A New Methodology for Adaptive pH Control

Abstract

Good pH control requires knowledge of the nonlinear process gain, or titration curve. For applications such as waste stream neutralization, the titration curve changes quickly, making online titration curve estimation essential. The titration curve is a complex function of waste stream composition, and direct estimation of parameters for a waste stream model is difficult. This paper presents a technique for estimation of waste stream chemical composition that uses as parameters a basis set of preselected building block waste stream models. The parameter choice linearizes the estimation problem. An adaptive pH controller is described that uses the estimation technique to identify a waste stream model online. The model is used to construct the process titration curve to provide a gain schedule for a PI controller. Results of pilot plant testing of this controller are presented.