MAFA Guidelines for Bulk Filling Silos – Minimise Dust and Pellet Damage
To ensure optimal combustion and maintain pellet integrity all the way to the burner, pellets must remain as intact as possible. Damaged pellets create dust, which leads to poor combustion and efficiency.
Key Steps for Proper Bulk Filling
- Start with Air Only
The driver should begin by using only drive air to create a cyclone effect inside the silo’s Cyclone. - Gradually Introduce Pellets
Open the feed or pellet valve after airflow is established, then adjust the air volume so the hose carries a dense flow of pellets. This reduces wear and tear. - Balance Air Pressure
Too little air causes hose vibration; too much air can damage pellets inside the Cyclone. - Long Hoses or Extensions
When using long hoses or bends in the filling pipe, more air is needed. This may slow unloading and slightly increase pellet breakage. - Start the Screw Early
If the silo is empty, MAFA recommends starting the screw 10–15 seconds before filling begins to ease start-up.
Following these steps ensures gentle filling, minimal dust, and maximum pellet quality.
- Bulk Filling Safety and Operating Procedure
- To ensure safe and efficient silo filling, follow these steps:
- Remove Protective Caps
Make sure the protective caps on the vent pipe and filling pipe are removed. - Ground the Bulk Truck
Connect the truck’s grounding cable to the silo to prevent static discharge. - Connect the Bulk Truck to the Silo
Secure all connections properly. - Attach the Bulk Hose
Connect the hose to the silo’s filling pipe. - Start Filling with Drive Air Only
Begin by releasing drive air to ensure free ventilation and avoid pressure buildup. - Gradually Introduce Material
Slowly open the feed valve to start material flow while maintaining proper air balance. - Reduce Air Pressure Before Completion
Cut back the air supply in time to avoid pressure surges from the truck at the end of filling. - Follow All Standard Bulk Filling Guidelines
Adhere to applicable safety and operational standards throughout the process.
In-Depth Guide: Pellet Filling and Bulk Handling Safety
Unloading powdered goods from a bulk truck to a silo is a high-risk operation. With speeds of nearly 1 ton per minute, material is transferred from the truck to the silo top, often positioned 15–20 meters above ground. This process requires significant energy.
Why Pneumatic Handling?
Pneumatic technology (compressed air) is the most common and efficient method for this demanding task. A truck-mounted air compressor pressurises a load-bearing pressure vessel, creating a powerful airflow that moves the powder through hoses and pipes to the silo receiver.
Safety Considerations
Due to the high pressure involved, the process must be carefully monitored to prevent uncontrolled surges that could stress the system beyond its design limits.
Consequences of poor handling include:
- Serious risks to personnel and equipment
- Dust emissions and contamination
- Damage caused by inadequate equipment or incorrect operation
Strict adherence to safety procedures and proper equipment maintenance is essential to ensure safe, efficient pellet filling.
Understanding the Risks of Pneumatic Bulk Filling Systems
When the driver connects the hose from the truck to the silo pipe, a pressure vessel system is created with a sender (truck) and a receiver (silo). The principle is simple: compressed air from the sender generates a powerful airflow to the receiver, carrying the powdered material to be unloaded.
However, this airflow can be unpredictable and dangerous if not properly controlled.
Shared Responsibility – Increased Risk
Because multiple parties share responsibility for the system and its operation, the risk of accidents with serious consequences increases.
Driver’s Responsibility
The driver controls the airflow and is therefore responsible for ensuring that the enormous energy stored in the truck’s tank does not cause an uncontrolled air surge.
Such a surge can open the relief valve and release dust and powder into the environment.
An uncontrolled air surge must never occur – the risk of severe accidents is significant.
Pressure and Airflow Dynamics in the Unloading Line
A typical unloading line consists of 4-inch pipes and hoses. During unloading, the airflow dynamics change significantly along the line:
- At the Hose Inlet (Point A)
Air enters at approximately 2 bar pressure. As soon as it expands into the pipeline, the pressure drops because the air needs more space, forcing the air velocity to increase. - Along the Pipeline
As the air moves forward, pressure continues to decrease while speed increases, converting pressure energy into kinetic energy. - At the Silo Inlet (Point B)
Near the silo roof, the air pressure is almost equal to atmospheric pressure. At this stage, pressure energy has been fully transformed into motion energy. - If Airflow Is Blocked
When the air cannot escape freely, its kinetic energy converts back into pressure, creating a surge that can stress the system.
This principle explains why proper airflow control is critical for safe and efficient pneumatic unloading.
