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STAR-CD digs miners out of trouble |
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| Brian Cannoo, CSIR, South Africa | |||||||||||
Not surprisingly, in addition to the inevitable methane release, this operation generates a large amount of coal dust. Not only are both the dust and methane unpleasant and dangerous to breathe, they are also highly flammable. For this reason, mining machinery is usually fitted with dust suppression and gas removal systems, including water sprays, airblowers, exhausts and scrubbers. The flow patterns involved are highly complex, being driven by air from the "Last Through Road" and the various air moving and dust control measures. Physical modeling of these flow patterns is close to impossible without expensive full-scale experiments, and even then, measurement is problematic and tends to be highly subjective. The prediction of the effectiveness of these measures becomes important when designing a new machine or changing the operating conditions. Voest Alpine Bergtechnik, one of the world's largest manufacturers of this equipment, has for the past several years gained an important edge by turning to CFD for these predictions. Over these years, techniques have been developed to make it possible to predict dust distribution using CFD without resorting to computationally expensive multiphase models. Essentially, these techniques involve modelling the dust-laden air as a second fluid that is allowed to mix with the background air, and the properties of the air flowing around the miner are derived from the properties of the mixture. A lot of creative work has been done in establishing the best and most economical way to introduce the dust into the model. In addition, user coding is used to apply the boundary conditions of the scrubbers and fans, in such a way that it is not necessary to model the inner workings of these items, while maintaining the dust and methane concentrations going in and out. The known efficiency of the scrubber is also applied to the model in this way. The figures show the geometry of a Bolterminer in a heading, and a mesh produced using pro-STAR. Contours of near-wall methane concentration are also shown, as well as an isosurface of a certain methane concentration and particle tracks. With CFD applied using the STAR-CD code, Voest Alpine Bergtechnik has been able to optimize many aspects of Bolterminer design, including the positioning and orientation of fans and other airmovers. For further information about CSIR’s consulting activities, contact: brian@starcd.za.net or visit: www.starsolutions.co.za |
