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Separator operation -educational videos

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Oil and gas separators 7 Parts

Part #1

Separators in oil and gas industry - Part #1 why we need separation and treatment in oil and gas fields ?

The text of the video


Petroleum Gases and Liquids are Called Hydrocarbon fluid because the main component of the petroleum fluid is the hydrogen and the carbon atoms.

Oil and gas wells produce a mixture of hydrocarbon gas, condensate or oil, salty water,
Also the mixture contains inorganic gases, such as nitrogen, carbon dioxide (CO2), and possibly hydrogen sulfide (H2S),
In addition to few solids, including sand from the reservoir, scale, and corrosion products from the tubing.

These mixtures are very difficult to handle, meter, or transport. In addition to the difficulty, it is also unsafe and uneconomical to ship or to transport these mixtures to refineries and gas plants for processing.

Further, hydrocarbon shipping tankers, oil refineries, and gas plants require certain specifications for the fluids that each receive. Also, environmental constraints exist for the safe and acceptable handling of hydrocarbon fluids and disposal of produced salt water.
It is therefore necessary to process the produced fluids in the field to yield products that meet the specifications set by the customer and are safe to handle.

The goal is to produce oil that meets the purchaser’s specifications that define the maximum allowable amounts of water, salt, and sulfur. In addition to the maximum allowable value of Reid vapor pressure and maximum allowable pour point temperature.

Similarly, the gas must be processed to meet purchaser’s water vapor maximum allowable content (Water dew point), hydrocarbon dew point specifications to limit condensation during transportation, in addition to the maximum allowable content of CO2, H2S, O2, Total Sulfur, Mercaptan, Mercury, and maximum gross heating value.

The produced water must meet the regulatory requirements for disposal in the ocean if the wells are offshore, or to meet reservoir requirements for injection into an underground reservoir to avoid plugging the reservoir or underground water contamination.

The specifications for the above requirements may include maximum oil in water content, total suspended solids to avoid formation plugging, bacteria counts, toxicity in case of offshore disposal, and oxygen content.

Phases that include (Gas- Oil – Water) in oil and gas production lines are not naturally 100% separated.
Part of the gases is free in field production or transportation lines, and another part is dissolved in the oil stream.
In the same time, part of the liquid produced is trapped in the gas stream.

Part# 2

1- The necessity of separation in oil field.
2- Separator Types (Horizontal – Vertical)
3- Separator function for 2& 3 phase separators.
4- Theory and technique of separation
5- Retention time (residence time ) for separation of each phase.

The text of the video

Separator Configurations

separators may be horizontal

A comparison between Horizontal and Vertical separators, will be presented later in this presentation, where, Advantages and disadvantages of each configuration will be discussed.

Terminology and general aspects of separation

Separators may be classified as
2 phase separators , in which the separator is designed to separate gases from liquid, and liquid from gases.
The two phases in this case are :
Gas and liquid.

Separators can go further to separate water from oil , and oil from water
In the last case separators are called three phase separators,
the three phases are:
– oil – and water.

Separation whether 2 or 3 phase separation is achieved by one or more of the following techniques:

Gravity separation, which depends on the density difference between phases
Coalescences , which depends on the growth of droplets caused by the
collision of the small droplets at a surface of a metal.
or growth after collision of small droplets in an electrical field.
Centrifugal force, which accelerate the gravity separation

Impingement, which depends on the separation caused by a collision of phases with a plate or a deflector.

The most important technique in separation is the
Gravity separation which depends on the difference in density between the phases to be separated as follows:

Crude oil is a complex mixture of hydrocarbons; its density usually ranges from 40 to 55 pounds per cubic foot.
Which is 0.65 to 0.9 kg/ liter

While, produced Water usually has a density about 65 pounds per cubic foot
which is about 1.05 Kg/ liter

density of gases is strongly changes due to temperature and pressure
for example
volume of 1 cubic feet of gas at 60 degree Fahrenheit ( 15 degree celiesius ) and pressure 35 psig ( 2.5 Barg)
is about 0.3 and its density is about 0.2 pounds per cubic foot ( which is 3.5 Kg per cubic meter)

While at the same temperature, and at pressure 100 psig ( 7 Barg) the gas volume is reduced to 0.1 cubic foot and the density is increased to 0.6 pounds per cubic foot ( which is 9 Kg per cubic meter)

Further increase in pressure to 500 psig (33 barg) will lead to more reduction in gas volume to reach 0.02 cubic foot , and the density will be 3 bounds per cubic foot (46 kg per cubic meter).
Whatever, the increase in gas pressure, still there is a big difference in densities between gases ( 3 lb/ cubic foot) and oil or water .

