GB2515169A

GB2515169A - Reactor

Info

Publication number: GB2515169A
Application number: GB1406931.4A
Authority: GB
Inventors: Gary Bevan Combes
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 2013-05-10
Filing date: 2014-04-17
Publication date: 2014-12-17
Also published as: WO2014181079A1; GB201406931D0; GB201308428D0

Abstract

A radial flow reactor 10 comprises: a cylindrical shell with first 14 and second 16 ends, one or more process fluid inlets 18 at the first end for receiving a process fluid, one or more process fluid outlets 36 at or adjacent the second end for discharging a reacted process fluid, and a catalyst containment means 22 within said shell that defines a peripheral void 30 and a central void 32, baffle means 26 to direct the flow of a process fluid entering through a process fluid inlet to the peripheral void then radially inwards to the central void and then to a process fluid outlet, wherein said central void contains a heat exchange unit 42 comprising a plurality of heat exchange tubes 44 or heat exchange plates connected to a tube sheet 46 that forms a header space 40 within the second end. The catalyst containment means may hold a particulate catalyst 20 and may be an annular bed within the reactor, the central void may be a cylindrical space. The catalyst bed may have a thickness of 0.1 0.4D where D is the internal diameter of the reactor. A method of use for the reactor is also disclosed.

Description

Reactor This invention relates to reactor in particular to a radial flow reactor suitable for carrying out catalysed reactions.

Radial flow reactors are known and generally comprise a cylindrical vessel with a process fluid inlet at one end and a process fluid outlet at the other and containing catalyst through which the process fluid flows radially. This is generally achieved by using catalyst containment means within the vessel that form a peripheral void around the bed of catalyst and also form a central void within the bed of catalyst. Baffles arranged in the reactor force the process fluid to flow into the peripheral void then through the catalyst then into the central void. Alternatively the process fluid may enter the central void and then pass through the catalyst to the peripheral void. The central and peripheral voids are in fluid communication with the inlet or outlet to allow the process fluid to enter and leave the vessel. Such reactors are described, for example, in US3620685.

US4181 701 discloses an ammonia converter for radial flow through two catalyst beds that has a heat exchanger mounted centrally in the vessel. A process stream of synthesis gas is obtained by combining, inside the converter, separate feed streams consisting of a shell stream serving to cool the converter shell, an exchange stream serving to cool the central heat exchanger, and a by-pass stream for final adjustment of the temperature of the process stream.

The process stream passes in succession radially through the first catalyst bed in an inwards direction, through the central heat exchanger for being cooled, and radially through the second catalyst bed.

US2004/0162357 discloses a reactor system for the production of methanol from synthesis gas comprising a first adiabatic reactor and a second cooled reactor having cooling means within the catalyst bed itself.

GB2I 22102 discloses a reactor for the catalytic production of e.g. ammonia or methanol, having at least one catalyst basket composed of an outer perforated wall, an inner perforated wall and a base; and within the inner wall a heat exchanger. Reactant gas enters the top of the reactor, passes axially and radially through the catalyst in the basket and reacts exothermically therein. Heat generated in the reaction in one catalyst basket is removed in the heat exchanger associated with that basket before the gas passes onto a further catalyst basket in which further reaction takes place.

However such arrangements are not suitable for all reactions and are complicated to fabricate and loadlunload. We have devised an arrangement that overcomes the problems of the prior art reactors.

Accordingly, the invention provides a radial flow reactor comprising: a cylindrical shell with first and second ends, one or more process fluid inlets at the first end for receiving a process fluid, one or more process fluid outlets at or adjacent the second end for discharging a reacted process fluid, and a catalyst containment means within said shell that defines a peripheral void and a central void, baffle means to direct the flow of a process fluid entering through the one or more process fluid inlets to the peripheral void then radially inwards through the catalyst containment means to the central void and then to the one or more process fluid outlets, wherein said central void contains a heat exchange unit comprising a plurality of heat exchange tubes or heat exchange plates connected to a tube sheet that forms a header space within the second end,.

The invention further provides a process using the reactor.

Unlike the aforesaid US41 81701, U82004/0162357 and GB21221 02, the heat exchange unit in the present invention comprises a plurality of heat exchange tubes or heat exchange plates connected to a tube sheet adjacent the second end that forms a header space within the second end, which is fluidly isolated from the shell such that a process fluid flowing through the reactor is prevented from entering the header space. This may reduce the need for external boilers and heat exchange apparatus. Furthermore, the embodiments depicted in GB21 221 02 use side-entry and exit ports for the cooling media through the shell wall. This decreases the integrity of the shell wall, and requires further stress relief in the design and construction of the reactor. Furthermore, in GB21 22102 the heat exchanger itself and the catalyst beds are shown to be supported from the base, which will require additional reinforcement not required in the present invention.

