Dusts from dry off-gas cleaning: comparison of flowability determined by angle of repose and with shear cells

The flowability of the dust separated in dry off-gas cleaning systems is an important characteristic for the design of dust storage and conveying equipment. The angle of repose is often used as an indicator for the flowability of granular material. In this study the results for the flowability obtained from the angle of repose and by the ratio of the consolidation stress to the unconfined yield strength were compared for 77 dusts from various dry off-gas cleaning systems. For dust with a Sauter mean diameter of > 5 μ m the flowability indicated by the angle of repose and the results of a shear test performed at a low pre-shear load correlated reasonably. For dusts with a smaller particle size such a correlation did not exist. The values of the angle of repose were scattered with no relation to the results of the shear test. The dependence of the angle of repose on the d ₃₂ described in the literature was confirmed for the coarser dusts only. For dusts with a smaller particle size such a relationship does not exist. For very fine dusts the angle of repose was even smaller. This effect was attributed to the visible small agglomerates formed during the angle of repose measurement. These agglomerates rolling down the slope prevented the formation of a steeper cone which limits the angle of repose.