1. THREE PHASE
SEPARATORS
By Muhammad Atif Ilyas

2. Three Phase Separators
Introduction
• Three phase separators are used to separate gas and two liquids of different
densities typically oil and water.
• They are a combination of Liquid - Liquid andVapor Liquid separators.
• They are typically employed in oil & gas fields in downstream of wells.

3. Three Phase Separators
Zones
Regardless of the internal configuration all liquid / liquid and gas / liquid / liquid
separators consist of three basic zones:
• Inlet section
• Liquid-liquid settling section
• Gas- Liquid Separation zone

4. Water
Oil
Inlet Nozzle(Three Phase Flow)
Water
Outlet
Nozzle
Oil Outlet
Nozzle
Gas Liquid
Separation
Zone
Liquid-Liquid
Separation
Zone
Oil
Water
Gas
Inlet
Zone
Three Phase Separator
General Figure

5. Factors Affecting
Separator Efficiency
• Flow Pattern at Separator Inlet
• Feed Pipe Geometry
• Inlet Device
• Entrainment
• Other Internals

6. Factors
Flow Pattern at Separator Inlet
• The amount of liquid entrained into the gas
phase as droplets is generally small for
most flow conditions, but will typically
begin to increase fairly rapidly as the
transition to annular flow is approached.
• Taking into account both
entrainment/droplet sizes and steadiness of
flow, sizing the feed pipe for
stratified/wave flow is desirable, if possible.
While Annular Flow is highly undesired.

7. Factors
Feed Pipe Geometry

8. Typical guidelines are:
• Provide 10 diameters of straight pipe upstream of the inlet nozzle without
valves, expansions/contractions or elbows.
• Path changing fittings must be avoided in the immediate upstream of
separator as it can change the flow regime and can also cause circulation of
flow.
• If a valve in the feed line near the separator is required, it should only be a
full port gate or ball valve.
Factors
Feed Pipe Geometry

9. • Inlet devices are typically selected and sized
based on the inlet momentum (sometimes
referred to as dynamic pressure) of the
separator feed stream.
• The intent is to reduce the energy/velocity
of the feed fluids to provide conditions
favorable for phase separation
Factors
Inlet Devices

10. Most Commonly used devices include
• Diverter Plates
• Half Pipe
• Vane Distributor
• Inlet Cyclone
Inlet
Devices

11. It can be used for flows with little gas load and
little tendency for foaming. Disadvantages
include
• Poor Bulk Separation
• Liquid Droplets get shattered
• Creates fine droplets which is undesired
Review of Inlet Devices
Diverter Plate

12. Half open pipes are the modified versions of
90° elbow devices suitable for both vertical
and horizontal separators, with slightly
improved bulk liquid removal and reasonable
gas distribution.
• In horizontal vessels, the last section of the
half open pipe should be horizontal;
pointing opposite to the flow direction in
the vessel and with its opening directed
upward.
• In vertical vessels, the last section is closed
and its opening is directed downward
Inlet Devices
Half Pipe

13. The inlet vane distributors work by smoothly
dividing the incoming flow into various segments
using an array of curved vanes.
The benefits of this device compared with
simpler deflectors such as deflector plates
include
• Reduced agitation and hence
• Improved phase operational performance
• More stable level control
• Reduced foaming.
Inlet Devices
Vane Distributor

14. The inlet cyclonic device is used in horizontal
and some vertical separators where there is a
requirement for
• High momentum dissipation
• Foam reduction
• High capacity
“Further comparison of inlet devices will be
discussed later on”
Inlet Devices
Inlet Cyclone

15. Comparison of
Inlet Devices

16. • Demisters
• Calming Baffles/Perforated Plates
• Coalescers
Factors
Other Internals

17. • The applicable entrainment
mechanism for a given set of
conditions is strongly dependent on
the liquid phase Reynolds number.
• For many separation applications, the
main liquid entrainment mechanism is
the shearing off of roll-wave crests .
• The onset of entrainment by this
mechanism would be expected to
coincide approximately with the
wavy/annular transition.
Factors
Entrainment

18. • Presence of impurities (paraffin, sand, scale, etc.)
• Foaming tendencies of the crude oil
• Corrosive tendencies of the liquids or gas.
• Operating and design pressures and temperatures
• ResidenceTime
Factors
Misc.

