Influence of CaO-SiO2-Al2O3 oxide system on the reduction behaviour of carbon composite pellet

In the present thesis, the effect of CaO-SiO2-Al2O3 oxide system on the reduction behaviour of carbon composite pellet was studied at iron-making temperatures between 1000oC and 1500oC. Compositional differences in the CaO-SiO2-Al2O3 ternary system were confirmed to influence the reactions occurring in composite pellets at high temperatures from 1350°C to 1500°C. Changes in physical appearance and off-gas composition during the in situ reaction experiments demonstrated a strong correlation between the oxide composition and internal reactions. Microscopic observation using light optical microscopy and scanning electron microscope confirmed the correlation between the morphological change of pellets and the compositional difference of oxide systems. Samples were also analysed by X-ray diffraction to investigate phase change during the reduction process. Impact of oxide chemistry was established as each pellet illustrated different state of iron oxide as a function of time. Physical property of pellet was confirmed to be largely influenced by its associated oxide binder systems selected for this study.The influence of compositional changes in the CaO - FeOt - (Al2O3) or (SiO2) ternary oxide system on the reaction kinetics of carbon composite pellet was investigated by using Thermo-Gravimetric Analyser (TGA) at temperatures from 1000oC to 1200°C. Measured CO and CO2 gas by infrared gas analyser and surface area change using BET analysis assisted with the reaction kinetics of carbon composite pellet at 1200oC. As a result, alumina increased the reduction rate of iron oxide by increasing surface area, while silica decreased reduction rate by reducing surface area of pellet samples. A modified reaction kinetic model taking into account both the Boudouard reaction and surface area variation was developed for a better understanding of reduction mechanisms occurring in carbon composite pellets. The effect of alumina and silica on the reaction behaviour of carbon composite pellet was investigated at 1000°C and 1100°C respectively. The overall reaction was divided into three stages according to phase transformation of iron oxide analysed by X-ray diffraction. The Boudouard reaction was largely influenced by alumina and silica that changed CO gas concentration resulting in different reduction behaviour of the pellets