FLASH CONVERTING SUSTAINABLE TECHNOLOGY NOW AND IN THE FUTURE

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1 International Peirce-Smith Converting Centennial Edited by: Joël Kapusta and Tony Warner TMS (The Minerals, Metals & Materials Society), 2009 FLASH CONVERTING SUSTAINABLE TECHNOLOGY NOW AND IN THE FUTURE Ilkka Kojo, Markku Lahtinen, Elli Miettinen Outotec Oyj PO Box 86, FI Espoo, Finland Keywords: Flash Converting, Continuous, Decoupling, Sulfur Capture, Energy Consumption, Sustainability, Environment Abstract The recent trends of decreasing energy consumption and environmental emissions and utilization of economies of scale are strong drivers favoring continuous copper converting processes. Flash Converting benefits from low off-gas volumes and low investment and operational costs for offgas treatment. Separate matte and blister furnaces allow the adaptation to concentrate quality changes and flexibility in layout and maintenance. The stationary blister copper bath in Flash Converting furnace is less aggressive to the furnace linings than agitated processes, resulting in low refractory consumption, long campaign life and high on-line availability. Copper Flash Converting has been successfully applied in Kennecott with a campaign life now exceeding five years. A second FCF was started at Xiangguang Copper in China in The process itself is proven, as its features are similar to those in FSF, Direct-to-Blister and Direct Outotec Nickel Flash Smelting (DON), with one significant difference: it is the easiest of all to operate. The paper presents differences between continuous Flash Converting and conventional converting based on recent experiences and studies. 383

2 Introduction Peirce-Smith converting has been the workhorse in copper converting for almost 100 years and is still the dominant converting process. The process has been developed continuously during the years and despite environmental, energy and labor cost pressures the process has still managed to compete with more modern converting technologies. However, the process has drawbacks such as fluctuating and lean SO 2 gas generation, a large amount of fugitive emissions, especially during loading and unloading of the vessel, tight timing between smelting and converting, which reduces the total on-line availability of the plant, a large number of furnace units with converter aisles and cranes, a short furnace brick lining life and in particular intermittent operation. In order to overcome the drawbacks of the batch Peirce-Smith converting process, Outokumpu started the development of a flash smelting type process for converting too. The concept of a Flash Converting process was first presented back in 1983 at the TMS Sulfide Smelting Symposium. The Kennecott-Outotec Flash Converting process was taken into operation in 1995 at Kennecott's Utah Smelter in conjunction with Outotec Flash Smelting. This paper summarizes the principles of Flash Converting and shows how the process is able to tackle the challenges of the copper smelting industry of today. Development of Blister Smelting Technologies Blister copper in one operation is the target at the Harjavalta smelter of Outokumpu Oy and the company metallurgists are coming close with their adaptation of flash smelting this news was published as long ago as 1953 [1], when Outokumpu was still operating the first Flash Smelting Furnace based on air preheating. However, it took a while before blister copper was purposely produced directly from concentrate: first in 1969 in the Outokumpu Technology (OT) pilot FSF and later in 1973 using Zairian and Polish concentrates. These test campaigns, which continued in 1976 with Polish concentrate, subsequently led to the start-up of the first commercial Flash Furnace producing blister copper at Glogow II in Poland in Later, during minipilot and pilot test campaigns were carried out for Australian bornitic-digenitic concentrate originating from the Olympic Dam ore body. Eventually this led to the construction and commissioning of the Olympic Dam smelter in June/July 1988, which was replaced with a new bigger Direct-to-Blister smelting line in To date, the OT Direct-to-Blister process has been practiced for close to 30 years and has proved to be reliable both at the KGHM and Olympic Dam smelters. The most recent Direct-to-Blister process started up in 2008 at Chingola, Zambia. In blister production mode, the inherent non-turbulent nature of the bath in Flash Technology provides protection for the refractory, thus providing campaign lives unrivalled by any other process. Some concentrates are more readily processed directly to blister than others, however, most concentrates available require smelting and converting to be done separately due to economic limitations. To overcome this, a joint development between Outokumpu (today Outotec) and Kennecott was started and the first continuous process for copper matte conversion to blister copper was successfully pilot-tested in Pori, Finland, in 1984 and further demonstrated in Flash Converting is identical with direct blister making from concentrate with high copper and low iron content. All the know-how acquired from the previous Direct-to-Blister Flash Smelting tests was utilized in planning and dimensioning the first commercial Flash Converting process, which started up at Kennecott Utah Copper Corporation (KUCC) in Salt Lake City in the summer of It is worth noting that in the Flash Converting process the same principles and similar types of equipment are used as in Flash Smelting and in Direct-to-Blister Flash Smelting. 384

