Energy Consumption in Copper Smelting: a New Asian Horse in the Race

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JOM, Vol. 67, No. 5, 2015 DOI: 10.1007/s11837-015-1380-1 Ó 2015 The Minerals, Metals & Materials Society

Energy Consumption in Copper Smelting: A New Asian Horse in the Race

P. COURSOL,1,5 P.J. MACKEY,2 J.P.T. KAPUSTA,3 and N. CARDONA VALENCIA4

1.—5N Plus Inc., Montreal, QC, Canada. 2.—P.J. Mackey Technology, Inc., Kirkland, QC, Canada. 3.—BBA Inc., Montreal, QC, Canada. 4.—Deltamet Consulting, Pointe-Claire, QC, Canada. 5.—e-mail: [email protected]

After a marked improvement in energy consumption in copper smelting during the past few decades, technology development has been slowing down in the Americas and in Europe. Innovation, however, is still required to further reduce energy consumption while complying with stringent environmental regulations. The bottom blowing smelting technology being developed in China shows success and promise. The general configuration of the bath smelting vessel, the design of high-pressure injectors, and the concentrate addition system are described and discussed in this article with respect to those used in other technologies. The bottom blowing technology is shown to be operating at a temperature in the range of 1160–1180°C, which is the lowest reported temperature range for a modern copper smelting process. In this article, it is suggested that top feeding of filter cake concentrate, which is also used in other technologies, has a positive effect in reducing the oxidation potential of the slag (p(O2)) while increasing the FeS solubility in slag. This reduction in p(O2) lowers the magnetite liquidus of the slag, while the in- creased solubility of FeS in slag helps toward reaching very low copper levels in flotation slag tailings. The application of high-pressure injectors allows for the use of high levels of oxygen enrichment with no requirements for punch- ing. Using a standard modeling approach from the authors’ previous studies, this article discusses these aspects and compares the energy consumption of the bottom blowing technology with that of other leading flash and bath smelting technologies, namely: flash smelting, Noranda/Teniente Converter, TSL (Isasmelt [Glencore Technology Pty. Ltd., Brisbane, Queensland, Aus- tralia]/Outotec), and the Mitsubishi Process (Mitsubishi Materials Corpora- tion, Tokyo, Japan).

technology configurations, remains an important INTRODUCTION topic for copper smelters. One of the biggest business stories of 2014 was The first published concept of bottom blowing the huge drop in the price of oil. Thus, the West smelting for nonferrous metals dates back to 1974 Texas Intermediate oil price dropped amid an oil and the paper by Paul E. Queneau and Reinhardt surplus and lower demand by almost 50% from ap- Schuhmann1 titled ‘‘The Q-S Continuous Oxygen proximately $100/barrel in the middle of 2014 to Converter.’’ The authors explained that the Q-S around $50/barrel by early 2015. For a large energy oxygen process invention was a response to the consumer such as a copper smelter, this provided challenges of the time (first oil crisis resulting in some relief to ever rising operating costs. However, high oil prices and pressure to fix sulfur dioxide analysts expect some rebound in the oil price later gases) to increase process efficiency by a systematic this year or into 2016. Hence, energy consumption use of oxygen with a substantial corresponding in smelting, examined in this article for a number of reduction in fossil fuel usage. Queneau and

1066 (Published online March 18, 2015) Energy Consumption in Copper Smelting: A New Asian Horse in the Race 1067

