Page 37 - Handbook of Energy Engineering Calculations

contains moisture, as is usually true, this moisture is added to the
combustion-formed moisture appearing in the products of combustion. Thus,
for 80°F (26.7°C) air of 60 percent relative humidity, the moisture content is
0.013 lb/lb (0.006 kg/kg) of dry air. This amount appears in the products of
combustion for each pound (kilogram) of air used and is a commonly

assumed standard in combustion calculations.

NATURAL GAS FUEL COMBUSTION IN A FURNACE

A natural gas has the following volumetric analysis at 60°F (15.5°C): CO =
2
0.004; CH = 0.921; C H = 0.041; N = 0.034; total = 1.000. This natural
2
2 6
4
gas is burned in a steam-boiler furnace. Determine the weight of air required
for theoretically perfect combustion, the weight of gas formed per pound
(kilogram) of natural gas burned, and the volume of the flue gas, at the boiler

exit temperature of 650°F (343°C), per pound (kilogram) of natural gas
burned; air required with 20 percent excess air, and the volume of gas formed
with this excess: CO percentage in the flue gas on a dry and wet basis.
2

Calculation Procedure:

1. Compute the weight of oxygen required per pound of gas
The same general steps as given in the previous calculation procedures will
be followed, except that they will be altered to make allowances for the

differences between natural gas and coal.
The composition of the gas is given on a volumetric basis, which is the
usual way of expressing a fuel-gas analysis. To use the volumetric-analysis
data in combustion calculations, they must be converted to a weight basis.
This is done by dividing the weight of each component by the total weight of

3
3
the gas. A volume of 1 ft (1 m ) of the gas is used for this computation. Find
3
3
the weight of each component and the total weight of 1 ft (1 m ) as follows,
using the properties of the combustion elements and compounds given in
Table 1:

TABLE 1 Properties of Combustion Elements *