La production d'énergie à partir de biomasse ligno-cellulosique via la technologie de gazéification est une option intéressante dans le contexte énergétique actuel. La combinaison d‘une pyrolyse rapide décentralisée de la biomasse pour produire les bio-huiles, suivie par le transport et le vaporeformage dans des bio-raffineries, est apparue comme l'une des méthodes économiquement les plus viables pour la production de gaz de synthèse (H2+CO). L‘objectif de ce travail est de combler le manque de connaissances concernant les processus de transformation physicochimique de l‘huile de pyrolyse en gaz de synthèse utilisant la gazéification non catalytique dans des réacteurs à flux entrainé. Il s‘agit d‘un processus complexe, mettant en oeuvre la vaporisation, les réactions de craquage thermique avec formation de gaz, de tars et de deux résidus solides : le char et les suies, qui sont des produits indésirables. Ceci est suivi par le reformage des gaz et des tars, ainsi que la conversion du char et des suies. Pour mieux comprendre le processus, la première étape de la gazéification (la pyrolyse), et par la suite l'ensemble du processus (pyrolyse + gazéification) ont été étudiés. L‘étude de la pyrolyse est focalisée sur l‘influence de la vitesse de chauffe, de la température ainsi que de la teneur en cendres dans la bio-huile, sur les rendements en char, tars et gaz. A très grande vitesse de chauffe le rendement en char est inferieur à 1%. Les cendres semblent favoriser les réactions de polymérisation et provoquent la diminution du rendement en gaz. Concernant la gazéification, l'effet de la température sur le rendement et la composition du gaz de synthèse a été étudié. Une augmentation de la température de réaction implique une augmentation du rendement en hydrogène et une conversion très élevée du carbone solide. Un calcul d'équilibre thermodynamique a montré que l'équilibre a été atteint à 1400°C. Finalement les mécanismes de formation et d‘oxydation des suies ont été étudiés expérimentalement sous différentes atmosphères : inerte (pyrolyse), riche en vapeur d‘eau (gazéification) et en présence d‘oxygène (oxydation partielle). Un modèle semi empirique est proposé et validé. Il est fondé sur la chimie détaillée pour décrire les réactions en phase gaz, une seule réaction basée sur la concentration de C2H2 pour décrire la formation des suies et principalement une réaction hétérogène pour décrire l‘oxydation des suies. / Energy production from ligno-cellulosic biomass via gasification technology appears as an attractive option in the current energy context. The combination of decentralized fast pyrolysis of biomass to produce bio-oil, followed by transportation and gasification of bio-oil in bio-refinery has appeared as one of the most economically viable methods for syngas (H2+CO) production. The objective of this work is to bridge the lack of knowledge concerning the physicochemical transformation of bio-oil into syngas using non catalytic steam gasification in entrained flow reactors. This complex process involves vaporization, thermal cracking reactions with formation of gas, tars and two solid residues - char and soot - that are considered as undesirable products. This is followed by steam reforming of gas and tars, together with char and soot conversion. To better understand the process, the first step of gasification (pyrolysis) and thereafter the whole process (pyrolysis + gasification) were studied. The pyrolysis study focused on the influence of the heating rate, the final pyrolysis temperature and the ash content of bio-oil on char, tars and gas yields. At the higher heating rate char yield is smaller than 1%. In addition, ash seems to promote polymerization reactions and causes a decrease of gas yield. Concerning gasification, the effect of temperature on syngas yield and composition was studied. An increase in the reaction temperature implies higher hydrogen yield and higher solid carbon conversion. A thermodynamic equilibrium calculation showed that equilibrium was reached at 1400°C. Finally, the soot formation and oxidation mechanisms were investigated through experiments in three different atmospheres: inert (pyrolysis), rich in steam (gasification) and in the presence of oxygen (partial oxidation). A semi-empirical model was proposed and validated. It is based on detailed chemistry to describe gas phase reactions, a single reaction using C2H2 concentration to describe soot formation and one main heterogeneous reaction to describe soot oxidation.

