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Publications (10 of 68) Show all publications
Kumar, T. K., Simonsson, M., Nurni, V., Ahmed, H., Andersson, C., El-Geassy, A.-H. A. & Björkman, B. (2018). Establishing a Novel Methodology to Correlate the Macroscopic and Microscopic Degree of Sintering inMagnetite Pellets during Induration. Steel Research International, 89(3), Article ID 1700366.
Open this publication in new window or tab >>Establishing a Novel Methodology to Correlate the Macroscopic and Microscopic Degree of Sintering inMagnetite Pellets during Induration
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2018 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 89, no 3, article id 1700366Article in journal (Refereed) Published
Abstract [en]

The quality of product pellets is a result of the physico-chemical phenomenainvolved in the induration process. Sintering is the primary phenomenon,and its degree or extent contributes substantially to the evolution of themetallurgical and mechanical properties of a pellet. During the induration ofmagnetite pellets, sintering proceeds through the oxidized and non-oxidizedmagnetite phases. Sintering of these phases has been previously studied ona single pellet at the macroscopic scale using an optical dilatometer. Adeeper understanding requires corroboration of these studies throughcharacterization at the microscopic scale. In the present work, the observationsrecorded at the microscopic scale are quantified using image processingtechniques to correlate them to the macroscopic measurements. Distancetransformation, which is an image processing principle, is adapted in a novelway to digitize the microstructures and to determine the degree of sinteringin a pellet quantitatively. This methodology has potential applications as ageneric tool to follow the sintering phenomenon and process kinetics at anystage during induration.

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
Keywords
Distance Transform, Induration, Optical Microstructures, Oxidized and Non-oxidized Magnetite Pellets, Sintering Degree
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-66590 (URN)10.1002/srin.201700366 (DOI)000426525900012 ()2-s2.0-85042594552 (Scopus ID)
Projects
Modeling of Physico-Chemical phenomena during Induration of Magnetite Pellet
Note

Validerad;2018;Nivå 2;2018-02-02 (andbra)

Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2018-05-16Bibliographically approved
Kiamehr, S., Ahmed, H., Nurni, V. & Seetharaman, S. (2017). Changes in Effective Thermal Conductivity During the Carbothermic Reduction of Magnetite Using Graphite. Metallurgical and materials transactions. B, process metallurgy and materials processing science, 48(3), 1502-1513
Open this publication in new window or tab >>Changes in Effective Thermal Conductivity During the Carbothermic Reduction of Magnetite Using Graphite
2017 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, no 3, p. 1502-1513Article in journal (Refereed) Published
Abstract [en]

Knowledge of the effective thermal diffusivity changes of systems undergoing reactions where heat transfer plays an important role in the reaction kinetics is essential for process understanding and control. Carbothermic reduction process of magnetite containing composites is a typical example of such systems. The reduction process in this case is highly endothermic and hence, the overall rate of the reaction is greatly influenced by the heat transfer through composite compact. Using Laser-Flash method, the change of effective thermal diffusivity of magnetite-graphite composite pellet was monitored in the dynamic mode over a pre-defined thermal cycle (heating at the rate of 7 K/min to 1423 K (1150 °C), holding the sample for 270 minutes at this temperature and then cooling it down to the room temperature at the same rate as heating). These measurements were supplemented by Thermogravimetric Analysis under comparable experimental conditions as well as quenching tests of the samples in order to combine the impact of various factors such as sample dilatations and changes in apparent density on the progress of the reaction. The present results show that monitoring thermal diffusivity changes during the course of reduction would be a very useful tool in a total understanding of the underlying physicochemical phenomena. At the end, effort is made to estimate the apparent thermal conductivity values based on the measured thermal diffusivity and dilatations.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-62263 (URN)10.1007/s11663-017-0944-6 (DOI)000400385900010 ()2-s2.0-85014026536 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-05-02 (andbra)

