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Title: three phase separator
Description: its study about spearator and studied about the process of separator
Description: its study about spearator and studied about the process of separator
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Petrofac
Flowlines and Manifolds
SECTION 3
THREE-PHASE SEPARATION
1
Introduction
1
...
1
6
Inlet Separation
Separation Systems
6
...
1
Pressure Control
8
...
1
Planned Shutdown
9
...
3
Startup After Emergency or Short-term Shutdown
High Pressure Relief Valves
Figures
3
...
2
3
...
4
3
...
6
Three-phase Horizontal Separator
Vertical Separator Internals
Three-phase Separator Internals
The Separation System
Production Train Separator and Instrumentation
Separator Pressure Control
Training Services
Page 1 of 13
© Petrofac 2010
Petrofac
Flowlines and Manifolds
1
INTRODUCTION
A separator is a vessel in which a mixture of fluids, that are not soluble in
each other, can be segregated
...
1
...
1
Vertical as shown in Figure 3
...
For separation of gas and liquid, the separator is referred to as a two-phase
type
...
Some wellstreams contain sand or other solid particles which are also
removed in a separator
...
Training Services
Page 2 of 13
© Petrofac 2010
Petrofac
Flowlines and Manifolds
2
FLOW PATTERNS
The flow in both horizontal and vertical separators is similar for two-phase
separators whereby the mixture enters at the side or end of the vessel, the
lighter fluid (usually gas) passes out at the top, and the heavier fluid is
withdrawn at the bottom
...
1; the fluid entering at
one end of the vessel and the liquids being allowed to settle out at the lefthand side of the vessel
...
The water layer remains on the left-hand side of the weir and is withdrawn
under separate level control
...
This type of problem can normally be overcome by using
demulsifying agents, chemicals that break down emulsions, in order to give
cleaner separation of the fluids
...
3)
...
The plate can be flat or dished, and as the inlet stream strikes it, the
liquid falls to the bottom and the gas flows around the plate
...
(2)
Mist Pads
Mist pads are most frequently used within gas-liquid separators to
remove the vapour mist from the gas
...
It is held in place by a sturdy grid frame which prevents it from
being swept out or torn by a sudden surge of gas flow
...
They are used in gas-liquid vessels to remove liquid from the gas by
causing small droplets to combine into larger drops which will
separate more readily
...
These allow the use of smaller vessels, which are just as
efficient as the larger vessels with longer residence times
...
They are also used in gas-liquid separation vessels and installed when
hydrate formation or paraffins would prevent the use of mist pads due
to blocking etc
...
The
separator usually contains an access hatch in order to allow
replacement of the elements
...
They impart a swirling action
to the inlet stream that concentrates the flow of the liquid phase onto
the wall of the device
...
They are normally located near to the
liquid level in the vessel
...
(9)
Water Jets
Water jets are sometimes referred to as sand jets
...
4
PRINCIPLES OF SEPARATION
Two factors are necessary for separators to function properly:
(1) The fluids that are to be separated must be insoluble with each other ie
they will not dissolve with each other
...
Separators depend upon the effect of gravity to segregate the fluids, if the
fluids are soluble in each other, no separation is possible by gravity alone
...
They must therefore be
segregated in a distillation process
...
Gas weighs far less than oil for the same volume, and will therefore
separate within a matter of seconds
...
(A typical specific gravity for oil is 0
...
)
Therefore the primary factor that affects separation of fluids is that of the
difference between their densities
...
3
...
Normally efficient separation of the oil, gas and water is achieved in a
series of stages:
Training Services
Page 6 of 13
© Petrofac 2010
Petrofac
Flowlines and Manifolds
5
...
The well fluid entering the vessel is subjected to a rapid and sudden change
of direction and velocity, when it strikes an inlet momentum breaker or
diverter plate
...
With the reduced operating pressure and enlarged space
available, this results in the liberation of flash gas and an oil mist which
rise, while the heavier slugs and large droplets of liquid fall to the bottom
of the tank
...
Test
separators are used to test the flow of individual wells and are
instrumented to measure flow of oil, water and gas
...
As the capacity of a separator is limited, it may be necessary to have a
number of separators to handle the well fluid flow
...
6
...
This water
percentage is called the water cut and if a platform is producing oil into
storage with a water cut of 13% then there is 87% oil going into storage
...
Provided the separators are not
overloaded and the design throughput of the process train can be
maintained, this is the better mode of operation
...
Training Services
Page 7 of 13
© Petrofac 2010
Petrofac
Flowlines and Manifolds
Figure 3
...
The
difference between two and three-phase separators is that on the threephase separator:
•
•
A weir is fitted
An additional level indicating controller (LIC) and level control valve
(LCV) are fitted
The weir forms a dam which creates a section where the water can separate
out of the oil
...
