Dissertations / Theses on the topic 'Modelli processo carbonio'

2009/2010
I suoli globalmente contengono circa 2500 Pg di C in forma minerale ed organica (ca 1550 Pg) ed il flusso annuo da e verso l’atmosfera – che attualmente contiene circa 760 Pg C – coinvolge circa 120 Pg di C. Questi scambi di carbonio sono clima-dipendenti; l’effetto del cambiamento climatico sui depositi di carbonio del suolo è perciò di importanza critica, in quanto anche piccole variazioni di un deposito di tale entità possono determinare importanti conseguenze sulla concentrazione di anidride carbonica in atmosfera, innescando meccanismi retroattivi positivi. Per fare delle previsioni sui cambiamenti dei depositi di carbonio per effetto dei cambiamenti climatici o di altre variabili è neccesario ricorrere a dei modelli; in particolare, per le stime a scala nazionale e regionale si impiegano dei modelli che operano a livello di ecosistema e che vengono abbinati a dei SIT. Vista la forte sinergia con la mitigazione e adattamento ai cambiamenti climatici, la ricerca è stata volta a stimare il potenziale di sequestro e accumulo di sostanza organica nei terreni agricoli del Veneto, con un occhio di riguardo per la gestione sostenibile. In secondo luogo, a fornire uno strumento per la contabilizzazione del sequestro di carbonio nei sistemi agricoli. Si è individuato nel GEFSOC Modelling Sistem uno strumento idoneo per il perseguimento di questi obiettivi; il GEFSOC MS integra due modelli meccanicistici ampiamente sperimentati – Century e RothC – ed il metodo empirico dell’IPCC e li interfaccia con un SOTER-DB e con un GIS. L’uso e la gestione del suolo ed i loro cambiamenti sono variabili fondamentali nel determinare il contenuto di carbonio nei depositi del terreno; poiché manifestano i loro effetti anche secoli dopo che si sono verificati, è necessario ricostruire la loro storia almeno negli ultimi 100 anni. Nel corso della ricerca è stato ideato e sperimentato per la prima volta in questo settore un approccio spazialmente esplicito alle transizioni di uso e gestione del suolo, utilizzando materiale cartografico di varia natura e completando la raccolta dati con statistiche agrarie e fonti storiche. Le simulazioni sono state fatte contemplando due diversi scenari di cambiamento climatico (PCM-B1 e Had3A1FI) spinti fino al 2100. L’analisi dei risultati prodotti evidenzia che i terreni più ricchi in carbonio sono maggiormente soggetti a perdite, mentre quelli poveri, anche se in misura modesta, incrementano il loro contenuto; la tendenza, quindi, è di avvicinarsi ad una maggiore omogeneità. Per quel che riguarda gli usi del suolo, seminativi ed aree agricole eterogenee sono le categorie che hanno manifestato tassi di incremento superiori. I tassi di variazione, comunque, sono tendenzialmente in calo e, per lo scenario di cambiamento climatico meno marcato, ad un certo punto (2070 ca) si portano su valori negativi: questo fatto si ripercuote sui depositi del terreno, che complessivamente mostrano un incremento nel lungo periodo, ma via via più contenuto, fino a raggiungere un massimo e quindi cominciare ad emettere negli ultimi decenni della simulazione. I depositi dei terreni sottoposti allo scenario di cambiamento più marcato, invece, non hanno subito flessioni ed hanno garantito, anche se in misura calante, il sequestro lungo tutto il periodo della simulazione. Questo dato può essere di qualche interesse nello studio degli effetti della temperatura sul rapporto produzione di biomassa-accumulo/decomposizione. L’analisi delle mappe dei depositi e dei tassi di variazione annua ad ettaro prodotte con la sperimentazione, ed il confronto delle stesse con carte del contenuto del carbonio nei terreni di doversa origine e natura, rivelano l’utilità dell’approccio spazialmente esplicito nella definizione delle transizioni dell’uso e gestione del suolo; è possibile infatti riconoscere, dalla zonizzazione, i tematismi che possono avere avuto un peso preponderante nel determinare peculiari situazioni; questo consente di indagarle, verificare la validità delle assunzioni fatte in fase di progettazione, modificare eventualmente la parametrizzazione e reindirizzare le simulazioni. Ad una livello di risoluzione comparabile a quello degli strati informativi di partenza. Alla luce della sperimentazione effettuata, si ritiene che il GEFSOC Modelling System meriti grande considerazione per quanto attiene la contabilizzazione del carbonio nei sistemi agricoli – problematica inevasa fino ad oggi in Italia; quale strumento a supporto del processo decisionale; per le possibili sinergie nella pianificazione di campionamenti e sperimentazioni attinenti; per l’approfondimento della ricerca nell’ambito delle relazioni tra clima e suolo.
XXIII Ciclo
1970

Gli impianti dell’industria di processo, durante il loro funzionamento, devono soddisfare requisiti relativi alla quantità realizzata ed alla qualità del prodotto finito. Nell’ottica del miglioramento continuo, l’ottimizzazione dei processi mira ad aumentare la produzione e/o la qualità del prodotto finito al fine di ottenere il massimo profitto. Il presente elaborato di tesi è stato sviluppato durante un tirocinio svolto presso il sito produttivo di Cabot Italiana. Esso ha avuto come obiettivo l’analisi dei dati di processo di un impianto dello stabilimento al fine di una loro migliore comprensione e dell’individuazione di correlazioni esistenti tra i dati stessi, indispensabile punto di partenza per lo sviluppo futuro di un modello matematico che possa prevedere il comportamento del sistema studiato e contribuire a miglioramenti del suo sistema di controllo. Il lavoro di tesi si articola in 7 capitoli. Il capitolo 1 è finalizzato alla presentazione sommaria dell’attività di tesi. Il capitolo 2 tratta in via generale i metodi di analisi dei dati, con un approfondimento sulle principali tecniche di pretrattamento dei dati e sull’Analisi delle Componenti Principali (PCA – Principal Component Analysis). Il capitolo 3 descrive la realtà di Cabot Italiana e ,nel dettaglio, la seconda parte della linea di processo 2 con il relativo sistema di controllo, che rappresenta il caso di studio considerato nel presente elaborato di tesi. Il capitolo 4 si focalizza sul metodo di gestione dei dati di processo, in particolare sui 2 software utilizzati nello stabilimento di Cabot Italiana: Aspen Process Explorer e AEMS Capability. Il capitolo 5 è interamente dedicato al pretrattamento dei dati di processo per il caso di studio considerato. Il capitolo 6 descrive l’applicazione della Principal Component Analysis al caso di studio. Infine, nel capitolo 7 sono riportate le considerazioni conclusive.

