Risks and Best Practices Associated with Syngas in Drum Dryers · Risks and Best Practices...

Risks and Best Practices Associated with Syngas in Drum Dryers

Prepared by Aon Risk Solutions / Cariboo Biomass Consulting ServicesGlen Visser, P.Eng, Aon Risk Control Services / Kevin Ericsson, PE, Chief Engineer, UNBCPresentation to Wood Pellet Safety Conference and Workshop – Safety in Action

Aon Risk Solutions (Mandatory) | Department/Practice (Optional)Proprietary and Confidential (Optional) | Date (Optional) 2

Biographies

Glen Visser, P.Eng., ARM, Sr Risk Control ConsultantAon Risk Solutions, VancouverConsiderable design and consulting experience in Pulp and Paper, Biomass Systems, Mechanical Systems, Fire Suppression, and Risk Management.

Aon Risk Solutions 3

Syngas


Definitions

“A definition is the enclosing a wilderness of idea within a wall of words.” Samuel Butler, 19th Century English author and poet.

§ Syngas (EnggCyclopedia) - Syngas is a mixture of Carbon Monoxide and Hydrogen which is the product of steam or oxygen gasification of organic material such as biomass. After clean up, syngas can be used to produce organic molecules such as synthetic natural gas (SNG-methane (CH4)) or liquid biofuel such as synthetic diesel. Syngas is the term generally used for mixture of combustible gases. So typically a syngas mixture will constitute of only hydrogen and carbon monoxide, with possibility of having carbon dioxide content sometimes. If the gasification product contains significant amount of non-combustible gases such as nitrogen and carbon dioxide, the term used for such mixtures is 'Producer Gas'.

– * note: The heating value of syngas varies from 11 to 18 MJ/m3 depending upon its constituents.

§ Producer Gas (EnggCyclopedia) - Producer gas is a mixture of combustible (Hydrogen, Methane and Carbon Monoxide) and non-combustible (Nitrogen, Carbon dioxide) gases. The heating value of producer gas varies from 4.5 to 6 MJ/m3 depending upon its constituents. Similar to syngas, producer gas is also produced by gasification of carbonaceous material such as coal or biomass. When atmospheric air is used as gasification agent, the producer gas consist mostly of carbon monoxide, hydrogen ,nitrogen, carbon dioxide and methane.

** note: heating value of natural gas varies from 35 to 43 MJ/m3


Definitions

§ Biomass Gasification (GSTC – Gasification and Syngas Technology Council) - The conversion of biomass or biosolids (sewage) into a gas that can be used to produce electricity and products. Biomass gasification differs in several aspects from traditional gasification. The plants are generally smaller in scale, use air instead of oxygen (or use plasma gasification) and require that the biomass be dried before being gasified.

§ Pyrolysis (Wikipedia) - Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen (or any halogen). It involves the simultaneous change of chemical composition and physical phase, and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating". Pyrolysis is a type of thermolysis, and is most commonly observed in organic materials exposed to high temperatures. It is one of the processes involved in charring wood, starting at 200–300 �C (390–570 �F)….


General Hazards

Off-Gassing (Low temperature)§ Any mass of wood accumulation

– Chip piles, Silo storage, Transport– In process – conveyors, dryers, metering and surge bins

§ Enhanced risks:– Species– Particle size– Biological processes / Microbial decay– Residence time– Heat, moisture– Containment

§ Hazards– Environmental – VOC release– Oxygen depletion– Toxicity– Fire / explosion– Buildup of tars


General Hazards

Gasification (High Temperatures)§ Pyrolysis / Combustion

– Produces …§ Enhanced risks:

– Heat, moisture content– Presence of air / oxygen– Fuel concentration (LEL/UEL)

§ Hazards– Environmental– Oxygen depletion– Toxicity– Fire / explosion– Hot exhaust gases


General Hazards

Wood Dust§ As produced

– Hammer mill– Saws

§ Wood breakdown– Long resident times in dry conditions

§ Hazards– Fire / Explosion (secondary & primary)– Layering causes over heating of electrical

equipment– Plugging of equipment / expansion when

moisture added


General Hazards

Ignition Sources§ Sparking

– Metals / stones / debris carried through ducting– Mechanical failures

§ Static Discharge– Ungrounded/unbonded equipment / ducting

§ Mechanical Equipment– Hot operating surfaces

§ Electrical Equipment– Over heating

§ Smoking– By employees, contractors, truck drivers

§ Smouldering / Fire flareups– Chip / hog / sawdust piles– Carried forward into process

§ Direct Firing – burners– Open flames or hot gases

HowisSyngasrelatedtothePelletindustry?Whyimportanttoday?

