UndergroundCoalGasification:Lookingaheadtocommercialisation

byMarcMostade,ManagingDirector,MostCoalEngineeringSprl,Belgium

publishedJune2011

Abstract

Undergroundcoalgasification (UCG)or In-situcoalgasification (ISCG) is thegasificationofcoal in-situ, which involves drilling boreholes into the coal and injecting water/air orwater/oxygen mixtures. It combines an extraction (mining) process and a conversion(gasification)processintoonestep,producingahigh-quality,affordablesyntheticgas,whichcan be used for power generation, ormanufacture liquid fuels, synthetic natural gas andindustrialchemicals.Stillintheearlystageofcommercialisation,UCGispoisedtobecomeafuturemajorcontributortotheenergymixincountriesaroundtheworld.

Introduction

Coalgasificationisawell-knownchemicalprocessthatconvertssolidcarbonaceousmaterialinto synthetic gas (syngas), which consists predominantly of combustible gases (e.g.methane (CH4), carbon monoxide (CO), and hydrogen (H2)). Gasification differs fromcombustion (orburning)becauseburning coal takesplace inexcessO2andproducesonlyCO2andwatersteam.

In theundergroundcoal gasification (UCG)application, air and/oroxygen is introduced tocoal while it is still in the ground by pumping it down boreholes (called injection wells),whicharedrilledintothecoalseamfromthegroundsurface(Figure1).

1. Making coal cleaner. The underground gasification of steeply dipping coal seams wasdemonstrated in a pilot project near Rawlins, Wyoming. In the underground coalgasificationprocess,airand/oroxygenisintroducedtothecoalwhileitisstillinthegroundbypumpingitdownboreholes(calledinjectionwells),whicharedrilledintothecoalseamfromthegroundsurface.Courtesy:PaulAhner.

MarcMostade,ManagingDirectorofMostCoal Engineering SPRL,Belgiumexplained thatonce syngas is formed in the coal seam, the syngas then flowsback to the surfaceunderpressureviaasecondborehole(theproductionwell),whichislinkedthroughthecoalseamtotheinjectionwell(Figure2). Alinkedinjectionwellandproductionwell iscalledaUCG“module,”whichisthecornerstoneofUCG.

2.Surfacing.Aftersyngasisformedinthecoalseam,itthenflowsbacktothesurfaceunderpressureviaasecondborehole(theproductionwell),whichislinkedthroughthecoalseamtotheinjectionwell.Courtesy:MarcMostade.

“Inmanyways, it is the relatively recentperfectionofdrillingandmethods for linking theinjectionandproductionwellsthathasledtothehugeresurgenceofinterestinUCGthatwearenowwitnessingacrosstheglobe,”hesaid.

CoalGasificationPilotProjects

Around theworld, thereare fivenotableundergroundcoalgasificationprojects invariousstagesofdevelopmentthatareworthwatching.

LincEnergyLtd.:ChinchillaPilotProject,Queensland,Australia

Linchashada “demonstration”UCGprojectatChinchilla,Queensland,Australia since thelate 1990s. Syngas was first produced in December 1999, and production continuedthereafter for two years. Since then, Linc has developed three additional modules atChinchilla. Generator3wascommissioned in2007 in tandemwith itsgas-to-liquids (GTL)demonstration plant that has successfully produced synthetic fuels. (Peter Bond, Linc’smanagingdirector,recentlycompleteda6,000-milejourneyacrossAustraliainacarfuelledbysyntheticdieselfromLinc’sGTLplant).Generator3isnowexhausted,butGenerator4iscurrentlyproducingsyngasandisexpectedtolastforanothertwoyears.

Lincnowownsover75%oftheUzbekUCGCompany,Yerostigaz,whichhasbeenoperatingtheworld’soldestUCGprojectatAngren,Uzbekistan. ThisprojecthasbeencontinuouslyproducingUCGsyngasforalocalelectricpowerstationformorethan40years.

