SCR脱硝超低排放NO_x均匀性优化及安全策略分析

Optimization on the Ultra-low NO_x Emission Uniformity and Analysis on the Safety Strategy of SCR Denitration System

为使超低排放改造后NOx排放浓度及氨逃逸量始终可控平稳,以某600MW燃煤机组超低排放改造后SCR脱硝系统为研究对象,针对SCR反应器出口与总排放口在线监测(CEMS)数据不一致的问题,进行分析与研究。通过对反应器出入口流场、NOx、NH3浓度场的测试,结合系统结构特征,分析问题出现的原因,制定优化调整方案并验证其有效性。研究结果表明,反应器入口氨氮摩尔比的不均匀性是导致反应器出口NOx浓度分布不均匀的主要原因。通过优化调整,有效改善了反应器出口NOx浓度分布的均匀性,降低了氨逃逸量,SCR反应器出口与烟囱总排放口NOx浓度CEMS监测数值基本一致。同时,根据试验得到的反应器出口NH3与NOx关系曲线,提出了NOx的最低安全控制浓度及最佳控制浓度,以便运行控制。

In order to keep the NOx emission concentration and ammonia escape volume within a controllable and stable range after the transformation of ultra-low emission of the SCR reactor,by taking the SCR denitrification system of a 600 MW coal-fired unit as the research object in the case studies,the inconsistency between the data of on-line monitoring (CEMS) measurement acquired from SCR reactor outlet and total discharge outlet is analyzed and investigated in this paper.Through the measurement and testing on the flow distribution at both the entrance and exit of SCR reactor,as well as the concentration field of NOx and NH3 with the structural characteristics of SCR denitrification system taken into account,the causes of the problems are explored,then the corresponding optimization and tuning scheme are formulated and the effectiveness of the scheme is verified.The results show that the heterogeneity of the molar ratio of ammonia to nitrogen at the inlet of SCR reactor is the main reason for the uneven distribution of NOx concentration at the outlet of SCR reactor.Through the optimization and tuning processes,the homogeneity of NOx concentration distribution at the outlet of SCR reactor is effectively improved,and the ammonia escape volume is reduced as well.The measurement data of the NOx emission concentration acquired by CEMS from SCR reactor outlet are basically consistent with the total discharge from the outlet of chimney.Meanwhile,based on the curve representing the relationship between NH3 and NOx concentration at the outlet of reactor SCR obtained by repeated experiments,this paper proposes both the minimum concentration for safety control and the optimal concentration of NOx safety-control,so as to facilitate the operation and control of SCR denitrification system in the later stage.