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Optical detection of ammonia inside a stack : Comparison of different techniques
No full textInternational audienceThe quantitative detection of pollutants in industrial emissions, in particular the emissions of biomass burners, requires different types of analyzers. Optical devices are usually sensitive to the transparency and dirtiness of the exhaust gases, so optical measurements are normally carried out by extracting the samples from the stacks. This paper has a twofold aim. First, we will prove that the molecular composition of the exhaust mixture (in particular the concentration of water and carbon dioxide) can deeply affect the outcome of optical analyzers, depending on the adopted detection technique. This is a critical issue, in particular with a view to the necessity of providing suitable reference methods for monitoring biomass burners emissions. Second, we will show how it is possible to measure inside an artificial stack by using an optical multipass cell located across the gas flow, even at 140 °C, or in presence of soot
Modeling organic aerosol over Europe in summer conditions with the VBS-GECKO parameterization : sensitivity to secondary organic compound properties and IVOC (intermediate-volatility organic compound) emissions
No full textInternational audienceThe VBS-GECKO (volatility basis set - Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere) parameterization for secondary organic aerosol (SOA) formation was integrated into the chemistry-transport model CHIMERE. Concentrations of organic aerosol (OA) and SOA were simulated over Europe for the July-August 2013 period. Simulated concentrations with VBS-GECKO were compared to results obtained with the former H2O parameterization implemented in CHIMERE and to observations from EMEP, ACTRIS and other observations available in the EBAS database. The model configuration using the VBS-GECKO parameterization slightly improves the performances compared to the model configuration using the former H2O parameterization. The VBS-GECKO model configuration performs well for stations showing a large SOA concentration from biogenic sources, especially in northern Europe, but underestimates OA concentrations over stations close to urban areas. Simulated OA was found to be mainly secondary (similar to 85 %) and from terpene oxidation. Simulations show negligible contribution of the oxidation of monoaromatic compounds to SOA production. Tests performed to examine the sensitivity of simulated OA concentrations to hydro-solubility, volatility, aging rates and NOx regime have shown that the VBS-GECKO parameterization provides consistent results, with a weak sensitivity to changes in the parameters provided by the gas-phase mechanism included in CHIMERE (e.g., HOx or NOx concentrations). Different scenarios considering intermediate-volatility organic compound (IVOC) emissions were tested to examine the contribution of IVOC oxidation to SOA production. At the continental scale, these simulations show a weak sensitivity of OA concentrations to IVOC emission variations. At the local scale, accounting for IVOC emissions was found to lead to a substantial increase in OA concentrations in the plume from urban areas. This additional OA source remains too small to explain the gap between simulated and measured values at stations where anthropogenic sources are dominant
Analytical methods for the determination of oil carryover from CNG/biomethane refueling stations recovered in a solvent
No full textInternational audienceVehicle gas is often compressed to about 200 bar at the refueling station prior to charging to the vehicle's tank. If a high amount of oil is carried over to the gas, it may cause damage to the vehicles; it is therefore necessary to accurately measure oil carryover. In this paper, three analytical methods for accurate quantification of the oil content are presented whereby two methods are based on gas chromatography and one on FTIR. To better evaluate the level of complexity of the matrix, 10 different compressor oils in use at different refueling stations were initially collected and analysed with GC and FTIR to identify their analytical traces. The GC traces could be divided into three different profiles: oils exhibiting some well resolved peaks, oils exhibiting globally unresolved peaks with some dominant peaks on top of the hump and oils exhibiting globally unresolved peaks. After selection of three oils; one oil from each type, the three methods were evaluated with regards to the detection and quantification limits, the working range, precision, trueness and robustness. The evaluation of the three measurement methods demonstrated that any of these three methods presented were suitable for the quantification of compressor oil for samples. The FTIR method and the GC/MS method both resulted in measurement uncertainties close to 20% rel. while the GC/FID method resulted in a higher measurement uncertainty (U = 30% rel.)
