Off-center unloading

by Emily Wilson
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Dear editor,

The article "Dangers of off-center silo unloading" (see World Grain, February 2000, page 62) was very informative and useful for technical people who handle silos. Our facility has a conical (hopper) bottom bin of 600 tonnes for handling soybeans. We are taking eccentric unloading from the cone to save power, but the bin is still intact in design after unloading from the side. We use the center unloading gate to empty out the bin.

Please advise whether this article is meant for flat bottom silos only. Can we continue unloading eccentric unloading of our bin?

Pradeep Sharma

General Manager,

M.P.Glychem Ind. Ltd., India

Editor's reply: Mark Myers of Brock, Grain and Feed Systems, Milford, Indiana, U.S., one of the authors of the article on off-center unloading, writes:

Off-center unloading will produce different results in bins or silos of varying diameters and heights. This is due in some part to the ratio of the height to the diameter. Regardless of whether the bin is a flat bottom or a hopper (cone) bottom, it should not be off-center unloaded unless it has been designed and equipped with a suitable side-draw system for off-center unloading.

Periodically we hear that off-center unloading without a side-draw system has been practiced for some period of time with no obvious negative impact. Depending on the bin height and diameter, structural failure may be not be immediate. However, the bin is still experiencing non-uniform stress for which it was not designed. The bin may survive these loads for days, months or in some cases even a few years. But when the flow channel intersects the wall of the silo, failure is expected.

We urge you to contact your silo manufacturer for a safety review and analysis of your specific circumstances. Your diligence may directly impact the safety and welfare of your employees, your family, or yourself.