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Electrostatics Separation TechnolgyProcess Solution Group
Description of Processes & Fundamentals
YOU DRILLED AN OIL WELL...
BUT ALSO PRODUCED.. GAS MUD SALT SAND WATER SULFUR CHEMICALS
TYPICAL PROCESS SCHEMEGAS PROCESSING BULK SEPARATION OIL TREATING WATER TREATING
CRUDE OIL TREATING CONSISTS OF . . . DEHYDRATION DESALTING(REMOVAL OF INSOLUBLE WATER)
(REMOVAL OF MINERAL CONTAMINANTS SOLUBLE IN WATER, AND OF SOLIDS)
DEHYDRATION DESALTINGCRUDE OIL
CRUDE OIL
CRUDE OIL DEHYDRATIONWATER IN A CRUDE OIL PRODUCTION STREAM CAN TAKE SEVERAL FORMS OIL RICH WATER RICH
EMULSIFIED WATER DISSOLVED WATER FREE WATER
STREAM SAMPLE
FREE WATERFree water is either water existing as the continuous phase, or water existing as relatively large dispersed droplets, both of which separate quickly from the oil phase
DISSOLVED WATERMEASURED WATER-IN-OIL SOLUBILITIES
TYPICAL WATER-IN-OIL EMULSION
Seen Through a Microscope
Droplet sizes range from sub-micron to several hundred microns.
Mechanism of Oil Dehydration A Three Step Process Coagulation Counteracting the Droplet Surface Films Flocculation Gathering the Destabilized Drops Together Sedimentation Gravitational Separation of the Phases
Mechanical Forces for Coalescence and Sedimentation
STOKES EQUATIONDescribes Sedimentation Velocity
V
g D ( 2 - 1 ) = 181
2
V = Sedimentation Velocity g = gravity D = Particle (or dispersed droplet) Diameter 1= Density of Continuous Phase 2= Density of Dispersed Phase 1 = Viscosity of Continuous Phase
DEHYDRATION OF CRUDE OILSACCOMPLISHED BY . . . DROP GROWTH OF THE DISPERSED PHASE SEPARATION OF THE LIQUID PHASES BY GRAVITY SETTLING
DROPLET GROWTH ACHIEVED BY COALESCENCEDiameter = 1 mm Volume = 0.5236 mm3 Surface Area = 3.1416 mm2
+Diameter = 1.260mm Volume =1.0472 mm3 Surface Area=4.98 mm2
TOTAL VOLUME UNCHANGED TOTAL SURFACE AREA ONLY 79% OF ORIGINAL
DROPLET COALESCENCESo why does an emulsion not rapidly coalesce and separate into distinct phases? An emulsion is a dispersion that has been stabilized.
WHAT IS AN EMULSION?EMULSIONS ARE TWO IMMISCIBLE PHASES, INTERDISPERSED BY MECHANICAL AGITATION, AND THE DROPLETS STABILIZED BY . . . VISCOSITY DENSITY DIFFERENCE DROPLET SIZES EMULSIFYING AGENTS STATIC ELECTRICAL CHARGE DESCRIBED BY STOKES LAW NOT DESCRIBED BY STOKES LAW
EMULSIFYING AGENTSEMULSIFYING AGENTS OIL HEAVY PARAFFINIC COMPOUNDS HEAVY NAPHTHENIC ACIDS PETROLEUM ACIDS ASPHALTIC COMPOUNDS ORGANIC SOLIDS INORGANIC SOLIDS WATER DROP
ELECTROSTATIC CHARGEIn a flowing process stream where water exists as a dispersed phase in an organic continuous phase, the water droplets tend to acquire a positive excess charge. This causes a repulsive force between droplets.
