A model for drobbles in drobble columns, based on the concept of phase space and the population balance equation, is presented. This model allows a consideration of the growth, breakage and coalescence of two-phase drobbles. The splitting step method is employed in the numerical calculation while the Monte Carlo method is used for handling the breakage and coalescence of drobbles. The vaporization height is a very important parameter in the engineering design of drobble columns with a vaporizing dispersed phase. Obviously this height has statistical characteristics. The model has been used for the simulation of vaporization height in this kind of system. The simulation results are in good agreement with experimental data not only qualitatively but also quantitatively. Detailed information about the variation of distribution density functions with column height is given both without and with consideration of the breakage and coalescence of drobbles.