Effects of 2CaO·SiO_2 and 2CaO Al_2O_3 SiO_2 on Primary Slag Melting of Sinters in the Cohesive Zone of a Blast Furnace

摘要

To investigate the relation between Al_2O_3 and the gas permeability resistance in a blast furnace, the effect of Al_2O_3 on the increment in the slag melt volume and the decrement in the temperature of the slag melt formation has been elucidated by comparing the reactions between liquid olivine and solid 2CaO·SiO_2 and between liquid olivine and solid 2CaO-Al_2O_3-SiO_2 at the constant temperature of 1 240℃, and eutectic reactions between FeO and 2CaO·SiO_2 and between FeO and 2CaO·Al_2O_3·SiO_2 at the constant heating rate of 10℃/min. The reaction temperature of 1 240℃ has been chosen because the effect of Al_2O_3 on the gas permeability is markedly observed at that temperature. The heating rate has been set to be 10℃/min as it is considered to be the approximate heating rate of burden in a blast furnace. The fraction of the liquid phase decreases from 38.3% to 30% for olivine-2CaOSiO_2 system, while it increases from 23.5% to 27.4% for olivine-2CaO·Al_2O_3·SiO_2 system in 10 min after the onset of heating. It is considered that the increment in the Al_2O_3 content of iron ores raises the amount of olivine-like slag melts around 1 240℃. The onset temperature of eutectic reaction for mixed FeO and C2AS powders is almost equal to that for mixed FeO and C2S powders when the temperatures are compared for powders with the average particle size smaller than around 40 μm. This implies that a negative effect of Al_2O_3, that is, lowering the temperatures of slag melt formation could be eliminated when the microstructures of sinters are fine enough.