EP1727617A1

EP1727617A1 - Corrugated criss-crossing packing structure

Info

Publication number: EP1727617A1
Application number: EP05739589A
Authority: EP
Inventors: Jean-Yves Thonnelier
Original assignee: Air Liquide SA; LAir Liquide SA a Directoire et Conseil de Surveillance pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2004-03-16
Filing date: 2005-03-10
Publication date: 2006-12-06
Also published as: CN1929909B; FR2867697B1; CN1929909A; WO2005092491A1; FR2867697A1; US20080036102A1; JP2007529306A; US8210505B2

Abstract

The invention relates to a corrugated criss-crossing packing structure for installations that transfer material and/or heat between a gas phase and a liquid phase, comprising a first surface (10), called the primary surface, having a number of parallel channels (11). According to the invention, this structure has a second surface (20), called the secondary surface, comprised of a number of secondary packing elements (21, 31), each secondary packing element being placed inside a channel (11) of said primary surface (10) and being formed separately from the first surface. The invention is for use in cryogenic distillation.

Description

The present invention relates to a corrugated-cross packing structure. In particular, it relates to a cross-corrugated packing structure for material and / or heat transfer installations between a gas phase and a liquid phase, and more particularly distillation such as cryogenic distillation. The invention finds a particularly advantageous application in the field of cryogenic distillation, in particular for separating gases from the air or also for separating mixtures containing hydrogen and carbon monoxide. In this type of application, the cross-corrugated packing structure is the benchmark for organized packing. It consists of a set of modules or "packs" each of which is formed by a stack of surfaces, or bands, waved obliquely alternately in one direction and in the other. The undulations of each surface, also called waves, are formed by parallel channels made from smooth or textured sheets, generally metallic, perforated or not. By way of example, a surface for cross-corrugated lining can be economically produced from a sheet of aluminum of standard quality by simple mechanical operations such as bending and perforation. In the case of distillation columns, the corrugated surfaces are contained in general vertical planes. The modules are most often rotated 90 ° around the axis of the column from one module to the next. The wavy-cross structure has imposed itself to date as the only one allowing the construction of columns of any size without deterioration of the intrinsic efficiency observed in small size. By varying the height of the undulations, we can adjust the density of the structure, expressed in m ² / m ³ . In doing so, we observe an evolution in the opposite direction of two properties whose optimization is however also sought, namely capacity and efficiency. Indeed, a dense structure with a high value in terms of m ² / m ³ will give a high-efficiency packing but which, by clogging easily, will offer a low capacity. Conversely, a sparse structure will allow the circulation of heavy loads, but with less efficiency. By playing on the density, we can define various types of packing structures that best adapt to the different cases considered, for example: - structures with high performance in efficiency are reserved for small columns, where the diameter is not the main parameter, - conversely, for very large devices, and if one wishes to obtain a maximum flow in a diameter imposed by construction and / or transport constraints, priority is given to the capacity, even if it means agreeing to an increase in height. In order to reduce the congestion effect limiting the capacity of the classically used corrugated-cross packing structures, WO 97/16247 proposes as corrugations for the surfaces of the S-shaped channels whose generatrices are curved at each end to become vertical at upper and lower edges of the module. This particular shape, which straightens the channels vertically at the interfaces between the packs, has made it possible to optimize the “efficiency-capacity” curve in the sense that, for the same structure in terms of general shape of the channels and density, the waterlogging limits have been pushed back by around 30%, without the efficiency being substantially affected. However, although it has marked considerable progress in the field of cross-corrugated linings, this latter S-shaped channel structure nevertheless retains the intrinsic limits, namely that by increasing the density of the channels, for to seek better efficiency, the spatial mesh is densified, and the capacity is reduced, and, conversely, by spacing the spatial mesh, the capacity is increased but by correlatively reducing the interfacial area and therefore the efficiency of gas-liquid exchanges. Also, the technical problem to be solved by the object of the present invention is to provide a cross-corrugated packing structure for cryogenic distillation plants, comprising a first surface, called primary surface, having a plurality of parallel channels, which would allow decisively pushing the limits inherent in currently known structures, including that described in WO 97/16247. The solution to the technical problem posed consists, according to the present invention, in that the secondary elements are formed separately from the first surface. The secondary elements can be removable. The design of this type of structure with two surfaces, and not with a single surface as in the structures of the state of the art, results from the merit of the applicant who has been able to realize that the limits of the known wavy-crossed linings are due to the fact that the single surface, said to be main in the context of the present invention, simultaneously performs two functions, on the one hand, on a "macroscopic" scale, the spatial organization in an infinity of crossed channels allowing exchanges between channels taking place face, and, on the other hand, on a "microscopic" scale, the exchanges of matter between gas phase and liquid phase. On the contrary, the invention dissociates these two functions which are then separated into a primary corrugated-cross structure with a large mesh, necessary and sufficient to ensure the