BestPractGuide_MethDrain_es31

8/8/2019 BestPractGuide_MethDrain_es31

1/86

ECONOMICCOMMISSIONFOREUROPE

METHANETOMARKETSPARTNERSHIP

BestPracticeGuidanceforEffective

MethaneDrainageandUseinCoalMines

ECEENERGYSERIESNo.31

UNITEDNATIONS

NewYorkandGeneva,2010


2/86

NOTE

Thedesignationsemployed and thepresentationof thematerial in thispublicationdonot

implytheexpressionofanyopinionwhatsoeveronthepartoftheSecretariatoftheUnited

Nationsconcerningthelegalstatusofanycountry,territory,cityorarea,orofitsauthorities,

orconcerningthedelimitationofitsfrontiersorboundaries.

Mentionofanyfirm,licensedprocessorcommercialproductsdoesnotimplyendorsementby

theUnitedNations.

UNITEDNATIONS

PUBLICATION

SalesNo.10.II.E.2

ISBN9789211170184

ISSN10147225

CopyrightUnitedNations,2010

Allrightsreservedworldwide


3/86

Foreword

Coalhasbeenanimportantsourceofglobalprimaryenergyproductionforthepasttwocenturies,and

theworldwillcontinue todependoncoalasanenergysource for the foreseeable future.Methane

(CH4) released during coal mining creates unsafe working conditions in many underground mines

around the world, with human fatalities an unacceptable consequence of many methanerelated

accidents.Effectivegasmanagement isnot limited tosafetyconcerns,however.Methaneventedto

theatmosphere,especially fromdrainage systems, isanenergy resource lost forever.The resulting

emissionsalsocontributetoclimatechange.Fortunately,solutionsforthesechallengescangohand

inhandusinganeffective,coordinatedresponse.

Although respected technical literatureonmethanemanagement iswidelyavailable for themining

professional, a single source of informed but accessible guidance for senior managers did not

previouslyexist.TheBestPracticeGuidanceonEffectiveMethaneDrainageandUse inCoalMines is

intendedtofillthiscrucialvoid.Recommendedprinciplesandstandardsoncoalminemethane(CMM)

captureandusearesetoutinaclearandsuccinctpresentationtoprovidedecisionmakerswithasolid

base of understanding from which to direct policy and commercial decisions. We believe such

knowledge iscriticaltoachievezero fatalitiesandexplosionriskwhileminimisingtheenvironmental

impactofCMMemissions.Changemuststartatthetop.

Theguidancedocumentcanalsobeusedbystudentsandeventechnicalspecialistsasanintroduction

tokeymethanemanagementprinciplesandreferences.Infact,aspartofthisoverallinitiative,several

organizations funded a reprint of the seminal Firedamp Drainage Handbook, a definitive technical

referencefirstpublishedbyVerlagGlckauffortheCommissionoftheEuropeanCommunitiesin1980.

We

wish

to

emphasize

that

theBest

Practice

Guidance

does

not

replace

or

supersede

national

or

internationallawsorotherlegallybindinginstruments.Theprinciplesoutlinedhereinareintendedto

provide guidance to complement existing legal and regulatory frameworks and to support

developmentofsaferandmoreeffectivepracticeswhereindustrypracticeandregulationcontinueto

evolve.

Thecontributorstothisprojectgavetheirtimefreelyandwillinglyinthedesiretopromoteincreased

safetyincoalmining.Inthelightofrecentaccidentsandinmemoryofallthefatalitiesofthepast,the

authorsexpressthehopethattheirworkwillcontributetoincreasinglysafercoalminingoperations.

February2010

UnitedNationsEconomicCommissionforEurope

MethanetoMarketsPartnership


4/86

Contents

Foreword.......................................................................................................................................................... iiiContents........................................................................................................................................................... ivAcknowledgements......................................................................................................................................... viiAcronymsandAbbreviations........................................................................................................................... ixGlossaryofTerms............................................................................................................................................. xiExecutiveSummary.........................................................................................................................................xiiiChapter1.Introduction .................................................................................................................................... 1

KeyMessages................................................................................................................................................11.1 ObjectivesofthisGuidanceDocument ................................................................................................11.2 TheIssues..............................................................................................................................................11.3 GasCapture,Utilisation,andAbatement .............................................................................................3

Chapter2.FundamentalsofGasControl.......................................................................................................... 5KeyMessages................................................................................................................................................52.1 ObjectivesofMineGasControl ............................................................................................................ 52.2 OccurrenceofGasHazards...................................................................................................................5

IgnitionofExplosiveMethaneMixtures.................................................................................................7 2.3 ReducingExplosionRisk........................................................................................................................72.4 RegulatoryandManagementPrinciples...............................................................................................9

EffectiveSafetyRegulatoryFramework.................................................................................................. 9Enforcement ...........................................................................................................................................9PermissibleGasConcentrationsforSafeWorkingConditions ............................................................... 9SafeTransportandUtilisationofGas ................................................................................................... 10RegulationstoReduceIgnitionRisk......................................................................................................11

Chapter3.Occurrence,Release,andPredictionofGasEmissionsinCoalMines..........................................12KeyMessages..............................................................................................................................................123.1 Introduction .......................................................................................................................................123.2 OccurrenceofGasinCoalSeams........................................................................................................12


5/86

3.3 TheGasReleaseProcess.....................................................................................................................133.4 RelativeGassinessofCoalMines........................................................................................................14 3.5 UnderstandingGasEmissionCharacteristicsofCoalMines...............................................................143.6 MeasurementoftheInSituGasContentofCoal...............................................................................15 3.7 PracticalEstimationofGasFlowsinCoalMines ................................................................................16

Chapter4.MineVentilation............................................................................................................................17KeyMessages..............................................................................................................................................174.1 VentilationChallenges ........................................................................................................................ 174.2 KeyVentilationDesignFeatures ......................................................................................................... 174.3

Ventilation

ofGassy

Working

Faces....................................................................................................18

4.4 VentilationSystemPowerRequirement.............................................................................................214.5 VentilationofCoalHeadings...............................................................................................................214.6 VentilationMonitoring .......................................................................................................................224.7 VentilationControl..............................................................................................................................22

Chapter5.MethaneDrainage ........................................................................................................................23Key

Messages..............................................................................................................................................23

5.1 MethaneDrainageandItsChallenges ................................................................................................23 5.2 BasicPrinciplesofMethaneDrainagePracticesEmployedWorldwide .............................................235.3 PreDrainageBasics.............................................................................................................................245.4 PostDrainageBasics...........................................................................................................................25 5.5 DesignConsiderationsforMethaneDrainageSystems......................................................................275.6 UndergroundGasPipelineInfrastructure...........................................................................................285.7 MonitoringofGasDrainageSystems..................................................................................................29

Chapter6.MethaneUtilisationandAbatement ............................................................................................30KeyMessages..............................................................................................................................................306.1 CoalMineMethaneandClimateChangeMitigation .........................................................................306.2 MineMethaneasanEnergyResource ...............................................................................................30 6.3

Use

Options.........................................................................................................................................31


6/86

6.4 AbatementandUtilisationofDrainedMethane ................................................................................32 6.4.1 Medium toHighMethaneConcentrationCMM .................................................................336.4.2 LowConcentrationDrainedMethane ..................................................................................346.4.3 PurificationTechnologiesforDiluteMethanefromDrainageSystems ................................346.4.4 Flaring ...................................................................................................................................35

6.5 AbatementorUtilisationofLowConcentrationVentilationAirMethane(VAM) .............................356.6 MethaneMonitoring...........................................................................................................................36

Chapter7.CostandEconomicIssues .............................................................................................................37KeyMessage ...............................................................................................................................................377.1 TheBusinessCaseforMethaneDrainage ..........................................................................................377.2 ComparativeCostsofMethaneDrainage...........................................................................................37 7.3 MethaneUtilisationEconomics .......................................................................................................... 387.4 CarbonFinancingandOtherIncentives..............................................................................................417.5 OpportunityCostofUtilisation...........................................................................................................437.6 EnvironmentalCosts ........................................................................................................................... 44

Chapter8.Conclusions

and

Summary

for

Policymakers ................................................................................45

Chapter9.CaseStudies ..................................................................................................................................47CaseStudy1:AchievingPlannedCoalProductionfromaGassy,RetreatLongwallwithSevereStrata

StressandaSpontaneousCombustionProneCoalSeamUnitedKingdom ............................................48CaseStudy2:HighPerformanceLongwallOperationsinAreaswithHighGasEmissionsGermany......50CaseStudy3:HighPerformanceLongwallOperationsinAreaswithHighGasEmissionsAustralia ...... 52Case

Study

4:

Reducing

Explosion

Risk

in

Room

and

Pillar

Mines

South

Africa......................................54

CaseStudy5:DevelopmentofaCMMPowerCoGeneration/EmissionAbatementSchemeChina......56CaseStudy6:VAMChina .........................................................................................................................5 7CaseStudy7:VAMAustralia....................................................................................................................59

Appendix1.ComparisonsofGasDrainageMethods .....................................................................................61References ......................................................................................................................................................66Additional

Resources ......................................................................................................................................68


7/86

AcknowledgementsSponsoringOrganizations

The United Nations Economic Commission for Europe (UNECE) is one of the five UN Regional

Commissions and provides a forum through which 56 countries of North America and Western,

Central,andEasternEuropeaswellasCentralAsiacometogethertoforgethetoolsoftheireconomic

cooperation.ThemainareasofUNECEsactivityare:economiccooperation,environmentandhuman

settlements, statistics, sustainableenergy, trade, industryand enterprisedevelopment, timber, and

transport. UNECE pursues its goals through policy analysis, the development of conventions,

regulations and standards, and the provision of technical assistance.

www.unece.org/energy/se/cmm.html

TheMethane toMarketsPartnership (M2M) is an internationalpublicprivatepartnershipwith 30

Partnercountries,plustheEuropeanCommission,establishedin2004andfocusedonpromotingcost

effectivemethaneemissionreductionsthroughrecoveryandusefromfourkeymethanesectors:coal

mining, landfills,oilandgas systems,andagriculture.TheCoalSubcommitteehasbrought together

keyexpertsincoalminemethanerecoveryandutilisationtoshareinformationaboutstateoftheart

technologies and practices through a number of workshops, trainings, study tours, and capacity

buildinginitiatives.www.methanetomarkets.orgStructure

ThisdocumentwasconceivedbyaSteeringCommittee,whoprovideddirectionandoverallvision,and

drafted by a Technical Experts Panel, consisting of five globally renowned experts in underground

ventilation

and

methane

drainage

at

coal

mines.

