Hydrogen is considered to be an important potential energy carrier; however, its advantages are unlikely to be realized unless efficient means can be found to produce it without generation of CO2. Sorption-enhanced steam methane reforming (SE-SMR) represent a novel, energy-efficient hydrogen production route with in situ CO2 capture, shifting the reforming and water gas shift reactions beyond their conventional thermodynamic limits. The use of fluidized bed reactors for SE-SMR has been investigated. Arctic dolomite, a calcium-based natural sorbent, was chosen as the primary CO2-acceptor in this study due to high absorption capacity, relatively high reaction rate and low cost. An experimental investigation was conducted in a bubbling fluidized bed reactor of diameter 0.1 m, which was operated cyclically and batchwise, alternating between reforming/carbonation conditions and higher-temperature calcination conditions. Hydrogen concentrations of >98 mole% on a dry basis were reached at 600°C and 1 atm, for superficial gas velocities in the range of ~0.03-0.1 m/s. Multiple reforming-regeneration cycles showed that the hydrogen concentration remained at ~98 mole% after four cycles. The total production time was reduced with an increasing number of cycles due to loss of CO2 -uptake capacity of the dolomite, but the reaction rates of steam reforming and carbonation seemed to be unaffected for the conditions investigated. A modified shrinking core model was applied for deriving carbonation kinetics of Arctic dolomite, using experimental data from a novel thermo gravimetric reactor. An apparent activation energy of 32.6 kJ/mole was found from parameter fitting, which is in good agreement with previous reported results. The derived rate expression was able to predict experimental conversion up to ~30% very well, whereas the prediction of higher conversion levels was poorer. However, the residence time of sorbent in a continuous reformer-calciner system is likely to be rather low, so that only a fraction of the sorbent is utilized, highlighting the importance of the carbonation model at lower conversions. A dual fluidized bed reactor for the SE-SMR system was modeled by using a simple two-phase hydrodynamic model, the experimentally derived carbonation kinetics and literature values for the kinetics of steam reforming and water gas shift reactions. The model delineates important features of the process. Hydrogen concentrations of >98 mole% were predicted for temperatures ~600°C and a superficial gas velocity of 0.1 m/s. The reformer temperature should not be lower than 540°C or greater than 630°C for carbon capture efficiencies to exceed 90%. Operating at relatively high solid circulation rates to reduce the need for fresh sorbent, is predicted to give higher system efficiencies than for the case where fresh solid is added. This finding is attributed to the additional energy required to decompose both CaCO3 and MgCO3 in fresh dolomite. Moreover, adding fresh sorbent is likely to result in catalyst loss in the purge stream, requiring sorbents with lifetimes comparable to those of the catalyst. Thermo gravimetric analysis (TGA) was used to study the reversible CO2-uptake of sorbents. In general, the multi-cycle capacity of the dolomite was found rather poor. Therefore, synthetic sorbents that maintain their capacities upon multiple reforming-calcination cycles were investigated. A low-temperature liquid phase co-precipitation method was used for synthesis of Li2ZrO3 and Na2ZrO3. Li2ZrO3 showed a superior multi-cycle capacity compared to Arctic dolomite in TGA, but the rate of reaction in diluted CO2 atmospheres was very slow. The synthesized Na2ZrO3 proved to have both fast carbonation kinetics and stable multi-cycle performance. However, regeneration in the presence of carbon dioxide was not easily accomplished. The findings of this thesis suggest that the bubbling fluidized bed reactor is an attractive reactor configuration for SE-SMR. Low gas throughput is the major disadvantage for this configuration, and operation in the fast fluidization regime is most likely to be preferred on an industrial scale of the process. Future work should focus on developing sorbents and catalysts that are suited for high velocity operation, with respect to reactivity and mechanical strength.

Includes bibliographical references. / [210] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis presents two advanced modelling studies which address some unresolved fluidized bed combustion (FBC) issues. In the first study, finite element methods are used to solve a transient continuum/percolation model of a single porous char and its surrounding boundary layer so as to generate temperature, O2,CO2, CO pressure and porosity distributions for over 100 different FBC conditions. In the second study, a new discrete approach for the determination of the diffusion coefficients of the fluid-solid system is described and used, based on moecular dynamics and percolation concepts. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1996

Thesis (M.S.)--West Virginia University, 1998. / Title from document title page. Document formatted into pages; contains xv, 98 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 84).

