Discontinuous Stills

The minimum possible volume of condensate and amount of heat required during the progress of distillation. - Table 105 shows that to produce 1 kilo of alcohol containing 94.61 per cent (by weight), more condensate must be produced and more heat supplied to the still the lower the alcoholic strength of the liquid to be distilled. But the amount of heat required does not steadily decrease as the alcoholic strength of the liquid to be distilled is increased. A minimum is reached when the alcoholic strength of the liquid to be distilled is about 26 per cent by weight. Above this strength the amount of heat required gradually rises again.

Supposing that the still be charged with alcohol of 90 per cent strength the amount of condensate and heat required per kilo of finished product will gradually fall until the alcoholic strength of the liquid left in the still has reached about 26 per cent by weight. After this point a steady rise takes place until towards the end of the distillation the amounts of condensate and heat required are very great. The condenser must, of course, be capable of providing the maximum amount of condensate required if an even output of finished product is required throughout the distillation. In the same conditions the source of heat must be capable of supplying the maximum heat requirements.

Number Of Plates Required In The Rectifying Column

As already stated, this depends on the strength of the liquid to be distilled, and on the strength of the finished product and the amount of heat abstracted by the condenser. Tables 106 and 107 give the theoretical optimum results obtained under various working conditions.

Continuous Stills

The Wash Column. - In this type of still the liquid to be distilled is supplied continuously at a steady rate to a wash column, the construction of which is similar to that of the rectifying column (see Figs. 104,121, 125,127). The wash flows on to the top plate of the column, and thence downward to the outlet, and leaves the column almost completely freed from alcohol. Live steam is the source of heat. It is supplied at the base of the column and causes the liquid on each plate to boil. The function of the wash column is to free the wash from alcohol as completely as possible. The heat required to do this increases as the alcoholic strength of the wash to be distilled increases (Table 108).

Table 105

Theoretical minimum amount of heat (in great calories) to be abstracted in the condenser from vapour entering it from a rectifying column, in order to produce 1 kilo of alcohol 94.61 per cent by weight, or 85.76 per cent by weight, from liquid in the still, the alcoholic strength of which varies from 0.052 per cent to 92.79 per cent by weight. The liquids treated are assumed to be already at their boiling points.