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Studies on dephosphorisation during steelmaking
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This work is aimed at understanding the thermodynamic principles influencing the phosphorus partition between slag and steel during steelmaking, particularly during refining of high-phosphorus hot metal using the basic oxygen steelmaking (BOS) process. Mapping of the slag path has been carried out using a mass balance model based on input conditions and off-gas analysis, which has been validated by intermediate measurements of slag and metal composition in an industrial basic oxygen furnace (BOF). The slag composition is found to vary over a wide range of basicity (%CaO/%SiO2) and iron oxide content. The partition of phosphorus increases with progress of refining but reduces during the intermediate period, corresponding to a decrease in iron oxide concentration and formation of “dry slag”. The phosphorus partition ratio increases again towards the end of the process. The equilibrium partition ratios for such conditions have been theoretically estimated using slag “model(s)”, based on the estimated slag compositions. It is seen that the partition ratio of phosphorus remains within 45% – 60% of the equilibrium value, showing a gradual decrease with progress of the refining process.

Equilibrium phosphorus partition ratios for slags containing low concentrations of MnO and Al2O3 have been experimentally determined, over the ranges of basicity and iron oxide concentration approximately corresponding to that observed in the typical BOS process. It is seen that the equilibrium phosphorus partition ratio is practically independent of basicity greater than 2.5 – 2.6, over the entire range of temperature and FeOx concentration studied. Variation of the activity of P2O5 with basicity and FeOx concentration has been investigated to explain the trends observed in the variation of phosphorus partition ratio. It is seen that the activity coefficient of P2O5 is lowest, and hence most conducive for removal of phosphorus from steel, over certain finite ranges of basicity and iron oxide concentration. It follows that the efficiency of dephosphorisation is likely to be maximum if the basic oxygen steelmaking process is operated within these ranges. Simultaneous with this work, mathematical correlations have been developed for estimation of P2O5 activity coefficient and phosphorus partition ratio as functions of slag composition. The correlations are compared with those proposed by earlier workers and are found to result in better predictions over certain composition ranges.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007.
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-4427ISBN: 978-91-7178-708-8 (print)OAI: oai:DiVA.org:kth-4427DiVA: diva2:12272
Public defence
2007-06-15, Sal B1, KTH, Brinellvägen 23, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100623Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2012-03-19Bibliographically approved
List of papers
1. Change in phosphorus partition during blowing in a commercial BOF
Open this publication in new window or tab >>Change in phosphorus partition during blowing in a commercial BOF
2007 (English)In: ISIJ International, ISSN 0915-1559, Vol. 47, no 5, 766-768 p.Article in journal (Refereed) Published
Keyword
SLAGS; IRON
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-7300 (URN)000246896900021 ()2-s2.0-34547183969 (Scopus ID)
Note
QC 20100623Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2011-10-03Bibliographically approved
2. Phosphorus partition between liquid steel and CaO-SiO2-P2O5-MgO slag containing low FeO
Open this publication in new window or tab >>Phosphorus partition between liquid steel and CaO-SiO2-P2O5-MgO slag containing low FeO
2007 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 38, no 3, 357-366 p.Article in journal (Refereed) Published
Abstract [en]

CaO-SiO2-FeOx-P2O5-MgO bearing slags are typical in the basic oxygen steelmaking (BOS) process. The partition ratio of phosphorus between slag and steel is an index of the phosphorus holding capacity of the slag, which determines the phosphorus content achievable in the finished steel. The influences of FeO concentration and basicity on the equilibrium phosphorus partition ratios were experimentally determined at temperatures of 1873 and 1923 K, for conditions of MgO saturation. The partition ratio initially increased with basicity but attained a constant value beyond basicity of 2.5. An increase in FeO concentration up to approximately 13 to 14 mass pet was beneficial for phosphorus partition.

Keyword
OXYGEN; STEELMAKING; SYSTEM; METAL; IRON
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-7301 (URN)10.1007/s11663-007-9057-y (DOI)000248511200002 ()2-s2.0-34547408242 (Scopus ID)
Note
QC 20100623Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2011-10-03Bibliographically approved
3. Phosphorus partition between liquid steel and CaO-SiO2-FeOx-P2O5-MgO slag containing 15-25 %FeO
Open this publication in new window or tab >>Phosphorus partition between liquid steel and CaO-SiO2-FeOx-P2O5-MgO slag containing 15-25 %FeO
2007 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 38, no 4, 623-630 p.Article in journal (Refereed) Published
Abstract [en]

CaO-SiO2-FeO2-P2O5-MgO bearing slags are typically used in the basic oxygen steelmaking (BOS) process. The partition ratio of phosphorus between slag and steel is an index of the phosphorus holding capacity of the slag, which determines the phosphorus content achievable in the finished steel. The influence of factors such as FeO content and basicity on the phosphorus partition ratio was investigated at two different temperatures. The partition ratio initially increased with basicity but remained constant beyond a basicity of 2.5 to 2.6. An increase in the FeO content up to 18 to 20 mass pct was beneficial for the phosphorus partition at a basicity level of 2 to 3, but a higher concentration of FeO resulted in a decrease in the phosphorus partition ratio; the FeO concentration corresponding to this transition varied with basicity and temperature. At even lower basicities, however, the equilibrium phosphorus partition showed either no change, or a marginally decreasing trend, with an increase in the FeO content.

Keyword
PIG IRON; OXYGEN; MGO; DISSOLUTION
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-7302 (URN)10.1007/s11663-007-9063-0 (DOI)000249847800015 ()2-s2.0-34548745807 (Scopus ID)
Note
QC 20100623Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2011-10-03Bibliographically approved
4. A model for activity coefficient of P2O5 in BOF slag and phosphorus distribution between liquid steel and slag
Open this publication in new window or tab >>A model for activity coefficient of P2O5 in BOF slag and phosphorus distribution between liquid steel and slag
2007 (English)In: ISIJ International, ISSN 0915-1559, Vol. 47, no 8, 1236-1238 p.Article in journal (Refereed) Published
Keyword
IRON
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-7303 (URN)10.2355/isijinternational.47.1236 (DOI)000248992600022 ()2-s2.0-35348856814 (Scopus ID)
Note
QC 20100623Available from: 2007-06-07 Created: 2007-06-07 Last updated: 2011-10-03Bibliographically approved

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