| 1. |
- Lu, Yu-Chiao, 1995-
(författare)
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Application of Hydrochar for Low-CO2 Emission Steel Production
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Steel is an indispensable material of the modern society and yet the production of steel is one of the largest anthropogenic CO2 emission sources on the planet. The conventional blast-furnace-basic-oxygen-furnace (BOF) process is responsible for generating 85% of the steel industry’s total CO2 emissions, which is the result of a high coal consumption rate for the reduction of iron ores and for providing the heat necessary for the high-temperature process. In order to meet the climate goal set by the Paris Agreement, the iron and steel industry must drastically decrease its CO2 emissions and aim at achieving net-zero emissions by 2050. Bioenergy is a form of renewable energy, and if it is managed sustainably throughout its life cycle, it can be considered carbon-neutral. Replacing fossil fuels with biofuels consumed during the steelmaking processes is one way to decrease CO2 emissions. However, this approach has not been widely adopted by steelmakers over the world due to the high price and the limited availability of wood-based biofuels. Hydrochar is a coal-like solid material that is produced from the hydrothermal carbonization (HTC) of biomass. It has attracted great interest from steelmakers due to its coal-like properties and the fact that it can be produced from a wide range of organic waste streams that can be found in almost every country. Previous studies focused on the use of hydrochar for the blast furnace process. This thesis therefore examines the potential use of hydrochar in the direct-reduction-electric-arc-furnace (DR-EAF) process, and particularly in two applications where the use of fossil coal is difficult to abate—the coal-based direct reduction of iron ore and the carburization of liquid steel in the EAF. This thesis begins with a characterization study of a hydrochar produced from lemon peel waste (LPH) and its comparison with a fossil reference material (anthracite) and two bio-reference materials (charcoal). The results reveal that LPH is a highly volatile material that is characterized by a low fixed carbon content and a medium calorific value. The volatile matter of LPH consists of gas, tar, and aqueous liquids, and contains approximately half of the total carbon and energy content of LPH. On the contrary, charcoal, anthracite, and the pyrolyzed char of LPH (PLPH) hardly emit any volatiles and are stable up to a high temperature (1200 °C). These materials are characterized by high fixed carbon contents and high calorific values, which makes them ideal fuel, carburizers, and reducing agents. On the other hand, LPH seems to be more efficient when it is applied in areas where its volatile matter content could be utilized to an advantage, such as to provide heating energy and to reduce metal oxides. Next, two hydrochars (produced from lemon peel and rice husk) were tested for coal-based direct reduction and their performance were compared to that of anthracite. Hematite-carbon mixtures prepared with varying fixed-carbon-to-oxygen ratios (C/O) were heated in nitrogen atmosphere up to 1100 °C for direct reduction. The hematite in briquettes with molar C/O ratios greater than 1.0 were completely reduced to metallic iron, whereas briquettes with C/O ratios equal to 0.4-0.5 were reduced by 63-86%. It was confirmed that the volatile matter released by the carbonaceous materials and the organic binder reduced hematite up to a maximum of 35% but the utilized fractions of the volatile matter were quite low (12-56%). As a result, the reduction of hematite was dominated by carbothermic reduction which involved fixed carbon. Thus, the efficiency of a carbonaceous material as a reducing agent for the coal-based direct reduction processes is still predominantly determined by its fixed carbon content. Then, LPH was tested for carburization of liquid iron in a laboratory setup under an inert atmosphere and its performance was compared with that of charcoal. Iron-carbon briquettes, which have higher apparent densities than the carbonaceous material itself, were utilized as carburizers with an aim to improve the carbon’s penetration depth in the liquid iron. The briquettes were experimented in two different ways to simulate the carbon addition practices in an EAF. With the first method, the briquettes were slowly heated from room temperature up to 1600 °C, which simulates the loading of carbon into an EAF at the beginning of a heat via a scrap bucket. With the second method, briquettes were directly charged into a pool of liquid iron. The results reveal that the carburization yield is predominantly determined by the fixed carbon content of the carbonaceous material, and when a more aggressive carbon addition method (e.g. direct charging) was used, there were additional carbon losses which lowered the