Ο Φώσφορος είναι από τα κυριότερα θρεπτικά συστατικά που συμβάλλουν στην ανάπτυξη των φυτών και άλλων βιολογικών οργανισμών. Η παρουσία του ωστόσο σε αυξημένα επίπεδα συγκεντρώσεων στα επιφανειακά ύδατα απορροής, συμβάλλει στην δημιουργία ανεπιθύμητου ευτροφισμού. Η επεξεργασία των αστικών υγρών αποβλήτων, πριν την τελική διάθεση τους στους υδάτινους αποδέκτες, για την απομάκρυνση του διαλελυμένου φωσφόρου, είναι απαραίτητη. Ουσιαστική ωστόσο συμβολή στην αειφόρο ανάπτυξη συνιστά η ανάκτηση του φωσφόρου με την μορφή προϊόντων τα οποία μπορούν να χρησιμοποιηθούν ως λιπάσματα. Αυτό αποτέλεσε και τον βασικό στόχο της παρούσας εργασίας. Συγκεκριμένα, στην παρούσα εργασία μελετήθηκε η δυνατότητα ανάκτησης των ανόργανων φωσφορικών από προσομοιωμένο αστικό υδατικό απόβλητο, με την κρυστάλλωση MgNH4PO4∙6H2O (Στρουβίτη). Διερευνήθηκε η δυνατότητα ανάκτησης του φωσφόρου με την μορφή στρουβίτη σε ρευστοποιημένη κλίνη με πληρωτικό υλικό πυριτικά στερεά. Η κρυστάλλωση έγινε σε υπέρκορα αλλά σταθερά διαλύματα και μελετήθηκε η μόνιμη κατάσταση η οποία μπορεί να αναπτυχθεί με συνεχή τροφοδοσία ανακύκλωσης του διαλύματος. Έγινε παραμετρική μελέτη των συνθηκών λειτουργίας της κλίνης με στόχο την μεγιστοποίηση της ανάκτησης φωσφόρου σε pH═6.5 και θ═25C. Το στερεό που καταβύθισθηκε από τα υδατικά διαλύματα, χαρακτηρίσθηκε με περίθλαση ακτίνων -Χ(XRD) και ηλεκτρονική μικροσκοπία σάρωσης (SEM). Διερευνήθηκε ο μηχανισμός της ετερογενούς πυρηνογενέσεως και αναπτύξεως κρυστάλλων στρουβίτη στην επιφάνεια του πληρωτικού υλικού της ρευστοποιημένης κλίνης με μετρήσεις του ρυθμού κρυστάλλωσης συναρτήσει του υπερκορεσμού. Οι μετρήσεις αυτές έδειξαν ότι το καθορίζον την ταχύτητα στάδιο ήταν η διάχυση των δομικών μονάδων στην επιφάνεια των κρυσταλλιτών του πληρωτικού υλικού, το οποίο ήταν καιτο υπόστρωμα για την κρυσταλλική ανάπτυξη. Η κρυσταλλική ανάπτυξη του στρουβίτη, έγινε επιλεκτικά στους κρυσταλλίτες του πληρωτικού υλικού. / Phosphorus is one of the most essential nutrients for the growth of plants and other organisms. However, the presence at high concentrations in surface waters, contributes to the development of eutrophication.The treatment of municipal wastewaters, before final disposal in aquatic systems, is necessary for the removal of dissolved phosphorus. Alternatively, phosphorus recovery in the form of solids which may be used as fertilizers is a significant contribution to the sustainable development.In the present work, it was attempted to recover P from simulated municipal wastewater in the form of struvite (MgNH4PO4∙6H2O) by crystallization in a fluidized bed reactor(FBR).Silicates (quartz and silica gel) were used as substrates in the FBR.The FBR was fed with kinetically stable solutions, supersaturated with respect to struvite. The solutions were introduced in the silicate bed by a peristaltic pump and were recirculated through a reservoir. Measurements of the solution pH and of the concentrations of Mg and P were used to monitor the process and for the measurement of induction times and rates of precipitation. A parametric study of the operating conditions, in the FBR was carried out in order to investigate the possibilities of P recovery at pH 6.50 and θ═25C. The mechanism of heterogeneous nucleation and crystal growth of struvite crystals on the surface of the filling particles(quartz)of the FBR, was investigated from measurements of the crystallization rate as a function of the solution supersaturation.In all cases the crystalline material forming out of the supersatured solutions was struvite and was identified by X-Ray Diffraction (XRD)and Scanning Electron Microscopy (SEM). The kinetics results suggested that the rate determining step was the diffusion of the structural units on the surface of the substrate particles. The induction times preceding the onset of the selective crystallization of struvite on the quartz particls in the FBR were inversely proportional with the solution supersaturation.From this dependence a value of ca. 22mJm^-2 was calculated for the surface energy of the overgrowth. Induction times were shorter and crystal growth rates were faster the higher the fluid velocity in the FBR, in agreement with literature reports.

