Flat-bottomed grain steel silo, also known as flat-bottomed steel silo or flat bottom silos, is a galvanized corrugated plate assembled steel silo with a flat bottom located on a cement platform. It is an advanced grain storage equipment widely used at present, mainly divided into two parts: the silo roof and the silo body. Large-capacity storage is a typical feature of flat-bottomed grain steel silo. The storage capacity of this flat-bottomed steel silo ranges from 39m³ to 29726m³. It is precisely because of this large capacity and small footprint that it is deeply loved by the vast storage industry, but there are also some problems that plague the operation of steel silos. Among these problems, the more common ones are low efficiency in entering and leaving the warehouse, easy wall hanging phenomenon and residual existence during the outbound storage. Today we mainly explain the preventive measures and treatment methods for the flat-bottomed steel silo to solve the wall hanging phenomenon during the outbound storage.
Reducing the wall hanging phenomenon during the outbound storage of flat-bottomed steel silos is a common challenge, especially when storing powdery, granular or sticky materials (such as cement, fly ash, mineral powder, grain, feed, etc.). Wall hanging will not only reduce the effective storage capacity and affect the measurement accuracy, but also cause the material to agglomerate and deteriorate, and even affect the smoothness of the discharge. In severe cases, manual cleaning is required, which poses a safety hazard.
The following are some strategies and methods to effectively reduce the phenomenon of wall hanging in flat-bottomed steel plate silos, which can be divided into design prevention, operation optimization and auxiliary measures:
I. Reasons for wall hanging
- 1. Gravity-free self-flow area: Flat-bottomed silos lack the steep slope of cone buckets, and materials cannot rely on gravity to slide naturally to the center.
- 2. Flow dead zone: The vicinity and corners of the silo wall are typical flow dead zones, and materials are very easy to be retained, compacted, and absorb moisture and agglomerate.
- 3. Limited unloading range: The suction or scraper system of the central unloading port has a limited coverage range, and it is difficult to effectively drive the edge materials.
- 4. Secondary arch risk: Even if the central material is extracted, the hanging material layer on the silo wall may form a "secondary arch foot" to hinder the upper material from falling.
II. Design prevention (solve from the source)
1. Optimize the silo wall design:
- Increase the cone angle: This is the most critical factor. The cone angle must be significantly greater than the material's angle of repose (angle of repose). For materials with poor fluidity, the cone angle usually needs to reach 60° or even 70° to ensure that the material can slide smoothly under gravity. Avoid using shallow cones.
- Optimize the cone shape: Use a hyperbolic cone (similar to the "square sky and round earth" transition) or a parabolic cone. This shape can reduce the shear stress and arch effect of the material in the cone transition area and promote material flow.
- Smooth inner wall treatment:
- Polishing treatment: Ensure that the steel plate weld is polished smoothly, the overall finish (Ra value) of the inner wall is as low as possible, and reduce the "anchor points" for material attachment.
- Special anti-sticking and wear-resistant coating: This is the most basic and most important measure. High-performance coatings (such as modified epoxy, polyurea, Teflon coating, UHMWPE liner) must be applied to the entire silo wall (especially the bottom and lower part of the side wall). The coating is required to be dense, low in surface energy, extremely low in friction coefficient, and wear-resistant. Apply a special coating with low friction coefficient, wear resistance, and anti-sticking (such as modified epoxy resin, polytetrafluoroethylene coating, and ultra-high molecular weight polyethylene coating) to the silo wall (especially the cone bucket part). This is a very effective and commonly used method.
- Finely grind the welds: All welds must be polished to be flush and smooth with the steel plate, eliminating any tiny protrusions.
- Avoid internal components: Any horizontal support beams, ladders, platforms and other components should be avoided inside the cone bucket area, which are the "hardest hit areas" for wall hanging and arching. When it must be set, it should be designed to be streamlined and coated with an anti-stick coating.
2. Choose a suitable discharge port:
- Sufficiently large size: The discharge port diameter must be large enough to prevent the formation of a stable material arch. Its size should be calculated and determined based on the material characteristics and flow requirements.
- Reasonable position: Make sure it is located at the center of the lowest point of the cone bucket to avoid eccentric design that causes flow asymmetry and wall hanging.
3. Air fluidization system (for powdered materials):
- Breathable layer/fluidizing rod: Lay breathable cloth or install fluidizing rod in the key areas of the cone bucket (especially near the discharge port and transition zone).
- Compressed air: When needed (such as when starting the discharge or feeling that the flow is not smooth), introduce low-pressure, dry compressed air to fluidize the material locally, destroy the material arch, and reduce the friction and adhesion with the silo wall. Pay attention to controlling the air pressure and duration to avoid excessive fluidization leading to material compaction.
4. Optimize the bottom plate design (key!):
- Slight inclination: Even if it is called a "flat bottom", a very slight overall slope (1°-3°) should be designed towards the center discharge port. This slight slope is crucial to promote the overall movement of the material to the center and can significantly reduce dead angles.
- Funnel-shaped/dish-shaped bottom: A better solution is to use a funnel-shaped bottom plate or a dish-shaped bottom plate. This is not a traditional cone bucket, but a concave arc or shallow cone in the center area formed on the basis of a flat bottom to guide the material to gather. Usually combined with center discharge.
- Center discharge port size and location: The size is large enough (to avoid arching) and is strictly located at the center of the lowest point.
III. Operation optimization (daily management)
1. Control material properties (if possible):
- Moisture control: Strictly control the moisture content of the material entering the warehouse. Moisture is the primary factor that causes the material to increase viscosity and agglomerate on the wall. Ensure that the material is below the safe storage moisture.