In this
example the oil level is controlled by the LIC-2 and its associated LCV
...
The controller is often at the interface level where the oil and
water meet
...
Emulsion is one of the main problem areas of threephase control in that it makes interface level control difficult
...
An example of an oil level gauge
or sightglass is shown in Figure 3
...
7
SEPARATOR INSTRUMENTATION
Within the limits of design and construction all separators have the same
basic instruments and controls as follows:
(1)
Pressure Indicator (PI)
Monitors the pressure in the separator with readout both locally and
remotely, the remote readout being transmitted to a central location
such as the Central control room (CCR) or local equipment room
(LER)
...
(3)
Pressure Safety Valve (PSV)
Relief valves are installed on each separator, one in service and the
other isolated
...
No alteration to this setting is allowed after
the relief valve has been certified
...
Training Services
Page 8 of 13
© Petrofac 2010
Petrofac
Flowlines and Manifolds
(5)
Gas Outlet Line
This is split into two streams - the gas to the recompression and
treating section and the gas to flare
...
The PIC
monitors and modulates the PCV as required
...
Generally this flow is a remote readout
in the control room on both indicator and recorder
...
This is another instrument which gives local
and remote readout in the control room
...
(10)
Drains
This gives the facility to manually drain down the separator through
the closed drain system
...
5
...
This valve is designed to close on a Low Low level being
detected in the upstream vessel, or a high pressure being detected
in the downstream vessel
...
Where crude cooling is installed prior to the final-stage separator this can
be fitted with:
•
High temperature alarm
•
High temperature shutdown
•
High integrity protection system (HIPS) - this provides an alternative
(electronic) means of shutdown as a backup to the high level
shutdown systems on the separators
Regardless of what function is being monitored the sequence for alarm and
shutdown is the same
...
If no corrective action is taken or the action is ineffective further
deterioration occurs and a shutdown results
...
Training Services
Page 10 of 13
© Petrofac 2010
Petrofac
Flowlines and Manifolds
8
...
Figure 3
...
Separator pressure control varies depending on the operating mode but the
first-stage separator will always be gas stream flow pressure
...
The PICs on each separator will be set slightly above the pressure the gas
plant is holding on them
...
As
soon as it reaches the pressure setpoint the controller opens the PCV to
route the excess gas to the flare
...
2
Level Control
The control of the oil level in the separator is the same regardless of
whether gas is being recompressed or flared
...
If the level rises, the controller opens the control valve;
conversely, the valve closes when the level falls
...
Where
possible, action to prevent an emergency shutdown, for example, cutting
back production to avoid high level trip, is good operating practice
...
9
...
Wells should be closed in slowly using the chokes prior to closing
their surface safety valve (SSV)
...
In this case, the
separator train must be depressurised, drained and isolated
...
Training Services
Page 11 of 13
© Petrofac 2010
Petrofac
Flowlines and Manifolds
Prior to restart after an emergency shutdown, not only must the cause of
the shutdown be cured but also the fault which created the cause
...
9
...
These checklists will include the following:
•
All utilities, including hydrate inhibitor, chemical injection, flare
systems (HP and LP), closed drains and produced water, are to be
available at the “battery limits”
•
Pressure purging with nitrogen up to a pressure of 2 barg at the initial
startup or following maintenance work where the system is air filled
until an oxygen content of 3% is achieved
•
Locked and interlocked valves are in their normal operating position
•
Spectacle blinds and spades are in their normal startup position
•
In line block valves are in the correct position as per the valve position
schedule in the operating manual
•
All instrumentation is fully commissioned, checked and ready for
service
•
ESD systems are to be at process level startup status
•
Power generation and distribution are to be at normal status, with
switchgear racked-in and deisolated
•
Safety detection and protection systems are to be at normal status
•
Control valve handwheels are disengaged
•
At least one main oil line booster pump and one main oil line are
ready for startup
•
A series of operational checklists for verification of pre-startup
requirements will be available for each system and subsystem
The importance of good communications between all involved sections
must be of the highest quality at all times, particularly at this startup
stage
...
3
•
Continuous visual checks for leaks are obviously most important at this
critical stage as pressure and temperatures increase to their normal
operating conditions
•
Separator off-gas will be flared initially
...
For example, after an emergency shutdown all manual block
valves will still be open
...
Training Services
Page 13 of 13
© Petrofac 2010
Petrofac
Training Services
© Petrofac 2010
Figure 3
...
2
© Petrofac Training Services / June 2010
Figure 3
...
4
© Petrofac Training Services / June 2010
Figure 3
...
6
© Petrofac Training Services / June 2010
Title: three phase separator
Description: its study about spearator and studied about the process of separator
Description: its study about spearator and studied about the process of separator