ENERGY SOURCES—ALTERNATIVES 307
level of 35–40 db (A) is acceptable, the critical level of noise
begins with 40 db (A), above 40 db the noise can reduce the
attention and concentration of working people. For working
places they are required by law to limit the noise level to:1) mainly intellectual work 55 db (A).
2) simple or mainly mechanical office work 70 db (A).
3) all other work in office or workshop 85 db (A).From 90 db (A) on it is required to wear ear protection.
Traffic noise, mainly from vehicular power plants, can
reach 90 db (A) in urban areas and on heavily traveled high-
ways, while a four-engine jet aircraft produces up to 120 db
(A) on take-off at a distance of 200 feet. In internal com-
bustion engines the sources of noise are the rapid combus-
tion of fuels, high-velocity gas discharges through exhaust
valves, and engine vibrations. The noise output is held down
by muffling of the exhaust gases and by acoustic lining of
the engine compartment. Turbine noises from both aircraft
engines and stationary power plants arise from high-speed
rotating components and high-velocity gas flows, and can
be controlled by reducing the fan blade tip speed, the use
of acoustic linings, and varying the geometry of the exhaust
nozzle.
The necessity to build power plants also in the vicin-
ity of towns and villages leads to expensive noise protection
equipment.ENERGY RESOURCESModification of fuel form and the substitution of alternate
energy resources are useful procedures for controlling envi-
ronmental effects. The selection among alternative resources
depends on their relative abundance, ease of recovery, con-
venience in handling, and economics. Some resources, such
as fossil and nuclear fuels, are present on earth in only finite
amounts and are not renewed to any extent, although in the
case of nuclear fuels the energy content of known reserves
may be quite large. The other major category of energy
resources involve energy that is supplied continually to the
biosphere over a geological time span, including geothermal
and tidal energy as well as solar energy and its derivatives,
wind, waves, and hydropower.
In 1980 the average cost of coal, oil, and natural gas at
their source was US $55–60 per ton, US $30–35 per bbl,
and $1.6–1.8 per 1000 ft^3 , respectively. Within the last years
these costs have drastically escalated and further adjustments
may be attributed to the cost of providing environmental pro-
tection systems and to governmental policy actions in spe-
cific areas such as mine safety, oil import quotas, and natural
gas price regulation. Current prices for nuclear fuel supplied
to fission reactors indicate a cost for this form of energy of
about US $1.8–2 per 10^6 Btu.
The cost of treating, refining, and transporting fuels adds
considerably to the price paid by the consumer for energy.
Figure 4 shows the portion of the cost of electrical energy,
produced in central station power plants, that is attributableto the transportation of coal, oil, and natural gas fuels and to
high-voltage electric transmission as a function of distance
and transport technique.^29 The spatial separation between
the location of resources and the centers of energy demand
poses the problem of optimal siting of fuel treatment, refin-
ing, and energy conversion activities and has been studied in
a geographical format by Manners.^30 Consideration of envi-
ronmental factors imposes additional constraints on such
siting problems.
A number of estimates of the abundance of energy
resources are available and have been assembled and refined
by Hubbert^31 of the US Geological Survey. The exploita-
tion of an exhaustible energy resource generally begins at a
low level and increases to a period of maximum utilization,
ultimately returning again to a low level as the resource is
depleted or as recovery costs become prohibitive. Of inter-
est with respect to an energy resource is the estimated time
of peak annual consumption and the time at which 90% of
the resource is expected to be consumed. The summation
of annual recovery over the entire recovery time span is the
ultimate recovery for that resource, Q ∞. The cost of obtaining
a resource increases as that resource is depleted. In general,
it is necessary to qualify any statement concerning resource
abundance with a definition of the cost constraints that are
assumed. In view of such difficulties, estimates of resource
availability vary widely.
The estimated supply of coal and nuclear fuels can pro-
vide the projected US needs over several centuries, while
Hubbert’s analyses indicate that over 90% of the oil and
natural gas resources may be consumed by the year 2015.
Others are much more optimistic about new discoveries of
oil and gas. Homan and Lovejoy^32 have reviewed the meth-
ods used in arriving at oil and gas supply estimates and com-
pare the results arrived at by several investigators.
Any estimate of the abundance of a certain energy
resource must however consider that the different pro-
cess of substitution in the meantime under way may rap-
idly change the global picture of the quantity of energy
resources. The process of substitution makes it necessary
to analyze alternative energy strategies and to formulate
a selected long-term strategy for each country or even
multinational areas.^33
Another pertinent characteristic of a specific fuel or
energy resource is its versatility. Some fuels can be modified
or treated with relative ease to provide a convenient form
and can be utilized in a wide spectrum of energy conversion
system while others may be limited in their periods of avail-
ability or in their adaptability. This characteristic accounts
more than any other for the great demand for natural gas
or oil and its derivative products. Coal, lignite, and their
products coals are burnable products of decomposition of
former vegetable substance in different phases of preser-
vation. Coals consist of more than 50% (weight) and more
than 70% (volume) of carbon and contain at maximum 30%
unburnable parts (ash). Coals have brown up to black color.
The vegetable substances produce first peat and then pro-
gressing through lignite, subbituminous, bituminous, and
anthracite stages. It has been estimated that there is aboutC005_006_r03.indd 307C005_006_r03.indd 307 11/18/2005 12:05:47 PM11/18/2005 12:05:47 PM