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Wretborn, Tobias. "Pyrolysis of Wood Chips : Influence of Pyrolysis Conditions on Charcoal Yield and Charcoal Reactivity." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-179.
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At a steel mill, charcoal from biomass is a potential substitute to coal as a reducing agent in the Blast Furnace. The steel industry accounts for 5 % of the global CO2 emissions. Charcoal, being a renewable fuel, has the potential to mitigate the steel industry’s contribution to global warming. If charcoal were to replace the pulverized coal injected into one of Sweden´s two blast furnaces an estimated 1,13 Mton raw biomass per year would be required, this is equivalent to 2,5 % of the total available biomass in Sweden the year 2020 . If this is to be realized, a well optimized pyrolysis process for charcoal production would be required, a process with high charcoal yield that minimize the biomass consumption. This report presents a study on pyrolysis of wood chips. The two main objectives of this work have been to find pyrolysis conditions, applicable in a real process, that increase the charcoal yield and also to investigate how the reactivity of the charcoal is affected by these conditions. A hypothesis with two approaches has been proposed and evaluated experimentally. It has been proposed that the charcoal yield is increased if the tar found in the pyrolysis gases are condensed and returned to impregnate the ingoing wood before undergoing a second pyrolysis step. Or, the charcoal yield is increased by letting the tar impregnate the outgoing charcoal before the two undergoes a second pyrolysis step. The hypothesis has been evaluated in a laboratory where pyrolysis has been conducted on chips from fir wood together with bio-oil. The bio-oil has been used to resemble tar. It has been concluded that by recycling tar the charcoal yield is increased. Pyrolysis of fir wood at 340 oC yields 32 % charcoal. If the wood is impregnated before the pyrolysis with an amount of bio-oil equivalent to a tar yield of 25 % the charcoal yield is increased to 37,7 %. It is possible to say, with 80 % confidence, that pyrolysis of wood and bio-oil gives a higher charcoal yield if the two undergoes pyrolysis while being in contact with each other instead of being separated. The charcoal yield is not increased by pyrolysis of charcoal impregnated with bio-oil. There is no difference in reactivity between charcoals from impregnated wood and plain wood.
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Makhadmeh, Leema al. "Coal pyrolysis and char combustion under oxy-fuel conditions." Aachen Shaker, 2009. http://d-nb.info/996033009/04.
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Gan, Yaodong. "Thermogravimetric Analysis of Coal Blends Under Conditions of Pyrolysis & Combustion." TopSCHOLAR®, 1989. https://digitalcommons.wku.edu/theses/2370.
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In recent years, the growing attention to coal quality by coal-burning utilities has led to an increase in coal blending. Coal blending is done with both economics and the quality of coal in mind. To assess the quality of coal, pyrolysis and combustion influencing thermal parameters, as measured in thermogravimetric analysis (TGA) experiments can be applied. The coal industry needs a study to determine relationships that may exist between the measured values of TGA thermal parameters in individual coals and those in the blends. The TGA thermal parameters are the weight loss, Tmax, Ti, T1/2, tmax, tbreak point, tcombustion end point, Rmax and residue. With these relationships, there exists the possibility of accurate prediction of values of these parameters in the coal blends. In this study, a series of coal blends were prepared and thermal parameters for the blends were measured to examine the additive or nonadditive nature of results obtained under both pyrolysis and combustion conditions using thermogravimetric analysis.
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Al-Makhadmeh, Leema [Verfasser]. "Coal Pyrolysis and Char Combustion Under Oxy-Fuel Conditions / Leema Al-Makhadmeh." Aachen : Shaker, 2009. http://d-nb.info/115983475X/34.
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Kong, Zhaoying. "Effects of pyrolysis conditions and biomass properties on leachability and recyclability of inorganic nutrients in biochars produced from mallee biomass pyrolysis." Thesis, Curtin University, 2014. http://hdl.handle.net/20.500.11937/1956.
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Using biochar as a soil amendment agent can recycle a majority of inherent inorganic nutrients in biomass to the soil, largely enhancing the overall sustainability of pyrolysis technology. This work investigates the effects of pyrolysis conditions and biomass properties on the leachability and recyclability of nutrients in mallee biochars. Understanding the relationships between biochar preparation conditions and biochar nutrients recyclability will aid the optimisation of suitable conditions to produce biochar with excellent leachability.
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Kelly, David Paul. "A study into the effects of pyrolysis fuels, pyrolysis conditions and the identification of chemical markers in grapes and wine as smoke taint." Thesis, Curtin University, 2014. http://hdl.handle.net/20.500.11937/1075.
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Taxonomically distinct vegetation fuels were used to generate smoke for fumigating grapevines to examine the influence of lignin makeup on smoke taint compounds that accrue in wine. Vegetation type had no effect on taint accumulation. Phenol, m-cresol and p-cresol glycoconjugates were closely associated with harsh smoke taint descriptors. While cultivars had similar smoke uptake sensitivity, winemaking method had distinct impact: red winemaking releases 80% of grape phenols compared to 20-35% for white winemaking.
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Somrang, Yatika. "Effect of operating conditions on product distributions and bio-oil ageing in biomass pyrolysis." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9202.
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Alternatives to petroleum-derived fuels are receiving significant interest in order to reduce dependence on finite resources of fossil fuels and to lower fossil-derived CO2 emissions. The present study addresses the production of bio-oil from biomass pyrolysis, one of the potential renewable substitutes to petroleum-derived fuels. The first objective of this work was to investigate the effect of pyrolysis operating parameters, i.e. temperature, heating rate and pyrolysis time, on product distributions in a wire-mesh reactor (WMR) which was designed to minimise secondary reactions. It has been found that high heating rate promotes melting of biomass and this facilitates volatile ejection, thereby resulting in high yield of large bio-oil molecules and high combustion reactivity of residual char. Maximum bio-oil yield is obtained at 500 °C for both rice husk and beech wood whereas a relatively low pyrolysis temperature, e.g. 350 °C, does not allow complete pyrolysis to take place. Chars produced from long holding time and high temperature tests show a decrease in the TGA combustion reactivity which is due to thermal annealing. The comparison between bio-oils obtained from the WMR and Gray-King retort demonstrates the impact of reactor configuration on the variation of bio-oil properties. The unstable nature of bio-oils provided the second objective of this work. The ageing behaviour of bio-oil and the use of organic solvents to improve the bio-oil properties have been investigated. Polymerisation plays a key role in bio-oil ageing and is enhanced by high temperature. Only slight changes in functional groups have been observed by 13C-NMR and FT-IR. UV-F results suggest that phenolic resin formation is one of the polymerisation reactions occurring during bio-oil ageing. With the addition of methanol and acetone to bio-oil, the extent of polymerisation decreases and NMR results indicate the formation of hemiacetals/acetals.
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Shen, Qiqing. "Rapid Pyrolysis of Raw and Pretreated Biomass under Conditions Pertinent to Pulverized Fuel Applications." Thesis, Curtin University, 2021. http://hdl.handle.net/20.500.11937/86933.
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This Ph.D. study investigates the rapid pyrolysis of biomass at high temperatures and the properties of derived char samples under various conditions. A novel drop-tube furnace was used to experimentally determine the accurate char yields after rapid pyrolysis at 1300°C, which is realized for the first time. Based on true char yield, the evolution of char properties was revealed, and the retention of inorganic species, the transformation of particle shape during rapid pyrolysis were quantified.
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McMasters, Brian Philip. "Effect of Fuel Chemical Composition on Pyrolytic Reactivity and Deposition Propensity under Supercritical Conditions." University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1398682863.
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Christodoulou, Mélina. "Pyrolyse de bois dans les conditions d'un lit fluidisé : étude expérimentale et modélisation." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0200/document.
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Ce travail s'inscrit dans le projet français de gazéification de la biomasse : le projet Gaya. C'est un vaste programme R&D partenarial coordonné par GDF SUEZ et soutenu par l'ADEME. L'objectif du projet Gaya est de développer une filière décentralisée de production de bio-méthane à partir de la gazéification de la biomasse selon un procédé thermochimique de deuxième génération. L'objectif de cette thèse est de réaliser un modèle de pyrolyse de biomasse représentatif des conditions du lit fluidisé de gazéification développé dans ce projet. Un pilote expérimental, le four à image, a été développé pour reproduire au mieux les conditions de chauffage d'un lit fluidisé à 850°C. Ce pilote permet de récupérer l'ensemble des produits de pyrolyse pour une analyse ultérieure. De là, les cinétiques des réactions de pyrolyse sont déterminées par modélisation des processus physico-chimiques et optimisation à partir des résultats expérimentaux. Le craquage des vapeurs primaires de pyrolyse éjectées de la particule de biomasse est étudié durant 300 millisecondes après leur éjection de la particule de biomasse. Ces expériences de craquage sont menées sur le montage expérimental combinant un réacteur tubulaire de pyrolyse et un réacteur parfaitement auto-agité de craquage. Le modèle développé permet de représenter la pyrolyse de la biomasse introduite dans le réacteur de gazéificationThis study contributes to the French biomass gasification project: Gaya project. It is a large R&D project financed by ADEME and coordinated by GDF SUEZ. The project GAYA will develop a demonstration platform for a new biomass gasification and methanation process. In this context, our objective is to build a biomass pyrolysis model, representative of the conditions encountered in the fluidized bed gasifier developed in this project. An experimental machine, the vertical image furnace, has been developed to reproduce the heat conditions of the fluidized bed gasifier at 850°C. This experimental model permits to collect all the pyrolysis products for a later analysis. Then, kinetics parameters are determined from both the physico-chemical process and the optimization of experimental results. The thermal cracking of condensable vapours, is studied during the first 300th milliseconds after their ejection from the biomass particle. For this purpose, cracking experiments are led on the experimental machine which combines a tubular pyrolysis reactor and a continuous self-stirred tank cracking reactor. The model developed allows us to represent the biomass pyrolysis introduced in the gasification reactor
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Guizani, Chamseddine. "Effects of CO2 on the biomass pyro-gasification in High Heating Rate and Low Heating Rate conditions." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2014. http://www.theses.fr/2014EMAC0010/document.
