An in-line approach to pH control of chemical effluent

Current practice and research into pH control principally entails the use of Continuous Stirred Tank Reactors (CSTRs). Researchers have typically adhered to the McMillian(1) plant design advice and over-designed plant. Whilst over-design does indeed damp out disturbances, it is expensive and leads to problems with control. However industry's need is for a cheap, but effective, solution to the problem. There are two criteria to be satisfied: good quality control and economical plant design. This paper outlines a minimal plant design consisting of an in-line injection system, a back mixing system and a variable transformation approach to controlling the pH. This approach uses an anti-logging technique which removes the non-linearity at source and yields an easier to handle linear signal. The technique is used in conjunction with advanced control methodologies.