Agricultural and Biosystems EngineeringConference Proceedings and Presentations Agricultural and Biosystems Engineering

7-2014

Techno-Economic Analysis (TEA) of Low-Moisture Anhydrous Ammonia (LMAA)Pretreatment Method for Corn StoverMinliang YangIowa State University, minlyang@iastate.edu

Kurt A. RosentraterIowa State University, karosent@iastate.edu

Follow this and additional works at: http://lib.dr.iastate.edu/abe_eng_conf

Part of the Agriculture Commons, and the Bioresource and Agricultural Engineering Commons

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Techno-Economic Analysis (TEA) of Low-Moisture AnhydrousAmmonia (LMAA) Pretreatment Method for Corn Stover

AbstractTechno-Economic Analysis (TEA) plays an important role in assessing economic performance and potentialmarket acceptance for new technologies. Previous work has shown that the construction and operation of acellulosic bioethanol plant can be very expensive. One of the largest cost categories is pretreatmentprocessing. The purpose of this study was to conduct a detailed cost analysis to assess low moisture anhydrousammonia (LMAA) pretreatment process at the commercial-scale, and to estimate the breakeven point inlarge-scale production. In this study, capital expenses, including annualized purchase and installation fees, andannual operating costs associated with each unit operation were determined. This research compared the unitcost per year between different scales of the LMAA process, and focused on exploring the optimal cost-effective point for this pretreatment method for bioethanol production.

KeywordsTechno-Economic Analysis, LMAA, Commercial-scale

DisciplinesAgriculture | Bioresource and Agricultural Engineering

This conference proceeding is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/abe_eng_conf/391

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An ASABE – CSBE/ASABE Joint Meeting Presentation

Paper Number: 141910976

Techno-Economic Analysis (TEA) of Low-Moisture Anhydrous Ammonia (LMAA) Pretreatment Method for Corn Stover

Minliang Yang

Department of Agricultural and Biosystems Engineering, Iowa State University,

3326B Elings Hall, Ames, IA, 50011, minlyang@iastate.edu..

Kurt A. Rosentrater, Ph.D.

Department of Agricultural and Biosystems Engineering, Iowa State University,

3327 Elings Hall, Ames, IA, 50011, karosent@iastate.edu.

Written for presentation at the 2014 ASABE Annual International Meeting

Sponsored by ASABE Montreal, Quebec Canada

July 13 – July 16, 2014

Abstract. Techno-Economic Analysis (TEA) plays an important role in assessing economic performance and potential market acceptance for new technologies. Previous work has shown that the construction and operation of a cellulosic bioethanol plant can be very expensive. One of the largest cost categories is pretreatment processing. The purpose of this studywasto conduct a detailed cost analysis to assess low moisture anhydrous ammonia (LMAA) pretreatment process at the commercial-scale, and to estimate the breakeven point in large-scale production. In this study, capital expenses, including annualized purchase and installation fees, and annual operating costs associated with each unit operation were determined. This research compared the unit cost per year between different scales of the LMAA process, and focused on exploring the optimal cost-effective point for this pretreatment method for bioethanol production.

Keywords. Techno-Economic Analysis, LMAA, Commercial-scale

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Introduction

Withanincreasingdemandforenergy,moreandmoreresearcheshavebeenfocused

onbioethanolproduction.Bioethanol,apromisingreplacementoffossilfuel,canbe

obtainedfromlignocellulosicbiomass,suchasenergycropsandresiduesfromarableland

(Singhetal.,2010).Typically,ethanolproductionfromlignocellulosicbiomassfollows

severalsteps:pretreatment,enzymatichydrolysis,fermentationofsugar,andethanol

recovery(Alviraetal.,2010).Amongtheethanolproductionprocess,pretreatmentis

regardedasthecriticalstepbecauseitisrequiredforefficienthydrolysis.Various

pretreatmentmethodshavebeendeveloped,suchasdiluteacid,hotwaterextraction,and

ammoniafiberexpansion(AFEX).Eachmethodhasitsownadvantagesanddisadvantages.