Les processus physiologiques déterminant la productivité forestière and l’allocation du carbone (C) entre les différents organes de l’arbre restent mal connus. La croissance forestière a longtemps été considérée comme limitée par le C, à travers un lien causal entre photosynthèse et croissance (contrôle de la croissance par la source de C). Ce paradigme C-centré est à l’origine des règles gouvernant l’allocation du C dans la plupart des modèles à base de processus (MBP). Cependant, le contrôle de la croissance forestière par la source de C a été remis en cause par un certain nombre d’études mettant en lumière que l’activité des méristèmes est plus sensible aux stress environnementaux (stress hydrique, température basse) que ne l’est l’assimilation du C (contrôle de la croissance par l’activité du puits). De plus, l’effet de la gestion, qui influe fortement sur le fonctionnement de la forêt and sa croissance, n’est pas pris en compte dans la plupart des MBP utilisés pour projeter le futur puits de C terrestre. Notre objectif principal dans cette thèse est d’améliorer notre connaissance des contraintes qui affectent - ou affecteront- la productivité ligneuse des forêts européennes, depuis l’époque actuelle jusqu’à la fin du 21ème siècle. Nous avons abordé cet objectif à travers l’amélioration du modèle CASTANEA, sur la base d’une analyse détaillée des déterminants de la productivité ligneuse annuelle des forêts françaises sur les 30 dernières années. Les espèces étudiées sont Fagus sylvatica, Quercus ilex, Quercus petraea, Quercus robur et Picea abies. Nos résultats suggèrent que la croissance annuelle des espèces étudiées est soumise à un contrôle complexe, impliquant des limitations par la source de C et par l’activité du puits. La variabilité inter-site de la fraction de C allouée à la croissance est principalement expliquée par un déclin lié à l’âge. La croissance annuelle à l’échelle de l’arbre est bien prédite par la taille des individus. Nous avons montré que l’asymétrie de la croissance, i.e., l’avantage des gros arbres dans la compétition pour les ressources, augmente avec la productivité, aux échelles inter-site et inter-annuelle. Sur la base de ces résultats, nous avons développé un nouveau schéma d’allocation du C dans le modèle CASTANEA. Le nouveau modèle a été capable de reproduire de manière satisfaisante la variabilité inter-annuelle et inter-site dans la croissance ligneuse aérienne le long de gradients environnementaux à l’échelle nationale. Le modèle a également été validé en utilisant une méta-analyse de mesure de réserves carbonées et des estimations satellitaires d’indices foliaires. Nos résultats indiquent que la représentation du contrôle de la croissance par l’activité du puits n’affecte pas les prédictions qualitatives de l’évolution de la productivité forestière européenne précédemment obtenues par les MBP C-centrés. Cependant, les MBP C-centrés sous-estiment certainement l’hétérogénéité spatiale des effets du changement climatique.Nous avons enfin utilisé notre nouvelle connaissance des déterminants de la croissance ligneuse annuelle à l’échelle de l’arbre (i.e., les règles empiriques de la compétition) pour calibrer un module simulant la croissance individuelle dans CASTANEA. Le modèle couplé a été utilisé pour évaluer l’effet potentiel de la gestion sur le fonctionnement des forêts et la croissance ligneuse à l’échelle de la France. Nous avons identifié les zones où la gestion pourrait être intensifiée pour réduire l’impact du changement climatique sur la productivité forestière nationale. Environ un quart des forêts françaises en hêtre et chênes tempérés sont en zone de forte vulnérabilité, zone dans laquelle la gestion pourrait donc être utilisée à profit pour limiter l’impact du changement climatique sur la récolte de bois
The processes that underlie forest productivity and C allocation dynamics in trees are still poorly understood. Forest growth has for long been thought to be C limited, through a hypothesized causal link between C supply and growth (source control). This C-centric paradigm underlies most of the C allocation rules formalized in process-based models (PBMs). However, the source limitation of growth has been questioned by several authors, arguing that meristem activities are more sensitive than C assimilation to environmental stresses (e.g., water deficit and low temperatures). Moreover, the effect of management, which strongly affects forest functioning and wood growth, is not accounted for in most of the PBMs used to project the future terrestrial C sink. Our main objective in this thesis was to move forward into our understanding of the constraints that affect - or will affect - the wood productivity in European forests, from present to the end of the 21 st century. We addressed this objective through the improvement of the representation of the forest productivity and C allocation in the CASTANEA PBM, building on a detailed analysis of the key drivers of annual wood productivity in French forests over the last 30 years (the species studied are Fagus sylvatica, Quercus ilex, Quercus petraea, Quercus robur and Picea abies). Our results supported the premise that the annual wood growth of the studied species is under a complex control including both source and sink limitations. The inter-site variability in the fraction of C allocatedto stand wood growth was predominantly driven by an age-related decline. At the tree level, we showed that annual wood growth was well predicted by the individual size. The size-asymmetry of growth, i.e., the advantage of big trees in the competition for resources, increased consistently with the whole stand productivity at both inter-site and inter-annual scales. On the basis of our findings, we developed a new C allocation scheme in the CASTANEA PBM, which integrate a combined source-sink limitation of wood growth. The new calibrated model captured both the inter-annual and inter-site changes in stand wood growth that was observed across national environmental gradients. The model was also successfully evaluated against a meta-analysis of carbohydrate reserve pools in trees and satellite-derived leaf area index estimates. Our results indicated that the representation of the environmental control of sink activity does not affect the qualitative predictions of the future of the European forest productivity previously obtained from source-driven PBMs. However, the current, source-driven generation of PBMs probably underestimates the spatial heterogeneity of the effects of climate change on forest growth that arise from sink limitations.Further, we successfully used our findings regarding the dependences of annual wood growth at tree level (i.e., empirical rules of tree growth competition) to calibrate a module for the simulation of the individual growth of trees in the CASTANEA model. The coupled model was used to assess the potential effects of management on forest functioning and wood growth across France. We identified the areas where management efforts may be concentrated in order to mitigate near-future drought impact on national forest productivity. Around a quarter of the French temperate oak and beech forests are currently in zones of high vulnerability, where management could thus mitigate the influence of climate change on forest yield

O alto custo do carvão ativado tem motivado a busca por materiais adsorvedores de baixo custo, como os subprodutos industriais. Neste sentido, o uso dos subprodutos industriais de xisto: finos de xisto (XC), xisto retortado (XR) e xisto retortado com pneus (XRP), proveniente do processo PETROSIX/PETROBRAS, e o catalisador exaurido (CAT), da unidade de FCC (Craqueamento Catalítico em Leito Fluidizado), foram caracterizados e utilizados neste trabalho na adsorção de compostos orgânicos de efluente líquido industrial. O objetivo geral deste estudo é modelar matematicamente o processo de adsorção de compostos orgânicos em xisto, catalisador exaurido de FCC e carvão ativado em pó, utilizando o modelo HSDM (Modelo de Difusão por Superfície Homogênea), e o comportamento hidráulico do sistema adsorvedor. A caracterização estrutural e química de várias amostras de xisto (finos de xisto, xisto retortado e xisto retortado com pneus) e do catalisador exaurido de FCC, além do desenvolvimento de um modelo computacional para a simulação do processo de adsorção são contribuições adicionais ao trabalho. Os resultados de caracterização dos adsorventes de xisto mostram que estes materiais são basicamente macroporosos e com área superficial em torno de 0,51 a 3,36 2 . 1 m g , além de apresentarem as mesmas estruturas cristalinas, e micrografias características dos argilominerais. Já o adsorvente CAT mostrou-se formado basicamente por faujasita, sílica e alumina, apresentando-se na forma de grânulos esféricos, irregulares e microporosos, com área superficial característica de materiais zeolíticos (148 e 155 2 . 1 m g ). Os ensaios de adsorção realizados nos efluentes sintéticos e industriais (Fenólico e Petroquímico) mostraram que existe potencial de aplicação dos subprodutos industriais de xisto e CAT na remoção de compostos orgânicos (corantes, fenóis e COT) destes efluentes. Os resultados das simulações obtidos do modelo proposto mostraram que o tratamento unicamente por adsorção em xisto ou CAT, tendo em vista os padrões ambientais de descarte de efluente (resolução CONAMA 357), é inviável. Isto por que a quantidade de adsorvente requerida é muito elevada. Entretanto, tais adsorventes podem ser utilizados na redução da carga orgânica de ambos os efluentes. Por questões de transporte, é indicado que cada subproduto industrial seja utilizado na própria indústria que lhe deu origem. Ou seja, o CAT é indicado para o tratamento do efluente Petroquímico e os adsorventes de xisto para o Fenólico.
The high cost of the activated carbon has motivated the search of low cost adsorbents such as industrial by-products. In this sense, the use of industrial by-products of oil shale: Oil Shale (XC), Pirolized Oil Shale (XR) and Pirolized Oil Shale with Tires (XRP), from PETROSIX/PETROBRAS, and the spent catalyst (CAT), from FCC (Fluid Catalytic Cracking) unit were characterized and used in this work in the adsorption of organics compounds of industrial liquid effluent. The main contribution of this thesis is to propose a mathematical model to the adsorption process of organic compounds in oil shale, spent catalyst of FCC and powdered activated carbon. This model is based on HSDM (Homogeneous Surface Diffusion Model) model and on the hydraulic behavior of the adsorbent system. Other contribution is the structural and chemical characterization of several samples of oil shale (oil shale, Pirolized oil shale and Pirolized oil shale with Tires) and of the spent catalyst of FCC. A computational model to simulate the adsorption process of these materials is also developed and can be considered an additional contribution of this work. Experimental and simulated results allow characterization of the oil shale adsorbent as basically macroporous and with superficial area about 0.51 to 3.36 m2.g-1. In addition, they present the same crystal structures and clay micrografies characteristics. The adsorbent CAT is composed basically by Faujasite, silica and alumina. They present spherical beads, irregular forms and micropores, with superficial area characteristics of zeolitic materials (148 and 155 m2.g-1). The adsorption tests realized in the synthetic and industrial effluents (Phenolic and Petrochemical) showed the potential of application of the industrial by-products of oil shale and CAT in the removal of organics compounds (dyes, Phenol and COT) of these effluents. In respect of environmental standards to effluents disposal (CONAMA resolution 357), simulations results, obtained with the proposed model, has demonstrated that the use of only oil shale or CAT is not viable, because the high quantity of adsorbents required. However, such adsorbents can be used in the reduction of organic loads in both effluents, when combined with other processes. Each adsorbent showed be used where it is produced because of transportation cost. The CAT is indicated for the treatment of Petrochemical effluent while the others adsorbents may be applied in the phenolic effluent treatment.

