Coal Lectures Series

Andrew W. CoxEnergy Intelligence & Marketing Research,

192 Sandyford Road,Newcastle upon Tyne NE2 1RN, United Kingdom.

Tel: 44 (0)191-261 5274cox.andrew421@googlemail.com

Coal Lectures Series – An Introduction

Since 1995 Energy Intelligence & Marketing Research [EIMR] has developed a wide range of teaching material on coal-related topics. The key themes include: coal formation; coal properties; coal as a fuel source; coal mining technologies; the markets for coal; coal-based electricity systems; pollution abatement technologies; clean coal technologies; coal capture and storage; coal-to-liquid fuels; the coal/energy sectors of several countries [including the United Kingdom and China]; plus the international coal trade.

A shortened version of a basic teaching module is enclosed.

In addition to the powerpoint presentations - a wide range of other supporting material is available - such as technical notes, case studies + video/movie clips.

Dr Andrew Cox and colleagues from EIMR can provide personal teaching and lectures to university courses - plus companies seeking continuing professional development – both in the UK and in other countries.

Please contact Dr Cox [cox.andrew421@googlemail.com] for further information.

Introduction toCoal Mining

Coal Mining TechnologiesVarious mining technologies are used throughout the world's coalfields.

The technology adopted in each mining project should be the one which will extract the coal at the lowest overall cost.

Mining commenced several hundred years ago by exploiting seams that reach the surface (outcrop). These were accessed by bell-pits or other simple mining techniques - such as bord and pillar (or room and pillar) extraction. Some of these techniques are still used by local non-mechanised miners in undeveloped coalfield areas throughout the world.

Extracting deeper coal seams led to the development of access by shafts and drifts - allowing large-scale extraction and removal of coal.

Modern Underground methods currently utilise longwall mining (either advancing or retreating systems) or continuous mining technologies.Sometimes other techniques may be used - such as auger mining.

The development of ventilation technology has also allowed coal extraction to take place at greater depths - as well as further from a mine’s main shafts and drifts. The development and planning of underground and surface mines during the last 30 years has increasingly employed design and modelling software.

Mining terms

Run of mine (ROM) production. This is the uncleaned output of a mine. In many mines ROM coal must undergo some form of washing and preparation to become the saleable product. ROM coal from surface mines usually has a lower level of ash and mineral matter - and so requires less preparation.

Panel. A block of coal in a seam that is worked by longwall mining. A typical panel might be 1000-2000m+ long and up to 300m wide. The dimensions of the panel are determined by the geological conditions in the mine – such as strata stability.

Pillar. A block of coal left behind in a coal seam to aid support of the overlying strata. Pillars may be needed to prevent excessive subsidence on the ground surface or to avoid excessive geological distortions in the mine workings. For example - a pillar is usually left between two panels of coal being extracted by longwall mining.

Drawing of Bell Pit MiningSource: http://www.sunnisidelocalhistorysociety.co.uk/

Collapse of early mine workings

Image of pitfallen land at Daisy Hill, County Durham [mid-1980s]

Longwall Mining

Longwall mining is a form of underground coal mining where a longwall face of coal is mined in a single slice (typically >1m thick). The longwall "panel" (the block of coal that is being mined) is typically 1-2 km long and 200m-300m wide.

The longwall shearer is a sophisticated machine with a rotating cutting drum that moves mechanically back-and-forth across the coal seam in the panel. The broken, loosened coal is dropped on to a series of conveyor belts for removal from the working area and is then transported up to the surface.. Self-advancing, hydraulic face supports temporarily hold up the roof whilst the coal is extracted. The roof over the area behind the face, from which the coal has been removed, is then allowed to collapse.The supports allow for high levels of production and safety. Many faces have a high degree of automation – with sensors monitoring the progress of the face, plus machine and environmental conditions.There are two types of longwall face systems – Advancing and Retreat.However - longwall mining takes place where geological conditions are relatively stable and where there is only a small inclination of the coal seams.

Diagram of Longwall mining operations

Headstock of a deep mine – access to mine shaft.

