coal mining

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.

 Historical mining of Coal:

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.