Empirical prediction of soil properties coupled with an understanding of soil processes, can uncover the complexity of the soil system. Digital soil mapping (DSM) has revolutionized the way soil information is delivered. While empirical DSM has greatly improved the quantitative prediction, we should be able to incorporate our physical and mechanistic understanding of the processes. Likewise, we should be able to use empirical knowledge to inform process-based models. This thesis delivers mechanistic and empirical models to improve the understanding of soil genesis and mapping of soil functional properties and finding the relationships between soil and environmental factors. Chapter 2 first critically reviews pedology models and DSM concepts, mapping soil classes, mapping soil profiles, mapping pedological features and processes, the relation between pedological knowledge and DSM, and the application of mechanistic pedological models in DSM. Chapter 3 investigates the use of a mechanistic pedogenesis model, State Space Soil Production and Assessment Model (SSSPAM) for modelling the spatiotemporal evolution of particle-size distribution (PSD). In Chapter 4, we used process-based understanding in a mechanistic model to help us make a better prediction of the 4D spatiotemporal distribution of SOC. Chapter 5 evaluates the proposition that soil properties can be evaluated at any depth by comparing the multi-layered 2.5D and 3D modelling with soil depth as a predictor variable. Chapter 6 investigates whether data provided from a rapid and non-destructive proximal sensor can be used to directly predict the provenance of soil samples. Overall, this thesis demonstrates that to comprehensively explain the complexity of the soils, their dynamics and relation to the soil-forming factors, it is beneficial to include knowledge of processes to model soil profile distribution and identify the unique pattern of soil distribution.

The weight saving benefits of carbon fibre composites have been keenly adopted by civil aviation, with over 50% of the weight of modern designs coming from the carbon fibre components. The rapid rise in demand for this new material has led to the development of fully automated manufacturing techniques, improving rate of production and repeatability of manufacture. However, this rapid development, combined with a constant drive for increased rate of manufacture from industry can result in the formation of critical defects in the more complicated structural components. Manufacturing complex aeronautical structures from carbon fibre leads to a number of interesting mechanical problems. Forcing a multi-layered laminate to conform to a curved geometry requires individual layers to move relative to one another in order to relieve various forming-induced stresses. If the layers are constrained the dissipation of these stresses in the form of interply shear is prevented and a wide range of defects can occur, compromising the integrity of the final component. One of the most important of these is fibre wrinkling, which is effectively the buckling of one or more layers within an uncured laminate. This buckle results in a localised change in fibre orientation, which can result in a significant knockdown in part strength. A large amount of research has been conducted on carbon fibre in its cured state, when it exists as elastic fibres in an elastic matrix. Manufacturing occurs when the material is uncured however, with modern processes typically using fibres which are pre-impregnated with resin in order to reduce void content and aid fibre placement. A ply of uncured material therefore consists of stiff elastic fibres suspended in a very weak liquid viscoelastic material, whose properties are hugely influenced by temperature and rate of deformation. This thesis builds a better understanding of the mechanics involved in forming, using a series of characterisation techniques developed drawing from techniques in the literature. Part of the process involves the fitting of a one-dimensional viscoelasto-plastic model to experimental test data in order to represent the material response when shearing two plies about their interface. This model shows the material response to be dominated by the viscoelastic resin at low temperatures, before becoming frictional and fibre dominated at higher temperatures. In terms of optimum formability, a region exists in the transition from the viscous to frictional behaviour at which resistance to forming is minimised. With this data alone, optimum forming parameters such as rate of deformation, pressure and temperature can be suggested based on the material being used, along with design parameters such as stacking sequence. Another important characteristic which must be understood when considering ply wrinkling is the bending stiffness of uncured prepreg, both as a single ply and when combined to form a small laminate. A wrinkle is in effect the buckling of a single or small number of plies within a laminate, therefore by understanding the bending stiffness and process-induced loading we can begin to predict whether or not wrinkles are likely to occur for a particular manufacturing regime. In order to assess bending stiffness, a modified Dynamic Mechanical Analysis process is employed, replacing the standard Engineers Bending Theory calculations with a Timoshenko element to capture the large degree of intraply shear experienced in the bending of uncured prepreg. Finally, a small laminate scale demonstrator is considered in which a 24-ply laminate is consolidated into a female tool in such a way as to induced maximum shear strain between the plies, in order that the optimum forming parameters predicted by the characterisation tests might be validated. A simple energy minimisation model is used to predict the variation in consolidation strain around the part due to resistance to shear, using material parameters from the model describing the inter-ply shear test data. These parameters are also used to inform a novel modelling technique which has been developed parallel to this thesis, which is validated against the experimental results, and shows how the characterisation techniques can be used to advance simulation methods aimed at reducing the development time for new carbon fibre components. This work provides a set of tests and methodologies for the accurate characterisation of the behaviour of uncured carbon fibre during forming. The models developed alongside these tests allow for a detailed interrogation of the results, providing valuable insight into the mechanics behind the observed material behaviour and enabling informed decisions to be made regarding the forming process in order that the occurrence of defects might be minimised. The primary aim has been to provide a set of vital input parameters for novel, complex process modelling techniques under development, which has been achieved and validated experimentally.

Ingeniero Civil
Los salares se ubican típicamente en la región altiplánica andina de Chile, Perú y Bolivia. Los sistemas acuáticos formados en ellos, corresponden usualmente a lagunas extremadamente someras, sometidas a condiciones ambientales desfavorables como bajo oxígeno atmosférico, alta oscilación térmica, alta radiación y fuertes vientos durante las horas del día. Estos ecosistemas están principalmente sustentados por la producción bentónica primaria, la que funciona como alimento para aves de la zona, como los flamencos, ave que se encuentra en estado vulnerable. Debido a lo anterior es que el trabajo de título realizado, consiste en la elaboración de un modelo hidrodinámico de la variación intradiaria de dióxido de carbono y oxígeno en el salar de Huasco, dinámicas que se ven afectadas por los flujos en la interfaz agua-sedimentos, los procesos biológicos de la columna de agua y los flujos en la interfaz aire-agua. El objetivo general es describir y cuantificar los procesos de transporte-reacción de dióxido de carbono y oxígeno en la zona, mediante la elaboración de un modelo hidrodinámico impermanente en 0D del salar, que permita obtener las evoluciones diarias para el oxígeno y el dióxido de carbono, para luego ser validado utilizando mediciones del terreno. El fin de la modelación es adquirir conocimiento acerca de estos fenómenos que pueden afectar considerablemente a los ecosistemas de la zona, únicos en el mundo, adaptados a condiciones climáticas extremas. Inicialmente se realizó un procesamiento de los datos obtenidos en dos campañas de terreno realizadas en los años 2015 y 2016, el que complementado con una revisión bibliográfica orientada a la hidro y biodinámica de sistemas someros, permitió plantear un modelo conceptual que simula las evoluciones intradiarias de dióxido de carbono y oxígeno. Luego se procedió a calibrar y validar el modelo con datos medidos, para finalmente realizar un análisis de sensibilidad que explique los procesos y parámetros más significativos del modelo. El principal resultado del trabajo, corresponde a un modelo que permite cuantificar las variaciones intradiarias de dióxido de carbono y oxígeno. Este modelo permite identificar que los procesos más importantes para el salar corresponden a la producción primaria, y a los flujos de masa en la interfaz aire-agua, tanto para el dióxido de carbono como para el oxígeno. En estos flujos se presentan inconsistencias entre lo que se sabe de la literatura y lo que se observa en el modelo, donde se presentan grandes diferencias entre las tasas de trasferencia en esta interfaz según el compuesto que se esté analizando.

