Thermodynamic analysis on the combination of supercritical carbon dioxide power cycle and transcritical carbon dioxide refrigeration cycle for the waste heat recovery of shipboard

With excellent physical properties, carbon dioxide has been widely employed as a working fluid in efficient energy conversion technologies, which are represented by supercritical carbon dioxide Brayton cycle and transcritical carbon dioxide refrigeration cycle. In this contribution, with the aim to recover the waste heat of shipboard, a combined system coupling carbon dioxide Brayton cycle and refrigeration cycle is proposed to simultaneously produce power and cooling. In order to alleviate the temperature mismatch in recuperator and effectively utilize the discharged heat of refrigeration cycle, low temperature recuperator and gas cooler are shared by power and cooling cycles. For this novel waste heat recovery system, thermodynamic and economic models are developed to conduct energy, exergy and economic analysis. Thereafter, key cycle parameters including gas cooler pressure, evaporation temperature and turbine inlet temperature are investigated to reveal the effects on the system performances. The obtained results indicate that the energy and exergy efficiencies of the proposed system are respectively 42.42% and 39.05% under design conditions. The corresponding average energy cost is 9.28 $/GJ. At lower evaporation temperature and higher gas cooler pressure, the advantages of low temperature recuperator can be fully utilized and more work is produced. However, lower cooling capacity is obtained. Furthermore, the turbine inlet temperature has no effects on refrigeration cycle, and the net work decreases with the increase of inlet temperature. These results will be beneficial to improve the design and performance of combined power and cooling system for future shipboard applications.