Gases in agro-food processes
 9780128125618, 0128125616, 9780128124659

Table of contents :
Content: Part 1: Introduction: 1.1. Modified atmosphere packaging and processing : a technology of the future for sustainable food preservation / Didier Majou --
1.2. Gases in the agro-food industry : from a regulatory perspective / Catherine Simoneau --
1.3. Gases in the agro-food chain : from field to fork / Patrick Lesueur. Part 2: Chemical and physical gases properties, gases production process, units: 2.1. Physicochemical properties of gas / Elise El Ahmar and Christophe Coquelet --
2.2. Industrial gas manufacturing, cylinder filling, bulk installations, piping, relief devices, and security / David Brian Burgner --
2.3. Special case of ozone (physicochemical properties, onsite generation technology / Mar Pérez-Calvo --
2.4. Special case of sulfur dioxide / Eric Poujol. Part 3: Heat and mass transfers : basics enthalpies calculation and the different transfer modes: 3.1. Heat and mass transfers : basics enthalpies calculation and the different transfer modes / Eric Ferret, Laurent Bazinet and Andrée Voilley. Part 4: Gases monitoring, safety: 4.1. Food safety management system : HACCP : risk assessment / Philippe Girardon, Flora Gabard and Heinz Peyer --
4.2. Online and offline gas control and leak detection / Laurent Michon. Part 5: Regulation: 5.1. Food grade gas regulation / Philippe Girardon. Part 6: Agriculture: 6.1. Animal production --
6.2. Vegetal production. Part 7: Food processing : all the food industry sectors: 7.1. Refrigeration --
7.2. Modified atmosphere packaging and controlled atmosphere packaging --
7.3. Gases in enology / Philippe Girardon --
7.4. Gases in breweries / Philippe Girardon --
7.5. Liquid food stuffs gas treatments --
7.6. Propellant gases for aerosols containers / Philippe Girardon --
7.7. Supercritical fluid applications in the food industry / Michel Perrut and Vincent Perrut --
7.8. Biotechnological processes. Part 8: Waste water treatment: 8.1. Gases for wastewater treatment in the food industry / Joerg Schwerdt and Markus Meier. Part 9: Sanitation: 9.1. Sanitation with ozone / Mar Pérez-Calvo. Part 10: Particular CO2 applications : cleaning, pH control: 10.1. CO2 cleaning and pH control in the food industry / Jan Vansant and Christian Rogiers. Part 11: Gases applications for safety prevention: 11.1. Safety improvement by means of gas applications : fire prevention in frozen food storages and grain silos / Philippe Girardon. Part 12: Market trends, prospectives, sustainable development, and R&D perspectives: 12.1. Application and perspectives in different world regions --
12.2. Industrial gases industries business overview / Philippe Girardon --
12.3. Sustainable development / Philippe Girardon --
12.4. Business to consumer gases applications / Philippe Girardon. Part 13: Conclusion and outlook: 13.1. Conclusion and outlook / Philippe Girardon.

Citation preview

GASES IN AGRO-FOOD PROCESSES

GASES IN AGRO-FOOD PROCESSES Edited By

REMY CACHON PHILIPPE GIRARDON ANDREE VOILLEY

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom © 2019 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-812465-9 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Cover photo by Jonathan Thevenet Cherrystone, Franc¸ois Vermeere. © 2018 Remy Cachon, Philippe Girardon, and Andree Voilley. Publisher: Charlotte Cockle Acquisition Editor: Nina Rosa de Araujo Bandeira Editorial Project Manager: Sara Pianavilla Production Project Manager: Nilesh Kumar Shah Cover Designer: Mark Rogers Typeset by SPi Global, India

Contributors Hermawan Dwi Ariyanto Department of Applied Biological Science, Kagawa University, Kita, Japan

Enrique Dacal ALTEC South West Europe, Air Liquide, Milano, Italy

Laurent Bazinet Department of Food Sciences, Institute of Nutrition and Functional Foods (INAF) and Dairy Research Center (STELA), Universite Laval, Quebec, QC, Canada

Guy Delhomme IMV Technologies, L’Aigle, France

Christian Beau

Serigne Gueye Diop Palais de la Republique, 1. Av. Leopold S. Senghor, Dakar, Senegal Sebastien Dupont Univ. Bourgogne FrancheComte, AgroSup Dijon, PAM UMR A 02.102, Dijon, France

IMV Technologies, L’Aigle, France

Laurent Beney Univ. Bourgogne Franche-Comte, AgroSup Dijon, PAM UMR A 02.102, Dijon, France Christine Boisrobert

Bruno Ebel Laboratoire Reactions et Genie des Procedes, CNRS-Lorraine University, UMR 7274, Vandoeuvre-le`s-Nancy, France

Air Liquide, Paris, France

David Brian Burgener CO2 & N2O, Air Liquide, Countryside; CO2 & N2O, Consulting Service Inc., Elmhurst, IL, United States

Elise El Ahmar Mines ParisTech, PSL University CTP, Centre of Thermodynamics of Processes, Fontainebleau, France

R emy Cachon Unit Biotechnology and Food Microbiology, AgroSup Dijon, Dijon, France; UMR Procedes Microbiologiques et Biotechnologiques, AgroSup Dijon, Univ. Bourgogne Franche Comte, Dijon, France Agne`s Camus

Eric Ferret Univ. Bourgogne Franche-Comte/ AgroSup Dijon, PAM UMR A 02.102, PMB/PAPC, Dijon, France Rayen Filali R&D, ALGAE NATURAL FOOD SAS, Illkirch-Graffenstaden, France

IMV Technologies, L’Aigle, France

G erald Cavalier Cemafroid/Tecnea, Fresnes; Association Franc¸aise du Froid (AFF), Paris; International Institute of refrigeration (IIR), Paris, France

Pablo Rodriguez Fonseca Agrosavia-Colombian Corporation for Agricultural Research, Research Center “La Selva”, Rionegro, Colombia

Philippe Cayot Food and Microbiological Processes (PAM) Research Centre, AgroSup Dijon, Dijon, France

Flora Gabard Air Liquide, Paris, France Philippe Girardon

Andr es Gonzalez IMV France

Son Chu-Ky School of Biotechnology and Food Technology (SBFT), Hanoi University of Science and Technology (HUST); International Joint Laboratory Tropical Bioresources and Biotechnology, Hanoi University of Science and Technology, Hanoi, Vietnam

Technologies,

L’Aigle,

Philippe Granvillain R&D, ALGAE NATURAL FOOD SAS, Illkirch-Graffenstaden, France Nathalie Guibert Cergy, France

Ecole de Biologie industrielle,

Paul Wan Sia Heng GEA-NUS Pharmaceutical Processing Research Laboratory, National University of Singapore, Singapore, Singapore

Christophe Coquelet Mines ParisTech, PSL University CTP, Centre of Thermodynamics of Processes, Fontainebleau, France

Phu-Ha Ho School of Biotechnology and Food Technology (SBFT), Hanoi University of Science and Technology (HUST), Hanoi, Vietnam

Didier Coulomb International Institute of Refrigeration, Paris, France Olivier Couture

Air Liquide, Paris, France

IMV Technologies, L’Aigle, France

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CONTRIBUTORS

Dominique Ibarra Paris Innovation Campus, Air Liquide, Les Loges en Josas, France

Tze Loon Neoh Department of Applied Biological Science, Kagawa University, Kita, Japan

Piyush Kumar Jha ONIRIS UMR GEPEA CNRS 6144, Nantes; Universite Bretagne Loire, Rennes, France

Manh Hieu Nguyen Vietnam Institute of Agricultural Engineering and Post-Harvest Technology (VIAEP), Hanoi, Vietnam

Phillip Kerckx VBS Sprl, Tubize, Belgium

Tien-Thanh Nguyen School of Biotechnology and Food Technology (SBFT), Hanoi University of Science and Technology (HUST), Hanoi, Vietnam

Mia Kurek Faculty of Food Technology and Biotechnology, Department of Food Engineering, Laboratory for Food Packaging, University of Zagreb, Zagreb, Croatia Francis A. Kurz R&D, ALGAE NATURAL FOOD SAS, Illkirch-Graffenstaden, France Alain Le-Bail ONIRIS UMR GEPEA CNRS 6144, Nantes; Universite Bretagne Loire, Rennes, France Richard LeBoucher France

IMV Technologies, L’Aigle,

Cl emence Lesimple IMV Technologies, L’Aigle, France Patrick Lesueur d’Ascq, France Herve Lonque

R&D,

Bonduelle,

Villeneuve

SEALED AIR, Epernon, France

Didier Majou Association de Coordination Technique pour l’Industrie Agro-alimentaire (Actia), Paris, France Phonkrit Maniwara Postharvest Technology Research Center, Faculty of Agriculture, Chiang Mai University, Chiang Mai, Thailand Christophe Marvillet IFFI (Institut Franc¸ais du Froid Industriel)/Cnam (Conservatoire National des Arts et Metiers), Paris, France Peter Meeus QHSE, Training & Expertise, EWS Group Antwerp, Antwerp; Entomologie fonctionnelle et evolutive, Gembloux Agro-Bio Tech— Universite de Lie`ge, Namur, Belgium Markus Meier Air Liquide Research & Development, LifeScience, Krefeld, Germany

Thi Minh Nguyet Nguyen Vietnam Institute of Agricultural Engineering and Post-Harvest Technology (VIAEP), Hanoi, Vietnam Thi Hanh Nguyen School of Biotechnology and ˙ Food Technology (SBFT), Hanoi University of Science and Technology (HUST), Hanoi, Vietnam Eric Olmos Laboratoire Reactions et Genie des Procedes, CNRS-Lorraine University, UMR 7274, Vandoeuvre-les-Nancy, France Shing Ming Ooi GEA-NUS Pharmaceutical Processing Research Laboratory, National University of Singapore, Singapore, Singapore Didier Pathier

Air Liquide, Paris, France

Mar P erez-Calvo Technical Direction, Cosemar Ozono, Madrid, Spain Michel Perrut Atelier Nyons, France

Fluides

Supercritiques,

Vincent Perrut Atelier Nyons, France

Fluides

Supercritiques,

Heinz Peyer Air Liquide, Paris, France Anh Tuan Pham Vietnam Institute of Agricultural Engineering and Post-Harvest Technology (VIAEP), Hanoi, Vietnam Eric Poujol GAZECHIM, Security Environment, Beziers, France Tongchai Puttongsiri King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand

WITT FRANCE, Morsang sur

Le-Ha Quan School of Biotechnology and Food Technology (SBFT), Hanoi University of Science and Technology (HUST), Hanoi, Vietnam

Caroline Moziar IM-BL Food Market, Air Liquide, Cambridge, ON, Canada

Jean-Patrice Quenedey Paris Innovation Campus, Air Liquide, Les Loges-en-Josas, France

Mamadou Ndiaye Molecules Group, Point E rue 4xB Immeuble 18B, Dakar, Senegal

Christian Rogiers Cold Jet LLC, Sr. VP Marketing, Loveland, OH, United States

Laurent Michon Orge, France

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CONTRIBUTORS

Elisabeth Rubin National Superior School of Decorative Arts, Paris, France Eric Schmitt IMV Technologies, L’Aigle, France Joerg Schwerdt Gas Injection in Liquids, Air Liquide Technology Center, Krefeld, Germany Isabelle Severin ENSBANA (AGROSUP); INSERM U 1231, AgroSupDijon, Dijon, France Catherine Simoneau European Commission, Joint Research Centre (JRC), Ispra, Italy Kevin C. Spencer Spencer International Consulting, Hinsdale, IL, United States Andrea Spizzica ALTEC South West Europe, Air Liquide, Milano, Italy Anthony Keith Thompson King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand Viet-Phu Tu School of Biotechnology and Food Technology (SBFT), Hanoi University of Science and Technology (HUST), Hanoi, Vietnam Fabrice Vaillant CIRAD—International Research Center in Agronomy for Development, UMR QUALISUD, Montpellier, France; Agrosavia-Colombian

Corporation for Agricultural Research, Research Center “La Selva”, Rionegro, Colombia Anne Linda Van L’Aigle, France Jan Vansant Belgium

Kappel IMV

Technologies,

Cold Jet LLC and VFB bvba, Leuven,

Andr ee Voilley Univ. Bourgogne Franche-Comte/ AgroSup Dijon, PAM UMR A 02.102, PMB/PAPC, Dijon, France Thi Nga Vu Vietnam Institute of Agricultural Engineering and Post-Harvest Technology (VIAEP), Hanoi, Vietnam Yves Wach e International Joint Laboratory Tropical Bioresources and Biotechnology, Hanoi University of Science and Technology, Hanoi, Vietnam; Univ. Bourgogne Franche-Comte, AgroSup Dijon, PAM UMR A 02.102; Pedagogic Unit Biotechnology and Food Microbiology, AgroSup Dijon, Dijon, France Hidefumi Yoshii Department of Applied Biological Science, Kagawa University, Kita, Japan

About the Editors

Prof. R emy Cachon has worked in the field of biotechnological processes since 1989. He is especially interested in the effects of gases on microorganisms and food quality, and in developing original processes using gases. His main fields of application are bioreactor modeling, lactic acid fermentation, alcoholic fermentation, production of yeast biomass, lactic starters and probiotics, food quality, and modified atmosphere packaging. Prof. Cachon has managed and participated in several R&D projects (national, international, and industrial). He is also actively involved in the training and supervision of graduate students. He has coauthored indexed articles, patents, technical papers, and congressional presentations. He is also regularly required as an expert for French and European research agencies. In France, AgroSup Dijon is one of the first  public “Grands Etablissements” for the training of engineers in the fields of agronomy and agrofood. It is part of the French Ministry of Food, Agriculture, and Forestry, and of the Ministries of Higher Education and Research. http:// www.agrosupdijon.fr Affiliations and Expertise Unit Biotechnology and Food Microbiology, AgroSup Dijon, Dijon, France. UMR PAM A 02.102, AgroSup Dijon, Universite Bourgogne Franche-Comte, France.

Philippe Girardon is an engineering graduate from Ecole Nationale Superieure de Biologie Appliquee a` la Nutrition et a` l’Alimentation, now part of AgroSup Dijon. He joined Air Liquide (AL) in 1979 as a food gases applications R&D engineer. His early work was in modified atmosphere packaging, specializing in gases for sterilization and fermentation. For 39 years he has worked at AL in the agrofood domain, ensuring that marketing and development promotes gas application technologies to AL affiliates and customers. He is part of the internal Technical Community Leaders program as an International Fellow. He belongs to the boards of the Professional Equipment Association and life science schools and has published several technical articles. He chaired the Food and CO2 Working Group in the European Industrial Gases Association (EIGA) in charge of watching legislation and elaborating relevant gas safety guidelines and food safety. Affiliations and Expertise Air Liquide (1979–2018), Food Processing, Microbiology, Fermentation, Cryogenics, Food Packaging, Gas Handling, Food Gas Application Technologies, Training, Knowledge Management.

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ABOUT THE EDITORS

Prof. Andree Voilley, Emeritus Professor. Voilley is recognized worldwide for her extensive knowledge of mass transfer in small molecules, such as water or aroma, as a function of complex biological matrix structures, and their relationship with hydration level and processing. She has directed more than 50 PhD dissertations. She coedited

“Flavor: From Food to Behaviors, Wellbeing and Health” (Elsevier, 2016), and “Flavour in Food” (Elsevier, 2006). Prof. Voilley is a member of the French Academy of Agriculture. Affiliations and Expertise AgroSup Dijon, Universite Franche-Comte, France.

Bourgogne

Preface

This book is the informal result of a discussion between three people: Remy Cachon, professor of biotechnology and biological processes at AgroSup Dijon; Andree Voilley, emeritus professor at AgroSup Dijon; and Philippe Girardon, with whom the working company partnered in researching the effect of the then-unexplored hydrogen gaseous molecule on biological systems as well as in teaching a course in modified atmosphere packaging for food engineers. Philippe Girardon always had a watchful eye toward AgroSup Dijon, where he earned his degree in engineering in food industries in 1977. Dijon is the capital of Burgundy as well as a gastronomic capital known for its vineyards with wines among the most prestigious in the world. A chapter is also dedicated to the gas applications in oenology between tradition and technology. This book could not have been written without the hindsight of 50 years of Food Industry, which is a short period in absolute terms. There are thousands of customers and users of food gases around the world, some of whom participated in the development of these applications from farm to the fork. This relatively recent industry will continue to be able to feed the planet with the diversity of its continents and cultures by offering more or less sophisticated products for all budgets as well as daily food safety. It represents a very large share of countries’ gross domestic product while employing millions of people around the world. Is not today’s much better food a reason for the longer life expectancy we enjoy now more so than half a century ago? We thank all those colleagues who responded enthusiastically by writing a chapter of this book

in their area of expertise. Also, we thank all the authors and experts in their domain who responded with spontaneity. These partners represent essential original equipment manufacturers (OEMs) of gas applications together with the scientists working on the basic physicochemical and biological knowledge of the implemented processes. These authors are a balance between the industrial and academic communities. Although there isn’t enough room in this work to develop in detail each topic, something that encyclopedic books do more in depth, the diversity of themes allows the reader to discover a sometimes new world through reminders of basic data and an original angle of attack that can give rise to cross-fertilization and inspiration for further innovation and development of the applications of the gas in the agro-food industries. We hope that students, teachers, researchers, industrialists, economists, and authorities may find interest in reading this work. Special acknowledgement from Philippe Girardon: “I dedicate this book to all my former colleagues (who) have inspired me during my career, which ended June 2018 in this wonderful Air Liquide Company where I discovered the world of gases and where I learned so much.” Special acknowledgment from Remy Cachon: “I dedicate this book to all the students and colleagues who motivated my interest with the use of gases in the food and biotechnology sectors. A particular thought for Professor Charles Divie`s who, at the beginning of my career as a

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PREFACE

researcher, encouraged me when I became interested in gases and their impact on the electrochemical activities of microorganisms.” Special acknowledgment from Remy Cachon and Andree Voilley: “Many thanks for AgroSup

Dijon, National Superior Institute of Agronomic Sciences, Food and the Environment for its support in our professional activity, and particular thanks for our colleagues from AgroSup Dijon for their kind cooperation in this book.”

C H A P T E R

1.1

Introduction: Modified Atmosphere Packaging and Processing; A Technology of the Future for Sustainable Food Preservation Didier Majou Association de Coordination Technique pour l’Industrie Agro-alimentaire (Actia), Paris, France

As shown in this remarkable book, gases are used in many food industry sectors (meat, fish, dairy products, ready meals, beverages, wine, bakery, etc.) with numerous applications that include cooling and deep freezing, inerting and carbonating beverages, hydrogenation of oils, and modified atmosphere packaging (MAP). Widely used since the late 1990s, MAP is a technique for preserving fresh or processed foods. By replacing air with other gases in the packaging, the process tends to slow down chemical or enzymatic oxidation reactions (on lipids and proteins) as well as reduce or inhibit the growth of pathogenic or spoilage aerobic and anaerobic bacteria, yeasts, molds, and viruses. The gases used in MAP are generally one or more of the following: carbon dioxide, nitrogen, and dioxygen. Which ones are used and their proportions depend on the gas properties, the applications, the objectives (extending shelf life or preserving color, texture, taste,

Gases in Agro-food Processes https://doi.org/10.1016/B978-0-12-812465-9.00001-3

etc.), the product’s characteristics or weight, the packaging material’s properties (permeability), the volume of headspace, the storage temperature, and the market price of the packaged product. However, consumers now want more natural, fresh, and minimally processed foods with fewer artificial additives, including preservatives. This consumer demand for high nutritional quality is a strong long-term trend. Moreover, increased use of cold technologies (chilling, freezing) around the world (China, India, etc.) will cause energy supply issues. In the long run, it will be necessary to find ways of offsetting these issues. In order to meet consumer expectations on the one hand, and the constraints of sustainability on the other, the intelligent application of hurdle technology needs to be further developed. A variety of major preservative technologies currently exist (e.g., temperature, pH, aw,

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1.1. INTRODUCTION: MODIFIED ATMOSPHERE PACKAGING AND PROCESSING

Eh, biopreservative bacteria) and the packaginggas couple must also become a key technology. However, in order for this couple to effectively preserve foods and/or allow them to mature, it is essential to improve MAP technology in addition to optimizing manufacturing processes. Companies expect an optimization of the choice of gas used (CO2, O2, N2) in MAP, the volume of gas in proportion to the weight of the food, and the permeability of the packaging materials. The challenge is to improve antibacterial efficacy, which will have consequences on shelf life, antioxidant protection, the quantity of packaging needed, the food-to-packaging ratio of the product to be transported, and the transportation cost per unit of sale. Therefore, films must have improved functionalities (selective permeability, sealing) while preventing the transfer of residual monomers to the foodstuff and also taking ecodesign (“from cradle to grave”) into account, and do that all at a reduced cost. In addition, research on the properties of gases and how they interact with films, food ingredients, and microorganisms must be developed beyond just their solubility. This requires a better understanding of reaction and diffusion mechanisms within real foods, with a particular focus on oxidation and its consequences. We must learn more about microorganisms’ metabolic growth conditions (aerobic, anaerobic, aeroanerobic) in relation to their ecosystem at chemical and microbiological levels. The selective pressure of the choice of gas on different species of bacteria and the interactions between species must be investigated. Thus, there is a need to further explain and quantify the effects of MAP in preserving food quality

(microbiology, organoleptics, nutritional composition). A decision-making tool based on key characteristics and mathematical models (gas diffusion, predictive microbiology, film permeability) would provide quick answers to these questions based on real food conditions. The French Technical Institute, ADRIA, coordinated the MAP’OPT project, which sought to design such a tool (2010–2014). The tool is still at the first demonstration stage. Its database must be enriched with data about the interactions between more microorganisms, packaging, and food to make it operational. Although three gases are generally used in MAP (CO2, O2, N2), the reducing properties of hydrogen with an admixture of nitrogen should be tested and applied on a larger scale in accordance with the work of Professor Remy Cachon (AgroSup Dijon, France). The modulation of the redox potential by H2 puts positive and negative selective pressure on bacteria on the one hand, and has an effect on the product’s chemical ecosystem with sensory or nutritional effects on the other hand. Modified atmosphere packaging must become modified atmosphere processing in production units. Inerting with nitrogen is used in wine making to limit the dissolution of oxygen and oxidation. Anoxia could also be used for other sensitive liquids such as fruit juices and oils. Milk, which has a particularly complex composition, would be a very interesting material to protect from oxidation in order to preserve its properties. So, we must continue to develop our understanding of modified atmosphere packaging and processing (MAPP). This is a technology of the future for sustainable food preservation.

1. INTRODUCTION

C H A P T E R

1.2

Introduction: Gases in the Agro-Food Industry; From a Regulatory Perspective Catherine Simoneau European Commission, Joint Research Centre (JRC), Ispra, Italy

The word gases can conjure up visions that are either misunderstood or not perceived to their right value, yet industrial gases have an important place in the agrofood chain. In agriculture, gases are used in both animal and vegetable production. In animal production, gases are used as anesthetics prior to slaughter or for oxygenation purposes in aquaculture. In vegetal production, they are used for enriching greenhouses; providing a controlled atmosphere for maturation, ripening, and storage; or toward the control of pests, for example. They also have postindustrial uses for wastewater treatments in the food industry. In food processing, gases such as nitrogen and carbon dioxide are used toward preservation, ripening, spoilage prevention, freezing, chilling, carbonation, and many more applications in a large number of foodstuffs such as bakery and dairy items, beverages, fish and seafood, fruits, vegetables, meats, poultry, prepared meals, and more. In particular, refrigeration processes such as chilling, freezing, subcooling, hardening, or cryogrinding use cryogenic industrial gases such as liquid nitrogen. Gases are also a key component of the

Gases in Agro-food Processes https://doi.org/10.1016/B978-0-12-812465-9.00002-5

preservation of minimally processed foods such as fish, meats, fruits, and vegetables. One foodprocessing application that uses industrial gases is modified atmosphere packaging (MAP), a process where a pure gas such as nitrogen or a gas mixture is placed as the breathable atmosphere in a package in order to slow down microbial growth or spoilage such as discoloration, oxidation, or moisture loss. Gases also provide inert environments, or together with hermetic sealing can serve as evidence markers for tampering (as interference with the packaging would be noticeable). From a regulatory standpoint, the basis at the European level for food safety is Regulation (EC) 178/2002, which stipulates the general principles and requirements of the EU food law, establishes the European Food Safety Authority, and lays down food-safety procedures. Those foodsafety procedures include traceability in the food chain in order to foster trust and enable consistent compliance from one actor to the next while ensuring the efficient and rapid withdrawal from the market of any food that poses health concerns to consumers. As a regulation, it was immediately binding upon publication

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1.2. INTRODUCTION: GASES IN THE AGRO-FOOD INDUSTRY; FROM A REGULATORY PERSPECTIVE

for member states of the European Union and cannot be modified unless at the EU level. The regulation gives a definition of food that “includes any substance that is intended to be, or is reasonably expected to be, ingested by humans.” The reference to “reasonably expected” is formulated to ensure that a substance that may be reasonably expected to find its way into the food supply chain but may also find its way into different industry sectors is handled with the same care as food until it is clear that it will not become a food. This implies that industrial gases such as nitrogen, oxygen, carbon dioxide, etc., in the production/distribution process have to be treated as if they are foods until specifically designated otherwise. It also confirms that food includes any substance intentionally incorporated into the food during its manufacture, preparation, or treatment. The European legislation therefore requires that foods, including gases supplied to the food industry, have to meet rigorous standards to ensure food safety. Food gases are defined as gases in liquid, gaseous, or solid form that are supplied to the food industry and used as additives, processing aids, or ingredients in contact with food. When used as a processing aid, food additives, or packaging gases, fall under Regulation EC 1333/2008. This regulation defines food additives and processing aids and prescribes labeling requirements. Food additives include packaging gases that include any gas, other than air, introduced into a container before, during, or after placing food in that container. It also includes propellants that expel a foodstuff from a container. The Regulation of food additives specifies purity criteria requirements. In addition, materials and articles intended to come in contact with food (food contact materials, FCMs) are all materials that are intended or likely to be in contact with food such as food packaging, kitchenware, and tableware as well as materials for food manufacturing, preparation, processing, storage, and distribution. They

can thus influence food safety and quality throughout the whole food supply chain. These materials fall under Regulation EC 1935/2004, which establishes the principles of safety assessment and management regarding the risk of chemical transfer from such materials into foods. While some materials are in addition covered by EU-wide specific measures, others can be overseen by national rules, depending on mutual recognition. The regulation sets out general requirements that all FCMs must be manufactured in accordance with good manufacturing practices (GMP) so that they are safe and do not change the properties of food in unacceptable ways. In the case of FCMs, separate rules on GMPs are laid down in Commission Regulation EC 2023/2006, which covers all stages of the supply chain including production, storage, repackaging, and distribution of food gases to the final user. In addition, food hygiene is paramount to food safety. In this context, Regulation EC 852/2004 provides measures and conditions necessary to control hazards and to ensure a foodstuff’s fitness for human consumption, taking into account its intended use. The primary responsibility for hygiene rests with the food business operators. They must ensure that all stages of production, processing, and distribution of food under their control satisfy the relevant hygiene requirements, which include the operation of food safety programs and procedures based on hazard analysis and critical control points (HACCP) principles. These considerations imply that the adequate uses of gases in the food industry include a number of regulatory frameworks and must respond to manufacturing and food safety requirements, including in terms of formulation components and their purity criteria as well as hygiene requirements, labeling, and traceability. In this overall multifaceted context, this book is quite unique in its kind and aims to provide extensive information on industrial gases in the agrofood processes.

1. INTRODUCTION

1.2. INTRODUCTION: GASES IN THE AGRO-FOOD INDUSTRY; FROM A REGULATORY PERSPECTIVE

The first set of chapters (Chapters 2-5) covers gas properties and the production of different food-grade gases as well as their safety. The second set of chapters (Chapters 6-7) provides extensive information on the use of industrial gases in agrofood processes, both in agriculture (animal and vegetable production) and food processing for all different food sectors. The third set of chapters (Chapters 8-11) covers

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wastewater treatment, sanitation, cleaning, and pH control in the food industry as well as fire prevention. The final chapters (Chapters 12-13) give market trends, development perspectives, and outlooks. This work therefore offers the reader comprehensive information that can be of use for academia, industries, risk assessors, or regulators.

1. INTRODUCTION

C H A P T E R

1.3

Introduction: Gases in the Agro-Food Chain; From Field to Fork Patrick Lesueur R&D, Bonduelle, Villeneuve d’Ascq, France

When I was first exposed to the topic of gases and food, my initial thoughts were going towards either the methane expelled by our global cattle or to the digestion of my lunch. When thinking about food and agriculture, the first things that come to mind are typically the soil, the seeds, the harvest, and the processing or packaging line. None of those comes with an obvious link to gases. So what is the interest for writing a book about gases and food? I was left pondering, and even moreso once I started to get my teeth into the topic. From wondering about the interest, I was quickly overwhelmed by the magnitude and breadth of the different usages of gases in agrofood processes. Basically, gases are used at every step of the food chain from field to fork and even as the “cradle to grave” one from “seed to waste.” Taking the example of fruits and vegetables, the breadth of gas applications can be quickly screened:

• In the agrisupply chain, for storage and ripening through a controlled atmosphere, for refrigeration, or for fire prevention in large storage areas. • In food processing, for decontamination, sanitation, refrigeration, or freezing. • In food packaging with modified atmosphere and shelf-life control and refrigeration. • And to justify my “seed to waste,” the cryoconservation of seeds or the running of any compost or sewage plant that will include oxygenation or reduction. And these are just a few examples for fruits and vegetables of which I’m aware. I could add to this short list the carbonation of beverages, the fermentation of many excellent beverages, foaming of dairy products, propellant in aerosol cans, using supercritical CO2 for dispersing fat during emulsification, etc. This ubiquitous usage of gases in agrofood is amazing. And any of the examples given above will involve the very basic laws of physics or biology. That is for one reason: gases are essential to life, gases are life as the atmosphere around our planet can demonstrate. And food

• In agriculture, to increase the productivity of the soil, as enrichment in greenhouses, or for pest control.

Gases in Agro-food Processes https://doi.org/10.1016/B978-0-12-812465-9.00003-7

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1.3. INTRODUCTION: GASES IN THE AGRO-FOOD CHAIN; FROM FIELD TO FORK

is basically life, hence the myriad and importance of gases in food production where gases are used to either promote life and growth, slow it down, or kill it. And the beauty of it because it evokes some very basics laws of physics is that the study of gases in food production will involve many ther-

modynamic laws and nice mathematical models in the world of food where many things are empirical and learned by experience. A nice change for any practitioner in the food industry like me and I hope you will—as I did—feel empowered to somehow rediscover the secret of life while reading this book.

1. INTRODUCTION

C H A P T E R

2.1

Physicochemical Properties of Gas Elise El Ahmar, Christophe Coquelet Mines ParisTech, PSL University CTP, Centre of Thermodynamics of Processes, Fontainebleau, France

List of Symbols A(T, v, n) fi G P R T Z x y v S H Hi

Helmholtz free energy [J mol1] fugacity of compound i in the mixing [Pa] Gibbs free energy [J mol1] pressure [Pa] gas constant [J/(mol K)] temperature [K] compressibility factor liquid mole fraction vapor mole fraction molar volume [m3 mol1] entropy [J mol1 K1] enthalpy [J mol1] Henry’s law constant [Pa/mol frac]

SUBSCRIPTS C cal exp i,j m v l

2.1.1 INTRODUCTION The goal of this chapter is to give the state of art concerning physicochemical properties of industrial gases used in agrofood processes. For example, these gases are CO2, N2, O3, and SO2. The chapter is divided into four parts. The first part concerns the fundamentals aspects in fluid thermodynamics (molecular interactions, chemical potential, and equilibrium conditions). The second part concerns the equation of state applied for these types of gas. The third part treats the gas solubility and Henry’s law constant correlations. The fourth part gives examples of phase diagrams (Pressure versus Temperature, Pressure versus Density, and Pressure versus Enthalpy) for pure

GREEK LETTERS ω acentric factor γi activity coefficient μi chemical potential of the component i in the phase [J mol1]

SUPERSCRIPT E Id 0 ∞

excess property ideal mixing reference fluid infinite dilution

Gases in Agro-food Processes https://doi.org/10.1016/B978-0-12-812465-9.00004-9

critical property calculated property experimental property molecular species mixing vapor phase liquid phase

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2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

gases and equilibrium properties of two mixtures. The chapter ends with a conclusion showing the utility of these properties for the design and the optimization of the agrofood processes.

2.1.2 FUNDAMENTAL ASPECTS IN FLUID THERMODYNAMICS: A REMINDER By definition, a phase diagram is a graphical representation of a physical or physical/chemical equilibrium and is a consequence of the chemical thermodynamics of the system. Because this equilibrium is dependent on the composition of the system, the pressure, and the temperature, a phase diagram should be able to tell us what phases are in equilibrium for any composition at any temperature and pressure of the system. Phase diagrams are essential in chemical engineering: a good understanding of phase diagrams leads to choosing or designing the best operating unit. There are many examples of diagram phase utility in chemical engineering. We can mention the distillation process. In fact, under heat effects, a fluid can dissociate into two phases or more. We also have liquid extraction based on the immiscibility between two liquids.

2.1.2.1 Molecular Interactions At the microscopic level, the two molecules can repulse and attract each other. These two classes of molecular interactions depend on the distance r between the cores of the molecules. The function linking force F(r) with the potential of interactions Γ(r) is expressed in Eq. (2.1.1): FðrÞ ¼

dΓ ðrÞ dr

2.1.2.1.2 Attractive Interactions According to the nature of the molecules (apolar, polar, ionic, etc.), there are many categories of attractive strengths. Let’s quote three categories: physical, quasichemical, and chemical (electrolyte). a. Physical interactions Between neutral (nonionic) molecules, van der Waals’ forces dominate the physical attractions. They are characterized by a potential of long-range low interaction. Van der Waals’ forces include three types: dispersion (London), dipole-dipole (Keesom), and induced dipole-dipole (Debye). • Dipole-dipole (Keesom) A polar molecule is electrically neutral but has a permanent electric dipole because of the difference in electronegativities of the atoms that form the molecule. The fact that the positive and negative poles attract each other causes an attractive force (see Fig. 2.1.1). The potential of interaction between two dipoles depends on the distance between two dipolar centers (r), their dipolar moments (μ), and the orientation of the dipolar moments. The potential of the average dipole-dipole interaction on all orientations can be expressed by Eq. (2.1.3):

(2.1.1)

where Γ(r) can be represented by the total of the repulsive and attractive contributions (Eq. 2.1.2): Γ ðrÞ ¼ Γ repulsion + Γ attraction

2.1.2.1.1 Repulsive Interactions When the distance between two molecules decreases, the latter ones repulse each other because of the presence of the electrons on their valence shell. The more the molecules approach, the more the potential for repulsive interactions increases. This potential approaches the infinite when the distance approaches zero.

(2.1.2)

Polar molecule

δ+ FIG. 2.1.1

δ−

Polar molecule

δ+

Dipole-dipole interaction.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

δ−

15

2.1.2 FUNDAMENTAL ASPECTS IN FLUID THERMODYNAMICS: A REMINDER

Polar molecule

δ+

δ−

δ+

δ−

FIG.

Apolar molecule

2.1.2

Induced

dipole-dipole

interaction.

δ+

δ−

δ+

δ−

Apolar polarizable molecule

Γ ij ¼ 

μ2i μ2j 1 3 kB T ð4πε0 Þ2 r6

Apolar molecule

(2.1.3)

where () indicates the attractive force, kB is Boltzmann’s constant, and ε0 the dielectric permittivity of the void.

δ−

• Induced dipole-dipole (Debye) All (polar or nonpolar) molecules are polarizable. A dipolar moment may happen when a molecule undergoes an electrical induction such as the presence of a polar molecule. The induced dipole is instantaneous and can attract another permanent dipole. Fig. 2.1.2 shows this type of interaction between a polar molecule and an apolar molecule. The average potential of interaction due to the induction of permanent dipoles can be expressed by Eq. (2.1.4): Γ ij ¼ 

αj μ2i + αi μ2j ð4πε0 Þ2 r6

(2.1.4)

The term “polarizability” (α) allows us to quantify the tendency of the formation of an instantaneous dipole within the (polar or apolar) molecule in the presence of a neighboring dipole. • Induced dipole-induced dipole (London) In an apolar molecule, the dipolar moment is statistically zero. But a temporary dipolar moment may happen through the instantaneously inhomogeneous distribution of electron density within a molecule (see Fig. 2.1.3).

δ+

δ−

δ+

Apolar molecule but temporally polarizable

FIG. 2.1.3

Induced dipole-induced dipole interaction

(dispersion).

The induced dipole-induced dipole interaction is generally called “dispersion.” The average potential of interaction of the dispersive interaction can be expressed by Eq. (2.1.5):   Ii Ij 3 αi αj (2.1.5) Γ ij ¼  2 ð4πε0 Þ2 r6 Ii + Ij where I is the first molecule ionization energy (i.e., the energy required to remove an electron from the molecule). This type of interaction exists between all the molecules because the polarizability and the first ionization energy of a molecule are never zero. It is the only universal type of attractive interaction. In addition to van der Waals’ forces, there are also other types of physical forces associated with the quadrupole such as dipole-quadrupole and quadrupole-quadrupole. Their contributions are often low, but they can be highly

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

16

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

O O

R

O

H

R

H

O

H

H

R O

O H

R

H

R

R H

O H

O

H

R O

R R

FIG. 2.1.4

Hydrogen links in an alcohol.

can be distinguished: monophasic homogeneous systems, for which composition and thermodynamics properties are identical in the whole space, and multiphase heterogeneous systems, for which thermodynamics properties changed brusquely at the interface. A phase is characterized by its temperature, its density, its pressure, and other thermodynamics properties (Gibbs energy, molar enthalpy and entropy, heat capacity, etc.). Phase is employed to distinguish the different states of matter. It exists mainly in three states: gas, liquid, and solid.

significant in some cases (e.g., CO2, N2, etc.) (Kontogeorgis and Folas, 2010).

2.1.2.3 Phases Transitions

b. Quasichemical interactions: hydrogen bonds

A phase transition is commonly used to describe the transition between different states of matter. Table 2.1.1 illustrates all the phase transitions between the solid, liquid, and vapor phases. A phase transition can be obtained by a change of the composition of the system, a change of temperature and/or pressure, or by the application of external strength. Consequently, composition, density, molar internal energy, enthalpy, entropy, refractive index, and dielectric constant have different values in each phase. But, temperature and pressure are identical concerning multiphase systems regarding the thermodynamic principle. So when two phases (or more) exist, we can speak about phase equilibria.

The quasichemical forces refer to Lewis’ acidbase interactions. The transfer of electrical charges between the molecules leads to the formation of bonds (about 10 kJ mol1) stronger than the physical forces (often below 1 kJ mol1), but weaker than the chemical bonds (100 to 1000 kJ mol1). The hydrogen bonds are a typical example of the quasichemical interactions. A hydrogen bond is established when a hydrogen atom bonded to a highly electronegative atom (e.g., oxygen, nitrogen, or fluorine) approaches another atom, also highly electronegative and carrying a free electric dipole. The hydrogen bonds are responsible for the formation of oligomers from monomers (see Fig. 2.1.4). This type of interaction is called “association” in thermodynamics. Depending on the nature of the molecular interactions, the fluid will adopt a behavior and propose several types of phase diagrams.

2.1.2.2 Phase Definition A phase is a homogeneous system composed of one pure component and/or a mixture of components. A system can be composed of one or several phases. Two kinds of systems

TABLE 2.1.1

Phases Transitions

Phase 1

Phase 2

Transition 1 ! 2

Liquid

Vapor

Boiling

Liquid

Solid

Solidification

Vapor

Liquid

Liquefaction

Vapor

Solid

Condensation

Solid

Vapor

Sublimation

Solid

Liquid

Melting

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

2.1.2 FUNDAMENTAL ASPECTS IN FLUID THERMODYNAMICS: A REMINDER

We have two types of phase transition: First order: Concerning this type of phase transition, we have an important variation of the molar entropy due to an exothermic or endothermic effect on the system. The temperature will stay constant. Consequently, diverging exists concerning  heat capacity and susceptibil∂V ). In other words, the first ity (χ T ¼  V1 ∂P T derivative of Gibbs free energy with regard to thermodynamics variables is discontinuous. Second order: There is no discontinuity of entropy. The heat capacity and susceptibility diverge. In other words, the first derivative of Gibbs energy with regard to thermodynamics variables is continuous but not the second derivative, which is discontinuous.

2.1.2.4 Variance The variance F of the system is determined from the Gibbs phases rule (Eq. 2.1.6). It is the picture of the degree of freedom of the system. F ¼ C + 2  φ,

(2.1.6)

with F, the number of degree of freedom, C, the number of components, and Φ, the number of phases in presence. Table 2.1.2 determines the degree of freedom for one compound. TABLE 2.1.2 (C ¼ 1)

Degree of Freedom for One Compound

2.1.2.5 Phase Diagram for Binary Systems The phase diagram is clearly defined compared to current species so compared to the various molecular interactions. Indeed, molecular species 1 interacts with another molecular species 1 but also with a molecular species 2. The interactions between 1 and 2 can be of a different nature. There are several scenarios that may present themselves for liquid-vapor equilibrium. Table 2.1.3 shows the different cases. Van Konynenburg and Scott (1980) have classified the mixture into six types considering van der Waals EoS and quadratic mixing rules. Fig. 2.1.5 presents the different types of phase diagrams. The transition between each type of diagram can be explained by considering the effect of size and the repulsive interaction. Fig. 2.1.6 gives a view of the phase diagram transitions.

2.1.2.6 Chemical Potential The chemical potential is one of the most important thermodynamic variables in the context of phase equilibrium. If we consider one phase with volume V which content N components, at temperature T and pressure P, the chemical potential μi of the component i in the phase is defined by Eq. (2.1.7): μi ðP, T, n1 , n2 , …, nC Þ

Number of Phases

Degree of Freedom

Variables

Vapor pressure, or melting or sublimation curves

2

1

T or P

Liquid, vapor, or solid

1

2

P and T

Triple point

3

0

Everything is fixed

Critical point

2

1

TC or PC

Region of the Phase Diagram

17

  ∂GðP, T, n1 , n2 , …, nC Þ ¼ ∂ni T , P, n j6¼i

(2.1.7)

where G ¼ H-TS is the Gibbs free energy of the phase. The expression for the infinitesimal reversible change in Gibbs free energy is given by Eq. (2.1.8): X μi dni : (2.1.8) dG ¼ VdP  SdT + i

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

18

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

Various Scenarios (Pressure Is Given With Arbitrary Unit Value)

7

40

6

35

Pressure

Pressure

TABLE 2.1.3

5 4 3 2

30 25 20 15 10

1

5

0

0 0

0.2

0.4

0.6

0.8

0

1

0.2

0.4

0.6

0.8

x, y

x, y

Ideal mixture

Positive deviation from ideal mixture

1

30

40 35

25

Pressure

Pressure

30 25 20 15

20 15 10

10

5

5 0

0 0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

x, y

Negative deviation from ideal mixture

0.8

1

Strong negative deviation from ideality

1.4

2.5

1.2

2

Pressure

1 0.8 0.6

1.5 1

0.4 0.5

0.2 0

0 0

0.2

0.4

0.6

0.8

0

1

0.2

0.4

0.6

0.8

x, y

x, y

Azeotropic mixture-Pressure minimum

Azeotropic mixture-Pressure maximum

2.5 2

Pressure

Pressure

0.6 x, y

1.5 1 0.5 0 0

0.2

0.4

0.6

0.8

1

x, y

Heteroazeotropic mixture

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

1

2.1.2 FUNDAMENTAL ASPECTS IN FLUID THERMODYNAMICS: A REMINDER

19

FIG. 2.1.5 Six types of phase behavior in binary fluid systems. C, Critical point; L, Liquid; V, Vapor; UCEP, Upper critical end point; LCEP, Lower critical end point. Dashed curve are critical.

Size effect (s)

TYPE V

TYPE I

TYPE IV

TYPE III S + MI

Size effect (s) H bonding TYPE VI

FIG. 2.1.6

VdP  SdT +

X

ni dμi ¼ 0:

(2.1.9)

i

TYPE II Molecular interaction effect (MI)

Moreover, P c from the Euler theorem we can write G¼ N i¼1niμi. So, the Gibbs-Duhem (Eq. 2.1.9) equation can be given from Eqs. (2.1.7), (2.1.8):

Molecular interaction effect (MI)

Evolution of phase diagrams.

2.1.2.7 Activity Coefficient and Fugacity The fugacity is defined from the variation of the chemical potential (Eq. 2.1.10); the mixing-free enthalpy can then be expressed with the help of the fugacities (see Eq. 2.1.11):

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

20

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

dμi ¼ RTd ln fi   X fi M G ¼ RT Ni ln 0 f i i

(2.1.10) (2.1.11)

The quotient of the fugacities in a mixing and in the referential state is called “activity” and is given by Eq. (2.1.12). fi ai ¼ 0 fi

(2.1.12)

In 1923, Lewis defined the ideal solution with Eq. (2.1.13) (with T and P): fiid ¼ fi0 xi

(2.1.13)

where fi is the fugacity of compound i in the mixing, the exponent id the ideal mixing, and 0 the pure body. So, for an ideal mixing, the activity comes down to the molar fraction (Eq. 2.1.14). a i ¼ xi

(2.1.14)

The activity coefficient (γ i) allows us to measure the distance between a mixing and the ideality compared to an ideal mixing. Usually, it is suitable to choose γ i ¼ 1 when xi ! 1. Therefore, γi ¼ γ∞ i when xi ! 0. By developing Eq. (2.1.11), we can show the free-excess enthalpy in the expression of the mixing-free enthalpy (Eq. 2.1.15): X X Ni RT ln ai ¼ GE + Ni RT lnxi GM ¼ i

i

Gα +Gβ are the Gibbs free energy of the phases α and β, respectively. At equilibrium, the Gibbs free energy must be at the minimum, that is to say (dG ¼ 0) (Eq. 2.1.17): dG ¼ dGα + dGβ ¼

X i

μαi dnαi +

X

μβi dnβi ¼ 0

i

(2.1.17) In a closed system, we have dnβi ¼  dnαi for each component i between phases α and β. For each chemical species, we can write Eq. (2.1.18).     μαi P, T, nα1 , nα2 , …, nαNC ¼ μβi P, T, nβ1 , nβ2 , …, nβNC (2.1.18) The equilibrium conditions of a multiphase mixture are equality of temperature, pressure, and chemical potential μi of each component i in all the phases in equilibrium. Thermodynamic models are used to calculate chemical potentials. Several types of equations of states can be used to calculate the thermodynamic properties of gas.

2.1.3 EQUATIONS OF STATE In this section, three types of equations of state (EoS) will be presented: Fundamental EoS, cubic EoS, and molecular model.

(2.1.15) The activity coefficient is linked to the freeexcess enthalpy with Eq. (2.1.16): X GE ðT, P, xÞ ¼ xi RTLnðγ i Þ (2.1.16)

2.1.2.8 Equilibrium Conditions We consider a multicomponent system in equilibrium between two phases (α and β), at temperature T and pressure P. The Gibbs free energy of this system is G ¼ Gα +Gβ, where

2.1.3.1 Fundamental Equations of State It is well known from Helmholtz energy that all thermodynamic properties can be calculated. Table 2.1.4 presents the thermodynamic properties obtained from Helmholtz free energy A(T, v, n). 2.1.3.1.1 Pure Fluids Fundamental equations of state are explained in terms of reduced molar Helmholtz free energy (Eq. 2.1.19).

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

21

2.1.3 EQUATIONS OF STATE

TABLE 2.1.4

Properties Calculation From Helmholtz Free Energy

Property

Relation   ∂A μi ¼ ∂ni V , T, nj

Chemical potential

  ∂A P¼ ∂V T  ! ∂ A= U ¼ 1 T  ∂ =T V

Pressure Internal energy

H ¼ A + TS   ∂A S¼ ∂T V

Enthalpy Entropy

G ¼ A  pV   ∂H CP ¼ ∂T p

Gibbs energy Isobaric heat capacity Cp

  ∂U ∂T V

Isochoric heat capacity Cv

CV ¼

Fugacity coefficient

ln φ ¼ Z  1  ln Z + ART  res  ∂A ðT, V, nÞ res  RT lnZ + ART ln φi ¼ ∂ni T, v, nj

res

Partial molar fugacity coefficient of component i in mixture

AðTr , ρr Þ Aid ðTr , ρr Þ Ares ðTr , ρr Þ ¼ + RT RT RT id ¼ a ðTr , ρr Þ + ares ðTr , ρr Þ

(2.1.19)

id

concerns ideal gas contribution and res concerns residual contribution. ρr and Tr are the reduced variables. Tillner-Roth and Baehr (1994) have proposed an expression concerning the Helmholtz free energy model (Eq. 2.1.20). Temperature and density are expressed in the dimensionless variables δ ¼ ρρ and τ ¼ TTr .

For some fluids, it is more convenient to use a virial type equation for state (Eq. 2.1.21) such as the Benedict Webb Rubin (Benedict et al., 1949, Eq. 2.1.22) or the modified BWR (Eq. 2.1.23) equations of state. Z ¼ 1 + Bρ + Cρ2 + Dρ3 + …

(2.1.21)

P (Z ¼ ρRT )

Z is the compressibility factor and is equal to one for an ideal gas; B, C, and D are the second, third, and fourth virial coefficients respectively. vr is the reduced molar volume.

r

X X   AðTr , ρr Þ ¼ ln ðδÞ + αi τti + αk τtk δdk exp γδlk RT i k (2.1.20)

Eq. (2.1.20) contains several adjustable parameters (αi and αk) and several adjustable exponents (tk, dk, and lk). Data are required to adjust these parame6 0. ters. Moreover, if lk ¼ 0, γ ¼ 0 and γ ¼ 1 if lk ¼

BWR:

    B C D c4 γ γ Z ¼ 1 + + 2 + 5 + 3 2 β + 2 exp  2 vr vr v r T r v r vr vr (2.1.22)    with B ¼ b1  b2 Tr  b3 T2  b4 T3 , r r  C ¼ c1  c2 =Tr + c3 =Tr3 , and D ¼ d1 + d2 Tr .

