Pollution from Power Plants


Coal Power plants

Coal is an organic sedimentary rock with terrestrial origin. Because it is derived from lignin, a plant material, it contains sulfur and nitrogen impurities along with metals.

Coal is abundant and supplies about half of the electricity in Illinois. We've already discussed the clean coal technology. We have the means to produce electricity from coal without introducing pollutants into the troposphere. It is more expensive and nearly all coal-fired power plants use the older, dirtier technology. Unfortunately, two of the nation's most polluting power plants are located in Illinois.

Coal is second only to automobiles in the production of NOx. Nitric oxide catalyzes the production of ground level ozone in the presence of sunlight and organic compounds. Smog is a threat to the health of humans and reduces agricultural productivity.

Particulate matter or soot is released when coal is burned. Fine particles, with a diameter of 2.5 micrometers or less, and coarse particles, with a diameter of 10 micrometers or less is produced. The irregular surfaces of these aerosols provide locations for SO2 and NOx to bind. Their high concentration on the particle surfaces promotes reactions that would have a much lower rate in the atmosphere and many of the surface reactions yield toxic or irritating chemical substances.

  • Burning of coal releases SO2 and NOx.

  • Oxidation of SO2 and NOx in air forms H2SO4 and HNO3, strong mineral acids.

  • These acids then dissolve in water droplets in clouds and acidic rain results.

  • This "wet deposition" reduces the concentration of sulfur and nitrogen oxides in the atmosphere but causes many problems on land and surface water. (More on this later.)

Mercury is a metallic pollutant released from coal combustion. Coal-burning power plants are the largest human-caused source of mercury emissions to the air in U.S., responsible for more than 40 % of mercury emissions (40-52 tons of mercury released every year in US).

When the mercury vapor finds its way into bodies of water, it is converted by bacteria into the more toxic compound, methyl mercury. This is a known neurotoxin. It causes mental retardation, seizures, cerebral palsy and death.

Burning coal in a power plant is less efficient than burning other fossil fuels and it makes more carbon dioxide per unit of electricity produced. As we've discussed, increasing CO2 levels in the atmosphere are responsible for global climate change.

Pollution Control

We have methods that allow us to remove many of the solids, liquids, and gases emitted from coal and other fossil fuel fired power plants but adding these pollution control devices costs money. Governments and other organizations can enforce limits on effluents or encourage/require the use of pollution control technology.

Pollution Reduction Technology:
  • Flue Gas Combustion Modification
      Modifying the oxygen content and/or the temperature of combustion can reduce the concentration of volatile organic compounds and partially oxidized nitrogen compounds.


  • Electrostatic Precipitators
      Solid or liquid particles supported in the effluent gas stream can pick up a charge and be trapped in an electrically charged filtering device..


  • Flue Gas Deacidifier
      Nitric and sulfuric acids are formed in fossil fuel combustion. These can be removed with wet scrubbers or by reaction with solid basic oxides.


Cap and Trade: the market approach

    We'll talk about this aspect of pollution control when we discuss the Clean Air Act. Cap-and-Trade sets a price on the ability to emit certain polluting compounds. Utilities can buy and sell these allowances.


Regulation

    State and federal governments have the ability to regulate the industries within their borders. Regulation relies on analytical chemistry to effluent quantities and concentrations of polluting substances in the air.


Cost

    How can we evaluate the benefits of pollution control relative to its costs?



Professor Patricia Shapley, University of Illinois, 2010