HEAT EXCHANGE REACTOR

Abstract: A heat exchange reactor including an outer shell (10) provided with process gas inlet (14) and outlet ports (15, 16) a plurality of reactor tubes (54) supported at their upper ends, header means (24) for supplying process gas from said header inlet port (14) to the upper ends of the reactor tubes (54), said means (24) including two or more primary inlet headers (24) disposed across the upper part of said shell (10), each primary inlet header (24) having a depth greater than its width, whereby said tubes (54) are supported, relative to the shell (10) directly or indirectly by said primary inlet headers (24).

Description: Heat exchange reactor This invention relates to a heat exchange reactor for effecting endothermic reactions which may be catalytic or non-catalytic One such type of reaction is catalytic steam reforming wherein a process gas, for example a mixture of a hydrocarbon feedstock and steam and/or carbon dioxide, is passed over a catalyst, for example nickel disposed on a suitable catalyst support such as alumina, zirconia or a calcium aluminate cement, disposed in tubes that are heated by a hot gas stream flowing past the tubes Another type of reaction is the reforming or cracking of hydrocarbons such as ethane, propane, butane and/or naphtha to form olefins wherein the hydrocarbon feedstock, often in admixture with a diluent such as steam, is passed through tubes, which are often free of catalyst, while the tubes are strongly heated Thermal cracking of the hydrocarbon feedstock takes place to give a product gas containing a mixture of lower hydrocarbons such as ethylene and propylene In a typical reactor, there may be 50 or more, for example 100 to 300, such tubes, each having a length of several metres, and during use the tubes are subjected to high temperatures, typically in the range 500-1100°C The weight of the tubes, the high temperatures and consequent thermal expansion, and any pressure differential between the interior and exterior of the tubes present significant mechanical problems in the reactor design One typical arrangement is described in US 4810472 wherein the reactor has a shell in which are mounted a plurality of reformer tubes with each reformer tube having a concentric double-tube configuration with a catalyst disposed in the annulus between an outer tube, herein termed a scabbard tube, and an inner tube, herein termed a bayonet tube The scabbard tubes are closed at their lower ends so that the process gas flows down through the annulus and then up through the central bayonet tube Surrounding each scabbard tube is a sheath tube so that the heating gas flows through the annulus between the sheath tube and the scabbard tube Tube plates extending across the area of the shell cross section are provided supporting the respective tubes and providing compartments keeping the inlet and outlet process gas and the heating gas separate In order to support the weight of the tubes, to minimise deformation in operation and to withstand any pressure differential between opposite sides of the tube plates, the latter, particularly the tube plates carrying the scabbard tubes which also carry the weight of the catalyst, are necessarily of substantial thickness and hence heavy and expensive We have devised an alternative arrangement that overcomes some of the mechanical problems Accordingly the present invention provides a heat exchange reactor including an outer shell provided with process gas inlet and outlet ports, a plurality of reactor tubes supported at their upper ends, header means for supplying process gas from said inlet port to the upper ends of the reactor tubes, said header means including two or more primary inlet headers disposed across the upper part of said shell, each primary inlet header having a depth greater than its width whereby said tubes are supported, relative to said shell, directly or indirectly by said primary inlet headers In one form of the invention the reactor is of the aforesaid double-tube type and the shell is provided with an inlet port for a heating gas In some processes the product process gas may be mixed with the heating gas so that the process gas outlet port forms the outlet port for the heating gas However generally the heating gas is not mixed with the process gas and so the shell is provided with a separate outlet port for the heating gas In another form of the invention, the reactor tubes are of a single tube configuration and their lower ends are connected to the process gas outlet port by means of tailpipes connected to an outlet manifold or to a tube plate provided at the lower part of the shell to provide a process gas off-take zone with the heating gas is supplied to the region above the tube plate Alternatively the tubes may extend through, but are not fastened to, a tube plate defining a products off-take zone at the lower end of the shell, so that sliding movement can occur between the tubes and the tube plate to accommodate the thermal expansion of the tubes A seal is generally necessary between the tubes and the tube plate, but where the heating gas is the reacted process gas after the latter has been subjected to further processing, the seal configuration described in US 5958364 may be employed In these arrangements using a tube plate at the lower part of the shell, since the tube plate does not have to carry the weight of the tubes, some of the mechanical problems associated therewith are significantly reduced In another arrangement, the reactor tubes are single tubes open at their lower ends so that the reacted process gas is discharged into the region outside the tubes In this case generally a