Simulated Blast Furnace Research Articles

Characterization of the burden behaviour of iron ore pellets mixed with nut coke under simulated blast furnace conditions

ABSTRACTIn the blast furnace, nut coke is utilized in a mixture with the ferrous burden to improve the gas permeability. Although applied in a broad range (10–40 mm, 2–23 wt-%), limited information is available on changed burden behaviour in its presence. In the present study, the detailed characterization was performed on the iron ore pellets quenched during sintering, softening and before complete melting. The quantified information of the phase distribution across the pellets is compared for the samples mixed with and without nut coke. The principal role played by the nut coke is on bringing higher reduction and lower sintering among the pellets. For the pellet mixed with nut coke, at the core, ∼25 vol.-% of the material is observed in a network arrangement. The core structure consists of a wüstite matrix (10–20 vol.-%) reinforced with the iron nuclei (5–15 vol.-%). On the contrary, in the absence of nut coke, the pellet core is observed being hollow.

An integrated approach for production of stainless steel master alloy from a low grade chromite concentrate

As an alternative process, the production of stainless steel master alloys in blast furnace (BF) exhibits high economic efficiency and great potential to use low-grade chromite resources. To produce desirable sinter products required by the blast furnace smelting process, sintering tests of ore mixtures made from a low grade South African chromite concentrate (Cr2O3/FeO = 1.99) and Chinese magnetite concentrate were performed in a sinter pot in terms of various sintering parameters including coke dosage, mix moisture, sinter basicity and proportion of magnetite concentrate, etc. An integrated process comprising “high pressure grinding rollers (HPGR) pretreatment, pelletizing, coke coating, pre-drying and non-fluxed sintering” steps was proposed based on the pellet-sintering technique. The quality of Cr-bearing sinters was evaluated. The results show that high quality Cr-bearing sinters can be obtained through the proposed process. Addition of 40% or more magnetite concentrate in ore blends promises to yield desirable sinters of proper chemical composition and good metallurgical properties required by the blast furnace smelting process. The smelting performance of the Cr-bearing sinter made from the 40% chromite and 60% magnetite mixture was assessed under simulated blast furnace smelting conditions. It is feasible to use the Cr-bearing sinters in blast furnace for stainless steel master alloy production. A stainless steel master alloy containing 71.75% Fe, 19.52% Cr and 7.84% C with phosphorus and sulfur contents (<0.015%) is obtained at Fe and Cr recovery rates of 92.55% and 87.53%, respectively, when smelting at 1550 °C for 60 min with slag compositions (10% Al2O3, 10% MgO and R2 = 1.0). The bonding mechanism of Cr-bearing sinters and the formation mechanism of liquid phase were further revealed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS). Both slag bonding (10 to 20% silicate) and solid bonding (recrystallization of spinel phase) contribute to the consolidation of the Cr-bearing sinters. Increasing the basicity of sinter made from 100% chromite concentrate or addition of magnetite concentrate in the ore blend at natural basicity lead to the formation of low-strength slag bonds, which generally reduces the sinter strength.

Biomethanation of blast furnace gas using anaerobic granular sludge via addition of hydrogen.

The high concentrations of CO (toxic) and CO2 (greenhouse gases) in blast furnace gas (a by-product of steelworks) reflect its low calorific value. In this study, anaerobic granular sludge was used to convert carbon from blast furnace gas to methane via exogenous hydrogen addition. The inhibition of methane production by CO partial pressure (PCO) was found to start from 0.4 atm. The intermediate metabolites from CO to methane including acetate, propionate, and H2 accumulated at higher CO concentrations in the presence of 2-bromoethanesulfonic acid. After the introduction of H2 and blast furnace gas, although the hydrogen partial pressure (PH2) up to 1.54 atm resulted in the maximum CH4 yield, the whole system was not stable due to the accumulation of a large amount of volatile fatty acids. The optimum PH2 on CH4 production from the simulated blast furnace gas, 5.32 mmol g−1 VSS, was determined at 0.88 atm in this study.

