Combined First and Second-Law Analysis of Gas Turbine Cogeneration System With Inlet Air Cooling and Evaporative Aftercooling of the Compressor Discharge

Abstract

A conceptual gas turbine based cogeneration cycle with compressor inlet air cooling and evaporative aftercooling of the compressor discharge is proposed to increase the cycle performance significantly and render it practically insensitive to seasonal temperature fluctuations. Combined first and second-law approach is applied for a cogeneration system having intercooled reheat regeneration in a gas turbine as well as inlet air cooling and evaporative aftercooling of the compressor discharge. Computational analysis is performed to investigate the effects of the overall pressure ratio rp, turbine inlet temperature (TIT), and ambient relative humidity φ on the exergy destruction in each component, first-law efficiency, power-to-heat ratio, and second-law efficiency of the cycle. Thermodynamic analysis indicates that exergy destruction in various components of the cogeneration cycle is significantly affected by overall pressure ratio and turbine inlet temperature, and not at all affected by the ambient relative humidity. It also indicates that the maximum exergy is destroyed during the combustion process, which represents over 60% of the total exergy destruction in the overall system. The first-law efficiency, power-to-heat ratio, and second-law efficiency of the cycle significantly vary with the change in the overall pressure ratio and turbine inlet temperature, but the change in relative humidity shows small variations in these parameters. Results clearly show that performance evaluation based on first-law analysis alone is not adequate, and hence, more meaningful evaluation must include second-law analysis. Decision makers should find the methodology contained in this paper useful in the comparison and selection of advanced combined heat and power systems.