Two-layer optimal control for goethite iron precipitation process

The goethite iron precipitation process is a very important part of the zinc hydrometallurgy process, where the most important is to control the oxygen volume. Therefore, this paper presents a two-layer optimal control method for goethite iron precipitation process. For the upper layer, oxygen utilization efficiency (OUE) in the process is firstly defined to measure the difference between the theoretical oxygen amount and its actual amount. On this basis, maximum OUE is the goal for optimizing the descent gradient of outlet concentration of ferrous ions. In the lower layer, least oxygen consumption and minimum error between outlet concentration of ions and the set value is the goal, and process dynamic model and process conditions are the constraints, optimal oxygen addition rate of each reactor is calculated. To overcome the impact of frequent fluctuations in production conditions on the control performance, a parameter adaptive correction approach is adopted to correct the model parameters. Finally, the actual OUE is used as the upper optimization parameter to update the outlet concentration of ferrous ions. Legendre pseudo-spectral method is adopted to calculate the optimization problem because of the multiple nonlinear constraints in the lower layer. Simulation results show that the two-layer optimal control method can achieve accurate process control and reduce oxygen consumption. © 2020, Editorial Department of Control Theory & Applications South China University of Technology. All right reserved.