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Mopani Copper Mines.  1937  2 x Reverbs, 4 x PS Converters  1956  3 x Reverbs, 5 PS Converters, 4 Anode Furnaces, 2 Casting Wheels  1972  36 MVA.

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Presentation on theme: "Mopani Copper Mines.  1937  2 x Reverbs, 4 x PS Converters  1956  3 x Reverbs, 5 PS Converters, 4 Anode Furnaces, 2 Casting Wheels  1972  36 MVA."— Presentation transcript:

1 Mopani Copper Mines

2  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   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)

3  Potential to treat > 420,000 tpa (ie toll)  New mines being developed in the region  Improve environmental performance  From no SO 2 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

4  Isasmelt furnace  850,000 tpa  Matte Settling Electric Furnace (MSEF)  850,000 tpa (equivalent) capacity (SMS Demag)  Acid Plant (Isasmelt offgas only)  1150 tpd (MECS)  Oxygen Plant  650 tpd (Air Products)  Fastest Isasmelt project  28 months from license agreement to feed on.

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6 ISASMELT CONCEPT Concentrates (CuFeS 2,Cu 2 S,CuCO 3.(OH) X, FeS 2,SiO 2, and others...) Flux (SiO 2,CaCO 3 ) Coal (C,CH 4 ) Water (H 2 O) Oxygen (O 2 ) Air (N 2,O 2 ) Diesel / Fuel Oil ISASMELT Furnace ISASMELT Lance Offgas (CO 2,SO 2,H 2 O,N 2 ) CuFeS 2 + O 2  Cu-Fe-S + FeO + SO 2 (FeS + 3Fe 3 O 4  10FeO + SO 2 ) FeS / 2 O2  FeO + 2SO 2 2FeO + SiO 2  2FeO.SiO 2 Matte Slag Matte-Settling Electric Furnace Slag Coating Smelting reactions Matte + Slag Slag box Post-combustion air (N 2, O 2 ) Granulation water

7  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

8  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 mix up feed materials!

9 CV124 (to bins) Feed bin building CV133 (to furnace)

10  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.  Reverts, Coal and Flux bins have 2 conveyors to measure accurately at low rates.

11 Cons feeders (x4) Flux, Reverts and Coal feeders

12  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

13  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:  Feed chute  Lance  Holding burner  Offgas  Copper blocks  Splash block  Tapping blocks (inner and outer) 13.3 m 4.4 m

14 Feed chuteLance port Holding burner port Splash block WHB

15 Feed chute Slag box (Lance port) Holding burner port

16 Feed chuteLance port Holding burner port Isasmelt furnace

17  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 Nm 3 /s (regardless of feed rate)  50 – 80% O 2  Process air from dedicated blower  Oxygen (95%+ O 2 ) from oxygen plant (650 tpd)

18 Tapping machine rails Head section Bend section

19  Furnace offgas cooled using a Waste Heat Boiler (WHB)  Furnace roof (inlet ~1,200 o C)  Cooling screen and Transition piece  Shaft 1  Shaft 2 (inlet ~600 o C)  Gas cooler (inlet ~400 o C) Transition piece Cooling screen Furnace roof Shaft 1Shaft 2 Gas cooler sprays To ESP

20  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.

21  General  12 MVA, 3 in line Electric Furnace  1092 mm Soderberg electrodes  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  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

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23  Concentrates  Mufulira (41%Cu, 12%Fe, 21%S, 12% SiO2)  Nkana (32%Cu, 22%Fe, 29%S, 7% SiO2)  Kansanshi (28%Cu, 27%Fe, 32%S, 5% SiO2)  Blend (32%Cu, 22%Fe, 29%S, 7% SiO2) (concentrate only)  Furnace feed  tph (Design 113 tph)  30-32%Cu in blended concentrate (excluding reverts)  7-9% Moisture (no water additions)  0-6 tph Silica  tph Coal (typically 2-3 tph)  0-25 tph Reverts  Paddle mixer not used

24  Lance  50-80% O 2  5 Nm 3 /s Total lance flow (design 7 Nm 3 /s)  Minimum lance air ~1.2 Nm 3 /s  35 lph diesel (average during smelting)  Products  o C  56-58% Cu in matte  0.8 SiO 2 :Fe  8% Fe 3 O 4 in slag  MSEF Products  Matte 58-60% Cu (1180 o C)  Slag 0.7% Cu (1250 o C)

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27 Rebrick Power failure, SAP Pumps Isasmelt roof leak Circ pumps, grab, electrodes O2 plant compressor No venting

28  General  22 month campaign duration  105 mm minimum brick thickness (~3 m)  Air cooling of shell during 2 nd 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

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31  Design  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  Performance  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)  2 nd Campaign Design  Anchors added to the top of the block

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33  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)

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35  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

36  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  2 nd 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)

37  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)  2 nd Campaign  Isasmelt style brick monitoring implemented for 2 nd 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

38  < February 07  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  ESP Rebuild  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

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40  Symptoms  ESP Exit temperature increases  Sulphur formation in gas cleaning plant  Factors  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)

41  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)

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43  Problem  Large water leak in the WHB’s 2 nd shaft  Cause  Gas cooler spray malfunctioned  Water impingement on tubes causing thinning  Damage and repairs  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

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45  Problem  Furnace roof leak (bottom of roof)  Cause  Consultant’s report indicated localised overheating, however cause is unknown  Damage and repairs  1 tube replaced  Lost time days (including reheating furnace)

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47  Problem  Furnace roof leak (top of roof)  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  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)

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49  Problem  WHB design exit temperature 700 o C  Actual exit temperature o C (under typical operating conditions)  Design condensing capacity35 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

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51  Mitigation  Increased demin storage from 10 to 70 m 3  Decrease lance flow from 7 to 5 Nm 3 /s  Concentrate blend requires less coal than design (very lucky)  Additional 10 MW condenser was installed.

52  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.

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