Dirceu Noriler

Nanoscale mixing during double-flame spray synthesis of heterostructured nanoparticles

The combination of two nanoparticle-producing flame reactors to a double-flame (DF) spray pyrolysis process is an attractive method for the high-temperature gas-phase synthesis of multicompound materials and heterostructures. It allows separate control of particle growth in the individual flames up to the intersection or mixing point where the formation of heterostructures takes place. The effect of mixing of the aerosol streams on the process temperature and product characteristics is investigated based on the example of Pt on TiO2. Temperatures were determined by Fourier-transform infrared spectroscopy and thermocouple measurements along with computational fluid dynamics, while the degree of mixing was investigated based on surface area, Pt-dispersion measurements, and transmission electron microscopy image analyses. The quadrat method in combination with the variation coefficient was used to quantify the uniformity of the Pt cluster distribution on the TiO2 support. For high intersection distances of the two flame jets and small intersection angles, nonuniform mixing of the compounds and the formation of large Pt particles are observed. For small intersection distances and large angles, a uniform Pt distribution was achieved. Based on these findings, process design rules were established which can be transferred to other material systems.

Numerical Simulation of Flame Spray Pyrolysis Process for Nanoparticle Productions: Effects of 2D and 3D Approaches

Nanoparticle production in flames was modeled in an Eulerian-Lagrangean framework, considering droplet evaporation and fuel combustion to predict the flame chemical species concentration and the flame temperature fields by means of Computational Fluid Dynamics (CFD). A mathematical model was carried out considering two-way coupling between the gas phase and the droplets. For the combustion model, the eddy dissipation concept model was applied, taking into account the droplets vaporization, the chemical reaction mechanisms, and the chemistry-turbulence interaction. 2D axisymmetric and 3D approaches were investigated in standard operations conditions. The initial conditions for the droplet sizes and droplet velocities were taken in experiment test facility by means of Laser-Diffraction. The grid independence study was made according to the Grid Convergence Index (GCI) methodology for both approaches. The droplets mass evaporated, temperature and velocities profiles were used to compare the 2D and 3D results. The results show similar behavior for both approaches, however, with some quantitative difference. The 2D approach showed lower temperature resulted by a larger mass fuel not evaporated and unburned.Copyright

Experimental and Numerical Investigation of a Reactive Absorption Column for Chlorine Gas Mitigation

Chlorine gas is extensively used in a variety of chemical processes as an end product or reactant, for instance, in the conversion of phthalocyanine dye. Reactive absorption (RA) columns can be applied for the treatment of the waste gas streams at the outlet of the reaction equipment, in order to satisfy the environmental regulations, and these should be prepared for potential accidents. The objective of this study was to evaluate an industrial-scale RA column for the treatment of chlorine gas stream in a phthalocyanine plant in the case of an accident. A coupled experimental and numerical study was performed. A factorial design was applied for the definition of a set of experimental conditions to be evaluated in a pilot-scale plant operated in the laboratory. The data collected were treated by means of the response surface methodology, and coupled numerical schemes allowed the determination of the mass transfer coefficient and the reaction rate constant. Finally, numerical studies were carried out to assess the industrial-scale column behavior. It was found that the industrial absorption column was able to treat a stream of chlorine at a flow rate of 900 kg/h with an efficiency of approximately 79%.

DESENVOLVIMENTO DE UMA UNIDADE EXPERIMENTAL PARA ESTUDOS EM TERMOSSIFÕES COM APLICAÇÃO DA TÉCNICA DE PIV PARA ANÁLISE DO ESCOAMENTO

RESUMO O escoamento induzido pelas forcas de empuxo em um termossifao e avaliado no presente estudo, com enfase na consolidacao de uma bancada experimental para constituicao de base empirica, a ser empregada na formulacao e validacao de modelos matematicos de CFD para este tipo de sistema. O termossifao da unidade experimental compreende um downcomer e um riser, que consistem em tubos de vidro enjaquetados, e um separador liquido-vapor. Como medida experimental, o perfil de velocidade axial na regiao do riser foi obtido por meio da tecnica de velocimetria por imagem de particula (PIV), para tres condicoes operacionais do regime monofasico e do bifasico, variando-se a temperatura de entrada da agua nas jaquetas do downcomer e do riser. Para o regime monofasico, o perfil de velocidade axial e caracterizado por velocidades mais altas na regiao proxima a parede em todas as condicoes avaliadas, seguindo o perfil esperado para a temperatura. Em regime bifasico, com o aumento do numero de bolhas formadas pela ebulicao do liquido, o perfil de velocidade axial torna-se mais uniforme ao longo do raio e a magnitude da velocidade aumenta significativamente, em comparacao aos resultados obtidos para o regime monofasico.

