An oil refinery
is an industrial process
plant where crude oil
is processed and refined into more
useful petroleum products
, asphalt base
, heating oil
and liquefied petroleum gas
Oil refineries are typically large sprawling industrial
complexes with extensive piping
running throughout, carrying streams of
between large chemical processing
Raw or unprocessed crude oil is not generally useful. Although
"light, sweet" (low viscosity, low sulfur
crude oil has been used directly as a burner fuel for steam vessel
propulsion, the lighter elements form explosive vapors in the fuel
tanks and are therefore hazardous, especially in warships
. Instead, the hundreds of different
hydrocarbon molecules in crude oil are separated in a refinery into
components which can be used as fuels
, and as feedstock in petrochemical
processes that manufacture such
products as plastics
such as nylon
are burned in internal combustion engines to provide
power for ships, automobiles, aircraft engines
, lawn mowers, chainsaws, and other machines.
Different boiling points
to be separated by distillation
. Since the lighter liquid products
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.
Oil can be used in a variety of ways because it contains
hydrocarbons of varying molecular
, forms and lengths such as paraffins
, and alkynes
While the molecules in crude oil include different atoms such as
sulfur and nitrogen, the hydrocarbons are the most common form of
molecules, which are molecules of varying lengths and complexity
made of hydrogen
and carbon atoms
, and a small number
of oxygen atoms. The differences in the structure of these
molecules account for their varying physical and chemical
properties, and it is this variety that makes crude oil useful in a
broad range of applications.
Once separated and purified of any contaminants and impurities, the
fuel or lubricant can be sold without further processing. Smaller
molecules such as isobutane
be recombined to meet specific octane
requirements by processes such as alkylation
, or less commonly, dimerization
. Octane grade of gasoline can also
be improved by catalytic
, which involves removing hydrogen from hydrocarbons
producing compounds with higher octane ratings such as aromatics
. 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
such as fluid catalytic cracking
, thermal cracking
, and hydrocracking
. The final step in gasoline
production is the blending of fuels with different octane ratings,
, and other properties
to meet product specifications.
Oil refineries are large scale plants, processing about a hundred
thousand to several hundred thousand barrel
of crude oil a day. Because of the
high capacity, many of the units operate continuously
, as opposed to processing
, at steady state
or nearly steady state for months
to years. The high capacity also makes process optimization
and advanced process control
Petroleum products are usually grouped into three categories: light
distillates (LPG, gasoline, naphtha), middle distillates (kerosene,
diesel), heavy distillates and residuum (heavy fuel oil,
lubricating oils, wax, asphalt). This classification is based on
the way crude oil is distilled and separated into fractions (called
) as in the above drawing.
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
- Vacuum Distillation unit
further distills residual bottoms after atmospheric
- 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 and cyclic hydrocarbons).
An important byproduct of a reformer is hydrogen released during
the catalyst reaction. The hydrogen is used either in the
hydrotreaters or the hydrocracker.
- Distillate Hydrotreater unit desulfurizes distillates (such as
diesel) after atmospheric distillation.
- Fluid Catalytic Cracker
(FCC) unit upgrades heavier fractions into lighter, more valuable
- Hydrocracker unit uses
hydrogen to upgrade heavier fractions into lighter, more valuable
- 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
- Coking unit (delayed coking, fluid coker, and flexicoker)
process 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
- 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
- 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
- Amine gas treater, Claus unit, and tail gas treatment for
converting hydrogen sulfide from
- 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
units and some type of further treatment (such as an activated sludge biotreater) to make such
water suitable for reuse or for disposal.
- Solvent refining units use solvent such as cresol or furfural to remove
unwanted, mainly asphaltenic materials from lubricating oil stock
(or diesel stock).
- Solvent dewaxing units remove the heavy waxy constituents
petrolatum from vacuum distillation
Flow diagram of typical refinery
The image below is a schematic flow
of a typical oil refinery that depicts the various
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
Schematic flow diagram of a typical
There are many process configurations other than that depicted
above. For example, the vacuum
unit may also produce fractions that can be
refined into endproducts such as: spindle oil used in the textile
industry, light machinery oil, motor oil, and steam cylinder oil.
As another example, the vacuum residue may be processed in a
to produce petroleum
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
- 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 pipeline 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
- Lubricants (produces light machine
oils, motor oils, and grease, 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
- 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
Siting/locating of petroleum refineries
The principles of finding a construction site for refineries are
similar to those for other chemical plants:
- The site has to be reasonably far from residential areas.
- Facilities for raw materials access and products delivery to
markets should be easily available.
- Processing energy requirements should be easily available.
- Waste product disposal should not cause difficulties.
For refineries which use large amounts of process steam and cooling
water, an abundant source of water is important. Because of this,
oil refineries are often located (associated to a port) near
navigable rivers or even better on a sea shore. Either are of dual
purpose, making also available cheap transport by river or by sea.
Although the advantages of crude oil transport by pipeline are
evident, and the method is also often used by oil companies to
deliver large output products such as fuels to their bulk
distribution terminals, pipeline delivery is not practical for
small output products. For these, rail cars, road tankers or barges
may be used.
