WO2008113740A1

WO2008113740A1 - Plate heat exchanger

Info

Publication number: WO2008113740A1
Application number: PCT/EP2008/052994
Authority: WO
Inventors: Mauro Ramazzotto
Original assignee: Metal Brain, Llc
Priority date: 2007-03-16
Filing date: 2008-03-13
Publication date: 2008-09-25
Also published as: EP2122287A1; ITTV20070043A1

Abstract

A plate heat exchanger characterized in that it comprises a plurality of heat-exchanger elements defined by a first plate and by a second plate joined together to form a first chamber for circulation of a first fluid and to define a portion of aninletheader and a portion of an outlet header for said first fluid, said plurality of heat-exchanger elements being set alongside one another and joined together and defining a plurality of gaps for passage of a second fluid, said heat exchanger having an inletsection and an outlet section for said second fluid, which are substantially orthogonal to said first and second plates.

Description

"IMPROVED HEAT EXCHANGER"

DESCRIPTION

The present invention relates to an improved heat exchanger. In particular, the present invention relates to a heat exchanger of the plate type, for a device for recovering the heat of the exhaust fumes of a boiler normally used in a domestic or industrial environment. As is known, boilers are thermal apparatuses traditionally used for heating water in a heating circuit or else water to be used by the users for personal requirement.

A boiler traditionally comprises a combustion chamber, housed in the proximity of which is a heat exchanger, generally referred to as primary heat exchanger, in order to carry out heating of the service water. The fumes produced following upon the phenomenon of combustion possess, as is known, a high thermal energy that advantageously can be recovered for the purpose of pre-heating the water entering the primary heat exchanger. This enables limitation of the amount of fuel consumed in so far as the thermal jump required becomes smaller, given the same final temperature required of the service water leaving the boiler. In order to recover said thermal energy, devices referred to as "fume-heat recovery devices" or sometimes also as "economizers" are traditionally used. They usually comprise heat exchangers, also referred to as "secondary heat exchangers", located within the boiler along the path used for exhaust of the combustion fumes outwards.

An example of boiler equipped with a secondary heat exchanger is described in the patent application N°. EP 0945688. In particular, in this technical solution, which is similar to many others of the sector, the secondary heat exchanger is constituted by a battery of tubes housed in a container inside the casing of the boiler. The tubes are internally traversed by the service water and are externally lapped by the combustion fumes conveyed within the container by means of a fan. Through a convection-conduction heat exchange, the thermal energy of the fumes is transferred from the fumes to the service water. In order to favour this heat exchange, the solution illustrated envisages the use of a partition wall that separates the inlet of the fumes from the outlet, enabling them to follow a predefined path.

Secondary heat exchangers of this sort present limits linked in particular to the modalities of production and assembly. They prove somewhat cumbersome and require, for their positioning, appropriate housings inside the boiler. The design and definition of the layout of the components of the boiler are hence markedly affected by the type of heat exchanger used and frequently call for laborious preliminary studies. To guarantee a better fume-water heat exchange and, at the same time, a considerable reduction in the overall dimensions, there have been introduced on the market heat exchangers of the plate type. Said heat exchangers have a series of juxtaposed plates so as to form two groups of distribution chambers. The chambers of each group are respectively traversed by the combustion fumes and by the service water. Said chambers are connected in alternation to one another to guarantee circulation of the fluids and carry out an effective heat exchange between said fluids. An example of a plate-type heat exchanger is illustrated in the Italian patent application N° . MI2004 AOOO 151.

Also plate heat exchangers of a known kind present some drawbacks that derive from the modalities of production and assembly commonly adopted.

