Presentation on theme: "Smelter start up of new ISA furnace and progress to date"— Presentation transcript:
1 Smelter start up of new ISA furnace and progress to date Mopani Copper Mines
2 Smelting at Mufulira - Developments 19372 x Reverbs, 4 x PS Converters19563 x Reverbs, 5 PS Converters, 4 Anode Furnaces, 2 Casting Wheels197236 MVA Electric Furnace, 1 x Reverb, 6 x PS Converters, 4 x Anode Furnaces, 2 x Casting Wheels, 1 x Holding Furnace36 MVA Electric Furnace, 4 PS Converters 4 Anode Furnaces, 2 Casting Wheels2006-PresentIsasmelt 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)1937 – Final production was blister
3 Project Motivation (Phase 1) Potential to treat > 420,000 tpa (ie toll)New mines being developed in the regionImprove environmental performanceFrom no SO2 capture to 50%Avoid ~6 m shutdown to rebuild old Electric FurnaceOld furnace at the end of its life.Old Electric Furnace failed during Isasmelt commissioningExporting concentrates difficult due to transport constraints
4 Project Description (Phase 1) Isasmelt furnace850,000 tpaMatte Settling Electric Furnace (MSEF)850,000 tpa (equivalent) capacity (SMS Demag)Acid Plant (Isasmelt offgas only)1150 tpd (MECS)Oxygen Plant650 tpd (Air Products)Fastest Isasmelt project28 months from license agreement to feed on.
7 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 dustWHB dust (mixed with reverts)Feed materials stored in separate stockpiles
8 Plant Description - Feed Preparation Feed materials reclaimed by front end loaderConveyed 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!
10 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.Reverts, Coal and Flux bins have 2 conveyors to measure accurately at low rates.
12 Plant Description - Feed Preparation Combined feed on CV131Paddle mixer installed, but normally bypassedFurnace 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 heatCoal reduction bin (furnace reductions)Reversible to bypass the furnaceFor weigher calibrationsFor unsuitable feed materials
13 Plant Description – Isasmelt Furnace Furnace refractory:13.3 m tall4.4 m internal diameter450 mm Cr-Mg (in most areas)100 mm insulation brickRoofBoiler tubes (part of WHB)Openings:Feed chuteLanceHolding burnerOffgasCopper blocksSplash blockTapping blocks (inner and outer)13.3 m4.4 m
17 Plant Description – Isasmelt Lance 18.1 m long350 mm body300 mm tipSingle swirlerInternal air and tip pressure pipesChanged after ~ 7 daysProcessTypical flow 5 Nm3/s (regardless of feed rate)50 – 80% O2Process air from dedicated blowerOxygen (95%+ O2) from oxygen plant (650 tpd)
20 Plant Description – Offgas ESP3 field ESP.3 perpendicular (to gas flow) drag link conveyors.Dust is pneumatically conveyed to feed system, and is directly recycled.Induced Draft (ID) FanSingle ID Fan.Precise control of furnace draftVariable speed drive.Inlet damper.
21 Plant Description – MSEF General12 MVA, 3 in line Electric Furnace1092 mm Soderberg electrodesTapping4 Matte tap holes (2 mud gun drills)2 Slag tap holes (manual tapping)Large pit for granulated slagReclaim slag with a grab craneFeed materials2 Return Slag Launders (PS Converter slag)1 Isasmelt Launder8 charge bins (coke and reverts)OffgasNaturally ventilatedCooled by dilution airDischarged without treatment
24 Operating Conditions Lance 50-80% O2 5 Nm3/s Total lance flow (design 7 Nm3/s)Minimum lance air ~1.2 Nm3/s35 lph diesel (average during smelting)ProductsoC56-58% Cu in matte0.8 SiO2:Fe8% Fe3O4 in slagMSEF ProductsMatte % Cu (1180 oC)Slag 0.7% Cu (1250 oC)
27 Plant Availability Rebrick No venting Sept+ No venting December – WHB roof leakJanuary – WHB pumps, Nation wide power failuresMarch – Circ pumps, Grab failures, Electrode Hydraulic Problems,May – O2 compressor failureAugust - RebrickCirc pumps, grab, electrodesO2 plant compressorIsasmelt roof leakPower failure, SAP PumpsRebrick
28 Isasmelt Rebrick General Wear control 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 blockUnusually symmetrical wearWear controlBrick 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 campaignGood match between physical measurements and calculationsPost combustion control very important for refractory above the splash blockInjecting air through the holding burner damages refractory, and probably the splash block
31 Splash Block performance DesignSingle piece, cast in Monel tubes4 cooling water passages (no air)Copper anchors on the bottom and front face of block4 thermocouples (3 in block, 1 between block and refractory)Temperature (copper) control by manipulating cooling water flowPerformance22 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 DesignAnchors added to the top of the block
