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Solution

The reflux of tower top is used to control the top temperature there by controls the purity of the overhead product. The amount of reflux compared to the product is known asa reflux ratio.

The major benefits and drwabacks to increasing the reflux ratio are :

When reflux ratio is increased, the amount of reflux increases. Reflux represents cooled, condensed top product returned to the tower top and, as such it is being reprocessed. The top product will therefore be purer. In general, the higher the reflux ratio, the fewer the number of trays required for a given separation.

However, too high a ratio may cause flooding in the tower resulting in poor separation and causing \'off-spec\' products throughout the system. The reflux rate is normally controlled by a temperature controller in the vapour outlet which operates a control valve in the reflux pump discharge. An increase in tower top temperature will cause the valve to open, increasing the reflux rate.