Powder or pellets?

Posted in: , on 6. Feb. 2003 - 18:39


I am working on a project dealing with the finishing section of a polyolefin plant.

We have safety concerns about storage of off grade reactor product. Is it better to store it as powder (and have about 10 different silos) or to store it after processing through an extruder under pellet shape? (the concern is about explosivity.)

And what are the most standard sizes for powder and pellet silos? Is there a big difference in price between the two?

I thank you in advance,




Posted on 12. Feb. 2003 - 11:27

If your main concern is explosability, you ought to consider that going for the pellet option may give you a false sense of security. If attrition of the pellets occurs there will still be fines present that may pose an explosion hazard. Have you had an assessment undertaken for the material? Depending upon the material, even a very low dust concentration may prove dangerous.

In terms of the difference in price for silos - it is all dependant upon the size required and the flow pattern that may develop within. Bear in mind that if you are considering a pellet silo there may be a risk of internal mass flow occuring - which carries the danger of the switch pressure (where the expanded flow channel intercepts with the vertical wall) occuring at an unreinforced section of the silo. This can, in some cases, lead to buckling. For a small vessel this may not be an issue - but it is worth bearing in mind for larger silos!

I hope that this helps in some way!

"Guide for the economic design of circular metal silos" by J Rotter, ISBN 0-419-23460-8 may be of interest to you.


Richard Farnish

The Wolfson Centre for Bulk Solids Handling Technology, Univ. Greenwich, UK

(not verified)

Re: Powder Or Pellets?

Posted on 14. Feb. 2003 - 01:09

Gwen ,

If the powder particle size has a fraction smaller than 100 microns , it will likely be explosive , Have you had any tests done to check , I can recommend places to do the work .

Pellets are easier to convey , store and will flow at shallower bin angles .

Silos for pellets require 45 degress , powders usually 60 degrees . Powders present arching and ratholing problems to get them to flow from the silo and can require dust collectors at the receiving vessels .

As already noted , Silos can be designed to several configurations , solid , segmented and with flow aids .

With more specifics, I can help you more . We would prefer to handle pellets or granules

(not verified)

Powder Or Pellets?

Posted on 17. Feb. 2003 - 05:24

Dear Gwen:

We are the world's largest manufacturer of open mouth packaging machinery, both of pellets and powders.

It may still be an explosive hazard with pellets, however the pellets are much easier to bag, and much less expensive. The automatic bagging of pellets may be only $75,000 vs as much as $300,000+ for powder. Also, the rates are much faster for pellets.


Sheldon Garriott

American-Newlong, Inc.

Phone: 317-787-9421