Double-section absorption heat pump for the deep recovery of low-grade waste heat

Abstract

Absorption heat pump is an effective option for industrial waste heat recovery. However, significant conflict between low evaporation temperature and high efficiency exists in conventional absorption heat pump, which limits its application in deep recovery of low-grade waste heat recovery. To address this issue, this paper presents the use of double-section absorption heat pump for low-grade waste heat recovery. Both theoretical and experimental researches are carried out to analyze the features of double-section LiBr-water absorption heat pump. Driven by hot water with temperature of 120.1 °C, the experimental prototype was able to extract thermal energy from the waste hot water by reducing its temperature from 45.0 °C to 15.9 °C, realizing a large temperature decrease of 29.1 °C for waste hot water. Meanwhile, the experimental prototype could heat water up to 52.5 °C for domestic heating application with capacity of 8666.4 kW and high coefficient of performance of 1.77. The excellent performance is attributed to the stepped generation/evaporation processes with gradient temperatures, which makes the double-section absorption heat pump achieve both higher efficiency for internal circulation and reduced irreversible loss for external circulation comparing with the conventional single-section absorption heat pump. This makes the double-section absorption heat pump an efficient way to realize the deep recovery of low-grade waste heat.