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Safety Features for Oil and Gas Separators[edit]

Oil andgas separators should be installed at a safe distance from other lease equipment. Where they are installed on

offshore platforms or in close proximity to other equipment, precautions should be taken to prevent injury to personnel

and damage to surrounding equipment in case the separator or its controls or accessories fail. The following safety

features are recommended for most oil and gas separators.

High- and Low-Liquid-Level Controls:

High- and low liquid-level controls normally are float-operated pilots that actuate avalve on the inlet to the separator,

open a bypass around the separator, sound a warning alarm, or perform some other pertinent function to prevent

damage that might result from high or lowliquid levels in the separator.

High- and Low-Pressure Controls:

High- and low pressure controls are installed on separators to prevent excessively high or low pressures from

interfering with normal operations. These high- and low-pressure controls can be mechanical, pneumatic, or electric

and can sound a warning, actuate a shut-invalve,open a bypass, or perform other pertinent functions to protect

personnel, the separator, and surrounding equipment.

High- and Low-Temperature Controls:

Temperature controls may be installed on separators to shut in the unit, to open or to close a bypass to a heater, or to

sound a warning should the temperature in the separator become too high or too low. Such temperature controls are

not normally used on separators, but they may be appropriate in special cases. According to Francis (1951), low-

temperature controls in separators is another tools used by gas producers which finds its application in the high-

pressure gas fields, usually referred to as "vapour-phase" reservoirs. Low temperatures obtainable from the

expansion of these high-pressure gas streams are utilized to a profitable advantage. A more efficient recovery of the

hydrocarbon condensate and a greater degree of dehydration of the gas as compared to the conventional heater and

separator installation is a major advantage of low-temperature controls in oil and gas separators.[19]

Safety Relief Valves:

A spring-loaded safety reliefvalve is usually installed on all oil andgas separators. These valves normally are set at

the design pressure of the vessel. Safety relief valves serve primarily as a warning, and in most instances are too

small to handle the full ratedfluid capacity of the separator. Full-capacity safety relief valves can be used and are

particularly recommended when no safety head (rupture disk) is used on the separator.

Safety Heads or Rupture Disks:

A safety head or rupture disk is a device containing a thin metal membrane that is designed to rupture when

thepressure in the separator exceeds a predetermined value. This is usually from 1 1/4 to 1% times the design

pressure of the separator vessel. The safety head disk is usually selected so that it will not rupture until the safety

reliefvalve has opened and is incapable of preventing excessive pressure buildup in the separator.

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The vapor-liquid separators which are generally used in industries might be classified into following:

1. Gravity separators

The separation process in this gravity separator occurs by settling and sedimentation and depends on gravitational

force. Liquid droplets or solid particles will settle out of a gas phase if the gravitational force acting on the droplet or

particle is greater than the drag force of the gas flowing around the droplet or particle. The same phenomenon

happens for solid particles in liquid phase and immiscible sphere of a liquid immersed in another liquid.

Gravitational forces control separation; the lower the gas velocity and the larger the vessel size, the more efficient the

liquid/gas separation. Because of the large vessel size required to achieve settling, gravity separators are rarely

designed to remove droplets smaller than 300 microns. Gravity separators are not recommended as the soul source

of removal if high separation efficiency is required. Gravity separators are sometimes also called scrubbers when the

ratio of gas rate to liquid rate is very high. These vessels have a small liquid collection section and are recommended

only for the following items: a. Secondary separation to remove carryover fluids from process equipment such as

absorbers and liquid dust scrubbers.

b. Gas line separation downstream from a separator and where flow lines are not long.

c. Miscellaneous separation where the gas-liquid ratio is extremely high

2. Centrifugal vapor-liquid separators

Utilize centrifugal action for the separation of materials of different densities and phases, might be built in stationary

and rotary types. In centrifugal separators, centrifugal forces act on droplets at forces several times greater than

gravity as it enters a cylindrical separator. Generally, centrifugal separators are used for removing droplets greater

than 100 m in diameter, and a properly sized centrifugal separator can have a reasonable removal efficiency of

droplet sizes as low as 10 m.

Centrifugal separators generally might be divided into three types: stationary vane separator, cyclone separator, and

inertial centrifugal separator. Cyclones and knock-out drums are recommended for waxy or coking materials.

Separator components

An oil/gas separator generally consists of following components

Inlet device located in pre-separation zone/section for priliminary phase separation;

Baffles downstream the inlet component to improve flow distribution;

Separation enhancement device located in the primary separation (gravity settling) section for major phase

separation;

Mist extraction device located in gas space to further reduce liquid content in the bulk gas stream;

Various weirs to control the liquid level or interface level;

Vortex breaker to prevent gas carryunder at outlet of liquid phase;

Liquid level/interface detection and control, etc.;

Gas, oil, water outlet;

Pressure relief devices