Design and Characterization of an Improved Screw-Assisted Rotary Feeding System for Aerosolization of Ultra-Small Quantities of Particulate Solids

Abstract

Many previous studies have examined solid-state particle discharge systems. However, several drawbacks have been encountered in terms of laboratory-scale particle feeding systems (e.g., high feeding rates, discontinuous feeding characteristics, the absence of long-term stability, and the use of high carrier gas volume rates). In this study, a state-of-the-art screw-assisted rotary feeding system was developed and evaluated in terms of aerosolization characteristics such as particle number concentration, geometric mean diameter, and geometric standard deviation. The various experimental conditions included changes in the rotational speed of the rotor, changes in the number of rotor grooves, and the existence or nonexistence of screw operation. Calcium carbonate (CaCO ₃ ) powder was selected as the discharged sorbent particle. To verify the performance of the designed feeding system, we measured number concentrations with and without operation of the screw. Uniformity (i.e., the steadiness of feeding characteristics over time) was analyzed using a condensation particle counter. As the rotational speed and the number of rotor grooves increased, the number concentration and the frequency of discharging sorbent particles increased, whereas the coefficient of variation decreased. However, when the loading time was less than the critical time (∼0.8 s), the number concentration decreased and the coefficient of variation increased again according to the rotational speed. Stability (i.e., the invariability of the size distribution in various rotational speeds of the rotor for three different rotors) was also analyzed using an aerodynamic particle sizer and a scanning mobility particle sizer. The results of both aerosol measurement and scanning electron microscopy analysis showed that the geometric mean diameter and the geometric standard deviation of aerosolized sorbent particles remained constant under all the experimental conditions. We also determined that the region in which the coefficient of variation was less than 0.1 was the stable operation region for this screw-assisted rotary feeding system.

Acknowledgments

This work was supported by Energy Resources Technology Development Projects of the Korea Energy Management Corporation (2007-C-CD27-P-02-1-000) and the BK21 Program of the South Korea Ministry of Education, Science, and Technology.