Control And Research On Process Water PH Valve Of Desulphurization And Dust Removal

With the continuous emissions of SO2, the total emissions of SO2 in China continue to face growing trend. In 2015, the emissions of SO2 are at about 19 million tons in our country. Therefore, it is necessary to implement some effective measures to reduce the emissions of SO2, which plays an important role on environmental governance in China. At present, limestone-gypsum wet flue gas desulphurization is widely used in wet desulphurization and dust removal technology. In the technical process of limestone-gypsum wet flue gas desulphurization, the slurry pH value in absorber tower is the key factor which has the critical effect. It not only affects the absorption rate of SO2, but also has a great relationship with the scaling of the system equipment, limestone dissolution and precipitation. However, the control projects of slurry pH value in absorber tower mostly are through manual adjustment of the valve opening of limestone slurry flow to make the pH value meet the requirement. The good or bad of this kind of pH value control system often has direct relations with the experience of site operator, which can bring about great inaccuracies to the system due to this mode of regulation. For this reason, in order to change this situation, the pH value of process water in desulphurization and dust removal technology was researched in this paper. In which the automatic control project of process water pH value was designed, which not only can make the system stable running, and significant energy saving effect. In this paper, the main research works are as follow:(1)Firstly, the limestone-gypsum wet flue gas desulphurization technical process was introduced, the influence of pH value to the limestone-gypsum wet flue gas desulfurization was analyzed. Beside, the relationship between the flow rate of limestone slurry and recirculation slurry pH value in absorber tower was given. On the basis of this principle, the pH value control plan was proposed.(2)The main components in the system such as servo motor, servo drive and centrifugal pump need to be selected, the parameters and performance of each component part need to be analyzed. After that, their respective mathematical model is established, combine all the parts, the mathematical model of the entire system can be established. From the two aspects of Nyquist stability criterion and Bode stability criterion, stable performance of the system was discussed. To analyze the controllability and observation of the system, the system state space model was established.(3)The PID control method was studied on system performance, the simulation model was established by applying the MATLAB/Simulink module, and then the simulation curve are obtained. According to the shortcomings of the PID control method, then the H∞ robust controller was designed, the model of the controller was described using the MATLAB programming, the robust controller can improve the quickness、stability and the anti-interference ability of the system.(4)In the flowing, this paper indicated the hardware solution of entire pH value control system, introduced the STM32 controller and control chip STM32F103RCT6, then each function module was designed on the controller development board.(5)According to the requirements of the system control, the entire software control scheme is proposed. For the convenient of programming, ST firmware library was used in this process. The entire program of control system was developed based on the Keil MDK application development environment. The method of modular programming was adopted to design the main program, PWM program, ADC sampling program and pH value judgment procedure.(6) Finally, A set of test device was adopted to verify the control project of process water pH value of desulphurization and dust removal. The principle diagram and circuit diagram of this test device are designed under the condition of satisfying control function. After completing the installation of the test bench, pH meter real-time acquisition data at the same time, this system can be run automatically. The experimental results showed that when the actual pH value of reaction vessel detected by pH meter was not equal to ideal pH 5.5, the rotate speed of servo motor was adjusted automatically in the system. That was to say, the alkali liquid flow into the reaction container was changed at the same time, made the liquid pH value in the reaction vessel meet ideal value eventually, which achieve the purpose of pH value control.The automatic control project of pH value of process water in desulphurization and dust removal technology based on STM32 and motor servo technology was researched in this paper. Firstly, the relationship between the flow rate of limestone slurry and recirculation slurry pH value in absorber tower was given. Besides, the mathematical model of entire control system was established. After that, the PID control method and H∞ robust control were implemented in this system, which can improve the quickness、stability and the anti-interference ability of the system greatly. Therefore, the control system of pH value of process water designed in this paper has certain reference significance to the desulphurization and dust removal technology in the future.