CarbonEnergyLtd.:BloodwoodCreekProject,Queensland,Australia

InOctober2008,CarbonEnergysuccessfullyproducedsyngasfromitsuniqueUCGmodulebasedontheparallelcontrolledretractableinjectionpoint(CRIP)method.Thetrial,whichranfor100days,reachedcoalgasificationratesofaround150tonnesperdayandproduceda high-quality syngas. Since then, Carbon Energy has installed one more module andconstructeda5-MWelectricpowerplanttobefedwithsyngasfromGenerator2.Generator1isnowbeingcarefullydecommissioned.

Plansforscalingupto25MWofelectricitygenerationareunderway,andasecondprojectinQueensland,knownastheBlueGumEnergyPark,isalsointheearlystagesofplanning.

SwanHillsSynfuels:Alberta,Canada

SwanHillsSynfuelsrecentlyproducedsyngasfromitspilotprojectinAlberta,Canada.Thisproject isthedeepestUCGpiloteverundertaken,atadepthof1,400meters,andisusingthelinearcontrolledretractinginjectionpointmethod.

ENNGroupCo.Ltd.:InnerMongolia,China

TheENNGroupCo.Ltd. (asubsidiaryoftheXinaocompany)producedsyngasfromapilotproject in Walanchabi City, Inner Mongolia, China, for 26 months, gasifying more than100,000tonsofcoal. Althoughnotmuch informationhasbeenmadeavailableaboutthisproject, it is known that there were initially seven injection and production wells, whichwerefirstfiredinOctober2007usingair.ENNisnowinitsfourthyearofoperationattheplant.

Eskom:Majuba,SouthAfrica

TheMajubaUCGprojecthasbeenproducingsyngassinceJanuary2007andbegandeliveringUCG syngas to co-fire with coal at the Majuba Power Station in late 2010. The projectcontributesabout3MWtotheoveralloutputof650MWfromtheelectricpowerstationusingthe linkedverticalwellmethod. Thisproject isnowthe longestrunningUCGtrial inthewesternworld. Plansare inplacetoexpandthefacilitiesto1,200MWeoutputs,with30%oftheplant’sfuelprovidedbysyngas.

TwoUCGMethods

ThetwomainmethodsusedtocarryoutUCGareoftenreferredtogenericallyasthelinkedvertical well (LVW) method and the controlled retracting injection point (CRIP) method.Both of these methods rely on a module of at least two linked boreholes to inject theoxidantandremovethesyngas.

The LVW method uses vertically drilled wells to access the coal seam and differenttechniquesto linktheboreholes. Incontrast, theCRIPmethodreliesonacombinationofconventionaldrillinganddirectionaldrillingtoaccessthecoalseam,andphysicallyformthelinkbetweentheinjectionandproductionwells.

Evidencefrompreviousandcurrenttrialssuggeststhatthetwobasicmethodsaregenerallysuited toexploitdifferentcoal resources. LVWmethodsaremoresuited to shallowcoalsseams,andCRIPmethodsaremoresuitablefordeepercoalseams.

There is a fairly equaldistributionofmethodsemployedonmodernUCGprojects aroundtheworld.

However,hepointedoutthat“onbalance,it’sfairtosaythattheLVWmethodiscurrentlyusedmore.”ItisusedinprojectsinUzbekistan,SouthAfrica,China,andNewZealand.Onthe other hand, the company Carbon Energy uses the parallel CRIP method in Australia;SwanHillsinCanadaisusingthelinearCRIPmethod;andLincEnergyhasexperimentedwithmostoftheavailabletechniques.

“As long as the techniques are deployed in properly selected sites (site selection isfundamentally important for UCG) and operated correctly, there are no major technicalchallengestothesetechniquesusedforUCG,”hesaid. “Muchoftheworknowadays is inrefining the techniques to increase both UCG efficiencies (mining and gasification) andreducecosts,ratherthaninovercomingmajortechnicalchallenges.”

UCG plants can produce syngas by exploiting coal resources located both onshore andoffshore(Figures3and4).

