This chapter presents latest
technological innovations applicable for in mining industries with emphasis on
mechanisation in coal mining industry. Coal Mining is done in
two major ways-Underground mining and Surface Mining. During the last 150 years
the mining technology has under gone extensive changes in India. In the very
first the extraction in Raniganj collieries of West Bengal were done in the shallow
opencast mines. But after continuous increasing demand of coal by the 1920s the
mining removed to underground method with the help of enhanced technology.
Apart from underground mining and surface mining, there are various types of
mining has introduce later time- board and pillar mining, long wall mining,
strip mining auger mining open pit mining etc.
The mining industry is confronted with a
number of well-known systemic challenges, including limited availability of
qualified labour (both local and expat), remote and difficult work environments
and the unending need to improve yields and reduce costs to meet competitive
challenges in an industry where there is limited pricing differentiation.
Mining companies has to understand their perspective on future industry trends
and their expectations for autonomous equipment. Three areas in which autonomy
could provide the most value were in improving overall mine performance,
increasing safety and reducing the aggregate labour requirements. The mining
industry typically operates in a cyclic fashion with periods of strong growth
followed by inevitable downturns. The industry is currently in the throes of a
downturn. In India, coal is the most important energy resource as also the main
contributor to the basket of commercial energy of the country. India is the
third largest coal producer in the world after China and USA. The biggest
reserves of coal are in the USA, Russia, China and India.1
A mining operation needs to
design and develop the necessary arrangement prior to its operation.
Any mining operation usually involves five steps. Exploration, by which the
presence of a mineral, its depth, quality etc. are determined; Project
development, in which primary development of project area takes place and road,
rail, power, water etc. are taken to the area; Mine operation, in which the
mineral is removed from the earth through different methods; Beneficiation or
processing of the mined mineral and the Mine closure, when the mine is abundant
after all the mineral which could be mined is extracted.2
In the context of coal, here we are
going to discuss mainly the mining operations. Coal Mining is done in two major
1. Underground mining
2. Surface Mining.
During last 150 years, the mining
technology has endured extensive changes in India. In the very beginning the
extraction in Raniganj collieries of West Bengal were done in the shallow
opencast mines. In response to the growing demand of coal by the 1920s the
mining shifted to underground method with the help of improved technology.
Underground mining is a method in which
coal is extracted from the earth by opening the earth surface at a point and
then going forward and deeper under the earth to extract the coal. There are
two main methods of underground mining, board and pillar (or room and pillar)
mining and long wall mining.
and Pillar Mining
The underground mining in India is
usually done by the ‘board and pillar’ (or room and pillar) method. In this
method a mesh of tunnels or galleries (a network of ‘rooms’) are first driven
into the coal seam, leaving coal pillars for roof support. Twenty to 30 per
cent of the coal reserve is extracted in this ‘development phase’. In the final,
‘depillaring’ phase, the pillars, which could be 40% of total coal, are also
extracted. If the surface area is free from human settlements, it is allowed to
subside in this phase. If the mine is under a town or a village, then the holes
are filled up with sand mixed with water. This process is called sand stowing.3
The drilling, blasting, cutting, loading, and transporting of coal ore from active
areas are carried out according to a mining plan.
Another underground method used now a
day in the developed countries is long wall mining. This method now used in the
countries like the USA and Australia. Long wall mining involves full extraction
of coal from a section of the seam or face using mechanical shearer (a cutting
machine) mounted on a steel conveyer that moves it along the face. “The
conveyer discharges the coal onto a conveyer belt for transport out of mine.
The long wall face crew, the shearer and the face conveyer are under a
continuous canopy of steel created by supports called shields. The shields,
face conveyer and shearer are connected to each other and move in a programmed
sequence so that the long wall face is always supported as the shearer
continuously cuts the coal in slices about 1 meter thick”. In long wall
mining over 75% of the deposit can be extracted from the panels of coal that
can extend 3 Km through the coal seams. The modem long walls are very capital
intensive (the equipment alone costs more than $52 million), highly
instrumented and automated, employ fewer than six workers at the face, and
produce more than 10000 thousand tons per shift. Generally the long wall mining
experiments have not been successful in the country4.
This method now in use in countries like Australia and the USA is not much in
use in India.
Surface method of extracting minerals
near the surface of the earth. Strip and auger mining are the two most common
surface methods of extracting coal in the United States. Open-pit mining is
sometimes used in thick shallow-lying western coal seams.
Strip mining is accomplished by two
techniques, area stripping and contour stripping. Where coal beds are
relatively flat and near the surface, as in much of the Western United States,
area stripping is the dominant technique. In area strip mining, overlying
material is removed from a seam of coal in long, narrow bands, or strips,
followed by removal of the exposed coal. With the exception of the first cut,
overburden from each cut is discarded in the previous cut from which the coal
has been removed.5
These parallel cuts continue across the coal seam until the thickness of the
overburden becomes too great to be removed economically or until the end of the
coal seam or property is reached. Both single and multiple seams, near the surface,
can be mined in this manner.
