WO2013108011A1

WO2013108011A1 - A compact catalytic reactor

Info

Publication number: WO2013108011A1
Application number: PCT/GB2013/050031
Authority: WO
Inventors: Michael Joseph Bowe; Iain Kenneth Baxter; Ioannis CHANIS
Original assignee: Compactgtl Limited
Priority date: 2012-01-16
Filing date: 2013-01-09
Publication date: 2013-07-25
Also published as: GB201200618D0

Abstract

A reactor (10) includes a reactor block (12) which defines a multiplicity of first channels (15) and defines a multiplicity of second channels (16) that are thermal contact with the first channels (15). The reactor block (12) is produced by a three- dimensional printing process from a powder. Catalytic inserts (22, 24) may then be introduced into the channels.

Description

A Compact Catalytic Reactor

This invention relates to a compact catalytic reactor suitable for performing a reaction which involves heat transfer. The reactor comprises first channels in thermal contact with second channels, so heat may be transferred between the first channels and the second channels. The invention also relates to a method of making such a compact catalytic reactor.

A plant and process are described in WO 2005/10251 1 (GTL Microsystems AG) in which methane is reacted with steam, to generate carbon monoxide and hydrogen in a first catalytic reactor; the resulting gas mixture is then used to perform Fischer-Tropsch synthesis in a second catalytic reactor. The reforming reaction is typically carried out at a temperature of about 800 °C, and the heat required may be provided by catalytic combustion in channels adjacent to those in which reforming is carried out, the combustion channels containing a catalyst which may comprise palladium or palladium/platinum on an alumina support in the form of a thin coating on a metallic substrate. The Fischer-Tropsch reaction, in contrast, takes place at about 200 °C, and is exothermic; the adjacent channels in this case carry a heat transfer fluid.

Reactors for performing such reactions, defining first channels in thermal contact with second channels, may be made by stacking a multiplicity of flat plates spaced apart by channel-defining spacers, and bonding the stack together. A variety of different channel-defining spacers have been proposed, such as castellated plates, or bars. An alternative method that avoids the need to stack multiple items, and avoids the need to bond items together by processes such as brazing, may be advantageous.

According to the present invention there is provided a method of forming a reactor, the reactor comprising a reactor block which defines a multiplicity of first channels and defines a multiplicity of second channels that are thermal contact with the first channels, wherein the reactor block is produced by additive layer manufacturing. The production process may be described as a three-dimensional printing process from a powder. The powder may be a metal powder. In one example the reactor block is produced by a process such as direct metal laser sintering. This process involves fusing together of very fine layers of metal powder using a focused laser beam. In one example the powder is deposited in layers of between 20 and 60 μηι, and each layer is then scanned with a high intensity laser beam so that the particles within the layer fuse together, and the layer fuses to the layer below.

Direct metal laser sintering involves gradually and repeatedly lowering a piston or support plate on which is repeatedly placed a thin layer of a powder of material, and scanning with a laser those portions of the layer of powder which are to be sintered together. After scanning the selective parts of each layer, the powder bed is lowered by one layer thickness, and the process repeated. Preferably the entire bed of powder is warmed up to slightly below the temperature required for sintering, so that the power required by the laser is reduced. This process is substantially identical to those referred to as selective laser metal sintering, or selective laser metal melting. An equivalent process, which may also be suitable, is electron beam melting.

The resulting reactor block is an integral structure, welded together throughout, and so avoids any brazed joints which impose a thermal limit on operations. In a modification of the process, the metal composition can be gradually varied throughout the reactor block. For example a more heat-resistant alloy may be used in forming channels in which combustion is to occur, while a less heat-resistant alloy may be used in channels that will experience a lower temperature. As another example, the material used to form the channels may be varied in accordance with the chemical composition or reactivity of the gases that are to pass through that part of the reactor.

The reactor is completed by incorporating appropriate catalysts in those channels in which a catalyst is required, that is to say in the channels in which a chemical reaction is to be performed catalytically. The catalyst may be deposited onto the wall of the channel. The catalyst may be incorporated into a ceramic support which is coated onto the wall of the channel. Alternatively or additionally the catalyst may be provided as a gas-permeable catalytic insert within the channel, and each such insert preferably includes a metal substrate. Preferably each such catalyst insert is shaped so as to subdivide the flow channel into a multiplicity of parallel flow sub-channels. Preferably each catalyst insert includes a ceramic support material on the metal substrate, which provides a support for the catalyst.