++++ ---
++++ ---
HOW CAN WE DESTABILIZE THE EMULSION AND INCREASE SETTLING RATE? Heat Chemistry Flow Regime Coalescing Surfaces Electrostatic Fields
Crude oil dehydration utilizes these principles to speed up the coalescence and separation of emulsified water from oil
BENEFITS OF HEATING Viscosity Increased Differential Density Increased Film Strength Weakened Chemical Reactivity Accelerated
Heat Chemistry Flow Regime Coalescing Surfaces Electrostatic Fields
BENEFITS OF HEATING
Heating can cause problem for heavy oil
DRAWBACKS OF EXCESSIVE HEATINGFUEL COST LOSS OF VOLUME LOSS OF GRAVITY INCREASED MAINTENANCE SAFETY
CHEMICAL TREATMENT Chemical additives called demulsifiers are typically injected into the crude oil stream to weaken the stabilizing film surrounding the water droplets
Heat Chemistry Flow Regime Coalescing Surfaces Electrostatic Fields
Chemical TreatmentRequirements: Deactivate Natural Surfactants Enhance Condensation of Interface Zone Modify Wetting of Solids Produce No Insoluble By-Products
Major Components: Demulsifier (Primary Ingredient) Wetting Agent (Used if solids are a problem)
Selection Methods for Demulsifiers Bottle Tests Most Common Method Measure Sedimentation Rate Estimate Resultant Oil Quality Vary Chemical Type and Dosage Electrostatic Bench Tests Measure Response of Emulsion to Electrostatic Field: Power Requirements & Sedimentation Rate Measure Resultant Oil Quality Vary Chemical Type & Dosage and Electrostatic Field Type
Bottle Test
Chemical Dossage Mixing
100 cc Emulsion Heating to process temperature 24 hours settling evaluation
cc Oil
cc Emulsion
cc Water
t=0
t = t1
Chemical analysis: Electrical susceptibility test
Equipment for electrical susceptibility test
Chemical analysis: Electrical susceptibility test
Graphical recorder
Test cell
Chemical analysis: Electrical susceptibility test
Chemical analysis: Electrical susceptibility testAmperage against test temperature0.200 0.190 0.180 0.170
Amperage (mA)
0.160 0.150 0.140 0.130 0.120 0.110 0.100 0 10 20 30 40 50 60 70 80 90
Petrozuata Lagotreco Jusepn
Temperature (C)
Chemical analysis: Electrical susceptibilitytest0,0000205000 0,0000190000
Relative Electrical Conductivity against temperature
Electrical Conductivity (mA/V)
0,0000175000
0,0000160000
Petrozuata Lagotreco Jusepin
0,0000145000
0,0000130000
0,0000115000
0,0000100000 0 10 20 30 40 50 60 70 80 90
Temperatura (C)
Comparative Results 19.5API Brazilian CrudeChemical Bottle Test Water in Oil% By Difference
Electrostatic Bench Test BS&WMeasured %
A B C D E
2.2 4.6 5.3 5.7 6
2.12 2.01 1.62 1.20 2.35
Red: Best Performance
DEMULSIFIERSCHEMICAL TANK AND PUMP
TREATER
WET CRUDE INLET
DEMULSIFIER IS INJECTED UPSTREAM OF THE TREATER
FLOW DISTRIBUTION
Heat Chemistry Flow Regime Coalescing Surfaces Electrostatic Fields
Flow distribution is critical to achieving uniform velocity and avoiding excessive turbulence
FLOW DISTRIBUTIONCollector Outlet Distributed Flow
UP-FLOWDistributor
Inlet
LONGITUDINAL-FLOW
Perforated Distributor Baffles
COALESCING SURFACES CAN SPEED UP SEPARATION
Heat Chemistry Flow Regime Coalescing Surfaces Electrostatic Fields
ACHIEVABLE WATER REMOVALTREATED CRUDE BS&W (%)100 FREE WATER KNOCKOUT 3-PHASE SEPARATOR TREATER or DESALTER 0.1 10 20 30 40 50 70 100 CRUDE OIL GRAVITY (DEG API)
10
1
USING AN ELECTROSTATIC FIELD TO CAUSE COALESCENCE
Heat Chemistry Flow Regime Coalescing Surfaces Electrostatic Fields
+
-
POLARIZATION OF DISPERSED DROPLETS
+Dipoles Align With The Field Droplet Elongates
ELECTROSTATIC EFFECTS
DIPOLAR ATTRACTIVE FORCE BETWEEN EQUAL SIZED DROPS 2 6
F=
6 KE r 4 d
F = Force of Attraction = Dielectric Constant E = Electric Field Strength r = Drop Radius d = Interdrop Distance
Notice the Limitations: Very Sensitive to Drop Size Operates Over Short Range
Critical Voltage GradientMaximum Voltage at which Specified Drop Size Can Exist
Ec < ( / d )
1/ 2
y/x>1.9 y x Drop is polarized by the electrostatic field Drop is more conductive than continuum Drop deforms to a prolate spheroid Drop splits when ratio of axes becomes too large Electrical charge on the drop promotes shattering or
ELECTROSTATIC FIELDS
There are two basic types of electrostatic field:
AC FIELD DC FIELD. . . and several possible variations of each
DROPLET BEHAVIOR IN AN AC FIELD
+
-
+
-
OPPOSITE POLES OF POLARIZED WATER DROPLETS ATTRACT, PROMOTING COALESCENCE
ELECTROSTATICALLY INDUCED FILM RUPTURE Absence of Electric Field Surface Stabilized by Film Coalescence Inhibited Drop Stretched by Field Surface Film Broken Coalescence Enhanced
AC -TYPE ELECTRODESTRANSFORMER OIL OUT
WATER OUT OIL IN
AC FIELD BENEFITS DIPOLAR ATTRACTION FILM STRETCHING WATER TOLERANCE
BUT THERE ARE LIMITATIONS MINIMAL DROP MOVEMENT LOW CHARGE DENSITY LIMITS ON USEFUL FIELD STRENGTH
DROPLET BEHAVIOR IN A DC FIELD
+ +Electrodes
+ Upward oil flow
-+
A single small water droplet
COALESCENCE IN A DC FIELD
+
-
+ -
- + UPWARD OIL FLOW
- +
COALESCING IN A DC FIELDOpposites Attract
DC FIELD BENEFITSMOST AC FIELD BENEFITS, PLUS . . . DROPLET TRANSPORT NET ELECTROSTATIC CHARGE BUT. . . MUST AVOID ELECTROLYTIC REACTIONS WATER TOLERANCE IS REDUCED
ELECTROSTATIC FIELDS: DUAL POLARITY
AC/DC (DUAL POLARITY) COALESCER
PLATE ELECTRODE ARRAY
INSULATOR HANGERS RAILS
ELECTRODE PLATES
DUAL POLARITYProvides Combined AC/DC Fields For Combined Benefits Drop Polarization Film Rupture Water Tolerance Drop Movement Drop Charge Density Minimizes Induced Corrosion
TRANSLATING PROCESS INTO EQUIPMENT
Heat Chemistry Flow Regime Coalescing Surfaces Electrostatic Fields
PROCESS EQUIPMENT DESIGN
PROCESS EQUIPMENT DESIGNWe have looked at the the principles the industry utilizes to achieve crude oil dehydration. Different equipment suppliers apply these principles in different ways. Following is an overview of NATCOGROUP equipment design, using these principles.
