Page 318 - Wastewater Solids Incineration Systems

Appendix A Combustion Fundamentals 279

TABLE A.1 Common secondary quantities in mechanical systems.

Item Definition Dimensions*
2
Area (Length) 2 m (sq ft)
3
Volume (Length) 3 m (cu ft)
Velocity Length/time m/s (ft/sec)
2
2
Acceleration Length/(time) 2 m/s (ft/sec )
2
Pressure Force/area Force/(length) 2 N • m (lbf/sq ft)
3
Density Mass/volume Mass/(length) 3 kg/m (lb/cu ft)
3
2
* sq ft 0.092 90 m ; cu ft 0.028 32 m ; ft/sec 0.304 8 m/s.
specific number of degrees to correctly reference temperatures to absolute zero as fol-
lows: °R °F 459.67 and K °C 273.15.

2.2 Fundamental Combustion Concepts
This section provides a discussion of various fundamental concepts that are essential
to a basic understanding of the combustion process. Included are an introduction to
combustion elements and atomic weights; molecules and molecular weights; the
ideal gas law; and the basic compositions of air and typical commercial fuels.

2.2.1 Combustion Elements and Atomic Weights
To date, scientists have identified 109 elements. Each element has a specific atomic
weight. Fortunately, most of these elements are not involved in sludge combustion.
The five most common elements encountered in sludge combustion are carbon,
hydrogen, oxygen, nitrogen, and sulfur. Table A.2 summarizes abbreviations and
atomic weights for these elements.
2.2.2 Molecular Weights
Carbon and sulfur are solids at room temperature, whereas hydrogen, oxygen, and
nitrogen are gases. A molecule of either carbon or sulfur contains a single atom. A mole-
cule of hydrogen, oxygen, or nitrogen contains two atoms. These are sometimes called
diatomic (di 2) gases. When writing the abbreviation for these gases, the subscript 2 is
used to indicate a gas molecule. While the correct atomic weight should always be used
in calculations, rounded off values are more commonly used in narrative discussions
and will be used in the example calculations presented in this appendix.
The molecular weights of solids, gases, or liquids that are a combination of the
five elements shown in Table A.2 can be easily calculated. Several illustrative exam-
ples of familiar compounds are shown in Tables A.3 and A.4.