The

draft

document

was

first

reviewed

by

a

StakeholdersAdvisoryGroup to ensure that messageswere clear and effective for seniordecision

makers,beforeundergoingaformaltechnicalpeerreviewprocess.

ExecutiveSteeringCommittee

PamelaFranklin,Cochair,M2MCoalSubcommittee

RolandMader,ViceChairman,UNECEAdHocGroupofExpertsonCoalMineMethane

RaymondC.Pilcher,Chairman,UNECEAdHocGroupofExpertsonCoalMineMethane

CarlottaSegre,Secretary,UNECEAdHocGroupofExpertsonCoalMineMethane

ClarkTalkington,

Former

Secretary,

UNECE

Ad

Hoc

Group

ofExperts

on

Coal

Mine

Methane

TechnicalExpertsDraftingGroup

BharatheBelle,AngloAmerican

DavidCreedy,SindicatumCarbonCapitalLtd.

ErwinKunz,DMTGmbH&Co.KG

MikePitts,GreenGasInternational

HilmarvonSchoenfeldt,HVSConsulting


8/86

StakeholderAdvisoryGroup

YuriyBobrov,AssociationofDonbassMiningTowns(Ukraine)

GraemeHancock,WorldBank

MartinHahn,InternationalLabourOrganization

HuYuhong,

State

Administration

for

Worker

Safety

(China)

SergeiShumkov,MinistryofEnergy(RussianFederation)

AshokSingh,CentralMinePlanning&DesignInstitute(India)

TechnicalPeerGroup

JohnCarras,CommonwealthScientificandIndustrialResearchOrganisation(Australia)

HuaGuo,CommonwealthScientificandIndustrialResearchOrganisation(Australia)

LiGuojun,TiefaCoalIndustryLtd.(China)

GlynPierceJones,TrolexLtd.(UK)

B.N.Prasad,

Central

Mine

Planning

&Design

Institute

(India)

RalphSchlueter,DMTGmbH&Co.KG(Germany)

KarlSchultz,GreenGasInternational(UK)

JacekSkiba,CentralMiningInstituteofKatowice(Poland)

TrevorStay,AngloAmericanMetallurgicalCoal(Australia)

OlegTailakov,InternationalCoalandMethaneResearchCenter,Uglemetan(Russian

Federation)

Inadditiontothoselistedabove,thesponsoringorganizationswishtoexpresstheirgratitudetoLuke

Warren,whoplayedanintegralroleintheinitialstagesofthisproject.


9/86

AcronymsandAbbreviations

CBM CoalbedMethane

CDM CleanDevelopmentMechanism

CERs CertifiedEmissionReductions

CFRR CatalyticFlowReversalReactors

CH4 Methane

CMM CoalMineMethane

CMR CatalyticMonolithReactor

CNG CompressedNaturalGas

CO2 CarbonDioxide

CO2e CarbonDioxideEquivalent

ERPA EmissionReductionPurchaseAgreement

ERUs EmissionReductionUnits

ESMAP EnergySectorManagementAssistanceProgram

GHG

Greenhouse

Gas

GWP GlobalWarmingPotential

IBRD InternationalBankforReconstructionandDevelopment

IC InternalCombustion

I&M InspectionandMaintenance

JI JointImplementation

kWh

Kilowatthour

LNG LiquefiedNaturalGas

l/s LitresperSecond

m Metre

m/s MetresperSecond

m3/d CubicMetresperDay

m3/s

CubicMetres

per

Second


10/86

mD Millidarcy(incommonusage,equivalenttoapproximately103(m)2)

MRD MediumRadiusDrilling

MSA MolecularSieveAdsorption

Mt Million(106)tonnes

Mtpa MillionTonnesperAnnum

MWe MegawattofElectricityCapacity

Nm3 NormalCubicMetres

PSA PressureSwingAdsorption

scfm StandardCubicFeetperMinute

t Tonne(metric)

t/d TonnesperDay

TFRR ThermalFlowReversalReactor

TRD TightRadiusDrilling

UNECE UnitedNationsEconomicCommissionforEurope

UNFCCC UnitedNationsFrameworkConventiononClimateChange

VAM VentilationAirMethane

VERs VerifiedEmissionReductions

USBM UnitedStatesBureauofMines


11/86

GlossaryofTerms

Withinthecoalandminegasindustry,thereisstillconfusionovertermsandabbreviationsusedwithin

and across differentjurisdictions. In addition to the terms listed here, the UNECE has prepared a

GlossaryofCoalMineMethaneTermsandDefinitionsthatismorecomprehensiveandhighlightshow

terminologyisusedindifferentregions

(www.unece.org/energy/se/pdfs/cmm/cmm4/ECE.ENERGY.GE.4.2008.3_e.pdf).

Airlockanarrangementofdoorsthatallowspassagefromonepartofamineventilationcircuitto

anotherwithoutcausingashortcircuit.

Auxiliaryventilationproportionofmainventilatingcurrentdirectedtothe faceofablindheading

(i.e.,entry)bymeansofanauxiliaryfanandducting.

Backreturn a temporary ventilation arrangement formed at the return end of a Uventilated

longwalltodivert

aproportion

ofthe

air

behind

the

face

toallow

access

for

gas

drainage

drilling

and

preventhighconcentrationgoafgasesencroachingonthefaceend.

Bleedershaftaverticalshaftthroughwhichgasladenairfromworkingdistrictsisdischarged.

Blindheadingadevelopmentroadwaywithasingleentrythatrequiresauxiliaryventilation.

Bordandpillar (roomandpillar)a methodofmining inwhich coal is extracted from a seriesof

headings,whicharetheninterlinkedleavingunminedcoalpillarstosupporttheroof.

Capture (drainage) efficiency the proportion of methane (by volume) captured in a methane

drainage

system

relative

to

the

total

quantity

of

gas

liberated.

Gas

liberated

comprises

the

sum

of

drainedgasplusgasemittedintothemineventilationair.Usuallyexpressedasapercentage,capture

(ordrainage)efficiencycanbedeterminedforasinglelongwallpanelorforawholemine.

Coal front gas gas released from the working seam coalface by the action of the coalcutting

machine.

Coalbedmethane(CBM)agenerictermforthemethanerichgasnaturallyoccurring incoalseams

typically comprising 80% to 95% methane with lower proportions of ethane, propane, nitrogen, and

carbondioxide.Incommoninternationaluse,thistermreferstomethanerecoveredfromunminedcoal

seamsusingsurfaceboreholes.

Coalminemethane(CMM)gascapturedataworkingcoalminebyundergroundmethanedrainage

techniques.Thegasconsistsofamixtureofmethaneandotherhydrocarbonsandwatervapour. It is

oftendilutedwithairandassociatedoxidationproductsdue tounavoidable leakageofair into thegas

drainageboreholesorgalleriesthroughmininginducedfracturesandalsoduetoairleakageatimperfect

jointsinundergroundpipelinesystems.Anygascapturedunderground,whetherdrainedinadvanceofor

aftermining,andanygasdrainedfromsurfacegoafwellsisincludedinthisdefinition.Preminingdrained

CMMcanbeofhighpurity.

Extraneousgasgasemissionsotherthancoalfrontgas.

FiredampalternativetermforCMM.


12/86

Gasdrainagemethodsforcapturingthenaturallyoccurringgasincoalseamstopreventitentering

mine airways. The gas can be removed from coal seams in advance of mining using predrainage

techniquesandfromcoalseamsdisturbedbytheextractionprocessusingpostdrainagetechniques.

OftenreferredtoasMethanedrainageifmethaneisthemaingascomponenttargettobecaptured.

Goaf(United

States:

gob)

broken,

permeable

ground

where

coal

has

been

extracted

by

longwall

coal

miningandtheroofhasbeenallowedtocollapse,thusfracturinganddestressingstrataaboveand,to

a lesserextent,below theseambeingworked.The termgob isgenerallyused in theUnitedStates;

elsewhere,goafisgenerallyused.

MethanedrainageSeeGasdrainage.

Naturalgastypicallyreferstogasextractedfromgeologicalstrataotherthancoalseams(i.e.,from

conventionalgasreserves).Thegascouldbecomposedmostlyofmethaneandmayhaveoriginally

migratedfromcoalseamsources.

Predrainage(preminedrainage)extractionofgasfromcoalaheadofmining.

Postdrainage(postminedrainage)extractionofgasreleasedasaconsequenceofmining.

Respirabledustmicroscopicparticlesofdustwhichcanenteranddamagethehumanlung.

Ventilationairmethane(VAM)methaneemittedfromcoalseamsthatenterstheventilationairand

isexhaustedfromtheventilationshaftatalowconcentration,typicallyintherangeof0.1%to1.0%by

volume.


13/86

ExecutiveSummaryTheworldhas reliedupon coal for a significantportionof itsprimary energyproduction since the

Industrial Revolution. The worlds major industrialised, emerging, and transitional economiesand

hence, theglobaleconomywillbedependentoncoalenergy resources for the foreseeable future.