FREE WATER KNOCKOUTGAS INLET
OIL
WATER
BATTERY OF VERTICAL TREATERS
VERTICAL TREATER (Cold climate options)INTERNAL FUNCTIONS DEGASSING MIST REMOVAL FREE WATER REMOVAL HEATING SECONDARY DEGASSING EMULSION COALESCING/SETTLING
TYPICAL TREATER FIRETUBE AND DRAFT SYSTEMSTACK HEAD TURBULATOR
STACK FIRETUBE AIR INTAKE/BURNER
CONE BOTTOM VERTICAL TREATEROPTIONAL ITEMS: CONE BOTTOM SAND JET RING HEATING BUNDLE SLOPED BAFFLES OUTSIDE LEVEL CONTROLS CROSS DRAIN
VFH TREATER (Vertical Flow Horizontal EQUALIZER GAS OUTLET Treater)INLET
OIL OUTLET
FIRETUBE FIRETUBE SHROUD FREE WATER OUTLET
SPREADERS
EMULSIFIED WATER OUTLET
FULL BAFFLE
PERFORMAX COALESCING PLATES
COALESCING SURFACESPERFORMAX MATRIX MATERIAL Polyvinylchlorid e Polypropylene Carbon Steel Stainless Steel
PERFORMAX TREATER (Horizontal Model)
DUAL POLARITY ELECTROSTATIC TREATER (VFH-CWW)
DUAL POLARITY ELECTROSTATIC TREATERS
SMALL OIL PRODUCTION BATTERY WITH SEPARATION AND TREATING
Dual Polarity Electrostatic Treater with Degasser
AC Field electrostatic dehydrators
Howe-Baker Electrostatic Dehydrators
AC Field electrostatic dehydrators
Petreco Electrostatic Dehydrators
AC Field electrostatic dehydrators
Kvaerner (HRI) Electrical treaters
Comparative suppliers analysisAC Field Proven technology in conventional desalting process Electrostatic dehydration/desalting under AC electric field Traditional desalting technology Lower comparative cost High oversizing design High sensitivity to emulsion tightness (high stability) and high water content High desalting multiple stages requirements Good technical support High control requirements
Dual Polarity Proven technology in conventional desalting process Electrostatic dehydration/desalting under Dual polarity (AC/DC) electric field and electrodynamic desalting process (exclusive technologies) Improved desalting technologies Higher comparative cost Optimal design (low oversizing) Low sensitivity to emulsion tightness (high stability) and high water content Low desalting multiple stages requirements Excelent technical support High control requirements
ELECTROMAX TREATER
ELECTROMAX CRUDE OIL DEHYDRATORCombines Electrical and Mechanical Coalescence High Flux Electrical Section Downflow Sedimentation Performax Mechanical Coalescer Dual Polarity Electrostatic Field Programmable Voltage Cycle Composite Electrodes Field Proven on Heavy and Difficult Oils
DUAL POLARITYTM DEHYDRATOR
TYPICAL ELECTRICAL ASSEMBLY
TECHNOLOGY
Following are some recent technology advancements that have significantly improved dehydration equipment performance.
