Dust Control Handbook for Industrial Minerals Mining and Processing

CHAPTER 2: WET SPRAY SYSTEMSProbably the oldest and most often used method of dust control at mineral processing operationsis the use of wet spray systems. In essence, as the fines are wetted each dust particle's weightincreases, thus decreasing its ability to become airborne. As groups of particles become heavier,it becomes more difficult for the surrounding air to carry them off. The keys to effective wetspray dust control are proper application of moisture, careful nozzle location, controlling dropletsize, choosing the best spray pattern and spray nozzle type, and proper maintenance ofequipment.In the vast majority of cases for mineral processing operations, the wet spray system used is awater spray system. Although the use of water sprays is a very simple technique, there are anumber of factors that should be evaluated to determine the most effective design for a particularapplication. The following two methods are used to control dust using wet sprays at mineralprocessing operations.Airborne dust prevention, achieved by direct spraying of the ore to prevent dust frombecoming airborne.Airborne dust suppression, which involves knocking down dust already airborne byspraying the dust cloud and causing the particles to collide, agglomerate, and fall outfrom the air.Most operations will use a combination of both of these methods in the overall dust control plan.PRINCIPLES OF WET SPRAY SYSTEMSTo use wet sprays effectively, it must be remembered that each ore type and application point isa unique situation and needs to be evaluated separately to achieve the optimal design. Forexample, wet sprays cannot be used with all ores, especially those that have higherconcentrations of clay or shale. These minerals tend to cause screens to blind and chutes to clog,even at low moisture percentages. Also, water cannot be used at all times throughout the year invarious climates where low temperatures may cause freezing.Water ApplicationWhen water is used to control dust, it has only a limited residual effect due to evaporation, andwill need to be reapplied at various points throughout the process to remain effective. Overapplicationin the amount/volume of moisture can be a problem in all operations and may impactthe equipment as well as the total process and transportability of the final product if shipped inbulk. In most cases, a properly designed spray system using finely atomized water sprays willnot exceed 0.1 percent moisture application [USBM 1987]; however, systems that addressprevention over larger areas with larger droplet sprays may add up to 1.5 percent moisture to theprocess.Wet Spray Systems 61