Oil and gas processing (Onshore)
Aug 19, 2014
Oil and gas processing (Onshore)
Oil & gas separation SEPARATOR:
• Pressure vessel separating well fluids into gaseous/ vapour and liquid components
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
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
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
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
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
Well Fluid from header
Gas to GDU/ Consumers
Produced water to ETP
Separator
Crude oil to dehydrator
Block diagram well fluids processing
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
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.
Well connection configuration
Multiphase HC mixture and water flowing through individual lines (preferred)
GGSWELL
WELLWELL
WELL
WELL
WELL
WELL
WELLWELL
Well connection configuration
Multiphase HC mixture and water flowing through interconnected lines (not preferred)
GGSWELL
WELL WELL
WELL
WELL
WELL
WELL
WELLWELL
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
Well connection configurationCentral Tank Form (CTF)
GGSWell
Well Well
Well
Well
Well
Well
WellWell
GGSWell
WellWell
Well
Well
Well
Well
WellWell
CTF
Pump
GGS
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
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
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.,
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
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
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
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:
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
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.
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
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
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.
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
SEPARATION
• Pressure• Temperature• Gas Oil Ratio (GOR)• Flow rate• Fluid properties like density, viscosity etc.
Depends on following factors:
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
Oil & gas separation
Principles of separation of “Gas from oil Settling Agitation Baffling Heat Chemicals
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
Gravity Separation
Diff. Liquid phases
PRINCIPLES OF SEPARATION (OIL FROM GAS) :
Diff. momentum
Diff. Densities
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) :
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) :
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)
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) :
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) :
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) :
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):
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 ):
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 ):
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 ):
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 ):
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 ):
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
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
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
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
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
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
2. Secondary or gravity separating section• Settling section• Reduced turbulence• Retention time
MAIN SECTIONS/COMPONENTS OF A SEPARATOR
• Straightening vanes/ Settling vanes
• Defoaming plates
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
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
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
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
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
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
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
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
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
General guidelines for use
Compressor KODFuel gas KODDegassing bootsAbsorber feed KOD
Production separator
3-Phase separationReflux drumFlare KOD
Vertical Horizontal
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
4. Centrifugal/compact separators
- Relatively new type of separators
- Technology still developing - Less efficient than other separators
SEPARATOR CONFIGURATION:
- Less maintenance is involved
- Less space is required - Light in weight - Less expensive
• Advantages
Centrifugal/compact separators
• Not suitable for large liquid slugs
• Efficiency not as good as other types
• Narrow operating flow range for highest efficiency
• Disadvantages
Centrifugal/compact separators
Comparison of separators
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.
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
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
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
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
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
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
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
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)
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.
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
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
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
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
Sizing of vertical separators Weight calculation
- Weight of the vessel can also be calculated from graph based on thickness, length and diameter.
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
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
Three phase separationTypes of separators
Vertical three phase separator
Horizontal 3 phase separator Inter-phase control with weir Inter-phase control with boot
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.
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
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
DETERMINATION OF SEPARATION STAGES:
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
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
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
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
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
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
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
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.
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
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
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.
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 .
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
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.
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.
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.
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.
Oil & gas separation
Controls of separators: Liquid level controllers for gas/ oil and
oil/water interfaces.
Gas back pressure control valves
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
Oil & gas separation
Accessories of separators: Pressure guages
Thermometers
Pressure reducing regulators
Level sight glasses
Safety head with rupture disk
Piping and tubing
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
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
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
Oil & gas separation
Problems in separation:
Foam management
Addition of foam depressants
Special designs for handling foaming
crude
Oil & gas separation
Problems in separation:
Paraffin
Reduces efficiency of separators
Can be removed by steam / solvents
Can be prevented by coating
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.
Oil & gas separation
Problems in separation:
Corrosion
Cause early failure of equipment
Most corrosive components in gases are
CO2 and H2S.
Oil & gas separationOperation and maintenance: Periodic inspectionInstallation of safety devicesSafety heads / rupture disksMist extractorsHydrate inhibitionCorrosive inhibitionparaffin controls
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
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
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
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
Oil & gas separationTROUBLE SHOOTING
LOW PRESSURE IN SEPARATOR
• Back pressure control valve not working• Leaking safety relief valve• Inlet valve closed
Oil & gas separationTROUBLE SHOOTING
HIGH PRESSURE IN SEPARATOR
• Back pressure control valve not working• Separator downstream valve closed• Plugged mist extractor
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
Oil & gas separationTROUBLE SHOOTING
MIST GOING OUT OF GAS LINE
• Vessel too small• Plugged mist extractor• High liquid level• Foaming problem
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
Oil & gas separationTROUBLE SHOOTING
EXCESS GAS GOING TO TANK WITH OIL
• Less retention time• Foaming oil• Too much pressure drop from separator to tank
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
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