Ammoniahasbeenchosenbecauseofitsdelignificationeffect(Kim&Lee,2007)and

swellingeffect(Mosieetal.,2005).In2011,anewmethodnamedlowmoistureanhydrous

ammonia(LMAA)hasbeenperformedinlabscale(Yooetal.,2011).Intheirstudy,LMAA

processresultedin89%ofthemaximumtheoreticalethanolyieldandshowedthe

potentialtodecreaseammoniaandwaterinputscomparedwithotherpretreatment

methods.

ThetechnicianreportpublishedbyNRELin2010entitledTechno‐economicanalysisof

biochemicalscenariosforproductionofcellulosicethanolcomparedfourdifferentmodelsof

pretreatmentprocessing(diluteacid,two‐stagediluteacid,hotwater,andammoniafiber

expansion(AFEX))(KabirKazietal.,2010).Itwasconcludedthatwithoutanydownstream

processvariation,diluteacidprocesshadthelowestproductvalue(PV)of$3.40/galof

ethanolin2007,whichwasequivalentto$5.15/galofgasoline.Oneyearlater,in2011,

theNationalRenewableEnergyLaboratory(NREL)haspublishedanothertechnicalreport

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entitledProcessdesignandeconomicsforbiochemicalconversionoflignocellulosicbiomass

toethanol(Humbirdetal.,2011)focusedondiluteacidpretreatmentprocess.Inthat

report,detailedbioethanolconversiondesignwasbuiltoneightspecificareas.The

minimumethanolsellingpricereportedfromNRELwas$2.15/gal,whichwasequivalent

to$3.27/galgasoline.Whenbrokedownintoprocesssections,$0.74/galwascontributed

fromthefeedstock,enzymeandwastewatertreatmenteachcontributed$0.34/gal,and

therest$0.73/galwascontributedfromtheremainingconversionprocessareas.Even

thoughthesellingpricewasstillhigherthanmarketprice,thelatteronewas$0.13/gal

lowerthanprevious.

Withtherecentdevelopmentofpretreatmenttechnologyandupdatedcostestimation,

anupdatedtechno‐economicanalysisofbiofuelproductionwasrequired.Asfarasthe

authorsknow,costanalysisbasedonlow‐moistureanhydrousammonia(LMAA)

pretreatmenthasnotbeenpublishedinanyjournalsyet.Thisresearchisfocusedon

estimatingunitcostsofbioethanolproductionbasedonLMAApretreatmentprocess,and

comparingitamongthreedifferentproductionscales.

Methods

Thisstudybeganbydevelopingprocessflowdiagrams(figure1),andalltheeconomic

andenvironmentalanalysiswerethencalculatedinanexcel‐basedspreadsheetwithan

accuracyof±30%(Coker,2010).Thewholeprocesswasdividedintosixsections:

feedstockhandling,ammoniationprocess,incubationprocess,simultaneous

saccharification&co‐fermentation(SSCF)process,evaporationprocess,andcombustor/

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burner.Wastewatertreatment,biomassandethanolstoragewerenotconsideredinthis

research.

ThisstudywasaderivativeestimationfromtheNREL’sreport(Humbirdetal.,2011).

What’smore,thecalculationwasbasedonaplantsizeof2,000metrictonne(MT)ofcorn

stoverperday;theothertwoscaleswere100MT/dand800MT/d,respectively.The

followingexponentialexpressionwasusedforscaling,inwhichtheexponentwasassumed

tobe0.6(Aden,etal.,2002).

Thisbioethanolplantwasassumedtowork24hoursperday,7daysperweek,and45

weeksannually,whichwas315onlineprocessingdayperyear.Themainproductofthe

plantwasethanol,andelectricitywasgeneratedasaby‐product.Othermajorassumptions

werelistedintable1below.

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Table1.Generalassumptions.

Feedstockcostis$36.25/drytonne.a

TheplantislocatedinthecenterofcornfarmlandinIOWA.

Electricitypriceis$0.0062/kWh.b

Waterpriceis$0.027/ft3.c

Powerefficiencyforequipmentisassumedtobe85%.

Heatlossisnotaccountedforintheenergybalancecalculations.

Buildingcostisnotconsideredinthisreport.

