Heat exchange reactor sealing device

Abstract

A tube sealing device suitable for use in a heat exchange reactor comprising one or more tubes is described, the tube sealing device comprising a seal tube and an inner tube disposed within the seal tube to provide an overlap region, the inner tube having within the overlap region (i) an internal constriction of reduced cross-sectional area forming a low pressure region, (ii) an expansion region adjacent the constriction of a cross-sectional area greater than the cross-sectional area of ​​the constriction, and (iii) one or more passageways through a wall of the inner tube connecting the low pressure region to an exterior of the inner tube, the tube sealing device further comprising one or more grooves formed around an inner surface of the seal tube in the overlap region corresponding to the low pressure region of the inner tube.

Description

[Technical field]

[0001] The present invention relates to a sealing device and the use of the sealing device in a heat exchange reactor, and to a process employing such an device, in particular a catalytic steam reforming process.

[0002] In heat exchange reactor apparatuses involving externally heated tubes, there is likely to be significant thermal expansion differences between the tubes carrying the process fluid and the means, such as tube sheets, that define the zones through which the heat exchange medium passes in heat exchange with the process fluid passing through the tubes. When the tubes are heated by a heat exchange medium flowing around the exterior of the tubes, which is at a lower pressure than the process fluid passing through the tubes, one solution has been to employ a seal device connected to each tube, comprising a seal tube and an inner tube movably disposed within the seal tube, which has a constriction providing a low pressure region, and also has a passage through the wall of the inner tube connecting the low pressure region with the exterior of the inner tube. In this way, mixing of the process fluid and the heat exchange medium is prevented or reduced. WO 9705947 discloses such an apparatus.

[0003] The applicant has discovered that by disrupting the flow of the heat exchange medium within the seal device by generating turbulence in the annular space between the outside of the inner tube and the inside of the seal tube, the amount of mixing of the heat exchange medium with the process fluid can be reduced.

[0004] Accordingly, the present invention provides a tube sealing device suitable for use in a heat exchange reactor comprising one or more tubes, the tube sealing device comprising a seal tube and an inner tube disposed within the seal tube to provide an overlap region, the inner tube having within the overlap region (i) an internal constriction of reduced cross-sectional area forming a low pressure region, (ii) an expansion region adjacent the constriction of a cross-sectional area greater than the cross-sectional area of ​​the constriction, and (iii) one or more passages through a wall of the inner tube connecting the low pressure region to an exterior of the inner tube, the tube sealing device further comprising one or more grooves formed around an inner surface of the seal tube in the overlap region corresponding to the low pressure region of the inner tube.

[0005] The invention further provides a heat exchange reactor comprising one or more heat exchange tubes comprising the tube seal device, and a process using the reactor and the tube seal device.

[0006] Heat exchange reactor apparatus including tube sealing devices are particularly useful where the heat exchange medium flowing around the exterior of the tubes is at a lower pressure than the process fluid passing through the tubes.

[0007] By providing grooves on the interior of the seal tube rather than on the exterior of the inner tube, fouling of the inner tube from material carried thereto by the heat exchange medium is reduced. This can improve the long-term performance of the tube seal device and simplify maintenance by allowing fouled seal tubes to be replaced during routine maintenance. Additionally, providing grooves on the interior of the seal tube allows for potentially more grooves to be present.

[0008] To further reduce mixing of the process fluid with the heat exchange medium, there may additionally be one or more grooves in the overlap region corresponding to the expansion region of the inner tube. The one or more grooves in the expansion region may be on the outer surface of the inner tube or on the inner surface of the seal tube. Preferably, the one or more grooves in the overlap region corresponding to the expansion region of the inner tube are disposed on the outer surface of the inner tube, because this simplifies manufacturing.

[0009] A heat exchange reactor apparatus including a tube seal device may include a process fluid supply zone, a heat exchange zone, and a process fluid withdrawal zone, first and second boundary means separating the zones from one another, and one or more heat exchange tubes fixed to one of the boundary means and extending through the heat exchange zones. A process fluid may flow from the process fluid supply zone through the one or more heat exchange tubes into the process fluid withdrawal zone. Each heat exchange tube is provided with a tube seal device. A seal tube of the tube seal device may be fixed to one of the boundary means. An inner tube of the tube seal device is provided on each heat exchange tube. The seal tube is disposed substantially coaxially with the inner tube such that the inner tube is in sliding engagement with its associated seal tube, thereby forming an overlap region.

