Full repowering of an existing fossil fuel steam power plant in terms of energy, exergy, and environmen for efficiency improvement and sustainable development

In this study, the feed-water-heating method is studied due to its numerous advantages for the repowering of 320 MW units at Isfahan power plant. In this method, only low-pressure heat exchangers or only high-pressure heat exchangers can be replaced with a new gas–water heat exchanger, or both can be replaced by two high-pressure and low-pressure heat exchangers. It is also possible to do the preheating of boiler feed water in parallel with existing heat exchangers and new heat exchangers. Each of this method has its own characteristics that have advantages and disadvantages. We first analyze the energy and exergy of the existing cycle and then analyze the methods used to feed-water-heating repowering. Various gas turbines are used for this work, and the results are expressed. Energy and exergy efficiencies are considered as objective functions, and finally, while considering other limiting parameters, it is recommended for each method of optimal gas turbine. The characteristics of the new heat exchangers are also described. In the first method, net efficiency of energy and exergy is increased relatively to 8.25% and 8.4%, respectively, and in the second method net efficiency of energy and exergy is increased relatively to 10.96% and 11.56%, respectively.