Constructiontimeandstart‐upperiodarenotconsidered.

Laborfeeisnotconsideredinthisreport.

Noleakagehappensduringthewholeprocess.

Insuranceandtaxareestimatedtobe1.5%oftheinstalledprice.

Annualinterestis6.0%inUSBank.d

Equipmentlifeexpectancyis10years.

Plantlifeis20years.

Electricalwiringandcontrolsfeeisassumedtobe4%ofthepurchaseprice.

Equipmentfreightisassumedtobe1%ofthepurchaseprice.

Overheadfeeis$0.16/ton.

Maintenanceandrepaircostareassumedtobe2%oftheinstallationfee.

Enzymepriceis$2/kg.ea. Availableat:http://msue.anr.msu.edu/news/corn_stover_what_is_its_worthb. Availableat:http://www.cityofames.org/index.aspx?page=113c. Availableat:http://www.cityofames.org/index.aspx?page=355d. Availableat:https://www.usbank.com/calculators/jsp/MortgageCompare.jsp#3e. Availableat:http://www.alibaba.com/showroom/cellulase‐enzyme.html

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Figure1.Overallprocessflowdiagram.

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Techno‐EconomicAnalysis(TEA)

TheTEAofthewholeprocesswasanalyzedforeachofthesixsections

mentionedinpreviousstudy.Equipmentcostswereobtainedfromindustry

quotationsandpreviousNRELreport(Adenetal.,2002).

Feedstockhandling

Thefeedstockusedinthisstudywascornstover.Table2showedthe

averagecomposition(%drybasis)ofcornstoverbasedonNRELstudies

(Humbirdetal.,2011).Inthisstudy,89%oftheglucosewasconvertedinto

ethanolfollowingthereaction: → 2 2 ,whichindicated

thattheyieldoftheethanolwas0.45gethanol/gglucose.Cornstoverwas

deliveredinbalesandthecostwas$36.25/dryton(Pennington,2013).

Table2.Cornstovercomposition.

Components  Composition (%) 

Extractives  14.65 

Glucan  35.05 

Xylan    19.53 

Galactan  1.43 

Arabinan  2.38 

Mannan  0.60 

Lignin  18.00 

Ash  4.93 

Acetate  1.81 

Protein  3.10 

Sucrose  0.77 

Moisture  20.00 

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Asfigure2showed,cornstoverbaleswerereceivedbybeltconveyors,

includingtransportconveyorsandunwrappingconveyors.Thentheunwrapped

feedstockistransporttohammermillwherethesizeofthematerialwas

reducedandbecamemorehomogeneous.

Sincetheplantsizewas2,000MT/d,twolinesofthetransportconveyorand

unwrappedconveyorswiththecapacityof45tons/hrwereusedtoreceivecorn

stover.Thenthestoverwasintroducedintothehammermillwiththecapacityof

75tons/hr.Waterwassprayedonthebiomassduringtransportingprocessto

washdirt,yettheamountwasnotconsideredhere.

LMAAPretreatmentandincubation

Beforegroundcornstoverwascontactedwithanhydrousammonia,

hydrolysateprocesswasconductedinordertoremoveaceticacidandpartof

furfural,whichmaybetoxictodownstreamfermentationmicroorganisms(Aden,

etal.,2002).Ammoniationwasdesignedfor20minutesofresidencetime,and

ammonialoadingwas0.1gammonia/drymatterbiomass.Ammoniatedstover

Figure2.Feedhandlingprocess

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wasthentransferredintoincubationtankfor3.5days.Afterincubation,solids

wereusedforsaccharificationandco‐fermentationprocess.Otherassumptions

forpretreatmentconditionswerelistedintable3below.Figure3and4werethe

flowchartsrepresentingtheammoniationandincubationprocess.SurplusNH3

fromincubationtankwasrecycledtoammoniationtank.

Table3.Pretreatmentconditions.*

Ammonialoading 0.1gNH3/DMbiomass

Waterloading 1g/DMbiomass

Residencetime 20minutes

Solidsintheammoniation 70%

Incubationtemperature 80°C

Incubationtime 3.5days(84hrs)

*Reference:Yooetal.,2011.

