Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Distillation is one of the most widely used processes for the separation of fluids with different volatilities. Due to the popularity of this process it is often assumed that the hydrodynamic behaviour inside distillation columns is well-defined. However, this is not always the case and this study therefore endeavoured to provide additional insight into the topic through a systematic investigation into the hydrodynamics and the capacity limitations of a sieve tray distillation column. The objective of the study was to measure and evaluate the effects of the following variables on entrainment and weeping: - Fluid flow rate (gas and liquid). - Plate geometry (i.e. hole diameter and fractional hole area). - Liquid properties (i.e. surface tension, viscosity and density). - Gas properties (i.e. viscosity and density). The hydrodynamic effects were evaluated at zero mass transfer in a pilot-scale tray column, by passing pure liquids and gases in counter current configuration. The pilot column was rectangular in shape with internal dimensions of 175 mm by 635 mm. A chimney tray was used to capture the weeping liquid, while a de-entrainment tray was used in combination with a mist eliminator pad to capture the entrained liquid. The fractional hole areas for the sieve trays under investigation were 7%, 11% and 15% and the hole diameters were 3.2 mm (⅛ in.), 6.4 mm (¼ in.) and 12.7 mm (½ in.). The experimental liquids were ethylene glycol, butanol, water and silicone oil, while the gases were air and carbon dioxide (CO2). These experimental measurements produced over 10 000 data points for entrainment and over 7 000 data points of weeping. The results were repeatable and the entrainment values compared reasonably well with previous data produced by Nutter (1971) and Uys (2012). The differences between entrainment for the different liquids were more significant in the spray regime than in the froth regime, and butanol was entrained more readily than silicone oil, ethylene glycol and water. Fluids that caused a larger spray layer in the dispersion zone produced more entrainment. Entrainment increased with decreasing liquid density, decreasing liquid surface tension and decreasing liquid viscosity. The more unstable the dispersion layer, the higher the entrainment. The liquid density strongly influenced weeping, i.e. weeping increased with increasing liquid density. On the other hand, gases with higher densities – and thus with a higher mass flow rates at similar volumetric flow rates through the sieve tray – displayed less weeping and more entrainment than less dense gases, because of an increased upward drag force on the fluids. When considering tray geometry and when operating in the spray regime, the magnitude of entrainment increased with decreasing fractional hole area, while the dependency of entrainment on fractional hole area was more prominent at lower fractional hole areas. When operating in the froth regime – typically above 23 m3/(h.m) – the fractional hole area had a relatively small influence on the magnitude of entrainment, while the cross-flowing liquid rate dominated related effects. In the spray regime, i.e. typically below 23 m3/(h.m), the entrainment increased with increasing sieve tray hole diameter, while hole diameter had a relatively small influence on entrainment at higher liquid flow rates between 23 and 60 m3/(h.m). However, at even higher liquid flow rates in the froth regime, i.e. above 60 m3/(h.m), the effect of hole diameter on the entrainment became more prominent again, with increased entrainment for smaller hole diameters. The effect of hole diameter on weeping differed with changing fluid combinations and the 12.7 mm hole size caused notably less weeping than the 3.2 mm and 6.4 mm trays at higher liquid flow rates. It is believed that weeping occurred preferentially at so-called localised high pressure zones on the sieve tray. At high gas and liquid flow rates, the resultant extended dispersion layer allows minimal intimate contact between the plate and the liquid (minimising such localized high-pressure zones). In effect, the liquid ‘jumps’ over the entire flow path length in the test rig, thus resulting in low weeping rates at high gas and liquid rates. The effects of fractional hole area and hole diameter on entrainment and weeping can be correlated with combinations of well-known hydrodynamic dimensionless numbers, such as the Weber number (We), Froude number (Fr) and Reynolds number (Re). Within the limitations of this study, the flow-Froude number was shown to be the most useful dimensionless number, since it displayed a monotonic relationship with magnitude of entrainment for different combinations of fluid systems and tray configurations. Furthermore, both the construction number and fluid density ratio could be used in a sensible manner to correlate some of the effects of tray geometry on entrainment. / AFRIKAANSE OPSOMMING: Distillasie word wêreldwyd