WO2002042704A1

WO2002042704A1 - Heat exchanger and chemical reactor

Info

Publication number: WO2002042704A1
Application number: PCT/GB2001/005131
Authority: WO
Inventors: Keith Thomas Symonds
Original assignee: Chart Heat Exchangers Limited
Priority date: 2000-11-22
Filing date: 2001-11-21
Publication date: 2002-05-30
Also published as: AU2002223851A1; GB0028410D0

Abstract

A heat exchanger and chemical reactor adapted to cause a first process fluid and a second reactant fluid to be mixed, the reactor comprising a bonded stack of plates, the stack containing a plurality of adjacent layers, each layer being formed of one or more plates, the plate(s) of each layer defining a passageway for fluid to travel across the layer from an inlet at a first edge of the plate(s) towards the opposite edge and back to an outlet at the first edge, the layers including a plurality of process fluid layers between temperature control fluids layers, a source of a reactant fluid being connected to the process fluid passageway at an inlet to or outlet from one of the process fluid layers, the inlets and outlets of the process fluid layers being arranged such that the direction of travel of process fluid is reversed between adjacent layers.

Description

HEAT EXCHANGER AND CHEMICAL REACTOR

This invention relates to a combined heat exchanger and chemical reactor, i.e. a reactor in which a first, process fluid can be mixed with a second, reactant fluid while passing through the reactor to cause the desired chemical reaction and thereby the desired product, third fluid. Cooling and/or heating may be applied, as appropriate, to cool an exothermic reaction and/or heat an endothermic reaction.

In our international patent application no. PCT/GB98/01565, publication no. WO 98/55812, there is described a heat exchanger and/or fluid mixing means which may be used as a chemical reactor. The basic heat exchanger/fluid mixing means described in that application comprises a bonded stack of plates, the stack comprising at least one group of main perforated plates, wherein at least two adjacent plates of the group of main perforated plates have their perforations aligned in rows with continuous ribs between adjacent rows and the adjacent plates are aligned whereby the rows of perforations in one plate overlap in the direction of the rows with the rows of perforations of an adjacent plate and the ribs of adjacent plates lie in correspondence with each other to provide discrete fluid channels extending across the plates, a channel corresponding to each row of perforations, the channels together forming one or more fluid passageways across the plates and the passageway(s) in the group of main perforated plates being separated from passageway(s) in any adjacent group of perforated plates by an intervening plate.

The intervening plate may contain holes positioned and dimensioned to provide controlled mixing of the fluids passing through the passageways of adjacent groups of plates. Thus a reactant fluid stream from one group of main perforated plates may be injected via the holes in the intervening plate into a process fluid stream in an adjacent group of main plates. Reaction caused by this injection can be controlled by the pressure differential between the two streams, the size, numbers and spacing of the injection holes and by sandwiching the process fluid stream between the reactant fluid stream and a coolant or heating layer stream, as appropriate.

Alternatively or additionally, inlets for the reactant fluid may be provided through inlets in peripheral borders of appropriate plates to feed the reactant into process fluid passageways.

The chemical reactors of WO 98/55812 have proved very suitable for chemical reactions that are relatively quick, i.e. which have fairly rapid reaction times. For chemical reactions of slower reaction time, the reactors can be adapted to increase residence time of the mixed reactant and process fluids within the reactor by increasing the number of times that the passageways in a group of main perforated plates traverse from a first edge of the plates to the opposite edge and change direction to return to the first edge and so on between the inlet and outlet of that group or layer of plates. For example, from four to sixteen passes across a layer may be used and the injection points where the fluids are mixed may be adjusted accordingly. For instance, it may be desirable not to introduce a second injection point in the stack until a position where the already mixed fluids have had the notionally ideal residence time for optimised reaction.

For chemical reactions that are particularly slow increasing the residence time by increasing the number of passes per layer may not be fully effective. There are practical limits imposed by the manufacturing techniques used to make compact reactors. Thus, in this type of known chemical reactor, a typical structure will have a plurality of groups of main perforated plates i.e. a plurality of layers of passageways for process fluid, between a coolant layer group and a reactant layer group. An unperforated solid intervening plate is positioned between each pair of adjacent groups or layers to prevent unwanted intermixing of the fluids in the various passageways. For example, there may be three process fluid layers above a reactant fluid layer and a coolant layer above the process layers. The process layers can conveniently be fed by integral extensions on an edge of each of their plates to form a feed tank into the passageways of the plates. The process fluid is, therefore, fed as three parallel streams across the plates and the residence time will effectively be the same as it would be for a single process layer. Thus increasing the number of process fluid streams into which reactant can be fed does not in this arrangement increase the time available for chemical reaction to take place.