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La présente étude porte sur les effets de CO2 sur la pyrolyse de la biomasse et la gazéification de chars dans des conditions de chauffe lente et de chauffe rapide. Dans la première partie de ce travail, nous avons étudié les effets du CO2 sur la réaction de pyrolyse rapide à haute température et évalué ses effets sur la vitesse de pyrolyse, sur le rendement de gaz ainsi que sur les propriétés du char. Nous avons aussi étudié la réaction de gazéification en atmosphère mixte en présence de CO2 et de H2O. Enfin, nous avons imaginé le cas hypothétique d’un gazogène au CO2 pur. Le cas d’une pyro-gazéification sous CO2 pur a été abordé au niveau de la particule de biomasse, expérimentalement et théoriquement par la modélisation numérique avec l’objectif de fournir des temps caractéristiques de pyrolyse et de gazéification, et de comprendre le déroulement de la pyro-gazéification sous CO2. Dans la deuxième partie, nous nous sommes intéressés à la question de la gazéification des chars obtenus par chauffe lente, en présence de CO2 avec deux objectifs principaux : d’une part, de fournir des données de réactivité dans des conditions opératoires de réacteurs de gazéification et d’autre part, de comprendre les mécanismes de réaction de gazéification sous CO2, H2O et leurs mélanges. Nous avons examiné l’influence de la taille des particules sur la vitesse de gazéification sous des atmosphères simples de CO2 et H2O en utilisant une approche basée sur le module de Thiele. Nous avons également étudié les effets de la température et de la taille des particules sur la gazéification du char sous atmosphères mixtes contenant CO2 et H2O à 900°C. Nous avons également abordé la question des atmosphères cycliques en examinant l’effet de la gazéification du char sous CO2 sur sa réactivité à H2O et vice versa. Pour mieux comprendre les mécanismes de gazéification dans des atmosphères simples et mixtes de CO2 et H2O, nous avons suivi l’évolution de la texture, de la structure et de la chimie de surface du char le long de la gazéification sous CO2, H2O et leurs mélanges. Des caractérisations chimiques, texturales et structurales ont été ainsi effectuées sur des particules de char partiellement gazéifiés à 20%, 50% et 70% de conversion sous CO2, H2O et leurs mélanges. Ces caractérisations conduisent à une meilleure compréhension du déroulement de la réaction de gazéificationThe present work deals about the effects of CO2 enriched atmospheres on biomass pyrolysis and char gasification reactions in High Heating Rate (HHR) and Low Heating Rate (LHR) conditions, at the biomass particle level. In the first part, we studied the effects of CO2 on the high temperature fast pyrolysis reaction and evaluate its effects on the pyrolysis rate, on the gas yield as well as on the char properties including chemical composition, texture and reactivity at 850°C. We focused also on the effects of CO2 on the HHR-char gasification reaction when injected as a co-reactant with steam. We studied the mixed atmosphere gasification reaction in CO2 and H2O for different atmosphere compositions. Finally, we imagined a hypothetical case of a pure CO2 operating gasifier. The case of a pure CO2 pyrogasification process was tackled experimentally and theoretically by numerical modelling with aim to provide pyrolysis and gasification characteristic reaction times, and to understand the unfolding of the global CO2 pyro-gasification reaction. In the second part, we were interested on the issue of LHR-char gasification in the presence of CO2 with two principal objectives: on one hand, providing reactivity data for practical gasification operations and on the other hand, understanding the gasification reaction mechanisms (in CO2, H2O and their mixtures) at the level of the char basic structural units (BSU). We examined the influence of particle size on the single atmosphere gasification in CO2 and H2O using the Thiele modulus approach. We also studied the effects of temperature and particle size on the char gasification in mixed atmosphere of CO2 and steam at 900°C. We also had a focus on the issue of cyclic atmosphere gasification and studied the effects of a prior CO2 gasification on the char reactivity towards H2O and vice versa. To further understand the char gasification mechanisms in single and mixed atmospheres of CO2 and H2O, we opted to monitor the evolution of the chemical, structural and textural char properties along the gasification in CO2, H2O and their mixtures. Deep char characterization were performed on small LHR-char particles partially gasified at 20%, 50% and 70% of conversion in CO2, H2O and their mixtures. These characterisations are of high interest as they shed light on the unfolding of the gasification reaction in CO2, H2O and their mixtures
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Ehrhardt, Jordan. "Allumage laser de poudres propulsives à vulnérabilité réduite : influence du taux de nitrocellulose sur les conditions de pyrolyse et d’inflammation." Thesis, Orléans, 2020. http://www.theses.fr/2020ORLE3135.
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Les poudres propulsives à vulnérabilité réduite ont été développées spécifiquement pour résister aux stimuli accidentels et remplacer les compositions classiques à base de nitrocellulose (NC). Néanmoins, aujourd’hui, les mécanismes mis en jeu, dictant le comportement de ces poudres propulsives, sont peu connus. Le phénomène d’allumage d’une poudre propulsive à vulnérabilité réduite inclut des phénomènes thermiques, physiques et chimiques très complexes. Ainsi, les poudres propulsives étudiées dans cette thèse sont des mélanges d’hexogène (RDX) et de nitrocellulose pour se concentrer sur l’interaction entre ces deux composés. De manière à préciser l’effet de la nitrocellulose sur l’allumage d’une poudre propulsive, trois compositions différentes sont étudiées. Ces poudres ont été préparées par un procédé d’extrusion. La phase gazeuse libérée lors de la pyrolyse est analysée par spectrométrie de masse à l’aide de deux dispositifs expérimentaux. Par la suite, l’allumage laser de ces poudres est étudié. À la lumière de propriétés de combustion comme la surpression ou le délai d’inflammation, certaines influences sont dégagées quant à l’impact de l’atmosphère gazeuse, de la puissance utilisée ou encore de la pression initiale. Les probabilités d’allumage sont calculées selon la méthode de Langlie. L’influence du graphitage en surface des grains se montre considérable, amenant une diminution de 95 % de l’énergie d’allumage. Numériquement, l’outil Reaction Mechanism Generator est utilisé pour générer le premier modèle de décomposition de la nitrocellulose. Ce modèle est, finalement, fusionné avec un modèle du RDX existant pour modéliser les surpressions obtenues expérimentalementLow vulnerability gun propellants are energetic materials specifically designed to resist unintended initiation stimuli and aim at replacing the usual nitrocellulose (NC) based ones. The different phenomena involved in the propellant’s ignition are numerous (thermal, chemical or physical) and not well known nowadays. Therefore, this study aims at investigating the pyrolysis and combustion phenomena of three propellants made of hexogen (RDX) and nitrocellulose (NC).These propellants were made through an extrusion process. The chemical species emitted during the pyrolysis process were analyzed by mass spectrometry using two experimental setups. Laser ignition is also investigated thanks to a laser diode. Depending on properties such as overpressure or ignition delay, influence of initial pressure, gas atmosphere or laser power are discussed. Ignition probabilities are calculated with the Langlie method. By adding carbon graphite on the surface of the propellant, the value of the ignition energy is decreased by 95 %. The “Reaction Mechanism Generator” tool has been exploited in order to build the first numerical model of NC decomposition. Eventually NC model has been merged with an already existing RDX model in order to simulate the overpressure experimentally obtained
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Ndiaye, Fatou Toutie. "Pyrolyse de la biomasse en réacteur cyclone - Recherche des conditions optimales de fonctionnement." Thesis, Vandoeuvre-les-Nancy, INPL, 2008. http://www.theses.fr/2008INPL013N/document.
