在超低排放要求下，SCR脱硝反应器的喷氨过量不仅影响经济性，还会引起空预器堵塞、电除尘积灰、布袋糊袋等问题。为提高SCR入口烟气速度和氨氮物质的量比的均匀性，对某电厂一台300 MW机组一侧SCR反应器进行计算流体力学的模拟和烟道流场优化。以Fluent为主要工具，在分析空塔模型和原导流板布置方案的基础上，对SCR烟道导流板结构进行优化、在喷氨格栅下游布置静态混合器，以实现首层催化剂前截面速度和氨氮物质的量比均匀分布。空塔方案速度相对标准偏差为26.1%，氨氮物质的量比相对标准偏差为24.8%，均达不到工程设计要求；原方案在SCR烟道渐扩处和转角处设置6组导流板，速度和浓度均匀性得到较大改善，速度相对标准偏差为13.9%，达到工程设计要求，而氨氮物质的量比相对标准偏差为15.3%，不符合小于10%的设计要求；优化方案布置的导流板消除了烟气在烟道转角处和渐扩处的漩涡、回流现象，同时安装静态混合器增强混合，使速度相对标准偏差减小至11.4%，氨氮物质的量比相对标准偏差为9.4%，SCR烟道内流场均匀性得到较大改善，速度和浓度均匀性达到设计要求。优化方案的压力损失为706 Pa，达到B级设计要求。合理布置导流板和静态混合器可以提高流场均匀性而不引起过大的压力损失，模拟结果对现场SCR流场优化具有借鉴和指导意义。

Under the requirements of ultra-low emission,the excessive injection of ammonia in the SCR DeNOx reactor not only affects the economy,but has also causes a series of operation and maintenance problems such as air preheater blockage,electrostatic precipitator fouling,and bag paste. In order to improve the uniformity of SCR inlet flue gas velocity and ammonia-nitrogen molar ratio,the computational fluid dynamics simulation and optimization research of flue flow field on one side SCR reactor of an old 300 MW unit in a certain power plant were carried out. Using Fluent as the main tool and based on the analysis of the empty tower model and the original deflector arrangement,the SCR flue deflector structure was optimized,and a static mixer was arranged downstream of the ammonia injection grid to achieve uniform cross-sectional velocity and ammonia-nitrogen molar ratio in the first layer of catalyst. The relative standard deviation of the velocity of the empty tower scheme is 26.1%,and the relative standard deviation of the ammonia-nitrogen molar ratio is 24.8%,all of which can not meet the engineering design requirements. In the original scheme,six groups of deflectors are set at the gradual expansion and corner of SCR flue,and the uniformity of speed and concentration is greatly improved,the relative standard deviation of the speed is 13.9%,which can meet the engineering design requirements,while the relative standard deviation of the ammonia nitrogen molar ratio is 15.3%,which can not meet the design requirements of less than 10%. The flow deflector arranged in the optimized scheme eliminates the vortex and reflux of flue gas at the flue corner and gradual expansion. Meanwhile,the static mixer is installed to enhance mixing,so that the relative standard deviation of velocity is reduced to 11.4%,and the relative standard of ammonia-nitrogen molar ratio to 9.4%. The uniformity of the flow field in the SCR flue has been greatly improved and the speed and concentration uniformity meet the design requirements. At the same time,the pressure loss of the optimized scheme is 706 Pa,which meets the B-level design requirements. The results show that the reasonable arrangement of the baffle and static mixer can improve the uniformity of the flow field without causing excessive pressure loss. The present work has reference value for the optimization of the on-site SCR flow field retrofit.

0 引言

1 SCR脱硝系统Fluent建模

   1.1 SCR系统基本概况

   1.2 网格划分

   1.3 数学模型与边界条件

   1.4 评价标准

2 各方案模拟结果与讨论

   2.1 空塔模拟

   2.2 原方案

   2.3 优化方案

   2.4 各方案模拟结果对比分析

3 结论