It is an object of the present invention to provide a heat exchanger and chemical reactor in which slow chemical reactions can be performed.

According to the invention in one aspect there is provided a heat exchanger and chemical reactor adapted to cause a first process fluid and a second reactant fluid to be mixed, the reactor comprising a bonded stack of plates, the stack containing a plurality of adjacent layers, each layer being formed of one or more plates, the plate(s) of each layer defining a passageway for fluid to travel across the layer from an inlet at a first edge of the plate(s) towards the opposite edge and back to an outlet at the first edge, the layers including a plurality of process fluid layers between a pair of temperature control fluid layers, a source of a reactant fluid being connected to the process fluid passageway at an inlet to or outlet from one of the process fluid layers, the inlets and outlets of the process fluid layers being arranged such that the direction of travel of process fluid is reversed between adjacent layers thereby to increase reaction residence time.

According to the invention in another aspect there is provided a method mixing a first process fluid and a second reactant fluid to form a reaction product, the method comprising mixing the process fluid and the reactant fluid in a reactor comprising a bonded stack of plates, the stack containing a plurality of adjacent layers, each layer being formed of one or more plates, the plate(s) of each layer defining a passageway for fluid to travel across the layer from an inlet at a first edge of the plate(s) towards the opposite edge and back to an outlet at the first edge, the layers including a plurality of process fluid layers between a pair of temperature control fluid layers, the inlets and outlets of the process fluid layers being arranged whereby the direction of travel of process fluid is reversed between adjacent layers, the method comprising passing the process fluid along the passageway of the plates and reversing the direction of travel between adjacent layers and supplying reactant fluid to the process fluid passageway at an inlet to or outlet from one of the process fluid layers thereby to increase reaction residence time.

Because the fluid or fluids are caused to travel across the face of the plates on a repeated basis there is enough opportunity for a slow reaction to take place within the reactor.

The plates are preferably rectangular and the invention will, for convenience, be more specifically described below with reference to rectangular plates. The plates can however be of another shape. Because the fluids travel across the plate or plates forming a single layer from a first edge of the plates and return to that edge to leave the layer, it will be appreciated that it is necessary to have an even number of passes back and forth across the layer.

Conveniently, the coolant layer inlets and outlets are positioned on the opposite side of the stack to the process fluid inlet and outlets.

By way of example only, the source of reactant fluid may be connected to join the flow of process fluid at its outlet from the first process fluid layer after the inlet for process fluid into the stack. Thus reactant fluid can conveniently be introduced at the same side of the stack as the process fluid and in a preferred embodiment is fed to join the process fluid as the latter leaves one process fluid layer to enter the next layer.

Preferably the plates have integral external extensions in the form of an exterior solid or apertured loop at or adjacent each of the four corners of the plates. The loops stack together on the outside of the stack of plates to form integral feed tanks for the fluids. Where a fluid needs to enter or leave a layer of plates, the extension loop opens into the plate passageways at that point. Where a fluid needs to by pass one or more layers of plates, the extension loops are closed off from those plate passageways.

Because the process fluid can change direction repeatedly and rapidly within a compact stack of layers, effective mixing with reactant can be achieved and residence time of the mixed fluids can be increased within a relatively compact structure. The number of layers of plates through which the mixed process and reactant fluids pass, and the number of passes across each layer of plates, can be chosen to provide the desired residence time to optimise the required reaction. A stack may conveniently have one or more cooling layers at its inlet end followed by a number of process/reactant layers without intervening cooling layers to enable the reaction with the reactant to proceed. Once the reaction is under way further process/reactant layers may then be interleaved with further coolant layers, as required, to prevent overheating of the reaction. As the reaction speed increases, the number and frequency of cooling layers may need to be increased.

The passageways into the layers of the stack may be formed, for example, by use of plates as described in WO 98/55812.

The invention is applicable to reactions which are slow. Examples include a biochemical reaction involving enzymes or where there is a fluid of a relatively high viscosity examples being oils, polymers and silicone compounds.

