Solve or Prevent Poor Flow - Jenike & Johanson

What is Poor Flow?

Two costly flow problems experienced in a silo, bin, or hopper are arching and ratholing.

Arching (bridging) occurs when an arch-shaped obstruction forms above the hopper outlet and stops flow. It can be an interlocking arch, where large particles mechanically interlock to form an obstruction, or a cohesive arch. A cohesive arch occurs when particles bond together due to effects of moisture, fines concentration, particle shape, temperature, etc.

Ratholing occurs when discharge takes place only in a flow channel located above the outlet. If the material being handled is cohesive, the material outside of this channel will not flow into it and may cake or agglomerate. Once the central flow channel has emptied, all flow from the silo stops.

Examples of Poor Flow

When & Where Can Poor Flow Occur?

These problems routinely occur in silos discharging in a funnel flow pattern, in which some material moves while the rest remains stationary. Funnel flow occurs when the sloping hopper walls of a silo are not steep enough and sufficiently low in friction for material to flow along them. Particles slide on themselves rather than the hopper walls.

Funnel flow:

Ratholing, if material is cohesive
Caking and material spoilage
Flooding of fine powders
First-in, last-out flow sequence
Sifting segregation effects worsened

The alternative silo discharge pattern is called mass flow, where upon withdrawal of any material, all of the material in the silo moves. Ratholing and stagnant material zones are not possible in mass flow hoppers.

Mass flow:

No ratholing
Uniform flow
No stagnant material
First-in, first-out flow sequence
Sifting segregation effects reduced

In mass flow, the hopper outlet must be sized to both prevent the formation of an arch and to allow the required discharge rate. See below for a video demonstration of funnel and mass flow patterns.

Expanded flow can develop when a mass flow hopper is placed beneath a funnel flow hopper. The mass flow hopper is designed to activate a large enough flow channel in the funnel flow hopper to overcome ratholing. This flow pattern can be effective for large diameter silos, as well as for gravity reclaim stockpiles.

Poor flow can have many implications, including: Why is Poor Flow a Problem?

Limited “live” capacity
Segregation of fines or dust
Idle equipment or process
Erratic or stopped flow
Powder flooding or flushing
Structure vibrations, quaking
Missed shipments or delays
Caking, agglomeration, wasted material

How can Jenike & Johanson Help Solve or Prevent Poor Flow?

The key to avoiding poor flow is to evaluate the flow properties of the material and to engineer an appropriate bulk material handling system.

We are prepared to assist you. Our team of experienced engineers and laboratory technicians have the knowledge, skills, and state-of-the-art tools and bulk material testing laboratories available for meeting your bulk material handling needs.

Explore our solutions to your poor flow needs, review case studies, or contact us so we can help you to solve or prevent costly powder or bulk solids flow problems.

Are you currently experiencing poor flow in your bulk handling process?