Dissertations / Theses on the topic 'Sieve trays'

An investigation has been made based on the measurements of the concentration profiles found from dynamic experiments to study axial and transverse mixing on sieve trays operating under froth, mixed and spray regimes. Two methods of tracer injection were employed, the line and point source tracer injection, and the experiments were carried out over a wide range of gas and liquid flow rates. Air and water were used as system fluids. Two different configurations of columns were used in the dispersion work in order to study the effect of the experimental configuration upon dispersion characteristics. The experimental results were analysed as appropriate for each configuration, the first by a one-dimensional axial plug flow model and the second by a two-dimensional axial and transverse plug flow model. An automatic method of optimization was employed to estimate the values of the longitudinal and transverse dispersion coefficients, and interstitial liquid velocities for each experiment. The variation in the liquid velocities were found to be quite considerable in the mixing studies. In the determination of the clear liquid height a new method was used to calculate the height of clear liquid in terms of the first moment of the dynamic response curve. The data were compared with those measured from manometric method.

Studies into gas-liquid flow patterns were carried out on commercial scale sieve trays where the ratio of froth depth to flow path length is typical of that found in practice. Experiments were conducted on a 2.44 m diameter air-water distillation simulator, in which flow patterns were investigated by direct observation, using directional flow pointers; by water cooling, to simulate mass transfer; and by height of clear liquid measurements across the tray. The flow rates used are typical of those found in practice. The approach adopted was to investigate the effect of the gas flow on the liquid flow by comparing water only flow patterns across an unperforated tray with air-water flow patterns on perforated trays. Initial gas-liquid contacting experiments on the 6.35 mm hole tray showed that, under certain conditions, the gas flow pattern beneath the test tray can have a significant effect on the tray liquid flow pattern such that gas-driven liquid circulation was produced. This was found to be a function of this particular air-water simulator design, and as far as is known this is the first time that this phenomenon has been observed. Consequently non-uniform gas flow effects were removed by modification of the gas distribution system. By eliminating gas circulation effects, the effect of the gas flow on the separation of liquid flow was similar to that obtained on the 1.0 mm hole tray (Hine, 1990). That is, flow separation occurred at the ends of the inlet downcomer which produced large circulating zones along the tray segments both on the non-perforated and perforated trays. The air when forced through the liquid, inhibited circulating flow such that it only occurred at high water inlet velocities. With the 6.35 mm hole tray, the growth and velocity of circulating flow was reduced at high superficial air velocities, and in the experiments to simulate distillation, liquid was in forward flow over most of the tray.

The thesis describes experimental work on the possibility of using deflection baffles in conventional distillation trays as flow straightening devices, with the view of enhancing tray efficiency. The mode of operation is based on deflecting part of the liquid momentum from the centre of the tray to the segment regions in order to drive stagnating liquid at the edges forward. The first part of the work was a detailed investigation into the two-phase flow patterns produced on a conventional sieve tray having 1 mm hole size perforations. The data provide a check on some earlier work and extend the range of the existing databank, particularly to conditions more typical of industrial operation. A critical survey of data collected on trays with different hole sizes (Hine, 1990; Chambers, 1993; Fenwick, 1996; this work) showed that the hole diameter has a significant influence on the flow regime, the size of the stagnant regions and the hydraulic and mass transfer performance. Five modified tray topologies were created with different configurations of baffles and tested extensively in the 2.44 m diameter air-water pilot distillation simulator for their efficacy in achieving uniform flow across the tray and for their impact on tray loading capacity and mass transfer efficiency. Special attention was given to the calibration of the over 100 temperature probes used in measuring the water temperature across the tray on which the heat and mass transfer analogy is based. In addition to normal tray capacity experiments, higher weir load experiments were conducted using a 'half-tray' mode in order to extend the range of data to conditions more typical of industrial operation. The modified trays show superior flow characteristics compared to the conventional tray in terms of the ability to replenish the zones of exceptionally low temperatures and high residence times at the edges of the tray, to lower the bulk liquid gradient and to achieve a more uniform flow across the tray. These superior flow abilities, however, tend to diminish with increasing weir load because of the increasing tendency for the liquid to jump over the barriers instead of flowing over them. The modified tray topologies showed no tendency to cause undue limitation to tray loading capacity. Although the improvement in the efficiency of a single tray over that of the conventional tray was moderate and in some cases marginal, the multiplier effect in a multiple tray column situation would be significant (Porter et al., 1972). These results are in good agreement with an associated CFD studies (Fischer, 1999) carried out by partners in the Advanced Studies in Distillation consortium. It is concluded that deflection baffles can be used in a conventional distillation sieve tray to achieve better liquid flow distribution and obtain enhanced mass transfer efficiency, without undermining the tray loading capacity. Unlike any other controlled-flow tray whose mechanical complexity impose stringent manufacturing and installation tolerances, the baffled-tray models are simple to design, manufacture and install and thus provide an economic method of retrofitting badly performing sieve trays both in terms of downtime and fabrication.

