Evolution of biomass char features and their role in the reactivity during steam gasification in a conical spouted bed reactor

Highlights: • The effect char porosity and metal content have on its reactivity is analyzed. • At 900 °C the porosity is faster developed, attaining high S_BET at lower conversion. • Porous structure influenced the reaction rate mainly at early stages. • For X > 0.6 the increase in reactivity is related to the catalytic effect of Ca and K. -- Abstract: A study was carried out on the effect the evolution of the porous structure and metal content have on the gasification rate during char gasification in a conical spouted bed reactor. Partially gasified samples at different temperatures (800–900 °C range) were collected at various conversion levels and characterized by different techniques (N₂ adsorption-desorption, ultimate/proximate analysis and X-ray Fluorescence). At 900 °C there is a fast development of the porous structure, attaining the highest BET specific surface area (S_BET) (633 m² g⁻¹) at low conversion. Char reactivity profiles revealed that the development of the porous structure influenced the reaction rate mainly at early stages, whereas the increase in the gasification rate for conversions higher than 60% (especially at 900 °C) was attributed to the catalytic effect of Ca, K and Fe (the main metals in the ashes).