COAL

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.

Coal: Plusses and Minuses

WHY USING COAL IS GOOD: 90% of FF in U.S. is coalAbundant domestic suppliesReduces reliance on imports

WHY USING COAL IS BAD: Burning coal releases lots of CO2 Coal burning causes acid rainCoal mining can damage waterways