3 Thus, having been in commercial operation, the Flash Converting Process is more mature than its age. It must be noted that besides the piloting tests, some of the development work was also carried out at laboratory scale at Outotec Research Oy in Pori, Finland, and at universities both in Finland and other countries. Thus the basic metallurgical principles of Flash Converting were well known before the design of the first commercial plant took place. These principles include flash reactions, slag chemistry, flow phenomena in the furnace, and the process thermodynamics and behavior of minor elements. However, the most important know-how and experience came from existing Direct-to-Blister Copper Flash Smelters in operation in Poland and in Australia. This development made the converting process continuous and sealed, thus providing all the process, environmental and economic advantages that come from continuous operation. Flash Converting Process The Flash Converting process has been described in previous papers [2-9], so only a short summary is given here. The flow sheet of the Flash Converting process combined with a Flash Smelting Furnace is shown in Figure 1. The dried concentrate is smelted in the Flash Smelting furnace using high oxygen enrichment even in this stage. The molten high-grade matte produced in the Flash Smelting furnace is conveyed by means of covered launders directly into granulation, where the matte is dispersed and granulated by means of high-pressure water jets. The Flash Smelting slag undergoes a slag treatment process for copper recovery. The matte granules are ground into a grain size sufficient for completing the reactions in the Flash Converting Furnace. CONC. BEDDING ACID PLANT STEAM DRYER WHB ESP FSF Slag Concentrator MATTE GRANULATION, GRINDING AND DRYING MATTE BEDDING SLAG GRANULATION ACID PLANT ANODE FURNACES FCF WHB ESP AF slag ANODE CASTING SCRAP MELTING FURNACE Figure 1 Flash Smelting - Flash Converting Process Flow Sheet. 385

4 The fine-grained matte is oxidized and smelted in the Flash Converting furnace to produce blister copper and slag using high oxygen enrichment or even pure technical oxygen. The Flash Converting furnace can operate autogenously even with high matte grades without using additional fossil fuels. The sulfur content of blister copper is controlled by the oxygen to matte ratio in the feed. Either silica or lime-based slag can be used. The copper content of the slag produced in the Flash Converting furnace is high, however, the small amount of slag generated can be fed back into the primary Flash Smelting furnace directly in granulated form, and thus, a separate slag treatment is not needed. Both flash furnaces produce an off-gas rich in SO 2. As a result of the high oxygen enrichment the volume of the off-gas is small. The off-gas flows continuously through cooling and cleaning steps to the sulfur recovery plant. Flash Converting Advantages The advantages of the continuous Flash Converting process compared to batch converting are summarized in Table I. Some of the benefits are discussed in more detail in the following section. Table I Advantages of the Flash Converting Process 1. Continuous and small off-gas flow rate Less gas cooling and cleaning Smaller investment costs at the acid plant Smaller operating costs at the acid plant Ease of fugitive gas control High SO 2 concentration in off-gas 2. Sealed process Fewer SO 2 emissions Smaller investment costs in fugitive gas handling Better working conditions 3. Separate smelting and converting Better total online availability No timing between smelting and converting Enables the use of Production Network 4. High capacity, small in size, single unit No converter aisle, no cranes Longer campaign life Less maintenance Lower investment costs 5. Continuous process Better process control Easier to operate 6. Proven Flash Smelting Technology and references Possibility to use pure oxygen 7. Continuous development Outotec is committed to continuous technology development 386