Several Factors Influence Hydrodynamic Design of Separators Inlet nozzle and momentum breaker design critical to efficient use of vessel volume Internal baffle positions improve flow distribution and prevent high fluid velocity paths Discharge nozzle designs affect fluid quality (vortex breakers may be inadequate) Computational Fluid Dynamics Provides Insight to Fluid Flow in Separators
Velocity Vectors Colored by Velocity Magnitude
Computational Fluid Dynamics State-of-the-Art Method to Solve Practical Problems
Complex Fluid Flow Analysis
Flow Visualization and Distribution Analysis
Key Separator Components for Control of Fluid Flow Patterns Inlet nozzle geometry and location Momentum dissipation devices (e.g., splash plate, vortex tubes, ) Solid (non-porous) weirs and dams Perforated plates Outlet nozzle geometry and location Vortex breakers or other directional flow devices
TIME
Box-Type Spreader with Open Bottom00 SECONDS
TIME
Box-Type Spreader with Open Bottom20 SECONDS
TIME
Box-Type Spreader with Open Bottom40 SECONDS
TIME
Box-Type Spreader with Open Bottom60 SECONDS
TIME
Box-Type Spreader with Open Bottom80 SECONDS
TIME
Box-Type Spreader with Open Bottom100 SECONDS
TIME
Box-Type Spreader with Open Bottom120 SECONDS
TIME
Box-Type Spreader with Open Bottom140 SECONDS
TIME
Box-Type Spreader with Open Bottom160 SECONDS
TIME
Box-Type Spreader with Open Bottom200 SECONDS
TIME
Box-Type Spreader with Open Bottom220 SECONDS
Perforated Plates in Separators Establish good fluid flow distribution to reduce short circuiting Control liquid sloshing for ship-mounted systems
Perforated Plates in SeparatorsDesign Criteria Fraction of open area as holes Hole size Hole pattern Open area under plate for sand migration Placement and number of plates within separator
Fluid Flow Paths Upstream and Downstream of a Perforated Plate Show Turbulence and Recirculation Patterns
Dual Perforated Plates Redistribute Flow Down Length of Separator
Separators on Floating Platforms are Subjected to Six Degrees of Motion4 5 61. Surge: Y 2. Sway: X 3. Heave: Z
3 1 24. Pitch: ZY 5. Roll: ZX
6. Yaw: XY
For CFD Simulation, Vessels Placed in Actual Position on Platform to Accurately Capture Vessel Movement Due to Wave Motion
Iso-surface Plot of Water/Oil Interface (Case #1) Iso-surface Plot of Water/Oil Interface (Case #1)
Spill-over due to Roll Motion
Time = 28.0 sec
Vessel Tail
Top of Weir Plate w/ Lip
Water Spill-over Reaches The Oil Outlet
Advanced Technology Reduces the Size of Downstream Separation Equipment Electrostatic treaters dehydrate crude oil in ever decreasing vessel sizes CFD provides insight to vessel hydrodynamics Vessel internals designed to cope with process upsets Water Treatment Systems become smaller, more efficient Improved designs for hydrocyclones extend turn-down range and remove smaller droplets CFD-assisted column flotation design improves IGF performance Can move IGF off-platform to save weight & space
SHROUDED-PIPE SPREADERPatented Shrouded Pipe Distributor Excellent momentum absorption Near perfect flow distribution No more than 5% flow recirculation
U.S. Patent 6,010,634
ELAPSED TIME = 30 SECONDS
MODEL RESULTS - Water Table w/ DyeOUTLET
STANDARD PIPE DISTRIBUTOR INTERFACE
SHROUDED PIPE DISTRIBUTOR
MODEL RESULTS - Water Table w/ DyeELAPSED TIME = 60 SECONDS
STANDARD PIPE DISTRIBUTOR
SHROUDED PIPE DISTRIBUTOR
Shrouded Inlet SpreaderTIME 00 SECONDS
Shrouded Inlet SpreaderTIME 20 SECONDS
Shrouded Inlet SpreaderTIME 40 SECONDS
Shrouded Inlet SpreaderTIME 60 SECONDS
Shrouded Inlet SpreaderTIME 80 SECONDS
Shrouded Inlet SpreaderTIME 100 SECONDS
Shrouded Inlet SpreaderTIME 120 SECONDS
Shrouded Inlet SpreaderTIME 140 SECONDS
Shrouded Inlet SpreaderTIME 160 SECONDS
Shrouded Inlet SpreaderTIME 180 SECONDS
Shrouded Inlet SpreaderTIME 200 SECONDS
Shrouded Inlet SpreaderTIME 220 SECONDS
Effects of Arcing Arcing is a Natural Part of the Process Arcs Momentarily Discharge a Steel Electrode Array Significant Arcing Results in Performance Loss Due to Compromise of the Field
A Means of Arc Control is Needed.
