Integrated design and control of chemical processes : part I : revision and clasification

[EN] This work presents a comprehensive classification of the different methods and procedures for integrated synthesis, design and control of chemical processes, based on a wide revision of recent literature. This classification fundamentally differentiates between “projecting methods”, where controllability is monitored during the process design to predict the trade-offs between design and control, and the “integrated-optimization methods” which solve the process design and the control-systems design at once within an optimization framework. The latter are revised categorizing them according to the methods to evaluate controllability and other related properties, the scope of the design problem, the treatment of uncertainties and perturbations, and finally, the type the optimization problem formulation and the methods for its resolution.[ES] Este trabajo presenta una clasificación integral de los diferentes métodos y procedimientos para la síntesis integrada, diseño y control de procesos químicos. Esta clasificación distingue fundamentalmente entre los "métodos de proyección", donde se controla la controlabilidad durante el diseño del proceso para predecir los compromisos entre diseño y control, y los "métodos de optimización integrada" que resuelven el diseño del proceso y el diseño de los sistemas de control a la vez dentro de un marco de optimización. Estos últimos se revisan clasificándolos según los métodos para evaluar la controlabilidad y otras propiedades relacionadas, el alcance del problema de diseño, el tratamiento de las incertidumbres y las perturbaciones y, finalmente, el tipo de la formulación del problema de optimización y los métodos para su resolución