op groot en klein skaal toegepas as ʼn metode om chemiese komponente van mekaar te skei, gebasseer op hul verskil in vlugtigheid. Die hidrodinamiese gedrag van vloeistowwe en hul damp binne ʼn distillasiekolom beïnvloed die effektiwiteit van die skeidingsproses. Hierdie studie beoog dus om bykomende insig te verskaf tot die hidrodinamika en kapasiteitsbeperkings van ʼn plaat-distilleerkolom. Die doelwit van die studie was om die invloed van die volgende veranderlikes op die meesleuring en deurdripping van vloeistowwe te ondersoek: - Gas- en vloeistof vloeitempo. - Plaatgeometrie (i.e. gatdeursnit en fraksionele deurvloei-area). - Vloeistofeienskappe (i.e. oppervlakspanning, viskositeit en digtheid). - Gaseienskappe (i.e. viskositeit en digtheid). Die hidrodinamiese studie is uitgevoer in ʼn reghoekige plaatkolom met interne afmetings van 175 mm x 635 mm. Die vloeistof en gasfases is in kontak gebring op ʼn teenstroom basis, met geen massa-oordrag wat plaasvind nie. ʼn Skoorsteenplaat het die vloeistof opgevang wat deurdrip terwyl ʼn ekstra plaat aan die bokant van die kolom die meegesleurde vloeistof opgevang het. Hierdie ekstra plaat is gebruik tesame met ʼn mis-elimineerder om al die meegesleurde vloeistof op te vang. Plate met verskillende deurvloei-areas (7%, 11% en 15%) en gat deursnitte (3.2 mm, 6.4 mm en 12.7 mm) is gebruik in die ondersoek. Die vloeistowwe wat gebruik is, sluit in etileen glikol, butanol, water en silikon olie. Lug en koolstofdioksied is as gasse gebruik. Die eksperimentele data het goeie herhaalbaarheid getoon en is vergelykbaar met die gepubliseerde data van Nutter (1971) en Uys (2012). Meer as 10 000 data punte is gemeet vir vloeistofmeesleuring en meer as 7 000 vir deurdripping. Die verskil in hoeveelheid meesleuring tussen die vloeistowwe, soos ondersoek in hierdie studie, was mees beduidend in die spoei-regime. Butanol is die meeste meegesleur, gevolg deur silikon olie en dan etileen glikol. Water is die minste meegesleur is. Vloeistowwe wat ʼn groter sproeivolume in die dispersielaag bo die plaat gevorm het, is die meeste meegesleur. Meesleuring het toegeneem met ʼn afname in digtheid, oppervlakspanning en viskositeit van die vloeistof. ʼn Onstabiele dispersielaag bo die plaat het meer meesleuring tot gevolg gehad. Vloeistofdeurdripping is sterk beïnvloed deur vloeistofdigtheid, i.e. deurdripping het sterk toegeneem met digtheid. Gasse met ʼn hoër digtheid veroorsaak weer ʼn afname in deurdripping a.g.v. die hoër opwaartse sleurkragte wat ʼn gas met hoë digtheid op die vloeistof uitoefen. In die sproei-regime (tipies by vloeistofvloeitempos laer as 23 m3/(h.m) is gevind dat meesleuring toeneem met ʼn afname in fraksionele deurvloei-area. Meesleuring se afhanklikheid van fraksionele deurvloei-area was meer beduidend by laer fraksionele deurvloei-areas. In die skuim-regime (tipies by vloeistofvloeitempos hoër as 23 m3/(h.m)) was die afhanklikheid van meesleuring op fraksionele deurvloei-area relatief klein. In die sproei-regime is gevind dat meesleuring toeneem met ʼn toename in gat deursnit, terwyl dieselfde veranderlike ʼn minder beduidende invloed op meesleuring getoon het by hoër vloeistofvloeitempos (tussen 23 en 60 m3/(h.m)). By vloeitempos hoër as 60 m3/(h.m) het meesleuring weer begin toeneem met ʼn afname in gat deursnit. By hoë vloeistofvloeitempos het die plaat met 12.7 mm gat deursnit aansienlik minder deurdripping getoon as plate met 3.2 mm en 6.4 mm deursnitte. Daar word vermoed dat deurdripping hoofsaaklik plaasvind by lokale hoëdruk gebiede op die plaat. By hoër vloeistof- en gasvloeitempos beslaan die dispersielaag ʼn groter volume en is daar dus minder gebiede van digte vloeistofkontak met die plaat, wat ʼn afname in die lokale drukgebiede veroorsaak. Dit lei tot ʼn afname in deurdripping by hoër gas- en vloeistofvloeitempos. Die invloed van fraksionele deurvloei-area en gatdeursnit op meesleuring en deurdripping korreleer goed met kombinasies van welbekende hidrodinamiese dimensielose getalle, i.e. die Webergetal (We), die Froudegetal (Fr) en die Reynoldsgetal (Re). Die vloei-Froudegetal is mees bruikbaar om die invloed van vloeistof-en-gas kombinasies en kolomuitleg op meesleuring te korreleer. Die konstruksiegetal asook die digtheidsverhoudings tussen vloeistof en gas kan op ʼn sinvolle manier aangewend word om van die invloede van plaatgeometrie op meesleuring te beskryf.