A general exergy balance equation that is applicable to any component of thermal systems has been formulated in this study. One of distinct features of this formulation is that the exergy involved in the component of any thermal system can be decomposed into exergy flows, entropy production flows, and the appropriate exergy rate terms such as fuel and available work. The exergy analysis based on this equation permits one to predict the thermal efficiency of the system, the exergy destruction in each component as well as the mass flow rate, the composition, and the temperature of the exhaust gases. We have examined the performance of a 1000 kW gas turbine cogeneration system when it is operated at part and full-load conditions through this analysis. We have also tested the effect of the inlet air temperature and the relative humidity of the inlet air on the performance of the system. The predicted values of the performances for the system have been compared with the actual performance data provided by the gas turbine manufacturer. It has been found that the measured data of net power and the properties of exhaust gases are in good agreement with calculation ones, differing by less than 3 percent. The exergy balance equation may be utilized in the exergoeconomic analysis to estimate the production costs depending on various input costs in a gas turbine cogeneration system.
IntroductionCogeneration may be defined as a thermal system that produces electrical and heat energy simultaneously from a single source of fuel (Baughn and Kerwin, 1987;Baughn and Bagheri, 1987). For industrial and domestic applications where both kinds of energy are demanded, this turns out to be a very effective energy-saving system (Lundberg, 1991). In this study, a general exergy balance equation that is applicable to any component of thermal systems has been formulated and the energy and exergy analysis based on this equation permit one to predict the thermodynamic performance of the system as well as to provide appropriate design data for the auxiliary components such as absorption refrigerators and cooling towers, which are needed for gas turbine cogeneration plants (Kim, 1995). This analysis also yields the thermal efficiency of the system, the exergy destruction in each component, the mass flow rate, the compositions and temperature of the exhaust gases at turbine outlet, and NO concentration with appropriate input data. In this analysis the mass, energy, and exergy balance in each component are strictly applied, which has never been done before. Previous exergy analysis (Dunbar et al., 1993;El-Masri, 1985) is a rather ideal and simplified approach in this sense.We have examined the performance of the gas turbine cogeneration system as well as the exergy destruction in each component in the system when it is operated at part and full-load conditions through this analysis. We have also tested the effect of the inlet air temperature, the relative humidity of the inlet air, and water or steam injection on the performance of the system. The...
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