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 negligible 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 12.27(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.

Problem 12.27(d)

(d) Solve the equations of part (c) for the unknown stream flow rates, component fractions and temperature of the air entering the dryer, and rate of heat transfer to the air in the furnace (kW).