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Page 1: Liquid and gas separation

Oil and gas processing (Onshore)

Page 2: Liquid and gas separation

Oil & gas separation SEPARATOR:

• Pressure vessel separating well fluids into gaseous/ vapour and liquid components

Page 3: Liquid and gas separation

Main facilities and operations in oil installation

1) Well head & choke 2) Flow lines 3) Manifold facilities 4) Testing of wells 5) Liquid and gas separation facilities 6) Oil and gas dehydration system7) Desalting8) Storage9) Shipment of products

Page 4: Liquid and gas separation

Main facilities and operations in GGS

- Oil and gas metering- Instrumentation and control system - Maintenance of equipments- Information & communication system- Utilities e.g. power, water and air- Office building- Fire fighting facilities- Transportation

Page 5: Liquid and gas separation

Oil & gas separationSEPARATORS OF PRODUCING FIELD:

• Oil & gas separator• Stage separator• Trap• Knock out vessel/drum/trap or

liquid knock out• Flash chamber /vessel/ trap• Expansion separator /vessel• Gas scrubber (dry/wet )• Gas filter ( dry/wet)• Filter /Separator

Page 6: Liquid and gas separation

Well head and well fluids

SBHPFBHPSBHT

FTHPFTHT

ABPABT

Choke 3.5”/4” 4/5 km.API 5L

Multiphase HC mixture with varying compositions and densities

Gas phase Liquid phase:

2 immiscible liquids

• Oil• Water

Page 7: Liquid and gas separation

HP TestMPHeaders

WELL#1

WELL#2

WELL#3

NRV

To HP separator

To MP separator

To test separator

NRV

NRV

Well manifold

PG

PG

PG

Page 8: Liquid and gas separation

Well Fluid from header

Gas to GDU/ Consumers

Produced water to ETP

Separator

Crude oil to dehydrator

Block diagram well fluids processing

Page 9: Liquid and gas separation

Utilization of gas and oil

• Gas is used for value added products- LPG- C2/C3- Gas to consumers

• Oil is supplied to refineries for distillation

Page 10: Liquid and gas separation

Classification of Installations

a) For one or two wells: well head installation (WHI) b) For many oil wells: group gathering station (GGS) c) For gas wells: gas collecting station (GCS) d) For oil storage and shipment : central tank farm (CTF) e) For gas shipment : gas compressor plant (GCP)f) For gas conditioning: Gas dehydration unit (GDU)

& gas sweetening unit (GSU)g) For water handling: Effluent treatment plant (ETP)h) Other plants: LPG recovery, C2-C3 unit, CSU etc.

Page 11: Liquid and gas separation

Well connection configuration

Multiphase HC mixture and water flowing through individual lines (preferred)

GGSWELL

WELLWELL

WELL

WELL

WELL

WELL

WELLWELL

Page 12: Liquid and gas separation

Well connection configuration

Multiphase HC mixture and water flowing through interconnected lines (not preferred)

GGSWELL

WELL WELL

WELL

WELL

WELL

WELL

WELLWELL

Page 13: Liquid and gas separation

Well connection configuration

Multiphase mixture flowing through well pads and group & test lines to GGS

GGS

WELL

WELL WELL

WELL

WELL

WELL

WELL

WELL

WELL

Pad Pad

Page 14: Liquid and gas separation

Well connection configurationCentral Tank Form (CTF)

GGSWell

Well Well

Well

Well

Well

Well

WellWell

GGSWell

WellWell

Well

Well

Well

Well

WellWell

CTF

Pump

GGS

Page 15: Liquid and gas separation

Typical PFD of GGS

HP MP Test

HP MP

TestOilStb.

Scrubber

KOD Flare

To consumers

To flare

Tank

Flare header

To ETP Pump

BH

BH

BH

HT

Bath heater

Heater treater

Page 16: Liquid and gas separation

Typical PFD of GCS

HP MP Test

MeOH or BH

HP MP

TestCond.Stb.

Scrubber

KOD Flare

Consumers

To flare

Tank

Cond.Stb.

