基于燃煤机组SCR系统普遍出现的性能不稳定、氨逃逸超标等问题，以具有代表性的某660 MW超临界煤粉锅炉SCR脱硝系统为例，拟结合喷氨格栅和驻涡型喷氨混合器特点，进行多维度的驻涡脱硝喷氨混合装置优化改造研究，并分析了烟气在烟道各位置流动、变化和相互混合的过程，提出了基于分级多效混合、多排分区、强制整流的优化方案。依据CFD模拟计算结果，提出的SCR脱硝系统的流场优化方案可以充分实现流场分布和NH₃/NO_x混合分布均匀的要求，即反应器内第1层催化剂入口截面NH₃/NO_x混合不均匀性低于5%；烟气气流速度不均匀性低于15%；烟气到达第1层催化剂的入射角小于10°。对原脱硝装置进行相应改造后，脱硝装置出口NO_x浓度总体分布均匀，平均浓度低于超低排放限值，且氨逃逸浓度远低于设计值3×10^-6,现场实测结果进一步验证了改造方案的可靠性。流场升级的改造方法对于指导大型燃煤机组SCR系统的超低排放改造具有借鉴意义。

Due to the problems of unstable SCR performance and excessive ammonia slip in coal-fired power plants,taking the SCR denitration system of a representative 660 MW supercritical pulverized coal boiler as an example,and combined with the characteristics of ammonia injection grid and stationary vortex ammonia injection mixer,the multi-dimensional optimization and transformation of the stationary vortex denitration ammonia injection mixing device was studied,and the process of flue gas flow,change and mutual mixing at various positions in the flue was analyzed. An optimization based on multi-effect staged mixing,zoning vortex ammonia injection and forced rectification was proposed. According to the CFD calculation results,the optimized design scheme of the SCR reactor system proposed in this paper can fully achieve the requirements of uniform flow field distribution and NH₃/NO_x mixed distribution. At the cross section in the first catalyst layer inlet,the coefficient of variance for flue gas flow velocity is less than 15%,and coefficient of variance for NH₃/NO_x mixing is less than 5%. The incident angle of the flue gas reaching the first catalyst layer is less than 10°. After the modification of the SCR reactor device,the overall distribution of NO_x concentration at the outlet of the denitrification device is uniform,the average concentration is lower than the ultra-low emission limit,and the ammonia escape concentration value is much lower than the design value 3×10^-6. The practical test results further verify the reliability of optimization method. Therefore,the upgrade idea and theoretical research method are of great significance to guide the ultra-low emission transformation of SCR system of large coal-fired units.

0 引言

1 计算模型

   1.1 机组情况

   1.2 计算模型

   1.3 模型设置

2 计算结果分析

   2.1 原脱硝系统计算结果

   2.2 优化改造方案计算结果

   2.3 优化改造结果

3 结论