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KASRAVAND vane mist extractors can be found throughout the industry as production separators, three phase separators, knock-out drums, and in a variety of other applications where liquid removal is required. The separator and scrubber offer KASRAVAND's Vanes mist extractors for high efficiency reliable free liquid and aerosol mist removal. Units are available with or without slug catching ability, in vertical and horizontal configurations. Design is available in all major design codes and certifications. Sizes are available from 6" through 120" diameter. |
KASRAVAND Vane Separators employ vane technology that consists of closely spaced metal plates that form a serpentine flowpath. Specially designed flow channels trap collected liquids and allow them to drain without having to flow across the gas stream, or against it. In its basic configuration, the VS offers the most compact and cost effective utilization of vane technology. Other than a drain box at the base of the vane bundle, there are no other internal components.
Application
The Vane Separator (VS) is used in application that require a high efficiency, low pressure drop mist eliminator to remove entrained liquid droplets from gas, steam, or air, and where liquid slugging does not normally occur. As a vane separator, the VS is not rated for solids removal, although if solid particles are entrained in along with liquid droplets, those particles that are slowed or stopped by the liquids on the vane surfaces will be drained along with the liquids.
VGS vane separators are recommended for:
- Replacement for mesh pad type separators
- Natural gas transmission or processing for the removal of amines, glycols, absorption or lubricating oil
- Interstage or discharge of reciprocating compressors
- Steam service for removal of condensate and oil
- Air service for the removal of water and compressor lubricating oil
- When high turndown from the gas flow design point is desired
- Chemical and petrochemical facilities for the recovery of product and pollution control.
Performance
KASRAVAND vane separators are designed to perform at high efficiency while operating over a wide range of flows. The VS will effectively arrest droplets as small as 5 microns. Efficiency is influenced by particle size distribution and liquid loading. When particle size is below 5 microns, an internal upstream mesh pad or vane agglomerator/coalescer may be utilized. This integral part of the separator will raise the removal efficiency up to 99.5% of liquid droplets 1 micron and larger.
Design
KASRAVAND vane separators are available in standard in-line configuration (inlet and outlet 1800 apart at the same elevation), or any of seven (7) alternate configurations, to meet the needs of different piping arrangements. Vane assemblies (also known as vane bundles) have far greater structural integrity and are more mechanically robust than mesh pads. These features, plus the inherently more open architecture and resistance to plugging, allow the vane separator to be applied successfully in pulsating service (reciprocating compressors). No maintenance is normally required for these designs. Vane blades are available in carbon steel, stainless steel, duplex, titanium, zirconium, Hastelloy, Inconel, Monel, and other alloys. All VS separators feature an internal liquid sump below the vane bundle. These features assure that removed liquids are shielded from the gas flow, avoiding re-entrainment. Pressure drops across vane elements seldom exceed 1/3 PSI .
The primary function of a separator is to separate the inlet components as completely as the operating conditions allow. A major factor in separator internal design is the method used to "scrub" the gas. Three principals are used in gas-liquid separation gravity, centrifugal force and impingement. Gravity separation is used in all separators, and is frequently used in combination with centrifugal force and/or impingement
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In the simplest form, a horizontal separator operates on this principle. The inlet steam is directed through or against some device to break the inlet jet and distribute the flow across the vessel. Most of the liquid will fall into the liquid section in the bottom half of the vessel in less than a vessel diameter of horizontal gas travel. |
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There will be small particles of mist that will stay suspended longer and those below 10x10-6 (10 microns) may not be caught at all, since small particles settle slowly. They can be separated better if:
- The flow is made less turbulent.
- The length of fall required before touching and wetting a surface is short.
These can be accomplished by using parallel PLATE ASSEMBLY VANES sloped to permit liquid drainage, as showing in figure 1. If the flow were laminar (Reynolds number below 2000) the velocity of setting would be determined by Stokes Law:
Where:
= Diameter of particle, ft.
= Density of gas, #ft cubed (Actual) |u = Viscosity, #/ft sec |
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Gas flow in separators is seldom laminar due to the very low viscosity of gas, so Stokes Law does not apply directly. An empirical equation based on Stokes is used and assumes all particles down to an acceptable size are separated.
V = Allowable gas velocity through separator, ft/sec
k = Empirical constant
The velocity is easily calculated. It is the actual volume of gas flowing in ft3/sec (not standard ft3/sec) divided by the cross-sectional vessel area devoted to gas, sq. ft.
The "K" value is empirically determined and is approximately:
0.16 x (sep. length, ft) 1/2 - Horizontal separators to 20' long with parallel plate vanes
0.35 - Vertical separators
0.35 - Wire mesh in vertical separators or columns
With this formula and the "K" values, it is possible to size vertical and horizontal separators to separate bulk liquid and mist particles from gas.
However, if the steam is cooling it may be loaded with a fog of very tiny particles which do not settle with gravity. These particles of liquid will wet any solid surface they strike. Placing a large surface area in the flow path in such a way that the chances of a collision with a particle is almost certain as a means of fog removal. This large area could be, in its most common form, a pad of wire mesh, 4 to 8 inches thick. One commonly used knitted and crimped mesh has a density of 9lb/ft3, consisting of stainless steel x .011" O.D. wires of stainless steel, and 85 sq. ft. wire surface area cu. ft.
Mesh will coalesce virtually all of the 10 micron particles, and larger, and perhaps half of the 3 micron particles. Mesh also collects paraffin, hydrates or solid particles, if present, resulting in eventual plugging of the mesh. For this reason mesh is used more often in clean gas streams, such as in the top of a glycol-gas contact column. The collection efficiency of mesh is calculable by a method described in a paper by B.J. Warner and Frank Scauzillo of Mobile and published in the 1963 Proceedings of the Gas Conditioning Conference of the University of Oklahoma.
The impingement technique can be used with much less plugging possibility by using a pack of closely spaced vertical plate assembly vanes shown in previous figure 1. This configuration creates many flow direction changes causing centrifugal force to drive the stream to the outside of each turn while creating a drain path on the inside of each turn. An 8" section of plate assembly vanes has a particle removal capability similar to mesh, and has far better drainage characteristics, resulting in less plugging
Plate assembly vane mist extractors can be used in several configurations of separators, as shown in figure 2. The horizontal vane bundle has the highest liquid handling capacity because it allows incoming liquid to fall to the bottom ahead of the vanes and allows space for coalesced liquid blown from the trailing edge to fall to the liquid section.
Separator Configurations Using Plate Assembly Vanes
Configuration "A"
Horizontal Separator Longitudal Flow K=0.65
The attached figure 3 shows capacities for horizontal plate assembly vanes and will essentially remove 99% of 10 micron and larger particles.
The centrifugal force technique is usually used in vertical separators. Gravity separation alone in a vertical separator is inherently inefficient because the liquid particles must fall downward counter-current to the rising gas stream, where in horizontal flow the particle falls across the gas flow.
These vertical separators have a high gas capacity but do not handle liquid well above approximately 20 BBLS/MMSCF. The pressure drop is relatively high and the economic advantage over a horizontal plate assembly vane separator is questionable.
Configuration "B"
Vertical Horizontal Flow Separator 20" Approximate Min I.D. K=0.45
Configuration "C"
Horizontal Cross Flow Separator 24" Approximate m in I.D. K=0.45
Operating Pressure vs Gas CapacityFor Horizontal Model Separator
(Plate Assembly Vanes)
Gas 50% Diameter of Vessel
Gas Sp. Gr. = 0.65: Op. Temp. = 100 deg. F.
