Limestone with a particle size of less than 5 mm was rapidly calcined in a high-temperature resistance furnace at 1623 K to simulate the conditions of rapid calcination of limestone at ultra-high temperature in a converter. In this study, the decomposition mechanism and calcination characteristics of small-sized limestone at steelmaking temperature were investigated. The study shows that the shrinking sphere or cylinder models with phase boundary reaction were found to be the best representation of limestone kinetic data, and the mechanism function equation is G(α) = 1 − (1 − α)ⁿ, n = 1/2 or 1/3. Limestone particles with a size of 0.18–1.0 mm can be quickly calcined to obtain a typical active lime microstructure and a high activity of more than 350 mL, which is the preferred limestone particle size range in the steelmaking process in which limestone powder is injected into the converter.

Converter blowing limestone powder making slag steelmaking process has the advantages of low carbon and high efficiency, and can realize the resource utilization of CO₂ in the metallurgical process, which is in line with the development direction of green metallurgy. Based on a thermogravimetric-differential thermal analyzer, the kinetic mechanism of decomposition of small limestone at steelmaking temperatures was investigated by a modified double extrapolation method. The results showed that with a higher rate of heating, limestone decomposition lagged, and decomposition temperature increased. Furthermore, the smaller the limestone particle size, the lower the activation energy of decomposition. Compared with N₂, air, and O₂, small limestone powder used for converter blowing could complete more rapid decomposition, and the time required for decomposition shortened by about 1/3, although the decomposition temperature increased in the CO₂. The limestone decomposition rate increased and then decreased at low to high CO₂ partial pressures. With a limiting link, the inhibition was more significant under high CO₂ partial pressure, but the reaction can be fully completed by 1000 °C. The decomposition type modeled was stochastic nucleation and subsequent growth. As the partial pressure of CO₂ increased from 25% to 100%, the number of reaction stages, n, increased.