The reactor comprises a cylindrical shell and first and second ends, which may be flat but are preferably domed. The internal diameter of the reactor may be in the range 0.5 to 6 metres, preferably 2 to 4 metres with a total length in the range ito 10 metres. The reactor may be fabricated from conventional materials such as steels suitable for use with the process fluids and capable of withstanding the process conditions. The reactor typically may be operated with the axis of the cylindrical shell aligned vertically, in which case the first and second ends may be described as the top or bottom ends. Preferably the first end is the bottom end and the second end the top end.

The reactor comprises one or more process fluid inlets. A single process fluid inlet at the first end is preferably located in-line with the axis of the cylindrical shell. A process fluid distributor may be connected to one or more of the inlets to distribute the process fluid evenly within the reactor. The one or more process fluid outlets are at or adjacent to the second end, for example on the shell near the second end. The one or more process fluid outlets open into the shell near the central void and allow a process fluid to flow from the central void from the reactor for recovery and further processing.

The reactor may be provided with a heat exchange fluid inlet and a heat exchange fluid outlet in orderto allow a heat exchange fluid to be fed to and discharged from the heat exchange tubes and/or heat exchange plates. The heat exchange fluid inlet and heat exchange fluid outlet are desirably located at the second end. There may be one or more heat exchange fluid inlets and one or more heat exchange fluid outlets. The heat exchange unit is connected to the second end by means of the tube sheet fixed within it. Preferably the second end is detachably mounted on the shell, for example by means of a flange assembly. In this way, the second end may be separated from the reactor shell along with the heat exchange unit, which facilitates inspection and repair and catalyst loading and unloading.

The present reactor preferably comprises a single catalyst containment means, which may contain one or more catalysts. Alternatively multiple catalyst containment means may be included within the reactor. The catalyst containment means is used to contain a particulate catalyst bed and may be arranged within the reactor to allow radial flow of process fluid through the catalyst bed from the peripheral void to the central void. Baffles within the reactor may be used to direct the flow of process fluid. Hence the catalyst containment means is desirably arranged within the shell such that a process fluid entering through a process fluid inlet passes to the peripheral void then radially inwards through the catalyst containment means to the central void and then to a process fluid outlet. Baffles may also be provided within the catalyst containment means to prevent by-pass of process fluid around the catalyst.

The catalyst containment means may be suspended within the shell and/or supported within the shell using conventional methods. In one embodiment, the catalyst containment means comprises an outer perforate cylinder and an inner perforate cylinder, desirably of about the same length, said cylinders mounted between two opposite non-perforate baffle plates, one baffle plate being of circular shape about the diameter of the outer cylinder and the other baffle plate being of annular shape with a width at least equal to the separation of the inner and outer cylinders, and preferably with a width equal to the distance between the inside wall of the shell and the inner perforate cylinder. The peripheral void is thus formed between the outer perforate cylinder and the inside wall of the shell, and the central void is provided within the inner perforate cylinder. In another embodiment, the catalyst containment means comprises a plurality of rigid peiforate chordal-, semi-circular-or C-shaped plates, or tubes formed by such plates in combination with rigid non-perforate back-plates, that are arranged around the inside wall of the shell in orderto provide the peripheral void. An inner perforate cylinder provides the central void, with non-perforate baffle plates mounted on said shaped plates or tubes and said central cylinder. This embodiment offers a number of advantages, particularly in larger reactors, for effective catalyst containment. The outer and inner perforate cylinders may be formed from a perforate mesh, grid or screen, preferably made form a commercially-available V-wire, with orifices desirably smaller than the catalyst particle size.

In use, the catalyst containment means contains a bed of one or more particulate catalysts.

The particulate catalysts are typically cylindrical pellets or extrudates which may be fluted or lobed and have one or more through holes extending there-through. The pellets or extrudates may have a width or diameter in the range 2-25 mm and an aspect ratio (i.e. length/diameter or width) «= 6.

The outside diameter of the catalyst bed contained by the containment means is less than the inside diameter of the reactor so that a peripheral void is formed around the catalyst bed. The catalyst containment means also form a central void within the catalyst bed, and are perforate so that a process fluid may flow from the peripheral void radially inwards through the catalyst bed to the central void. The central axis of the bed is desirably the same as that of the reactor.

Thus, the catalyst containment means desirably holds the particulate catalyst as an annular bed within the reactor and the central void is a cylindrical space. The thickness of the catalyst bed is preferably in the range 0.1 to 1.5 metres depending on the size of the vessel. Preferably the bed thickness is in the range O.1-O.4D where D is the internal diameter of the reactor.