With the continuing trend towards miniaturization, micro milling plays an increasingly important role in fabrication of freeform and high-accuracy micro parts or components directly and cost-effectively. The technology is in kinematics scaled down from the conventional milling, however, existing knowledge and experiences are limited and comprehensive studies on the micro tooling performance are essential and much needed particularly for the process planning and optimization. The cutting performance of micro tools is largely dependent on the dynamic performance of machine tools, tooling characteristics, work material properties and process conditions, and the latter three aspects will be focused in the study. The state of the art of micro milling technology with respect to the tooling performance has been critically reviewed, together with modelling work for performance prediction as well as metrology and instrumentation for the performance characterization. A novel 3D finite element method taking into account the geometry of a micro tool, including the tool diameter, rake angle, relief angle, cutting edge radius and helix angle, has been proposed for modelling and simulation of the micro milling process. Validation through well-designed micro milling trials demonstrates that the approach is capable of characterizing the milling process effectively. With the support of FEM simulation developed, the tooling geometrical effects, including those from helix angle, rake angle and cutting edge radius with influences on cutting forces, tool stresses, tool temperatures, milling chip formation and temperatures have been comprehensively studied and compared for potential micro tool design and optimization purposes. In an effort to prolong the tool life and enhance the tooling efficiency, DLC and NCD coatings have been deposited on micro end mills by PE-CVD and HF-CVD processes respectively. Corresponding cutting performance of these coated tools have been assessed and compared with those of WC micro tools in both dry and wet cutting conditions so as for better understanding of the coating influence on micro tools. Furthermore, the cutting characteristics of the DLC coated and uncoated tools have been analysed through verified plane-strain simulations. The effects of coating friction coefficient, coating thickness and UCT have been determined and evaluated by design of simulation method. Mechanical, chemical and physical properties of a work material have a direct influence on its micro-machinability. Five most common engineering materials including Al 6061-T6, C101, AISI 1045, 304 and P20, have been experimentally investigated and their micro milling behaviours in terms of the cutting forces, tool wear, surface roughness, and micro-burr formation have been compared and characterized. Feed rate, cutting speed and axial depth of cut constitute the complete set of process variables and they have significant effects on the tooling performance. Fundamental understanding of their influences is essential for production engineers to determine optimum cutting parameters so as to achieve the maximum extension of the tool life. 3D FE-based simulations have been carried out to predict the process variable effects on the cutting forces, tool stresses, tool temperatures as well as micro milling chip formation and temperatures. Furthermore, experimental approach has been adopted for the surface roughness characterization. Suggestions on selecting practical cutting variables have been provided in light of the results obtained. Conclusions with respect to the holistic investigation on the tooling performance in micro milling have been drawn based on the research objectives achieved. Recommendations for future work have been pointed out particularly for further future research in the research area.

Orientadores: Teresa Massako Kakuta Ravagnani, Sergio Persio Ravagnani
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: A redução dos níveis de dióxido de carbono (CO2) é de suma importância, tanto para o combate à poluição atmosférica proveniente de atividades industriais, como no tratamento de correntes gasosas em processos químicos. O método clássico para captura de CO2 engloba sua absorção reativa em solução de aminas, conduzida em colunas de borbulhamento, spray ou recheio. Porém, desvantagens como a formação de espuma e dispersão de fase constituem problemas operacionais significativos desses processos. Alternativamente, módulos de membrana de fibras ocas seriam equipamentos mais adequados para esse fim, apresentando como vantagens uma grande área interfacial e flexibilidade operacional. Nesse sentido, o presente estudo buscou realizar a simulação do processo de absorção de CO2 em módulos de membrana, utilizando soluções aquosas de2-amino-2-metil-1-propanol (AMP), dietanolamina (DEA) e metildietanolamina (MDEA). A modelagem matemática do sistema utilizou expressões da taxa de reação e equações de balanço de massa diferenciais. A resolução numérico-computacional do modelo foi conduzida mediante aplicação dos métodos de colocação ortogonal e de Michelsen, tendo sido implementada em linguagem Fortran. O processo foi estudado em diversas condições operacionais para a análise de sensibilidade paramétrica e os resultados indicam, com base nas características dos diferentes sistemas, as melhores condições gerais de operação. Dentre as aminas consideradas como solventes reativos, as maiores taxas de absorção de CO2 foram previstas com o uso de AMP. Entretanto, sua concentração radial, à saída do módulo de membrana, apresentou forte incidência do fenômeno de depleção da solução absorvedora. Os principais parâmetros que incrementaram a taxa de absorção e, conseqüentemente, a eficiência do módulo de membrana, foram a velocidade de escoamento do líquido absorvente, as concentrações iniciais de CO2 e de amina, o raio interno e o comprimento das fibras.
Abstract: The decrease in the carbon dioxide (CO2) levels is extremely important to avoid atmospheric pollution, from industrial activities, and to the gaseous treatment in several chemical processes. The classical process to the CO2 sequestration involves its reactive absorption into amine solutions, which are carried on bubble, spray or fixed bed columns. However, some disadvantages, such as foam formation and phase dispersion, are serious operational problems to be avoided. Alternatively, membrane modules are supposed to be mode adequate equipments to that aim, which some advantages are great interfacial area and operational flexibility. Under this context, the present study intended to provide the simulation of the CO2 absorption process in hollow fiber membrane module, by using a-amino-2-methyl-1-propanol (AMP), diethanolamine (DEA) and methyldiethanoamine (MDEA) aqueous solutions. The mathematical modeling is based on the inherent rate expressions of the reactive system, besides the differential mass balance equations. The numerical and computational solution was developed by applying the orthogonal collocation and Michelsen methods, which were compiled in Fortran language. The idealized process was studied based on a given standard operational condition, besides a parametric sensibility analysis. The main results, to each sorption system, show the best general conditions to the process operation. Under the standard operation, among the alkanolamines considered as reactive solvents, the best CO2 absorption rate were calculated by using the AMP solution. Nevertheless, its radial concentration tends to suffer the incidence of depletion phenomena in their aqueous solution. The best performance credited to the AMP solution were also confirmed, where the main parameters that increased the absorption rate were the absorbent liquid flow velocity, the initial CO2 and amine concentration, the fibers inner radius and length.
Mestrado
Sistemas de Processos Quimicos e Informatica
Mestre em Engenharia Química

La metodologia LCA rappresenta lo strumento chiave delle politiche europee per la valutazione degli impatti ambientali di prodotti e servizi durante il loro intero ciclo di vita. Essa è ampiamente impiegata, tra l’altro, per la valutazione dei servizi professionali di pulizia per questo motivo sono state elaborate delle linee guida (Product Category Rules, PCR) specifiche. Il principale obiettivo della tesi è l’elaborazione di un modello analitico per la valutazione del ciclo di vita del servizio di pulizia professionale svolto presso il Politecnico di Torino. Il modello è stato realizzato per valutare e confrontare gli impatti derivanti da tre possibili scenari di miglioramento del servizio elaborati in ottica Ecolabel. Il secondo obiettivo della tesi è testare l’adeguatezza del modello tramite sua implementazione nel software GaBi con i dati relativi al servizio in esame. La struttura del modello è basata sulla letteratura di riferimento (PCR di settore e EPD di servizi di pulizia) ma viene adattata alle esigenze dello studio a supporto del processo di sostituzione della fornitura secondo i protocolli Ecolabel. Il servizio è diviso in tre fasi: processi di upstream, core e downstream, rispettivamente riguardanti la produzione e il trasporto degli articoli di pulizia, l’erogazione del servizio e il fine vita dei prodotti impiegati. I processi inclusi nel modello sono stati selezionati perché influenzati da una variazione del protocollo di pulizia. I risultati ottenuti dallo studio sono relativi alla categoria d’impatto "Riscaldamento globale con orizzonte temporale di 100 anni (GWP100)" e risultano coerenti con la letteratura: la fase di maggior impatto è quella di core, seguita da upstream e poi downstream. Il modello risulta dunque idoneo all’obiettivo dello studio. Le fasi successive del progetto, escluse dall’elaborato, prevedono l’impiego del modello come base per lo svolgimento della LCA degli scenari Ecolabel, garantendo un solido confronto tra risultati.

Arsenic contamination of circum-Himalayan groundwater is leading to one of the greatest humanitarian disasters of modern times, poisoning at least 70 million people who are mostly poor and rural. The groundwater is hosted in Holocene aquifers consisting of Himalayan sediments deposited by the great Asian rivers in deltaic environments. Arsenic is released when organic material (OM) reacts with the iron-oxide minerals co-deposited in the sediments onto which arsenic is adsorbed. The source of OM is one of the most important questions facing researchers and policy makers. There are generally accepted to be three potential sources of OM: 1) sedimentary bound OM (SOM) co-deposited with sediments; 2) thermally mature petroleum upwelled from reservoirs below the aquifers; 3) dissolved organic carbon (DOC) some of which might be drawn in to the aquifer through modern pumping and irrigation. In this thesis the nature of organic material in the aquifer is researched and the processes and timescales which lead to arsenic release are studied. Here evidence for a new conceptual model of arsenic release is presented. Isotopic tracing combined with a new geochemical model and organic geochemical techniques, shows that OM driving arsenic release pre-dates agriculture in the region and was from natural grasslands in the early Holocene. The geochemical model utilises strontium isotopes to correct the radiocarbon age of dissolved inorganic carbon (DIC) to find only the age and isotopic signature of DIC from oxidation of organic material. This shows that DIC from oxidation of OM was from the early Holocene and had an isotopic signature consistent with the early Holocene SOM in this region. A study of the sediments in the region built upon a geomorphological history shows that the most oxidised SOM is from early Holocene sediments. Thus both techniques separately indicate that pre-agricultural organic material drove arsenic release. This conceptual model however reveals the "arsenic sand paradox", because whilst release is from early Holocene clays, today highest concentrations of arsenic are in younger sands. Explaining this paradox is the most important next step leading on from this research.

