HEAT EXCHANGER

Abstract: A first portion of the assembly is formed of one or more first perforated plates (26), to define a first series of slots (36) and a second series of slots (46), each slot (36) of the first series being positioned between a pair of slots (46) of the second series, defining first passageways through the first portion for a first fluid and second passegeways through the first portion for a second fluid. A second portion of the assembly is formed of one or more second plates (20, 22, 20A) being perforated to define a first (36, 36B) and a second (46, 46B) series of slots corresponding to the slots of the first plate(s) each slot (46, 46B) of the second series opening at each of its ends into a feeder slot (40A, 40B) extending around the second plate adjacent its periphery, the feeder slot (40A, 40B) being connected to an inlet (24) or an oulet (34) for the second fluid.

Description: DESCRIPTION HEAT EXCHANGER This invention relates to heat exchangers. It is particularly concerned to provide a heat exchanger that can be used as a packed bed catalytic reactor or for the cooling or recuperation of heat f om gas flues, e.g. of ovens for the manufacture of a variety of products, e.g. bread, and for food processing and furnaces used for heat treatment. However, it will be appreciated that the invention is not intended to be limited to such uses and a structure of the invention may be used, for example, as a "bulk fluid" heat exchanger wherein one of the fluids passing through the structure comprises granules or powder constituents. Structures of the invention may equally, if desired, be used to exchange heat between two liquids, two gases or between a gas and a liquid. Nevertheless, the invention will for convenience be more particularly described with reference to packed bed catalytic reactors. In a packed bed catalytic reactor it is necessary to pass a first fluid or mixture of fluids, which is to react in a desired manner, into contact with a bed of a catalyst which promotes the reaction. The reaction may be exothermic, in which case it may be necessary to cool the reacting fluid(s), or endothermic, in which case it may be necessary to heat the fluid(s) to promote the desired reaction. In both instances, it will be appreciated that a heat exchanger structure may usefully be employed so that heat may be added to or taken f om the fluid(s) passing into contact with the catalytic material. Known heat exchanger constructions for use as packed bed catalytic reactors are generally based on existing tube and shell technology and hence are not as efficient in terms of performance per unit volume as would be reactors of more compact construction. It is, therefore, one object of the present invention to provide an improved construction that is particularly useful as a packed bed catalytic reactor. It is a further object of the invention to provide an improved heat exchanger construction that is particularly useful for the cooling or recuperation of heat from oven flues. Accordingly, in one aspect, the invention provides a stacked assembly of plates, the stack having an inlet and an outlet for a first fluid and an inlet and an outlet for a second fluid, a first portion of the length of the assembly being formed of one or more first perforated plates, each first perforated plate being perforated to define a first series of slots spaced across the plate and a second series of slots spaced across the plate, each slot of the first series being positioned between a pair of slots of the second series, whereby the slots of the first series define first passageways through the first portion of the length for a first fluid and the slots of the second series define second passageways through the first portion of the length for a second fluid, the first series of passageways being connected to said inlet and outlet for the first fluid, a second portion of the length of the assembly being formed of one or more second perforated plates, each second perforated plate being perforated to define a first and a second series of slots corresponding to the slots of the first plate(s) so as to provide continuing passageways in line with the first and second passageways of the first portion, each slot of the second series opening at each of its ends into a feeder slot extending around the second plate adjacent its periphery, the feeder slot being connected to an inlet or an outlet for the second fluid. In another aspect the invention provides a heat exchanger comprising a stacked assembly of plates as defined in the immediately preceding paragraph. In a yet further aspect the invention provides a perforated plate for a heat exchanger, the plate being perforated to define a first series of slots spaced across the plate and a second series of slots spaced across the plate, each slot of the first series being positioned between a pair of slots