Whenever there is a contact between gas and liquid in the column, there will be maximum chances of entrainment. It’s just entrapment of one substance by another one along with contaminants. Such mist and liquid droplets cannot be vented off directly to the atmosphere. And it can lead to serious losses of the process fluid and equipment damage in mass transfer operations.

This entrained component can be easily get separated by using demister pad. This pad can directly convert entrained vapours/mist into liquid and traps the vapours to get vented off with gas. It helps to collect entrained vapours in the form of liquid drops and separates it from gaseous mixture. The main working principle of Demister is to separate liquid by coalescing smaller liquid droplets from the gasses and allow it to get drop into the liquid pool.

Coalescing of smaller liquid droplets is due to different types obstructions made in the path of vapours. It allows vapours to pass through obstruction where the pressure drops created in the vapour leads to formation of liquid droplet, and only gasses to flow from the demister device by the mechanical separation.

Demister pad can also be called as mist eliminator, mist pad, wire mesh demister, catching mist and mesh mist eliminator also. Demister pad can install directly on the outlet of the top vapour or at the top of the packing tower.

Working Principle of Demister Pad

When mist in the gas rises at constant speed, then the mist eliminator works where, vapour strikes the mesh surface filament and liquid start coalescing. After some time, liquid droplet size goes up and it gets isolated from the filament

Application of Demister Pad

This Demisters can mainly use in,
1. Distillation columns
2. Absorption columns
3. Oil Mist Separation
4. Steam Boilers
5. Gas and Air scrubbers
6. Knockout Drums
7. Effluent gas treatment in Sulphuric Acid Factories.
8. Vacuum Towers and Drying Towers.

Mesh Type Demister Pad

In this type of pad, vapours just strikes the mesh filaments of mist and initiates the coalescing of small droplets. And further, it leads to dropdown of droplet to the pool. Main advantages of demister pad to increase mass transfer efficiency and to reduce board spacing.

Advantages

1. Relatively Inexpensive.
2. Efficient at removing particles down of specific size.

Subtypes of the Mesh Type Demister Pad

Different types of Mesh Type Demister pad are classified on the basis of mesh density has been mentioned in the below chart-

Style Material Application Wire

Diameter

mm

Mesh density

Kg/m3

Surface Area

m2/m3

Voidage

%

Nominal Micron Rating*
SCM-A1 Metals Very high efficiency in clean service 0.15 195 650 97.5
SCM-A2 Metals Fine droplet removal in clean service 0.15 145 480 98.2
SCM-A3 Metals General purpose, clean service 0.15 112 375 98.6
SCM-B1 Metals Optimum efficiency & pressure drop 0.275 195 355 97.6
SCM-B2 Metals General purpose, not totally clean 0.275 170 310 97.9
SCM-B3 Metals Heavy duty e.g. oil & gas separators 0.275 145 265 98.2
SCM-C1 Metals Light fouling 0.275 110 200 98.6 10µ
SCM-C2 Metals Moderate fouling 0.275 80 145 99.0 12µ
SCM-C3 Metals Heavy fouling e.g. evaporators 0.275 50 90 99.4 15µ
SCM-PP1 Polypropylene Acid mists 0.25 75 1120 93.0
SCM-PP2 Polypropylene Chemical Scrubber towers 0.25 50 750 95.3
SCM-T Teflon Very corrosive services 0.25 64 480 97.0
SCM-PP3 Polypropylene Low pressure drop e.g. air scrubbers 0.25 33 490 96.9 10µ
SCM-A1X Metal/PP Mix Mist removal of polar/Non- polar mixtures 0.25 200 625 95.6

Mist Eliminator

Mist Elimination, removal of liquid droplets from the vapour is one of the most commonly encountered process. Unfortunately, Mist Eliminators are most ignored commodities to available technologies and design parameters. The well-engineered mist eliminators can reduce liquid carryover by a factor of one hundred or more relative to a standard unit, drop head losses by more than 50%, increases capacity by factors of three or four. Overall approach is to cost effective operation by avoiding solvent losses, emissions and extending equipment life and maintenance cycles using proven and cost effective techniques.

Vane Type Mist Eliminator

In this type, the bends of the vane allows the vapour to flow from various directions, and helps to break inertia, momentum. Where liquid droplets strike the adjacent vanes and starts coalescing the droplets.

Applications:
  • Used when the Solid particles present in the process fluid.
Advantages
  • Used for viscous, suspended solid or large droplet size vapours.
  • Provides high efficiency at low pressure drop.
Specifications
  • Simple structure.
  • Lightweight and easy to transport.
  • High porosity, less pressure drops.
  • Large surface area and high separating efficiency.
  • Easy to install, operate and maintain.
  • Durable and long service life.
  • Corrosion and rust resistance.

Selection Criteria

When solids are present in the gas then demister pad can’t be a choice. Selection of Vane type mist eliminator will be the perfect option. Further selection is depending upon pressure drop, efficiency of the device. We aredesigning each device with wellcustomized and specialized software for getting optimized efficiency and pressure drop calculation for particular applications.

TYPES –

In Mist Eliminator device, more the passes, more will be the efficiency of separation. That’s why different types of the devices can be a choice as per the process requirement.

1. VV TYPE-

Comprises plate type vanes for entrained droplet separation.

2. VH1 TYPE-

Comprises one extra vane for better effective mass transfer.

3. VH2 TYPE-

Comprises two extra supporting vane plates with respect to angle of vanes to get more optimized results.