Dust capture for small coal particles (<2.5µm) can be improved if one takes advantage of electrostatic charges that resides on the surface of coal dust particles and on the surface of water spray droplets used to capture coal dust. Traditional dust capture methods that use water sprays are ineffective in capturing small dust particles since the motion of small dust particles is governed by electrostatic forces. If additives such as ionic surfactants could be added to water that would enhance the surface charge on water spray droplets, dust capture with water sprays could be improved. The results presented show that n-sodium octyl sulfate causes the greatest charge enhancement versus the longer chained n-sodium dodecyl sulfate and n-sodium octadecyl sulfate. This can be explained by considering the factors that lead to droplet charge enhancement. Those factors are the mass of surfactant ions at the droplet surface, and the diffusion rate of the surfactant ions from the bulk droplet to the surface of the droplet. Sodium octyl sulfate will have a faster diffusion rate to the droplet surface because of its relatively short length, and will also maximize the mass balance of surfactant ions at the drop surface.

Present day water spray based dust removal technologies do not effectively remove respirable submicron coal and silica dust particles in the underground coal mines causing Coal worker’s pneumoconiosis (CWP). The objective of this research was to study the electrostatic charges present in the airborne coal dust in order to develop efficient water spraying based dust removal technology where water drops charged using ionic compounds and surfactants would be used to capture the oppositely charged coal particles. In an experimental scrubbing column, coal particles dispersed in an air stream by a Fluidized Bed Aerosol Generator were captured by water drops sprayed by an atomizer. Characterization studies performed using an Aerodynamic Particle Sizer and Aerosol Electrometer showed that airborne coal particles have a significant amount of positive charge with an average of 140 elementary units of charge. The capture efficiencies of the water drops evaluated were found to be higher than those predicted by previously determined mathematical models. It was predicted that apart from the effects of Brownian diffusion, interception and impaction, the effect of Coulombic attraction was present and the charge of the water drops was predicted to be between - 2 x 10-6 C and -2 x 10-4 C.