MXPA97006722A - Heat exchange apparatus and proc - Google Patents

Abstract

The present invention relates to heat exchange apparatus, which includes a process fluid feed zone, a heat exchange zone and a process fluid discharge zone, first and second boundary means separating such zones a on the other, a plurality of heat exchange tubes attached to one of the boundary means and extending through the heat exchange zone, whereby the process fluid can flow from the process fluid feed zone , through the heat exchange tubes and to the process fluid discharge zone and for each heat exchange tube, one seal tube attached to the other medium of the limit means, each seal tube attached to the other means of the limit means, each seal tube being arranged substantially coaxial with its associated heat exchange tube, so that each seal tube is in sliding engagement with its exchange tube. or associated heat, thereby defining an overlapping region, wherein the heat exchange and the seal tubes overlap each other, whereby the thermal expansion of the heat exchange tubes can be accommodated within the overlapping region characterized in that the The inner tube of the heat exchange tube and its associated seal tube is provided with an inner constriction of the reduced transverse area forming a low pressure region, a region of transverse area expansion greater than that of the downstream constriction, in the direction of the flow of process fluid, from the low pressure region, and one or more passages through the inner tube wall connecting the low pressure region to the outside of the inner tube, the passages being located within the overlap region, thus providing a path of flow for the fluid from the heat exchange zone through the overlapping region towards the region e low pressure inside the inter tube

Description

HEAT EXCHANGE AND PROCESSING APPARATUS DESCRIPTION OF THE INVENTION This invention relates to a heat exchange and process apparatus and in particular to a process and apparatus in which a significant differential thermal expansion can exist between tubes carrying a process fluid and media, such as a tube sheet, defining a boundary of the zone through which a heat exchange medium passes in the heat exchanger with the process fluid passing through the tubes. In a heat exchanger of the above type, a process fluid is passed from a process fluid supply zone, through heat exchange tubes disposed within a heat exchange zone defined by a cover to through which passes a heat exchange medium, and then into a discharge zone of process fluid. Means, such as tube sheets, are provided to separate the zones. In this way, a tube sheet can separate the heat exchange zone through which the heat exchange medium of a zone, such as a plenum chamber, passes, communicating with the interior of the heat exchange tubes. to allow the supply of process fluid to the tubes or the discharge of the process fluid from the tubes. An alternative arrangement involves the use of collector pipes arranged within the heat exchange zone to define the process fluid feed zone: the process fluid is fed to the collector pipes from where it flows into and through the exchange tubes of heat. Similarly, the collecting pipes can be provided for the discharge of the process fluid from the pipes. Alternatively, there may be a combination of tube sheets and collecting pipes, for example, the process fluid may be fed into the heat exchange tubes from a plenum chamber separated from the heat exchange zone through a sheet of heat. tube, while the collector pipes are provided disposed within the heat exchange zone for the discharge of the process fluid from the tubes. Such tube or collector sheets herein are referred to as limit means since they define boundaries between the heat exchange zone and the process fluid supply and the discharge zones. In some applications, such as reforming hydrocarbon vapor, the heat exchange tubes are of considerable length, typically several meters, and there is a large temperature difference, usually several hundred ° C, for example 500 to 1000 ° C or more, between the cold, ie the ambient state and the normal process operation. As a result, the tubes are longitudinally expanded by a considerable amount, usually 10 cm or more, relative to the cover to which the limit means are attached. The normal practice is to provide tabs at one or both ends of the tubes to allow for such differential expansion, so that the tabs, instead of the tubes themselves are attached to the limit means. Alternatively, bellows arrangements are usually employed to allow such expansion. However, tails or bellows arrangements capable of adapting to differential expansion of the order of 10 cm or more present practical difficulties. In some types of heat exchange apparatus, the heat exchange medium is the process fluid that has passed through the tubes, but which has been subjected to an additional process before being used as the medium for exchange of heat. hot. For example, the tubes can be filled with a steam reforming catalyst and a hydrocarbon supply material mixed with the steam is passed through the tubes; the latter are heated through a heat exchange medium to supply the heat necessary for the endothermic primary steam reforming reaction to give a primary reformed gas. The resulting primary reformed gas after being subjected to partial oxidation, wherein the primary reformed gas is partially combusted with oxygen or air and, in some cases, the process known as secondary reforming, is then passed through a bed of secondary reforming catalyst. The resulting partially combusted gas, w term includes secondary reformed gas, is then used as the heat exchange medium to heat the tubes. An example of this type of process and heat exchange apparatus for effecting primary reformation is described in GB 1 578 270. In a modification of this type of process, the limit means at the outlet end of the exchange tubes of heat are omitted. The tubes open towards an area in w a gas such as air or oxygen is introduced, so that partial combustion of the primary reformed gas occurs and the resulting partially combustion gas passes back to the tubes by heating the latter. Examples of this type of process and apparatus are described in US 2 579 843, US 4 919 844 and GB 2 181 740. Since this type of arrangement avoids the problems associated with the differential thermal expansion of the tubes, nevertheless , presents problems where it is desired to pass the partially combustion gas through a bed of secondary reforming catalyst before using the partially combustion gas to heat the tubes. Proposals have also been made, for example in US 4 337 170 and US 5 264 202, to use this type of reformer, wherein the heat exchange tubes are "open at the ends" at the outlet end, So that the reformed gas coming out of the tubes is in communication with the heat exchange zone, to effect the reformation of a supply material by passing the supply material, and steam through the tubes, w are heated by the primary reformed gas produced in a conventional reformer. The US Pat. No. 4,337,170 mentioned above also suggests that the primary reformed gas of the conventional reformer may be subjected to secondary reforming before being mixed with the gas emanating from the tubes of the heat exchange reformer and used as the heating medium. . In the present invention, these problems are overcome by providing boundary means with seal tubes, w are coupled with the heat exchange tubes, but to w they are not fastened, so that the seal tubes provide a positional location for Heat exchange tubes, while allowing sliding movement between heat exchange seal tubes to adapt to differential expansion. However, there is inevitably a leakage path between the zones on both sides of the limit means, through the gap spaces between the seal tubes and the heat exchange tubes necessarily provided to allow such sliding movement. Due to the high temperatures normally encountered during use, the provision of a leak-proof, sliding seal, for example, gas-tight, for this gap of clear presents problems. The leakage path allows the process fluid, for example, the primary reformed gas, to pass to the heat exchange medium, for example partially combustion gas, or vice versa. The direction of the leak will, of course, depend on the relative pressures of the process fluid and heat exchange medium. Generally, when the heat exchange medium is the product of further processing of the process fluid, the process fluid will be at a higher pressure than the heat exchange medium, for example as a result of pressure drops encountered during the passage. of the process fluid through additional processing before being used as the heat exchange medium. This means that the predominant leakage will be from the process fluid to the heat exchange medium, which means that some of the process fluid will be derived from the additional processing. Such derivation of the additional processing is generally undesired. Thus, when the process gas is the primary steam product by reforming a hydrocarbon supply material into the tubes, the methane content of the primary reformed process gas is typically 10% or more by volume, while the product secondary steam reforming the primary reformed gas typically has a methane content of less than 1%, usually less than 0.5% by volume. If 5% of the process gas leaks into the heat exchange zone, ie, is diverted to the secondary reforming stage, the resulting mixture of the secondary reformed gas and the leaked primary reformed gas could have a methane content typically of double that of the secondary reformed gas. Not only does this mean that a significant amount of methane has not been reformed, but also this "sliding" methane generally acts as an inert gas in subsequent processes such as ammonia synthesis, thus making the latter less efficient. An arrangement has been advised in which, although the heat exchange is at a slightly lower pressure than the process fluid exiting the tubes, the predominant leakage is from the heat exchange medium into the process.