The heat exchange unit comprises a plurality of heat exchange tubes or heat exchange plates through which a heat exchange fluid may be passed. Thus the heat exchange unit may comprise a plurality of U-shaped tubes, bayonet tubes, helical tubes, flat heat exchange plates or concentric heat exchange plates, or a combination thereof connected to the heat exchange fluid inlet and the heat exchange fluid outlet. The number and spacing of tubes andlor plates may be in accordance with conventional heat exchanger design principles.

In order to improve heat transfer, the tubes or plates may be finned to increase their surface area. In addition or alternatively, a sheath tube may be mounted around a portion of the heat exchange tubes or plates that causes the process fluid passing into the central void to flow along the heat exchange tubes or plates.

In the present invention, the heat exchange tubes or plates are connected to a tube sheet located at the second end. The tube sheet forms a header space within the second end, which is fluidly isolated from the shell such that the process fluid flowing through the reactor is prevented from entering the header space. As the heat exchange tubes are connected to the tube sheet at the second end, the heat exchange fluid inlet and/or heat exchange fluid outlet preferably are also located at the second end.

The heat exchange fluid inlet and heat exchange fluid outlet are fluidly isolated from the process fluid inlet and the one or more process fluid outlets, i.e. the heat exchange fluid is not mixed with the process fluid passing through the reactor. Accordingly, the one or more process fluid outlets may be located below the tube sheet, or the one or more process fluid outlets may be connected to the tube sheet and the second end so as to provide a path for the cooled reacted process fluid from a space near the central void through the header space to the second end from where it may be recovered. This embodiment may provide a simpler, lower cost second end design.

Preferably the heat exchange unit comprises a tube bundle, which may comprise one or more transverse baffles to improve heat transfer between the process fluid and the heat exchange fluid.

In a preferred embodiment, the heat exchange unit comprises a plurality of bayonet tubes connected to a tube sheet fixed adjacent to the second end that forms a header space within the second end, said tubes extending from the tube sheet through the central void to a position adjacent the first end. The bayonet heat exchange tubes comprise an outer tube with an open end attached to the tube sheet and a closed end at the position adjacent the first end, and an inner tube within the outer tube extending through the outer tube to a position adjacent the closed end. Heat exchange fluid may flow in though the outer tube and then out through the inner tube, or vice-versa. Accordingly, the inner tube may be connected to the heat exchange fluid outlet and the outer tube to the header space and the header space connected to the heat exchange fluid inlet, or vice-versa.

The advantages of the reactor according to the present invention include: 1) The footprint on the plant is smaller.

2) Less ancillary piping and instrumentation is required.

3) The internal components remain fully accessible for maintenance and reloading the catalyst.

4) It can reduce the maximum vessel temperature by virtue of water that can be vaporised to remove heat.

5) It can be retrofitted to an existing process.

A process using the reactor described herein comprises the steps of: (i) feeding a process fluid to a process fluid inlet of the reactor, (U) passing the process fluid from the process fluid inlet to the peripheral void, (Hi) passing the process fluid radially inwards from the peripheral void through a catalyst contained by the catalyst containment means to the central void to form a reacted process fluid, (iv) passing the reacted process fluid from the central void to a process fluid outlet, (v) and recovering a reacted process fluid from the process fluid outlet, wherein the process fluid is passed through the heat exchange unit before it is passed to the process fluid outlet.

The reactor may be used for any catalysed reaction, in particular for exothermic reactions, in which the heat exchange unit is used to apply cooling. Accordingly in a preferred embodiment the catalysed reaction is exothermic and the heat exchange unit cools the reacted process fluid in the central void.

In a particularly preferred embodiment, the heat exchange fluid is water. The reactor then may be described as a radial flow reactor comprising an integral boiler with a boiler feed-water header with heat exchange tubes or plates arranged to cool reacted process fluid within the central void. The integral boiler preferably comprises a plurality of bayonet heat exchange tubes, comprising an outer tube and an inner tube as described above, suspended from a tube sheet adjacent the second end. The tube sheet forms a head space within the reactor at the second end to which the water may be fed or from which saturated steam recovered. The head space is preferably connected to one or more boiler feed water inlets that provide boiler feed water to the head space and thence to the tubes. The water, typically at a suitable pressure to match that of the process fluid, may be fed to the outer tube or the inner tube but is preferably the outer tube as this provides improved cooling efficiencies and may be simpler to fabricate. The water is heated as it passes down through the outer tube in heat exchange with the process fluid and is at least partially converted to steam. The water/steam then passes up through the inner tubes to be collected and discharged from the reactor via the heat exchange fluid outlet. Preferably the inner tubes are connected to a header located within the boiler feed water head space to a saturated steam outlet in the second end. In an alternative embodiment, the boiler feed water is fed to the header and thence the inner tubes and saturated steam/water is discharged from the outer tubes into the head space from which it is recovered.