of the second series, each slot of the second series opening at each of its two ends into a feeder slot extending around the plate adjacent its periphery. In one embodiment the assembly has a third portion of its length formed at the other end of the first portion, the plate(s) of the third portion being of a similar construction to the plates of the second portion with the feeder slot being connected to an outlet or an inlet accordingly for the second fluid. If desired, the, or each, plate of the third portion is positioned to have its inlet or outlet on the opposite side of the assembly to the outlet or inlet of the first portion, whereby the second fluid must cross the assembly from one side to the other between the second fluid inlet and outlet. The first fluid is conveniently the fluid to contact the catalyst when the structure of the invention is to be used as a packed bed catalytic reactor and the catalyst will, therefore, be packed into the first series of passageways through the assembly. The second fluid, correspondingly, will be a coolant or a source of heat, as required. Similarly for cooling or heat recuperation purposes, the flue gases will be passed along the first series of passageways and the fluid to remove heat therefrom will be passed along the second series of passageways. The plates may be of any suitable shape, e.g. they may be discs, i.e. they may be circular in plan, and the slots may be arcuate or linear. In another preferred embodiment of the invention, the assembly of plates includes at one or each end thereof a perforated closure or end plate. The closure plate may, for example, have a first series of slots corresponding to the first passageways, whereby the first fluid can flow uninterrupted through the closure plates, but no slots corresponding to the second passageways, whereby the second fluid is diverted into the inlet and/or outlet provided into or out of the second plate(s). Conveniently all the plates may be of the same external dimensions in plan so that they can be readily assembled together to provide the desired passageways through the assembly. The plates may conveniently all be of the same thickness, e.g. from 1 mm to 12 mm. However, this is not essential and it may be found advantageous in particular circumstances to use plates of different thickness in the assembly. The plates may be brazed or bonded together to form the stack. For example, the plates may be of clad aluminium or of stainless steel. The required perforations may be cut, for example, by high pressure water jet or by etching, blanking or laser cutting. The perforated plates can then be vacuum brazed or bonded together and any required inlet and outlet connections and tanks can be welded to the bonded stacked assembly. The feeder slot may extend entirely around the plate adjacent its perimeter, i.e. in a continuous slot without end, or it may extend around the majority of the perimeter but have its two ends separated by a short solid region of plate. It will be appreciated that each perforated plate will have a solid peripheral region extending around its perimeter and that each slot will be surrounded by a solid region of plate except at the open ends of the second slots where they open into the feeder slot. Adjacent solid regions extending between adjacent pairs of first slots may, therefore, need to be connected together by one or more strengthening tie bars extending across an intervening second slot. One such a tie bar may conveniently be positioned towards each open end of the second slot. Similarly, the feeder slot is defined inside a solid edge portion around the perimeter of the plate. If it is desired to feed into the second fluid inlet from a side of the plate, then a gap must be provided in the solid edge portion for that purpose, thereby providing an inlet into the feeder slot. However, this may not be necessary if it is desired to feed into the feeder slot in the direction of the thickness of the plate rather than transversely to that direction. If a gap is provided in the solid edge portion, then one or more tie bars may be needed, preferably adjacent that gap to connect the solid edge portion to a solid region at the inside perimeter of the feeder slot. Of course, if the feeder slot extends continuously around the plate, then one or more tie bars will in any event be needed to extend across the feeder slot between the solid edge portion of the plate and a solid region at the inside perimeter of the feeder slot. Whether or not tie bars will be needed across the first and second slots will be determined by the rigidity of the perforated plates and hence will be determined by their material and their thickness. It will be appreciated that in order to bond the stack together effectively, there should be little or no undue movement of any solid regions of the plate out of the plane of the plate during handling. It