According to the present invention, there is provided a heat exchange apparatus which includes a process fluid feed zone, a heat exchange zone and a process fluid discharge zone, first and second boundary means separating such zones between them, a plurality of heat exchange tubes attached to one of the boundary means and extending through the heat exchange zone, whereby the process fluid can flow from the process fluid feed zone , through the heat exchange tubes and to the process fluid discharge zone, and for each heat exchange tube, one seal tube attached to the other of the limit means, each seal tube being substantially disposed and coaxially with its associated heat exchange tube, so that each seal tube is in sliding engagement with its associated heat exchange tube, thereby defining a translucent region. Apparent, where the heat exchange and the seal tubes overlap each other, so that the thermal expansion of the heat exchange tubes can be adapted within the overlapping region, the inner tube of the heat exchange tube and its associated seal tube being provided with an inner constriction of reduced cross-sectional area forming a low pressure region downstream, in the direction of the flow of such process fluid, of the constriction, a region of expansion of cross-sectional area greater than that of the constriction downstream thereof, and one or more passages through the wall of the inner tube connecting the low pressure region to the outside of the inner tube, the passages being located within the overlapping region, thus providing a path of flow for the fluid from the heat exchange zone through the overlapping region to the low pressure region within the tube internal The invention also provides a process in which a process fluid is subjected to a processing step comprising the feeding of a process fluid to a process fluid supply zone separated from the heat exchange zone by means of of limit, to pass such process fluid from the process fluid feed zone, through a plurality of heat exchange tubes that extend through the heat exchange zone, in which the process fluid is subjected to heat exchange with a heat exchanger medium in the heat exchange zone, by passing the process fluid from the heat exchange tubes to a process fluid discharge zone separated from the heat exchange zone through second limit means, by subjecting the process fluid from the process fluid discharge zone to the desired processing step, and by passing the fluid of p processed process resulting through the heat exchange zone as the heat exchange medium, the heat exchange tubes being fastened to one of the limit means and, for each heat exchange tube, a tube of heat exchange is provided. seal attached to the other of the limit means, each seal tube being disposed substantially coaxially with its associated heat exchange tube, so that the seal tube is in sliding engagement with its associated heat exchange tube, thereby defining an overlapping region, where the heat exchange and the seal tubes overlap each other, so that the thermal expansion of the heat exchange tubes can be adapted within the overlapping region, the inner tube of the exchange tube of heat and its associated seal tube being provided with an inner constriction of reduced cross-sectional area forming a low pressure region downstream, in the of the process fluid flow, of such constrictionK. , a region of transverse area greater than that of the constriction downstream thereof, and one or more passages through the wall of the inner tube connecting such low pressure region to the outside of the inner tube, the passages being located within the overlapping region thus providing a flow path for the fluid from the heat exchange zone through the overlapping region to the low pressure region within the inner tube, the process is operated in such a way that the pressure of the process fluid Processed feed to the heat exchange zone is greater than the pressure in the low pressure region, so part of the processed process fluid fed into the heat exchange zone, passes through the clear space and the passages towards the region of low pressure. The process and the apparatus are of particular utility for reforming through steam, hydrocarbons, in which a mixture of hydrocarbon and steam supply material is passed through a heat exchange tube, which contain a reforming catalyst steam in order to form a primary reformed gas, which is then subjected to a partial combustion with a gas containing oxygen, for example, air, and the resulting partially combustion gas is used as the heating fluid in the area of heat exchange. Preferably, the partially combustion gas is passed through a bed of a secondary reforming catalyst, in order to effect further reformation, before being used as the heat exchange fluid. As a result of the constriction of one of the inner heat exchange and seal tubes, a low pressure region is formed within the inner tube downstream of the constriction: appropriately dimensioning the constriction, the pressure in the low pressure region, when it is in normal operation, it can be made lower than the pressure in the heat exchange zone, so that there is a flow of heat exchange medium, for example, the product of the secondary reformation of the process fluid taken from the area of discharge of process fluid, of the zone of heat exchange through the clear space and through the passages to the region of low pressure. Downstream of the low pressure region, the process fluid expands in the expansion region giving a process fluid pressure greater than that in the low pressure region. Consequently, there will also be a backflow, or recirculation, of process fluid from the outlet end of the inner tube, through the clear space, into the passages and into the low pressure region. The seal of preference is provided in the boundary means between the heat exchange zone and the process fluid discharge zone. In this way, the seal tubes are attached to the limit means, while the heat exchange tubes are attached to the limit means, for example, the tube sheet, between the process fluid inlet zone and the zone of heat exchange. This is particularly preferred when the heat exchange medium is the result of further processing of the process fluid from the process fluid discharge zone and the process fluid undergoes a substantial pressure drop as it passes through the tubes of heat exchange, for example, where the latter contains a catalyst: in such cases, it may be difficult to provide the pressure reduction given by the constriction to that exceeded from the pressure drop encountered as the process fluid passes through through the heat exchange tubes plus any pressure drop that the process fluid undergoes during further processing before it is employed as the heat exchange medium. However, providing the seal in the boundary media between the process fluid inlet zone and the heat exchange zone, may have advantages in some cases. For example, when the process fluid undergoes a chemical reaction as it passes through the heat exchange tubes, the process fluid at the inlet end of the heat exchange tubes may have a different density allowing it to obtain a greater reduction of pressure through the constriction and / or the composition may be such that the process fluid is less corrosive at the inlet end of the heat exchange tubes. In addition, the temperature at the inlet end of the heat exchange tubes may be lower, so that the seal is operating at lower temperatures. The seal tubes can be arranged so that the heat exchange tubes slide inside the seal tubes; in such a case, the heat exchange tubes are the internal tubes and have the constriction inside them. In this case, the seal tubes can be projected towards the heat exchange zone of the boundary means or they can extend from the boundary means towards the zone, i.e. the process fluid inlet or the discharge zone, over the other side of the limit means. The heat exchange tubes can extend from the limit means to which they are fastened, through the heat exchange zone, and through the seal tubes attached to the other limit means, and can be projected towards the area , that is, the process fluid inlet or the discharge zone, on the other side of the limit means to which the seal tubes are attached. Alternatively, the seal tubes may be arranged so that they slide inside the heat exchange tubes. In this case, the seal tubes are the internal tubes and have the constriction inside them. In this case, the seal tubes extend towards the heat exchange zone from the limit means to which they are fastened.

