Latin Abstract :
The paper illustrates the eects of recycle streams on the controllability of integrated plants and the improvement of performance
made possible by a direct compensation of the recycle. A procedure for the decomposition of the global process in a part repre-
senting the process without recycle and in a part representing the recycle is presented. This is the key issue for evaluating the rele-
vance of the recycle and to reduce the control system to two blocks: a regulator, depending on the process without recycle, plus a
recycle compensator. The design of this control scheme is much easier with respect to a speci®c regulator computed for the global
process and allows to achieve relevant improvement of performance with respect to a standard PI regulator. This is clearly illu-
strated for a SISO reference case, where process parameters are changed to create situations of particular evidence, and have been
con®rmed in the application to the two MIMO benchmarks, proposed in literature: the two reactors in series (W.H. Ray, Advanced
Process Control, McGraw±Hill, New York, 1981, pp. 219±224), and the two reactors plus three distillation columns (M.L. Luyben,
W.L. Luyben, Design and control of a complex process involving two reaction steps, three distillation columns and two recycle
streams, Ind. Eng. Chem. Res. 34 (1995) 3885±3898). For a full evaluation of the eectiveness of the proposed control system, the
eect of the uncertainty, of the approximated structure of the compensator, as well as possible improvements by including partial
adaptive features in the control system, are also taken into consideration.
NaturalLanguageKeyword :
recycle , Compensators , Decentralized Control , ntegrated plants
