In bulk material systems that are operated with abrasive material, material abrasion inevitably occurs on the inner wall of the silo. This material abrasion is naturally determined by the raw material and always allows conclusions to be drawn about the flow behavior.
The design and material type of the silo system is decisive for the mass flow and core flow behavior. In the area of mass flow, abrasive material is likely to cause significantly increased abrasion. The abrasion must be assigned to the type of bulk material – the more abrasive the bulk material, the better the silo must be protected by baffle plates or wear protection. In so-called core flow silos, material abrasion is only limited. The advantage is clear: abrasion is significantly reduced. Disadvantage – massive build-up can occur due to thermal bridges, which can be dangerous for hygroscopic materials.
The results for those difficulties are manifold and depend on the bulk solids properties as well as the local boundary conditions. Sometimes a core flow silo with too rough and/or flat walls can be converted into a mass flow silo by coating or lining the walls with a suitable material or replacing them with sufficiently steep walls, or by placing a suitable installation in the hopper. If the core flow is caused by the discharge device, a technological direction of the discharge device can be useful, e.g. in the case of a screw conveyor, replacing the existing screw with a constant pitch by one with a pitch that increases in the conveying direction.
As is always the case, all (costly) modifications, especially those to the hopper walls, should be checked prior to the version using measured bulk solids properties. The bulk solids properties can be used to predict which hopper inclination is mandatory for mass flow during a specific hopper wall surface for the bulk solids under consideration, or with which degree of lining or coating mass flow can be achieved within a given hopper wall inclination, or with which additional aids (e.g. internals) mass flow can be achieved.
This work can of course be done for you by experienced specialists. Nevertheless, it is often essential to know as much as possible about a silo in order to better understand the complications that arise and to be able to better assess proposed solutions from all kinds of suppliers. The most important information for this is knowledge of the flow profile, i.e. the type in which the bulk material flows in the silo.
Fig. 1 – Massive corrosion of the silo inner wall
Depending on the condition of a particular component, further surface preparation may be required. A specialist must determine the degree of flash rust and remove oil and dirt residues, as well as loose or damaged coating areas.
The most important thing here is to create a comparable overall appearance – dirt residues, impurities and rust must not form strong partial stains or shading, as this would be visible in the aftermath.
Proper preparation of the surface ensures longer safety for subsequent coating systems and prevents further work that has not been taken into account.
Fig. 2 – Loss of material due to corrosion – panels are already peeling off
In contrast to pure liquids, the behavior of a bulk material cannot be described solely by specifying its material composition. This has long been clear from the fact that, in addition to the chemical composition, there is a wealth of other variables that influence the flow properties of a bulk material.
Some of those variables that can hardly be recorded without exception are e.g:
- Particle size distribution,
- Moisture,
- Particle shape (e.g. spherical, platelet, rod-shaped; smooth/rough particle surface).
In addition to the composition of the bulk material, the current state of solidification also plays a fundamental role. For example, a bulk solid behaves like a liquid in a fluidized state (e.g. in a fluidized bed) and like a solid in a compacted state (e.g. tablet, briquette). When storing and conveying bulk solids, there are usually states in addition to these extremes: here we are dealing with loose to fully compacted bulk solids, whose mechanical characteristics relevant to storage and conveying are verbalized below.
Our range of services also includes the refurbishment of silo systems as well as the refurbishment of tank and fluid storage systems. At Natusch & Thiedemann Siloreinigung GbR, your equipment is in expert hands.
Our services include all essential measures for professional concrete refurbishment as well as all preparatory work and protective measures.
This includes
- Qualified concrete analysis
- Determination of carbonation depths
- Sandblasting work
- High and ultra-high pressure water jetting
- Grouting
- Corrosion protection
- Coatings
- Sealing
- Joint restoration
