Automatic batchwise fractionation of feeds comprising a mixt. of substances (esp. crude oil) is carried out in one or more sequences, each sequence being effected at a constant pressure =atmospheric pressure. Each sequence comprises (a) progressively vaporising the feed mixt by heating it in a vessel connected to a distn. column, (b) intermittently withdrawing distillate from the top of the column, (c) separating the distillate into fractions, (d) condensing the fractions and collecting them in a receiver, (e) opt. measuring the wt. or vol. of the fractions collected, and (e) opt. using the measured values to calculate the material balance of the distn. The improvement comprises adjusting the heat supply so as to maintain a constant pressure drop (DELTA P) between the bottom and top of the column during a given sequence. Since the rate of liq. withdrawal remains constant at constant DELTA P, continual adjustments by the operator to maintain the required distillate withdrawal rate are not necessary; distn. times can be reduced by =50%.
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