Air scrubbers are air pollution control devices that use liquid to remove particulate matter or gases from an industrial exhaust or flue gas stream. In comparison to other air pollution control devices, scrubbers are a very efficient way of removing solids, mists, and gases while also providing cooling. They are also capable of handling volatile gases safely. However, scrubbers suffer from high levels of corrosion and produce slurry waste streams which are less convenient for recycling and disposal.
Scrubbers are devices that use a liquid to capture and remove pollutants. Through a nozzle or orifice a scrubbing liquid is introduced into the gas stream. The droplets capture the dust particles. This increases the size and mass of the particles, making them easier to collect in a filter or separation process. The scrubbing liquid absorbs and neutralizes gaseous pollutants. Suspended liquid is typically recovered in mist collectors and recycled through the system.
A key parameter in the design of scrubbers is the liquid-to-gas ratio. It is commonly expressed in gallons per minute (gpm) of liquid divided by actual cubic feet per minute of gas. This ratio is determined by the solubility of the gas pollutants, the amount of pollutants and particulate matter in the gas stream, and the mass transfer characteristics of the tower. Increasing the liquid to gas ratio increases the collection efficiency of the system, so finding the optimum ratio is important for balancing performance with operating costs.
Packed bed or packed tower scrubbers are systems which contain one or more layers of packing material to increase gas-liquid contact, such as Kempac’s Tri-Pack style, plastic pall ring, or plastic saddle packing. Gas streams enter in the bottom of the chamber and flow upward or horizontally through the packing as scrubbing liquid is distributed uniformly to the packing material. Once through the packing, cleaned gas passes through a mist eliminator while the waste liquid/slurry falls to the bottom by gravity. Some packed towers designed for
Packed bed scrubbers are primarily gas absorbers and are the most effective scrubbers for treating gas streams with gaseous pollutants. They can collect solids, but are not often used for this purpose because wet dust collecting in the beds would require unreasonable maintenance. One of the key design considerations for packed scrubber towers is the selection of the type of random packing and the material or type of resin. Kemflo offer several styles of plastic random packing in a variety of resins to meet your application. Kempac plastic random packing is available in a Tri-Pack style packing which is available in 1”, 2” and 3.5”, a plastic pall ring packing that is available in 1”, 2” and 3.5” and a plastic saddle packing which is available in 1” 2” and 3”.
There are multiple styles of scrubbers to consider. Stationary or enclosed scrubbers are housed in their own building or enclosure. These are typically used to treat process exhaust gases from industrial waste streams before they are released into the atmosphere. Portable scrubbers are small units used for local cleansing and cleaning applications. In addition to small size, they may have wheels or handles to make them easier to transport. Skid or base plate mounted scrubbers are designed to be placed on a skid or plate positioned on the floor. These scrubbers frequently contain transport features such as forklift slots for movement around a facility. Trailer or truck scrubbers are mounted on a trailer or truck for mobile spot dust or fume abatement.
Performance specifications are the ratings assigned by a manufacturer that describe the scrubber’s performance. These are the specifications most important for industrial buyer to consider when selecting a suitable scrubber for their application.
- Airflow or gas flow rate defines the acceptable flow rate or range of flow rates of the gas stream through the scrubber, measured in cubic feet per minute (cfm).
- Liquid or water flow rate defines the intended flow rate or range of flow rates of the scrubber liquid in the system, often described in gallons per minute (gpm). It may be given as a liquid-to-gas ratio (L/G). It determines the amount of water used by the scrubber, which will have a large impact on the operating costs of the system.
- Minimum particle size filtered indicates the minimum diameter of particulate matter that a dust collector is capable of capturing, measured in micrometers (µm). This rating effectively defines the range of capability of the collection device.
- Efficiency, collection efficiency, or capture rate defines the percentage of particulate matter and/or gaseous pollutants in the filtered gas stream that is effectively removed by the scrubber. Efficiencies can vary widely for different types of scrubbers and different gas streams.
In addition to performance criteria, there are other parameters to consider when selecting scrubbers for a particular application. These include material compatibility and operating temperature.
- Material compatibility – It is important to ensure the materials used in the construction of the scrubber are compatible with the chemical (acidity, reactivity) and physical (abrasivity) properties of the gas stream. Applications where the scrubbing liquid contains additional chemicals or substances may make it necessary to use specialty materials with high corrosion or chemical resistance.
- Operating temperature – Although scrubbers are often designed to provide cooling or quenching of hot gas streams, these devices still are limited to a certain range of temperatures, above or below which they may not operate effectively.
For more information on Kempac plastic random packing product line including the Tri-Pack style, plastic pall ring or plastic saddle packing please visit our website at www.kempac-packing.com.