Cogeneration Improves Separation Efficiency

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