Today,coalsupplies25%ofglobalprimaryenergy,40%ofglobalelectricity,andalmost70%of the

worlds steelandaluminum industry. The InternationalEnergyAgency (IEA)projects thatemerging

economieswillseeenergydemandgrow93%by2030,drivenlargelybydemandgrowthinChinaand

India,andcoalisexpectedtobetheleadingfueltomeetthisgrowingdemand(IEA,2009).

With the continued dependence on coal production, coal extraction is expected to become

increasinglychallenginginmanypartsoftheworldasshallowreservesareexhaustedanddeeperand

more gassy seams are mined. Yet societies are demanding and expecting safer mine working

conditions, and greater environmental stewardship from the coal industry. The application of best

practicesformethanedrainageanduseiscriticaltoreducemethanerelatedaccidentsandexplosions

thatalltoooftenaccompanycoalmining,whilealsocontributingtoenvironmentalprotectionthrough

reductionofgreenhousegas(GHG)emissions.

CoalMineMethanePosesSafetyandEnvironmentalChallenges

The global coal industry, national governments, trade unions, and worker safety advocates are

concernedthatthefrequencyandseverityofmethaneexplosions,especially inemergingeconomies,

areunacceptablyhigh.Goodminingpracticesneed tobe transferred toallcountries toensure that

risksaremanagedprofessionallyandeffectively.Nomine,even in themostdevelopedcountries, is

freefromsafetyrisks.Regardlessoflocationorminingconditions,itispossibletosignificantlyreduce

theriskofmethaneaccidents.

Methaneisanexplosivegasintherangeof5%to15%methaneinair.Itstransport,collection,oruse

withinthisrange,orindeedwithinafactorofsafetyofatleast2.5timesthelowerexplosivelimitand

at least two times the upper limit, is generally considered unacceptable because of the inherent

explosionrisks.

Effectivemanagementof methane risks at coalmines can alsohave the benefit of contributing to

reducedorminimisedGHGemissions.Coalmines area significant emissions sourceofmethane, a

potentGHGwithaglobalwarmingpotential(GWP)ofmorethan20timesthatofcarbondioxide(IPCC,

2007).Methanetotals14%ofglobalanthropogenicGHGemissionsandcoalminesrelease6%ofglobal

anthropogenicmethane

emissions,

orabout

400

million

tonnes

ofcarbon

dioxide

equivalent

(MtCO2e)

peryear.CMMemissionsareprojected to increase through2020 (MethanetoMarkets,2008; IPCC,

2007;EPA,2006a),withestimatesashighas793MtCO2eby2020(ESMAP,2007).

MethaneOccurrenceandControl

Methanerichgases,generallycontaining80%to95%methaneatundergroundminingdepths,occur

naturallyincoalseamsandarereleasedasCMMwhencoalseamsaredisturbedbyminingactivities.

CMMonlybecomesflammableandcreatesanexplosionhazardwhenallowedtomixwithair.

Emissions of large volumes of carbon dioxide also occur from coal mines in some geologic

environments(e.g.,

Australia,

South

Africa,

France,

and

Central

Europe).

This

coal

seam

carbon

dioxide

canhaveimportantimplicationsforoverallminedegasificationmanagementstrategies.


14/86

Goodsafetypracticeincoalminesistoreduceexplosionriskbypreventingtheoccurrenceofexplosive

mixtureswherepractical,andbyrapidlydilutingthemtosafeconcentrations(i.e.,throughventilation

systems).Wheregasflowsaresohighthattheyexceedthecapacityofthemineventilationsystemto

ensureadequatedilutionofmethaneinthemineair,gasshouldbecollectedthroughaminedrainage

systembeforeitcanenterthemineairways.

Good practice for mine methanedrainage systemsmeansboth selection of a suitable gas capture

method and proper implementation and execution of the mine drainage system. Following good

practicewillensurethatCMMcanbesafelycaptured,transported,and (ifappropriate)utilised,ata

concentrationatleasttwicethatoftheupperexplosivelimit(i.e.,atorover30%methane).

RegulatoryApproachestoMethaneControl

A risk assessment approach to minimising explosion riskscombined with strong enforcement of

robustventilationandutilisationsafetyregulationscanleadtosubstantiallyimprovedquantitiesand

qualitiesofcapturedgas.

Furthermore, establishment and enforcement of safety regulations governing gas extraction,

transport,andutilisationwillencouragehighermethanedrainagestandards, increasedcleanenergy

production,andgreateremissionreductions.

PredictionofUndergroundMethaneReleases

Gas flows into underground coal mines under normal, steadystate conditions are relatively

predictable in certain geological andmining conditions, although there is significant variation from

country to country. Lack of reliable gas emission prediction methods for deep and multipleseam

mining continues to be a significant challenge due to the complex mininginduced interactions

between

strata,

groundwater,

and

gas.

Nonetheless,

proven

methods

for

projecting

gas

flows,

gas

capture,ventilation requirements,andutilisationpotentialarewidelyavailableand shouldbeused

routinelyinmineplanning.

Bytheirverynature,unusualemissionandoutbursteventsarenoteasilypredicted,buttheconditions

underwhichtheycanoccurarereasonablywellknown.Therefore,followinggoodpracticeallowsfor

moreeffectivemanagementoftheserisks.

Any mining activity can sometimes disturb adjacent natural gas reservoirs, leading to unwanted

methanereleasesthatcanbeasmuchas twice thoseexpected fromcoalseamsourcesalone.Such

situationscanbeidentifiedatanearlystagebycomparingmeasuredandpredicteddata.

TheRoleofVentilationSystems

The maximum rate of coal extraction that can be safely achieved on a gassy working coalface is

determinedprimarilybythecombinationoftwofactors:1)themineventilationsystemscapacityto

dilutegaseouspollutants toacceptableconcentrations,and2) theefficiencyof theminesmethane

drainagesystem.

Operating costs are a key driver in designing the overall mine degasification scheme. The power

consumed inprovidingundergroundmineventilation isamongthemostcostlyoperationalexpenses

at a mine; it is proportional to the airflow volume cubed. Therefore, introducing a gas drainage

system

or

increasing

its

effectiveness

often

represents

a

lowercost

option

than

increasing

ventilationairvolumes.


15/86

MethaneDrainage

Thepurposeofmethanedrainage istocapturegasathighpurityfrom itssourcebefore itcanenter

themineairways. From a strictly regulatoryperspective,only enough gasneeds tobe captured to

ensurethatthecapacityoftheventilationairtodilutegaseouspollutants isnotexceeded.However,

there is a strong case for maximising gas capture to achieve enhanced safety, environmental

mitigation,andenergyrecovery.

Methanecanbecapturedbeforeandafterminingbypre andpostdrainagetechniques,respectively.Pre

drainage istheonlymeansofreducinggas flowdirectly from theminedseam.Forthisreason,pre

drainage isespecially important iftheseambeingextracted isthemaingasemissionsource,but it is

generally only feasible in seams of medium to highpermeability. Postdrainage methods involve

interceptingmethanethathasbeenreleasedbyminingdisturbancebeforeitcanenteramineairway.

Postdrainage techniques all involve accessing the zoneofdisturbance aboveand also sometimes

belowthe worked coal seam. Postdrainage may involve drilling from the surface or from

underground.

Lowcaptureefficienciesofthedrainagesystemandexcessiveingressofairtothemineworkingsresult

from the selectionofunsuitablegasdrainagemethodsand from thepoor implementationof these

methods. These, in turn, negatively affect both gas transport and utilisation by producing gas

concentrationssometimesatlevelsthatarenotconsideredsafe(e.g.,below30%methane).

Theperformanceofmethanedrainagesystemscanbesignificantly improvedthroughacombinationof

properinstallationandmaintenance,regularmonitoring,andsystematicdrilling.

There is a strong business case for installing and operating highefficiency methane gas drainage

systems.Successful

methane

control

isakey

factor

inachieving

profitability

ofgassy

underground

coal

mines.

Basedonexperiences in coalminesworldwide, investment ingoodpracticegasdrainage systems

resultsinlessdowntimefromgasemissionproblems,saferminingenvironments,andtheopportunity

toutilisemoregasandreduceemissions.

MethaneUtilisationandAbatement

CapturedCMMisacleanenergyresourceforwhichthereareavarietyofuses.FigureES1summarizes

thedistributionofknownCMMprojectsgloballythatareoperating,underdevelopment,planned,or

wereoperatingpreviously.Thesefiguresarebasedonadatabaseofmorethan240projectsglobally,

compiledbytheMethanetoMarketsPartnership.Asthe figure indicates,powergeneration,natural

gaspipelineinjection,andboilersarethedominantprojecttypes(basedonnumberofprojects).

FigureES1DistributionofCMMUses inGlobalProjects.This figurerepresentsthetotalnumberof

CMMprojectsreportedtoMethanetoMarketsthatareactiveorunderdevelopmentglobally,based

ontypeofenduse.


16/86

(Source:MethanetoMarketsPartnership,2009)

Purificationtechnologies

have

been

developed

and

are

extensively

used

(e.g.,

inthe

United

States)

to

remove any contaminants fromhighqualityCMMtypicallyproduced from predrainagetomeet

stringentpipelinequality standards (EPA,2009). Formanyother gasenduseapplications, thehigh

costs associated with purifying drained gas may be unnecessary and can be avoided by improving

undergroundmethanedrainagestandards.

Withtheproperequipmentandprocedures,unuseddrainedgascanbesafelyflaredtominimiseGHG

emissions.Flaringconvertsmethane,whichhasaGWPofmorethan20comparedtocarbondioxide,

whichhasaGWPofone(IPCC,2007).

