What is Coal and How Coal is Formed ?

Coal is a solid, black, readily combustible fossil fuel that contains a large amount of carbon-based material – approximately 50% of its weight.

Coal has been used as an energy source for nearly 2000 years. For example, coal was widely used for home heating in early 17th century England. But the Industrial Revolution dramatically increased the demand for coal. Specifically, James Watt’s improvements to the steam engine made coal useful for doing work.

By the 1830’s coal mining was a booming industry in the eastern United States with coal supplied for industry and steam locomotives on newly developed rail roads.

In 2010 coal accounted for 9.2% of Canada’s primary energy production. Coal in the modern world is the most widely used and abundant fossil fuel. Coal exhibits a 109 year reserve to production ratio (as of 2012). The total amount of coal reserves is approximately 10 tonnes, the United States is home to the largest individual coal reserves.

What is Coal ?

Coal is a rock formed from the decomposition of plant life. It is primarily composed of carbon, with many other trace elements. Coal’s high energy density and extensive reserves found in nature make it useful as a fuel for electricity generation in coal-fired power plants, and in some places, heating.

Coal is considered low-cost in that to build a coal fired power plant, extract coal from the ground and to burn it does not cost a company as much as other fuel processes (because of the externalities that it ignores). Coal is also plentiful; there is a large reserve globally. This has lead to the people burning a lot of coal for centuries, which we continue to do today.

Coal formation began several hundred million years ago (check out chronozoom) under environmental conditions vastly different than the ones present today. Acidic waters slowed the decay of organic matter and allowed this dead organic matter, mainly plankton, to accumulate in layers. The old material was then pushed deep into the ground while being covered with sediment and eventually formed into a crumbly brown material referred to as peat. This peat contains some of the energy that was generated by photosynthesis when the plants were alive.

Geological processes buried this peat further, the high pressures and temperatures caused material to lose much of its hydrogen and oxygen atoms, resulting in a carbon rich material referred to as coal. Major types of coal include anthracite, lignite, sub-bituminous and bituminous coal. The type of coal is a function of where it is formed and how far evolved it is, anthracite and bituminous coal are the most developed types of coal and are therefore almost entirely composed of carbon.

How Coal is Formed ?

The formation of coal takes a significant amount of time (on the order of a few million years), and the first coal-bearing rock units appeared about 290-360 million years ago, at a time known as the Carboniferous or “coal-bearing” Period. As well, there are extensive coal deposits from the Cretaceous age – about 65 to 144 million years ago.

The formation of coal begins in areas of swampy wetlands where groundwater is near or slightly above the topsoil. Because of this, the flora present produces organic matter quickly – faster in fact than it can be decomposed. In these areas, layers of organic matter are accumulated and then buried. It is these layers of organic material that then form coal. The energy in coal initially comes from the Sun, and is energy from sunlight trapped by dead plants.

Coal formed millions of years ago when the earth was covered with huge swampy forests where plants – giant ferns, reeds and mosses – grew. As the plants grew, some died and fell into the swamp waters. New plants grew up to take their places and when these died still more grew. In time, there was thick layer of dead plants rotting in the swamp. The surface of the earth changed and water and dirt washed in, stopping to decaying process. More plants grew up, but they too died and fell, forming separate layers. After millions of years many layers had formed, one on top of the other. The weight of the top layers and the water and dirt packed down the lower layers of plant matter. Heat and pressure produced chemical and physical changes in the plant layers which forced out oxygen and left rich carbon deposits. In time, material that had been plants became coal.

Process

The process that creates coal varies slightly in different areas depending on the plants and conditions that are present, but the overall process is similar. There are two main phases in coal formation: peatification and coalification. Bacterial activity is the main process that creates the peat during peatification. Increasing temperature and pressure from burial are the main factors in coalification. To form coal, the following steps are followed:

Plant matter in mires and wetlands, such as ferns, shrubs, vines, trees, and algae dies and accumulates on the surface. Initially the organic matter is decomposed by bacteria, yielding carbon dioxide and methane.
The plant matter becomes buried, and are no longer exposed to air. Anaerobic bacteria then starts to decompose the material. Burial and accumulation can occur for several thousands of years, producing several meters of partially decayed plant matter known as peat.
When this peat is deeply buried, water and other compounds is squeezed out from the increasing pressure and the lowest quality of coal, lignite, begins for form.
Continued burial, resulting in increasing pressures and temperatures, causes this low quality lignite coal to be transformed into higher quality “black coals”. First lignite becomes sub-bituminous coal, then bituminous coal, and finally the highest quality anthracite coal. As these transformations occur, the amount of water and other compounds in the coal decreases and the coal becomes more dense. Along with this comes a higher carbon concentration.