[0010] Each inner tube of the tube sealing device is provided with (i) an internal constriction of reduced cross-sectional area forming a low pressure region within the inner tube, (ii) an expansion region of cross-sectional area greater than the cross-sectional area of ​​the constriction downstream of the constriction, and (iii) one or more passages through the wall of the inner tube connecting the low pressure region to the exterior of the inner tube, the passages being located within the overlap region, thereby providing a flow path for fluid from the heat exchange zone through the overlap region and into the low pressure region within the inner tube.

[0011] Each pipe seal device includes one or more grooves formed around the inner surface of the seal pipe in an overlap region that corresponds to the low pressure region of the inner pipe.

[0012] In the above types of heat exchange reactors, the process fluid is passed from the process fluid supply zone through one or more heat exchange tubes disposed in a heat exchange zone defined by a casing through which the heat exchange medium passes, and then into a process fluid withdrawal zone. Means such as tube sheets are provided to separate the zones. As such, the tube sheets may separate the heat exchange zone through which the heat exchange medium passes from a zone such as a plenum chamber that communicates with the interior of the heat exchange tubes to allow the supply of process fluid to the tubes or the withdrawal of process fluid from the tubes. An alternative configuration involves defining the process fluid supply zone using header pipes disposed in the heat exchange zone, the process fluid being supplied to the header pipes from which it flows into and passes through the heat exchange tubes. Similarly, header pipes may be provided for the withdrawal of process fluid from the tubes. Alternatively, there may be a combination of tube sheets and header pipes. Such tube sheets or headers are referred to herein as boundary means, since they define the boundaries between the heat exchange zone and the process fluid supply zone and the process fluid withdrawal zone.

[0013] By providing an inner tube on the heat exchange tube and by connecting a seal tube to an interface means within the heat exchange reactor, longitudinal movement caused by thermal expansion and contraction of the heat exchange tube can be accommodated.

[0014] In use, due to the low pressure region within the inner tube, the heat exchange medium may be drawn into the interior of the inner tube where it mixes with the process fluid flowing through the inner tube.

[0015] A heat exchange reactor may contain one or more heat exchange tubes, for example 1-10 tubes, while a heat exchange reactor used, for example, in a steam reforming process, may contain tens or even hundreds of tubes, for example 10-2000 tubes. The tubes may have an internal diameter of 25-150 mm and the wall thickness of the tubes may range from 2-13 mm depending on the size of the tube. The tubes may be 5-15 meters long. At such lengths, especially 10-15 meters, longitudinal expansion is particularly problematic without the use of tube sealing devices. The tubes may be manufactured from a suitable metal, such as stainless steel. The heat exchange reactor may be equipped with one or more transverse baffles to move the heat exchange medium in a serpentine manner through the heat exchange zone, thereby enhancing heat exchange.

[0016] The tube seal device comprises an inner tube. The inner tube may be connected to one end of the heat exchange tube or may be formed as an end of the heat exchange tube. The inner tube may have the same diameter as the heat exchange tube or preferably have a narrower diameter than the heat exchange tube. The inner tube may be polygonal or cylindrical, but is preferably shaped such that a uniform clearance space is formed between the outer surface of the inner tube and the inner surface of the seal tube at the overlap region. The inner tube has an internal constriction forming a low pressure region within the tube and an enlarged portion adjacent the constriction forming an expansion zone within the tube. One or more passages through the wall of the inner tube connect the low pressure region to the exterior of the inner tube. There may be 1 to 20 passages connecting the low pressure region to the exterior of the inner tube. The passages are desirably equally spaced to open into the clearance space between the inner tube and the seal tube. In use, the device is oriented such that the expansion zone is downstream of the low pressure zone. For example, in a vertical downflow configuration where the tube seal device is located at the lowest end of the heat exchange tube, the expansion zone will be below the constriction of the inner tube. The relative sizes of the constriction, low pressure region, and expansion region depend in part on the size of the tube. For example, in one embodiment including a heat exchange tube with an internal diameter of about 100 mm, the section of the tube forming the inner tube may have an internal dimension of about 25 mm tapering internally to a constriction of about 12 mm internal diameter that opens into a low pressure region with an internal diameter of about 18 mm and a length of about 108 mm. At the end of the low pressure region, the inner tube may flare from a diameter of 18 mm to an outer diameter of about 31 mm over a length of about 78 mm. Twelve equally spaced passages of 3 mm diameter may be provided between the low pressure region and the exterior of the inner tube.