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Les procédés conventionnels de transformation thermique de la biomasse sont conçus pour la production d’huiles ou de gaz riches en CO, CO2, H2 et hydrocarbures légers à des fins énergétiques ou chimiques. Le pilote de pyrolyse rapide utilisé dans cette étude comporte un réacteur cyclone, chauffé à ses parois, et capable de mettre en oeuvre la pyroliquéfaction ou la pyrogazéification par le simple jeu des conditions opératoires. Les produits de réaction (charbon, huiles et gaz) sont récupérés et analysés. Les bilans de matière massiques et élémentaires (C, H, O) bouclent de façon très satisfaisante. Les basses températures de paroi et faibles débits de gaz vecteur favorisent la pyroliquéfaction. La production d’huiles augmente avec le débit de biomasse. La taille des particules a une faible influence sur les sélectivités en gaz, liquides et charbon. Un modèle de fonctionnement du cyclone est établi en tenant compte de l’hydrodynamique des phases gaz et solide ainsi que des lois de transferts de chaleur paroi-gaz et paroi-solides dans le cyclone. Ce modèle inclut également un schéma cinétique de pyrolyse rapide intégré dans un modèle de décomposition de la particule, ainsi qu’un modèle de craquage des vapeurs. Validé successivement sur la cellulose puis sur le bois, il permet de prédire les variations des sélectivités en fonction des conditions opératoires. Le modèle montre que les réactions de craquage se déroulent majoritairement dans une mince couche limite proche des parois chaudes. On propose deux lois générales (pyrogazéification et pyroliquéfaction) regroupant les différents paramètres opératoires contrôlant les performances du réacteurThe usual processes of biomass thermal upgrading are designed for the production of bio-oils or of gases rich in CO, CO2, H2 and light hydrocarbons for energy or chemical productions. The laboratory-scaled set-up used in this study includes a cyclone reactor, heated at its walls and able to carry out the fast pyroliquefaction or pyrogazeification by simply changing the operating conditions. The reaction products (charcoal, liquids and gases) are recovered and analyzed. The masses and elementary (C, H, O) balances closures are very accurate. Pyroliquefaction conditions are favoured by low walls temperatures and small carrier gas flowrates. The bio-oils fractions increase with the biomass flowrate. The particles size has only a weak influence on gas, liquids and charcoal selectivities. A model representing the cyclone behaviour is established by taking into account the hydrodynamics of the gases and solids, and the wall-gas and wall-solids heat transfer laws inside the cyclone. This general model includes also a model of particle decomposition (scheme of fast pyrolysis in competition with heat transfers) and a model of vapours cracking. Validated successively with cellulose and then with wood, it allows to predict the variations of the selectivities according to the operating conditions. The model shows that the cracking reactions occur mainly inside a thin boundary layer close to the hot walls. Two laws (pyrogazeification and pyroliquefaction) gathering the various operational parameters that control the performances of the reactor are finally proposed
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Shurtz, Randy C. "Effects of Pressure on the Properties of Coal Char Under Gasification Conditions at High Initial Heating Rates." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2877.
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The effects of elevated pressure and high heating rates on coal pyrolysis and gasification were investigated. A high-pressure flat-flame burner (HPFFB) was designed and built to conduct these studies. The HPFFB was designed to provide an environment with laminar, dispersed entrained flow, with particle heating rates of ~10^5 K/s, pressures of up to 15 atm, and gas temperatures of up to 2000 K. Residence times were varied from 30 to 700 ms in this study. Pyrolysis experiments were conducted at particle heating rates of ~10^5 K/s and maximum gas temperatures of ~1700 K at pressures of 1 to 15 atm. A new coal swelling correlation was developed that predicts the effects of heating rate, pressure, and coal rank on the swelling ratio at heating rates above ~10^4 K/s. A coal swelling rank index system based on 13C-NMR chemical structural parameters was devised. The empirical swelling model requires user inputs of the coal ultimate and proximate analyses and the use of a transient particle energy balance to predict the maximum particle heating rate. The swelling model was used to explain differences in previously reported bituminous coal swelling ratios that were measured in facilities with different heating rates. Char gasification studies by CO2 were conducted on a subbituminous coal and 4 bituminous coals in the HPFFB. Pressures of 5, 10, and 15 atmospheres were used with gas compositions of 20, 40, and 90 mole % CO2. Gas conditions with peak temperatures of 1700 K to 2000 K were used, which resulted in char particle temperatures of 1000 K to 1800 K. Three gasification models were developed to fit and analyze the gasification data. A simple 1st-order model was used to show that the measured gasification rates were far below the film-diffusion limit. The other two models, designated CCK and CCKN, were based on three versions of the CBK models. CCKN used an nth-order kinetic mechanism and CCK used a semi-global Langmuir-Hinshelwood kinetic mechanism. The two CCK models fit the HPFFB gasification data better than the 1st-order model. The fits of the gasification data with CCK and CCKN were comparable to each other. The fit of the data in CCK suggests that Knudsen diffusion may have influenced the gasification rates in the HPFFB experiments. The gasification rate parameters in each of the three models were correlated with coal rank. 13C-NMR parameters were used to estimate a structural parameter of the coal char. Char-CO2 gasification rate coefficients correlated better with this NMR-based char structure index than it did with the carbon and oxygen content of the parent coal.
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Ehsan, Abbasi Atibeh. "A Study On The Catalytic Pyrolysis And Combustion Characteristics Of Turkish Lignite And Co-processing Effects With Biomass Under Various Ambient Conditions." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614512/index.pdf.
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In this study the catalytic pyrolysis and combustion characteristics of Turkish coal samples in O2/N2 and O2/CO2 (oxy-fuel conditions) ambient conditions were explored and the evolution of emissions during these tests was investigated using non-isothermal Thermo-gravimetric Analysis (TGA) technique combined with Fourier Transform Infrared (FTIR) spectroscopy. Potassium carbonate (K2CO3), calcium hydroxide (Ca(OH)2), iron (III) oxide (Fe2O3) and iron (III) chloride (FeCl3) were employed as precursors of catalysts to investigate the effects of potassium (K), calcium (Ca) and iron (Fe). Furthermore the effects of these catalysts on calorimetric tests of Turkish coal samples were investigated.
TGA-FTIR pyrolysis tests were carried out in 100 % N2 and 100 % CO2 ambient conditions which are the main diluting gases in air and oxy-fuel conditions. Lignite pyrolysis tests revealed that the major difference between pyrolysis in these two ambient conditions was observed beyond 720
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Atmani, Léa. "Study of organic matter decomposition under geological conditions from replica exchange molecular dynamics simulations." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0104/document.
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Pétrole et gaz proviennent de la décomposition de la matière organique dans la croûte terrestre. En s’enfouissant, les résidus organiques se décomposent en un solide poreux et carboné, appelé kérogène et en un fluide composé d’hydrocarbures et de petites molécules telles que de l’eau. Le processus de formation du kérogène n’est pas totalement élucidé et une modélisation aiderait à une meilleure compréhension à la fois de sa structure et de sa composition et serait utile à l’industrie pétrolière.Dans le présent travail, nous adoptons une approche thermodynamique ayant pour but, à l’aide de simulations numériques, de d’étudier la décomposition de précurseurs de kérogène d’un type donné –ici le type III- dans les conditions d’un réservoir géologique. La méthode dite de Replica Exchange Molecular Dynamics (REMD) est appliquée pour étudier la décomposition de cristaux de cellulose et de lignine. Le potentiel d’interaction ReaxFF et le code LAMMPS sont utilisés. La REMD est une façon de surmonter de larges barrières d’énergie libre, en améliorant l’échantillonnage de configurations d’une dynamique moléculaire conventionnelle à température constante, en utilisant des états générés à températures supérieures.En fin de simulation, les systèmes ont atteint un état d’équilibre entre deux phases : une phase riche en carbone, composée d’amas de macromolécules, que nous appelons « solide » et d’une phase riche en oxygène et en hydrogène, composée de petites molécules, que nous dénommons « fluide ». L’évolution des parties solides de nos systèmes coïncide avec celle d’échantillons naturels de kérogènes de type IIIIn deep underground, organic residues decompose into a carbonaceous porous solid, called kerogen and a fluid usually composed of hydrocarbons and other small molecules such as water, carbon monoxide. The formation process of the kerogen remains poorly understood. Modeling its geological maturation could widen the understanding of both structure and composition of kerogen, and could be useful to oil and gas industry.In this work we adopt a purely thermodynamic approach in which we aim, through molecular simulations, at determining the thermodynamic equilibrium corresponding to the decomposition of given organic precursors of a specific type of kerogen –namely type III- under reservoir conditions. Starting from cellulose and lignin crystal structures we use replica exchange molecular dynamics (REMD) simulations, using the reactive force field ReaxFF and the open-source code LAMMPS. The REMD method is a way ofovercoming large free energy barriers, by enhancing the configurational sampling of a conventional constant temperature MD using states from higher temperatures.At the end of the simulations, we have reached for both systems, a stage where they can clearly be cast into two phases: a carbon-rich phase made of large molecular clusters that we call here the "solid" phase, and a oxygen and hydrogen rich phase made of small molecules that we call "fluid" phase.The evolution of solid parts for both systems and the natural evolution of a type III kerogen clearly match. Evolution of our systems follows the one of natural samples, as well as the one of a type III kerogen submitted to an experimental confined pyrolysis
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Rungta, Meha. "Carbon molecular sieve dense film membranes for ethylene/ethane separations." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/50121.
