Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

The purpose of this study was to determine whether the fluctuations of concentration in the exit stream for a RTD were statistically random. A 460ml one inlet, one outlet CSTR (Continuous Stirred Tank Reactor) was set up to perform the RTD (Residence Time Distribution) test. A electrical conductivity probe capable of measuring concentration variations in volume elements of the order of 3.00 x 10⁻⁵ml was used to detect the tracer {sodium chloride) response. Flow rates ranging from 52 (ml/min) to 213 (ml/min) and agitation speeds from 0.00 rpm to 200 rpm were covered. The C-curve (concentration curve) was found to be reproducible to within ± 5 % at agitation speed greater than 20 rpm. The fluctuations for a C-curve were extracted and standard deviation was used to characterize these fluctuations. The fluctuations were found to be not random statistically and the standard deviation of fluctuation was reproducible to within ± 8%. / M.S.

The prime objective of a current research project at the University of Natal is to develop a novel autothermal fluidised bed coal gasifier which is capable of efficiently producing synthesis quality gas (rich in hydrogen and carbon monoxide) from discard of duff coal resources using air and steam as the reactant gases. The development of this gasifier was initially motivated to utilise the ever increasing supply of discard coal in South Africa which represents a significant potential source of energy and currently poses severe environmental pollution hazards caused by spontaneous combustion and wind erosion of the discard coal dumps. Recently, however, the gasifier has been considered for the conversion of more general coal resources in an Integrated Coal Gasification Combined Cycle process (IGCC) for the production of electricity. The knowledge of the kinetics of steam gasification of local coal resources is of vital importance to the design of this gasifier. However, no such kinetic data are available of which the author is aware. This thesis presents the following contributions to the overall knowledge of the gasifier (a) The development of a micro reactor to measure the rate of reaction of the steam gasification of coal-char at temperatures of up to l000oC and pressures up to 5 bar absolute; (b) Kinetic studies using the microreactor on the steam gasification of coal-chars derived from Bosjesspruit and Transvaal Navigation coal samples. The following principal results were obtained with Bosjesspruit coal-char : The rate of steam-char gasification is very sensitive to variations in the temperature of reaction in the range 840°C to 920°C. Neither the rate of steam-char gasification nor the product gas composition are affected by the steam partial pressure in the range 1.8 to 4.8 bar absolute; The concentrations of the H2 and CH4 components of the product gas stream rapidly approached their respective equilibrium compositions, whereas the concentrations of CO and CO2 gradually approach their respective equilibrium compositions during gasification at a rate which is typical of the stoichiometry of the Boudouard reaction. The average product gas composition is independent of the temperature of reaction in the range 840°C to 920°C and is approximately 49% H2, 32% CO, 17% CO2 and 2% CH4 on a molar basis; The steam gasification kinetic data are well described by a fundamental Arrhenius-type volumetric reaction model at (c) temperatures of up to 920°C. The value of the activation energy for the reaction is 146 kJ/gmol, which indicates that the gasification kinetics are controlled by the rates of the chemical reactions (ie. C + H2O = CO + H2 and C + CO2 = 2CO) at temperatures up to 920o C; There are no major differences between the kinetics measured for Bosjesspruit coal-char and those reported in the literature for foreign coal-chars. The experimental results obtained for the steam gasification of char derived from Transvaal Navigation coal show that the concentrations of both the Hz and the CH4 in the product gas stream rapidly attain their respective equilibrium values and remain approximately constant throughout gasification, whereas the concentrations of CO and CO2 gradually approach their respective equilibrium values during the course of gasification and almost attain equilibrium concentrations as the conversion of carbon nears completion. The rate of steam gasification of this char is therefore also controlled by the rate of the Boudouard reaction. The mathematical development of a steady-state, one-dimensional compartment model of the gasifier. The model is also presented in the form of a Fortran 77 computer program which is designed to run on a personal computer. The program is capable of simultaneously solving the overall material and energy balances of the gasifier to a tolerance of l% within 15 minutes when using a microprocessor which operates at 10 Mhz. (d) The gasifier simulation program is currently being used in the design of a pilot scale gasifier which is intended to demonstrate the capability of the process on a continous basis of operation. (e) Experimentation on the air-steam gasification of Bosjesspruit coal using a mini-pilot scale gasifier. These experiments have successfully demonstrated the feasibility of the production of a gas stream which is rich in hydrogen and carbon monoxide. The composition of the product gas stream compares well with the predictions of the simulation model of the gasifier. / Thesis (Ph.D.)-University of Natal, Durban, 1990.