La capture du dioxyde de carbone (CO2) en postcombustion est une stratégie importante pour la limitation de l’effet de serre. Le procédé de référence est l’absorption du CO2 dans des solutions aqueuses aminées, suivie par une étape de stripage du solvant. La technologie mature associée à ce procédé est la colonne à garnissage. Toutefois, afin de rendre le procédé plus attractif, il convient de l’intensifier en réduisant le volume des équipements et le coût énergétique associé. Les contacteurs membranaires à fibres creuses (CMFC) constituent une alternative aux colonnes à garnissage. Les CMFC permettent de développer d’importantes aires spécifiques conduisant potentiellement à une intensification des transferts gaz-liquide. Ainsi, l’utilisation des CMFC réduirait la taille des installations, mais aussi diminuerait la consommation énergétique par la diminution de la quantité de vapeur de stripage. Cependant, l’utilisation de CMFC dans les étapes d’absorption et de stripage dans des conditions industrielles a été peu étudiée. Afin de combler cette lacune, des modèles à différents niveaux de complexité : monodimensionnel, bidimensionnel, isotherme et adiabatique ont été développés, comparés et validés. Ceci afin d’identifier le niveau de complexité approprié. Les résultats de simulation ont mis en évidence le potentiel d’intensification des CMFC dans l’étape d’absorption et aussi de stripage, se traduisant par une réduction en volume de 4 à 10 fois par rapport aux colonnes à garnissage. Néanmoins, les CMFC peuvent difficilement réduire le coût énergétique du procédé étant donné que l’étape de stripage fonctionne dans des conditions très proches de la limite thermodynamique
Post-combustion CO2 capture (PCC) is an important strategy in mitigating greenhouse effect. The reference process in PCC is the CO2 absorption into amine aqueous solutions, followed by the regeneration (or stripping) of the solvent. The robustness of packed columns makes it the standard technology for both absorption and stripping steps. However, the treatment of large quantities of flue gases requires itself equipment of a large size. Hollow fibre membrane contactors (HFMC) are considered as one of the most promising strategies for intensified CO2 absorption process, due to their significantly higher interfacial area than that of packed columns, allowing to reduce the equipment size. In addition, this would reduce the energy penalty of the process by reducing the required amount of stripping steam. However, despite the potential advantages of HFMC, very few investigations have studied implementing this technology for PCC within an industrial framework. To fill this lack, the performances of both absorption and stripping steps using HFMC under industrial conditions were estimated by modelling and simulation. To identify the optimal modelling strategy, transfer models with different levels of complexity were developed ranging from one-dimensional isothermal single-component to two-dimensional adiabatic multi-component. Simulation results of both absorption and stripping steps revealed that, compared to traditional packed columns, contactor volume reduction factors comprised between 4 and 10 might be achieved using HFMC. However, since the stripping operating conditions are very close to thermodynamic equilibrium, HFMC can hardly reduce the energy consumption of the process

Bisphenol A (BPA) is widely used in the production of plastics, epoxy resins and polycarbonates. It is a toxic, endocrine disruptor compound. Different studies have shown the presence of BPA in several environmental systems, classifying it as a worldwide persistent pollutant which may act synergistically with other pollutants. In this context, advanced oxidation processes (AOP) have received great attention due to their ability to degrade pollutants with such characteristics, through their transformation into less hazardous compounds or even their mineralization. Although there are investigations on the use of AOPs for BPA degradation, systematic studies on the effects of process variables, coupled with the statistical interpretation of the results are virtually non-existent. Furthermore, to the best of our knowledge, a rigorous kinetic model has not yet been proposed for the degradation of this pollutant by the H2O2/UV process. The objective of this work was to evaluate BPA degradation by the H2O2/UV process, investigating the effects of the initial H2O2 concentration and the specific rate of photons emission (EP,0) by means of a Doehlert experimental design, combined with the response surface methodology. The experiments were performed in a photochemical tubular reactor equipped with a 254-nm UV lamp, for [H2O2]0 and EP,0 in the ranges 1.6-9.6 mmol L-1 and 0.87 × 1018-3.6 × 1018 photons L-1 s-1, respectively. Total BPA degradation was achieved after 60 min of irradiation in all experiments. The best conditions were [H2O2]0 = 7.6 mmol L-1 and EP,0 = 3.6 × 1018 photons L-1 s-1, for which the best performance was obtained regarding the BPA degradation rate, BPA degradation after 15 min, and the second highest TOC removal after 180 min. However, in most experiments less than 75% TOC removal was observed, with 95% mineralization obtained only for the superior [H2O2]0 and EP,0. A mathematical model was developed, considering the reactor characteristics and the radiation field, based on the line source with parallel emission (LSPP) approach, in combination with the radiative transfer equation (RTE), mass balances, and a detailed kinetic model of the H2O2/UV process. The steady-state approximation was applied for all radical species. In the estimation of unknown kinetic constants, the non-linear least squares method was employed. The model was able to satisfactorily fit experimental BPA and H2O2 concentrations as a function of time. This work shows that the H2O2/UV process is a good alternative for BPA removal from aqueous streams, with total degradation of the target compound and adequate percent mineralization under optimal operating conditions. Such conditions may serve as first guidelines for pilot-plant and industrial processes operation. In addition, simulations using the proposed kinetic model may provide useful information for the design and scale-up of pre- or post-treatment of effluents containing this pollutant.
O bisfenol A (BPA) é amplamente utilizado na fabricação de plásticos, resinas epóxi e policarbonatos. Trata-se de um composto tóxico e um desregulador endócrino. Diferentes estudos evidenciam a presença do BPA em diversos compartimentos ambientais em todo planeta, identificando-o como um poluente persistente e resistente à degradação biológica, que apresenta efeitos sinergéticos com outros poluentes. Nesse contexto, os processos oxidativos avançados (POA) têm recebido atenção devido a sua capacidade em degradar poluentes com tais características, transformando-os em compostos menos perigosos ou até mesmo mineralizando-os totalmente. Apesar de haver trabalhos na literatura acerca da utilização de POA para degradação de BPA, estudos sistemáticos dos efeitos de variáveis de processo junto com a interpretação estatística dos resultados são virtualmente inexistentes. Além disso, até onde se sabe um modelo cinético rigoroso ainda não foi proposto para a degradação desse poluente por meio do processo H2O2/UV. Este trabalho teve por objetivo avaliar a degradação do BPA pelo processo H2O2/UV, investigando os efeitos da concentração inicial de H2O2 e da taxa específica de emissão de fótons (EP,0) por meio de um projeto experimental Doehlert, combinado com a análise de superfície de resposta. Os experimentos foram realizados em um reator tubular fotoquímico equipado com uma lâmpada UV de 254 nm, para [H2O2]0 e EP,0 entre 1,6-9,6 mmol L-1 e 0,87 × 1018 - 3,6 × 1018 fótons L-1 s-1, respectivamente. Todos os experimentos sob H2O2/UV resultaram em total degradação do BPA após 60 min de irradiação. Nesse caso, as melhores condições foram [H2O2]0 = 7,6 mmol L-1 e EP,0 = 3,6 × 1018 fótons L-1 s-1, para as quais se obteve o melhor desempenho quanto à taxa de degradação de BPA e à remoção após 15 min, e a segunda maior remoção de COT após 180 min. Entretanto, na maioria dos experimentos menos de 75% de remoção de COT foram observados, com 95% de mineralização obtida apenas para os maiores [H2O2]0 e EP,0. Elaborou-se um modelo matemático que considera as características do reator utilizado e o campo de radiação, baseado no modelo de fonte linear de emissão em planos paralelos (LSPP), combinado à equação de transferência radiativa (RTE), aos balanços materiais e a um modelo cinético detalhado do processo H2O2/UV. Foi empregada a aproximação de estado estacionário para todas as espécies radicalares. Na estimativa das constantes cinéticas desconhecidas, utilizou-se o método de mínimos quadrados não linear. Esse modelo foi capaz de ajustar satisfatoriamente as concentrações experimentais de BPA e de H2O2 em função do tempo. Este trabalho mostra que o processo H2O2/UV constitui uma alternativa conveniente para a degradação de BPA em matrizes aquosas, com total degradação do composto alvo e porcentagem de mineralização adequada nas condições ótimas de operação. Tais condições podem servir como diretrizes iniciais de processamento em escalas piloto e industrial. Por sua vez, simulações empregando o modelo matemático proposto permitem gerar informações úteis para projeto e aumento de escala de processos de pré- ou pós-tratamento de efluentes contendo esse poluente.