Schuhmann adopted the following key concepts in The number of SKS lead reactors in China quickly their process design: grew after 2002; Stephens7 reported that the SKS lead furnace had been described ‘‘as the smelting Continuity—to limit capital and operating costs section of a QSL reactor.’’ As for the SKS copper Autogenous—by using oxygen to lower energy 5 furnace, Kaixi Jiang et al. described it as similar in and fossil fuel consumption design to the Noranda Reactor, contrasting with the Single off-gas of minimal volume—to lower costs fact that ‘‘the air in the copper matte layer is blown of sulfur fixation into the furnace via the oxygen guns set in the Bottom blowing—to attain optimal solid–liquid– furnace bottom.’’ These oxygen ‘‘guns’’ are essen- gas contact tially Savard–Lee-type shrouded injectors with Countercurrent flow of matte and slag—to compressed air as shrouding gas. The process at achieve bath oxidation and slag reduction in a Dongying is now known as the bottom blowing single vessel smelting (BBS) process. Several other copper smel- An elongated, kiln-like vessel—to improve heat ters in China have since adopted the SKS/BBS and mass transfer. technology. It has also been reported that the tech- In 1989, Queneau2 provided historical insights into nology is being evaluated as an alternative for some the conceptual phase of the Q-S process develop- copper smelters in Chile. ment mentioning that a key driver that triggered The goal of this article is to discuss the SKS/BBS the search for a new nonferrous smelting process technology features and to evaluate the energy re- was the invention of the Savard–Lee shrouded in- quirements for this technology compared with other jector and its success in steel refining. In fact, modern smelting technology. To do so, the approach Queneau and Schuhmann3 had filed their patent in used by Kellogg and Henderson8 and Coursol 1973 and entered into a collaborative agreement et al.9,10 is used. In this approach, all technologies with Savard, Lee, and Canadian Liquid Air that are compared on the same basis, with the same same year, forming QSOP Inc. (Queneau–Schuh- concentrate, flux and coal composition, this allows mann Oxygen Process). evaluating both the electrical and thermal energy With a lack of interest from the copper industry, required to operate a smelter from concentrate to QSOP found support from Werner Schwartz of anode for a given technology. Lurgi, leading to a QSOP-Lurgi agreement in 1974 for the development of the QSL (Queneau–Schuh- BOTTOM BLOWING SMELTING mann–Lurgi) lead smelting reactor. After 15 years TECHNOLOGY (SKS/BBS) of efforts in the laboratory and in pilot and demon- General Description stration plants, including further developments of the Savard–Lee injectors, the QSL became the first The SKS/BBS reactor, as shown in Fig. 1,isa bottom blown smelting vessel commercialized in cylindrical vessel with gravity top feeding of wet nonferrous pyrometallurgy with lead smelting re- concentrate through several ports. The injectors are actors installed in 1990 in Canada (Trail Smelter of all located on one side of the furnace, whereas the Cominco Ltd.), Germany (Stolberg Smelter of Ber- off-gas mouth, matte, and slag tap holes are on the zelius), and China (Baiyin Smelter of CNIEC), and opposite side. This arrangement creates a two-zone in 1991 in Korea (Onsan Smelter of Korea Zinc). A bath: an agitated oxidation zone below the feed more complete story of the QSL development from ports and a quiescent settling zone above the matte patent to commercial implementation was reported tap hole. Two auxiliary burners are located on each by Kapusta and Lee.4 end wall and are used during start-up or stand-by. The Chinese industry developed its own bottom The mouth is small compared with existing bath blowing reactor in the 1990s. China Nonferrous smelting reactors because operating at high oxygen Metal Industry’s Foreign Engineering and Con- struction Co. Ltd. and China ENFI Engineering (ENFI) first piloted their ShuiKouShan (SKS) lead smelting technology in 1999 at