Inside a maze of silver towers and pipes is a fascinating factory that
changes hydrocarbon molecules to make gasoline.
A refinery is a factory. Just as a paper mill turns lumber into legal pads or a
glassworks turns silica into stemware, a refinery takes a raw material--crude oil--and
transforms it into gasoline and hundreds of other useful products.
A typical large refinery costs billions of dollars to build and millions more to
maintain and upgrade. It runs around the clock 365 days a year, employs between 1,000 and
2,000 people and occupies as much land as several hundred football fields. It's so big and
sprawling, in fact, that workers ride bicycles from one station to another.
Chevron has five gasoline-producing "Factories" in the United States
and another in Burnaby, British Columbia. ChevronTexaco has refining
capacities worldwide of over two million barrels per day.
These world class operations had surprisingly humble origins. In 1876, company pioneers
used wagons and mules to haul two primitive stills to a spot near Pico Canyon, Calif., the
site of California's first producing oil wells. The stills, each about the size of a
garage, were used to heat oil at the prodigious rate of 25 to 40 barrels a day. This
"oil boiling" produced kerosene, lubricants, waxes and gasoline--a clear,
lightweight liquid that generally was discarded as a useless byproduct. (Read
more about Chevron's first refineries in the History section.)
Gasoline's lowly status rose quickly after 1892, when Charles Duryea built the first
U.S. gas-powered automobile. From then on, the light stuff from crude oil became the right
stuff.
Today, some refineries can turn more than half of every 42-gallon barrel of crude oil
into gasoline. That's a remarkable technological improvement from 70 years ago, when only
11 gallons of gasoline could be produced. How does this transformation take place?
Essentially, refining breaks crude oil down into its various components, which then are
selectively reconfigured into new products.
This process takes place inside a maze of hardware that one observer has likened to
"a metal spaghetti factory." Employees regulate refinery operations from within
highly automated control rooms. Because so much activity happens out of sight, refineries
are surprisingly quiet places. The only sound most visitors hear is the constant, low hum
of heavy equipment.
The complexity of this equipment varies from one refinery to the next. In general, the
more sophisticated a refinery, the better its ability to upgrade crude oil into high-value
products. Whether simple or complex, however, all refineries perform three basic steps:
separation, conversion and treatment.
Modern separation--which is not terribly different from the "cooking" methods
used at the Pico Canyon stills--involves piping oil through hot furnaces. The resulting
liquids and vapors are discharged into distillation towers, the
tall, narrow columns that give refineries their distinctive skylines.
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. These tarlike
fractions, called residuum, are literally the "bottom of the barrel."
The fractions now are ready for piping to the next station or plant within the
refinery. Some components require relatively little additional processing to become
asphalt base or jet fuel. However, most molecules that are destined to become high-value
products require much more processing.
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. This also is where a refinery makes money, because
only through conversion can most low-value fractions become gasoline.
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.
Fluid catalytic cracking, or "cat cracking," is the basic
gasoline-making process. Using intense heat (about 1,000 degrees Fahrenheit), low pressure
and a powdered catalyst (a substance that accelerates chemical reactions), the cat cracker
can convert most relatively heavy fractions into smaller gasoline molecules.
Hydrocracking applies the same principles but uses a different catalyst,
slightly lower temperatures, much greater pressure and hydrogen to obtain chemical
reactions. Although not all refineries employ hydrocracking, Chevron is an industry leader
in using this technology to cost-effectively convert medium- to heavyweight gas oils into
high-value streams. The company's patented hydrocracking process, which takes place in the
Isocracker unit, produces mostly gasoline and jet fuel.
Some Chevron refineries also have cokers, which use heat and moderate pressure
to turn residuum into lighter products and a hard, coallike substance that is used as an
industrial fuel. Cokers are among the more peculiar-looking refinery structures. They
resemble a series of giant drums with metal derricks on top.
Cracking and coking are not the only forms of conversion. Other refinery processes,
instead of splitting molecules, rearrange them to add value. Alkylation, 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. Chevron's patented
reforming process is called Rheniforming for the rheniumplatinum catalyst used.
Back when Chevron's founders boiled crude oil to get kerosene, they didn't have to
worry about customer specifications or government standards. Today, however, a major
portion of refining involves blending, purifying, fine-tuning and otherwise improving
products to meet these requirements.
To make Chevron 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. Technicians also add Techron,
Chevron's patented performance additive, and dyes that distinguish the various grades of
fuel.
Refining has come a long way since the oil boiling days of Pico Canyon. By the time a
gallon of gasoline is pumped into a car's tank, it contains more than 200 hydrocarbons and
additives. All that changing of molecules pays off in a product that ensures smooth,
high-performance driving.
You can view an illustration showing a refinery's most
important processes.
Ever wonder what are the key factors in running a refinery? Read a quick lesson in refinery economics to find out.
Almost half of every barrel of crude oil ends up as something other than gasoline. Here
are a few.