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The current work focused on defining the material science options to fabricate novel, high performing ethylene/ethane (C₂H₄/C₂H₆) separation carbon molecular sieve (CMS) dense film membranes. Three polymer precursors: Matrimid®, 6FDA-DAM and 6FDA:BPDA-DAM were used as precursors to the CMS membranes. CMS performances were tailored by way of tuning pyrolysis conditions such as the pyrolysis temperature, heating rate, pyrolysis atmosphere etc. The CMS dense film membranes showed attractive C₂H₄/C₂H₆ separation performance far exceeding the polymeric membrane performances. Semi-quantitative diffusion size pore distributions were constructed by studying the transport performance of a range of different penetrant gases as molecular sized probes of the CMS pore structure. This, in conjunction with separation performance data, provided critical insights into the structure-performance relationships of the CMS materials. The effects of testing conditions, i.e. the testing temperature, pressure and feed composition on C₂H₄/C₂H₆ separation performance of CMS dense films were also analyzed. These studies were useful not just in predicting the membrane behavior from a practical stand-point, but also in a fundamental understanding of the nature of CMS membrane separation. The study helped clarify why CMS membranes outperform polymeric membrane performance, as well as allowed comparison between CMS derived from different precursors and processing conditions. The effects on C₂H₄/C₂H₆ separation in the presence of binary gas mixture were also assessed to get a more realistic measure of the CMS performance resulting from competition and bulk flow effects. The current work thus establishes a framework for guiding research ultimately aimed at providing a convenient, potentially scalable hollow fiber membrane formation technology for C₂H₄/C₂H₆ separation
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Lassalle, Francis. "Conception et mise en oeuvre d'un reacteur d'epitaxie gainas/inp par la methode aux hydrures, analyse des conditions de croissance." Clermont-Ferrand 2, 1987. http://www.theses.fr/1987CLF2D193.
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Reacteur permettant la croissance de couches epitaxiques dans le systeme (ga,in,as,p) par transport en phase vapeur et par la methode aux hydrures (ph::(3),ash::(3),h::(2),hcl,in,ga). Sa conception autorise la realisation d'heterostructures a interfaces abruptes en conservant une geometrie de reacteur monochambre. Analyse des conditions de croissance du ternaire gainas sur support inp (100). Mise en evidence de l'effet du non equilibre entre les especes as::(2) et as::(4) sur la presence d'un depot parasite en amont de l'echantillon et sur les caracteristiques du depot. Proposition d'un modele rendant compte de l'influence des cinetiques de reactions de surface sur la composition en gallium de gainas
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Norberg, Elin. "Effekten av olika typer av biokol på metallers löslighet i förorenad urban jord." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-392512.
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Förorenade markområden utgör ett stort miljöproblem som orsakar spridning av toxiska metaller till grund- och ytvatten. Samtidigt är många metaller toxiska för djur och människor, vilket gör att markmiljön kan påverkas och risker för människors hälsa uppkommer om de vistas på platsen. I Sverige finns idag över 80 000 förorenade områden och saneringstakten anses inte vara tillräckligt snabb. Metallerna koppar (Cu), bly (Pb) och zink (Zn) hör till de allra vanligasteme tallföroreningarna i jord. Lösligheten av dessa är avgörande för hur biotillgängliga deär samt i hur stor utsträckning de kan spridas till yt- och grundvatten. Biotillgängligheten och halterna i yt- och grundvattnet har i sin tur stor betydelse för hur stor exponeringen blir för människor och djur. Biokol är ett organiskt material som genomgått kemisk omvandling i en syrefattig miljö vid höga temperaturer. Dessa framställningsbetingelser gör att biokol har stora möjligheter att fastlägga metaller genom adsorption till funktionella grupper på dess yta. Samtidigt fungerar biokol som ett jordförbättrande medel. Det anses även kunna lagra kol i upp till 1000 år och därmed fungera som en kolsänka. Biokol kan dessutom tillverkasav organiskt avfall vilket gör att avfallsströmmen minskar när detta framställs. I studien har sex olika biokol blandats in i en jord förorenad med Cu, Pb och Zn. Syftet var att undersöka hur inblandningen påverkade lösligheten av metallerna. Samtidigt testades också fastläggningen av metallerna till tre rena biokol. Det visade sig att lösligheten förändrades när biokolen blandades in i jorden. I pH-intervallet 4 - 6 minskade lösligheten av alla metaller. Det framkom att ett av biokolen var bättre på att fastläggametallerna än de andra. Detta biokol kom från anläggningen i Högdalen, Stockholm och var framställt av trädgårdsavfall.Contaminated ground constitutes an environmental problem that causes spread of metals to groundwater and surface water. Many of the contaminating metals are toxic to animals and humans and their spreading can cause negative effects on soil environment. In Sweden there are more than 80 000 contaminated sites and the decontamination rate is considered to be too slow. The metals copper, zinc and lead are some of the most common contaminants in soils. The solubility of these metals affects how bioavailable they are and how much they can spread to groundwater and surface water. Bioavailability and concentration in water is crucial for the exposure of metals to humans and animals. Biochar is an organic material that has been chemically transformed in an environment with little or no oxygen, at high temperatures. Due to these conditions, biochar is efficient for reducing the solubility of metals through adsorption to functional groups on its surface. Biochar also improve soil fertility, and it might also remain in the soil up to 1000 years and acts as a carbon sink. Furthermore, biochar can be produced from organic wastes and thus production of biochar can contribute to a reduced waste stream. In this study, six different samples of biochar were mixed with a contaminated soil containing copper, lead and zinc. The aim was to investigate how the adding of biochar would affect the solubility of the metals, since the solubility is crucial for the spread of metals and their bioavailability. The sorption of the metals in three pure samples of biochar was also tested. It was found that the solubility changed when biochar was addedto the soil. In the pH range 4 - 6, the solubility decreased for each metal. One of thebiochar samples had better sorption capacity in the soil than the others. This biochar was produced from garden wastes in Högdalen, Stockholm.
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Ndiaye, Fatou Toutie Lédé Jacques Ferrer Monique. "Pyrolyse de la biomasse en réacteur cyclone - Recherche des conditions optimales de fonctionnement." S. l. : INPL, 2008. http://www.scd.inpl-nancy.fr/theses/2008_NDIAYE_F_T.pdf.
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Benyattou, Abdelkader. "Thermohydrolyse de solutions d'aluminium III, conditions d'apparition de phases solides : caractérisations physico-chimiques des précipités." Lyon 1, 1994. http://www.theses.fr/1994LYO10071.
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La thermohydrolyyse, obention d'une phase solide par ebullition prolongee d'une solution initialement homogene, peut etre une technique interessante. Elle assure une bonne reproductibilite et limite la dispersion des proprietes texturales des solides obtenus. Des hydroxysulfates appartenant a la famille des alunites peuvent se former par thermohydrolyse de solutions de sulfate d'aluminium. L'influence de la composition des solutions a ete etudiee. Il est clairement etabli que l'alunite se forme en presence des cations na#+ ou nh#4#+ mais non pas en presence de li#+. Le rendement de precipitation croit lorsque les rapports so#4#2#-/al#3#+ avec (na#+ -o) et na#+ (ounh#4#+)al#3#+ augmentent. Une diminution rapide du ph apparait en meme temps que la temperature augmente: a l'ebullition le ph se stabilise pendant toute la duree de l'hydrolyse. L'utilisation des constantes d'hydrolyse et de complexation generalement admises, l'exploitation des spectres de la rnn de #2#7 al qui montrent le role du complexe al(h#2o)#5so#4#+, ont conduit a proposer un mecanisme dans lequel se forme d'abord l'anion al#3(h#2o)#8(os)#6(so#4)#2#-. Ensuite il se deshydrate et precipite avec l'alcalin, si ce dernier est suffisamment volumineux. La composition des solides obtenus depend etroitement de celle de la solution mere, la variation des parametres cristallins peut etre directement lies a la concentration des ions sodium de la solution. Par pyrolyse a l'air a environ 900c, les alubates conduisent a l'oxyde d'aluminium, al#2o#3 pour la natroalunite et al#2o#3 pour l'ammonialunite. La precipitation simultanee des ions mg#2s+ et al#3#+ par cette technique conduit a ph 12, a l'hydroxyde double mg#4al#2(08)#1#4, 3h#2o. Les conditions de synthese tres dures entrainent la formation de phases parasites. La modification du rapport al#3/mgh#2#+ entre 0,5 et 0,8
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Mounkassa, Michel Arsène. "Contribution à l'évaluation toxicologique des produits de thermolyse des matériaux dans diverses conditions de ventilation." Rouen, 1991. http://www.theses.fr/1991ROUEA002.
