Theoretical and Applied Aspects of Biomass Torrefaction. For Biofuels and Value-Added Products PDF
Preview Theoretical and Applied Aspects of Biomass Torrefaction. For Biofuels and Value-Added Products
THEORETICAL AND APPLIED ASPECTS OF BIOMASS TORREFACTION For Biofuels and Value-Added Products THEORETICAL AND APPLIED ASPECTS OF BIOMASS TORREFACTION For Biofuels and Value-Added Products STEPHEN GENT MICHAEL TWEDT CHRISTINA GEROMETTA EVAN ALMBERG Butterworth-HeinemannisanimprintofElsevier TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UnitedKingdom 50HampshireStreet,5thFloor,Cambridge,MA02139,UnitedStates ©2017ElsevierInc.Allrightsreserved. Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans,electronic ormechanical,includingphotocopying,recording,oranyinformationstorageandretrievalsystem, withoutpermissioninwritingfromthepublisher.Detailsonhowtoseekpermission,furtherinformation aboutthePublisher’spermissionspoliciesandourarrangementswithorganizationssuchasthe CopyrightClearanceCenterandtheCopyrightLicensingAgency,canbefoundatourwebsite: www.elsevier.com/permissions. Thisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightbythe Publisher(otherthanasmaybenotedherein). Notices Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchandexperience broadenourunderstanding,changesinresearchmethods,professionalpractices,ormedicaltreatment maybecomenecessary. Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluating andusinganyinformation,methods,compounds,orexperimentsdescribedherein.Inusingsuch informationormethodstheyshouldbemindfuloftheirownsafetyandthesafetyofothers, includingpartiesforwhomtheyhaveaprofessionalresponsibility. Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors, assumeanyliabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproductsliability, negligenceorotherwise,orfromanyuseoroperationofanymethods,products,instructions,or ideascontainedinthematerialherein. LibraryofCongressCataloging-in-PublicationData AcatalogrecordforthisbookisavailablefromtheLibraryofCongress BritishLibraryCataloguing-in-PublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary ISBN:978-0-12-809483-9 ForinformationonallButterworth-Heinemannpublications visitourwebsiteathttps://www.elsevier.com/books-and-journals Publisher:JoeHayton AcquisitionEditor:RaquelZanol EditorialProjectManager:AnaClaudiaGarcia ProductionProjectManager:MohanaNatarajan Designer:MarkRogers TypesetbySPiGlobal,India DEDICATION We dedicate this book to our loved ones. BIOGRAPHIES OF AUTHORS Dr. Stephen Gent is an associate professor of mechanical engineering at South Dakota State University. He has been engaged in a variety of theo- reticalandappliedresearchprojectspertainingtoproductandprocessreal- ization. These projects include developing torrefaction technologies for converting agricultural residues to value-added products, developing fast pyrolysisstrategiesforproducingbiooilfromnonfoodoilseedmeals,study- ing and computationally predicting the moisture release of corn in contin- uous flow drying for improved drying efficiency and throughput, developinganalyticaltoolsandprocessesforimprovingthedesignofsystems that grow algae for biofuels, and developing computational fluid dynamics modeling techniques for agricultural and biomedical applications, among others. He has an established publishing and funding record in which he has authored over 40 peer-reviewed publications and has been a PI or Co-PIonavarietyofprojectsfundedbytheNationalScienceFoundation, the US Department of Transportation, and private industry. Dr. Gent has taught a variety of courses in thermal-fluids science and energy systems, including thermodynamics, fluid mechanics, and computational fluid dynamics. Michael Twedt is a registered professional engineer and has been per- formingfeasibilitystudiesandanalyzingenergyandbioenergysystemssince 1992.Inthistimehehasconductedover400energyefficiencyandrenew- ableenergyintegrationassessmentsonregionalpublicandprivatefacilities. Mr. Twedt is the president of BTU Engineering, where he leads energy engineeringprojectsfocusedoninnovativeenergyefficiencyandrenewable energy systems. Mr. Twedt holds BS and MS degrees in mechanical engi- neering and has a passion for energy efficiency and renewable energy sys- tems. He teaches engineering courses at South Dakota State University andservesasthedirectorfortheEnergyAnalysisLabwhereheleadsnovel research projects dealing with energy conversion, wind energy develop- ment, bioprocessing, and bioenergy conversion such as torrefaction. Mr. Twedt has authored a number of published papers concerning bio- energy conversion and is a regular invited speaker on various energy and bioenergy topics. He has taught a variety of energy and systems-related mechanical engineering courses such as Renewable Energy Systems, xi xii BiographiesofAuthors Analysis and Design of Industrial Systems, Thermodynamics, HVAC Design, and Mechanical Systems Design. ChristinaGeromettaisaninstructorofmechanicalengineeringatSouth