Discharge Problems:

Discharge problems often occur when silo design and bulk solid are not well suited to each other. Only few powders and bulk solids can easily be discharged from a 'standard silo' with a slope angel of 30° against the vertical and an outlet diameter of e.g. 300 mm.
Typical problems appearing are: arching, ratholing, segregation and time consolidation.

Generally two different flow profiles can be observed when bulk solids are discharged from silos:

Mass flow Funnel flow
Criteria of distinction During discharge the bulk solid slides along the hopper walls. Ideally the whole surface of the filling drops evenly. During discharge the bulk solid doesn't slide along the hopper walls. Only the bulk solid above the outlet is in motion. A more or less central flow funnel arises.
Characteristic shape of hopper long steep funnel short flat funnel
Discharge problems occuring arching, time consolidation arching, time consolidation, ratholing, segregation, irregular flow, flooding
Additional features narrow residence time distribution, "first-in first-out" wide residence time distribution, formation of "dead" zones

Retrofit of Discharge Aids:

By retrofitting discharge aids many discharge problems can easily be eliminated. If it is critical that flow aid devices should be easy to install from the outside, variable to arrange and adjustable to operate, our Pulsors present the perfect solution.
Please contact us for this purpose ...

The application of discharge aids nearly always is the most reasonable option if discharge problems shall be eliminated.

Silo construction / modification:

When silos are designed the knowledge of the following parameters are important from the aspect of trouble-free discharge:

  1. Which is the required hopper slope and which material has the hopper to be made from to ensure mass flow ?
    (To achieve mass flow the hopper slope angel and the coefficient of friction between bulk solid and wall material are the decisive factors)
  2. Which is the minimum outlet size to prevent arching ?
    (The maximum diameter of a stable arch depends on the bulk solid's unconfined yield strength and its density.)
  3. How change the bulk solid's flow properties during storage time ?
By measuring characteristical parameters of a bulk solid, such as unconfined yield strength, density and coefficient of friction, in accordance with the standardised Jenike shear test procedure, answers to the questions mentioned above can be given.
Please contact us for this purpose ...