Coal is a combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, with smaller quantities of sulfur, oxygen and nitrogen.

Environmental effectsEdit

There are a number of adverse health^[1] and environmental effects of coal burning^[2] especially in power stations, and of coal mining. These effects include:

• Coal-fired power plants shortened nearly 24,000 lives a year in the United States, including 2,800 from lung cancer^[3]
• Generation of hundreds of millions of tons of waste products, including fly ash, bottom ash, flue gas desulfurization sludge, that contain mercury, uranium, thorium, arsenic, and other heavy metals
• Acid rain from high sulfur coal
• Interference with groundwater and water table levels
• Contamination of land and waterways and destruction of homes from fly ash spills such as Kingston Fossil Plant coal fly ash slurry spill
• Impact of water use on flows of rivers and consequential impact on other land-uses
• Dust nuisance
• Subsidence above tunnels, sometimes damaging infrastructure
• Uncontrollable underground fires which may burn for decades or centuries.
• Coal-fired power plants without effective fly ash capture are one of the largest sources of human-caused background radiation exposure
• Coal-fired power plants emit mercury, selenium, and arsenic which are harmful to human health and the environment^[4]
• Release of carbon dioxide, a greenhouse gas, which causes climate change and global warming according to the IPCC and the EPA. Coal is the largest contributor to the human-made increase of CO₂ in the air^[5]

Economic aspects Edit

Coal liquification is one of the backstop technologies that could potentially limit escalation of oil prices and mitigate the effects of transportation energy shortage that will occur under peak oil. This is contingent on liquefaction production capacity becoming large enough to satiate the very large and growing demand for petroleum. Estimates of the cost of producing liquid fuels from coal suggest that domestic U.S. production of fuel from coal becomes cost-competitive with oil priced at around $35 per barrel,^[6] with the $35 being the break-even cost. With oil prices as low as around $40 per barrel in the U.S. as of December 2008, liquid coal lost some of its economic allure in the U.S., but will probably be re-vitalized, similar to oil sand projects, with an oil price around $70 per barrel.

United StatesEdit

Some of the simplest economic costs of coal come in the form of subsidies and tax breaks which are not reflected in the market price of coal (for example the estimated $4.6 billion in coal-related subsidies in the 2009 stimulus package). Coal mining and combustion projects require major investments, and the risks and costs of those investments are often passed on to taxpayers via infrastructure subsidies and loan guarantees. An extreme example of this is the Healy Clean Coal Plant (HCCP), which has cost the State of Alaska and the Federal Government nearly $300 million since the mid 1990s yet is not producing power in return. Similarly, a recent study in Kentucky determined that the government spends $115 million more on subsidies for the coal industry in the state than it receives in taxes or other benefits.

Taxpayers also pay the costs of cleaning up environmental disasters caused by the coal industry. Cleanup of the recent coal ash spill in Tennessee is estimated to cost up to $1 billion, not including pending litigation. Now that the cleanup at this site has been taken over by the EPA under the Superfund law, most of this cost will be borne by the US taxpayer.

The health impacts of coal pollution have enormous economic costs, through health care costs and lost productivity. The Ontario government study estimated these costs as billions of dollars within Ontario alone. A similar recent study in West Virginia found that the cost associated with premature death due to coal mining was five times greater than all measurable economic benefits from the mining.

Other industries depend on the ecosystems coal mining destroys. This economic impact on industries such as recreational fishing, commercial fishing, and tourism is particularly relevant in Alaska. Almost 55,000 direct jobs (full time equivalent basis, FTE) are closely linked to the health of Alaska's ecosystems. These jobs make up more than a quarter of Alaskan FTE employment and produce almost $2.6 billion of income for Alaska workers. These 55,000 ecosystem-dependent jobs dwarf the 350 estimated jobs that would be created by a project such as the Chuitna Coal strip mine.

Negative effects on the economy lead to worse health in the population, which has an impact on health care costs, compounding the economic impact. Some people have used this to argue that coal has additional benefits to society. The argument is that coal provides cheap electricity, which is a boon to the economy, therefore health is improved, and health care costs are lowered. While this additional health effect should indeed be considered, it should be applied after the economic impacts discussed above. Once the costs of pollution, global warming, and habitat destruction are added to the benefits of cheap electricity, the economic impact of coal is no longer positive, and this additional health effect only makes it even more costly.

