Performance comparison of different heat pumps in low-temperature waste heat recovery

Abstract

The recovery of low-temperature waste heat can greatly reduce the fossil energy consumption, among whose technologies heat pumps show excellent energy saving effect and environmental friendliness. There are four commercial types of heat pumps, the absorption heat pump (AHP), absorption heat transformer (AHT), steam jet pump (SJP) and mechanical heat pump (MHP). To compare the energy performance of the four types of heat pumps in low-temperature waste heat recovery (WHR), simulation models for these heat pumps are established by Aspen Plus. The heat demand of the user side is described by a heat ratio (the ratio of the user side heat demand to the waste heat). The energy performance of four kinds of heat pumps in low-temperature WHR is compared and analyzed by the coefficient of performance (COP), exergy efficiency and annual savings of standard coal. The results show that when the heat ratio is higher than about 0.5, the MHP has the best energy performance. When the heat ratio is lower than about 0.5, the AHT is the best, for it can not only meet the heat demand of the user side, but make full use of the waste heat source as well. The performance of SJP is always better than that of AHP. Combined with qualitative economic analysis, it is recommended that the SJP is a good choice when HR is higher than about 0.7, otherwise the AHT is a suitable choice. This study can provide references for choosing a suitable heat pump in the low-temperature WHR.