Document Lg7noD0noy6Mx6QOVaebxbyEb

486 CHAPTER 33 1960 Guide boiling point, (4) Burning index" based on API gravity and SO percent distillation point, and (5) Estimated Carbon* Hydrogen ratio12 based on API gravity aniline point, and boiling point. Various investigators have shown correlation between one or more of these indexes and the performance of fuel oils in oil burners. Experiments conducted with the Oil Heat Insti tute Reference Test Unit" indicated good correlation between the smoking tendency of fuel oils and API gravity, burning index, Diesel index, and hydrogen-carbon ratio for a limited number of oils in laboratory apparatus simulating a pressureatomizing burner. These results are shown graphically in Fig. 3. Smplring tendency is given here in terms of smoke-spot Fig. 3 .... Correlation of Burning Qualities of Fuel Oils with Four Combustion Indexes reflectance, the light reflectance of a smoke-6oiled filter paper. A high reflectance, relative to a clean filter paper, indicates low smoking tendency. COt/U is the observed CO, divided by the ultimate or maTinuim theoretical CO* expressed as a percentage. Reid and Hersberger" have related burning qualities and burning index for various oils in a wall-flame burner. Cauley and Delgass" cite test results on combustion indexes obtained with vaporizing burners. The present ex perimental data are probably too meager as yet to correlate adequately any one of these indexes with burning qualities of oil fuel for &L1 types of burners. Few attempts have been made to suggest limits for any of these fuel oil indexes for particular applications, even though correlations between them and burning qualities have been observed. Experiments have shown that the rate of thermal decom position or cracking of hydrocarbons becomes appreciable at a temperature of approximately 6S0 F at atmospheric pres sure. Thus distillate fuel oils, whose end point approximates this temperature, cannot be completely evaporated in vapor izing-type oil burners at atmospheric pressure without leav ing a residue. A complete distillation curve cannot usually be determined for fuel oils containing fractions that evaporate above 680 F. Since No. 1 grade fuel oil in Commercial Standard CS12-48 has a raAwmuin end point of 625 F, although an end point this high is rare, it can in most cases be completely evapo rated in atmospheric vaporizing burners without cracking. although occasionally an oil is found that undergoes cracking at temperatures below 625 F. By the same criterion, No. 2 grade fuel oil in the Commercial Standard, which can have a moTTiniim Higt.illfltinn temperature of 675 F at the 90 per cent point, would generally be cracked in a vaporizing burner. Vaporizing-type burners, therefore, can use only No. 1 fuel oil with assurance that thermal decomposition will not occur during combustion. On the other hand either No. 1 or No. 2 fuel oils may be employed in high- or low-pressure atomizing burners when the temperatures developed in the combustion chamber are high enough to assure complete combustion, even if the fuel oil is thermally decomposed. In vaporizing burners there is complete evaporation of fuel before it is exposed to intense heat. Thorough mixing of the air and gasified fuel promote complete combustion with out smoke and with a minimum of excess air. In pressuretype burners good atomization of the fuel, good mixing of the atomized oil with the air, air turbulence, and high com bustion chamber temperatures (preferably red hot) promote smokeless combustion with a minimum of excess air. Natural draft burners depend on the motivating force of a chimney to induce enough air into the burner for complete combustion. Forced draft burners are supplied with com bustion air by mp*ns of a blower or fan; the chimney merely conducts the flue gases outdoors and prevents leakage of flue gases into the building. More details on the operation of the different kinds of oil burners and on chimneys and draft will be found in Chapters 34 and 36 respectively. FUEL GASES Fuel grafts employed for various heating and air condition ing processes throughout the United States fall into three broad classifications: natural, manufactured, and liquefied petroleum. Natural gas is a mixture of several combustible and, usually, a small percentage of inert gases obtained from geologic formations. Manufactured gas is made by the distillation or cracking of oil or coal, by the steam-carbon reaction, or by combinations of these processes. Liquefiedpetroleum gases (propane and butane) are higher hydrocar bon gases normally obtained as a by-product of oil refineries or by stripping natural gas. These two compounds are gen erally gaseous under usual atmospheric conditions although they can be liquefied by the application of moderate pres sures at normal temperatures. In American gas practice the heating value of a gas and also appliance efficiencies are based on the gross heating value. This value is the number of Btu liberated by complete combustion, at constant pressure, of one cubic foot of gas saturated with water vapor and measured at 60 F and 30 in. of mercury, with air at the same temperature and pressure. Products of combustion are cooled to the initial temperature of the gas and air and the water formed by combustion of free and