L’azoto è uno dei prodotti principali dell’industria chimica, utilizzato principalmente per assicurare un sicuro stoccaggio di composti infiammabili. Generatori con sistemi PSA sono spesso più economici della tradizionale distillazione criogenica. I processi PSA utilizzano una colonna a letto fisso, riempita con materiale adsorbente, che adsorbe selettivamente un componente da una miscela gassosa. L’ossigeno diffonde molto più velocemente dell'azoto nei pori di setacci molecolari carboniosi. Oltre ad un ottimo materiale adsorbente, anche il design è fondamentale per la performance di un processo PSA. La fase di adsorbimento è seguita da una fase di desorbimento. Il materiale adsorbente può essere quindi riutilizzato nel ciclo seguente. L’assenza di un simulatore di processo ha reso necessario l’uso di dati sperimentali per sviluppare nuovi processi. Un tale approccio è molto costoso e lungo. Una modellazione e simulazione matematica, che consideri tutti i fenomeni di trasporto, è richiesta per una migliore comprensione dell'adsorbente sia per l'ottimizzazione del processo. La dinamica della colonna richiede la soluzione di insiemi di PDE distribuite nel tempo e nello spazio. Questo lavoro è stato svolto presso l'Università di Scienze Applicate - Münster, Germania. Argomento di questa tesi è la modellazione e simulazione di un impianto PSA per la produzione di azoto con il simulatore di processo Aspen Adsorption con l’obiettivo di permettere in futuro ottimizzazioni di processo affidabili, attendibili ed economiche basate su computazioni numeriche. E' discussa l’ottimizzazione di parametri, dati cinetici, termodinamici e di equilibrio. Il modello è affidabile, rigoroso e risponde adeguatamente a diverse condizioni al contorno. Tuttavia non è ancora pienamente soddisfacente poiché manca una rappresentazione adeguata della cinetica ovvero dei fenomeni di trasporto di materia. La messa a punto del software permetterà in futuro di indagare velocemente nuove possibilità di operazione.

This thesis presents a new stratigraphic forward numerical model to simulate the carbonate production of marine sedimentary basin through ecological model which is implemented in the SIMSAFADIM-CLASTIC program. This ecological model is based on the Generalized Lotka Voltera equations that model the population evolution of species. These populations are controlled by biological factors (growth rate, carrying capacity and interaction among species), and by the environmental conditions (light, energy of the medium, nutrients, bottom slope and concentration of clastic sediments in suspension) which are combined forming a unique environmental factor that downscale the intrinsic rate of growth. The algorithm to apply in the code uses an explicit Runge-Kutta numerical method of order (4)5 to solve the differential equations formulated in the ecological model. Finally, a 3D visualization output files for the interpretation and analysis are generated using the VTK format. The obtained code has been applied in three sample experiments in order to discuss the possibilities and the limitations of the code. The first example is the model of a theoretical basin. The results are compared with real cases. The second example is an actual basin sited in western Mediterranean Sea. The results are discussed to show the applicability and the limitations of the model. The third example applies several configurations to the Aptian Galve sub-basin (Maestrat Basin, E Iberia), allowing to define the environmental conditions.

De 20 största massabruken i Sverige släpper tillsammans ut ungefär 20 miljoner ton CO2 per år. Dessa utsläpp har biogent ursprung och anses därför vara klimatneutrala. Massa- och pappersindustrin är därmed en lämplig kandidat för implementeringen av BECCS (eng. Bioenergy with Carbon Capture and Storage) och har en betydande potential att nå de, av den svenska regeringen, uppsatta klimatmålen som säger att Sverige inte ska några nettoutsläpp av växthusgaser till atmosfären senast år 2045. I detta examensarbete simulerades kemiska absorptions- och desorptionsprocesser med MEA som lösningsmedel genom att tillämpa den hastighetsbaserade metoden i en rigorös modell i Aspen Plus. Stripper- och absorptionsmodellerna validerades innan standardprocessen modifierades till en konfiguration som möjliggör värmeintegration av koldioxidinfångningens överskottsvärme med, exempelvis, ett sulfatmassabruk. Avskiljningsgraden och laddning hos den mättade lösningen användes som prestandaindikatorer för att validera absorptionskolonnerna. Återkokarens energiåtgång och laddning hos den omättade lösningen användes somprestandaindikatorer för att validera stripperkolonnerna. Samtliga kolonner dimensionerades för att erhålla 90 vikt% avskiljningsgrad. Olika flödeshastigheter av lösningsmedlet testades för att säkerställa effektivt nyttjande av packningen i absorptions- och stripperkolonnerna. Lämpliga temperaturnivåer för värmeintegration, inom och utanför, koldioxidinfångningen erhölls genom att utvärdera olika varianter av en stripper-overhead-kompression konfiguration. Utvärderingen av den modifierade MEA processen tog hänsyn till potentialen för ångbesparing och energieffektivisering. Resultat från simuleringarna tyder på att den modifierade strippern skulle kunna ge besparingar på upp emot 11 % i ånganvändning. Energibesparingar i samma storleksordning kunde även erhållas genom värmeintegration mellan koldioxidinfångningen och en särskild process i ett referensbruk. Implementering av BECCS-konceptet på det här sättet skulle därmed kunna bli ett mer attraktivt alternativ för den svenska massa- och pappersindustrin att bekämpa klimatförändringarna.
The 20 largest pulp mills in Sweden emit around 20 million tonnes of CO2 per year. These emissions are considered carbon-neutral since they originate from biogenic sources. The pulp and paper industry is therefore a good candidate for the application of BECCS (Bioenergy with Carbon Capture and Storage) and has the potential to play a significant role for reaching the long-term mitigation target set by the Swedish government that Sweden should be climate-neutral by year 2045. In this thesis, a MEA-based chemical absorption and desorption process was rigorously modelled in Aspen Plus using the rate-based method. Validation of the absorber and stripper model was conducted before the standard process was modified to a configuration that enables heat integration of a significant amount of excess heat from the capture process in, for example, a Kraft pulp mill. CO2 removal rate and rich solvent loading were used as performance indicators to validate the absorber columns. The reboiler duty and lean solvent loading served as performance indicators in the stripper validation. The columns were dimensioned considering 90 wt% capture rate. Efficient use of the entire packing in the absorber and stripper columns was ensured by testing different solvent flow rates. Suitable temperature levels for heat integration, within and across the capture plant, were obtained through an assessment of different versions of a stripper overhead compression configuration. The evaluation of the modified MEA processes took into account the steam conservation potential and energy efficiency potential. The simulation results indicate that the modified stripper may lead to savings of up to 11% in steam consumption. Heat integration between the capture plant and a specific process in a reference Kraft pulp mill resulted in energy savings of the same order of magnitude. Thereby, making the BECCS concept a more attractive solution for the Swedish pulp and paper industry to mitigate climate change.