Effect of mixing charge of highly reactive semicoke nut on the reaction of high Al2O3 ferrous burden in blast furnace

ABSTRACTIn order to improve the performance of blast furnace ironmaking when using the high Al2O3 iron ore, the technology of mixing charge of high reactive semicoke nut with ferrous burden was proposed and systematically investigated at laboratory scale in the present paper. The CO2 gasification activation energy of semicoke ranged from 136.5 to 150.3 kJ mol−1, which was lower than that of the traditional coke. At the temperature of 1200°C, the reduction degree of ferrous burden increased a little with the addition of semicoke nut and the consumption ratio of semicoke was 14.0 wt-% under the simulated blast furnace ironmaking condition. The mixing charge of semicoke could obviously reduce the softening beginning temperature, increase the melting temperature and improve the permeability compared with the standard and traditional coke mixing charge samples. During the total softening and melting process, about 90 wt-% of the semicoke nut and 45 wt-% of the traditional coke nut were consumed, respectively. The experiment results indicated that the mixing charge of high reactive semicoke nut could obviously improve the performance of blast furnace ironmaking when using high Al2O3 ferrous burden and the semicoke was more effective than traditional coke.

Effect of diboron trioxide on the crushing strength and smelting mechanism of high-chromium vanadium–titanium magnetite pellets

The effect of diboron trioxide (B2O3) on the crushing strength and smelting mechanism of high-chromium vanadium–titanium magnetite pellets was investigated in this work. The main characterization methods were X-ray fluorescence, inductively coupled plasma–atomic emission spectroscopy, mercury injection porosimetry, X-ray diffraction, metallographic microscopy, and scanning electron microscopy–energy-dispersive X-ray spectroscopy. The results showed that the crushing strength increased greatly with increasing B2O3 content and that the increase in crushing strength was strongly correlated with a decrease in porosity, the formation of liquid phases, and the growth and recrystallization consolidation of hematite crystalline grains. The smelting properties were measured under simulated blast furnace conditions; the results showed that the smelting properties within a certain B2O3 content range were improved and optimized except in the softening stage. The valuable element B was easily transformed to the slag, and this phenomenon became increasingly evident with increasing B2O3 content. The formation of Ti(C,N) was mostly avoided, and the slag and melted iron were separated well during smelting with the addition of B2O3. The size increase of the melted iron was consistent with the gradual optimization of the dripping characteristics with increasing B2O3 content.

Effect of charcoal addition on the properties of a coke subjected to simulated blast furnace conditions

A pilot oven produced coke with the addition of 7.5wt% charcoal (bio-coke) and the similarly produced base blend coke were subjected to gasification and annealing under the simulated blast furnace conditions. The effect of charcoal addition on the coke properties after gasification and annealing was characterised using Raman spectroscopy, ultra-micro indentation and tensile testing. The addition of charcoal significantly increased the coke reactivity with CO2 as a result of its increased surface area by charcoal. The addition of charcoal made no further contribution to the devolatilisation or mineral reactions of coke during annealing. The charcoal particles were well preserved after annealing at 2273K, but preferentially consumed in the gasification. Annealing temperature had less effect on the graphitisation of the charcoal component compared to the coexisting inert maceral derived component (IMDC) and reactive maceral derived component (RMDC). The charcoal addition had no effect on the microstructure and microstrength of coexisting microtextural types during annealing and gasification. The charcoal presented a higher resistance to fracture than IMDC and RMDC under annealing conditions. The addition of charcoal did not deteriorate the coke resistance to strength degradation under the thermal load of blast furnace. However, charcoal addition caused more severe degradation by gasification as demonstrated by more reduction in the tensile strength of the bio-coke. This was attributed to the preferential solution loss reaction of the charcoal particles leaving voids which coalesced the pores in coke, thereby increasing the defects that cause stress concentration under loading.

Investigation of Reduction Mechanism and Kinetics of Vanadium Titanomagnetite Carbon Composite Hot Briquette at 1173-1373 K

The isothermal reduction of vanadium titanomagnetite carbon composite hot briquette, simulated Blast Furnace condition at the temperature range of 1173–1373 K, is investigated in an electric resistance furnace. The samples reduced at different temperature are characterized by X-ray diffraction (XRD). The phase transitions during reduction process can be described as follows: Fe3O4 → FeO → Fe; Fe2.75Ti0.25O4 → Fe2.5Ti0.5O4 → Fe2TiO4 → FeTiO3 → TiO2; FeTiO3 → TiO2; Fe2VO4 → V2O3; FeCr2O4 → Cr2O3. Then, model fitting methods are used to evaluate the apparent activation energy during this process. The reduction process can be divided into three stages, and the apparent activation energies of the three stages are 40.26, 66.46, and 90.96 kJ mol−1, respectively. The rate controlling step of the initial stage is gas diffusion and interfacial chemical reaction. However, as the reduction proceeding, the rate controlling steps of the intermediate and final stage are gradually transformed to interfacial chemical reaction.