O Φώσφορος είναι βασικό συστατικό των αστικών αποβλήτων, ο οποίος συγκεντρώνεται στους υδάτινους αποδέκτες προκαλώντας κυρίως προβλήματα ευτροφισμού. Τα παγκόσμια αποθέματα ορυκτού φωσφόρου μειώνονται λόγω της αυξημένης ζήτησης, έτσι κρίνεται απαραίτητο η κατά κάποιον τρόπο ανακύκλωση του. Μια από τις εναλλακτικές και πολλά υποσχόμενες μεθόδους για την ανάκτηση του φωσφόρου από την επεξεργασία των υγρών αποβλήτων είναι η δέσμευση του φωσφόρου, μέσω της κρυστάλλωσης, υπό την μορφή φωσφορικών αλάτων όπως ο στρουβίτης (ΜgNH4PO4.6H2O). O στρουβίτης χρησιμοποιείται απευθείας ως βραδέως αποδεσμευόμενο λίπασμα, το οποίο λόγω της χαμηλής του διαλυτότητας, εξασφαλίζει, την ελεγχόμενη παροχή θρεπτικών συστατικών φωσφόρου και αζώτου, απαραίτητων για την ανάπτυξη των φυτών. Στη παρούσα εργασία, δοκιμάστηκαν δύο τύποι αντιδραστήρων, ένας αντιδραστήρας ρευστοποιημένης κλίνης (FBR) και ένας αντιδραστήρας διαλείποντος έργου (Batch) με συνθετικό απόβλητο σε pH 6.50 στους 25οC. Η στοιχειομετρική αναλογία 1:1:1 των πλεγματικών ιόντων του στρουβίτη, Mg:N:P, διατηρήθηκε σε όλα τα πειράματα. Η καταβύθιση στρουβίτη σε υπέρκορα διαλύματα εξαρτάται κυρίως από τον υπερκορεσμό της καταβυθιζόμενης φάσης, τη θερμοκρασία και τη παρουσία ξένων ιόντων ή επιμολύνσεων. Πραγματοποιήθηκαν πειράματα αυθόρμητης καταβύθισης του στρουβίτη σε συνθήκες σταθερού pH για τον καθορισμό του εύρους της μετασταθούς περιοχής. Η γνώση αυτή είναι απαραίτητη για τον καθορισμό των συνθηκών διεξαγωγής πειραμάτων. Τα αποτελέσματα από τους δύο τύπους αντιδραστήρων, δεν παρουσίασαν διαφορές στους χρόνους επαγωγής γεγονός το οποίο υποδεικνύει την αυξημένη σημασία της πυρηνογένεσης και την μικρότερη σημασία της ρευστοδυναμικής του συστήματος. Στους δύο τύπους αντιδραστήρων μελετήθηκε ο ετερογενής σχηματισμός του στρουβίτη σε συνθήκες σταθερού pH 6.50, σε σταθερά υπέρκορα διαλύματα συνθετικού αποβλήτου, χρησιμοποιώντας ως φύτρα για την εκκίνηση της κρυσταλλικής ανάπτυξης, quartz, άμμο και στρουβίτη. Με υπόστρωμα quartz, παρατηρήθηκε μείωση του ρυθμού καταβύθισης αυξανομένης της ποσότητας τόσο σε αντιδραστήρα batch όσο και σε FBR, λόγω της επιβραδυντικής δράσης των πυριτικών ιόντων. Με υπόστρωμα άμμου, παρατηρήθηκε υπερδιπλάσια αύξηση του ρυθμού καταβύθισης για τη διπλάσια ποσότητα φύτρων, το οποίο συνηγορεί στην υπόθεση της δευτερογενούς πυρηνογένεσης. Τα μεγαλύτερα ποσοστά ανάκτησης φωσφόρου της τάξεως ~40% και καταβύθισης στρουβίτη από 70-100% είχαμε σε αντιδραστήρα ρευστοποιημένης κλίνης με υπόστρωμα στρουβίτη. Η χρήση υποστρώματος άμμου είχε αποτελέσματα παραπλήσια με τα αντίστοιχα τα οποία ελήφθησαν με την χρησιμοποίηση φύτρων κρυσταλλικού στρουβίτη. Η εισαγωγή σωματιδίων quartz στα υπέρκορα διαλύματα για την δημιουργία πυρήνων κρυστάλλωσης στρουβίτη είχε ως αποτέλεσμα την συγκριτικά μικρότερη απομάκρυνση φωσφόρου και κρυστάλλωση στρουβίτη. Σε λιγότερα από 700min λειτουργίας των αντιδραστήρων, στα υπέρκορα διαλύματα στα οποία είχαν εισαχθεί φύτρα στρουβίτη, η καταβυθιζόμενη ποσότητα στρουβίτη ήταν η μέγιστη δυνατή. Συγκρίσιμα αποτελέσματα ελήφθησαν με την εισαγωγή άμμου στα υπέρκορα διαλύματα. Το καταβυθιζόμενο στερεό χαρακτηρίστηκε με μεθόδους περίθλασης ακτίνων-X και ηλεκτρονική μικροσκοπία σάρωσης. Στα πειράματα batch, το καταβυθιζόμενο στερεό ήταν στρουβίτης, ενώ στα FBR σε υπόστρωμα 20g quartz σε χαμηλό υπερκορεσμό καταβυθίστηκε μικρή ποσότητα φωσφορικού μαγνησίου και σε υπόστρωμα 5g στρουβίτη σε υπερκορεσμό Ω=1.65 παρατηρήθηκε