1,721,169 research outputs found
Fingerprint of a submerged-arc furnace: Optimising energy consumption through data mining, dynamic modelling and computational fluid dynamics
No full textThis study imparts a scientific perception of a phosphorous-producing submerged arc furnace never seen before; a proverbial fingerprint that can improve problem identification, disturbance diagnostics, process prediction, dynamic modelling and model predictive control of this type of furnace. It successfully incorporates accurate, multi-field thermodynamic-, kinetic- and industrial data with computational flow dynamic calculations; thus further unifying the sciences of kinetics and equilibrium thermodynamics. The true power of this study is the extensive and methodical validation that ensures industrially endorsed results. To facilitate all this the author spent six uninterrupted months at an industrial plant (Thermphos International), twice walked inside a cold submerged-arc furnace, gathered and analysed more than thirty-four mineralogical samples, managed an extensive and insightful sampling campaign on the slag streams, performed feed material porosity tests and had thirteen additional temperature probes installed inside the furnace lining. The author also scrutinised over years of industrial data, inspected many industrial drawing and partook in countless valuable conversations with industrial and technical experts to guarantee, not only a valuable scientific contribution, but one that is deep-rooted in authentic engineering principles.Mechanical Maritime and Materials Engineerin
Experimental Study of the Melting and Reduction Behaviour of Ore Used in the HIsarna Process
No full textThe HIsarna is a coal-based smelting reduction process for ironmaking to drastically reduce CO2 emission and is one of the most promising alternative ironmaking processes under development in the world. The furnace consists of two inter-connected reactors: i) a smelting cyclone, ii) a smelting reduction vessel. The smelting cyclone is expected to provide about 20 % pre-reduction degree through thermal decomposition and reduction. However, as a new technology still at its development stage, the iron ore behaviour in the smelting cyclone is not well studied. Three HIsarna pilot plant campaigns have been conducted successfully during the years of 2011-2013 at the Tata Steel site in IJmuiden, the Netherlands. The laboratory study has been carried out in the same period at Delft University of Technology as part of the research programme of the Matrials innovation institute M2i, to focus on the thermal decomposition and reduction kinetics of individual particles in the smelting cyclone of the HIsarna, forming the main part of this thesis. In this study, a special experimental set-up has been designed and commissioned: the high temperature drop tube furnace (HTDF). The HTDF was used to investigate the reduction mechanism at high temperature of individual ore particles without agglomeration. The reaction gas is a mixture of CO, CO2, H2 and N2, and the composition is controlled with mass flow controllers. The gases are firstly guided into a gas mixing station and form a flow of gas mixture. And then the gas mixture is split up into two flows. A small flow of the gas mixture enters the syringe pump feeder as particle carrier gas. The other flow is preheated to 773 K through a pre-heat furnace before entering the electrically heated furnace. The particle feed rate is controlled by a syringe pump feeder. The individual iron ore particles from the syringe pump feeder pass through a water-cooled injection probe before entering the hot zone. The iron ore reduction takes place during the flying time of the particle in the hot zone. The off-gas and the partially reduced particles are received by a water-cooled sampling probe. Finally, the iron ore particles are collected by a sample collector. The study of the thermal decomposition behaviour of hematite ore started with a theoretical evaluation. The experimental study has been conducted with the TGA-DSC analyser and in a high temperature horizontal furnace at a steady state. The individual particle thermal decomposition behaviour has been investigated in the HDTF under different conditions. The theoretical evaluation shows that, in the inert gas environment, the lowest start thermal decomposition temperature of Fe2O3 could be room temperature when the partial pressure of oxygen is close to zero bar. The thermal decomposition of Fe2O3 can be accelerated when the temperature is higher than 1473 K. The thermal decomposition of pure Fe3O4 can also take place at room temperature when the partial pressure of oxygen is close to zero bar and the thermal decomposition can be accelerated when the temperature is higher than 1673 K. These results have been confirmed by the following experimental studies. From the TGA-DSC analysis, it was found that a sharp weight loss in a short time appears on the TG curve. However, the weight loss is quite small during the time elapsed after the sharp weight loss stage. The experimental study in the horizontal furnace provided accurate results of the thermal decomposition degree of hematite ore at different temperatures and holding times by chemical titration. The thermal decomposition degree of iron ore increases with the increase of temperature. At the same temperature, the thermal decomposition degree of iron ore increases slowly with the increase of holding time (1 h, 2 h and 3 h). In addition, no significant difference was observed between the results at 1673 K and 1773 K. Furthermore, whether the sharp weight loss stage occurs and how much of the thermal decomposition degree could be achieved in the smelting cyclone has been further tested with the HTDF. The effects of different inert gases: N2, Ar, CO2 (CO2 is the primary gas in the pilot plant besides CO), temperature, residence time, and particle size on the final thermal decomposition degree were studied. It was found that the sharp weight loss stage observed in the TGA-DSC experiments can be mostly achieved in the HTDF in the CO2 gas rather than N2 and Ar. For example, at 1750 K in CO2 gas, the thermal decomposition degree of iron ore in the HTDF is around 10.8 % which is slightly lower than the value of 12.6 % obtained