The metal substrate provides strength to the catalyst insert and enhances thermal transfer by conduction. Preferably the metal substrate is of a steel alloy that forms an adherent surface coating of aluminium oxide when heated, for example a ferritic steel alloy that incorporates aluminium (eg Fecralloy (TM)). The substrate may be a foil, a wire mesh or a felt sheet, which may be corrugated, dimpled or pleated; the preferred substrate is a thin metal foil for example of thickness less than 150 μηι, which is corrugated to define the longitudinal sub-channels. Depending on the size of the flow channels, the substrate may comprise either a single corrugated foils or an assembly of foils, which may be bonded together.

Where the foils are corrugated, the corrugations may be square, rectangular, trapezoidal or hexagonal in cross-section; or arcuate or sinusoidal; or they may be of zigzag shape, defining triangular corrugations, or a sawtooth shape, for example with sloping portions connected by flat peaks. The corrugations typically run parallel to the length of the foils. In some alternative configurations, the corrugations may be non-parallel or even perpendicular to the length of the foil.

Preferably the first flow channels and the second flow channels extend in parallel directions, within a reactor block, as this simplifies the method of

manufacture. By way of example the reactor block may define flow channels that are of length at least 300 mm, more preferably at least 500 mm, but usually no longer than 1000 mm. A suitable length is between 500 mm and 700 mm, for example 600 mm. To ensure good thermal contact in the reactor block, both the first and the second flow channels may be between 10 mm and 2 mm high (in cross-section); and each channel may be of width between about 3 mm and 25 mm. The reactor block preferably provides the requisite structure to ensure that the reactor can resist any differential pressures and thermal stresses that may be applied during operation, so that the catalyst insert does not have to provide structural support. Consequently the catalyst inserts can be non-structural, as they do not have to hold the walls of the channels apart during operation. The flow channels may be square in cross-section, or may be of height either greater than or less than the width; the height refers to the dimension in the direction in the direction for heat transfer. For example the reactor block might be 0.5 m wide and 1 .0 m long, or 0.6 m wide and 0.8 m long; and it may define channels 7 mm high and 6 mm wide, or 3 mm high and 10 mm wide, or 10 mm high and 5 mm wide. These dimensions are merely exemplary, and the skilled person will recognise that many different shapes and sizes are equally suitable. Arranging the first and second flow channels to alternate in the stack helps ensure good heat transfer between fluids in those channels. The catalyst structures are inserted into the channels, and can be removed for replacement.

In additional aspects, the invention provides a reactor block made as described above; and a reactor incorporating this reactor block. The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 shows a perspective view, partly in section, of a reactor block of the invention suitable for a chemical process involving reactions in both the first and second flow channels;

Figure 2 shows a sectional view of an alternative reactor block of the invention, suitable for a chemical process in which a reaction takes place in only the first flow channels; and

Figure 3 shows a sectional view of an alternative reactor block of the invention, suitable for a chemical process in which a reaction takes place in only the first flow channels.

Referring to figure 1 there is shown a reactor 10 which would be suitable for use for a chemical process where reactions occur in both the first and second flow channels, one reaction being endothermic and the other exothermic. For example it would be suitable for use as a steam/methane reforming reactor, or for use in a steam/methane reforming reactor, in which case catalytic steam/methane reforming would occur in the first flow channels, and catalytic combustion in the second flow channels. The reactor 10 includes a reactor block 12 formed by direct metal laser sintering of a corrosion resistant high-temperature alloy. The reactor 10 is shown in an orientation which may be suitable for its use, in which the channels extend horizontally, but the reactor block 12 may be made with the channels extending vertically. The reactor block 12 is a single integral block of the alloy, and it defines a multiplicity of channels 15, 16 that are each of rectangular cross-section, and which extend parallel to each other, being defined by horizontal webs 17 and vertical fins 18 (in the orientation as shown), so the channels 15 are in horizontal rows alternating with horizontal rows of channels 16. In this example all the channels 15, 16 are of the same size, which in this example is 6 mm high and 7 mm wide. The webs 17 and the fins 18, in this example, are each of thickness 0.9 mm. At the sides of the reactor block 12 are thick sidewalls 20, of thickness 15 mm in this example. The channels 15 and 16 are distinguished, in this example, by their use.

The reactor block 12 may be formed with the channels 15, 16 extending vertically, starting on a base plate of the corrosion resistant high-temperature alloy which defines rectangular apertures corresponding exactly to the desired positions of the channels 15 and 16. The block is formed by depositing a thin layer of metal powder over the entire area, and then scanning over the surface with a high intensity laser to sinter the metal powder together and to the underlying material in those regions that are to form the webs 17 and the fins 18 of the block 12. Since the channels 15 and 16 extend vertically, the webs 17 and the fins 18 are self supporting. Powder deposition and laser scanning are repeated a very large number of times to create the entire block 12. Each thin layer may for example be of thickness between 10 μηι and 100 μηι, more preferably between 20 μηι and 60 μηι, for example 40 μηι. The un-sintered powder is then emptied out of the channels 15 and 16.

