安全工程专业中英文文献翻译煤炭自燃.docx
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安全工程专业中英文文献翻译煤炭自燃.docx
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安全工程专业中英文文献翻译煤炭自燃
Spontaneouscombustionofcoal
Coalundergoesslowoxidationonexposuretoairatambienttemperatures,withtheevolutionofheat,gasesandmoisture,theheatgenerated,ifnotdissipated,givesrisetoanincreaseinthetemperatureofthecoal.Asthetemperatureofthecoalrises,therateofoxidationincreases.Ifthisisallowedtoproceeduncheckeditcaneventuallyresultintheignitionofthecoal.Thisoxidationprocessisknownasspontaneouscombustionorspontaneousheatingorself-heating.Self-heating,therefore,occurswhentherateofheatgenerationexceedstherateofoxidation.
Duringrecentyearstherehasbeenarenewedinterestinthespontaneouscombustionofcoalinallcoalminingcountriesparticularlybecauseoftheuseofcavingmethodsandthethickerseamsbeingmined.Large-scalebulkstorageandbulktransportofcoalhavealsobecomemoreimportantwiththeincreaseincoaltrade.
Evaluationofthepotentialofcoalforspontaneouscombustion
Severalmethodshavebeenusedtoevaluatethepotentialofcoalforspontaneouscombustionbutnoneisclearlysuperior.Themostcommonmethodsusedaredescribedblow.
Oxygenabsorption
Inthismethod,acoalsampleisplacedinacontainerandoxygenorairisaddedtoit.Theamountofoxygenabsorbedbythecoalisestimatedfromtheanalysisofthegaseousreactionproducts.Thetemperatureincreaseperunitofoxygenconsumedindicatespotentialofcoalforspontaneouscombustion.
Heatingrate/crossing-pointtemperature
Inthismethod,acoalsampleisplacedinabathandheatedataconstantrate.Initially,thetemperatureofthecoallagsbehindthetemperatureofthebathbutascoalbeginstoself-heat,thetemperatureofthecoalfirstcoincideswithandthenexceedsthetemperatureofthebath.Thecrossing-pointtemperatureisknownasthe‘relativeignitiontemperature’.Usually,thecrossing–pointtemperatureisusedasameasureofthepotentialofcoalforspontaneouscombustionalthoughtheindexbasedontheratioofheatingratetocrossing-pointtemperatureismoresuitablebecausethespontaneouscombustionpotentialofcoalnotonlydependsontheignitiontemperaturebutalsoontherateofheatgeneration.
Adiabaticcalorimetry
Inthismethod,acoalsampleisplacedinaninsulatedbath,andthewholesystemisheatedtoapre-selectedtemperature.Oxygenorairisthenaddedtoitandoxidationofthecoalraisesitstemperature.Sincenoheatislosttothesurroundings,thechangeinthetemperatureofthecoalinagiventime,thetimeneededtoreachapre-selectedtemperature,ortheamountofheatgeneratedperunittimeindicatesthepotentialofcoalforspontaneouscombustion.
Isothermalcalorimetry
Inthismethod,acoalsampleisplacedinalargebathheldataconstanttemperature.Heatgeneratedinthecoalsampleduetospontaneouscombustionismeasuredbythermocouplesanddissipatedintherelativelylargeheatsink.Theamountofheatgeneratedperunittimegivesanindicationofthepotentialofcoalforspontaneouscombustion.
Factorscontributingtospontaneouscombustion
Coalcharacteristics
Somecoalsaremorepronetospontaneouscombustionthanothers.Therateofoxidationofcoaldependsuponmanyfactors,includingrank,presenceofpyrite,particlesize,moisturecontent,temperature,extentofpreviousoxidationofcoalandthecompositionoftheambientair.
Itisgenerallyacceptedthatastherankofcoaldecreases,theriskofspontaneouscombustionincreases.
Thepresenceofpyriteincreasesthepotentialofcoalforspontaneouscombustion,particularlywhenthepyriteconcentrationexceeds2%andwhenitisveryfinelydistributed.Pyriteacceleratesspontaneouscombustionbyswellingandcausingdisintegrationofthecoalmass,therebyincreasingthesurfaceareaavailableforoxidation.
Thesmallerthecoalparticle,thegreatertheexposedsurfaceareaandthegreaterthetendencytowardspontaneouscombustion.Friablecoalswhichproduceaconsiderableamountoffineswhenminedaremorevulnerabletospontaneouscombustion.
Thechangesinmoisturecontentofthecoalaffectthepotentialofcoalforspontaneouscombustion.Ithasbeenfoundthattherateofoxidationincreaseswithanincreaseinmoisturecontent.Also,wettingisanexothermicprocessanddryingisanendothermicprocess.
Airflowrate
Forspontaneouscombustiontodevelop,therateofheatgenerationshouldbemorethantherateofheatdissipation.Atveryhighairflowratesalmostunlimitedoxygenfortheoxidationofcoalisavailablebutdissipationoftheheatgeneratedbyoxidationisveryefficient.Alowflowraterestrictstheamountofoxygenavailable,butdoesnotallowtheheatgeneratedtobedissipated.Acriticalflowrateisonethatprovidessufficientoxygenforwidespreadoxidationbutdoesnotdissipatetheheatgenerated.