Flare header

To ETP Pump

Page 17: Liquid and gas separation

Oil & gas separation

Fluid 0API (cP)

Oil 6 – 50 5 - 90,000

Condensate 50 - 120 2 - 6

Gas 0.5 - 0.9 0.011 - 0.024

WELL FLUIDS:• Mixture of oil, gas and water / Free gas

• Impurities / Extraneous material Nitrogen, CO2, H2S etc., Water, Paraffin Sand, silt etc.,

Page 18: Liquid and gas separation

Oil & gas separation

Separated crude oil

Depending on retention time,

Free gas content in separated oil = 1.5% to 20%

Water content of separated Oil = 0.05% to 8%

Quality improvement possible by chemical,

equipment, techniques and procedures

Quality of separated fluids

Page 19: Liquid and gas separation

Oil & gas separation

Separated water:Depending on retention time,Oil content in eff. Water = 0.004% to 2.0%Special methods and separating techniques can improve water quality.Difference in sp.gr. of oil and water less than 0.2 results in limited and incomplete separation.

Quality of separated fluids

Page 20: Liquid and gas separation

Oil & gas separation

Separated Gas:For a separator with suitable mist extractor, Oil content in separated gas = 0.101 to 1.0

gal/mmscf In case of gas scrubbers oil content in effluent

gas should be less than 0.1 gal/mmscf.

Quality of separated fluids

Page 21: Liquid and gas separation

Oil & gas separation

Measurement

Oil in separated gas

Gas in separated oil

Water in separated oil

Oil in effluent water

Instrument

Laser liq. Particle spectrometer

Nucleonic densitometer

BS&W monitor

Ultraviolet absorption unit/

Solvent extraction/

Infrared absorbence.

Instruments for measuring quality of separated fluids:

Page 22: Liquid and gas separation

Functions of separators

Primary functions1. Removal of oil from gas

2. Removal of gas from oil

3. Removal of oil from water

Secondary functions1. Maintain optimum

pressure

2. Maintain liquid seal

Oil & gas separation

Page 23: Liquid and gas separation

Oil & gas separationProcess of separation: Separation of bulk liquid from gas Reduction in gas velocity to allow liquids to drop out Scrubbing of the gas Retaining liquids long enough for free gas

separation Controlling and maintaining gas oil interface. Removal of all products from their respective out

lets.

Page 24: Liquid and gas separation

Classification of separators

Configuration

VerticalHorizontalSpherical

Low pr. Sep.(10 - 225psi)Med. Pr. Sep.(225 - 750 psi)High pr. Sep.(750 - 1500 psi)

Application Function Principle ofprimary sep.

Operating pressure

Test sep.Prodn. Sep.L.T.S.Elevated sep.Stage sep.Metering sep.Foam sep.

2-phase3-phase

Gravity sep.Impingement/coalescence sep.centrifugal sep.

Oil & gas separation

Page 25: Liquid and gas separation

Oil & gas separation

Stage separation of oil and gas: Series of separators operating at sequentially

reduced pressures. Liquid is discharged from high pressure separator

into the next lower pressure separator Aims at maximum recovery of liquid hydrocarbon

and maximum stabilization of separated fluids. Economics limits the no. of stages of separation to

3 to 4

Page 26: Liquid and gas separation

Oil & gas separation

Stabilization of crude oil : Operation of separator under vacuum / at high temp.

Liquid discharged completely stabilized

Liquid recovery comparable to that of 4-6 stage

separation

Results in increased profit for highly volatile liquids

Initial cost of stabilizer less than initial cost of multiple

stage oil and gas separators.

Page 27: Liquid and gas separation

SeparatorsBenefits of separation Separated gas, crude oil and produced water

can be processed easily at low cost Removal of water helps in reducing damage

due to corrosion Less costly MOC can be used if water is

removed Less energy is required to move single

phases

Page 28: Liquid and gas separation

SEPARATION

• Pressure• Temperature• Gas Oil Ratio (GOR)• Flow rate• Fluid properties like density, viscosity etc.

Depends on following factors:

Page 29: Liquid and gas separation

Oil & gas separation

Principles of separation of “Oil from gas” Density difference Impingement Change of flow direction Change of flow velocity Centrifugal force Coalescence Filtering

Page 30: Liquid and gas separation

Oil & gas separation

Principles of separation of “Gas from oil Settling Agitation Baffling Heat Chemicals

Page 31: Liquid and gas separation

PRINCIPLES OF SEPARATION:Based on one or more of the following:Removal of Oil from Gas Removal of Gas from Oil

Gravity Separation SettlingImpingement Agitation

Change of flow direction BafflingChange of flow velocity Heat

Filtering ChemicalsCoalescence

Centrifugal

Page 32: Liquid and gas separation

Gravity Separation

Diff. Liquid phases

PRINCIPLES OF SEPARATION (OIL FROM GAS) :

Diff. momentum

Diff. Densities

Page 33: Liquid and gas separation

Gravity Separation:

Terminal / Free settling velocity of droplet

Vt = [4 g Dp (l - g) / 3 g C’]

Max. allowable gas velocity

PRINCIPLES OF SEPARATION (OIL FROM GAS) :

Page 34: Liquid and gas separation

Impingement :

If a flowing stream of of gas containing liquid

mist is impinged against a surface, the liquid

mist may adhere to and coalesce on the surface.

