Water Sprays or Garden Hose Technology is the oldest form of "dust control". These systems are designed to wet the material before dust is generated. However, there are several issues that makes these systems ineffective.
- Many materials do not take up water very well. It is nearly impossible to wet the material evenly.
- Water spray and mist system droplets are too large to capture airborne particles.
- Over-wetting can create material handling issues like belt tracking and carry-back.
- Water spray will freeze preventing cold weather operation.
- Nozzles tend to plug due to the higher pressure drop at the nozzle discharge making solids come out of suspension at the nozzle tip.
- Water Sprays create a BTU penalty to materials used for fule such as coal or biomass adding to the cost of power generation adding as much as 5% moisture to the fuel. See Moisture Addition by Weight Chart.
Misting Systems are not Fog Systems. Misters use very high water pressure (600 to 1200 psi) to squeeze the water through orifices as small as .006 of an inch. Our Dry Fog system essentially produces droplets in the 1-10 micron size range (dry fog is defined as 1-10 micron droplets). See Droplet Size Chart The dust that becomes airborne and is of concern to health and environmental officials is called PM-10 or particulate matter 10 microns or smaller. A like size droplet to dust particle size (PM-10) is essential as it is this like size that dramatically increases the opportunity for the dry fog/water droplet to impact the airborne dust. Larger droplets (mist 20 to 100 microns) have proven to be ineffective in treating airborne particulate due to the slip stream effect created by the droplet being larger than the dust. This concept was first explored by the Colorado School of Mines in in the 1970s with the results being published in a 1976 Issue of Coal Age Magazine