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Par la mise en oeuvre d'un appareillage complet de laboratoire permettant d'une part l'analyse physio-chimique des porduits de dégradation thermique des matériaux (modèle feu), d'autre part par l'exposition et l'analyse du comportement des animaux (modèle animal), la dynamique de production des toxiques et des réponses biologiques a pu être étudiée sur une série de matériaux utilisés dans le bâtiment et en aéronautique. Cette étude a montré que les risques liés à la thermodégradation des matériaux appartenant à une même famille chimique peuvent être différents. Il faut donc se référer à une exposition animale pour juger de la toxicité d'un matériau. Celle-ci ne doit pas être déduite à partir des résultats des études réalisées sur les matériaux voisins. L'influence de la ventiliation des enceintes de thermolyse a pu ensuite être appréciée. Sur l'ensemble des dangers potentiels d'ordre physico-chimique, l'influence de la ventilation se manifeste particulièrement sur l'inflammabilité et les émissions de CO et CO2. Sur le plan biologique, l'effet de la ventilation est plus marqué sur la mortalité. En prenant en compte toutes les données expérimentales, un classement des différents matériaux a été décrit en fonction du risque global.
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El, Ouachini Abdelkrim. "Etude de la détection des molécules neutres générées par ablation laser dans différentes conditions de longueur d'onde et d'irradiance." Metz, 1998. http://www.theses.fr/1998METZ053S.
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Les travaux menés ont pour objectif de présenter la conception de dispositifs expérimentaux permettant le couplage direct ou indirect entre la pyrolyse laser (Py laser) de matériaux organiques et leur analyse par chromatographie en phase gazeuse couplée à la spectrométrie de masse (GC/MS). Après avoir fait le point sur les techniques de pyrolyse analytique et sur le phénomène d'interaction laser-matière, ce mémoire décrit plus particulièrement l'instrumentation utilisée et les montages conçus au laboratoire pour mettre en place les deux types de couplage entre Py laser et GC/MS. Afin de mettre en évidence le rôle de la longueur d'onde et de l'irradiance, la partie expérimentale de ce travail s'est articulée autour de deux axes complémentaires. Le premier a consisté à étudier la réactivité d'agrégats carbones Cn de petite taille (n < 20) formes lors de l'interaction laser-graphite à une irradiance de 2. 10[à la puissance]9 W. Cm[à la puissance]-2 en présence de benzène en phase liquide ou gazeuse, utilisé pour piéger et solubiliser les composes formes. Ceux-ci sont concentrés avant d'être analysés : il s'agit d'un couplage Py laser - GC/MS indirect. La variation des paramètres expérimentaux (longueur d'onde du laser, état physique du benzène) a permis d'estimer leur influence sur la nature et la taille des molécules obtenues. Les résultats montrent l'importance du dimère C2 dans les processus de formation des agrégats carbonés. Le second axe de recherche a consisté à évaluer les performances d'une microcellule d'ablation laser et du système de transfert direct des pyrolysats vers l'appareil d'analyse. Au moyen de cette interface, nous avons réalisé la Py laser-GC/MS de cinq polymères synthétiques à une irradiance de 10[à la puissance]8 W. Cm[à la puissance]-2, plus faible que dans le cas de l'étude des Cn pour éviter les fragmentations excessives. Une empreinte caractéristique de la cible irradiée est obtenue pour chaque type de matériauThe purpose of this thesis is to present the conception of experimental devices which allow the direct or non-direct coupling between laser pyrolysis (Py laser) of organic materials and their analyses by Gas Chromatography/Mass Spectrometry (GC/MS). The report describes more precisely the instrumentation and the ablation cells used for the connection between Py laser and GC/MS. Two main laser probe parameters are studied under two complementary axes : the laser wavelength and the power density. The first experimental part consisted in the study of carbon clusters Cn (n < 20) reactivity generated during laser-graphite target interaction. The power density was fixed at 2. 10 9 W. Cm-2 and under liquid or gaseous benzen. The synthetized compounds are solubilized in benzen and concentrated before analysis. This approach is described as an non direct coupling between Py laser and GC/MS. It has been possible to show the influence of the laser experimental parameters (wavelength of the laser, physical state of benzen) on the size and on the composition of the generated clusters. Such way confirms the C2 cluster agregation process. From these results, a new ablation rnicrocell connected directly to the GC/MS has been conceived. By using a such on-line coupling, Py laser-GC/MS of five synthetic polymers were realized under 10 8 W. Cm-2. Such lower power density was necessary to avoid some carbon clusters fragmentation processes which could be a negative effect for samples identification
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Abraham, Grégory. "Etude et développement d'une méthode d'analyse par spectroscopie infrarouge appliquée à la pyrolyse d'hydrocarbures en conditions supercritiques et transitoires." Thesis, Orléans, 2009. http://www.theses.fr/2009ORLE2056/document.
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Un système d'échangeur à contre-courant, utilisant un carburant –endothermique-, est envisagé pour répondre au refroidissement d’un super statoréacteur. La mesure du débit de carburant décomposé et chauffé ainsi que celle de la composition chimique est nécessaire. Ceci permettra de contrôler et optimiser le fonctionnement d’un tel moteur, puisque sa poussée est principalement déterminée par la nature et le débit des espèces brûlées. La mise en place d’une méthode de caractérisation du fluide fait l’objet de cette étude. L’utilisation d’un spectromètre infrarouge à transformée de Fourier permet une analyse non intrusive des produits de pyrolyse. Cette technique est associée à un banc expérimental permettant la dégradation thermique d’un hydrocarbure en condition supercritique (jusque 60 bar, de 550°C à 900°C). Une méthode est réalisée pour obtenir une mesure quantitative et en ligne des produits majoritaires de la phase gazeuse. Celle-ci est basée sur un étalonnage avec les gaz majoritaires (méthane, éthylène, éthane, propylène et propane) et un traitement quantitatif de type CLS (Classical Least Square). La méthode est ensuite appliquée à l’étude de la pyrolyse en condition supercritique de différents hydrocarbures (alcanes linéaires purs et kérosènes du commerce). Les résultats de cette méthode sont comparés à ceux donnés par une technique chromatographique, et présentent de bonnes concordances (généralement moins de 5 % d'écart). Une approche en transitoire de la décomposition du n-dodécane par spectroscopie infrarouge a permis de suivre qualitativement l’évolution des produits de pyrolyseA system of heat hexchanger against the current, using an endothermic fuel, is considered to answer the cooling of a SCRAMJET engine. The measure of the mass flow rate of pyrolysed and heated fuel as well as the chemical composition is necessary. This will allow to control and to optimize the functioning of such engine, as his thrust is in most cases determined by the nature and the flow rate of burned species. This study bears on the development of a method of characterization of fluid. The use of a Fourier transformed infrared spectrometer allows a not interfering analysis of the products of pyrolysis. This technology is linked to an experimental bench allowing the thermal degradation of a hydrocarbon in supercritical condition (to 60 bar, from 550°C to 900°C). A method is accomplished to acquire a quantitative and online measure of the majority products of gaseous phase. This one is based on a calibration with majority gases (methane, ethylene, ethane, propylene and propane) and a quantitative treatment of CLS type (Classical Least Square). Method is then applied to study pyrolysis in supercritical condition of different hydrocarbons (linear alkanes and kerosenes of trade). The results of this method are compared with those given by a chromatographic technique, and introduce good agreement (less than 5 % of distance). An approach in transitional of the decomposition of the n-dodécane by infrared spectroscopy allowed to follow qualitatively the evolution of the pyrolysis products
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Placet, Vincent Perré Patrick. "Conception et exploitation d'un dispositif expérimental innovant pour la caractérisation du comportement viscoélastique et de la dégradation thermique du bois dans des conditions sévères." [S.l.] : [s.n.], 2006. http://www.scd.uhp-nancy.fr/docnum/SCD_T_2006_0102_PLACET.pdf.
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Elie, Marcel. "Effets des conditions temps-température et de la matrice minérale sur l'évolution de matières organiques de type II et III au cours de la pyrolyse en milieu confiné." Nancy 1, 1994. http://www.theses.fr/1994NAN10315.
