Which component uses exhaust gases to preheat feedwater in a boiler system?

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The main idea is heat recovery: using hot exhaust to raise the temperature of feedwater before it enters the boiler. The economizer does this. It’s a heat exchanger placed in the path of the boiler’s exhaust gases, so as the hot flue gases pass through, they transfer heat to the incoming feedwater. This preheats the water, reducing the energy the boiler must use to convert cold water into steam, which improves overall boiler efficiency and lowers fuel consumption and emissions.

In contrast, an air preheater uses exhaust heat to warm the combustion air, not the feedwater, so it doesn’t preheat the water going into the boiler. The turbine rotor cooling assembly is focused on removing heat from the turbine components, not conditioning feedwater. And the boiler feed pump increases the water pressure, but it does not provide the heat transfer needed to preheat the feedwater.