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- Kumar, TK Sandeep, 1986-, et al.
(författare)
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Developing the Oxidation Kinetic Model for Magnetite Pellet
- 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. 162-172
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation is a vital phenomenon for magnetite pellets in their excursion through the furnace during induration. One of the pre-requisites for magnetite pellets to achieve homogeneously structured good quality pellets is to have complete oxidation before sintering begins. Partially oxidized magnetite pellets, upon sintering, might result in inhomogeneous structured pellets which could be detrimental to pellet quality. It is necessary to understand the mechanisms responsible for magnetite oxidation, and hence, it is intended in this study to investigate experimentally as well as develop a mathematical model based on oxidation kinetics. Oxidation of pellets is largely influenced by the oxidation kinetics of particles and hence should be studied at particle as well as at pellet scale. The principles of the Grain Model have been adopted to develop the Oxidation Model at pellet scale, whereas the particles’ oxidation follows the Avrami Kinetic Model. Isothermal oxidation experiments performed Thermogravimetric Analyzer showed that oxidation rate of magnetite at pellet scale contained two peaks. They were complemented well by oxidation rates predicted from the model. Further, the pellet was investigated microstructurally at pellet and particle scale to substantiate the findings from the experiments and the model. The oxidation model developed is used to predict the progression of oxidation in the magnetite pellet with respect to the reaction time at three different temperatures (873 K, 973 K, and 1073 K (600 °C, 700 °C, and 800 °C)) and at four levels of oxygen (0.21, 0.30, 0.60, and 1.00 atm) in the oxidizing gas.
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| 4. |
- Kumar, TK Sandeep, et al.
(författare)
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Effect of Heating Rates on the Sintering of Oxidized Magnetite Pellets during Induration
- 2015
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Kumar, TK Sandeep
(författare)
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Evolution of the flux combination for pelletization of high alumina iron ore fines
- 2013
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Konferensbidrag (refereegranskat)abstract
- During mining of iron ore, huge amount of fines is being generated which needs to be pelletized to use them in blast furnace for iron making process. Pellet quality plays a vital role in decreasing coke rate and increasing the blast furnace productivity. Indian iron ores are suffering from high amount of alumina, which is a deleterious constituent in both pelletizing as well as iron making process. Flux used plays a crucial part in determining pellet quality. Silicate fluxes like pyroxenite and olivine shows improvement in high temperature metallurgical properties but still could not met the desired quality due its improper assimilation, and high content of alumina in iron ore. Carbonate fluxes like limestone or dolomite is more often used in pelletization for alternative iron making processes. Thermodynamic modeling and experiments helped in the evolution of the new tailor-made combination of carbonate and silicate minerals which together provides an attractive solution to achieve sustainable pelletizing with desired quality pellets, and substantiated by their microstructures. During firing, the carbonate mineral dissociates and reacts with high alumina iron ore to form liquid bonding phase in the pellet improving its strength at room and low temperatures up to 600oC (i.e., CCS and RDI), while the silicate mineral forms high melting point phase which keeps the pellet quality intact even at high temperatures beyond 1000oC (i.e., Softening temperature). These superior quality pellets improves the productivity by 12%, mitigate the pellet fines generation by 35%, and decreases the blast furnace coke rate, hence low CO2 emissions.
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| 6. |
- Kumar, TK Sandeep
(författare)
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Investigation of Sintering Kinetics of Magnetite pellets during Induration
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the measures of development and economy of a nation is its per capita consumption of steel, and the demand is fulfilled by iron ore. In the context of increasing environmental constraints and ores becoming leaner and leaner, recycling and utilization of ore fines becomes necessary. Pelletization, being one of the major agglomeration techniques is increasingly practiced across the world to produce agglomerates that can be fed into the metallurgical furnaces (say blast furnaces) for subsequent processing. In Europe, Sweden has the richest iron ore deposits, and mining and metals production contributes majorly to its net export. LKAB operates with magnetite ore bodies in the northern Sweden to produce magnetite pellets (26 MTPA) exports about 70 % of its product to the European Steel producers. Therefore, constant efforts are necessary to maintain and improve the quality of magnetite pellets, and it is necessary to enhance the understanding on the reaction kinetics and mechanisms responsible while producing pellets.Magnetite pellets prepared from the fines are indurated (heat hardened) 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 doctorate project is undertaken to systematically understand these processes in isolation to the extent possible and quantify them seeking the physics. With this motivation, the current study is focused on investigating the sintering phenomena involved during induration of magnetite pellet.Experiments with single pellets were designed to understand and quantify the sintering behavior of oxidized magnetite (hematite) and magnetite independently. The kinetics of sintering can be described using power law (Ktn) and Arrhenius (ln(TK^((1/n)) )=lnK' - Q/RT ) equations. In the experiments, a single pellet was exposed to different thermal profiles in a controlled atmosphere, and their in-situ shrinkage was captured continuously by a novel technique using Optical Dilatometer. It was found that the sintering behavior captured by shrinkage of the pellet can be quantified using 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 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. The isothermal sintering kinetic equation is also extended to predict the non-isothermal sintering for both oxidized magnetite and magnetite, and validated with the laboratory experiments. This is further useful in predicting the sintering state of pellets during induration in the plant scale operations.
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| 7. |
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| 8. |
- Kumar, TK Sandeep, et al.
(författare)
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Sintering Mechanism of Magnetite Pellets during Induration
- 2016
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 9. |
- Kumar, TK Sandeep, et al.
(författare)
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Studying the Sintering Behavior of Oxidized Magnetite Pellet During Induration
- 2015
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Ingår i: AISTech 2015. - Warrendale, PA : Association for Iron & Steel Technology. - 9781935117476 ; , s. 611-618
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Konferensbidrag (refereegranskat)abstract
- Pelletization is by far the leading agglomeration technique practiced in Sweden and also across the world for magnetite fines. Magnetite pelletization provides an added advantage in terms of energy generated from exothermic nature of magnetite oxidation. Swedish steel industries pioneered in operating their blast furnaces with cent percent pellets. This makes it necessary to understand the entire process of pelletization, where green pellets are strengthened through heat hardening process known as induration for subsequent use in iron making units such as blast furnace and direct reduced iron processes.
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| 10. |
- Nurni, Viswanathan, et al.
(författare)
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A methodology to quantify the physico-chemical phenomena during induration of a single magnetite pellet
- 2017
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Konferensbidrag (refereegranskat)abstract
- Induration of magnetite pellet involves three important phenomena, namely oxidation, sintering and associate heat transfer; these phenomena are interdependent on determining the final quality of the pellet. In order to study the sintering a novel optical dilatometric method was used. These studies were performed separately for magnetite and completely oxidized magnetite. Further, the sintering phenomena was modeled taking cues from powder metallurgy literature. In order to study the oxidation kinetics, TGA analysis were conducted both at powder and pellet scales at sufficiently low enough temperatures so that sintering effects are minimized. Interesting results that has not been reported earlier have been observed and these results could be explained using available gas-solid reactions models both at powder and pellet scales. Once the sintering and oxidation models were validated independently, they were integrated along with heat transfer model to realize a comprehensive induration model. These efforts have resulted in a Single Magnetite Pellet Induration Model (SPIM) which in principle can be used for optimizing raw material mix as well as the process parameters at the reactor scale.
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