VANE MIST ELIMINATORS / CHEVRON DEMISTERS

Description

Operation Principle of Demister
For example, gas from liquid (L) converts to vapors (V) in distillers.
When vapors rise, the surface of liquid breaks to generate micro particles of liquid and deliver them with gas through demister.
In this process, micro particles increased in volume due to inertial collision principle on the surface of vanes.
When the gas stream passes through the vane demister and change direction, the liquid droplets are unable to change direction as quick as the gas due to their momentum.
So the liquid droplets impact on the chevron blade and then coalesce and form large droplets until drain away.
The inertia of the liquid droplets forces the entrained liquid droplets to impact on the vane surfaces where they form a liquid film and drain.
Particles that contain impurities free fall due to the weight of impurities.
Gas come through demister or contain liquid particles release as pure gas to the top of demister.

Overview
Effective separation of vapor and liquid is a primary requirement for efficient industrial processing.
With a vast range of fluids, physical properties, pressures, temperature, and flow-rates to cover, the mist eliminators offer effective separation across the board.
Mist eliminator is also called as demister and separator.
It is a type of filter that separates and removes mist or dust from fluid and a chemical reaction accelerator.
Demister can be semi-permanent, made of various materials according to condition of usage and its structure is very simple for convenient installation and repair.

Characteristics
Beside wire mesh pad, vane pack mist eliminators are the most widely used internals when the need is to separate liquid droplets carried by gaseous streams, which the liquid droplets are larger than 8 μm.
In the working principle, the vane demisters are different from the wire mesh pad demisters.
Vane, also known as Chevron, or corrugated plate type mist eliminators consist of a series of closely spaced zig-zag corrugated blades of plate, they are assembled as banks of parallel vane profiles.
They are to provide passage for vapor flow and profiled with angles to provide sufficient change of direction for liquid droplets to impact, coalesce and drain from the surfaces of the plates.
That force mist laden gas to follow serpentine paths.
Liquid drainage in the vane demister occurs outside the gas flow.
Vane pack mist eliminators are high capacity and high efficiency separators, they collect essentially 100% of all particles bigger than 20 to 40 microns in diameter, depending on the design parameters.
These equipment are generally not perfectly efficient for mist droplets smaller than about 20 microns, but they are sturdier than mesh pads and impose less pressure drop.
In the same environments, where the small solid particles present, vane demisters are the better choice for liquid and gas separator than the wire mesh pad demisters.
Simple Vane Pack profiles are particularly suitable for applications with a significant risk of fouling due to solid particles or high viscosity liquids in the feed.
Sectional installation of the vane banks allows installation and removal through the vessel manway.
Vane arrays can be mounted horizontally or vertically.
They are preferred in applications involving high vapor velocities, low available pressure drop, viscous or foaming liquids, lodging or caking of solids, slugs of liquid, or violent upsets.
They are sometimes used in combination with wire mesh pad demisters for optimum performance in special situations.
The gas with entrained liquid droplets flows between the vanes of separator.
The specifically designed channels form an inertial force trapping by impact all the mist and droplets.
The abrupt change in airflow direction produces an inertial force that affects the entrapped droplets.
The droplets are ejected from the gas stream by inertial force, impacting against the outer wall of the channel, forming a film on the channel wall.
This film then drains back to the circuit or collection channel via basic gravity, and coalesce to a size where they drop down and are collected and removed.
Vane arrays can be mounted horizontally or vertically.
They are preferred in applications involving high vapor velocities, low available pressure drops, viscous or foaming liquids. slugs of liquids, or violent upsets.
The vanes are rigid in construction and suitable for several services which may include high vapor velocity, high vibration, high temperature, high corrosion, or particulate fouling.
Engineered vane units commonly replace original wire mesh pad mist eliminators when one of these following conditions occurs:
-    Capacity of conventional wire mesh pad is exceeded.
-    High vapor capacity.
-    Low pressure drop.
-    Effective removal of high liquid loads.
-    Short service life and increased pressure drop due to mesh fouling.
-    Excessive corrosion of mesh wire occurs.

Mist Eliminator Design
The design of vane mist eliminators depends on many factors, but a preliminary sizing can be undertaken relatively easily using proprietary K factors in the same way as for wire mesh demisters.

Face area although it should be treated with caution and confirmed with us before actual use, the following:

Vvme = K . { (ρL - ρV ) / ρV } 0.5
Where:
Vvme = Max. velocity in vanes, m/s
K = K-factor, m/s
ρL = Density of liquid, kg/m3
ρV = Density of vapor, kg/m3
And:
Avme (m2) = Q (m3/s) / vvme (m/s)

Pressure Drop
The disadvantage of using the more expensive, pocketed designs is that the pressure drop is higher. To estimate the pressure drop, the following method can be used:
ΔP = C . (ρL – ρV) . K* K

Features and Benefits of Vane Demisters
Suitable for applications where solids or sticky and viscous liquids are present and would plug a wire mesh pad demister.
Suitable for both vertical and horizontal gas flow.
Good collection efficiency in low pressure drop and vacuum applications.
Suitable for higher liquid and gas loads.
High capacity, it can improve 30% to 100% more capacity than the wire mesh demister pad.
High filtering and separating efficiency.
Durable and long service life.
Resistance to fouling.
High tensile strength.
Custom-made design available

Materials
Available in varieties of metal and plastic material as follows:
1. Metal: SS304, SS304L, SS316, SS316L, others as request
2. Plastic: PP (Poly Propylene), PE (Poly Ethylene)

Specifications of Vanes
Vane thickness: 0.46 mm, 0.90mm, etc. depend on the material, type, and style
Vane height: 5", 8", 170mm, 235mm, etc. depend on the material, type, and style
Profile depth: 1/2" - 3/8", etc. depend on the material, type, and style
Vanes spacing: 20mm, 25mm, 30mm, 35mm, etc. depend on the material, type, and style

Applications of Vane Demisters
Vane demisters are widely used in various applications to separate liquid droplets from gas streams, in all applications where a contact between liquid and flowing gas, the vane demister can supply a good performance. Additional, tiny mist droplets can be carried away with the gas.
It is widely used in the foaming system and high liquid viscosity system in refineries, chemicals, petrochemicals, pharmaceuticals, dyes and intermediates, aromatics and other process industries.

Typical Applications of Vane Demisters
• Low Pressure Evaporators
• Refinery Vacuum towers
• Scrubbers in flue gas desulfurization (FGD) systems
• Pulp and Paper mills
• Sugar refinery