Plate heat exchangers of a known type envisage, in fact, the provision of a dual distribution circuit for bringing the two fluids into thermal contact with one another. To obtain said dual circulation of fluids, each plate is in general equipped with at least four openings, provided, alternately, for inlet/outlet of the first fluid (for example, the combustion fumes) and for the passage, in the two directions, of the second fluid (for example, water). Each of said openings is provided with appropriate connection collars, which extend in a direction perpendicular to the surface of the plates so that corresponding to the juxtaposition of the plates is the formation of passages between one chamber and the other for the aforesaid fluids. In general, there are present further openings to enable recovery of the condensate that is formed inside the chambers for passage of the combustion fumes.

It has been found in practice that said relatively complex structure of the heat exchanger leads to non-negligible head losses, in particular as regards the passage of the combustion fumes.

This can lead obviously to a reduction of the global efficiency of the boiler.

Furthermore, it has been found that the industrial production of said heat exchangers involves relatively high costs precisely on account of the considerable number of machining operations to which the plates must be subjected to obtain, by juxtaposing them, the double fumes-water distribution circuit.

On the basis of the foregoing, there emerges the need to have available new plate heat exchangers, in particular for heat-recovery devices, that will be economically advantageous, easy to assemble, and of contained volume.

Consequently, the main aim of the present invention is to provide a plate heat exchanger, which will enable the drawbacks just referred to above to be overcome.

In the framework of the above aim, a purpose of the present invention is to provide a plate heat exchanger that may be obtained with a limited number of components that can easily be assembled together.

Another purpose of the present invention is to provide a plate heat exchanger that will present a high degree of reliability and that will guarantee an efficient heat exchange between combustion fumes and water, designed for service uses.

A further purpose of the present invention is to provide a plate heat exchanger that will be easy to integrate in a heat-recovery device or economizer, in a boiler for domestic or industrial use.

Not the least important purpose of the present invention is to provide a plate heat exchanger that will present a relatively simple structure and that will be relatively easy to produce industrially at competitive costs.

The above task and purposes, as well as other purposes that will emerge clearly from the ensuing description and from the attached plates of drawings are provided, according to the invention, by a heat exchanger, according to what is specified in the following claim 1.

The plate heat exchanger, according to the present invention, envisages the creation of just one distribution circuit for bringing the fluids of the heat exchanger into thermal contact with one another, minimizing, for each plate, the number of openings for passage of fluids. In particular, the plates are coupled together so as to form just one circuit for the circulation of a first fluid, for example water, in a plurality of chambers. A second fluid, for example the combustion fumes of a boiler, is brought into thermal contact with the first fluid by means of a series of lateral gaps made in the structure of the heat exchanger and alternating with said plurality of chambers. Said gaps develop in a direction substantially parallel to the surface of the plates of the heat exchanger.

This enables a heat exchanger to be obtained having an extremely compact structure, which is very efficient from a thermal standpoint, with high flexibility of design and easy to assemble and produce at an industrial level.

Further characteristics and advantages of the present invention may be perceived more clearly with reference to the description provided in what follows and to the annexed plates of drawings, which are provided purely by way of illustrative and non-limiting example and in which:

Figures Ia-Ib are schematic illustrations of a first perspective view and a second perspective view of a first embodiment of a heat exchanger according to the present invention;

Figure 2 is a schematic illustration of a longitudinal cross-sectional view of a second embodiment of a heat exchanger according to the present invention; Figure 3 is a schematic illustration of a first cross-sectional view of the heat exchanger of Figures Ia-Ib;

Figure 4 illustrates an enlarged detail of Figure 3;

Figure 5 is a schematic illustration of a second cross-sectional view of the heat exchanger of Figures Ia-Ib;

Figure 6 illustrates an enlarged detail of Figure 5;

Figure 7 is a schematic illustration of a third cross-sectional view of the heat exchanger of Figures Ia-Ib;

Figure 8 illustrates an enlarged detail of Figure 7;

Figure 9 illustrates an enlarged detail of the heat exchanger of Figure 2;

Figures 10a- 10b are schematic illustrations of a first and a second perspective view of a heat-exchanger element in the heat exchanger of Figures Ia-Ib;

