(69b) Determine the Flow Properties of Bulk Materials to Prevent Flow Problems

Authors: 
Cabrejos, F., Universidad Técnica Federico Santa María
In many mining and industrial processes where large quantities of crushed ores and non-degrading bulk materials are handled and stored, silos, hoppers, stockpiles, feeders and chutes are widely used because they are economical and reliable (if properly designed and operated). However, they are not free of trouble and may experience flow problems such as arching, ratholing, erratic flow, limited storage capacity, limited discharge flow rate, caking, segregation and/or flooding.

Testing provides the best method to characterize a bulk material and its handling properties for proper equipment and system selection, design and operation. Hence, we strongly recommend performing laboratory tests with representative samples of the material (or materials) to be handled in a silo, hopper, stockpile, feeder and/or chute including cohesive strength, wall friction, compressibility, permeability, and other parameters such as bulk density, internal friction, chute, repose and draw down angles of the material, tested at similar conditions to those to exist in the plant including different moisture levels, consolidating pressure, storage time at rest, etc.

The purpose of this article is to highlight a proven, scientific method that can be utilized to ensure reliable storage, flow and discharge of bulk solids in silos, hoppers, stockpiles, feeders and chutes based on the Jenike flow-of-solids theory and laboratory testing. Knowledge of the flow properties of the material handled provides a design basis to ensure mass flow, avoid arching and prevent the formation of “ratholes” even if handling wet cohesive materials. The effect of an increase in water content of the ore is also discussed in details with experimental results.