Effect of Temperature and Gas Mixtures on Cementite Formation During the Carburization of Hydrogen-Reduced DRI

摘要

The iron and steel industries are undergoing a transformation from fossil (carbonaceous) to fossil-free technology, in which hydrogen is used as a reducing gas to produce directly reduced iron (DRI). However, since it is necessary to include carbon in the DRI to achieve smooth and efficient smelting operations, it is imperative to understand the effect of varying gas mixtures (CO, CH4, CO2, and H-2) on the carburization behavior of hydrogen-reduced DRI between 600 and 800 degrees C. The statistical method of D-Optimal was adopted to design the experiments, analyze the responses, and establish the correlation with the input factors. The experiments were performed in a thermogravimetric analyzer at the single pellet scale. Carburized DRIs were further analyzed under an optical microscope, and the cementite content was determined with the help of macroscopic image analyses. In this study, it was found that the gas mixtures dominated by CH4 are the fastest to carburize at higher temperatures (800 degrees C), and DRI is carburized relatively faster by CO than by CH4 at lower temperatures (600 degrees C). Additionally, CO is more likely to deposit carbon on the surface, and H-2 seems to promote the carburization rate, while CO2 lowers the rates of carburization and carbon deposition. This study helps in establishing the composition of carburizing gas mixtures in correspondence to chosen temperatures, and the compositions might depend on the desired product, such as cold DRI or HBI. [GRAPHICS] .