The temperature-dependent release of volatile inorganic species from Victorian brown coals and German lignites under CO2 and H2O gasification conditions

To promote the use of abundant low rank coal resources, and to assist with the design, development and optimisation of hot gas cleaning and downstream processes, it is necessary to understand the release mechanisms of volatile inorganic species from low rank coals under high temperature gasification conditions. Although a significant amount of work has been reported under combustion and oxygen lean gasification conditions, these studies do not sufficiently explain the role of the gasification reagents CO2 and H2O in the mechanisms. Therefore, gasification experiments under 20% CO2 and 20% H2O in He were conducted at 1100 °C, 1200 °C and 1400 °C for two Victorian brown coals and four Rhenish lignites. Hot gas analysis was conducted by online molecular beam mass spectrometry to determine the intensity, relative quantity and timing of the release of volatile species of interest. Two overlapping phases were clearly observed from the results - devolatilisation and char gasification. Major species detected were 23Na+, 34H2S+, 35Cl+, 36HCl+, 39K+/39NaO+, 58NaCl+, 60COS+/60NaCl+, and 64SO2+. The release during devolatilisation was essentially independent of the bulk gas atmosphere and constituted the majority of Na and Cl species. The release of S-species occurred predominantly during gasification under both CO2 and H2O atmospheres by similar but distinct mechanisms, and was directly affected by the absence, presence and concentration of the gasification reagents.