By a wide range of manufacturing, domestic, and industrial activities.
Construction, agriculture, and mining are contribute most to atmospheric dust levels.
In minerals processing operations. during broking, dumping, crushing, grinding, screening, belt conveying, transferring, stocking, loading and milling materials to a finer size and movement of workers and machinery.
The amount of dust emitted by these activities depends on the physical characteristics of the material and the way in which the material is handled.
Fibrogenic dust is so named because it is a kind of dust that has fibber like tendencies. Fibrogenic dust is biologically toxic and if retained in the lungs can impair the lungs, ability to function properly.
Nuisance dust, or inert dust contains less than 1% quartz, its low content of silicates, having little adverse effect on the lungs. Any reaction that may occur from it is potentially reversible. However, excessive concentrations of it in the workplace may cause invisibility, unpleasant deposits in eyes, ears, and nasal passages and injury to the skin or mucous membranes by chemical or mechanical action.
Respirable dust are small enough to penetrate the nose and upper respiratory system and deep into the lungs, beyond the body's natural clearance mechanisms of cilia and mucous and are more likely to be retained.
Inhalable dust which enters the body, but is trapped in the nose, throat, and upper respiratory tract. The median aerodynamic diameter of this dust is about 10 µm.
Total dust includes all airborne particles, regardless of their size or composition.
“ Prevention is better than cure" but prevention of dust in the bulk material handling operation is an impossible task, properly designed bulk material handling components can play an important role in reducing dust generation, emission, and dispersion.
Reduces the dust concentration by the use of uncontaminated fresh air.
Simple measures such as providing shrouds, covers, or enclosures around a dust source help to contain dust emissions or allow the existing dust control system to operate more efficiently.
Here we describe some of the commonly used processing and bulk material handling equipment, their major dust emission points, and measures to prevent or reduce dust generation, emission, dispersion and control.
Surface wetting affected by droplet size and impact velocity. Surface wetting can be increased by reducing the droplet diameter and increasing the number of droplets and by increasing the impact velocity (by increasing the system's operating pressure).
We use nozzles in our system that produce drops in the 200 to 500 µm range to create a light rain effect.
Most important among components in a system are the spray nozzles.Following factors must be considered.
1-Droplet size, distribution is the most important variable for proper dust control. The droplet size decreases as the operating pressure increases.
2-Droplet velocity , higher drop velocities are desirable, especially in high-velocity air streams and where the nozzle is not located close to the target. Drop velocity is dependent upon drop size: Small drops may have a higher initial velocity, but the speed diminishes quickly. Larger drops retain velocity longer and can travel further.
3- Spray Pattern, Nozzles produce different types of spray patterns with varying characteristics.
Full cone nozzle product droplets that maintain a high velocity over a distance. They are useful for providing a high velocity spray when the nozzle is located distant from the area where dust control is desired.
Hollow-cone nozzles, produce a circular ring of water. Drops are generally smaller than other nozzle types and are used in locations where dust is widely dispersed. Reduced clogging is an added benefit of hollow-cone nozzles because its orifice is larger than other nozzle types.
Flat-spray nozzles, produce relatively large droplets that are delivered at a high pressure and tapered-edge, rectangular or even spray pattern. These nozzles useful for wet dust suppression systems and typically used in narrow or rectangular enclosed spaces.
Hydraulic fine-spray nozzles, produce a fine mist or fog. Hydraulic fine spray nozzles are preferred in most areas because operating costs are lower since compressed air is not required. They are useful for airborne dust control systems.
Air atomizing nozzles , produce finer drops, are effective in locations where dust particles are extremely small and the nozzles can be located in close proximity to the dust source.
4- Spray Angle Each nozzle has a jet spray angle , Spray angle and spray pattern will yield a specific coverage, determining how many nozzles are needed and their relative placement. In most applications, a spray angle between 55° and 70° offers the best coverage .
5-Flow rate of water through the nozzle depends on operating pressure. In order to determine the increase in moisture on materials being sprayed, the flow rate of the spray nozzles must be ascertained.
Screens are used to sort material according to size.
Dust is generated in all dry screening processes. However finer material produces more dust.
Screen emit dust from top and discharge.
Dust generated by screens cannot be altered. However, properly enclosed and removable enclosure can reduce dust emissions that consists of a special rubber cloth, rubber moulding, and simple metal hardware.
We recommend water spray system for screen at discharge end only. We place the spray nozzle at discharge end or as required at site.