Geologicalfactors
Thepresenceoffaultsincoalseamsoftencontributestothedevelopmentofheatingincoalminesbyallowingairandwatertomigrateintothecoalseams.Zonesofweaknesswhichusuallydevelopintheareaaroundthefaultsalsoaidinthedevelopmentofheating.
Thetemperaturesofthestrataincreasewithdepth.Therefore,theoxidationratewillincreasewithdepth,makingdeeperseamsmorevulnerabletospontaneouscombustion.Ontheotherhand,thehigherrankofcoalfoundintheseseamsdecreasesthechancesofheating.
Thickcoalseamsareoftenconsideredtohavemorepotentialforspontaneouscombustionbecausetheworkingoftheseseamsisinvariablyaccompaniedbyhighlossesofcoalinthegoafareas.Thelowthermalconductivityofcoalcomparedwiththatofshaleorsandstoneisalsoacontributoryfactor.
Whenacoalseamunderashallowoverburdenismined,thegoafareasbecomeconnectedtothesurfacebycracksandfissures.Airandwaterfromthesurfacecangainaccesstothecoalandincreasethepotentialforspontaneouscombustion.Similarly,whenmulti-seamsincloseproximityareworked,thecracksandfissuresdevelopedintheinterveningstrataincreasethepotentialforspontaneouscombustionofthesurroundingunminedseams,particularlytheunderminedseams.
Miningpractice
Someofthemostcommonplaceswherespontaneousheatingsoccuraregoafareasandunconsolidatedwastes,packwallahighproportionofcoal,theedgesofgoaveswherehighstratapressurecausescrushing,rooffallsandfloorheaves,crushedpillars,regulatorsdoorsandaircrossingsandconstrictionsintheroadways.
Coalleftingoafareasisveryliabletospontaneouscombustionastheairmovementthereisverysluggish,andanyheatgeneratedasgresultofoxidationwillnotberemoved.
Incoalmines,coalisleftintheroofand/orfloortosupporttheweakadjoiningstrataorbandsofinferiorqualitycoalwhichareleftunmined.Howeveronlongstanding,rooffallsandfloorheavesoccurcausinglarge-scalecrushingoftheleftcoalandcreatingconditionssusceptibleforheating.
Pillarsthathavebeenstandingforalongtimearepronetoheating,particularlywhentheyareliabletocrushing.
Regulators,doorsandaircrossingsarepointsofhighairleakage,theairmovingthroughthefracturesinthesolidcoalaroundthem.Thegreaterthepressuredifferenceacrossthem,thegreatertheleakage.Constrictionsofmineroadwaysalsocauseleakageofair.Changesinventilation,eitherintentionaloraccidental,maycauseexcessiveairleakagesormaysuddenlybringmoistairintocontactwithdrycoal.
Goafareas,wherealargeamountofcoalisleftandparticularlywhereableederventilationsystemisusedtocleargasfromthegofa,presentoptimalconditionsforspontaneousheating.
Incubationperiod
Theterm‘incubationperiod’generallyimpliesthetimerequiredfortheoxidationofcoal,insuitablecircumstances,tocauseariseintemperaturetoitsignitionpoint.Itdependsonthecharacteristicsofthecoal,theairleakageandtheheataccumulationintheenvironment.Forlow-rankcoals,thetimeperiodgenerallyvariesbetween3and6months,butwithhigh-rankcoalstheperiodvariesbetween9and18months.Theincubationperiodcanbeextendedbyreducingfissurationand/orairleakage.Underadverseconditions,theperiodcanbelessthan2weeks,especiallywithlow-rankcoals.
Preventionofspontaneouscombustion
Preventionofspontaneouscombustionisbasedontwofactors:
(1)eliminationofcoalfromtheareaand
(2)controlofventilationsoastoexcludeoxygenentirelyfromthearea,ortosupplyasufficientflowofairtodissipatetheheatefficientlyasitisgeneratedandbeforeacriticaltemperatureisreached.Themethodsadopteddependuponthelocalsituation.
Mininglayout
Whendesigningmininglayoutsforseamsliabletospontaneousheatingitisessentialthatthegenerallayoutofthemineissimpleandthateachareacanbequicklyandeffectivelysealedoff.Therelativepositionsofthevariousdistrictsintheseamandsurroundingseamsmustalsobetakenintoaccount.Itisessentialtofollowdescendingorderofextractionwhenminingmultipleseams.
Thepanelsystemisanappropriateoneforminingseamsliabletospontaneouscombustion.Thissystemfacilitateseffectivesealingwithafewstopping.Thesizeandconfigurationofthepanelsdependuponthemethodofmining,theseamcontoursandothergeologicalconsiderations.Ifnecessary,thepanelsmustbeofasizewhichwouldpermitcompleteextractionwithintheincubationperiod.Thesizeofpanelbarriersneedstobesufficientforstability.
Whenworkingseamsbythebordandpillarmethod,thesizeofthepillarsmustbesufficienttoavoidexcessivecrushing.Thisalsoappliestocoalpillarsleftatthestartoflongwallfaces.
Whenwo
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