The concurrent spreading of a boundary layer type diffusion flame is studied. The impossibility of obtaining a low velocity laminar flow without any perturbation induced by buoyancy has lead to the development of an experimental apparatus for use in micro-gravity facilities. Based on previous experimental observations, an original numerical approach has been developed showing, first the dominating role of the radiative heat transfer on the structure of the flame and second the major role of the soot on the extinction phenomenon at the flame trailing edge. The influence of the forced flow velocity, the fuel injection velocity and oxygen concentration on the geometry of the flame has been examined by imaging of CH* and OH* radicals spontaneous emission. Laser-Induced Incandescence (LII) is used to determine the soot field concentration in the flame. The soot formation has been studied by Laser Induced Fluorescence (LIF) of Polycyclic Aromatic Hydrocarbons (PAHs). The interaction between the reaction zone and the field of soot formation/oxidation is taken into account to analyze the flame length. These results can be used as the experimental input data for a future complete validation of numerical model simulating the soot formation and oxidation in this kind of flame.

Le catalyseur quatre voies est destiné à diminuer simultanément les émissions d’hydrocarbures, de monoxyde de carbone, d’oxydes d’azote et de suies par l’intermédiaire d’un seul monolithe catalytique. Plusieurs études sur ce type de catalyseur ont montré que la présence d’oxydes d’azote entraîne une diminution de la température d’oxydation des suies. Cependant, l’effet de la présence d’eau sur l’adsorption des oxydes d’azote n’est pas encore clair, surtout en présence de suies. Les travaux présentés dans ce manuscrit ont pour but de mettre en évidence l’influence de la présence d’eau et/ou de suies sur le fonctionnement de catalyseur «piège à NOx». Les résultats obtenus montrent que la présence d’eau entraîne une inhibition de la fonction oxydante du catalyseur, une diminution de la quantité de stockage des oxydes d’azote, et une inhibition de la formation des espèces adsorbées de surface. Ces phénomènes ont été attribués à la voix réactionnelle spécifique en présence d’eau associée à l’adsorption des oxydes d’azote. Les résultats obtenus sur le mélange noir de carbone et catalyseur montrent que la présence de noir de carbone induit une diminution de stockage des oxydes d’azote. De plus, cet effet se trouve plus important en contact fort. Les expériences réalisées sur l’adsorption des oxydes d’azote en présence simultanée de noir de carbone et d’eau ont montré un effet non cumulé de l’eau et du noir de carbone. Ce phénomène a été attribué à une compétition entre l’action de l’eau qui favorise la formation de nitrate de cœur à partir des nitrates faiblement liés et l’action du noir de carbone qui tend à déstabiliser les nitrates faiblement liés pour former les carbonates. / The four ways catalyst is used to decrease the emissions of hydrocarbon, carbon monoxide, nitrogen oxides and soot by a monolithic catalyst. Several researches on this type of catalyst have shown that the presence of nitrogen oxides involves a decrease of the soot oxidation temperature. However, the effect of the presence of water on the nitrogen oxides adsorption is not clear yet, especially with the presence of soot. The works presented in this manuscript are intended to study the influence of the presence of water or/and soot on the performance of the catalyst NOx trap. The results showed that the presence of water involves an inhibition of the oxidation function of catalyst, a decrease of the capacity of the NOx storage, and an inhibition of the formation of the surface adsorbed species. It is attributed to a special reactive way in the presence of water linked to the adsorption of nitrogen oxides. The results obtained on the mix of carbon black and catalyst showed that the presence of carbon black induce a decrease of the NOx storage capacity of catalyst. Besides, this effect was more important with a tight contact between carbon black and catalyst. The experiments realized on the adsorption of nitrogen oxides with the presence of carbon black and water simultaneously showed an effect not accumulated of the water and the carbon black. This phenomenon is attributed to a competition between the action of water which favors the formation of the bulk nitrate from the weak-linked nitrates and the action of carbon black which tend to destabilize the weak-linked nitrates to form the carbonates.

