Energy, Environment, and Industrial Development Michael B. McElroy Frederick H. Abernathy Lecture 14 April 3, 2006

Sunlight + CO2 + H2O  CH2O + O2 Photosynthesis: a mechanism for conversion of solar energy to chemical potential energy Sunlight + CO2 + H2O  CH2O + O2 Coal is formed as organic matter is withdrawn from contact with atmospheric O2 and subjected to high temperatures and pressures organic matter oxygen released to atmosphere

The ultimate product may be represented by: CH2O  C + H2O As plant matter is subjected to higher pressures and temperatures, its chemical composition is altered The sequence involves sequential loss of H and O and enrichment of the relative abundance of C The ultimate product may be represented by: CH2O  C + H2O graphite

Sequence of transformations in coal formation: Peat  lignite (brown coal)  sub-bituminous  bituminous  semi-bituminous  anthracite  graphitic

Lignite Lowest rank of coal. Used almost exclusively for steam-electric power generation Brownish-black in color with high inherent moisture content – sometimes as high as 45% Heat content ranges from 9 ~ 17 million BTU/ton. Computed on a moist, mineral matter free, basis.

Sub-bituminous coal Intermediate between lignite and bituminous Color ranges from dull, dark brown, to black. Relatively soft and crumbly 20~30% inherent moisture content Heat content 17 ~ 24 million BTU/ton on moist, mineral-matter free, basis. Major US source in Powder River Basin of Wyoming. Used mainly for electric power generation

Bituminous coal Most abundant US source Moisture content < 20% Heat content 21~30 million BTU/ton Dense, black, matter Used for power generation but also for heat and as a source of coke

Anthracite coal Hard, brittle, black, lustrous color High in C with low content of volatiles Moisture content < 15% Heat content 22~28 million BTU/ton, average for US 25x106 BTU/ton

Primary sources of coal in the US: Appalachia, Mid-west, West Sulfur content of western coal is relatively low, typically about 0.7% Sulfur content of Eastern coal is relatively high, typically 3~4% Up to 1970, Eastern sources dominated US production. More recent shift to Western sources Coal consumption in US is dominated now by electric power production. Prior to 1945, railroads and residential heating were comparable to power generation

Origins of Coal Products of land-based plants Recall that life expanded to land at about 440x106 yr BP (November 25, 7am) Carboniferous period 360~290x106 yr BP England at that time was close to the equator

320 Ma (Paleozoic/Carboniferous/Pennsylvanian/Bashkirian/Yeadonian) 410 Ma (Paleozoic/Silurian/Pridoli) Picture source: Windley, Brian F. The Evolving Continents. West Sussex: John Wiley & Sons Ltd., 1995. Figures adopted from http://www.dinosauria.com/dml/maps.htm

Origins of Coal Think of primitive jungles with massive trees – lepidodendron, sigillaria (see story in Coal – Barbara Freeze) Slow decay led to preservation of large quantities of plant material Decay often took place in environments flooded episodically with sea water Sea water is high in sulfur

Origins of Coal Decay resulted in depletion of oxygen. SO42- would have been reduced. Sulfur retained often in form of pyrite, FeS2. Pyrite is the most abundant sulfide mineral, sometimes known as “fool’s gold”. In addition to combustible C, coal contains variable amounts of Ca, Mg, K, S, Cl and other chemical elements bound up in mineral form.

Environmental problems associated with coal Problems with mining:  black lung disease  mine collapse  explosions CH4, CO  CO2  flooding Residues from mining  pollution of soils and waters  devastation of landscapes

Environmental problems associated with coal Problems with coal combustion  particles released to air  soot  sulfur  mercury, etc

Acid Rain Combustion of coal converts S to SO2 SO2 in the atmosphere is oxidized to H2SO4 (sulfuric acid) SO2  x-4 = 0, x = 4 H2SO4  x+2-8=0, x = 6 In rain H2SO4  H+ + H+ + SO42- pH of rain in equilibrium with atmospheric CO2  pH = 5.6

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http://www.eia.doe.gov/oiaf/ieo/figure_56.html

Coal consumption: Top 25 countries http://www.nationmaster.com/red/graph-T/ene_coa_con#

http://www.eia.doe.gov/oiaf/ieo/figure_55.html