Distillation Column

Abstract

This distillation column comprises a cross-corrugated packing module formed from strips having corrugations that define channels (14), each channel lying between two main peaks (12; 10) and each channel having two channel legs (16) that are joined together by a top main peak (10; 12). The strip (2) comprises an inverted portion (22) which lies within the cross section of one of the channels (14) and which includes a first intermediate peak (26) oriented in the opposite direction to the top main peak (10; 12). The inverted portion (22) includes a second intermediate peak (28; 30) oriented in the direction of the top main peak (10; 12). Application to air distillation installations.

Description

The present invention relates to a distillation column comprising at least one cross-corrugated packing module comprising a plurality of strips with their channel orientations inverted from one strip to the next, the strip being made of a sheet material and being of the type comprising corrugations that form alternately first main peaks directed along a first direction and second main peaks directed along the opposite direction, the corrugations defining channels, each channel lying between two first or second adjacent main peaks forming edge peaks of the channel, and each channel having two channel legs that are joined together by a top main peak, the channels having a general orientation that is inclined to a general flow direction of the said liquid, the strip furthermore comprising at least one inverted portion which lies entirely within the cross section of one of the channels and which joins together the two channel legs, the inverted portion comprising a first intermediate peak oriented-in the opposite direction to the top main peak of the channel.

The term “packing” is understood to mean a device intended for mixing a phase and/or for bringing several phases flowing co-currently or countercurrently into contact with one another. A heat and/or mass exchange and/or a chemical reaction may in particular take place in the packing. One particular application of the invention lies in the columns separating gas mixtures, especially air distillation columns.

Mentioned in the prior art are air distillation installations comprising cross-corrugated packing modules, which are also called “packs”. The modules comprise corrugated metal sheets placed vertically, the corrugations of which sheets are oblique with respect to a general fluid flow direction in the installation and are inclined alternately, generally crossed at 90°, from one sheet to another.

The packing modules are slipped into the distillation column so that the sheets of one module are angularly offset with respect to the sheets of an adjacent module about the axis of the column, generally by 90° from one module to another.

To improve the exchange between a liquid and a gas, which are flowing through the packing module, it has been proposed in the prior art to have openings that are made in the corrugated metal sheets. These openings lead to a change in the flow of the gas from one side of the metal sheet of the packing to the other and improve exchange with the liquid.

A packing strip of this type is known from document EP-A-1 029 588, the corrugations of which form peaks and valleys joined together by corrugation legs defining channels. This strip includes inverted portions, also called “serrations”, which lie within each channel, each inverted portion forming a single intermediate peak. The inverted portion defines an angle of 90° with each corrugation leg to which it is joined.

When this strip is manufactured by bending a thin flat metal sheet, the material forms tears or pleats. The finished packing strip therefore deviates from its desired geometrical shape, thereby reducing the mass or heat exchange performance of the finished strip.

Document U.S. Pat. No. 4,670,196 also describes a corrugated packing strip provided with inverted portions, which has the same drawbacks.

The object of the present invention is to alleviate the above drawbacks and to propose a packing strip that is easy to manufacture from a thin flat metal sheet and results in substantial heat and/or mass exchange.

For this purpose, the subject of the invention is a column according to claim 1.

According to particular embodiments, the strip of the column according to the invention includes one or more of the following features:

• • the inverted portion comprises a third intermediate peak oriented in the direction of the top main peak, the second and third intermediate peaks lying on either side of the first intermediate peak;
  • seen in cross section taken perpendicular to the orientation of the channel, the inverted portion is joined at a point to each of the channel legs and the developed length of the channel and the developed length of the inverted portion, which are measured between the two points, are approximately identical;
  • the cross section of the inverted portion comprises a first circular arc, which forms the first intermediate peak, and second and third circular arcs, which form the second and third intermediate peaks, and lying between the first circular arc and each of the second and third circular arcs is an intermediate straight section of the inverted portion, which straight section is joined tangentially to the associated circular arcs;
  • the cross section of the channel comprises a main circular arc that forms the top main peak and two main straight sections which join tangentially to the main circular arc;
  • the radius of curvature of the main circular arc is equal to the sum of the radii of curvature of the first, second and third circular arcs and the angle between each of the intermediate straight sections and the associated main straight section is equal to the angle between the main straight sections;
  • the channel has a height which is measured between the top main peak of the channel and a plane lying between the two adjacent main peaks of the channel and the distance between the top main peak and the first intermediate peak is approximately equal to ⅔ times the height; and
  • the strip is made of a bent metal sheet.

