Oil - How Oil Is Refined

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.