will be appreciated that references herein to a continuous slot are meant to include a slot with one or more tie bars across it. Thus a feeder slot may extend continuously around the plate but be sub-divided into a series of sub-slots by tie bars. Where one or more tie bars is necessary in the second plates, it will be necessary to utilise at least two different second plates. Although they may be essentially of the same slotted construction, they differ in the positioning of their tie bars so that when two such second plates are stacked together, although their feeder slots and first and second passageway slots respectively align with each other, their tie bars are offset from each other. By this means, fluid can flow over the tie bars whereas if the tie bars were located together, flow across the stack would be prevented. Injection plates may be provided in the stack whereby one or more further fluids can be injected into the first fluid as it passes through the stack. A typical injection plate may be a modified first type of plate in which an injection channel is provided in the form of a groove extending only partially into the thickness of the plate. The groove may extend from an edge of the plate to pass adjacent the ends of the first slots that lie towards that edge of the plate and then branch grooves from the main groove may extend into each slot. Because the groove does not extend completely through the thickness of the plate it will be sealed by contact between that plate and solid regions of an adjacent plate in the stack. Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic elevation of a heat exchanger of the invention; Figure 2 is a plan view of an end plate for use in the heat exchanger of Figure 1; Figure 3 is a plan view of a first perforated plate for use in the heat exchanger of Figure 1; Figure 4 is a plan view of one second perforated plate for use in the heat exchanger of Figure 1; Figure 5 is a plan view of a second type of second perforated plate; Figure 6 is a plan view of a third type of second perforated plate; Figure 7 is a plan view of a fourth type of second perforated plate; and Figure 8 is a plan view in enlarged scale of a portion of the plate of Figure 4. In Figure 1 a heat exchanger is formed of a stacked assembly 10 of perforated plates. The individual plates are described in greater detail below with reference to Figures 2 to 8. The stack 10 has an inlet end 12 and an outlet end 14 for flow therethrough of a first fluid which is to pass in the direction of arrow A. Where the stack is to be used as a catalytic reactor, the first fluid passageways will be packed with a catalyst. Where the stack is to be used for heat recuperation purposes, they will not normally be packed with catalyst. An end plate 18 is positioned at each end of the stack of plates. Plate 18 is described in more detail below with reference to Figure 2. Where the first passageways are packed with catalyst, a mesh cover may be positioned immediately below plate 18 at the outlet end of the stack to retain the catalyst therein. Stacked in succession above end plate 18 are, firstly, a second type of perforated plate 20, a modified second type of perforated plate 22 and another second type of perforated plate 20 A, identical to plate 20. Plates 20, 20A and 20 form the aforesaid second portion of the length of the assembled stack and provide an inlet 24 for a second fluid, e.g. a coolant, into the stack. Plates 20 and 22 are described in more detail below with reference to Figures 4 and 5 respectively. Immediately above plate 20A are ten identical first type of perforated plates 26, forming the aforesaid first portion of the length of the assembled stack. A plate 26 is described in more detail below with reference to Figure 3. Above plates 26 is a further assembly of a further second type of perforated plate 30, a modified further second type of perforated plate 32 and another second type of perforated plate 30A, identical to plate 30. Plates 30, 32 and 30A provide an outlet 34 for the second fluid from the stack and form the aforesaid third portion of the length of the assembled stack. Plates 30 and 32 are described in more detail below with reference to Figures 6 and 7. The first type of perforated plates 26 are as illustrated in Figure 3. Each plate is circular in plan and has a first series of linear slots 36 through its thickness and segmental slot 36A at each end of the row of slots 36. Each slot 36 extends between a pair of parallel chords 37 defining a land 39 across the plate. The ends of each slot 36 lie inside a solid perimeter edge portion 38 of the plate and a continuous slot 40 extends around the plate between solid perimeter edge 38 and the ends of slots 36. At one side, the plate has two adjacent lugs 42, 42A. These lugs line up with corresponding lugs in other plates of the stack. Slot 40 has a spaced series