What are Oil and Gas Separators?

What is a Separator?

?A separator is a pressure vessel used to separate well fluids produced from oil and gas wells into gaseous and liquid components in the oil field. Hydrocarbon streams are made up of a mixture of gas, liquid hydrocarbons, and free water at the wellhead. In most cases, it's best to divide these phases as soon as possible so that the two or three phases can be handled separately. The liquids are separated from the gas phase bypassing the good stream through an oil-gas water separator.

SEPARATION PROCESS OF Separators:?????

Introduction: The crude oil mixture is collected from the well, using by flowline. It will be reaching to gathering center. A gathering center is a facility to collect crude oil mixture from the wells, coming to a single head. According to pressure, it is divider and feeding to various production separators.

The separator is a mechanical vessel/equipment as shown below figure. The Inlet is a crude oil mixture (Oil, Gas, and Water). It is separated by the gravity and pressure difference like GAS, OIL & WATER.?

PRIMARY GAS-LIQUID SEPARATION PROCESS:

Separators are mechanical devices used for the primary separation to remove and collect liquid from natural gas, which is normally accomplished with the aid of centrifugal force.

WHAT DOES A SEPARATOR DO????????????????????

The figure explains the mixture of OIL, GAS, and WATER that it is in emulsion form entering to a static vessel so that Gas is lighter than the liquid and it will move to topside within a resonant type and liquid itself is a water and oil (emulsion mixture) still for separation which will take certain time. Water is heavier than oil, water will settle down and oil will be in the middle. This is the basic principle of a separator.

When the well fluid is entering from the inlet and inside arrangements are called separator internals working like a mechanical helper. The mechanical internal devices help accelerate better/perfect suppression. It will also be breaking the emulsion due to pressure difference or gravity difference; Gas will immediately travel to the top of the Gas Outlet.?

Separators are sometimes called:??????

1.???Scrubbers

2.???Accumulators

3.???Flash tanks

4.???Knock Out drums (KO drums).

Separator CLASSIFICATION:???????????????????????

The below figure describes the classification of the separator as Vertical, Horizontal, and Spherical. It is classified according to pressure, quantity/volume of gas, or oil.

The separator is classified into Phases and by Shape as follows. These separators are used in companies for different operations on the atmospheric separator, medium pressure separator, high-pressure separator according to the well fluid pressure.

By Phase:

Three Phase – Gas, Oil, and Water

Two-Phase – Gas and Oil

?By Shape:

Horizontal, Vertical, and Spherical

THE MAIN FUNCTIONS OF AN OIL-GAS FIELD SEPARATOR ARE:??

?To cause primary phase separation of gas from liquid and continue by removing entrained liquids from gas.

Sufficient time is allowed in the separator for gas to be released from oil as well as to permit the separation of oil and water.

The controls provide to prevent the gas from escaping with the liquids.

To discharge the separated fluids, form the vessel in such a manner that re-mixing of any of the fluids is impossible.

PHYSICAL FACTORS FOR SEPARATORS TO FUNCTION:??

The three physical factors are necessary for separators to function and accelerate to get better results for separation.

1.???Gravity

2.???Fluid insolubility

3.???Difference in fluid densities

• Gas is very much lighter than crude oil, and in a separator gas and oil will separate in a few seconds.
• Because of the vast difference in density between gas and crude oil, almost all the gas instantly separates from crude oil in the separator.
• Approximately 90% of gas from liquid separation occurs instantly, this is known as primary separation or flash separation.
• ?Some liquid remains in the gas in the form of a fine mist, this entrained liquid must be removed for separation to be completed.
• ?If the mist is not removed from the gas phase in the separator, the liquid will settle out in the gas outlet flow line, possibly in a burner, and cause a hazardous condition. Also, an amount of crude oil production will be lost.

WHAT ARE SEPARATION STAGES?????????????????

There are two stages in the process of separation of gas from liquid.