Persistent organic pollutants (POPs) is a group of chemicals that are toxic, undergo long-range transport and accumulate in biota. Due to their persistency the distribution and recirculation in the environment often continues for a long period of time. Thereby they appear virtually everywhere within the biosphere, and poses a toxic stress to living organisms. In this thesis, attempts are made to contribute to the understanding of factors that influence the distribution of POPs with focus on processes in the marine environment. The bioavailability and the spatial distribution are central topics for the environmental risk management of POPs. In order to study these topics, various field studies were undertaken. To determine the bioavailable fraction of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated naphthalenes (PCNs), and polychlorinated biphenyls (PCBs) the aqueous dissolved phase were sampled and analysed. In the same samples, we also measured how much of these POPs were associated with suspended particles. Different models, which predicted the phase distribution of these POPs, were then evaluated. It was found that important water characteristics, which influenced the solid-water phase distribution of POPs, were particulate organic matter (POM), particulate soot (PSC), and dissolved organic matter (DOM). The bioavailable dissolved POP-phase in the water was lower when these sorbing phases were present. Furthermore, sediments were sampled and the spatial distribution of the POPs was examined. The results showed that the concentration of PCDD/Fs, and PCNs were better described using PSC- than using POM-content of the sediment. In parallel with these field studies, we synthesized knowledge of the processes affecting the distribution of POPs in a multimedia mass balance model. This model predicted concentrations of PCDD/Fs throughout our study area, the Grenlandsfjords in Norway, within factors of ten. This makes the model capable to validate the effect of suitable remedial actions in order to decrease the exposure of these POPs to biota in the Grenlandsfjords which was the aim of the project. Also, to evaluate the influence of eutrophication on the marine occurrence PCB data from the US Musselwatch and Benthic Surveillance Programs are examined in this thesis. The dry weight based concentrations of PCB in bivalves were found to correlate positively to the organic matter content of nearby sediments, and organic matter based concentrations of PCB in sediments were negatively correlated to the organic matter content of the sediment.

Soot particles are a major absorber of shortwave radiation in the atmosphere. They exert a rather uncertain direct and semi-direct radiative effect, which causes a heating or in some cases a cooling of the atmosphere. The mass absorption coefficient is an essential quantity to describe this light absorption process. This work presents new experimental data on the mass absorption coefficient of soot particles in the troposphere over Central Europe. Mass absorption coefficients were derived as the ratio between the light absorption coefficient determined by multi angle absorption photometry (MAAP), and the soot mass concentration determined by Raman spectroscopy. The Raman method is sensitive to graphitic structures present in the particle samples, and was calibrated in the laboratory using Printex90 model particles. The mass absorption coefficients were determined for a number of seven observation sites, ranging between 3.9 and 7.4 m²/g depending on measurement site and observational period. The highest values were found in an continentally aged air mass in winter, where we presumed soot particles to be present mainly in internal mixture. The regional model WRF-Chem was used in conjunction with a high resolution soot emission inventory to simulate soot mass concentrations and absorption coefficients for the Central European Troposphere. The model was validated using soot mass concentrations from Raman measurements and absorption coefficients. Simulated soot mass concentrations were found to be too low by around 50 %, which could be improved by scaling the emissions by a factor of two. In contrast, the absorption coefficient was positively biased by around 20%. Adjusting the modeled mass absorption coefficient to measurements, the simulation of soot light absorption was improved. Finally, the positive direct radiative forcing at top of the atmosphere was found to be lowered by up to 70% for the model run with adjusted soot absorption behaviour, , indicating a decreased heating effect on the atmosphere.

An experimental study was performed to study soot formation and evolution in atmospheric, laminar, coflow, diffusion flames of Jet-A1, Synthetic Paraffinic Kerosene and their surrogates. Light extinction, rapid thermocouple insertion and thermophoretic sampling followed by transmission electron microscopy and atomic forced microscopy were used to obtain soot volume fraction profiles, temperature profiles and soot morphologies, respectively. Different soot evolution processes were observed on the flame centerline and on a streamline with a significantly different temperature history. Formation and agglomeration of the first soot particles are different on the two streamlines. Transparent liquid-like particles are produced in large volumes in the early regions of the flame centerline where T < 1500 K; these particles are undetectable by the extinction method with the wavelength of 632.8 nm. Most of the currently used computational soot models do not predict the liquid-like nature of nascent soot particles which has major effects on the modeling.

An experimental study was performed to study soot formation and evolution in atmospheric, laminar, coflow, diffusion flames of Jet-A1, Synthetic Paraffinic Kerosene and their surrogates. Light extinction, rapid thermocouple insertion and thermophoretic sampling followed by transmission electron microscopy and atomic forced microscopy were used to obtain soot volume fraction profiles, temperature profiles and soot morphologies, respectively. Different soot evolution processes were observed on the flame centerline and on a streamline with a significantly different temperature history. Formation and agglomeration of the first soot particles are different on the two streamlines. Transparent liquid-like particles are produced in large volumes in the early regions of the flame centerline where T < 1500 K; these particles are undetectable by the extinction method with the wavelength of 632.8 nm. Most of the currently used computational soot models do not predict the liquid-like nature of nascent soot particles which has major effects on the modeling.

