Lage Jonsson

Slag-metal reactions during ladle treatment with focus on desulphurisation

Abstract Within several cooperative projects, KTH (Royal Institute of Technology), Ovako Steel AB, and MEFOS have investigated the desulphurisation of bearing steel during vacuum degassing. The work includes thermodynamic calculations of the slag-metal equilibrium, CFD modelling of slag-metal reactions, and plant trials. Results from the various studies are presented and discussed in this paper. Models for predicting slag properties (sulphide capacity, viscosity, and oxide activities) in liquid slags as functions of slag composition and temperature have been used for the calculation of data which have been employed in static and dynamic modelling of sulphur refining. The results from static modelling show that the method allows fast and easy evaluation of the theoretical desulphurisation conditions during degassing at Ovako Steel AB, as well as theoretical determination of the parameters that have the greatest influence on the equilibrium sulphur distribution. The conclusion from dynamic modelling is that the vacuum degassing operation can be described dynamically with the present knowledge of sulphide capacity, sulphur distribution, viscosity, and oxide activities of ladle slags if this knowledge is combined with fluid flow modelling to derive the overall kinetics. The presented model approaches have been found useful in understanding the sulphur refining process at Ovako Steel AB. The dynamic modelling concept is also believed to have potential for dynamic descriptions of other slag-metal reactions in steelmaking.

The Use of an Enhanced Eulerian Deposition Model to Investigate Nozzle Clogging During Continuous Casting of Steel

Nozzle clogging caused by the build-up of non-metallic inclusions on ceramic walls is a serious industrial problem during continuous casting of steel. The current theoretical study uses the extended Eulerian model to predict the inclusion deposition rate in a submerged entry nozzle (SEN). The model considers Brownian and turbulent diffusion, turbophoresis, and thermophoresis as transportation mechanisms. First, the steel flow in a tundish was simulated using a three-dimensional CFD model. The obtained flow parameter in a SEN was then put into the Eulerian deposition model to predict the deposition rate of non-metallic inclusions. Thereafter, the deposition rates of different-size inclusions in the SEN were predicted and compared. The result shows that the steel flow is non-uniform in the SEN of the tundish. This leads to an uneven distribution of the inclusion deposition rates at different locations of the inner wall of the SEN. In addition, large size inclusions among the size of inclusions considered show a large deposition rate, due to the strong effect of turbophoresis.

Fundamental decarburisation model of AOD process

Abstract A mathematical fluid flow model of gas injection in an argon–oxygen decarburisation (AOD) converter process has been coupled with a high temperature thermodynamic model. The current model is a further enhancement of an earlier developed three-dimensional, three-phase model, to also include some thermodynamics of the process. The model is based on fundamental transport equations and includes separate solutions for the steel, slag and the gas phases and their coupling by friction. The AOD model has been used to predict the first injection stage of decarburisation in an AOD converter. The predictions have been found to agree well with the corresponding results from an industrial process control model. One of the important observations from the simulations was that large concentration gradients of carbon exist in the AOD at an early stage and as the first injection step approaching its end the carbon gradients diminish. Also, the results show, in accordance with theory, that the local decarburisation rate is decreased at elevated pressures.

Numerical and Physical Study on a Cylindrical Tundish Design to Produce a Swirling Flow in the SEN During Continuous Casting of Steel

A new tundish design was investigated using both water model experiments and numerical simulations. The results show that the Reynolds Stress Model simulation results agree well with the Particle Image Velocimetry-measured results for water model experiments. A strong swirling flow in the Submerged Entry Nozzle (SEN) of the new tundish was successfully obtained, and the tangential velocity in the region near SEN inlet could reach a value of around 3.1 m/s. A high value of the shear stress was found to exist on the SEN wall, due to the strong swirling flow inside the SEN. This large shear stress leads to the dissipation of the rotational momentum of the steel flow. Thus, the maximum tangential velocity of the steel flow decreases from 3.1 m/s at around the SEN inlet to 2.2 m/s at a location close to the SEN outlet. In addition, the near-wall region has a high pressure, which is larger than the atmospheric pressure, due to the centrifugal effect. The calculated swirl number, with the value of around 1.6 at SEN inlet, illustrates that the current design can produce a similar strong swirling flow compared to the swirl blade method and the electromagnetic stirring method, while this is obtained by simply changing the steel flow path in tundish instead of using additional device to influence the flow.

