The iron- and steelmaking is the largest energy consuming in the industrial sectors. The high ene... more The iron- and steelmaking is the largest energy consuming in the industrial sectors. The high energy consumption is associated with emission of CO2 and other pollutants. The most common ironmaking process used in the world is the blast furnace which contributes around 70 % of the world’s steel production. Recently, blast furnace has undergone tremendous modifications and improvements to reduce the energy consumption and CO2 emissions. The modifications are being focused on two main approaches: (1) development of top charging materials and (2) injections of auxiliary fuels through blast furnace tuyeres. The present chapter will discuss the recent modifications and development in the top charging burden and how it could participate in minimizing the energy consumption and CO2 emissions for more efficient and sustainable iron and steel industry. The injection of auxiliary fuels will be discussed in details in another chapter. The enhancement of burden material quality and its charging mode into the blast furnace has resulted in a smooth and efficient operation. Recently, the usage of nut coke in the modern blast furnace is accompanied by higher production and lower reducing agent rates. An efficient recycling of in-plant fines by its conversion into briquettes with proper mechanical strength is applied in some blast furnaces to exploit the iron- and carbon-rich residues. Nowadays, novel composite agglomerates consist of iron ores and alternative carbonaceous materials represent a new trend for low-carbon blast furnace with lower dependence on the conventional burden materials. The recent investigations demonstrated that the novel composites are able to reduce the thermal reserve zone temperature in the blast furnace and consequently enhance the carbon utilization through its higher reactivity compared to fossil fuels. The top charging of bio-reducers and hydrogen-rich materials into the blast furnace is one of interesting innovations to mitigate the CO2 emissions. Although some of previous approaches are recently applied in the modern blast furnace, others are still under intensive discussions to enhance its implementations.
Abstract Pure Fe2O3 and Fe2O3 doped with 2, 4, and 6 mass% of MnO2 (>99%) compacts annealed at... more Abstract Pure Fe2O3 and Fe2O3 doped with 2, 4, and 6 mass% of MnO2 (>99%) compacts annealed at 1473 K for 6 h were isothermally reduced with H2 at 1073–1373 K. The O2 weight loss resulted from the reduction of compacts was continuously recorded as a function of time using thermogravimetric analysis (TGA). High pressure mercury porosimeter, optical and scanning electron microscopes, X-ray phase analysis and vibrating sample magnetometer were used to characterise both the annealed and reduced samples. In MnO2 containing samples, manganese ferrite (MnFe2O4) was identified. The rate of reduction of pure and doped compacts increased with temperature and decreased with the increase in MnO2 content. Unlike in pure compacts, the reduction of MnO2 containing samples was not completed and stopped at different extents depending on MnO2 (mass%). At initial reduction stages, the decrease in the rate was due to the presence of poorly reducible manganese ferrite (MnFe2O4) phase which was partially reduced to iron manganese oxide (FeO0.899, MnO0.101) at the final stages. The reduction mechanism was predicted from the correlation between the reduction kinetics and the structure of partially reduced samples at different temperatures. The reduction of pure and doped samples was controlled by a combined effect of interfacial chemical reaction and gaseous diffusion mechanism at their initial stages. At final stages, the interfacial chemical reaction was the rate controlling mechanism.
ABSTRACT One of the most important factors to increase the economic efficiency of the blast furna... more ABSTRACT One of the most important factors to increase the economic efficiency of the blast furnace process is to reduced coke losses (undersieve product known as nut coke). In recent years there has been increased interest in mixing nut coke in the sinter layers. In order to clarify the influence of nut coke on sinter reducibility, sinter and sinter–nut coke mixtures were isothermally reduced with 30%CO–70%N2 at 1173–1523 K using a muffle furnace supported by an on-line gas analyser. Reflected light microscopy, scanning electron microscopy and X-ray technique were used to characterise the microstructure and the different phases developed in the original and reduced sinter. Sinter reduced without nut coke participation exhibited reduction retardation at elevated temperatures (>1373 K) while the presence of nut coke prevented such phenomena. The rate controlling mechanism of sinter and sinter–nut coke mixture was predicted from the correlation between apparent activation energy calculations, mathematical modelling derived from gas–solid reaction model and microstructure examination.
