Abstract:
Minerals and mineral products are the backbone of most industries.
Coal is an organic sediment
consisting of a complex mixture of substances. It has a lot of commercial and industrial
applications.
It is an energy giving non-renewable source of energy. Mining of coal is one of the oldest
industrial
operation. The mining
method selected for exploitation is determined mainly by the characteristics
of the coal deposit and the limits imposed by safety, technology,
environmental concerns, and
economics. Geologic conditions play a key role in selecting the
method. Coal is friable and loose in its
structure. The methods of mining of coal varies from deposit to
deposit. This report highlights the
coal mining methods, their significances, issues of concern and
the stages of using coal after mining.
Introduction:
Coal is a readily combustible rock containing more than 50 percent
by weight of carbonaceous
material, formed from compaction and induration of variously
altered plant remains similar to those in
peat. Most coal is fossil peat. Peat is an unconsolidated deposit
of plant remains from a water-
saturated environment such as a bog or mire; structures of the
vegetal matter can be seen, and, when
dried, peat burns freely.
Coal is the most abundant fossil fuel on Earth. Coal is found in beds or seams
interstratified with
shales, clays, sandstones, or (rarely) limestones. The Coal
deposits in India are of two distinct
geological ages. The earliest coal deposits are of Permian age
formed about 270 million years ago. At
that time South Africa , South America , Antarctica , Australia
, India and Madagascar formed a
landmass called Gondwanaland. Coal formed in Gondwanaland are
known as Gondwana Coal . Other
deposits of Tertiary age (30-60 million years) have been formed
comparatively recently. These are
known as Tertiary Coal .
Coal is extracted from the ground by coal mining. Since 1983, the
world's
top coal producer has been China.
Ancient people mined coal by picking and scraping and used it for
heating, cooking, and in
ceremonial chambers as early as the 12th century AD; in the 14th century they used it
industrially in
pottery making. Small-scale
mining of surface coal deposits dates back thousands of years. The
Romans were exploiting all major coalfields by the late 2nd century AD. Coal was mined in America
in the early 18th century, and commercial mining started around 1730
in Midlothian, Virginia.
Coal-cutting machines were invented in the 1880s. Before this
invention, coal was mined from
underground with a pick and shovel. By 1912, surface mining was
conducted with steam shovels
designed for coal mining.
Coal mining has had many developments over the recent years, from the
early days of men tunneling, digging and manually extracting the
coal on carts, to large open cut and
long wall mines.
The various methods of mining a coal seam can be classified under
two headings, surface
mining and underground mining.
Top ten
coal producers (2018)
|
|||
PR
China
|
3550 Mt
|
Russia
|
420 Mt
|
India
|
771 Mt
|
South
Africa
|
259 Mt
|
USA
|
685 Mt
|
Germany
|
169 Mt
|
Indonesia
|
549 Mt
|
Poland
|
122 Mt
|
Australia
|
483 Mt
|
Kazakhstan
|
114 Mt
|
Source:
IEA Coal Information 2019
|
Methods of extraction
The most economical method of coal extraction from coal seams
depends on the depth and quality of
the seams, and the geology and environmental factors. Many coal deposits are extracted from
both
surface and underground mines.
Surface mining and deep underground mining are the two basic
methods adopted for mining coal. The choice of mining method
depends primarily on depth of burial,
density of the overburden and thickness of the coal seam. Seams
relatively close to the surface, at
depths less than approximately 180 ft (50 m), are usually
surface mined. Coal that occurs at depths of
50 to 100 m are usually deep mined, but in some cases surface
mining techniques can be used. Coals
occurring below 100
m are usually deep mined.
Feasibility of coal mining
The technical and economic feasibility of coal mining are
evaluated based on the following:
a) regional geological conditions;
b) overburden characteristics;
c) coal seam continuity, thickness, structure, quality, and
depth;
d) strength of materials above and below the seam for roof
and floor conditions;
e) topography (especially altitude and slope);
f) climate;
g) land ownership as it affects the availability of land for
mining and access;
h) surface drainage patterns;
i) ground water conditions;
j) availability of labor and materials;
k) coal purchaser requirements in terms of tonnage, quality,
and destination; and
l) capital investment.
Auxiliary and unit operations:
Those activities which are essential to maintain safe and
productive operating conditions both at the
working faces and in all parts of the mine are known as auxiliary
operations.
These include ground control, ventilation, haulage, drainage,
power supply, lighting, and
communications. Those activities which are conducted sequentially
in a production cycle—
i.e., cutting and hauling the coal and supporting the immediate exposed
roof after coal removal—are
called unit operations.