PRINCIPLES OF SEPARATION (OIL FROM GAS) :

Page 35: Liquid and gas separation

Change of flow direction:

Change in flow direction: Change in inertia

Gas assumes change in direction readily

Liquid gets retarded and flow back

PRINCIPLES OF SEPARATION OIL FROM GAS :PRINCIPLES OF SEPARATION (OIL FROM GAS)

Page 36: Liquid and gas separation

Change of flow velocity:

Change in flow velocity: Change in inertia

Increase / decrease in velocity: High inertia liquid moves away from gas

PRINCIPLES OF SEPARATION OIL FROM GAS :PRINCIPLES OF SEPARATION (OIL FROM GAS) :

Page 37: Liquid and gas separation

Filtering :

Porous filters are effective to remove liquid mist.

Uses the principles of impingement, change in direction, change in velocity and coalescence.

PRINCIPLES OF SEPARATION OIL FROM GAS :PRINCIPLES OF SEPARATION (OIL FROM GAS) :

Page 38: Liquid and gas separation

CoalescingCoalescing of small droplets (mist/fog)

PRINCIPLES OF SEPARATION :

Settling by gravity

Formation of large droplets

PRINCIPLES OF SEPARATION OIL FROM GAS :PRINCIPLES OF SEPARATION (OIL FROM GAS) :

Page 39: Liquid and gas separation

Centrifugal force:

Fluids allowed to flow in circular motion at high velocity.

Centrifugal force throws liquid mist outward against the walls of the vessel.

PRINCIPLES OF SEPARATION OIL FROM GAS :PRINCIPLES OF SEPARATION (OIL FROM GAS):

Page 40: Liquid and gas separation

Settling :

Non solution gas separate on adequate retention time

Optimum removal of gas – if body of oil is thin

PRINCIPLES OF SEPARATION (GAS FROM OIL ):

Page 41: Liquid and gas separation

Agitation/Baffling:

Controlled agitation helps removing non solution gas

Disperses oil in such a manner that gas readily escapes

Allows gas bubbles coalesce and separate

PRINCIPLES OF SEPARATION (GAS FROM OIL ):

Page 42: Liquid and gas separation

Heat :

Hydraulically retained gas releases on reduction of surface tension or viscosity

Heat reduces surface tension and viscosity of oil.

PRINCIPLES OF SEPARATION (GAS FROM OIL ):

Page 43: Liquid and gas separation

Chemical :

Hydraulically retained gas releases on reduction of surface tension or viscosity

Certain chemicals can reduce surface tension and foaming tendency of oil.

PRINCIPLES OF SEPARATION GAS FROM OIL :PRINCIPLES OF SEPARATION (GAS FROM OIL ):

Page 44: Liquid and gas separation

Centrifugal force :

Heavier oil is thrown outward against wall of vortex retainer and gas occupies inner portion.

Properly designed vortex allow gas to ascend and liquid to flow downward

PRINCIPLES OF SEPARATION GAS FROM OIL :PRINCIPLES OF SEPARATION (GAS FROM OIL ):

Page 45: Liquid and gas separation

1. Two phase separator Separation of liquid (oil + water) and gas

CLASSIFICATION OF SEPARATORS:

2. Three phase separator Separation of liquid and gas Separation of water and oil

Page 46: Liquid and gas separation

MAIN SECTIONS/COMPONENTSOF A SEPARATOR

1. Primary separating section

2. Secondary or gravity separating section

3. Coalescing section4. Sump or liquid section

HORIZONTAL SEPARATOR

CA B

D

Two Phase Inlet Gas Outlet

Liquid Outlet

Mesh Pad

B

D

A

Mesh Pad

VERTICAL SEPARATOR

Liquid Outlet

Gas Outlet

Two phaseInlet

A – Primary SeparationB – Gravity SettlingC – CoalescingD – Liquid Collecting

Page 47: Liquid and gas separation

Oil & gas separation

Components of oil and gas separators: Primary separation device and /or section

Secondary gravity settling section

Mist extractor

Gas out let

Liquid settling section

Page 48: Liquid and gas separation

Oil & gas separationComponents of oil and gas separators: Oil out let Water out let Vortex breakers Back pressure control valve Level control valves Pressure relief valves

