Types of coal, their origin, coal ranking

1. Unit 1: Classification & Ranking
of Coal
Prepared by:
Ankur Sachdeva
AP(ME)

2. What is Coal?
• Coal is highly carbonaceous fossil fuel
that has been produced as a result of
vegetable debris under favorable
conditions of high temperature and
pressure over million of years.
• It is chiefly composed of C, H, N and O
besides non-combustible inorganic matter.

3. What is Coal
• Also called black gold.
• Found in sedimentary strata [layers of soil].
• Contains carbon, volatile matter,
moisture and ash [in some
cases Sulphur and phosphorous]
• Mostly used for power generation and
metallurgy.
• Coal reserves are six times greater than oil and
petroleum reserves.

4. Global Coal Reserves

5. Coal-fields in India

6. Carboniferous Coal
• Most of the world’s coal was formed
in Carboniferous age [350 million years ago]
[Best quality coal].
• Carboniferous age: In terms of absolute time, the
Carboniferous Period began approximately 358.9
million years ago and ended 298.9 million years
ago. Its duration is approximately 60 million
years.
• The name Carboniferous refers to coal-bearing
strata.

7. Coal Age
• Carboniferous coal was produced by bark-bearing
trees that grew in vast lowland swamp forests.
• Vegetation included giant club mosses, tree ferns,
great horsetails, and towering trees with strap-
shaped leaves.
• Over millions of years, the organic deposits of this
plant debris formed the world's first extensive
coal deposits—coal that humans are still burning
today.

8. Types of Vegetation
Tree Ferns
Bark
Great Horsetails Giant Club Mosses

9. Marsh & Swamp
• A marsh is a wetland which
is characterized mineral
soils which are poorly
drained, and plant life
composed of mainly
grasses.
• Defining Characteristics:
– It is constantly flooded with
water from a specific source
• A swamp is a wetland which
is characterized by
waterlogged soils which are
interspersed with areas of
dry land.
• Defining Characteristics:
– They usually have an
abundance of trees
Marsh
Swamp

10. Bog & Fen
• A bog is a wetland with a
sealed clay bottom which
prevents water from
seeping out.
• Defining characteristic
– They lack nutrients and are
unable to support life
• A fen is a wetland which is
formed when groundwater
seeps into a depression
• Defining characteristic
– Water from underground
seeps into the depression
through a crack in the clay
bottom.
Fen
Bog

11. Origin of Coal
• Coal formed millions of years ago when the earth was covered with
huge swampy [marshy] forests where plants – giant ferns and
mosses – grew.
• As the plants grew, some died and fell into the swamp waters.
• New plants grew up to take their places and when these died still
more grew.
• In time, there was thick layer of dead plants rotting in the swamp.
• The surface of the earth changed and water and dirt washed
in, stopping the decaying process.
• More plants grew up, but they too died and fell, forming separate
layers. After millions of years many layers had formed, one on top
of the other.
• The weight of the top layers and the water and dirt packed down
the lower layers of plant matter.
• Heat and pressure produced chemical and physical changes in the
plant layers which forced out oxygen and left rich carbon deposits.
In time, material that had been plants became coal.

12. Origin of Coal

13. Coal Formation

14. Coal Formation
• The transformation of the vegetable debris to coal
takes place in two stages:
(a) Biochemical or peat stage: During this stage,
the plant materials were attacked by various micro
organisms.
(b) Chemical stage or metamorphism: In this
stage, the peat deposit buried under sedimentary
deposits lose moisture and volatile components
under the effect of high temperature and pressure.
• The peat gets enriched in carbon whereas its
oxygen content decreases.

15. Coal Formation

16.  Coals are mainly classified on the basis of their degree
of coalification from the parent material, wood.
 When wood is converted into coal, there is gradual
increase in the concentration of carbon and decrease in
the percentage of oxygen and nitrogen.
 Coal is given a ranking depending upon the carbon
content of the coal from wood to anthracite.
Wood Peat Lignite Bituminous coal Anthracite
Increase in carbon contents, Calorific value and hardness
Decrease in H, O, S, N, contents and volatile matter
16
Classification of Coal

17. Coal Ranking
• The wide, shallow seas of the Carboniferous
Period provided ideal conditions for coal
formation, although coal is known from most
geological periods.
• The exception is the coal gap in the Permian–
Triassic extinction event, where coal is rare.
• Coal is known from Precambrian strata, which
predate land plants — this coal is presumed to
have originated from residues of algae.

18. Coal Ranking
• Coal rank is the measure of
the degree of organic
metamorphism(coalification)
of a coal, ranging from low-
rank peat to high-rank meta-
anthracite.

19. Composition of Different Coals

20. PEAT
• First stage of transformation.
• Contains less than 40 to 55
per cent carbon == more
impurities.
• Contains sufficient volatile
matter and lot of
moisture [more smoke and
more pollution].
• Left to itself, it burns
like wood, gives less heat,
emits more smoke and leaves
a lot of ash.

21. LIGNITE
• Brown coal.
• Lower grade coal.
• 40 to 55 per cent carbon.
• Intermediate stage.
• Dark to black brown.
• Moisture content is high
(over 35 per cent).
• It undergoes SPONTANEOUS
COMBUSTION [Bad. Creates
fire accidents in mines]

22. SUB-BITUMINOUS COAL
• Sub-bituminous coal,
whose properties range
from those of lignite to
those of bituminous coal,
is used primarily as fuel
for steam-electric power
generation and is an
important source of light
aromatic hydrocarbons for
the chemical synthesis
industry.

23. BITUMINOUS COAL
• Soft coal; most widely available
and used coal.
• Derives its name after a liquid
called bitumen.
• 40 to 80 per cent carbon.
• Moisture and volatile content (15
to 40 per cent)
• Dense, compact, and is usually of
black colour.
• Does not have traces of original
vegetable material.
• Calorific value is very high due to
high proportion of carbon and
low moisture.
• Used in production of coke and
gas.

24. STEAM COAL
• “Steam coal" is a grade
between bituminous coal
and anthracite, once
widely used as a fuel for
steam locomotives.
• In this specialized use, it
is sometimes known as
"sea-coal" in the US.
Small steam coal (dry
small steam nuts or
DSSN) was used as a fuel
for domestic water
heating.

25. ANTHRACITE COAL
• Very little volatile matter.
• Negligibly small proportion
of moisture.
• Semi-metallic lustre.
• Ignites slowly == less loss of
heat == highly efficient.
• Ignites slowly and burns
with a nice short blue
flame. [Complete
combustion == Flame is
BLUE == little or no
pollutants. Example: LPG]
• In India, it is found only in
Jammu and Kashmir and
that too in small quantity.