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- El-Tawil, Asmaa
(författare)
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Bio-coal as an alternative reducing agent in the blast furnace
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 4. |
- Hu, Xianfeng, et al.
(författare)
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Carbothermic reduction of synthetic chromite with/without the addition of iron powder
- 2016
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 56:12, s. 2147-2155
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Tidskriftsartikel (refereegranskat)abstract
- Carbothermic reduction of chromite is an important industrial process for extracting chromium from the chromite. To have a better understanding of the effect of iron on the carbothermic reduction of chromite, the reduction of synthetic chromite (FeCr2O4) by graphite with/without the addition of iron powder was investigated in this paper by Thermogravimetric Analysis (TGA) in argon atmosphere. The fractional reduced samples were examined by SEM/EDS and XRD analysis, and the reduction process was thermodynamically and kinetically evaluated. The experimental results show that the iron powder addition enhances the reduction of FeCr2O4 and this effect increases when increased amounts of iron powder are added. This phenomenon is attributed to the in situ dissolution of chromium into the iron and mixed carbide (Cr,Fe)7C3, which can decrease the activity of the nascent chromium formed by the reduction of the FeCr2O4. The experimental results indicate that the reduction of FeCr2O4 with up to 80 wt.% iron powder addition is likely to be a single-step process and the kinetic analysis suggests that the reduction reaction is likely to be either (a) chemical reaction at the surface of FeCr2O4 or (b) diffusional dissolution of the product (FeCr2) into the iron/alloy particles or the mixed control of (a) and (b).
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| 5. |
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| 6. |
- Hu, Xianfeng, et al.
(författare)
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Direct Alloying Steel with Chromium by Briquettes Made from Chromite Ore, Mill Scale, and Petroleum Coke
- 2017
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Ingår i: Steel Research International. - : Wiley-VCH Verlag. - 1611-3683 .- 1869-344X. ; 88:5
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the effectiveness of using briquettes made from chromite ore, mill scale, and petroleum coke for direct chromium alloying is tested by induction furnace trials carried out in three different scales. The experimental results show that steel scrap can be alloyed with chromium by the chromite ore in the briquettes and the Cr yield from the chromite ore increases with the increase in mill scale addition to the briquettes: the more mill scale is added to the briquettes, the lower the mass ratio of Cr to (Cr + Fe) would be, leading to a higher Cr yield from the chromite ore. Specifically, the maximum Cr yield from the chromite ore is 99.9% when the mass ratio of Cr to (Cr + Fe) in the briquettes is 0.05, and being 93.0% when the ratio is 0.10. However, when the ratio of Cr to (Cr + Fe) in the briquettes reaches 0.20, the maximum Cr yield is only 67.1%. The reduction of chromite ore under the present experimental conditions is promoted by a solid-state reduction mechanism.
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| 7. |
- Hu, Xianfeng, et al.
(författare)
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Exploring the capability of muon scattering tomography for imaging the components in the blast furnace
- 2018
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 58:1, s. 35-42
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Tidskriftsartikel (refereegranskat)abstract
- Knowing the distribution of the materials in the blast furnace (BF) is believed to be of great interest for BF operation and process optimization. In this paper calibration samples (ferrous pellets and coke) and samples from LKAB’s experimental blast furnace (probe samples, excavation samples and core-drilling samples) were measured by the muon scattering tomography detector to explore the capability of using the muon scattering tomography to image the components in the blast furnace. The experimental results show that it is possible to use this technique to discriminate the ferrous pellets from the coke and it is also shown that the measured linear scattering densities (LSD) linearly correlate with the bulk densities of the measured materials. By applying the Stovall’s model a correlation among the LSD values, the bulk densities and the components of the materials in the probe samples and excavation samples was established. The theoretical analysis indicates that it is potential to use the present muon scattering tomography technique to image the components in various zones of the blast furnace.
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