Respirable coal dust control using surfactants, with special emphasis on a liquid spray system

As a result of extensive research and development programs which have been carried out since a mandatory respirable dust standard of 2 mg/m{dollar}sp3{dollar} was enacted in 1969 under the Federal Mine Safety and Health Act, considerable progress has been made in dust control technology. These programs have helped coal mines to meet the dust standards by, for example, improved efficiency in water sprays and scrubber technology. But some mines, particularly those with longwall sections, are still not able to comply. In addition, the incidence of pneumoconiosis does not yet seem to be declining even under the standard (Sinha, 1982; Attfield, 1993). It has been suggested that this is because existing technology may not be effective in controlling finer dust particles (below 3 microns), the size range primarily responsible for pneumoconiosis.; In this study, surfactants were used to increase the effectiveness of water sprays in capturing both coarse and fine dust particles. The effectiveness of the surfactant in wetting coal clearly depends upon both the type of surfactant and the type of coal. The nonionic surfactant Surfynol proved to be the best at capturing coal dust because it reduces dynamic surface tension in a mobile environment such as that found with airborne dust. The collection efficiencies for different types of coals were strongly influenced by the sulfur content of each coal.; Nonionic surfactants tend to give better coal wetting qualities due to a good balance between hydrophilic head groups and lipophilic tail groups, and are not sensitive to the mine water environment. Wetting performances with nonionic surfactant solutions were significantly improved (up to 215 percent) by adding bases such as sodium hydroxide and potassium hydroxide.; Results showed that the most effective surfactants increased the ability to suppress overall coal dust levels by up to about 93 percent when compared with plain water. More critically, the best surfactant suppressed fine dust particles (below 3 microns) up to 125 percent more effectively than plain water.; The surfactants improve wetting by reducing the surface tension of the water and by converting the hydrophobic coal surface to a hydrophilic state through adsorption. The addition of surfactant did not impact droplet size and velocity. Therefore, the improved dust collection efficiency by adding surfactants to water must be achieved not by the change in droplet parameters but by the improved wettability.; A factorial design and subsequent analysis was used to evaluate the venturi-scrubber system used to mix water sprays with the air containing respirable dust. Results showed that the pump injection pressure had more impact on the suppression performance for lignite than for bituminous and anthracite coals, while increased wetting agent concentration yielded a higher collection efficiency for bituminous and anthracite coals than for lignite coal. Also, the significant increase in the collection efficiency achieved by increasing the surfactant concentration decreased gradually at increased pump pressures.