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Recycling of Blast Furnace Sludge within the Integrated Steel Plant: Potential for Complete Recycling and Influence on Operation
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ore-based steelmaking generates various residues including dust, sludges, scales and slags. Internal and external recycling has allowed for 68-90 % of the dust, sludges and scales to be recycled. However, several residues are landfilled despite containing elements valuable as raw material in the production of steel. One such residue is the blast furnace (BF) sludge which has a chemical composition dominated by iron and carbon. In 2008, the annual worldwide landfilling of BF sludge was estimated to 8 million metric tons in dry weight. Furthermore, as the iron production via the BF route has increased significantly since 2008, the landfilling of BF sludge could be even higher as of today. Thus, the potential to reclaim valuable iron and carbon while improving the raw material efficiency is substantial.

Traditionally, in-plant recycling of residues generated in the integrated steel plant is conducted via the sinter or, in the case of pellet-based BFs, via cold-bonded briquettes and injection in the BF tuyeres. The challenges in recycling BF sludge via these routes are the fine particle size distribution, the high water content and the zinc content. Of these challenges, the latter is the main concern as too high zinc loads in the BF lead to increased reductant rates, reduced lining life of carbon-based bricks and scaffold formation, which may disturb the process. The challenge regarding zinc has previously been addressed by pretreating the sludge, generating a low-zinc and high-zinc fraction where the former has been recycled to the BF via the sinter or cold-bonded pellets. Although pretreatment and recycling of the low-zinc fraction have been achieved in industrial scale, the reported sludges are generally coarse in size and high in zinc. Furthermore, recycling of pretreated BF sludge to the BF utilizing cold-bonded briquettes has not been reported and the internal recycling of the high-zinc fraction has not been considered.

In the present thesis, newly produced BF sludge with a fine particle size distribution and low zinc content was characterized finding that a majority of the zinc was present in weak acid soluble phases and that the finest fraction of the sludge carried most of the zinc. Based on these findings, the BF sludge was pretreated using sulfuric acid leaching, hydrocycloning and tornado treatment, respectively. Sulfuric acid leaching was the most effective method in selectively separating zinc from the iron, carbon and solids. However, both hydrocycloning and tornado treatment were successful in generating a fraction low in zinc.

The low-zinc fraction of the tornado-treated BF sludge was incorporated in cold-bonded briquettes and tested for strength, swelling and intrinsic reducibility. Furthermore, the briquettes were charged as basket samples in the LKAB Experimental Blast Furnace (EBF) in order to study the behavior in actual BF conditions. The results suggested that the low-zinc fraction of the BF sludge could be added to the briquettes without negatively affecting the performance of the briquettes in the BF. The results were confirmed in industrial-scale trials where non-treated BF sludge was added to cold-bonded briquettes in an amount that would facilitate complete recycling of the low-zinc fraction. Charging these briquettes to the BF did not induce any negative effects on the process or the hot metal (HM) quality.

The high-zinc fraction of the tornado-treated BF sludge was added in self-reducing cold-bonded agglomerates and studied in technical-scale smelting reduction experiments aiming at recycling to the HM desulfurization plant. The experiments suggested that melt-in problems could be expected when using either briquettes or pellets. Nonetheless, industrial-scale trials were performed aiming to study the feasibility of recycling cold-bonded briquettes to both the HM desulfurization plant and basic oxygen furnace (BOF). These trials suggested that a substantial amount could be recycled without affecting the final quality of the steel. However, additional experiments were identified to be required in order to enable 100 % recycling of the high-zinc fraction of the tornado-treated BF sludge.

Based on the results from the experimental work, a holistic concept to completely recycle the BF sludge within the integrated steel plant was suggested.

Place, publisher, year, edition, pages
Luleå University of Technology, 2019. , p. 104
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
URN: urn:nbn:se:ltu:diva-75651ISBN: 978-91-7790-419-9 (print)ISBN: 978-91-7790-420-5 (electronic)OAI: oai:DiVA.org:ltu-75651DiVA, id: diva2:1344770
Public defence
2019-10-18, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, JK21069Available from: 2019-08-22 Created: 2019-08-22 Last updated: 2019-09-13Bibliographically approved
List of papers
1. Characterization and Upgrading of a Low Zinc-Containing and Fine Blast Furnace Sludge: A Multi-Objective Analysis
Open this publication in new window or tab >>Characterization and Upgrading of a Low Zinc-Containing and Fine Blast Furnace Sludge: A Multi-Objective Analysis
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2017 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 57, no 2, p. 262-271Article in journal (Refereed) Published
Place, publisher, year, edition, pages
The Iron and Steel Institute of Japan, 2017
Keywords
blast furnace sludge, recycling, characterization, zinc, hydrocyclone, leaching
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-59991 (URN)10.2355/isijinternational.ISIJINT-2016-512 (DOI)000396642300008 ()2-s2.0-85013916025 (Scopus ID)
Funder
Swedish Energy Agency
Note

