In the world of dust abatement with nebulized water, understanding and improving the interaction between water droplets and dust particles is very important as it allows to maximize dust abatement without a significant increase in humidity.
The keys to effective wet spray dust control are the proper application of moisture, careful nozzle location, controlling droplet size, choosing the best spray pattern and spray nozzle type and proper maintenance of equipment.
To use wet sprays effectively, it must be remembered that each type of dust and application point is a unique situation and needs to be evaluated separately to achieve the optimal result. Also, water cannot be used at all times throughout the year in various climates where low temperatures may cause freezing.
Humidity
When water is used to control dust, it has only a limited residual effect due to evaporation, and will need to be reapplied at various points throughout the process to remain effective. Overapplication in the amount/volume of moisture can be a problem in all operations and may impact the equipment as well as the total process and transportability of the final product if shipped in bulk. In most cases, a properly designed spray system using finely atomized water sprays will not exceed 0.1 percent moisture application [USBM 1987]; however, systems that address prevention over larger areas with larger droplet sprays may add up to 1.5 percent moisture to the process.
How does dust behave?
It is important to observe that the vast majority of dust particles created during crushing are not released into the air, but stay attached to the surface of the broken material. Therefore, adequate wetting is extremely important because it ensures that the dust particles stay attached to the broken material. Uniformity of wetting is also an important issue for an effective system. By far the best dust reductions can be achieved by spraying the ore with water and then mechanically mixing the ore and water together to achieve a uniformity of wetting.
Position of nozzles
Due to the unique characteristics of each application, there are no hard and fast rules for specifically locating spray nozzles in dust control applications; however, optimal spraying can be achieved by taking few things into consideration.
- For airborne dust prevention, the nozzles should be located at an optimum target distance from the material, far enough to provide the coverage required but close enough so that air currents do not carry the droplets away from their intended target.
Moreover, the droplet size also needs to be considered when setting the correct target distance. - For airborne dust suppression, nozzles should be located to provide maximum time for the water droplets to interact with the airborne dust.
- For wet dust prevention systems, nozzles should be located upstream of the transfer point where dust emissions, in most cases, are being created.
- Care should be taken to locate nozzles for the best mixing of material and water.