This paper introduced the primary research on the method of using limestone instead of lime for slagging during BOF steelmaking. The study showed that the heat is sufficient for limestone to completely replace lime on the condition that the ratio of hot metal to ferrous scrap is adjusted properly. According to thermodynamic calculations, the partial pressure of CO2 at the hot metal surface at the early stage of converter steelmaking is close to 0 and nearly all the CO2 can react with elements in hot metal, producing CO and reducing O2 consumption. Slag with high oxidizability, high basicity and relatively low temperature can be formed quickly by using limestone, which is advantageous for dephosphorization. Industrial tests showed the endpoint Lp rises with the proportion of lime replaced by limestone increasing. CO2 volume expands by 4000~30000 times when limestone is heated at extremely high speed in converter, resulting in the fragmentation of some parts of limestone and the increase of the contacting area of limestone and slag. The unreacted core model with surface exfoliated was introduced.

Some industrial trials of utilizing limestone as a new kind of slag-making agent instead of lime for slagging during LD-steelmaking process are discussed and analyzed in the present work. The results indicate that with oxygen blowing time being unchanged, slag forming rate increased significantly and final steel compositions and temperature reached the required standard during the steelmaking process with limestone used, compared with the process by using lime. The preliminary success achieved from industrial tests gave strong evidence that the idea of using limestone instead of lime for slagging is feasible and this new steelmaking method with limestone used, which saves energy and reduces CO2 emissions, can be successfully applied into industrial production. Thus, the application of this new method can not only sharply reduce energy consumption and emission of dust and CO2, but also bring significant environmental and economic benefits.

Variations of decomposition rate and decomposition layer thickness of six spherical limestone particles with different sizes are calculated and compared with each other by the experiments and model of static decomposition of limestone under constant temperature. The results indicate that: the decomposition process of limestone can be explained by unreacted core model (UCM) when it is heated sharply; the decomposition rate of large particle is greater than that of small one; the smaller particle size, the larger decomposition layer thickness in unit time.

In this paper, firstly, the morphology characteristics of aggregated Al2O3 inclusion were quantitatively described by fractal dimension and hydrodynamic radius. Then, a general collision-agglomeration model was established to describe the collision and agglomeration process of Al2O3 inclusions with different morphology characteristics. The results showed that: in the collision and agglomeration process of Al2O3 inclusions with different morphology characteristics, the number density of monomer inclusion decreases with time, but that of new aggregated inclusions, firstly increases to the maximum value, then decreases sharply; the smaller the fractal dimension of new aggregated inclusion, the more rapid decrease of number density of monomer inclusion and the larger agglomeration rate of new aggregated inclusions. so in order to accelerate the removal rate of micro inclusion particles, it is a viable way that keeping the fractal dimension of new aggregated inclusions at an appropriate value, not too small.

The Micro agglomeration process of liquid inclusion particles in static steel was simulated based on VOF model of fluent software. The results were indicated that: two liquid inclusion particles, which are apart from a certain surface distance, can aggregate into a larger new inclusion particle; in order to promote liquid inclusion particles aggregate and accelerate inclusions flotation to be removed, the following measures can be taken: shortening the inclusion particle surface spacing, reducing the steel viscosity and controlling the composition of liquid inclusion in high interfacial tension area.