[0017] In the overlap region between the inner surface of the seal tube and the outer surface of the inner tube, there is a clearance space, for example an annular gap. This allows the inner tube to move freely longitudinally within the seal tube. The thickness of the gap between the inner surface of the seal tube and the outer surface of the inner tube portion of the heat exchange tube may be about 0.1-0.5 mm. For example, in the above embodiment, the gap may be about 0.2 mm.

[0018] The pipe sealing device also includes a seal tube, which may be polygonal or cylindrical, but preferably has the same shape as the inner tube so that a uniform clearance space is maintained. A pipe sealing device including a cylindrical seal tube and a cylindrical inner tube is preferred as it is simpler to manufacture and more suitable for use at high temperatures under pressure.

[0019] The pipe seal device includes one or more grooves on an inner surface of the seal pipe. The one or more grooves on the inner surface of the seal pipe are formed on the inner surface of the seal pipe in an overlap region corresponding to the low pressure region of the inner pipe. The one or more grooves on the inner surface of the seal pipe may be formed as crenellations, i.e., having a square or rectangular configuration, or the grooves may be U-shaped, V-shaped, or any combination thereof. Square or rectangular grooves may provide improved turbulence in the overlap region.

[0020] The grooves may be formed by cutting one or more channels into the inner surface of the sealing tube device. Alternatively, the grooves may be formed without cutting, for example, by using a layered arrangement of rings of different inner diameters on the inside of the sealing tube device, or by rolling a grooved profile into the sealing tube device.

[0021] The size of the grooves may be 2-20 mm wide, for example 6-14 mm wide and 1-7 mm deep, depending on the size of the tube and the thickness of the tube wall. Desirably, the depth of the grooves is about 50% or less of the wall thickness of the tube for strength reasons. In the overlap region corresponding to the low pressure region of the inner tube, there may be 1-30 grooves located on the sealing tube, for example 2-25 grooves, preferably 5-20 grooves. This is an improvement over devices where the grooves are located on the inner tube and the number of grooves in this region is limited to 8 or less by the size of the inner tube. By locating the grooves on the inner wall of the sealing tube, the grooves may extend beyond the low pressure region.

[0022] In addition, there may be one or more grooves in the overlapping region corresponding to the expansion region of the inner pipe. Whether the one or more grooves are on the outer surface of the inner pipe or on the inner surface of the seal pipe, they may be formed as crenellations, i.e. having a square or rectangular form, or the grooves may be U-shaped, V-shaped, or any combination thereof. The size of the grooves in this region may also be 2-20 mm wide, for example 6-14 mm wide and 1-7 mm deep. The number of grooves in the expansion region may be the same as or greater than the number of grooves in the low pressure region. For example, there may be 1-30 grooves, for example 2-25 grooves, preferably 5-20 grooves located on the inner surface of the seal pipe or the outer surface of the inner pipe in the overlapping region corresponding to the expansion region of the inner pipe.

[0023] The one or more grooves are desirably positioned to impede the flow of gas through the pipe seal device. The one or more grooves may be positioned perpendicular to the flow of process fluid through the inner pipe, or the grooves may be formed in a helical fashion, such as a screw thread.

[0024] When there is more than one groove in either the low pressure region or the expansion region, they are preferably parallel to each other.

