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wet scrubber
What Is Wet Scrubber?
Wet scrubbers are filtration systems that are used to remove harmful particles from industrial exhaust gases (flue gas), ahead of their release into the atmosphere.
Wet scrubbers are widely used in any type of industrial facility where air pollutants are produced.
How Do Wet Scrubbers Work?
Wet scrubbers use water based absorption to remove pollutants from exhaust gases. Firstly;
— The polluted gas is moved through the packed bed and water or water based solvents, which are misted from above.
— Then, as the gases are misted with the solvent, the heavier pollutants attach to the solvent liquid and are separated from the gas.
— The solvent is stored in a metal container and extracted through the bottom. While the treated gas is moved through mist filters to capture any droplets before it leaves the scrubber.
Which Pollutants Can A Wet Scrubber Control?
Inorganic Fumes, Vapors and Gases
Wet scrubbers are widely used in many industries to regulate floating gases, vapors and fumes. In large quantities, such pollutants can be the cause of environmental disorders and detrimental health effects when they’re released to the atmosphere unfiltered. Wet scrubbers can remove some of the most detrimental air pollutants as listed in the image above.
Volatile Organic Compounds
Wet scrubbers are also effective in removing volatile organic compounds. These are artificial chemicals, generated during specific manufacturing processes, particularly those used to produce paint, pharmaceuticals or refrigerants. VOC chemicals, some of which can cause severe health effects over time or in a short period, become trapped in particular liquids or solids and release into the air eventually.
Particulate Matter
Encompassing a large variety of solid particles and liquid droplets, particulate matters can be as large as 10 micrometers or as small as 2.5 micrometers, sometimes even smaller. Alongside wet scrubbers, our electrostatic filtration units are very effective in filtering particulate matter.
Hazardous Air Pollutants
Hazardous or toxic air pollutants have tested or suspected major health implications. Some of them may cause cancerous growth, birth defects and other concerns. Keeping them from the atmosphere is imperative for ensuring public health and safety.
Some examples of these harmful pollutants are listed below.
Benzene: It’s a pollutant found in gasoline that is highly inflammable and rapidly evaporative. Ingesting it or breathing it in will cause internal cells to malfunction and impair bone marrow’s ability to produce sufficient red blood cells, causing anemia. Which can also cause the immune system to be weakened.
Perchloroethylene: This pollutant is released into the atmosphere particularly by dry cleaning or metalworking facilities. It’s colorless and non-flammable, with a sweet odor. High-level exposure can lead to nervous system failures, resulting in unconsciousness or death.
Methylene chloride: Also called dichloromethane, methylene is a solvent and paint stripper. Exposure to this pollutant may cause cancer, suffocation or cognitive impairment.
Where Can A Wet Scrubber Be Used?
A wet scrubber is a necessity in a wide range of industrial environments thanks to its air filtration capabilities.
However, in some industries wet scrubbers are essential. These industries may include but are not limited to:
Food and Agriculture
Electroplating
Acid Plants
Fertilizer Plants
Steel Mills
Asphalt Plants
What Are Wet Scrubbers Made Out Of?
Wet scrubbers can comprise of various materials such as metals or plastics.
Designating the correct materials for a wet scrubber is critical in reducing concerns of cost such as corrosion or rusting.
Some of the most popular materials used in constructing a wet scrubber are listed below.
Cast Iron:
An economical alternative, cast-iron scrubbers may integrate FRP or stainless steel lining to improve corrosion resistance.
Cast Iron Alloys:
A nickel containing cast-iron alloy has better corrosion resistance. When exhaust gas is high temperature or consists of abrasive material, it’s a good material to build a wet scrubber.
Stainless Steel:
Stainless steel, a temperature-resistant material, is ideal for high-temperature environments. However, it’s best to use a different material if hydrochloric acids are present.
Fiberglass-reinforced Plastic:
Effective in both alkaline and acidic environments, FRP is an economic and lightweight alternative. It’s most suitable for low to medium temperature environments and inorganic components. Owing to its high corrosion resistance, it is a good liner material for steel corrosion prevention.
