A modified equilibrium stage model for simulating and designing packed distillation columns has been developed. The new model incorporates mass transfer efficiency and convective heat transfer along the packed bed. This results in a set of simultaneous (MESHEC) equations to replace the classic MESH equations. By solving the MESHEC equations, detailed temperature, flowrate and composition profiles in the column can be determined. Furthermore, the new model is based on the well established methods of calculation for the equilibrium stage and mass transfer efficiency. Thus, it is more practical and efficient than the nonequilibrium model, which requires the precise input of mass transfer coefficients. The model presented in this paper can also be extended to simulate the plate columns and even absorption and extraction operations.