CROSS-CORRUGATED PACKING MADE FROM METAL FOAM

Abstract

Disclosed is a packing made up of a stack of plates, having been shaped to form corrugations in the plate and assembled to form a cross-corrugated packing block for a mass and/or heat transfer application, wherein the material of the packing plates is an open-pore metal foam, and in that the specific surface area of the packing is greater than 500 m2/m3 and in that the thickness (e) of the plate is less than 2 mm before the shaping operation.

Claims

1-13. (canceled)

14. A packing made from a stack of leaves having been shaped to form corrugations in the leaf and assembled to form a pack of packing for a mass and/or heat transfer application, the material of the packing leaves being a metal foam, wherein the leaves are assembled to form a cross-corrugated pack of packing, the material of the packing leaves is an open-pore metal foam, in that the specific surface area of the packing is greater than 500 m.sup.2/m.sup.3, and in that the thickness of the leaf is less than 2 mm before the shaping operation.

15. The packing as claimed in claim 14, wherein the specific surface area of the packing is greater than 700 m.sup.2/m.sup.3.

16. The packing as claimed in claim 14, wherein the thickness of the leaf before it enters the press is less than 0.6 mm before the bending operation.

17. The packing as claimed in claim 14, wherein that the metal foam material consists predominantly of nickel.

18. The packing as claimed in claim 14, wherein the metal foam material consists predominantly of copper.

19. The packing as claimed in claim 14, wherein the metal foam material consists of an alloy of FeCrAl type.

20. The packing as claimed in claim 14, wherein the metal foam material consists of an alloy of NiCrFeAl type.

21. The packing as claimed in claim 14, wherein the metal foam material has a pore density of between 10 and 130 ppi.

22. The packing as claimed in claim 14, wherein the metal foam material has a pore density of between 30 and 80 ppi.

23. A process for separating the air gases by cryogenic distillation in an air separation unit, the process comprising the steps of: operating a first column at a first pressure thermally connected to a second column operating at a second pressure lower than the first pressure and an optional third column connected to the second column by a pipe conveying argon-enriched gas, wherein at least one of the second column and the third column contain the packing as claimed in claim 14 sending a flow of air that is to be separated to the first column, sending an oxygen-enriched fluid and a nitrogen-enriched fluid from the first column to the second column, withdrawing a second nitrogen-enriched fluid from the second column, withdrawing a second oxygen-enriched fluid from the second column, wherein a length travelled by a liquid produced by air separation progressing by capillary action through the foam during the residence time for which the liquid resides in the packing body being greater than ten times the pitch (b) of the corrugation of the leaf.

24. The process as claimed in claim 23, wherein the metal foam packing is used in a gas-liquid material exchange column section, where the liquid reflux is less than 20 m.sup.3/h/m.sup.2.

25. The process as claimed in claim 24, wherein the metal foam packing is used in a gas-liquid material exchange column section, wherein the liquid reflux is less than 10 m.sup.3/h/m.sup.2.

26. The process as claimed in claim 23, wherein the length travelled by the liquid produced by air separation progressing by capillary action through the foam during the residence time for which the liquid resides in the packing body is greater than 15 times the pitch (b) of the corrugation of the leaf.

27. The process as claimed in claim 26, wherein the length travelled by the liquid produced by air separation progressing by capillary action through the foam during the residence time for which the liquid resides in the packing body is greater than 20 times the pitch (b) of the corrugation of the leaf.

28. The process as claimed in claim 23, further comprising the third column, and further comprising the step of sending an argon-enriched fluid from the second column to the third column.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

[0058] FIG. 1 schematically indicates the typical geometry of cross-corrugated packings.

[0059] FIG. 2 indicates the various geometric parameters of a corrugation of a cross-corrugated packing.

[0060] FIG. 3 depicts the material structure of a woven metal and of a metal foam.

[0061] FIG. 4 depicts the invention described below through an example of use in a process for separating air gases using distillation. This is depicted using a simplified diagram in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

[0062] FIG. 1 illustrates part of a packing module made up of a stack of corrugated leaves 1, 2 oriented in such a way that the corrugations are crossed from one leaf to the next. Each leaf is identical and the stack is constructed by turning round one leaf in two. The corrugations illustrated in FIG. 2 have a pitch b, a height h, a thickness e, a corrugation-side developed length s and a bend angle β between two sides of a corrugation.

[0063] According to the prior art, the leaves are made of perforated aluminum or of gauze (FIG. 3A). According to the present invention, the leaves are made of metal foam (FIG. 3B) with open pores. The specific surface area is greater than 500 m.sup.2/m.sup.3, preferably greater than 700 m.sup.2/m.sup.3.

[0064] The thickness e of the leaf before entering the press is less than 2 mm, preferably less than 0.6 mm before entering the press to form the bent leaf.

[0065] The metal foam material may consist predominantly of nickel or predominantly of copper.

[0066] The metal foam material may consist of an alloy of FeCrAl type or of an alloy of NiCrFeAl type.

[0067] The metal foam material has a pore density of between 10 and 130 ppi, preferably between 30 and 80 ppi.

