Size Distribution Measurement of Airborne Coal Dust by Optical Particle Counters

Abstract

An optical particle counter has been calibrated for size distribution measurement of airborne coal dust particles. A differential electrical mobility analyzer was used with a fluidized bed dust feeder to produce uniform coal dust particles of a known size for calibration for particles <2.4 μm. For larger particles, the optical counter was calibrated with a microscopic technique. The output pulse height of the optical counter was found to be significantly lower for coal particles than for spherical oil drops of the same particle size. The geometrical standard deviation, σg, of the output pulse height distribution of the optical counter for monodisperse aerosols was found to increase from about 1.1 for spherical oil particles to about 1.8 for the irregularly shaped coal particles. Although this broadening effect reduced the ability of the counter to resolve small particle size differences, a numerical inversion procedure was developed which allowed the original size distribution to be recovered.