Advances in pH Modeling and Control

Many chemical and biological processes have pH control loops. Good pH control can be important for product quality as well as environmental compliance. The extraordinary rangeability and sensitivity of pH as a concentration measurement poses exceptional challenges in many aspects of pH design and implementation. Advances in dynamic modeling, basic control, and advanced control embedded in a Distributed Control System are introduced and illustrated with field test results for a plant waste treatment pH system. Examples are also presented on how these advances can be potentially used to reduce the project and operating costs for multi-stage pH systems. This paper details how models and control strategies are integrated in a DCS and used for an extensive variety of purposes. The model is used initially offline in a virtual plant to explore and prototype process control improvements running 10 to 100 times faster than real time. The improvements can be equipment, piping, and control system changes that reduce the capital and maintenance cost and reagent consumption that meet process objectives. An innovative configuration of a standard model predictive control is then developed to adapt model parameters to match up key process variables between the model and the plant. Test results and examples show how running and adapting the model online can provide increased monitoring and diagnostic besides control capability