In the current study, a factorial design is used to investigate the effect of total iron and sili... more In the current study, a factorial design is used to investigate the effect of total iron and silica on the metallurgical performance of different grades of manganese ores. The derived mathematical formulations are applied to estimate the reduction disintegration index (RDI+6.3, RDI+3.15, and RDI−0.5), reduction index (total reduction index (RIT), manganese reduction index (RIM), and iron reduction index (RIF)), and softening-melting property (start of softening (TS1), end of softening (TS2), start of melting (Tm1), and end of melting (Tm2)) of manganese ores. The RDI+6.3 and RDI+3.15 are increased with the individual effect of SiO2 and the interaction effect of iron with silica, while they are decreased as the total iron increased. The high-Fe high-SiO2 manganese ore showed the highest RIT and RIF. The RIM was almost identical in all manganese ores. The presence of high content of SiO2 resulted in a narrow softening range (62–83°C), while the high-Fe high-SiO2 manganese ore exhibite...
Minimizing the coke consumption in the blast furnace is the key to achieve both ecological and ec... more Minimizing the coke consumption in the blast furnace is the key to achieve both ecological and economic aspects by reducing the CO2 emissions and the overall hot metal production cost. Complementary injection of cheaper auxiliary fuels and waste materials into the blast furnace via tuyeres has been greatly modified in the recent years to reduce the expensive coke consumption. Nowadays, most of the blast furnaces all over the world use pulverized coal at different injection rates. The greatest influence of coal injection on lowering the production cost and enhancement of hot metal production rate has led to further investigations on the injection of various other auxiliary materials including coke oven gas, converter gas, blast furnace dust, waste plastics, charcoal and torrefied biomass. In addition, trials on the injection of iron ore fines, low reduced iron and BOF slag have been recently studied. The injection rate of auxiliary materials into the blast furnace should be optimized to attain the minimum coke consumption and stable operation. The present chapter will discuss the influence of various materials injection on the blast furnace operation. The injection limit and changing of the blast furnace operating conditions, hot metal quality and coke consumption will be explained based on the experimental trials and mathematical modelling.
Page 1. Volume Changes of Iron Oxide Compacts under Isothermal Reduction Conditions Compacts made... more Page 1. Volume Changes of Iron Oxide Compacts under Isothermal Reduction Conditions Compacts made from chemically grade Fe2O3 were fired at 1473K for 6 hrs. The fired compacts were isothermally reduced either by hydrogen or carbon monoxide at 10731373K. ...
Numerical prediction is performed on the reduction of wüstite under simulated blast furnace condi... more Numerical prediction is performed on the reduction of wüstite under simulated blast furnace conditions using factorial design approach. Wüstite sinter samples with different basicity (0.5, 1.0, and 2.0) are reduced with a gas mixture consisting of 30% CO, 10% H2, 5% CO2, and 55% N2 at 950–1100°C. In all cases, the reduction degree of wüstite increased with basicity and temperature. A 23 factorial design is applied to derive a regression model based on the experimental data of acidic (CaO/SiO2 = 0.5) and basic (CaO/SiO2 = 2.0) wüstite which is reduced at 950°C and 1100°C for 5 and 35 min. The developed mathematical model is applied to predict the reduction degree of wüstite at different basicity (0.5, 1.0, and 2.0), interval of time (5–35 min), and temperatures (950, 1000, 1050°C, and 1100°C). In general, the results of the driven models are found to be in good agreement with the experimental data of reduction of wüstite in many cases. The MATLAB program is used to carry out the requ...
The foundry industry is currently facing challenges to reduce the environmental impacts from appl... more The foundry industry is currently facing challenges to reduce the environmental impacts from application of fossil fuels. Replacing foundry coke with alternative renewable carbon sources can lead to significant decrease in fossil fuel consumption and fossil CO2 emission. The low bulk density, low energy density, low mechanical strength and the high reactivity of biocarbon materials are the main factors limiting their efficient implementation in a cupola furnace. The current study aimed at designing, optimizing and developing briquettes containing biocarbon, namely, biocarbon briquettes for an efficient use in cupola furnace. Laboratory hydraulic press with compaction pressure of about 160 MPa and stainless-steel moulds (Ø = 40 mm and 70 mm) were used for compaction. The density, heating value, energy density, mechanical strength and reactivity of biocarbon briquettes were measured and evaluated. The compressive strength and splitting tensile strength of biocarbon briquettes were mea...
