WO2002047808A1

WO2002047808A1 - Heat exchanger/chemical reactor

Info

Publication number: WO2002047808A1
Application number: PCT/GB2001/005515
Authority: WO
Inventors: Keith Thomas Symonds
Original assignee: Chart Heat Exchangers Ltd
Priority date: 2000-12-12
Filing date: 2001-12-12
Publication date: 2002-06-20
Also published as: AU2002222200A1; GB0030201D0; GB0129713D0

Abstract

A heat exchanger/chemical reactor comprises a stack of perforated metal plates (10). The central region (15) of the plates (10) has been etched to provide a plurality of apertures (15A) defining an arrray of adjacent column precursors (16) together and to the border region (11). Each column precursor (16) is hollow in that it has a longitudinally-extending passageway (18) through its lengh. Radial grooves (19) extend from central passageway (18) to form radial flow paths from the central passageways to be apertured regions (15A) of the plate. Each column precursor (16) has equi-spaced grooves (19). Process fluid can be passed through a stack of plates (10) in the direction indicated by arrow B and reactant fluid can be passed through central passageways (18) to emerge, as indicated by arrows B from grooves (19) into apertures (15A) where it mixes with the process fluid.

Description

HEAT EXCHANGER/ CHEMICAL REACTOR

This invention relates to heat exchangers and is particularly concerned with heat exchangers of the so-called "pin-fin" type and with heat exchangers of that type that are intended for use as chemical reactors, i.e. in which a reactant fluid is fed into a process fluid inside the heat exchanger.

"Pin-fin" type heat exchangers have been well known in principle for many years and consist essentially of a stack of thin metal plates, adjacent pairs of plates in the stack being separated by a plurality of spaced columns - or pins, which act as the heat exchanger fins, i.e. they create the desired secondary surfaces. Fluid flowing through the stack passes between adjacent pairs of plates and is forced to follow a tortuous path to flow around the pins in its travel from one side of the stack to the other. Such flow, and the turbulence caused by the pins, leads, theoretically, to good heat transfer properties for the stack.

The pins are essentially columns of solid metal which have to be bonded at their ends to a pair of plates so that the pins are sandwiched between and perpendicular to the plates. The plates form the primary surfaces of the heat exchanger and separate different flow streams and the pins, as indicated above, provide secondary surface areas.

Preferably, the pins need to be bonded, e.g. by brazing, welding, diffusion bonding or any other possible means, in a manner to minimise surface contact resistance. In practice, however, it has proved difficult to make a satisfactory pin- fin stack. It has proved difficult to maintain the pins at their correct spacing relative to each other while creating the necessary conditions, e.g. of temperature and pressure, for satisfactory bonding of the plates and the pins to take place.

In our international patent application number PCT/GB99/01622 publication number WO 99/66280 it is, therefore, described an improved pin-fin heat exchanger that can be accurately and consistently manufactured to the required tolerances while having improved heat exchange capability. In that international patent application is described a heat exchanger comprising a stack of parallel perforated plates, each plate of the stack having perforations, in which the perforations define an array of spaced column precursors, of thickness equal to the plate thickness, the column precursors being joined together by ligaments, each ligament extending between a pair of adjacent column precursors, the ligaments having a thickness less than the plate thickness, the column precursors of any one plate being coincident in the stack with the column precursors of any adjacent plate whereby the stack is provided with an array of individual columns, each column extending perpendicularly to the plane of the plates, whereby fluid flowing through the stack is forced to follow a tortuous flow path to flow around the columns.

The top and bottom of the stack may each be closed by a conventional solid plate, and inlet, outlet, header tank and like features may be provided as required to form the desired heat exchanger. Side plates or bars of the stack may conveniently be formed by the stacking of unperforated border regions around the edges of individual plates of the stack, the unperforated border regions being integrally formed as part of the plate. A plurality of stacks of the invention of WO 99/66280 may be joined together, each stack of perforated plates being separated from an adjacent stack by an unperforated, i.e. solid, plate, whereby two or more fluid streams may pass separately through the multi-stack to achieve desired heat transfer between the streams.

