Environmental discharge criteria and dispersion estimation for mine ventilation exhaust stacks

Water droplets emitted from mine ventilation discharge points can have a detrimental impact on the environment, and are being recognised as an important source of emission at mine sites. Furthermore, this can lead to poor fan performance, fan wear and reduced fan efficiency, which in turn translates into an increase in overall operating cost. Droplets are the result of groundwater seepage and/or condensation entrained in the gas stream. Harmful dusts may be incorporated in these droplets. The larger droplets then associated with these dust particles increase their settling velocity and thus dispersion can be substantially reduced. This paper addresses the issues associated with the characterisation of particle size distribution and illustrates energy losses due to droplets in vertical shafts using pneumatic conveyor calculations. Measuring techniques and abatement technologies are also highlighted. Keywords: mining, ventilation, dispersion, droplet, entrainment