SECTION TWO
COAL MINING
>> Coal is mined by two methods – surface or ‘opencast’mining and underground or ‘deep’ mining. >>
The choice of mining method is largely
determined by the geology of the coal deposit.Underground mining currently accounts forabout 60% of world coal production, althoughin several important coal producing countriessurface mining is more common. Surface
mining accounts for around 80% of productionin Australia, while in the USA it is used forabout 67% of production.
Underground Mining
There are two main methods of undergroundmining: room-and-pillar and longwall mining.In room-and-pillar mining, coal deposits aremined by cutting a network of ‘rooms’ into thecoal seam and leaving behind ‘pillars’ of coal tosupport the roof of the mine. These pillars canbe up to 40% of the total coal in the seam –although this coal can sometimes be recoveredat a later stage. This can be achieved in what isknown as ‘retreat mining’, where coal is minedfrom the pillars as workers retreat. The roof isthen allowed to collapse and the mine isabandoned.
Longwall mining involves the full extraction ofcoal from a section of the seam or ‘face’ usingmechanical shearers. A longwall face requires
The Coal Resource: A Comprehensive Overview of Coal7
careful planning to ensure favourable geologyexists throughout the section before
development work begins. The coal ‘face’ canvary in length from 100-350m. Self-advancing, hydraulically-powered supportstemporarily hold up the roof while coal is
extracted. When coal has been extracted fromthe area, the roof is allowed to collapse. Over75% of the coal in the deposit can be
extracted from panels of coal that can extend3km through the coal seam.
The main advantage of room–and-pillarmining over longwall mining is that it allowscoal production to start much more quickly,using mobile machinery that costs under $5million (longwall mining machinery can cost$50 million).
The choice of mining technique is site specificbut always based on economic considerations;differences even within a single mine can leadto both methods being used.
Surface Mining
Surface mining – also known as opencast oropencut mining – is only economic when thecoal seam is near the surface. This methodrecovers a higher proportion of the coal
8World Coal Institute
Definition
Overburden is the layer ofsoil and rocks (strata)between the coal seams andthe surface.
Definition
DWT – Deadweight Tonneswhich refers to thedeadweight capacity of aship, including its cargo,bunker fuel, fresh water,
stores etc.
deposit than underground mining as all coalseams are exploited – 90% or more of the coalcan be recovered. Large opencast mines cancover an area of many square kilometres anduse very large pieces of equipment, including:draglines, which remove the overburden; powershovels; large trucks, which transport
overburden and coal; bucket wheel excavators;and conveyors.
The overburden of soil and rock is first
broken up by explosives; it is then removed by draglines or by shovel and truck. Once thecoal seam is exposed, it is drilled, fracturedand systematically mined in strips. The coal is then loaded on to large trucks orconveyors for transport to either the coal preparation plant or direct to where it will be used.
Coal Preparation
Coal straight from the ground, known as run-of-mine (ROM) coal, often contains unwantedimpurities such as rock and dirt and comes in amixture of different-sized fragments.
However, coal users need coal of a consistentquality. Coal preparation – also known as coalbeneficiation or coal washing – refers to thetreatment of ROM coal to ensure a consistentquality and to enhance its suitability forparticular end-uses.
The treatment depends on the properties ofthe coal and its intended use. It may requireonly simple crushing or it may need to gothrough a complex treatment process toreduce impurities.
To remove impurities, the raw run-of-mine coalis crushed and then separated into various sizefractions. Larger material is usually treatedusing ‘dense medium separation’. In this
process, the coal is separated from other
impurities by being floated in a tank containinga liquid of specific gravity, usually a
suspension of finely ground magnetite. As thecoal is lighter, it floats and can be separatedoff, while heavier rock and other impuritiessink and are removed as waste.
The smaller size fractions are treated in anumber of ways, usually based on differencesin mass, such as in centrifuges. A centrifuge isa machine which turns a container around veryquickly, causing solids and liquids inside it toseparate. Alternative methods use the
different surface properties of coal and waste.In ‘froth flotation’, coal particles are removed ina froth produced by blowing air into a waterbath containing chemical reagents. Thebubbles attract the coal but not the wasteand are skimmed off to recover the coalfines. Recent technological developmentshave helped increase the recovery of ultrafine coal material.
Longwall mining involves thefull extraction of coal from asection of the seam usingmechanical shearers.Photograph courtesy of Joy Mining Machinery.
The Coal Resource: A Comprehensive Overview of Coal9
The way that coal is transported to where itwill be used depends on the distance to becovered. Coal is generally transported byconveyor or truck over short distances. Trainsand barges are used for longer distances
within domestic markets, or alternatively coalcan be mixed with water to form a coal slurryand transported through a pipeline.
transportation, in sizes ranging from
Handymax (40-60,000 DWT), Panamax (about60-80,000 DWT) to large Capesize vessels(about 80,000+ DWT). Around 700 milliontonnes (Mt) of coal was traded internationallyin 2003 and around 90% of this was seabornetrade. Coal transportation can be very
expensive – in some instances it accounts forup to 70% of the delivered cost of coal.
