An economizer located in the path of the gases of combustion increases boiler efficiency by approximately how much for each 10°F rise in feed water temperature?

The function of an economizer is to preheat the feedwater entering the boiler by using waste heat from the flue gases. This process increases the overall efficiency of the boiler system because it reduces the amount of fuel needed to heat the water to the desired steam temperature.

When the feedwater temperature rises, the energy input required from the fuel to achieve boiling is reduced. The approximately 1% increase in boiler efficiency for each 10°F rise in feedwater temperature reflects the direct relationship between the temperature of the feedwater and the amount of thermal energy required to convert that water to steam. This principle is crucial in steam plant operations, as maximizing the thermal efficiency of the system leads to better performance and lower operational costs.

Hence, a rise in feedwater temperature due to the economizer's operation translates to less fuel consumption, effectively increasing the boiler's thermal efficiency by about 1% for every incremental increase of 10°F in the feedwater temperature.