the ShuiKouShan lead smelter in Hunan Province. Commercial engineering and construction took place in 2001 and successful commissioning in 2002. The SKS copper process was first adopted in 2001 and commissioned commercially at the Sin Quyen Copper Complex in Vietnam in 2008 with a capacity of just 10,000 t/a of anode copper. The second implementation of the technology, and first in China, took place in 2008 at the Dongying Fangyuan Nonferrous Metals Co., Ltd. (Dongying) with an original copper concentrate smelting capacity of 32 dry t/h or 55,000 t/a of an- 5,6 Fig. 1. Schematics of SKS/BBS copper process from Yao and ode copper. Jiang.11 1068 Coursol, Mackey, Kapusta, and Valencia enrichment produces lower volumes of process off- reactor and Teniente converter operations. The gases. original design capacity of the Dongying furnace Cui et al.12 provided a complete description of the was 55,000 t/a of anode copper at 55% oxygen, and bottom blown oxygen smelting process at Dongying. its current capacity has reached 100,000 t/a as the The cylindrical furnace is 4.4 m in diameter by oxygen enrichment reached 75%. 16.5 m in length. The oxygen ‘‘lances’’ are positioned The inherent low level of nitrogen in the blast is in two rows at the bottom of the furnace with five frequently perceived as a weakness of high-oxygen lances in the lower row at 7° to the vertical and the injection due to the diminished mixing of the bath. A four lances in the upper row at 22°. This provides a comparison with the operating oxygen top-blown– 15° angle between the two rows. A photograph of the nitrogen-bottom stirred vessel at Vale’s Copper Cliff Dongying furnace is given in Fig. 2. smelter in Sudbury is opportune at this point. The oxygen lances or guns used to inject the blast Marcuson, Diaz, and Davies reported the use of five are Savard–Lee-type shrouded injectors with simi- porous plugs, each with nitrogen flow rates of lar design and configuration as the original QSL 14 Nm3/h.16 The total flow rate of nitrogen for stir- injectors developed by Lurgi and Air Liquide in the ring was 70 Nm3/h, which was evidently sufficient 1970s.4 The tips of the injectors are built with a to provide stirring in a 135-t semiblister bath (cor- gear-like design as shown on Fig. 3a (drawing) and responding to a specific blowing rate of 0.52 Nm3/h/t Fig. 3b and c (photographs) for the reactors built by of the melt). In this later case, the top blown oxygen ENFI. The principle of the lances is to inject high- flow rate was approximately 5330 Nm3/h. With an oxygen-enriched air or pure oxygen in the central SKS/BBS furnace operating at 75% oxygen, the to- bore and first or two annuli of grooves and a cooling tal blast rate is approximately 19,160 Nm3/h, cor- medium in the outer ring of grooves (e.g., air or ni- responding to the Dongying vessel to a specific trogen). All streams are injected at sonic velocity. blowing rate of 70 Nm3/h/t of melt. These conditions The lance design at Dongying has been slightly provide nitrogen in the order of 4,790 Nm3/h for modified to reduce the pressure requirement of the stirring, a sizeable amount compared with the por- oxygen streams to achieve sonic velocity.13 ous plugs in the Copper Cliff case. By comparison, The oxygen enrichment achieved to date with the the Noranda Process reactor in Canada has a SKS/BBS reactors is in the range 50–75%, which is specific blowing rate of about 130 Nm3/h/t of melt. significantly higher than for the current Noranda The lance life was reported in 2013 by Xiaohong Hao et al. to be 30–60 days14 and in 2014 by Johnny Zhang et al. to be up to 6 months.17 This discrep- ancy highlights the importance of a proper lance design to ensure sonic velocity is achieved, and a controlled bath chemistry and temperature is needed to limit lance and refractory wear. Dongying has achieved the most advanced developments in the operation of its SKS/BBS furnace. This operation has therefore been selected in this article as the reference for energy comparison of the SKS/BBS furnace to the Noranda and Teniente reactors.

