EFFICIENCY andSUSTAINABILITYin the ENERGYand CHEMICALINDUSTRIESSECOND EDITIONScientific Principlesand Case StudiesGREEN CHEMISTRY AND CHEMICAL ENGINEERINGSeries Editor: Sunggyu LeeMissouri University of Science and Technology, Rolla, USAEfciency and Sustainability in the Energy and Chemical Industries: Scientic Principlesand Case Studies, Second Edition Krishnan Sankaranarayanan, Hedzer J. van der Kooi, and Jakob de Swaan AronsProton Exchange Membrane Fuel Cells: Contamination and Mitigation StrategiesHui Li, Shanna Knights, Zheng Shi, John W. Van Zee, and Jiujun ZhangProton Exchange Membrane Fuel Cells: Materials Properties and PerformanceDavid P. Wilkinson, Jiujun Zhang, Rob Hui, Jeffrey Fergus, and Xianguo LiSolid Oxide Fuel Cells: Materials Properties and Performance Jeffrey Fergus, Rob Hui, Xianguo Li, David P. Wilkinson, and Jiujun ZhangCRC Press is an imprint of theTaylor & Francis Group, an informa businessBoca Raton London New YorkEFFICIENCY andSUSTAINABILITYin the ENERGYand CHEMICALINDUSTRIESSECOND EDITIONKrishnan SankaranarayananHedzer J. van der KooiJakob de Swaan AronsScientific Principlesand Case StudiesCRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742 2010 by Taylor and Francis Group, LLCCRC Press is an imprint of Taylor & Francis Group, an Informa businessNo claim to original U.S. Government worksPrinted in the United States of America on acid-free paper10 9 8 7 6 5 4 3 2 1International Standard Book Number-13: 978-1-4398-1471-0 (Ebook-PDF)Thisbookcontainsinformationobtainedfromauthenticandhighlyregardedsources.Reasonableefforts havebeenmadetopublishreliabledataandinformation,buttheauthorandpublishercannotassume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint.Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmit-ted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, includingphotocopying,microfilming,andrecording,orinanyinformationstorageorretrievalsystem, without written permission from the publishers.Forpermissiontophotocopyorusematerialelectronicallyfromthiswork,pleaseaccesswww.copyright.com(http://www.copyright.com/)orcontacttheCopyrightClearanceCenter,Inc.(CCC),222Rosewood Drive,Danvers,MA01923,978-750-8400.CCCisanot-for-profitorganizationthatprovideslicensesand registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged.Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe.Visit the Taylor & Francis Web site athttp://www.taylorandfrancis.comand the CRC Press Web site athttp://www.crcpress.com To our children and grandchildren who may witness the emergence of a sustainable societyviiContentsPreface .....................................................................................................................xvAbout This Book .................................................................................................. xixAcknowledgments .............................................................................................. xxiAuthors ............................................................................................................... xxiiiI PartBasics1Introduction ..................................................................................................... 3References ......................................................................................................... 62Thermodynamics Revisited ......................................................................... 72.1The System and Its Environment ........................................................ 72.2States and State Properties ................................................................... 72.3Processes and Their Conditions ......................................................... 82.4The First Law ......................................................................................... 82.5The Second Law and Boltzmann ...................................................... 112.6The Second Law and Clausius .......................................................... 122.7Change in Composition ..................................................................... 132.8The Structure of a Thermodynamic Application ........................... 18References ....................................................................................................... 213Energy Consumption and Lost Work ................................................... 233.1Introduction ......................................................................................... 233.2The Carnot Factor ................................................................................ 243.3Lessons from a Heat Exchanger ........................................................ 253.4Lost Work and Entropy Generation ................................................. 293.5Conclusion ............................................................................................ 31References ....................................................................................................... 314Entropy Generation: Cause and Effect ..................................................... 334.1Equilibrium Thermodynamics ......................................................... 334.2On Forces and Flows: Cause and Effect ........................................... 344.3Cause and Effect: The Relation between Forces and Flows .......... 364.4Coupling ............................................................................................... 384.5Limited Validity of Linear Laws ....................................................... 404.6Conclusion ............................................................................................ 46References ....................................................................................................... 46viiiContents5Reduction of Lost Work ............................................................................... 475.1A Remarkable Triangle ....................................................................... 475.2Carnot Revisited: From Ideal to Real Processes ............................. 495.3Finite-Time, Finite-Size Thermodynamics ...................................... 545.4The Principle of Equipartitioning ..................................................... 555.5Conclusions .......................................................................................... 58References ....................................................................................................... 58I PartIThermodynamic Analysis of Processes6Exergy, a Convenient Concept.................................................................... 636.1Exergy ................................................................................................... 636.2The Convenience of the Exergy Concept ......................................... 666.2.1Out of Equilibrium with the Environment: What It Takes to Get There ................................................................. 676.2.2Out of Equilibrium with the Environment: What It Takes to Stay There ................................................................ 686.2.3Dissipative Structures ........................................................... 696.2.4Physical and Chemical Exergy ............................................. 706.3Example of a Simple Analysis ........................................................... 716.4The Quality of the Joule ..................................................................... 746.5Example of the Quality Concept ....................................................... 776.6Conclusions .......................................................................................... 80References ....................................................................................................... 817Chemical Exergy ........................................................................................... 837.1Introduction ......................................................................................... 837.2Exergy of Mixing ................................................................................. 837.3Chemical Exergy ................................................................................. 847.3.1Reference Components from Air ......................................... 857.3.2Exergy Values of the Elements ............................................. 867.3.3Chemical Exergy Values of Compounds ............................ 887.3.4The Convenience of the Chemical Exergy Concept .......... 897.4Cumulative Exergy Consumption .................................................... 907.5Conclusions .......................................................................................... 91References ....................................................................................................... 928Simple Applications ..................................................................................... 93References ..................................................................................................... 105ContentsixII PartICase Studies9Energy Conversion ..................................................................................... 1099.1Introduction ....................................................................................... 1099.2Global Energy Consumption ........................................................... 1109.3Global Exergy Flows ......................................................................... 1129.4Exergy or Lost Work Analysis......................................................... 1159.5Electric Power Generation ............................................................... 1159.5.1Steam Plants.......................................................................... 1169.5.2Gas Turbines ......................................................................... 1169.5.3Combined Cycle ................................................................... 1179.5.4Nuclear Power ...................................................................... 1189.5.5Hydropower .......................................................................... 1209.5.6Wind Power .......................................................................... 1209.5.7Solar Power ........................................................................... 1219.5.8Geothermal Energy ............................................................. 1219.6Coal Conversion Processes .............................................................. 1219.6.1Fixed or Moving Beds ......................................................... 1229.6.2Suspended Beds ................................................................... 1229.6.3Fluidized Beds ...................................................................... 1229.6.4Thermodynamic Analysis of Coal Combustion .............. 1239.6.5Discussion ............................................................................. 1249.6.6Coal Gasifcation .................................................................. 1259.7Thermodynamic Analysis of Gas Combustion ............................ 