Basic design of a double-pipe unit type internally heat integrated distillation column (HIDiC)

Distillation is not only the most energy consumer but also the most frequently-adopted separation operation in chemical industries since it separates a mixture only by the difference among vapor pressures (boiling points) of components. So distillation is often called as the king of separation processes. Therefore, research and development of technologies on energy savings of distillation is an extremely important and eternal mission for chemical engineers. In 1978, Secondary Reflux Vaporization (SRV) system, that is an ingenious technology of energy saving for the distillation, was proposed by Dr. Mar in USA. In the SRV system, the rectifying section is pressurized to elevate its temperature level to be higher than that for the stripping section, and these two sections are contacted with each other like a heat exchanger. This structure makes the rectifying section a heat source or a side heater for the stripping section. If the temperature difference and the contact between these two sections are appropriate, a great energy saving can be expected by the SRV system. However, this system has not been put into practical use at that time and R&D had not been continued. In the nearly time in Japan, Heat Integrated Distillation Column (HIDiC), that is almost equivalent to the SRV system, has been investigated by numerical simulations. A lot of papers for the HIDiC have been reported by Prof. Takamatsu and Dr. Nakaiwa et al. until now. In these papers, some possibilities of operation of HIDiC without a reboiler and a condenser, that is called an ideal HIDiC operation, are shown to obtain the best energy saving from thermodynamic point of view. After long R&D period, a pilot plant of the HIDiC was built and operated at last in 2005 . Since the feed flow rate of the HIDiC pilot plant is about 2000 kg/h, it is rather a commercial scale column. The consecutive operation of the pilot HIDiC for 1000 hours has already been achieved. The energy consumption of the pilot HIDiC has been saved at less than 40% of a conventional distillation column with the same scale. In this paper, the structure and the detail of the pilot HIDiC are shown, and its basic design strategy is explained.