Hydrodynamic model for controlled cycling in tray columns

Abstract The paper describes a model for controlled cycling in tray columns. Gas phase dynamics and hydrodynamic relations are included in the proposed model. The model has been simulated on a digital computer. Gas phase dynamics is found to play an important role for cyclic operation of distillation columns, while as the effect of gas phase dynamics can be ignored for absorption columns. In a 5-tray distillation column reasonable separation between liquid and vapour flow periods can be achieved, but with increasing number of trays the switch-over from one period to another becomes less ideal. For a ten tray column the flow situation is unacceptable. The simulations also show that the plug flow condition in the liquid flow period is most difficult to satisfy in the top and bottom of the column. The risk of flooding on some trays and other trays running dry increases when the numbers of trays increases. Finally it is shown that the hydrodynamic behaviour may be improved by changing the geometry of some of the trays.