燃煤电厂SCR脱硝系统喷氨优化模拟

Optimization Simulation of Ammonia Injection in SCR DeNO_(x)System of Coal-Fired Power Plant

为提高某660 MW机组SCR(选择性催化还原)脱硝反应器出口NO_(x)质量浓度分布均匀性,文中以SCR出口NO_(x)质量浓度分布相对标准偏差最小为优化目标,提出了一种基于动力学模型的最优喷氨策略。将现场实测数据作为入口边界条件,耦合反应器内的湍流流动、组分输运和化学反应,进行了CFD数值模拟计算。对氨流动特性进行可视化分析,并定义喷氨格栅分区/喷嘴的流动影响系数,结合基于SCR反应动力学模型建立的出口NO_(x)浓度分布与入口NH3浓度的数学关系,直接求解优化矩阵方程,可得到喷氨格栅不同分区或不同喷嘴的最优可控喷氨流量。模拟结果表明:均匀喷氨方式下,不同分区氨氮浓度混合匹配度不高,SCR反应器出口NO_(x)质量浓度相对标准偏差达到40.1%,分布均匀性较差;按文中提出的方法进行喷氨优化后,出口NO_(x)质量浓度相对标准偏差下降至6.8%,出口均匀性大幅提高,既能实现NO_(x)压线排放满足环保要求,又可避免出现脱硝效率过高和过低的区域。文中通过数值模拟的方式将流场可视化,通过定量求解各阀门喷氨量进行喷氨优化,可以为实际电厂喷氨优化调试提供理论参考,降低调整的盲目性。

To improve the uniformity of NO_(x)mass concentration distribution at the outlet of SCR(selective catalytic reduction)denitration reactor of a 660 MW unit,this paper proposed an optimal ammonia injection strategy based on the kinetic model with the objective of minimizing the relative standard deviation of NO_(x)mass concentration distribution at the outlet of SCR.The on-site measured data was used as the inlet boundary condition,and CFD numerical simulation calculations were conducted by coupling turbulent flow,component transport,and chemical reactions in the reactor.The ammonia flow characteristics was visually analyzed,and the flow influence coefficient of the ammonia injection grid partition/nozzle was defined.The optimal controllable ammonia injection flow of different partitions or nozzles of the ammonia injection grid can be obtained by directly solving the optimization matrix equation,and combining the mathematical relationship between the outlet NO_(x)concentration distribution and the inlet NH3 concentration,which is based on the SCR reaction kinetics model.The simulation results show that under the uniform ammonia injection mode,the mixing matching degree of ammonia nitrogen concentration in different zones is not high,the relative standard deviation of NO_(x)mass concentration at the outlet of SCR reactor reaches 40.1%,and the uniformity of NO_(x)mass concentration distribution at the outlet is poor.After the optimization of ammonia injection according to the method proposed in the paper,the relative standard deviation of NO_(x)mass concentration at the outlet decreases to 6.8%,and the uniformity of the outlet is greatly improved.This can not only realize the pressure line emission of NO_(x)to meet environmental requirements but also avoid areas with high and low denitrification efficiency.The flow field was visualized through numerical simulation in the article,and ammonia injection optimization was carried out by quantitatively solving the ammonia injection volume of each valve.This can provide theoretical reference for actual ammonia injection optimization debugging in power plants and reduce the blindness of adjustment.