SMELTER START UP OF NEW ISA FURNACE
AND PROGRESS TO DATE
Mopani Copper Mines
SMELTING AT MUFULIRA - DEVELOPMENTS





1937
 2 x Reverbs, 4 x PS Converters
1956
 3 x Reverbs, 5 PS Converters,
4 Anode Furnaces, 2 Casting Wheels
1972
 36 MVA Electric Furnace, 1 x Reverb, 6 x PS Converters,
4 x Anode Furnaces, 2 x Casting Wheels, 1 x Holding Furnace
1991-2006
 36 MVA Electric Furnace, 4 PS Converters
4 Anode Furnaces, 2 Casting Wheels
2006-Present
 Isasmelt Furnace, 12 MVA Slag cleaning furnace
5 x PS Converters,
 2 x 400 tonnes Anode furnace, 1 x twin casting wheel(commissioned in March 2009)
PROJECT MOTIVATION (PHASE 1)

Potential to treat > 420,000 tpa (ie toll)
 New

mines being developed in the region
Improve environmental performance
 From

no SO2 capture to 50%
Avoid ~6 m shutdown to rebuild old Electric Furnace
 Old
furnace at the end of its life.
 Old
Electric Furnace failed during Isasmelt
commissioning
 Exporting
concentrates difficult due to transport
constraints
PROJECT DESCRIPTION (PHASE 1)

Isasmelt furnace


Matte Settling Electric Furnace (MSEF)


1150 tpd (MECS)
Oxygen Plant


850,000 tpa (equivalent) capacity (SMS Demag)
Acid Plant (Isasmelt offgas only)


850,000 tpa
650 tpd (Air Products)
Fastest Isasmelt project

28 months from license agreement to feed on.
PROJECT DESCRIPTION
Equipment Legend
Smelter Upgrade- Phase1
MCM
Concentrators
Sulphuric Acid Plant
(1150tpd)
Tail gas to
Atmosphere
Smelter Upgrade- Phase2
Offgas to
Atmosphere
Concentrate
Purchased
concentrate,
coal and fluxes
Concentrate
storage
Diesel
Cons,
reverts,
flux,
coal
Offgas
Coke
Discard slag
to
Dump
Isasmelt furnace
(850,000tpa)
Oxygen
Oxygen Plant
(650tpd)
Matte,
Slag
Matte Settling
Electric Furnace
Matte
Slag
Offgas
to
Atmosphere
PS Converters
) 4 to 5
(upgrade from
Blister
Fire Refining and
Casting
(install2 x 400t AFs,
80 tph casting wheel
)
Reverts
Anode Copper
to
Refinery
Post-combustion air (N2, O2)
ISASMELT
CONCEPT
Oxygen (O2)
Air (N2,O2)
Offgas
(CO2,SO2,H2O,N2)
Diesel / Fuel Oil
Slag box
Concentrates
(CuFeS2,Cu2S,CuCO3.(OH)X,
FeS2,SiO2, and others . . .)
Flux (SiO2,CaCO3)
Coal (C,CH4)
Slag
Coating
Water (H2O)
Smelting reactions
CuFeS2 + O2  Cu-Fe-S + FeO + SO2
(FeS + 3Fe3O4  10FeO + SO2)
ISASMELT
Lance
FeS2 + 5/2O2 
ISASMELT
Furnace
Matte-Settling
Electric
Furnace
Matte +
Slag
FeO + 2SO2
2FeO + SiO2  2FeO.SiO2
Slag
Matte
Granulation
water
PLANT DESCRIPTION - FEED PREPARATION

Feed materials:








Concentrates (Mopani and toll)
Reverts (<25 mm)
Silica flux (sand)
Limestone flux (not normally used)
Coal (5-20 mm)
Isasmelt ESP dust
WHB dust (mixed with reverts)
Feed materials stored in separate
stockpiles
PLANT DESCRIPTION - FEED PREPARATION


Feed materials reclaimed by front end
loader
Conveyed to storage bins:





Concentrate (4 x 150 t)
Flux (2 x 80 t)
Reverts (1 x 180 t)
Coal (1 x 50 t)
Don’t Hopper
mix up feed materials!
CV121
CV123
CV124
Front End
Loader
Cons
(x4)
CV134 (Shuttle)
Flux
(x2)
Coal
Stockpiles
To Furnace
Reverts
PLANT DESCRIPTION - FEED PREPARATION
Feed bin building
PLANT DESCRIPTION - FEED PREPARATION
Feed materials are accurately measured
(±2%) and controlled by the PWCS.
 Feed rate is controlled by variable speed
drives.
 Flexible system allows quick blend
changes.
Con
Con
Con
Con
Reverts
Coal
Flux
Flux
ESP
BN108
BN109
BN115
BN116
BN113
BN112
BN111
BN110
Dust
 Reverts, Coal and Flux bins have 2
conveyors to measure accurately at low
rates.

