When silica, limestone, cement, aggregate, and other respirable dust particles that range in diameter from 0.1 to 70 microns are airborne, they create a safety and health concern, as well as an aesthetic nuisance. As a source of physical discomfort, lost materials, and wear on conveying pulleys, idlers, belting, and motors, such dust often can be a significant factor in lowered productivity and added operating and maintenance costs.

When the initial plant design or modifications to contain dust have not worked properly, some operators resort to air-lift or scrubbing systems. Baghouses, wet scrubbers, and cyclones are expensive in terms of capital cost and maintenance. In addition, you have the added cost of rehandling the collected fines or slurry.

Dust suppression, on the other hand, is a less expensive technology that uses water sprays to create fine water droplets. These water droplets impinge the fines, collect them, and then settle back onto the conveyor or stockpile. Therefore, without resorting to chemical additives, the use of compressed air atomizing nozzles can remove particulate with a minimum volume of water in stationary, as well as portable installations. As well, additional wetting agents or foaming surfactants can be used to extend the suppression effect over long multiple transfer point conveyors.

One development in the industry's campaign to control fugitive particles is a dry fog dust suppression system from TurboSonic. The system agglomerates dust at the source through a fine spray of thousands of tiny droplets. The system can be installed at breakers, crushers, and screws as well as transfer points.

A TurboSonic dust suppression system includes Sonicore atomizing nozzles, a source of compressed air, a sequencing circuit, linear actuators, or on-off controls depending upon site requirement. The dry fog dust suppression system controls respirable particulates 0.1 to 3 microns diam. as well as larger airborne particles, according to TurboSonic. These fines are considered the principal source of dust clouds, haze, andaccompanying low levels of visibility. In most applications where respirable dust particles can be settled out of the atmosphere quickly, the TurboSonic system makes it unnecessary to add a tension-active chemical to the water.

The nozzles are air-driven acoustic oscillators that atomize liquids by passing them through a field of high-frequency soundwaves. The air then expands through a convergent/divergent section into a resonator cap where it is reflected back to primary shock-wave. The result of this is an intense field of sonic energy focused between the nozzle body and the resonator cap. According to Turbosonic, this approach allows a minimum volume of water to be used.

For example, a TurboSonic dust suppression system was given the job of suppressing siliceous dust at a quarry producing 100 tons of silica sand each day. With the help of 13 Sonicore nozzles strategically located in the feeding sieves of three rollercone gyratory crushers, the dust particles were agglomerated and settled down as the silica sand was discharged from the crushers to the conveyors.

In conclusion, TurboSonic holds that the dry fog suppression system offers industry users the following:

* less product wetting than conventional water spray systems (less than 0. 5%);

* wetting agents and their controls eliminated;

* no conveyor belt wetting or accompanying tracking problems;

*less conveyor downtime and fewer conveyor belt replacement parts;

* nozzles operate on low-pressure air and water to eliminate need for pumping systems;

* improved working conditions enables compliance with applicable health and safety regulations;

* cleaning and maintenance costs reduced; and

* permits recovery of spilled materials.