WO1984002973A1

WO1984002973A1 - Heat exchanger in plate construction

Info

Publication number: WO1984002973A1
Application number: PCT/FI1983/000003
Authority: WO
Inventors: Risto Saari
Original assignee: Risto Saari
Priority date: 1983-01-17
Filing date: 1983-01-17
Publication date: 1984-08-02
Also published as: EP0133427A1

Abstract

A heat exchanger for transferring heat from a first fluid to a second fluid. The heat exchanger (103) has been formed of plates (13, 14) between which have been established alternatingly a first interstice (11) and a second interstice (12). Each first interstice (11) communicates directly with a space (101) containing first fluid. At least part of the second interstice (12) communicates directly with a space (102) containing second fluid. In a multiple effect heat exchanger, the plates of the heat exchanger of a given effect have been pressed against each other with a force perpendicular against the plates, and the plate stack thus produced has been pressed with a force parallel to the plates between two frames, both frames having the shape of a closed circuit. The heat exchanger (103) is applicable in evaporators, of which further a multiple effect distilling apparatus can be compiled.

Description

Heat exchanger in plate construction

The present invention concerns a heat exchanger intended for heat transfer from a first fluid to a second fluid, composed of plates between which alternatingly a first interstice and a second interstice have been established.

A significant application range of. the invention is the distilling of fresh water from seawater. The heat exchangers of distilling plants are usually constructed either of tubes or of plates. The overwhelming majority of heat exchangers employed towards seawater distillation are tube heat exchangers. Evaporators and condensers in plate construction have so far been used to a rather limited extent. They have usually been applied in embodiments where the heating agent in the evaporator is a liquid and the cooling agent in the condenser is likewise a liquid. This is for instance the case in a few marine evaporators. In those evaporators, however, where the heating agent is condensing vapour, as for instance in vapour compression distillation or in multiple effect distillation, plate heat exchangers have not been used as a rule.

The limited use of plate heat exchangers is due to the relatively great area of the vapour flow passages, in particular at low temperatures. It is common practice, in plate heat exchangers, to introduce and remove the substances participating in the heat exchange through apertures in the heat exchanging plates and end plates. The vapour flow passage must then be relatively of greater size accordingly as the number of plates in the heat exchanger increases. At low temperatures, when the specific volume of the vapour is high, this has the consequence that in a large plate heat exchanger containing a plurality of plates nearly all of the surface area is used up by the vapour flow passages if there is vapour both on the primary and the secondary side. Therefore they are not being used in applications of that kind.

The object of the invention is to provide a heat exchanger in plate construction which enables the evaporators to be used also in applications of this type. It is also an object of the invention to provide a multiple effect distilling plant which can be assembled of evaporators in which a heat exchanger according to the present invention is used. It is still one object of the invention to provide a condenser which has been constructed of a heat exchanger according to the invention.

The aims of the invention are achieved by the aid of a heat exchanger mainly characterized in that each first interstice communicates directly with a space containing first fluid, and that at least part of the second interstices directly communicates with a space containing second fluid.

The other characteristic features of the heat exchanger of the invention have been stated in claims 2 to 9.

The heat exchanger of the invention has been applied in an evaporator, and the characteristic features of such an evaporator are stated in claims 10 to 13.

The characteristic features of a multiple effect distilling apparatus assembled of an evaporator according to the invention are stated in claims 14 and 15.

The characteristic features of a condenser assembled of a heat exchanger according to the invention are stated in claims 16 and 17.

By the problem solution of the invention, numerous significant advantages are gained. Firstly, one achieves a structure which is substantially more compact and has a better space economy than conventional constructions, as well as ease of maintenance and fitness for being series-produced. Furthermore, the invention enables the plate heat exchanger also to be used in larger multiple effect distilling plants by conducting the primary vapour directly into the interstices between plates and, on the other hand, the secondary vapour out therefrom, in which case the heat exchanger can even be constructed so that the vapour passages do not pass through its plates at all.

The invention is described in detail with reference to certain advantageous embodiments of the invention, presented in the figures of the attached drawings, but to which the invention is not meant to be exclusively confined.

Fig. 1 presents an evaporator conforming to the principle of the invention, as a schematic axonometric drawing.

Fig. 2 presents an advantageous embodiment of the heat exchanging plates used in the heat exchanger of the invention, viewed from the front.

Fig. 3 presents a stack of plates assembled of heat exchanging plates as shown in Fig. 2, as a schematic axonometric drawing.

Fig. 4a presents an embodiment of the gaskets associated with the heat exchanger of the invention, in cross section.

