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

2. 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Coal is formed as organic matter is withdrawn from contact with atmospheric O2 and subjected to high temperatures and pressures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

3. 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

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

5. 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.

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

14. 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.

15. 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

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

17. 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

19. Figure 18.5
Figure 18.5

20. Figure 18.5 continued
Figure 5 continued

21. Figure 18.6
Figure 18.6

22. Figure continued
Figure continued

24. Coal consumption: Top 25 countries