Various embodiments of the invention are illustrated with reference to the accompanying drawings in which Figure 1 is a diagrammatic cross section of a heat exchange apparatus according to a first embodiment of the invention, wherein the limit means are sheets of tube, Figure 2 is a cross section of the lower end of one of the tubes of the first embodiment, showing the associated tube sheet and the seal tube, and Figure 3 is a diagrammatic cross-sectional view, similar to the Figure 1, but of a second embodiment, in which the limit means carrying the seal tubes are a collector. Figures 4 to 6 are diagrammatic cross sections of several alternative seal arrangements. In Figure 1, there is shown a heat exchange apparatus, such as a heat exchange reformer, having an external insulated pressure cuirass 10 enclosing four zones 11, 12, 13, 14 defined by the walls of the shell and the tube sheets 15, 16, 17. The zone 11, a process fluid supply zone, is defined by the walls of the shell and the tube sheet 15, and is provided with a supply supply conduit 18. and has a plurality of heat exchange tubes, for example, reforming tubes, 19, fastened to and extending downward from the tube sheet 15. The number of tubes used will depend on the scale of operation: although only five tubes are shown in Figure 1, there can typically be 50 or more such tubes. For steam reforming, the tubes 19 will be filled with a suitable steam reforming catalyst, for example nickel on a support of a refractory material such as alumina, zirconia or a calcium aluminate cement. The reforming catalyst is usually in the form of randomly configured units packed in the tubes. Typically, the configured units have a maximum dimension of less than about one fifth of the diameter of the reforming tube and may be in the form of cylinders having a passage, or preferably more than one passage, extending longitudinally through the cylinder. Zone 12, a zone for discharging heat exchange medium, forms the second part, smaller than the heat exchange zone, and is defined by the walls of the shell and the tube sheets 15 and 16. The tubes of heat exchange 19 extend through the zone 12 and through the tube sheet 16. Each tube 19 is provided with a surrounding annular sleeve 20, fastened to and extending downwardly from the tube sheet 16. The inside of the sleeves 20 communicates with the zone 12, so that the heat exchange medium passing into the space between the inner wall of the sleeve 20 and the outer wall of the tube 19 associated with that sleeve, can pass into the zone 12. The zone 12 is also provided with an outlet conduit 21 of heat exchange medium. The zone 13 is the first, larger part of the heat exchange zone and is limited by the walls of the shell 10 and the tube sheets 16 and 17. An inlet conduit 22 of heat exchange medium is provided in the lower end of the zone 13. The tubes 19 extend through the zone 13 and through the tube sheet 17 at the lower end of the zone 13. Each sleeve 20 is open at its lower end and ends towards the end bottom of the zone 13, so that the heat exchange fluid supplied to the zone 13 through the conduit 22 can enter the annular space between the inner surface of the sleeve 20 and the external surface of the tube 19 associated therewith. The tubes 19 each have a portion 23 of reduced cross section at the lower ends below the sleeves 20 and passing through the tube sheet 17. The area 14, the discharge zone of process fluid, is defined by the walls of the shell 10 and the tube sheet 17, and is provided with a process fluid outlet conduit 24. The lower portions 23 of the tubes 19 pass through the tube sheet 17 and are open at their lower ends 25 (see Figure 2) thus allowing the process fluid from the tubes 19 to pass into the zone 14 and from this Thus, it can be seen that, considering the two portions 12, 13 of the heat exchange zone as an individual heat exchange zone, the process fluid inlet zone 11 it is separated from the heat exchange zone through the tube sheet 15 by forming the limit means to which the heat exchange tubes 19 are clamped, and the heat exchange zone is separated from the discharge zone of the heat exchanger. process fluid 14 through the tube sheet 17 through which the ends of the heat exchange tubes 19 pass. As shown in Figure 2, the lower portions 23 of the tubes 19 are not attached to the T sheet ubo 17. So that the thermal expansion of the heat exchange tubes 19 relative to the shell 10 can be adapted, each tube portion 23 extends towards a seal tube 26 attached to the tube sheet 17 and extending towards the region 14. The portion 23 of the tube 19 extending towards the seal tube 26 forms an overlap region having a small gap of clear 27 between the outer surface 28 of the lower portion 23 of the tubes 19 and the inner surface 29 of the seal tube 26 associated therewith. Typically, this clear is of the order of 0.05 to 3 mm. Within the overlapping region, where the tube portion 23 is inside the seal tube 26, the interior of the lower portion 23 of the tube 19 has a conical section 30 leading to a cylindrical constriction region 31 of cross sectional area reduced. Typically, the cross-sectional area of this constriction region 31 is approximately 15-50% of the cross-sectional area of the lower portion 23 of the tubes 19. Downstream of the constriction region 31 a cylindrical low pressure region 32 of a transverse area greater than that of the constriction region, but smaller than that of the lower portion 23 of the tubes 19. The lower portion 23 of the tubes 19 terminates in an internally enlarged region 33. Within the overlap region, passages 34 are provided through the wall of the lower portion 23 of the tubes 19, communicating with the low pressure region 32 downstream of the constriction region 31. Providing the process fluid pressure that flows from the tubes 19 at the entrance of the conical region 30 is not too much greater than the pressure of the heat exchange medium entering the zone 13 through the conduit 22, through the proper selection of the dimensions of the region of constriction 31 and the low pressure region 32, it is possible to provide that, in normal operation, the pressure in the low pressure region 32 resulting from the process fluid flow through the constriction region 31 to the low region pressure 32, is less than the pressure of the heat exchange medium entering the heat exchange zone 13 via the conduit 22. Consequently, there will be a flow of the exchange medium of heat from the zone 13, through the gap 27 in the overlap region and through the passages 34, into the region of low pressure 32. The pressure at the outlet end 25 of the heat exchange tubes 19 also will be greater than that in the low pressure region 32, and there will also be a recirculation flow of process fluid from the outlet end of the heat exchange tube 19 through the gap 27 and the passages 34 to the region of low pressure 32. It will be appreciated that since the heat exchange medium is allowed to leak past the tube sheet 17 into the low pressure region, rather a narrow gap gap is provided between the seal tube 26 and the lower portion 23 of the heat exchange tube 19, a larger gap can be employed with a simple mechanical seal allowing sliding movement. The failure of the seal will thus allow the flow of the heat exchange medium beyond the seal to the low pressure region 32. In this way, an adequate packing allowing the sliding movement at the upper end of the seal tube 26 can be provided. in the gap 27 between the outer walls 28 of the lower portion 23 of the tube 19 and the inner wall of the seal tube 26 to further reduce the leakage of the heat exchange medium from the zone 13 to the area 14. that it is not essential that the heat exchange tubes 19 have lower portions 23 of reduced cross section, ie the tubes 19 can be of a total cross section over the passage through the tube sheet 17 with the seal tubes 26 appropriately dimensioned, the provision of a lower portion 23 of reduced cross section facilitates the design and construction of "leakage" trajectories. In an alternative arrangement, the sleeves 20 and the tube sheet 16 are omitted so that the heat exchange zone is not divided into a larger heat exchange portion and a lower heat exchange medium outlet portion, but it is simply a single zone through which the heat exchange medium flows from the inlet conduit 22 and exits through the outlet conduit 21. In the embodiment of Figure 3, the lower pipe sheet 17, the zone of Process fluid discharge 14 and process fluid outlet conduit 24 of Figure 1, are replaced by a series of collection pipes 35 connected to an output conduit 36 of process fluid extending through the wall of the container. The heat exchange medium enters the container at the lower end through the conduit 22 and passes, through the spaces between the adjacent collector pipes 35 and beyond the lower ends of the pipes 19, towards the sleeves 20. Seal tubes 26 are fastened to the collection pipes 35 and extend upwards from the collection pipes 35 to the heat exchange zone 13. The seal arrangement is similar to that in Figure 2 except that, as mentioned in above, the tube sheet 17 is omitted and the seal tubes 26 extend upwardly from the collection pipes 35. Figures 4, 5 and 6 show alternative arrangements with the seal at the upper end of the process fluid feed of the heat exchange tubes. The direction of flow of process fluid is indicated by the arrow A. In these arrangements, not shown in Figures 4 to 6, the heat exchange tubes 19 are attached to the limit means, for example, a tube sheet or collector pipes, separating the heat exchange zone from the process fluid discharge zone. In the embodiments of Figures 4 and 5, the seal tubes 37 are attached to the tube sheet 15 forming the boundary means between the input zone 11 of process fluid of the second smaller portion 12 of the exchange zone of hot. In Figure 4, the seal tubes extend downward from the tube sheet 15 to the portion 12 of the heat exchange zone, while in Figure 5, the seal tubes extend from the tube sheet 15. to the inlet zone 11 of process fluid. In the arrangement of Figure 6, the seal tube 37 is disposed within the upper end of the heat exchange tube 19. In each of these arrangements, the interior of the inner tube, i.e. the heat exchange tube 19 in Figures 4 and 5, and seal tube 37 in Figure 6, is provided with a constriction, a low pressure region, a region of expansion, and passages through the inner tube walls in a manner similar to that described in the foregoing with respect to Figure 2. In these arrangements, the heat exchange medium may flow from the portion of the zone. of heat exchange 12 through the gap of clear between the heat exchange tube 19 and the seal tube 37, through the passages to the region of low pressure downstream of the constriction within the interior of one of the tubes . In an example calculated using the embodiment of Figures 1 and 2, a natural gas is desulfurized by the addition of a small proportion of a hydrogen / nitrogen mixture recovered from the ammonia purge gas and passed through a bed of a hydrodesulfurization catalyst and a bed of a zinc oxide acting as an absorbent for hydrogen sulfide. Steam is added and the resulting mixture (stream A), preheated to 406 ° C, is fed to the process fluid feed zone 11 of a reformer through line 18 and primary reformed in heat exchange tubes 19 of an internal diameter of 125 mm and a length of 10 m, containing a steam reforming catalyst randomly packed with nickel on a support of calcium aluminate cement in the form of cylinders with a length of 17.6 mm and a diameter of 14.0 mm, which has four axially extended cylindrical passages with a diameter of 4.0 mm. The catalyst was supported on a restriction grid placed at the upper end of the transition region, where the reforming tubes were reduced in diameter to form the lower portions 23, so that the lower portions 23, which have a diameter internal 25 mm, were free of catalyst. The temperature and pressure of the reformed process gas (stream B) entering the lower portion 23 of the reformer tubes 19, were 722 ° C and 40.0 absolute bars, respectively. The resulting reformed gas was passed through the constriction region 31 and the low pressure region 32, giving an increase in pressure of 38.6 bars absolute, in the region of low pressure and a pressure of 39.3 absolute bars at the end of outlet 25 of the tubes 19. As described in the following, there is a leakage current C of gas from the heat exchange zone 13 to the discharge zone 14 of process fluid through the passages 34 and the region low pressure 32. The reformed process gas (stream D) consisting of stream B plus leakage current C, was then fed via conduit 24 to a secondary reformer, where it was subjected to partial combustion with a stream of air E, which was preheated to 650 ° C, and subjected to secondary reformation by passing the partially combustion mixture through a randomly packed bed of a secondary secondary reformer catalyst. l supported on calcium aluminate cement cylinders. The secondary reforming catalyst cylinders had a length of 17.6 mm, a diameter of 14.0 mm and had four cylindrical axially extending passages with a diameter of 4.0 mm. The secondary reformed gas (stream F), at a pressure of 38.8 bars absolute, and at a temperature of 970 ° C was then fed to the zone 13 for heat exchange through line 22. The part (stream C) of the reformed gas secondary current F escape from zone 13 to zone 14 through passages 34 and low pressure regions 32, while the remainder (stream G) was used as the heat exchange medium by heating the exchange tubes of heat 19 as the stream G was passed through the annular space within the sleeves 20 to the zone 12. The temperature of the product gas (stream H) leaving the zone 12 through the conduit 21, was 530 ° C. The lower portion 23 of the tubes had an internal dimension of 25 mm, tapering towards a constriction region 31 of an internal diameter of 12 mm and expanding towards the region of low pressure 32 with an internal diameter of 18 mm and a length of 108 mm. The open end of the enlarged tube with a diameter of 18 mm from the low pressure region 32 to the outer diameter of 31 mm from the lower portion 23 of the tubes 19 with a length of 78 mm. Twelve recirculation passages 34 with a diameter of 3 mm were provided between the low pressure region 32 and the annular heat gap 27. The thickness of the annular gap 27 between the seal tubes 26 and the outer surface 28 of the portion lower 23 of tubes 19 was 0.2 mm. The length of the lower portions 23 of the tubes 19 and the seal tubes 26 was sufficient so that the recirculation passages 34 and the open ends 25 of the tubes 19 were inside the seal tubes 26 both from the start, is say, with the appliance at room temperature and at a normal operating temperature. It was calculated that, at the normal operating temperature, despite the pressure of the stream B at the inlet to the conical region 30 which was 1.2 bar above the pressure of the secondary reformed gas, stream F, which enters the zone 13, about 3% of the reformed process gas leaving the open ends 25 of the tubes 19 was recirculated through the gap 27 and the recirculation passages 34, and about 3% of the secondary reformed gas (stream F) ) which enters from zone 13, was also passed, as a leakage current C, through the tube sheet 17 towards the low pressure region 32 through the gap 27 and the passages 34. The speeds of flow (rounded almost 0.1 kmoles / h) of the components of the different currents, together with the temperatures and current pressures, are shown in the following Table I.

