南师大锅炉原理课件2-3 煤的特性及其对锅炉工作的影响

2025/6/2212.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响1.Heatingvalue发热量Gross(higher)heatingvalue(HHV)isdefinedastheheatreleasedfromcombustionofaunitfuelquantity(mass),withtheproductsintheformofash,gaseousCO2,SO2,nitrogenandliquidwater,exclusiveofanywateraddedasvapor. 高位发热量(Qgr)：单位质量的煤完全燃烧时所放出的热量，包括产生的水蒸汽汽化潜热的发热量(kJ/kg)。Thenet(lower)heatingvalue(LHV)iscalculatedfromtheHHV.Itistheheatproducedbyaunitquantityoffuelwhenallwaterintheproductsremainsasvapor. 低位发热量(Qnet)：单位质量的煤完全燃烧时所放出的热量，不包括水蒸汽的汽化潜热后的发热量(kJ/kg)

。2025/6/2221.Heatingvalue发热量Watercomesfrom:

thereactionofhydrogenandoxygenH与氧的反应moisture(Mar)inthefuel燃料中的含水量MarTherelationshipofHHVandLHVbasedonthedifferentanalysisbases.各成分分析基准的高位/低位发热量间的关系2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/223Basisconversionofheatingvalue发热量基准转换对高位发热量而言，水分只是占据了质量的一定份额，而使发热量降低；采用表2-1的换算系数进行换算。对低位发热量而言，水分不仅占据了质量的一定份额，而且还要吸收汽化潜热，必须考虑汽化潜热的影响，采用表2-2换算关系，(推导过程自学)低位发热量先转换成同基的高位发热量；通过换算系数进行不同基高位发热量换算；再换回要求的同基的低位发热量。发热量测定：一般用氧弹法(adiabaticbombcalorimeter)测定，测出的为定容发热量。定容发热量减去硫酸和硝酸的溶于水的放热量，为定压发热量。锅炉计算一般用定压发热量。2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/224Approximatecalculationofheatingvalue近似计算

Accordingtotheultimateanalysis根据元素分析Mendeleevformula门捷列夫公式ChinaCoalResearchInstituteformula煤科院公式Theerrorbetweencalculationandmeasurement计算值与实测值的误差当Ad≤

25%时，Qnet,ar≤600kJ/kg当Ad>25%时,Qnet,ar≤800kJ/kg2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2251.Heatingvalue发热量Standardcoalequivalent

标准煤的发热量(煤当量)Standardcoal:aspecifiedcoalwhosenetheatingvalueaccordingtotheasreceivedbasisis7000kcal/kgor29308kJ/kg.Standardcoal标准煤:

一种假想的煤，规定收到基低位发热量为7000kcal/kg(29308kJ/kg)，国际上法定的能量折算单位。Standardcoalconsumption

标准煤消耗量：

2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响

kg/h2025/6/2261.Heatingvalue发热量Convertedcomposition折算水分、折算灰分和折算硫分在讨论杂质(水分、灰分)对锅炉工作的影响时，使用其折算值更合理。燃料燃烧每放出单位热量（常取1000kcal或1兆焦）所对应的水份、灰份、硫份的量称为煤的折算水份、折算灰份和折算硫分。1）折算水分：煤低位收到基发热量中每4186.8kJ热量所对应的水分。

%；大于8％为高水分燃料2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2271.Heatingvalue发热量Convertedashandsulfur折算灰分和折算硫分2）折算灰分：煤低位收到基发热量中每4186.8kJ热量所对应的灰分。 %；＞4％为高灰分燃料3）折算硫分：煤低位收到基发热量中每4186.8kJ热量所对应的硫分。 %；＞0.2%为高硫分燃料2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2282.Volatilematter挥发分Component组成

Hydrocarbon碳氢化合物hydrogen氢气COH2SO2N2

氮气CO2等2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2292.Volatilematter挥发分Characteristics特点VMdecreaseswithincreasingofcoalification,suchas:VMoflignite>40%,anthracite≤8%. 挥发分含量随煤化程度加深而减少;ReleasetemperatureofVMincreaseswithcoalification.