Preliminary investigation of influence of temperature on decarburisation using fundamental AOD model

Abstract A high temperature thermodynamics model was earlier coupled with a fundamental mathematical model describing the fluid flow in an argon–oxygen decarburisation (AOD) converter and was initially validated for an idealised temperature description. More specifically, a linear average temperature relation was used such that the temperature would be isolated from other effects such as reactions and mixing. Thereafter, the effect of the starting temperature on the decarburisation was studied. The purpose is to provide some initial knowledge about how temperature affects the decarburisation in an AOD converter. The results suggest that the thermodynamic limit for carbon concentration after reaching the carbon removal efficiency (CRE) maxima is vertically translated downwards at higher temperatures. Furthermore, when plotting the mass ratio between CO and CO2, there is an indication of a point that may relate to a CRE maximum.

The Behavior of Impurities During Producer Gas Implementation as Alternative Fuel in Steel Reheating Furnaces: A CFD and Thermo-Chemical Study

The use of available and cheap industrial producer gases as alternative fuels for the steel reheating furnaces is an attractive topic for steel industry. The application of producer gases for such ...

Erratum to: A Mathematical Modeling Study of Tracer Mixing in a Continuous Casting Tundish

Specifically, in the transport equations for the mass fraction of water, tracer, and the scalar (Eqs. [7], [8], and [13], respectively). The density properties were the density of the mixture in Eq. [10] instead of the density of the water or the tracer itself. Second, the update of one of the result in the article. Regarding the result (1) KCl density only (OD) in Table II and the text in p. 179: ‘‘Apart from the KCl molecule diffusion, the mesh difference could also, to some extent, influence the differences in the results.’’ The result (1) KCl density only (OD) was based on a mesh of 168 9 71 9 70 grids, while the other results (2) through (5) were based on a mesh of 193 9 79 9 117 grids. A new simulation for the (1) KCl density only (OD) were recently made based on a mesh of 193 9 79 9 117 grids to maintain the consistency. It was difficult to distinguish the difference between the RTD curves of the case that implemented with density only (OD) and the case implemented with both density and KCl molecule diffusion (KMD). To conclude, all the properties of tracer (except for the density) that implemented in the CFD model could not affect the calculated RTD curves.

On the Implementation of Producer Gases as Alternative Fuels in Steel Reheating Furnaces

During the past decades, combustion of producer gases from other facilities has been introduced as one of the promising techniques in steel furnaces. The impurities inside producer gases are responsible for a low quality steel production due to formation of the molten ash that forms sticky layers of solutions on steel surfaces. Therefore, a comprehensive investigation is needed before a full implementation of producer gases inside the industrial furnaces. In this paper, the effects of impurities inside the gasified biomass flue gases are thermodynamically investigated regarding temperature zones inside a reheating furnace. After that, the high temperature agent combustion (HiTAC) is investigated as a solution for a steel batch reheating furnace to reduce the side effects of using the producer gases. Finally, computational fluid dynamics (CFD) is used as a numerical technique to compare four different producer gases in the studied furnace. The temperature distribution is validated with existing literature data. It shows a good agreement with a 5% error in the heating and a 10% error in the soaking zones of the reheating furnace. The comparison of simulation results assists in the understanding of the chemical and thermal behavior of different gases and provides useful data for the furnace fuel optimization.Copyright

Various consequences regarding hypothetical dispersion of airborne radioactivity in a city center

In case of dispersion of airborne radioactive material in a city center a number of questions will prompt for an answer. While many questions can get their answers in due course of time based on results of tests and sampling, a good understanding of the quantitative effect of dispersion will be very helpful to rescue staff, in particular in the early stage. In the following dose and dose rate estimates are presented for three scenarios including dispersion of radioactivity in a city center. In one case the activity is released in an open place, in another from a roof and in the third case from a source on a street where the wind is blowing along the street. In each case, at specific positions, estimates are made of dose from inhalation, and dose rates for contamination on skin as well as from radioactive particles deposited onto ground, walls and roofs (external exposure) in the city center. It should be noted that the deposition pattern in urban areas varies greatly which means that the consequences are difficult to predict. The dispersion is influenced by recirculation behind tall buildings and diverted flow close to street-ends, which have significant effects on the deposit pattern. Regarding the relative importance of contributions to total dose it is found that inhalation could play a major role for long term effects while dose to skin might dominate acute effects.

Growth of Small Alumina Clusters during Ladle Deoxidation

The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions.Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles.In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow.The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.