The manufacturing of the cement begins with the extraction and the preparation
of raw material from raw material quarrying to feeding the raw material in to preheater.
The raw meal silo performs two functions; on one hand it acts as raw meal storage
and ensures that the kiln is supplied with raw meal even during the raw mill stoppages.
On the other hand, it has task of homogenizing the raw meal produced by the
raw mill to ensure that the kiln can produce consistent quality of clinker. The
principal of the homogenization is the storage of horizontal layers, each have
different quality characteristics, followed by the vertical blending of these layers
during extraction from the silo.
In the typical blending silo, the feeding takes place through the parallel distributor
installed on silo top from more than 6 inlets ensuring the controlled buildup of the
different material layers. The bottom of the silo has different outlets (6 or 8)
depending upon the size of the silo, with aeration system for the easy flow of material.
The capacity of the storage silo is decided based on the capacity of the kiln, type
of raw mill grinding facility (Vertical roller mill or Roller press or Ball mill), its
availability, storage days required to store the raw meal due to major breakdown in
the grinding system and the type of pre mill feeding blending and homogenization.
2.1 Raw Meal Silo
2.1.1 Norms for Raw Meal Silo sizing
Various cement plant consultants give various selection criteria for blending/ storage
silos capacity. Here are a few.
- Holtec
As per the Holtec standard norms the capacity of the raw meal silo should be,
Clinker capacity per day x Clinkerisation factor x Storage norms
The standard storage norm for the raw meal is 1.5 storage days.
For example, for 4500 TPD kiln capacity the storage silo capacity would be
as below, 4500 x 1.54 x 1.5 days = 10395 tons. - Holcim
As per Holcim, the followings are the design parameters for silo capacity
selection.
Raw mill down time- As discussed in detail later in the document.
Requirement of homogenizing quality
As per Holcim 24-hour storage capacity of the Raw meal silo is more than
adequate to meet the kiln demand.
So the Minimum capacity is 1-day kiln feed recoverable storage.
Raw meal silo capacity = 24 Hours x kiln feed rate (t/hour)
2. Selection of Capacity of Raw Meal Silo, Cement Silo & Fly Ash Silo
SILO, FLY ASH SILO