3.Hittingpaydirt.Thisdiagramillustratesthecontrolledretractableinjectionpoint(CRIP)method being used to access a coal seam onshore. The CRIP method relies on acombination of conventional drilling and directional drilling to access the coal seam and

physically form the link between the injection and production wells. Source: UCGAssociation

4. Going to the sea depths. UCG plants can also be constructed with injection andproductionwellsthatcanaccesscoalseamslocatednear-offshore.Source:UCGAssociation

TheLinkedVerticalWellMethod

TheLVWmethodusesgenerallyreversecombustion(RC):Thecoalisignitedfromoneoftheverticalwellsandairisintroducedintothecoalfromtheotherwell.Thecombustionfrontthenmovestowardtheair,forminglinkagesbetweenthewellsbyprogressivelyconsumingsmall amounts of coal and forming tube-like channels as it goes. Once the linkage isestablished,forwardcombustion(wherethecombustionfrontmovesinthesamedirectionastheinjectedair/oxygentowardtheproductionwell)isusedtogasifythecoal.

“An advantage of the RC-LVWmethod is that it is relatively inexpensive, as no expensivedirectionaldrillingisrequiredtolinkthewells,”hesaid.

ItisalsopossiblewithRC-LVWtousegreater-diameterinjectionandproductionwellsthanwith the CRIP methods because no deviated in-seam drilling (where large boreholediametersareadisadvantage)isrequired.ThismeansthatgreatersyngasflowratescouldbeachievedusingRC-LVWthanwithCRIPatshallowdepths(<300meters).

AdisadvantageoftheRC-LVWmethodisthat,becauseitreliesonthenaturalpermeabilityof coals, it is not particularly well suited to low-permeability coal, or deeper coal seams(>300 meters), which tend to be under great pressure and consequently have reducedpermeability, according to him. The reliance on natural permeabilitymay also force the

linkagetotakeunpredictablepaths,asthelinkagewilllikelyfollowpre-existingfracturesorpathsoflowpermeability.Furthermore,itismoredifficulttoensurethatthelinkageinthecoalseamismaintainedcloseaspossibletothebaseoftheseamusingthismethod.

“This is important because early UCG trials using the RC-LVW method showed strongevidencethatmaintainingtheinjectionpointatalowpositioninthecoalseamisessentialforobtaininggoodsyngasqualityandhighmining/gasificationefficiencies,”hesaid.

TheControlledRetractingInjectionPointMethod

The modern CRIP techniques use a combination of conventional and directional drillingtechniques todrill and completeboth the injectionandproductionwells, hepointedout.Thevertical sectionof theCRIPmodule injectionwell isdrilled toapredetermineddepth,afterwhichdirectionaldrillingisusedtodeviatetheholeanddrillalong,andatbottomof,thecoalseam.

“WiththeCRIPtechnique,thelocationoftheinjectionpointcanbepreciselycontrolledandretractedbackalongthebottomofthecoalseam,”henoted.“Thisisofbenefitbecauseitallowsforfreshcoaltobeaccessedeachtimethesyngasqualitydropsasaresultofcavitymaturation.”

ThemaindifferencebetweenthelinearandparallelCRIPmethodsisintheproductionwelldesign:

• ThelinearCRIPconceptusesaverticalproductionwell locatedat least300mfromthedeviatedinjectionwell. Thein-seamsectionoftheinjectionwell isdrilledsuchthatitintersectstheproductionwell.

• TheparallelCRIPmethodusesadeviatedin-seamproductionwelldrilledparalleltothe injection well with an inter-well spacing of around 30 m. The two wells aredeviatedatapredeterminedin-seamlengthtowardathirdverticallydrilledignitionwell,whichisusedtoinitiategasification.

GasificationefficiencydropsastheUCGreactorgrowsbecausemoreandmoreofthebarrenroofrockisexposed,whichconductsheatawayfromthereactorandimpactssyngasquality,hesaid.TheCRIPmethodallowsfortheinjectionpointtoberetractedbackwithinthecoalseamwhentheefficiencydrops.

“The large spacing between the injection and production wells also means that fewerboreholesarerequiredtogasifyacertainvolumeofcoal,andsotheCRIPmethodshaveasmallersurfaceimpactthanLVWmethods,”hesaid.

Furthermore, as the CRIPmethods do not rely on natural coal permeability to create thelinkage, thismethodcanbeusedatgreatdepths (1,400mdeephasbeenachievedat theSwan Hills project in Alberta, Canada), significantly increasing the resource base for UCGaroundtheworld.