Page 49: Liquid and gas separation

Oil & gas separation

Essential features of separators: Inlet baffle / Impingement baffle / divertor Adequate liquid capacity to handle liquid

surges Adequate vessel diameter and height for

vapor disengagement Internal baffle / defoaming plates Demister pad / mist eliminator

Page 50: Liquid and gas separation

1. Primary separating section

• Separate bulk portion of free liquid from inlet stream

• Inlet diverter / Inlet baffle / Impingement baffle

MAIN SECTIONS/COMPONENTS OF A SEPARATOR

Inlet Diverter

Vane typeMist Extractor

VaporOutlet

Dv

Downcomer

Liq. Outlet

Two phaseInlet

Page 51: Liquid and gas separation

2. Secondary or gravity separating section• Settling section• Reduced turbulence• Retention time

MAIN SECTIONS/COMPONENTS OF A SEPARATOR

• Straightening vanes/ Settling vanes

• Defoaming plates

Page 52: Liquid and gas separation

3. Coalescing section• Coalescer or mist

extractor/demister pad• Interwoven mesh• Gets plugged very easily with

heavier hydrocarbons or deposits

• Requires frequent cleaning

MAIN SECTIONS/COMPONENTS OF A SEPARATOR

Knitted wire mesh type

Page 53: Liquid and gas separation

3. Coalescing section• Coalescer or mist

extractor/ demister pad

MAIN SECTIONS/COMPONENTS OF A SEPARATOR

Vane type

• Does not require frequent cleaning

• Better suited to crudes having high wax and deposition tendency

Page 54: Liquid and gas separation

4. Sump / Liquid Collection Section• Receiver for all liquid separated from

well fluid in first 3 sections• Minimum level required for liquid

controls• Requirement of surge volume for

degassing or slug removal

MAIN SECTIONS/COMPONENTS OF A SEPARATOR

Vortex breaker

Page 55: Liquid and gas separation

SEPARATOR CONFIGURATION:

1. Vertical separator2. Horizontal separator3. Spherical separator4. Centrifugal separator5. Compact Separators/Hydro-cyclones

• Vertical and Horizontal type separators are the most common in the oil industry

Page 56: Liquid and gas separation

1. Vertical Separator (Advantages)

SEPARATOR CONFIGURATION:

• Low to medium GOR streams• When relatively large liquid

slugs are expected• Incidence of sand, paraffin, wax• Limited plot space• Ease of level control is desired• Full diameter for gas & liq. flow

Page 57: Liquid and gas separation

Vertical separators Disadvantages

- Larger diameter for given gas capacity

- More difficult to skid mount and ship

- More difficult to reach and service top

mounted devices

Page 58: Liquid and gas separation

2. Horizontal Separator (Advantages)

SEPARATOR CONFIGURATION:

• High to medium GOR streams• Less difficult to skid mount and ship• Larger volume of gas• Foaming crude• 3- separation

Page 59: Liquid and gas separation

Horizontal separators Disadvantages

Only part of shell available for gas

separation Occupies more area Liquid level control is more critical More difficult to clean produced

sand

Page 60: Liquid and gas separation

SEPARATOR SELECTION CRITERIA:

Vertical Separator Horizontal SeparatorLow to medium GOR Medium to high GORWhen large liquid slugs are expected

For larger volumes of gas

Incidence of sand, paraffin or wax

For foaming crude

Limited plot space For 3- separationEase of level control is desired

Page 61: Liquid and gas separation

General guidelines for use

Compressor KODFuel gas KODDegassing bootsAbsorber feed KOD

Production separator

3-Phase separationReflux drumFlare KOD

Vertical Horizontal

Page 62: Liquid and gas separation

SEPARATOR CONFIGURATION:

3. Spherical Separator• Most commonly used for

separation of large vol. of gas from extremely small vol. of liquid

• High pressure service where compactness is desired

• Limited liquid surge capacity

Page 63: Liquid and gas separation

4. Centrifugal/compact separators

- Relatively new type of separators

- Technology still developing - Less efficient than other separators

SEPARATOR CONFIGURATION:

Page 64: Liquid and gas separation

- Less maintenance is involved

- Less space is required - Light in weight - Less expensive

• Advantages

Centrifugal/compact separators

Page 65: Liquid and gas separation

• Not suitable for large liquid slugs

• Efficiency not as good as other types

• Narrow operating flow range for highest efficiency

• Disadvantages

Centrifugal/compact separators

Page 66: Liquid and gas separation

Comparison of separators

Page 67: Liquid and gas separation

Separator design guidelines

Sufficient residence time for both oil and water is provided to enable separation of water from oil and oil from water.

