CaseStudy– utilisingbiogasforprocessheat

BiogasfromHeatusingFoodProcessingWaste/AgResiduesBioenergyAustraliaBiogasWorkshops

PresentationContent

• ManagingH2S– doyouneedpretreatment?• Gastrain– whatsafetydevicesarerequired?• Dualfuelboiler– howtooperatethroughoutcycle?

WheredoesH2Scomefrom?

• Q- WhatcausesH2S?• A– SulphurcompoundswhenanaerobicallydigestedwithasourceofhydrogenandsulphatereducingbacteriawillpreferentiallydecomposetohydrogensulphidebeforemethanogenicbacteriacanmakemethaneorCO2.

• Q– Wheredothesulphurcompoundscomefrom?• A– DigesterFeedstock(cellularmatter,solubleforms),CIPchemicals

• Q– Howtominimisepriortoconsideringpretreatment?• A– MinimisesulphurcompoundsinCIPchemicals,sourcesegregateveryhighstreamsifpossible.

TypicalbiogasH2Sconcentrations

• Brewerywastewater– 2,000ppm(1,000ppmwithacampaigntoreducesulphurinCIPchemicals)• Pulpandpaperwastewater– 15,000– 25,000ppm• Municipalsludgedigestion– 1,000– 3,000ppm• Dairy– 1,000– 4,000ppm• Abattoirbiogas– 1,000– 10,000+ppm(highlydependentonprocessingandanimal)• Agriculturalwastebiogas(highlydependentonfeedstock)– 3,000–10,000ppm

• IfH2Sisconsistentlyabove2,000ppm,pre-treatmentisadvisable

UnderstandingSOx corrosion• Keycombustionequationsforbiogas

1.)CH4 +2O2 ->CO2 +2H2O2.)H2S+O2 ->SO2 +H2O3.)SO2 +H2O->H2SO3

CorrosionoccurswhenH2SO3 condensestoH2SO4(Sulphuricacid)

• CorrosionissueswithbiogasatH2Sconcentrationsof2,000ppmcanbemanagedifburnsequenceiscontrolled

• However- CheckthatstackemissionSOx limitsarenotexceeded

• Understandingsulfuricaciddewpointminimum~130Cfromgraphabove.

• ExtremelyimportantforheatrecoverymoduleinCHP– H2Spretreatment iscriticaltopreventcorrosionbyexhaustgases

DualFuelBoiler– startup sequence

• Dualfuelisidealastheinitial1hourofoperationutilisesaH2Sfreefueltogetthestacktemperatureabove130C.

SO2 +H2O->H2SO3(remainsingasphase)

• Oncestacktemperatureisabove130Csulfuricacidwillnotcondense– switchfuelsourcetobiogas• Boilerbackupfuelsourcerequiredregardlessforredundancy• LPG,LNG,CNGallgoodoptions

DualFuelBoiler– shutdownsequence

• Iffuelisblendedinasingleburner,ensurebiogasisnotusedoverthelast30minutestopurgeanyremainingSox inline• Ideallyalsopurgethebiogaslinewithnaturalgastopreventdamagetofeedpipeworkwhenoffline• Flarebiogaswhenbiogasisavailableandheatorpowerisnotrequired• SameconsiderationsforCHPengineapplications– exhaustgastemperatureinheatrecoverymoduleshouldnotbebroughtdowntoolowwithoutcompletepre-treatmentforH2Sremoval.

KeyBiogasTrainequipment

• BoilersandburnermanagementsystemsareregulatedunderAS2593,AS1228.Therearesomeconcessionsifitisahotwaterratherthansteamboiler• OtherdevicescoveredbyTypeBAS3814• Biogastrainfromthecollectionpointtoboilershouldinclude:condensatetrap,biogasblower,biogasregulator,flowmeter,pressuretransmitter,isolationvalves,doubleblockvalvewithleakdetection• Chillingmayberequiredtoreducedewpointhowevercanbemanagedifpipingdistancebetweenblowerandboilerisshortandapositivedisplacementblowerisused• IfH2Sisgreaterthan2,000ppm,pretreatment likelyadvisableviaeitherThiopaq,ironspongeoractivatedcarbon(dependingonconcentration)

ThankYou

• Pleasecomeandsayhelloafterwards!

• Anyquestions/enquiries- Digestionequipment,biogastreatment,CHP

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