5 Benefits Achievable by Using Flash Converting The oxygen enrichment potential of matte processing can be fully utilized in Flash Converting, whereas in PS converting large amounts of nitrogen must be used as coolants, resulting in very high off-gas amounts, as seen in Figure 2. The fluctuating off-gas streams of PS converting result in large levels of poorly utilized off-gas handling capacity. The stable off-gas stream of the Flash Converting process enables significant savings in acid plant investment costs. The combined gas volume of Flash Smelting and Flash Converting furnaces is less than 80,000 Nm 3 /hr, similar to the volume of a single Peirce-Smith converter [4]. Figure 2 Required Off-Gas Treatment Capacity for Producing 200,000 tpa of Copper [9]. Flash Converting produces a gas stream with much higher SO 2 concentration that enables a compact off-gas line and acid plant size and low operational costs [10]. The SO 2 concentrations of the off-gases in PS and Flash Converting are compared in Figure 3. Figure 3 Comparison of SO 2 Concentration in Off-Gases, Vessel Online Availability and Vessel Campaign Life for Peirce-Smith and Flash Converting. 387

6 In Flash Converting, significant energy and labor costs are saved in comparison to those needed in the PS converting practice for continuous vessel maintenance, relining, and reheating. Vessel availability time in Flash Converting is significantly higher than that of one single Peirce-Smith converter and complete shutdowns and relinings are needed much less often. The decoupling availability of the FSF-FCF line further reduces production time losses due to maintenance. Matte can be stored during FCF repair and the stored matte processed during FSF repair. The acid plant can be operated throughout the entire maintenance period. The stable bath and effective cooling of the Flash Converting Furnace minimize the refractory wear in comparison to the intensively stirred baths typical of PS converting and lancing techniques. A typical interval for PS converter relining is one year, whereas in Flash Converting over five years have been proven and values of close to ten years are expected. The refractory consumption per tonne of produced copper varies from 1.5 to 4.5 kg in PS converting [11], whereas in Flash Converting it is minimal in the order of magnitude of 0.25 kg per tonne of produced copper, as seen in Figure 4. Figure 4 Refractory Consumption per Tonne of Copper Produced in Peirce Smith Converting and Flash Converting. Safety is a very important aspect in favor of Flash Converting. The highly automated system without hot metal cranes and ladles and a high amount of fugitive gases increases workplace safety and hygiene. High degrees of automation also decrease the labor requirements of flash converting. One important aspect is also the economies of scale, which favor a minimum number of furnaces and process steps. This results in significant savings in both investment and operational costs. The FCF is easier to operate than the FSF due to the constant feed material quality. The FSF concentrate changes frequently in such a way that oxygen demand for desired matte grade varies +/- 20 % (see Figure 5). In modern Flash Smelting furnaces it is possible to produce matte that is fairly homogeneous with respect to copper content (+/- 1%). A good blending further evens out matte grade deviation and the FCF feed matte grade can thus be regarded as virtually constant. The oxygen demand variation is much lower in the FCF than in the FSF, as shown in Figure 6, making the process much more stable. In both furnaces oxygen is almost totally consumed in the 388

7 reaction shaft and strict control is therefore possible. At the beginning at Kennecott the blister oxygen was measured for control purposes. This is now no longer necessary, as the copper content of the slag is the only necessary control parameter along with temperature measurements. When the copper in slag varies between 18 and 22 %, the sulfur in blister varies roughly between 0.3 and 0.1 %, respectively. One may speculate that it is difficult to reach the desired end point, because of the sensitiveness of the oxygen demand. However, the produced blister copper content variation is insignificant. What changes is the slag copper oxide content, which acts as a control buffer. The ease of process operation enables stable operation, high online availability, stable SO 2 concentration in the off-gas and, of course, long campaign life. Figure 5 An Example of Calculated FSF Matte Grade as a Function of Oxygen Coefficient for Various Concentrate Copper Contents. Figure 6 An Example of Calculated FCF Slag Copper Content as a Function of Oxygen Coefficient for Various Matte Grades. 389

