An oil refinery is an industrial process plant where crude
oil is processed and refined into more useful petroleum products, such as
gasoline, diesel fuel,
asphalt base, heating oil, kerosene, and liquefied petroleum
gas.[1][2] Oil refineries are typically large sprawling industrial complexes with extensive piping running throughout, carrying streams
of fluids between large chemical processing units.
Operation
Crude oil is separated into fractions by
fractional distillation. The
fractionating column is cooler at the top than at the bottom because the fractions
at the top have lower
boiling points than the fractions at the bottom. The heavier
fractions that emerge from the bottom of the fractionating column are often broken up (
cracked) to make more useful products. All of the fractions are subsequently routed to other
refining units for further processing.
Raw oil or unprocessed ("crude") oil is not 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 fuels
and lubricants, and before some of the byproducts could be used in petrochemical processes to
form materials such as plastics, and foams. Petroleum fossil fuels are used in 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 hydrocarbons 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, forms 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 atoms. 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 purified of any contaminants and impurities, the fuel or lubricant can be sold without any further
processing. Smaller molecules such as isobutane and propylene or butylenes can be recombined to meet specific
octane requirements of fuels by processes such as alkylation
or less commonly, dimerization. Octane grade of gasoline 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.
Oil refineries are large scale plants, processing from about a hundred thousand to several hundred thousand barrels of crude oil per day. Because of the high capacity, many of the units are operated continuously (as
opposed to processing in batches) at steady state or approximately steady
state for long periods of time (months to years). This high capacity also makes process
optimization and advanced process control very desirable.
Major products of oil refineries
Most products of oil processing are usually grouped into three categories: light distillates (LPG, gasoline, naptha), middle
distillates (kerosene, diesel), heavy distillates and residuum (fuel oil, lubricating oils, wax, tar). This classification is
based on the way crude oil is distilled and separated into fractions (called distillates and residuum) as can be seen in the above drawing.[2]
Common process units found in a refinery
- Desalter unit washes out salt from the crude oil before it enters the atmospheric
distillation unit.
- Atmospheric Distillation unit distills crude oil into fractions. See Continuous
distillation.
- Vacuum Distillation unit further distills residual bottoms after atmospheric
distillation.
- Naphtha Hydrotreater unit uses hydrogen to
desulfurize naphtha from atmospheric distillation. Must hydrotreat the naphtha before sending to a Catalytic Reformer unit.
- Catalytic Reformer unit is 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 distillates (such as diesel) after atmospheric distillation.
- Fluid Catalytic Cracking (FCC) unit upgrades heavier fractions into lighter,
more valuable products.
- Hydrocracker unit uses hydrogen to upgrade heavier fractions into lighter, more
valuable products.
- Visbreaking unit upgrades heavy residual oils by thermally cracking them into lighter,
more valuable reduced viscosity products.
- Merox unit treats LPG, kerosene or jet fuel by oxidizing mercaptans to organic disulfides.
- Coking unit processes very heavy residual oils into gasoline and diesel fuel, leaving
petroleum coke as a residual product.
- Alkylation unit produces high-octane component for gasoline blending.
- Dimerization unit converts olefins into higher-octane gasoline
blending components. For example, butenes can be dimerized into isooctene which may subsequently be hydrogenated to form isooctane. There are also other uses for dimerization.
- Isomerization unit converts linear molecules to higher-octane branched molecules for
blending into gasoline or feed to alkylation units.
- 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 vessels or bullets (horizontal vessels with rounded ends.
- Storage tanks for crude oil and finished products, usually cylindrical, with some sort of vapor emission control and
surrounded by an earthen berm to contain spills.
- Amine gas treater, Claus unit, and tail
gas treatment for converting hydrogen sulfide from hydrodesulfurization into elemental sulfur.
- Utility units such as cooling towers for circulating cooling water, boiler plants for steam generation, instrument air systems for pneumatically
operated control valves and an electrical
substation.
- Wastewater collection and treating systems consisting of API separators, dissolved air flotation (DAF)
units and some type of further treatment (such as an activated sludge
biotreater) to make such water suitable for reuse or for disposal.[3]
Flow diagram of typical refinery
The image below is a schematic flow diagram of a typical oil refinery that
depicts the various unit processes and the flow of intermediate product streams that
occurs between the inlet crude oil feedstock and the final end products. The diagram depicts
only one of the literally hundreds of different oil refinery configurations. The diagram also does not include any of the usual
refinery facilities providing utilities such as steam, cooling water, and electric power as well as storage tanks for crude oil
feedstock and for intermediate products and end products.[1][4][5][6]
Schematic flow diagram of a typical oil refinery
Specialty end products
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").
- Lubricants (produces light machine oils, motor oils,
and greases, adding viscosity stabilizers as
required), usually shipped in bulk to an offsite packaging plant.
- Wax (paraffin), used in the packaging of frozen foods,
among others. May be shipped in bulk to a site to prepare as packaged blocks.