Methane

that

is

not

captured

by

the

drainage

system

is

diluted

in

the

mine

ventilation

air

and

is

emittedtotheatmosphereasdiluteventilationairmethane(VAM),typicallyatconcentrationsof1%

or lessmethane.Despitethis lowconcentration,collectivelyVAM isthesingle largestsourceofmine

methaneemissionsglobally.Thermaloxidationtechnologieshavebeen introducedatdemonstration

andcommercialscalesatseveralsitesglobally(e.g.,Australia,China,andtheUnitedStates)toabate

theseemissions(andinonecase,toproduceelectricityfromthedilutemethane).Othertechnologies

tomitigateVAMemissions(e.g.,catalyticoxidation)areemergingandunderdevelopment.

CostandEconomicIssues

Effectivegasdrainagereducestherisksofexplosions,andhenceaccidentrisks.Reducingtheserisksin

turn

reduces

their

associated

costs.

Costs

of

methane

related

accidents

vary

widely

from

country

to

countrybutaresignificant.Forexample,a10%workstoppageoridlingatagivenmineduetoagas


17/86

relatedincidentoraccidentcouldleadtoUS$8milliontoUS$16millionperyearinlostrevenuesata

typical highproduction longwall mine. Additional costs of a single fatal accident to a large mining

operationcould range fromUS$2million tomorethanUS$8million through lostproduction, legal

costs,compensation,andpunitivefines.

Atthe

same

time,

gas

drainage

creates

an

opportunity

for

gas

recovery

and

utilisation.

Such

energy

recoveryprojects canbeeconomical in theirown right through saleof thegasor its conversion to

electricity,vehiclefuel,orothervaluablegasfeedstocks.

Gas recovery and utilisation projects are increasingly also including revenue streams from carbon

emission reduction credits in the form of Verified Emission Reductions (VERs), Certified Emission

Reductions (CERs),orother credits suchasemission reductionunits (ERUs).Thesepotential carbon

financingoptionsmaybeacriticalfactorinmakingsomeCMMutilisationprojectseconomicallyviable

thatwouldbeotherwise financiallyunattractive. Inaddition,carbon financingmayprovide theonly

revenue streams for abatementonly projects, such asVAMoxidation (without energy recovery)or

CMMflaring.

VAM can also be used for power generation. At this time, VAMderived power generation is not

commercially feasible without carbon revenues or other incentives, such as preferential electricity

pricingorportfoliostandards.

Currently,investmentdecisionsatmostminesarelikelytofavourexpansionincoalproductionrather

thandevelopingCMMutilisationprojects(particularlypowergeneration)duetothehighopportunity

costof investing inpowergeneration capitalequipmentand infrastructure.Tomeetenvironmental

protection targets in the future, however, mine owners may be required to improve gas drainage

performancebeyond

the

level

strictly

required

tomeet

the

mines

safety

needs.

Such

improvements

in

the drainage system that yield relatively highquality gas may provide an additional incentive for

investmentingasrecoveryandutilisationprojects.

Conclusions

Aholisticapproachtomanagingmethanereleasesintocoalmineworkingsandsubsequentemissions

into the atmosphere will have a number of beneficial impacts on overall mine safety, mine

productivity,andenvironmentalimpacts,particularlywithregardtoGHGemissions.

Globalapplicationoftheaccumulatedknowledgeonmethaneoccurrence,prediction,control,

andmanagementthatiscurrentlyavailablewillimproveminesafety.Implementationofgood

practices for methane drainage could substantially reduce explosion risks resulting from

methaneincoalmines.

Thereisastrongbusinesscaseforinstallingandoperatinghighefficiencygasdrainagesystems

basedontheircontributionstoincreasemineproductivity.Becausesuchsystemswillincrease

theavailabilityofgoodqualityCMM, therecanalsobeastrongbusinesscase forexploiting

andrecoveringenergyfromthecapturedgas.

Emissionsofmethane,animportantGHG,fromundergroundcoalminescanbesignificantly

reducedby

utilising

the

drained

gas,

flaring

the

gas

that

cannot

be

used,

and

mitigating

VAM

emissionsbyoxidation.


18/86

Chapter1.Introduction

KeyMessages

Regardlessofconstraints,mineworkersafetyisparamountandshouldnotbecompromised.

Ariskassessmentapproachtominimisingexplosionrisksshouldbecombinedwithstrongenforcement

ofrobustventilationandutilisationsafetyregulations.

Ideally,moderncoalminingcompaniesrecognisethebenefitsofadoptingaholisticgasmanagement

systemthatconstructively integratesundergroundgascontrol,methaneutilisation,andreductions in

greenhousegas(GHG)emissions.

1.1 ObjectivesofthisGuidanceDocument

Thisdocumentaimstoprovideguidancetomineownersandoperators,governmentregulators,and

policymakers in the design and implementation of safe, effective methane capture and control in

underground coal mines. It is intended primarily to encourage safer mining practices to reduce

fatalities,injuries,andpropertylossesassociatedwithmethane.

An importantcobenefitofeffectivemethanedrainageatcoalmines is toallow for the recoveryof

methane tooptimise theuseofotherwisewastedenergy resources.Thus,an importantmotivation

behindthedevelopmentofthisguidancedocument isto facilitateandencouragetheutilisationand

abatement of coal mine methane (CMM) to reduce GHG emissions. Ultimately, adoption of these

practiceswillhelptoenhancethesustainabilityandlongtermfinancialpositionofcoalminesglobally

by:

Strivingtoachieveagoalofzerofatalities,injuries,andpropertylosses.

Demonstrating the global coal industrys commitment to mine safety, climate change

mitigation,corporatesocialresponsibility,andgoodcitizenship.

EstablishingaglobaldialogueonCMMcaptureanduse.

Creatingcriticallinkagesamongcoalindustry,government,andregulatoryofficials.

IncorporatingeffectiveCMMcaptureasapartofaneffectiveriskmanagementportfolio.

Thisguidancedocument is intentionallyprinciplesbased.That is, itdoesnotattempt topresenta

comprehensive,prescriptive approach thatmaynot adequately account for sitespecific conditions,

geology,andminingpractices.Theauthorsrecognizethereisnouniversalsolutionandtherefore,have

establishedabroadsetofprinciplesthatcanbeadaptedasappropriatetoindividualcircumstances.In

general,thetechnologiesforimplementingtheseprinciplescontinuetoevolveandimproveovertime.

Internationalindustrybestpracticesareoutlinedinthisdocumentasappropriate.

This document is not intended to serve as a comprehensive, detailed technical methane drainage

manual.Referencesandadditionalresourcesareprovidedattheendofthisdocument.

1.2 TheIssues

Coal

is

an

essential

energy

resource

in

both

industrialised

countries

and

emerging

economies.

Meeting

thevoraciousenergydemand,particularlyinsomerapidlygrowingeconomies,hasplacedpressureon


19/86

coalmines to increase theirproductionsometimes to levelsbeyondwhat canbe safely sustained,

leadingtostressesonoverallminingoperationsandcompromisingsafety.Thepresenceofmethanein

coalminespresentsaserioussafetyconcernthatneedstobemanagedprofessionallyandeffectively.

Whilemethaneexplosions inundergroundcoalminesareveryrareoccurrences inmanycoalmining

countries,theystillcausethousandsofminefatalitiesandinjurieseveryyear.

Manydeathscan result froma single incident.Table1.1 showssomeof themost serious fatalcoal

mineexplosions thathaveoccurred in several countries since2000.Witheffectivemanagementof

minemethane,suchtragediescanbeeliminated.

Table1.1MajorCoalMineExplosionIncidents,Post2000

Country Date CoalMineNumberof

Fatalities

China 14February2005 Sunjiawan,Haizhoushaft,Fuxin 214

Kazakhstan 20September2006 Lenina,Karaganda 43

Russia 19March2007 Ulyanovskaya,Kemerovo 108

Ukraine 19November2007 Zasyadko,Donetzk 80

USA 2June2006 Sago,WestVirginia 12

Accidentscanoccurwhenmethaneenterstheminespacefromthecoalseamandsurroundingstrata

asaresult

ofthe

disturbance

created

by

the

mining

operation.

The

amount

ofgas

released

into

the

mine is a function of both the rate of coal extraction and the in situ gas content of the coal and

surroundingstrata.

National regulatory agencies set maximum limits for the methane concentration in underground

airways.Thus,methanereleasesintothemineworkingscanbealimitingfactorforcoalproduction.

Guidanceisurgentlyneededtohelpgovernmentsswiftlyimplementsaferworkingpracticestoreduce

thehazardposedbymethane inunderground coalmines.Basedonavailabledata, there isa large

range in the fatality rate of underground coal mining in different countries around the world. For

instance, the rateof fatalitiespermillion tonnescoalminedmaydifferbya factorofmore than30

timesfromonecountrytoanother.1

No coal mine is free from safety risks. Gasrelated incidents can occur in even the most modern

undergroundcoalmines.Advancedtechnology reduces the riskofworker fatalities fromexplosions,

but technology alone is insufficient to solve the problem. Management, organisational structure,

workerparticipation,training,andregulatoryandenforcementsystemsareallessentialcomponents

1Basedon2008data(officialstatistics)forundergroundcoalminingfatalitiesinChinaandtheUnitedStates.In

2008,Chinareported3,215fatalitiesper2,565billiontonnesofundergroundcoalmined(assuming95%ofthe

total reported 2.7 billion tonnes is from underground coal mined), for 1.25 fatalities per million tonnes

underground

coal

mined

(SAWS,

2009).

In

2008,

the

United

States

reported

12

fatalities

from

underground

coal

mines,withproductionof324million tonnes, for0.037 fatalitiespermillion tonnesunderground coalmined

(MSHA,2009).


20/86

of an effective risk management process. Knowledge and understanding of the basic principles of

methanegascontrolisfundamentaltodesigneffectivecontrolsandsystems.Ultimately,allexplosion

accidentsareamanifestationoffailuretoeffectivelyimplementsafepracticesandprocedures.

