Life cycle techno-enviro-economic assessment of dual-temperature evaporation transcritical CO2 high-temperature heat pump systems for industrial waste heat recovery

Replacing fuel-fired boilers by using efficient heat pump plants to recover industrial waste heat is an effective solution to achieve the dual carbon target. Three novel transcritical CO2 high-temperature heat pump systems (Ej-Evap2-A, Ej-Evap2-B, and Ej-Evap2-C) are proposed in this study, by introducing the technique of dual -temperature evaporation realized with an ejector for cascade heat absorption from the heat source. Consid-ering the application in the scenario of industry requirement of hot water heating, the life cycle performances of the new proposed heat pump systems and fuel-fired boilers are comprehensively studied from the perspectives of energetic, emissions, and economic. A sensitivity analysis about the new configuration heat pump system is also conducted considering the variation in electricity and coal price. The results demonstrate there exists an opti-mum discharge pressure that maximizes the coefficient of performance (COP). Ej-Evap2-C shows a maximum COP of 4.85, which is 14.40% higher than the baseline CO2 heat pump system (Base), and the exergy efficiency of Ej-Evap2-C is 7.86-15.19% higher than that of Base. Among the eight heating methods including coal-fired boilers (CFB), gas-fired boilers (GFB), electric heating boiler (EHB) and five kinds of CO2 heat pump systems, Ej-Evap2-C shows the least pollutant emissions and life cycle cost. Furthermore, Ej-Evap2-C has the shortest payback period of fewer than 7 years compared with the CFB. The dual-temperature evaporation CO2 high -temperature heat pump is promising to substitute traditional fuel-fired boilers to generate high-temperature fluid in the future.

Automated summary

This study proposes three novel transcritical CO2 high-temperature heat pump systems that achieve cascade heat absorption from the heat source through the technique of dual-temperature evaporation with an ejector. The life cycle performances of the new heat pump systems and fuel-fired boilers are comprehensively studied considering energetic, emissions, and economic perspectives. Results show that Ej-Evap2-C has the highest coefficient of performance (COP) and exergy efficiency, and the least pollutant emissions and life cycle cost among different heating methods. The dual-temperature evaporation CO2 high-temperature heat pump is a promising alternative to traditional fuel-fired boilers for generating high-temperature fluid in the future.