We can notice, the difference in density between oil and water is less than the difference in densities between gases and any of the produced liquids.
The targets of the 2 phase separation are:
to remove liquid droplets from Gas- and remove gas bubbles from Liquid.
The liquid droplets entrained in gas stream must fall down to the liquid surface
It will take less than 5 seconds in small diameter separators, at low pressure.

and up to 15 seconds in case of high diameter separators, at high pressure

the gas stream, has to stay in the separator a residence time more than the time of liquid droplets fall.
Calculations for the time required for droplet separation, are usually based om 100 or 140 micron droplet diameter.

Larger droplet fall down faster, hence consumes less time to reach the liquid level.

The only restriction for the liquid droplet , while falling down is the viscosity of gas, which is of a low value, and will not make a remarkable effect on the droplet velocity.
For the Gas bubble entrained in the liquid,
due to the density difference, the gas bubble will ascend leaving the liquid zone to the gas area,
Due to the viscosity of surrounding liquid, the gas bubble will take much more time to ascend, than the time required for the liquid droplet to fall down.

The gas bubble, may need up to 4 minutes to ascend and leave the liquid surface, depending on the viscosity of the liquid.

Therefore, liquid residence time in two phase separator, usually ranges from 1 minute for light crude oil ( low viscos liquid) to about 4 minutes for high viscos – low API crude oil.

in horizontal separators
Gravitational force is perpendicular to the drag force caused by fluid movement.
The falling direction of the droplet will be in an angle between gravitational force and drag force.
Also the ascending direction of the gas bubble will be in angle between drag force caused by liquid movement and buoyancy or gravitational force.

in vertical two phase separators:
The same concept is applied as in horizontal separators.
The only difference is that :
The flow of gas stream, and the drag force caused by the gas flow, is in the opposite direction of the gravitational force ( or the falling path of the liquid droplet), hence there is a limit for speed for the gas flowing upward, to allow liquid droplet separation by gravity force.

In other words, The drag force, caused by gas movement, must be less than the gravity force downward, for separation to occur.
Therefore, in a vertical separator design, there is a minimum diameter used for each calculation.

A bigger Diameter – increase flow area – hence reduce flow velocity, consequently reduces the drag force.
The same concept is applied for a gas bubble ascending in liquid stream, which is affected by drag force caused by liquid movement downward.

let’s remember that: this is not the same in the horizontal separators, because the drag force is perpendicular to the falling direction – not opposite to it.

For 3-phase separation
In addition to removal of liquid droplets from Gas- and removal of gas bubbles from Liquid as in 2 phase separation it is also design to Remove Water from Oil and Oil from Water.

Removing liquids from gas stream will consume 5:15 seconds, as in 2 phase separation.
Removing gas bubbles from liquid stream will consume also from 1 to 4 minutes as in 2 phase separation

The difficulty, or the critical path is to remove water from oil, where it will consume from 20 to 30 minutes.
depending on the oil viscosity, and the density of oil (API degree).

The more the difference in densities between oil and water the faster the separation will be.
in vertical separators 3 phase separation.
The same concept of horizontal 3 phase separation is applied, except we have to consider the maximum flow speed – or – the minimum diameter required – as we mentioned for the two phase separators.

Gravity separation depends on the difference in density between phases
For example
@ 100 Psig the densities of the 3 phases are as follows:
Water 65 lb/cu ft.
Oil 50 lb/cu ft. (Average)
Gas 0.6 lb/cu ft. @ 100 psig
Therefore, it’s much easier and faster to separate gases from liquids, than to separate water from oil.
Gravity Separation also, depends on the Viscosity of the continuous phase.

For example

To separate gas trapped in a liquid phase, the gas bubble has to move upward through the viscous liquid.
While, Separation of liquid from the gas phase is much easier and faster, since the viscosity of the gas phase will not restrict the dropping of liquid drop downward.
According to Stok’s Law, and similar equations usually used in gravity separation
Velocity of separated droplets

(V) α is directly proportional to the (Density difference)
and is indirectly proportional to the diameter of the droplet or bubble,
and indirectly proportional to the viscosity of the continuous phase (in which the droplet or bubble will move through),

Therefore, We can conclude that :
1- Increase in Density difference will enhance separation.
( Gas is easily separated from Liquids,
It is easier to separate Water from light crude oil than from heavier crude oil “Lower API).
2- Viscous crude oil, is harder in water separation.
3- Small droplet sizes are harder to be separated.
4- Increasing temperature, will reduce viscosity and therefore enhance separation.
5- three phase separator size is bigger than 2 phase separators for the same liquid fluid, because, an oil room is added, and more residence (retention) time will need to separate water from oil.
6- Reducing the separator operating pressure, will increase gas volume, consequently, reduce retention time of gas inside separator.
7- Separators working at higher pressure, will treat more gas than the same size at low pressure, due to reduction in gas volume.