- Particle size control: Avoid too much ultrafine powder, which easily absorbs moisture and increases viscosity. Consider adding flow aids if necessary (the impact on material performance needs to be evaluated).
- Prevent segregation: Optimize the feeding method (such as multi-point feeding, using a center tube or dispersion cone), reduce the particle size stratification and segregation of the material in the warehouse, and prevent fine powder from concentrating on the warehouse wall.
2. Standardize feeding and discharging operations:
- "First in, first out" principle: Avoid long-term static storage of materials in the warehouse. The longer the material is stored, the more likely it is to agglomerate and hang on the wall due to compaction, moisture absorption, temperature changes, etc. Try to keep the material flowing.
- Emptying operation: Before planned maintenance or material change, try to completely empty the material in the silo. This is one of the most effective operations to prevent long-term wall hanging and caking. Avoid long-term operation at low material level.
- Avoid the "thin waist" phenomenon: When discharging, try to keep the material level above the transition area between the straight section of the silo and the cone bucket (the "thin waist" area), or let the material level pass through this area quickly. This area is a high-incidence area for wall hanging and arching.
- Smooth discharge rate: Avoid drastic fluctuations in the discharge rate. Too fast may cause material compaction, and too slow is not conducive to destroying the potential arch structure. Using variable frequency controlled feeding equipment (such as rotary valves, vibrating feeders) helps to stabilize the discharge.
3. Regular cleaning (preventive maintenance):
Even with good design and operation, slight wall hanging may accumulate. A plan should be made to conduct a thorough cleaning inspection regularly (such as annually or according to material characteristics). Use downtime to remove the material layer attached to the silo wall. Safety regulations (such as limited space operations, dust explosion prevention, energy isolation, etc.) must be strictly followed when clearing the warehouse. Personnel are strictly prohibited from entering at will!
IV. Auxiliary measures (solving wall hanging that has occurred)
1. Silo wall vibrator:
- Install high-frequency pneumatic or electric vibrators on the outside of the silo wall (especially the transition zone in the upper and middle parts of the cone bucket and the area prone to wall hanging).
- When the discharge starts or the flow is not smooth, start the vibrator for a short time and intermittently. Vibration can effectively destroy the adhesion between the material and the silo wall and cause the wall-hanging material to fall off.
- Key points: Choose the appropriate model (frequency, exciting force), installation location and quantity. Avoid continuous vibration, otherwise the material may be compacted more tightly, which is counterproductive and damages the silo structure.
2. Air cannon:
- Install air cannons at key points prone to wall hanging and arching (such as the upper part of the cone bucket, the transition zone, and above the discharge port).
- Use the high-pressure gas shock wave released instantly to strongly destroy the material arch and adhesion layer. The effect is usually more "violent" than the vibrator, suitable for stubborn wall hanging or arching.
- Key points: Accurately design the installation position, angle and release pressure. A high-quality compressed air system and control system are required. Pay attention to noise and safety when using.
3. Mechanical dredging (use with caution):
- Under the premise of ensuring safe isolation (materials, energy) and ventilation and qualified inspection, tools such as long poles can be used for external auxiliary dredging from manholes or inspection ports. Personnel are strictly prohibited from entering the dangerous area below the hanging material.
- There are specially designed warehouse cleaning robots or robotic arms that can be used for specific scenarios, but the cost is relatively high.
Summary and suggestions
- 1. Prevention first: The most economical and effective method is to fully consider the material characteristics in the design stage, use large cone angles, smooth inner walls (coatings), suitable discharge port sizes, and avoid internal obstacles. This is the fundamental solution to the problem of wall hanging.
- 2. Daily management is the key: Strictly control the moisture content of materials, implement the "first in, first out" principle, empty the materials as much as possible, and avoid long-term operation at the "thin waist" material level, which can significantly reduce the occurrence of wall hanging.
- 3. Auxiliary equipment is effective but conditional: Vibrators and air cannons are effective tools for dealing with wall hanging, but they must be correctly selected, installed and used (short-term, intermittently), otherwise they may be ineffective or harmful. Think of them as preventive and remedial measures, not alternatives to design defects.
- 4. Safety first: Any form of warehouse clearance operation is extremely dangerous! Strict operating procedures must be formulated to implement safety measures such as energy isolation, ventilation detection, and monitoring and rescue. Auxiliary means that do not enter the warehouse (vibrators, air cannons) are preferred.
- 5. Targeted solutions: The best solution needs to be formulated after a comprehensive evaluation based on the specific material characteristics of the storage (particle size, moisture, viscosity, repose angle), the specific structure of the steel silo (size, cone angle, inner wall treatment), site conditions and budget. There is no one-size-fits-all approach.
A few suggestions from Shelley Steel Silo
- 1. Clarify the specific materials stored and their key characteristics (especially moisture, particle size distribution, repose angle).
- 2. Check the structure of the existing steel silo (especially the cone angle, inner wall smoothness, discharge port size, and whether there are components inside).
- 3. Evaluate the current operation process (feeding, discharging, emptying, and storage cycle).
- 4. Based on the above information, prioritize operational management optimization (such as strengthening moisture control and strictly enforcing emptying), and then evaluate whether it is necessary to add auxiliary equipment (vibrator/air cannon) or make modifications (such as inner wall coating).
By systematically applying the above strategies, the phenomenon of flat bottom silos hanging on the wall during outbound storage can be significantly reduced, storage efficiency can be improved, production can be guaranteed to be smooth, and maintenance costs and safety hazards can be reduced. I hope the above explanation can help you solve the problem of steel silos hanging on the wall in the future.
Written by
Shandong Shelley Grain Steel Silo Co., Ltd
Editor Jin
www.grainstoragesilos.com
WhatsApp : +86-18653877118
Email : shelley@cnshelley.com
