RIO TINTO KENNECOTT SMELTER 20 YEARS STRONG! Arsenio Enriquez, Glen Hogendoorn, David Krippner, Mike Loveless, Colin Nexhip, Kenly Ochoa Rio Tinto Kennecott LLC David B George Rio Tinto Technology & Innovation 4700 Daybreak Parkway, South Jordan, 84095, Utah, USA ABSTRACT The Rio Tinto Kennecott Copper (RTKC) Smelter near Salt Lake City, Utah is entering its 20 th year of operation since the Smelter Modernization Project in the early 1990 s when flash smelting and Kennecott- Outotec Flash Converting was first implemented. During this period, the Smelter has seen a number of innovative technical developments, year on year improvements in safety, health, environmental emissions reductions, greatly improved asset management and productivity improvement practices, and successful planning and execution of major maintenance shutdowns. The paper will describe key safety and operational performance over the last 20 years, treatment of very low grade copper concentrate, blister copper production, power production from waste heat/co-generation, and large scale sulfuric acid production. Technology developments around furnace integrity and condition monitoring, optimized slag chemistry, increased capability in copper scrap melting, and recovery of rhenium from furnace gas cleaning scrubber blow-down solution, will also be discussed. During Sept-Nov 2014 the Smelter executed its largest maintenance shutdown, which included a complete rebuild of the Flash Smelting Furnace and replacement of the concentrate dryer, furnace waste heat boiler and sulfuric acid plant modifications, and significant upgrades to the anode casting plant. HEALTH SAFETY & ENVIRONMENT Kennecott is committed to Zero Harm and continues to make improvements in protecting its people, our process, and the environment. In 2013 RTKC, the Bingham Canyon Mine experienced the largest open pit slide ever; nobody was injured in the event due to planning and preparation for the slide which was predicted in advance. This slide event (see Figures 1A & 1B) triggered significant changes in the operating plan and re-focused efforts on safety. The mine resumed production within 2 weeks and full production in less than 6 months. Key points from the mine slide and the resulting business recovery phase have been: All personnel safe and out of harms way before and during the slide Monitoring and planning preceded failure (slide was predicted ahead of time) Slide outcome: o +150 million tonnes of material o Material behaved differently than anticipated o Equipment damage in pit bottom o Crusher/conveyor were intact o Conveyor tunnel confirmed undamaged
Cornerstone waste ore mining operations re-started on April 13 th Ore production restart April 27 th Continued safety improvement during the complex open pit slide recovery activities and the significant rescaling of the RTK business after the event led to Kennecott receiving the prestigious Rio Tinto CEO Safety Award in 2013. Figure 1A: Manefay slide at RTKC Bingham Canyon Mine (April 2013) Figure 1B: Recovery and remediation of the slide was rapid, demonstrating business resilience In 2012 and 2013 the RTKC Smelter set a new safety record, achieving 960 days without a Lost Time Injury. In total, 3.6 million man-hours were worked without an LTI during 2012/2013; and a new All Injury Frequency Rate (AIFR) record low of 0.27 was established. [Note: The AFIR is based on incidents per 200,000 hours which is equvalent to 100 people working full time]
The environmental performance of the Smelter continues to improve on an already excellent performance (see Figure 2). Annual sulfur dioxide emissions over the last 20 years show a downward trend in spite of the Smelter treating ever lower concentrate grades with higher sulfur content. Over the last 6 years the sulfur dioxide emissions have varied between 26 kg/hr and 45 kg/hr SO 2 against a permitted limit of 96 kg/hr. The sulfuric acid plant tail gas is now normally below 50 ppm SO 2 and often in the 30 ppm range; a third of the original design emission rate and accomplished without tail gas scrubbing. Overall sulfur capture is in excess of 99.93% of the input sulfur and the RTKC Smelter remains one of the very cleanest smelters in the world, if not the cleanest. Figure 2: RTKC Smelter