Process Chemistry Although most modern smelting vessels accom- Fig. 2. SKS/BBS furnace at Dongying (Source: Yao and Jiang.11) plish a similar task of producing a high-grade

Fig. 3. (a) Drawing of lance tip from Hao et al.,14 and (b, c) Photographs from July 2013 ENFI presentation.15 Energy Consumption in Copper Smelting: A New Asian Horse in the Race 1069 matte, the chemistry can vary significantly from one trend as function of the matte grade for different Fe/ technology to another. In the BBS furnace case, SiO2 ratios in slag from a bath reactor such as the several factors seem to affect positively slag chem- Teniente Converter. The thermodynamic calcula- istry, leading to low copper levels in the furnace slag tions assume all sulfur is soluble as FeS, but the and favorable oxygen consumption figures. A few of copper sulfidic dissolution is yet to be modeled ap- these aspects are discussed next. propriately. At 70% matte grade and a Fe/SiO2 ratio of 1.8, the expected %S soluble in slag is 0.7 wt.%, Impact of Matte Grade which is lower than the level of 1.1 wt.% reported by Zhao et al.6 for the BBS slag, which must account for The smelting furnace matte grade is important both Cu and Fe sulfidic dissolution. for the process chemistry. A matte grade higher The sulfur solubility in slag can have a positive than 77% leads to higher soluble copper in slag in impact by forming recoverable matte droplets dur- the oxidic form, whereas operating at a matte grade ing slag cooling and solidification, if the slag is so- lower that 70% leads to moderate copper levels in lidified at a sufficiently low cooling rate.20 Figure 5a slag, predominantly in the form of soluble sulfidic shows the microstructure of a rapidly cooled slag copper.18 In the BBS process, the operating matte sample, in which sulfide exsolution led to a phe- grade is in a range where the lowest soluble losses nomenon called ‘‘copper fog.’’ In the copper fog for- are observed, which is generally between 70 and mation, the small sulfide particles are trapped 75% Cu.18 A reasonably low total copper in slag is between olivine and terminal glass (final slag to observed in the BBS furnace, indicating less than solidify in a glassy state during the solidification 5 wt.% matte entrained in slag.6 Given that the process) and are quite hard to recover by milling approach taken for slag cleaning is by milling and and flotation. On the contrary, when the slag is so- flotation, a high copper recovery is expected, with a lidified under a controlled slow cooling rate, as copper content in tailings reported at 0.26%.6 practiced by several smelters worldwide, this results in a much coarser microstructure and the FeS Solubility in Slag and Impact on Copper growth of droplets (e.g., due to coalescence phe- Recovery nomena). Hence, higher Cu recoveries can be ob- The bulk sulfur content in slag of the BBS reactor tained. Figure 5b shows a coarse microstructure was reported to be 1.7 wt.%,6 whereas the bulk with matte droplets formed during cooling slag and copper content of the slag was reported to be a large entrained matte droplet with sulfide exso- 2.9 wt.%.6 These numbers appear low from the au- lution texture. thors’ viewpoint and are expected to vary as a function of slag quality and matte grade. If one as- sumes all copper is present as matte entrained in the Feeding on Slag Instead of Submerged Injection slag, then the %Cu/%S ratio should be maintained at In the BBS furnace case, the fresh feed is added as 3.4. If a significant level of copper oxide is present in a wet concentrate onto the slag surface. Under these the slag, then the ratio should be higher. In the BBS conditions, it is conceivable to obtain a lower p(O2)in furnace, the %Cu/%S ratio is 1.71, indicating that the slag than in the matte because of the addition of another sulfide species is soluble or entrained in the fresh concentrate from the top, as long as mixing is slag. Previous publications have discussed FeS so- adequate, yet not overly intense. With more intense lubility in copper smelting slag and its sig- mixing, the p(O2) of both phases would be nearly the nificance.18,19 Figure 4 shows the sulfur solubility same (closer to equilibrium). Melting of the concentrate within the slag can contribute to maintaining the dissolved copper oxide content to quite low levels and, furthermore, to controlling the magnetite level 0.7 of the slag. In the BBS furnace case, the reduced 0.6 Fe/SiO2=1.6 bath agitation due to the higher oxygen enrichment Fe/SiO2=1.4 and lower blowing rates (or, a lower total off-gas 0.5 Fe/SiO2=1.8 volume expressed as m3/m3 of melt) can provide fa- 0.4 vorable conditions in the slag to minimize the slag 0.3 liquidus (lower p(O2) and a higher level of soluble FeS). Although the Teniente Converter with sub- 0.2 merged injection generally operates near 1225– %S in Slag as FeS%S in 0.1 1250°C, the Noranda Reactor and the Isasmelt fur- 0.0 nace (Glencore Technology Pty. Ltd., Brisbane, 0.5 2.0 3.5 5.0 6.5 8.0 9.5 Queensland, Australia) using wet feed addition from %Fe in matte the top operate at 1200°C and 1180°C, respectively, which can lead to a significant improvement in the Fig. 4. Calculated sulfur solubility (as FeS) in the Teniente converter refractory protection and heat balance of these ves- slag. Effect of Fe/SiO ratio and %Fe in matte at T = 1250°C. 2 sels. The BBS technology, operating with top feeding (p(SO2) = 0.25 atm, [Al2O3]slag = 4.0 wt%, [ZnO]slag = 2.1 wt.%, 19 [MgO]slag = 0.8 wt.%, [CaO]slag = 0.8 wt.%). and high oxygen enrichment levels, seems to push 1070 Coursol, Mackey, Kapusta, and Valencia

