Superheated steam generation with open hybrid absorption-compression heat pump cycle

Energy used for steam generation accounts for a large share of industrial energy consumption. Combining steam generation with heat pump is an energy-saving approach, but this combination suffers from excessive output temperature and reduced COP in producing superheated steam. This study proposes an open hybrid absorption-compression heat pump (OHACHP) cycle to achieve efficient superheated steam generation with low-grade ambient heat source. The proposed cycle coupled the open vapor compression with closed cascaded absorption-compression heat pump cycle. Cascaded heat pump cycle extracts low-grade heat from the environment and improve the heat grade. Feed water is heated and vaporized through multi-stage heating by condensation heat and absorption heat, and then further compressed into high pressure superheated steam. Aiming at generating superheated steam of 200 kPa utilizing ambient heat of 30 °C, an optimized COPall of 1.84 can be achieved, with coupling temperature between absorption and compression heat pump sub-cycle of 67 °C, feed water flow rate of 100 kg/h and output temperature of 179 °C. The corresponding relationship between superheat and efficiency with the impact of operational parameters is investigated. Comparing with existing closed hybrid absorption-compression heat pump system, the OHACHP cycle demonstrates its capability to operate at minimum ambient temperature of 10 °C and maximum temperature lift of 170 °C. The different steam generation pathway makes the OHCHP cycle advantageous in high superheated steam production.