Ignitability and combustibility of Yallourn pyrolysis char under simulated blast furnace conditions

In this paper we have examined the potential of Yallourn brown coal char (collected from an industry-scale pyrolyser) to be used as a pulverized coal injection (PCI) fuel, its size-dependent properties, ignitability and combustibility under the simulated conditions of the blowpipe-tuyere section in a blast furnace. The combustion of individual sizes for Yallourn char was tested in a lab-scale drop-tube furnace (DTF) using pre-heated hot gas with a temperature up to 1000°C, and a particle residence time as short as 0.6s. Computational fluid dynamics (CFD) modelling was further conducted to optimize the char combustion conditions via sensitivity analysis. Irrespective of the pyrolysis condition, Yallourn char is superior over bituminous coal for being used as a top grade PCI fuel, due to its higher calorific value (7500–8110kcal/kg), lower ash content (<10wt%), high ash melting temperatures (>1550°C), and abundance of iron (>40wt% in ash). The performance of Yallourn char is also superior over bituminous coal under the simulated blast furnace conditions, for a rapid ignition and burnout even for a coarse char size of 300μm under the stoichiometric O2/C molar ratio and using low blast temperatures of 800–1000°C. All these are beneficial for reducing the energy consumption related to particle pulverization and the amount of oxygen for the combustion. With regard to the Yallourn char ignition and combustion in the hot gas, a minimum 6wt% volatile content is essential for a stable and rapid ignition of the volatiles at a gas temperature of 1000°C or below, since homogeneous ignition is predominant at low temperatures. However, once the blast temperature rises to 1200°C, the dependence on volatile content turns insignificant due to the dominance of the heterogeneous ignition, high C-O2 reactivity for the solid char, as well as the minimized pore diffusion control due to the large porosity (52.0–63.1%) of the Yallourn char tested here.

Coke Reactivity in Simulated Blast Furnace Shaft Conditions

Despite the fact that H2 and H2O are always present in the gas atmosphere of a blast furnace shaft, their role in the solution-loss reactions of coke has not been thoroughly examined. This study focuses on how H2 and H2O affect the reaction behavior and whether a strong correlation can be found between reactivity in the conditions of the CRI test (Coke Reactivity Index) and various simulated blast furnace shaft gas atmospheres. Partial replacement of CO/CO2 with H2/H2O was found to significantly increase the reactivity of all seven coke grades at 1373 K (1100 °C). H2 and H2O, however, did not have a significant effect on the threshold temperature of gasification. The reactivity increasing effect was found to be temperature dependent and clearly at its highest at 1373 K (1100 °C). Mathematical models were used to calculate activation energies for the gasification, which were notably lower for H2O gasification compared to CO2 indicating the higher reactivity of H2O. The reactivity results in gas atmospheres with CO2 as the sole gasifying component did not directly correlate with reactivity results in gases also including H2O, which suggests that the widely used CRI test is not entirely accurate for estimating coke reactivity in the blast furnace.

A Novel Technique for Making Cold Briquettes for Charging in Blast Furnace

Different metallurgical wastes are generated during pyro processing of iron ore, which is used for making sponge iron or hot metal and for producing steel. Apart from these wastes, coke fines are generated during the coke making, and iron ore fines are generated during mining of iron ore. Although iron ore fines are used for making pellet after beneficiation still, it generates a huge quantity of iron ore waste during beneficiation with comparatively lower iron content. In the present study, briquettes are made by a stiff extrusion process from metallurgical waste like iron ore fines and coke fines with the addition of Portland cement as a binder and clay as a rheology modifier. Physical properties of the briquettes are evaluated, and reducibility of the briquettes is studied in comparison to lumpy iron ore. Phase analysis and microstructural analysis of the briquettes and lumpy iron ore are carried out after firing at different temperatures in the simulated blast furnace condition. Physical and mineralogical properties are correlated with the reducibility of the briquettes and lumpy iron ore. Briquettes made by a stiff extrusion process show a better mechanical strength fired at a different temperature to take the load of burden and better reducibility than lumpy iron ore. The briquettes after self-curing are charged to a 23 mt3 blast furnace which shows encouraging results.