yield. In the final part of the thesis, two types of hydrochars (those produced from orange peel and green waste) and an anthracite were applied for carburization tests in a pilot-scale EAF. Carbonaceous materials were either top-charged into the EAF at the beginning of a heat, or injected as powder via a lance directly into liquid steel after scrap meltdown. The results show that hydrochar and anthracite has a similar carburization yield (based on fixed carbon) when the same carbon addition method was used, and the carburization yields achieved by top-charging were higher than that achieved by lance injection. Based on the results obtained in this thesis, three main conclusions are drawn. Firstly, hydrochar can completely replace fossil coal as a reducing agent for the direct reduction of iron ores and as a carburizing agent in the EAF process. However, it is more efficient to use pyrolyzed hydrochar than to use pristine hydrochar since the fixed carbon content of the material mostly determines its substitution ratio for anthracite. Secondly, some negative impact of the ash content of hydrochar has been identified in this study. For example, the reduction rate of hematite-carbon composite mixture is lowered by the hindering effect of ash on carbothermic reduction. Furthermore, ash increases the slag volume and decreases the slag’s basicity in the EAF. Hydrochars produced from fruit peel wastes (lemon peel, orange peel) have lower ash contents than hydrochars produced from plant wastes (rice husk, green waste) and are more suitable to be applied directly in steelmaking processes. Lastly, the substitution of anthracite with charcoal or hydrochar lowers the total amount of sulfur introduced into the EAF. The increase in the amount of phosphorous introduced into the EAF resulting from the addition of hydrochar can be resolved either by controlling the amount of hydrochar added, or by lowering the phosphorous content of hydrochar through additional impurity reduction treatment following the HTC process, which should be investigated in future studies.
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| 2. |
- Bi, Yanyan
(författare)
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Three Dimensional Determinations of Inclusions in Ferroalloys and Steel Samples
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As the requirements on material properties increase, there has been a demand on an additional knowledge on the effect of impurities in the ferroalloyson the steel cleanness. Thus, the number, morphology, size and composition of inclusions in sixdifferent ferroalloys (FeTi, FeNb, FeSi,SiMn, LC and HC FeCr) were investigatedin this study. This was done in three dimensions (3D) by using a SEM in combination with EDS after electrolytic extraction of the ferroalloy samples. Theresults show that thenon-metallic and metallic inclusions can besuccessfully analyzed on the surface of a film filterafter a separation of the inclusions from the matrix. Overall, the inclusions canbe divided into two categories depending on the melting point. Furthermore, the possible transformation of different kinds of inclusions after their addition to the liquid steel canalso be determined.The inclusions and clusters in steel samples of two similar steel grades of high-silicon non-calcium treated (HSiNC) stainless steels were also 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: a low Al steel (LAl) and a high Al steel (HAl). Spherical (SP), irregular and regular (IR) inclusions and clusters (CL) were observed in the samples from both heats. It wasfound 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-Al2O3spherical inclusions. The compositions of irregular and regularinclusions and clusters in steel samples of a high Al steel were mostly MgO·Al2O3spinel, but also complex sphericalinclusions containing Al2O3-MgO-CaO-SiO2. In addition, the phase stabilitydiagram based on Darken’s quadratic formalism and Redlich-Kister type polynomial was estimated for both heats at a non-infinite solution.It is known that clusters in liquid steel have a harmful effect on the casting process and the quality of the final steel product. Therefore, 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 differentholding times after the addition of a mischmetal. The morphology, composition, number and size of clusters in PT and IH steel samples were analyzed and compared as a function of the 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 μm. In addition, the size and number of most clusters in PT are larger than those in IH samples.Largesize inclusions are recognized to be crucially harmful for the mechanical properties of steel products. Therefore, predictionsof the maximum size of Al2O3-CaO spherical inclusions in an Fe-10 mass% Ni alloy have been examined based on two dimensional (2D) and three dimensional (3D) investigations. The effects of the number of measurements and unit volume on the estimated 3D results were also investigated.