μικρή ποσότητα newberyite. / Phosphorus is one of the main components in the municipal wastewater, which can lead to problems such as eutrophication in the water reservoirs. The known reserves of phosphorus rocks are decreasing because of the high worldwide demands. Thus, it is necessary to recycle phosphorus from wastewater. Τhe crystallization of struvite is An attractive and new alternative method for phosphorus recovery. Struvite may be used as a slow-release fertilizer because of its relatively low solubility and the presence of both ammonia and phosphorus which through dissolution nutrients available to plants. In the present work, two types of reactors, a fluidized bed reactor (FBR) and a stirred tank reactor were used for the investigation of phosphorus recovery in synthetic wastewater at pΗ 6.50, 25οC. The stoichiometric molar ratio at the constituent ions was 1:1:1 through out the experiments of the present work. The extent of struvite precipitation depends on the solution supersaturation with respect to the precipitating solid, the temperature and the presence of foreign ions or substrates in the solution. The spontaneous precipitation of struvite was studied in both types of reactors at a constant pH 6.50 in order to determine the metastable zone width. This provided knowledge of the stable supersaturated solutions domain where heterogenous nucleation experiments can be done, in order to evaluate nucleation experiments can be done, in order to evaluate the relative ability of substrates to induce the crystallization of struvite. For the two type’s reactors, no significant differences were measured for the induction time, preceding precipitation. This suggested that hydrodynamics is not very important for the conditions of the present work. The heterogeneous formation of struvite was investigated at constant supersaturation and of pH in synthetic wastewater in both types of reactors. The seeds included quartz, sand and synthetic struvite. A decrease in the rate of struvite precipitation was found in both reactors with the use of quartz seeds due to the retardation effect of silicon ions. The use of sand seeds increased the rate of precipitation, while increasing the amount of substrate, resulted in a disproportionate increase at the respective rates of precipitation, suggesting a secondary nucleation process. Phosphorus recovery reached almost 40% and precipitation of struvite from 70 to 100% in the FBR filled with struvite. Sand gave similar results with struvite. The recovery of phosphorus and precipitation with quartz seeds were low, perhaps because of the inhibition effect of the silicon ions. Experiments, in which struvite seeds were used to seed supersaturated solutions, resulted in the precipitation the maximum amount of struvite in less than 700min. The experiments with sand seeds were quite close from the previous experiments especially in high supersaturation values. Finally, the precipitated solid characterized with XRD and SEM. In the batch series, the precipitated solid was struvite but for the FBR experiments a small amount of magnesium phosphate, for supersaturation Ω= 1.65 with 20g quartz seeds and a small amount of newberyite for 5g struvite seeds in supersaturation value 1.65, were obtained. These findings suggested that the problem is complex and kinetic stabilization of metastable mineral phases may be formed at very specific conditions.

