Energetic and Exergetic Performance Evaluation of a Gas Turbine–Powered Cogeneration System Using Reverse Brayton Refrigeration Cycle for Inlet Air Cooling

Abstract

A conceptual gas turbine–powered cogeneration system is proposed where a reverse Brayton refrigeration cycle is employed for compressor inlet air cooling that can reduce the inlet air temperature close to 0° C or lower, which cannot be achieved through evaporative and absorption inlet cooling techniques, respectively. The conservation of energy (first law of thermodynamics) and the quality of energy (second law of thermodynamics) are both investigated for the system under various operating conditions. The results indicated that both energetic and exergetic efficiencies of the cogeneration cycle are considerably varied with the change in the extraction pressure ratio, extracted mass rate, turbine inlet temperature, and process heat pressure, and least affected by the ambient relative humidity. Exergy analysis of the proposed cogeneration shows that maximum exergy is destroyed during the combustion and steam generation process, which represents more than 87% of the total exergy destruction in the overall cogeneration cycle. Comparison of the cogeneration and noncogeneration cycle shows that the first-law and second-law efficiencies of the cogeneration cycle are 64 and 40% higher than the efficiencies of the noncogeneration cycle for a given extraction pressure ratio. Further, it is shown that the gas-turbine cycle coupled with the reverse Brayton refrigeration cycle for inlet air cooling provides higher energy efficiency than the gas turbines coupled with other commonly used inlet air-cooling systems. The results provide information about the research and development priorities in the future for gas-turbine performance enhancement.