Visit inside CF-silo To know its components

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CF Raw Meal Silo

How it works 

The CF (Controlled Flow) silo is a continuously operating system for homogenization and storage of cement raw meal, where the material is extracted simultaneously at different flow rates from a number of outlets in the silo bottom. The CF system, including suitable kiln feed equipment, ensures stable kiln feed composition at minimum power consumption and investment cost. The efficient performance of the CF homogenizing silo results in stable kiln operation so that changes in kiln speed or firing rate are rarely needed and stable coating in the kiln is maintained. In order to ensure high homogenization efficiency, all the raw meal in a silo must be kept in constant movement towards the outlets. Furthermore, the raw meal must pass through the silo in flow zones with different residence time. The CF silo complies with these demands. It extracts raw meal at different rates from several outlets in the silo bottom and mixes the stream from these outlets. The CF silo’s extraction system is governed by a programmable control unit. This enables the selection of optimum flow rate distribution based on local requirements and conditions.





Unique design

The unique characteristic of the CF silo is the design of its bottom. As shown in figure 1, the silo bottom is divided into seven identical hexagonal sections. At the center of each hexagonal sections an outlet with a large conical coverage of steel. These steel cones are designed to maintain an optimal flow pattern during extraction of the raw meal, which influences homogenizing efficiency.



In addition, the cones are designed to relieve the pressure above the outlets and to ensure extraction from the aerated part of the silo bottom (see figure). Each of the seven sections is divided into six triangular segments. So the bottom consists of a total of 42 segments, all of which are provided with aeration units. These 42 separate segments represent 42 individual areas from which the material is extracted in a preset sequence of shorter duration than the residence time in the tank below the silo. Wide flow zones with varying material sinking velocity are formed above the cones covering the outlets, and this further improves homogenization. Layers of raw meal of varying chemical composition are fed to the silo. The variations in extraction rate/residence time mean that these layers are broken up as they proceed down through the silo. The resulting raw meal product, extracted from the silo during any stage  of the extraction sequence, will there- fore be a mixture of raw meal components of different chemical composition.


Optimal flow and homogenizing efficiency

Each of the seven outlets is provided with a shut-off valve by which extraction from a given outlet can be started and stopped together with the aeration of the appertaining segments. Slide gates are provided to facilitate the maintenance of the shut-off valves.



Homogenizing factor

The homogenizing factor H is the most commonly used term to describe the efficiency of a homogenizing silo. H represents the ratio between the inhomogeneity before and after the silo.The homogenizing factor H is defined as:







Determining homogenizing factor 

The following calculation shows how the homogenizing factor is determined at a CF silo in operation. The first graph shows the chemical variation of the material entering the silo; the second graph shows the variation of the material at the silo output.



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