Coal

Coal is a black or brownish-black mineral deposit formed as the result of the decay and compression of organic plant matter through geological action over millions of years. This fossil fuel has been a critical source of energy and heat for thousands of years. Coal was the fuel which powered the industrial revolution of the 17th and 18th centuries, and it continues to be a vital source of energy today. The enduring interest in coal has largely been driven by its low cost, relative accessibility, and abundance.. Currently, coal is used as the primary fuel in the steel industry (about 70% globally) and accounts for approximately 35% of the global electric power output.

Geological conditions - such as the depth of burial, vegetation type, and length of burial – alter the properties of the coal. Higher densities of carbon and lower levels of moisture increase the hardness and energy content of a given coal. As a result, coal is classified into four ranks, which are determined by the degree of transformation of the original plant material to carbon. In descending order of carbon content, one finds:

• Anthracite coal is the hardest of all coals, and has the greatest energy content. It is not currently mined in Canada, although deposits can be found in northern British Columbia and the Yukon.
• Bituminous coal is the second rank of coal and accounts for 46% of the coal production in Canada. It is the primary type of coal that is used in the steel and electricity industries. It can be found in British Columbia, Alberta, and the Maritimes.
• Sub-bituminous coal is the third rank of coal and accounts for about 38% of Canada's coal production. It is softer than bituminous coal and contains a higher moisture content. It is abundant in Alberta and is mainly used for electricity generation.
• Lignite, the final rank of coal, has the lowest energy content and is also used for thermal electricity generation. It is mostly mined in Saskatchewan.

All of these ranks reflect different stages of coal development. Ancient plant deposits that have been subjected to high pressure and temperature over long period of times will result in a drier coal with a greater energy content. Thus, anthracite is the oldest type of coal.

Mining, Extraction and Refinement

The thought of coal mining often evokes images of the coal-streaked faces of miners as they work deep within dark mining shafts. Many technological advances have been made since then to improve the safety and efficiency of coal mining. These technologies are tailored as a function of the accessibility of the coal deposits. For instance, vertical or horizontal shafts allow miners and equipment to reach deep coal deposits. Conversely, shallow coal deposits are mined using either open pit or strip mining techniques, depending on the shape of the deposit.

Following its extraction, coal can then be refined to improve its relative value. For instance, coal can be cooked at high temperatures in the absence of air within “cokers” to remove moisture, tars, oils and gases. The resulting product, termed “coke”, is typically used in the steel industry. Coal can also be processed to produce other types of fossil fuels including gasoline, diesel and kerosene.

Pollution and Environmental Impact

Coal is considered the dirtiest of all fossil fuels and contributes to the emission of significant amounts of pollutants that affect our health, environment and economy. A memorable demonstration of the impacts of coal combustion can be found in the London Smog of 1952,  during which thousands of people died as a result of poor air quality. Even today, coal-powered industries continue to be a major source of particulate matter (PM), sulphur dioxide (SO₂), nitrogen oxides (NO_x), mercury and greenhouse gases such as carbon dioxide emissions.

A number of emission control technologies are available to limit the environmental impacts of coal combustion. For instance, large amounts of fly ash (suspended particulate matter) can be collected using electrostatic precipitators. This fly ash is then either shipped to dumping sites, used as backfill for mining operations, or incorporated in concrete as an alternative to cement. The heavier bottom ash, which is collected at the bottom of the furnace, is typically sent to special landfill sites to prevent the migration of pollutants.

Sulphur dioxide is also a major pollution concern from the combustion of coal and a major cause of acid rain. The combustion of low-sulphur coal, such as that found in Alberta and British Columbia, limits SO₂ emissions to a certain extent. In addition, the installation of scrubbers in furnace stacks can significantly reduce sulphur emissions prior to their release in the atmosphere.

In recent years, the development and deployment of carbon capture-and-storage technologies has been outlined as a means of mitigating climate change. Pre-combustion, post-combustion, and oxyfuel techniques are being developed to capture a virtually pure stream of CO₂ (a greenhouse gas), which can then be sequestered in geological formations.

Finally, coal mining can lead to significant physical disturbance of the environment. In order to access coal deposits, large tracts of land must be cleared and excavated, especially in the case of surface mines, leading to a disturbance of the local wildlife and vegetation. Several ecological initiatives have been undertaken to minimize this disturbance and to reclaim the disturbed areas.