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:
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 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)
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
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!
CV124 (to bins) Feed bin building CV133 (to furnace)
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.
Cons feeders (x4) Flux, Reverts and Coal feeders
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
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
Feed chuteLance port Holding burner port Splash block WHB
Feed chute Slag box (Lance port) Holding burner port
Feed chuteLance port Holding burner port Isasmelt furnace
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)
Tapping machine rails Head section Bend section
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
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.
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
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)
Rebrick Power failure, SAP Pumps Isasmelt roof leak Circ pumps, grab, electrodes O2 plant compressor No venting
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
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
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)
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
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)
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
< 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
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)
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)
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
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)
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)
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
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.
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.