Simultaneous Process and System Control Design: An Actual Industrial Case

Abstract

In view to reducing capital needs and energy costs, a chemical plant was designed with highly integrated process unit operations. Because of the high level of heat integration, during the design phase special emphasis was put on the controllability of the system, especially at startup, shutdown and upset conditions.

In this paper the design and control of the process heater, being the main heat source of the plant, will be discussed. Two questions were to be answered: i) what is the optimal heater design, and ii) what is the best control structure, i.e. which controlled variable should be paired to which manipulated variable. The heater design and controllability was studied as stand alone unit as well as integrated unit. Dynamic modelling and controllability behaviour was studied using SpeedUp and Speecon software packages.

The present work showed that heavy integrated processes ask for controllability analysis at the design stage. Based upon controllability data, it appeared that a heater consisting of parallel heat sections was to be preferred over a serial positioning of these sections. Furthermore it was concluded that controllability analysis should cover complete process networks. This was illustrated by the fact that the best control structure of the integrated heater was the one that come out as the least good for the stand alone unit.