Optimal operation of Petlyuk distillation: Steady-state behavior (Reprinted from Journal of Process Control, vol 9, pg 407-424, 1999)

The "Petlyuk" or "dividing-wall" or "fully thermally coupled" distillation column is an interesting alternative to the conventional cascaded binary co lumns for separation of multi-component mixtures. However, the industrial u se has been limited, and difficulties in operation have been reported as on e reason. With three product compositions controlled, the system has two de grees of freedom left for on-line optimization. We show that the steady-sta te optimal solution surface is quite narrow, and depends strongly on distur bances and design parameters. Thus it seems difficult to achieve the potent ial energy savings compared to conventional approaches without a good contr ol strategy. We discuss candidate variables which may be used as feedback v ariables in order to keep the column operation close to optimal in a "self- optimizing" control scheme.