In ore-based steelmaking, blast furnace (BF) dust is generally recycled to the BF via the sinter ... more In ore-based steelmaking, blast furnace (BF) dust is generally recycled to the BF via the sinter or cold-bonded briquettes and injection. In order to recycle the BF sludge to the BF, the sludge has to be upgraded, removing zinc. The literature reports cases of recycling the low-zinc fraction of upgraded BF sludge to the BF. However, research towards recycling of the high-zinc fraction of BF sludge within the ore-based steel plant is limited. In the present paper, the high-zinc fraction of tornado-treated BF sludge was incorporated in self-reducing cold-bonded briquettes and pellets. Each type of agglomerate was individually subjected to technical-scale smelting reduction experiments aiming to study the feasibility of recycling in-plant residues to the hot metal (HM) desulfurization (deS) plant. The endothermic reactions within the briquettes decreased the heating and reduction rate leaving the briquettes unreduced and unmelted. The pellets were completely reduced within eight minute...
The H2/CO ratio in the reducing gas of iron ore pellets is one of the most important factors that... more The H2/CO ratio in the reducing gas of iron ore pellets is one of the most important factors that affect the efficiency of the direct reduction processes. The magnitude effect of this ratio on the reduction is still not clear compared with the reduction time and temperature. In the current study, a 2 3 factorial design was used to elucidate the reduction potential of different ratios of H2/CO in the reduction process at different temperatures and time. A regression model has been developed based on the experimental data of iron ore pellets that reduced with simulated Midrex, Hyl, and Syngas at 850 o C and 1050 o C. The reduction time was selected at 1.0 and 15 minutes in all trails. The H2/CO ratios in the applied reducing gas were equal to 0.4, 1.0, 1.6, and 2.6. The results showed that the reduction time has the highest positive effect followed by the applied temperature and then H2/CO ratio. The mutual interaction combination between time and temperature was higher than that between H2/CO ratio with either time or temperature. The lowest positive effect on the reduction processes was exhibited by the mutual interaction between all of operational parameters which are represented in H2/CO ratio, temperature, and time. The developed mathematical model was tested against various experimental data to estimate its efficiency in the prediction of the reduction degree. The predicted values of the reduction process by the current mathematical model were found in a good agreement with experimental results in many cases. The Matlab program was used to carry out the required calculations.
ABSTRACT The mitigation of CO2 emissions has become a global priority in the iron and steel indus... more ABSTRACT The mitigation of CO2 emissions has become a global priority in the iron and steel industry. One promising solution to decrease CO2 emissions is recycling of the blast furnace top gas to be reused in the reduction of iron oxide. In this study, iron oxide compacts were reduced isothermally with simulated conventional blast furnace top gas (BFTG: 20%CO, 20%CO2, 5%H2, 55%N2) at 700–900uC using a thermogravimetric technique. The reduction reached 30–34% depending on the applied temperature. The compacts were reduced completely to wu¨ stite (Fe0?925O or Fe0?971O) with a few grains of metallic iron, which appeared only at 900uC. To investigate the reduction behaviour at the later stages, the compacts reduced with BFTG at 900uC were followed by isothermal reduction with simulated blast furnace shaft gas (BFSG: 30%CO, 5%CO2, 10%H2, 55%N2) at 950–1100uC. The total reduction extents were increased to 66–90% at 950–1100uC respectively. The remaining unreduced wu¨ stite (Fe0?974O) has a higher Fe/O ratio compared with that formed by reduction with BFTG. At the initial stages of reduction, the rate controlling mechanism was interfacial chemical reaction, while at the later stages, solid state diffusion was the rate controlling mechanism. Reflected light microscope, scanning electron microscope, X-ray diffraction and Poresizer techniques are used to estimate the reduction kinetic and mechanisms.