1289.7.1Exergy In ............................................................................... 1289.7.2Air Requirements ................................................................. 1289.7.3Exergy Out ............................................................................ 1309.7.4Effciency ............................................................................... 1329.7.5Discussion ............................................................................. 1339.8Steam Power Plant ............................................................................ 1349.9Gas Turbines, Combined Cycles, and Cogeneration .................... 1359.9.1Gas Turbines ......................................................................... 1369.9.2Thermodynamic Analysis of Gas Turbines ..................... 1369.9.3Combined Cycles, Cogeneration, and Cascading ........... 1379.9.4Example ................................................................................. 1389.10Concluding Remarks ........................................................................ 139References ..................................................................................................... 140 10Separations ................................................................................................... 14110.1Introduction ....................................................................................... 14110.2Propane, Propylene, and Their Separation .................................... 14110.2.1Single-Column Process ....................................................... 142xContents10.2.2Double-Column Process ..................................................... 14210.2.3Heat Pump Process .............................................................. 14310.3Basics ................................................................................................... 14410.3.1Flash Distillation .................................................................. 14410.3.2Multistage Distillation and Refux .................................... 14510.4The Ideal Column: Thermodynamic Analysis ............................. 14910.5The Real Column............................................................................... 15210.6Exergy Analysis with a Flow Sheet Program ............................... 15510.7Remedies ............................................................................................ 15710.7.1Making Use of Waste Heat ................................................. 15710.7.2Membranes ........................................................................... 15810.7.3Other Methods ..................................................................... 15910.8Concluding Remarks ........................................................................ 160References ..................................................................................................... 161 11Chemical Conversion ................................................................................. 16311.1Introduction ....................................................................................... 16311.2Polyethylene Processes: A Brief Overview .................................... 16411.2.1Polyethylene High-Pressure Tubular Process .................. 16611.2.2Polyethylene Gas-Phase Process ........................................ 16711.3Exergy Analysis: Preliminaries....................................................... 16811.4Results of the HP LDPE Process Exergy Analysis ....................... 16911.5Process Improvement Options ........................................................ 17111.5.1Lost Work Reduction by the Use of a Turbine ................. 17211.5.2Alternative to the Extruder ................................................ 17211.5.3Process Improvement Options: Estimated Savings ......................................................................... 17311.6Results of the Gas-Phase Polymerization Process Exergy Analysis .............................................................................................. 17411.7Process Improvement Options ........................................................ 17511.7.1Coupling Reactions and Chemical Heat Pump System .................................................................................... 17611.7.2Exergy Loss Reduction by Recovering Butylene and Ethylene from Purge Gas ............................................ 17711.7.3Heat Pump and Preheating of Polymer ............................ 17711.7.4An Alternative to the Extruder .......................................... 17911.7.5Process Improvement Options: Estimated Savings ........ 18011.8Concluding Remarks ........................................................................ 181References ..................................................................................................... 181 12A Note on Life Cycle Analysis ................................................................. 18312.1Introduction ....................................................................................... 18312.2Life Cycle Analysis Methodology .................................................. 18412.2.1Goal and Scope ..................................................................... 18412.2.2Inventory Analysis .............................................................. 186Contentsxi12.2.3Impact Assessment .............................................................. 18712.2.4Interpretation and Action ................................................... 18812.3Life Cycle Analysis and Exergy ...................................................... 18812.4Zero-Emission ELCA ........................................................................ 18912.5Concluding Remarks ........................................................................ 191References ..................................................................................................... 191I PartVSustainability 13Sustainable Development ......................................................................... 19513.1Sustainable Development ................................................................ 19513.1.1Three Views .......................................................................... 19713.1.2Some Other Views ............................................................... 19713.2Nature as an Example of Sustainability ........................................ 19813.3A Sustainable Economic System ..................................................... 20013.3.1Thermodynamics, Economics, and Ecology .................... 20013.3.2Economics and Ecology ...................................................... 20313.3.3Natures Capital and Services ............................................ 20513.3.4Adjustment of the Gross National Product ...................... 20613.3.5Intermezzo: Thermodynamics and EconomicsA Daring Comparison and Analogy ..................................... 20613.4Toward a Solar-Fueled Society: A Thermodynamic Perspective ......................................................................................... 21113.4.1Thermodynamic Analysis of a Power Station ................. 21113.4.2Some Observations .............................................................. 21313.4.3From Fossil to Solar ............................................................. 21313.5Ecological Restrictions ..................................................................... 21413.5.1Ecological Footprint............................................................. 21413.5.2Waste ...................................................................................... 21813.6Thermodynamic Criteria for Sustainability Analysis ................. 22113.6.1Introduction .......................................................................... 22113.6.2Sustainable Resource Utilization Parameter ................ 22213.6.3Notes on Determining Depletion Times and Abundance Factors ...................................................... 22713.6.4Exergy Effciency .............................................................. 22813.6.5The Environmental Compatibility ................................. 22913.6.6Determining Overall Sustainability ................................. 23213.6.7Related Work ........................................................................ 23413.7Conclusions ........................................................................................ 234References ..................................................................................................... 235 14Effciency and Sustainability in the Chemical Process Industry ..... 23914.1Introduction ....................................................................................... 23914.2Lost Work in the Process Industry ................................................. 239xiiContents14.3The Processes ..................................................................................... 24214.4Thermodynamic Effciency ............................................................. 24314.5Effcient Use of High-Quality Resources ....................................... 24414.6Toward Sustainability ...................................................................... 24514.7Chemical Routes ................................................................................ 24614.8Concluding Remarks ........................................................................ 247References ..................................................................................................... 248 15CO2 Capture and Sequestration .............................................................. 25115.1Introduction ....................................................................................... 25115.2CO2 Emissions ................................................................................... 25115.3The Carbon Cycle .............................................................................. 25415.4Carbon Sequestration: Separation and Storage and Reuse of CO2 .............................................................................. 25615.5Carbon Capture Research ................................................................ 25815.6Geologic Sequestration Research .................................................... 25915.6.1Oil and Gas Reservoirs ....................................................... 25915.6.2Coal Bed Methane ................................................................ 26015.6.3Saline Formations ................................................................ 26015.6.4CO2 Mineralization .............................................................. 26115.6.5Effciency of CO2 Capture and Sequestration .................. 26115.7Carbon Tax and Cap-and-Trade ...................................................... 26115.8Concluding Remarks ........................................................................ 262References ..................................................................................................... 262 16Sense and Nonsense of Green Chemistry and Biofuels .................... 