hatch reduction technology tms presentation 2015
TRANSCRIPT
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MAEGMA STEEL
November 2006
Recent Technology Developments in Smelter Power Reduction &
Pot-life Extension
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Will Berends, Director, Hatch Technologies GroupSmelter Power Reduction
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• Engineering, Services & Technology• Mining& Metals, Energy, Infrastructure• ~10,000 persons worldwide• >50 offices in > 20 countries
www.Hatch.ca3
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Hatch Light Metals GroupServices• Capital Projects: EPCM Services
• Operational Services: In-plant resources
• Technical Consulting Services: Process, equipment, facilities, infrastructure environment,
• Management Consulting Services: Investment due diligence, owner representative
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Hatch Technologies GroupIndependent Supply of Hatch Proprietary Technology• Bauxite Tube Digester
• Ferronickel Smelting Furnaces
• Mineral Processing Autoclaves
• Steel Production ‘Coilbox’
• Smelter Power Reduction Technology
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Our Lawyer’s Disclosure Statement
Please note: Thetechnology described herein is protected by one or more issued or pending international patents.
CA 2,838,113US 62119508CN201420801618.3RU2014149274GCC2014/28532PCT CA2014/051178Etc.
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Aluminum Smelting – COMPLEX!
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Key Metrics:- Power Consumption Kwh/Kg- Current Efficiency %- Potlife (Time or Tons)- SPL, Emissions
Key Operating Parameters:• Potline Amperage • Pot Voltage drop, Anode, Bath ACD, Cathode• Bath Chemistry & Superheat• Frozen Bath Ledge & Cathode wear• Potlife – failure by runouts, metal purity (Si, Fe, etc.)• Anode Effect, Pot-Noise, CE%• Net Carbon Consumption
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Process Operating Parameters
PotLineAmperage KA
Pot Voltage Drop
ACD upper limit
ACD lower limit
No sideledge
Poor alumina dissolution, frozen bath in corners
Bath Superheat. range
Poor CE%, pot noise, Anode effect
Wasted energy
Normal operating window
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Hatch: Smelter Power ReductionRetrofit & New Installation
Anode Assembly• Stub to Carbon iron
connection
Potshell Heat Balance +/-• Cooling & Insulating
Cathode Assembly• Iron connection to
improve current distribution
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Hatch: Smelter Power Reduction
Anode Assembly• Stub to Carbon iron
connection
Potshell Heat Balance +/-• Cooling & Insulating
Cathode Assembly• Iron connection to
improve current distribution
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Anode Assembly Voltage Drop:Stub To Carbon Contact Resistance
Steel Stub
Grey cast iron ‘Thimble’
Carbon Anode
Iron cracking from shrinkage
Shrinkage Gap betweeniron and carbon
Initial Voltage drop of ‘cold’ iron connection >200 mV,Average Voltage drop reported to be >80 mV over anode cycle
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Typical vs. Desired STC voltage drop over anode cycle
Hours Anode Cycle Days
Time
Voltage drop
2 4 6 8 1210 14 1816 20 22 24 2 4 6 8 10 12 16 18 2014 22 24
Typical Amperage pickup
Typical Contact resistance
Typical STC voltage drop
Desired STC Voltage Drop
Desired Contact Resistance ??
Objective: to reduce Stub to Carbon voltage drop over initial heatup and full anode cycle
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Low Resistance Anode Assembly
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Main issues for contact resistance & voltage drop
• Contact resistance:– Contact area– Contact pressure– Surface conditions of stub– Cleanliness of stubhole– Stub preheat at casting– Iron Shrinkage Gap– Iron Thimble thickness– Iron expansion (phase
change, %Carbon Equiv.)– Nail size & quantity &
location– Operating temperature
Iron shrinkage gap
Top surface of carbon anode
Cast Iron
Steel stub
Current flow
Stubhole Anchors
Stubhole groove
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‘Gap’ between thimble and anode, with and without ‘Stubhole Anchors’
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Stubhole Anchor ‘in-situ’ test
‐Measure mV drop across gap
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Stripped Iron Thimble fragments with Stubhole Anchors
High carbon nails survived iron casting and 21 day reduction anode cycle
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Initial Thimble Anchor test observations
Head of nail encased by cast iron Profile indicates:
- early iron solidification adjacent to nail
- small volume loss into carbon during cycle
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8 Stubhole Anchor In-situ Test: voltage drop
0
20
40
60
80
100
120
140
160
180
200
2 4 6 8 10 12 20
mV
drop
First 20 Hours after Anode Setting
Average with no anchors
Average with 8 anchors/stubhole
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8 Stubhole Anchor In-situ Test: voltage drop
0
10
20
30
40
50
60
70
80
90
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
mV drop
21 days anode cycle
Average with no anchors
Average with 8 anchors/stubhole
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0
20
40
60
80
100
120
1600 1800 2000 2200 0 200 400
mV
drop
Anode with 20 anchors/stubhole
20 Stubhole Anchor In-situ Test: voltage drop
Anode with no anchors/stubhole
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Cathode Slot Anchors: Resistance μΩ vs Temp°C
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
5 100 200 300 400 500 600 650 700 750 800 850 900
Res
ista
nce
mic
ro-o
hms μΩ
Temperature °Celsius
Cathode slice with no anchors
150mm Cathode slice with 6 anchors
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Anode Assembly Options: Stubhole Bottom
