Document ZJRv2D1VYn7zD7zBpkeMyQj2Z

HEATINC VENTILATING AIR CONDITIONING GUIDE 1942 Table 2. Flame Temperature Data Appearance op Flame Red, visible in daylight.Light red.__ ..... ................................. Orange-red................................. Oransre-vellow......................... Yellow-white........................ Bright white. ............................ Temperature Deo F 975 2012 2192 2372 2550 process. The luminosity of a flame is caused by the heating to incan descence of unconsumed particles of combustible matter in the gases, and the higher the temperature of these particles the whiter the flame. Table 2 gives some approximate flame temperature data. AIR AND COMBUSTION The weight of air required for the perfect combustion of a pound of fuel may be determined by use of the ultimate analysis of the fuel as applied to Equations 2 to 4. The various elements are expressed in percentages by weight. Solid and Liquid Fuels: Pounds air required per pound fuel = 34.56 -f- ----- -f- Gaseous Fuels: Pounds air required per pound fuel.= 2.46 CO + 34.56 H, + 17.28 Cff, 13.29 Off, + 14.81 C,ff. + 16.13 CtH, + 6.10 H,S - 4.32 0, (2) W When the analysis is given on a volumetric basis the equation is expressed as follows: Cubic feet air required per cubic foot gas <= 2.39 (CO + H,) + 9.56 C/1* + 11.98 CjHi + 14.35 CtH, + 16.74 CJJt - 4.78 0, (4) Equations 5 and 6 may be used as approximate methods of determining the theoretical air requirement for any fuel. Pounds air required per pound fuel = 0.755 X Va--(5) Cubic feet air required per unit fuel = Hating valrefBtu per unit) (6) Approximate values for the theoretical air required for different fuels' are given in Table 3. It is customary to make use of the analysis of the products of com bustion to determine the amount of flue gas produced and the actual amount of air supplied for combustion. The analysis of flue gases has been well described in various publications of the Bureau of Mines and in the literature and the details of Orsat manipulation need not be considered in this discussion. (See Chapter 35.) The weight of dry flue gas per pound of fuel burned is used in com bustion loss calculations and may be determined by Equation 7. 160 CHAPTER 8. COMBUSTION AND FUELS P_ound.s dj ry aflue gas per pound. ,fue1l = -H----C--O---,--+- 38 O, + 7C(OC)O---+-----H--,)- _* ^,, (7) Values for CO%, Oi, CO and Nt are percentages by volume from the flue gas analysis and' C is the weight of carbon burned per pound of fuel corrected for carbon in the ash. EXCESS AIR Because the real measure of the efficiency of combustion is the relation existing between the amount of air theoretically required for perfect com bustion and the amount of air actually supplied, a method of determining the latter factor is of value. Equation 8 will give reasonably accurate results, for most solid and liquid fuels, for determining the amount of air supplied per pound of fuel. 3.036 Nt PnnnH<s rlrv air surmlied oer DOund of fuel -- Values for C02, CO and N are percentages by volume from the flue gas analysis and C is the weight of carbon burned per pound of fuel corrected for carbon in the ash. The difference between the air actually supplied for combustion and the theoretical air required is known as excess air. Per cent excess air Air supplied -- Theoretical air Theoretical air (9) Since the calculation is usually made from Orsat readings, Equation 10 will be found to be a convenient statement of this relationship. Table 3. Theoretical Air Requirements Solid Fuel Pounds Aib Per Pound Fuel 9.6 11.2 10.3 6.2 11.2 Fuel On, Pounds Air Per Gallon Fuel 102.6 104.5 106.5 112.0 114.2 Gaseous Fuels 161 Cubic Feet Air Per Cubic Foot Gas 10.0 4:4 4.4 2.1 5.2