ABSTRACT 1300uC and prereduced at 900uC using low potential reducing gas (LPRG; 20%CO, 20%CO2, 5%... more ABSTRACT 1300uC and prereduced at 900uC using low potential reducing gas (LPRG; 20%CO, 20%CO2, 5%H2 and 55%N2). The prereduced sinters were subsequently reduced to metallic iron at 950– 1100uC using relatively high potential reducing gas (HPRG; 30%CO, 5%CO2, 10%H2 and 55%N2). Both LPRG and HPRG were selected to simulate the gas composition in the blast furnace upper and lower shaft respectively. High pressure mercury porosimeter, X-ray phase analysis, optical and scanning electron microscope were used for the analysis of the prepared and reduced sinters. In the original basic sinter, calcium ferrite (CaFe2O4) and dicalcium silicate (Ca2SiO4) phases were identified as well as the main Fe2O3 phase, whereas wollastonite [Ca2?87Fe0?13(SiO3)3] and silica (SiO2) were formed in the acidic sinter. The prereduction in sinters with LPRG at 900uC resulted in the formation of wu¨ stite (Fe0?902O) phase. The subsequent reduction in wu¨ stite sinters to metallic iron using HPRG at 950–1100uC was found to be the highest for basic sinter and the least for acidic sinter. The higher reduction rate of basic sinter was attributed to the enhancement of wu¨ stite reducibility through the formation of calcium ferrites. The lower reduction rate of wu¨ stite in acidic sinter was attributed to the formation of hard reducible fayalite (Fe2SiO4) and ferrobustamite [(Ca0?5Fe0?5)SiO3] phases. The rate controlling mechanism during the reduction process was estimated by the correlation between apparent activation energy calculation and microstructure investigations.
ABSTRACT Fe2O3/C compacts prepared by mixing of nanosized Fe2O3 (40–150 nm) with charcoal in a mo... more ABSTRACT Fe2O3/C compacts prepared by mixing of nanosized Fe2O3 (40–150 nm) with charcoal in a molar ratio of 1 : 4 were isothermally reduced at 950–1100uC in argon gas flow. The rate of reduction was calculated from the direct measurements of the mass–loss using TG technique. In addition, the QMS gas analyser was used to monitor CO and CO2 concentrations in the off gases. The different phases developed in the composites were identified by X-ray diffraction and their structures were microscopically examined. The effect of temperature and particle size of Fe2O3 on the reduction rates was studied. The reduction of Fe2O3 was found to proceed in a stepwise manner up to metallic iron. Alternatively, the carbon solution loss reaction resulted from the gasification of charcoal plays a significant role in the carbothermic reduction process. Incubation periods were detected in QMS analysis at the beginning of reduction process. The charcoal volatiles interfered with the O2 weight loss measurements, upon applying TG technique, resulting higher values of total weight loss than that measured by QMS. Comparison of the reduction testing techniques shows the differences in the actual reduction extents. The reduction kinetics were correlated with the microstructure of the reduced products and directed to the elucidation of the reduction mechanism.
The iron- and steelmaking is the largest energy consuming in the industrial sectors. The high ene... more The iron- and steelmaking is the largest energy consuming in the industrial sectors. The high energy consumption is associated with emission of CO2 and other pollutants. The most common ironmaking process used in the world is the blast furnace which contributes around 70 % of the world’s steel production. Recently, blast furnace has undergone tremendous modifications and improvements to reduce the energy consumption and CO2 emissions. The modifications are being focused on two main approaches: (1) development of top charging materials and (2) injections of auxiliary fuels through blast furnace tuyeres. The present chapter will discuss the recent modifications and development in the top charging burden and how it could participate in minimizing the energy consumption and CO2 emissions for more efficient and sustainable iron and steel industry. The injection of auxiliary fuels will be discussed in details in another chapter. The enhancement of burden material quality and its charging mode into the blast furnace has resulted in a smooth and efficient operation. Recently, the usage of nut coke in the modern blast furnace is accompanied by higher production and lower reducing agent rates. An efficient recycling of in-plant fines by its conversion into briquettes with proper mechanical strength is applied in some blast furnaces to exploit the iron- and carbon-rich residues. Nowadays, novel composite agglomerates consist of iron ores and alternative carbonaceous materials represent a new trend for low-carbon blast furnace with lower dependence on the conventional burden materials. The recent investigations demonstrated that the novel composites are able to reduce the thermal reserve zone temperature in the blast furnace and consequently enhance the carbon utilization through its higher reactivity compared to fossil fuels. The top charging of bio-reducers and hydrogen-rich materials into the blast furnace is one of interesting innovations to mitigate the CO2 emissions. Although some of previous approaches are recently applied in the modern blast furnace, others are still under intensive discussions to enhance its implementations.
