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Heating Ventilating Air Conditioning Guide 1939 Additional secondary air is introduced around the flame by draft inspi ration. In the luminous flame burner, which is sometimes used, all of the air for combustion is brought in contact with the flame as secondary air. The importance of bringing the secondary air into intimate contact with the gas is noted. Some makes of burners use radiants or refractories to convert some of the energy in the gas to radiant heat by utilizing the principle of surface Table 9. Representative Properties of Gaseous Fuels. Based on Gas at 60 F and 30 in. Hg. Gab Btu per Cd Ft Low (Gross) (Net) Specific Gravitt, Am -- 1.00 Am Required for Combus tion, (Co Ft) Products of Combustion Cubic Feet Total CO, HjO with N, Ulti mate CO, Dry Basis Theoretical Flame Tem pera tceg, (dbg Fahb) Natural gas-- California 1200 1087 0.67 11.26 1.24 2.24 12.4 12.2 3610 Natural gas-- Mid-Conti nental 967 873 0.57 9.17 0.97 1.92 10.2 11.7 3580 Natural gas-- Ohio 1130 1025 0.65 10.70 1.17 2.16 11.8 12.1 3600 Natural gas-- Pennsylvania 1232 1120 0.71 11.70 1.30 2.29 12.9 12.3 3620 Retort coal gas 575 510 0.42 5.00 0.50 1.21 5.7 11.2 3665 Coke oven gas 588 521 0.42 5.19 0.51 1.25 5.9 11.0 3660 Carbureted water gas 536 496 0.65 4.37 0.74 0.75 5.0 17.2 3815 Blue water gas 308 281 0.53 2.26 0.46 0.51 2.8 22.3 3800 Anthracite pro ducer gas 134 124 0.85 1.05 0.33 0.19 1.9 19.0 3000 Bituminous producer gas 150 140 0.86 1.24 0.35 0.19 2.0 19.0 3160 Oil gas 575 510 0.35 , 4.91 y 0.47 1.21 5.6 10.7 3725 combustion. The radiants also serve as baffles in directing the flow of the products of combustion. Since one of the main functions of a gas burner is to properly proportion the air and gas, any marked change in the gas composition which affects the specific gravity necessitates a readjustment of the burner. It is necessary to supply a greater amount of air when the specific gravity of a gas is increased. The quantity of air given in Table 9 is that required for theoretical combustion, blit with a properly designed and installed burner the excess air can be kept low. The division of the air into primary and secondary is a matter of burner design and the pressure of gas available, and also of the type of flame desired-.' ' .182 Chapter 9. Combustion and Fuels :r gas ratio has a decided effect upon flame propagation. It is 1 ne (jjat the gas will flow out of the burner ports fast enough so that "Aflame cannot travel back into the burner head, i.e. flash back, but the 1 *ty must not be so high that it blows the flame away from the port. veTh maximum and minimum flow speeds from burner ports which may rmitted are known to be very close together when air-gas mixtures theoretical proportions are being supplied to the burner. As the air-gas t o is lowered, and the mixture becomes more gas rich, the limiting raids become further apart, until with 100 per cent gas, in an all-yellow flame flash back cannot occur and a much higher velocity, is needed to blow off the flames. REFERENCES Fuels and Their Combustion, Haslam and Russell (McGraW Hill Co., 1926). Principles of Combustion in the Steam Boiler Furnace, Arthur D. Pratt, (Babcock and Wilcox Co.). Bureau of Mines Publications: Bulletin No. 97, Sampling and Analyzing Flue Gases, by Henry Kreisinger and F. K. Ovitz. Report of Investigations (R.I. 2980), Coke as a Domestic Heating Fuel, by P. Nicholls and B. A. Landry. . Bulletin No. 276, Five Hundred Tests of Various Coals in House-heating Boilers, by P. Nicholls, S. B. Flagg and C. E. Augustine. Report of Investigations (R.I. 3283), Quality of Anthracite as Prepared at Breakers, 1935. Technical Paper No. 80, Hand Firing Soft Coal under Power-Plant Boilers, by Henry Kreisinger. Technical Paper No. 303, Value of Coke, Anthracite, and Bituminous Coal for Gener ating Steam in a Low-pressure Cast-iron Boiler, by John Blizard, James Neil and F. C. Houghten. Anthracite Industries Laboratories Publications: Report 2015, Comparison of Sizes, Egg, Stove and Chestnut Anthracite. Report 2018, Domestic Survey. Report 2062, Utilization of Anthracite for Domestic Heating. Report 2204, The Crater Method of Firing. Report 2403, Anthracite Industries Manual. An Experimental Investigation of the Use of Oil for the Treatment of Coal, by Ralph A. Sherman and J. M. Pilcher (A.S.M.E. Transactions, February, 1938). Handbook of Oil Burning, by Harry F. Tapp, American Oil Burner Association. Industrial Gas Series, Combustion, American Gas Association. Comfort Heating, American Gas Association. Tests of Gas Home-Heating Equipment, by R. B. Leckie and C. H. B. Hotchkiss (Purdue University, Engineering Bulletin Research Series No. 36). PROBLEMS IN PRACTICE 1 What effect does moisture in fuels have on their efficiency? With any solid fuel, latent and sensible heat are lost at the stack when moisture is dried out of the fuel in burning, and when its hydrogen is burned. Therefore, such fuels as sub-bituminous coal and lignite, which are high in moisture content, have a low efficiency. However, these efficiencies may be improved if the stack gases are cooled to room temperature, t>y heating the feed water, for example. 183