Reactor for carrying out heterogeneously catalysed gas phase reactions, and use of the reactor

Abstract

The invention relates to a reactor for carrying out heterogeneously catalyzed gas-phase reactions, having an internal element (11, 35) or a plurality of internal elements (11, 35) which are arranged in succession in the flow direction of the gas mixture of the heterogeneously catalyzed gas-phase reaction through the reactor (10), where the internal elements extend over the entire reactor cross section, wherein the one or more internal elements (11, 35) is/are at least partly made of a fiber composite ceramic material.

Claims

1. A reactor for carrying out heterogeneously catalyzed gas-phase reactions, having an internal element or a plurality of internal elements which are arranged in succession in the flow direction of the gas mixture of the heterogeneously catalyzed gas-phase reaction through the reactor, where the internal elements extend over the entire reactor cross section, wherein the one or more internal elements are at least partly made of a fiber composite ceramic material, where the fiber composite ceramic material is composed of a ceramic matrix in which ceramic fibers are embedded; wherein the ceramic matrix and the ceramic fibers are composed of an oxide ceramic.

2. The reactor according to claim 1, wherein the one or more internal elements comprise internal elements for accommodating a heterogeneous catalyst and optionally additional quiescent elements through which the reaction gas does not flow and which do not comprise any catalyst material.

3. The reactor according to claim 1, wherein the reactor is designed for carrying out heterogeneously catalyzed gas-phase reactions at reaction temperatures of 600-1500 C.

4. The reactor according to claim 1, wherein the reactor has a cylindrical reactor wall.

5. The reactor according to claim 1, wherein the reactor cross section in the regions in which the one or more internal elements are arranged is greater than 0.25 m.sup.2, with the maximum reactor cross section being in the range from 5 to 50 m.sup.2.

6. The reactor according to claim 1, wherein the one or more internal elements arranged in succession in the flow direction of the gas mixture of the heterogeneously catalyzed gas-phase reaction through the reactor are made in one piece, as one-piece basket having a closed vertical side wall and a perforated bottom.

7. The reactor according to claim 6, wherein the one or more internal elements are in each case made as a one-piece basket having a closed vertical side wall and a perforated bottom, where the closed vertical side wall of the one-piece basket merges at its upper end with a horizontally angled annular plate which serves to position the one-piece basket on a rest, where the rest is configured as an annular console which is fastened to the inside of a reactor wall.

8. The reactor according to claim 7, wherein a seal which is formed by one or more layers of fiber mats or fiber tapes is provided between the horizontally angled annular plate and the rest.

9. The reactor according to claim 7, wherein the rest is configured as a step section which is integrated into they reactor wall and comprises a vertical side wall and a horizontal annular protuberance projecting into the interior of the reactor.

10. The reactor according to claim 1, wherein the one or more internal elements arranged in succession in the flow direction of the gas mixture of the heterogeneously catalyzed gas-phase reaction through the reactor have a multipiece construction.

11. The reactor according to claim 10, wherein the one or more multipiece internal elements arranged in succession in the flow direction of the gas mixture of the heterogeneously catalyzed gas-phase reaction through the reactor are configured as a plurality of individual gratings and/or as a plurality of individual baskets which in each case have their own side walls and perforated bottoms, with the gratings and/or the baskets being arranged on supports which allow passage of the gas mixture of the heterogeneously catalyzed gas-phase reaction.

12. The reactor according to claim 11, wherein the baskets are sealed against one another and/or against the inside of the reactor wall by means of an insulation material.

13. The reactor according to claim 11, wherein the supports are configured as spaced T-supports, or as support elements having a wave-like profile and a plurality of openings for passage of the gas mixture of the heterogeneously catalyzed gas-phase reaction.

14. The reactor according to claim 11, wherein both the one or more multipiece internal elements arranged in succession in the flow direction of the gas mixture of the heterogeneously catalyzed gas-phase reaction through the reactor and also the supports are made of fiber composite ceramic materials, but with the fiber composite ceramic material for the supports having a higher strength than the fiber composite material for the one or more multipiece internal elements arranged in succession in the flow direction of the gas mixture of the heterogeneously catalyzed gas-phase reaction through the reactor.

15. The reactor according to claim 1, wherein two, three or more internal elements which are arranged in succession in the reactor so as to allow the gas mixture of the heterogeneously catalyzed gas-phase reaction to flow through them are provided where the reactor wall has a conical geometry.

