Unsteady-State Processing

Abstract

Benefits can be obtained by deliberately operating a process in the unsteady state. Increases in efficiency and capacity of columns and flattening of velocity profiles in packed beds are some of the advantages over conventional steady-state processing. Examples are given from work in distillation, extraction, crystallization, ion exchange, and reaction engineering Unsteady-state processing promises to be an interesting area 58 INDUSTRIAL AND ENGINEERING CHEMISTRY

Membrane Separation of Gases Using Steady Cyclic Operation

“…In recent years there have been numerous suggestions and demonstrations of advantages to be had by operating various chemical processes in an unsteady-state fashion. Schrodt (1967) illustrate this point. Of particular relevance here is the consideration of a steady cyclic ion-exchange process given by Simmons and Spinner (1969).…”

Cyclic distillation technology - a mini-review

“…The authors mention a number of interesting problems posed by periodic operation: overall material and mass balances must be maintained; in contrast to conventional operation, where only small changes of flow rates are required, periodic operation modifies the inputs between minimum and maximum values; it is necessary to control not only the actual flow rate, but also the total amount of flow of each input (this is particularly important during the liquid drain period); there must be stable hydrodynamic operation of the column; the liquid drain time must be carefully chosen to maintain the desired holdup; some method of product composition measurement is necessary. According to Schrodt, both instantaneous and averaged measurements are necessary, as the control mechanism must maintain both the repeating pattern of the instantaneous variables and their average.…”

On the theory of dynamic plug‐flow processes: Inlet control and distributed trajectory control

“…Thus, if only the inlet state can be controlled, (case (A) ) the attainable sets for periodic and steady-state operations are indicated by SR and SR= respectively. Clear Iy, (21) where the bracket stands for any of the three classes of possible control actions.…”