Coal mines are a significant emissions source of methane, a potent GHG with a global warming

potential(GWP)

ofmore

than

20

times

that

ofcarbon

dioxide

(IPCC,

2007).

Methane

accounts

for

14%

ofglobalanthropogenicGHGemissions,andCMMemissionscontribute6%ofglobalanthropogenic

methane emissions or close to 400 million tonnes of carbon dioxide equivalent (MtCO2e) annually

(EPA,2006a;IPCC,2007;MethanetoMarkets,2008).CMMemissionsareprojectedtoincreaseto793

MtCO2eby2020(ESMAP,2007).Morethan90%oftheseCMMemissionsarefromundergroundmines

(EPA, 2006b); of which about 80% is emitted in very dilute form (typically less than 1% methane)

throughthemineventilationair.

Technologiesalreadyexistthatcouldsignificantlyreducemethaneemissions fromcoalmining.Their

successfulimplementationrequiresleadershipfromgovernments,suitablefinancingmechanisms,and

thecommitment

ofthe

global

coal

mining

industry.

1.3 GasCapture,Utilisation,andAbatement

Gas capture and use in coal mines is not new, although there have been major improvements in

technologyanditsapplicationoverseveralcenturies.Thefirstrecordedmethanedrainageoccurredinthe

UnitedKingdomin1730.Moremodern,controlledmethanedrainagesystemswereintroducedinEurope

inthefirsthalfofthetwentiethcentury.2Utilisationofminegasforlightingmayhaveoccurredasearlyas

the18thcenturyandwasrecordedinthe1880s.

Bythe1950s,systematicandeffectivegascapturemethodsthatwereoriginallydeveloped inGermany

were being used throughout Europe. Since the 1960s, increasing use has been made of drained gas,

initiallyformineboilersand industrialprocessesandthen later forpowergeneration,pipelinegas,and

towngas.

Figure1.1illustratesathreedimensionalschematic,incutawayperspective,ofanundergroundcoalmine

workingsandsurfacefacilities.Thisgraphicshowsthecomplexityandinterrelatedaspectsofthemines

undergrounddrainageandgascollectionsystemswiththesurface facilitiesneededtoconvertCMMto

electricity.Thegraphicalsoillustratesthesimultaneousabatementofventilationairmethane(VAM)from

themineventilationshafts.

2TheseincludedsystemsintheUpperSilesianbasininPolandin1937andinGermanyin1943.


21/86

Figure1.1SchematicofanUndergroundCoalMineDrainageSystemandSurfaceFacilities forEnergy

RecoveryandAbatementofCMM

(CourtesyofGreenGasInternational)

Currently, therearehundredsofCMMgas recoveryandutilisationprojectsaround theworld thatare

operatingorunderdevelopment.Forinstance,theMethanetoMarketsPartnershipestimatesthatmore

than240projectshaveoperated,arecurrentlyoperating,orare indevelopment inabout14countries

globally(2009).ThemostprevalentuseforCMMisforpowergeneration;otherusesincludeboilerfuel,

injectiontonaturalgaspipelines,towngas,industrialgas,feedstockforconversiontovehiclefuelssuchas

liquefiednaturalgas(LNG)orcompressednaturalgas(CNG),andcoaldrying.

Insomecases,methanethatcannotbeeconomicallyrecoveredandusedduetoimpracticalsitespecific

conditionsormarketsisdestroyed(i.e.,flaredandtherebyconvertedtocarbondioxide).Thisreducesthe

GWP of the emissions. These emission reductions also have the potential to generate revenue from

carboncreditsinsomecountries,throughbothvoluntaryandcompliancecarbonmarkets.


22/86

Chapter2.FundamentalsofGasControl

KeyMessages

Establishing and enforcing regulationsfor safe gas extraction, transport, and utilisation encourages

highermethane

drainage

standards,

as

well

as

increased

clean

energy

production

and

greater

emission

reductions.

There is tremendous global industry knowledge about and experience with managing methane

explosionrisks.

Safeworkingconditions ingassymineenvironmentscannotbeachievedsolelythrough legislationor

eventhemostadvancedtechnology.Rather,rationalandeffectivemanagementsystems,management

organisation,andmanagementpracticesarefundamentaltosafeoperations.Othercriticalelementsof

mine safety are appropriate education and trainingfor bothmanagement and theworkforce, and

encouragingworker

input

as

work

safety

practices

are

adopted.

2.1 ObjectivesofMineGasControl

Theprimaryaimofgascontrolsystemsistopreventexplosionsandasphyxiationrisksinunderground

coal mines. Controlling methane at an active longwall face so that methane concentrations in the

return airway do not exceed 1% generally requires only using ventilation techniques. However, if

highermethaneflowsareexpectedfromtheworkingface,acombinationofventilationandmethane

drainagemustbeused.Bestpracticegascontrolforsafetywillenhancegasutilisationprospects.

Protectionmeasuresareavailabletoreducethepropagationofanexplosionafterithasoccurredand

areimportant

second

lines

ofdefence.

Post

failure

methane

mitigation

isno

substitute

for

prevention,

however,whichisthefocusoftheseguidelines.

2.2 OccurrenceofGasHazards

Methanerich gases, generally containing between 80% and 95% methane, occur naturally in coal

seams and are released whenever these are disturbed by mining. Coal seam gas only becomes

flammableandcreatesanexplosionhazardwhenallowedtomixwithair.

Emissionsof largevolumesofcarbondioxidearealsoencountered incoalmines insomegeological

environments. Carbon dioxideis heavier than air and toxic at concentrations above 5% in air, but

physiologicaleffectscanbeexperiencedatconcentrationsaslowas1%.

Methane iscolourless,odourless,andtasteless;therefore,ameasurementdevice isneededtoconfirm

its presence. Methane is flammable when it is mixed with oxygen in a range of concentrations as

showninFigure2.1.

Atatmosphericpressure,themostexplosiveconcentrationofmethaneinairis9.5%byvolume.Inthe

confinedconditionsunderground,themaximumexplosionpressurecanincreaseastheunburnedgas

iscompressedaheadoftheflamefront.

Inoxygen

deprived

environments,

such

ascan

occur

insealed

goafs,

explosive

mixtures

can

only

form

if air is added. When present at higher concentrations, methane is an asphyxiant due to air


23/86

displacement. As underground coal mines are confined, ignition of a substantial accumulation of

methaneinvariablyleadstoanexplosion.

Figure2.1FormationofExplosiveMixtures

(Source:Moreby,2009;basedonCoward,1928)

Methanehasa tendency to stratifyand formhorizontal layersnear the roofofmineworkingswhere

thereare insufficientlyhighventilationvelocitiestoprevent layering.Thisphenomenonoccursbecause

methaneislighterthanair,withadensityofonly0.55thatofair.Inmanyinstances,anairvelocityof0.5

metrespersecond(m/s)willpreventlayeringbuttherearesomecircumstanceswherethisairvelocity

will

be

insufficient.

Ventilation

designers

should

be

aware

of

variables

that

inhibit

the

layering

of

methane, sucha layerwidth, inclinationof roadway, gasemission rate,andairflow rate (Creedy&

Phillips,1997;Kissell,2006).

Insomecircumstances,wheremixingisnottakingplacedueto insufficientairvelocity,methanelayers

can formand floweitherwith the floworagainst the flowof theventilation stream.Thesemethane

layersmaypropagate flame rapidly, thus increasing the riskand severityofexplosionsbyprovidinga

pathway between ignition sources and large accumulations of flammable mixtures (e.g., in longwall

goafs).Oncemethaneismixedwithair,however,itwillnotseparatespontaneously.

Mine

operators

actively

isolate

areas

of

mines

that

are

no

longer

being

worked

(i.e.,

workedout

longwallsandsometimesgoafsofactive longwalls)fromthemineventilationsystembyconstructing


24/86

barriersorseals.Theseventilationbarriersorsealsareinvariablyimperfectduetogroundmovement

andwillnotcompletelypreventgasemissionsfromentering intotheactivemineworkings.Explosive

gas mixtures can accumulate behind ventilation seals and will flow into airways as a result of

ventilationfluctuationsorbarometricpressuredepressions.

Highrisk

areas

inacoal

minewhere

coal

seam

methane

passes

through

the

explosive

rangeare

in

the goaf (gob)behind longwall faces and in the cutting zoneofmechanised coalcuttingmachines.

Explosivemixturescanalsoformwithinbadlydesignedorpoorlyoperatedmethanedrainagesystems

duetoexcessiveairbeingdrawnin.

Roomandpillarmineworkings(withnopillarrecovery)tendtodisturbconsiderablylowervolumesof

adjacent strata than longwall methods; therefore, these mines tend tobe less gassy than longwall

mines.Roomandpillarminesarenotnecessarily lessat risk fromexplosions,however,due to the

difficultiesofachievingadequate ventilationofworking faces.Thepredominantmethane source in

roomandpillarworkingsistheworkedseamitself.Layersofflammablegasmixturescanarise inthe

roofasaresult

ofinadequate

ventilation

ofblind

headings

and

emissions

from

roof

sources

(see

Case

Study4).

IgnitionofExplosiveMethaneMixtures

Methaneair mixtures can be ignited by a number of sources: electrical sparks, high temperatures

causedbysteelstrikingquartziticrock,adiabaticcompressionfromfallsofrock,aluminiumimpacting

oniron,lightningstrikes,smokingmaterials,explosivesanddetonators,spontaneouscombustion,and

nakedflames.

Theuseofincreasinglypowerfulrock andcoalcuttingmachineryinmoderncoalmineshasgivenrise

tothe

serious

problem

offrictional

ignitions.

The

high

frequency

ofmethane

ignitions

caused

by

rock

andcoalcuttingtoolscomparedtoothersourcesindicatesthetechnicaldifficultyinachievingabsolute

controlofgashazards.