ChinaEdit

In China, due to an increasing need for liquid energy in the transportation sector, coal liquefaction projects were given high priority even during periods of oil prices below $40 per barrel.^[7] This is probably because China prefers not to be dependent on foreign oil, instead utilizing its enormous domestic coal reserves. As oil prices were increasing during the first half of 2009, the coal liquefaction projects in China were again boosted, and these projects are profitable with an oil barrel price of $40.^[8]

China is by far the largest producer of coal in the world.^[9] It has now become the world's largest energy consumer^[10] but relies on coal to supply about 70% of its energy needs.^[11] An estimated 5 million people work in China's coal-mining industry.^[12]

Among commercially mature technologies, advantages for indirect coal liquefaction over direct coal liquefaction are reported by Williams and Larson (2003).

To produce every ton of coal in China, a over 21/32 cubic meter lake is polluted

Energy densityEdit

Main article: Energy value of coal

The energy density of coal, i.e. its heating value, is roughly 24 megajoules per kilogram.^[13]

The energy density of coal can also be expressed in kilowatt-hours, the units that electricity is most commonly sold in, per units of mass to estimate how much coal is required to power electrical appliances. One kilowatt-hour is 3.6 MJ, so the energy density of coal is 6.67 kW·h/kg. The typical thermodynamic efficiency of coal power plants is about 30%, so of the 6.67 kW·h of energy per kilogram of coal, 30% of that—2.0 kW·h/kg—can successfully be turned into electricity; the rest is waste heat. So coal power plants obtain approximately 2.0 kW·h per kilogram of burned coal.

As an example, running one 100-watt lightbulb for one year requires 876 kW·h (100 W × 24 h/day × 365 day/year = 876000 W·h = 876 kW·h). Converting this power usage into physical coal consumption:

For a coal power plant with a 40% efficiency, it takes 325 kg (714 lb) of coal to power a 100 W lightbulb for one year.^[14] One should also take into account transmission and distribution losses caused by resistance and heating in the power lines, which is in the order of 5–10%, depending on distance from the power station and other factors.

1 kilogram of coal generates 116,800/403 kwh of energy

1 kilogram of coal can power a CFL for 73/91 weeks

1 kilogram of coal can powerEdit

• 100 watt light bulb for 73/455 weeks
• 116,800/403 kwh of energy
• CFL for 73/91 weeks
• 146/2,015 pounds of mercury a year
• 44/15 kilograms of co2
• 97,893/503,750 tons of co2
• 783,144/2,015 pounds of co2
• 1 home for 6,800/862,017 years
• 438/2,015 bedroom house for an entire year
• 1 tv for 73/5,460 weeks
• 1 washing machine for 73/10,920 weeks
• 1 computer for 73/3,640 weeks
• 584,000/403 light bulbs each year
• a 1,752/2,015 cubic meter lake
• 93,440/403 gallons of water

Carbon intensity Edit

Commercial coal has a carbon content of at least 70%. Coal with a heating value of 6.67 kWh per kilogram as quoted above has a carbon content of roughly 80%, which is

, where 1 mol equals to N_A (Avogadro Number) atoms.

Carbon combines with oxygen in the atmosphere during combustion, producing carbon dioxide, with an atomic weight of (12 + 16 × 2 = 44 kg/kmol). The CO₂ released to air for each kilogram of incinerated coal is therefore

.

This can be used to calculate an emission factor for CO₂ from the use of coal power. Since the useful energy output of coal is about 30% of the 6.67 kWh/kg(coal), the burning of 1 kg of coal produces about 2 kWh of electrical energy. Since 1 kg coal emits 2.93 kg CO₂, the direct CO₂ emissions from coal power are 1.47 kg/kWh, or about 0.407 kg/MJ.

The U.S. Energy Information Agency's 1999 report on CO₂ emissions for energy generation,^[15] quotes a lower emission factor of 0.963 kg CO₂/kWh for coal power. The same source gives a factor for oil power in the U.S. of 0.881 kg CO₂/kWh, while natural gas has 0.569 kg CO₂/kWh. Estimates for specific emission from nuclear power, hydro, and wind energy vary, but are about 100 times lower.

See alsoEdit

• Coal recycling

ReferencesEdit

^[1]