33 MSEF Rebrick General Wear control Expected refractory life was 5-10 yearsAfter 2 years side walls required replacement (partial)Roof required replacement due to furnace explosionsWear controlBrick monitoring thermocouples were initially installed (SMS Design)3 separate brick monitoring locations spontaneously leaked Remaining openings were closed with refractory and a steelAdditional thermocouples were not installed mid campaign due to cooling jacket design (steel cooling jacket behind working lining)
35 MSEF Performance Charging Accretions Input launders directed towards dead corners resulting in launder blockagesBurners required to prevent launder blockagesAccretionsNo accretions on the side walls (no refractory protection)Bottom accretions of up to 1 metreAccretions largest in non active areas of the furnaceRegular pig iron additions required to control accretions
36 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 delaysMatte taphole inserts (Cr-Mg, installed in outer tapping block) require replacement every 4 days. Therefore only 3 working tapholesMatte tapholes can not be closed manually2nd mud gun installed to prevent run awaysTaphole design being improved (eliminating outer tapping block inserts)Tapholes require deep repair every 1-2 months (requires a 24 hour shutdown)
37 MSEF Performance Refractory Disappointing performanceLow grade brick used by SMS Demag (400 mm RHI ESD)Unable to monitor brick wear, operating parameters not optimisedTechnical focus on other areas (due to many other problems)2nd CampaignIsasmelt style brick monitoring implemented for 2nd campaignImproved process controlHigher grade bricks (RHI FG)Consider jacket design change if wear rate can’t be controlledTarget refractory life is >= 2 Isasmelt campaigns
38 Problems – ESP Damage < February 07 ESP Rebuild Post Rebuild ESP exit temp intermittently > inlet temperature (believed to be instrumentation problems)ESP inspections (external) did not identify problemShutdown February 2007 to inspect and repair ESP (ESP could not maintain KVs)ESP internals found to be beyond repairAcid plant not commissioned at this stageESP RebuildSeptember – November 07 (US$1.4M)ESP bypassed for rebuildAdditional dust load to gas cleaning plant required daily shutdowns to remove dust from scrubbersPost RebuildNo further damageESP’s performance improved, but still struggles to hold KVs at times
40 Problems – Post Combustion SymptomsESP Exit temperature increasesSulphur formation in gas cleaning plantFactorsCoal rate (high rates increase problems)Post combustion airExcessive dust in ESP (high dust levels in hoppers cause problems)ConsequencesPotential damage to ESP (none since Nov 2007)Damage to gas cleaning pumps (very sensitive to S)
41 Problems – Post Combustion DetectionSAP Gas Cooling Tower pump discharge pressure increases (indicates weak acid coolers are blocking)ESP exit temperature increasesGlass rod test (least reliable)PreventionImplemented post combustion air flow smelting interlockImplemented 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)
43 Problems – WHB Leak (May 07) Large water leak in the WHB’s 2nd shaftCauseGas cooler spray malfunctionedWater impingement on tubes causing thinningDamage and repairs6 tubes replacedRepair time 5 days (poor welding technique)ActionsImplemented logic to detect failure (using existing instruments)Modified spray design (sprays heads were dissolving)Regular thickness testing of tubes around sprays
47 Problems –Roof Damage (May 08) Furnace roof leak (top of roof)CauseHolding burner hoist rope failed, dropping holding burnerWeb ripped off tube causing small leakLeak noticed about 10 hours after hoist failureDamage and repairTube weldedWeb not reattached (concerned about differential expansion causing leaks)Furnace partially cooledLost time ~19 hours (including furnace recovery)ActionsHolding burner carriage stopper relocated (was too low)Minor repairs to roof during rebrick (tubes were not straightened)Hoist replaced (original rope was under designed)
49 Problems – WHB Capacity WHB design exit temperature 700 oCActual exit temperature oC (under typical operating conditions)Design condensing capacity 35 tphRequired condensing capacity ~50 tph (for design conditions)Demin capacity 5 tphIt is not possible to operate under design conditionsAvailability 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 transferVery clean (Pb, Zn, As) concentrates
51 Problems – WHB Capacity MitigationIncreased demin storage from 10 to 70 m3Decrease lance flow from 7 to 5 Nm3/sConcentrate blend requires less coal than design (very lucky)Additional 10 MW condenser was installed.
52 Smelter Projects HFO Conversion Aisle debottlenecking Currently using diesel for the holding burner, lance and launder burnersCommissioning of HFO on the holding burner is in progress.Aisle debottlenecking3 x 55 tonne Main Aisle CranesMechanical punching machines are being commissioned.
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