Nonlinear dynamic matrix control for high‐purity distillation columns

Abstract

AbstractThe performance of Dynamic Matrix Control (DMC) for different product purity distillation columns is studied and compared with a conventional multiloop proportional‐integral control structure (LV). The load‐rejection capability (regulatory response) of DMC becomes worse than that of the conventional structure as product purity increases. Large load disturbances take the highly nonlinear system away from the nominal linear model, adversely affecting the performance of DMC. The LV structure is less sensitive to process nonlinearities. However, simple nonlinear output transformations suggested by the fundamental design equations of the process give models that are quite insensitive to nonlinearities of the process. This results in a nonlinear version of DMC that has better performance than the standard DMC and it is much simpler than the gain and time constant scheduling DMC or adaptive DMC. The complexity of DMC when it is applied on systems with very large time constants is also addressed. Suggestions to overcome this problem are proposed.