Anders Tilliander

Removal of hydrogen, nitrogen and sulphur from tool steel during vacuum degassing

Abstract The removal of hydrogen, nitrogen and sulphur during vacuum degassing of a tool steel grade was studied. Both slag and steel samples were collected before and after vacuum treatment for 10 heats. From these, the chemical compositions of steel and slag were determined. Thereafter, the removal rates of sulphur, hydrogen and nitrogen were calculated. For sulphur and hydrogen only first order reaction models were considered. However, for nitrogen both first order and second order kinetic models were studied. The results showed that the removal of hydrogen and nitrogen can be described with first order reaction models. However, the removal rate of sulphur follows the equilibrium sulphur content at all stages during the vacuum degassing. It is also clear that after 10 min of degassing the hydrogen and nitrogen removal is more or less finished for the studied steel grade. However, the sulphur refining can still be carried out for longer times to reach lower values.

In situ studies of agglomeration between Al2O3-CaO inclusions at metal/gas, metal/slag interfaces and in slag

Abstract Studies of inclusion behaviour at the metal/slag interface is of great importance for the steel industry in order to achieve better control of both the size and amount of the inclusions, as well as improving the steel quality and the casting process. In this work agglomeration of liquid Al2O3–CaO particles at both steel/argon gas and steel/slag interfaces was studied with a confocal scanning laser microscope. In addition, agglomeration of liquid Al2O3–CaO–SiO2 inclusions present in the slag was investigated. The results showed that liquid inclusions more easily agglomerated to semiliquid inclusions than to liquid inclusions. Moreover, the agglomeration of liquid particles was found to be improved remarkably when the particles were present in the slag compared to when they were in the steel/slag interface.

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.

KTH Steel Scrap Model – Iron and Steel Flow in the Swedish Society 1889–2010

Abstract KTH Steel Scrap Model calculates material flows of iron and steel in the Swedish society based on statistics, mass balance and mass flow analysis and industry knowledge. The material flows of iron and steel were calculated for external scrap consumption, internal scrap, domestic steel scrap arising and net flow of iron and steel into the Swedish society. Model output on external steel scrap consumption and domestic steel scrap arising was compared to an earlier analysis done by Jernkontoret for the timeline 1980–2009. The results show that mass balance calculations are area wise corresponding to consumption figures based on trade statistics. In addition the difference in trend is assumed to be mainly due to stocking effect. Furthermore it is shown that mass balance and mass flow models could be used as a tool to calculate apparent scrap consumption based on crude steel production figures by process type.

Influence of ladle slag additions on BOF process performance

Abstract A plant trial has been performed, with recycling of ladle slag to the LD converter at SSAB EMEA, Luleå, Sweden. The effect of ladle slag addition on the slag and steel composition, together with the slag weight, was investigated with sampling both during the blow and at blow end. The addition of ladle slag resulted in an increase in slag weight between 1 and 2 t throughout the blow and an increase of 3 wt-% in the slag Al2O3 content. This indicated that the ladle slag melted during the initial stages of the blow and enhanced the early slag formation. Lime additions were reduced with 3·5 kg t−1 liquid steel without drawbacks on the phosphorus or sulphur refining. Heats with added ladle slag had an increase in blowing time with ∼4% and an increased tendency for slopping. However, this can be handled by different lance and addition programmes.

Experimentally determined temperatures in blast furnace hearth

Abstract In this study temperature measurements have been carried out at blast furnace no. 2 at SSAB Oxelösund. The temperature was measured in the hearth lining and at the outer surfaces of the hearth wall and bottom. The lining temperature was measured using permanently installed thermocouples and surface temperatures were measured using a hand held thermocouple. The aims of the study were to find a correlation between lining and surface temperatures as well as to find a method to determine the surface temperature based on readings from lining thermocouples. The overall conclusion is that the bottom and wall surface temperatures can be determined based on lining temperatures.