Discretization approach

학위논문(박사)--서울대학교 대학원 :공과대학 화학생물공학부(에너지환경 화학융합기술전공),2019. 8. 이원보.In recent years, many researchers in chemical engineering have made great efforts to develop mathematical models on the theoretical side that are consistent with experimental results. Despite these efforts, however, establishing models for a system with complex phenomena such as multiphase flow or stirred reactors is still considered to be a challenge. In the meantime, an increase in computational efficiency and stability in various numerical methods has allowed us to correctly solve and analyze the system based on the fundamental equations. This leads to the need for a mathematical model to accurately predict the behavior of systems in which there is interdependence among the internal elements. A methodology for building a model based on equations that represent fundamental phenomena can lower technical barriers in system analysis. In this thesis, we propose three mathematical models validated from laboratory or pilot-scale experiments. First, an apparatus for vaporizing liquid natural gas is surrounded with a frost layer formed on the surface during operation, and performance of the apparatus is gradually deteriorated due to the adiabatic effect. Because the system uses ambient air as a heat sink, it is necessary to consider the phase transition and mass transfer of water vapor, and natural gas in the air in order to understand the fluctuation of system characteristics. The model predicts the experimental data of a pilot-scale vaporizer within a mean absolute error of 5.5 %. In addition, we suggest the robust design methodology and optimal design which is able to maintain the efficiency under the weather conditions for a year. Two or more data analysis techniques including discrete waveform transformation and k-means clustering are used to extract features that can represent time series data. Under the settings, the performance in the optimized desgin is improved by 22.92 percentage points compared to that in the conventional system. In the second system, the continuous tubular crystallization reactor has advantages in terms of production capacity and scale-up compared with the conventional batch reactor. However, the tubular system requires a well-designed control system to maintain its stability and durability, and thus; there is a great deal of demand for the mathematical model of this system. We were able to estimate crystal size distribution by considering the population balance model simultaneously with several heat exchanger models. The model constructed based on the first principle reaction scheme successfully predicted the results from the full-factorial experiment. The experiments were conducted with LAM (L-asparagine monohydrate) solution. In the prediction, the average crystal length and standard deviation were within 20% of the results of an experiment where the crystals were not iteratively dissolved in the liquid but maintained a low-level supersaturation. Furthermore, to confirm the controllability of the crystal size distribution in the system, we replaced the LAM solution with HEWL (Hen-egg white lysozyme) solution. Finally, we propose a multi-compartment model to predict the behavior of a high-pressure autoclave reactor for polymer production. In order to simulate a complex polymer synthesis mechanism, the rotation effect of impellers in the reactor on polymerization and the influence caused by polymerization heat were sequentially evaluated. As a result, This model turned out to be able to predict the physical properties of the polymers produced in an industrial-scale reactor within 7% accuracy. In this thesis, all three systems are distributed parameter systems which can be expressed as partial differential equations for time and space. To construct a high order model, the system was interpreted based on discretization approach under minimal assumptions. This methodology can be applied not only to the systems suggested in this thesis but also to those consisting of interpdependent variables. I hope that this thesis provides guidance for further researches of chemical engineering in nearby future.최근에 몇 년에 걸쳐서 많은 연구자들이 이론을 기반으로 실험 결과와 일치하는 수학 모델을 개발하고자 많은 노력을 기울여 왔다. 하지만 이런 노력에도 불구하고 다상 흐름 혹은 교반 반응기와 같은 복잡한 현상을 내포한 시스템을 위한 모델을 수립하는 것은 여전히 화학 공학 분야에서 쉽지 않은 일로 여겨진다. 이 와중에 다양한 수치적 방법에서의 계산 효율의 증가와 안정성의 향상은 기본방정식에 기초한 시스템을 정확하게 해결하고 분석할 수 있게 해주었다. 이로 인하여 내부 요소들 간의 상호 의존성이 존재하는 시스템의 거동을 정확하게 예측하기 위한 수학적 모델의 필요성이 부각되었다. 기본 현상들을 표현할 수 있는 방정식들을 기반으로 모델을 구축하기 위한 방법론은 시스템 해석에 있어서 기술적 장벽을 낮출 수 있다. 이 학위 논문에서 우리는 실험실 또는 파일럿 규모의 실험으로부터 입증된 세 가지 수학적 모델을 제안한다. 첫 번째로, 공기를 사용하여 액상의 천연가스를 기화시키는 장치는 운전 도중에 기화기 표면에 서리 층이 형성되고 그로 인한 단열 효과로 장비의 성능이 서서히 저하된다. 시스템은 주변 공기를 열 흡수원으로 사용하기 때문에 시스템 특성의 변동을 파악하기 위해서는 공기 중 수증기 및 천연 가스의 상전이 및 전달 현상을 동시에 고려하여야 한다. 제시된 수학적 모델에 의해 예측한 결과는 파일럿 규모 기화기로부터 얻은 실험 데이터와 5.5% 평균 절대 오차를 보였다. 이에 더하여, 앞에서 제시한 기화기 모델을 이용하여 1년 동안의 기상 조건에서 운전 효율을 유지하면서 지속 운전이 가능한 기화기의 설계 방법과 결과를 제안하였다. 이산 파형 변환과 k-평균 군집화를 포함하는 두 가지 이상의 데이터 분석 기법을 사용하여 시계열 데이터를 대표할 수 있는 특징을 추출한다. 추출된 특징 아래에서 최적화된 디자인은 기존 제시된 안에 비해 22.92% 만큼 향상된 성능을 보여주었다. 두 번째 시스템은 신 제약 기술 공정인 연속 관형 결정화 반응기는 기존에 널리 쓰이던 회분식 반응기에 비하여 생산 속도 및 스케일 업 측면에서 장점이 많다. 하지만 제어기술이 기반이 되어야한다는 점에 있어서 그 도입이 늦어졌고 이에 따라 자연스럽게 개발된 모델 또한 전무하다. 우리는 이 장치에서 결정 크기 분포를 추산하기 위한 인구 균형 모델을 열 교환 모델과 동시에 고려하여 결정 크기 분포를 추산할 수 있었다. 제 1원리 결정 반응식을 기반으로 구축된 모델은 완전 요인 배치법을 기반으로 실험된 데이터를 성공적으로 예측하였다. 결정이 액상에 용해되지 않으면서 낮은 수준의 과포화 상태를 유지한 실험에 대해서는 평균 결정 길이와 표준편차가 실험 결과와 20% 이내의 오차를 보였다. 앞에서 모델의 검증에 사용된 데이터가 LAM (L-아스파라긴 일 수화물)용액으로부터 얻어진 것이었다면 이후에는 HEWL (달걀 흰자 리소자임)를 사용하여 제품의 결정 크기 분포의 조절 가능성을 보였다. 마지막으로 폴리머 생산을 위한 고압 오토클레이브 반응기의 거동을 예측하기 위한 다중 구획 모델을 제안하였다. 복잡한 고분자 합성 메커니즘을 모사하기 위하여 반응기 내 임펠러의 회전이 중합에 미치는 효과와 중합 열로 인한 영향력을 순차적으로 평가하였다. 제안된 모델은 3D 구조를 가진 산업화된 반응기에서 생산된 두 가지 고분자의 물성을 7%이내 정확도로 예측할 수 있다. 본 학위논문에서는 다루는 시스템은 모두 분포 정수계 시스템으로 시간과 공간에 대하여 편미분방정식으로 표현할 수 있다. 고차 모델을 구축하기 위해 이산화 접근법을 기반으로 최소한의 가정 하에 시스템을 해석하였다. 이는 논문에 제시한 시스템 뿐만 아니라 시공간에서 예측 어려운 분포를 가지는 변수를 가진 모든 시스템에 대하여 적용이 가능하다. 이 논문이 앞으로 화학 공학 분야의 시스템을 해석하는 데 있어서 더 발전된 연구를 위한 지침서가 되기를 희망한다.Abstract i Contents iv List of Figures viii List of Tables xii Chapter 1 1 Introduction 1 1.1 Research motivation 1 1.2 Research objective 3 1.3 Outline of the thesis 4 1.4 Associated publications 9 Chapter 2 10 Distributed parameter system 10 2.1 Introduction 10 2.2 Modeling methods 11 2.3 Conclusion 16 Chapter 3 17 Modeling and design of pilot-scale ambient air vaporizer 17 3.1 Introduction 17 3.2 Modeling and analysis of frost growth in pilot-scale ambient air vaporizer 24 3.2.1 Ambient air vaporizer 24 3.2.2 Experimental measurement 27 3.2.3 Numerical model of the vaporizer 31 3.2.4 Result and discussion 43 3.3 Robust design of ambient air vaporizer based on time-series clustering 58 3.3.1 Background 58 3.3.2 Trend of time-series weather conditions 61 3.3.3 Optimization of AAV structures under time-series weather conditions 63 3.3.4 Results and discussion 76 3.4 Conclusion 93 3.4.1 Modeling and analysis of AAV system 93 3.4.2 Robust design of AAV system 95 Chapter 4 97 Tunable protein crystal size distribution via continuous crystallization 97 4.1 Introduction 97 4.2 Mathematical modeling and experimental verification of fully automated continuous slug-flow crystallizer 101 4.2.1 Experimental methods and equipment setup 101 4.2.2 Mathematical model of crystallizer 109 4.2.3 Results and discussion 118 4.3 Continuous crystallization of a protein: hen egg white lysozyme (HEWL) 132 4.3.1 Introduction 132 4.3.2 Experimental method 135 4.3.3 Results and discussion 145 4.4 Conclusion 164 4.4.1 Mathematical model of continuous crystallizer 164 4.4.2 Tunable continuous protein crystallization process 165 Chapter 5 167 Multi-compartment model of high-pressure autoclave reactor for polymer production: combined CFD mixing model and kinetics of polymerization 167 5.1 Introduction 167 5.2 Method 170 5.2.1 EVA autoclave reactor 170 5.2.2 Multi-compartment model of the autoclave reactor 173 5.2.3 CFD simulation of mixing effects in the autoclave reactor 175 5.2.4 Region-based dividing algorithm 178 5.2.5 Polymerization kinetic model 182 5.3 Results and discussion 191 5.4 Conclusion 203 5.5 Appendix 205 Chapter 6 210 Concluding Remarks 210 6.1 Summary of contributions 210 6.2 Future work 211 Appendix 214 Acknowledgment and collaboration declaration 214 Supplementary materials 217 Reference 227 Abstract in Korean (국문초록) 249Docto

