煤粉锅炉污染物限值排放综合控制系统研究

燃煤锅炉产生的SO2、NOx是大气污染物的重要组成部分,随着环境形势的日益严峻,国家环保政策对电站锅炉和中小型工业锅炉的污染物排放标准提出了更高要求。煤粉工业锅炉烟气净化系统采用手动调节方式控制,系统惯性大,已不能满足最新环保排放标准。针对这些问题,基于可编程控制器(PLC)和以太网通讯架构,结合神东矿区某煤粉锅炉站限值排放改造工程,设计了集成化的污染物排放控制系统。在分析各系统工艺流程的基础上,分别提出了脱硫、脱硝系统的优化控制策略。脱硫系统基于站内原有NGD系统进行改造,增加了脱硫剂储运设备,在灰钙循环和增湿活化控制的基础上设计了自动脱硫剂补充和调节逻辑。脱硝系统增设了臭氧制备和输送装置,采用SNCR-臭氧协同方式,并设计了串级启动和自动投送控制逻辑。控制系统采取分布式硬件架构部署,采用西门子SIMATIC系列PLC作为主控制器,基于优化的控制逻辑,分别组态脱硫子系统、SNCR子系统及臭氧子系统。通过以太网络构建通讯子网,共享各子系统内部数据,以保证设备之间的安全联锁,以及脱硫、脱硝系统对锅炉负荷情况的跟踪响应,试验结果表明,控制系统能够在起炉后10 min内将SO2浓度控制在100 mg/m^3以内,在锅炉变负荷工况条件下可维持SO2浓度低于设定限值。多台锅炉连续运行时,各炉脱硫剂缓冲仓平均用料周期约为80 min,平均补充周期约为4.5 min,平均等待时间约为7 min,控制逻辑能够保证脱硫剂连续不间断供给。起炉后控制系统依次投入SNCR及臭氧系统,自动调节尿素溶液和臭氧的投加量,能够在20 min内将NOx浓度控制在100 mg/m^3以内。与改造前相比,锅炉站长周期运行时SO2、NOx排放浓度均显著下降,由100~200 mg/m^3降低至50~100 mg/m^3;根据运行期间80 h数据,SO2排放浓度平均值由163.55 mg/m^3降低至72.54 mg/m^3,NOx排放浓度平均值由160.85 mg/m^3降至71.06 mg/m^3,均满足国家与地方的环保排放标准。污染物排放波动性较改造前亦有所降低,SO2浓度标准差由21.04降至18.14,NOx浓度标准差由25.09降至15.84。

Research on integrated limited pollutant emission control system of pulverized coal fired boiler

The SO2 and NOxproduced by coal fired boiler are important components of air pollutant.With increasingly serious environmental situation,the national environmental protection rules put forward higher requirements for the emission standards of both utility boiler and middle and small industrial boiler. The flue gas purification system of pulverized coal fired industrial boiler has large inertia by using manual control mode,which can not meet the latest environmental standards.In view of these problems,combined with limited pollutant emission modification project of certain Shendong boiler station,an integrated pollutant emission control system based on programmable logic controller( PLC) and ethernet was designed.The optimal control logic of desulfurization and denitration system were proposed through analyzing process flow of certain systems.The desulfurization system was on the basis of original NGD system,the storage and transportation device of desulfurizer was added,and the automatic desulfurizer supplying and regulating control logic based on ash calcium circulation and humidification activation of desulfurization system were proposed.By installing ozone generator and conveying unit,denitration system was implemented with SNCR-Ozone cooperative method,then the cascaded start-up and automatic addition control logic were designed.Control system was deployed with distributed hardware,then subsystems of desulfurization,SNCR,and ozone system were configured based on optimized control logic using SIEMENS SIMATIC series PLC.The Ethernet network is used to build the communication subnet and share the internal data of each subsystem,so as to enable interlock protection and the tracking response of the desulfurization and denitrification system to the boiler load.The results show that the control system is able to maintain SO2 concentration below 100 mg/m^3 in 10 min after the boiler started,and keep the value under the preset limit at variable load. During continuous operation of several boilers,the average consumption time of desulfurizer surge bins is about 80 min,the average supply time is about 4.5 min,and the average waiting time is about7 min,which ensures the nonstop supply of the desulfurizer.The control system starts SNCR and ozone system in succession after the boiler started,adjusts dosing quantity of urea and ozone automatically,and maintains NOxconcentration below 100 mg/m^3 in 20 min. Compared with that before the transformation,the SO2 NOxemission of the station decreases significantly in long period operation,the concentration of which reduces from 100-200 mg/m^3 to 50-100 mg/m^3;according to operation data during 80 h,the average SO2 emission concentration value decreases from 163. 55 mg/m^3 to 72. 54 mg/m^3,meanwhile the average NOxemission concentration value decreases from160.85 mg/m^3 to 71.06 mg/m^3,which meets the national and local environmental standards.In addition,the fluctuation of pollutant emission is also reduced compared with that before the transformation,and the standard deviation of SO2 concentration value decreases from21.04 to 18.14,meanwhile the standard deviation of NOxconcentration value decreases from 25.09 to 15.84.