This work is aimed at understanding the thermodynamic principles influencing the phosphorus partition between slag and steel during steelmaking, particularly during refining of high-phosphorus hot metal using the basic oxygen steelmaking (BOS) process. Mapping of the slag path has been carried out using a mass balance model based on input conditions and off-gas analysis, which has been validated by intermediate measurements of slag and metal composition in an industrial basic oxygen furnace (BOF). The slag composition is found to vary over a wide range of basicity (%CaO/%SiO2) and iron oxide content. The partition of phosphorus increases with progress of refining but reduces during the intermediate period, corresponding to a decrease in iron oxide concentration and formation of “dry slag”. The phosphorus partition ratio increases again towards the end of the process. The equilibrium partition ratios for such conditions have been theoretically estimated using slag “model(s)”, based on the estimated slag compositions. It is seen that the partition ratio of phosphorus remains within 45% – 60% of the equilibrium value, showing a gradual decrease with progress of the refining process. Equilibrium phosphorus partition ratios for slags containing low concentrations of MnO and Al2O3 have been experimentally determined, over the ranges of basicity and iron oxide concentration approximately corresponding to that observed in the typical BOS process. It is seen that the equilibrium phosphorus partition ratio is practically independent of basicity greater than 2.5 – 2.6, over the entire range of temperature and FeOx concentration studied. Variation of the activity of P2O5 with basicity and FeOx concentration has been investigated to explain the trends observed in the variation of phosphorus partition ratio. It is seen that the activity coefficient of P2O5 is lowest, and hence most conducive for removal of phosphorus from steel, over certain finite ranges of basicity and iron oxide concentration. It follows that the efficiency of dephosphorisation is likely to be maximum if the basic oxygen steelmaking process is operated within these ranges. Simultaneous with this work, mathematical correlations have been developed for estimation of P2O5 activity coefficient and phosphorus partition ratio as functions of slag composition. The correlations are compared with those proposed by earlier workers and are found to result in better predictions over certain composition ranges. / QC 20100623

In the present work, viscosities and sulphide capacities of high alumina blast furnace slags were investigated. The systems investigated were four component CaO-SiO2-MgO-Al2O3 quaternary system, CaO-SiO2-MgO-Al2O3-TiO2 and CaO-SiO2-MgO-Al2O3-CaF2 quinary systems. Viscosities of high alumina blast furnace slags were experimentally determined by the rotating cylinder method using Brookfield digital viscometer model LVDV-II+ pro. Experiments were conducted in the temperature range of 1573- 1873 K. The effects of temperature, basicity, TiO2, CaF2 and silica activity of slags on viscosity were studied. Viscosity decreases with basicity for high alumina blast furnace slags with increase in basicity and CaF2. At higher basicity (~0.8), slag viscosity decreases even with small amount of TiO2 (~2%) addition in the slag. With increase in silica activity in the range of 0.1 to 0.4,viscosity of slag increases and the increase is steeper below liquidus temperature. Sulphide capacity of the slag was measured using gas-slag equlibria. The liquid slag was equilibrated with Ar-CO-CO2-SO2 gas mixture. The slag systems studied were the same as in the case of viscosity measurements. Experiments were conducted in the temperature range of 1773 to 1873 K. Effect of temperature, basicity, MgO,TiO2 and CaF2 contents of slags on sulphide capacity were studied. As expected, sulphide capacity was found to increase with increase in temperature and basicity. At higher experimental temperature (~ 1873 K) TiO2 was found to decrease the sulphide capacity of slags. But, at lower temperature, there was no significant effect of TiO2 on the sulphide capacity. Sulphide capacity increases with increase in MgO content of slag if MgO content is more than 5%. Based on above experimental data, models were developed for estimation of viscosity and sulphide capacity of blast furnace slags. These models were later on applied for designing the slags for achieving the optimum slag characteristics so that slag volume can be reduced. With the help of these models slag volume was reduced to the extent of 5-10 kg per ton hot metal and also silicon content of the hot metal was reduced by around 10% with some improvement in slag viscosity and sulphide capacity of the slag. / QC 20100818

During the production of steel the oxide inclusion content partly depends on the reaction of the melt with the furnace lining, the ladle lining and the pouring system. The refractory material may be eroded by the molten steel and slag as well as corroded through chemical reactions with the slag and molten steel and the deoxidation products. In this report the effects of revolution speed, temperature and steel composition on the rate of dissolution of commercial MgO-C refractory samples into Al-deoxidised molten steel and CaOAl2O3- SiO2-MgO slag were examined by the rotating cylinder method. The study also includes tests with slag were doloma refractory samples are examined by the same method. Cylinders of MgO-C refractory material were immersed in to steel that was deoxidised by adding metallic aluminium. This was carried out in the temperature range of 1873 to 