Fig. 4b likewise presents an embodiment of the gaskets associated with the heat exchanger of the invention, in cross section.

Fig. 5a likewise presents an embodiment of the gaskets associated with the heat exchanger of the invention, in cross section.

Fig. 5b likewise presents an embodiment of the gaskets associated with the heat exchanger of the invention, in cross section.

Fig. 6 shows the section along the line VI-VI in Fig. 7.

Fig. 7 shows the section along the line VII-VII in Fig. 6.

Fig. 8a shows the section along the line VIII-VIII in Fig. 6, the multiple effect distilling apparatus of the invention having been applied in connection with multiple effect distilling. Fig. 8b shows the section along the line VIII-VIII in Fig. 6, the multiple effect distilling apparatus of the invention having been applied in connection with multi-stage flash distilling.

Figs 9a and 9b present a detail A, respectively B in Fig. 8a, of the evaporator of the invention, for separation of droplets from the vapour.

Referring now to Fig. 1, the partition 19 divides the evaporator into two spaces 101 and 102. The space 101 is the primary space, filled by the primary vapour when the evaporator is in operation, and the space 102 is the secondary space, which is filled by the secondary vapour with lower pressure and temperature. Furthermore, in the figure is seen a plate heat exchanger 103, consisting of alternating heat exchanging plates 13 and 14 and of gaskets 15 between these plates. The heat exchanger is so constructed that between the plates two kinds of interstices are established. The interstices 11 communicates through apertures 17 with the primary space 101. The interstices 12, again, are not in communication with the primary space 101 but only with the secondary space 102. The interstices 11 communicate furthermore by smaller flow passages 18 also with the secondary space 102. The evaporator comprises moreover a means for supplying the evaporating liquid into the interstices 12. This means, which in practice may be a jet nozzle or a perforated tube, has been omitted from the figure, for the sake of clarity.

It is thus understood that when the evaporator is in operation, the evaporating liquid flows in the interstices 12, and the heating vapour fills the spaces 11. As the heating vapour condences on the heat exchanging plates 13 and 14, evaporating liquid will evaporate in equivalence in the interstices 12 to become secondary vapour, which is free to become distributed in the secondary space 102. The liquid to be distilled which has not evaporated runs down on the bottom of the secondary space 102 and is removed from there. The condensate that has formed from the primary vapour flows from the interstices 11 through the apertures 17 to the bottom of the primary space 101 and is therefrom removed with a means not depicted. Thus, the principle of Fig. 1 is that the first interstices 11 of the heat exchanger 103 communicate directly with the primary space 101 and the second interstices 12 communicate directly with the secondary space 102. One avoids hereby the necessity of cutting large vapour passages through the heat exchanging plates.

The uncondensable gases present in the primary steam would eventually fill the interstices 11 and inhibit the operation of the heat exchanger 103 if they had not the escape route through the passages 18 into the secondary space 102.

Plate heat exchangers are usually constructed of plates and of resilient gaskets associated with their interstices. In Fig. 2 is shown a simple embodiment according to which the plate heat exchanger 103 conforming to the principle of Fig. 1 may be constructed in practice. The front side of the heat exchanging plate 14 corresponds to the primary interstice 11 in Fig. 1, which has been encircled with a gasket 15, this gasket having one or several small flow passages 18 for uncondensable gases. The interstice 11 is open at the bottom. The interstice which is created on the front side of the next heat exchanging plate 13, again, is closed at the bottom by a gasket 16, but open in other directions. The space between it and the preceding plate corresponds to the secondary interstice 12 of Fig. 1.

The heat exchanger 103 is assembled by stacking in alternation such heat exchanging plates, for instance as shown in Fig. 3 upon a frame 20. The frame 20 carries a gasket 21 making the circuit of the frame at exactly that point where the gaskets 15 and 16 end on the edge of the heat exchanging plates. Hereby the edges of the plates are uniformly sealed against the gasket 21, as shown in Fig. 4a. The gaskets 15 and 16 may also extend out over the heat exchanging plates, as can be seen in Fig. 4b.

In the embodiment of Fig. 3, the plate stack assembled upon the frame 20 is pressed together with force F₁, in practice using end plates and bolts. It is thereafter urged with force F₂ against the frame 20, whereby the gasket 21 seals the margins of the stack all around, connecting the interstices 11 with the space 101 and the interstices 12 with the space 102. The frame 20 may also be positioned in another direction with reference to the stack, instead of under it. This particular direction is in most instances the most convenient in view of assembling the stack.