Fossil fuel combustion produces fly-ash particles that are released into the atmosphere and deposited in the environment. A particularly characteristic kind of fly-ash is spheroidal carbonaceous particles. They are composed of an amorphous carbon matrix in which other elements are dispersed. The elemental carbon content makes them very resistant to chemical degradation and these particles can be relatively easily extracted from sediment and soil samples using a method described in this thesis. The distribution of spheroidal carbonaceous particles in lake sediment profiles, surface sediments and forest soils has been studied. Cores from several Swedish lakes have been analysed and, although the lakes are from different parts of the country, consistent trends in the deposition of the carbonaceous particles have been found. The analyses of dated cores show that the carbonaceous particle deposition in the sediments follows the same general pattern as statistics for Swedish coal and oil combustion over the last two centuries. This indicates that the sediment records reflect the history of the atmospheric deposition of particulate pollutants from fossil fuel combustion. Analysis of surface sediment samples provides an integrated picture of the deposition over the preceding few years and can be used to indicate the contemporary geographical pattern of deposition from the atmosphere. Two sets of surface sediment samples (0-1 cm) were analysed. One comprised samples from 66 lakes around Sweden's second largest city, Gothenburg, and showed very high carbonaceous particle concentrations within a distance of 50 to 100 km from the city. The second set comprised surface sediment samples from 114 lakes distributed all over Sweden. This survey of Sweden demonstrated a geographical north-south gradient with more than a hundred times higher particle concentrations in the south than in the north. This distribution is similar to the distribution of other air pollutants (data obtained from a moss survey and an air monitoring program) and suggests that carbonaceous particles in palaeolimnological investigations of air pollution, can be used as tracers for pollutants that are otherwise difficult to determine in lake sediments. Spheroidal carbonaceous particles also accumulate in soils, and forest soil samples can be used for geographical surveys of particle deposition. In Swedish podzol soils the particles mainly accumulate in the thin organic horizon and concentrations in this layer reflect the total deposition since industrialisation, although most will have been deposited during the last few decades. Since the spheroidal carbonaceous particle record in Swedish lake sediments has a characteristic temporal pattern, carbonaceous particle profiles can be used for indirect dating of recent sediment cores. Analyses of multiple sediment cores from three lakes demonstrate that carbonaceous particles can also be used for studies of sediment distribution in lake basins. Results from Gårdsjön indicate that the acidification of the lake changed sediment distribution processes from a normal sediment focusing regime to a more even distribution of sediments over the lake bottom. Liming of the lake seems to have restored normal sedimentation processes. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1992, Härtill 8 uppsatser</p> / digitalisering@umu

No description available.

The objective of this study was onboard testing of a mixed metal oxide diesel soot oxidation catalyst composing of oxides of lead and cobalt previously developed in our lab, by mounting a diesel particulate filter (DPF), which is coated with this catalyst, to the exhaust stream of a diesel vehicle. Commercial wall flow type DPF&rsquo / s (Corning EX-80) were coated with the catalyst by a slurry wash-coating procedure and then mounted on the exhaust stream of a diesel light duty vehicle (LDV) provided by TOFAS (FIAT Doblo 1.9 JTD). These vehicles were driven on the rollers of the chassis dynamometer at constant speed and gear for two different loading conditions and on a standard driving cycle (NEDC) in the Test and Emission Laboratory of TOFAS-FIAT. The exhaust gases were analyzed for NOx, CO, CO2, THC and PM. The pressure drop caused by the filter was monitored during these tests as an indication of soot accumulation on the filter with the help of pressure sensors placed before and after the filter. Also temperatures before, inside and after the filter were monitored by means of thermocouples. Three different filters were tested in this manner: (1) Monocoated (CoOx), (2) Sequential PbOx coated over CoOx (PbOx/CoOx), (3) Simultaneously coated (PbCoOx). Also tests with the uncoated filter were performed to determine the pressure drops as a result of non-catalytic soot oxidation. The performances of the catalytic filters were evaluated by determining the temperature at which the soot oxidation rate on the filter equals the soot production rate in the engine (balance point temperature-Tbal). This temperature was used for comparing the catalytic activity of the supported catalyst with that of the powder form tested in the laboratory, i. e. Tpeak. The results of the onboard test were in parallel with the previous laboratory studies with similar catalytic activity temperatures. The continuous regeneration temperatures (Tbal) obtained in onboard tests with PbOx/CoOx and PbCoOx filters of about 370oC, which was close to the values attained in the lab study with the same mixed metal oxide catalyst having a Tpeak value of 385oC. Also the PM emissions during the tests were complying with the current EURO-IV emission limits.