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Minimum Ignition Temperature (MIT) characterizes the ignition sensibility of a dust cloud. This work assesses the role of a standard Godbert-Greenwald furnace in the agglomeration/deagglomeration and fragmentation phenomena. Several organic powders and different dispersion pressures were tested. The average residence time varied from 120 to 330 ms according to the amount of powder injected and the pulse pressure. Entanglement was observed for coarser cellulose particles, while surface cohesion forces characterised the agglomerates of finer cellulose, glucose and ascorbic acid. The latter was characterised by fragmentation, especially at 0.5 and 1 bar(g). Biot, Pyrolysis and Damköhler numbers were used to analyse the effects of cellulose agglomeration and deagglomeration. At 600 K, the pyrolysis is the rate-limiting step, but from 700 K, the external heat transfer becomes the rate-limiting step, which would not happen without agglomeration. Due to the particle size distribution evolution, but also to turbulence and residence time variation, MIT can vary by 50 °C. [ABSTRACT FROM AUTHOR]

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. [Display omitted] [ABSTRACT FROM AUTHOR]

Biomass is a renewable energy source which may provide a significant contribution to the reduction of fossil fuels consumption and the associated environmental impacts. The use of agricultural or agro-industrial waste such as solid residues from olive oil production is particularly relevant since it may combine several benefits. Gasification is a promising waste-to-energy technique for this type of lignocellulosic residues. The technology however is adapted to a relatively limited panel of solid waste fuels of defined specifications, which must therefore be characterized properly to assess their adaptation. The purpose of this research was to analyze and compare three different olive mill solid residues by complementary techniques such as Fourier transform infrared spectroscopy (FTIR) and thermochemical methods, in order to characterize these residues as potential fuels for gasification. The results obtained underlined the complex nature of the residues and indicated that they were mainly organic, with very little mineral matter. In addition to the major organic components (cellulose, hemicelluloses and lignin), the presence of several minor organic constituents was shown by thermogravimetry coupled to differential scanning calorimetry and FTIR. The gas produced from pyrolysis was analyzed by gas chromatography and mass spectrometry. It was found to contain several degradation products from lignocellulosic material and olive oil, such as hydroxyacetone, furfural and methoxyphenols. The influence of the olive oil extraction process (two-phase or three-phase) was also demonstrated. It was shown that the thermochemical degradation of olive mill residues followed a complex pathway but the composition of the residues met the requirements for gasification for most parameters. • Despite their different origins, the olive mill residues showed strong similarities. • Some differences were notably attributed to oil extraction process. • Thermochemical degradation was characterized by TG-DSC and Py-GC/MS. • The presence of residual olive oil was evidenced, increasing heating value. • The residues characteristics met most requirement parameters for gasification. [ABSTRACT FROM AUTHOR]