{"id":1942,"date":"2012-04-20T12:21:13","date_gmt":"2012-04-20T16:21:13","guid":{"rendered":"http:\/\/epcamr.org\/home\/?page_id=1942"},"modified":"2024-02-13T16:15:49","modified_gmt":"2024-02-13T21:15:49","slug":"coal-types-formation-and-methods-of-mining","status":"publish","type":"page","link":"https:\/\/epcamr.org\/home\/content\/reference-materials\/coal-types-formation-and-methods-of-mining\/","title":{"rendered":"Coal Types, Formation and Methods of Mining"},"content":{"rendered":"
\"coalage\"<\/a>

Legend: CAMBRIAN, ORDOVICIAN, SILURIAN, DEVONIAN, MISSISSIPPIAN, PENNSYLVANIAN, PERMIAN, TRIASSIC, JURASSIC, CRETACEOUS, TERTIARY, QUATERNARY.<\/p><\/div>\n

\"cwreserves\"<\/a>

World Wide Contemporary Coal Reserves by Continent<\/p><\/div>\n

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Coal\u00a0is\u00a0an organic sediment consisting of a complex mixture of substances<\/em>. \u00a0Depending upon the evolutionary developmental phase of coal formation\u00a0there are:<\/p>\n

<\/a>Four kinds of coal<\/span><\/p>\n

\"peatcoal\"<\/a>The first evolutionary phase is peat which is little more than\u00a0wood pulp that has been badly decomposed. There are large deposits of \u00a0peat in the Scandinavian countries and Greenland. One can strip mine it \u00a0since it is basically very close to the ground level. \u00a0The\u00a0problem with peat is that it has a very low British Thermal Units (BTU)\u00a0production per pound of the fuel burned. In addition, strip mining is\u00a0ecologically very destructive unless the mining company makes a conscious effort to restore the countryside. \u00a0Strip mining<\/span>\u00a0is the process of scraping the coal from the top surface of the ground<\/em>.<\/p>\n

The second phase in the evolutionary development of coal is<\/em> lignite<\/span>. \u00a0Lignite is found in great quantities in the Western part of the US. \u00a0Again lignite is not particularly efficient in producing energy per mass of \u00a0fuel. There have been quite a bit of effort recently in the liquification and\u00a0gasification of lignite. \u00a0Liquification<\/span> converts lignite into liquid crude petroleum<\/em>. \u00a0Gasification<\/span> plants convert lignite into natural gas products<\/em>.\u00a0The conversion process is quite expensive, and with the present cost of\u00a0other forms of fuel, it is economically infeasible. However, if other fuels\u00a0become too expensive, this could be a more economical process. Other\u00a0research has been conducted investigating other uses of lignite such\u00a0as a fertilizer in hydroponic plant growth. \u00a0Hydroponics<\/span> is the use of nutrient containing water instead of\u00a0soil in the growth of plant life<\/em>.<\/p>\n

A third phase in this coal development is<\/em> bituminous<\/span>\u00a0(soft coal) which is\u00a0one of the two stages\u00a0 used as a fuel in generating electrical power. \u00a0The fourth and final phase results in the formation of<\/em> anthracite<\/span>\u00a0(hard coal). \u00a0If anthracite coal was placed under more heat and pressure, it would eventually be compressed into a diamond.<\/p>\n

<\/a>Two broad categories of coal and peat<\/span><\/p>\n

Humic<\/span> – More common and originates from peat deposits consisting mostly of organic debris deposited “in situ” –\u00a0in its original place (autochthonous)<\/em>.<\/p>\n

Sapropelic<\/span> – Derived from redeposited (allochthonous) resistant plant fragments<\/em> such as spores or aquatic plants.<\/p>\n

The sapropelic coals can be further subdivided into:<\/p>\n

Cannel coal<\/span> – Made\u00a0<\/em>up principally of uniformly sized plant fragment<\/em>s (eg. spores)<\/p>\n

Boghead coal<\/span> – Consists mainly of alginite<\/em> (an algae “coal maceral”\u00a0–\u00a0dehydrogenated plant fragments).<\/p>\n

\"peat\"<\/a>The type of original plant input, the availability of nutrients, climatic conditions, the level of the water table, the pH and Eh conditions all help to determine the type of peat that\u00a0is formed\u00a0(and eventually the mine drainage that comes from the bed).<\/p>\n

Peat<\/span> is formed from the deposition of organic material with a restricted supply of oxygen<\/em>. Peat forming environments are known generally as ‘mires’.<\/p>\n

Mires may be classified as limnic or paralic:<\/div>\n
<\/div>\n
Paralic deposits<\/span> \u00a0– there was a hydrological connection with the sea at the time of peat deposition.<\/em> Mires may be found along coastal lowlands; as back barrier lagoons, estuaries and deltas.<\/div>\n

Limnic deposits<\/span> –\u00a0Peat forming environments isolated from the sea<\/em> (inland swamps and lakes).<\/p>\n

Every part of the ecosystem of the peatland or mire may be represented in the peat, including the large trees, herbaceous shrubs, grasses, aquatic plants and the micro-organisms that break down the organic material.<\/p>\n

For a coal to be developed, the peat has to be buried and preserved. The process that converts peat to coal is called<\/em> coalification<\/span>. The degree of coalification which has taken place determines the rank of the coal.<\/p>\n

<\/a>Formation of Coal (aka.\u00a0Coalification)<\/span><\/p>\n

The transformation of plant material into coal takes place in two stages, biochemical degradation and physico-chemical degradation.<\/p>\n

