A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace （RHF）. In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account...A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace （RHF）. In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account. The behaviors of iron metallization and dezincification were analyzed by the numerical method, which was validated by experimental data of the direct reduction of pellets in a Si-Mo furnace. The simulation results show that if the production targets of iron metallization and dezincification are up to 80% and 90%, respectively, the furnace temperature for high-temperature sections must be set higher than 1300~ C. Moreover, an undersupply of secondary air by 20% will lead to a decline in iron metallization rate of discharged pellets by 10% and a decrease in dezincing rate by 13%. In addition, if the residence time of pellets in the furnace is over 20 min, its further extension will hardly lead to an obvious increase in production indexes under the same furnace temperature curve.展开更多
The reduction process of MgO-fluxed pellets was investigated and compared with traditional acidic pellets in this paper. Based on the piston flow concept and experimental data, a kinetic model fitting for the gas-soli...The reduction process of MgO-fluxed pellets was investigated and compared with traditional acidic pellets in this paper. Based on the piston flow concept and experimental data, a kinetic model fitting for the gas-solid phase reduction of pellets in tubular reactors （blast furnace, BF） was built up, and the equations of reduction reaction rate were given for pellets. A series of reduction experiments of pellets were carried out to verify the model. As a result, the experimental data and calculated result were fitted well. Therefore, this model can well describe the gas-solid phase reduction process and calculate the reduction reaction rate of pellets. Besides, it can give a better explanation that the reduction reaction rate （reducibility） of MgO-fluxed pellets is better than that of traditional acidic pellets in BF.展开更多
The optimized use of MgO flux in the agglomeration of high-chromium vanadium-titanium magnetite was investigated system- atically through sinter and pellet experiments. MgO was added in the form of magnesite. When the...The optimized use of MgO flux in the agglomeration of high-chromium vanadium-titanium magnetite was investigated system- atically through sinter and pellet experiments. MgO was added in the form of magnesite. When the content of MgO in the sinter was in- creased from 1.95wt% to 2.63wt%, the low-temperature reduction degradation index increased from 80.57% to 82.71%. When the content of MgO in the pellet was increased from 1.14wt% to 2.40wt%, the reduction swelling index decreased from 15.2% to 8.6%; however, the com- pressive strength of the oxidized pellet decreased dramatically and it was 1985 N with an MgO content of 1.14wt%. This compressive strength does not satisfy the requirements for blast-furnace production. When all of the aforementioned results were taken into account, the sinter with a high MgO content （2.63wt%） matching the pellet with a low MgO content （less than 1.14wt%） was the rational burden structure for smelting high-chromium vanadium-titanium magnetite in blast furnaces.展开更多
Lump lime as a fiux material in a basic oxygen furnace （BOF） often creates problems in operation due to its high melting point, poor dissolution property, hygroscopic nature, and fines generation tendency. To allevi...Lump lime as a fiux material in a basic oxygen furnace （BOF） often creates problems in operation due to its high melting point, poor dissolution property, hygroscopic nature, and fines generation tendency. To alleviate these problems, fluxed lime iron oxide pellets （FLIP） containing 30% CaO were developed in this study using waste iron oxide fines and lime. The suitable handling strengths of the pellet （crushing strength： 300 N; drop strength： 130 times） of FLIP were developed by treating with CO2 or industrial waste gas at room temperature, while no separate binders were used. When the pellet was added into hot metal bath （carbon-containing molten iron）, it was decomposed, melted, and transformed to produce low melting oxidizing slag, because it is a combination of main CaO and Fe2O3. This slag is suitable for facilitating P and C removal in refining. Furthermore, the pellet enhances waste utilization and use of CO2 in waste gas. In this article, emphasis is given on studying the behavior of these pellets in hot metal bath during melting and refining along with thermodynamics and kinetics analysis. The observed behaviors of the pellet in hot metal bath confirm that it is suitable and beneficial for use in BOF and replaces lump lime.展开更多
Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was con...Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was constructed to study the reduction kinetics of iron oxides and ZnO in the dust composite pellets. It was validated by comparing the calculated values with experimental results. The effects of furnace temperature, pellet radius, and pellet porosity on the reduction were investigated by the model. It is shown that furnace temperature has obvious influence on both of the reduction of iron oxides and ZnO, but the influence of pellet radius and porosity is much smaller. Model calculations suggest that both of the reduction of iron oxides and ZnO are under mixed control with interface reactions and Boudouard reaction in the early stage, but only with interface reactions in the later stage.展开更多
A method of preparing iron carbide by reducing magnetite pellets with H2-CO mixtures is presented. The results show that an over 90 percent conversion ratio of iron carbide can be reached at 973 K and 1073 K under the...A method of preparing iron carbide by reducing magnetite pellets with H2-CO mixtures is presented. The results show that an over 90 percent conversion ratio of iron carbide can be reached at 973 K and 1073 K under the suitable atmosphere. The reaction process to prepare iron carbide from magnetite pellets can be divided into two stages: reduction of magnetite pellets and carburization of reduction products. The carbon deposition has a great influence on the formation of iron carbide. In order to get a high conversion ratio of iron carbide, the relative weight loss value (m) should be controlled between 0.5 to 0.8.展开更多