Available from: 2017-03-02 Created: 2017-03-02 Last updated: 2018-07-10Bibliographically approved
Kumar, T. S., Nurni, V., Ahmed, H., Andersson, C. & Björkman, B. (2017). Erratum to: Estimation of Sintering Kinetics of Magnetite Pellet Using Optical Dilatometer [Letter to the editor]. Metallurgical and materials transactions. B, process metallurgy and materials processing science, 48(1), 743-745
Open this publication in new window or tab >>Erratum to: Estimation of Sintering Kinetics of Magnetite Pellet Using Optical Dilatometer
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2017 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, no 1, p. 743-745Article in journal, Letter (Refereed) Published
Abstract [en]

Authors have used a new way for measuring bulk volume based on the image (pixel) analysis named as Light Table Imaging (LTI), and subsequently bulk densities and porosities. Authors lately found that there was a slight error in calibrating the scale (known distance) to pixel measurement and understand the need to communicate the error and subsequent corrections.  

Place, publisher, year, edition, pages
Springer, 2017
Keywords
Metallurgical process, Manufacturing engineering
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-60524 (URN)10.1007/s11663-016-0843-2 (DOI)000392295500071 ()2-s2.0-84992365208 (Scopus ID)
Available from: 2016-11-17 Created: 2016-11-17 Last updated: 2018-07-10Bibliographically approved
Kumar, T. S., Nurni, V., Ahmed, H., Andersson, C. & Björkman, B. (2017). Erratum to: Estimation of Sintering Kinetics of Oxidized Magnetite Pellet Using Optical Dilatometer (ed.) [Letter to the editor]. Metallurgical and materials transactions. B, process metallurgy and materials processing science, 48(1), 746-748
Open this publication in new window or tab >>Erratum to: Estimation of Sintering Kinetics of Oxidized Magnetite Pellet Using Optical Dilatometer
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2017 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, no 1, p. 746-748Article in journal, Letter (Refereed) Published
Abstract [en]

Authors have used a new way for measuring bulk volume based on the image (pixel) analysis named as Light Table Imaging (LTI), and subsequently bulk densities and porosities. Authors lately found that there was a slight error in calibrating the scale (known distance) to pixel measurement and understand the need to communicate the error and subsequent corrections.  

Place, publisher, year, edition, pages
Springer, 2017
Keywords
Chemical engineering - Metallurgical process and manufacturing engineering
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-60075 (URN)10.1007/s11663-016-0844-1 (DOI)000392295500072 ()2-s2.0-84992723871 (Scopus ID)
Available from: 2016-11-01 Created: 2016-11-01 Last updated: 2018-09-28Bibliographically approved
Ahmed, H., Nurni, V. & Björkman, B. (2017). Isothermal reduction kinetics of self-reducing mixtures (ed.). Ironmaking & steelmaking, 44(1), 66-75
Open this publication in new window or tab >>Isothermal reduction kinetics of self-reducing mixtures
2017 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 44, no 1, p. 66-75Article in journal (Refereed) Published
Abstract [en]

Isothermal reduction of haematite carbon mixtures was investigated at temperatures 750–1100°C under inert atmosphere. Mass loss curves proved the stepwise reduction of haematite to metallic iron. The non-linear feature of haematite to magnetite reduction kinetics was observed and an activation energy of 209 kJ mol−1 was calculated. Irrespective of carbon-bearing material type, reduction rate of magnetite was linear. Activation energy values were calculated to be 293–418 kJ mol−1. Significant increase in the reduction kinetics in the last step (Wustite reduction) was observed and explained by the catalytic effect of freshly formed metallic iron. During the initial stages of wustite reduction, the activation energy values were calculated to be in the range of 251–335 kJ mol−1 for all carbon-bearing materials.

