There are four major types of basic configurations of separators, generally available from manufacturers: vertical, horizontal single tube, horizontal double tube, and spherical. Each type has specific advantages, and selection is usually based on which one will accompolish the desired resutls at the lowest cost.
Vertical
A vertical separator is often used on low to intermediate gas-oil ratio well streams and where relatively large slugs of liquid are expected. It will handle greater slugs of liquid without carryover to the gas outlet, and the action of the liquid level control is not as critical. A vertical separator occupies less floor space, an important consideration where space might be expensive as on an offshore platform. Due to the greater vertical distance between the liquid level and the gas outlet, there is less tendency to revaporize the liquid into the gas phase. However, because the natural upweard flow of gas in a vertical vessel oppposes the falling droplets of liquid, it takes a larger-diameter separator for given gas capacity than a horizontal vessel. Also v ertical vessels are more expensive to fabricate and ship in skid-mounted assembles.
In operation an inlet diverter spreads the inlet fluids against the vertical separator sheel in a thin flim and, at the same time, imparts a centrifugal motion to the fluids. This provides the desired momentum reduction and allows the gas to escape from the thin oil film. The gas rises to the top of the vessel, and the liquids fall to the bottom. Some small liquid drops will be swept upward with the rising gas stream. These drops are separated by a centrifugal baffle arrangement below the gas-outlet connection.
Horizontal Single Tube
The horizontal separator may be the best separator for the money. The horizontal separator has a much greater gas-liquid interface area consisting of a large, long, baffled gas separation section which permits much higher gas velocities. This type of separator is easier to skid-mount and service, and requires less piping for field connections and a smaller diameter for a given gas capacity. Several separators can be stacked easily into stage-separation assembilies, minimizingspace requirements.
In operation, gas flow horizontally and, at the same time, falls toward the liquid surface. The gas flows in the baffle surfaces and forms a liquid film that is drained away to the liquid section of the separator. The baffles need only be longer than the distance of liquid trajectory travel at the design gas velocity. The liquid level control placement is more critical than in a vertical separator, and surge space is somewhat limited. Horizontal separators are almost always used for high gas-oil ratio well streams, for foaming well streams, or for liquid-from-liquid separation.
Horizontal Double Tube
A horizontal double-tube or double-barrel separator has all the adavantages of a normal horizontal separator plus a much higher liquid capacity. Incoming free liquid is immediately drained away from the upper section into the lower section. The upper section is filled with baffles, and gas flow is straight through and at higher velocities.
Spherical
Spherical separators offer an inexpensive and compact vessel arrangement. However, these types of vessels have a very limited surge space and liquidsetting section. The placement and actions of the liquid level control in this type of vessel is very critical.
Three-phase or oil-gas-water separation can be easily accomplished in any type of separator by installing either special internal baffling to construct a water leg or water siphon arrangement, or by using an interface liquid level control. A three-phase feature is difficult to install in a spherical separator due to the limited internal space available.
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