Coals are classified into three main ranks, or types: lignite, bituminous coal, and anthracite. These classifications are based on the amount of carbon, oxygen, and hydrogen present in the coal. Coal is defined as a readily combustible rock containing more than 50% by weight of carbon. Coals other constituents include hydrogen, oxygen, nitrogen, ash, and sulfur. Some of the undesirable chemical constituents include chorine and sodium. In the process of transformation (coalification), peat is altered to lignite, lignite is altered to sub-bituminous, sub-bituminous coal is altered to bituminous coal, and bituminous coal is altered to anthracite.

Lignite – is the lowest rank of coal – which means that it has the lowest heating value and lowest carbon content. Although lignite is more solid than peat it crumbles when shipped long distances. Most lignite in the U.S. is in North and South Dakota, Montana, and Texas. Lignite is used to generate electricity. Other uses include generating synthetic natural gas and producing fertilizer products.

Bituminous – is intermediate in rank and sometimes called soft coal. It appears smooth when you first see it, but look closer and you’ll find it has many layers. It is the most abundant kind of coal. It has a high heating value, but it also has a high sulfur content. More than 80% of the bituminous coal produce in the U.S. is burned to generate electricity. Other major coal users are the cement, food, paper, automobile, textile and plastic industries. Another important industrial use is to provide coke for iron and steel industries. Bituminous coal derivatives, or by-products can be changed into many different chemicals form which we can make paint, nylon, aspirin and many other items.

Anthracite – is the highest rank of coal which means that it has the highest heating value and highest carbon content. It is very hard, deep black, and looks almost metallic because it is brilliantly glossy. Anthracite burns longer, with more heat and with less dust and soot than other types of coal. The primary market for anthracite is for heating homes. Nearly all of the anthracite in the U.S. is in Pennsylvania, but there are some small beds in other states.

What is coal, what are the types of coal, and what coal is used for ?

Coal is primarily used as fuel to generate electric power in the United States. The coal is burned and the heat given off is used to convert water into steam, which drives a turbine. In 2012, about 39 percent of all electricity in the United States was generated by coal-fired power plants, according to the U.S. Energy Information Administration.

Certain types of coal can also be used for metallurgical processes, like forging steel, smelting metals, or even in smelting sands, which are used to cast metal. Finally, coal can be burned to provide heat for individual homes.

Coal is abundant in the U.S., is relatively inexpensive, and is an excellent source of energy and byproduct raw materials. Because of these factors, domestic coal is the primary source of fuel for electric power plants in the U.S., and will continue to be well into the 21st century. In addition, other U.S. industries continue to use coal for fuel and coke production and there is a large overseas market for high-quality American coal.

Because humans have used coal for centuries, much is known about it. The usefulness of coal as a heat source and the myriad of byproducts that can be produced from coal are well understood. The continued and increasingly large-scale use of coal in the United States and in many other industrialized and developing nations has resulted in known and anticipated hazards to environmental quality and human health. As a result, there is still much to be learned about the harmful attributes of coal and how they may be removed, modified, or avoided to make coal use less harmful to humans and nature. These issues of coal quality have not been examined carefully until recently.

Coal is a sedimentary rock made predominantly of carbon that can be burned for fuel. Coal is readily combustible, black or brownish-black, and has a composition that, including inherent moisture, consists of more than 50 percent by weight and more than 70 percent by volume of carbonaceous material. It is formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geologic time.

Coal is found all over the world including our country, predominantly in places where forests and marshes existed prehistorically, before being buried and compressed over millions of years. Some of the largest deposits, though, are located in areas of the Appalachian basin in the eastern U.S., the Illinois basin in the mid-continent region, and throughout the Rocky Mountain basins in the western U.S.

What are the types of coal?

There are four major types (or “ranks”) of coal. Rank refers to steps in a slow, natural process called “coalification,” during which buried plant matter changes into an ever denser, drier, more carbon rich, and harder material. The four ranks are:

Anthracite: The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter.
Bituminous: Bituminous coal is a middle rank coal between subbituminous and anthracite. Bituminous usually has a high heating (Btu) value and is the most common type of coal used in electricity generation in the United States. Bituminous coal appears shiny and smooth when you first see it, but look closer and you may see it has layers.
Subbituminous: Subbituminous coal is black in color and dull (not shiny), and has a higher heating value than lignite.
Lignite: Lignite coal, aka brown coal, is the lowest grade coal with the least concentration of carbon.