COMPOSITE ELECTRODES
Conventional electrodes are constructed of Steel. Composite Electrodes are made of plastic
COMPOSITE ELECTRODES
+
-
+
-
CONDUCTIVE STRIP
PLASTIC PLATE
COMPOSITE ELECTRODES
CONDUCTIVE STRIP TAPERED VOLTAGE FIELD
COMPOSITE ELECTRODES PROVIDE ADDITIONAL TOLERANCE FOR WATER AND CONDUCTIVITY FIBER REINFORCED THERMOPLASTIC CONSTRUCTION RELIANCE ON SURFACE CONDUCTIVITY QUENCH ELECTRICAL ARCS PROVIDE FIELD GRADIENT INCREASE INTENSE-FIELD RETENTION TIME PROVIDE HIGHLY STABILIZED ARRAY
LOAD-RESPONSIVE CONTROLLERPOWER SUPPLY REQUIREMENTS PROTECTION MUST PROTECT ELECTRICAL COMPONENTS IN CONDUCTIVE ENVIRONMENTS FLEXIBILITY ABILITY TO HANDLE VARYING FEEDSTOCK AVAILABILITY MINIMAL DOWNTIME IN CHALLENGING CONDITIONS
LOAD-RESPONSIVE CONTROLLERConventional means of transformer protection: reactor in primary circuitR SF O TO R M C EA ER
POWER SUPPLY
TR
R
A
HI VOLTAGE TO PROCESS
N
LOAD RESPONSIVE CONTROLLERAnother way to control power time-based voltage chopping
Voltage
Crude Oil Conductivity Maintains Heat Dissipation Rating Functions During Process Upset Condition Preserves Coalescing Effect Microprocessor design allows field modulation
Slow Modulation Voltage Cycle
Field Control by Load Responsive Controller (LRC)
Modulated Dual Polarity Benefits
Modulation offers the Following Improvements:Added Coalescing Power More Effective on Smaller Drops Better Drop Growth Higher Water Tolerance Increased Tolerance to Conductive Oils
Modulated Fields - Terminology Threshold Voltage Gradient Voltage Gradient Necessary to Initiate Coalescence Critical Voltage Gradient Limiting Maximum Voltage Gradient at Which a Drop of a Specified Diameter Can Exist Modulation Frequency Affects Drop Transport Drop Relaxation Field Decay
State-of-the-Art Technology: Modulation of the Electrostatic Field
Slow Speed Modulation (as in EDD) Used to Control Drop Size Distribution Pulse Modulation Used to Energize Drop Surfaces Base Frequency Control Used to Limit Field Decay
Effects of Pulse Modulation & Base Frequency
Energizes Drops at Resonant Frequency Deformed Drops More Readily Coalesced Allows Adjustment for Physical Parameters Interfacial Tension (Pulse Modulation) Oil Conductivity (Base Frequency) Density Viscosity
Resonant Frequency Oscillation High frequency electrostatic field applied Marangoni Effect produces localized circulation in drop
Electrophoretic movement becomes oscillatory Drop deforms Surface free energy counters interfacial tension Drop surface becomes highly reactive Coalescence enhanced by reduced energy barrier
Field Decay in Conductive OilsLimits Coalescence Performance
+
VoltageIncreasing Conductivity
Effect of Base Frequency on Voltage DecayIncreases Coalescence Performance
1
1
sin ( z )
s i nz ) (
1 0 z 20
1 0 z 20
Low FrequencyNote deep RC discharge between voltage peaks.
High FrequencyNote shallow RC discharge between voltage peaks.
Low FrequencyNote deep RC discharge between voltage peaks.
High FrequencyNote shallow RC discharge between voltage peaks.
EXAMPLE OF IMPROVED TECHNOLOGY BENEFITPROBLEM: Increased capacity was needed through existing desalting units in Africa, and shipping quality specifications had to be maintained. SOLUTION: AC Treaters were Retrofitted with Dual Polarity Electrode system. RESULTS: Capacity increased from 50,000 BPD to 100,000 BPD and shipping quality was maintained.
EXAMPLE OF IMPROVED TECHNOLOGY BENEFITPROBLEM: Existing North Sea DUAL POLARITY dehydrator designed for 60,000 BPD, but production had increased to 100,000 BPD SOLUTION: Retrofit unit with Composite electrodes Retrofit unit with Pipe/Deflector spreader RESULT: Capacity increased to 100,000 BPD
DEHYDRATION DESALTINGCRUDE OIL
CRUDE OIL
THE SALT PROBLEMMineral salts are often carried in solution in the water which is emulsified in the oil. In addition there are often small amounts of insoluble solids carried in the oil or water phases. OILSALT IN WATER
THE SALT PROBLEMWHERE DOES THE SALT COME FROM? IN THE FIELD, IT COMES FROM THE FORMATION IN THE REFINERY IT IS EITHER RESIDUAL SALT REMAINING AFTER FIELD DEHYDRATION, OR IS SEA WATER WHICH HAS CONTAMINATED THE OIL
THE SALT PROBLEMTHE RESIDUAL WATER CONTAINS MINERAL SALTS. SALT IS A PROBLEM IN THE FOLLOWING WAYS . . . 1. IT PROMOTES CORROSION 2. IT FOULS HEATERS, HEAT EXCHANGERS, PUMPS AND TOWER TRAYS 3. IT POISONS CATALYSTS IN REFINERY UPGRADING PROCESSES
THE SALT PROBLEMTYPICAL SALT-IN-OIL REQUIREMENTS
FORCORROSION SALT DEPOSIT FOULING CORROSION SALT DEPOSIT FOULING CATALYST POISONING
OILFIELD: 10 - 25 PTB REFINERY: 0.5 - 3 PTB
(PTB = pounds of salt per 1000 bbls of oil)
THE SALT PROBLEM
THE SALT PROBLEM
S/O =
0.35 x S/W x W/L 1 - W/L
S/O = salt-to-oil (PTB) S/W = salt-to-water (mg/l water salinity) W/L = water-to-total liquid (volume fraction)
THE SALT PROBLEMDEHYDRATION ALONE IS INSUFFICIENT TO MEET THE SALT REMOVAL REQUIREMENTS IN MANY CASESPTB (POUNDS OF SALT PER 1000 BBLS OF OIL)200g/ l 0 m ,0 0
20 0
100
.00 0 10
g/l 0m
/l 0 mg 0 50,0
TYPICAL FIELD REQUIREMENTS TYPICAL REFINERY REQUIREMENTS
0
0.1
0.2 0.3 0.4 0.5 RESIDUAL WATER (%)
0.6
DESALTING FUNDAMENTALS0.35 x S/W x W/L 1 - W/L
S/O =
This formula suggests that there are two parameters that determine salt-in-oil: Water Salinity Water Fraction of the Stream
DESALTING FUNDAMENTALSWater fraction can be reduced by simple dehydration, using principles already discussed. To reduce water salinity, it must be diluted.