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

22

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

mBWR: P¼

9 X

" αn ρn + exp

 # 15 ρ 2 X ρC

n¼1

MR n°1: αn ρ2n17

X

A0 ¼

n¼10

Eq. (2.1.22) contains several parameters (12) β, γ, bi, ci and dj (where i ¼ 1–4 and j ¼ 1–2). Eq. (2.1.23) also contains several adjustable parameters (αn). All parameters must be adjusted on experimental data (equilibrium properties or densities) using a specific algorithm (objective function to minimize, numerical methods). Using these equations of state, it is possible to calculate the Helmholtz free energy. Considering Eq. (2.1.19), the residual term can be calculated and is given in Eq. (2.1.24). ares ðT, vÞ ¼

1 RT



v¼∞

RT P v

X

C0 ¼

1

=2

E0 ¼

X



1

xi b i





1

xi d i

=3

i

dv

(2.1.24)

X

γ¼

T

1

xi γ i

=2

X

1

xi a i

=3

=3

1

xi c i

X

,α ¼

1

xi αi

1  R

ðT T0

cid p T

,

!2 ,

,

=3

!2 ,

i

!2

i

The determination of ideal term requires the calculation of the isobaric heat capacity (Eq. 2.1.25). hid sid ρT 1 aid ðT, vÞ ¼ 0  0  1 + ln + RT R ρ0 T0 RT

!2

!2

i

!2

=2

xi D0i

i

,c ¼

i

X

X

!2

=3

1

i

,a ¼

x i E0 i

i

X

, D0 ¼

!2

=2

x i B0 i ,

i

!2

xi C0i 1

X

,B0 ¼

xi A 0 i

i

X

!2

=2

i

(2.1.23)

ðv

1

(2.1.27) MR n°2:

ðT cid p dT T0

XX

A0 ¼

i

dT

B0 ¼

1



2.1.3.1.2 Mixtures Helmholtz free energy can also be split into ideal and residual terms (Eq. 2.1.26).

xi B0i , C0 ¼

A ð Tr , ρ r , x Þ ¼ a ð Tr , ρ r , x Þ RT ¼ aid ðTr , ρr , xÞ + ares ðTr , ρr , xÞ (2.1.26) For the mixture, one possibility is to directly use the previous equations of state, but mixing rules have to be considered. For example, with the BWR equations of state, the following mixing rules (MR) can be used (Eqs. 2.1.27, 2.1.28).

XX i

E0 ¼

1

1

1

xi a i

=3

i



X

1

xi c i

α¼

 1  kij ,

i

2

 2

=3

1

1

,b ¼

xi α i

 2

1



xi xj C0i C0j





2

2

3 1  lij ,

2

4 1  mij ,

5 1  nij ,

X

1

xi b i

=3

i

!2

=3

1

j

1

!2

i

X

i



xi xj E0i E0j

j

X

XX

xi xj D0i D0j

j

XX i



2

j

X

D0 ¼



xi xj A0i A0j

i

(2.1.25)

1

2

,d ¼

X

1

xi d i

=3

!2 , !2

i

!2 ,γ ¼

X

1

xi γ i

=2

, !2

i

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

(2.1.28)

23

2.1.3 EQUATIONS OF STATE

Generally, in order to have the best prediction of thermodynamic properties, it is useful to consider binary interaction parameters (kij, lij, mij, and nij). Also, the determination of these interaction parameters requires numerous experiments for the mixture (equilibrium properties and densities). The second possibility is to consider the multifluid approximation. This approach was introduced by Tillner-Roth (1993). It applies mixing rules to the Helmholtz free energy of the mixture components (Eq. 2.1.29).  X  id res x a ð T , ρ , x Þ + a ð T , ρ , x Þ aðTr , ρr , xÞ ¼ j r r r r j j j + xj lnxj +

X X

xp xq Fpq aEpq

(2.1.29)

p¼1 q¼p + 1

P P E Δares is called the pq ¼ p¼1 q¼p + 1 xp xq Fpq apq departure function from ideal solution. p and q are the component index. It is an empirical function fitted to experimental binary mixture data. In this departure function, the Fpq parameters take into account the behavior of one binary pair with another. If only vapor liquid equilibrium properties are available, aEpq is considered to be equal to zero (Mac Linden and Klein, 1996). With the multifluid approximation, it is important to calculate the new critical properties that correspond to the mixture studied as reducing parameters are used. Eqs. (2.1.30), (2.1.31) detail one type of mixing rule. TCmel ¼

XX

 0:5 kT, pq xp xq TCp TCq

(2.1.30)

p¼1 p¼1

VCmel ¼

XX p¼1 p¼1

kv, pq xp xq

1=3  1=3 3 1  VCp + VCq 8 (2.1.31)

kT, pq and kv, pq are adjustable parameters. Kunz and Wagner (2012) proposed different mixing rules (Eqs. 2.1.32, 2.1.33).

TCmel ¼

X

x2i TCi +

XX

2xp xq βTpq γ Tpq

p¼1 p¼1

i

0:5 xp + xq  TCp TCq 2 βTpq xp + xq VCmel ¼

X i

x2i VCi +

XX

(2.1.32) xp xq βvpq γ vpq

p¼1 p¼1

1=3  1=3 3 xp + xq 1   V + V Cp Cq β2vpq xp + xq 8

(2.1.33)

βT,pq, βv,pq, γ T,pq and γ v,pq are adjustable parameters. Using these different equations, the thermodynamic properties are calculated with a high degree of accuracy, particularly if the composition approaches a mole fraction of 1, as high accuracy equations of state for the components are used. The main disadvantage of this model is the number of parameters to be adjusted. So, the number of experimental data requires to fit them.

2.1.3.2 Cubic Equations of State The first tests done in the 19th century were related to the study of the gases. The first thermodynamic model that allowed us to understand the behavior of the gases is the model of the perfect gas (Eq. 2.1.34). Pv ¼ RT

(2.1.34)

The determination of this state equation is based on the kinetic theory whose assumptions are:    

The gas is assimilated to a monoatomic gas. Speed isotropy. Uniform molar density. No interaction between the molecules (the pressures are relatively low).

This model is similar to an EoS because it connects the various intensive variables (P, T, v). Unfortunately, it has a limited gas use. Later, Van der Waals (1873) attempted to take into account the interactions between molecules.

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24

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

Considering the repulsive and attractive forces, he proposed changing the kinetic pressure with (attractive a negative molecular pressure a v2 interactions between molecules, where a is the energy parameter). The expression of the molecular pressure results from the expression of the potential of interaction between the molecules. With the perfect gas equation, the volume becomes zero when the pressure gets very high. Therefore, he also took into consideration the repulsive interactions via the molar covolume b. The equation for the pure substance is given by Eq. (2.1.35):  a (2.1.35) P + 2 ðv  bÞ ¼ RT v where a is the attraction parameter (called energy parameter) and b the molar covolume. The determination of a and b is done at the critical point where (see Eq. 2.1.36):  2    ∂P ∂ P ¼ ¼0 (2.1.36) ∂v T ∂v2 T We then can find: a¼

27 R2 TC2 1 RT C PC v C ; b¼ ; ZC ¼ ¼ 0:375 RT C 64 PC 8 PC

This equation was the first to reveal the existence of a liquid-vapor phase transition and to report on the existence of a critical point. It represents the properties of the liquid phase less than those of the vapor phase. In order to better show the thermodynamic properties of the fluids (vapor tensions and volumes), other researchers have proposed to modify the Van der Waals equation (VdW). The cubic equations are only improvements of the VdW equation (more particularly of the expression of the molecular pressure that comprises the attractive parameter a). In 1949, Redlich and Kwong proposed a first modification. In 1972, Soave modified the expression of the attractive term and used a temperaturedependent function. Soave, Redlich, and Kwong’s equation (SRK), which applies for

apolar (or slightly polar) compounds, is given by Eq. (2.1.37):   aðT Þ ðv  bÞ ¼ RT (2.1.37) P+ ðv + bÞv The determination of the a and b parameters of this equation is done the same way we do for the Van Der Waals one at the critical point. R2 TC2 RT C ; Ωa ¼ 0:42748; b ¼ Ωb ; PC PC 1 Ωb ¼ 0:086640; Zc ¼ 3 a ¼ Ωa

This equation allows us to better correlate the experimental data in a wider field and to improve the representation of the critical zone. In 1976, Peng and Robinson proposed another modification of the attractive term. This equation is generally used for polar compounds (also used for hydrocarbons) and gives results that are closer to experimental results (mainly for volumetric properties) than those of the SRK equation. The expression of Peng and Robinson’s equation (PR) is given by Eq. (2.1.38):   aðT Þ ðv  bÞ ¼ RT (2.1.38) P+ 2 ðv + 2bv  b2 Þ As for a and b, we get: a ¼ Ωa

R2 TC2 RT C ; Ωa ¼ 0:47236; b ¼ Ωb ; PC PC Ωb ¼ 0:07780; ZC ¼ 0:3074

Other cubic EoS have been developed; we can cite Patel and Teja (1982), Trebble and Bishnoi (1987), and Coquelet et al. (2016). In 1986, Trebble and Bishnoi made a comparative study of the two cubic EoS (SRK and PR). Table 2.1.5 show the comparisons about the pressures and the liquid and vapor volumes in absolute relative mean value (ΔY ¼ j(Yexp  Ycal)/Yexp j). We can note that the SRK cubic equation does not allow us to make a very precise

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

25

2.1.3 EQUATIONS OF STATE

TABLE 2.1.5 Ranges on the Calculation of Vapor Pressures and of Liquid and Vapor Molar Volumes Authors

Δ(psat)/%

Δ(vliq)/%

Δ(vvap)/%

Soave (1972)

1.5

17.2

3.1

Peng and Robinson (1976)

1.3

8.2

2.7

calculation of the liquid volumes. The vapor pressures are generally well calculated because the researchers have developed alpha functions that make the attractive term a vary with temperature. In 1972, Soave added the following alpha function (Eqs. 2.1.39, 2.1.40) in order to improve the calculation of the vapor pressures (and of the liquid and vapor volumes). TR is the reduced temperature and ω the acentric factor: h  i2 1=2 αðT Þ ¼ 1 + m 1  TR (2.1.39) m ¼ 0:480 + 1:574ω  0:175ω2

(2.1.40)

Other alpha functions have been developed; we can cite Stryjek and Vera (1976), Mathias and Copeman (1983), Twu et al. (1995a,b), and Coquelet et al. (2004). Recently Jaubert and coworkers [Le Guennec et al. (2016, 2017)] proposed a new method to characterize alpha function and defined new parameters for the Twu et al. alpha function. 2.1.3.2.1 Mixing Rules The mixing rules must be able to take into account the ideal and nonideal characteristics of the solutions. With the two-parameter cubic equations, the objective is to calculate again the a and b parameters, considering the mutual influence of the various compounds. The first set of mixing rules is that of Van der Waals, which corresponds to what is commonly called “classical mixing rules.” Starting from the state equation, developing the virial about the volume and applying the statistical thermodynamics, we have Eq. (2.1.41):



XX i

xi xj aij

(2.1.41)

j

 P pffiffiffiffiffiffiffi where aij ¼ ai aj 1  kij ;b ¼ i xi bi kij is called the binary interaction parameter of the decoupling constant. This parameter must take into account the fact that the attractive interactions between compounds i and j are different from those between i and i and j and j. Several mixing rules have been developed. We will present two of them (Huron-Vidal and Wong-Sandler mixing rules). Their authors have taken into account models based on the calculation of the activity coefficient (excess-free enthalpy) and models by state equation. Indeed, the first ones are adapted to the low-pressure treatment of polar and/or nonpolar bodies while the state equations give satisfying results only for apolar bodies but without any pressure limitation. Thus, they have written (Eq. 2.1.42): gEγ ðT, P ! ∞Þ ¼ gEEoS ðT, P ! ∞Þ

(2.1.42)

and v ¼ b when P ! ∞. This mixing rule has been presented by Huron and Vidal (1979): ! X X  ai  E + gP¼∞  C ; b ¼ xi xi b i ; a¼b bi i i r1  r2  C¼  1  r1 Ln 1  r2 where r1 and r2 depend on the chosen state equation. Wong and Sandler (1992) have kept the classical mixing rules obtained with the development of the virial. However, as for the Huron-Vidal mixing rule, the equality of excess-free enthalpies, according to the processing with state equation and activity coefficient, allows us to obtain another relation between the attraction parameter a and the molar covolume b. Starting from that, we can also write from Helmholtz free energy (Eq. 2.1.43):

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

26

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

aEEOS ðT, P ! ∞, xÞ ¼ aEγ ðT, P ! ∞, xÞ

(2.1.43)

On the other hand, the authors have considered that the free energy depends less from the pressure than from the free enthalpy. Thus, they have written Eq. (2.1.44): aEγ ðT, P ! ∞, xÞ ¼ aEγ ðT, P ¼ 1 Bar, xÞ

(2.1.44)

In fact, the fundamental relation of the thermodynamics is written (Eq. 2.1.45): g ðT, P, xÞ ¼ a ðT, P, xÞ + Pv E

E

E

(2.1.45)

They have considered that, at low pressure, the PvE product is insignificant compared to aE. Consequently, they have obtained (Eq. 2.1.46): aEEOS ðT, P ! ∞, xÞ ¼ aEγ ðT, P ! ∞, xÞ ¼ aEγ ðT, P ¼ 1 Bar, xÞ (2.1.46) ¼ gEγ ðT, P ¼ 1 Bar, xÞ Thus, after having written the mixing-free energy, we come to Wong-Sandler’s mixing rule (see Eqs. 2.1.47, 2.1.48, and 2.1.49):  XX a  xi xj b  RT ij i j (2.1.47) b¼ 0X a i 1 xi bi gEγ ðT, P, xÞC B i C 1B @ RT + CRT A and

 the NRTL model: A local composition model based on the lattice theory.  the UNIQUAC model: Also based on the concept of local composition.  the UNIFAC model: a group contribution model. The gE can also be calculated by the Redlich and Kister (1948) form given by Eq. (2.1.50): gE ¼ x1 ð1  x1 Þ

2 X

ðRTGn ð2x1  1Þn Þ

where Gn(n ¼ 0–2) are the adjustable parameters. 2.1.3.2.3 NRTL Model (Nonrandom Two Liquids) Proposed in 1968 by Renon and Prausnitz, this model is based on mixing internal energy according to the local compositions. The expressions of the activity coefficients and of the free-excess enthalpy are given by Eqs. (2.1.51), (2.1.52), respectively: X τj, i Gj, i xj j

Lnðγ i Þ ¼ X

Gj, i xj

j

+

0

X

(2.1.48)

with

  a  1  a   a   1  kij b ¼ + b b RT ij 2 RT i RT j (2.1.49) 2.1.3.2.2 Activity Coefficient Models We need activity coefficient models to calculate Gibbs energy. For this reason, different models have been developed, called “activity coefficient models” or “GE models.” We can cite:

Gk, j τk, j xk

1

X Gi, j xj B C Bτi, j  kX C X @ A G x G x k, j k k, j k j k

 XX a a  b xi xj b  ¼ RT RT ij i j

(2.1.50)

n¼1

Ci , j ; τj, i ¼ RT

k



(2.1.51)  ; Ci, i ¼ 0 

C αj, i RTj, i

Gi, j ¼ Exp  Cj, i X X xj Exp αj, i RT   Cj, i (2.1.52) gE ¼ xi X Ck, i i j xk Exp αk, i RT k

with

We can notice that we have six parameters for a binary mixing αi, j and Ci, j which are likely to be adjusted from experimental data. Generally, the parameters αij are set (0.2 or 0.3 and even 0.5, which corresponds to mixture families). Other researchers have created the UNIQUAC model, which has fewer parameters.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

27

2.1.3 EQUATIONS OF STATE

2.1.3.2.4 The UNIQUAC Model (UNIversal QUAsi Chemical) Abrams and Prausnitz (1975) developed this model. As for the NRTL model, the UNIQUAC model is based on the concept of local composition. They have considered that each constituent could be decomposed into segments (parameter ri) and that the interactions depend on the external surface of the constituents (surface parameter qi). Thus, by writing the mixing internal energy, they have shown two excess-free enthalpies that take into account the interactions between the constituents (residual excess-free enthalpy) and size parameters (ri and qi) of each constituent (combinatory excess-free enthalpy). The expressions of the activity coefficients are given by Eqs. (2.1.53, 2.1.54, and 2.1.55): Lnðγ i Þ ¼ Lnðγ i Þcombinatory + Lnðγ i Þ Residual (2.1.53) with Lnðγ i Þ

Combinatory

    Φi z Θi + qi Ln + li ¼ Ln xi Φi 2 Φi X  xj lj xi j (2.1.54)

where

li ¼ ðri  qi Þ 2z  ðri  1Þ; Θi ¼ Xi

x qi

Moreover,

xj qj

xi ri ; Φi ¼ X ; z ¼ 10 x j rj

j

2

j

0

3

1

X Θj τij 7 X 6 7 @ X Lnðγ i Þ Residual ¼ qi 6 Θj τji A  5 41  Ln Θk τkj j j k

(2.1.55)

The expression of the excess-free enthalpy is given by Eqs. (2.1.56), (2.1.57), and (2.1.58): g ¼g E

E,combinatory

gE, combinatory ¼ RT

"

X i

+g 

xi Ln

E, residual

(2.1.56)

  Φi zX Θi xi qi Ln + xi Φi 2 i

#

0 0 11 X X E, residual g ¼ RT @ qi xi Ln@ Θj τji AA (2.1.58) i

j

Thus, the UNIQUAC model requires knowledge of only two parameters for each binary. The volume and surface parameters (Van der Waals surface and volume) have been determined from the volumes and the surfaces of the molecules. Despite everything, if we do not have any experimental data, we cannot make predictive calculations. From the UNIQUAC model, the researchers have developed predictive models based on the contributions from groups. One of the first predictive models is the UNIFAC model. 2.1.3.2.5 The UNIFAC Model (UNIquac Fonctional Group Activity Coefficient) The UNIFAC model was proposed by Fredenslund et al. in 1975. Its principle is founded on that of the UNIQUAC model, that is to say the excess-free enthalpy can be decomposed into two free enthalpies, combinatory and residual. However, the authors have taken into account interactions between groups instead of taking into account interactions between constituents, knowing that a constituent is an assembly of these groups. Thus, in the framework of a binary, for example, we must not consider a two-compound solution anymore but a group solution. The whole difficulty is in the UNIFAC decomposition of the molecule. The values of the binary interaction parameters are generally available in the literature and they are constantly updated. The expression of the residual activity coefficient is Eqs. (2.1.59, 2.1.60, and 2.1.61):  i   X ðiÞ h ðiÞ ¼ υ Ln ð Γ Þ  Ln Γk Ln γ residual k i k k

(2.1.59) 3

2

! X X Θm Ψkm 7 6 X LnðΓk Þ ¼ Qk 41  Ln Θm Ψmk  5 Θn Ψnm m m

(2.1.57) 2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

n

(2.1.60)

28

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

where: Xm Qm Θm ¼ X Xn Qn

(2.1.61)

n

and Xm is the molar fraction of the group in the mixing and υkis the number of k under-groups present in the mixing.  a  mn Ψmn ¼ Exp  (2.1.62) T where amn is the interaction parameter between the various undergroups. As for the combinatory term, ri and qi are calculated by simple additivity rules: X X ri ¼ υm, i Rm ;qi ¼ υm, i Qm m

m

where Rm and Qm are the volume and surface parameters of each undergroup.

2.1.3.3 Molecular Model Based on Wertheim’s (1984) statistical theory of associative fluids, Chapman et al. (1989, 1990) developed the first EoS SAFT (Statistical Associating Fluid Theory) called SAFT-0. Many versions exist today, such as LJ-SAFT (1994), SAFT-VR (1997), Soft-SAFT (1997), PC-SAFT (2001), etc. The various versions differ mainly in the choice of the reference fluid, the radial

Segment of hard spheres

distribution function, and explicit expressions of the terms of disruption. The PC-SAFT (Gross and Sadowski, 2001, Perturbed-Chain Statistical Associating Fluid Theory) EoS will be presented in this section. Each molecule is considered as a chain of spherical segments that is not inevitably identified as an atom. The u(r) interaction potential between the segments of a chain corresponds to a modification of the potential of square wells (proposed by Chen and Kreglewski, 1977) (Eq. 2.1.63). 8 ∞ r < ð σ  s1 Þ > > > < 3ε ðσ  s1 Þ  r < σ (2.1.63) uðrÞ > ε σ  r < λσ > > : 0 r  λσ where r is the distance between two segments, σ the diameter of the segment, ε the depth of the potential trough, and λ the reduced width of the well (s1 ¼ 0.12σ). The compressibility factor is the total of the three terms (Eq. 2.1.64). Z ¼ 1 + Zseg + Zchain + Zasso

The first term takes into account the repulsive and attractive interactions. Fig. 2.1.7 shows the PC-SAFT different contributions. The repulsive interactions are studied with a hard sphere model. The Boublik (1970) and Association

Polarity Dispersion

Chain’s formation

FIG. 2.1.7

(2.1.64)

Illustration of the various PC-SAFT contributions. 2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

29

2.1.3 EQUATIONS OF STATE

Mansoori et al. (1971) expressions are used (Eqs. 2.1.65, 2.1.66); Zseg ¼ mZhc + Zdisp

(2.1.65)

ξ 3ξ1 ξ2 3ξ32  ξ3 ξ32 + (2.1.66) Z ¼ 3 + 1  ξ3 ξ0 ð1  ξ3 Þ2 ξ0 ð1  ξ3 Þ3 P where ξn ¼ π6 ρ i xi mi dni and d is the collision diameter corresponding to a chain segment while m is the number of segments for each chain. The chain term is calculated with the help of Eq. (2.1.67): hc

Z

chain

¼

X i

∂ ln ghc ii xi ðmi  1Þρ ∂ρ

(2.1.67)

ghc ii is the function of radial distribution for the segments of the compound i in a system of hard spheres. As for the dispersive part, Barker and Henderson’s (1967) theory is used while taking as a reference the chain of hard sphere segments. The dispersive interactions are only a disturbance in the reference state. They are applied to molecules having several segment chains. This allows the PC-SAFT model to be used for the study of the polymers. We have Eq. (2.1.68): Adisp A1 A2 ¼ + NkT NkT NkT

(2.1.68)

where A1 and A2 are the first and second range contributions, k Boltzmann’s constant. They are determined from the following relations (Eqs. 2.1.69, 2.1.70), which can be applied to any interaction potential.   ∞   ð A1 σ 2 ε eðxÞghc m; x x2 dx σ3 u ¼ 2πρm kT d NkT

  eðxÞghc m; x σd x2 dx eðxÞ ¼ uðεxÞ; I1 ¼ u with x ¼ σr , u 1 " # ∞   Ð ∂ hc σ 2 eðxÞg m; x d x dx . and I2 ¼ ∂ρ u Ð∞

1

ghc is the distribution function allowing us to know the number of molecules in a certain volume element. In the PC-SAFT theory, I1 and I2 can be estimated from weighted sums. Finally, the compressibility factor of the dispersive part is written by Eq. (2.1.71): ∂ðηI1 Þ 2 3 m εσ ∂η

∂ðηI2 Þ  πρm C1 + C2 ηI2 m2 ε2 σ 3 (2.1.71) ∂η  1 ∂Zhc hc 1 2 3 with C1 ¼ 1 + Z + ρ ; C2 ¼ ∂C ∂η ; m εσ ∂ρ ε  XX ij ¼ xi xj mi mj σ 3ij m2 ε2 σ 3 kT i j  ε 2 XX ij ¼ xi xj m i m j σ 3ij : kT i j Zdisp ¼ 2πρ

The associative term is directly deduced from Wertheim’s expressions. If we take into account two spherical segments having an association site A, the associative bond can occur only when the distance and orientation are favorable. The association is modeled by a square well interaction potential centered on site A. Two parameters are required: parameter εasso, which corresponds to the depth of the well, and parameter κ asso, which characterizes the association volume (linked to the range of the interaction). These parameters allow us to calculate XA, a molar part of the molecules that is not associated with site A.

1

(2.1.69)  1 A2 ∂Zhc ¼ πρm 1 + Zhc + ρ NkT ∂ρ 3 2 ∞   ð σ 7 6 eðxÞghc m; x x2 dx5 ∂4 u d  2 ε 1 m2 σ3 ∂ρ kT

Z

asso

¼

X i

2

3 "

# X X ∂XAj  1 xi 4 ρj  0:5 5 ∂ρi T, ρk6¼i XAj A j j

(2.1.72) (2.1.70)

This model allows us to calculate, for each kind of associative molecule, the thermodynamic properties. Parameters of binary interactions

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

30

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

allowing us to calculate m2 εσ 3 and m2 ε2 σ 3 can be adjusted from experimental data.

2.1.4 GAS SOLUBILITY The solubility of a gas in a liquid is often proportional to its partial pressure in the gas phase. The equation that describes this observation is commonly known as Henry’s law. At high pressure, the effect of the pressure is not negligible and it is necessary to consider how Henry’s constant depends on pressure. In 1935, Krichevsky and Kasarnovsky showed how to explain the correct Henry’s law (H) (Eq. 2.1.73).  V     f ðT, P, yH2 O Þ ¼ ln H T, Psat ln solute solvent xsolute v∞ + solute Psolute RT (2.1.73) v∞ solute is the molar volume at infinite dilution of the solute. It can be obtained with Eq. (2.1.74):  2 3 ∂P 6 ∂nsolute 7 6   T, V, nsolvent 7 v∞ ¼  (2.1.74) 6 7 solute 4 ∂P 5 ∂v T, nsolute , nsolvent n ¼0 solute

It is common to estimate the solubility of a species in a solvent mixture by using the solubility of the same species in each of the pure solvents that comprises the mixture. The global Henry’s coefficient is determined by using a relation that includes each Henry’s coefficient. The unsymmetrical normalized activity coefficient and Gibbs’ energy are used to determine the following relation (Prausnitz et al., 1999) (for this example a ternary mixture is used with the solvent, composed of 1 and 3, and the solute, 2) (Eq. 2.1.75): lnðH2, mixture Þ ¼ x1 lnðH2,1 Þ + x3 lnðH2,3 Þ  a13 x1 x3 (2.1.75)

a13 is a parameter that can be estimated from the vapor–liquid equilibrium data for the solvent mixture. Consequently, it is sometimes customary to define an excess Henry’s constant E (Eq. 2.1.76): Hi,mixture m X  E    xj ln Hi, j ¼ lnðHi, mixture Þ  ln Hi,mixture j¼1

(2.1.76) Concerning the Henry’s law constant at solvent vapor pressure, it is necessary to consider a temperature dependency. Several correlations can be found in the open literature (see Carroll, 1999). For example, an exponential expression (Eq. 2.1.77) can be considered. It is inspired from the expression used by Yaws et al. (1990) or the Design Institute for Physical Properties (DIPPR) equation n°101, which was obtained from Dauber et al. (2000)   B ln Hicor ¼ A + + ClnðTÞ + DT T

(2.1.77)

Harvey also proposed another correlation to estimate Henry’s law constant coefficient in a large range of temperature for pure water (Eq. 2.1.78)     Harvey ¼ ln Psat ln Hi water +

A Bð1  Tr Þ0:355 + + Ceð1Tr Þ Tr0:41 Tr Tr (2.1.78)

In 1999, Yaws et al. (1999) proposed a correlation to predict the Henry’s law constant at atmospheric pressure (Eq. 2.1.79). Parameters for CO2, N2, and SO2 are presented in Table 2.1.6. Fig. 2.1.8 presents the evolution of the Henry’s law constant as a function of temperature for the three molecules.   B log HiYaws ¼ A + + ClogðT Þ + DT T

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

(2.1.79)

31

2.1.5 APPLICATION TO INDUSTRIAL FLUIDS

TABLE 2.1.6 mol Fraction

Henry’s Law Constant for CO2, N2, and SO2 in Pure Water According to Yaws et al. (1999), Hi is in atm/

Name

A

B

C

D

Tmin /K

Tmax/ K

Carbon dioxide

69.4237

3796.46

21.6694

0.000478857

273.15

353.15

Nitrogen

78.8622

3744.98

24.7981

0

273.15

350.15

Sulfur dioxide

22.3423

1987.11

5.6854

0

283.15

323.15

FIG. 2.1.8

Evolution of Henry’s law constant of CO2, N2, and SO2 as a function of temperature.

2.1.5 APPLICATION TO INDUSTRIAL FLUIDS In the following section, three phase diagrams (Pressure versus Temperature, Pressure versus Density and Pressure versus Enthalpy) of some gases used in the food industry (CO2, N2, O3 and SO2) and their uses (Girardon, 2004) will be presented. In order to illustrate the application of thermodynamic to the representation of equilibrium properties of mixtures, two binary systems have been investigated. The first one concerns the binary system CO2 + water and the second one concerns the binary system CO2 + ethanol.

2.1.5.1 CO2 Carbon dioxide is used in food processing, preservation, and packaging. Its main applications are the carbonation of soft drinks and the monitoring of temperatures in deep freezing and transport (due to its ability to be stored in snow or ice forms). Figs. 2.1.9 and 2.1.10 present two phase diagrams of pure CO2. A fundamental EoS is used (REFPROP v10.0 software from the National Institute of Standards and Technology). Fig. 2.1.11 gives the pressure enthalpy phase diagram. Its critical properties are 304.13 K and 73.77 bar.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

32

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

8.0 7.0

Pressure/MPa

6.0 5.0 4.0 3.0 2.0 1.0 0.0 225

FIG. 2.1.9

235

245

255

265 275 Temperature /K

285

295

305

Pressure temperature phase diagram of CO2.

9.0 8.0 7.0

Pressure/MPa

6.0 5.0 4.0 3.0 2.0 1.0 0.0 0

5

10

15

20

25

30

Density/mol.dm–3

FIG. 2.1.10

Pressure density phase diagram of CO2. At 243.3, 304.13 and 310.21 K.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

33

2.1.5 APPLICATION TO INDUSTRIAL FLUIDS

8.0

7.0

6.0

Pressure/MPa

5.0

4.0

3.0

2.0

1.0

0.0 0

5000

10000

15000

20000

25000

Enthalpy/Jmol–1

FIG. 2.1.11

Pressure enthalpy phase diagram of CO2 at 243.3, 304.13 and 310.21 K. Reference: h ¼ 0 at ¼0 K.

2.1.5.2 N2 Nitrogen is proving to be a beneficial ingredient for the prepared foods sector, with a range of creative applications that includes freezing, packaging, mixing, coating, and grinding. Nitrogen can be used to process a wide variety of foods including fruits, vegetables, pasta, dairy products, baked goods, and prepared meals. Figs. 2.1.12 and 2.1.13 present two phase diagrams of pure nitrogen. A fundamental equation of state is used (REFPROP v10.0). Fig. 2.1.14 gives the pressure enthalpy phase diagram. Its critical properties are 126.19 K and 33.96 bar.

2.1.5.3 O3 Ozone is particularly suited to the food industry because of its ability to disinfect microorganisms without adding additional chemicals to the

treated food, or to the water used or the atmosphere in which the food is stored. Figs. 2.1.15 and 2.1.16 present two phase diagrams of pure SO2. A cubic equation of state (Peng Robinson Equation of state implemented in Simulis Thermodynamics software from Prosim, France) is used. Fig. 2.1.17 gives the pressure enthalpy phase diagram. Its critical properties are 261 K and 55.7 bar.

2.1.5.4 SO2 Sulfur dioxide is the most widely used additive in winemaking. It is also used as an additive in the food industry in general (dry fruits, mustard, prepackaged food preparation, shellfish, cereals). Its main functions are to inhibit or kill unwanted yeasts and bacteria, and to protect wine from oxidation. Figs. 2.1.18 and 2.1.19

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

4.0

3.5

Pressure/MPa

3.0

2.5

2.0

1.5

1.0

0.5

0.0 60

FIG. 2.1.12

70

80

90 100 Temperature/K

110

120

130

Pressure temperature phase diagram of N2.

8.0

7.0

6.0

Pressure/MPa

5.0

4.0

3.0

2.0

1.0

0.0 0

FIG. 2.1.13

5

10

20 15 Density/mol.dm–3

25

30

35

Pressure density phase diagram of N2 at 88.33, 126.19 and 128.72 K.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

8.0

7.0

6.0

Pressure/MPa

5.0

4.0

3.0

2.0

1.0

0.0 –5000 –4000 –3000 –2000 –1000

0

1000

2000

3000

4000

5000

Enthalpy/Jmol–1

FIG. 2.1.14

Pressure enthalpy phase diagram of N2 at 88.33, 126.19 and 128.72 K. Reference: h ¼ 0 at ¼0 K.

6.0

5.0

Pressure/MPa

4.0

3.0

2.0

1.0

0.0 190

200

210

220

230

240

250

260

270

280

Temperature/K

FIG. 2.1.15

Pressure temperature phase diagram of O3.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

8.0

7.0

Pressure/MPa

6.0

5.0

4.0

3.0

2.0

1.0

0.0

FIG. 2.1.16

0

5000

10000

15000 20000 Density/mol.dm–3

25000

30000

Pressure density phase diagram of O3 at 208.80, 261 and 266.22 K.

8.0

7.0

Pressure/MPa

6.0

5.0

4.0

3.0

2.0

1.0

0.0 –25000

–20000

–15000

–10000

–5000

0

Enthalpy/Jmol–1

FIG. 2.1.17

Pressure enthalpy phase diagram of O3 at 208.80, 261 and 266.22 K. Reference: h ¼ 0 at T ¼ 298.15 K, ideal gas.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

9.0 8.0 7.0

Pressure/MPa

6.0 5.0 4.0 3.0 2.0 1.0 0.0 200

250

300

350

400

450

Temperature/K

FIG. 2.1.18

Pressure temperature phase diagram of SO2.

10.0 9.0 8.0

Pressure/MPa

7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0

0

5

10

15

20

25

30

Density/mol.dm–3

FIG. 2.1.19

Pressure density phase diagram of SO2 at 301.45, 430.64 and 439.25 K.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

38

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

10.0 9.0 8.0

Pressure/MPa

7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 –10000 –5000

FIG. 2.1.20

0

5000

10000 15000 20000 25000 30000 35000 Enthalpy/Jmol–1

Pressure enthalpy phase diagram of SO2 at 301.45, 430.64 and 439.25 K. Reference: h ¼ 0 at ¼0 K.

present two phase diagrams of pure SO2. A fundamental equation of state is used (REFPROP v10.0). Fig. 2.1.20 gives the pressure enthalpy phase diagram. Its critical properties are 430.64 K and 78.84 bar.

2.1.5.5 Binary Systems 2.1.5.5.1 CO2-H2O Fig. 2.1.21 presents the phase diagram at 298.28 K. The CO2 + water binary system is classified as type II according to Van Konynenburg and Scott (1980). The Peng Robinson equation of state associated with the modified Huron Vidal Mixing rules and NRTL activity coefficient model is used to correlate the experimental data. Experimental data are from Nakayama et al. (1987) and Valtz et al. (2004). As we can see, the solubility of CO2 is perfectly predicted but not the water content in the liquid-liquid region.

2.1.5.5.2 CO2-C2H5OH Fig. 2.1.22 presents the phase diagram of the CO2 + ethanol binary system at 293.15 K. The same equation of state was used. Experimental data are from Secuianu et al. (2008). As we can see, the model is in good agreement with the experimental data and so the ethanol content can be easily predicted.

2.1.6 CONCLUSION Throughout this chapter, we presented the fundamentals aspects in fluid thermodynamics (molecular interactions, chemical potential, and equilibrium conditions) and various thermodynamic models (fundamental EoS, cubic EoS, and molecular model). These models are at the heart of all developments and optimization of industrial processes and energetic

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

39

10,000

10,000

9000

9000

8000

8000

Pressure/kPa

Pressure/KPa

REFERENCES

7000 6000 5000 4000 3000 2000

7000 6000 5000 4000 3000 2000

1000

1000

0 0

0.2

0.4

0.6

0

0.8

1

0.98

0.985

0.99

(B)

X1, Y1

(A)

0.995

1

X1, Y1

FIG. 2.1.21 Vapor liquid equilibrium of CO2 (1) + Water (2) binary system at 298.28 K. (A) complete phase diagram; (B) zoom around pure CO2 vapor pressure. (Δ): Valtz et al., (◊): Nakayama et al., solid line: Peng Robinson equation of state prediction.

7000 6000

Pressure/kPa

5000 4000 3000 2000 1000 0

0

0.2

0.4

0.6

0.8

1

X1, Y1

FIG. 2.1.22

Vapor liquid equilibrium properties of the CO2 (1) + Ethanol (2) binary system at 293.15 K. (Δ): Secuianu et al. (2008), solid line: Peng Robinson equation of state prediction.

efficiency. Phase diagrams help to define the best process and to show how one can articulate the unit operations according to the temperature, pressure, and composition conditions. The study of the phase diagrams also helps to understand the physicochemical phenomena in order to improve the functioning of the separation units: knowledge of the molecular aspects helps in the development of tomorrow’s processes.

References Abrams, D.S., Prausnitz, J.M., 1975. Statistical thermodynamics of liquid mixtures: a new expression for the excess Gibbs energy of partly or completely miscible systems. AICHE J. 21, 116–128. Barker, J.A., Henderson, D., 1967. Perturbation theory and equation of state for fluids: the square-well potential. J. Chem. Phys. 47 (8), 2856–2861. Benedict, M., Webb, G.B., Rubin, L.C., 1949. An empirical equation for thermodynamic properties of light hydrocarbons and their mixtures. J. Chem. Phys. 8, 334–344.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

40

2.1. PHYSICOCHEMICAL PROPERTIES OF GAS

Boublik, T., 1970. Hard sphere equation of state. J. Chem. Phys. 53, 471–478. Carroll, J.J., 1999. Henry’s law revisited. Chem. Eng. Progr. 95, 49–56. Chapman, W.G., Gubbins, K.E., Jackson, G., Radosz, M., 1989. SAFT: equation-of-state solution model for associating fluids. Fluid Phase Equilib. 52, 31–38. Chapman, W.G., Gubbins, K.E., Jackson, G., Radosz, M., 1990. New reference equation of state for associating liquids. Ind. Eng. Chem. Res. 29 (8), 1709–1721. Chen, S.S., Kreglewski, A., 1977. Applications of the augmented van der Waals theory of fluids. I. Pure fluids. Ber. Bunsen-Ges. 81, 1048–1052. Coquelet, C., Chapoy, A., Richon, D., 2004. Development of a new alpha function for the Peng–Robinson equation of state: comparative study of alpha function models for pure gases (natural gas components) and water-gas systems. Int. J. Thermophys. 25 (1), 133–158. Coquelet, C., El Abbadi, J., Houriez, C., 2016. Prediction of thermodynamic properties of refrigerant fluids with a new three-parameter cubic equation of state. Int. J. Refrig. 69, 418–436. Dauber, T.E., Danner, R.P., Sibu, H.M.I., Stebbins, C.C., Oscarson, J.L., 2000. Physical and Thermodynamic Properties of Pure Chemicals. DIPPR, Taylor & Francis. Girardon, P., 2004. Utilisation des gaz industriels en agroalimentaire. Techniques de l’ingenieur. Agroalimentaire 2, 1–22. F1275. Gross, J., Sadowski, G., 2001. Perturbed-chain SAFT: An equation of state based on perturbation theory for chain molecules. Ind. Eng. Chem. Res. 40, 1244–1260. Huron, M.J., Vidal, J., 1979. New mixing rules in simple equations of state for representing vapour-liquid equilibria of strongly non ideal mixtures. Fluid Phase Equilib. 3, 255–271. Kontogeorgis, G.M., Folas, G.K., 2010. Thermodynamic Models for Industrial Applications: From Classical and Advanced Mixing Rules to Association Theories. Wiley, Chichester, UK. Kunz, O., Wagner, W., 2012. The GERG-2008 wide range equation of state for natural gases and other mixtures: an expansion of GERG-2004. J. Chem. Eng. Data 57, 3032–3091. Le Guennec, Y., Lasala, S., Privat, R., Jaubert, J.N., 2016. A consistency test for α-functions of cubic equations of state. Fluid Phase Equilib. 427, 513–538. Le Guennec, Y., Privat, R., Lasala, S., Jaubert, J.N., 2017. On the imperative need to use a consistent α-function for the prediction of pure-compound supercritical properties with a cubic equation of state. Fluid Phase Equilib. 445, 45–53. Mac Linden, M.O., Klein, S.A., 1996. A next generation refrigerant properties database. In: International Refrigeration and Air Conditioning Conference Paper 357, pp. 409–414.

Mansoori, G.A., Carnahan, N.F., Starling, K.E., Leland, T.W., 1971. Equilibrium thermodynamics properties of the mixture of hard spheres. J. Chem. Phys. 54, 1523. Mathias, P.M., Copeman, T.W., 1983. Extension of the Peng Robinson equation of state to complex mixtures: evaluation of the various forms of the local composition concept. Fluid Phase Equilib. 13, 91–108. Nakayama, T., Sagara, H., Arai, K., Saito, S., 1987. High pressure liquid-liquid equilibria for the system of water, ethanol and 1,1-difluoroethane at 323.2 K. Fluid Phase Equilib. 38, 109–127. Patel, N.C., Teja, A.S., 1982. A new cubic equation of state for fluids and fluid mixtures. Chem. Eng. Sci. 37, 463–473. Peng, D.Y., Robinson, D.B., 1976. A new two parameters equation of state. Ind. Eng. Chem. Fundam. 15, 59–64. Prausnitz, J.M., Lichtenthaler, R.N., Gomes de Azevedo, E., 1999. Molecular Thermodynamics of Fluid-Phase Equilibria. Prentice Hall PTR, New Jersey. ISBN: 0-13977745-8. Redlich, O., Kister, A.T., 1948. Thermodynamics of nonelectrolyte solutions – x-y-t relations in a binary system. Ind. Eng. Chem. 40 (2), 341–345. Secuianu, C., Feroiu, V., Geancentsa, D., 2008. Phase behavior for carbon dioxide + ethanol system: experimental measurements and modeling with a cubic equation of state. J. Supercrit. Fluids 47, 109–116. Soave, G., 1972. Equilibrium constants for modified RedlichKwong equation of state. Chem. Eng. Sci. 4, 1197–1203. Stryjek, R., Vera, J.H., 1976. PRSV: an improved PengRobinson equation of state for pure compounds and mixtures. Can. J. Chem. Fundam. 15, 59–64. Tillner-Roth R., 1993 PhD. University of Hannover, Germany. Tillner-Roth, R., Baehr, H.D., 1994. J. Phys. Chem. Ref. Data 23, 657–729. Trebble, M.A., Bishnoi, P.R., 1987. Development of a new four-parameter equation of state. Fluid Phase Equilib. 35, 1–18. Twu, C.H., Coon, J.E., Cunningham, J.R., 1995a. A new generalized alpha function for a cubic equation of state. Part 1. Peng Robinson equation. Fluid Phase Equilib. 105, 49–59. Twu, C.H., Coon, J.E., Cunningham, J.R., 1995b. A new generalized alpha function for a cubic equation of state. Part 2. Redlich-Kwong equation. Fluid Phase Equilib. 105, 61–69. Valtz, A., Chapoy, A., Coquelet, C., Paricaud, P., Richon, D., 2004. Vapour-liquid equilibria in the carbon dioxidewater system, measurement and modelling from 278.2 to 318.2K. Fluid Phase Equilib. 226, 333–344. Van der Waals, J.D., 1873. Over de Continuiteit van den € Gas- en Vloestoftoestand. (Uber die Kontinuitt€at des Gas- und Fl€ ussigkeitszustands). Dissertation, Universit€at Leiden, Niederlande, deutsche € Ubersetzung, Leipzig.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

FURTHER READING

Van Konynenburg, P.H., Scott, R.L., 1980. Critical lines and phase equilibria in binary van der Waals mixtures. Philos. Trans. R. Soc. 298, 495. Wertheim, M.S., 1984. Fluids with highly directional attractive forces. I. Statistical thermodynamics. J. Stat. Phys. 35, 19–34. Wong, D.S.H., Sandler, S.I., 1992. A theoretically correct mixing rule for cubic equation of state. AIChE 38, 671–680. Yaws, C.L., Hopper, J.R., Wang, X., Rathinsamy, A.K., Pike, R.W., Hansen, K.C., 1999. Calculating solubility and Henry’s law constant for gases in water. Chem. Eng., 102–105. Yaws, C.L., Yang, H.C., Hopper, J.R., Hansen, K.C., 1990. Organic chemicals: 168 water solubility data; keep these values at your fingertips for engineering and environmental impact studies. Chem. Eng., 115–118.

Further Reading Blas, F.J., Vega, L.F., 1997. Thermodynamic behaviour of Homonuclear and Heteronuclear Lennard-Jones chains

41

with association sites from simulation and theory. Mol. Phys. 92 (1), 135–150. Fredenslund, A., Jones, R.L., Prausnitz, J.M., 1975. Group contribution estimation of activity coefficients in non ideal-liquid mixtures. AICHE J. 21, 1086–1099. Gil-Villegas, A., Galindo, A., Whitehead, P.J., Mills, S.J., Jackson, G., Burgess, A.N., 1997. Statistical associating fluid theory for chain molecules with attractive potentials of variable range. J. Chem. Phys. 106 (10), 4168–4186. Krichevsky, I.R., Kasarnovsky, J.S., 1935. Thermodynamical calculations of solubilities of nitrogen and hydrogen in water at high pressures. J. Am. Chem. Soc. 57, 2168–2171. Redlich, O., Kwong, J.N.S., 1949. On the thermodynamics of solutions. V. An equation of state. Fugacities of gaseous solutions. Chem. Rev. 44, 233–244. Renon, H., Prausnitz, J.M., 1968. Local composition in thermodynamic excess function for liquid mixtures. AICHE J. 14, 135–144. Trebble, M.A., Bishnoi, P.R., 1986. Accuracy and consistency comparison of ten cubic equations of state for polar and non polar compounds. Fluid Phase Equilib. 29, 465–474.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

C H A P T E R

2.2

Industrial Gas Manufacturing, Cylinder Filling, Bulk Installations, Piping, Relief Devices, and Security David Brian Burgener*,† †

*CO2 & N2O, Air Liquide, Countryside, IL, United States CO2 & N2O, Consulting Service Inc., Elmhurst, IL, United States

2.2.1 GAS PRODUCTION

as a cryogenic liquid to a customer bulk tank. Bulk liquid nitrogen can be consumed either for freezing or vaporized as a compressed gas. A cryogenic gas plant will manufacture nitrogen, oxygen, and argon at capacities ranging from 50 to 1000+ tons/day. Fig. 2.2.1 shows the schematic of a typical ASU. The process starts with a large air compressor that pressurizes the air to 6.75bar (98 psi). The air is then cooled and dried to remove the moisture and carbon dioxide, which would freeze inside the distillation column. The cold air condenses by passing through a large heat exchanger with the outgoing cold gases to form liquid air at 173°C ( 279°F). The distillation column is a tall, highly specialized process that consists of a medium-pressure lower column and a low-pressure upper column. The liquid air is distilled into pure nitrogen in the top of the mediumpressure column. The oxygen is purified in the upper low-pressure column. Argon concentrate at 10% is either vented or sent to an external

Food gases are generally produced remotely and delivered to the customer as a bulk liquid, compressed gas, or solid, as in the case of carbon dioxide “dry ice.” In some special instances, gases may be manufactured onsite for direct delivery to the customer piping system. This includes the use of porous membranes and pressure swing adsorption for the production of nitrogen. Large nitrogen gas users can have onsite cryogenically assisted distillation of compressed air. Large hydrogen customers my manufacture onsite using the cracking of methane gas using the methane-water shift reaction.

2.2.1.1 Cryogenic Production of Nitrogen, Oxygen, and Argon at an ASU Gases such as oxygen, nitrogen, and argon are manufactured by cryogenic distillation in large air separation plants (ASUs), and are then delivered

Gases in Agro-food Processes https://doi.org/10.1016/B978-0-12-812465-9.00005-0

43

# 2019 Elsevier Inc. All rights reserved.

44

2.2. INDUSTRIAL GAS MANUFACTURING, CYLINDER FILLING, BULK INSTALLATIONS, PIPING, RELIEF DEVICES, & SECURITY

FIG. 2.2.1

Typical air separation manufacturing process.

purifier. The medium pressure nitrogen exits the column and is passed through a turboexpander, which produces additional cooling that helps condense the incoming air in the heat exchanger (see Chapter 10). The pure gases exit the column and proceed to a liquefier where pure nitrogen liquid (LIN) or pure oxygen liquid (LOX) and pure argon liquid (LAR) is manufactured and stored to be loaded into vacuum-insulated tanker trucks for delivery to bulk customer tanks.

2.2.1.2 Compressed Liquified Gases— (Carbon Dioxide and Nitrous Oxide) 2.2.1.2.1 Carbon Dioxide Manufacturing Carbon dioxide (CO2) is typically created as a byproduct of other manufacturing processes such as the manufacture of ammonia, ethanol

for fuel, and refinery hydrogen production. The raw gas typically enters the CO2 plant at low pressure with a purity of 99 + % saturated with water. The manufacturing steps for CO2 vary based upon the impurities in the incoming raw source. See Fig. 2.2.2 for a typical plant process schematic. The following steps are a typical plant process: • Removal of condensed water or liquids. • Two-stage compression to approximately 300 psig (20.7 bar). • Removal of impurities based upon the raw gas source. This can include sulfur, air, alcohols, and hydrocarbons. The steps used could include distillation columns, carbon adsorption, and catalytic oxidation of residual hydrocarbons (not shown).

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

45

2.2.1 GAS PRODUCTION

Vent Noncondensibles

LCO2 storage 230psi (15.6Bar)

CO2 condenser

Distillation column

Activated carbon

Sulfur removal

Dryer

NH3 refrigeration Cooling water

NH3 chilling

NH3 chilling

Raw CO2 (99%) Cooling water

Cooling water Water Removal

1st Stage compression

FIG. 2.2.2

2nd Stage compression

Typical carbon dioxide manufacturing process.

• The gas is dried to a dew point of approximately 80°F ( 62°C). • Activated carbon removes odors and residual impurities. • Condensed to a liquid using ammonia refrigeration. • Distillation of the liquid to remove dissolved gases. 2.2.1.2.2 Nitrous Oxide Production Nitrous oxide (N2O) is manufactured by thermally decomposing pure ammonium nitrate into nitrous oxide, water, and ammonia. This is a highly specialized process that requires accurate control of temperatures and pressures to prevent a runaway reaction that could become explosive. The typical manufacturing steps are as follows: 1. Make or receive liquid ammonium nitrate (LAN). 2. Heat liquid ammonium nitrate in a temperature-controlled reactor at close to 500 °F (260°C).

