According to the Canadian site Energy Education:
“An oil refinery is an industrial plant where crude oil
is separated into a variety of different, useful substances through a variety
of chemical separation steps.”
Many refineries extract the full range of petroleum
products. Others focus on a limited number of particular products, such as
asphalt plants and petrochemical plants.
The general steps in refining
crude oil include fractional distillation, chemical processing, treating,
blending, and storage. Other analyses separate refining into three main
processes: separation, conversion, and treatment. Energy Education describes
the fractional distillation process that extracts the different hydrocarbon
products by temperature as follows:
“Fractional Distillation: Crude oil
enters the refinery through a series of pumps and first stops at a heater. In
this heater, the crude oil is heated to around 370°C. After the crude oil has
been heated and is vaporized, it travels to a distillation tower. Inside these
towers the vaporized crude oil is separated into fractions by utilizing their
different boiling points. As the vaporized crude oil travels up the tower,
fractions with different boiling points condense at different levels,
separating different components of the oil. Lighter fractions like butane and
propane are collected at the top with heavier fractions collected at the bottom.”
Chemical processing is used
in some newer refineries to break long hydrocarbon chains into shorter ones, a
process known as conversion.
“In a vessel known as a hydrocracker, heavier petroleum
fractions are exposed to heat and pressure in the presence of a catalyst to
break up long hydrocarbon chains. This is useful as it converts some of the
heavier fractions into more useful fractions, such as gasoline, jet fuel, and
propane.”
Treating refers mainly to
removing sulfur and other impurities. Many crudes contain high levels of
sulfur. Removing the sulfur makes the oil burn cleaner and more efficiently.
De-sulfurization units are employed at many refineries. However, these are
expensive to construct, costing hundreds of millions of dollars, and
potentially raising the cost of needed products like gasoline. Government
mandates for sulfur removal have been contentious over the past several years
and have pulled back somewhat. Hydrogen is used in desulfurization.
Blending creates different
composite products like gasoline with different octane ratings. On-site storage
is followed by distribution via pipeline, rail, or truck.
“In refineries, unprocessed crude oil is separated into
a variety of different useful products. Although crude oil is not useful by
itself, when separated a large number of useful hydrocarbons are obtained,
primarily gasoline, diesel fuel, heating oil, jet fuel, kerosene, and propane.
In addition to this, crude oil yields other important products such as natural
gas liquids, petrochemical feedstocks, petroleum coke, heavy fuel oil, asphalt,
lubricating oils, naphthas, and waxes. Because all of these useful products are
obtained through the refining process, the refining of oil is an incredibly
important step in the oil and gas industry.”
All refineries have
atmospheric distillation units that separate products based on boiling points,
but more advanced ones, about 80% of all refineries now, also have vacuum
distillation units where the pressure is lowered below atmospheric pressure to
extract products. At low pressures, the boiling point of the atmospheric
distillation units’ “bottoms” is low enough that lighter products can vaporize
without cracking or degrading the oil.
A vacuum distillation unit is depicted below.
Gasoline was originally
discarded in early refining, as kerosene was a more desirable product. Crude
oil is a mixture of many hydrocarbon compounds, including paraffins,
naphthenes, and more. Paraffins are the most common component in both crude
oils and refined products such as gasoline. In every barrel (42 gallons) of
crude oil, there are about 20 gallons of gasoline that can be extracted. The
heavier extracts from distillation remain at the bottom of the tower. These are
known as gas oils and are less valuable products that can be “cracked” via
heat, pressure, and catalysts into lighter hydrocarbons. Excess light
hydrocarbons from refining, like naphtha, can be combined with heavier
hydrocarbons to make desired products. According to Slash Gear:
“While no two barrels of crude oil are the same, roughly
42% of each barrel will ultimately become gasoline, on average. Another 27%
becomes diesel fuel, meaning that nearly three quarters of each barrel makes
its way to the gas pump in one form or another. About 6% of each barrel becomes
jet fuel, 5% becomes tar-like heavy fuel, 3% becomes light fuel, and 2% becomes
other hydrocarbon fuels.”
“After all of the fuels have been removed, you're left
with about 14% of the original barrel. About 4% of that will become asphalt
used to make roads and sidewalks. The last 10% gets spread around to just about
every industry on the planet and is where we get petroleum products from
plastics to perfumes and everything in between.”
Other products made from refined crude oil include plastics
(although most are now made from the natural gas liquid known as ethane),
antifreeze, car tires, clothing, fertilizers, paint, soap, yarn, nylon, a whole
host of petrochemicals, and much more.
References:
From
Crude to Unleaded: How Gasoline is Made. Cassidy Ward. Slash Gear. January 11,
2024. From Crude To Unleaded: How Gasoline
Is Made (slashgear.com)
Oil
Refinery. Energy Education. Oil refinery - Energy Education
Oil
and petroleum products explained. Refining crude oil. Energy Information
Administration. Last updated: February 22, 2023. Refining crude oil - the refining
process - U.S. Energy Information Administration (EIA)
Petroleum
refining processes. Wikipedia. Petroleum refining processes -
Wikipedia
Vacuum
distillation is a key part of the petroleum refining process. Energy Information
Administration. December 10, 2012. Vacuum distillation
is a key part of the petroleum refining process - U.S. Energy Information
Administration (EIA)
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