flow rate and the homogeneity of the flows, in particular in large columns, and a secondary structure, attached to the interior of the primary structure, specifically improving gas-liquid exchanges, without seeking an effect of spatial organization. More precisely, knowing that the density of a cross-corrugated lining varies in 1 / h if h is the height of the channels, the invention allows, for a target density which would be obtained with a height h for a conventional structure at a single surface, to achieve the same final density but with a distribution of the surface between the primary surface, wavy-cross, and the secondary surface housed in the channels of the primary surface. We can thus imagine a primary surface of wavy structure with a height of 2 hours, thus providing half of the total surface targeted, and a secondary surface providing the other half, or more generally, as provided by the invention, a distribution between (1 -x) of primary surface and x of secondary surface (0 <x <1). The description which follows with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be implemented. Figure 1 is a perspective view of a first embodiment of a cross-corrugated packing structure according to the invention Figure 2 is a side view of the structure of Figure 1. Figure 3a is a perspective view of a secondary lining element of the structure of FIG. 1. FIG. 3b is a perspective view of a variant of the lining element of FIG. 3a. Figure 4 is a sectional view of a variant of the structure of Figure 1 including fixing tabs. Figure 5 is a perspective view of a second embodiment of cross-corrugated lining structure according to the invention. Figure 6 is a side view of the structure of Figure 5. Figure 7a is a top view of a secondary packing element of the structure of Figure 5. Figure 7b a perspective view of the element secondary lining of Figure 7a. Figure 8 is a side view of a variant of the structure of Figure 5 including fixing tabs. In Figure 1 is shown in perspective a portion of corrugated-crossover packing structure intended to equip cryogenic distillation installations, in particular for separating gas mixtures. This structure comprises a first surface 10, or primary surface, having undulations formed, in the example of FIG. 1, by parallel channels 11 whose section has the shape of an equilateral triangle as shown in FIG. 2. The structure of FIG. 1 also includes a second surface 20, or secondary surface, made up of a plurality of secondary packing elements 21, each secondary element 21 being disposed inside a channel 11 of the primary surface 10 As can be seen in FIG. 3a, and in the variant of FIG. 3b, the secondary packing element 21 has a periodic structure along the channel 11 of the primary surface 10. In general, the secondary elements 21 of Figures 3a and 3b can be made from flat metal strips, or fire it bacon, by cutting, perforating, and / or folding separate from the first surface. More specifically, in the exemplary embodiments of FIGS. 3a and 3b, the secondary elements 21 are obtained from a strip of height 2r sectioned at regular intervals over half of its height, leaving a heel 211, 211 '. The sectioned parts are alternately folded right and left equilaterally to form the wings 212 ′, 212 ″. In the case of FIG. 3b, the heel 211 ′ carries equidistant perforations 213. The secondary elements 21 thus obtained are housed inside the channel 11 according to the arrangement shown in FIG. 2. In this embodiment, the elementary mesh of the structure is formed by the two sides of the equilateral triangle forming the channel 11. Taking into account that each face of the channel participates in two channels, the section per channel 11 of primary surface is proportional to π 3, r being the radius of the circle circumscribed to the equilateral triangle of FIG. 2. On the other hand, the section of the secondary element 21 is proportional The distribution of section between primary surface 10 and secondary surface 20 is therefore made in a ratio of (1 -x) to x with x close to 0.5, here x = 0.464. In the variant of f igure 3b, the ratio (1-x) / x is lower, but remains of the order of 1. According to the embodiment of FIG. 5, the primary corrugated primary surface 10 is identical to that of FIG. 1 with an equilateral triangular elementary channel 11. On the other hand, the elementary element 31 of the secondary surface 30 of the lining structure is cut from a strip according to the plane of FIG. 7a, then folded to form corrugations in accordance with FIG. 7b which will be housed in the channel 11 The section of the secondary surface 20 is here less than in the previous case. We also introduce a more significant restriction of the section offered to the gas (in the first example, the secondary surfaces are strictly parallel to the flow of the gas), we thereby introduce a exchange element between channels, the gas deflected by the inclined surface forming an obstacle being redirected towards the opposite channel. As shown in Figures 4 and 8, the secondary elements 21 and 31 'can be snapped into the channel 11 by means of tabs 40, 40' arranged on the secondary elements 21, 31 'and inserted in openings 41 formed through the walls of the channel 11. Of course, there are very numerous variants to the basic shapes which have just been described with reference to the appended drawings, either by varying the folding steps and the angles, or even by adding to the secondary structure additional folds forming deflector flaps. Another family of solutions consists in placing twisted strips forming secondary elements with a worm structure. Whatever their shape, the secondary surfaces are therefore individual elements to be housed in each channel. The S-shape of the new linings as described in international application No. WO 97/1624 constitutes a happy closure of the channels at their ends: once the lining module is constructed, the secondary surface elements will be trapped in the channels, even if they are not physically attached to it. Once the secondary elements have been placed in the channels of a packing strip, one strip out of two must be turned over to mount it crossed with the previous one. The strip to be turned over may be temporarily covered by a flat face, the whole turned over on the other corrugated strip, and the flat face then removed by sliding.