• NotjustPelletindustry– anyprocesswhereheatisappliedtowood.Plywooddryers,OSB&MDFdryers,evenindustrialwoodfurnaces.

• HistoryofA.S.M.E.

• Copyright- CaribooBiomassConsultingServices

Equipmentmaintenance

WoodPelletPlantProcess

GasBurner

• Safetyinterlockscanbebypassed.EG:Flamedetectorunreliable.

• Gasburnerassemblynotinspectedregularlybyregulators.

• Combustionairsupplydamperscanovertimebecomeoutofcalibration.


WoodFiredEnergySystem

• Combustionairsupplyportscanbecomecloggedduetoslag/klinker buildup

• Causesthecombustortoburninefficiently• Sendsmorethannormalsparkstobecarriedoverintothedryingsystem

• Causesissueswiththedryingsysteminthatmorethannormalsparkscanbedetectedbythedryersparkdetectionsystemcausingextrawatertobesprayedintothedryeroutlet.


WoodFiredEnergySystem(continued…)

• Extrawaterresultsin…• Woodfiberthatisoutofspecortoomoist,whichinturncancausethedryeroperatortoaddmoreheattothedryerinanattempttodryoutthefiberandgetthemoisturebackwithinspec.

• Woodfiberthatwilllaydowninsidethedryerdischargepiping,causingadominoeffectandincreasedbuilduptothepointthatthedryerhotgasflowbecomesrestrictedcausingfibertostayinthedryerdrumtoolongwhichwillcauseadryerfire.

• Toomuchwateraccumulatinginthedryerdrumfromthedryersystemdelugewillcausethedryerdrumdrivetotriponoverload.Thiscancausethedryerdrumtowarpduetometalfatiguefromoverheating.


Dryerinfeed airlock

• Airlockcanjamsuddenlyfromtoomuchfeedorabigpieceofwoodormetal.Thiscanbeanissueifthedryeroperatordoesn’tgettheheatsupplytothedryershutoffimmediately.ItcouldleadtoadryerfireinthedryerdrumorinthecycloneandductingbetweenthecycloneanddryerIDfan.

• Airlockwipescanbecomeworntothepointwhereexcessiveamountsof“Trampair”cangetintothedryerprocessgasstream,causingahigherthannormaloxygenconcentration.Thiswillpromotesparklifeandfiresaswellascausemoreheatthannormaltoberequiredtomeetdryeroutputandfibermoistures.

• In-consistentwoodmix(Reallygreentosuddenlyreallydry)cancausedryerfires.


Dryerhotgasinlet

• Inletdelugeandorloadspraynozzlescanbecomedisconnected(Expansion/contraction)orwornoutwhichmakesatomizationofwatersprayin-effective.

• Thesolenoidvalvethatturnsthewaterontothedelugeorloadspraynozzlescanleakby– causinganartificialloadonthedryerresultinginin-consistentfibre moistures,whichinturncanresultinthedryeroperatorincreasingtheheatsupplytothedryer,whichcancauseexcesssparkingonthedryeroutlet,whichcouldpotentiallycauseafire.(Tattletale)

• Thewatersupplytothedryerinletdelugeorloadspraycanbecomefrozeninoutdoorapplicationsmakingfireprotectionnon-existent.

• Thedryerdruminletsealcanwearovertimeandstarttoleak.Thiscausesexcessairortrampairtobedrawnintothedryerdrumandhotgasstream.Anelevatedoxygenconcentrationinthesespaceswillonlypromotecombustionandinefficientdryeroperation.


DryerDrum

• Overtime,dryerflightscanbecomedetachedcreatingacatchpointforfibreandcausesparksand/ordryerfires.

• Ifadryerdrumdriveisofavariablefrequencydrivetype,sometimesafterpoweroutagesthemotordrivesettingscandefaultbacktooriginalcausingthedrumspeedtobeincorrect.Thiscanleadtoexcessivesparkingontheoutletofthedryer.

• Toomuchwateraccumulatinginthedryerdrumfromthedryersystemdelugewillcausethedryerdrumdrivetotriponoverload.Thiscancausethedryerdrumtowarpduetometalfatiguefromoverheating.(Weightinthebottom,heatinthetop)

• Weldingrepairsinthesevesselscanbetrickyduetoconfinedspacerequirementsandlimitedaccessespeciallyontriplepassrotarydryers.Also,ifthereismorethanonedryerinseriesconnectedtothesameheatsource,adequatedoubleblock&bleedmansafeisolationdampersmustbeinplacebeforeaninternalrepaircantakeplaceonanysingledryer.


