轮机英语课件lesson 14

Lesson14BoilerMountingsandMaintenance

boilermountings(配件)Certainfittingsarenecessaryonaboilertoensureitssafeoperation.Theyareusuallyreferredtoasboilermountings.The

mountings

usuallyfoundonaboiler

are:SafetyvalvesThesearemountedinpairstoprotecttheboileragainst(from)overpressure.OncethevalveliftingpressureissetinthepresenceofaSurveyor验船师itislockedandcannotbechanged.Thevalveisarrangedtoopenautomaticallyatthepre-setblowoffpressure起阀压力.MainsteamstopvalveThisvalveisfittedinthemainsteamsupplylineandisusuallyofthenon-returntype.AuxiliarysteamstopvalveThis

isasmallervalvefittedintheauxiliarysteamsupplyline,and

isusuallyofthenon-returntype.Feedcheckorcontrolvalve(给水止回阀或控制阀)Apairofvalvesarefitted:oneisthemainvalve,theothertheauxiliaryorstandby.Theyarenon-returnvalvesandmustgiveanindicationoftheiropenandclosedposition.WaterlevelgaugeWaterlevelgaugesor‘gaugeglasses’arefittedinpairs,atoppositeendsoftheboiler,theconstructionofthelevelgaugedependsontheboilerpressure.AirreleasecockThesearefittedintheheaders,boilerdrum,etc.,toreleaseairwhenfillingtheboilerorinitially初始的raisingsteam.SamplingconnectionAwateroutletcockandcoolingarrangementisprovidedforthesamplingandanalysisoffeedwater.Blowdownvalve(排污阀)Thisvalveenableswatertobeblowdownoremptiedfromtheboiler.Itmaybeusedwhenpartiallyorcompletelyemptyingtheboiler.Scumvalve(上排污阀)Ashallow(浅的)dish盘positionedatthenormalwaterlevelisconnectedtothescum(泡沫、浮渣)

valve.Thisenablestheblowing吹downorremovalofscum浮渣andimpurities杂质fromthewatersurface.Whistle汽笛stopvalveThisisasmallborenon-returnvalvewhichsuppliesthewhistlewithsteamstraightfromtheboilerdrum.Watertubeboilers,becauseoftheirsmallerwatercontentinrelationtotheirsteamraisingcapacity,requirecertainadditionalmountings:AutomaticfeedwaterregulatorFittedinthefeedlinepriortothemaincheckvalve,thisdeviceisessentialtoensurethecorrectwaterlevelintheboilerduringallloadconditions.Boilerswithahighevaporationratewilluseamultiple-element多因素feedwatercontrolsystem.LowlevelalarmItisadevicetoprovideauditory听觉的warningoflowwaterlevelconditions.SuperheatercirculatingvalvesActingalsoasairvents,thesefittingsensureaflowofsteamwheninitiallywarmingthroughandraisingsteamintheboiler.Sootblowers(吹灰器)Operatedbysteamorcompressedair,theyareacttoblow

