<br />The energy fuels that involve a refining process
<br />distinct from both extraction and subsequent conver-
<br />sion or consumption are nuclear fuels and oil
<br />(including shale oil and synthetic oil from coal), and
<br />are described in the following section.
<br />Water demands in the nuclear fuel cycle have been
<br />calculated by the Atomic Energy Commission (1972)
<br />on the basis of annual requirements of a typical
<br />I,OOO-mw light-warer reactor steam-electric plant
<br />operating 80 percent of the time. Of a total consump-
<br />tion of 163 million gallons (617 thousand m'), 65
<br />million gallons (246 thousand m'), or about 40 per-
<br />cent, is assigned to the uranium-ore milling stage,
<br />almost entirely as evaporation from tailings ponds. The
<br />remaining consumption of water occurs mainly in
<br />evaporative cooling in the uranium enrichment plant,
<br />which is normalized to 90 million gallons (341 thou-
<br />sand m') annually for a I,OOO-mw plant. The
<br />remaining 8 million gallons (30 thousand m') is
<br />assigned in about equal proportions to the production
<br />of uranium hexafluoride and reprocessing of used fuel
<br />elements. Not included in the above water consump-
<br />tion caJcu)ations is water consumed at power plants
<br />supplying electricity for the enrichment process. This
<br />annual power requirement is estimated at 310,000
<br />mwhr (megawatt hours) that, if produced in a fossil-
<br />fuel plant, would indicate an evaporative requirement
<br />of roughly 160 million gallons (604 thousand m'). To
<br />keep this demand in proper perspective, it should be
<br />remembered that the electrical power produced by the
<br />model I,OOO-mw nuclear station annually (at 80 per.
<br />cent load factor) amounts to about 22 times the
<br />energy consumed to produce an annual fuel require-
<br />ment for a 1,000.mw station (U.S. Atomic Energy
<br />Commission, 1972, p. D5).
<br />Water demand for petroleum refining is highly varia-
<br />ble, depending upon such factors as process employed,
<br />refinery design, and cost and availability of water.
<br />A sampling of refineries producing 30 percent of the
<br />petroleum products in the United States in 1955 (OilS,
<br />1963, p. 299), indicated an average withdrawal demand
<br />of 468 gallons (1.76 m') of water per barrel (42
<br />gallons or 0.159 m') of crude-oil input. Some 90
<br />percent of this water was used in cooling processes at
<br />various stages of refining. A more meaningful measure
<br />of water demand, however, is the consumptive use,
<br />which averaged 39 gallons (0.14 m') of water per
<br />barrel of crude-oil input, or roughly I volume of
<br />water consumed per 1 volume of crude. Of this
<br />consumption, 7J percent was accounted for in
<br />evaporative cooling, 26 percent as boiler feed water,
<br />and the remaining 3 percent for sanitary and other
<br />in-plant uses.
<br />
<br />CONVERSION
<br />
<br />Conversion embraces the concept of changing an
<br />energy raw material into a more usable form of energy.
<br />Examples include burning of coal, gas, or oil to produce
<br />electricity, or converting energy of nuclear fission to
<br />electricity. Other examples include changing coal or oil
<br />into gas, a cleaner, more convenient fuel for space heat-
<br />ing, or even changing coal into a form of oil for further
<br />refining. Much of the present emphasis on conversion
<br />seeks to use fuels abundant in the United States, such as
<br />coal and oil shale, to meet the present energy crisis with-
<br />out sacrificing air quality objectives. Gene-rally. this
<br />involves processing near the site of extraction to produce
<br />a nonpolluting fuel which can be transported to a distant
<br />market. Alternatively, the coal can be used near the
<br />mine to produce electricity for transport to market.
<br />The processes of particular interest in the present
<br />energy shortage are coal gasification, coal liquefaction,
<br />oil-shale retOTting, use of geothermal energy for electric
<br />generation, and increased use of coal-burning plants and
<br />nuclear reactors for power generation. fn each mode
<br />considerable flexibility is possible in plant design, proc-
<br />ess employed, and location of processing facilities with
<br />respect to site of extraction, source and use of water,
<br />and location of market. It is impractical, if not impossi.
<br />ble, to assign rigid values of water use per unit of energy
<br />produced to all processes because of economic trade-
<br />offs, but ranges of water demand are useful for planning
<br />purposes. Moreover, in electric-power generation the
<br />need for high fuel efficiency generally dictates water
<br />demand within close limits; accordingly, water demand
<br />for electric generation can be estimated reasonably well.
<br />
<br />STEAM-ELECTRIC GENERATION
<br />
<br />The most efficient method of meeting large steady
<br />electric demand (base load) is by use of a steam turbine
<br />to drive a generator (Ilg. I). The steam may be produced
<br />from geothermal wells, by burning coal, oil, or gas, or by
<br />heat given off by nuclear fission, The power output of a
<br />steam turbine is greatly increased by reducing the pres-
<br />sure on the outlet side of rhe turbine_ This is done by
<br />use of a condenser, which lowers the temperature of the
<br />exhaust steam, causing condensation and thus signifi-
<br />cantly reducing the pressure. The cooling capacity
<br />needed for the condensation phase accounts for the
<br />greatest consumption of water in the entire energy.
<br />production process.
<br />Various systems are used for condenser cooling-
<br />once-through circulation. cooling ponds, sprayers, wet
<br />cooling towers, dry cooling towers, and combinations of
<br />the preceding systems. Once-through cooling commonly
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