COAL IN SOUTH AFRICA
In the chemistry of turning plant material into coal, the first stage is biochemical decomposition (humification). Bacterial breakdown of the soluble components, mainly cellulose, results in enrichment of the more resistant, waxy leaf coatings, spores, pollen, fruit and algal remains. Decomposition also expels some gasses originally contained in the rotting matter – principally water, carbon dioxide and methane – leaving organic residues rich in carbon.
The second stage starts when the plant deposits are progressively buried beneath substantial amounts of mud, sand and silt. As depth of burial increases, so too does pressure (compaction).
As a result of the earth’s internal heat flow, temperature also increases with depth. Progressive physical and chemical changes are brought about by the increased temperature and pressure (coalification). The degrees of change result in distinguishable stages of coal quality, or rank, which reflect the maturity of the coal. The different quality stages are Lignite, Bituminous, Anthracite and Graphite.
These four main levels of ranks – Lignite, Bituminous, Anthracite and Graphite – have a certain set of physical parameters which are chiefly controlled by moisture, volatile content, ash and fixed carbon content as well as different swelling characteristics.
[/content-box] [content-box bg_color=”#000000″ class=”tt tb pl-5 pr-5 text-center”]COMPOSITION OF COAL
To understand the distribution of varying densities within the overall coal composition, a breakdown of the coal’s constituents needs to be understood. The natural constituents can be divided into two main groups:
- The Organic Fraction, which can be further subdivided into microscopically identifiable macerals, namely the Liptinite, Vitrinite and Inertinite.
- The Inorganic Fraction, which is comprised of sediment and minerals, commonly identified as ash subsequent to combustion.