Figures 1 Ia-I Ib are schematic illustrations of a first and a second perspective view of a first plate of the heat-exchanger element of Figures 10a- 10b;

Figures 12a- 12b are schematic illustrations of a first perspective view and a second perspective view of a second plate of the heat-exchanger element of Figures 10a- 10b;

Figures 13 a- 13b are schematic illustrations of a first perspective view and a second perspective view of a heat-exchanger element in the heat exchanger of Figure 2;

Figures 14a- 14b are schematic illustrations of a first perspective view and a second perspective view of a first plate of the heat-exchanger element of Figures 13a- 13b; and

Figures 15 a- 15b are schematic illustrations of a first perspective view and a second perspective view of a first plate of the heat-exchanger element of Figures 13a- 13b. With reference to the above figures, a plate heat exchanger according to the present invention, in both of the embodiments 1, 1' described in what follows, comprises a plurality of heat- exchanger elements 2 that are defined by a first plate 3 and a second plate 4, the structure of which will be described in greater detail in what follows.

The plates 3 and 4 are joined together to form a chamber 5 for circulation of a first fluid, for example water. The plates 3 and 4 moreover define a portion of an inlet header 6 and a portion of an outlet header 7 of said first fluid. As may be seen from the figures, the heat-exchanger elements 2 are set alongside one another and joined together, and define a plurality of gaps 8 for passage of a second fluid, which is for example constituted by the combustion fumes of a boiler. One of the peculiarities of the heat exchanger of the present invention is that it has an inlet section 10 and an outlet section 11 of the second fluid substantially orthogonal to the plates 3 and 4.

It may be seen therefore how the heat exchanger of the present invention presents a very simple structure. In practice, the plates are joined to provide just one circuit for circulation, constituted by the various chambers 5 connected together through the inlet header 6 and two outlet header 7, which develop along two mutually parallel axes perpendicular to said plates.

The various heat-exchanger elements 2 deriving from the union of two plates are in turn joined together to form a plurality of gaps 8 for passage of the second fluid, whence it emerges that the structure of the heat exchanger presents as a series of chambers 5 alternating with the gaps

8.

The water (which in general constitutes the first heat-exchange fluid) enters the heat exchanger through the header 6, fills the chambers 5, traversing them from left to right, and comes out of the heat exchanger through the outlet header 7. At the same time, the second heat-exchange fluid, normally constituted by the combustion fumes of a boiler, enters the heat exchanger 1 through the inlet section 10, traverses the gaps 8 (from right to left in the heat exchanger 1 of

Figures Ia-Ib or in a perpendicular direction, coming out of the plane of cross section of the heat exchanger 1 ' of Figure 2), and comes out of the heat exchanger through the outlet section

11. There is thus obtained within the heat exchanger a heat exchange between the two fluids that flow substantially in countercurrent with respect to one another.

Preferably, in order to maximize the heat exchange and maintain the circulation of the fluids in countercurrent, the first, inlet, header 6 of the first fluid is positioned in the proximity of the outlet section 11 of the second fluid, whilst the second, outlet, header 7 is positioned in the proximity of the inlet section 10 of the second fluid.

With reference to the above figures, there will now be described some possible embodiments of the plates 3 and 4 that make up each heat-exchanger element 2 in the heat exchanger according to the invention, in both of the embodiments 1, 1' described.

The first and second plates 3, 4 have a substantially rectangular geometry. The first plate 3 has a first surface of contact 30 with the first fluid and a second surface of contact 31 with the second fluid. Furthermore, said first plate 3 has a first hole 32 and a second hole 33 for passage of said first fluid.