It is useful to site refineries in areas where there is abundant
space to be used by the same company or others, for the
construction of petrochemical plants, solvent manufacturing (fine
fractionating) plants and/or similar plants to allow these easy
access to large output refinery products for further processing, or
plants that produce chemical additives that the refinery may need
to blend into a product at source rather than at blending
Safety and environmental concerns
The refining process releases numerous different chemicals into the
; consequently, there
are substantial air pollution
emissions and a notable odor
accompanies the presence of a refinery. Aside from air pollution
impacts there are also wastewater concerns, risks of industrial accidents
such as fire and
explosion, and noise health
due to industrial
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.
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
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. 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 CEPSA 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 radius and the CEPSA refinery in Santa Cruz on
the island of 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.
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.
Corrosion problems and prevention
Petroleum refineries run as efficiently as possible to reduce
costs. One major factor that decreases efficiency is corrosion of
the metal components found throughout the process line of the
hydrocarbon refining process. Corrosion
causes the failure of parts in addition to dictating the cleaning
schedule of the refinery, during which the entire production
facility must be shut down and cleaned. The cost of corrosion in
the petroleum industry has been estimated at US$3.7 billion.
Corrosion occurs in various forms in the refining process, such as
pitting corrosion from water droplets, embrittlement from hydrogen,
and stress corrosion cracking from sulfide attack. From a materials
standpoint, carbon steel is used for upwards of 80% of refinery
components, which is beneficial due to its low cost. Carbon steel
is resistant to the most common
forms of corrosion, particularly from hydrocarbon impurities at
temperatures below 205o
C, but other corrosive chemicals
and environments prevent its use everywhere. Common replacement
materials are low alloy steels
, with stainless steels
containing more chromium
dealing with more corrosive environments. More expensive materials
commonly used are nickel
, and copper
These are primarily saved for the most problematic areas where
extremely high temperatures or very corrosive chemicals are
Corrosion is fought by a complex system of monitoring, preventative
repairs and careful use of materials. Monitoring methods include
both off-line checks taken during maintenance and on-line
monitoring. Off-line checks measure corrosion after it has
occurred, telling the engineer when equipment must be replaced
based on the historical information he has collected. This is
referred to as preventative management.
On-line systems are a more modern development, and are
revolutionizing the way corrosion is approached. There are several
types of on-line corrosion monitoring technologies such as linear
polarization resistance, electrochemical noise
resistance. On-Line monitoring has generally had slow reporting
rates in the past (minutes or hours) and been limited by process
conditions and sources of error but newer technologies can report
rates up to twice per minute with much higher accuracy (referred to
as real-time monitoring). This allows process engineers to treat
corrosion as another process variable that can be optimized in the
system. Immediate responses to process changes allow the control of
corrosion mechanisms, so they can be minimized while also
maximizing production output. In an ideal situation having on-line
corrosion information that is accurate and real-time will allow
conditions that cause high corrosion rates to be identified and
reduced. This is known as predictive management.
Materials methods include selecting the proper material for the
application. In areas of minimal corrosion, cheap materials are
preferable, but when bad corrosion can occur, more expensive but
longer lasting materials should be used. Other materials methods
come in the form of protective barriers between corrosive
substances and the equipment metals. These can be either a lining
of refractory material such as standard Portland cement or other
special acid-resistant cements that are shot onto the inner surface
of the vessel. Also available are thin overlays of more expensive
metals that protect cheaper metal against corrosion without
requiring lots of material.
oil refineries in the world were built by Ignacy Łukasiewicz near Jasło, Austrian
Empire (now in Poland) from 1854
to 1856, 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.
first large refinery opened at Ploesti (today known
as Ploieşti), Romania, in
1856-1857, with US
After being taken over by Nazi Germany
, the Ploesti refineries were
bombed in Operation Tidal Wave
by the Allies
during the Oil Campaign of World War II
early large refinery is Oljeön, Sweden (1875), now
preserved as a museum at the UNESCO world heritage site Engelsberg and part of the Ecomuseum Bergslagen.
point, the refinery in Ras
Arabia owned by Saudi Aramco
was claimed to be the largest oil refinery in the world.
of the 20th century, the largest refinery was the Abadan Refinery in Iran.
refinery suffered extensive damage during the Iran-Iraq war
. The world's largest refinery
complex is the "Centro de Refinación de Paraguaná" (CRP) operated
in Venezuela with a production
capacity of (Amuay , Cardón and Bajo Grande 16,000 bpd).
SK Energy's Ulsan refinery in
Korea with a capacity of and Reliance Petroleum's Jamnagar Refinery in India with are the
second and third largest, respectively.
Oil refining in the United States
Early refineries in the U.S. processed crude oil to recover the
. 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 US Environmental
(EPA) were not subject to any environmental
protection regulations. Today, national and state legislation
requires refineries to meet stringent air and water cleanliness
standards. In fact, oil companies in the U.S. perceive obtaining a
permit to build a modern refinery to be so difficult and costly
that no new refineries have been built (though many have been
expanded) in the U.S. since 1976. Some attribute increasing
dependence in the U.S. on imports of finished gasoline, to lack of
new refineries. On the other hand, studies have revealed that
accelerating mergers among the refineries have further reduced
capacity, resulting in tighter markets particularly in the