<p>Consideration has been given to the problem of calculation of the processes of heat transfer in a binary-distillation column (of the entropy production and heat-transfer coefficients for each of the four heat exchangers). The dependence of the column′s capacity on the expenditure of heat with account of the heat-transfer processes has been obtained for the case where the composition of product flows is fixed and the processes are irreversible. Reversible estimates of the expenditure of heat have been obtained for an arbitrary system of rectification columns during the separation of a multicomponent mixture. These estimates require a knowledge of only the composition of the flows entering the system of columns and going out of it and of the maximum temperature in the boiler and the minimum one in the dephlegmator for columns making up the system in question.</p>