Enough free space is left at the top for separation of liquid from gas.

Page 68: Liquid and gas separation

SEPARATOR SPECIFICATIONS:

Retention time for liquid-liquid separation

• Retention time determines the liquid capacity of a separator

• API 12J recommendations are available for specifying retention time for 2- phase and 3- separator

Page 69: Liquid and gas separation

SEPARATOR SPECIFICATIONS:

Retention time for liquid-liquid separation

• API 12J allows equal retention times for both oil and water

• If problems such as foaming, wax, or slug flows are encountered, additional retention time may have to be considered

Page 70: Liquid and gas separation

Retention time (min.)Oil API Gravity

2 to 410 - 20

1 to 220 – 30

1Above 35

API RECOMM. FOR 2- SEPARATION

SEPARATOR SPECIFICATIONS :

Retention time for liquid-liquid separation

10 to 20Below 35, Sep temp > 80 oF

Retention time (min.)Oil API Gravity

20 to 30Below 35, Sep temp > 60 oF

5 to 10Below 35, Sep temp > 100 oF

3 to 5Above 35

API RECOMM. FOR 3- SEPARATION

Page 71: Liquid and gas separation

Holdup time:SIZING CRITERIA FOR A SEPARATOR

• Time it takes to reduce the liquid level from NLL to LLL, while maintaining a normal outlet flow without feed make-up

• Based on the reserve required to maintain good control and safe operation of downstream facilities

T

T

Di

h1h2h3h4

h5

h6

h7

h8

HLA

HLL

NLL

LLL

LLA

Page 72: Liquid and gas separation

SIZING CRITERIA FOR A SEPARATORSurge time :

• Time it takes for the liquid level to rise from NLL to maximum or HLL, while maintaining a normal feed flow without any outlet flow

• Based on requirements to accumulate liquid as a result of upstream or downstream variations, e.g. slugs

• Normally, surge time is taken as ½ of holdup time

T

T

Di

h1h2h3h4

h5

h6

h7

h8

HLA

HLL

NLL

LLL

LLA

Page 73: Liquid and gas separation

Design conditions for pressure vessels

Operating Pr (Bar)0-1010-3535-70> 70

Design Pr (Bar)MOP + 1 BarMOP + 10%MOP + 3.5%MOP + 5%

MOP: Maximum operating pressure

Pressure

Page 74: Liquid and gas separation

Design conditions for pressure vessels

Temperature Max design temperature = Max op. temp +

15 oC Min Design temperature = Min op. temp – 5

oC Note: Minimum design temperature must take into account of depressurization of the vessel

Page 75: Liquid and gas separation

Sizing of vertical separators Calculate settling velocity

vs = k [ (l - v )/ v ]1/2

l = Liquid density, kg/m3 v = Vapour density, kg/m3 vs = settling velocity, m/s k = correlating factor (Find out from table)

Page 76: Liquid and gas separation

Sizing of vertical separators

Derate calculated settling velocity by 85% for design margin.

Calculate internal diameter Di= [ 4Q/vs]1/2

Where Di = Internal dia, mm Q = Flow rate, M3/s Round the ID to nearest 50 mm.

Page 77: Liquid and gas separation

Sizing of vertical separator Height calculation

h1= Max 15% of dia. or 400mmh2= 150mm for mesh padh3= max ( 50% of dia. or 600mm)h4= 400mm +d/2; d: inlet nozzle,mmh5= calculate based on 1-2 min residence time at maximum liquidh6= calculate based on 4-5 min hold up timeh7= calculate based on 1-2 min residence time h8= 300mm for bottom connection, 150mm for side connectionHt= h1+ h2 + h3 + h4 + h5 + h6 + h7 + h8

TT

Di

h1h2h3h4

h5

h6

h7

h8

HLA

HLL

NLL

LLL

LLA

Page 78: Liquid and gas separation

Sizing of vertical separators Wall thickness

t = {PDi / (2SE-1.2P)}+ C

Di = Internal dia., mm t = wall thickness, mm P = design pressure, barg

E = joint efficiency (use 1.0 for seamless shells 0.85 otherwise)S = Max allowable stress, bar

C = Corrosion allowance, mm

Page 79: Liquid and gas separation

Sizing of vertical separators Weight calculation

- Shell weight with ellipsoid head

Wt= s (tDiHt+2x1.09xDi2)x10-9

WhereWt= Bare vessel weight with ellipsoid head, Kg s = CS density = 7865.55 Kg/m3

Page 80: Liquid and gas separation

Sizing of vertical separators Weight calculation

- Shell weight with dished head

Wt = s(tDiHt+2x0.842xDi2)x10-9

where:Wt= bare vessel weight with dished head, Kg

s= CS density = 7865.55 Kg/m3

Page 81: Liquid and gas separation

Sizing of vertical separators Weight calculation

- Weight of the vessel can also be calculated from graph based on thickness, length and diameter.

