Exhaust gas cleaning systems, commonly referred to as scrubbers, are pollution control devices used to remove harmful substances from exhaust gases before they are released into the atmosphere. These systems are particularly prevalent in industries such as marine shipping and power generation, where large amounts of emissions are produced.

Here's how scrubbers typically work:

1. Gas Contact: Exhaust gases containing pollutants, such as sulfur oxides (SOx), nitrogen oxides (NOx), particulate matter, and other harmful compounds, are directed into the scrubber system.

2. Scrubbing Medium: Within the scrubber, the exhaust gases come into contact with a scrubbing medium. This medium can be water, chemicals, or a combination of both, depending on the specific pollutants targeted for removal.

3. Chemical Reactions: The pollutants in the exhaust gases react with the scrubbing medium. For example, sulfur dioxide (SO2) reacts with water to form sulfuric acid (H2SO4) in wet scrubbers. Chemical reactions may neutralize, dissolve, or transform pollutants into less harmful substances.

4. Particle Removal: Particulate matter, such as ash or soot, may be captured by the scrubbing medium through mechanisms like impingement, interception, or diffusion.

5. Separation: After the scrubbing process, the cleaned gas is separated from the scrubbing medium. In wet scrubbers, this separation is typically achieved through a mist eliminator or demister to remove excess water droplets.

6. Disposal or Treatment: The captured pollutants in the scrubbing medium must be disposed of or treated appropriately. This may involve further chemical treatment, filtration, or safe disposal methods to prevent environmental contamination.

Scrubbers can be categorized into several types based on their design and operation:

1. Wet Scrubbers: These scrubbers use liquid (typically water or a chemical solution) to remove pollutants from the exhaust gas stream through absorption or chemical reaction. Wet scrubbers are effective for removing acidic gases like sulfur dioxide (SO2) and particulate matter.

2. Dry Scrubbers: Dry scrubbers use dry sorbents, such as lime or activated carbon, to chemically react with and neutralize pollutants in the gas stream. Dry scrubbers are suitable for removing acidic gases like sulfur dioxide (SO2) and can be advantageous in situations where water usage is restricted or challenging.

3. Hybrid Scrubbers: Hybrid scrubbers combine elements of both wet and dry scrubbing technologies to achieve higher efficiency in pollutant removal. They may use a combination of liquid and dry sorbents to capture a wider range of pollutants.

Scrubbers play a crucial role in reducing air pollution and ensuring compliance with environmental regulations by significantly reducing harmful emissions from industrial processes and exhaust sources. However, their effectiveness, cost, and environmental impact depend on various factors such as the specific pollutants targeted, the type of scrubber used, and the operational conditions.

What is the difference between a wet scrubber and a dry scrubber?

Wet scrubbers and dry scrubbers are two common scrubbers for exhaust gas purification systems. Their working principles and application scenarios are different.

Wet scrubbers usually use water or alkaline solution as the scrubbing liquid, and are contacted with the exhaust gas through sprays or packed towers. The pollutants in the exhaust gas react chemically with the washing liquid or are adsorbed, thereby achieving the purpose of purifying the exhaust gas. This method is suitable for removing particulate matter, sulfides, nitrogen oxides and other pollutants, but it requires a large amount of water resources and produces waste liquid that needs to be treated.

Dry scrubbers do not use washing liquid, but remove pollutants in exhaust gas through filtration, electrostatic adsorption or catalytic conversion. This method is suitable for treating exhaust gas with lower humidity and less water content, and can avoid water pollution and corrosion problems, but the removal effect of certain pollutants may not be as good as that of wet scrubbers.

When choosing a scrubber, you need to choose the appropriate type based on the characteristics of the exhaust gas and the purification requirements. At the same time, the design and operation of scrubbers also need to take into account factors such as the type, concentration, flow rate, temperature, and pressure of pollutants to ensure purification effects and economy.