Nils Å. I. Andersson

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.

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.

A Comparative CFD Study on Simulating Flameless Oxy-Fuel Combustion in a Pilot-Scale Furnace

The current study presents a method to model the flameless oxy-fuel system, with a comparative approach, as well as validation of the predictions. The validation has been done by comparing the predicted results with previously published experimental results from a 200 kW pilot furnace. A suction pyrometer has been used to measure the local temperature and concentrations of CO, CO2, and O2 at 24 different locations. A three-dimensional CFD model was developed and the validity of using different submodels describing turbulence and chemical reactions was evaluated. The standard model was compared with the realizable model for turbulence, while Probability Density Function (PDF) with either chemical equilibrium or the Steady Laminar Flamelet Model (SLFM) was evaluated for combustion. Radiation was described using a Discrete Ordinates Model (DOM) with weighted-sum-of-grey-gases model (WSGGM). The smallest deviation between predictions and experiments for temperature (1.2%) was found using the realizable model and the SLFM. This improvement affects the prediction of gaseous species as well since the deviation between predictions and experiments for CO2 volume percentages decreased from 6% to 1.5%. This provides a recommendation for model selections in further studies on flameless oxy-fuel combustion.

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 role of process control on the steel cleanliness

The possibilities of obtaining a good process control in order to reach a good cleanliness of the steel were studied based on plant trials. Steel and slag samples were taken from two steel grades with a slightly different composition, but with similar processing conditions. Thereafter, the chemical compositions of the steel and slag samples were determined. The results show that the sum of the FeO and MnO was found to be a clear indicator for when reoxidation had taken place. No conclusive indicator was found to predict the extent of slag carry-over from the electric arc furnace. However, most of the variation in deoxidation seem to originate from the accuracy of the slag raking. Steel grades with low amounts of deoxidisers such as C and Si naturally were found to result in higher oxygen contents at the start of deoxidation. Furthermore, calculations of oxygen activities in the steel melt were made and the results were compared to measurements with varying results. Overall, the results indicate that calculation of oxygen activities with multivalence slag species such as Fe and Cr requires additional measurements to obtain accurate results.

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 ...

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