An innovative hybrid structure of solar PV-driven air separation unit, molten carbonate fuel cell, and absorption–compression refrigeration system (Process development and exergy analysis)

Abstract

The regasification of liquefied natural gas provides considerable cold energy that would have practical potential in different industrial fields and makes a suitable option for integrating with cryogenic air separation systems that requires a significant amount of energy. In this research, two-column cryogenic air separation units are driven with solar photovoltaic panels to produce oxygen and nitrogen. The gaseous natural gas feeds a molten carbonate fuel cell (MCFC), producing electricity and heat. The heat is recovered by an absorption–compression refrigeration cycle (ACRC) to supply a high-intensity cooling load at −67 °C. The proposed scheme is designed to provide 1781 kmol/h oxygen, 8574 kmol/h nitrogen, 136 MW electrical power, and 13.09 MW cooling load. The thermal efficiency of the whole combined structure and the electrical efficiency of the fuel cell are 51.07% and 51.93%, respectively. The exergy analysis illustrates that the solar photovoltaic collectors and heat exchanges are the two most exergy destructive components compared to others. The exergy efficiency and irreversibility of the developed hybrid process are 52.77% and 160.5 MW, respectively. The effect of working temperatures has been studied on the performance of the molten carbonate fuel cell, including voltage, power density, and efficiency. The exergy and thermal efficiencies of the proposed system increase up to 56.18% and 55.05%, respectively with an increase of LNG molar flow rate from 892 to 992 kmol/h.

Keywords

• Photovoltaic panel
• Air separation unit
• Molten carbonate fuel cells
• Refrigeration system
• Exergy analysis
• Thermal integration