Question 79Steam Plants - 1st Asst/Chief

The correct answer is B) the dew point temperature of the stack gas. The minimum feed water inlet temperature to a boiler economizer is determined by the dew point temperature of the stack gas. This is because the economizer is designed to extract heat from the hot flue gases before they are expelled through the stack. To avoid condensation and corrosion in the economizer, the feed water inlet temperature must be above the dew point temperature of the stack gas. The other options are incorrect because they do not directly determine the minimum feed water inlet temperature. Radiant heat transfer in the furnace, superheater outlet temperature, and the surface area of the third stage heater are not the primary factors that influence the minimum feed water inlet temperature for the economizer.