Gas-tight, heat-permeable multilayer ceramic composite tube

Abstract

The present invention relates to a gastight multilayer composite tube having a heat transfer coefficient of >500 W/m.sup.2/K and comprising at least two layers, namely a layer of nonporous monolithic oxide ceramic and a layer of oxidic fiber composite ceramic, a connecting piece comprising at least one metallic gas-conducting conduit which in the longitudinal direction of the composite tube overlaps in a region at least two ceramic layers, where the one ceramic layer comprises a nonporous monolithic ceramic and the other ceramic layer comprises a fiber composite ceramic, and also the use of the multilayer composite tube as reaction tube for endothermic reactions, radiation tubes, flame tubes or rotary tubes.

Claims

1. A multilayer composite tube, comprising: a first layer comprising a nonporous monolithic oxide ceramic; and a second layer comprising oxidic fiber composite ceramic, wherein the tube has a heat transfer coefficient of >1000 W/m.sup.2/K in a temperature range of from 500 to 1700 C., wherein the second layer has a thickness in a range of from 0.5 mm to 3 mm, wherein the first and second layers are joined frictionally or adhesively to one another and form one component, and wherein the oxidic fiber composite ceramic is a matrix comprising (a) oxidic ceramic particles and (b1) oxidic and/or (b2) nonoxidic ceramic fibers.

2. The tube of claim 1, wherein a total wall thickness made up of the at least two layers is from 0.5 mm to 50 mm.

3. The tube of claim 1, having an internal tube diameter in a range of from 20 mm to 1000 mm.

4. The tube of claim 1, having an open porosity of <5%.

5. The tube of claim 1, wherein a thickness of the second layer is less than 25% of a total wall thickness.

6. The tube of claim 1, wherein a modulus of elasticity of the nonporous monolithic oxide ceramic is greater than a modulus of elasticity of the oxidic fiber composite ceramic.

7. The tube of claim 1, wherein a thermal conductivity of the nonporous monolithic oxide ceramic is greater than a thermal conductivity of the oxidic fiber composite ceramic.

8. The tube of claim 1, wherein the oxidic fiber composite ceramic comprises SiC/Al.sub.2O.sub.3, SiC/mullite, C/Al.sub.2O.sub.3, C/mullite, Al.sub.2O.sub.3/Al.sub.2O.sub.3, Al.sub.2O.sub.3/mullite, mullite/Al.sub.2O.sub.3, mullite/mullite, or a mixture thereof.

9. The tube of claim 1, wherein the second layer has a thickness less than 50% of a total wall thickness.

10. The tube of claim 1, wherein the fibers of the oxidic fiber composite ceramic have a diameter in the range of from 10 to 12 m.

11. The tube of claim 1, which is impregnated or coated with polymer, a nonporous ceramic, pyrolytic carbon, and/or a metallic material in a peripheral region.

12. The tube of claim 1, configured to overlap at least in a region of at least one layer of the tube in a longitudinal direction with a metallic gas-conducting conduit.

13. The tube of claim 1, wherein the nonporous monolithic oxide ceramic comprises at least 70 wt. % aluminum oxide.

14. A double-tube reactor suitable for endothermic reactions, the reactor comprises: a first and a second of the tube of claim 1 arranged such that an outer composite tube encloses an inner composite tube, and configured such that the inner composite tube is open at both ends and the outer tube is closed at one end.

15. A multilayer connecting piece, comprising: a first layer comprising a nonporous monolithic ceramic; and a second layer comprising a fiber composite ceramic, wherein the multilayer connecting piece has a heat transfer coefficient of >500 W/m.sup.2/K, wherein the first and/or the second layer has been impregnated or coated with a polymer, a nonporous ceramic, a pyrolytic carbon, a metallic material, or a mixture thereof, in a peripheral region before a transition to another material.

16. A multilayer connecting piece, comprising: a metallic gas-conducting conduit, which in a longitudinal direction at least partially overlaps at least one layer of the tube of claim 1.