Abstract Pure Fe2O3 and Fe2O3 doped with 2, 4, and 6 mass% of MnO2 (>99%) compacts annealed at... more Abstract Pure Fe2O3 and Fe2O3 doped with 2, 4, and 6 mass% of MnO2 (>99%) compacts annealed at 1473 K for 6 h were isothermally reduced with H2 at 1073–1373 K. The O2 weight loss resulted from the reduction of compacts was continuously recorded as a function of time using thermogravimetric analysis (TGA). High pressure mercury porosimeter, optical and scanning electron microscopes, X-ray phase analysis and vibrating sample magnetometer were used to characterise both the annealed and reduced samples. In MnO2 containing samples, manganese ferrite (MnFe2O4) was identified. The rate of reduction of pure and doped compacts increased with temperature and decreased with the increase in MnO2 content. Unlike in pure compacts, the reduction of MnO2 containing samples was not completed and stopped at different extents depending on MnO2 (mass%). At initial reduction stages, the decrease in the rate was due to the presence of poorly reducible manganese ferrite (MnFe2O4) phase which was partially reduced to iron manganese oxide (FeO0.899, MnO0.101) at the final stages. The reduction mechanism was predicted from the correlation between the reduction kinetics and the structure of partially reduced samples at different temperatures. The reduction of pure and doped samples was controlled by a combined effect of interfacial chemical reaction and gaseous diffusion mechanism at their initial stages. At final stages, the interfacial chemical reaction was the rate controlling mechanism.
ABSTRACT One of the most important factors to increase the economic efficiency of the blast furna... more ABSTRACT One of the most important factors to increase the economic efficiency of the blast furnace process is to reduced coke losses (undersieve product known as nut coke). In recent years there has been increased interest in mixing nut coke in the sinter layers. In order to clarify the influence of nut coke on sinter reducibility, sinter and sinter–nut coke mixtures were isothermally reduced with 30%CO–70%N2 at 1173–1523 K using a muffle furnace supported by an on-line gas analyser. Reflected light microscopy, scanning electron microscopy and X-ray technique were used to characterise the microstructure and the different phases developed in the original and reduced sinter. Sinter reduced without nut coke participation exhibited reduction retardation at elevated temperatures (>1373 K) while the presence of nut coke prevented such phenomena. The rate controlling mechanism of sinter and sinter–nut coke mixture was predicted from the correlation between apparent activation energy calculations, mathematical modelling derived from gas–solid reaction model and microstructure examination.
In the current study, a factorial design is used to investigate the effect of total iron and sili... more In the current study, a factorial design is used to investigate the effect of total iron and silica on the metallurgical performance of different grades of manganese ores. The derived mathematical formulations are applied to estimate the reduction disintegration index (RDI+6.3, RDI+3.15, and RDI−0.5), reduction index (total reduction index (RIT), manganese reduction index (RIM), and iron reduction index (RIF)), and softening-melting property (start of softening (TS1), end of softening (TS2), start of melting (Tm1), and end of melting (Tm2)) of manganese ores. The RDI+6.3 and RDI+3.15 are increased with the individual effect of SiO2 and the interaction effect of iron with silica, while they are decreased as the total iron increased. The high-Fe high-SiO2 manganese ore showed the highest RIT and RIF. The RIM was almost identical in all manganese ores. The presence of high content of SiO2 resulted in a narrow softening range (62–83°C), while the high-Fe high-SiO2 manganese ore exhibite...
Minimizing the coke consumption in the blast furnace is the key to achieve both ecological and ec... more Minimizing the coke consumption in the blast furnace is the key to achieve both ecological and economic aspects by reducing the CO2 emissions and the overall hot metal production cost. Complementary injection of cheaper auxiliary fuels and waste materials into the blast furnace via tuyeres has been greatly modified in the recent years to reduce the expensive coke consumption. Nowadays, most of the blast furnaces all over the world use pulverized coal at different injection rates. The greatest influence of coal injection on lowering the production cost and enhancement of hot metal production rate has led to further investigations on the injection of various other auxiliary materials including coke oven gas, converter gas, blast furnace dust, waste plastics, charcoal and torrefied biomass. In addition, trials on the injection of iron ore fines, low reduced iron and BOF slag have been recently studied. The injection rate of auxiliary materials into the blast furnace should be optimized to attain the minimum coke consumption and stable operation. The present chapter will discuss the influence of various materials injection on the blast furnace operation. The injection limit and changing of the blast furnace operating conditions, hot metal quality and coke consumption will be explained based on the experimental trials and mathematical modelling.
Page 1. Volume Changes of Iron Oxide Compacts under Isothermal Reduction Conditions Compacts made... more Page 1. Volume Changes of Iron Oxide Compacts under Isothermal Reduction Conditions Compacts made from chemically grade Fe2O3 were fired at 1473K for 6 hrs. The fired compacts were isothermally reduced either by hydrogen or carbon monoxide at 10731373K. ...
