A novel approach to promptly control product quality in precise distillation columns based on pressure dynamic modeling

Abstract

For distillation columns, a temperature is controlled to hold product quality while the column is operated at constant pressure. In practice, absolute stability of temperature and pressure is unachievable, whereas the product quality, namely, product composition, fluctuates with the variation of them. By analyzing phase equilibrium, the composition fluctuation, caused by slight temperature and pressure variation, cannot be ignored for precise distillation column. Thus, a novel approach is proposed to improve the performance of product quality control. For preliminary, the freestanding pressure dynamic model is established via calculating vapor molar holdup. The modeling method is applied to a commercial ethylene column, and the veracity and reliability of the dynamic model is improved. For principal part, the complementary control strategy is proposed on the basis of the improved dynamic behaviors. Besides qualitative analysis, 2 scenes that contain tight control for external disturbance and transition control for internal regulating are discussed to verify the feasibility and progressiveness of product quality control with complementary structure.