What is a Worst-case Powder

Posted in: , on 24. Feb. 2010 - 23:09

Dear Colleagues,

In order to test out a general design of a fluidized hopper bottom aeration cone, we will be looking for some representative powders that would serve as a proxy for some of the common bulk materials that could be a challenge to discharge from a hopper.

Can you recommend some typical and challenging powders that are rather cohesive and are prone to "hanging up," bridging, arching and rat-holing? I would be looking for materials that are not too exotic and easy to buy and test. For example, it would be easy to go the store and buy cake flour, but it might be useful to demonstrate that we can successfully fluidize and discharge a material known to be more difficult. I am not looking for impossible powders like super wet materials etc., just ones that are known to be a bit of a challenge.

Our discharge technology uses multiple layers of stainless steel mesh sintered together to form a porous plate. We can "dial in" a specific flow rate per unit area and a specified mesh pore size. We form the porous plate into a cone and locate it inside a conical vessel (hopper bottom) with appropriate air inlets.

Thank you for your help!


Powder Etc.

Posted on 25. Feb. 2010 - 12:05

prussiate of soda

milled talc

minus thirty mesh Halite fines

minus thirty mesh evaporated salt fines dust

ammonium nitrate

hydrated lime- you will have fun with this one

hammer milled limestone fines

fugititve powdered sugar dust below 30 mesh

brown sugar dust

silica dust from mining operations

from roof drill dust

rock drill fines minus thirty mesh

being the dust vacuumed from the roof drill hole

carbide mining bit dust

carborundum grinding wheel dust from carbide bit grinding

limestone dust minus thirty mesh

cycloned and wet or dry bituminous coal dust

marble stone dust from stone cutting with wire saws or stone circular saws

both dry and wet.

Hematite fines below 30 mesh

Bituminous fly ash-top ash section to bag house and precipitator.

there are lots more if you so desire to have another list

leave payment in cookies on the stoop

Thank You

Posted on 25. Feb. 2010 - 03:21

Dear Izaharis,

Thank you for your reply.

Which of these would be simplest and most affordably obtained and could be used for a reasonably challenging (but not impossible), relevent test of a generalized design?

Seems like milled talc might be easy to obtain, and perhaps can be handled with minimum precautions such as disposable face mask?

Thank you again,


p.s. would gladly provide cookies


Posted on 26. Feb. 2010 - 05:11


1. Powdered confectioners sugar.

2. Johnson & Johnson baby powder or its equivalent

3. hydrated lime 50 lb. bag

4. agricultural lime/50 lb. bag

(you may be able to buy a 5-10 lb bag at a farm store that sells plants and vegetable seedlings in season.)

5. rock salt fines- any bag size of mined deicing salt( 30 mesh

6 pan cake flour/bisquick

3M dust masks-N95 type only 10 to a box from www.gemplers.com

Hope you are good at herding cats.

Black strap molasses cookies

Re: What Is A Worst-Case Powder

Posted on 26. Feb. 2010 - 11:07

Just asking for difficult powders for aeration doesn't sound very scientific. Geldart Classification is normally used to determine how well the material will respond to aeration. Certain groups respond very well to aeration and some don't. Just take materials form the difficult group and test.

Sintered metal, Ceramic, porous woven polyester membranes etc. have been used for a long time for this application. Sintered metal ones are not preferred as they get blind much faster then woven synthetic ones .


The Worst Is Yet To Come!

Posted on 2. Mar. 2010 - 12:45

The worst case material is the one which you thought you had already designed for before you tried out your design.

Re: What Is A Worst-Case Powder

Posted on 4. May. 2010 - 11:44


You may try it with fine milled untreated Ammonium phosphate or Ammonium sulfate in the micron area like it is used as raw material in fire extinguishing powders. it should have most of the properties you are looking for.

Worst Case Powder

Posted on 17. May. 2010 - 09:57

I would suggest a fine ground limestone as it is inert, stable, cheap and readily available. It is used as a reference material for Jenike testing, but verified samples for this putpose are not inexpensive. An alternative is titanium dioxide, available in various grades, but all tend to be cohesive due totheir fine particle composition.