Cogeneration Improves Separation Efficiency

For\nmost distillation systems, the heat pump (HP) compressor, upgrading\nthe heat from the condenser’s lower temperature to the reboiler’s\nhigher temperature, uses electrical energy that is only a fraction\nof the reboiler heat, thereby making such processes highly efficient.\nHowever, the electricity utilized to power the HP compressor is typically\ndissipated as waste heat in cooling water. Here, we propose a novel\nstrategy termed “Separation Cogeneration” whereby most\nof the electrical energy supplied to the HP compressor is recovered\nas steam or process heat at or higher than the reboiler temperature.\nThrough simulations of several industrially relevant distillations,\nwe find that 79% to nearly 90% of the supplied compressor electrical\nenergy can be recovered as usable steam/process heat. This is a remarkably\nhigh first-law efficiency of the distillation cogeneration system\nand is likely to make it the most efficient among the alternative\nprocesses for separations, where distillation can be used. Furthermore,\nthe availability of alternative HP schemes leeway in the choice of\napproach temperature across the reboiler heat exchanger and the distillation\ncolumn pressure along with the potential use of multieffect distillation\nprovide a great deal of flexibility in adjusting the temperature at\nwhich steam/process heat could be recovered. Through several industrially\nrelevant case studies, we demonstrate that for a given separation\nand generation of the associated steam, the separation cogeneration\nrequires nearly 40% less electricity when compared to the two-step\nprocess using conventional HP distillation and steam generation using\nelectricity. The separation cogeneration strategy holds promise to\nfurther the decarbonization goal of the industrial sector, facilitating\nthe efficient utilization of electricity and reducing greenhouse gas\nemissions.