Master of Science / Mercury is the most mysterious planet in the inner Solar System, suggested by observations from the MESSENGER mission. These observations shine a light on potential processes occurring within Mercury as it evolved over time. Scientific instruments aboard MESSENGER indicate that Mercury has a very thin surface layer of broken rocks, a thin crustal layer covered by lavas erupted from a melt formed in a relatively thin, FeO poor mantle, and a large metal rich core made from Fe and some quantity of a light element. These conditions are different than those seen on Earth: a thick crust covered by a layer of varied thickness made up of loose unconsolidated rocks and dust, a large mantle with more FeO, and a smaller core to planet ratio. To understand how these non-Earth like conditions affect how the planet's interior changes with time, a modified evolution model was created to track the changes in heat and chemistry within Mercury. This model accounts for complications like a dynamic core density that changes with a growing inner core, the formation method of the inner core, and the FeO poor mantle composition. Using this model offers illumination on the conditions Mercury experienced after it formed. This model is limited, but results suggest that Mercury's mantle began at an initial mantle temperature of 1600 K, and a mantle reference viscosity of 1021–1022 Pa s, indicating the mantle was less likely to flow easily. Model results also suggest the core contained some sulfur from 0.05–8.9 wt.% S, derived from the MESSENGER data. BepiColombo, a new Mercury mission, will provide some perspectives on the interior of Mercury, leading to more detailed information about conditions present after planetary formation and the effect of non-Earth like conditions on a planet's interior as it cools.

A novel study on the investigation of three very common atmospheric sulphur species relevant to the Mpumalanga Highveld subregion was conducted. Long-term in situ measurements were applied in the diurnal and seasonal evaluation of the observed sulphur species. Ambient pollutant concentrations and surface meteorological data were collected at an air quality monitoring station at Elandsfontein. Elandsfontein air quality monitoring station was ideal for the observations due to its high elevation within the Mpumalanga Province surrounded by few rolling hills and negligible windbreaks which easily allows for extensive plume-contact with the surface during convective daytime mixing. The temporal characteristics of the sulphur species have been assessed relative to one another with varying meteorological conditions. The diurnal and seasonal concentration variations were used to describe the physical characteristics exhibited by the compounds over Elandsfontein. Pollution roses were used to target the source of the major release points and areas of these sulphur species relative to the Elandsfontein monitoring station. Gas and particle concentrations were analysed in relation to varying meteorological parameters with a view to ascertaining the sulphur transformation and concentration distribution in the planetary boundary layer. Particulate sulphate distribution has been modelled through multivariate regression analyses in relation to three meteorological parameters, namely, wind speed, relative humidity and ambient temperature for the various seasons observed over southern Africa. This study has shown that hydrogen sulphide, sulphur dioxide and sulphate species are present throughout the year in the Mpumalanga Highveld at notably significant levels. The presence of ambient particulate sulphate has been shown to result from the combination of chemical interactions during long-range aerosol transport; atmospheric recirculation processes shown from back trajectories over the southern Africa sub-region, as well as the variation in the removal mechanisms and rates for the different seasons throughout the year. These transport and removal processes all contribute to the overall sulphur mass balance in the planetary boundary layer. Dosage of the three sulphur species was evaluated to provide data for sulphur pollution loading that could form a basis for health and vii environmental impact assessments over the area. In view of the characteristic patterns displayed by particulate