More Questions and Answers

Q: Our current dilute-phase pneumatic conveying system is degrading the particles in the friable agglomerated product we’re handling and thus destroys our desired particle size distribution. Is there a way to reduce this product attrition?

A: Mike Weyandt, Nol-Tec, says: Product degradation in a pneumatic conveying system is directly related to the velocity at which the product is transferred. The higher the velocity, the more the product will degrade from the transfer. The basis of dilute-phase system design lies in providing a motive gas flow above the conveyed product’s saltation velocity, thus keeping the individual particles entrained. This velocity is based mainly on the product’s bulk density and particle size.

It's possible that you could slow down your existing system by reducing the conveying gas speed while still running in a dilute-phase mode. This may bring some reduction in degradation. However, if you fall below the product's saltation velocity, performance will be adversely affected through plugging or a greatly reduced conveying rate.

The better alternative is to convert your system to a dense-phase design if space constraints allow. Dense-phase systems operate well below the product saltation velocity, ideally likened to an extrusion process. However, the reduced gas flow removes the need to provide a higher-pressure-differential motive gas source. But before going through this retrofit, it would be best to conduct dense-phase conveying testing with a potential equipment supplier to determine the amount of product degradation that you'll have with the dense-phase design.

Nol-Tec is a Minnesota-based supplier of pneumatic conveying, bulk material handling, and integrated process control equipment.