Environmental Engineering Reference
In-Depth Information
Cooling Towers
Cooling towers discharge waste heat from turbine-cooling water to the atmosphere through a
variety of means. Wet cooling towers allow hot water to cascade through numerous layers of fill
material in walled structures, while circulating cooler air through the water either using fans or
naturally. Heat is exhausted at the top of the tower. Natural draft towers may be 350 to 550 feet
tall and mechanical draft towers are typically fifty to sixty-five feet tall (Christman et al. 1980,
227). Cooling towers may produce a plume of wet air that, under unfavorable meteorological
conditions, may create a ground fog, reducing visibility nearby and creating a driving hazard at
night, so wet-dry towers heat the plume and partially cool incoming water in an attempt to reduce
this effect. Dry cooling towers circulate water through a closed system comparable to a radiator
on an automobile, transferring heat to air via radiation and convection to avoid this problem; this
type of tower is rare in the United States (Christman et al. 1980, 227).
Every electric power generating plant has an industrial water treatment plant to treat incoming
water before it is introduced into equipment; various agents are used to minimize corrosion, buildup
of mineral scale, and organic materials. Small quantities of waste, some of which is chemical waste,
are generated from routine operation and maintenance of electric generator cooling systems and
water treatment plants. These include ash transport water, metal cleaning waste, boiler blowdown
(e.g., cleaning water used to remove particles of corrosion and scale), cooling tower blowdown,
construction site and material storage runoff, and several low-volume waste streams (e.g., scrub-
ber waste water, water treatment plant waste, in-plant drainage systems) (Christman et al. 1980,
228). Consequently, chemical effluent limitations for the utility industry restrict the discharge of
acidity, polychlorinated biphenyls (PCBs), total suspended solids, oil, grease, chlorine, copper,
iron, zinc, chromate, and phosphorous under the Clean Water Act (33 U.S. Code § 1316). These
environmental costs are converted to dollar costs as a matter of regulatory policy. Yet other unpriced
environmental costs of utilizing coal total $180 to $530 billion per year, enough to double or triple
the dollar costs of coal if they were included in our electric bills (Epstein et al. 2011).
COSTS OF COAL UTILIZATION
Dollar Costs
U.S. consumption of coal was about 1.048 billion short tons in 2010, up from about 997.5 million
short tons in 2009 (USEIA 2011b, Table 7.1). The market cost to consumers for coal energy in
calendar year 2009 was estimated at a bit over $45.8 billion, and a little over $49.4 billion in 2008
(Table 3.5). Federal subsidies and tax expenditures for coal were estimated at almost $1.36 billion
for FY2010 (USEIA 2011c, xiii), including $1.2 billion for electricity production (xviii). Efforts
to develop synthetic liquid fuels from coal received no subsidies in FY2010, a drastic reduction
from over $3 billion in subsidies and tax expenditures from FY2007 (xiv).
Coal has been described as a “sick industry” in relative decline during the twentieth century
through the mid-1970s (Davis 1993, Ch. 2), beset by persistent labor and environmental problems
as it shifted production from underground mines to surface mines and later shifted its underground
mines from pick and shovel to longwall operations. The resulting price instability had long made
it difficult for any but the largest operations to survive. One result was a long-term trend toward
consolidation of the industry into fewer, ever-larger firms, a trend that continues today. The deliv-
ered price of coal varies according to the distance from the mine to the boiler in which it is burned,
and the adequacy of rail and barge facilities. For example, the delivered price per ton of coal to
 
Search WWH ::




Custom Search