(183e) Towards the Practical Application of the Internally Heat-Integrated Distillation Columns (Hidic)

The imperatives of global warming and sustainable development demand efficient energy utilization in all aspects of life. The chemical processing industry, as an intensive energy consumer, is a major contributor to CO2 emissions. It accounts for 25% of the energy consumed by industries overall in Japan, while the distillation process accounts for up to 50% of the energy consumed by this industry. To abate its impacts and achieve the targets designated by the Kyoto Protocol, the development of energy-efficient distillation processes has a potentially very important role. So far, many modifications of distillation columns have been proposed and utilized in the chemical industries. Among such new developments of distillation processes, an internally Heat-Integrated Distillation Column (HIDiC) is one of the promising alternatives. In Figure 1, a conceptual configuration for the HIDiC has been created. The column's stripping and rectifying sections are separated, but connected through internal heat exchangers. To accomplish internal heat transfer from the rectifying section to the stripping section, the rectifying section is operated at sufficiently higher pressure than the stripping section to give higher temperatures throughout its length. To adjust the pressures, a compressor and a throttling valve are installed between the two sections. Owing to the heat integration, a proportion of the latent heat transported in the rectifying section is transferred to the stripping section, thereby generating both the reflux flow for the rectify ing section and the vapor flow for the stripping section. Thus the condenser and reboiler are, in principle, not needed; and operation at zero external reflux is theoretically possible. Developments of HIDiC The early concept of the HIDiC was proposed by Prof. Haselden with examples of gas separations in 1958. In the concept, the compressed feeds or products from a distillation column can be utilized as an energy source for the distillation columns and it leads to a reduction of the energy requirement of the process. The idea was reintroduced in 1970's as a Secondary Reflux and Vaporization (SRV) method by Prof. Mah et al. and the general configuration of the today's HIDiC was established. At that time, the Japanese government was paying a lot of efforts to overcome the two energy crisis in 1970's, since almost all energy resources have been imported from other countries. Therefore, there were large demands on the technology for energy savings from all industries in Japan. Since 1980's, researches on distillation columns with the SRV method have been carried out under the name of the HIDiC in Japan (Nakaiwa et al., 2003). They further analyzed and modified the original arrangement of the SRV method. From 1990's, a national project on the HIDiC in Japan was conducted. In the project, the structure, the performance, the dynamic response and the control strategy for the HIDiC were investigated by both experiments and simulations. With an example of benzene-toluene separation, an energy saving of 30 % in average was achieved by the prototype HIDiC. It was operated even without any condensers, i.e., at zero reflux condition for more than 100 hours. Since then, the commercialization of the HIDiC becomes the next big target. From 2002, the next phase of national project on the HIDiC, with Maruzen Petrochemical, Kimura Chemical Plants, Kansai Chemical Engineering, Taiyo Nissan, Kobelco, and AIST (project leader) has been started to industrialize the HIDiC as a key technology for the energy savings of chemical industries. In the project, there is a plan to separate the twelve-component hydrocarbons, which is one of the real mixtures in a chemical complex, by the pilot HIDiC (Figure 2). The reduction of CO2 emission by the HIDiC is estimated to be more than 50% compared with the conventional column, resulting from the pilot plant experiment. A cryogenic air separation by the HIDiC is another important subject of Japanese HIDiC project. It is in progress by Taiyo Nissan. A HIDiC project in the Netherlands has been also conducted in 2002 by Dr. Olujic et al. in the Delft University of Technology, and British Petroleum., DSM, Akzo-Novel, Shell, ABB Lummus and Sulzer also participated in the project. They have shown that the energy saving of 90 % will be achieved if the HIDiC is applied to the separation of propylene and propane (C3 splitter). They have also experimental setups for testing the hydraulics of the HIDiC. As well as the Japanese HIDiC project, the commercialization of the HIDiC is in sight.

References

Haselden, G. G., "An Approach to Minimum Power Consumption in Low Temperature Gas Separation," Trans. Inst. Chem. Eng., 36, 123-132 (1958) Mah, R. S. H., J. J. Nicholas, Jr., and R. B. Wodnik, "Distillation with Secondary Reflux and Vaporization: A Comparative Evaluation," AIChE J., 23, 651-658 (1977)

Nakaiwa, M., K. Huang, A. Endo, T. Ohmori, T. Akiya, and T. Takamatsu; "Internally Heat-Integrated Distillation Columns: A Review," Chem. Eng. Res. Des., 81, 162-177, (2003) Olujic, Z., F. Fakhri, A. de Rijke, J. de Graauw and P.J. Jansens, "Internal Heat Integration - The Key to An Energy-conserving Distillation Column," J. Chem. Tech. Biotechnol., 78, 241-248 (2003)