CV125
CV126
CV135
CV136
CV140
CV139
CV130
CV131
CV138
CV129
CV137
CV128
CV127
To furnace
PLANT DESCRIPTION - FEED PREPARATION
Cons feeders
(x4)
Flux, Reverts and
Coal feeders
PLANT DESCRIPTION - FEED PREPARATION



Combined feed on CV131
Paddle mixer installed, but normally bypassed
Furnace feed conveyor (CV701)

Retractable and reversible to prevent heat damage (fires)



Conveyor always runs unless retracted.
Otherwise the belt will catch on fire from
furnace radiant heat
Coal reduction bin (furnace reductions)
Reversible to bypass the furnace


For weigher calibrations
For unsuitable feed materials
Coal reduction
bin
CV701
CV131
(mixed feed)
Paddle mixer
CV133
Retractable &
Reversible
CV132
Bypass
bunker
Isasmelt
furnace
PLANT DESCRIPTION – ISASMELT FURNACE

Furnace refractory:





13.3 m tall
4.4 m internal diameter
450 mm Cr-Mg (in most areas)
100 mm insulation brick
Roof


Boiler tubes (part of WHB)
Openings:





13.3 m
Feed chute
Lance
Holding burner
Offgas
Copper blocks


Splash block
Tapping blocks (inner and outer)
4.4 m
PLANT DESCRIPTION – ISASMELT FURNACE
Feed chute
Lance port
Holding
burner port
WHB
Splash block
PLANT DESCRIPTION – ISASMELT FURNACE
Feed chute
Slag box
(Lance port)
Holding
burner port
PLANT DESCRIPTION – ISASMELT FURNACE
Feed chute
Lance port
Holding
burner port
Isasmelt
furnace
PLANT DESCRIPTION – ISASMELT LANCE

Lance







18.1 m long
350 mm body
300 mm tip
Single swirler
Internal air and tip pressure pipes
Changed after ~ 7 days
Process




Typical flow 5 Nm3/s (regardless of feed rate)
50 – 80% O2
Process air from dedicated blower
Oxygen (95%+ O2) from oxygen plant (650 tpd)
PLANT DESCRIPTION – ISASMELT TAPPING
Tapping machine
rails
Bend
section
Head
section
Shaft 1
Shaft 2
PLANT DESCRIPTION – OFFGAS

offgas cooled using a
Waste Heat Boiler (WHB)
Furnace
Furnace roof (inlet ~1,200 oC)

Cooling screen and Transition piece

Shaft 1
oC)

Shaft
2
(inlet
~600
Transition piece

Gas cooler (inlet ~400 oC)

To ESP
Cooling screen
Furnace roof
Gas
cooler
sprays
PLANT DESCRIPTION – OFFGAS

ESP




3 field ESP.
3 perpendicular (to gas flow) drag link conveyors.
Dust is pneumatically conveyed to feed system, and is directly
recycled.
Induced Draft (ID) Fan


Single ID Fan.
Precise control of furnace draft


Variable speed drive.
Inlet damper.
PLANT DESCRIPTION – MSEF

General



Tapping





4 Matte tap holes (2 mud gun drills)
2 Slag tap holes (manual tapping)
Large pit for granulated slag
Reclaim slag with a grab crane
Feed materials




12 MVA, 3 in line Electric Furnace
1092 mm Soderberg electrodes
2 Return Slag Launders (PS Converter slag)
1 Isasmelt Launder
8 charge bins (coke and reverts)
Offgas



Naturally ventilated
Cooled by dilution air
Discharged without treatment
MATTE SETTLING ELECTRIC FURNACE
OPERATING CONDITIONS


Concentrates
 Mufulira
 Nkana
 Kansanshi
 Blend
(41%Cu, 12%Fe, 21%S, 12% SiO2)
(32%Cu, 22%Fe, 29%S, 7% SiO2)
(28%Cu, 27%Fe, 32%S, 5% SiO2)
(32%Cu, 22%Fe, 29%S, 7% SiO2)
(concentrate only)
Furnace feed
 70-115 tph (Design 113 tph)
 30-32%Cu in blended concentrate (excluding reverts)
 7-9% Moisture (no water additions)
 0-6 tph Silica
 1-4.5 tph Coal (typically 2-3 tph)
 0-25 tph Reverts
 Paddle mixer not used
OPERATING CONDITIONS

