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3.0 Electrolyzer Assembly
Uhde Technology
• Uhde Electrolyzer Design
• Pretreatment and installation
• Bubble tests
• Start-up
Uhde Electrolyzer Cell Design
Uhde Electrolyzer Single Element
Element Insertion to
FullElectrolyzer
BM2.7 Narrow Gap 0.4 mm
Uhde Pretreatment and Assembly
• Unroll membranes in to alkaline water, 4-6 gpl NaOH• When ready for assembly, drill membrane bolt holes• Anode awaiting assembly is on table which must be flat and
level– Pour one liter of alkaline water in anode for humidification
• Membrane is placed on to the anode half shell• Using four pins to guide cathode, it is carefully placed on top
of the anode/membrane• See diagrams for placement of PTFE cords and gasket• Bolts are tightened to specified torque
Pretreatment and Assembly• Element is placed in special clamp for pressure test.• This pressures both sides to 3500 mm to check for
external leaks (15 minutes)• Next (bubble test 1), only cathode side is pressured
to 400 mm; anode inlet hose is placed in ~35 mm water.
• If no bubbles in 2 minutes, element passes• Element is transported horizontally and placed in
horizontal storage. If no horizontal storage available, may be placed in rack (electrolyzer) in vertical orientation.
Assembly into Electrolyzer
• Assembled elements can be stored indefinitely
• Bubble test one is repeated on assembly to assure no damage in storage, transport, or installation
Low power test
• Recommended at every start-up• Cell voltages are measured at 2.7 ka• Old/new elements/membranes must be
segregated and averaged• Acceptable voltage deviations from average
< 300 mV• High deviation elements must be removed
and remembraned
New Plants
• Maintain at 5.4 Ka (2 Ka/m2) for
minimum 12 hours
4.0 Membrane Electrolysis
Membrane Single Cell Element
AnolyteOutlet
CatholyteOutlet
ChlorineProduct Hydrogen
DepletedBrine
CausticProduct
H2 &NaOH
Cl2 &NaCl
Na+
H+
OH–
OH–
OH–
H2O
Cl–
Na+
Na+
Cl–
Caustic Feed
(NaOH)
Brine Feed
(NaCl)
AnodeChamber
CathodeChamber
Membrane
DIH2O
AnolyteOutlet
CatholyteOutlet
ChlorineProduct Hydrogen
DepletedBrine
CausticProduct
H2 &NaOH
Cl2 &NaCl
Na+
H+
OH–
OH–
OH–
H2O
Cl–
Na+
Na+
Cl–
Caustic Feed
(NaOH)
Brine Feed
(NaCl)
AnodeChamber
CathodeChamber
Membrane
DIH2O
How Does the Membrane Work?The membranes are CATION exchange membranes having functional
groups which are negatively charged. Cations and polar molecules move freely through the membrane under the influence of electric fields, concentrations, temperatures, and other gradients.
Anions are repelled by the membrane because of its fixed negative charges. This is the fundamental reason that the membrane can transport cations with little resistance, and offer a nearly impassable barrier to anions.
Neutral species, such as water, are not repelled by the membrane and can be carried through the membrane along with cations.
Sodium ions (Na+) are cations, so they’re electrically attracted to the negative cathode. Being cations, they pass freely through the membrane from the anode side to the cathode side, carrying with them current and water.
Hydroxide ions (OH-) are anions, so they’re repelled by the membrane They really want to go to the anode because it’s positive, and opposites attract. But the membrane won’t let them. The efficiency of the membrane to reject the hydroxide ions is called “current efficiency”.
Membrane Cross Section
Inefficiency By-Products
Membrane Cross Section
Membrane Pinhole
Current Efficiency Change with Time Example
CE
Time
As Current Efficiency Drops the Inefficiency By-Products Increase
Time
O2
ClO3
HOCl
Current Efficiency
Effects of Membrane Damage
Occurrence ofMembrane Damage
Time
O2
ClO3
HOCl
CurrentEfficiency
Co
nce
ntr
atio
n
TYPICAL MEMBRANEELECTROLYSIS PROCESS
SCHEMATIC
Primary BrineTreatment
SecondaryFiltration
Ion ExchangeBrine
Treatment
Saturation Salt Storage Ultra-PureBrine Storage
Hydrogento Processing
Cl2 Gasto Processing
30-32%NaOH
CausticCirculation
BrineDechlorination
ChlorineBrine
Separation
Cell Roomand
Renewal
Rectifier
HCl
Vent
NaOHHClDI H2O
NaOHNa2CO3
Flocculant
ProcessH2 O
Cl2
SulfateControl
NaOH
Na2 SO3
Cl2
H2 0 H2 0
H2 0
NaOHH2
NaOH
NaClCl2
Cl2
HCl
H2
D.I.H20