电站锅炉水冷壁高温腐蚀成因与对策研究

亚临界以上参数的大型电站锅炉水冷壁温较高,低NOx分级燃烧技术的应用使主燃烧区域处于贫氧状态,往往导致严重的高温腐蚀。选取某300 MW电站锅炉发生高温腐蚀后的水冷壁管为研究对象,通过割管取样、电镜表征分析等手段,对高温腐蚀原因、类型进行了研究。研究结果表明,腐蚀产物中含有大量FeS,属于典型的硫化物型腐蚀。腐蚀管样表面覆盖有肉眼可见的蓝色、黄绿色物质,其主要成分为铁的氧化物、铁的硫化物以及锌的硫化物;硫化物在蓝色物质中主要为FeS晶体,晶体尺寸大小在10～20μm,呈现规则六方晶体结构;黄绿色物质则主要为ZnS,同时,腐蚀管样表面还发现大量未燃尽碳颗粒,表明炉内配风不合理,存在火焰中未燃尽的煤粉和飞灰颗粒刷墙现象。燃烧器改造后,进行了冷态空气动力场烟花调试,发现整体切圆状况良好,符合设计要求,无偏离炉膛几何中心。一次风切圆直径为790 mm,基本与设计值吻合,各层气流相对舒展,无明显贴壁现象,炉内烟花模拟的火焰充满度良好,炉内空气动力场状况明显改善;从改造后热态运行结果看,锅炉对煤种适应性有极大改善,燃烧稳定性和防结渣能力均有较大提升,在贫煤50%掺烧比例下,锅炉出力可保持800 t/h以上连续运行,看火孔火焰均匀,未发现大块连续结焦现象,高温腐蚀现象明显减轻。 The water wall temperature of large utility boilers with sub-critical and above parameters is generally high.The application of low NOx staged combustion technology leads to the oxygen deficiency in the primary combustion zone,which often causes serious high temperature corrosion.The sample of the water wall tube after high temperature corrosion was cut off from a 300 MW utility boiler for characterization analysis.The cause and the classification of high temperature corrosion were discussed.The results show that the corrosion products contain a large amount of FeS,which belongs to typical sulfide corrosion.Blue and yellow-green products are covered on the tube surface,whose main composition are iron oxides and sulfides.The iron sulphides in the blue products are FeS while in yellow-green products are ZnS.The FeS presents a hexagonal crystal and with a size of 10-20 μm.Meanwhile,large amount of unburned fly ash particles were found at the surface of the sample tube,indicating that the air distribution in the furnace were irrational and the flame brushing walls phenomenon was existent.After the reconstruction of the burners,the cold aerodynamic field using fireworks in furnace was conducted.It is found that the whole tangential circle is in good condition and does not deviate from the geometric center of the furnace,which meets the design requirements.The diameter of imaginary primary air tangential circle is 790 mm,which basically coincides with the design value.The air flow in each layer is relatively stretched,and no obvious brushing walls phenomenon is observed.The imaged flame is full of the furnace and the condition of the aerodynamic field is obviously improved.The hot state operating results show that the adaptability to coal change is greatly improved,the combustion stability and anti-slagging ability are greatly improved.The boiler can be continuous operated above 800 t/h load under 50% blending ratio of lean coal.The flame colour is uniform and no large continuous coking phenomenon was found.The high temperature