Steady-State Noninteracting Controls for Distillation Columns: an Analytical Study

Abstract

Using the Eduljee equation (19754, approximate steady-state decoupling algorithms for dual composition control are developed analytically for binary columns. Use of the algorithms in multicomponent columns is also discussed. These algorithms agree very well with exact decoupling results. The fact that complete decoupling probably cannot be realized in dual composition control of high purity columns is shown analytically. The relationships presented should be useful in future studies and applications of decoupling control to distillation columns.

Approximate solutions for distillation rating and operating problems using the Smoker equations

“…Shinskey (1977) advocates the use of this much simpler approach for column control analysis. Jafarey et al (1980) also discuss its use in steady-state decoupling analysis.…”

Feasibility of Decoupling in Conventionally Controlled Distillation Columns

“…This factor contains both steady-state and dynamic elemerits. The subject of the dynamic effect of [1 -(P12P21/P11P22)] is treated in a future paper (McAvoy, 1980). In this paper a less general approach which only considers the steady-state value of this factor will be taken in order to give a simple explanation of decoupling.…”

“…Three recent studies (Jafarey and McAvoy, 1978;McAvoy, 1979;Jafarey et al, 1980), however, have questioned whether decoupling can be achieved in certain columns.…”

“…All of these studies are based upon considering steady-state column performance. Jafarey and McAvoy (1978) and Jafarey et al (1980) showed that in practice it may not be feasible to completely decouple both composition loops in a column. Although two decoupling relationships exist, they turn out to be almost identical for high purity towers and thus it may not be possible to implement both of them simultaneously.…”

“…Since the results of Jafarey and McAvoy (1978), McAvoy (1979), and Jafarey et al (1980) were based on steady-state considerations only, a series of dynamic column simulations was run to verify their conclusions. Three columns having a low, moderate, and high sensitivity as defined by McAvoy (1979) were chosen for study.…”