Page 329 - Wastewater Solids Incineration Systems

290 Wastewater Solids Incineration Systems

Calculating the volume at standard conditions for each component of the flue gas:

0.0725 lb-mole CO 379.5 cu ft/(lb-mole) 27.51 cu ft CO 11.4%
2 2
0.0650 lb-mole H O 379.5 cu ft/(lb-mole) 24.67 cu ft H O 10.2%
2 2
0.0209 lb-mole O 379.5 cu ft/(lb-mole) 7.95 cu ft O 3.3%
2 2
0.4779 lb-mole N 379.5 cu ft/(lb-mole) 181.36 cu ft N 75.1%
2 2
Total 241.48 cu ft 100.0%
These calculations demonstrate that volume percent and mole percent are equal.
The volume and mole percents tabulated above are calculated on a wet basis. Often,
it is necessary to calculate volume percents on a dry basis for emissions reporting and
other purposes. The shortcut formula for excess air requires dry volume percent
oxygen. This is calculated by subtracting the volume of H O from the total and
2
recomputing the relative percentage of the remaining components as follows:
Wet volume % O 7.95 cu ft O 2/241.48 cu ft 100 3.29% O
2 2 2, wet
Dry volume % O 7.95 cu ft O /(241.48 cu ft 24.67 cu ft) 100 3.67% O
2 2 2,dry
From the previous formula for XS air:
XS air 3.67% O /(20.9% 3.67% O ) 21.3%
2, dry 2, dry
The actual basis for the combustion calculation was 20% XS air. As can be seen,
the above shortcut method introduced a slight error. However, as stated previously,
it is generally adequate for emission rate computations.

4.1 Adiabatic Flame Temperature

The adiabatic flame temperature is the temperature that would be reached with perfect
stoichiometric combustion (0% excess air), zero heat loss, and no disassociation of flue
gas molecules. The adiabatic flame temperatures of natural gas and no. 2 oil are between
1927 and 2065°C (3500 and 3750°F). These extremely high temperatures for dry fuels are
of academic interest but do not play a role in sludge incineration calculations.

4.2 Theoretical Temperature of the Products of Combustion
The theoretical temperature of the products of combustion (TTPC) is the temperature
(calculated) that would be reached if a wet or dry fuel was burned with zero heat
loss. In some cases, especially for a high moisture sludge cake with no auxiliary fuel,
the TTPC may be well below the temperatures required to produce actual burning
and a flame. For any given fuel or fuel combination, the flame temperature at zero