Page 82: Liquid and gas separation

Nozzle sizing of separatorsInlet nozzle Size based on normal volumetric flow + 10% Limit inlet velocity to 7-13 m/s Round nozzle diameter to nearest standard size

Gas outlet Size based on normal flow arte Limit velocity to 15-30 m/s

Liquid outlet Normal flow rate + 10% Limit velocity to 1-3 m/s for HC

2-4 M/S for water

Page 83: Liquid and gas separation

SEPARATOR DESIGN :Horizontal 2-Separator

• Calculate settling velocity Vs

• Vessel diameter required for droplet separation D1= Qg/.Vs.F.(L/D)

• Vessel dia. required for sufficient liquid residence time D2= 316Qltres/3.(L/D)

• Select max. of D1 or D2.

Qg - Gas flow rate at Pr.& T – m3/sQl - Tot. liq. Flow rate - m3/sVs - settling velocity - m/sD - Vessel Dia. - mL/D – Vessel design ratioF - Security factor (0.85)tres – liquid residence time - s

Page 84: Liquid and gas separation

Three phase separationTypes of separators

Vertical three phase separator

Horizontal 3 phase separator Inter-phase control with weir Inter-phase control with boot

Page 85: Liquid and gas separation

Design guidelines for 3-ph separator

Settling time for separation of oil from water and water from oil is calculated based on: minimum particle size flow rates density difference fluid viscosities.

Page 86: Liquid and gas separation

SEPARATOR DESIGN :Horizontal 3-Separator

When heavy liquid volume is not substantial ( 15-20% by wt.)

When almost equal vol. of light and heavy liq. are present

Page 87: Liquid and gas separation

DETERMINATION OF SEPARATION STAGES:

• Usually carried in more than one stages• Separation of HC mixture into vapor and liquid

in two or more equilibrium phases at successively lower pressures

• Storage tank is considered as one stage of separation

• In actual field practice, 2 or 3 stage separation is considered to be optimal

• More stable stock tank liquid• Enhanced liquid recovery

Page 88: Liquid and gas separation

DETERMINATION OF SEPARATION STAGES:

Page 89: Liquid and gas separation

Tota

l GO

R, s

cf/b

sto

DETERMINATION OF SEPARATION STAGES :• TOTAL GOR : Ratio of total cumulative gas recovered

from all stages per bbl of stock tank oil produced• Total GOR varies with no.

of stages for a given crude

• Total GOR is lower for more no. of stages

• When total GOR is lower, more of light fractions remain in oil, thus increasing oil API gravity, thereby yielding higher income

Page 90: Liquid and gas separation

SEPARATOR SPECIFICATIONS:

Separator efficiency

• With mesh type ME, efficiency of 98-99% with droplet size smaller than 100

Liquid carryover in gas

• Generally < 2 – 5 % by volume

Gas content in oil

• < 300 – 500 mg/l due to environmental restrictionsOil content in water

Page 91: Liquid and gas separation

SEPARATOR SPECIFICATIONS:

• Max oil level < 0.65 x ID• Normal oil level = 0.5 x ID, or 1 min. retention time

between max. and normal oil level• Low oil level = 0.1 x ID, or 12” from bottom, or safe

height from normal water level to prevent water carry-through; whichever is greater

Liquid levelsOil level

• Height corresponding to water retention time (1 to 2 min. normally), or 12”; whichever is greater

Water level

Page 92: Liquid and gas separation

PREVENTIVE MAINTENANCE OF SEPARATORS :

Regular checks should include:

• Check liquid levels

• Check pressures and temperatures

• Daily

• Check pressure relief valves

• Yearly

• Lubricate valves• Clean gauge columns• Check drum valves• Check level control valves• Replace broken gauge glasses

and pressure gauges whenever reqd.

• Check back pressure controls

• Periodically

Page 93: Liquid and gas separation

Oil & gas separation

Sizes and Capacities : Efficiency of separators(accepted norms):

Liquid carry over of 10 droplet size in gas <

0.1 gal/ mmscf.

