抄録
A heat-driven distillation process combined with evaporators and condensers was proposed for the improvement of separation performance and the reduction of energy consumption. In this process, a rectifying stage is divided into an evaporator and a condenser and the mass transfer between these phase converters can be controlled by the recycle flow rates, RCj and REj, which are adjusted by the supply of heat to the evaporator and the release of heat from the condenser. Binary distillation of methanol and water was computed for a 12-stage heat-driven distillation system. The increase in the recycle flow rates was very effective for improving the separation performance. When the recycle flow rates were increased from 1 to 5 mol/s, the separation factor of methanol was increased to about 230 times, however, the energy consumption was also increased to about 5 times, because of the increase in the supply of heat to the evaporators. Such energy consumption was reduced drastically by the introduction of internal heat-exchange process between the evaporator and the condenser, in which the heat generated by the isentropic compression of vapor phase in the condenser was utilized to the vaporization of liquid in the evaporator. The pressure of each condenser was adjusted appropriately under the condition that total exergy loss was minimized. Then, the sum of external heat provided to the evaporators was reduced to zero and the sum of works required for the compression of vapor flows to the condensers was evaluated as less than 4% of energy consumption of conventional distillation system with the same separation performance. These results suggest that the heat-driven distillation system introducing the internal heat-exchange is valuable as a new energy-saving technology.