In an embodiment of WO 99/66280 which is intended for use as a chemical reactor, a plurality of the stacks of that invention are provided in which adjacent fluid streams are separated not by an unperforated plate but by a plate having perforations to allow controlled injection of fluid at higher pressure from one stream into fluid at lower pressure in an adjacent stream. Thus a reactant fluid may be injected into a process fluid to achieve the desired chemical reaction as the process fluid passes through the heat exchanger. Appropriately positioned coolant fluid layers may take away heat of reaction for exothermic reactions or similar layers may provide heat for endothermic reactions.

Although chemical reactors of WO 99/66280 have proved to be of significant effectiveness, we have now found that improvements in the mixing efficiency of the process and reactant fluids may be achieved by further modifications of the structure of perforated plates in the stack.

Accordingly in one aspect the present invention provides a heat exchanger or chemical reactor apparatus comprising a stack of parallel perforated plates, each plate having perforations, which define an array of spaced apart column precursors of thickness equal to the plate thickness, the column precursors of adjacent plates being joined together by ligaments, each ligament extending between a pair of adjacent column precursors, the ligaments having a thickness less than the plate thickness, the column precursors of any one plate being coincident in the stack with the column precursors of any adjacent plate whereby the stack is provided with an array of individual columns, each column extending perpendicularly to the plane of the plates whereby fluid flowing through the stack is forced to follow a tortuous flow path around the columns, some at least of the column precursors being hollow to provide a passageway inside the hollow columns and some at least of the hollow column precursors having at least one radial flow path from their hollow interior to the outside whereby a fluid in the hollow columns emerges to mix with fluid flowing across the stack.

In another aspect the invention provides a perforated plate having an array of spaced column precursors, the column precursors being of thickness equal to the plate thickness and being joined together by ligaments extending between parallel plates, each ligament extending between a pair of adjacent column precursors, the ligaments having a thickness less than the plate thickness and some at least of the column precursors being hollow and having at least one radial flow path from their hollow interior to their outer surface.

In another aspect, the invention provides a method of carrying out heat exchange or chemical reaction in apparatus comprising a stack of parallel perforated plates, each plate having perforations which define an array of spaced apart column precursors of thickness equal to the plate thickness, the column precursors being joined together by ligaments, each ligament extending between a pair of adjacent column precursors of adjacent plates, the ligaments having a thickness less than the plate the column precursors of any one plate being coincident in the stack with the column precursors of any adjacent plate whereby the stack is provided with an array of individual columns, each column extending perpendicularly to the plane of the plates, whereby fluid flowing across the stack is forced to follow a tortuous flow path around the columns; at least some of the column precursors being hollow to provide a longitudinal passageway inside the hollow columns and at least some of the hollow column precursors having at least one radial flow path from the hollow interior to the outside, the method comprising passing a first fluid across the stack and passing a second fluid through the passageways in the hollow columns to emerge from the hollow columns to mix with the first fluid.

Preferably the first fluid is a liquid and the second is gas.

It will be appreciated, therefore, that when the plates are stacked together, at least one adjacent, abutting pair of plates will form columns some or all of which will each have a longitudinal passageway. Where there are more than two perforated plates in the stack, all of the plates may have hollow column precursors in coincidence with hollow column precursors of adjacent plates so that the hollow columns, in a preferred embodiment, extend completely through the thickness of the stack. However, this is not essential provided that at least a pair of adjacent plates at one end of the stack form hollow columns so that longitudinal passageways in the hollow columns extend to an end surface of the stack.

If desired, all of the column precursors of a plate may be hollow so that all the columns formed between adjacent pairs of plates are hollow. However, this is not essential and, depending on the amount and distribution of reactant fluid required, only a proportion of the columns may need to be so formed.

A stack of plates of the invention may be closed at one end by an unperforated plate whereby a fluid passing through the stack, e.g. a process fluid, may be separated from a fluid, e.g. a coolant, passing through passageways defined on the opposite side of the unperforated plate. At the other end of the stack of plates of the invention, the stack may be closed by a perforated plate whose perforations are holes positioned to coincide with the positions of the hollow columns. Thus fluid, e.g. reactant fluid, passing on the opposite side of this perforated plate can pass through those holes into the hollow columns and then, via the radial flow paths, can flow out of the hollow columns into the process fluid.

The size of the columns and their positions relative to each other can readily be determined by the skilled man of the art from heat transfer, pressure drop and mechanical loading conditions. Similarly the number and position of the hollow columns and of the radial passageways may be determined as required for the particular process and reactant fluids under consideration.

