Separation of fluid mixtures in multiple distillation columns

摘要

The method for the separation of a fluid mixture contg. at least one more volatile component and at least one less volatile component which comprises introducing the fluid mixture at a first pressure as a first feed stream into a first distillation column having at least one sepn. stage above the feed point and withdrawing a first overhead vapour and a first bottoms liquid. The first bottoms liquid is flashed to a second pressure, and is then fed to a second distillation column. A second overhead vapour enriched in the more volatile component and a second bottoms liquid enriched in the less volatile component are withdrawn. At least a portion of the first overhead vapor is condensed and at least a portion of the resulting first condensate is returned to the first column as reflux. The cooling duty for condensing the first overhead vapour is provided by indirect heat exchange with either (1) fluid at an intermediate point in the second column or (2) at least a portion of the resulting flashed first bottoms stream prior to the second distillation column. Either the temp. at the bottom of the first column is equal to the temp. at the bottom of the second column and the temp. at any other point in the first column is between the highest and lowest temps. in the second column or the temp. at any point in the first column is between the highest and lowest temps. in the second column. The combined molar flow rate of the two overhead vapours is more than 50% of the molar flow rate of the first feed stream.