Abstract: Despite its obvious advantage of energy conservation, thermally coupled distillation has not been widely used in industry since 1960s. The reason for its limited application and its future prospect are investigated by simulation study of the operational performances. For systems to be separated with different degrees of "Separation Difficulty Ns", the operational performances of thermally coupled distillation towers are quite different. Only the operational performances of those thermally coupled distillation towers with a lower degree of separation difficulty are acceptable for industrial use. The multiple solutions for Petlyuk columns are also discussed. The confi-gurations and operational performances of possible solutions are quite different Only the one with optimal performance should be chosen as the design basis.