Abstract

Reflux policies were calculated for a batch distillation process in which a fixed quantity and purity of a multicomponent product was required. The policies calculated, neglecting hold-up, were the constant reflux, constant overhead purity and minimum time methods of operation, the latter were similar and predicted that the constant reflux ratio time of 12·35 hr could be reduced by 3 hr using either of these variable reflux schemes. Experiments on a 30 theoretical stage industrial batch still processing a 10 component turpentine mixture showed that hold-up could not be ignored, even though this totalled less than 4 per cent of the initial still charge. A sub-optimal control scheme was therefore found which took hold-up into account. Using this policy the plant produced the required product in 10 hr 40 min compared with 12 hr 20 min using a constant reflux, a saving of 13·5 per cent. ln both cases the product was the same.

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