INTEGRATED CALORIMETRIC TECHNIQUES APPLIED TO RUNAWAY REACTIONS ANALYSIS

The main objective of this thesis is the study of runaway reactions and their preventive and protective measures. The experimental approach is focused on the integration of calorimetry, a well consolidated technique in process safety assessment, with other techniques in order to overcome possible limitations and to obtain additional information about the process conditions. The first results obtained during this work are about the efficiency of the stability criteria for thermal runaway present in literature. The reaction under study was the esterification of the acetic anhydride and methanol catalysed by sulfuric acid and analysed in isoperibolic conditions as a function of jacket temperature and catalyst quantity. This mild runaway reaction represents a severe test for the reactor stability criteria. The main result was the advantage of using sensitivity based criteria because they are suitable to on-line implementation aimed at the early detection of thermal explosions. An Early Warning Detection System based on divergence criterion, which is a sensitivity based one, was applied to the data deriving from experiments on the decomposition of the hydrogen peroxide in quasi-isothermal versus runaway mode. This system was analyzed with a pseudo adiabatic calorimeter modified in our laboratory in order to study the effect of the pressure on the decomposition. The runaway reaction developed by the peroxide decomposition is very rapid and exothermic, so it was possible to test the criterion in conditions very similar to those of a full scale thermal explosion incident. The data obtained experimentally were also used to evaluate the possibility of the use of a screening instrument for vent sizing and this was found to be the greater limitation of this cost efficient technique. The rest of the thesis was dedicated at the investigation of real industrial incidents involving highly reactive substances that often undergo undesired exothermic reactions during their transport, storage or process: monomers. The first incident analysed was the self-polymerisation of commercial 63% divinylbenzene in different conditions of temperature and oxygen quantity in order to prove that an overfilling of the tank or an excessive storage temperature can make the inhibition mechanism ineffective and lead to self-initiated runaway polymerisation. The second incident was about the runaway polymerisation of methyl methacrylate added with accelerators. The experimentation allowed us to prove that accelerators affect the polymerisation rate even if with no initiator is present in the system This has been a significant finding because of the novelty of the process that has been often cause of incidents in the last years. A model of the system was formulated and the results of the simulations helped us in establishing the potential hazards associated with the use of accelerators in resin manufacture. In conclusion this work dealt with the currently relevant problem of runaway reactions and their different aspects, including possible preventive and protective measure by an experimental integrated approach, trying to find solutions that can be concretely implemented in industrial scale reactors to improve process safety of highly reactive systems