Validerad; 2017; Nivå 2; 2017-03-10 (andbra)

Available from: 2016-10-27 Created: 2016-10-27 Last updated: 2019-09-13Bibliographically approved
2. Upgrading of Blast Furnace Sludge and Recycling of the Low-Zinc Fraction via Cold-bonded Briquettes
Open this publication in new window or tab >>Upgrading of Blast Furnace Sludge and Recycling of the Low-Zinc Fraction via Cold-bonded Briquettes
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2019 (English)In: Journal of Sustainable Metallurgy, ISSN 2199-3823, no 3, p. 350-361Article in journal (Refereed) Published
Abstract [en]

Depending on the operation of the blast furnace (BF), the main outlet of zinc from the furnace is more or less via the BF dust and sludge. As the dust is recycled to the BF, the sludge has to be de-zinced prior to recycling to prevent the accumulation of zinc in the BF. De-zincing and recycling of the low-zinc fraction via sinter have been reported. However, no research con-cerning recycling of upgraded BF sludge via cold-bonded briquettes has been performed. In the present study, a fine-grained BF sludge with low zinc content, generated by a BF operating on a ferrous burden of 100% pellets, was upgraded using the tornado process. The process simultaneously dried and separated the BF sludge into a high-zinc and a low-zinc fraction. The feasibility of recycling the low-zinc fraction to the BF using cold-bonded briquettes was studied on a laboratory-scale BF shaft simulator. On comparison with a reference briquette, the experiments indicated that 10 wt% of the upgraded BF sludge can be added to the briquette without negatively affecting the reducibility. Higher additions were found to render the briquette less reduced compared to the reference under test conditions corresponding to the central part of the BF. The strength of the briquettes was not compromised with the addition of the upgraded BF sludge, and a decision to study the briquettes in the LKAB experimental blast furnace was made in order to evaluate the behavior under actual BF conditions.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Blast furnace sludge, Recycling, Upgrading, De-zincing, Cold-bonded briquettes, Laboratory-scale blast furnace
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-73899 (URN)10.1007/s40831-019-00225-x (DOI)000483723600008 ()2-s2.0-85065727551 (Scopus ID)
Funder
Swedish Energy Agency, JK21069
Note

Validerad;2019;Nivå 2;2019-09-27 (johcin)

Available from: 2019-05-10 Created: 2019-05-10 Last updated: 2019-09-27Bibliographically approved
3. Recycling of Blast Furnace Sludge to the Blast Furnace via Cold-Bonded Briquettes: Evaluation of Feasibility and Influence on Operation
Open this publication in new window or tab >>Recycling of Blast Furnace Sludge to the Blast Furnace via Cold-Bonded Briquettes: Evaluation of Feasibility and Influence on Operation
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2019 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460Article in journal (Refereed) Epub ahead of print
Abstract [en]

Ore-based steelmaking generates various residues including dusts, sludges, scales and slags. Recycling of these residues within the process or via other applications is essential for sustainable production of steel. In blast furnace (BF) ironmaking, the gas-cleaning equipment generally recovers the particles in the off-gas as dust and sludge. Traditionally, the dry dust is recycled via the sinter or, in the case of pellet-based BF operation, via cold-bonded briquettes and injection. As the BF sludge mainly consists of iron and carbon, this residue is of interest to recycle together with the BF dust. However, depending on how the BF is operated, these two residues are more or less the major outlet of zinc from the furnace. Thus, to limit the recycled load of zinc, both materials cannot be recycled without dezincing the sludge prior to recycling. Dezincing and recycling of the low-zinc fraction of BF sludge via sinter have been reported whereas recycling via cold-bonded briquettes has not been performed. In the present study, cold-bonded briquettes containing the low-zinc fraction of dezinced BF sludge were charged as basket samples to the LKAB Experimental Blast Furnace (EBF). The excavated basket samples from the quenched EBF suggested that additions of up to 20 wt.% of upgraded BF sludge was feasible in terms of reducibility and strength. Based on these results, BF sludge were added to cold-bonded briquettes and charged in industrial-scale trials. The trials indicated that the annual generation of BF sludge, after dezincing, could be recycled to the BF.