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Une roche mère du toarcien du bassin de paris (broyée, sèche, humide), son kérogène isole et un charbon de la Mahakam ont été matur2s artificiellement en milieu confiné afin d'étudier les effets de la présence de matrice minérale, de la présence d'eau et du couple temps-température lors de la maturation thermique de la matière organique. 224 pyrolyses ont été réalisées sur ces différents précurseurs dans des conditions temps-température variables: 5 heures < t < 100 jours ; 203c < t < 508c. Les résultats obtenus indiquent que: la plupart des paramètres géochimiques sont décalés entre le kérogène et la roche mère en raison des propriétés de rétention des minéraux argileux ; l'influence catalytique des minéraux argileux est plus faible pour une roche mère que pour un mélange artificielle (kérogène + minéraux argileux) ; la présence d'eau (12%) induit un enrichissement du bitume résiduel en hydrocarbures ; l'eau intervient directement dans les processus de transfert d'hydrogène lors de la dégradation de la matière organique en milieu confiné ; le temps et la température ne sont pas des paramètres interchangeables. En effet, la dégradation des composes polaires s'intensifie avec la durée de pyrolyse alors que la dégradation des hydrocarbures est plus sensible à l'utilisation de températures élevées. Ces résultats montrent la nécessité de prendre en compte les différents facteurs (présence de matrice minérale, rôle de l'eau, effets combinés du temps et de la température) dés lors qu'il s'agit d'extrapoler
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Kretz, Thierry. "Etude de la cristallisation de silicium amorphe obtenu par pyrolyse de disilane par lpcvd dans des conditions ultra-pures. Application a la realisation de transistors mos en couche minces." Université Louis Pasteur (Strasbourg) (1971-2008), 1993. http://www.theses.fr/1993STR13216.
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L'objectif de ce travail est d'elaborer des transistors en couches minces en silicium polycristallin a gros grains, a partir de couches amorphes de haute purete realisees dans un reacteur de type uhvcvd et cristallisees thermiquement en phase solide. Les materiaux amorphes elabores a partir du gaz disilane, decompose a des temperatures variant de 460 a 540c, sont compares aux depots a base de gaz silane obtenus par pyrolyse a 550c. Les analyses sims revelent que les concentrations en oxygene et en carbone dans ces depots sont de plus de deux ordres de grandeur inferieures a celles rapportees dans la litterature pour des depots lpcvd. Par spectrometrie raman, nous montrons que pour une vitesse de depot identique, le silicium amorphe realise a partir du gaz disilane presente un degre de desordre structural superieur au silicium amorphe genere par le gaz silane. La cristallisation en phase solide des couches amorphes de haute purete est ensuite etudiee. L'evolution de la texture <111> des couches polycristallines en fonction des conditions de depot est determinee par diffraction de rayons x dans la configuration (-2). Une methode de suivi in situ (dans le four de recuit) de l'evolution de la conductance des couches, en fonction de la duree de recuit, combinee avec des observations en microscopie electronique de la variation de la taille des grains, pour differentes temperatures de cristallisation, nous permet de remonter aux energies d'activation du taux de nucleation, e#n, et de la vitesse de croissance, e#g, des cristallites. Les valeurs de e#n et e#g sont en bonne correlation avec la difference de taille de grains (plus d'un ordre de grandeur) observee entre les couches a base de silane et celles a base de disilane. Finalement nous montrons que l'utilisation du gaz disilane permet d'ameliorer les caracteristiques electriques (mobilite, tension de seuil, pente sous le seuil) des transistors en couches minces en silicium polycristallin
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Placet, Vincent. "Conception et exploitation d'un dispositif expérimental innovant pour la caractérisation du comportement viscoélastique et de la dégradation thermique du bois dans des conditions sévères." Phd thesis, Université Henri Poincaré - Nancy I, 2006. http://tel.archives-ouvertes.fr/tel-00116612.
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D'origine biologique, le bois présente des propriétés fortement variables rendant sa caractérisation parfois complexe. Une meilleure connaissance du comportement rhéologique et en particulier des propriétés viscoélastiques du bois est nécessaire au développement ainsi qu'à l'amélioration des processus de transformation et de fabrication de matériaux à base de bois utilisant ces propriétés.Ainsi, l'objectif majeur de cette thèse est de caractériser le comportement différé du bois vert dans des conditions thermiques et hydriques contrôlées. Un dispositif expérimental parfaitement adapté aux spécificités du bois, et en particulier à son anisotropie et son hygroscopie, a été développé. Cet appareil, appelé WAVET (Environmental Vibration Analyser for Wood) assure la détermination des propriétés viscoélastiques du bois par des essais harmoniques en flexion simple encastrement pour des fréquences comprises entre 5.10-3 Hz et 10 Hz. Dimensionné pour fonctionner jusqu'à des pressions de l'ordre de 5 bars, il permet d'effectuer des essais en milieu anhydre ou saturé pour des températures variant de 0°C à 140°C.
Les résultats expérimentaux collectés à l'aide de cet appareil sur diverses essences tempérées permettent de mettre en évidence l'influence de nombreux paramètres sur les propriétés rhéologiques et notamment au niveau de la température de ramollissement, à savoir l'essence, la direction matérielle, le type de bois (normal/réaction), ou encore la structure anatomique et macromoléculaire.
L'étude de la dégradation thermique du bois saturé en eau dévoile des modifications biochimiques importantes au sein de ce biopolymère. Il apparaît clairement que les propriétés de rigidité et d'amortissement du bois traité thermiquement en milieu aqueux évoluent en fonction de la sévérité du traitement et de la structure native des macromolécules constitutives.
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Mathis, Etienne. "Evaluation du risque d'inflammation de gaz imbrûlés au cours d'un incendie en milieu sous-ventilé." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2016. http://www.theses.fr/2016ESMA0012/document.
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Lors du déclenchement d’un incendie en milieu clos, la quantité d’oxygène du local décroît, entrainant une combustion incomplète. Des gaz chauds imbrûlés peuvent alors s’accumuler dans le local ou dans les gaines de ventilation et un accident thermique peut survenir suite à un apport d’air frais. Ce travail, réalisé pour AREVA, vise à quantifier et d’analyser ce risque, afin de pouvoir le prédire et le prévenir. Tout d’abord, une étude bibliographique a été réalisée afin de définir les paramètres d’auto-inflammation à partir du modèle de Frank-Kamenetskii. Celui-ci permet, après un bilan d’énergie, l’établissement d’un paramètre critique, δC, d’auto-inflammation du mélange. δC réunit la géométrie, la température (et la température ambiante) et la composition du mélange à l’auto-inflammation.Puis, la dégradation thermique du Polyéthylène Haute Densité en fonction de la densité surfacique de flux incident à la surface du matériau et de la sous-ventilation a été caractérisée (cinétique de dégradation, productions gazeuses). Le Cône Calorimètre à Atmosphère Contrôlée a été employé.Ce travail expérimental a permis d’obtenir plusieurs mélanges gazeux suivant les conditions. La dernière partie de l’étude a permis, à partir de δC, de poser le volume de mélange via le rayon comme critère d’auto-inflammabilité des mélanges. En imposant une température, en faisant varier la fraction volumique de chaque gaz combustible entre sa LII et LSI le risque d’accident thermique a été définiAfter the beginning of a fire in a closed room, the oxygen rate in the atmosphere decreases. This implies an incomplete combustion and unburnt gases production. These ones may accumulate in the room or in ventilation pipes, and, after mixing with fresh air, auto-ignite. This could trigger a thermal accident such as backdraft. This present work, conducted for AREVA, aims to analyse this hazard and provide some methods to predict and prevent it. First, a bibliographical research, was carried on to define a mixture’s auto-ignition parameters. This study was based on Frank-Kamenetskii’s model: after establishing the energetics balance between the heat produced by combustion, and the one consumed by conduction, an auto-ignition critical parameter, δC, was defined. It reunites the system’s geometry, temperature (or the room temperature) and composition.Then, the High Density Polythene degradation in a Controlled Atmosphere Cone Calorimeter was studied. The effect on the material’s degradation of under-ventilation and of the energy brought has been tested through the oxygen concentration in the atmosphere and the incident heat flux.During this work many different gas mixtures were analyzed. On the ground of δC formula, the final step was to set the volume, through the radius (characteristic size of the system), as an auto-ignition parameter. Making the concentration of each combustible varying between the LFL and UFL and imposing the temperature allowed to predict this hazard
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Boissiere, Francois Patrice. "Influence of pyrolysis conditions on macropore structure of char particles." Thesis, 1993. http://hdl.handle.net/1911/13694.
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A systematic analysis of the structure of char particles produced from an Illinois #6 coal was carried out. Coal particles were pyrolyzed in a hot-stage reactor under inert (N$\sb2$) and reactive (5% O$\sb2$ / 95% N$\sb2$) atmospheres at various heating rates (0.1, 1 and 10$\sp\circ$C/s) and final heat treatment temperatures (500 and 700$\sp\circ$C). Image analysis procedures were used to measure the size and macroporosity of the particles, and the surface area and size distribution of the macropores.
High heating rates and the addition of oxygen resulted in larger particle swelling and increased the macroporosity, the surface area and the fraction of large macropores with thin walls. Heat treatment temperatures had smaller effects on char particle structure. Our data confirm the strong effects of pyrolysis conditions on char reactivity during combustion in the diffusion-limited regime. They also provide the necessary parameters for char combustion models.
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Ismail, Ahmad Faris. "The effect of process conditions on coal pyrolysis and char reactivity." Thesis, 1994. http://hdl.handle.net/1911/16741.