The subject of the invention is also a process for manufacturing a strip made of folded metal sheet, of the type comprising corrugations that form alternately first main peaks directed along a first direction and second main peaks directed along the opposite direction, the corrugations defining channels, each channel lying between two first or second adjacent main peaks forming edge peaks of the channel, and each channel having two channel legs that are joined together by a top main peak, the channels having a general orientation that is inclined to a general flow direction of the said liquid, the strip furthermore comprising at least one inverted portion which lies entirely within the cross section of one of the channels and which joins together the two channel legs, the inverted portion comprising a first intermediate peak oriented in the opposite direction to the top main peak of the channel, the inverted portion furthermore including a second intermediate peak oriented in the direction of the top main peak, as defined above, characterized in that the process comprises the following step:

• • (a) a flat metal sheet is bent, thus forming a corrugated metal sheet comprising the channels;
  • (b) at the location of at least one inverted portion of the strip, two slits are cut in the sheet, across a line of top main peaks; and
  • (c) the portion located between the two slits is bent in the inverse manner to the corrugation, thus forming the inverted portion.

A better understanding of the invention will be gained by reading the following description, given solely by way of example and with reference to the appended drawings, in which:

FIG. 1 is a schematic view, in longitudinal section, of a mass and/or heat exchange column according to the invention, comprising cross-corrugated packing modules;

FIG. 2 is a plan view of part of a packing strip of a column according to the invention;

FIG. 3 is a perspective view of part of the strip of FIG. 2; and

FIG. 4 is a sectional view of the strip along the line IV-IV of FIG. 2, on a larger scale.

FIG. 1 shows a mass and/or heat exchange column EC according to the invention, having a vertical general axis X-X. The column EC is for example a cryogenic distillation column, especially an air distillation column.

The column EC comprises, at its upper end UE, a liquid inlet LI emerging in a liquid header LH which distributes the liquid over the cross section of the column EC, and a vapour outlet VO. At its lower end LE, it comprises a vapour inlet VI and a liquid outlet LO. The column EC furthermore includes a cylindrical shell S.

The column EC defines a general fluid flow direction D_f, which runs vertically.

A packaging module PM1, which favours the spreading of the liquid transversely to the X-X axis, is placed in the shell S directly below the header LH. Such a module PM1 is known per se and is for example a packing module comprising a cross-corrugated packing with perforations or striations.

A plurality of packing modules PM2 according to the invention is placed in the shell S beneath the module PM1. A bottom support BS holds the packing modules PM1, PM2 in place.

Each packing module PM2 comprises a multitude of corrugated packing strips 2. The strips 2 have a mid-plane P (see FIG. 4) lying parallel to the general direction D_f. The strips 2 of a module PM2 are placed against one another and in such a way that the planes P lie parallel to one another. The planes P of the packing strips of two adjacent modules PM2 are angularly offset about the X-X axis, preferably by approximately 90°.

FIG. 2 shows part of a packing strip 2.

The strip 2 has two parallel edges, an upper edge 4 and a lower edge 6, which lie perpendicular to the direction D_f.

The strip 2 also has corrugations 8 which form alternately first main peaks 10, directed in one direction (see FIG. 4) relative to the general mid-plane P of the strip 2, and second main peaks 12, directed in the opposite direction relative to the plane P. In this case, the second peaks 12 form valleys.

The corrugations 8 form identical but alternately inverted channels 14, each channel lying between two first 10 or two second 12 main peaks. The channels 14 are open alternately in one of the two aforementioned directions and then in the other. The intermediate main peak 12 or 10 forms the top main peak of the channel 14 in question, whereas the two adjacent peaks 10 or 12 form the channel edge peaks. Two adjacent main peaks 10, 12 are joined together by a channel leg 16 of straight section. The channels 14, and consequently the peaks 10, 12, lie along a channel direction D_c that is inclined at an angle δ to the edges 4,6 (see FIG. 2). The directions D_c of two adjacent strips 2 of a module PM2 are inverted one with respect to the other.

In cross section, taken perpendicular to the direction D_c, as shown in FIG. 4, each channel 14 has a first circular arc 18 of radius of curvature r1, which forms the top main peak 10. A main straight section 20 of the channel leg 16 is joined tangentially to this circular arc 18 on either side of the latter. This straight section 20 has a length d1 measured between the join 24 (see below) and the circular arc 18. The two straight sections 20 make an angle γ between them.

The strip 2 furthermore includes, in each channel 14, a multitude of identical inverted portions 22.

