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

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

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

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

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

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

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

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

Current Density/Current flow modelTypical cathode assembly Hatch ‘Arc-Cast’ Cathode Assembly

Full thickness new cathode

½ thickness worn cathode 56

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

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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The EndThank you

WBerends@Hatch.ca

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