Cs. Bildea et Ac. Dimian, Interaction between design and control of a heat-integrated distillation system with prefractionator, CHEM ENG R, 77(A7), 1999, pp. 597-608
This paper analyses the relationship between the design and control of a he
at-integrated distillation set-up consisting of a prefractionator and a sid
e stream main column. The separation of a pentane-hexane-heptane mixture wi
th moderate purity requirements is considered. Both forward and reverse hea
t-integration schemes are investigated. Different designs are possible, dep
ending on the light/heavy split in the prefractionator and the heat-integra
tion scheme. They are similar with respect to energy consumption, but very
different with respect to dynamic behaviour. The differences are studied us
ing frequency-dependent controllability analysis, as well as carrying out c
losed-loop simulation, in the presence of large feed composition disturbanc
es. Thus, it is found that the forward heat-integration is much easier to c
ontrol, using only temperature measurements. The low-cost design with a sma
ll prefractionator has the best closed-loop performance. The reverse heat-i
ntegration can be controlled only if a composition analyser of the side str
eam is available; a sharp light/heavy split in the prefractionator gives be
tter disturbance rejection. The superior dynamic behaviour of the forward h
eat-integration scheme was confirmed by the study of a high purity separati
on of the benzene-toluene-xylene mixture.