The non-isothermal reduction mechanisms of pyrite cinder-carbon composite pellets were studied at laboratory scale under argon （Ar） atmosphere. The composite pellets as well as the specimens of separate layers conta...The non-isothermal reduction mechanisms of pyrite cinder-carbon composite pellets were studied at laboratory scale under argon （Ar） atmosphere. The composite pellets as well as the specimens of separate layers containing pyrite cinder and coal were tested. The degree of reduction was measured by mass loss. The microstmctures of the reduced composite pellets were characterized by scanning electron mi- croscopy （SEM）. It is found that the reduction processes of the composite pellets may be divided into four stages： reduction via CO and H2 from volatiles in coal at 673-973 K, reduction via H2 and C produced by cracking of hydrocarbon at 973-1123 K, direct reduction by carbon via gaseous intermediates at 1123-1323 K, and direct reduction by carbon at above 1323 K. Corresponding to the four stages, the apparent activation energies （E） for the reduction of the composite pellets are 86.26, 78.54, 72.01, and 203.65 kJ.mol-1, respectively.展开更多
Analytical-reagent-grade Al2O3 was added to magnetite ore during the process of pelletizing, and the methods of mercury intru-sion, scanning electron microscopy, and image processing were used to investigate the effec...Analytical-reagent-grade Al2O3 was added to magnetite ore during the process of pelletizing, and the methods of mercury intru-sion, scanning electron microscopy, and image processing were used to investigate the effect of Al2O3 on the compressive strength of the pellets. The results showed that, as the Al2O3 content increased, the compressive strength of the pellets increased slightly and then decreased gradually. When a small amount of Al2O3 was added to the pellets, the Al2O3 combined with fayalite （2FeO＆#183;SiO2） and the aluminosilicate （2FeO＆#183;2Al2O3＆#183;5SiO2） was generated, which releases some iron oxide and reduces the inhibition of fayalite to the solid phase of consolidation. When Al2O3 increased sequentially, high melting point of Al2O3 particles hinder the oxidation of Fe3O4 and the recrystallization of Fe2O3, making the internal porosity of the pellets increase, which leads to the decrease in compressive strength of the pellets.展开更多
A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions in...A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm （TDMA）. In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.展开更多
Direct reduction of low-grade lateritic bauxite was studied at high temperature to recover Fe and beneficiate AlzO3 slag. The re- sults show that a metallization rate of 97.9% and a nugget recovery rate of 85.1% can b...Direct reduction of low-grade lateritic bauxite was studied at high temperature to recover Fe and beneficiate AlzO3 slag. The re- sults show that a metallization rate of 97.9% and a nugget recovery rate of 85.1% can be achieved when the reducing and melting tempera- tures are 1350 and 1480℃, respectively. Moreover, a higher-grade calcium aluminate slag （A1203 = 50.52wt%） can also be obtained, which is mainly composed of ct-A1203, hercynite （FeAI：O4）, and gehlenite （Ca2A12SiO7）. In addition, high-quality iron nuggets have been produced from low-grade lateritic bauxite. The nugget is mainly composed of iron （93.82wt%） and carbon （3.86wt%）, with almost no gangue （slag）.展开更多
Iron nugget and boron-rich slag can be obtained in a short time through high-temperature reduction of boron- bearing iron concentrate by carbonaceous material, both of which are agglomerated together as a carbon compo...Iron nugget and boron-rich slag can be obtained in a short time through high-temperature reduction of boron- bearing iron concentrate by carbonaceous material, both of which are agglomerated together as a carbon composite pellet. This is a novel flow sheet for the comprehensive utilization of boron-bearing iron concentrate to produce a new kind of man-made boron ore. The effect of reducing agent species （i.e., carbon species） on the reduction and melting process of the composite pellet was investigated at a laboratory scale in the present work. The results show that, the reduction rate of the composite pellet increases from bituminite, anthracite, to coke at temperatures ranging from 950 to 1300~C. Reduction temperature has an important effect on the microstructure of reduced pellets. Carbon species also affects the behavior of reduced metallic iron particles. The anthracite-bearing composite pellet melts faster than the bituminite- bearing composite pellet, and the coke-bearing composite pellet cannot melt due to the high fusion point of coke ash. With anthracite as the reducing agent, the recovery rates of iron and boron are 96.5% and 95.7%, respectively. This work can help us get a further understanding of the new process mechanism.展开更多
基金financially supported by the National Key Basic Research and Development Program of China(No. 2012CB720405)
文摘A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace （RHF）. In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account. The behaviors of iron metallization and dezincification were analyzed by the numerical method, which was validated by experimental data of the direct reduction of pellets in a Si-Mo furnace. The simulation results show that if the production targets of iron metallization and dezincification are up to 80% and 90%, respectively, the furnace temperature for high-temperature sections must be set higher than 1300~ C. Moreover, an undersupply of secondary air by 20% will lead to a decline in iron metallization rate of discharged pellets by 10% and a decrease in dezincing rate by 13%. In addition, if the residence time of pellets in the furnace is over 20 min, its further extension will hardly lead to an obvious increase in production indexes under the same furnace temperature curve.