Table Flow rate (kmol / h). temperature (° C), and pressure (bar abs.) of the current A B C D E F G H CH, 560.0 428.2 0.5 428.7 0.0 15.5 15.0 15.0 C? 23.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C, H, 4.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C | H? A 3.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CO 0.0 69.3 12.6 8 0 0.0 421.1 408.5 408.5 CO, 3.0 137.3 6.5 143.9 0.4 218.3 211.8 211.8 H.O 1719.1 1381.1 45.4 1426.4 46 1511.8 1466.5 1466.5 H. 256.8 960.9 52.8 1013.7 0.0 1759.2 1706.5 1706.5 N: 113.5 113.5 36.2 149.7 1055.5 1205.2 1169.0 1169.0 or, 0.0 0.0 0.0 0.0 284.0 0.0 0.0 0.0 Ar 0.0 0.0 0.4 0.4 12.6 13.0 12.6 12.6 Tßmp. 406 722 970 732 650 970 970 530 I j Pressure | 43.7 40.0 38.8 39.3 40.0 38.8 38.8 38.3 In a calculated comparative example, it was assumed that the lower portion of the tubes 23 had no constriction region or low pressure region or no recirculation passage, but had a diameter of 25 mm, internal, for its entire length. The reformed gas leaving the end 25 of the tubes in this way was at a pressure of 40.0 bars absolute, so that the gas leak was from the area 14 of discharge of process fluid through the annular gap 27 towards zone 13 heat exchange. The flow rates (rounded to almost 0.1 kmoles / h) of the components of the different currents, together with the temperatures and current pressures, are shown in the following Table II.

