Gasification reaction kinetics on biomass char obtained as a by-product of gasification in an entrained-flow gasifier with steam and oxygen at 900-1000 °C

The purpose of this study was to investigate the gasification kinetics of biomass char, such as the wood portion of Japanese cedar char (JC), Japanese cedar bark char (JB), a mixture of hardwood char (MH) and Japanese lawngrass char (JL), each of which was obtained as a by-product of gasification in an entrained-flow type gasifier with steam and oxygen at 900-1000 °C. Biomass char was gasified in a drop tube furnace (DTF), in which gasification conditions such as temperature (T_g), gasifying agent (CO₂ or H₂O), and its partial pressure (P_g) were controlled over a wide range, with accompanying measurement of gasification properties such as gasification reaction ratio (X), gasification reaction rate (R_g), change of particle size and change of surface area. Surfaces were also observed with a scanning electric microscope (SEM). By analyzing various relationships, we concluded that the random pore model was the most suitable for the biomass char gasification reaction because of surface porosity, constant particle size and specific surface area profile, as well as the coincidence of R_g, as experimentally obtained from Arrhenius expression, and the value is calculated using the random pore model. The order of R_g was from 10⁻² to 10⁻¹ s⁻¹, when T_g = 1000 °C and P_g = 0.05 MPa, and was proportional to the power of P_g in the range of 0.2-0.22 regardless of gasifying agent. Reactivity order was MH > JC > (JB, JL) and was roughly dependent on the concentration of alkali metals in biomass feedstock ash and the O/C (the molar ratio of oxygen to carbon) in biomass char.