10.2 Coal

Jeff Simpson

Learning Objectives – By the end of this chapter, you should be able to do the following.

  • Explain the conditions under which coal formed, when it formed, and what it formed from.
  • Explain why anthracite coal is preferred as a fuel source to peat or lignite.
  • Explain the changes from peat to lignite to bituminous to anthracite.
  • Name and explain why there are two different types of coal mines. 
  • Describe the principle ways that we use coal. 
  • Explain how electricity is generated from coal.
  • Explain the use of and problems with the disposal of coal ash as well as one possible new use.
  • Explain how our civilization has been built by burning coal.
  • List several health and environmental, health, and social consequences associated wit coal extraction.

 

The black lump below, a piece of coal, has made our modern civilization possible. Societies around the world have burned coal for centuries as it has been a plentiful, widely distributed, fuel with high energy content. However, the extraction and burning of coal also has produced severe consequence for the environment and societies.

 

Fig. 10.2.1 – A lump of coal. (Not from my Christmas stocking.) 

 

What Is Coal and How Did It Form?

 

Video 10.2.1 – How Coal Made Us Rich and Why it Needs to Go (8:21)

 

Main Points from the Video
Many new coal plants will stop being used before the end of their normal life, becoming stranded assets, a financial liability

Coal resources in Wales often are cited as one reason for the rise of Britain (and later the United States) in the industrial revolution.1 Coal, the first fossil fuel to be widely used, forms mostly on land in swampy areas next to rivers and deltas in areas with humid tropical to temperate climates. The vigorous growth of vegetation leads to an abundance of organic matter that accumulates within stagnant water and thus does not decay and oxidize. This condition in which dead organic matter is submerged in oxygen-poor water must be maintained for centuries to millennia in order for enough material to accumulate to form a thick layer. At some point, the swamp deposit is covered with more sediment — typically because a river changes its course or sea level rises. As more sediments are added, the organic matter starts becomes compressed and heated. Compressed plant material is called peat. Peat has been used as a fuel for centuries.

 

Fig 10.2.2 – Peat consists of partially decayed organic matter. The Irish have long mined peat to be burned as fuel though this practice is now discouraged for environmental reasons. 

 

Peat gatherers at Westhay, Somerset Levels in 1905
Fig 10.2.3 – Peat gatherers at Westhay, Somerset Levels in 1905

Over time, given pressure and heat, peat can turn into the low-grade type of coal called . Lignite forms at depths between a few 100 m and 1,500 m and temperatures up to about 50°C. Between 1,000 m to 5,000 m depth and temperatures up to 150°C m, coal forms (Figure 20.3.1d). At depths beyond 5,000 m and temperatures over 150°C, coal forms. As the coal becomes more compressed and heated, water, volatiles, and oxygen are driven out and the percentage of carbon increases, leading to a more desirable fuel product. Much of the coal being burned today in India is low-grade coal and results in significant air pollution, health issues, and deaths.

 

Types of coal - peat, lignite, bituminous, and anthracite.
Fig 10.2.4 – Types of Coal

 

coal seam
Fig 10.2.5 – A seam of bituminous coal at Point Aconi, Nova Scotia. The plant material that formed this coal was deposited in the Pennsylvanian Period about 299-323 million years ago. Photo by Michael C. Rygel, Wikimedia Commons.

 

How is Coal Mined?

Strip Mines – When a seam of coal coal is closer than ~100′ to the surface, the overburden, the rock covering the coal, is blasted away and the coal is scooped up. This type of mine requires the fewest employees and can extract vast amounts of coal in a short time. However, this works only when the sedimentary rock layers that contain the coal are close to the surface such as in the Black Thunder Coal Mine in Wyoming, USA.

 

surface coal mine in Wyoming, USA
Fig 10.2.6 – A surface coal mine in Wyoming, United States. The USA has the world’s largest coal reserves. Mining coal this way is safer and requires less labor. gHowever, not all coal deposits are close enough to the surface to extract this way.

