The Influence of Wet vs Dry Scrubbers on Air Pollution
The two types of scrubbers both work by treating exhaust gasses. There are, however, differences between the mechanisms that each type of scrubber uses and the pollutants they are most effective at neutralizing. It’s necessary to know how these systems work and their pros and cons before making a decision on which scrubber is right for you.
There are several types of wet scrubber that remove pollutants from exhaust gasses. The different types of wet scrubbers all work by wetting the gas to separate contaminants. Acids and contaminants can be effectively removed from water using wet scrubbers.
There are different ways in which wet scrubber types expose exhaust gasses to liquid. There are the following types of wet scrubbers:
- Bed scrubbers packed in boxes
- Venturi scrubbers
- Spray towers
- Chambers for cyclone spraying
- Orifice scrubbers
All wet scrubbers are dependent on the amount of exhaust gas to liquid based on the surface area contact of the gas with the liquid. A scrubber’s performance is also influenced by the pressure and speed of the incoming exhaust gas. What the unit removes from the exhaust gas is also determined by the scrubbing liquid. While water is the most common liquid, caustic scrubbing liquid may be an alternative for facilities that need to remove acids from exhaust gases.
There are different types of scrubbers with varying uses and performance levels. For this reason, you must understand the specific operation of each type of wet scrubber before understanding how they work.
The packed bed scrubber, also known as a packed tower, sends gas through the beds of tower packing. The scrubbing liquid sprays down on top of the gas as it moves upward through the beds. The type of packing makes a significant difference in the surface contact between gas and liquid in these scrubbers. The gas continues to move up through a mist eliminator section of the tower, where the pollutants are collected, allowing the clean gas to exit.
Tower packaging can be made from a variety of materials and shapes. According to the composition and design of the tower, the best type to use will vary. In an ideal tower packing, gas will be in direct contact with liquid and excessive pressure falls will be prevented.
A Venturi scrubber uses a high-pressure hourglass-shaped chamber to pass exhaust gases. It introduces a low-pressure chemical into the exhaust stream. The high pressure of the gas transforms the scrubbing liquid into a fine mist, trapping gaseous and particulate matter in droplets. This type of scrubber, however, requires a lot of power to compensate for the high-pressure drops.
The jet scrubber is a variation of the Venturi scrubber. The scrubbing liquid is delivered at high pressure into the narrowest part of the scrubber with this type. This method overcomes the extreme pressure drops, but it is not as efficient as a standard Venturi scrubber.
In order to remove pollutants from gases, spray towers use a simple method. During the cleaning process, the exhaust passes through a chamber with multiple spray nozzles that create mists of the scrubbing liquid. The size of the droplets must be carefully controlled to ensure maximum pollution capture and removal from the gas. The gas is expelled through the top of the chamber. The liquid then recirculates through a treatment system before returning to the tower after treating the gas.
Compared to other types of towers, spray towers have a lower power consumption because of their simplistic operation. Unfortunately, these towers do not remove particulates from gas as efficiently as other towers. To reuse the liquid, facilities need to treat it first. Finally, spray towers require heavy maintenance to keep the spray nozzles clear to produce the required droplet size.