Oil refinery
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View of Shell Oil Refinery in Martinez, California. |
An
oil refinery is an industrial
process plant where
crude oil is processed and refined into useful
petroleum products, such as
gasoline and
diesel fuel.
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Crude oil is separated into fractions by fractional distillation. The fractionating column is cooler at the top than at the bottom so the vapours can condense more easily while the moving up the column. The heavier fractions that emerge from the bottom of the fractionating column are often broken up (cracked) to make more useful products. |
Raw oil or unprocessed ("crude") oil is not very useful in the form it comes in out of the ground. Although "light, sweet" (low viscosity, low sulfur) oil has been used directly as a burner fuel for steam vessel propulsion, the lighter elements form explosive vapors in the fuel tanks and so it is quite dangerous, especially so in
warships. For this and many other uses, the oil needs to be separated 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
ship,
automobile and
aircraft engines. These different
hydrocarbons have different
boiling points, which means they can be separated by
distillation. Since the lighter liquid elements are in great demand for use in internal combustion engines, a modern refinery will convert heavy liquid and lighter gaseous elements into these higher value products using complex and energy intensive processes.
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.Hydrocarbons are molecules of varying length and complexity made of only
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.
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.
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Asphalt*
Diesel fuel*
Fuel oils
*
Gasoline*
Kerosene*
Liquid petroleum gas (LPG)
*
Lubricating oils
*
Paraffin wax*
TarOil refineries are typically large sprawling
industrial complexes with extensive
piping running throughout. The refining process releases numerous different chemicals into the
atmosphere; consequently, there are substantial
air pollution emissions
[AP 42, Compilation of Air Pollutant Emission Factors] and a notable
odor normally accompanies the presence of a refinery. Aside from air pollution impacts there are also wastewater concerns,
upset risks of fire and explosion, and both
occupational noise and environmental
noise health effects.
The public has demanded that many governments place restrictions on contaminants that refineries release, and most refineries have installed the equipment needed to comply with the requirements of the pertinent environmental protection regulatory agencies. In the
United States, there is strong pressure to prevent the development of new refineries, and no major refinery has been built in the country since
Marathon's Garyville facility in
1976. However, many existing refineries have been expanded during that time. It is likely that more stringent conditions will be placed on refineries in the future worldwide, leading to a change in the
net energy balance of production against petroleum and in favor of
ethanol fuel. These environmental restrictions and pressure to prevent construction of new refineries have also contributed to rising fuel prices in the Unites States.
Environmental and safety concerns mean that oil refineries are sometimes located some distance away from major urban areas. Nevertheless, there are many instances where refinery operations are close to populated areas and pose health risks such as in
Tenerife, Spain
[Smoke, oil spills and now radiation - whatever next? www.atan.org ], which is sited in a densely-populated city center and next to the only two major evacuation routes in and out of the city. In
California's Contra Costa County and
Solano County, a shoreline necklace of refineries and associated chemical plants are adjacent to urban areas in
Richmond,
Martinez, California,
Pacheco,
Concord,
Pittsburg,
Vallejo and
Benicia, with occasional accidental events that require "shelter in place" orders to the adjacent populations.
*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. Must hydrotreat the naphtha before sending to a Catalytic Reformer Unit.)
*
Catalytic Reformer Unit (contains catalyst used to convert the naphtha-boiling range molecules into higher octane reformate (reformer product). The reformate has higher content of aromatics, olefins, and cyclic hydrocarbons). An important byproduct of a reformer is hydrogen released during the catalyst reaction. The hydrogen is used either in the hydrotreaters and hydrocracker.)
*Distillate Hydrotreater Unit (desulfurizes distillate (diesel) after atmospheric distillation)
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Fluid Catalytic Cracking (FCC) Unit (upgrades heavier fractions into lighter, more valuable products)
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Hydrocracker Unit (upgrades heavier fractions into lighter, more valuable products)
* Coking unit (processes asphalt into gasoline and diesel fuel, leaving coke as a residual product)
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Alkylation unit (produces high octane component for gasoline blending)
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Dimerization Unit
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Isomerization Unit (chemically combines two smaller propane/butane/pentane molecules to form a gasoline molecule)
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Steam reforming Unit (produces hydrogen for the hydrotreaters or hydrocracker)
*Liquified gas storage units for propane and similar gaseous fuels at pressure sufficient to maintain in liquid form - these are usually spherical or bullets (horizontal cylinder with rounded ends).
*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
*Utility units such as
cooling towers for circulating cooling water, boiler plants for steam generation, and
wastewater collection and treating systems to make such water suitable for reuse or for disposal.
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
pipeline inspection gauges ("pigs").
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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.
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Sulfuric acid finishing and shipping. This is a useful industrial material, usually prepared and shipped as the acid precursor
oleum, a byproduct of sulfur removal from fuels.
*Bulk
tar shipping for offsite unit packaging for use in tar-and-gravel roofing.
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Asphalt unit. Prepares bulk asphalt for shipment.
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Asphalt concrete unit. Mixes asphalt with aggregate on demand to truck hot for local road surfacing use.
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 or
agrichemicals.
The world's first oil refinery opened at
Ploieşti,
Romania in
1856 [WORLD EVENTS: 1844-1856 www.pbs.org]. 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. Since, they have been rebuilt, and currently pose somewhat of an environmental concern.
Another early example is
Oljeön, now 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.
Early US refineries processed crude oil to recover the
kerosene. Other products (like gasoline) were considered wastes and were often dumped directly into the nearest river. The invention of the automobile shifted the demand to gasoline and diesel, which remain the primary refined products today. Refineries pre-dating the EPA were very toxic to the environment. Strict legislation has mandated that refineries meet modern air and water cleanliness standards. In fact, obtaining a licence to build even a modern refinery with minimal impact on the environment (other than CO2 emmissions) is so difficult and costly that no new refineries have been built in the United States since 1976. As a result, the US is becoming more and more dependent on the imports of finished gasoline, as opposed to incremental crude oil.
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A refinery at night. The gas flare is in the center of the picture. |
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Air pollution*
AP 42 Compilation of Air Pollutant Emission Factors*
Cooling tower*
Ethanol fuel*
Gas flare*
List of oil refineries*
Net energy balance*
Refinery*
Complete, detailed refinery description*
Petroleum Refinery Planning and Optimization Using Linear Programming*
Student's Guide to Refining*
Finance*
Global refinery shortage shifts power balance*
Discover Petroleum, an educational site from the UK
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Short introduction to oil refining in a slideshow*
Ecomuseum Bergslagen - history of Oljeön, Sweden
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An example flowchart of fractions from crude oil at a refinery
*[
1] Guide to Refining
*[
2]
*[
3]
