R. Todd Swinderman, Martin Engineering, examines how improved conveyor design and operation can significantly reduce dust emissions and operational costs in bulk material handling.
Dust is not just a workplace safety issue, it is also an operational expense. Emissions foul rolling components, machinery, and equipment air intakes, leading to frequent servicing, unplanned downtime, equipment replacements, and additional labour. These factors unnecessarily drive up operational costs, especially when effective methods and technologies exist to control and suppress dust emissions before they become airborne and create these risks.
Reducing dust emissions might seem as simple as mitigating the amount of dust created in processing, but that is easier said than done. This is because there are so many sources that need to be managed. Once bulk materials are crushed and ground, the resulting fine particles become increasingly difficult to manage, especially as material is transferred between stages of production – through conveyor transfer points or as it is discharged onto stockpiles.
Where do the dust emissions come from?
Conveyors are a major source of dust emissions, but they can also aid in reducing fugitive dust. For example, pit crushing and overland conveying from a limestone quarry emits less dust compared to truck haulage. Even unprocessed limestone is prone to particulate emissions and, in some cases, may require an enclosed conveyor belt system.
When haulage involves a conveyor belt, dust generation primarily occurs during loading and discharge, and how these stages are managed plays a critical role. Closed conveyors are very useful for preventing contamination and protecting the cargo from the elements, but they still have to be opened and closed for loading and discharge. Passive dust reduction strategies include:
Shorter or directed drops
Transfer chutes positioned over loading zones reduce the impact of cargo as it hits the belt, decreasing turbulence and minimising the release of dust within the loading area.
Managing the flow
While rock boxes are a common solution, they can be prone to clogging. Experienced engineers often recommend sloped transfer systems that slow the material flow, minimising impact energy and the air induction that contributes to dust. Properly managing flow also includes loading material at the centre of the belt, which reduces shifting and improves belt tracking.
Preventing belt sag between idlers
The belt can dip slightly between idlers, creating gaps between the belt and skirting, causing the release of dust and fines in the loading zone. Using an impact cradle with shock-absorbent polyurethane bars reduces impact strain on the belt and creates an even belt plane with no gaps between the skirting and belt. Cradles can extend along the entire length of the stilling zone.
Fully enclosed transfers
By completely enclosing the loading and settling zone, dust is contained. Items like dust curtains and dust bags can then be added to control airflow and capture dust.
How does the belt affect dust?
The speed and design of a conveyor belt play a significant role in dust generation. Various recommendations exist for optimal belt speeds depending on the characteristics of the bulk material being transported. ANSI/CEMA 550-2003 ‘Classification and Definitions of Bulk Materials’ outlines miscellaneous properties of bulk materials that would contribute to a decision to use a lower belt speed.
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