10World Coal Institute
Graded embankment to act as baffle against
noise and dustTopsoil and subsoilstripped by motor scrapers
and carefully storedOverburden from benchesdug by shovels and hauled
by dump trucks
Overburden being excavated
by dragline
Surface Coal Mining Operations and Mine Rehabilitation
Measures are taken at every stage of coaltransportation and storage to minimise
environmental impacts (see Section 5 for moreinformation on coal and the environment).
Safety at Coal Mines
The coal industry takes the issue of safety veryseriously. Coal mining deep underground
involves a higher safety risk than coal mined inopencast pits. However, modern coal mines have rigorous safety procedures, health andsafety standards and worker education andtraining, which have led to significantimprovements in safety levels in both
underground and opencast mining (see graph onpage 11 for a comparison of safety levels in UScoal mining compared to other industry sectors).There are still problems within the industry.The majority of coal mine accidents and
fatalities occur in China. Most accidents are insmall scale town and village mines, often
illegally operated, where mining techniques arelabour intensive and use very basic equipment.The Chinese government is taking steps toimprove safety levels, including the forced
Froth flotation cells atGoedehoop Colliery are usedfor fine coal beneficiation.Photograph courtesy of Anglo Coal.
The Coal Resource: A Comprehensive Overview of Coal11
Spoil pileDragline bucketunloads burden
Dragline backfill levelled by Tipping overburden from benchesSubsoil andtopsoil beingreplaced Grass and trees
closure of small-scale mines and those that failto meet safety standards.
Injury Rates in Selected US Industries, 2003 (per 100 full-time employees)
Source: Bureau of Labor Statistics, US Department of Labor
Coal Mining & the Wider Community
Coal mining generally takes place in rural areaswhere mining and the associated industries areusually one of, if not, the largest employers inthe area. It is estimated that coal employs over7 million people worldwide, 90% of whom are indeveloping countries.
Not only does coal mining directly employmillions worldwide, it generates income andemployment in other regional industries thatare dependent on coal mining. These industriesprovide goods and services into coal mining,such as fuel, electricity, and equipment, or aredependent on expenditure from employees ofcoal mines.
Large-scale coal mines provide a significantsource of local income in the form of wages,community programmes and inputs intoproduction in the local economy.
However, mining and energy extraction cansometimes lead to land use conflicts and
difficulties in relationships with neighbours andlocal communities. Many conflicts over land usecan be resolved by highlighting that mining isonly a temporary land use. Mine rehabilitationmeans that the land can be used once again forother purposes after mine closure.
SECTION TWO END
SECTION TWO
COAL MINING
>> Coal is mined by two methods – surface or ‘opencast’mining and underground or ‘deep’ mining. >>
The choice of mining method is largely
determined by the geology of the coal deposit.Underground mining currently accounts forabout 60% of world coal production, althoughin several important coal producing countriessurface mining is more common. Surface
mining accounts for around 80% of productionin Australia, while in the USA it is used forabout 67% of production.
Underground Mining
There are two main methods of undergroundmining: room-and-pillar and longwall mining.In room-and-pillar mining, coal deposits aremined by cutting a network of ‘rooms’ into thecoal seam and leaving behind ‘pillars’ of coal tosupport the roof of the mine. These pillars canbe up to 40% of the total coal in the seam –although this coal can sometimes be recoveredat a later stage. This can be achieved in what isknown as ‘retreat mining’, where coal is minedfrom the pillars as workers retreat. The roof isthen allowed to collapse and the mine isabandoned.
Longwall mining involves the full extraction ofcoal from a section of the seam or ‘face’ usingmechanical shearers. A longwall face requires
The Coal Resource: A Comprehensive Overview of Coal7
careful planning to ensure favourable geologyexists throughout the section before
development work begins. The coal ‘face’ canvary in length from 100-350m. Self-advancing, hydraulically-powered supportstemporarily hold up the roof while coal is
extracted. When coal has been extracted fromthe area, the roof is allowed to collapse. Over75% of the coal in the deposit can be
extracted from panels of coal that can extend3km through the coal seam.
The main advantage of room–and-pillarmining over longwall mining is that it allowscoal production to start much more quickly,using mobile machinery that costs under $5million (longwall mining machinery can cost$50 million).
The choice of mining technique is site specificbut always based on economic considerations;differences even within a single mine can leadto both methods being used.
Surface Mining
Surface mining – also known as opencast oropencut mining – is only economic when thecoal seam is near the surface. This methodrecovers a higher proportion of the coal
8World Coal Institute
Definition
Overburden is the layer ofsoil and rocks (strata)between the coal seams andthe surface.
Definition
DWT – Deadweight Tonneswhich refers to thedeadweight capacity of aship, including its cargo,bunker fuel, fresh water,
stores etc.
deposit than underground mining as all coalseams are exploited – 90% or more of the coalcan be recovered. Large opencast mines cancover an area of many square kilometres anduse very large pieces of equipment, including:draglines, which remove the overburden; powershovels; large trucks, which transport
overburden and coal; bucket wheel excavators;and conveyors.