sulphate, multivariate mathematical models have been developed on a seasonal basis with variations in meteorological parameters. This was seen to predict an accuracy of up to 70 % of the particulate sulphate loading for different seasons over the South African Highveld. In order to understand the chemical interactions of atmospheric sulphur species, it is important to be able to predict the route taken and expected products of transformation on any given condition. Theoretical analyses of the chemical thermodynamic properties of the known reacting species and a well-established approach were used in predicting reaction paths and establishing the possible and feasible products of chemical transformation in relation to the ambient temperature. The determination of reaction paths and possible products of chemical transformation provides a measure of the relative importance of the reacting species and the mechanism of reaction. Gas-, aqueous-phase and radical reactions involving sulphur (IV) were investigated with a view to establishing their relative importances. Thermochemical properties of several sulphur-containing compounds not available in the literature have been generated for evaluation of Gibbs free energy (ΔG) and enthalpy (ΔH). An electronic energy structural approach has been applied to model for ΔG and ΔH of 88 sulphur species in 90 chemical reactions comprising gas-phase, aqueousphase and radical reactions. Modelling was evaluated for their relative importances over a temperature range of –100 °C to +100 °C. The temperature range is well above the known tropospheric temperature range to account for variations in the atmospheric environment. To further comprehend the chemistry of sulphur with regards to distribution of the species in the atmosphere, a kinetic model is developed and incorporated into a dispersion model. The kinetic evaluation of the oxidation rate of SO2 to sulphate has been determined with advection and dispersion over the Elandsfontein area. Gas-phase transformation with advection and dispersion has been used to evaluate the extent of the distribution of SO2 relative to the major contributing sources. The dry deposition was considered to be the dominant removal mechanism. It was assumed that the reaction rate was second order in concentration and that the rate of deposition was first order. The oxidation rates obtained for the seasons were 10.9 % h-1 for summer; 8.83 % h-1 for autumn; 6.56 % h-1 for winter; viii 10.8 % h-1 for spring, while an overall rate of 9.6 % h-1 was obtained for the one year study period. The transformation rate model produced a reaction constant and an activation energy of 4.92 x 10-6 μg m-3 s-1 and 36.54 kJ kg-1 for summer; 3.939 x 10-6 μg m-3 s-1 and 43.89 kJ kg-1 for autumn; 2.90 x 10-6 μg m-3 s-1 and 115.69 kJ kg-1 for winter; 4.82 x 10-6 μg m-3 s-1 and 43.29 kJ kg-1 for spring, while for the year 4.29 x 10-6 μg m-3 s-1 and 34.31 kJ kg-1. A Gaussian puff unsteady state Lagrangian dispersion model with reflection at the surface and inversion layer was applied for concentration diffusion. The Lagrangian dispersion model with dry deposition was a better prediction of the observed data than the models from previous studies using a first order rate constant with or without deposition rate.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo deste trabalho é a aplicação de um Planejamento Fatorial Completo, ferramenta estatística que auxiliará a obter dados empíricos para otimizar um tratamento termoquímico, a cementação. Partindo-se de um levantamento da profundidade de camada cementada e da dureza de uma corrente de aço de baixo teor de carbono, usada para amarração, e para resistir à abrasão reproduziu-se uma nova cementação, variando-se seus parâmetros de influência, para se alcançar o ponto ótimo, definindo o melhor aço e o melhor processo. Foram realizados dois planejamentos, um fatorial 2 e dois 2, comparando o comportamento do processo na prática em relação aos resultados teóricos de uma simulação computacional, que permite a obtenção das curvas de enriquecimento de carbono, baseado na segunda Lei de Fick, para várias condições de contorno. Os perfis teóricos de cementação apresentaram valores de profundidade efetiva próximos aos valores obtidos experimentalmente, evidenciando o planejamento realizado.

