Energy and exergy analysis of an absorption power cycle

The thermal efficiency of a power cycle is drastically reduced when the temperatures of the heating and cooling fluids approach, which is the case of cycles run by waste heat streams and low temperature solar or geothermal systems. In this work, an absorption LiBr–H2O power cycle is analysed and compared to a conventional Rankine cycle operating between two heat sources at similar temperatures. The absorption power cycle is found to improve the thermal efficiency, and this improvement in efficiency is higher for lower temperature differences between the heating and the cooling external fluids. The relative efficiency improvement of the absorption cycle is as high as 40% operating with a similar turbine to that of the conventional Rankine cycle. The exergy destruction of both the absorption and the conventional cycle was also analysed. In a conventional Rankine cycle, the constant temperature at which phase change occurs leads to higher temperature differences between the operating fluid and the heating and cooling external fluids, producing high exergy destruction. The absorption cycle permits a better temperature match, reducing the exergy destruction. Therefore, the exergetic efficiency of the absorption power cycle is around 10% higher than that of the conventional Rankine cycle. •A LiBr–water absorption power cycle is proposed.•The absorption cycle can operate with low heating and cooling temperature difference.•The absorption cycle permits a better match of temperatures in the heat exchangers.•The LiBr–H2O cycle has better thermal and exergetic efficiencies than a Rankine cycle.