19. Configurations
There are two main configurations of three phase separators
• Horizontal
a) HorizontalThree Phase Separator with Boot
b) HorizontalThree Phase Separator with Overflow weir
c) HorizontalThree Phase Separator with Bucket and Overflow weir
d) HorizontalThree Phase Separator with coalescer
• Vertical

20. • Horizontal separators are almost always used for high GOR wells, for
foaming well streams and for liquid-liquid separation.
Configurations
Horizontal Separators

21. • A vertical separator can handle relatively large liquid
slugs without carryover into the gas outlet.
• It thus provides better surge control and is often used
on low to intermediate gas-oil ratio (GOR) wells and
wherever else large liquid slugs and more sands are
expected
Configurations
Vertical Separators

22. Configurations
HorizontalThree Phase Separators with Boot
• A horizontal separator with a boot is
commonly used for gas-liquid-liquid
separation where a small amount of
water is present in hydrocarbon liquid
• Because the surge volume spans the
entire vessel length this configuration
handles slugs well as long as the
settling region is sufficient for the
heavy phase to settle into the boot as
the slug is separated.
• In the most common configuration
the interface is maintained

23. Configurations
HorizontalThree Phase Separators with Overflow
Weir
• A settler with a single overflow weir is
a common configuration for gas-
liquid-liquid separation, where the
liquid-liquid interface is well defined.
• Where slugs are possible the
submerged weir is preferred. In this
design the overall level will rise and
liquid residence time will increase
when a slug enters the separator

24. • A settler with a “bucket”, and an
overflow weir, is commonly
used for applications where a
small amount of hydrocarbon is
to be separated from water.
Configurations
HorizontalThree Phase Separators with Overflow
Weir and Bucket

25. Configurations
HorizontalThree Phase Separators with Coalescer
• Coalescer internals can be used
with all of the above horizontal
three phase separator
configurations.
• The design is best suited for
separation of difficult-to-
separate dispersions and for
high outlet product quality
specifications

26. FactorsThat Determine
Vessel Orientation
Feature Vertical Horizontal
Compact separator Yes Yes
Small footprint Yes -
Small liquid surge drum Yes -
Solid removal with liquid Yes -
Small capacity flare KO drum Yes -
Gas dominated services Yes -
Liquid dominated services - Yes

27. Feature Vertical Horizontal
Three phase separation - Yes
Liquid-liquid separation - Yes
High liquid degassing residence
time
- Yes
Pigging and slug flow separation - Yes
Foaming feed - Yes
High liquid surge capacity - Yes
Large capacity flare KO drum - Yes
Solid removal through jetting - Yes
High liquid and vapor flow rates Yes Yes
FactorsThat Determine
Vessel Orientation

28. • Have good bottom-drain and clean-out facilities.
• Can handle more sand, mud, paraffin, and wax without plugging.
• Fewer tendencies for entrainment.
• Has full diameter for gas flow at top and oil flow at bottom.
• Occupies smaller plot area..
Advantages of
Vertical Separators

29. • Advantages of these separators are:
• Require smaller diameter for similar gas capacity as compared to vertical
vessels.
• No counter-flow (gas flow does not oppose drainage of mist extractor).
• Large liquid surface area for foam dispersion generally reduces turbulence.
Advantages of
Horizontal Separators

30. • Providing sufficient time to allow the immiscible gas, oil, and water phases
to separate by gravity.
• Providing sufficient volume in the gas space to accommodate rises in the
liquid level that result from the surge in the liquid flow rate.
• Allowing for variation in the flow rates of gas, oil, and water into the
separator without adversely affecting separation efficiency.
• Increasing gas flow yields improved droplet capture, but also increases re-
entrainment which results in liquid carryover and limits separation capacity.
Tidbits for
Separator Sizing

31. Data and Information Required
to Specify and Size Separators
• Separator environment: wellhead, offshore, gas plant
• Service: K.O. drum, gas-liquid separator, surge, flash drum, reflux drum, crude oil
separator, solids removal
• Physical space limitations
• Typical sizing parameters for this service
• Separator effluent requirements / separation efficiency needed: Bulk liquid
removal and/or fine mist removal.
• Effect of separation efficiency on downstream equipment
• Conditions of service: clean, fouling, or potentially plugging service determines
types of entrainment separation devices that may be considered

32. Data and Information Required
to Specify and Size Separators
• Operating Conditions: gas and liquid flow rates, operating temperature and
pressure, gas and liquid physical properties
• Design factor for sizing:Typically design factor is based on either maximum
operating flow rate alone or operating flow rate plus a factor.This decision
should be based on specific service and project criteria
• Liquid residence time requirements for de-gassing or other needs for this
service based on experience or specific project criteria
• Liquid-liquid settling time requirements

