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Cement Powder Silo Storage Issues

Getting to grips with Bulk Solids (e.g. cement, lime, etc.) Flow Issues.

Storage Silos Bulk Storage Flow

It is quite common for engineers to understand the ‘Bulk Solids Flow’. Sure, they can enter a couple of numbers into a complicated formula and get a result which indicates optimal discharge. Unless you are getting a highly trained engineer to design your bulk solids storage silos, you may be ‘walking down a dark path’. Flow behaviour becomes an issue if the design isn’t perfect; resulting in material caking on the side walls of the storage silo. This is all before the particle size, moisture content, temperature and time of storage is taken into account.

As a result, quality, productivity and safety may become an issue further down the line.

Bulk Solids Flow Summaries

Storage silos, storage bins and hoppers witness two different flow profiles, according to studies. Mass Flow & Funnel Flow. Mass flow indicates full flow of powder throughout the discharge all the way to the opening of the silo (Optimal). However, the alternative is Funnel Flow. This process indicates an issue with the walls of the silo, storage, tank; where the wall is too rough or too flat. Cement and Aggregate product sticks to the walls of the silo, resulting in a ‘dead zone’ on either side. Remove “dead zones’ as early as possible to return the plant to the highest production efficiency.

 

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Flow Complications for Storage Silos, Bin & Hoppers.

  • Arching’ – Sometimes, you may come across a situation where bulk solid flow has stopped altogether. You may notice that a section just above the outlet has been hollowed with an ‘Arch’ of bulk solid some way up into the silo. Adhesion forces between the particles causes product to join together; resulting in the ‘arch’.  Thankfully, this issue can be rectified in design by using a large outlet suitable for the flow of product. (This may be necessary to keep in mind if buying second hand storage silos).
  • ‘Ratholing’ – This term is related to the ‘Funnel Flow’ summary mentioned above. The bulk solid flows directly down through the path of least resistance, all the while leaving behind ‘dead zones’ on the sides of the storage silos. Longer periods of bulk storage increases the possibility of ‘Ratholing’ occurring in your product. If not emptied at regular time periods, this could cause a strong time consolidation leading to more and more build up in the storage silo or hopper.
  • ‘Segregation’ – Segregation occurs when bulk solids are distributed throughout the silo by particle size.  This is obviously less than ideal as it leads to inconsistent flow of material and possibly inconsistent product being sold.

Silo Design

If designed properly, a mass flow storage silo, aggregate bin or hopper will generally not have any of the issues mentioned above. However, there is the possibility of arching occurring in ‘Mass Flow’ silos. ‘Funnel Flow’ silos become a victim of the issues mentioned above due to incorrect angled walls/cone.  This means that taking the time to care for the design may prevent retrofits, shutdowns and lost revenue.