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No. of bitstreams: 1 chaucanes_pam_me_ilha.pdf: 4074329 bytes, checksum: b4e87799b76f0a2635d5a1511a22d2f0 (MD5) Previous issue date: 2017-10-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este estudo mostra o funcionamento dos processos de oxidação de matéria orgânica junto com os processos simultâneos de nitrificação e desnitrificação (SND) dentro do reator aeróbio de leito fluidizado de tubos concêntricos com uma terceira câmara para gerar condições anóxicas (necessárias para garantir o processo de desnitrificação). O reator foi operado por um período de 140 dias, durante o qual a remoção de demanda química de oxigênio (DQO) e de nitrogênio total (NT), atingiu 80% e 44% respectivamente, para um tempo de detenção hidráulica (TDH) de 3 horas. A configuração dos diâmetros dos tubos concêntricos resultou em diferentes relações de áreas e, portanto em diferentes vazões para cada câmara. Na operação do reator foram aplicadas duas relações de vazões alterando o nível de esgoto dentro do reator. Os efeitos destas relações de vazões, alterou a concentração de oxigênio dissolvido (OD) entre os compartimentos aeróbio e anóxico do reator e a relação C:N, as quais foram estudadas durante o funcionamento deste sistema. Os resultados indicaram que a relação de vazões 2(4,8: 3,8: 1 para as câmaras 1, 2 e 3, respectivamente) beneficiou as remoções de DQO e NT. A concentração de OD no compartimento aeróbio apresentou valores médios de 3,57 ± 1,24 mg.L -1 , e no topo da câmara 3, a concentração de OD foi de 1,41 ± 0,78 mg.L -1 . As relações C:N que apresentaram maiores eficiências de remoção de NT foram as superiores a 10, sendo a máxima remoção de T na relação C:N de 17. O tempo de retenção celular (TRC) alcançado no reator foi de 3,16 ± 3,07 dias. Neste trabalho de pesquisa foi concluído que a configuração de três câmaras concêntricas para o reator aeróbio de leito fluidizado beneficia a remoção de NT, tornando este reator uma alternativa para o tratamento de águas residuárias domésticas. / This study shows the operation of the organic matter oxidation processes together with the simultaneous processes of nitrification and denitrification (SND) inside the aerobic fluidized bed reactor of concentric tubes with a third chamber to generate anoxic conditions (necessary to guarantee the denitrification process). The reactor operated over a period of 140 days, during which chemical oxygen demand (COD) and total nitrogen (TN) removal reached 80% and 44% respectively, for a 3 hour hydraulic detention time (HDT). The configuration of the diameters of the concentric tubes resulted in different area ratios and therefore in different flow rates for each chamber. In the reactor operation were applied two flow ratios, altering the sewage level inside the reactor. The effects of these flow rates were changing the concentration of dissolved oxygen (DO) between the aerobic and anoxic compartments of the reactor and the C: N ratio, which was studied during the operation of this system. The results indicated that the ratio of flows 2 (4.8: 3.8: 1 for chambers 1, 2 e 3, respectively) benefited the COD and TN removal. The DO concentration in the aerobic compartment presented average values of 3.57 ± 1.24 mg.L-1 , and on top of chamber 3, the DO concentration was 1.41 ± 0.78 mg.L-1 . The C:N ratios that showed higher nitrogen removal efficiencies were higher than 10, with the maximum TN removal at the C:N ratio of 17. The cell retention time reached (CRT) in the reactor was 3.16 ± 3.07 days. In this research, was concluded that three concentric chambers configuration for the aerobic fluidized bed reactor benefits the TN removal, became this reactor an alternative in domestic wastewater treatment.