Note:DMdenotesdrymatter.

Figure3.Ammoniationprocessflowdiagram.

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Figure4.Incubationprocessflowdiagram.

Thewashedandgroundcornstoverwasfedtotwoscrewconveyorswith

fourwaterpumpsforhydrolysisinthisprocess.Thentwoholdtankwiththe

capacityof15,000galeachwereusedbecauseofammoniationresistancetime.

Foreveryhalfanhour,stoverwasfedtotheammoniationtank.Anhydrous

ammoniawasinletintothetankbytwopumps.Afterthis,ammoniatedcorn

stoverwastransferredinto10incubationtankswiththecapacityof100,000gal

each.Hydrolysatefromincubationwasdeliveredtosaccharificationprocessby

fourbeltconveyors.Wastewaterwascollectedandtreatedwithbothanaerobic

andaerobicdigester,whichwillnotbediscussedinthisstudy.

Saccharificationandco‐fermentationprocess

Hydrolysatefrompretreatmentwasfedtothesaccharificationtankalong

withenzymes.Aftersaccharification,themicroorganismZ.mobilis,grownina

seedtank(figure5),wasusedasthebiocatalystinthefermentationprocess.

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Then,theseedinoculum,nutrients,andsaccharifiedslurrywereaddedtothe

ethanolfermenter(figure6).

Figure5.Seedproductionprocessflowdiagram.

Figure6.Saccharificationandco‐fermentationprocessflowdiagram.

Inthesaccharificationprocess,five1,000,000‐gallontankswereused.The

enzymeloadingwascalculatedbasedonthecellulosecontentandtarget

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hydrolysisconversionlevel.Acoolerwasusedforsaccharifiedslurry.Other

assumptionswerelistedintable4below.

Table4.Saccharificationconditions.*

Temperature 65°C

Residencetime 2days

Celluloseloading 12FPU/gcellulose

Numberofcontinuoustrains 1

*Reference:Adenetal.,2002.

Intermsofseedproductionprocess,10%ofthesaccharifiedslurrywassent

forseedproduction(Adenetal.,2002).Twotrainswereusedforturn‐around

timeforeachseedfermenterfor12hours;fivefermenterswereneededineach

train.Otherassumptionswerelistedintable5below.

Table5.Seedproductionconditions.*

Numberoftrains 2

Numberoffermenter 5/train

Maxfermentervolume 10,000L

Minfermentervolume 100L

Cornsteepliquorlevel 0.5%

Diammoniumphosphatelevel 0.67g/Lbroth

*Reference:Adenetal.,2002.

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Fermentationprocesswasconductedinfive1,000,000‐galethanol

fermenters.Thetotalresidencetimewasassumedtobe36hours.The

fermenterswerecooledbeforedistillationandevaporationprocess.Table6

listedtheassumptionsusedinthefermentationprocess.

Table6.Fermentationconditions.*

Microorganism Z.mobilis

Residencetime 36hrs

Numberoffermenter 5

Temperature 41°C

Cornsteepliquorlevel 0.25%

Diammoniumphosphatelevel 0.33g/Lbroth

*Reference:Adenetal.,2002.

Evaporation

Duringthisprocess,molecularsievesanddistillationwereusedforethanol

recovery.Figure7belowrepresentedthisprocess.

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Figure7.Distillationandevaporationprocessflowdiagram.

Fivebeercolumnswiththecapacityof1,000Lwereusedindistillation

processtoremovethedissolvedCO2andmostofthewater.Theethanolwas

collectedasvaporfromthebeercolumnandfedtorectificationcolumn. After

rectification,overheadvaporofethanolwasgiventomolecularsieveadsorption

unit.Nicepieceswerecontainedinthisunit,suchasproductcooler,condenser,

andmolecularsievecolumns.Themixturewascondensedandreturnedtothe

rectificationcolumn.

Liquidsfrombeercolumnwassenttothe1stevaporator,about24%ofthe

waterenteringcouldbeevaporated(Adenetal.,2002).Thentheslurrywasfed

tothe2ndevaporator,about44%ofthewatercouldbeevaporated.The3rd

evaporatorcouldevaporatenearly76%ofthewater.Thefinalvaporwas

condensed,andsolidsweresenttoburner.