 

Video 10.2.2 – World’s Biggest Mine: Inside US Coal at the North Antelope Rochelle Mine, Wyoming (5:17)


Mountaintop Removal
– When coal-bearing sedimentary rocks are in an area that has been incised (cut) by streams rather than being flat as shown above, a process called mountaintop removal is used as in this area near Danville, West Virginia, USA. The Land of Mountaintop Removal (2:57) by Smithsonian shows how 500 mountains and 3200 streams in the Appalachian Mountains near West Virginia have been destroyed by mountaintop removal. But this process, like strip mining, is more cost effective and safer than underground mining. (The Shocking Danger of Mountaintop Removal | Michael Hendryx TED Talk (13:44) is a fascinating look at the findings of science and the work of mining companies to cover up those findings.)

 

Video 10.2.3 -How Mountaintop Mining Affects Life and Landscape in West Virginia (9:24)

 

Underground Mining – When coal is too far below the surface to access easily, vertical shafts are drilled until the coal seam is reached. Then horizontal drifts or tunnels allow miners remove the coal from the mine. This form of mining is the most dangerous due the possibility of a mine collapse or the ignition of methane leaking from the coal seam. Additionally, miners are exposed to airborne silica dust (from the rock) and coal. Over years, this leads to black lung disease and silicosis. (See Mining the Navajo Nation and Big Money, Black Lung, and Doctors for the Coal Companies.)

 

Underground and Surface Mining Methods
Fig 10.2.7 – Underground and Surface Mining Methods (Image courtesy of University of Kentucky)

 

Fig 10.2.8 – A miner, begrimed and sweaty, wearing just a pair of trunks and a helmet, works the coal face in an underground mine with a large drill in Britain in 1942. The steel props which hold up the roof of the tunnel can be seen on the right of the photograph.


Where Coal Is Found?

Coal is mined today near the surface where, during the Carboniferous period, the conditions were correct for plants to grow, die, and stack up. Not all countries have access to coal. This unequal distribution of a prized fossil fuel led during World War II to Germany looking far and wide for more coal to fuel its war effort.

 

Fig 10.2.9 – Major world coal deposits.

 

 

Arizona Mines
Fig10.2.10 – Arizona’s major coal deposits are in the northeastern part of the state near Kayenta. (Arizona Geological Survey)

 

The coal deposits and mines in northeastern Arizona fueled the Navajo Generating Station near Lake Powell and Page, AZ. The mining of those same deposits required the extensive pumping of groundwater, causing many Navajo families to have to haul water and leading to lung disease for many of the workers. But the coal also provided jobs.


Coal Power Plants 

Once coal is mined, it is used primarily in smelting, the making of steel, or – the major use at 2/3 – producing electricity. As of 2022, worldwide there were about 6593 coal-fired power stations generating ~ 1/3 of the world’s electricity. Many of these plants are not fully utilized, some existing only for statistical purposes. Though the amount of coal being burned is increasing slowly, that trend is about to reverse.

Coal Plant Parts
Figure 10.2.11 – Idealized schematic of a typical coal power plant. Note that the image omits the air pollution and the coal ash piles.

In the plant, coal is pulverized to a fine powder and them shot into a boiler. A 500 MW plant may shoot 250 tonnes per hour under full load. That is 152 pounds of coal per second. Each of the three former coal units at the Navajo Generating Station near Page, Arizona when fully operating used 300 pounds/second.

As the coal contains some silica from the rock where it was mined, the very expensive pipes in a coal plant are worn down quickly and have to be replaced.

The boilers create steam which turns a turbine which turns a generator to make electricity in a process that may have begun 400,000,000 years ago when the sun’s energy combined elements and molecules in growing plants, after which the plants died, were buried in the absence of oxygen, and were pressed and heated. Nearly 400,000,000 later, we break apart those original solar bonds to release turn chemical energy which becomes thermal energy which becomes mechanical energy and, finally electrical energy. In the process a lot of pollution is released.