Table II Flow rate (kmol h), temperature fC), and pressure (bar ata.) Of the current A? C 0 E F G H CH. 560.0 428.2 21.4 406.8 0.0 14.2 35.6 35.6 CzH, 23.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C.H, 4.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C < H10 32 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CO 0.0 69.3 3.5 65.9 0.0 388.1 391.6 391.6 C02 3.0 137.3 6.9 130.4 0.4 201.2 208.1 208.1 H, 0 1719.1 1381.1 69.1 1312.0 4.4 1393.7 1462.7 1462.7 H, 256.8 960.9 48.0 912.8 0.0 1620.8 1668.8 1666.8 N. 113.5 113.5 5.7 107.8 1003.9 1111.7 1117.4 1117.4 o. 0.0 0.0 0.0 0.0 270.1 0.0 0.0 0.0 Ar 0.0 0.0 0.0 0.0 12.0 12.0 12.0 1Z0 Temp. 406 722 722 722 650 970 961 515 Pressure 43.7 40.0 40.0 40.0 40.0 38.8 39.3 38.8 The above processes, involving primary and secondary air reforming, are designed to produce reformed gas for use in the production of ammonia. Since in an ammonia plant, the reformed gas is normally subjected to the exchange reaction, in which essentially all of the carbon monoxide reacts with steam to produce carbon dioxide and hydrogen, the amount of hydrogen that can be obtained (the hydrogen equivalent), which in turn determines the amount of ammonia that can be produced, is equal to the sum of the hydrogen and carbon monoxide contents of stream H. Due to leakage of gas from discharge zone 14 of process fluid to the heat exchange zone 13 in the case of comparison, the temperature of the gas used as the heat exchange medium is reduced. Also in the comparison of the flow rate to the secondary reformer is reduced and thus less air has to be used to obtain the outlet temperature of the secondary reformer. This in turn means that the amount of gas (stream F) leaving the secondary reformer is reduced, and thus, in spite of increasing, it is rather extinguished, by the leakage current C, the quantity of gas (stream G). ) available for use as the heat exchange medium is reduced. This reduction in quantity and temperature of the heat exchange medium, current F, means that in order to obtain the same amount of reformation in the heat exchange tubes 19, the temperature of the product gas, stream H, leaving the reformer through conduit 21 is smaller, thus reducing the amount of heat that has to be recovered from that gas stream. The salient points that emerge from the above comparison can be seen in the following Table III.

