New Electrostatic Technology for Desalting Crude Oil

NPRA Spring National March 2006

New Electrostatic Technology for Desalting Crude Oil

• Gary W. Sams PE–Director Research & Development

• Kenneth Warren PhD–Chief Process Consultant - Electrostatics

NPRA Spring National March 2006

Desalter Performance Issues

• Opportunity Crudes• Heavy crude oils• Increased temperatures• Increased oil conductivity• Soluble Water

NPRA Spring National March 2006

Oil Desalting

• Critical Variables include:– Flow, Temperature, – Water Content, Solids– Mix Water Injection Points– Mixing Energy Requirements– Recycle Water Schemes– Electrostatic Field Type

NPRA Spring National March 2006

Process StagesChemicals – Electrostatic Fields – Hydraulics

• Coagulation– Requires Chemical Reaction

• Flocculation– Assisted by Electrostatic Forces

• Sedimentation– Depends Upon Vessel Flow Regime, Drop

Size & Viscosity

NPRA Spring National March 2006

Partnership for Drop Growth

Chemicals Remove the Barriers…

Electrostatics Provide the Muscle…

NPRA Spring National March 2006

Selection of Electrostatic Fields

• AC – Conventional & Deep-field• DC (Only with refined products)• Combination AC/DC• Modulated AC/DC Fields• Bi-Modal Modulation

NPRA Spring National March 2006

Electrostatic Forces• Dipolar Attraction: Electrical

force produced by positive and negative centers on induced dipoles of water drops.

• Electrophoresis: Electrically induced movement of polar bodies in a uniform field toward closest electrode.

• Dielectrophoresis: Movement of polar bodies induced by a divergent electric field toward increasing gradient.

+ -

+ -

+ -

+ +

+

+

- -

-

-

NPRA Spring National March 2006

Critical Voltage Gradient

x

y

y/x>1.9

• Polarized by the electrostatic field

• Deforms to a prolate spheroid

• Splits when ratio of axes becomes too large

or

Maximum Voltage at which Specified Drop Size Can Exist

2/1)/( dEc γε<

( - )

( + )

NPRA Spring National March 2006

AC Electrostatic Dehydrators

Viscous Drag

Weight

Dipolar Attraction

+ +- -

Dielectrophoretic Force ** Only Exists with Divergent Field

-+

Electrophoretic Force

NPRA Spring National March 2006

Dipolar Attractive ForceBetween Equal Sized Drops

2

4

66 EKd

rF ε=F = Force of Attraction

e = 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 Gradient Cannot Be Exceeded

NPRA Spring National March 2006

Drop Forces in Uniform DC Field

Viscous Drag

Weight

Dipolar AttractionElectrophoretic

Force

++ --+

NPRA Spring National March 2006

Drop Forces in Non-Uniform Field

Viscous Drag

Weight

Dipolar Attraction

Electrophoretic Force+

Dielectrophoretic Force:

+-+-

Holds Drops in Field Until Weight Overcomes Suspending Force

NPRA Spring National March 2006

} Bulk Water Removal

AC/DC Electrostatic Field

NPRA Spring National March 2006

Coalescence in an AC/DC Field

+

Residual Drops from AC Field

- + - +

+ --+

Electrical Ground Reference

NPRA Spring National March 2006

AC/DC Electrostatic Dehydrator• Separation via Stokes’ Law Sedimentation• Multiple Coalescing Forces Grow Drops

– Brownian Collisions– Dipolar Attraction– Electrophoretic Movement– Dielectrophoretic Movement (Only in Divergent Fields)

• Drop Size “Cut Point” Defined by Balance of Dragand Weight

• Larger Mean Drop Size Than Previous Dehydrators

NPRA Spring National March 2006

Electrostatic Field Terminology• Threshold Voltage Gradient

– Voltage Gradient Necessary to Initiate Coalescence

• Critical Voltage Gradient– Maximum Voltage Gradient at which a Specific

Diameter Drop Can Exist

• Modulation Frequency Affects– Drop Transport as function of oil conductivity– Drop Distortion as function of interfacial tension– Field Strength as function of applied voltage