Fig. 5. (a) Fine microstructure showing ‘‘copper fog’’ (bright dots). (b) Coarser microstructure obtained by slow cooling of the slag, leading to high copper recovery by flotation (Cu2S and Cu-Fe sulfide [bright phases], fayalite [gray columnar crystals], terminal glass [dark gray phase between the fayalite blades], and magnetite crystals [intermediate grey crystals shown in (b)]). the concept observed in other top feeding technolo- important, as most of the remaining iron sulfide gies toward a reduced mixing intensity, leading to needs to be oxidized during converting. This is il- even lower operating temperatures, reported to be in lustrated by reaction 3. the 1160–1180°C range.6–17 The mineralogy of reverts added to the smelting unit can also lower tonnage oxygen usage and SO2 Operating at High Oxygen Enrichment generation. For example, adding metallic copper in the form of reverts, copper scrap, or spent anodes Higher oxygen enrichment has the benefit of re- can reduce both the SO produced during smelting leasing more heat during the smelting process and of 2 and tonnage oxygen usage. This can be referred to allowing more reverts or low-grade materials to be as ‘‘sulfur sequestration’’ and obviously has an im- recycled in the smelting vessel. It also has the ad- pact on the FeS oxidation mechanism, changing vantage of providing a lower mixing level in the from reaction 3 to 4. Similarly, Cu O contained in smelting vessel and reducing the off-gas volume. One 2 reverts from the converter aisle or anode furnaces should also note that these conditions reduce the risk represent a source of oxygen and therefore can also of foaming during periods when the slag contains significantly reduce tonnage oxygen consumption. excessive levels of solid magnetite. One drawback of This is illustrated by reaction 5. using high oxygen enrichment is the increase in Finally, in a deficient heat balance situation, coke OPEX and CAPEX for oxygen production. addition is used for closing the heat balance. Most of this coke entering the smelting unit exits as CO gas Oxygen Usage in Copper Smelting 2 with trace levels of CO; hence, the oxygen required From practical experience with modern smelting for this reaction contributes to the total specific O2 technologies, the oxygen usage factor (or oxygen consumption. efficiency) in most technologies is in the 95–99% range. Although much lower oxygen usage per ton- ðÞFeS2 feedþO2ðfreeboardÞ ¼ ðÞFeS matteþSO2 (1) ne of concentrate can apparently be observed in some cases, clearly an oxygen efficiency over 100% is not possible. Differences can be explained by the ðÞFeS þ3=2O ¼ ðÞFeO þSO2 (2) factors discussed next. It is noted that a lower feed 2ðfreeboardÞ slag specific oxygen consumption was observed in the BBS furnace case.17 When concentrate is fed to a smelting unit from the ðÞFeS matteþ3=2O2 ¼ ðÞFeO slagþSO2 (3) top (Noranda Reactor, El Teniente Converter, BBS furnace, etc.), the freeboard air or gas can react with the concentrate if sufficient oxygen is available. This ðÞFeS þ2CuðÞ þO ¼ ðÞFeO þðÞCu S phenomenon is illustrated by reactions 1 and 2. The matte matte 2 slag 2 matte chalcopyrite, bornite, and chalcocite present in the (4) concentrate can be oxidized following similar me- chanisms. Although this is not the major oxidation mechanism, it can make a significant difference in ðÞFeS matteþCu2O ¼ ðÞFeO slagþðÞCu2S matte (5) specific oxygen consumption for a given feed. The concentrate mineralogy obviously has a significant impact on the oxygen requirements. Main- The preceding discussion is helpful in under- ly, the input FeS2 and FeS equivalent are very standing the lower published and observed oxygen Energy Consumption in Copper Smelting: A New Asian Horse in the Race 1071 use in the BBS furnace compared with the Noran- Appropriate data were also taken from Kellogg da–Teniente reactor as indicated by Zhang et al.17 and Henderson,8 and updated information was used in other cases. Examples of auxiliary unit op- METHODOLOGY-ENERGY CALCULATIONS erations include producing tonnage oxygen, com- pressing Peirce Smith Converter (PSC) injection air, The methodology adopted to evaluate smelting delivering low-pressure air to burners, moving pro- energy in this study was based in part on the ap- cess off-gas, drying concentrate and other materials, proach used by Kellogg and Henderson,8 which was and transporting and injecting fine solids suspended reviewed for modern smelting technologies by in a stream of gas (dense phase transportation of Coursol et al.9,10 In these last two studies, the au- solid particulates). thors reviewed the energy consumption (electrical The standard conditions used for the calculation and thermal) and compared modern technology of energy requirements for each of the chosen pro- performances in specific configurations, process cesses are presented in Table II and are identical to copper concentrate, and finished anodes. In total, 12 the ones taken in previous studies.9,10 These pro- different flowsheet configurations were compared. A cesses include the assay of a standard copper con- Metsim model (METSIM; Proware, Tucson, AZ) centrate and the data relative to fluxes and fuels. previously developed by Tripathi et al.21 was used as a basis for designing several other models and for comparing technologies on the same basis. Heat and mass balance and energy consumption data were then computed for each process for subsequent analysis and comparison. Process ‘‘boundary limits’’ were as follows: Inputs: wet concentrate, flux, and Table II. Standard conditions used in the Metsim other consumables delivered to the smelter day model bins; and Outputs: copper anodes, sulfuric acid, acid plant tail gas, cleaned fugitive gas released to at- Item and data mosphere, and cleaned slag. Waste heat recovery Concentrate analysis (dry basis): 30.5% Cu, 28.5% Fe, from process gas streams was included as part of the 31.5% S, 5% SiO2,2%Al2O3 study. In this work, the same approach was used to Concentrate moisture content: 10% H2O compare the BBS technology with other modern Flux analysis (dry basis): 88% SiO2, 2% CaO, 6% Al2O3, technologies. Energy consumption in auxiliary unit 2% MgO, and 2% Fe3O4 Flux moisture: 3% H2O operations and energy equivalent for process sup- 3 plies were computed from a set of unit energy con- Natural gas: 37.3 MJ/Nm Coal: 28.4 MJ/kg sumption factors. These are presented in Table I Ambient conditions: 0°C, 760 mmHg based on data from Refs. 9 and 10.