2.3 ReducingExplosionRisk

Highlighting theunderlyingprinciplesofexplosionprevention isamajor goalof this guidance.This

knowledge is essential for effective programme design for controlling gas risks in coal mines. The

principlesdescribedhereinare synonymouswith thoseembedded in the riskmanagement systems

that modern mining companies have implemented in striving towards zero accidents and zero

explosions.

Managementofcoalminegasexplosionrisks involvesa largenumberofdifferentactivities(seeBox

2.1),necessitatinggoodorganisationandclearallocationofresponsibilities.


25/86

Reducingexplosion riskbypreventing theoccurrenceofexplosivemixtureswhereverpossibleand

takingmeasurestoensureseparationofexplosivemixtures frompotential ignitionsourcesarethe

bestsafetypracticesincoalmines.

Controllingthedilution,dispersion,anddistributionofflammablegasesincoalminestominimisethe

availabilityoffuelforignitioniscritical.Therisksassociatedwithflammablegasesinundergroundcoal

minescanbeminimised inseveralways:bydilutingthemtosafeconcentrationswithventilationair;

byusingproprietarydevices toventilatecoalcuttingmachines;bydivertinggasaway fromworking

areas;and,

where

necessary,

by

capturing

gas

inboreholes

orgas

drainage

galleries

before

itcan

enter

mineairways.

Thefundamentalprinciplesofreducingexplosionriskareasfollows:

Whereverpossible,preventoccurrenceofexplosivegasmixtures (e.g.,useofhighefficiency

methane drainage methods, prevention and dispersal of methane layers by ventilation

velocity).

Ifexplosivegasmixturesareunavoidable,minimise thevolumesofexplosivemixtures (e.g.,

rapiddilutioninventilationairtopermissiblemethaneconcentrations).

Box2.1TypicalCoalMineGasExplosionRiskControlsandProcedures

Useofflameproofelectricalequipmentandcables

Controlofexplosivesandtheirusebelowground

Provisionofadequatefireandrescuefacilities

Gasdrainage

planning,

design,

and

implementation

Controlofthedischargeofdrainedmethanegas

Controlofaccesstothemineanditsworkingareas

Restrictionofcontrabandintheundergroundenvironment

Inspectionofundergroundworkings

Provisionofantistaticmaterials

Supervisionofminingoperations

Useandmaintenanceofmechanicalandelectricalplant

Provisionforrestrictingtheuseofunsuitableequipment

Supervisionofmechanicalandelectricaloperations

Restrictionofsmokingmaterialsbelowground

Ventilationplanning

Controlofthemineventilation

Monitoringandmeasurementofminegasconcentrations

Useofauxiliaryventilation

Degassingofheadings

Frictionalignitionprecautions

Provisionofmethanedetectors

Qualificationsofemployees

Safetytraining

Provisionofexplosionsuppressionbarriers

Postingofwarning

signs

and

notices


26/86

Separateunavoidablegasmixtureoccurrences frompotential ignitionsources (e.g.,byusing

specially designed faceend ventilation systems to prevent gas accumulations near electric

motorsoravoidinguseofelectricityinlongwalldistrictreturnairways).

Avoidignitionsourcesasmuchaspossible(e.g.,unsafeelectricdevices,nakedflames,smoking).

Controlgasemissionsfromworkedout,sealedareasoftheminebyusinggasdrainagemethods

regulatedtomaintaingaspurityandbydraininggastoaccommodatefluctuationsinbarometric

pressure.

2.4 RegulatoryandManagementPrinciples

EffectiveSafetyRegulatoryFramework

An effective safety regulatory framework will provide coherent and clear guidance to the industry

under theaegisofa leadsafetyauthority,withclearlydefined rolesand responsibilitiesthatdonot

overlapwiththoseofotherauthorities.

Comprehensivecoal

mine

gas

safety

regulations

provide

no

guarantee

ofsafe

working

conditions.

To

be effective, regulations must be understood, applied, and enforced by mine inspectors, mine

management,supervisorystaff,andmineworkers.Proactiveriskmanagementandbottomupsafety

responsibilitiesarethekeystopreventionofgasaccidents.Officialsandminerscanonlybeproactiveif

they understand the underlying principles of gas emission and control processes. Training and

knowledge transferare thereforenecessary elementsofa successful safetyprogramme, aswell as

ready access to factual reportson gas incidentsand their causes. Safetymanagement and training

shouldencompassbothmineemployeesandcontractors.

Enforcement

Effective

government

inspectors

audit

mine

safety

conditions

by

conducting

detailed

underground

inspections,providingexpertguidancetominemanagement,reviewingtheefficacyofregulations,and

ensuringcompliancewiththeregulationsbyworkingwithmineoperatorstocorrectanydeficiencies

or penalise those who conspicuously ignore regulations and endanger life. Effective safety and

regulatorymanagementsystemsalsoinvolvethosewhoaremostaffectedbyfailuretocontrolgas,the

minersthemselves.Toensurethemosteffectiveriskmanagement,emphasismustbeonaccidentor

incidentpreventionratherthanpunishmentafteranevent.

Successfulmanagementofhealthandsafetyrisksnotonlyinvolvestheregulatoryauthoritiesandthe

mine operator, but must include the mine workers as equal participants. As outlined in the

International

Labour

OfficesCode

of

Practice

on

Safety

&

Health

in

Underground

Coal

Mines

(ILO,

2006),workersareentitled toa safeworkingenvironment, including theability to reportpotential

hazards without fear of retribution. Moreover, as partners in developing safe working conditions,

workersareobligatedtosupportsafeworkingpracticesandmaintainasafeminingenvironment.

PermissibleGasConcentrationsforSafeWorkingConditions

Prescriptive regulations shouldbeusedsparingly,as theycanstifle innovation.Theyarejustifiedby

physical imperatives such as the explosive range of flammable mine gases in air. All coal mining

countriessetupper limitsofpermissiblemethaneorflammablegasconcentrationsthatshouldnotbe

exceededinmineairways.Someapplydifferentmandatorygasconcentrationlimitsindifferentpartsof

acoal

mine

depending

on

the

activity

and

the

risk

ofexplosive

levels

being

reached,

and

set

minimum


27/86

safe concentrations for transporting and using gas to minimise the risk of underground explosions

(Table2.1).

Table2.1SelectedExamplesofRegulatoryandAdvisedFlammableMethaneConcentrationLimits

Limiting

flammable

methane

concentration[%]

Australia China Germany Indiah

South

Africa

United

Kingdom USA

Factors

ofsafetya

Maximumbelow

whichworkingis

permittedin

general

1.25 1.0 1.0 1.25 1.4 1.25 1.0 3.65.0

Maximumbelow

whichworkingis

permittedin

returnairways

2.0b 1.5

g 1.5 0.75 1.4 2.0

b 2.0

b 2.56.7

Minimum

permittedfor

utilisation

nae

30

25

naf

naf

40

25c

1.72.7

Minimumfor

underground

pipelinetransport

nae na 22 na

f na

f na

e na

d 1.5

(a)Factorsofsafetyindicatetherangeofmultiplesbelowthelowerexplosivelimitof5%orabovetheupperexplosivelimitof

15%methaneinair;

(b)Ifnoelectricity;

(c)TheUnitedStateshandlesmethanedegasificationintheventilationplan,therearenocodesorregulations;

(d)Notconsideredaproblemaslowerconcentrationgoafgasesaregenerallydrainedatsurfacewells;

(e)Determinedbylocalriskassessment;

(f)Fewornoapplicationssonotaddressed;

(g)2.5%

for

anon

travelling

return;

(h)InIndia,methanestandardsarespecifiedinIndianCoalMineRegulation1957,whichisbasedonMinesAct1952.

The precise action levels for gas concentrations by themselves are insufficient to ensure safe mine

conditions.Itisjustasimportanttoidentifysuitablelocationsatwhichtheconcentrationsaremeasured,

the procedures to be used for measurement, and the actions to be taken as a consequence of the

measurements.Mininglegislationinindustrialisedcountriesgenerallyfocusesonmonitoringandcontrol

effortsinproportiontothedegreeofexpectedrisk.

SafeTransportandUtilisationofGas

Transport

and

use

of

explosive

mixtures

of

gas

is

hazardous

due

to

the

dangers

of

propagating

an

explosionintotheworkingareasofamine.Nationalminesafetyregulationsvaryintheirassessment

of the minimum methane concentration considered safe for transport and utilisation, which varies

from25%to40%amongcountries.A factorofsafetyofat leasttwotimestheupperexplosive limit

(i.e.,30%orgreatermethaneconcentration)isgenerallyacknowledgedasagoodpracticeminimum.3

Accidentsinvolvingpipelinescarryingmethaneatconcentrationswellabovetheupperflammablelimit

donotresultinexplosionsbecausethegasisattoohighapuritytoburn;inthesecases,afireatthe

gas/air interfacecanbeextinguishedbyfirefightingtechniques. Incontrast,an ignitionof lowpurity

3Afactorofsafetyofatleast2.5belowthelowerexplosivelimitofmethane(i.e.,below2%methane)isagood

practicemaximum,intheabsenceofelectricity;ahigherfactorofsafetybeingnecessaryifelectricityisinuse.


28/86


29/86

Chapter3.Occurrence,Release,andPredictionofGas Emissions in

CoalMines

KeyMessages

Methanegasflowsintocoalminesundernormal,steadystateconditionsaregenerallypredictable.

Unusualemissionandoutbursteventsarenoteasilypredicted,buttheconditionsunderwhichtheycan

occurarereasonablywellknown.Detailedmethodsforreducingrisksundertheseconditionshavebeen

developedandshouldbeappliedwhereversignificantrisksare identified. Insuchcircumstances,safe

workingconditionsdependontherigorofimplementationandmonitoringofgascontrolmethods.

