Coal and Electricity
“Coal is dirty!” – Sierra Club
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 ____________________________________________________
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.
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 –____________________________________________in the process)
E. To generate electricity in the United States, we use the following sources of primary energy:
Coal – 45%
Natural Gas – 23%
Nuclear Fuels – 20%
_________________________________________
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
______________________________________________
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,________________________________________.
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, ___________________.
F. As peat is compressed, first lignite coal is formed. Further compression yields sub-bituminous and bituminous coal.
After even more pressure and time, ___________________________________
G. The four types of coal are based on age and energy quality.
Name of Coal Type
Lignite
Age of Coal
Youngest (baby coal)
Sub-bituminous
Second youngest (teenage coal)
Bituminous
Second oldest (adult coal)
Anthracite
Oldest (elderly coal)
Energy Quality of Coal
Least dense type of coal, lowest
amount of energy per kilogram
Slightly more dense than lignite
Moderately dense, moderate
amount of energy per kilogram
Most dense type of coal, highest
amount of energy per kilogram
II. Coal (Continued)
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. ___________________________________________
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 __________________________________________.
c) Bituminous – “Soft” coal – most frequently used in electricity generation. Mined mostly in _________________________
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.___________________________________________.
__________________________________15,000 BTUs per pound!
H. Coal contains a number of impurities that are released when it is burned, __________________________
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 __________________________________, 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
_____________________________________________.
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 ________________________________________________________________________.
III. Electricity Generation
A. Many types of fossil fuels, as well as nuclear fuels, can be used ______________________________________.
B. Regardless of the type of fuel used, all thermal power plants work the same way – they convert stored potential energy into
electricity.
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 ____________________________________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 ________________________________
B. We can use technology on coal-fired power plants to_______________________________________.
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.
D. Particulates can be removed using either an electrostatic precipitator or a scrubber.
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_________________________.