The overburden of soil and rock is first
broken up by explosives; it is then removed by draglines or by shovel and truck. Once thecoal seam is exposed, it is drilled, fracturedand systematically mined in strips. The coal is then loaded on to large trucks orconveyors for transport to either the coal preparation plant or direct to where it will be used.
Coal Preparation
Coal straight from the ground, known as run-of-mine (ROM) coal, often contains unwantedimpurities such as rock and dirt and comes in amixture of different-sized fragments.
However, coal users need coal of a consistentquality. Coal preparation – also known as coalbeneficiation or coal washing – refers to thetreatment of ROM coal to ensure a consistentquality and to enhance its suitability forparticular end-uses.
The treatment depends on the properties ofthe coal and its intended use. It may requireonly simple crushing or it may need to gothrough a complex treatment process toreduce impurities.
To remove impurities, the raw run-of-mine coalis crushed and then separated into various sizefractions. Larger material is usually treatedusing ‘dense medium separation’. In this
process, the coal is separated from other
impurities by being floated in a tank containinga liquid of specific gravity, usually a
suspension of finely ground magnetite. As thecoal is lighter, it floats and can be separatedoff, while heavier rock and other impuritiessink and are removed as waste.
The smaller size fractions are treated in anumber of ways, usually based on differencesin mass, such as in centrifuges. A centrifuge isa machine which turns a container around veryquickly, causing solids and liquids inside it toseparate. Alternative methods use the
different surface properties of coal and waste.In ‘froth flotation’, coal particles are removed ina froth produced by blowing air into a waterbath containing chemical reagents. Thebubbles attract the coal but not the wasteand are skimmed off to recover the coalfines. Recent technological developmentshave helped increase the recovery of ultrafine coal material.
Longwall mining involves thefull extraction of coal from asection of the seam usingmechanical shearers.Photograph courtesy of Joy Mining Machinery.
The Coal Resource: A Comprehensive Overview of Coal9
The way that coal is transported to where itwill be used depends on the distance to becovered. Coal is generally transported byconveyor or truck over short distances. Trainsand barges are used for longer distances
within domestic markets, or alternatively coalcan be mixed with water to form a coal slurryand transported through a pipeline.
transportation, in sizes ranging from
Handymax (40-60,000 DWT), Panamax (about60-80,000 DWT) to large Capesize vessels(about 80,000+ DWT). Around 700 milliontonnes (Mt) of coal was traded internationallyin 2003 and around 90% of this was seabornetrade. Coal transportation can be very
expensive – in some instances it accounts forup to 70% of the delivered cost of coal.
10World Coal Institute
Graded embankment to act as baffle against
noise and dustTopsoil and subsoilstripped by motor scrapers
and carefully storedOverburden from benchesdug by shovels and hauled
by dump trucks
Overburden being excavated
by dragline
Surface Coal Mining Operations and Mine Rehabilitation
Measures are taken at every stage of coaltransportation and storage to minimise
environmental impacts (see Section 5 for moreinformation on coal and the environment).
Safety at Coal Mines
The coal industry takes the issue of safety veryseriously. Coal mining deep underground
involves a higher safety risk than coal mined inopencast pits. However, modern coal mines have rigorous safety procedures, health andsafety standards and worker education andtraining, which have led to significantimprovements in safety levels in both
underground and opencast mining (see graph onpage 11 for a comparison of safety levels in UScoal mining compared to other industry sectors).There are still problems within the industry.The majority of coal mine accidents and
fatalities occur in China. Most accidents are insmall scale town and village mines, often
illegally operated, where mining techniques arelabour intensive and use very basic equipment.The Chinese government is taking steps toimprove safety levels, including the forced
Froth flotation cells atGoedehoop Colliery are usedfor fine coal beneficiation.Photograph courtesy of Anglo Coal.
The Coal Resource: A Comprehensive Overview of Coal11
Spoil pileDragline bucketunloads burden
Dragline backfill levelled by Tipping overburden from benchesSubsoil andtopsoil beingreplaced Grass and trees
closure of small-scale mines and those that failto meet safety standards.
Injury Rates in Selected US Industries, 2003 (per 100 full-time employees)
Source: Bureau of Labor Statistics, US Department of Labor
Coal Mining & the Wider Community
Coal mining generally takes place in rural areaswhere mining and the associated industries areusually one of, if not, the largest employers inthe area. It is estimated that coal employs over7 million people worldwide, 90% of whom are indeveloping countries.
Not only does coal mining directly employmillions worldwide, it generates income andemployment in other regional industries thatare dependent on coal mining. These industriesprovide goods and services into coal mining,such as fuel, electricity, and equipment, or aredependent on expenditure from employees ofcoal mines.
Large-scale coal mines provide a significantsource of local income in the form of wages,community programmes and inputs intoproduction in the local economy.
However, mining and energy extraction cansometimes lead to land use conflicts and
difficulties in relationships with neighbours andlocal communities. Many conflicts over land usecan be resolved by highlighting that mining isonly a temporary land use. Mine rehabilitationmeans that the land can be used once again forother purposes after mine closure.
SECTION TWO END