Numerical prediction is performed on the reduction of wüstite under simulated blast furnace condi... more Numerical prediction is performed on the reduction of wüstite under simulated blast furnace conditions using factorial design approach. Wüstite sinter samples with different basicity (0.5, 1.0, and 2.0) are reduced with a gas mixture consisting of 30% CO, 10% H2, 5% CO2, and 55% N2 at 950–1100°C. In all cases, the reduction degree of wüstite increased with basicity and temperature. A 23 factorial design is applied to derive a regression model based on the experimental data of acidic (CaO/SiO2 = 0.5) and basic (CaO/SiO2 = 2.0) wüstite which is reduced at 950°C and 1100°C for 5 and 35 min. The developed mathematical model is applied to predict the reduction degree of wüstite at different basicity (0.5, 1.0, and 2.0), interval of time (5–35 min), and temperatures (950, 1000, 1050°C, and 1100°C). In general, the results of the driven models are found to be in good agreement with the experimental data of reduction of wüstite in many cases. The MATLAB program is used to carry out the requ...
The foundry industry is currently facing challenges to reduce the environmental impacts from appl... more The foundry industry is currently facing challenges to reduce the environmental impacts from application of fossil fuels. Replacing foundry coke with alternative renewable carbon sources can lead to significant decrease in fossil fuel consumption and fossil CO2 emission. The low bulk density, low energy density, low mechanical strength and the high reactivity of biocarbon materials are the main factors limiting their efficient implementation in a cupola furnace. The current study aimed at designing, optimizing and developing briquettes containing biocarbon, namely, biocarbon briquettes for an efficient use in cupola furnace. Laboratory hydraulic press with compaction pressure of about 160 MPa and stainless-steel moulds (Ø = 40 mm and 70 mm) were used for compaction. The density, heating value, energy density, mechanical strength and reactivity of biocarbon briquettes were measured and evaluated. The compressive strength and splitting tensile strength of biocarbon briquettes were mea...
In ore-based steelmaking, blast furnace (BF) dust is generally recycled to the BF via the sinter ... more In ore-based steelmaking, blast furnace (BF) dust is generally recycled to the BF via the sinter or cold-bonded briquettes and injection. In order to recycle the BF sludge to the BF, the sludge has to be upgraded, removing zinc. The literature reports cases of recycling the low-zinc fraction of upgraded BF sludge to the BF. However, research towards recycling of the high-zinc fraction of BF sludge within the ore-based steel plant is limited. In the present paper, the high-zinc fraction of tornado-treated BF sludge was incorporated in self-reducing cold-bonded briquettes and pellets. Each type of agglomerate was individually subjected to technical-scale smelting reduction experiments aiming to study the feasibility of recycling in-plant residues to the hot metal (HM) desulfurization (deS) plant. The endothermic reactions within the briquettes decreased the heating and reduction rate leaving the briquettes unreduced and unmelted. The pellets were completely reduced within eight minute...
The H2/CO ratio in the reducing gas of iron ore pellets is one of the most important factors that... more The H2/CO ratio in the reducing gas of iron ore pellets is one of the most important factors that affect the efficiency of the direct reduction processes. The magnitude effect of this ratio on the reduction is still not clear compared with the reduction time and temperature. In the current study, a 2 3 factorial design was used to elucidate the reduction potential of different ratios of H2/CO in the reduction process at different temperatures and time. A regression model has been developed based on the experimental data of iron ore pellets that reduced with simulated Midrex, Hyl, and Syngas at 850 o C and 1050 o C. The reduction time was selected at 1.0 and 15 minutes in all trails. The H2/CO ratios in the applied reducing gas were equal to 0.4, 1.0, 1.6, and 2.6. The results showed that the reduction time has the highest positive effect followed by the applied temperature and then H2/CO ratio. The mutual interaction combination between time and temperature was higher than that between H2/CO ratio with either time or temperature. The lowest positive effect on the reduction processes was exhibited by the mutual interaction between all of operational parameters which are represented in H2/CO ratio, temperature, and time. The developed mathematical model was tested against various experimental data to estimate its efficiency in the prediction of the reduction degree. The predicted values of the reduction process by the current mathematical model were found in a good agreement with experimental results in many cases. The Matlab program was used to carry out the required calculations.
