A mixture of 75 mole% methane and 25 mole% hydrogen is burned with 25% excess air. Fractional conversions of 90% of the methane and 85% of the hydrogen are achieved; of the methane that reacts, 95% reacts to form CO2 and the balance reacts to form CO. The hot combustion product gas passes through a boiler in which heat transferred from the gas converts boiler feedwater into steam.
(a) Calculate the concentration of CO (ppm) in the stack gas.

(b) The CO in the stack gas is a pollutant. Its concentration can be decreased by increasing the percent
excess air fed to the furnace. Think of at least two costs of doing so. (Hint: The heat released by the combustion goes into heating the combustion products; the higher the combustion product temperature, the more steam is produced.)