Energy and exergy analyses of partial repowering of a natural gas-fired steam power plant

In this paper, the feed water heating repowering of a natural gas-fired steam power plant is investigated. To do this, three separate cases including replace of low pressure, high pressure and both low and high pressure feed water heaters with new heat exchangers and a gas turbine have been suggested. Energy and exergy efficiencies have been used as objective functions, and cycle-tempo flow sheet software has been used to simulate the cycle of power plant. According to the obtained results, the maximum exergy efficiency has been achieved in replacement all feed water heaters with two heat recovery heat exchangers. In this case, gas turbine model westinghouse-401 is the best option; in which net energy and exergy efficiencies increase from 33.42% and 32.58% in simple cycle to 38.39% and 37.2% in repowered cycle, respectively. Moreover, output power will increase from 200 MW to 285.9 MW.