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Energy and environmental optimization of some aspects of EAF practice with novel process solutions
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of the present thesis is to optimize the electric arc furnace (EAF) practice from an environmental view point. Two aspects that meet the requirements of the secondary steelmaking industries today, viz. Mo alloying with maximum retainment of the alloying element in molten steel and optimization of foaming by carbonate addition with a view to optimize the energy need of the process. Both these aspects would also have a significant impact on the process economy.

Iron molybdate (Fe2MoO4) has been synthesized from commercial grade materials and proposed as a new potential precursor for steel alloying with Mo. The thermal stabilities of different molybdates, viz. Fe2MoO4, CaMoO4 and MgMoO4, were studied using thermogravimetry analysis (TGA). It was found that Fe2MoO4 is the most stable one and doesn’t evaporate in Ar atmosphere when heating up to 1573 K.

The synthesis of Fe2MoO4 requires high temperature (1373 K) and long holding time (up to 16 hours). In a view of this, the possibilities for in-situ formation of Fe2MoO4 and CaMoO4 from their precursor mixtures were studied with the aid of high-temperature X-ray diffraction (XRD) and TGA analysis. Laboratory and industrial trials on steel alloying with Mo were conducted using precursor mixtures as sources of Mo. It was found that the mixture, which contains FeOx, MoO3 and C (Fe2MoO4 precursor), can provide the Mo yield up to 98 % at both the laboratory as well as industrial trials. The Mo yields even in the case of C+MoO3 and C+MoO3+CaO mixtures were around 93 % in these trials. The higher yield for the MoO3+C+FeOx mixture was attributed to the stabilization of Mo in the precursor (marked by the decrease in the Gibbs energy of Mo) and the readiness to dissolve in the steel bath.

The heat effect of the slag foaming with carbonates addition was studied at 1623 and 1673 K with the aid of thermal analysis technique with a new crucible design. Experiments were conducted by adding limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. It was found that the decomposition energies for dolomite and limestone for the studied slag composition are in the range 56-79 % of theoretical values, which is linked to the energy saving effect of slag foaming. No influence of sample shape on decomposition energy was found both for limestone and dolomite.

The kinetics of slag foaming by limestone particles was studied at 1773 K with the aid of X-ray imaging system. A model was proposed to describe the decrease in foam height with time on the basis of CaO shell formation during decomposition reaction.

The energy impact of limestone and raw dolomite addition was examined in a 100-ton EAF. It was found that, in the case of addition of carbonates after the scrap is completely molten; the endothermic heat effects for limestone and dolomite (2255 and 2264 kJ/kg respectively) were only 70 % from theoretical values. This is indicative of the resistance to heat transfer due to increased foaming.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , viii, 53 p.
Keyword [en]
Molybdates, slag foaming, steel alloying, EAF, carbonate decomposition
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-24486ISBN: 978-91-7415-721-5 (print)OAI: oai:DiVA.org:kth-24486DiVA: diva2:350412
Public defence
2010-10-08, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100914Available from: 2010-09-14 Created: 2010-09-10 Last updated: 2010-12-03Bibliographically approved
List of papers
1. MoO3 Evaporation Studies from Binary Systems towards Choice of Mo Precursors in EAF
Open this publication in new window or tab >>MoO3 Evaporation Studies from Binary Systems towards Choice of Mo Precursors in EAF
2010 (English)In: Steel Research International, ISSN 1611-3683, Vol. 81, no 9, 784-791 p.Article in journal (Refereed) Published
Abstract [en]

The evaporation rate of molybdenum oxide from mixtures with CaO or MgO was studied in the temperature range 300-1573 K. The investigations were carried out using high temperature X-ray diffraction and thermogravimetry. Further, additions of these precursors to molten steel in the laboratory scale and the Mo yield achieved were determined. The X-ray studies show that the calcium molybdate is formed from the oxide mixture in the temperature interval 773-873K, which precedes the beginning of evaporation of MoO3. Results of thermogravimetric studies with mixtures CaO and MgO with MoO3 as well as the compounds CaMoO4 and MgMoO4 confirm the above results. Addition of various molybdenum precursors, viz, the mixtures of carbon with pure MoO3, CaMoO4 and MgMoO4, as well as oxide mixtures (CaO + MoO3, MgO + MoO3) show that the highest yield was observed for CaMoO4 + C and MoO3 + C mixtures, while MgO + C + MoO3 mixture showed much lower yield.

