An Adaptive Feedforward Control Algorithm for Computer Control of Wastewater Neutralization

Abstract

The purpose of this paper is to show the development and testing of an adaptive feedforward control of a wastewater neutralization process. The adaptive controller is compared to a nonlinear proportional - integral-derivative (NPID) controller developed by Shinskey and Myron (1970). The process and controllers were simulated on a digital computer. The adaptive controller utilizes two pH probes, a feedforward probe and a feedback probe, with the latter used in the adaptive calculations of the feedforward gain. The feedback measurement provides the adaptive controller with a form of reset action.The process simulated for control combines a strong (hydrochloric) and weak (carbonic) acid neutralized by a strong base (sodium hydroxide). The adaptive controller was shown to give superior responses both for step changes in the strong acid and in the weak acid (buffer) concentration. One particular advantage of the adaptive controller is that it requires only two tuning parameters, while many controllers in use today require five or more tuning parameters.The sensitivity of the adaptive control to changes in certain parameters (probe noise and lag, valve hysteresis and lag, and dead time) was studied, as was the effect of a step change in flow rate to the system. Noise in the feedforward pH probe and the dead time between the reagent addition and the feedback probe had the largest effect on the adaptive controller performance.