Theimportanceofnotonlyinstallingundergroundmonitoringforoperationalminesafetyreasonsbut

gatheringandusingthedataforsafetyplanningcannotbeoverstated.

3.1

Introduction

Modern, highproduction coal mines encounter increasingly high gas flows as their coal extraction

rates increaseand theyworkdeeper,highergascontent coal seams.Knowledgeof theoccurrence,

emissioncharacteristics,andexpectedgasflowsfromacoalmineasafunctionofthecoalproduction

rate is essential for safety, mine planning, ventilation, gas utilisation, and GHG emission control

purposes.

3.2 OccurrenceofGasinCoalSeams

Thenaturallyoccurringgasfound incoalseamsconsistsmainlyofmethane(typically80%to95%)with

lowerproportionsofheavierhydrocarbongases,nitrogen,andcarbondioxide.Themixturesofmethane,

water vapour, air, and associated oxidation products that are encountered in coal mines are often

collectivelytermed"minegas."

Methanewasformed incoalseamsasaresultofthechemicalreactionstakingplaceasthecoalwas

buried at depth. Plant debris such as that found in modern swamps will slowly change from wet,

organicdetritustocoal,ifthematerialbecomesburiedatasufficientdepthandremainscoveredfora

lengthoftimethroughaprocessknownascoalification.Thegreaterthetemperature,pressure,and

durationof coalburial, thehigher the coalmaturity (i.e., rank) and the greater theamountof gas

produced.Muchmore gaswasproducedduring this coalificationprocess than isnow found in the

seams. The gas lost during the coalification process has been emitted at ancient land surfaces,

removedinsolutionbygroundwaterpassingthrough,orhasmigratedandbeentrappedinthepore

spacesandstructuresinsurroundingrocks.Thisgasmayhaveaccumulatedinadjacentporousstrata

suchassandstonesormayhavebeenadsorbedbyorganicshale.Thesereservoirrockscanbecome

significant sourcesof gas flows into themine if these gasbearing layersare sealedby surrounding

impermeablestrataandremainundisturbeduntilminingtakesplace.Methaneoccurs inmuchhigher

concentrationsincoalcomparedtoanyotherrocktypebecauseoftheadsorptionprocess,whichenables

methanemoleculestobepackedintothecoalsubstancetoadensityalmostresemblingthatofaliquid.In

averticalsequenceofcoalseams,methanecontentoften increasessystematicallywithdepthandrank.

Gascontent

depth

gradients

vary

from

coalfield

tocoalfield

and

reflect

the

geologic

history

ofthe

basin

in


30/86

which the coal formed. In some coal basins, methane contents increase with depth, finally reach a

maximumandthendecreasebelowthislevel.

3.3 TheGasReleaseProcess

The

gas

that

is

naturally

produced

and

stored

in

coal

and

surrounding

strata

can

be

released

ifdisturbedbyminingactivity.Therateandamountofgasreleaseddependsontheinitialamountofgas

inthecoal(gascontent),thedistributionandthicknessofcoalseamsdisturbedbymining,thestrength

ofthecoalbearingstrata, thegeometryof themineworkings,the rateofcoalproduction,andcoal

seampermeability.Totalgasflowvariesproportionallytotherateofdisturbanceofstratabymining

activity. Inaparticulargeologicalsetting,therefore,the totalvolumesofgas releasedduringmining

increase proportionally with the increase in the rate of coal extraction. In certain circumstances,

however,rapidejection,oroutbursts,ofcoalandgasandsuddenemissionsofgascanalsooccur.

Some coal seams mined in Australia and elsewhere have adsorbed substantial amounts of carbon

dioxideaswell

asmethane.

Where

these

coal

seams

are

mined,

outbursts

may

occur

atalower

total

insitugascontentofthecoalseamthanwouldbeexpectedifonlymethanewaspresent.Therefore,the

insitucontentofbothgasesshouldbemeasuredtoassesstheneedforpredrainage.

Europeanstudies(Creedyetal,April1997)haveshownthatadestressedarchorzoneofdisturbance,

withinwhichgasisreleased,formsabovealongwalltypicallyextending160mto200mintotheroof

andbelowthelongwalltoabout40mto70mintothefloor.Figure3.1isapictureofaplastermodel

showingthedistressingofoverlyingmaterialafteravoidspacewascreated.Thismodellingprocedure

isusefulindeterminingthemagnitudeofdestressingthattakesplaceandtheheightabovethevoid

thatnoticeablebedseparation,fractureopening,andotherformsofstratarelaxationoccurs,thereby

increasingthe

permeability

and

creating

pathways

for

gas

migration.

Various

theories

and

empirical

modelshavebeendevelopedtorepresentthisprocess.

Figure3.1ModelSectionParalleltotheLongwallFaceShowingtheStrataFracturedasaResultof

RemovingtheCoal,ThusFormingtheGoaf

(ModeledafterGaskell,1989)

Coalseamextraction leadstosubsidenceatthesurface.Whilealltheseamsbetweena longwalland

thesurfacewillbedisturbed,onlygaswithinadestressedarchenterstheworkings.Boreholesfrom

thesurfaceandshallowexcavationswillsometimesencounterreleasedcoalseamgasthatwouldnot


31/86

normally be emitted during mining. Gas production may then occur. However, the borehole or

excavation can also serve as a migration pathway for gas not captured, resulting in surface and

subsurfacehazards.

3.4 RelativeGassinessofCoalMines

Thespecific(orrelative)emissionrateiscommonlyusedtorepresentthegassinessofamine,or

ofa longwalldistrict.Itusesthesameunitsasgascontent(i.e.,cubicmetresofmethaneemittedper

tonneofcoalorm3/t),but it isconceptuallyverydifferent.4Thespecificemissions represent the total

volumeofmethanereleased fromallsourcesdividedbythetotalamountofcoalproducedduringa

referencedperiodof time, ideallyaweekormore. Inotherwords, thismeasurement is reallycubic

metres (m3)ofmethaneemittedper tonne (t)ofcoalminedoveranygivenperiodof time.Thegas

beingemitted,andmeasured, iscomingnotjust fromthecoalthat isbeingextracted,butallofthe

strata that is disturbed and becomes relaxed as the void left by the mining process collapses.

Generally, coal mines with specific emissions of 10 m3/t and higher are considered gassy. Specific

emissionsashigh

as50

m3/t

to100

m3/t

have

been

encountered

inmines

insome

countries,

such

as

theUnitedKingdomandtheUnitedStates,buttheselevelsareexceptional(Kisselletal,1973).

3.5 UnderstandingGasEmissionCharacteristicsofCoalMines

Peakflowsofgasoccurinthereturnairwaysofworkingdistrictsduringthecoalfacecuttingcycleand

following roof caving as longwall supports are advanced. Statistical studies have shown that these

peaks typically rise up to 50% above the mean (Creedy et al, April 1997). Gaspredictionmethods

commonlyusethisrelationshipinestimatingthevolumeofairthatwillbenecessaryinordertomeet

mandatorygasdilutionrequirements.

Thevolumeofgasreleased fromanycoaldisturbedbyminingdecreasesovertime,whilecontinued

miningactivityaddsnewgassources.Theresultantemissionsarethereforedeterminedbythesumof

allthesourcesovertime.Asaconsequence,thespecificemission(i.e.,theamountofgasemittedper

tonne of coal mined) can increase over the life of a longwall. When coal production stops, gas

continues todesorb from the coal seamand flow from thenoncoal strata,butatadeclining rate.

Whenaminecommencescoalextractionaftera fewdaysofstoppage,gasemissionwillbe initially

lowerthanatsteadyproduction.

Most empirical emission calculations assume steadystate coal production and uniform emission

characteristics. While this approach suits most planning needs, mine operators must also consider

other lesspredictable factors.Therefore,riskcontrolmethodsarecriticaltoreducethe likelihoodof

seriousoccurrences.Forexample, suddenoutburstsofgasandcoal (and sometimes rock) from the

workedseamareencounteredincertainmineswithhighgascontentsandlowpermeabilitycoal.The

principalgeologicalandminingfactors,whichgiverisetothehighestriskofanoutburstoccurrence,

canoftenbe identified,but theactual incidence cannotbepredictedwithany certainty.Coalmine

managementcanaddressthissafetyissuebyimplementingrigorousoutburstpreventionandcontrol

methods. These methods typically involve reducing the gas content of the coal to below a critical

amountbydrainingthegasbeforemining.

4GascontentisdefinedanddescribedinSection3.6.


32/86

Suddenemissionsofgascanoccurfromthefloorofalongwallworking,eitherontothefaceorintothe

roadwaysneartheface.Thistypeofemissionisconsideredespeciallylikelywhenthefloorcontainsa

strong sandstone bed and another coal seam lies within 40 m to 60 m below the working seam.

Althoughpredictinganoccurrence isproblematic,prevention cangenerallybeassuredbydrillinga

regularseriesoffloorboreholestopreventaccumulationofgaspressure.

Suddenemissionsandoutburstscancauseconsiderabledamageandresultininjuriesandfatalities.If

theair/methanemixtureisintheflammablerange,sparksfromrockstrikingmetalscanalsoignitethe

minegas.

Coalmineworkings can sometimesdisturbnatural gas reservoirs, leading toemissionsup to twice

thoseexpectedfromcoalseamsourcesalone.Thenaturalgasreservoirsmaybestrata interbedded

withthecoalseamsandoccurringasanormalpartofthecoalbearingsequence,butbecausegeologic

processesobstructedorsealedoffgasmigrationpathways,thetrappedgas issubsequentlyreleased

duringmining.Suchsituationsarenoteasily identifiedbeforemining,butmineoperatorsshouldbe

vigilantabout

this

possibility

by

comparing

measured

and

predicted

data.

