Coalescers
When oil or other liquid hydrocarbons are mixed with water tiny droplets are created within one continuous liquid phase. This mixture will separate by itself only very slowly or not at all.
To separate such a mixture into different phases or components the physical method of coalescence is used.
Essentially the small droplets are brought in contact with each other to form larger droplets. These larger droplets can then be separated more easily, for instance by gravitation due to the different density of water and oil.
Types of coalescer systems
The tiniest fuel droplets are coalesced inside the special coalescer-fiberbed to form larger drops. Due to their difference in density these drops ascend into the collecting dome, from where the fuel is taken out for further use.
The drops flow along a path, which can be calculated during the design to assure that they are not drawn into the water outlet.
To remove water from fuel Repack-elements are used.
For high flow rates and low pressure drops they maintain moderate to good separation efficiencies during long operating times. Repack coalescers will remove free water with an efficiency of approximately 98% or better, depending on the Repack material used. The outlet concentration of the water in the fuel will be less of 100 ppm water or better.
The Repack element works as a depth element. The coalescence takes place inside the complete element, not only at the surface or within a thin layer. It is therefore used for long-time applications, usually several years before replacement.
In addition to the coalescence the Repack coalescer may be used as a particle filter.
Due to the large amount of Repack material there is space for many particles without clogging the system. Typically particles of less of 30-40 µm diameter will be removed.
They are concentrated at the top of the corrugated plates and will rise through the weep holes to the other collected oil above the plate-stack.
These plate-stacks are installed in the Coalescing plate-stack systems (CPS).
Our CPS are much more efficient and more compact than empty-tank type separators. In empty tank type separators only oil droplet of 100 – 150 µm and larger can be removed. Their outlet concentration may still contain a low quality of about 150 mg/l oil, whereas coalescing plate separators may be designed to remove droplets down to 10 – 20 µm or less with an outlet concentration down to 10 mg/l or less.
When it is necessary to remove oil or other hydrocarbons from water, coalescing plate-stack systems are often a good solution. They remove the oil using only gravity and a clever process design. They have a long operating life and require little maintenance. They contain no consumable items such as filter cartridges.
The recovered oil often has a sufficient quality to be recyclable.
The separation efficiency of the coalescing plate pack system is based on the maximum upward path for the oil droplets of only 6 or 12 mm and the wave form of the plates (corrugation) and therefore the wavelike but laminar flow path.
After a maximum of only 6 or 12 mm, respectively, the small oil droplets reach the plate above their respective flow channel, where they are captured by the hydrophobic/oliophilic material and thus removed.
The 2-stage coalescer contains coalescer cartridges as well as separator cartridges. The carefully selected types, numbers and lengths of the cartridges assure the optimized separation for each individual application.
Similar to the one-stage-coalescer small water droplets at the inlet are distributed/dispersed in the continuous hydrocarbon phase. The mixture flows through the coalescing stage, where the small droplets are united to larger drops (via coalescence).
In the second stage the system lets only pass the organic phase. The water is thus efficiently separated, the large water drops sink to the bottom and are removed at a separate outlet.
The 2-stage coalescer is the system of choice when the maximum efficiency is wanted. It is also used to assure that particles are kept away from the hydrocarbon product, for instance in turbine fuel.
