Explain the concept of economizer in power plant.

An economizer in a power plant is a heat exchanger that recovers waste heat from the flue gas (the exhaust gases exiting the boiler) to preheat the boiler feedwater. Boiler feedwater is the water that is fed into the boiler to be converted into steam. By preheating the feedwater, the economizer reduces the amount of fuel needed to raise the water to its boiling point and then convert it into steam. This improves the overall efficiency of the power plant. The economizer is typically located in the flue gas duct between the boiler and the air preheater (another heat recovery device). The flue gas passes over the economizer tubes, transferring heat to the feedwater flowing inside the tubes. This cools the flue gas before it is released into the atmosphere and increases the temperature of the feedwater entering the boiler. In short, economizers reduce energy consumption and improve energy performance.