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What is a Refinery?
Separation
Conversion
Treatment
Storage
WHAT IS A REFINERY? |
A refinery is a factory. Just as a paper mill turns lumber into paper, a refinery
takes crude oil and turns it into gasoline and hundreds of other useful products.
A typical refinery costs billions of dollars to build and millions more to maintain
A refinery runs twenty-four hours a day, 365 days a year and requires a large
number of employees to run. A refinery can occupy as much land as several hundred
football fields. Workers ride bicycles to move from place to place inside the
complex.
The world needs gasoline and petroleum products to move merchandise and people;
help make plastics; and do many other things. Today, some refineries turn more
than half of every 42-gallon barrel of crude oil into gasoline. How does this
transformation take place? Essentially, refining breaks crude oil down into
its various components, which then are selectively reconfigured into new products.
All refineries perform three basic steps: separation,
conversion, and treatment.
Heavy petroleum fractions are on the bottom, light fractions are on the top. This allows the separation of the various petrochemicals. Modern separation involves piping oil through hot furnaces. The resulting liquids and vapors are discharged into distillation towers.
Inside the towers, the liquids and vapors separate
into components or fractions according to weight and boiling point. The lightest
fractions, including gasoline and liquid petroleum gas (LPG), vaporize and rise
to the top of the tower, where they condense back to liquids. Medium weight
liquids, including kerosene and diesel oil distillates, stay in the middle.
(Heavier liquids, called gas oils, separate lower down, while the heaviest fractions
with the highest boiling points settle at the bottom.)
The finishing touches occur during the final treatment. To make gasoline, Cracking
and rearranging molecules adds value to the products. This is where refining's
fanciest footwork takes place--where fractions from the distillation towers
are transformed into streams (intermediate components) that eventually become
finished products. The most widely used conversion method is called cracking
because it uses heat and pressure to "crack" heavy hydrocarbon molecules into
lighter ones. A cracking unit consists of one or more tall, thick-walled, bullet-shaped
reactors and a network of furnaces, heat exchangers and other vessels.
Cracking and coking are not the only forms of conversion. Other refinery processes,
instead of splitting molecules, rearrange them to add value. Alkylation’s, for
example, makes gasoline components by combining some of the gaseous byproducts
of cracking. The process, which essentially is cracking in reverse, takes place
in a series of large, horizontal vessels and tall, skinny towers that loom above
other refinery structures. Reforming uses heat, moderate pressure and catalysts
to turn naphtha, a light, relatively low-value fraction, into high-octane gasoline
components.
The finishing touches occur during the final treatment. To make gasoline,
refinery technicians carefully combine a variety of streams from the processing
units. Among the variables that determine the blend are octane level, vapor
pressure ratings and special considerations, such as whether the gasoline will
be used at high altitudes.
Both the incoming crude oil and the outgoing final
products need to be stored. These liquids are stored in large tanks on a tank
farm. Pipelines carry the final products from the tank farm near the refinery
to other tanks all across the country.
All of these activities are required to make the gasoline that powers our cars, the diesel fuel that brings our food to market, and the jet fuel that flies our planes. These provide us with the energy we need to get from place to place quickly and comfortably.
Last Revised: October 2006
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