Compared to packings trays are more cost effective column internals because they create a large interfacial area for mass transfer by the interaction of the vapour on the liquid. The tray supports a mass of froth or spray which on most trays (including the most widely used sieve trays) is not in any way controlled. The two important results of the gas/liquid interaction are the tray efficiency and the tray throughput or capacity. After many years of practical experience, both may be predicted by empirical correlations, despite the lack of understanding. It is known that the tray efficiency is in part determined by the liquid flow pattern and the throughput by the liquid froth height which in turn depends on the liquid hold-up and vapour velocity. This thesis describes experimental work on sieve trays in an air-water simulator, 2.44 m in diameter. The liquid flow pattern, for flow rates similar to those used in commercial scale distillation, was observed experimentally by direct observation; by water-cooling, to simulate mass transfer; use of potassium permanganate dye to observe areas of longer residence time; and by height of clear liquid measurements across the tray and in the downcomer using manometers. This work presents experiments designed to evaluate flow control devices proposed to improve the gas liquid interaction and hence improve the tray efficiency and throughput. These are (a) the use of intermediate weirs to redirect liquid to the sides of the tray so as to remove slow moving/stagnant liquid and (b) the use of vapour-directing slots designed to use the vapour to cause liquid to be directed towards the outlet weir thus reducing the liquid hold-up at a given rate i.e. increased throughput. This method also has the advantage of removing slow moving/stagnant liquid.