- Sulfur (or sulfuric acid), byproducts of sulfur
removal from petroleum which may have up to a couple percent sulfur as organic sulfur-containing compounds. Sulfur and sulfuric
acid are useful industrial materials. Sulfuric acid is usually prepared and shipped as the acid precursor oleum.
- Bulk tar shipping for offsite unit packaging for use in tar-and-gravel roofing.
- Asphalt unit. Prepares bulk asphalt for shipment.
- Petroleum coke, used in specialty carbon products or as solid fuel.
- Petrochemicals or petrochemical feedstocks, which are often sent to
petrochemical plants for further processing in a variety of ways. The petrochemicals may
be olefins or their precursors, or various types of aromatic
petrochemicals.
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
or agrichemicals.
Safety and environmental concerns
The refining process releases numerous different chemicals into the atmosphere;
consequently, there are substantial air pollution emissions[7] and a notable odor normally accompanies the
presence of a refinery. Aside from air pollution impacts there are also wastewater concerns,[3] risks of industrial accidents
such as fire and explosion, and noise health effects due to industrial noise.
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, Louisiana facility in
1976. However, many existing refineries have been expanded during that time. Environmental
restrictions and pressure to prevent construction of new refineries may have also contributed to rising fuel prices in the United
States[8]. Additionally, many refineries (over 100 since
the 1980s) have closed due to obsolescence and/or merger activity within the industry itself. This activity has been reported to
Congress and in specialized studies not widely publicised.
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
the Campo de Gibraltar, a Spanish state owned refinery near the towns of
Gibraltar, Algeciras, La
Linea, San Roque and Los Barrios with a
combined population of over 300,000 residents within a 5 mile radius and the CEPSA refinery in Santa Cruz on the island of
Tenerife, Spain[9] 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, Pacheco, Concord, Pittsburg, Vallejo and Benicia, with occasional accidental events
that require "shelter in place" orders to the adjacent populations.
History
The world's first oil refineries were set up by Ignacy Łukasiewicz near
Jaslo, Austrian Empire (now in Poland) in the years 1854-56[10][11] but they were initially small as there was no real demand for
refined fuel. As Łukasiewicz's kerosene lamp gained popularity the refining industry grew
in the area.
The first large oil refinery opened at Ploieşti, Romania in
1856.[12] 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 US Army Air Forces in
Operation Tidal Wave, August 1, 1943. Since then 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.
At one time, the world's largest oil refinery was claimed to be Ras Tanura,
Saudi Arabia, owned by Saudi Aramco. For most of the
20th century, the largest refinery of the world was the Abadan refinery in Iran. This refinery suffered extensive damage during the war Iran-Iraq war.
The world's largest refinery complex is the "Centro de Refinación de Paraguaná" (CRP) operated by PDVSA in Venezuela with a production capacity of 956,000 barrels per day (Amuay 635,000 bpd,
Cardón 305,000 bpd and Bajo Grande 16,000 bpd). SK Corporation's Ulsan refinery in South Korea with a capacity of 840,000 bpd and
Reliance Petroleum's refinery in Jamnagar, India with 660,000 bpd are the second and third largest, respectively.
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 permit to build even a modern refinery with minimal impact on the environment (other than CO2
emissions) is so difficult and costly that no new refineries have been built (though many have been expanded) in the United
States since 1976. As a result, some believe that this may be the reason that the US is becoming more and more dependent on the
imports of finished gasoline, as opposed to incremental crude oil. On the other hand, studies have revealed that accelerating
merger activity in the refining and production sector has reduced capacity further, resulting in tighter markets in the United
States in particular.
See also
A refinery at night. The gas flare is in the center of the picture.
References
- ^ a b Gary, J.H. and Handwerk, G.E.
(1984). Petroleum Refining Technology and Economics, 2nd Edition, Marcel Dekker, Inc. ISBN
0-8247-7150-8.
- ^ a b Leffler, W.L. (1985).
Petroleum refining for the nontechnical person, 2nd Edition, PennWell Books. ISBN 0-87814-280-0.
- ^ a b Beychok, Milton R. (1967).
Aqueous Wastes from Petroleum and Petrochemical
Plants, 1st Edition, John Wiley & Sons. LCCN
67019834.
- ^ Guide to Refining from Chevron Oil's website
- ^ Refinery flowchart from Universal Oil Products' website
- ^ An example flowchart of fractions from crude oil at a refinery
- ^ AP 42, Compilation of Air Pollutant Emission Factors
- ^ Behind high gas prices: The refinery crunch
- ^ Smoke, oil spills and now radiation - whatever next?
- ^ Frank, Alison Fleig (2005).
Oil Empire: Visions of Prosperity in Austrian Galicia (Harvard Historical Studies). Harvard University Press. ISBN
0-674-01887-7.
- ^ Warsaw University timeline
- ^ WORLD EVENTS: 1844-1856 www.pbs.org
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