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Mass transfer efficiency in distillation, absorption and stripping depends on both thermodynamic efficiency and hydrodynamic behaviour. Thermodynamic efficiency is dependent on the system kinetics while hydrodynamics is the study of fluid flow behaviour. The focus of this thesis is the hydrodynamic behaviour in tray columns, which affects entrainment. In order to isolate hydrodynamic behaviour from the thermodynamic behaviour that occurs inside sieve tray columns, investigations are conducted under conditions of zero mass transfer. When the gas velocity is sufficiently high to transport liquid droplets to the tray above, entrainment occurs. The onset of entrainment is one of the operating limits that determines the design of the column and thus impacts on the capital cost. By improving the understanding of the parameters that affect entrainment, the design of the tray and column can be improved which will ultimately increase the operability and capacity while reducing capital costs. Existing correlations predicting entrainment in sieve tray columns are based on data generated mainly from an air/water system. Previous publications recommend that more testing should be performed over larger ranges of gas and liquid physical properties. An experimental setup was therefore designed and constructed to test the influence of the following parameters on entrainment: 1. gas and liquid physical properties 2. gas and liquid flow rates 3. tray spacing The experimental setup can also measure weeping rates for a continuation of this project. The hydrodynamic performance of a sieve tray was tested with air and water over a wide range of gas and liquid flow rates and at different downcomer escape areas. It was found that the downcomer escape area should be sized so that the liquid escaping the downcomer always exceeds a velocity of approximately 0.23 m/s in order to create a sufficient liquid seal in the downcomer. For liquid velocities between 0.23 and 0.6 m/s the area of escape did not have an effect on the percentage of liquid entrained. It was also established that entrainment increases with increasing gas velocity. The rate at which entrainment increases as the gas velocity increase depends on the liquid flow rate. As soon as the liquid flow rate exceeded 74 m3/(h.m) a significant increase in entrainment was noted and the gas velocity had to be reduced to maintain a constant entrainment rate. This is because the increased liquid load requires a longer flow path length for the froth to fully develop. The undeveloped froth, caused by the short (455 mm) flow path, then creates a non-uniform froth that is pushed up against the column wall above the downcomer. Consequently, the froth layer is closer to the tray above resulting in most of the droplets ejected from the froth reaching the tray above and increasing entrainment. By reducing the gas velocity, the froth height and ejecting droplet velocity is reduced, resulting in a decrease in entrainment. The results from the experiments followed similar trends to most of the entrainment prediction correlations found in literature, except for the change noted in liquid flow rates above 74 m3/(h.m). There was, however, a significant difference between the experimental results and the correlations developed by Hunt et al. (1955) and Kister and Haas (1988). Although the gas velocities used during the air/water experiments were beyond the suggested range of application developed by Bennett et al. (1995) their air/water correlation followed the results very well. The entrainment prediction correlation developed by Bennett et al. (1995) for non-air/water systems was compared with the experimental air/water results to test for system uniformity. A significant difference was noted between their non-air/water prediction correlation and the air/water results, which motivates the need for a general entrainment prediction correlation over a wider range of gas and liquid physical properties. Based on the shortcomings found in the literature and the observations made during the experiments it is suggested that the influence of liquid flow path length should be investigated so that the effect on entrainment can be quantified. No single correlation was found in the literature, which accurately predicts entrainment for a large range of liquid loads (17 – 112 m3/(h.m)), high superficial gas velocities (3 – 4.6 m/s) and different gas and liquid physical properties. It is therefore recommended that more work be done, as an extension of this project, to investigate the influence of gas and liquid physical properties on entrainment (under zero mass transfer conditions) for a large range of liquid (5 – 74 m3/(h.m)) and gas (2 – 4.6 m/s) flow rates. In order to understand the effect of droplet drag on entrainment, tray spacing should be varied and increased to the extent where droplet ejection velocity is no longer the mechanism for entrainment and droplet drag is responsible for droplet transport to the tray above. Since it is difficult and in most cases impossible to measure exact gas and liquid loads in commercial columns, another method is required to measure or determine entrainment. Since liquid hold-up was found to be directly related to the entrainment rate (Hunt et al. (1955), Payne and Prince (1977) and Van Sinderen et al. (2003) to name but a few), it is suggested that a correlation should be developed between the dynamic pressure drop (liquid hold-up) and entrainment. This will contribute significantly to commercial column operation from a hydrodynamic point of view.