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| 3. |
- Davydenko, Arkadiy
(författare)
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Some aspects of recycling of rest products and slag foaming in the EAF during stainless steel production
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An efficient stainless steel making industry is defined by different factors such as an efficient utilisation of energy in the Electric Arc Furnace (EAF). This requires a good by slag foaming practice and an utilisation of waste products from own production facilities. In the following study, briquettes applied for a combined slag foaming and waste product recycling in the EAF were investigated in both laboratory and industrial scales. More specifically, briquettes were characterised and used for slag foaming in the EAF. The recipes of the briquettes were made based on a literature review and previous experience. Afterwards, the composition and density of briquettes were defined and compared to calculated data. Moreover, weight reduction experiments were made on a laboratory scale at temperatures up to 1500°C in an argon atmosphere in order to characterise the products (metal, slag and gas) produced by briquettes. The calculations were also compared to experimental data. Thereafter, briquettes with different densities and pet-coke addition were tested on an industrial scale to study slag foaming in the EAF process during a stainless steel production. The slag foaming tendencies were determined based on visual estimations of slag foaming, determinations of the slag density before and after additions of different briquettes, and by calculating a foaming index. Moreover, the influence of the main parameters of the briquettes (composition, density) and the furnace slag (composition, basicity and etc.) on slag foaming was studied. Investigation of briquettes made on laboratory and industrial scales provided the following main results: the density of briquettes can successfully be verified, briquettes have different mechanical properties depending on the materials used for production of briquettes, briquettes yield different amounts of metal and gas. Moreover, it was found that the heavy briquettes (containing FeCr) produce about half the amount of gas compared to the light briquettes (without FeCr). The main part of the gas was generated during the first 2-3 min. Also, the valuable metals can be recovered from briquettes; recipes of briquettes can be optimized based on the amount of metal droplets in briquettes and the total utilisation of carbon. In addition, it was found that both heavy and light briquettes can be used for slag foaming. The highest slag foaming rate was obtained for slags with a basicity in the range of 1.31-1.49.
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| 4. |
- Du, Hongying, 1991-
(författare)
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Evaluations of Non-metallic Inclusionsin Ca-treated Steels and Their Effect on the Machinability
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent decades, a considerable development of steel with respect to the performance of steel has taken place, which also has resulted in large challenges to process these steel grades. Therefore, it is essential to make suitable modifications of non-metallic inclusions (NMI) in the steelmaking process and to have a good control of its characteristics to meet the target mechanical properties and to obtain a good machinability. Based on a case of 316L stainless steel trials with a calcium modification to improve the machinability of steel, the influence and contribution of different NMIs on the machinability were discussed. First, based on the Thermo-Calc calculation results with respect to the appropriate range of Ca additions, steel is produced by an additional Ca treatment at the end of the ladle treatment. In order to evaluate non-metallic inclusions and their influence on machinability tests, steel samples were collected from rolled bars produced by the conventional production route (316R) and an experimental trial with Ca treatment (316Ca). The metal chips generated during the machining test were also collected for the evaluation of chip breakability and NMIs characteristics after machining. In addition, the Electrolytic extraction (EE) technology is used to extract NMIs from steel and chip samples. Then, a three-dimensional (3-D) study is performed on the inclusions collected on a membrane filter using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The morphology, size, number, frequency, and composition of non-metallic inclusions are studied. Four main types of inclusions were found in the 316Ca steel: Type I (elongated MnS), Type II (oxy-sulfides with hard oxide cores), Type III (soft elongated oxides), and Type IV (hard undeformed oxides).The results show that the morphologies of NMIs in stainless steel chips were significantly changed after cutting. Overall, three different main shapes of NMIs were found: i) Group I having similar shapes, ii) Group II stretched inclusions having very thin film-like (Group II-a) and fractured stretched morphologies (Group II-b), and iii) Group III brittlely fractured inclusions. The total areas of MnS and SO inclusions in the secondary deformation zone of the chips were significantly increased (by up to 2-3 times) compared to that of the reference steel sample before the cutting test. It was found that the morphologies of NMIs during machining depend on the location in chips, the workpiece material, as well as the applied cutting speed. This results in different temperatures and metal matrix deformation degrees during machining. In addition, the chip breakability and chip tool contact length of the reference steel and the experimental steel were evaluated and compared with the characteristics of NMIs in the two steels. A new weight-measurement-based method was developed. The results show that the 316Ca steel generally has a better machinability compared to the reference 316R steel. However, the chip-tool contact length results show that the modification of NMIs for machinability improvements is only beneficial in some machining processes. The 316R steel was preferred at low cutting speeds, whereas the 316Ca steel was preferred at high cutting speeds. The different characteristics of NMI in the various cutting conditions and materials lead to different behaviors and functions of NMI during processing. Finally, the possible application of PDA/OES in the steelmaking process was also evaluated. This online survey method developed in the industry during recent years provides a high possibility for implementing a rapid screening of the NMI content and shows the potential of establishing an online control of NMI during the processing of steel.
