Influence of the pyrolysis heating rate on the steam gasification rate of large wood char particles

This work was carried out in order to quantify the impact of the pyrolysis heating rate both on the properties of the residual charcoal and on the behaviour during gasification by H2O of the charcoal. The experiments were conducted on 10 mm diameter beech wood spheres, pyrolysed at atmospheric pressure under heating rates covering the range from very slow, 2.6 K min−1, to very rapid, over 900 K min−1, i.e. the highest value that can be reached. When charcoal is submitted to gasification at 20% H2O in N2 at 1200 K, the ratio of the times for complete conversion reach 2.6. Such a difference is considerable as far as an industrial application is concerned. The initial properties of the charcoal such as apparent density, porosity, and pore surface area obtained by N2 or Ar adsorption were measured in order to explain the differences in gasification kinetics within the charcoal. The charcoal particles exhibit densities as different as 219–511 kg m−3 and porosities between 87 and 70% for charcoal prepared at 900 and 2.6 K min−1 respectively. The specific surface area is higher than 600 m2 g−1 for three charcoals. Influence of ash content of the initial charcoals, at 1.6–2.7%, is also regarded with particular attention to explain the observed differences in gasification kinetics.