| 1. |
- Ahmed, Hesham M., et al.
(författare)
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Kinetics and Mathematical Modeling of Hydrogen Reduction of NiO-WO(3) Precursors in Fluidized Bed Reactor
- 2011
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 51:9, s. 1383-1391
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, Fluidized bed reduction of NiO-WO(3) precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H(2)O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.
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| 2. |
- Ahmed, Hesham M., et al.
(författare)
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On The Kinetics of Hydrogen Reduction of NiO-WO3 Precursors in Fluidized Bed- A Modeling Approach
- 2011
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Ingår i: ISIJ International. - 0915-1559 .- 1347-5460. ; 51:9, s. 1383-1391
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, Fluidized bed reduction of NiO-WO3 precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H2O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.
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| 3. |
- Arzpeyma, Niloofar, et al.
(författare)
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Mathematical Modeling of Scrap Melting in an EAF Using Electromagnetic Stirring
- 2013
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:1, s. 48-55
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Tidskriftsartikel (refereegranskat)abstract
- Numerical modeling has been used to investigate the influence of electromagnetic stirring on melting of a single piece of scrap in an eccentric bottom tapping (EBT) electric arc furnace (EAF). The heat transfer and fluid flow in the melt for both conditions with and without electromagnetic stirring were studied. The buoyancy and electromagnetic forces were considered as the source terms for momentum transfer in the studied conditions. The enthalpy-porosity technique was applied to track the phase change of a scrap piece defined in the EBT region of the furnace. Different scrap sizes, preheating temperatures, stirring directions and force magnitudes were considered, and the heat transfer coefficient was estimated from the heat transfer rate at the melt-scrap interface. The results showed that electromagnetic stirring led to a reduced melting time and an increased heat transfer coefficient by a factor of four. The results for Nusselt number versus Grashof number for natural convection and Reynolds number for electromagnetic stirring were compared with those obtained through correlations from previous studies.
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| 4. |
- Bi, Yanyan, et al.
(författare)
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Evolution of Different Inclusions during Ladle Treatment and Continuous Casting of Stainless Steel
- 2013
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:12, s. 2099-2109
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Tidskriftsartikel (refereegranskat)abstract
- The inclusions and clusters in steel samples of two similar steel grades of high-silicon non-calcium treated (HSiNC) stainless steels were investigated and compared during ladle treatment and continuous casting. Samples of liquid steel and slag were taken at different stages of the ladle treatment and casting during two plant trials: Low Al steel (LAI) and High Al steel (HAI). After electrolytic extraction of the steel samples, characteristics of inclusions and clusters (such as morphology, composition, size and number) were investigated in three dimensions (3D) by SEM in combination with EDS. Moreover, the composition of typical inclusions and clusters was analyzed on a polished cross section of steel samples. Spherical (SP), irregular and regular (IR) inclusions and clusters (CL) were observed in the samples from both heats. It was found that the morphology and composition of inclusions and clusters in both heats were significantly changed during the ladle treatment and casting. Most of inclusions (44-98%) in a Low Al steel are MgO-CaO-SiO2-Al2O3 spherical inclusions. The compositions of IR inclusions and clusters in steel samples of a High Al steel were mostly MgO center dot Al2O3 spinet, but also the complex SP inclusions containing Al2O3-MgO-CaO-SiO2. In addition, phase stability diagram based on Darken's quadratic formalism and Redlich-Kister type polynomial was estimated for both heats at a non-infinite solution.
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| 5. |
- Bi, Yanyan, et al.
(författare)
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Three Dimensional Evaluations of REM Clusters in Stainless Steel
- 2014
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 54:6, s. 1266-1273
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Tidskriftsartikel (refereegranskat)abstract
- It is known that clusters in liquid steel have a harmful effect on the casting process and the quality of the final steel product. In this study, clusters. of rare earth metals (REM) were investigated in steel samples of a S30185 stainless steel grade from a pilot trial (PT, 250 kg) and from an industrial heat (IH, 100 t). Samples were taken from the liquid steel at different holding times after the addition of mischmetal. Thereafter, REM clusters collected on film filters after electrolytic extraction and filtration were investigated in three dimensions (3D) by SEM in combination with EDS. The morphology, composition, number and size of clusters in PT and IH steel samples were analyzed and compared as a function of holding time. It was found that typical clusters with regular and irregular inclusions were the main type of clusters (69%-98%) in all PT and IH steel samples. The composition of inclusions in clusters corresponded mostly to REM-oxides. The size of clusters that were observed in different samples varied mainly from 2 to 23 mu m. In addition, the size and number of most clusters in PT are larger than those in IH samples. Furthermore, the formation mechanisms and evolution of different type of REM clusters were discussed in both PT and IH heats.
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| 6. |
- Brämming, Mats, et al.
(författare)
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BOS vessel vibration measurement for foam level detection
- 2011
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 51:1, s. 71-79
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Tidskriftsartikel (refereegranskat)abstract
- In the BOS process liquid slag together with dispersed metal droplets, solid particles and process gases form an expanding foam. Certain process conditions may lead to excessive foam growth, forcing foam out through the vessel mouth, an event commonly known as 'slopping'. Slopping results in loss of valuable metal, equipment damage and lost production time. In the early 1980s a system for foam level and slopping control was installed at SSAB's steel plant in Luleå, a system based on the correlation between BOS vessel vibration in a narrow low frequency band and foam development. The technique, in this case with an accelerometer mounted on the trunnion bearing housing, soon showed its usefulness, for example when adapting existing lance patterns to a change in oxygen lance design from a 3-hole to a 4-hole nozzle. Estimating the actual foam height in the BOS vessel was of great importance in the recently completed RFCS funded research project "IMPHOS" (Improving Phosphorus Refining). Based on the earlier positive experiences, it was decided to further develop the vessel vibration measurement technique. Trials on an industrial size BOS vessel type LD/LBE have been carried out, this time with a tri-axial accelerometer mounted on the vessel trunnion. FFT spectrum analysis has been used in order to find the frequency band with best correlation to the foam level development. The results show that there is a correlation between vessel vibration and foam height that can be used for dynamic foam level and slopping control. © 2011 ISIJ.
