TheinventionoftheincandescentlightbulbbyThomasA.Edisonin1879createdademandforacheap,readilyavailablefuelwithwhichtogeneratelargeamountsofelectricpower.Coalseemedtofitthebill,anditfueledtheearliestpowerstations(whichweresetupattheendofthenineteenthcenturybyEdisonhimself).Asmorepowerplantswereconstructedthroughoutthecountry,therelianceoncoalincreased.SincetheFirstWorldWar,coal-firedpowerplantshaveaccountedforabouthalfoftheelectricityproducedintheUnitedStateseachyear.In1986suchplantshadacombinedgeneratingcapacityof289,000megawattsandconsumed83percentofthenearly900milliontonsofcoalminedinthecountrythatyear.Giventheuncertaintyinthefuturegrowthofnuclearpowerandinthesupplyofoilandnaturalgas,coal-firedpowerplantscouldwellprovideupto70percentoftheelectricpowerintheUnitedStatesbytheendofthecentury. 　　Yet,inspiteofthefactthatcoalhaslongbeenasourceofelectricityandmayremainoneformanyyears(coalrepresentsabout80percentofUnitedStatesfossil-fuelreserves),ithasactuallyneverbeenthemostdesirablefossilfuelforpowerplants.Coalcontainslessenergyperunitofweightthannaturalgasoroil;itisdifficulttotransport,anditisassociatedwithahostofenviron****lissues,amongthemacidrain.Sincethelate1960'sproblemsofemissioncontrolandwastedisposalhavesharplyreducedtheappealofcoal-firedpowerplants.Thecostofamelioratingtheseenviron****lproblemsalongwiththerisingcostofbuildingafacilityaslargeandcomplexasacoal-firedpowerplant,havealsomadesuchplantslessattractivefromapurelyeconomicperspective. 　　Changesinthetechnologicalbaseofcoal-firedpowerplantscouldrestoretheirattractiveness,however.Whereassomeofthesechangesareevolutionaryandareintendedmainlytoincreasetheproductivityofexistingplants,completelynewtechnologiesforburningcoalcleanlyarealsobeingdeveloped.看下面的网址或许对你有点启示