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Universidade Federal de Sao Carlos
Distillation is one of the most important and used separation techniques of components at industrial level, applied in a wide range of processes. 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. Nowadays, with the necessity of rethink the energetic use owing to the massive usage of natural resources, new regulations of pollutant emissions, environmental issues and market competition; the enhancement of the distillation process has become essential to the refineries, petrochemicals and a variety of other sectors of the industry. Empirical studies about the flow dynamics in distillation columns are rare due to the large dimensions of this equipment and the high investment, including measurement instrumentation. This lack of experimental data makes difficult the appropriate understanding of the mechanisms that occur in this equipment, as flow patterns and degree of separation, as well as the relation between both. Nevertheless, to improve the distillation process performance is necessary to deeply know the dynamics of the multiphase flow existing on each tray of the column, where the contact between the phases indeed happens. In this study, was proposed the computational simulation of sieve trays of distillation columns using CFD s tools (Computational Fluid Dynamics). The main aim was to conceive a model capable to predict the hydrodynamics and the more volatile component transfer between the liquid and the vapor. Furthermore, the regions that possibly interfere on obtaining higher efficiencies were pointed out. For that, tridimensional, transient and multiphase models with the Euler- Euler framework were used. The main results show liquid velocity profiles, volumetric fraction, clear liquid height, mass fraction and efficiency. The results presented agreement with the literature. In general, the fluid dynamics results obtained here highlight the significance of the application of models that represent the complex behavior existing on sieve trays, since this crucially influence in the separation degree of the process. The CFD evidenced to be and valuable tool to study this sort of flow on columns internals and can be applied in the design and optimization of those equipment.
A destilação é uma das mais importantes técnicas de separação de componentes empregada a nível industrial nos mais diversos processos. Sua suma importância dá-se na capacidade de purificar 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. Atualmente, com a necessidade de se repensar o uso energético, com as novas políticas de emissão de poluentes, da preocupação com o ambiente e a concorrência de mercado; o aperfeiçoamento do processo de destilação tem se tornado essencial para as refinarias, petroquímicas e diversos setores da indústria. Estudos empíricos sobre o escoamento em colunas de destilação são raros, em parte devido às grandes dimensões destes aparelhos e ao alto investimento em equipamentos e instrumentos de medição. Esta carência de dados experimentais dificulta o entendimento adequado dos mecanismos que ocorrem neste equipamento, como os padrões de escoamento e o grau de separação, assim como a relação entre estes dois. Contudo, para que se possa melhorar o processo destilatório, é necessário conhecer a fundo a dinâmica do escoamento multifásico existente em cada prato da coluna, onde de fato ocorre o contato íntimo entre as fases. Neste estudo, foi proposta a simulação computacional de pratos perfurados de colunas de destilação usando ferramentas de CFD (Computational Fluid Dynamics). O principal objetivo foi conceber um modelo capaz de prever a hidrodinâmica do prato e a transferência do componente mais volátil entre o líquido e o vapor. Além do mais, foram apontadas as regiões no prato que possivelmente interferem na obtenção de maiores eficiências de estágio. Para isso, foram usados modelos 3D, transientes e multifásicos com abordagem Euler-Euler. Os principais resultados mostram os perfis de velocidade, fração volumétrica, altura de líquido claro, fração mássica e eficiência, os quais apresentaram concordância quando comparados com a literatura. Em geral, os resultados fluidodinâmicos obtidos neste estudo ressaltam a importância da aplicação de modelos que representem o complexo comportamento encontrado em pratos perfurados, já que estes influenciam decisivamente no grau de separação do processo. CFD demonstrou ser uma ferramenta valiosa para estudar o fluxo em internos de torres de destilação e pode ser aplicado para projeto e otimização destes equipamentos.

The distillation point efficiencies for the alcohol-water binary, ternary and quaternary systems were measured using a modified Oldershaw column. This column is expanded above the tray to separate the newly formed bubbles from the column wall, thus eliminating the surface tension induced wall effects for positive systems and discouraging wetted wall effects. The excessive and recirculating foam and froth found in the conventional Oldershaw column is due to these wall effects and does not represent conditions in large scale distillation. The point efficiencies measured using this column for the system methanol/water were lower than the point efficiencies deduced from the composition profiles across a large and narrow rectangular distillation column using an eddy diffusion model. The narrow rectangular column had a liquid flow path length of about one meter, thus avoiding stagnant zones and flow non-uniformities. The lower efficiencies were due to the shorter contact time between the gas and the liquid. This contact time was increased markedly by fitting an outlet weir to the modified Oldershaw column, thus increasing the tray liquid hold-up and the point efficiencies. These point efficiencies were about 10 per cent lower than those on the large tray at a similar value of the F. Factor. The eddy diffusion model predicted rectangular tray efficiencies about 10 to 20 per cent lower than those measured, when using the improved modified column point efficiencies. Using a suitable model, the improved point efficiencies were scaled-up to the conditions existing on the rectangular tray. This resulted in the large tray values of 2 to 4 per cent lower tray efficiencies than those measured. The surface tension effect on the point efficiencies of the binary systems MeOH/n.PrOH using the original modified Oldershaw column in the absence of wall effects using the concept of the Marangoni stabilising index. The surface tension of these systems were measured using a glass thermometer. The system MeOH/H20 had the highest Marangoni index and showed the highest point efficiencies throughout the composition range, with the EtOH/H2O/n.PrOH, with low values of the Marangoni index, showed comparable point efficiencies throughout the composition range. These systems demonstrate all the possible types of surface tension behaviour. The effects of the outlet weir height and hole size on the point efficiencies in the rectangular column operating under similar hydrodynamic conditions were also investigated using the system MeOH/H2O. There was an increase in point and tray efficiencies on increasing the outlet weir height from 2 mm to 12.7 mm. There was also small increase in point and tray efficiencies on decreasing the hole size from 6.4 mm to 1 mm at the expense of higher pressure drops. The point efficiencies of these trays under different hydraulic conditions were in the range 85 to 95 per cent, with subsequent high tray efficiencies. This provides further evidence of the high tray efficiencies available to the design engineer if the detrimental effects of stagnant zones and flow non-uniformities were eliminated. Two highly non-ideal ternary systems and quaternary system were also studied using the original modified Oldershaw and the rectangular columns. Considerable differences between the individual component point efficiencies were observed. These differences are probably caused by the interactive nature of the mass transfer in these systems. These systems also exhibited equal component point efficiencies in parts of the composition range, which illustrates the composition dependency of these systems. The individual component tray efficiencies for these systems were noticeably different, even with equal component point efficiencies operating across the tray. These differences were simulated using the eddy diffusion model, highlighting the effects of limited liquid back mixing on the tray. The composition profile for the system MeOH/EtOH/H20 were predicted and compared with the measurements across the rectangular column using three methods derived from the original Maxwell and Stephan mass transfer equations. These predictions were in good agreement with the measurements. However, as the comparison is only based on a one meter flow path length, the actual design of distillation column using these methods would be conservative. The prediction of the composition profiles using the point efficiencies from the original version of the modified 0ldershaw column yielded a similar observation for both the ternaries and the quaternary system. An expanded aluminium tray (Expamet 607A) was also subject to preliminary efficiency tests in the rectangular column. This material has corrugated angled holes, thus encouraging the liquid flow across the tray by using the vapour momentum. This material showed much lower pressure drops, due to its high open area compared with conventional sieve trays, and discourages weeping and entrainment.

