Parametric study of an ethanol–water distillation column with direct vapour recompression heat pump

Heat pumps have been used to reduce energy consumption in distillation columns. However, the effects of some parameters have not been taken into consideration in the determination of energy consumption in such systems. Perhaps this is one of the reasons for little or no application of the system in ethanol which is fast becoming a competitive fuel to petrol. The study reported here considers the effect of pressure increase across the compressor, column heat loss and the overall heat transfer coefficient of reboiler–condenser as an explicit function of Prandtl, Reynolds and Nusselt numbers. This was to study the overall influence of these parameters on energy consumption and energy effectiveness (coefficient of performance). An ethanol–water conventional distillation column with direct vapour recompression was used as a case study. Results showed that when these parameters were included in the model equation, there was an increase in compressor power input and total energy consumption while the energy effectiveness reduced. Also, the comparison of the two systems showed that while the values of the column heat loss, reboiler heat transfer rate, total energy consumption and overall heat transfer coefficient were greater for the actual (VRCΔP) system, the coefficient of performance and the heat pump distribution factor were more for the control (VRC) system. The significance of this work is the provision of information for the determination of energy effectiveness as well as appropriate capacity of the auxiliary equipment.