26516.1Introduction ....................................................................................... 26516.1.1What Is Green ....................................................................... 26516.1.2What Is Biomass ................................................................... 26616.1.3Biomass as a Resource ......................................................... 26716.1.4Structure of This Chapter ................................................... 26816.2Principles of Green Chemistry ........................................................ 26816.3Raw Materials .................................................................................... 26916.3.1Biomass .................................................................................. 27016.3.2Recycling ............................................................................... 27216.4Conversion Technologies ................................................................. 27316.4.1Combustion........................................................................... 27416.4.2Pyrolysis ................................................................................ 27516.4.3Gasifcation ........................................................................... 27516.4.4Upgrading Biomass ............................................................. 27716.5How Green Are Green Plastics ....................................................... 27816.5.1Optimism in the United States .......................................... 27816.5.2Initiatives in Europe ............................................................ 27816.5.3From a Hydrocarbon to a Carbohydrate Economy ......... 28016.5.4Feelings of Discomfort ........................................................ 280Contentsxiii16.5.5Short Memory: Ignorance or Not Welcome ..................... 28316.6Biofuels: Reality or Illusion .............................................................. 28316.6.1Multidisciplinarity ............................................................... 28316.6.2Second-Generation Biofuels ............................................... 28716.6.3The Fossil Load Factor ........................................................ 28816.6.4Sustainability and Effciency.............................................. 28916.6.5Algae ...................................................................................... 29016.6.6The Future ............................................................................. 29016.6.7Sense or Nonsense? Discussion ......................................... 29116.7Concluding Remarks ........................................................................ 294References ..................................................................................................... 295 17Solar Energy Conversion........................................................................... 29917.1Introduction: Lighting the Way .................................................. 29917.2Characteristics ................................................................................... 30317.3The Creation of Wind Energy ......................................................... 30717.4Photothermal Conversion ................................................................ 31117.5Photovoltaic Energy Conversion ..................................................... 31317.6Photosynthesis ................................................................................... 31517.7Concluding Remarks ........................................................................ 317References ..................................................................................................... 319 18Hydrogen: Fuel of the Future ................................................................... 32118.1Introduction ....................................................................................... 32118.2The Hydrogen Economy .................................................................. 32118.3Current Hydrogen Economy ........................................................... 32418.4Conventional Hydrogen Production from Conventional Sources ............................................................. 32418.5Hydrogen from Renewables ............................................................ 32518.6Hydrogen as an Energy Carrier ...................................................... 32518.7Hydrogen as a Transportation Fuel ................................................ 32518.8Effciency of Obtaining Transportation Fuels ............................... 32618.9Challenges of the Hydrogen Economy .......................................... 32818.10Hydrogen Production: Centralized or Decentralized ................. 32918.11Infrastructure .................................................................................... 32918.12Hydrogen Storage ............................................................................. 33018.13Fuel Cells as a Possible Alternative to Internal Combustion ...... 33218.14Costs of the Hydrogen Economy .................................................... 33218.15Concluding Remarks ........................................................................ 334References ..................................................................................................... 334 19Future Trends .............................................................................................. 33719.1Introduction ....................................................................................... 33719.2Energy Industries .............................................................................. 33819.3Chemical Industries .......................................................................... 340xivContents19.4Changing Opinions on Investment ................................................ 34119.5Transition............................................................................................ 34319.6Concluding Remarks ........................................................................ 344References ..................................................................................................... 345Epilogue ............................................................................................................... 347Problems .............................................................................................................. 349Index ..................................................................................................................... 359xvPrefaceForsomeofus,theenergycrisisofthe1970sand1980smaystillbefresh inourmemory.Thecrisiswasofpoliticalorigin,notoneofrealshortage. Thedevelopedcountriesrespondedbyfocusingonincreasingenergyeff-ciency, at home and in industry, and by taking initiatives to make them less dependentonliquidfossilsfromtheMiddleEast.Morethaneverbefore, attentionshiftedtocoalasanalternativeenergyresourceitsexploration, production,transportation,andmarketing.Massiveresearchanddevelop-ment programs were initiated to make available clean and effcient coal uti-lization and more easily handled materials as gaseous and liquid conversion products. Obviously, large multinational oil companies played an important roleintheseinitiatives,astheyconsideredenergy,notoil,theirultimate business.At the same time, there was growing concern worldwide for the environ-ment. With the industrial society proceeding at full speed with mass produc-tion and consumption, the world became aware that this was accompanied bymassemissionofwaste.Airpollution,waterpollution,deteriorationof the soil, and so forth became topics that started worrying us immensely. The irreversibility of most of our domestic and industrial activities seemed to ask a price for remediation that could become too high, if not for the present generations,thenforlaterones.Thisinsightdevelopedasenseofrespon-sibilitythatwentbeyondpolitical,national,orotherspecifcinterestsand seemedtobesharedbyallawareworldcitizens.Earlier,andtriggeredby activitiesoftheClubofRome,computersimulationsshowedthepossible limits to growth for a growing world population with limited resources. The 1987 Brundtland Report [1] emphasized our responsibility for future genera-tions and pointed to the need for sustainable development. This showed the emergence of a trilemmawith economic growth, need for resources, and care for the environment in a delicate balance. The sun as a renewable source of energy became more and more prominent, as exemplifed in Japans mas-sive New Sunshine Program and by the emergence of green chemistry, a development to fulfll our needs for chemicals in a sustainable way.Our desire to write this book originated from the aforementioned need to increase the energy effciency of industrial processes. Of all factors that are importanttoourfuture,energymaywellbethesingle-mostcriticalprob-lem that we have to face in the twenty-frst century. Octave Levenspiel, the famous American chemical engineer and scientist, has emphasized that no sensibledecisiononenergyanditstransformationcouldbewellfounded without understanding the concepts of thermodynamics. After all, thermo-dynamics is the ultimate science of the transformation of energy and matter, irrespective of whether we talk about industrial, ecological, or even economic xviPrefacesystems.Fromitsscientifcconcepts,thermodynamicshasemergedasthe ultimateaccountantofenergy.Thermodynamics,inparticularthesecond law, seemed indispensable to fnd ones way in a labyrinthor so it seemsofresourceandprocessalternatives.Butwiththeemergenceoftheworld-widecallforsustainability,ourinterestextendedtoincludefactorsother than effciency to deal with this concept. In doing so, we discovered that in nature and its cycle of life, energy and chemistry are more or less synony-mous, and that nature has its own ways to be sustainable. However complex its ways and processes, nature is the prime example of sustainability and the source of inspiration for developing from an industrial society to what some liketocallametabolicsociety:asocietythatmakesuseofanimmaterial energy source and recycles its products, including its waste. This is not only afascinatingchallengebut,moreimportantly,anecessity!Effciencywill still be an important factor, as there are serious indications that the worlds ecological opportunity to exploit the sun as a resource is limited.AngelaMerkel,physicistandformerGermanMinisterofEnvironment, defnedsustainabledevelopmentasusingresourcesnofasterthanthey can regenerate themselves and releasing pollutants to no greater extent than natural resources can assimilate them [2].Living systems are out of equilibrium with the dead and inorganic envi-ronment. Thermodynamics provides us with some very useful concepts to tellushowfaroutofequilibriumasystemisandwhatittakestomain-tainthisstate.ThelateFrenchscientistBernardSpinnerpointedoutthat these concepts allow us to integrate the environment into the analysis of any system we are interested in, a wonderful thermodynamic principle: always study the system in interaction with its environment. Science, in this instance thermodynamics, can hardly offer society something better to live in har-mony with the Environment. In conclusion, the main objective of this book is to study the effciency and sustainability of industrial systems. In doing so, we will be looking at these systems through the glasses of thermodynamics and apply this impressive science wherever possible. In this second edition, thebooksstructureofBasics,ThermodynamicAnalysisofProcesses, Case Studies, and Sustainability has been unaffected, but a few things havechanged.Whereverrelevant,problemshavebeenaddedtoachapter, testing the students on understanding, reproduction, and application of the discussedconcepts.InPartII,specialattentionhasbeengiventothepos-sibility of integrating the environment into the thermodynamic analysis of the systems or processes considered. The authors are no experts on climate but accept the fact that the emissions of CO2 are increasing at an increased rate.