A STUDY OF A HEAT-PUMP DISTILLATION COLUMN SYSTEM

The thermodynamic efficiency of a distillation column is usually quite low while at the same time the energy consumption is high. This is due to the fact that the separating agent in the distillation process depends directly on the amount of energy used and the recovery of this energy is often low. A brief survey has been carried out of the possibilities of improving the energy conservation quotient and increasing the thermodynamic efficiency for a single distillation column system utilizing various heat pump arrangements, paying attention to the various aspects of both open and closed types of systems. The use of more elaborate systems involving intermediate heat exchangers is, theoretically, necessary in order to achieve a higher thermodynamic efficiency; in practice, however, these systems do not always turn out to be economically viable when compared with simpler arrangements. Computer simulations of different heat pump configurations and distillation columns were performed and it was found that it is possible to attain a substantial decrease in energy consumption. It is also noted that the thermodynamic efficiency of the system can be increased by installing a heat pump using a binary non-azeotropic mixture to the distillation column. However, the exact amount of this increase depends, to a certain extent, on the way thermodynamic efficiency is defined. Owing to the lack of measured physical data in the literature for such mixtures, comparisons have also been made between experimentally determined equilibrium data for non-azeotropic mixtures of halogenated hydrocarbons and theoretically calculated data based on the Lee-Kesler-Plocker equation of state. These comparisons show that the equation of state used in the simulations is suitable for calculations of enthalpy and equilibrium data but there is a large deviation in liquid volume calculations.