Time required for
Gravity separation

The required time to separate a 150 micron droplet of liquid entrained in the gas phase is less than 15 seconds at 1000 psig – large diameter separators.
and less than 5 seconds @ 100 Psig- small separators.

Therefore, the residence or retention time of gas in separators must be more than the time required for separation process.
 Liquid required residence time to separate a bubble of 150 micron gas from liquid phase is ranging from 1 : 4 Minutes (Depends of temperature, and viscosity of liquid).

Liquid residence time to separate water from oil is usually 20 – 30 minutes.
depends on oil density, temperature, and viscosity.

For the above residence time consideration
API 12 J
presented tables for recommended retention time in separators as we can see:
Liquid retention time range is from 1: 4 minutes – to separate gases from liquid.

To separate free water from oil the retention time ranges extend to 30 minutes.

All separated water, are the free water existing, not emulsified water; which require more treatment through heating and electrostatic heaters, or desalting.

 Sizing of separators usually, is based on 20-30 minutes; liquid residence time for 3-phase separators.
And about 1:4 minutes for 2-phase separators.

 Additional residence time in separators, will not be effective in reducing the water content in oil.
 After about 20 : 30 minutes, an equilibrium is reached and further water separation will not be achieved.

As it is clear from the graph
in the beginning
separation rate of free water from oil is very high
then the rate is decreased with time
till reaching an equilibrium after about 30 minutes, where more residence time, will result in a very small increase in separated water.

further processing is required in oil and gas processing, to achieve the required crude oil specs.

a heater treater usually exists Downstream the separator,
to heat the emulsion, hence, reducing the crude oil viscosity, and allow more water separation.
Then a fresh or low salinity water usually added to the crude oil ( wash water) , and the crude oil is pumped to a desalting vessel, which separate the small water droplets, by applying an electrical field.
Electrical voltage affect the water droplets, and help in coalescing droplets together to enhance separation.

Further gas treatment may be required which include
acid gas treatment which is known as gas sweetening
Dehydration of natural gas
Condensate recovery

 In the previous session
We explained :
1- The necessity of separation in oil field.
2- Separator Types (Horizontal – Vertical)
3- Separator function for 2& 3 phase separators.
4- Retention time (residence time ) for separation of each phase.
 Next
Separation Internal Components.
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More Videos will be added soon

In different oil and gas categories
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Part # 3

Separation in oil and gas industry - Part #3 Separator internals

The text of the video

Separation in oil and gas industry part 3
Separator Internals
Whether the separator is vertical or horizontal,
a group of internal devices are usually installed to enhance separation and to allow smooth operation.

1- Inlet Diverters

is the First component the fluid will meet is: the
Inlet diverters serve to impart flow direction of the entering vapor/liquid stream and provide primary separation between liquid and vapor. There are many types of inlet diverters such as
• Diverter plate
• Half-pipe
• Reversed pipe (elbow)
• Dished head
• Vane-type
• Cyclonic

baffle plates,
vane, and
centrifugal diverters.

 Inlet Diverters have different shapes, and techniques, all serve to impact flow direction of the entering vapor/liquid stream and provide primary separation.

The main functions of the inlet device are:
• Reduce the momentum of the inlet stream and enhance flow distribution of the gas and liquid phases.
• separate the bulk liquid phase Efficiently.
• Prevent droplet shattering and re-entrainment of bulk liquid phase.

2- Defoaming Plates :
Separators may be equipped with defoaming plates, which serve to force the foam to pass through a series of inclined parallel plates or tubes. To break the foam bubbles.

3- Wave Breakers :
are perforated baffles or plates that are placed perpendicular to the flow located in the liquid collection section of the separator. These baffles dampen any wave action that may be caused by incoming fluids.

The wave actions in the vessel must be eliminated so level controls, level switches, and weirs may perform properly.

4- Vortex Breakers :
Horizontal separators are often equipped with vortex breakers, which prevent a vortex from developing when the liquid control valve is open. To prevent gas escape with liquids when the control valve is open.

5- Sand Jets and Drains:
In horizontal separators, one worry is the accumulation of sand and solids at the bottom. To remove the solids, sand drains are opened, and then high-pressure fluid, is pumped through the jets to agitate the solids and flush them down the drains.

