Abstract: The SO_2 and NO_xproduced 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/m3 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 NO_xconcentration below 100 mg/m~3 in 20 min. Compared with that before the transformation,the SO_2\ NO_xemission 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 SO_2 emission concentration value decreases from 163. 55 mg/m~3 to 72. 54 mg/m~3,meanwhile the average NO_xemission 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 SO_2 concentration value decreases from21.04 to 18.14,meanwhile the standard deviation of NO_xconcentration value decreases from 25.09 to 15.84.