Definition
Wet scrubbers accomplish particulate collection by employing water or another liquid as the collection media. There are many scrubber designs, but most particulate scrubbers work by creating a wetted target for particle collection. This wetted target plate can be a bed of water or a zone where the particle and water droplet collide.
Benefits of wet scrubbers are their ability to perform in various moisture and temperature conditions, their resistance to chemical corrosion, and their low maintenance needs. However, wet scrubbers require a significant amount of water, which must be disposed of along with the collected particulate.
This lowers the collection efficiency and increases the energy costs. Settling ponds are one common method of collected particulate disposal in the mineral processing industry, and the water from these ponds can often be reused within the operation.
The types of wet scrubbers
Venturi Scrubbers
Venturi scrubbers are a type of wet scrubber and consist of a venturi-shaped inlet and a separator. Dust-laden air is accelerated to velocities between 12,000 and 36,000 fpm in the throat of the venturi. These high velocities atomize the coarse water spray and create pressure drops ranging from 5 to over 15 inches wg. The venturi can be ceramic-lined for abrasive applications. The extreme turbulence promotes collision between water droplets and dust particles in the throat of the venturi. An inertial separator then removes these agglomerates.
Impingement Plate Scrubbers
In another type of wet scrubber—an impingement plate scrubber—the exhaust passes upward through openings in perforated plates, which hold a layer of water. An impingement baffle is located above each hole, resulting in the formation of small droplets. Intimate gas/liquid contact results in efficient particle collection. A pressure drop of 4 inches wg is typical.
Spray Tower Scrubbers
Gravity spray tower scrubbers employ atomized water, which falls counter-current through a rising dust-laden air stream, to remove dust particles. These scrubbers are generally of lower efficiency and operate at pressures of 1 to 2 inches wg. They are approximately 70 percent efficient on 10-μm particles and above with poor efficiency on particles smaller than 10 μm. However, they are capable of treating high dust concentrations without becoming plugged.
Wet Cyclone Scrubbers
Similar to a dry cyclone, wet cyclone scrubbers use centrifugal forces to throw particles on the collector’s wetted walls. Water is introduced from the top of the scrubber to wet the walls and wash the particles away. Pressure drops for these collectors range from 2 to 8 inches wg with good efficiency for removing particles 5 μm and larger.
Reference
NIOSH Mining Program Report of Investigations, « Dust Control Handbook for Industrial Minerals Mining and Processing» Second Edition.