SyngasCostComparison

Thecostofproducingsyngasonaperunitenergybasisisverycloselylinkedtoanumberofkeyvariables,andsoitisnotreallypossibletogiveoneoverallfigureappropriateforallUCGprojects,heexplained.

One of the most important variables is coal seam thickness. This is because the cost ofproducingsyngasis linkedcloselytothecostof installingamodule(apairof injectionandproductionwells),andsothemorecoalamodulecangasify,whichisafunctionofcoalseamthickness,thelowerthecoststoproducesyngas.

“It is possible to give a rough idea of costs for specific projects, so the UCGA recentlyproducedapricecomparisonwithotherenergy-producingtechnologiesinresponsetoaUKgovernment-sponsoredreportentitled‘UKElectricityCostsUpdate,June2010,’”hesaid.

TheUCGAusedthesamemethodstocalculatethecostsforUCGasthoseusedinthereporttoensurea faircomparison(Figure5). Theseandothercostestimates, includingworkbyLawrenceLivermoreNationalLaboratory,consistentlyshowUCGtobeverycompetitivewithexistingmaturecoal-orgas-firedelectricitygenerationtechnologies.ItisworthpointingoutthateconomicswillonlyimproveasUCGdevelopsintoamatureindustry.

5. A cost-effective option. This cost estimate showsUCG tobe competitivewithexistingmaturecoal-ornaturalgas–firedelectricitygenerationtechnologies.Notethat1.00Euro=$1.4320USD,May2011. ForUCG,nopayment for thevalueofcoal is included,and thecost of UCG includes the cost of 90-plus% carbon capture and storage. Source: UCGAssociation

TheImpactofLowNaturalGasPricesonUCGDeployment

“Historically, lownaturalgasprice isoneof themaincontributing factors fordelaying thecommercialisation of UCG,” he said. “Nowadays, with the advances made in directionaldrillingandother technologies, theproductionof syngasona calorific valueperunit costbasisismuchmorecompetitivewithnaturalgas,evenrelativelycheapnaturalgas.”

“Sincethebeginning,theUCGAhashadaworldmapdetailingalltheinterestinUCGaroundthe globe,” he said. “There are many reasons why UCG is attractive to coal-bearingcountries:

• Some countries, such as Poland, rely on coal to produce the vastmajority of theirpower. As the amount of economically minable coal declines, UCG is becomingincreasinglyattractive;

• Another key driver for interest in UCG in Europe is energy security concerns,particularlyinthosecountriesthatrelyonRussiafortheirnaturalgassupplies;and

• Othercountries,suchasChina,IndiaandSouthofAfrica(e.g.SouthAfrica,Botswana,Namibia),simplyrequirehugeamountsofenergytofueltheireconomicexpansion.Asthesecountriescontainvastquantitiesofcoal,muchofitunminable,UCGisbeingdevelopedaspartoftheenergymix.

“Incontrast,wearealsoseeinginterestfromenergy-richregions,suchasAlbertainCanada.Albertahashugeoil sand reservesand isnot shortofenergy,”he said. “Albertaalsohasvery large quantities of very deep unminable coal, which is suitable for UCG, so manycompaniesarelookingtoexploitthisvaluableresource.”

ObstaclestoDeployment

There are fewUCG-specific technical issues that need to be overcomebecause, in recentyears, the technologies havematured to a stagewhere companies are nowmoving frompilotstagetoacommercialstage,hesaid.Inhisopinion,“whatweneedtoseenowismoreprojects moving into the commercial stage to give investors more confidence in thetechnologyandfundmoreprojects.”

“Thisiscloselylinkedtoanotherchallengeweareseeing:Therecurrentlyisonlyahandfulofpeople with direct experience of UCG,” he said. “These people generally reached theirprofessionalpeakinthelast‘phase’ofUCGdevelopmentbetweenthe1970sandlate1990s.Therefore, we now need a new generation of UCG experts to develop UCG in the 21stcentury.

