The world uses gasoline and petroleum products to move merchandise and people, help make plastics, and do many other things. At a refinery, different parts of the crude oil are separated into useable petroleum products. 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
Heavy petroleum components or "fractions" are on the bottom; light fractions are on the top. This difference in weights 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 fractions according to weight and boiling point.
Conversion
Cracking and rearranging molecules takes a heavy, low-valued feedstock — often itself the output from an earlier process — and change it into lighter, higher-valued output such as gasoline. This is where refining fanciest footwork takes place — where fractions from the distillation towers are transformed into streams (intermediate components) that eventually become finished products.
Treatment
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.
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