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.

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 (PhD)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Distillation column design and operation require understanding of both the hydrodynamic and thermodynamic behaviour and limitations. One of the hydrodynamic aspects that negatively influence separation efficiency in the distillation column is entrainment of the liquid with the rising vapour or gas. Inaccurate entrainment predictions will lead to poor separation efficiencies in the column and consequently over design of the column diameter and/or height has to be incorporated. This has a significant impact on the capital cost due to the size and scale of industrial columns. Therefore, small improvements in entrainment prediction will lead to large savings in capital investment. Previous research published in the open literature focused primarily on the influence of gas and liquid flow rates and, tray geometry on entrainment for the air/water system. Consequently the non-air/water database is small and consists of data obtained from various tray and column geometries. As a result the accuracy of current entrainment prediction models is questionable for systems other than air/water. Therefore, the first objective of this work was to investigate whether current prediction models perform well for systems other than air/water. To prove this air/water, air/ethylene glycol and air/silicon oil data were measured and compared with current prediction correlations. It was found that current prediction models perform poorly for the air/ethylene glycol and air/silicone oil systems. At the same time a new observation was made with regard to froth development and behaviour inside the column. The observation shows that liquid flow rate has a nonmonotonic influence on entrainment, caused by the short (475mm) tray flow path. The second objective was to examine the influence of gas physical properties on entrainment. New entrainment data were measured by individually contacting air, CO2 and SF6 with water and ethylene glycol, while n-butanol was contacted with CO2 and SF6. The data was compared with current prediction models which performed poorly for SF6 results. This shows the inability of these models to predict entrainment for gas systems with high densities. Modified Reynolds and Froude numbers were developed to show the influence of gas physical properties on entrainment. Low modified Reynolds numbers and large modified Froude numbers resulted in high entrainment. The third objective was to determine the influence of liquid physical properties on entrainment. New entrainment data were measured using CO2 with Isopar G, n-butanol, water, silicone oil and ethylene glycol. Current prediction models compared poorly to the data and did not include the influence of liquid viscosity on entrainment. It was found that viscosity had an intricate non-monotonic influence on entrainment. The fourth and final objective was to correlate the influence of gas and liquid properties on entrainment as determined by the previous two objectives. To make the dataset more complete, entrainment was measured for four tray spacings using CO2/Isopar, CO2/nbutanol, air/ethylene glycol, CO2/ethylene glycol, air/silicone oil and CO2/silicone oil (over 1700 data points). Two new correlations are presented to predict the fraction of liquid entraining with the rising gas (L’/G with R2 = 85%) and the fraction of liquid entering the tray that entrains (L’/L with R2 = 92%). The performance of the L’/G correlation (R2 = 85%) is vastly superior to two other prominent correlations (R2 = 61% and 23%). This correlation can be implemented to predict entrainment successfully for different tray geometries by combining the predicted influence of tray geometry, by Kister and Haas (1988), with results from the newly developed correlation. All four objectives are presented as manuscripts for journal publication and serve as alone standing documents.