3. Cool the raw N2O gas to condense water and residual ammonia. 4. Pass the gas through wet chemical stripper towers to wash out multiple impurities with potassium permanganate and sodium hydroxide. 5. Compress to 300 psig (20.7 bar). 6. Dry to a dew point of 60°F ( 51°C) or lower. 7. Condense into liquid at +10°F ( 12°C). Note that steps 5–7 above are similar to the CO2 process as indicated in 2. See CGA and EIGA documents for more information (CGA G 8.4, 2016; EIGA 175/16, n.d.). 2.2.1.2.3 Onsite Membrane Production of Nitrogen Porous membrane bundles can be installed onsite to produce nitrogen gas with a purity level of 90 + %. The system has purity limits created by the separation process. An air compressor increases the pressure to approximately

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

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2.2. INDUSTRIAL GAS MANUFACTURING, CYLINDER FILLING, BULK INSTALLATIONS, PIPING, RELIEF DEVICES, & SECURITY

150 psig (10.3 bar), .which is then passed through a series of porous membrane bundles that allows the smaller oxygen, carbon dioxide, and water molecules to permeate through the membrane, leaving the larger nitrogen molecules to pass through. This production method is excellent for use with long-term preservation of fruits and vegetables where lower purities are acceptable (see Fig. 2.2.3). Capacity can be increased by adding additional bundles and purity can be increased by placing bundles in series. The bundles have a fairly long life if properly maintained and if no oil is allowed to plug the pores of the membranes. 2.2.1.2.3.1 PRESSURE SWING ADSORPTION

Large nitrogen users can install onsite production of nitrogen using pressure swing adsorption. Air is compressed and sent to multiple beds containing zeolites and activated carbons, which selectively adsorb the nitrogen from the air to create an oxygen-rich vent gas. The recovered nitrogen can exceed purities of 99.9%. Units can produce up to 100,000 cfm (2830 m3).

2.2.1.2.4 Cylinders and Cylinder Filling Smaller food gas customers usually consume gases in cylinders or cylinder banks before growing into a bulk or onsite system. There are basically three methods of delivery for small supplies of gases. 1) Cylinders of compressed gas (nitrogen, oxygen, hydrogen, and mixed gases) that are always maintained as a gas because their liquid boiling temperatures are at cryogenic temperatures, well below ambient temperature. 2) Cylinders filled with compressed liquified gases (CLGs such as carbon dioxide, nitrous oxide), which are stored as a liquid at elevated pressure and ambient temperature (CGA G6.3, n.d.). 3) Liquid cylinders that are insulated and contain a small quantity of either cryogenic liquid or CLGs. These contain larger volumes than standard compressed gas cylinders because of the increased density of the liquid. Cylinders are typically filled at either a manufacturing plant or a trans-fill location from a bulk tank. Liquid is withdrawn from the bulk

Compressed air in 150 psig (10.2 bar)

Compressed air in 120 psig (8.2 bar)

Vent oxygen, water, CO2 to atmosphere

FIG. 2.2.3

Gaseous nitrous membrane bundle.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

2.2.1 GAS PRODUCTION

FIG. 2.2.4

47

Typical cryogenic gas process and instrumentation drawing (P&ID).

tank and pumped up to high pressures with a positive displacement piston pump. Cryogenic liquids such as nitrogen and oxygen are pressurized to approximately 2000 psi (138 bar), and are then passed through a vaporizer and introduced into typical steel cylinders. The cylinders are available in many sizes per local and regional regulations. The user is able to determine how much gas remains by monitoring the decrease of the internal pressure. There is a direct relationship between the volume remaining and the cylinder pressure. These types of cylinders are filled to a specific pressure as indicated by national and international standards. Standard steel cylinders will be permanently stamped in the neck area, near the valve with the appropriate regulatory specification designation as well as the number of dates that it was retested. Full cylinders that exceed their required retest date can be used, but they can not be refilled until tested. CLGs such as carbon dioxide are withdrawn from a bulk tank as a refrigerated liquid at 0°F

( 18°C) and pressurized with a piston pump that increases the pressure to approximately 800 psi (55 bar), which is then pumped directly into similar steel cylinders. The liquid is allowed to equilibrate with ambient temperature. These cylinders are filled only by weight because the internal pressure varies with changes in ambient temperature. The cylinder provides gas by boiling the liquid inside until the last drop is consumed. At that point, the cylinder is empty and pressure decreases extremely rapidly. For this reason, pressure can not be used as an indication of the quantity of product that remains. Carbon dioxide cylinders require more frequent retesting because in a carbonated beverage service, water can back flow into the cylinder, creating carbonic acid that weakens the cylinder due to internal corrosion. Liquid cylinders are somewhat of an intermediate solution for small gas users that are not yet large enough to have a bulk installation. These are typically vacuum-insulated stainless steel pressure vessels that can deliver either liquid or gas to the point of consumption. This makes them

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2.2. INDUSTRIAL GAS MANUFACTURING, CYLINDER FILLING, BULK INSTALLATIONS, PIPING, RELIEF DEVICES, & SECURITY

more versatile for customers that require a small volume of freezing as well as compressed gas. Cylinders are delivered individually or on forklift-compatible pallets. These are typically connected to a manifold at the customer location and piped to the point of use. Larger gas users may consider using tube trailers, which are essentially extremely large cylinders (tubes) that are permanently attached to a truck chassis and are exchanged as needed.

Pressure Vessel Code, n.d.). The vacuum space is typically 3–4 in. thick (7.6–10 cm) and contains a radiant heat insulation system. The insulation and inner vessel are encased inside a vacuumresistant outer steel jacket that also provides structural support for the entire tank. There are two primary types of radiant heat shields on bulk vacuum tanks: perlite and super insulated. 2.2.2.1.1 Perlite Insulation

2.2.2 BULK TANKS AND SUPPLY Industrial gases are supplied in bulk to food customers from a number of different style tanks. Most bulk food gas customers lease or rent their onsite storage tanks. Specialty food gases may be supplied by large tube trailers filled with compressed gases. An example of a typical gas use bulk nitrogen P&ID and an example of a gas use bulk CO2 P&ID are shown in Fig. 2.2.5.

2.2.2.1 Vacuum-Insulated Tanks Cryogenic liquids such as nitrogen, oxygen, and hydrogen are stored at extremely cold temperatures (< 150°F [ 101°C]). Almost all cryogens are stored at customer sites in vacuum-insulated containers. The inner pressure vessel is typically made from stainless steel or another low-temperature nickel steel alloy (EN 1252, n.d.; EN 1797, n.d.; ASME Boiler &

FIG. 2.2.5

One of the most popular cryogenic insulating systems is perlite, which is heat-expanded volcanic rock. It is economical and provides excellent insulation in conjunction with a deep vacuum. It does tend to settle or shift inside the vacuum space as the inner vessel expands and contracts as product is added or withdrawn. The normal vacuum level on a perlite tank is 50– 100 μm. If the vacuum level degrades, perlite tanks lose efficiency, but the perlite still retains most of its inherent insulation capabilities. 2.2.2.1.2 Superinsulation This is a lighter, thinner form of insulation that consists of multiple layers of reflective aluminum foil sandwiched between an inert spacer material. The tank and internal piping are wrapped with these layers to provide radiant heat protection. An SI-insulated tank has about one-half the heat leak of a perlite tank. The typical vacuum level is approximately 15 μm, which

Typical CO2 bulk tank gas process and instrumentation (P&ID). 2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

2.2.3 INSTALLATION AND LOCATION

is much lower than that required by a perlite tank. If the vacuum degrades on an SI tank, there is a very significant reduction in insulating value with a large increase in venting losses. All cryogenic tanks have some form of overpressure protection system to protect the vacuum space from overpressurization. This is either in the form of a lift plate on the top of the tank that is sealed by an O-ring that opens at a positive pressure, or a rupture disc that fails at low positive pressures. This is required to protect the outer vessel from any leaks that might be created by the piping that is inside the insulation space. This overpressure protection system is also the primary source of vacuum leaks. Any evidence of loss of vacuum, such as increased venting or frost spots on the exterior shell, should immediately be investigated and repaired. This is both for operational efficiency as well as the safety and integrity of the tank itself.

2.2.2.2 Urethane or Conventional Insulation Compressed liquefied gases (CLG) such as carbon dioxide (CO2) and nitrous oxide (N2O) are stored as a liquid at much warmer temperatures (> 20°F [ 30°C]) and therefore can use more conventional insulating materials. The most important thing is to maintain a good vapor barrier to prevent ambient moisture from migrating into the cold insulation and damaging the insulation. Holes or defects in the outer vapor barrier should be repaired immediately to prevent frost spots or water saturating the insulation. Wet insulation increases the tank external heat load, and may cause external rust and corrosion of low alloy steel pressure vessels. Most of the urethane-insulated tanks have mechanical refrigeration systems that allow storing the bulk liquid indefinitely without any venting losses. The refrigeration systems require electrical power and routine maintenance, but can counteract external heat loads caused by pumping and circulating systems that are used in food chilling or freezing applications.

49

The industrial gas industry has started using both vacuum-insulated and mechanically insulated bulk tanks for CO2 and N2O customers, so the choice of tank insulation becomes one of cost to purchase and maintain as well as the cost of any venting losses from a vacuum tank with intermittent use.

2.2.2.3 Tube Trailers Food gases such as hydrogen and helium may be delivered by tube trailers that can be exchanged as they become empty or repressurized by another delivery trailer. These trailers must meet national transportation regulations and local permitting and siting requirements. See NFPA 55 or EU regulations for special setback and security requirements.

2.2.3 INSTALLATION AND LOCATION Bulk gas systems are typically installed outside food-processing facilities adjacent to the building and a road or parking area. All regulatory jurisdictions classify the food gas storage systems as hazardous materials. This means that there are local and national regulations regarding where such systems can be installed and how far they might have to be from various hazards. In North America, the National Fire Protection Association (NFPA) provides national codes for most industrial gas installations (NFPA 55 Compressed Gases and Cryogenic Fluids Code) (NFPA 55, 2016) and provides specialized installation and setback information on gas systems. In the EU, this is provided by local regulations. The International Building Code (IBC) (International Code Council, n.d.) is used to provide regulations regarding foundations and structures for industrial gas systems. Bulk gas installations typically require permitting by the authority having jurisdiction

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

50

2.2. INDUSTRIAL GAS MANUFACTURING, CYLINDER FILLING, BULK INSTALLATIONS, PIPING, RELIEF DEVICES, & SECURITY

(AHJ) to insure that the installation is safe and that all local regulatory requirements are met. The majority of the installations are outdoors in an area where there is good ventilation to disperse any vented gases and away from any fire and other hazards. There are hazards such as spillage of cryogenic liquids, asphyxiation, release of oxidizers, and combustible gases that all must be evaluated by a knowledgeable person. In rare cases where an installation must be indoors or in a restricted courtyard, it is required that a thorough risk assessment be completed to determine whether the site is safe and suitable (see CGA P-41 Locating Bulk Storage Systems in Courts (CGA P-41, n.d.) for further guidance). Release of cryogenic liquids, cold gases, oxidizers, and flammables inside and in areas with limited natural ventilation can be extremely hazardous. Indoor or courtyard installations require that all relief devices be vented outside to a wellventilated area and the area must be continuously monitored for oxygen deficiency or hazardous atmosphere. The relief devices on most bulk tanks may not be sized to handle the increased flow capacity required to be installed in an area that could be engulfed in fire. The user should verify that the original tank manufacturer can certify that the relief system meets all local and national regulations for indoor or hazardous installation.

2.2.3.1 Foundations Bulk food gas installations require that a proper foundation be installed to support the weight of the tank as well as any accessories that come with the installation. A certified structural engineer or another qualified person needs to verify that an existing concrete foundation meets all local and national regulations. Many locations have special foundation requirements that include natural upset conditions such as earthquakes, hurricanes, high

winds, excessive frost, and substandard soil conditions. Those may require larger foundations, increased bolting, or frost skirts in colder climates to prevent lifting of the foundation caused by freezing soil moisture. 2.2.3.1.1 Unloading Pad Cryogenic liquids and oxidizers such as O2 and N2O require a concrete unloading pad adjacent to the fill gate. A typical pad is a minimum of 12 ft.  12 ft. (3.7  3.7 m) (NFPA 55, 2016) (see Fig. 2.2.6). Care should be taken to locate the unloading pad such that the rear wheels of the trailer are supported on the concrete, yet the area at the rear of the trailer where the hose connections are located should align with the security gate and allow any spillage to be captured by the concrete pad. Oxidizers require that all foundation expansion joints are filled with an oxygen-compatible sealant (see Fig. 2.2.7 detail).

2.2.3.2 Site Security and Lighting Typical bulk installations have a 6 ft. (2 m) high locked security fence around the perimeter to keep unauthorized personnel from entering the area. There can be random discharges of cold gases or liquids from the installation during normal operation and keeping untrained persons away is important. See Fig. 2.2.8 for examples of typical security fencing for bulk gas systems. Generally, there should be two gates or entry/ exit points that allow a delivery driver or service technician an alternate method of escaping from the area of the bulk gas system should there be a release of gases while inside the enclosed area. Emergency exits from the adjacent facility and air intakes should not be installed near the bulk installation. This may be further restricted by local and national regulations (NFPA 55, 2016). The use of fence slats or methods of hiding the installation is strongly discouraged because it

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

2.2.3 INSTALLATION AND LOCATION

51

FIG. 2.2.6

Typical one hose fill bulk cryogenic tank installation with unloading pad, security fencing, and guard posts.

FIG. 2.2.7

Typical bulk CO2 tank installation with security fencing and guard posts.

can restrict air flow and inhibit the correct operation of ambient vaporizers (CGA P-41, n.d.). The lock that secures the site is typically one that is keyed to the gas supplier’s distribution network. If the site is secure and no fencing is required, then an alternative can be to lock the fill valves in order to deny unauthorized access to the system. This is required to eliminate the potential for adulteration of the food-grade product as required by national regulations.

The installation should have adequate night lighting to allow night deliveries and to provide site security. Most bulk systems regularly receive deliveries during the night or during hours where natural lighting may not be sufficient. 2.2.3.2.1 Guard Posts (Bollards) Guard posts or guard rails are required per NFPA 55 (NFPA 55, 2016) (see Chapter 4) in North America where the bulk tank and

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

52

2.2. INDUSTRIAL GAS MANUFACTURING, CYLINDER FILLING, BULK INSTALLATIONS, PIPING, RELIEF DEVICES, & SECURITY

auxiliary equipment may be subject to impact from vehicular traffic or other motorized equipment (see Fig. 2.2.8 for more details).

2.2.3.3 Telemetry Most bulk suppliers install some form of telemetry that is able to communicate the tank liquid levels and other optional parameters such as pressure and valve operation. These typically use cell phone technology to indicate when a tank needs to be filled so that as the customer consumption varies, the supplier is able to optimally schedule deliveries to prevent running out. Customers may be asked to provide a dedicated phone line in remote areas that don’t have adequate cell coverage at the site to provide the data to allow optimal scheduling.

2.2.3.4 Emergency Shutoffs Bulk gas systems should have manual valves or automated control systems marked and designated as emergency shutoffs. Those devices should be properly labeled to allow access in an emergency. Certain gases such as hydrogen have special remote shutoff requirements, as indicated in local or national regulations (NFPA 55, 2016) (see Chapters 10 and 11).

2.2.3.5 Low-Temperature Protection Systems Food gas users that vaporize cryogenic fluids must provide low-temperature protection of their gas-distribution piping. This is required by NFPA 55 (NFPA 55, 2016) and CGA in North America as well as EIGA in Europe to prevent extremely cold cryogen from being transported into the gas delivery system that could cause embrittlement of nonresilient materials as well as a freezing hazard. This type of protection is typically installed by the gas supplier as a part of the leased equipment at the bulk tank site.

2.2.4 PRESSURE-REDUCING REGULATORS Gas users typically require a supply pressure lower than the bulk tank normal operating pressure. This is achieved by installing a pressurereducing regulator manifold, which typically has two regulators so that if one fails, the second can immediately be brought online by manipulating the correct bypass valves. High-pressure sources such as carbon dioxide, nitrous oxide, and HP hydrogen tubes typically require special larger-capacity relief valves downstream of the pressure-regulation system to protect the piping from overpressurization should the regulator fail in the open position. A qualified industrial gas technician should verify via a risk assessment and calculations that the relief valve protecting the customer supply line is sufficiently large enough to prevent overpressurization of the piping and all components connected to the main piping system. Oversizing regulators can make proper sizing of downstream line safety valves much more difficult. Regulators can be spring or pilot operated and shall have elastomers and diaphragms chosen from materials compatible with the gas and that can withstand the normal expected discharge temperature of the autorefrigeration effect of the expanding gases. It may be necessary in some cases to install a trim heater in the gas delivery system to prevent regulator damage or condensation on the exterior of the indoor process piping. This is especially true with CO2 and N2O systems because in lowtemperature winter conditions, the gas can recondense back to a liquid, causing the formation of solid “dry ice” that could block the piping and cause embrittlement. A typical method of installation is to invert the spring chamber of the regulator(s). This allows any condensed moisture to drain, preventing corrosion and freezing during ambient temperatures below freezing.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

2.2.4 PRESSURE-REDUCING REGULATORS

Typical security fencing and gates for bulk gases.

FIG. 2.2.8

53

54

2.2. INDUSTRIAL GAS MANUFACTURING, CYLINDER FILLING, BULK INSTALLATIONS, PIPING, RELIEF DEVICES, & SECURITY

2.2.5 RELIEF VALVES AND TESTING 2.2.5.1 Tank Primary Relief Valves The bulk tank requires that the primary relief device shall be sized to meet national regulations for pressure vessels and they must be tested and maintained by those same standards. In North America, the American Society of Mechanical Engineers Pressure Vessel Code (ASME Code) (ASME Boiler & Pressure Vessel Code, n.d.) or the Canadian code (Canadian Standards Association, n.d.) covers pressure vessel construction, the National Board of Inspection Code (NBIC) (National Board Inspection Code – NBIC, n.d.) covers the testing and field verification of safety relief devices, and CGA S 1.3 (S-1.3, n.d.) indicates the sizing criteria for those devices. In the EU, safety relief devices are covered by EN 4126 Safety Devices for Protection against excessive pressure (EN 4126, n.d.). Relief devices are required to be tested or replaced on a regular basis. In North America, this is generally every 5 years. In other countries, the time varies and the method of proof testing also varies. If the tank is leased or rented, then periodic relief device testing generally is the responsibility of the tank owner/operator, but this is determined by supply contracts. The Compressed Gas Association (CGA for NA) and the European Industrial Gas Association (EIGA for the EU) guidelines require that bulk industrial gas storage tanks have at least two primary relief devices active at all times. The primary device is typically set at the maximum allowable working pressure (MAWP); a secondary device can be set from 120 to 150% of the MAWP, depending upon local codes and regulations. Cryogenic tanks typically have a single spring-loaded “pop” relief device set at the MAWP, and a frangible or rupture disc set at 150%. Compressed liquefied gases such as CO2 and N2O do not use rupture discs because the

failure of the disc will cause the formation of solid “dry ice” or cause extremely low internal temperatures colder than the pressure vessel is designed to handle. Relief devices should communicate directly to the very top of the vessel, so that there is sufficient vapor space to allow for the expansion of the internal liquid as it warms and expands. Relief device piping should not pass through the cold liquids because thermal conduction could cause external moisture to freeze inside the relief valve and prevent proper operation. Any piping installed on the outlet of relief devices must be evaluated by a qualified professional to insure that back pressure created by such piping does not exceed 10% of the set pressure at the full flowing condition (ASME Appendix M) (ASME Boiler & Pressure Vessel Code, n.d.). If external vent piping is installed, it typically must be at least one size larger than the outlet of the relief device. Relief devices need to be installed such that there is no net thrust created by the operation of the device that might rotate or dislodge the device. All external piping should either be pitched downward toward the point of discharge or include a drain hole to prevent condensation for freezing inside the outlet piping. It is recommended that a three-way diverter be placed underneath the primary relief devices so that the devices can be removed/replaced without having to remove the vessel from service. A means of depressurizing the space underneath the valve should be provided to guarantee no residual pressure exists. There should always be an equivalent capacity device present on the opposite side of the diverter to insure continuous protection of the vessel. The inlet to all safety relief devices should never be reduced or decreased. The generally accepted standard for inlet pressure losses to a relief device at full-flowing conditions is 3% of the set pressure. Any reduction of the inlet of the diverter will generally fail that calculation.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

55

2.2.5 RELIEF VALVES AND TESTING

2.2.5.2 Thermal Relief Valves (National Board Inspection Code – NBIC, n.d.) Bulk food gas systems require a thermal relief device between every positive shutoff point (hand valves, check valves, regulating valves, etc.) in the piping where liquid could be present. Cryogenic liquids and CLGs when trapped between valves will increase pressure by orders of magnitude in a matter of seconds if in warm ambient temperatures. Pressures can quickly increase to the failure pressure of piping or components. All liquid piping needs to be protected with thermal relief valves that have vapor traps incorporated into the design so that they do not become covered with external water ice created from moisture in the ambient air. Water ice accumulation can prevent the relief valve from opening in cases where liquid is trapped, and this could lead to catastrophic failure. See Fig. 2.2.9 for a typical recommended installation. Relief valves in food gas service in many cases do not reseat properly when actuated. It is good practice to have spares available to allow for quick replacement should they fail to reseat. This is especially true for cryogens and CO2.

Thermal relief valves installed prior to pressure-reducing devices should be set at a pressure higher than the MAWP of the bulk tank and less than the MAWP of the piping system and components in the system. Good engineering practice is to set spring-operated relief valves installed on liquid and gas piping operating at bulk tank pressure approximately 100 psi (6.9 bar) higher than the MAWP of the tank. This allows the bulk tank relief system to control the piping pressure while protecting the piping from trapped liquid or a component failure. Relief valves set lower than the bulk tank primary relief device could open before the main tank and discharge large quantities of liquid product before attempting to reseat. This can create asphyxiation and freezing hazards surrounding the bulk tank installation. Rupture discs are not recommended as relief devices to protect process piping from overpressurization caused by the expansion of cold liquid. They fail open and will not reclose, and could vent the entire contents of the bulk system. The primary customer pipeline protection safety valve is typically installed outside at the bulk tank location. Any discharges will

Typical pressure relief device insulated liquid food gas piping

Vapor trap

Pressure relief device Accumulated water ice

Best discharge down

Good

Incorrect

FIG. 2.2.9

Best practice installations of thermal safety devices on cold or insulated piping systems.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

56

2.2. INDUSTRIAL GAS MANUFACTURING, CYLINDER FILLING, BULK INSTALLATIONS, PIPING, RELIEF DEVICES, & SECURITY

therefore be outside in a well-ventilated area to prevent any unsafe accumulation of gases inside the food-processing area. All relief devices that are installed indoors or in confined areas must be vented outside to meet local and national safety regulations. Combustible gases such as hydrogen and ethylene will require specialized external vent stacks to discharge the hazard safely away from buildings and personnel (NFPA 55, 2016; CGA G 5.5, n.d.) (see Chapters 10 and 11). See CGA and EIGA gas specific documents for further information.

2.2.6 VAPORIZERS Almost all food gas bulk installations require some form of vaporizer. They are used to provide gas to the end use point or to maintain the bulk tank pressure as product is withdrawn or cold liquid is added. Cryogenic tanks (N2, O2, H2) almost universally use ambient aluminum/stainless finned vaporizers to utilize the over 300°F (150°C) typical temperature difference between the liquid boiling temperature and the ambient. Compressed liquefied gases are stored at temperatures around 0°F ( 15°C) and typically utilize electric-based vaporizers. There is not enough temperature gradient between the bulk liquid and the ambient temperature for ambient air vaporizers to be effective. Cryogenic ambient vaporizers in continuous service will accumulate large quantities of water ice. This can create a number of problems that food gas users need to consider. • The weight of the accumulated ice increases foundation loading and increases wind resistance, especially in the cooler months. • They must be sized to handle the maximum instantaneous flow in order to prevent cryogenic liquid being discharged into the piping (see low-temperature protection). • The vaporizers may have to be deiced after extended use. Note that the extremely cold ice on the vaporizer is quite strong and can cause











serious injury to those technicians deicing fins. Adequate ground clearance is required to prevent the accumulated water ice from expanding and damaging the vaporizer or extracting the mounting bolts out of the foundation. Siting can be important to achieve desired capacity. The optimal location is facing the sun with generous clearances and excellent air flow. Installations in shaded or protected areas with minimal air flow will require a larger vaporizer. Large users may need to consider two or more vaporizers with switching valves to allow one to thaw while another is operating. Vaporizers need to be installed far enough away from bulk tanks, walls, and restrictions so that air has sufficient space to circulate around the cold coils and transfer heat to vaporize the liquid gas. Electric vaporizers typically use cast aluminum blocks or direct exposure to heater elements to vaporize the material. Nitrous oxide should NEVER have sources of heat >300°F (150°C) in direct contact. This could lead to a disassociation reaction that could lead to an explosion (see CGA G-8.4 Safe Practices for the Production of Nitrous Oxide From Ammonium Nitrate). Popular alternate vaporizing means for CLGs are water and steam. When sizing an electric vaporizer for CO2 and N2O, a good estimate of capacity is 25 lbs. hr1/Kwh (64 kg hr1/Kwh).

2.2.7 PIPING AND RELATED COMPONENTS Suitable supply piping for food gases depends upon a number of factors: • Piping materials must be compatible with the gas or liquid being consumed. Most food gases are pure dry gases and not corrosive to the interior of piping systems. Consult the

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

57

2.2.7 PIPING AND RELATED COMPONENTS













Handbook of Compressed Gases, by the Compressed Gas Association, or the Safety Data Sheets (SDS) for the gases in question to verify piping compatibility. Outdoor piping should either be of corrosionresistant materials or protected from corrosion. Indoor process piping should meet the food cleanliness standards required by the process and food regulation standards (typically stainless or copper). Liquid cryogen piping must be insulated to preserve the cooling capacity of the cryogen. Piping downstream of cryogenic vaporization systems must either be resilient to cold temperatures or adequate low temperature shutoff protection must be installed. The supply system MAWP typically determines the wall thickness of the process piping. Piping downstream of pressure-reducing regulation systems can be of lower working pressures, but must be protected from

regulator failure by adequately sized relief devices (see relief valve sizing). In many cases, the choice of piping material is more determined by the skills and resources of the person completing the installation. The second consideration is the potential for external corrosion or reaction with the surrounding atmosphere. Installation and inspection of process piping is controlled by local and national regulations. In North America, this is typically ASME B31.3 (ASME B 31.3, 2016; ASME B 31.8, n.d.) and in Europe, EN 13445 (EN 13445, n.d.). Pneumatic testing of newly installed piping is suggested following guidelines from local and national process piping regulations. Hydrotesting of piping for industrial gas systems is discouraged because of the potential for contamination of the system with residual water that could freeze in contact with cold gases or liquids (Table 2.2.1). The following types of pipes and fittings are not acceptable for bulk cryogenic service: Carbon steel (not resilient at low temperatures). PVC and CPVC piping (see note below).

TABLE 2.2.1 Suggested Food Gas Piping Materials. Bulk cryogenic liquids and gases (LN2, LOX, GH2, LH2 1000 Hz). In Fig. 2.3.2, you can see the schema of a corona discharge: Because 85%–95% of the electrical energy supplied to a corona discharge ozone generator produces heat, some type of method is required for the removal of this. In addition, adequate cooling significantly affects the energy efficiency of the ozone generator, so most of the corona discharge systems use air, water, or both as cooling methods.

2. CHEMICAL AND PHYSICAL GASES PROPERTIES, GASES PRODUCTION PROCESS, UNITS

2.3.5 TECHNOLOGIES FOR GENERATION IN SITU

FIG. 2.3.2

FIG. 2.3.3

69

Corona discharge.

“Corona effect” diagram.

At the heart of a corona discharge is the dielectric. The electrical charge diffuses on this dielectric surface, creating an electrical field, or “corona.” A corona effect diagram can be seen in Fig. 2.3.3. The most important thing for ozone systems by corona discharge is appropriate preparation of the air. The gas that supplies the ozone generator must be very dry (minimum 62°C dew point, the temperature at which the water vapor contained in the air starts to condense, producing dew, mist, or any type of cloud), because the presence of moisture affects the production of ozone and leads to the formation of nitric acid. Nitric acid is highly corrosive to critical internal parts of a corona discharge ozone generator, and can cause premature failure and significantly increase maintenance frequency. The relative production of ozone decreases as the moisture content of the air increases. Of the above-mentioned ozone technologies, none has a clear advantage. However, to help reduce the field for a particular application, we should consider the amount of ozone required in that application. For many years now, thanks to the fact that it is possible to work at high frequency as well as the progress made in electronics, there has been a change from

using large transformers at low frequency and valves to smaller ozone equipment. That smaller equipment consumes less energy and has very low dissipation of heat at P sec Inner vessel

Outer jacket

Gas P*

Pressure build coil

Outside vaporizer

Liquid Interspace under vacuuh

T*

P reglee

Pressure regulator opeh if P < P sec Gas usage Liquid usage

Filing hanifold FIG. 6.1.2.9

Liquid oxygen tank draft.

and the active oxygen requirement when it is swimming, feeding, and digesting the food. The oxygen intake rate (OIR) is correlated by exponential functions with water temperature and the body weight of fish by a general formula: OIR ¼ K W m Tn OIR ¼ oxygen intake rate in mg of oxygen per kg of fish weight per h W ¼ individual body weight or average unitary weight in the population in g

T ¼ water temperature in degrees Celsius K, m, n ¼ coefficients that vary depending on fish species Some examples of this correlation can be found for Gilt-head sea bream (Sparus aurata), European seabass (Dicentrarchus labrax), Atlantic salmon (Salmo salar), and rainbow trout (Oncorhynchus mykiss) in the following tables (Fig. 6.1.2.11). OIR is difficult to measure and there are not many studies in this field, but still it is possible to find approximated values for some fish

6. AGRICULTURE

142

FIG. 6.1.2.10

6.1. ANIMAL PRODUCTION

Air Liquide’s ASU.

European seabass (Dicentrarchus labrax) Gilt-head sea bream (Sparus aurata) Rainbow trout (Oncorhynchus mykiss)

K

m

n

2.85

–0.247

1.25 (1)

300.81

–0.2829

0.0232 (2)

249

–0.142

0.024 (2)

(1) OIR = K Wm Tn, OIR in mg of O2 per kg of total weight per hour, W fish individual weight in g and T temperature in ºC (2) OIR = K Wm 10nT, OIR in mg of O2 per kg of total weight per hour, W fish individual weight in g and T temperature in ºC From Alain Belaud - École Nationale Supérieure Agronomique de Toulouse (INP-ENSAT)

T (ºF)

K

50 50

OIR = K Wm Tn, OIR in weight units of DO per 100 weight units of fish weight per day, W fish individual weight in lbs and T temperature in ºF From Richard W. Soderberg - Flowing Water Fish Culture

FIG. 6.1.2.11

OIR formulas for different species.

species. The Oxygen Table in FishBase (Froese and Pauly, 2016) is a large collection of OIRs for more than 300 species with close to 7000 records for standard and active metabolisms. Despite the fact that OIR is clearly linked to feed intake, the calculation based on this parameter is not very accurate. The ratio of oxygen to feed consumption is higher when the fish are fed low rations, infinite indeed when not

fed at all, and lower when fed at demand. Besides, the protein percentage and the caloric content of feed trigger oxygen consumption. Different authors report a wide range of 0.25– 0.75 kgO2/kgfeed depending on the formulation and feeding ratio with an average of 0.35 kgO2/kgfeed. Available oxygen is a common concept in aquaculture, understood as the amount of

6. AGRICULTURE

6.1.2.5 FACTORS AFFECTING OXYGEN REQUIREMENT OF FISH

oxygen naturally provided by the water that can be profited by the fish, that is to say the difference between the DO in the inlet and the minimum due in the outlet of a rearing unit. DOa ¼ Q ðDOin  DOout Þ 103 where DOa is the available DO in kg/h; Q is the water flow in m3/h; DOin is the concentration of DO in the inlet of a rearing unit in mg/L; DOout is the concentration of DO in the outlet of a rearing unit in mg/L. The DO concentration to be maintained in the outlet varies depending on the requirements of each species and the fish size, but should be a minimum of 3–6 mg/l. The actual oxygen requirement in a tank, raceway, or pond can then be figured out from the total needs minus available oxygen. AOR ¼ OIR B 106  DOa where AOR is the actual oxygen requirement in kg/h B is the biomass in a rearing unit in kg When dimensioning aeration or oxygenation equipment, it is recommended to consider the worst possible conditions, that is to say, the highest biomass, highest temperature, less water flow, and lowest DOin, including possible oxygen depletions. The oxygen consumption of microorganisms must be added if water is reused from a previous rearing unit, as is usually the case in freshwater fish farms. In closed-loop circuits (RAS), the elimination of organic matter increases the oxygen consumption significantly, making necessary an additional application in the biological treatment of the depuration system. An approximate estimation can be calculated as: MOD ¼ 1:3 BOD5 Q 103

143

where MOD is the oxygen demanded by microorganisms in kg/h; BOD5 is the biochemical oxygen demand in mg/L; Q is the water flow in m3/h. Finally, the transfer efficiency of the application equipment must be taken into account in order to choose the adequate capacity and figure out the total oxygen and/or energy consumption.

6.1.2.5 FACTORS AFFECTING OXYGEN REQUIREMENT OF FISH 6.1.2.5.1 Body Size Small fish with a fast growth rate have a more active metabolism than bigger fish and so OIR is exponentially higher in fingerlings. For instance, at 15°C a rainbow trout of 50 g consumes 330 mgO2/kg/h while a 500 g fish consumes only 240 mgO2/kg/h. Nevertheless, the AOR is determined by the biomass, and so the first fish consumes all in all 16.5 gO2/h and the latter 124.5 gO2/h. Therefore, the oxygen needs are much lower in hatchery and nursery tanks than in growing ponds.

6.1.2.5.2 Water Temperature Fish are ectothermic animals, meaning that their body temperature is approximately that of the environment. Temperature rules metabolic activity and OIR, and there again they are exponentially correlated. Following the former example, a trout of 50 g consumes 225 mgO2/kg/h at 10°C and 430 mgO2/kg/h at 20°C. Different species of farmed fish grow in a wide range of temperatures, sometimes even changing in the consecutive development stages. A differentiation is generally done between warm water species thriving at temperatures of 22–32°C and cold water species at 14–17°C.

6. AGRICULTURE

144

6.1. ANIMAL PRODUCTION

As expected in their natural environment, cold water species demand more oxygenated water than warm water species. Sea bass, sea bream, tilapia, or eel, being warm water species, are adapted to tolerate DO levels as low as 2– 3 mg/L (30% saturation) for relatively long periods of time, unlike salmon, trout, or turbot, which don’t endure concentrations below 5– 6 mg/L (60% saturation). In any case, it is demonstrated that keeping 100% saturation at all times improves growth, feed conversion rate, and resistance to diseases in both warm and cold water species. It is remarkable that there is a contradictory coincidence between oxygen availability and requirements in nature. When the temperature is higher and the fish demand more oxygen, the DO saturation is lower. This is a major reason to count on adequate oxygenation systems with best performances in order to maintain healthy fish at all times.

6.1.2.5.3 Species Fish are unable to absorb oxygen from the water below a certain level known as the threshold limit. In the boundaries of this value, fish become lethargic and their swimming turns sluggish. This condition stresses the fish and alters the immune response in the long term, making them more susceptible to diseases. If the limit is exceeded, death by asphyxia occurs after a variable time depending on the species. Although there are interespecific variations in the resistance to low DO concentrations, the main difference between cold water and warm water species has already been commented upon.

6.1.2.5.4 Salinity Different species of farmed fish live in fresh, brackish, or salt water, and some move from one to the other during their life cycle, such as salmon from fresh to salt water (anadromous) and eel just

the opposite (catadromous). Both species are euryhaline, being more tolerant to changes in salinity as long as they are gradual, while stenohaline species have not evolved this capacity. In any case, osmoregulation is necessary for both freshwater and salt water fish, in fresh water to prevent the loss of salts from their body and in salt water to hold back the loss of water. This metabolic activity consumes energy, and so the more similar water salinity is to blood plasma, the less energy and oxygen consumption. For most euryhaline species, the minimum osmotic effort can be found in brackish water with intermediate salinities between 11 and 22 g/L. The oxygen requirement must be increased when fish are transferred to different salinities, for instance when adapting salmon smolts to salt water (Fig. 6.1.2.12).

6.1.2.5.5 Feed The feeding ratio (FR) is expressed as kg of feed per 100 kg of fish per day. It is inversely proportional to fish size and directly proportional to temperature (although it decreases above the optimal temperature for the species). OIR goes parallel to FR, undergoing a peak when the fish is feeding that lasts for some hours during digestion until the complete assimilation of the food. Some authors have registered peaks of 1.2–1.5 over basal oxygen consumption persisting 4–6 h after feeding. In intensive fish farming where fish are fed at demand during light hours, OIR should be considered at its maximum most of the time. Fish adapt their feeding behavior according to oxygen levels. When DO is low, they stop feeding and hence growing, trying to save oxygen for basic physical activity. Fish should only be fed at maximum when oxygen is fully available, and conversely, the feeding ratio and diet must be adapted to low oxygen availability in order to avoid possible hypoxia. The best growth and conversion rate are achieved when oxygen and feed are supplied

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Temp (ºC)

Sal (g/L)

DO (mg/L)

8 –17

0 – 35

6

Rainbow trout (Oncorhynchus mykiss)

10 –17

0 –35

6

Adriatic sturgeon (Acipenser naccarii)

18 –22

0 –3

6

Common Carp (Cyprinus c arpio)

20 –32

0 –3

3

T ilapia (Oreoc hromis niloticus)

25 –32

0 –3

3

Eel (Anguila anguila)

23 –27

0 – 35

4

Atlantic s almon (Salmo salar)

T urbot (Psetta maxima)

14 –17

30 –40

5

European sea bass (Dicentrarchus labrax)

22 –27

30 –40

5

Meag re (Argy rosomus reg ius)

16 –26

30 –40

5

Gilthead sea bream (Sparus aurata)

22 –26

30 –40

5

Senegalese sole (Solea senegalensis)

18 –22

30 –35

5

Shrimp (Penaeus japonicus)

26 –28

25 –30

4

Temp: Optimum growing temperature

FIG. 6.1.2.12

Sal: Optimum growing salinity

DO: Minimum dissolved oxygen concentration

Temperature, salinity, and DO for different species.

with self-demand feeders and adequate oxygenation systems, letting the fish regulate their intake by satiety.

6.1.2.5.6 Activity Swimming is the major oxygen-consuming activity in fish. A strong current requires extra energy and oxygen supply, reducing growth rate. Water velocity is a controlled parameter in fish farming that must meet a compromise between the self-cleaning of the waste in the rearing units and the unnecessary swimming effort. A rate of 0.6–1.1 body lengths per second is usually adopted as an adequate water velocity.

6.1.2.6 OXYGENATION SYSTEMS As a general rule, intensive aquaculture facilities need to enrich water with extra amounts of oxygen in order to keep high densities of fish in

good condition, taking it from the air or using pure oxygen (with purities over 96%). Both aeration and oxygenation equipment are designed to increase the interphase surface, the turbulence, and the oxygen gradient. This chapter will focus on some of the available oxygenation equipment.

6.1.2.6.1 Jet Platforms Cascades are natural aeration systems using slopes to produce small jets and drops of water over the surface of a pond. They are normally used in freshwater fish farms for the reoxygenation of water with the oxygen nearly exhausted from a previous rearing unit. The amount of oxygen that a cascade can provide is figured out from the transfer rate formula, where kLa depends on the height of the slope, the depth of the reception pond, the temperature of the water, and the interphase surface.

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As an example, given a freshwater flow with an oxygen concentration of 5.5 mg/L at 15°C, a cascade of 1 m height will provide at best some extra 2.3 mg/L of oxygen, with 77.6% saturation in the pond overall. Jet platforms are devices that improve this effect using pure oxygen inside an enclosure built in civil works, stainless steel, or another water-resistant material. An upper chamber receives the water from an inlet canal. Several nozzles in the bottom of the chamber produce jets that pass through a closed oxygen atmosphere, penetrating into the water surface of the oxygenation chamber below and drifting inside small oxygen bubbles. Nondissolved bubbles are later decanted and returned to the oxygenation chamber (Fig. 6.1.2.13). A good performance can be achieved from a slope between water layers of 0.7 m, although

Oxygen inlet

Inlet channel

it is also conditioned by the water depth in the pond. Slopes over 1 m can supersaturate water around 200% at nearly any temperature with high efficiency and no energy cost. Jet platforms are usually chosen wherever there is a natural slope as the most profitable and cost-effective equipment, and must be tailored according to each site.

6.1.2.6.2 U-tube The U-tube is an oxygenation system built in civil works where water is driven by gravity through a tube going underground to a variable depth, normally more than 5 m. Oxygen is injected near the surface by a diffuser, creating small bubbles that drift down to the bottom to be efficiently dissolved, helped by the hydrostatic pressure. The oxygenated water is then

Oxygen purge

h1 L1

Jet

h2

Oxygen chamber

h3 L2 Bubble decanter Mixing chamber

FIG. 6.1.2.13

Jet platform.

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Fish pond

147

6.1.2.6 OXYGENATION SYSTEMS

driven up to the surface by an ascending tube. Descending and ascending speeds must be carefully calculated in order to prevent bubbles from coming up in the first tube and drifting outside in the second. A minimum slope of 0.5 m is necessary to keep the water circulating. Instead of a U-shaped tube, a descending pipe inside a well fulfills the same function, saving space. The capacity and performance of the U-tube is conditioned by the depth of the well and the hydrostatic pressure achieved (Fig. 6.1.2.14).

6.1.2.6.3 Bicone Bicone is a closed pressurized reactor patented by Air Liquide for a high efficient dissolution of gases with a low head loss. Inlet water is

Inlet channel

pumped through a pipeline where oxygen is injected. The pipe enters the Bicone, driving the water up to the top, filled with oxygen gas. The oxygen bubbles drift by the flow down to the bottom where they are dissolved, and the oxygenated water comes out of the Bicone after a calculated retention time. Due to the shape of the Bicone, the speed of the water in the upper part is faster than in the lower part, pushing nondissolved bubbles down and creating a zone of intense mix that increases the efficiency. Bicones are fabricated in stainless steel, plastic, or fiberglass for a wide range of water flows from 30 to 900 m3/h and different pressures, depending on the oxygen requirement (Fig. 6.1.2.15).

Oxygen inlet

Oxygen purge

L1 Oxygen chamber Bubble decanter L2

FIG. 6.1.2.14

Graphic U-tube.

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Outlet channel

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6.1. ANIMAL PRODUCTION

BICONE ®

O2 O2

Recirculation pump

Pumping basin

Gravity pipe Fish basin

Bicone installation

Bicone FIG. 6.1.2.15

Graphic bicone.

6.1.2.6.4 Porous Diffusers Porous diffusers for aquaculture are fabricated in ceramic, plastic (EPDM, polyurethane, silicone, PTFE, etc.) or sintered stainless steel to produce fine bubbles less than 2 mm in diameter with different capacities, depending on the total perforated surface. Transfer efficiency is conditioned by bubble size, among other factors. Small bubbles have more contact surface than big bubbles in relation to their volume. When the diffuser is placed in the bottom of a pond, small bubbles also have slower ascending speed and more contact time. It is therefore important to produce as many small bubbles as possible, avoiding coalescence that could make them bigger. However, there is a lower limit in diameter because the gas in bubbles less than 500 μm may not overcome the surface tension and would not be dissolved.

Pure oxygen has a much better performance than air in diffusers because of the higher partial pressure and the reduction of total gas volumes to 20% for the same amount of oxygen transferred. In addition, oxygen gas from the liquid supply already has the necessary pressure to be driven and injected without additional compression. Diffusers with oxygen are normally used as a support system, for instance, to treat the fish with some medication in bath (DO level must be maintained while water flow is stopped), or in case of an electricity breakdown in pumped water facilities (Fig. 6.1.2.16). They may also be installed inside pipes in order to dissolve oxygen if conditions in the pipeline are suitable, or to disperse it in other equipment such as Bicones or U-tubes. Tanker trucks for transporting living fish at long distances also use diffusers with oxygen supplied by small cryogenic vessels or bundles of cylinders (Fig. 6.1.2.17).

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6.1.2.6 OXYGENATION SYSTEMS

FIG. 6.1.2.16

Graphic efficiency of porous diffusers.

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149

150

FIG. 6.1.2.17

6.1. ANIMAL PRODUCTION

FOTO Tanker truck for fish transport.

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6.1.2.6 OXYGENATION SYSTEMS

References Froese, R., Pauly, D., 2016. The Oxygen Table in Fish Base. FishBase. version (10/2016), www.fishbase.org.

Further Reading Anon. Technics used for intensive rearing and alimentation of fish and shellfish. n.d. A. Belaud. n.d. Syste`mes de recirculation et leurs application en aquaculture—Oxygenation de l’eau. INP, ENSAT, France. Food and Agriculture Organization of the United Nations, 2016. Aquaculture and Fisheries Report 2016 Summary. FAO. R. Francis-Floyd. n.d. Dissolved Oxygen for Fish Production. University of Florida. Kepenyes, J., 1984. Recirculation Systems and Re-use of Water in Aquaculture. Fish Culture Research Institute, Szarvas, Hungary.

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Kepenyes, J., Va´radi, L., 1984. Aeration and Oxygenation in Aquaculture. Fish Culture Research Institute, Szarvas, Hungary. Lawson, T.B. (Ed.), 1995. Fundamentals of Aquacultural Engineering. Springer, USA, ISBN: 978-1-4613-0479-1. Mallya, Y.J., 2007. The effects of dissolved oxygen on fish growth in aquaculture. Kingolwira National Fish Farming Centre, Fisheries Division. Ministry of Natural Resources and Tourism, Tanzania. Segovia, E., Mun˜oz, A., Flores, H., 2012. Water flow requirements related to oxygen consumption in juveniles of Oplegnathus insignis. Latin Am. J. Aquat. Res. 40 (3), 766–777. Soderberg, R.W., 1982. Aeration of water supplies for fish culture in flowing water. Prog. Fish-Cult. 44 (2), 89–93. Subramanian, S., 2013. Feed intake and oxygen consumption in fish. PhD thesis, Wageningen University, Wageningen. Tucker, C., 2005. Pond Aeration. Southern Regional Aquaculture Center, USA.

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C H A P T E R

6.2

Vegetal Production

Gases in Agro-food Processes https://doi.org/10.1016/B978-0-12-812465-9.00013-X

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# 2019 Elsevier Inc. All rights reserved.

S U B C H A P T E R

6.2.1 CO2 for Greenhouses Philippe Girardon Air Liquide, Paris, France

6.2.1.1 INTRODUCTION Boosting the CO2 level in commercial greenhouses has been in use for more than 40 years. The most common approach was to recover the CO2 from the flue gases resulting from burning the natural gas (for example, from piping distribution of methane or from liquefied propane in a vessel) that was used for heating the greenhouses. The combination of these cleaner fuels and improved burners enabled recovery of the CO2 to become one of the largest selfproductions of “industrial” CO2 made directly by the user. In the hotter summer period when no heating is required, the question was the cost of producing CO2 from combustion compared to the cost of industrial CO2 proposed by the gas industry. Further trends were to use higher levels of CO2. Initially, most systems aimed to keep the levels comparable to those found in the outside air, but growers obtained much higher yields from their crops by the use of around 2–3 times the ambient air CO2 levels. Today, greenhouse heating technology management consists of matching the CO2 production according to night and day frequency

periods with heat store use. Typically, the heating system runs during the day, producing the necessary CO2 while pumping the heat into a heat store. At night, the heating system is switched off and the heat store gives the necessary heating back to the greenhouse.

6.2.1.2 HIGH TECH GREENHOUSE MANAGEMENT Recent greenhouse designs consist of closed construction and ventilation provided by only mechanical systems, full air control, heat pumps and heat storage, temperature and humidity control, tight control of CO2, nutrient solution irrigation, and use of artificial lighting. Such interrelated systems are very efficient in terms of energy use and CO2 consumption while providing optimum growing conditions for the highest crop yields. Maximizing growth does not necessarily produce more fruit or flowers. Tomatoes fruit is one of the major products grown under plant production in greenhouses vs open field (Fig. 6.2.1.1).

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6.2.1.4 PHOTOSYNTHESIS BACKGROUND

FIG. 6.2.1.1

155

Tomatoes fruit is one of the major products grown under plant production in greenhouses vs open field.

6.2.1.3 INFLUENCE OF CO2 AND FUEL COSTS In the 1970s, the escalation of fuel prices and a progressive fall in the market price for CO2 resulted in a change in the economics of the application in favor of “external” CO2 use.

6.2.1.4 PHOTOSYNTHESIS BACKGROUND Plant growth is the result of photosynthesis in which light energy from the sun is used as a source of energy for the synthesis of organic

matter from atmospheric CO2 and water. Chemically, this phenomenon, which is accompanied by oxygen production by the plant, can be represented by the formula below: 6H2 O + 6CO2 + light energy ! C6 H12 O6 + 6O2 This equation shows that CO2 is one of the three main factors that combine to produce the organic elements necessary to the constitution of the structure of the plant. The reverse reaction is breathing in use among all living organisms, and which is to burn carbohydrates by releasing water, CO2, and energy. Green elements absorb CO2 normally present in the air at a concentration of 0.03% in volume on

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6.2. VEGETAL PRODUCTION

average (300 ppm) through pores (stomata) in the plant cells. This value is less than the optimum of that required for the growth of plants. If the concentration falls to 0.012%–0.015% (120–150 ppm), this will even stop photosynthesis. There are many other carbohydrates and organic compounds that are formed together with mineral nutrients and water to build the plant tissues and organs.

6.2.1.5 ADVANTAGES OF CO2 ENRICHMENT Without the outside input of CO2, this critical level can be reached in a few hours in a greenhouse full of plants. CO2 enrichment allows restoring the minimum content required. The results are variable according to the cultivated species and varieties. Researchers and growers rapidly found that much higher rates of growth were possible with elevated CO2 levels. Enrichment of CO2 from 300 up to about 800 ppm can ensure an increase of yield both in weight and number of fruits, faster development giving earlier harvesting, better bloom color quality, more vigorous stems, healthy growth with improved disease resistance, and longer lasting flowers, as indicated in Tables 6.2.1.1–6.2.1.4. In these tables the advantages of CO2 enrichment are recorded for the following specific crops: tomatoes, cucumbers, lettuce, peppers, and roses for the main. The role of illumination is not negligible as shown in the following curves, knowing that due to dissipation of sun energy caused by the water in air, there is a big gap between theoretical availability and reality. This is mostly in northern countries, for example, 1000 watt m2 on the Earth’s surface at the equator versus 150 in Benelux (Fig. 6.2.1.2).