Gas carried through oil - 2 to 5% by volume

Oil content of effluent water < 300 - 500 mg/l

Page 94: Liquid and gas separation

Oil & gas separationSizes and Capacities : Recommended retention time:

Oil gravity Retention time o API (min.)

2-Phase> 35 1Separators 20-30 1-2

10-20 2-4

3-Phase >35 3-5separators Below35

100+o F 5-10 80+o F 10-20

60+o F 20-30

Page 95: Liquid and gas separation

Oil & gas separationSizes and Capacities : Liquid levels

Maximum oil level : < 0.65 I.D.

Normal oil level : 0.5 I.D. or 1 min. retention time between max. and normal liq. Level Low oil level : 0.1 I.D. or 12” from bottom

Water/ inter face level : Water retention time of 1-2

min. or 12” which ever is greater

Page 96: Liquid and gas separation

Oil & gas separationSizes and Capacities : Design data required:

Separator operating temperature and pressure

Gas : Flow rate, Sp. Gr., acid gas content

Oil : Flow rate, Sp. Gr., viscosity,

Water : Flow rate, Sp. Gr., viscosity, corrosion

and scaling tendencies.

Page 97: Liquid and gas separation

Sizes and Capacities :

• Design data required:

– Water : Flow rate, Sp. Gr., viscosity, corrosion and scaling

tendencies.

– Impurities : Quantities and description of deposits and scales

– Vessel : Type, Pr. Rating, corrosion allowance, connections and

coatings.

– Accessories: Codes to be followed, safety devices, and

instrumentation desired.

Oil & gas separation

Page 98: Liquid and gas separation

Oil & gas separation

Gas capacity Based on max. allowable gas velocity

Max. allowable vap. Velocity (Vs)

(Vs) = K ( L - V / V )

Where K= 4gDp / 3Cd

Page 99: Liquid and gas separation

Oil & gas separation

Oil capacity Calculation based on retention time of the

liquid in the vessel sufficient to obtain equilibrium between liquid and gas.

Liquid settling volume (W)W = VL (t x 1440)

Where VL = Liquid capacity, bbl/d t = retention time, min.

Page 100: Liquid and gas separation

Oil & gas separation

Design considerations: Sized for maximum flow rates Should take care of : Heads/ slugs and pumping requirements Pumping , gas lift and naturally flowing

wells .

Page 101: Liquid and gas separation

Oil & gas separation

Capacity of vertical and horizontal

separators: Nomographs/Curves available

To size the separator

To determine the volume of fluid for a given

separator

• Suitable for preliminary sizing

Page 102: Liquid and gas separation

Oil & gas separationCapacity of vertical and horizontal

separators: Gas capacity : Does not vary directly with a

change in shell length.

The gas capacity of a horizontal separator is

proportional to its length.

The liquid capacities depend on the liquid

retained in the settling section of the

separators.

Page 103: Liquid and gas separation

Oil & gas separationSelection criteria of separators:

Vertical separator applications

Well fluids having low GOR.

Well fluids having sand, etc.,

Where limitation of space exits

Slug flow from wells

Down stream and upstream equipment.

Page 104: Liquid and gas separation

Oil & gas separationSelection criteria of separators: Horizontal separator applications

Separation of water from oil

Foaming crude oils

Well fluids with high GOR

Wells with relatively uniform flow

Skid mounted or trailer mounted

Stacking of multiple units.

Page 105: Liquid and gas separation

Oil & gas separation

Selection criteria of separators: Spherical oil and gas separator applications

Well fluids having high GOR and constant flow

rate

Installations where both vertical and

horizontal space/height limitations exist.

As gas scrubbers down stream of process

units.

Page 106: Liquid and gas separation

Oil & gas separation

Controls of separators: Liquid level controllers for gas/ oil and

oil/water interfaces.

Gas back pressure control valves

Page 107: Liquid and gas separation

Oil & gas separation

Valves of separators: Oil discharge control valve

Water discharge control valve

Drain valves

Block valves

Pressure relief valves

Valves of sight glasses

Page 108: Liquid and gas separation

Oil & gas separation

Accessories of separators: Pressure guages

Thermometers

Pressure reducing regulators

Level sight glasses

Safety head with rupture disk

Piping and tubing

Page 109: Liquid and gas separation

Oil & gas separation

Safety features in separators: High and low liquid level controls

High and low pressure controls

High and low temperature controls

Safety relief valves

Rupture disks

Page 110: Liquid and gas separation

Oil & gas separation

Problems in oil and gas separation: Foaming of crude oil

Encasing of gas in thin film of oil

Crudes that are likely to foam crudes with o API < 40 Operating temp < 160 0 F Crude viscosity > 50 cP