Place, publisher, year, edition, pages
Iron and Steel Institute of Japan, 2019
Keywords
blast furnace sludge, recycling, cold-bonded briquettes, pilot-plant scale blast furnace trials, industrial-scale blast furnace trials
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-75198 (URN)10.2355/isijinternational.ISIJINT-2019-080 (DOI)
Funder
Swedish Energy Agency, JK21069
Available from: 2019-07-03 Created: 2019-07-03 Last updated: 2019-08-22
4. The Potential of Recycling the High-Zinc Fraction of Upgraded BF Sludge to the Desulfurization Plant and Basic Oxygen Furnace
Open this publication in new window or tab >>The Potential of Recycling the High-Zinc Fraction of Upgraded BF Sludge to the Desulfurization Plant and Basic Oxygen Furnace
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2018 (English)In: Metals, ISSN 2075-4701, Vol. 8, no 12, article id 1057Article in journal (Refereed) Published
Abstract [en]

In ore-based steelmaking, blast furnace (BF) dust is generally recycled to the BF via the sinter or cold-bonded briquettes and injection. In order to recycle the BF sludge to the BF, the sludge has to be upgraded, removing zinc. The literature reports cases of recycling the low-zinc fraction of upgraded BF sludge to the BF. However, research towards recycling of the high-zinc fraction of BF sludge within the ore-based steel plant is limited. In the present paper, the high-zinc fraction of tornado-treated BF sludge was incorporated in self-reducing cold-bonded briquettes and pellets. Each type of agglomerate was individually subjected to technical-scale smelting reduction experiments aiming to study the feasibility of recycling in-plant residues to the hot metal (HM) desulfurization (deS) plant. The endothermic reactions within the briquettes decreased the heating and reduction rate leaving the briquettes unreduced and unmelted. The pellets were completely reduced within eight minutes of contact with HM but still showed melt-in problems. Cold-bonded briquettes, without BF sludge, were charged in industrial-scale trials to study the recycling potential to the HM deS plant and basic oxygen furnace (BOF). The trials illustrated a potential for the complete recycling of the high-zinc fraction of BF sludge. However, further studies were identified to be required to verify these results.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
recycling, blast furnace sludge, smelting reduction, desulfurization, basic oxygen furnace, cold-bonded briquettes, cold-bonded pellets, low-sulfur binders
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-72426 (URN)10.3390/met8121057 (DOI)000455072100081 ()2-s2.0-85058575555 (Scopus ID)
Conference
8th International Congress on Science and Technology in Ironmaking — 8th ICSTI 2018, September 25 to 27 2018, Vienna.
Note

Konferensartikel i tidskrift

Available from: 2019-01-02 Created: 2019-01-02 Last updated: 2019-08-22Bibliographically approved
5. A Holistic and Experimentally-Based View on Recycling of Off-Gas Dust within the Integrated Steel Plant
Open this publication in new window or tab >>A Holistic and Experimentally-Based View on Recycling of Off-Gas Dust within the Integrated Steel Plant
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2018 (English)In: Metals, ISSN 2075-4701, Vol. 8, no 10, article id 760Article in journal (Refereed) Published
Abstract [en]

Ore-based ironmaking generates a variety of residues, including slags and fines such as dust and sludges. Recycling of these residues within the integrated steel plant or in other applications is essential from a raw-material efficiency perspective. The main recycling route of off-gas dust is to the blast furnace (BF) via sinter, cold-bonded briquettes and tuyere injection. However, solely relying on the BF for recycling implicates that certain residues cannot be recycled in order to avoid build-up of unwanted elements, such as zinc. By introducing a holistic view on recycling where recycling via other process routes, such as the desulfurization (deS) station and the basic oxygen furnace (BOF), landfilling can be avoided. In the present study, process integration analyses were utilized to determine the most efficient recycling routes for off-gas dust that are currently not recycled within the integrated steel plants of Sweden. The feasibility of recycling was studied in experiments conducted in laboratory, pilot, and full-scale trials in the BF, deS station, and BOF. The process integration analyses suggested that recycling to the BF should be maximized before considering the deS station and BOF. The experiments indicated that the amount of residue that are not recycled could be minimized.

Place, publisher, year, edition, pages
Basel: MDPI, 2018
Keywords
Recycling, Cold-bonded briquettes, Blast furnace, Desulfurization, Basic oxygen furnace, Dust, Sludge, Fines
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-71130 (URN)10.3390/met8100760 (DOI)000448658700024 ()2-s2.0-85054764975 (Scopus ID)
Funder
Swedish Energy Agency
Note

Validerad;2018;Nivå 2;2018-10-19 (marisr)

Available from: 2018-10-08 Created: 2018-10-08 Last updated: 2019-08-22Bibliographically approved

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