EnvironmentalChallenges

Theenvironmentalchallengesarewellunderstood,asaresultofthesignificantknowledgegained from previous UCG trials. These include groundwater contamination, subsidence,surfacecontamination,andgasemissions. Theycanbemanaged,however,bycarefulsiteselection, the correct operation of the UCG module, and by the use of appropriateengineeringmaterials/surfaceplants,accordingtoMostade.Safetyisalsooftenmentionedas a challenge, although experience is showing that with good process monitoring andcontrolofoperations,safetyissuesarenodifferentthanthoseinotherprocessindustries.

UCGSafetyIssues

Undergroundcoalgasification(UCG)isinherentlysaferthanconventionaloilandgasorcoalexploitationmethods.Akeysafetyconcernforoilandgasworkersistheriskofablowoutduringdrilling,followedbyignitionoftheoiland/orgas,causingafire.Aswaswitnessedin

theGulfofMexicoin2010,blowoutsorwellfailuresduringoffshoreoilandgasdrillingcancreatesignificantsafetyissuesandhavethepotentialforcausingsignificantenvironmentalimpacts.

TheriskofablowoutduringdrillingforUCGissignificantlylowerthanforoilandgasdrilling,as the target coal formation is not a pressurised hydrocarbon reservoir. The risks are,therefore,morecomparablewithcoalbedmethanedrilling.Althoughitdoesentailtheriskofhittingpocketsofpressurisedgas,coalmethanedrillingoverall is intrinsicallysaferthanoilandgasdrilling.

Comparedwithcoalmining,UCGisalsosignificantlysafer.Themostobviousreasonisthatnopeoplearerequiredtoworkunderground.Coalmining,especiallyinsomecountries,isan extremely dangerous activity because of the risks of a mine collapsing, or methaneleakingintominegalleries.InUCG,allthepeoplearelocatedonthesurfaceinpurpose-builtfacilitiesthataredesignedtominimisetheriskofharm.

Perhapsthemostsignificantrisk inUCG is fromsyngas leaking fromsurfacepipes. Safetysystems, however, such as continuous carbon monoxide monitoring or emergencyprocedures thatmay include diverting syngas to a flare, help to reduce these risks. As aresult, there’s no reason to think that a commercial UCG plantwill be less safe than anymodernenergyorchemicalprocessingplant.

GroundwaterContamination.Contaminants,suchasbenzeneandotherhydrocarbons,canbe produced duringUCG by a natural process called coal pyrolysis. Coal pyrolysis occursduring the breakdown of coal at temperatures less than those required for gasification.DuringUCG, thiswill likelyhappenwithin the coal at adistance less than0.5m from thecoalface.

“AsUCGtakesplacebelowthegroundwaterlevel,ina‘groundwaterbubble,’thereisariskthat some of the contaminants could leave the UCG reactor and impact groundwaterresources,” he said. “It is possible, however, to stop contaminants from entering thegroundwaterbyensuringthatwateronlyflowsintotheUCGcavity,becausecontaminantswillnotbetransportedagainstthedirectionofflow.”

Selecting theappropriatesite forUCG isof fundamental importance,andacorrectly sitedUCGprojectwouldnotbelocatedanywherenearanaquiferusedtoextractwaterforuse.Thesuitabilityofasitewithrespecttoassessingriskstoaquiferscanbedeterminedusinganumberofexistingandwell-testedmethods,soitisrelativelystraightforwardtoavoidhigh-risklocationsinthefirstplace.

Subsidence. Ground subsidence is the propagation of the UCG cavity toward the surfacefollowing collapse of the cavity roof rocks. The distance that subsidence can propagate isstronglydependentoncavitysize,thedepthtothecavity,andthemechanicalpropertiesoftherocksoverlyingthecavity. Significantsurfacesubsidencehasnotbeenobserved inallUCG trials; in fact, it is very rare. Site selection is one of themost important factors inmanaging the risks fromsubsidence. Coal seamdepth is critical,andseams>300mdeepminimisetheriskstothesurface.Itisalsonecessarytotargetcoalseamswithstrong,fullyconsolidatedroofrocksthatcanresisttheeffectsofsubsidence.

