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. CoalD. 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 sub-bituminous 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 EmissionsD. 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.