After forming the reactor block 12, catalyst inserts 22 or 24 (only one of each are shown in Figure 1 ), carrying a catalyst for the respective reaction, are inserted into the channels 15 and 16 respectively. These inserts 22 and 24 comprise a metal substrate and a ceramic coating acting as a support for the active catalytic material. The metal substrate of each insert 22, 24 comprises a stack of corrugated foils and flat foils occupying the respective flow channel 15 or 16, each foil being of thickness less than 0.2 mm, for example 100 μηι; the stacks shown in figure 1 consist of three corrugated foils separated by two flat foils, bonded together. The channels 15 and 16 in this example are 6 mm high and 7 mm wide, while the catalyst inserts 22 and 24 in this case are 5.4 mm high and 6.6 mm wide, so providing a degree of clearance from the walls of the channels 15 and 16. This is necessary to allow for tolerances in manufacture of the reactor block 10. More generally, the webs 17 may typically of thickness between 0.5 and 4 mm, for example between 1 mm and 2.5 mm; and the fins 18 may be of thickness between 0.25 mm and 3.5 mm. The height of the fins 18 would typically be in the range 2-12 mm, as the height should be sufficiently small for good heat transfer, but sufficiently large to be able to insert the catalytic insert 22 or 24. Although only five channels are shown as being defined in each horizontal row in figure 1 , in a practical reactor there might be many more, for example over seventy channels in a reactor block 10 of overall width about 500 mm. Referring now to figure 2 is shown an alternative design of reactor 30 which would be suitable for a chemical process in which a reaction takes place in only the first flow channels, and in which a coolant is passed through the second flow channels. This would, for example, be suitable for performing partial oxidation (POX) of a hydrocarbon gas, or for Fischer-Tropsch synthesis, as these are both exothermic reactions. Fischer-Tropsch synthesis is carried out at an elevated pressure, typically at least 1 .8 MPa; the preferred reaction conditions are a temperature of between 215^ and 235°C, and a pressure in the range from 2.1 MPa up to 2.7 MPa, for example 2.6 MPa. The reactor 30, includes a reactor block 32 formed by direct metal laser sintering of a metal alloy suited to the chemical reaction conditions; the reactor block 32 is shown in section, and only in part. The reactor block 32 may be made with the channels extending vertically, but it may be used with the channels in a different orientation. The structure will be described in the orientation shown in the figure 2, as if the channels extend horizontally. The reactor block 32 is a single integral block of the alloy, and it defines a multiplicity of channels 33, 34 which extend parallel to each other. The first flow channels 33 are shown in horizontal rows, defined by horizontal webs 35 and vertical fins 36. The vertical fins 36 in this example are of thickness 1 .2 mm, and the spacing between the horizontal webs 35 defining the height of the first flow channels in this example is 5 mm; that height is typically in the range between 2 mm and 10 mm. In this example the vertical fins 36 are spaced apart at 10 mm gaps, so the first flow channels 33 are each 5 mm high and 10 mm wide. The second flow channels 34 are triangular in cross-section, defined between the horizontal webs 35 by alternately inclined fins 37. The inclined fins 37 in this example are of thickness 0.75 mm, while the spacing between the horizontal webs 35 defining the height of the second flow channels 34 in this example is 2 mm; that height is typically in the range between 1 mm and 4 mm for good heat transfer. As described above in relation to the reactor block 12, the reactor block 32 may be formed with the channels 33, 34 extending vertically, starting on a base plate of the same material as the block is made of, and which defines rectangular and triangular apertures corresponding exactly to the desired positions of the channels 33 and 34. The block 32 is formed by depositing a thin layer of metal powder, and then scanning over the surface with a high intensity laser to sinter the metal powder together and to the underlying material in those regions that are to become the block 32. This is repeated a very large number of times to create the entire block 32. Each thin layer may for example be of thickness between 10 μηι and 100 μηι, more preferably between 20 μηι and 60 μηι, for example 20 μηι or 40 μηι. The un-sintered powder is then emptied out of the channels 33 and 34.