The process may be operated in an up-flow or down-flow arrangement. In a preferred arrangement the process fluid is passed through the reactor in an up-flow arrangement, i.e. the first end is at the bottom and the second end at the top. The advantage of an upward flow design is that any particulate material in the process fluid feed will not collect at the base of the radial bed, which reduces the risk of particulate fouling leading to hotspots within the reactor and the potential for side reactions.

The present invention is able to provide a longer path length for the heat exchange, courtesy of the volume provided in the header space at the second end to collect the cooled process fluid before it exits the vessel. For demanding heat removal applications, this extra length allows the reactor to meet necessary duty with fewer tubes or plates and thus fewer connections in the tube-sheet. This also reduces the cost of the reactor. Moreover, the present invention may provide an inherently safer design for those exothermic reactions in which runaway reactions can take place because of the enhanced heat transfer arising from the header at the second end. Compared to GB2122102, should the feed of the water to the reactor fail, the integrated feed storage in the head in combination with a thermo-siphon effect may enable the continued removal of heat from the bed. Moreover fluctuation of the process fluid outlet temperature may be reduced.

The process fluid fed to the reactor is preferably a synthesis gas, which may be reacted over a suitable synthesis gas conversion catalyst to either change the hydrogen content of the synthesis gas, convert carbon oxides present in the synthesis gas into methane or form methanol or ammonia, which may be recovered downstream. Thus in one embodiment the catalyst is a water-gas shift catalyst and the reactor is therefore a water-gas shift reactor. In another embodiment the catalyst is a methanation catalyst and the reactor is therefore a methanation reactor. In another embodiment the catalyst is a methanol synthesis catalyst and the reactor is therefore a methanol synthesis reactor. In yet another embodiment the catalyst is an ammonia synthesis catalyst and the reactor is therefore an ammonia synthesis reactor.

Preferably the synthesis gas comprises hydrogen, carbon monoxide and/or carbon dioxide, and optionally steam.

In a particularly preferred embodiment, the reactor is used for the water-gas shift reaction, especially a so-called sour-shift water gas shift reaction, used to increase or decrease the hydrogen content of synthesis gases. The reaction may be depicted as follows; H20+CO -* H2-FC02 This reaction is exothermic, and conventionally it has been allowed to run adiabatically, with control of the exit temperature governed by feed gas inlet temperature and composition. Side reactions can occur, particularly methanation, which is usually undesirable. To avoid this, the shift reaction requires considerable amounts of steam to be added to ensure the desired synthesis gas composition is obtained with minimum formation of additional methane. The cost of generating steam can be considerable and therefore there is a desire to reduce the steam addition where possible. Moreover, in CO-rich feeds, temperature control of the exiting gas is problematic and unwanted side reactions can occur. The present invention offers an improved process where temperature may be better controlled and unwanted side reactions minimised.

We have found that the disadvantages of the previous water-gas shift processes may be overcome using a water-gas shift stage operated using the radial-flow reactor of the present invention.

In a preferred embodiment, the process fluid fed to the reactor is a synthesis gas mixture comprising hydrogen, carbon oxides and steam and containing one or more sulphur compounds, having a ratio, R, defined as R = ([H2]-[C02])/([CO]+[C02]) «= 0.6 and a steam to carbon monoxide ratio S 1.8. The synthesis gas may be produced by gasification of a carbonaceous feedstock, such as coal, petroleum coke or another carbon-rich feedstock such as biomass. Before the synthesis gas is subjected to the water-gas shift reaction, it is preferably cooled, optionally filtered and then washed to remove particulates such as coal ash.

The R ratio in the synthesis gas is preferably«= 0.6, more preferably in the range 0.1 to 0.6, most preferably in the range 0.2 to 0.6. R may readily be calculated from the molar quantities of the components in the synthesis gas feed. The synthesis gas may comprise one or more sulphur compounds such as hydrogen sulphide or carbonyl sulphide. In order that a sour shift water-gas shift catalysts remain suitably sulphided, the sulphur content of the synthesis gas fed to the water-gas shift catalyst may desirably be >2SOppm.

If the synthesis gas does not contain enough steam for the water-gas shift process, steam may be added to the synthesis gas, for example by live steam addition or saturation or a combination of these. The steam to carbon monoxide ratio (i.e. molar ratio) of the synthesis gas mixture fed to the water-gas shift catalyst may be up to 3 or higher, but is preferably «= 1.8 and more preferably is in the range 0.2 to 1.8, most preferably 0.7 to 1.8. In some embodiments, it may be desirable to operate with a ratio in the range 0.95 to 1.8.

The water-gas shift catalyst may be any suitably stable and active water-gas shift catalyst.

