Harmful effects of coal burning

Combustion of coal, like any other compound containing carbon, produces carbon dioxide (CO₂) and nitrogen oxides (NO_x) along with varying amounts of sulfur dioxide (SO₂) depending on where it was mined. Sulfur dioxide reacts with oxygen to form sulfur trioxide (SO₃), which then reacts with water to form sulfuric acid. The sulfuric acid is returned to the Earth as acid rain.

Emissions from coal-fired power plants represent the largest source of carbon dioxide emissions, a primary cause of global warming. Coal mining and abandoned mines also emit methane, another cause of global warming. Since the carbon content of coal is much higher than oil, burning coal is a more serious threat to global temperatures. Many other pollutants are present in coal power station emissions. A study commissioned by environmental groups claims that coal power plant emissions are responsible for tens of thousands of premature deaths annually in the United States alone. Modern power plants utilize a variety of techniques to limit the harmfulness of their waste products and improve the efficiency of burning, though these techniques are not subject to standard testing or regulation in the U.S. and are not widely implemented in some countries, as they add to the capital cost of the power plant. To eliminate CO₂ emissions from coal plants, carbon capture and storage has been proposed but has yet to be commercially used.

Coal and coal waste products including fly ash, bottom ash, boiler slag, and flue gas desulferization contain many heavy metals, including arsenic, lead, mercury, nickel, vanadium, beryllium, cadmium, barium, chromium, copper, molybdenum, zinc, selenium and radium, which are dangerous if released into the environment. Coal also contains low levels of uranium, thorium, and other naturally-occurring radioactive isotopes whose release into the environment may lead to radioactive contamination. While these substances are trace impurities, enough coal is burned that significant amounts of these substances are released, paradoxically resulting in more radioactive waste than nuclear power plants.

Due to its scientifically accepted connection with climate change , the world's reliance on coal as an energy source, and health concerns in areas with poor air pollution controls, The Economist recently labeled the burning of coal "Environmental Enemy No. 1."

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Energy density

The energy density of coal is roughly 24 Megajoules per kilogram. It is perhaps more useful to put this into another unit of energy, kilowatt-hours. This is the unit that electricity is most commonly sold in. In that case, the energy density of coal is 6.67 kW*hours/kg.

One can put this information to use to figure out how much coal is needed to power things. For example, running one 100 Watt computer for one year requires this much electricity:

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The maximum Thermodynamic efficiency of coal power plants is about 30%. Of the 6.67 kW*hours of energy per kilogram of coal, about 30% of that can successfully be turned into electricity - the rest is waste heat. Coal power plants obtain ~2.3 kW*hours/kg of burned coal.

Plugging in this information one finds how much coal must be burned to power a typical computer for one year:

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It takes 838 pounds of coal to power a computer for one full year.

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