Decomposition And Dissolution Behavior Of Limestone In Early Converter Slag

Compared to the conventional lime steelmaking mode,adding limestone directly into the converter is considered to have many advantages such as energy conservation,emission reduction of CO2,and lower production cost.However,less systematic research work has been done on the decomposition and dissolution behavior of limestone under the condition of conveter steelmaking.Effects of slag temperature,stirring speed and limestone size on the rates of decomposition and dissolution of limestone are investigated based on high temperature kinetic experiment.Macro-kinetic models of decomposition and dissolution of limestone in the salg are developed and the rate-controlling steps are decided.Meanwhile,by combining with the research work on the microstructure of decomposed layer from limestone,the mechanisms of decomposition and dissolution of limestone are investigated,and the main results are as the followings.(1)Slag temperature and limestone size play important roles on the decomposition rate of limestone.Under the condition of slag basicity of 0.5 and stirring speed of 100r/min,for the limestone in the size of 10mm,the decomposition rate at 1400? is as 1.51-3.76 times as that at 1300?.The total decomposition time of limestone in 15mm is as 1.5 times as that in 10mm.(2)No obvious influence of stirring speed on the decomposition and dissolution rate has been noted,which indicates resistance of heat and mass transfer within the external boundary layer can be neglected.(3)The limestone decomposition rate in the early converter slag is a mixed control of chemical reaction and heat conduction through the CaO layer and the activation energy of decomposition is about 159.416kJ/mol.(4)The grain size of the generated lime increases with the increament of slag temperature and decomposition time.At the temperature range of 1300? to 1400?,the grain size of the generated lime varies from 0.594 to 0.919?m for the decomposition time of 90s to 270s,which is smaller than the grain size of 1 to 3?m of the calcined CaO.Moreover,the porosity of the generated lime decreases slightly with the increament of slag temperature and decomposition time.The porosity of the generated lime is 37.91%at 1300? for 90s,then decreases to 35.49%at 1400 ?,which are comparable to the 35.28%of calcined lime and considered to be favourable for the slag formation(5)Slag temperature and basicity play an important role on the dissolution rate of limestone.The dissolution rate increases with the increament of temperature,while decreases with the increase of slag basicity.The dissolution rate at 1400 ? is as 3.16?3.39 times as that at 13 00 ?.And the dissolution rate in the slag with basicity of 0.5 is as 1.35?1.61 times as that with basicity of 1.0.(6)The dissolution reaction is confirmed as the rate-controlling step of limestone dissolution process,and the activation energy of dissolution is about 457.893kJ/mol.(7)An enriching region of CaO-FeO is found at the interface CaO-molten slag,which increases with the temperature while decrease with the slag basicity.Meanwhile,the region of immersed molten slag is found inside the limestone,indicating that the dissolution process of limestone can be considered as the dissolution of CaO into the molten slag together with slag penetration.