Chapter 2Coal As A Substance

Content

• Physical description

– Macroscopic

– Microscopic

– Mineral Content

• Coalification (Rank)

– Coalification

– Causes

• Coal Quality

– Chemical Prop

– Combustion Prop

– Physical Prop

– Coal Oxidation

• Classification of Coals

Physical Description of Coals

Physical Description of Coals

•Coal is sediment, organoclastic in nature, composed of

lithified plant remains and combustible material

•Coal constituents can be divided into macerals, organic

equivalent of minerals and mineral matter.

•Coal rank is the degree of diagenesis or coalification that a

coal has undergone by burial and tectonic effect

•Term brown coal is used for low rank coal such as lignite to

subbituminous coal

•Black/hard coal is bituminous to anthracite coal

•Coal is divisible into humic coals and sapropelic coals

– Humic coals mixture of macroscopic plant debris, typically have

banded appearence

– Sapropelic coals composed of restricted variety of microscopic plant

debris, homogenous appearence

Macroscopic Description of Coals

•Humic coals

– Term that used for description is lithotypes

Macroscopic Description of Coals

• Durain (dull, grainy texture, tough)

• Fusain (dull black, charcoal texture, hands get dirty)

• Clarain (bright, satiny texture, brittle)

• Vitrain (bright, black, glassy, brittle).

Macroscopic Description of Coals

•

Macroscopic Description of Coals

•

Macroscopic Description of Coals

•

Macroscopic Description of Coals

• Fusain

Macroscopic Description of Coals

• Sapropelic Coals

– Products of biological and physical degradation in coal peat forming

environment with addition materials such as spore and algae

– Cannel coal

– Boghead coal

Microscopic Description of Coals

• Macerals or organic units can be divided into 3 groups :

– Huminite / vitrinite : woody materials

– Exinite / liptinite : spores, resin and cuticles

– Inertinite : oxidized plant material

• Coal may be made up largely of a single maceral or more usually

association of macerals. These associations when studied

microscopically are called microlithotypes

• lithotype can only be recorded if it forms a band > 5 µm than

microlithotypes

Microscopic Description of Coals

•

Microscopic Description of Coals

•

Microscopic Description of Coals

•

Microscopic Description of Coals

•

Mineral Content of Coals

• The mineral content of coal is the noncombustible inorganic

fraction

• Detrital (clastic) or autighenic mineral (CaCO3, apatite and clays)

– Detrital mineral ---> transported into swamp by air or water

• Example : quartz, carbonate, iron and clay minerals

• Process : water with mineral ---> flooding ---> coal swamp ---> laid down on top of

the organic materials ---> mineral-rich parting in coals

• How about the wind ? ---> tonsteins (kaolinite rich sed. Rock)

– Authigenic minerals ---> during or after deposition / coalification.

• Example : calcium-iron minerals (calcite, ankerite, sideritem pyrite, quartz), clay

minerals

• Clay minerals content : < 20 % ( Coal); 20 – 60 % (carbargilite); > 60 % (no coal /

argillaceous shale

Coalification (Rank)

• Coalification : alteration vegetation to peat then transformation to

various rank in coal

• Process : Biochemical and Geochemical Stage (metamorphisme)

• Biochemical process : peat to brown coal (lignite)

• Geochemical process : carbon content increase then H and O

decrease.

– Result : water loss and compaction

– Produce methane and carbon dioxide

Coalification (Rank)

•

Coalification (Rank)

• Causes :

– Temperature, such as :

• Direct contact with intrusion, loss volatile, methane, water and oxygen

• Associated with the depth of burial

– Time

• Degree of coalification is less when the sediment subsided rapidly and

the cooking time was short

– Pressure

• Phsyco-structural coalification

• Decrease porosity and moisture content

– Radioactivity

• Uranium / thorium contact

Coal Quality

• means : those chemical and physical properties of a coal that

influence its potential use

• coal quality depend on chemical properties and physical

properties of coal

• the quality of coal is determined by the make-up of the original

macerals, mineral content and the degree of coalification

• some countries have standard procedure to measure chemical

and physical properties of coals.

Chemical properties of coal

• coal can be regarded as being made up of moisture, pure coals

and mineral matter

•

Source

http://www.uky.edu/KGS/coal/coalcomp.htm

http://www.kgs.ku.edu/Publications/Bulletins/102_1/06_

petro.html

http://www.slideshare.net/adhlino_bono/coal-mine

http://www.thefossilforum.com/index.php?/topic/42202-

fusain-evidence-of-a-forest-fire-307-mya-

edited/?hl=fusain

http://geology.com/articles/coal-through-a-

microscope.shtml

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Source

http://www.uky.edu/KGS/coal/coalcomp.htm

http://www.kgs.ku.edu/Publications/Bulletins/102_1/06_

petro.html

http://www.slideshare.net/adhlino_bono/coal-mine

http://www.thefossilforum.com/index.php?/topic/42202-

fusain-evidence-of-a-forest-fire-307-mya-

edited/?hl=fusain

http://geology.com/articles/coal-through-a-

microscope.shtml