PRODUCTION ENHANCEMENT AND OPERATION PARAMETER S OPTIMIZATION OF THE FLASH SMELTING FURNACE BASED ON NUMERICAL SIMULATION

Transcription

1 Third International Conference on CFD in the Minerals and Process Industries CSIRO, Melbourne, Australia 10-1 December 003 PRODUCTION ENHANCEMENT AND OPERATION PARAMETER S OPTIMIZATION OF THE FLASH SMELTING FURNACE BASED ON NUMERICAL SIMULATION Xin-feng LI and Tianyuan XIAO National CIMS Engineering Research Center, Tsinghua University, Beijing , China ABSTRACT An extensive study of the coer flash smelting furnace has been undertaken. It aims at increasing the throughut of the flash smelting furnace and imroving the smelting erformance. In this aer a mathematical model, which incororates the transort of momentum, heat and mass and reaction kinetics between gas and articles and reactions between gas and gas, is emloyed to simulate the henomena in flash smelting furnace. After numerical simulation and otimization, a set of good oeration arameters, which can increase roduction safely and efficiently, was achieved. And the rule of 3C was found to be a very valid method to imrove the smelting erformance. The otimization took a notable effect in Jinlong flash smelting furnace. Key word: Simulation, Numerical, Flash smelting furnace, Otimization NOMENCLATURE A d C D C g h H c H r H s k m S Φ T u v Y Ф ρ Γ Φ ε rofile area of the article article drag coefficient secific heat caacity of the article gravity vector gas secific enthaly convective heat source radiative source chemical reaction heat source turbulent kinetic energy mass of the article source term for variable Ф temerature of article gas velocity comonent article velocities gas mass fraction. variable density of the fluid exchange coefficient for variable Ф dissiation rate of turbulent kinetic energy INTRODUCTION Flash smelting rocess, develoed by Outokumu, is considered to be one of the most imortant innovations in coer metallurgy in the 0 century. In flash smelting rocess, the concentrate, along with recycled dust, flux, is fed into the vertical reaction shaft from the CJD burner, where the oxygen-enriched air is injected too. In the reaction shaft (RS) the articles are quickly disersed and heated by the RS wall and the gas until decomosition. Then, the concentrate articles react with gas hase to redetermined oxidation degree. After the reaction shaft, the concentrate disengage from the gas stream and form the slag and mate layers on the bottom of the settler. Gas stream leaves the furnace via the utake and ass through a waste heat boiler (WHB) and electrostatic reciitators (EP) before assing to a acid lant. Today, more throughuts are demanded by metallurgical lants in order to meet the need of modernization and increasing caacities and rocess intensity. Some examles of increased caacity are shown in the Table 1 and the data shown in the table 1 are not the maximum obtainable caacity increases [1]. There is still a great otential for increasing caacities, rocess intensity, energy saving and increasing the life time of concentrate burner and reaction shaft. Numerical simulation has effectively imroved our understanding of the henomena about flash smelting [- 9]. It can handle the comlications of two-hase flow of articles and gas and chemical reactions, and consider heat and mass transfer, turbulence and radiation, and the consequences of high temerature. And it is also used to otimize the design of concentrate burner [10]. Smelter Country Production(% of Original caacity) Huelva Sain More than 400 Harjavalta Finland More than 300 Saganoseki Jaan More than 300 Tamano Jaan More than 00 Hamburg Germany More than 00 Kosaka Jaan More than 00 Guixi China More than 150 Toyo Jaan More than 150 Hidalgo United States More than 150 Onsan South Korea More than 150 Olymic Dam 1 Australia More than 150 Table 1: Examles of caacity increase of some flash smelters MATHEMATICAL MODEL Basic Model To describe the henomena occurring in flash smelting furnace, the conservation equation for the transort of mass, momentum and energy are written for each hase. The gas hase is viewed from an Eulerian framework and all the gas-hase governing equations were written in general form [5]: ρφ + div( ρu Φ) div( ΓΦ gradφ) = S (1) Φ t In the resent modeling, the thirteen equations were solved (Ф =1, u, v, w, k, ε, h, Y O, Y S, Y SO, Y CO, Y HO, Y oil ) in a steady state roblem. The article hase is viewed from a Largrangian framework and the momentum equation for a article Coyright 003 CSIRO Australia 155