The

importance

ofnot

only

installing undergroundmonitoring foroperationalmine safety reasonsbut gathering andusing the

dataforsafetyplanningcannotbeoverstated.

3.6 MeasurementoftheInSituGasContentofCoal

Planning gas drainage and ventilation systems to ensure safe mining requires knowledge of the

amount of gas adsorbed in the coal substance and, to a negligible extent, the amount of gas

compressedinthelargerporespaces.Gascontentisexpressedinvolumeofgascontainedpermassof

coal substance in situ (m3/t) and should not be confused with specific emissions.5 The general

approachfor

measuring

the

gas

content

istoobtain

and

seal

coal

samples

incanisters

inasfresh

a

stateaspossible.Thesesamplesaremaintainedatnearreservoirtemperaturewhilegasisallowedto

desorb.Themeasuredreleaserateallowsestimationofthegas lostpriortosampling.Figure3.2 isa

diagram showing an apparatus designed to collect and measure gas as it is desorbed from coal

containedbyasealedcanister.Theprocedureforusingthissystem includescollectingthesampleof

coal fromaboreholeand sequestering the coal ina canister.Periodically, thegas in the canister is

allowed to flow into the measuring cylinder and the volume of gas measured and recorded. The

compositionofthegasmaybeanalyzedbycapturingasampleandsubmittingitforchemicalanalysis.

Thegasremaining inthecoalafterthe initialtests isdeterminedbycrushingthecoalandmeasuring

thequantityreleased.TheU.S.BureauofMines(USBM)gascontentmeasurementmethodisthemost

commonlyused

technique

and

usually

requires

aperiod

ofdays

toseveral

weeks

(Diamond

&Levine,

1981).QuickdesorptionmethodshavebeendevelopedinEuropeandAustraliatoproviderapidresults

tosuitoperationalminingneeds(Janas&Opahle,1986).Inaddition,forlowpermeabilitycoals,partial

pressureandstatisticalmethodshavealsobeendevised (Creedy,1986).Becausecoalseams include

mineralmatteraswellascoalsubstance(gas ispredominantlyadsorbedonorganicsubstances),gas

contents are generally adjusted to an ashfree basis. The gaseous components are sometimes

measuredseparately;inmostinstances,thegasispredominantlymethane.Typicalmethanecoalseam

contentsfoundinnaturerangefromtracelevelstoaround30m3/t.

5Themeasureofgasemittedduringminingoperationscomparedtotheamountofcoalproduced.


33/86

Figure3.2GasContentMeasurementEquipment(AustralianStandard)

(BasedonDiamond&Schatzel,1998)

3.7 PracticalEstimationofGasFlowsinCoalMines

Rigoroustheoreticalgasemissionflowandsimulationmodelshavebeendevelopedwithinacademia

andbyresearchinstitutes.Forpracticalpurposes,minesgenerallyuseempiricalgasemissionmodels

that have been proven to be very reliable when used in conjunction with local knowledge and

expertise. These models require inputs of parameters including seam gas contents, mechanical

propertiesof the rockand coal strata,mininggeometry,andcoalproduction rates.Users canbuild

their own models using published information, or they can purchase proprietary software. Flow

estimates are expressed in either relative terms of cubic metresof gas releasedper tonneof coal

mined(specificemissionsinm3/t)orinabsoluteterms,asasteadystateflowrateofcubicmetresper

minute(m3/min)orlitrespersecond(l/s).

Modelsmaypredicttheeffectsofincreasedcoalproductionratesongasflows.Theycanalsoforecastthe

maximumcontrollablegasflowandtheassociatedmaximumcoalproductionaffectedbythefollowing

parameters:

Thestatutoryflammablegasconcentrationlimitinlongwalldistrictreturnairways.

Ventilation air quantities available and airflow volumes that can be circulated around the

workingdistricts.Theairflowvolumethatcanbedeliveredtoaworkinglongwalldependson

thenumberof roadways,ventilation configurationof theproductiondistrict,andmaximum

acceptablevelocity

for

miner

comfort.

Thegasdrainagecapturethatcanbeconsistentlymaintained,ifgasdrainageisused.


34/86

Chapter4.MineVentilation

KeyMessages

Mineventilationsystemsarecriticalcomponentsofanoverallsystemtoeffectivelyremovemethane

frommine

workings.

A

mine

ventilation

system

is

designed

to

achieve

three

objectives:

1)

deliver

breathablefreshair to theworkers,2)controlmineair temperatureandhumidity,and3)effectively

diluteorremovehazardousgasesandairbornerespirabledust.

Improvementstomethanedrainagesystemscanoftenprovideamorerapidandcosteffectivesolution

tominegasproblemsthansimplyincreasingtheminesairsupply.

4.1 VentilationChallenges

Achievingeffectiveventilation in coalmines isultimately the factor that limits coalproductionata

given

mine.

The

maximum

rate

of

coal

extraction

that

can

be

safely

achieved

on

a

gassy

working

coalface isdeterminedby thecombinationofventilation capacity todilutepollutants toacceptable

concentrationsandmethanedrainageefficiency.

Ventilation is the primary means of diluting and dispersing hazardous gases in underground mine

roadways.Airvelocitiesandquantitiesareoptimised toensuredilutionof gas,dust,andheat.The

greaterthefreshairquantitysuppliedtothecoalface,thegreatertheinflowofgasthatcanbediluted.

Thisdilutionprocessisinherentlylimitedbyairavailabilitywithinthemineandmaximumtolerableair

velocities.

Ventilationpressureisproportionaltothesquareoftheairflowvolume.Amodestriseinairquantity

thereforerequires

asignificant

increase

inpressure,

which

leads

togreater

leakages

across

goafs

and

ventilationdoors.Excessiveleakageflowsacrossthegoafsmayalsoincreasespontaneouscombustion

risksandcanimpairgasdrainagesystems.

The volume of air required to ventilate the underground workings and the permissible level of

pollutants is often mandated by local government agencies. A ventilation system that is designed

simplytocomplywith legalminimumairflowsorairvelocitiesmaybe inadequateforthepurposeof

maintainingasafeandsatisfactoryenvironmentinanactivemine.Forthisreason,ventilationsystem

designspecificationsmusttakeintoaccounttheexpectedworstcasepollutantlevels.

Methane

is

considered

the

principal

pollutant

and

the

most

hazardous

gas

for

ventilation

system

specifications. If the selected ventilation system design is capable of removing or satisfactorily

controllingtheprimarypollutant,itisassumedthatthelesserpollutantswillbeadequatelycontrolled

orremovedatthesametime.

4.2 KeyVentilationDesignFeatures

Generally,air isdrawn(sucked)throughaminebyexhaustfans locatedonthesurface.Thus,theair

pressure in the mine is below atmospheric pressure. In the event of fan failure, the ventilation

pressureintheminerises,preventinganinstantaneousreleaseofgasfromworkedareas.


35/86

Thedeeperandmoreextensivethemine,themorecomplextheventilationcircuitandthegreaterthe

propensity for leakage losses through communicatingdoors in theminebetween intakeand return

airways. Thus complex, larger mines have limited quantities of fresh air available for use in blind

headingsandonworkingcoalfaces,whichrequirestheuseofauxiliaryventilationducts.Nevertheless,

sufficientairmustbesuppliedtoallowheadingstobeventilatedinparallelandnotinseries;withthe

latterarrangement,agasprobleminoneheadingwillberapidlytransmittedtothenext.Bestpractice

istomakearrangementsforthesupplyofelectricitytobecutofffromallworkingplacesdownstream

ofaworkingplaceinwhichthemethaneconcentrationhasexceededthestatutorymaximum.

Ventilation requirementsaredynamic.Ventilationairdemand increasesasamine isdevelopedand

theareabeingventilated increases, sometimes requiring installationofadditionalventilationshafts,

upgradingfans,orenlargingexistingairways.

Proprietarysoftwareisavailableformodellingventilationnetworks.Actualpressureandflowsurveys

should be made at regular intervals to calibrate the model and check the system performance as

changesare

made.

Wheneverpossible,theventilationsystemshouldbedesignedsothatthevariousventilationsplits

orbranchesarenaturallybalanced.Thisactionreducestheneedtoinstallflowcontroldevicessuchas

air locks.Theopeningandclosingofsuchdevicestoallowthepassageofpersonnelhasaprofound

effectontheairflowsinthebranch.

Thesurface fan(s)shouldbedesigned tosatisfythemineventilation requirements.Surface fanscan

generally be adjusted within certain limits to ensure that they meet the requirements without

suffering aerodynamic instability. Older surface fans installed at some mature mines are often

operatingattheir

design

maximum

duty.

Insuch

cases,

any

increase

inairflows

tothe

more

remote

partsoftheminecanonlybeachievedbyimprovementstotheventilationairnetwork.

4.3 VentilationofGassyWorkingFaces

Differentcoalfacelayoutscontrolthegas,dust,andheatthatresultfromcoalextractionwithvarying

degreesofeffectiveness.Theprincipalgasrisksareassociatedwithareasofcoalworkingsinwhichthe

seamhasbeenpartiallyorwhollyextracted(whetherbylongwallorroomandpillarmethods)andare

no longersafelyaccessible(i.e.,goafs).All longwallorpillarrecoveryoperationsare indirectcontact

with minedout areas where methane, oxygendeficient air, and other hazardous gases can

accumulate. These gases includemethanenot capturedby gasdrainage,plus continuing emissions

fromcoalleftinthegoaf.

Thesegasesarehandledinoneoftwoways.First,theymaybeallowedtoenterthemineairstream

where sufficient air is available to dilute the maximum expected gas flows in the airways to safe

concentrations(Figure4.1).Asanexampleonlya longwallwithUv

BestPractGuide_MethDrain_es31

Documents

Transcript of BestPractGuide_MethDrain_es31