Three Phase Separators

1. THREE PHASE
SEPARATORS
By Muhammad Atif Ilyas

2. Three Phase Separators
Introduction
•Threephaseseparatorsareusedtoseparategasandtwoliquidsofdifferent
densitiestypicallyoilandwater.
•TheyareacombinationofLiquid-LiquidandVaporLiquidseparators.
•Theyaretypicallyemployedinoil&gasfieldsindownstreamofwells.

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 atSeparator Inlet
•Theamountofliquidentrainedintothegas
phaseasdropletsisgenerallysmallfor
mostflowconditions,butwilltypically
begintoincreasefairlyrapidlyasthe
transitiontoannularflowisapproached.
•Taking into account both
entrainment/dropletsizesandsteadinessof
flow,sizingthefeedpipefor
stratified/waveflowisdesirable,ifpossible.
WhileAnnularFlowishighlyundesired.

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. Theinletvanedistributorsworkbysmoothly
dividingtheincomingflowintovarioussegments
usinganarrayofcurvedvanes.
Thebenefitsofthisdevicecomparedwith
simplerdeflectorssuchasdeflectorplates
include
•Reducedagitationandhence
•Improvedphaseoperationalperformance
•Morestablelevelcontrol
•Reducedfoaming.
Inlet Devices
Vane Distributor

14. Theinletcyclonicdeviceisusedinhorizontal
andsomeverticalseparatorswherethereisa
requirementfor
•Highmomentumdissipation
•Foamreduction
•Highcapacity
“Furthercomparisonofinletdeviceswillbe
discussedlateron”
Inlet Devices
Inlet Cyclone

15. Comparison of
Inlet Devices

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

17. •The applicableentrainment
mechanismforagivensetof
conditionsisstronglydependenton
theliquidphaseReynoldsnumber.
•Formanyseparationapplications,the
mainliquidentrainmentmechanismis
theshearingoffofroll-wavecrests.
•Theonsetofentrainmentbythis
mechanismwouldbeexpectedto
coincideapproximatelywiththe
wavy/annulartransition.
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
•Residence Time
Factors
Misc.

19. Configurations
There are two main configurations of three phase separators
•Horizontal
a)Horizontal Three Phase Separator with Boot
b)Horizontal Three Phase Separator with Overflow weir
c)Horizontal Three Phase Separator with Bucket and Overflow weir
d)Horizontal Three 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
Horizontal Three Phase Separators with Boot
•Ahorizontalseparatorwithabootis
commonlyusedforgas-liquid-liquid
separationwhereasmallamountof
waterispresentinhydrocarbonliquid
•Becausethesurgevolumespansthe
entirevessellengththisconfiguration
handlesslugswellaslongasthe
settlingregionissufficientforthe
heavyphasetosettleintothebootas
theslugisseparated.
•Inthemostcommonconfiguration
theinterfaceismaintained

23. Configurations
Horizontal Three Phase Separators with Overflow
Weir
•Asettlerwithasingleoverflowweiris
acommonconfigurationforgas-
liquid-liquidseparation,wherethe
liquid-liquidinterfaceiswelldefined.
•Whereslugsarepossiblethe
submergedweirispreferred.Inthis
designtheoveralllevelwillriseand
liquidresidencetimewillincrease
whenaslugenterstheseparator

24. •Asettlerwitha“bucket”,andan
overflowweir,iscommonly
usedforapplicationswherea
smallamountofhydrocarbonis
tobeseparatedfromwater.
Configurations
Horizontal Three Phase Separators with Overflow
Weir and Bucket

25. Configurations
Horizontal Three Phase Separators with Coalescer
•Coalescerinternalscanbeused
withalloftheabovehorizontal
three phase separator
configurations.
•Thedesignisbestsuitedfor
separationofdifficult-to-
separatedispersionsandfor
highoutletproductquality
specifications

26. Factors That Determine
Vessel Orientation
Feature Vertical Horizontal
Compactseparator 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 dominatedservices - Yes

27. Feature Vertical Horizontal
Threephase separation - Yes
Liquid-liquidseparation - Yes
Highliquid degassing residence
time
- Yes
Piggingand slug flow separation - Yes
Foamingfeed - Yes
Highliquid surge capacity - Yes
Largecapacity flare KO drum - Yes
Solid removalthrough jetting - Yes
High liquid and vapor flow rates Yes Yes
Factors That 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. •Advantagesoftheseseparatorsare:
•Requiresmallerdiameterforsimilargascapacityascomparedtovertical
vessels.
•Nocounter-flow(gasflowdoesnotopposedrainageofmistextractor).
•Largeliquidsurfaceareaforfoamdispersiongenerallyreducesturbulence.
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)Without Wire mesh
b)With Wire Mesh
•Liquid-Liquid Separation Zone
a)Conventional
b)With Boot
c)With Overflow Weir
Criterion for
Horizontal Three Phase Separator Sizing

35. •Checkthatthevaporvelocitysatisfiesthefollowingequationinorderto
avoidentrainment.Theareausedforthevaporvelocityshallbethevertical
cross-sectionalareaabovehighliquidlevel.
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 levelu
L
H
u
h t
1
1
Vapor Liquid Separation Zone
Without Mesh

36. •Theminimumvaporspaceabovethehighliquidlevelshouldbelargerthan
15%ofthedrumdiameteror300mm,whicheveristhegreatertoavoid
entrainmentofliquid
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.uK
DR
a
g
g


100


 L Q
u
a
a
1
10003600


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 mesh03 11. . uu u
awm a u
wm
015. m/s 




















2
1000
1
3600
LQ
u
a
wm wmu
Vapor Liquid Separation Zone
With Mesh

39. •Checktheliquidvelocitywhichisgivenbyfollowingequationinorderto
avoidentrainmentofheavierliquid.Terminalvelocityofheavierdroplets
shallbeestimatedbyu
L
H
u
h 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. •Checkthelighterliquidvelocityinthiszoneforheavierdropletseparation.
Liquid-Liquid Separation Zone
With Overflow Weiru
L
H
u
h
s
t
1

44. Any questions ? Hope you don’t 