Page 111: Liquid and gas separation

Oil & gas separation

Problems in separation:

Foaming of crude oil

Effects of foamingReduces the capacities of oil and gas

separatorsCarry over of oil in gasControl of liquid levels

Page 112: Liquid and gas separation

Oil & gas separation

Problems in separation:

Foam management

Addition of foam depressants

Special designs for handling foaming

crude

Page 113: Liquid and gas separation

Oil & gas separation

Problems in separation:

Paraffin

Reduces efficiency of separators

Can be removed by steam / solvents

Can be prevented by coating

Page 114: Liquid and gas separation

Oil & gas separation

Problems in separation:

Sand / silt / mud etc.,

Reduces capacities of separators

Sand removal by periodic draining

Salt removal by mixing crude with water

and draining the water.

Page 115: Liquid and gas separation

Oil & gas separation

Problems in separation:

Corrosion

Cause early failure of equipment

Most corrosive components in gases are

CO2 and H2S.

Page 116: Liquid and gas separation

Oil & gas separationOperation and maintenance: Periodic inspectionInstallation of safety devicesSafety heads / rupture disksMist extractorsHydrate inhibitionCorrosive inhibitionparaffin controls

Page 117: Liquid and gas separation

Oil & gas separationOperation and maintenance in oil and gas

separation: High capacity operations Pressure shock loads Throttling of discharge liquids Pressure guages Guage cocks and glasses Cleaning of vessels

Page 118: Liquid and gas separation

Oil & gas separation

PREVENTIVE MAINTENANCE OF SEPARATORS

• Check liquid levels• Check pressure & temperatures• Replace broken guage glasses & pressure guages

� Daily

� Periodically• Lubricate valves• Clean guage columns• Check level control valves• Check back pressure valves

� Yearly• Check pressure relief valves

Page 119: Liquid and gas separation

Oil & gas separationTROUBLE SHOOTING

LOW LIQUID LEVEL

• Fluid dump valve opening too wide or trim

cut out• Drain valve opening or leaking• No fluid entering

Page 120: Liquid and gas separation

Oil & gas separationTROUBLESHOOTING

HIGH LIQUID LEVEL

• Fluid control dump valve closed or plugged• Block valve around dump valve closed• Inlet valve to next vessel closed• Separator overloaded

Page 121: Liquid and gas separation

Oil & gas separationTROUBLE SHOOTING

LOW PRESSURE IN SEPARATOR

• Back pressure control valve not working• Leaking safety relief valve• Inlet valve closed

Page 122: Liquid and gas separation

Oil & gas separationTROUBLE SHOOTING

HIGH PRESSURE IN SEPARATOR

• Back pressure control valve not working• Separator downstream valve closed• Plugged mist extractor

Page 123: Liquid and gas separation

Oil & gas separationTROUBLE SHOOTING

ALL THE OIL GOING OUT OF GAS LINE

• Dump valve not open/partially open• Blocked valve closed in piping to tank • Separator or piping plugged

Page 124: Liquid and gas separation

Oil & gas separationTROUBLE SHOOTING

MIST GOING OUT OF GAS LINE

• Vessel too small• Plugged mist extractor• High liquid level• Foaming problem

Page 125: Liquid and gas separation

Oil & gas separationTROUBLE SHOOTING

FREE GAS GOING OUT OF OIL/WATER VALVE

• Too low level in separator• Dump valve not seating• Block valve around dump valve passing

Page 126: Liquid and gas separation

Oil & gas separationTROUBLE SHOOTING

EXCESS GAS GOING TO TANK WITH OIL

• Less retention time• Foaming oil• Too much pressure drop from separator to tank

Page 127: Liquid and gas separation

Oil & gas separationTROUBLE SHOOTING

OIL/CONDENSATE & WATER NOT SEPARATING IN 3 PHASE SEPARATOR

• Paraffin problem hampering water from being free• Not enough retention time• Interface level control not working properly• Leak in adjustable weir• Adjustable weir height to be adjusted

Page 128: Liquid and gas separation

Oil & gas separation

TROUBLE SHOOTING DIAPHRAGM OPER. DUMP VALVE NOT OPERATING

• Pilot failure• Supply gas failure• Out of adjustment• Broken valve stem• Plugged tubing• Ruptured diaphragm• Leak in line from pilot to valve