EDI How it work - songvietwater.com cat/EDI How it work... · GE – Training – What Is EDI & How...
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Electrodeionization (EDI)
Transcript of EDI How it work - songvietwater.com cat/EDI How it work... · GE – Training – What Is EDI & How...
Electrodeionization (EDI)
Introduction to EDI
Process Principles
Electrodeionization (EDI) process removes ionizable species from liquids using
Definition
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ionizable species from liquids using electrically active media and using an electrical potential to influence ion transport.
Why EDI?
Continuous water purificationwithout regeneration chemicals:
...Reverse Osmosis replaces primary
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...Reverse Osmosis replaces primary cation/anion exchange
...Electrodeionization replaces mixed bed ion exchange
EDI EVOLUTION
Pretreatment Cation IX Anion IX Mixed Bed
Caustic
Acid
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Pretreatment Mixed Bed
CausticAcid
R.O. EDI
R.O.
Pretreatment
Role of EDI in RO/EDI Systems
RO initial demineralization step
> remove ionic impurities, particles, high molecular
weight organics
> rejection relative to feed
– ca. 95-99% rejection
EDI final demineralization step
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EDI final demineralization step
> remove residual ionic and ionizable impurities
> must meet absolute specifications (resistivity,
sodium, silica, boron)
… EDI must meet ABSOLUTE specifications
Introduction to EDI
GE currently has more than 100,000 gpm installed capacity.
EDI in general is offered by virtually every water treatment company
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Widely adopted across many industries
Approved by leading industry experts, i.e., Intel, Fuji, AEP ProServ, etc.
Introduction to EDI
Proven in a wide range of demanding applications:
>Power / Utilities / Boiler Feed Water
>Biotechnology / Pharmaceuticals
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>Semiconductor / Electronics
>Surface Finishing (Automotive, etc.)
>Consumer Goods & Cosmetics
>General Industry
How EDI Works
MIXED BED vs EDI
Product Water
Product Water
Regenerated Resin
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EDI Stack
Feed Water
Feed Water
Exhausted Resin
Transition Zone
Process Principles
Cation exchange membranes
Anion exchange membranes
All EDI Devices have the following:
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Anion exchange membranes
Spacers
Electrodes
Cation/Anion exchange resin
Electrodialysis(Continuous Process)
Cathode (-)
Cation-Transfer Membrane
Anion-Transfer
DemineralizedProduct
Na+
Na+
Cl-
Na+
Na+Na+
Na+
Cl- -
- - - - -
Cl-
Anode (+)
Anion-Transfer Membrane
ConcentrateCation-Transfer Membrane
Na+
Na+
Cl-Na+
Na+
Cl-
Cl
Na+Na+
Cl-Cl-
Cl-Cl-
Cl-Cl-
+ + + + +
Na+ Na+Na+
CaCa++++ NaNa++MgMg++++ HH++
High-
- - - -Cathode (-)
CO2Cation-Exchange Membrane
Process Principles
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HCOHCO33--SOSO44
== ClCl-- OHOH--HSiOHSiO33-- COCO33
==
High-
Purity
Product
WaterHCO3
-
+ + + +Anode (+)
SiO2
CO2
Na+
SO4=
Cl-Ca++
Anion-Exchange Membrane
Cation-Exchange Membrane
Ion Exchange
Cation
Resin
Na+
H+
Dilute Chamber
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Resin
Anion
Resin
Cl-
H+
OH-H2O+
Water Splitting & Regeneration
OH-
H2O
H+ OH-H+
Dilute Chamber
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Resin ResinOH-H+
Na+ Cl-
OHH+
Cation
Resin Na+
H+
H+H+
- +
Dilute Chamber – Ion Migration
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Anion
Resin
Cation
membrane
Anion
membrane
OH-
OH-Cl- OH-
- +
CH3
N+
CH3
CH3
CH3
N+
CH 3
CH3
CH3
N+
CH 3
CH3 Cl
-
Mobile Counter Anions
Water-Filled Passage
Fixed Cation Sites
Polymer Support Structure
Cl-
Cl-
Anion-Exchange Membrane
Ion-Exchange Membranes
Today there are 2 standard types of membranes:-Heterogeneous-Homogeneous
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Mobile Counter Cations
Water-Filled Passage
Fixed Anion Sites
Polymer Support Structure
S O-
O
O
S O-
O
O
S O-
O
O Na+
Na+
Na+
Cation-Exchange Membrane
-Homogeneous
Cations can’t pass
through anion
membrane and
Concentrate Chamber
Anion membrane Cation membrane
Dilute
ChamberNa+
H+
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membrane and
anions can’t pass
through cation
membrane
Dilute
Chamber
Cl-
OH-
Concentrate Chamber
Dilute
Chamber
Dilute
Chamber
Cl-
Na+
Cl-
Na++
+-
-
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Anion membrane Cation membrane
Cl-
OH- H+
Cl- +
+-
-
High pHLow pH
pH Extremes
• 2 to 9 times the number of H+ and OH-
ions as other (contaminant) ions
• Concentrate chamber side of Cation
membrane is at low pH (many H+ ions)
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membrane is at low pH (many H+ ions)
• Concentrate chamber side of Anion
membrane is at high pH (many OH-
ions)
• High pH levels can facilitate scaling!
