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- Kumar, T K Sandeep, 1986-, et al.
(författare)
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Establishing a Novel Methodology to Correlate the Macroscopic and Microscopic Degree of Sintering inMagnetite Pellets during Induration
- 2018
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Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 89:3
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Kumar, T K Sandeep, 1986-, et al.
(författare)
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Experimental Characterization of Sintering Mechanism using Optical Dilatometer and Push Rod Dilatometer : A Comparative Study
- 2017
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Konferensbidrag (refereegranskat)abstract
- In Iron and Steel industries, sintering process is used in producing agglomerates either as iron ore sinter or as heat hardened iron ore pellets. It is also used extensively used in producing ceramic or metallic powder compacts as well as in additive manufacturing processes. The thermal excursion of the green powder compact determines the extent of sintering and its subsequent evolution of desired properties. Therefore, it is necessary to understand the sintering phenomena for a single green compact. Sintering phenomena of iron ore pellets – magnetite and hematite are investigated in this study using two types of dilatometers. Optical Dilatometer has been used to study in-situ intrinsic sintering kinetics of pellets experimentally at different temperatures, and compared with that of widely used Push Rod Dilatometer. Unlike optical dilatometer, push rod dilatometer uses a load to keep the rod in contact with the compact. Interestingly, it has been found that the intrinsic sintering characteristics changes with the load imposed. These findings can also be extended to other materials manufactured by sintering phenomenon. Understanding on sintering mechanisms of material compacts with and without load will help in evaluating kinetic parameters considering the conditions compact encounter in further applications, and design accordingly.
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| 4. |
- Kumar, T K Sandeep, 1986-, et al.
(författare)
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Investigating the Oxidation Phenomena of Magnetite Pellet
- 2017
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Konferensbidrag (refereegranskat)abstract
- Induration of magnetite pellet is a complex physico-chemical process involving oxidation, sintering and the heat transfer phenomena. Often, these phenomena happen simultaneously and influence each other in the induration furnace. It could be because of the highly exothermic nature of oxidation phenomena that can result in significant temperature gradients inside the pellet and sintering might begin much earlier that it is ideally supposed to. This could results in the formation of pellets with heterogeneous phases and crystallographic properties such as duplex structure, and results in the inferior quality of pellets across the bed. In order to predict the optimum thermal profile to achieve homogenous good quality pellets on consistent basis, it is necessary develop a model based on the kinetics of each of these phenomena. This will help to identify and optimize the responsible process parameters during induration accordingly. Subsequent to the investigation of sintering kinetics of magnetite pellets, the current study focuses on the oxidation phenomena. The reaction mechanisms for oxidation of magnetite pellets is dependent primarily on factors such as temperature and oxygen content in the oxidizing gas, etc. Isothermal oxidation of magnetite at pellet scale has been studied experimentally using Thermogravimetric Analyzer (TGA) by inserting the single pellet directly into the isothermal zone of the furnace. It has been found that the oxidation phenomena in the magnetite pellets is a multi-stage phenomena dominated by distinct mechanisms depending on varying extent of oxidation with respect to temperature and oxygen content.
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| 6. |
- Kumar, T.K. Sandeep, 1986-, et al.
(författare)
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Investigation of Magnetite Oxidation Kinetics at the Particle Scale
- 2019
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 50:1, s. 150-161
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Tidskriftsartikel (refereegranskat)abstract
- The induration of magnetite pellets is a complex physico-chemical process that involves oxidation, sintering, and heat transfer. The thermal- and gas-composition profile that is experienced by the pellet in an induration reactor could result in the formation of a homogenous or heterogeneous pellet structure, which could affect the pellet quality. The oxidation kinetics of magnetite pellets from sintering studies have been studied at two levels, namely, the pellet scale and at the particle scale, and the findings of the latter are presented here. The rate of oxidation of the magnetite concentrate depends primarily on temperature, oxygen content in the oxidizing gas, and particle size. These factors are investigated in this study. It was found that the oxidation of the magnetite concentrate is comprised of two distinct stages, a primary stage with high rates followed by a secondary stage where rates decrease significantly. The isothermal oxidation behavior as analyzed by the Avrami kinetic model was found to fit better than the shrinking-core model. The partially oxidized particles were examined microstructurally to supplement the experimental and model results. The Avrami kinetic model for isothermal oxidation was extended to non-isothermal profiles using the superposition principle, and the model was validated experimentally.
