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HEATING VENTILATING AIR CONDITIONING CUIDE 1940 combustion are not cooled to the dew-point and the higher calorific value cannot be obtained. FLAME The appearance of the flame or products of combustion may serve as an1 approximate measure of the temperatures developed in the combustion 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 Formulae 3 to 5. The various elements are expressed in percentages by weight. Table 2. Flame Temperature Data Appearance op Flame Red, visible in daylight........ ...........................................,,................. Light red. _ ............................................................. ............................... Orange-red................................................................................................ Orange-yellow......................................... ................................................. Yellow-white.- ............................................. ........................ Temperature Deo F 975 1832 2012 2192 2372 2550 Solid and. Liquid Fuels: Pounds air required per pound fuel = 34.56 -Cg- + IlH + --0 \J + --S Gaseous Fuels: Pounds air required per pound fuel = 2.46 CO + 34.56 Ht + 17.28 CH, + 13.29 C,H, + 14.81 CsH, + 16.13 CJ1, + 6.10 H,S - 4.32 0, (3) (4) When the analysis is given on a volumetric basis the formula is'express ed as follows: Cubic feet air required per cubic foot gas = 2.39 (CO + Hi) + 9.56 CH, + 11.98 C,H, + 14.35 C,H, + 16.74 CiH, - 4.78 O, ,,, w Formulae 6 and 7 may be used as approximate methods of determining the theoretical air requirement for'any fuel. Pounds air required per pound fuel = 0.755 X ---r`^1C Va*Ue^^|u Per Pun(^) (g) Cubic feet air required per unit fuel = Calorific value (Btu per unit) (7) 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 gets produced and the actual 160 CHAPTER 9. COMBUSTION AND FUELS 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 45.) The weight of dry flue gas per pound of fuel burned is used in com bustion loss calculations and may be determined by Formula 8. 11 CO,+ 8 0,+ 7 (CO + N,) ,, r Pounds dry flue gas per pound fuel 3 (CO, + CO) * (8) Values for CO,, 0,, 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. Table 3. Theoretical Air Requirements Solid Fuel Anthracite...................... Semi-bituminous coal.-- Bituminous coal............ Lignite.... ........................ Coke--........................ :-- Founds Air Pee Pound Fuel . 9.6 11.2 10.3 6.2 11.2 Fuel Oil Commercial Standard No. l._ ............................................. Commercial Standard No. 2.................................................. Commercial Standard No. 3.--................................:............ Commercial Standard No. 5. ............................................... Commercial Standard No. 6-- ............................................. Pounds Air Per Gallon Fuel 102.6 104.5 106.5 112.0 114.2 Gaseous Fuels Cubic Feet Am Per Cubic Foot Gas 10.0 4.4 4.4 2.1 5.2 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. Formula 9 will give reasonably accurate results, for most solid and liquid fuels, for determining the amount of air supplied per pound of fuel. Pounds dry air supplied per pound of fuel 3.036 N, (CO, + CO) X (9) Values for CO2, 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. 161