ABSTRACT The mitigation of CO2 emissions has become a global priority in the iron and steel indus... more ABSTRACT The mitigation of CO2 emissions has become a global priority in the iron and steel industry. One promising solution to decrease CO2 emissions is recycling of the blast furnace top gas to be reused in the reduction of iron oxide. In this study, iron oxide compacts were reduced isothermally with simulated conventional blast furnace top gas (BFTG: 20%CO, 20%CO2, 5%H2, 55%N2) at 700–900uC using a thermogravimetric technique. The reduction reached 30–34% depending on the applied temperature. The compacts were reduced completely to wu¨ stite (Fe0?925O or Fe0?971O) with a few grains of metallic iron, which appeared only at 900uC. To investigate the reduction behaviour at the later stages, the compacts reduced with BFTG at 900uC were followed by isothermal reduction with simulated blast furnace shaft gas (BFSG: 30%CO, 5%CO2, 10%H2, 55%N2) at 950–1100uC. The total reduction extents were increased to 66–90% at 950–1100uC respectively. The remaining unreduced wu¨ stite (Fe0?974O) has a higher Fe/O ratio compared with that formed by reduction with BFTG. At the initial stages of reduction, the rate controlling mechanism was interfacial chemical reaction, while at the later stages, solid state diffusion was the rate controlling mechanism. Reflected light microscope, scanning electron microscope, X-ray diffraction and Poresizer techniques are used to estimate the reduction kinetic and mechanisms.
ABSTRACT 1300uC and prereduced at 900uC using low potential reducing gas (LPRG; 20%CO, 20%CO2, 5%... more ABSTRACT 1300uC and prereduced at 900uC using low potential reducing gas (LPRG; 20%CO, 20%CO2, 5%H2 and 55%N2). The prereduced sinters were subsequently reduced to metallic iron at 950– 1100uC using relatively high potential reducing gas (HPRG; 30%CO, 5%CO2, 10%H2 and 55%N2). Both LPRG and HPRG were selected to simulate the gas composition in the blast furnace upper and lower shaft respectively. High pressure mercury porosimeter, X-ray phase analysis, optical and scanning electron microscope were used for the analysis of the prepared and reduced sinters. In the original basic sinter, calcium ferrite (CaFe2O4) and dicalcium silicate (Ca2SiO4) phases were identified as well as the main Fe2O3 phase, whereas wollastonite [Ca2?87Fe0?13(SiO3)3] and silica (SiO2) were formed in the acidic sinter. The prereduction in sinters with LPRG at 900uC resulted in the formation of wu¨ stite (Fe0?902O) phase. The subsequent reduction in wu¨ stite sinters to metallic iron using HPRG at 950–1100uC was found to be the highest for basic sinter and the least for acidic sinter. The higher reduction rate of basic sinter was attributed to the enhancement of wu¨ stite reducibility through the formation of calcium ferrites. The lower reduction rate of wu¨ stite in acidic sinter was attributed to the formation of hard reducible fayalite (Fe2SiO4) and ferrobustamite [(Ca0?5Fe0?5)SiO3] phases. The rate controlling mechanism during the reduction process was estimated by the correlation between apparent activation energy calculation and microstructure investigations.
ABSTRACT Fe2O3/C compacts prepared by mixing of nanosized Fe2O3 (40–150 nm) with charcoal in a mo... more ABSTRACT Fe2O3/C compacts prepared by mixing of nanosized Fe2O3 (40–150 nm) with charcoal in a molar ratio of 1 : 4 were isothermally reduced at 950–1100uC in argon gas flow. The rate of reduction was calculated from the direct measurements of the mass–loss using TG technique. In addition, the QMS gas analyser was used to monitor CO and CO2 concentrations in the off gases. The different phases developed in the composites were identified by X-ray diffraction and their structures were microscopically examined. The effect of temperature and particle size of Fe2O3 on the reduction rates was studied. The reduction of Fe2O3 was found to proceed in a stepwise manner up to metallic iron. Alternatively, the carbon solution loss reaction resulted from the gasification of charcoal plays a significant role in the carbothermic reduction process. Incubation periods were detected in QMS analysis at the beginning of reduction process. The charcoal volatiles interfered with the O2 weight loss measurements, upon applying TG technique, resulting higher values of total weight loss than that measured by QMS. Comparison of the reduction testing techniques shows the differences in the actual reduction extents. The reduction kinetics were correlated with the microstructure of the reduced products and directed to the elucidation of the reduction mechanism.
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