Document QJ86gNj96nn1zpMjb89r7VgmE

v 312 CHAPTER 16 1946 Guide Table 8. 1 Commercial Standard No. Approximate Gravity and. Calorific Value of Standard Grades of Fuel Oil Approximate Gravity Range A. P. I. Calorific Value Btu Per Gallon 1 38-40 136,000 2 34-36 138,500 3 28-32 141,000 5 18-22 148,500 6 14-16 152,000 general use, for small fire-pots where the fuel depth is not over 20 in., is that which passes over a 1 in. screen and through a 1}4> in. screen. For large fire-pots where the fuel can be fired over 20 in. deep, coke which passes over a 1 in. screen-and through a 3 in. screen can be used, but a coke of uniform size is always more satisfactory. Large sizes of coke should be either mixed with fine sizes or broken up before using. FURNACE VOLUME fi si J 3i The principal requirements for a hand-firedfurnacaare that it shall have enough grate area and correctly proportioned combustion space. The. amount of grate area required is dependent upon-the desired combustion rate. The furnace volume is influenced by the kind of coal used. Bituminous coals, on account of their long-flaming characteristic, require more space in which to burn the gases of combustion completely than do the coals low in volatile matter. For burning high volatile coals provision should be made for mixing the combustible gases thoroughly; so that combustion is complete before the gases come in contact with the relatively cool heating surfaces.- An abrupt change in the direction of flow tends to mix the gases of combustion more thoroughly. Anthracite requires com-' paratively little combustion space. CLASSIFICATION OF OILS The Commercial Standard Specifications for Fuel Oils (CS 12-40) of the U. S. Department of Commerce are given m Table 7. These speci fications conform with American Society for Testing Materials Tentative .Specifications for Fuel Oils D396-38T. The A.P.I. gravity of oil is of interest in it& relationship to the calorific value and these data are given in Table 8. COMBUSTION OF OIL , With oil, as with any kind of fuel, efficient heat production requires that all combustible matter in the fuel shall be completely consumed and that it shall be done with a minimum of excess air. The combustion of oil is a rather rapid chemical reaction. Excess air provides an over supply of oxygen so that all of the oil will be completely oxidized and thus produce all the heat possible. The use of unreasonable quantities of air in excess of theoretical combustion requirements results in lowered efficiencies due to increased stack losses. Such losses, if not accompanied by unbumed products of combustion, may be offset somewhat by in creasing the secondary heating surfaces of the heat absorbing medium, boiler or furnace. Oil is a highly concentrated fuel composed mainly of Filp.Is and Combustion Table 9. Representative Properties of Gaseous Fuels. Based on Gas at 60 F and 30 in. Hg. 313 Ga3 Btu per Cu Ft (Gross) Low (Net) Specific Grayitt, Am = 1.00 for Combus tion, (CuFt) Natural gas-- California 1200 1085 0.67 Natural gas-- Mid-Conti nental 970 870 0.57 Natural gas-- Ohio 1130 1025 0.65 Natural gas-- Pennsylvania 1130 1025 0.71 Retort coal gas 570 510 0.42 Coke oven gas 590 520 0.42 Carbureted water gas 540 495 0.65 Blue water gas 300' 280 0.53 Anthracite pro ducer gas .135 125 0.85 Bituminous producer gas 150 140 0.86 Oil gas 575 510 0.35 11.26 9.17 10.70 11.70 5.00 5.19 4.37 2.26 1.05 1.24 4.91 -Products of Combustion Cubic Feet COi s0 Total with tfi Ulti mate COi Dry Basis Flame Tem perature, (F DEO) 1.24 2.24 12.4 12.2 3610 0.97 1.92 10.2 11.7 3580 1.17 2.16 11.8 12.1 3600 . 1.30 0.50 0.51 2.29 1.21 1.25 12.9 5.7 5.9 12.3 11.2 11.0 3620 3665. 3660 0.74 0.75 5.0 17.2 3815 0.46 0.51 2.8 22.3 3800 0.33 0.19 1.9 19.0 3000 0.35 0.19 2.0 19.0 3160 0.47 1.21 5.6 10.7 3725 hydrogen and carbon. In its liquid form oil cannot burn. It must be converted into -a. gas of vapor by some means. If the excess air is to be kept within efficient limits, air must be supplied in carefully regulated quantities. The air and oil vapor must be thoroughly mixed to get a rapid and complete chemical reaction. The better the mixing, the less excess air will be needed. The combustion must take place in a space that maintains the temperatures high so the reaction will be completed. CLASSIFICATION OF GAS Gas is broadly classified as being either natural or manufactured:' Natural gas is a mechanical mixture of several combustible and inert gases rather than a chemical compound. Manufactured gas as dis tributed is usually a combination of. certain proportions^ gases produced by two or more processes. Representative properties of gaseous fuels commonly used in domestic heating are presented in Table 9. Natural gas is the richest of the gases and contains from 80 to 95 per cent methane, with small percentages of the other combustible hydrocarbons. In addition, it contains from 0.5 to 5.0 per cent of COt, and from 1 to 12 or 14 per cent of nitrogen. The heat value varies from . 1000 to 1200 Btu per cubic foot, th.e majority of natural gases averaging about 1000 Btu per cubic foot. Table 9 shows typical values for thefour main oil fields, although values from any one field vary materially. '