A number of new mining methods, such as LTCC and wider faces, have ramped up this year in Australia. What are the ramifications of this now and in the long term?
Longwall Top Coal Caving (LTCC) is being utilised to achieve higher resource recovery albeit with potential for higher dilution. The potential productivity of a LTCC face remains relatively unproven presently in Australian conditions and regulatory environment.
While an effective method for maximizing coal resource recovery (up to 80% of the seam remaining after the initial shearer pass), top coal caving may take some time before it is widely embraced by the Australian industry. There are potential issues with untrained labour (both operators and maintenance), increased dust generation from the caving process and significant dilution. One advantage for thick seam coal mines prone to spontaneous combustion is that by leaving less roof coal in the goaf the risk of spontaneous combustion is reduced. Top coal caving methods are generally less productive on a shift or day basis than one pass shearing methods.
The time required for the un-sheared coal to crush and fail is dependent upon several factors including coal strength, location in the face line, depth of cover, and strength of roof strata. Coal generation from the LW face cannot be sped-up as is the case with single pass shearing systems. Another potential limitation of top coal caving methods is in highly gassy seams, where the caving process promotes a sharp increase in methane gas emissions.
The widening of longwall faces was an inevitable move in the Australian coal mining industry as it has been in other countries. Due to increasing depth, and more difficult mining conditions, development rates and development floats have been reduced at many longwall mines.
Clearly a wider face reduces the development metre to longwall tonne ratio, hence placing less reliance on development sections to sustain high production rates.
Down-sides of the wider faces include significantly higher capital costs as the roof supports are the largest capital component of an UG LW mine, increasingly more powerful main/tailgate drives to move the larger chain and coal on the chain.
The more powerful equipment results in more heat at the longwall face (which is already an issue in QLD mines and many are already moving to refrigeration methods to keep temperatures below statutory levels, particularly in development). There are relatively fewer simple, un-faulted deposits remaining that are suitable for a longwall installation; the wider faces further reduce mine plan flexibility and resource recovery.
Despite these issues, we expect to see more LW installations with wider face widths as newer generation faces replace older equipment.
A number of junior and mid-tier coal explorers and producers are currently carrying out exploration, feasibility studies and bringing mines onto line. What does this mean for consultants, and for the Australian industry as a whole?
Many of the Junior coal producers run much leaner technical and planning teams, therefore providing opportunities for consultants to assist with all phases of planning, mine design and project implementation. However, the Juniors typically don’t have the significant operating budgets and sustained reliable revenues of the major producers hence limiting the attractiveness of using consultants.
Generally, the activities of the Juniors are a healthy development for the Australian industry as a whole and should result in many opportunities for consulting assignments.
In your eyes what is the most important R&D project (private or publicly funded) happening at the moment and why?
In our opinion, projects attempting to increase development rates and increase LW and CM availabilities would be the most important. Many longwalls in Australia are running at less than 50% availability and LW development rates need to improve if higher LW performance is to improve in the future.
What progress has been made in improving the way roof falls are managed?
Even with increased focus on higher roof support density there remain instances of major and potentially catastrophic roof falls in longwall mining operations. Longwall roof falls are being better managed with the implementation of several techniques to:
1. avoid face falls in the first place
2. minimise the impact of falls
3. management of major falls.
The foremost progress in improving the management of falls is in the areas of prediction and prevention and in procedures for mining through potentially fall prone ground.
Prediction allow for the longwall manager to prepare for hazardous areas principally by completing maintenance and other tasks before attempting fall prone ground and scheduling personnel during this time to maximize the time dedicated to mining. These actions, which permit mining through hazardous areas with minimal delays, are effective because of the nature of rock failure.
That is, roof stata deteriorate over time and because of the faster mining retreat rates, abutment stresses have less time to adversely affect the face and gateroads.
Management also reduces the probability of falls on the face by minimizing tip to face distance and selecting appropriate shields. Shield manufactures have helped in this regard by increasing pontoon foundation loading, increasing tip loads, stabilizing the shield, increasing support density and speed of advance.
Management has also improved its understanding of conditions and their impact on longwall operations including evaluation of conditions that cannot be mined through in which case arrangements are made to improve ground conditions or to move around the feature. Techniques to improve ground conditions include advance drilling and pumping of micro-fine cements and grouts and PUR injection long before the longwall approaches the hazardous ground.
Once a fall on the face occurs, quick response time is needed to minimize face deterioration. Supervisors must be involved in personnel and contractor management. Techniques including surface and in mine drilling and pumping of micro-fine cements and grouts, PUR injection, and cavity fill foam injection, which are now undertake immediately after the fall.
Gate road stability is another key to high longwall production rates. In this area, improvements include increasing support density and lowering reaction time when falls occur. Of note, are the increased use of cutable cribs, cable bolts, self-drill bolts, and the early injection of grouts before hazardous areas deteriorate. Early installation of support systems and the use and improvements in gate shields add to management’s tools for developing stable gateroads.