Iron-based and copper-based water-gas shift catalysts are well known and may be used. Such catalysts operate with the iron or copper in a reduced form. Alternatively manganese-based catalysts may be used. In particular so-called "sour shift" catalysts may be used, in which the active components are metal sulphides. Preferably the water-gas shift catalyst comprises a supported cobalt-molybdenum catalyst that forms molybdenum sulphide in-situ by reaction with hydrogen sulphide present in the synthesis gas stream. The Co content, expressed as CoO, is preferably 2-10% wt and the Mo content, expressed as MoO3, is preferably 5-20% wt.

Alkali metal promoters may also be present at 1-10% wt. Suitable supports comprise one or more of alumina, magnesia, magnesium aluminate spinel and titania. The catalysts may be supplied in oxidic form, in which case they require a sulphiding step, or they may be supplied in a pre-sulphided form. Particularly preferred sour shift catalysts are supported cobalt-molybdate catalysts such as KATALCOTM KB-Il available from Johnson Matthey PLC, which comprises about 3% wt. CoO and about 10% wt. MoO3 supported on a particulate support containing magnesia and alumina.

The synthesis gas and steam mixture is passed at elevated temperature and pressure, preferably temperatures in the range 190 to 420°C more preferably 200 to 400°C, and pressure up to about 85 bar abs, over the bed of water-gas shift catalyst. The flow-rate of synthesis gas containing steam may be such that the gas hourly space velocity (GHSV) through the bed of sulphur-tolerant water-gas shift catalyst in the first reactor may be »= 6000hour1.

The water-gas shift reaction occurs, consuming carbon monoxide and steam and forming carbon dioxide and hydrogen.

If desired, a by-pass stream of synthesis gas may by-pass the reactor to be mixed with the cooled reacted process fluid recovered from the one or more process fluid outlets.

The reactor may be used alone, but is preferably used in combination with other water-gas shift reactors. In a preferred embodiment, the reactor is used in combination with one or more adiabatic or gas-cooled reactors, each containing a suitable water-gas shift catalyst.

The heat exchange unit within the reactor of the present invention may be used to generate steam for use in the water-gas shift process, or in downstream or upstream processes. Thus where the heat exchange unit is a boiler, a portion of the steam recovered from the one or more heat exchange fluid outlets may be combined with the synthesis gas fed to the process fluid inlet.

The resulting shifted gas stream may be subjected to further processing including the steps of cooling the shifted gas stream, ora mixture of the shifted gas stream and a bypass stream, to below the dew point to condense water; separating the resulting condensate therefrom to form a dry shifted gas stream; feeding the dry shifted gas stream to a gas-washing unit operating by means of counter-current solvent flow, to produce a product synthesis gas enriched in hydrogen; and collecting the product synthesis gas from the washing unit.

After such further processing to remove water and adjust the carbon dioxide content, the product synthesis gas may be used in downstream processes for the production of methanol, dimethylether (DME), Fischer-Tropsch (Fl) liquids or synthetic natural gas (SNG). Where a higher degree of water-gas shift is required, for example when making hydrogen for ammonia synthesis or a low carbon content fuel for combustion in a gas turbine, additional water-gas shift steps may be performed.

The invention is further illustrated by reference to the accompanying drawings in which; Figure 1 is a cross-section of a reactor according to a first embodiment of the invention, and Figure 2 is a cross-section of a reactor according to a second embodiment of the invention.

In Figure 1, a reactor 10 comprises an elongate cylindrical shell 12 aligned vertically with first domed end 14 at the bottom and a second domed end 16 at the top.

The first end 14 has a process fluid inlet pipe 18 positioned in line with the vertical axis of the reactor.

The shell 12 contains an annular catalyst bed 20, e.g. a particulate sour shift catalyst, disposed within a catalyst containment means comprising an outer perforate cylinder 22 and an inner perforate cylinder 24, arranged coaxially within the shell and mounted between a first non-perforate circular baffle plate 26 near the first end 14 and a second non-perforate annular baffle plate 28 near the second end 16. The catalyst 20 is disposed between the inner 24 and outer 22 perforate cylinders. In an alternative embodiment the outer perforate cylinder may be replaced by a plurality of rigid perforate chordal-, semi-circular-or C-shaped plates, or tubes formed by such plates in combination with rigid non-perforate back-plates, that are arranged around the inside wall of the shell 12. The diameter of the first circular baffle plate 26 is about that of the outer perforate cylinder 22. The second annular baffle plate 28 extends from the inside of the shell 12 to a position beyond the inner perforate cylinder 24. In order to prevent by-pass due to catalyst settling, the second annular baffle plate 28 may be provided with a vertical baffle (not shown) that extends downwards into the surface of catalyst bed. A peripheral void 30 is formed between the outside of the outer perforate cylinder 22 and the inside wall of the shell 12. A central void 32 is formed within the inner cylinder 24.

The second end is detachably mounted on the shell 12 by means of a flange assembly 34 located above the annular baffle plate 28. The catalyst containment means may therefore be supported within the shell 12 from the flange assembly 34 by connection to the baffle plate 26.