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| 5. |
- Ericsson, Ola
(författare)
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An Experimental Study of a Liquid Steel Sampling Process
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the steelmaking process samples are taken from the liquid steel, mainly to assess the chemical composition of the steel. Recently, methods for rapid determination of inclusion characteristics (size and composition) have progressed to the level where they can be implemented in process control. Inclusions in steel can have either good or detrimental effects depending on their characteristics (size, number, composition and morphology). Thereby, by determination of the inclusion characteristics during the steelmaking process it is possible to steer the inclusion characteristics in order to increase the quality of the steel. However, in order to successfully implement these methods it is critical that the samples taken from the liquid steel represent the inclusion characteristics in the liquid steel at the sampling moment. The purpose of this study is to investigate the changes in inclusion characteristics during the liquid steel sampling process. Experimental studies were carried out at steel plants to measure filling velocity and solidification rate in real industrial samples. The sampling conditions for three sample geometries and two slag protection types were determined. Furthermore, the dispersion of the total oxygen content in the samples was evaluated as a function of sample geometry and type of slag protection. In addition, the effects of cooling rate as well as oxygen and sulfur content on the inclusion characteristics were investigated in laboratory and industrial samples. Possibilities to separate primary (existing in the liquid steel at sampling moment) and secondary (formed during cooling and solidification) inclusions depending on size and composition were investigated. Finally, in order to evaluate the homogeneity and representative of the industrial samples the dispersion of inclusion characteristics in different zones and layers of the samples were investigated. It was concluded that the type of slag protection has a significant effect on the filling velocity and the sampling repeatability. Furthermore, that the thickness of the samples is the main controlling factor for the solidification rate. It was shown that top slag can contaminate the samples. Therefore, the choice of slag protection type is critical to obtain representative samples. It was shown that the cooling rate has a significant effect on the number of secondary precipitated inclusions. However, the number of primary inclusions was almost constant and independent on the cooling rate. In most cases it is possible to roughly separate the secondary and primary oxide inclusions based on the particle size distributions. However, in high-sulfur steels a significant amount of sulfides precipitate heterogeneously during cooling and solidification. This makes separation of secondary and primary inclusions very difficult. Moreover, the secondary sulfides which precipitate heterogeneously significantly change the characteristics (size, composition and morphology) of primary inclusions. The study revealed that both secondary and primary inclusions are heterogeneously dispersed in the industrial samples. In general, the middle zone of the surface layer is recommended for investigation of primary inclusions.
