Avalanche Time of Granular Flows in Rotary Kilns

Abstract

Discrete avalanching is the dominant motion of granular beds in industrial rotary kilns. The avalanche time is an important parameter influencing the heat-and material transfer inside the kiln. Experiments are conducted on a rotating cylinder to measure the time evolution of avalanches. Nonspherical particles (rice) and low filling degrees are used in order to simulate the operating conditions in industrial kilns. The difference between the average critical angle and stop angle of the avalanche is found to be in the range of 7°-9°, i.e., much higher values than ever reported in literature. As the filling degree is three times increased, the average critical angle is found to be approximately constant, whereas the average stop angle is slightly increased and the avalanche time is increased by 20 %. For all experimental configurations, the average avalanche time occupies about 35 %-38 % of the total circle time (elevation time plus avalanche time). Experimental data are used to test theoretical models from different authors. Comparison demonstrates that the models proposed by Mellmann and Davidson et al. can predict well the increasing tendency of average avalanche time with filling degrees. The former has higher accuracy with errors less than 5 % for all experiments. Results of this work are useful for kiln design and further theoretical studies on dynamics of granular avalanches.

Powder flowability characterisation at preheating temperature in additive manufacturing

“…The movement of powder in the drum is affected by many factors such as the filling rate, Froude number F r and powder physical parameters, which are complicated and directly affect the avalanche time [24]. Typically, a low avalanche time implies good powder flowability.…”

Measurements of solid volume fraction and granular temperature at granular avalanches in a drum

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Three-Dimensional Simulation of the Effects of Demolition Waste Recycling into Rotary Cement Kilns

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