6- Mist extractors or mist eliminators or demister, are names of an equipment used to remove the liquid droplets and solid particles from the gas stream.

Separators sizing are usually based on the removal of 100 micron and bigger liquid droplet.
Designing a vessel to remove smaller sizes, is not practical or economical.

To remove small liquid droplets, smaller than 100 micron, a mist extractor is used at the gas outlet inside the separator.

Impingement-Type Mist Extractor (wire mesh) is the most widely used type of mist extractors.
These types consist of baffles, wire meshes, and micro-fiber pads.
Impingement-type mist extractors may involve just a single baffle or disc installed in a vessel.

Baffles (Vane Type) mist extractor
This type consists of a series of baffles, vanes, or plates between which the gas must flow. The most common is the vane or chevron-shape,
The vanes force the gas flow to be laminar between parallel plates that contain directional changes. The surface of the plates serves as a target for droplet impingement and collection.

Other Types of Mist extractors include:
Arch-plate-type mist extractor.

Centrifugal mist extractor

Coalescing Pack-type mist extractor.
Next - we will present
Separator control and safety equipment.
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Part #4

Separation in oil and gas industry - Part #4 Separator Control
Pressure control - Liquid level control .
In addition to other types of separators. scrubbers, slug catchers... etc.

The text of the video
Separation in oil and gas industry part 4
Separator controls
and other types of separators
Gas–oil separators are generally equipped with the following control devices
* Liquid Level Controller
* Pressure Control Valve
* Pressure Relief Valve
* Shut down valve

The two Factors to be controlled in separator operations are: Pressure & Liquid Level.
Pressure is maintained constant or controlled by a
pressure control valve,
The pressure control valve (PCV) is an automatic backpressure valve that exists on the gas stream outlet. The valve is set at a prescribed pressure. It will automatically open or close, allowing more or less gas to flow out of the separator to maintain a fixed pressure inside the separator.

The liquid level controller (LLC) is used to maintain the liquid level inside the separator at a fixed height.
In 3-Phase Separators, two level controllers exist
one for the water interface, and the second is for oil level.
The same two level controllers exist in 3-Phase vertical Separators

Pressure Relief Valve & Rupture Disks
The pressure relief valve (PRV) is a safety device that will automatically open to vent the separator if the pressure inside the separator exceeded the design safe limit.
the Rupture Disk : consists of a thin diaphragm held between flanges. The disk is designed to rupture and relieve pressure when exceeded.

Shut down valves: are usually installed at the inlet of separator to protect the vessel by preventing the incoming flow in case of vessel high pressure or high liquid level.
Other types of separators

A double-barrel horizontal
A double-barrel horizontal separator is a variation of the horizontal separator.
They are commonly used in applications where there are high gas flow rates and where there is a possibility of large liquid slugs, e.g., slug catchers.

A single barrel separator with a liquid “boot” or “water pot” at the outlet end is a special case of a two-barrel separator

A Filter separator is another type of separator that is frequently used in some high-gas/low liquid flow applications. They can be either horizontal or vertical in configuration. Filter separators are designed to remove small liquid and solid particles from the gas stream.

A scrubber is a two-phase separator, that is designed to recover liquids carried over from the gas outlets of production separators or to catch liquids condensed due to cooling or pressure drops. Liquid loading in a scrubber is much lower than that in a separator.
Typical applications include: upstream of mechanical equipment such as compressors.

A slug catcher, is a special case of two-phase gas-liquid separator that is designed to handle large gas capacities and liquid slugs on a regular basis, and it is commonly used in gas gathering pipelines.

Slug Catcher, may be designed as a large Double Barrel Separator.

Selection of a type of a separator

When flow variability is very high - a slug catcher is the only choice, which may be followed by another separator.
When the gas oil ration is high – scrubber is the choice, and if it is very high, a filter separator is the best choice.
Next part will be
Separator operations -
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Separators in oil and gas processing

Part #5
2 phase separator operations

Operation of two phase separators

The text of the video

Here we see a simplified animation for a typical 2 phase separator
The fluid enters the separator and hits the inlet diverter, causing a sudden change in velocity and direction
The initial separation of liquid and vapor occurs at this point.
The force of gravity, causes the heavy liquid droplets to fall down to the liquid collection section.
This liquid collection section holds the liquid for a retention time required to evolve the dissolved and entrained gases and raise to the vapor space.
This part also provides a surge volume, is necessary to handle intermittent slugs of liquids.
The separated liquid then leaves the vessel through liquid dump valve, which is regulated by level controller
The level controller senses changes in liquid level and controls the dump vale accordingly.

