Abstract
The aim of this study is to evaluate the performance of combined cycle power plants in full and part-load operations in terms of energy, exergy and environment. The environmental analysis is performed using life cycle assessment method. Two different strategies are selected to control the gas turbine under part-load conditions, including Turbine Exhaust Temperature (TET) constant and Turbine Inlet Temperature (TIT) constant modes. Results show that gas turbine has a higher efficiency in TET constant mode. But, combined cycle shows a better efficiency in TIT constant mode. Exergy analysis results show that combustion chamber has the highest rate of exergy destruction, both in full and part-load operation. With reducing the load, total exergy destruction of the plant is decreased which is due to lower fuel consumption. Also reducing the load by 50% leads to 2.47% and 6.36% reduction in exergy efficiency of the plant in TIT and TET constant modes, respectively. Therefore, in terms of energy and exergy, it is suggested to use the TIT constant mode for part-load operation of the gas turbine within a combined cycle. But in terms of environmental analysis, results show that more emissions are produced in TIT constant mode, due to higher fuel consumption.
Highlights
Power generated in power plants should always adjust with electricity demand
Since in Turbine Inlet Temperature (TIT) constant mode, turbine outlet temperature increases with load reduction, the outlet flue gas has higher energy content and in this situation more steam is produced in the HRSG
Exergy analysis showed that among all components, combustion chamber has the highest rate of exergy destruction, both in full-load and part-load
Summary
Power generated in power plants should always adjust with electricity demand. Since electricity demand is fluctuating throughout a day, sometimes the power plants have to operate under part-load conditions. Bakalis et al [17] performed an exergy analysis on a combination of micro gas turbine and solid oxide fuel cell at full and part-load conditions and calculated exergy destruction and exergy efficiency of each component. They utilized variable speed control strategy in part-load condition. Energy, exergy and environmental analyses are performed on a combined cycle power plant at full and part-load operation and exergy destruction and exergy efficiency of each component and the whole plant is calculated. The two selected strategies are compared based on environmental analysis
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