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.

The 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.

The present paper reports the experimental results of the fast pyrolysis of biomass performed in a cyclone reactor heated at its walls. The conditions of pyroliquefaction are chosen (walls temperature between 900 and 983 K) in order to enhance bio-oils production. Their yields reach 74% while those of char and gases are respectively 10% and 16%. The bio-oils are condensed and trapped at different temperatures. Three main fractions are recovered: heavy oils, light oils and aerosols. Their physicochemical properties (water and particles content, viscosity, density, pH, fraction of pyrolytic lignin and elementary molar composition) as well as stability during storage are measured and compared with literature. The results show very different behaviours according to the types of oils fractions.

This paper reports the results of experiments performed on the flash pyrolysis of lignin samples submitted to controlled heat flux densities (short flashes of a concentrated radiation). Two types of lignins are used: Kraft and Organocell lignins. Microscopic observations of the reacted samples reveal the formation of an intermediate liquid compound that precedes the further formation of char, vapours and gases. The rates of mass loss and the production rates of the products are determined for both lignins. The results are compared to each other and to those obtained in former similar studies made with cellulose.The analyses of the produced gases reveal high syngas and H-2 contents (respectively 87 and 50 mol%). This composition is compared to results obtained in other different thermal conditions with lignins and other types of biomasses. The possible mechanism of hydrogen formation is further discussed. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

The continuous self stirred tank reactor is a well known suitable device for studying the kinetics of high-temperature gas phase reactions. Temperature and composition are uniform at any point of the reactor, and for a given residence time, it is easy to calculate the values of kinetic constants from a very simple mathematical model. The aim of the present paper is to report the first experimental results obtained on the thermal cracking of vapours produced by the pyrolysis of biomass. The experiments are carried out between 836 and 1303K and under mean residence times ranging from 0.3 to 0.5 s. The calculated activation energy (59kJmol-1) and preexponential factor (1930s-1) are in good agreement with those obtained by other authors operating in more usual devices, but needing the solving of more sophisticated models.

The image furnace technology has been applied to the study of the first steps of biomass flash pyrolysis. The experiments performed with small pellets of cellulose show that the reaction primarily passes through the intermediate of short lifetime liquid species (ILC). The quantitative study of the variations of the sample mass loss and of the mass of ILC reveals the existence of a transient period followed by a steady-state regime resulting from an equilibrium between cellulose decomposition into ILC and ILC vaporization. A mathematical model has been solved in parallel. The results agree very well with the experimental measurements and yield additional information on the temperatures of cellulose pyrolysis and of ILC vaporization.

The present paper reports first experimental results showing that it is possible to produce zinc from the thermal reduction of zinc oxide in the presence of cellulose. The experiments are performed in a solar simulator where small pellets of ZnO+cellulose mixtures are submitted to a brief controlled concentrated radiation. The reaction is very fast and occurs at temperatures that are more than 1000 K lower than those corresponding to the direct ZnO splitting. Several possible reaction mechanisms are discussed and it is concluded that the ZnO reduction seems to involve interactions with the liquid species formed during cellulose thermal depolymerization. Side experiments performed in less severe conditions with an electric furnace confirm the low temperatures of reaction. In order to errand the results to the more practical case of biomass, it is suggested to continue similar experiments with other components such as lignin.

It is possible to use concentrated solar energy for producing zinc by direct high temperature dissociation of ZnO. The purpose of the present paper is to show that the overall efficiency of such a process as well as the quality of the products may be controlled by several chemical and physical factors such as heat and mass transfer efficiencies, hydrodynamics and reactor design. The results of three complementary experimental approaches are reported. They are interpreted in connection with simplified models in order to describe the controlling processes occurring in the high temperature and quench sections of the reactor. One of the conclusions is that zinc can be recovered by condensation on the cold walls of a heat exchanger and/or under the form of small dispersed particles. Finally, it is shown that the reactor design must be optimized inside the perspective of a given future use of zinc.

It is possible to dissociate samples of zinc oxide at high temperature by using a concentrated radiation as a best source. However, the reoxidation radiation between the products is very fast and it is hence necessary to cool down very rapidly (quench) the gases. The present paper describes two experimental methods of analysis owned at measuring the quench efficiency (i.e. the fraction of zinc recovered). The accuracy of both methods is first presented. Then, preliminary results obtained in an image furnace are given. It is concluded that it is necessary to optimize the quench reactor in order to enhance to efficiency of zinc production.

This paper reports the first results of experiments and modelling of the radiant flash pyrolysis of cellulose. Small samples are exposed to brief flashes of a concentrated radiation, at the focus of an image furnace operating with a 5 kW xenon lamp associated to two elliptical mirrors. The mean heat flux densities may be higher than 107 W m−2. The microscopic observations of the sample after the flash reveal the presence of short life time liquid species formed for flash durations lower than about 1 s. These products which are liquid in pyrolysis conditions are solid at room temperature, where they show a good stability. They are soluble in water. For longer flashes, they give rise to vapours escaping in the gas phase, while practically no char is formed. These results show that, if in biomass pyrolysis, lignin is known to give rise to a liquid phase, it is also the case for cellulose. A first simple modelling of these experiments is proposed. It relies on heat and mass balances at the sample level, on the Broido–Shafizadeh (BS) model and on experimentally estimated values of some of the optical characteristics of cellulose (reflectivity and absorptivity). Indeed, cellulose is a highly reflecting and weakly absorbing (semi-transparent) material. These properties must be necessarily taken into account in any predictive calculation (only a small fraction of the incoming flux is effectively absorbed by cellulose). The calculated values of the times of beginning and end of the reaction are compared with the results of the experiments. The good agreement confirms that the intermediate products have life times shorter than about 1 s at the reaction temperature, predicted to be close to 750 K.

Partial oxidation of n-butane was carried out in a self-stirred reactor in the homogeneous gas phase under atmospheric pressure at 600–700 K. The influence of space time (0.8 to 5 s) and of the fraction of oxygen in the reactants was studied, either with premixed or with unmixed reactant feed. It was found that the selectivity in the required products (formaldehyde, methanol, acetic acid) with respect to water was essentially favoured by operation at low temperature. A kinetic ‘tendency model’ is shown to account for the dependence of selectivity upon various experimental parameters and for the ‘ignition’ of the reactor. This model relies on a limited number of stoichiometric equations but keeps the essential features of the very complex reaction system. With this model, we are able to simulate the reaction under new experimental conditions (reactor type, inlet temperature, feed composition, space time) and to optimize the yield in required products.