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The Potential of Recycling the High-Zinc Fraction of Upgraded BF Sludge to the Desulfurization Plant and Basic Oxygen Furnace
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
SSAB Europe, Luleå.
Swerim AB, Luleå, Sweden; Central Metallurgical Research and Development Institute, Cairo, Egypt.
Swerim AB, Luleå, Sweden.
Vise andre og tillknytning
2018 (engelsk)Inngår i: Metals, ISSN 2075-4701, Vol. 8, nr 12, artikkel-id 1057Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
MDPI, 2018. Vol. 8, nr 12, artikkel-id 1057
Emneord [en]
recycling, blast furnace sludge, smelting reduction, desulfurization, basic oxygen furnace, cold-bonded briquettes, cold-bonded pellets, low-sulfur binders
HSV kategori
Forskningsprogram
Processmetallurgi
Identifikatorer
URN: urn:nbn:se:ltu:diva-72426DOI: 10.3390/met8121057ISI: 000455072100081Scopus ID: 2-s2.0-85058575555OAI: oai:DiVA.org:ltu-72426DiVA, id: diva2:1274703
Konferanse
8th International Congress on Science and Technology in Ironmaking — 8th ICSTI 2018, September 25 to 27 2018, Vienna.
Merknad

Konferensartikel i tidskrift

Tilgjengelig fra: 2019-01-02 Laget: 2019-01-02 Sist oppdatert: 2019-08-22bibliografisk kontrollert
Inngår i avhandling
1. Recycling of Blast Furnace Sludge within the Integrated Steel Plant: Potential for Complete Recycling and Influence on Operation
Åpne denne publikasjonen i ny fane eller vindu >>Recycling of Blast Furnace Sludge within the Integrated Steel Plant: Potential for Complete Recycling and Influence on Operation
2019 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Luleå University of Technology, 2019. s. 104
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
HSV kategori
Forskningsprogram
Processmetallurgi
Identifikatorer
urn:nbn:se:ltu:diva-75651 (URN)978-91-7790-419-9 (ISBN)978-91-7790-420-5 (ISBN)
Disputas
2019-10-18, 09:00 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Swedish Energy Agency, JK21069
Tilgjengelig fra: 2019-08-22 Laget: 2019-08-22 Sist oppdatert: 2019-09-13bibliografisk kontrollert

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