KINETIC-STUDY OF THE FLASH PYROLYSIS OF ALMOND SHELLS IN A FLUIDIZED-BED REACTOR AT HIGH-TEMPERATURES

Two correlation models have been developed and applied to simulate the primary and secondary reactions (assuming first order kinetics for bo th reactions) as well as the heat transfer in the pyrolysis of almond shells in a system with a fluidized bed reactor. The biomass is discha rged onto the hot sand fluidized bed. The primary decomposition takes place during the fast heating of the particle inside the sand fluidize d bed. The cracking of the volatiles evolved takes place in the upper part of the reactor, from the top of the sand bed to the heat of the r eactor. The first model calculates the kinetic constants of the primar y and secondary reactions in the pyrolysis. The apparent activation en ergy for the primary reaction is very low, showing the effect of the h eat transfer. The primary kinetic constant obtained should be consider ed as a correlation constant, including both the chemical reaction and the heat transfer. A second model was developed with different assump tions concerning distinct kinetic expressions for the primary reaction s obtained from the Pyroprobe 100 and TGA, considering heat transfer t o the particle. The heat transfer from the fluidized bed to the almond shell particles as well as that from the wall of the reactor to the v olatiles has also been considered. The model reproduces the experiment al data very well and the constants obtained compare favorably with pu blished data, both for kinetic constants and for heat transfer numbers .