Theoretical and Applied Aspects of Biomass Torrefaction. For Biofuels and Value-Added Products

213 Pages·2017·11.64 MB·English

by  Stephen Gent

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
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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