1973C° and at rotational speeds of 100 to 800 rpm for different holding times. The experimental results show that the rate of dissolution of MgO-C refractory materials increased with the temperature, rotational speed and immersion time. This supports the assumption that the diffusion of magnesium through the slag boundary layer formed around the refractory samples would be the rate-determining step. Mass transfer coefficients calculated on the basis of experimental results are in good agreement with earlier published results for pure ceramics. A formation of a thin oxide layer at the interface was found. It is due the reaction between magnesium vapour and the CO generated by the reaction MgO and C in the refractory walls. The oxide inclusions formed in the steel have been shown to mainly consist of MgO, Al2O3 and a mixture of them. The rate of dissolution of solid MgO-C into liquid CaO-Al2O3-SiO2-MgO slag at different temperatures was studied under conditions of forced convection by rotating cylindrical refractory specimens in a stationary crucible containing the molten slag similar to the MgO-C refractory/steel experiments. The corrosion rate was calculated from the change in diameter of the cylindrical specimens. The specimens were rotated for 15 to 120 minutes at speeds of 100 to 400 rpm in the molten slag. The rate of corrosion increased with temperature and with rotating speed of the rod and decreased when the slag was nearly saturated with MgO. The experimental results confirm the assumption that the diffusion of magnesium oxide through the slag phase boundary layer controls the corrosion process. The corrosion mechanism seems to be the dissolution of elements in the refractory materials into the slag, followed by penetration into the pores and grain boundaries. Finally, grains are loosened from the refractory into the slag. The investigation of doloma and doloma-carbon showed that the dissolution of magnesia into the slag was determining the corrosion rate. As for the other experiments, steel/MgO-C refractory and slag/MgO-C refractory, the corrosion rate was calculated from the change in diameter of the cylindrical specimens. The specimens were rotated for 15 to 120 minutes at speeds of 100 to 400 rpm in the molten slag. The results from the study showed that refractory materials that were impregnated with carbon had a much better slag resistance than the refractory that contained no carbon. This is due to the higher wetting angle between carbon and slag. Corrosion of MgO-C refractories in different gas atmospheres consisting of air, Ar, CO or Ar/CO was also studied. Experiments were carried out in the temperature range 1173 K to 1773 K and for holding times between 2 to 120 min. The reaction rate of the MgO-C material was determined from measurements of the weight loss of the samples. The results showed that the refractory weight loss increased with an increased temperature or an increased holding time. The thermodynamic conditions and the experimental results show that magnesium gas and carbon monoxide gas should form during ladle refining of steel when the refractory material consists of MgO-C. / QC 20100813

Today’s problems with emissions of green house gases, land filling of waste and depletion of the oil reserves calls for new energy systems based on alternative fuels like biomass and waste. Gasification is an attractive technology for the use of such solid fuels. Conventional gasification, in the vast majority of cases, uses in-reactor heat release from combustion of part of the feedstock, possibly coupled with a limited preheating of the agent, to obtain the necessary temperatures in the gasifier bed. During recent years, a new gasification technology, using highly preheated gasification agents (> 1273 K), has been developed. The extra heat brought into the process by the high temperature agent reduces the amount of feedstock that has to be oxidized to supply the necessary heat and the use of highly preheated agents has previously proven to have several positive effects on the fuel gas quality.In difference to the previous work on gasification with highly preheated agents, this thesis primarily focuses on the fundamental aspects namely, mass conversion, heating and ignition. It starts by considering single fuel particles or thin beds of fuel particles inserted into highly preheated agents. Mass conversion, heating and ignition are reported in function of the temperature and oxygen concentration of the agent and formulas for the prediction of ignition time and ignition mechanism are developed. The perspective is then widened to include the whole gasifier bed. Simulations of fixed bed batch gasification using highly preheated agents are performed with a mathematical model and used to study how the high agent temperature influences the mass conversion, devolatilisation front rate and the temperature distribution in the fixed fuel bed. Further, the gas quality and gasification efficiency are studied by means of large scale experiment. Ultimately, a thermodynamic analysis of the whole autothermal gasification system, including both a regenerative preheating system and the gasifier, is made.The particle study reports results from experiments with wood and coal and agents consisting of mixtures of nitrogen and oxygen in various proportions. It is shown that an increase in agent temperature from 873 K to 1273 K make the conversion process faster, mostly due to an early onset of the devolatilisation (fast drying) but also due to an increased devolatilisation rate (at least in the case of wood). The time to ignition also decreases significantly, particularly so