The gasket 21 may easily suffer damage when the plate stack is being pressed together. This may be avoided for instance in the way shown in Figs 5a and 5b. The gasket 21 is a resilient flexible tube like a bicycle inner tire, inserted uninflated on the bottom of a groove provided in the frame 20 (Fig. 5a) and permitting the heat exchanging plates 13 and 14 to be freely moved along the frame 20. When the plate stack has been pressed together, pressure is applied to the interior of the gasket 21, whereby it is urged intimately against the edges of the plates and of the gaskets associated with these (Fig. 5b).

Figs 6 and 7 illustrate schematically a possible way in which the heat exchanger 103 of a multiple effect distilling apparatus can be assembled. Figs 6 and 7 illustrate two effects positioned one upon the other. The plate stack is assembled upon the ring 20. Connected with the ring 20 are fixed end wall 22 of the plate stack and quides 24 upon which the stack is partly assembled before being pressed together. This is accomplished with the aid of a movable end wall 23, which is connected with the fixed end 22 by bolts passing through lugs 25. The gasket 21 in the frame 20 is urged, in the way shown in Figs 5a and 5b, against the edges of the plates. The frame 20 carries also on its underside a similar gasket 21 which in its turn is urged against the top edge of the plate stack thereinunder. The stacks may be brought into register with each other e.g. by means of pins 44 in the fixed end plates.

The plate stacks assembled in the way just described may comprise many kinds of plates and gaskets, depending on what heat exchange process they are used for. Figs 8a and 8b show, as examples, the application of the invention in the two best-known multiple stage distilling processes. The application of Fig. 8a is the multiple effect distilling, where the vapour produced in a given effect is condensed in the next distilling effect operating at a lower pressure level, where thus this vapour serves as heating steam. Each distilling effect comprises in alternation interstices 11, serving as condensers, and interstices 12, serving as evaporators. In Fig. 8a, an evaporator has been depicted in the upper distilling effect and a condenser in the lower effect. Gaskets 26 separate both the evaporator and the condenser from ambience with the aid of the frame 20 and gaskets 21. The liquid to be evaporated flows through small apertures 28 in the gasket 27 into the space 12, where it runs as thin film down along the surface of the plate. At the same time, part of it evaporates as the vapour from the preceding effect condenses on the opposite side of the heat exchanging plate. The mixture of vapour and liquid thus produced flows through apertures 37 on either side of the gasket 29 into the space confined by the frame 20. The vapour flows through a droplet separator 36, of any previously known design, and through the aperture 38 remaining between the gaskets 32, to the condenser 11 of the next effect, where it condenses to become distillate.

The distillate departs through a small aperture 35 in the gasket 34 to the condenser of the next effect therebelow (not depicted). The evaporator plates have at the equivalent point a gasket 30, which prevents the distillate from flowing to the evaporator and conducts it through a cut-out 31 in the margin of the plate to the aperture 38 leading to the condenser therebeside. Similarly, the condenser plates carry gaskets 32, which prevent the access of the liquid to be distilled to the condenser and conduct it through cut-outs 33 in the margin of the plate up above the gasket 27 of the evaporator plate therebeside, and thence further through apertures 28 to the evaporator therebeside.

Fig. 8b shows two effects of a multiple effect condenser which may for instance be used in multi-stage flash distilling. Each effect comprises in alternation interstices 11 and 12. Gaskets 41 separate the interstices 12 from ambience. The interstices 12 communicate at both ends with space confined by the ring 20 and gaskets 21. The interstices 11, in turn, have been isolated by gaskets 42 from the space defined by the frame 20. They are instead open to ambient space. The mode of operation of this condenser is that the cooling liquid flows from one stage to another through the interstices 12. The vapour condenses in the interstices 11, and the uncondensable gases escape into a passage formed by apertures 39 and gaskets 40. In the multi-stage distilling apparatus the frames 20 are connected to the partitions 43 between stages. A single-stage equivalent design may be used for instance as a turbine condenser.

Separation, from the vapour discharging from the evaporator, of the liquid droplets present therein may also be effected as shown in Figs 9a and 9b. The vapour discharge aperture 37 (Fig. 8a) has been divided by slanting gaskets 45 into a plurality of smaller apertures 48, which deflect the vapour flow to the left in the figure. The gaskets 45 have at their lower end pockets 46 in which the droplets entrained with the vapour accumulate. Adjacent to these pockets, holes 47 have been provided in the plate 13, these holes conducting the liquid over to the side of the neighbouring condenser. Here, the gasket 34 is divided into two branches 34a and 34b, and the liquid flows through the groove 49 between them and through the aperture 50 to one side of the frame 20 without being admixed to the vapour discharging through the apertures 48.

