Document mp8j8aBVaao17YD8m2ROp37od

Hcri 340 CHAPTER 14 1955.G&&55.-J Fuels and Combustion 341 A. Indexes based on a single physical test: (1) API gravity7, (2) Aniline.point* (3) Institute of Petroleum smoke test,,(4) Carbon-Hydrogen ratio based on hue-gas analysis or ultimate analysis, and (5) Percent aromatics determined by sulfuric'acid absorption tests*. ! B. Indexes based on two or more physical tests: (1) i/iesel index' based on API gravity and aniline point, (2) Institute of Petroleum cetane number 10 based on the API gravity and 50 percent distillation point, (3) Universal Oil Products, characteri zation factor" based on specific gravity and average boiling point; (4) Burning index11 based on API gravity and 50 percent distillation point, and (5) Estimated Carbon: Hydrogen ratio11 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 o Smoke Spot Reflectonce for 60% of Ultimate CO* A Per Cent of Ultimate GO* for 60% Relative Reflectance ' fuel oil indexes for particular'applications, even though correlations be tween them and burning qualities have been observed. In other words, none of the above mentioned indexes has yet gained sufficiently wide usage to replace the grading of oils by Commercial Standard, CS12-48. Experiments have shown that thermal decomposition or cracking of hydrocarbons begins at a temperature of approximately 680 F at atmos pheric pressure, although the temperature of cracking varies somewhat above and below this value. Thus pure distillate fuel oils, whose end point does not exceed this temperature, can usually be completely evaporated in vaporizing-type oil burners at atmospheric pressure without leaving a residue or without cracking of the hydrocarbons. Fuel oils that cannot be completely evaporated below 680 F are likely to undergo cracking in vaporizing type burners, with the resulting possibilities of smoky combus tion and residues in the oil burner. 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 maxi mum end point of 625 F, it can in most cases be completely evaporated 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 maximum distillation temperature of 675 F at the 90 percent point, would frequently be cracked in a vaporizing burner. How ever some No. 2 fuel oils do not crack before complete evaporation takes place. Vaporizing-type burners can generally 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. 20 40 60 100 BURNING INDEX Fig. 4. Correlation of Burning Qualities of Fuel Oils with Four Combustion Indexes In vaporizing burners, preheating of the combustion air and fuel, com plete evaporation of fuel before it is exposed to intense heat, and thorough mixing of the air and gasified fuel promote complete combustion without smoke and with a minimum of excess air. In pressure-type burners pre heating of the combustion air, a maximum of air turbulence, good atomiza-ofthe fuel, and high combustion chamber temperatures (preferably red hot) promote smokeless combustion with a minimum of excess air. j^atural draft burners depend on the motivating force of a chimney to induce enough air into the burner for complete combustion. Forced draft conducted with the Oil Heat Institute Reference Test Unit14 indicated go0^ (l'iirnr? are supplied with combustion air by means of a blower or fan; correlation between the smoking tendency of fuel oils and API gravity, burning index, Diesel index, and hydrogen-carbon ratio for a limited num ber of oils in laboratory apparatus simulating a pressure-atomizing burner. These results are shown graphically in Fig. 4. Smoking tendency is giv ^ e chumicy merely conducts the flue gases outdoors and prevents leakage ,. J*ue gases inside the building. More details on the operation of the 1 erent kinds of oil burners and on chimneys and draft will be found in napters 15 and 17 respectively. here in terms of smoke spot reflectance, the light reflectance of a smokesoiled filter paper. A high reflectance, relative to a clean filter paPr> FUEL GASES indicates low smoking tendency. COz/U is the observed COz divided by uel gases employed for various heating and air conditioning processes the ultimate or maximum theoretical COz expressed as a percentage. Rem mar,Uf U^ United States fall into three broad classifications: natural, and Hersberger12 have related burning qualities and burning index lor various oils in a wall-flame burner. Cauley and Delgass13 cite test resu on combustion indexes obtained with vaporizing burners. The pres comh* an<^ liquefied petroleum. Natural gas is a mixture of several from US , e. ases an.d, usually, a small percentage of inert gases obtained in 2fW ^C fr'Hnations. Natural gas is produced in significant amounts experimental data are probably too meager as yet to correlate adequately Qki,,, sta*'es- Texas is by far the largest producer, followed by Louisiana, Lany one burners. of these indexes Few attempts with have burning qualities of oil fuel been made to suggest limits for for all any toyfpethses0,e ; nC iade <vfna' California, Kansas, and West Virginia. by the distillation or cracking of oil or coal, Manufactured gas is by the steam carbon. rj III I