Optimization-Based Input/Output Linearizing Control Strategy for a pH Process with Multiple Titrant Streams

This work develops a control strategy to handle coupling effects between the level and pH for a pH process with multiple titrant streams. The feedback controller is formulated based on a nonlinear optimization problem of an input/output (I/O) linearization for output tracking. In order to calculate the control actions and estimate the state disturbances simultaneously, an integrated disturbance estimator is combined into the developed control structure. The proposed controller is applied to control the outlet pH and liquid level of a reactor system to achieve desired setpoints by adjusting outflow and titrating streams. Control performance of the developed control system is investigated by experimentation with a continuous bench-scale pH process that is operated under servo and regulatory problems of disturbances in the feed and titrant streams. Experimental results show that the developed controller can force the process to the desired setpoints effectively and handle the pH process with disturbances when fluctuations in pH and inlet flow of the reactor are present.