A need was identified for a set of basic design tools for Multi-Effect Distillation (MED) plant evaporators. This led to an investigation into the different types of evaporators as well as further research on horizontal falling film evaporators as used in the MED process. It also included the theory on these types of evaporators. In order not to duplicate existing design tools, an investigation was also performed on some of the tools that are currently available. The first set of tools that were developed were tools, programmed in EES (Engineering Equation Solver), for the vacuum system and the evaporator. These programs can be used to simulate different parameters (like different mass flows and temperatures). That enables the correct selection of components for the vacuum system and can be used to address sizing issues around the evaporator. It can also be used to plan the layout of the plant. The second of the design tools was developed by designing and building a flow pattern test section. From the flow pattern test section a set of curves for the wetted length under different conditions was obtained which can be used in order to design the sieve tray. This set of curves was found to be accurate for municipal as well as seawater and can be used in the design of the sieve tray of the evaporator. Further development can be done by implementing the figures of the wetted length into a simulation package like, for example, Flownex (a system CFD (Computational Fluid Dynamics) code that enables users to perform detail design, analysis and optimization of a wide range of thermal-fluid systems). The background gained from the study done on the evaporator can also be implemented into such a package. This could solve the problem of different design packages by creating a single design package with all of the above mentioned options included. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

A need was identified for a set of basic design tools for Multi-Effect Distillation (MED) plant evaporators. This led to an investigation into the different types of evaporators as well as further research on horizontal falling film evaporators as used in the MED process. It also included the theory on these types of evaporators. In order not to duplicate existing design tools, an investigation was also performed on some of the tools that are currently available. The first set of tools that were developed were tools, programmed in EES (Engineering Equation Solver), for the vacuum system and the evaporator. These programs can be used to simulate different parameters (like different mass flows and temperatures). That enables the correct selection of components for the vacuum system and can be used to address sizing issues around the evaporator. It can also be used to plan the layout of the plant. The second of the design tools was developed by designing and building a flow pattern test section. From the flow pattern test section a set of curves for the wetted length under different conditions was obtained which can be used in order to design the sieve tray. This set of curves was found to be accurate for municipal as well as seawater and can be used in the design of the sieve tray of the evaporator. Further development can be done by implementing the figures of the wetted length into a simulation package like, for example, Flownex (a system CFD (Computational Fluid Dynamics) code that enables users to perform detail design, analysis and optimization of a wide range of thermal-fluid systems). The background gained from the study done on the evaporator can also be implemented into such a package. This could solve the problem of different design packages by creating a single design package with all of the above mentioned options included. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

Submitted by Regina Correa (rehecorrea@gmail.com) on 2016-09-21T20:17:28Z No. of bitstreams: 1 TeseGHJ.pdf: 12148265 bytes, checksum: 1180759f1c9f8691c3ce486239959cf5 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-23T18:39:16Z (GMT) No. of bitstreams: 1 TeseGHJ.pdf: 12148265 bytes, checksum: 1180759f1c9f8691c3ce486239959cf5 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-23T18:39:23Z (GMT) No. of bitstreams: 1 TeseGHJ.pdf: 12148265 bytes, checksum: 1180759f1c9f8691c3ce486239959cf5 (MD5) / Made available in DSpace on 2016-09-23T18:39:31Z (GMT). No. of bitstreams: 1 TeseGHJ.pdf: 12148265 bytes, checksum: 1180759f1c9f8691c3ce486239959cf5 (MD5) Previous issue date: 2016-03-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / The development of the design of chemical processes has received increasing improvement, incorporating sophisticated mathematical models, which allowed better simulation of its real behavior. Distillation is one of the most important and used separation techniques of components at industrial level, applied in a wide range of processes and its perfect working and optimization are economically crucial factors. Its great importance is due to the capacity of purify components of a mixture using the volatility difference among them as driving force. However, this technique represents 40% of the total energy consumption of an industrial facility. Some of models used for this, such as the models based on equilibrium and non-equilibrium stage concepts, usually