The Research And Application Of Advanced Control Technology For SCR DeNOx System Of The Coal-fired Power Plant

At present,the poor quality of automatic control of ammonia spraying was considered as the common technical problems in the SCR system of coal-fired power,which can easily lead to damage of ash corrosion at cold end of air preheater and other operational problems.The objective of inhibiting the formation of ammonium bisulfate and improving the safe and stable operation performance of the unit with ultra-low emission retrofit could be realized by optimizing control of ammonia spraying to achieve the lower ammonia slip.Based on the denitrification control system transformation project corresponding to the unit 2 of Shenhua Guohua Shouguang power plant with 1023MW,the most feasible ammonia spraying control scheme was put forward after deeply understanding the development direction and characteristics of advanced control of SCR system in coal-fired power plants.Combined with the reaction mechanism of the SCR system,the operation status of the unit and the conventional control scheme of ammonia spraying,the following conclusions were obtained.The control scheme of fixed molar ratio control was not conducive to ensuring high precision control of NOx emissions,according to easily cause environmental emissions exceeding the standard.In view of the fact that the measured inlet NOx concentration varies greatly and of high hysteresis,the quality of ammonia spraying control would be relative low when the measured NOx concentration was introduced directly.The method of setting the control parameters relying on the static physical characteristics of the system was proved as not reasonable,which was not conducive to achieve the good matching between the control characteristics and the characteristics of the controlled object.The distortion of the measurement of the key operating parameters,such as inlet and outlet NOx concentration should be accordingly dealt,otherwise,it is not conducive to improving the automatic control quality.As a result,the advanced integrated control scheme of SCR for ammonia spraying was proposed in this research.Firstly,the design method and simulation results of improved cascade control scheme were given based on Smith prediction and state variable compensation technique.Then the PID controller in the main loop of the improved cascade control scheme was replaced by the generalized predictive controller,and the design method along with its simulation result was provided.Finally the intelligent feedforward control technology was developed to achieve the dynamic compensation for two types of disturbances,which were the great fluctuation of inlet NOx concentration and the distortion disturbance measured by NOx analyzer.Consequently,timely and reasonable ammonia spraying was realized at the source of the reaction.The advanced integrated control scheme of SCR for ammonia spraying proposed in this paper has been successfully applied to the domestic 1023MW ultra-supercritical units in Shenhua Guohua Shouguang power plant.The software design and development was carried out based on the optimized control scheme,and it was invested in industrial application finally accompanied by the configuration of related hardware in the light of the actual situation of SCR system in this plant.The engineering application results showed that the advanced control scheme could effectively improve the dynamic response quality,and improve the control effect of NH3 significantly,which could provide a reference path for the transformation of ammonia spraying in other power plants of the same type.