Effects of particle size, dust concentration and dust-dispersion-air pressure on rock dust inertant requirement for coal dust explosion suppression in underground coal mines

Experimental investigations of the minimum ignition energy and the minimum ignition temperature of inert and combustible dust cloud mixtures.

Experimental investigation on effects of particle size, dust concentration and dust-dispersion-air pressure on minimum ignition temperature and combustion process of coal dust clouds in a G-G furnace

Deflagration explosions of coal dust clouds and flammable gases are a major safety concern in coal mining industry. Accidental fire and explosion caused by coal dust cloud can impose substantial losses and damages to people and properties in underground coal mines. Hybrid mixtures of methane and coal dust have the potential to reduce the minimum activation energy of a combustion reaction. In this study the Minimum Explosion Concentration (MEC), Over Pressure Rise (OPR), deflagration index for gas and dust hybrid mixtures (K st ) and explosive region of hybrid fuel mixtures present in Ventilation Air Methane (VAM) were investigated. Experiments were carried out according to the ASTM E1226-12 guideline utilising a 20 L spherical shape apparatus specifically designed for this purpose. Results obtained from this study have shown that the presence of methane significantly affects explosion characteristics of coal dust clouds. Dilute concentrations of methane, 0.75–1.25%, resulted in coal dust clouds OPR increasing from 0.3 bar to 2.2 bar and boosting the K st value from 10 bar m s −1 to 25 bar m s −1 . The explosion characteristics were also affected by the ignitors’ energy; for instance, for a coal dust cloud concentration of 50 g m −3 the OPR recorded was 0.09 bar when a 1 kJ chemical ignitor was used, while, 0.75 bar (OPR) was recorded when a 10 kJ chemical ignitor was used. For the first time, new explosion regions were identified for diluted methane-coal dust cloud mixtures when using 1, 5 and 10 kJ ignitors. Finally, the Le-Chatelier mixing rule was modified to predict the lower explosion limit of methane-coal dust cloud hybrid mixtures considering the energy of the ignitors.

Effects of ignition energy on fire and explosion characteristics of dilute hybrid fuel in ventilation air methane

Float coal dust is produced during the coal mining process in underground mines. If it is entrained, the float coal dust presents a dangerous explosion hazard to miners when it reaches the minimum explosible concentration and is ignited. However, coal dust can be inerted if properly mixed with generous amounts of pulverized rock dust such as limestone to result in a homogeneous dust mixture with a total incombustible content (TIC) ≥80%. In the United States, it is mandatory for the rock dust to be 100% passing through a 20 mesh (841 μm) sieve and 70% or more passing through a 200 mesh (75 μm) sieve. Laboratory experiments have been conducted using the National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) 20-L and the Fike Corporation 1-m 3 explosion chambers. Coal and rock dust samples were prepared by sieving and were used to investigate the effect of particle size on explosibility and inerting effectiveness. The results from both chambers show that large coal particles >60 mesh (>250 μm) do not explode/ignite at dust concentrations up to 600 g/m 3 , and limestone rock dust particles >200 mesh (>75 μm) require a significantly higher TIC of 90% to inert Pittsburgh pulverized coal (PPC). This data illustrates the significance of particle size for preventing coal dust explosions and the importance of measuring particle size as well as TIC (which includes moisture as well as incombustibles) to determine the true explosibility of a dust sample.

Yi Wu

Papers

Experimental investigations of coal dust-inertant mixture explosion behaviors

Experimental investigation of dust MEC measurement