provide useful results, but consider empirically many of the fluid dynamics phenomena by assuming a perfect mixture in each phase. Due to the development of the Information Technology (IT), in the numerical methods and improvement in models of multiphase flows, the investigation of complex turbulent flow problems is possible. One way to investigate these problems is to use the Computational Fluid Dynamics (CFD) tecniques. Therefore, it was adopted for this study a CFD model, with the main objective of evaluating the transport phenomena for the isothermal (water-air) and non-isothermal (ethanol-water) flows through the CFD techniques to simulate a distillation sieve tray. The proposed models had the following characteristics in common in the modeling: heterogeneous, three-dimensional, shear stress transport as turbulence model, and Eulerian-Eulerian approach at 1 atm. The continuity and momentum conservation equations were used to describe the isotherm model and for non-isothermal model it was added the energy and chemical species conservations equations. The simulated sieve trays geometries were based on experimental work of Solari e Bell (1986), to which it were observed the influence of the inlet downcomer presence or not on sieve tray. The results for isotherm flow showed the velocity profiles, the volume fractions, and clear liquid height under the influence of the inlet downcomer. For the non-isotherm flow, the results showed moreover the hydraulic parameters, the temperature profiles and ethanol mass fractions for vapor flow rates. Thus, the simulations of the isothermal system indicated a strong influence of the liquid velocity profile for the domain with downcomer inlet. In the non-isothermal system it was possible to determine the separation efficiency, which varied with the vapor flow rates on the sieve tray. The proposed methodology in this work proved to be appropriate and the computational fluid dynamics techniques presented to be an important tool in the design and optimization of sieve trays. / O desenvolvimento de projetos de processos químicos tem recebido aperfeiçoamento cada vez maior, incorporando modelos matemáticos mais sofisticados, os quais possibilitam uma maior aproximação do seu comportamento real. A destilação é uma das mais importantes técnicas de separação de componentes empregada a nível industrial nos mais diversos processos e o seu perfeito funcionamento e otimização são fatores economicamente cruciais. Sua importância dá-se na capacidade de separar os componentes de uma mistura utilizando a diferença de volatilidade entre eles como força motriz. Entretanto, trata-se de uma técnica que representa cerca de 40% da energia consumida em uma planta industrial. Alguns modelos utilizados nesses dispositivos, tais como os modelos baseados em conceitos de estágios de equilíbrio e não-equilíbrio, geralmente fornecem resultados úteis, mas consideram empiricamente muitos fenômenos fluidodinâmicos e assumem uma mistura perfeita em cada fase. Com o avanço da Tecnologia de Informação (TI), dos métodos numéricos e aperfeiçoamento em modelos de fluxos multifásicos, é possível a investigação de problemas complexos de escoamentos turbulentos. Uma das formas de investigar esses problemas é a aplicação das técnicas da Fluidodinâmica Computacional (CFD). Dessa maneira, foi adotado para o presente trabalho um modelo de CFD, tendo como objetivo principal a avaliar os fenômenos de transportes para os escoamentos isotérmico (água-ar) e não isotérmico (etanol-água) através das técnicas de CFD na simulação de um prato perfurado de destilação. Os modelos propostos, possuem em geral, as seguintes características em comum: modelo heterogêneo, tridimensional, modelo de turbulência shear stress transport e abordagem Euleriana-Euleriana a 1 atm. As equações da continuidade e de conservação da quantidade de movimento foram empregadas no modelo isotérmico e para o modelo não isotérmico foram adicionadas as equações de conservações de energia e das espécies químicas. Os domínios computacionais foram baseados no trabalho de Solari e Bell (1986), onde foram observados a influência da presença ou não do downcomer de entrada no prato perfurado. Os resultados para o escoamento isotérmico mostraram os perfis de velocidades de líquido, as frações volumétricas e a altura de líquido claro sob a influência do downcomer de entrada. Para o escoamento não isotérmico, os resultados mostraram, além dos parâmetros hidráulicos, os perfis de temperatura e das frações mássicas de etanol para várias vazões de vapor. Assim, as simulações do sistema isotérmico indicaram uma forte influência do perfil de velocidade de líquido na entrada prato para o domínio com downcomer. No sistema não isotérmico foi possível determinar a eficiência de separação, a qual variou com a vazão de vapor no prato. A metodologia proposta neste trabalho foi adequada para aplicações em internos de coluna de destilação, mostrando-se uma ferramenta viável e importante no desenvolvimento e otimização de pratos perfurados.