8 Sustainability of Copper Smelting In a recent study [12] the different aspects of sustainability were reviewed. According to this study, the copper smelter operators valuated the following indicators to be the most important economic indicators of their operations: Operation Costs, Profit/Total Income Ratio, ROCE (Pretax operating profit/capital employed) and Online Time (% of available time). All these aspects are strongly supported by the continuous nature of the Flash Converting Process. In addition to that, the online time and especially the campaign life of the Flash Converting Process can be compared to that of Flash Smelting, which is the benchmark of this industry: ten year campaign compared to less than a year for batch converting. Of the social indicators the most important were the Number of Fatal Accidents (# of fatalities per year), Accident Frequency Rate (# of accidents per 1 million hours worked) and Overall Working Conditions. The operational safety issues, and more specifically the overall working conditions, of a Flash Converting plant are on a totally different level compared to that of a plant, in which molten materials are transported to converters by ladles and cranes. In Flash Converting, all molten materials are transported via launders, which can easily be covered to collect the fugitive emissions. Of the environmental indicators the most important were Specific SO 2 Emissions (kg SO 2 /t Cu), Copper Recovery (as % of total Cu), Specific Net Energy Consumption (MJ/t Cu), Specific Heavy Metals Discharges to Water and Number of Exceeding Local and/or National Emission Limits. It is easy to understand that all these factors are important and can most easily be tackled in a process which collects all the process gases efficiently and in which the off-gas is treated in a sulfuric acid plant. In Flash Converting the sulfur dioxide content of the gas is in range of % SO 2 whereas in bath converting the gas strength is only 3-12 % SO 2 : this means much more efficient sulfur capture, but also much lower and cheaper gas handling equipment cost. The Flash Converting process can be determined to belong to the group of Environmentally Sound Technology or, in the OECD definition, of Cleaner Technologies, i.e. technologies which protect the environment, are less polluting, use all resources in a more sustainable manner, recycle more of their wastes and products, and handle residual wastes in a more acceptable manner than the technologies for which they were substitutes. Environmental and Carbon Footprint The emission regulations are becoming tighter and tighter. However, today several copper producers are providing their sustainability reports based on voluntary reporting and some companies have provided Life Cycle Assessment (LCA) reports of their operation. An impact category is a class representing environmental issues of concern into which the LCA results may be assigned (EN ISO 14042, 1997). The following six standard impact categories, often used in Life Cycle Assessments, have been quantified in this Life Cycle Inventory: Use of Energy and Resources: Primary Energy Climate Change: Global Warming Potential Acidification of Land and Water Resources: Acidification Potential Eutrophication: Eutrophication Potential Destruction of Ozone Layer: Ozone Depletion Potential Formation of Photochemical Oxidants: Photochemical Ozone Creation Potential 390

9 Today, and for the near future, there is pressure for cathode copper producers to be able to show the environmental and carbon dioxide footprint of their copper production process, starting from mine operations and ending with semis producers (who also have to generate their life cycle inventory and assessment reports (LCI/LCA)). According to some earlier LCI analysis, most of the carbon dioxide is released in the mining and concentration steps followed by the energy production facilities. Metal production, i.e. smelting, converting and refining, produces less emissions than the carbon dioxide emissions generated by transportation of concentrate alone! Production Network Concept Besides its ability to allow easy and efficient control of fugitive emissions, the Flash Converting process offers one additional option to further decrease a smelter carbon footprint: the use of the Production Network concept, which takes advantage of the decoupling feature. As the matte and blister making processes are no longer correlated to each other in place or time, a separate market is possible for matte. One or several smelters may be used as matte source for one FCF. This gives some flexibility for balancing off-gas capacities, for example, among those smelters. The FSF and the FCF may be run totally independently of each other. Matte can be produced next to the mine, which reduces the concentrate transportation costs. In brown-field projects, decoupling enables minimal production time losses. A new larger Flash Furnace can be built next to the existing plant. No long shut downs will be needed since the new Flash Furnace can be operated with the existing PS converters until the old Flash Smelting Furnace has been modified into a Flash Converting Furnace, as seen in Figure 7. CONC. BEDDING NEW FSF ACID PLANT STEAM DRYER WHB ESP Slag Concentrator SLAG GRANULATION PEIRCE-SMITH CONVERTERS WHB ESP OLD FSF TO BE MODIFIED INTO FCF ANODE FURNACES ANODE CASTING AF slag Figure 7 Phase 1: New FSF Built Next to Existing Plant and Producing Matte for the PS Converters while Existing FSF is Being Modified into a Flash Converter. 391