Place, publisher, year, edition, pages
Taylor & Francis, 2017
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-15632 (URN)10.1080/03019233.2016.1165497 (DOI)000396712800010 ()2-s2.0-84978512250 (Scopus ID)f2a254cc-072d-4113-99c6-307f557fb0bb (Local ID)f2a254cc-072d-4113-99c6-307f557fb0bb (Archive number)f2a254cc-072d-4113-99c6-307f557fb0bb (OAI)
Note

Validerad; 2017; Nivå 2; 2016-12-20 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-11-19Bibliographically approved
Kumar, T. S., Nurni, V., Ahmed, H. M., Andersson, C. & Björkman, B. (2016). Estimation of Sintering Kinetics of Magnetite Pellet Using Optical Dilatometer (ed.). Metallurgical and materials transactions. B, process metallurgy and materials processing science, 47(1), 309-319
Open this publication in new window or tab >>Estimation of Sintering Kinetics of Magnetite Pellet Using Optical Dilatometer
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2016 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, no 1, p. 309-319Article in journal (Refereed) Published
Abstract [en]

During induration of magnetite pellets, oxidation of magnetite followed by sintering of the oxidized magnetite (hematite) is desirable. Sintering of magnetite which hampers the oxidation of magnetite is aimed to be kept as low as possible. In succession to our earlier study on sintering behavior of oxidized magnetite (hematite), this paper focusses on the sintering behavior of magnetite phase in isolation with an objective to estimate their kinetic parameters. The pellets prepared from the concentrate of LKAB’s mine, which majorly contains (>95 pct) magnetite, are used for the sintering studies. Optical Dilatometer is used to capture the sintering behavior of the magnetite pellet and determine their isothermal kinetics by deducing the three parameters, namely—activation energy (Q), pre-exponential factor (K′), and time exponent (n) with the help of power law and Arrhenius equation. It is interesting to find that the time exponent (n) is decreasing with the increase in sintering temperature. It is also interesting to note that the activation energy for sintering of magnetite pellet shows no single value. From the present investigation, two activation energies—477 kJ/mole [1173 K to 1373 K (900 °C to 1100 °C)] and 148 kJ/mole [1373 K to 1623 K (1100 °C to 1350 °C)]—were deduced for sintering of magnetite, suggesting two different mechanisms operating at lower and other at higher temperatures. The estimated kinetic parameters were used to predict the non-isothermal sintering behavior of magnetite using the sintering kinetic model. Predicted results were validated using experimental data.

Keywords
Chemical engineering - Metallurgical process and manufacturing engineering, Kemiteknik - Metallurgisk process- och produktionsteknik
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-14333 (URN)10.1007/s11663-015-0505-9 (DOI)000368692300031 ()2-s2.0-84958180660 (Scopus ID)db037374-5a60-4d9a-9d90-01338adc1d16 (Local ID)db037374-5a60-4d9a-9d90-01338adc1d16 (Archive number)db037374-5a60-4d9a-9d90-01338adc1d16 (OAI)
Note

Validerad; 2016; Nivå 2; 20151122 (kamsan)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-12-14Bibliographically approved
Kumar, T. S., Nurni, V., Ahmed, H., Andersson, C. & Björkman, B. (2016). Sintering Mechanism of Magnetite Pellets during Induration (ed.). In: (Ed.), : . Paper presented at International Conference on Process Development in Iron and Steelmaking : 13/06/2016 - 15/06/2016.
Open this publication in new window or tab >>Sintering Mechanism of Magnetite Pellets during Induration
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2016 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