of tie bars 41 anchoring it between edge 38 and the central region of the plate. Each plate also has a second series of linear slots 46 through its thickness. Each slot 46 extends across a land 39 of the plate the land being defined, as indicated above, between adjacent pairs of chords 37, i.e. each slot 46 lies between an adjacent pair of slots 36. Slots 46 and slot 40 are fed with second fluid, e.g. coolant, by means of second plates to be described below with reference to Figures 4 and 5, and can thereby provide cooling between slots 36 (and 36 A) and around the exterior of the stack. Each slot 46 opens at each of its ends into continuous slot 40 and each slot 46 has a number of tie bars 48 extending across its width and spaced along its length. Thus each slot 46 is divided into a number of sub-slots. The slots 36 and the slots 46 (and slot 40) of plates 26 form respective passageways for the first fluid and the second fluid when the plates are stacked together. One second type of plate 20 is shown in Figure 4. Plate 20 is also circular in plan and has a first series of linear slots 36' and 36A' identical to the slots 36 and 36A in plate 26. Plate 20 also has a second series of slots 46' corresponding in size and location to slots 46 of plate 26. Slots 36', 36A' and 46' lie inside a solid peripheral margin 38' and slots 46' open into a feeder slot 40 A extending continuously around and adjacent the perimeter of the plate. Slot 40 A has tie bars 41A and slots 46' have tie bars 48A. Feeder slot 40A is fed from an inlet hole 44 in a lug 42A' corresponding in location to lug 42 of plate 26. (A second lug 42' corresponding in location to lug 42 of plate 26 also carries a hole 44A but this is not connected to feeder slot 40A.). Inlet hole 44 will correspond directly with the inlet 24 shown in Figure 1. It will be appreciated that an assembly of two or more plates such as plate 20 in direct contact with each other would prevent flow of second fluid around the feeder slot 40 A as the tie bars 41 A nearest to inlet 44 would stack together to form a barrier to flow and so prevent flow into slots 46'. Flow along slots 46' would also be prevented by the stacking together of their tie bars 48A. A modified type of second plate, perforated as shown in Figure 5, is therefore utilised. In Figure 5 plate 22 is similar to plate 20 in that it has identical series of slots 36B and 36B' corresponding to slots 36' and 36A' and has slots 46B corresponding to slots 46'. It also has a feeder slot 40B into which slots 46B open, slot 40B extending continuously around the plate perimeter inside solid peripheral margin 38B. Plate 22 is also provided with tie bars 48B in slots 46B and tie bars 41B in feeder slot 40B for the same reason as in plate 20. However, the tie bars in plate 22 are spaced at different intervals compared with those in plate 20. The tie bars of adjacent plates do not, therefore, stack together when the plates are assembled together but lie apart so that second fluid can flow under and over them to pass around the feeder slots and along the second slots of the stacked plates. Feeder slot 40B is in communication with an inlet hole 44B in lug 42B corresponding in location to hole 44 and lug 42A' in Figure 4 and again, corresponding directly with inlet 24 of Figure 1. A second lug 42C with a hole 44C corresponding in location to lug 42' and hole 44A of Figure 4 is provided but is not connected to the feeder slot 40B. When three plates 20, 22 and 20 are stacked together in the assembly, therefore, second fluid can pass via inlet 24 through inlet holes 44 and 44B into feeder slots 40A and 40B to travel completely around the feeder slots and across the second slots 46', 46B. This flow is shown and described in more detail below with reference to Figure 8. The skilled man of the art will readily be able to size the passageways formed by slots 40 A, 40B, 46' and 46B so that adequate flow takes place completely around the feeder slots and across the second series of slots. Thus it will be appreciated that not all the second slots need be of the same width and, generally speaking, slots further from the inlet holes may be wider than those adjacent the inlet holes. The closure plates 18 used at each end of the stack is shown in Figure 2. It has a solid perimeter 50 inside which is a first series of slots 56 and 56A corresponding to slots 36, 36', 36B and 36A, 36A' and 36B' of plates 20, 22 and 26 so that flow of first fluid through the stack is not interrupted. It also has solid unperforated lands 58 between adjacent pairs of slots 56 and between adjacent slots 56 and 56A, i.e. it has no slots corresponding to second fluid slots 46, 46' and 46B in lands 39 in plates 26, 20 and 22. The second fluid flow channels, therefore, are closed off at each end of the stack and the second fluid flows into the stack via inlet 24 and holes 44 and 44B as