8/8/2019 Rank of Coal
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Prepared by: Izhar Mitha l J iskani 09 MN 98
Rank of Coal
Coal is complex combination of material, and the combination has
great difference fromone formation or deposit to another.
These differences result from:1. The varying types of vegetation
from which the coal originated.2. The depth of burial and the
temperature and pressure at those depths.
3. The length of time the coal has been forming in the
deposit.
Following are ranks of coal in progressive order.
1. Lignite
Lignite often referred to as brown coal and may be represented
as immature coal. It is
considered as the lowest rank of coal; and used almost
exclusively as a fuel for steam-
electric power generation. It is brownish-black in color and has
a high inherent moisturecontent sometimes as high as 66%, and also
high ash content (50%). Lignite is a
geologically young coal which has lowest carbon content (25-35%)
that produces less
than 8,300 BTUs per pound. It has a high content of volatile
matter which makes it easierto convert into gas and liquid
petroleum products than higher ranking coals. However, its
high moisture content and susceptibility to spontaneous
combustion can cause problems
in transportation and storage. Because of its low energy
density, brown coal is inefficient
to transport and is not traded extensively on the world market
compared with higher coalgrades. Lignite is typically mined by
stripping methods and burned in power stations
constructed very close to any mines known as mine-mouth power
plant.
2. Sub-bituminous coal
It is intermediate in rank between lignite and bituminous coal
and is used primarily as
fuel for steam-electric power generation. It contains 35 to 45%
percent carbon and the
heat content of sub-bituminous coals range from 8300 to 11,500
BTu/lb. This coalgenerally has a lower sulfur content than other
types, which makes it attractive for use
because it is cleaner burning.
3. Bituminous coal
Bituminous coal or black coal is a relatively soft coal
containing a tar like substancecalled bitumen. It is of higher
quality than lignite and poor than anthracite coal,
extensively used in iron and steel manufacturing. Bituminous
coal is an organicsedimentary rock formed by digenetic and
sub-metamorphic compression of peat
material. It is often with well-defined bands of bright and dull
material.
SOCIETY OF MINING ENGINEERS
Department of Mining Engineering,Mehran University of
Engineering & Technology, Jamshoro
8/8/2019 Rank of Coal
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Prepared by: Izhar Mitha l J iskani 09 MN 98
4. Anthracite
It is nearly pure form of carbon Used primarily for residential
and commercial spaceheating. Anthracite is the highest rank of
coal. Its hard, brittle, lustrous black texture
contains a high percentage of fixed carbon and low percentage of
volatile matter. Its high
carbon content (86 to 99%) allows to burn hot and long and it
has a heating value ofnearly 16,000 BTUs/lb.
SOCIETY OF MINING ENGINEERS
Department of Mining Engineering,Mehran University of
Engineering & Technology, Jamshoro