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| 6. |
- Jarnerud, Tova, 1976-
(författare)
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Utilization of recovered lime-containing materials from pulp and paper industries as slag formers in stainless steel production
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, major efforts have been made to develop a more circular economy. The desire to reuse, remanufacture and recycle materials are important for the development towards a sustainable society. An extended lifespan of materials helps to reduce the amount of waste kept in landfills, as well as to reduce the extraction of natural resources. Pulp and paper and steel industries are two of the largest export industrial sectors in Sweden. It is well known that the pulp and paper industries also generates large amounts of organic and inorganic wastes, of which a significant part is kept in landfills. Year by year deposit of wastes in landfills is becoming more difficult to handle and expensive due to stronger regulations and requirements regarding the environment. During Electric Arc Furnace (EAF) and Argon Oxygen Decarburization (AOD) stainless steelmaking operations, burnt lime (primary lime) is charged together with other slag forming materials in the furnace or converter to attain a specific basicity of the slag and to achieve purification from unwanted elements by chemical reactions in the steel.However, a number of CaO-containing wastes from pulp/paper mills can be used as slag formers in steelmaking processes to replace the currently used burnt natural lime, since the use of this primary lime does not conform with the closing the loop idea that is being prioritized in modern society. This thesis presents results from preliminary experiments for examining the replacement of primary lime with secondary lime from pulp and paper production waste as slag formers in EAF and AOD converters. The obtained results showed a possibility of using up to 30% CaO from secondary lime as a replacement for primary lime in the EAF. Furthermore, the amount of ferrosilicon alloys additions can be decreased by up to 3kg/ton of steel. For the AOD process the use of secondary lime doesn´t have any negative effects on the decarburization process and reduction process. Furthermore, it has similar desulphurization functions as the primary lime. However, the phosphorus content in the metal was slightly increased. Thus, the replacement ratio of secondary lime will be limited by the acceptable phosphorus level in the final steel due to higher phosphorus content in wastes from pulp and paper mills compared to that in primary lime. Moreover, it was revealed during this study that slags from AOD converters can be used as binding agents for briquetting of these secondary lime materials. These results shows that waste/by products from two major industries can be used to make metallurgical briquettes, uniting two major industrial sectors in a circular symbiosis towards a more sustainable future.
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| 7. |
- Kellner, Hans, 1989-
(författare)
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Study of Non-metallic Inclusion in Alloy 825
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is well known that inclusions affect the properties of steels and alloys. Therefore, it is important to understand what type of inclusions that exist and how they behave and especially with a focus on large size inclusions. Thus, the large size non-metallic inclusions in ferroalloy FeTi70R were investigated in two dimensions (2D) by using scanning electron microscopy (SEM) in combination with an energy dispersive technique (EDS). It was found that the FeTi70R ferroalloy contain complex oxide inclusions consisting mostly of CaO, SiO2 and TiOx. Furthermore, experimental trials were performed to investigate how these inclusions behaved when entering a melt. More specifically, a comparison between pure Fe and an Alloy 825 grade were made. These results determined the parameters effect on the transformation of the inclusions in the melt.The large size non-metallic inclusions in Alloy 825 during the ladle treatment were investigated during industrial trials by using both two dimensional (2D) and three dimensional (3D) microscopic investigations. The results showed that inclusions consisted of spherical oxides and clusters made up of oxides and nitrides. Further investigations found that the spherical inclusions were transformed from existing NMI in the FeTi70R ferroalloy and slag particles. As for the clusters, they originate from deoxidation products. Furthermore, small inclusions precipitated in the local zones around the added FeTi70R ferroalloy and titanium nitrides. Investigations also found that only Al2O3-MgO and TiN clusters exist after casting.Industrial trials were performed during the last period of the ladle treatment and using a combined electromagnetic (EMS) and gas (GS) stirring. The purpose to investigate the effect of different EMS directions on the agglomeration and on the removal of Al2O3-MgO and TiN clusters. The investigations were then performed in 3D after an electrolytic extraction of the metal samples. The results show that electromagnetic stirring in the upwards direction is best for the agglomeration of the Al2O3-MgO and TiN clusters. However, electromagnetic stirring in the downwards direction is more effective to remove clusters from the melt. This is in agreement with the theoretical predictions based on Stokes’, Brownian and Turbulent collisions. Also, the calculations showed that for Al2O3-MgO clusters with sizes <20 μm the Turbulent collision is the defining factor for agglomeration. However, both Stokes’ and Turbulent collisions are dominant for larger inclusions. For the TiN clusters, turbulent collisions is the dominant factor.Further investigations with more heats and stirring modes were done by using 2D microscopic investigations. More specifically, the number, size, composition and morphology of different inclusions were determined by using SEM in combination with EDS and Inca Feature analyses. The results show that the EMS in downwards direction with a 0.04 m3 min-1 gas flow rate promotes a general removal of Al2O3-MgO and TiN inclusions. Furthermore, that the upwards EMS direction promotes a drastically increase of inclusions having an equivalent size smaller than 11.2 μm. Moreover, the stirring with a 0.02 m3 min-1 gas flow rate has a better removal rate for both downwards and upwards stirring directions compared to the stirring with a 0.04 m3 min-1 gas flow rate. However, no influence on the inclusion composition and morphology could be seen from the different stirring modes.
