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RU-2861344-C2 - REFORMING CENTRE PIPE

RU2861344C2RU 2861344 C2RU2861344 C2RU 2861344C2RU-2861344-C2

Abstract

FIELD: gas industry. SUBSTANCE: invention relates to a reforming centre pipe, wherein at least part of the inner surface has a roughened portion having a roughness Ra of from 12.5 mcm to 500 mcm, wherein the roughness Ra is the arithmetic mean deviation of the surface. The reforming centre pipe extends along an axial length, and the inner surface of the roughened portion comprises a group of grooves. The deviation of the grooves from the circumference of the inner surface of the pipe is up to 10°. The invention also relates to a reforming system. EFFECT: preventing gas entrainment from the grooves, thereby preventing the formation of turbulent eddies in the grooves. 20 cl, 7 dwg, 1 tbl

Inventors

  • FLAO, Dominik
  • FISHER, Berri

Dates

Publication Date
20260505
Application Date
20220406
Priority Date
20210407

Claims (20)

  1. 1. An axial reforming tube in which at least a portion of the inner surface has a rough section having a roughness Ra of 12.5 μm to 500 μm, wherein the roughness Ra is the arithmetic mean deviation of the surface;
  2. wherein the axial reforming pipe extends along the axial length, and the inner surface of the rough section contains a group of grooves, and
  3. In this case, the deviation of the grooves from the circumference of the inner surface of the pipe is up to 10°.
  4. 2. The axial reforming tube according to claim 1, wherein at least a portion of the tube is a roughened section having an inner surface with a roughness Ra of at least 25 μm.
  5. 3. An axial reforming pipe according to claim 1 or 2, in which the deviation of the grooves from the circumference of the inner surface of the pipe is up to 5°.
  6. 4. A reforming axial tube according to any one of the preceding claims, wherein the group of grooves is formed as one or more helical grooves.
  7. 5. An axial reforming tube according to any of the preceding claims, wherein the sides of the grooves are inclined relative to a plane perpendicular to the axial length at a side angle of from 0° to 50°.
  8. 6. An axial reforming pipe according to claim 5, in which the sides of the grooves are inclined relative to a plane perpendicular to the axial length at a side angle of from 0° to 30°.
  9. 7. The axial reforming tube according to claim 5 or 6, wherein the side angle is at least 10°.
  10. 8. An axial reforming pipe according to one of paragraphs 5, 6 and 7, in which the side angle is up to 25°.
  11. 9. An axial reforming tube according to any one of the preceding claims, wherein the axial length of the bottom of the grooves is from 50% to 200% of the depth of the grooves.
  12. 10. An axial reforming tube according to any of the preceding claims, wherein the grooves are separated by ridges and the axial length of the ridges is from 50% to 100% of the depth of the grooves.
  13. 11. A reforming axial tube according to any of the preceding claims, in which the grooves are separated by ridges and sharp edges are formed between the ridges and the sides of the grooves, wherein the sharp edges have an average radius of curvature of up to 20 µm.
  14. 12. An axial reforming tube according to any of the preceding claims, wherein the rough section extends along the entire length of the tube.
  15. 13. An axial reforming pipe according to any one of paragraphs 1-11, wherein said pipe comprises a smooth section with a roughness Ra of up to 3.2 μm, connected to a rough section.
  16. 14. The axial reforming tube according to claim 13, wherein the rough section is connected between two smooth sections.
  17. 15. A reforming axial tube according to any of the preceding claims, wherein said tube has a length of at least 700 mm.
  18. 16. A reforming axial pipe according to any of the preceding paragraphs, wherein the internal diameter of the pipe is up to 350 mm.
  19. 17. A reforming axial tube according to any one of the preceding claims, wherein said tube has a length of at least 2 m and an internal diameter of from 95 mm to 280 mm.
  20. 18. A reforming axial tube according to any of the preceding claims, wherein said tube has a length of at least 2 m and an internal diameter of from 95 mm to 250 mm.