A cold-flow vibated-bed microreactor system, operating at the room temperature and atmospheric pressure, was built and tested. The purpose of this microreactor was to simulate gas- and solid-mixing in a hot-flow microreactor system. The latter is being developed to study carbon deposition rates for continuous Fischer-Tropsch synthesis from a low H₂:CO gas with rapid switching of catalyst between gas atmospheres. The cold-flow microreactor consisted of three chambers with vertical sliding baffles that shift catalyst between the smaller, center reaction chamber and two outer chambers. The results show that the solid mixing within each chamber is essentially complete within one second after transfer of catalyst. The solid mixing was independent of gas flow and gas flow rate. Results of gas-mixing studies show that gas transfer between chambers of the microreactor was due to the transfer of gas within the interstices of transferred catalyst particles. During rapid baffle-switching intervals, complete gas mixing within each chamber occurred. The amount of gas transferred from the center chamber to each outer chamber was nearly constant and increased only slightly with feed gas rate to the center chamber. For the gas feed rates tested, the percentage of gas fed to the center chamber that transferred to each outer chamber was low, ranging from 1.2 to 4.9 percent. The results of this study are significant to the further development of the "sliding-baffle" microreactor for continuous Fischer-Tropsch synthesis, from a low H₂:CO gas. The microreactor will give important information on the rate of carbon deposition in a system that switches catalyst between two gas atmospheres. / M.S.

Orientador: Milton Mori / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-09-11T21:07:59Z (GMT). No. of bitstreams: 1 Bastos_JaciCarloSchrammCamara_M.pdf: 4360168 bytes, checksum: 100c57a7c93213cf37fcdab4ee05e24f (MD5) Previous issue date: 2005 / Resumo: A presente pesquisa apresenta a modelagem matemática e a simulação de uma operação de fluidização rápida em um longo duto cilíndrico vertical, operação importante em vários processos industriais, sendo que sua principal aplicação está vinculada ao craqueamento catalítico do petróleo para a conversão em gasolina. Tem como objetivos a obtenção de uma compreensão contínua e o conhecimento do desenvolvimento do escoamento gás-sólido, bem como a soma de experiências às pesquisas em escala industrial motivados pela possível predição do desempenho deste tipo de escoamento. O modelo tridimensional, turbulento e bifásico usado para a predição do escoamento gás-sólido, consiste num conjunto de equações de conservação da massa e momento para cada uma das fases, formuladas seguindo a aproximação Euleriana-Euleriana. As variáveis fluidodinâmicas foram estimadas pela solução do modelo, com o emprego de correlações empíricas da literatura e disponibilizadas pelo código computacional de CFD, para garantir o fechamento do modelo e sua solução numérica. Desde de que a predição da dinâmica do escoamento complexo, em dutos com alto fluxo ascendente de sólidos não é possível por meio somente de equações fundamentais, a maioria dos modelos requerem entradas empíricas, as quais somente são adquiridas com a experimentação. Estes dados foram obtidos dos estudos de PÄRSSINEN e ZHU (2001). A geometria e a malha numérica estrutural do duto vertical foram geradas pelo software (CAD) ICEM, subdividido em DDN (geometria) e Hexa (malha). A adaptação do modelo matemático para a geração do modelo numérico foi alcançada com o uso do simulador comercial CFX 5.7. Os resultados obtidos foram avaliados com respeito à teoria apresentada ao longo da dissertação, sendo finalmente feita uma comparação entre as predições numéricas com o modelo e dados experimentais da literatura / Abstract: The present research presents the mathematical modeling and the simulation of an operation of fast fluidization in a long vertical cylindrical duct line, which is an important operation in many industrial processes, where its main application is tied with the catalytic cracking of oil for gasoline synthesis. It has as objective the attainment of a continuous understanding and knowledge of the development of the gas-solid flow, as well as adding of experiences to research of industrial scale equipments motivated by the possibility of prediction of the performance of this type of flow. The three-dimensional, turbulent and two-phase model used for the prediction of the gas-solid flow, consists of a set of conservation equations of mass and momentum for each phase, which was formulated following the Eulerian-Eulerian approach. The fluid dynamics variables was estimated by the solution of the model with the use of correlations found in the literature and available in the computational CFD code, in order to guarantee the closure of the model and its numerical solution. Since the prediction of the dynamics of the complex flow in ducts with high ascending solid flow is not possible by solely using the basic equations, the majority of the models require the setting empirical, parameters which are acquired only with experimentation. These data were obtained from the studies of PÄRSSINEN and ZHU (2001). The geometry and the structural numerical mesh of the vertical duct was generated by the software (CAD) ICEM, subdivided in DDN (geometry) and Hexa (meshing). The adaptation of the mathematical model for the numerical model generation was reached with the use of the commercial simulator CFX 5.7. The results were evaluated with respect to the theory presented along this dissertation, where comparisons between the numerical predictions with the model and experimental data from the literature were performed. / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

