The mist eliminator, also known as a demister or entrainment separator, is an essential component in a scrubber or wet gas cleaning system. Its primary function is to remove liquid droplets (mist) from a gas stream, ensuring that the gas leaving the scrubber is clean and free from contaminants. Scrubbers are commonly used in industrial applications to remove pollutants, particulates, and gases from exhaust air.

Mist eliminator works within a scrubber:

1. Gas Inlet: Polluted or contaminated gas enters the scrubber from an industrial process.

2. Liquid Injection: The scrubber introduces a liquid, often water or a specific chemical solution, to the gas stream. This liquid reacts with and absorbs the contaminants in the gas.

3. Contacting and Mixing: The gas and liquid mix together, creating a turbulent environment where the pollutants come into contact with the liquid. This process allows the contaminants to dissolve or be captured within the liquid.

4. Mist Formation: During the gas-liquid interaction, mist or fine droplets of the liquid can form and become entrained in the gas stream. These mist droplets need to be removed to ensure that the cleaned gas is free from any liquid carryover.

5. Mist Eliminator Stage: The mist eliminator, typically placed downstream of the gas-liquid contacting and mixing section, captures and separates these mist droplets from the gas. It consists of various components such as vanes, wire mesh, or other structures designed to intercept and coalesce the mist droplets. These components provide a large surface area for the droplets to collect and merge, eventually forming larger droplets that are too heavy to remain entrained in the gas. These larger droplets then drip back into the liquid phase of the scrubber.

6. Clean Gas Outlet: After passing through the mist eliminator, the gas stream is now cleaner and free from the liquid droplets. It exits the scrubber as a treated and purified gas.

Mist eliminators are crucial for maintaining the efficiency and effectiveness of wet scrubbers, as they prevent liquid carryover, which could potentially lead to issues like corrosion, clogging, or environmental non-compliance. The design and choice of mist eliminator depend on factors such as the type of contaminants being removed, the gas flow rate, and the specific requirements of the industrial process.

Few common styles of scrubber defoggers:

1. Wire Mesh Demister Pads:

• Wire mesh demister pads are widely used in scrubber defoggers. They consist of layers of woven wire mesh designed to capture mist or droplets from the gas stream.

• Gas containing mist or fog passes through the wire mesh, and the mist droplets coalesce and collect on the mesh surfaces.

• These demister pads are commonly used in vertical or horizontal gas scrubbers and are easy to install and maintain.

2. Vane Type Defoggers:

• Vane type defoggers use a series of vanes or blades arranged in the gas stream.

• The vanes force the mist-laden gas to change direction multiple times, allowing the mist droplets to impact and collect on the vane surfaces.

• Vane defoggers are effective at removing mist from gas streams and are used in various industrial applications.

3. Fiber Bed Defoggers:

• Fiber bed defoggers use a bed of fibers or packing material to capture mist and droplets.

• Gas passes through the fiber bed, and the mist droplets are captured on the fibers through impaction and coalescence.

• These defoggers are often used in acid gas scrubbers and other applications where fine mist removal is crucial.

4. Cyclonic Defoggers:

• Cyclonic defoggers use a cyclone separator design to remove mist and liquid droplets.

• The gas stream enters the cyclonic chamber and is forced to spin in a cyclonic motion. This causes the mist to separate from the gas and collect at the bottom of the cyclone.

• Cyclonic defoggers are effective for applications with high gas flow rates and where a compact design is necessary.

5. Mesh-Pad Type Defoggers:

• Mesh-pad type defoggers combine wire mesh demister pads with vane technology.

• They consist of a mesh pad positioned in the gas stream with vanes located behind it.

• The mesh pad captures mist droplets, and the vanes enhance the coalescence process, making them highly efficient.

6. Impingement Plate Defoggers:

• Impingement plate defoggers utilize a series of plates or baffles in the gas stream.

• The mist-laden gas is forced to impact on the plates, and the mist droplets coalesce and run down the plate surfaces.

• They are suitable for applications where high mist removal efficiency is required.

The choice of scrubber defogger style depends on factors such as the gas flow rate, the nature of the mist or fog to be removed, space constraints, and the specific needs of the industrial process. Each style has its advantages and limitations, and the appropriate design should be selected based on the unique requirements of the application.