The radial flow passageways from a hollow column precursor may conveniently be one or more grooves extending from its longitudinal passageway to the outer surface. By way of example only, four grooves may be equi-spaced around a central hollow passageway.

The fluid passageways for coolant and for reactant fluids which lie adjacent the process fluid passageways may be formed in any convenient manner. Thus, if desired, all the passageways may be formed of pin-fin type construction, i.e. the passageways for coolant and reactant may be formed of stacks of plates according to WO 99/66280 while the passageways for reactant fluid are formed according to the present invention. In an alternative example, the passageways for reactant and/or coolant fluid may be formed as described in International patent application no. PCT/GB98/01565, WO 98/55812. If desired, the process fluid passageways may contain catalyst to promote a desired chemical reaction, the catalyst, for example, being coated onto the passageway surfaces.

Preferably the ligaments of one plate of each pair of adjacent plates of the present invention are displaced relative to those of the other plate of the pair whereby more turbulent fluid flow channels are provided through the stack, i.e. around the columns and under or over each ligament.

Thus while the flow is in the general direction of the plane of the plates in that the fluid crosses the plate from one edge to an opposite edge thereof, additional turbulence is caused by flow under and over the ligaments.

Preferably the perforations in the plates, the reduced thickness of the ligaments, the hollow column passageways and the radial flow paths are all produced by photochemically etching, such a technique being well known in the art.

As indicated above, it is preferred that at least two different patterns of ligaments are used so that the ligaments do not completely coincide through the stack. Preferably at least two different plates are provided, i.e. the plates have different ligament patterns. Thus a tortuous flow path through the stack is provided not only around and normal to the longitudinal axes of the columns but also across the surfaces of the ligaments.

The column precursors, and hence the columns, may, in a preferred embodiment, be of circular transverse cross-section but this is not essential and any other desired cross- section may be utilised, e.g. elliptical, square, rectangular, triangular and so on, by appropriate choice of the pattern to be etched or otherwise formed in the plate. As indicated above, the size, i.e. cross-sectional area, the pitch of the columns, and also the bore of the central passageways and the radial flow passageways, can be varied widely to suit particular circumstances and the skilled man of the art will readily be able to determine dimensions and arrays appropriate to a particular need. Similarly, the thickness and width of the ligaments, the thickness of the plates and the number of plates in the stack may be determined to achieve a required result.

The thickness of the ligaments may be chosen to cause more or less interruption to fluid flow as required. Thus variations in the velocity of and turbulence in the fluid flow may be achieved by appropriately designed plate patterns. Increased heat transfer (and associated pressure drop) may, therefore, be achieved by appropriate changes to the ligament dimensions. Thus thinner ligaments may be employed when it is desirable to minimise such effects.

The plates may be circular, rectangular or of any other desired shape in plan and may be formed of any suitable material, usually metal, that can be made, e.g. by etching, to the desired column and ligament patterns. The plates of a stack are preferably all of the same material and are preferably thin sheets of metal of e.g., 0.5 mm thickness or less. The material is preferably stainless steel but other metals, e.g. aluminium, copper, titanium or alloys thereof, may be used.

The components of a stack may be bonded together by diffusion bonding or by brazing or by any other suitable means. Diffusion bonding, where possible, may be preferred but, in the case of aluminium, which is difficult to diffusion bond, brazing may be necessary. It is then preferable to clad the aluminium surfaces, e.g. by hot-roll pressure bonding, with a suitable brazing alloy, in order to achieve satisfactory bonding by the brazing technique, although other means to provide the braze medium may be used, e.g. foil or vapour deposition.

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 plan view of one perforated plate according to the invention;

Figure 2 is an enlarged view of a portion of the central region of the plate of Figure 1 ;

Figure 3 is a section on line Ill-Ill of Figure 2;

Figure 4 is a section on line IV-IV of Figure 2;

Figure 5 is a section through the plate of Figure 1 at an edge region thereof;

Figure 6 is a similar view to Figure 2 of another perforated plate according to the invention;

Figure 7 is a diagrammatic illustration in section of a chemical reactor/heat exchanger of the invention; and

Figure 8 is an enlarged view of a portion of Figure 7. In Figures 1 to 5 is shown a thin perforated metal plate 10 of generally rectangular shape and having an unperforated border region 11 around its perimeter. Four integral loops 12, one adjacent each corner of the plate, define apertures 13 which, when a stack of similar plates is assembled, form tanks through which inlets and outlets to and from the stack can be positioned.

