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International audience; 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 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.

International audience; There are many different ways to convert biomass into liquid fuels, mostly referred to as bio-oils. This paper presents the analysis of bio-oils produced by hydrothermal liquefaction and fast pyrolysis of beech wood. Both processes have a wide panel of parameters that can be optimised influencing the oil quality. Results of the analysis show that both oils have high acidities. Iodine values indicate a high degree of unsaturations. These two qualities seem to be inversely proportional in the case of pyrolysis oils. In the case of hydrothermal conversion, additives to adjust the pH such as sodium hydroxide increase oil yields, lower its viscosity but do little to further improve the quality of the oils. For pyrolysis oils, increasing the severity does reduce acidity but at the expense of more unsaturations and a loss in yield. The results show that without extensive upgrading or refining, commercial fuel standards cannot be met. Specific norms and standards are being elaborated for pyrolysis used in specific installations. This paper shows how detailed analysis can help to optimise process parameters with an objective that goes beyond the mass or energy yield.

International audience; This study, performed in the context of GAYA project, focuses on the development of a simple predictive model about steam gasification of char from woodchips fast pyrolysis. A semi-empirical model was developed through experiments in a macro thermogravimetric analyzer which owns the peculiar ability of fast heating, as well as to deal with macro-size particles and higher mass loads compared to conventional TGA. The experimental results show that gasification is controlled by chemical kinetics and internal transfer phenomena. During gasification, char particles can be considered as isothermal in a given range of temperatures and particle sizes, more likely for low values. The gasification model was based on the effectiveness factor, which involves the chemical kinetics and diffusion rate. The chemical kinetics were expressed by a classical Arrhenius law, whereas empirical expressions from mathematical fitting of the experimental data were established for the diffusion coefficient and surface function. The diffusion coefficient from this work is suspected to probably include supplementary rate limiting phenomena, apart from steam porous diffusion, such as H2 inhibition and/or the decrease of temperature within char particles because of the endothermic character of gasification. The model globally predicts with accuracy the gasification rate in typical operating conditions of a fluidized bed reactor. For its simplicity and reliability, this approach can be used for the modelling of char gasification in the conditions of interest.

Char and soot characterization was performed for samples obtained from beech particles pyrolysis in a drop tube reactor at various temperatures and residence times. Firstly, an experimental study was performed and highlights the variation of char and soot composition and reactivity with operating conditions. A structure ordering with temperature for soot samples was also experimentally put into evidence. These variations are believed to be consequence of structural changes during char thermal annealing and soot formation process, affecting both carbonaceous matrix and mineral matter. Secondly, a semi-empirical model was developed and validated with thermogravimetry experiments. This model was then used for conversion time estimation in conditions representative of an entrained flow reactor, and shows that a complete conversion of char and soot is possible in a few seconds under severe operating conditions.

International audience; Wood particle conversion in a drop tube reactor was studied between 1000 °C and 1400 °C, both with experiments and simulations using a comprehensive model. Particular attention was paid to the influence of steam on the gasification process, and to the wood particle size. The model included a description of the different phenomena involved in biomass conversion: pyrolysis, gas phase reactions, soot formation and carbonaceous solid gasification. Satisfactory results were obtained in comparison with experiments. The addition of steam in the atmosphere influenced char, tar, soot and gas yields, especially at 1200°C and 1400°C. These changes were linked to char and soot steam gasification, and to gas phase reactions, among which hydrocarbons steam reforming and water-gas shift. At 1400°C, with 25 mol% H$_2$O and after a residence time of 4.4 s, the char seems to be completely gasified, while the soot yield still represents about 5 wt% of the initial dry biomass. Wood particle size in the range 0.35-0.80 mm was experimentally shown to have no influence on products yields for a residence time of a few seconds.

Wood sawdust gasification experiments were performed in a steam fluidized bed at 800 °C between 2 and 10 bar. An evolution of gas yields with time was measured during the tests, and especially an increase of hydrogen and carbon dioxide yields. This test duration effect was ascribed to char build-up in the bed. As tests proceed, the contribution of char steam gasification to gas yield increases, and the catalytic effect of char on hydrocarbons and tar conversion and on water–gas shift reaction is enhanced. As total pressure increases from 2 to 10 bar, hydrogen, carbon dioxide and methane yields increase by 16%, 53% and 38% respectively, whereas carbon monoxide yield decreases by 33%. The changes in gaseous yields with pressure can be partly explained by the influence of pressure on gas phase reactions (acceleration of water–gas shift kinetics and change in hydrocarbon reactions). The increase of methane yield with pressure is rather suggested to be linked to a change in secondary pyrolysis reactions scheme under high pressure.

Biomass gasification at temperatures below 1273 K produces gas which contains methane and too much tar for Fischer–Tropsch synthesis. The aim of this study is to investigate methane conversion at high temperature. Experimental tests were performed between 1273 and 1773 K, with a mixture of gas representative of wood pyrolysis at 1100 K (main components only: CO, CO2, CH4, H2, H2O). Two different kinetic schemes were used to predict the gas composition, and PAH molecules formation. For a residence time of 2 s in the reactor, the gas must be heated to at least 1650 K to reach a methane conversion rate of 90%. A parametric study was performed at 1453 K, by varying the initial methane, steam and hydrogen contents, so as to find out which components are the most influent on methane conversion and soot production.