In the dryer air furnace, a natural gas containing 92.5 mole% methane, 4.8% ethane, and the remainder propane is burned with 20% excess air. The fuel enters the furnace at 25°C and the air enters at 27°C, 1 atm, and 60% relative humidity. Essentially all of the fuel is consumed, and the flue gas contains a negligi-ble amount of carbon monoxide. Heat is transferred from the hot combustion products through the furnace wall to the dryer air. The combustion products leave the furnace at 250°C. Calculate the fuel feed rate (kg/h) required to achieve the heating rate calculated in Problem 27(d). (Suggestion: Assume a fuel feed of 100 mol/s. calculate the energy transfer corresponding to this basis of calculation, and then scale the results to determine the actual fuel feed rate.)