combined hydrogen is condensed to the liquid state. Classification of Gases Natural gas contains from 55 to 98 percent methane with various percentages of higher hydrocarbons, chiefly ethane. In addition to these components, non-combustible gases such as carbon dioxide, nitrogen, and helium are sometimes pres ent. Percentages of the different components vary with the area from which natural gas is withdrawn. They may even vary slightly from any given well during its lifetime but these variations are inconsequential insofar as the utilization of the gas is concerned. Heating values of natural gases vary from 900 to 1400 Btu per cu ft but the usual range for use is from Fuels and Combustion 487 Table 6.... Analyses of Natural Gos Distributed in Various Cities* Coiufrtuenf* of Cot*1--Pereenf by Volume cST* *0^Metfione No. City CM, CtH* Solone CtHu CO, o. N, Specific Grarity Bto per co ft. Dry* (Grottf 1 Akron, Ohio 2 Atlanta, Ga. 3 Baltimore, Md. 4 Canton, Ohio 5 Cheyenne, Wyo. 6 Cincinnati, Ohio 7 Cleveland, Ohio 8 Columbus, Ohio 9 Dallas, Texas 10 Denver, Colo. 88.00 94.95 93.80 88.00 72.40 93.70 88.00 95.70 85.00 73.70 8.10 1.30 3.60 8.10 5.70 0.40 0.33 0.90 0.40 3.40 3.90 8.10 2.90 7.10 5.40 0.60 0.40 2.40 3.30 0.20 0.10 0.70 0.20 1.20 0.10 0.20 0.50 1.20 0.10 0.09 0.10 0.20 0.10 0.14 0.10 trace 0.10 0.10 0.40 0.10 0.70 0.70 0.60 0.70 0.80 0.70 1.30 0.60 0.15 0.10 0.10 0.10 2.30 2.39 0.40 2.30 17.10 0.614 0.5974 0.602 0.614 0.700 1052 1008 1062 1052 971 0.90 2.30 0.10 4.00 16.15 0.605 0.614 0.609 0.650 0.692 1071 1052 1037 1079 973 11 Detroit, Mich. 12 Houston, Texas 13 Kansas City, Mo. 14 Los Angeles, Calif. 15 Memphis, Tesa. 71.70 93.94 79.21 85.10 92.80 14.50 2.88 4.54 7.40 4.20 0.69 2.71 3.10 0.80 0.44 1.53 0.40 0.20 0.13 0.48 0.10 0.10 0.12 0.10 0.10 1.30 0.10 0.10 1.00 0.20 13.50 0.62 11.31 3.80 0.80 0.690 0.605 0.684 0.648 0.600 999 1069 1024 1089 1049 16 Milwaukee, Wis. 17 Minneapolis, Minn. 18 New Orleans, La. 19 Oklahoma City, Okia. 20 Omaha, Neb. 72.20 72.02 92.89 83.23 75.78 6.30 15.55 3.23 7.91 4.97 3.80 1.15 2.82 3.24 1.00 0.59 0.75 2.12 0.24 0.43 0.19 0.10 0.49 0.24 0.20 0.07 0.96 0.14 16.70 12.26 1.22 3.66 13.55 0.703 0.681 0.611 0.679 0.685 975 1002 1065.7 1068 1011 21 Pittsburgh, Pa, 22 Pueblo, Colo. 23 St. Louis, Mo. 24 San Diego, Calif. 25 San Francisco, Calif. ' 90.12 74.90 87.60 80.24 86.50 5.64' 5.20 7.40 12.70 6.90 1.39 3.20 0.48 1.10 1.60 0.30 2.90 _ -0.30 0.07 0.10 0.04 0.10 0.04 trace 0.68 0.30 1.00 2.05 0.50 0-10 1.58 15.20 4.00 2.97 2.80 0.6176 0.684 0.610 0.672 0.640 1071 975 1027 1083.5 1090 26 Toledo, Ohio 27 Tulsa, Okla. 28 Washington, D. C. 29 Wichita, Kan. 30 Youngstown, Ohio 95.70 78.44 87.40 79.62 88.00 2.90 13.72 7.10 . 6.40 8.10 1.35 2.80 1.42 0.40 0.47 0.90 1.12 0.20 0.05 0.40 0.48 0.10 0.14 0.10 1.30 0.20 0.20 0.10 0.70 1.20 0.10 0.10 0.10 4.57 1.20 10.62 2.30 0.609 0.663 0.630 0.660 0.614 1037 1073 1131 1051 1052 * This table ebetneted bom unpnbUabcd maniweript of tnd ed., Oo* Bnointon? Handbook, American Gal Annexation. ' b These are avenge analyses ss of November, 1951. The gal may vary considerably from this average. As dm supplies may be received from other sources, the analyses may change in the future. ' At 60 F and SO in. Hg, abeolute pressure. To convert to a saturated bass, deduct 1.7S pescent--i-e., 17J from 1000,19 from 1100 1000 to 1050 Btu (gross) per cu ft. Properties of natural gas as distributed in various cities are shown in Table 6. Manufactured gases such as coke oven and carburetted water gas, which were distributed with a beating value of 500 to 600 Btu per cu ft (gross), are no longer common in large communities due to the widespread availability of natural gas. Mixed gases are a result of increased distribution of natu ral gas, through transcontinental transmission lines, into areas having existing manufactured gas facilities. In such in stances some gas companies supply a 600 to 800 Btu mixture. Liquefied petroleum gases, such as propane and butane or mixtures thereof have calorific values ranging from 2500 to 3200 Btu per cu ft. Propane is generally available by the bottle or cylinder, or in bulk in tank truck, truck transport or tank car lots. Butane is generally not available in cylinders. In such cases the liquid evaporates when pressure is relieved, the heat necessary for vaporization being obtained from the surrounding air or ground. As butane boils at 32 F some pro vision is necessary for maintaining the gas above this tem perature or for lowering the partial pressure by dilution if the gas is utilized in colder climates. Propane, with a boiling point of --40 F, may be served in localities where temperatures sub stantiallybelow freezing are encountered. When employed for heating purposes, these gases are usually delivered by tank truck into bulk storage pressure vessels of sufficient size to give the customer an adequate supply of fuel. Both gases, mixed with air, or in undiluted form, are also extensively em ployed by gas companies to augment their base load supplies during peak load periods. In some smaller communities, where gas manufacturing plants are not economically feasible and natural gas is unavailable, liquefied petroleum gases or lique fied petroleum gas-air mixtures are supplied through mains in much the same manner as manufactured or natural gas.