Table I. Unit energy parameters used in this study

Item Unit energy References Steam dryer 2 t steam/t water evaporated 9 Conversion of steam to electricity at smelter 6.25 kg of steam/kWha 9 Tonnage oxygen production (300 kPa) 285 kWh/t of oxygen 22 Tonnage oxygen production (600 kPa) 321 kWh/t of oxygen Authors Compress tuyere air (600 kPa) 0.126 kWh/Nm3 Authors Compress tuyere air (110 kPa) 0.05 kWh/Nm3 8 Compress lance air (60 kPa) 0.03 kWh/Nm3 9 Process off-gases handling 0.0085 kWh/Nm3 9 Fan-secondary gases 0.002 kWh/Nm3 24 Furnace cooling water 3 kWh/t Cu 9 Matte granulation and handling 9 kWh/t of matte 9 Slag granulation and handling 3 kWh/t of slag 9 Matte comminution and handling 10 kWh/t of matte 9 Lighting and miscellaneous power (allowance) 30 kWh/t of Cu 8 Acid plant operation (double contact) [(646.8/%SO2) + 63.7] kWh/t of acid 8 Energy-Flux (90 MJ + 3 kWh)/t of flux 8 Energy-limestone calcination (CaO ﬂux) 7000 MJ/t of CaO 9 Energy-wear steel in slag milling 20.7 MJ/kg of steel 23 Energy-pig iron 15.5 MJ/kg of pig iron 9 aBased on a rate of 5 kg steam/kWh and an operational efﬁciency of 80% to account for potential losses on start-up/standby, etc. 1072 Coursol, Mackey, Kapusta, and Valencia

Brief Description of Processes Assumptions of 37 wt.% Cu.25 With an oxygen enrichment of 43%, (Noranda Reactor Versus BBS Technology) the heat balance was closed with a slag temperature of 1244°C. These conditions, given as a reference, Each process route also included the following are the same conditions as presented by Coursol ‘‘standard’’ unit operations: (I) complete secondary et al.10 gas collection and cleaning, (II) anode refining and In the BBS furnace case, with shrouded tuyeres, casting, and (III) process gas treatment in a double- it is possible to achieve oxygen enrichment as high contact acid plant with acid delivery to storage as 75 vol.%. By using this technology allowing for tanks. As noted above, heat recovery from process higher oxygen enrichment, the coke addition in the off-gases was also used. Concentrate and other solid smelting unit was reduced to zero, and the slag process streams requiring drying were treated in concentrate grade was reduced to 15 wt.% Cu al- steam dryers using waste heat steam. Surplus lowing a lower %Cu in slag tailings (0.26 wt.%) to be steam was assumed to generate electricity. The assumed. The lower grade of slag concentrate pro- flowsheet configuration used for the BBS process vides a greater tonnage of cold material to be added, was identical to the configuration used for the No- thus being available to absorb excess smelting heat randa Process by Coursol et al.10 Figure 6 shows the as a consequence of the relatively high level of flowsheet configuration used in both the Noranda oxygen enrichment used. Thus, with the two chan- Reactor and the BBS furnace cases for the mass ges mentioned above, an oxygen enrichment level of balance calculations. 63% is allowed to close the heat balance and obtain In both simulations, Noranda and BBS, a feed a slag temperature of 1180°C. rate of 126.8 t/h of a standard filter cake concentrate was assumed (10% moisture, 114 t/h dry basis), were fed to the smelting vessel. The total heat RESULTS losses for both smelting units were fixed at 7 MW. The two flowsheet had the exact same configura- Tables III and IV show the results of energy and tions as shown in Fig. 6. A few differences in process fossil fuel consumption for the Noranda Reactor and data between the two cases are listed next. the BBS furnace cases, respectively. Separate col- In the Noranda Reactor case, with normal tuyere umns for electric energy, expressed in kWh/t of technology (low pressure and nonshrouded), the anode copper, and fuel, expressed in MJ/t of anode oxygen enrichment is limited to 45 vol.% to mini- copper, are provided in these tables. The fuel mize risks on tuyere line integrity. The maximal equivalents of electrical energy were calculated us- coke addition to the vessel is limited to ap- ing a power plant efficiency of 38%.9 In the tables, proximately 2 t/h from practical experience. In this the numbers for items such as fuel, oxygen, com- simulation, the Fe/SiO2 ratio in the slag was set to pressed air, secondary gases, and fugitive gases 1.42. The final copper losses in slag tailings were correspond to respectively overall smelter con- assumed to be 0.39 wt.% at a slag concentrate grade sumption or production.

Fig. 6. Model flowsheet configuration used for the Noranda flowsheet and the BBS flowsheet. Energy Consumption in Copper Smelting: A New Asian Horse in the Race 1073

Table III. Energy requirements for the Noranda reactor case with Peirce–Smith converters and slag ﬂotation (slightly modiﬁed from Ref. 10 for consistency with following BBS furnace case)

Electrical Fuel Total Item kWh/t Eq MJ/t MJ/t MJ/t Fuel 0 0 4088 4088 Tonnage oxygen 256 2427 0 2427 High pressure air 135 1276 0 1276 Process gas handling 61 576 0 576 Secondary and fugitive gas handling 76 720 0 720 Supplies, steel, etc. 2 17 39 56 Milling slag 160 1515 0 1515 Acid production 401 3800 0 3800 Lighting and miscellaneous 30 284 0 284 1120 10,614 4127 14,741 Steam credit À176 À1669 À1669 944 8946 13,072

Table IV. Energy requirements for the BBS furnace case with Peirce–Smith converters and slag ﬂotation

Electrical Fuel Total Item kWh/t Eq MJ/t MJ/t MJ/t Fuel 0 0 2331 2331 Tonnage oxygen 298 2824 0 2824 High-pressure air 133 1255 0 1255 Process gas handling 48 459 0 459 Secondary and fugitive gas handling 76 720 0 720 Supplies, steel, etc. 1 12 39 51 Milling slag 160 1518 0 1518 Acid production 360 3413 0 3413 Lighting and miscellaneous 30 284 0 284 1107 10,486 2370 12,857 Steam credit À129 À1223 À1223 978 9263 11,634

The calculations performed in this study and selected data from previous studies9,10 are shown in Table V.

Table V. Comparison between energy consumption for copper production (concentrate to anode) for the reverberatory furnace and for selected modern copper smelting technologies

Processing route Electric energya Fossil fuela Totala KH-hot calcine reverberatory8 2173 15,935 18,108 Flash smelting–flash converting–slag flotation9 9266 1518 10,784 Isasmelt–Peirce–Smith converting-rotary slag cleaning9 6903 4175 11,078 Mitsubishi Process (Mitsubishi Materials Corporation, Tokyo, Japan)9 8508 2498 11,006 Noranda–Teniente with dry feed + slag flotation9 10,088 2657 12,746 Noranda reactor (filter cake) + PSCs + slag flotation 8946 4127 13,072 Bottom blowing smelting (filter cake) + PSCs + slag flotation 9263 2370 11,634 aAll energies are expressed in MJ/t of anode copper. 1074 Coursol, Mackey, Kapusta, and Valencia