historical SO 2 emissions (note plant modernization was in 1995) OPERATIONAL PERFORMANCE The Kennecott smelter is a captive smelter and thus must respond to changes in mine and concentrator output including wide swings in concentrate production rates and grade over relatively short periods to maximize the Enterprise Value to Rio Tinto. The original flash smelting furnace maximum design capacity was 150 tonnes per hour of total charge (not including recycled dust) based on an average concentrate grade of 26.8%. The Smelter now operates routinely at 240 tonnes per hour of feed with periods in excess of this tonnage. The true limits of the flash smelting furnace are not known but gas handling, sulfur capture and slag handling, are likely the most important bottlenecks. The original design concentrate grade was 26.8% copper but changes in concentrator operation and evolution of mining has led to much lower grade concentrate with high levels of either pyrite or gangue. The Smelter now treats concentrate ranging from a low of 16% copper to a high of over 30% copper with
average grade ~ 22% copper. Treating this very low grade concentrate required development of new strategies to manage furnace heat balance while still using high levels of oxygen enrichment. Multiple bottleneck constraints had to be considered including the maximum acid plant sulfur capacity of 43 tonnes per hour. Flash Smelting Furnace Performance Over the years the RTKC Smelter has improved its capability to smelt more complex feed stocks such as lower grade copper concentrate, lower Cu/S ratio in feed, and more elevated impurity levels such as SiO 2, As, Pb and Bi. This has been achieved through improvements in process control, chemistry control, and improved blending of feed stocks, and also adoption of new coolant blends such as FS slag (in addition to C-Slag that has traditionally been used as coolant) and purchased secondary material. At times the total coolant load has been 25% of the total charge, dispelling the myth that flash furnaces cannot process secondary materials without a Pierce-Smith converter. Historical FSF online times achieved are shown in Figure 3 (note Smelter Shutdown years were 2006/2008/2010/2012/2014). Given the aforementioned challenges associated with the massive slide and business interruption from the Bingham Canyon Mine, the RTKC Smelter undertook the FSF throughput improvement project. This was a 3 month mandate project intended to safely, and sustainably, increase capability to process higher rates of more complex grade/quality concentrate through the FSF by reducing scheduled and unscheduled downtime and improving ability to operate at or above usual target feed rates. Increasing throughput capability and eliminating FSF process related bottlenecks provided the following benefits: Improved concentrate inventory management and blending Process all concentrate received from the RTKC Copperton Concentrator Utilize excess plant capacity to process third-part concentrate ( keep the Smelter full ) Faster recovery from furnace maintenance outages Increased copper output and reduce processing costs per pound of copper Standardized furnace inspections (quality and time focus) and maintenance activities Feed System reliability (dense phase pneumatic conveying systems) Acid plant capability (better gas grade control to support higher FS feed rates) In terms of process control, the historical FSF control model consisted of an Excel-based heat and mass balance model and a Visual Basic-coded user interface (built in-house in 1999). Recently, the RTKC Smelter completed a control platform modernization in order to avert impending obsolescence of software and loss of technical support with the old furnace control system. The project was completed through collaboration with Metso-Cisa. Several all-time throughput records were also attained for the FSF during 2013, such as of 5,565 tonnes of dry feed in a 24 hour period, and a monthly record of 138,968 tonnes of dry feed; both records achieved in October 2013. Acid production also reached an all-time monthly record of 94,807 tonnes in 2013 and was directly related to best performance for acid plant online time, and improved FSF throughput as a result of the project mandate efforts.