away

sootandtheproductsofcombustionfromthetubesurfaces.Severalarefittedinstrategic关键的，战略的places.Thesoot-blowerlance喷头isinserted,sootisblownandthelanceiswithdrawn.Generalmanagementprinciplesandoperatingproceduresarewellknownandmustbealwaysbeingfollowedtoavoidboilermishaps事故.Withmanysmallpackage组件，包boilers,theautomaticcontrolsequenceusuallyensuresthattheboilerfireisinitiallyignitedfromadieseloilsupply,andchangedovertotheusualsourcewhenignitioniscompleted.Withgoodmanagement,tofacilitate方便subsequent随后startingfromcold,thefuelsystemoflargeboilerswillhavebeenflushedthroughwithdieseloilwhentheboilerwasonlightdutyimmediatelypriortobeingsecured停止.Whenburningsuchdieselfuelitisessentialforsafetythatonlythecorrect(small)burnertip喷嘴shouldbeused.Itshouldbekeptinmindthatiffiredoesnotlight,immediatelyshutofffuelandventfurnace.Completeignitionoffuelinthefurnaceisessential.Theburnerflame,thesmokeindicatorandthefunnelshouldbefrequentlyobserved.Withsatisfactorycombustion,theflameshouldappearincandescent白亮的，耀眼的withanorangeshade橙色灯罩attheflametip尖,andafaint微弱brownish褐色haze薄雾shouldshowatthefunnel.Ifonfirstignitiontheflameisuncertain,badlyshapedandseparatedfromtheprimaryswirler旋流器,momentary瞬间openingorclosingofairregister寄存器maycorrect.ThepHvalueoftheboilerfeedwatershouldbekeptbetween8and9andtheboilerdensitylessthan300ppm.But,ifwatersamplesshowaheavyconcentrationofsuspendedmatter悬浮物,shortblow-downsof20secondsdurationshouldbegivenuntilthesludgecontentisseenreduced。Theboilershouldbeblowndownwhentheoilburnerisoperating,thewaterlevelloweredandthenrestoredtoprovethefunctioningofthelowwatercut-outandtheoilburnerstart-upequipment.Theboilerscumvalve上排污阀shouldalsobeoperatedatthistimetokeepthewaterlevelclearfromfloatingscum.Fuelburnercomponents部件andigniterelectrodes电极shouldbecleanedweeklyandthefurnaceexaminedtoensurethattherearenoexcesscarbondeposits.Tubesintheexhaustgassectionoftheboilershouldbebrushedthroughataboutsix-monthlyintervals,andthoseintheoil-burningsectionperiodicallyexaminedandcleanedasnecessarywithawirebristle短毛brush钢丝毛刷.Withcorrectfeedwatertreatment,blow-downproceduresandsludgecontentsinwatersamplesatastablelevel,itshouldnotbenecessarytowashoutthewatersideoftheboilermorethanonceeverythreeorfourmonths.Boilerfiresmaybeoutforlongperiodswhenashipisatseaandtheboilersteamingmaintainedbyheatinputfromwasteheatrecoveryplant.Thisoperationisfreefromhazard危险,butfeedwaterandboilerwatertreatmentmustbemaintainedtopreventinternaldeterioration恶化orscaleformation.Waterlevelcontrollersmustbekeptoperabletoprotectexternalsteam-usingplantfromwater“carry-over“汽水共腾danger.Ifaboilerisisolatedfromthesteam-usingsystemitmustbekepteitherincloseddrystorage储存保管withasuitableinternaldesiccant干燥剂,orcompletelyfulloftreatedwater,orunderalowsteampressurepreferably最好maintainedbyasteam-heatedcoil.Regulartestingofboilerprotectivedevicesmustbeimplemented实施.Frequentcomparisonofdrum-mountedandremote-readingwaterlevelindicators:discrepancies差异betweenthesehavecontributedto导致failuresbecauseofoverheatingthroughshortage缺少ofwater,whenaboilerwasbeingoil-fired.Ifindoubtastothetrueboilerwaterlevel,i.e.whetherawaterlevelindicatorsightglassiscompletelyfullorempty,whenaunitisbeingoil-firedthefireshouldbeimmediatelyextinguisheduntilthetruelevelisresolved.Proceduresshouldbepredetermined预先定andfollowedintheeventofshortageofwater,bulging膨胀orfracture裂纹ofplatesorfurnace,orburstingofwatertubes.Ingeneral,firesshouldbeimmediatelyextinguishedbyremotetripping跳闸offuelsupplyvalves;forceddraught气流airpressuremaintainedifthereisanyriskofescapingsteamenteringtheboilerroom;stempressurerelievedifmetallicfracturesseempossible;andboilerwaterlevelmaintained,wherepracticable,untiltheboilerbeginstocooldown.Regularoperationofsootblowers,iftherearefitted,whentheboilerisonoil-firedoperation.