FIG. 4 shows one of these inverted portions 22. The inverted portion 22 lies entirely within the cross section of the channel 14, that is to say that the portion of the strip 2, which lies inside the thickness e of the corrugation legs 16, does not form part of the inverted portion 22. The inverted portion 22 joins the two legs 16 of the channel 14 together and is joined to them at two joins 24. It forms a first intermediate peak 26 directed in the opposite direction to the top peak 10 of the channel, and two intermediate peaks, a second intermediate peak 28 and a third intermediate peak 30, which are oriented in the direction of the top main peak 10 and lie on either side of the intermediate peak 26.

The cross section of the inverted portion 22 comprises three circular arcs 32, 34, 36. The circular arcs 34, 36 have the same radius of curvature r2 and form the second 28 and third 30 intermediate peaks, whereas the circular arc 32 has a radius of curvature r3 (>r2) and forms the first intermediate peak 26. Extending between the circular arc 32 and each of the circular arcs 34, 36 is a straight section 38 of the inverted portion 22, which straight portion is joined tangentially to each of the circular arcs 32, 34, 36. The straight sections 38 have the same length d2.

Advantageously, the circular arcs 34, 36 are joined tangentially to the channel legs 16. As a consequence, there is little stressing of the metal sheet during deformation.

Each of the two straight sections 38 makes an angle a with the adjacent corrugation leg 16.

The developed length of the inverted portion 22 is identical to the developed length of the two main straight sections 20 and of the circular arc 18. Thus, the material is not stretched, or only slightly so, during bending.

Moreover, the channel 14 has a height h which is measured between the top main peak 10 of the channel and a plane Q defined by the two adjacent main peaks 12. The distance d4 between the top main peak 10 and the first intermediate peak 26 is approximately ⅔ of the height h. In other words: $d4=\frac{2}{3}h.$

Thus, the first intermediate peak 26 lies approximately at the location of the barycentre B of the cross section of the channel. It is at this point that there is the highest concentration of mass or the highest temperature of a gas flowing in the channel 14. Consequently, the strip 2 results in substantial heat and/or mass exchange.

In addition, the channel 14 and the inverted portion 22 are symmetrical with respect to a plane of symmetry A, perpendicular to the planes P and Q, the plane of symmetry being defined by the top main peak 10 and the first intermediate peak 26.

In order for the criterion of identical developed lengths to be respected, the following geometrical condition has to be satisfied.

In the case (not shown) in which α=γ:
r1=2r2+r3.

In the case shown in FIG. 3, the angles α and γ are not the same. In this case, the following conditions have to be satisfied: $d1=\frac{K^{\prime }-K\sin \left(\alpha -\frac{\gamma }{2}\right)}{\sin \left(\frac{\gamma }{2}\right)-\sin \left(\alpha -\frac{\gamma }{2}\right)}\mathrm{and}d2=d1-K,\mathrm{where}K=r2\left(\pi -\alpha \right)+r3\left(\frac{\Pi }{2}-\alpha +\frac{\gamma }{2}\right)-r1\left(\frac{\Pi }{2}-\frac{\gamma }{2}\right)\mathrm{and}$ $K^{\prime }=r2\left[\cos \left(\frac{\gamma }{2}\right)+\cos \left(\alpha -\frac{\gamma }{2}\right)\right]+r3\cos \left(\alpha -\frac{\gamma }{2}\right)-r1\cos \left(\frac{\gamma }{2}\right).$

The radii of curvature r1, r2, r3 of the corrugation 8 and of the inverted portion 22 are preferably at least 1 mm and in particular at least 2 mm, thereby making it easier to form the inverted-portion 22 without material rupture.

The strip 2 according to the invention is manufactured according to a process comprising the following steps:

• • (a) a flat metal sheet is firstly bent, thus forming a corrugated sheet that includes the channels 14;
  • (b) two slits are then cut in the sheet at the location of each inverted portion 22;
  • (c) finally, the portions lying between two slits are bent in the opposite manner to the corrugation, thus forming the inverted portions 22.

Owing to the presence of at least one second intermediate peak, the strip 2 is only slightly deformed at the joins 24. There is therefore little likelihood of the strip 2 tearing at these joins. Because the developed length of the corrugation 8 is the same as that of the inverted portion 22 between the joins 24, the finished strip 2 is smooth and has a thickness e which is approximately the same over its entire surface. In addition, a risk of the strip 2 fracturing during bending is low.

As a variant, the slits are cut before the flat sheet is bent, so that step (b) is carried out before step (a).

Also as a variant, steps (b) and (c) are carried out at the same time. Thus, it is unnecessary to synchronize the cutting and bending tools for the inverted portion.