Seismic repeaters linked to weak rock-mass creep in deep excavation mining
No full textInternational audienceSeismic repeaters are a phenomenon rarely observed in mining environments. In this study, we show that repeaters and associated aseismic slip can be the governing mechanism behind seismic triggering in response to excavation mining, providing new perspectives for rethinking and improving standard procedures for seismic rock burst hazard assessment and mining monitoring. Evidence comes from an extensive multiplet analysis on dense spatiotemporal microseismic event clusters (-2.5 < M-w < 1) that was recorded by a local microseismic network at the Lappberget orebody in the Garpenberg mine in Sweden at around 1 km depth. Analysis involved template matching, clustering, double-difference relocation, source parameter and mechanism estimation, as well as interevent time analysis. The results show that almost 80 per cent of the analysed events can be interpreted as seismic repeaters. Source mechanisms demonstrate systematic strike-slip faulting with a significant reverse faulting component, indicating that triggering of the repeaters is sensitive to increases in the horizontal compressive stresses. We suggest that seismic repeaters represent brittle frictional parts (asperity) of creeping, planar shaped, pre-exiting structures of several metres composed of weak rock-mass materials (e.g. talc) associated with strengthening friction behaviours. This repeater model and the here used definition of asperity thus slightly differs from its meaning in classical seismological models where repeating events are related to the locked fault patches along a creeping fault. In addition, we identified different asperity types for the different repeater families that we interpret as different friction properties. Some multiplet families represent rather a transitional case between multiplet and repeater occurrences that might imply a mixture of weakening and strengthening friction processes, that is, creep and brittle rupture along neighboured plane shaped anisotropies in a heterogeneous rock mass. The exact nature of asperities and seismic and aseismic coupling of the rock mass as well as the propagation mechanism of strain and stress associated with short-term (days to weeks) and long-term (months to years) post-blast creep remains uncertain and needs to be addressed by future investigations. The understanding of these processes is particularly important for assessing hazard of larger dynamic ruptures
Pool evaporation : Experimental tests at medium-scale with gasoline
No full textInternational audiencePool evaporation is a major source of flammable vapour clouds. Predicting the evaporation rate of a liquid hydrocarbon pool is therefore a key issue of dispersion modelling for safety concerns. This paper presents small- and medium-scale experiments of pool evaporation carried out with liquid hydrocarbons (pentane, heptane), hydrocarbon “gasoline-like” mixtures and gasoline. Liquid mass loss was measured and the evaporation rate deduced with its evolution in time. Other observations are highlighted, regarding the evolution of liquid temperatures, mixture compositions, and scale effects like the influence of pool length on surface evaporation rate. Comparisons with well-known correlations are then shown. The authors finally suggest a new semi-empirical correlation with a set of parameters fitted on the performed experiments
Usefulness of the transgenic cyp19a1b-GFP zebrafish model to refine the zebrafish embryo acute toxicity test (ZFET)
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Establishing a Diagnosis: Inventorying, Monitoring and Assessing
No full textInternational audienceImproving air quality is a major challenge for public health and the environment. Assessing the contribution of agricultural activity to air pollution and the resulting impacts is a prerequisite for recommending mitigation practices. More important, their long-term adoption can only be justified by performing a real-time assessment of their effectiveness. Since the 1990s, using emission indicators, air contamination levels and environmental impacts has indeed become a widespread means of supporting decision-making at different levels, risk management and public policy assessment. However, this assessment is made difficult owing to the complex network of processes involved and the variability in pollutant emission and deposition. This chapter first details the methodologies implemented for emission inventories, used to better target the largest contributing sources, to check whether national commitments have been met, and to assess the trends. It also presents observation networks established to monitor background air pollution, deposition as precipitation, gases and particles in rural and forest areas, and impacts on terrestrial ecosystems. Finally, it outlines the indicators used to assess the impacts of agricultural practices on human and ecosystem health via the atmospheric compartment and it gives examples of their practical use to manage pollution risks, evaluate agricultural practices or compare agricultural products
Subsidence prediction of reinforced soil layer by geosynthetic using large-scale 1g physical model
No full textInternational audienceAbstract. Subsidence can result from the collapse of underground cavities. The impact of the movements on existing structures and infrastructures is generally dramatic. Geosynthetic sheets (RG) can be used to reduce their impact. This paper focuses on the use of large-scale physical modelling to study the subsidence mechanisms and to estimate the RG efficiency for cohesive or granular soil layers. The results have shown that the RG reduced the ground movement even under important overload. The deformation of the RG and the surface settlement depend both on the soil type and overload intensity. The experimental results are compared to analytical solutions proposed to design the RG for cohesive and granular soils. Stress distribution on the RG was investigated. The analytical and experimental results are rather similar, that shows the relevance of the analytical models to predict the behaviour of reinforced soil layers
Compressive response of a very low density polyurethane foam using Split Hopkinson Pressure Bars and high speed imaging