in the horizontal furnace. This is because the fine iron ore particles could be heated up faster in CO2 gas than in N2 and Ar gas due to the strong radiation properties (emission and absorption) of CO2 gas. Temperature plays an important role in determining the iron ore thermal decomposition which dramatically goes up with the increase of temperature. However, there is no significant influence of particle size and residence time on the thermal decomposition degree observed, when the particle diameter is smaller than 250 µm. It indicates that the thermal decomposition of iron ore quickly takes place in the first 210 ms. Based on the results of thermal decomposition of iron ore particles, the individual particle reduction mechanism of hematite ore in the smelting cyclone has been investigated with the HTDF. Under the studied experimental conditions, the maximum reduction degree of iron ore particle is in the range of 23-30 %. Before reaching the reduction equilibrium state, the reduction degree of iron ore goes up with the increase of residence time and temperature, and decreases with the increase of Post Combustion Ratio (CO2 + H2O)/(CO + CO2 + H2+ H2O). The gas-solid particle reaction takes place in all the studied residence times at 1550 K and 1600 K, and at 1650 K in the residence times of 210-970 ms. The 100 % gas-molten particle reduction takes place at 1700 K in the residence times of 700-2020 ms and in all the studied residence times at 1750 K. The reduction degree of iron ore in the first 210 ms is the combined result of reduction and thermal decomposition. During the reduction process, quantities of micro pores were formed due to the different crystal structures of hematite, magnetite and w?stite. The micro pores could accelerate the reduction process. The reaction mechanism of iron ore reduction at high temperature has been revealed through the kinetic analysis. The kinetic model was determined by microscopic examination. The unreacted shrinking core model was applied to both gas-solid particle reaction and gas-molten particle reaction. The rate controlling step of gas-solid particle reduction was obtained by the model-fitting method and confirmed by the model-free method, and the rate controlling step of gas-molten particle reduction and mixed reduction was obtained by the model-fitting method. The reaction rate controlling step was found to be the chemical control for gas-solid particle reduction, mixed reduction and gas-molten particle reduction from a macrokinetics point of view. Through further study, the rate controlling step of gas-solid particle reduction was found to be mass transport of cations and electrons inside the matrix along the interfaces from a microkinetics point of view. The most typical operating conditions of the smelting cyclone of the HIsarna process have been studied in this study and the fundamental understanding of the reduction kinetics of the individual iron ore particle is presented in this thesis. At the same time, new questions about the reactions and the reactor systems have been raised like the reduction mechanism of bigger particle size, reduction behaviour of ‘particle swarms’, the particles’ collision behaviour and so on. The further laboratory study seems significant for future development of the HIsarna process.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin
DEM-CFD Modelling of the ironmaking blast furnace
No full textMaterials Science & EngineeringMechanical, Maritime and Materials Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
AI2O3 in steel and its transformation with calcium
No full textMaterials Science and EngineeringMechanical, Maritime and Materials Engineerin
Microstructural Changes in Brazing Sheet due to Solid-Liquid Interaction
No full textAluminium brazing sheet is the material of choice to produce automotive heat exchangers. Although in Dutch the official translation of aluminium brazing sheet is “aluminium hardsoldeerplaat” the English name is used in the industry. Aluminium brazing sheet is basically a sandwich material and consists of an aluminium core alloy, typically an AA3XXX alloy (containing Mn) or an AA6XXX alloy (containing Mg and Si) with a clad alloy of the AA4XXX (containing Si) series. The core alloy gives the final product the desired properties after brazing. The core alloys are designed in such a way that after the brazing cycle, the condition is reached where the core has its optimum properties. Properties like strength and corrosion resistance are the main engineering parameters. Typically the core alloy is single side or both side clad and the thickness of the clad alloy ranges between 5 and 20% of the total thickness. The AA4XXX alloy used for aluminium brazing sheet has a melting range between 570°C and 610°C while the melting range of a typical AA3XXX core alloy lies above 610°C. This difference in temperature between the two alloys is used to join complex shaped products in “one shot”. At the brazing temperature, typically around 600°C, the AA4XXX clad alloy is completely molten. Due to capillary forces and surface tension differences, the molten clad alloy will flow to connect adjacent pieces. The process by which joining is taking place is called the brazing process. During this brazing process liquid metal from the clad alloy is in close contact with the solid core alloy. At this stage an interaction between the two phases can take place. Several types of interaction between the two phases can take place but the interaction that is referred to as Liquid Film Migration is the topic of study in this thesis. Liquid Film Migration is, however, not the only name given in literature to what seems to be the same interaction. Liquid Film Migration is causing a significant change in microstructure and element distribution of the core alloy. These changes are detrimental to the corrosion resistance of the final product. Although the name Liquid Film Migration was given to the process responsible for the observed changes no conclusive evidence has been presented to confirm the existence of a liquid film in aluminium brazing sheet. The literature available on Liquid Film Migration in aluminium brazing sheet has given some information on the conditions favourable for Liquid Film Migration to occur. These conditions