33. Data and Information Required
to Specify and Size Separators
• Inlet slug size and frequency
• Surge time requirements
• Nature of fluids being contained: hazardous properties (toxic, flammable,
lethal, etc.) and corrosively
• Mechanical design conditions: design pressure and temperature, corrosion
allowance, material of construction, minimum design metal temperature,
and any project specific requirements

34. • Vapor Liquid Separation Zone
a) WithoutWire mesh
b) WithWire Mesh
• Liquid-Liquid Separation Zone
a) Conventional
b) With Boot
c) With OverflowWeir
Criterion for
HorizontalThree Phase Separator Sizing

35. • Check that the vapor velocity satisfies the following equation in order to
avoid entrainment. The area used for the vapor velocity shall be the vertical
cross-sectional area above high liquid level.
ut = terminal velocity of liquid droplet (m/s)
uh = horizontal vapor velocity (m/s)
L1 = distance between vapor inlet nozzle and vapor outlet nozzle (mm)
H1 = height of vapor section(the section above the high level
u
L
H
uh t
1
1
Vapor Liquid Separation Zone
Without Mesh

36. • The minimum vapor space above the high liquid level should be larger than
15% of the drum diameter or 300 mm, whichever is the greater to avoid
entrainment of liquid
Vapor Liquid Separation Zone
Without Mesh

37. • Maximum allowable velocity at wire mesh pad is calculated by following formula
• Vapor velocity passing through wire mesh pad shall be equal to or smaller than
maximum allowable velocity. Actual pad length is larger than required pad length
by 100 mm for support plate.
L2 = L1 + 100
• Height from high liquid level to underside of wire mesh (H1) shall be 0.50L1 or
minimum 150 mm to avoid re-entraining from liquid surface.
u K
DR
a
g
g
 

100
 


L Q
u
a
a
1
1000 3600


Vapor Liquid Separation Zone
With Mesh

38. • Check that the velocity through
mesh pad is kept high enough for
good separation.
=Vapor velocity at wire mesh
0 3 11. .   u u ua wm a uwm  0 15. m/ s





















2
1000
1
3600
LQ
u a
wm
wmu
Vapor Liquid Separation Zone
With Mesh

39. • Check the liquid velocity which is given by following equation in order to
avoid entrainment of heavier liquid. Terminal velocity of heavier droplets
shall be estimated by
u
L
H
uh t
1
1
Liquid-Liquid Separation Zone
Conventional
 
u
gD
t
P h

2
18
 




40. • Total liquid flow rate (sum of heavier and lighter)
shall be used for liquid velocity (uh ). Sectional
area (A1) for liquid velocity shall be based on
H1+H2.
• (4)The minimum vapor space above the high
liquid level should not be less than 15% of the
drum diameter or 300 mm, whichever is the
greater for avoiding entrainment of liquid.
• (5) Lighter Liquid Low Level (LLL) should be
separated at least 200 mm from Heavier Liquid
High Interface Level (HIL). Outlet nozzle of higher
liquid should be extended above HIL by min. 100
mm.
Liquid-Liquid Separation Zone
Conventional

41. • Holding time of heavier liquid in boot (from low interface level (LIL) to high
interface level (HIL)) shall be minimum five (5) minutes as a guideline.
Minimum height from LIL to HIL shall be 300 mm.
• Minimum boot diameter shall be 250 mm (10") for good operability of
heavier draw off. Commercial pipe up to 24" should be applied from
economical standpoint.
• Maximum boot diameter shall be 1/3 of the drum inside diameter. When
larger diameter is required, consult mechanical engineer
Liquid-Liquid Separation Zone
With Boot

42. • LS (length of separation zone) should be no
less than 0.85D (diameter). A approximate LS
from inlet nozzle to boot center can be given
as follows.
• L1 : nozzle nominal diameter (mm) + 200
• L2 : Boot diameter (d) + outlet nozzle nominal
diameter + 0.1*drum diameter + 350
• L3 : nozzle nominal diameter (mm) + 200
• Calculate and check LS
• LS = L - (L1 + L2 + L3), LS0.85D
• Criteria for Uh is checked
Liquid-Liquid Separation Zone
With Boot

43. • Check the lighter liquid velocity in this zone for heavier droplet separation.
Liquid-Liquid Separation Zone
With Overflow Weir
u
L
H
uh
s
t
1

44. Any questions ? Hope you don’t 