AFRIKAANSE OPSOMMING: Distillasie kolom ontwerp en bedryf vereis begrip van beide die hidrodinamiese en termodinamiese gedrag en beperkings. Een van die hidrodinamiese aspekte wat skeiding doeltreffendheid negatief beïnvloed in die distillasie kolom is meesleuring van die vloeistof met die stygende dampe of gas. Onakkurate meesleuring voorspellings sal lei tot swak skeiding doeltreffendheid in die kolom en gevolglik word die ontwerp van die kolom deursnee en / of hoogte beinvloed. Dit het 'n beduidende impak op die kapitale koste as gevolg van die grootte en skaal van industriële kolomme. Klein verbeterings in meesleuring voorspelling sal dus lei tot groot besparings in kapitaal belegging. Vorige navorsing gepubliseer in die oop literatuur het hoofsaaklik gefokus op die invloed van gas- en vloeistof vloeitempos en plaat geometrie op meesleuring vir die lug/water sisteem. Gevolglik is die nie-lug/water databasis klein en bestaan van die data wat verkry is uit verskeie plaat en kolom-geometrieë. As gevolg is die akkuraatheid van die huidige meesleuring voorspelling modelle vir stelsels anders as lug/water te betwyfel. Daarom is die eerste doel van hierdie werk om ondersoek in te stel of die huidige voorspelling modelle goed presteer vir stelsels anders as lug/water. Om dit te bewys was lug/water, lug/etileenglikol en lug/silikon olie data gemeet en vergelyk met die huidige voorspelling korrelasies. Daar is bevind dat die huidige voorspellings modelle swak presteer vir die lug/etileenglikol en lug/silikon olie. Op dieselfde tyd was 'n nuwe waarneming gemaak met betrekking tot dispersie ontwikkeling en gedrag binne die kolom. Die waarneming toon dat vloeistof vloeitempo 'n nie-monotoniese invloed op meesleuring het, veroorsaak deur die kort (475mm) plaat vloei pad lengte. Die tweede doelwit was om die invloed van gas fisiese eienskappe op meesleuring te ondersoek. Nuwe meesleuring data was gemeet deur individuele kontak van lug, CO2 en SF6 met water en etileenglikol, terwyl n-butanol slegs met CO2 en SF6 inkontak gebring was. Die eksperimentele resultate word vergelyk met die huidige voorspellings modelle wat swak presteer invergelyking met SF6 resultate. Dit toon die onvermoë van hierdie modelle om meesleuring vir gas stelsels met hoë digthede te voorspel. Gemodifiseerde Reynolds en Froude getalle was ontwikkel om die invloed van gas fisiese eienskappe op meesleuring aan te toon. Lae gemodifiseerde Reynolds getalle en groot gemodifiseerde Froude getalle lei na hoë meesleuring. Die derde doelwit was om die invloed van vloeistof fisiese eienskappe op meesleuring te bepaal. Nuwe meesleuring data is gemeet deur gebruik te maak van CO2 met Isopar G, nbutanol, water, silikon olie en etileenglikol. Huidige voorspellings modelle vergelyk swak met die data en sluit nie die invloed van vloeistof viskositeit op meesleuring in nie. Daar is gevind dat viskositeit 'n ingewikkelde nie-monotoniese invloed op meesleuring het. Die vierde en finale doelwit was om die invloed van die gas en vloeistof eienskappe op meesleuring soos bepaal deur die vorige twee doelwitte te korreleer. Om die datastel meer volledig te maak, is meesleuring vir vier plaat spasiërings met CO2/Isopar, CO2/n-butanol, lug/etileenglikol, CO2/ethylene glycol, lug/silikon olie en CO2/silikon olie (meer as 1700 data punte gemeet). Twee nuwe korrelasies word aangebied om die fraksie vloeistof wat meegesleur word met die stygende gas (L’/G met R2 = 85%) en die fraksie vloeistof wat die plaat binnetree wat meegesleur word (L’/L met R2 = 92%) te voorspel. Die prestasie van die L’/G korrelasie (R2 = 85%) is aansienlik beter as twee ander prominente korrelasies (R2 = 61% en 23%). Hierdie korrelasie kan suksesvol geïmplementeer word om meesleuring vir verskillende plaat geometrieë te voorspel deur die voorspelde invloed van plaat geometrie deur Kister en Haas (1988), met die resultate van die nuut ontwikkelde korrelasie te kombineer. Al vier doelwitte word as manuskripte vir joernaal publikasie aangebied en dien as alleenstaande dokumente.

