Research On NO_x Optimized Control And Engineering Application For Denitration System In Coal-fired Unit

China is a resource-based country dominated by coal.In the combustion process,coal produces a large amount of NOx,SO₂,PM,heavy metals and other pollutants,which is an important factor causing air pollution and haze in China and seriously affecting the natural environment,people’s life and health in China.The Chinese government attaches great importance to environmental protection and actively promotes the implementation of the policy of ultra-low emission of air pollutants,which has achieved remarkable results.The stable and efficient operation of the denitrification system is the key point for reaching the standard of NOx emission concentration of the flue gas of coal-fired power plants.Due to the nonlinear and hysteresis characteristics of the denitrification system,under the existing PID control mode,the NOx concentration exported from the denitrification system fluctuates greatly,and the emission concentration exceeds the standard frequently.Therefore,it is unable to reach the ultra-low emission standard in a stable manner.In the actual operation,excessive ammonia spraying is used to ensure the NOx emission concentration at the export reaches the standard,which increases the operating cost of the denitration system.In this paper,SNCR-SCR denitration system is taken as the research object to carry out the following research work aiming at the urgent problems of high fluctuation of NOx emission from export and high cost of denitration caused by the nonlinear,hysteresis and poor PID control tenability of denitration system:First,in view of the SNCR-SCR NOx emission concentration of outlet of the denitration system issue such as difference of volatility,device control,study the characteristics of the traditional PID control method,analyzed the denitration system entry/exit NOx concentration affect the characteristic parameter,is put forward based on the prediction of NOx concentration denitration system optimization control method,system optimization control model has been established,in order to further develop denitration optimization control system set up research provides the theoretical support.Second,taking a 220t/h circulating fluidized bed boiler SNCR-SCR denitration system as the research object,the main equipment to carry out the denitration system reformation,the foundation work of hard software upgrades,studied the functional building,and put forward the system structures,the key problems and solutions,to build the denitration optimization control system,in view of the typical working condition of boiler operation to optimize denitration system debugging,export NOx concentration before and after the contrast analysis of the optimal control of volatility,comparison results show that the optimization control mode standard general export NOx concentration decreases more than 77%,significantly reduce NOx concentration of outlet of the denitration volatility,It provides data support for further long-term engineering application of denitrification optimization control system.Thirdly,for the engineering application of denitration optimization control system,the long-term operation analysis was carried out on the rated load of 220t/h and 130t/h coal-fired units respectively.By comparing the actual engineering application effects before and after the optimization control,the quality of the optimized control system was verified.The specific research conclusions include:under the optimized control method,the concentration distribution of export NOx concentrates near the given value of export NOx.Compared with the original control method,the standard deviation of export NOx emission concentration decreases by 65.7%and 43.6%,respectively,which realizes the precise control of export NOx emission concentration.The optimized control mode can realize the real-time standard of export NOx emission concentration to ultra-low emission standard,and the material consumption cost of denitrification system can be saved by 25%and 20%respectively,and the operating cost of denitrification system can be significantly reduced.