2 moving in a surrounding fluid is given by dv m = CDρ ( u v) u v Ad / + mg () dt The energy equation for a single article in the resence of convective, radiative and chemical reaction sources is given as follows: m dt dt C = Hc + Hr + Hs (3) Coer concentrate combustion In order to create a comrehensive mathematic model, a sub model is necessary to be created and integrated into the basic model. The sub model is required to describe the decomosition and combustion of the concentrate, labile sulfur s combustion and ancillary oil combustion in flash smelting furnace. A) The decomosition reactions occur after articles reaching the decomosition temerature. The decomosition reactions are endothermic and roduce the intermediate roducts FeS and S. FeS =FeS +1/ S (4) CuFeS =CuS + FeS + 1/S B) The labile sulfur from the chalcoyrite and yrite combusts with the oxygen and releases heat to the gas hase, reaction heat is released to the gas; Partial FeS combusts with the oxygen and roducts FeO and SO. At the same time, reaction releases heat to the articles directly; C) Slag blow reaction. (5) S + O =SO (6) D) Slag blow reaction. FeS + 3/O =FeO + SO (7) FeO + SiO =FeO (SiO ) (8) Oil is necessary when the combustion heat of concentrate could not meet the need of the flash smelting rocess. CxH y+(x+y/4)o =xco +y/ho (9) SOLUTION ALGORITHM Figure 1 shows the overall PSIC strategy to solve the gas and article equations. All inut data were read including details of gas and article comositions, article sizes, boundary conditions and roerties of article and gas. A first assumtion of the source terms in the gas hase equations to zero is made, and gas equations are solved in Eulerian framework under this assumtion. When the Eulerian equations are converged, the article equations are calculated in Lagrangian framework and the reactions of article are calculated. New source terms for all gas hase equations are comuted and these source terms are under-relaxed before returning to the Eulerian calculations. One cycle of the algorithm in which the Eulerian calculations are converged and the Lagrangian calculations comute the new source terms is called a article-iteration. Overall convergence is achieved when the source terms do not change from one article-iteration to the next. The numerical simulation of the flash smelting rocess was carried out with CFX-4, which is a general-urose commercial CFD code for fluid flow, heat transfer and combustion rocesses.. Start Eulerian calculations read the gas and article comositions, article sizes, boundary conditions and roerties of article and gas Lagrangian calculations Particle reaction Assume S φ =0 N New S φ Converged End Y Figure 1: Overall solution algorithm of the mathematical model 156

3 SIMULATION AND OPTIMIZATION The shaft of Jinlong smelting furnace is 5m in diameter and 6.64m tall from the to of the shaft to the bottom. The height from the bottom of shaft to the matte surface is 1.5m. A central jet distributor (CJD) burner is ut at the to of the reaction shaft where the concentrate is fed into RS. The comonents and the chemical analyses of concentrate are showed in table. Table 3 gives the diameter distribution of the concentrate, resectively. In order to find a good oeration arameter to satisfy the need of roduction enhancement and imrove the smelting erformance, a series of simulation study of the coer flash smelting rocess has been undertaken. Table 5 shows the artial oeration arameter of the flash smelting furnace and simulation results. In table 4, the oeration arameter 1 is the real condition used in the Jinlong flash smelting furnace before roduction enhance. Parameter is used in Jinlong smelter after roduction enhancement without otimizing the oeration arameter. This arameter has been roved to do harm to the wall of the RS. The detailed discussion of these two simulations is resented elsewhere [6]. Parameter 3 is the best oeration arameter achieved from a series of numerical simulation. Comared with result of the arameter 1 and, the simulation result of arameter 3 has the highest articles temerature and smallest radius of articles distribution. It benefits for the article melt and increasing the lifetime of RS. Figure : Temerature in Flash Smelting Furnace The temerature distribution of simulation condition 3 in the flash smelting furnace is resented in Figure. The highest temerature is 11K. The temerature in the lower art of the shaft is more or less uniform, excet near the central line of the flash shaft. However, in the uer art of the shaft, esecially near the burner, large gradients exist. The contours in Figure 4 show that the temerature higher than 1650K. This zone lies at the center of the flash furnace under the CJD burner. This zone in simulation arameter 3 is the bigger than that of other oeration arameters because of the effect of lower distribution air seed and higher ratio of O c /O o. Clearly, it benefits for the melting and reactions of concentrate articles.. NO. Feed /t h -1 Weight/t d -1 Comonent/(%) Cu S Fe SiO CaO MgO Coer concentrates Slag concentrates SiO FSF dust WHB dust Table : comonents of concentrate Oil for RS/kg h -1 Ratio of O c /O o Table 3: Concentrate diameter distribution (µm) distributed air velocity /m s 1 oxygen enrichment rate of rocess air Highest temera -ture of article/k Radius of articles distribution/m Table 4: artial simulation conditions and result Almost all the articles seem to react in a very narrow region. This is seen more obviously from the mass fractions of O and SO, show in Figures 3 and 4. After the oxygen-enriched air and the central oxygen is injected from CJD burner, the concentration of oxygen decreases raidly. The SO concentration is very high in all regions of the flash furnace, esecially below the CJD burner, excet for the area near the oxygen injector and oil burner. The maximum mass fraction of SO is 77.5%. Figure 3: O Content in Flash Furnace 157

