应用SCR氨喷射技术解决空预器硫酸氢铵堵塞问题

Application Study of Ammonia Injection Technology on Solving ABS Block Problem of Air Heater

某350 MW机组SCR增加催化剂按照NO_x超低排放运行时,发生了空预器硫酸氢铵ABS严重堵塞问题,分析发现SCR入口烟道截面的NH_3/NO摩尔比分布不均匀导致局部氨逃逸过大是主要原因。为此,采用CFD数值模拟方法对SCR喷氨格栅(AIG)进行了优化设计改造,并通过现场试验对AIG喷氨流量分配进行了优化调整。测试结果表明,脱硝反应器出口NO_x浓度分布相对标准偏差由改造前的49%降低至11%以内,顶层催化剂上方烟道截面的NH_3/NO_x摩尔比分布相对标准偏差小于3.1%,消除了局部过高的氨逃逸浓度峰值,减轻了空预器ABS堵塞风险。

Serious ABS block occurs at air pre-heater in a 350 MW unit after operating under super-low NOx emission, with back-up catalyst layer added. Study reveals the major reason is NH3/NOx non-uniform distribution at SCR inlet duct, leading to excessive local NH3 slip. Therefore, by means of CFD（Computational Fluid Dynamics） method, design optimization and retrofit of SCR AIG（Ammonia Injection Grid） system is carried out,in succession with AIG tuning through field test. The test results show that after retrofit, the relative standard deviation of NOx distribution at SCR outlet is reduced from 49% to 11%, the relative standard deviation of NH3/NOx mole ratio upstream of top catalyst layer is below 3.1%,with local excessive NH3 slip eliminated, which decreases the crisis of air pre-heater ABS block.