According to a variant (not shown), the intermediate peak 26 is placed close to the barycentre B of the cross section of the channel 14, for example at a distance from this point B of less than 0.20 times the height h of the channel 14. Thus, the intermediate peak 26 remains within a high concentration or high temperature region.

Depending on the embodiments, the packing strip 2 according to the invention also includes the following features:

• • in cross section taken perpendicular to the orientation of the channel 14, the inverted portion 22 is continuous over its entire developed length;
  • the inverted portion 22 joins the channel legs 16 without a sharp edge;
  • the second 34 and third 36 circular arcs are joined to the channel legs 16 tangentially;
  • the channel 14 has a height h which is measured between the top main peak 10, 12 of the channel and a plane Q lying between the two edge main peaks 12, 10 of the channel, the area of the cross section of the channel 14 has a barycentre B, and the first intermediate peak 26 of the inverted portion 22 is located at a distance from the barycentre that is less than 0.20 times the height h;
  • the channel 14 and the inverted portion 22 are symmetrical with respect to a plan of symmetry A defined by the top main peak 10 and by the first intermediate peak 26;
  • the thickness e of the strip 2 is approximately the same over its entire surface.

The invention also relates to a cryogenic distillation installation and in particular to an air distillation installation comprising at least one packing module as defined above.

Claims

1-9. (canceled)

10. A distillation column comprising at least one cross-corrugated packing module comprising a plurality of strips with their channel orientations inverted from one strip to the next, the strip being made of a sheet material and being of the type comprising corrugations that form alternately first main peaks directed along a first direction and second main peaks directed along the opposite direction, the corrugations defining channels, each channel lying between two first or second adjacent main peaks forming edge peaks of the channel, and each channel having two channel legs that are joined together by a top main peak, the channels having a general orientation that is inclined to a general flow direction of the said liquid, the strip furthermore comprising at least one inverted portion which lies entirely within the cross section of one of the channels and which joins together the two channel legs, the inverted portion comprising a first intermediate peak oriented in the opposite direction to the top main peak of the channel, wherein the inverted portion furthermore includes a second intermediate peak oriented in the direction of the top main peak.

11. The column of claim 10, wherein the inverted portion of the strip comprises a third intermediate peak oriented in the direction of the top main peak, the second and third intermediate peaks lying on either side of the first intermediate peak.

12. The column of claim 10, wherein, seen in cross section taken perpendicular to the orientation of the channel, the inverted portion of the strip is joined at a point to each of the channel legs and in that the developed length of the channel and the developed length of the inverted portion, which are measured between the two points, are approximately identical.

13. The column of claim 11, wherein the cross section of the inverted portion of the strip comprises a first circular arc, which forms the first intermediate peak, and second and third circular arcs, which form the second and third intermediate peaks, and in that lying between the first circular arc and each of the second and third circular arcs is an intermediate straight section of the inverted portion, which straight section is joined tangentially to the associated circular arcs.

14. The column of claim 10, wherein the cross section of the channel of the strip comprises a main circular arc that forms the top main peak and two main straight sections which join tangentially to the main circular arc.

15. The column of claim 13, wherein the radius of curvature of the main circular arc is equal to the sum of the radii of curvature of the first, second and third circular arcs and in that the angle between each of the intermediate straight sections and the associated main straight section is equal to the angle between the main straight sections.

16. The column of claim 10, wherein the channel has a height which is measured between the top main peak of the channel and a plane lying between the two adjacent main peaks of the channel and in that the distance between the top main peak and the first intermediate peak is approximately equal to ⅔ times the height.

17. The column of claim 10, wherein the strip is made of a folded metal sheet.

18. A process for manufacturing a strip made of folded metal sheet, of the type comprising corrugations that form alternately first main peaks directed along a first direction and second main peaks directed along the opposite direction, the corrugations defining channels, each channel lying between two first or second adjacent main peaks forming edge peaks of the channel, and each channel having two channel legs that are joined together by a top main peak, the channels having a general orientation that is inclined to a general flow direction of the said liquid, the strip furthermore comprising at least one inverted portion which lies entirely within the cross section of one of the channels and which joins together the two channel legs, the inverted portion comprising a first intermediate peak oriented in the opposite direction to the top main peak of the channel, the inverted portion furthermore including a second intermediate peak oriented in the direction of the top main peak, wherein the process comprises the following steps:

a) a flat metal sheet is bent, thus forming a corrugated metal sheet comprising the channels;

b) at the location of at least one inverted portion of the strip, two slits are cut in the sheet, across a line of top main peaks; and

c) the portion located between the two slits is bent in the inverse manner to the corrugation, thus forming the inverted portion.