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Self-Reduction Behavior of Bio-Coal Containing Iron Ore Composites
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering. Central Metallurgical Research and Development Institute, P.O Box 87, Helwan, 11421 Cairo, Egypt.ORCID iD: 0000-0002-2358-7719
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering. Swerim AB, 971 25 Luleå, Sweden.ORCID iD: 0000-0003-3363-351x
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
2020 (English)In: Metals, E-ISSN 2075-4701, Vol. 10, no 1, article id 133Article in journal (Refereed) Published
Abstract [en]

The utilization of CO2 neutral carbon instead of fossil carbon is one way to mitigate CO2 emissions in the steel industry. Using reactive reducing agent, e.g., bio-coal (pre-treated biomass) in iron ore composites for the blast furnace can also enhance the self-reduction. The current study aims at investigating the self-reduction behavior of bio-coal containing iron ore composites under inert conditions and simulated blast furnace thermal profile. Composites with and without 10% bio-coal and sufficient amount of coke breeze to keep the C/O molar ratio equal to one were mixed and Portland cement was used as a binder. The self-reduction of composites was investigated by thermogravimetric analyses under inert atmosphere. To explore the reduction progress in each type of composite vertical tube furnace tests were conducted in nitrogen atmosphere up to temperatures selected based on thermogravimetric results. Bio-coal properties as fixed carbon, volatile matter content and ash composition influence the reduction of iron oxide. The reduction of the bio-coal containing composites begins at about 500 °C, a lower temperature compared to that for the composite with coke as only carbon source. The hematite was successfully reduced to metallic iron at 850 °C by using bio-coal, whereas with coke as a reducing agent temperature up to 1100 °C was required.

Place, publisher, year, edition, pages
MDPI, 2020. Vol. 10, no 1, article id 133
Keywords [en]
devolatilization, torrefied biomass, bio-coal, volatile matter, reduction, blast furnace
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
URN: urn:nbn:se:ltu:diva-78186DOI: 10.3390/met10010133ISI: 000516827800133Scopus ID: 2-s2.0-85078498833OAI: oai:DiVA.org:ltu-78186DiVA, id: diva2:1416582
Note

Validerad;2020;Nivå 2;2020-03-30 (alebob)

Available from: 2020-03-24 Created: 2020-03-24 Last updated: 2020-04-02Bibliographically approved
In thesis
1. Bio-coal as an alternative reducing agent in the blast furnace
Open this publication in new window or tab >>Bio-coal as an alternative reducing agent in the blast furnace
2020 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The steel industry is aiming to reduce CO2 emissions by different means; in the short-term, by replacing fossil coal with highly reactive carbonaceous material like bio-coal (pretreated biomass) and, in the longer term, by using hydrogen. The use of bio-coal as part of top charged briquettes also containing iron oxide has the potential to lower the thermal reserve zone temperature of the Blast furnace (BF) and, due to improved gas efficiency, thereby give a high replacement ratio to coke.

In order to select a suitable bio-coal to be contained in agglomerates with iron oxide, the current study aims at investigating the devolatilization behavior and related kinetics of different types of bio-coals. In addition, the aim is to investigate the self-reduction behavior of bio-coal-containing iron ore composite under inert condition and simulated blast furnace thermal profile.

In the BF the temperature of the top-charged material will increase rather quickly during the descent in the upper part. Ideally, all the carbon and hydrogen contained in the top-charged bio-coal should contribute to the reduction. The devolatilization of bio-coal is thus important to understand and to compare between different types of bio-coal.

To explore the devolatilization behavior for different materials, a thermogravimetric analyzer equipped with a quadrupole mass spectrometer was used to monitor the weight loss and off-gases during non-isothermal tests for bio-coals having different contents of volatile matter. The samples were heated in an inert atmosphere up to 1200°C at three different heating rates: 5, 10 and 15°C/min. The thermogravimetric data were evaluated by using the Kissinger–Akahira–Sonuse (KAS) iso-conversational model and the activation energy was determined as a function of the conversion degree. Bio-coals with both low and high content of volatile matter can produce reducing gases that can contribute to the reduction of iron oxide in bio-agglomerates. Bio-coals containing a higher content of catalyzing components such as CaO and K2O will enhance the devolatilization and release of volatile matter at a lower temperature. 

The self–reduction of composites was investigated by thermogravimetric analyses in argon atmosphere up to 1100°C and evolved gases were monitored by means of quadrupole mass spectroscopy. Composites with and without 10% bio-coal and sufficient coke breeze to keep the C/O molar ratio equal to one were mixed and Portland cement was used as a binder. To explore the effect of added bio-coals, interrupted vertical tube furnace tests were conducted in a nitrogen atmosphere at temperatures selected based on thermogravimetric results, using a similar thermal profile as for the thermogravimetric analyzer. The variation between fixed carbon, volatile matter contents and ash composition for different types of bio-coal influences the reduction of iron oxide.

The results showed that the self-reduction proceeds more rapidly in the bio-coal-containing composite and that the volatile matter could have contributed to the reduction. The self-reduction of bio-coal-containing composites started at 500°C, while it started at 740°C with coke as the only carbon source. The hematite was successfully reduced to metallic iron at 850°C with bio-coal present as a reducing agent, but not until 1100°C when using coke.

Use of bio-coal with high content of volatile matter but low content of catalyzing elements as potassium, sodium and calcium in bio-agglomerates for the BF can be recommended because it enhances the self-reduction of iron oxide, e.g., wustite was detected by XRD analysis in samples treated up to 680°C. Bio-coal with low content of volatile matter, low alkalis, low phosphorous and high content of fixed carbon will also be suitable to use in the BF.

 

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2020. p. 67
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
Devolatilization, torrefied biomass, bio-coal, volatile matter, reduction, blast furnace
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-78301 (URN)978-91-7790-569-1 (ISBN)978-91-7790-570-7 (ISBN)
Presentation
2020-06-05, C305, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-05-15Bibliographically approved

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El-Tawil, Asmaa A.Ahmed, Hesham M.Sundqvist Ökvist, LenaBjörkman, Bo

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