Gasification and gasifier

principle of gasification, gasification process, gasifier, types of gasifier

1. Subject: Renewable Energy
and Green Technology
Topic: Gasification &
Gasifier
by
Dr. Sanjay Singh Chouhan
Assistant Professor
College of Agriculture, JNKVV,
Powarkheda, Hoshangabad

2. Principles of Gasification
•Gasificationisdefinedastheconversionofbiomassintoa
gaseous-energycarrierbymeansofpartialoxidationatthe
elevatedtemperature.
•Thisprocessinvolvesasequenceofchemicalandthermal
reactionsliketheoxidationandreduction.
•Gasificationprocessconvertsolidbiomasswithalimitedquantity
ofairintoProducergas.

3. Producer Gas
•Producergas,thegasgeneratedwhenwood,charcoalorcoalis
gasifiedwithair,consistsofsome40%combustiblegases,mainly
carbonmonoxide,hydrogenandsomemethane.Therestarenon-
combustibleandconsistsmainlyofnitrogen,carbondioxideandwater
vapor.
•Producergasisamixtureofcombustible{Hydrogen(13-19%),Methane
(1-5%)andCarbonMonoxide(18-22%)}andnon-combustible{Nitrogen
(45-55%),Carbondioxide(9-12%)}gases.
•Theproducergashasacalorificvaluerangingfrom1000to1200
kcal/Nm
3
.
•Thegasalsocontainscondensabletar,acidsanddustasimpurities.
Theseimpuritiesmayleadtooperationalproblemsandabnormalengine
wear.

4. Gasification Process

5. Important Parameters Affecting the
Gasification
1.Shape and size of the biomass fuel
and fuel bed structure,
2.Moisture content
3.Volatile matter content
4.Ash content
5.Ash composition, its moisture cont.
6.Energy content

6. Disadvantage
1.Thegasificationsystemhastobe
designedspecificallytosuit
thermo-chemicalcharacteristics
ofbiomass,
2.Thetechnologyismore
complicatedthan direct
combustionprocess.

7. Gasification Process of Biomass

8. Gasification Reactions
1.ThedehydrationorDryingprocessoccursataround100-150°C.
Typicallytheresultingsteamismixedintothegasflowandmaybe
involvedwithsubsequentchemicalreactions.
2.ThePyrolysisprocessoccursataround200-500°C.Volatilesare
releasedandproducedcharandgaseousproduct(CO,CO
2,H
2and
hydrocarbon)resultinginupto70%weightlossforcoal.
3.Inoxidationzone,thecombustionprocessoccursasthevolatile
productsandsomeofthecharreactwithoxygentoprimarilyform
carbondioxideandsmallamountsofcarbonmonoxide,which
providesheatforthesubsequentgasificationreactions.

9. 4.IntheReductionzone,otherreactionslikestem-carbon,water-
gasshiftandlimitedextenthydro-gasificationandmethanation
reactionstakesplacewhichbalancestheconcentrationsof
carbonmonoxide,steam,carbondioxideandhydrogen.

10. Pyrolysis of
Carbonaceous Fuels
Gasification of Char

11. Thermo-chemical Process in Gasifier

12. Types of Gasifiers
1) Fixed -bed gasifiers
A.Updraft gasifiers
(Counter current)
B.Downdraft gasifier
(Co-counter current)
C.Crossdraftgasifier
(Cross current)
2) Fluidized -bed gasifiers.

13. Updraft Gasifier

14. Updraft gasifier
•Airflowisupwardandthegasleavesatthetop.
•Nearthegrateatthebottomthecombustionreactionsoccur,
whicharefollowedbyreductionreactions.
•Intheupperpartofthegasifier,heatingandpyrolysisofthe
feedstockoccurasaresultofheattransferbyforcedconvection
andradiationfromthelowerzones.
•Thetarsandvolatilesproducedduringthisprocesswillbe
carriedinthegasstream.
•Ashesareremovedfromthebottomofthegasifier.

15. Advantage of updraft
1.Itissimpleindesign.
2.Ithasclearlydefinedzonesforvariousreactions
3.Itsefficiencyisveryhighbecausehotgasespassthroughentire
fuelbed.
4.Highcharcoalburn-outandinternalheatexchangeleadingto
lowgasexittemperatures.
5.Thepossibilityofoperationwithmanytypesoffeedstock
(sawdust,cerealhulls,etc.).
6.Thegasisusedfordirectheatapplications,inwhichtarscan
simplyburnt.