Made available in DSpace on 2016-06-02T19:56:47Z (GMT). No. of bitstreams: 1 4497.pdf: 8936250 bytes, checksum: a23101fb063b44abfcf0e8b680623fc7 (MD5) Previous issue date: 2012-03-26 / The development of the design of chemical processes has received increasing improvement, incorporating sophisticated mathematical models, which allowed better simulation of its real behavior. The distillation column is one of the most widely used separation equipment in the industry and therefore, its perfect working and optimization are economically crucial factors. Thus, the study of the hydrodynamic in distillation column sieve trays has increased over the years with the purpose to optimize the flow patterns, which is of great importance on the mass and energy transfer efficient. Due to the development of powerful computers, advances in numerical methods and improvement in models of multiphase flows, the investigation of complex flow problems is possible. One way to investigate these problems is to use Computational Fluid Dynamics. Thus, in this work we used commercial package CFD software to predict the hydrodynamics in a sieve tray, with the main objective to evaluate the velocity fields and compare them with the experimental work of Solari and Bell (1986). We proposed a two-fluid model with Eulerian-Eulerian framework, three-dimensional (3D), steady-state and the standard k-ε turbulence model for air/water system at 1 atm. The continuity and momentum conservation equations were used to describe the gas and liquid phases. The simulated sieve tray geometry was based on experimental work of Solari e Bell (1986). The simulation domain included the downcomer region. New sieve tray geometry design was proposed to evaluate the hydrodynamics. The results show the velocity profiles, volume fractions and liquid recirculation zones on the sieve tray for several combination of liquid and gas flow rates. The simulation indicated the presence of recirculation and stagnation zones, and it reproduced satisfactorily the results of Solari e Bell (1986) and the new geometry design reduced the liquid recirculation zones on tray. The proposed methodology in this work proved to be appropriate and the Computational Fluid Dynamics (CFD) techniques presented to be an important tool in the design and optimization of sieve trays. / O desenvolvimento de projetos de processos químicos tem recebido aperfeiçoamento cada vez maior, incorporando modelos matemáticos mais sofisticados, os quais possibilitam uma maior aproximação do seu comportamento real. A coluna de destilação é um dos equipamentos de separação mais empregados na indústria e por isso, o perfeito funcionamento e otimização são fatores economicamente cruciais. Deste modo, o estudo da hidrodinâmica de pratos perfurados em coluna de destilação vem crescendo ao longo dos anos, no intuito de otimizar os fluxos de escoamento, que tem uma grande importância sobre a eficiência na transferência de massa e energia. Com o desenvolvimento de poderosos computadores, avanços em métodos numéricos e aperfeiçoamento em modelos de fluxos multifásicos, é possível a investigação de problemas complexos de escoamentos. Uma das formas de investigar esses problemas é a utilização da Fluidodinâmica Computacional. Assim, neste trabalho foi utilizado um pacote comercial de CFD para prever a hidrodinâmica em um prato perfurado, tendo como objetivo principal avaliar os campos de velocidades e compará-los com o trabalho experimental de Solari e Bell (1986). Foi proposto um modelo de duas equações com abordagem Euleriana-Euleriana, tridimensional (3-D), estado estacionário e o modelo de turbulência k-ε padrão para um sistema ar/água a 1 atm. As equações da continuidade e de conservação de quantidade de movimento foram empregadas no modelo para descrever a fase líquida e a fase vapor. A geometria do prato perfurado foi baseada no trabalho experimental de Solari e Bell (1986), na qual foi incluída a região do downcomer. Uma nova geometria de prato foi proposta para observar a hidrodinâmica. Os resultados mostram os perfis de velocidades, frações volumétricas e zonas de recirculação de líquido no prato perfurado para várias combinações de vazões de líquido e vapor. A simulação indicou a presença de zonas de recirculação e estagnação. A simulação reproduziu satisfatoriamente os resultados experimentais de Solari e Bell (1986) e a nova geometria reduziu as zonas de recirculação de líquido no prato. A metodologia proposta neste trabalho foi adequada e a técnica da Fluidodinâmica Computacional mostrou-se uma ferramenta viável e importante no desenvolvimento e otimização de pratos perfurados.

A glicerina é um composto de grande utilidade em muitas áreas de aplicação. Atualmente, a maior fonte de glicerina é como subproduto da produção do biodiesel. Em 2010 o Brasil foi o segundo maior produtor de biodiesel no mundo com 2,4 milhões de m3. Estima-se que 10% da produção de biodiesel é glicerina bruta e destes 10%, aproximadamente entre 30% e 60% correspondem à glicerol. As impurezas são formadas por água, sais orgânicos e inorgânicos, ésteres e álcoois, e traços de glicerídeos. Como as aplicações mais nobres da glicerina requerem uma glicerina isenta de impurezas, novas rotas de purificação da glicerina bruta vem sendo estudadas. Neste sentido, o Laboratório de Separações Térmicas e Mecânicas da EPUSP propôs uma nova rota de purificação em 2008, na qual a ultima etapa é a desidratação de uma solução glicerol-água por meio de destilação trifásica usando tolueno como arrastador. O objetivo do presente trabalho foi estudar o comportamento deste tipo