Large particles of wood (N1 cm) may contain char at the surface of the
particle andwet wood in the interior of the particle. Up to this point, char
combustion has been within a specific region (approx 0.15 m tall), and
only a negligible amount of oxygen reaches the wood portion of the bed.
Most pyrolysis occurs when wood temperatures reach 300 to 450 °C. The
gas profiles are at t=1h as shown in Fig. 4. At the gasifier entrance
(x=0.0m), oxygen and nitrogen enter the gasifier at 35 °C. Char
combustion reactions consume the oxygen in the first 0.1 m of the
gasifier, and CO is produced. The mass fraction of nitrogen drops in this
region because additional gases are being produced from the combustion
reaction. These combustion gases (CO and N2) travel through the gasifier.
At x=0.48m, the gases enter the wood region, where water vapour is
being released fromdryingwood particles. Themass fraction ofN2 and CO
drop from x=0.48mtothegasifier exit at x=1.08mdue to the additional
mass of water vapour.
The gas profiles are similar at t=2 h as shown in Fig. 5. The x-location
represents the original location within the bed. Oxygen is nowconsumed
fromx=0.038mto x=0.200 m, indicating that the first 0.038 mof char
have been consumed. A small amount of tars and light pyrolysis gases are
released in the top portion of the gasifier.