A heat-driven distillation (HDD) system, in which each rectifying stage is divided into an evaporator and a condenser, was proposed for improving both the separation performance and the energy-saving effect. In this system, the mass transfer can be controlled by the internal flows of vapor and liquid, which are generated by the supply of heat to the evaporator and the release of heat from the condenser, respectively. Binary distillation of methanol and ethanol by a HDD system with 12 sets of evaporators and condensers was computed. The separation performance was improved by increasing the internal flow rates. When the internal flow rates were increased 5 times (from 1 to 5 mol/s), the overall separation factor of methanol at the appropriate recycle ratio was increased similar to 22 times. Then, the energy consumption was also increased in proportion to the increase in the internal flow rates; however, it was reduced drastically by introducing the internal heat-exchange processes, in which heat generated by the isentropic compression of the vapor phase in the condensers is utilized for the vaporization of liquid in the evaporators. The pressures of the condensers were adjusted under the condition that total exergy loss was minimized. Then, the heat supplied to the evaporators was close to zero. The energy consumption is only the compression work of the condensers and is evaluated as similar to 10% of the heat supplied to the reboiler of a conventional distillation system with the same separation factor, under the conditions that the internal flow rates and the heat transfer area of internal heat exchangers are 2 mol/s and 5 m(2), respectively. A large energy-saving effect is expected for the HDD system.