Ignitability and Combustibility of Yallourn Pyrolysis Char Blended with Pulverized Coal Injection Coal under Simulated Blast Furnace Conditions

Pulverized coal injection (PCI) is a widely used blast furnace technology aimed at reducing costs and increasing productivity. The prospect of blending PCI coal with a lower cost char, derived from Yallourn brown coal, is evaluated in this study by means of thermogravimetric analysis (TGA), flat-flame burner reactor, and drop-tube furnace experiments at four different blending ratios as well as computational fluid dynamics (CFD) modeling. Yallourn char has desirable properties compared to PCI coal, including a lower ash content and a higher heating value, although the reactivity is lower and the ignition temperature is higher. Because the combustion behavior of a blend is not always easily predicable based on the performance of the individual parent fuels, two Yallourn char samples (YC-1 and YC-2) are analyzed after blending with PCI coal at four ratios. According to the particle ignition time, a maximum of 40 wt % is allowable for YC-1 char which is comparably reactive with the commercial PCI coal. Howev...

Coke Degradation under Simulated Blast Furnace Conditions

Three metallurgical cokes made from coking coals over a significant range in rank were subjected to treatment with blast furnace-like gas composition-temperature profile to 1 673 K, annealing under N2 to 2 273 K and gasification with subsequent annealing at 1 873 and 2 273 K. The degradation of cokes after reaction and annealing was characterised using I-drum tumbling, tensile testing, ultra-micro indentation and X-ray diffraction. Both gasification and annealing decreased the mechanical strength of coke. Compared with annealing at 1 673 K, gasification at same temperature caused larger degradation for all three cokes, and the effect was more significant on more reactive coke. In the annealing process, degradation of the cokes occurred through the entire coke lump and resulted in both tensile strength and I-drum tumbling strength decreasing simultaneously. In the process of gasification under the blast furnace-like conditions, degradation took place through the whole piece of coke with high reactivity; however, the degradation of coke with low reactivity was more severe at the periphery than in the core and therefore gasification had a minimal effect on the core of the coke and its tensile strength, but had a much stronger effect on I600. Microstrength of coke decreased significantly with increasing annealing temperature. The change of microstrength of coke upon gasification, which occurred at relatively low temperatures, was marginal. The cokes after gasification with subsequent annealing had similar microstrength and graphitisation degree compared to those subjected only to annealing at the same temperature.

Softening and Melting Behavior of Ferrous Burden under Simulated Oxygen Blast Furnace Condition

The softening and melting behavior of sinter, pellet and mixed burden was researched through high temperature reaction tests under load simulating traditional blast furnace (T-BF) and oxygen blast furnace (OBF) conditions. The results indicated that compared with T-BF, the softening zone of sinter and pellet became wide, but the melting zone became narrow in OBF. The permeabilities of both sinter and pellet were improved in OBF. Under the condition of OBF, the temperature of softening zone of mixed burden was increased by 63 K, but the temperature of melting zone was decreased by 76 K. Therefore, the permeability of material layer was significantly improved. This was mainly caused by the change of the melting behavior of pellet. In addition, the quality of dripping iron in OBF was much better than that of T-BF.

Analysis of the Rheological Behaviour of Selected Semi-Solid Slag Systems in Blast Furnace Flow Conditions

Abstract The rheological properties of liquid and semi-solid systems of slag and hot metal in a blast furnace are extremely important from the perspective of their dripping in the unit. The rheological nature and the values of the dynamic viscosity coefficient of liquid and semi-solid phases - slag and hot metal - determine the permeability of the zones in which those systems exist. The modelling of dripping processes and e.g. static and dynamic holding/retention of liquid in the bed, requires an accurate description of the rheological behaviour of slag and iron systems. Determining the liquid flow through the lump bed of the blast furnace is based on the assumption that liquids in the unit in the whole range of their occurrence are similar to a Newtonian ideal liquid. This study presents an analysis of the findings of high-temperature rheometric measurements of CaO-SiO2-Al2O3-MgO systems, liquid, semi-solid slags of the blast furnace type doped with TiO2 and solids in the form of TiN. The tests were performed within a temperature range of 1310-1490°C. Also measurement results for glycerol solutions with concentrations of 86% and 100% at the ambient temperature, simulating blast furnace slags with various contents of solids - PC, anthracite - are presented.

