Underground » Detection and Prevention of Fires and Explosions
This project investigated the level of stone dusting required to inert Australian coals for the purposes of preventing the propagation of a coal dust explosion. A large number of coal samples were obtained from Australian mines and tested to determine individual inerting levels and other explosibility factors. These properties were correlated against other coal properties such as volatile content and vitrinite reflectance. The impacts of ignition energy in the test apparatus and of the presence of methane presence were also examined.
From the results obtained, it is clear that the inerting requirements for individual coals are not correlated to volatile content or any other common coal property as previously thought. For the range of coals mined by underground methods in Australia, the individual inerting requirement varies from 83% to 85% total incombustible content (TIC) which is the stone dust plus ash and moisture from the coal. Only at very low volatile content was there a lower requirement being 77% TIC at less than10% volatile content.
The impact of methane is to increase the inerting requirement by 5% TIC for the first 1% of methane present.
Minimum explosible concentrations varied from 30 to 50gm/m3 and were unrelated to other coal properties. This is equivalent to a layer about to 0.15mm thick in a roadway 3m high.
Large-scale testing of one of the Australian coals was undertaken at the Klopperbos facility in South Africa to be compared against the results obtained in the laboratory. The results obtained indicated an inerting requirement of between 81.8% and 86.3% compared to the laboratory results of 84.3% at 5kJ ignition energy.
The implications of the results obtained need to be considered in light of recent measurements of dust fallout in longwall panel returns. It is expected that to be able to achieve the levels of inerting indicated by this work program would require up to fivefold increase in stone dust application rates. This is probably impractical, significant further work should be undertaken to find alternative dust suppression methods.