(An) experimental study of distillation column control using the KDAX system

Abstract

Distillation columns are the most widely used separation processes in the chemical and petrochemical industries. The existence of a great number of published articles dealing with various aspects of distillation column control also is ample evidence of the importance that industry and the academic control community have given to this subject. Recently, for the increasing demands of high product quality, minimization of waste and low energy consumption, better performance and tighter control of distillation columns is getting more important. Most conventional control techniques are developed on the assumptions that systems are regarded as being linear and time-invariant. Mainly, they use some simple linear mathematical models to describe the characteristics of systems. However, the real systems are not linear and time-invariant, thus this fact imposes the inherent limitations on the achievable control performance whenever linear controllers are used. Therefore, when applying linear controllers, we must have accurate models of real systems and frequently restrict them to operate in confined operation ranges. The control problems with distillation columns, especially for high-purity product, have been so severe that many process designers try to avoid making high-purity products out of both ends of a column simultaneously. Top and bottom composition control of binary separation has been proved to be particularly difficult because of the interactions between control loops. Due to these interactions many studies have been concerned only with the control of overhead product or bottom product composition. It is a very common practice in the chemical industry to build two columns instead of one and to provide large intermediate tanks to handle recycle flow between these columns. Pure products are produced out of one end of each column. This practice increases both capital investment and energy costs. Although decentralized control structure (especially multi-loop SISO ...