Ce travail de thèse porte sur l’étude et le développement de matériaux adaptés pour la conversion et le stockage thermochimique de l’énergie solaire concentrée à haute température (400-1200°C), en utilisant des réactions solide-gaz réversibles. Ce type de stockage peut être associé aux centrales solaires thermodynamiques pour la génération d’électricité. Une étude bibliographique a permis d’identifier et de sélectionner les matériaux les plus adaptés possédant une densité d’énergie élevée pour le stockage thermochimique, suivant les critères de domaine de température et de non-toxicité requis. Les matériaux sélectionnés sont des oxydes métalliques (de Fe, Mn, Co, Cu), ainsi que des carbonates et des hydroxydes (de Ca, Sr, Ba). Les travaux ont porté ensuite sur les équilibres thermodynamiques des systèmes afin de prévoir les températures de transition et capacités de stockage théoriques. Une étude expérimentale a également été effectuée avec pour objectifs de déterminer précisément les niveaux de température, capacités de stockage en oxygène et enthalpies pour chaque réaction, et de démontrer leur réversibilité complète sur plusieurs cycles successifs. Des oxydes métalliques mixtes (systèmes binaires de Co-Cu, Co-Fe, Mn-Fe, Mn-Co, Mn-Cu) et des pérovskites substituées sur sites A et B ont été développés afin d’optimiser les propriétés redox des matériaux pour le stockage thermochimique. Concernant les carbonates et les hydroxydes de Ca, Sr, Ba, l’addition d’un agent stabilisant (MgO) a permis d’améliorer la stabilité des matériaux et la réversibilité des réactions au cours des cycles. Enfin, un nouveau réacteur thermochimique solaire, permettant la conversion en continu de particules réactives solides, a été validé expérimentalement et optimisé dans le cas de la décomposition de CaCO3 pour le stockage de l’énergie solaire. / This PhD thesis deals with the study and development of suitable materials for thermochemical conversion and storage of concentrated solar energy at high temperature (400-1200°C), by using reversible solid-gas reactions. This type of storage can be associated with solar thermal power plants. A bibliographic survey was performed to identify and select the most promising materials with a high energy storage density for thermochemical storage, based on different required criteria. The selected materials are metal oxides (of Fe, Mn, Co, Cu), carbonates and hydroxides (of Ca, Sr, Ba). The work then focused on the thermodynamic equilibria to determine the theoretical transition temperatures and energy storage capacities of the selected materials. An experimental study was carried out in order to determine the reaction temperatures, oxygen storage capacities and enthalpies for each reaction, and to demonstrate their complete reversibility upon cycling. Mixed metal oxides (binary systems of Mn-Fe, Co-Fe, Co-Cu, Mn-Cu, Mn-Co) and A- and B-site substituted perovskites were developed to optimize their thermochemical energy storage properties. Regarding carbonates and hydroxides of Ca, Sr, Ba, the addition of a stabilizing agent (MgO) allowed improving the materials cycling stability and reactions reversibility during successive cycles. Finally, a novel lab-scale solar reactor was experimentally tested in order to investigate the continuous decomposition of CaCO3 particles for thermochemical solar energy storage application.

<p>Black liquors are presently combusted in recovery boilers where the inorganic cooking chemicals are recovered and the energy in the organic material is converted to steam and electricity. A new technology, developed by Chemrec AB, is black liquor gasification (BLG). BLG has more to offer compared to the recovery boiler process, in terms of on-site generation of electric power, liquid fuel and process chemicals. A prerequisite for both optimization of existing processes and the commercialization of BLG is better understanding of the physical and chemical processes involved including interactions with the refractory lining. The chemistry in the BLG process is very complex and to minimize extensive and expensive time-consuming studies otherwise required accurate and reliable model descriptions are needed for a full understanding of most chemical and physical processes as well as for up-scaling of the new BLG processes. However, by using these calculated model results in practice, the errors in the state of the art thermochemical data have to be considered. An extensive literature review was therefore