Document pvzyr84q33aQ59wkdQwkvzdk

HEATING VENTILATING AIR CONDITIONING GUIDE 1943 Table 9. Representative Properties of Gaseous Fuels. Based on Gas at 60 F and 30 in. Hg. Gas - CoBtc feb Ft High Low (Gross) (Net) SpEctnc Grayitt Aib = Am Reqotbed fob Combus tion, (Cc Ft) Products or Combustion . Cubic Feet Total CO* BtO with AT* Ulti mate COi Dry Basis Theoretical Flame Tem perature, (deo F) 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 0.47 1.21 5.6 10.7 3725 type of burner part of the air required for combustion is mixed with the gas as primary air, the air and gas mixture being fed. to the burner ports. 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. The radiants.also serve as baffles in directing the flow of the products of combustion. The quantity of air given in Table. 9 is that required for theoretical combustion, but 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. The air gas ratio has a decided effect upon flame propagation. It is' necessary that the gas will flow oiit of the burner ports fast enough so that the flame cannot travel back into the burner head, i.e. flash back, but the velocity must not be so high that it blows the flame away from the port. 184 CHAPTER 8. COMBUSTION AND FUELS The maximum and minimum flow speeds from burner ports which may be permitted are known to be very close together when air-gas mixtures in theoretical proportions are being supplied to the burner. As the air-gas ratio is lowered, and the mixture becomes more gas rich, the limiting speeds 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. SOOT The deposit of soot on the flue surfaces of a boiler or heater acts as an insulating layer over the surface and reduces the heat transmission to the water or air. The Bureau of Mines Report of Investigations No. 3272 shows that the loss of seasonal efficiency is not as great as has been believed and usually is not over 6 per cent because the greater part of the heat is transmitted through the combustion chamber surfaces. The Bureau of Standards Report BMS 54 points out that, although the decrease in efficiency of an oil fired boiler due to soot deposits is relatively small the attendant increase in stack temperature may become excessive. The soot accumulation clogs the passages and reduces the draft; the loss of efficiency from this action may be considerably greater than from the reduction in heat transfer. 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.). Smoke-Producing Tendencies in Coals of Various Ranks, by H. J. Rose and F. P. Lasseter (A.S.H.V.E. Transactions, Vol. 45, 1939, p. 329). 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. National Bureau of Standards Publication: Report BMS 54, Effect of Soot on the Rating of an Oil-Fired Heating Boiler, by R. S. Dill and P. R. Achenbach. Anthracite Industries Laboratories Publications: Report 2015, Comparison of Sizes, Egg, Stove and Chestnut Anthracite. Report 2018, Domestic Survey. 185