Temperatures of Wood Particles in a Hot Sand Bed Fluidized by Nitrogen

The thermal history undergone by cylindrical beech wood particles, injected in a sand bed fluidized by nitrogen has been recorded. Experiments have been carried out by varying particle diameter ( d = 2−10 mm) and bed temperature ( T r = 712−1107 K). The rate of volatile release becomes significant for temperatures above 625−650 K and is always completed for temperatures below 675−825 K. Devolatilization causes a strong reduction in the heating rate which, at the particle center and for the most intense reaction activity, is comprised between 0 and 25 K/s. For the conditions typical of fast pyrolysis (bed temperatures of 800−1100 K and particle sizes of 2−6 mm), the yields of char are 10−18% and the devolatilization times (corresponding to a conversion of 95%) 18−45s. Furthermore, in qualitative agreement with previous analyses carried out for coal particles, these are well predicted by an empirical power-law relation: t v = 0.8e 1525/ T r d 1.2 s, over the entire range of experimental conditions examined.