de destilação em uma coluna modulada com três pratos perfurados. Nesta coluna avaliou-se o layout de pratos e as melhores condições de operação. Os resultados, obtidos com este estudo, constituem uma contribuição importante para o projeto básico de coluna de destilação trifásica. As séries experimentais foram planejadas sequencialmente empregando-se planejamento estatístico de experimentos (DOE). Como variáveis de processo foram estudadas a vazão de vapor do tolueno (kg/h), vazão de alimentação de glicerina (kg/h) e concentração de glicerol na alimentação (% em massa). Como variáveis geométricas foram estudadas a área livre do prato () e a altura de vertedouro (Hw). O desempenho da coluna foi avaliado mediante o incremento da concentração de glicerol (em relação à concentração de glicerol na alimentação) e a concentração de glicerol no fundo da coluna (estas duas variáveis de resposta são dependentes entre si). A influência das variáveis de processo e geométricas nas respostas estudadas permitiram a construção de modelos estatísticos, e o melhor deles foi comparado com os modelos de não equilíbrio (NEQ) e de equilíbrio (EQ) obtidos por simulação no programa ASPEN PLUS. O modelo de não equilíbrio está baseado nas equações de Maxwell-Stefan, que utiliza a abordagem de Eckert e Vanek (2001) e a correlação de Chen-Chuang (1993), para estimar os coeficientes binários de transporte de massa. O modelo de equilíbrio utiliza as equações MESH (Material balance, Equilibrium, mole fraction Summation, and Heat balance). Conclusivamente, pode-se afirmar que as variáveis operacionais exercem maior influência do que as variáveis geométricas na desidratação da glicerina. As melhores condições foram: a vazão de vapor de tolueno de 23,5 kg/h, vazão de alimentação de glicerina de 2,2 kg/h e concentração de glicerol na alimentação de 50 % glicerol em massa, usando o layout L5 com área livre de 0,04 e altura de vertedouro de 70 mm. Os valores preditos pelo modelo estatístico (obtido com dados experimentais) e pelo modelo de NEQ representaram o comportamento da desidratação da glicerina por destilação trifásica à pressão atmosférica usando tolueno como arrastador, na coluna de pratos perfurados estudada. O modelo de EQ superestimou os valores reais. / Glycerine is a material of outstanding utility with many areas of application. Currently, the largest source of glycerine is as a by-product of biodiesel production. In 2010, Brazil was the second largest biodiesel productor in the world with 2.4 million m3. It is estimated that 10% of biodiesel is raw glycerine, and of this 10%, approximately between 30% and 60% corresponds to glycerol. The impurities are formed by water, organic and inorganic salts, esters and alcohols, and traces of glycerides. Although many attempts have been made to use raw glycerine, it is still necessary to purify it for of the most applications; hence new routes of glycerine purification have been studied. In this way, the Laboratory of Thermal and Mechanical Separations of EPUSP have proposed a new route of purification in 2008, where the last step is the dehydration of glycerol-water solution by three-phase distillation using toluene as entrainer. The aim of the present work was to study the behavior of the three-phase distillation using a modulated column with three sieve trays. In this column, the tray layout and the best operating conditions were evaluated. The results achieved in this study are an important contribution to the basic design of three-phase distillation column. Experimental series were designed sequentially employing a statistical design of experiments (DOE). The process variables studied were the vapor flow rate of toluene (kg/h), feed flow rate of glycerine (kg/h) and the feed glycerol concentration (% wt.). The geometric variables studied were the fractional hole area () and the weir height (Hw). The column performance was evaluated by the increment of glycerol concentration (in relation to the feed glycerol concentration) and the bottom glycerol concentration (these two variables are mutually dependent responses). The influence of process and geometric variables allowed the empirical models building, in which the best model was compared with the non-equilibrium (NEQ) and equilibrium (EQ) models obtained by the simulator ASPEN PLUS. The non-equilibrium model is based on Stefan-Maxwell equations, which uses the approach of Eckert and Vanek\'s (2001) and the Chen-Chuang correlation (1993), to estimate the binary coefficients of mass transport. The equilibrium model is based on the MESH equations (Material balance, Equilibrium, mole fraction Summation, and Heat balance). Finally, it can be stated that the operating variables have more influence than the geometric variables in the glycerine dehydration. The best conditions were: vapor flow rate of toluene of 23.5 kg/h, feed flow rate of glycerine of 2.2 kg/h and feed glycerol concentration of 50% wt., using the fractional hole area of L5 of 0.04 and weir height of 70 mm. The predicted values obtained by the statistical model and by the non-equilibrium model represented the behavior of the glycerine dehydration by three-phase distillation at atmospheric pressure using toluene as entrainer in the sieve tray column studied. The equilibrium model (EQ) overpredicted the real values.

