| -With the rapid growth of economy,Emissions of nitrogen oxides(NO_x)in thermal power plants are also increasing year by year,which bring some threat to the human health and the natural environment.In recent years,the state has made more stringent requirements on NO_x emissions to coal-fired power plants.Therefore,it is very important to study the safety,environmental protection and economic nitrogen oxides removal technology.Selective catalytic reduction technology has the advantages of simple design,convenient control and high efficiency of denitrification,which is widely used in coal-fired power plant.For a long time,the research of SCR denitrification system mainly focuses on the research of the principle of denitrification,the catalyst,the flow field of the reactor and so on.The research on the control method of SCR system has not been paid enough attention to.But the control precision of the system is not only to determine whether the flue gas emission is satisfied to the standard,but also affects the operation cost of the power plant.This paper studies the dynamic process of SCR denitrification system.Based on adsorption desorption and chemical reaction,my paper constructed the denitration system mechanism model.At the same time,I connect the feed-forward control and Dynamic matrix control method.And the input and output constraints are added to design the optimal control system of the ammonia injection quantity based on the mechanism model to improve the control precision of the ammonia injection quantity.The thesis is carried out from the following three parts:This paper expounds the dynamic matrix control algorithm,considering the constraint conditions for the existence of SCR denitration system in actual operation,the design of DMC cascade control loop are analyzed by simulation of dynamic matrix control parameters on the control effect.Secondly,this paper introduces the basic principle and characteristics of the least square support vector machine.Introduce the SCR system layout,process flow and reaction principle and introduce two kinds of ammonia injection quantity control method: Fixed molar ratio control mode and Control mode of NO_x fixed value for the outlet of the denitrification reactor.A conventional PID control scheme is completed based on the design of the control mode of the export NO_x fixed value.And through simulation,combined with the simulation curve and the actual operating characteristics of the power plant,the characteristics of SCR denitrification system and the shortcomings of the existing control schemes are analyzed and summarized.The dynamic principle of SCR reaction process is analyzed,and the mechanism model of SCR system is established.The input parameters of denitration system is influenced by boiler combustion state seriously,and chemical reaction in SCR r eactor,outlet NO_x detection as well as the adjustment of the injection valve exist inertia and delay,which only feedback control is difficult to achieve accurate and fast adjustment of the export concentration of NO_x on the change of the condition.Therefore,based on the historical data of the power plant,the boiler side can be used as the input,and the output of the ammonia is used as the output,and the NO_x concentration model of boiler outlet is constructed by using the least square support vector machine algorithm.The model is used as an intelligent feed-forward controller and convert outlet NO_x concentration into valve opening signal.According to the parameter variation of boiler side,the model output the real time feed-signal in response to the change of the side condition of the boiler.Combining feed-forward control with dynamic matrix control,I design the optimal control system of ammonia injection quantity based on the mechanism model.The simulation results show that this model can control the whole working condition of NO_x concentration,and reduce the ammonia escape. |
PDF Full Text Request