Intelligent Optimization Control Of Wet Flue Gas Desulfurization Process Based On CPS Framework

A large amount of coal is burned in the power generation process of coal power plants.The flue gas generated during coal combustion is continuously discharged into the air.The flue gas contains a lot of sulfur dioxide which is one of the main pollutants that cause acid rain and air pollution.Limestone-gypsum wet flue gas desulfurization is one of the most efficient and mature desulfurization technologies at present,and it has been widely used in the desulfurization field at home and abroad.In this technology,the liquid absorbent contacts with the flue gas to absorb the sulfur dioxide in the flue gas,so as to achieve the purpose of flue gas desulfurization.However,wet flue gas desulfurization process is complex,and it involves multiple complex chemical reactions.During the operation of the desulfurization system,many system parameters are uncertain due to external interference,and the relationship between the parameters is complicated.In addition,the automation level of the existing wet desulfurization system is not high,and some control links even require manual adjustment.Considering these factors,it is necessary to study the control system of the desulfurization process to improve the automation level of the wet flue gas desulfurization process.Based on the desulfurization system data of a coal-fired power plant in Beijing,the cyber-physical systems(CPS)technology is introduced into the existing flue gas desulfurization system control,and the data-driven control algorithms such as model-free adaptive control are used to track and control the desulfurization process.The main research schemes and novelty of the thesis are as follows:(1)Wet flue gas desulfurization system is a complex system involving a series of chemical and physical processes.There are many complex control links in the desulfurization process.In order to improve the intelligent level of wet flue gas desulfurization process and optimize the process flow of wet flue gas desulfurization,firstly,the sensing,computation,communication and other technologies of CPS are introduced into the desulfurization system.By integrating the sensing data,network communication and other information resources with the physical resources in wet flue gas desulfurization system,a CPS framework of wet flue gas desulfurization process is designed.Then the decision-making control scheme of the flue gas desulfurization system under CPS framework is studied,and a variety of data-driven control algorithms are proposed,which are used for the tracking control of important links in the flue gas desulfurization process.Finally,the application flow of the data-driven control scheme proposed in this paper in the wet flue gas desulfurization system based on the CPS architecture is described in detail.(2)In the wet flue gas desulfurization process,the pH change process of absorption tower slurry is complex,and it is difficult to establish an accurate mathematical model.Considering the modeling complexity of the absorption tower slurry pH and the large amount of process data generated and stored during the operation of the system,a model-free adaptive control scheme based on compact form dynamic linearization(CFDL-MFAC)is designed by using the input and output data of the absorption tower slurry pH controlled system in this paper.According to the nonlinear and large lag characteristics of the pH change process of absorption tower slurry,combined with the advantages of model-free adaptive control algorithm and predictive control algorithm,a model-free adaptive predictive control algorithm based on compact format dynamic linearization(CFDL-MFAPC)is used in the pH control process of absorption tower slurry.The simulation results show that compared with PID control algorithm,CFDL-MFAC algorithm can obtain higher pH tracking accuracy of absorption tower slurry.When the CFDL-MFAPC algorithm is adopted,the tracking accuracy and convergence speed of absorption tower slurry pH to the set value are better.(3)Due to various interference factors in the pH control process of absorption tower slurry,it is easy to cause the parameters and even the structure of the controlled system to jump.To solve this problem,a model-free adaptive control scheme based on switching strategy is proposed in this paper,and the convergence of the system is analyzed.In this scheme,multiple model free adaptive controllers are established for the slurry pH controlled system with jump parameters to deal with the operating conditions corresponding to different jump parameters.It is turned out that this method can switch different controller for different jump parameters in the absorption tower slurry pH control process,so as to realize the fast tracking control of slurry pH.Through this method,the overshoot can be reduced and the control quality can be improved.(4)For multiple input and multiple output wet flue gas desulfurization process,a model-free adaptive control algorithm based on full-format dynamic linearization(FFDL-MFAC)is used to track and control it.Firstly,a mathematical model of the wet flue gas desulfurization system with two inputs and two outputs is established based on the data-driven modeling method.Then a FFDL-MFA controller is designed.Finally,in the simulation experiment,the FFDL-MFAC algorithm is compared with the CFDL-MFAC algorithm and the PID control algorithm to show the superiority of the method.(5)Considering that the load jump of coal-fired power units has a great impact on the desulfurization efficiency,a model free adaptive control scheme with switching mechanism is proposed for multiple input and multiple output wet flue gas desulfurization system.In the scheme,firstly,the operating conditions of desulfurization system are divided based on the load of coal-fired power units,and the mathematical models of two input and two output wet flue gas desulfurization system under different operating conditions are established.Then the MFA controllers of desulfurization system under multiple operating conditions are established respectively.Finally,a switching index function is designed to switch the controller of desulfurization system according to different operating conditions,so that the desulfurization system is always controlled by the most appropriate controller.The simulation results show that this method can effectively reduce the transient error of desulfurization system output and improve the desulfurization effect.