described above. It flows out of the stack as described below with reference to Figures 6 and 7. Plate 50 has lugs 52, 52A with holes 54, 54A corresponding in position to those of the other plates. These do not have a flow function but help to ensure adequate bonding together of the plates to form the desired completed stacked assembly. In Figure 6 is shown another second type of perforated plate 30. This is essentially of the same construction as plate 20 except in respect of its outlet hole and lug. Thus the inlet and outlet to the stack, contrary to as shown in Figure 1, are shown to be on the same side of the stack. This is useful in certain circumstances, e.g. difficulty of access all around the stack, where it may be necessary to position the inlet and outlet at the same side of the stack. However, this is not essential and it may be desired in many circumstances to position the inlet and outlet on opposite sides of the stack as is shown in Figure 1. Thus plate 30 has a series of first fluid slots 36C, 36C and second fluid slots 46C and a continuous feeder slot 40C, all corresponding to those of plate 20. Slots 46C have tie bars 48C and slot 40C has tie bars 41C. Solid outer periphery 38C has two lugs 42C and 42B' positioned in the stack in correspondence with the lugs of plates 20 and 20 A. The lugs 42C, 42B' each has a hole 44C, 44B' respectively and of these only hole 44C is connected to feeder slot 40C. Hole 44C is an outlet hole enabling second fluid to proceed to an outlet similar to outlet 34 of Figure 1 but on the same side of the stack as inlet 24. As with plates 20 and 22, a second plate 32 is required to be stacked with plate 30 to prevent stacking together of their tie bars should identical plates be used. Plate 32 is shown in Figure 7. It differs from plate 22 in the same manner that plate 30 differs from plate 20. Thus the lug and hole for outlet purposes do not correspond to the ones used in plate 20. Thus plate 32 has a series of first fluid slots 36D, 36D', and second fluid slots 46D and a continuous feeder slot 40D, again corresponding to the slots of plate 22. Slots 46D have tie bars 48D and slot 40D has tie bars 41D. These tie bars are positioned at different intervals in their respective slots to the tie bars of plate 30. Thus in a stack of plates 30, 32, 30A (30A being identical to 30) second fluid can flow between the slots 46D and 40D to the outlet by passing under and over the staggered tie bars. Plate 32 has two lugs 42B" and 42C" each with a hole 44B" and 44C" respectively. Hole 44C" communicates with feeder slot 40D thereby providing an outlet route but hole 44B" is again not connected to the feeder slot. Thus it can be appreciated that the stack of Figure 1 provides a through route via the channels of the first series of slots for a first fluid and a second fluid through route via inlet 24, the feeder slots 40A, 40B, the second series of slots and circumferential slots 40 through the stack to outlet feeder slots 40C, 40D to the outlet 34. Where it is desired to have the inlet and outlet on opposite sides of the stack, it may be preferable to provide all the plates with two diametrically opposed pairs of lugs so that the lugs stack together along the complete length of the stack on both sides of the stack for bonding purposes, although one of such pairs of lugs on each plate is unnecessary for flow purposes. In Figure 8, a portion of the second fluid flow path into the plate 20 of Figure 4 is shown in greater detail, the flow being indicted by the arrows. Second fluid enters through hole 44 in lug 42A' and travels into feeder slot 40A via a short feeder slot 45. Its flow splits to proceed in both directions around feeder slot 40A and, passing under and over tie bars 41 A (which are spaced from corresponding tie bars in adjoining plates in the stack) proceeds around the feeder slot to the far side of the plate (not shown).. As the fluid passes the entry to each slot 46', its flow splits to provide a stream along that slot, passing under and over tie bars 48A until it rejoins the feeder slot in the far side of the plate. The fluid continues its travel longitudinally through the stack via the passageways formed by the slots in plates 26. It will also be appreciated that the invention can be varied widely from the embodiments shown, e.g. in respect of the number and width of the slots and the number and positioning of the tie bars. In the embodiments shown, the first fluid slots have been shown much wider than the second fluid slots. This arrangement is particularly useful for the cooling of oven flue gases. However, different width ratios may be appropriate for different end uses. Moreover, as indicated above, the width of the second series of slots may vary from slot to slot - or the width of the entries to those slots may vary - to ensure appropriate temperature distribution throughout the stack.

