Mist Eliminators


Mist Elimination
Mist eliminators have been widely used in process equipment to remove entrained liquid droplets. The most commonly used de-entrainment device is a mesh pad mist eliminator. When mesh pad mist eliminator cannot be used in fouling service and/or high liquid load condition, vane pack mist eliminator is highly recommended. A combination of vane and mesh pad is used as an option to increase efficiency where the exiting gas stream requires very small amounts of entrainment.
Liquid Droplets Formation
Regarding the droplet formation, there are three primary mechanisms as below.

• Mechanical Action
• Condensation
• Chemical Reaction

Liquid droplets can be formed by contact between gas and liquid in a mass transfer operation, or by condensation on the surface of heat exchanger. Droplets can be also formed from gas phase reactions which yield a liquid product. The liquid droplet size depends on the mechanism which entrainment can be generated as shown in the chart. Droplet size is essential for a proper mist eliminator design.
Removal of Entrained Liquid Droplets
In the removal of entrained liquid from a gas stream, 100% efficiency often cannot be achieved. The extent and nature of the shortfall which is acceptable depends on the process objectives, which may be categorized as follows :

✔ Avoid carry over of liquid which could cause damage to downstream equipment, eg. by accumulated liquid slugging into a reciprocating compressor.

✔ Avoid carry over of specific components in the entrained liquid :

• product contaminants (eg. colored molecules)
• process contaminants (eg. which would poison catalyst in a downstream process)
• high value circulating process materials (eg. selective solvents, or catalyst solutions)
• solids in solution which polymerize (these may cause blockage in downstream equipment)

Removal of the specific components may be required to a very high efficiency, but carry over of liquid which does not contain these components may well be quite acceptable.

Applications of Mist Eliminators
In most cases, the entrainment should be removed to protect equipment damage and prevent potential process or environmental contamination. Use of mist eliminators is an effective solution to liquid entrainment problems in many process applications described below.

Protect downstream equipment

Mist eliminators protect downstream corrosion and damage to equipment such as compressors, blowers, driers, and turbines.

Improve product purity

Mist eliminators improve the purity of overhead gas and side draw-off liquid in packed and trayed towers.

Prevent contamination

Mist eliminators prevent the poisoning of expensive downstream catalysts and potential contamination problems.

Increase recovery of valuable chemicals

Mist eliminators reduce losses of expensive chemicals such as glycols, amines, or solvents in absorption and regeneration towers.

Reduce environmental pollution

Mist eliminators help reduce droplet emissions from acid plants to environmentally acceptable levels.

Mesh Pad Mist Eliminators

Mesh pad mist eliminators are fabricated from fine wire which is crimped to form a double layer. This double layer material is then either rolled into a cylinder or layered to form the desired thickness of mesh pad. This arrangement provides free volumes of 90 to 99% with surface areas from 160 to 2000 m2/m3. As the vapor carrying the entrained liquid passes through the mesh, the liquid droplets impinge and adhere to the fine wire, coalesce, and drain by gravity.

• High efficiency with low pressure drop
• Easy to install in all process equipment
• Most cost-effective solution

Materials of Construction
• Stainless Steels
• Nickel Alloys
• Titanium
• Aluminum
• Copper
• Polypropylene
• Fluoroplastics

Separation Mechanisms
On mesh pads, liquid droplets in the entering gas stream are captured by three mechanisms: Inertial Impaction, Direct Interception, and Brownian Diffusion.

Inertial Impaction occurs when the droplets have sufficient momentum and cannot follow the gas stream. Direct Interception occurs if the gas streamlines carrying the droplets are close to the wire for contact. Diffusion results when the droplet mass is very low and the droplets are deposited by Brownian motion on the wire surface.

Droplets larger than 1 micron are removed by impaction and interception, whereas droplets smaller than 1 micron are removed mainly by diffusion.

※ If the entire table is not visible, you can scroll the table left and right to check the entire table..

Density, kg/㎥ Surface Area, ㎡/㎥ Voids, % Hanbit Soltech Equivalent Mesh Style
Metal mesh mist eliminators
80 157 99.0 HST-80 931 (708) B 7CA
120 210 98.5 HST-120 422    
128 459 98.4 HST-128 326 (194)   3BF
144 282 98.2 HST-144 431 (172) A 4CA
193 375 97.5 HST-193 421 (709) C 4BA
220 905 97.2 HST-220      
432 2000 94.6 HST-432 333   X-100
Plastic mesh mist eliminators
42 360 97.0 HST-193P   F  
64 430 96.5 HST-300T 221 D 8T

Vane Pack Mist Eliminators

Vane pack mist eliminators are high capacity droplet separators consisting of plates with parallel chevron profiles. These mist eliminators are generally not efficient for droplets smaller than about 20 microns, but they are suitable for applications with high vapor velocities, low available pressure drop, viscous liquids or a significant risk of fouling due to solid particles. The vane packs are classified into various styles depending on the direction of the gas flow and the features of the vane profile.

• High capacity with low pressure drop
• Ideal for viscous liquids or fouling service
• Mechanically durable construction

Materials of Construction
• Stainless Steels
• Carbon Steel
• Nickel Alloys
• Titanium
• Polypropylene
• Fluoroplastics

Separation Mechanisms
Vane pack is a kind of impingement separators that capturing droplets by inertial impaction.

The vane profiles allow the gas to change direction several times from inlet to outlet. The changes in gas flow direction combined with inertia of the entrained liquid droplets cause impingement of the droplets onto the plate surface. The liquid droplets impinge and adhere to the surface at each curve, eventually coalescing into larger droplets which then drain by gravity.

With vertical flow, collected liquid drips from the bottom of the vane and falls through the rising gas. With horizontal flow, a drainage path is required at the bottom of the vane.

Double Pocket Vane Pack
Double pocket vane packs offer higher capacity and efficiency than standard vanes. Liquid droplets separated from the gas flow are collected in special pockets that prevent liquid re-entrainment. This design allows more efficient mist removal and increases the gas handling capacity. The Double pocket vane is applied for debottlenecking of existing equipment or the new vessel design, which can reduce the vessel size.

※ If the entire table is not visible, you can scroll the table left and right to check the entire table..

Profile Z - profile C - profile Z – profile w/ hooks C – profile w/ pockets
Flow Direction Vertical Vertical or Horizontal Horizontal Vertical or Horizontal
K-values 0.50 ft/s 0.55-0.75 ft/s 0.65 ft/s 1.00 ft/s
Efficiency Medium Medium Medium - High High
Pressure drop Low Low Low Moderate
Applications General use Low cost General use Horizontal scrubbers Debottlenecking