A glicerina é um composto de grande utilidade em muitas áreas de aplicação. Atualmente, a maior fonte de glicerina é como subproduto da produção do biodiesel. Em 2010 o Brasil foi o segundo maior produtor de biodiesel no mundo com 2,4 milhões de m3. Estima-se que 10% da produção de biodiesel é glicerina bruta e destes 10%, aproximadamente entre 30% e 60% correspondem à glicerol. As impurezas são formadas por água, sais orgânicos e inorgânicos, ésteres e álcoois, e traços de glicerídeos. Como as aplicações mais nobres da glicerina requerem uma glicerina isenta de impurezas, novas rotas de purificação da glicerina bruta vem sendo estudadas. Neste sentido, o Laboratório de Separações Térmicas e Mecânicas da EPUSP propôs uma nova rota de purificação em 2008, na qual a ultima etapa é a desidratação de uma solução glicerol-água por meio de destilação trifásica usando tolueno como arrastador. O objetivo do presente trabalho foi estudar o comportamento deste tipo de destilação em uma coluna modulada com três pratos perfurados. Nesta coluna avaliou-se o layout de pratos e as melhores condições de operação. Os resultados, obtidos com este estudo, constituem uma contribuição importante para o projeto básico de coluna de destilação trifásica. As séries experimentais foram planejadas sequencialmente empregando-se planejamento estatístico de experimentos (DOE). Como variáveis de processo foram estudadas a vazão de vapor do tolueno (kg/h), vazão de alimentação de glicerina (kg/h) e concentração de glicerol na alimentação (% em massa). Como variáveis geométricas foram estudadas a área livre do prato () e a altura de vertedouro (Hw). O desempenho da coluna foi avaliado mediante o incremento da concentração de glicerol (em relação à concentração de glicerol na alimentação) e a concentração de glicerol no fundo da coluna (estas duas variáveis de resposta são dependentes entre si). A influência das variáveis de processo e geométricas nas respostas estudadas permitiram a construção de modelos estatísticos, e o melhor deles foi comparado com os modelos de não equilíbrio (NEQ) e de equilíbrio (EQ) obtidos por simulação no programa ASPEN PLUS. O modelo de não equilíbrio está baseado nas equações de Maxwell-Stefan, que utiliza a abordagem de Eckert e Vanek (2001) e a correlação de Chen-Chuang (1993), para estimar os coeficientes binários de transporte de massa. O modelo de equilíbrio utiliza as equações MESH (Material balance, Equilibrium, mole fraction Summation, and Heat balance). Conclusivamente, pode-se afirmar que as variáveis operacionais exercem maior influência do que as variáveis geométricas na desidratação da glicerina. As melhores condições foram: a vazão de vapor de tolueno de 23,5 kg/h, vazão de alimentação de glicerina de 2,2 kg/h e concentração de glicerol na alimentação de 50 % glicerol em massa, usando o layout L5 com área livre de 0,04 e altura de vertedouro de 70 mm. Os valores preditos pelo modelo estatístico (obtido com dados experimentais) e pelo modelo de NEQ representaram o comportamento da desidratação da glicerina por destilação trifásica à pressão atmosférica usando tolueno como arrastador, na coluna de pratos perfurados estudada. O modelo de EQ superestimou os valores reais. / Glycerine is a material of outstanding utility with many areas of application. Currently, the largest source of glycerine is as a by-product of biodiesel production. In 2010, Brazil was the second largest biodiesel productor in the world with 2.4 million m3. It is estimated that 10% of biodiesel is raw glycerine, and of this 10%, approximately between 30% and 60% corresponds to glycerol. The impurities are formed by water, organic and inorganic salts, esters and alcohols, and traces of glycerides. Although many attempts have been made to use raw glycerine, it is still necessary to purify it for of the most applications; hence new routes of glycerine purification have been studied. In this way, the Laboratory of Thermal and Mechanical Separations of EPUSP have proposed a new route of purification in 2008, where the last step is the dehydration of glycerol-water solution by three-phase distillation using toluene as entrainer. The aim of the present work was to study the behavior of the three-phase distillation using a modulated column with three sieve trays. In this column, the tray layout and the best operating conditions were evaluated. The results achieved in this study are an important contribution to the basic design of three-phase distillation column. Experimental series were designed sequentially employing a statistical design of experiments (DOE). The process variables studied were the vapor flow rate of toluene (kg/h), feed flow rate of glycerine (kg/h) and the feed glycerol concentration (% wt.). The geometric variables studied were the fractional hole area () and the weir height (Hw). The column performance was evaluated by the increment of glycerol concentration (in relation to the feed glycerol concentration) and the bottom glycerol concentration (these two variables are mutually dependent responses). The influence of process and geometric variables allowed the empirical models building, in which the best model was compared with the non-equilibrium (NEQ) and equilibrium (EQ) models obtained by the simulator ASPEN PLUS. The non-equilibrium model is based on Stefan-Maxwell equations, which uses the approach of Eckert and Vanek\'s (2001) and the Chen-Chuang correlation (1993), to estimate the binary coefficients of mass transport. The equilibrium model is based on the MESH equations (Material balance, Equilibrium, mole fraction Summation, and Heat balance). Finally, it can be stated that the operating variables have more influence than the geometric variables in the glycerine dehydration. The best conditions were: vapor flow rate of toluene of 23.5 kg/h, feed flow rate of glycerine of 2.2 kg/h and feed glycerol concentration of 50% wt., using the fractional hole area of L5 of 0.04 and weir height of 70 mm. The predicted values obtained by the statistical model and by the non-equilibrium model represented the behavior of the glycerine dehydration by three-phase distillation at atmospheric pressure using toluene as entrainer in the sieve tray column studied. The equilibrium model (EQ) overpredicted the real values.