further gas is introduced into the shell and with which the reacted process gas is mixed Thus the further gas may be a hot gas from another source, e g another reformer, for example as described in US 4337170, or an oxidant gas, e g air, oxygen-enriched air, or substantially pure oxygen, which is introduced to effect partial combustion, and hence heating of the reacted process gas to provide the heating gas In all these arrangements, in the present invention the weight of the reactor tubes is borne relative to the shell, by two or primary inlet headers extending across the upper part of the shell These primary inlet headers serve the dual purpose of carrying the weight of the reactor tubes and providing part of the conduit required to supply the process gas from the process gas inlet port to the reactor tubes The primary inlet headers need to be of such size that they can carry the weight of the reactor tubes across the span of the shell, which may have a diameter of several metres without undue distortion even at the high temperatures encountered during use and to withstand any pressure differential across their walls often there will be a significant pressure differential with the pressure inside the primary inlet headers being substantially more, e g up to 50 bar or more, than the pressure outside the primary inlet headers In order to minimise their mass however, in the present invention, the primary inlet headers are in the form hollow pipes of an elongated cross section so that their depth is greater than their width preferably at least twice their width in order to withstand the bending forces arising during operation Preferably only two such support members are employed The primary inlet headers may be supported directly by the shell, e g rest upon flanges thereon, or indirectly from a suitable structure supported on the shell The primary inlet headers support the reactor tubes directly or indirectly In a preferred arrangement, the hollow primary inlet headers which are connected to the process gas inlet port, carry, and communicate with, a plurality of hollow secondary inlet header conduits and the reactor tubes are carried by, and communicate with, the secondary inlet header conduits In this arrangement, where the reactor tubes are of a double-tube configuration as described above, the outer, i e scabbard, tubes are carried by, and communicate with the secondary inlet header conduits, while the inner, i e bayonet tubes, may be supported in like fashion by the outer, scabbard, tubes and connected to primary and/or secondary outlet header conduits by non-load bearing pipes, or may be carried by such primary and/or secondary outlet header conduits In either case the primary and secondary outlet conduits are preferably supported directly or indirectly by the primary inlet headers Suitable means such as bellows may be used to form a gas-tight connection between the process gas inlet and outlet ports and the primary inlet and outlet headers while still allowing movement to accommodate thermal expansion The invention is illustrated by reference to the accompanying drawings wherein Figure 1 is a diagrammatic vertical section through a reactor in accordance with the invention, Figure 2 is a diagrammatic plan of the reactor of Figure 1 with the upper portion of the shell removed, Figure 3 is an enlarged section along the line ll-ll of Figure 2 Figure 4 is a section along line Ill-Ill of Figure 3 Figure 5 is an enlarged section of the arrangement of supporting the primary inlet headers relative to the shell in an alternative embodiment As shown in Figures 1 to 4, the reactor comprises an outer shell having an upper section 10 and a lower section 1 1 Each section has a lining of refractory insulation 12, 13 The upper section 10 has an inlet port 14 for process gas and outlet ports 15 and 16 for process gas and heating gas respectively The lower section has an inlet port 17 for heating gas at its lower end The lower section is provided with a perforate arch member 18 above the heating gas inlet port 17 in use, the region 19 immediately above the arch 18 is filled with an inert particulate material, such as alumina spheres, to act as a flow distributor Located on the upper edge of the lower section 11 of the shell is a flanged ring member 20 carrying a tube assembly A tube sheet 21 is welded to the lower edge of the ring member 20, and a pair of box beams 22, having a depth greater than their width, are disposed beneath the tube sheet 21 and welded thereto The primary purpose of these box beams is to support the tube sheet 21 against bowing and to carry sheath tubes as described hereinafter However in this embodiment, as described hereinafter, the ends of the box beams 22 also support the primary inlet headers and reactor tube assembly relative to the lower section 11 of the shell Since the weight of the assembly is borne by the ends of the box beams 22, tube sheet 21 may be of relatively light gauge construction , As shown in Figure 3, pairs of trunnions 23 are welded to the tube sheet 21 immediately above each box beam 22 towards the ends thereof Hollow primary process gas inlet headers 24, having an elongated cross section so that their depth is substantially greater than their width, are disposed above and extend along, the box beams 22 and are mounted via supporting legs 25 and pins 26 journalled in the trunnions 23 This allows for differential thermal expansion between the primary inlet headers 24 and the tube sheet 21 As shown in Figures 1 and 2, the headers 24 are connected at one end by a process gas inlet conduit 27 which in turn is connected, via conduit 28, to the process gas inlet port 14 in