Page 556 - Environment: The Science Behind the Stories

only make emissions worse; oil sands are estimated to gen- also gain more power from coal with less pollution through
erate 14–20% more greenhouse gas emissions than conven- a process called gasification, in which coal is converted into
tional oil, and shale oil is still more polluting. a cleaner synthesis gas, or syngas, by reacting it with oxygen
Besides modifying our climate, fossil fuel emissions affect and steam at a high temperature. In an “integrated gasification
human health. Combusting coal high in mercury content emits combined cycle” process, syngas from coal is used to turn a
mercury that can bioaccumulate in organisms’ tissues, poi- gas turbine and also to heat water to turn a steam turbine.
soning animals as it moves up food chains (pp. 391–392) and The U.S. government and the coal industry have each
presenting health risks to people. Gasoline combustion in auto- invested billions of dollars in clean coal technologies for new
mobiles releases pollutants that irritate the nose, throat, and power plants, and these have helped to reduce air pollution
lungs. Some hydrocarbons, such as benzene and toluene, cause from sulfates, nitrogen oxides, mercury, and particulate matter
cancer in laboratory animals and likely in people. Gases such (pp. 476–477). If these technologies were applied to the many
as hydrogen sulfide can evaporate from crude oil, irritate the older plants that still pollute our air, they could help even
eyes and throat, and cause asphyxiation. Crude oil also often more. At the same time, the coal industry spends a great deal
contains trace amounts of known poisons such as lead and arse- of money fighting regulations and mandates on its practices.
nic. As a result, workers at drilling operations, refineries, and in As a result, many power plants are built with few clean coal
other jobs that entail frequent exposure to oil or its products can technologies, and these plants will continue polluting our air
develop serious health problems, including cancer. for decades. Moreover, many energy analysts emphasize that
The combustion of oil in our vehicles and coal in our these technologies may make for “cleaner” coal but will never
power plants releases sulfur dioxide and nitrogen oxides, result in energy production that is completely clean. Some
which contribute to industrial and photochemical smog argue that coal is an inherently dirty way of generating power
(pp. 482–483) and to acid deposition (pp. 491–493). Fossil and should be replaced outright with cleaner energy sources.
fuel pollution is intensifying in developing nations that are
industrializing rapidly as they grow in population. In contrast,
air pollution from fossil fuel combustion has been reduced in Can we capture and store carbon?
developed nations in recent decades as a result of laws such as
the U.S. Clean Air Act and government regulations to protect Even if clean coal technologies were able to remove every
public health (Chapter 17). In these nations, public policy has last chemical contaminant from power plant emissions, coal
encouraged industry to develop and install technologies that combustion would still pump huge amounts of carbon diox-
reduce pollution, such as catalytic converters that cleanse vehi- ide (CO ) into the air, intensifying the greenhouse effect and
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cle exhaust (see Figure 17.15, p. 478). Wider adoption of such worsening global climate change. This is why many current
technologies in the developing world would reduce pollution efforts focus on carbon capture followed by carbon storage or
there considerably. carbon sequestration (p. 526). This approach consists of cap-
turing carbon dioxide emissions, converting the gas to a liquid
form, and then sequestering (storing) it in the ocean or under-
Clean coal technologies aim to reduce ground in a geologically stable rock formation (FIGURE 19.16).
air pollution from coal Carbon capture and storage (abbreviated as CCS) is being
attempted at a variety of new and retrofitted facilities. The
Burning coal emits a variety of pollutants unless effective pol- world’s first coal-fired power plant to approach zero emis-
lution control measures are in place. The composition of emis- sions opened in 2008 in Germany. This Swedish-built plant
sions from coal combustion depends on chemical impurities removes its sulfate pollutants and captures its carbon dioxide,
in the coal, and coal deposits vary in the impurities they con- then compresses the CO into liquid form, trucks it 160 km
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tain, including sulfur, mercury, arsenic, and other trace metals. (100 mi) away, and injects it 900 m (3000 ft) underground into
Coal from the eastern United States tends to be high in sulfur a depleted natural gas field. CHAPTER 19 • FOSSIL FUELS, THEIR IMPA CT S, AND ENERGY CONSERVATI ON
because it was formed in marine sediments, and sulfur is pre- In North Dakota, the Great Plains Synfuels Plant gasi-
sent in seawater. Most coal in China is even more sulfur-rich. fies its coal, then sends half the CO through a pipeline into
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At coal-fired power plants, scientists and engineers are Canada, where a Canadian oil company buys the gas to inject
seeking ways to cleanse coal of sulfur, mercury, and other impu- into an oilfield to help it pump out the remaining oil. The
rities. Clean coal technologies refer to an array of techniques, North Dakota plant also captures, isolates, and sells seven
equipment, and approaches that aim to remove chemical con- other types of gases for various purposes.
taminants during the process of generating electricity from Currently the U.S. Department of Energy is teaming
coal. Among these technologies are various types of scrubbers, up with seven energy companies to build a prototype of a
devices that chemically convert or physically remove pollut- near-zero-emissions coal-fired power plant. The $1.3-billion
ants (see Figure 17.16, p. 479). Some scrubbers use minerals FutureGen project aims to design, construct, and operate a
such as magnesium, sodium, or calcium in reactions to remove power plant that burns coal, produces electricity, captures
sulfur dioxide (SO ) from smokestack emissions. Others use 90% of its carbon dioxide emissions, and sequesters the CO
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chemical reactions to strip away nitrogen oxides (NO ), break- underground. The project, located in Meredosia, Illinois, will
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ing them down into elemental nitrogen and water. Multilayered pump CO more than 1200 m (three-quarters of a mile) under-
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filtering devices are used to capture tiny ash particles. ground beneath layers of impermeable rock. If this showcase
Another clean coal approach is to dry coal that has high project succeeds, it could be a model for a new generation of
water content in order to make it cleaner-burning. We can power plants across the world. 555

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