Flue gas exit temperature from the
air preheater can range from 250 to
350°F depending on the acid dew
point temperature of the flue gas,
which is dependent on the concentration of vapor phase sulfuric acid and moisture. For power plants equipped with wet FGD systems, the flue gas is further cooled to approximately 125°F as it is sprayed with the FGD reagent slurry. However, it may be possible torecover some of this lost energy in the flue gas to preheat boiler feedwater via use of a condensing heat exchanger.