10 In the final stage, the new FSF feeds the old furnace that has been modified into a Flash Converter while the PS converters can be removed (see Figure 8). CONC. BEDDING NEW FSF ACID PLANT STEAM DRYER Slag Concentrator SLAG GRANULATION WHB ESP MATTE BEDDING PEIRCE-SMITH CONVERTERS WHB ESP SLAG OLD FSF MODIFIED INTO FCF ANODE FURNACES ANODE CASTING AF slag Figure 8 Phase 2: New FSF Feeding Old FSF Modified into a Flash Converter. Experience of Kennecott and Yanggu The world s first Flash Converter has been running at Kennecott Utah Copper for well over a decade with an expected campaign life reaching that of Flash Smelting Furnaces. A single Flash Smelting Flash Converting line replaced three Noranda Reactors and four PS converters, and doubled the production capacity. As environmental regulations became considerably more stringent, the FSF-FCF technology was chosen as the solution to meet the standards and to ensure the ability to increase future capacity without compromising the environmental performance of the facility [4]. After a learning period of a few years and some technical and operational changes, the last campaign life at Kennecott was over five years. Before the last shutdown, there was an option to continue feeding to the FCF, but the FSF went for a major overhaul and a decision was made to stop the FCF as well. A modest silica addition to the calcium ferrite slag makes the slag so much less aggressive to an extent that the sidewall refractory remains in good condition. In Flash Smelting the reaction shaft is the place for turbulence, whereas the melt is relatively quiescent, which in turn protects the settler brick lining. The hearth was still in good condition. All the above factors plus good process control combined with the fact that the furnace is easy to operate will make future campaign lives as long as those of Flash Smelting Furnaces. During the last five-year campaign over 2.1 Mt of matte was processed and the ongoing campaign of over two years has so far processed almost 1 Mt of matte. During its existence the Kennecott-Outotec Flash Converter has processed a total of over 5 Mt of matte, i.e. about 3.5 Mt of copper. 392

11 Yanggu Xiangguang Copper is the second copper smelter in the world to adopt the Flash Converting technology and process (see Figure 9). Shandong Yanggu Xiangguang Copper Co. Ltd. started production on September 29, One of the main reasons for the decision favoring Outotec Flash smelting and the Kennecott-Outotec Flash Converting process for the greenfield smelter in China was the increasing environmental concern. With the Flash Converting process, the sustainable operation provides the smelter an environmental license to operate for decades to come. Flash Converting offers continuous smelting and converting with an efficient use of oxygen, minimum sulfur dioxide emissions and low operating cost. The project was planned to reach an overall production capacity of 400,000 tons, with 200,000 tons in its first phase. Figure 9 Yanggu Xiangguang Copper Smelter. The production of the Xiangguang Copper FSF-FCF process reached its design capacity smoothly and met the environmental standards, marking a successful application in China of only the second Double Flash copper smelting process in the world. Xiangguang s productive practice shows that FSF-FCF copper smelting technology is an advanced and mature process, a highly effective and environment-friendly copper smelting technology, and the direction into the future for the copper smelting process. The Double Flash has outstanding features in terms of energy savings, low investment and production costs, high automation and labor productivity, good potential expansion capacity and environment protection performance, especially by avoiding flue gas pollution and SO 2 fugitive emissions. It combines the most advanced copper smelting and acid manufacturing technologies to utilize resources and energy maximally, without impacting the environment. The production and energy consumption indices and comprehensive resource utilization rate have reached the leading domestic or advanced international level. A clean site environment and 99% sulfur recovery rate have enabled Xiangguagn Copper to become one of the cleanest and most environment-friendly copper smelter in the world. Xiangguang Copper is therefore the only smelter to have the honor of being a National Ten Key Environment Friendly Project in the Chinese non-ferrous metal industry in As far as we know, this award is the highest environmental protection honor there is for a construction project in China [13]. 393