16. A method comprising carrying out heterogeneously catalyzed gas-phase reactions in the reactor according to claim 1.

17. The reactor according to claim 1, wherein the reactor is designed for carrying out heterogeneously catalyzed gas-phase reactions at reaction temperatures of 800 to 1000 C.

18. The reactor according to claim 1, wherein the reactor cross section in the regions in which the one or more internal elements are arranged is greater than 1 m.sup.2, with the maximum reactor cross section being in the range from 10 to 30 m.sup.2.

19. The reactor according to claim 6, wherein the one or more internal elements are in each case made as a one-piece basket having a closed vertical side wall and a perforated bottom, where the closed vertical side wall of the one-piece basket merges at its upper end with a horizontally angled annular plate which serves to position the one-piece basket on a rest, where the rest is configured as an annular console which is welded to the inside of a reactor wall.

20. A reactor for carrying out heterogeneously catalyzed gas-phase reactions, having an internal element or a plurality of internal elements which are arranged in succession in the flow direction of the gas mixture of the heterogeneously catalyzed gas-phase reaction through the reactor, where the internal elements extend over the entire reactor cross section, wherein the one or more internal elements are at least partly made of a fiber composite ceramic material, where the fiber composite ceramic material is composed of a ceramic matrix in which ceramic fibers are embedded; wherein the ceramic matrix and the ceramic fibers are composed of an oxide ceramic; and wherein the ceramic fibers have a diameter in the range of from 10 to 12 m.

Description

(1) The drawings show:

(2) FIG. 1 a schematic longitudinal section through one embodiment of a reactor according to the invention with a first variant of a one-piece internal element;

(3) FIG. 2 a view corresponding to FIG. 1 of a second variant of a one-piece internal element;

(4) FIG. 3 a view corresponding to FIG. 1 of a third variant of a one-piece internal element;

(5) FIG. 4 a detail of FIG. 3;

(6) FIG. 5 a view corresponding to FIG. 1 of a fourth variant of a one-piece internal element;

(7) FIG. 6 a view corresponding to FIG. 1 of a fifth variant of a one-piece internal element;

(8) FIG. 7 a view corresponding to FIG. 1 of a sixth variant of a one-piece internal element;

(9) FIG. 8 a view corresponding to FIG. 1 of a seventh variant of a one-piece internal element;

(10) FIG. 9 a longitudinal section through a conical reactor having three one-piece internal elements arranged in succession;

(11) FIG. 10 a schematic longitudinal section through a preferred embodiment of a reactor having a multipiece internal element;

(12) FIG. 11 a section along the line A-A in FIG. 10;

(13) FIG. 12 a section along the line B-B in FIG. 10;

(14) FIG. 13 a view corresponding to FIG. 10 of a second variant of a multipiece internal element;

(15) FIG. 14 a view corresponding to FIG. 10 of a third variant of a multipiece internal element;

(16) FIG. 15 a variant of a support for multipiece internal elements in longitudinal section; and

(17) FIG. 16 a perspective view of the support of FIG. 15.

(18) In the figures, components in the various embodiments which perform the same or a corresponding function are denoted by the same reference numerals.

(19) FIG. 1 shows a longitudinal section through a part of a reactor 10 in which a one-piece internal element 11 is arranged. In the example depicted, the one-piece component 11 is configured as a basket 12 which is bounded at the side by a vertical side wall 13 and on the underside by a perforated bottom 14. The vertical side wall 13 of the basket 12 goes over at the top into a horizontally outward-angled annular plate 15 which rests on a rest 16 which is joined to the wall 17 of the reactor 10, for example by welding. The annular plate 15 of the basket 12 is sealed against the rest by means of a seal 18. Catalyst material 19, which can, for example, be in the form of a bed of catalyst particles or in the form of a monolithic catalyst is present in the basket 12. The basket 12 can be covered at the top by a noble metal gauze 20. The arrow 21 indicates the flow direction of the gas stream of the heterogeneously catalyzed gas-phase reaction through the reactor 10.

(20) In the embodiment of the reactor of the invention depicted in FIG. 2, a weighting element 22, for example one or more covering blocks or a circumferential covering ring, is additionally provided above the horizontally angled annular plate 15 in order to ensure secure positioning of the noble metal gauze and the catalyst bed.

