Speaking at AJM’s sixth longwall conference in March, Peter Hetherington, head of engineering and Phil Garner, operations director spoke of recent lessons learned at the Yorkshire colliery and some of the technology the mine has used to overcome problems.

 

Daw Mill will be one of eight remaining core UK Coal mining operations servicing the UK’s domestic power market once the recently announced spate of mine closures are finalised.

 

The Joy 2x850t supports with a working range of 2-5.4m are among the largest powered supports ever used in Europe and couldn’t go underground as a complete unit. Two re-assembly stages were completed before the chocks were installed on the face. The installation of 301’s involved the transportation of 6,500 tonnes of steelwork and 1300 vehicle movements.

 

In the development of the 5m extraction height ‘301’ longwall face the mine recorded several firsts such as the drivage of a lateral roadway using an Austrian method. This incorporated an Anderson RH45 roadheader to drive a 4.5m circular roadway which was supported by 55mm to 200mm of sprayed concrete.

 

Faceline drivage was a first for the UK coal mining industry. Prior to the current 301 longwall face the widest face driven solely on roof bolts was 6.5m. In contrast, the Daw Mill 295m wide faceline is 4m high and 8.2m wide, supported by roof bolts at 2.6 bolts per square metre.

 

Mining started in April last year but by May a previously unidentified geological feature started to show up on the coal face which slowed production until January. Tongue in cheek, Garner described it as “a sedimentary feature of indeterminate origin.” This fault developed towards the tail gate and eventually affected 60% of the coal seam.

 

Among several problems experienced when mining began was with clearance and at times the AFC was stalled for days with rock from large cavities. Lumping caused coal flow problems on the stage loader and pile ups at the headframe and crusher.

 

The mine management decided it was not economic to relocate around the fault and that mining through the fault was the best way forward. By January this year production had increase as the seam returned to its normal section.

 

Attempts to map the sequence on the panel have included the use of in-seam seismic reflection but this did not identify the compactional seam disturbance. It did provide trend information on a 3m normal fault which was proved in the tailgate.

 

An in-seam seismic transmission survey gave a vague zone where seam disturbance may be possible but did not clearly delineate the feature. The most successful technique appeared to be 3D seismic tomographics. While the results most closely match the actual shape of the disturbance a disadvantage is that the images can be produced by changes in stress or fracturing.

 

The mine plan is to operate the face at 70,000 tonnes per week, with a target of 3Mt per annum.