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A New Toolbox for Optimising Converter Aisle Operation

Pascal Coursol and Phillip Mackey Consultants-Extractive Metallurgy

Xstrata Process Support

Presented at the Copper 2010 ConferenceJune 8th, Hamburg, Germany

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Presentation Outline

• How were Peirce Smith converters operated/controlled in period 1920-1990

• Development of new tools in the last 20 years

– Process Modelling Tools

– Process control Tools

• How far can we go with Peirce Smith converters ??

– Further improvements possible

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How were Peirce Smith converters operated/controlled in period 1920-1990

• Visual end point detection (flame) from earliest times

• Systematic air flow and temperature measurements 1950s onwards

• Gaspé puncher 1960s, higher matte grades, concentrate injection

• Some control on flux addition-still variable, poor slag control

• Introduction of primary and secondary hooding (SO2 recovery)

• Mass and energy balance modeling

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Modern Modeling Tools

• Slag Chemistry Modelling (Factsage)

– Slag Liquidus, optimal %Fe/SiO2 ratio and temperature...

• Flowsheet Analysis (METSIM)

– Heat and mass balance

– Minor element deportment

– Blow by Blow Modelling (METSIM)

Minimise metal losses in slag

Optimise heat balance

Process more reverts

• Logistics/scheduling (ARENA)

– Consider maintenance and equipment availability, personnel as regards plant capacity calculations

• Finite element modelling

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Slag Chemistry Modeling

• Find optimal operating conditions (%Fe/SiO2, T, %O2)

• Impact of minor components in converting flux (CaO, Al2O3, MgO...)

Modelling tools are useful to perform slag chemistry

calculations and better understand the converters slag

chemistry

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Factsage SoftwareSlag Chemistry ModelingImpact of %Fe/SiO2

1150

1175

1200

1225

1250

1275

1300

1325

1350

0.7 0.9 1.1 1.3 1.5 1.7 1.9

%Fe/SiO2 in Slag

Tem

pera

ture

(0C

)

Liquid

Slag

Liquid +

Spinel

Liquid

+Silica

Impact of the %Fe/SiO2 in Slag on Slag Liquidus ([Cu]matte=68%, [Fe]matte=6.8%,

[ZnO]slag=4.0%, [CaO]slag=3.3%, [Al2O3]slag=2.0%, [MgO]slag=0.8%, P(SO2)=0.25;

the open star indicates present operating conditions)

Similar graphs can

be prepared for

each blow and

considering minor

slag components.

Optimal operating

conditions can be

deduced.

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Slag Chemistry ModelingImpact of %CaO in Slag (Factsage)

Impact of %CaO on the Copper blow slag liquidus. (5% Al2O3, 3.5% ZnO, 1%MgO, 7.5%PbO,

and p(SO2)=0.25 atm). The star indicates approximate present operating conditions at site.

CaO “robs” the SiO2

and raises the

magnetite liquidus

CaO + 2SiO2 =

Ca2SiO4

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Flowsheet Modeling-METSIM

• Impact of changing operating conditions in converters and smelting furnace

– Matte grade

– Furnace %Fe/SiO2

– Oxygen enrichment

– Dust Recycling

– Reverts recirculation

– ...

• Techno-economical evaluations can be performed directly in METSIM or on an EXCEL sheet where the METSIM data are exported

• Other similar softwares are available (HSC, Aspen,..)

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Flowsheet Illustration for Isasmelt + PS Converting + Slag Cleaning

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Converter Blow by Blow Analysis-METSIM

Parameters to optimize in a blow sequence

• Amount of matte in each blow (tonnes)

• Amount of reverts or recyclable per blow (tonnes)

• Coke rate (tonnes) and oxygen enrichment (%)

• Specific blowing rate for each blow (Nm3/tonne)

• Silica flux added at each blow (target %Fe/SiO2)

• Magnetite level in slag

• ...

From a simple mass balance model and from basic plant

data, it is reasonably easy to optimise the blowing sequence

for converters.

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Converter Blow by Blow Analysis METSIM Steady State (3 blows, heat losses distributed between blows)

Air+

O2

Air+

O2

Air+

O2

Blow 1

Blow 2

Blow 3

Matte 1st blow

+ slag left

Matte 2nd blow

+ slag left

Matte from smelting unit

Flux, coke, reverts

Flux, coke, reverts

Flux, coke. reverts

Blister Copper

to Anode

Furnaces

Recyclable Materials

Slag 3rd blow

Slag to slag

cleaning

process

Slag 3rd blow

Slag 3rd blow

Sla

g 2

nd

blo

w

Slag 2nd blow

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Scheduling Aspects of a Converter Aisle

• Some factors influencing converter aisle and smelter capacities

• Scheduled/unscheduled maintenance

• Cranes, acid plant, oxygen plant…

• Matte availability (smelting unit reliability)

• Shift change (operators)

• Blowing rates, oxygen enrichment

• Casting wheel preparation time

• Vessel availability (relining),…

The plant processing steps need to be coordinated in order to

reach the maximal capacity.

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Sudbury Smelter Capacity Project (ARENA scheduling model)

Capacity study to go from 66ktpy Nickel to 85

ktpy. Debottlenecking study with the ARENA

software to confirm a viable solutionThe solution to reach

85ktpy was found to

be a combination of

the following

parameters:

•Increased slag

cleaner capacity

•Increased converter

blowing rate

•Increased matte

granulation capacity

Screen Shot of the Sudbury Smelter ARENA Model

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Horne Smelter Capacity Project (ARENA Model)

Screen Shot of the Horne Smelter ARENA Model

Study to increase copper capacity from 180ktpy

to over 200ktpy. Debottlenecking study with the

ARENA software to confirm a viable solution.