A positioning lug 14 is integrally formed centrally of each of the four edges of the plate to assist assembly into a stack of plates.

The central region 15 of the plate inside border 11 has been etched to provide a plurality of apertures 15A (Figure 2) defining an array of column precursors and ligaments, the ligaments joining adjacent column precursors together and to the border region 11. A portion of central region 15 is shown in greater detail in Figure 2.

In Figure 2 an array of column precursors 16 and ligaments 17 is shown and a single column precursor at edge 11 of the plate is shown in Figure 5. The column precursors are circular in plan and of height equal to the thickness of the plate.

The ligaments 17 have been etched to half the thickness of the plate.

Each column precursor 16 is hollow in that it has a longitudinally-extending passageway 18 through its length. Radial grooves 19 extend from central passageway 18 to form radial flow paths from the central passageways to the apertured regions 15A of the plate. Each column precursor has four equi-spaced grooves 19 although, as indicated above, it is not necessary for every column precursor to be so provided and the number of grooves may be varied as desired. The grooves have been etched to half the plate thickness as shown in Figures 3 and 4.

Process fluid can be passed through a stack of plates such as plates 10 in the direction indicated by arrow A in Figure 2 and reactant fluid can be passed, as will be explained in greater detail below, through central passageways 18 to emerge, as indicated by arrows B in Figure 2, from grooves 19 into apertures 15A where it mixes with the process fluid.

An alternative arrangement of column precursors and ligaments is shown in Figure 6. Here the central region 25 of the plate has been etched to provide a plurality of apertures 25A with a different pattern of ligaments 27. Again, each column precursor has a central through passageway 28 which leads via four equi-spaced grooves 29 into apertures 25A. The column precursors have the same profile as those of Figure 2 and their sectional views (not shown) are the same as shown in Figures 3 and 4.

Ligaments 27 have been etched to half the plate thickness as have the grooves 29. In this instance, therefore, the ligaments have been positioned to be co-extensive with the base of the grooves.

As with the plate portion illustrated in Figure 2, process fluid passed through a stack of plates of the type shown in Figure 6, which flow is indicated again by arrow A can be mixed with reactant fluid passing through central passageways 28 and grooves 29 into apertures 25A, as illustrated by arrows B.

If desired a stack of plates to form the flow passageways for the process fluid may be made of an alternating array of plates of Figures 2 and 6. Thus the ligaments of adjacent plates will not coincide throughout the stack to provide greater turbulence in the flow passages whereas the column precursors do coincide throughout the stack.

In Figure 7 is shown a chemical reactor/heat exchanger of the invention. It has an outer coolant layer 30 defined between two unperforated plates 31 and 32, a reactant fluid layer 33 defined between unperforated plate 32 and a perforated plate 34, a process fluid layer 35 defined between perforated plate 34 and an unperforated plate 36, a central coolant layer 37 defined between unperforated plates 36 and 38, another reactant fluid layer 39 defined between unperforated plate 38 and a perforated plate 40, another process fluid layer 41 defined between perforated plate 40 and an unperforated plate 42 and another outer coolant layer 43 defined between unperforated plates 42 and 44.

Coolant flow is indicated by the arrows C, reactant fluid flow by the arrows D and process fluid flow by the arrows E. The process fluid is shown travelling through the reactor in the opposite direction to flow of coolant and reactant fluid. Although not essential, this improves the cooling effect and the mixing of the reactant and process fluids.

It will be appreciated that the arrangement of coolant/reactant process/coolant layers may be repeated in the reactor more than the two times illustrated.