Cathode chemistry_
2H2O + 2e- = 2OH-(aq) + H2(g)↑↑↑↑
• Hydrogen gas formation
• 7.0 mL(STP)/Amp/minute
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Cathode
• 7.0 mL(STP)/Amp/minute
• High pH
• Scaling is possible
Anode chemistry+
• Oxygen gas formation
2H2O = 4H+(aq) + O2(g)↑↑↑↑ + 4e-
(2Cl-(aq) = Cl2 (g) ↑↑↑↑ + 2e-)
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Anode
• Oxygen gas formation• 3.5 mL (STP)/Amp/minute
• Trace Chlorine formation• 1-2 ppm in Eout (400 uS/cm NaCl)
• Low pH
Process Principles- EDI ProcessFeed
HSiOHSiO33-- COCO33
== OHOH--ClCl--SOSO44== NONO33
-- HCOHCO33--
Anion Membrane
NaNa++CaCa++++ MgMg++++ HH++ Na+Na+
Cation Membrane
Anode Waste
Concentrate
Anode (+)
High Purity Water
HSiOHSiO33--
COCO33== OHOH--ClCl-- NONO33
-- HCOHCO33-- HSiOHSiO33
--SOSO44==
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HH++
-
Cation Membrane
Anion Membrane
High Purity Water
CaCa++++ MgMg++++ NaNa++
HH++
Concentrate
Cathode(-)
Cathode Waste
Concentrate
COCO33== OHOH--ClCl-- NONO33
-- HCOHCO33-- HSiOHSiO33
--SOSO44==
Demineralization with EDI
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E-CellTM Flow Path
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Concurrent Processes in EDI• Ion exchange occurs as per usual kinetic &
thermodynamic factors – therefore the process is driven by the same factors that occur in a Mixed Bed Vessel
• Ions in the IX resin migrate toward the electrodes,
through IX membranes and into C-chambers
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through IX membranes and into C-chambers
> Impurity ions trapped in C-chambers by membranes
> H+ and OH- recombine to give H2O
• Water splitting produces H+ and OH- ions resulting
in continuous regeneration
Concurrent Processes in EDI
• Water splitting produces a continuous flux of H+
and OH- ions resulting in continuous regeneration
• Electrode flow is captured separately from C Bleed due to trace chlorine and hydrogen gas
• Scaling can occur if design limits exceeded
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• Scaling can occur if design limits exceeded
Key EDI Operating Parameters
Feed water composition
> ionic/ionizable impurities (pH inside IX)
> Ubiquitous CO2 => design on TEA (vs TEC)
Applied current
> Key stoichiometric quantity (=IX capacity in MB IX)
> Drives water splitting and ion removal
> Determined by
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> Determined by
– target product quality (resistivity, silica, …)
– impurity concentration and flow rate
– ionic charge on impurities inside IX medium
Flow rate
> dilute solution => film diffusion limiting
– flow ↑↑↑↑ => residence time↓↓↓↓ & diffusion layer ↓↓↓↓
PretreatmentReverse Osmosis Permeate required to minimize:> Scaling
> Organic fouling
> Particulate and colloidal plugging
> Chemical cleaning
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Other Possible Pretreatment Combines w/ RO treatment> MicroFiltration/UltraFiltration
> Cartridge Filters (CF)
> Degasification – Membrane/NaOH Injection/Forced Draft
> UV TOC Destruct (UV)
> Softeners
Feed Water Requirements
• Ion loading levels higher than 65 uS/cm, and CO2
higher than 8 ppm, will easily overwhelm the EDI
ionization processes that are required to achieve
high product water resistivity and to remove species
such as silica and boron.