煤的挥发分析出温度随煤化程度加深而升高，如依次为lignite褐煤、bituminouscoal烟煤、leancoal贫煤、anthracite无烟煤；FastIgnition,stablycombustionofcoalshavinghighVM.挥发分含量高，着火迅速，燃烧稳定；VMwillaffectfurnacestructureandoperationofboiler.挥发分大小影响锅炉炉膛结构和运行方法；Animportantindicatorofcoalclassification,作为煤的重要分类依据。

2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2210Coalrank煤种VdafVMreleaseTemp逸出温度(℃)IgnitionTemp着火温度(℃)lignite褐煤>40130~170250~450Bituminouscoal烟煤20~40170~320400~500Leancoal贫煤10~20370~390600~700anthracite无烟煤<10380~400>7002.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响Therelationshipoftemperatureswithcoalrank2025/6/22113.

Cokecohesiveness

煤的焦(粘)结性煤的焦(粘)结性对层燃炉运行影响较大。2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/22124.Ashfusibility灰的熔融性(pp20;pp21-5)Ashfusibilityhassignificanteffectsonboilersafeoperatingandboilerefficiency. 灰的熔融性对锅炉运行的经济性和安全性有很大影响1)定义：灰在加热时，由固态逐渐向液态的转化特性。Thecharacteristicsofsolidashconvertingtoliquidashwhenashisheated.Themeasurementofashfusibilitytemperaturesisbyfarthemostwidelyusedmethodforpredictingashbehavioratelevatedtemperature.2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/22134.Ashfusibility灰的熔融性2)Measurementmethod测定方法Anashsample(dp<0.2mm)ispreparedbyburningcoalunderoxidizedconditionsattemperatureof799to899C.Theashispressedinamoldtoformatriangularpyramid(cone)20mminheightwitha7mmtriangularbase. 取粒度小于0.2mm的空气干燥样，按GB212-1991规定完全灰化，然后研磨至0.1mm以下，制成三角锥。Theconeisheatedinafurnaceatcontrolledratetoprovideatemperatureincreaseof8ºCperminute.Theatmosphereinthefurnaceisregulatedtoprovideeitheroxidizingorreducingcondition.2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/22142.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响4.Ashfusibility灰的熔融性(pp20;pp21-6)Whenthesampleisheated,fourdeformationtemperaturesarereportedasfollows:Initialdeformationtemperature,DT变形温度Softeningtemperature,ST软化温度Hemisphericaltemperature,HT半球温度Fluidtemperature,FT流动温度STHT一般使用ST作为表征灰的熔融性的温度。在锅炉设计时，为避免炉膛出口结渣，要求出口烟温应比ST低100℃。2025/6/22153)Furnacedesignforashremoval(p21-2)Historically,twodistinctlydifferenttypesoffurnacedesignwereusedtohandletheashfromcoalfiringinlargeutilityboilers.Thesearecommonlyreferredtoas:Thedry-ashordry-bottomfurnace.固态排渣炉Theslag-taporwet-bottomfurnace.液态排渣炉Inadry-bottomunitmostoftheash,typically70to80%,isentrainedinthefluegasandcarriedoutofthefurnace.Thisportionoftheashiscommonlyknownasflyash.2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/22163)Furnacedesignforashremoval(p21-2)Someoftheflyashiscollectedinhoppersarrangedundertheeconomizerandairheaters,wherecoarseparticlesdropoutofsuspensionwhengasflowdirectionchanges.Thefinerashparticlesremaininsuspensionandarecarriedoutoftheunitforcollectionbyparticulatecontrolequipment.Theremaining20to30%oftheashthatsettlesinthefurnace,orisdislodgedfromthefurnacewalls,iscollectedinahopperformedbythefrontwallandrearwalltubepanelsatthebottomofthefurnace.Thisbottomashisdischargedthrougha3to4ft(0.9to1.2m)wideopeningthatspanstheentirewidthofthehopper.2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/22173)Furnacedesignforashremoval(p21-2)Theslag-taporwet-bottomfurnace,whichwereoriginallydevelopedtoresolveashdepositionandremovalproblemswhenfiringcoalswithlowashfusiontemperaturesindry-bottomfurnaces.Theseunitsareintentionallydesignedtomaintainashinafluidstateinthelowerfurnace.Moltenashiscollectedonthefurnacewallsandothersurfacesinthelowerfurnaceanddrainedcontinuouslytoopeningscalledslag-tapsinthefurnacefloor.Watertankspositionedbeneaththeslag-tapssolidifytheliquidashfordisposal.2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/22183)Furnacedesignforashremoval(p21-2)Theapplicationofslag-tapunitsforpulverizedcoalfiringbegantodecline(减少)inthelate1940s,primarilyduetodesignimprovementsindry-bottomunitsthatminimizedashdepositionproblems.Slag-tapunitsequippedwithCyclonefurnacescontinuedtobeapplieduntiltheearly1970swhenthefederalCleanAirActmandatedcontrolofnitrogenoxides(NOx)emissions.Thehighfurnacetemperaturesrequiredforwet-bottomoperationwerehighlyconducive(有利于)toNOformation.Allmodernpulverizedcoal-firedboilersusethedry-bottomarrangement.2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2219Fig.1:Thecoal-firedboilerBottomash:20~30%flyash:70-80%2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2220Ashdeposition(pp21-3)Regardlessofthefiringmethod,whencoalisburned,arelativelysmallportionoftheashwillcausedepositionproblems.Ashpassingthroughtheboilerissubjecttovariouschemicalreactionsandphysicalforceswhichleadtodepositiononheatabsorbingsurface.Theprocessofdepositionandthestructureofdepositsarevariableduetoanumberoffactors.Particlecomposition,particlesizeandshape,particleandsurfacetemperatures,gasvelocity,flowpatternandotherfactorsinfluencetheextentandnatureofashdeposition.Dueprimarilytothedifferencesindepositionmechanismsinvolved,twogeneraltypesofhightemperatureashdepositionhavebeendefinedasslaggingandfouling.

