The principle of hybridizing a solid/gas thermochemical refrigeration cycle with a power cycle is extended to two novel hybrid cycles (called operating modes). They can be driven by low-grade heat, and they allow storing this energy and converting it predominantly into mechanical power. For this purpose, they integrate an original autothermal power production during their discharging step, which is deeply analyzed. In addition, depending on the operating mode, power can be produced in both charging and discharging steps and an additional cold production can be provided. A deep thermodynamic study was carried out to assess the performance of these cycles, for 103 solid/gas pairs. These cycles allow converting low-grade heat sources from 87 °C to 250 °C. The maximal energy and exergy efficiencies for power and cold cogeneration are 0.24 and 0.40, respectively, and the maximal exergy density is 722 kJ/kgNH3. The part of power production reaches 62% (when it occurs only in discharging step) to 78% (when it occurs in both steps).
This paper investigates several new hybrid cycles combining a solid/gas sorption refrigeration cycle with a Rankine cycle, and targeting three key functions: they are able to recover low-grade heat (for instance industrial waste heat), to store this energy, and to convert it into cold and/or power. Five operating modes have been designed, for either prevailing cold production or power generation. A thermodynamic analysis was performed to evaluate their energy and exergy performances, for a wide variety of reactive salts in the thermochemical system. Depending on the different modes and reactants, these hybrid thermochemical cycles can operate at temperatures as low as 87 °C. The share of power in total energy production lies between 0 and 30% for prevailing cold production modes, and between 50 and 100% for prevailing power generation modes. The energy and exergy efficiency reach 0.61 and 0.41, respectively. The energy storage density reaches about 170 kWh per m 3 of storage system. In some cases, additional power generation occurs during the charging step. Alternative systems performing the same functions and based on commercial systems have been designed and compared with hybrid thermochemical cycles. This comparison highlights that the energy storage density is lower for hybrid cycles. However, the global energy efficiency can be higher for hybrids, especially for prevailing cold production modes where it can be 34 % higher than for the alternative commercial system.
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