Page 331 - Wastewater Solids Incineration Systems

292 Wastewater Solids Incineration Systems

This heat is often referred to as sensible heat. The specific heat of common flue
gases over temperatures of general interest in sludge incineration (60 to 2200°F) is not
constant and there are numerous equations that have been developed to quantify this
variation. To determine the average specific heat these equations for specific heat
must be integrated over the temperature range of interest.
For this appendix, this often complex mathematical integration step will be elim-
inated and the following fourth power polynomial equations for enthalpy (60°F base)
will be used. The enthalpy (h) at any temperature (T) between 60 and 2200°F may be
calculated as follows:

h X X T X T X T X T
0 1 2 2 3 3 4 4
where X , X , X , X , and X are constants used in the equation.
0 1 2 3 4
Polynomial equations such as the one above are easily programmed into a
spreadsheet. The five equation constants are unique for each gaseous compound
and are tabulated in Table A.13 for the more common gaseous compounds found
in flue gases.
Application of these constants in the basic equation gives the enthalpy of each
compound at the selected temperature. Table A.14 summarizes the computed values
of enthalpy for the more common gaseous compounds found in flue gases at temper-
atures from 60 to 2200°F.
It is important not to use these simplified polynomial equations outside their range
of applicability (60 to 2200°F), as significant errors may be introduced. Figure A.1
depicts the variations in enthalpy calculated from these equations in graphical format
over their range of applicability.
The heat of vaporization of water at 60°F is taken as 1059.7 Btu/lb. When ash is a
constituent in the flue gas that must be considered, it does have a fairly constant spe-

TABLE A.13 Enthalpy constants for common flue gases (60°F base).
Constant CO O N H O SO
2 2 2 2 2
X 11.781 55 12.985 06 14.846 22 27.141 43 8.687 84
0
X 0.192 338 0.215 133 0.247 333 0.451 462 0.142 168
1
X 6.815 10 –5 2.151 10 –5 1.230 10 –6 1.399 10 –5 4.466 10 –5
2
X 1.890 10 –8 1.731 10 –9 8.612 10 –9 1.565 10 –8 1.425 10 –8
3
X 2.357 10 –12 2.947 10 –13 1.928 10 –12 2.760 10 –12 1.947 10 –12
4