Injection of Flux into the Blast Furnace via Tuyeres for Optimising Slag Formation.

Ma, Jiawei

doi:10.2355/isijinternational.39.697

Cited by 17 publications

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“…To decrease the variations in slag basicity and the slag amount in the cohesive zone, Ma 1) has proposed injection of fluxes through the tuyeres, instead of charging them from the top, to improve slag formation in the blast furnace. The basicity B2 of primary slag of the pellet, bosh slag, tuyere slag and final slag will then be 1.0, 1.1, 0.9 and 1.2, respectively.…”

Section: )mentioning

confidence: 99%

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The Melting Properties of Tuyere Slags with and without Flux Injection into the Blast Furnace.

Ökvist

2001

ISIJ International

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A laboratory study concerning the melting properties of tuyere slags has been conducted. The meltingpoint measurements of various specimens, consisting of coke ash, coal ash and fluxes (BOF slag, burnt lime and burnt dolomite), corresponding to the tuyere slags formed in front of the tuyeres with or without flux injection, have been performed in a high-temperature microscope. Theoretical estimations of melting points have been made based on the chemical composition of the tuyere slag specimens.The results have shown that injection of fluxes has quite a positive effect on the melting properties of the tuyere slag. The melting point of the tuyere slag decreases and the temperature interval between softening and complete melting of the tuyere slag becomes narrower. Compared to the injection of burnt lime and burnt dolomite, the injection of BOF slag will result in still better tuyere slag properties in terms of lower flow point and narrower temperature interval between softening and melting. The differences in melting behaviour in the tuyere slag specimens indicate that injection of BOF slag will also give the tuyere slag a lower viscosity compared to injection of burnt lime or burnt dolomite at the same levels of slag basicity B2.KEY WORDS: flux injection; tuyere slag; melting-point measurements.powder mixture of flux and iron ore did decrease the Si content. The positive effect of flux powder was explained by SiO absorption by the flux powder. 5) In another study on injection of iron ore fines it was found that the Si content was decreased as a result of increased partial pressure of oxygen in the end of the raceway. If sinter fines containing CaO was used the effect was higher. 6) In another study of the injection, a mixture of iron ore and coal or a water slurry containing iron ore resulted in decreased Si content of hot metal. The oxidation degree of the slag in the hearth and bosh was considered to be a key factor controlling Si content of hot metal.7) The different results achieved in the iron ore injection studies might be explained by the particle size of the injected iron ore.8) The original oxidation degree of slags in the bosh and the hearth will affect the result. 5)When a very fine grain size of iron ore is used, the reduction in the raceway will be efficient and the amount of residual FeO limited.The use of injection of flux via tuyeres in order to obtain smooth slag formation in the blast furnace results in a decrease in the volume of bosh slag and prevents the formation of a bosh slag with excessive basicity.1-3) At normal blast furnace operation, the tuyere slag, formed by the ash content in fuels combusted in front of the tuyeres, is very acidic and has a high viscosity. The injection of fluxes via the tuyeres makes it possible to increase the basicity of the tuyere slag to an appropriate level and improve its melting properties. A lower tuyere slag viscosity might improve the drainage of the slag through the voids in the coke bed. 9,10) The aim of this laboratory study is to determine the influe...

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Section: )mentioning

confidence: 99%

“…[1][2][3] At normal blast furnace operation, the tuyere slag, formed by the ash content in fuels combusted in front of the tuyeres, is very acidic and has a high viscosity. The injection of fluxes via the tuyeres makes it possible to increase the basicity of the tuyere slag to an appropriate level and improve its melting properties.…”

Section: )mentioning

confidence: 99%

The Melting Properties of Tuyere Slags with and without Flux Injection into the Blast Furnace.

Ökvist

2001

ISIJ International

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“…Occasionally, reduction of gas/liquid permeability in the bosh zone during high PCR/low slag volume operations has been reported. [2][3][4] For high PCR/low slag volume operation, the gas/liquid permeability should be estimated with considering the slag chemistry, and it can be indirectly predicted by investigating the viscosity of bosh slags.…”

Section: Introductionmentioning

confidence: 99%

Influence of MgO and Al2O3 Contents on Viscosity of Blast Furnace Type Slags Containing FeO