Claims

1. Corrugated-cross packing structure for material and / or heat transfer installations between a gas phase and a liquid phase, comprising a first surface (10), called primary surface, having a plurality of parallel channels (11), said structure comprising a second surface (20), called secondary surface, consisting of a plurality of secondary packing elements (21; 31), each secondary packing element being arranged inside a channel (11) of said primary surface (10) characterized in that the secondary elements are formed separately from the first surface.

2. A packing structure according to claim 1, characterized in that. said secondary packing elements (21; 31) have a periodic structure along the channels (11) of the primary surface (10).

3. A lining structure according to claim 2, characterized in that said secondary elements (21; 31) of lining are made from flat metal strips.

4. lining structure according to claim 3, characterized in that said flat metal strips are cut and / or perforated and / or folded.

5. A lining structure according to claim 4, characterized in that said metal strips are folded alternately to the left and to the right in the shape of a Y.

6. Upholstery structure according to claim 5, characterized in the heel of the Y-shape carries periodic perforations (213).

7. lining structure according to claim 4, characterized in that said flat metal strips are cut and folded so as to form corrugations.

8. A lining structure according to claim 3, characterized in that said flat metal strips are twisted.

9. A packing structure according to any one of claims 1 to 8, characterized in that said secondary packing elements (21, 31 ') carry tabs (40, 40') for snap fastening in the channels (11) of the primary surface.

10. A packing structure according to any one of claims 1 to 9, characterized in that the channels of the primary surface have an S shape.

11. Lining structure according to any one of claims 1 to 10, characterized by a section distribution (1-x) / x between primary surface and secondary surface with x close to 0.5.