Theoretical Analysis of Transcritical HTHP Cycles with Low GWP HFO Refrigerants and Hydrocarbons for Process Heat up to 200 ℃

摘要

Transcritical heat pump cycles are suitable for processes that require large temperature glides on the heat sink,such as air or hot water heating. Refrigeration systems or hot water heat pumps often apply transcritical CO_2cycles. For industrial waste heat recovery with high temperature heat sources, transcritical CO_2 heat pumpsare not suitable. This study investigates the feasibility of low GWP HFO refrigerants and hydrocarbons for thedelivery of process heat up to 200 ℃ using transcritical HTHP cycles. Steady-state models with IHX andparallel compression have been developed to analyse the cycle performance for heating air from 30 to 200 ℃and water from 100 to 200 ℃. The design aspects of the main cycle components are discussed, especiallycompressor and refrigerant-oil selection. The analysis shows that the gas cooler pressure is the most importantoptimization parameter to achieve highest efficiency up to 3.5. The transcritical cycle with IHX is easy tocontrol and is technically feasible with one or two compression stages. R1233zd(E), R1224yd(Z) and R600are considered the best refrigerant candidates.