Characteristics of gasification chars - Results from a screening campaign

Despite several useful characteristics like high carbon content, large BET surface area and narrow particles size distribution, the solid residues from wood gasification, i.e. gasification chars, are rarely used and commonly considered as wastes. Furthermore, marketing of these materials is hampered by a limited knowledge base on their characteristics from different gasification technologies, an incomplete understanding on influencing factors and a lack of standardization both for the material itself and the analytical procedures that have to be employed for their characterization. To provide a basis for standardization and future utilization perspectives, a screening was performed covering a wide range of gasification technologies. The samples were analyzed for ash content, moisture, volatiles, fixed carbon and elemental composition as well as the content of polycyclic aromatic hy-drocarbons (PAHs) and volatile aromatic hydrocarbons. In total, analysis data of 118 gasification char samples from plants of 17 different gasification plant manufacturers have been evaluated. The results indicate a wide variation in the characteristics of gasification chars both with respect to ash and carbon content, i.e. 3.9%-100% and 0.9-92.5%, respectively. Particularly high levels of organic contaminants are associated with samples originating from cold gas filtration with PAH contents of up to 130 g kg(-1) and post-treatment would be necessary in most cases to qualify these materials for material applications. Hot gas filtration and thermal post-treatment was found to result in gasification chars with substantially lower levels of organic contaminants. For these materials, the PAH contents rarely exceeded 2 g kg(-1).