Clogging of granular materials in narrow vertical pipes discharged at constant velocity

Significance Statement

Clogging is a hazard whenever granulate solids are conveyed in narrow conduits. This is clearly evident if there is a bottleneck in the duct (as in the case of silos), but even in an unimpeded straight conduit, the flow can be arrested due to the formation of arches. This is precisely, the scenario investigated in this work which is inspired in a real case of ore pass. Ore passes are vertical or inclined pipes dug out of rock mass, commonly used in underground mining to transport the ore or waste from one level of the mine to another using the gravity driving force. Despite the important advantages of this transportation method (economic, landscape, environmental…) it may become problematic because of the formation of domes that block the flow of material.

Based on a robust statistical analysis, the authors evidence that a sufficiently large pipe diameter (in relation with the particle size) will prevent clogging development (at least in the lifetime of the mine). The figures given will surely depend on the material properties but can be used as the starting point whenever a new design of underground transport has to be performed. Finally, the effect of the pipe inclination and the extraction velocity are investigated revealing that clogging can be reduced by increasing the extraction rate and inclining the pipe at an angle that deviates from the vertical

Journal Reference

Granular Matter, October 2015, Volume 17, Issue 5, pp 545-551. 

Alvaro Janda1,2 , Iker Zuriguel 1, Angel Garcimartín 1, Diego Maza 1 

[expand title=”Show Affiliations”]
  1. Departamento de Física, Facultad de Ciencias, Universidad de Navarra, 31080, Pamplona, Spain
  2. School of Engineering, University of Edinburgh, King’s Buildings, Edinburgh, EH9 3JL, UK
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Abstract

We report experimental results for pipe flow of granular materials discharged through vertical narrow tubes by means of a conveyor belt placed at the bottom. When the diameter of the tube is not much larger than the particle size, the system clogs due to the development of hanging arches that are able to support the weight of the grains above them. We find that the time it takes to develop a stable clog decays exponentially, which is compatible with a clogging probability that remains constant during the discharge. From this, and making an analogy with the discharge of silos, we introduce the avalanche size, measured in terms of the number of discharged tubes before the system clogs. The mean avalanche size is found to increase as the tube diameter is enlarged, the velocity of the conveyor belt grows, and the tube tilt deviates from the vertical.

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