The process fluid layers are each formed of a stack of plates of the invention, portions 50 of eight such plates being shown in Figure 7 and in larger scale for layer 35 in Figure 8. Each plate 50 has a structure similar to the structures shown in Figures 1 and 2 or 6 and, therefore, has a number of apertures (not shown) defined between the ligaments (not shown) and column precursors (indicated as portions 50). The column precursors of the plates stack together to form individual columns extending vertically to the plane of the plates and for the full thickness of the stack of eight plates. Each column precursor has a centrally-disposed longitudinal passageway 51 and four equi-spaced grooves 52 (only two of which are visible for each plate in Figures 7 and 8) extending from the central passageway to the apertures outside the column precursors. The eight passageways 51 together form a central passageway extending through the complete thickness of the stack of eight plates. At one end this central passageway is blocked by the unperforated plate 36. At the other end the central passageway coincides with a hole 53 through plate 34. By this means reactant fluid from layer 33 can flow into the process fluid layer 35 through hole 33, the central passageway formed by longitudinal passageways 51 and the grooves 52. The passage of reactant fluid into the process fluid layer is indicated by the smaller arrows d.

Thus reactant fluid can be introduced into the process fluid not only adjacent plate 34 but at positions across the layer 35 to a position adjacent layer 36. By this means much more efficient mixing can be achieved across the whole of layer 35 regardless of how many plates are stacked to form that layer. This may be of particular benefit if it is desired to mix a reactant gas into a process liquid.

Plates 50 need not be identical but may alternate as pairs of plates with different ligament arrangements.

Not all the column precursors of plates 50 need be hollow so that injection of reaction fluid need not take place at every column in the stack. However, it may be preferred to standardise with the plates all having hollow column precursors and the number of hollow columns accessible to injection of reactant fluid being determined by the number of holes in the perforated plates 34 or 40. Thus some of the hollow columns may be cut off from reactant fluid by being covered by a solid plate portion. The hollow columns may be made of solid metal or other material. The passageways therein need not be straight. The exit ports of the hollow columns may be different from what is shown, and ports may be present between the ends of the columns.

Claims

1. Heat exchanger or chemical reactor apparatus comprising a stack of parallel perforated plates, each plate having perforations which define an array of spaced apart column precursors of thickness equal to the plate thickness, the column precursors of adjacent plates being joined together by ligaments, each ligament extending between a pair of adjacent column precursors of adjacent plates, the ligaments having a thickness less than the plate thickness, the column precursors of any one plate being coincident in the stack with the column precursors of any adjacent plate whereby the stack is provided with an array of individual columns, each column extending perpendicularly to the plane of the plates, whereby fluid flowing across the stack is forced to follow a tortuous flow path around the columns; at least some of the column precursors being hollow to provide a passageway inside the hollow columns and at least some of the hollow column precursors having at least one radial flow path from the hollow interior to the outside, whereby a fluid in the hollow column emerges to mix with the fluid flowing across the stack.

2. Apparatus according to Claim 1 , wherein the stack of plates is closed at one end by an unperforated plate.

3. Apparatus according to Claim 2, wherein at the other end of the stack of plates is closed by a perforated plate.

4. Apparatus according to any preceding Claim, wherein the radial flow passageways from a hollow column precursor is provided by one or more grooves extending from the passageway to the outer surface.

5. Apparatus according to any preceding Claim, wherein the ligaments of one plate of a pair of adjacent plates are displaced relative to those of the other plate of the pair.

6. Apparatus according to any preceding Claim, wherein process fluid passageways contain catalyst coated onto the passageway surfaces.

7. Apparatus according to any preceding Claim, wherein the plates of a stack are thin sheets of metal of e.g. 0.5 mm thickness or less.

8. A perforated plate having an array of spaced column precursors of thickness equal to the plate thickness and being joined together by ligaments extending between parallel plates, each ligament extending between a pair of column precursors, the ligaments having a thickness less than that of the plate thickness and some at least of the column precursors being hollow and having at least one radial flow path from their hollow interior to their outer surface.

9. A method of carrying out heat exchange or chemical reaction in apparatus comprising a stack of parallel perforated plates, each plate having perforations which define an array of spaced apart column precursors of thickness equal to the plate thickness, the column precursors being joined together by ligaments, each ligament extending between a pair of adjacent column precursors of adjacent plates, whereby fluid flowing across the stack is forced to follow a tortuous flow path around the columns; at least some of the column precursors being hollow to provide a longitudinal passageway inside the hollow columns and at least some of the hollow column precursors having at least one radial flow path from the hollow interior to the outside, the method comprising passing a first fluid across the stack and passing a second fluid through the passageways in the hollow columns to emerge from the hollow columns to mix with the first fluid.

10. A method according to Claim 9, wherein the first fluid is a liquid and the second is a gas.