多变截面SCR脱硝系统优化改造

为了解决某电厂600 MW机组选择性催化还原(SCR)脱硝系统存在脱硝效率低以及空气预热器磨损严重的问题,利用数值模拟分析该问题的原因,对该机组SCR脱硝装置进行了优化改造。结果表明:在省煤器出口水平扩张段的多变截面烟道采用小角度、多片数方法设计导流板,消除了水平扩张段的涡流低速区和高速区,提高了喷氨上游烟气流动的均匀性,并且使水平扩张段的流动阻力降低;对比涡流静态混合式喷氨、线性喷氨和分区喷氨,分区喷氨可以更好地控制首层催化剂入口氨氮摩尔比分布的均匀性,进而提高脱硝效率、减少氨逃逸;在SCR脱硝反应器出口到空气预热器入口增加导流板可以提高空气预热器入口烟气流速分布的均匀性,减轻空气预热器的磨损。

Optimization and Retrofit of a SCR Denitrification System with Variable Cross Sections

To solve the problems of low denitrification efficiency in the selective catalytic reduction(SCR)denitrification system and severe abrasion in the air preheater of a 600 MW power unit,the problems were analyzed by numerical simulation,following which,the SCR denitrification system was optimized and retrofitted.Results show that the design of multi-disc guide plates arranged at small angles in the variable cross-section duct at economizer outlet could help to eliminate the vortex caused by the difference of gas velocities between front and rear wall,improve the gas velocity distribution in the upstream of ammonia injection area and reduce the flow resistance in the area.By comparing the vortex static mixing ammonia injection,the linear ammonia injection and the partition ammonia injection,the way of partition ammonia injection is found to be able to effectively improve the distribution of the mole ratio of NH3 to NOx in the first-layer catalyst,resulting in an increase in denitrification efficiency and a decrease in ammonia slip.Moreover,the gas velocity distribution at the inlet of air preheater could be improved,while the abrasion in the air preheater could be relieved,by arranging guide plates in the duct between the outlet of SCR denitrification reactor and the inlet of air preheater.