TABLE 6.2.1.1 Optimum CO2 Content for Some Products Plants Grown

CO2 Concentration (ppm)

VEGETABLES Tomatoes

600–1000

Cucumbers

800–1000

Lettuce

1000

Melons

1000

PLANTS IN POTS Begonias

800

Hydrangeas

1500–2000

St-Paulia

800

GREEN PLANTS Ficus

800

Croton

800

CUT FLOWERS Roses

800

Mums

800–1000

Tulips

1200

Eyelets

800

TABLE 6.2.1.2 Additional CO2 Average Registered, and Estimated Value for a 400 ppm CO2 Concentration kg CO2 (m22 year21)

kg CO2 (m22 day21)

4

11  103

TABLE 6.2.1.3 Impact of CO2 on the Production of Cucumbers From Mid-March to Mid-August CO2 concentration (ppm)

400

1000

Number of fruits (m2 week1)

2

2.3

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6.2.1.6 TYPICAL INSTALLATION

TABLE 6.2.1.4

Total Consumption of CO2 (Fumes + Additional) According to the CO2 Concentration CO2 Concentration 600 ppm 22

kg CO2 (m

21

year )

1000 ppm 22

kg CO2 (m

21

day )

22

kg CO2 (m

21

year )

kg CO2 (m22 day21)

Peppers

6.5

17.8  102

12.7

35  103

Tomatoes

6.1

16.8  103

12.7

35  103

Roses

6.7

18.3  103

12.7

35  103

Photsynthesis rate (mg CO2/m3/s)

2

300

1.8

250

1.6 1.4

200

1.2

150 100

1 0.8 0.6

50

0.4 0.2

Watt/m2

CO2 concentration (ppm) FIG. 6.2.1.2

Photosynthesis rate at different levels of illumination and CO2 concentration.

6.2.1.6 TYPICAL INSTALLATION CO2 is usually supplied into the circulating airstream from a liquid CO2 tank (18 bar pressure). The pipes used for CO2 distribution inside the greenhouse are those used for the CO2 stream coming from the fume recovery, whatever the heating or nonheating period. The CO2 passes

through a hand valve prior to injection directly into the ventilation air stream. In such a configuration, the injected liquid CO2 will produce a fine spray of solid CO2 snow and gas into the airstream. The warm air easily provides the heat necessary to ensure rapid sublimation of the snow particles. When the heater is switched off, a specific CO2 heater must be used to avoid any

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6.2. VEGETAL PRODUCTION

liquid CO2 encroachment in the airstream pipe causing possible material embrittlement. The most common method of CO2 distribution throughout the greenhouse is the use of a very lightweight tube made from a plastic film (for example, polyethylene) perforated at regular intervals to provide the necessary flow rates. These plastic film-forming tubes are lying on the floor at the bottom of the vegetable plants and rooting medium.

6.2.1.7 SAFETY The concentration of CO2 in the greenhouse atmosphere controlled from the normal atmospheric level of around 340 ppm up to around 2000 ppm is well below the 5000 ppm permissible exposure limit. The basic safety interlock is that CO2 cannot be injected unless the ventilation system is operating.

6.2.1.9 CONCLUSION AND PERSPECTIVES 6.2.1.9.1 Vertical Vegetal Greenhouses In the recent past, a few companies have been involved in closed growing equipment that integrate state-of-the art technologies: fluorescent lighting with an output wavelength optimized for vegetable growth, air-conditioning systems that maintain a constant temperature and moisture level, tracking control of growth, and sterilization systems for packing material. Strategic interests for these companies are probably based on LED lighting technology development appearing in that sector versus traditional lighting. Refer to Toshiba and Philips communication: https://www.toshiba.co.jp/about/press/ 2014_09/pr3001.htm http://www.lighting.philips.com/main/ products/horticulture On another side, a vertical greenhouse concept has been developed in the trend of urbanization of agriculture.

6.2.1.8 ECONOMICS In order to optimize the product yields, growers worked with research institutes and consultants to find the optimum economic conditions according to the costs of fuels and CO2 that can fluctuate depending of the periods versus the market selling price of the vegetable that is also subject to fluctuation at different periods of the year. The professionals did this atmosphere optimization like they did for the whole growing process, for example, the rooting medium, the hydroponic watering composition, the lighting, the variety selection, etc. There is no room for independent parameter evaluation, everything being linked. Practically, a breakeven assumption was estimated a few years ago with the following figures: fuel barrel equivalent price and CO2 price per ton both around 100€, meaning accurate management of combustion versus pure CO2 uses by the farmer.

6.2.1.9.2 Hygiene The plant factories described above in close to sterile conditions minimizing germ contamination and the consequences on food safety can contribute to extend the freshness and shelf life of vegetables, which is a major concern for retailers, convenience stores, and supermarkets. Could we observe in the future a more integrated production step for fresh-cut salad plants? The hydroponic nutrient flow brought to the culture is a source of contamination when recycled. Generally, it is steamed for sterilization before controlling the three macronutrients used by plants. These macronutrients are nitrogen (N), phosphorus (P), and potassium (K), NPK for short. Ozonation has been tested as an alternative solution with an onsite generator. See the related chapter on ozone sanitation.

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6.2.1.9 CONCLUSION AND PERSPECTIVES

159

FIG. 6.2.1.3 Homogeneous blooming can be obtained with ethylene boosting during the ripening step of tomato growth.

6.2.1.9.3 Ripening of Tomatoes Recent European legislation banned the use of ethephon (C2H6ClO3P), a plant growth regulator promoting fruit ripening, abscission, and flower induction as well as generating ethylene used at the last step in the ripening of tomatoes before picking. Tests regarding replacement by gaseous ethylene are being validated and legal approval is being sought through some technical

centers, growers, and universities, mostly in Belgium (Fig. 6.2.1.3).

6.2.1.9.4 Influence of Other Gases Complete gas control management in a perspective of growing optimization points out a last parameter concerning oxygen content in hydroponic solutions with some encouraging results on some varieties.

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6.2.2 Controlled Atmospheres for Fruit and Vegetable Storage and Ripening Tongchai Puttongsiri, Anthony Keith Thompsona King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand

6.2.2.1 INTRODUCTION The postharvest effects of gases on fresh fruits and vegetables was first referred to as “gas storage” (Kidd and West, 1927), but in the 1930s, that was changed to “controlled atmosphere (CA) storage”. The scientific basis for the effects of gases during the storage of fresh fruit and vegetables probably began at the University of Montpellier in France in 1819 (Berard, 1821). They found that fruit absorbed O2 and gave out CO2 and showed that climacteric fruit stored in atmospheres containing no O2 did not ripen, but if they were held for only a short period and then placed in air they continued to ripen. In the 1860s, Benjamin Nyce experimented in the United States with modifying the atmosphere in an apple store by making it airtight. Franklin Kidd and Cyril West carried out experiments in the early 20th century on CA storage and by 1920 were able to set up trials at a farm in the United Kingdom to test their laboratory findings in small-scale commercial practice. In 1929, a commercial CA store for apples was built by a grower in the United Kingdom. By 1938, there were more than 200 commercial CA stores for apples in the a

United Kingdom (Thompson, 2010). Currently, CA storage is increasingly used on an increasing number of fresh fruits and vegetables in an increasing number of countries. An enormous number of papers have been published in the scientific literature on postharvest science and technology; some journals are even exclusively dedicated to the subject. This chapter attempts to review the role of gases in the postharvest science and technology of fresh fruits and vegetables.

6.2.2.2 PRESTORAGE EFFECTS The condition of fruits and vegetables before being put into store can have a profound effect on their postharvest life. Harvest maturity, especially with climacteric fruit such as apples, needs to be specified before harvesting them for longterm storage. Some cultivars are known to have a longer storage life than others and the responses of different crops to levels of O2 and CO2 may vary considerably. Also, some chemical treatments can be applied to them to control diseases and physiological disorders while rendering them less sensitive to ethylene.

Formally: Cranfield University, Cranfield, United Kingdom.

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6.2.2.3 CONTROL OF GASES IN CA STORES

6.2.2.3 CONTROL OF GASES IN CA STORES The optimum levels O2, CO2, and other gases, especially ethylene and water vapor, vary between different types of fruits and vegetables and even between cultivars and areas of production. These have been determined to some degree and data is presented for some in many publications, for example Thompson (2010). Many recommendations may not reflect the optimum conditions but rather the most suitable conditions in relation to the technology available at the time. Development of technology that enables O2 levels to be maintained safely at very low levels has led to improved conditions in storage, especially ultralow oxygen (ULO) storage, that is, O2 levels of 1% or less. The first experiments in the early part of the 20th century on the effects of gases on fresh fruits and vegetables used metal cylinders of compressed gas that had been made up with the various proportions of the gases to be studied. Subsequently, gas levels in commercial CA stores were measured by frequently extracting a sample of the store air, analyzing it in an Orsat gas analyzer or other equipment, and adjusting the levels manually. This method was clearly laborious and did not permit sufficient accuracy in controlling the gas levels in the store. Currently, the atmosphere in many modern CA stores is regularly analyzed automatically for CO2 levels, using an infrared gas analyzer and O2 levels with analyzers using electrochemical cells or sometimes a paramagnetic analyzer. The analyzers are monitored and controlled by a computer, which can then automatically adjust their levels. This method is based on prior knowledge of the optimum gas combination that suits the type and cultivar of fruit or vegetable to be stored. Subsequently, systems and equipment have been developed that use the physiological responses of the fruit or vegetable to determine the optimum gas level and also to control it. Yearsley et al. (1996) concluded that determining lower

161

O2 limits on the steady-state internal atmosphere of the apples estimated the true lower O2 limit more accurately than those estimated from the store atmosphere. Equipment to determine the chlorophyll fluorescence (CF) and respiratory quotient (RQ) have been developed to measure physiological responses for this purpose. Temperature interacts with gas levels on the effects on fruits and vegetables during storage. Kidd and West (1927) reported that there is evidence that CA storage is only successful when applied at low temperatures. Standard refrigeration units are therefore integral components of CA stores. In commercial practice for long-term CA storage, the store temperature is initially reduced to 0°C for a week or so, whatever the subsequent storage temperature will be. This would clearly not be applicable to fruits and vegetables that can suffer from chilling injury at relatively high temperatures (10–13°C). Also, CA stores are normally designed to a capacity that can be filled in 1 day, so fruits are loaded directly into the store and cooled the same day. In the United Kingdom, the average CA store size was given as about 100 tons with variations between 50 and 200 tons, in continental Europe about 200 tons, and in North America about 600 tons (Bishop, 1996). In the United Kingdom, the smaller rooms are preferred because they facilitate the speed of loading and unloading.

6.2.2.3.1 Water Vapor Most fruits and vegetables require high humidity when kept in storage. Generally, the closer the humidity is to saturation the better, so long as moisture does not condense on the fruit or vegetables as this might result in disease infection. A major reason for comparatively low humidity developing in a store is that the cooling coils on the refrigeration unit are set at too high a temperature differential from the required store air. This results in condensation on the cooling coils that can cause desiccation

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from the fruit or vegetables. Evaporator coil refrigerant temperature, store humidity, cooldown period, and mass loss rates in a commercial 1200 bin apple store were studied by Hellickson et al. (1995). They reported that stores in which the evaporator coil refrigerant temperatures were dictated by cooling demand resulted in a significantly longer time required to achieve the desired humidity than stores in which the evaporator coil temperatures were controlled by a computer. A whole range of humidifying devices can also be used to increase the humidity in the store, including spinning disc and sonic humidifiers. In a laboratory experiment, Dijkink et al. (2004) described a system that could maintain humidity very precisely in 500-L containers. They were able to maintain 90.5  0.1% RH using a hollow fiber membrane contactor and a liquid desiccant.

contact equally with all the fruit in the room. At the same time, the CO2 given off by the fruit, which can impede ripening initiation, is not allowed to concentrate around the fruit. The application of ethylene can be as a liquid, for example, Ethrel, which is sprayed on fruit and hydrolyzed to produce ethylene. Gas cylinders containing ethylene under pressure are also used. Typical mixtures are 95% N2 and 5% ethylene. The method of application was to meter the gas into the ripening room containing the fruit through a pipe. Currently, ethylene generators are most commonly used (Fig. 6.2.2.1). These are devices that give a slow release of ethylene over a protracted period, commonly 16 h. The generators are used by placing them in the ripening room, pouring a liquid provided by the manufacturer into a container within the generator, and plugging the generator into an

6.2.2.3.2 Ethylene Ethylene is synthesized by plant cells. In climacteric fruit, the biosynthesis of ethylene initiates ripening. Ripening rooms have been used for climacteric fruit (especially bananas) that are harvested in a preclimacteric state and subsequently placed in a ripening room and exposed to ethylene gas under controlled conditions. They are also used for degreening citrus fruits. The primary requirements for ripening rooms are that they should have a good temperature control system, have good and effective air circulation, be gas tight, and have a good system for introducing fresh air and ethylene gas. Over the past few decades, in some countries there has been an increasing demand for all the fruit being offered for sale in a supermarket to be of exactly the same stage of ripeness so that it has an acceptable and predictable shelf life. This has led to the development of a system called “pressure ripening.” The system involves the circulating air in the ripening room being channeled through boxes of fruit so that exogenous ethylene gas, which initiates ripening, is in

FIG. 6.2.2.1 ripening.

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Catalytic ethylene generator used in fruit

6.2.2.3 CONTROL OF GASES IN CA STORES

electrical supply. The liquid is probably ethanol because if ethanol is heated in the presence of a copper catalyst, ethylene gas is produced. Ethylene can also have negative effects on fresh fruits and vegetables, especially when accumulated in stores. For example, Wills et al. (1999) showed that the postharvest life of some nonclimacteric fruit and vegetables could be extended by up to 60% when stored in an atmosphere containing less than 5 parts per billion ethylene compared with those stored in 100 parts per billion. Solomos and Biale (1975) showed that exposure to ethylene during storage results in an increased respiration rate (Table 6.2.2.1). 1-Methylcyclopropene (1-MCP) is used commercially to slow the ripening of fruits in store. Its mode of action involves 1-MCP tightly binding to the ethylene receptor sites in plant cells, thereby blocking the effects of ethylene by inhibiting the activities of ACC (1-aminocyclopropane-1carboxylic acid). This also delays the peaks in the ACC synthase activity and ACC concentration TABLE 6.2.2.1 Effects of Ethylene on Respiration Rate of Selected Crops Respiration Rate (μL O2 g21 h21) Crop

Control

Ethylene

Apple

6

16

Avocado

35

150

Beet

11

22

Carrot

12

20

Cherimoya

35

160

Grapefruit

11

30

Lemon

7

16

Potato

3

14

Rutabaga

9

18

Sweet potato

18

22

163

as well as gene expression of enzymes and of ethylene receptors at the transcript level (Ma et al., 2009). N-dimethylaminosuccinamic acid (DPA, Daminozide, Alar, B9, or B995) is a plant growth regulator. Treated apples were shown to be less sensitive to ethylene than nontreated apples during storage, but this response varied between cultivars (Knee and Looney, 1990). However, it has been withdrawn from the market in several countries because of suggestions that it might be carcinogenic. Aminoethoxyvinylglycine (AVG) is used in apple orchard sprays to inhibit their ethylene biosynthesis. Its mode of action is to inhibit the activity of ACC-synthase. McIntosh apples sprayed with AVG were shown to have a delayed onset of the climacteric during subsequent storage (Robinson et al., 2006). There are various ways in which ethylene can be removed from stores, including absorption, reaction, ozone scrubbers, and catalytic converters. Filters are available commercially in several forms that can be placed in the air circulation system. These contain an active alumina carrier impregnated with potassium permanganate that oxidizes the ethylene (Fig. 6.2.2.2). Catalytic converters remove ethylene by chemical reaction. Air from the store is passed through a device (Fig. 6.2.2.3) where it is heated to more than 200°C in the presence of an appropriate catalyst, usually platinum (Wojciechowski, 1989).

6.2.2.3.3 Carbon Dioxide

Adapted from Solomos, T., Biale, J.B., 1975. Respiration in fruit ripening. Colloq. Int. C. N. R. S. 238, 221–228.

When CO2 levels in store are too high, fruit or vegetables can be damaged. The optimum CO2 level in store varies for different crops and situations (Thompson, 2010). There are many different types of scrubbers that can remove CO2 from CA stores, but they can basically be divided into two types. One uses a chemical that reacts with CO2 and thus removes it from the store; this is sometimes called “passive scrubbing.” The other is renewable, sometimes called “active scrubbing.” Passive scrubbing is where bags or pallets, usually calcium hydroxide, are placed

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FIG. 6.2.2.2 Ethylene-absorbing potassium permanganate granules, (A) a filter blanket containing granules (B). Reproduced with permission of Molecular Products Limited.

FIG. 6.2.2.3 Portable Tubamet Swingcat ethylene scrubber in use in a wholesale packhouse in the United Kingdom in the 1990s.

inside the store, where they can keep CO2 levels low (usually about 1%). For greater control, the bags or pallets of lime may be placed in a separate airtight small room. When the CO2 level in the store is above that which is required, a fan draws the store atmosphere through the room containing the bags of lime until the required level is reached. In passive scrubbers, the time taken for the levels of these two gases to reach the optimum (especially for the O2 to fall from 21 kPa in fresh air) can reduce the maximum storage life of the crop. It is common therefore to fill the store with the crop, seal it, inject N2 gas until the O2 has reached the required level, and then maintain it in the way described above. The N2 may be obtained from large liquid N2 cylinders or from N2 generators (Fig. 6.2.2.4). Active scrubbers use molecular sieves and activated carbon that can hold CO2 and organic molecules such as ethylene. When fresh air is passed through these substances, the molecules are released. This means that they can be used in a two-stage system where the store air is being passed through the substance to absorb the CO2 and ethylene while the other stage is being cleared by the passage of fresh air. After an appropriate period, the two stages are reversed. Hydrated aluminum silicate or aluminum calcium silicate is used. The regeneration of the

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6.2.2.3 CONTROL OF GASES IN CA STORES

FIG. 6.2.2.4

165

Nitrogen generator used to reduce the O2 level in CA stores.

molecular sieve beds can be achieved when they are warmed to 100°C to drive off the CO2 and ethylene. This system of regeneration is referred to as “temperature swing” where the gases are absorbed at low temperature and released at higher temperature. Regeneration can also be achieved by reducing the pressure around the molecular sieve, which is called “pressure swing.” During the regeneration cycle, the trapped gases are usually ventilated to the outside. Burdon et al. (2005) reported that the method of CO2 control may affect the volatile composition of the room atmosphere, which in turn may affect the volatile content of fruit. They compared activated carbon scrubbing, hydrated lime scrubbing, N2 purging, and storage in air on kiwi stored at 0°C in 2 kPa O2 + 5 kPa CO2. After storage, the fruits were allowed to ripen at 20°C and the volatile profiles differed between CA stored and air stored fruits, and also among fruits from the different CO2 scrubbing systems. However, the different CO2 scrubbing systems did result in measurable differences in ripe fruit volatile profiles.

6.2.2.3.4 Oxygen The way that traditional CA storage systems were operated was that the rooms were sealed and when the O2 reached the level required for the particular crop through respiration, it was maintained at that level by frequently introducing fresh air from outside. Sharples and Stow (1986) reported that tolerance limits were set at 0.15% for O2 levels below 2%, and 0.3% for O2 levels of 2% and above. With continuing equipment development, the precision with which the set levels of CO2 and O2 can be maintained is increasing. With recent developments in the control systems used in CA stores, it is possible to control O2 levels close to the theoretical minimum. This is because modern systems can achieve a much lower fluctuation in gas levels, and ULO storage (levels around 1%) is now common. If the O2 level in CA stores is too low, the type of respiration of the fruit can change from aerobic respiration to fermentation, producing various volatiles including acetaldehyde, ethyl acetate,

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and ethanol. Considerable advantages have been shown in storing fruit as close as possible to that low O2 point, called the anaerobic compensation point (ACP) (Bishop, 1996; Prange et al., 2014). North and Cockburn (1975) describe detection for ethanol in CA stores using indicator tubes that could be connected to an alarm system so that when fermentation was just beginning, the O2 level could be slightly increased to prevent the fruit from being damaged. This technology was subsequently developed and Schouten et al. (1997) described a system that he called “dynamic control of ultra low O2 storage” based on headspace analysis of ethanol levels that were maintained at less than 1 μL L1 where O2 levels were maintained at 0.3–0.7 kPa in the store. This method of monitoring and control is called “dynamic controlled atmosphere” (DCA) storage (Prange et al., 2014). Therefore DCA uses the responses of actual fruits or vegetables being stored as monitors of the store atmosphere instead of an arbitrary setting of the O2 and CO2 levels in the store that had been based on previous experience and experimentation. The ACP is the critical internal O2 concentration where the metabolism of the fruit or vegetable reaches a level that results in fermentation. Two methods of detecting the ACP were described by Gasser et al. (2008) based on RQ and chlorophyll fluorescence (CF) signal monitoring, which were used to detect the critical O2 concentration during DCA storage. DCA storage under a stress atmosphere maintained a flat fluorescence (Fα) baseline while those with lower O2 produced an Fα spike. O2-induced Fα shifts occurred quickly at the lower O2 limit of the fruit and were measurable but returned quickly to the prestressed level when the O2 level was raised above the lower O2 limit (Prange et al., 2002, 2003). A commercial technology called HarvestWatch based on CF measurement of stress, which occurs when there is insufficient O2 for aerobic metabolism, has been developed, commercialized, and patented. Prange et al. (2014)

TABLE 6.2.2.2 The Effects of Time in Storage on the Lower Oxygen Limit Detected by Dynamic Controlled Atmosphere-Chlorophyll Fluorescence (DCA-CF) on Four Apple Cultivars Lower O2 Limit (kPa) Apple Cultivar

October 10–19

December 1–4

Delicious

0.85

0.47

Golden Delicious

0.92

0.45

Honeycrisp

0.90

0.50

Empire

0.90

0.88

Adapted from Prange, R.K., Wright, A.H., DeLong, J.M., Zanella, A., 2014. History, current situation and future prospects for dynamic controlled atmosphere (DCA) storage of fruits and vegetables, using chlorophyll fluorescence. Acta Hortic. 1012, 905–915.

used DCA-CF to calculate the lower O2 limit for apples and showed that this varied between cultivars and was also reduced considerably during storage (Table 6.2.2.2). Another method developed for ULO storage is Safepod, which has also been patented and commercialized. Yearsley et al. (1996) investigated the internal levels of concentrations of acetaldehyde, ethyl acetate, and ethanol in stored apples as a means of determining their ACP and fermentation threshold in order to ascertain their optimum CA conditions. They concluded that determining lower O2 limits on the steady-state internal atmosphere of the apples estimated the true lower O2 limit more accurately than those estimated from the store atmosphere. They considered, therefore, that the fermentation threshold RQ represented the safest estimate of the true lower O2 limit for optimizing storage atmospheres.

6.2.2.3.5 HarvestWatch HarvestWatch is commercial CA technology based on CF measurement of stress that has been patented and commercialized. Isostore is software that incorporates the HarvestWatch signals, CO2, O2, and temperature data into a

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167

FIG. 6.2.2.5 Chlorophyll fluorescence (HarvestWatch) showing the system (A) and individual kennels with avocados readily prepared to be placed in the store (B). Reproduced with permission of Robert Prange.

single real-time display. Samples of fruit are placed in plastic boxes called “kennels” that are placed among the fruit to be stored (Fig. 6.2.2.5). Each kennel has appropriate monitoring equipment that is linked to a computer for monitoring and control of O2 levels in the store. CF is light reemitted by chlorophyll molecules during return from excited to nonexcited states (DeEll et al., 1999). Prange et al. (2003) reported that “a new chlorophyll fluorescence (F) sensor system called FIRM (fluorescence interactive response monitor) was developed that measures F at low irradiance. This system can produce a theoretical estimate of Fo at zero irradiance for which they have coined a new fluorescence term, Fα. The ability of Fα to detect fruit and vegetable low-O2 stress was tested in short-term (4-day) studies on chlorophyllcontaining fruit. In all of these fruit and vegetables, Fα was able to indicate the presence of low-O2 stress. As the O2 concentration dropped below threshold values of 0 to 1.4 kPa, depending on the product, the Fα value immediately and dramatically increased. At the end of the short-term study, O2 was increased above the threshold level, whereupon Fα returned to approximately pre-stressed values.” Prange et al. (2003) reported a study with apples stored at 0.9, 0.3, or 1.5 kPa O2 for 9 months using

HarvestWatch. The apples stored at 0.9 kPa had the highest firmness, lowest concentration of fermentation volatiles, and lowest total disorders. Sensory ratings for off-flavor, flavor, and preference indicated no discernible differences among the three O2 storage conditions. Burdon et al. (2008) reported that CF in avocados remained constant at 0.8 at 6°C in O2 levels down to 1 kPa. However, below that O2 level, the CF rapidly dropped to 0.68 within 24 h. When the fruit was kept for 6 days, then returned to a nonstressed atmosphere, the CF rapidly returned to 0.8. They also found that after DCA storage, using CF, the avocados ripened in 4.6 days at 20°C compared with 7.2 days for “static” CA stored fruit and 4.8 days for fruit stored throughout in air.

6.2.2.3.6 Safepod Storage Control Systems Ltd. developed Safepod (US Patent 8739694, Canadian Patent CA2746152). Each Safepod holds around 60– 70 kg of fruit. It is exposed to the same storage conditions as the rest of the store but is isolated from the store’s atmosphere at regular intervals. The control is based on stress detection on the 60–70 kg representative sample of fruit. The Safepod sits in the CA store and thus has the same temperature, humidity, pressure, and

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FIG. 6.2.2.6 Safepod unit (A) and Safepod ready for loading into a ULO store (B). Reproduced with permission of David Bishop, Storage Control Systems Ltd.

atmosphere as the store (Fig. 6.2.2.6). Periodically, the valves are closed and the fruit inside is then tested for CO2 produced and O2 consumed and its RQ is calculated using Safepod software. The RQ is then used as a basis to make the necessary small adjustments to the overall conditions of the store (Thompson and Bishop, 2016). Wollin et al. (1985) had previously discussed the possibility that RQ may be used to calculate the lowest O2 level that can be tolerated in fruit storage to be incorporated in an automated CA system. RQ is the measure of moles CO2 evolved to moles O2 absorbed in plant cells. It is 1 when the substrate in carbohydrate but lower for lipids and proteins. Burton (1952) measured RQ in potatoes stored at 10°C in 5–7 kPa CO2 for up to 14 weeks. The increased CO2 reduced both O2 uptake and CO2 output by about 25%–30%, but the RQ was unaffected and remained close to 1. Bessemans et al. (2016) described DCA storage to control O2 and CO2 in storage containers for apples, based on measurements of RQ. Ethanol concentrations in the fruit were found to be very low (21°C) and deniable inspected on the presence of live insects.

Bulk containers with biorice, infested with rice weevil. 60% CO2, 21 days exposure at 21°C.

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FIG. 6.2.3.9

185

Sealing the loading hatches and mounting tubes for gas injection, measurement, and temperature control.

Air samples were taken on a daily basis. The O2 and CO2 concentrations of a container treated that way can be seen in Fig. 6.2.3.10. These techniques are very well suited to treat organic products. The weak point is that temperature control is extremely important to keep the exposure time commercially acceptable. Nitrogen can also be used as a gas for such operations, but at a much higher dosage. With N2, we will have to go to at least 99% gas concentration, leaving a maximum of 1% oxygen. Especially in museums, where artifacts are very valuable and vulnerable, mostly nitrogen is used because it’s absolutely harmless to the artifacts. Longer exposure times are for those purposes less important. Nitrogen is mostly generated by a nitrogen separator. Oxygen is taken out of the air by this machine and released back into the ambient air. The pure nitrogen is used to flush the fumigation chambers and to maintain the low oxygen

level. Fig. 6.2.3.11 shows an example of a nitrogen fumigation under sheets. In Fig. 6.2.3.12, we see the preparation of a treatment in a gastight fixed chamber. In such installations, the temperature can also be raised in order to reduce the exposure time.

6.2.3.4 HIGH-PRESSURE CARBON DIOXIDE TREATMENTS One of the main disadvantages of treatments with inert gases is the long exposure time needed to kill all insect stages. The solution here is the use of carbon dioxide under high pressure in an autoclave (see Fig. 6.2.3.13). Such autoclaves can be constructed to take palletized goods (horizontal construction) or bulk products (vertical construction). Carbon dioxide is injected at pressures mostly between 20 and 30 bar. Exposure periods

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FIG. 6.2.3.10

Carbon dioxide and oxygen concentration during treatment of a biorice container. CO2 > 60%; O2 < 10%.

FIG. 6.2.3.11

Low oxygen treatment of highly valuable organic coffee with a nitrogen separator. 6. AGRICULTURE

6.2.3.4 HIGH-PRESSURE CARBON DIOXIDE TREATMENTS

FIG. 6.2.3.12

Treatment of exotic herbs in a chamber for low oxygen treatment.

FIG. 6.2.3.13

High-pressure CO2 treatment in an autoclave.

range between 2 and 3 h, depending on the pressure used. Due to the high pressure, the carbon dioxide is “pumped” into the body of the insects (all stages). Mortality is caused by a kind of

187

acidification of the body fluids. At the end of the treatment, the pressure is released relatively rapidly. The dissolved CO2 in the body fluids will try to escape the same way as when shaking

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and opening a soda bottle. Sometimes insects, and also insect eggs, literally explode during this phase of the process. This is a quick treatment method, but the capacity is low. Of course the investment cost of the autoclave, pumps, and tanks will have a serious impact on the exploitation costs. Organic products or products with high added value will be the targets for this technique. For example, the company Martin Bauer (Germany) has two horizontal autoclaves connected to each other. At the end of the fumigation cycle in one of them, the carbon dioxide is pumped in the other one as the start of that other cycle. This results in the use of less gas and thus cost savings.

6.2.3.5 LOW-PRESSURE PRESERVATION AND FUMIGATION TREATMENTS The opposite of high pressure is low pressure. Treatments at very low pressures (20 millibar) showed very promising results for stored product protection. Even insect eggs were killed in

FIG. 6.2.3.14

relatively short times. However, such low pressures cannot easily be obtained and maintained in commercial circumstances. Also, there are very few to no commercially available containers or packaging that can withstand such low pressures for a longer time. On the other hand, we now have strong barrier films with extremely low oxygen permeability. With the appropriate sealing devices, we can make from these foils bigbag-size bags. The aim is very clear: lower the partial oxygen pressure by a partial vacuum in such a way that the insects cannot find enough oxygen to breathe normally. As we already know, insects have no lungs, so they can’t actively take in the air they need to get their oxygen. All their stigmata will now be opened completely, desperately searching for enough air. At that moment, we add another “weapon” into the battle: we flush with either carbon dioxide or nitrogen, and then we go back to low pressure. With every cycle of “flushing and vacuumizing,” the oxygen content goes down. See Fig. 6.2.3.14. After that, the whole suffocation process can also be enhanced by raising the temperature. The higher the temperature, the higher the

Long-term insect control using VacQPack technology.

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FIG. 6.2.3.15

Sealing the special valve after vacuumizing.

activity and metabolism of the insects and the higher their oxygen demand. With their spiracles wide open, they will also lose a lot of water because the vapor pressure of the gas mixture is very low. This effect plays an evenly important role in insect mortality. Low oxygen in vacuumizing big bags not only has an effect on insect control, but by reducing the oxygen content, there will be less oxidation of the free fatty acids in the product, so deterioration processes can be slowed down or even inhibited. This means a significant increase in the shelf life of the product. Also, mold forming will be inhibited because the moisture content inside the packaging will be significantly diminished by replacing the ambient air with completely dry gases during each flushing cycle. Of course, the semivacuum has to be kept during the whole storage period. Four factors will determine the quality of the system:

• Oxygen permeability of the foil used. • Quality of the seals in the foil. • Presence and/or quality of a valve for extraction/injection. • Kind of cargo. All those operations can be carried out using either nitrogen or carbon dioxide as the flushing agent. They both have advantages and disadvantages. In such specialized markets, it’s advisable to ask for an expert opinion (Fig. 6.2.3.15).

6.2.3.6 CONCLUSIONS Inert gases for pest control are already well established. However, creativity is very important in these subjects. There are still so many subjects that are not investigated yet… Quite a challenge!!!

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S U B C H A P T E R

6.2.4 Algae Culture Philippe Granvillain, Rayen Filali, Francis A. Kurz R&D, ALGAE NATURAL FOOD SAS, Illkirch-Graffenstaden, France

6.2.4.1 CO2, GLOBAL WARMING, AND INDUSTRIAL EMISSIONS One major cause of global warming is now widely known as the large and steady increase of the CO2 level in the atmosphere since the advent of the industrial revolution in the mid1800s. The CO2 level, one of the prime sources of the greenhouse gas emission effect, rose over the past 40 years due to the exponential emissions of flue gases from industrial plants and fossil fuel modes of transportation. A typical industrial flue gas contains up to 20% CO2. Even though many nations, citizens, and NGOs worldwide have tried to limit the production of excessive levels of CO2, the exponential rise of the worldwide population has boosted the global demand for more products, impairing the efforts of global CO2 reduction. Carbon biological sequestration is one of the promising ways to reduce the excess CO2 from the atmosphere and industrial plants. Complete physical techniques are already well known and implemented: absorption, adsorption, cryogeny, and membranes (Velea and Dragos, 2009). Today, the cost to capture the CO2 produced by a standard thermal power facility is still too high, $128–967 per tons of carbon (IEA, n.d.), and therefore not economically sustainable. The only way to bring down the cost of capture is to both capture and fix efficiently the CO2 by a

system that may be a chemical, geological, or biological one, and turn CO2 into useful commercial molecules. Thus, CO2 from industrial processes might be valorized as one component for a new process, considered as belonging to the context of the circular economy. Hence, extensive studies have been carried out since then for CO2 sequestration. CO2 gas may be generated in agrofood facilities such as breweries, malthouse plants, or any plant where some fermentation processes are involved. The sequestration of the CO2 emissions by the food-processing industry is a promising step because no toxic byproduct gases such as SOx and NOx are produced, unlike those produced by power plants or boilers. One of the most promising ways for CO2 biofixation concerns the application of microalgae cells. Indeed, microalgae are photosynthetic microorganisms that are able to convert carbon dioxide into biomass, oxygen, and high-value molecules. Thus, many studies are focused on CO2 mitigation by cultures of microalgae strains. This biological process doesn’t require any separation and/or purification step of CO2 from flue gases: those can be directly used in the culture, and save around 70% of the total cost of CO2 fixation. The industrial CO2 emissions may be a valuable and potentially cheap source of carbon for growing plants and algae as a whole. Microalgae culture is considered a

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6.2.4.2 CARBON SOURCE FOR A BIOLOGICAL SYSTEM: CARBONATE SYSTEM

promising way for CO2 biofixation, also called CO2 capture, mitigation, sequestration, or removal. However, many flue gases contain other toxic gases such as SOx and NOx, which are toxic with a 50 ppm concentration for microalgae growth (Lee and Lee, 2003). Then, some upstream treatment might be necessary before using such gases in cultivation. Moreover, several flue gases usually contain particulate matter, heavy metals, and halogen acids that could end up in the biomass harvested that could not be used as valuable end products.

6.2.4.2 CARBON SOURCE FOR A BIOLOGICAL SYSTEM: CARBONATE SYSTEM Carbon dioxide is naturally dissolved into aqueous liquid, where it is slowly hydrated to form the diacide form, or carbonic acid: H2CO3 (pKa 2.84). It should be noted that CO2(aq) and H2CO3 are hard to distinguish. Then, H2CO3 dissociates quickly to form another mineral aqueous form: HCO3  , called bicarbonate ion, featuring a pKa of 6.35 (Dreybrodt et al., 1997). Bicarbonate quickly loses its last H+ at a pH above 10.33 representing its last pKa. This growth of living microorganisms depends on the carbon source, in the form of carbon dioxide, bicarbonate, and carbonate. The equilibrium of these forms on the aqueous solution is related to the carbonate system, considering the pH of the medium. To summarize, in an aqueous liquid environment where pH ranges from 6.35 to 10.33, which is suitable and experimentally observed for microalgae cultivation, the predominant form of the inorganic carbon is HCO3  , as summarized in Fig. 6.2.4.1. The carbon dioxide transfer from the gas to the liquid defines the quantity of the CO2 absorbed, which depends on the diffusion rate constant (kL), the effective mass transfer area (α), and the driving force concentration difference (ΔCO2). Thus, the CO2 mass transfer rate

191

FIG. 6.2.4.1 CO2 dissociation equations in aqueous solution (Aslam and Mughal, 2016).

NCO2 (mg L1 h1) is related to the volumetric gas-liquid mass transfer coefficient and CO2 concentration upon the following formula:   NCO2 ¼ kL α C∗CO2 L  CCO2 L where kL is the liquid-phase mass transfer coefficient (m h1), α is the specific area available for the mass transfer (m1), CCO2L∗ (mg L1) is the carbon dioxide concentration in CO2 in equilibrium with the outlet gas phase, given by Henry’s law, and CCO2L (mg L1) is the carbon dioxide concentration in the liquid (Markl, 1977). Current studies try to increase kL and α in order to raise the CO2 mass transfer rate by various sparging strategies and PBR configurations. Because of its acidic feature, and as displayed in Fig. 6.2.4.1, CO2 solubility also depends on the pH of the solution. Naturally, as gas solubility increases as the temperature decreases, a lower temperature promotes CO2 solubility; the outcome is the same for applying a higher inlet (sparging) gas pressure. But what is less known is that the more salt presence in the culture media, the less CO2 solubility (Liu et al., 2013). It should be noted that CO2 gas solubility is much higher than for O2 gas by a magnitude of 100: 1496 g CO2 L1 under pressure of 1 atmosphere at 25°C in water, explaining why the CO2 mass transfer from the gas form to liquid is rather fast (Aslam and Mughal, 2016). To conclude, the use of that kind of carbon source, either CO2 or HCO3  , by microalgae is therefore one of the envisaged credible ways to CO2 biofixation. This chemical process enables a better assimilation of the carbon by

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microalgae, and therefore illustrates perfectly the CO2 sequestration. This mineral carbon therefore turns into the organic form thanks to the microalgae metabolic way.

6.2.4.3 BIOLOGICAL MECHANISM FOR CO2 FIXATION BY MICROALGAE Microalgae are microorganisms that convert light energy and carbon sources into biomass and other high-value molecules. The primary metabolism is the photosynthetic activity. Photosynthesis by microalgae represents a bioenergetics process, unlike that developed by terrestrial plants. The mechanism of CO2 fixation is rather simple: the mineral form of carbon goes through the plasmatic membrane thanks to an active transport; the same phenomenon is carried out with the chloroplast membrane. The key enzyme involved for CO2 utilization into the well-known Calvin cycle is the Rubisco, which stands for ribulose-1,5-bisphosphate carboxylase/oxygenase (only the carboxylase aspect for fixing CO2 is of interest in this chapter) and is mainly responsible of the CO2 fixation efficiency (Badger and Spalding, 2000). The CO2 concentrating mechanism, or CCM, was a concept created to help understand the many ways all aerobic photosynthetic cells use for carbon fixation, which aim to set suitable conditions for the Rubisco carboxylation performances (Broda, 1975). Several components constitute the CCM: the active capture of CO2, the energy supply during photosynthesis (energy biological system ATP/NADPH), the intermediary species of CO2 (essentially HCO3  ), the CO2 release mechanism outside the cell by flowing (for cyanobacteria, that CO2 could be absorbed again into the cell by a recycling process), the CO2 concentrating section around Rubisco, the loss of CO2 diminution in CO2 generation sit by carbonic anhydrase, and the kinetic properties alteration of Rubisco (Badger

and Spalding, 2000). Interestingly, the intermediary species of the CO2 CCM component is HCO3  , which is localized into the chloroplast stroma for the microalgae eukaryotic cell and into the cytoplasm for the cyanobacteria cell. It should be noted that both the CO2 and HCO3  present in the aqueous media would potentially be absorbed and fixed by the microalgae cell. Another major enzyme involved in that process, the carbon anhydrase, turns HCO3  into CO2 into the cell. The local rise of the CO2 level enables the Rubisco to function well for producing the very first organic components. Fig. 6.2.4.2 shows an overview of the mechanisms involved for cyanobacteria (Ducat et al., 2011).

6.2.4.4 MICROALGAE CULTURE Cultivating microalgae is both a science and an art. As a science, since the 1960s, the literature has plenty of technical articles describing various cultivation system designs developed for specific microalgae strains, cultures conditions, and applications. As an art, it is common to think an effective microalgae cultivation as the right combination of three components: the right choice and selection of microalgae species, the identification and optimization of the microalgae environmental conditions, and the suitable culture system. About the selection of the microalgae and depending on the application, the most considered criteria concern the specific growth rate and high tolerance of the microalgae strains to an industrial flue gas containing high levels of CO2, NOx, and SOx, and potentially the tolerance to high temperature that usually comes with supplying flue gas. To select the right strain to be studied or produced, it is interesting to recoup both a bibliographical work with primary cultivation trials that might be performed into a laboratory photobioreactor, or microplates as displayed in the Fig. 6.2.4.3.

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193

FIG. 6.2.4.2 Overview of cyanobacterial organization: (A) cross-section of a cyanobacteria: Synechococcus elongatus, (B) diagram of the complexes involves in the light-dependent ETC (Ducat et al., 2011).

FIG. 6.2.4.3

Microplate used for screening microalgae cultivation at Algae Natural Food, Riquewihr, France.

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In regard to the right strains to use, selected strains are either isolated, identified, and purified from natural and various habitats, or should be bought from a public or private microalgae bank. A strategy for improving cultivation systems is to perform physiological stress on the strains, such as severe culture conditions like pH, temperature, and light, to isolate the robust algae cells that deserve to be inoculated for further cultivation. However, genetic manipulation on microalgae cells to improve performance cultivation is not a current and global way of research, nor is it recommended for that purpose. Three microalgae cultivation modes are used so far: microalgae cells may grow (1) autotrophically, where mineral compounds and light are used, (2) heterotrophically, where organic compounds such as glucose and a dark mode is used, and (3) mixotrophycally, which is a blend of the first two modes, like using organic compounds and light to grow microalgae. Modes (1) and (3) are related to the purpose of that chapter being using flue gases for cultivation. Regarding the microalgae environmental condition, one of the most important steps concerns the identification of the optimal growth parameters and the composition of the medium. Water salinity is linked to the type of water, which may be freshwater, marine water, or hypersaline water. It also may display various minerals in different concentrations that would eventually affect cultivation and the nutritive medium that should be complemented. Moreover, for massive microalgae cultivation, the current stream of R&D is to valorize agrofood wastewaters with high mineral and biocomponent composition in order to avoid using artificial nutritive media to be bought and added to the cultivation. Formulation of wastewater for microalgae culture is more challenging as it represents a complex liquid system combining both minerals and organic parts, from small molecules to huge ones, and in equilibrium in a particular pH and temperature. Light is the second

major component to be addressed. Usually, cultivation uses natural sum beam and respects a light-dark cycle, called the photoperiod. Geographical aspects such as the latitude of the cultivation area, the season, and the time of the day determine the daily access of light for suitable growth. Artificial light may be used either for extra illumination supply, especially during winter or for Northern regions, or when an absolute industrial cultivation control is required by the commercial client, which is the case for highvalued molecules or microalgae extracts for the cosmetics industry. Then sparging rate, gas distribution, mixing quality, air quality, and composition are considered. This is not only to provide a suitable mass transfer of CO2 as a primary source of carbon, but also to avoid microalgae cell sedimentation, especially for those not equipped with flagella, that would impair growth because of the limitation of light access and bacteria development. Concerning the cultivation systems, two major systems are usually utilized: ponds or photobioreactors. Ponds, also called open ponds or open systems, may take many forms such as a natural pond where microalgae develop more or less monospecifically, that is, for one specific strain, as is the case for some African lakes where Spirulina develops naturally and is taken out and eaten by local inhabitants. Artificial ponds are also well known with a so-called raceway, typically designed in a U-shape. Other names exist such as round ponds or racetracktype ponds. Many sizes, lengths, deepnesses, and designs exist, from the lab scale to hundreds of cubic meters. The latter design represents the least expensive cultivation system for massive microalgae cultivation. Indeed, for artificial ponds, a mere large hole dug in the soil with a liner, all of which is equipped with a mechanical system to circulate the culture to avoid cell sedimentation, is the minimum required to produce microalgae for a low Capex. Working on, harvesting, and cleaning such a system displays a low Opex as well. However, a large area is

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6.2.4.4 MICROALGAE CULTURE

needed for setting up ponds, and this may represent a real issue where access to land is either difficult because of the topography, or expensive. Also, the growth productivity is usually low as the ratio of illuminated surface on useful culture volume is unfavorable. Moreover, because of their design, ponds are open to whatever comes from the air such as pollution, aerosols, etc., which would eventually contaminate the microalgae cultivation, including by other microalgae species. This explains why it is so difficult to cultivate a single microalgae strain in such a system usually required by the client. Finally, ponds display a poor ability to control culture parameters, such as controlling the light beam or water quality. For all the reasons

195

mentioned above, the microalgae biomass usually obtained in raceway ponds is not that much, around 0.5–1 g L1. This is unlike photobioreactors, which can display up to 4 g L1 (Davis et al., 2011), even though this high cell concentration induces serious shading phenomena that greatly limit the growth. From an area perspective, the productivity may attain 96 g m2 d1, giving a theoretical value of 350 ton ha1 year1 (Zamalloa et al., 2001). From an area perspective, the productivity may attain 96g m2 d1, giving a theoretical value of 350 ton ha1 year1 (Zamalloa et al., 2001). From the photobioreactor perspective, also called a closed system, many strategic designs have been developed for decades, such as the ones displayed in Fig. 6.2.4.4, and further

FIG. 6.2.4.4 Some photobioreactor designs: (A) flat PBR, (B) biocoil 1000 L tubular PBR, (C) plastic bag, and (D) air-lifted tubular PBR (Andersen, 2005).

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creation and development of designs and equipment are the current research. The simplest one is the column photobioreactor. It may be made of soft plastic forming a plastic bag, which is the cheapest photobioreactor to be made because these are industrially manufactured as rolls from which the operator can cut the proper length to get the volume wanted for microalgae cultivation. It may also be made of plain plastic.

6.2.4.5 CO2 BIOFIXATION BY MICROALGAE: MICROALGAE SPECIES AND PERFORMANCES CO2 biofixation by microalgae depends on the right selection of microalgae strain to be cultivated into its proper cultivation system (specific customized pond or PBR) and optimized under the local environment (sunlight access, fresh or seawater, wastewater) and specific parameters (sparging rate and quality, pH control, nutritive medium). The scientific literature is full of references to microalgae tolerance for high levels of CO2 (Tang et al., 2011) and those used for CO2 mitigation such as Botryococcus braunii, Chlorella vulgaris, Chlorella kessleri, Chlorocuccum littorale, Scenedesmus sp., Chlamydomonas reinhardtii, and Spirulina sp. (Aslam and Mughal, 2016), even though strain selection is not easy because of their morphology, growth features, or various environmental factors (Velea and Dragos, 2009). Specifically, it regularly describes such a performance with the microalgae Chlorella. Indeed, the strain C. vulgaris features an outstanding capacity to fix CO2 at a pace of more than 6 g L1 d1 (Cheng et al., 2006). It has also been demonstrated than the strain Chlorella sp. can also remove nitrogen oxides and sulfur dioxides from gas and CO2 at a pace of 0.8–1 g L1 d1 (Keffer and Kleinheinz, 2002), and it has been confirmed that Chlorella is a great CO2 removal algae (Chiu et al., 2008).

Microalgae uses CO2 for two main reasons: creating and developing its own cell organites for biomass productivity or for assuring that its own metabolism (Chiu et al., 2009) can survive and develop, and where carbon mitigation may be lowered, as demonstrated for some species where optimal CO2 removal occurred at 1%, even though higher biomass productivity is observed beyond that CO2 rate (Ramanan et al., 2010). Moreover, the more CO2 is used for microalgae growth, the more lipids and fatty acids the latter may produce, representing an obvious environmental and economical field of interest for mankind. Indeed, several microalgae show an increase production of polyunsaturated fatty acids (PUFAs) and total lipids when sparged with 30%–50% of CO2 (Chiu et al., 2008; Tang et al., 2011), which could be caused by a diminution of the O2 level affecting enzymatic desaturation (Vargas et al., 1998). For instance, Chlorella concentrated fatty acids starting from 0.04% up to 4%–5% of CO2 (Tsuzuki et al., 1990). Generally, it is now accepted by the scientific community that a level of CO2 that ranges from 0.2% to 5% in the gas flow is recommended to achieve sufficient biomass productivity for most microalgae species. For instance, Nannochloropsis occulata grows well at 2% of CO2 but its growth is stopped at 5% (Hsueh et al., 2007). Some species develop well with sparging gas containing between 5% and 20% of CO2, which is considered a significant level. However, a level above 20% which is considered high, may impair the cultivation and reduce biomass productivity (Silva and Pirt, 1984; Lee and Tay, 1991), even though it depends on the microalgal cell concentration and pH (Chiu et al., 2008, 2009; Olaizola, 2003). Finally, few specific strains grow quickly under a CO2 level up to 20%. It has even been shown that some microalgae displayed a high rate of photosynthesis when grown under 40% of CO2 concentration, and may show a good CO2 tolerance up to 100% of CO2 (Matsumoto et al., 1997; Olaizola, 2003).