In Europe, Sweden has the richest magnetite ore deposits. The mined magnetite ore is ground, beneficiated and pelletized to make the process sustainable and environment friendly. These pellets are subsequently processed in blast furnaces, and hence the optimum pellet quality is of utmost important. Magnetite green pellets are indurated (heat hardened) in either rotary kiln or straight grate induration furnace to attain the quality standards in terms of strength and other metallurgical properties. The quality of magnetite pellet is primarily determined by the physico-chemical changes the pellet undergoes as it makes excursion through the gaseous and thermal environment in the induration furnace. Among these physico-chemical processes, the oxidation of magnetite phase and the sintering of oxidized magnetite (hematite) and magnetite (non-oxidized) phases are vital. Rates of these processes not only depend on the thermal and gaseous environment the pellet gets exposed in the induration reactor but are also interdependent on each other. Therefore, a systematic study has been done to understand these processes in isolation to the extent possible and quantify them seeking the physics.Optical Dilatometer was used in a novel way to design the experiments on single pellets, exposed to different thermal profiles, in order to quantify the sintering of oxidized magnetite and non-oxidized magnetite, independently. Power law (Kt^n) and Arrhenius (푙n(TK(1^n) = ln K' - Q/RT) equations quantifies sintering behavior by estimating three isothermal kinetic parameters, namely – activation energy (Q), pre-exponential factor (K’) and time exponent (n). The values of activation energy and time exponent derived suggests that sintering of oxidized magnetite (hematite) is a single dominant diffusion mechanism, whereas sintering of unoxidized magnetite might be a combination of two distinct mechanisms; one operating at lower temperatures and the other at higher temperatures. The isothermal sintering kinetic equation is also extended to predict the non-isothermal sintering, and validated with the laboratory experiments. This will be further useful in predicting the sintering state of pellets during induration in the plant scale operations.

National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-39755 (URN)e9e2c0d6-7bf6-4ae5-97b6-c5ac75daba41 (Local ID)e9e2c0d6-7bf6-4ae5-97b6-c5ac75daba41 (Archive number)e9e2c0d6-7bf6-4ae5-97b6-c5ac75daba41 (OAI)
Conference
International Conference on Process Development in Iron and Steelmaking : 13/06/2016 - 15/06/2016
Note

Godkänd; 2016; 20160616 (kamsan)

Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-05-28Bibliographically approved
Wang, L., Nurni, V., Muhmood, L., Kapilashrami, E. & Seetharaman, S. (2016). Some Aspects of Interfacial Phenomena in Steelmaking and Refining (ed.). Metallurgical and materials transactions. B, process metallurgy and materials processing science, 47(4), 2107-2113
Open this publication in new window or tab >>Some Aspects of Interfacial Phenomena in Steelmaking and Refining
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2016 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, no 4, p. 2107-2113Article in journal (Refereed) Published
Abstract [en]

Unique experiments were designed to study the surface phenomena in steelmaking reactions. The concept of surface sulfide capacities and an understanding of the surface accumulation of surface-active species, based on experimental results, are presented. In order to understand the flow phenomenon at slag/metal interface, experiments were designed to measure the interfacial velocity of S on the surface of an iron drop immersed in an aluminosilicate slag using the X-ray sessile drop method. The oscillation of the iron drop in the slag due to the change in the surface concentration of sulfur at the slag–metal interface was monitored by X-ray imaging. From the observations, the interfacial velocity of sulfur was evaluated. Similar experiments were performed to measure the interfacial velocity of oxygen at the interface as well as the impact of oxygen potential on the interfacial velocity of sulfur. The interfacial shear viscosity and the dilatational modulus were also evaluated. In a study of the wetting of alumina base by iron drop at constant oxygen pressure under isothermal condition, the contact angle was found to be decreased with the progress of the reaction leading to the formation of hercynite as an intermediate layer creating non-wetting conditions. In the case of silica substrate, an intermediate liquid fayalite layer was formed

National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-8698 (URN)10.1007/s11663-016-0631-z (DOI)000379510000005 ()2-s2.0-84961116475 (Scopus ID)73b68140-5fd6-4aca-8e6a-7742bdf07b58 (Local ID)73b68140-5fd6-4aca-8e6a-7742bdf07b58 (Archive number)73b68140-5fd6-4aca-8e6a-7742bdf07b58 (OAI)
Note