Dryeroutletductingandelbow

• Theoutletdelugenozzlepipinginsidethedryerductingcanwearfromabrasivewoodfiberwearingthroughthemetalovertime.Thiscancausethepipingtobecomecloggedwithfiberleavingthedelugelineun-useable.

• Typicallytheoutletelbowor“flat-back”iswherefiberwilllaydownfirstinupsetconditionsandoftenwoodfiberwillcatchfireinthislocationfromitsittingthere.

• Anoutletelbowwillusuallyhaveacleanoutaccesshatch.Thishatchistheonethatisopenedmostfrequentlytocleanoutfiberortoinspectforconfirmationofbuilduporafire.


Dryeroutletductingandoverheadducting

• Greconfiberopticsense&extinguish- sense,deluge&abortsensingeyescanbecomedirtyorcoveredoverwithpitchand/ortarmakingthesensingeyeunreliable.Thiscanleadtosparksgettingintothedryercyclone&outletconveyorsand/ordrybins.

• Thewatersupplytothesense&extinguishnozzlescanbecomediminishedifthestrainersonthewatersupplylinesbecomecloggedorifthesolenoidvalvesbecomedysfunctional.TheGreconspraynozzlesalsobecomewornovertimecausingthemtonotfunction(Spray)properlytothepointwherefibre cangetintoanozzleandclogitentirely.

• Dryeroutletthermocouplescanbecomewornfromfibre wearingonthem&fail– causingtheoutletdelugetogooffun-necessarily.Thiswillcausethedryertobeshutdownaswellasfibertoaccumulateintheoutletelbowandoverheadducting,whichwillrequiremanualcleanout.


Dryeroutletductingandoverheadducting(cont…)

• Anywoodfiberlayingdownintheoverheadductingcaneventuallybecarriedoverintothecycloneinlargeclumpsandcausethecycloneoutfeedairlocktoclog&triporcausematerialtobridgeabovetheoutfeedairlockwhichinturnwillcauseacycloneplug.Ifnotdetected– fibercanthenbecarriedoverintothedryerIDfanandeventuallyendupinpollutionabatementequipmentsuchasElectrostaticFilterBeds(EFB’s)orWetElectrostaticPrecipitators(WESP’s).Thisinitselfcancausefiresandawholelistofotherproblems.

• Inmostapplications– theoverheadductinghasaccesshatchesforcleaningoutbuiltupfibre thathasaccumulatedfromexcessiveGrecon“Sense&Extinguish”events.Theseaccesshatchesareusedtogetinandcleanoutthefiber,ofteninaveryhotenvironmentaswellasaveryriskyconfinedspaceenvironment.

• Theoverheadductingsometimeswillhave“ExplosionHatches”.HatchesthataredesignedtoreleaseenergyinaStratificationevent.Althoughtheseeventscanattimesbeminor,theseexplosionhatchessometimesaredamagedfromaneventorarenotcompletelysealedupafterwardscausing“Trampair”togetintothedryerprocessgases.Thiscausestheoxygenconcentrationtobeabovenormal,creatinganenvironmentthatwillpromotesparklifeandfires.


DryerCyclone

• Woodfiberfineswillaccumulateontothecycloneinnertube.Ifsparksgetthroughtothecyclone,oftenthesparkswillcatchinthefinesandcreateasmouldering event.Thisareacansmolderforhoursduetotheloweroxygenconcentrationintheprocessgasstream.

• Attimes,thedryerwillhavetobeshutdownandanemployeesentuptothetopofthecycloneinanextremelyhotenvironment(Ifthecycloneisinsideabuilding)toopentheinspectionhatchesontopofthecyclonetoextinguishthesmolderingfineswithafirehose.Thisareaisoftenonlyaccessiblebymanliftorshipladders.Ifanemployeewentdownformedicalreasonsontopofacyclone– arescuewouldbeverydifficult.

• Cycloneairlockrubberwiperscanbecomewornovertimeandcontributeto“Trampair”.Wornairlockwipeswillalsocontributetofinescarryover&buildupintodownstreamducting,fans,dampersandpollutionabatementequipmentandbecomepotentialfuelforafire.


DryerCyclone(cont…)

• Eachcyclonetypicallyhasanexplosionpanelonthetopengineeredtopreventthecycloneitselffromcomingapart.Sometimestheseexplosionpanelscanbeblowncompletelyoffandbecomeaprojectile.Sometimestheseexplosionpanelswillstartleakingfromsmallstratificationeventsandwillberepairedin-house.Theleakingpanelswillcontributeto“Trampair”.

