Chlor Alkali Coatings
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Transcript of Chlor Alkali Coatings
1
CHLOR-ALKALI COATINGS
AND
REFURBISHMENT SERVICES
By Dr Derek C Armstrong
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KEY FACTS
INEOS manufactures all its own coatings
All INEOS coatings can be tailored to customers membrane cycles
Anodes – 8, 10, 12 years
Cathodes – 8, 10, 12, 15, 16 years
INEOS coatings are currently installed in the following electrolysers
• INEOS
• UHDE
• AK
• MGC
INEOS HAS BEEN MANUFACTURING CHLOR ALKALI ELECTRODES FOR 118 YEARS
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INEOS ANODE COATINGS
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Anode Coatings
� A layer of conductive, catalytic material applied to the surface of a titanium anode to promote chlorine evolution at low voltage
� Applied in layers followed by stoving (thermal decomposition)
� Key components are RuO2, IrO2
� Voltage performance dependent on
surface area
� Surface shows a ‘cracked’ structure
� Lost by 2 mechanisms
� Mechanical loss
� Alkaline wear
SEM of INEOS anode coating 1.5K magnification
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Anode Coatings – Features to consider in Coating Selection
Feature What is it? Impact ?
Over-potential Additional voltage generated by the surface resistance of the coating
Higher over potentials mean higher power consumption- adds to operating cost
Alkali Wear Resistance
Resistance to loss of Ruthenium, the critical catalytic element, during operation
High alkali wear = short anode life, or more expensive anodes as suppliers add more RuO2
High Chlorate in brine
ClO3- is produced as a by
product of Cl2 productionPotentially environmentally damaging and discharge may be limited
Higher chemical usage in chlorate destruction system
Higher rates of corrosion in caustic evaporators as higher levels of chlorate in caustic soda.
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INEOS Anode Coating – LOW CHLORINE OVER POTENTIAL
INEOS ANODE coatings have been designed to provide a chlorine over-
voltage of 20-30mV lower than typical commercial coatings. This represents a
1% power saving for customers (eg based on $80 per MWh a 100kte plant
would save $120k/year)
20
25
30
35
40
45
50
55
60
0 1 2 3 4 5 6 7 8
chlorine over-voltage (mV)
Time
Chlorine over-voltage
INEOS ANODE COATING
TYPICAL COMMERCIAL ANODE COATING
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INEOS Anode Coating – LOW ALKALINE WEAR
Accelerated Alkaline Wear Test - Voltage Rise - 20kA/m2 Current Density
0
1
2
3
4
5
6
7
8
9
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
Duration (Hours)
Voltage ( V )
CP304 CompetitorINEOS
INEOS ANODE coatings have been designed to provide significantly superior alkaline
wear performance over other commercially available chlor-alkali anode coatings.
With the move to zero gap where the membrane lies directly up against the membrane
good alkaline wear resistance in very important for coating life as the surface of the
membrane is alkaline.
Time
StandardCommercialcoating
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INEOS Anode Coating – LOW CHLORATE IN BRINE
INEOS Competitor
Chlorate (g/l) 0.05 0.3
Hypochlorite (g/l) 0.8 1.5
INEOS ANODE coatings have been designed to provide a very low level of
chlorate (and hypochlorite) in brine.
This translates to less chemical usage for chlorate destruction but more
importantly lower chlorate in caustic, stopping evaporator corrosion.
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INEOS CATHODE COATINGS
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Cathode Coatings
� A layer of conductive, catalytic material applied to the surface of a cathode to promote hydrogen evolution at low voltage.
� Key components are many and vary dependent upon the supplier.
e.g. RuO2, Raney nickel, Pt group metal oxides, Nickel Oxides, sulfides, carbides.
� Applied using a range of techniques depending upon the coating type.
e.g. “spray-bake”, electro deposition, plasma spray, electroless plating, catholyte additive.
� Total coating thickness 200microns to
>1 micron depending upon type.
� Best have a high ratio of catalytic area
to apparent area.
� Loss mechanisms are� Wear
� Reverse current dissolution
� poisoning
SEM of INEOS cathode coating – 4K magnification
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Typical Progression of Cathode Coating Wear
• Non-precious metal coatings normally last 4-8 years
• INEOS precious metal coating shows virtually no loss (warrantied for 16 years)
• >18 years experience in our FM mono-polar technology
• 13 years experience on BICHLOR™ with no measurable loss
Cathode coating loading vs time on load - schematic
0
100
0
time on load
% of starting catalyst remaining in
coating
Non-precious metal coating
INEOS precious metal coating
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The INEOS CATHODE Coating has an exceptionally high resistance to
reverse currents making it the ideal cathode coating for all zero gap
electrolysers.
Coating totally failed
-0.350
-0.300
-0.250
-0.200
-0.150
-0.100
-0.050
0.000
0 100 200 300 400 500 600 700 800
E(V) verus RHE
Test Cycles
Accelerated Cathode Durability Data85°C 32% NaOH (Data HF Resistance Corrected)
INEOS cathode coating Competitor cathode coating
High resistance to reverse currents
Non precious metal cathode coating
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Features of INEOS Cathode Coatings in summary
Feature INEOS vs Competitor
Over potential In trials in other technologies INEOS’ over potential at start-up is the same as non precious metal coatings but demonstrates better performance over a longer lifecycle.
Resistance to reverse currents at shutdown
INEOS cathode coatings lose no catalyst when subjected to reverse current..
Non precious metal coatings are known to be attacked by reverse currents
Resistance to impurity poisoning
High surface area minimises the sensitivity to impurity damage.
Any poisoning that does occur tends to be reversible (e.g. at shutdown)
Lifetime Experience indicates INEOS cathode coatings will last for >16 years
Proven in FM mono-polar electrolysers over 18 years,
13 years (and counting) without weight loss in BICHLOR™ bipolar electrolysers
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INEOS REFURBISHMENT CAPABILITY
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INEOS Refurbishment Facility
• A new purpose built facility commissioned in Q1 2013.
• First delivery within 4 weeks from initial receipt of pans.
• Smaller batches can be accommodated in a shorter lead time.
• In addition to modular type electrolysers, different types of structures may be processed for example mercury and large fly screen meshes.
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Refurbishment Process
� Receipt and identification
� Pre-work inspection & assessment (Recorded in database)
� Refurbishment - Repair (Mesh, Flange and Pan repair)
� Surface preparation
� Coating
� Final quality inspection
� Packing & Dispatch
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Inspection
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Expert Welding
Fine ‘jewellery’ type welding by experts
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Refurbishment – Flange and electrode damage/corrosion
crevice corrosionflange corrosion
Corrosion at compression points Corrosion of louver
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Louvre Replacement
Sections of corroded louvre are removed and replaced
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Inlet Repair
Corrosion to outlet pipe
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Inlet Repair
Completed Repair
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Key Steps – Surface Preparation
ANODE
CATHODE
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Pan/Element Washing
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In-Pan/Element Coating
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In-Pan/Element Coating
Flange protected by coating
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Final Inspection
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Finished Product – Preparing for Shipment
SUMMARY
INEOS CAN PROVIDE :-
� STATE OF THE ART COATINGS• Long life• Robust against wear, reverse currents and impurities• Low over voltage
� COMPREHENSIVE RE-COATING AND REFURBISHMENT SERVICE