Jerad Heitzler, Training Manager, Martin Engineering, writes about controlling dust at conveyor transfer points to protect worker health and to extends equipment life and boost operational efficiency.
Transfer points are critical connections between key stages of cement manufacturing, but they are notorious as a source of fugitive dust. After all, whenever materials like crushed limestone, shale or clinker drop onto a moving conveyor, dust emissions are inevitable, aren’t they? Not necessarily.
When loose materials hit a moving conveyor belt, the impact causes some of the cargo to disperse, particulates become airborne, and the subsequent air turbulence forces the dust toward the nearest opening. If the environment isn’t sealed, the dust-filled air creates a serious workplace health and safety hazard, a problem that’s exacerbated if dust is allowed to build up.
Dust emissions don’t just create a harmful environment for those working in the area. Abrasive particulates make their way into exposed machine parts and rolling components, causing them to wear quicker, seize and require replacement sooner. Particulates also clog air intakes of nearby equipment, further raising the need for maintenance and downtime. Then as it settles, dust builds up to cover walkways and stairs, engulfing control units, obscuring signage and, in some cases making access for maintenance impossible without a full shutdown and clean-up.
Often, the biggest issue is the team’s lack of understanding of the underlying sources of dust at transfer points. In fact, there are just three factors that cause dust in any minerals processing plant:
a. Material degradation from crushing and milling, as well as transfer and movement, which creates an abundance of fine particles that become airborne.
b. Air flow through the plant is a key factor in carrying airborne particulates and this can be controlled with the right design, considering material speed, volume and fall.
c. Transfer point design is one of the main causes of dust emissions and spillage on conveyor systems, often exacerbated due to desired increases in productivity.
Best practices for transfer point dust control
- Avoid belt sag with impact cradle support. For each transfer point, support the belt the entire length of the chute wall so it doesn’t sag away from skirting. The pressure from air turbulence is enough to push dust and fines out of these gaps, causing excessive dust and spillage.
- Use wearliners to increase system life. Modern chute designs raise the height of the chute, providing more room for dust to settle in the stilling zone and allowing space for an external wearliner. Without it, the rubber skirting takes the force of falling materials which lowers the equipment’s life.
- Seal the environment with belt skirting. Single skirting should be cut to the belt’s trough angle for a tighter seal and mounted externally for easy and safe adjustment. Self-adjusting skirting has spring-driven latches that offer slight downward pressure for reduced maintenance. Dual skirting offers a single skirt with a rubber flap that provides a second layer of sealing and protection from spillage and emissions.
- Use dust collection only when necessary – ‘Passive dust control’ uses engineered solutions such as controlled loading, wearliners, skirting, curtains and modular enclosures first. When there are length or space restrictions for chutes, which prevent an extended settling zone, dust bags and mechanical air cleaners are still effective, but they can require more maintenance, so sealing at source is better.
- Slow the exiting air velocity. Some flow of air is still going to be exiting the system, but the key is slowing it to under 200 fpm (1 m/s), slow enough to allow for settlement happen. Adding a tail panel and curtains is essential to this but simply adding them at the ends does not accomplish the proper stilling environment required. Understanding the air flow and then strategic placement is the key to reducing exiting air velocity.
Conclusion
Improving workplace air quality in a cement plant seems like a challenge but eliminating dust delivers numerous benefits, notably in health and safety, housekeeping, efficiency, productivity and cost reduction. Of course, conveyor transfer points are not the only source of dust. However, as one of the most prevalent generators of particulate emissions in any bulk handling operation, addressing these is an excellent place to start.
By following best practices using modern and well-designed retrofitted components, and expert advice from experienced technicians, operators can tackle dust in a methodical way. Once the major dust sources are addressed, it becomes easier to identify emissions from other parts of the operation with the ultimate goal of a clean, efficient and
safe operation.
About the author:
As programme manager and lead instructor for Martin Engineering’s FOUNDATIONS™ Training Workshops, Jerad Heitzler is a leader in helping the industry learn how to make the handling of bulk materials cleaner, safer and more productive.
