310 ENERGY SOURCES—ALTERNATIVES
Other estimates are higher than this by a factor of 2 or 3. The
world resources are felt to be between 1350 and 2100 10 9
bbl. Peak annual recovery and the 90% depletion point are
projected to be attained by the years 1995 and 2000, respec-
tively, for the US and 2000 and 2050 for the world, consider-
ing that the processes of saving and substitution have begun.
Petroleum resources may be extended considerably by the
recovery of this fuel from shale oil. About 80 10 9 bbl of oil
can be recovered in the US under present conditions, using
shale with a content of oil of more than 10 gallons per ton.
The total US resources of shale oil in place with more than
10 gallons of oil per ton is figured at 1430 10 9 bbl. Before
a substantial production could be achieved, however, high
investments must be affected—and prototype plants of semi-
industrial and industrial size would have to be constructed.
A wide range of control of product yield is available
in the oil refining process. Separation of light and heavy
fractions are generally performed by distillation into lique-
fied petroleum gas (mostly propane and butane), gasoline,
kerosine, fuel oil, and residual crude. The normal yield of
gasoline from a typical crude is about 15% but this can be
increased substantially by thermal and catalytic cracking
techniques. In 1968 the average gasoline yield from US
refineries was 45% of the crude oil consumption. Petroleum
can also be used to produce methane, hydrogen, ammonia,
methanol, and other clean fuels that are being studied for
various applications including mobile power plants.
The sulfur content of crude oil is generally concentrated
by refining operations in the heavier fractions, such as the
residual oil used to fuel central station power plants. Table
13 gives the 1966 crude oil production in the US by area
and sulfur content of the original crude. Since much crude
oil and petroleum product is imported, similar information
on foreign production is given in Table 14. Sulfur may be
removed from oil by several techniques including delayed
coking, solvent deasphalting, and hydrogen treatment.Natural Gas and Natural Gas LiquidsThe principal component of natural gas delivered to the con-
sumer is methane. As recovered in the field the gas contains
hydrocarbons of the composition C n H 2n+2 (methane, ethane,
propane, butane, and pentane), natural gas liquids, and other
gases such as hydrogen sulfide (H 2 S) and, in some cases,
helium. The H 2 S content varies from field to field and is
removed to recover and sell the sulfur. Natural gas resources
are classified into nonassociated, associated, and dissolved
categrories depending on whether the gas exists alone, in a gas
cap with oil beneath it, or dissolved in oil. About 75% of the
gas reserves are in the nonassociated category. Gas associated
with oil generally provides pressurization of the oil pool and
stimulates its recovery, so the gas is usually left in place until
the oil is depleted. Natural gas liquids (NGL) are recoverable
from the gas and supplement other liquid fuel resources.
The ultimate recovery, Q ∞ , of natural gas in the US is
estimated by Hubbert at about 1200 10 12 ft^3 and for the
world at 8000 to 12,000 10 12 ft^3. Cumulative productionthrough 1969 was about 400 10 12 ft^3 in the US. On the
basis of these figures, the year of peak annual recovery will
be about 2000 and 90% of the resources will be consumed
by the year 2025.Uranium and ThoriumNatural uranium has an isotopic makeup of 0.711% uranium-
235, 0.006% uranium-234, and the balance is uranium-238.
Only uranium-235 among the naturally occurring isotopes
is fissionable to any extent and natural uranium must be
enriched in this isotope to between 2 and 3% to provide fuel
for current nuclear reactors. If only the naturally occurring
uranium-235 were utilized in fission reactors, the nuclear
industry could be limited, for economic reasons, to those
US resources of U 3 O 8 that are recoverable at a suitable cost.
These are estimated at 660,000 tons and would furnish only
about 232 10 15 Btu of energy. Fortunately, it is possible to
extend the degree of utilization of our uranium resources by
converting the abundant uranium-238 isotope into fissionable
plutonium-239. Thorium, which is available in large quanti-
ties, can also be converted into a fissionable isotope, in this
case uranium-233. These conversion processes, involving
the capture of neutrons by the fertile isotopes, may be car-
ried out in power producing reactors, which are called breed-
ers if the amount of new fissionable generated is greater than
that consumed, or converted if the amount generated is less
than that consumed. Breeding is required in order to fully
utilize uranium-238 and thorium-232 resources and makes
the economics of nuclear power less dependent on the cost
of fuel resources. There are estimated to be about 25 10 6
tons of U 3 O 8 in the US recoverable at reasonable costs and
eventual utilization of all of this natural uranium, including
the uranium-238 isotope after conversion into plutonium-
239, would develop some 1.25 10 21 Btu of energy.Fusion ResourcesThere are several fusion processes that are currently under
study or in development as a source of energy but none
have been attained in a controlled reactor. These reac-
tions depend on the hydrogen isotope deuterium, D, in
seawater as a primary fuel. One process, the D–D reac-
tion involves the feeding of deuterium into a magnetically
confined high temperature plasma and has the net result
of converting five deuterium atoms into one atom each of
helium-4, helium-3, and hydrogen, in addition to two neu-
trons, releasing 24.9 MeV of energy in the process. AnD + T→^4 He + n + 17.58 MeV
D + T→^3 He + n + 3.27 MeV
D + D→ T + p + 4.04 MeValternate and, in theory, easier reaction to obtain is the D–T
reaction which involves the fusion of one atom of deuterium
and one atom of tritium to produce an atom of helium-4, one
neutron, and 17.6 MeV of energy. The neutrons generated
in the D–T reactor must be captured in a lithium-6 blanketC005_006_r03.indd 310C005_006_r03.indd 310 11/18/2005 12:05:47 PM11/18/2005 12:05:47 PM