Mineral crushing and screening operations can be major sources of airborne dust due to the inherent nature of size reduction and segregation processes. Without adequate solutions, workers' health can be seriously compromised over time.
(Relative emission rate ratios of crushing and screening equipment)
In this article, we take a closer look at how to prevent dust in Crushing and Screening operations.
CRUSHING: how can you control the dust?
Crushing creates smaller sized material with an attendant increase in surface area, which will be dry. Thus, material wetted prior to crushing for dust control will likely have to be wetted again to address the additional dry surface area.
Wet dust control methods for crushing operations, involve wetting the process material before crushing, after crushing, or both. This is essentially treating the crushing operation as two transfer points, the feed side and discharge side.
The nozzles used depend by type of control, Hollow cone nozzles should be used when dust suppression (reduction of airborne dust) is desired, with spray patterns arranged to cover the entire area of the dust cloud. When prevention of airborne dust is desired in a static application such as a bin or hopper, full cone nozzles should be used with spray patterns overlapping the entire surface of the material to be wetted.
The mechanical action of crushers can generate air movement; i.e., jaw crushers can have a bellows-type effect. A method to estimate maximum generated airflow from this type of crusher has been described [Burton 1999]
Where D = diameter of the hammer assembly from the tip to tip, feet; and W = the width of the hammers, feet.
The volume of air generated per minute (cfm) is then the product of AGEN REV and shaft RPM.
SCREENING: how can you control the dust?
Screening operations can produce high levels of dust because smaller sized material is handled. Airborne dust is generated from the vibrating screen decks that accomplish the size separation. Additionally, material must fall some distance as part of the separation process, and some dust will be suspended by this process. Dust control for screening systems is similar to that for crushers, although wet systems are generally not used due to blanking of the screen openings by the wet material. Screens should be totally enclosed, and water suppression systems (when compatible with the process) or dust collection and exhaust systems should be incorporated.
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- NIOSH . Handbook for dust control in mining. By Kissell FN. Pittsburgh, PA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, NIOSH Information Circular 9465, DHHS, (NIOSH) Publication No. 2003–147.
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- Dust control Handbook for industrial mineral mining and processing