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Influence of Ladle-slag Additions on BOF-Process Parameters
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The influence of ladle-slag additions on the BOF-process performance were investigated in plant trials. The aim of the study was to recycle ladle slag from secondary steelmaking to the LD-converter to save lime and improve the slag formation. More specifically, two plant trial campaigns covering in total 83 heats, whereof 47 with ladle-slag additions and 36 without ladle-slag additions, were performed.

 Slag and steel sampling of the process were performed at tapping as well as during blowing at 15, 35, and 65% of the total blowing time. During the first campaign, ladle slag was added through the chute and lime reductions were made manually to correct for the ladle-slag addition.

 In the second campaign, a development of the approach was made to suite a normal production practice. More specifically, the ladle slag was added through the weight-hopper system and implemented in the process-control system. In this way, the lime additions were reduced automatically by approximately 260 kg per heat. Moreover, the heat balance was compensated with a reduction in the iron-ore consumption. Additionally, the lance program was modified and the lance was lowered in the initial stages of the blow.

 On the positive side, it was found that no demerits in the metallurgical performance of the process occur when ladle slag is recycled to the BOF-process. Furthermore, only slight affections on the slag composition were found, mainly with respect to the Al2O3 and FeO-content. In addition, the ladle slag was shown to melt during the initial stages of the blow. This contributed to an increased slag weight both during the blow and at tapping. However, a negative effect on the blowing time was experienced during the trials. Although, this effect was more pronounced during the first campaign and could be reduced with a controlled heat balance during the second campaign.

 

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , xii, 28 p.
Keyword [en]
BOF, slag formation, ladle slag, recycling, steel, composition, energy
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-33270ISBN: 978-91-7415-961-5OAI: oai:DiVA.org:kth-33270DiVA: diva2:414283
Presentation
2011-05-04, Sal B1, KTH, Brinellvägen 23, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20110503Available from: 2011-05-03 Created: 2011-05-02 Last updated: 2011-05-03Bibliographically approved
List of papers
1. Influence of ladle slag additions on BOF process performance
Open this publication in new window or tab >>Influence of ladle slag additions on BOF process performance
2012 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, Vol. 39, no 5, 378-385 p.Article in journal (Refereed) Published
Abstract [en]

A plant trial has been performed, with recycling of ladle slag to the LD converter at SSAB EMEA, Lulea, Sweden. The effect of ladle slag addition on the slag and steel composition, together with the slag weight, was investigated with sampling both during the blow and at blow end. The addition of ladle slag resulted in an increase in slag weight between 1 and 2 t throughout the blow and an increase of 3 wt-% in the slag Al2O3 content. This indicated that the ladle slag melted during the initial stages of the blow and enhanced the early slag formation. Lime additions were reduced with 3.5 kg t(-1) liquid steel without drawbacks on the phosphorus or sulphur refining. Heats with added ladle slag had an increase in blowing time with similar to 4% and an increased tendency for slopping. However, this can be handled by different lance and addition programmes.

Keyword
ladle slag, recycling, slag formation, LD converter
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-33298 (URN)10.1179/1743281211Y.0000000021 (DOI)000304538100009 ()2-s2.0-84861973611 (ScopusID)
Note
QC 20120326. Updated from submitted to published.Available from: 2011-05-03 Created: 2011-05-03 Last updated: 2012-06-25Bibliographically approved
2. Influence of ladle slag additions on BOF process under production conditions
Open this publication in new window or tab >>Influence of ladle slag additions on BOF process under production conditions
2012 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, Vol. 39, no 5, 318-326 p.Article in journal (Refereed) Published
Abstract [en]

The influence of recycled ladle slag on the basic oxygen furnace (BOF) process under production conditions was investigated in plant trials. More specifically, 25 heats with ladle slag additions and 23 heats without ladle slag additions were studied. Both steel and slag samples were collected, from which the chemical compositions were determined. In addition, several process parameters were monitored. Overall, it was found that recirculation of ladle slag during normal production conditions works fine. On the positive side, it was seen that the steel quality concerning the phosphorus and sulphur contents of liquid steel has, in accordance with previous studies, not been affected by the ladle slag additions. Furthermore, no major differences in the slag composition occur when the recycling of ladle slag to BOF is performed. Finally, in comparison to previous studies, the increased tendency for slopping when adding ladle slag could be eliminated with a change in the lance schedule. However, on the negative side, it was seen that the addition of ladle slag leads to an increased blowing time due to lower iron ore additions. Moreover, the slag weight at tapping increased due to an increased weight of added slag formers.

Keyword
BOF, ladle slag, recycling, steel, composition.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-33299 (URN)10.1179/1743281211Y.0000000073 (DOI)000304538100002 ()2-s2.0-84861967683 (ScopusID)
Note
QC 20120625. Updated from manuscript to article in journal.Available from: 2011-05-03 Created: 2011-05-03 Last updated: 2012-06-25Bibliographically approved
3. A theoretical study of the effect of ladle-slag additions on the BOF process
Open this publication in new window or tab >>A theoretical study of the effect of ladle-slag additions on the BOF process
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A Case study has been performed using the commercial Multi‐Phase equilibrium (MPE) software. The aim was to study the effect on the energy balance of an industrial BOF converter when recycling of ladle slag is made to the process. A reference simulation was made with typical process parameters of an industrial converter without the addition of ladle slag. The energy penalty of recycling ladle slag to the process was found to be 1728 MJ. Moreover, five different options to obtain an energy balance in the converter were studied. The results showed that either the scrap weight could be decreased by 1.5t, or the iron‐ore addition could be reduced with 380 kg. These two solutions offered consistent metallurgical performance in the process, but had drawbacks due to a decreased yield and an increased blowing time respectively. It was also found that the chemical energy released from the process could be increased, by oxidizing FeO or adding FeSi. However, this had negative effects on the process time as well as the steel quality. The most beneficial way for the BOF process to compensate for the energy loss is to reduce the tapping temperature with 12°C. This will also have positive effects on the phosphorus removal in the process. The results also showed that 200 kg per heat of burnt lime could be saved thanks to the recirculation of ladle slag. However, concluding remarks on the environmental and economical effect of the different options to compensate for the energy penalty needs to be assessed by a Life Cycle Analysis in the future to which this study can act as a useful guide.

 

Keyword
Energy balance, simulation, ladle slag, recycling, BOF
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-33300 (URN)
Note
QS 2011Available from: 2011-05-03 Created: 2011-05-03 Last updated: 2011-05-03Bibliographically approved

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