Q: Is continuous haulage the answer to improved roadway development rates?
A: Continuous haulage systems (CHS) are one of the elements of improved development rates; however, it is likely that more immediate and more significant gains will be achieved at most mines through improved application of process management and process improvement disciplines, the pursuit (and maintenance) of fit-for-purpose equipment designed to optimise existing roadway development processes, and the introduction of self-drilling bolts.
Simulation studies conducted by OEMs show that in gateroad development with shuttle cars the roadway development process is “bolting constrained” for the first 70 metres or so from the shuttle car shunt where the shuttle car can return to the continuous miner after discharging or shunting before the bolting cycle (or part cycle) is completed.
The development process then typically becomes “haulage (shuttle car) constrained” once the haulage distance from the shunt increases beyond 70m, and the bolting cycle (or part cycle) is completed before the shuttle car returns to the continuous miner.
Studies show that the metres per operating hour (MPOH) rate begins to deteriorate once the process becomes haulage constrained.
Over a typical longwall gateroad pillar cycle a “current best practice” shuttle car mine initially operates at a rate of 8MPOH when bolting constrained at the start of the cycle, which progressively reduces to 3MPOH at the end of the pillar cycle once it becomes haulage constrained (and averages 5MPOH for the full pillar cycle).
In these best practice instances, a CHS could be utilised to maintain advance rates at, say, 8MPOH over the complete cycle; however, few mines are operating at these best practice rates due to factors such as a lack of process management, equipment not being fit for purpose, and mining conditions.
Typical operating rates across mines are in the 2–3MPOH range, with the number of operating hours (50–60 hours per week) being significantly fewer than the result being achieved in best practice mines (80 hours or more per week). Hence there is significant potential to improve performance by improving operating rates (MPOH) and improving process uptime (hours) without necessarily introducing a CHS.
At the last round of ACARP Roadway Development Workshops (August 26, 27 and 29, 2008) Chris Wilkinson (Mine Consultancy Services) noted that in South Africa some 27 bord and pillar development units were producing in excess of 1 million tonnes per annum each (equivalent to 40km per continuous miner); however, only three miner units utilised a CHS, with the balance using shuttle cars (typically three shuttle cars per unit).
Process management and control was considered a key factor in the higher levels of performance achieved in South Africa, together with the application of place change mining with small pillar dimensions. Wilkinson also noted that 40m/shift was both achievable and sustainable in gateroad development in Australian longwall mines with fit-for-purpose equipment and a good application of process control and improvement, with moderate to high levels of roof support, while using a shuttle car based haulage system.
The secret is to optimise the shuttle car loading time, roof bolting cycle time, shuttle car “away time”, and to reduce non-production time.
The introduction of self-drilling bolts provides the opportunity to reduce bolting cycle times due to the reduced number of process steps required to install a bolt, coupled with reduced variation in bolting cycle times from the fewer number of steps and tool changes.
Improved onboard hydraulics on new generation continuous miners also allows the sustained operation of up to six bolting rigs simultaneously and, coupled with improved ergonomics on these machines, is likely to result in sub-six-minute bolting cycle times.
This reduction in bolting cycle times will lead to improved MPOH rates, providing shuttle car operations are optimised, or if a CHS is employed.
At the March 2008 Roadway Development Workshop, Richard Porteous (Xstrata Coal NSW) also reported on benchmarking studies conducted within Xstrata’s NSW mines (which were recently extended to include the company’s Queensland mines), with the studies reinforcing the view that significant gains can be achieved by utilising fit-for-purpose equipment that is designed to optimise and match the bolting cycle, shuttle car loading time, shuttle car capacity and operating speeds and discharge rates (shuttle car “away time”), and also postulated on the gains to be achieved from self-drilling bolts and CHS.
Q: Industry seems to be showing a lot of confidence in the new technology. Is industry rushing into this or are their decisions based on good facts?
