Rigorous investigation of heat pump assisted distillation

Abstract

In this work a propylene-propane splitter assisted by a heat pump of the vapour recompression type is investigated by rigorous methods. Two schemes, a single compressor scheme and a double compressor scheme in parallel arrangement, are scrutinised and compared to the conventional stand alone column. The investigation includes parametric study, operability assessment and an estimation of the role of heat pump in minimising flue gas emissions. The parametric study of the influences of the column top pressure and the pressure lift of the heat pump on the economics shows, for both schemes at the optimal conditions, practically the same annual total cost, which is about 37% cheaper than the conventional stand alone column.

The operability of the system is investigated by degrees of freedom analysis and steady state controllability parameters. The operability considerations show that in the case of the double compressor scheme, the column pressure can be independent of the threshold temperature of the condenser. Thus the column pressure can be determined to satisfy the optimum separation parameters. Due to this operability reason, the double compressor scheme is preferred to the single compressor scheme. The heat pump share in reducing flue gas emissions is estimated. It is found that about 60% of the flue gas emissions can be minimised when using a heat pump.