Steam Generating High Temperature Heat Pumps: Best Practices, Optimization Strategies and Refrigerant Selection for Performance Improvement

The present paper provides a general overview of the state of the art of steam generating heat pumps (SGHPs) technology employed in the industrial field. Recommended best practices and optimization procedures for overall performance improvement of compression closed-loop-based systems are described in detail, as well as the main modifications of the thermodynamic heat pump cycle. Once the main configurations of SGHPs are described, the different concepts are compared in terms of supply temperature ranges; cases of comparison among different concepts are reviewed, and techno-economic barriers are also discussed. The working fluids (including natural refrigerants) commonly selected for these steam generating systems are presented along with their uses. Moreover, zeotropic refrigerant mixtures and new potentially usable mixtures are mentioned. After that, refrigerant selection criteria for high temperature heat pumps are also discussed. Then, using an internal heat exchanger, refrigerant injection technique and super heating in lubricated compressors are herein presented as best practices for general performance improvement. Regarding thermodynamic cycle modifications, basic auto-cascade and quasi-two-stage compression cycles are discussed along with further improvements suggested in the specialized literature. Lastly, optimization strategies useful to enhance the heat pumps’ design and based on TOPSIS method, advanced exergy analysis, exergy-based cost minimization and combined design are analyzed.