Kinetics Of Decomposition And Slagging Of Limestone In The Primary Blowing Period Of Converter

Energy consumption and environmental problem can not only be eliminated by using limestone instead of lime during BOF steelmaking process,but also the reduction of metallurgical effect caused by the slaking and pulverization of lime can be solved,and its prospect of industrial application is board.Compared with the slag formation steelmaking process with lime in converter,some scientific proclems are need to be clarified for the steelmaking process in converter by substitution of lime with limestone at the initial exploratory period of industrial application.According to the characteristics of steelmaking process in converter by substitution of lime with limestone,the calculation of material and heat balance was carried out in the present work.Meanwhile,by high temperature experiment combination with SEM and EDS analysis methods,the effects of temperature and basicity of molten slag on the kinetics of decomposition and slagging of limestone in the primary blowing period of converter were investigated.The controlling step of decomposition and dissolution process of limestone in molten slag in converter was discussed,and the slagging mechanism of limestone was also studied.The following conclusions were made.Based on the calculation results of material and heat balance for the steelmaking process in converter by substitution of lime with limestone,the consumption amount of scrap decreased and the consumption amount of hot metal increased with the increment of substitution ratio of limestone.The consumption amount of O2 gas increased slightly but the slag composition was basically unchanged.Meanwhile,Not only the mount of converter gas increased,but also the CO content in the gas increased,and the heat value of conveter gas increased.1 kg limestone could provide 0.077 kg of oxygen and had the same cooling effect of 1.21kg scrap.During the primary blowing period of converter,temperature played an important role on the decomposition rate of limestone in molten slag and the decomposition rate of limestone increased with the increment of temperature.While the effect of slag basicity on the decomposition process was not obvious.Under the present conditions of different temperatures and basicities of molten slag,there still existed the undecomposed CaCO3 region in the central area of limestone samples within 90s.During the decomposition and slagging process of limestone,a CaO-FeO reaction layer was formed between the interface of molten slag and produced lime.With the increment of temperature for the same reaction time and slag basicity,the thickness of the CaO-FeO reaction layer increased and the produced lime dissolved more quickly.While the thickness of CaO-FeO reaction layer became less with the increment of slag basicity,and the dissolution rate of produced lime decreased.The controlling step of limestone decomposition was considered to be the internal diffusion of CO2 through the produced CaO layer,and while the dissolution rate was controlled by CaO diffusion in molten slag.The total process including decomposition and slagging process of limestone was considered to be the dissolution of produced lime in the slag.In the present work,the decomposition activation energy EDe of limestone was 12.20 kJ/mol and the dissolution activation energy E of the produced lime was 180.01 kJ/mol.