[0025] The invention relates to a process comprising the steps of: (a) feeding a process fluid to a heat exchange reactor having a process fluid feed zone separated from a heat exchange zone by a boundary means; (b) passing the process fluid from the process fluid feed zone to one or more heat exchange tubes extending through the heat exchange zone, the process fluid being subjected to heat exchange with a heat exchange medium at a lower pressure than the process fluid passing through the tubes in the heat exchange zone; (c) passing the process fluid from the heat exchange tubes to a process fluid withdrawal zone separated from the heat exchange zone by a second boundary means; (d) subjecting the process fluid from the process fluid withdrawal zone to further processing steps; and (e) passing the resulting treated process fluid as a heat exchange medium through the heat exchange zone. wherein each of the one or more heat exchange tubes is secured to one of the interface means and engages the other of the interface means by a tube seal device comprising a seal tube secured to the other of the interface means and an inner tube connected to each heat exchange tube and disposed within the seal tube to provide an overlap region, the inner tube having within the overlap region (i) an internal constriction of reduced cross-sectional area forming a low pressure region, (ii) an expansion region of cross-sectional area greater than a cross-sectional area of ​​the constriction downstream of the low pressure region in a flow direction of the process fluid, and (iii) one or more passages through a wall of the inner tube connecting the low pressure region to an exterior of the inner tube, the tube seal device including one or more grooves formed around an inner surface of the seal tube in the overlap region corresponding to the low pressure region of the inner tube.

[0026] In the process, a portion of the treated process fluid fed to the heat exchange zone enters a tube seal device and passes through one or more passages into a lower pressure region.

[0027] In the process, the heat exchange medium is a process fluid that has been passed through the tubes but has been subjected to further processing before being used as a heat exchange medium, preferably including a step in which the process fluid is heated such that the heat exchange medium donates heat to one or more heat exchange tubes.

[0028] The tube sealing device is particularly useful in heat exchange steam reformers, or gas-heated reformers, i.e., heat exchange reactors that contain one or more externally heated tubes containing a steam reforming catalyst through which the reformer feed is passed to generate synthesis gas, and in which the heat exchange medium is used to heat the tubes. In such processes, the heat exchange medium is typically at a lower pressure than the reformer feed.

[0029] The process and apparatus are particularly useful for the steam reforming of hydrocarbons, in which a mixture of a hydrocarbon feedstock and steam is passed through heat exchange tubes containing a steam reforming catalyst, such as a nickel-containing steam reforming catalyst, to form a primary reformed gas, which is then subjected to partial combustion with an oxygen-containing gas, and the resulting partially combusted gas is used as a heat exchange medium in the heat exchange zone. Preferably, the partially combusted gas is passed through a bed of a secondary reforming catalyst for further reforming before being used as a heat exchange medium.

[0030] As a result of the constriction in the inner tube, a low pressure region is formed in the inner tube. By appropriately sizing the constriction, the pressure in the low pressure region during normal operation can be lower than the pressure in the heat exchange zone, so that the heat exchange medium, e.g., secondary reforming products of the process fluid removed from the process fluid removal zone, flows from the heat exchange zone through the interstitial space between the seal tube and the inner tube, through said passages in the wall of the inner tube, and into the low pressure region. Downstream of the low pressure region, the process fluid expands in an expansion region providing a higher process fluid pressure than the low pressure region. As a result, it is also possible for the process fluid to flow back or recirculate from the outlet end of the inner tube, through the interstitial space, into the passages, and into the low pressure region.

[0031] The tube seal device is preferably provided at the boundary means between the heat exchange zone and the process fluid withdrawal zone. Thus, the seal tube is preferably fixed to the boundary means, while one or more heat exchange tubes, including the inner tube, are fixed to the boundary means between the process fluid inlet zone and the heat exchange zone, for example to a tube sheet. In this configuration, the inner tube is formed at the end of the heat exchange tube adjacent to the boundary means between the heat exchange zone and the process fluid withdrawal zone, and thus engages with the seal tube at this boundary means to form the tube seal device. This is particularly preferred when the process fluid undergoes a substantial pressure drop when passing through the heat exchange tube, for example when the heat exchange tube contains a catalyst. The seal tube may protrude from the boundary means into the heat exchange zone, or may extend from the boundary means back into the process fluid withdrawal zone on the opposite side of the boundary means.

