MEMBRANE TUBE

Abstract

A membrane tube is provided for the permeative separation of a gas from gas mixtures. The membrane tube has at least two membrane tube sections, each with a porous, gas-permeable, metallic, tubular support substrate, and a membrane which is selectively permeable for the gas to be separated off. The tube also has, applied to the support substrate around the circumference, at least one connecting section which is gastight at least on the surface and by way of which the two adjacent membrane tube sections are joined, and at least one spacer in the region of the connecting section. The spacer projects in the radial direction to above the membrane.

Claims

1-15. (canceled)

16. A membrane tube element for a permeative separation of a gas from a gas mixture, the membrane tube element comprising: a membrane tube section having a porous, gas-permeable, metallic, tubular support substrate, said tubular support substrate having an end face; a membrane that is selective for the gas to be separated off applied around a circumference of said membrane tube substrate; at least two connecting parts that are gastight at least on a surface thereof; said tubular support substrate being joined at each end face thereof to a respective connecting part; and at least one spacer disposed at one of said connecting parts, said at least one spacer projecting in a radial direction to above said membrane.

17. A membrane tube for a permeative separation of a gas from a gas mixture, the membrane tube comprising: at least two membrane tube sections each having a porous, gas-permeable, metallic, tubular support substrate and a membrane that is selectively permeable for the gas to be separated off and that is applied around a circumference of said support substrate; at least one connecting section that is gastight at least on a surface and configured to join two adjacent said membrane tube sections to one another; and at least one spacer disposed in a region of said at least one connecting section and projecting in a radial direction to above said membrane.

18. The membrane tube according to claim 17, wherein said spacer projects radially circumferentially above said connecting section.

19. The membrane tube according to claim 17, wherein said spacer is annular.

20. The membrane tube according to claim 17, wherein said spacer is connected to wais connecting section by a material bond and/or by a positive-locking connection.

21. The membrane tube according to claim 17, wherein said connecting section is joined to said support substrate by a material bond.

22. The membrane tube according to claim 17, wherein said spacer is made of a metallic material.

23. The membrane tube according to claim 17, wherein precisely one spacer is provided per connecting section.

24. The membrane tube according to claim 17, wherein said connecting section is formed of two connecting parts which are each joined to a respective said membrane tube section.

25. The membrane tube according to claim 17, which comprises an intermediate piece having said spacer installed thereon and arranged between said two connecting parts.

26. The membrane tube according to claim 17, wherein said spacer is an element having been formed by buildup welding.

27. The membrane tube according to claim 17, which comprises an end cap disposed to close off said membrane tube, said end cap being gastight at least on a surface thereof and being joined to said support substrate or connecting section.

28. The membrane tube according to claim 16, which comprises an end cap disposed to close off said membrane tube, said end cap being gastight at least on a surface thereof and being joined to said support substrate or connecting section.

29. A membrane tube system, comprising: at least two membrane tubes according to claim 17 disposed parallel to one another; wherein said spacers are each arranged at a height of said connecting section of adjacent membrane tubes.

30. The membrane tube system according to claim 28, wherein at least two spacers of directly adjoining membrane tubes are arranged at the same height.

31. The membrane tube system according to claim 28, wherein said membrane tubes are arranged within an outer tube.

Description

[0030] Further advantages and useful aspects of the invention can be derived from the following description of working examples with reference to the accompanying figures.

[0031] The figures show:

[0032] FIG. 1a: a schematic view of a membrane tube element according to the invention;

[0033] FIG. 1b: an enlarged section of the region denoted by I in FIG. 1 in the transition region between membrane tube section and connecting part in a schematic cross-sectional view;

[0034] FIG. 2: a schematic view of a membrane tube system according to a first embodiment of the invention;

[0035] FIG. 3: a schematic view of a membrane tube system according to a second embodiment of the invention;

[0036] FIG. 4: a schematic view of a membrane tube system according to a third embodiment of the invention;

[0037] FIG. 5a: a schematic view of a membrane tube system according to a fourth embodiment of the invention;

[0038] FIG. 5b: an enlarged section of the region denoted by II in FIG. 5a around the spacer in a cross-sectional view.