No full textTo mitigate the disastrous effects of a blast wave, the use of layered claddings with thermal insulating materials could be a very economical solution. The present paper focuses on the study of the mechanical behaviour of a very low density insulating polyurethane foam (30 kg/m^3) under compressive loading. Static compressive tests are conducted with a press and nylon Split Hopkinson Pressure Bars (SHPB) are used to investigate the dynamic behaviour over a wide range of engineering strain rates from 10^{-5} to 10^3 s^{-1}. In addition to traditional displacement and strain measurements, the Digital Image Correlation (DIC) technique is used to observe the inhomogeneous strain fields. To better represent the mechanical state in the foam due to blast loadings, oedometric compression tests are also conducted. The foam response, showing a linear elastic stage, followed by a plastic plateau and a densification is shown to be transversely isotropic, heterogeneous and strain rate sensitive
Nouvelles considérations sur l'explosivité des nanopoudres : un nano-grain de sable dans les rouages des standards
No full textThe small size of nanoparticles implies a high specific surface area, which induces original properties when compared to micropowders, such as chemical, mechanical, optical or biological properties. Among these new specificities, nanoparticles are subjected to weak cohesion forces, such as van der Waals, electrostatic or capillary forces, which cause them to agglomerate in a reversible way. However, dust explosions require the dispersion of the dust in the air, which can lead to a breakage of these agglomerates. The aim of this work is then to study the influence of nanoparticles specificities, notably the agglomeration, on their ignition sensitivity and explosion severity, and evaluate the adequacy of the international standard methods to determine these parameters when it comes to nanoparticles. Four types of powders were chosen to highlight the specific behavior of each type of combustible powder: carbon black, nanocellulose, aluminum and carbon-coated silicon. The powders were characterized by Scanning Electron Microscopy (SEM), specific surface measurement and helium pycnometer, and their particle size distribution (PSD) was measured before and after dispersion using different methods. The mean surface diameter, used to consider the high surface area of nanoparticles, considerably decreases after the injection in the 20L sphere, i.e the standard equipment to measure the explosion severity of a dust. This observation highlighted the necessity to characterize the dust after injection in the 20L sphere, to accurately evaluate the explosion risk. Ignition and explosion tests were conducted in standard conditions, but also by varying the powder preparation (aging, drying, sieving, agglomeration), and the operating conditions (dispersion procedure, ignition energy, initial turbulence). Specific behaviors related to the powder nature (carbonaceous, organic or metallic) were then observed, discussed, and alternative measurement methods were proposed. For instance, alternative dispersion nozzles were tested to provide a better cloud homogeneity or to reproduce industrial release conditions. Dispersion procedure and ignition source should be adapted to the minimum ignition energy of the nanopowders to avoid both pre-ignition and overdriving. Variation of the ignition delay time can be helpful to obtain the most conservative results. One of the main proposals consists in the consideration of the laminar burning velocity as a standard characteristic of the explosion severity. Experiments were conducted in a flame propagation tube and a vented 20L sphere to evaluate the unstretched burning velocity of nanocellulose. The results were then compared to an existing correlation based on the pressure-time evolution during standard experiments. Furthermore, a flame propagation model, initially designed for hybrid mixtures, was adapted to the flame propagation in a cloud of organic nanoparticles, showing consistent results with the experiments.La petite taille des nanoparticules induit une grande surface spécifique, qui procure des propriétés inédites, notamment chimiques, mécaniques, optiques ou biologiques, comparées aux particules micrométriques. Parmi ces nouvelles spécificités, les nanoparticules sont soumises à des forces de cohésion plus intenses, telles que des forces de van der Waals, électrostatiques ou capillaires, ce qui les amène à s’agglomérer de manière réversible. Cependant, une explosion de poussières nécessite une dispersion de la poudre dans l’air, ce qui peut mener à une fragmentation de ces agglomérats. L’objectif de ce travail est ainsi d’étudier l’influence des spécificités des nanoparticules, notamment de l’agglomération, sur leur sensibilité à l’inflammation et leur sévérité d’explosion, et d’évaluer l’adéquation des méthodes définies par les standards internationaux pour la détermination de ces paramètres concernant les nanoparticules. Quatre types de poudres ont été considérées pour étudier le comportement spécifique de chaque type de combustible: noirs de carbone, nanocellulose, aluminium et silicium enrobé de carbone. Les poudres ont été caractérisées au repos, et leur distribution de tailles de particules a été mesurée avant et après dispersion à l’aide de méthodes complémentaires. Le diamètre moyen en surface diminue significativement après l’injection dans la sphère de 20L, i.e l’équipement standard utilisé pour mesurer la sévérité d’explosion. Cette observation prouve la nécessité de caractériser la poudre après injection dans la sphère de 20L, pour évaluer le risque de manière fiable. Des essais d’inflammation et d’explosion ont été réalisés dans des conditions standards, mais aussi modifiant la préparation de la poudre (vieillissement, séchage, tamisage, agglomération) ainsi que les conditions opératoires (procédure de dispersion, énergie d’inflammation, turbulence initiale). Des comportements spécifiques liés à la nature de la poudre (carbonée, organique ou métallique) ont été observés, discutés, et des méthodes alternatives de mesure ont été proposées. Par exemple, la procédure de dispersion et la source d'inflammation doivent être adaptées à l'énergie d'allumage minimale des nanopoudres pour éviter à la fois les phénomènes de pré-inflammation et ‘d’overdriving’. Enfin, l’une des principales propositions consiste à considérer la vitesse laminaire de flamme comme un paramètre standard représentant la sévérité d’explosion. Des tests ont été réalisés dans un tube de propagation de flamme et dans une sphère éventée pour évaluer la vitesse non étirée de la nanocellulose. Les résultats obtenus ont alors été comparés à une corrélation existante basée sur les paramètres obtenus lors d’essais standards. De plus, un modèle de propagation de flamme, initialement développée pour des mélanges hybrides, a été adapté pour représenter la propagation de flamme dans un nuage de nanoparticules et a montré des résultats en adéquation avec les résultats expérimentaux