Carbon Steel:
One of the most popular choices for wet scrubbers, carbon steel is best effective against dust or non acidic pollutants.
Polyvinyl chloride:
A material you might find in some components of a wet scrubber, such as the spray nozzle or the packed bed. PVC is only effective in low-temperature environments because it can’t stand excessive heat.
Furfuryl alcohol resin:
Furfuryl alcohol resin has strong acid & alkali resistance and is very effective against organic pollutants.
Choosing Wet Scrubber Materials & Lining
The designation of construction materials for the wet scrubber will depend on factors such as the application, type of pollutants and other priorities.
Where initial expenses are concerned, some materials will be more economical than others. Cast iron for instance, is the cheapest material where initial costs are concerned.
Yet, using a corrosion-resistant material instead my justify a higher initial cost with its longevity in some cases.
SOME INTERNAL LINING OPTIONS FOR WET SCRUBBERS
Carbon graphite:
Very suitable for small capacity wet scrubbers, carbon graphite is a popular choice for simpler applications.
Teflon:
Effective in very high-temperature settings and other extreme conditions, Teflon is a popular and reliable choice.
Kynar:
For specifically targeting chlorinated hydrocarbons, a Kynar-lined FRP wet scrubber is a fine choice.
How Targeted Pollutants Affect Wet Scrubber Design
As air pollutants are varied in different aspects such as size, shape and electric charge, the wet scrubber design will differ in order to effectively capture the targeted contaminants. Some of these factors are listed below:
Packet Bed Height
Packed bed scrubbers are effective against inorganic fumes, gases and odors. A packed-bed wet scrubber’s efficiency may be between 50 and 95%. The packed bed height size factor can differ with the specific contaminant targeted and the efficiency goals of the application. Packed bed height impacts the how long the gas is in contact with the solvent liquid, which increases the absorption of the particle.
Scrubbing Liquid Type
Solvent liquid content is another factor that affects scrubber design. Acidic contaminants require a caustic scrubber solvent, whereas caustic pollutants call for an acidic one. The electric charge of the solvent influences what type of pollutants it attracts and binds to. Naturally, which solvent will be most effective will depend on the specific pollutants a facility generates.
Liquid Flow Rate
This factor is the proportion of solvent liquid to gas treated. A greater volume of solvent droplets will ensure more contaminants are captured, up to a point. So, a facility that generates relatively high amount of air contaminants, might require a wet scrubber with a high liquid flow rate.
Target Gas Velocity
The speed at which the polluted gas moves through the wet scrubber affects contaminant collection efficiency. Inertias of higher levels will cause more collisions and impactions, which results in more captured pollutants. Different targeted particles may necessitate different velocities. Naturally, higher velocities require a stronger force and more energy. Making wet scrubbers with velocities both more expensive to buy and operate.
The Advantages of A Wet Scrubber
Low Pressure Drop
The change in pressure as the gas passes through the scrubber is called the pressure drop. A low pressure drop will be critical for the efficiency, which in turn will extend the scrubber’s life and reduce cost. Minimizing pressure drops is one of the traits of the most efficient wet scrubber systems.
High Mass-Transfer Efficiency
The amount of pollutants a wet scrubber can remove from the air is directly proportional to the amount of material it can move through it. A greater pollutant filtration can be achieved by a high-mass transfer efficiency.
Packing Height or Type Adjustments
Different types and heights of packing in a scrubber will work the most efficient against different contaminants, removing more particles from the air and improving mass travel.
Low Costs
In terms of both initial application and operating, wet scrubbers have low costs when compared to other pollution controlling solutions.
Small Space Requirements
Wet scrubber systems take relatively small space in most cases, since a singular application can remove various types of pollutants. Which minimizes cost and infrastructure concerns at the same time.
Effective Against Particulate Matter as Well as Gases
Wet scrubbers not only remove harmful gases from the air but also particulate matters, which may include allergens or illness-causing smoke and soot. Wet scrubber’s effectiveness in dealing with both pollutant types provide environmentally safe and breathable air way beyond the facility itself.