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6.2.4.5 CO2 BIOFIXATION BY MICROALGAE: MICROALGAE SPECIES AND PERFORMANCES

rate of more than 1 g CO2 L1 d1 for Chlorella sp. (freshwater species) and Chlorococcum littorale (marine species) (Murakami and Ikenouchi, 1997). The main criterion to quantify the CO2 mitigation from a biological system is to determine the CO2 efficiency, given by the following formula (Chiu et al., 2009):

That CO2 tolerance limitation could be explained either by the stress the CO2 high level represents for microalgae photosystem II, which is inhibited (Xu et al., 2003), or by the rise of the osmotic pressure on the microalgal cell (Soletto et al., 2008). It should be noted that CO2 tolerance surprisingly depends on nutrients and light as well (Soletto et al., 2008). Identification of a strain that grows under a higher CO2 level is one of the current research methods. Using a lab photobioreactor, researchers demonstrated that some microalgae absorb CO2 gas generated by coal power plants. One of the parameter used to demonstrate sequestration performances is the CO2 conversion efficiency into algal biomass. For instance, 1.5 kg of CO2 may be transformed into 1 kg dry weight of Chlorella (Velea and Dragos, 2009); a similar observation gives 2 tons of CO2 generating 1 ton of microalgae biomass (Stepan et al., 2002). Another scientific source reported a CO2 fixation TABLE 6.2.4.1

197

CO2 efficiency ð%Þ ¼

ðCO2 influent  CO2 effluentÞ∗ 100%=CO2 influent

Table 6.2.4.1 illustrates the CO2 efficiency for some microalgae species. According to Table 6.2.4.1, the CO2 removal rate is similar to the CO2 fixation rate, RCO2, measured in (g CO2 m3 h1), and can be related to the carbon content CC, in g/g of cell dry weight, of the microalgae biomass by the following formula (Yun et al., 1997): RCO2 ¼ CC μL ∗ ðMCO2 =Mc Þ

CO2 Removal Efficiency From Some Microalgae Species (Aslam and Mughal, 2016)

Microalgae Species

Cultivation System

Temperature (°C)

Lipid Content (% Dry Weight)

Chlorella sp.

Sequential bioreactor

27

18–48

15

1

85.6

Andersen (2005) and Velea and Dragos (2009)

Chlorococcum littorale

Fate PBR

25

19.3

20

0.4

16.7

Ono and Cuello (2007), Ramanan et al. (2010), and Andersen (2005)

Monoruphidium minutum

Flask

25



13.6

1

90

Silva and Pirt (1984) and Soletto et al. (2008)

Nannochloropsis sp. Cylindrical glass PBR

25–27

35.7

2–15

0.17

11–47

Lee et al. (2000) and Sierra et al. (2008)

Spirulina sp.

30

4–16.6

6

0.22

53.29

Andersen (2005), Rodolfi et al. (2009), Roncallo et al. (2012), and Sanchez Miron et al. (2000)

Tubular PBR

CO2 Concentration (%)

CO2 Growth Rate Removal (g L21 d21) (%)

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Reference

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6.2. VEGETAL PRODUCTION

where μL is the volumetric growth rate (g dry weight m3 h1) in the linear growth phase, and MCO2 and Mc are, respectively, the molecular weight of CO2 and C. However, it has been observed that the fixation rate of CO2 by microalgae is low. Usually, the flue gas generated by a plant is high in temperature: the strains to be chosen should therefore be thermotolerant, like the ones that naturally grow in hot spring water or that grow well around or above 30°C. Hence, a microalgae cultivation area should be set up next to such an industrial gas-emitting plant. For instance, hot spring water Chlorella in Japan has been cultivated under a CO2 level of at least 40% and 42°C (Wang et al., 2008). Regarding the cyanobacteria Spirulina sp., the productivity attained under 12% of CO2 was 0.22 g L1 d1 with a yield of 3.50 g L1 DW (Murakami and Ikenouchi, 1997). Another example is for preselected Scenedesmus and Chlorella that have been grown under 50% of CO2 with a good growth rate (Hanagata and Takeuchi, 1992).

6.2.4.6 THE USE OF NOX AND SOX BY MICROALGAE For untreated flue gases displaying upper levels of CO2, SOx, and NOx, the common scientific approach is to select strains that are capable of biologically resisting such gases and that present a high growth rate along with a sufficient cell density (IEA, n.d.). Otherwise, the culture may be at least inhibited and eventually die.

Also, the more tolerant the strain to those untreated gases, the less the potential cost of gas pretreatment is considered. A good example concerns the new Chlorella called KR-1, which has not been inhibited under 100 ppm of NO, 50 ppm of SO2, and 20% of CO2 (Lee et al., 2002; Sung and Lee, 1998). Table 6.2.4.2 gives insight into such a tolerance with microalgae growth performance.

6.2.4.7 TOLERANCE AND REMOVAL OF NOX FROM MICROALGAE The biofixation process of NO and NO2 is quite efficient during the exponential phase of the microalgal culture, but might inhibit the growth if added too early at the beginning of the growth. Several parameters are considered when studying the NOx tolerance. Among them, the microalgae strain selection is one of the most considered parameters; the growth phase and NOx concentration at a given flow rate are also important parameters (Aslam and Mughal, 2016). Nitrogen oxide NO represents the most of NOx from flue gases, more than 90%, and is interesting to be eliminated by a microalgal system because of its poor aqueous solubility ( Jin et al., 2005). To avoid this limitation, researchers added chelatant agents to turn the NO in gas form into an aqueous and stable form, like a metal-nitrosyl complexes. For instance, adding ethylenediaminetetraacetic acid chelated with

TABLE 6.2.4.2 Growth Features of Microalgae Suitable for CO2 Absorption Under Toxic Gases (Aslam and Mughal, 2016; Lee and Lee, 2003) Microalgae

CO2 (%)

NOx (ppm)

SOx (ppm)

Growth Rate in Linear Phase (g L21 day21)

C. littorale

70

50

30

0.47

Chlorella HA-1

20

100

50

0.51

Chlorella KR-1

30

100

100

0.78

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6.2.4.8 TOLERANCE AND REMOVAL OF SOX FROM MICROALGAE

Iron (II): Fe(II)EDTA to NO(g) rapidly generates the aqueous form of NO: Fe(II)EDTA-NO(aq) ( Jin et al., 2008). Other chelating agents may be used: nitrilotriacetic acid (NTA), methyliminodiacetic acid (MIDA), or dimercaptopropanesulfonic acid (DMPS). However, adding such a chelating agent might be considered a micropollutant and might impair the subsequent use of the microalgal biomass. Moreover, it has been demonstrated that the NOx removal rate is quite low in a microalgal system, for example, 0:74gNOx mreactor 3 d1 (Van Den Hende et al., 2011), and does not represent a major way to get rid of it. Some complexes are also unstable under long sunlight exposure, which is the case for iron EDTA (Lockhart and Blakeley, 1975). Nannochloropsis sp. cultivation removed half the NOx present at 300 ppm from flue gases (Yoshihara et al., 1996). It should be noted that NO partially oxidized into the aqueous molecule of NO2 by reacting with dioxygen generated from the algae culture during photosynthesis, and therefore may inhibit the cultivation of microalgae (Matsumoto et al., 1997).

6.2.4.8 TOLERANCE AND REMOVAL OF SOX FROM MICROALGAE Microalgae are known to be more sensitive to SOx uptake and can easily be inhibited. Also, the SO2 may be literally toxic for some species (Lee et al., 2000). The admitted threshold for SO2 is 50 ppm for many strains (Yanagi et al., 1995). This is partly due to the decrease of the cultivation media pH following SOx sparging; for instance, 400 ppm of sulfur dioxide SO2 decreases the pH to 4, sufficiently acidic to stop microalgae growth (Matsumoto et al., 1997; Stepan et al., 2002). But the process is not irreversible: adding some basic chemical agents such as NaOH increases pH and the culture grows normally, even with SOx (Matsumoto

199

et al., 1997). Another reason for that potential detrimental effect is the anion bisulfite HSO3ðaqÞ  concentrations, as this plays the role of oxidizing or reducing agent. That could eventually generate highly oxidative molecules that can damage microalgae organites and biomolecules and therefore can stop microalgae growth. HSO3ðaqÞ  is formed by easily dissolving SO2 in gas form with carbonate CO3ðaqÞ 2 . An illustration about the toxicity concerns concentrations below 104 mg L1 of NaHSO3, the aqueous form of sulfur HSO3ðaqÞ  is a good S-source for B. braunii once oxidized into sulfate SO4 2 , the preferred form for microalgae assimilation; but a level above 104 mg L1 of NaHSO3 is shown toxic for that microalgae (Yang et al., 2004). This can be explained by the oxidative entities, such as hydroxyl radicals, superoxide anions, or hydrogen peroxides, that are formed during the oxidation from HSO3  to SO4 2 and cause the peroxidation of the lipids building membranes and bleaching of chlorophyll (Giordano et al., 2005). So, an artificial rise of pH during cultivation, to at least pH 6, should limit the formation of HSO3  and its potential detrimental consequences on cultivation (Lee et al., 2000). Not much scientific data has been released so far about the removal rate of SO2 by microalgae. Besides, it is a common practice in the microalgae world to use the vessel volumes per minute (vvm) as a measure of the flow rate; this is merely the standard gas that is a gas volume running per minute, the gas flow rate, but also per bioreactor volume. A study displayed a rate of only 3.2 mg SO2 L1 d1, conveyed into a very low gas flow rate of 0.0050 vvm containing 572 mg N m3 SO2 from flue gas. As expected, the SO4 2 increased at the same time from 50.7 to 54.9 mg L1 in the liquid cultivation media (Van Den Hende et al., 2011). From an industrial perspective, once the biomass is harvested from culture, the remaining cultivation media would be discharged for subsequent water treatment. However, a higher sulfate level would not let that wastewater be eligible for treatment

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because of regulations, which is for instance from 90 to 150mgSO4 2 L1 . This constitutes a roadblock for flue gas SO2 removal, much more so than microalgae SO2 tolerance (Aslam and Mughal, 2016).

6.2.4.9 EFFECTS OF EXTERNAL PARAMETERS 6.2.4.9.1 Mass Transfer, Flow, and Mixing For a microalgal cultivation system, mass transfers involves the absorption by the microalgae (solid phase) of the nutritive components dissolved in the cultivation media (liquid phase) and including CO2 both in gas form (gas phase) and aqueous form (HCO3  ) (liquid phase), as summarized in Fig. 6.2.4.5. Optimization comes both from new theoretical equations (Sanchez Miron et al., 2000) and experiments by varying CO2 concentration, bubble size, gas flow rate, gas holdup, and superficial aeration velocity. CO2 removal is enhanced when the adequate algae species is used under optimized operating conditions, as illustrated in Table 6.2.4.3 for Chlorella sp. (Chiu et al., 2008). It has also been demonstrated that a gradual supply of CO2 for microalgae cultivation to a significant level could increase the growth and CO2 removal rate more than a constant rate. This

FIG. 6.2.4.5 Mass transfer involved in a microalgae system (Velea and Dragos, 2009).

TABLE 6.2.4.3 CO2 Removal for Chlorella sp. (Chiu et al., 2008) CO2 (v/v)

CO2 Removal Efficiency (%)

2

58

5

27

10

20

15

16

can be explained by a better adaptation of the microalgae for CO2 tolerance (Yun et al., 1996). The optimal aeration rate recommended, embodied by the gas volumetric flow rate per unit volumetric culture medium (vvm), ranges from 0.025 to 1, and depends on the species and PBR configuration. In that configuration, 5%–10% (v/v) of CO2 seems to be effective for a satisfying CO2 removal by microalgae (Sierra et al., 2008). Above that range, the aeration rate will eventually cause shear stress due to bubble generation, coalescence, and breakup.

6.2.4.9.2 Artificial and Natural Light Two common strategies exist about the light supply for microalgae cultivation: (1) natural light and (2) artificial light. The main interest of the latter is that the light is controlled by operators both in intensity (measured in W m2 or μmol m2 s1, even in lux, which provides an idea about light intensity but is not recognized as a thorough light measure), and light beam direction (meaning the right incident angle into the microalgae culture). This approach may be used whenever strict cultivation control is required, typically for producing high-value compound purposes, that is, in the biotech, cosmetics, or health industry, or to supply extra light at natural light when the season, weather, or production site location is unfavorable. However, the main roadblock is the cost of artificial light because it is usually high in Capex and

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6.2.4.10 VALUABLE COMPOUNDS FROM MICROALGAE

Opex, where a high power supply consumption is needed to operate that kind of lighting. Current development about artificial light is the utilization of LEDs, optical fibers, and thorough work on the photoperiod, which is the right balance between dark and light duration for a period of time and for a given strain. When thinking in terms of a large-scale cultivation area, the most economical way to supply light is obviously the use of sunlight, which is the cheapest way to supply light for a massive cultivation facility. For instance, the highest light intensity is 1100 W m2 at midday (Miyake et al., 1999). Stated otherwise, a typically sunny day in France gives around 1350 μmol m2 s1 (80,000 lux). Interestingly, only dozens of μmol m2 s1 are enough to let the microalgae cell do its photosynthesis overcoming its respiration mode, and then starting to produce biomass and growth; for example, only 34μmol m2 s1 are enough to yield a maximum cell density of 37.5 106 cell mL1 for the strain Nannochloropsis sp. in a 25-cm diameter vertical photobioreactor (Roncallo et al., 2012). Unfortunately, sunlight is not constant during the course of the days, seasons, or latitudes. Moreover, as that way for lightening is used for outdoor open pond cultivation, sunlight comes with UV-radiations those might damage microalgae cells (Chen et al., 2008), and also implies a day-night cultivation mode where half of the period of time of a culture is not illuminated. All those factors largely impair the cultivation and explain why the growth rate is low in such a cultivation mode. That general lack of light energy impairs the light conversion efficiency, impacting the metabolism of microalgae cells where the biocomposition of algae is modified; that is, the carbohydrate content decreases for Chlorella pyrenoidosa at night (Ogbonna and Tanaka, 1998).

6.2.4.9.3 Temperature Temperature greatly influences the microalgae cultivation performance because it is directly linked to enzyme optimum functioning

201

and therefore, metabolism. Hence, it is common to cultivate Spirulina strains under 35°C in situ for achieving maximum productivity; that explains why such a strain is massively produced in sunny regions and inside a greenhouse to promote high temperature for cultivation. Another example is for the Nannochloropsis strain, which grows better when the temperature is less than 25°C. However, the flue gas used as a CO2 inlet usually comes with very high temperatures, usually around 120°C (that is, in power plants). For such a cultivation mode, the strategy is to select strains tolerant to high temperature to both assure a workable biomass production and to save on the cost of cooling flue gases (Ono and Cuello, 2007). Therefore, either mesophilic microalgae, where optimal growth occurs between 13°C and 45°C, or thermophilic ones that range from 42°C to 75°C, with both displaying a high tolerance to CO2, are the best candidates for achieving significant biomass production when using flue gases. The main issue of working at those high temperatures is eventually water evaporation of the cultivation medium that concentrate dissolved nutritional salts, increase the shadowing effect by rising the cell density, and might impact the pH, perturbating the smooth run of the microalgae cultivation.

6.2.4.10 VALUABLE COMPOUNDS FROM MICROALGAE By choosing specific microalgae with high CO2 fixation capability and growth rate, the valorization of the microalgae biomass can be considered for the production of valuable and sellable biocompounds, CO2 level increase may at least be offset, no saying decreasing on the long run. Clearly, there are two ways to value biocompounds produced by microalgae when grown for CO2 biofixation. The first consists of recovering compounds that may be edible, either for the

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6.2. VEGETAL PRODUCTION

feed or the food industry. This may be possible only when CO2 gas from an agroplant is used for microalgae culture, which does not usually occur unless treated flue gas is used. Thus, many feed additives such as antioxidants, amino acids, pigments, crude proteins, PUFAs, and pharmaceuticals may be obtained from such cultivation. Selling prices per kg are usually higher than those of nonedible compounds, potentially reaching $100,000 per kg for very high value products. The other way is to extract compounds for nonedible utilization, and this is the preferred way when using CO2 from flue gas containing toxic SOx and NOx. For the latter, hydrocarbons may be extracted by solvent in order to make some biofuels by thermochemical liquefaction. Another way is to mix a synthetic polymer with microalgae to produce new building material. This was done by mixing C. vulgaris with polyvinylchloride into molds to create new structures (Velea and Dragos, 2009), but again, the economic yield has to be thoroughly checked.

6.2.4.11 CONCLUSION So much work has been done so far to understand the mechanism of absorption and use of various gases by microalgae, and especially the flue gas ones. By that way, microalgae are fully entering into a new business model, the circular economy, where algae should be grown industrially in a very large scale in a profitable way while using a massive quantity of flue gas with a beneficial environmental impact. Hence, the issue about gas transportation for making that algae cultivation concept true. The new business model should be based on a solid, win-win, and durable industrial partnership between a large-scale algae producer and an industrial plant wanting to get rid of its gas for various reasons. Worldwide, very rare microalgae producers have already installed their algae culture plant aside to an industrial flue gas producer; Algae Natural Food from

Riquewihr, France, has done it since 2014 by setting up its Spirulina cultivation facilities next to a malting plant in Strasbourg, France, that produces malt for the beer industry from barley. In that business model, Algae Natural Food uses not only the rinsing water from barley as the liquid base to cultivate Spirulina inside, saving hundreds of cubic meters of fresh water, but also it uses calorific energy that the malting plant produces to keep the right cultivation temperature, especially during winter, and of course the CO2 gas coming from the respiration of barley during the germination into malt process. The short distance between the algae cultivation platform and the malting plant enables getting a low CAPEX and OPEX for production microalgae, and consequently offers an attractive selling price for the food and feed industries. Reusing byproducts of plants such as flue gases in order to restart new primary biological productions as microalgae not only permits industrially acting in an economically friendly way, but also significantly decreases production costs and opens new markets. The circular economy fully applies here and is now a reality for producing microalgae that way, and will develop for the next generations to come.

References Andersen, R.A., 2005. Algal Culturing Techniques, first ed. Academic Press. Aslam, A., Mughal, T.A., 2016. A review on microalgae to achieve maximal carbon dioxide (CO2) mitigation from industrial flue gases. Int. J. Res. Advent Technol. 4, 12–29. Badger, M.R., Spalding, M.H., 2000. In: Leegood, R.C., Sharkey, T.D., von Caemmerer, S. (Eds.), Photosynthesis: Physiology and Metabolism. Kluwer, pp. 369–397. Broda, E., 1975. The Evolution of Bioenergetic Processes. Pergamon Press, Oxford, pp. 135–137. Chen, C.Y., Saratale, G.D., Lee, C.M., Chen, P.C., Chang, J.S., 2008. Phototrophic hydrogen production in photobioreactors coupled with solar-energy-excited optical fibers. Int. J. Hydrogen Energy 33 (23), 6886–6895. Cheng, L., Zhang, L., Chen, H., Gao, C., 2006. Carbon dioxide removal from air by microalgae cultured in a membranephotobioreactor. Sep. Purif. Technol. 50 (3), 324–329.

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Chiu, S.Y., Kao, C.Y., Chen, C.H., Kuan, T.C., Ong, S.C., Lin, C.S., 2008. Reduction of CO2 by a high-density culture of Chlorella sp. in a semicontinuous photobioreactor. Bioresour. Technol. 99 (9), 3389–3396. Chiu, S.Y., Kao, C.Y., Tsai, M.T., Ong, S.C., Chen, C.H., Lin, C.S., 2009. Lipid accumulation and CO2 utilization of Nannochloropsis occulata in response to CO2 aeration. Bioresour. Technol. 100 (2), 833–838. Davis, R., Aden, A., Pienkos, P.T., 2011. Techno-economic analysis of autotrophic microalgae for fuel production. Appl. Energy 88 (10), 3524–3531. Dreybrodt, W., Eisenlohr, L., Madry, B., Ringer, S., 1997. Precipitation kinetics of calcite in the system CaCO3 H2O CO2: the conversion to CO2 by the slow process H+ + HCO3 ! CO2 + H2O as a rate limiting step. Geochim. Cosmochim. Acta 61 (18), 3897–3904. Ducat, D.C., Way, J.C., Silver, P.A., 2011. Engineering cyanobacteria to generate high-value products. Trends Biotechnol. 29 (2), 103–195. Giordano, M., Beardall, J., Raven, J.A., 2005. CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. Annu. Rev. Plant Biol. 56, 99–131. Hanagata, N., Takeuchi, T., 1992. Tolerance of microalgae to high CO2 and high temperature. Phytochemistry 31, 3345–3348. Hsueh, H.T., Chu, H., Yu, S.T., 2007. A batch study on the bio-fixation of carbon dioxide in the absorbed solution from a chemical wet scrubber by hot spring and marine algae. Chemosphere 66 (5), 878–886. IEA, n.d. Carbon Dioxide Capture From Power Stations. www.ieagreen.org.uk. Jin, Y., Veiga, M.C., Kennes, C., 2005. Bioprocesses for the removal of nitrogen oxides from polluted air. J. Chem. Technol. Biotechnol. 80 (5), 483–494. Jin, H.F., Santiago, D.E., Park, J., Lee, K., 2008. Enhancement of nitric oxide solubility using Fe(II) EDTA and its removal by green algae Scenedesmus sp. Biotechnol. Bioprocess Eng. 13 (1), 48–52. Keffer, J.E., Kleinheinz, G.T., 2002. Use of Chlorella vulgaris for CO2 mitigation in a photobioreactor. J. Ind. Microbiol. Biotechnol. 29 (5), 275–280. Lee, J.-S., Lee, J.-P., 2003. Review of advances in biological CO2 mitigation technology. Biotechnol. Bioprocess Eng. 8, 354–359. Lee, Y., Tay, H.S., 1991. High CO2 partial pressure depresses productivity and bioenergenetic growth yield of Chlorella pyrenoidosa culture. J. Appl. Phycol. 3, 95–101. Lee, J.H., Lee, J.S., Shin, C.S., Park, S.C., Kim, S.W., 2000. Effects of NO and SO2 on growth of highly-CO2-tolerant microalgae. J. Microbiol. Biotechnol. 10 (3), 338–343. Lee, J.S., Kim, D.K., Lee, J.P., Park, S.C., Koh, J.H., Cho, H.S., Kim, S.W., 2002. Effects of SO2 and NO on growth of Chlorella sp. KR-1. Bioresour. Technol. 82 (1), 1–4.

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Liu, R., Liu, Y., Z, C., 2013. Development of an efficient CFDsimulation method to optimize the structure parameters of an airfilt sonobioreactor. Chem. Eng. Res. Des. 91 (2), 220–221. Lockhart, H.B., Blakeley, R.V., 1975. Aerobic photodegradation of iron (III)-(ethylenedinitrilo) tetraacetate (ferric EDTA). Implications for natural waters. Environ. Sci. Technol. 9 (12), 1035–1038. Markl, H., 1977. CO2 transport and photosynthetic productivity of a continuous culture of algae. Biotechnol. Bioeng. 19 (12), 1851–1862. Matsumoto, H., Hamasaki, A., Sioji, N., Ikuta, Y., 1997. Influence of CO2, SO2 and NO in flue gas on microalgae productivity. J. Chem. Eng. Jpn. 30 (4), 620–624. Miyake, J., Wakayama, T., Schnackenberg, J., Arai, T., Asada, Y., 1999. Simulation of the daily sunlight illumination pattern for bacterial photo-hydrogen production. J. Biosci. Bioeng. 88 (6), 659–663. Murakami, M., Ikenouchi, M., 1997. The biological CO2 fixation and utilization project by rite—screening and breeding of microalgae with high capability in fixing CO2. Energ. Convers. Manage. 38, S493–S497. Ogbonna, J.C., Tanaka, H., 1998. Cyclic autotrophic/heterotrophic cultivation of photosynthetic cells: a method of achieving continuous cell growth under light/dark cycles. Bioresour. Technol. 65 (1), 65–72. Olaizola, M., 2003. Microalgal removal of CO2 from flue gases: changes in medium pH and flue gas composition do not appear to affect the photochemical yield of microalgal cultures. Biotechnol. Bioprocess Eng. 8 (6), 360–367. Ono, E., Cuello, J.L., 2007. Carbon dioxide mitigation using thermophilic cyanobacteria. Biosystem Eng. 96 (1), 129–134. Ramanan, R., Kannan, K., Deshkar, A., Yadav, R., Chakrabarti, T., 2010. Enhanced algal CO2 sequestration through calcite deposition by Chlorella sp. and Spirulina platensis in mini-raceway pond. Bioresour. Technol. 101 (8), 2616–2622. Rodolfi, L., Chini Zittelli, G., Bassi, N., Padovani, G., Biondi, N., Bonini, G., Tredici, M.R., 2009. Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor. Biotechnol. Bioeng. 102 (1), 100–112. Roncallo, O.P., Garcia Freites, S., Paternina Castillo, E., Bula Silvera, A., Cortina, A., Acuna, F., 2012. Comparison of two different vertical column photobioreactors for the cultivation of Nannochloropsis sp. J. Energy Res. Technol. 135, 1–7. Sanchez Miron, A., Garcia Camacho, F., Contreras Gomez, A., Grima, E.M., Chisti, Y., 2000. Bubble-column and airlift photobioreactors for algal culture. AIChE J. 46 (9), 1872–1887. Sierra, E., Acien, F.G., Fernandez, J.M., Garcia, J.L., Gonzales, C., Molina, E., 2008. Characterization of a flat

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plate photobioreactor for the production of microalgae. Chem. Eng. J. 138 (1), 136–147. Silva, H., Pirt, S.J., 1984. Carbon dioxide inhibition of photosynthetic growth of Chlorella. J. Gen. Microbiol. 130, 2833–2838. Soletto, D., Binaghi, L., Ferrari, L., Lodi, A., Carvalho, J.C.M., Zilli, M., Converti, A., 2008. Effects of carbon dioxides feeding rate and light intensity on the fed-batch pulsefeeding cultivation of Spirulina platensis in helical photobioreactor. Biochem. Eng. J. 39 (2), 369–375. Stepan, D.J., Shockey, R.E., Moe, T.A., Dorn, R., 2002. Carbon Dioxide Sequestering Using Microalgal System. University of North Dakota. Sung, K.D., Lee, J.S., 1998. Isolation of a new highly CO2 tolerant fresh-water microalga Chlorella KR-1. Korean J. Chem. Eng. 15, 449–450. Tang, D., Han, W., Li, P., Miao, X., Zhong, J., 2011. CO2 biofixation and fatty acid composition of Scenedesmus obliquus and Chlorella pyrenoidosa in response to different CO2 levels. Bioresour. Technol. 102 (3), 3071–3076. Tsuzuki, M., Ohnuma, E., Sato, N., Takaku, T., Kawaguchi, A., 1990. Effects of CO2 concentration during growth on fatty acid composition in microalgae. Plant Physiol. 93 (3), 851–856. Van Den Hende, S., Vervaeren, H., Desmet, S., Boon, N., 2011. Bioflocculation of microalgae and bacteria combined with flue gas to improve sewage treatment. New Biotechnol. 29 (1), 23–31. Vargas, M.A., Rodriguez, H., Moreno, J., Olivares, H., Del Campo, J.A., Rivas, J., Guerrero, M.G., 1998. Biochemical composition and fatty acid content of filamentous nitrogen-fixing cyanobacteria. J. Phycol. 34 (5), 812–817. Velea, S., Dragos, N., 2009. Biological sequestration of carbon dioxide from thermal power plant emissions, by aborbtion in microalgal culture media. Rom. Biotechnol. Lett. 14 (4), 4485–4500. Wang, B., Li, Y., Wu, N., Lan, C.Q., 2008. CO2 bio-mitigation using microalgae. Appl. Microbiol. Biotechnol. 79 (5), 707–718. Xu, M., Chen, S., Liu, G., Hu, Z., 2003. Pilot study of physiological and morphological acclimation of Scenedesmus armatus under extreme high CO2 stress. Wuhan Bot. Res. 22 (5), 439–444. Yanagi, M., Watanabe, Y., Saiki, H., 1995. CO2 fixation by Chlorella sp. HA-1 and its utilization. Energ. Convers. Manage. 36 (6), 713–716. Yang, S., Wang, J., Cong, W., Cai, Z., Ouyang, F., 2004. Effects of bisulfite and sulfite on the microalga Botryococcus braunii. Enzyme Microb. Technol. 35 (1), 46–50. Yoshihara, K.I., Nagase, H., Eguchi, K., Hirata, K., Miyamoto, K., 1996. Biological elimination of nitric oxide

and carbon dioxide from flue gas by marine microalga NOA-113 cultivated in a long tubular photobioreactor. J. Ferment. Bioeng. 82 (4), 351–354. Yun, Y.S., Park, J.M., Yang, J.W., 1996. Enhancement of CO2 tolerance of Chlorella vulgaris by gradual increase of CO2 concentration. Biotechnol. Tech. 10 (9), 713–716. Yun, Y.S., Lee, S.B., Park, J.M., Lee, C.I., Yang, J.W., 1997. Carbon dioxide fixation by algal cultivation using wastewater nutrients. J. Chem. Technol. Biotechnol. 69 (4), 451–455. Zamalloa, C., Vulsteke, E., Albrecht, J., Verstraete, W., 2001. The techno-economic potential of renewable energy through the anaerobic disgestion of microalgae. Bioresour. Technol. 102 (2), 1149–1158.

Further Reading Benemann, J.R., 1997. CO2 mitigation with microalgae systems. Energ. Convers. Manage. 38, S475–S479. Brown, L.M., 1996. Uptake of carbon dioxide from flue gas by microalgae. Energ. Convers. Manage. 37 (6), 1363–1367. De Morais, M.G., Costa, J.A.V., 2007a. Biofixation of carbon dioxide by Spirulina sp. and Scenedesmus obliquus cultivated in a three-stage serial tubular photobioreactor. J. Biotechnol. 129 (3), 439–445. De Morais, M.G., Costa, J.A.V., 2007b. Carbon dioxide fixation by Chlorella kessleri, C. vulgaris, Scenedesmus obliquus and Spirulina sp. cultivated in flasks and vertical tubular photobioreactors. Biotechnol. Lett. 29 (9), 1349–1352. De Morais, M.G., Costa, J.A.V., 2007c. Isolation and selection of microalgae from coal fired thermoelectric power plant for biofixation of carbon dioxide. Energ. Convers. Manage. 48 (7), 2169–2173. Giavarini, C., Maccioni, F., Santarelli, M.L., 2010. CO2 sequestration from coal fired power plants. Fuel 89 (3), 623–628. Hu, Q., Kurano, N., Kawachi, M., Iwasaki, I., Miyachi, S., 1998. Ultrahigh-cell-density culture of a marine green alga Chlorococcum littorale in a flat-plate photobioreactor. Appl. Microbiol. Biotechnol. 49 (6), 655–662. Iwazaki, I., Hu, Q., Kurano, N., Miyachi, S., 1998. Effect of extremely high-CO2 stress on energy distribution between photosystem I and photosystem II in a “highCO2” tolerant green algae, Chlorococcum littorale and intolerant green alga Stichococcus bacillaris. J. Photochem. Photobiol. B: Biol. 44 (3), 184–190. Mata, T.M., Martins, A.A., Caetano, N.S., 2010. Microalgae for biodiesel production and other applications: a review. Renew. Sustain. Energy Rev. 14 (1), 217–232.

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S U B C H A P T E R

6.2.5 Liquid Nitrogen: A Sustainable Solution to Cryopreserve Life ` s Camus, Olivier Couture, Anne Linda Van Kappel, Guy Delhomme, Clemence Lesimple, Agne Andres Gonzalez, Richard LeBoucher, Christian Beau, Eric Schmitt IMV Technologies, L’Aigle, France

6.2.5.1 WHY CRYOPRESERVING? It would not be a surprise for a lab operator not to be amazed when he looks at cryopreserved cells coming back to life after years in liquid nitrogen. As a step back in time, the heat provided gradually melts ice crystals, wakes up complex biochemical machinery, and finally brings back life. In 1949, when Polge et al. successfully exploited the cryoprotective effect of glycerol to freeze the first mammalian cell (a spermatozoa, supposedly programmed to die fast), they definitely reached a milestone toward time control. Thanks to the following discoveries in this field, cryopreservation has led to many applications in animal research, farming, and health. Year after year, research has allowed the freezing of embryos, ovarian tissue, oocytes, and testicular tissue while providing precious tools to manage species and breeds. Today, this method is widely used in artificial insemination of cattle, small ruminants, equine, swine, fish, pets (that is, dogs), and endangered species (to help maintain biodiversity). Cryopreservation applied to artificial insemination plays a decisive role in the management of animal genetic resources, which is “the need to ensure that livestock can continue fulfilling

the roles that make them so important to the lives and livelihoods of so many people around the world, and that the value embodied in livestock biodiversity is not lost.” (FAO, 2012). It makes it possible to recreate a breed from conserved cells, even if only a small proportion of the breeds in the world can be considered as properly preserved: cattle (16% of breeds), goats (9%), sheep (9%), pigs (9%), and chickens (3%). Thawed cells (spermatozoa, oocyte, and embryos) give back genetics to first create new ancestors and later to optimize genetic diversity, minimizing inbreeding and genetic drift. In commercial breeding programs of animal species, cryopreservation is used to store the genetics of some individuals, to store alleles of interest, and more generally to collect images of past genetics. It is therefore possible to grow the family of a male, test their performance (milk production, meat yield, and disease resistance), and come back to the gene bank to collect straws full of marketable genetics. In a genetic environment of rapid adaptation to domestication, evolution, and selection, frozen straws are a freeze-frame of husbandry. When you control time, you can control distance. Cryopreservation deeply changed the artificial insemination industry, allowing male gametes to travel the world. It was the beginning

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of the globalization of genetics and the dispersion of some bull genes. One of the first famous bulls, Hanoverhill Starbucks, who was born in Port Perry on April 26, 1979, provided 685,000 straws sold in 45 countries. The record has now been set by Toy Story (May 1, 2001), who provided 2.4 million doses of frozen semen. Today, breeders use cryopreservation to manage the genetics of their population as well as to optimize fertility, health control, and hygiene. The holy trinity is a cell medium, a freezing curve, and an adapted container. Liquid nitrogen, Cassou straws (Cassou et al., 1994), and cryoprotectants are all choices that shaped the industry of different species and their history.

6.2.5.2 ARTIFICIAL INSEMINATION AND SEMEN PACKAGING 6.2.5.2.1 A Brief History of AI Artificial insemination (AI) in viviparous species dates back quite a long time, perhaps as far back as 1320 AD where an Arab chieftain purportedly mated mares with natural sponges using the sperm collected in the vagina of mares belonging to rival groups. The first reported successful insemination was performed on a bitch by Lazzaro Spallanzani of Italy in 1780 (Heape, 1897; Spallanzani, 1785; Walters et al., 2009). Spallanzani has since been known as the inventor of AI. In 1897, the British zoologist Walter Heape successfully inseminated rabbits, dogs, and horses. After pioneering semen work in the late 1890s on birds, cattle, horses, and sheep, Russia’s Ilya Ivanovich Ivanov in 1922 developed the first semen extender (a liquid medium where sperm cells are better preserved in time) and methods of artificial insemination similar to those we know today (Ombelet and Robays, 2015). Most of Ivanoff’s work was taken over by Viktor Milovanov, another Russian scientist who, in 1931, mass

bred almost 20,000 cows in Russia using AI. In 1938, Milovanov established major cattle breeding projects in Russia, a country known today as the first country having performed AI on a large scale (Ombelet and Robays, 2015). The later part of the 1930s was therefore the true start of AI. In 1936, Denmark’s Eduard Sorensen established the world’s first bovine AI cooperative with some 1100 cows (Bartlett, 1946; Foote, 2002). Sorensen invented the first “straw” (made of oat) in order to package semen inside (Foote, 2002), and F.J. Perry established the first AI cooperative in North America in 1938. Shortly after, the planet saw a massive increase of AI cooperatives being set up worldwide. Indeed, the dairy cattle industry proved to be the largest beneficiary of AI as AI brought four major advantages to the industry: (1) Fast genetic improvement of livestock using genetically superior sires (Walters et al., 2009), (2) Control of diseases (Critser and Russel, 2000; Knight and Abbott, 2002), (3) Increased fertility rates (Kuczynski et al., 2001; Nalesnik et al., 2004), and (4) Maintenance of genetic diversity (Critser and Russel, 2000; Walters et al., 2009).

6.2.5.2.2 Semen Packaging: Past and Present Up to the mid-1960s, glass ampules (Fig. 6.2.5.1) were the container of choice, whether frozen on dry ice or in LN2. However, besides the issues mentioned above, glass ampules had several problems, such as breaking easily or having lower fertility results due to their large volume/surface area (sperm cells freeze/thaw better when the volume surface ratio of the container decreases). In 1964, Robert Cassou of France, then founder and director of one of the first AI cooperatives in that country (L’Aigle 1947), revolutionized the AI industry by manufacturing a small 1.2-mL tube made of extruded PVC and a plug with a “tripartite” plug

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6.2.5.2 ARTIFICIAL INSEMINATION AND SEMEN PACKAGING

FIG. 6.2.5.1

207

First semen conditioning structure: glass ampules.

(Fig. 6.2.5.2). The straw was sealed at the opposite end first with polyvinylic alcohol, then mechanically by ultrasound. With the straw, the production of one center went from a few thousand doses to many tens of thousands per day. The “French straw,” as it became known worldwide, could at the same time be printed on (for bull identification), filled (diluted semen with extender and glycerol), sealed (to prevent diseases while in LN2 tanks), frozen on LN2

vapors or programmable freezers, preserved for a virtually unlimited time, thawed in a water bath (to prepare the insemination), loaded into a breeding gun, and its volume expelled thanks to a simple plunger system in the breeding gun. All the above advantages yielded more fertility results as well as ease of record keeping (Figs. 6.2.5.3 and 6.2.5.4). A genial multifunction container was born.

FIG. 6.2.5.2

straws.

FIG. 6.2.5.3 Medium and ministraws.

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IMV IS4 equipment to fill, seal, and print

208

FIG. 6.2.5.4

6.2. VEGETAL PRODUCTION

0% loss IMV Genom’X filling and sealing

equipment.

In 1964, while Nagase of Japan and Dr. Ed Graham from the University of Minnesota were developing a competing system known as the pellet (Nagase and Graham, 1964, Fig. 6.2.5.5), the straw rapidly became the container of choice. Even though the pellet proved to have good fertility results (Maxwell et al., 1980, 1995), its processing, use, and difficulty in labeling were far more cumbersome than the straw. The pellet is today seldom used, mostly only in Russia, Ukraine, and Cuba. More than 50 years after its invention, the straw is still the uncontested container of choice to spread genetics worldwide.

FIG. 6.2.5.5

As mentioned, it was first produced in 1964 in a 1.2-mL format to match the ampule format of the time. Then, in 1968, technological advances in extrusion allowed making the same small tube in 0.5 mL, a similar volume to that used with ampules (1 mL: Curtiss breeders in, 0.75 mL: Tri-State Breeders, then American Breeders Service with 0.5 mL). It was mentioned earlier that the volume/surface ratio is important to freeze living cells more successfully. Eight years after the birth of the French straws and 4 years after the engineering of the medium straw (0.5 mL), Cassou introduced the “ministraw” in 1972 with a total volume of 230 μL (0.23 mL) (Table 6.2.5.1). The thermal exchange during freezing being better than other enclosed systems, it was proven that ministraws (“quarter cc straws”) had better conception rates than medium straws (“.5 cc straws”). Furthermore, the ministraw took less space than any other container previously used. By 1976, most of Europe had switched to the ministraw. TABLE 6.2.5.1 Straw Classification Area (mm2)

Useful Volume (μL)

Volume/ Surface Ratio

Medium (0.5 mL)

1152

500

2304

Mini (0.25 mL)

823

210

3919

Straw Type

Another storage container for semen: pellet making.

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6.2.5.3 FREEZING TECHNIQUES

6.2.5.3 FREEZING TECHNIQUES 6.2.5.3.1 Semen Cooling in Early Times In the late 1930s and throughout the 1940s, bull sperm was cooled down to 5°C using egg yolk-phosphate, then sodium citrate (Philipps, Lardy, Salisbury), as a sperm membrane protector (Watson and Martin, 1973; Foote, 2002). Diluted semen used for insemination was kept in glass tubes. Balloons containing slushed ice were wrapped around the tube. It was then wrapped in insulating material in order to keep the temperature cool for a day or so (Fig. 6.2.5.6A and B). At that time, most inseminations were carried out the same day or within 3 days at

FIG. 6.2.5.6

209

the latest. Back then, we already knew that colder was better. In 1949, the United Kingdom’s Polge et al. discovered that semen could be successfully frozen with the addition of glycerol in the preserving media. This disruptive finding forever changed the cattle AI industry and to this date, bovine frozen semen represent >98% of all inseminations worldwide. Back in those days, dry ice was used to keep small glass ampules filled with semen frozen at 79°C (Bratton et al., 1955). However at 79°C, biological changes still occur in the sperm cells, making them obsolete after some time. The use of dry ice was also inconvenient due to the required frequent resupply.

(A) Fresh semen tubes (Cornell, 1941). (B) Semen tubes being prepared for dispatch (Cornell, 1941).

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Scientists had shown that keeping cells at ultralow temperatures, as with liquid nitrogen (LN2), stopped all metabolism. Although LN2 was first liquefied in 1883 by Polish physicists Wroblewsi and Olszewski (Sarangi, 1987) and the “dewar” (a vacuum flask) invented by James Dewar from the United Kingdom in 1892 (Freiman and Bouganim, 2005), it is not until the mid-1950s that large, efficient LN2 containers were made available to the AI world. J. Rockefeller Prentice, owner of American Breeders Service, personally funded the American Cyanamid Corporation (a division of Linde) to develop an efficient insulated container, which they supplied to him in 1952. LN2, with a boiling temperature of 196°C/ vapor of 140°C showed that sperm survival, at this ultralow temperature, could be essentially indefinite. In 1952, American Breeders Service of De Forest, Wisconsin, collected and froze the first bull semen in liquid nitrogen. “Cottonade Emmet” produced offspring well into the 1980s. The combination of being able to successfully freeze semen and the availability of LN2 storage containers was the cornerstone of the development of the AI industry.

6.2.5.3.2 Generalities About Reproductive Tissue Freezing (Saragusty and Arav, 2011 for Review) Cryopreservation is the process of preserving living cells by controlled cooling to cryogenic temperatures where chemical reactions are slowed down to an extent that cells can be preserved for a very long period. An integral part of cryopreservation is the warming of the cells to bring them back to physiological temperature and to normal functioning. The cryopreservation process is characterized by two phase transition temperatures (Fig. 6.2.5.7). The first one is the freezing temperature (Tf). Above this temperature, the cryopreservation medium is still liquid. When cooling under the Tf, ice crystals appear and grow until

FIG. 6.2.5.7 Phase transitions during the cryopreservation process. Tf, freezing temperature; Tg, glass transition temperature, Tg 0 , amorphous glassy state.

the second phase transition temperature, the glass transition temperature (Tg). At this stage, the freezing medium is in a rubbery state (ice and cryo concentrate solution). When reaching the Tg, the growth of ice crystals stops and the sample turns into an amorphous glassy state (Tg ’ ), in which no change occurs anymore. Living cells contain large quantities of water and water molecules tend to form ice crystals when cooled to subzero temperatures. To avoid damaging ice crystal formation in freezing cells, the cells are dehydrated before and in the cooling process. To avoid damage from dehydration—the so-called osmotic stress— cryoprotectants are used to replace the water in the cells and to bind the water molecules. Much research has been done on the development of cryopreservation techniques for different types of cells to find the right balance between ice crystal formation and osmotic stress. Cryoprotectants are chemicals and may also affect cells when exposed at higher concentrations and temperatures. The development of artificial insemination techniques has become possible with the development of cryopreservation of spermatozoa.

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As mentioned earlier, Polge, Smith, and Parkes described the use of glycerol to freeze spermatozoa (Polge et al., 1949). Also, offspring by artificial insemination using frozen-thawed semen was reported in 1951 for cows (Stewart, 1951,) and in 1957 for pigs (Hess et al., 1957) and horses (Barker and Grandier, 1957). The use of frozen semen was developed for the species where the results were at least comparable with those achieved by natural mating and where commercial advantages existed. The development was also made possible in regions where cryogenic gasses were available and transport systems adapted.

2.5% to 10%. According to the type of tissue, the cryopreservative solution can be added to the semen at 34°C just after the collection (cattle), at room temperature (embryos), or at 4°C (cattle and swine). Germplasms are then kept at 4°C equilibration temperature (from a few minutes to 24 h) to allow osmotic exchanges between the cells and the freezing medium, then filled in straws before freezing. The freezing process traditionally follows three phases. First, the sample undergoes a slow cooling rate (3–60°C/min, respectively, for embryos and equine semen) from the equilibration to the supercooling temperature (approximately minus 7–10°C). At this stage, the solution, under the freezing temperature, is still in a liquid state. To limit the supercooling amplitude, crystallization can be induced to initiate the first ice crystal. The “seeding” can either be controlled at a set temperature by contact with a colder surface, shock, or chemical additive or uncontrolled to occur spontaneously. The cooling rate applied is then from 0.3°C/min for embryos to 60°C/min for certain spermatozoa, inducing a rubbery state. The slope allows the control of the size and the shape of ice crystals until 35°C (embryos) or 110 °C (semen).

6.2.5.3.3 Slow Freezing and Programmable Freezers (For Example, Holt, 2000; Pegg, 2007; Saragusty and Arav, 2011) 6.2.5.3.3.1 Slow Freezing (See Fig. 6.2.5.8) Germplasms are extended in cryopreservative solution to be gradually exposed to cryoprotectant agents and to reach the requested number of spermatozoa per dose. With the slow freezing technique, the concentration of cyoprotectant agent varies from

Time (s) 0 20

100

200

300

Liquid state

0

Temperature (°C)

–20

Super cooling

–40 –60 –80

Rubbery state /ice crystal grows

–100 –120 –140

Glassy state/ solid state

–160

FIG. 6.2.5.8

400

Freezing temperature/nucleation

Slow cooling slope.

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500

212

6.2. VEGETAL PRODUCTION

This phase is crucial to maintain cell survival. In the sample, only pure water will turn into ice. The cells and all solutes will form the “unfrozen fraction.” The concentrations of cryoprotectants, sugar, and salt will increase while the volume of unfrozen fraction decreases. Finally, the sample is transferred into liquid nitrogen to stop ice crystal growth and maintain the sample under the glass transition temperature (130°C). 6.2.5.3.3.2 Programmable Freezers The cryopreservation process has to follow a very precise and controlled succession of events to prevent cell death. To control precisely the cryopreservation process, IMV Technologies has designed special programmable freezers

FIG. 6.2.5.9

(Digitcool, capacity of 45–5300 straws according to the size), composed of four different parts: a temperature regulator, software to program the regulator and monitor the freezing, an isolated chamber, and an autopressurized tank. According to the wanted slope, the regulator controls the quantity of liquid nitrogen injected from the autopressurized tank into the chamber, thanks to a special solenoı¨d valve. The control of the temperature inside the isolated chamber and inside the sample is managed via two temperature probes (Figs. 6.2.5.9 and 6.2.5.10). Liquid nitrogen is injected on a squirrel cage fan and pulverized on the side. The cooled air flow is pushed along the sides of the chamber

Digitcool programmable freezer (IMV technologies) functioning.

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6.2.5.3 FREEZING TECHNIQUES

FIG. 6.2.5.10

213

IMV Digitcool programmable freezer. Up to 5250 straws frozen in LN2 per cycle.

to the top and then downward through the sample racks (inversed chimney effect).

6.2.5.3.4 Vitrification (Pegg, 2007; Sakai and Engelmann, 2007; Saragusty and Arav, 2011) Vitrification is the transformation of a liquid to a glass state. For liquid biological samples, it means a transformation into a solid without formation of ice crystals. It can be obtained by ultrafast cooling and/or chemical reactions. The water present in germplasm cells and embryos will be transformed into ice crystals when cooled to subzero temperatures. As indicated before, these ice crystals may lead to potentially lethal mechanical and osmotic damage to the cells. To avoid formation of ice crystals, it is therefore necessary to block the regrouping of water molecules in crystals. It can be done by ultrafast cooling—molecules do not have time to move—or by increasing the viscosity of the liquid so that molecules cannot move easily. Ultrafast cooling can be obtained by plunging small volumes of liquid directly into liquid nitrogen. The glass state is unstable and water molecules may form ice crystals in the warming process as soon as the temperature allows

molecules to move—above the glass transition temperature of water, 130°C. Therefore, it is very important to maintain constant cryogenic temperatures. Storage in liquid nitrogen is the best way to maintain samples at stable cryogenic temperatures. When the biological sample is to be recovered, the warming process has to be very fast in order to avoid formation of ice crystals (devitrification) during the warming up from the cryogenic to the positive temperatures. Vitrification has developed in cryopreservation of embryos and oocytes because of better survival, fertilization, and reimplantation rates, first in human IVF but more and more in veterinary applications. Embryos and oocytes are prepared with stepwise baths of increasing concentrations of cryoprotectants to diminish the concentration of free water in the cells and therefore the risk of icecrystal formation. Vitrification straws (Cryo Bio System) are composed of a very thin carrier for a droplet of a maximum 0.5 μL that is placed in a very thin straw. The cell is placed on the carrier in the straw and vitrified by plunging it directly in liquid nitrogen. For warming, the carrier is withdrawn from the straw and immediately plunged in a warmed recovery fluid that brings the cell from the glass state to the liquid state and washes out progressively the cryoprotectants.

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6.2.5.3.5 Storage Germplasms are stored under glass transition temperature (920,000 ministraws. 6. AGRICULTURE

6.2.5.5 TARGET ANIMAL SPECIES

species, but the spermatozoa modifications are never fully reversible and the reproductive efficiency of the frozen semen remains below that of the fresh one. 6.2.5.4.1.2 Oocyte (See Saragusty and Arav, 2011 for Review) Techniques for oocyte cryopreservation are much less developed than for semen or embryos (FAO Guidelines, 2012). Oocytes are, by nature, less prone to cryopreservation than spermatozoa: their larger size makes them more sensitive to chilling and intracellular ice crystallization, and the presence of the Zona Pellucida (protection envelop of the oocyte), acting as a supplementary barrier, may interfere with the diffusion of cryoprotectants. In addition to this simple physics phenomenon, the cryopreservation process may impact the oocyte’s structure in various ways: (1) The Zona Pellucida can be hardened during the freezing process, making it impossible for the spermatozoa to fertilize the oocyte. (2) The maturation process is interrupted by cryopreservation, altering the quality of the oocyte and compromising its viability and fertility after thawing. Despite these difficulties, successful freezingthawing processes exist in a great number of animal species (cattle and pigs: Critser et al., 1997 for review; goats: Le Gal, 1996), leading to viable birth of progeny in cattle (for example, Abe and Hoshi, 2005; Otoi et al., 1995) and horses (Maclellan et al., 2002).

6.2.5.4.2 Embryos (Saragusty and Arav, 2011 for Review) An embryo is a pluricellular structure, increasing the risk of ice formation during the freezing process. The main advantage of embryo cryopreservation is that it allows the dispersion of both male and female genetics. Two methods that reduce this risk are used for embryo cryopreservation: the embryos may be exposed to a high concentration of

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cryoprotectant and submitted to a fast cooling rate (vitrification), or to a low concentration of cryoprotectant and submitted to a slow cooling rate, allowing the dehydration of cells during the process and leading to the formation of ice in the extracellular matrix only. The choice of the freezing process depends on the species’ characteristics. Along with the intrinsic characteristics of the species, the stage of the embryo’s development has an impact on its resilience to cryopreservation; morulae or young blastocysts resist better than older embryos.

