Conveyor Dust Control: Best Practices for Transfer Points

It does not matter if it is from a silo, hopper or another conveyor – when dry bulk material is dropped onto a moving conveyor belt, dust emissions are inevitable.

A common problem is many operators’ lack of understanding of what causes dust. Most solutions focus on suppressing and collecting dust, but years of field study and experience show that to improve air quality at transfer points, it is more effective to address the root causes by taking a comprehensive view of the function and design of the material transfer process.

Elements of a transfer chute

A transfer chute should include several essential components that reduce material spillage and dust, help the cargo to settle in the centre of the belt, and assist dust in settling back into the cargo flow or into a dust collection system. These components comprise cradles, wear liners, skirting, raised enclosures, and strategically positioned dust curtains.

Some manufacturers offer modular transfer chute enclosures that can be quickly and economically retrofitted for changes in production during scheduled downtime. Extending the transfer chute enclosure provides more space for the turbulent air and dust to settle.

Externally facing wear liners and skirting allow easy access for significantly safer maintenance. Although the normal lock-out/tag-out procedures are required, external servicing eliminates the need for chute entry and drastically reduces the amount of downtime.

Respirable dust

If you can see the particulates floating in the air, they are not small enough to be respirable, meaning they do not surpass the body’s natural defences and enter deep into the lungs, causing serious damage and health issues. Nuisance particulate matter (PM) smaller than 200 µm (micrometres in diameter) – roughly the size of normal household dust – is light enough to remain airborne on ambient air currents. When PM reaches 100 µm – approximately the size of a cross-section of a human hair – it becomes invisible to the naked eye. At 10 µm or smaller, the particulate is considered 'respirable'.

Conveyor enclosures that are properly sealed and retrofitted with three curtain zones incrementally slow the airflow and allow dust to settle. Field tests show a drastic reduction in emissions of both nuisance and respirable dust.

Identifying the root causes of dust

Many operators have the misperception that, in the inherently dirty business of mining, processing and handling bulk materials, dust control is a futile battle that can never be overcome.

Airflow through the transfer point is achieved by adjusting the loading angle and the proper placement of dust curtains. With a centred and sloped or spoon-shaped loading configuration, the cargo is eased onto the belt with less impact. Proper placement of curtains creates zones where air is slowed, allowing dust to settle back into the cargo stream.

Material degradation increases small fines in two ways. As raw material is processed through crushers or mills, it is reduced in size and dust becomes more prevalent. Degradation can also be caused by the impact of material upon transfer, resulting in it breaking apart.

Poor transfer point design for current production expectations is perhaps the largest cause of dust. Increases in production require either a greater volume of conveyed material or higher belt speeds. If the system is not graded for these expectations, dust becomes the bellwether for a host of other issues.

Best practices for belt conveyor dust control

• Avoid belt sag – support the belt the entire length of the enclosure so it does not sag away from the skirting. The pressure from air turbulence is enough to push dust and fines out of these gaps.
• Wear liners increase the conveyor system’s life – modern chute design raises the height of the chute, providing more room for dust settling in the stilling zone and also space to place the external wear liner.
• Install belt skirting to seal the environment – single skirting should be cut to the belt’s trough angle for a tighter seal. Self-adjusting skirting has spring-driven latches that offer slight downward pressure. Dual skirting offers a single skirt with a rubber flap that provides a second layer of sealing.
• Seal before adding dust collection devices – 'passive dust control' uses engineered design solutions such as controlled loading, wear liners, skirting, curtains and modular enclosures first.
• Slow the exiting air velocity – a flow of air will still be prevalent exiting the system, but the key is slowing it to under 200 fpm (1 m/s) – slow enough to reduce emissions. Adding a tail panel and curtains is essential to this, and strategic placement is the key to slowing exiting air velocity.

Conclusion

Improving workplace air quality may seem like a daunting task, but achieving it increases compliance, morale and safety. Conveyor transfer points are not the only source of dust, but as one of the most prevalent generators of particulate emissions in any bulk handling operation, they are an excellent place to start. By following best practices using modern and well-designed retrofitted components, operators can tackle dust by a process of elimination. Once large emission sources are addressed, it is easier to identify dust from other parts of the operation – with the ultimate goal of a clean and efficient workplace, high staff morale and an exemplary safety record.

Read the article online at: https://www.drybulkmagazine.com/special-reports/29102025/conveyor-dust-control-best-practices-for-transfer-points/