12 Conclusions In greenfield smelter projects, one small, continuous, high-intensity reactor is the clear choice over three or four large, low-intensity vessels. Often the environmental regulations require that the least polluting process option be favored. The possibilities for a large capacity increase without major modifications or further investment is another major benefit of the Flash Converting process. In the future, more stringent environmental regulations will drive the industry towards continuous converting. Replacing existing PS facilities with an FSF-FCF line and modifying Flash Smelting Furnaces into Flash Converting Furnaces is a viable option for capacity increase in a sustainable and economical way. As Bill Imrie stated in 1993 in a conference presentation about Flash Converting [14]: Now, rarely will a production corporation plead that improved environmental measures are impracticable, unjustified or contrary to business survival. From a business perspective, the key question is how the cost for environmental compliance can be offset when generally there is no directly attributable revenue gain from the additional pollution control equipment. It now seems timely to rethink philosophy and to be particularly alert to opportunities where solutions to greater environmental challenges can be combined with measures that also achieve improved economic competitiveness. Today, Flash Converting has shown that the motivation to change the way of thinking was correct and that environmental benefits achieved by Flash Converting are not only benefits for Nature but for the copper producers themselves. Flash Converting offers comprehensive solutions for copper producers in sustainable and economical way now and in the future. References 1. F. Benidetz, Flash Smelting Improves, Engineering and Mining Journal, 154 (1952) 10, D.B. George, Continuous Copper Converting A Perspective and View of the Future, Sulfide Smelting 2002, ed. R.L. Stephens and H.Y. Sohn, (Warrendale, PA: The Minerals, Metals & Materials Society (TMS), 2002), P. Hanniala, I.V. Kojo and M. Kytö, The Kennecott-Outokumpu Flash Converting Process: Facts and Fictions, Converting, Fire Refining and Casting, ed. J.D. McCain and J.M. Floyd, (Warrendale, PA: The Minerals, Metals & Materials Society (TMS), 1994), D.B. George, J.R. Gottling and C.J. Newman, Modernization of Kennecott Utah Copper Smelter, Copper-Cobre 95 International Conference, Volume IV Pyrometallurgy of Copper, ed. W.J. Chen, C. Diaz, A.Luraschi and P.J.Mackey, (Montreal, Canada: The Metallurgical Society of CIM, 1995), M. Kytö, I.V. Kojo and P. Hanniala, Flash Converting Technology Meeting Challenges of the Next Century, (Presented at the SME 1997 Annual Meeting Converting Practices Short Course, Denver, February 1997). 6. P. Hanniala, I.V. Kojo and M. Kytö, Kennecott-Outokumpu Flash Converting Process Copper by Clean Technology, Sulphide Smelting '98 Current and Future Practices, (Warrendale, PA: The Minerals, Metals & Materials Society (TMS), 1998),

13 7. I.V. Kojo, A. Jokilaakso and P. Hanniala, Flash Smelting and Converting Furnaces High Intensity Reactors with Outokumpu Design, JOM, 52 (2000) 2, I.V. Kojo, A. Jokilaakso and P. Hanniala, Outokumpu Flash Smelting Technology and the Production Network Concept, Rudy i Metale Niezelazne, 45 (2002) 12, J. Tuominen and I.V. Kojo, Blister Flash Smelting Efficient and Flexible Low-Cost Continuous Copper Process, Converter and Fire Refining Practices, ed. A. Ross, T. Warner and K. Scholey, (Warrendale, PA: The Minerals, Metals & Materials Society (TMS), 2005), I.V. Kojo and H. Storch, Copper Production with Outokumpu Flash Smelting: An Update, Sohn International Symposium on Advanced Processing of Metals and Materials Vol. 8: International Symposium On Sulfide Smelting 2006, ed. F. Kongoli, R. Reddy, (Warrendale, PA: The Minerals, Metals & Materials Society, 2006), W.G. Davenport, M. King, M. Schlesinger and A.K. Biswas, Extractive Metallurgy of Copper, 4 th edition, Pergamon, L. Aspola, Sustainability Indicators in Copper Smelting Processes, M.Sc. Thesis, Helsinki University of Technology, 16 May W.P. Imrie, J.A. Murray and R.H. Richards, Bold Vision Can Yield Enhanced Environmental Performance and Establish Competitive Operating Economics - A Smelter Modernization Case Study, First National Meeting for Evaluation of Environmental Impact, Comision Nacional del Medio Ambiente, Santiago, Chile, 8-10 Nov