ANÁLISE NUMÉRICA DO USO DE ANÉIS DEFLETORES INTERNOS SOBRE O ESCOAMENTO GÁS-SÓLIDO EM RISERS DE FCC

RESUMO O escoamento gas-solido em risers de FCC e caracterizado por uma regiao diluida no centro e uma regiao densa em catalisador, proxima as paredes. Este comportamento, caracterizado com a heterogeneidade do campo de fracao volumetrica, e responsavel pelo contato ineficiente entre o gas e as particulas de catalisador. Uma alternativa para homogeneizar a fracao volumetrica de solidos na regiao de mistura e a insercao de aneis defletores internos na regiao de entrada do riser. Este trabalho analisa a insercao de aneis defletores em formato de aerofolio na regiao de entrada do riser para redirecionar o escoamento de particulas solidas. Para isso, foram realizadas simulacoes numericas utilizando abordagem Euleriana-Euleriana, com modelo de turbulencia k-e. A homogeneidade da distribuicao de solidos na secao transversal do riser foi avaliada a partir do seu desvio-padrao. Com auxilio das simulacoes numericas e da aplicacao da ANOVA, verificou-se que o menor desvio-padrao e obtido com aneis de 10mm de espessura.

EXPERIMENTAÇÃO NUMÉRICA E FÍSICA DA EROSÃO EM CICLONES

RESUMO A erosao e o desgaste mecânico na parede dos equipamentos por particulas transportadas por escoamento de fluido. Este fenomeno representa um grave problema nas unidades de FCC (craqueamento catalitico fluido), especialmente em ciclones, reduzindo a vida util do equipamento e causando paradas nao programadas. Assim, o objetivo deste trabalho e analisar a erosao causada pelo impacto das particulas de catalisador de FCC em uma geometria de ciclone otimizada para operar com altas vazoes, mediante a realizacao de estudos experimentais conjugados com estudos de simulacao numerica. O escoamento gas-solido foi estudado por meio da abordagem euleriana-lagrangeana com o modelo de turbulencia RSM-SSG (Reynolds Stress Model – Quadratico). A taxa de erosao foi calculada por dois modelos de erosao. Experimentacoes fisicas foram realizadas para validar os resultados numericos com ciclones construidos em gesso para acelerar o processo de erosao. Os resultados numericos apresentaram boa concordância qualitativa com os dados experimentais, mostrando a regiao na parede do ciclone onde a erosao e mais evidente e, de forma quantitativa em alguns dos casos estudados.

Novel Atomization Process for Large Scale Nanoparticle Production by Flame Spray Pyrolysis

An advanced atomizer concept to obtain larger production rates of nano-particles by the Flame Spray Pyrolysis process (FSP) is investigated. In the conventional FSP process (external mixing gas/liquid nozzle) production rates may be varied by increasing the precursor feed rate and/or the precursor concentration. However, both measures typically result in the formation of larger nanoparticles. These effects may be avoided by the development and integration of advanced atomizer concepts. The aim is to address the spray structure in a way that keeps the flame height constant and modifies the flame width. Therefore, the time scales and the residence time-temperature histories of droplets and nanoparticles are expected to be similar while the production rate is increased. The atomizer concept for creation of a modified spray and flame combines a swirling liquid film generation that is atomized with an external swirling gas flow.In the first step a hollow cone of liquid ligaments and primary droplets is generated through a conventional pressure-swirl nozzle. The liquid phase is atomized in the second step, by the expanding gas of a circular ring nozzle. To study the main characteristics of the combined atomizer in model experiments, water and water/glycerol mixtures are used as the liquid phase and air as the gas phase. For investigation of the atomizer and spray properties, the relation between liquid outlet angle, inlet angle of the gas, the gas/liquid flow rates, the spray cone geometry and droplet size distribution are investigated. The spray structure and the breakup of the film are analyzed by high speed images. Laser diffraction is used to measure the droplet size distribution in the spray.A numerical model is developed and used to simulate the cold gas flow and spray distribution as in the adapted atomizer concept. The Eulerian-Lagranian approach is solved by means of a computational fluid dynamics (CFD) code. The process parameters such as liquid composition, liquid and gas flow rates are varied to meet the specific requirements of the nanoparticle production in the FSP process. The experimental and numerical investigation showed that an enlarged and steady spray resulted from an increased outlet angle of the liquid and gas swirl. Increased tangential velocities increase the entrainment of surrounding gas, widening and providing a more uniform velocity profile to the spray. Spray droplet mean diameters resulted in the desired range of ≤ 20 μm.Copyright

Prediction of Efficiencies Through Simultaneous Momentum, Mass and Energy Transfer Analyses in a Distillation Sieve Tray by CFD Techniques

Abstract The main objective of this work is to apply a CFD model under Eulerian-Eulerian framework for gas-liquid flows, with capability to predict the momentum, mass and thermal phenomena of multiphase flows. A two-phase, three-dimensional and transient model with chemical species, energy and momentum conservation balances have been applied for predicting volume fractions, velocity, pressure, temperature and concentration fields, of two-phase flows on sieve distillation tray. The mathematical model was applied in the CFD commercial code for numerical studies, with the construction of a particular numerical grid and with proper sub-routines in FORTRAN language for the closure equations of the model. The results show the profiles as a function of the time and of the position in the distillation sieve tray. The model implemented in this work allows direct application to predict efficiencies in distillation plates, more specifically point, plate, component and global efficiencies.