NPRA Spring National March 2006

• Electrophoretic Force = 53 dynes• Drag = Weight = 0.01 dynes• Dipolar Force = 0.004 dynes• Dielectrophoretic Force = 0.002 dynes

Process ConditionsLow Oil Conductivity

750 Micron “Cut Point” Droplet5 kV / in Peak Voltage Gradient0.5% BS&W - Homogeneous

Magnitude of Electrostatic Forces

NPRA Spring National March 2006

Conductivity in Crude OilsSources of Conductivity• Excess water in the electrode zone• Polar compounds in the oil• Solids-Stabilized dispersions

Effects of Conductivity – Performance Loss• Excessive arcing• Parasitic electric currents to the Interface• Loss of electrostatic field

NPRA Spring National March 2006

AC/DC Field Decay in Conductive Oils

Increasing Conductivity

Vol

tage

+

-

NPRA Spring National March 2006

Conductivity Tolerant Designs

• Current-limiting Composite Electrodes• Electrostatic Field Modifications• Solids Removal Systems

– Mud-wash Systems (Sand Jets)– Interface Sludge Drains

NPRA Spring National March 2006

Composite Electrode Array

NPRA Spring National March 2006

Laboratory Pilot Tests

0.430.65805Diluted Bitumen

0.29NA

(Current Limit Exceeded)

6031Arabian Heavy

0.72 – 0.921.2 – 1.56015Maya

Outlet BS&W%

Composite Electrode

Outlet BS&W %

Steel Electrode

Flux (BPD/ft2)

Inlet BS&W

%Crude

NPRA Spring National March 2006

Pilot Testing Facility

NPRA Spring National March 2006

High Reactance TransformerConventional Transformer Protection

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100

Voltage, % of Full Scale

Cur

ren

t, %

of F

ull

Sca

le

Operating Range

NPRA Spring National March 2006

Low Reactance TransformerPermits Voltage Modulation

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100

Voltage, % of Full Scale

Cur

ren

t, %

of F

ull

Sca

le

Operating Range

NPRA Spring National March 2006

Modulated AC/DC Benefits

Modulation Improvements:• Added Coalescing Power• More Effective on Smaller Drops• Enhanced Drop Growth• Higher Water Tolerance• Tolerant of Conductive Oils

NPRA Spring National March 2006

Advanced Electrostatic Field ModulationEstablished Technology• Slow Speed Modulation (as in EDD®)

– Shifts Size Distribution to Larger Drops

Latest Technology• Pulse Modulation (1 to 20 Hz)

– Oscillates Drop Surfaces• Base Frequency (800 to 1600 Hz)

– Used to Limit Field Decay

NPRA Spring National March 2006

Benefits of Bi-Modal Dehydration Pulse & Base Frequency

• Energizes Drops at Resonant Frequency• Deformed Drops Coalesce More Readily• Allows Adjustment for Physical Parameters

• Pulse Modulation - Interfacial Tension,Density, Viscosity

• Base Frequency - Oil Conductivity

NPRA Spring National March 2006

Resonant Frequency Oscillation

• Electrophoretic movement becomes oscillatory and deforms drops• Surface free energy counters interfacial tension• Drop surface becomes highly reactive• Coalescence enhanced by reduced energy barrier

• High frequency electrostatic field applied• Marangoni Effect produces localized circulation in drop

NPRA Spring National March 2006

Dual Frequency® Field Results

0

0.1

0.2

0.3

0.4

0.5

0 20000 40000 60000 80000 100000 120000

Dual Pola

rity (A

C/DC) w/ C

ompo

site

Dual Frequency (Bi -M

odal) w/ C

omposite

Capacity (BOPD)

Out

let B

S&

W (

%)

NPRA Spring National March 2006

Dual Frequency Technology

• Sustains electrostatic field• Optimizes frequencies based on crude• Improves droplet mobility• Increases droplet coalescence• Achieves reduced water content

NPRA Spring National March 2006

Dual Frequency® Advantages

• Reduced outlet BS&W by 30 to 95%• Tested on oils between 17 & 40 API.

• Reduces outlet salt by similar amounts• Easy retrofit to existing AC/DC dehydrators

or desalters• Easily optimized to process conditions.

NPRA Spring National March 2006

Leadership in Electrostatic Technology