Knitted Wire Mesh Pads can be used as effective coalescers in both Liquid-Liquid and Vapour-Liquid service. Mesh Pad style, face velocity and configuration will depend on the specific application.

Liquid-Liquid Applications

Mixtures of immiscible liquids can generally be separated by a process of settling as a result of the density difference between the two phases. However gravitational settling becomes increasingly difficult as the droplet size of the dispersed phase decreases.The settling process can be enhanced considerably by passing the dispersion through a suitable coalescer pad. Liquid-Liquid separator vessels are usually arranged horizontally as shown right.
The Coalescer Pack is used to enhance the separation of Liquid Dispersions and consists of layers of composite materials chosen to suit service conditions. Generally a metallic wire monofilament is co-knitted with a fibre material which has a surface which is preferentially wetted by the dispersed phase. For hydrocarbon in water dispersions, a thermoplastic fibre is preferred and for water in hydrocarbon dispersion a specially treated glass fibre is used. It is therefore always important to know which is the dispersed phase in the mixture. Whilst the right choice of fibre material ensures maximum collection of the dispersed droplets, the effect of the difference in surface free energies of the monofilament wire and fibre materials in close proximity promotes droplet coalescence. Dispersions of droplets sized over 1000 microns tend to be very unstable and separate apidly under gravity. Dispersions of droplets sized below 10 microns tend to be very stable and do not easily separate. Wire Mesh Coalescers as shown above are very effective in coalescing all droplets as small as 30 microns into droplets greater than 1000 microns. The Coalescer Pack should be sized as follows:
Generally similar principles apply to Coalescer Pads in vertical Liquid-Liquid Extractor columns. A 150mm thick pad of composite knitted wire mesh, preferentially wetted by the dispersed phase, installed above the packed section will coalesce dispersed phase droplets hence improving phase separation and reducing entrainment.

Vapour-Liquid Applications

Standard Knitted Wire Mesh Mist Eliminators can be designed to remove almost 100% of all liquid droplets greater than 5 microns from vapour streams. Liquid droplets smaller than 5 microns however are not easily removed. The installation of a properly designed Coalescer below the Mist Eliminator will affect the removal of 98% of all liquid droplets down to 2 microns. The Coalescer Pad is normally composite material consisting part monofilament and part staple fibre yarn exhibiting along its length the ends of the staple fibres. The ends of these fibres are much smaller in diameter than either the yarn into which they are spun as well as being smaller in diameter than the monofilament. The mass of fibrous ends reduces the streamline effect on the gas flow and traps the fine droplets which subsequently coalesce into larger droplets. These larger droplets are re-entrained by the gas stream but are easily removed by a conventional mist eliminator installed downstream.

Competitive Advantage

The advantages of the Saiptech coalescers are:

• Compact solutions
• Maximize overall liquid separation
• Excellent turndown performance
• Low pressure drop
• Clean & fouling service available
• Maintenance free
• Removable through Man Way