Gas and liquid contact apparatus – Contact devices – Wet baffle
Reexamination Certificate
1999-10-28
2001-12-04
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Wet baffle
C261S113000, C261SDIG007
Reexamination Certificate
active
06325360
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a structured packing for producing intimate contact of fluids, for example liquid—liquid, liquid-gas, or gas—gas, particularly in a mass and/or heat exchange apparatus. More particularly, the invention relates to a structured packing assembly for enhancing contact between a first fluid having a predominantly downward direction of flow, and a second fluid, the packing having a plurality of juxtaposed sheets.
BACKGROUND OF THE INVENTION
Structured packings in general have a well-defined geometry of discrete flow channels facilitating theoretical estimation of the performance of the transfer device. Structured packings of various designs have been known in the chemical industry for decades. They are generally known to offer a lower resistance to flow than bulk (random) packing, and lend themselves to easy installation within a mass exchange chamber. Structured packing elements may be constructed of corrugated of fluted plates, such as known e.g., from U.S. Pat. Nos. 4,929,399 to Lockett et al.; 5,407,607 to Mix; 5,188,773 to Chen et al; 5,624,733 to McKeigue et al. and 5,132,056 to Lockett et al.
In most of the prior art solutions, the corrugations, folds or flutings are arranged at an angle to the vertical, or the axis of the column or tower. This has the effect of non-uniform distribution of the liquid flow over the surface of the packing plates.
U.S. Pat. No. 2,042,127 to Sayles describes a structured packing assembly composed of a number of generally vertically disposed, parallel, generally flat sheets arranged in superimposed tiers. The assembly features collectors disposed at the top of a tier for distribution of down-flowing liquid over both sides of the subjacent plates. It is noted that Sayles advocates the sheets being disposed as close as possible to prevent cascading, or free-fall of liquid through the packing.
U.S. Pat. No. 1,561,044 to Alexander proposes a structured packing assembly also composed of a number of parallel flat sheets having projections extending all between adjacent sheets perpendicularly to the sheets and serving as spacers therebetween.
While the parallel-sheet concept of Sayles and Alexander is useful, there is still a need in the mass/energy transfer industry for a simple, low weight (low material cost) and large surface area (high efficiency interphase transfer) structured packing with a relatively low pressure drop. It is also important that vapour and liquid be able to transfer between sheets so that uniform liquid and vapour distribution over the column or tower cross-section be maintained. The uniform distribution of fluids is essential for achieving high efficiency of mass transfer. The ease of assembly and placement in the exchange apparatus (e.g., a tower) as well as the structural quality of the packing are also of importance. Additional desired features of a structured packing are good wetting of the sheet surface by the fluid(s), or minimization of so-called “dry zones” in the assembly, and improved cross-flow between adjacent flow channels.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a packing assembly for enhancing contact of a first fluid and a second fluid passing therethrough, the first fluid usually having a generally downward direction of flow when passing through said assembly, the packing assembly comprising:
a plurality of juxtaposed generally flat sheets disposed generally parallel to each other to form generally flat channels for the flow of the fluids therethrough,
a plurality of projections protruding from said sheets and arranged in said channels,
wherein said projections comprise at least one fluid-spreading projection and a plurality of sheet-spacing projections, the at least one fluid-spreading projection extending angularly from one sheet towards an adjacent sheet preferably without contacting the adjacent sheet. The projections are preferably punched out of the sheets without cut-out losses. The fluid-spreading projection may extend upwardly or downwardly, at an acute angle or an obtuse angle relative to the surface of the respective sheet, and specifically relative to the original position of the projection before punching and bending.
The spacing projections extend between adjacent sheets in a bridging relationship at a generally right angle to the planes of the respective sheets. The general symmetry line of the spacing projections is preferably at an angle to the horizontal to minimize hold-up or entrapment of the first fluid on the spacing projections. The angle to the horizontal can be selected in a broad range, from a few degrees to almost 90°.
Preferably, the contact between the spacing projections and the adjacent sheets is by abutment only. A permanent attachment is feasible but not preferable for ease of construction, especially if multiple spacers are involved.
Since the spacing and spreading projections, called hereinafter also tabs, extend away from the flat, vertical surfaces of the sheets, their down-turned surfaces may not be wetted properly in operation by the downward flowing liquid. Dry zones on those surfaces may result. In order to minimize the occurrence of such dry zones, the packing assembly may comprise means for enhancing contact of at least the first, downward flowing fluid with the down-turned surfaces of the packing assembly that would normally give rise, in operation, to “dry zones” of the assembly. The means may be embodied by a plurality of perforations in the spacing and spreading projections, and/or by a specific design of the projections themselves e.g., by their appropriate bending. Also, perforations (or weep holes) may be provided in at least some of the flat portions of the sheets to provide fluid communication between both sides of the sheets. The perforations may be of a size allowing liquid flow (“weep holes”), while others may be of a size allowing both liquid and gas flow therethrough. The perforations on the projections (tabs) or entire sheets enhance the uniformity of distribution of down-flowing liquid between two sides of a sheet and reduce the occurrence of a dry, non-wetted zone on the downward-facing part of a tab that does not come in direct contact with the down-flowing liquid. Additionally, a perforated assembly is obviously lighter than an analogous non-perforated one. The number of perforations and their size are such as not to compromise substantially the mechanical strength of the sheets and of the assembly.
The perforations should not be equated with slots that remain from the punching of the tabs out of the sheets.
Preferably, the projections are formed as integral part of the sheets and are disposed in a regular arrangement over the surface of said sheets such as to promote uniform distribution of at least one of the fluids passing through the assembly over the surface of the sheet.
REFERENCES:
patent: 1561044 (1925-11-01), Alexander
patent: 2042127 (1936-05-01), Sayles
patent: 4276242 (1981-06-01), Chen et al.
patent: 4296050 (1981-10-01), Meier
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patent: 4842778 (1989-06-01), Chen et al.
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patent: 5057250 (1991-10-01), Chen et al.
patent: 5063000 (1991-11-01), Mix
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patent: 5132056 (1992-07-01), Lockett et al.
patent: 5185106 (1993-02-01), Chen et al.
patent: 5188773 (1993-02-01), Chen et al.
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patent: 5441793 (1995-08-01), Süess
patent: 5458817 (1995-10-01), Lang
patent: 5500160 (1996-03-01), Süess
patent: 5578254 (1996-11-01), Mix
patent: 5624733 (1997-04-01), McKeigue et al.
patent: 5637263 (1997-06-01), Lang et al.
patent: 5644932 (1997-07-01), Dunbobbin et al.
patent: 5653126 (1997-08-01), Harada et al.
patent: 5975503 (1999-11-01), Chuang et al.
patent: 1292424 (1991-11-01), None
patent: 1327306 (1994-03-01), None
patent: 294281 (1981-04-01), None
patent: 29 42 481 A1 (1981-04-01), None
patent:
Chuang Karl Tze-Tang
Lillico Douglas Alexander
Rajan Varagur S. V.
Alberta Research Council Inc.
Bushey C. Scott
Rodman & Rodman
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