Coal-fired electricity is the most used source to create electricity and, until 2014, it had the fastest growth wordwide (IEA, Coal Information 2015).
Coal forms through the process of coalification, where peat undergoes several changes as a result of bacterial decay, compaction, heat and time. Peat is the plant remains from a water-saturated environment, such as a bog or a mire. This process happens in a water-saturated environment because only in this particular environment there is a lack of oxygen which favours a specific bacterial decay. The degree of alteration of the peat marks the rank of the coal, broadly divided into low-rank coals, such as lignite and sub-bituminous coals, which have lower calorific value and higher moisture levels, and high-rank coals, bituminous and anthracite coals (also known as hard coal), which have more carbon and higher energy content.
Coal mining methods can be either through underground mines: drift, slope and shaft mining or surface-mines: area, contour, mountain top removal and auger mining. Coal mining equipment makes the largest human-built machines on the planet.
Leaving aside other applications from coal, we will discuss how coal is used in electricity production. After coal is mined, coal is taken to power plants through trains and conveyor belts. Coal is then blown in a combustion chamber of a boiler and burned at around 1,400 degrees Celsius. Surrounding the walls of the boiler are pipes filled with water, which are heated to make superheated high-pressure steam. The steam passes through a turbine, causing it to rotate, that turns a generator, creating electricity. Efficiencies of these power plants can reach 46% (EURACOAL, 2013).
In short, merits of coal are abundance, affordability, reliability of fuel supply, easy to store and transport. Drawbacks are land disturbance during mining for surface mines and the release of harmful pollutants during burning.