Attrition of Bulk Solids in Pneumatic Conveying: Mechanisms and Material Properties

Abstract

In the approach presented, attrition of bulk solids in pneumatic conveying is regarded as a result of a process function (stress conditions) and a material function (influence of material properties). The paper focuses on dilute phase conveying (homogeneous flow) and in the first part describes the determination of the process function by employing computational fluid dynamics (CFD). In the second part, experimental results for the determination of the material function by means of simulating the previously identified stress modes of impact and friction under well-defined stress conditions are presented. Contrary to what was expected initially, the numerical simulations as well as experimental results indicate that sliding friction is apparently of importance in dilute phase conveying. This conclusion can be drawn from the low calculated impact angles in a pipe bend (r B /D=5; D=80 mm), which lie between 10 and 35°. Consequently, the tangential impact velocity components ranging from 32 to 40 m/s are considerably higher than the normal ones (5 to 22 m/s). These results are confirmed by observations made in experiments to determine the material function. The relative attrition behavior of four different polypropylenes under pure sliding friction conditions closely resembles that observed in attrition experiments carried out in a pipe bend of the above geometry, while differences are observed for normal impact conditions.