PROCESS DIAGRAM
(^1) Heated
crude oil is
pumped into
fractionation
tower.
(^2) Fractionation
tower separates
crude oil
products based
on boiling
points.
(^4) Compounds
with lowest
boiling points
rise highest in
the tower.
(^3) Compounds
with the highest
boiling points
are produced
lowest in the
tower.
Lowest boiling point
Gases
Gasoline
Fractionation
tower
Petroleum products
Aviation fuel
Kerosene
Condensed
liquid
Heating oil
Diesel oil
Lubricants
Asphalt
Highest boiling point
Heated
crude
oil
Condensation
cap
Condensation
cap
hydrocarbon compounds. In addition to being used for
fuel, oil is used to produce petrochemicals, compounds
that can be converted into products such as fertilizers,
plastics, paints, pesticides, medicines, and synthetic fi-
bers. During petroleum refining, the compounds are
separated into different products—such as gases, jet
fuel, heating oil, diesel, and asphalt—based on their
different boiling points (}ÕÀiʣǰn).
Compared to petroleum, natural gas contains only
a few hydrocarbons: methane and smaller amounts of
ethane, propane, and butane. Propane and butane
are separated from the natural gas, stored in pres-
surized tanks as a liquid called liquefied petroleum
gas, and used primarily in rural areas as fuel for
heating and cooking. Methane is used to heat resi-
dential and commercial buildings, to generate elec-
tricity in power plants, and for a variety of purposes in
the organic chemistry industry.
Natural gas use is increasing in four main areas:
electricity generation, transportation, commercial
cooling, and as a feedstock for producing plastics and
fertilizers. Natural gas is often used in cogeneration,
an efficient process in which natural gas is used to
produce both electricity and steam; the heat of the ex-
haust gases provides energy to make steam for water
and space heating.
As a fuel for trucks, buses, and cars, natural gas offers
significant environmental advantages over gasoline or
diesel: Natural gas vehicles emit 33 percent less
carbon dioxide, 80 to 93 percent fewer hydro-
carbons, 70 percent less carbon monoxide, 90
percent fewer toxic emissions, and almost no
soot. As of 2011, the United States had more
than 150,000 vehicles running on compressed
natural gas. The city of Los Angeles has the largest fleet
of natural gas–powered transit buses in North America.
Worldwide, there were more than 10 million natural gas
vehicles in 2011.
Natural gas efficiently fuels residential and commer-
cial air-cooling systems. One example is the use of natu-
ral gas in a desiccant-based (air-drying) cooling system,
which is ideal for restaurants and supermarkets, where
humidity control is as important as temperature control.
The main disadvantage of natural gas is that deposits
are often located far from where the energy is used. Be-
cause it is a gas and less dense than a liquid, natural gas
costs four times more to transport through pipelines than
crude oil. To transport natural gas over long distances, it
Petroleum refining
U }ÕÀiʣǰn
✓✓THE PLANNER
424 CHAPTER 17 Nonrenewable Energy Resources