Energy Performance Comparison between Power and Absorption Refrigeration Cycles for Low Grade Waste Heat Recovery

Power cycles converting waste heat to electricity and absorption refrigeration cycles converting waste heat to cooling are widely used for low grade waste heat recovery in the process industry. It is significant to choose an appropriate cycle to recover waste heat at different temperatures. In this paper, a comparison is performed between a Kalina cycle and a LiBr-H2O absorption refrigeration cycle considering low-temperature waste heat sources at different temperatures, and the optimal conditions of these two waste heat utilization technologies are determined. Because power and cooling are different kinds of energy with different energy levels, a novel indicator, the amount of mechanical work, is used to evaluate the cycles to reasonably compare the energy performance of the cycles. The cooling generated by an absorption refrigeration cycle is converted into mechanical work required by a compression refrigeration cycle under the same cooling output. Results show that when the waste heat source temperature is from 100 to 175 degrees C, it is proper to choose a LiBr-H2O absorption refrigeration cycle; when temperature range is 175 to 200 degrees C, the Kalina cycle is preferable.