between 873 and 1073 K. Further, it is shown that the higher the agent temperature, the more pronounced was also the tendency of the coal particles to heat significantly faster in oxygen diluted conditions (5,10 and 21% oxygen) than in inert (0% oxygen) or oxygen rich conditions (30, 50, 80 and 100% oxygen). An increase in agent temperature is also shown to reduce the dependency of the process on the oxygen concentration, at least in diluted conditions (5-21% oxygen). The results also indicate that for coal an increase in the oxygen concentration, specifically in the region above the atmospheric concentration, leads to a decreased dependency on the agent temperature. It is finally shown in the experiments with agent temperatures of 1073 and 1273 K that a flame is promptly formed even in very low concentrations of oxygen.The gasifier study reports results from simulation of batch air gasification and experiments in both batch and continuous up-draft fixed bed gasifier with wood and waste derived fuel and air and mixtures of air and steam. It is shown that the conversion process is faster the higher the air temperature. In particular somewhere between air temperatures of 623 K and 803 K the process behaviour changes. In fact, the devolatilisation rate is significantly increased in this region while it increases less sharply with air temperature below and above this temperature window. The temperature distribution in the bed shows less sharp gradients at high temperature (> 803 K) than at low temperatures (< 623 K). It is also showed experimentally and in fairly large scale that the use of highly preheated air for the gasification of biomass and waste derived fuels can produce - in continuous mode – relatively high yields of product syngas with relatively high fractions of combustible gases and probably also low content of tar. The efficiency of the gasification under these conditions, even when the extra heat input in the preheated agent is considered in the computation of the gasification efficiency, is shown to be comparable to that of conventional gasification techniques. The results also shows that with the use of steam in the agent, the content of hydrogen can be further increased with respect to gasification with only preheated air.In base of the results of the particle study and the gasifier study it is shown that a there exists two regimes of operation in function of the agent temperature, separated by the minimum agent temperature to guarantee spontaneous ignition regardless of the particle temperature. The value of this temperature depend on material properties and the kinetics of the reaction, thus also on the oxygen concentration. When agent temperatures below the minimum agent temperature to guarantee spontaneous ignition regardless of the particle temperature are used, the drying and devolatilisation are mainly controlled by the heat released by reactions. The heating of the fuel particles and their devolatilisation are relatively slow and the devolatilisation rate is highly oxygen dependent. In a fixed bed, the devolatilisation front rate is low and the bed is characterised by significant temperature gradients.When the agent temperature is higher than the minimum agent temperature to guarantee spontaneous ignition regardless of the particle temperature, the drying and devolatilisation are mainly controlled by the convective heat transfer from the preheated agent and the released volatiles ignite very fast even in diluted conditions. This results in very efficient heat transfer to the fuel particles. In the fixed fuel bed the process is characterized by a high devolatilisation front rate. Thus, the temperature gradients in the bed are significantly reduced and the gasification can be said to be thermally homogeneous. Thanks to high rates of heat transfer and mass conversion, the heating value of the dry produced syngas is high with high concentrations of combustible species. The ignition of the volatiles and the high temperatures all along the bed presumably contributes to the reduction of the tar content even in up-draft configurations. The high temperatures also allows for operation with reduced air – to – fuel ratios which further increased the value of the produced gas (thanks to less dilution by nitrogen).The system study presents a concept for an autothermal system including both preheating and gasification. Results from a thermodynamic analysis of such a system are reported. Autothermal operation of a thermally homogeneous gasifier is possible only in a twin component system in which the gasifier is coupled to a preheating system able to reach preheating temperatures well above the minimum agent temperature to guarantee spontaneous ignition regardless of the particle temperature. It is shown that to reach certain temperature levels of the gasification air, heat exchange between product gas and air is not enough and the preheating system has to improve the temperatures involved, for example by burning part of the produced gas in a regenerative preheater. Further, it is shown that in comparison to gasifier without such a system for additional preheating, the autothermal Thermally Homogeneous Gasification system has the ability to significantly improve the gas quality (in terms of heating value of the dry gas) without losing energy- or exergy efficiency to an appreciable extent. / QC 20100903

