Process Control Under Variable Flow and Volume

Abstract

Models of continuous flow vessels with variable volume and flow are studied and their control algorithms developed. It is shown that the weighting functions of many vessels which are time-variable under such conditions, are invariant with regard to new, composite variables which are introduced. The validity of the basic assumption on invariability of the flow pattern under flow and volume variations is shown valid for several, analytically known cases. The approach is extended to arbitrary, non-analytic response functions obtained by measurements. Automatic controllers are then introduced for processes with variable liquid volume and flow. Both the feedforward and feedback controllers developed in terms of the new variables have constant parameters and eliminate correctly the effects of the disturbance variables in control of concentration or other material property. The corresponding gain scheduling controllers are also presented which operate in terms of the time. Both types of controllers appear easy to implement in hardware and software. Industrial buffer vessels, natural water reservoirs and physiological systems are stated as potential applications of modelling and control, and extensions to chemical reactors are discussed.