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Modelling of Nitrogen Intrusion into an AOD Converter at the Reduction Stage Caused by Suction Oscillation in the Ventilation Hood
Author(s) -
Tang Yong,
Fabritius Timo,
Härkki Jouko
Publication year - 2004
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.200405783
Subject(s) - suction , pressure drop , nitrogen , ventilation (architecture) , steelmaking , environmental science , materials science , mechanics , mechanical engineering , engineering , metallurgy , chemistry , physics , organic chemistry
Some AOD operators doubt that unusual high nitrogen content in low nitrogen grade stainless steel may come from the entrapped nitrogen of air through the gap between hood and AOD converter under some unsteady conditions. This paper modelled the unsteady condition caused by pressure jumping in the ventilation system of an AOD vessel in order to investigate the possible nitrogen intrusion inside the converter. Commercial CFD code, FLUENT6.1, was applied to study the gas flow field, thermal conditions and species transfer in the computing domain. The stainless steelmaking converters in AvestaPolarit's stainless steel plant in Finland, named AOD1 and AOD2, were simulated respectively. The modelling was carried out at the reduction stage of the AOD process, in which only argon is blown from the bottom tuyeres. The results show that most hot gas from the AOD converter escapes to the atmosphere as the local relative pressure in the ventilation hood jumps to a high value. The temperature inside the hood climbs suddenly when the suction ability of the ventilation system drops and the direction of the exhaust gas flow reverses. Because of different geometric location between hood and converter, the air can intrude further into AOD1 converter than into AOD2. Therefore, the high nitrogen fraction area also projects deeper inside AOD1. Although gas containing a high nitrogen fraction can be entrapped inside the converter due to a dramatic drop in suction ability in the ventilation system, the present research suggests that the area rich in nitrogen is so limited inside AOD that the mass fraction of nitrogen does not exceed 5% near the melt bath surface.