DakotaStateUniversity.SheobtainedherMSinMechanicalEngineering, with an emphasis on thermo-fluid systems, in 2014. During this time she researched the potential of corn stover to be used as a biochar for SDSU’s EnergyAnalysisLab,andassistedinconductingenergyassessmentsforsev- eralprivateandpublicfacilities.Asaninstructor,Ms.Geromettateachesthe Measurements and Instrumentation course and specializes in research that use analytical chemistry instruments in renewable energy applications. Evan Almberg is an engineer in the power and energy sector and brings experience from the design, maintenance, and analysis of industrial processing and distribution systems. Holding a MS and BS in mechanical engineering, along with specializations in Sustainable Energy Systems and Thermo-Fluids, Mr. Almberg has performed various research projects in the areas of bioenergy. These projects include investigating distributed torrefaction systems, producing pyrolysis biooils, and analyzing energy- intensive drying strategies. Mr. Almberg has coauthored technical papers focusingonthetopicsofthermochemicalconversionandagriculturaldrying approaches, performed comparative fuel studies of ethanol-blended fuels and conventional gasoline for the State of South Dakota Office of Fleet andTravelManagement,andalsooperatedlab-scaleprocessingandthermo- chemical reactor systems to produce value-added biooils at South Dakota State University’s Biofuels Laboratory. ACKNOWLEDGMENTS WewouldfirstliketothanktheDepartmentofMechanicalEngineeringat SouthDakotaState Universityandourdepartmenthead,Dr.Kurt Bassett, for accommodating us to complete this book and for providing laboratory space and resources to pursue our research and analytical efforts in torrefaction. Second, we would like to thank past and current students in our engi- neeringcourses.Theytrulymadeteachinganenjoyableexperienceandhel- pedusrealizetheimportanceofprovidingabalancedapproachinteaching theoreticalprinciplesandapplyingtheseprinciplestopracticewhiledevel- oping this book. We especially would like to thank all past and current students who worked closely with us on research activities, whether it was conducting experiments, developing simulations, collecting literature, or writing manuscripts. Their efforts were truly appreciated! Third, we would like to thank all our colleagues with whom we have pursuedourprofessionalendeavors.Wehaveengagedincountlessconver- sations,contemplatednumerousideas,andenjoyedgettingourhandsdirty intheprocess.Withouttheirtechnicalsupport,wewouldnotbewherewe are at today. Finally,wewouldliketothankourfamiliesandclosefriendswhohave provided unconditional support and love throughout our lives. We espe- ciallyliketothankMelissaGentandDawnTwedtforaddressingtheneeds at home while we spent countless nights, weekends, and holidays to write the book. We are truly blessed! xiii CHAPTER ONE Introduction to Thermochemical Conversion Processes The objectives of this chapter are to: (cid:129) Provideanintroductionanddefinebiomass,bioenergy,andvalue-added bioproducts, (cid:129) Review unit systems between SI and the English unit system that are incorporated in this text, (cid:129) Identifyandclassifytheprocessesforproducingbiofuelsandvalue-added products from biomass feedstocks, (cid:129) Summarize and contrast thermochemical processes, and (cid:129) Provide a historical perspective of torrefaction. 1.1 MOTIVATION—A NEED FOR SUSTAINABLE ENERGY AND PRODUCTS Our planet is estimated to have over 7.39 billion people as of early 2016.AccordingtoprojectionsbytheUnitedNations,thepopulationwill reach 10 billion by the year 2060. This exponential population growth is certainlyatestamenttoouradvancesinmechanization,automation,health care, and nutrition, among others. In addition, advances in transportation and communication have transformed our world to be highly intercon- nected, interdependent, and globalized. Progression of these technologies hasreliedgreatlyontheutilizationofnaturalresourcesforcreatingproducts and powering our society. Prior to the 20th century, most of our energy was derived from nonpetroleum sources, namely wood, coal, and animal- derived fats and oils. As the 20th century progressed, our energy sources evolved to use greater amounts of petroleum, and many of the products we use on a daily basis are derived from petroleum. Asoursocietyprogressesthroughthe21stcentury,therehasbeenagreat dealofconcernonhowourworldcanmeetthechallengesofprovidingthe energyandproductsinwhichwehavebecomeaccustomedallwhilebeing good stewards of our planet. The term sustainability has entered our TheoreticalandAppliedAspectsofBiomassTorrefaction ©2017ElsevierInc. 1 http://dx.doi.org/10.1016/B978-0-12-809483-9.00001-4 Allrightsreserved. 