Interrelation of packing and mixed phase flow parameters with liquid residence time distribution

Glaser, M. B.; Lichtenstein, Ira

doi:10.1002/aic.690090107

Cited by 8 publications

(2 citation statements)

References 9 publications

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“…However, there have been relatively few data reported for gas-liquid flow, and the great majority of these concern countercurrent air-water flow through Raschig rings. Examples include work by Sater andLevenspiel (1966), Ruszkay (1962), Hoogendoorn and Lips (1965) Data on holdup and axial mixing in cocurrent downflow are scanty and include the work of Glaser and Lichtenstein (1963), Schiesser andLapidus (1961), andReiss (1967).…”

Section: (29)mentioning

confidence: 99%

Two-Phase Cocurrent Downflow in Packed Beds

Hochman¹,

Effron²

1969

Ind. Eng. Chem. Fund.

131

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These calculated CV's were then empirically correlated by the relationship 0.7 m A(CV) = 19.5 [ & I where A(CV) = 51.7 -CV. Figure 5 illustrates the excellent fit of this empirical correlation to the calculated CV values.Equation 29 enables a consistent set of parameters q and m to be chosen to simulate a given amount of breakage, as given by the CV from an experimental CSD. Thus, if the level of breakage, y, were independently determined, Equation 29 would permit the selection of a consistent value of m giving the same effect on the CV as measured experimentally. Such a simple breakage model, calibrated in this way, could be inserted in the complete equations describing CSD-Le., Equation 3 together with a mass balance and appropriate nucleationgrowth rate kinetics.Crystal breakage, classified product removal, and decrease in linear growth rate with crystal size all skew CSD, producing a narrower size range of crystals than would be expected from Equation 1. In practice it might be difficult to distinguish among these three possible factors. The presence of solids classification can be determined by careful sampling of both the crystallizer suspension and discharge, comparing both CSD and total solids content between suspension and discharge samples. Changes in linear growth rate with size can be determined by studying the growth of single crystals in the laboratory or inferred by the absence of the other two factors. Crystal breakage can usually be established from microscopic examination of various screen fractions and from experience with handling the solid phase material-e.g., amount of breakage encountered in screening and/or in standardized crushing tests. Recent work (Austin, 1967) in the area of crushing and grinding indicates that a promising way of independently measuring breakage in a real crystal suspension would be to follow the history of a narrow size range of radioactively tagged crystals. Such direct measurement has obvious advantages over the indirect method of inferring birth and death functions from the over-all affect on CSD, and would allow the formulation of more realistic breakage models. Such refined models, as they become available, can be used to predict CSD using Equation 3, as illustrated in this paper. I t appears to be of interest to extend these CSD calculations, using such experimental or postulated breakage models. An example of the latter case would be the random breakage model, outlined above. AcknowledgmentThe writer thanks H. Wengrow and B. Fairchild for their help and patience in assisting the writer to adapt Program AMOS to this problem. Free computer time was made available through the University of Florida Computing Center. Cocurrent trickle flow was investigated in a 6-inch diameter column packed with 3/~e-inch glass beads usingNz and MeOH. Liquid-and gas-phase residence-time distribution measurements were made, and for comparison with previous work were characterized by an effective axial dispersion coefficient and mean residence time. Radial variations in both liquid ...

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Section: (29)mentioning

confidence: 99%

Two-Phase Cocurrent Downflow in Packed Beds

Hochman¹,

Effron²

1969

Ind. Eng. Chem. Fund.

131

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“…As another example we will briefly consider some data from a 1-foot mixed phase reactor simulation unit. The tracer curves were from the same equipment used in the study of Glaser and Lichtenstein (5). The two runs included one in which the bed was faulted.…”

Section: Analysis Of Data From Faulted Bedmentioning

confidence: 99%

Tracer Tests in Flow Systems

Bischoff¹,

McCracken²

1966

Ind. Eng. Chem.

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The influence of axial dispersion on carbon dioxide absorption tower performance

Brittan

Woodburn

1966

AIChE Journal

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Carbon dioxide was absorbed from mixtures with nitrogen by countercurrent contact with water in an experimental packed tower. Radial and axial gas concentration profiles were determined from measurements made within the packing. Substantial gas phase channeling was observed. Characterizing the gos flow regime by both piston flow and axial diffusion models yielded mass transfer data and computed axial gas concentration profiles. Differences between the mass transfer results for the two models allowed the influence of axial dispersion to be assessed. Comparison of the piston flow and axially dispersed profiles with the experimental profiles enabled conclusions to be drawn regarding the applicability of the axial diffusion model and the accuracy of available dispersion parameter values.The axial diffusion model appears to be a satisfactory representation of the process. The dispersion coefficients used were found to be too high, which emphasizes shortcomings in the transient response experiments yielding dispersion coefficients. The influence of dispersion on the performance was found to be only moderately adverse. The effect increases with increasing liquid rate, decreasing gas rate, and decreasing packing height. It is improbable that the effect is large enough to account for the difference between industrial scale performance and that predicted from available mass transfer correlations.The spread of fluid element residence times prevailing in an absorption tower invalidates the piston flow assumption inherent in existing design techniques. The resulting longitudinal dispersion will, in some measure, have an adverse influence on the performanoe. The magnitude of this effect has not as yet been determined, however. For carbon dioxide absorbers, in particular, it has been speculated that the wide discrepancy between the actual industrial scale performance and that predicted from standard mass transfer correlations (19,28,31) is due to axial dispersion of the gas phase. In two-phase operation of this nature, substantial gas phase mixing will be induced by the countercurrent liquid flow, particularly at the high water rates necessary to achieve satisfactory absorption of relatively insoluble gases such as carbon dioxide. Published gas-side dispersion coefficients for twophase operation are scarce, but those available (11, 12) would indicate the effect of dispersion on the performance to be significant, especially if projected into the range of industrial liquid rates. The values of dispersion coefficients such as these, obtained from transient response experiments, have not been verified by application to steady state systems of practical interest. Consequently, their accuracy is subject to some question, and they cannot be employed to make definitive predictions.The study described in this paper presents data to indicate the degree to which axial dispersion will affect absorption tower performance. By using published dispersion coefficients, the investigation serves also as a test of their accuracy. The evidence upon...

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Interrelation of packing and mixed phase flow parameters with liquid residence time distribution

Abstract: xc = mole fraction of ith compox, = mole fraction of low-boiling n = total pressure, lb./sq. in. abs. p. = critical molar density of mixp'c = pseudocritical molar density pem = critical molar density of pure nent component ture, g.-moles/cc. of mixture, g.-moles/cc. methane, g.-moles/cc.

Cited by 8 publications

References 9 publications

Two-Phase Cocurrent Downflow in Packed Beds

Two-Phase Cocurrent Downflow in Packed Beds

Tracer Tests in Flow Systems

The influence of axial dispersion on carbon dioxide absorption tower performance

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