Document 3MOam1ObmNmNJDQdQ329aab3

304 CHAPTER 16____________--A 1948 Guide Table 6. - Representative .Properties of Gaseous Fuels, Based on Gas-at 60 F and 30 in. Hg. Gab Natural gas--1 ;Btu per Cu Ft High (Gross) Specific Aib Required Gratot. Aib * Low (Net) . 1.00 fob Combus tion, (Co Ft) dir. Products Combustion * Cubic Feet Total COt BtO with Nt Ulti mate COt Dry Theoretical Flams Tem perature, (F dbg) -1200 1085 0.67 11.26 .1.24 2.24 12.4 12.2 3610 Natural gas-- Mid-Conti* nental 970 870 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 1130 1025 0.71 11.70 1.30 2.29 12.9 .12.3 3620 Retort coal gas 570 510 0.42 5.00 0.50 1.21 5.7 11.2 3665 Coke oven gas , .590 Carbureted water gas 540 520 0.42 495 0.65 5.19 4.37 0.51 1.25 5.9 11.0 0.74 0.75 5.0 17.2 3660 - 3815.., Blue water gas 300 280 0.53 2.26 . 0.46 0.51 2.8 22.3 3800 Anthracite pro- ducergas 135 125 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 0.47 121. 5.6 10.7, 3725 : four, main oil fields, although values from any one field vary materially. Table ,6 .also gives.the calorific values of the more common .types of ' 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 leaye.`;cbhsiderableTatitude 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. However, in any community the variations in gas composition are held within suitable limits so that the performance of: approved gas. appliances will not be adversely affected. , FUNDAMENTAL PRINCIPLES OF COMBUSTION Combustion may be defined as the chemical combination of a substance with oxygen with a resultant evolution of heat. The. rate of combustion depends partly upon the specific rate of reaction of the combustible substance with oxygen, partly upon the rate.at which.oxygen is supplied, and upon the temperature obtained due to surrounding conditions. 1 Complete combustion is obtained when all of the combustible elements in the fuel are oxidized with all of the oxygen with which they can combine. All of the oxygen supplied may not be utilized;. Perfect combustion is defined as the result of supplying'the required Fueb and Combustion 305 amount of oxygen for combination with all of the combustible elements of the fuel and utilizing all of the oxygen so supplied. The oxygen required for the process of combustion is obtained from air which is a. mechanical mixture of oxygen, ni trogen .and small amounts -of carbon dioxide, water vapor and inert gases. These inert gases are generally included with the nitrogen, and for engineering purposes the values given herewith may be used. ' :' Bt Volume, Per Gent OilOxygen, ........... . . ..................................... ......................... 1 Nitrogen, Ni... ....... .............. .................. 20.9 79.1 Bt Weight, Per Cent 23.15 i 76.85 . The combination of oxygen with the combustible elements and com pounds of a fuel is in accordance with fixed laws. In the case of perfect; combustion the reactions and resultant combinations are shown in Table 7.- The most important condition governing the process of combustioni is temperature. It is necessary to bring a combustible substance to its ignition temperature before it will unite in chemical combination with' oxygen to produce combustion. The ignition temperatures for several of the combustible constituents of fuels are presented in Table 7. ' HEAT OF COMBUSTION As previously stated, the process of combustion results in the evolution of heat. The heat generated by the complete combustion of a unit of fuel is constant for a given- combination of combustible elements and com pounds, and is known as the heal of combustion, calorific value, or heating value of the fuel. The heat of combustion of the several substances found in the more common fuels is given in Table 7. The calorific value of a fuel may be determined either by direct measure-' ment of the heat evolved during combustion in a calorimeter, or it may be computed-from the ultimate analysis and the heat of . combustion of- the,several chemical elements in the fuel. When the heating value ofa fuel is determined in a calorimeter the water vapor is condensed- and the ' latent heat of vaporization is included in the heating value of the fuel: : The heating value so determined is termed the gross or higher; heating value and this is.what is ordinarily meant when the heating value ofa; fuel is specified. In burning the fuel, however, the products of combus tion are not cooled to the dew-point and the higher heating value cannot, be utilized. . \ '. When combustion is complete, the carbon in the fuel unites with oxygen l to form carbon dioxide; GOs, the hydrogen unites with oxygen to form , water vapor, IhO, and the nitrogen, being inert, passes through the reaction without change. When combustion, is incomplete, some of the r carbon may unite with oxygen to form carbon monoxide,- CO, and some of the'hydrogen and hydrocarbon gases may not'be burned at'all. When carbon monoxide or other combustible gases are present in the flue gases, considerably less heat is produced per unit of fuel.consumed,and a lower combustion efficiency is obtained. Incomplete combustion may result from any or all of the following three conditions: I.-Inadequate air supply. ' 2. Insufficient mixing of the air and gases. 3. A temperature too low to produce ignition or maintain combustion: