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Steam power plants play a key role in electricity generation throughout the world. Their performance is strongly dependent on the boilers performance and feedwater heater network. In this study, exergoeconomic analysis is performed on a steam power plant in Iran and effects of adding a new feedwater heater to the cycle are investigated through exergy and exergoeconomic analyses. In this respect, two configurations are considered, in the first one the new feedwater heater is placed before the first existing feedwater heater and in the second configuration, the new feedwater heater is placed after the last one. Performance of the system in these two new configurations is studied and then compared with the base case condition. Also an optimization algorithm is applied to each configuration and the base case condition. The results show that boiler has the highest rate of exergy destruction. Also in terms of exergoeconomic analysis, boiler has a high value of relative cost different which 45% of it is because of exergy destruction cost. Comparison between the results shows that adding the new feedwater heater increases the exergy efficiency of the plant, but if it placed after the last feedwater heater, it can reduce the product cost rate of the plant as well. Optimization results reveal that placing the new feedwater heater in this position can reduce the product cost rate by 0.16% and increase the exergy efficiency by 0.33%.

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.