6.2.5.5 TARGET ANIMAL SPECIES 6.2.5.5.1 Bovine The bovine species is the primary target of germplasm and embryo cryopreservation (the first calf produced using cryopreserved semen was born in 1951, Curry, 2000). The artificial insemination using frozen semen represents nowadays >98% of the estimated 300 million yearly cattle AI in the world. More than 500 million semen doses are produced each year. For each collected ejaculate, an average of 400 straws is filled in, meaning potentially 400 cows inseminated. When using frozen semen, the pregnancy rate varies generally from 40% to 65%, depending on several parameters including the breed, age, feeding, management, and geographic location of the cow. In order to maximize the chance to obtain heifers (optimization of genetic performance and interval between generations), it is now possible for breeders to access frozen sexed (sorted) semen (8% of the insemination in 2014) and embryos (350,000 transfers/year). Two main techniques are used in bovine embryo production. With in vivo embryo production, heifers are superovulated and inseminated. After 7 days, uterine horns are “washed” (flushing techniques) and embryos collected. If the cow was inseminated with conventional (nonsorted) semen, embryos can be sexed and

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genotyped before freezing. The second technique, in vitro production, is mainly used in South America (Brazil, Argentina, Japan). Oocytes of cows with high genetic value are collected and fertilized in vitro. Embryos are then transferred in recipient cows (milking cow or lower genetic heifer). In bovine embryo cryopreservation, slow freezing is less constraining than vitrification. With slow freezing, the embryo can be directly transferred from the straw to the cow, whereas vitrification requires the removal of the cryoprotectants, which are toxic for the embryo.

6.2.5.5.2 Fish Use of cryopreservation in aquatic species started in the 1980s and rapidly spread to more than 200 species. Today, the largest volume of freezing comes from (1) reproductive practices in aquaculture, (2) breeding program management in aquaculture, and (3) conservation of genetic resources and endangered species. Milt cryopreservation is now fully integrated into reproductive practices of cultured marine and freshwater aquatic species by simplifying broodstock management (Martı´nez-Pa´ramo et al., 2016) and is used to: • Get milt available all-year round in nitrogen tanks, independently of male maturation control through hormone induction or photoperiod control. • Transport genetic resources in straws between hatcheries or from the wild. • Optimize the fertility of sperm when milt can be collected at its highest quality and limit risk of senescence. With the fast development of salmonid breeding programs, cryopreservation became a classical tool for aquaculture geneticists. The technique is used to: • Optimize the mating plans when male genetics can be repeatedly used in different crosses. • Improve the accuracy of estimated breeding values through progeny testing, when the

male genetics of the father are accessible for years. • Control of inbreeding in a selected population. • Conserve valuable genetic candidates. • Estimate the yearly cost effectiveness of a breeding program, when ancestor milt has been successfully frozen. Finally, conservation of aquatic genetic resources offers a chance to preserve species listed as threatened or endangered. With the help of reproductive biotechnologies, cryopreservation would help to further reconstruct the original strain, population, or diversity.

6.2.5.5.3 Porcine In swine species, cryopreservation is mostly used in the context of genetic line preservation, international breeding exchanges, and preservation of rare specimens. Considering the decreased number of doses per ejaculate (15 versus 30–50 in fresh semen), the lower farrowing rate and litter size with frozen semen, and the relatively long preservation of fresh semen in boars (up to 7 days), semen freezing is mostly used on high-value sows or species/breed preservation (Curry, 2000). Countries such as Vietnam, Laos, and Indonesia receive a rather important ratio of their genetic replacement via frozen semen coming mainly from the United States or Canada. South Africa routinely receives high-value genetics in frozen straws as well. Pig embryos have long been the most difficult embryos to cryopreserve because of their extreme sensitivity to chilling and high lipid content. Some studies focused on overcoming these difficulties, leading to live piglets derived from cryopreserved embryo transplantation (for example, Bertelot et al., 2000; Dobrinsky et al., 2000; Nagashima et al., 2007). Swine embryos remain, however, very difficult to cryopreserve, and regarding the cost/benefit balance, cryotransfer is not recommended (FAO Guidelines, 2015).

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6.2.5.7 CONCLUSION/PERSPECTIVES

6.2.5.5.4 Caprine Domesticated goats have been associated with mankind for more than 10,000 years (Ensminger and Parker, 1986), in particular in poor rural areas. Because of its frugal needs in terms of water and food and its efficiency in absorbing poor quality roughage, goats are particularly appreciated and valuable in developing areas with harsh environments (Table 2). Goats are used in meat and fiber (Mohair, Cashmere) production, but mainly for milk. The total goat milk production approaches 15 million metric tons (MT), representing only 2% of the total amount of milk production (cows, buffaloes). Of this production, 83% comes from developing countries and only 3% from Europe (mostly for cheese production). As a species of interest mostly in developing countries (table 1, FAOSTAT, 2008), goats have not been subjected to the same genetic improvement pressure as cattle and no strategy has yet been organized to solve the seasonality problem of reproduction to ensure a regular milk supply (Dubeuf and Bozayoglou, 2009). However, given the increased interest for milk production in developed countries (France principally), a genetic improvement program using frozen semen AI has been settled, especially for the Alpine and Saanen breeds. France was the pioneer country in the field of goat breeding technologies, with the first artificial insemination using fresh semen in 1954 and the first use of frozen semen for AI as soon as 1968 (CAPGENES). Nowadays, 400,000 AIs using frozen semen are conducted every year in goats, with 80,000 of them in France.

Of the bovine straw production, 80% is made in ministraws and 20% in medium straws. There is a continual propensity to go from medium to mini in all countries. This trend that started in 1972 continues. Today, only a dozen countries are using medium straws for bovine semen. These countries include the United States (partial), Japan, Pakistan, Argentina, and the Philippines. More than 90% of all straws sold and frozen in the world are for bovine, because not all species are kept frozen. Furthermore, due to suboptimal results, physiology, economics, or logistics, straws are still not used on some species. For example, the swine industry where AI is used extensively uses fresh semen in bags of toothpaste-type tubes. Frozen swine semen is done in medium straws or in larger straws, but freezing swine semen remains very selective and rare. When done, it is usually for foreign exports where live animal cannot be imported. Equine semen is mostly used fresh. Frozen equine semen, only exploited for sport horses, is processed in medium straws outside the reproductive season. While ovine is mostly fresh semen in straws, caprine is frozen. Rabbit is also a species where mostly fresh semen is used. Other species that are routinely frozen are camelids, fish milt, or canines and felines. Poultry semen is used fresh as frozen semen results are poor. In addition to the above, more than 500,000 bovine embryos are frozen yearly using specific ministraws and 500,000 are transferred fresh.

6.2.5.7 CONCLUSION/ PERSPECTIVES

6.2.5.6 ECONOMICAL STAKE Today, more than 500 bovine semen collection centers in more than 110 countries process hundreds of millions of straws yearly for bovine insemination. In more than 98% of the cases, the doses are frozen in LN2 vapor or in programmable freezers, using liquid nitrogen.

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Today, the bovine semen industry is a multibillion euro business and it is growing, largely in Asia (India) or on the African continent. Moreover, thanks to heat synchronization protocols, the beef industry—much larger than the dairy cow business—is using more and more AI frozen in liquid nitrogen.

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AI with frozen semen is the single main genetic transfer system that helps poorer populations access descript genetics. Using superior semen can double the milk production of a sub-Saharan cow breed. AI with frozen semen helps feed the world by unlocking the potential of small dairy stakeholders.

References Abe, H., Hoshi, H., 2005. Evaluation of bovine embryos produced in high performance serum-free media. J. Reprod. Dev. 49, 193–202. Bailey, J., Bilodeau, J.F., Cormier, N., 2000. Semen cryopreservation in domestic animals: a damaging and capacitating phenomenon. J. Androl. 21, 1–7. Barker, C., Grandier, J.C., 1957. Pregnancy in a mare resulted from frozen epididymal spermatozoa. Can. J. Comp. Med. Vet. Sci. 21, 45–51. Bartlett, J., 1946. Artificial insemination of dairy cattle. In: Problem of Fertility: Proceedings of the Conference on Fertility. Princeton University Press, p. 206. Bratton, R., Foote, R., Cruthers, J., 1955. Preliminary fertility results with frozen bovine spermatozoa. J. Dairy Sci. 38, 40–46. Cassou, R., Cassou, M., Cassou, B., 1994. Tube known as straw, for cryogenically preserving biological samples. Biotechnol. Adv. 12, 156. Critser, J., Russel, R., 2000. Genome resource banking of laboratory animal models. Inst. Lab. Anim. Res. J. 41, 183–186. Critser, J.K., Agca, Y., Gunasena, K.T., 1997. The cryobiology of mammalian oocytes. In: Karow, A.M., Critser, J.K. (Eds.), Reproductive Tissue Banking: Scientific Principles. Academic Press, New York, pp. 329–357. Curry, M., 2000. Cryopreservation of semen from domestic livestock. Rev. Reprod. 5, 46–52. Dubeuf, J.P., Bozayoglou, J., 2009. An international panorama of goat selection and breeds. Livest. Sci. 120, 225–231. FAO, 2012. Cryoconservation of Animal Genetic Resources. FAO Animal Production and Health Guidelines No. 12, Rome. FAOSTAT, 2008. http://www.fao.org/faostat/en/#home. Foote, R.H., 2002. The history of artificial insemination: selected notes and notables. J. Anim. Sci. 80, 1–10. Freiman, A., Bouganim, N., 2005. History of cryotherapy. Dermatol. Online J. 11, 9. Heape, W., 1897. The artificial insemination of mammals and subsequent possible fertilisation or impregnation of their ova. Proc. R. Soc. Lond. 61, 52–63. Hess, E.A., Teague, H.S., Ludwick, T.M., Martig, R.C., 1957. Swine can be bred with frozen semen. Ohio Farm Home Res. 42, 100.

Holt, W., 2000. Basic aspects of frozen storage of semen. Anim. Reprod. Sci. 62, 3–22. Knight, J., Abbott, A., 2002. Mouse genetics: full house. Nature 417, 785–786. Kuczynski, W., Dhont, M., Grygoruk, C., Grochowski, D., Wolczynski, S., Szamatowicz, M., 2001. The outcome of intracytoplasmic injection of fresh and cryopreserved ejaculated spermatozoa—a prospective randomized study. Hum. Reprod. 16, 2109–2113. Le Gal, F., 1996. In vitro maturation and fertilization of gaoat oocytes frozen at the germinal vesicle stage. Theriogenology 45, 1177–1185. Maclellan, I., Carnevale, E., Coutinho da Silva, M., Scoggin, C., Bruemmer, J., Squires, E., 2002. Pregnancies from vitrified equine oocytes collected from superstimulated and nonstimulated mares. Theriogenology 58, 911–919. ´ ., Labb, C., Zhang, T., Martı´nez-Pa´ramo, S., Horva´th, A Robles, V., Herra´ez, P., Suquet, M., Adams, S.L., 2016. Aquaculture 462, 1–9. Maxwell, W., Curnock, R., Logue, D., Reed, H., 1980. Fertility of ewes following artificial insemination with semen frozen in pellets or straws, a preliminary report. Theriogenology 14, 83–89. Maxwell, W., Landers, A., Evans, G., 1995. Survival and fertility of ram spermatizia frozen in pellets straws and minitube. Theriogenology 43, 1201–1210. Nagase, H., Graham, E.F., 1964. Pelleted semen: comparison of different extenders and processes on fertility of bovine spermatozoa. In: VICAR Meeting. International Congress on Animal Reproduction and Artificial Insemination, Trento, pp. 387–389. Nalesnik, J., Sabanegh, E., Eng, T., Buchholz, T., 2004. Fertility in men after treatment for stage 1 and 2A seminoma. Am. J. Clin. Oncol. 27, 584–588. Ombelet, W., Robays, J., 2015. Artificial insemination history: hurdles and milestones. Facts Views Vis. ObGyn 7, 137–143. Otoi, T., Yamamoto, K., Koyama, N., Suzuki, T., 1995. In vitro fertilization and development of immature and mature bovine oocytes cryopreserved by ethylene glycol with sucrose. Cryobiology 32, 455–460. Pegg, D., 2007. Principles of cryopreservation. In: Day, J.G., Stacey, G. (Eds.), Cryopreservation and Freeze-Drying Protocols, second ed. Humana Press Inc., Totowa, USA, pp. 39–57. Polge, C., Smith, A., Parkes, A., 1949. Revival of spermatozoa after vitrification and dehydration at low temperature. Nature 164, 666. Sakai, A., Engelmann, F., 2007. Vitrification, encapsulationvitrification and droplet-vitrification: a review. Cryoletters 28, 157–172. Saragusty, J., Arav, A., 2011. Current progress in oocyte and embryo cryopreservation by slow freezing and vitrification. Reproduction 141, 1–19.

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FURTHER READING

Sarangi, S., 1987. Cryogenic storage of hydrogen. In: Dahiya, R.P. (Ed.), Progress in Hydrogen Energy. Reidel Publishing Company, pp. 123–132. Spallanzani, L., 1785. Experiences pour servir a` l’histoire de la generation des animaux et des plantes (etc.). Chirol. Stewart, D., 1951. Storage of bull spermatozoa at low temperatures. Vet. Rec. 63, 65–66. Walters, E., Benson, J., Woods, E., Crister, J., 2009. The history of sperm cryopreservation. In: Pacey, A., Tomlinson, J. (Eds.), Sperm Banking: Theory and Practice. Cambridge University Press, pp. 1–10.

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Watson, P., Martin, C., 1973. Artificial insemination of sheep: the effect of semen diluent containing egg yolk on the fertility of ram semen. Theriogenology 6, 559–564.

Further Reading Webb, D.W., 1992. Artificial insemination in dairy cattle. University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS.

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C H A P T E R

7.1

Refrigeration

Gases in Agro-food Processes https://doi.org/10.1016/B978-0-12-812465-9.00014-1

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# 2019 Elsevier Inc. All rights reserved.

S U B C H A P T E R

7.1.1 Refrigeration Process Technologies Didier Coulomb International Institute of Refrigeration, Paris, France

7.1.1.1 INTRODUCTION Refrigeration plays a key role in food processing, both for the production and the preservation of foodstuffs. Various technologies have been developed, especially since the 19th century, and continue to evolve, mainly due to environmental constraints. Most refrigeration technologies use gases.

7.1.1.1.1 From Natural to Artificial Refrigeration Since ancient times, refrigeration has been used in Europe, the Middle East, and East Asia to preserve and transport food through the use of snow or ice. The snow could be used to preserve the seafood during storage or transport. Ice could be collected in cold areas (glaciers, etc.) or in frozen water in winter, and then used for transport or storage in coolers until the end of summer. There was even an “industrialization” of the collection of ice in the 19th century, which stopped at the beginning of the 20th century, replaced by the rise of artificial refrigeration. Technical experiments to artificially create cold were developed throughout the 19th century, following the scientific discoveries of the 18th and 19th centuries. The main sector using refrigeration remains food.

These refrigeration technologies have been and continue to be perfected and will be described in their present form hereinafter. However, the fundamentals of these techniques and the different techniques used remain the same.

7.1.1.1.2 Artificial Refrigeration Systems Producing cold by means of a refrigeration system consists of modifying its own thermodynamic equilibrium (characterized by its volume, pressure, temperature, etc.), thanks to an energy supply, in mechanical or thermal form, by releasing cold and heat. This technology relies on the first two principles of thermodynamics: conservation of energy in a closed system, and the impossibility of transferring heat from a cold body to a hot body without energy compensation. This second principle, expressed in different ways (entropy), gives cold production particular features compared with traditional heat production, and explains the complexity and broad spectrum of refrigeration systems. The different processes for cold production can be classified, as shown in Figs. 7.1.1.1 and 7.1.1.2, based on the energy source used. Indeed, the nature of the energy source is fundamental and determines the constraints and possibilities linked to the refrigeration system.

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7.1.1.1 INTRODUCTION

FIG. 7.1.1.1

FIG. 7.1.1.2

225

Methods of artificial refrigeration in the form of work W.

Methods of artificial refrigeration in the form

of heat Q.

Systems Consuming Mechanical (Electric) Energy

W1 They are used for juice concentration. W2 These are the most simple and widespread systems for food preservation, ice water production, and air conditioning, and heat pumps use this type of cycle. W3 System using several successive cycles, with various refrigerants, to lower the temperature.

W4 System in which the phase change takes place at ambient temperatures. W5 Using zeotropic mixtures with several components for low temperatures. W6 System in which the active fluid remains gaseous; these cycles are mostly used for air conditioning of aircraft and low temperatures. W7 System in which refrigerant evaporation is replaced by vapor desorption outside a solution and condensation by vapor absorption once again by the solution. W8 and W9 systems using the Peltier or magnetocaloric effects; they are rarely used, and employed only in very specific applications. System Q Consuming Thermal Energy

Q1 System without suction-vapor recovery (vacuum cooling). Q2 System in which the air is dehumidified before being cooled by water vaporization.

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Q3 System using an ejector as a suctioncompression system. Q4 System in which the mechanical compressor is replaced by a thermocompressor (absorber + boiler). Q5 Water + ammonia absorption cycle in which hydrogen compensates for the pressure differences of the refrigerant (domestic absorption refrigerators). Q6 and Q7 System in which refrigerant vapor sorption occurs intermittently on the surface of a solid (adsorption) or within a liquid (absorption). Q8 System similar to Q6 and Q7 but in which refrigerant vapor is the result of the chemical breakdown of a compound. Q9 In the previous systems, the state of the working fluid periodically undergoes a phase change that implies that the vapor can be liquefied in the selected temperature range. In order to avoid this constraint, two (or more) chemical reactors containing compounds reacting with the refrigerant at various temperatures are used. Q10 System combining a Stirling heat engine and a Stirling gas cooler. Q11 In order to avoid the law of vapor pressure, as in Q9, in this continuous absorption cycle, the evaporator is replaced by a desorber and the condenser is replaced by an absorber; the refrigerant remains in the gaseous state. Q12 Q9-type system, but here, the physical phenomena used are absorption and desorption of a vapor in two different types of absorbent. Q13 Systems combining a Seebeck-effect electric generator and a Peltier module. Q14 Very widespread system in which a heat engine is employed (using petrol or diesel) in order to drive a mechanical refrigeration system, generally a compressor (refrigerated trucks).

7.1.1.1.2.1 Thermal Energy-Based Systems For example: solar energy, energy recovered from heat rejecting systems, etc. This is mainly the case in sorption systems (absorption or adsorption). A fluid called refrigerant evaporates, absorbing heat and thus producing cold. It is then absorbed or adsorbed into a solution with solid granules. This process is part of a cycle similar to a vapor compression cycle. Thermochemical and thermoelectrical systems are also worth mentioning. The primary heat can also drive a mechanical system; in that case see the following paragraph on mechanical energy-based systems. It is namely the case of car or truck engines, which drive a refrigeration system allowing the refrigerated transport of foodstuffs. 7.1.1.1.2.2 Mechanical Energy-Based Systems Today, some mechanical energy-based systems are (still) limited to specific applications, such as gas cycles, where the refrigerant remains in a gaseous state, Peltier effect systems or magnetocaloric systems. However, their operation is similar to that of vapor compression systems. In a magnetocaloric system, during the magnetization, the electron spins of a magnetocaloric material are oriented and the material warms up. Through a reverse effect, the demagnetization cools it down. The magnetocaloric material plays the same role as the refrigerant in a vapor compression system. Here is the general principle of a vapor compression machine (Fig. 7.1.1.3): The cycle described above operates in a closed circuit. It produces cold on one side and heat on the other. Usually, only cold is used. Heat can however be used in the case of a heat pump (Fig. 7.1.1.4). Coefficient of performance (COP): Φcold/Pmec is the ratio between the cooling capacity Φcold and the mechanical energy provided to the system, Pmec

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FIG. 7.1.1.3

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General principles of a vapor compression system.

In a vapor compression refrigeration machine, there are four essential parts:  An evaporator where heat is transferred from the medium to be cooled to the refrigerant at low pressure.  A compressor driven by a motor, almost always an electrical motor.  A condenser for transferring heat from the refrigerant at high pressure to the surroundings.  A metering device (expansion valve or throttling valve) to regulate the flow of refrigerant and decrease the pressure from condenser pressure to evaporator pressure. Inside the machine, the refrigerant, which undergoes phase changes in the evaporator and in the condenser, is circulated. Although the cold is produced within the evaporator, the critical element for the efficiency of the system (apart from the fluid, which will be

discussed later) is in fact the compressor. Several types of compressors have been developed (piston, screw, scroll, etc.) in an ever-innovating sector. The compressor must be adapted to the refrigerant used in order to achieve the best efficiency (Fig. 7.1.1.5). The refrigeration machine includes mechanical elements (compressor, condenser, expander, evaporator, heat exchangers, tanks, pumps, etc.) and elements that allow it to operate (refrigerant, oil). But other elements matter. The way cold is distributed is also very important. The cold can be used immediately. It can also be used as a cold source for a second machine (cascade system) in order to progressively reach a temperature a single system could not reach. It is also possible to exchange the cold produced with a harmless fluid, free of any hazard (glycol water, ice slurry), that will supply cold to a space open to the public; this neutral fluid is called secondary refrigerant.

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

Thermodynamic systems

With a visible change of state of the refrigerants(s)

Closed transformation (cycle)

Open transformation

Open ejection

Open sorption

Q1

Without a visible change of state of the refrigerant (s)

Thermochemical cycles

Continuous

Q11Resorption

Q12 Gas-on-solid adsorption desorption

Q5 Diffusion-

absorption systems

absorption systems

FIG. 7.1.1.4

absorption cycles

Discontinuous

Q4 Continuous

Q14 Heat engine + mechanical refrigeration system

Discontinuous

Q9 Reactor couples

With ejection systems Q3

Continuous

Vapor or gas sorption cycles

Vuilleumier cycles Q10

Sorption cycles

Q8 Reactor + evaporator condensor

Thermoelectric systems

Gas thermodynamic cycles

Single refrigerant

Q2

Thermochemical cycles

Q6 Discontinuous absorption systems

Q13 Thermoelectric generators

Q7 Discontinuous absorption systems

Basic refrigeration machine.

Thermoelectric systems

Thermodynamic systems

Magnetic systems

Without a visible change of state of the refrigerant(s)

With a visible change of state of the refrigerant(s)

Closed transformation (cycle) Thermodynamic gas cycles

open transformation

Vapor or gas sorption cycles

W9 Magnetocaloric generators

Several refrigerants

Single refrigerant

W1 Vapor compression Separate

Mixed

W6 Stirling Brayton, Ericson gas cycles, pulse tube thermoacoustic system, MacMahon

W7 Desorption, absorption compression cycles

W2 Single-or multistage compression cycles

W4 Zeotropic mixture cycles

W3 Cascade cycles

W5 Integrated cascade cycles

FIG. 7.1.1.5

Carrier screwcompressor. 7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

W8 Peltier effect systems

7.1.1.1 INTRODUCTION

We will then discuss the primary refrigerant issues. The insulation systems are obviously complementary to the cooling systems in order to avoid energy losses as much as possible.

7.1.1.1.3 Refrigerants Each fluid has different thermodynamic properties: its volume, temperature, and pressure are linked through parameters that are specific to it, and that determine the characteristics of the refrigerating machine cycle. Moreover, the chemical properties of the fluids can have important consequences on the materials used to build the refrigerating machine (corrosion, for example) or on the environment if these fluids are not confined in the machine: toxicity, flammability, greenhouse effect, and interaction with the stratospheric ozone layer. Only certain fluids are therefore suitable for efficient use in a particular application. The installation must also be designed in such a way as to minimize the possible impact of the refrigerant on human health and the environment. Indeed, the fluid must be handled during its manufacture, installation, maintenance of the installation, and potential destruction. The fluid can also leak; the installations are not necessarily leakproof, especially in the connections of the circuit setup (seals). Many fluid mixtures are used to optimize the desired characteristics; however, they imply risks due to possible poor miscibility (one component tends to leak more than another, etc.) But the number of possible fluid types remains limited. They can be classified as follows:  “Natural” fluids as they can be found in nature or almost: carbon dioxide (CO2), ammonia (NH3), hydrocarbon (mainly isobutane, propane, propene).

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 Chlorofluorocarbons (CFCs): they were developed from the 1930s and quickly replaced different fluids that presented various health hazards.  Following the discovery of the stratospheric ozone depletion (1974) and the implementation of the Montreal Protocol (1987), these fluids were gradually banned from developed and then developing countries. In case of leakage, they had the disadvantage of destroying the stratospheric ozone layer and being very powerful greenhouse gases at the same time.  Hydrochlorofluorocarbons (HCFCs): with a smaller impact on the stratospheric ozone layer, they gradually replaced CFCs, which are similar in terms of physiochemical properties, from the 1970s through the early 2000s. However, they will gradually be phased out by 2030; they are also included in the Montreal Protocol.  Hydrofluorocarbons (HFCs): they have virtually no impact on the stratospheric ozone layer and have therefore not been included in the Montreal Protocol. But they are greenhouse gases like CFCs and HCFCs. After a step up in the 1990s, they are gradually replacing the previous ones. But since the Kigali Agreement (2016), their use must be significantly reduced in the next 20–30 years.  Hydrofluoroolefins, which are unsaturated HFCs with a very low greenhouse effect, are just beginning to be used. Since the agreements on the stratospheric ozone layer and then global warming, natural refrigerants are on the rise, but they require various precautions when designing the installation and using it. Ammonia corrodes copper; it is also toxic and very slightly flammable. Carbon dioxide is toxic at high concentrations, but above all it exerts high pressure on materials. Hydrocarbons are highly flammable.

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7.1.1.2 CONCLUSION In conclusion, refrigeration process technologies are moving fast because of environmental constraints such as global warming; the whole refrigeration sector represents 7.8% of global greenhouse gas emissions and 37% are due to the emission of fluorinated gases. The agrofood processes are only one part. However, refrigeration technologies are similar to other equipment of the cold chain as well as in air conditioning for instance, and all technologies will move

simultaneously. Vapor compression systems will most likely continue to be the main technology for the next decades. The other ones will remain marginal but their share will increase as many technical developments are underway. Gases used in vapor compression technologies will be adapted. These changes will have consequences on the whole systems, especially regarding security issues, because most replacement refrigerants present risks of flammability, toxicity, or high pressure.

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7.1.2 CO2 in Closed Loop Christophe Marvillet IFFI (Institut Franc¸ ais du Froid Industriel)/Cnam (Conservatoire National des Arts et Metiers), Paris, France

Carbon dioxide is used in closed circuits, mainly for energy use in food processing applications and especially for cold applications, that is to say at temperatures below ambient and that can go down to close to 40°C. The two major functions provided by this fluid CO2 in refrigeration systems are:  Use as a secondary coolant, that is to say the transport of thermal energy from a point of use (heat source) to a point of cold production (heat sink) at temperatures, according to applications, between 10°C and 40°C.  Use as a refrigerant that flows in the circuit of the refrigeration equipment, is compressed in the compressor in the vapor phase, evaporates in the evaporator in the liquid/ vapor phase, and allows in this equipment the effective production of cold, that is to say the absorption of heat at low temperature from the medium or fluid to be cooled. The increasing use of CO2 in refrigeration systems in recent years is due not only to the specific characteristics of this fluid—in particular its low impact on the environment—but above all to the new regulatory constraints that apply to HFC refrigerants (hydroflurocarbons) which have major impacts on the environment

and on secondary fluids based on alcohol, synthetic, or silicone oils also concerned by environmental constraints but also by their unsuitability for agrofood uses. In this chapter, we will discuss the following points:  The specific properties of CO2 as a coolant and refrigerant and the advantages/ limitations of this fluid in the intended applications.  The use of CO2 as a secondary coolant by recalling the architecture of energy systems, the main design rules of these systems, and the precautions to be taken when using this fluid for these uses.  The use of CO2 as a refrigerant by recalling the main refrigeration cycles in which it can be valued and the main design rules of these systems.

7.1.2.1 THE CARBON DIOXIDE THERMODYNAMICAL AND THERMOPHYSICAL PROPERTIES Carbon dioxide is an inorganic compound whose chemical formula is CO2, the molecule having a linear structure of the form O]C]O.

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Under normal conditions of temperature and pressure, it presents itself as a colorless, odorless gas with a pungent flavor. At atmospheric pressure, it sublimates at 78.5°C (passage from the solid state to the gaseous state), but does not melt (passage from the solid state to the liquid state). The liquid phase can only exist at pressure above the minimum pressure of 519 kPa, and in a temperature range of 56.6°C (triple point) to 31.1°C maximum at 7.38 MPa (critical point). Fig. 7.1.2.1 shows the diagram pressure/temperature of two-phase CO2 equilibrium data (gas/solid, liquid/solid, and liquid/gas). The latent heat values are the following:  Vaporization: at 0°C the latent heat is equal to 234.5 kJ/kg, at 16.7°C to 276.8 kJ/kg, and at 28.9°C to 301.7 kJ/kg.  Fusion: at 56.6°C the latent heat is equal to 199 kJ/kg.

It will be noted that one of the particular points of CO2 lies, whether for secondary coolant or refrigerant uses, by the high-pressure values encountered with this fluid in the temperature range of 10°C to 80°C, the range of temperature used in refrigerating equipment. In comparison, with traditional fluids, we note:  For secondary coolant use, glycol mixtures in liquid form, for example, only require pressures not exceeding 300 kPa, whereas a CO2 circuit can reach values of several MPa, depending on the temperatures reached.  For refrigerant uses, Table 7.1.2.1 shows the comparison of CO2 saturation pressures with the refrigerants commonly used and highlights the very important values achieved with this fluid. The thermodynamical properties of CO2 have an important impact on fluid manipulation. Prior to charging, the system must be evacuated

Pressure (bar)

10,000 Solid

1000

Supercritical fluid

Liquid

100 Critical point

10 Gas Triple point

1 200

250

300

350

400

Temperature (K)

FIG. 7.1.2.1

Diagram pressure-temperature for carbon dioxide.

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7.1.2.1 THE CARBON DIOXIDE THERMODYNAMICAL AND THERMOPHYSICAL PROPERTIES

TABLE 7.1.2.1 Saturated Pressure (Bar) for CO2 and Traditional Refrigerant for Refrigeration Systems 250°C

240°C

235°C

210°C

+30° C

CO2

6.83

10

12

26.5

72.1

NH3

0.41

0.72

0.93

2.91

11.7

R507

0.8

1.41

1.74

4.52

14.6

first. Also, it’s important to never brake the vacuum with liquid CO2 because the spontaneous evaporation has a severe cooling effect and generates a risk of brittleness and thermal shock of the materials. To avoid the formation of solid CO2, it is strongly recommended to charge the plant with gaseous CO2 up to approximately 10 up to 20 bars. The thermophysical properties that must be analyzed are those that condition the design of the technical equipment of refrigerant fluid

TABLE 7.1.2.2 (A AND B)

circuits or refrigerating machines. These properties are:  The densities of the liquid and vapor phases, which determine the size of pipes and active elements such as pumps and compressors.  The thermal capacities and thermal conductivity of the liquid and vapor phases, which determine the size of the exchangers (evaporator, condenser).  The viscosity of the liquid and vapor phases, which condition the pressure losses in the fluid circuits and the dimensions of the pumps and other technical equipment. Here again, we distinguish two distinct uses:  As a coolant, a comparison (Table 7.1.2.2A) of properties of CO2 and a water-MEG (mono ethylene glycol) mixture is made.  As a refrigerant, a comparison (Table 7.1.2.2B) of the properties of CO2 and a “traditional” fluid HFC404a is realized.

Thermophysical Properties of Saturated CO2 Density (kg/ m3)

Fluid (2a)

233

Heat Capacity (kJ/ kg K)

Thermal Conductivity (W/m K)

Dynamic Viscosity (kg/m s)

(A) Properties of secondary fluid: CO2 versus water + MEG at 10°C Water + MEG (0.7/0.3)

Liquid

1047

3627

0.43

0.0065

CO2

Liquid + vapora

981 (71)

2.3 (1.5)

0.12 (0.016)

0.00013(0.000017)

Fluid (2b)

Density (kg/ m3)

Heat Capacity (kJ/ kg K)

Thermal Conductivity (W/ m K)

Dynamic Viscosity (kg/ m s)

(B) Properties of refrigerant: HFC507 vs CO2 at 10°C HFC507

Liquid + vapora

1193 (23.2)

1.34 (0.93)

0.078 (0.011)

0.0002 (0.00001)

CO2

Liquid + vapora

981 (71)

2.3(1.5)

0.12 (0.016)

0.00013(0.000017)

a

Values for vapor are in bracket.

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Carbon dioxide has undeniable qualities as a secondary coolant, especially due to its application conditions of +15°C to 50°C with interesting thermophysical properties: low viscosity in the liquid phase, and high thermal capacity and conductivity in the liquid phase, as shown in Table 7.1.2.2. These real qualities can moreover be valorized by use in the form of a liquid-vapor mixture, which makes it possible to use the evaporation enthalpy and to very significantly reduce the flow rate of circulating fluid. The advantage of such a device lies in the very high heat-carrying power of the fluid due to the use of the latent heat of the coolant fluid (CO2). Therefore, the thermal power transported per unit volume (of the liquid phase) of CO2 is more than 20 times higher than that transported, with a temperature difference of 5°C, by a performing monophasic secondary coolant, that is to say water/MEG. Such a difference results in substantial gains in terms of piping and pump dimensions, pumping energy, and the elimination of the temperature variation on the exchangers, which makes it possible to raise the evaporation temperature of the primary fluid by 4 at 6 K, reduce the size of the compressors, and improve system performance by about 15%. Carbon dioxide also shows good qualities as a refrigerant because of high latent heat of evaporation and high vapor density, which allow a strong reduction of circuit and compressor size. The thermal conductivity of liquid CO2 is significantly higher that of HFC507A, a traditional refrigerant in low-temperature refrigeration machines. The refrigeration cycle with CO2, due to the low value of the critical temperature, may show supercritical conditions. In these conditions, as can be seen in Fig. 7.1.2.2, supercritical CO2 shows atypical evolution of thermophysical properties:  Dramatic increase of isobaric heat capacity and thermal conductivity at pressure between 74 and 86 bars. This has to be taken

into account for high-pressure gas cooler design.  Strong change of viscosity and density for temperature between 31°C and 41°C; this has great impact on the heat exchangers design.

7.1.2.2 THE CARBON DIOXIDE ENVIRONMENTAL IMPACTS For many years, halogenated hydrocarbons (CFC, HCFC, HFC) have been used as refrigerants in refrigeration systems. We know that stratospheric ozone is destroyed by chlorine transported at these altitudes by halogenated hydrocarbons, which have a long life in the atmosphere. This is mainly from CFCs but also, to a much less extent, from HCFCs. We also know that it is this criterion that has led the international community to ban these chlorinated compounds. The action of each compound on stratospheric ozone is characterized by the ODP (ozone depletion potential), the potential for destroying ozone. The values of the ODP are generally given with reference to R-11, (CCl3F) one of the CFCs that is the most aggressive from this point of view. Only refrigerants having a zero ODP should continue in use. Table 7.1.2.3 gives ODP values reported in CO2, HFC, and HCFC. Greenhouse gases are essential for people living on our planet; in their absence, we would have a temperature much too low to be habitable (18°C). However, an excess of these gases, hindering the exit (toward the cosmos) of terrestrial radiation, can, in the long run, cause a slow warming, that is dangerous for our world. Aside from the well-known greenhouse gases (water vapor, CO2, methane, nitrogen oxides, etc.), the halocarbon refrigerants have a very significant action. Their influence is much greater than, for example, that of CO2, whose greenhouse effect is the best known. The greenhouse effect of a compound is characterized by the global warming potential, GWP. Table 7.1.2.3 gives

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7.1.2.2 THE CARBON DIOXIDE ENVIRONMENTAL IMPACTS

FIG. 7.1.2.2 Thermophysical properties of supercritical CO2 against temperature and P absolute pressure. (a) Isobaric Heat Capacity, (b) Dnsity, (c) Viscosity, (d) Thermal Conductivity.

TABLE 7.1.2.3

Environmental Impact of Various Refrigerants

Fluid

Fluid Composition and Designation

Normal Boiling Temperature (°C)

Critical Temperature (°C)

ODP (1 for R11)

GWP (100 Years)

Ammonia

NH3 (R717)

33.35

132.4

0

1

Carbon dioxide

CO2 (R744)

31

0

1

Water

H2O (R718)

100

374

0

Propane

C3H8 (R290)

42.1

96.7

0

20

Isobutane

C4H10 (R600a)

11.7

134.7

0

20

Trichlorofluoromethane

CFCl3 (R11)

23,7

198

1

4750

Chlorodifluoromethane

CClF2CF3 (R115)

39.2

80

0.04

1790 Continued

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7.1. REFRIGERATION

Environmental Impact of Various Refrigerants—cont’d

Fluid

Fluid Composition and Designation

Normal Boiling Temperature (°C)

Critical Temperature (°C)

ODP (1 for R11)

GWP (100 Years)

R502

R22/R115 (48.8/51.2)

45.3

81.5

0.3

4600

R507A

R125/R43a (50/50)

46.7

70.6

0

3800

R404A

R125/R143a/R134a (44/52/4)

46.2

72

0

3700

R407C

R32/R125/R134a (23/ 25/52)

43.6

86

0

1700

GWP values reported in CO2 and CFC, HFC, and HCFC; these relationships change with the time period envisaged because CO2 molecules and those of gaseous refrigerants considered do not disappear from our atmosphere at the same speed. For comparisons with CO2, we generally adopt a reference period of 100 years. The GWP translates the greenhouse effect (consequence of leakage or nonrecovery). The compression refrigeration systems generate a greenhouse effect indirectly, linked to their electricity consumption (CO2 emission during electricity production). Many of the proposed neorefrigerants, such as HFCs, that have GWP are considered to be too important, which leads to the wish for the exclusive use of natural fluids: CO2, water, ammonia, propane, butane, etc.

7.1.2.3 RISKS AND SAFETY INSTRUCTIONS FOR CO2 USE Outside ambient air today contains about 0.04% of CO2. Nevertheless, at a certain concentration in the air, this gas is dangerous or even deadly because of the risk of asphyxiation or acidosis, although CO2 is not chemically toxic. The exposure limit value is 3% over a period of 15 min. This value should never be exceeded. Beyond that, the health effects are all the more

serious as the CO2 content increases. Thus, at 2% of CO2 in the air, the respiratory amplitude increases. At 4%, the respiratory rate accelerates. At 10%, visual disturbances, tremors, and sweating may occur. At 15%, it is a sudden loss of consciousness. At 25%, respiratory arrest results in death. Inhalation of concentrated carbon dioxide causes a blockage of ventilation, sometimes described as a violent feeling of strangulation or breathlessness, respiratory distress, or chest tightness, which can quickly lead to death if exposure is prolonged. Because carbon dioxide is a colorless, heavy gas accumulating in layers, it is difficult to detect by an inexperienced person. In high concentrations approaching 50%– 100%, such as those found in artificial carbon dioxide arrays of occupational origin, there may be a nervous breakdown and immediate loss of consciousness, followed by fast death in the absence of outside help. These accidents present a high risk of further tragedy, as witnesses can rush to help the victim without thinking about their own safety and become victims of intoxication too. Recommendations: The limit value of exposure to CO2 in the workplace (ELV) corresponds to “limit values of exposure to workstations” at a concentration of 0.5% by volume. Please note that CO2 not only has an asphyxiating effect

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7.1.2.4 CO2 COOLING AND REFRIGERATION LOOP CONCEPTION AND DESIGN

but acts directly on the metabolism in our body, even if there is still enough oxygen in the ambient air. The concentration of CO2 must be monitored by taking measurements; control of the oxygen content gives a false impression of safety. Another harmful effect of carbon dioxide on the human body is that of cold. If CO2 cooled by detente comes into contact with the skin in the form of ice/dry ice, it can cause frostbite, that is, painful cold burns. Sensitive skin tissues, such as the cornea, are particularly at risk. Ice formation in pipes and piping or valves may also pose a mechanical hazard to people in the vicinity. Recommendations: Please follow exactly the working instructions for handling CO2. Protect your skin by wearing appropriate protective clothing and gloves. Wearing safety glasses can effectively protect the corneas from cold burns. The following safety measures are indicated:  Inform your employees of the special dangers of CO2.  Employees working in the vicinity of applications using CO2 must be trained and instructed accordingly so that they can correctly interpret alarms and their own observations. Develop detailed job descriptions and risk analysis for sectors using carbon dioxide.  Ensure the tightness of installations using CO2, and remedy any leakage without delay. CO2 emissions from technical equipment or safety valves must be vented to the open air. Premises with CO2-based facilities must have efficient ventilation, especially if they are below ground. This ventilation equipment must be regularly maintained and checked.  A CO2 monitoring and alarm system must be installed in premises where installations using this gas are located. The surveillance and alarm systems must be checked

237

regularly, and periodic maintenance must be carried out by the company that set them up.  In the event of a sudden escape of CO2, leave the premises immediately, especially if they are located in the basement (pits, cellars), because the risk of CO2 accumulation is particularly high there.  Do not enter rooms where large amounts of CO2 have accumulated with a self-contained breathing apparatus. This also applies when there are injured people in the room who need urgent rescue. Fixed CO2 extinguishing systems must be put into service for control purposes or for necessary intervention only if there is no one in the area where risks exist. If the carbon dioxide can enter other premises through pipes, openings in the wall, ventilation, or air conditioning, these premises are also considered risk areas.

7.1.2.4 CO2 COOLING AND REFRIGERATION LOOP CONCEPTION AND DESIGN 7.1.2.4.1 Carbon Dioxide Cooling Loop Carbon dioxide has undeniable qualities as a secondary coolant, especially due to its application conditions of +15°C to 50°C with interesting thermophysical properties: low viscosity and high thermal capacity in the liquid phase. These real qualities can moreover be valorized by use in the form of a liquid-vapor mixture, which makes it possible to use the evaporation enthalpy and to very significantly reduce the flow rate of circulating fluid. Under these conditions of use, Fig. 7.1.2.3 shows a piping diagram of a technical device in which a CO2 refrigerant circuit is associated with an ammonia, CO2, or HFC cold production unit. Thus, the fluid to be cooled yields thermal energy and allows vaporization of the liquid CO2 (for example at 36°C). The vapor phase produced is sent to the evapocondenser, the exchanger

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7.1. REFRIGERATION

Chiller

CO2 loop

FIG. 7.1.2.3

CO2 coolant circuit scheme.

ensuring the heat transfer between the CO2 coolant loop and the cold production unit, and then condensed at a saturation temperature close to that of 36°C for the example considered. The condensate—substantially subcooled—is circulated by a pump and sent back to the exchanger in contact with the fluid to be cooled.

7.1.2.4.2 CO2 Refrigeration Cycles Significant developments have been made in the last 10 years for new CO2 systems taking advantage of the low GWP of this fluid and its classification as a safe refrigerant (A1 under EN 378). The drawbacks of CO2 are well known and are mainly related to its low critical temperature of 31°C. This low critical temperature leads to a trans-critical cycle when delivering heat at higher temperature. Efficient developments of CO2 are summarized here after.  A transcritical cycle (Fig. 7.1.2.4) with an intermediate heat exchanger is a basic cycle

with a low-pressure stage at subcritical conditions. The machine is composed of an evaporator at low pressure, a gas cooler at very high pressure (about 80–110 bar), and an intermediate heat exchanger HX. The HP regulation valve has to regulate the optimum value of high pressure (for a maximum cycle efficiency) in the gas cooler.  For low-temperature applications, a cascading system when condensing CO2 (Fig. 7.1.2.5) at a temperature lower than 31°C, and possibly around 10°C to 0°C, CO2 systems show high energy performances due to efficient thermophysical properties (low viscosity and high thermal conductivity) and the development of cascading systems. Those cascading systems use CO2 at evaporating temperatures varying between 50°C and 35°C associated with a high-temperature refrigerating system (of the cascade) using either ammonia or HFCs have led to very efficient systems in the food industry.  In parallel with this effort, a number of laboratories and industries have developed new possible solutions using ejectors in order to improve the energy efficiency. Developments of expansion turbines have also been proposed for the same purpose: limitation of expansion losses. As shown in different publications, high-efficiency expansion has to be studied in parallel with heat recovery by a liquid/vapor heat exchanger. The two options are in competition for improvement of energy efficiency.  The development of heat exchangers is driven by high-efficiency heat exchange and the decrease of material quantities (for mass production components, the mass of the material is a key parameter for the price). The trends are obvious: the thickness of copper tubes has been reduced to 0.3 mm, the thickness of aluminum fins is in the range of 0.1 mm, the diameters have been constantly reduced, and high efficiency fins, groove

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239

7.1.2.4 CO2 COOLING AND REFRIGERATION LOOP CONCEPTION AND DESIGN 1-2: Compression 2-3: Isobaric heat removal 3-4: Isonthalpic expansion of high-pressure fluid 4: Separation of phases (liquid and gas) 5-8: Isonthalpic expansion of flash gas 6-7: Isonthalpic expansion of liquid 7-1: Isobaric evaporation and superheating

HP regulation value

3

(HX) Gas cooler

2

Pressure (bar)

Critical point Liquid receiver Compressor 6

Evaporator

5

4 7

8

1

Specific enthalpy (kJ/kg)

FIG. 7.1.2.4

CO2 single-stage transcritical cycle.

CO2 medium temperature loop

Gas cooler/ condenser

Co2 low temperature loop

Cascade heat exchanger Heat reclaim

HP control ETX

PR HX

Receiver ETX

ETX

Co2 medium temperature evaporator

FIG. 7.1.2.5

Co2 low temperature evaporator

CO2 cascade cycle.

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7.1. REFRIGERATION

tubes, have led to improvement by a factor 2– 3 the heat exchange coefficient of air-torefrigerant heat exchangers in the last 20 years. In parallel with those developments, condensers have been designed with extruded microchannel aluminum tubes. Those tubes are brazed with accordionlouvered fins, leading to a significantly higher heat transfer coefficient.

7.1.2.5 CONCLUSION In just a few years, CO2 has become a major fluid in refrigeration equipment, particularly in food-processing plants, due to future

prohibitions on HFC (hydrofluorocarbons) fluids that present an excessive GWP. The introduction of CO2 as a coolant or refrigerant strongly modifies, due to the increased complexity of the systems, the design rules of the installations as well as the modalities of driving and maintenance. The deployment of these technologies in Europe and more widely on other continents where the prohibition rules are less severe presupposes a mastery of the rules of design, construction, security, and implementation of this fluid through rigorous respect of the cleanliness and lack of moisture in the CO2 circuits.

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7.1.3 Application—Freezing of Foodstuffs Alain Le-Bail*,†, Piyush Kumar Jha*,† *ONIRIS UMR GEPEA CNRS 6144, Nantes, France † Universite Bretagne Loire, Rennes, France

7.1.3.1 INTRODUCTION: BASICS OF FOOD FREEZING PROCESS Food freezing is an important and widely used process. Apart from drying, it is the most efficient means to extend the shelf life of food. Freezing has been used for centuries in cold regions and cold seasons as a method for preserving food. Freezing stops or slows the growth of most bacterial species. Freezing prevents microorganism growth by turning the liquid water of the food into ice, therefore rendering this water unavailable for microorganism growth. This results in longer preservation and a great reduction of decomposition of the food. The main component of most frozen food products is water, and understanding the freezing process of the water contained in food is a key element to understanding the freezing process of the food itself. The phase diagram is a good representation of the physical phenomenon that occurs during the freezing of food and water. A standard phase diagram of a food item is presented below. The diagram in Fig. 7.1.3.1 shows a phase diagram of a typical food product. The different phases are represented on a diagram showing the temperature as a function of the concentration or titer of the aqueous phase of the food (mass of dry matter per total mass). On the blue curve

(gray in the print version), Tm represents the evolution of the initial freezing temperature as a function of concentration. The thick black line shows the evolution of the temperature—titer followed by food during freezing. At point A, the first crystals of ice appear. From point A to point B, a phenomenon of cryoconcentration occurs; the formation of the ice crystals causes the residual solution to increase in titer and its freezing temperature to drop. At point B, the maximum cryoconcentration is reached at temperature Tm0 . Below this temperature, it is no longer possible to crystallize more water. If the food is cooled beyond its maximum cryoconcentration point, it will reach the point C corresponding to the glass transition temperature Tg0 . The temperature Tm0 is often in the range of 30°C to 40°C and therefore temperature is lower than the reference frozen storage temperature of 18°C. At this temperature, which is above Tm0 , the freezable water will not be fully frozen for most foods. The function describing the evolution of the fraction of freezable water effectively frozen as a function of temperature (assuming an initial freezing temperature of 1°C) and an end-offreezing temperature Tm0 of 40°C is shown in Fig. 7.1.3.2. The calculation has been done according to Le-Bail et al. (2008), based on Fikiin (1998) and Fikiin and Fikiin (1999). It shows that 96.9%

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7.1. REFRIGERATION

FIG. 7.1.3.1 Phase diagram of a food item. For given dry matter content, the evolution of concentration and temperature of the aqueous phase is drawn with the first ice crystal formed in A, maximal cryoconcentration in B, and glass transition in C.

FIG. 7.1.3.2 Graph showing the evolution of the fraction of freezable water frozen as a function of the temperature, assuming an initial freezing temperature of TIFP ¼ 1°C and an end of freezing temperature of Tm0 ¼ 40°C.

of the freezable water is frozen at 18°C. The International Institute of Refrigeration considers that a food is “frozen” if (a) 80% of the freezable water is frozen, or (b) below the temperature of 10°C. In the case shown in Fig. 7.1.3.2, the temperature of 10°C can be considered as 80% of frozen water corresponds to 4.6°C. The most

restrictive value, that is to say the lowest value, must be considered. The maximum crystallization zone, on which the quality of a deep-frozen food is set, in particular in terms of the size of the ice crystals, is therefore within this range covering the gap between the initial freezing temperature and Tm0 .