After forming the reactor block 32, catalyst inserts 38 (only three are shown in Figure 2), carrying a catalyst for the exothermic reaction, are inserted into each of the channels 35. These inserts 38 comprise, in this example, a metal substrate and a ceramic coating acting as a support for the active catalytic material; this may be a corrugated 50 μηι thick foil (typically of thickness in the range from 20-150 μηι) with a ceramic coating acting as a support for the catalytic material. Each insert 38 is shown as consisting of a single such corrugated foil, but as an alternative each insert 38 might consist of a stack of corrugated foils and flat foils occupying the flow channel 35, like the inserts 22 and 24 described above. In use of the reactor 30, the gas mixture to undergo the exothermic reaction would be passed through the first flow channels 33, and a coolant passed through the second flow channels 34. Referring now to figure 3 there is shown a reactor 40 with some features in common with the reactor 30, identical features being referred to by the same reference numerals. The reactor 40 includes a reactor block 42 formed by direct metal laser sintering of a suitable metal alloy; the reactor block 42 is shown in section, and only in part. The reactor block 42 may be made with the channels extending vertically, but it may be used with the channels in a different orientation. The structure will be described in the orientation shown in the figure 3, as if the channels extend horizontally. The reactor block 42 is a single integral block of the alloy, and it defines a multiplicity of channels 43 and 34 which extend parallel to each other. The first flow channels 43 are shown in horizontal rows, defined by horizontal webs 35 and bars 44. The bars 44 in this example are of width 5 mm and of height of 5 mm, and the spacing between the bars 44 in this example is 35 mm. Hence the first flow channels 43 are each 5 mm high and 35 mm wide. The second flow channels 34 are triangular in cross-section, defined between the horizontal webs 35 by alternately inclined fins 37. The inclined fins 37 in this example are of thickness 0.75 mm, while the spacing between the horizontal webs 35 defining the height of the second flow channels 34 in this example is 2 mm; that height is typically in the range between 1 mm and 4 mm for good heat transfer.

The reactor block 42 may be made in the same way as the reactor blocks 12 and 32 described above, with the channels 43 and 44 extending vertically. After emptying the un-sintered powder from the channels 43 and 44, catalytic inserts 46 (only two are shown) are then inserted into each flow channel 43. The inserts 46 are shown as single corrugated foils of the height of the channel 43, but might instead consist of a stack of corrugated foils and substantially flat foils.

In the reactor blocks 12, 32 and 42 the channels 15, 16, 33 and 43 have their largest transverse dimension parallel to the plane of the horizontal webs 17, 35. In an alternative arrangement, not illustrated, the channels may have their largest transverse dimension perpendicular to the plane of the webs 17, 35. In either case the width of the channels is preferably between about 4 and 20 mm. Each reactor block 12, 32 and 42 may for example be 1 .3 m by 1 .3 m, or 1 .2 m by 0.8 m, in plan view perpendicular to the direction of the channels, so the channels would be 1 .3 m long or 0.8 m long, respectively. Preferably the channels 15, 16, 33 and 43 are no more than 1 .5 m long, and preferably at least 0.3 m long.

Since the channels 15, 16, 33 and 43 are required to accommodate a catalyst insert 22, 24, 38 or 46, the channel is preferably of rectangular or square cross-section at least along that portion of its length in which the catalyst is to be inserted, as it is somewhat simpler to make a catalyst insert to fit a rectangular channel than to fit a differently-shaped channel. However, if the channel has an end portion in which and through which no such insert has to pass, then that end portion of the channel may have a different cross-sectional shape. So, considering the reactor block 32, at one end of the reactor block 32 the first flow channels 33 might change into a channel of circular cross-section; there may be a gradual transition between a rectangular cross-section and a circular cross-section. It will also be appreciated that such end portions may extend in a different orientation. For example at one end the first flow channels 15 of the reactor 10 may change direction through 90 °, to communicate with an outlet port at one side of the block 12. Similarly, at one end the second flow channels 16 of the reactor may also change direction through 90 °, to communicate with an outlet port at one side of the block 12; this may be at the same end as for the first flow channels 15, or may be at the opposite end. This can simplify the supply of fluids to or from the channels 15 and 16.

Claims

1 . A method of forming a reactor, the reactor comprising a reactor block which defines a multiplicity of first channels and defines a multiplicity of second channels that are thermal contact with the first channels, wherein the reactor block is produced by additive layer manufacturing.

2. A method as claimed in claim 1 wherein the block is formed from a metal powder.

3. A method as claimed in claim 1 or claim 2 wherein the reactor block is produced by direct metal laser sintering.

4. A method as claimed in any one of the preceding claims wherein during production of the reactor block the channels extend vertically.

5. A method as claimed in any one of the preceding claims wherein the reactor block is produced from a metal powder, and the properties of the powder are varied through the block.

6. A reactor comprising a reactor block wherein the reactor block is made by a method as claimed in any one of the preceding claims.

7. A reactor as claimed in claim 6 also comprising catalyst inserts within each of the channels in which a chemical reaction is to be performed catalytically.