Published in Australia's Longwalls
Daw Mill is one of eight deep mines owned by UK Coal earmarked for continuing coal production against a backdrop of major restructuring currently taking place in Britain’s remaining deep coal mining industry. UK Coal is the largest coal producing company in the United Kingdom, outputting14.8 million tonnes in 2003, and a further 3.1Mt from its surface mines.
Last year Daw Mill’s proposal for aid was one of 14 schemes put forward to the government. In late 2003 the UK Government offered a total of £36.5 million in Investment Aid to access more than 70Mt of reserves at UK Coal collieries. The aid amounts to a maximum of 30% of project costs.
Daw Mill was offered £9.6 million towards a total project cost of £41.4 million to access over 32.8Mt of reserves. Work will include the development of over 3,200m of underground roadways and the purchase of a second set of face equipment to maintain continuity of production.
Daw Mill works the Warwickshire Thick seam, a combination of six separate seams forming up to 7m of extractable coal. At a cutting height of 5m, Daw Mill is believed to be cutting one of the thickest sections in the world, and the face is equipped with the largest powered supports ever used in Europe. These are 172 Joy Mining Machinery 850 tonne roof supports, spaced at 1.75m with a cutting range of 2-5.4m, each weighing 32t. The control system is Joy’s RS20.
Supports are supplied from a RMI pumping system based on three pumps each capable of delivering 66 gallons per minute for a total delivery of 198 gallons/min at 5000psi, depending upon demand. The shearer is an all-electric Eickhoff SL 500 with five motors at a voltage of 3300volts. Daw Mill’s 301’s longwall face has a cutting length of 295m.
The Joy stage loader is rated at 1.8 metres per second with a capacity of 2000 tonnes per hour while the Joy armoured face conveyor incorporates 2 x 750kW drives. Initially, the AFC couldn’t cope with overload generated by the geological conditions as the torque was not optimised. To address this problem Turbo technology transmissions (TTT), which is a Voith coupling, was installed on both AFC gearboxes, providing high torque capacity with no load electrical start. Once torque was increased overload problems were largely solved.
Power to the face is supplied by an Allenwest Wallacetown AW2000 load centre supplying 8 x 3300 volt drives, 2 x 1100 volt drives and 8 x 110 volt power supplies. 301’s gate conveyor is about 3000m long with one main drive and two tripper drives. The conveyor transports 1800tph over a length of 3400m with a lift of 150m.
Production was limited by coal clearance, which was 800tph up the drift belt. This was upgraded to 1200tph in 2003.
Last year the mine also focused on improving coal preparation performance by reorganising the conveyor system. Until then Daw Mill was producing coal to 23 specifications with ‘exotics’, some 30% of output going to industrial and domestic customers and the remaining 70% to power stations. Run of mine coal was transported on 5.8km conveyors.
This reordering has seen a reduction in screen processes from 35 to 20, conveyors reduced from 78 to 59, and the network shortened to 4.6km. This has improved plant availability by over 20%
The introduction of fibre optics to enable high-speed data communications has helped to improve productivity at the mine. With its multitude of sensors, a modern installation such as the current 301’s panel can require 1,924 digital inputs and 2,154 analogue inputs. The mine’s earlier outstation could only cope with a maximum of 128 digital inputs, 24 analogue inputs and 8 relay controls. One driver for the high-speed network was the installation of a multiple power tripper conveyor on the maingate system. The increase in speed in the communication systems allows the variable motors to react much quicker to changes in tension in the conveyor, allowing smoother speed control.
Utilising SCADA fibre controls, data communication speed has been increased from 60 to 600 millisec (ethernet) on 301’s development conveyor, which will give faster reaction times to the Breurer motors.
The mine employs 480 staff with a small number of contractors operating a three shift system based on 7.25 hours per shift, five days a week.
301’s was developed using single entry roadways as the maingate and tailgate. The tailgate was developed by a Joy ED15 bolter miner with Hydramatic rigs. Roadways are 4m high, 5.2m wide, driven up to 3,120m in length. Bolting density of 2.6 bolts per square metre was adopted.
Production for 2003 totalled 2.145Mt, the third highest annual output achieved at the mine and the best ever for a single face. Production from 301’s face in the last quarter was in excess of 714,000t.
By the end of March 2004, the face had produced over 2.7Mt and following an intensive maintenance and improvement programme to the power loader, AFC, stage loader and coal gate conveyor, output is being maintained at over 60,000t per week, with a projected total colliery output of over 2.70Mt for 2004. By its finish, 301’s is expected to produce over 5.22Mt
The use of 3D surface seismic surveys is being successfully used to prove the geological structure and avoid any seam anomalies. In 2003 a survey was completed that has proven 30’s Area, which is currently being developed to replace 301’s. In addition another major 3D survey is about to be undertaken to confirm the geological structure of 300’s Area. Inseam seismic surveys are also used to prove forward as roadway development takes place.
To support the face production, around 5000m of annual replacement development is planned. Single gate roads are being developed that are over 3km in length utilising bolter miners. The investment programme includes the purchase of a new Voest Alpine ABM25 heading machine that will be delivered later this year.
The face is currently working some 6.6km from the mine entries and the working area extends some 5km further to the west and south. Fifteen tonne Clayton and 28t Hunslet BoBo electric locomotives are used to transport men and materials to the working area. Materials are then deployed using a fleet of free steered vehicles. Man-riding within the developments is provided by the installation of double-deck two-way conveyor belt man-riders. In the operational face district a SMV Driftrunner personnel module is used. This diesel powered free-steered people carrier ferries the 12-man team to the production face. The investment program includes the extension and enhancement of the transport systems.