Table III Leakage from zone 13 Leakage from zone 14 to zone 14 to zone 13 (invention) (comparison) H2 equivalent of current H 2115.0 kmol / h 2060.4 kmol / h Methane content of the current H 0.3% 0.7% Total current flow D 3244.6 kmol / h 2935.8 kmol / h Air used 1357.2 kmol / h 1290.8 kmol / h Total current flow G 4989.8 kmol / h 4896.1 kmol / h Current temperature G 970 ° C 961 ° C Current temperature H 530 ° C 515 ° C As can be seen from Table III that the hydrogen equivalent, and therefore the potential production of ammonia, for the case of the invention is about 2.65% greater than the case of comparison. In addition, the amount of ammonia that can be produced also depends on the methane content of the reformed gas, since methane represents an inert material in the subsequent ammonia synthesis; an increase in the methane content of the reformed gas, as in the case of comparison, means that the amount of purge required in the subsequent ammonia synthesis circuit has to be increased, with the consequent reduction in the amount of ammonia produced. Consequently, the amount of ammonia that can be produced in the case according to the invention will be significantly more than 2.6% greater than the comparison case, although it was described in the foregoing mainly in relation to the heat exchange reformation, It will be appreciated that the invention is also useful in other heat exchange applications, where a considerable differential thermal expansion has to be adapted and the leakage of the heat exchange medium into the process fluid is not the objection. heat of feed / effluent, for example where the feed to a process step such as a Exothermic reaction, for example, methanol or ammonia synthesis, is heated through heat exchange with the effluent from the process step. In such cases, the heat exchange tubes may be catalyst free unless it is desired, as in the reforming process mentioned above, that a catalytic reaction is carried out in the process fluid while the latter undergoes the exchange of hot.

