Environmental Engineering Reference
In-Depth Information
markets. The TransAlaska line, also 120 cm in diameter,
is 1280 km long and annually moves about 100 Mt of
crude oil from the North Slope to Anchorage.
Natural gas is not as easily transported as crude oil
(Poten & Partners 1993; IEA 1994). The specific energy
needed for its pumping is about three times that of en-
ergy required to move crude oil. The longest and widest
natural gas pipelines (6500 km long and up to 142 cm in
diameter) carry fuel from the supergiant fields of Med-
vezh'ye, Urengoy, Yamburg, and Zapolyarnyi in the
Nadym-Pur-Taz gas production complex in Western
Siberia to European Russia and then all the way to
Western Europe, with the southern branch going
to northern Italy and the northern branch to Germany
and France. Undersea links are practical only over
short and shallow stretches, as in the North Sea (bringing
the gas to Scotland and the Continent) and across the
Sicilian Channel and the Messina Strait to Italy (bringing
Algerian gas to Europe).
Natural gas is stripped of any undesirable ingredients,
most often H
2
S and moisture, before it is compressed
and piped, and this preparation can be accomplished
with minimal land requirements. The throughput power
densities of gas-processing plants may be as high as 70
kW/m
2
and rarely are below 50 kW/m
2
. Pipelines usu-
ally need a 25-30 m corridor for construction; afterwards
only access strips of up to 10 m may be necessary. Com-
pressor stations take up to 20,000 m
2
at 80-120-km
intervals; pumping stations claim up to ten times as
much area every 100-160 km (the TransAlaska line has
11 of them, one every 116 km). Aggregate U.S. data
and assumptions of 7-10-m right-of-ways for operating
lines prorate to average throughputs of 200-300 W/m
2
for natural gas and 350-480 W/m
2
for crude oil. Major
lines do much better. Even with a 30-m right-of-way
the TransAlaska line has maximum design throughput
power density of 3.7 kW/m
2
, and its actual maximum
in the year 2000 prorated to 1.7 kW/m
2
(Alyeska
2003).
While modern coal preparation is just a set of simple
physical procedures, crude oils undergo a complex pro-
cess of refining, a combination of physical and chemical
treatments. Refining separates the complex mixture of
hydrocarbons into more homogeneous categories and
adds value to final products. During straight thermal dis-
tillation light naphtha (pentanes to heptanes) boils away
at 27-93
C, heavy naphtha (compounds with up to 10
C atoms) at 93-177
C; then comes kerosene (jet fuel)
at up to 325
C, followed by light (diesel) gas oil and
heavy gas oil (up to 565
C). Residual solids (coke, as-
phalt, tar, waxes) boil only above 600
C. Early refining
relied strictly on heat (delivered as high-pressure steam
at 600
C) to separate major fractions. Given the quality
of dominant flows, this produced largely medium and
heavy products, and without an effective technical solu-
tion the extent of driving and flying would have
remained restricted because of crude oil quality.
In 1913, William Burton patented thermal cracking of
crude oil, which relied simply on the combination of heat
and high pressure to break heavier hydrocarbons into
lighter mixtures. A year later Almer M. McAfee patented
the first catalytic cracking process, which used aluminum
chloride to break long-chained molecules into shorter,
more volatile chains. But because the relatively expen-
sive catalyst could not be recovered, thermal cracking
remained dominant until 1936, when Sun Oil put on
line the first catalytic cracking unit, designed by Eug`ne
Houdry,
to produce high-octane gasoline (Houdry