the shell upper section 10 via bellows means (not shown) to accommodate thermal expansion The tube sheet 21 , and box beams 22, may be coated with thermal insulation 29, 30 (omitted for clarity in Figures 1 and 2) A plurality of secondary process gas inlet headers 31 of circular cross-section extend laterally through and are welded to the primary process gas inlet headers 24 This form of construction has the ancillary benefit that the portion of secondary headers 31 passing through the primary inlet headers 24 serves to strengthen the latter against the outward bowing that might result when, as is often the case, there is a significant pressure differential across the walls of the primary inlet headers 24 In order to achieve the closest packing of the tubes consistent with ease of welding access, alternate secondary headers 31a are located at the lower part of the primary headers 24 while the intermediate secondary headers 31 b are located at the upper part of primary headers 24 Perforations, e g slots 32 or other orifices are provided through the wall of secondary inlet headers 31 to provide a flow path for process gas from the interior of primary inlet headers 24 into secondary inlet headers 31 Supported by brackets 33 on the primary process gas inlet headers 24 are a pair of primary process gas outlet headers 34 which are connected at one end by a process gas outlet conduit 35 which in turn is connected to the process gas outlet port 15 in the upper shell section 10 via conduit 36 and bellows (not shown) to accommodate thermal expansion As shown in Figures 3 and 4, a plurality of reactor tubes 37 extend downwards from the secondary headers 31 In order to facilitate replacement of tubes from above (since access to the underside of the secondary headers is liable to be restricted), the reactor tubes 37 are disposed in sleeves 38 extending through and welded to the upper and lower sides of secondary inlet headers 31 Reactor tubes 37 are a sliding fit within sleeves 38 and are welded thereto at their upper ends 39 only Thus there is no weld between reactor tube 37 and the lower end 40 of sleeve 38 A cap 41 is welded to the top of sleeve 38 Hence by removing cap 41 and the weld at the upper end 39 of tube 37 the reactor tube 37 can be lifted up out of sleeve 38 Since there is no weld between the lower end 40 of sleeve 38 and reactor tube 37, it is not possible to provide slots in the sleeve 38 and reactor tube 37 to provide a path for the process gas to flow from the interior of secondary header 31 into reactor tube 37 since leakage would be liable to occur between the lower end 40 of sleeve 38 and the exterior surface of reactor tube 37 To provide a path for the process gas to flow from the interior of secondary inlet header 31 into reactor tube 37, orifices 42 and 43 are provided in the upper part of the wall of secondary inlet header 31 and in a portion of sleeve 38 extending up from the upper part of the wall of secondary inlet header 31 respectively and a cowl 44 is welded on to the top of the secondary inlet header 31 between adjacent sleeves 38 to form a conduit 45 permitting process gas to flow from secondary inlet header 31 , through orifice 42, into conduit 45 and thence through orifice 43 into reactor tube 37 Cowl 44 has the additional benefit of strengthening the secondary inlet headers 31 against bending So that the process gas can flow along the secondary inlet headers 31 past the sleeves 38 extending therethrough, the sleeves have an exterior diameter less than the interior diameter of secondary inlet headers 31 so that, as shown in Figure 4, spaces 46 are provided between the interior wall of secondary inlet header 31 and the sleeve 38 Each reactor tube 37 is of the double-tube configuration, being closed at its lower end 47 and having an inner tube 48, open at its lower end, extending down through the reactor tube 37 Where the process is catalytic, in use, the catalyst is disposed in the annular space between the tubes 37 and 48 and is supported by a catalyst restraining grid 49 adjacent the lower end of tubes 37, 48 The upper end of inner tube 48 is provided with an elbow 50 projecting through the wall of sleeve 38 below cap 41 Elbow 50 is welded to a pipe 51 connected to secondary process gas outlet headers 52 extending laterally through the primary process gas outlet headers 34 Perforations, e g slots, 53 are provided through that part of the wall of the secondary outlet headers 52 that is within the primary outlet headers 34 to permit flow of gas from the secondary outlet headers 52 into the primary outlet headers 34 Depending from, and welded to, tube sheet 21 are a plurality of sheath tubes 54 one for each reactor tube 37 These serve to define an annular zone outside each reactor tube 37 Since sheath tubes merely have to support their own weight and are not subject to any significant pressure differential they may be made of relatively light gauge material Thus, in operation, process gas is fed through process gas inlet port 14 into the primary process gas inlet headers 24 via conduits 28 and 27, and thence, via slots 32, secondary process gas inlet headers 31 and orifice 42, conduit 45, and orifice 43 into the annular space in the reactor tubes 37 between the interior wall thereof and the associated inner tube 48 The process gas undergoes the desired reaction and then passes up inner tube 48 and into process gas outlet headers 52 via pipe 51 , the secondary process gas outlet header 52 and slots 53 The process gas then leaves the vessel via conduits 35 and 36 and process gas outlet port 15 The heating gas is fed to the vessel via inlet port 17, and after flow through perforate