Sändningsförloppet omfattar olika faser och nedan följer en beskrivning av dem.
Pre-Delivery Safety Measures
Correct Goods
The delivery note must be presented when the receiver has staff on-site. This ensures:
- The type of goods and quantity match the order.
- The receiver can confirm that the load will fit in the designated silo.
Correct Silo
The receiver must clearly mark which silo pipe should be used.
A recommended safety measure is to use locking caps on pipes, especially when unloading at unmanned locations.
Why this matters:
Delivering the wrong product can cause significant financial damage and operational disruption.
A misdelivery into a full silo creates a sudden hazard that the driver may not be able to manage in time.
Pressurisation Process
Air is injected into the fluidisation system, which disperses it finely into the powder. This occurs at the bottom of the tank near the discharge opening, causing the powder to transition into an almost fluid-like state.
When the pressure gauge reaches the operating pressure of 2 bar, it’s time to start the sending process.
Start the Sending Process
- Activate Ejector Air (a)
Begin by fully opening the ejector air to create a strong airflow in the discharge assembly. - Open the Discharge Damper (b)
Perform this step with a smooth yet firm motion to start material flow. - Adjust Ejector Air
Once the sending process is underway, reduce the ejector air to a level determined by the driver.- Different unloading conditions require different amounts of ejector air.
- The key is to use as little ejector air as possible without causing blockages in the pipeline.
Tip: Proper adjustment ensures efficient unloading, minimal wear, and reduced risk of pellet damage.
Sending Phase – Critical Safety and Control
During the sending phase, the amount of air supplied by the compressor equals the volume of air and material leaving the container.
- Stable Pressure (a)
The system pressure must remain stable throughout the process. As the vessel empties, the energy potential increases, reaching its maximum when the tank is empty. - Monitor Material Level (b)
The driver must carefully track how the level drops inside the tank. A simple method is to tap the tank with a rubber mallet to check the remaining material.
Safety Alert
Given the enormous energy stored in the tank, the driver must stay extremely vigilant during the entire sending phase and remain within reach to quickly close the discharge damper if needed.
Stopping the Sending Process – Critical Safety Step
A critical moment occurs when resistance in the unloading line starts to drop because material flow decreases or becomes uneven. Every driver must learn how to determine the right time to close the discharge damper — and this must happen before the tank is completely empty.
Why?
An uncontrolled air surge must be prevented. Relying on the silo’s relief valve as a signal is not acceptable, as it causes dust emissions during every unloading.
Key Warning Signals
- Pressure Gauge Movement
The needle begins to tremble and move downward. - Change in Sound
The airflow noise changes in tone. - Feel the Flow
With a foot on the unloading hose, you can sense a change in flow.
Tip: Act immediately when these signals appear to avoid dusting and prevent dangerous pressure surges
Silo Equipment – Essential Components for Safe and Efficient Operation
MAFA offers a complete range of silo equipment designed for durability, safety, and optimal performance in bulk handling. Key components include:
- Filters – For clean airflow and dust control during filling and ventilation.
- Safety Valves – Prevent overpressure and protect the system.
- Level Sensors – Monitor material levels for accurate inventory and automation.
- Pressure Switches & Alarms – Ensure safe operating conditions and provide alerts.
- Hose Valves & Couplings – Secure connections for pneumatic filling.
- Filling Pipes & Hoses – Robust solutions for efficient material transfer.
- Ladders & Access Equipment – Safe inspection and maintenance access.
Our equipment is engineered for pellet storage, feed handling, and bioenergy applications, ensuring reliability in demanding environments.
B – Filter
Ensures clean airflow by capturing dust and fine particles during filling and ventilation.
C – Safety Valve
Protects the system by releasing excess pressure to prevent damage or accidents.
D – Level Sensor
Monitors material levels inside the silo for accurate inventory control and automated alerts.
E – Alarm
Provides a warning signal for critical conditions such as overfill, pressure issues, or system faults.
F – Pressure Switch
Detects and controls pressure changes in the system to maintain safe operating conditions.
G – Hose Valve
Controls airflow and material flow through the hose during filling or unloading.
H – Filling Pipe
The main pipe used for connecting the bulk truck and transferring material into the silo.
I – Hose Coupling
Secure connection point between the hose and the filling pipe for safe material transfer.
J – Hose / Hose Clamps
Flexible hose and clamps ensure a tight seal and prevent leaks during pneumatic handling.
K – Ladder
Provides safe access for inspection and maintenance of the silo and its components
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