(21) The rest 16 is located in a region of the reactor 10 which is subject to particular thermal stress, since the heterogeneously catalyzed gas-phase reaction also proceeds in this region. Reliable fastening of the rest 16 to the inside of the reactor wall 17 is therefore technologically demanding. In the embodiment depicted in FIG. 3, this problem is solved by the reactor wall 17 being made up of a plurality of parts and having a step section 23 which is installed in the reactor wall 17 at the height of the internal element 11 and is joined to the remainder of the reactor wall by means of welds 24. The step section 23 of the reactor wall 17 has a side wall 25 and an annular protuberance 26 which projects inward and is configured in one piece with the side wall 25 and forms the rest for the internal element. The side wall 25 extends vertically above and below the annular protuberance 26 and thus forms part of the reactor wall. The step section 23 with its inward-projecting protuberance 26 can be configured as a turned or milled workpiece. In the interests of clarity, the workpiece forming the step section 23 is shown again in isolation in FIG. 4. Since the welds 24 are located at a greater distance from the region which is particularly thermally stressed in the vicinity of the basket 12, high-temperature problems in fastening of the rest in the embodiment depicted in FIG. 3 can be avoided more easily.

(22) FIG. 5 depicts a fourth variant of a reactor having a one-piece internal element. The internal element 11 is again configured as a basket 12, but in contrast to the variants of FIGS. 1-3 the vertical side wall 13 is not angled horizontally to form an annular plate at its upper end in order to hang the basket 12 on the rest 16 and instead the basket 12 is seated entirely, once again via a sealing ring 18 arranged inbetween, on the rest 16.

(23) The longitudinal section of FIG. 6 shows a further preferred embodiment of a one-piece internal element 11 configured as a basket 12, where an insulation element 27 composed of high-temperature ceramic is provided between the side wall 13 of the basket 12 and the rest 16 so as to thermally protect the inside of the reactor wall 17, in particular the side wall 25 of the step section 23. In the example depicted, the rest 16 is shown as part of a turned step section 23 as has been described in more detail in connection with FIG. 3. Of course, such an insulation element can also be used with rests 16 as have been depicted in FIGS. 1, 2 and 5.

(24) FIG. 7 shows a longitudinal section through a further preferred embodiment having a one-piece internal element 11, with the wall 17 of the reactor 10 once again being made of a plurality of parts. In the upper and lower sections 28, 29 of the reactor wall which are subject to less thermal stress, the reactor wall consists of inexpensive normal steel. In the region of the internal element 11, the reactor wall 17 consists of an intermediate ring 30 made of high-temperature steel. In the example depicted, the upper and lower wall sections 28, 29 have connection flanges 31, 32 between which the intermediate ring is pressed in via sealing elements 33. In these regions, the reactor 10 can also be taken apart in a simple manner for maintenance purposes.

(25) A further improvement of the variant of FIG. 7 is depicted in FIG. 8, where a weld lip seal 34 is additionally provided in the region of the intermediate ring 30 made of high-temperature steel of the reactor wall 17.

(26) FIG. 9 shows a longitudinal section through a further preferred embodiment of a reactor 10 according to the invention. In this variant, three one-piece internal elements 11 which are arranged in succession in the flow direction and configured as baskets 12 are, by way of example, arranged in the reactor 10, as has already been described in detail in connection with the variant of FIG. 1. In the example depicted, the reactor wall 17 tapers from the top downward, so that the individual baskets 12 can easily be taken out through an upper assembly opening (not shown) of the reactor 10 despite the rests 16 which are fixed to the reactor wall 17. Devices, which are not shown in FIG. 9, for injecting intermediate gas, offtake device or mixing devices can be provided between the individual internal elements E.

(27) FIG. 10 shows a longitudinal section through a further preferred embodiment of the reactor 10 of the invention having one internal element. In this variant, the internal element is configured as a multipiece internal element 35. The individual parts of the multipiece internal element 35 are formed by gratings 36 which are arranged on ceramic supports 37, 38 which in turn rest on the rest 16. Catalyst material 19 is installed, for example as a bed as shown in FIG. 10, on the gratings 36. However, the catalyst material can also be, for example, Installed in monolithic form on the gratings 36. The gratings 36 have a mesh-like or other perforated structure which ensures firstly that the gas stream can pass through and also that the catalyst material is retained on the gratings. The gratings 36 are preferably arranged at a particular distance from one another, so that thermally induced changes in the dimensions can be compensated.