Description

AREA OF TECHNOLOGY The present invention relates to axial reaction tubes for reforming, in particular, but not exclusively, to axial reaction tubes for steam reforming of methane. LEVEL OF TECHNOLOGY Steam methane reforming is a process commonly used to produce hydrogen from natural gas. For example, steam and methane are heated to temperatures between 700°C and 1000°C and pressures between 3 bar and 400 bar, passed over a nickel catalyst, and the highly endothermic reaction CH 4 + H 2 O → CO + 3 H 2 produces hydrogen, carbon monoxide, and some carbon dioxide. A moderately exothermic water-gas shift reaction involving a catalyst produces carbon dioxide and additional hydrogen from carbon monoxide and water: CO + H 2 O ↔ CO 2 + H 2 . The carbon dioxide can then be absorbed via pressure swing absorption, producing essentially pure hydrogen. Steam methane reforming is typically performed in axial-flow reforming tubes (also known as catalytic reforming tubes or reforming vessels). Axial-flow reforming tubes are also used in other reforming processes, including ammonia and methanol production. During operation, the reaction tubes of steam methane reformers are typically positioned vertically within a reforming furnace (a refractory-lined chamber). The reforming tubes are made of alloy steel capable of withstanding the pressures and temperatures at which reforming occurs and ensuring high rates of heat transfer through the tube wall from the external heat source to the gas passing through the tube. An example of a material used for the manufacture of axial reforming tubes is H39WM, a heat-resistant austenitic stainless steel manufactured by Paralloy Limited containing 0.4% carbon, 25% chromium, 35% nickel, and 1% niobium. Due to the increased strength of axial reforming tubes and the increased ratio of the internal surface area to volume, which affects the heat transfer between the internal surface of the tube and the gas passing inside, axial reforming tubes are typically characterized by a large length compared to the internal diameter, for example, 13 m in length with an internal diameter of 10 cm. During operation, gas flows along the reformer's reaction tube, generally along its axis. The steam methane reforming reaction occurs where the reactant passes over the catalyst, and as the gas moves along the reformer's axial tube, it leaks around the catalyst. Gas also moves along the tube's inner surface. Typically, the catalyst has a high surface area to volume ratio and is preferably shaped to provide a relatively low pressure drop for gas passing through the catalyst bed. Axial reforming tubes are typically manufactured using centrifugal casting, and the inner surface is formed by smooth boring, for example, with a roughness Ra (where Ra is the average arithmetic surface deviation) of 3.2 μm to 1.6 μm, which can correspond to a roughness Rt (where Rt denotes the range of experimentally obtained roughness values) of 13 μm to 6.3 μm. It is generally believed that boring the inner surface with a grinding finish reduces gas flow resistance along the inner tube surface and maximizes the yield of reformed products. ESSENCE OF THE INVENTION The present invention provides a reforming axial tube and a reforming system as defined in the appended claims. According to the first aspect, the invention provides an axial reforming tube, wherein at least a part of the inner surface has a rough section having a roughness Ra of from 12.5 μm to 500 μm, wherein the roughness Ra is the arithmetic mean deviation of the surface; wherein the axial reforming tube extends along the axial length, and on the inner surface of the rough section there is a group of grooves; wherein the deviation of the grooves from the circumference of the inner surface of the tube is up to 10°. According to a second aspect, the invention provides a reforming system comprising a reforming axial tube corresponding to the first aspect. The inner surface of the roughened section may have a roughness Ra of at least 25 μm. The inner surface of the roughened section may have a roughness Ra of at least 50 μm. The inner surface of the roughened section may have a roughness Ra of at least 100 μm. The deviation of the grooves from the circumference of the inner surface of the pipe can be up to 5°. A groove group may include one or more spiral grooves. The groove flanks may be inclined relative to the plane perpendicular to the axial length at a flank angle of 0° to 50°. The groove flanks may be inclined relative to the plane perpendicular to the axial length at a flank angle of 0° to 30°. The flank angle may be at least 10°. The flank angle may be up to 25°. The axial length of the groove bottom can range from 50% to 200% of the groove depth. The grooves may be separated by ridges, and the axial length of the ridges may be from 50% to 100% of the groove depth. The grooves can be separated by ridges, forming sharp edges between the ridges and the sides of the grooves,