Study On Reaction Mechanism And Distribution Law Of Alkali Metal In BF Smelting Process

In recent years, with the rapid growth of iron and steel production, many blast furnaces had to use raw materials of low price, which has high content of alkali metal and sulphur, thus alkali and sulphur load of BF increased sharply, the dealkalization and desulfurization task become aggravated; Meanwhile, the slag amount is maintained at a low level, the contradiction between dealkalization and desulfurization become more acute, the circulation and enrichment of alkali metal in blast furnace increases, the alkali metal hazards to blast furnace production becomes worse. Therefore, the study on the reaction mechanism and distribution law of alkali metal in blast furnace smelting process has important theoretical significance and application value.The alkali metal balanced survey is carried out taking the large blast furnace of Handan Iron and Steel Co. Ltd. as the object. The results show that:the alkali metal load of blast furnace is much higher, because the alkali metal content of iron ore and fuel are much higher. Dealkalization ratio of slag is not high, resulting in the harm of alkali metal to blast occurs. The experiments of alkali metal adsorption and thermodynamic simulation results show that:The alkali metal oxide reduction zone mainly exists in high temperature region, the charge not only don’t absorb alkali but also volatile the absorbed alkali metal. As the temperature rises in the high temperature region, K2O·Fe2O3 content decreases gradually, Na (g) and NaCN (g) content increases. The charge adsorption of alkali metal is sufficient in the medium temperature zone, Na2CO3 gradually decreases, and the amount of alkali vapors is little. The amount of alkali metal charge adsorption decreases fast in low temperature region, potassium is mainly in combination with iron oxide; sodium is mainly in the form of Na2CO3 and NaCN.The potassium sulfide capacity of the BF slag containing alkali metals was determined using gas-slag equilibrium techniques, the results reveal:As binary basicity of slag increases, potassium capacity decreases, sulfide capacity increases and potassium sulfide capacity first increases and then decreases. As MgO content of slag increases with fixed binary basicity, potassium capacity increases, sulfide capacity and potassium sulfide capacity first increase and then decrease. As MgO content of slag increases with fixed ternary alkalinity, sulfide capacity increases, both potassium capacity and potassium sulfide capacity decrease. As Al2O3 content of slag increases, potassium capacity increases, sulfide capacity and potassium sulfide capacity decrease. As temperature increases, potassium capacity and potassium sulfide capacity decrease, sulfide capacity increases. As SO2 pressure increases, potassium capacity decreases both sulfide and potassium sulfide capacity first increase and then decrease. As potassium pressure increases, potassium capacity, sulfide capacity, potassium sulfide capacity decrease all.FetO activity of BF slag containing alkali metal is determined using gas-slag-metal equilibrium techniques, the calculating model of FetO activity is established based on the coexistence theory of slag structure, the calculated results are in agreement with experimental results. The results showed that:As binary alkalinity increases, FetO activity of slag increases. As MgO content increases with fixed basicity, FetO activity decreases. As MgO content increases with fixed ternary basicity, FetO activity decreases. As Al2O3 content increases, FetO activity decreases. Increasing FetO activity of slag is unfavorable to dealkalization, but is in favor of desulfurization.According to Handan Iron and Steel Co. Ltd. production conditions, the simulation experiment of BF slag dealkalization and desulfurization is carried out. The results show that:the basicity has the greatest impact on dealkalization and desulfurization of slag, but the two impacts is conflict, increasing basicity is conducive to desulfurization, but not conducive to dealkalization. MgO content increases with fixed binary basicity, sulfur distribution coefficient and dealkalization rate increase and then decrease. As temperature increases, sulfur distribution coefficient increases, dealkalization rate decreases. As slag ratio increases, sulfur distribution coefficient and dealkalization rate both increase. As reaction time increases, sulfur distribution coefficient increases, dealkalization rate decreases. The suitable slagging system and operating parameters of BF:binary basicity is around 1.11, MgO content is about 10%, Al2O3 content is about 15%, hearth temperature is 1480-1500℃, slag ratio is about 0.36, the tapping time is 100-120min. The quality of hot metal could be ensured, the slag dealkalization rate is greater than 80% in this condition, and thus the alkali metal hazards to BF could be eliminated.