Open Cut » Overburden Removal
The previous project outcomes (C25041) supported the potential for DynaCut technology to be effective and economically competitive at a large scale for surface coal mining. This phase aimed to progress the de-risking process through additional cutting trials with a modified cutting system, as well as advance mining system concepts and establish key design criteria for the next-generation DynaCut test machine.
Cutting tests were performed using the DynaCut test machine and sandstone sample blocks cemented into a cutting bunker. The rocks spanned two domains: ~20 MPa UCS and ~30 MPa UCS. The machine was modified to allow variation of the oscillating dynamics of the cutting disc, to test the hypothesis that reconfiguring the way that the cutting energy is applied to the rock may improve the efficiency of cutting, and therefore the overall performance of the system, in overburden materials. The testing comprised over 200 individual cuts, providing 29 test cuts in the sandstone blocks.
Key performance metrics for the cutting tests were the ICR (instantaneous cutting rate) and SE (specific energy of cutting). Whilst increasing the total cutting power (via increased oscillation frequency and/or increased energy per cutter cycle with a higher oscillating mass) delivered improved cutting rates, the key finding was that the cutting efficiency could indeed be significantly improved by simply reconfiguring the way that total power was delivered. In fact, the most efficient cutting was achieved by increasing the oscillating mass whilst simultaneously reducing the oscillation frequency, delivering a reduction in SE of about 25%, without any detrimental effect on the cutting rate.
Cutter designs for overburden materials were also advanced during this project. Whilst a sharper or more aggressive cutter is generally required for weaker/softer materials, there is a balance between this sharpness and the strength of the cutter body, and therefore different designs may still be required for different domains of overburden materials. Features of the cutting face and rock mass, such as free surfaces and mechanical discontinuities, also offer potential for further enhancement of overall excavation performance through considered cut sequencing and path planning.
A process of engineering review, combined with further conceptualisation of potential surface mining systems, provided clarification of the key requirements and design features for an up-scaled test machine. It was determined that the upper limit of a single cutter unit, without major re-engineering of the core components, is likely to be a cutter of about 1m diameter with a cartridge about three times more powerful than the current system.
High-potential commercial systems include a surface longwall style system and mobile machine style system. An upscaled surface longwall style system with two shearers could potentially cut at a rate of about 2300 bcm/h (ICR). For the mobile machine style of cutting system, an up-scaled single-cutter machine could potentially cut at a rate of about 540 bcm/h (ICR), whilst a much larger multi-cutter machine might be capable of >2000 bcm/h.
Previous economic evaluations for future high-capacity commercial production systems were revised, indicating a total all-in cost of $3.01/bcm for a mobile machine-based system, and $2.95/bcm for a surface longwall style system. These revised cost estimates further strengthen the potential competitiveness of DynaCut, with the all-in cost for conventional mining in the same scenario being about $3.00/bcm.
A more comprehensive performance and cost assessment was also performed, with a case study deposit scenario and various scales of lower-capacity single-cutter machines with multiple material transport systems. Whilst the OpEx and CapEx of the DynaCut systems are typically higher than that of conventional mining, there are systems that are likely very competitive on an OpEx basis e.g. DynaCut-conveyor system: $4.40-$5.50/bcm; baseline system: $4.60-$5.00/bcm. CapEx estimates for the complete DynaCut system fleets ($46M to $68M) were also higher than for the baseline system ($34M). Various benefits offered by continuous cutting (e.g. potential for steeper pit slopes, increased coal recovery, elimination of blasting-related impacts) must be considered alongside the simple metrics of OpEx and CapEx. Applying basic examples of these to the case study mining scenario actually resulted in the DynaCut-conveyor system outperforming the baseline drill/blast/load operation, despite having higher OpEx and CapEx per bcm.
The ultimate scale of the individual cutting units of a DynaCut system may not be as large as originally envisaged, and it may be feasible to base an MVP (minimum viable prototype) for initial deployment on an existing platform. The MVP ideally requires a larger cutter (towards 1m diameter), and needs improved mobility and stability, whilst allowing more continuous operation and appropriate cuttings management.
The outcomes of this phase are extremely encouraging, highlighting that there is likely much additional potential to be discovered as the DynaCut technology is further tested, developed and refined. An extended site deployment opportunity with a suitable prototype machine is a pivotal requirement for de-risking the continued development of the technology for application in surface coal mining, and accelerating adoption into suitable operations.