Coal - Energy Policy Analysis: A Conceptual Framework - page 28

industrial locations that use coal, a steady flow of fuel into boilers tends to keep operating costs
low, so to meet fluctuations in demand and possible delays in shipping, extra coal is kept on-site
in stockpiles. Daily and hourly fluctuations in consumption are met by a small storage pile near
the boiler, and a larger intermediate stockpile is maintained on-site to handle holidays or trans-
portation difficulties. A seasonal reserve is often built up during summer months to handle higher
winter consumption levels for heating, except at electric generating stations in southern climates
where peak demand may be experienced during summer for air conditioning. Electric utilities,
coke production plants, other industrial boilers, producers, and distributors together stockpiled a
year-end total in 2010 of almost 233.6 million tons at thousands of locations nationwide (USEIA
2011a, Table 27).
Coal storage stockpiles are potential sources of water pollution from precipitation runoff, and
air pollution from coal fires and fugitive dust. Moisture and air in contact with coal cause oxida-
tion of pyrites and marcasite to sulfuric acid, and rain washes some of this acid into surface and
groundwater (Christman et al. 1980). Concentrated “slugs” of acid drainage may be released
immediately after rainfall. Sulfuric acid produced by weathering of high-sulfur coals reduces the
pH of streams, and the resulting increased acidity stresses aquatic organisms. Runoff contains fine
coal particles, various minerals, and trace elements, increasing suspended sediments in receiving
streams and aquifers and altering their chemistry. Fugitive dust of fine coal particulates may be
blown from coal stockpiles whenever a breeze blows. Fires in stockpiles provide uncontrolled
emissions of smoke, particulates, and regulated pollutants such as sulfur dioxide, nitrogen oxides,
and carbon monoxide, which are hazardous to human health. If smoke containing high concen-
trations of sulfur dioxide comes in contact with nearby vegetation, it may be visibly harmed by
acid deposition.
COAL COMBUSTION
Coal-fired electricity generating plants accounted for about 30.4 percent of summer installed
generating capacity at 1,445 generating units and generated about 44.7 percent of the electricity
produced in the United States during 2010 (USEIA 2011d, Table 1.1.A, Table 2.1.A). Each power
plant requires dedication of several hundred to a few thousand acres of land to a single industrial
use for the boiler and generator, coal storage and handling facilities, water storage and purifica-
tion, pollution control equipment, and solid waste handling and storage facilities, access to which
must be limited for safety reasons.
At a typical coal-fired electric generating unit, crushed coal is first pulverized to a powder
about the consistency of a fine face powder. A mixture of finely pulverized coal and air is blown
into a combustion chamber at the base of a boiler and ignited as it passes through a burner flame,
as illustrated in Figure 2.3. Above the combustion zone of the boiler, water is pumped through
banks of metal tubes, which transfer heat from burning gases to the water, which leaves the boiler
as superheated steam, which turns a turbine and drives an electrical generator. Lower-pressure
steam leaving the turbine is fed into a cooling system that extracts residual heat and recycles
condensed water back to the boiler for reuse, yielding an overall system efficiency of 36 to 40
percent (Perry 1973).
Environmental Costs of Coal Combustion
Environmental costs of coal combustion include deterioration of air quality in the form of airborne
particulates, sulfur oxides, nitrogen oxides, lead, unburned hydrocarbons, carbon monoxide, carbon