Electricity and Coal
Information Directly from Friedland
and Relyea
I. Electricity Basics
A. Coal, oil, and natural gas are primary sources
of energy. Electricity is a secondary source of
energy, meaning we obtain it from the
conversion of a primary source.
B. Approximately 40% of the energy used in the
US is used to generate electricity. Because of
the second law of thermodynamics, only 13%
of this energy is actually available for end
uses.
I. Electricity Basics
C. Energy efficiency is the ratio of the amount of
work that is done to the total amount of
energy that is introduced into the system in
the first place.
D. The process of generating electricity is
therefore only about 35% efficient (only about
35% of the total energy input is turned into
electricity – 65% of the energy is lost in the
process)
I. Electricity Basics
E. To generate electricity in the United States,
we use the following sources of primary
energy:
Coal – 45%
Natural Gas – 23%
Nuclear Fuels – 20%
Hydroelectric Dams – 7%
Other Renewables – 4%
II. Coal
A. Coal is the fuel most commonly used for
electricity generation in the United States.
B. Coal is formed from the remains of swamp
plants that have died between 50 to 350
million years ago, and have decomposed
anaerobically (without oxygen).
II. Coal
C. When organisms die, decomposers break
down most of the material aerobically, and
the nutrients get recycled into the food web.
However, in places such as swamps, river
deltas, and the ocean floor, a large amount of
detritus may build up quickly in an anaerobic
environment. Under these conditions,
decomposers can’t break everything down.
II. Coal
D. As layers of sediment are then laid down,
heat and pressure builds up, and eventually
(over millions of years) fossil fuels can form.
E. The precursor to coal is called peat, and is
made up of partially decomposed organic
material, including mosses.
II. Coal
F. As peat is compressed, first lignite coal is
formed. Further compression yields subbituminous and bituminous coal. After even
more pressure and time, anthracite coal
forms.
G. The four types of coal are based on age and
energy quality.
Name of Coal Type
Age of Coal
Energy Quality of Coal
Lignite
Youngest (baby coal). Soft
coal with wood-like texture
Least dense type of coal,
lowest amount of energy
per kilogram.
Sub-bituminous
Second youngest (teenage
coal)
Slightly more dense than
lignite
Bituminous
Second oldest (adult coal)
Moderately dense,
moderate amount of
energy per kilogram
Anthracite
Oldest (elderly coal)
Most dense type of coal,
highest amount of energy
per kilogram. Very intense
heat, also called hard coal.
Empirical formulas for Coal
C137H97O9NS for Bituminous Coal
C240H90O4NS for high-grade Anthracite
a) Lignite – Very low heating value but still used
for some electricity generation. Most is mined
in Texas, Louisiana, and Montana. Lignite is
about 35% water., and 4,000 to 8,000 BTUs
per pound. Also called “Brown Coal.”
b) Sub-bituminous – Lower sulfur than
bituminous, also heating values of 8,300 and
13,000 BTUs-per-pound. 90% of the coal in
the U.S. is bituminous or sub-bituminous.
Usually found in the Western states or Alaska.
c) Bituminous –
“Soft” coal – most frequently used in electricity
generation. Mined mostly in Appalachia and
the Midwest.
d) Anthracite – “Hard” coal. Formed only when
bituminous coal is put under extreme pressure
– usually with the folding of mountain ranges.
Found in the US. primarily in 15 counties
Pennsylvania. Used for some electricity
generation and in space heating. 15,000 BTUs
per pound!
H. Coal contains a number of impurities that are
released when it is burned, including sulfur.
I. Sulfur content varies by coal type, from 0.4 to
4% of coal mass. Lignite and anthracite have
relatively low sulfur content, while bituminous
coal has a much higher sulfur content.
J. Burning coal also releases mercury, radioactive
particles, and large particulates.
K. Because coal is 60 to 80% carbon, when it is
burned most is converted into CO2. When it is
burned, coal produces far more CO2 than oil
or natural gas.
L. Anything not completely burned remains
behind as coal ash – 3 – 20% of the mass of
burned coal is left behind as coal ash.
M. This large amount of leftover coal ash is
often stored by large coal-fired power plants,
mixed with water in holding ponds.
N. A coal- ash holding pond in Knoxville, TN
broke in 2008 and spilled 1.1 billion gallons of
coal ash, covering 300 acres with toxic sludge.
This was one of the worst spills of a liquid
toxin in US history.
Coal Type Comparisons
*From The Indiana Center for Coal Technology Research
III. Electricity Generation
A. Many types of fossil fuels, as well as nuclear
fuels, can be used to generate electricity.
B. Regardless of the type of fuel used, all
thermal power plants work the same way –
they convert stored potential energy into
electricity.
III. Electricity Generation
C. Major features of a typical coal-burning
power plant include a boiler, where fuel is
burned.
D. The burning fuel transfers energy to water,
which becomes steam.
E. The kinetic energy of the water molecules in
the steam is transferred to the blade of a
turbine, a large device that looks like a giant
fan with a lot of blades.
III. Electricity Generation
C. Major features of a typical coal-burning
power plant include a boiler, where fuel is
burned.
D. The burning fuel transfers energy to water,
which becomes steam.
E. The kinetic energy of the water molecules in
the steam is transferred to the blade of a
turbine, a large device that looks like a giant
fan with a lot of blades.
IV. Reducing Coal Emissions
A. Burning coal releases sulfur in the form of
sulfur dioxide (SO2) which causes acid rain.
The particulates released from coal are a
major public respiratory health hazard, and
the mercury released is a major
environmental and health hazard. The
carbon dioxide released from burning coal is
a major driver of climate change.
IV. Reducing Coal Emissions
B. We can use technology on coal-fired power
plants to reduce some of these emissions.
C. Sulfur can be removed from coal exhaust by
fluidized bed combustion, in which coal is
burned next to calcium carbonate, which
absorbs a lot of the sulfur dioxide.
IV. Reducing Coal Emissions
D. Particulates can be removed using either an
electrostatic precipitator or a scrubber.
Kelly Steinheuer, 8 of Coorparoo, taking her cystic fibrosis medication at
the kitchen table. Her parents Robyn and Darren fear dust and
particulates from coal trains running through their suburb are making
her illness worse. Picture: Liam Kidston. Source: The Courier-Mail
E. An electrostatic precipitator uses electrically
charged plates to collect particulates via
charge from the coal exhaust stream –
particulates are trapped and do not exit.
F. A scrubber passes coal exhaust through a
water misting system, and particulates are
caught and collected in a water system.