performed to update the data needed for unary, binary and higher order systems. The results from the review reviled that there is a significant range of uncertainty for several condensed phases and a few gas species. This resulted in experimental re-determinations of the binary phase diagrams sodium carbonate-sodium sulfide (Na2CO3-Na2S) and sodium sulfate-sodium sulfide (Na2SO4-Na2S) using High Temperature Microscopy (HTM), High Temperature X-ray Diffraction (HT-XRD) and Differential Thermal Analysis (DTA). For the Na2CO3-Na2S system, measurements were carried out in dry inert atmosphere at temperatures from 25 to 1200 °C. To examine the influence of pure CO2 atmosphere on the melting behavior, HTM experiments in the same temperature interval were made. The results include re-determination of liquidus curves, in the Na2CO3 rich area, melting points of the pure components as well as determination of the extent of the solid solution, Na2CO3(ss), area. The thermal stability of Na2SO3 was studied and the binary phase diagram Na2SO4-Na2S was re-determined. The results indicate that Na2SO3 can exist for a short time up to 750 °C, before it melts. It was also proved that a solid/solid transformation, not reported earlier, occurs at 675 ± 10 °C. At around 700 °C, Na2SO3 gradually breaks down within a few hours, to finally form the solid phases Na2SO4 and Na2S. From HTM measurements a metastable phase diagram including Na2SO3, as well as an equilibrium phase diagram have been constructed for the binary system Na2SO4-Na2S. Improved data on Na2S was experimentally obtained by using solid-state EMF measurements. The equilibrium constant for Na2S(s) was determined to be log Kf(Na2S(s)) (± 0.05) = 216.28 – 4750(T/K)–1 – 28.28878 ln (T/K). Gibbs energy of formation for Na2S(s) was obtained as ΔfG°(Na2S(s))/(kJ mol–1) (± 1.0) = 90.9 – 4.1407(T/K) + 0.5415849(T/K) ln (T/K). The standard enthalpy of formation of Na2S(s) was evaluated to be ΔfH°(Na2S(s), 298.15 K)/(kJ mol–1) (± 1.0) = – 369.0. The standard entropy was evaluated to be S°(Na2S(s), 298.15 K)/(J mol–1 K–1) (± 2.0) = 97.0. Analyses of used refractory material from the Chemrec gasifier were also performed in order to elucidate the stability of the refractory lining. Scanning electron microscopy (SEM) analysis revealed that the chemical attack was limited to 250-300 μm, of the surface directly exposed to the gasification atmosphere and the smelt. From XRD analysis it was found that the phases in this surface layer of the refractory were dominated by sodiumaluminosilicates, mainly Na1.55Al1.55Si0.45O4.</p>

Black liquors are presently combusted in recovery boilers where the inorganic cooking chemicals are recovered and the energy in the organic material is converted to steam and electricity. A new technology, developed by Chemrec AB, is black liquor gasification (BLG). BLG has more to offer compared to the recovery boiler process, in terms of on-site generation of electric power, liquid fuel and process chemicals. A prerequisite for both optimization of existing processes and the commercialization of BLG is better understanding of the physical and chemical processes involved including interactions with the refractory lining. The chemistry in the BLG process is very complex and to minimize extensive and expensive time-consuming studies otherwise required accurate and reliable model descriptions are needed for a full understanding of most chemical and physical processes as well as for up-scaling of the new BLG processes. However, by using these calculated model results in practice, the errors in the state of the art thermochemical data have to be considered. An extensive literature review was therefore performed to update the data needed for unary, binary and higher order systems. The results from the review reviled that there is a significant range of uncertainty for several condensed phases and a few gas species. This resulted in experimental re-determinations of the binary phase diagrams sodium carbonate-sodium sulfide (Na2CO3-Na2S) and sodium sulfate-sodium sulfide (Na2SO4-Na2S) using High Temperature Microscopy (HTM), High Temperature X-ray Diffraction (HT-XRD) and Differential Thermal Analysis (DTA). For the Na2CO3-Na2S system, measurements were carried out in dry inert atmosphere at temperatures from 25 to 1200 °C. To examine the influence of pure CO2 atmosphere on the melting behavior, HTM experiments in the same temperature interval were made. The results include re-determination