SEPARATION AND PROCESSING OF OIL WATER AND NATURAL GAS

There are many characteristics you must know in order to construct a right separator especially the interior of a separator. Here, you have to take into account and consideration on how to build it.

Internal Construction of Separators:

  • The principal item of construction that should be present is a good liquid gas separator are the same, regardless of the overall shape or configuration of the vessel. Some of these features are as follows:
  • A centrifugal inlet device where the primary separation of the liquid and gas is made.
  • A large setting section of sufficient lenght or height to allow liquid droplets to settle out of the gas stream with adequate surge room for slugs of liquid.
  • A mist extractor or eliminator near the gas outlet to coalesce small particles of liquid that will not settle out by gravity.
  • Adequate controls consisting of level contro, liquid dump valve, gas back pressure valve, safety relief valve, pressure gauge, gauge glass, instrument gas regulator, and piping.

The bulb of the gas-liquid separation occurs in the inlet centrifugal separating section. Here, the incoming stream is spun around the walls of a small cylinder, which would be the walls of the vessel in the case of a vertical or spherical separator. This subjects the fluid to a centrifugal force up to 500 times the force of gravity. This action stops the horizontal motion of the free liquid entrained in the gas stream and forces the liquid droplets together where they will fall to the bottom of the separator into the settling section.

The settling section lets the turbulence of the fluid stream subside and allows liquid droplets to fall to the bottom of the vessel due to the difference in the gravity between the liquid and gas phases. A large open space in the vessel is adequate for this purpose. Introduciong special quieting plates or baffles with narrow openings only complicates the internal construction of the separator and provides places for sand, sludge, paraffin, and other materials to collect and eventually plug the vessel and stop the flow. The separation of liquid and gas using the centrifugal inlet feature and a large, open settling section produces a more stable liquid product, which can be contained in atmospheric or low-pressure storage tanks. Minute scrubbing of the gas phase by use of internal baffling or plates may produce more liquid to be discharged from the separator, however the product will not be stable since light ends will be entrained in it., incurring more vapor losses from the storage system.

Another major item required for good and complete liquid-gas separation is a mist eliminator or extractor near the gas outlet. Small liquid droplets that will not settle out of the gas stream, because of little or no gravity difference between them and the gas phase, will be entrained and pass out of the separator with the gas. This can be almost eliminated by passing the gas through a mist eliminator near the gas outlet, which has a large surface impingement area. The small liquid droplets will hit the surfaces, coalesce, and collect to form larger droplets that then drain back to the liquid section in the bottom of the vessel. A stainless steel woven-wire mesh mist eliminator is probably the most efficient type since it removes up to 99.9% or more of the entrained liuquids from the gas stream.

Types of Separators

There are four major types or basic configurations of separators, generally available from manufacturers: Vertical, Horizontal single tube, Horizontal double tube, and spherical. Each type has specific advantages, and slection is usually based on which one will accomplish the desired results 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.

CONVENTIONAL VERTICAL SEPARATOR

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, and important consideration where space might be expensive as on an offshore platform. Because of the greater vertical distance betwwen the liquid level and the gas outlet, there is less tendency to revaporize the liquid into the gas phase. Nevertheless, because the natural upward gas flow in a vetical vessel opposes the falling droplets of liquid, it takes a larger-diameter separator for given gas capacity than a horizontal vessel. Also, vertical vessel are more expensive to fabricate and ship in skid-mounted assemblies.

 Horizontal Single Tube:

This 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 that permits much higher gas velocities.

CONVENTIONAL HORIZONTAL SEPARATOR

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 assemblies, minimizing space requirements.

In operation, gas flows in the battle 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 desing gas velocity. The liquid level control placement is more critical than a vertical separator, and surge space is somewhat limited. Horizontal separators are almost always used for high GLR well streams, for foaming well streams, or for liquid-from- liquid separation.

Horizontal double tube:

A horizontal double-tube has all the advantages 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.

CONVENTIONAL HORIZONTAL DOUBLE-BARREL SEPARATOR

Spherical:

An Spherical separator offers an inexpensive and compact vessel arrangement. However, these types of vessels have a very limited surge space and liquid settling section. The placement and action of the liquid level control in this type of vessel is very critical.

SPHERICAL LOW-PRESSURE SEPARATOR

Three phase horizontal separator:

For another, 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.

CONVENTIONAL HORIZONTAL THREE-PHASE SEPARATOR

A three-phase feature is difficult to install in a spherical separator because of the limited internal space available. With three-phase operation, two liquid level controls and two liquid dump valves are required. Three-phase separators are used commonly for well testing and in instances where free water readily separates from the oil or condensate.

From an evaluation of the advantages and disadvantages of the various types of separators, the horizontal single-tube separator emerged as the one that gives the most efficient operation for high liquid loadings, vertical separators should be considered.

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