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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.

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Coal

COAL


What is it

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)


Usage

Usage

Most of the coal used in the U.S. (90%) is used to generateelectricityAlmost all of the remainder is used to make heat and coke for industrial processesVery small amounts (less than 1%) go toward home and building heatWe 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

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 poundAlmost complete conversion means that it had to be buried verydeep at some point, if not stillIn the U.S., anthracite is found primarily in 13 counties in Pennsylvania


Bituminous

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; influxof ocean water into swamp brought a lot of sulfur into thedeposits  a lot of sulfur dioxide formed when burnedBituminous is our largest single variety of coal in the U.S.


Subbituminous

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  stripminingMost of it is found in the western U.S.


Lignite

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 deeplyFound chiefly in South and West


Coal mining

Coal mining

Found in “seams” underground that often run parallel to the surface

UNDERGROUND MINING:

Dig out coal seam from underground

STRIP MINING:

Get to coal seam by removing soil on top of it


Coal

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)


Coal

STRIP MINING

Use large machinery to remove overburden covering shallow seamMust remediate land after coal removed

Cheaper, safer, not much else you can do with shallow coal


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

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

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 hugeAll of Wyoming’s contribution comes from 20 mines


Coal

Coal: Uses

Used primarily in developed world for electricity production

GLOBAL ENERGY PRODUCTION:

25%

U.S. ENERGY PRODUCTION:

57%


Combustion pollution

Combustion Pollution

As with all fossil fuels, burning coal produces CO2High sulfur coals (bituminous) produce SO2, which turnsinto sulfuric acidCoal burns most efficiently if burned at high temperatures

High temperatures produce a lot of NOx, as nitrogen in aircombines with oxygen


Removing sulfur

Removing Sulfur

Sulfur attached to other chemicals (iron pyrite) can be removedby crushing and washingOrganic sulfur (sulfur attached to coal molecules) could be removed before burning chemically, but expensiveScrubbers - pass flue gas through crushed limestone and watersolution; SO2 combines with calcium in water to form calcium sulfate (gypsum)


Clean burning coal

Clean Burning Coal

Removing NOx from flue gas not that easy; better not to produce itCan be removed with chemical scrubber, but expensiveStaged combustion - initially burn coal at low temperaturesuntil nitrogen has been bled from coal; then move to high temperature burner once nitrogen reducedFluidized 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 liquefaction

Coal Gasification and Liquefaction

Coal 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.


Coal

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 CO2

Coal burning causes acid rain

Coal mining can damage waterways


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