Study On Coordination Control Of Cement Closed Circuit Grinding Process

Cement grinding process is an important link in cement production,which directly affects the quality of cement.However,due to the characteristics of cement grinding process and the diversity of cement mixtures in China,the stability of cement grinding process is poor and it is difficult to operate stably for a long time.Therefore,it is of great significance to study the control of cement grinding.The process of cement closed-circuit grinding includes two subsystems: pre-grinding and final grinding.In this paper,the mathematical model is established respectively,and fuzzy PID and sliding mode control algorithm are used to control the subsystem separately.In order to reduce the adjustment conflict between the subsystems and maintain the dynamic balance between the two systems,a coordination controller is designed to enhance the coordination between the two subsystems,and optimization control system is developed.The main research work is as follows:(1)Based on the analysis of process mechanism of cement closed-circuit grinding system and historical data processing,the key parameters of pre-grinding system and final grinding system are selected.In the pre-grinding system,considering the non-linearity of the closed-loop structure,the BP neural network method is used to establish the mathematical model with the feed quantity as input and the material level value as output.In the final grinding system,considering that the adjustment parameters of the equipment fluctuate less frequently,the least square support vector machine(LS-SVM)method is used to establish a mathematical model with the rotational speed of the circulating fan as input and the amount of powder returned as output.The mathematical models of the two subsystems are simulated to verify the fitness of the models.(2)Based on the mathematical model of the pre-grinding system established by(1),the fuzzy PID algorithm is used to design the pre-grinding system controller.Taylor Expansion is carried out for the mathematical model of the final grinding system;the sliding mode control algorithm is used to design the controller for the final grinding system.Aiming at the disturbance factors of the system,a state observer is designed.Finally,a simulation study of the controller is carried out to verify the effectiveness of the controller.(3)Aiming at the problem of lack of coordination among subsystems and difficulty of maintaining dynamic equilibrium state,a coordination controller was designed for cement grinding system by combining multi-objective optimization algorithm.The upper coordination layer divides the working condition area for the whole system by analyzing the return powder amount and the steady flow bin material level,and determines the weight of the objective function.Then the multi-objective optimization algorithm is used to determine the stable flow bin material level and the expected amount of return powder under different working conditions and output to the control layer.The lower control layer receives the expectation from the coordination layer,changes the tracking instruction of the subsystem,and completes the tracking control of the subsystem.Simulation results verify the effectiveness of the coordination controller.(4)Combined with the on-site process of cement plant,and taking coordinated control and bang-bang control strategy as the core,this paper presents the coordinated optimization control system scheme of cement closed-circuit grinding process.A coordinated optimization control system was developed in C# software environment with OPC technology and malvern laser particle size analyzer,and it put into use in cement factory,obtained good result.