• · Overtime,thecyclonebottomsectionitselfcanbecomewornfromwearandholeswillbecomeevidentandindicatedbyfibre leaks.Theseleaksareoftenpatchedfromtheoutside.Asthecyclonewearsmore&moreiteventuallyhastobere-linedontheinsideorreplacedaltogether.Theproblemcanbethatthestructuralintegrityofthecyclonecanbecomecompromisedifthewearislefttoolong.

• · Ifthecycloneisinanoutdoorenvironment,thereisriskofthedelugelinesbecomingfrozenifthewatersupplylinesarenotheattracedand/orinsulated.Everyfallandatregularintervalsthroughoutthewintermonths,theheattraceshouldbeverifiedtobeworkingandallinsulationisintact.Frozenwatersupplylines=nofireprotection.


Dryercyclonedischargeducting• Finesandtarcanaccumulateinthisductingposingathreatascombustiblematerial.Ifthisductingisnotinsulated,itwillinsulateitselffromtheinsidewithaneventhickerbuildupoffines.

• Potentialsourceofwherefireswillstartandcansmoulder forhoursbeforeittakesoff.

• SomecompanieshaveaddedaGreconsensorinthisductalongwithamanualdelugeforaddedsafety.Thekeythinghereisthatifsparksaredetected,thatanoperatormanuallydelugethisductwithsmallamountsofwater,otherwisetoomuchwaterwilloverloadtheIDfanandcauseittotrip.TheIDfantrippingwillpotentiallycausethefiretoreallytakeoff.


Creosotebuildupinachimney

Conditionsthatcausecreosotebuildup

• Non-insulatedducts.• Highpercentageoffinesintheprocess.• Cycloneairlockwipesnotmaintained.(Airleakingby)• Typeofspeciesbeingprocessed.(Pine,Aspen,Birch,Fir)


DryerIDFan

• Finesandtarcanaccumulateonthefaninletdamperscausingthemtojamand/orfail.Today,mostplantshaveanIDfanthatisonavariablefrequencydrivewhichwilleliminatetheneedfordampers.

• Finesandtarcanaccumulateonthefanblades.Overtime,thiswillcausethefantomovelessandlessairthroughtheentiredryingprocessandcaneventuallycausefibertolaydownintheducting,eventuallycausingplugs&fires.Thiswillalsocausethefireprotectionsystem(Sense&extinguish)tobeoutoftime– inthesensethatiftheairintheductingismovingslower,whenasparkissensedtheextinguishingnozzlewillspraytoosoonpotentiallymissingthesparkaltogether.Thebuilduponthefanbladescanalsocausethefanimpellertobecomeoutofbalanceandiflefttoolongwillcausefanbearingstofail.Regularcleaningisamust.


DryerAbortDamper

• ThisabortdampertypicallyisinstalledasameansofisolatingthedryingprocessfrompollutionabatementequipmentsuchasaWetElectrostaticPrecipitator(WESP)oranElectrifiedFiltrationBed(EFB).

• Ifadryercyclonebridgesundetectedatthebottomandwoodfiberisnolongerallowedtodischarge,itwilleventuallyfillthecyclone(Ifapluggedcyclonedetectorisfaulty– whichiscommon,theabortgatewillnotautomaticallybypassandwillcarrythefiberoverintothepollutionabatementequipment).Thiscanalsocausemajorproblemsinthepollutionabatementequipmentincludingfires.


PollutionAbatementEquipment

• Iftheinternaltemperatureofthisequipmentisallowedtooperatebelowthedewpointtemperatureoftheprocessgasses– (typically~200’For93.3’C)thetarsandresinswillbuildupinsideonthehighvoltageplatesorgravel.This,overtimewillcausetheequipmenttooperatelessefficientlyandabuildupoftars,resins,andwoodfiberfineswillaccumulatecreatingasourceoffuelforafireandorexplosion.

• Thisequipmentrequiresfrequentinspectionandcleaning– whichrequiresrigidlockoutandconfinedspaceprocedures,especiallywhentheriskofafirestartinginthisequipmentisatitshighestwhenstartinguporshuttingdownadryerordryers.Anin-attentiveoperatorcouldallowthetemperaturesinsidethisequipmenttogettoohotwithnomoistureintheprocessgassestodissipatetheoxygen(>250’for121’C)andcausespontaneouscombustion.Oftenthisequipmentcanbesmouldering whenitisbeinginspected,repairedorcleaned.

• Oftenthisequipmenthasinadequatefiresuppressiontodealwithfiresadequatelyespeciallyinrelationtodealingwithhighvoltage.

