Organic Rankine cycles combined with thermochemical sorption heat transformers to enhance the power output from waste heat

Abstract A novel integrated power generation system is proposed in this work, which combines an organic Rankine cycle (ORC) with a thermochemical sorption heat transformer (TSHT), to improve power generation from low temperature heat sources. The TSHT lifts the temperature of the residual heat not captured by the ORC, and makes the upgraded heat available for evaporation of additional working fluid. Contextually, the ORC operates with an increased evaporation pressure and thermal efficiency compared to a standalone ORC using the same heat source. The overall effect is a net gain in power, because the degree of heat extraction is no longer limited by the improved thermal efficiency of the power cycle. The performance of the novel concept is explored for selected combinations of reactive salts in the TSHT and working fluids in the ORC, for utilization of waste heat in the range 100–230 °C. The results of the thermodynamic optimization show a 12–18% improvement in power output compared to the standalone ORC. The investment on the TSHT is recovered in less than ten years and generates an internal rate of return in the range 8.7–26.6%. This demonstrates the benefit of integrating thermochemical heat sinks/sources into low temperature power cycles.