Alternatively, the containment means may be supported on plate 26 from the first end 14.

The second end 16 comprises two opposed process fluid outlets 36 located above the flange assembly 34 that open into the space above the baffle plate 28, and a tube sheet 38 located above the outlets 36 that extends horizontally across the second end to form a header space above it within the second end. A plurality of bayonet heat exchange tubes depend from a central portion of the tube sheet 38, into the central void 32 to a position near the circular baffle plate 26. Only three tubes are depicted, but in practice a tube bundle comprising 10's or 100's of tubes may be used. The bayonet tubes each comprise an outer tube 42 with an open end connected to the tube sheet 38 which opens into the header space 40 and a closed end, and an inner tube 44 that extends from a position near the closed end of the outer tube 42 to a header assembly 46 located within the header space 40. The header 46 connects the inner tubes 44 to a heat exchange fluid outlet pipe 48 in the second end 16 above the tube sheet 38.

A heat exchange fluid inlet pipe 50 is also provided in the second end above the tube sheet 38 for feeding a heat exchange fluid into the header space 40.

A sheath tube 52 is mounted around the tubes 42. The sheath tube extends from the tube sheet 38 to a position near the closed end of the tubes 42. In this embodiment, the annular baffle plate 28 of the catalyst containment means extends towards the sheath lube 52 to provide a seal therewith and a plurality of orifices 54 are provided in the sheath tube between the baffle plate 28 and tube sheet 38.

In use a process fluid, such as a synthesis gas derived from coal gasification, is fed into the reactor 10 via process fluid inlet 18 in the first end 14 and is directed by baffle plates 26 and 28 to the peripheral void 30 within the shell 12. The process fluid then passes radially inwards through the catalyst 20, e.g. a sour shift catalyst, disposed within the catalyst containment means where reactions take place, to the central void 32. The resulting reacted process fluid is then directed to the closed ends of the bayonet tubes 42 by means of the sheath tube 52 and baffle plates 26, 28. The reacted process fluid flows upwards along the surface of the outer tubes 42 within the sheath tube 52 where it is cooled in heat exchange with water under pressure flowing through the tubes 42. The cooled reacted process fluid passes through orifices 54 in the sheath tube 52 and thence to the process fluid outlets 36, from which the reacted process fluid may be recovered.

Boiler feed water is fed into the header space 40 in the second end 16 by means of the heat exchange fluid inlet 50. The feed water passes through the outer tubes 42 where it is heated in heat exchange with the reacted process fluid and is converted at least partly into steam. The steam and water pass to the inner tubes 44 and thence to the header 46 and heat exchange fluid cutlet 48 in the second end. In an alternative embodiment, the inlet 50 and outlet 48 are reversed such that the water is fed in though pipe 48 then via header 46 to the inner tubes 44 and thence outer tubes 42 which discharge the heated water/steam to the header space 40 from which it is collected via pipe 50.

In Figure 2, the second end of the reactor has been adapted by moving the process fluid outlets from below the tube sheet 38 to the tube sheet itself. The remaining features of the reactor are the same as in Figure 1. Hence in Figure 2 the reactor 60 comprises an elongate cylindrical shell 12 aligned vertically with first domed end 14 at the bottom and a second domed end 16 atthe top.

The first end 14 has a process fluid inlet 18 positioned in line with the vertical axis of the reactor.

The second end is detachably mounted on the shell 12 by means of a flange assembly 34 located above the annular baffle plate 28. The catalyst containment means may therefore be conveniently supported within the shell 12 from the flange assembly 34 by connection to the baffle plate 28. Alternatively, the containment means may be supported on plate 26 from the first end 14.

The second end 16 comprises a tube sheet 38 located above the flange assembly 34 that extends horizontally across the second end to form a header space 40 above it within the second end. Two process fluid outlet pipes 62 are attached towards the periphery of the tube sheet 38 that open into the space above the baffle plate 28 and extend to the second end 16.

A plurality of bayonet heat exchange tubes depend from a central portion of the tube sheet 38, into the central void 32 to a position near the circular baffle plate 26. Only three tubes are depicted, but in practice a tube bundle comprising 10's or 100's of tubes may be used. The bayonet tubes each comprise an outer tube 42 with an open end connected to the tube sheet 38 and a closed end, and an inner tube 44 that extends from a position near the closed end of the outer tube 42 to a header assembly 46 located within the header space 40. The header 46 connects the inner tubes 44 to a heat exchange fluid outlet pipe 48 in the second end 16 above the tube sheet 38. A heat exchange fluid inlet 50 is also provided in the second end above the tube sheet 38 for feeding a heat exchange fluid into the header space 40.