<p>The topic of this thesis is estimation of the dynamic changes of the surface temperatureand heat flux during heating processes by using an inverse method. The local transient surface temperature and heat flux of a steel slab are calculated based on measurements in the interior of the slab.</p><p>The motivations for using an inverse method may be manifold. Sometimes, especially in the field of thermal engineering, one wants to calculate the transient temperature or heat flux on the surface of a body. This body may be a slab, or billet in metallurgical applications. However, it may be the case that the surface for some reason is inaccessible to exterior measurements with the aid of some measurement device. Such a device could be a thermocouple if contact with the surface in question is possible or a pyrometer if an invasive method is preferred. Sometimes though, these kinds of devices may be an inappropriate choice. It could be the case that the installation of any such device may disturb the experiment in some way or that the environment is chemically destructive or just that the instruments might give incorrect results. In these situations one is directed to using an inverse method based on interior measurements in the body, and in which the desired temperature is calculated by a numerical procedure.</p><p>The mathematical model used was applied to experimental data from a small scale laboratory furnace as well as from a full scale industrial reheating furnace and the results verified that the method can be successfully applied to high temperature thermal applications.</p>

The present dissertation describes the efforts directed towards the development of computational tools to support process modeling. This work is also a further development of the Thermoslag® software developed in the Division of Materials Process Science, KTH. The essential parts of the thesis are a) development of a semi-empirical model for the estimation of the molar volumes/densities of multicomponent slags with a view to incorporate the same in the model for viscosities and b) further development of the viscosity model for application towards fluoride- and manganese containing slags, as for example, mould flux slags and manganese slags used in ferromanganese production. c) estimating fluoride emissions from industrial slags and mould fluxes. d) study the reaction between carbon particles, hematite containing slags and in oxygen containing atmosphere. The model for the estimation of molar volume is based on a correlation between the relative integral molar volume of a slag system and the relative integral molar enthalpies of mixing of the same system. The integral molar enthalpies of the relevant systems could be evaluated from the Gibbs energy data available in the Thermoslag® software. The binary parameters were evaluated from experimental measurements of the molar volumes. Satisfactory correlations were obtained in the case of the binary silicate and aluminate systems. The model was extended to ternary and multi component systems by computing the molar volumes using the binary parameters. The model predictions showed agreements with the molar volume data available in literature. The model was used to estimate the molar volumes of industrial slags as well as to trace the trends in molar volume due to enable prediction of molar volumes of slags that are compatible with the thermodynamic data available. With a view to extend the existing model for viscosities to F--containing slags, the viscosities of mould flux slags for continuous casting in steel production have been investigated in the present work. The measurements were carried out utilizing the rotating cylinder method. Seven mould fluxes used in the Swedish steel industry and the impact of Al2O3 pick up by mould flux slags on viscosities were included in the study. The results showed that even relatively small additions of Al2O3 are related with a significant increase in viscosity. A similar experimental technique was employed to estimate the viscosity of twelve synthetic slags corresponding to composition of the raw materials used in ferromanganese production. The flow rate of the liquid slag, which is determined by the slag viscosity, is an important parameter affecting the reduction rate of manganese oxide. The results show a clear correlation between manganese oxide content and viscosity. An increase of MnO in the slag lowers the viscosity. The measured viscosities have also been connected to the structure of the silicates. The fluoride loss from the binary slag systems Al2O3-SiO2, CaO-SiO2 and MgOSiO2 with additions of CaF2 was studied by thermogravimetric (TGA) studies. The Arrhenius activation energy for the evaporation reaction of fluorides was found to be dependent on temperature and slag chemistry for the slags studied. A correlation between the activation energy for fluoride evaporation and activity of SiO2 in the slag melt was established. This relationship obtained for the binary systems appears also to be suitable for the ternary systems Al2O3-CaO-SiO2 with CaF2 addition, which indicates a possibility to estimate the fluoride emissions from industrial slags and mould fluxes. A Confocal Scanning Laser Microscopy was used to investigate the reaction between carbon particles in hematite containing slags and in oxygen containing atmosphere. Experiments with varying temperature and slags with varying FeOx content were carried out. The general trends were that the particle size decrease was more rapid with increase of FeOx amount and/or temperature was increased. / QC 20100812

