Liquid liquid coalescers are physical separation devices that function on the principle of “Intra-Media Stokes Settling” or “Direct Interception”.
Traditionally, gravity separators were used to handle emulsions before the use of coalescing media became commonplace. In this equipment, differences in densities of the two liquids cause droplets to rise or fall by their buoyancy. The greater the difference in densities, the easier the separation becomes. Rising (or falling) droplets are slowed by frictional forces from viscous effects of the opposing liquid.
Whether engineering a new coalescer vessel, or debottlenecking an existing separator, full knowledge and understanding of the basic principles involved are required. The design should be treated as a system design rather than an equipment design, as, neglecting this fundamental principle may result in inadequate performance. Often overlooked are the capabilities of properly selected and designed internals for the enhancement of simple gravity separation, location of coalescing equipment’s due to mechanical constraints, residence time as the length needs to be as short as possible, velocities of continuous & dispersed phase as the diameters are fixed, potential of fouling due to presence of solid, inversion point etc.
In principle, meshes, co-knits of wire and yarns; and wire and glass wools all depend primarily on Direct Interception where a multiplicity of fine wires or filaments collect fine droplets as they travel in the laminar flow streamlines around them. In general, they can capture smaller droplets than those that depend on enhanced Stokes Settling. A general rule with Direct Interception is that the size of the target should be close to the average sized droplet in the dispersion. Finer coalescing media allow for the separation of finer or more stable emulsions. Note that fine media will also capture or filter fine solid particulates from the process stream.
Therefore, unless the emulsion is very clean, an upstream strainer or filter is needed to protect a high efficiency coalescer.
Parallel Plate Coalescer comprised of parallel plates with a specific plate angle (typically 45° or 60°) and is used to accelerate gravity separation based on “Stokes Law” or the Stokes Settling principle. The plate spacing and the plate angle varies depending upon the service, efficiency requirements and the fluids physical properties.
Intra media stokes settling relies on stokes settling and the flow is divided in smaller channels based on the plate spacing, and the distance the dispersed droplet needs to travel is the function of plate spacing and plate angle. This division in smaller channels reduces the Reynolds number (laminar regime), which favors liquid-liquid separation and the distance a specific droplet needs to travel to coalesce with other droplet is reduced, which helps in reduction of residence time subsequently the footprint of the separator.
The parallel plate coalescer is often used in practice not only due to the gain in separation efficiency and reduced vessel sizes, but also due to the capabilities to handle solids which are commonly present in the feed. The design for the parallel plate coalescer can account for potential solids in the feed and include features to mitigate the fouling and offer longer runtimes between shutdowns or cleaning cycles.
Stokes Pak™ Coalescer, is corrugated foil similar to structured packing. It poses higher surface area than plate pack, however, is less intolerant of solids as compared to parallel plate pak coalescer, and hence are more commonly used for moderate fouling services. It is generally arranged with vertical sheets and are available with different surface area, crimp height and angle. The surface of the foil is smooth without any dimples and perforations.
Stokes-Pak™ Coalescer is available is variety of surface area ranging from 125 m2/m3 upto 250 m2/m3. Higher surface area is also available depending upon specific requirements.
The AMACS MAXSWIRL™ Hydrocyclone, typically made out of duplex, is an axial flow hydrocyclone wherein that the swirl is generated in the same (axial) direction of the flow through the cyclone. Traditional hydocyclones generate the swirling flow by tangential inlet(s), which are perpendicular to the flow inside the hydrocyclone liner.
The oily water entering the inlet of the cyclone will be forced into a rotation by a static swirl element. This aero dynamically designed swirl element generates high centrifugal forces (G-Forces) and these high G-forces, in combination with a stabilised flow, result in high separation efficiencies. Due to the centrifugal forces, the light liquid phase (oil) will be forced inwards by the heavier liquid phase (water) that itself is forced outwards. In the tapered section of the hydrocyclone, an oil core is created which together with a small percentage of the water changes direction and exits the hydrocyclone at the front, through a small channel in the swirl element (reject side). The main stream of the water, essentially free from oil, will flow further through the tapered section towards the water outlet nozzle where a flow control valve will provide a back pressure to ensure a proper hydraulic balance.
AMACS Coalescing Media is available in a wide range of metallic alloys (ex. 304 SS, 316 SS, Monel, Alloy 20, duplex and Hastelloy) and polymers (ex. Polypropylene, Dacron and Teflon) and Fiberglass. Our applications engineers are happy to assist you in selection of the appropriate coalescing media for your process.