Due to the current market conditions with record coal prices being recorded, increasing amounts of pressure has been placed on coal producing companies to optimise product output in an attempt to maximise profit. This has lead companies to assess areas of their operations to determine bottlenecking or regions where production is limited due to a certain process, system or applications. One such area which has been identified to have detrimental affects on underground coal production is mining through dykes or hard igneous intrusions. This causes delays and equipment damage due to the use of unsuitable soft rock equipment (e.g. continuous minors and shearers).
One alternate method that has been identified is companion excavation, this involves using impact hammers to fragment the hard rock material and allow the coal specific equipment to excavate coal.
To assess the potential implementation of this technology in underground coal mines initial scoping must be carried out. This involves analysing a series of performance data obtained from Rammer Sandvik Corporation. This data provides hammer performance rates for a series of selected hammers in numerous hard rock materials experienced during coal mining. As the focus of this study is centred on dyke materials, dolerite excavation has been evaluated extensively.
It has been identified that subsequent research is required to fully analyse this topic. This must involve the mechanical design of a suitable system / unit to be employed on both the longwall and development faces. This will assist the selection of a suitable range of hammers to be used based on the underground working area constraints. This must also evaluate the associated issues such as, deployment and mobilisation, equipment optimisation and the required energy needed to operate the unit.
To get a clear indication of how the results relate to coal mining they have been converted to both longwall and development scenarios. These have also been compared to a real life case experienced at Anglo Coal’s Dartbrook Colliery.
The results show that based on the specific conditions production rates can be significantly improved while mining through dyke affected material. This conclusion has be reached due to the fact that a lot of the hammers return advance rates greater then that of the shearer, and thus normal conditions can be assumed. The hypothetical results for Dartbrook show that advance rates during mining of dyke affected material is around one quarter of current normal condition rates, with the use of an impact hammer these results can be improved and normal rates achieved. Another major finding of the project is that through the use of companion excavation maintenance costs can be significantly reduced as the hard rock is not affecting the tensile style of excavation created by the shearer and continuos miner.
Due to the amount of flexibility and the capacity to utilise larger equipment, the development application of this technology is believed to hold the greatest potential. This is due to the fact that implementation will only require the attachment of a suitable unit to an LHD machine.
Companion excavation can be seen to be a viable option for overcoming the coal extraction issues created by dykes and other hard rock occurrences. With the current market conditions for both thermal and coking coals this method could increases site production by reducing losses and therefore increase site value, a goal which should be a target for all companies.