The liquid steel sampling method is one of the commonly used procedures in monitoring the steelmaking process. Besides it can be used for analyzing the dissolved alloys, hydrogen content and oxygen content, it can be also employed to monitor the inclusion characteristics at the steelmakings. Here, a crucial point is that the steel sampler should be filled and the metal solidifies without changing the inclusion characteristics. Therefore, the objective of this work is to fundamentally understand the liquid steel sampling process by means of analyzing and modeling the two-phase flow during the sampler filling process, and verifying the mathematical model by using the experimental data. The present dissertation presents an experimental and theoretical study of the filling process of both the lollipop-shaped sampler and the rectangular-shaped sampler. Firstly, a physical modeling by using a water model has been carried out to fundamentally investigate the flow pattern inside the sampler vessels during its filling. The flow patterns were obtained by a PIV system. Then, a mathematical model has been built to theoretically understand the phenomena. The commercial CFD code was used. Here, different turbulence model have been compared between the realizable k-ε turbulence model and Wilcox k-ω turbulence model. It concludes that the Wilcox k-ω turbulence model agrees well with the PIV measurements.HH Thus, the preferred it was further employed to predict the turbulent flow inside the production lollipop-shaped sampler fillings. It is important to find that the average collision volume in the production steel sampler without solidification at filling is about 30 times higher than that in a ladle furnace. In the end, the whole sampling system was modeled. The initial solidification during the filling was taken into account. Focus was on the influence of the initial solidification on the inclusion concentrations. A discrete phase model was used to simulate the movement of inclusions in the liquid steel. Some selected different sized primary inclusions that exist in the ladles at a steelmaking process were simulated. The same method of studying the filling procedure of the lollipop-shaped sampler was further applied to comprehensively investigate the rectangular-shaped sampler. / QC 20100908

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No description available.

The aim of this thesis work is to increase the knowledge of phenomena taking place during the initial stage in a top blown converter. The work has been done in a few steps resulting in four different supplements. Water model experiments have been carried out using particle image velocimetry (PIV) technology. The system investigated was a fundamental top blown converter where an air jet was set to impinge on a water surface. The flow field of the combined blown case, where an air jet was introduced through a bottom nozzle, was also captured by the PIV. The work clearly showed that the flow field caused by an impinging top blown jet alone could not match that of the bottom blown case. The main re-circulation loop (or vortex) was investigated with respect to position and it was found that an increased flow rate pushes the center of the re-circulation loop downwards into the bath. However, for the top-blown case there is a point when the flow rate is too large to cause a distinguishable re-circulation loop since the jet becomes more plunging (i.e. penetrates deep into the bath) than impinging, with large surface agitation and splashing as a result.A numerical model with the same dimensions as the experimental system was then created. Three different turbulence models from the same family were tested: standard-, realizable- and a modified-(slight modification of one of the coefficients in order to produce less spreading of the air jet) k-ε turbulence model. It could be shown that for the family of k-ε turbulence models the difference in penetration depth was small and that the values corresponded well to literature data. However, when it comes to the position of the re-circulation loop it was shown that the realizable k-ε model produced better results when comparing the results to the experimental data produced from the PIV measurements, mentioned earlier.It was then shown how the computational fluid dynamics (CFD) model could be coupled to thermodynamics databases in order to solve for both reactions and transport in the system. Instead of an air-water system, a gas-steel-slag system was created using the knowledge obtained in the previous simulation step described above. Reactions between gas-steel, gas-slag, steel-slag and gas-steel-slag were considered. Extrapolation of data from a few seconds of simulation was used for comparison to experimental data from the literature and showed reasonable agreement. The overall conclusion was that it is possible to make a coupling of the Thermo-Calc databases and a CFD software to make dynamic simulations of metallurgical processes such as a top-blown converter.A parametric study was then undertaken where two different steel grades were tested; one with high initial carbon content (3.85 mass-%) and one with lower carbon content (0.5 mass-%). The initial silicon content was held constant at 0.84 mass-%. Different initial temperatures were tested and also some variation in initial dissolved oxygen content was tried. It was found that the rate of decarburization/desiliconization was influenced by the temperature and carbon concentration in the melt, where a high temperature as well as a high carbon concentration favors decarburization over desiliconization. It was also seen that the region affected by a lower concentration of alloys (or impurities) was quite small close to the axis where the impinging jet hits the bath. Add the oscillating nature of the cavity and it was realized that sampling from this region during an experiment might be quite difficult. / QC 20100720