Figure 4 show the FSF improvements achieved during the 3 month mandate project, whereby tons per operating hour, total (short) tons of concentrate processed and FSF online time were improved. Figure 5 shows the FSF live process control dashboard to diagnose instantaneous bottlenecks/constraints in the process, allowing more effective utilization of FSF capacity and capability in real time. Figure 3: Historical FSF on-line time Figure 4: Typical step-change improvements achieved during the FSF throughput project
Figure 5: FSF live process control dashboard to diagnose instantaneous bottlenecks/constraints in the process, allowing more effective utilization of FSF capacity and capability Flash Converting Furnace Performance Historical FCF online times are shown in Figure 6 (note Smelter Shutdowns in 2006/2008/2010/2012/2014). Figures 7-9 show historical trends for %Cu in slag control, CaO/Fe flux ratio, and %S in blister copper; respectively. Figure 10 shows historical copper anode production. It is worth noting that the full capacity of the FCF at RTKC is not normally utilized. This allows more flexibility in scheduling maintenance. The FCF consists of 10 blister tap-holes and 2 slag tap-holes, and was completely rebuilt in 2012 and included modifications to tap-block window, with a more robust design being the outcome. Work efforts have continued in order to mitigate potential safety concerns associated with tap-hole copper leakage and have also resulted in productivity improvements and added cost benefits across the Smelter. The frequency of tap-hole repairs have reduced from twice a month schedule to once every two months without compromising its integrity. The work involved that contributed to this success included consistent tap-hole rotation, continuous improvement of blister/slag tapping techniques, and improvement of insert brick quality. A semi-automated tapping device has also proven to be beneficial, allowing the furnace tappers to lance straight and reduce likelihood of damaging surround brick and tap-hole water-cooled faceplates.
Tap-hole rotation and proper tapping techniques have always been an integral part of the FCF operation best practices, and recent efforts have been focused around further operational standardization and consistency through continuous operator training, standard work assessments, and regular audit procedures to ensure operational consistency. Several different types of tap-hole brick qualities have also been tested since April 2012, as an alternative to traditional silicon carbide bricks. Among the qualities tested, alumina chrome bricks have yielded encouraging results, with an insert life improvement from an average of 2,500 (short) tons of blister tapped, to 9,000 tons of blister tapped before an insert change-out is required (also leading to increased furnace on-line time and reduced maintenance costs). The lance pipe burned/consumed per 100 tons blister tapped has also shown a significant reduction from a typical consumption of 7 bars, and currently reduced to 4.5 lance pipes per 100 tons blister tapped. This also reflects the more favorable tapping conditions experienced through better accretion control in the FCF. Improvements to operation and control of the FCF continue to be made, particularly as relates to slag chemistry. In recent years the Smelter has deliberately implemented measures to dramatically reduce entrained %SiO 2 (as a contaminant) in FSF matte, which in turn has dramatically improved FCF slag accretion control, and required lower CaO/Fe flux, as well as improved furnace tapping conditions (less burn bars required per 100 ton of blister tapped). Control of magnetite in slag has also improved, with lower %Fe 3 O 4 in slag due to better lime/flux control; which in turn helped improve tapping conditions and also maximize available furnace blister capacity. Improved control of %S in blister is also a direct result of improved copper in slag control in the FCF. Flash converting process technology is also increasingly being internationally recognized, with several new plants constructed (for instance in China) now utilizing FCF technology. Figure 6: Historical FCF on-line time
Figure 7: Historical copper in slag control in the FCF Figure 8: Historical CaO/Fe slag control in the FCF
Flash Converting Blister Sulfur 95% CI for the Mean median 3200 3000 Parts per Million 2800 2600 2400 2200 2000 2006 2007 2008 2009 2010 2011 2012 2013 2014 Figure 9: Historical sulfur in blister copper control in the FCF Figure 10: Historical copper production (note shutdowns in 2006/2008/2010/2012/2014)
