A study of industrial steel making dusts: melting behaviour and interactions with refractory bricks

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Kemian tekniikan korkeakoulu | Master's thesis
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Date

2020-08-18

Department

Major/Subject

Sustainable Metals Processing

Mcode

CHEM3026

Degree programme

Master's Programme in Chemical, Biochemical and Materials Engineering

Language

en

Pages

83+45

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Abstract

Understanding the behaviour of alkali metals and halogens at high temperaturescombined with their effect on refractories is important for efficient and safe operatingof Electric Arc Furnaces (EAF). In this work the behaviour of alkali metals andhalogens in industrial EAF dusts was investigated at temperatures between 800°Cand 1400°C. The dusts were first heated for 1, 2, 4 and 8 hours at 800°C and 1200°C under a reducing atmosphere of 90% CO/10%CO2to determine the effect of theheating time. The dusts were then heated for 2 hours at 1200°C, 1250°C and 1300°C under the same reducing atmosphere. Analyses of the industrial dusts were performed using a combination of SEM-EDSand image analyses software on BSE pictures. The analyses were performed to betterunderstand the melting behaviour of the dusts and the behaviour of fluorine, chlorine,sodium and potassium. It was found that melting in the EAF dusts starts in thetemperature region of 1250-1300°C. Depending on the composition of the dust, thena molten fraction of 25-50 % forms. The AOD dust had a molten fraction at 1200°Cof about 30 %. Due to the industrial nature, the concentrations of the investigatedelements were low in the raw material and thus also in the samples. Fluorine wasfound in high levels in the melted phase of the AOD dust. In the EAF dusts fluorinewas found in a solid spinel phase. Sodium was mostly found in the slag phase inlow concentrations. Potassium was only found in the slag phase of one EAF dustand some spots of the other EAF dusts slag phase. Chlorine was not present in thesamples after heating. The interaction between the dusts and refractories was investigated by conductinga study where the effects of a synthetic dust on four types of refractories at 1300°Cunder the same reducing atmosphere were analysed. The synthetic dust containedhigh concentrations of potassium, fluorine and chlorine. The refractory samples wereRadex OX6 (Cr-MgO), Radex S (MgO), Resistal RK30 (Al-Cr) and Durital E90(Al-Si). The refractory samples were analysed using a combination of visual analysesand SEM-EDS. From the four refractories tested with the highly concentrated synthetic dust, itwas found that the two refractories containing no chrome were severely penetratedby potassium. The two chrome containing refractories were only affected to a depthof 5 mm. The Durital E90 refractory was the most affected in its shape where theothers suffered less from expansion.

Description

Supervisor

Jokilaakso, Ari

Thesis advisor

Kekkonen, Marko

Keywords

refractory wear, corrosion, alkali metal, halogen, image analysis software, AOD

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Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-202008245180

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[dipl] Kemian tekniikan korkeakoulu / CHEM