Silo cleaning and inspection of blast furnace slag silo plant

Silo cleaning and inspection of blast furnace slag silo plant

Siloreinigung und Inspektion in einem Hüttensandsilo

Metallurgical or slag sand is produced by granulating thermally liquefied blast furnace slag with water and/or air. It is a fine-grained (< 5 mm), glassy unipolar by-product of pig iron production in the blast furnace. Blast furnace slag consists of approx. 30-45 % CaO, 30-45 % SiO2, 5-15 % Al2O3, 4-17 % MgO, 0.5-1 % S and traces of other elements. The exact composition varies depending on the materials used in the blast furnace.

Silo cleaning and inspection is associated with increased risks and only specialists are allowed to work in these areas.

The plant operator must check whether the service provider has a written rescue concept, CSE documentation, risk assessment and access qualifications before commissioning the work. If this documentation is not available, the service provider should not be commissioned, as the risk of a fatal accident at work is too high. Extract from DGUV

Silo cleaning and silo inspection is of great importance in these bulk solids storage systems, as the bulk solids are highly abrasive (Mohs 6-7). In high-frequency systems with a high flow volume, there are increased abrasive influences on the inner wall of the silo. These lead to heavy material abrasion and jeopardize silo stability. For this reason, recurring wall layer thickness measurements and the installation of wear protection elements are important for operational safety. In the course of this operation, the objective was to remove heavy build-up from the silo ceiling and silo wall and to expose the silo cone.

Depending on the design of the bulk material cone, the material core flow behavior of compacted material lumps is at risk and discharge blockage occurs. In the course of a silo inspection, material blockage can be detected and prevented at an early stage. As a rule, most blast furnace slag silo systems are more than 30 years old and are therefore susceptible to material blockages caused by older layers of material. We remove these layers of material and thus significantly reduce the risk of blockages. Depending on the type of silo construction, the wall layer thicknesses are measured and documented for material fatigue – comparative values are therefore possible.

If there is increased material degradation of the silo wall, the installation of baffle plates or wear protection lining is recommended. Once the silo wall has been completely worn through, statically effective remedial measures are difficult or costly. Such a silo failure is of serious economic significance for the plant operator and must be avoided at all costs.

The flow of bulk material can be controlled by installing baffle plates. Controlled core flow behavior in the silo significantly reduces the abrasion properties, as the material is only moved in and out of the core and the friction on the walls is very low. However, pressure and moisture conditions can lead to increased material adhesion to the silo wall during core flow behavior, which can significantly reduce the storage capacity of a silo system after years.

For this reason, these material build-ups, which protect the silo wall from abrasive influences, must be removed. Unfortunately, the disadvantage of the material-friendly core flow behavior is that these build-ups increase annually and thus considerably limit the silo capacity.

In summary, it is regrettable that although the core flow behavior protects the silo wall from abrasive influences, this process ensures that the silo system eventually builds up so much material on the wall that a silo blockage can occur. For this reason, we advise our customers to install wear protection plates. If the silo system is equipped with wear protection plates, the silo wall is sustainably protected against abrasive influences. Silo closures caused by old, slipped material are very rare in lined silo systems.

The use of wear protection plates with reduced adhesion means that there is only minimal material build-up. Depending on the bulk material, however, it may be necessary to replace or refurbish the wear protection after a certain period of use. Good wear protection solutions can be partially rehabilitated and are replaced or repaired selectively depending on wear.


The core flow behavior in bulk solids silos is good for protecting the silo wall with abrasive materials. However, it builds up permanently and can lead to silo closure or considerable material layer thicknesses. (rat hole)

If the silo system is equipped with baffle plates and wear protection, the material flow can be influenced. Adhesions on the silo wall do not lead to layer build-up. The silo wall is sustainably protected against wear.

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