Vapor flowing at high velocity carries liquid particles with it. This phenomenon is called “entrainment”. A demister pad is an entrainment eliminator. In simple words, a demister pad is a “liquid-vapour separator”. A properly installed demister can achieve up to 99.9% separation efficiency, with a nominal pressure drop.
Demisters can reduce the residence time required to separate a given liquid droplet size thereby reducing the volume and associated cost of separator equipment. Demisters are often used where vapor quality is important in regard to entrained liquids; particularly where separator equipment costs are high (e.g., high pressure systems) or where space or weight savings are advantageous.
The principle of demister operation is based on having a large number of obstacles intercepting entrained droplets in a vapor flow. This large number of obstacles must provide minimum drop in pressure over the removal system.
The demister is employed where the liquid droplet size is below 10 microns. The pad is made up of knitted mesh of metallic or synthetic material. The vapor is made to pass through this mesh, causing the vapor to flow freely but the liquid droplets being entangled due to inertia.
The droplets stick to the mesh surface for a brief period of time. As more and more droplets collect, they coalesce into a larger droplet, gaining weight and eventually falling off due to gravity. The vapour thus separated is almost free of liquid.
Material Of Construction:
Some of the commonly used materials are:
The demister pad is designed depending on factors like vapour-velocity, liquid particulate size, fluid viscosity, surface tension, temperature, pressure and pressure drop required, nature of fluid passing through, man-hole size, ease of handling, etc.
The demister pads come in various sizes and forms depending on the shape of the vessels they are to be fitted on. Small sized demisters are directly knitted while larger sized are cut into segments and held together by grids and supporting rods. These accessories help in easy handling of the pad. The segment size of the demister usually depends up on the man-hole size provided on the vessel.
The formation of mist leads to process inefficiencies, downstream damages to vessels as well as product loss. A properly designed demister pad is employed for one or more of the following reasons:
We manufacture the following types of mist eliminators in our facilities:
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