Coal Mine Rock Dust Dispersibility Tests after Absorbing Moisture
Richard Gilmore, Colorado School of Mines; Jürgen Brune, Colorado School of Mines
Pulverized limestone dust, also called rock dust, is used in United States underground coal mines to prevent and suppress coal dust explosions. The 2010 explosion of the Upper Big Branch mine left 29 miners dead and underscored the coal dust explosion hazard in the coal industry. For rock dust to be effective, it must be easily dispersible by the forces of a methane or coal dust explosion. Moisture in the mine environment and water droplets from the dust suppression water sprays can cause caking of the rock dust requiring frequent reapplication of fresh dry rock dust. Rock dust suppliers have developed hydrophobic rock dust that repels water in an effort to remain dispersible even after wetting. Researchers at the Colorado School of Mines performed rock dust dispersibility tests in a full-size explosion test drift. Researchers used detonating cord to generate wind speeds of 30 to 50 m/s, the minimum required for propagating coal dust explosions. Three rock dust types are tested that meet United States standards: a conventional United States standard rock dust, a rock dust product meeting more stringent specifications for use in German mines and a hydrophobized rock dust product. Tests are conducted with dry-applied rock dust and dry-applied, then misted with water, rock dust. Results show that the conventional United States standard and German standard rock dust products partially agglomerate in larger chunks that may not be effective in suppressing a coal dust explosion, while hydrophobic rock dust retains dispersibility.