Orientador: Tsunao Matsumoto / Resumo: Este estudo mostra o funcionamento dos processos de oxidação de matéria orgânica junto com os processos simultâneos de nitrificação e desnitrificação (SND) dentro do reator aeróbio de leito fluidizado de tubos concêntricos com uma terceira câmara para gerar condições anóxicas (necessárias para garantir o processo de desnitrificação). O reator foi operado por um período de 140 dias, durante o qual a remoção de demanda química de oxigênio (DQO) e de nitrogênio total (NT), atingiu 80% e 44% respectivamente, para um tempo de detenção hidráulica (TDH) de 3 horas. A configuração dos diâmetros dos tubos concêntricos resultou em diferentes relações de áreas e, portanto em diferentes vazões para cada câmara. Na operação do reator foram aplicadas duas relações de vazões alterando o nível de esgoto dentro do reator. Os efeitos destas relações de vazões, alterou a concentração de oxigênio dissolvido (OD) entre os compartimentos aeróbio e anóxico do reator e a relação C:N, as quais foram estudadas durante o funcionamento deste sistema. Os resultados indicaram que a relação de vazões 2(4,8: 3,8: 1 para as câmaras 1, 2 e 3, respectivamente) beneficiou as remoções de DQO e NT. A concentração de OD no compartimento aeróbio apresentou valores médios de 3,57 ± 1,24 mg.L -1 , e no topo da câmara 3, a concentração de OD foi de 1,41 ± 0,78 mg.L -1 . As relações C:N que apresentaram maiores eficiências de remoção de NT foram as superiores a 10, sendo a máxima remoção de T na relação C:N de 17. O te... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This study shows the operation of the organic matter oxidation processes together with the simultaneous processes of nitrification and denitrification (SND) inside the aerobic fluidized bed reactor of concentric tubes with a third chamber to generate anoxic conditions (necessary to guarantee the denitrification process). The reactor operated over a period of 140 days, during which chemical oxygen demand (COD) and total nitrogen (TN) removal reached 80% and 44% respectively, for a 3 hour hydraulic detention time (HDT). The configuration of the diameters of the concentric tubes resulted in different area ratios and therefore in different flow rates for each chamber. In the reactor operation were applied two flow ratios, altering the sewage level inside the reactor. The effects of these flow rates were changing the concentration of dissolved oxygen (DO) between the aerobic and anoxic compartments of the reactor and the C: N ratio, which was studied during the operation of this system. The results indicated that the ratio of flows 2 (4.8: 3.8: 1 for chambers 1, 2 e 3, respectively) benefited the COD and TN removal. The DO concentration in the aerobic compartment presented average values of 3.57 ± 1.24 mg.L-1 , and on top of chamber 3, the DO concentration was 1.41 ± 0.78 mg.L-1 . The C:N ratios that showed higher nitrogen removal efficiencies were higher than 10, with the maximum TN removal at the C:N ratio of 17. The cell retention time reached (CRT) in the reactor was 3.16 ± 3.... (Complete abstract click electronic access below) / Mestre

Les minerais d’uranium sont généralement peu concentrés avec des teneurs en uranium inférieures à 1%. Pour éviter le transport inutile de tonnages importants sur de longues distances, des opérations de purification et de concentration s’effectuent à proximité immédiate des sites miniers. Après purification, l’uranium est précipité pour conduire à un concentré solide appelé couramment « Yellow-Cake » et contenant entre 70 et 76% d’uranium. Cette thèse apporte une contribution à l’étude du procédé de précipitation du Yellow-Cake, sous forme de peroxyde d’uranium, en réacteur à lit fluidisé. Afin de mieux comprendre tous les mécanismes mis en jeu au cours de la précipitation, nous avons développé des méthodes permettant de mettre au point un modèle de solubilité, de compléter les données cinétiques et de proposer un modèle décrivant le procédé de précipitation en réacteur à lit fluidisé. Les cinétiques de nucléation et de croissance cristalline ont été déterminées par Planteur (2013). L’identification de la loi cinétique d’agglomération consiste en la détermination du noyau d’agglomération en fonction des paramètres influençant le mécanisme d’agglomération. Plus précisément, dans le cas du peroxyde d’uranium, le mécanisme d’agglomération est caractérisé par un noyau d’agglomération constant par rapport à la taille des particules, mais proportionnel à la vitesse de croissance cristalline (ordre 1 vis-à-vis de la sursaturation) et une vitesse d’agglomération freinée significativement par une augmentation du taux de cisaillement. L’étude expérimentale du procédé de précipitation du peroxyde d’uranium en réacteur à lit fluidisé a porté sur l’influence des conditions opératoires sur la qualité du produit final obtenu : vitesse d’agitation, capacité du réacteur et teneur en sulfate. À partir des données expérimentales obtenues en réacteur à lit fluidisé sur une installation