8 - Characteristics of Respirable Coal Dust Particles

Abstract

Respirable coal dust particles range from one nanometer to ten micron. Their Reynolds number (defined as R=dvσ , where, d is the particle diameter; v is the settling velocity in air, and σ is the kinematic viscosity of air) is typically less than one and mean free path, l on the order of 10-5 cm. Particle motions when their radius, r, is much larger, equal to, or much smaller than l are individually addressed. Settling velocity is defined and mathematically derived. Respirable dust is divided into settling and nonsettling portions. Particles less than 0.5 micron (unit density) do not settle down and remain afloat. The aerodynamic shape factor, defined as the ratio of projected diameter to Stoke's diameter, was determined to be 1.42 on an average for fine coal particles. The mass distribution of coal particles and experimental procedures for its determination are discussed. Anthracite appears to have more fine dust (less than 1 micron) than lower rank coals. It leads to about 1.43 times higher rate of deposition in the lungs, increasing the chances of coal worker's pneumoconiosis (CWP). Finally, the chemical composition of respirable dust is discussed. Silica and iron sulfate appear to be more significant than coal dust itself in the growth of CWP.