The solution to reach

200+ktpy was found to

be a combination of the

following parameters:

•Reduced preparation

time casting wheel

•Variable casting rate to

“piggy back” a new

anode charge on the one

casting

•Number and

availability of operating

vessels identified

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Finite Element Modelling (Converters, slag cleaner, Anode furnace, casting,...)

• Modeling of PSCs and Anode furnaces

• Burner selection/optimization

• Feed entrainment in freeboard

• Tap hole design to minimize entrainment of matte in slag during tapping (diameter, slag/matte levels,…)

• Selection of correct lining materials (thermal profile, heat flux calculations)

• Mechanical stress and impact of thermal expansion during start-up (refractory spacers)

• Environmental Aspects

• Stack dispersion and in-plant hygiene

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Finite Element Modelling-Velocity fields in a smelting/converting vessel

Variable velocity

fields inside a

smelting/converting

vessels can lead to

solid entrainment

and localized hot

spots .

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Process Control ToolsSome suggestions….

The following are considered important in maximizing the performance of converters

1. Matte grade control in smelting furnace

2. Fe/SiO2 control in converter slag

3. %Fe in matte at the end of each blow

4. Level of magnetite in slag

5. Slag or matte temperature

Optimal conditions can be identified with the models, but an adequate control strategy is required in order to reach these conditions.

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Matte Grade Control in Smelting furnaces

• Feed blending to reduce variability at the smelting furnace

• Good matte sampling and frequent analysis of the %Fe in matte

• Correction of matte and slag assays for entrainment (e.g. correction to remove the %Fe in matte related to entrained slag)

• Adjust O2 enrichment and/or coke addition to correct the smelting furnace temperature rather than changing the %Fe in matte

Constant matte grade to the converter aisle will facilitate optimization of the converters

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%Fe/SiO2 Control in Converters

• Optimal slag conditions depend strongly on the accuracy of the flux addition in the converters.

• Batch addition vs continuous addition

• Accuracy, reproducibility

• Proper Flux Selection

• Minor gangue components (MgO, Na2O, CaO, Al2O3,…) tend to increase the flux requirements, but may enhance smeltability.

• Size distribution impacts smeltability and carryover

• In cases where the heat balance need to be satisfied, lowering the flux to improve the heat balance may not be the best solution

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%Fe in Matte at the End of Each Blow

• Many factors affect slag quality and metal losses in a converter cycle. It is better to control all the inputs to reach a better performance.

• Matte grade from the smelting unit

• Accuracy on added materials (flux, slag, reverts,..)

• Slag left in the vessel after each blow

• Air leakage at the tuyeres.

• There are control tools to maintain performance even when the feed is variable.

• Example: SEMTECH instrumentation-tracking of trace components (PbS, PbO and CuOH) in the converter off-gas and temperature.

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PbS increases immediately upon start of cycle: Rapid fayalite formation, minimized magnetite formation.

Very high PbO and CuOH, PbS decreases to zero: Spinel formation, increased foaming risk.

Addition of fresh matte: Slag recovers, cycle terminated properly.

Converter Cycle (SEMTECH)

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Smelter Year Number and Type of FurnaceDegerfors Jernverk 1990 1 Alloy steel converter

Boliden Mineral 1994 3 PS Copper converter

Norddeutsche Affinerie 1994 2 PS Copper-Lead converter

(Phelps Dodge Hidalgo 1996 3 PS Copper converter; Smelter shut down)

Norddeutsche Affinerie 1997 3 PS Copper converter

Chuquicamata 1998 4 PS Copper cvonverter

Norddeutsche Affinerie 2000 2 Anode furnace

(Hüttenwerke Kayser 2000 2 PS Scrap recycling converter; Furnaces shut down)

Mount Isa 2002 4 PS Copper converter; OPC not in use)

Boliden Harjavalta 2004 4 PS Copper converter

Atlantic Copper 2004 4 PS Copper converter

Onahama Smelting 2006 5 PS Copper converter

(Thai Copper 2006 3 Hoboken copper converter; Smelter shut down)

La Caridad 2007 3 PS Copper converter

Southern Peru Copper 2007 4 PS Copper converter

Cumerio 2007 3 PS Copper converter

Tamano 2007 3 PS Copper converter

Doe Run 2008 2 PS Copper converter

Lonmin 2009 3 PS Copper-Nickel-PGM converter

Kazzinc 2010 2 PS Copper converter

Toyo 2010 4 PS Copper converter

Xstrata Falconbridge 2010 2 PS Copper-Nickel converter

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Process Control Tools-Modern Tools

• Magnetite analyzer (Satmagan) to obtain magnetite level in slag after each blow

• Portable X-Ray analyzer for rapid determination of the %Fe in Matte and %Fe/SiO2 in slag

• Slag/matte temperatures

• Tuyere pyrometer available for matte temperature

• Optical pyrometer can be installed in Converter Hoods

• Oxygen enrichment and coke/fuel addition used to obtain the proper end-point temperature

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How far can we go with the Peirce-Smith Converters ?

• Further improvements are possible in PSC operation

• Slag chemistry and impact of minor components on magnetite formation and Cu losses

• Optimal cycle to maximize slag cleaning and reverts processing during PSC cycles

• Good process control (Flux, %Fe matte, SEMTECH(end point),%Fe3O4 slag (Satmagan),..)

• Limitation compared to continuous converting

• PSCs require matte and slag transfer by ladles and emissions are harder to control

• Continuous converters can allow a better energy efficiency (heat losses per ton of anode Cu)