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Pellet flow in hoppers

Q: How do you measure the flow ability of pellets in a hopper? Please show any details or illustrations.

A: The problem that pellets have is the presence of fines and angel hair. The typical shear cell (rotating, Schulze or cross flow, Jenike) is used on small particles, which are the cause of most poor flow conditions. There are some large-scale shear cells for particles above 20 mesh. The only one that I'm familiar with is at the Jenike and Johanson San Luis Obispo facility in California.

Clean pellets flow fine as long as the walls are 10-15 degrees above the angle of slide. That angle of slide can be determined by placing pellets on a sheet of the wall material of construction and lifting the sheet until the pellets slide off. A thin layer is all that is needed (no more than 2-3 pellets deep). This "rule" does not apply if the pellets have a significant amount of fines (over 50 ppm). To maintain mass-flow, which is usually desired, the shear flow properties need to be determined through tests. Pellets often do not require mass-flow as long as they don't age or the bins are routinely emptied.

The equipment to run these tests can be purchased, but unless you do a lot of testing, it would not be cost effective. Try Jenike and Johanson (North and South America) or the Key Centre for Bulk Solids and Particle Flow at the University of Wollongong (Australia). There are other test centers in Europe. It looks like you are in the South East Asia area, so the Australia location may be your best choice.

Details on the theory of flow ability testing can be found in Bulletin No. 123 of the Utah Engineering Experimental Station at the University of Utah. The title is Storage and Flow of Solids by Andrew W. Jenike. It was first published in 1964 and has been revised about a dozen times, so be sure to get the latest revision.

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