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


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


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


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


Thick Cell• Introduced in 1996• First thick cell sold

to OEMs• Plate and frame Courtesy: GE Water


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-


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


Spiral Wound EDI – Design #1

Courtesy: Dow Chemical


Spiral Wound – Design #2

Courtesy: Christwater


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


EDI System Design

• Multiple

Stack vs.

Single

Stack



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


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


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


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


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


System Design

ROEDI

STORAGE

ROEDI

STORAGERO

STORAGE

High Pressure

Pump

High Pressure

Pump

EDI Feed

Pump


System Design

ROEDI

STORAGERO

STORAGE

Booster

Pump

ROEDI

STORAGERAW

WATER

EDI Reject

High Pressure

Pump

High Pressure

Pump

EDI Feed

Pump


Current Efficiency

• Current Efficiency governs all EDIs

• Voltage is only a potential

• Current does the work

Ohm’s Law

E=IR


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


Current Efficiency• Simplified Equation

Source: Ionpure


Variables to be Monitored

• Pressure

• Temperature

• Flow rates

– Dilute

– Concentrate

– Electrode

• Voltage

• Amperage

• Conductivity

• Resistivity


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

)


• 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


Seasonal Effects

• Geography

• Naturally occurring events

• Feed water source variability

– Chlorine

– Chloramines

– Hardness

– pH

– Temperature


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


Most notable in the diluting compartment

•Decrease in flow



Most notable outside of active membrane area

•Decrease in flow



•Increase in electrical resistance

An oxidation attack will irreversibly damage EDI

•Decrease in flow



Most notable in the concentrate department


Organic Fouling

Current at

Constant Voltage

Time

EDI

EDI Product Resistivity


Scaling

ΔP in Concentrate

and Electrode

Time

Pressure

Current

Current


Oxidation

ΔP in Dilute

Time

Pressure

Current

Current


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


“Bringing Clarity to the Turbid Waters of Technology”SM

by Chris Gallagher

[email protected]

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.

fundamentals of electrodeionization (edi) technology...electrodeionization process •edi is not a...

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