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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.

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.

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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.

碩士
東海大學
化學系
91
The catalytic reaction between trans, trans, cis- 1, 5, 9- cyclododecatriene and hydrogen gas has been studied using nickel containing mesoporous molecular sieve MCM-41. The catalysts of Ni/Si-MCM-41 and Ni/Al-MCM-41 were characterized with various techniques of XRD, TEM, gas sorption analyzer, NH3-TPD, H2-TPR, solid state NMR, CO-chemisorption and FT-IR to obtain the catalyst properties, viz. the structure, the surface area, the acidity, the reducibility and the metal dispersion. Increasing the SiO2/Al2O3 mol ratio enhances the structural order and the surface area but diminishes the acid amount. An increase of nickel content in Ni/Si-MCM-41 enlarges the acid amount, the adsorbed CO and the peak area of H2-TPR except the largest amount of nickel (15%) probably due to the packing of nickel metal. With Ni (15%)/MCM-41 catalysts, the textures of nickel packing were obtained from the results of TEM and TPR. Based on FT-IR measurements, the catalysts were found to contain Lewis acid sites. The catalytic reaction was performed at 10 bar and 50~80℃ in a stirred batch reactor. The system is free of diffusional limitation at a stirring speed larger than 800 rpm and the better catalytic activity is attained by using polar solvent. The conversion of reactant increases with the catalyst weight, the reaction temperature and the nickel content. Decreasing the SiO2/Al2O3 mol ratio of Ni(15%)/Al-MCM-41enhances the catalytic activity, implying the positive effect of catalyst Lewis acidity. After reactions the Ni/MCM-41 catalysts show a decrease of BET surface area, structural order, acid amount and area of high temperature peak in TPR. Accordingly, the regenerated catalysts exhibit lower activities.

碩士
東海大學
化學系
91
(1)Theoretical calculation using density functional B3LYP correlation- exchange is employed to study the structure of different sizes of the VAPO-5 clusters. The results indicate that the substitution of either the phosphorus site or aluminum site of the AFI framework by vanadium is in general not feasible. The isolates vanadium was found to exist as a mono-oxo(V4+=O)(Of)4 species for reduced, dehydrated VAPO-5 and as di-oxo V5+O4 species for calcined, dehydrated VAPO-5. (2)The topological analyses of the internal rotation of three different series of monorotor molecules are investigated in this paper. The bifurcation descriptions indicate that the types of catastrophe and topological regions are related to the generic form of potential energy function , and the critical points. When the double-barrier energy functions are represented as the third-order generic polynomial of the reduced reaction corrdinate, the process is isomorphic to the elementary fold catastrophe. Similarly, when the triple-barrier energy functions are represented as the fourth-order generic polynomial of the reduced reaction coordinate, the process is isomorphic to the elementary cusp catastrophe.