The applications presented above are merely examples of the embodiments of the invention, and the invention should not be considered confined to them only. For instance, in its connection all expedients known in the art for constructing plate heat exchangers may be applied, for instance shaping of the plates, eminences to lie against gasketless plate margins, etc. The invention is in principle applicable in all those heat exchange processes in which tube heat exchangers have been used heretofore.

Claims

1. Heat exchanger (103) for transferring heat from a first to a second fluid, composed of plates (13,14) between which have been alternatingly established a first interstice (11) and a second interstice (12) , characterized in that each first interstice (11) communicates directly with a space (101) containing first fluid, and that at least part of the second interstices (12) communicate directly with a space (102) containing second fluid.

2. Heat exchanger according to claim 1, characterized in that each plate (13,14) has at most one pass-through aperture.

3. Heat exchanger according to claim 1 or 2, characterized in that at least part of the gaskets (15,16) separating the plates (13,14) of the heat exchanger (103) extend up to the edge of the plate or there-beyond.

4. Heat exchanger according to any one of claims 1 to 3, characterized in that the plates of the heat exchanger (103) have been pressed together with a force (F₁) perpendicular against the plates and the plate stack thus produced has been pressed against the edges of a frame (20) forming a closed circuit, with a force (F₂) parallel to the plates.

5. Heat exchanger according to any one of claims 1 to 3, characterized in that the plates of the heat exchanger (103) of a given effect have been pressed against each other with a force (F₁) perpendicular to the plates and the plate stack thus produced has been pressed with a force (F₂) parallel to the plates between two frames (20) , both frames (20) having the form of a closed circuit.

6. Heat exchanger according to claim 4 or 5, characterized in that to the frame (20) is fixedly connected one end plate (22) of the plate stack.

7. Heat exchanger according to claim 4,5 or 6, characterized in that with the frame (20) are connected guides (24) on which the movable end (23) of the plate stack has been disposed to move.

8. Heat exchanger according to claim 4 or 5, characterized in that the frame (20) comprises at least one gasket (21) with the shape of a closed circuit.

9. Heat exchanger according to claim 8, characterized in that the pressure exerted by the gasket (21) on the frame (20) against the edges of the plate stack is changeable after assemebly of the plate stack.

10. An evaporator, consisting of a primary space (101) filled by primary vapour, a secondary space (102) filled by secondary vapour and a heat exchanger (103) composed of plates (13,14), between said plates having been established in alternation a first interstice (11) and a second interstice (12) , a means for supplying liquid to be distilled into the second interstices (12), a means for removing liquid to be distilled from the secondary space (102) and a means for removing condensate from the primary space (101) , characterized in that the first interstices (11) communicate directly with the primary space (101) and at least part of the second interstices (12) communicate directly with the secondary space (102) .

11. Evaporator according to claim 10, characterized in that the first interstices (11) communicate with the secondary space (102) or with another space in which prevails a pressure lower than that in the primary space (101), through at least one passage (18,35) of which passage or passages the flow cross section is substantially less than that of the passage (17,38) by which the respective first interstice (11) communicates with the primary space (101) .

12. Evaporator according to claim 10, characterized in that the second interstices (12) communicate with the primary space (101) by one or several flow passages (28), of which the combined flow cross section is substantially less than that of the flow passage (37) by which said second interstices (12) communicate with the secondary space (102) .

13. Evaporator according to claim 12, characterized in that in the flow passages (37) through which said second interstices (12) communicate with the secondary space (102) have been provided one or several apertures (47) leading into the adjacent first interstice (11) , these apertures leading to a space (49) isolated form the rest of said first interstice (11), this space in its turn communicating by one or several apertures (50) with the secondary space (102) .

14. A multiple effect distilling apparatus assembled of evaporators according to claim 10,11,12 or 13, characterized in that the consecutive distilling effects have been assembled on top of each other and mutually connected by means of frames (20) with the shape of a closed circuit.

15. Distilling apparatus according to claim 14, characterized in that in the frame (20) connecting the effects has been disposed a means (36) separating droplets from the vapour.

16. Condenser assembled of heat exchangers according to any one of claim 1 to 9, characterized in that the first interstices (11) communicate with a space containing vapour that is to be condensed and the second interstices (12), with a flow passage for the cooling liquid.

17. Condenser according to claim 16, characterized in that the heat exchanging plates have in their central part one or several holes (39) for removing uncondensable gases.