Orientador: Milton Mori / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-10T23:15:40Z (GMT). No. of bitstreams: 1 Rosa_LeonardoMachadoda_D.pdf: 1367270 bytes, checksum: 1819e68c66a949c1c8fae024725df552 (MD5) Previous issue date: 2008 / Resumo: A aplicação de Fluidodinâmica Computacional (CFD) em operações industriais vem aumentando sensivelmente, em razão desta auxiliar no projeto de novos equipamentos, bem como a otimização dos já existentes. O presente trabalho apresenta uma série de simulações tridimensionais, bifásicas e adiabáticas, utilizando-se o modelo de dois-fluidos para o cálculo do escoamento gás-sólido em risers de diferentes tamanhos ¿ um com as dimensões de 10m de altura e 76mm de diâmetro interno, e outro com 18m de altura e 50mm de diâmetro interno. Utilizou-se o modelo k-epsilon para tratar a fase gasosa como turbulenta. Foram considerados os modelos cinéticos de 4 lumps e 10 lumps para o cálculo das taxas de craqueamento catalítico presentes no reator. Dados experimentais para comparação do escoamento foram obtidos em literatura, e os resultados obtidos mostram que, para a correta predição dos fenômenos presentes no interior de um riser, deve-se levar em consideração também as reações de craqueamento, visto que a alteração da composição química da fase gasosa interfere diretamente no comportamento dinâmico do escoamento / Abstract: The application of Computational Fluid Dynamics (CFD) in industrial operations has been increased not only in the project of new equipments but also in the optimization of the existing ones. The present work shows a set of tridimensional two-phase and adiabatic conditions, using the two-fluids model for the calculation of gas-solids flow in a high-flux risers of two different geometries, one with 10m of height and 76mm of internal diameter, and the second with 18m of height and 50mm of internal diameter. The k-epsilon model was applied to consider the influence of turbulence over the gas phase. The four-lump and ten-lump schemes kinetic models were used to predict the catalytic cracking reactions in the two different reactors. The riser with 10m of height and 76 mm of internal diameter had two entrances, one for particles inlet and one for the organic materials. The size of mesh for this case was 584.000 control volumes. The second riser studied with geometry of 18m of height and 50mm of internal iameter had one entrance for vapor, one for organic materials, and a third for particles inlet. The mesh generated over this geometry was considered 650.000 control volumes. The numerical results of gas-solids dispersion flow in a high-flux were compared with the xperimental data from the work of P¨arssinen and Zhu (2001), the four lump scheme for he mass concentration of chemical species was compared with the work of (ALI et al., 997), and the ten lump scheme was compares with the work of NAYAK et al. (2005). The catalytic cracking reactions models show an important role in the prediction of all henomena present in the reactor. The simulated results show that the kinetics models are important not only because of the variation of the gas phase and the temperature profiles inside the reactor but also because these parameters interfere directly in the dynamic behavior of the gas-solid flows / Doutorado / Desenvolvimento de Processos Químicos / Doutor em Engenharia Química