4 Figure 4: SO Content in Flash Furnace Figure 5 shows the article trajectories and temerature. After the articles leave the CJD burner, they fall down with the rocess oxygen-enriched air and dro into the slag and matte layers at the bottom of the settler. Clearly, lower distribution air seed makes the concentration of articles and few articles hit the wall of RS directly. It benefit for the collision and reactions among articles, increasing the lifetime of RS and keeing the coer flash smelting furnace working in safe status. At the same time, few articles leave the flash smelting furnace, which means the decreasing of dust rate. The article temeratures are also shown in Figure 5. Particles are injected and heated to decomosition temerature by radiation and convection from oil combustion, the shaft wall and hot circulating gas. The highest temerature reached by the articles is 1880K and the eak temerature is higher than that of other simulation condition because of the lower distribution air seed and higher ratio of O c /O o. The higher temerature of articles is good for the melt and reaction of articles. Availability of FSF Dust Rate of FSF Oil consumtion electric ower consumtion July Aug Se Oct Nov Dec Table 5: The imroving of smelting erformance in the flash smelting furnace after otimization CONCLUSION Numerical simulation has been used to otimize the roduct in flash smelting furnace. The conclusions can be summarized as follows: The study resented in this aer, shows that the reactions of concentrate take lace in a very narrow lace below the CJD burner. The concentration of the concentrate articles, concentration of oxygen and concentration of temerature are good for the smelting erformance. This is named the rule of 3C. Numerical simulation and otimization is one of very effective methods for the roduction enhancement, the smelting erformance imrovement. ACKNOWLEDGEMENTS The authors are grateful to the Jinlong Smelter for financial suort. The authors also want to thank Dr. Phili Stoford of AEA Technology for his kind hel in rogramming and valuable advice. Figure 5: Particle Trajectories and Temerature EFFECT OF OPTIMIZATION Through numerical simulation, the roduction enhancement and oeration arameter s otimization is achieved. Table 5 shows the imroving of smelting erformance in flash smelting furnace after otimization. The feed of the concentrate increased from 65 to 80 ton er hour. Dust rate decreased from 7.5% to less than 5.5%. Availability of the flash smelting furnace increased from 87% to 95%. Oil consumtion decreased from 30 to less than 13.7 kg er ton concentrate. And the electric ower consumtion by the slag cleaning electric furnace (SCEF) decreased from the 80 to 50 kilo watt er hour. REFERENCES 1. ILKKA V. KOJO, AI JOKILAAKSO, and PEKKA HANNIALA, Flash Smelting and Converting Furnaces: A 50 Year Retrosect[J], JOM, 000, Vol.5(5) JORGENSEN, F.R.A. and P.T.L. KOH, Combustion in Flash Smelting Furnaces[J], JOM 001, Vol.53(5) LI XINFENG, MEI CHI, XIAO TIAOYUAN, Numerical Simulation analysis of Guixi Coer flash smelting furnace[j], Rare Metals, Vol.1(4) 00, LI XINFENG, MEI CHI, XIAO TIANYUAN, Numerical modeling of Jinling CJD burner coer flash smelting furnace[j], Journal of University of Science and Technology Beijing, Vol.9(6), 00, LI XINFENG, MEI CHI, Study on Mathematical Model of Multistage and Multihase Chemical Reactions in Flash Furnace[J], Transactions of Nonferrous Metals Society of China, LI XINFENG, Analysis and Otimization of Coer flash smelting furnace rocess[d] Changsha, Central South University

5 7. LI XINFENG, MEI CHI, Study on the Influence of Oeration Parameters in Flash Smelting Furnace Using Virtual Simulation System [J], Transactions of Nonferrous Metals Society of China, PERWZ-TELLO, MANUEL, HONG YONG SOHN, Exerimental Investigation and Three- Dimensional Comutational Fluid-dynamics Modeling of the flash converting Furnace Shaft: art II: Formulation of Three-Dimensional Comutational Fluid-Dynamics Model Incororating the article-cloud Descrition[J], Metallurgical and Materials Transactions B, 001, Vol3b(5), AHOKAINEN, T., JOKILAAKSO, A., Numerical Simulation of the Outokumu Flash Smelting Furnace Reaction Shaft [J], Canadian Metallurgical Quaterly. Vol.37(3-4), 1998, VARNAS. S.R., N. KEMORI, and P.T.L. KOH, Evaluation of Nickel Flash Smelting Through Piloting and Simulation [J], Metallurgical and Materials Transactions B, Vol. 9B(1). 1998,

6 160