With pollution on the rise, the need to abate harmful contaminants and stay in compliance with the Clean Air Act is of upmost importance. For this reason, companies are turning to experienced vendors that focus on air pollution control technologies to help keep them in compliance. While there are many viable options, many times, a wet scrubber fitted with quality mist eliminators will be suggested as a safe and effective way to remove pollutants and odors from exhaust streams. A properly designed scrubber will be highly successful in removing contaminants before they reach the atmosphere, therefore keeping companies in compliance and avoiding shutdowns.
A scrubber system is used in the removal of harmful and hazardous particulates from industrial gas streams before they are released into the environment. Scrubbers can be engineered to safely remove solids, mist, and gases while at the same time providing cooling. Valuable product may also be recovered in the scrubber preventing product loss.
There are two different types of commonly designed scrubbers, wet and dry. In dry scrubbing, solids or slurries are used to bind contaminants. Dry scrubbing is less common than wet scrubbing and could be used in situations where there is no option for a wet scrubber. In wet scrubbing, liquids are used to wash the contaminants.
In a wet scrubber, a fan is used to forcefully guide the polluted gas stream through the inlet side of the scrubber via pipes and ductwork. The dirty gas will meet the liquid solution, typically water, but sometimes a mixture or a chemical wash. The liquid solution is most often sprayed from a nozzle. As the gas meets the liquid solution, particles will stick together and form larger particles or droplets. The vessel will be fitted with mist eliminators or packing which will serve as a filter. The particles or droplets will collect on the filter. At this point, they will fall to the bottom of the stack where they can be collected for removal.
This is called the absorption phase also known as “scrubbing”. In this phase, the gas components have turned to liquid. Depending on the process, chemicals or micro-organisms are added to the scrubbing liquid to neutralize the gases that are dissolved in the liquid. Lastly, the clean air stream that remains will pass through the mist eliminator and exit through the outlet side of the scrubber into the atmosphere.
Wet scrubbers are unique in the sense that they can handle gaseous and particulate contaminants in one technology. Wet scrubbers are extremely safe, they can be designed to handle high temps, high humidity, corrosive chemicals, and liquids.
Any industry with a high level of air toxins or odors will benefit from a properly designed scrubber system. Industries that burn fossil fuels to create energy or industries that use acid waste products and chemical reactions typically use a wet scrubber to stay in compliance.
There will be many considerations to the design. The scrubber will either be vertical or horizontal and incorporate a system fan, recycle pump, instrumentation and controls, mist eliminators, and exhaust stack. A scrubber should be corrosion resistant. Select scrubbing liquids will be used, depending on the chemicals or pollutant that needs to be targeted, such as ammonia, sulfur, and chlorine. The scrubber design will depend on the operating process conditions, flow rate, temperature, concentration, removal efficiency, and the chemicals being removed.
Wet scrubbers will only function properly and optimally if the mist eliminators or packing are the best quality, design, and fit. Packing materials must be lightweight and durable, not interact with the chemicals and the material must have a path for the liquid to flow as well as allow for the contact between the liquid and the gas. If the liquid cannot flow, you will have high-pressure drop which will impact performance and efficiency.