pilote, un modèle de réacteur parfaitement mélangé avec séparation de la phase solide (MSSPR) est développé avec succès pour le procédé de précipitation du peroxyde d’uranium. Le modèle proposé peut ensuite être mis à profit pour dimensionner les précipitateurs à lit fluidisé du type MSSPR / Currently exploited uranium deposits contain less than 1% of uranium. Once uranium ore has been extracted, it is transported to a processing plant. Purification and concentration are required in order to reduce the cost of uranium transportation. The precipitation of uranium present inside mill leach solutions produces a solid known as yellow cake. This precipitate contains around 75% uranium. This PhD thesis deals with the yellow cake precipitation process in a fluidized-bed reactor. The process produces uranium peroxide. We develop methods for studying the kinematic mechanisms that take place during the precipitation process. We provide a global model of the uranium peroxide precipitation process in a fluidized-bed reactor. Planteur (2013) studies the kinematics of uranium peroxide nucleation and crystal growth. His thesis work presents a parametric study that quantifies the influence of operating parameters on the agglomeration mechanism. The uranium peroxide agglomeration kernels are found to be particle size-independent, directly proportional of the crystal growth rate, and inversely proportional to the average shear rate. Our experiment stresses the influence of key operating parameters on the yellow cake precipitation in a fluidized-bed reactor. We investigate the effects of stirring speed, feed flow, and sulfate concentration on the uranium peroxide precipitation. We use our experimental results for modeling the precipitation process. We propose a model called Mixed Suspension Separated Product Removal (MSSPR). The successful application of this model reveals its potential for sizing fluidized-bed reactors at the industrial scale

The research determined that the improved heat transfer characteristics of a fluidized bed reactor (FBR) will allow the use of cobalt catalyst for high temperature Fischer-Tropsch synthesis (HTFT). Cobalt was loaded onto a gamma alumina support, the catalyst was characterized using TPR, BET/BJH, XRD, and PSA to track changes in the catalyst morphology. The reactor was characterized to determine the minimum fluidization velocity and the maximum velocity prior to entering lean phase fluidization with pneumatic transport of the catalyst. The highest minimum fluidization velocity was found to be about 2800 sccm, there was no maximum velocity found for the reactor setup. Once characterized, the reactor was operated at pressures of 145, 217.6, and 290.1 psig, a syngas flow rate of 4000 sccm, and at temperatures of 330 and 350 °C. The optimal conditions found in this study were 330 °C and 217 psig. At these conditions CO conversion was 83.53 % for a single pass. Methane, CO2, and light gases (C2 - C4) selectivities were at low rates of 31.43, 5.80, and 3.48 % respectively. Alcohol selectivity at these conditions was non-existent. The olefin and wax selectivities were the lowest of the data set at 7.05 and 3.18 % respectively. Liquid transportation fuels selectivity was the highest at 56.11 %.

L’étude multi-échelle d’un lit fluidisé gaz-particule est réalisée afin de comprendre les raisons de la mauvaise prédiction de la combustion dans ce type de réacteur. Dans un premier temps, des simulations numériques directes à l’échelle de quelques particules montrent le couplage entre la fraction volumique de particules et la fraction massique des espèces dans l’écoulement. Ensuite, une analyse des équations flitrées en LES montre qu’un terme de corrélation fluide-particule apparaît lorsque l’on explicite le taux de réaction gaz-particules. On comprend alors que si ce couplage n’est pas pris en compte correctement dans les simulations aux grandes échelles, le résultat ne peut pas être bon. Des simulations numériques à l’échelle du réacteur sont alors réalisées avec différents maillages pour tenter de mettre en évidence les effets de sous-maille liés à ce couplage à l’échelle des petites structures solides dans l’écoulement. / The multiscale study of a reactive gas-solid fluidized bed is performed to understand the reason of the bad prediction of the combustion in such a reactor. First, Direct Numerical Simulations at the particle array lenght scale show the dependency of the species mass fraction released in the gas phase on the solid volume fraction. Then, the analysis of the filtered continuity equations for the eulerian granular model highlights that a fluid-particle coupling term appears when expliciting the heterogeneous reaction rate. Therefore, we understand the need to take this coupling into account in large scales simulations to obtain good results. Computations at the lab-scale reactor are eventually performed using different grid refinements in order to try to highlight the subgrid terms due to this coupling at the small solid structure scale.