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| 8. |
- Muwanguzi, Abraham Judah Bumalirivu
(författare)
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Investigating the parameters that influence the behaviour of natural iron ores during the iron production process
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the iron production processes, sinters and pellets are mostly used as raw materials due to their consistency with respect to physical and chemical properties. However, natural iron ores, as mined, are rarely used directly as a feed material for iron processing. This is mainly due to the fact that they have small contents of iron and high concentration of impurities. Moreover, they swell and disintegrate during the descent in the furnace as well as due to low melting and softening temperatures. This work involves an investigation of the parameters that influence the use of natural iron ores as a direct feed material for iron production. Furthermore, it points out ways in which these can be mitigated so as to increase their direct use in iron production.Natural iron ore from Muko deposits in south-western Uganda was used in this study. Initially, characterisation of the physical and chemical properties was performed, to understand the natural composition of the ore. In addition, investigations were done to study the low temperature strength of the ore and its behaviour in the direct reduction zone. Also, simulations were performed with three models using the experimental data from the direct reduction experiments in order to determine the best model for predicting the direct reduction kinetics of natural iron ores.Chemical analyses showed that the Muko ore represents a high grade of hematite with an Fe content of 68% on average. The gangue content (SiO2+Al2O3) in 5 of the 6 investigated iron ore samples was < 4%, which is within the tolerable limits for the dominant iron production processes. The S and P contents were 0001-0.006% and 0.02-0.05% respectively. These can be reduced in the furnace without presenting major processing difficulties. With respect to the mechanical properties, the Muko ore was found to have a Tumble Index value of 88-93 wt%, an Abrasion Index value of 0.5-3.8 wt% and a Shatter Index value of 0.6-2.0 wt%. Therefore, the ore holds its form during the handling and charging processes.Under low temperature investigations, new parameters were discovered that influence the low temperature strength of iron oxides. It was discovered that the positioning of the samples in the reduction furnace together with the original weight (W0) of the samples, have a big influence on the low temperature strength of iron oxide. Higher mechanical degradation (MD) values were obtained in the top furnace reaction zone samples (3-25% at 500oC and 10-21% at 600oC). These were the samples that had the first contact with the reducing gas, as it was flowing through the furnace from top to bottom. Then, the MD values decreased till 5-16% at a 500oC temperature and 6-20% at a 600oC temperature in the middle and bottom reaction zones samples. It was found that the obtained difference between the MD values in the top and other zones can be more than 2 times, particularly at 500oC temperature. Furthermore, the MD values for samples with W0 < 5 g varied from 7-21% well as they decreased to 5-10% on average for samples with W0 ≥ 5 g. Moreover, the MD values for samples taken from the top reaction zone were larger than those from the middle and bottom zones.During direct reduction of the ores in a H2 and CO gas mixture with a ratio of 1.5 and a constant temperature, the reduction degree (RD) increased with a decreased flow rate until an optimum value was established. The RD also increased when the flow rate was kept constant and the temperature increased. An optimum range of 3-4g was found for natural iron ores, within which the highest RD values that are realised for all reduction conditions. In addition, the mechanical stability is greatly enhanced at RD values > 0.7. In the case of microstructure, it was observed that the original microstructure of the samples had no significant impact on the final RD value (only 2-4%). However, it significantly influenced the reduction rate and time of the DR process.The thermo-gravimetric data obtained from the reduction experiments was used to calculate the solid conversion rate. Three models: the Grain Model (GM), the Volumetric Model (VM) and the Random Pore Model (RPM), were used to estimate the reduction kinetics of natural iron ores. The random pore model (RPM) provided the best agreement with the obtained experimental results (r2 = 0.993-0.998). Furthermore, it gave a better prediction of the natural iron oxide conversion and thereby the reduction kinetics. The RPM model was used for the estimation of the effect of original microstructure and porosity of iron ore lumps on the parameters of the reduction process.