Claims (10)

1. A heat exchange apparatus, characterized in that it includes a process fluid supply zone, a heat exchange zone and a process fluid discharge zone, first and second limit means separating such zones from one another, a plurality of heat exchange tubes fastened to one of the boundary means and extending thr the heat exchange zone, whereby the process fluid can flow from the process fluid feed zone, thr the heat exchange tubes and to the process fluid discharge zone, and for each heat exchange tube, a seal tube attached to the other of the limit means, each seal tube being disposed substantially coaxially with its associated heat exchange tube, so that each seal tube is in sliding engagement with its associated heat exchange tube, thus defining an overlapping region, wherein the exchange of heat and the seal tubes overlap each other, so that the thermal expansion of the heat exchange tubes can be adapted within the overlapping region, the inner tube of the heat exchange tube and its associated seal tube being provided with an inner constriction of reduced cross-sectional area forming a region of low pressure downstream, in the direction of the process fluid flow, of the constriction, a region of expansion of transverse area greater than that of the constriction downstream thereof , and one or more passages thr the wall of the inner tube connecting the low pressure region to the outside of the inner tube, the passages being located within the overlapping region, thus providing a flow path for the fluid of the exchange zone of heat thr the overlapping region to the region of low pressure inside the inner tube.

2. The heat exchange apparatus according to claim 1, characterized in that the limit means comprises a tube sheet thr which the tube is expanded.