[0032] In steam reforming, the hydrocarbon feedstock is typically a methane-containing gas. During the reforming process, methane reacts with steam to produce hydrogen and carbon oxides. Any hydrocarbons present containing two or more carbon atoms are converted to methane, carbon monoxide, and hydrogen. The steam reforming reaction takes place in tubes over a steam reforming catalyst at temperatures above 350°C, and typically the process fluids leaving the tubes are at temperatures in the range of 650-950°C. The heat exchange medium flowing on the outside of the tubes may have a temperature in the range of 500-2000°C.

[0033] The present apparatus and process can be used as part of a process for the production of hydrogen, methanol, dimethyl ether, olefins, ammonia, urea, or hydrocarbon liquids (e.g. diesel fuel) obtained by Fischer-Tropsch synthesis. Thus, the reformed gas mixture obtained using the apparatus of the present invention or in the process of the present invention may be subjected to further process steps, including steps of hydrogen separation, methanol synthesis, dimethyl ether synthesis, olefin synthesis, ammonia synthesis, or hydrocarbon liquid synthesis. Known processes can be used to achieve these steps.

[0034] Although described above primarily with respect to heat exchange steam reforming, it will be appreciated that the invention is also useful in other heat exchange applications where significant thermal expansion differences must be accommodated and leakage of the heat exchange medium into the process fluid is undesirable. Examples include feed / effluent heat exchangers where the feed to a process step, such as an exothermic reaction, e.g., methanol or ammonia synthesis, is heated by heat exchange with an effluent from the process step. In such cases, the heat exchange tubes may not contain a catalyst, unless it is desired that a catalytic reaction be performed on the process fluid while it is undergoing heat exchange, as in the reforming process described above. [Brief description of the drawings]

[0035] The invention is further explained by reference to the accompanying drawings.

[0036] [Figure 1] 1 is a schematic cross-sectional view of a heat exchange reactor including a tube sealing device according to one embodiment of the present invention, where the boundary means is a tube sheet. [Diagram 2] 1 is a cross-sectional view of a tube sealing device according to one embodiment of the present invention.

[0037] 1 shows a heat exchange steam reformer having an outer insulated pressure shell 10 enclosing three zones 11, 12, 13 defined by shell walls and tube sheets 14 and 15. Zone 11, a process fluid supply zone, is defined by shell walls 10 and tube sheet 14. Zone 11 is provided with a process fluid supply conduit 16 and has a plurality of vertical tubes 17 fixed to and extending downwardly from tube sheet 14. The number of tubes employed depends on the scale of operation and although only five tubes are shown, there may typically be 50 or more such tubes. Tubes 17 are filled with steam reforming catalyst 18, for example perforated cylindrical pellets of refractory oxide supported nickel catalyst and / or structured steam reforming catalyst. Zone 12, a heat exchange zone, is defined by shell walls 10 and tube sheets 14 and 15. Heat exchange tubes 17 extend through heat exchange zone 12 and engage tube seal device 20. The tube seal devices 20 each comprise a seal tube 21 fixed to the tube sheet 15 and engage with a catalyst-free inner tube portion 22 extending from the bottom of the catalyst-filled tubes 17 in the heat exchange zone 12. The heat exchange zone 12 is supplied with a heating medium, e.g., synthesis gas produced by autothermal reforming or secondary reforming, via a conduit 23 located within the shell 10 near the bottom of the tubes 17. The heating medium passes upwardly through the heat exchange zone exchanging heat with the tubes 17 and is then removed from the heat exchange zone 12 via a conduit 24 located within the shell 10 near the top of the tubes 17. A transverse baffle 25 serves to redirect the heating medium horizontally across the reformer to enhance heat exchange with the tubes 17. A process fluid withdrawal zone, zone 13, is defined by the walls of the shell 10 and the tube sheet 15. The tube seal devices 20 are open ended and extend through the tube sheet 15 into the withdrawal zone 13. The reformed gas passes from tube 17 through tube seal device 20 into withdrawal zone 13 from where it is removed by process fluid withdrawal conduit 26 .