• Oftenthevendorsdonotprovideadequatetrainingforoperatingandmaintainingthisequipment.Thisislearnedbytrialanderror.


PollutionAbatementEquipment(cont…)

• Astheequipmentagesandexperienceswearand/orfiresitbecomessusceptibletoholesandallowstrampairtoinfiltrateintotheunits.Thiscanprovideoxygentopotentialfires.Itwillalsopromotelowerinternaltemperatureswhichinturnwillforceoperationstooperatetheirunitsatbelowdewpointtemperature– whichinturnwillcausefurtherproblemsasmentionedabove.

• Tarsandresinsmixedwithcombustiongasesbecomeacidic,whichovertimewillcorrodethemetalsurfacesofpollutionabatementequipmentunlessstainlesssteelisusedinmanufacturing.

• INEFB’s,oftengravelbedswillform“pockets”ofgravelthatstopmovingfromsticktarbuildup.Thisinturnwillforcethehighvoltagecagesto“shift”andcausetheceramicinsulatorstobreak.Thiswilldisablethehighvoltagefortheeffectedbedcausingtheefficiencyoftheunittobecomeverypoor.Thiswillcauseeventualbuildupofwoodfiberinsidetheunit,becomingfuelforanypotentialfire.


PollutionAbatementEquipmentDischarge

• Becauseoftheductingsometimesnotbeinginsulated,tarandresinsbuildupmorethanusualontheinsideofthedischargeductingprovidingfuelforpotentialfires.Thistarandresinbecomecorrosiveandovertimewillrotoutdischargestacksmakingthemunstableandunsafe.

• Often,firesuppressioninthisdischargeductingisinadequate.

• TheBoosterfansordischargefansneedtobecleanedoftenforreasonsmentionedearlier.


SafetyInterlocks(Wooddryingequip.)Discussion

• Lowoxygen(Warningthenshutdown)• Hightemperature.(Warningthenshutdown)• Lowairflow.(Differentialpressureacrosscycloneorfan)

• Mandatorycalculated&programmedvesselpurge(Pre-start,post–stop)afterO2isabove10%

• Mandatory2nd operatorduringstart-up&Shut-down.


OperatorTrainingDiscussion

• Documentedtrainingprocessrequiredthatiseffective.(Testing&demonstratedabilities)

• WatchdogSoftwarerequired(ProcessNet)• ConsequencesforCulpablebehaviorrequired.(Supervisorsincluded)

• ConsequencesforCulpablebehaviourontheTradesside.(Supervisorsincluded)

• Documented&managedprocessforPLC,Ladderlogicquickfixes/changes.

• ConsequencesforCulpablebehaviourontheTradessideforbypassingequipmentsafetyinterlocks.(Supervisorsincluded)

• Overallexperiences.


FireProtectionMaintenance

Grecon&Firefly• https://youtu.be/OovrSFud2A8 Grecon

• https://youtu.be/BigFGxZewjw Grecon

• https://youtu.be/J7nRCnP1-88 Firefly

Fiberopticandheatsensors Nozzles

DryermaintenanceDiscussionØFancleaning.

ØDampercleaning.ØThermocouplecalibrations.(overdryingofmaterial)

ØMoisturemetercalibrations.(overdryingofmaterial)

ØDamperactuatorcalibration/linkagecheck.ØAirlockwipechangeout.(Finescarryover)ØDryerdruminternals/flightinspection.ØDryerdrumspeedcalibration.ØDryersubstitutionloadanddelugenozzlecheck.ØNewequipmentcommissioning.Ø Copyright- CaribooBiomassConsultingServices

Standards• NFPA67- GuidelineonExplosionProtectionforGaseousMixturesinPipeSystems.

• NFPA68- StandardonExplosionProtectionbyDeflagrationVenting.

• NFPA69– StandardonExplosionPreventionSystems.(Coversthedesign,construction,operation,maintenanceandtestingofsystemsforthepreventionofdeflagrationexplosionsbymeansofthefollowingmethods:(a)controlofoxidantconcentration;(b)controlofcombustibleconcentration;(c)explosionsuppression;(d)deflagrationpressurecontainment;(e)sparkextinguishingsystems)

• Groundwatertestingformethane.• Qualificationsforoperatorswithemphasisonresponsibility&accountability.(SimilartoaPowerEngineerorMechanicalEngineer)

• Insurancecompanies.


Questions/Thank youImportant: This report contains proprietary and original material which, if released, could be harmful to the competitive position of Aon Reed Stenhouse Inc. Accordingly, this document may not be copied or released to third parties without Aon’s consent.

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