Coal-fired power stations emit over 10 Gt of CO2 each year (~1/5 of world greenhouse gas emissions or 40% of the energy emissions) and are the single largest cause of climate change. More than half of all the coal-fired electricity in the world is generated in China, though China is beginning to consolidate and phase out coal plants. Coal plants remain profitable only because the externalized environmental and health costs are not included. If damage to our health and environment were included in the cost of coal power, coal would be phased out immediately. We allow our atmosphere to be a free dumping ground. Our leaders ignore this issue. As more countries move away from coal, hundreds of billions of dollars that have been invested in coal plants will become stranded assets, something that concerns investors.


Coal Ash

Coal ash is what is left over from the burning of coal in coal-fired power plants. In 2014, coal ash is one of the largest types of industrial waste generated in the US with ~130 million tons of coal ash generated in 2014. Some coal ash is used in making wallboard, concrete, roofing materials, and bricks in a way that minimizes the toxic materials contained from escaping into the surrounding environment. Other coal ash is used structural fills/embankments where the stability of those toxic materials is more in question. About 60% of all coal as is place in on-site impoundments or landfills where is will be contained forever… hopefully. However, major coal ash spills in Kingston Tennessee and Eden, NC have shown this is not the case. The Kingston spill [GE] alone cost over $1,000,000,000 to clean up. In the coming decades, more coal ash sites will suffer the same fate. Is using fossil fuels really worthwhile?

Tennessee Valley Authority Fly Ash containment failure on 23 December 2008 in Kingston, Tennessee
Fig 10.2.12 – Tennessee Valley Authority Fly Ash containment failure on 23 December 2008 in Kingston, Tennessee. Cleanup of this one spill cost over one billion dollars. 

 

Coal ash includes, fly ash (fine, powdery material composed mostly of silica made from the burning of finely ground coal in a boiler), bottom ash (coarse angular ash too large to be carried up into the smoke stacks so it forms in the bottom of the coal furnace), boiler slag, molten bottom ash from slag tap and cyclone type furnaces that turns into pellets that have a smooth glassy appearance after it is cooled with water), flue gas desulfurization material (remains from the process of reducing sulfur dioxide emissions from a coal-fired boiler that can be a wet sludge consisting of calcium sulfite or calcium sulfate or a dry powered material that is a mixture of sulfites and sulfates) and other products.

Coal ash contains contaminants like mercury, cadmium and arsenic which can pollute streams, groundwater, and our atmosphere. The waste that we have left behind from burning coal will be with us for thousands of millennia. Contamination of groundwater from coal ash has occurred in Texas. A report found that the groundwater around coal-fired plants across the state contains levels of pollutants like arsenic, boron, cobalt or lithium that would make it unsafe for human consumption. It also found that almost none of the impoundments where plants dispose of spent coal are lined properly — one of the requirements of the 2015 Coal Ash Rule. Despite rules being in place, many fossil fuel companies try to work around them or just ignore them and they most often are not held accountable.

Average Heavy (Toxic) Metal Content of Coal

Mercury (Hg) 0.10±0.01 ppm
Arsenic (As) 1.4 – 71 ppm
Selenium (Se) 3 ppm

However, this is some potential good news. We need a reliable supply of some elements called rare earth elements for our new gadgets such as smart phones, LED lights, electric motors, and batteries. Despite their name, rare earth elements (REEs) not not that rare, but they are concentrated in only a few locations leading to supply chain issues and international tensions. A possible solution is to mine coal ash. Researchers have reported a simple method for recovering REEs from coal fly ash which has similar elemental concentrations as the raw ores. Until now, extracting these precious elements was complicated and hazardous. Researchers report that environmentally benign and reusable ionic liquids can selectively dissolve rare-earth oxides over other metal oxides. The ionic liquid can be recovered easily. Researchers have extracted >77% of the REEs from fresh coal ash and 97% from weathered ash that had spent years in a storage pond.