‐ Adds bottom surface to contact area- Ridges may be formed into bottom
for iron breakage during stripping
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Anode Assembly Options : Stubhole Wall Grooves
- Nails in grooves do not interfere with anode assembly
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Anode Assembly Options : Stubhole Bottom & pedestal
‐ Adds partial bottom surface to contact area- Pedestal is formed into bottom
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Low Cost Production Equipment
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Low Cost Production Equipment
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High speed robotic cell with auto nail reloading
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Benefits of Stubhole Anchors• Lower STC resistance
= lower power consumption = $ power savings
• Distributes current more evenly through all stubs, may enable higher line current
• Lower temperature at iron connection = lower carbon airburn, lower stub wear & toe-in
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Questions?
How to proceed?– Hatch will work with interested smelter to
conduct in-situ tests and determine energy savings
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Hatch: Smelter Power Reduction
Anode Assembly• Stub to Carbon iron
connection
Potshell Heat Balance +/-• Cooling & Insulating
Cathode Assembly• Iron connection to
improve current distribution
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Magnetic Mounted PotshellCooling Fins &
Insulating Blankets
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Balancing heat transfer through the potshell
Objectives:1. Cooling Sidewalls:
– To increase the protective lining of frozen bath– To reduce shell thermal deformation.
2. Heating Corners: – To reduce the frozen bath ‘toe’ at the corners:– To reduce high current density and cathode
corrosion– To reduce metal pad turbulence and pot noise
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Potshell Sidewall & EndwallCooling
Frozen Bath Ledge on sidewall
Anode
Molten Bath
Metal Pad
Cathode & Potlining
Bath Cover
Frozen Bath ‘Toe’ on cathode
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Sidewall and Corner damage
SiC sidewall damage
SiC sidewall damage
Potlining & Sidewall damage34
Toe
Ledge
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Hatch Magnetic Mounted Cooling Fins‐ Extruded anodized aluminum
- Hi-temp magnets with spring mounting
- Dust shield
- Graphite coating to increase radiation heat transfer from potshell
- Convenient to install or remove manually
- No maintenance or operating cost
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Cooling rate : Fin/No Fin
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ANSYS modelled temperature diffusion under cooling fin
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Cooling Fin testing: thermal image
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Operating Issues
• Holding power– Alnico magnet has highest curie point, spring mount adjusts for differential thermal expansion
• Rusty/dirty potshell – black heat sink absorbs radiation heat from potshell
• Dust – shield prevents blocking of airflow over fins
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When to apply fins to potshell
• Treat hotspots: on older pots to delay runout, may be used with forced air for more intensive cooling
• Maintain ledge thickness: fins along metal zone maintain frozen ledge to extend pot-life
• Potline current increase: add to potshell to offset extra heat from increase in potlinecurrent KA
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Cathode Corner Corrosion
Advanced cathode corrosion in corner from high current density beside ledge ‘toe
Photo Reference:•Century Aluminum, Light Metals 2004• Hydro Aluminum, Norway Today
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Bath Toe
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Potshell Corner Insulation
Cathode Surface Corner Planview
Anode Shadow
PotshellSidewall
Edge of frozen bath ‘Toe’ on
cathode surface
Potshell EndwallCold Corners: Area of high current density and cathode corrosion
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Insulating Potshell CornersProblem:- Extra potshell surface area loses heat:
causes bath ‘Toe’ to extend over cathode surface in corners
- ‘Toe’ causes increased current density: around ledge ‘toe’ plus related cathode corrosion
- ‘Toe’ causes MHD induced turbulence: of metal pad and related potnoise, reduces current efficiency
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Potshell Corner Insulating
Cathode Surface ‐ Corner Planview
Anode Shadow
PotshellSidewall
Edge of frozen bath ‘Toe’ on
cathode surface
PotshellEndwall
Cold Corners:Area of high current density and cathode corrosion
Anode Shadow
Edge of frozen bath ledge on cathode surface Corner Blankets:
To reduce frozen bath ledge and reduce peak current density in corners
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Magnetic Mounted Blanket- Non-flammable Silica cloth- Ferrous and/or Samarium cobalt magnets- Easy to manually apply or remove
- No maintenance or operating costs
- Can be multilayered or add quilting
- Custom sizes available
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Cooling rate: Blanket/No Blanket
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Blanket thermal testing
270C 330C
350C
Internal view
Double layer
Single layer
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When to use blankets• Treat cold corners: to reduce bath ‘toe’ to
– Reduce MHD induced metal turbulence– Reduce cathode wear from high current density
• When reducing power: to conserve heat
• To reduce temperature variance: balance sidewall versus corner temperature – can reduce superheat in bath
• Potline current increases: while operating higher power pots at low power prior to line current increase.