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243

7.1.3.3 CRYOGENIC FREEZING: FASTER THAN MECHANICAL FREEZING

After having described what happens in food during freezing, let’s move on to the techniques to achieve a freezing process. In the food industry, depending on how the cold is generated, two types of techniques are commonly used to freeze food products:  Mechanical freezing (or air freezing): In this type of freezer, the cold is generated with a refrigerating machine mainly made of a compressor, a condenser (warm heat exchanger), an evaporator (cold heat exchanger), and a pressure reducer. This system needs energy, electricity in most cases, to run. The temperature commonly achieved with this freezer is 40°C.  Cryogenic freezing (or flash freezing): In this case, the cold is generated by the injection of a cryogen, for example, liquid nitrogen or liquid carbon dioxide. The cryogen is delivered to the freezing industry in a tank and this tank is connected to the freezer with an insulated pipe. Producing cold consists of opening a valve and injecting cryogenic fluid into the freezer. No extra energy is required (in fact the cryogenic fluid contains the energy for producing the cold). The temperatures commonly achieved with this system start from 50°C and go down to 100°C. In the case of direct contact between liquid nitrogen and food, the temperature can even drop down to 196°C (temperature of liquid nitrogen boiling at atmospheric pressure). The very low temperature we can achieve with this technique makes cryogenic freezing much faster than mechanical freezing. That’s why cryogenic freezing is sometimes called flash

freezing. The coming parts will describe the advantages and disadvantages of the cryogenic freezing technique for the food industry.

7.1.3.3 CRYOGENIC FREEZING: FASTER THAN MECHANICAL FREEZING Thanks to the very low temperature we can achieve in a cryogenic freezer, the freezing process is much faster than in a mechanical (or air) freezer. In the study of Anon and Calvelo (1980), we can see that freezing meat with a cryogenic freezer offers real benefits thanks to a faster freezing rate. Fig. 7.1.3.3 shows critical freezing time as a function of the product thickness. The critical freezing time is the time spent between 1°C (initial freezing temperature) and 7°C (80% of freezable water frozen) (Anon and Calvelo, 1980). With cryogenic freezing, the heat transfer can be higher; the temperature gradient is for sure significantly higher. As a result, the critical freezing time is shorter. 10,000

Near centre Near surface 1000

Critical time tc

7.1.3.2 CRYOGENIC AND MECHANICAL: TWO COMMON TECHNIQUES TO ACHIEVE FREEZING

Air freezing Near centre

100

Cryogenic freezing

10

Near surface

1 1

10

100

Product thickness (mm) FIG. 7.1.3.3 Critical freezing time tc as a function of food thickness in mm.

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7.1. REFRIGERATION

7.1.3.4 LESS DEHYDRATION AND LESS WEIGHT LOSS DURING FREEZING AND STORAGE Another important difference between cryogenic (fast) freezing and mechanical freezing is the impact on the dehydration during freezing. The cryogenic freezing process prevents the drying out of the goods and the consequent undesirable weight loss. For instance, Rodezno et al. (2013) found that cryogenically frozen catfish fillets had a lower freezing loss (0.37%) during freezing than the catfish fillets frozen by blast freezing (0.45%). Similarly, Boonsumrej et al. (2007) reported that freezing under cryogenic conditions (70°C to 100°C) reduces the freezing losses by 18%–47% when compared to airblast conditions (at 28°C and the air velocity of 4, 6, and 8 m/s). Moreover, when compared to the air blast freezing process, the cryogenic freezing process reduced the moisture losses during the storage period (Rodezno et al., 2013). The higher freezing rate of the cryogenic freezing process causes an ice crust formation at the surface of the product at the beginning of the freezing process. This ice crust acts as a glaze (thin protecting layer), which reduces moisture transfer from food to the atmosphere (Rodezno et al., 2013). Lower dehydration results in less product weight loss and better economic results.

7.1.3.5 GENERATION OF VISIBLE CRACKS IF EXCESSIVE FREEZING RATE Broadly speaking, the high freezing rate of cryogenic freezing has a good effect on the product. But it can also have negative impacts. When a product is too quickly frozen, the external layer of the food being frozen is exposed to compressive stress during water-to-ice-transition (until maximum freeze concentration temperature is

reached). Then this ice has to support tensile stress due to contraction during further cooling. The layer being frozen moves into the direction of the center of the product and has to support compressive stress (Fig. 7.1.3.4). The differential between the compressive and tensile stresses results in cracks if the tensile stress passes the rupture stress of the frozen material. This is described in Fig. 7.1.3.5. One way to prevent such risk is to allow stress relaxation for some time (typically a few minutes are sufficient) before further cooling. All these phenomena have been described in the papers from Shi et al. (1998a,b, 1999) or again in the work of Tremeac et al. (2007) and further studies. A temperature plateau at around 40°C (food temperature) during freezing will allow stress relaxation before further cooling to a lower temperature. The temperature of 40°C is proposed as it corresponds to the maximum

0.03

0.025

0.02

0.015

eT

244

0.01

0.005

0 −200

−150

−100

−50

0

T (°C) FIG. 7.1.3.4 Coefficient of linear expansion of water during solidification. Water expands during crystallization and then contracts. This antagonist expansion/contraction can be responsible for cracks in frozen matrices.

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7.1.3.6 SMALLER ICE CRYSTAL IN FOOD PRODUCTS

245

FIG. 7.1.3.5 Scheme representing the impact of fast freezing on mechanical stress in the case of a cylindrical or spherical geometry. Pictures showing cracked potatoes on the right have been taken by Shi et al. (1999).

ice concentration for a majority of food systems; meanwhile it is above the glass transition. Indeed, the food system becomes very brittle and fragile below the glass transition temperature. Another possible way to avoid such cracks could be the use of electromagnetic radiation during the cryogenic freezing process (Anese et al., 2012). In this case, the torque exerted by electromagnetic radiation can displace water molecules from the equilibrium state in a cluster and, thereby, may inhibit or retard spontaneous ice nucleation. The inhibition of ice nucleation at the external layer of the food would allow faster heat transfer from the outside environment to the inside of the food product. As a result, most of the ice crystals would form at the same time, and thus, development of mechanical stresses (both compressive and tensile stress) could be minimized and crack formation may be avoided.

7.1.3.6 SMALLER ICE CRYSTAL IN FOOD PRODUCTS The freezing process is often associated with damage. The sources of damage are believed to be associated with ice formation, either directly (e.g., mechanical effects) or indirectly (e.g., changes in solute concentration in the unfrozen phase); through migration of water from the cell interior to the cell exterior, producing cell shrinkage and membrane damage; through changes in gas solubility; and by phase transformation in nonaqueous membrane components (e.g., lipids) (Reid, 1997). In general terms, rapid freezing techniques are thought to form smaller ice crystals within the product structure, offering minimal quality changes. Whereas, the slow freezing process produces larger ice crystals and increases the damage to the food products. However, high freezing rates (cryogenic freezing) do not

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necessarily result in better product quality: the higher temperature difference between the cooling medium and products during the quick freezing process may have negative effects, due to considerable internal strain, surface ruptures, and cell structural changes. The aforementioned facts can be well understood by referring to Table 7.1.3.1. Moreover, the quality of the cryogenically frozen product also depends on the temperature consistency during transportation and storage. The cryogenically frozen products can be more sensitive to the temperature variations than the conventionally frozen products, due to the delicate matrix of ice crystals formed in the initial stages of cryogenic freezing and the higher temperature difference between frozen product and storage environments (Estrada-flores, 2016).

7.1.3.7 GOOD PRESERVATION OF MICROSTRUCTURE AT 280°C Image analysis is a powerful tool to determine the microstructure of food products. The structural examination helps to monitor the following parameters that can influence the

product quality: ice crystal size; ice crystal shape; level of damage the cells suffer during freezing/storage/thawing; redistribution of solutes; and degree of heterogeneity of the foodstuff, which thereby helps to draw out important correlations between the microstructure and the mouth texture (Wilson, 1991). In general, cryogenic freezing produces numerous small ice crystals, both in intercellular and intracellular domains, and hence reduces the freezing damage. But sometimes cryogenic freezing with a very high freezing rate causes cracking of the product, resulting in an inferior quality product. Chassagne-Berces et al. (2009) conducted a comparative study between the conventional freezing method (20°C) and two cryogenic freezing methods: (i) freezing by gas nitrogen convection at 80°C and (ii) freezing by immersing in liquid nitrogen (LN2, boiling point ¼  196°C). The changes in cellular structure were tracked by three different imaging methods: (i) the macrovision imaging method was used to determine the changes at a tissue level, (ii) confocal microscopy was used to visualize the vacuolar integrity at the cellular level, and (iii) cryo-scanning electron microscopy (C-SEM) was used to determine the ice

TABLE 7.1.3.1 Impact at Three Different Levels of Structure of Three Different Freezing Processes: Freezing at 20°C, 80°C Thanks to Nitrogen Gas Convection, and at 196°C by Immersion in Liquid Nitrogen (Chassagne-Berces et al., 2009) Structure Levels Cell Wall

Cell

Tissue

Organ

Freezing Protocols

Composition Modification

Vacuole Integrity

Cellular Structure

Puncture

Compression

At 20°C (0.9°C/min)

+++

Destroyed

Collapsed cell wall, tearing

++

++

At 80°C (8.1°C/min)

+

Destroyed

Tissue preservation

+

+

At 196°C (310°C/ min)

++

Destroyed

Tissue preservation, breakage

+++

+

Softening

Puncture and compression are the two texture parameters analyzed here. Amplitude of structure level modification (+++ high, ++ medium, + low).

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7.1.3.7 GOOD PRESERVATION OF MICROSTRUCTURE AT 80°C

crystal size. The macrovision images clearly indicated that freezing at 20°C produces large changes of the cellular structure: cell walls seem to be collapsed and a larger number of bigger intercellular spaces were formed (Fig. 7.1.3.6). When freezing at 80°C, the cellular structure is very close to the fresh one. When freezing at 196°C in liquid nitrogen, a long and thin tissue crack appears. Similarly, the confocal laser imaging of the frozen-thawed sample showed that none of the freezing protocols was able to preserve the vacuole intact. Moreover, C-SEM

247

images showed that freezing at 20°C produced relatively large ice crystals compared to both cryogenic freezing conditions. Freezing at 196°C using liquid nitrogen produced more small ice crystals in the apple sample than freezing at 80°C. In another study, Anese et al. (2012) reported that the sample frozen in an air blast freezer shows ice crystals mostly in the intercellular domain while the product frozen by cryogenic freezing shows ice crystals both in the intercellular and intracellular domains. In addition, the

FIG. 7.1.3.6

Macroscopic images of apple parenchyma tissue sections before and after freezing. (A) Fresh apple, (B) thawed apple after freezing at 20°C, (C) thawed apple after freezing at 80°C, and (D) thawed apple after immersion in liquid nitrogen. A tissue crack is pointed out by an arrow. The field of view was 5.5–7.25 mm (Chassagne-Berces et al., 2009).

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cryogenically frozen sample shows large surface fractures oriented in the direction of the meat fibers.

7.1.3.8 FOOD TEXTURE CLOSE TO THE FRESH ONE AT 270°C The most observable change happening to the product during freezing/thawing is the loss of its texture. The cryogenic freezing processes have both positive and negative impacts on the texture of the product, depending on the freezing rate. Normally, the cryogenic freezing process tends to preserve the texture of food products, but the use of a very high freezing rate such as dipping in liquid nitrogen may lead to crack development in the product, which deteriorates the texture of the food products. The studies on the effect of the cryogenic freezing process on the texture are exposed below. In their study, Kidmose and Martens (1999) reported a positive impact on the texture of steam-blanched carrots when frozen with a cryogenic technique. In their study, it was found that the blast freezing process (at 24°C) caused more tissue damage (i.e., tissue showing holes and large cracks between cells and excessive wrinkling of cell walls) and resulted in a softer texture product than cryogenic freezing at 70°C. In another study, the cryogenic freezing process was found to better maintain the textural stability of the rice flour/tapioca starch blend gel system (Seetapan et al., 2015). In this study, it was observed that the gel frozen via cryogenic freezing keeps its integrity when compressed. This was proven by the homogeneous distribution of small ice-rich domains. In contrast, the slow-rate freezing process causes gel fracture due to an inhomogeneous microstructure with the presence of larger ice-rich domains. Chassagne-Berces et al. (2009) found that the textural loss of apple fruit depends on the freezing rate. According to the mechanical test

applied at the organ level, freezing at 80°C causes less deformation of texture than other freezing protocols (at 20°C and a liquid nitrogen-immersed sample). For instance, freezing at 80°C generates less degradation (54%) in firmness than freezing at 20°C (79%) or immersion in liquid nitrogen (91%) during the puncture tests. The compression test shows that freezing at 80°C and immersion in liquid nitrogen makes less Young’s modulus decrease (97%) than freezing at 20°C (99%). At this point, we have to mention that the puncture test evaluates local fracture behavior (Chassagne-Berces et al., 2009). In the case of freezing by immersion in liquid nitrogen, the higher temperature difference between the sample and cryogenic fluid generates cracks in the sample, mainly at the level of vascular bundles where the cell size is smaller, and this might result in larger deformation during the puncture test. For the compression test, the situation is different. It evaluates the deformability of the tissue taken as a whole (Chassagne-Berces et al., 2009). The results of this compression test are closely associated with the cellular structure degradation obtained by macrovision analysis (Fig. 7.1.3.6). Similar to Chassagne-Berces et al. (2009), Anese et al. (2012) also reported cracking of a meat sample when frozen by the cryogenic freezing method (liquid nitrogen spray). The creation of large surface fractures in the direction of meat fibers had a bad effect on the texture of the meat. When defrosted, cryo-frozen samples were more firm than the air blast frozen samples. In the literature, there are two contradictory results available related to the change in the texture of the meat product during freezing-thawing. The first hypothesis suggests that during freezing-thawing the meat product, tenderness increases. This is due to the breakdown of muscle fiber caused by the enzymatic action during proteolysis, aging, and loss of the structural integrity caused by the ice crystal formation (Farouk et al., 2004; Leygonie et al., 2012). However, Lagerstedt et al. (2008) and

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7.1.3.11 SLOWER LIPID OXIDATION DURING COLD STORAGE

Leygonie et al. (2012) proposed that the loss of fluid during thawing results in less water needed to hydrate the muscle fibers; thus, a greater quantity of fiber per surface area seems to increase the toughness of the meat. In the study of Anese et al. (2012), the increase in firmness of a cryo-frozen meat sample during thawing can be attributed to a higher drip loss than the air blast frozen sample.

7.1.3.9 FEWER OR LARGER DRIP LOSSES The graph in Fig. 7.1.3.7 shows that the drip loss rate is low for a very short critical freezing time, then it increases and then decreases. There is thus an optimal freezing rate to reduce the drip losses. This was attributed by the authors to cracks in the frozen structure. This confirms the results from Shi et al. and Tremeac et al. (2007). The cryogenic freezing processes can either decrease or increase drip loss. The crack development during the freezing process acts as a determining factor for the drip loss increase or decrease. For instance, Boonsumrej et al. (2007) observed less loss during thawing for the cryogenically frozen sample than for the air blast frozen sample. In contrast, Anese et al. (2012) reported a higher drip loss for the cryogenically frozen sample. The higher drip loss in the case of the cryogenically frozen meat sample was attributed to the large surface fractures that occurred in the direction of meat fibers during the freezing process. Another parameter to judge the microstructure deterioration and drip losses is the salt soluble protein (SPP). The SPP was reported to be higher in the cryogenically frozen sample than in the air blast frozen sample, indicating less protein denaturation during the cryogenic freezing process (Boonsumrej et al., 2007).

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7.1.3.10 LESS CELL WALL DEGRADATION Freezing processes also affect the cell wall sugar composition of fruits. For instance, Chassagne-Berces et al. (2009) observed a reduction in the proportion of cell wall neutral sugars and uronic acids of apple during freezing and thawing. Slow freezing (at 20°C) creates more damage than the other freezing conditions (80° C and dipped in liquid nitrogen). The main sugars, the amounts of which were modified after freezing at 20°C, concern the arabinose representative of pectin and mannose, which is cellulosic-hemicellulosic sugar. The reduction in the arabinose content as a consequence of freezing-thawing could be due to the loss of arabinan from the rhamnogalacturonan I domains of pectin, which is supposed to participate in the cell wall mechanical characteristics by forming an interaction with the cellulose (Zykwinska et al., 2005). Thus, modification of pectins and hemicelluloses might have contributed to the collapse of the cell walls, resulting in cell separation with the presence of larger intercellular spaces in samples frozen at 20°C (Fig. 7.1.3.6). Kidmose and Martens (1999) observed no significant difference in sugar composition between cryogenic and blast-frozen carrot samples.

7.1.3.11 SLOWER LIPID OXIDATION DURING COLD STORAGE The cryogenic freezing process can also delay lipid oxidation during storage of frozen food products. For instance, the thiobarbituric acid (TBA) value of the catfish fillets frozen cryogenically was found to be significantly lower (0.94 mg MDA/kg fillet) than in the fillets frozen

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FIG. 7.1.3.7

7.1. REFRIGERATION

Drip losses in function of the critical freezing time tc.

by air blast freezing (1.25 mg MDA/kg fillet) after 6 months at 20°C 1°C (Rodezno et al., 2013). Similar observations were reported by Boonsumrej et al. (2007) for a tiger shrimp sample. The reduction in lipid oxidation during frozen storage in the case of cryogenically frozen products can be attributed to (i) slow diffusion of oxygen between the surface of samples and the surrounding area due to the barrier effect provided by the ice layer formed on the surface of cryogenically frozen sample; and (ii) a lesser amount of damage caused to the cellular structure during freezing (Rodezno et al., 2013).

7.1.3.12 VARIABLE IMPACT ON COLOR AND FLAVOR The impact of the cryogenic freezing process on the color and the flavor depends on the product and the freezing rate. Colors and flavors are highly affected by a large number of enzymatic reactions. These reactions can be affected by liquid concentration changes as well as cell wall and cell structure deterioration during freezing. For many fruits and vegetables, a slow freezing rate leads to significant color and flavor changes, making the frozen food product

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7.1.3.13 CONCLUSION

unappealing. But most good air freezers and of course all cryogenic freezers can provide a high enough freezing rate so the frozen product offers the right color and preserved flavors. For some fruits and vegetables such as mushrooms and green beans, the higher freezing rate of cryogenic freezers improves the texture of the frozen product, which can result in a better feeling of color and flavor for the consumer. In Table 7.1.3.2, a test (Archer and Kennedy, 1998) shows the impact of freezing rate (slow to very quick freezing) on the sensory characteristics of a product (cooked green beans). We can see that only slow freezing, when the freezing process last more than 12 h, leads to significant color and flavor changes. For some products such as meat or fish, the freezing rate can affect their visual aspect. Too fast cryogenic freezing leads to the formation of very fine ice crystals, especially at the surface of the product. These smaller ice crystals scatter light more effectively than larger crystals. This results in a lighter colored product surface. This can be a disadvantage for most products, which are supposed to have a nice colored surface, or an advantage for white products. At that point, we have to mention that this effect is subjected to temperature fluctuation and will often disappear during cold storage. TABLE 7.1.3.2 Texture, Color, and Flavor Changes After Slow to Very Quick Freezing (Archer and Kennedy, 1998) Time for Core to Reach 220°C

Sensory Characteristics of Cooked Product

Type of Freezing

12 h

Loss of texture, color, and flavor adversely affected

Slow freezing

Very quick frozen beans offer the best sensory characteristics.

This visual impact depends on the meat itself. Another study showed that the cryogenic process tends to cause minimal color losses on meat (Rodezno et al., 2013).

7.1.3.13 CONCLUSION When compared with mechanical freezing, cryogenic freezing offers much colder temperatures and as a result much higher freezing rates. This impacts the quality of the frozen food as follows:  Cryogenic freezing causes less dehydration and less weight loss during freezing but also during cold storage.  Due to ice expansion, cryogenic freezing generates cracks in the product when the freezing rate is too high.  Fast cryogenic freezing leads to smaller ice crystals in the product.  In relation with the ice crystal size, cryogenic freezing at 80°C causes almost no microstructure deterioration, the wall cells are kept intact, and the texture of the defrosted product is close to that of a fresh product. When a product is frozen at warmer or colder temperatures, these advantages disappear.  The impact of cryogenic freezing on the drip losses is complex. A very short freezing time leads to very low drip losses while a short freezing time leads to high drip losses and a long freezing time leads to medium drip losses.  Cryogenic freezing delays the lipid oxidation during cold storage. All in all, cryogenic freezing is a powerful technique for freezing food. It offers a large range of freezing rates and a large range of temperatures (down to 196°C). A food product frozen with a cryogenic technique and the right parameters can be significantly better in terms of quality. Dehydration, microstructure

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damage, texture degradation, and drip losses can be clearly minimized. But with the wrong parameters, when the freezing rate is too high or the temperature is too low, cryogenic freezing can lead to a frozen product that is not better in terms of quality. Ice expansion can cause visible product cracks as well as microstructure and texture damage. So, depending on the food product, its size, its composition, its structure, and its texture, the right parameters should be found for cryogenic freezing to get the best of this powerful technique and achieve a high-quality product.

References Anese, M., Manzocco, L., Panozzo, A., Beraldo, P., Foschia, M., Nicoli, M.C., 2012. Effect of radiofrequency assisted freezing on meat microstructure and quality. Food Res. Int. 46, 50–54. Anon, M.C., Calvelo, A., 1980. Freezing rate effects on the drip loss of frozen beef. Meat Sci. 4, 1–14. Archer, G.P., Kennedy, C.J., 1998. Maximising Quality and Stability of Frozen Foods: A Producers Guide to the State of the Art. Concerted Action CT96-1180. (Report 2). Boonsumrej, S., Chaiwanichsiri, S., Tantratian, S., Suzuki, T., Takai, R., 2007. Effects of freezing and thawing on the quality changes of tiger shrimp (Penaeus monodon) frozen by air-blast and cryogenic freezing. J. Food Eng. 80, 292–299. Chassagne-Berces, S., Poirier, C., Devaux, M.F., Fonseca, F., Lahaye, M., Pigorini, G., Girault, C., Marin, M., Guillon, F., 2009. Changes in texture, cellular structure and cell wall composition in apple tissue as a result of freezing. Food Res. Int. 42 (7), 788–797. Estrada-flores, S., 2016. Cryogenic freezing of food. In: Reference Module in Food Science. Elsevier, pp. 1–9. Farouk, M.M., Wieliczko, K.J., Merts, I., 2004. Ultra-fast freezing and low storage temperatures are not necessary to maintain the functional properties of manufacturing beef. Meat Sci. 66 (1), 171–179. Fikiin, K.A., 1998. Ice content prediction methods during food freezing: a survey of the Eastern European literature. J. Food Eng. 38 (3), 331–339. Fikiin, K.A., Fikiin, A.G., 1999. Predictive equations for thermophysical properties and enthalpy during cooling and freezing of food materials. J. Food Eng. 40, 1–6. Kidmose, U., Martens, H.J., 1999. Changes in texture, microstructure and nutritional quality of carrot slices during blanching and freezing. J. Sci. Food Agric. 79, 1747–1753.

˚ ., Enf€alt, L., Johansson, L., Lundstr€ Lagerstedt, A om, K., 2008. Effect of freezing on sensory quality, shear force and water loss in beef M. longissimus dorsi. Meat Sci. 80 (2), 457–461. Le-Bail, A., Chapleau, N., De-Lamballerie, M., Vignolle, M., 2008. Evaluation of the mean ice ration as a function of temperature in an heterogenous food; application to the determination of the target temperature at the end of freezing. Int. J. Refrig. 31 (5), 816–821. Leygonie, C., Britz, T.J., Hoffman, L.C., 2012. Impact of freezing and thawing on the quality of meat: review. Meat Sci. 91 (2), 93–98. Reid, D.S., 1997. Overview of physical/chemical aspects of freezing. In: Erickson, M.C., Hung, Y.C. (Eds.), Quality in Frozen Food. Springer, Boston, MA. Rodezno, L.A.E., Sundararajan, S., Solval, K.M., Chotiko, A., Li, J., Zhang, J., Alfaro, L., Bankston, J.D., Sathivel, S., 2013. Cryogenic and air blast freezing techniques and their effect on the quality of catfish fillets. LWT—Food Sci. Technol. 54, 377–382. Seetapan, N., Limparyoon, N., Gamonpilas, C., Methacanon, P., Fuongfuchat, A., 2015. Effect of cryogenic freezing on textural properties and microstructure of rice flour/tapioca starch blend gel. J. Food Eng. 151, 51–59. Shi, X., Datta, A.K., Throop, J.A., 1998a. Mechanical property changes during freezing of biomaterial. Trans. ASAE 41 (5), 1407–1414. Shi, X., Datta, A.K., Mukherjee, Y., 1998b. Thermal stresses from large volumetric expansion during freezing of biomaterials. Trans. ASME 120, 720–726. Shi, X., Datta, A.K., Mukherjee, S., 1999. Thermal fracture in a biomaterial during rapid freezing. J. Therm. Stresses 22, 275–292. Tremeac, B., Datta, A.K., Hayert, M., Le-Bail, A., 2007. Thermal stresses during freezing of a two-layer food. Int. J. Refrig. 30 (6), 958–969. Wilson, A.J., 1991. Microscopical methods for examining frozen foods. In: Bald, W.B. (Ed.), Food Freezing: Today and Tomorrow. first ed. Springer-Verlag, London, pp. 97–112. Zykwinska, A.W., Ralet, M.C.J., Garnier, C.D., Thibault, J.F.J., 2005. Evidence for in vitro binding of pectin side chains to cellulose. Plant Physiol. 139 (1), 397–407.

Further Reading Adamkiewicz, M., Rubinsky, B., 2015. Cryogenic 3D printing for tissue engineering. Cryobiology 71, 518–521. Kim, N.K., Hung, Y.-C., 1994. Freezing-crack in foods as affected by physical properties. J. Food Sci. 59 (3), 669–674. Mallett, C.P., 1993. Frozen food technology. Springer. ISBN: 978-0-7514-0072-4.

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FURTHER READING

Mellor, M., 1980. Mechanical properties of polycristallince ice. In: Tryde, P. (Ed.), Physics and Mechanics of Ice. Springer-Verlag, New York, NY. Mellor, M., Cole, D.M., 1982. Deformation and failure of ice under constant stress or constant strain-rate. Cold Reg. Sci. Technol. 5, 201–219. Michel, B., 1978. The strength of polycristallince ice. Can. J. Civ. Eng. 5 (3), 285–300.

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Pham, Q.T., Le-Bail, A., Tremeac, B., 2006. Analysis of stresses during the freezing of spherical foods. Int. J. Refrig. 29 (1), 125–133. Pounder, E.R., 1965. The Physics of Ice. Oxford Pergamon Press.

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S U B C H A P T E R

7.1.4 Cryogenic Refrigeration

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S U B C H A P T E R

7.1.4.1 Cryogenics for Food Freezing, Chilling, and Temperature Control Applications Philippe Girardon*, Caroline Moziar†, Didier Pathier* †

*Air Liquide, Paris, France IM-BL Food Market, Air Liquide, Cambridge, ON, Canada

7.1.4.1.1 REFRIGERATION WITH CRYOGENIC FLUIDS When deep freezing or cooling needs to be done quickly and must meet industrial production rates as well as sanitary and veterinary standards, it should be necessary in each project to ask the following question: should we implement a refrigerating machine using “mechanical cold” or use a cryogenic refrigerant at a lower temperature, allowing direct contact with the products? In the first case, the product is in contact with a cold environment (from the air) at a temperature lower than its freezing temperature, and is maintained in the time needed to reach a low enough temperature. Mechanical refrigeration uses loops of refrigerant (CFC, HCFC and NH3), the air being cooled via a heat exchanger, then follows a strong convection of air. In the second case, the refrigerants of natural origin (liquid nitrogen or carbon dioxide) are used in direct contact with the product. The principle of their transfer of energy to the food product according to the nature of the fluid is: Liquid nitrogen (LN2) in a fine spray of liquid to 196°C. In the case of liquid carbon dioxide (LCO2), the rapid pressure drop from 20 bar (20°C) of the liquid to the atmospheric

pressure gives a mixture of gas and solid particles (CO2 snow), the whole being 78.5°C. The use of these low temperatures accompanied by high coefficients of convection depends on the heat transfer modes (e.g., direct immersion in a liquid nitrogen bath, speeds of the cold gas in contact with products). The application of these fluids can be done in specific devices designed for cooling or freezing or in food processing such as mixers or grinders for temperature control. In any user facility, we distinguish a part related to the implementation of the fluid (gas storage tank, thermally insulated pipeline), a part related to application (e.g., the freezing equipment), the extraction of the cold gas to outside the building, and the safety instruments to prevent asphyxiation.

7.1.4.1.2 IMPLEMENTATION 7.1.4.1.2.1 Storage of Cryogenic Fluid Liquid nitrogen is stored at 196°C under 2 bars absolute in an insulated tank (vacuum insulation), always installed outside buildings. It should be located as close as possible to the application to avoid costly pipe lengths and input of heat sources. The nitrogen tank storage

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area must be accessible by the fluid delivery vehicles. According to the needs estimated in the fluid and in order to have sufficient autonomy, a tank of suitable size is installed. Different sizes exist from a few tons to up to 100 tons of liquefied gas. The tank is equipped with accessories allowing the filling, storage, and pressurization of liquid nitrogen in the best conditions of operation and safety. This equipment generally remains the property of the supplier for reasons of responsibility, maintenance, and retest purposes. This facility is not subject to the regulation of sites classified in major countries. Carbon dioxide for cryogenic applications is conventionally stored as a liquid at 20°C under 20 bars in tanks insulated and kept cold with the help of a compressor fridge. Vacuumed insulation tanks similar to those of liquid nitrogen storage are also used. In this case, it is not necessary to provide a source of cold at all times.

7.1.4.1.2.2 Transfer of Cryogenic Fluid Through Pipelines Transfer lines should be as short as possible and with a minimum of elbows, vertical up and down sections, and changes of diameter to avoid gaseous phase generation. This gaseous phase mixed with a liquid phase giving application process issues when immediate cold for a short period is required. To minimize the introduction of heat in the pipe, it may be recommended to use a vacuumed insulated line. As an alternative, polyurethane-foamed insulation pipe is also possible. The choice between these two types of materials will depend on the nature of the fluid (maximum insulation for liquid nitrogen, polyurethane for liquid carbon dioxide) and the distance between the tank and the application point of use. Despite all the precautions done with the piping design, it can still be necessary to separate the generated gaseous phase from the liquid

phase by means of a phase separator, one or more if necessary located at the highest point of the layout in a way to always get a stable refrigeration process efficiency.

7.1.4.1.2.3 Cold Gas Generation From Cryogenic Liquid Liquid nitrogen when vaporized by spraying generates an important volume of nitrogen gas. Under atmospheric pressure, 1 L of liquid nitrogen by itself releases 680 L of nitrogen gas at 0°C, which an extraction system retrieves and returns outside the building. When CO2 snow or dry ice is sublimated, 500 L of cold gas are generated per kilogram of solid CO2. The cold gas generated by liquid nitrogen vaporization or solid CO2 sublimation evacuated is diluted with ambient air or heated with an electric wire to avoid icing and the extraction duct obstruction.

7.1.4.1.2.4 Safety This section covers a fundamental aspect related to the use of cryogenic fluids, which by themselves spraying or sublimating to generate a large amount of gas, and which, if they are not taken out of the workshops in best practices, may decline the oxygen level, the latter causing a risk of anoxia for personnel at the same time. We will remind that a value of 16% of inhaled air oxygen content causes respiratory discomfort in humans. A content of 6% of oxygen is fatal. This risk is even more devious because nitrogen is odorless and colorless; CO2 causes tingling and is toxic beyond 3%, in addition to the risk of anoxia. In order to ensure the safety of people in the place of use, an oxygen sensor is recommended. When using a CO2 fluid, an additional specific sensor is also recommended. This gas safety monitoring is connected to an alarm system (visual and audible alarms) and fluid supply cut off (Fig. 7.1.4.1.1) .

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7.1.4.1.3 CALCULATION OF THE ENERGY NEEDS

FIG. 7.1.4.1.1

257

Oxygen safety detector installed in a freezing work shop.

It can be useful to refer to the labor code in order to comply with the local law. The industrial gas supplier is legitimate for all information and advice in this domain. In addition to the risk of anoxia, low temperatures can cause burns if the body is splashed with liquid nitrogen on the parts that are not protected by equipment such as cryogenic gloves, tight boots, and safety glasses, or would be in contact with a cold surface such as a noninsulated pipe or with frozen foodstuffs for a long time.

7.1.4.1.3 CALCULATION OF THE ENERGY NEEDS 7.1.4.1.3.1 Units First of all, we see a few reminders about the units used in work, energy, and heat quantity domains. According to Wikipedia:  The SI unit of work is the Joule (J), which is defined as the work expended by a force of one Newton through a displacement of one meter.  The dimensionally equivalent Newton meter (N m) is sometimes used as the measuring unit for work, but this can be confused with the unit Newton meter, which is the measurement unit of torque. Usage of N m is

discouraged by the SI authority because it can lead to confusion as to whether the quantity expressed in Newton meters is a torque measurement or a measurement of work.  Non-SI units of work include the erg, the foot-pound, the foot-poundal, the kilowatt hour, the liter-atmosphere, and the horsepower-hour. Due to work having the same physical dimension as heat, occasionally measurement units typically reserved for heat or energy content, such as therm, BTU, and calorie, are utilized as a measuring unit. 1 Joule (symbol J) ¼ 1 m2 kg s2 1 kilojoule (symbol kJ) ¼ 1000 J Non-SI unit details for expressing heat quantities; • The calorie (symbol Cal):  corresponds to the increase from 14.5°C to 15.5°C, the temperature of a gram of water at atmospheric pressure.  Also known as the “small calorie” or “gram calorie.”  Conversion factor: 1 Cal ¼ 4.1868 J. • The kilocalorie (symbol kcal):  Corresponds to the increase from 14.5°C to 15.5°C, the temperature of a kilogram of water at atmospheric pressure.

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7.1. REFRIGERATION

 Also known as the “large calorie.”  Conversion factor: 1 kcal ¼ 4.1868 kJ.  1 kilocalorie (kcal) ¼ 1000 Calorie (cal). • The Frigorie (symbol fg):  The energy removed from one 1 kg of water to cool it from 15.5°C to 14.5°C at atmospheric pressure.  It is a negative kilocalorie.  Conversion factor: 1 fg ¼  4.1868 kJ.  Hence, one Frigorie (fg) ¼  1000 cal ¼ –1 kcal. • The therm (symbol th): equals 1000 kcal.  Conversion factor: 1 th ¼ 4186.8 kJ. The power is expressed in watts (symbol W). A watt corresponds to the work of one Joule performed in one second: 1 W ¼ 1 J s1.  A kilowatt corresponds to the work of one kilojoule performed in one second: 1kW ¼ 1 kJ s1 ¼ 1000 W  Horsepower (symbol ch): power provided by a horse carrying a 75-kg load at walking speed (3.6 km h1 or 1 m s1). 1 ch ¼ 75  9:81  1 ¼ 735:5 W There is another work unit defined based on the watt: the kilowatt hour (symbol kWh). This corresponds to the work of one kW for one hour. As 1 kW ¼ 1 kJ s1, a kilowatt hour therefore equals 3600 kJ or 3600/4.18 ¼ 860 kcal.  1 kWh ¼ 3600 kJ ¼ 860 kcal (work or energy)  1 W ¼ 1 J s1 ¼ 860 cal h1 ¼ 0.86 fg h1 (power)

7.1.4.1.3.2 Energy and Gas Consumption Equivalence The amount of heat necessary for cooling or freezing a product is the difference in enthalpy between the initial state and the final state of the product.

 Generally, in the case of a cooling without a change of state of a material, this energy is given by the following formula:  Q energy per kg ¼ specific heat capacity ðrated C or CP Þ  dT Q is expressed legally (International Standard) in Joules (kJ). CP in kJ kg1 °C1. dT ¼ temperature difference between the initial state and the final state (°C).  When there is a change of state, this energy is calculated by using: • The specific heat above the freezing level: Cs in kJ kg1 °C1. • The latent heat due to the change of state (transformation of water into ice for food products): L in kJ kg1. • The specific heat below the freezing level: Cg in kJ kg1 °C1. • The initial temperature: Ti in °C. • Freezing temperature: Tc in °C. • The final temperature: Tf in °C. For food products, this energy is linked to their composition:  Water content.  Fat content.  Dry extract content. This energy is given most frequently by the CHAIM formula: Q ¼ (Cs  ΔT1) + L + (Cg  ΔT2). This is used to determine the difference in enthalpy between the fresh and frozen food product as a result of a change in state of the water (from liquid into ice), when the fat, water, and solid contents of the product are known. • Specific heat above the freezing point (kJ kg1 °C1): Cs ¼ ½2:09 ð%fatÞ + 1:25 ð%solidÞ + 4:18 ð%H2 OÞ

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7.1.4.1.3 CALCULATION OF THE ENERGY NEEDS

• Latent heat of fusion or solidification (kJ kg1): L ¼ 334:4 ð%H2 OÞ • Specific heat below the freezing point (kJ kg1 °C1): Cg ¼ ½2:09 ð%fatÞ + 1:25 ð%solidÞ + 2:09 ð%H2 OÞ This means that the total energy required to change the food product from state A (fresh) to state B (frozen) is equal to:  Q ¼ ðCs  ΔT1 Þ + L + Cg  ΔT2 with: • ΔT1: temperature difference expressed in °C between the initial temperature and the freezing temperature of the product. • ΔT2: temperature difference expressed in °C between the freezing temperature of the product and the final temperature. Example: Deep freezing fish from +10°C to 28°C. • Freezing point: 2°C. • H2O: 70%. • Fat: 10%. • Solid: 20%. Cs ¼ ð2:09  0:10Þ + ð1:25  0:20Þ + ð4:18  0:70Þ ¼ 0:209 + 0:25 + 2:926 ¼ 3:385kJkg1° C1 L ¼ 0:7x334:4 ¼ 234kJkg1 Cg ¼ ð2:09  0:10Þ + ð1:25  0:20Þ + ð2:09  0:70Þ ¼ 0:209 + 0:25 + 1:463 ¼ 1:922kJkg1° C1 Total heat load removal for the product is: Q ¼ ð3:385x12Þ + ð1:922x26Þ + 234 ¼ 324:6kJkg1 From this amount of calculated heat, we can determine the liquid nitrogen or liquid carbon

259

dioxide consumption by using the MOLLIER diagrams for liquid nitrogen and liquid carbon dioxide (see Fig. 7.1.4.1.2). The cooling energy of cryogenic fluid is given by the difference in enthalpy to the temperatures of the fluid and gaseous phase extracted during the freezing step. It is this energy that will be used for the calculation of consumption of fluid. In other words, the heat energy absorbed to allow the fluid vaporization depends on the liquid’s state of equilibrium, defined by its pressure and temperature. In practice, the following are identified:  The liquid’s enthalpy in its initial state through the pressure in the storage tank, assuming that the liquid is in a state of temperature equilibrium with this pressure.  The enthalpy of the gas in its final state through the temperature of the gases extracted from the application device, assuming that this gas is at atmospheric pressure. The difference between these two enthalpies gives us the quantity of heat exchanged during transformation. They are marked on the graph according to the main fluid storage conditions and the gas extraction temperatures. If the extraction of cold nitrogen temperature is 60°C, the result will be: 324.6/320  1 L of liquid nitrogen (kg of fish)1. In the case of liquid CO2, the result will be 1 kg LN2 (kg of fish)1. In addition to the specific energy needed to freeze the products, it is important to take into account the technical energy consumption of the device, consisting of cooling the equipment and maintaining it in freezing temperature operation as well as gas losses related to the gas supply pipeline and gas storage tank. These values are not negligible, and they depend on the frequency of stops and restarts of operations as when beginning the process or after cleaning between two shifts.

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Enthalpy in kj/kg 400

400

390

390

380

380

370

370

360

360

350

350 340

340 N2 1 barg tank pressure N2 2 barg N2 3 barg N2 4 barg N2 5 barg CO2 12 barg CO2 14 barg CO2 16 barg CO2 17 barg CO2 19 barg

330 320 310 300 290 280 –60

FIG. 7.1.4.1.2

–50

–40

–30

–20 –10 0 10 Exhaust gases temperature in °C

20

30

330 320 310 300 290 40

280

Mollier diagram for nitrogen and carbon dioxide used for cryogen consumption calculation.

7.1.4.1.4 DIFFERENT METHODS OF HEAT TRANSFER There are three types of heat transfer methods that are used in cryogenics: immersion, spraying, and convection. Immersion heat transfer methods are used only with liquid nitrogen where the food product is dipped into 196°C liquid for quick freezing or crust freezing applications. Some products are extremely sensitive to these ultralow temperatures, which means that they will crack or shatter (also known as thermal shock) if the contact time is too long. Spraying methods are more commonly used whereby liquid nitrogen is sprayed or CO2 snow is deposited directly onto the food product. In order to increase the rate of heat transfer and subsequently reduce the freezing time of the product, convection methods created by

rotating fan blades are also used in conjunction with a spraying method. Many types of cryogenic freezing and chilling equipment are designed based on the spray-convection philosophy. Fig. 7.1.4.1.3 gives the refrigeration capacity for the two gases used in cryogenics: nitrogen and carbon dioxide. There are several types of heat transfers when using cryogenic fluids, as mentioned in Table 7.1.4.1.1.

7.1.4.1.4.1 Direct Contact With Liquid Nitrogen Immersion is to dip the foodstuff in a liquid nitrogen bath. The heat transfer coefficient (HTC) depends on the size, shape, and surface area of the product. The heat exchange is usually

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7.1.4.1.4 DIFFERENT METHODS OF HEAT TRANSFER

FIG. 7.1.4.1.3

261

Cooling capacity of liquid nitrogen and liquid carbon dioxide.

TABLE 7.1.4.1.1

Different Types of Heat Transfer for Liquid Nitrogen and Carbon Dioxide

Fluid

Type of Transfer

Details

Liquid nitrogen

Contact liquid/ product

Immersion in a liquid nitrogen bath

Convection after spray

Snow generation from liquid CO2 depressurization, sublimation into gaseous carbon dioxide and convection

Contact solid/ product

Direct contact between CO2 snow and product

Carbon dioxide snow

Liquid nitrogen spraying through nozzles or holes and convection

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7.1. REFRIGERATION

constrained by the phenomenon of calefaction. The calefaction in the case of liquid nitrogen is characterized by the presence of a film of gaseous nitrogen vapor, generated by boiling (vaporization by formation of vapor bubbles) between the “warm” product and the fluid that is either a liquid or a mix of liquid and vapor phases. Immersion heat transfer mode can reach about 200 W m2 K1. As a spray, HTC can be more important than immersion as the calefaction phenomenon does not occur. However, this transfer depends on other important factors, especially the physical state of the liquid nitrogen (its pressure and temperature, liquid/gas proportion) as well as the fitting of spray (type of nozzle, spray distance). Further note that the spray is limited with a wrapping insulation around the product.

7.1.4.1.4.2 Gaseous Convection Heat exchanges take place between the gas from the evaporation of liquid nitrogen or sublimation of solid carbon dioxide, the cooled air, and the product. Formulas involving dimensionless numbers (Reynolds, Prandtl, Nusselt, etc.) can be used to calculate the transfers. Several factors are taken into account, including: • The size of the product (advantage for small products that have a higher surface area to volume ratio). • Air speed impacted by fan blade rotation. • The difference in temperature between the product and the cold source. Typical HTC with spray-convection systems is between 60 and 100 W m2 °K1. A satellite of convection is jet “impingement” of a liquid or gas onto a surface on a continuous basis. This mode of heat transfer has been tested extensively for many years and is still an ongoing pursuit. Some issues, among them noise

reduction, are still being improved. Impingement jets can be air-powered or use liquid nitrogen. High speed jet impingement on a foodstuff surface creates a thin boundary layer, and thus a high heat transfer coefficient up to 300 W m2 K1; more than with a liquid nitrogen immersion bath.

7.1.4.1.4.3 Direct Contact With Solid Carbon Dioxide Solid CO2 under a snow state (when liquid CO2 is depressurized) transfers its energy when sublimating into a gaseous form and surrounding the product to be chilled or frozen. It is then possible to perform an intimate mixing between CO2 snow or CO2 dry ice and the product to improve the heat transfer.

7.1.4.1.5 APPLICATIONS Cryogenics are used throughout a food manufacturing operation in order to address quality, processing, shelf life extension, and food preservation issues. There are two main applications for cryogenics: as a preservation refrigerant for freezing, chilling, and temperature control, or as a processing aid for sauce coating, shaping, liquid pelletizing, slicing, crystallizing, grinding, and glazing.

7.1.4.1.5.1 Advantages of Using Cryogenics The advantages of cryogenic refrigeration versus mechanical refrigeration are well known in the industry. The colder temperatures from cryogenic refrigerants contribute to higher yields by rapidly locking in the product’s moisture content so that there is very little weight loss from dehydration. The colder temperatures also enhance product quality by freezing the product faster. Faster freezing results in the formation of

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7.1.4.1.5 APPLICATIONS

smaller ice crystals, which causes less damage to the cellular structure and helps to retain the product’s initial texture, color, and flavor profile. The economic viability of cryogenic refrigeration is largely dependent upon the type of food products that are being processed and the freezing capacity requirements of the customer. In order to justify the freezing cost of cryogenics, the food product should be: • High in moisture content and high in value such as the protein category, which includes meat (beef, pork, lamb, etc.), poultry, fish, and seafood products, or • The food product should be a value-added, further processed item such as ice cream or ready meals (entrees, pizzas, pastas). Low-value commodity-type foods, such as fruits and vegetables, are typically not a good fit for cryogenics because the profit margins are too small to support the freezing costs that are associated with cryogenics. Furthermore, cryogenic refrigeration is better suited to freezing capacity requirements of up to 800 kg h1 and, as a result, small to medium processors are usually ideal candidates because companies may be trying to minimize their risk or are looking for an upfront investment with a minimal capital outlay. Other advantages for using cryogenic refrigeration, in addition to faster freezing time, fewer dehydration losses, and improved product quality, include: • Lower initial cryogenic equipment investment, especially where rental options are provided. • Greater processing flexibility for a wide range of food products using the same piece of equipment. • Lower maintenance costs of the cryogenic equipment. • Fewer floor space requirements for cryogenic equipment, due to a faster freezing time.

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• Customized cryogenic equipment solutions depending upon the product or the process. One of the challenges for using cryogenic refrigeration instead of mechanical refrigeration is the higher freezing or operating cost due to the fact that cryogenics are expendable refrigerants rather than a closed-circuit refrigeration system. The freezing cost with cryogenics can be approximately 2–5 times more than that with mechanical systems due to the moisture content and the temperature profile (initial versus final temperature) of the product, and the price of the cryogen (which varies by geography and by volume requirements). When cryogenics are compared to mechanical refrigeration, it is important to offset the higher cryogenic operating costs against the cost savings of less product dehydration, improved product quality, increased productivity, less rework, reduced downtime, and reduced labor requirements that are usually associated with a cryogenic refrigeration system. If cryogenic refrigeration is used as a processing aid, it is usually easier to justify the higher operating costs because there are very few alternative solutions. For instance, sauce coating of Individual frozen particles, pelletizing of juices, and grinding and shaping of applications can only be done using cryogenic solutions. A quick start-up time can also be factored into the arguments in favor of cryogenics.

7.1.4.1.5.2 Dehydration and Water Losses Example: Analysis of comparatives water losses of a product such as minced beef meat: water loss during the mechanical freezing is 1.31% while in cryogenic freezing the water loss is 0.47%, leading to a favorable balance of +0.84% in favor of cryogenics, which at the price of the product is not negligible. Beyond these figures, it should be noted that any comparison is difficult because of

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264

7.1. REFRIGERATION

a multitude of parameters and must be carried out in parallel in real conditions.

7.1.4.1.5.3 Ice Crystal Incidence Freezing implies phase changes. The aqueous component of the tissues separates in two phases: ice and solution increased in solute concentration. The presence of ice crystals and the concentration of the solution can have significant effects on the final quality of the product. In addition to ice formation, an additional complexity is introduced: tissues are made of cells. There are at least two distinct environments—intracellular and extracellular media— separated by a system of membranes. These two systems interact with the phase state of the aqueous system. a. Freezing occurs in the extracellular medium first; if cell membranes are intact, ice doesn’t penetrate the cell. b. As the concentration of extracellular medium is increasing and water can permeate through the membrane, an osmotic exchange occurs, so water will leave the intracellular medium, forming additional extra cell crystals. This is the osmotic dehydration of the cell. c. Intracellular concentration increases as the water is removed from the cell to equilibrate extracellular concentration. d. If water cannot be exported sufficiently rapidly, internal seeding of ice and ice growth will occur. Once ice forms within the cell, the concentration of extra- and intracellular unfrozen medium matches and there is no longer an osmotic force for water transport. In slow freezing, there is sufficient time for a large removal of water from the cell to the extracellular medium. This increases the

concentration of the cell content, creating cell dehydration with no ice crystallization within the cell, then large ice crystal growth in the extracellular medium. The consequence is severe cell dehydration with cell shrinkage, damages in membrane properties, and an undesirable reaction due to a high concentration of intracellular solution and extracellular crystallization sources of tissue distension. Due to cell membrane damage consequent to the freezing process, this water doesn’t return to the cell upon thawing and becomes drip loss. In fast freezing, there isn’t enough time to remove the water from the cell. When heat is removed rapidly, ice forms rapidly and tends to be small and unsteady. Ice forms both within the cell and in the extracellular medium, and osmotic water transfer is limited.

7.1.4.1.5.4 Freezing of Foods Freezing is a method of preserving food by lowering the temperature to below the freezing point of water (0°C or 32°F) so that the liquid water phase is converted to ice, which essentially stops any bacterial growth and allows the food to be stored for longer periods of time. Different freezing methods have been used in recent decades such as brine immersion solutions, blast and contact freezing systems with mechanical refrigeration, or immersion and spray-convection systems with cryogenics. Note that if all the microorganism growth is definitively stopped below this admitted 18°C temperature, they are not killed and several enzyme types can still react in the foodstuff media such as proteases. Description of the different cryogenic machine concepts are located further in this chapter.

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7.1.4.1.5 APPLICATIONS

7.1.4.1.5.5 Chilling of Foods Chilling is a preservation technique where raw or processed foods are cooled from their initial temperature to between 0°C (+32°F) and +4° C (+40°F) in order to slow the growth of bacteria and delay spoilage. Because bacteria multiply exponentially at temperatures between +4°C (+40°F) and +60°C (+140°F), the proper chilling of foods is essential for eliminating any risk of foodborne illness. Descriptions of the different cryogenic machine concepts are located further in this chapter.