Embodiments of the invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which:

Figure 1 is a diagrammatic exploded view of a single stack of plates comprising a chemical reactor of the invention;

Figure 2 is a plan view of an end plate for use in a stack of Figure 1 ;

Figure 3 is a plan view of one plate for use in a fluid passageway layer of the stack; Figure 4 is a plan view of another plate for use with the plate of Figure 3 in a layer of the stack;

Figure 5 is a plan view of another plate for use with the plates of Figures 3 and 4 in a layer of the stack; and

Figure 6 is an enlarged plan view of the central region of a plate similar to the plates of Figures 3, 4 and 5.

In Figure 1 the stack comprises an end plate 10, (which itself may be a stack of thin plates), a coolant layer of plates 12, a separator or intervening plate 14, a layer of process fluid plates 16, a separator plate 18, a layer of reactant/process fluid plates 20, a separator plate 22, another layer of reactant/process fluid plates 24, a separator plate 26, another layer of reactant/process fluid plates 28, a separator plate 30, a coolant layer of plates 32, a separator plate 34, another process/reactant layer of plates 36, a separator plate 38, another coolant layer 40, a separator plate 42, a final coolant layer 44 and one or more top end plates 46.

It will be noted that each plate is rectangular and has an extension loop adjacent each of its four corners. As will be explained below, these loops control flow of the three fluids, coolant, process and reactant, through the stack.

As shown in the drawings, each layer of plates, other than end plates and separator plates, has a "four pass" passageway for fluid, i.e. the fluid enters at one edge of the plates, adjacent a corner, crosses to the opposite edge, turns and re-crosses back to the first edge, returns again to the opposite edge and finally returns to the first edge where it leaves that layer adjacent the other corner of the first edge.

As indicated above, the number of passes and the number of layers can be varied to suit the particular circumstances.

The flow of coolant through the stack is indicated by arrows A and A', flow of process fluid is indicated by arrows B, flow of reactant by arrows C and flow of mixed process and reactant fluids by arrows D.

One end plate of layer 10 is shown enlarged in Figure 2. This plate, 100, has a solid imperforate central region 101 to prevent escape of coolant fluid from the adjacent layer 12 in the stack.

Plate 100 has four extension loops 102, 103, 104, 105, each being adjacent a corner of the plate. (These and similar extensions on other plates in the stack are referred to herein as "loops" although not all of them have a through hole or perforated central region. Some of the "loops" are imperforate, i.e. solid, and so, strictly speaking, are lugs not loops.). The loops are in pairs, one pair 102, 103 being at a first edge 100A of the plate and the other pair 104, 105 being at the opposite edge 100B of the plate.

Loop 105 is an imperforate loop so that no fluid flow takes place through that loop. Loops 102, 103 and 104 each have a through hole 102A, 103A, 104A through which fluid can flow. Reference to Figure 1 will show that coolant flow A passes through the hole of loop 104, process fluid flow B passes through the hole of loop 102 and reactant fluid flow C passes through the hole of loop 103. Plate 100 also has four location lugs 106, each containing a hole, one lug being located centrally on each edge of the pate. These lugs correspond to similarly positioned lugs on all the plates of the stack whereby the plates may be readily assembled to form the stack. Plate 100 also has an identification tab 107 which is positioned on one edge face of the plate. This tab position represents an easily-identifiable visual code representing the specific arrangement of extension loops on the plate. By this means it can be identified for assembly at the correct position in the stack before the stack is bonded.

In Figures 3, 4 and 5 are shown respectively plates 120A, 120B and 120C. Coolant layer 12 in Figure 1 is formed from six plates stacked above plate 100 in the order 120A, 120B, 120C, 120A, 120B, 120C. (An enlarged version of a similar plate is shown in Figure 6 and will be described in more detail below.).

Plate 120A, Figure 3, has a central region with a peripheral border 121, the central region defining a four-pass passageway from an inlet extension loop 124 to an outlet extension loop 125 on the same edge of the plate. Extension loops 122 and 123 on the opposite edge of the plate are closed off from the fluid passageways by portions 121 A, 121 B of border 121 whereas these border portions have been removed from within loop 124 and 125. Loops 124 and 125 are, therefore, inlet and outlet loops respectively and loops of the type of loops 122 and 123 will be referred to as bypass loops.

The plate has four location lugs 126 with holes, the lugs corresponding to those of plate 100, and an identification tab 127. Plates 120B and 120C of Figures 4 and 5 respectively are of essentially the same construction as plate 120A but differ in the position of the slots 128 that are formed in rows across the central regions of the plates. As can be seen by a comparison of the rows of slots in Figures 2, 3 and 4, when plates 120A, 120B and 120C are stacked together, the slots of adjacent plates will overlap. This forms the fluid passageways as described in greater detail below with reference to Figure 6.