Development and experimental validation of CPOx reforming dynamic model for fault detection and isolation in SOFC systems

2013 - 2014In the present work an investigation of the reforming technologies available for Solid Oxide Fuel Cell (SOFC) systems and their basic concepts has been carried out, with the aim to describe, test and simulate the reforming process for fault diagnosis application. The final aim of a fault diagnosis activity for SOFC systems is to reach the required criteria for a commercial application, which, besides long lifetime and performance, include high reliability and safety at reasonable costs. The achievement of these targets is necessary to contribute promoting the SOFC technology and finally starting a mass production phase. In this thesis, the attention has been focused on the reforming reactor, responsible for the conversion of the inlet fuel in hydrogen, suitable source fuel for the SOFC. In particular, the Catalytic Partial Oxidation (CPOx) process has been analyzed. The CPOx reforming mechanism is the most attractive technology for the production of syngas or hydrogen in small-medium scale SOFC applications and Micro Combined Heat and Power (μCHP) systems. This is due to the ability of the CPOx reaction to be carried out in compact reactors with rapid dynamic response and with low heat capacity. The reaction is slightly exothermic and therefore does not require external heat to take place. In addition, CPOx technology does not require steam, as the media required for the reforming reaction is air, which is easily available for residential application. This mainly means that CPOx is independent from an external water source and any heating source. The hydrocarbon is both oxidized to CO2 and H2O, either partially or completely, and also converted to synthesis gas by endothermic steam reforming (according to the indirect CPOx mechanism). Despite these advantages, catalytic partial oxidation is less efficient than steam reforming. This indicates that it is most suitable for applications in which the system simplicity has the priority with respect to the hydrogen yield. The high surface temperatures can cause a local loss of activity of the catalyst, leading to the instable performance of the entire reactor. Nevertheless, in the CPOx process even a small difference in the operating air and fuel flow rates could lead to carbon deposition or oxidation of the catalyst, with serious consequences for the SOFC system and for the stack itself. It is therefore extremely important to develop a diagnosis tool able to investigate these phenomena and to detect and isolate the faults that may verify inside the reactor. The most common fault events likely to occur inside a CPOx reformer for SOFC applications have been analyzed through a Failure Mode and Effect Analysis (FMEA) and a Fault Tree Analysis (FTA). These analyses are aimed at identifying the main events responsible for the catalyst deactivation, together with their causes and effects on the SOFC system performance. The Catalytic Partial Oxidation mechanism has then been explored from both modelling and experimental points of view, with the aim to simulate the reforming process and identifying the thermodynamic optimal operating conditions at which natural gas may be converted to hydrogen. At the same time, the main fault scenarios likely to occur during the reforming phase have been analyzed, both in experiments and during simulations, to evaluate the capability of the developed model in performing effective fault detection and isolation for on-board diagnostic application. The CPOx dynamic model developed is based on the minimization of Gibbs free energy and can be easily reconfigured for describing a steam reforming mechanism. The simulation results give useful indication on how operating parameters such as the input conditions of reactants (inlet compositions and temperature) affect the reaction equilibrium and, in turn, the products composition and reactor outlet temperature. A sensitivity analysis for different operating conditions has been carried out. The transient behavior of the reforming reaction and the information about methane conversion and hydrogen selectivity complete the set of model results. The dynamic CPOx model has been validated through experimental data and its behavior during transients has been carefully analyzed during the variations in the set-points of operating phases. Both test data and reactor design were part of the activities performed within the EFESO project, funded by the Italian Ministry of Economic Development and led by Ariston Thermo Spa. The model results demonstrate that the CPOx dynamic model represents a useful tool for fault diagnosis application and its results provide an interesting benchmark for the design and working parameters of a CPOx reforming system for SOFC application. [edited by author]XIII n.s

