coal
DESCRIPTION
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 coal comes from the Carboniferous period of geologic time (180-360 mya). Usage. - PowerPoint PPT PresentationTRANSCRIPT
What is it?
Woody substances buried in an oxygen-deprived; heat and pressureconvert wood to carbon; process may give off water and methane
Most coal comes from the Carboniferous period of geologic time(180-360 mya)
UsageMost of the coal used in the U.S. (90%) is used to generateelectricity
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 haveWe 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 verydeep at some point, if not still
In the U.S., anthracite is found primarily in 13 counties in Pennsylvania
BituminousSecond 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; influxof ocean water into swamp brought a lot of sulfur into thedeposits 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 fairlyvariable (8,300-11,500 BTU’s per pound)
Coal has not undergone a lot of conversion, which means it cannever have been buried deep stripmining
Most of it is found in the western U.S.
LigniteCarbon 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
World Estimated Recoverable Coal Source: U.S. Dept. of Energy(Million Short Tons)
Region/CountryRecoverable Anthracite and
BituminousRecoverable Lignite and
SubbituminousTotal Recoverable
CoalNorth America 130,186 149,320 279,506
Central & South America 8,489 13,439 21,928
Western Europe 1,571 34,918 36,489
Eastern Europe & Former U.S.S.R. 122,170 157,607 279,778
Middle East 462 0 462
Africa 55,294 192 55,486
Asia & Oceania 212,265 114,999 327,264
World Total 530,438 470,475 1,000,912
Coal StatesOver 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 hugeAll of Wyoming’s contribution comes from 20 mines
Top Coal-Producing States (2009)
(Thousand Short Tons)
State Amount
Wyoming 431,107
West Virginia 136,971
Kentucky 107,338
Pennsylvania 57,979
Montana 39,486
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 CO2
High sulfur coals (bituminous) produce SO2, which turnsinto sulfuric acid
Coal burns most efficiently if burned at high temperatures
High temperatures produce a lot of NOx, as nitrogen in aircombines with oxygen
Removing SulfurSulfur attached to other chemicals (iron pyrite) can be removedby 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 watersolution; SO2 combines with calcium in water to form calcium sulfate (gypsum)
Clean Burning Coal
Removing NOx 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 temperaturesuntil nitrogen has been bled from coal; then move to high temperature burner once nitrogen reduced
Fluidized bed - finely crushed coal mixed with limestone to burnwhile floating in air; limestone removes sulfur while coal burnsat cooler temperature; efficiency increased by using coal as if a gas (turbine plus steam turbine)
Coal Gasification and LiquefactionCoal is the most abundant fossil fuel, but its solid nature makes ithard 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.