Energy and exergy analyses of a novel power cycle using the cold of LNG (liquefied natural gas) and low-temperature solar energy

• A solar collector and liquefied natural gas cold energy are used effectively.
• A novel oxy-fuel power generation cycle is successfully simulated and analyzed.
• Exergy efficiency expressions are developed for the hybrid system components.

A new cogeneration system which uses CO2 (carbon dioxide) as a working fluid is proposed and analyzed. The system has high efficiency and no CO2 and other emissions. Thermal energy from a low temperature solar energy collector and the cold of LNG (liquefied natural gas) can be effectively utilized together. The system consists of a subcritical Rankine-like cycle, a solar collector and LNG vaporizing subsystems. By utilizing the LNG vaporization subsystem as the cycle cold sink, the cycle condensation process can be achieved at a temperature much lower than the ambient. Also, high-pressure liquid CO2 ready for disposal can be withdrawn from the cycle without consuming additional power. The effects of several key thermodynamic parameters on the system performance are examined based on various performance criteria. The results show that the performance of the system can be improved by adjusting the turbine inlet temperature, the LNG flow rate and the main heat characteristics of the solar energy system. Also, with a regenerator added to the cycle, a performance improvement is obtained that permits a reduction in the solar collector area. The energy and exergy efficiencies of the overall system are determined to be 60.1% and 61.3%, respectively.