Practical Column Design Guide by M. Nitsche & R. Gbadamosi

Author:M. Nitsche & R. Gbadamosi
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

What is more difficult is analytic control of the distillate composition in which the concentration constantly changes and the optimum setting of the reflux ratio, in order to achieve the desired distillate composition and yield with a low-energy input. Therefore, the analyses must be performed constantly, manually, or with a process chromatograph in order to optimize the reflux ratio. In a stepwise increase of the reflux equilibrium disturbances in the column can occur. A uniform change of the reflux rate is recommended.

For two-component separations a constant concentration dependent control can relatively simply be achieved with a DVP controller. The top composition is thereby held constant and the reflux is increased permanently according to the additional separation task. Alternatively, the reflux ratio can be controlled depending on the batch temperature or the temperature difference between top and bottoms. The start-up of a batch distillation is such that the initial contents of the batch are heated to boiling temperature and then the equilibrium in the column is set at total reflux. Subsequently, distillate take-off begins. Special problems

When dimensioning a batch distillate unit the ratio between batch volume and hold up of column and condenser is very important. If the still is underdesigned a reasonable separation or yield cannot be achieved. Therefore, it makes sense to choose a column with low hold up and a top condenser. If a still is too small only short distillation periods are allowed.

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