+
=
DESALTING FUNDAMENTALS Basic desalting consists of two sub-processes: 1st - Dilution - of the dispersed brinewith a water of lesser salinity (called wash water or dilution water)
2nd - Dehydration - removal of the diluteddispersed brine by oil dehydration
DILUTION OF DISPERSED BRINEDesalting Chemical injection Wet Crude Oil Inlet To desalter vessel for dehydration
Wash water Injection
Mixing by Continued Rough hydraulic or hydraulic Dispersing mechanical Coalescence of wash agitation, water usually a Mixing Valve
THE MIXING VALVEDifferential Pressure Controller DPC
To Desalter Crude Flow Mixing Valve Static Mixer (Optional) is occasionally installed either upstream or downstream of the mixing valve
MIXING VS. DEHYDRATION IN DESALTING
DESALTER BASIC FLOW SCHEMEDesalted Oil Discharge
Single Stage Desalter
Crude Oil Inlet Wash Water Inlet
Mix Valve
Brine Discharge
CONSERVATION OF WASH WATERThere are several reasons why wash water must be conserved: Supply of fresh or near-fresh water is often scarce, particularly in the producing field. Disposal of effluent water is often costly, and needs to be minimized. Too much total water can cause desalter electrodes to short-circuit.
SOURCES OF WASH WATERRefinery Condensate from towers Cooling water Utility water Field Deep fresh-water formations Shallow groundwater River water Sea water (often must be de-salinated)
DUAL POLARITY DESALTER (typical)
DOUBLE VOLT AC ELECTROSTATIC COALESCERPower Unit 1Phase A Phase B Earth
Power Unit 2Phase B Phase C Earth
Power Unit 3Phase C Phase A Earth
Grid 1
Grid 2
Grid 3
Earth
Power Unit Primary ConnectionsDELTAPower Unit 3
Grid ConnectionsPower Unit 1
Power Unit Secondary ConnectionsGrid 1Power Unit 1 Power Unit 2
Phase APower Unit 1
Grid 1 DELTA STARPower Unit 3
Phase B Phase CPower Unit 2
Grid 3Power Unit 3
Grid 2Power Unit 2
Grid 3 Earth
Grid 2
TRIGRID AC ELECTROSTATIC COALESCERPower UnitPhase A Phase B Earth
Grid 1 Earth Grid Grid 2
Earth
Power Unit Primary ConnectionsPhase A
Grid ConnectionsPower Unit Grid 1
Power Unit Secondary ConnectionsEarth
Phase B Grid 2 Earth Grid 1 Grid 2
TRIVOLT AC ELECTROSTATIC COALESCERPower Unit 1Phase A Phase B Earth
Power Unit 2Phase B Phase C Earth
Power Unit 3Earth Phase C Phase A
Grid 1
Grid 2
Grid 3
Earth
Power Unit Primary Connections
Grid ConnectionsPower Unit 1 Power Unit 2 Power Unit 3
Power Unit Secondary ConnectionsGrid 1
Phase APower Unit 1
DELTA
STAR Grid 1Power Unit 2
Power Unit 1 Power Unit 2
Phase B Phase C
Grid 2 Grid 3
Power Unit 3
Grid 3 Earth
Grid 2
HIGH VOLTAGE ASSEMBLYOverflow with liquid seal Oil Level Glass Disconnect Link High Pressure Bushing Continuous Vent 10 ANSI Class 300 lb Power Inlet nozzle Vessel Wall Power Connector Rod Weight Pick-up bucket
Power Unit
Electrode Insulator Assembly
DESALTER SIZINGFLOW
OIL FLOW (BPD) AREA = DESIGN FLUXDESIGN FLUX OBTAINED FROM...