Use of volume correlation model to calculate lifetime of end-of-life steel

Abstract A new mathematical model for calculating the lifetime of steel on an annual basis, called the volume correlation model is presented. The model compares the quantities of scrap collection with the steel consumption as well as evaluates the time difference between the two data sets. The lifetime of steel was calculated for the collected end-of-life steel amounts. The calculations were performed by assuming a full recovery of the steel consumption or a non-re-circulated accumulated steel stock in society denoted the full and true lifetime of steel. Based on the volume correlation model, the lifetime of steel was calculated for the total steel, low alloyed and special steel, and stainless steel in Sweden between 1898 and 2010. Previous studies on the lifetime of steel are based on experimental measurements and numerical calculations. The full lifetime of the total amount of steel from previous studies is 31 and 35 years for the years 2000 and 2006 respectively. Based on the volume correlation model the lifetime for the total steel amount, when assuming a full recovery of the material, was calculated as 34 and 37 years for these two years. This indicates that the lifetime of steel from the volume correlation model is in a similar range, but slightly higher, compared to previously reported data. The present results show that the model could be an alternative method to calculate the lifetime of steel and other recyclable materials on an annual basis. Results show that the lifetime of the total steel amount has continuously increased between 1975 and 2010. This indicates that the accumulated steel stock in society is still large enough to withstand the high collection rate of steel scrap. Furthermore, that there are as yet no lack of untapped resource of end-of-life steel scrap assets in Swedish society.

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.

Influence of ladle slag additions on BOF process under production conditions

Abstract The influence of recycled ladle slag on the basic oxygen furnace (BOF) process under production conditions was investigated in plant trials. More specifically, 25 heats with ladle slag additions and 23 heats without ladle slag additions were studied. Both steel and slag samples were collected, from which the chemical compositions were determined. In addition, several process parameters were monitored. Overall, it was found that recirculation of ladle slag during normal production conditions works fine. On the positive side, it was seen that the steel quality concerning the phosphorus and sulphur contents of liquid steel has, in accordance with previous studies, not been affected by the ladle slag additions. Furthermore, no major differences in the slag composition occur when the recycling of ladle slag to BOF is performed. Finally, in comparison to previous studies, the increased tendency for slopping when adding ladle slag could be eliminated with a change in the lance schedule. However, on the negative side, it was seen that the addition of ladle slag leads to an increased blowing time due to lower iron ore additions. Moreover, the slag weight at tapping increased due to an increased weight of added slag formers.

Use of Physical Modelling to Study How to Increase the Production Capacity by Implementing a Novel Oblong AOD Converter

There is no known example of an AOD converter with oblong cross sections in the literature. Changing the geometry of the converter vessel, from the traditional circular cross sections, to increase converter volume could potentially influence the performance of the converter and in particular the decarburisation rate. To study the feasibility of implementing an oblong converter, physical modelling was used to study the fluid flow of the proposed converter configuration, geometry and number of tuyeres, and the potential influence on the decarburisation rate. Two water models were employed using water containing NaOH and gas injected through six or eight tuyeres as fluids. In the model, CO2 gas was injected and the reaction of CO2 and NaOH was indirectly measured by detecting the pH value of the water. The mixing time is considered to be a good indicator of the decarburisation as kinetics will be diffusion controlled in the latter period of the process. The following three configurations were studied: (i) a circular converter with six tuyeres, (ii) an oblong converter with six tuyeres, and (iii) an oblong converter with eight tuyeres. The mixing time can be used to evaluate the different converter configurations. The average CO2 concentrations based on several experiments, differed by less than 5% between the circular and oblong models after 165 s of injection of air and CO2. The results also showed that no difference in mixing time could be found when using 6 and 8 tuyeres, respectively in the oblong model, where the CO2 concentrations differed by less than 2% after 165 s of injection time of air and CO2. Based on the findings, it has been observed that the influence of converter geometry on mixing time is small, it was concluded that decarburisation rate is likely to be the same irrespectively of converter geometry.