Document 1QkwqjbDxw7209BambqQa2JpK

American Society of Heating and Ventilating Engineers Guide, 1934 manufactured gas. Most states have legislation which controls the distri bution of gas and fixes a minimum limit to its heat content. The gross or higher calorific value usually ranges between 520 and 545 Btu per cubic foot, with an average of 535. A given heat value may be maintained and yet leave considerable latitude in the composition of the gas so that as distributed the composition is not necessarily the same in different dis tricts, nor at successive times in the same district. There are limits to the variation allowable, because the specific gravity of the gas depends on its Table 3. Representative Properties of Gaseous Fuels Gas __________ Based, on Gas at 60 F and 30 in. Hg.. Bru per Cu Ft High Low (Gross) (Net) Specific Geatitt Ant = 1.00 Air Required for Combus tion, (Cu Ft) Products of Combustion Cubic Feet Total COt BiO wIift,h Ulti mate COt* Dry Bass -- Theoretical Flame Tem perature, (deg Fahb) 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 Carburetted 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 Oilgas 575 510 0.35 . 4.91 0,47 1.21 5.6 10.7 3725 composition, and too great a change in the specific gravity necessitates a change in the adjustment of the burners of small appliances. . Table 3 shows that a large proportion of the products of combustion when gas is burned, may consist of water vapor, and that the greater the proportion of water vapor, the lower the maximum attainable CO% by gas analysis. The table also shows that a low calorific value'does not neces sarily mean a low flame temperature since, for example, natural gas has a theoretical flame temperature of 3600 F and blue water gas of 3800 F, although it has a calorific value less than one-third that of natural gas. The quantity of air given in Table 3 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. 376 Chapter 28 AUTOMATIC fuel burning equipment Stokers, Residential Stokers, Apartment House Stokers, Com mercial Stokers, Domestic Oil Burners, Air and Oil Supply, Atomi zation, Type of Flame, Ignition, Boilers for Domestic Oil Burners, Commercial Oil Burners, Gas-Fired Appliances, Gas Boilers, Warm Air Furnaces, Space Heaters, Conversion Burners, Gas Appliances, Installation Features LABOR saving, automatic, mechanical equipment for the efficient combustion of coal, oil, and gas is considered in this chapter. MECHANICAL STOKERS Assuming the same intelligence in handling the fire, coal can be burned more efficiently on a mechanical stoker than on any kind of hand-fired grate. This does not necessarily mean that a stoker installation may be more economical, because the amount of coal burned may be so small or the cost of the installation so high that the savings with stokers may not be sufficient to pay for the investment. The operation of burning coal in volves uniformity in stoking, proper distribution over the fuel bed, admission of air as required to all parts of the fuel bed, and disposal of the ash. The handling of the volatile gas is largely a matter of furnace design but since this gas forms a considerable portion of the heating value of the coal, it may also be said that the proper handling of this gas is a function of firing. All mechanical stokers must provide means of taking care of these several functions in order fully to serve their purpose. Classifications of Stokers Stokers may be divided into four types according to their construction and operation, namely, (1) overfeed flat grate, (2) overfeed inclined grate, (3) underfeed side cleaning type, and (4) underfeed rear cleaning type. They may also be classified according to their uses. The following classification has been adopted by the U. S. Department of Commerce: Class 1. Residential (Capacity less than 100 lb coal per hour). Class 2. Apartment houses and small commercial heating jobs (Capacity 100 to 200 lb coal per hour). Class 3. General commerical heating and small high pressure steam plants (Capacity 200 to 300 lb coal per hour). Class 4: Large commercial and high pressure steam plants (Capacity over 300 lb per hour). Overfeed Flat Crate Stokers This type is represented by the various chain grate stokers. These 377