Economizers on Boilers
An economizer is a heat exchanger that transfers heat from flue gases on the outside of the exchanger tubes to boiler feedwater on the inside.
Boilers with economizers generally cool the flue gas temperatures from the 600°F to 800°F range to stack temperatures of about 300°F to 350°F.
A stack temperature of 300°F is also near the minimum temperature to avoid corrosion from sulfuric acid condensation in the cold end of the unit. These minimum temperatures are determined by the sulfur content of the fuel, the excess air, and the moisture of the flue gas.