Coal can also be considered as an economic source of strategically important elements, such as Ge, Ga, U, V, Se, and are earth elements, Y, Sc, Nb, Au, Ag, and Re, as well as base metals Al and Mg.

 

Coal and Methane Releases 

The process of mining coal releases large amounts of methane into the atmosphere. Even abandoned coal mines emit methane into the atmosphere. This is a concern as methane is a putting green house gas, 25 times more powerful than carbon dioxide.

 

Fig 10.2.13 – The EPA reports that underground coal mines release 36,500,000 cubic feet of methane or more per year. Surface mines do emit methane do not have to report these data. The 2019 measured methane releases were equivalent to 34,206,291 metric tons of CO2. That is the equivalent of 7.5 million cars or more than 3 times all the carbon dioxide from all the passenger vehicles in Arizona. 

 

What is the Future for Coal?

As late as the 1980s, coal provided over half the electricity in the US, but by 2022 that fraction had fallen to 22%. The burning of coal for electricity in the US should continue to decline, though there will be some instability due the variable price of natural gas.

In the industrialized world, coal use is declining, though China and India use vast quantities of coal. Many in the industrialize world point at China and ask, “Why should we stop using coal when China isn’t?” The simple answer is that we have exported much of our manufacturing and thus our coal pollution to other countries. We get affordable items, people have jobs, but our pollution is exported and not identified with us.

As the world moves toward cleaner source of energy, coal use is expected to decline, though there will continue to be a need for coal in the making of steel, both for heat at as a source of carbon to cobine with iron to make steel. Eventually, hydrogen may be able to take the place of coal in industrial heat.

 

Fig 10.2.13 – Coal Production by Region

 

The amount of coal consumed each second by the world is equivalent to ~400 barrels of oil, but the future of coal is less bright.

 

Video 10.2.4 – Why Coal Has No Future (2:21)

 

Coal and Health

The burning of this much coal results in many illnesses and early deaths, mainly from air pollution. Peer-reviewed research published in Nature showed that emissions from fossil fuels killed over 1,000,000 people around the world in 2017 with half of those deaths attributable to emissions from coal.

Coal miners often suffer from silicosis and black lung disease, and, in some cases, the coal mining companies deny worker compensation.

 

Coal and Jobs

The mining of coal use to employ almost 180,,000 workers. Now that number under 38,000 and falling as power plants that once used coal are turning to methane, wind, solar, and nuclear.

 

Coal Jobs in the US
Fig 10.2.13 – Coal jobs in the USA. [Source]

 

Advantages of Coal Power
1. It creates jobs.
2. It is a concentrated source of energy.
3. It can run 24 hours a day.

Disadvantages of Coal
1. The burning of coal is major source of CO2.
2. The burning of coal releases toxic metals (As, Hg, Cd) into the air, water and soil.
3. The burning of coal releases small particulates, PM 2.5, that get into our water, blood and brain.
4. The mining of coal is destructive to habitats including mountaintops and streams.
5. Coal generates over 100,000,000 tons of ash/year containing Hg, U, Th, As and other heavy metals in the US.
6. Coal plants are slow to ramp up and down.
7. Coal plants are not very efficient. Only ~40% of the energy in a piece of coal becomes electricity. The coal plant itself is one of the biggest users of its own energy, using up to 8% by some accounts. (Running all those motors and pumps take a lot of electricity.)
8. Electrical power must travel long distances through transmission lines, incurring more losses and resulting in even lower efficiency.
9. Operating a coal plants requires more maintenance and more manpower decreasing profitability.
10. Sulfur from burning coal leads to acid rain, though scrubbers in the US remove much of the sulfur.
11. People living near coal mines and plants have adverse heath effects.
12. Coal-fired power plants cause nearly 24,000 premature deaths/yr in the US.  Annual health costs in Europe from coal plants are €42.8 billion, or $55 billion. These externalized costs are not paid by the utility but are borne by the citizens.
13. Subsidence leading to infrastructure damage  can occur above coal mines.
14. Coal-fired power plants release more radioactivity via their emissions that a nuclear power plant.