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

Abstract

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...

The Effect of BOF Slag and BF Flue Dust on Coal Combustion Efficiency

“…The negative effects of a decreased combustion efficiency in the raceway can be counteracted by an improved permeability caused by the consumption of unburnt char and coke fines by FeO 6,12) supplied by the BOF slag. The improved melting properties of tuyere slag 17) can as well be expected to improve the permeability. The mixture of BOF slag and high volatile coal will have a lower volatile content compared to coal only, which will have an effect on the ignition of coal.…”

“…A laboratory study on the effect of different basic fluxes-BOF slag, burnt lime and burnt dolomiteon the melting properties of tuyere slag shows that the addition of basic fluxes in general, and BOF slag particularly, improves the melting properties of coal and coke ash in terms of a decreased melting point and a decreased softening and melting temperature interval. 17) There are no sinter plants in operation in Sweden. Inplant fines are mainly recycled as cold bonded agglomerates.…”

Influence of Basicity and FeO Content on Viscosity of Blast Furnace Type Slags Containing FeO

“…4) Although the viscosities of CaO-SiO 2 -Al 2 O 3 (-MgO) slags have been measured by several researchers, [5][6][7] the range of basicity in these studies was limited to approximately C/S≈0.6-1.3 in view of tapped slag composition. Recently, the viscosities of the CaO-SiO 2 -Al 2 O 3 -MgO-FeO slags with C/Sϭ1.2-1.5 were measured by Sugiyama. 2) However, the viscosities of slags containing FeO were measured only at CaO/SiO 2 ϭ1.2, and these results were applied to other basicity regions by extrapolation.…”

Viscosity of Highly Basic Slags

“…For example, slag viscosity is important in BOF steelmaking and blast furnace ironmaking in terms of slag fluidity. [5][6][7] In addition, the chemical composition of molten oxide mixtures affects the life span of metallurgical refractories. For instance, slag composition should be optimized to expand the life of the BOF vessel lining by improving the slag coating technology of the vessel.…”