Bench-Top Apparatus to Examine Factors that Affect Dust Generation

Abstract

A bench-top apparatus was designed and built to investigate factors that affect dust generation. The apparatus allows the investigation of process variables, material properties, and the size distribution of generated dust, thus addressing the limitations of other bench-top dustiness testers. The controlled testing of hazardous materials is also possible in this air-tight device. The apparatus consists of a dust generation section and a dust measurement section. Materials are introduced to the generation section at various drop heights and flows by an injection slide. Dust is generated by the impact of the falling material and the release of air entrained with the falling stream of material. The generated dust is drawn through an elutriator, which removes particles 25 μm and greater in aerodynamic diameter. The size distribution of the residual dust is measured for particles between 1.4 and 15 μm in aerodynamic diameter with a cascade impactor.

The effects of material drop height, mass flow, and moisture content were investigated for four granular materials: ground limestone, titanium dioxide, glass beads, and lactose. For each material, a simple model was developed to describe the size-specific dust generation rate. Increases in material drop height caused a roughly proportional increase in the dust generation rate for all four materials. Material flow had little effect on dust generation. Changes in moisture content, which affect the interparticle binding forces, strongly influenced the dust generation rate. Decreased dust generation was found in all cases where material moisture content increased. Although an increase in dust generation normally results from reductions in moisture content, some dried samples showed a decrease in the dust generation rate. This could have occurred due to the formation of solid, interparticle bridges of soluble materials, or due to increased electrostatic effects, as the material dried.