Functional Mechanism Of A Separator In Oil & Natural Gas

A separator is a mechanical device for the removal and accumulation of liquids of different specific gravities from natural gas.

Separation Process:

All separators are generally divided into four sections/categories involving separation procedures.

• Primary separation section
• Secondary separation section
• Liquid accumulation section
• Mist extractor section

1.Primary Separation Section –

Primary separation section is the portion of the vessel around the inlet of the Separator internals where the energy entering the good stream gets dissipated. The fundamental purpose of this section of Separator internals and their mechanical components is to make the initial separation of liquid from gas employing varied method deflectors or baffles. Most of the liquid is shifted towards the liquid accumulation section of Separator internals with larger quantities of liquid, large liquid drops immediately fall off owing to gravitational pull.

In vertical separators, an inlet deflector propels liquid to change direction towards the vessel shell where it spreads out in the thin film, enabling the breaking out of solution gas.

In horizontal separators, the liquid is generally directed against a deflector plate either dish-shaped or not. The liquid collected in Separator internals is thrown against the vessel shell for diverting it from the main gas stream and permitting fast release of solution gas. On some occasions, baffles are employed to break the liquid streams into smaller ones and droplets for the rapid release of solution gas.

2.Secondary Separation Section –

The area of the separator immediately beyond inlet deflector, between the liquid accumulation section of the Separator internals and mist extractor is termed the secondary separation section. Here, gas’s velocity and liquid are minimized due to increased cross-sectional areas, enabling liquid particles to fall towards liquid accumulation section as an outcome of gravitational force on liquid particle mass.

In vertical separators, a gas velocity that extends up, counters the gravitational pull effect on liquid particles stored in Separator internals exerting resistant force on particles. The particle settles in the bottom if both the particle and gravitational force are large. Minute particles get carried along with gas as entrainment leaving separator, if not removed by another device like a mist extractor. In horizontal separators, force is exerted at right angles to gravitational force not causing any hindrance to particles’ fall to liquid accumulation section of Separator internals. The particles’ path is diagonal or trajectory towards the separator outlet. Horizontal separators should be large enough in cross-section and long enough so that reduction of gas velocity and diagonal paths for the bulk of liquid particles are able to carry them into the liquid accumulation section. Allowing velocity for the secondary separation section has already been augmented by field tests of different types of separators. Sizing is based on the allowable velocity for gas stream in the secondary separation section. Most of the liquid particles that’re unable to drop out of a gas stream, generally get removed from gas stream via mist extractor of Separator internals.

3.Liquid Accumulation Section –

Liquid accumulation section of Separator internals constitutes three major categories-liquid level controller, dump valves, control valves, and sight glasses. Liquid retention time is usually one minute for two-phase separation allowing time for solution gas to break out of the accumulated liquid. In vertical separators, the baffle plate is positioned between liquid accumulation collected in the Separator internals and the secondary separation section. Horizontal separators normally utilize approximately half of this section for liquid accumulation, having less instantaneous surge capacity compared to vertical separators, with liquid retention time being three minutes for three-phase separation.

However, liquid outlet connections, be it in vertical or horizontal separators are generally located as far as it can be from inlet ensuring maximum liquid retention time for solution gas release-connections designed and formulated with anti-vortex baffles or siphon-type drains for preventing vortex development. Vortex development at the liquid outlet causes gas to be re-entrained in liquid being discharged.

4.Mist Extractors-

There’re three kinds of mist extractors being part of Separate internals, most commonly used in oil and gas separators-knitted wire mesh, vane, and centrifugal. Mist extractors make small minute particles transform into larger droplets. As the gas stream passes through the mist extractor, the mist extractor surface gets wetted with entrained liquid particles, and continued contact with wet surfaces combines to form larger droplets. This action is fostered by changing of direction forced on gas by extensive, long and windy paths to get through the mist extractor. When droplets reach the proper size for overcoming the lifting force imposed by gas velocity, they tend to fall into the Separator internals liquid accumulator section.

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