An efficiency test of a boiler fired by fuel No. 2 indicated a flue gas temperature of 700°F and excess air of 40 percent. The annual fuel consumption of the boiler is 85,000 gallons/year. The cost of fuel No.2 is $1.15/gal.

a. Estimate the efficiency of the boiler as well as the percentage in CO₂ and O₂ of the flue gas.

b. Determine the new boiler efficiency and the annual cost savings in fuel use if the percentage of O2 in the flue gas is reduced to 3 percent and the stack temperature is set to 500°F.

c. Determine the payback period of installing an automatic control system at a cost of $8,500 to maintain the same efficiency throughout the life of the boiler.