Separators

[h=Mist Extractors]3[/h] The two types of mist extractors most commonly used in oil and gas separators are knitted wire mesh and vane. Mist extractors cause small entrained particles to form into larger droplets. As the gas stream passes thru the mist extractor, the surfaces of the mist extractor itself are wetted with the entrained liquid particles. Continued contact with the wetted surfaces causes coalescing into larger droplets. This action is promoted by the changing of direction forced on the gas by the tortuous path it must take to get thru the mist extractor. When the droplets reach sufficient size to overcome the lifting force imposed by the gas velocity, they will fall into the liquid accumulator section of the separator. The standard mist extractor for KW International separators is the knitted wire mesh.
[h=Knitted Wire Mesh Mist Extractors]3[/h] Knitted wire mesh mist extractors consist of horizontal or vertical pads of knitted stainless steel or monel wire mesh either in layers or wound for insertion into the separator. On vertical separators the pad is placed in the horizontal position near the top of the vessel. Horizontal separators use vertical pads near the gas outlet end of the separator. The pads are generally 4" to 6" thick and can vary in bulk density depending upon the particle size to be removed and the efficiency of removal desired. Wire mesh mist extractors normally are designed to remove 99% of all liquid particles which are 10 microns or larger.
[h=Vane Type Mist Extractors]3[/h] Vane type mist extractors are the most efficient. They are standard on KW International vertical scrubbers where large volumes of gas must be handled with small liquid loads and are available in any type of KW International separator. Vane type mist extractors consist of a series of parallel impingement baffles which provide the surface area for the small entrained particles to collide and coalesce into larger drops. The vanes are also arranged to cause the gas stream to change direction and velocity; creating a centrifugal force and thereby improving the collection and coalescing of the small liquid particles. Vane type mist extractors are the best units to use with wellstreams containing paraffin or wax since they do not plug as readily as the knitted wire mist units.
[h=Separators: Three-Phase Operation]3[/h] Three-phase operation in vertical and horizontal separators requires different internal construction to assure dependable operation. Experience has proven that it is wise to use a longer retention time to obtain better water-oil separation. The standard retention time for 3 phase separator design is 3 minutes. This results in a reduction of the overall liquid capacity for any given size separator as compared to 2-phase operation which is based on one minute liquid retention time. Separation of the water and oil is simply due the specific gravity difference of the two liquids. A separator cannot separate water and oil that exists as an emulsion. The water and oil must be as free liquids in the separator. In the vertical separator, three-phase operation is similar to the two-phase operation previously discussed except that all the separated liquids drop on to a divider or isolation baffle located above the liquid accumulation section. From this baffle the liquids flow through a down comer into the liquid section where the water and oil are released below or near the water-oil interface. This assures that the water does not have to settle through the separated clean oil, thereby providing efficient oil-water separation.
Three-phase operation in horizontal separators varies from the two-phase operation in the liquid zone only. Instead of being controllable as in the two-phase separator, the liquid level in the 3-phase separator is set by the oil spillover height. There are two types of construction used in three phase separators. These are "oil spill-over baffle" and "bucket and weir". The water-oil interface level in the bucket and weir system is not controllable unless the weir height is made to be adjustable.
The oil spill over type operates with a gas-liquid interfacial control for the oil and water-oil interfacial control for the water.
The bucket and weir type arrangement is used so that a gas-liquid interfacial control is used on the oil and the water in their own separate compartments for positive control.
In horizontal three phase separators, since the liquid top level is usually set by a baffle at 50% of the vessel cross-section the gas capacity of a given size will usually be reduced compared to a horizontal two phase separator. This applies to both types of three-phase design in the liquid section.