Abstract: The stability time and control effect of traditional proportional integral (PI) control for fractionator of diesel hydrorefining unit with complex process and strong coupling of the system are not good. Based on the original PI scheme of fractionator of diesel hydrorefining unit in a domestic petrochemical enterprise, a model predictive control (MPC) co-PI control scheme was proposed. The results showed that the control scheme of MPC and PI could improve the dynamic performance of the device, and the oscillation frequency of PI control was similar to that of MPC control scheme when the feed rate and steam rate of stripper fluctuate, but the stability time and the control maximum deviation of MPC were smaller. For disturbances of ±10% feed rate, the maximum temperature relative deviation of PI control and MPC scheme was 3.48% and 0.07%, the stability time was 3.5 h and 1.5 h, and the value of absolute error integral (IAE) was 7.30 and 0.23, respectively, and the control effect of MPC was better than that of PI control. At the same time, the feasibility of MPC and PI control was verified, which showed that MPC combined PI control was more suitable for advanced control of fractionator of diesel hydrorefining unit.

Key words: simulation, product quality, PI, model predictive control, fractionation unit