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预热器

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  预热(re)器的低(di)温腐蚀(shi)机理
  燃料中(zhong)的硫(liu)在燃烧(shao)后(hou)生成(cheng)(cheng)二氧(yang)化(hua)硫(liu)(SO2),其中(zhong)有(you)少量(liang)的SO2(只(zhi)占SO2的1%左右)又会(hui)进一步氧(yang)化(hua)而形成(cheng)(cheng)三氧(yang)化(hua)硫(liu)(SO3)。由于(yu)三氧(yang)化(hua)硫(liu)在烟(yan)气(qi)(qi)中(zhong)存在,则(ze)使烟(yan)气(qi)(qi)的露(lu)点(dian)温(wen)(wen)度升高,即三氧(yang)化(hua)硫(liu)和(he)烟(yan)气(qi)(qi)中(zhong)水(shui)蒸(zheng)气(qi)(qi)化(hua)合,生成(cheng)(cheng)硫(liu)酸蒸(zheng)汽(qi),露(lu)点(dian)温(wen)(wen)度大为升高。当含有(you)硫(liu)酸蒸(zheng)汽(qi)的烟(yan)气(qi)(qi)流经低温(wen)(wen)受(shou)热面(mian)(mian)(空气(qi)(qi)预(yu)(yu)热器),受(shou)热面(mian)(mian)金属(shu)壁(bi)温(wen)(wen)低于(yu)硫(liu)酸蒸(zheng)气(qi)(qi)的露(lu)点(dian)时, 则(ze)在受(shou)热面(mian)(mian)金属(shu)表(biao)面(mian)(mian)结硫(liu)酸露(lu)(也即在预(yu)(yu)热器低温(wen)(wen)冷端波纹板(ban)上结硫(liu)酸露(lu)),并腐蚀受(shou)热面(mian)(mian)金属(shu)。
  蒸汽(qi)开始凝结的(de)温度称为露(lu)点(dian)(dian)(dian),通常烟气(qi)中水蒸气(qi)的(de)露(lu)点(dian)(dian)(dian)称为水露(lu)点(dian)(dian)(dian);烟气(qi)中硫酸(suan)蒸气(qi)的(de)露(lu)点(dian)(dian)(dian)称为烟气(qi)露(lu)点(dian)(dian)(dian)(或酸(suan)露(lu)点(dian)(dian)(dian))。
  水(shui)露(lu)点取决于(yu)水(shui)蒸气(qi)(qi)在烟(yan)(yan)气(qi)(qi)中的分(fen)压力,一般为30-60℃,即(ji)使煤中水(shui)分(fen)很大(da)时,烟(yan)(yan)气(qi)(qi)水(shui)露(lu)点也(ye)不超过66℃。一旦(dan)烟(yan)(yan)气(qi)(qi)中含(han)SO3气(qi)(qi)体,则使烟(yan)(yan)气(qi)(qi)露(lu)点大(da)大(da)升高,如烟(yan)(yan)气(qi)(qi)中只(zhi)要含(han)有0.005%(50ppm)左右(you)的SO3,烟(yan)(yan)气(qi)(qi)露(lu)点即(ji)可高达130-150℃或以上。