*Andsoanewchapterisdedicatedtothissubjectwithspecialatten-tion for the removal and storage of CO2. A CO2-free industry emerging from hydrocarbon resources could imply an industry based on H2, a topic to which another new chapter has been devoted. Chapter 12 on life cycle analysis has * Nature, 458, 10911094, April 29, 2009.Prefacexviibeen extended to include the fate of the quality of energy during the cycle of the process or product. The separate chapters on biomass conversion and greenchemistryhavebeenintegratedintoonenewchapter.Thechapter Economics, Ecology and Thermodynamics (Chapter 18 in the frst edition) has now been absorbed into the other chapters, as economics, ecology, and thermodynamicsshouldalwaysbeconsideredsimultaneously.Frequently, researchersconsidereconomicsasanafterthought,andthoseskilledin economics and business are not fully aware of the physical constraints that follow from the laws of thermodynamics.Finally, the senior authors (HJvdK and JdSA) have invited their former stu-dentandjuniorcoauthor(KS)toassumetheresponsibilityoffrstauthor. His youth, exceptional skills, and critical scientifc and engineering attitude willensurethathoweverdistractedwemaybebyshort-termeventsand wisdom, in the long term, scientifc truth will prevail.Krishnan SankaranarayananHedzer J. van der KooiJakob de Swaan AronsReferences1.Brundtland,G.H.Ourcommonfuture,Theworldcommissiononenviron-mental development, Oxford University Press: Oxford, U.K., 1987.2.Angela Merkel, Science 1998, 281, 5375, 336337.xixAbout This BookIn the last three decades, important political events and authoritative reports have drawn our attention to the limits of economic growth, and caused grow-ing concern on our living environment, the latter even taking global dimen-sions with issues as climate change and reduction of biodiversity. Most of us now seem to be aware that our technological and economic activities should servealsothequalityofournaturalenvironment.Thisisoftencalledsus-tainable development. The question is now what, more precisely, is meant by this. The term becomes more relevant with talk of alternative energy sources, hydrogen, CO2, and terms such as green. This book aims to quantify these terms,determinethefeasibilityandpossibilityofclaims,andallowfora rational evaluation and discussion based on sound scientifc principles.This book answers this question for industrial processes, in particular those in the energy and chemical industry. Having a long experience in joint efforts withindustryandwithteaching,theauthorsusethefundamentallawsof thermodynamics as a point of departure. They contrast the present industrial societywiththeemergingmetabolicsociety,inwhichmassproductionand consumption are in harmony with the natural environment through closure ofmaterialcycles.Theseareultimatelydrivenbytheprimarynewenergy source, the sun. This book provides keys to a quantifcation of process effciency and sustainability. This is illustrated in case studies, examples, and problems.Thebookismeantforthepracticingengineerandanybodyelsewhois interested or engaged in the transition from a fossil-based, non-sustainable industrytoasustainable,low-wasteindustrybasedonrenewableenergy and resources. Thus, it is hoped, the book itself will contribute to the devel-opment of a sustainable society.xxiAcknowledgmentsTheauthorswishtoacknowledgethevarioususefulcontributionsto thisbookbyDr.Ir.SanderLems.Wealsowishtothanktheparents (K. Sankaranarayanan and Kokila Sankaranarayanan) and wife (Ayshwarya Srinivasan) of the frst author (KS) for all the support during the fnal phase of the book and the wife (Kozue Takamura) of the third author (JdSA) for all the help with the typing and editing of the documents.xxiiiAuthorsKrishnanSankaranarayananreceivedhisMScatDelftUniversityof Technology,theNetherlandsandhisPhDatPrincetonUniversity,New Jersey.AtDelft,hedidanextensivestudyoftheenergyeffciencyofthe polyolefnindustry,forwhichactivityDSMactedashost.Heiscurrently groupheadreactorengineeringandmixingatExxonMobilResearchand Engineering, Fairfax, Virginia.HedzerJ.vanderKooireceivedhisMScandPhDdegreesfromDelft UniversityofTechnologyandspecializedinphaseequilibria.Inthelast decade,heworkedcloselytogetherwithSankaranarayananonthesub-jectofthisbook,assistedbymanystudents.Heiscurrentlyactiveinthe Department of Architecture at Delft University of Technology.JakobdeSwaanAronsreceivedhisMScandPhDdegreesfromthe DelftUniversityofTechnology,theNetherlands.Hespentsome20years withShellInternational,beforehewasappointedtothechairofApplied ThermodynamicsandPhaseEquilibriaatDelftUniversityofTechnology. HeisanelectedmemberoftheRoyalNetherlandsAcademyofArtsand Sciences,andanhonoraryprofessoroftheBeijingUniversityofChemical Technology,China.From2003to2009,heservedaschairinthechemical engineering department of Tsinghua University, Beijing, China. Much of his inspirationwasdrawnfromhismanyvisitstoJapananditsresearchcen-ters. He received the Hoogewerff Gold Medal for his lifetime contributions to process technology in 2006.I Part BasicsLearn the fundamentals of the game and stick to themJack Nicklaus, golf legendInChapter2,wepayarenewedvisittothermodynamics.Wereviewits essentialsandthecommonstructureofitsapplications.InChapter3,we focusonso-calledenergyconsumptionandidentifytheconceptsofwork available and work lost. The last concept can be related to entropy produc-tion,whichisthesubjectofChapter4.Thischaptershowshowsomeof the fndings of nonequilibrium thermodynamics are invaluable for process analysis. Chapter 5 is devoted to fnite-time fnite-size thermodynamics, the application of which allows us to establish optimal conditions for operating a process with minimum losses in available work.31IntroductionSome years ago, we were teaching an advanced course in thermodynamics to process engineers of a multinational industry. Subjects included phase equilib-ria, the thermodynamics of mixtures, and models from molecular thermody-namics applied to industrial situations. Some participants raised the question whethersometimecouldbespentonthesubjectoftheexergyanalysisof processes. At that time this was a subject with which we were less familiar because energy-related issues fell less within the scope of our activities. We fell back on a small monograph by Seader [1] and the excellent textbook by Smith et al. [2], who dedicated the last chapter of their book not so much to exergy buttothethermodynamicanalysisofprocesses.Conceptssuchasidealwork, entropy production, and lost work were clearly related to the effcient use of energy in industrial processes. The two industrial examples givenone on the liquefaction of natural gas, the other on the generation of electricity in a natural gas-fred power stationlent themselves very well not only for illustrative pur-poses but also for applying the exergy concept and exergy fow diagrams [3,4]. Thelatterconceptsappealedtousbecauseoftheirinstrumentalandvisual power in illustrating the fate of energy in the processes (Figure 1.1).Afterthisexperienceinindustry,westartedtoincludethesubjectin advancedcoursestoourownchemicalengineeringstudentsatDelft UniversityofTechnology.Acolleaguehadpointedouttousthatthe design of a process is more valuable if the process has also been analyzed foritsenergyeffciency.Formechanicalengineers,whoweretradition-ally more engaged in energy conversion processes, this was obvious; for chemical engineers, until then more concerned with chemical conversion processes,thiswasrelativelynew.Thesubjectgrewinpopularitywith our students because it became more and more obvious that the state of theenvironmentandenergyconsumptionarecloselyrelatedandthat excessive energy consumption appeared to be one of the most important factors in affecting the quality of our environment.In performing such an analysis, either for industry, or out of our own curi-osity, we became more and more aware of the very important role that the secondlawisplayinginourdailylivesandhowthethermodynamicsof irreversible processes, until then for us a beautiful science but without sig-nifcant applications, appeared to have a high engineering content. Atkins statement that the second law is the driving force behind all change [5] had a lasting impact on us, as much as Goodsteins suggestion [6] that the second lawmaywellturnouttobethecentralscientifctruthofthetwenty-frst 4Effciency and Sustainability in the Energy and Chemical Industriescentury. We discovered the importance of the relation between results from classical, engineering, and irreversible thermodynamics as we have tried to make visible in what we like to call the magic triangle behind the second law (Figure 1.2).Later,whenwewerestruckbytheobservationthatcomplexindus-trial schemes and life processes or living systems have much in common, ExchangerSep./Val.2184Liquid CH4534495262622100010378118722220Compression3FIGURE 1.1Grassmann diagram for the Linde liquefaction process of methane. One thousand exergy units of compression energy result in 53 exergy units of liquid methane. The thermodynamic eff-ciencyofthisprocessis5.3%.Thearrowedcurves,benttotheright,showthelossesinthe various process steps.The magic triangle behind thesecond lawEngineeringthermodynamicsIrreversiblethermodynamicsSgen > 0W lost=T0SgenS gen=iJiXiFIGURE 1.2Themagictrianglebehindthesecondlaw.Therelationbetweenresultsfromclassical, engineering, and irreversible thermodynamics (see Chapter 4).Introduction5ourattentionwasagainattractedtothemeaningofthesecondlaw andtheroleofentropyproduction.Thisledustothetopicofenergy flow in biology and the invaluable monographs by Schrdinger [7] and Morowitz[8].Thispartofoureducationhadcomeinatimelyfashion, as became apparent when, more and more often, the words sustainabil-ityandsustainabledevelopmentwerebroughtinrelationwiththe efficientuseofenergy.Wewereforcedtoseeouranalysisinthelight of these concepts and to make efforts to extend our analysis to indicate, in quantitative terms, the extent to which processes or products are not onlyefficientbutalsocontributetosustainability.Onceagainwewere stimulated by ideas and questions from colleagues within multinational