A mesure que l'intérêt mondial pour les énergies renouvelables s'intensifie, la production de biogaz ne cesse de croître, car elle est une source renouvelable et propre. La technologie de séparation par adsorption modulée en pression (Pressure Swing Adsorption ou PSA) se présente alors comme une des technologies intéressantes permettant la valorisation du biogaz en biométhane. La grande flexibilité du procédé PSA est liée en une certaine manière à sa complexité avec plusieurs paramètres de design et opératoires contrôlant les performances de l’unité de séparation. L’identification de ces paramètres par une approche expérimentale est pratiquement impossible et une phase d’étude numérique est primordiale pour dimensionner l’unité, concevoir le cycle de pression et déterminer les conditions optimales de fonctionnement, avant tout essai expérimental. L’objectif général de la thèse a été centré sur le développement d’outils de simulation d’un procédé de purification de biométhane par technologie PSA.Dans un premier temps, une simulation basée sur une modélisation dynamique monodimensionnelle non isotherme a été mise en place. Elle fait appel à un modèle cinétique d’adsorption de double force motrice (bi-LDF) pour décrire les échanges de matière intragranulaires. Le choix de l’adsorbant s’est porté sur un tamis moléculaire de carbone (CMS-3K) permettant d’assurer une grande sélectivité cinétique du dioxyde de carbone vis à vis du méthane (CH4). Le cycle PSA a été optimisé pour obtenir une récupération du CH4 de 92 % avec une consommation d'énergie spécifique modérée de 0,35 kWh/Nm3, tout en respectant les spécifications de pureté d’injection dans le réseau national (97 % de CH4). Les performances obtenues sont ainsi compatibles avec une exploitation industrielle. Ce cycle est composé de cinq colonnes et de quinze étapes incluant trois équilibrages et un recyclage de gaz de purge.Le développement d’un modèle numérique multidimensionnel (3D) et multi-échelle (colonne/grain/cristal) permettrait d’estimer les limites des hypothèses et des corrélations utilisées dans les simulateurs usuels. La première étape consiste à simuler l’écoulement du gaz dans un lit d’adsorbant ayant une morphologie la plus réaliste possible. Ainsi, lors de la seconde partie du travail de thèse, un lit constitué de billes inertes a été généré numériquement par calcul DEM (modélisation par éléments discrets) pour une colonne de taille de laboratoire. L’emploi d’OpenFOAM (logiciel CFD) a permis de calculer l’écoulement tridimensionnel d’un traceur dans la colonne. En parallèle une étude expérimentale du front de percée a été menée pour un lit de mêmes dimension et caractéristiques. Les temps de percée et les coefficients de dispersion-diffusion calculés et mesurés sont similaires. Cependant la simulation présente quelques divergences de la concentration du traceur localement dans la colonne, en raison de difficultés de maillage. L’étape suivante consistera à prendre en compte des interactions grains-fluide en considérant des grains poreux d’adsorbant
As global interest in renewable energy intensifies, biogas production continues to grow as a clean, renewable source. Pressure Swing Adsorption (PSA) is considered as one of the most interesting technologies for the valorization of biogas into biomethane. The great flexibility of the PSA process is linked in some way to its complexity with several design and operating parameters which control the performance of the separation unit. The identification of these parameters by an experimental approach is practically impossible. A numerical study stage is essential for sizing the unit, designing the pressure cycle and identifying the optimal operating conditions before any experimental test.The general objective of the thesis was focused on the development of simulation tools for a biomethane purification process using PSA technology.In a first stage, a simulation based on one-dimensional non-isothermal dynamic model, where the intragranular mass transfer kinetics was modelled using a double driving force (bi-LDF) approximation, was implemented. A carbon molecular sieve (CMS-3K) was selected. This adsorbent ensures a high kinetic selectivity of carbon dioxide with respect to methane (CH4). The optimized cycle, composed of five columns and fifteen steps including three equalization steps and a purge gas recycling allowed a CH4 recovery of 92% with a moderate specific energy consumption of 0.35 kWh/Nm3 , at the same time respecting the grid injection specifications (97% CH4 purity ). The performance obtained is thus compatible with industrial operation.The development of a multidimensional (3D) and multi-scale (column/grain/crystal) numerical model would serve to evaluate the limits of the assumptions and correlations used in usual simulators. The first step consists in simulating the gas flow in an adsorbent bed having a reaslistic stacking.. Thus, an inert packed bed was numerically generated by DEM calculation (discrete element modeling) for a column of laboratory size. The use of OpenFOAM (CFD software) allowed to calculate the three-dimensional tracer gas flow in the column. In parallel an experimental study of the breakthrough curves was carried out using a bed having the same dimensions and characteristics. The breakthrough times and the dispersion-diffusion coefficients calculated and measured were similar. However the simulation showed some divergences in the concentration of the tracer locally in the column, due to difficulties in meshing. The next step will consist in taking into account grain-fluid interactions by considering porous adsorbent grains

Cette thèse porte sur l'étude de la réaction d'hydrogénation du dioxyde de carbone vers des hydrocarbures gazeux et liquides sur un catalyseur supporté K-Fe/Al2O3. Le sujet s'inscrit dans le cadre des technologies Power-to-X qui visent à stocker les excès d’énergie électrique issue des énergies renouvelables sous forme de composés chimiques gazeux et liquides. En particulier, l'électricité est utilisée pour produire de l'hydrogène via l’électrolyse de l'eau, puis l'hydrogène obtenu est utilisé pour convertir le dioxyde de carbone en hydrocarbures. Ces hydrocarbures peuvent avoir des applications comme matière première dans l'industrie chimique ou comme carburants dans le domaine des transports. L'hydrogénation du dioxyde de carbone est une réaction catalytique, généralement réalisée sur des catalyseurs à base de fer, et s’effectue en deux étapes : d'abord, le dioxyde de carbone est converti en monoxyde de carbone via la réaction inverse de conversion eau-gaz (RWGS), puis le monoxyde de carbone est transformé en hydrocarbures via la synthèse Fischer-Tropsch (FT). L'une des principales contraintes de cette réaction est sa faible sélectivité, car une grande variété d'hydrocarbures peut être obtenue. Pour une éventuelle application de ce procédé à l'échelle industrielle, il est nécessaire de comprendre comment la sélectivité de la réaction pourrait être orientée vers la formation des produits visés. Dans ce travail, une étude expérimentale à l'échelle du laboratoire a été réalisée dans un lit fixe continu et un protocole analytique qui permet la quantification de tous les produits obtenus a été développé. De plus, nous avons développé un modèle macro-cinétique qui décrit avec une approche semi-empirique la formation de tous les produits considérés ; et un modèle micro-cinétique, qui contribue à apporter un éclairage sur les mécanismes de réaction possibles. Enfin, nous avons modélisé un réacteur à plus grande échelle avec des approches hétérogène et pseudo-homogène et nous avons simulé le procédé global pour estimer son bilan carbone et son efficacité énergétique
This thesis is focused on the study of the carbon dioxide hydrogenation reaction towards gaseous and liquid hydrocarbons over a supported K-Fe/Al2O3 catalyst. The subject is part of the framework of the Power-to-X technologies that aim at storing surplus electric power derived from renewable energy into the form of gaseous and liquid chemical compounds. In particular, the electricity is used to perform the water electrolysis to produce hydrogen, then the obtained hydrogen is used to convert carbon dioxide into hydrocarbons. These hydrocarbons can have applications as feedstock in the chemical industry or as fuels in the transport field. The carbon dioxide hydrogenation is a catalytic reaction, generally performed over Fe-based catalysts, consisting in two steps: first, carbon dioxide is converted into carbon monoxide via the reverse water-gas shift reaction (RWGS), and then it is further transformed into hydrocarbons via the Fischer-Tropsch synthesis (FT). One of the main constraints of this reaction is its low selectivity, as a variety of hydrocarbons can be obtained. For an eventual application of this process at the industrial scale, it is necessary to deeper understand and better describe the selectivity of the reaction to optimize the productivity of the desired products. In this work, we have carried out an experimental study of the reaction in a lab-scale fixed bed reactor and developed an analytic protocol that allows the quantification of all the products obtained. Moreover, we have developed a macro-kinetic model that describes with a semi-empirical approach the formation of all the products considered; and a micro-kinetic model, that contributes to give insights about the reaction mechanism. Finally, we have modelled a scaled-up reactor with a heterogeneous and a pseudo-homogeneous approach and we have simulated the global process to estimate its carbon and energy efficiencies

Le présent travail est réalisé dans le cadre de l’étude d’un procédé industriel de densification de matériaux composites carbone/carbone (C/C) destinés aux freins d’avion. Une préforme poreuse de fibres de carbone baigne dans un précurseur liquide et elle est chauffée par induction électromagnétique radio-fréquence. Le précurseur porté à ébullition dans l’espace poral crée un dépôt de carbone dans les zones les plus chaudes ; ce dépôt constitue la matrice du composite. On propose une modélisation physico-chimique de ce procédé afin d’en assurer le contrôle et l’optimisation. Le travail a consisté à développer un solveur couplant l’induction électromagnétique avec les transferts de masse, de chaleur, de mouvement et d’espèces chimiques, en incluant l’ébullition et le dépôt chimique. Le modèle inclut le circuit électrique complet permettant d’effectuer le chauffage : il permet donc de suivre en temps réel et de façon non destructive l’avancement de la densification par l’évolution des grandeurs électriques. Une formulation originale adaptée à la représentation simultanée du liquide, du gaz et de la zone en ébullition a été développée et implémentée avec succès dans un logiciel commercial d’éléments finis. Les résultats de la simulation sont comparés avec les données obtenues sur le moyen expérimental, avec un bon accord. Enfin, la simulation est utilisée pour proposer des pistes d’amélioration du procédé, en altérant la géométrie du dispositif de chauffage par induction et en modifiant la stratégie de pilotage en puissance
This work has been carried out in the frame of the study of an industrial process for the manufacturing of carbon/carbon (C/C) composite aircraft brake discs. A porous preform made of carbon fibres is immersed in a liquid precursor and is heated by Radio-Frequency electromagnetic induction. The boiling precursor enters the porous preform and yields a carbon deposit in the hottest zones; this deposit will be the carbon matrix of the composite. A physico-chemical process model is proposed in the aim of ensuring its control and optimisation. The work consisted in developing a numerical solver coupling electromagnetic induction heating with heat, mass and species balances accounting for boiling, diffusion and chemical deposition reactions. The model includes the complete electrical circuit of the heating device: it therefore allows real-time, non-destructive monitoring of the infiltration progress through the evolution of the electrical properties. An original formulation has been designed to simultaneously describe the liquid, the gas and the boiling zone; it has been implemented in a commercial Finite Element software package and validated physically with respect to experimental data, with a good agreement. Finally, the simulation software has been used to propose directions for process improvements, through alterations of the inductive heating device geometry or of the heating power supply program