2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2221Ashdeposition(pp21-3)Slagging(结渣)istheformationofmolten,partiallyfusedorresolidifieddepositsonfurnacewallsandothersurfacesexposedtoradiantheat.Slaggingcanalsoextendintoconvectivesurfaceifgastemperaturesarenotsufficientlyreduced.Fouling(污垢、积灰)

isdefinedastheformationofhightemperaturebondeddepositsonconvectionheatabsorbingsurfaces,suchassuperheatersandreheaters,thatarenotexposedtoradiantheat.Ingeneral,foulingiscausedbythevaporizationofvolatileinorganicelementsinthecoalduringcombustion.Asheatisabsorbedandtemperaturesareloweredintheconvectivesectionoftheboiler,compoundsformedbytheseelementscondenseonashparticlesandheatingsurface,formingagluewhichinitiatesdeposition.2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2222Ashdeposition(pp21-3)AreaswhereslaggingandfoulingcanoccurareshowninFig.2Figs.3and4showheavilyslaggedandfouledsurfaces.2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/22234)Influencingfactorsonashfusibility影响因素分析(pp21-4)MineralogicalcompositionTherearenostandardizedmethodsthatareusedroutinelyfordeterminingthespecificmineralconstituentsofcoal.Mineralogicalanalysisrequirestheuseofalowtemperatureashingtechniquetoseparatethemineralmatterfromtheorganicportionofthecoal.Standardhightemperatureashingprocedureswouldsignificantlyalterthemineralforms.However,anumberofresearchers,usingavarietyoflowtemperatureashingmethodsandsophisticatedanalyticaltechniques,haveidentifiedanenormousvarietyofmineralspeciesincoal,encompassingtheentirespectrumofthesemineralsfallintooneofseveralgroups:clayminerals(aluminosilicates),sulfides/sulfates,carbonates,chlorides,silica/silicatesandoxides.SomeofthemorecommonmineralsinthesegroupsareshowninTable2.2.3Coalcombustioncharacteristics

§2-3煤的特性及其对锅炉工作的影响2025/6/2224clayminerals(aluminosilicates),sulfides/sulfates,carbonates,chlorides,silica/silicatesoxides.2025/6/2225ChemicalcompositionBecausebothquantitativeandqualitativeevaluationofmineralmatterformsareextremelydifficult,relativelysimplechemicalanalysesarecommonlyusedtodeterminethepercentagesofthemajorelementsintheash.ElementalashanalysisisperformedonacoalashsampleproducedinaccordancewiththeASTM3174ashingprocedure.Pulverizedcoalisburnedinafurnacewithanoxidizingatmosphereat1292to1382F(700to750C).Theelementspresentintheasharequantitativelymeasuredusingacombinationofemissionspectroscopyandflamephotometryandarereportedasweightpercentsoftheiroxides.Coalashconsistentlyfoundtobecomposedmainlyofsilicon,aluminum,iron,

andcalciumwithsmalleramountsofmagnesium,titanium,sodiumandpotassium.TheelementalanalysisalsoidentifiesphosphorusasP2O5andsulfurassulfurtrioxide(SO3).SulfurisreportedasSO3becauseitisnormallypresentasth