DESIGN FLOW AREA
SIZING STANDARDS LOCAL HISTORICAL NORMS PILOT TESTS
PILOT TESTSNatcos HTU dehydration/desalting pilot unit in the Tulsa R&D facility simulates field or refinery dehydration and desalting processes; tests conventional and state-of-the-art technologies
PILOT TESTS
LIMITATIONS OF SINGLE STAGE DESALTERS
To maintain reasonable wash water requirements, the inlet stream can contain only a small amount of dispersed brine. To reduce high inlet brine concentrations, a dehydrator is placed upstream.
DEHYDRATOR/DESALTER FLOW SCHEMEOutlet Oil
Emulsion Inlet Effluent Water Wash Water Mix Valve EffluentWater
TWO STAGE DESALTERS
WITH INTER-STAGE RECYCLE
Brine Recycle
THREE STAGE DESALTERS WITH INTER-STAGE RECYCLEWhere extreme wash water conservation or deeper desalting is required, three stages may be used
INTERNAL RECYCLESingle Stage Desalter with Internal RecycleDesalted Oil Discharge
Crude Oil Inlet
Mix Valve Internal Recycle
Recycle Pump Brine Discharge
Wash Water Inlet
INTERNAL RECYCLETwo Stage Desalters with Internal and Inter-Stage RecycleFirst Stage Second Stage Desalted Oil Discharge
Crude Oil Inlet
Mix Valve
Mix Valve
Recycle Pump
Inter-Stage Recycle Brine Discharge Wash Water Inlet Internal Recycle
INTERNAL RECYCLEThree Stage Desalters with Internal and Inter-Stage RecycleFirst Stage Crude Oil Inlet Second Stage Third Stage Oil Discharge
Brine Discharge
Wash Water Inlet
REFINERY DESALTING
PRODUCER A
PRODUCER C
REFINERY
PRODUCER B PRODUCER D
FIELD DESALTERS(3) 2-Stage Trains At Sea Side, Egypt
FIELD DESALTERS
1st and 2nd Stages, Mid-East
REFINERY DESALTERS
2-STAGE, Mid-East
DESIGN AND OPERATIONAL CONSIDERATIONSSEPARATION OF SUSPENDED SOLIDS CHEMICAL TREATMENT WATER WASH REMOVAL OF SEPARATED SOLIDS SAND JETS (MUD WASH SYSTEM) INTERFACE SLUDGE DRAINS
DESIGN AND OPERATIONAL CONSIDERATIONSAVOID CRYSTALLINE SALT In the producing field, it is caused by low watercontent wells being flashstripped during degassing. In the refinery it is caused by heating a low watercontent crude to where the water solubility exceeds available water.
AVOIDING SALT CRYSTALLIZATION AND DEPOSITION IN REFINERY DESALTERSFEEDSTOCK TANKS CHARGE PUMPS HEATERS DESALTERS
SMALL AMOUNT OF WASH WATER INJECTED UPSTREAM OF HEATERS
WASH WATER SUPPLY
Solids Control Sources of Solids Formation Fines & Precipitated Scale Precipitated Asphaltenes Solids Partitioned Between Oil and Water Phases Chemical Treatment May Help Some Remain in the Vessel Interface Sludge Bottom Sediments Removal Is Essential For: Control of Conductivity Maintenance of Flow Distribution
Solids Removal
Interface Sludge DrainOperated As Required
Mud Wash (Sand Jet) SystemScheduled Operation
TECHNOLOGY
ADVANCED DESALTING TECHNOLOGIE S
ELECTRO-DYNAMIC DESALTER
Combines 5 Essential Process Technologies: Dual Polarity Electrostatic Dehydrator Start with a proven technology Composite Plate Electrodes Provide high water tolerance Load Responsive Controller Controls field strength Counterflow Dilution Water Process Provides multi-stage contact Electrostatic Mixing Process Focuses mixing energy only on dispersed phase
ELECTRO-DYNAMIC DESALTER
ELECTRO-DYNAMIC DESALTERWASH WATER INLET OUTLETOIL COLLECTOR
WASH WATER HEADER
...................................COMPOSITE ELECTRODES SPREADER
INLET
WATER OUTLET
ELECTRO-DYNAMIC DESALTER - LOAD RESPONSIVECONTROLLER
ELECTRO-DYNAMIC DESALTER PC BASED LOAD RESPONSIVE CONTROLLER LOCAL MAY BE LOCALOR REMOTE Transformer, SCRs and Firing Board Diodes NATCO Control Board and Diagnostic Display Junction Box DEDICATED OR PORTABLE PC With LRC Program and Monitoring Software
Control Feedback AC Power
LRC Control Software
LRC Programming/ Monitoring Software3
ELECTRO-DYNAMIC DESALTER COUNTERFLOW WASH WATER PROCESS
ELECTRODE PLATES
WASH WATER HEADER DOWNWARD WATER FLOW
UPWARD OIL FLOW
ELECTRO-DYNAMIC DESALTER
TYPICAL SINGLE STAGE EDDCOUNTERFLOW WASH WATER INLET
OIL OUTLET
CRUDE OIL INLET FIRST WASH WATER INLET MIX VALVE
BRINE OUTLET
EDD IN FAR EAST REFINERY
EDD IN FAR EAST REFINERY
EDD IN FAR EAST REFINERY
Dual Frequency Technology Transformer Three phase design Low reactance Increases power utilization up to 70%.
