Since 1984 nameplate capacity of a typical longwall has increased from 1.25 million tonnes per annum, 2,000t/h, to 3Mtpa and 3,000t/h. Current specifications focus on 6Mtpa and 4,500t/h.
Similarly, 20 years ago a standard block had a face width of 200m and a length of 2,000m. Today face width of 300m are becoming common, with 400m on the drawing board. Block lengths of 6,000m-8,000m figure on many mine plans today; the so-called ‘super blocks.’
These trends pose equipment challenges, Merriman said. The dilemma is whether to specify equipment for one block or specify it for longer duty. The OEM has to design equipment with a high overall life coupled to availability and a long overhaul interval.
Technical issues to do with making AFCs longer are related to controlled starting, chain management and chain oscillations. Equipment designs of power transmission losses are sometimes overlooked as a problem. Merriman said in some instances voltage drops of over 20% were possible.
“It is important for the equipment designer to specify motors that can still produce adequate pull-out torque… at a nominal voltage of 4.0 to 4.5 x full load torque The jeopardy for not doing so is to end up with an AFC that may not start under end-to end loaded conditions, irrespective of face spall. Not a good idea on a long and/or high face,” Merriman said.
He also briefly outlined the concept of broadband chain Joy is pursuing to overcome chain oscillation. (A more detailed article on broadband is due to be published in the June 2003 edition of Australia’s Longwalls.)
To complete an 8,000m by 400m wide super block a shearer will travel more than 3,200 kilometers (with haulage) which makes a clear case for a reliable haulage system. This means the shearer drivers will also travel this distance collectively thus emphasising the importance of using tools like memory cut and roof support initiation.
Merriman said further optimisation opportunities exist in the areas of life cycle management/maintenance. Most underground operations have access to copious amounts of data but this is commonly still used retrospectively – the ‘black box recorder’ which is interrogated if something goes wrong.
“What’s missing in the underground industry at present seems to be the person dedicated to the on-line analysis. The data is available, it’s just not looked at until it is too late,” Merriman said.
Other industries, such as surface mining use such information in a more pro-active way to plan maintenance. This is the way towards predictive diagnostics.