Research On Na₂SO₄Regeneration Control Method In Acid Pickling Of Cold Rolling Mill

Along with the development of technology of stainless steel acid pickling, neutral electrolyte becomes the mainstream. While it improves the unevenness of the strips, the drainage of waste electrolyte also causes serious pollution to the environment for the highly toxic hexavalent chromium ions. Therefore, reasonable recycling of waste electrolyte becomes more and more important as well as meets national requirements on sewage discharge.Based on the process of stainless-steel acid pickling, this thesis introduces treatment process of Na2SO4waste electrolyte, and its mechanism of chemical reactions. By analyzing programs in control system of pickling line, we got the control objectives of PH value and Oxidation Reduction Potential (ORP), which characterizes concentration of hexavalent chromium ions in the solution. As low and stable PH value acts as prerequisite in removal section of haxalevant chromium ions, the thesis ensures removal rate of haxalevant chromium ions by adding reducing agent to adjust ORP, thus dual-loop ratio control system is established with PH acts as primary controlled value and ORP as secondary. With traits of long latency and the change of model parameters in the process of regulating PH value, adding reducing agent and chemical reaction, the thesis tries to lead into Fuzzy PID Control as intelligent control algorithm for PH-loop control system. In this case, it meets the requirements of real-time control as online turning of PID parameters and removes reliance on mathematical models for controllers. And also, for ORP, in order to exclude the disturbance caused by electrolyte, the thesis chooses Internal Model Control to improve its robustness with its model coming from Nernst Equation.By means of simulation tool of Matlab, the thesis analyzes fuzzy PID control and Internal Model Control for their dynamic response and robustness. In this case, the thesis can reach the final conclusions firstly, fuzzy PID controller achieves a better control effect; Secondly, Internal Model Control has an improvement in robust performance, compared to conventional PID controller.