[0068] One industrial application of this packing is the separation of air gases using cryogenic distillation. The process is indicated schematically in FIG. 4. A flow of air enters the main exchanger at a pressure close to 6 bar. It has been purified beforehand to remove the water and carbon dioxide that it contained in the atmosphere.

[0069] It is cooled by flowing in the counter-flow direction with respect to the products leaving the cryogenic distillation stage. A more or less complex system of compressors and turbines provides top-up cooling. This compensates for the loss of frigories caused by the temperature offset at the cold end of the exchanger, the inputs of heat and the possible production of liquid. The latter is not indicated in the diagram.

[0070] The cooled air at its dew point then enters a medium-pressure first distillation column 3 where rectification takes place producing, at the top of the column, a medium-pressure flow of gaseous nitrogen. At the bottom, an oxygen-enriched liquid is extracted to be distilled in a second column 4 at a low pressure, which is to say a pressure close to atmospheric pressure.

[0071] In this stripping second column 4, the liquid is further enriched with oxygen to achieve a commercial purity in the bottom. From this second column 4 there may be extracted a flow of a mixture of oxygen and of argon which is then distilled in two or three successive columns in order to obtain argon with a commercial purity. These columns are not indicated in the diagram.

[0072] In order to obtain a reflux of liquid in the medium-pressure column 3, the nitrogen is condensed in a heat exchanger. Similarly, in order to obtain an upflow of gas in the low-pressure column 4, the oxygen is vaporized, likewise in a heat exchanger. In practice, it is the one same heat exchanger which on one side condenses the liquid nitrogen and on the other vaporizes the liquid oxygen. It is in order for this to be thermodynamically possible that the first column 3 is at a medium pressure where the nitrogen liquefaction temperature is slightly above the boiling point of oxygen at atmospheric pressure.

[0073] In order to increase the nitrogen extraction rate, a reflux of liquid nitrogen from the top of the medium-pressure column 3 is sometimes added to the low-pressure column 4 in order to produce a little more nitrogen at the top. One or two liquid reflux connections are also generally added at an intermediate height in order to optimize the profiles of the flow rates in the columns and increase the overall efficiency of the process.

[0074] The hydraulic conditions of the low-pressure column 4 entail relatively low liquid reflux values, typically of below 25 m.sup.3/h/m.sup.2 at the bottom and up to less than 10 m.sup.3/h/m.sup.2 at the top. The packings used are relatively dense, having a specific surface area that may exceed 500 m.sup.2/m.sup.3.

[0075] Under such conditions and without major modification to the packing production system, it is possible to replace material that generally takes the form of perforated aluminum sheets with corrugated leaves made of metal foam. At the bottom of the low-pressure column 4, the value obtained for the length I.sub.cap travelled, by a liquid, by capillary action is 135 mm, namely 15 times the value of the pitch b of the corrugation. Experimental testing has demonstrated that, for no change in processing capacity, the reduction in height of the packed sections, namely the height of a leaf 1, 2, may exceed 15%.

[0076] The argon columns also have low liquid reflux, of the order of 15 m.sup.3/h/m.sup.2, and in general, very dense packings, notably of a specific surface area in excess of 700 m.sup.2/m.sup.3. In the same way as for the low-pressure column, it is possible to use a packing made of metal foam. The value obtained for I.sub.cap is 126 mm, namely 20 times the value at the base b of the corrugation. With these high densities, the height reduction may exceed 25% without impairing the processing capacity.

[0077] The volume savings expected through use of the present invention are even greater when the packing has a greater density. The spreading effect promoted by the metal foam is all the more significant when the surface area to be irrigated is great.

[0078] Liquid oxygen has a surface tension of less than 13.2 mN/m, liquid argon less than 12.6 mN/m and liquid nitrogen than 8.9 mN/m at atmospheric pressure. The tension decreases with pressure: at 5 bar, the surface tension values for the same liquids are 8.7, 8.1 and 5.3 mN/m.

[0079] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0080] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0081] “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.

[0082] “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0083] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0084] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0085] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

TABLE-US-00001 TABLE 1 Key Symbol Unit Description a.sub.p m.sup.2/m.sup.3 Specific surface area b m Pitch, base of a corrugation e m Sheet thickness g m/s.sup.2 Acceleration due to gravity h m Corrugation height h.sub.pack m Height of a pack of packing l.sub.cap m Length travelled by capillary action r.sub.pore m Mean pore radius s m Corrugation- side developed length t.sub.resL s Liquid residence time U.sub.Le m/s Effective liquid velocity U.sub.Ls m/s or Surface m.sup.3/h/m.sup.2 liquid velocity α.sub.L ° Angle of greatest slope of packing wrt horizontal β ° Corrugation bend angle δ m Nusselt film thickness ε Level of voids in packing μ.sub.L Pa .Math. s Liquid viscosity ρ.sub.L kg/m.sup.3 Specific mass (density) of liquid σ.sub.L N/m Liquid surface tension τ Level of perforation of the sheet