arch 18 and the packing in the flow distributor region 19, flows up the annulus between each sheath tube 54 and its associated reforming tube 37, into the space above tube sheet 21 From there it leaves the vessel via heating gas outlet port 16 Where a catalyst is employed, in order to load and discharge the catalyst from the reactor tubes, the caps 41 can be removed by removing the welds at the top of sleeves 38 If it is necessary to remove the inner tube 48 from a reactor tube 37, cap 41 and any catalyst are removed and the elbow 50 disconnected from pipe 51 The elbow at the top of inner tube 48 can then be pushed into the interior of sleeve 38 and then inner tube, with its elbow 50, lifted out of sleeve 38 and reactor tube 37 In an alternative embodiment shown in Figure 5, the primary inlet header 24 is supported directly on a flange 55 provided on the inner wall of the flanged ring member 20 which in turn is supported on a flange 56 on the lower portion 1 1 of the shell In this embodiment, the shell is shown with an external cooling jacket 57 through which a suitable coolant medium, for example boiling water, is circulated This ensures that the shell is maintained at a temperature not much above 100°C, even though the heating gas inside the shell may be at a temperature of for example 900°C or more The thermal gradient is borne by the layer of insulation 13 In use sheath tubes 54 and the primary inlet headers 24 inevitably are at a relatively high temperature and necessarily have metal-to-metal contact with the flanged ring member 20 By providing a sufficient depth to the flanged ring member, the thermal gradient therein can be maintained at an acceptable level

Claims: Claims 1 A heat exchange reactor including an outer shell provided with process gas inlet and outlet ports, a plurality of reactor tubes supported at their upper ends, header means for supplying process gas from said inlet port to the upper ends of the reactor tubes, said header means including two or more primary inlet headers disposed across the upper part of said shell, each primary inlet header having a depth greater than its width, whereby said tubes are supported, relative to said shell, directly or indirectly by said primary inlet headers 2 A heat exchange reactor as claimed in claim 1 wherein there are two primary inlet headers 3 A heat exchange reactor as claimed in claim 1 or claim 2 wherein the primary inlet headers have a depth at least equal to twice their width A heat exchange reactor as claimed in any one of claims 1 to 3 wherein each primary process gas inlet header is provided with a plurality of secondary process gas inlet headers extending laterally through and supported by the primary process gas inlet headers 5 A heat exchange reactor as claimed in claim 4 wherein each secondary process gas inlet header has a plurality of reactor tubes depending from and supported by the secondary process gas inlet headers 6 A heat exchange reactor according to claim 5 wherein each secondary process gas inlet header is provided with a plurality of sleeves extending vertically therethrough, each sleeve having an external diameter less than the internal diameter of the secondary process gas inlet header and being welded to both the upper and lower parts of the walls of its associated secondary inlet header and extending above the upper wall of said secondary inlet header, and a reactor tube is located within each sleeve and welded thereto only at the upper end of said reactor tube, a cowl member extending between the upper extensions of adjacent sleeves is welded to said upper extensions and to the upper wail of said secondary inlet header, thereby defining a conduit between adjacent sleeves above said secondary inlet header and orifices are provided through the upper wall of said secondary inlet header and through the upper extensions of said sleeves thereby providing a gas flow path from said secondary inlet header to said reactor tube via said orifices and said conduit A heat exchange reactor as claimed in any one of claims 1 to 6 wherein a tube sheet is provided extending across the shell and the reactor tubes extend through said tube sheet A heat exchange reactor as claimed in claim 7 wherein each reactor tube is provided with a surrounding sheath tube supported by and extending downwardly from said tube sheet A heat exchange reactor as claimed in any one of claims 1 to 8 wherein each reactor tube is of a double tube construction having an outer tube closed at its lower end and an inner tube open at its lower end extending substantially the length of the outer tube, thereby providing an annular space between the outer tube and the inner tube A heat exchange reactor as claimed in claim 9 wherein the inner tubes of the reactor tubes are connected at their upper ends to the process gas outlet port A heat exchange reactor as claimed in claim 10 wherein the inner tubes are connected to process gas outlet headers supported by the primary process gas inlet headers A heat exchange reactor as claimed in claim 11 wherein each primary process gas inlet header supports a primary process gas outlet header connected to the process gas outlet port and each primary process gas outlet header is provided with a plurality of secondary process gas outlet headers extending laterally through and supported by the primary process gas outlet header, and each secondary process gas outlet header is connected to a plurality of the inner tubes

Inventors: DAVIES RAYMOND, DAVIES, RAYMOND
Applicants: DAVIES RAYMOND, ICI PLC, DAVIES, RAYMOND, IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 2001
Main classification: B01J8
IPC codes: B01J8, C01B3, F28F9