Advanced process control of a B-9 Permasep® permeator desalination pilot plant

An experimental application of advanced control and optimization on a hollow-fiber membrane module (B-9 Permasep (R) permeator by DuPont) is presented. The objective of the study was to compare the performance of standard proportional-integral (PI) control with the performance of a constrained model predictive control (CMPC). A proper control strategy, whether PI or CMPC, should allow for the manipulation (servo control) of the product flow rate while maintaining product quality. In doing so, a plant can adjust the production of water to meet demand. Several PI control experiments involving set point changes in product flow rate and conductivity (a measure of quality) were conducted. It was found that PI control was unable to properly control the quality of the product by means of manipulating the pH of the feed. The PI controller over-compensated for offset in product conductivity. In contrast, CMPC displayed superior performance in the control of the pilot plant by holding the process outputs within specified bounds; especially the feed pH which prevented the conductivity PI control loop from becoming unstable. Furthermore, CMPC was able to maximize the product flow rate by 13.6% while improving the conductivity (quality) by 1.1%.