(37d) Detailed Gasification Process of Biomass-Derived Char and Gasification Mechanism

To effectively utilize renewable biomass resources, gasification technology is being actively developed. Many studies have been performed regarding the gasification of biomass-derived char (i.e., biochar), where the gasification rate varies greatly with experimental device and biomass type, even when the same gasification temperature is used. In addition, the pore development mechanism during gasification i.e., the relation between the gasification reaction rate and interface area, has been rarely studied. Herein, the gasification rate of biochar with H2O and CO2 gasifying agents using same experimental apparatus and char samples were investigated. The development of micro- and mesopores in the biochar during gasification with gasifying agents was examined in detail. The results showed that (1) in case of wooden biochar, the gasification rate constant was approximately 3–10 times higher under H2O gasifying agent than under CO2 agent at 1073–1273 K; (2) the specific surface area of the micro and mesopores increased with proceeding H2O and CO2 gasification, and the reaction rate is proportional to the interface area during the gasification process; and (3) on the other hand, in the case of grass biomass-derived char, the increased specific surface area of the pores was less than 1/3 that of the woody biomass-derived char (< X=0.5), and the surface area of grass biomass-derived char was saturated near X = 0.5. The grass biomass-derived char consisted mainly of leaf sheaths, which are aggregates of vents. Because gasification agents can easily pass through vents, the reaction mechanism in grass biomass-derived char was predicted to be similar to that on its external surface.