industries. All these elements and influences can be found in this book and its structure.PartIofthisbook,Basics(Chapters2through5),reviewsthemain results of classical thermodynamics and identifes the important concepts of ideal work, lost work, and entropy generation, from using and combin-ing the frst and second laws for fowing systems. Having identifed these concepts, we further interpret them in everyday technical terms by using the main results of irreversible thermodynamics. After reviewing possible waystominimizetheworklost,weconcludethispartbygivingatten-tion to the thermodynamic cost of performing a process in fnite time and space.Part II, Thermodynamic Analysis of Processes (Chapters 6 through 8), discusses the thermodynamic effciency of a process and how effciency can be established and interpreted. A very useful thermodynamic prop-erty, called exergy or available work, is identifed that makes it relatively easytoperformandintegratetheenvironmentintosuchananalysis. Some simple examples are given to illustrate the concept and its applica-tion in the thermodynamic or exergy analysis of chemical and nonchemi-cal processes.PartIII,CaseStudies(Chapters9through12),takestheseillustrations abitfurther,namely,bydemonstratingtheanalysisforsomeofthemost important processes in industry: energy conversion, separations, and chemi-cal conversion. Chapter 12 briefy discusses the concept of life cycle analysis, whichaimstocomparetheconsolidatedinputsandoutputsofaprocess or a product from the cradle to the grave [9], and its extension to include the minimization of process irreversibilities in a so-called exergetic life cycle analysis [10].Part IV, Sustainability (Chapters 13 through 18), deals with the topics of sustainable development, effciency, and sustainability in the chemical pro-cess industry and a very topical topic, carbon dioxide (CO2). The sense and nonsense of green chemistry and biofuels is expounded in this part as well, followed by solar energy conversion and musings on hydrogen in the fnal chapter of this part.Chapter 19, contains the authors thoughts on what the future may hold.6Effciency and Sustainability in the Energy and Chemical IndustriesReferences1.Seader,J.D.ThermodynamicEffciencyofChemicalProcesses,IndustrialEnergy-ConservationManual1,Gyftopoulos,E.P.(ed.),MITPress:Cambridge,MA, 1982.2.Smith,J.M.;VanNess,H.C.; Abbott,M.M.IntroductiontoChemicalEngineering Thermodynamics, 4th edn., The McGraw-Hill Companies Inc.: New York, 1987.3.Sussman, M.V. Availability (Exergy) Analysis, A Self Instruction Manual, Mulliken House: Lexington, MA, 1985.4.de Swaan Arons, J.; van der Kooi, H.J. Exergy analysis, adding insight and preci-sion to experience and intuition. In Precision Process Technology. Perspectives for PollutionPrevention,Weijnen,M.P.C.andDrinkenburg,A.A.H.(eds.),Kluwer Academic Publishers: Dordrecht, the Netherlands, 1993, pp. 83113.5.Atkins, P.W. Educating chemists for the next millennium. ChemTech, 1992, July, 390392.6.Goodstein, D. Chance and necessity. Nature 1994, 368, 598.7.Schrdinger,E.WhatIsLife?CambridgeUniversityPress:Cambridge,U.K., 1980.8.Morowitz, H.J. Energy fow in biology. In Biological Organisation as a Problem in Thermal Physics, OxBow Press: Woodbridge, CT, 1979.9.Ayres, R.U.; Ayres, L.W.; Martinas, K. Exergy, waste accounting, and life-cycle analysis. Energy 1998, 23, 355363.10.Cornelissen,R.L.Thermodynamicsandsustainabledevelopment.PhDthesis, Twente University, Enschede, the Netherlands, 1997.72Thermodynamics RevisitedInthischapter,webriefyreviewtheessentialsofthermodynamicsand itsprincipalapplications.Wecoverthefrstandsecondlawsanddiscuss themostimportantthermodynamicpropertiesandtheirdependenceon pressure,temperature,andcomposition,beingthemainprocessvariables. Change in composition can be brought about with or without the transforma-tion of phases or chemical species. The common structure of the solution of a thermodynamic problem is discussed.2.1The System and Its EnvironmentIn thermodynamics, we distinguish between the system and its environment. The system is that part of the whole that takes our special interest and that we wish to study. This may be the contents of a reactor or a separation column or a certain amount of mass in a closed vessel. We defne what is included in the system. The space outside the chosen system or, more often, a relevant selected part of it with defned properties, is defned as the environment.Next, we distinguish between closed, open, and isolated systems. All are defned in relation to the fow of energy and mass between the system and its environment. A closed system does not exchange matter with its environ-ment, but the exchange of energy (e.g., heat or work) is allowed. Open systems mayexchangebothenergyandmatter,butanisolatedsystemexchanges neither energy nor mass with its environment.2.2States and State PropertiesThe system of our choice will usually prevail in a certain macroscopic state, which is not under the infuence of external forces. In equilibrium, the state canbecharacterizedbystatepropertiessuchaspressure(P)andtempera-ture(T),whicharecalledintensiveproperties.Equally,thestatecanbe characterizedbyextensivepropertiessuchasvolume(V),internalenergy (U), enthalpy (H), entropy (S), Gibbs energy (G), and Helmholtz energy (A). 8Effciency and Sustainability in the Energy and Chemical IndustriesThese properties are called extensive because they relate to the amount of massconsidered;oncerelatedtoaunitamountofmass,theyalsobecome intensive properties.The equilibrium state does not change with time, but it may change with loca-tion as in a fowing system where P, T, and other state properties can gradually change with position. Then we speak of a steady state. If the state temporarily changes with time, as in the startup of a plant, we call it a transient state.Ifanisolatedsystemisinanonequilibriumstate,itspropertieswill usuallydifferfromitsequilibriumpropertiesanditwillnotbestable. Ifsuchasystemcanabsorblocalfuctuations,itisinametastablestate; otherwise, the system and state are called unstable (Figure 4.2).2.3Processes and Their ConditionsOften our system of interest is engaged in a process. If such a process takes place at a constant temperature, we speak of an isothermal process. Equally, theprocesscanbedefnedasisobaric,isochoric,isentropic,orisenthalpic ifpressure,volume,entropy,orenthalpy,respectively,remainsunchanged during the process. A process is called adiabatic if no heat exchange takes placebetweenthesystemanditsenvironment.Finally,aprocessiscalled reversible if the frictional forces, which have to be overcome, tend to zero. The unrealistic feature of this process is that energy and material fows can take place in the limit of driving forces going to zero; for example, in an iso-thermalprocess,heatcanbetransferredwithoutatemperaturedifference within the system or between the system and its environment. In a real pro-cess, frictional forces have to be overcome, requiring fnite driving forces as P, T, G, or when driving forces are already present in the system, this leads to processes where spontaneously is given in to such forces in a spon-taneousexpansion,mixingprocess,orreaction.Suchprocessesarecalled irreversible processes and are a fact of real process life. As we will see later, thetheoryofirreversiblethermodynamicsidentifestheso-calledthermo-dynamicforces,forexample,(1/T)insteadofT,andtheassociatedfow ratein this instance, the heat fow rate Q.2.4The First LawThermodynamics is solidly founded on its main laws. The frst law is the law of conservation of energy. For a closed system that receives heat from the envi-ronment, Qin, and performs work on the environment, Wout, we can writeThermodynamics Revisited9 = in outU Q W (2.1)Heat and work are forms of energy in transfer between the system and the environment. If more heat is introduced into the system than the system per-forms work on the environment, the difference is stored as an addition to the internalenergyUofthesystem,apropertyofitsstate.Inamoreabstract way,thefrstlawissaidtodefnethefundamentalthermodynamicstate property, U, the internal energy.Equation 2.1, in differential form, can be written as in outdU Q W = (2.2)The -character is used to indicate small amounts of Q and W because heat and work are not state properties and depend on how the process takes place between two different states.If the process is reversible and the sole form of work that the system can exert on its environment is that of volume expansion, then revout. dW PdV =If, in addition, the process is isobaric, PdV = d(PV) and revin( ) dQ d U PV dH = + = (2.3)The enthalpy H is defned as H = U + PV and is a property of state derived fromthefundamentalpropertyU.Ifheatisstoredreversiblyandisobari-callyinasystem,itisstoredasanincreaseinthesystemsH-value.Hhas been defned for our convenience; it has no fundamental meaning other than that, under certain conditions, its change is related to the heat absorbed by thesystem.Itcanbeshownthatthespecifcheatatconstantvolumeand pressure, cv and cp, respectively, can be expressed as andv pV PU Hc cT T = = (2.4)For process engineering and design, it is important to know how enthalpy is a function of pressure, temperature, and composition. The last variable is discussed later. It can be found in any standard textbook that the differential of H can be expressed as a function of the differential of T and P as follows: pPVdH c dT V T dPT = + (2.5)The frst term depends on what is sometimes called the caloric equation of state,describinghowintramolecularproperties,thepropertieswithinthe molecules,areafunctionofthestatevariables.Theexpressioninbrackets requires the mechanical equation of state, which expresses the dependency of a property, for example, V on the intermolecular interactions, the interactions 10Effciency and Sustainability in the Energy and Chemical Industriesbetween molecules. Process simulation models usually contain information and models for both types of equation of state.Most often, we are not interested in the absolute value of H, but rather in its change, tr H. The subscript tr refers to the nature of the change. If the change involves temperature and/or pressure for a one-phase system only, no subscript is used for . But in case of a phase transition, of mixing, or of a chemical reaction, the subscript is used and may read vap for vaporization, mix for mixing, or r for reaction, and so forth.When a superscript is used as in trH, it indicates that the change in H is considered for a transition under standard pressure, which usually is chosen as1bar.Inthecaseofchemicalreactions,thesuperscriptreferstostan-dard pressure and to reactants and products in their pure state or otherwise defned standard states such as infnitely dilute solutions.Finally, we present the frst law for open systems as in the case of streams fowing through a fxed control volume at rest [1] = + + + + + + 2in2outin out sh,in sh,out22ii i icvjj j jdU um h gzdtum h gzQ Q W W

