Study of Ni/Char Catalyst for Biomass Gasification in an Updraft Gasifier: Influence of Catalyst Granular Size on Catalytic Performance

In order to examine whether catalyst granular size was a factor for tar removal and syngas composition enhancement, three Ni/char catalysts with 90-100 mesh (Ni/SC), 50-60 mesh (Ni/MC), and 20-30 mesh (Ni/LC) size were prepared with a mechanical mixing method and tested in an updraft gasifier. Reforming parameters investigated were the reaction temperature (650-850 degrees C), the Ni loading (5-20% of the weight of char support), and the gas residence time (0.1-1.2 s). It was found that the catalyst granular size affected the diffusion of reactants, as well as of products. Ni/SC, Ni/MC, and Ni/LC removed more than 96.5% of the tars in syngas at 800 degrees C reforming temperature, 15 wt. % Ni loading, and 0.3 s gas residence time. Tar removal efficiencies increased with the decrease of Ni/char granular size, which can be attributed to the higher active surface area with the Ni/SC catalyst. As the catalyst granular size was increased, the H-2 content in the syngas was increased and the CO content was significantly decreased. The total amount of combustible gases (H-2, CO, and CH4) obtained in the syngas with Ni/MC was higher than with Ni/SC or Ni/LC. It was concluded that Ni/char, especially Ni/MC, can be considered as an effective and inexpensive catalyst for biomass gasification tar removal and syngas conditioning.