Advancing Longwall Faces

Face advances away from roadway

RetreatLongwall Faces

Main Roadways

Two parallel tunnelsare driven away fromthe main roadwayand then connectedat the longwall faceto create a panel. The face works back – retreats - to the mainroadway.

Underground mine plan - showing layout of roadways and longwall panels

Longwall face, Kellingley Colliery, Yorkshire, UKSource: Coal Authority

Longwall face, Daw Mill Colliery, West Midlands, UKSource: Coal Authority

Roof bolting and additional roof support are used in most large underground mines

Examples of Rock Bolts – used to stabilise roofs and walls of underground mines

Hydraulic face supports

Self-advancing, hydraulic face supports. They move forward as the cutting face advances.

Mine AutomationRemote control, automation and monitoring, are widely used throughout larger coal mines. All information is fed into a computer network system which can be monitored at the control room on the surface. In the UK mining engineers call this the Mine Operating System [MINOS]. These systems, which improve efficiency and safety, already control transport systems and monitor temperature, mine gas concentrations and ventilation underground. Similar systems are deployed to monitor and control a range of mining operations at the coalface.

Continuous Miners

Continuous miners were first introduced in the late 1940s – allowing a significant increase in speed and efficiency of extracting coal. They now extract the majority of coal from US underground mines - and are used in mines throughout the world.

These machines are designed to remove coal from the seam and to load it into shuttle cars and then conveyor belts in a continuous process. This allows the coal to be rapidly removed from the working area and transported to the surface.

The continuous miner has a large rotating steel drum equipped with tungsten carbide teeth that cut coal from the seam. Standard continuous miners can extract coal at a rate of several tonnes a minute depending upon the seam thickness. Newer, more powerful continuous miners are highly productive and can be remotely controlled - being designed for a variety of seam and mining conditions.

The standard working layout is a “room and pillar” system – where the mine is divided into a series of 6-9 metre “rooms” or work areas which are cut into the coal seam with pillars of coal left standing to help support the roof.

Rock bolts, typically 1 to 3 metres long steel bolts, are inserted into holes drilled into the roof at regular intervals to bind the strata together and ensure support. Where the geological conditions permit, the pillars are subsequently extracted [“robbed”] - allowing very high levels of coal extraction.

Diagram of a mine with longwall and continuous mining system

Room and Pillar working – utilising continuous mining systems

The front of the continuous miner [above] – which cuts coal from the seam . The coal is carried to the back into a shuttle car [see below] which transfers it to a conveyor belt.

Joy continuous miner in one of Sasol Group’s mines, South Africa

Auger Mining

This is a method for recovering coal by boring into a coal seam at the base of strata exposed by excavation. It is normally one of the lowest-cost techniques of mining, it is limited to horizontal or slightly pitched seams that have been exposed.

Augering is usually associated with surface mining, recovering coal for a limited depth beyond the point where stripping become uneconomic because the seam of coal lies so far beneath the surface - or under land that can't be strip-mined/opencasted due to environmental and planning constraints.

An auger removes coal by drilling or cutting horizontally into the coal seam. They are usually either single auger or double auger mining equipment - which can reach depths of up to 1000 ft from the initial entry point into the seam. 

Some auger systems have also been developed for extracting coal from seams in underground mines.

Surface MiningSurface mining has rapidly developed during the second half of the 20th Century as larger earthmoving equipment has evolved.The new technologies allow large surface mines to produce millions of tonnes of coal per year.Extraction depths of surface mining are dependent upon the overburden ratio (the ratio of overburden moved to the volume of coal recovered) and the market price obtained for the coal - which is also dependent on the quality of the final product.A wide range of mining equipment is used in surface mining.

Large surface mining excavator – used in lignite mining. This excavator weighs 13,400 tonnes; has a height of 96m and a crew of 3. It can excavate 240,000 tonnes per day. It takes 2 years to assemble the excavator on site prior to coal production.

HambachMine,Germany

Shotton Opencast Site, Northumberland, UK

Ffos-y-Fran surface mine, South Wales, UK