Like parts on plates 120A, 120B and 120C have been given the same reference numerals.

In the stack of Figure 1 coolant having passed through the hole in loop 104 divides on reaching layer 12, some of the coolant passing upwardly (stream A) through inlet loops 124 and some passing from loops 124 to enter and pass through layer 12 as indicated by the arrows. This coolant leaves layer 12 from outlet loops 125 to form a second stream A' of coolant passing up the stack.

Above layer 12 is a separator plate 14. This plate has a solid, imperforate central region 141 to enclose coolant in layer 12 between itself and end plate 10. Plate 14 has four extension bypass loops 142, 143, 144 and 145 corresponding in position to the extension loops of the other plates and each of these four loops has a central aperture to allow through flow of one each of the two coolant streams (through loops 144 and 145), the process fluid stream (through loop 142) and the reaction fluid stream (through loop 143). The plate also has four positioning lugs 146 and an identification tab 147. Above plate 14 is a layer 16 formed from six plates. These plates are identical to the six plates 120A, B, C, A, B, C, of layer 12 except for their extension loop arrangements and the position of their identification tabs 167.

In the plates of layer 16, extension loops 164 and 165 are closed off from the passageways across the plates, i.e. are bypass loops, so that the two coolant streams from the plates below continue unhindered on their passage on the outside of this portion of the stack. Extension loops 162 and 163 open into the passageways across the plates, loops 162 providing an inlet and loops 163 an outlet. Thus process fluid in stream B enters layer 16 through the inlet of loops 162 and after four passes across the plates leaves through the outlet of loops 163. Moreover, as shown, reactant stream C joins the process fluid by passing through loops 163 and a combined process/reactant stream D continues up the stack.

The next plate, plate 18, is another separator plate having a solid imperforate central region 181. Its extension loop 182 is imperforate and prevents process fluid continuing straight up the stack but diverts it into the passageways of layer 16. Its loop 183 has a central aperture to allow flow of streams B and C, i.e. combined stream D to continue. Similarly loops 184 and 185 are apertured to allow the two coolant streams to continue. Again, plate 18 has four positioning lugs 186 and an identification tab 187.

Above plate 18 is a layer of plates 20 of identical construction to layer 16. Process/reactant stream D does a four-way pass across layer 20. However, this flow is in the reverse direction to that across layer 16 and this is achieved by separator plate 22 above layer 20. Separator plate 22 is identical to separator plate 18 except for the arrangement of its extension loops. Loops 224 and 225 are apertured, as in plate 18, to allow continuing flow of coolant streams A and A'. Extension loop 223 is imperforate whereas loop 222 is apertured. Thus stream D enters layer 20 at inlet loops 203 and leaves at outlet loops 202, i.e. the entry and exit ports are transposed in comparison with layer 16, thereby reversing the direction of flow of the combined process fluid/reactant stream D.

Layer 24 above plate 22 is identical to layer 16. The two streams A and A' of coolant, therefore, pass through its bypass loops 244 and 245 and continue up the stack while stream D enters through inlet loops 242 and exits through outlet loops 243. Separator plate 26 above layer 24 is identical to plate 18 and so has the same extension loop arrangement to allow flow into the inlets of loops 242 and out of loops 243, i.e. its loop 262 is imperforate and its loop 263 is apertured. Loops 264 and 265 are also apertured to allow continuing flow of the coolant streams.

Layer 28 above separator plate 26 is identical to layer 20 and hence, in conjunction with plate 30 above it, which is identical to plate 22, again reverses the direction of flow of stream D, which enters at inlet extension loops 283 of layer 28 and leaves at outlet loops 282. Thus extension loop 303 of plate 30 is imperforate and loops 302, 304, 305 are apertured to allow through flow of their respective streams.

Above plate 30 is a coolant layer 32. This has six plates similar to the plates of coolant layer 12. However, these plates of layer 32 are different in respect of the arrangement of their extension loops and the position of their identification tab 327. Loops 324 and 325 are apertured to form respectively an inlet into and an outlet from the layer 32 whereby coolant from stream A passes through that layer and can cool the stream D in adjacent process/reactant layers above and below. The coolant leaves outlet loops 325 where it joins coolant stream A¹ passing up the stack. This aperture arrangement is as in layer 12. Loops 322 are apertured but are bypass loops so that stream D continues up the stack without entering the passageways in the plates of layer 32. Extension loops 323 are solid, i.e. imperforate.