A: At the September 2007 Roadway Development Workshop, Xstrata (David Gibson) noted that it had analysed its roadway development process at Beltana and determined that the only way forward for it to improve upon current best practice development rates and to sustain a higher level of performance was through the introduction of a CHS. Xstrata representatives have also visited a number of CHS in the US and appear to have “done their homework”.
Caledon have introduced and developed a mining process that maximises straight cutting cycles and minimises cut through breakaways (a process that typically impacts development rates) and have utilised a CHS to offset the potential haulage constraints associated with longer roadways, while optimising overall recovery rates within a geotechnically complex environment. The Sandvik presentation at the August 2008 Roadway Development Workshop would suggest that they are very close to getting it right.
Aquila is similarly unique (for Australia) in that it is operating in a seam thickness of 1.6–1.7m, and while they have been able to sustain production rates in excess of 800m per week in these conditions with shuttle cars in a place change mining system, improvement upon those rates and the sustainability of improved rates is a challenge when operating shuttle cars in a low seam horizon.
At the recent ACARP Workshop, Chris Wilkinson did note that introduction of a CHS was not necessarily straightforward, and that another and different range of issues were introduced than that experienced with shuttle car haulage.
It is also reasonable to say that CHS technology is now more mature than it was in the 1980s and 1990s; hence it is likely that these new generation systems will have overcome many of the technology shortfalls of earlier generation systems. The challenge is likely to be in the OEM’s ability to support the technology and hardware in current market conditions.
A further technological development that may be utilised to enhance the potential successful introduction of CHS in Australia (and other countries) is the ability to simulate operation of the equipment within a virtual world to identify potential design and operational problems well before any metal is cut (the University of Wollongong is utilising such technologies in their current ACARP-funded project to automate bolting operations and the installation of steel mesh).
Q: How are things being done differently this time compared to when the technology failed about a decade ago?
A: There is a better understanding of the roadway development process and what can be achieved through proper application of fit-for-purpose equipment, while there is also a recognition of the importance of getting ownership of the technology and hardware at an operator level. As noted above, CHS technology is now more mature than it was in the 1980s and 1990s, hence it is likely that these new generation systems will have overcome many of the technology shortfalls of earlier generation systems.
The Longwall Automation project also demonstrated the importance of having competent, professional champions to champion the introduction of the technology. I also anticipate that companies committed to the successful introduction of new technologies will commit appropriate resources and are expected to perhaps be less tolerant of their champions being anything less than successful.
Q: Where do you see the future of continuous haulage going in Australia?
A: Firstly, I expect that best practice mines will successfully introduce and embrace new generation CHS and establish industry benchmark performance levels. These companies will also be able to integrate these systems with new technologies developed as part of the proposed CM2010 project to leverage further gains.
Significant cultural change will be necessary in other mines if they are to establish a suitable platform to successfully capitalise on the introduction of new technologies, particularly in regard to their approach to involvement of personnel, their pursuit (and maintenance) of fit-for-purpose equipment specifically designed to optimise the mine’s roadway development process, and their application of process management and process improvement.
Mining conditions at some mines are also likely to limit the introduction of new generation CHS on an economic basis, with shuttle car based haulage systems (and even remotely operated shuttle cars) being able to readily match the achievable development performance in adverse conditions associated with depth, stress, gas, geological structures, and resulting high density support regimes.
The continuing application of shuttle car based haulage systems will offer a low risk, low capital and maintenance cost alternative to many mines. The development of remote operating systems for shuttle cars, as is being considered by one South Coast NSW mine (similar to the technology employed on LHDs in underground metalliferous mines), may also provide the enabling technology required for a remotely operated mining system, albeit at possibly lower system production capacity.
Clearly, it will be interesting in 10 years or so to reflect back upon the next decade to see what unfolded and what were the drivers of change. With the development of additional production capacity being committed on almost a daily basis across the industry, will a lower than projected rate of growth of coal demand (due to heightened environmental concerns) drive new mines to pursue higher technology, higher capacity mining systems as a means of remaining competitive in the market, or will continuing skills shortages constrain the industry from realising its market potential?