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The effect of process conditions on coal pyrolysis and char reactivity is systematically studied using the thermogravimetric reactor equipped with in-situ video microscopy imaging (TGA/VMI). This system provides a complete time-registered record of the history of single coal particles as they are sequentially pyrolyzed and combusted in the reactor. Three coals are investigated: Illinois #6, Utah Blind Canyon, and Wyodak-Anderson seam.
An image analysis procedure was developed to monitor the transient swelling pattern of the two plastic coals (Illinois and Utah). Particle swelling increases with increasing pyrolysis heating rate and increasing particle size. When pyrolyzed in reactive atmospheres, these coals exhibit less plasticity and less "bubbling", but they swell more. The maximum devolatilization rate occurs during the stage of vigorous "bubbling." Since the Wyodak coal is not plastic, it does not swell during pyrolysis.
Process conditions affect char ignition behavior. Particles will ignite more easily when the observed reaction rates are high and heat removal rates are low. During combustion in the presence of intraparticle diffusional limitations, we observed that large char particles and chars produced at high pyrolysis heating rates ignite more easily. Increased particle sizes slow the heat removal rates, while high pyrolysis heating rates produce chars with larger macroporosities and macropore surface areas thus enhancing the reaction rates. Chars produced in reactive pyrolysis atmospheres appear to be more reactive and ignite more easily. Experiments at low temperatures show that the pyrolysis heating rate, particle size, and pyrolysis atmosphere do not affect the reactivity pattern in the kinetic control regime.
We also developed a steady-state mathematical model for char particle ignition. Model parameters were obtained from structural measurements for the Illinois #6 chars. The model predicts that the ignition temperature decreases with decreasing gas flow rate and increasing pyrolysis heating rate, increasing oxygen concentration and increasing particle size. Model predictions are in excellent agreement with our experimental data.
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Benfell, Katharine Elaine. "Assessment of char morphology in high pressure pyrolysis and combustion." Thesis, 2001. http://hdl.handle.net/1959.13/1312422.
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Research Doctorate - Doctor of Philosophy (PhD)Drives to reduce carbon dioxide emissions and improve efficiency make pressurised gasification an attractive option in future coal utilisation technologies. Process conditions in pressurised gasification differ from conventional entrained flow combustion in pressure, atmosphere, peak temperature and heating rate, yet there is sparse literature concerning coal behaviour under pressurised conditions. Previous work suggests that bituminous coals can show enhanced plasticity at high pressures and this phenomenon may not be predicted by standard tests of coking properties. Previous modelling of char reactivity and burnout in combustion and gasification has failed to take account of the petrographic variability of coals. Current work to improve the predictive capacity of these models requires evaluation of the effects of different macerals and of char preparation pressure on char behaviour. Prior studies of whole coals subjected to high pressure and high temperature conditions have shown that daughter char morphology is influenced by particle heating rate, the size distribution of the feed coal, furnace pressure, feed rate, coal rank and the parent coal petrography. Chars were produced by pyrolysis at 1100 or 1300 °C and 1, 5, 8, 10 and 15 atm furnace pressure, and by combustion at 1100 °C and 1 atm furnace pressure, from a suite of East Australian bituminous coals. The characteristics of the chars and their parent feed coals were quantified using semi-automated image analysis, as well as petrographic, particle size and chemical analyses. Relationships between the morphology of the chars and properties of the parent coal and furnace pressure were established. Daughter char morphology and volatile yield was found to be related to the petrographic composition of the parent feed coals, their full reflectance profiles and the char preparation pressure. Chars derived from vitrinite-rich lithotypes and those prepared under high pressure conditions show larger mean diameters, porosities, sphericities and proportions of porous char types. Volatile yield is related to the vitrinite content of the lithotype. A parameter derived from full coal reflectograms proves to be effective for prediction of char morphology and trends in volatile yield. The Carbon Burnout Kinetic model is improved in its predictive value by including parent coal vitrinite content as an input parameter and could be further improved by utilising the full coal reflectogram parameter.
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Rathnam, Renu Kumar. "Pulverised coal combustibility in simulated oxyfuel (O₂/CO₂) and air (O₂/N₂) conditions." Thesis, 2012. http://hdl.handle.net/1959.13/936144.
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Research Doctorate - Doctor of Philosophy (PhD)The need for reducing emissions on a large scale to mitigate climate change has led to the development of new carbon capture and storage (CCS) technologies such as oxyfuel combustion. Oxyfuel combustion, as the name suggests, is a technology in which fuel is burnt in oxygen rather than air to reduce the nitrogen content of the flue gas and thereby producing a concentrated stream of carbon dioxide almost ready for sequestration. In oxyfuel combustion a part of the flue gas, concentrated in CO₂, is recirculated back into the furnace mainly to reduce the high furnace temperatures. Hence, the combustion atmosphere is mainly O₂/CO₂ under oxyfuel conditions whereas in conventional air combustion, the atmosphere is mainly O₂/N₂. This major difference in the combustion conditions (the high CO₂ concentrations) affects major processes such as fuel combustion, heat transfer, and emissions inside the furnace. Hence, further development of this technology greatly relies on understanding the combustion and other processes under O₂/CO₂ conditions, with high CO₂ levels, as most current data and models available from air combustion may not suit pulverised coal combustion under oxyfuel conditions. This study deals in studying the combustion of pulverised coal in both O₂/CO₂ and O₂/N₂conditions concurrently. Data from the current study will help understand pulverised coal combustion under oxyfuel conditions and also enable direct comparison with the results obtained under air conditions. Coals of different ranks obtained from various regions of the world were selected to widen the scope of the study. In total, eight coals were used for the experiments, out of which three of them were mainly studied. Coals ranged from lignite to semi-anthracite and were obtained from were obtained from Australia, South Africa, Poland, and Germany. The combustion rates and reactivities were measured using a Drop Tube Furnace (DTF) and a Thermogravimetric analyser (TGA). The coal samples were analysed using proximate, ultimate, and petrographic analyses. Particle size measurements and scanning electron microscope studies were carried out on coal and char samples. Internal surface area measurements were performed on char samples. Chars were formed in the DTF at 1400 °C in N₂ and CO₂ atmospheres for the isothermal TGA tests. Combustion measurements were mainly carried out in the DTF and TGA under various O₂ levels, ranging from 0 to 21% v/v basis, in O₂/N₂ and O₂/CO₂ atmospheres to simulate air and oxyfuel conditions respectively. Furnace temperatures were also varied in the DTF and the TGA tests in the range of 1000 to 1400 °C and 800 to 1000 °C respectively. Coal burnouts were measured in the DTF tests and char combustion rates were estimated from the coal burnout data. The char mass loss rates were measured in the TGA tests for reactivity assessment. Results from the current studies show that the char-CO₂ gasification reaction plays an important role under O₂/CO₂ conditions. Higher or similar volatile yields and coal/char burnouts were measured under CO₂ and O₂/CO₂ atmospheres respectively, in DTF experiments, in comparison to N₂ and O₂/N2₂conditions respectively. The results from the DTF experiments were supported by higher mass loss rates and endothermic reactions indicated in O₂/CO₂ atmospheres during TGA experiments. The effect of the char-CO₂ gasification reaction depended on the coal type, furnace (particle) temperatures, and O₂ levels in the gas. The lower rank lignite tested in the study exhibited significantly higher mass loss/burnout under O₂/CO₂ conditions when compared to the other higher rank coals used in the study. The increase in mass loss rates/burnouts due to the char-CO₂ gasification was enhanced by lower O₂vlevels and higher furnace temperatures. While the diffusion of O₂ in CO₂ is slower than that in N₂, similar burnouts and combustion rates were observed in O₂/N₂ and O₂/CO₂ conditions. Under diffusion limited conditions, at very high particle temperatures, the char combustion rates are slower under O₂/CO₂ conditions, however, the char-CO₂ gasification reaction may compensate for the slower diffusivity. However, this depends on the coal type/rank as well, as the char-O₂ oxidation is comparatively faster and under diffusion limited conditions, the char-CO₂ gasification may not have sufficient residence time to have a significant effect on the char combustion rate. This study has shown that the char-CO₂ gasification reaction may contribute to the overall char combustion rate under O₂/CO₂ conditions depending on the O₂ level, the particle temperature, and the coal type. Under practical combustion conditions, as simulated in the current study using the DTF experiments, there may not be major differences in the coal burnout in air and oxyfuel conditions due to the reasons mentioned above. Even though the coal burnouts may appear similar apparently, the mechanisms of coal combustion including the volatiles release and combustion, char formation, and char combustion, have to be modelled specifically for O₂/CO₂ conditions in order to understand and predict the coal burnout and emissions. The char-CO₂ gasification reaction should be included in the models. Experimental data from the current study may be used for future modelling studies under O₂/CO₂ conditions.
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Bhatia, Tania. "Phase Evolution In The MgO-MgAl2O4 System Under Non-Equilibrium Processing Conditions." Thesis, 1997. http://etd.iisc.ernet.in/handle/2005/2136.
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Chen, Yen-Chang, and 陳延昌. "Study on the development of a novel fast pyrolysis unit for converting biomass to bio-oil and the optimal operational conditions." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/85316280510628599936.
