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

Abstract

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.