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MINING OF THIN COAL SEAMS DEVELOPMENT WINNING OF PANELS PAST ATTEMPTS (MACHINES USED) AUTONOMOUS MINING MACHINES CASE STUDY

DEVELOPMENT Thin Seam Mining methods which as the name suggests is used for mining seams with thickness less than 1.5 metres. Thin seam differs in that it involves forming smaller pillars Each mining “panel” forms up to seven roadways. The miner cuts these road ways in a sequence that allows a mobile bolting machine to come in after the mineral has been removed for up to 15 metres

To support the roof the miner is driven on the tracks (fitted) to another roadway where it cuts another 15 metres. This is known as the “cut and flit” method. In this system, the pillars of coal are not removed by pillar extraction methods. This mining system achieves a higher-than-normal recovery of the resources on the advance. Extraction is done by machines like mole miners, full face miners and scraper boxes

WINNING OF PANELS ROOM AND PILLAR METHOD 8.4 m wide rooms. 5 holes- 66 mm dia- Airdox tubes capable of pull of 2.6 m. 2. LONGWALL METHOD Advancing longwall preferred. High capacity, but light AFCs are used. Low height chocks and shields are used. For the extraction of panel, in-web shearers and ploughs are in use (down to 0.9 m thickness).

PAST ATTEMPTS MOLE MINERS 2. FULL FACE MINERS 3. SCRAPER BOXES

MAIN EQUIPIMENTS USED MOLE MINER It is fully autonomous machine and remotely operated. This technology is composed of several sub systems like haulage for coal removal, ventilation, monitoring, and control and pushing system. This method has advantage that personnel need not to enter in extraction zone.

MOLE MINER (contd) The cutting height is not more than 5 ft. This equipment has been successfully used in USA, UK and former USSR. This miner is itself propelled.

COLLINS MINER The cutting head of this miner is composed of three overlapping auger blades. The blades are driven by single 120 HP electric motor. Small flight convey the cut coal to the belt conveyor behind machine. Entire machine is mounted on skid plates that are connected to the main plate, by hinges in front and by lifting jacks at the rear. In this method numerous consecutive parallel entries are driven to obtain desired production.

FULL FACE MINER These machines span the entire width of mining face. Machine is advanced or retreated along the width at one time. There must be personnel on the working face for the purpose of maintenance. The size of equipment is limited according to the its application. Example of full face miners are Mine wall, In seam miner.

Sandvik full face miner Source:www.flickr.com

Full face miner Source:www.toreuse.com

Scraper Boxes It is one of the simplest long wall type system. It is made up of a box that is open at the top, front and bottom. The scraper box blade is hinged into the rear of the box. To give the system more reach multiple scrapers are usually employed on the same face.

Scraper boxes Source:www.hub4.com

OTHER MACHINES Low profile thin seam miner-Includes a main frame mounting a lower transverse axis rotary cutter. Oscillating disc machine with steering-used specially for ores of non ferrous metals, comprising at least one drilling head pivoted about a vertical axis.

PROBLEMS Steering of the machines is based on the floor horizon and the operator has no indication of thinning of seam until the machine is cutting roof stone. By the time operator realizes that the machine is cutting roof by observing the material in conveyor severe damage to the roof already takes place. Occasionally thin slabs of roof material falls on the top of machine or behind it. The fallen roof materials often cause serious problems in coal transportation which can hamper production and operation.

AUTONOMOUS MINING MACHINES Complete automation is a prerequisite because of the limited height of the faces. For navigation : face, local, and global. guidance system are to align the equipment at the face, achieve proper guidance during cutting. Some Technologies used: Coal-Rock Interface Detection (CID) Technologies. Continuous Miner Guidance Technologies.

CID TECHNOLOGIES Detects the coal-rock interface at the boundary of the seam Numerous types of CID technologies include: Natural Gamma Radiation (NGR)- Coal has lower amount of radio activity Vibration- Sensors mounted on machines Infrared- Different types of strata release different amount of infrared radiation while being cut Optical / video sensors- video cameras and image analysis equipment Radar- Attenuation of Doppler radar pulses. Pick force- Energy required to break different types of rock is different.