(2.6)V1P1, T1u1V2z1z2Datum levelHeat exchangerTurbineSection 1.Qin.WoutSection 2P2, T2u2zFIGURE 2.1Changes in steady-state fow.Thermodynamics Revisited11Foroneingoingandoutgoingstreaminthesteadystate(Figure2.1),this equation simplifes into 2in out2um H g z Q W + + =

(2.7)wherem. refers to the mass fow rate consideredu is the velocity of the fowing systemz is its height in the gravitational feld2.5The Second Law and BoltzmannThesecondlawisassociatedwiththedirectionofaprocess.Itdefnesthe fundamental property entropy, S, and states that in any real process the direc-tionoftheprocesscorrespondstothedirectioninwhichthetotalentropy increases,thatis,theentropychangeofboththesystemandenvironment should in total result in a positive result or in equation formenvironment generatedS S S + = (2.8)generated0 S > (2.9)In other words, every process generates entropy. The best interpretation, in our opinion, of this important law is given by adopting a postulate by Boltzmann: ln S k = (2.10)Thisequationexpressestherelationbetweenentropyandthethermody-namic probability , where k is Boltzmanns constant. If in an isolated vessel, flled with gas, at t = 0 half of the molecules are nitrogen, the other half are oxygen, and all nitrogen molecules fll the left half of the vessel whereas all oxygen molecules fll the right half of the vessel, then this makes for a highly unlikely distribution, that is, one of a low thermodynamic probability 0. As time passes, the system will evolve gradually into one with an even distri-bution of all molecules over space. This new state has comparatively a high thermodynamic probability , and the generated entropy is given by = = generated final original0ln S S S k (2.11)12Effciency and Sustainability in the Energy and Chemical IndustriesStandard textbooks give ample examples of how can be calculated [1].Noticethatthedirectionoftheprocessandtimehavebeendetermined: This has been called the arrow of time [2]. Time proceeds in the direction of entropy generation, that is, toward a state of greater probability for the total ofthesystemanditsenvironment,which,inthewidestsense,makesup the universe. Finally, we wish to point out that an interesting implication of Equation 2.10 is that for substances in the perfect crystalline state at T = 0 K, the thermodynamic probability = 1 and thus S = 0.2.6The Second Law and ClausiusAs the frst law is sometimes referred to as the law that defnes the funda-mental thermodynamic property U, the internal energy of the system, the sec-ond law is considered to defne the other fundamental property, the entropy S. Classical thermodynamics, via Clausiuss thorough analysis [3] of thermody-namic cycles that extract work from available heat, has produced the relation between S and the heat added reversibly to the system at a temperature T: revinQdST= (2.12)This relation plays an important role in the derivation of the universal and fundamental thermodynamic relationdU TdS PdV = (2.13)whichisoftencalledtheGibbsrelation.Thisrelationisinstrumentalin connectingthechangesbetweenthemostimportantthermodynamicstate properties.FromthisrelationthedifferentialdScanbeexpressedasthefollowing function of the differentials of pressure and temperature: PPC VdS dT dPT T = (2.14)P, T, and also composition are the state variables most often used to charac-terize the state of the system, as they can be easily measured and controlled. As we show in Part II, Equations 2.5 and 2.14 are important to perform the thermodynamicanalysisofaprocess 0298 TS ,whichexpressesthechange inentropyofareactionat298 Kandatstandardpressure.Thereactionis defned to take place between compounds in their standard state, that is, in the Thermodynamics Revisited13most stable aggregation state under standard conditions, like liquid water for water at 298 K and 1 bar. Analogous to Equation 2.6, for the frst law for open systems, the second law reads in outgeneratedin outi i j jcvk ldSmS mSdtQ QST T = + +

(2.15)and simplifes to Equation 2.8 for single fows in and out the control volume in the steady state.Finally,equilibriumprocessescanbedefnedasprocessesbetweenand passing states that all have the same thermodynamic probability. On the one hand,theseprocessesproceedwithoutdrivingforces;ontheotherhand, and this is inconsistent and unrealistic, there is no incentive for the process to proceed. These imaginary processes function only to establish the mini-mum amount of work required, or the maximum amount of work available, in proceeding from one state to the other.2.7Change in CompositionSofarourdiscussionofthermodynamicconceptshasreferredtosystems thatdidnotseemtochangewithcomposition,onlywithpressureP,tem-perature T, or the state of aggregation. Thermodynamics, however, is much more general than being limited to these conditions, fortunately, for changes incompositionaretheruleratherthantheexceptioninengineeringsitu-ations.Purehomogeneousphasesmaymix,andahomogeneousmixture may split into two phases. A homogeneous or heterogeneous mixture may spontaneouslyreacttooneormoreproducts.Inallthesecaseschangesin composition will take place. This part of thermodynamics is usually referred to as chemical thermodynamics, and its spiritual father is Josiah Willard Gibbs[4].IthasbeenthemeritofLewis[5]todecipherGibbsachieve-mentsandtotranslatetheseintoreadilyapplicablepracticalandcompre-hensible concepts such as the Gibbs energy of a substance i, or the individual thermodynamicpotential i,fugacityfi,oractivityai,conceptsnowwidely usedinprocessdesign.Thethermodynamicorchemicalpotentialcanbe consideredtobethedecisivepropertyforanindividualmolecularspecies transport or chemical behavior. It has been one of the main achievements of Prausnitz et al. [6] to be instrumental in quantifying thermodynamic proper-ties for ready application by taking into account the molecular characteristics 14Effciency and Sustainability in the Energy and Chemical Industriesandpropertiesofthosemoleculesmakingupthemixtureinaparticular thermodynamicstate.Thisbranchofthermodynamicsisoftenreferredto asmolecularthermodynamics,andmanyconsiderPrausnitzasitsmost prominent founding father.If a mixing process or chemical transformation is brought about, sponta-neously or by applying work on the system, the process will take place with entropy generation:generated0 S > (2.9)and the total entropy will tend to a maximum value that will be reached for the equilibrium state.Indeed,fordifferentmolecules,whichotherwisearenearlythesame, suchasisomers,ormoleculesofaboutthesamesize,polarity,orother properties, the thermodynamic probability of the mixed state at the same PandTismuchlargerthanthatoftherespectivepurestates(inmolar units): mixedmix generatedseparatedln S S R = = (2.16)with mixed >>> separated.If the change is in composition only, at constant P and T, and confned to the system we wish to consider, for instance, in a mixer, separation column, orareactor,thenasystempropertyG,theGibbsenergy,canbeidentifed and has been defned as follows: G U TS PV + (2.17)It has the property that in time (t) and at constant pressure and temperature it tends to a minimum value that will be reached when the system has reached equilibrium (Figure 2.2);GPTtFIGURE 2.2TheGibbsenergyGon approaching equilibrium.Thermodynamics Revisited15 ,minP TG (2.18)or ,0P TdGdt (2.19)Ifweconsiderachemicalreactionthattakesplaceinahomogeneous mixture, the equilibrium composition of the mixture can be found from theequalityconditioninEquation2.19ifthedependenceofGonthe composition is known.If the process of mixing takes place with negligible change of the internal energy U and volume V, we speak of ideal mixing and it can be shown then that for 1 mol of mixture =idealmix lni iS R x x (2.20)in whichxi is the molar fraction of constituent i in the mixtureR is the universal gas constantFor an ideal mixture, mixUideal and mixV ideal are zero for mixing at constant P and T, and so mixGideal is given by idealmixlni iG RT x x = (2.21)Notice that mixH ideal is also zero and thus, with Equation 2.3 in mind, ideal mixing at constant P and T will take place without heat effects.For deviations from ideal mixing, the excess property ME is defned as idealmix mixEM M M = (2.22)AnimportantexcesspropertyistheexcessGibbsenergyGE.Manymod-elshavebeendevelopedtodescribeandpredictGEfromthepropertiesof the molecules in the mixture and their mutual interactions. GE models often refer to the condensed state, the solid and liquid phases. In case signifcant changes in the volume take place upon mixing, or separation, the Helmholtz energy A, defned as A U TS (2.23)anditsexcesspropertyAEarethepreferredchoicesfordescribingthepro-cess. This requires an equation of state that expresses the volumetric behav-iorofthemixtureasafunctionofpressure,temperature,andcomposition. 16Effciency and Sustainability in the Energy and Chemical IndustriesFor the models most applied in practice for GE and AE, the reader is referred to Ref. [7].Partialmolarpropertiestakeaspecialplaceinthethermodynamicsof mixtures and phase equilibria. They are defned as , ,( )jiiP T n inMMn (2.24)Thebest-knownexampleisthepartialmolarGibbsenergy,betterknown astheearlier-mentionedthermodynamicpotential.Thethermodynamic potential of component i in a homogeneous mixture is = , ,( )ji iiP T n inGGn (2.25)An important condition for phase equilibria is i i i= = = (2.26)or in terms of the fugacity in mixtures i if f = = (2.27)in which equations, the primes indicate the respective phases. Fugacity and activity(seebelow)aredirectlyrelatedtothethermodynamicpotential. The latter property has the dimension of Joules per mole, whereas fi has the dimension of pressure and ai is dimensionless.The last equation, applied to a vaporliquid equilibrium, reads satsat sat( )expi ii i i i i iV P Py P x PAT = (2.28)which simplifes to Raoults law for ideal gas behavior, for which the fugacity coeffcients i and satiare equal to 1, and ideal mixing in the liquid state, for which the activity coeffcient i equals 1, and the Poynting factor (the expo-nential in Equation 2.28), with iV the liquid-phase molar volume is approxi-mately unity: sati i iy P x P = (2.29)The fugacity coeffcient i can be calculated from a valid equation of state; the activitycoeffcienticanbederivedfromanapplicableGEexpression.The activity ai is the product of i and xi.Thermodynamics Revisited17The property known as the Gibbs energy G, and defned by Equation 2.17, playsanimportantroleindescribingontheonehandthetransformation between phases where species stay the same but distribute differently over the phases present, such as vapor and liquid, and on the other hand in trans-formationswherespecieschangeidentity,thechemicalreaction.Chemical reactionsandphasetransformationsbothproceedinthedirectionsthat fulfll Equations 2.18 and 2.19.For a chemical reactionA B j kv A v B v J v K + + + + (2.30)inwhichviisthestoichiometriccoeffcientofspeciesi,defnedaspositive for a product and negative for a reactant, it can be shown that progress of the reaction can be characterized by a reaction property, the so-called degree of advancement of reaction, which is defned as [1] iidndv = (2.31) and the chemical reaction velocity vchem are related by chemdvdt= (2.32)Equilibrium is reached for (Figure 2.3) 0dGd=(2.33)and chem0 v = (2.34)FIGURE 2.3TheGibbsenergyGandthe degreeofadvancementof reaction .eqGPT18Effciency and Sustainability in the Energy and Chemical IndustriesIf G is known as function of composition, the position of the chemical equi-librium can be determined with the help of Equation 2.33, which is instru-mental in fnding the equilibrium composition. It can be shown that chemical equilibrium is characterized by the equation 0i iv = (2.35)From this, the chemical equilibrium constant at temperature T 0iviTifKf = (2.36)can be identifed as 0lnT r TRT K G = (2.37)The dependency on T is given by = 0ln(1/ )T r Td K Hd T R (2.38)KnowledgeofthesechangesinstandardGibbsenergyandenthalpy allowsonetocalculatetheequilibriumcompositionanditsvariationwith temperature.2.8The Structure of a Thermodynamic ApplicationWe now briefy discuss how thermodynamics can work for us or, better, how thermodynamics functions to solve a problem where it can help to provide theanswer.Wewishtoillustratethisforarelativelysimpleproblem:how much work is required to compress a unit of gas per unit time (Figure 2.4) from a low to a high pressure. Figure 2.5 schematically gives the path to the answer and the structure of the solution. In fact, the same steps will have to be taken to apply thermodynamics to problems such as the calculation of the heat released from or required for a process, of the position of the chemical or phase equilibrium, or of the thermodynamic effciency of a process.In our case, the task is to calculate the amount of work required to com-pressagasatpressureP1andtemperatureT1toapressureP2.Weturnto the frst law in the version of Equation 2.7, which allows us to translate the original, technical, question into one of thermodynamics:Thermodynamics Revisited19 = +in outW H Q (2.39)Weassumethatthecompressionisadiabatic:itwilltakeplacewithout exchange of heat with the environment, Qout = 0. So the frst law tells us that Win is known if we know the change in enthalpy of the gas. For this we need to know how the gas enthalpy is a function of pressure and temperature.Assuming, for simplicity, that the gas behaves like an ideal gas, for which the enthalpy is not a function of pressure, we end up with the relation 2 1( )pH c T T = (2.40)by which we have also assumed that the specifc heat at constant pressure, cp, is not a function of temperature. Unfortunately, we do not know T2, and for that we turn to the second law. As the process takes place adiabatically, we write Equation 2.8 in the versionP1, T1, H1WinP2, T2, H2FIGURE 2.4The compressor.Required stepsTask 1. Translation2. Fundamental relations3. Models4. Handleable relations5. Retrieval, estimationbasic dataand parameters6. Computation CompletionFIGURE 2.5Thestructureofathermodynamic application.20Effciency and Sustainability in the Energy and Chemical Industries 0 S (2.41)First, we assume that the process takes place reversibly, and thus rev0 S =(2.42)Withtheassumptionsthatthegasbehavesasanidealgasandcpisnota function of temperature, we may write rev2 2rev1 1ln lnpT PS c RT P = (2.43)Theseequationsallowustocalculate rev2T , rev H,andthus revinW,thework required if the compression had taken place reversibly. But in the real process S > 0, and according to Equation 2.43, T2 must be larger than rev2Tand H > rev H. Thus, revin inW W > . Usually, this is expressed in the compressors effciency revinin1WW < (2.44)When this effciency is known, and for a specifc compressor it usually is, Win can be calculated and with this T2. If we now turn again to Figure 2.5, thefundamentallaws(step1)wereinstrumentalintranslatingthetask, whereasthefundamentalrelations(step2)thatexpresshowHandSare functions of P and T provide us with equations to proceed to the answer. Usually, the gas does not behave as an ideal gas and we need models (step 3) for what we earlier called the mechanical equation of state and the caloric equation of state. This will lead us to what we call handleable, as opposed to abstract, equations. The abstract equations do not allow us to calculate anything, but the handleable equations allow us to perform calculations ifweknowsomenumbers.Givencertainbasicdata,fromexperimentor predicted, and associated parameters, such as for expressing cp as a func-tion of temperature (step 5), these equations allow us to perform the com-putation (step 6) to complete the task and come up with the answer to the original question. Steps 1 and 2 are extensively discussed in textbooks of chemical engineering thermodynamics [1], step 3 falls within the subdisci-pline of molecular thermodynamics [6], and step 5 falls within that of the prediction of thermodynamic properties as a function of composition and basedonthemolecularstructureofthemixturesconstituentsandtheir mutual interactions [7].We conclude this example with the observation that the second law for real processes expresses that entropy generation is positive and that the implica-tion is that the real amount of work required is larger than that calculated for Thermodynamics Revisited21the reversible or ideal(ized) process. This suggests a relation between entropy generation and excess work. This relation is of fundamental signifcance for the subject of this book, as we will demonstrate later.References1.Smith,J.M.;vanNess,H.C.; Abbott,M.M.IntroductiontoChemicalEngineering Thermodynamics, 4th edn., McGraw-Hill: New York, 1987.2.Blum, H.F. Times Arrow and Evolution, Harper: New York, 1962.3.Carnot, S. Refections on the Motive Power of Fire and Other Papers on the Second Law ofThermodynamics,Clausius,R.andClayperon,E.(eds.),DoverPublications: New York, 1960.4.Gibbs,J.W.ThermodynamischeStudien,WilhelmEngelmannVerlag:Leipzig, Germany, 1982.5.Lewis,G.N.;Randall,M.Thermodynamics,Pitzer,K.S.andBrewer,L.(eds.), McGraw-Hill: New York, 1961.6.Prausnitz,J.M.;GomesdeAzevedo,E.;Lichtenthaler,R.N.Molecular ThermodynamicsofFluidPhaseEquilibria,3rdedn.,PrenticeHall:Englewood Cliffs, NJ, 1999.7.Reid,R.C.;Prausnitz,J.M.;Poling,B.E.ThePropertiesofGasesandLiquids,5th edn., McGraw-Hill: New York, 2001.233Energy Consumption and Lost WorkIn this chapter, we show that it is not so much energy that is consumed but itsquality,thatis,theextenttowhichitisavailableforwork.Thequality of heat is the well-known thermal effciency, the Carnot factor. If quality is lost,workhasbeenconsumedandlost.Lostworkcanbeexpressedinthe products of fow rates and driving forces of a process. Its relation to entropy generationisestablished,whichwillallowuslatertoarriveatauniversal relation between lost work and the driving forces in a process.3.1IntroductionWe all know what is meant by energy consumption. Most of us pay energy billsandweacceptthatwearechargedforconsumingenergyjustaswe arechargedforconsumingotherthings.Butareweconsumingenergy? According to the frst law of thermodynamics, energy cannot be created nor annihilated. Then what is it that we consume if it is not energy?Inawaythesituationcanbecomparedwithconsumingfood.Ifwe madeathoroughanalysisoffoodconsumption,wewouldconclude that it is not its mass that we have consumed, as the mass balance is not affected.Norisittheenergythatwehaveconsumedasaproperlyper-formedenergybalancewillshow.ThisledSchrdinger[1]tohissome-whatdesperatequestion:Ifitismassnorenergythatweextractfrom food then what is it ?As should become clear from the following sections, it is not energy that we consume but its quality, by which is meant the extent to which energy is available for performing work. In the spontaneous combustion of natu-ral gas, mass and energy are conserved, but the work stored and available in the chemical bonds of the gas will, to a large extent, get lost. By energy consumptionwemeanconsumptionofordecreaseinavailablework. Lossofavailableworkiscalledlostwork,Wlost.Asweshallshow,lost workcan,inthermodynamicterms,beidentifedastheproductofthe entropygeneratedandtheabsolutetemperatureoftheenvironmentT0. This is expressed in the remarkable relation known as the GouyStodola relation [2,3].24Effciency and Sustainability in the Energy and Chemical Industries3.2The Carnot FactorCarnotallowedustoanswerthefollowingquestion:Whichpartofheat Q,availableatatemperatureT>T0,canatmostbeconvertedintouseful work? Provided the process is cyclic and conducted reversibly, the maximum amount of work available is given by 0 maxout1TW QT = (3.1)The factor 1 (T0/T) is often called the thermal effciency, but we prefer to call it the Carnot factor.* For example, if heat is supplied at 600 K and the temperature of the environment is 300 K, the Carnot factor is 1/2. We could also say that in this instance the quality q of every Joule of heat is 1/2 J/J, if we wish to express that at most half of the Joule of heat supplied can be made available for useful work with respect to our environment at T0: maxout 01W TqQ T= = (3.2)SowedefnethequalityofheatsuppliedatatemperaturelevelT>T0as themaximumfractionavailableforusefulwork.Baehr[4]hascalledthis part of heat the exergy of heat. The remaining part is unavailable for useful work and is called anergy. It is the minimal part of the original heat that will be transferred as heat min0Qto the environment. In Baehrs terminology, we could say that in this instance the ideal heat engine would achieve the fol-lowing separation between useful and useless Joules: 0 0max minout 01exergy anergyT TQ Q QT TW Q = + = += + (3.3)Overall, the cycle takes up an amount of energy Q, produces an amount of work maxoutW , and releases an amount of heat max minout 0Q W Q =at the tempera-ture T0 to the environment.This equation very clearly expresses the quality aspects of heat and must have tempted Sussmann [5] to a statement much inspired by Orwell in his * The minimum amount of work, mininW , required to transfer to the environment the amount of heat leaked in from the environment at T0 into a reservoir maintained at a temperature T < T0 is minin 0(( / ) 1) W Q T T = .Energy Consumption and Lost Work25famousnovelAnimalFarm[6]:AllJoulesareequalbutsomeJoulesare more equal than others. But, in a more earnest sense, this observation can also be found in discussions on energy policy [7]: The quality of energy (i.e., exergy)and not only the quantityas an objective and clear starting point, must be included in making policy choices.Later it will become clear why this observation is important and how far-reachingtheimplicationisofmakinguseofthedistinctionbetweenboth quantity and quality of the various Joules involved in a process.Equation3.3isanexpressionofthefrstlawofthermodynamicsforthe separationinusefulanduselessenergyoftheenergyfromheat.Equation 3.1 is clearly not an expression of the frst law but, as we shall see later, an implicationofthesecondlaw.Inthiscontext,itisworthrecallingBaehrs formulation of the frst and second laws [4]:1.The sum of exergy and anergy is always constant.2.Anergy can never be converted into exergy.This unusual and much less-known formulation of the main laws of thermo-dynamics serves the purpose of this book very well.3.3Lessons from a Heat ExchangerSome important lessons from engineering thermodynamics can be learned from the thermodynamic analysis of a heat exchanger. For illustrative pur-poses we assume that the heat is exchanged between a condensing fuid at a temperature Thigh and an evaporating fuid at a temperature Tlow, with Thigh > Tlow > T0 (Figure 3.1). The mass fow rates have been chosen such that within the exchanger all high-temperature fuid condenses and all low-temperature fuid evaporates. The heat exchanger is not supposed to exchange heat with the environment and thus operates adiabatically. For steady-state operation, if changes in kinetic and potential energy are small compared to the enthalpy changes, the energy balance can be written according to Equation 2.7 ashigh high low low0 m H m H + = (3.4)Theamountofheatexchangedandtakenupbytheevaporatingfuidper unit of time, the heat fow rate Q, is positive and is given by low lowhigh highQ m Hm H= =

