Reactor/separator processes with recycle .1. Candidate control structure for operability

The economic and environmental considerations often lead to more stringent process design. In terms of plant operation. this means the existence of recycle structures in processing plants. The steady-state and dynamic behaviors of the reactor/separator system differ significantly from their individual unit counterparts. A notable difference is the limited throughput handling capability when the control structure (selection of controlled and manipulated variables) is not appropriately chosen. Since the extra work. resulting from load change, is not evenly distributed among process units. this imbalance leads to large deviations in some process variables. Analyses are given to illustrate this effect and a control structure is proposed to overcome this disturbance rejection problem. Furthermore, a systematic tuning procedure is also proposed to find the controller parameters in plantwide control. A reactor/separator process is used to illustrate effectiveness of the balanced control structure and controller tuning procedure. Simulation results show that the balanced scheme can handle large load changes while maintaining good dynamic performance. Copyright (C) 1996 Elsevier Science Ltd