Supression de polvos

INTRODUCTION TO DRY FOG AGGLOMERATIVE DUST SUPPRESSION
PRINCIPLE OF OPERATION
The DSI dry fogging system, agglomerates (attaches) the airborne dust particles to micron sized water droplets so that the particles become heavy enough to be returned to the product stream by the force of gravity. Unlike water spray systems, dry fogging uses very little water and does not wet the process material,only the airborne dust. No expensive surfactant or binding type chemicals is required. Dust control efficiencies can be as good as a dust collection system, but with lower capital, installation, and operating cost. The reason the DSI dry fog system works so efficiently is due to our ability to atomize water into micron-sized droplets of similar size to the dust particles that are of concern. Theeffectiveness of like size droplets is easily understood from the illustration below. “Consider a water droplet about to impinge on a dust particle, or what is aerodynamically equivalent, a dust particle about to impinge on a water droplet, as shown in the drawing. If the droplet diameter is much greater than the dust particle, the dust particle simply follows the air streamlines around the droplet,and little or no contact occurs. In fact, it is difficult to impact micron-size particles on anything, which is why inertial separators do not work well at these sizes. If, on the other hand, the water droplet is of a size that is comparable to that of the dust particle, contact occurs as the dust particle tries to follow the streamlines. Thus the probability of impaction increases as the size ofthe water spray droplets decreases.” COAL AGE Magazine, April 1976 To achieve agglomeration at the dust source point, two conditions need to exist; 1.) Enough water droplets of the same size as the dust particles have to be generated and 2.) Both dust particles and water droplets have to be contained in the same area so that agglomeration can occur. The following two sections will explain how theDSI system achieves these two conditions.
RESONATING CHAMBER

COMPRESSED AIR REFLECTED AIR STREAM

FOG NOZZLES
The design of the DSI system is based on a unique nozzle that can produce a very dense fog of 1-10 micron size water droplets that literally blanket the dust source and keep the dust particles from becoming airborne. It is important to note that the DSI dry fogging system wets thedust, not the material!
WATER

SONIC SHOCK WAVE

CONVERGE/DIVERGE ORIFICE

The DSI nozzle is an air driven device for fogging liquids by passing them through a field of high frequency sound waves. This is accomplished by compressing air upstream of a specially designed converge section of the nozzle. The result is an air stream that will accelerate past the speed of sound in the divergesection. When it passes the speed of sound, a primary shock wave is generated at the mouth of the nozzle. To enhance the fogging capability, a resonating chamber in the path of the air stream reflects the air stream back at itself to amplify the primary shock wave. Once the shock wave is generated, water is delivered through annular orifices where it is sheared into relatively small droplets. OVER >>>These small droplets are then carried by the primary air stream into the shock wave and exploded into thousands of micron size fog droplets. The air then escapes around the resonating chamber and carries the droplets downstream in a soft, low velocity fog pattern. The nozzle has no moving parts and is constructed of 100% stainless steel to provide years of trouble free service. Dissolvedminerals pass through the nozzle without clogging and any undissolved solids are easily filtered out by our system. The following diagram and table give the operating parameters of our DSN series of nozzles.

FOG CONTAINMENT
As explained in the “PRINCIPLE OF OPERATION” section, both the dust particles and the fog droplets have to be contained in the

NOZZLE SPECIFICATIONS
NOTE: ALL NOZZLES ARE...