Kerosene
Kerosene is that fraction of crude petroleum that boils between about 330° to 550° F (183° to 305° C) (i.e. the distillate cut between gasoline and heavy fuel oil). What is usually thought of as kerosene, the domestic fuel or "range oil" commonly used for space heaters, is only a small part of this fraction. Diesel fuel, aviation jet fuel, and No. 1 and No. 2 heating oils also come from this general boiling range.
History
Petroleum was discovered by Drake in Pennsylvania in 1859. It is a mixture of hydrocarbon compounds ranging from highly flammable volatile materials like propane and gasoline to heavy fuel oil, waxes, and asphalt. It was soon discovered that crude oil could be separated by distillatoin in to various factions according to their boiling point (molecular weight). Kerosene, a middle distillate, was the first product made from petroleum that had a substantial commercial market. The Pennsylvania crudes happened to be low in sulfurous and aromatic components, so the straight run (unrefined) distillate was relatively odorless and clean-burning. The distillate rapidly replaced whale oil in lamps, and coal in home room heaters, and by 1880 kerosene accounted for 75 percent by volume of the crude oil produced. However, after the turn of the century, the advent of electric lights soon made kerosene lamps obsolete. Later, central home heating based on heating oil and natural gas largely replaced space heating based on kerosene, wood, and coal.
By 1980 production of "range oil" type kerosene was less than one percent of the crude oil refined. By the end of the twentiteth century, kerosene's use for space heating, water heating, cooking, and lighting was largely limited to camps, cabins, and other facilities remote from centralized energy sources. Kerosene is a relatively safe fuel, but to prevent fires care must be taken not to tip over operating kerosene appliances. While burner designs have been improved to minimize accidental upset, carbon monoxide formation is still a potential hazard. This deadly gas can result from use of dirty, poorly maintained burners or if the heater is used in a space with insufficient ventilation.
Kerosene is also used as a solvent for herbicides and insect sprays. However, most of the kerosene fraction in crude oils is used to make Diesel engine fuel and aviation jet fuel.
Properties
Kerosene is an oily liquid with a characteristic odor and taste. It is insoluble in water, but is miscible with most organic solvents. Structurally, it is composed mostly of saturated hydrocarbon molecules containing twelve to fifteen carbon atoms. When a sweet (low sulfur content) paraffinic crude oil is cut to the proper boiling range in a refinery's atmospheric pipe still, the resulting kerosene may only require a drying step before use. However, if the crude oil contains aromatic ring compounds like xylenes, they must be eliminated by solvent extraction because they burn with a smoky flame. Olefinic (unsaturated) molecules in this boiling range must also be removed by refining, usually by hydrogenation. These compounds tend to form color bodies and polymerize, thus imparting poor storage stability. Sulfur compounds are undesirable because of their foul odor and formation of air polluting compounds. They can also be removed by hydrogenation.
Other important properties include flash point, volatility, viscosity, specific gravity, cloud point, pour point, and smoke point. Most of these properties are related directly to the boiling range of the kerosene and are not independently variable. The flash point, an index of fire hazard, measures the readiness of a fuel to ignite when exposed to a flame. It is usually mandated by law or government regulation to be 120° or 130° F (48° or 72° C). Volatility, as measured by the boiling range, determines the ease with which the fuel can evaporate in a burner or lamp. Viscosity measures the fuel's resistance to flow, and thus determines the ease with which it can be pumped or atomized in a burner nozzle. Specific gravity is the ratio of the weight of a given volume of fuel to the same volume of water. Denser, higher gravity fuels have higher heating values. Typical kerosenes have heating values of about 139,000 BTU per gallon. Cloud and pour points indicate the temperature at which the precipitation of waxy constituents affect performance in cold climates. As wax begins to form (cloud point) there is danger of plugging fuel nozzles and filters. At an even lower temperature (the pour point), enough wax has formed so that the fuel sets up and can no longer flow as a liquid. The smoke point is the flame height in millimeters at which a kerosene lamp begins to smoke.
Other properties of interest are carbon residue, sediment, and acidity or neutralization number. These measure respectively the tendency of a fuel to foul combustors with soot deposits, to foul filters with dirt and rust, and to corrode metal equipment. Cetane number measures the ability of a fuel to ignite spontaneously under high temperature and pressure, and it only applies to fuel used in Diesel engines. Typical properties of fuels in the kerosene boiling range are given in Table 1.
Because of its clean burning characteristics, kerosene commands a higher price than other fuels in its boiling range.
| | Kerosene | Diesel Fuel | #2 Heating Oil |
| Gravity, A.P.I. | 40 | 37 | 34 |
| Boiling Range, °F. | 325 - 500 | 350 - 650 | 325 - 645 |
| Viscosity, SSU @ 100° F. | 33 | 35 | 35 |
| Flash Point, °F. | 130 | 140 | 150 |
| Sulfer, Weight Percent | 0.05 - 0.12 | 0.30 | 0.40 |
Equipment
The technology of kerosene burners is quite mature. The most popular kerosene heater is the perforated sleeve vaporizing burner or range burner (Figure 1). It consists of a pressed steel base with concentric, interconnected grooves and perforated metal sleeves, between which combustion takes place. Kerosene is maintained at a depth of about 1/4 inch in the grooves. As the base heats up, oil vaporizes from the surface, and the flame lights from asbestos wicks. Combustion air is induced by natural draft. The flame is blue, and the burner is essentially silent, odorless, and smokeless.
For larger capacity space heaters vaporizing pot burners are used (Figure 2). They consist of a metal pot perforated with holes for combustion air. Oil flows into the bottom of the pot by gravity, and is vaporized from the hot surface. Fuel vapors mix with primary air from the lower holes, then with additional secondary air in the upper section, and burn at the top of the vessel. Between periods of high demand, pot burners idle at a low fire mode. The flames burn in the bottom section of the pot, at a fraction of the high fire fuel feed rate, using only primary air. Thus no extraneous pilot light or ignition source is required for automatic operation.
Kerosene lamps have a flat cloth wick. Flame height is determined by the height of the wick, which is controlled by a ratchet knob. A glass chimney ensures both safety and a stable, draft-free flame.
Bibliography
Gary, J. H., and Handwerk, G. E. (1993). Petroleum Refining Technology and Economics, 3rd ed. New York: M. Dekker.
Ramose, D. (1983). Kerosene Heaters. Blue Ridge Summit, PA: Tab Books.
U.S. Consumer Product Safety Commission. (1988). What You Should Know About Kerosene Heaters. Washington, DC: U.S. Government Printing Office.
Wood, Q. E. (1986). Quaker State Roots Go Deep in World's First Oil Field. New York: Newcomen Society of the United States.
Yergin, D. (1991). The Prize: the Epic Quest For Oil, Money and Power. New York: Simon & Schuster.
This is the complete article, containing 1,251 words
(approx. 4 pages at 300 words per page).
