Research On Predictive Control And Simulation Of PH Value Based On The Confection Process Of Sodium Nitrate

The pH value is the scale unit of solution acidity. In lots of chemical industrial production process, the control quality of pH value influences both quality and quantity of corresponding products directly, and holds the important status in the industrial process control. However, the pH neutralization process is a typical kind of complex process, its specific characteristic, which is strongly nonlinear, time-varing, large time delay, has made it very hard to build an accurate mathematical model for the very process. Using the regular control methods can not make a quick and precise response during variational process of the reaction. Considered above, it is very hard to implement effective control and impact. The predictive control method is suitable well for those industrial production process, which is complicated relatively and not easy to obtain the accurate model, the control effect is quite good, and also has better robustness. In the article, with predictive control theory, the author has analyzed and researched the control problem of the pH value based on the confection process of sodium nitrate during Acrylon manufacture.At first, based on the reaction mechanism of electrochemistry during the process, the reaction situation of acid-base neutralization had been analyzed deeply. And according to the equation of charge balance, the mechanism model of acid-base neutralization, which is designed for the research of sodium nitrate confection process, has been derived. On the base of mechanism model, the simulation model is created with the help of software module--Simulink in MATLAB, and then the simulation model is utilized on the analysis of the nonlinear feature of pH neutralization process and the response of system disturbance.After that, the structure feature of Hammerstein model, the typical nonlinear model, has been studied. The author has chosen the structure of polynomial function, which is the most simple and widen applied, to describe the static nonlinear element of process. Then, the principle of least-squares has been used in the off-line identification for parameter estimation, followed by the on-line recursive least-square method with forgettable factor, which can adapt to identify the pH neutralization process and to adjust the parameter of Hammerstein dynamic linear sector.At the end, the valid estimated parameters under the validation of various data are adopted to take real-time control simulation of the target with the combination of model predictive control strategy. And the author has compared with the traditional method—PID in the aspect of control effects. The result indicates that, according to the experimental equipment of sodium nitrate confection pH neutralization process, the predictive controller based on Hammerstein model has shorter response duration, less overshoot and static error. In that case, the nonlinear control problem of pH value has been solved well under this advanced control theory.