of liquidus curves, in the Na2CO3 rich area, melting points of the pure components as well as determination of the extent of the solid solution, Na2CO3(ss), area. The thermal stability of Na2SO3 was studied and the binary phase diagram Na2SO4-Na2S was re-determined. The results indicate that Na2SO3 can exist for a short time up to 750 °C, before it melts. It was also proved that a solid/solid transformation, not reported earlier, occurs at 675 ± 10 °C. At around 700 °C, Na2SO3 gradually breaks down within a few hours, to finally form the solid phases Na2SO4 and Na2S. From HTM measurements a metastable phase diagram including Na2SO3, as well as an equilibrium phase diagram have been constructed for the binary system Na2SO4-Na2S. Improved data on Na2S was experimentally obtained by using solid-state EMF measurements. The equilibrium constant for Na2S(s) was determined to be log Kf(Na2S(s)) (± 0.05) = 216.28 – 4750(T/K)–1 – 28.28878 ln (T/K). Gibbs energy of formation for Na2S(s) was obtained as ΔfG°(Na2S(s))/(kJ mol–1) (± 1.0) = 90.9 – 4.1407(T/K) + 0.5415849(T/K) ln (T/K). The standard enthalpy of formation of Na2S(s) was evaluated to be ΔfH°(Na2S(s), 298.15 K)/(kJ mol–1) (± 1.0) = – 369.0. The standard entropy was evaluated to be S°(Na2S(s), 298.15 K)/(J mol–1 K–1) (± 2.0) = 97.0. Analyses of used refractory material from the Chemrec gasifier were also performed in order to elucidate the stability of the refractory lining. Scanning electron microscopy (SEM) analysis revealed that the chemical attack was limited to 250-300 μm, of the surface directly exposed to the gasification atmosphere and the smelt. From XRD analysis it was found that the phases in this surface layer of the refractory were dominated by sodiumaluminosilicates, mainly Na1.55Al1.55Si0.45O4.

The Multidisciplinary University Research Initiative (MURI) research at Texas A and M University is concerned with the experimental characterization of non-thermal and non-chemical equilibrium systems in hypersonic (Mach greater than 5) flowfields using experimental diagnostics, and is an interdisciplinary collaboration between the Chemistry and Aerospace Engineering departments. Hypersonic flight conditions often lead to non-thermochemical equilibrium (NTE) state of air, where the timescale of reaching a single (equilibrium) Boltzmann temperature is much longer than the timescale of the flow, meaning that certain molecular modes such as vibrational modes, may be much more excited than the translational or rotational modes of the molecule leading to thermal-nonequilibrium. A nontrivial amount of energy is therefore contained within the vibrational mode, and this energy cascades into the flow as thermal energy, affecting flow properties through the process of various vibrational-vibrational (V-V) and vibrational-translational (V-T) energy exchanges between the flow species. The research is a fundamental experimental study of these NTE systems and involves the application of advanced laser and optical diagnostics towards hypersonic flowfields. The research is broken down into two main categories: the application and adaptation of existing laser and optical techniques towards characterization of NTE, and the development of new molecular tagging velocimetry techniques which have been demonstrated in an NTE flowfield, but may be extended towards a variety of flowfields.

The need for effective disposal of huge volumes of industrial waste is becoming more challenging due to expected imposition of stringent pollution control regulations in the near future. Thermochemical conversion, particularly gasification of organics in the waste is considered the best route from the perspective of volume reduction and prevalent eco-friendly concept of waste-to-energy transformation. It is considered imperative to have adequate understanding of basic combustion features as a part of the thermochemical conversion process, leading to gasification. The aim of this thesis is to understand the fundamental combustion processes associated with one of the top listed hazardous wastes from distilleries (Biochemical Oxygen Demand (BOD) ~ 40,000 - 50,000 mg/L), commonly known as vinasse, stillage or spent wash, through experiments and modeling efforts. Specially designed experiments on distillery effluent combustion and gasification are conducted in laboratory scale reactors. As an essential starting point of the studies on ignition and combustion of distillery effluent containing solids consisting of 62 ± 2 % organics and 38 ± 2 % inorganics (primarily sugarcane derivatives), the roles of solids concentration, drop size and ambient temperature were investigated through experiments on (1) liquid droplets of 65 % and 77 % solids (remaining water) and (2) spheres of dried effluent (100 % solids) of size 0.5 mm to 20 mm diameter combusted at ambient temperatures of 773 to 1273 K. The investigation reveals that the droplets burn with two distinct regimes of combustion, flaming and char glowing. The ignition delay ‘t1’ of the droplets increased with size as is in the case of non-volatile droplets, while that of bone-dry spheres was found to be independent of size. The ‘t1’ decreased with increase in solids concentration. The ignition delay has showed an Arrhenius dependence on temperature. The initial ignition of the droplets and the dry spheres led to either homogeneous (flaming) or heterogeneous (flameless) combustion, depending on the ambient temperature in the case of sphere and on solid concentration and the ambient temperature, in the case of liquid droplets. The weight loss during the flaming combustion was found to be 50 - 80 % while during the char glowing it was 10-20 % depending on the ambient temperature. The flaming time tc is observed as tc~ d2c , as in the case of liquid fuel droplets and wood spheres. The char glowing time tc' is observed as tc ~ d2c as in the case of wood char, though the inert content of effluent char is as large as 50 % compared to 2 - 3 % in wood char. In the case of initial flameless combustion, the char combustion rate is observed to be lower. The heterogeneous char combustion in quiescent air in controlled temperature conditions has been studied and modeled using one-dimensional, spherico-symmetric conservation equations and the model predicts most of the features of char combustion satisfactorily. The measured surface and core temperatures during char glowing typically are in the range of 200 to 400 K and are higher than the controlled temperature of the furnace. Based on the results of single droplet combustion studies, combustion experiments were conducted in a laboratory scale vertical reactor (throughput ranging from 4 to 10 g/s) with the primary aim of obtaining sustained combustion. Spray of effluents with 50 % and 60 % solids (calorific value 6.8 - 8.2 MJ/kg), achieved by an air blast atomizer, was injected into a hot oxidizing environment to determine the parameters (ambient temperature and air-fuel ratio) at which auto-ignition could occur and subsequently studies were continued to investigate pre-ignition, ignition and combustion processes. Effluent with lower solids concentration was considered first from the point of view of the less expensive evaporator required in the field conditions for concentration and a spin-off in terms of better atomization consequently. Three classes of experiments were conducted: 1) Effluent injection from the wall with no auxiliary heat input, 2) Effluent injection with auxiliary heat input and 3) effluent injection within kerosene enveloping flame. Though individual particles in the spray periphery were found to combust, sustained spray combustion was not achieved in any of the three sets of experiments even with fine atomization. While conducting the third class of experiments in an inclined metallic reactor, sustained combustion of the pool resulting of accumulated spray seemed to result in large conversion of carbon. This led to the adoption of a new concept for effluent combustion in which the residence time is controlled by varying reactor inclination and the regenerative heat transfer from the product gases supplies heat for endothermic pre-ignition process occurring on the bed. Combustion and gasification experiments were conducted in an inclined plate reactor with rectangular cross section (80 mm x 160 mm) and 3000 mm long. A support flame was found necessary in the injection zone in addition to the regenerative heat transfer. Effluent with 60% solids was injected as film on the reactor bed. This film disintegrated into fine particles due to induced aerodynamic stretching and shear stripping. Combustion of individual particles provided exothermic heat profile and resulted into high carbon conversion. However, effluent clogging in the cold injection zone hindered system from attaining steady state. Effluent injected directly on the hot zone caused it to remain mobile due to the spheroidal evaporation and thus assuaging this problem. Improved mass