\"cyclotherm\"<\/a><\/p>\n

Biochemical degradation<\/span> involves chemical decomposition of botanical matter assisted by organisms<\/em>.<\/p>\n

In tropical environments, this process may be faster, since the warm moist conditions are ideal for the organisms that assist in this process such as bacteria and fungi. However plant growth is also more rapid and so the increased rate of decomposition may be balanced by plant growth. In tropical conditions high rates of evaporation need to be coupled with high precipitation to maintain plant growth and peat accumulation.<\/p>\n

In cooler climates the growth rate of vegetation may be cyclical in nature and slower since the seasonal variation in conditions is greater. The conditions are less ideal for fungi and bacteria so the slower growth rate is matched by a slower rate of biochemical degradation.<\/p>\n

Humification affects the soft contents of the plants cells before the cell walls, which consist of cellulose, hemicellulose and lignin which is the most resistant compound. \u00a0Humification begins with the oxidation of plant matter and attack by aerobic organisms such as fungi, insects and aerobic bacteria. \u00a0Hydrocarbons are extracted from the tissue and the material left behind is relatively enriched in oxygen and carbon. Semifusinite, an inertinite maceral may be formed in this manner. \u00a0Various humic substances are formed at this time, these are acidic in nature. If this continues the plant material will be completely degraded into carbon dioxide and water. \u00a0When the plant material or degraded plant material is buried below the ground water table aerobic organisms and oxidation can no longer attack the material. Anaerobic bacteria may still decompose the plant matter until it reaches a depth or conditions unsuitable for these organisms. Anaerobic bacteria utilise the oxygen in the plant matter, so all molecules may be attacked even the more resistant compounds. However the softer tissue may be more rapidly affected.<\/p>\n

Biochemical coalification ends at the rank of sub-bituminous coal, when humic substances have polymerised.<\/p>\n

Physico-chemical coalification<\/span> which follows is caused by conditions of burial<\/em> (ie. heat and pressure).<\/p>\n

The overburden which is deposited, the heat flows in the earth’s crust and tectonic heat and pressure change the chemistry and structure of the altered organic material. The same conditions are applied to all the coal\u00a0macerals. \u00a0Water is squeezed out and pore size is reduced as pressure increases and oxygen and hydrogen are released during thermal cracking. Water and carbon dioxide are the first products released. \u00a0When rank reaches medium volatile bituminous coal demethanation begins.<\/p>\n

<\/div>\n

<\/a>Concept of Coal Rank<\/span>
\nThe rank of a coal refers to the degree of coalification endured by the organic matter. It is estimated by measuring the moisture content, specific energy, reflectance of vitrinite or volatile matter (these are known as rank parameters). See Table 1 for details of the different rank stages.
\nTable 1. From Diessel (1992) indicates the difference in rank parameter with increase in rank.<\/p>\n

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Rank Stages<\/center><\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n
\u00a0\u00a0<\/span><\/td>\n%carbon<\/span><\/td>\n%volatile matter<\/span><\/td>\nspecific energy<\/span><\/td>\n% in situ moisture<\/span><\/td>\n% vitrinite<\/span><\/td>\nreflectance random max<\/span><\/td>\n<\/tr>\n
wood\u00a0<\/span><\/td>\n50<\/span><\/td>\n>65<\/span><\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
peat<\/span><\/td>\n60\u00a0<\/span><\/td>\n>60<\/span><\/td>\n14.7<\/span><\/td>\n\u00a075.0<\/span><\/td>\n200.<\/span><\/td>\n20<\/span><\/td>\n<\/tr>\n
brown coal<\/span><\/td>\n71<\/span><\/td>\n52<\/span><\/td>\n23<\/span><\/td>\n30<\/span><\/td>\n0.40<\/span><\/td>\n0.42<\/span><\/td>\n<\/tr>\n
sub-bituminous<\/span><\/td>\n80<\/span><\/td>\n40<\/span><\/td>\n33.5<\/span><\/td>\n5 0.<\/span><\/td>\n60<\/span><\/td>\n0.63<\/span><\/td>\n<\/tr>\n
high volatile bituminous coal<\/span><\/td>\n86<\/span><\/td>\n31<\/span><\/td>\n35.6<\/span><\/td>\n3<\/span><\/td>\n0.97<\/span><\/td>\n1.03<\/span><\/td>\n<\/tr>\n
medium volatile bituminous coal<\/span><\/td>\n90<\/span><\/td>\n22<\/span><\/td>\n36<\/span><\/td>\n<1<\/span><\/td>\n1.47<\/span><\/td>\n1.58<\/span><\/td>\n<\/tr>\n
low volatile bituminous coal<\/span><\/td>\n91<\/span><\/td>\n14<\/span><\/td>\n36.4<\/span><\/td>\n1<\/span><\/td>\n1.85<\/span><\/td>\n1.97<\/span><\/td>\n<\/tr>\n
semi-anthracite<\/span><\/td>\n92\u00a0<\/span><\/td>\n8<\/span><\/td>\n36<\/span><\/td>\n1<\/span><\/td>\n2.65<\/span><\/td>\n2.83<\/span><\/td>\n<\/tr>\n
anthracite<\/span><\/td>\n95<\/span><\/td>\n2<\/span><\/td>\n35.2<\/span><\/td>\n2<\/span><\/td>\n6.55<\/span><\/td>\n7<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Methods of Mining<\/span><\/p>\n

Underground Coal Mining<\/span>
\n\"ugmine\"<\/a><\/p>\n