Overburden removal is usually
accomplished in the United States with draglines and shovels. Much of the
overburden contains layers of shale, limestone, or sandstone and must be
blasted before it can be removed. After the overburden is removed, coal is
usually drilled and blasted, then loaded into coal haulers with either a shovel
or front-end loader.
Contour stripping is practiced on steep
terrain mostly in the Appalachian Coal Region. The method consists of removing
overburden from the coal bed with the first cut at or near the outcrop, and
proceeding around the hillside. Overburden is stacked along the outer edge of
the bench. After the uncovered bed is removed (successive cuts, usually two or
three) are made until the depth of the overburden becomes too great for economic
recovery of the coal. Contour mining creates a shelf or bench on the side of
the hill. On the inside, it is bordered by the high wall, ranging in height
from a few feet to more than 100 feet, and on the outer side, by a high ridge
Equipment used for contour stripping is smaller in size and load capacity than
that used for area stripping. Bulldozers and front-end loaders are often used
for overburden removal at these operations.
In the eastern United States, auger
mining is used on hillside terrain. It requires a surface cut (removal of
overburden and a portion of the coal bed) to allow the auger access to the bed.
It is also used to recover part of the coal left from underground mining. In
the western United States, auger mining is used in conjunction with strip
mining. Coal mining by the auger method entails boring horizontal or
near-horizontal holes in an exposed face of the coal, and loading the coal
removed by the auger. Single, dual, or triple auger heads can remove up to 90
inches of coal for a distance of over 200 feet. Augering is generally used to
supplement recovery at contour or strip mines when the overburden becomes too
great to be economically removed. It is also used where the terrain is too
steep for overburden removal and where recovery by underground methods would be
impractical or unsafe7.
In open-pit mining, overburden is
removed and placed outside the mining area. The overburden can be removed with
either scrapers or shovels loading into trucks. Mining begins by drilling and
blasting waste rock to expose the coal seams, excavating additional overburden,
and removing and transporting the coal. The pit increases in size and depth as
mining progresses, and it is unusual that overburden, once removed, is ever
returned to the pit. The open pit method is sometimes used in coal mining where
numerous seams lie parallel to each other and outcrop on relatively flat
Mountaintop removal mining (MTR), often
referred to as mountaintop mining/valley fills, is a form of surface mining
that involves extreme topographic change to the summit or summit ridge of a
mountain. It is most closely associated with coal mining in the Appalachian
Mountains, located in the eastern United States. The process involves the
removal of up to 1,000 vertical feet of overburden to expose underlying coal
seams. The overburden is often scraped into the adjacent drainage valleys in
what is called a valley fill.8
Because of its destructive nature, MTR
is controversial and is protested by environmentalists, local residents, and
others. Controversy over the practice stems from both the extreme topographical
and ecological changes that the mining site undergoes, as well as from the
storage of waste material generated from the mining and processing of the coal.
It is also essentially impossible to raconteur the site to pre-mine conditions
during reclamation. Waivers are often given to mining companies in these
cases to use the leveled area for alternate industrial uses. Proponents of MTR
point to its efficiency, job creation, and increase of flat land in areas where
there is often little.9
The practice of mountaintop removal mining is not recommended and will not be
discussed further in this section.
Opencast mining is a type of surface
mining, which entails removing the vegetation, top soil and rock (called
overburden materials) above the mineral deposit, removing the deposit and
reclaiming the affected land for post mining land use. Opencast mining
equipment’s are Heavy Earth Moving Machines (HEMMs) e.g. scrapers, bulldozers,
drills, shovels, front end loaders, trucks, cranes, draglines etc. Opencast
mining today is characterized by very large equipment (e.g. trucks that can
haul more than 300 tons of rocks, loading shovels with buckets greater than 36
cubic meters, draglines with buckets greater than 120 cubic meters) and modem
technology for planning, designing, monitoring and controlling operations. In
India more than 85% of the coal production is currently from opencast mines.
Coal production through opencast mining increased from 19.8 million tons (25%
of total production) in 1973-7 4 to 3 73.13 million tons (86% of total
production) in 2006-07. Whereas, the production through underground mining
increased from 58.4 mts in 1973-74 to 74 million tons in 1993-94 and has been
declining since then. It came down to 58 million tons in 2006-2007.10
After coal is removed, it typically goes
on a conveyor belt to a preparation plant that is located at the mining site.
The plant cleans and processes coal to remove dirt, rock, ash, sulfur, and
other unwanted materials, increasing the heating value of the coal. The coal
may also be sorted by quality and size. Once the coal is processed it is
shipped to wherever it is needed, typically by rail, but also by truck or barge
or even a coal-slurry
pipeline. Transportation methods depend on the distance to be traveled and
access to existing transportation systems.