Keyword
calcium and magnesium molybdates evaporation, steel alloying, Mo yields, calcium molybdate formation
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24516 (URN)10.1002/srin.201000055 (DOI)000281912200013 ()2-s2.0-77956601719 (Scopus ID)
Note
QC 20100913. Uppdaterad från in press till published (20101203).Available from: 2010-09-13 Created: 2010-09-13 Last updated: 2010-12-03Bibliographically approved
2. Synthesis and characterization of Fe2MoO4 as a precursor material for Mo alloying in steel
Open this publication in new window or tab >>Synthesis and characterization of Fe2MoO4 as a precursor material for Mo alloying in steel
2011 (English)In: Steel Research International, ISSN 1611-3683, Vol. 82, no 3, 269-276 p.Article in journal (Refereed) Published
Abstract [en]

Iron molybdate (Fe2MoO4) has been studied as a new potential precursor for Mo additions in high alloy steel processing. Fe2MoO4 was synthesized by high temperature reactions between MoO3, FeOx and carbon by holding the mixture first for 23 hours at 873K and then for 16 hours at 1373 K. The Fe2MoO4 syntheses were carried out with pure reagents as well as commercial grade materials supplied by steel industry. A thermodynamic analysis of the stabilities of the various phases in the Fe-Mo-O-C quaternary was carried out. The synthesis processes, leading to the Fe2MoO4 formation from the precursors and further reduction by carbon were studied with the aid of thermogravimetric analysis (TGA), high-temperature X-ray diffraction (HT-XRD) and evolved gas analysis by gas chromatography (GC). The maximum temperature in the case of all the experiments was 1373 K. It was found that the reactions between the precursor components start already above 873 K. The precursor mixture from commercial grade materials offers an economically advantageous process route with high Mo yield in steel.

Keyword
Fe2MoO4, Mo alloying, Synthesis, Characterization, Mo yields
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24518 (URN)10.1002/srin.201000158 (DOI)000289061100015 ()2-s2.0-79952234376 (Scopus ID)
Note
QC 20100913 Uppdaterad från submitted till published (20110420).Available from: 2010-09-13 Created: 2010-09-13 Last updated: 2011-04-20Bibliographically approved
3. Fe2MoO4 as a precursor material for Mo alloying in steel: (Part II): Upscaling test
Open this publication in new window or tab >>Fe2MoO4 as a precursor material for Mo alloying in steel: (Part II): Upscaling test
2011 (English)In: Steel Research International, ISSN 1611-3683, Vol. 82, no 8, 886-897 p.Article in journal (Refereed) Published
Abstract [en]

The Mo yield when using three different alloying mixtures (MoO3 +C; MoO3 +C + FeOx; and MoO3+ C + CaO) was tested both in laboratory experiments (16 g and 0.5 kg scale) and industrial trials (3 ton scale). The alloying is based on in-situ formation of compounds of Mo in the mixtures from molybdenite concentrate with industrial grade Fe 2O3. Thermogravimetry (TGA) and X-ray diffraction (XRD) analyses were performed to identify the reduction steps and final products of the alloying mixtures. At least two steps of mass change were discovered during the reduction of all tested mixtures by carbon. The Mo yield for MoO3 + C mixture is 93% which was confirmed by both laboratory and industrial experiments. The Mo yield for MoO3 + C + CaO mixture is around 92% during 16 g scale laboratory and 3 ton scale industrial tests. The best results were obtained in the case of the mixture which contained FeOx, MoO3 and C, resulting in the Mo yield up to 98% at all the experiment scale levels. It was found that the combination of both lower evaporation and fast reduction by carbon of the mixture along with further dissolution in steel are necessary to provide high Mo yield during steel alloying. The calculated mass balance of 3 ton trial heats showed that only a small part of initial Mo amount (8-13 ppm) has gone into slag. Copyright