Reduction Behavior of Pellet under Simulated Oxygen Blast Furnace Condition

The reduction behavior of pellet was researched through the programming apparatus under simulated conditions of oxygen blast furnace (OBF) and traditional blast furnace (T-BF). The results indicated that compared with traditional blast furnace, the reduction starting temperature of pellet decreased by 60 °C under oxygen blast furnace condition. The reduction degree of pellet could almost reach 100% under oxygen blast furnace condition when the temperature reached 1100 °C, whereas it was only 82. 49% in traditional blast furnace. The content of carbon in pellet of oxygen blast furnace was about 5 times more than that of traditional blast furnace. In addition, the microstructure at the periphery and core of pellets after reaction was characterized by means of SEM and EDS.

Mathematical Analysis of the Reduction of Wüstite at Different Basicity Using Factorial Design

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 required calculations.

Reduction behaviour of ferrous burden under simulated oxygen blast furnace conditions

The reduction behaviour of sinter and pellets was investigated by a programmable reduction apparatus to simulate the traditional blast furnace (TBF) and the oxygen blast furnace (OBF). The starting temperature for reduction of sinter and pellet in the OBF decreased 60 and 150°C compared with that in the TBF and, by the time the temperature reached 1100°C the reduction degree of sinter and pellet was 100.0 and 98.7% in the OBF compared to 94.0 and 83.1% in the TBF. The trends of the reduction rate of sinter and pellet were consistent in OBF and TBF. There are two peak values at about 60 and 80 min and in the OBF the third peak value of pellet emerged at 40 min. In addition, the mineral microstructures of the ferrous burden were characterised by means of SEM and the area proportion of metallic iron zone was obtained by SEM photos.

カルシウムフェライトの反応過程を考慮した焼結鉱ガス還元モデル(6界面未反応核モデル)

Reducible oxides containing iron in iron ore sinter are hematite, magnetite and quaternary calcium ferrite (abbreviated by CF), which is the complex crystalline mineral produced from Fe2O3, CaO, SiO2 and Al2O3. Equilibrium diagram for CF reduction with CO-CO2 gas mixture is a little but significantly different from the one for pure iron oxides. In previous analyses for reduction reaction of iron oxides in a blast furnace, however, sinter has been treated as pure iron oxides; existence of CF has been ignored. Reduction steps for CF can be written asCF (= ‘Fe2O3’) → ‘Fe3O4’ → ‘FeO’ → ‘Fe’,which are much the same as pure iron oxides, where ‘Fe2O3’, ‘Fe3O4’, ‘FeO’ and ‘Fe’ designate hematite, magnetite, wustite and iron stages of CF, respectively. However, a reported variation of gas composition with temperature measured in a blast furnace shows that the gas composition in the thermal reserve zone is a little higher than the wustite / iron equilibrium, the reduction potential of which is less than that of ‘FeO’ / ‘Fe’ equilibrium and hence ‘FeO’ cannot be reduced to ‘Fe’. In the present work, gaseous reduction model for sinter is developed in consideration of CF reaction process; unreacted-core shrinking model for six interfaces is proposed to take into account reaction process of CF as well as pure iron oxides. Trial comparison of the calculated reduction curve with our previously reported experimental data under simulated blast furnace conditions shows rather good agreement.

Reduction Behavior of Cold-bonded Briquettes under Simulated Blast Furnace Conditions

Reduction Behavior of Cold-bonded Briquettes under Simulated Blast Furnace Conditions

Effect of basicity on wüstite sinter reducibility under simulated blast furnace conditions

In this study, synthetic sinters with different basicity (CaO/SiO2 = 0, 0·5 and 2·0) were prepared at 1300°C and prereduced at 900°C 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 950–1100°C 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 900°C resulted in the formation of wüstite (Fe0·902O) phase. The subsequent reduction in wüstite sinters to metallic iron using HPRG at 950–1100°C 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 wüstite reducibility through the formation of calcium ferrites. The lower reduction rate of wüstite 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.