Progressive inhibition of C plus H 2 O reaction in wood char packed bed by in-situ evolving H 2: Experimental insights and theoretical analysis

Previous research on Char reactions with gas phase compounds under micro-thermogravimetry systems shows that hydrogen inhibits heterogeneous char reactions. However, its impact on larger gasification systems with evolving hydrogen profiles remains largely unexplored. This study examines a macro-scale wood char bed to understand the influence of in situ evolving hydrogen on char reactions. When subjected to a specific steam flux, carbon conversion and pore morphology changes are mainly confined to the bed's upstream, with the downstream char retaining its original characteristics. Numerical investigations reveal over 75 % of species production and consumption occurs within the initial 20 % of bed height. Fourier-transform infrared spectroscopy confirms hydrogen-induced inhibition in downstream segments, showing a shift from C-OH to C-H bonds. Particle-scale analysis indicates significantly higher rates of hydrogen diffusion and adsorption compared to H 2 O , impeding downstream C + H 2 O reactions. Increased temperature, higher reactant concentrations, or reduced residence time can overcome this inhibition, enhancing conversion rates. These findings are critical for optimizing steam-to- biomass ratios in oxy-steam gasification systems for generating hydrogen-rich syngas.