Comprehensive evaluation and analysis of coal used for direct reduction in rotary kiln

Abstract

To explore the coal types appropriate for direct reduction in rotary kiln, this paper focuses on three distinct coal types—lignite, bituminous coal, and anthracite—as the subjects of our experiments. The aim is to comprehend their pyrolysis properties and evaluate their suitability for direct reduction in rotary kiln. First, the requirement of coal quality in direct reduction process of rotary kiln was analyzed. Pyrolysis experiments and thermogravimetry–mass spectrometry (TG–MS) analyses of different coal types were carried out. Brunauer–Emmett–Teller (BET) method and thermogravimetry–differential scanning calorimetry (TG–DSC) were employed to analyze pore structure characteristics reactivity of the coals at different ranks. Furthermore, In order to further characterize properties of coals at different ranks，X-ray diffraction (XRD) was employed to analyze the molecular configuration of the raw coal and resulting coke samples after pyrolysis. Finally, a comprehensive evaluation system for coal was established by comparing the pyrolysis products, pore structural parameters, and gasification reactivity of coals at different ranks. The results indicate that the proportions of pyrolysis gas from lignite and bituminous coal are relatively high. The char of lignite has the largest BET surface area and total pore volume. In the gasification stage, the maximum weight loss rate of lignite reaches 5.89(%·min⁻¹) for the first time at 894℃.The crystallite structure parameters confirm the accuracy of pore parameters and gasification reaction results from the microscopic perspective. Comprehensive analysis shows thatlignite have the highest pyrolysis gas content was, the largest BET specific surface area and total pore volume, and the lowest peak temperature of gasification rate, which is undoubtedly more suitable for the direct iron reduction process in rotary kiln.