• Particulates will clog inlet screens and occupy the
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• Particulates will clog inlet screens and occupy the
available void volume in the resin bed.
• Organics can foul anion resins and prevent ion
exchange from proceeding.
Feed Water Requirements
Parameter E-Cell Ionics EDIConductivity 25mg/l (as CaCO3) TEA <40 mS/cm
CO2 Included in TEA <8 mg/l
Hardness <0.50mg/l (as CaCO3) <0.25mg/l (as CaCO3)
Silica <0.50mg/l <1.0mg/l
TOC <0.50mg/l <0.50mg/l
Total Chlorine <0.05mg/l <0.10mg/l
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Total Chlorine <0.05mg/l <0.10mg/l
Temperature 10 – 35 deg C 10 – 38 deg C
pH 4 – 12 4 – 12
Fe, Mn, H2S <0.01mg/l <0.01mg/l
Turbidity <1 NTU <1 NTU
Typically all EDI state approximately the same inlet feed water requirements.
RecoveryRecovery = Product flow
Feed flow
Feed flow = Product flow + Makeup
= Product flow + E Out + C Bleed
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Recovery = Product flow
Product flow + E Out + C Bleed
Flow meters on E-Cell System:
D Out, E Out, C Bleed (& Cin)
Recovery
300
400
500
600
700
800
Tim
e B
etw
een
Cle
an
ing
s (
days)
8 h/d 5 d/week
12 h/d 5 d/week
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Figure 4.4: Cleaning intervals as a function of E-Cell feed hardness and
operating schedule.
0
100
200
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Hardness (ppm as CaCO3)
Tim
e B
etw
een
Cle
an
ing
s (
days)
24 h/d 7 d/week
RecoveryFor ALL types of EDI systems, recovery depends on Feed Hardness
Higher feed hardness => lower recovery
Lower recovery reduces scaling potential
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Lower recovery reduces scaling potential
> By reducing hardness of Concentrate Stream
Recovery set via Concentrate Bleed
Operation of Standard Systems
Similar to a RO
•Set up proper flows and pressures during start-up
•Set appropriate current
•During operation of system monitor & trend: flows,
pressures, current, voltage, product resistivity and
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pressures, current, voltage, product resistivity and
concentrate conductivity
•Depending on trending and feed water quality
cleanings will be required.
Benefits & Limitations of EDI
Benefits over Mixed Bed Technology
1. No bulk storage of regeneration chemicals.
2. No waste neutralization required
3. Facility footprint/overhead can be significantly
reduced.
4. Affords complete control over water system in
house – nothing leaves or comes into plant.
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house – nothing leaves or comes into plant.
5. No risk of cross contamination with other customer
resins.
6. Reduction of EHS risks
7. Continuous, not batch operation. Stable water
quality over time.
Limitations of EDI
Number 1 reason EDI systems fail in the field is feed water hardness.
>High hardness leads to scaling which can lead to thermal damage.
>To counter this, E-Cell has developed
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>To counter this, E-Cell has developed a trending spreadsheet to help protect your system.
>System needs to be cleaned in a timely manner.
Limitations of EDI
Number 1 reason EDI systems produce poor product
quality in the field is CO2 in the feed water.
> The resin within the stack can be
overwhelmed
> Most people only look at conductivity into the
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> Most people only look at conductivity into the
EDI system, but fail to look at CO2 because it
is not readily checked.
> To counter this, ensure that a proper
projection is completed on the feed water.
> CO2 should be checked at regular intervals.
Hach has a very easy test kit that can be
used.
Feedwater must be RO direct-coupled quality
Physical, biological and chemical contamination must be prevented
> Physical: PVC shavings; metal shavings; dirt; dust; pollen; welding debris; resin beads/fines
Limitations of EDI – Feed Water
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dust; pollen; welding debris; resin beads/fines
> Chemical: oxidizers such as chlorine; polyvalent cations, such as iron, manganese
Sources of contamination: open storage tank, degasifier, or softener without filtration before E-Cell