Validerad; 2016; Nivå 2; 20160321 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Rozario, A., Nurni, V. & Basu, S. (2015). Draining of gas bubbles at interface between two liquids-some observations (ed.). In: (Ed.), X. Wang (Ed.), Proceedings of the 6th International Congress on the Science and Technology of Steelmaking: ICS 2015, Beijing, China; 12 - 14 May 2015. Paper presented at International Congress on the Science and Technology of Steelmaking : 12/05/2015 - 14/05/2015 (pp. 328-331). : The Chinese Society for Metals
Open this publication in new window or tab >>Draining of gas bubbles at interface between two liquids-some observations
2015 (English)In: Proceedings of the 6th International Congress on the Science and Technology of Steelmaking: ICS 2015, Beijing, China; 12 - 14 May 2015 / [ed] X. Wang, The Chinese Society for Metals , 2015, p. 328-331Conference paper, Published paper (Refereed)
Abstract [en]

In steelmaking operations, slag foaming plays an important role in energy efficiency, heat transfer and process kinetics. A cold model simulation of slag foaming phenomenon in steel making operation was conducted to understand the effect of viscosity, density and interfacial energy between steel and slag on foaming. The experimental study was conducted at room temperature using water and oils of different viscosities which represent steel and slag respectively. Experiments on individual bubble motion across water-oil interface showed that the residence time of bubble at the interface increased with increase in interfacial tension. It also showed the foam index was influenced by the carryover of water across the interface by gas bubbles which in turn depend on the velocity of gas, density and viscosity of the mediums. Foaming experiments with oil phase only showed that the foaming height increased with increase in viscosity and decreased with further increase in viscosity by varying the gas velocity. Foam index in the oil phase experiments decreased with increase in gas velocity. But in water-oil system, the trend was entirely different from only oil phase experiment showing that the foam height and foam index not only depends on viscosity, density difference between the phases but also on the amount liquid transfer that takes place across the interface which affects the residence time of the bubbles

Place, publisher, year, edition, pages
The Chinese Society for Metals, 2015
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-35055 (URN)96f59b0a-7c36-4a2e-8d03-6e674fa046bc (Local ID)9780000000002 (ISBN)96f59b0a-7c36-4a2e-8d03-6e674fa046bc (Archive number)96f59b0a-7c36-4a2e-8d03-6e674fa046bc (OAI)
Conference
International Congress on the Science and Technology of Steelmaking : 12/05/2015 - 14/05/2015
Note
Godkänd; 2015; 20160526 (andbra)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-05-28Bibliographically approved
Kumar, T. S., Ahmed, H., Nurni, V., Andersson, C. & Magnusson, G. (2015). Effect of Heating Rates on the Sintering of Oxidized Magnetite Pellets during Induration (ed.). In: (Ed.), : . Paper presented at European Steel Technology and Application Days : METEC 16/06/2015 - 19/06/2015.
Open this publication in new window or tab >>Effect of Heating Rates on the Sintering of Oxidized Magnetite Pellets during Induration
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2015 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

Magnetite pellet induration is a combination of complex physicochemical phenomena – oxidation, sintering and theheat transfer associated with them. Depending on the pellet properties and the environment it encounters duringthe induration, the oxidation and sintering course may vary and the mechanisms will interact. To be able to predict their course and control it, the kinetics of these phenomena needs to be understood. One approach is to determine the kinetics of the phenomena in isolation. The present investigation is aimed to predict and studying the sintering behavior of oxidized magnetite (hematite) pellets exposed to different heating rates. Experiments have been carefully performed at three different heating rates to capture the sintering behavior during induration using an optical dilatometer, and also used for validation.

National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-34576 (URN)8cf53bf5-9b3c-4fb4-affc-6b13c7793886 (Local ID)8cf53bf5-9b3c-4fb4-affc-6b13c7793886 (Archive number)8cf53bf5-9b3c-4fb4-affc-6b13c7793886 (OAI)
Conference
European Steel Technology and Application Days : METEC 16/06/2015 - 19/06/2015
Note

Godkänd; 2015; 20150617 (kamsan)

Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-05-28Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0278-1333

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