Above layer 32 is a separator plate 34 having bypass loops 342, 344 and 345 corresponding to loops 322, 324 and 325 and an imperforate loop 343 corresponding to loop 323.

Above separator plate 34 is a layer 36 formed from six plates identical to those of layer 24. Separator plate 38 above layer 36 is identical to plate 26. Thus its imperforate loop 382 diverts flow into inlet loops 362 and its apertured loop 383 allows flow out from outlet loops 363 to continue up the stack. Its apertured loops 384, 385 allow continued flow of the coolant streams A and A'.

A coolant layer 40 lies above plate 38. This has a similar plate arrangement to the previous coolant layers but has a different extension loop arrangement. Loops 402 are imperforate and loops 403 are bypass loops to allow stream D to bypass this layer. Loops 404 are inlet loops to allow coolant from stream A into the layer and loops 405 are outlet loops where the coolant exits to join stream A'.

Separator plate 42 above layer 40 has an imperforate extension loop 422 and bypass loops 423, 424 and 425 for the process/reactant stream D, coolant stream A and coolant stream A' respectively. This plate is identical to plate 38. Above plate 42 is a final coolant layer 44. This is identical to layer 40. It allows coolant from stream A through the layer via inlet loops 444 and they exit to join stream A'; through outlet loops 445. Loop 442 is imperforate and loop 443 is a bypass loop for the process/reactant stream D. Coolant stream A does not continue beyond layer 44. It is stopped, other than passing through layer 44, by imperforate loops 464 of top closure plates 46. Thus a single coolant stream A' and product stream D exit the stack. Plates 46 above layer 44 have two imperforate extension loops 462, 464 and apertured loops 463 and 465 to permit outflow of streams A' and D.

In Figure 6, perforated plate 500 for use in the invention is of rectangular shape, having four edges 500A, 500B, 500C, 500D. It has a series of perforations in the form of elongated slots 51 1 through its thickness. The slots 511 lie in parallel rows forming four main groups of rows extending across the plate between edges 500A and 500C. As shown there are 16 rows of slots in each group of rows but it will be appreciated that more or less rows of slots per group (and more of less groups across the plate) may be employed, if desired.

Transverse bars or flow interrupters 512 separate each slot from adjacent slots on the same row. (It will be appreciated that bars 512, which are shown normally across the plate, could if desired be angled.). Narrow fins or ribs 513 extending in the direction of the slots separate each slot in a row from a slot in an adjacent row.

An unperforated border region 514 extends around the edges of the plate.

Positioning lugs 17 are integrally-formed at the mid-region of each edge 500A, 500B, 500C, 500D. As the rows of slots 511 of the first group from inlet A approach the border 514 at edge 500C, an L-shaped slot 519A turns its row through a right angle so that the row which ran parallel to edge 500D now continues parallel to edge 500C. A second L-shaped slot 519B then turns each row through a second right angle so that the rows, now forming the second group of rows, continue back across the plate parallel to edge 500D. This pattern is repeated when the second group of rows of slots approaches the border at edge 500A, with L-shaped slots 519C turning the rows to continue parallel to edge 500A and then L- shaped slots 519D turning the rows again to run parallel to edge 500B.

Finally, when the rows approach the border at edge 500C again, they are turned by L- shaped slots 519E to run parallel to edge 500C and then by L-shaped slots 519F to run parallel to edge 500B to reach outlet B.

It will be appreciated in the case of plates 120A , 120B and 120C of Figures 3, 4 and 5 that the transverse bars are out of alignment from one plate to the next. Thus when a plurality of plates such as plates 120A, 120B 120C is superposed one on the other with their edges aligned, the transverse bars 512 of one plate will be sufficiently out of alignment with those of the other plates so as not to overlap therewith. Flow channels are, thereby, provided along the rows of slots as the transverse bars do not prevent flow. Because the fins or ribs 513 of the superposed plates are aligned, each row of slots provides a discrete flow channel separated from adjacent flow channels.