Keyword
Fe2MoO4, industrial test, Mo yields, steel alloying
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24520 (URN)10.1002/srin.201100026 (DOI)000294444800002 ()2-s2.0-79961157127 (Scopus ID)
Note
Updated from submitted to published. QC 20120326Available from: 2010-09-13 Created: 2010-09-13 Last updated: 2012-03-28Bibliographically approved
4. Foaming in Electric Arc Furnace: Part I: Laboratory Studies of Enthalpy changes of Carbonate Additions to Slag Melts
Open this publication in new window or tab >>Foaming in Electric Arc Furnace: Part I: Laboratory Studies of Enthalpy changes of Carbonate Additions to Slag Melts
2011 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 42, no 1, 20-29 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, a modified thermal analysis technique was used for studying the heat effect of slag foaming with carbonates addition. Experiments were conducted by sinking limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. The heat effects of dolomite and limestone decompositions were determined at 1623 K (1350 A degrees C) and 1673 K (1400 A degrees C). It was found that the decomposition energy for dolomite and limestone for the studied slag composition is in the range of 56 to 79 pct of theoretical values, which is linked to the energy-saving effect of slag foaming. No influence of sample shape on decomposition energy was found for both limestone and dolomite.

Keyword
Decomposition energy, Electric arc furnace, Energy-saving effect, Enthalpy change, Heat effect, Laboratory studies, Molten Slag, Sample shape, Slag compositions, Slag foaming, Slag melt, Temperature changes, Theoretical values, Thermal analysis techniques, Carbonates, Decomposition, Electric arcs, Furnaces, Limestone, Thermoanalysis
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24522 (URN)10.1007/s11663-010-9447-4 (DOI)000286942500005 ()2-s2.0-79951512284 (Scopus ID)
Note
QC 20100913 Uppdaterad från submitted till published (20110318).Available from: 2010-09-13 Created: 2010-09-13 Last updated: 2011-03-18Bibliographically approved
5. Foaming in Electric Arc Furnace: Part II: Foaming visualization and Comparison with Plant trials
Open this publication in new window or tab >>Foaming in Electric Arc Furnace: Part II: Foaming visualization and Comparison with Plant trials
2012 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 43, no 5, 1078-1085 p.Article in journal (Refereed) Published
Abstract [en]

The kinetics of slag foaming by limestone particles was studied at 1773 K (1500 A degrees C) with the aid of an X-ray imaging system. Two models were implemented to describe the decrease in foam height with the time on the basis of the lowering of the average temperature and CaO shell formation during decomposition reaction. The energy impact of carbonate additions was studied on an industrial scale in a 100-ton electric arc furnace (EAF). It was found that, in the case of the addition of carbonates after the scrap is completely molten, the heat effects for limestone and dolomite (2255 and 2264 kJ/kg, respectively) were only 70 pct from theoretical values. Comparing these values with similar additions during the scrap melting stage shows that the energy requirements in the case of carbonate additions to steel bath are much smaller. It was found from the trial heats with dolomite addition to the steel bath that the partial substitution of lime by raw dolomite can be made without an increase in energy consumption.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24523 (URN)10.1007/s11663-012-9690-y (DOI)000308822100008 ()2-s2.0-84869879147 (Scopus ID)
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research
Note

Updated from "Submitted" to "Published" QC 20121016

Available from: 2010-09-13 Created: 2010-09-13 Last updated: 2012-10-16Bibliographically approved

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