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博士國立臺灣大學
機械工程學研究所
99
A novel fast pyrolysis reactor for converting biomass into bio-oil has been developed in this study. A reaction chamber equipped with a single tapered screw extruder was designed for simultaneous feeding and pyrolyzing the biomass. The screw extruder is chain-driven by a motor with adjustable rotation speed. In the system development, the aim is to have the capability and simplicity to achieve high production rate, so that it can be easily scaled up with low cost. Moreover, the screw extruder was made of a special type of cast iron having excellent heat resistance and low thermal expansion coefficient, so distortion or warp and hence interference of the screw extruder can be prevented during the operation. The effect of pyrolysis temperature (ranging from 460~560oC) on bio-oil yield was investigated for cedar, camphor and jatropha trees. The experimental results, indicate that the highest bio-oil yields of 42.9 wt% can be obtained for cedar tree with 18.73 MJ/kg HHV at 520oC. For camphor and jatropha trees, the highest bio-oil yields respectively reach 49.6 wt% with 19.14 MJ/kg HHV at 500oC and 41.6 wt% with 31.41 MJ/kg HHV at 560 oC. The effects of process parameters of camphor tree biomass grain size (ranging from 0.425 to 3.35mm), rotational speed (ranging from 20 to 60rpm) and the pyrolysis temperature (ranging from 400 to 550 oC) on the yield of bio-oil were investigated in this study by using a fast pyrolysis reactor with a single tapered screw extruder. This study gives the optimal pyrolysis temperatures and rotational speeds for different grain sizes to achieve peak bio-oil yield. The results indicate that higher feed rates are required for larger grain sizes to achieve peak bio-oil yields. Taguchi experimental design method and the SPSS (Statistical Package for Social Sciences) multiple regression analysis software were employed to analyze the effects of key process parameters for camphor. The results showed that the optimal pyrolysis temperature depends on the grain size and rotation speed. (1) At fixed 20rpm feed rare, the pyrolysis temperature was varied from 400 to 550oC for different grain sizes to attain the optimal pyrolysis temperatures. For the grain size of 0.425~0.6mm and 0.6~0.85mm, the peak bio-oil yields were obtained at 470oC respectively with 60.4wt% and 58.2wt%. In addition, at 500oC the peak bio-oil yields reached 50.2wt%, 57.6wt%, 52.5wt%, 53.0wt%, 50.8wt% respectively for the grain sizes of <0.425mm, 0.85~1.18mm, 1.18~1.70mm, 1.70~2.50 mm and 2.50~3.35mm. (2) At constant temperature of 500oC, the rotation feed rate was varied from 20 to 60 rpm for different grain sizes. Based upon the experimental results was then conducted to evaluate the effect of rotational speed, ranging from 20rpm to 60rpm, on the yield of bio-oil for different biomass grain sizes. The results show that different optimal pyrolysis temperatures and rotational speeds are required for different grain sizes to achieve peak liquid yield. In addition, when larger grain sizes were used, higher feed rates were required to achieve peak bio-oil yield, implying that a significant increase in productivity is resulted. This implies that the productivity of bio-oil can be significantly increased in the current system. For the case of 2.5~3.35mm grain size, which corresponds to an optimal rotational speed of 40rpm, the production rate was estimated to be around 4kg/h. From the experiments, we can see the production yield and high heating value of the bio-oil were influenced by the process parameters (grain size, pyrolysis temperature, and biomass feed rate). The S/N ratios were obtained using Taguchi’s methodology. Here, the intended objective is to obtain higher product yields. Hence, the larger the better type S/N ratio was used to transform the yields of the bio-oil. Therefore, the SPSS multiple regression analysis was performed to obtain the regression formulae that correlate the production yield (Y, dependent variable) with the process parameters (pyrolysis temperature, X1：450oC, 470oC and 500oC , feed rate, X2：20rpm, 40rpm and 60rpm, and grain size, X3：0.425mm, 1.70mm and 3.35mm). The regression formula model is as follows: Y = a + b1X1 + b2X2 + b3X3 + e, where a is the interception, b1, b2, and b3 are the regression factors, and e is the random error. The obtained formula is: Ycamphor = 1409.04+0.00672X12–0.0519X22–6.253X32 + 0.0071X1X2–0.133X1X3+ 0.157X2X3–6.221X1+ 87.99X3
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GLASS, MICHEAL WALTER. "STEREOLOGICAL ANALYSIS OF THE MACROPORE STRUCTURE OF CHARS PRODUCED UNDER VARIOUS PYROLYSIS CONDITIONS AND THE INFLUENCE OF MACROPORE STRUCTURE ON CHAR GASIFICATION RATES IN THE PRESENCE OF STRONG DIFFUSIONAL LIMITATIONS." Thesis, 1987. http://hdl.handle.net/1911/16059.
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The effects of pyrolysis heating rates, particle size and ash upon the macropore structure of coal-derived chars were investigated for an Illinois #6 and a lignite coal. A new direct method was used to characterize the macropore structure of the chars. Polished cross-sections of char particles were analyzed with an integrated video microscopy/digital image processing system. Pore size analysis combined a stereological model and digital image processing techniques to overcome the limitations of indirect methods. Obtained results were used to investigate the effects of the macropore structure on global gasification rates under conditions of strong intraparticle diffusional limitations. Simulations employed a two-dimensional discrete model and image processing techniques to treat the reaction of the complex pore structures observed.
The coals were pyrolyzed in nitrogen to 900$\sp\circ$C with a microcomputer- controlled, heated wire-mesh reactor at heating rates between 0.1$\sp\circ$C/s and 1000$\sp\circ$C/s. The Illinois #6 char showed an increasingly complex macropore structure as the heating rate was increased. Measurements revealed a definite shift toward the formation of cellular structures with thin-walled large and small cavities. Pyrolysis heating rates had virtually no effect on the macropore structure of lignite chars. Three fractions of Illinois #6 coal with different particle sizes were also pyrolyzed at 10$\sp\circ$C/s. The char from the smallest size fraction exhibited a few large primary cavities but very little secondary pore formation was present. In contrast, the chars from the larger size fraction contained a large amount of secondary pores. The presence of ash during the pyrolysis process appeared to have very little effect on the development of the macropore structure.
Discrete modeling of char gasification with strong diffusional limitations showed that the wide variation of macropore structure exhibited by the Illinois #6 chars had a marked effect on the global gasification rates. An increase in the amount of secondary pores formed at the higher heating rates and larger particle sizes produced much more pronounced maxima in the rate vs conversion curves.
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Xavier, Isaac de Melo Jr. "Electron energy-loss spectroscopy study of polyatomic molecular systems under pyrolytic conditions." Thesis, 1989. https://thesis.library.caltech.edu/8005/2/Xavier%2C%20Jr_1989.pdf.
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The technique of variable-angle, electron energy-loss spectroscopy has been used to study the electronic spectroscopy of the diketene molecule. The experiment was performed using incident electron beam energies of 25 eV and 50 eV, and at scattering angles between 10° and 90°. The energy-loss region from 2 eV to 11 eV was examined. One spin-forbidden transition has been observed at 4.36 eV and three others that are spin-allowed have been located at 5.89 eV, 6.88 eV and 7.84 eV. Based on the intensity variation of these transitions with impact energy and scattering angle, and through analogy with simpler molecules, the first three transitions are tentatively assigned to an n → π* transition, a π - σ* (3s) Rydberg transition and a π → π* transition.
Thermal decomposition of chlorodifluoromethane, chloroform, dichloromethane and chloromethane under flash-vacuum pyrolysis conditions (900-1100°C) was investigated by the technique of electron energy-loss spectroscopy, using the impact energy of 50 eV and a scattering angle of 10°. The pyrolytic reaction follows a hydrogen-chloride α-elimination pathway. The difluoromethylene radical was produced from chlorodifluoromethane pyrolysis at 900°C and identified by its X^1 A_1 → A^1B_1 band at 5.04 eV.
Finally, a number of exploratory studies have been performed. The thermal decomposition of diketene was studied under flash vacuum pressures (1-10 mTorr) and temperatures ranging from 500°C to 1000°C. The complete decomposition of the diketene molecule into two ketene molecules was achieved at 900°C. The pyrolysis of trifluoromethyl iodide molecule at 1000°C produced an electron energy-loss spectrum with several iodine-atom, sharp peaks and only a small shoulder at 8.37 eV as a possible trifluoromethyl radical feature. The electron energy-loss spectrum of trichlorobromomethane at 900°C mainly showed features from bromine atom, chlorine molecule and tetrachloroethylene. Hexachloroacetone decomposed partially at 900°C, but showed well-defined features from chlorine, carbon monoxide and tetrachloroethylene molecules. Bromodichloromethane molecule was investigated at 1000°C and produced a congested, electron energy-loss spectrum with bromine-atom, hydrogen-bromide, hydrogen-chloride and tetrachloroethylene features.