[0039] FIG. 1a depicts an example of a membrane tube element for the permeative separation of a gas to be separated off (e.g. H.sub.2) from a gas mixture (e.g. steam-reformed natural gas, containing CH.sub.4, H.sub.2O, CO.sub.2, CO, H.sub.2, etc.), with the region denoted by I in FIG. 1a in the transition region between membrane tube section and connecting part being shown enlarged in FIG. 1b. The membrane tube element 10 has a tubular membrane tube section 11 and a tubular connecting part 14, 14 at each of the end faces. The two connecting parts 14, 14 serve for gastight connection to supply or discharge tubes of the gas separation plant or for joining to a further membrane tube element in order to form, as indicated in the subsequent FIG. 2, a membrane tube made up of a plurality of membrane tube elements connected in series. As shown in FIG. 1b, the membrane tube section 11 is made up of a tubular, porous, gas-permeable, metallic support substrate 12 (e.g. composed of ITM) along the (circular) end face of which the tubular connecting part 14 made of solid metal (e.g. steel) is joined via an adhesive bond, for example a welded join. The support substrate 12 and the connecting parts 14, 14 can also be configured as integral or monolithic component, e.g. composed of a porous, gas-permeable base material, with the outside surface of the connecting parts subsequently having to be made gastight. Gastightness on the surface can, for example, be achieved by application of a coating or a sealing composition or by melting of the surface of the porous base material of the connecting part 14, 14.

[0040] A membrane 13 (e.g. made of Pd) which is selectively permeable to the gas to be separated off and, (apart from the permeability for the gas to be separated off) forms a seal in the region of the support substrate; extends over the entire cylindrical outer surface of the porous support substrate. To suppress interdiffusion effects which occur between the metallic support substrate 12 and the membrane 13 (which is normally likewise metallic in the case of H.sub.2 being separated off) at high operating temperatures, two ceramic, gas-permeable, porous intermediate layers 16, 16 (e.g. made of sintered 8YSZ) are arranged between the support substrate 12 and the membrane 13 and extend over the entire gas-permeable surface of the support substrate. This second intermediate layer 16 extends slightly beyond the first intermediate layer 16 and ends directly on the connecting part 14. The first intermediate layer 16 has a smaller average pore size than the support substrate 12, and the second intermediate layer 16 has an even smaller average pore size compared to the first intermediate layer 16. The second intermediate layer 16 serves to provide a sufficiently smooth substrate for the subsequent membrane 13. This subsequent membrane 13 extends beyond the two intermediate layers 16 and 16 and ends directly on the connecting part 14, which ensures reliable sealing even in the transition region between support substrate 12 and connecting part 14. The sealing between support substrate 12 and connecting part 14 is effected analogously.

[0041] In the case of the present membrane tube element 10, a spacer 15 in the form of a collar is provided on a connecting part 14. In the present example, the connecting part 14 has been produced from a thick-walled tube from which a tube section having the collar 15 was turned.

[0042] Further embodiments of the spacer can be seen in FIG. 2 to FIG. 5. In these figures, sections of a membrane tube system (module) 30 having three membrane tubes 20 are shown in each case. The figures depict only a section, both in respect of the number of membrane tubes in a module (a plurality of membrane tubes, typically up to several hundred membrane tubes, are usually installed parallel to one another as a bundle within an outer tube in a module) and in respect of an individual membrane tube (only that part of a membrane tube where two membrane tube elements abut is depicted). An individual membrane tube consists of a plurality of membrane tube elements which are arranged in series and are connected by a material bond (German: stoffschlssig) at the end faces to the connecting parts. In the embodiments depicted, they are welded together at the end faces by means of a laser; the welded seam is denoted by 17 in the figures. The membrane tubes are mechanically fixed (not shown) at least on one side and can there be connected to connection conduits of the plant (not shown). To delimit the outer process gas space, the individual membrane tubes are usually arranged within an enclosing outer tube (not shown).

[0043] FIGS. 2 to 5 each depict three membrane tube sections which are formed by the juxtaposition of membrane tube elements 10, 10. The two connecting parts 14, 14 of adjacent membrane tube elements 10, 10 form the connecting sections 21. A spacer 15; 15, 15 which projects in the radial direction above the membrane is provided for each connecting section. The connecting sections 21 of adjacent membrane tubes correspond to one another, i.e. are arranged at the same height; in the working examples shown, the spacers are also arranged at the same height. The spacers are dimensioned so that in the case of stresses as normally occur during transport, on start-up or during operation, any mechanical contact between adjacent membrane tubes occurs exclusively via spacers and the membranes of adjacent membrane tubes cannot touch one another. The spacers 15; 15; 15 also act as spacers from the enclosing outer tube.