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| 7. |
- Bäcke, Linda
(författare)
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Modeling the Effect of Solute Drag on Recovery and Recrystallization during Hot Deformation of Nb Microalloyed Steels
- 2010
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 50:2, s. 239-247
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Tidskriftsartikel (refereegranskat)abstract
- The effect of solute drag on recovery and recrystallization during hot deformation of Nb microalloyed steels has been modeled using a newly developed microstructure model. The model is based on dislocation theory and the calculated dislocation density determines the driving force for recrystallization. Subgrains act as nuclei for recrystallization and have to reach a critical size and configuration in order for recrystallization to start. In the model, the solute drag effect of Nb in solution is described. Nb retards both dislocation and grain boundary movement giving retardation in both recovery and recrystallization. Calculations were compared to experimental results from axisymmetric compression tests combined with stress relaxation. In order to model the effect of solute drag, the experiments were carried out at temperatures where precipitation of Nb(C, N) should not occur. The calculated flow stresses for the compression tests show good fit with experimental data. Also, the calculated results of the relaxation tests show good agreement with experimental data.
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| 8. |
- Deng, Zhiyin, et al.
(författare)
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Attachment of Liquid Calcium Aluminate Inclusions on Inner Wall of Submerged Entry Nozzle during Continuous Casting of Calcium-Treated Steel
- 2014
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 54:12, s. 2813-2820
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, inclusions in calcium-treated steel after RH treatment, in the tundish and in bloom were studied. Only two types of inclusions were detected in all steel samples, namely liquid calcium aluminate inclusions and inclusions of two phases with spinel in the center surrounded by the liquid calcium aluminate. The attachment of the inclusions on the inner surface of SEN was investigated for two types of refractory materials. The results indicated that liquid calcium aluminate inclusions could attach on the wall of SEN, when the refractory had big grain size and big cavities on the surface. On the other hand, tiny grain size and smooth surface of the SEN showed no attachment of the inclusions. The different behaviors of the two types of SEN were well explained using the results of flow calculation in the nozzle. The mechanism of the attachment was also discussed based on the experimental results and the CFD calculation. The tiny nodules formed on the surface of the inner nozzle due to inclusion attachment could be a source of macro inclusions.
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| 9. |
- Dwarapudi, Srinivas, et al.
(författare)
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Development of cold bonded chromite pellets for ferrochrome production in submerged arc furnace
- 2013
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:1, s. 9-17
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Tidskriftsartikel (refereegranskat)abstract
- Pelletizing of Indian chromite ores is more challenging due to their high refractory nature. High Cr/Fe ratio and high MgO content in these ores demand high firing temperatures and longer firing cycles but often result in low strength fired pellets. Aim of this study was to develop cold bonded chromite pellets for smelting in submerged arc furnace (SAF) from chromite fines using suitable binder that induce less gangue into the pellets but cures quickly. Different binders were studied through laboratory pelletizing experiments for their suitability for cold bonding the pellets. As result, a composite binder comprising dextrin and bentonite, was found to be suitable and pellets made from the same were tested for their low and high temperature behavior. Electron and optical micro structural studies with image analysis were carried out to find out the type and amount of phases formed in the chromite pellets during high temperature reduction. High temperature reduction studies revealed that pellets were resistant to disintegration up to 1200°C. Pilot scale arc furnace trials were also carried out to compare the performance of cold bonded pellets (CBPs) with sintered chromite pellets and found that for a constant power input, smelting rate was faster for CBPs than sintered pellets. Loss of Cr to slag was reduced in case of cold bonded pellets usage.
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| 10. |
- Grip, Carl-Erik, et al.
(författare)
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Application of Pinch Analysis in an Integrated Steel Plant in Northern Sweden
- 2013
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:7, s. 1202-1210
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Tidskriftsartikel (refereegranskat)abstract
- The energy system in a modern integrated steel plant is a complicated network of units exchangingenergy and matter with each other. System studies using process integration tools are important to avoidsub-optimization. At the steel plant in Luleå such studies have been carried out using a MILP-based mathematicalprogramming tool (reMIND), mainly because of its inherent flexibility for handling combinedflows and reactions of both matter and chemical, thermal and mechanical energy. There are, however,areas where the energy system is dominated by creation, transport and exchange of thermal energy, andwhere pinch analysis can be expected to be a valuable tool. For this reason a pinch targeting study wascarried out for the plant site of the integrated steel plant in Luleå. The coke plant and the iron making/steelmaking plant were both studied with three ambition levels of possible improvements. The study confirmedthat pinch analysis is a powerful tool for targeting energy savings in areas where thermal energyflows dominate the local energy system, e.g., the gas cleaning area at the coke plant. The study also indicatedthat a connection between the energy systems in the coke plant and the iron making/steelmakingwould be valuable. This is not 100% feasible because of distance, but, a common steam net could add adegree of flexibility.
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