Thesteamsupplylinemustbethoroughly彻底warmed,anddrainedbeforetheblowersareused,theair/fuelratioincreasedthroughouttheaction,andblowersgreasedafteruse.Immediateinvestigation调查ofanyhighsalinityalarmsincondensatesystem,andelimination消除ofanysaltwateroroilcontaminationofboilerfeedwatersystem.Safetyprecautionstakenbeforeenteringaboilerconnectedtoanotherboilerundersteam.Themainenginemaybekeptinoperationwiththeboilerdryandthegasespassingthroughtheexhaustgassection.Ifthisistobedoneforaprolongedperioditisadvisable可取toallowacurrentofairtoflowthroughtheboilerbyremovingmanhole,sightholeandmudhole泥浆孔covers.Ifrefillingahotboilerthemainenginespeedshouldbereducedtoslowforhalfanhourandthefeedwatersuppliedbeashotaspossible;thereafter其后themainenginemaybebroughtuptopoweroverasimilarperiod.Boilerstart-upForboilersofthedirect-fired直燃式,smoketubetypethestepsarerelevant.WithScotch苏格兰boilers,circulationshouldbecommencedassoonastheboilergetswarm,usingthecirculatingpump,andworkingpressureshouldnotberaisedinlessthan12hours(preferably最好24hours)toreduceexpansionstresses.Timerequiredforotherboilertypeswillvarywithconstructionandwatercontent,butitisalwaysdesirable可取的toheatthroughevenly均匀的andifnecessaryblowdownsomeofthecontentstoseatodisplace替换coldwaterfromthelowestpartoftheboilershell,tominimizetemperaturedifferentialsandthermalstressesinthepressureparts.Forproceduresforlarge,watertubeboilersandtestingofprotectivedevicesforalarm,logic逻辑andcontrolsystemsarerelevanttomodernauxiliaryboilers.RaisingsteamTheboilershouldbefilledtonormallevel(1/2glass)whenthefeedcontrolvalveisautomaticallyclosedandthepanelindicatinglightextinguished熄灭.Theforceddraughtfan鼓风机shouldbestartedandairpassedthroughthefurnaceforseveralminutesto"purge"itofanyexhaustgasoroilvapors.Theoperatingburnercannowbelitandadjustedtoprovidealowfiringratewithgoodcombustion.Thefueloilpressureandforceddraughtpressureshouldbemaintainedtoensuregoodcombustionwithafullsteadyflame.Whenwaterlevelnearsthetopofthegaugeglass,duetoexpansion,theinitiallevelshouldberestored恢复bydrainingoffwaterthroughthescumvalve.Whenadrumpressureofabout210kg/m2hasbeenreached,thedrumairventmaybeclosed.Theboilermustbebroughtslowlyuptoworkingpressureinordertoensuregradualexpansionandtoavoidoverheatingthesuperheaterelementsanddamaginganyrefractorymaterialduetoexpansionstresses.Thetimerequiredwillvarywithboilertypesandconstruction.Ifnecessaryblowdownsomeofthecontentstoseatodisplace替换coldwaterfromthelowestpartoftheboilershell,tominimizetemperaturedifferentialsandthethermalstresses.Themainandauxiliarysteamlinesshouldnowbewarmedbycrackopeningoftheboilermainandauxiliarystopvalves.Whenthelinesarehotclosethedrains.Inadditionthewaterlevelgaugesshouldbeblownthroughandcheckedforcorrectreading.Whenthesteampressureisabout300kg/m2belowthenormaloperatingvalue,thesafetyvalvesshouldbeliftedandreleasedusingtheeasingGear减压装置.Onceatoperatingpressure,theboilermaybeputonloadandthesuperheatercirculatingvalvesclosed.Allothervents,drainsandbypassesshouldthenbeclosed.Thewaterlevelintheboilershouldbemaintained.BoilerShut-DownThisoperationmayhavetobedonenormallyattheendofavoyageorinemergency.Fornormalshutdownthesuitableprocedureis:Carryoutsootblowing,ifpermissible.Changecombustioncontrolfromautomatictomanual.Changefuelsupplytodieseloil;shutsteamofffuelheatersandtraceheating.Closeburnersupplyvalvesandmainfuelshutoffvalve.Purgeboilerfurnaceswithairforthreetofiveminutes;stopforceddraughtfan.Closesteamstopvalvesonboilerwhenpressureisreduced.Drainboilerwhenithascooleddownorfillwithtreatedwater.Steamsystemsmaybewarmedthroughassteamisbeingraisedontheboilerby:·openingsteamrangedrainstobilgeandtosteamtraps;·openingsteamlinevalvestotherequiredservices;·crackingopenboilerstopvalvewhendrumpressureis2bar;·throttlingsteamlinedrainsasrangewarmsthrough;·openingboilerstopvalvefullbeforeauxiliariesarestarted;·closingsteamlinedirectdrainsandsteamtrapbypassesontrappedlineswhenlinesarehot.Wasteheatrecovery(回收)system(W.H.R)Generationofelectricpowerfromasteamturbo-generatorandthesupplyofsaturatedsteam(饱合蒸汽)toheatingservicesbyexhaustgasheatrecoverysystemsiseffectedinmanyships.ThetypeofW.H.R.unit