Celebrating 20 years of flash smelting and converting! Since the start-up of the modernized Smelter in 1995, the facility has smelted ~22.6M tonnes of dry feed to the FSF, producing ~4.6M tonnes of blister copper. Here the copper production is enough to outfit 22 million homes, produce 6.1 billion computers, or 266 billion cell phones. The Smelter has also produced ~16.1M tonnes of sulfuric acid since startup in 1995, and remains one of the largest (if not largest) sulfuric acid producers in North America. The Smelter was also designed to recover waste heat in the form of steam and produces ~66% of its own power needs through co-generation (35MW steam turbine generator). Over the 20 year history of the Smelter, ~3,000 GWh of electricity have been produced enough to power homes in Salt Lake City for almost 3.5 years or all the homes in New York City for 70 days. Tables 1 & 2 describe historical production totals since the 1995 start-up of the Smelter, and also various production records achieved (monthly and daily); respectively. FSF Total Dry Feed 22,616 kt Blister Copper 4,593 kt Power Generation 3,001 GWh Sulfuric Acid 16,176 kt Table 1: Cumulative production by RTKC Smelter since 1995 start-up FSF Total Dry Feed (24 hr) 5,565 tonnes (Oct 2013) FSF Total Dry Feed 138,968 tonnes (Oct 2013) Sulfuric Acid 94,807 tonnes (Oct 2013) FSF Slag 74,581 tonnes (Oct 2013) Blister Copper 29,384 tonnes (Nov 2009) Copper Anodes 29,277 tonnes (Aug 2010) Table 2: Production records set by RTKC Smelter. [Note all are monthly records except FSF dry feed over 24hrs] Anode quality improvements Chemical impurity levels of anodes a RTKC are among the highest in the world, yet production of ASTM Grade 1 cathode is possible due to precipitation of bismuth and antimony as a complex of arsenates in the porous anode slime layer (formed with elevated lead in anode). Specifications have evolved over years, and impurity and physical anode specifications are shown in Tables 3&4. These are among the highest impurity anodes produced by any major smelter. The variability in the impurity levels also is a function of the ore mined and can vary widely below the range listed below. Chemical Range/Tolerance Lead 3500 ppm Bismuth 700 ppm Arsenic 1000 2500 ppm Oxygen* 1500 +/- 500 ppm Sulfur* 50 ppm Table 3: Chemical specifications of copper anodes
Physical Requirement Weight 338-354 kg Surface Protrusions 6.4 mm from vertical plane Edge Protrusions < 6.4 mm Taper < 12.7 mm Ears 12.7-24.4 mm Table 4: Physical specifications of copper anodes As part of Kennecott Smelter continuous improvement initiative, an Anode Quality Mandate was initiated during the second quarter of 2014 aimed towards 100% good physical quality anodes leaving the Smelter. The RTKC Mandate technique is based on a 90 day program involving employees from across the business and at all levels of management and shop floor employees. The concept is to lock down a plan and deliver value and sustain the improvements made. Here the physical quality specification was reexamined and tolerances on anode weights, protrusions and ear thickness were re-evaluated. The succeeding efforts focused on improvements to meet the agreed Smelter and Refinery physical specifications. These includes work related to master mold quality, anode mold quality and mold life, casting spoon quality, casting wheel pour curve and maintenance of casting wheel auxiliary equipment. The results of quality improvements in reduced anode reject rates, is shown below in Figure 11. Figure 11: Anode reject rate decreased as a result of the quality mandate project
FCF side-wall accretion thickness monitoring TECHNOLOGY & INNOVATION Installation of a furnace sidewall diagnostic (PCA based) system now allows real-time magnetite side-wall thickness prediction, which brings new capability to furnace integrity monitoring for the FCF. This technology was developed by Hatch and the system improves furnace safety by providing real-time information of sidewall accretion condition enabling more informed operating decisions. It can also provide early detection of abnormal process measurements due to sensor failures or abnormal process drifts - adding confidence to existing methods of furnace integrity monitoring. Remote tapping of FS matte The RTKC Smelter has historically relied on very manual intensive methods to tap matte from the FSF. It typically involved 1-2 operators at a time, use of oxygen burning lances and requiring close proximity to the working tap-hole, resulting in higher exposure to heat stress and potential for burns from molten matte. Although RTKC has proven the practice to be safe over the years there has always been interest in taking the step to a more automated process, therefore reducing the workload on the operators, removing them from the direct line of fire, and decreasing exposure to off-gas and metal splash from tap-holes. There is also value from improved safety, hygiene and reduced heat stress, as well as more consistent burning and longer life of tap-hole inserts (resulting in higher furnace online times). Lewis Australia, an engineering firm specializing in automated equipment, worked with RTKC engineers to develop a compact matte tapping machine. Initial trials were encouraging (Figure 12) and two mechanized tap-hole opening and closing machines were installed during the 2014 Shutdown. Figure 12: Prototype testing of matte tapping system. Full scale design utilizes wireless remote controls