Primary Separation:

The large difference between the densities of gas and crude oil, about 95% separation occurs almost instantly. This is called primary separation. Some of the crude oil remains in the gas as a fine mist.

Secondary Separation:

The most difficult function of a gas/liquid separator is to remove the oil mist from the gas. The mist cannot be removed unless the fine droplets in the mist can be made to join (to coalesce) to make large drops that become heavy and fall out of the gas.

Coalescing devices are used in the separator to make these fine droplets join. In a coalescing device, the liquid sticks to the surface of the device and combines with other drops to eventually form a drop large enough to fall out.

PROBLEM CAUSED BY POOR SEPARATION???

Poor operation of the separator can cause downstream problems. For example, liquid can settle out in gas lines, possibly in a burner system, causing serious problems in the downstream equipment.

If gas remains in the liquid, it can cause cavitation in pumps and increase pressure in vessels.

Retention Time (Residence Time)

Gas bubbles in the liquid will break out of the crude oil phase in most oil production separators in 30 to 60 seconds. Therefore, the separator is designed so that the liquid stays inside the vessel for 30 to 60 seconds. The length of time that the liquid stays inside the separator is called the liquid residence time or the time required for gas to bubble out of the liquid.

A tangential inlet or internal diverter is used to cause a spinning motion of the incoming gas. A properly designed separator will also provide for the release of the entrained gases from the accumulated hydrocarbon liquids. The objective of ideal separator selection and design is to separate the hydrocarbon stream into liquid-free gas and gas-free liquid. Ideally, the gas and liquid reach a state of equilibrium at the existing conditions of Pressure and Temperature within the vessel.

SEPARATOR CONTROL SYSTEM?????????????????????

Control systems are important to all process equipment to make sure each piece of equipment works safely and efficiently.

The control system controls the important process variables with a set point to achieve the best operating values.

The important process variables in the separator are pressure and level. Pressure controlled by a Pressure Control Valve (PCV) installed in the Gas outlet and Liquid level controlled by Level Controlled Valve (LCV) installed in the liquid outlet line.?

Safeguard SYSTEM???????????????????????????????????????

Safeguard systems are an important part of the process plant and equipment, which operate the plant safe and efficient level.

Safeguards activate alarms and provide an automatic shut down of all inlets and blow down all gas outlets in any abnormal conditions.

Safeguard system protects personnel, plant, and the environment from abnormal operating conditions, like pressure high/low, level high/low, temperature high/low, high vibration, gas leak, fire, or instrumentation pressure low.

Examples of safeguard systems are shut down valves, different alarms, switches, etc.

?SEPARATOR OPERATION????????????????????????????????

With the separator in normal service, the following checks should be made.

Observe the various level, pressure, temperature, and flow control instruments to see that they are controlled within the proper desired ranges.

Diaphragm operated control valves should be stroked occasionally to see that they will fully open or close without restriction.

Gauge glasses should be drained and cleaned occasionally to prevent the build-up of scale and debris in the lines. The build-up of scale and debris in the lines could cause false readings.

The pressure drop across demister pads and other coalescing devices should be monitored for an increase, which indicates a build-up of solids, and the need to clean or replace the devices.

TROUBLESHOOTING SEPARATORS????????????????

A process of elimination finds the cause of an operating problem. Each event, which can cause the problem, is checked until the cause is found. The proper sequence for checking the various causes is to eliminate the easy ones first. These are the instruments, (pressure gauges, control valve positions, controller output pressures, gauge glasses, flow meters, etc.).

In making these checks, make sure that the instruments are working properly and not giving a false reading. Once the easy causes are checked and eliminated, the most difficult causes are checked.

Another important of troubleshooting is that of maintaining an overall view of the total

process, and not just the troublesome equipment.

Problems at the front-end of a plant often show up at the back-end. Find the source of the problem before attempting to fix it.

For more information please contact JMS-Johar Manufacturing Services; [email protected] or call +971545759109