et al. 2004

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The viscosities of CaO-SiO 2 -Al 2 O 3 -MgO-FeO slag were measured under conditions of C/Sϭ1.35-1.45, 10-18 mass% Al 2 O 3 , 3.5-10 mass% MgO and 5 mass% FeO. The bosh slag with 10 mass% Al 2 O 3 content had the lowest melting temperature and the widest solid-liquid coexisting region at about 5 mass% MgO, while in case of 14 mass% Al 2 O 3 , an increase in a MgO content from about 3.5 to 10 mass% raised the melting point of bosh slag. The viscosity of bosh slag also exhibited a minimum value at about 7 mass% MgO at temperatures above 1 723 K. However, it was not significantly changed with varying MgO content. On the hand, with increasing Al 2 O 3 content, the viscosity of bosh slag increased at a fixed C/S and MgO content. Based on the melting temperature and the behavior of viscosity at a fixed temperature, it could be proposed that the MgO and Al 2 O 3 contents in bosh slag should be maintained around 5 and 10 mass%, respectively, for high pulverized-coal ratio (PCR) and low slag volume operations in blast furnace.KEY WORDS: viscosity; bosh slag; blast furnace; slag volume reduction; slag structure; FT-IR. 100 rpm) were employed in 1 773 K to ensure that viscosity values were independent of rotation speed. All measurements were performed with cooling and holding temperature. The holding time for reaching equilibrium state was more than 30 min at each experimental temperature. A metal flange was utilized to fill the gap between the viscometer and the mullite reaction tube, and an Ar gas (0.4 L/min) was flown into the reaction chamber. After viscosity measurements were completed, the slag samples were reheated up to 1 773 K, and held for more than 3 h. Then, the slag sample was quenched to analyze slag composition and to measure the infrared spectra of the slag. According to the composition analysis of post-measurement slag using X-ray Fluorescence (Bruker-SRS3400), there was no significant change in any component of slags (less than 1 %).In order to confirm the reproducibility of viscosity values, some experiments for the same composition were carried out three times. The results show that differences between measurements were lower than 0.2 dPa · s (less than 0.5 %). Infrared Spectra MeasurementThe structure of the investigated slags was analyzed by FT-IR spectroscopy (JASCO, FT/IR-300 E). FT-IR trans- ISIJ International, Vol. 44 (2004) mitting spectra were recorded in the 4 000 -400 cm Ϫ1 range using a spectrometer equipped with a KBr (deuterated triglycine sulfate with potassium bromide windows) detector. A spectral resolution of 4 cm Ϫ1 was chosen. Each 2.0 mg sample was mixed with 200 mg of KBr in an agate mortar, and then pressed into 13 mm diameter pellets. The spectrum for each sample represents an average of 20 scans, which were each normalized to the spectrum of the blank KBr pellets. The FT-IR spectra were analyzed by computer software. Results and DiscussionIn the present study, the effects of MgO and Al 2 O 3 contents on the viscosities of the CaO-SiO 2 -Al 2 O 3 -MgO-FeO slags were investigate...

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“…The amount of the BOF-slag added is about 3% of the amount of pellet. Theoretical analyses conducted by Professor Ma 4) have shown that top-charged BOF-slag can improve slag formation when using olivine pellets, but does cause problems when using 100% self-fluxed pellets. For the latter, the top-charged BOF-slag with the primary slag phases from the pellets can form high-basicity bosh slag, especially when segregation of BOF-slag occurs.…”

Section: Introductionmentioning

confidence: 99%

“…One of the major reasons has been theoretically attributed to the worsening of the softening and melting properties of the pellet in the furnace, resulting from the top-charging of the fluxes together with pellets. 4) Conventionally, the major slag formers used at SSAB Luleå are BOF-slag and limestone, top-charged together with pellets. The amount of the BOF-slag added is about 3% of the amount of pellet.…”

Section: Introductionmentioning

confidence: 99%

Softening and Melting Characteristics of Self-fluxed Pellets with and without the Addition of BOF-slag to the Pellet Bed.

Zuo

2000

ISIJ International

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When using 100 % self-fluxed pellets in the blast furnace burden, top charged fluxes, especially the BOFslag, may cause irregularities in operation. The major reason has been theoretically attributed to the problematic slag formation in the furnace. As the melting of pellets is the first step of the slag formation process, the softening and melting properties of LKAB's self-fluxed pellets with and without addition of fluxes are studied experimentally.The results show that the softening and melting properties of the two types of LKAB's self-fluxed pellets are quite suitable for blast furnace operation. Contrarily, the melting-down characteristics of BOF-slag are variable and harmful to the slag formation under a reducing atmosphere. Adding 5 % BOF-slag to the selffluxed pellets can considerably worsen the softening and melting properties of pellets. It can either increase the softening and melting temperature interval substantially or cause the precipitation of solid phases, mainly di-calcium silicates, in the slag. It is quite likely that the resulting slag will therefore become very viscous, even entirely blocking the melting down of the pellets up to a temperature 1 520°C.

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Injection of Flux into the Blast Furnace via Tuyeres for Optimising Slag Formation.

Cited by 17 publications

References 1 publication

The Melting Properties of Tuyere Slags with and without Flux Injection into the Blast Furnace.

The Melting Properties of Tuyere Slags with and without Flux Injection into the Blast Furnace.

Influence of MgO and Al2O3 Contents on Viscosity of Blast Furnace Type Slags Containing FeO

Softening and Melting Characteristics of Self-fluxed Pellets with and without the Addition of BOF-slag to the Pellet Bed.

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