Access to a coal seams:
Accesses to a coal seam, called portals, are the first to be
completed and generally the last to be
sealed. A large coal mine
will have several portals.
Their locations and the types of facilities installed in them
depend on their principal use, whether for
worker and material transport, ventilation, drainage and power
lines, or emergency services. In many
cases, the surface facilities near a portal include bathhouses
and a lamp room; coal handling, storage,
preparation, and load-out facilities; a fan house; water- and
waste-handling systems; maintenance
warehouses; office buildings; and parking lots.
There are three types of portal adopted in coal mining as drift,
slope, and shaft.
Drift Mining
Drift mining is a process of accessing precious geological
material, like coal, by cutting into the side
of the earth, rather than tunneling directly downwards. Drift
mines have flat entries into the coal seam
from a hillside.
Drift mines are different from slope mines, which have a tending
opening from the
surface to the coal vein. If likely, while, drifts are driven at
just a slight predispose so that removal of
material may be helped out by gravity.
Slope mining:
Slope mining is a method of accessing valuable geological
material, such as coal or ore.
A sloping access shaft travels downwards towards the desired
material. Slope mines differ
from shaft and drift mines, which access resources by tunneling
straight down or horizontally,
respectively. In slope mining, the primary access to the mine is
on an incline.
Where the coal seam does not outcrop but is not far below the
surface, it is accessed by driving
sloping tunnels through the intervening ground.
Slopes are driven at as steep an angle as is practicable for
transporting coal by belt. Commonly, a pair
of slopes is driven (or a slope is divided into two separate
airtight compartments) or ventilation and
material transport. Where
the minimum coal-seam depth exceeds 250 to 300 metres, it is common to
drive vertical shafts. (Poor ground conditions are another factor
in selecting a shaft over a slope.)
Shaft Mining:
Shaft mining is a form of underground mining where shafts are
pushed vertically from top to bottom
to excavate the ores and minerals. It is also called shaft
sinking. It is best suited for concentrated
minerals such as iron, coal, etc. which can be found at the depth
of the earth's surface. It is found
mostly all over the world. Shaft sinking refers to shallow shafts
and it is different from a deep shaft.
Shafts, too, may be split into separate compartments for fresh
air, return air, worker and supply
transport, and coal haulage.
Capital and operating costs for coal haulage are lowest in a drift
access.
Roof support:
In modern mechanized mines, roof bolting is the most common method
employed.
Steel bolts, usually 1.2 to 2 metres long and 15 to 25 millimetres
in diameter, are inserted in holes
drilled into the roof by an electric rotary drill and are secured
by either friction or resin.
The bolts are set in rows across the entry, 1.2 to 1.8 metres
apart.
Failure to support the roof of a mine is the greatest cause of
accidents in mining.
Rockbolts
Rock bolts and cables have been used in supporting the underground
excavations for decades and are
still the most reliable means of support.
In coal mining, the surrounding strata is weakened and fractured around mine openings in
underground mines due to
the in situ stress redistribution.
The main purpose of rockbolt reinforcement
is to improve the
internal load bearing strength of the rock mass to support itself.
Rockbolt performance is
influenced by the rockbolt type, anchorage system, strata lithology and other
geological conditions.
Roof support at the face (the area where coal is actively mined)
is intended to hold the immediate roof
above the coal face.
Several theories explain how roof bolts hold the roof.
Theories of Rock Bolting. In coal mining, the surrounding strata is weakened and fractured
around
mine openings in underground mines due to the in situ stress
redistribution. The main purpose of
rockbolt reinforcement is to improve the internal load bearing
strength of the rock mass to support
itself.
These include the beam theory (roof bolts tie together several
weak strata into one),
the suspension theory (weak members of the strata are suspended
from a strong anchor horizon), and
the keying-effect theory (roof bolts act much like the keystone in
an arch).
Haulage:
Haulage is the business of transporting goods by road or rail. It
includes the horizontal transport
of ore, coal, supplies, and waste, also called cartage or drayage. The vertical transport of the
same
with cranes is called hoisting.
Coal haulage, the transport of mined coal from working faces to the
surface, is a major factor in underground-mine efficiency.
It can be considered in three stages:
a) Face or section haulage, which transfers the coal from the active working faces; b)
intermediate
or panel haulage, which transfers the coal onto the primary or main haulage;
and c) the main haulage
system, which removes the coal from the mine.
In room-and-pillar systems, electric-powered, rubber-tired
vehicles called shuttle cars haul coal from
the face to the intermediate haulage system.
In some semimechanized or manual longwall operations, chain
haulage is used.
