Page 49 - Handbook of Energy Engineering Calculations

4, times the proportion of N in the air, or 0.79. The excess O passes through
2
2
the furnace and adds to the combustion products and is computed as shown in
the tabulation. Subtracting the total moisture, 3430 mol, from the total (or

wet) combustion products gives the moles of dry combustion products.

Related Calculations. Use this method for molal combustion calculations for
all types of fuels—solid, liquid, and gaseous—burned in any type of furnace
—boiler, heater, process, or waste-heat. Select the correct factors from Table

3.

ESTIMATING THE TEMPERATURE OF THE FINAL
PRODUCTS OF COMBUSTION

Pure carbon is burned to carbon dioxide at constant pressure in an insulated
chamber. An excess air quantity of 20 percent is used and the carbon and the
air are both initially at 77°F (25°C). Assume that the reaction goes to

completion and that there is no dissociation. Calculate the final product’s
temperature using the following constants: Heating value of carbon, 14,087
3
Btu/lb (32.74 × 10 kJ/kg); constant-pressure specific heat of oxygen,
nitrogen, and carbon dioxide are 0.240 Btu/lb (0.558 kJ/kg), 0.285 Btu/lb m
m
(0.662 kJ/kg), and 0.300 Btu/lb (0.697 kJ/kg), respectively.

Calculation Procedure:

1. Establish the chemical equation for complete combustion with 100
percent air
With 100 percent air: C + O + 3.78N → CO + 3.78N , where approximate
2
2
2
2
molecular weights are: for carbon, MC = 12; oxygen, MO = 32; nitrogen,
2
MN = 28; carbon dioxide, MCO = 44. See the Related Calculations of this
2
2
procedure for a general description of the 3.78 coefficient for N .
2
2. Establish the chemical equation for complete combustion with 20 percent

excess air
With 20 percent excess air: C + 1.2O + (1.2 × 3.78)N → CO + 0.2O +
2
2
2
2