International audienceThe aim of the present paper is to validate Lagrangian and Eulerian modeling approaches of biomass fast pyrolysis from comparison with experimental measurements. Wood samples are submitted during measured times to a controlled and concentrated radiation delivered by an image furnace. The heat flux densities are close to those encountered when wood is surrounded by hot bed particles in a dual fluidized bed (DFB) gasifier. In the image furnace, the sample is placed inside a transparent quartz reactor fed by a cold carrier gas. The volatile matter (condensable vapors and gases) released by the solid is quenched inside the reactor. It is hence possible to selectively study primary pyrolysis phenomena occurring at the solid level. All the pyrolysis products (char, vapors, and gases) are recovered, and their masses are measured as a function of the flash time allowing the assessment of mass balances. The yield of vapors does not significantly depend on the available heat flux density, unlike the gases and char yields. The experimental results are compared to data derived from two different modeling approaches. Their basic assumptions are discussed from characteristic time values which reveal the controlling phenomena. Mass transfer limitations are neglected in comparison with heat transfer and chemical phenomena. The first type of pyrolysis model relies on an original Lagrangian approach where mathematical equations of heat and mass balances are written with the assumptions that wood and char form two distinct layers. In the second one, a classical Eulerian approach is considered: equations are directly written at the whole particle level. The results of the two models as well as the experimental data (sample mass losses and product yields) are in quite good agreement

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Many kinds of solids (e.g., biomass, thermoplastic and coal) thermally decompose according to similar types of kinetic pathways. They usually include a first step giving rise to more or less stable solid or liquid species followed by competitive reactions with formation of the final products (solids, vapours, and/or gases). In order to be extended to several types of solids, the present pyrolysis model relies on an original dimensionless Lagrangian approach. Mathematical equations of mass and heat balances are written in the assumptions that non-volatiles products form distinct layers which are separated by each other by moving interfaces that propagate towards the inner parts of the sample. The conditions required to apply this Lagrangian approach to solid thermal decomposition are discussed. The time evolution of pyrolysis products and sample internal temperature profiles are obtained by numerical solving of equations written in a reduced form. The first results of simulations performed in a large range of dimensionless parameters values (thermal Thiele, Biot and thermicity criteria) are reported. It is pointed out that variations of reduced masses as a function of reduced time significantly depend on operating conditions (particularly thermal Thiele and Biot numbers). The results of the model are finally compared to experimental data reported in the literature for cellulose fast pyrolysis. The agreement is quite good considering the uncertainties with which the physicochemical parameters are known from the literature.

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In the near future, in France, new regulations will govern the emissions of gaseous effluents. The furniture industry will be affected. Different wood wastes, from furniture, were burnt in an open cone calorimeter. Several configurations of wood (whole-wood and shredded wood samples) were studied: wood chips, wood fibers, and boards. The efficiency of combustion appears to be well correlated with the apparent density of these materials. Temperature evolution was followed during the combustion of these materials. The temperature histories show that increasing the apparent density of compounds strongly improves the heat transfer into the materials. The maximum rate of heat release (HRR) increased with increasing apparent density. Moreover, gases in the exhaust were analyzed. The combustion becomes complete when waste was compressed to obtain boards. For example, carbon monoxide emissions from wood boards were 45% less than from wood fibers.