are residual strain in the core alloy present at the peak brazing temperature and a small grain size of the core alloy. This thesis focussed on the occurrence of LFM in brazing sheet and the possible mechanism and driving forces behind it. Two different core alloys with the same clad alloy were processed and studied for their susceptibility to Liquid Film Migration. Conditions were created that according to literature should result in different degrees of Liquid Film Migration. Brazing took place in a standard brazing furnace or in a salt bath. The salt bath would enable a kinetic study since time and temperature are well controlled. The study of the samples after brazing indeed showed a different response to the applied processing. The main observation was that the onset of recrystallization of the core alloy plays a major role in the occurrence of Liquid Film Migration. A detailed study of the liquid film showed the accumulation of constituents and dispersoids which were originally present in the core alloy. The measured diffusion profiles of silicon in front of the liquid film coincide with theoretical diffusion profiles as if they originated from a moving boundary. From the diffusion profiles of silicon, the kinetics of the moving liquid film was extracted resulting in an inverse square root dependence of the velocity with time. An estimation of the energies available in the system showed that the coherency strain energy could not be the driving force for Liquid Film Migration in aluminium brazing sheet. Most likely the energy is supplied by the reduction of the (sub)grain size. This is supported by the fact that strained samples that do not recrystallize during brazing are the ones showing the highest degree of Liquid Film Migration. Based on these findings, the residual strain present in the form of sub-grains or dislocations is considered to provide the energy for the movement of the liquid film. A qualitative assessment of the residual strain present in samples after brazing supported the hypothesis that indeed this residual strain is the energy source needed for the movement of the liquid film. The mechanism behind liquid film migration has been found to be similar to the recrystallization process caused by Strain Induced Boundary Migration. It was presented that lowering the surface energy between grains by a liquid film would allow the boundary to move at lower dislocation densities compared to a non liquid infiltrated grain boundary. Recrystallization would reduce the dislocation density taking away the driving force to spport liquid film migration. Liquid film migration and strain induced boundary migration are both in competition for the same energy. Strain induced boundary migration can take place during the whole brazing cycle while liquid film migration only can occur in the presence of a liquid. This means that the clad alloy has to be at least partly molten to allow wetting of the grain boundaries. When recrystallization by strain induced boundary migration takes place no liquid film migration will occur. A theoretical approach to determine the velocity of the liquid film was in reasonable agreement with the observations. The main obstacle to completely quantify liquid film migration is the uncertainty of the development of the film thickness in time. As demonstrated, recrystallization plays a critical role in the onset of liquid film migration. A through Process Model was used to determine if such model could be used to predict recrystallization based on thermal mechanical process input parameters and alloy chemistry. Unfortunately the model lacks sensitivity to predict the onset of recrystallization in this study. However the model contains all necessary modules to ensure that after fine tuning for this application, more predictive power can be expected.Light Metal ProcessingMechanical, Maritime and Materials Engineerin
Mould powders for high speed continuous casting of steel
No full textLight Metals ProcessingMechanical, Maritime and Materials Engineerin
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Recycling of Glass Fibre Reinforced Aluminium Laminates and Silicon Removal from Aerospace Al Alloy
No full textAerospace aluminium alloys (7xxx and 2xxx series Al alloy) is one of the important Al alloys in our life. The recycling of aerospace Al alloy plays a significant role in sustainable development of Al industry. The fibre reinforced metal laminates GLARE including 67 wt.% 2024 Al alloy was used as upper fuselage in Airbus A380, but the solution for GLARE recycling is not available. Thermal recycling which uses high temperature to decompose the resin and separate the reinforcement fibres and fillers, has been used in the thermal delamination of Lacomet (one member of fibre metal laminates family). Similar to the thermal recycling of Lacomet, a practical solution for GLARE recycling in laboratory-scale was developed in this research.The recycling of GLARE consists of two steps. The first step is the separation of S2-glass fibre and 2024 Al sheets after the decomposition of resins in GLARE under thermal condition, the decomposition behaviour as well as the decomposition kinetics of resins in GLARE were studied. The second step is the re-melting and refining of the separated 2024 Al sheets, the critical influence factors such as the salt flux composition, refining temperature, the size of 2024 Al scrap and the ratio of salt flux to scarp were discussed in this research. Si is a harmful impurity for aerospace Al alloys, and Si concentration is strictly controlled in aerospace Al alloys. But a small amount of Al alloy scrap with high Si concentration is usually mixed together with aerospace Al alloy scrap during the recycling of aerospace Al alloys, thus Si concentration in final secondary aerospace alloys exceeds the upper limit of nominal concentration. Besides the improvement of the efficiency of scrap classification, the removal of impurity Si from recycled aerospace Al alloys is also an option to improve the quality of secondary aerospace Al alloys. In this research, the first attempt on Si removal from Al in laboratory-scale was conducted by using Ti addition method.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin
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