Combustor/burner

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Thepurposeofthisprocesswastoburnsolidsorby‐productsdownstream

forelectricitygeneration.Alltheremainingligninandhemicellulosefromthe

feedstockwereburntinthefluidizedbedcombustor.Ageneratorwasusedto

generateelectricity.Theflowdiagramofthisprocesswasshowninfigure8.

Figure8.Burningprocessflowdiagram.

ResultsandDiscussion

Thetechno‐economicanalysis(TEA)ofthecellulosicethanolplantwas

conductedonthreedifferentscalesbasedoncornstovercapacity:100MT/d,

800MT/dand2,000MT/d.Resultsshowedthatthelargertheplantscale,the

lowertheproductcost,whichwasillustratedinfigure9.Theapproximate

ethanolyieldperyearincompatiblewiththecornstovercapacitywas2.5

MMgal/y,20MMgal/y,and50MMgal/y,respectively.Thelowestcostofethanol

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was$3.86/galforacommercialplantof50MMgalethanolyieldperyear,which

wasstillhighercomparedwithmarketgasolineprice($3.704)(U.S.Energy

InformationAdministration,2014).However,thiscostwouldbemuchhigherin

realcommercialscalesincethewastewatertreatment,storagecost,andutility

costwerenotconsideredinthisstudy.Intermsofthesmallscaleethanolplant

(2.5MMgal/y),theethanolcostwouldbe$5.08/gal;and$4.28/galformedium

scaleethanolplant(20MMgal/y).

Figure9.Costperunitethanolindifferentscales.

Intermsofcostpertonoffeedstock,asshowninfigure11,thelargerthe

plantsize,thelowertheunitcost.Forsmallscale,thecostperunitfeedstockwas

$451.27;formediumscale,itdecreasedto$380.85;and$342.79/tonofcorn

stoverforlargescaleethanolproduction.

$5.08

$4.28$3.86

$‐

$1.00

$2.00

$3.00

$4.00

$5.00

$6.00

0 500 1000 1500 2000 2500

Cost($/gal)

Ethanolplantscale(MTcornstover/d)

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Figure10.Costperunitfeedstockindifferentscales.

Detailedreportforthe2000MTcornstover/dplantwithethanolproduction

of50MMgal/ywasshownintable7.

Table7.TEAreportof50MMgal/yethanolproductionplant.

$451.27

$380.07$342.79

$‐

$50.00

$100.00

$150.00

$200.00

$250.00

$300.00

$350.00

$400.00

$450.00

$500.00

0 500 1000 1500 2000 2500

Cost($/ton)

Ethanolplantscale(MTcornstover/d)

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Detailedreportforthe800MTcornstover/dplantwithethanolproduction

of20MMgal/ywasshownintable8.

Table8.TEAreportof20MMgal/yethanolproductionplant.

Detailedreportforthe100MTcornstover/dplantwithethanolproduction

of2.5MMgal/ywasshownintable9.

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Table9.TEAreportof2.5MMgal/yethanolproductionplant.

Conclusions

Inthisstudy,thecellulosicbioethanolplantbasedonsixmajorprocessing

sectionswasbuiltinthreedifferentscales:100MTcornstover/d,800MTcorn

stover/d,and2,000MTcornstover/d.Afterthetechno‐economicanalysis,the

resultshowedthatthelargertheethanolplant,thelowertheunitcostbothin

$/galofethanoland$/tonoffeedstock.However,theminimumethanolselling

costobtainedfromthisstudywasstillhighcomparedwiththecurrentgasoline

price.Inordertofurtherreducetheunitcosttomakebioethanolmore

competitive,improvementsinprocessdesignandethanolconversionrateneed

tobemade.Asthedevelopmentofbiorenewableenergyindustryandthe

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techno‐economicanalysis,lowerpriceinbioethanolcouldbeachievedinthe

nearfuture.

Acknowledgements

This study was funded by the United States Department of Transportation, under

contract DTOS59-07-G-00054.

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