Comparison of entrained flow CO₂ gasification behaviour of three low-rank coals – Victorian brown coal, Beulah lignite, and Inner Mongolia lignite

This study compared the entrained flow CO₂ gasification behaviour of three lignites from around the world. The coals include Victorian brown coal-Yallourn, one American lignite-Beulah, and one Chinese lignite-Inner Mongolia. The comparison is made through gasification performance-gas composition and carbon conversion, pollutant gas emission, char characterization, and mineral matter transformation. The gasification experiments were carried out at a wide range of temperatures (1000–1300 °C), input CO₂ concentrations (10–40% CO₂), and residence times (5–7 s) using a high-temperature entrained flow reactor. The increase in temperature, input CO₂ concentrations, and residence time increased the CO concentration and carbon conversion. The three coals had a very similar gas composition on N₂ and CO₂ free basis with high CO concentration (approximately 92–96%) at 1200 °C. Beulah lignite obtained nearly 100% carbon conversion at 1100 °C and 20% CO₂, Yallourn coal at 1200 °C and 20% CO₂, and Inner Mongolia lignite at 1300 °C and 20% CO₂ or at 1200 °C and 40% CO₂. Yallourn coal released the least HCN, NH₃, and H₂S, Beulah lignite released the most NH₃, and Inner Mongolia released the most H₂S. At high carbon conversion of 99%, the particle size of D(0.9) was still high (∼50 µm) because of particle agglomeration. The inorganic mineral matter behaviour of each coal at high temperature varied markedly due to the significant differences in coal ash composition. However, the common mineral transformation found for all three coals was the decomposition of CaSO₄. Mineral transformations during CO₂ gasification tended to increase ash fusion temperature and enhance gasification reactivity.