Claims: CLAIMS 1. A stacked assembly (10) of plates, the stack having an inlet (12) and an outlet (14) for a first fluid and an inlet (24) and an outlet (34) for a second fluid, characterised in that a first portion of the length of the assembly is formed of one or more first perforated plates (26), each first perforated plate (26) being perforated to define a first series of slots (36) spaced across the plate and a second series of slots (46) spaced across the plate, each slot (36) of the first series being positioned between a pair of slots (46) of the second series, whereby the slots (36) of the first series define first passageways through the first portion of the length for a first fluid and the slots (46) of the second series define second passageways through the first portion of the length for a second fluid, the first series of passageways being connected to said inlet (12) and outlet (14) for the first fluid, a second portion of the length of the assembly being formed of one or more second perforated plates (20, 22, 20A), each second perforated plate (20, 22) being perforated to define a first (36, 36B) and a second (46, 46B) series of slots corresponding to the slots of the first plate(s) so as to provide continuing passageways in line with the first and second passageways of the first portion, each slot (46, 46B) of the second series opening at each of its ends into a feeder slot (40A, 40B) extending around the second plate adjacent its periphery, the feeder slot (40A, 40B) being connected to an inlet (24) or an outlet (34) for the second fluid. 2. A stacked assembly according to Claim 1, characterised in that a third portion of the length of the assembly at the opposite end of the first portion to the second portion is formed of one or more plates (30, 32, 30A) of similar construction to the plates of the second portion with the feeder slot being connected to an outlet (34) or an inlet (24) accordingly for the second fluid. 3. A stacked assembly according to Claim 2, characterised in that the or each plate (30, 32, 30A) of the third portion is positioned to have its inlet (24) or outlet (34) on the opposite side of the assembly to the inlet (24) or outlet (34) of the first portion. 4. A stacked assembly according to Claim 1, 2 or 3, characterised in that the plates (20, 22, 20A, 30, 32, 30A) are circular in plan and the slots (36, 46) are linear. 5. A stacked assembly according to any preceding claim, characterised in that it includes a perforated end plate (18) at one end thereof, the end plate (18) having a first series of slots (56) corresponding to the first passageways but no slots corresponding to the second passageways. 6. A stacked assembly according to any preceding claim, characterised in that the plates (20, 22, 20A, 30, 32, 30A) are all of the same thickness. 7. A stacked assembly according to any preceding claim, characterised in that adjacent solid regions (39) of plate extending between adjacent pairs of first slots (36, 36', 36B) are connected together by one or more tie bars (48, 48A, 48B) extending across an intervening second slot (46, 46' 46B). 8. A stacked assembly according to Claim 7, characterised in that one such tie bar (48A, 48B) is positioned adjacent each open end of the second slot (46', 46B) of a second plate (20, 22). 9. A stacked assembly according to any preceding claim, characterised in that the feeder slot (40A, 40B) extends entirely around its plate (20, 22) adjacent its perimeter and one or more tie bars (41 A, 4 IB) extend across the feeder slot (40A, 40B) to connect together its inside and outside perimeters. 10. A stacked assembly according to Claim 8 or 9, characterised in that it includes two different second plates (20, 22), each with tie bars (48A, 48B) across their second slots (46', 46B), the plates differing in the positions of their tie bars whereby when the plates are stacked together, their feeder slots (40A, 40B) and first and second passageway slots (36', 36B; 46', 46B) align respectively with each other but their tie bars (48A, 48B) are offset from each other. 11. A stacked assembly according to any preceding claim, characterised in that it includes an injection plate being a modified first type of plate to contain an injection channel in the form of a groove extending only partially into the thickness of the plate and communicating into one or more first slots. 12. A stacked assembly according to Claim 11, characterised in that the groove is a main groove extending from an edge of the plate to pass adjacent the ends of the first slots and branch grooves from the main groove extend into the first slots. 13. A heat exchanger comprising a stacked assembly of plates (10) according to any one of the preceding claims. 14. A perforated plate (20, 22) for a heat exchanger, characterised in that the plate (20, 22) is perforated to define a first series of slots (36', 36B) spaced across the plate and a second series of slots (46', 46B) spaced across the plate, each slot (36', 36B) of the first series being positioned between a pair of slots (46', 46B) of the second series, each slot (46', 46B) of the second series opening at each of its two ends into a feeder slot (40A, 40B) extending around the plate adjacent its periphery.

Inventors: SYMONDS KEITH THOMAS, SYMONDS, KEITH, THOMAS
Applicants: CHART HEAT EXCHANGERS LTD, SYMONDS KEITH THOMAS, CHART HEAT EXCHANGERS LIMITED, SYMONDS, KEITH, THOMAS
Application year: 2001
Main classification: F28F3
IPC codes: B01J19, F28F3