Materials flow through concrete storage silos in different ways depending on the construction, cone angles, contents and a variety of other factors.
Mass flow silos are generally for coal or other materials with segregation problems. With the mass flow pattern, the first materials in are the last materials out. This is important with materials like coal, when you need to keep the coal moving within the silo to minimize the risk of spontaneous combustion.
The mass flow pattern allows for the materials to move down the silo as a column with no flow channels. This eliminates stagnant, non-moving materials and/or the effects of segregation of materials stored within the silo. The cone angle will be between 68-72 degrees depending on the material being stored.
Funnel flow silos are used for more granular types of materials where material degradation is not a worry. Funnel flow silos are generally 20-30% less expensive than mass flow silos.
With this type of silo, the first materials in are the first materials out. Upon emptying there is a flow channel in the middle allowing the material to drain first and the side material to flow into the channel as the silo empties. This can create flow channels in some materials and can potentially make the product susceptible to segregation issues. The cone angles for the funnel flow silos are 45-60 degrees.
Expanded flow silos offer the same benefits as the mass flow pattern, but for less cost. These are good for materials that don’t need to be stored very long. They feature a 45-60 degree angle tapering into a 68-72 degree cone angle.
These silos have a similar effect as the mass flow except they may require that dead material captured within the silo be fully emptied periodically.
Fluidized flow silos are used for fine powders. The material is aerated with a large volume of air pumped into the bottom of the silo, making it act like a fluid as it is discharged out of the bottom of the silo. The discharge angles are only 5-10 degrees.