Chemical looping combustion for carbon capture

Among the well-known state-of-art technologies for CO2 capture, Chemical Looping Combustion (CLC) stands out for its potential to capture with high efficiency the CO2 from a fuel power plant for electricity generation. CLC involves combustion of carbonaceous fuel such as coal-derived syngas or natural gas via a red-ox chemical reaction with a solid oxygen carrier circulating between two fluidised beds, air and fuel reactor, working at different hydrodynamic regimes. Avoided NOx emissions, high CO2 capture efficiency, low CO2 capture energy penalties and high plant thermal efficiency are the key concepts making worthy the investigation of the CLC technology. The main issue about the CLC technology might concern the cost of the solid metal oxides and therefore the impact of the total solid inventory, solid make-up and lifetime of the solid particles on the cost of the electricity generated. A natural gas fired power plant embedding a CLC unit is presented in this work. Macro scale models of fluidised beds (i.e. derived applying macroscopic equations) are developed and implemented in Aspen Plus software. Kinetic and hydrodynamic phenomena, as well as different operating conditions, are taken into account to evaluate their effect on the total solid inventory required to get full fuel conversion. Furthermore, a 2D micro scale model of the fuel reactor (i.e. derived applying partial differential equations), making use of a CFD code, is also developed. The results, in terms of the effect of the different kinetic and hydrodynamic conditions on the outlet gas conversion, are compared with the results using the macro-scale model implemented in Aspen Plus. Based on the micro scale (CFD) outcomes, the macro scale model is enhanced to capture the main physics influencing the performance of the fuel reactor. Thus, the improved macro scale model is embedded into different power plant configurations and mass and energy balances are solved simultaneously. Thermal efficiency evaluations for the different plant arrangements are carried out. A detailed economic evaluation of the CLC power plant is undertaken by varying two relevant parameters: fuel price and lifetime of the solid particles. The effect of the aforementioned parameters on the Levelised Cost Of Electricity (LCOE) is investigated and the resulting outcomes are critically discussed

Numerical and Experimental Investigation of Liquid and Gas/Liquid Flows in Stirred Tank Reactors