The separated gas flows over the inlet diverter, and horizontally travels in the gravity section

As the gas flows through the section, small drops of liquid which were entrained in the gas and not separated by the inlet diverter , are separated out by gravity and fall to the gas liquid interface

Some of the drops of such small diameter, are not easily separated in the gravity settling section.
However , before the gas leaves the vessel it passes through a coalescing section, or mist eliminator.
In this section, metal vanes, wire mish, or closely spaced plates are used to coalesce the very small droplets of liquid, and cause them to fall into the liquid collection section.
The pressure of the separator is maintained by a pressure controller.
The pressure controller senses changes in pressure in the separator, and send a signal to either open or close a pressure control valve accordingly.
By controlling the way in which gas leaves the vapor space of the vessel, the pressure in the vessel is controlled.

Normally, horizontal separators are operated half full of liquid to maximize the surface area of the gas liquid interface.

Vertical 2 phase separator

The production separator separate free gases from the liquid stream at specific pressure and temperature.
The vertical 2 phase separators, include a primary separation section ( which is the Inlet diverter )

Secondary separation section (gravity area)
Liquid accumulation section

Mist extraction section
A level control and safety devices.

The primary separation section, removes the bulk of the liquid in the inlet stream .
first, slugs and large liquid particles are removed to minimize gas turbulence and re-entrainment of liquid particles.
To do this, the velocity and direction of fluid changed , Centrifugal force created either by inlet baffle, or internal piping, allows change allows a change in flow direction and also a reduction in stream velocity

after stream velocity has been reduced, gravity causes a large liquid droplets from the gas in the secondary separation section.

The efficiency of the this section depends on the gas and liquid properties, particle size and degree of turbulence.
Some designs use a straightening vanes here to reduce this turbulence.

Before the gas leaves the vessel, the mist extractor section removes the very small droplets of liquid in a final separation step.
The mist extractor can be a series of vanes, wire mesh pad, or special chamber called a cyclonic passage.
Now recent designs use a wire mesh pad.
Liquids are collected in a liquid accumulation section.
By design , the liquid has minimum disturbance from the flowing gas stream.

Two things determine the capacity here:
the volume of one stream surges and the time the liquid must remain for efficient break out of solution gas .
That is the gas dissolved or entrained in the liquid in the well stream fluid.

As the liquid level controller reacts to the accumulated liquid level, it triggers the liquid level control valve.
The liquid is sent to storage, or for further processing.
Separators also have sight glasses to monitor the liquid level.
This devices, allow the operator to check levels, check operation of the dump valves.

Separators are equipped with several safety devices.
This may include a relief valve, or rupture disk.
They all mounted near the top of the vessel.

As in the horizontal separator, the pressure is controlled by a pressure control valve at the gas outlet line.

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Separators in oil and gas processing
Part #6
Operation of three phase separators

Content Text

3 phase separator’s operation
The major difference between two phase Vertical separator and three phase vertical separator is the water accumulation section.
Here is the top portion of liquid accumulation section collects oil
and the bottom portion collects water
Both areas has its own liquid level controller and liquid control valve
The well stream enters the vessel in the upper portion
Stream direction and velocity are change by baffles
as the gas and liquid vapor rise, baffles, straightening vanes and mist extractor remove the water droplets
Gas leaves the separator near the top
Oil and water fall to the accumulation section
where the gravity separates the oil from the water
since the settling time is longer than gas oil separation, the liquid must remain in this section longer than in two phase separators. This requires a larger liquid accumulation section.
Oil leaves the vessel through a liquid level control valve in the oil portion of the accumulation section
Water leaves the separator through a different level control valve
Both the oil and water valves have liquid level controllers

Liquid level controller is critical in three phase separation, the oil water interface must be contained within ranges or the oil dump valve will begin to dump water rather than oil.
On the other hand, in malfunction of the liquid level controller or valve in the water section, could cause water and oil to be dumped into the waste water .

Three phase separator may be vertical, or horizontal
Sometimes the liquid level is controlled by either one or two weirs.
a weir is a dam like structure, designed to keep liquid at a given level
In a separator with one weir, the weir maintains the combined liquid level, however both the water and oil levels are maintained through individual level controllers and valves
With two weirs, one maintains the oil level, and the other the water level
Each liquid is dumped through individual level controller and valve.
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separators in oil and gas industry
part #7
two phase vertical separator components

separators in oil and gas industry
part #8
Difference between two and three phase separators
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separation in oil and gas industry part - #9- three phase separator operation2.

separation in oil and gas industry part - #10- separator operation problems.

separation in oil and gas industry part - #11- Stage separation
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