fundamentals of electrodeionization (edi) technology...electrodeionization process •edi is not a...
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Fundamentals of
Electrodeionization (EDI)
Technology
By Chris Gallagher
Applied Water Solutions, Inc.
WQA 2008
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Electrodeionization Process
• EDI is not a filter but an electrochemical process
that removes ionized and ionizable species
• EDI can replace mixed bed ion exchange
• EDI performance is directly effected by:
– Total ionic load in the feed water
– Temperature
– Needs a DC voltage source to create an electric current
– Flow rate
• Current Efficiency governs all EDIs
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Year 0 1 2 3 4 5 6 7 8 9 10
Maintenance
Evaluation Issues
Considerations/
Recommendations
Filter replacement every 6 months
Cleaning frequency increases through time
Replace Carbon
Pump Seals
Calibration
Membrane
Replacement
Replace Motor
Replace Pump
Update Instruments
Replace Valves
Decrease in Throughput
Variability in Feed Source
Stricter Water Standards
New regulations prohibiting certain discharge
Increase Demand for High Purity Water
Revise PM program Revise PM program
Membrane
Replacement
New System Investment
Rebuild Existing System
Reevaluate technologies
Reduce Chemical Use
Environmental Issues
Maintenance CostsReliability
Initial Capital
Investment
Life of a Water System
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Type of EDIs
Thick Cell• Introduced in 2001• Plate and frame
Spiral Wound• Limited market share
• Higher efficiency
Circular Enclosure• Innovative design• Plate and frame
Thin Cell• Introduced in late 80s• Plate and frame• First sold to OEMs
Courtesy: Electropure
Courtesy: Ionpure Technologies
Courtesy: Omexell
Courtesy: Ionpure Technologies
Thick Cell• Introduced in 1996• First thick cell sold
to OEMs• Plate and frame Courtesy: GE Water
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Process Principles
AN
OD
E (
+)
CA
TH
OD
E (
-)
EX
CH
AN
GE
ME
MB
RA
NE
EX
CH
AN
GE
ME
MB
RA
NE
Purifying
Concentrate
PurifyingConcentrateConcentrate
PurifyingPurifying
Cl-
HCO3-
OH-
CO3-
HCO3-
Ca++
Mg++
Na+
H+
Cl-
CO3-
HCO3-
Mg++
Na+
H+
ElectrodeElectrode
Ca++
HCO3-
HCO3-
HCO3-
Ca++
OH-
OH-
Ca++
Na+
H+
OH-
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Flow Path of EDIs
AN
OD
E (
+)
CA
TH
OD
E (
-)
Conc Purifying Conc
ED
EDI Dilute Filled
EDI All Filled
AN
OD
E (
+)
CA
TH
OD
E (
-)
Conc Purifying Conc
AN
OD
E (
+)
CA
TH
OD
E (
-)
Conc Purifying Conc
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Spiral Wound EDI – Design #1
Courtesy: Dow Chemical
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Spiral Wound EDI – Design #1
Courtesy: Dow Chemical
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Spiral Wound – Design #2
Courtesy: Christwater
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EDI System Design
Multiple Stack vs.
Single Stack
• 50 gpm standard
• 15 gpm standard
• 10 gpm standard
• <10 gpm standardCourtesy: GE Infrastructure,
Water & Process
Technologies
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EDI System Design
• Multiple
Stack vs.
Single
Stack
Courtesy: Ionpure Technologies
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Feed Water Requirements for EDI Supplier 1 Supplier 2 Supplier 3 Supplier 4
Source: RO water RO water RO water RO water
Feed
Conductivity:
< 40 µS/cm 4-30 µS/cm < 40 µS/cm na
Concentrate
Conductivity:
> 20 µS/cm
(varies)
> 10 µS/cm
(varies)
na 250 - 1000
µS/cm
Hardness: < 0.25 ppm
as CaCO3
< 1.0 ppm < 1.0 ppm < 2.0 ppm
Silica: < 1.0 ppm < 0.5 ppm < 1.0 ppm < 1.0 ppm
TOC: < 0.5 ppm < 0.5 ppm < 0.5 ppm < 0.5 ppm
Pressure: 20 to 50 psi < 60 psi 20 to 100 psi 36 to 100 psi
Temperature: 10 to 35oC 5 to 35oC 5 to 45oC 5 to 38oC
pH: 4 to 10 5 to 9.5 4 to 11 5 to 9
Chlorine: < 0.1 ppm < 0.05 ppm < 0.02 ppm < 0.05 ppm
Fe, Mn, Sulfide: < 0.01 ppm < 0.01 ppm < 0.01 ppm < 0.01 ppm
CO2 < 10 ppm < 5 ppm na < 10 ppm
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Feed Water Concentration LimitsParameter RO EDR
TDS (as NaCl) rejection rates 97-99% removal ~50% removal
Iron (dissolved) 0.3 mg/l 0.3 mg/l
Manganese (dissolved) 0.05 mg/l 0.1 mg/l
H2S 0.1 mg/l 0.1 mg/l
Aluminum 0.1 mg/l 0.1 mg/l
Free Chlorine ( RO Composite Polyamide Membranes)
Homogeneous Ion Exchange Membranes
< 0.1 mg/l 0.5 mg/l cont
30.0 mg/l max
shock
Free Chlorine (Max, Cellulose Acetate Blend Membranes) 1.0 mg/l NA
Oil 0.0 mg/l 2.0 mg/l
COD 4 – 18 mg/l (as O2) 50 mg/l (as O2)
TOC < 2.0 mg/l 15.0 mg/l
Turbidity 0.1 – 0.4 NTU 0.5 – 2.0 NTU
SDI15 (Continuous) < 3.0 10-12
SDI15 (Max, Intermittent) 4.0 – 5.0 15
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Typical GuidelinesWater Standards / Guidelines
Microelectronics Power ASTM Pharmaceutical
electronics grade
QR 1.2
Type I Type
II
USP27
Conductivity
(S/cm)
.0546 <0.10 <0.056 <1.0 <1.3
Resistivity (M-cm) 18.2 >10.0 18.0 >1.0 >0.769