Voltage Control Voltage levels can be optimized. Pulse waveform can be selected.
Frequency Control Base Frequency Pulse Frequency
Dual FrequencyCompact Electrostatic Dehydrator Modulation of the Electrostatic Field Slow Speed Modulation Used to Control Drop Size Distribution High Speed Modulation Used to Energize Drop Surfaces
Dual FrequencyCompact Electrostatic Dehydrator High Speed Modulation of Field
Energizes Drops at Resonant Frequency Deformed Drops More Readily Coalesced Allows Adjustment for Physical Parameters Interfacial Tension Oil Conductivity Density Viscosity
Dual FrequencyCompact Electrostatic DehydratorBenefits: Incremental improvement, over existing best in class electrostatic technology. Allows the operator to minimize planned capital expansions: Increases processing capacity of existing vessels. Allows processing of difficult, highly conductive, viscous oils and/or oil blends. Debottleneck offshore platforms where minimization of space, weight and performance are critical.
Dual FrequencyCompact Electrostatic DehydratorCharacteristics:The transformer consists of three primary components, packaged in a single oil-filled enclosure (three phase, 480 volts (50 / 60 Hz)). First, the 480 volts is conditioned to produce a variable amplitude and variable frequency voltage supply for the primary of the transformer. Second, the medium frequency transformer steps up the input voltage to a secondary voltage level necessary to promote effective coalescence. Third, the secondary voltage is rectified into positive and negative half-wave outputs. These polarized, half-wave voltages are then applied to the electrodes to create the benefits of both AC and DC fields.
Dual FrequencyCompact Electrostatic DehydratorA PC-based process controller defines the voltage production. To highly conductive crude oils: Increasing frequency to maximize the energy delivered to the oil dehydration process. Using a medium frequency transformer overcomes the voltage decay associated with conventional 50/60 Hz transformers. Where the interfacial tension between the oil and water is low: Adjust the waveform minimize destruction of the water droplets normally caused by the application of 50/60 Hz power. Reducing the frequency of the waveform and the selection of the shape of the voltage waveform allow to achieve the best dehydration results.
Dual FrequencyCompact Electrostatic Dehydrator In wet crude oils (low effective impedance, rapid voltage decay): Reduces voltage decay and effectively sustains the applied voltage. Seting the minimum and maximum voltage levels to increase the percentage of the entrained water that is swept by the electrostatic voltage. Maximize the droplet growth to promote a rapid sedimentation rate and reach the smallest water to develop a surface charge and promote coalescence. Reducing the voltage to a minimum level will maximize the droplet growth to promote a rapid sedimentation rate.
Dual FrequencyCompact Electrostatic DehydratorPC-based Dual Frequency load responsive control system can control:
The output of the transformer to produce an infinite variety of waveform configurations. The unique waveform generated is optimized to the specific oils physical properties, and enables higher treatment rates and lower BS&W levels than conventional technology.
Demulsification vs. FrequencyDemulsification, % 100 80 60 40 20 0 0 500 1000 1500 2000 Frequency, Hz 1000 V 3000 V
Data from German Researchers
International Chemical Engineering, Vol. 33, no. 1, January, 1993
Dual FrequencyThe Latest Development
Combines Modulation Modes Maximum Drop Growth & Vessel Flux Optimized for Crude Oil Characteristics More Efficient Power Utilization Easy Retrofit
Dual Frequency Field Test Results
0.5
0.4
Outlet BS&W (%)
0.3
0.2
0.1
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P
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m Co y
sit po
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0 0 20000 40000 60000 80000 100000 120000
Capacity (BOPD)
Dual Frequency Results
Dual Frequency Applications
Retrofits to existing installations: Especially Dual Polarity (External Changes) Increased performance: BS&W and/or Capacity
Refinery market where: Highly conductive crudes cannot be desalted Space is a constraint
Offshore production facilities where: Space is limited Weight increases deck construction & expense
Dual Frequency Advantages Reduced outlet BS&W by 30 to 95% Tested on oils between 17 & 40 API.
Allows an increase in vessel throughput from 50 to 100%. Easy retrofit to existing Dual Polarity dehydrators or desalters Estimated 2000 vessels currently in service.
Replaces steel and vessel volume with advanced electrostatic controls Easily optimized to process conditions.
Dual FrequencyCompact Electrostatic Dehydrator
Dual Frequency TM Compact Coalescer Technology
Conventional A/C 14 x 65
Current State-of-the-Art Technology 12 x 40
Dual FrequencyTM 10 x 26
Coalescing Droplets
Example: 80,000 BOPD 32 API Crude 4 cps Viscosity Inlet: 5% BS&W Outlet: 0.5% BS&W