3.0 electrolyzer assembly - 4.0 electrolysis

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