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 both reactions) as well as the heat transfer in the pyrolysis of almond shells in a system with a fluidized bed reactor. The biomass is discharged onto the hot sand fluidized bed. The primary decomposition takes place during the fast heating of the particle inside the sand fluidized 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 reactor. The first model calculates the kinetic constants of the primary and secondary reactions in the pyrolysis. The apparent activation energy for the primary reaction is very low, showing the effect of the heat transfer. The primary kinetic constant obtained should be considered as a correlation constant, including both the chemical reaction and the heat transfer. A second model was developed with different assumptions concerning distinct kinetic expressions for the primary reactions obtained from the Pyroprobe 100 and TGA, considering heat transfer to 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 volatiles has also been considered. The model reproduces the experimental data very well and the constants obtained compare favorably with published data, both for kinetic constants and for heat transfer numbers.