Effect of Droplet Size, Charge and Presence of Surfactants on Coal Dust Capture

Prolonged exposure to respirable coal and silica dust particles in coal mine dust is the primary cause of Coal worker's pneumoconiosis (CWP). After a steady decline over the past years, the prevalence of CWP is on the rise in recent years. The occurrence rate of CWP is directly rehted to the to the exposure level to respirable coal dust, and a lowering of the coal-mine dust level standard from 2.0 to 1.0 7ngjm3 has been proposed to reduce the rate. To achieve a lower dust level, newer technologies are needed. Existing technologies based on plain water sprays are not effective for the removal of airborne small particles (i.e., size less than 10 11m, or more specifically less than 2.5 11m) that pose the highest risk. This is because of large, charge neutral droplets involved in the sprays, and the hydrophobic nature of coal particles. We postulate that airborne coal particles carry significant amounts of charge, and therefore, these particles can be effectively captured by charged water droplets generated during spraying by the addition of ionic compounds. The objective of the proposed research is to understand the factors that control the capture of respirable coal particles in water droplets with an aim to develop an efficient water droplet based technology for the removal of coal mine dust. To achieve the objectives of the proposal we will (i) examine the effect of the presence of coal wetting agents in collecting droplets on the capture efficiency of coal particles, (ii) measure chaf'~e distribution in airborne coal particles to establish whether the mechanism based on Coulombic attraction can be used to capture these particles, (iii) examine whether spray droplets can be charged either negatively or positively by the addition of ionic surfactants or other ionic compounds (e.g., ionophores, and ionic liquids), and (iv) measure capture efficiency of charged droplets exposed to charged coal particles. To obtain fundamental understanding of the mechanisms involved in the capture of particles by a droplet, we propose to use an electrodynamic balance to examine the capture efficiency of single charged droplets suspended in a stream of well-characterized coal particles. In addition, we will use linear streams of highly monodisperse droplets to measure the capture of coal particles with high temporal resolution. Such a system provides a unique space-time relation; thus, by examining droplets at several distances from the generation point the capture of particles by a droplet with time can be deciphered.