[0038] In use, a process fluid comprising hydrocarbons and steam is fed at high temperature and pressure through conduit 16 to process fluid feed zone 11 and from there down through catalyst-filled tube 17. It is heat exchanged with a heat carrier in heat exchange zone 12, where the steam reforming reaction takes place. The gas mixture undergoing reforming passes through tube 17 and from there through tube seal device 20 to withdrawal zone 13, from where it is removed by withdrawal conduit 26. The reformed gas recovered from withdrawal conduit 26 is subjected to further processing, in particular being heated by autothermal reforming or secondary reforming, and the further processed gas is sent as heat exchange medium via conduit 23 to the heat exchange reformer. The pressure of the heat exchange medium fed through conduit 23 is lower than the gas passing through tube 17.

[0039] In Fig. 2, a tube seal device 20 is shown oriented vertically and arranged for downward flow through the device according to the embodiment shown in Fig. 1. The tube seal device 20 comprises an outer seal tube 21 and an inner tube 22. The inner tube 21 is located inside the seal tube 22 to provide an overlap area and is free to slide vertically. In use, the inner tube 22 is fixed to the bottom 30 of the heat exchange tube. The junction of the bottom 30 of the heat exchange tube and the inner tube 22 has an inner diameter of 25 mm and does not contain catalyst. The inner tube 22 tapers from an inner diameter of 25 mm to a constriction 31 with an inner diameter of 12 mm and expands from the constriction 31 to a low pressure region 32 with an inner diameter of 18 mm and a length of 108 mm. The inner tube expands from a diameter of 18 mm in the low pressure region 32 to an outer diameter of 31 mm in the expansion region 33 over a length of 78 mm. Twelve passages 34, each having a diameter of 3 mm, are provided between the low pressure region 32 downstream of the narrowed portion 31 and an annular gap 35 between the inner surface of the seal pipe 21 and the outer surface of the inner pipe 22. The thickness of the annular gap 35 between the seal pipe 21 and the outer surface of the inner pipe 22 is 0.2 mm.

[0040] The seal tube 21 includes seven parallel 7 mm wide square cut grooves 36 cut into the inner surface of the seal tube 21 facing the inner tube 22 at the overlap region. The grooves extend from a location in the low pressure region 32 adjacent the passage 34 upwardly towards and beyond where the inner tube 22 is connected to the lowermost portion 30 of the heat exchange tube. It will be appreciated that providing the grooves in this manner allows for many more grooves to be present than if the grooves were cut on the outer surface of the inner tube 22.

[0041] In this embodiment, six further parallel 7 mm wide right angle cut grooves 37 are cut into the outer surface of the inner tube 22 from adjacent the passages 34 downward towards the expansion region 33 .

[0042] The length of the inner tube 22 and the seal tube 21 are such that at start-up, i.e., both when the device is at ambient temperature and when it is at normal operating temperature, the passage 34 and the open end of the inner tube 22 are within the seal tube 21.

[0043] A flange 38 is provided at the bottom of the seal tube 21 beyond the end of the overlap region to enable the tube seal device 20 to be secured to the tubesheet.

Claims

1. 1. A tube sealing device suitable for use in a heat exchange reactor comprising one or more tubes, the tube sealing device comprising: a seal tube; and an inner tube disposed within the seal tube to provide an overlap region, the inner tube having within the overlap region: (i) an internal constriction of reduced cross-sectional area forming a low pressure region; (ii) an expansion region adjacent the constriction, the expansion region having a cross-sectional area greater than a cross-sectional area of ​​the constriction; and (iii) one or more passages through a wall of the inner tube connecting the low pressure region to an exterior of the inner tube; the tube sealing device further comprising one or more grooves arranged to impede the flow of gas through the tube sealing device, the one or more grooves being formed around an inner surface of the seal tube in the overlap region corresponding to the low pressure region of the inner tube.

2. The pipe sealing device of claim 1 , wherein one or more grooves are additionally provided in the overlap region corresponding to the expansion region (33) of the inner pipe (22).

3. 3. The pipe sealing device of claim 2, wherein the one or more grooves in the expansion region are provided on an outer surface of the inner pipe (22) or on the inner surface of the sealing pipe (21), preferably on the outer surface of the inner pipe.

