Oil refinery

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View of the Tosco (ex Valero, originally Shell) Martinez oil refinery
View of the Tosco (ex Valero, originally Shell) Martinez oil refinery

An oil refinery is an industrial process plant where crude oil is processed and refined into useful petroleum products.



Raw oil or unprocessed ("crude") oil is not very useful in the form it comes in out of the ground. It needs to be broken down into parts and refined before use in a solid material such as plastics and foams, or as petroleum fossil fuels as in the case of automobile and airplane engines.

Oil can be used in so many various ways because it contains hydrocarbons of varying molecular masses and lengths such as paraffins, aromatics, naphthenes (or cycloalkanes), alkenes, dienes, and alkynes.

Crude oil is separated into fractions  by fractional distillation. The heavier fractions, that emerge from the bottom of the fractionating column are often broken up (cracked) to make more useful products.
Crude oil is separated into fractions by fractional distillation. The heavier fractions, that emerge from the bottom of the fractionating column are often broken up (cracked) to make more useful products.

Hydrocarbons are molecules of varying length and complexity made of hydrogen and carbon. Their various structures give them their differing properties and thereby uses. The trick in the oil refinement process is separating and purifying these. All these different hydrocarbons have different boiling points, which means they can be separated by distillation.

Once separated and any contaminants and impurities have been removed, the oil can be either sold without any further processing, or smaller molecules such as isobutane and propylene or butylenes can be recombined to meet specific octane requirements by processes such as alkylation or less commonly, dimerization. Octane can also be improved by catalytic reforming, which strips hydrogen out of hydrocarbons to produce aromatics, which have much higher octane ratings. Intermediate products such as gasoils can even be reprocessed to break a heavy, long-chained oil into a lighter short-chained one, by various forms of cracking such as Fluid Catalytic Cracking, Thermal Cracking, and Hydrocracking. The final step in gasoline production is the blending of fuels with different octane ratings, vapor pressures and other properties to meet product specifications.

Products of oil refinery

Safety and environmental concerns

MiRO refinery at Karlsruhe
MiRO refinery at Karlsruhe

Oil refineries can become very large and sprawling complexes with vast numbers of pipes running throughout the facility. The refining process can cause many different chemicals to be released into the atmosphere - consequently a notable odor may accompany the presence of a refinery. Environmental groups have lobbied many governments to increase restrictions on how much material refineries can release, and many refineries have installed equipment and changed practices to lessen the environmental impact. In the United States, there is strong pressure to prevent the development of new refineries, and none have been built in the country for more than three decades. Many existing refineries have been expanded during that time however.

Environmental and safety concerns mean that oil refineries are usually located a safe distance away from major urban areas. Nevertheless, there are potentially dangerous exceptions to this rule, a particularly notable one being the Santa Cruz refinery 1 (Tenerife, Spain), which is sited in a densely-populated city center and next to the only two major evacuation routes in and out of the city.

Common process units found in a refinery

  • Atmospheric Distillation Unit (distills crude oil into fractions)
  • Vacuum Distillation Unit (further distills residual bottoms after atmospheric distillation)
  • Naphtha Hydrotreater Unit (desulfurizes naphtha from atmospheric distillation)
  • Catalytic Reformer Unit (uses hydrogen to break long chain hydrocarbons into lighter elements that are added to the distiller feedstock)
  • Distillate Hydrotreater Unit (desulfurizes distillate (diesel) after atmospheric distillation)
  • Fluid Catalytic Converter Unit
  • Dimerization Unit
  • Isomerization Unit
  • Gas storage units for propane and similar gaseous fuels at pressure sufficient to maintain in liquid form - these are usually spherical
  • Storage tanks for crude oil and finished products, usually cylindrical, with some sort of vapor enclosure and surrounded by an earth berm to contain spills

Specialized end product units

These will blend various feedstocks, mix appropriate additives, provide short term storage, and prepare for bulk loading to trucks, barges, product ships, and railcars.

  • Gaseous fuels such as propane, stored and shipped in liquid form under pressure in specialized railcars to distributors.
  • Liquid fuels blending (producing automotive and aviation grades of gasoline, kerosene, various aviation turbine fuels, and diesel fuels, adding dyes, detergents, antiknock additives, oxygenates, and anti-fungal compounds as required). Shipped by barge, rail, and tanker ship. May be shipped regionally in dedicated pipelines to point consumers, particularly aviation jet fuel to major airports, or piped to distributors in multi-product pipelines using product separators called "pigs".
  • Lubricants (produces light machine oils, motor oils, and greases, adding viscosity stabilizers as required), usually shipped in bulk to an offsite packaging plant.
  • Wax, used in the packaging of frozen foods, among others. May be shipped in bulk to a site to prepare as packaged blocks.
  • Sulfuric acid finishing and shipping. This is a useful industrial material, usually prepared as oleum, a byproduct of sulfur removal from fuels.
  • Bulk tar shipping for offsite unit packaging for use in tar-and-gravel roofing.
  • Asphalt unit. Prepares bulk asphalt for shipment.
  • Asphalt concrete unit. Mixes asphalt with aggregate on demand to truck hot for local road surfacing use.

Co-plant siting

Frequently a chemical plant will be sited adjacent to a refinery, utilizing intermediate products as feedstocks for the production of specialized materials such as plastics and various toxic materials used in agribusiness


The world's first oil refinery opened at Ploieşti, Romania in 1856 [1]. Several other refineries were built at that location with investment from United States companies before being taken over by Nazi Germany during World War II. Most of these refineries were bombarded by the US Air Force in Operation Tidal Wave, August 1, 1943.

Another early example is Oljeön preserved as a museum at the UNESCO world heritage site Engelsberg. It started operation in 1875 and is part of the Ecomuseum Bergslagen.

The largest oil refinery in the world is in Ras Tanura, Saudi Arabia, owned by Saudi Aramco. The city was originally built as a sea port, but actually developed because of the huge refinery area. For most of the 20th century the largest refinery of the world was that of Abadan in Iran.

A refinery at night
A refinery at night

See also

External links

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