Theoretical study on the effect of axial liquid backmixing on distillation in a packed column

Based on proper assumptions, an approximate but sufficiently accurate formula for evaluating HETP (the height equivalent to a theoretical plate) involving liquid axial backmixing effect is presented. A new dimensionless number, designated as backmixing characteristic number, is introduced. The effective effect of liquid backmixing on separation efficiency of a distillation column is pronounced with increasing the axial liquid backmixing coefficient and with decreasing the overall HTU (height of a transfer unit) for vapor phase and the liquid effective velocity. The incremental factor of HETP is determined only by backmixing characteristic number and vapor-liquid equilibrium constant. The computing formula and graph for the incremental factor of HETP are given.