distribution was achieved by displacing nozzle laterally in a cycle, actuated by a mechanism. Consistent injection led to sustained effluent combustion with resulting carbon conversion in excess of 98 %. The typical gas fractions obtained during gasification condition (air ratio = 0.3) were CO2 = 14.0 %, CO = 7.0 %, H2 = 12.9 %, CH4 - 1 % H2S = 0.6 - 0.8 % and about 2 % of saturated moisture. This composition varied due to variation in temperature (± 30 K) and is attributed to combined effect of local flow variations, shifting zones of endothermic processes due to flowing of evaporating effluent over a large area. In order to minimize this problem, experiments were conducted by injecting effluent at higher solids (73 % solids is found injectable). The effluent was found to combust close to the injection location-due to the reduced ignition delay and lower endothermic evaporation load helped raising the local temperature. This caused the pyrolysis to occur in this hottest zone of the reactor with higher heating rates resulting in larger yield of devolatilized products and improved char conversion. Effluent combustion was found to sustain temperature in the reactor under sub-stoichiometric conditions without support of auxiliary heat input and achieved high carbon conversion. These results inspired the use of higher concentration effluent, which is also known in the case of wood to have improved gasification efficiency due to reduction in moisture fraction. In addition, the recent studies on the sulfur emission in the case of black liquor combustion in recovery boilers have revealed that with increase in solids concentration, release of sulfur in gas phase is reduces. The required concentration can be carried out using low-grade waste heat from the reactor itself. It was found through experiments that, even though spray ignition occurred at this concentration, the confined reactor space prevented the spray from attaining sustained combustion. This led to the conduct of experiments in a new vertical reactor with adequate thermal inertia, essential to prevent variations in local temperature to reach a steady state gasification and required space to accommodate the spray. The results of the experiments conducted in the vertical reactor in which effluents with 73 % solids, heated close to the boiling point and injected as fine spray in a top-down firing mode are consolidated and reported in the thesis in detail. Single particle combustion with enveloping faint flame was seen unlike stable flame found in coal water slurry spray combustion. Sustained gasification of gas-entrained particles occurred at reactor temperature in the range of 950 K - 1000 K and sub-stoichiometric air ratio 03 - 0.35 without the support of auxiliary fuel. The typical gas fractions obtained during gasification condition (air ratio = 0.3) were CO2 = 10.0 -11.5 %, CO - 10.0 - 12.0 %, H2 - 6.7 - 8.0 %, CH4 = 1.75 % H2S = 0.2 - 0.4 % and about 2 % of saturated moisture. The carbon conversion obtained was in the range of 95 - 96 %. These experiments have provided the conditions for gasification. The extraction of potassium salts (mostly sulfates, carbonate and chloride) from the ash, using a simple water leaching process, was found to recover these chemicals to as high an extent as 70 - 75 % of total ash. In summary it is concluded that increasing the solid concentrations to as high levels as acceptable to the system (~ 75 %) and introducing as a fine spray of heated material (~ 363 K) into furnace with air at sub-stoichiometric conditions in a counter current combustion reactor will provide the frame work for the design of a gasification system for vinasse and similar effluent material. The thesis consists of seven chapters. Chapter 1 introduces the problem and motivation of the work presented in the thesis. Literature review is presented in Chapter 2. The Chapter 3 deals with the single particle combustion studies. The results of effluent spray combustion experiments conducted in a laboratory scale vertical reactor are presented in Chapter 4. The results of combustion and gasification experiments conducted in another variant of a reactor, namely, inclined flat plate rectangular reactor is consolidated in Chapter 5. The results of gas-entrained spray gasification experiment of higher concentration effluent injected as spray in the vertical reactor are presented in Chapter 6. The general conclusions and scope for the future work are presented in the concluding chapter 7.