2 TheoreticalandAppliedAspectsofBiomassTorrefaction vocabulary as of late, so much that it is even being used in marketing and advertising for a variety of products. Many researchers, entrepreneurs, policymakers, and others have been pursuingseveralpathwaysandtechnologiesforaddressingthemonumental challenges of providing sustainable energy and products from biobased materials. Several pathways have focused on converting lower valued materials, e.g., municipal wastes, agricultural and forestry residues, grasses and energy crops raised on marginal land, etc., into higher value energy sources or value-added products. The production of biofuels and value-added products has two primary conversion pathways—biochemical and thermochemical. Biochemical conversion(commonintheproductionofethanolfromsugarcaneorcorn feedstocks) take place in controlled environments and relies on the use of enzymesandfermentationtobreakdownthefeedstockintoproductssuch as ethanol. Thermochemical conversion pathways, on the other hand, rely on chemical reactions that take place under controlled temperatures and pressurestoconvertthefeedstockintobiofuels,buildingblocksforbiofuels and value-added products. Despite the interest and advancements in technologies that promote sustainable energy and products, there have been numerous obstacles that need to be addressed. First, many of the proposed conversion technologies are quite involved and require large-scale processing plants to be econo- mically viable. The scalability of these processing plants, while inherently challenging, is possible. However, large-scale plants become increasingly complicatedtooperateandmaintain,whichrequirespecializedtechnicians, engineers, and managers. Second, which is related to the first, is that large, centralized processing facilities require large amounts of feedstock. What makesthisespeciallychallengingisthelogisticsaspectofharvesting,collec- ting, transporting, and preprocessing the feedstock even before it arrives at the facility for conversion. This book advocates a different pathway for producing value-added productsandfuels—torrefaction.Torrefaction,also knownasmild pyrolysis, is a thermochemical conversion process that introduces a solid feedstock within an elevatedtemperatureoxygen-limitedenvironment andupgrades it to a more energy dense, storable product. Torrefaction is achieved at a temperature of 200–300°C (392–572°F), in which the feedstock is slowly heated, causing the feedstock to release moisture and volatile gases. The end products include (1) a solid biochar material, similar to charcoal and (2) combustible off gases, commonly referred to as torr-gas, both of which IntroductiontoThermochemicalConversionProcesses 3 may be burned for thermal energy at a later time. A third product of torrefaction,wasteheat,maybeutilizedforacolocatedprocess.Asanadded benefit, all the end products of torrefaction are biobased and renewable. Torrefaction of biomass increases the energy density of the product, which can be stored indefinitely without spoilage or degradation while the excess lower-value, off gas may be burned for thermal energy and be utilized for other applications. Traditional torrefied materials, including biochar pellets derived from woody residues, have been investigated and utilized as an alternative to coal due to its similar material properties. Torrefied agricultural residues, energy crops, woody residues, and even municipal wastes have a similar potential for being a viable energy source while providing a pathway for producing value-added products. As explained later in the text, torrefaction is a pathway that can be employed in a rural environment (farmstead or community-based processingplant),whichgreatlyimprovesthelogisticsaspectsoftheproduct. Inaddition,torrefactiontechnologiesdonotrequireparticularlyspecialized equipment, especially when compared with fast pyrolysis, gasification, or biochemical systems. The remainder of this chapter will provide a brief overviewofbioenergy,biomassandthebioeconomy,andbiomassconver- siontechnologies.Inaddition,thischapterwillreviewcommonlyusedunits and terminology pertaining to torrefaction, thermochemical conversion technologies, and the history of torrefaction. 1.2 BIOBASED ENERGY AND PRODUCTS Bioenergyisasustainablealternativeenergyplatformthatisproduced through the conversion of biobased materials derived from organic matter. Collectively, these materials are referred to as biomass. Biomass is one of the largest contributors to sustainable energy production, accounting for an estimated 10% of the total global energy production [1]. Moreover, biomassiscurrentlytheonlyrenewableresourceavailablefortheproduction of biofuels (grain ethanol and biodiesel). The demand for biofuels and bioenergy is only expected to increase due to increasing energy demands and legislative actions. In the United States, the Energy Independence Act of 2007 (EISA 2007) mandates the production of 36 billion gallons per year (BGY) of biofuels by 2022 [2]. This act incorporates a revision totheRenewableFuelStandard(RFS),allocating14BGYtonextgenera- tion(nonfood)sources,suchaslignocellulosicbiomass.Fig.1.1outlinesthe
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