Gas and liquid contact apparatus – Contact devices – Wet baffle
Reexamination Certificate
2000-07-25
2002-08-06
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Wet baffle
C261SDIG007
Reexamination Certificate
active
06427985
ABSTRACT:
The invention relates to a structured packing for heat exchange and mass transfer between a liquid and a gas in a column. For heat exchange and mass transfer between liquid and gaseous media, in particular for the separation of mixtures by distillation, plate columns and packed columns are used in industry. The two types differ with respect to the hydrodynamic operating conditions.
In the case of plate columns, in each case a bubbling layer forms on the individual plates where predominantly the liquid is the continuous phase and the gas the disperse phase. Between the individual plates are free spaces in which predominantly the gas is the continuous phase.
The mode of operation of packed columns differs from plate columns with respect to hydrodynamics. In this case it is not the liquid but the gas which forms the continuous phase. The liquid runs as a film downward over the packings.
Structured packings are made up of a multiplicity of individual layers of packing elements, such as metal sheets, expanded metals and wire fabrics, which are disposed vertically to one another in a regular structure and are usually held together in a composite by attachments such as metal wires, thin metal rods or metal sheet strips. Usually the packing elements themselves have a geometric structuring, for example in the form of folds or circular holes of from about 4 to 6 mm in diameter. The openings act to increase the flood limit of the packing and to make a higher column load possible.
Examples are packings of the types “Mellapak”, CY and BX from Sulzer AG, CH-8404 Winterthur, or types A3, BSH or B1 from Montz GmbH, D-40723 Hilden. The folds of the packing elements of these packings run linearly and at an angle of from about 30° to 45° to the longitudinal axis of the packing. The foldings of the packing elements lead to a cross-channel structure within the structured packing.
DE 196 05 286 A1 describes a special development in which this angle is further decreased to values of from 3° to 14° in order to reduce the pressure drop of the packings as far as possible in the case of applications at high vacuum (approximately 1 mbar top pressure).
In the prior art, structured packings are known which are catalytically active. A catalytically active distillation packing in a conventional shaping is, for example, the packing “KATAPAK” from Sulzer AG, CH-8404 Winterthur.
Structured packings are usually provided as individual packing layers which are then arranged in the column stacked one above the other. The packing layers usually have a height of from about 0.17 m to about 0.30 m.
In the prior art, a structured packing called “Montz” A
2
from Montz GmbH, D-40723 Hilden is known, which has folded packing elements with curved fold courses. Within a packing element, the gradient of these fold courses varies over the height of the packing element. In this case the layers of the packing elements alternate so that in each case one packing element in which the gradient of the fold line is greatest at the bottom end of the packing layer alternates with a packing element in which the gradient of the fold line is greatest at the top end of the packing layer. The internal geometry of the packing layer is therefore constant over its height. However, this packing type, in comparison with the usual structured packings, has an unfavorable separation efficiency.
Because of the industrial importance of heat exchange and mass transfer processes in chemistry and process engineering, in particular separation by distillation, a multiplicity of technical developments are aimed at improving heat exchange and mass transfer columns, in particular distillation columns. Important criteria for an efficient economic heat exchange and mass transfer column, in particular distillation column, are its price, its throughput performance for the gas and liquid stream and the separation efficiency based on the height of the column. It is usually characterized as the number of theoretical plates per meter of column height (n
th
/m) or as the height equivalent to a theoretical plate (HETP).
It is an object of the present invention to increase the throughput and economic efficiency of heat exchange and mass transfer columns, in particular for distillation purposes.
We have found that this object is achieved by a structured packing for heat exchange and mass transfer between a liquid and a gas in a column having at least one packing layer with a first, lower end and a second, upper end, the packing layer having an internal geometry which varies over its height so that by suitably setting the liquid and gas flow rates in a first, in particular lower, region of the packing layer a bubbling layer having a predominantly disperse gas phase forms in a targeted manner and simultaneously in a second, in particular upper, region of the packing layer a film flow of the liquid having a predominantly continuous gas phase forms in a targeted manner.
The internal geometry is therefore, in contrast to structured packings of the prior art, not constant over the height of the packing layer.
The hydrodynamic operating states described can be achieved by the resistance to flow varying over the height of the packing layer. Preferably the first, optionally lower, region of the packing layer has a higher resistance to flow than the second, optionally upper, region of the packing layer.
The first region of the packing layer is preferably situated in a lower region of the packing layer and the second region of the packing layer is preferably in an upper region of the packing layer. For the purposes of the present invention, the first, optionally lower, region and the second, optionally upper, region of the packing layer preferably extend over the entire cross-sectional area of the packing layer. The first, lower, region of the packing layer can be bound directly to the lower end of the packing layer and the second, upper region of the packing layer can be bound directly to the upper end of the packing layer. In a preferred embodiment, the first, optionally lower, region of the packing layer is connected directly to the second, optionally upper, region.
In the context of the present invention a structured packing is preferred in which the packing layer has touching flat packing elements, in particular metal sheets, expanded metals, wire fabrics and knitted meshes, having folds of defined courses, the fold courses or tangents to the fold courses being at a larger angle to the longitudinal axis of the packing layer in the first region of the packing layer than in the second region of the packing layer. Particularly preferably, the fold courses or the tangents to the fold courses of the packing elements are at an angle of from about 45° to about 75° to the longitudinal axis of the packing layer in the first region of the packing layer and from about 10° to about 45° in the second region. Very particularly preferably, the fold courses or the tangents to the fold courses are at an angle of from about 60° to about 70° to the longitudinal axis of the packing layer in the first region of the packing layer and from about 30° to about 45° in the second region.
The folds can have, at least in sections, a curved or linear course.
In a preferred embodiment, the folds are curved in a shape of monotonic course, so that the tangents to the fold courses are at an angle of from about 45° to about 75°, preferably from about 60° to about 70°, to the longitudinal axis of the packing layer at the lower end of the packing layer, this angle of the tangents to the fold courses decreasing upwardly to values of from about 10° to about 45°, preferably from about 30° to about 45°, to the longitudinal axis of the packing layer.
The structured packing can also be designed such that the fold courses are linear in sections, the fold courses preferably being at an angle of from about 45° to about 75°, particularly preferably from about 60° to 70° to the longitudinal axis of the packing layer in the first region of the packing layer and the angle of the fold courses to the longitudinal axis of the
Kaibel Gerd
Stammer Achim
Stroezel Manfred
BASF - Aktiengesellschaft
Bushey C. Scott
Keil & Weinkauf
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