Distillation efficiencies on a large sieve plate with small‐diameter holes

Biddulph, Michael W.; Dribika, M. M.

doi:10.1002/aic.690320817

Cited by 12 publications

(26 citation statements)

References 21 publications

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“…Improvement of the theoretical models to allow for such effects (Porter et al, 1972;Lockett et al, 1973;Lockett and Safekourdi, 1976;Lim et al, 1974) has achieved reasonable success. On the other hand improvement in the hydraulic behavior of large circular trays to avoid such effects could also lead to significantly higher tray efficiencies, as demonstrated by Biddulph and Dribika (1986). However the first part of the problem, the prediction of point efficiency, has received less attention.…”

Section: Introductionmentioning

confidence: 93%

“…32, No. 11 (Kreis and Raab, 1979;Biddulph and Dribika, 1986). Chan and Fair (1982), improving on the AIChE method, developed a correlation for the volumetric vapor-phase mass transfer coefficient in terms of vapor diffusivity, liquid holdup, and fractional approach to flooding.…”

Section: Introductionmentioning

confidence: 99%

“…In the present work the large rectangular tray, previously described and used in the study of MeOH-H,O system by Biddulph and Dribika (1986), had a small width and long flow path to avoid flow nonuniformities and stagnant zones. In addition the two columns had trays with similar hole size and percent free area.The results presented in this work indicate that the laboratory Oldershaw column having one sieve tray and external downcomers can be used to obtain an approximation of the point efficiencies on a similar large tray, and can be used in conjunction with an eddy diffusion model (Biddulph, 1975b(Biddulph, , 1977Biddulph and Dribika, 1986) to relate these point efficiencies to the tray efficiencies. This would result in a conservative design provided that allowance is made for other factors, such as nonuniform flow patterns or stagnant regions, or that they are eliminated.…”

mentioning

confidence: 95%

“…The results presented in this work indicate that the laboratory Oldershaw column having one sieve tray and external downcomers can be used to obtain an approximation of the point efficiencies on a similar large tray, and can be used in conjunction with an eddy diffusion model (Biddulph, 1975b(Biddulph, , 1977Biddulph and Dribika,…”

mentioning

confidence: 97%

“…This is in agreement with the results of Fair et al (1983), who studied the scale-up of plate efficiencies from a laboratory Oldershaw column with internal downcomers containing various trays, where the point efficiencies of large industrial conventional trays were deduced using an eddy diffusion model, and did not allow for the existence of liquid flow nonuniformities and stagnant zones. In the present work the large rectangular tray, previously described and used in the study of MeOH-H,O system by Biddulph and Dribika (1986), had a small width and long flow path to avoid flow nonuniformities and stagnant zones. In addition the two columns had trays with similar hole size and percent free area.…”

mentioning

confidence: 99%

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Scaling‐up distillation efficiencies

Dribika

Biddulph

1986

AIChE Journal

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This paper describes a study of the possibility of using point efficiencies, measured in a small laboratory column, in the scale-up of distillation efficiencies. The conditions on a large rectangular tray were closely duplicated in a small glass Oldershaw column with one sieve tray having similar hole size and percent free area. Point efficiencies on the large rectangular sieve tray were deduced from the composition profiles and compared with the point efficiencies measured in the small column. A simple relationship between the two columns was found in terms of the froth heights and liquid holdups. The results demonstrate that the slightly lower point efficiencies measured in the Oldershaw column could be used in conjunction with a mathematical mass transfer model based on the eddy diffusion concept, to relate the point efficiencies to the tray efficiences, resulting in a conservative design provided either that allowance is made for other factors, such as nonuniform flow patterns and stagnant zones, or that these are eliminated. A wide range of composition was covered using the two systems MeOH-nPrOH and EtOH-nPrOH operating in the froth region. M. M. Dribika, M. W. BiddulphUniversity of Nottingham Department of Chemical Engineering University Park, Nottingham, England SCOPEThe prediction of the performance of a large-scale distillation tray column is difficult, particularly if a new system is being processed. It is a problem that has attracted a considerable amount of attention over many years. However, the prediction of tray efficiency is still a very uncertain part of the design unless operating data from a similar size column distilling a similar system are available. The problem is that both mass transfer characteristics and tray hydraulic considerations are involved, and so the tray efficiency is a function of system and tray size. This paper is concerned with the mass transfer part of the problem. It describes a study of the relationship betwen point efficiencies, measured in a small glass Oldershaw Column, and the efficiencies inferred at points along a rectangular tray with a liquid flow path length of about 1 m. The tray used is a sieve type with small hole sizes typical of those used in the cryogenic distillation of air. The hole sizes and percent free area in the two trays being compared are similar. CONCLUSIONS AND SIGNIFICANCEThe relationship between point efficiencies measured in a small laboratory column and the point efficiencies that actually exist on a large rectangular tray were studied using two systems, MeOH-nPrOH and EtOH-nPrOH, and covering a wide range of composition. The composition profiles across the tray were measured and used to infer the values of point efficiencies using a mathematical mass transfer model based on the eddy diffusion concept.Similar conditions to those on the large rectangular 1864November 1986 sieve tray were used in a small Oldershaw column with one sieve tray and external downcomers. The results indicate that the point efficiencies obtained on the large rectangu...

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Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 95%

mentioning

confidence: 97%

mentioning

confidence: 99%

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Scaling‐up distillation efficiencies

Dribika

Biddulph

1986

AIChE Journal

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Limitations of the equilibrium theory of countercurrent devices

1987

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In the analysis of countercurrent adsorption processes, an equilibrium theory in which local equilibrium between the fluid and the adsorbent phases is assumed has been used in the past to determine the composition of the pinch state that would be obtained for long columns. It is shown that this equilibrium theory is deficient and that certain mass transfer parameters, which are lost in the procedure by which the model equations for the equilibrium theory are formulated, can have a profound effect on the composition of the pinch.

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Multicomponent efficiencies in two types of distillation column

1988

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A study of the efficiencies of two plate distillation columns is reported. One column had three rectangular trays with a flow path length of about 1 m, the other was a modified glass Oldershaw column with one tray of 38 mm dia. Tray efficiencies were measured in both columns and point efficiencies were deduced for the rectangular column.The systems studied were ternary and quaternary mixtures of alcohols and water. The results showed that for thermodynamically nonideal systems significant differences existed among the individual component point efficiencies. In the case of an ideal system the component point efficiencies were effectively equal, but tray efficiencies were different due to differing volatilities and composition profiles across the large trays.This study illustrates the need to allow for the above effects in largecolumn designs for multicomponent systems. The possibility of using laboratory-scale point efficiencies in these designs is explored.

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Distillation efficiencies on a large sieve plate with small‐diameter holes

Cited by 12 publications

References 21 publications

Scaling‐up distillation efficiencies

Scaling‐up distillation efficiencies

Limitations of the equilibrium theory of countercurrent devices

Multicomponent efficiencies in two types of distillation column

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