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Oil - How Oil Is Refined

capacity crude utilization distillation

Before oil can be used by consumers, crude oil, lease condensate, and natural gas plant liquids must be processed into finished products. The first step in refining is distillation, in which crude oil molecules are separated according to size and weight.

During distillation, crude oil is heated until it turns to vapor. (See Figure 2.3.) The vaporized crude enters the bottom of a distillation column, where it rises and condenses on trays. The lightest vapors, such as those of gasoline, rise to the top. The middleweight vapors, such as those of kerosene, rise about halfway up the column. The heaviest vapors, such as those of heavy gas oil, stay at the bottom. The vapors at each level are then condensed to liquid as they are cooled. These liquids are drawn off, and the processes of cracking and reforming further refine each portion. Cracking converts the heaviest fractions of separated petroleum into lighter fractions to produce jet fuel,

TABLE 2.1

Refinery capacity and utilization, selected years, 1949–2003
Operable refineries
Year Number1 Capacity2 (thousand barrels per day) Gross input to distillation units (thousand barrels per day) Utilization3 (percent)
1Through 1956, includes only those refineries in operation on January 1; beginning in 1957, includes all "operable" refineries on January 1.
2Capacity on January 1.
3Through 1980, utilization is derived by dividing gross input to distillation units by one-half of the current year Januray 1 capacity and the following year January 1 capacity. Percentages were derived from unrounded numbers. Beginning in 1981, utilization is derived by averaging reported monthly utilization.
R=Revised.
P=Preliminary.
Web Pages: For data not shown for 1951–1969, see http://www.eia.doe./emeu/aer/petro.html. For related information, see http://www.eia.doe.gov/oil_gas/petroleum/info_glance/petroleum.html.
SOURCE: "Table 5.9. Refinery Capacity and Utilization, Selected Years, 1949–2003," in Annual Energy Review 2003, U.S. Department of Energy, Energy Information Administration, Office of Energy Markets and End Use, September 7, 2004, http://www.eia.doe.gov/emeu/aer/pdf/aer.pdf (accessed September 28, 2004)
1949 336 6,231 5,556 89.2
1950 320 6,223 5,980 92.5
1955 296 8,386 7,820 92.2
1960 309 9,843 8,439 85.1
1965 293 10,420 9,557 91.8
1970 276 12,021 11,517 92.6
1971 272 12,860 11,881 90.9
1972 274 13,292 12,431 92.3
1973 268 13,642 13,151 93.9
1974 273 14,362 12,689 86.6
1975 279 41,961 12,902 85.5
1976 276 15,237 13,884 87.8
1977 282 16,398 14,982 89.6
1978 296 17,048 15,071 87.4
1979 308 17,441 14,955 84.4
1980 319 17,988 13,796 75.4
1981 324 18,621 12,752 68.6
1982 301 17,890 12,172 69.9
1983 258 16,859 11,947 71.7
1984 247 16,137 12,216 76.2
1985 223 15,659 12,165 77.6
1986 216 15,459 12,826 82.9
1987 219 15,566 13,003 83.1
1988 213 15,915 13,447 84.7
1989 204 15,655 13,551 86.6
1990 205 15,572 13,610 87.1
1991 202 15,676 13,508 86.0
1992 199 15,696 13,600 87.9
1993 187 15,121 13,851 91.5
1994 179 15,034 14,032 92.6
1995 175 15,434 14,119 92.0
1996 170 15,333 14,337 94.1
1997 164 15,452 14,838 95.2
1998 163 15,711 15,113 96.5
1999 159 16,261 15,080 92.6
2000 158 16,512 15,299 92.6
2001 155 16,595 15,369 92.6
2002 153 16,785 R15,180 R90.7
2003P 149 16,757 15,505 92.5

motor gasoline, home heating oil, and less-residual fuel oils, which are heavier and used for naval ships, commercial and industrial heating, and some power generation. Reforming is used to increase the octane rating of gasoline.

Refining is a continuous process, with crude oil entering the refinery at the same time that finished products leave by pipeline, truck, and train. Although storage tanks surround refineries, they have limited storage capacity. If there is a malfunction and products cannot be processed, they may be burned off (flared) if no storage facility is available. While a small flare is normal at a refinery or a chemical plant, a large flare, or many flares, likely indicates a processing problem.

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