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| 7. |
- Kumar, T. K. Sandeep, 1986-
(författare)
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Investigations on the Physico-Chemical Phenomena during Induration of a Magnetite Pellet
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the era of globalization with increasing environmental awareness, sustainable utilization of the available resources is a necessity; iron ores are no exception. Pelletization, being one of the increasingly practiced agglomeration techniques for the iron ore fines as well as other solid wastes from steel plants. The pellets produced are further fed into the metallurgical furnaces for subsequent processing. Induration is the vital cog in the process of pelletization, especially for magnetite ore fines. Induration of magnetite pellet is a complex physico-chemical phenomenon involving oxidation, sintering and the associated heat transfer.Rates of these processes not only depend on the thermal and gaseous environment the pellet is exposed to in the induration reactor but are also interdependent on each other. A doctorate project was undertaken to systematically understand these processes in isolation to the extent possible and seek their physics by quantifying them with the overall objective of creating a single pellet model. Isothermal experiments on single pellet scale were designed to understand the sintering and oxidation behavior of magnetite pellets independently.Sintering behavior of oxidized magnetite and non-oxidized magnetite pellets have been evaluated by continuously capturing their in-situ shrinkage using an Optical Dilatometer. The pellets were exposed to different thermal profiles in the defined range of temperature. The kinetics of sintering phenomenon was estimated with the help of power law and Arrhenius equations. The values of activation energy and time exponent derived suggests that sintering of oxidized magnetite (hematite) is dominated by a single diffusion mechanism, whereas sintering of magnetite showed two distinct mechanisms; one operating at lower temperatures and the other at higher temperatures. Further, in order to predict the sintering state of pellets during induration in plant scale operations, the isothermal sintering kinetic equation is also extended to predict the non-isothermal sintering. Thereafter, the predicted profiles were validated with the laboratory experiments, and found to be in fair agreement. Subsequently, these macroscopic sintering behaviors is correlated to quantitative microstructural characterization. This was done by quantifying the mosaic optical microstructures of pellet using the principle of distance transform.Oxidation behavior of magnetite was studied by investigating the kinetics at both at particle and pellet scales. Isothermal experiments were designed with Thermo Gravimetric Analysis (TGA) at sufficiently low enough temperatures so that sintering effects are minimized. The experimental results were analyzed by Shrinking Core Model (SCM) and Avrami Kinetic Model (AKM). It was found from the fit that oxidation at particle scale suitably follows Avrami mechanism, which infers that the rate of oxidation is primarily determined by the rate of nucleation initially followed by the rate of growth. The activation energy of 226 kJ/mol suggests solid-state diffusion mechanism. These findings were corroborated by the microstructural evaluation of particles, where, the hematite crystals were seen growing in some preferred directions.Further, the Pellet Oxidation Model is developed on the principles of grain model for gas-solid reactions by incorporating the derived particle oxidation kinetics with gaseous diffusion. Interestingly, it was found from the experiments as well as from the model that there exist two peaks in oxidation rate curves for magnetite pellet oxidation. The intensity of the peaks increases with the temperature and shifts towards lower times. After investigating different cases, it was found that these peaks were attributed to the initial thermal transient as the pellet is lowered from room temperature into the isothermal zone of the reactor as well as initial high rates of oxidation at the particle scale. The earlier rise of peaks in the rate of oxidation curves for the pellets determined experimentally as compared to the model output could be because of the presence of large fraction of fine particles (size distribution) in the pellet instead of mono-sized particles. These findings were substantiated by microstructural investigations at pellet scale and particle scale. Thereafter, pellet oxidation model is used to predict the oxidation behavior of the pellets treated at higher oxidation temperature or enriching the oxygen content in the oxidizing gas. It is further intended to integrate the oxidation models and sintering models along with the associated heat transfer to develop the comprehensive Single Pellet Induration Model (SPIM). SPIM can be used as a tool to simulate the induration behavior of magnetite pellet at any stage during processing. In future, SPIM can be incorporated into the reactor scale models improving their efficiency, considering the raw material variability.
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