Exhaust gas from a chemical process flows at a rate of 8,000 actual cubic feet per minute (acfm) from point A at 250°F and 1 atm pressure. It flows through a circular duct to a fan at which point the pressure is increased by 4 inches of water (gage), and then flows to an incinerator. Fuel gas is burned at a rate of 75 pounds per hour and the temperature of the incinerator exhaust gas is 1200°F.
(a) Assuming both the process exhaust and the incinerator exhaust streams have properties similar to air (specifically, the heat capacity is similar to air), calculate the enthalpy that has been added by burning the fuel in Btu/hr.
(b) Assuming that you can recover heat from the incinerator exhaust as the exhaust gases cool to 500°F, how much money can you save by recovering that heat (in $/day), assuming that the heat is worth $7.00 per million Btu.
Hint #1: "gage" is sometimes also spelled "gauge" and is the pressure increase above atmospheric pressure. Given that 1 atm = 406.8 in. H2O, an increase of 4 in. H2O corresponds to an increase in the pressure to 410.8 in H2O.
Hint #2: You may find it easiest to do this problem using SI units.