TOC (ppb) <50 100 50 <500
Silica (ppb) <5 <10 <3 <3 none
Bacteria (cfu/ml) <10 none <100
Chloride (ppb) <0.1 <10 1 5 none
Sulfate (ppb) 0.1 <10 none
Sodium (ppb) <0.5 <10 1 5 none
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Concentrate Compartment• Recirculation
– Concentration of reject
– Flow rate considerations
• Brine Injection
– Addition of NaCl
Purifying Conc
100 gpm
90 gpm
Purifying Conc
Reject
Purifying Conc
Reject
Reject
5-10 gpm
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Hydraulic/ Pressure Considerations
• Reverse Osmosis Design
– RO Pump Sizing
– Permeate Back Pressure
• Break Tanks
– Pre EDI
– Post EDI
• EDI
– Pressure drop across EDI varies with
manufacturer
– EDI back pressure varies with manufacturer
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System Design
ROEDI
STORAGE
ROEDI
STORAGERO
STORAGE
High Pressure
Pump
High Pressure
Pump
EDI Feed
Pump
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System Design
ROEDI
STORAGERO
STORAGE
Booster
Pump
ROEDI
STORAGERAW
WATER
EDI Reject
High Pressure
Pump
High Pressure
Pump
EDI Feed
Pump
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Current Efficiency
• Current Efficiency governs all EDIs
• Voltage is only a potential
• Current does the work
Ohm’s Law
E=IR
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Current Efficiency• Detailed Equation (1)
Where
current utilization efficiency, %
z = charge of ion
F = Faraday’s constant, 96,485 Amp-s/mol
Qf = diluate flow rate, L/s (=gpm/15.85)
Cdinlet = diluate ED cell inlet ion concentration, mol/L
Cdoutlet = diluate ED cell outlet ion concentration, mol/L
N = number of cell pairs
I = applied current, Amps
Source: Ionpure
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Current Efficiency• Simplified Equation
Source: Ionpure
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Variables to be Monitored
• Pressure
• Temperature
• Flow rates
– Dilute
– Concentrate
– Electrode
• Voltage
• Amperage
• Conductivity
• Resistivity
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Performance Data Collection• Daily
• Weekly
• Monthly
• Seasonal Effects
RO
Co
nd
uctivity
(ED
I F
ee
d)
Temperature
EDI
RO
ED
I Co
nd
uctiv
ity
(Qu
ality
)
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• Some conditions that effect system performance:
– Water temperature
– Feed salinity
• Normalization adjusts data to fit specific operating
conditions.
• Changes in normalized performance represent a
real change in system performance.
• Normalization makes it easy to see real changes in
the performance of a system.
Normalization
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Seasonal Effects
• Geography
• Naturally occurring events
• Feed water source variability
– Chlorine
– Chloramines
– Hardness
– pH
– Temperature
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TroubleshootingPretreatment
Organic
Fouling
Particulate
FoulingBiofouling
Oxidation
AttackScaling
Sym
pto
ms
•Decrease in performance
•Increase in electrical resistance
Most notable in the diluting compartment
•Decrease in flow
•Increase in pressure drop
•Decrease in performance
Most notable in the diluting compartment
•Decrease in flow
•Increase in pressure drop
•Decrease in performance
Most notable outside of active membrane area
•Decrease in flow
•Increase in pressure drop
•Decrease in performance
•Increase in electrical resistance
An oxidation attack will irreversibly damage EDI
•Decrease in flow
•Increase in pressure drop
•Decrease in performance
Most notable in the concentrate department
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Organic Fouling
Current at
Constant Voltage
Time
EDI
EDI Product Resistivity
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Scaling
ΔP in Concentrate
and Electrode
Time
Pressure
Current
Current
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Oxidation
ΔP in Dilute
Time
Pressure
Current
Current
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Three Important Factors of CE
• Flow Rate
– Higher flow rates, less
residence time
– Kinetics change
– Pressure drop
• Feed Water
– Total ionic load
– Temperature• Current
– Voltage
– Directly affects performance
CASE E (Volts) I (Amps) R (Ohms) Quality
(Meg-ohm)
Initial
Condition
300 3
#1 300 2
#2 400 3
#3 200 3
#4 400 4 No Change
15
No Change
No Change
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“Bringing Clarity to the Turbid Waters of Technology”SM
by Chris Gallagher
cgallagher@appliedwatersolutions.com
Questions?
Disclaimer
The speaker represented the information included in this presentation as being valid at the time it was presented. Applied Water Solutions makes every effort to provide timely and accurate information. Nevertheless, mistakes and confusions may occur. Applied Water Solutions and the author does not assume liability for the accuracy or reliability of the information provided in here.
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