Lance
 50-80% O2
 5 Nm3/s Total lance flow (design 7 Nm3/s)
 Minimum lance air ~1.2 Nm3/s
 35 lph diesel (average during smelting)

Products
 1170-1190 oC
 56-58% Cu in matte
 0.8 SiO2:Fe
 8% Fe3O4 in slag

MSEF Products
 Matte
 Slag
58-60% Cu (1180 oC)
0.7% Cu (1250 oC)
CONCENTRATE TREATMENT FROM START UP
REVERTS TREATMENT FROM STARTUP
60
50
Overall operating time
Operating time - without aisle and power constraints
100
No venting
80
Rebrick
O2 plant compressor
Isasmelt roof leak
10
Power failure, SAP Pumps
Circ pumps, grab, electrodes
40
% of total time
PLANT AVAILABILITY
Isasmelt Operating Time
90
70
30
20
0
Oct-08
Sep-08
Aug-08
Jul-08
Jun-08
May-08
Apr-08
Mar-08
Feb-08
Jan-08
Dec-07
Nov-07
Oct-07
Sep-07
Aug-07
Jul-07
Jun-07
May-07
Apr-07
Mar-07
Feb-07
Jan-07
Dec-06
Nov-06
ISASMELT REBRICK

General






22 month campaign duration
105 mm minimum brick thickness (~3 m)
Air cooling of shell during 2nd year (offtake side of furnace)
Low wear above the splash block
Unusually symmetrical wear
Wear control






Brick monitoring thermocouples (important)
and thermal imaging (not very important, just looking for hotspots)
High wear during the first 7 months (high temps, poor slag chemistry)
Wear rates controlled for remainder of campaign
Good match between physical measurements and calculations
Post combustion control very important for refractory above the splash block
Injecting air through the holding burner damages refractory, and probably the
splash block
ISASMELT REBRICK – WEAR PROFILE
ISASMELT REBRICK
SPLASH BLOCK PERFORMANCE

Design






Performance




Single piece, cast in Monel tubes
4 cooling water passages (no air)
Copper anchors on the bottom and front face of block
4 thermocouples (3 in block, 1 between block and refractory)
Temperature (copper) control by manipulating cooling water flow
22 months without leaks or apparent damage (apart from anchors)
Cooling water flow does vary (occasionally) to control copper temperature
(uncertain if it makes any difference to block’s life)
Post combustion air injection via the holding burner heats the top surface of the
block (all slag melts leaving a bare block)
2nd Campaign Design

Anchors added to the top of the block
SPLASH BLOCK PERFORMANCE
MSEF REBRICK

General




Expected refractory life was 5-10 years
After 2 years side walls required replacement (partial)
Roof required replacement due to furnace explosions
Wear control



Brick monitoring thermocouples were initially installed
(SMS Design)
3 separate brick monitoring locations spontaneously leaked
Remaining openings were closed with refractory and a steel
Additional thermocouples were not installed mid campaign due to
cooling jacket design
(steel cooling jacket behind working lining)
MSEF REBRICK – WEAR PROFILE
MSEF PERFORMANCE

Charging
Input launders directed towards dead corners resulting
in launder blockages
 Burners required to prevent launder blockages


Accretions
No accretions on the side walls (no refractory
protection)
 Bottom accretions of up to 1 metre
 Accretions largest in non active areas of the furnace
 Regular pig iron additions required to control accretions

MSEF PERFORMANCE

Matte tapping






Initial tapping arrangement (4 tapholes, 1 ladle at a time)
was a major production constraint, matte bogie installed to
minimise tapping delays
Matte taphole inserts (Cr-Mg, installed in outer tapping
block) require replacement every 4 days. Therefore only 3
working tapholes
Matte tapholes can not be closed manually
2nd mud gun installed to prevent run aways
Taphole design being improved
(eliminating outer tapping block inserts)
Tapholes require deep repair every 1-2 months
(requires a 24 hour shutdown)
MSEF PERFORMANCE

Refractory

Disappointing performance
 Low
grade brick used by SMS Demag (400 mm RHI ESD)
 Unable to monitor brick wear, operating parameters not
optimised
 Technical focus on other areas (due to many other problems)

2nd Campaign
 Isasmelt
style brick monitoring implemented for 2nd campaign
 Improved process control
 Higher grade bricks (RHI FG)
 Consider jacket design change if wear rate can’t be controlled
 Target refractory life is >= 2 Isasmelt campaigns
PROBLEMS – ESP DAMAGE