(28) The section depicted in FIG. 11 along the line A-A in FIG. 10 demonstrates the arrangement of the gratings 36 in a horizontal plane in the reactor 10. The shape and number of the gratings 36 is not subject to any restrictions but is selected so that the internal cross section of the reactor 11 is filled very completely with the required play between the gratings. In the section depicted in FIG. 12 along the line B-B in FIG. 10, it can be seen that in the depicted example the ceramic supports 37 have a cross section having a double-T geometry. The supports 37 are configured as straight-line supports in the example depicted. The supports 38 at the periphery can, for example, have a U-shaped cross section, with the base of the U being in contact with the inside of the reactor wall 17. The supports 38 at the periphery can also be configured as supports having a double-T geometry. In the schematic drawing of FIG. 12, both variants are depicted. The supports 38 at the periphery are preferably configured as segments and are fitted to the inside of the reactor wall 17 over an appropriate length.

(29) FIG. 14 shows a longitudinal section through a further preferred embodiment of the reactor 10 of the invention having a multipiece internal element 35. In this embodiment, the multipiece internal element consists of baskets 39 which rest directly on the straight-line supports 37 having a double-T geometry and the supports 38 at the periphery. The ceramic baskets 39 are filled with catalyst material 19 in the form of catalyst beds or monolith catalysts. The baskets 39 of the multipiece internal element also have a perforated bottom 40 and optionally a noble metal gauze 41 at the top of the baskets 39. However, the noble metal gauze 41 is not provided. A particularly preferred use of the noble metal gauze is, for example, in nitric acid oxidation where the gauze itself serves as catalyst and the catalysts in the baskets bring about purification of the reaction gas to a certain extent. Like the gratings of FIGS. 10-12, the number and shape of the baskets 39 is such that they completely fill the internal cross section of the reactor with the appropriate play between the baskets. Since catalyst material 19 is present only in the baskets 39, the gaps between the baskets 39 have to be filled with a joint filling material 43, for example in the form of a high-temperature fiber mat, so that a bypass of the gas stream is prevented. The gap at the periphery between the baskets and the inside of the reactor wall 17 is also filled with a filling material 43, preferably with an insulation material.

(30) In the embodiment depicted in FIG. 14, the multipiece internal element consists both of ceramic baskets 39 which are filled with catalyst material in the form of catalyst beds or monolith catalysts and also of ceramic gratings 36. The baskets 39 rest on the gratings 36, while the gratings 36 are, as in the variants of FIGS. 10-12, supported by ceramic supports 37, 38. Once again, a high-temperature-resistant joint filling material 43 in the form of high-temperature fiber mats has been introduced into the gaps between the baskets 39. In the example depicted, the base area of the baskets 39 corresponds to the base area of the gratings 36, but the respective base areas can also be selected independently of one another, so that, for example, a basket 39 can extend over a plurality of gratings 36.

(31) The oxide-ceramic supports or support elements can have a variety of shapes. While supports 37 having a double-T shape or supports 38 having a U-shape were depicted in the previously described embodiments, FIGS. 15 and 16 show ceramic supports 44 which have a perforated structure having a wave-like profile. Here, FIG. 15 shows a cross-sectional view with a grating 36 arranged on the supports 44 and FIG. 16 shows a perspective view of the supports 44 without grating. In the example depicted, each support 44 consists of a single wave. Joining of a plurality of supports 44 at their longitudinal edges 45 forms the periodic structure depicted. In this way, large-area support structures for reactors can be produced more simply on an industrial scale. However, it is also possible to produce single supports 44 which consist of a plurality of wave trains. In addition, it can be seen that the supports 44 have openings 46 through which the gas of the gas-phase reaction can flow.

(32) The invention will now be illustrated with the aid of an example of a heterogeneously catalyzed gas-phase reaction.

(33) An ammonia/air mixture (12.5% by volume of NH.sub.3, 87.5% by volume of air) is fed to the ammonia combustion furnace in which, as depicted in FIG. 1, a one-piece internal element is installed. The basket has an internal diameter of 3.52 m. The reactor is operated at an ammonia/air mixture throughput of 3650 standard m.sup.3/h and per m.sup.2 of catalyst gauze area. The temperature of the ammonia/air mixture entering the reactor is 28.4 C. and the pressure upstream of the platinum catalyst gauze in the reactor is 1089 mbar (abs.). At the platinum catalyst gauze, the ammonia burns at temperatures of about 880 C. to form the reaction product which is then passed through the catalytically active packing in the basket and comprises nitrogen monoxide as main component and small amounts of dinitrogen monoxide N.sub.2O (nitrous oxide). The nitrous oxide concentration in the reaction product immediately downstream of the platinum catalyst gauze, i.e. before reaching the catalytically active packing in the basket, is about 1000 ppm. The platinum gauze is followed by the basket which comprises a 150 mm deep layer of all-active catalyst extrudates, with these extrudates having a star-shaped cross section, a diameter of about 6 mm and a length of from 5 to 30 mm and consisting of a mixture of CuO, ZnO and Al.sub.2O.sub.3. The basket has a lateral delimitation which is about 250 mm high.

