what is Coal

Coal

According to ICCP (International Commission for Coal Petrology) in 1963 define coal as “a combustible sedimentary rock formed from plant remains in various stages of preservation by processes which include the compaction of the material buried in a basins, initially of moderate depth” It is clear that it is the combination of organic constituents (Plant remains, vesicular and non vesicular part) and inorganic (minerals of rock).

                                                                                      OR

Coal: sedimentary rock formed from the partial decay of plants remains in swamp or big environment in 
humid tropical     environment/water saturated environment.

Aerobic decay soon depleted the water of oxygen Anaerobic decay by bacteria is similar in capability with aerobic one but due to waste so the product of bacteria it become toxic (because it remain in its place) partially decomposed plant material remains in a state of arrested decay___in this stage material is

peat___lignite___sub-bitumeous___bitumeous___anthracite = rank

Coal is produced from type iii kerogin
Kerogen is precursor of hydrocarbon insoluble in petroleum solvent that generate liquid petroleum when heated.

Oil window = 60 – 120°c
Gas window = 120 – 220 °c
Coal window = above 220 °c

Composition of coal C , H , O with minor sulfur & nitrogen.

                            

Coalification Process

The alteration undergone during burial, when referring to coal, Coalification
Coalification is a combination set of biological, physical and
chemical processes, and is comprised of five successive but
overlapping stages, which in return give series of coal ranks.

1.Peatification
2. Dehydration
3. Bituminization
4. Debituminization
5. Graphitization

There are no sharp divisions between stages. These five stages also
correspond more or less to the evolutionary stages described by
Tissort and Welte (1984):

Peatification and dehydration correspond to diagenesis,
bituminization and debituminization to catagenesis, and
graphitization to metagenesis.

The above five stages, plant remains proceed from peat, lignite,
sub-bituminous coal, bituminous coal, anthracite coal, to graphite (a
pure carbon mineral).

Rank of Coal:

These terms (peat, lignite, sub-bituminous, bituminous and
anthracite) are used to represent different stages of the coalification
process, indicating the rank of the coal.

Constituents of Coal

1.      Megascopic Constituents: Terms as ingredients or lithotypes and can be divided into

i.                   Humic Coal: Humic coal more common, pass through peat stage.

Derived mainly from megascopic parts of the plant debris (wood,
leaves or bark) deposited under oxic to sub-oxic condition.

This coal is banded, lustreous dark brown and black and can be
classified into: vitrain, clarain, durain, fusain.

ii.                 Sapropelic Coal:

This coal is unbanded, dull in appearance, they do not pass throuh
peat stage but follow the diagenetic pathway.

Derived mainly from microscopic parts of the plant (spores, resins,
waxes and algal materials) under sub-oxic to anoxic condition.

This coal may occur as lenses or thin layers (within humic coal) and can be classified into: boghead and cannel coals.

2. Microscopic Constituents

The microscopic constituents are termed as “macerals”: it is define by Stope, 1935 and is derived from Latin word “macerare”

meaning minerals. It is the equivalent word for mineral in rock.

The microscopic constituents are derived from different organs or
tissues of plant.

A maceral coal has different physical and chemical properties and
can be classified into three groups according to greyness in
reflected light

i.                    Liptinite (dark grey):

Derived mostly from algae or spores, pollens, cuticles, and resins in the original plant material.

They are known to have the richest hydrogen content and the
highest petroleum potential.

ii. Vitrinite (medium to light grey)

Derived from wood, bark, and roots.

They contain less hydrogen than the liptinites do, but higher than
inertinites.

ii.                  Inertinite (white and may be very bright)

which are mainly oxidation products of the other macerals and are
consequently richer in carbon.

Coals can contain different relative proportions of liptinites,
vitrinites and inertinites, each having its own molecular
compositions, and a given capacity to generate oil and gas.