Perforated Plate Weeping

Zanelli, S.; Bianco, R.

doi:10.1016/0300-9467(73)85043-9

Cited by 13 publications

(16 citation statements)

References 3 publications

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“…The frequency of these oscillations was approximately 1 cycle/s and was dependent on the vapor and liquid flow rate. Similar frequencies have been reported by Zanelli and Del Bianco (1973). Biddulph and Stephens (1974) identified three regimes at increasing gas velocities.…”

Section: Fluid Oscillationsupporting

confidence: 83%

Mass transfer on a single sieve plate column operated with periodic cycling

Duffy

Furzer

1978

AIChE Journal

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A single sieve plate column operated with periodic cycling was mathematically modeled using the assumption of zero weeping rate and plug ,flow of liquid during the liquid drain period. Zero weeping rates could only be obtained by introducing baffles to control fluid oscillations on the plate. Experimental measurements of the ratio of the slopes of the equilibrium and operating lines A, the Murphree plate efficiency B , the fraction of the liquid holdup transferred per cycle T , and the separation factor X on a computer controlled column provided the first reliable confirmation of the improvements in separating ability, predicted by the theory. G. SCOPEThe mathematical modeling of the unsteady state mass transfer processes on a sieve plate column demonstrates that larger mass transfer driving forces are available than with steady state operation. These larger driving forces result in improved rates of mass transfer and superior overall column performance. The magnitude of the improvements can be quantitatively measured by comparing the number of plates required in the unsteady state case with the steady state case. For normal operating flow conditions, the theory predicts that the steady state case will require twice the number of plates. The theoretical advantages of using unsteady state conditions lead to columns containing 50% of the expected number of plates. These major improvements in reducing column height and capital expenditure exceed those available by improved plate contacting efficiency or modifications to the plate geometry.Mass balances satisfying a list of simple assumptions are used to describe the unsteady state processes occurring during the vapor-liquid contacting time. However, to achieve liquid flow through the column, it is necessary to reduce the vapor flow rate to zero for short periods to allow liquid to transfer to the plate below. The movement of liquid in the column during this liquid drain period can be described by the discrete residence time distribution (DRTD). The most desirable DRTD is for ideal plug flow, when all of the liquid holdup on a plate is transferred to the plate below, with no mixing with any other liquid stream. Multiple sieve plate columns have been shown to have a spread about the mean time in the DRTD and in an unmodified form do not satisfy the plug flow assumption required by the theory during the liquid drain period. The spread in the DRTD provides a quantitative measure of departures from plug flow and accounts for the inability of previous experimental results on distillation columns to achieve the separation predicted by the theory.The only column configuration which provides zero spread in the DRTD and satisfies the plug flow assumption is a single sieve plate column. In addition to this advantage, the single sieve plate can be used to obtain the plate efficiency, an unltnown parameter in the theoretical solution. The single sieve plate geometry provides the basic experimental equipment for the testing of the theory of periodic cycling of plate columns. CON...

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Section: Fluid Oscillationsupporting

confidence: 83%

Mass transfer on a single sieve plate column operated with periodic cycling

Duffy

Furzer

1978

AIChE Journal

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“…Qualitative confirmation of the observations of Zanelli and Del Bianco (1973) on variations in hydrostatic head and their effect on weeping was obtained. In addition, it has been observed that full wave oscillations remove the stagnant zones on trays, near the column walls.…”

Section: Vehfp G D 3 P~supporting

confidence: 76%

“…When the underside of the tray was observed under conditions of stable biphase with weeping, the weeping did appear to come from localized groups of holes, in spurts. These localized groups varied around the tray, and appeared to be 10 to 20 cm apart, tending to confirm the observation of Zanelli and Del Bianco (1973). When the gas flow rate was raised, and full-wave oscillation occurred, all the weeping came from the major peaks, at the walls and along the center line of the tray.…”

Section: Some General Observations On Tray Behaviorsupporting

confidence: 70%

“…Foss and Gerster ( 1956), Plank ( 1958), McAllister et al (19S8), andBarker andSelf (1962) all reported the situation where a large peak strikes one wall of the column at the same instant as a trough appears at the opposite wall. This has also been observed by Zanelli and Del Bianco ( 1973). All these earlier studies used trays of fairly small dimension, up to about 0.3m in diameter.…”

Section: Vehfp G D 3 P~supporting

confidence: 64%

“…Recently Zanelli and Del Bianco (1973) have reported a study of perforated plate weeping. A single hole in the perforated plate was studied and drop frequencies noted.…”

Section: Some General Observations On Tray Behaviormentioning

confidence: 99%

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Oscillating behavior on distillation trays‐II

Biddulph

1975

AIChE Journal

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This paper describes an extension of an earlier study on oscillations which can develop on distillation trays. The oscillations take the form of violent lateral movements of the gas/liquid biphase, and they are generally undesirable for good column performance. It has been found that lower density gases need higher velocities to initiate oscillation, and vice versa for higher densities. The predictive method for the onset of oscillations proposed previously appears to remain valid for the range of gas density covered, and for small hole size trays. The presence of oscillations has been shown to increase weeping significantly.

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Experimental study and modeling of weeping rate in rectangular large‐scale valve trays

et al. 2019

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Weeping is an important hydraulic parameter that needs to be considered for valve trays and for calculations in the distillation field. Therefore, the accurate prediction of weep rate is crucial for the optimal design of valve trays. First, the effects of gas and liquid loads and weir height on weep rate, tray pressure drop, and actual bubbling area were studied in a 1.5 m × 0.61 m cold simulator. Second, the weep modes on the valve tray were analyzed in detail. A theoretical model was then derived to calculate weeping. The model showed a clear relationship between the weep rate and the fractional bubbling area. The experimental data showed that the weir height substantially affected the orifice coefficient of the liquid passing through the valve. Finally, the relation between weir height and orifice coefficient was obtained by fitting the experimental data. The agreements were good, and the maximum deviations were approximately 25%.

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Perforated Plate Weeping

Cited by 13 publications

References 3 publications

Mass transfer on a single sieve plate column operated with periodic cycling

Mass transfer on a single sieve plate column operated with periodic cycling

Oscillating behavior on distillation trays‐II

Experimental study and modeling of weeping rate in rectangular large‐scale valve trays

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