[0044] In the case of the membrane tubes 20 in FIG. 2 to FIG. 4, the membrane tubes are arranged close together but at a distance from one another with a small gap between the spacers of adjacent membrane tubes in the installed state. This assists the flow of the process gases in the outer region. In the variant depicted in FIG. 5, the spacers are already in mechanical contact in the normal positioning, as a result of which a more compact construction of the module is made possible. The spacers of adjacent membrane tubes are, however, not joined to one another but allow, in particular, axial movements in order to be able to compensate for mechanical stresses caused, for example, by different thermal expansion, as can occur, for example, during start-up of the plant.

[0045] FIG. 2 shows a membrane tube system based on membrane tube elements from the working example in FIG. 1. The connecting section 21 consists of a tubular connecting part 14 which is welded at a connecting part 14 to a collar of the adjoining membrane tube element 10. The spacer can, as in the working example of FIG. 3, be realized by means of an intermediate piece 18 which is welded in between the two connecting parts 14, 14. The intermediate piece is made of a thick-walled tube section from which a sheath having a central collar has been turned. This working example has advantages in the manufacture of the individual membrane tube elements since these then do not have a collar and are therefore easier to manufacture.

[0046] In the working example of FIG. 4, the spacer 15 can be configured as an annular welded seam by the circumferential welded seam by means of which the two connecting parts are joined being made thicker. In this variant, only one welding operation is necessary in order to both join the membrane tube elements and also realize the spacer.

[0047] FIG. 5a shows, in a side view, an embodiment in which the spacer 15 is realized by means of a spacing disk. As shown in the enlarged depiction in FIG. 5b, a connecting part 14 has an outer thread on its periphery into which the other connecting part 14 has been screwed by means of a corresponding peripheral internal thread and a spacing disk 15 threaded in between. The spacing disk is welded on both sides to the connecting parts at the circumferential welded seams 17.

[0048] The production of the membrane tube elements as is used for the above-described membrane tube system but also for the other working examples will be discussed briefly below. A support substrate in the form of a porous tube made of ITM and having an external diameter of 10 mm, a length of 100 mm, a porosity of about 40% and an average pore size of <50 m is welded at both end faces to a tubular connecting part made of solid steel and having the same external diameter by laser welding. To homogenize the welded transitions, the component obtained is heat treated at a temperature of 1200 C. under a hydrogen atmosphere. After smoothing of the surface by means of sandblasting, an 8YSZ powder having a d80 of about 2 m is, to produce the first intermediate layer, prepared in a suspension suitable for a wet-chemical coating process, for example with addition of dispersant, solvent (e.g. BCA [2-(2-butoxyethoxy)ethyl] acetate, obtainable from Merck KGaA Darmstadt) and binder. The connecting parts are subsequently covered up to the welded seam and the first intermediate layer is applied by dipcoating to the beginning of the welded seam. After drying, the covering is removed from the gastight surface of the connecting parts and the component obtained is subsequently sintered at a temperature of 1300 C. under a hydrogen atmosphere, as a result of which the organic constituents are burnt out, sintering of the ceramic layer takes place and the porous, sintered ceramic first intermediate layer 16 is obtained. The production of the second intermediate layer 16 is carried out analogously, with a finer 8YSZ powder being used and a somewhat lower viscosity of the suspension than in the case of the first intermediate layer being set. The second intermediate layer is likewise applied by dip coating. The second intermediate layer completely covers the first intermediate layer and ends directly on the connecting parts. The component obtained is sintered at a temperature of 1200 C. under a hydrogen atmosphere, as a result of which the organic constituents are burnt out, sintering of the ceramic layer takes place and the porous, sintered, ceramic second intermediate layer is obtained. A Pd membrane is subsequently applied by means of a sputtering process. It completely covers the second intermediate layer and also the first intermediate layer underneath. Finally, a further Pd coating is applied on top of the sputtered Pd layer by means of an electrochemical process in order to seal the sputtered layer and achieve the required gastightness.

[0049] The present invention is not restricted to the embodiments depicted in the figures. The structure described is suitable not only for separating off H.sub.2 but also for separating off other gases (e.g. CO.sub.2, O.sub.2, etc.). Furthermore, it is possible to use alternative membranes such as microporous, ceramic membranes (Al.sub.2O.sub.3, ZrO.sub.2, SiO.sub.2, TiO.sub.2, zeolites, etc.) or dense, proton-conducting ceramics (SrCeO.sub.3-, BaCeO.sub.3-, etc.). Furthermore, a spacer can be provided within a membrane tube system at the height of neighboring connecting sections of a plurality of membrane tubes only at each second connecting section, so that the spacers in each case ensure the distance to the neighboring connecting section (and not to a neighboring spacer). Based on the axial direction of a membrane tube, it is also possible, for example, a spacer to be provided only at each second or third connecting section.