A sheath tube 52 is mounted around the tubes 42. The sheath tube extends from the tube sheet 38 to a position near the closed end of the tubes 42. In this embodiment, the annular baffle plate 28 of the catalyst containment means extends towards the sheath tube 52 to provide a seal therewith and a plurality of orifices 54 are provided in the sheath tube between the baffle plate 28 and tube sheet 38.

In use a process fluid, such as a synthesis gas derived from coal gasification, is fed into the reactor 10 via process fluid inlet 18 in the first end 14 and is directed by baffle plates 26 and 28 to the peripheral void 30 within the shell 12. The process fluid then passes radially inwards through the catalyst 20, e.g. a sour shift catalyst, disposed within the catalyst containment means where reactions take place, to the central void 32. The resulting reacted process fluid is then directed to the closed ends of the bayonet tubes 42 by means of the sheath tube 52 and baffle plates 26, 28. The reacted process fluid flows along the surface of the outer tubes 42 within the sheath tube 52 where it is cooled in heat exchange with water under pressure flowing through the tubes 42. The cooled reacted process fluid passes through orifices 54 in the sheath tube 52 and thence to the process fluid outlets 62.

Boiler feed water is fed into the header space 40 in the second end 16 by means of the heat exchange fluid inlet 50. The feed water passes through the outer tubes 42 where it is heated in heat exchange with the reacted process fluid and is converted at least partly into steam. The steam and water pass to the inner tubes 44 and thence to the header 46 and heat exchange fluid outlet 48 in the second end. In an alternative embodiment, the inlet 50 and outlet 48 are reversed such that the water is fed in though pipe 48 then via header 46 to the inner tubes 44 and thence outer tubes 42 which discharge the heated water/steam to the header space 40 from which it is collected via pipe 50.

In order to maintain the reactor the second end 16 comprising the outlets 62, and heat exchange unit 38, 40, 42, 44, 46, 46, 50, 52, 54 may be detached from flange assembly 34 on the shell 12, to give access to the catalyst containment means 20, 22, 24, 26, 28.

The invention is further illustrated by reference to the following calculated Example.

Example 1

A water-gas shift reactor according to Figure 1 in which the outer perforate cylinder was replaced by a plurality of perforate scalloped plates around the periphery of the catalyst bed was modelled in order to establish the appropriate reactor parameters for a coal-to-methanol process. The required heat removal duty was 9799 kW.

A dry synthesis gas at a flow of 9126 kmol/h and pressure of 38.8 bara was mixed with steam at a Steam:CO ratio of 0.8 and passed through the reactor containing a Co/Mo sour shift catalyst.

The synthesis gas composition consisted of: Component Dry gas mole fraction in feed Co 0.593 CO2 2.19x102 COS 7.26x104 H2S 8.41x103 Ar 1.OlxlO-2 N2 6.07x102 NH3 3.42x103 CH4 4.15x104 H2 0.301 The CO conversion was 14.3% resulting in a temperature rise from 280°C to 344°C.

The diameter of the reactor was 2500mm ID. The design used bayonet tube heat removal using 2" OD tubes and 1" OD internal tubes. In this design theywere either un-finned orfinned using 20 fins of 6mm height per tube. A distance between tubes of 15mm was used in calculations (pitch/do = 1.29). A triangular pitch was selected. A draft tube of 5mm thickness was used, with an annular gap of typically 220mm between the sheath and the centre pipe.

Examples of design appear below.

Sour shift Catalyst Volume (m3) 13.16 Bed height(m) 7.28 Bed depth (m) 0.28 Number of tubes 145 Finned U,W/m2.K 328 HTA, m2 388 Heat removal delivered (%) 149 UnFinned U,W/m2.K 173 HTA,m2 161 Heat removal delivered (%) 33 Water flowrate, kg/s 6.3 Steam raised bara 16 Length of tubes, m 7 Water flowrates estimated for a 0.8 VF return line from a saturated boiler feed water feed.

Steam generated at 16 bara.

The results demonstrate that the finned tubes offer a considerable improvement in heat removal compared to un-finned tubes. The un-finned tubes would require an additional heat exchanger to meet the required duty, although this would be smaller than the case where the reactor did not comprise an integral boiler.

