Mass flow and funnel flow silos

Section summary
1. Definition
2. Pros and cons of each design

1. Definition

Hoppers / Silos can be classified in 2 types : mass flow silos and funnel flow silos. This classification is done according to the flow pattern of bulk solids in the silos. In funnel flow, the product located at the center of the silo will move much faster than the product located at the sides. In mass flow silos, in contrary, all particles will move at the same speed, which means that the distribution of residence time in the silo will be reduced, whereas it can be very large with funnel flow hoppers.

Figure 1 : Bin discharge patterns

2. Pros and cons of each design

Table 1 : Pros and Cons of mass and funnel flow design [1]

Hopper type Advantages Disadvantages
Funnel flow Can offer larger capacity with a reduced height (cone walls angles are flatter than with mass flow hoppers)
Reduced abrasion of hopper walls since particles at wall do not move
Hoppers are sensitive to arching and ratholing making discharge unpredictable (issues can be mitigated with disharging aids)
Risks of formation of archs, then collapse of archs that can cause structural issues to large silos
Collapse of arches can fluidize the whole silo and make the product suddenly flow very quickly
Silos sensitive to segregation
Mass flow First in - First out, particles have more or less the same residence time in the silo
No arching, stable flow output
Less segregation (density is stable at outlet, important for feeder design)
Flooding happen rarely since arches are not stable to form
Can require tall geometries that may not fit in the installation
May not be possible for all materials - use of discharging aids is then to consider

Source [1] Principles of Powder Technology, M.J. Rhodes, 1990

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