16. Disadvantage
1.Unsuitableforhighvolatilefuels.
2.possibilityofcloggingintheequipment,whichcanleadto
oxygenbreak-throughanddangerous,explosivesituations.
3.Necessitytoinstallautomaticmovinggrates.
4.theproblemsassociatedwithdisposalofthetarcontaining
condensatesthatresultfromthegascleaningoperations.

17. Downdraft
Gasifier

18. Downdraft Gasifier
•Asolutiontotheproblemoftarentrainmentinthegasstream
hasbeenfoundbydesigningco-currentordowndraught
gasifiers
•Primarygasificationairisintroducedatorabovetheoxidation
zoneinthegasifier.
•Theproducergasisremovedatthebottomoftheapparatus.

19. Advantage
1.Themainadvantageofdowndraughtgasifiersliesinthe
possibilityofproducingatar-freegassuitableforengine
applications.
2.Downdraught gasifiers suffer less from environmental objections
than updraught gasifiers.
Disadvantage
1.Thegasleavesatrelativehightemperature,hencegasifier
efficiencyisless.
2.Notsuitableforhighashfuels,highmoistureandlowashfusion
temperature.

20. Cross-draft
Gasifier

21. Cross-draft gasifier
•Cross-draughtgasifiersareanadaptationfortheuseofcharcoal.
•Charcoalgasificationresultsinveryhightemperatures(1500°C
andhigher)intheoxidationzone.
•Incrossdraughtgasifiersinsulationagainstthesehigh
temperaturesisprovidedbythefuel(charcoal)itself.
•Inacross-draftgasifier,airisfedintothegasifierthrougha
horizontalnozzle
•Theresultingfuelgasisdischargedthroughaverticalgrateonthe
oppositesideoftheairinjectionlocation.

22. •Thebiomasscanbefedtothegasifiereitherfromthetopor
fromtheside.
•Thereactionsinthecross-draftgasifieraresimilartothe
downdraftgasifier.
Advantage of crossdraft
1.Gatenotrequired.
2.Singleairblower
3.Ashformedduetohightempraturefalltothebottomanddoes
notrequirecleaningoperation.
Disadvantage
1.Thegasleavesatrelativehightemperature,hencegasifier
efficiencyisless.

23. Fluidized bed gasifier
•Theoperationofbothupanddowndraughtgasifiersis
influencedbythemorphological,physicalandchemical
propertiesofthefuel.
•Problemscommonlyencounteredare:lackofbunkerflow,
slaggingandextremepressuredropoverthegasifier.
•Adesignapproachaimingattheremovaloftheabove
difficultiesisthefluidizedbedgasifier.

24. Fluidized bed Gasifier

25. •Ingeneral,thefluidizedbedgasifierisatallrefractorylinedunit.
•Theheighttodiameterratioofafluidizedbedreactoris10:1.
•Theinertmaterialslikesandorashmaybeusedasafluidizing
medium.
•Airisblownthroughabedofsolidparticlesatasufficientvelocity
tokeeptheseinastateofsuspension.
•Thebedisoriginallyexternallyheatedandthefeedstockis
introducedassoonasasufficientlyhightemperatureisreached.
•Thisfuelparticlesquicklymixedwiththebedmaterialandalmost
instantaneouslyheateduptothebedtemperature.
•Asaresultofthistreatmentthefuelispyrolysedveryfast,

26. •Mostsystemsareequippedwithaninternalcycloneinorderto
minimizecharblow-outasmuchaspossible.
•Ashparticlesarealsocarriedoverthetopofthereactorand
havetoberemovedfromthegasstreamifthegasisusedin
engineapplications
•Theoutputofabiomassgasifiercanbeusedforavarietyof
directthermalapplicationssuchascooking,drying,heating
water,andgeneratingsteam.
•ItcanalsobeusedasafuelaftercleaningforI.C.Enginesto
obtainmechanicalshaftpowerorelectricalpower.
•Theconversionefficiencyofagasifierisusuallyaround75%.

27. Thanks for listening…..
JNKVV-College of Agriculture, Powarkheda 27