< February 07






ESP Rebuild




ESP exit temp intermittently > inlet temperature
(believed to be instrumentation problems)
ESP inspections (external) did not identify problem
Shutdown February 2007 to inspect and repair ESP
(ESP could not maintain KVs)
ESP internals found to be beyond repair
Acid plant not commissioned at this stage
September – November 07 (US$1.4M)
ESP bypassed for rebuild
Additional dust load to gas cleaning plant required daily shutdowns to remove dust
from scrubbers
Post Rebuild


No further damage
ESP’s performance improved, but still struggles to hold KVs at times
PROBLEMS – ESP DAMAGE
PROBLEMS – POST COMBUSTION

Symptoms



Factors




ESP Exit temperature increases
Sulphur formation in gas cleaning plant
Coal rate (high rates increase problems)
Post combustion air
Excessive dust in ESP (high dust levels in hoppers cause problems)
Consequences


Potential damage to ESP (none since Nov 2007)
Damage to gas cleaning pumps (very sensitive to S)
PROBLEMS – POST COMBUSTION

Detection




SAP Gas Cooling Tower pump discharge pressure increases
(indicates weak acid coolers are blocking)
ESP exit temperature increases
Glass rod test (least reliable)
Prevention




Implemented post combustion air flow smelting interlock
Implemented ESP dT interlock (Outlet temp – Inlet temp)
Installing CO, O2, NO monitor at WHB exit (in progress)
Post combustion fan operates at maximum rate, so additional post combustion
air is provide by increasing furnace draft
(not very efficient)
PROBLEMS – POST COMBUSTION
PROBLEMS – WHB LEAK (MAY 07)

Problem


Cause



Gas cooler spray malfunctioned
Water impingement on tubes causing thinning
Damage and repairs



Large water leak in the WHB’s 2nd shaft
6 tubes replaced
Repair time 5 days (poor welding technique)
Actions



Implemented logic to detect failure (using existing instruments)
Modified spray design (sprays heads were dissolving)
Regular thickness testing of tubes around sprays
PROBLEMS – WHB LEAK (MAY 07)
PROBLEMS – WHB ROOF LEAK (DEC 07)

Problem


Cause


Furnace roof leak (bottom of roof)
Consultant’s report indicated localised overheating,
however cause is unknown
Damage and repairs


1 tube replaced
Lost time - 6.5 days (including reheating furnace)
PROBLEMS – WHB ROOF LEAK (DEC 07)
PROBLEMS –ROOF DAMAGE (MAY 08)

Problem


Cause




Holding burner hoist rope failed, dropping holding burner
Web ripped off tube causing small leak
Leak noticed about 10 hours after hoist failure
Damage and repair





Furnace roof leak (top of roof)
Tube welded
Web not reattached
(concerned about differential expansion causing leaks)
Furnace partially cooled
Lost time ~19 hours (including furnace recovery)
Actions



Holding burner carriage stopper relocated (was too low)
Minor repairs to roof during rebrick (tubes were not straightened)
Hoist replaced (original rope was under designed)
PROBLEMS –ROOF DAMAGE (MAY 08)
PROBLEMS – WHB CAPACITY

Problem








WHB design exit temperature
700 oC
Actual exit temperature
400-500 oC
(under typical operating conditions)
Design condensing capacity
35 tph
Required condensing capacity
~50 tph
(for design conditions)
Demin capacity
5 tph
It is not possible to operate under design conditions
Availability would be limited to ~33%
Cause (probable)


Fouling on the hot side of the boiler tubes much less than
design, resulting in higher than design heat transfer
Very clean (Pb, Zn, As) concentrates
PROBLEMS – WHB CAPACITY
Blow off to
atmosphere
Air Cooled Condenser
Blow off valve
Steam
Condensate
Steam Drum
Makeup water
Heat surfaces
PROBLEMS – WHB CAPACITY

Mitigation
 Increased
demin storage from 10 to 70 m3
 Decrease lance flow from 7 to 5 Nm3/s
 Concentrate blend requires less coal than design
(very lucky)
 Additional 10 MW condenser was installed.
SMELTER PROJECTS

HFO Conversion



Currently using diesel for the holding burner, lance and launder burners
Commissioning of HFO on the holding burner is in progress.
Aisle debottlenecking


3 x 55 tonne Main Aisle Cranes
Mechanical punching machines are being commissioned.
THANK YOU