Claims

Claims.1. A radial flow reactor comprising: a cylindrical shell with first and second ends, one or more process fluid inlets at the first end for receiving a process fluid, one or more process fluid outlets at or adjacent the second end for discharging a reacted process fluid, and a catalyst containment means within said shell that defines a peripheral void and a central void, baffle means to direct the flow of a process fluid entering through the one or more process fluid inlets to the peripheral void then radially inwards through the catalyst containment means to the central void and then to the one or more process fluid outlets, wherein said central void contains a heat exchange unit comprising a plurality of heat exchange tubes or heat exchange plates connected to a tube sheet that forms a header space within the second end.
2. A reactor according to claim 1 wherein the second end is detachably mounted on the shell.
3. A reactor according to claim 1 or claim 2 wherein the catalyst containment means comprises an outer perforate cylinder and an inner perforate cylinder, said cylinders mounted between two opposite non-perforate baffle plates, one baffle plate being of circular shape having a diameter of the outer cylinder and the other baffle plate being of annular shape with a width at least equal to the separation of the inner and outer cylinders,
4. A reactor according to claim 1 or claim 2 wherein the catalyst containment means comprises a plurality of rigid perforate chordal-, semi-circular-or C-shaped plates, or tubes formed by such plates in combination with rigid non-perforate back-plates, that are arranged on the inside wall of the reactor in order to provide the peripheral void and an inner perforate cylinder to provide the central void, with non-perforate baffle plates mounted on said shaped plates and said central cylinder.
5. A reactor according to any one of claims 1 to 4 comprising a particulate catalyst disposed within said catalyst containment means.
6. A reactor according to claim 5 wherein the catalyst containment means holds the particulate catalyst as an annular bed within the reactor and the central void is a cylindrical space.
7. A reactor according to claim S or claim 6 wherein the catalyst bed has a thickness in the range O.1-O.4D where D is the internal diameter of the reactor.
8. A reactor according to any one of claims I to 7 wherein one or more process fluid outlets are located below the tube sheet, or the one or more process fluid outlets are connected to the tube sheet and the second end so as to provide a path for a process fluid from a space near the central void through the header space to the second end.
9. A reactor according to any one of claims I to 8 wherein the heat exchange unit comprises a plurality of bayonet heat exchange tubes extending from the tube sheet through the central void to a position adjacent the first end.
10. A reactor according to any one of claims ito 9 wherein the tubes or plates are finned to increase their surface area.
11. A reactor according to any one of claims 1 to 10 wherein a sheath tube is mounted around a portion of the heat exchange tubes or plates that causes the process fluid passing into the central void to flow along the heat exchange tubes or plates.
12. A process using a reactor comprising the steps of: (i) feeding a process fluid to a process fluid inlet of a reactor, said reactor comprising a cylindrical shell with first and second ends, one or more process fluid inlets at the first end and one or more process fluid outlets at or adjacent to the second end, and a catalyst containment means within said shell that defines a peripheral void and a central void, baffle means to direct the flow of a process fluid entering through a process fluid inlet to the peripheral void then radially inwards to the central void and then to a process fluid outlet, wherein said central void contains a heat exchange unit comprising a plurality of heat exchange tubes or heat exchange plates connected to a tube sheet that forms a header space within the second end, (ii) passing the process fluid from the process fluid inlet to the peripheral void, (iU) passing the process fluid radially inwards from the peripheral void through a catalyst contained by the catalyst containment means to the central void to form a reacted process fluid, (iv) passing the reacted process fluid from the central void to the one or more process fluid outlets, (v) and recovering a reacted process fluid from the one or more process fluid outlets, wherein the process fluid is passed through the heat exchange unit before it is passed to the one or more process fluid outlets.
13. A process according to claim 12 wherein the heat exchange fluid is water.
14. A process according to claim 12 or claim 13 wherein the process fluid comprises a synthesis gas.
15. A process according to acclaim 14 wherein the catalyst is selected from the group consisting of a water-gas shift catalyst, a methanation catalyst, a methanol synthesis catalyst and an ammonia synthesis catalyst.
16. A process according to any one of claims 12 to 15 wherein the process fluid is a synthesis gas mixture comprising hydrogen, carbon oxides and steam and containing one or more sulphur compounds, having a ratio, R, defined as R = ([H2]- [C02])I([CO]+[C02]) «= 0.6 and a steam to carbon monoxide ratio «= 1.8, and the catalyst is a sulphur-tolerant water gas shift catalyst.
17. A process according to claim 16 wherein the synthesis gas and steam mixture is passed at a temperatures in the range 190 to 420°C and pressure up to about 85 bar abs, over the bed of water-gas shift catalyst.
18. A process according to claim 16 or claim 17 wherein the reactor is used in combination with one or more adiabatic or gas-cooled reactors, each containing a suitable water-gas shift catalyst to produce a shifted synthesis gas stream.
19. A process according to claim 18 further comprising the steps of: (i) cooling the shifted synthesis gas stream obtained from the one or more further stages of water-gas shift, or a mixture of the shifted gas stream and a bypass stream, to below the dew point to condense water, (ii) separating the resulting condensate therefrom to form a dry shifted gas stream, (Ui) feeding the dry shifted gas stream to a gas-washing unit operating by means of counter-current solvent flow, to produce a product synthesis gas enriched in hydrogen and (iv) collecting the product synthesis gas from the washing unit.