COAL. What is it? Woody substances buried in an oxygen-deprived; heat and pressure convert wood to carbon; process may give off water and methane Most.
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What is it? Woody substances buried in an oxygen-deprived; heat and pressure convert wood to carbon; process may give off water and methane Most coal comes from the Carboniferous period of geologic time (180-360 mya)
Usage Most of the coal used in the U.S. (90%) is used to generate electricity Almost all of the remainder is used to make heat and coke for industrial processes Very small amounts (less than 1%) go toward home and building heat We use about 1,000 million short tons of coal a year; we have We have an estimated 500,000 million short tons of reserves Source: DOE, http://www.eia.doe.gov/cneaf/coal/reserves/appendixa_taba1.html
Coal Types Anthracite - the hardest variety of coal; 86-98% carbon When burned, produces very little ash; extremely high heat value of 15,000 BTU’s per pound Almost complete conversion means that it had to be buried very deep at some point, if not still In the U.S., anthracite is found primarily in 13 counties in Pennsylvania
Bituminous Second hardest variety of coal; large range of carbon content (45-86% carbon); still has extremely high heat value (10,500-14,000 BTU’s per pound) Most bituminous coal was formed in swamps near ocean; influx of ocean water into swamp brought a lot of sulfur into the deposits a lot of sulfur dioxide formed when burned Bituminous is our largest single variety of coal in the U.S.
Subbituminous Carbon content getting fairly low (35-45%); heating value fairly variable (8,300-11,500 BTU’s per pound) Coal has not undergone a lot of conversion, which means it can never have been buried deep stripmining Most of it is found in the western U.S.
Lignite Carbon content very low (25-35%); heating values also low (4,000-8,300 BTU’s per pound) As with subbituminous, never has been buried deeply Found chiefly in South and West
Coal mining UNDERGROUND MINING: Dig out coal seam from underground Found in “seams” underground that often run parallel to the surface STRIP MINING: Get to coal seam by removing soil on top of it
UNDERGROUND MINING Dig shaft to depth of seam, then follow seam and mine it out DANGERS: Cave-ins Inhalation of coal dust particles (black lung)
STRIP MINING Use large machinery to remove overburden covering shallow seam Must remediate land after coal removed Cheaper, safer, not much else you can do with shallow coal
Strip mining: Impacts ACIDIC MINE DRAINAGE After mining, bedrock and soil replaced on site Rainwater flows through disturbed rock and soil and accumulates pollutants Runoff with low pH and high metal content pollutes streams and lakes
Coal reserves The United States has the largest reserve of coal in the world. Current usage is about 1 billion short tons per year
Coal States Over 1,400 mines in the U.S. About 60/40 on strip mines vs. traditional subsurface mines About 70% of the coal comes from stripmining, some quite huge All of Wyoming’s contribution comes from 20 mines Top Coal-Producing States (2009) (Thousand Short Tons) StateAmount Wyoming431,107 West Virginia136,971 Kentucky107,338 Pennsylvania57,979 Montana39,486
Coal: Uses GLOBAL ENERGY PRODUCTION: 25% U.S. ENERGY PRODUCTION: 57% Used primarily in developed world for electricity production
Combustion Pollution As with all fossil fuels, burning coal produces CO 2 High sulfur coals (bituminous) produce SO 2, which turns into sulfuric acid Coal burns most efficiently if burned at high temperatures High temperatures produce a lot of NO x, as nitrogen in air combines with oxygen
Removing Sulfur Sulfur attached to other chemicals (iron pyrite) can be removed by crushing and washing Organic sulfur (sulfur attached to coal molecules) could be removed before burning chemically, but expensive Scrubbers - pass flue gas through crushed limestone and water solution; SO 2 combines with calcium in water to form calcium sulfate (gypsum)
Clean Burning Coal Removing NO x from flue gas not that easy; better not to produce it Can be removed with chemical scrubber, but expensive Staged combustion - initially burn coal at low temperatures until nitrogen has been bled from coal; then move to high temperature burner once nitrogen reduced Fluidized bed - finely crushed coal mixed with limestone to burn while floating in air; limestone removes sulfur while coal burns at cooler temperature; efficiency increased by using coal as if a gas (turbine plus steam turbine)
Coal Gasification and Liquefaction Coal is the most abundant fossil fuel, but its solid nature makes it hard to use in many applications Gasification and liquefaction convert coal to gaseous and liquid fuels, respectively, by heating coal in the presence of oxygen and/or steam.
Coal: Plusses and Minuses WHY USING COAL IS GOOD: 90% of FF in U.S. is coal Abundant domestic supplies Reduces reliance on imports WHY USING COAL IS BAD: Burning coal releases lots of CO 2 Coal burning causes acid rain Coal mining can damage waterways