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

Abstract

International audienceWoody 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 degrees C), woody biomass particle size (370-640 mu m) 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 degrees C for the 370 mm 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 degrees C, increasing the particle size from 370 mm to 640 mu m 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. (C) 2017 Elsevier Ltd. All rights reserved

Biomass Chars: The Effects of Pyrolysis Conditions on Their Morphology, Structure, Chemical Properties and Reactivity

“…The D band position shifts to lower wavenumbers as pyrolysis temperature increases (from 1363 cm −1 at 500 • C to 1327 cm −1 at 1400 • C), while the G band position shifts to higher wavenumbers when increasing the pyrolysis temperature (from 1576 cm −1 at 500 • C to 1596 cm −1 at 1400 • C). This tendency was also observed previously during the characterization of chars prepared by cellulose slow pyrolysis at different temperatures [28]. This "red shift" in the D band peak position is more pronounced for low temperature chars, which have the highest contents of oxygenated defects structures [29].…”

The Heat Treatment Severity Index: A new metric correlated to the properties of biochars obtained from entrained flow pyrolysis of biomass

“…The EFR experimental set-up was previously described in details in [26,27]. It consists of an alumina tube inserted in a vertical electrical heater with three independent heating zones.…”

“…• The first one is related to medium temperature pyrolysis (500, 550 and 600°C) aiming at maximizing the bio-oil production [26].…”

“…In previous related works, we studied the evolution of chars properties obtained after pyrolysis of 370 µm beech wood particles in an entrained flow reactor in a temperature range between 500°C and 1400°C [26,27]. These chars were characterized for their chemical composition (Elemental analysis), structure (Raman spectroscopy) and reactivity towards oxygen (thermogravimetric analysis) [28].…”

“…The biochars were prepared by an entrained flow pyrolysis of 370 µm beech wood particles between 500°C and 1400°C [26,27], and characterized for their chemical composition, structure and reactivity [28]. Leaning on the modeling results validated with the pyrolysis experiments in [26,27], which provide data on the biomass particle pyrolysis and residence times, and on the biochar properties described in our previous work [28], we searched for a suitable expression of a severity index that could be related directly on the measured biochar properties. This work is a first attempt for the investigation of this idea.…”