Balancing Diameters of Distillation Column with Vapor Feeds

Methods for balancing distillation vapor loads to achieve smaller, more-uniform diameters are developed for vapor feeds and the largest calculated diameter in the enriching section. The diameter can be reduced by (i) cooling the entire feed, (ii) cooling or condensing part of the feed while leaving the other part vapor (two-enthalpy feed), or (iii) condensing vapor inside the column with an intermediate condenser. For distillation of a saturated vapor feed of 10 mol % ethanol and 90 mol % water, the use of a two-enthalpy feed resulted in a 58% reduction in column volume with the same purity and no increase in energy use . Examples are also shown for methanol−water and n -butane−propane distillations.