Cyclic Operation of Flash and Column Flash Distillation

Cyclic distillation can increase the column efficiency that is evident from either more separation with the same number of stages or fewer stages for the same separation. Cyclic flash distillation, the single stage limit of cyclic distillation without reflux, is batch distillation with repeated charges of feed. Continuous flash distillation is normally a single stage separation technique, but one variant, column flash distillation, has multiple stages. Column flash distillation is not a common separation process, but it is used commercially during partial condensation of hydrocarbon gas mixtures. In traditional batch distillation, the still pot is heated, and some of the batch is boiled away. A second batch operating method first loads the still pot with liquid feed, and then, vapor feed is added. A third method combines the previous two methods. Although traditional simple batch distillation requires significantly less energy than continuous flash distillation, batch distillation is rarely employed because it is believed that it is difficult to interface batch operations with the continuous processes in continuous plants. In this paper, binary separations by the following systems are compared: batch distillation, conventional flash distillation, continuous column flash distillation, and cyclic column flash distillation. The results show significant improvement when batch distillation or continuous column flash distillation replaces continuous conventional flash distillation and very modest improvement when cyclic column flash distillation replaces continuous column flash distillation.