Multi-variable Control for HPAL Using Nonlinear Multivariable Decoupling PID Control based on Predictive Model

Abstract

High pressure acid leaching process is the use of strong acid slurry in the high temperature & pressure conditions, and acid leaching to useful metal ions process. It is a typical multiple-input multiple-output system. The efficiency of acid leaching is sensitively influenced by temperature, pressure and level of the autoclave, and in general the single loop PI method is always adopted for designing each loop controller. But due to the coupling effects among those variables, the method cannot control the temperature, pressure and level stable, which result in the decrease of efficiency of acid leaching. By analyzing high pressure acid leaching characteristics a nonlinear decoupling predictive control approach is employed based on mechanistic models established. The method has been successful applied to a real large-scale abroad nickel hydroxide cobalt smelt plant. The results demonstrate that the method can effectively and steadily control the temperature, pressure and level of the autoclave at their targets nearby, and improve the efficiency of acid leaching.