Les réacteurs à cuve agitée (STR) sont couramment utilisés dans les industries pétrolières, chimiques, biochimiques, pétrochimiques, minières et métallurgiques. De nos jours, ralenties par des facteurs et des barrières tant économiques qu’environnementaux, ces industries sont ardemment à la recherche de procédés efficaces et fiables permettant de minimiser le gaspillage d’énergie et de matières premières ainsi que la production de sous-produits indésirables et nocifs. De fait, la recherche de lignes directrices pour la mise à l’échelle de tels procédés, du laboratoire à l’échelle industrielle, est devenue une tâche indispensable pour les ingénieurs des procédés. Les procédures classiques de conception et de mise à l’échelle des STR supposent que les paramètres hydrodynamiques sont constants à travers le réacteur (hypothèse du “mélange parfait”). Cette hypothèse est assez simpliste et sans doute abusive, particulièrement pour les STR de grands volumes. Il est reconnu que la conception et la mise à l’échelle d’équipements de procédé peuvent difficilement être couronnées de succès sans la prise en compte de l’hydrodynamique locale. Une compréhension de l’hydrodynamique et du mélange est donc essentielle pour la conception et la mise à l’échelle précises des STR. L’objectif général de cette étude a par conséquent été d’améliorer la compréhension de l’hydrodynamique à l’intérieur des STR et d’aider la conception et la mise à l’échelle de tels systèmes. Pour atteindre cet objectif, une combinaison judicieuse de divers outils de conception incluant la modélisation compartimentale (CM), la mécanique des fluides numérique (CFD) et la mécanique des fluides expérimentale (EFD) a été utilisée. Comme le taux de dissipation de l’énergie cinétique de turbulence () affecte de façon importante la performance des STR, la première partie de cette thèse a été consacrée aux effets des conditions opératoires et de la mise à l’échelle sur la distribution de dans les STR. Les résultats de simulations CFD monophasiques par la méthode des volumes finis sur des STR équipés d’une turbine Rushton (RT) ont été utilisés pour déterminer les paramètres d’un modèle à deux zones compartimentales qui y décrit l’inhomogénéité de la turbulence. Une méthode améliorée a été proposée pour trouver la frontière entre deux régions caractéristiques. A l’aide de cette méthode, les effets de divers critères classiques de mise à échelle ont été étudiés. Il a été observé que la distribution de et, en conséquence, les paramètres du modèle compartimental changent considérablement lorsque les critères classiques de mise à l’échelle ont été suivis. Par la suite, la méthode non-intrusive dite du suivi de particules radioactives (RPT) a été utilisée pour une analyse exhaustive de l’écoulement parfaitement turbulent du fluide dans un STR de laboratoire équipé d’une turbine RT ou d’une turbine à pales inclinées (PBT). Cette étude couvre les descriptions eulérienne et lagrangienne du mouvement du fluide. Les mesures RPT du champ d’écoulement turbulent dans un STR agité par une turbine RT ont été comparées à des mesures laser et à des résultats de simulations CFD de modèles de turbulence basés sur une méthode de RANS (Reynolds-Averaged Navier-Stokes). Un bon accord a été trouvé entre toutes les méthodes pour les profils de vitesse moyenne tridimensionnelle prédits et mesurés en tous points du STR. La technique RPT a été utilisée pour la première fois pour mesurer le champ d’écoulement turbulent dans une cuve agitée par une turbine PBT. Deux indices de mélange, un basé sur le concept d’indépendance stochastique et l’autre sur le concept statistique de perte de mémoire dans les procédés de mélange, ont été utilisés pour mesurer le temps de mélange à l’aide des données RPT. Cette étude montre que la technique RPT s’avère très prometteuse pour étudier les écoulements turbulents et les caractéristiques du mélange dans les STR, ainsi que pour évaluer la validité des modèles numériques. La RPT a aussi été utilisée pour valider un modèle CFD simulant les écoulements turbulents monophasiques. Les résultats de ce modèle ont été utilisés comme une condition initiale pour des simulations CFD plus complexes d’écoulement turbulent gaz-liquide dans des STR qui présentées dans la dernière partie de la thèse. Finalement, la troisième partie de la thèse présente le développement d’un modèle multi-échelle d’écoulement gaz-liquide comme outil pour la conception et la mise à l’échelle de STR. Le modèle est basé sur la compartimentalisation du STR en zones et l’utilisation de simulations simplifiées d’écoulement gaz-liquide moins coûteuses en temps calcul. Ce modèle a prédit la valeur moyenne du coefficient volumique de transfert de matière (kLa) dans chaque zone à l’aide de paramètres hydrodynamique locaux y figurant (c.-à-d. rétention de gaz et le taux de dissipation de l’énergie cinétique de turbulence du liquide). La validité du modèle à chaque étape a été scrupuleusement évaluée à l’aide de données de la littérature. Le modèle proposé a été capable de prédire le coefficient volumique global de transfert de matière à l’intérieur du STR avec une bonne précision. À l’aide de ce modèle, il est apparu que les contributions de chaque zone au transfert de matière global à l’intérieur du STR peuvent changer considérablement en modifiant les conditions opératoires et la mise à l’échelle. Il a été estimé que, en accroissant le volume du STR, le kLa global avait diminué d’au moins 20% suite à une mise à l’échelle classique. L’originalité scientifique du présent travail repose sur (a) l’introduction d’une nouvelle méthode pour trouver la localisation de la frontière entre deux zones compartimentales caractéristiques des STR qui y décrivent l’inhomogénéité de la turbulence, (b) l’investigation systématique des effets des conditions opératoires et des différentes approches de mise à l’échelle sur le degré d’inhomogénéité de la turbulence dans les STR équipés de turbine RT, (c) les études expérimentales exhaustives sur les écoulements turbulents dans des STR à l’aide de la technique RPT pour les turbines RT et PBT, (d) l’introduction d’une nouvelle méthode pour la mesure non-invasive du temps de mélange dans les STR basée sur le concept statistique de perte de mémoire, (e) le développement d’un modèle multi-échelle pour les écoulements gaz-liquide comme outil de conception et de mise à l’échelle du STR, et (f) l’examen attentif de l’impact des conditions opératoires et de la mise à l’échelle