mainlyfittednowadaysformediumtolargeoutputs

ismade

ofhorizontalextended(分布)surfacesteeltubes,force-circulatedwithwatertakenfromanoilfiredboilerandreturnedaswater/vapouremulsion(混合液).Theboilerisfiredwheneverthedemandforsteamexceedsthatavailablefromexhaustgasheating.Additional

heat

extractionfrom(提取)theexhaustgases

can

be

effected

byaddinganeconomizersection(节能器)totheunitinplantswherethearrangementpermitsthesupplyofcooledcirculatingwaterorfeedwaterattheeconomizerinlet.Similar

results,butwithsomedisadvantages,can

be

obtained

byproducinglow-pressuresteamfromaseparateheatexchangeunit

atthetailendofthegasstream.CirculationoftheW.H.R.plant(equipment)mustbemaintainedatalltimeswhenthemainengineisonload.Alsoitmustbecontinuedforat

leasttwohoursaftertheenginehasbeenstopped

toensurethat

thatanycombustionmaterialfromtheexhaustgas

whichdepositedontheheatingsurfacesisthoroughlycooledbelowtheignitionpoint.

Circulationshouldbestoppedandthesystemsecured(关闭)onlyifalongstayinportisexpected.Whenleavinganintermediateport,ifthesystemhasbeendepressurized(减压),circulationoftheW.H.R.unitshouldbecommencedbeforethemainenginesarestarted,andanyairliberated(释放)bythehotcirculatingwater(shouldbe)releasedfromtheheaderairvents.Whensootblowersarefittedtotheunit,thefiresshouldbelitintheoil-firedboilertomaintainsteampressure,thesteamlinesdrainedandthesootblowersoperatedoncedailyatsea.Intervalsbetweenblowingmaybeextendedwhenobservationofthefunnel(烟囱)showsthatsootdischargeissmall.Aguidetotheireffectivenessisgivenbyachangeinthefunnelexhausttemperatureimmediatelyaftersootbloweroperation.Waterwashingoftheheatingsurfacemustalsobecarriedoutatintervalsofthreemonths,orsuchlesserintervalsasmaybedecideduponfromsightingofthesurfaceduringintermediateinspections.ThedrainprovidedatthelowestpointoftheinlettrunkimmediatelybelowtheW.H.R.unitmustbeprovedclearpriortoandduringthewashingoperation.Ataconstantmainenginepowerlevel,W.H.R.systemshavearisingpressurecharacteristiconafallingsteamdemandwhichaffordssomecontrol.Theoutputcanbereducedbybypassingthefeedheateroneitherthefeedwaterorcirculatingwatersides,soincreasingthetemperatureattheeconomizerinletandreducinggas/watertemperaturedifferencesinthisheatexchangersection.Otherautomaticormanualcontrolarrangementsmay