(3.5)26Effciency and Sustainability in the Energy and Chemical Industriesand this amount fows spontaneously from Thigh to Tlow. At the high tempera-ture its exergy, or available work as Americans prefer to call it, is 0highhigh1TW QT = (3.6)At the low temperature its quality has decreased and the available work is now less: 0lowlow1TW QT = (3.7)Thus, the exchange of heat has taken place with a rate of loss of available work: lost high low0 0high low0low high1 11 1W W WT TQT TQ TT T= = =

(3.8)or per unit mass instead of per unit time: lost 0low high1 1W Q TT T = (3.8a)VThighTlowLT0m highm low VLQFIGURE 3.1Aheatexchangerinwhichtheheatof condensationofafuidatThighistrans-ferred to an evaporating fuid at Tlow. We assume that Thigh > Tlow > T0.Energy Consumption and Lost Work27FromFigure3.2,inwhichtheCarnotfactorhasbeenplottedagainstthe amount of heat transferred, we can conclude that the work lost is represented bytheenclosedareabetweenthetemperaturelevelsThighandTlowandthe points of entry and exit.ThefactorbetweenbracketsinEquation3.8canbeidentifedasthe driving force for heat transfer, but instead of the familiar T = Thigh Tlow, our equation suggests that the thermodynamic driving force is (1/T) = (1/Tlow) (1/Thigh), and thus Equation 3.8 shows that the amount of work lostistheproductofT0andtheproductof(Q)and(1/T),namely,the product of the fow rate and its driving force. This last product is one of themanythatcanbeidentifedwiththehelpofirreversiblethermody-namics, as we will show in Chapter 4. Another interesting observation is the following. If a body or fow isothermally absorbs a positive amount of heat, Qin at a temperature T, then its change in entropy is given by inQST = (3.9)With this equation in mind, we can read the last part of Equation 3.8a as lost 0 low high 0( ) W T S S T S = + = (3.10)in which S is the entropy change of the heat exchanger. As the heat exchanger operates adiabatically, there is no associated change in entropy of the envi-ronment, S0 = 0, and thus the second law according to Equation 2.8 reads11T0T0TQTH1T0TLFIGURE 3.2The enclosed area represents the amount of lost work in this plot of the Carnot factor against the heat transferred.28Effciency and Sustainability in the Energy and Chemical Industries generatedS S = (3.11)This allows us to write Equation 3.10lost 0 generatedW T S = (3.12)Thisremarkable,simplerelationbetweentheworklostandtheentropy produced in a process dates back to close to the beginning of the twentieth century, when it was independently derived by Gouy [2] and Stodola [3].This equation is not restricted to the process of heat exchange but instead hasauniversalvalidity.Thisisshowninthenextsection.Theextentto which heat exchangers can contribute to the work lost in a process is clearly illustratedinFigure3.3.Hereweobservethat,fortheprocessofmaking ice,nearly45%ofthecompressorworkislostintheevaporatorandcon-denseroftheammoniarefrigerationcycle.Notmanyprocessengineers associate lost work with heat exchange, but this example strikingly shows that they should.Asmentionedbefore,thisthermodynamicanalysissuggeststhat(1/T), not T, is the driving force behind heat fow, contrary to everyday engineer-ing practice. We may then write that to a frst approximation1802 kWelectricIce 1180 kWAmmoniaAmmonia1180 kW494 kW2572 kW1991 kW1882 kW410 kW581 kW109 kW208 kW1180 kWWater0 kWCompressorCondensorValveEvaporatorFIGURE 3.3A refrigeration cycle to make ice from water with ammonia as the working fuid or energy car-rier. Nearly 45% of the compression power is lost due to heat exchange in the evaporator and the condenser.Energy Consumption and Lost Work29 1HQ k AT= (3.13)in whichkH is the overall thermodynamic heat transfer coeffcientA is the surface of exchangeIf we introduce this expression in Equation 3.8, we can write 2lost 01HW k A TT = (3.14)This equation tells us that the amount of work lost in a heat exchanger is in the frst instance proportional to the square of the driving force, and so if one wishes to be more economical with energy, the driving force should be made smaller. On the other hand, Equation 3.13 shows us that if we have to fulfll a certain heat transfer duty Q, the reduction of (1/T) must be compensated eitherbyanexchangermaterialwithbetterheatconductionproperties (a larger kH) or with a larger surface for transfer. It is interesting how these simpleequationsexpresstheeconomicneedofoptimizingbetweencapi-talcostandthecostofenergy.Thepowerfulroleofthermodynamicshere becomes somewhat tempered by the role of economics. Both disciplines play a decisive role in the ultimate design of the heat exchanger.3.4Lost Work and Entropy GenerationWeconsiderasteadyfowingmediumonwhichanamountofworkis exerted,Win(Figure3.4).Heatisonlyexchangedwiththeenvironmentat atemperatureT0.Weassumethatthefowisnotundergoingsignifcant P1, T1P2, T2WinQ0FIGURE 3.4Workandheatareexchangedwiththe environmentwhileafuidisbrought fromcondition1atP1,T1tocondition2 at P2, T2.30Effciency and Sustainability in the Energy and Chemical Industrieschangesinvelocitynorinheightandthereforeneglectthemacroscopic changes in kinetic and potential energy. The frst law then reads according to Equation 2.39in 0= W H Q + (3.15)The second law reads generated 0S S S = + (3.16)We combine the equations, making use of the relation 000QST = (3.17)and after eliminating Q0 and S0, we arrive at the following equation:in 0 0 generatedW H T S T S = +(3.18)H and S express the changes in the fows enthalpy and entropy from state 1 to state 2, for example, 2 2 1 1( ) ( ) H H P T H PT = (3.19)Theminimumamountofworktoaccomplishthischangeinconditionsis apparently given by minin 0W H T S = (3.20)ThesecondlawstatesthatSgenerated>0;hencetherealamountofwork required must be larger: minin in 0 generatedW W T S = +(3.21)The amount of work lost in the process is defned as minlost in inW W W (3.22)and thus we arrive at the relationlost 0 generatedW T S = (3.23)Thisrelationholds,ofcourse,forthegeneralexchangeofworkandheat betweenafowingmediumanditsenvironment.Theabstractformulation of the second law as inEnergy Consumption and Lost Work31generated0 S > (3.24)hasfoundhereaclearandnonambiguoustranslationintotermswidely understood in the everyday world. After all, lost work in any process makes us rely more on energy resources such as coal, oil, natural gas, nuclear fuel, andsoon.Knowingthepricesoffuel,wecanthuseventranslateentropy generationintotermsofmonetaryunits,butthentheconceptbecomesas shaky as the value of a currency, and so we shall refrain from doing this. But the observation has to be made.At this point the need arises to become more explicit about the nature of entropygeneration.Inthecaseoftheheatexchanger,entropygeneration appears to be equal to the product of the heat fow and a factor that can be identifed as the thermodynamic driving force, (1/T). In the next chapter we turn to a branch of thermodynamics, better known as irreversible ther-modynamics or nonequilibrium thermodynamics, to convey a much more universal message on entropy generation, fows, and driving forces.3.5ConclusionThe quality of heat is defned as its maximum potential to perform work with respecttoadefnedenvironment.Usually,thisistheenvironmentwithin whichtheprocesstakesplace.TheCarnotfactorquantitativelyexpresses which fraction of heat is at most available for work. Heat in free fall from a higher to a lower temperature incurs a loss in this quality. The quality has vanishedatT0,thetemperatureoftheprevailingenvironment.Lostwork can be identifed with entropy generation in a simple relation. This relation appears to have a universal value.References1.Schrdinger,E.M.WhatIsLife?CambridgeUniversityPress:Cambridge,U.K., 1944.2.Gouy, G. J. Phys. 1889, 8, 501.3.Stodola, A. Steam and Gas Turbines, McGraw-Hill: New York, 1910.4.Baehr, H.D. Thermodynamik, Springer-Verlag: Berlin, Germany, 1988.5.Sussmann,M.V.Availability(Exergy)Analysis,3rdedn.,MullikenHouse: Lexington, MA, 1985.6.Orwell, G. Animal Farm, Penguin Longman Publishing Company: London, U.K., 1945.7.Annual Report of the Dutch Electricity Producers (SEP), 1991.334Entropy Generation: Cause and EffectIn this chapter, we frst introduce the principles of irreversible or nonequilib-rium thermodynamics as opposed to those of equilibrium thermodynamics. Then, we identify important thermodynamic forces X (the cause) and their associated fow rates J (the effect). We show how these factors are responsible for the rate with which the entropy production increases and available work decreases in a process. This gives an excellent insight into the origin of the incurredlosses.Wepayattentiontotherelationbetweenfowsandforces and the possibility of coupling of processes and its implications.4.1Equilibrium ThermodynamicsEquilibrium thermodynamics is the most important, most tangible result of classical thermodynamics. It is a monumental collection of relations between state properties such as temperature, pressure, composition, volume, internal energy, and so forth. It has impressed, maybe more so overwhelmed, many totheextentthatmostwereleftconfusedandhesitant,ifnottosaypara-lyzed, to apply its main results. The most characteristic thing that can be said about equilibrium thermodynamics is that it deals with transitions between well-defned states, equilibrium states, while there is a strict absence of mac-roscopicfowsofenergyandmassandofdrivingforces,potentialdiffer-ences, such as difference in pressure, temperature, or chemical potential. It allows, however, for nonequilibrium situations that are inherently unstable, out of equilibrium, but kinetically inhibited to change. The driving force is there, but the fow is effectively zero.Some confusion may arise from the discussion of so-called reversible pro-cesses. Reversible processes take place in the limit of all driving forces going tozero.Mostofustacitlyaccepttheterminologyofheatisisothermally transferred only to become aware in daily engineering practice that there isnosuchthingasisothermalheattransfer.Indailyengineeringpractice, heat transfer needs a temperature gradient, mass transfer needs a gradient in the thermodynamic potential, and chemical conversion needs a nonzero affnity between products and reactants. In fact, all heat exchanger