Despite significant efforts have been directed toward reducing waste generation and encouraging alternative waste management strategies, landfills still remain the main option for Municipal Solid Waste (MSW) disposal in many countries. Hence, landfills and related impacts on the surroundings are still current issues throughout the world. Actually, the major concerns are related to the potential emissions of leachate and landfill gas into the environment, that pose a threat to public health, surface and groundwater pollution, soil contamination and global warming effects. To ensure environmental protection and enhance landfill sustainability, modern sanitary landfills are equipped with several engineered systems with different functions. For instance, the installation of containment systems, such as bottom liner and multi-layers capping systems, is aimed at reducing leachate seepage and water infiltration into the landfill body as well as gas migration, while eventually mitigating methane emissions through the placement of active oxidation layers (biocovers). Leachate collection and removal systems are designed to minimize water head forming on the bottom section of the landfill and consequent seepages through the liner system. Finally, gas extraction and utilization systems, allow to recover energy from landfill gas while reducing explosion and fire risks associated with methane accumulation, even though much depends on gas collection efficiency achieved in the field (range: 60-90% Spokas et al., 2006; Huitric and Kong, 2006). Hence, impacts on the surrounding environment caused by the polluting substances released from the deposited waste through liquid and gas emissions can be potentially mitigated by a proper design of technical barriers and collection/extraction systems at the landfill site. Nevertheless, the long-term performance of containment systems to limit the landfill emissions is highly uncertain and is strongly dependent on site-specific conditions such as climate, vegetative covers, containment systems, leachate quality and applied stress. Furthermore, the design and operation of leachate collection and treatment systems, of landfill gas extraction and utilization projects, as well as the assessment of appropriate methane reduction strategies (biocovers), require reliable emission forecasts for the assessment of system feasibility and to ensure environmental compliance. To this end, landfill simulation models can represent an useful supporting tool for a better design of leachate/gas collection and treatment systems and can provide valuable information for the evaluation of best options for containment systems depending on their performances under the site-specific conditions. The capability in predicting future emissions levels at a landfill site can also be improved by combining simulation models with field observations at full-scale landfills and/or with experimental studies resembling landfill conditions. Indeed, this kind of data may allow to identify the main parameters and processes governing leachate and gas generation and can provide useful information for model refinement. In view of such need, the present research study was initially addressed to develop a new landfill screening model that, based on simplified mathematical and empirical equations, provides quantitative estimation of leachate and gas production over time, taking into account for site-specific conditions, waste properties and main landfill characteristics and processes. In order to evaluate the applicability of the developed model and the accuracy of emissions forecast, several simulations on four full-scale landfills, currently in operative management stage, were carried out. The results of these case studies showed a good correspondence of leachate estimations with monthly trend observed in the field and revealed that the reliability of model predictions is strongly influenced by the quality of input data. In particular, the initial waste moisture content and the waste compression index, which are usually data not available from a standard characterisation, were identified as the key unknown parameters affecting leachate production. Furthermore, the applicability of the model to closed landfills was evaluated by simulating different alternative capping systems and by comparing the results with those returned by the Hydrological Evaluation of Landfill Performance (HELP), which is the most worldwide used model for comparative analysis of composite liner systems. Despite the simplified approach of the developed model, simulated values of infiltration and leakage rates through the analysed cover systems were in line with those of HELP. However, it should be highlighted that the developed model provides an assessment of leachate and biogas production only from a quantitative point of view. The leachate and biogas composition was indeed not included in the forecast model, as strongly linked to the type of waste that makes the prediction in a screening phase poorly representative of what could be expected in the field. Hence, for a qualitative analysis of leachate and gas emissions over time, a laboratory methodology including different type of lab-scale tests was applied to a particular waste material. Specifically, the research was focused on mechanically biologically treated (MBT) wastes which, after the introduction of the European Landfill Directive 1999/31/EC (European Commission, 1999) that imposes member states to dispose of in landfills only wastes that have been preliminary subjected to treatment, are becoming the main flow waste landfilled in new Italian facilities. However, due to the relatively recent introduction of the MBT plants within the waste management system, very few data on leachate and gas emissions from MBT waste in landfills are available and, hence, the current knowledge mainly results from laboratory studies. Nevertheless, the assessment of the leaching characteristics of MBT materials and the evaluation of how the environmental conditions may affect the heavy metals mobility are still poorly investigated in literature. To gain deeper insight on the fundamental mechanisms governing the constituents release from MBT wastes, several leaching experiments were performed on MBT samples collected from an Italian MBT plant and the experimental results were modelled to obtain information on the long-term leachate emissions. Namely, a combination of experimental leaching tests were performed on fully-characterized MBT waste samples and the effect of different parameters, mainly pH and liquid to solid ratio (L/S,) on the compounds release was investigated by combining pH static-batch test, pH dependent tests and dynamic up-flow column percolation experiments. The obtained results showed that, even though MBT wastes were characterized by relatively high heavy metals content, only a limited amount was actually soluble and thus bioavailable. Furthermore, the information provided by the different tests highlighted the existence of a strong linear correlation between the release pattern of dissolved organic carbon (DOC) and several metals (Co, Cr, Cu, Ni, V, Zn), suggesting that complexation to DOC is the leaching controlling mechanism of these elements. Thus, combining the results of batch and up-flow column percolation tests, partition coefficients between DOC and metals concentration were derived. These data, coupled with a simplified screening model for DOC release, allowed to get a very good prediction of metal release during the experiments and may provide useful indications for the evaluation of long-term emissions from this type of waste in a landfill disposal scenario. In order to complete the study on the MBT waste environmental behaviour, gas emissions from MBT waste were examined by performing different anaerobic tests. The main purpose of this study was to evaluate the potential gas generation capacity of wastes and to assess possible implications on gas generation resulting from the different environmental conditions expected in the field. To this end, anaerobic batch tests were performed at a wide range of water contents (26-43 %w/w up to 75 %w/w on wet weight) and temperatures (from 20-25 °C up to 55 °C) in order to simulate different landfill management options (dry tomb or bioreactor landfills). In nearly all test conditions, a quite long lag-phase was observed (several months) due to the inhibition effects resulting from high concentrations of volatile fatty acids (VFAs) and ammonia that highlighted a poor stability degree of the analysed material. Furthermore, experimental results showed that the initial waste water content is the key factor limiting the anaerobic biological process. Indeed, when the waste moisture was lower than 32 %w/w the methanogenic microbial activity was completely inhibited. Overall, the obtained results indicated that the operative conditions drastically affect the gas generation from MBT waste, in terms of both gas yield and generation rate. This suggests that particular caution should be paid when using the results of lab-scale tests for the evaluation of long-term behaviour expected in the field, where the boundary conditions change continuously and vary significantly depending on the climate, the landfill operative management strategies in place (e.g. leachate recirculation, waste disposal methods), the hydraulic characteristics of buried waste, the presence and type of temporary and final cover systems.

L’objectif de cette thèse est de contribuer à l’optimisation de la production de méthanol par hydrogénation de CO₂ en synthétisant des nouveaux catalyseurs sous forme d’extrudés pour un usage industriel. Six catalyseurs à base de Cu et ZnO supportés sur de l’alumine et des ZSM-5 ont été préparés et testés. A 36 bar et sous chauffage conventionnel, le CuZnO/Al₂O₃ a montré le meilleur rendement en méthanol. Un procédé industriel basé sur ce catalyseur a été proposé et optimisé. L’influence de l’extraction de l’eau et du méthanol du milieu réactionnel en utilisant deux réacteurs en série au lieu d’un a été étudié et il a été trouvé que cela augmente le rendement en méthanol considérablement. Sous plasma à DBD et à 1 bar, le Cu/Al₂O₃ donne des meilleures conversions de CO₂, alors que le CuZnO/ZSM-5 montre des meilleurs rendements en méthanol. Cela a été attribuée à la conductivité ionique et à la constante diélectrique des matériaux
The objective of this thesis is to contribute to the optimisation of the production of methanol by hydrogenation of CO₂ by synthesising new catalysts in the form of extrudates for industrial use. In this regard, six Cu-ZnO based catalysts supported on alumina and ZSM-5 were prepared and tested. At 36 bar and under conventional heating, the CuZnO/Al₂O₃ showed the best methanol yield. An industrial process based on this catalyst has been proposed and optimised. The influence of extracting water and methanol from the reaction medium using two reactors in series instead of one was investigated and it was found to increase methanol yield considerably. Tests at atmospheric pressure and under DBD plasma showed that the Cu/Al₂O₃ gives better CO₂ conversions, while the CuZnO/ZSM-5 showed better methanol yields. This was attributed to the ionic conductivity and the dielectric constant of the catalysts