4. The pipe sealing device according to any one of claims 1 to 3, comprising 1 to 30 grooves, preferably 5 to 20 grooves, located on the sealing pipe (21) in the overlap region corresponding to the low pressure region (32) of the inner pipe (22).

5. The pipe sealing device of any one of claims 1 to 4, wherein the one or more grooves (36) have a square or rectangular configuration, or are U-shaped, V-shaped, or any combination thereof.

6. A heat exchange reactor comprising one or more heat exchange tubes (17) comprising a tube sealing device according to any one of claims 1 to 5.

7. 7. The heat exchange reactor of claim 6, comprising a process fluid supply zone (11), a heat exchange zone (12), and a process fluid withdrawal zone (13), first and second boundary means (14) separating said zones from one another, one or more heat exchange tubes (17) fixed to one of said boundary means and extending through said heat exchange zones, and a tube sealing device (20) for each heat exchange tube, said tube sealing device comprising a seal tube (21) and an inner tube (22), said seal tube of said tube sealing device fixed to one of said boundary means and disposed substantially coaxially with said inner tube such that said inner tube is in sliding engagement with its associated seal tube thereby forming an overlap region.

8. 8. The heat exchange reactor of claim 7, wherein the heat exchange tubes contain a steam reforming catalyst.

9. 9. The heat exchange reactor according to claim 7 or 8, wherein the pipe sealing device is fixed to the boundary means (15) between the heat exchange zone (12) and the withdrawal zone (13).

10. 10. A heat exchange reactor according to claim 8 or 9 in the form of a heat exchange steam reformer operatively connected to partial combustion means designed to effect partial combustion of the process fluid after it has passed through the tubes and to supply the partially combusted gas to the heat exchange steam reformer as a heat exchange medium.

11. 11. The heat exchange reactor of claim 10, wherein the partial combustion means comprises a reforming catalyst bed through which the partially burned gas passes before being supplied to the heat exchange reformer as the heat exchange medium.

12. 1. A process comprising: (a) feeding a process fluid to a heat exchange reactor having a process fluid feed zone (11) separated from a heat exchange zone (12) by a boundary means (14); (b) passing the process fluid from the process fluid feed zone through one or more heat exchange tubes (17) extending through the heat exchange zone, the process fluid being subjected to heat exchange with a heat exchange medium at a lower pressure than the process fluid passing through the tubes in the heat exchange zone; (c) directing the process fluid from the heat exchange tubes to a process fluid withdrawal zone (13) separated from the heat exchange zone by a second boundary means (15); (d) subjecting the process fluid from the process fluid withdrawal zone to further processing steps; and (e) passing the resulting treated process fluid as the heat exchange medium through the heat exchange zone (12), wherein each of the one or more heat exchange tubes (17) is one of the boundary means. and an inner pipe (22) connected to each of the heat exchange tubes and disposed within the seal tube to provide an overlap region, the inner pipe having within the overlap region: (i) an internal constriction of reduced cross-sectional area forming a low pressure region (32); (ii) an expansion region (33) of greater cross-sectional area than a cross-sectional area of ​​the constriction downstream in a flow direction of the process fluid of the low pressure region; and (iii) one or more passages (34) through the wall of the inner pipe connecting the low pressure region to the exterior of the inner pipe, the pipe seal device including one or more grooves (36) arranged to impede the flow of gas through the pipe seal device, the one or more grooves being formed around an inner surface of the seal pipe (21) in the overlap region corresponding to the low pressure region of the inner pipe.

13. 13. The process of claim 12, wherein the heat exchange reactor comprises a heat exchange reformer including one or more externally heated tubes including a steam reforming catalyst through which a reformer feed is passed to produce synthesis gas, and the heat exchange medium used to heat the tubes is at a lower pressure than the reformer feed.

14. 14. The process of claim 13, wherein the heat exchange steam reformer is operatively connected to partial combustion means designed to effect partial combustion of the process fluid after it has passed through the tubes and to supply the gas after said partial combustion to the heat exchange steam reformer as a heat exchange medium.

15. 15. The process of claim 14, wherein the partial combustion means comprises a reforming catalyst bed through which the partially burned gas passes before being supplied to the heat exchange reformer as the heat exchange medium.

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