Rhenium recovery from acid plant blow-down by continuous ion exchange RTKC smelts copper concentrate containing trace amounts of the rare metal rhenium which is associated with molybdenum in the Bingham Canyon orebody. There is a a potential yield of ~ 1,000 kg/annum of recoverable rhenium. When copper concentrate is smelted the rhenium volatilizes in the flash smelting process off-gas process and is recovered in the Acid Plant Blow-down (APB). APB is treated in the Hydromet Plant along with refinery bleed solutions to recover copper while fixing bismuth and other impurities in a form suitable for discharge to tailings. Rhenium is recirculated to the smelter and can build to high levels approaching 50 mg/l (averages 20 mg/l) in the APB. Rhenium is, without a recovery plant, ultimately lost to the Hydromet Plant tails. The Smelter recently commissioned a new plant to recover Rhenium and the plant has been integrated with the existing Hydromet Plant (HMP). Plant controls allow any fraction of the APB to be delivered to the rhenium plant or the Hydromet Plant liquor distribution system. The chemical composition of the APB and the nature and quantity of the suspended solids can change quickly. A clarifier followed by an automated sluicing vertical leaf filter produce polished liquor that is advanced to the Continuous Ion Exchange (CIX). The Ionex CIX system includes 36 resin columns, the Rotating Distributor Apparatus (RDA) and the regeneration system and its controls (Figure 13 shows the RDA). The system is fully automated and can be operated with minimal operator attention. The CIX system includes the following functional zones: Loading, Wash Displacement, Pre-elution, Elution, Rinse and Conditioning (Protonation). Recovery of Rhenium at the KUC Smelter is another example of innovation and value-add via new process technology. Figure 13: Rotary Distributor Apparatus as part of the system for Rhenium recovery
Copper anode fire-refining and scrap melting using Praxair Co-Jet technology The Kennecott anode furnaces are some of the largest in the world with a maximum capacity of 650 (short) tons of blister copper. The blister copper from the FCF contains higher sulfur, typically 2000 ppm, than blister produced by the Pierce-Smith converting process (<500ppm) but much less than the Mitsubishi MI process (6000+ ppm). The FCF blister also contains high levels of dissolved oxygen making it relatively easy to de-sulfurize the blister. Three techniques are used to enhance sulfur removal during the initial stage of refining. First the stoichiometry of the pure oxygen-gas burner is adjusted to produce an oxygen rich atmosphere, second the anode furnaces are equipped with 6 porous gas injection plugs and third the refining system is Steam-Gas Refining (SGR) which offers excellent sulfur removal during the reduction (poling) step. SGR is based on the controlled metering of superheated steam and natural gas which is injected into the anode furnace through two stainless steel tuyeres. Typical refining times including oxidation, any slag skimming and reduction are less than 4 hours for a 550 tonne charge and often less than 2.5 hours. This technology has been licensed to Outotec. The Smelter continues to improve copper scrap melting capability (see Figure 14) through application of Co-Jet technology, and in collaboration of technical developments with Praxair. The Praxair Co-Jet technology continued to add value to RTKC through increase secondary scrap treatment and flexibility to operating practice. The challenge in moving forward is to maintain this capability and flexibility while improving Anode Furnace campaign life. Additional burner development since 2012 related to burner design and flame setting control have led to positive results on maintaining the furnace refractory integrity. Additional process developments in this area, such as tuyere-less refining, are anticipated. Figure 14: Utilization of Co-Jet technology to enhance copper scrap melting rates
Shutdown scope & execution 2014 SMELTER MAINTENANCE SHUTDOWN The longest and largest ever planned Smelter Shutdown occurred in Sept-Nov 2014, and was innovative and also critical to the future operation, and involved more than 2,000 employees and contractors. RTKC Smelter reset the asset health of critical, larger equipment like the FSF and concentrate dryer. The innovative FSF rebuild (which included elimination of roof refractory brick) is a unique design to manage hotter feed at higher throughput rates and processing of lower grades of copper concentrate. Improvements being made to the acid plant, ensuring worlds-best practice/environmental assurance around sulfur capture, as well as production assurance in sustaining throughput rates going forward. The Smelter is also working to increase the amount of time before acid plant shutdowns are required (moving from 2 years, to every 3 years). Below is a summary of various improvements that were undertaken: 1. FSF Rebuild: Designed uniquely for the challenges associated with dropping head grade to manage the heat management/loading BAT (Best Available Technology), such as : Improvements to refractory grade in worst heat effected zones Installation of water cooled gas phase elements Full BIC element roof design; Inconel clad throat elements New feed delivery system and new burner design (designed for ~235 tph) Upgraded jacket cooling water supply system Oxygen injection to settler for minimization of throat accretions (minimize if not eliminate need for throat blasting) Figure 15: New FSF under construction (October 2014) 2. Concentrate Dryer Replacement: Issues over the last year with accelerated wear on the existing dryer due to the need to process crushed FS-slag as coolant significantly impacted life expectancy. The dryer has processed over 22 million tonnes of feed and the integrity of the vessel had become a concern. The decision was made to replace the dryer shell and upgrade other aspects of the dryer.
