NO_x浓度分布在线监测系统研发及应用

Development and Application of Online Monitoring System for NO_x Concentration Distribution

选择性催化还原(selective catalytic reduction,SCR)烟气流场和NOx浓度分布不均匀,导致现有NOx在线监测系统单点测量结果代表性差和多点混合测量结果无法满足喷氨的分区调整控制,且难以为精准喷氨提供可靠的数据支持,极大制约SCR在线优化水平的提高,为此研发了烟气NOx浓度分布在线监测系统。首先依据喷氨区布置由多组网格化取样探头组成的取样分区,以巡回检测的方式实现SCR出口双侧烟道全截面的NO浓度分布在线监测;继而同步得到各测点截面NO与O2混合浓度值、截面浓度相对标准偏差、浓度分布云图及NO、O2、CO浓度测量值等信息;最后将该系统所测数据应用于SCR运行在线优化,而且结合喷氨调节阀的自动控制,进一步实现喷氨的动态分区智能控制,提升SCR运行在线优化水平,严格控制氨逃逸,降低空预器堵塞、引风机电耗增加甚至腐蚀等风险。该系统已在某电厂700MW机组上进行成功应用。

SCR flue gas field and uneven distribution of NO x concentration has caused poor representativeness of single-point measurement result of current NO x online monitoring system and failure of multi-point mixed measurement result in satisfying partition adjustment control for ammonia injection, which can not provide reliable data support for accurate ammonia injection and greatly restricts improvement of SCR online optimization level. Therefore, an online monitoring system for NO x concentration distribution is developed. Firstly, according to ammonia injection partition, sampling zones consisting of multigroup of gridding sampling probes are arranged and a way of cyclic detection is used to realize online monitoring of NO x concentration distribution on the total cross-section of flue at both sides of SCR outlet. Then information such as mixed concentration value of NO and O 2 on the cross-section of each measurement point, relative standard deviation of cross-section concentration, concentration distribution cloud map, measurement values of concentration of NO, O 2 and CO and so on is synchronously displayed. Finally the measured data of the system is applied for online optimization of SCR. Meanwhile, by automatic control of ammonia control valve, it is able to realize intelligent control of dynamic partition for ammonia injection, promote online optimization of SCR operation, strictly controll ammonia escape and reduce risks of blocking of the air pre-heater, power consumption increase of the induced draft fan even corrosion. This system has been successfully used in a 700 MW unit in one power plant.