sur les valeurs du coefficient volumique local de transfert de matière. Les découvertes de cette étude ont permis de mettre en lumière les paramètres hydrodynamiques importants pour la conception et la mise à l’échelle des STR. À cet égard, il est permis de croire que des améliorations significatives dans leur conception pourront être réalisées à l’aide du modèle multi-échelle proposé étant donné qu’il considère à la fois le champ d’écoulement effectif et des paramètres hydrodynamiques locaux. ---------- Stirred tank reactors (STRs) are widely used in the petroleum, chemical, biochemical, petrochemical, mineral and metallurgical industries. Nowadays, submerged by both economic and environmental drivers and barriers, industries urge for efficient and reliable processes in order to minimize the waste of energy and raw materials, as well as the production of un- desirable and harmful by-products. As a result, finding adequate rules for scaling up such processes from the laboratory to an industrial scale has become a crucial task for process engineers. The conventional procedures for design and scale-up of STRs assume that the values of hydrodynamic parameters are constant in the entire reactor (”well-mixed” assump- tion). This assumption is quite rudimentary and may even be far-fetched, particularly for large-scale STRs. It is well known that the design and scale-up of process equipment can barely be successful without taking local hydrodynamics into account. An understanding of the hydrodynamics and mixing is thus essential for the precise design and scale-up of STRs. The overall objective of this study was to gain insight into the hydrodynamics prevailing in STRs, and help improve the design and scale-up of such systems. To meet this objective, strategic combinations of various design tools, including compartmental modeling (CM), computational fluid dynamics (CFD) and experimental fluid dynamics (EFD), were used. As the turbulent energy dissipation rate (ε) significantly affects the performance of STRs, the first part of this thesis presents the effects of operating conditions and the scale-up on the distribution of ε in STRs. The results of single-phase finite-volume CFD simulations of STRs equipped with a Rushton turbine (RT) were used to determine the parameters of a two- compartment model that describes the turbulent non-homogeneities therein. An improved method was proposed to find the boundary between the two characteristic regions. Using this method, the effects of various conventional scale-up criteria were investigated. It was observed that the distribution of ε and, as a result, the compartmental model parameters change considerably when conventional scale-up rules were followed. Next, so-called radioactive particle tracking (RPT) as a non-intrusive measurement technique was used for the comprehensive analysis of the fully turbulent fluid flow in a laboratory- scale STR equipped with an RT or a pitched blade turbine (PBT). This study covers the Eulerian and Lagrangian descriptions of fluid motions. The RPT measurement of the turbulent flow field in an STR agitated by an RT was benchmarked with CFD simulations of RANS-based turbulence models and laser-based measurements. A good agreement was found between all the methods for the measured and predicted 3D mean velocity profiles at all locations in the STR. The RPT technique was used to measure the turbulent flow field in a tank agitated by a PBT for the first time. Two mixing indices, one based on the concept of stochastic independence and the other on the statistical concept of memory loss in mixing processes, were used to measure mixing times using RPT data. This study shows that the RPT technique holds great promise for investigating turbulent flows and the mixing characteristics of STRs, and for assessing the adequacy of numerical models. RPT also was used to validate a CFD model for simulating single-phase turbulent flow. The results of this model were used as an initial condition for more complex CFD simulations of gas/liquid turbulent flow in the STRs presented in the last part of the thesis. Finally, the third part of this thesis presents the development of a multiscale gas/liquid flow model as a tool for the design and scale-up of STRs. The model was based on the compartmentalization of the STR into zones and the use of simplified less computationally intensive gas/liquid flow simulations. It predicted the mean value of the local volumetric mass transfer coefficient (kLa) in each compartment based on the local hydrodynamic parameters therein (i.e., gas hold-up and liquid turbulent energy dissipation rate). The adequacy of the model at each step was carefully assessed using experimental data drawn from the literature. The proposed model was able to predict the overall volumetric mass transfer coefficient in the STR with good adequacy. Using this model, it was shown that the contributions of each compartment to the overall mass transfer inside the STR could be changed considerably by altering the operating conditions and scale-up. It was also estimated that by increasing the STR size the overall volumetric mass transfer coefficient decreased by at least 20% following a conventional scale-up rule. The scientific novelty of the current work lies in: (a) the introduction of a new method for finding the location of the boundary between the two characteristic compartments of STRs that describes the turbulent non-homogeneities therein, (b) the systematic investigation of the effects of operating conditions and different scale-up approaches on the extent of turbu- lent non-homogeneities in STRs equipped with an RT, (c) the comprehensive experimental investigations of the turbulent fluid flows in STRs using RPT for both RT and PBT impellers, (d) the introduction of a novel method for the non-invasive measurement of mixing time in STRs based on the statistical concept of memory loss, (e) the development of a multiscale gas/liquid flow model to serve as a tool for the design and scale-up of STRs, and (f) the scrutinization of operating conditions and scale-up impacts on the local volumetric mass transfer coefficient values. The findings of this study have shed light on the hydrodynamic parameters that are important for the design and scale-up of STRs. In this regard, it is also believed that significant design improvements can be achieved by using the proposed multiscale model as it considers the actual flow field and local hydrodynamic parameters