Mine Conveyors:
Belt conveyors have been used for mineral transport below ground
in mines. It started more
vigorously after the time of the First World War. Their use
continued to grow, aligned to the move
from pillar and stall to longwall mining systems. They were initially used to replace horses and
rope
haulages for the more efficient transportation of minerals in
mines. The available records show that
there were 1356 km of belt conveyors installed in British coal
mines in 1948 which rose to 2692 km
by 1953. A typical present-day large coal mine has some 30 km of
belt conveyors. Individual belt
conveyor installations vary widely in their design, capacity and
duty.
Mine Ventilation:
Underground mine ventilation provides a flow of air to the
underground workings of a mine of
sufficient volume to dilute and remove dust and noxious gases and
to regulate the temperature. The
source of gases are
equipment that runs on diesel engines, blasting with explosives and sometimes,
the ore body itself. Mine ventilation is done to provide oxygen to
the miners and to dilute, render
harmless, and carry away dangerous accumulations of gases and
dust. In some of the gassiest mines,
more than six tons of air are circulated through the mine for
every ton of coal mined. Air circulation is
achieved by creating a pressure difference between the mine
workings and the surface through the use
of fans. Fresh air is conducted through a set of mine entries (called
intakes) to all places where miners
may be working. After passing through the workings, this air (now
termed return air) is conducted
back to the surface through another set of entries (called
returns).
Monitoring and control:
Advancements in sensor technology and in computer hardware and
software capabilities are finding
increasing application in underground coal mines, especially in
the monitoring and control of
ventilation, haulage, and machine condition.
Longwall shearers and shields can be remotely operated, and
continuous miners have also been
equipped with automatic controls.
The atmospheric environment is remotely monitored for air
velocity, concentrations of various gases,
and airborne dust; fans and pumps are also monitored continuously
for their operational status and
characteristics.
Health, safety, and environment:
Code of practice for occupational safety and occupational health
in coal mining - prescribes
responsibilitys of the state, coal miners, employers, managers,
supervisors and surveyors; covers
notification and reporting system for occupational accidents and
occupational diseases, protective
equipment, ventilation, precautions to take against explosions,
fires and dust, use of explosives,
electricity, equipment and machinery, first aid, rescue, training
needs, etc.
Coal mining in India:
Coal mining in India began in 1774 when John Sumner and Suetonius
Grant Heatly of the East India
Company commenced commercial exploitation in the Raniganj
Coalfield along the Western bank
of Damodar river.
The first proposal for
regulation of mining in India came
in 1890, which was introduced by
Lord
Cross, who at that time was the Secretary of State of India, later
in 1894 for the first time Inspector of
Mines was appointed for the purpose of management and supervision.
In the year 1901, first Mine Act enacted in India which was only
applicable to the mines situated in
British India, which
was accompanied with
establishment of “Bureau
of Mines Inspection”
in
Kolkata. Since then Mine Act has been re-enacted in 1923, 1928 and
1935.
The mineral resources in India consist of Coal, Iron ore,
Manganese, Mica, Bauxite, Titanium ore,
Chromite, Diamonds, etc. India is the third largest producer of
Coal and Lignite & Barytes and the
largest producer of mica in the world. India is also ranked among
the top producers of Iron ore,
Bauxite, Manganese ore and Aluminium.
In 2003-2004 India has produced 355 million tones of coal all of
which has been consumed internally.
Coal India Limited is a State owned company which contributes a
bulk percentage in the Coal
production. As on 31 March 2015, India had estimated coal reserves
of 306.6 billion metric tons
(338.0 billion short tons), the fifth largest coal reserves in the
world.
For this reason, coal mining worldwide is heavily regulated
through health and safety laws.
In coal mining—particularly underground coal mining—there are numerous conditions that can
threaten the health and safety of the miners. The operation of the
mining sector in India is governed
by the Mines and Minerals (Development and Regulation Act, 1957,
the Mines Act, 1952 and the
rules and regulations framed under them.
Legal aspects of Coal Mining:
The Coal Mines (Nationalisation) Act, came in 1973. The Administration of the Coal Mines
(Conservation and Development) Act, came in 1974 (28 of 1974).
Coal mining, world over, is highly regulated industry due to
presence of many inherent, operational
and occupational hazards. Coal Mine Safety Legislation in India is
one of the most comprehensive
and pervasive statutory framework for ensuring occupational health
and safety (OHS). Compliance of
these safety statutes is mandatory.
Conclusion:
Coal mining has had many developments over the recent years.
Technological advancements have
made coal mining today more productive than it has ever been. To cope up
with the technology and
to extract coal as efficiently as possible, the mining personnel
must be highly skilled and well trained
in the use of complex, state-of-the-art instruments and equipment. It is also necessary to know
all
these coal mining methods.
1 Comments