Mining Institute of Kola Science Center of Russian Academy of Sciences (Apatity, Russia):

Kozyrev S. A., Head of Laboratory, Doctor of Engineering Sciences, e-mail: skozirev@goi.kolasc.net.ru
Amosov P. V., Senior Researcher, Candidate of Engineering Sciences

The article discusses a question of natural ventilation of deep open pits, with a principal task of provision of standard hygienic and sanitary conditions in pit atmosphere, which would ensure safe and efficient work. General tendencies of open pits deepening, growth of pit vehicles efficiency and increasing of power plants' capacity lead to worsening of problem of natural ventilation of deep open pits. The parts of open pits, which are difficultly ventilated in recirculated zone, are situated at tranches driving, ramps and working sites of benches at open pit bottom. According to this, air contamination level in face space of the given working sites considerably depends on direction of ventilating air flow. Therefore, knowledge of particularities of air flows distribution at deep open pits space under different surface meteorological situations allow to predict the open pits atmosphere conditions. Authors suppose that it is impossible to determine actual distribution of aerodynamic parameters at in-pit space volume, due to its large volumes. However, according to the modern experience, research of deep open pits’ aerodynamics should be carried out, using the software, creating CFD-models (ANSYS, COMSOL etc). This paper presents the results of 2D modelling of velocity fields’ structure for Tsentralnyy and Glubokiy open pits, «Apatit» JSC, Zheleznyy open pit and Kovdor Ore Dressing and Processing Enterprise. This modelling was carried out, using CFD-models. The following thumb sections of the open pit were calculated: North — South, Northeast — Southwest, Northwest — Southeast and West — East. Direct and reverse direction of air flow was modelled (eight situations). Analysis of numerical tests (velocity fields, profiles of velocity components near the open pit foot and benches, angle of air flow expansion) determined the following facts:
- large vortex is clearly seen in the central part of open pits;
- formation of smaller vortexes is possible in the open pit deep part in some situations;
- reverse flows can occur at some parts of the open pit slopes (large benches);
- velocities at the open pit bottom are rather slow (some cm/sec).
For example, at wind velocity of 2,5 m/sec on surface, velocity of air flow at the open pit’s bottom is 0,015–0,08 m/sec. According to numerical modeling results, weakening of air flows on deep open pits bottom is more significant, in comparison with average-deep open pits. Boundary of recirculated zones in open pits with difficult mountain relief doesn’t correspond to its standard determination by air flow expansion angle, with reverse flows along the open pit bottom. The vortex flows in the pit’s upper part are formed, impeding removal of harmful impurities.

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