Also, there is peat. Peat is not actually coal, but rather the precursor to coal. Peat is a soft organic material consisting of partly decayed plant and, in some cases, deposited mineral matter. When peat is placed under high pressure and heat, it becomes coal.

Different coal types are all minerals and rocks made largely of carbon. This fossil fuel generates ~40% of the world’s electricity and about 25% of the world’s primary energy. However, not all coal used is the same; it comes in different quantity levels of carbon—which dictates the quality of the coal.

Higher quality coal produces less smoke, burns longer, and provides more energy than lower quality coal.

The table below includes the carbon contents, and energy densities of coal. In addition, it states the moisture content before drying, and the amount of volatile content, after it’s dried.

Table 1: Types of Coal
Coal	Dry, Carbon content (%)	Moisture content before drying (%)	Dry, volatile content (%)	Heat Content (MJ/kg)
Anthracite	86-92	7-10	3-14	32-33
Bituminous coal	76-86	8-18	14-46	23-33
Sub-Bituminous coal	70-76	18-38	42-53	18-23
Lignite	65-70	35-55	53-63	17-18
Peat	<60	75	63-69	15

The following is an overview of the different grades of coal, ordered from lowest to highest quality. Please see their main pages to learn more about each type.

What it is used for ?

In 2019, about 539 million short tons (MMst) of coal were consumed in the United States. On an energy content basis, this amount was equal to about 11.3 quadrillion British thermal units (Btu) and to about 11% of total U.S. energy consumption. Although coal use was once common in the industrial, transportation, residential, and commercial sectors, today the main use of coal in the United States is to generate electricity.

The electric power sector accounts for most of U.S. coal consumption.

U.S. coal consumption by consuming sector by amount and percentage share of total in 2019

Electric power—539.4 MMst—91.8%
Industrial total—47.1 MMst—8.0%
- Industrial coke plants—17.9 MMst—3.1%
- Industrial combined heat and power—11.2 MMst—1.9%
- Other industrial—17.9 MMst—3.0%
Commercial—0.9 MMst—less than 1%
Residential and transportation—each less than 1 MMst—less than 1%

U.S. coal consumption peaked in 2007 and declined in most years since then, mainly because of a decline in the use of coal for electricity generation.

How to Make Steam-Activated Charcoal ?

Steam-activation is primarily used for coconut charcoal and coal.

In the production of steam-activated charcoal, first the coconut shell or coal is heated to create a char. This char is then “activated” in a furnace at high temperatures of 1,700° to 1,800°F with steam in the absence of oxygen. In the steam-activation process, all volatile compounds are removed, and at the same time layer after layer of carbon atoms are pealed off, enlarging the existing internal pores, and leaving behind a carbon skeleton. The carbon + steam reaction results in producing hydrogen gas and carbon monoxide (C+H₂O=H₂ +CO). As the carbon monoxide gases off it takes carbon atoms with it. Typically 3 pounds of raw charcoal will produce 1 pound of activated charcoal. This is a perfect example of the saying “Less is More”. Less carbon atoms yields More internal space.

How to Make Steam-Activated Charcoal ?

Once the activated charcoal is cooled off, to remove the soluble ash content, it may be either “water-washed”* (which requires a lot of water) or it is “acid-washed” (to remove the acid-soluble ash content) and then repeatedly “water-washed” to remove any trace of the acid solution.
(*Not to let anything go to waste, the charcoal “vinegar” is sometimes collected and sold as commercial ascetic acid or processed into table vinegar.)

Because of the very high temperatures required for steam activation (600 – 1,200 °C), temperatures you cannot achieve in a conventional oven (260 °C), this method is all but limited to industrial technology.

Another huge limiting factor is the cost of production. The world uses a tremendous amount of Activated Charcoal annually and so production needs to be on an industrial scale that can produce millions of tons of AC at a very low price.

This is typically done in large rotating steel cylinder kilns (up to 180ft long producing up to 12.5 metric tonnes/hour) with a sophisticated delivery system of heat and steam. If money were not an issue, then individuals would need to first design an even more sophisticated miniature version. There would be the issue of washing/rinsing, the disposal of waste ash from the pyrolysis, managing the exhaust gasses, and other challenges. The net product would far exceed the cost of the mass-produced product, and quality would likely also be an issue, since cooking temperatures and times are quite critical. Aside form the fascination of building one’s own, it seems the cost would be prohibitive to make steam-activated charcoal “at home”.

So, how can you make steam activated charcoal? It should be obvious that, for small personal quantities, you are not set up for the technical challenges or the financial outlay. Well then, how can you make chemically activated charcoal? Is it less expensive and easier?