ÅTERANVÄNDA AOD-SLAGG I LJUSBÅGSUGNEN

Melting steel scrap and alloys in an electric arc furnace (EAF) is the first step in stainless steel production. Further processing of the liquid steel is then carrying out in an Argon Oxygen Decarburisation (AOD) converter. The main objective of the treatment in the AOD converter is to reduce the carbon content to a target value by injecting an oxygen-argon mixture. During this decarburisation step unavoidably some chromium and other alloying elements with high affinity to oxygen are oxidised and ends up in the slag. To obtain an acceptable yield of these alloying elements is necessary to reduce the slag in the AOD converter after the decarburisation with either aluminium or ferrosilicon. In the case of aluminium reduction, the final slag after reduction is generally composed of lime (CaO) and aluminium oxide (Al2O3). The denomination of the slag is Al-reduced AOD-slag and at the moment this has no practical use and is stored as landfill. Therefore, the slag ought to be recycled due to financial and environmental reasons. Within the present work, recirculation of Al-reduced AOD-slag to the EAF as slag former has been examined by theoretical analysis and practical trial using a small rotating kiln. The main aim of the thermodynamic calculations was to investigate how much of the Al-reduced AOD-slag is needed to reduce the activity of silicate in the slag and thereby depressing the loss of chromium to the slag. The second phase of the study was designed to investigate the effect of added Al-reduced AOD slag on refractory wear during trials in a rotary kiln. During these trials the kiln was lined with four different types of bricks, supplied by the three companies participating in this project – Vargön Alloys AB, Outokumpu Stainless AB Avesta and Sandvik Materials Technology. The thermodynamic calculations disclose that a significant decrease of the activity of SiO2 could be observed with only 5 weights per cent addition of Al-reduced AOD-slag. Furthermore, the result showed that 15 weight per cent of Al-reduced AOD-slag in the EAF slag can be recycled to the EAF without a large impact on the refractory material. Additionally, X-ray diffraction investigations of the Al-reduced AOD-slag showed that there was no metal contamination.Key words: AOD-slag, slag recycling, refractory wear, slag activities, EAF-slag.Validerat; 20151119 (global_studentproject_submitter

ÅTERANVÄNDA AOD-SLAGG I LJUSBÅGSUGNEN

Melting steel scrap and alloys in an electric arc furnace (EAF) is the first step in stainless steel production. Further processing of the liquid steel is then carrying out in an Argon Oxygen Decarburisation (AOD) converter. The main objective of the treatment in the AOD converter is to reduce the carbon content to a target value by injecting an oxygen-argon mixture. During this decarburisation step unavoidably some chromium and other alloying elements with high affinity to oxygen are oxidised and ends up in the slag. To obtain an acceptable yield of these alloying elements is necessary to reduce the slag in the AOD converter after the decarburisation with either aluminium or ferrosilicon. In the case of aluminium reduction, the final slag after reduction is generally composed of lime (CaO) and aluminium oxide (Al2O3). The denomination of the slag is Al-reduced AOD-slag and at the moment this has no practical use and is stored as landfill. Therefore, the slag ought to be recycled due to financial and environmental reasons. Within the present work, recirculation of Al-reduced AOD-slag to the EAF as slag former has been examined by theoretical analysis and practical trial using a small rotating kiln. The main aim of the thermodynamic calculations was to investigate how much of the Al-reduced AOD-slag is needed to reduce the activity of silicate in the slag and thereby depressing the loss of chromium to the slag. The second phase of the study was designed to investigate the effect of added Al-reduced AOD slag on refractory wear during trials in a rotary kiln. During these trials the kiln was lined with four different types of bricks, supplied by the three companies participating in this project – Vargön Alloys AB, Outokumpu Stainless AB Avesta and Sandvik Materials Technology. The thermodynamic calculations disclose that a significant decrease of the activity of SiO2 could be observed with only 5 weights per cent addition of Al-reduced AOD-slag. Furthermore, the result showed that 15 weight per cent of Al-reduced AOD-slag in the EAF slag can be recycled to the EAF without a large impact on the refractory material. Additionally, X-ray diffraction investigations of the Al-reduced AOD-slag showed that there was no metal contamination.Key words: AOD-slag, slag recycling, refractory wear, slag activities, EAF-slag.Validerat; 20151119 (global_studentproject_submitter