7.1.4.1.5.6 Particular Uses of Cryogenic Refrigeration As mentioned above, there are two main applications for cryogenics: as a refrigerant for freezing, chilling, and temperature control in order to preserve food from spoilage, and as a processing aid for coating, shaping, pelletizing, slicing, crystallizing, grinding, and glazing. Descriptions of the different cryogenic machine concepts are located as following. 7.1.4.1.5.6.1 Freezing of Liquid Foods Liquid or semiliquid food products such as ice cream spheres, egg products, etc., can be frozen into free-flowing pellets with a consistent size and shape using specially designed liquid nitrogen freezers. The liquid nitrogen flow within the equipment can be controlled by a pressure-sensing level gauge that operates in conjunction with a solenoid valve and a programmable logic controller (PLC) panel. When equipped with a liquid nitrogen pump, the liquid nitrogen is recirculated back to the pelletizing channel in order to create a continuous flowing river cocurrent of liquid nitrogen flow (Figs. 7.1.4.1.4 and 7.1.4.1.5). Pellets under sphere forms are generated by peristaltic liquid pumps with a large series of needles generating the right drop dimensions.

265

7.1.4.1.5.6.2 Individual Quick Freezing (IQF) Individual quick freezing (IQF) technology is an important part of the frozen food market because the quality of the product is not compromised. IQF technology locks in the moisture, shape, and freshness of smaller food items while ensuring reliable food safety and a natural appearance. Individual quick freezing can be used to freeze protein products (sliced/diced poultry and beef; raw or marinated poultry and meat products such as chicken breasts, fillets, and wings; meatballs, shrimps, scallops, etc.), prepared foods (pizza toppings; pasta products such as ravioli and tortellini; egg products), and high value fruits and vegetables. The main IQF product categories in proportion are fruits (21%), seafood (20%), vegetables (19%), and poultry (15%). Approximately 48% of IQF products are consumed directly by the consumer (business to consumer) while about 52% are used in the processing of prepared food products, either by another manufacturer or by the food-service industry (business to business). IQF products can be frozen with either cryogenic or mechanical refrigeration systems. 7.1.4.1.5.6.3 Sauce Coating Another outstanding example is combining both types of prepared foods requested by the consumer and the adaptation of existing equipment to accomplish a specific operation of cryogenics. Sauce-coated IQF products, into portion, was born from demands to keep homogeneous and similar sauce/product bases ratio whatever the quantities of food it is liked for thawing at lunch time. Sauce coating means freezing of sauce layers onto already frozen products. The finished product is convenient and easy to prepare for the home consumer or food-service operator. The interest for potential customers is adding value to an existing product so that the end user can reduce the culinary effort required.

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7.1. REFRIGERATION

Ventilator

Insulation

Pelletizing channel

Dropper unit

Product

Conveyor belt

Return channel for liquid nitrogen

Liquid nitrogen pump

Weighting and packaging

FIG. 7.1.4.1.4

Liquid nitrogen pelletizing unit.

FIG. 7.1.4.1.5

Pelletized ice cream.

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7.1.4.1.5 APPLICATIONS

Compared to IQF products, sauce coating must bring sufficient added value to justify the additional cost. This is a list of recipes that the food industry proposes:  Macaroni and spaghetti products, pasta, rice (paella, Cantonese rice), and potatoes in combination with other products.  Vegetables.  Diced meat and poultry.  Seafood; scallops, shrimp, and shellfish. The equipment used is a tumbler from different original equipment manufacturers (OEMs) such as Armor Inox, Lutetia, Henneken, Dohmeyer, GEA, etc. (Fig. 7.1.4.1.6 and Table 7.1.4.1.2) The operating principle is:  Batch production.  The IQF products are introduced already frozen.  Mixing with liquid sauce to coat the pieces.  Alternated injections of sauce and decryogenic fluid in the rotating cylinder.  A surface crusting effect of the sauce appears on the pieces.

 Liquid sauce introduction and cryogenic fluid injection are repeated, depending on the desired sauce coating layer rate. Each piece is coated with sauce and frozen.  Loading and unloading by the same end.  Applicable for sauce content up to 100%.  Cycle duration of 45 min. 7.1.4.1.5.6.4 Subcooling for Glazing Glazing involves the formation of a protective layer of ice around the surface of frozen seafood and raw poultry products (i.e., boneless chicken breasts) in order to prevent oxidation and dehydration (which can lead to freezer burn) during frozen storage. The ice is formed by dipping the frozen product into potable water or by using a water spray, usually after the surface of the product has been subcooled in a cryogenic freezer. Subcooling the surface of the product ensures the required water pick-up in order to form the glaze and transfers the right amount of cold so that the glaze is fully hardened by the time the product has reached the packaging operations, thus eliminating any risk that the products will refreeze together in the package. The amount of glazing is determined by the

Production cycle Sauce injection

Liquid nitrogen injection

Temperature

10°C

Sauce

Coated products

–18°C

IQF products

Loading of products into cryomix

FIG. 7.1.4.1.6

–18°C

Ingredient mixing

Production cycle of IQF sauce coating in an Armor Inox special tumbler Cryomix brand.

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Time

268 TABLE 7.1.4.1.2

7.1. REFRIGERATION

Different Process Details of Recipe References

IQF Products (218°C)

Type of Sauce

Sauce Temp. (°C)

Coating Percenta

Final Temp. (°C)

Final Batch Weight

Process Cycle Timeb

Total Cycle Timec

Liquid Nitrogend (L/kg)

Mediterranean mixed fried

Oil base

30°C

6%

20°C

850 kg

25 min

45 min

2.5

Paella

Paella sauce

10°C

30%

20°C

975 kg

55 min

Pasta-liquid sauce introduction and cryogenic fluid injection are repeated depending on the desired sauce coating layer. Each piece is coated with sauce and frozen.

Carbonara

Forestiere mixed fried

Bechamel

Various vegetables

Tomato sauce

Cabbage

Bechamel

Cabbage

Bechamel

a b c d

2.8

30%

2.5

25%

20°C

1000 kg

60 min

2.4

45%

30°C

800 kg

75 min

3.0

27°C

30%

25°C

500 kg

20 min

2.7

90°C

20%

50°C

500 kg

36 min

6.5

15°C

Compared to final batch weight. Cryogenic process cycle time. Including loading and unloading. Consumption per whole coated product.

manufacturer in order to ensure the protection of the product without being perceived as a means of deceiving the consumer or improving their profits. 7.1.4.1.5.6.5 Crust Freezing Before Slicing or Dicing Crust freezing with liquid nitrogen or CO2 prior to slicing or dicing is typically used for the following types of products: luncheon (or deli) meats, fish products (i.e., smoked salmon), cheese products, cooked meat and poultry products (i.e., pizza toppings, fajita strips), or raw primal meat products (i.e., pork, beef, lamb, bone-in or boneless). In many cases, cryogenics has replaced the use of mechanical systems because the food product can be more easily crust frozen on a “just-in-time” basis. Using cryogenics for this process delivers better slicing

or dicing characteristics along with improved hygiene, product yields, appearance, weight control, and process efficiency. Normally, a crust freeze depth of approximately 6–10 mm into the surface of the product, prior to the slicing or dicing operation, will give the best results. 7.1.4.1.5.6.6 Hardening in the Ice Cream Industry There are several different cryogenic hardening applications that can be used in the ice cream industry, such as: (i) Immersion hardening of the ice cream novelty, using a liquid nitrogen immersion freezer, prior to a liquid chocolate coating application in order to quickly solidify the chocolate to the surface of the product. If the ice cream novelty is immersed in the liquid nitrogen for too long, then the chocolate

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7.1.4.1.5 APPLICATIONS

269

FIG. 7.1.4.1.7

Difference of chocolate coating quality according to the liquid nitrogen bath immersion time (left: 1–2 s in liquid nitrogen immersion, right: 4–5 s in liquid nitrogen immersion).

FIG. 7.1.4.1.8

Ice cream stick made of several layers that need subcooling between each next coating.

coating will subsequently crack (Fig. 7.1.4.1.7). (ii) Liquid nitrogen dipping tanks for coating ice cream bars with multiple layers of fruit or juice coating (Fig. 7.1.4.1.8). The ice cream bar is first dipped into a specially designed tank of liquid nitrogen in order to harden the surface so that when the bar is dipped into the next tank of coating, it

solidifies and freezes very quickly due to the transfer of the extreme cold from the ice cream. A second liquid nitrogen dipping tank then follows, along with another fruit or juice coating application. A third dipping tank is typically used to subcool the surface of the bar so that it can be packaged without smearing the surface of the coating.

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7.1. REFRIGERATION

(iii) Hardening the surface of ice cream in cones or containers using specially designed liquid nitrogen spray systems prior to the application of chocolate, fruit sauces, or other liquid toppings in order to prevent melting of the ice cream so that it retains its shape (Fig. 7.1.4.1.9). The same equipment in the figure above can also be used to harden the chocolate glaze or coating that is deposited inside a sugar cone prior to the ice cream filling operation. By quickly solidifying the glaze with a liquid nitrogen spray, this process ensures that there is an even thickness of coating around the inside of the cone that

FIG. 7.1.4.1.9

Liquid nitrogen spray unit for ice

provides a moisture barrier between the ice cream and the cone so that the cone does not become soggy in texture during its shelf life. (iv) Hardening of high-end, specialty ice cream cakes (Fig. 7.1.4.1.10) prior to a chocolate coating application to quickly solidify the coating by the transfer of cold from the surface of the ice cream to the chocolate. This process ensures that the ice cream underneath doesn’t melt and then bleed through the chocolate coating, which would then look visually unattractive to the consumer.

FIG. 7.1.4.1.10 Frozen cake hardening in a batch freezer.

cream cones.

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7.1.4.1.5.7 Cryogrinding Cryogrinding is the act of cooling or chilling a material and then reducing it to a smaller particle size. The process utilizes the effects of liquid nitrogen to brittle materials prior to and during the grinding process. The cryogrinding process does not alter or damage the chemical composition of the food product in any way and can help reduce losses of volatile components or heatsensitive constituents. This process is primarily used for the cryogrinding of spices such as pepper, cinnamon, ginger, cumin seed, nutmeg, clove, etc., in order to: (i) Prevent the loss of essential oils by means of the lower operating temperatures from liquid nitrogen. The temperature in the grinding zone can rise to more than 90°C, resulting in a loss of essential oils and therefore an inferior quality ground product. (ii) Prevent clogging and gumming of the mill. Spices such as cinnamon, clove, and nutmeg contain high levels of fat while capsicum, chili, etc., contain high levels of moisture, which can cause clogging and gumming of the mill that results in a lower productivity rate and quality of the ground product. (iii) Reduces oxidation and related degradation. Aromatic substances in spices or food materials can oxidize and become rancid due to the cyclone effect of the air in the vicinity of the grinding zone. In addition, the oxidation process can be accelerated on the newly exposed surfaces of the foodstuff, which is created by the grinding action. The main advantages of cryogrinding include smaller more uniform particle sizes, increased productivity, reduced power consumption, minimal loss of volatile components and essential oils, and improved aroma of the product. The cryogrinding system consists of a precooling unit and a grinding unit. The cryogenic

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precooler is a cooling device that consists of a screw auger within an insulated enclosure along with a system to introduce the liquid nitrogen as the refrigeration source. The precooler is designed to remove the heat from the food product prior to entering the grinder. The cold liquid nitrogen gas from the precooling unit is then usually redirected to the grinder chamber in order to minimize thermal reactions with the material and to reduce the loss of volatile components during grinding (Fig. 7.1.4.1.11).

7.1.4.1.5.8 Prilling Nitrogen in its cryogenic form can sometimes be used in very specific fields such as the production of pharmaceutical or nutritional particles. In order to protect active ingredients from oxidation or high temperature, encapsulation is one solution. These particles include the active element inside by means of cryogenic prilling. Liquid nitrogen is used to cool down the product initially melted and sprayed into small droplets. The liquid droplets quickly turn into solid beads of different sizes and properties. In the pharmaceuticals and nutritional supplements markets, to make the pills easier to swallow and to get a better release of the active ingredient within the body, several studies have been carried out on the stabilization and formulation of these ingredients. The animal feed ingredient domain is also of concern to look for solutions to stabilize and hide the taste and off-flavors of some molecules, the target being to make healthy food with the desired nutritional properties while remaining appetizing for the animal. 7.1.4.1.5.8.1 General Operating Principle According to the following figures (Figs. 7.1.4.1.12–7.1.4.1.14), the cryogenic prilling consists of the following steps:  Melting: the first important step of this process is to make a consistent liquid mixture of the product to be granulated. The product

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N2

1

4 2

T

LN2 3

FIG. 7.1.4.1.11

Cryogrinder schema.

FIG. 7.1.4.1.12

Diagram of a cryogenic prilling system with a freezing step in cold gaseous nitrogen. 7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

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FIG. 7.1.4.1.13

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Diagram of a cryogenic prilling system with a freezing step by direct contact of the droplets with liquid

nitrogen.

FIG. 7.1.4.1.14

Cryogenic prilling system.

must be melted and its viscosity low enough to tolerate the following steps. A balance must be found for the right temperature. Indeed, temperature level influences several

parameters such as viscosity, droplet generation performance, effectiveness of the active ingredient, further freezing time, and freezing energy quantity. The formulation of

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the mixture is the second key point of this step as the active ingredient has to be protected by another ingredient (the matrix), thanks to a homogeneous distribution of the sensitive component that will be kept in the final solid form.  Jet generation: the melted product (mix) is then divided into precise droplets. A spray nozzle (needles) working under accurate pressure delivers a defined range of droplet sizes. In that case, the size distribution curve is often a fairly flat bell curve covering a wide range of diameters. Droplet generation: when accurately calibrated particles are needed, vibration under a specific frequency or an alternating electric field is applied to the needles.  Freezing: Once formed, the droplets fall from the top of a tower to the bottom. During this fall, the droplets are in contact with a very cold atmosphere, which by thermal exchange causes their cooling and solidification into beads. Thanks to the liquid nitrogen

FIG. 7.1.4.1.15

temperature, the vaporized nitrogen gaseous phase in contact with the droplets is 180°C, leading to a small cooling tower design. A shorter freezing time can be obtained with liquid nitrogen injection near the melted product injection.  Particle recovery: the solidified particles are collected at the bottom of the tower. 7.1.4.1.5.8.2 Types, Sizes, and Shapes of Generated Particles The three types of particles presented below are obtained by different cryogenic prilling process specifications and differ in size and shape (Fig. 7.1.4.1.15). Particles have a diameter ranging from 60 to 300 μm. The product and liquid nitrogen are sprayed in the same zone, allowing extremely fast freezing but leading to the deformity of the particles. As a result, all particles are not spherical (Fig. 7.1.4.1.16). In that case, the freezing step is slower but achieved in much less turbulent conditions.

Spheres obtained by nonmonodispersed cryogenic prilling and freezing with direct liquid nitrogen

contact.

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FIG. 7.1.4.1.16

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Nonmonodispersed cryogenic prilling when freezing is achieved in a cold gaseous nitrogen atmosphere.

The shape of the droplets is frozen in quiet conditions, without contact and chock with liquid nitrogen droplets. The droplets keep their spherical shape during their fall in the cooling tower. The size of the beads varies from 100 to 2000 μm with a higher proportion of beads having a diameter ranging from 600 to 2000 μm (Fig. 7.1.4.1.17). Droplets are formed under a defined vibration frequency perturbation that sequences the droplets with a fixed diameter. As a result, the perfect spherical beads have a similar diameter chosen from 600 to 2000 μm. Broadly speaking, all these cryogenic prilling techniques (cooling by contact with gaseous nitrogen or with liquid nitrogen, prilling monodispersed or not) produce beads or particles with a uniform or matrix composition. The particles are uniform when the melted product is pure. They have a matrix structure when the melted product is a mixture of an active ingredient and a support ingredient (excipient). In that case, the particles play the role we want them to play: the active ingredient is encapsulated and

protected by the solidified excipient. The particle sizes can go from 60 to 2000 μm. Many active molecules can be successfully encapsulated with this technology such as ginger extracts, analgesics, antiinflammatories, caffeine, vitamins, iron, and copper salts.

7.1.4.1.5.9 Temperature Control During Manufacturing 7.1.4.1.5.9.1 Case of Minced Meat in Mixers In use in many unit processes of food industries, temperature control maintains the temperature of the product, which rises as a result of the transmission of heat by the energy of agitation, pumping, mixing, cutting, and grinding. This energy can be dispersed by cold air ventilation or by a circuit of cold water or glycol-based refrigerant. In the case of the blenders, a jacket around the vessel (that is, a mixer) is often not sufficient. Also, a direct injection of refrigerating cryogenic fluid in the product is more effective whether it is CO2 snow made with a snow horn

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FIG. 7.1.4.1.17

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Monodispersed cryogenic prilling when freezing is achieved in cold gaseous nitrogen.

positioned in the cover or liquid nitrogen sprayer. In both cases, it should be an extraction of the cold gas generated after transmission of their energy. Variants are to bring these fluids at low points. As the measurement and control of temperature cannot be done easily by an accurate physical measurement (risk of grubbing up of any probe), the setting of quantities of frigories to bring is essential. The injection doesn’t take place continuously but alternatively by a set of valves, each observing a break between two injections. Mixing is a very common process used in many sectors of the food industry, the aim being to create a homogenous product from its ingredients. The combination of mixing with a cooling action is a particularly useful process that can be used for one or more of three different cooling needs:

(b) Preventing a product from warming due to the energy being put into mix of the product, that is, nearly all mixing processes absorb power, and this power input will have a direct heating effect on the product. In many cases in the food industry, the warming of the product would have unacceptable consequences, that is, the product becomes too warm for the next stage of the process while there is an increased rate of microbial growth, the product viscosity changes, etc. (c) Some processes require that the product should have a certain viscosity in order for the process to work in an optimum way, that is, most hamburger forming machines work best with a semifrozen material as a warmer product is too fluid, which results in too much variation in the formed product shape and/or weight.

(a) Cooling a product that enters the mixing process at too high a temperature, that is, nonchilled ingredients mixed together producing a product that needs to be chilled for the next stage of the process.

In different parts of the food industry, various techniques to give the product the required temperature for the process stage that follows mixing have been developed. These include (Fig. 7.1.4.1.18):

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FIG. 7.1.4.1.18

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Global view of a meat mixer equipped with a bottom liquid cryogenic gas injection.

 Adding chilled water, brine, or water ice to the product.  Using overchilled ingredients.  Using some frozen ingredients in the product. 7.1.4.1.5.9.1.1 PROCESS DESCRIPTION PRINCIPLES AND FEATURES OF THE PROCESS During mixing, the temperature of

the food product in the mixer is reduced by the injection of a liquid cryogenic gas into the mass of product. Liquid nitrogen or liquid carbon dioxide are the gases that can be used. When liquid nitrogen is injected, it initially generates some “flash gas” due to its pressure

dropping below its storage pressure (or its “saturated vapor pressure,” to use the correct term) and the remainder of the liquid is cooled during the pressure drop to approx. 196°C (320°F). The liquid nitrogen is mainly injected into the mass of the food product. As the food product is much warmer than the liquid nitrogen, heat is transferred to the liquid nitrogen, which boils very rapidly, creating a large volume of cold nitrogen gas. With the mixing action, the gas moves through the mass of the product until it reaches the surface and is released into the atmosphere above the product. During this movement and mixing, more heat is transferred from the food product to the cold gas. A small

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proportion of the liquid nitrogen will often follow an upward path between the food and the wall of the mixer, with the heat being absorbed by the liquid nitrogen from both the food and the mixer. When liquid carbon dioxide is injected into the mixer, it also creates “flash gas” due to the pressure drop, but liquid carbon dioxide cannot exist at atmospheric pressure. Instead, it cools and creates a mixture of solid carbon dioxide (often called CO2 snow or dry ice) particles at around 78.5°C (109°F) and carbon dioxide gas at the same temperature. When solid carbon dioxide is heated, it sublimates (changes from solid to gas without going through a liquid phase). The solid carbon dioxide can also be pushed through the product mixture in a different way to the mixing action that is achieved with liquid nitrogen. Again, the cold gas moving through the product provides additional cooling to the product. Both cryogens can thus create very rapid and effective cooling of the food product during mixing. FEATURES OF TOP AND BOTTOM INJECTION SYSTEMS A top-injection liquid nitrogen sys-

tem uses an arrangement of one or more nozzles to spray liquid nitrogen onto the top surface of the product to be cooled. The product is moved and mixed, bringing a continuously renewed product surface into contact with the liquid nitrogen spray. Most of the liquid nitrogen is evaporated by heat at the surface of the product, as little liquid nitrogen is mixed into the mass of the product to effect cooling within the mass of the food product. In the main, the cold nitrogen gas does not pass through the product mass, and only a little heat transfer is achieved between the product and the gas at the surface of the product before the gas passes out of the mixer into the exhaust system. If the spraying rate is too high, the product surface may be overcooled, making mixing more difficult and giving an unevenly cooled product.

A top injection liquid carbon dioxide system uses an arrangement of one or more snow horns to deposit dry ice snow onto the top surface of the product to be cooled. The rate of sublimation of the snow is relatively slow, so the mixer is usually able to mix the dry ice snow into the product mass. Snow horns can create small flakes of light snow that can be carried away by the exhaust gas stream without ever touching the product to be cooled. If the snow production rate is too high, the product surface may be overcooled, making mixing more difficult and giving an unevenly cooled product. Due to the easier mixing of the dry ice snow when compared to the effect of mixing with top injection of liquid nitrogen, it is easier to produce a reasonably good liquid carbon dioxidebased top injection system than it is to do so with liquid nitrogen. When compared with top and bottom injection, systems:  Deliver more cooling effect from a given quantity of liquid cryogen. In a liquid nitrogen system, the evaporation occurs in the product mass and the flash and evaporated cold gas passing through the product absorb much more heat from the food. No liquid nitrogen is ever likely to be carried away by the exhaust stream. In a liquid carbon dioxide system, the sublimation occurs in the product mass and the flash and sublimed gas passing through the product absorb much more heat from the food. No dry ice snow is ever likely to be carried away by the exhaust system.  Provides faster, more even cooling. The injection of cryogen is done from several points in the product mass where the mixing effect is strong. This enables the product to be cooled faster and more evenly than with top injection systems. With the carbon dioxidebased system, the high velocity direct injection into the product mass creates much

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finer dry ice snow particles, which results in particularly rapid and even cooling. The mixing paddles of the mixer are not subjected to as much direct cooling. They get less cold and less product freezes onto the blades, so the blades better maintain the mixing action planned by the mixer manufacturer.  As the exhaust gases are warmer, the management of the exhaust duct is easier. LIQUID CARBON DIOXIDE AND LIQUID NITROGEN BOTTOM INJECTOR FEATURES A

system consists of a number of injector assemblies that are welded directly onto the lower part of the mixer. Injectors are designed to be easy to clean and are constructed of food-grade materials that consist of a stainless steel fixing sleeve, a flow control orifice, a valve that opens and closes at preset pressures, a hygienic “dairy clamp” to hold the assembly together, and a short flexible connection hose from the liquid cryogen supply via a control valve and safety cut-off valve. The injectors have to be positioned correctly in the mixer so as to be as effective as possible to have easy demounting for cleaning, compatible with aggressive food industry cleaning materials. The system can be fitted onto many types of new or existing mixers at the customer location. It is compatible with a large range of common mixer brands such as Alco, GEA, Haarslev, Innotec, KS, Laska, or Weiler. A few details in the assembly differ between liquid nitrogen and liquid CO2 usage, such as the type of nozzle and the insulation with a flanged PTFE part in the case of liquid nitrogen. The normal configuration is to use one process control valve per injector or pair of injectors. Implementation of the systems: The injectors are positioned to inject the liquid cryogen at a slight downward angle into the mass of the product, aiming slightly below the axis or axes of the mixing element. This gives a longer path of the liquid and gas to pass

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through the product, and makes the injectors self-draining for wash water. The number of points of injection has to be calculated based upon the specification of the mixer and the process requirements. 7.1.4.1.5.9.1.2 OTHER CASES OF TEMPERATURE CONTROL THROUGH FOOD PROCESSING

Minced beef meat isn’t the only concern for temperature control during cutting-mixing operations. Poultry filets mixing before nuggets forming, sausages meat, fish before p^ate forming, sauce and salads mixing and kneading bread dough need such cryogenic process. The principle described above is the same except the type of mixing machine, which can be different with a lower height bowl than for minced meat mixing. When using small height for mixing, top cryogenic fluid injection is best, such as for dough breading, which is of a compact texture and is done in a particular machine.

7.1.4.1.5.10 Cryogenic Crystallization of Fats Cryogenic Crystallization of fat is typically a processing aid cryogenic application based on physical state change of texture from a melted (around 60°C) to a solid form (ambient temperature). The product is atomized to produce liquid droplets of the desired size within a cooling chamber (tower), usually using airatomizing nozzles. The droplets are sprayed through a matching spray of liquid and gaseous nitrogen at 196°C to solidify them in a few milliseconds. Further cooling is performed by contact between the solidified droplets and the cold nitrogen gas produced in the previous stage. The powder obtained may be stored under controlled conditions to allow time for the desired crystal structure to develop. The product is typically around 20–200 μm in diameter. The powder produced can be mainly amorphous or be predominantly α crystals, which,

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depending on the production and storage conditions, may change to β crystals. Hydrogenated vegetable fats, baking improvers, bakery shortenings, milk and dairy fats, confectionery fats, and many others are the concerned ingredients.

7.1.4.1.6 REVIEW OF THE MOST COMMON EQUIPMENT TYPES 7.1.4.1.6.1 Cooling and Freezing Equipment Cryogenic application equipment covers a wide range of principles, different builders, and several brands. The manufacturers are generally of independent ownership more or less linked to the different industrial gas companies (IGC) for all or part of their equipment range. Most freezers can be grouped into the following: liquid nitrogen immersion freezers, freezer cabinets, inline freezers, IQF freezers, spiral freezers, or pelletizers. Some application machines can be batch processes such as cabinets and tumblers. The continuous ones are represented by inline (also called straight) tunnels. Variations of continuous machines are represented by multipass (also called three-belt, three-deck, and three-tier) and spiral machines (helical belt forming drum). Another category dedicated to IQF is made of several concepts of conveying and heat transfer mode combinations such as fluidization, tumbling, liquid nitrogen immersion, screwing, multibelt conveying, immersion, and vibration mix.

7.1.4.1.6.2 Cooling or Freezing in Batch Freezers They consist of:  An enclosure without a threshold, and isolated polyurethane foam with a stainless-

steel coating designed to receive different international standard carts.  Fans or turbines for ventilation, and ramp(s) with nozzles for injection of liquid nitrogen or liquid CO2 that relaxation at atmospheric pressure will turn into snow. Liquid nitrogen is injected directly inside the cabinet following a flow proportional to the energy needs of the products. The turbines or the fans provide a rapid vaporization of liquid nitrogen or a scattering of dry ice to give a homogenization of temperatures throughout the interior. The capabilities deal with a few tens to a hundred kilograms of product per operation cycle. The cycle time depends on product mass and levels of initial and final temperatures to reach.

7.1.4.1.6.3 Cooling and Freezing With In-Line Tunnels The inline tunnels are devices used for the freezing, chilling, and crust freezing of food products by spraying a cryogenic fluid (liquid nitrogen or liquid CO2), which become cold gas or snow. These cold gases contribute to cooling or freezing operations by convection. An inline tunnel consists of an insulated enclosure crossed by a conveyor in stainless steel mesh supported by a frame. The enclosure is made of an insulated U-shape in two parts, a cover and a bottom frame (see Figs. 7.1.4.1.19 and 7.1.4.1.20). The insulation quality has some impact on performance and gas consumption, with the main factor of performance being gas confinement and gas exhaust temperature. Depending on design and manufacturing, the enclosure can accept very low temperatures (e.g., down to 130°C). Convection control is assumed thanks to a relevant arrangement of fans and their rotation speed. Exhaust gas balance (hood and exhaust piping design, speed of exhaust fans) and gas

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FIG. 7.1.4.1.19

Inline tunnel enclosure made of a polyurethane insulated U-shape.

FIG. 7.1.4.1.20

Inline cryogenic tunnel.

confinement (baffles) have a huge impact on safety and efficiency. For liquid nitrogen, the fluid is injected directly inside the tunnel through a flow proportional valve according to the needs of the product enthalpy. The conveyor moves the food stuffs to be frozen inside the cold area, where we distinguish different zones: A prespray injection can be (optional) used for upstream crust freezing.

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A prerefrigeration area: products enter the tunnel and absorb the frigories made by countercurrent gaseous nitrogen phase convection. A spray area: Liquid nitrogen is sprayed through a set of nozzles in order to guarantee homogeneous liquid nitrogen coverage and cold contribution to freeze the products. In this zone, nitrogen vaporization happens. The products absorb at this level the largest

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part of the frigories for liquid into solid phase water transformation. Stabilization between surface and depth of the product. This equilibrium may be completed after coming out of the tunnel. For liquid carbon dioxide injection, there is only a snow spray area with an associated gaseous phase. Then a stabilization step happens.

7.1.4.1.6.4 Equipment for Dealing With Individual Cases 7.1.4.1.6.4.1 Liquid Nitrogen Immersion Bath Immersion freezers typically use a conveyor belt, loaded with solid product, to carry product through a liquid nitrogen bath. They are used mainly in IQF applications to partially or fully freeze food products. Upon exiting the immersion freezer, the product is usually conveyed to another freezer where the product is fully frozen, that is, a mix of a liquid nitrogen bath and a mechanical system freezer. While tunnel freezers and immersion freezers have been used successfully for IQF applications, both have their advantages and disadvantages. Because the freezing agent is liquid nitrogen rather than recirculated gaseous nitrogen, immersion freezers can achieve higher production rates than tunnel freezers. Immersion freezers can remove heat at approximately 500–800 W m2 °C1, whereas tunnel freezers are in the 35–50 W m2 °C1 range. The main disadvantage of immersion freezers is that they are less efficient with nitrogen, using 3–4 kg of nitrogen per kg of product while regular tunnel freezers can use approximately 1 kg of nitrogen per kg of product. It has been designed specifically for high value, sticky, wet, IQF products in solid, semisolid, or liquid form such as ice cream pellets, bacteria cultures, diced cheese, BBQ sauce, or hard-boiled eggs.

7.1.4.1.6.4.2 Flat Belt in Line Tunnels Handling and conveying of soft, deformable, soggy, sticky and highly watered product before further processing is common in food processing. In order to give them some rigidity by means of more fat content solidification, it can be efficient to decrease quickly their temperature by cold application. Cryogenics is an appropriate means using the above-mentioned equipment. To avoid any marks coming from the metallic meshes of a standard in line tunnel belt, a flat belt can be used made of a polyester or polyethylene material, taking into account that the intended material must comply with the low temperatures of cryogens. When further process consists of slicing or cubing, crust freezing is an option in order to give more productivity and matter savings. Last, when brined products are frozen by a mechanical refrigeration, a prior crust freezing step enables the water to be blocked, forming an ice coating limiting the later evaporation. Brined poultry filets and quenelles are among the concerns. 7.1.4.1.6.4.3 Individual Quick Frozen (IQF) Machines The market for small, individually frozen products occupies a niche among frozen products. The term IQF has now come into everyday usage, and IQFs are treated as a specific class of IFP (intermediate food products). These are preparations used to make fresh or frozen precooked dishes aimed at end consumers or manufacturers: finely minced beef, raw or cooked beef granules and balls, diced meat and poultry, cheese cubes, bacon bits, peeled prawns, shredded surimi, sliced sausage, and pieces of fruit and vegetables. These intermediate products are used by a vast range of operators, including the fast food and food-

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processing industries, to make a host of different dishes such as mixed salads, pizzas, sauces, pasta in sauce, etc. Their usefulness lies in being very easy to use and conserve. Indeed, the frozen state enables the supply flow and thereby the stocks to be managed according to demand for the end product without losses, as could be the case with fresh intermediate products. Furthermore, by virtue of their grading and small size (diameter or side measuring from a few millimeters to a few centimeters), they readily lend themselves to precision automatic dosing due to their frozen state, preventing unwanted sticking together of the elements, as would be the case for nonfrozen products. As with all food product freezing operations, the user is faced with the choice between mechanical and cryogenic refrigeration. Given the relatively small production flows of IQF, cryogenics may provide an advantage in terms of investment, flexibility, water loss, and general quality. IQF technologies are made of several concepts of conveying and heat transfer mode combination such as fluidization, tumbling, liquid nitrogen immersion, screwing, multibelt conveying, immersion, and vibration mix.  Fluidization is based on what exists with mechanical systems.  The screwing principle is based on a fixed cylinder (cigar) with an internal helical screw moving the products inside in a continuous process.  Tumbling is a similar process to screwing but discontinuously without the screw inside, the cylinder rolling with a fixed paddle in order to agitate the product. Freezing in a tumbler is using a deviation of churn for muscle brining and massing of ham in use in the delicatessen industry.  Multipass belt tunnels.

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7.1.4.1.6.4.4 Cryogenic Sauce Coating of IQF Products The equipment used is a churn that is also used for cooked ham processing at the brining/muscle massage step. Batch process manages sequences including periods of cryogenic fluid injection and periods of injection of sauce in the rotating tumbler, allowing IQF products to be coated with successive thin sauce layers until 100% sauce weight.

7.1.4.1.7 HOW TO DECIDE BETWEEN MECHANICAL AND CRYOGENIC CHILLING-FREEZING When analyzing a chilling or freezing project, the apparent high cost of cryogenic fluids and the technical improvements in mechanical systems are important factors in the industrial and financial decision to choose the most advantageous technology at a given time. We can consider that despite the merits of cryogenic chilling, the first reflex, or even the overall trend, is in favor of mechanical refrigeration for various reasons. Even if cryogenics is still superior in terms of quality and speed, its technical and financial flexibility of assets are not always known to most novices. The number of users of mechanical systems is currently estimated at 90% compared to only 10% for cryogenics in the field of frozen food. Several factors need to be taken into account in this choice: hourly and mostly annual profile production, cleaning time, investment capabilities (Capex), available space or overall machine dimensions, frame time before production startup, utility fluid cost, added value of the product enabling paying for the cryogenic quality, etc. On the top of these criteria, the main lever of differentiation between the two technologies is

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the possible water losses when a long residence time happens in mechanical systems, leading to a larger dehydration rate compared to cryogenics, this one having a much shorter residence time. The difference can be up to 5% for beef patties mechanically frozen versus almost 0% with cryogenics. This consideration is valid with raw products such as meat, fish, fruits, and vegetables, but not so relevant when prepared with added ingredients such as water-based sauces. It can be considered that some opportunity for cryogenic refrigeration involves specific equipment developed for nontraditional, innovative products that only customizers can manufacture in a short timeframe and in small numbers that can easily be included in production lines. Furthermore, cryogenics remains preferential or even inescapable for cooling or temperature control in customer processes such as mincemeat grinding or crusting before slicing. Simulation and calculation tools show that in many cases, a cryogenic freezing project may be profitable in conditions that appear to be pessimistic.

7.1.4.1.7.1 Product Data A large number of data must be taken in consideration to compare mechanical and cryogenic refrigeration technologies as; production capacity, number of operating hours in the year, input and chilling or freezing temperature (generally from 18°C to 25°C). The time taken to set up the system before reaching the nominal production capacity; the duration of the project, which is often the service life of the range; or the desired level of visibility are also considered. Weight loss: this aspect is of capital importance in the final result. A quick reminder: cryogenic chilling, due to its short processing time, causes less evaporation of the product’s free water. In addition, the greater instantaneous chilling power (for example, by submersion or spraying with liquid nitrogen) enables water

to be trapped by surface crusting. Data exist in written documentation, completed by the capitalization of industrial experiences. This difference may represent a few percent (from 1% to 4%) compared to mechanical chilling, which, in the final analysis with the product selling price, offers a major substantiation lever for choosing cryogenics for the duration of the project.

7.1.4.1.7.2 Equipment Data The final temperature and desired flow rate help to automatically calculate the refrigeration capacity to be installed expressed in kW and the enthalpy represented in kg of liquid nitrogen or kg of CO2 for the cryogenic fluids. The value of the equipment sold or rented is preestablished in tables or can be entered directly from the actual values as well as their depreciation period and the bank loan rates in the case of purchase. In the case of mechanical cold, the freezer values (linear tunnel, spiral, or fluidizer) are dissociated from those of compressors using ammonia (R717), or with a cooler like R404A, or even cascade cycles R717 + CO2, by also incorporating civil engineering (concrete slabs, building, etc.). Some options are not neglected such as stainless-steel finishing, cleaning-in-place systems (CIP), or upward and downward conveyor systems in the case of spiral freezers. Similarly, some costs of administrative files (authorization for storage of dangerous fluids or those subject to authorization) are to be planned in certain countries according to local regulations.

7.1.4.1.7.3 Consumables In addition to the values of fluid prices (gas, washing water, and defrosting water) and electricity, the levels of inflation of these variables are also taken into account. Bear in mind that in many areas electricity costs are currently

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prone to high inflation, particularly in countries with no major energy resources (including electrical). Table 7.1.4.1.3 (adjacent page) summarizes in a simplified way the results of two simulations carried out on quite basic products showing contrary conclusions. The main items whose levers have a considerable effect can be summarized as follows:  Initial investment in the case of mechanical chilling. TABLE 7.1.4.1.3

 Consumption of liquid nitrogen.  Difference in product weight loss during processing related to the product’s added value.  Maintenance, water consumption, and the current bank interest rates are minor in the final analysis. We notice that a difference in product weight loss of around 3% between the two technologies can drive back the economic boundary between cryogenic and mechanical chilling, which

Economical Comparison Between Mechanical and Cryogenic Chilling and Freezing

Product Production Cost

Technology Cryogenic Freezing

Technology Cryogenic Chilling

Selling price

Minced beef

Mechanical Chilling

Potatoes

Mechanical Chilling

Initial temperature

4°C

4°C

10°C

10°C

Final temperature

18°C

18°C

18°C

18°C

Enthalpy difference (kcal/kg)

72

72

77

77

Energy represented by kg of liquid nitrogen/kg of product

0.88



0.95



Hourly capacity (kg/h)

1000

1000

2000

2000

Annual capacity (T)

1800

1800

2700

2700

Refrigeration theoretical power (kW)

83.69

83.69

181

181

Duration before reaching nominal capacity (years)

1

1

1

1

Expected duration of the project (years)

5

5

5

5

Freezer investment (€)

108,000

297,000

295,000

384,000

Investment in compressors (€)

0

230,000

0

275,000

Civil engineering (€)

5000

15,000

5000

15,000

Administrative costs

0

0

0

0

Annual rental of cryogenic gas storage (€)

15,000

0

15,000

0

Cryogenic fluid supply line investment (€)

20,000

0

20,000

0

Investment in safety devices (detectors, extraction of cold gases)

25,000

0

25,000

0

Electricity cost (€/kWh)

0.047

0.047

0.047

0.047 Continued

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7.1. REFRIGERATION

TABLE 7.1.4.1.3

Economical Comparison Between Mechanical and Cryogenic Chilling and Freezing—cont’d

Product Production Cost

Technology Cryogenic Freezing

Technology Cryogenic Chilling

Selling price

Minced beef

Mechanical Chilling

Potatoes

Mechanical Chilling

Liquid nitrogen molecule cost (€/kg)

0.08

0

0.08

0

Liquid nitrogen or electricity annual energy cost (€)

130,000

20,000

420,000

35,000

Loss of water from the product during processing (%)

0.5

3

0.5

2

Value of weight loss/year (€)

55,000

340,000

35,000

135,000

Annual consumption of process and washing water (€)

100

1000

100

1000

Annual maintenance (€)

2000

8000

2000

8000

3

3

3

3

Depreciation periods (years)

5

5

5

5

Cost of processing per kg (€)

0.139

0.276

0.107

0.061

Annual advantage/disadvantage (€)

245,000

245,000

247,000

247,000

Bank rates (%) a

a

The depreciation period may vary according to the type of investment.

requires this value to be carefully estimated. This appraisal is reinforced or attenuated by the price of liquid nitrogen. This in part relates to its geographical availability insofar as the production site is located more or less close to an air liquefaction factory. Lastly, the opportunity for the gas company to offer second-hand equipment and to rent it also generates substantial savings.

7.1.4.1.8 LIST OF NAMES OF CRYOGENIC EQUIPMENT MANUFACTURERS Not all IGCs design their own branded freezing equipment ranges, which are subcontracted by specialized exclusive or nonexclusive OEMs. Nevertheless, the main players are doing it. When OEMs are independent from the IGCs, they propose to everybody a catalogue of

standard cryogenic equipment fitting with almost all cryogenic applications, including for cryobiology and pharmaceutical sectors. IGCs and final customers are using a lot their service competencies for repairing, retrofitting, and prototype designing. Air Liquide: https://www.airliquide.com Linde: https://www.the-linde-group.com Praxair: http://www.praxair.com Air Products: http://www.airproducts.com Messer: https://www.messergroup.com Sol: http://www.solgroup.com Airgas: http://www.airgas.com Nippon Sanso: https://www.tn-sanso.co.jp/ en Dohmeyer: https://dohmeyer.com CES: http://www.cesgroup.com Serap: http://www.groupeserap.com Packo: http://www.packoindustry.com/fr/ home

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

7.1.4.1.9 CONCLUSION—PERSPECTIVES

Buse: http://www.buse-group.com/home/ company/buse-group/ This is a nonexhaustive list.

7.1.4.1.9 CONCLUSION— PERSPECTIVES Food cryogenics for chilling, freezing, and temperature control in food processing are a very wide sector in the food industry. The number of applications described above is not exhaustive, as frequently the several players involved (gas companies and clients) discover new territories. This technology is competitive with mechanical refrigeration while its specific

287

niches are well identified. The economic situation is subject to fluctuation for both technologies, according to energy cost (electricity) in the different geographies, environmental and safety constraints (e.g., ammonia storage), and available space in the workshops in favor of compact cryogenic installations. The economic evaluation must be done case by case, even for a similar product, due to a different situation specific to each user. Nevertheless, when quality is considered as a priority for premium foodstuffs, cryogenics is best, like when there are no ways to do differently such as with coating, meat mixers, and temperature control. More than competing, the association of the two technology modes must be looked at more closely in the future.

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

S U B C H A P T E R

7.1.4.2 Particular Case of Chefs “Cryogenic Cooking” Elisabeth Rubin National Superior School of Decorative Arts, Paris, France

7.1.4.2.1 INTRODUCTION: LIQUID NITROGEN USED FOR COOKING FOR MORE THAN 100 YEARS The first person who wrote about using liquid gas to freeze food is the British cook Agnes B. Marshall (1855–1905). She probably knew of James Dewar’s conferences and experiences before writing in the magazine The Table (August 24, 1901): “Liquid air will do a wonderful thing, but as a table adjunct its powers are astonishing and persons scientifically inclined may perhaps like to amuse and instruct their friends as well as feed them when they invite them to the house. By the aid of liquid oxygen, for example each guest at the dinner party may make his or her own ice cream at the table by simply stirring with a spoon the ingredients of ice cream with a few drops of liquid air that has been added by the servant: one drop in a glass will more successfully freeze champagne than two or three lumps of ice.” She probably did not try this and she would not have been able to use liquid oxygen (which is much more dangerous than liquid nitrogen), and furthermore, the “few drops” as she wrote probably would not have been enough to freeze anything.

In 1994, the American physician Peter Braham wrote an article in the Scientific American journal about using liquid air to make ice cream. Since 1993, the French chemist Herve This wrote many books about the chemical and physical phenomenon of cooking called molecular cooking. Liquid nitrogen is often described as the way to make the best ice cream or sorbet. Indeed, the deep/flash freezing makes the crystals so small, that the result is a very smooth sensation in the mouth with a wonderful taste. At the same time, some famous chefs began to use liquid nitrogen in their restaurants: Pierre Gagnaire and Thierry Marx (both French), Ferran Adria (Spanish), Heston Blumenthal (British), and, a few years later, Kristof Coppens (Belgian).

7.1.4.2.2 DIFFERENT USES OF LIQUID NITROGEN FOR COOKING Chefs can use liquid nitrogen to freeze and solidify an ingredient and delay its cooking inside a big piece of meat or a cake (Figs. 7.1.4.2.1 and 7.1.4.2.2). They can also grind any soft ingredients to decorate plates and use it as a kind of topping.

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

7.1.4.2.3 LIQUID NITROGEN TO MAKE ICE CREAM

FIG. 7.1.4.2.1

Individual cake with soft chestnut cream in the middle.

FIG. 7.1.4.2.2

Fruit jelly crumbs.

As an example, citrus pulp can be separated into very small juice pockets. These can be preserved in a common freezer (at 20°C) and be used at any time as a fresh fruit. More importantly, citrus prepared and preserved this way will keep its color, taste, and vitamins (Fig. 7.1.4.2.3). Or it can be used to make a sculpture with cream by dropping or molding to create a voluminous dessert base (Figs. 7.1.4.2.4 and 7.1.4.2.5).

289

Liquid nitrogen is also most commonly used by chefs to make the smoothest and tastiest ice creams and sorbets (even with added salt or alcohol) (Fig. 7.1.4.2.6).

7.1.4.2.3 LIQUID NITROGEN TO MAKE ICE CREAM The first commercial liquid nitrogen ice cream makers appeared just before 2010. In San Francisco, Robyn Sue Fisher, with an MBA

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

290

7.1. REFRIGERATION

FIG. 7.1.4.2.3

Citrus pulp before and after flash freezing.

FIG. 7.1.4.2.4

A nest made of cream dropped into liquid nitrogen.

FIG. 7.1.4.2.5 Half sphere made of strawberry juice.

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

7.1.4.2.4 LIQUID NITROGEN USED IN FRONT OF THE PUBLIC…

FIG. 7.1.4.2.6

291

Gazpacho sorbet.

from Stanford University, started selling her Smitten Ice Cream out of a Radio Flyer wooden wagon. Her homemade ice cream that fused nostalgia and science was made to order. Today, Fisher presides over a half-dozen Smitten Ice Cream shops in the Bay Area and Los Angeles, with more than 120 employees. At the same time in Camden Town (a famous tourist place) in London, the first liquid nitrogen ice cream shop appeared: Chin Chin Laboratorists, which now has three shops in London. Since 2010, dozens of shops have opened each year all over the world. Each shop is equipped with cryogenic containers of several hundredliter capacity and a vacuum-insulated line that brings liquid nitrogen into the electric mixer. The opening of this kind of ice cream shop is growing exponentially. The advantages are both the quality of the product and the spectacular way it is produced: it is instantaneous and has the theatrical effect of “freezing white fog.” Most of the time, the ice cream or sorbets are made to order to show the process and to guarantee the freshness of the product. But some ice cream makers keep their ice cream in a freezer for a quicker service. This is quite impossible

with a sorbet without any additive. In a common freezer, the sorbet would totally solidify (like a stone), because of the high-water content.

7.1.4.2.4 LIQUID NITROGEN USED IN FRONT OF THE PUBLIC… It is not only ice creams and sorbets that can be made instantaneously and directly before the public. Quickly dipping a bite-size cube or “bouchee” into liquid nitrogen produces an interesting effect and a direct contrast between texture and taste. The cold temperature momentarily solidifies and reduces the taste of the part that has been put into the liquid nitrogen. 1 or 2 s is enough and the “bouchee” then must be taken off with a skimmer (Figs. 7.1.4.2.7 and 7.1.4.2.8). Then, once out of the liquid nitrogen—after chewing, the inside and outside of the “bouchee” are mixed, to reveal a spectacular scale of sensation and taste! A common recipe consists of holding a bitesized piece of food with a wooden stick. This piece of food is first dipped in a tasty sauce (so it is all coated) before it is dipped for a few

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

292

FIG. 7.1.4.2.7

7.1. REFRIGERATION

Skimmer with a “bouchee” after dipping in liquid nitrogen.

liquid nitrogen) is crunchy and the taste is momentarily amplified. While chewing, this crunchy cold part will mix with the inside so that many blended tastes will then progressively appear in the mouth (Figs. 7.1.4.2.9 and 7.1.4.2.10). It is also sometimes interesting to add toppings such as nuts or grilled sesame crumbs. Another classic effect using liquid nitrogen is the “Dragon Effect.” For example, if you dip a small piece of meringue into liquid nitrogen for at least 10 s, the air trapped inside it will become very cold. If you then exhale through your nose while you bite the meringue, you should produce fog from your nostrils. This is great fun, but of course does not add to the overall experience of eating specific foods prepared using liquid nitrogen (Figs. 7.1.4.2.11 and 7.1.4.2.12). FIG. 7.1.4.2.8

Open Nutella bouchee after two 2 s dipping in liquid nitrogen.

seconds into liquid nitrogen. Then it is important to eat the food quickly before the extreme cold temperature penetrates the food. Because of the cold temperature, the tasty sauce coating the food (that has been in direct contact with the

7.1.4.2.5 LIQUID NITROGEN FOR DINNER! Agnes B. Marshall imagined that “each guest at the dinner party may make his or her own ice cream at the table.” In fact, this would not be

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

7.1.4.2.5 LIQUID NITROGEN FOR DINNER!

FIG. 7.1.4.2.9

FIG. 7.1.4.2.10

Foie gras coated with Balsamic reduction dipped into liquid nitrogen.

Shrimp coated with spicy sauce and nut crumbs.

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

293

294

7.1. REFRIGERATION

FIG. 7.1.4.2.12 FIG. 7.1.4.2.11

Dragon effect.

Meringue just after dipping.

possible as each guest would need to stir liquid nitrogen at the dinner table and this would be dangerous and need many safety precautions to prevent the risk of an accident. However, it is possible to organize a fondue party with specially adapted equipment: a large table with a withdrawal system to dispense the liquid nitrogen (in the center of the table) and covered with a transparent dome to avoid any possible projection of liquid nitrogen into the eyes. Each guest would then be able to dip their own “bouchee” coated with sauce (into the liquid nitrogen) while holding it safely with a long wooden stick (Fig. 7.1.4.2.13).

7.1.4.2.6 EQUIPMENT AND SAFETY CONSIDERATIONS TO USE LIQUID NITROGEN FOR COOKING 7.1.4.2.6.1 Risks for Users Nitrogen is the biggest component of the air that we breathe, so while it is totally safe to breathe, it is dangerous when manipulated as a liquid because of the extreme temperature. The first risk to the user concerns frostbite: in the liquid phase, liquid nitrogen is very cold at 196°C. It immediately freezes any surface that it comes into contact with—especially when it is

7. FOOD PROCESSING: ALL THE FOOD INDUSTRY SECTORS

7.1.4.2.6 EQUIPMENT AND SAFETY CONSIDERATIONS TO USE LIQUID NITROGEN FOR COOKING

FIG. 7.1.4.2.13

295

Liquid nitrogen safe fondue dinner party.

wet. It is also very unsafe to look at liquid nitrogen being dispensed, so any person using this product in close proximity (