基金financially supported by the Natural Science Foundation of China(Nos.51374061 and 51074040)
文摘The reduction process of MgO-fluxed pellets was investigated and compared with traditional acidic pellets in this paper. Based on the piston flow concept and experimental data, a kinetic model fitting for the gas-solid phase reduction of pellets in tubular reactors （blast furnace, BF） was built up, and the equations of reduction reaction rate were given for pellets. A series of reduction experiments of pellets were carried out to verify the model. As a result, the experimental data and calculated result were fitted well. Therefore, this model can well describe the gas-solid phase reduction process and calculate the reduction reaction rate of pellets. Besides, it can give a better explanation that the reduction reaction rate （reducibility） of MgO-fluxed pellets is better than that of traditional acidic pellets in BF.
基金financially supported by the National Natural Science Foundation of China (Major Program, No. 51090384)the National High Technology Research and Development Program of China (Nos. 2012AA062302 and 2012AA062304)+1 种基金the Fundamental Research Funds for Central Universities (Nos. N110202001 and N130602003)the Northeastern University Cultivation Project of Excellent Doctoral Dissertation
文摘The optimized use of MgO flux in the agglomeration of high-chromium vanadium-titanium magnetite was investigated system- atically through sinter and pellet experiments. MgO was added in the form of magnesite. When the content of MgO in the sinter was in- creased from 1.95wt% to 2.63wt%, the low-temperature reduction degradation index increased from 80.57% to 82.71%. When the content of MgO in the pellet was increased from 1.14wt% to 2.40wt%, the reduction swelling index decreased from 15.2% to 8.6%; however, the com- pressive strength of the oxidized pellet decreased dramatically and it was 1985 N with an MgO content of 1.14wt%. This compressive strength does not satisfy the requirements for blast-furnace production. When all of the aforementioned results were taken into account, the sinter with a high MgO content （2.63wt%） matching the pellet with a low MgO content （less than 1.14wt%） was the rational burden structure for smelting high-chromium vanadium-titanium magnetite in blast furnaces.
基金financial assistance received from the Department of Science and Technology (Government of India) for carrying out this investigation
文摘Lump lime as a fiux material in a basic oxygen furnace （BOF） often creates problems in operation due to its high melting point, poor dissolution property, hygroscopic nature, and fines generation tendency. To alleviate these problems, fluxed lime iron oxide pellets （FLIP） containing 30% CaO were developed in this study using waste iron oxide fines and lime. The suitable handling strengths of the pellet （crushing strength： 300 N; drop strength： 130 times） of FLIP were developed by treating with CO2 or industrial waste gas at room temperature, while no separate binders were used. When the pellet was added into hot metal bath （carbon-containing molten iron）, it was decomposed, melted, and transformed to produce low melting oxidizing slag, because it is a combination of main CaO and Fe2O3. This slag is suitable for facilitating P and C removal in refining. Furthermore, the pellet enhances waste utilization and use of CO2 in waste gas. In this article, emphasis is given on studying the behavior of these pellets in hot metal bath during melting and refining along with thermodynamics and kinetics analysis. The observed behaviors of the pellet in hot metal bath confirm that it is suitable and beneficial for use in BOF and replaces lump lime.
基金financially supported by the National Basic Research Program of China (No. 2012CB720401)the National Key Technology Research and Development Program of China (No. 2011BAC01B02)
文摘Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was constructed to study the reduction kinetics of iron oxides and ZnO in the dust composite pellets. It was validated by comparing the calculated values with experimental results. The effects of furnace temperature, pellet radius, and pellet porosity on the reduction were investigated by the model. It is shown that furnace temperature has obvious influence on both of the reduction of iron oxides and ZnO, but the influence of pellet radius and porosity is much smaller. Model calculations suggest that both of the reduction of iron oxides and ZnO are under mixed control with interface reactions and Boudouard reaction in the early stage, but only with interface reactions in the later stage.