Orientador: Milton Mori / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-26T06:44:29Z (GMT). No. of bitstreams: 1 AlvarezCastro_HelverCrispiniano_D.pdf: 5280150 bytes, checksum: 96fb29e2849d11c06890186cb8af2f51 (MD5) Previous issue date: 2014 / Resumo: Conversão de matéria-prima e rendimento são estudados através de um modelo 3D que simula o principal reator do processo de craqueamento catalítico fluidizado (FCC). Fluidodinâmica computacional (CFD) é usada como técnica com abordagem Euleriana-Euleriana para prever o comportamento do riser da FCC. O modelo considera 12 grupos com desativação do catalisador dada por coque e envenenamento por nitritos alcalinas e adsorção aromático policíclico para estimar o comportamento cinético, o qual partindo de uma determinada matéria prima, se craquea a diversos produtos. Composições diferentes para matérias-primas foram consideradas. Para validação o modelo foi comparado com dados experimentais em condições de operação industrial. O modelo é capaz de representar com precisão a geração de produtos para as diferentes condições de operação consideradas. Todas as condições consideradas foram resolvidos usando o solver Ansys CFX 14.0. As diferentes variáveis do processo de operação e efeitos hidrodinâmicos do riser industrial de craqueamento catalítico fluidizado (FCC) foram avaliadas. As previsões do modelo são apresentados e comparadas; conversão e produtos são apresentados. Recomendações para criar condições para obter maior rendimento do produto no processo industrial foram dadas / Abstract: Feedstock conversion and yield products are studied through a 3D model simulating the main reactor of the fluid catalytic cracking (FCC) process. Computational Fluid Dynamic (CFD) is used with Eulerian-Eulerian approach to predict the fluid catalytic cracking behavior. The model considers 12 lumps with catalyst deactivation by coke and poisoning by alkaline nitrides and polycyclic aromatic adsorption to estimate the kinetic behavior which, starting from a given feedstock, produces several cracking products. Different feedstock compositions are considered. The model is compared with sampling data at industrial operation conditions. The simulation model is able to represent accurately the products behavior for the different operating conditions considered. All the conditions considered were solved using a solver Ansys CFX 14.0. The different operation process variables and hydrodynamic effects of the industrial riser of a fluid catalytic cracking (FCC) are evaluated. Predictions from the model are shown and comparison with experimental conversion and yields products are presented; recommendations are drawn to establish the conditions to obtain higher product yields in the industrial process / Doutorado / Engenharia de Processos / Doutor em Engenharia Química

Aujourd’hui, la transplantation est le seul traitement efficace proposé aux patients souffrant d’une insuffisance hépatique fulminante. La nécessité de disposer d’un système de suppléance hépatique transitoire apparaît donc indispensable. C’est dans cet axe que se sont développés les systèmes qualifiés de foies bio artificiels (BAL). Leur principale caractéristique est d’incorporer un bioréacteur hébergeant des cellules pouvant restaurer l’activité hépatiques dans son ensemble. A l’heure actuelle, les hépatocytes primaire humains (HEP) issus de foies de donneurs non transplantables sont considérées comme le meilleur choix. Cependant, leur utilisation reste limitée par leur faible disponibilité et la difficulté à les maintenir différenciés en culture in vitro. Pour remédier à ce dernier point, l’approche la plus prometteuse semble être une co-culture des hépatocytes avec les cellules non parenchymateuses afin de recréer un environnement proche des sinusoïdes hépatiques. Ce travail de thèse repose sur la mise en place d’une nouvelle approche de co-culture tridimensionnelle sous la forme de sphéroïdes, d’HEP primaires avec les principaux types de cellules non-parenchymateuses (les cellules de Kupffer, les cellules endothéliales et les cellules étoilées) selon des proportions spécifiques. Puis de leurs encapsulations dans des billes d’alginate et leurs cultures au sein d’un bioréacteur à lit fluidisé. Ce modèle s’est révélé pertinent et approprié à maintenir les fonctions hépatiques dans le temps. Bien que beaucoup d’optimisation reste à définir, ce travail exploratoire témoigne de l’intérêt de cette approche intéressante pour le progrès des systèmes BAL. / Liver shortage makes transplantation inapplicable to all acute liver failure patients. Bioartificial Iiver (BAL) devices represent a temporary solution for these patients which are thereby bridged tilt Iiver transplantation or regeneration BAL treatment offers blood purification and substitution of metabolic functions through the activity of hepatocytes (HEPs), which are integrated in the device within acclimating containers, so-called bioreactors. Primary human hepatocytes are the ideal cell type to use in BAL, but they are scarcely available and difficult to maintain in vitro. Co-culture of HEPs with supporting cells has been proposed as the most promising strategy for preserving HEP behaviors in in vitro conditions. In fact, assisting cells types hold their ability to influence functional responses of the HEPs by providing them with cues of the native organ.This PhD work proposed a novel approach of co-culture for the functional sustain and preservation of the HEPs in the environment of the fluidized bed bioreactor (designed in our Iaboratory). Definition of this model took inspiration from the cellular organization in the organ; therefore, it employed three major sinusoidal non-parenchymal cell populations (liver sinusoidal, Kupffer, and hepatic stellate cells) which, together with HEPs, were cultured with three-dimensional arrangement (spheroids) and according to specific proportions. The resulting model was characterized in terms of functional benefits for the HEPs, and then applied in the microenvironment of alginate beads, which provide cells with immunological and mechanical protection in the fluidized bed bioreactor. This spheroidal multi-cultured model revealed its potentiality in sustaining in vitro HEP behaviors over time. Although much remains to be refined, this model may represent an interesting approach for the progress of BAL