6. B. Zhao, Z. Cui, and Z. Wang, Fourth International Sym- CONCLUSION posium on High-Temperature Metallurgical Processing, ed. T. Jiang, J.Y. Hwang, P.J. Mackey, O. Yucel, and G. Zhou From an energy perspective, our calculations (Warrendale, PA: TMS-AIME, 2013), pp. 3–10. indicate the BBS/SKS technology to be superior to the 7. R. Stephens, Proceedings of the International Symposium on Noranda/Teniente smelting vessels and to be nearly Lead and Zinc Processing, ed. T. Fujisawa, J.E. Dutrizac, equivalent to other highly efficient technologies: A. Fuwa, N.L. Piret, and A.H-J. Siegmund (Tokyo: The flash smelting, Isasmelt, and the Mitsubishi Process. Mining and Materials Processing Institute of Japan, 2005), pp. 45–71. The calculated specific energy data presented in 8. H.H. Kellogg and J.M. Henderson, Extractive Metallurgy of Table V are not only for smelting but also for Copper, Vol. I, ed. J.C. Yannopoulos and J.C. Agarwal treating concentrate through to anode copper; (Warrendale, PA: TMS-AIME, 1976), pp. 373–415. hence, the results of all technologies can be im- 9. P. Coursol, P.J. Mackey, and C. Dıáz, Proceedings of Copper 2010,Vol.2—Pyrometallurgy I (Clausthal-Zellerfeld: GDMB, proved by optimizing peripheral equipment. The 2010), pp. 649–668. authors believe that more work needs to be done 10. P. Coursol, P.J. Mackey, and C. Dıáz (Paper presented at the regarding better converting technologies and anode 50th Conference of Metallurgists, Montreal, QC August 2011). furnace design to further reduce energy usage. 11. S. Yao and C. Jiang, Proceedings of the Bill Davenport Oxygen enrichment, a dominant aspect in improv- Honorary Symposium held during the Conference of Metal- lurgists 2014 (COM2014), ed. E. Ozberk and E. Partelpoeg, ing energy efficiency, has been incorporated in most (Montreal, QC: The Metallurgy and Materials Society of modern technologies, and the industry now has to CIM, 2014). search elsewhere while reaching even higher en- 12. Z. Cui, Z. Wang, and B. Zhao, Proceedings of Copper 2013, richment levels. Converting, fire refining, waste International Copper Conference, Vol. III (Book 2)—The Nickolas Themelis Symposium on Pyrometallurgy and Pro- heat recovery, and oxygen/acid production are all cess Engineering, ed. R. Bassa, R. Parra, A. Luraschi, and key areas to allow further improvements in energy S. Demetrio (Santiago: The Chilean Institute of Mining efficiency and energy usage. Engineers, 2014), pp. 351–360. The Noranda Reactor and Teniente Converter 13. J.P. Kapusta, Private visit at the Dongying Fangyuan have been work horses in Canada and Chile during smelter and lance manufacturing machine shop, November 2014. the last 40 years. Much attention has been placed in 14. X.Hao,Z.Lu,K.Wei,Z.Zhang,L.Hu,B.Li,Z.Wen,F.Su,and increasing productivity but with no major change in Y. Yu, Proceedings of Copper 2013, International Copper Con- vessel configuration or injector technology. The ference, Vol. III (Book 2)—TheNickolasThemelisSymposium current practical limitation in oxygen enrichment on Pyrometallurgy and Process Engineering, ed. R. Bassa, R. Parra, A. Luraschi, and S. Demetrio (Santiago: The Chilean with low-pressure, nonshrouded tuyeres is consid- Institute of Mining Engineers, 2014), pp. 451–459. ered near to 45% O2. It is believed that high-pres- 15. China ENFI Engineering Corporation, Oxygen Bottom sure injectors and/or shrouded tuyeres added to the Blowing Copper Smelting Technology (SKS), online pre- Noranda–Teniente Converter can provide sig- sentation, http://wenku.baidu.com/view/4a6be5990029bd64 nificant benefits in terms of energy efficiency, with 783e2cf1.html. 16. S.W. Marcuson, C. Diaz, and H. Davies, JOM 46, 61 (1994). attendant improvements in environmental perfor- 17. J. Zhang, X. Guo, Z. Wang, and Z. Cui, Proceedings of the mance. Using this approach, such vessels located in Bill Davenport Honorary Symposium Held During the Chile could improve operational and environmental Conference of Metallurgists 2014 (COM2014), ed. E. Ozberk performance and better energy efficiency with likely and E. Partelpoeg, (Montreal: The Metallurgy and Materials Society of CIM, 2014). a low capital investment. 18. M. Nagamori, Metall. Trans. B 5, 531 (1974). ACKNOWLEDGEMENT 19. N. Cardona, P. Coursol, P.J. Mackey, and R. Parra, Can. Metall. Q. 50, 319 (2011). The authors would like to acknowledge the con- 20. P.W. Godbehere and C. Ferron (Paper presented at the 112th tribution of Dr. Carlos Diaz in previous publications AIME Annual Meeting, Atlanta, GA, March 1983). 21. N. Tripathi, P. Coursol, S. Morissette, and P.J. 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