Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Reexamination Certificate
1999-06-25
2001-08-28
Loney, Donald J. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
C428S184000, C261S105000, C261S112200, C261SDIG007
Reexamination Certificate
active
06280819
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a structured packing having particular application to a method of separating air in which the packing is formed of a plurality of corrugated sheets and a plurality of flat, planar members alternating with and located between the corrugated sheets to inhibit vapor turbulence. More particularly, the present invention relates to such a structured packing in which the corrugated sheets and the flat, planar members have perforations sized to inhibit vapor and liquid flows but to allow for pressure equalization through the packing.
Structured packing has found wide spread use in a variety of distillations including those involved in the separation of air into its component parts. Distillations are conducted within distillation columns filled with mass transfer elements to bring ascending vapor phases into intimate contact with descending liquid phases of mixtures to be separated. As the ascending phase rises and contacts the descending liquid phase, it becomes evermore enriched in the more volatile components of the mixture to be separated. At the same time the descending liquid phase becomes ever more concentrated in the less volatile components of the mixture to be separated. In such fashion, systems of distillation columns can be used to separate various mixture components. For instance, in case of air separation, nitrogen is separated from oxygen is a double distillation column unit. Argon is then separated from oxygen in an argon column that is attached to a lower pressure column of such double distillation column unit.
Structured packings are widely used as mass transfer elements within distillation columns due to their low pressure drop characteristics. Structured packings generally include corrugated sheets of material in which the sheets are placed in a side by side, relationship with the corrugations of adjacent sheets crisscross-crossing one another. In use, the liquid phase of the mixture to be separated is distributed to the top of the packing and spreads out throughout the packing as a descending film. The vapor phase of such mixture rises through the corrugations contacting the liquid film as it descends.
There have been many attempts in the prior art to increase the efficiency of structured packings, that is, to decrease the height of packing equal to a theoretical plate. Obviously, the lower the height, the more efficient the packing. At the same time, structured packing with a low HETP inherently has an increased pressure drop over less efficient packings. One such structured packing is disclosed in U.S. Pat. No. 4,597,916 in which the corrugated sheets are separated from one another by flat, perforated sheets that extend throughout the packing. It is thought by the inventors herein that the flat perforated sheets of this packing increase efficiency both by providing additional interfacial area for vapor-liquid contact and by increasing turbulence in the vapor flow and therefore the degree of mixing between vapor and liquid phases. Transverse mixing is also increased by perforations that are specifically designed to promote liquid and vapor flow in a transverse direction of the packing.
As will be discussed, Applicants have designed a structured packing that unlike the prior art, is optimized not for efficiency, but rather, for smooth vapor flow. Through such optimization, the Inventors herein have found that it is possible to increase the capacity of the packing and therefore, use such packing in a more efficient cost effective manner.
SUMMARY OF THE INVENTION
The present invention provides a structured packing comprising a plurality of corrugated sheets and a plurality of flat, planar members alternating with and located between the sheets to inhibit turbulence in vapor ascending through said structured packing. The plurality of planar members are positioned so that at least lowermost transverse edges of the planar members and the corrugated sheets are situated at least proximal to one another as viewed when the structured packing is in use. Each of the planar members and the corrugated sheets has perforations sized to inhibit liquid and vapor flows but to allow pressure equalization.
Pairs of the planar members can be located between the corrugated sheets and spaced apart from one another so that the uppermost and the lowermost transverse edges of the planar member and the corrugated sheets are aligned. Additionally, the planar members may sized with lengths and widths equal to those of the corrugated sheets.
In any embodiment, each of the perforations can have a diameter in a range of between about 5% and about 40% of a channel width of corrugations of the corrugated sheets as measured between adjacent peaks or troughs of the corrugations. This diameter can be between about 5% and about 20% of the channel width. Preferably the diameter is about 10% of the channel width of corrugations. Furthermore, the perforations can constitute an open area of the planar members in a range of between about 5% and about 20% of a total area of the planar members. Such open area of the planar members can be between about 7% and about 15% of the total area. Preferably, the open area of the planar members is about 10% of the total area.
It has been found by the inventors herein that a structured packing designed in the manner set forth above functions with a slightly higher HETP than structured packings of the prior art. This is surprising considering the fact that the packing with the intermediate planar members has a greater surface area than similar packing not incorporating such planar members. A further unexpected feature is that a packing of the present invention will flood at higher vapor rates. There are various criteria that are used to describe the flooding condition, for instance, excessive pressure drop. In all cases if HETP is plotted against F-Factor (where F-Factor is a product of the superficial vapor velocity and the square root of the vapor density) flooding is evidenced by a rapid rise of the slope of the curve. Such a rise in HETP is indicative of the vapor supporting the descending liquid thereby choking the column and disrupting the separation. This increase in the flooding point allows higher flow rates through the column and therefore for a given volume of packing, greater production. This allows for thinner columns using less packings or columns that can handle a greater throughput. The reason for such operation is that the planar member and opening design of the present invention acts to inhibit turbulence in the vapor flow ascending through the structured packing.
REFERENCES:
patent: 4597916 (1986-07-01), Chen
patent: 5350566 (1994-09-01), Stingaro
patent: 5474832 (1995-12-01), Massey
patent: 0 036 944A (1981-10-01), None
Kooijman Hendrik Adriaan
Krishnamurthy Ramachandran
McKeigue Kevin
Cheung Wan Yee
Loney Donald J.
Pace Salvatore P.
The BOC Group Inc.
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