Les travaux présentés dans cette thèse concernent le développement d’un procédé de stockage d’énergie thermique haute température par voie thermochimique en vue d’une application dans une centrale solaire à concentration. Un état de l’art des technologies de stockage d’énergie thermique haute température par voie thermochimique a permis de définir le couple réactionnel et la technologie les mieux adaptés au procédé. Ainsi, la réaction réversible Ca(OH)2(s) = CaO(s) + H2O(g) est mise en oeuvre dans un réacteur à lit fluidisé. Une étude expérimentale a permis de démontrer la faisabilité du procédé en stockant et en déstockant l’énergie à une même température et en mettant en oeuvre 50 cycles de charge/décharge de l’énergie sans perte de réversibilité. L’utilisation d’un modèle monodimensionnel couplant les phénomènes chimiques, thermiques et hydrodynamiques à l’intérieur du réacteur a permis de mettre en évidence l’influence des conditions opératoires sur les performances du système. Les premiers pas vers une extrapolation industrielle font l’objet de la dernière partie de ces travaux, en présentant l’analyse énergétique d’une centrale solaire à concentration intégrant le procédé de stockage développé et en présentant une étude expérimentale mettant en oeuvre un solide de type industriel dans le réacteur. / This PhD thesis concerns the development of a high temperature thermochemical heat energy storage process for an application in concentrated solar power plants. A literature review allows the identification of both the best reaction couple and technology to operate the process. Thus, the Ca(OH)2(s) = CaO(s) + H2O(g) reversible reaction is carried out in a fluidized bed reactor. The experimental study demonstrated the process feasibility. Thermal energy has been charged and discharged at the same temperature and 50 cycles have been performed without any loss of reversibility. A 1D model coupling the chemical, thermal and hydrodynamic phenomena inside the reactor has been developed to study the operating parameter effects on the process performance. The last section of this work deals with the first steps towards an industrial scale-up. An energetic analysis of a concentrated solar power plant integrating the developed storage process is detailed as well as the reactions implementation with an industrial solid.

Für den ökonomischen Erfolg konzentrierender Solarkraftwerke und für die Effizienz-steigerung der Industrie durch Weiterverwendung von Abwärme sind skalierbare Hochtemperatur-Wärmespeicher zu vertretbaren Kosten unabdingbar. Bisher sind für dieses Anwendungsgebiet nur sensible Speicher kommerziell verfügbar. Denen gegenüber besitzen chemische Speicher zahlreiche Vorteile. Sie bieten höhere Speicherdichten, geringere Wärmeverluste, die Möglichkeit zur Wärmetransformation durch Variation des Reaktionsdrucks und eine Vielzahl von Reaktionssystemen für eine optimale Prozess-integration. Jedoch befinden sie sich noch in der Entwicklungsphase. Die reversible Gas-/Feststoffreaktion von Calciumoxid und Wasserdampf zu Calcium-hydroxid geschieht bei Temperaturen von 400 – 600 °C und ist damit optimal für solarthermische Anwendungen geeignet. Für die Entwicklung eines Speichers ist neben der thermochemischen Charakterisierung des Speichermaterials ein effizientes, skalierbares Reaktorkonzept nötig. Ein Reaktor mit bewegtem Reaktionsbett ermöglicht die Trennung der zwei charakteristischen Speichergrößen Leistung und Kapazität und stellt damit einen wirtschaftlichen Speicher in Aussicht. Die vorliegende Arbeit befasst sich mit Aufbau und Inbetriebnahme eines neuen Teststandes, in welchem ein innovatives Reaktordesign erprobt werden soll. Sie beschreibt die Auslegung einer planaren Reaktorgeometrie, die einen Schwerkraftfluss des Bettes und die Modularisierung für größere Anlagen gewährleistet. Bei Vorversuchen stellt sich die homo-gene Bewegung des Reaktionsbettes aufgrund dessen Kompressibilität als schwierig heraus. Der angestrebte homogene Massenfluss des Reaktionsmaterials kann durch die ursprünglich eingesetzten Feindosiereinheiten nicht erzielt werden. Sie zeigen sich jedoch für die Temperierung des Speichermediums und die Gasdichtheit des Reaktionsraumes als geeignet. Das homogene Ausfließen wird einer separaten Austragshilfe zugeteilt, welche konstruiert und umgesetzt wird. Experimente mit einem Schaureaktor identifizieren eine Zahnwelle als beste Option. Für einen kommerziellen Speicher wird ein Schlitzschieber empfohlen. Ebenso erfolgen Auslegung und Errichtung der peripheren Anlagenteile, wie z.B. die Fertigung eines Druckhalters zur Steuerung der Reaktionstemperatur. Am Teststand werden somit alle Vorbereitungen abgeschlossen, um Heißversuche bei Reaktionstemperatur durchzuführen.