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Benefits of Fins & Blankets
• Balancing potshell thermal transfer and internal refractory temperature
• Localized control of frozen bath ledge thickness +/-
• Treatment of hot spots to extend potlife• Reduction of Toe induced high current
density and related metal turbulence, potnoise, and cathode corrosion
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Questions?
How to proceed:• Hatch offers smelters a free set of fins &
blankets for one cell as part of a 2 day pot trial
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Hatch: Smelter Power Reduction
Anode Assembly• Stub to Carbon iron
connection
Potshell Heat Balance +/-• Cooling & Insulating
Cathode Assembly• Iron connection to
improve current distribution
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Uneven Current distribution = Uneven cathode wear
Typical ‘W’ wear pattern from uneven current density over cathode surface
Ref: Aluminerie Alouette Ref: NTNU, Hydro
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Cathode Pothole corrosion
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High peak current density along sidewall drives pothole corrosion, that accelerates with age
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New Iron Connection for Cathode Assembly
Reference: Typical iron connection on 3-4 sides of collector bar
Hatch ‘Arc-Cast’: 2 sided iron connection with arc profile of contact surface
The ‘Arc-Cast’ iron connection provides uniform resistance over the length of the cathode.
Higher CVD is offset by improved current efficiency, lower ACD, lower cathode corrosion rate.54
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Current distribution: Reference vs. ‘Arc-Cast’ iron profile100% full thickness cathode
50% thickness cathode ‘W’ profile
*220 KA cell current density modelling by KAN-NAK
‘Arc-Cast’
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1:3 1:6 ratio, peak current rises 2X 1:1.2 ratio, peak current remains low
Half cathode model
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Current Density/Current flow modelTypical cathode assembly Hatch ‘Arc-Cast’ Cathode Assembly
Full thickness new cathode
½ thickness worn cathode 56
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Reduced Lorentz Force in Metal Pad
*220 KA cell current density modelling by KAN-NAK
Referencecathode Force density = max 774.5 n/m³
‘Arc-Cast’ cathode Force density = max 712.2 n/m³
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Reduced Metal Pad VelocityReference cathode Max.velocity = 13.1 cm/s
‘Arc-Cast’ cathode Max.velocity = 6.1 cm/sDecrease of 54%
*220 KA cell current density modelling by KAN-NAK58
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Potential Benefits of Hatch ‘Arc-Cast’ Cathode Assembly• Lower velocity and turbulence in metal pad
provides:– Lower pot noise & higher current efficiency– Enables lower ACD to save power, 1 mm ACD~25+mV– More stable operation to increase line current– Lower cathode wear by abrasion
• Lower peak current density and variation provides:– Lower cathode wear from Aluminum Carbide formation– More even cathode wear for longer potlife, reduce SPL
• Even current distribution: May be customized for problem areas, up/downstream or near risers
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Questions?
How to proceed?• Hatch will work with interested smelters to:
– Estimate the achievable current distribution for their cell technology
– Prototype and test cathode assemblies – Pilot reline of test pot(s).– Performance monitoring, controls optimization – Potline implementation with debottlenecking,
(power, carbon, alumina, etc.)
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Process Operating Parameters
PotLineAmperage KA
Pot Voltage Drop
ACD upper limit
ACD lower limit
No sideledge
Poor alumina dissolution, frozen bath in corners
Bath Superheat. range
Poor CE%, pot noise, Anode effect
Wasted energy
Normal operating window
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Process impact of Hatch technologyVoltage Drop,
ACD upper limit
ACD lower limitFins improve
sideledge
Enlarged operating window
Blankets reduce temperature variation of sides vs. corners
Arc‐CastCathode Assembly improves metal pad stability PotLine
Current KA
Wider Bath Superheat. Range
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HATCH Recent Technology Developments in Smelter Power Reduction & Pot-life Extension
Anode Stubhole AnchorsMagnetic Fins & Blankets
‘Arc-Cast’ Cathode Assembly
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