文摘A method of preparing iron carbide by reducing magnetite pellets with H2-CO mixtures is presented. The results show that an over 90 percent conversion ratio of iron carbide can be reached at 973 K and 1073 K under the suitable atmosphere. The reaction process to prepare iron carbide from magnetite pellets can be divided into two stages: reduction of magnetite pellets and carburization of reduction products. The carbon deposition has a great influence on the formation of iron carbide. In order to get a high conversion ratio of iron carbide, the relative weight loss value (m) should be controlled between 0.5 to 0.8.
文摘The non-isothermal reduction mechanisms of pyrite cinder-carbon composite pellets were studied at laboratory scale under argon （Ar） atmosphere. The composite pellets as well as the specimens of separate layers containing pyrite cinder and coal were tested. The degree of reduction was measured by mass loss. The microstmctures of the reduced composite pellets were characterized by scanning electron mi- croscopy （SEM）. It is found that the reduction processes of the composite pellets may be divided into four stages： reduction via CO and H2 from volatiles in coal at 673-973 K, reduction via H2 and C produced by cracking of hydrocarbon at 973-1123 K, direct reduction by carbon via gaseous intermediates at 1123-1323 K, and direct reduction by carbon at above 1323 K. Corresponding to the four stages, the apparent activation energies （E） for the reduction of the composite pellets are 86.26, 78.54, 72.01, and 203.65 kJ.mol-1, respectively.
基金financially supported by the National Key Basic Research and Development Program of China(No.2011BAC01B02)
文摘Analytical-reagent-grade Al2O3 was added to magnetite ore during the process of pelletizing, and the methods of mercury intru-sion, scanning electron microscopy, and image processing were used to investigate the effect of Al2O3 on the compressive strength of the pellets. The results showed that, as the Al2O3 content increased, the compressive strength of the pellets increased slightly and then decreased gradually. When a small amount of Al2O3 was added to the pellets, the Al2O3 combined with fayalite （2FeO＆#183;SiO2） and the aluminosilicate （2FeO＆#183;2Al2O3＆#183;5SiO2） was generated, which releases some iron oxide and reduces the inhibition of fayalite to the solid phase of consolidation. When Al2O3 increased sequentially, high melting point of Al2O3 particles hinder the oxidation of Fe3O4 and the recrystallization of Fe2O3, making the internal porosity of the pellets increase, which leads to the decrease in compressive strength of the pellets.
基金the Fundamen-tal Research Funds for Central Universities(No.FRF-SD-12-013A)the State Key Laboratory of Advanced Metallurgy,China
文摘A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm （TDMA）. In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.
基金financially supported by the International Scientific and Technological Cooperation and Exchange Projects of China (No. 2013DFG50640)
文摘Direct reduction of low-grade lateritic bauxite was studied at high temperature to recover Fe and beneficiate AlzO3 slag. The re- sults show that a metallization rate of 97.9% and a nugget recovery rate of 85.1% can be achieved when the reducing and melting tempera- tures are 1350 and 1480℃, respectively. Moreover, a higher-grade calcium aluminate slag （A1203 = 50.52wt%） can also be obtained, which is mainly composed of ct-A1203, hercynite （FeAI：O4）, and gehlenite （Ca2A12SiO7）. In addition, high-quality iron nuggets have been produced from low-grade lateritic bauxite. The nugget is mainly composed of iron （93.82wt%） and carbon （3.86wt%）, with almost no gangue （slag）.
基金support by the National Natural Science Foundation of China(No.51274033)
文摘Iron nugget and boron-rich slag can be obtained in a short time through high-temperature reduction of boron- bearing iron concentrate by carbonaceous material, both of which are agglomerated together as a carbon composite pellet. This is a novel flow sheet for the comprehensive utilization of boron-bearing iron concentrate to produce a new kind of man-made boron ore. The effect of reducing agent species （i.e., carbon species） on the reduction and melting process of the composite pellet was investigated at a laboratory scale in the present work. The results show that, the reduction rate of the composite pellet increases from bituminite, anthracite, to coke at temperatures ranging from 950 to 1300~C. Reduction temperature has an important effect on the microstructure of reduced pellets. Carbon species also affects the behavior of reduced metallic iron particles. The anthracite-bearing composite pellet melts faster than the bituminite- bearing composite pellet, and the coke-bearing composite pellet cannot melt due to the high fusion point of coke ash. With anthracite as the reducing agent, the recovery rates of iron and boron are 96.5% and 95.7%, respectively. This work can help us get a further understanding of the new process mechanism.
