The dust lifting mechanism and dust flame propagation modelling

In underground coal mining or iron sulfide operations as well as many industrial facilities, combustible dust layers accumulate on floors, horizontal ledges, surfaces of machinery, and above false ceilings. Dust layers can easily be lifted into suspension by weak explosions or pressure waves. Some examples of typical causes are a small methane gas explosion in an underground mine, the blast wave from an explosive charge in a sulfide mine operation, cleaning operations, a strong gust of wind because of an open window or door in a processing plant, or a leak from a compressed gas system. Once a dust cloud is created, there is always a high probability of ignition leading to a flash fire or a propagating dust explosion. Furthermore, if the dust cloud is formed within a confined space that contains obstacles, the propagating dust flame will accelerate, possibly leading to a dust-to-detonation transition. Therefore, this research program focuses on understanding and modelling the dust lifting process. The overall long-term objective is to better predict the dust explosion hazard and thereby develop strategies to prevent them from occurring or to mitigate their consequences. The experimental program will investigate the mechanism of dust lifting as a function of the nature of the particles (density, type and shape), thickness of the dust layer, particle size distribution; shock wave propagation velocity; and presence of obstacles. Some experiments will be done in a standard 20-L dust explosion chamber to better understand the dispersion of non-standard dusts (e.g. low density cellulosic fibers) which are currently not well-understood. Additionally, experiments in a purpose built shock tube will allow high-speed Schlieren photography for visualization of the dust lifting process. All these experiments will enable development of a suitable model to describe the dust lifting, dispersion, and mixing process for implementation in a Dust Explosion Simulation Code. This simulation code will allow prediction of explosibility characteristics from standard testing of various dusts as well as prediction of the dust explosion hazard within process equipment and facilities.