be

controllingflowthroughanexhaustgasbypassductbymeansofdampers(档板),and,whensub-dividedinletheadersareprovided,byclosingoneormoreoftheisolatingvalvessupplyingcirculatingwatertoseparatesectionsofthesteamgenerator.Valvesmustbefullyopenorfullyshutandnotleftinanintermediateposition.Ifthemainenginespeedissuddenlyreducedorcircumstancesdictateanemergencyenginestop,thepotentialforsteamgenerationfromtheW.H.R.unitwillobviouslyreduceorcease.CochranspheroidverticalboilerSpannerverticalboilerAconsiderableamountofresidualheatinitiallyremainsintheheatedmetalofthesteamgenerator/economizerandinthewaterintheboilerdrumandcirculatingsystem.Thisallowssteamgenerationatafallingpressuretocontinueforsomeminutesafteranemergencyenginestop.Theprecisetimeavailablecanbestbeestablishedbytrials,buttypicalinstallationstestshaveshownthataturbo-generatorsuppliedwithsteamfromaW.H.R.plantwillcontinuetocarrythefullsealoadforperiodsuptoabout12minutes.Thisusuallygivesampletimetobringon-linealternativesourcesofsupplyforheatandpowertoallowfor:(a)automaticstartingofadieselgeneratorand/orlightingoffaboilerfireintheeventofsteampressurefallingtoapre-setlevelorbridgecontrolapplicationofaspeedreduction;(b)preferentialtrippingofpowersuppliestonon-essentialcircuitsinsimilarevents;(c)automaticloadsharingwithadiesel-drivengeneratorset;(d)initiatingof(a)or(c)fromanenginecontrolroom;(e)operationofoverridecontrolsonboiler-firingcircuitsloallowmanually-controlledlighting-offifautomaticignitionispreventedbyhighorlowwaterlevelautomaticcut-outs.Intheunlikelyeventofasteamgenerator/economizertubeleakingwhileatsea.itmaybenecessarytodeferrepairsortubeisolationuntilitisconvenienttostopthemainengineforaperiodoruntilarrivalinport,butifheavyleakageisobservedthemainengineshouldbestoppedimmediately.Thecirculatingpumpshouldthenbestopped,thesteamgenerator/economizerisolatedanddrained,and,preferably,thetubeswaterwashedorsootblownifblowersarefitted.ThemainenginemaythenberestartedafterprovingthatwaterisnotpresentintheexhaustsystembeforetheW.H.R.unit.Similarproceduresshouldbefollowedifitisnecessarytostopcirculationduetoleakagesexternaltotheunit,or,iftheassociatedboilerorcirculatingpumpisinoperable.Insuchcasesthemainenginemaybestoppedwhenitissafetodosobut,wheneverpossible,circulationmustbecontinueduntilthisisdone.Withsomeinstallationsshipbuildersmayhaveprovidedemergencysteamingconnectionsforuseundersuchconditions,whichwillbeshownontheirsteamandfeedsystemdiagrams.Thesteamgenerator/economizermaybesafelyoperatedinthe"dry-fired"conditionaftercleaninguntilsuchtimeasthecirculationisrestarted,shouldoperatingrequirementsmakethisnecessary.However,thesootblowingprocedureatseaandwaterwashinginportmuststillbecarriedoutwheninthisdry-firedconditionaftercleaning.FireshaveoccurredinW.H.R.unitsofvariousmakesandtypesduetoabuild-upofcombustibledepositsandtheirsubsequentignition.Similarfireshaveoccurredinairheatersandeconomizersofmanyboilersforthesamereason.Althoughtheproblemisthesamethereissomedifferenceinrecommendedprocedures.Thefollowingguide-linesarethereforeprefferedontheprevention,causes,detectionandfightingofsuchfiresinW.H.R.units.Suchhazardswillnot,ofcourse,occurifdieunitiskeptclean.A.PreventionoffiresPreventionoffiresisasimplematterofmaintainingnormalgoodcombustionoffuelinthemainengine,keepingtheW.H.R.unitclearofunduesootdepositsbywaterwashingandregularuseofsootblowerswhenfitted,andmaintainingcirculationofwaterthroughtheunit.B.CausesoffiresTheexhaustgasesfromanydieselenginecontainacertainamountofcombustiblematterresultingfromthecombustionprocessandthecarry-overofalubricantorcoolingoil.Thebulkoftheashcontentintheburntfuelremainsentrainedintheexhaustgasstream,butasmallamountmaydepositontheelementsoftheunit.Suchsootdepositonthesteelfinsisnormallyverylightandfriableandwillbedislodgedbythegasflowwhentheengineisrestarted.Theremaybeadditionaldepositsonhorizontaltubesurfaceswhicharenotvisiblewhenthesurfaceiscursorilyviewedandwhichmaynotbesoeasilydislodgedbythegases.Intotal,theseunseendepositsmayformasubstantialbaseofcombustiblematerial.Inanenginewithfaultyfuelorexhaustvalves,unburntfuelcanbecarriedoverintothegasstrew.Othercombustiblematerialmaybeaddedfromcarbondepositswhichmaybreakawayfromtheexhaustvalvecagesorports,etc.,andmaydepositastheexhaustgasesare