Figure 16A: New concentrate dryer installation Figure 16B: New concentrate dryer installation 3. Anode Refining & Casting: Several improvements are being made in the Anodes area to help support current operability issues and the shift to a 3 yearly outage philosophy Higher grade refractory in refining furnace Additional porous plugs (currently 6, moving to 8) to optimize refine times New barite spray system (anode quality improvement initiative) Upgraded control system, wheel-house and casting wheels
4. FSF WHB (Waste Heat Boiler): Replacing the first ~40 feet of the radiation and convection zones New style Omega tubes (heavy duty; improved impact and corrosion capability) Redesign with elimination of the boiler tubes in the throat section (eliminate tube leaks in area historically responsible for 80% of tube failures) Application of Inconel spray coating of tubes to facilitate de-slagging and provide higher erosion resistance 5. Acid Plant & Powerhouse: Replacement and re-design of Superheater to minimize gas leaks in feed plenum and transition section from converting tower Replacement of and redesign Cold Inter-Pass Heat Exchanger to eliminate tube fatigue and baffle impingement due to gas flow New high efficient mist eliminators in Final Absorption Tower to minimize opacity and acid mist carryover in tail gas Upgrade to control systems for Acid Plant turbine blowers to minimize plant downtime associated with control equipment issues. Major overhaul and inspection on the 35 MW STG (Steam Turbine Generator) Replacement of tubes on dump condenser this will allow plant to run at higher capacity when STG is offline Figure 17: Acid plant modifications during 2014 Smelter Shutdown (note good luck rainbow)
CONCLUSIONS The Rio Tinto Kennecott Smelter is a captive smelter and thus must respond to changes in mine and concentrator output including wide swings in concentrate production rates and grade over relatively short periods to maximize the Enterprise Value to Rio Tinto. Since the start-up of the modernized Smelter in 1995, the facility has smelted ~22.6M tonnes of dry feed to the FSF, producing ~4.6M tonnes of blister copper. Improvements to operation and control of the FCF continue to be made, particularly as relates to slag chemistry, and tap-hole insert life. Flash converting process technology is also increasingly being internationally recognized, with several new plants constructed (for instance in China) now utilizing FCF technology. The Smelter recently reset the asset health of critical, larger equipment such as installation of a new FSF (with new burner and air-slide systems) and a new gas-fired concentrate dryer. The innovative FSF design (which included elimination of roof refractory brick) will further enable processing of hotter and lower grade feed at sustained higher throughput rates. The Smelter also continues to demonstrate a capacity for innovation such as a new plant to recover Rhenium from off-gas/acid streams, remote tapping of FSF matte, enhanced melting of copper scrap utilizing Co-Jet technology, and FCF sidewall accretion thickness monitoring in real-time. All of these operational practices and innovative technologies, coupled with the experience and operating know-how gained over the last 20 years, will help drive even further improvements at RTKC for the next 20 years! ACKNOWLEDGMENTS The authors would like to acknowledge the contribution of Shelley Ferrari, Mark Taylor, and Ryan Walton from RTKC Smelter, and also Mike Rockandel from Rio Tinto Technology & Innovation. The authors would also like to thank Outotec Oy for a fruitful technology partnership over the years.