Biomass fast pyrolysis in a drop tube reactor for bio oil production: Experiments and modeling

Woody biomass fast pyrolysis in Entrained Flow Reactor (EFR) is studied both with experiments in a lab-scale drop tube reactor (DTR) and simulations with a 1-D model. The parameters of the study are temperature (450-600 °C), woody biomass particle size (370-640 µm) and gas residence time (12.6-20.6 s). The most critical phenomena affecting the bio-oil yield are considered in the model: heating of the biomass particles, slip velocity of the biomass particles varying with biomass/char properties, biomass pyrolysis and tar cracking. The analyses of all products - char, bio-oil and gas - also brought information on the advancement of the pyrolysis and cracking for the different tests. The reactor temperature and particle size were found to have a major influence on the pyrolysis product distribution. The production of bio-oil reaches a maximum of 62.4 wt.% at 500 °C for the 370 µm particles. The particle conversion advancement is then estimated at 94% at the reactor exit. The bio-oil yield is lower at higher temperatures for a constant particle size due to tar cracking. At 550 °C, increasing the particle size from 370 µm to 640 µm induces a decrease of the bio-oil yield from 48.3 to 34.8 wt.%, which was shown to be due to incomplete pyrolysis of the particles, because of a too short residence time as well as a too long heating time of particles. The pyrolysis conditions - temperature, particle size - were not found to have any significant influence on the bio-oil properties, such as acidity.