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 (Tr ) 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: tv ) 0.8e1525/Trd1.2 s, over the entire range of experimental conditions examined.