Carnot Cycle and Heat Engine Fundamentals and Applications II

This second Special Issue connects both the fundamental and application aspects of thermomechanical machines and processes. Among them, engines have the largest place (Diesel, Lenoir, Brayton, Stirling), even if their environmental aspects are questionable for the future. Mechanical and chemical processes as well as quantum processes that could be important in the near future are considered from a thermodynamical point of view as well as for applications and their relevance to quantum thermodynamics. New insights are reported regarding more classical approaches: Finite Time Thermodynamics F.T.T.; Finite Speed thermodynamics F.S.T.; Finite Dimensions Optimal Thermodynamics F.D.O.T. The evolution of the research resulting from this second Special Issue ranges from basic cycles to complex systems and the development of various new branches of thermodynamics

Microreactor system for reaction development and online optimization of chemical processes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 162-175).Developing the optimal conditions for chemical reactions that are common in fine chemical and pharmaceutics is a difficult and expensive task. Because syntheses in these fields have multiple reaction pathways, a significant number of experiments are required to determine the conditions that maximize the yield of the desired product. With few exceptions, these experiments have been performed in flask reactors. The goal of this thesis research was to improve the efficiency and the accuracy of these reaction optimization investigations through the use of an automated microreactor system. Previous studies have illustrated the benefits of silicon microreactors for the study of chemical reactions. Such advantages include the small reactor volume and the continuous flow operations that enable microreactors to achieve a high throughput rate of experiments while using minute amounts of expensive material. Heat and mass transfer rates in microreactors are orders of magnitude larger than those in traditional laboratory equipment, thus rendering microreactors ideal tools for accurate reaction optimization and kinetic investigations. Moreover, the integration of chemical and physical sensors with microreactors permits accurate monitoring of the reaction progress. Combining these measurements with appropriate feedback algorithms offers a means to automate experiments and to perform real-time optimization and kinetic modeling of chemical reactions. Several automated microreactor systems were developed in this thesis research to improve reaction development. One such system was used in the multidimensional screening investigation of densely functionalized heterocycles. As demonstrated in this example, the use of an automated microreactor system greatly improved the speed and efficiency involved in reaction library development. Incorporating a feedback algorithm into the system operations provided a method for rapid reaction optimization. With throughputs as high as one experiment performed and analyzed per 10 minutes, rapid multi-variable reaction optimization was demonstrated for several chemistries. It was also possible to quickly and accurately extract the kinetics of a reaction by incorporating model-based optimization approaches. The results from these optimization studies were used to scale up reaction production by factors as large as 500 in a mesoflow reaction system. Future extensions for automated microflow systems were identified, and the technology developed in this thesis research was used to optimize a two-step synthesis and to more efficiently study reactions that produce solid by-products.by Jonathan Patrick McMullen.Ph.D

Colloidal Nanoparticles Tethered by Oligomers and Short Polymers in Organic and Polymeric Media

Nanoparticles and related nanomaterials are increasingly being utilized in technological applications. Controlling the dispersion and organization of these advanced materials is crucial towards realizing their full potential. In this dissertation, we employ methods of tethering oligomers and short polymers to the surfaces of spherical nanoparticles and 2D crystals. ZnO quantum dots are spherical nanoparticles which are direct bandgap semiconductors (3.37 eV) with large exciton binding energies (60 meV) and show strong photoluminescence. We show that poly (methyl methacrylate) grafted onto ZnO quantum dots via radical polymerization yields polydisperse brushes that are particularly effective in forming stable, fine dispersions in melt-blended nanocomposites. Nanocomposites prepared via this method exhibit tunable properties in refractive index, glass transition temperature and energy bandgap as a result of their linear dependence on ZnO concentration. It is further shown that the glass transition behavior of these nanocomposites is analogous to that of polymer thin films. α-ZrP nanoplatelets are 2D crystals which are being studied for use as a catalyst, drug delivery agent, proton conductor, nanofillers for nanocomposites, etc. Exfoliated α-ZrP nanoplatelets of large aspect ratios tethered by polyoxyalkyleneamines form photonic structures in high polar, aprotic solvents. The polyoxyalkyleneamines form a brush layer on the nanoplatelets allowing the formation of lamellar phases with large d-spacings. Bragg reflection by the mesomorphic structures in the visible wavelengths gives rise to iridescence with brilliant colors that are tunable by adjusting the concentration of nanoplatelets. In epoxy, α-ZrP nanoplatelets tethered by polyoxyalkyleneamines self-assemble into smectic phase when spray-coated onto polyimide substrates. These spray-coated thin films of smectic α-ZrP/epoxy exhibit excellent gas barrier properties that perform consistently in low and high humidity conditions. The highly ordered nanoplatelets are aligned parallel to the substrate forcing gas molecules to traverse a tortuous path resulting in a reduction of permeability in the film. Observations of the occurrence of liquid crystalline phases in the bulk α-ZrP/epoxy liquid shows that the self-assembly behavior of these smectic α-ZrP are consistent with the predictions of Onsager’s theory