Continuous Miner Guidance Technologies Laser Based Miner Guidance Ultrasonic Continuous Miner guidance Modular Azimuth Positioning System

Case study: Southern coalfields (new south wales) Source: map mines.jpg

NRE NO. 1 COLLIERY The NRE No. 1 Colliery (formerly South Bulli Colliery) was acquired by Gujarat NRE Coke Ltd, through its subsidiary Gujarat NRE Australia Pty Ltd. in December 2004. The mine located in the Southern Coalfields of New South Wales, approximately 10 kilometers north of Wollongong and around 60 kilometers south of Sydney in Australia will ensure a steady supply of high quality raw material for its coke ovens operations in India in a highly volatile environment and provide insurance against price volatility. The Colliery will also create employment in the Illawarra area and in India with benefits to both the nations.

The NRE no1 colliery SOURCE:gujarat NRE.com

Mine Geology The mine spread over 6421 hectares and having reserves of around 300 million tonnes of coking coal comprises three coal seams, the Bulli seam, which occurs at the top of the Illawarra Coal Measures, the Balgownie seam, some 8 to 10 metres below it, and the Wongawilli seam, which lies between 22 and 25 metres below the Balgownie seam. Two minor seams, the Cape Horn seam and the Hargraves seam, lie between the Balgownie and Wongawilli seams, but are too thin to have any economic significance. The average seam thickness of the Bulli, Balgownie and Wongawilli seams are 2.01 metres, 1.25 metres, and 9.75 metres respectively, though only the basal 2.5 metres of the Wongawilli seam is regarded as the working section. The Bulli seam has been worked extensively in the mine area for almost 120 years, the Balgownie seam was worked between 1967 and 1982 and again in 2002. There has been no systematic production from the Wongawilli seam in this colliery. Both the Balgownie and the Wongawilli seams are largely untapped resource

MINING METHODS Gujarat NRE has adopted new approaches to mining in the NRE No 1 Colliery as compared to what was being practiced by the earlier owners. Where mining has for a number of decades been conducted using Longwall mining, it intends to use Pillar extraction method to increase the recovery level in the remaining levels. While mining in the colliery has always been concentrated on the Bulli seam, the Balgownie and the Wongawilli seams have hardly seen much activity. Pillar extraction mining in the Bulli seam uses the Continuous Miner method supported by BLS breaker line support. Continuous miner is a speedy and efficient process having high productivity and is designed for a variety of seams and mining conditions. The continuous miner cuts a network of “rooms” into the seam. As the rooms are cut, the continuous miner simultaneously loads the coal onto a shuttle or ram car where it will eventually be placed on a conveyor belt that moves it to the surface. The roof is supported by installation of steel “roof bolts” into the stone above the coal seam, and pillars of coal are left behind to support the roadways. These pillars are later removed with the continuous miners and the roof is allowed to collapse in a controlled manner. The breaker line support helps to provide a safe working environment near the continuous miner by pushing upwards against the roof.

The company further intends to mine the Wongawilli seam also using Longwall Mining Machines. It proposes to mine the Balgownie seam using Thin Seam Mining methods which as the name suggests is used for mining coal seams with thickness less than 1.5 metres. Hence, this method is most suitable for mining Balgownie seam, the thickness of which ranges from 0.46 to 1.5 metres. Thin seam differs in that it involves forming smaller pillars of coal that would be found in the Bulli or Wongawilli seam. Each mining “panel” forms up to seven roadways. The miner cuts these road ways in a sequence that allows a mobile bolting machine to come in after the coal has been removed for up to 15 metres, and to support the roof the miner is driven on the tracks (fitted) to another roadway where it cuts another 15 metres. This is known as the “cut and flit” method. In this system, the pillars of coal are not removed by pillar extraction methods. This mining system achieves a higher-than-normal recovery of the resources on the advance.

continous miner (Tamrock Inc. 1998)

Shearer in long wall panel Source:larry whipper people power.com

REFERENCES : www.bounty.com www.energy.vt.edu www.gujaratnre.com.au www.toreuse.com www.flickr.com Mapmines.jpg www.hub4.com www.energy.vt.edu/Publications/report9901.html www.cdc.gov/niosh/mining/pubs/pubreference/outputid578.htm