3. The heat exchange apparatus according to claim 1, characterized in that the limit means comprise collector pipes connected to a process fluid discharge conduit.

4. The heat exchange apparatus according to any of claims 1 to 3, characterized in that each heat exchange tube is coupled within its associated seal tube.

5. The heat exchange apparatus according to any of claims 1 to 4, characterized in that the heat exchange tubes are fastened to the boundary means between the process fluid inlet zone and the heat exchange zone.

6. The heat exchange apparatus according to any of claims 1 to 5, characterized in that it is in the form of a heat exchange reformer operatively connected to the partial combustion means designed to effect partial combustion of the process fluid after that the latter has passed thr the tubes and to supply the gas, after partial combustion, to the heat exchange reformer as the heat exchange fluid.

7. The heat exchange apparatus according to claim 6, characterized in that the partial combustion means includes a bed of secondary reforming catalyst thr which the partially combustion gas passes before the supply thereof to the heat exchange reformer. as the heat exchange fluid.

8. A process in which a process fluid is subjected to a processing step characterized in that it comprises feeding a process fluid to a process fluid supply zone separated from the heat exchange zone by means of limit means, passing such process fluid from the process fluid feed zone, through a plurality of heat exchange tubes that extend through the heat exchange zone, in which the process fluid is subjected to heat exchange with a heat exchange medium in the heat exchange zone, by passing the process fluid from the heat exchange tubes to a process fluid discharge zone separated from the heat exchange zone at through second limit means, by subjecting the process fluid from the process fluid discharge zone to the desired processing step, and passing the resulting processed process fluid through the heat exchange zone as the medium of heat exchange, the heat exchange tubes being fastened to one of the limit means and, for each heat exchange tube, a seal tube attached to the other of the means is provided of limit, each seal tube being disposed substantially coaxially with its associated heat exchange tube, so that the seal tube is in sliding engagement with its associated heat exchange tube, thereby defining an overlapping region, wherein Heat exchange and seal tubes overlap each other, so the thermal expansion of the heat exchange tubes can be adapted within the overlap region, the inner tube of the heat exchange tube and its seal tube associated being provided with an inner constriction of reduced cross-sectional area forming a region of low pressure downstream, in the direction of the process fluid flow, of such constriction, a region of expansion of cross-sectional area greater than that of the downstream constriction of the same, and one or more passages through the wall of the inner tube that connect such low pressure region to the outside of the tube internal, the passages being located within the overlapping region thus providing a flow path for the fluid from the heat exchange zone through the overlapping region to the low pressure region within the inner tube, the process is operated in such a way that Thus, the pressure of the processed process fluid fed into the heat exchange zone is greater than the pressure in the low pressure region, so that part of the processed process fluid fed into the heat exchange zone passes through from the clear space and the passages to the low pressure region.

9. The process according to claim 8, characterized in that the steam reforming of a hydrocarbon supply material, in which the process fluid fed to the process fluid feed zone comprises a mixture of hydrocarbon supply material and steam, the heat exchange tubes are attached to the boundary means between the process fluid feed zone and the heat exchange zone and contain a steam reforming catalyst and the seal tubes are attached to the media. limit by separating the heat exchange zone from the process fluid discharge zone, whereby the mixture is subjected to steam reforming in the heat exchange tubes to give a stream of primary reformed gas, by passing the flow of primary reformed gas from the heat exchange tubes to the process fluid discharge zone, subjecting the primary reformed gas from the z A partial discharge of process fluid with a gas containing oxygen and passing the resulting partially combustion gas through the heat exchange zone in order to heat the heat exchange tubes.

10. The process in accordance with the claim 9, characterized in that the partially combustion gas is passed through a bed of a secondary reforming catalyst before being fed to the heat exchange zone. SUMMARY A heat exchange and process apparatus, particularly a primary heat exchange reformation with the primary reformed gas that is subject to partial combustion (and optionally secondary reforming) and the resulting partially combustion gas that is used as the exchange medium of heat to supply the heat required for primary reformation. The apparatus includes process fluid inlet (11) and outlet (14) zones separated from the heat exchange zone (13) through limit means such as tube sheets (15, 16, 17) or collector pipes (35). A plurality of heat exchange tubes (19) for a process fluid, extending through the heat exchange zone (13) from one of the limit means (15, 16) and slidably engaging the other means of heat exchange. limit (17) with the seal tubes (26) attached to the other limit means (17) The interior of the inner part of the seal tube (26) and its associated heat exchange tube (19) is provided with a constriction (31) of reduced cross-sectional area forming a low pressure region (32) downstream of the constriction , a region (33) of cross-sectional area expansion greater than that of the constriction (31) downstream thereof, and one or more passages (34) through the wall of that inner tube connecting the low-pressure region to the outside of the inner tube. The passages (34) are located within the overlap region of the seal tube (26) and the heat exchange tube (19) in order to provide a leakage flow path for the heat exchange medium from the zone of heat exchange, through the overlapping region and the passages, towards the low pressure region.