(34) Samples of the reaction product can be taken directly after the platinum catalyst gauze (offtake point 1) and in the middle of the reactor downstream directly beneath the bottom of the basket (offtake point 2) and also at the periphery of the reactor downstream directly beneath the outer peripheral region of the bottom of the basket (offtake point 3) and analyzed to determine the nitrous oxide concentration by the GC/MS method. A further offtake point 4 is installed downstream after the basket and a subsequent waste heat exchanger unit.

(35) In the experiment for comparative purposes, the same basket design (same dimensions) once in the conventional variant made of metal and in the case according to the invention made of an oxidic high-temperature fiber ceramic is used.

COMPARATIVE EXAMPLE 1 (NOT ACCORDING TO THE INVENTION)

(36) In the continuous process, an ammonia/air mixture as described above is reacted using a metallic basket made of Inconel 600 (material number 2.4816).

(37) In the peripheral region of the basket, the catalytically active packing has a funnel-shaped depression in the form of a trough having a depth of 96 mm. The height of the remaining bed in the peripheral region above the bottom is now only 54 mm (before the beginning of the experiment it was 150 mm).

(38) The measured nitrous oxide concentration at the offtake point 3 directly underneath the funnel-shaped depression is 676 ppm of nitrous oxide, and at the offtake point 2 the measured nitrous oxide concentration is 186 ppm, so that the average measured nitrous oxide concentration downstream after the metallic basket and the waste heat exchanger unit installed downstream at the offtake point 4 is 227 ppm.

EXPERIMENTAL EXAMPLE 1 (ACCORDING TO THE INVENTION)

(39) The comparative experiment according to the invention was carried out using a corresponding basket made of an oxide-ceramic high-temperature fiber ceramic.

(40) The basket was produced by infiltrating an oxide ceramic fiber fabric made of Nextel 610 with an Al.sub.2O.sub.3-comprising slip and laminating this onto a pattern having the desired basket geometry. After drying at 100 C., the dried material was removed from the pattern and fired at 1250 C.

(41) In the continuous process, an ammonia/air mixture is reacted as described above.

(42) The peripheral region in the ceramic basket now has only a small funnel-shaped depression in the form of a trough having a depth of 37 mm in the catalytically active packing, the height of which in the peripheral region of the ceramic basket is now only 113 mm (before the beginning of the experiment it was 150 mm).

(43) The measured nitrous oxide concentration at the offtake point 3 directly underneath the funnel-shaped depression is 316 ppm of nitrous oxide, and at the offtake point 2 the measured nitrous oxide concentration is 190 ppm, so that the average measured nitrous oxide concentration downstream after the oxide-ceramic basket and the waste heat exchanger unit installed downstream at the offtake point 4 is 199 ppm.

(44) It can be seen that the tendency of the catalyst bed to undergo funnel formation is significantly reduced by the use of a basket made of high-temperature fiber ceramic because of the low thermal expansion of the oxide-ceramic basket and, correspondingly, the nitrous oxide concentration in the gas stream can be significantly reduced as a result of the lower bypass stream.

LIST OF REFERENCE NUMERALS

(45) 10 Reactor 11 One-piece internal element 12 Basket 13 Vertical side wall 14 Perforated bottom of the basket 12 15 Annular plate 16 Rest 17 Reactor wall 18 Seal 19 Catalyst material 20 Noble metal gauze of the basket 12 21 Arrow indicating the flow direction 22 Weighting element 23 Step section of the reactor wall 24 Weld 25 Side wall 26 Annular protuberance 27 Insulation element 28 Upper wall section 29 Lower wall section 30 Intermediate ring 31 Upper connection flange 32 Lower connection flange 33 Sealing element 34 Weld lip seal 35 Multipiece internal element 36 Grating 37 Straight-line ceramic support 38 Peripheral ceramic support; preferably U-profile, fitting the wall 39 Basket 40 Side wall of the basket 39 41 Perforated bottom of the basket 39 42 Noble metal gauze of the basket 39 43 Joint filling material in the form of high-temperature fiber mats 44 Wave-shaped ceramic support 45 Longitudinal edge of the support 44 46 Opening