Thus when the superposed plurality of plates is bonded between a pair of unperforated or separator plates, a group of independent, discrete flow channels will form a passageway which crosses and re-crosses four times through the layer so formed. Fluid can,

Claims

therefore, enter the stack in the direction of arrows A (Figure 6) via a suitable inlet, e.g. as described above, and leave from the same edge in the direction of arrows B via a suitable outlet, e.g. as described above.It will be appreciated that a second or additional injection sites for reactant can be built into the stack, each further injection point being positioned to ensure that the notionally ideal residence time for the previously mixed process and reactant fluids has been achieved before further reactant is introduced.It will also be appreciated that, if desired, the coolant flow across the coolant layers may be reversed in direction from one coolant layer to the next in a similar manner to that described above for the process fluid layers in order to better control the coolant circulation.The structures of the invention have significant advantages, particularly for slow reaction processes. Not only do they enable rapid and frequent changes of direction for the mixed process and reactant stream, which increased turbulence can greatly assist promotion of the reaction, the changes or direction can be achieved in a compact design which is virtually impossible to achieve in a heat exchanger of conventional design. Moreover, the reactant can be introduced through a large inlet formed by the stacked extension loops of a plurality of plates, thereby enabling significant mixing to take place from a single inlet. This latter feature is particularly useful for fluids of high viscosity.The invention is not limited to the embodiment shown. The plates need not be rectangular. The number and disposition of the plates will be varied according to need. The reactor could have fluid supply means at locations other than the corner extensions. The feed systems for the fluids may be different from that shown. CLAIMS

1. A heat exchanger and chemical reactor adapted to cause a first process fluid and a second reactant fluid to be mixed, the reactor comprising a bonded stack of plates, the stack containing a plurality of adjacent layers, each layer being formed of one or more plates, the plate(s) of each layer defining a passageway for fluid to travel across the layer from an inlet at a first edge of the plate(s) towards the opposite edge and back to an outlet at the first edge, the layers including a plurality of process fluid layers between temperature control fluid layers, a source of a reactant fluid being connected to the process fluid passageway at an inlet to or outlet from one of the process fluid layers, the inlets and outlets of the process fluid layers being arranged such that the direction of travel of process fluid is reversed between adjacent layers.

2. A reactor according to Claim 1 , wherein the fluids are arranged to travel in an even number of passes across a layer.

3. A reactor according to Claim 1 or 2, wherein the plates are generally rectangular and have extensions at least some of which define means for the passage of the process fluid or reactant fluid.

4. A reactor according to Claim 3, wherein the extensions are in the form of an exterior solid or apertured loop adjacent each of the four corners of the plates whereby the loops stack together on the outside of the stack of plates to form integral feed tanks for the fluids.

5. A reactor according to any preceding Claim, wherein inlets and outlets for a coolant temperature control layers are positioned on the opposite side of the stack to the inlet and outlets for the process fluid layers.

6. A reactor according to Claim 4, wherein the reactant fluid is introduced at the same side of the stack as the process fluid and is fed to join the process fluid as the latter leaves one process fluid layer to enter the next layer.

7. A reactor according to Claim 6, wherein the source of reactant fluid is connected to the stack to join the flow of process fluid at its outlet from the first process fluid layer.

8. A reactor according to any preceding Claim, comprising layers for process fluid, for coolant, for reactant, for separation and for process/reactant.

9. A reactor according to Claim 8, comprising an end plate layer, a coolant layer, a separator layer, a process fluid layer, a separator layer, a reactant/process layer, a separator layer, a reactant/process layer, a separator layer, a reactant/process layer, a separator layer, a coolant layer, a process/reactant layer, a separator layer, a coolant layer, a separator layer, and a coolant layer and an end plate layer.

10. A method mixing a first process fluid and a second reactant fluid to form a reaction product, the method mixing the process fluid and the reactant fluid in a reactor comprising a bonded stack of plates, the stack containing a plurality of adjacent layers, each layer being formed of one or more plates, the plate(s) of each layer defining a passageway for fluid to travel across the layer from an inlet at a first edge of the plate(s) towards the opposite edge and back to an outlet at the first edge, the layers including a plurality of process fluid layers between a pair of temperature control fluid layers, the inlets and outlets of the process fluid layers being arranged whereby the direction of travel of process fluid is reversed between adjacent layers, the method comprising passing the process fluid along the passageway of the plates and reversing the direction of travel between adjacent layers and supplying reactant fluid to the process fluid passageway at an inlet to or outlet from one of the process fluid layers.

11. A method according to Claim 10, including causing the fluids to travel in an even number of passes back and forth across the layer.