Particle Size Distribution in a Godbert-Greenwald Furnace: Experiments and Modelling

During a dust dispersion, the particle size distribution (PSD) depends on several factors such as the turbulence, the initial particle size and shape as well as the dust concentration. As a consequence, when determining safety parameters using standard procedures, its potential evolution should be considered. Different powders were chosen: glucose, starch, ascorbic acid, glass beads and cellulose. A Godbert-Greenwald furnace was used to disperse the powders and determine their minimum ignition temperature (MIT) according to ISO/IEC 80079-20-2:2016 standard. The PSD of each powder was determined in-situ at different locations using a laser diffraction sensor. Some powders showed clear signs of breakage, as for glucose whose mean diameter decreases from 166 to 76 µm during its dispersion. On the contrary, many samples tended to agglomerate, e.g. starch and cellulose. For instance, the d90 of starch can even be quadrupled under certain conditions. Agglomeration occurs especially for fine dusts due to strong inter-particles forces (e.g. starch) or for elongated fibres due to entanglement phenomenon (e.g. cellulose). During a powder dispersion in the Godbert-Greenwald furnace, the PSD evolves not only as a function of time but also along with its location. The impact of the glass elbow on PSD variation has notably been highlighted by placing the G-G furnace horizontally. For powders showing strong tendency to agglomeration or breakage, the influence of the dispersion pressure has also been studied. The role of such PSD modification on the MIT has been measured and, depending on the dispersion procedure, temperature differences of more than 50°C have been observed. The agglomerate strength was assessed using three models (from Rumpf, Weiler and Kendall works) and compare to the deagglomeration stress exerted on the powders. In the case of cohesive powders, fibres or brittle dusts, attention should be paid to the PSD evolution during MIT determination

Détection semi-quantitative du virus BK chez les receveurs de greffon rénal (approche préliminaire en vue de la mise en oeuvre d'une technique quantitative de routine)

BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Inégalités économiques: (Rapport du CAE n.33)

This report gives a detailed picture of economic inequality in France today. It analyses their origins, assesses the impact of redistributive mechanisms and indicates which are the appropriate instruments of policy in the fight against inequality. The second report, Thomas Piketty concerns the distribution of tax revenues in France in the twentieth. These reports are followed by comments from Michel Dollé, Mireille Elbaum, Jacques Freyssinet and Firoella Kostoris Padoa Schioppa. We finally found eight additional returning to some of the topics discussed

Study of flash pyrolysis and combustion of biomass powders using the Godbert-Greenwald furnace : an essential step to better understand organic dust explosions

An organic dust explosion is a heterogeneous system on a space and time scale. Predicting the parameters characteristic of its severity needs experimental and theoretical approaches to find the optimal compromise between consistency with reality and modelling time. A hybrid method is proposed to study flash pyrolysis and combustion of several organic powders (cellulose, wheat starch, oak wood, Douglas fir and olive pomace). A Godbert-Greenwald furnace was employed to perform the experiments to mimic the fundamental characteristics of a dust explosion: high particle heating rate, high reaction temperature and short residence times. At 973 K, the residence time is a critical parameter: the large particles of cellulosic compounds (wood, cellulose) do not reach their pyrolysis temperature and only fibres smaller than 20 or 30 µm are fully converted. As the particle size distribution of starch is smaller, heat transfer is not directly the limiting phenomenon but rather the strong tendency for powders to agglomerate during pyrolysis. At higher temperatures, secondary reactions of primary tars are evidenced, stressing the influence of the pyrolysis stage and leading to heterogeneous combustion. The composition of the pyrolysis gases as a function of the nature of the powder and the temperature was also determined. A lumped-kinetic model adapted to dust explosion was developed and validated for cellulose. The kinetics constants corresponding to levoglucosan to permanent gases and cellulose to char and water reactions are significantly different from those proposed by the literature, demonstrating that dust explosion kinetic parameters must be obtained under conditions consistent with such phenomenon

Mechanisms and kinetics of methane thermal conversion in a syngas

International audienceIn order to optimize H2 and CO production from biomass gasification, the thermal decomposition of methane in a reconstituted syngas was investigated in a tubular reactor at 130 kPa, for a gas residence time of 2 s and as a function of temperature (1000-1400 °C), CH4 (7, 14%), H2 (16, 32%), and H2O (15, 25, 30%) initial mole fractions. H2 showed an inhibiting effect on CH4 conversion whereas H2O had few effects. Three detailed elementary mechanisms were used to predict the methane conversion rate and to identify the key reaction pathways. Flow rate analyses showed that carbon oxidation occurs mainly by addition of OH radicals on C2 compounds. OH radicals are mainly produced by CO2 (CO2 + H ) CO + OH). The inhibiting role of H2 on CH4 conversion is explained by a competition between the OH radicals consumption channels (H2 + OH ) H2O + H). The competition between thermal conversion of methane and reforming of unsaturated C2 explains the soot formation