17. The piece of claim 16, further comprising: a first tube region comprising the metallic gas-conducting conduit; a second tube region which adjoins the first tube region and has an outer layer of fiber composite ceramic and an inner metallic layer or has an outer ceramic layer and an inner metallic layer; a third tube region which adjoins the second tube region and has a sandwich structure comprising a metallic layer, a nonporous monolithic ceramic layer, and a fiber composite ceramic layer; and a fourth tube region which adjoins the third tube region and comprises the tube comprising the layer of the nonporous monolithic ceramic and the layer of the fiber composite ceramic.

18. The piece of claim 16, further comprising: a first tube region comprising the metallic gas-conducting conduit; a second tube region which adjoins the first tube region and has a sandwich structure comprising an inner ceramic layer, a middle metallic layer, and an outer ceramic layer or comprising an inner ceramic layer, a middle ceramic layer, and an outer metallic layer, one of the ceramic layers comprising a nonporous monolithic ceramic layer and the other ceramic layer comprises a fiber composite ceramic layer; and a third tube region which adjoins the second tube region and comprises the tube comprising the layer of the nonporous monolithic ceramic and the layer of the fiber composite ceramic.

19. A process for producing synthesis gas by at least one of: reforming hydrocarbons with steam, carbon dioxide, or both; coproducing hydrogen and pyrolysis carbon by pyrolysis of hydrocarbons; preparing hydrocyanic acid from methane and ammonia or from propane and ammonia; preparing one or more olefins by steam cracking of hydrocarbons; and coupling methane to form ethylene, acetylene, and benzene, wherein the process occurs in at least one apparatus comprising the multilayer composition tube of claim 1.

20. A reaction tube, comprising: the tube of claim 1.

Description

(1) The figures show:

(2) FIG. 1a a schematic depiction of a gastight multilayer composite tube having a variable diameter,

(3) FIGS. 1b/1c/1d a schematic depiction of the connecting pieces,

(4) FIG. 2 a schematic depiction of a variant of the solution consisting of two concentric tubes,

(5) FIG. 3a a schematic depiction of a gastight multilayer sandwich tube having a variable diameter,

(6) FIGS. 3b/3c a schematic depiction of the connecting pieces.

(7) The following abbreviations are used: 1: nonporous monolithic ceramic 2: fiber composite ceramic 3: sealed region in the fiber composite ceramic 4: metal sections 5: overlap joint between the metal section and the nonporous monolithic ceramic

EXAMPLE 1 (COMPARATIVE EXAMPLE)

(8) The test specimen was a tube having a monolithic wall composed of dense -alumina (product of Friatec having the product number 122-11035-0) and having the following dimensions (external diameterinternal diameterlength): 35 mm29 mm64 mm. The heat transfer coefficient of the tube wall was, based on the inside of the wall: k.sub.loc=9200 (W/m.sup.2/K). The tube was exposed to the flame of a welding torch. The welding torch was supplied with acetylene and oxygen and equipped with a welding head type Gr3, A, 6-9, S2.5 bar. The flame was set neutrally with a stoichiometric ratio =1.15 air/acetylene. The torch tip was directed perpendicularly at the tube wall at a distance of 50 mm. After about 3 seconds, the tube fractured. The test was therefore ended. This test confirmed the thermal shock sensitivity of monolithic ceramics.

EXAMPLE 2

(9) The test specimen was a tube having a two-layer wall. The wall of the core tube consisted of dense monolithic -alumina (product of Friatec having the product number 122-11035-0) with the following dimensions (external diameterinternal diameterlength): 35 mm29 mm64 mm. A layer of fiber composite ceramic (ceramic sheet type FW12) having a layer thickness of about 1 mm was wrapped around the core tube. The heat transfer coefficient of the tube wall was, based on the inside of the wall: k.sub.loc=3120 (W/m.sup.2/K). The tube was exposed to the flame of a welding torch. The welding torch was supplied with acetylene and oxygen and equipped with a welding head type Gr3, A, 6-9, S2.5 bar. The flame was set neutrally with a stoichiometric ratio =1.15 air/acetylene. The tip of the torch was directed perpendicularly at the tube wall at a distance of 50 mm. In this case, a white-hot spot having a length of about 25 mm (T>1300 C.) was formed on the outer wall of the tube within 4 seconds. The flame was taken away from the tube after 20 seconds and after another 30 seconds was again directed at the tube for 20 seconds. The tube withstood this thermal shock without damage.