TherisksofsurfacesubsidencefromUCGareanalogoustothosefromconventionalmining,andsotherearemanystandard,well-acceptedtechniquesforassessingthisrisk. ThefactthatUCG is increasingly carriedoutatdepthsgreater thanconventionalmining,however,lowerstheriskofsurfacesubsidencecomparedwithtraditionalminingtechniques.

Surface Contamination. Risks to theenvironment fromUCGat the surfaceareessentiallyrestrictedtohowcontaminantsarehandledoncetheyarecondensedoutwiththewaterinthe syngas. UCG “black water” is no different from the wastewater produced duringconventionalsurfacecoalgasification.Therefore,technologiesthatcantreatthewaterarewellestablishedandreadilyavailable.

AtmosphericEmissions.TheemissionsfromUCGareessentiallynodifferentthanfromanyothermodern industrial process using coal, and so existing, tried and tested technologiescan be employed to reduce atmospheric emissions. Emissions from a UCG plant are,however,considerablylowerthanfromconventionalcoalmines,becausenocoalisbroughttothesurface,andmethaneemissions(oftenassociatedwithcoalmining)areminimised.

PermittingIssuesforUCGProjects.

It iswellwithin the interestsofUCGoperators todemonstrate clearly thatno impacts togroundwater resources on- or off-site will occur as a result of UCG, he said. Impacts toaquifers from any contamination will have serious implications for a project under itsenvironmentalpermittingregime.Forexample,aregulatorcouldorderaprojecttostopallUCGactivities if ithasbreached itspermitting conditions. Additionally, theUCGoperatorwouldlikelyhavetopaythesignificantcostsassociatedwithaquiferremediationaswellasexposeitselftotheriskoflitigationfromadjacentlandowners.

All UCG operators are aware of these issues and, consequently, ensure that numerousmonitoringwellsaredistributedthroughout their sites. Maintaininggroundwater levels iscriticalforthelong-termsustainabilityofUCGprojects.Therefore,groundwatermonitoringwellshavetobeonUCGsitesirrespectiveoftheiruseforgroundwaterqualitymonitoring.Typically,groundwatermonitoringwellsarepositionedatthesiteperiphery,aswellasoff-site, whenever feasible. This allows UCG operators to demonstrate that they are notimpactingaquifers.

LookingAhead

Oneof thecurrenthindrances towidespreaddeploymentofUCGaround theworld is theuncertain regulatory environment in some areas, he said. Countries and regions withexistingUCGregulations (orwithotherexistingpolicies thatcanbeeasilyadaptedtodealwithUCGprojects)willhaveanadvantageoverothers.

He pointed out that “it is clear that countries such as the UK, China, India, Turkey, U.S.(Wyoming),Australia,andCanadaaremovingforwardwiththeirregulationsandstimulatinginterestinUCGprojects.”Thosecountrieswithabundant,unminablecoalreservessuitablefor UCG and a strong need for affordable energy, such as China and India, will probablyundertake widespread deployment of UCG first. Currently, five UCG projects are beingcarriedoutinAustralia,China,Canada,andSouthAfrica.

“WeareattheearlystageofcommercialisationofUCG.AsmoreandmoreprojectsaroundtheworldprovethatUCGproducesaffordable,clean,andefficientenergy,theuseofUCGintheworldwillnaturallygrowbothintheshortandlongterm,”hesaid.“Otherfactors,suchas energy security and carbonemissions,will likely have an impacton thedeploymentofUCG,butprobablyinthelongerterm.”

MarcMostade also emphasised the impact that the successful implementation of carboncaptureandsequestration (CCS)couldhaveonUCG’s futuredevelopment. “In the longertimeframe,itisourfirmbeliefthatCCSwillbecomecommercial,andgivenUCG’sinherentbenefits forcarboncapture (e.g.CO2canbecapturedrelativelycheaply fromoxygen-firedUCGsyngasathighpressure),thistrendwillseeUCGbeingincreasinglyexploitedinremoteregionssuchasthesouthernpartofAfrica,”hesaid.

MarcMostadewould liketoacknowledgethecontributionsof the followingpeople:ShaunLavis,seniorgeoscientist;andPaulAhner,seniorUCGtechnician.