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| 9. |
- Nabeel, Muhammad, 1987-
(författare)
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A study of micro-particles in the dust and melt at different stages of iron and steelmaking
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dust particles generated due to mechanical wear of iron ore pellets and clusters formed in molten stainless steel alloyed with rare earth metals (REM) are considered in this study. Firstly, the influence of the characteristics of iron ore pellets, applied load on a pellet bed and partial reduction of the pellets on the size distribution of the generated dust was investigated. Secondly, REM clusters are investigated to evaluate the size distribution of the clusters. Also, an extreme value distribution (EVD) analysis has been applied for the observed REM clusters.The large sized pellets showed 10-20% higher wear rate than small sized pellets during wear in a planetary mill. Moreover, an increase of ~67% was observed in the friction and dust generation in the pellet bed as the applied load increased from 1 to 3 kg. Also, it was observed that a higher friction in the pellet bed can lead to an increased amount of airborne particles. The mechanical wear experiments of pellets reduced at 500 °C (P500) and 850 °C (P850) showed that P500 pellets exhibit ~16-35% higher wear rate than unreduced pellets. For the P850 pellets, the wear is inhibited by formation of a metallic layer at the outer surface of the pellets. The mechanism of dust generation has been explained using the obtained results.A reliable cluster size distribution of REM clusters was obtained by improving the observation method and it was used to explicate the formation and growth mechanism of REM clusters. The results show that the growth of clusters is governed by different types of collisions depending on the size of the clusters. For EVD analysis three different size parameters were considered. Moreover, using the maximum length of clusters results in a better correlation of EVD regression lines compared to other size parameters. Moreover, a comparison of predicted and observed maximum lengths of clusters showed that further work is required for the application of EVD analyses for REM clusters.
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| 10. |
- Sidorova, Elena, 1991-
(författare)
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Non-metallic inclusions in pipeline steels and their effect on the corrosion resistance
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focus on investigations of the influence of non-metallic inclusions on corrosion in steel samples taken at different stages of the steel production when producing pipeline steels. The electrolytic extraction technique was used to extract inclusions from these steel samples and thereafter studying them using scanning electron microscopy in combination with energy dispersive microscopy. This approach enabled three-dimensional evaluations of different non-metallic inclusions present in two metal samples of low-carbon Ca-treated pipeline steels. The modification of the inclusion characteristics was investigated and compared for steel samples taken from various stages of the smelting production process. Thereafter, the corrosion resistance of these steels was discussed depending on the characteristics of non-metallic inclusions present in the steel. In addition, this study also presents a new method of soft chemical extraction for qualitative and quantitative evaluations of the initial corrosion processes of a steel matrix surrounding various non-metallic inclusions. The results showed that the initial dissolution of the steel matrix started in areas surrounding CaS inclusions or inclusion phases containing a CaS phase. Furthermore, the results showed that no dissolution of the metal matrix surrounding CaO·Al2O3 and TiN inclusions could be detected. Key words: pipeline steels, Ca-treatment, non-metallic inclusions, electrolytic extraction, corrosion, chemical extraction.
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