In the same way, the second plate 4 has a third surface of contact 40 with the first fluid and a fourth surface of contact 41 with the second fluid. Moreover defined on the surface of the second plate 4 are a third hole 42 and a fourth hole 43 for passage of the first fluid. The holes 32, 33, 42 and 43 are substantially of the same dimensions and are positioned so that, when the plates are set on top of one another and joined, their axes will be substantially coincident, thus providing a channel for passage of the first fluid perpendicular to the surface of the plates. Preferably, the holes 32 and 33 are positioned, respectively, in the proximity of a first edge 310 and a second edge 320 of the first plate, said edges 310, 320 being set opposite to one another. In the same way, the holes 42 and 43 of the second plate 4 are, respectively, positioned in the proximity of a first edge 410 and a second edge 420, set opposite to one another, of said second plate 4. As may be seen, the first edges 310, 410 of said first and second plates 3, 4 advantageously define the outlet section 11 of the second fluid, whilst the second edges 320, 420 define the inlet section 10 of the second fluid.

With reference to Figures 10a- 12b, it may be noted how, in the heat exchanger 1 according to the first embodiment illustrated in Figures Ia-Ib, the first plate 3 has a third edge 330 and a fourth edge 340, set opposite to one another, bent in the direction of the same surface. With reference to Figures 11a and l ib, the edges 330 and 340 are bent in the direction of the surface 30 and form with said surface 30 an angle greater than 90°. In the same way, with reference to Figures 12a and 12b, also the second plate 4 has a third edge 430 and a fourth edge 440, set opposite to one another, bent in the direction of the same surface (in this case the surface 41) and forming with said surface 41 an angle greater than 90°.

In this case, the coupling between two plates to form a heat-exchanger element 2 is such that the edges 330 and 340 of one plate come to couple together by means of superposition with the edges 430, 440 of an adjacent plate.

With reference to Figures 13a-15b, it may be noted how, in the heat exchanger 1 ' according to the second embodiment illustrated in Figure 2, the first plate 3 has a third edge 330 and a fourth edge 340, set opposite to one another but not bent (Figures 14a- 14b). In this embodiment, the plate 3 has, in a position corresponding to the surface 31 , in contact with the second fluid, one or more reliefs 311 projecting in a direction substantially perpendicular to the surface 31. Said reliefs 311 are particularly useful for facilitating coupling of two heat-exchanger elements 2, superimposed on one another. The reliefs 311, moreover advantageously function as spacers to prevent any undesirable squeezing of the gaps 8 during assembly of the heat-exchanger elements 2.

With reference to Figures 15a and 15b, the second plate 4 has a third edge 430 and a fourth edge 440, set opposite to one another, bent in the direction of the same surface (in this case, the surface 41) and forming with said surface 41 an angle greater than 90°. The second internal plate comprises also inner edges 410a, 420a, 430a, 440a, respectively parallel to the edges 410, 420, 430 and 440, to define a seat 40a designed to facilitate coupling of the plate 4 with the plate 3 to form a heat-exchanger element 2. The inner edges of the seat 40a are designed to couple, respectively, with the edges 310, 320, 330, and 340 of the plate 3. In both of the embodiments 1 , 1 ' of the heat exchanger according to the invention, the union between the different plates 3-4 is very simple and at the same time very effective. As may be seen, in fact, the union between the plates 3-4 is obtained simply by setting them alongside one the another. The sealed fixing can then be obtained with traditional techniques, for example welding or brazing.

With reference now to Figures 10a- 15b, in both of the embodiments 1, 1 ' of the heat exchanger according to the invention, the first hole 32 and the second hole 33 of the first plate 3 preferably have, respectively, a first edge 321 and a second edge 331 that develop from said second surface 31 of contact with said second fluid. In the same way, with reference to Figures 4a and 4b, the third hole 42 and fourth hole 43 have, respectively, a third edge 421 and a fourth edge 431 that develop from said fourth surface 41 of contact with said second fluid. The dimensions and the shaping of the edges 321, 331, 421, 431 are such that, when the various plates and the various elements are joined together to form the heat exchanger, the edge 321 of the hole 32 of the first plate 3 will come to fit into the edge 421 of the hole 42 of the second plate 4. In the same way, the edge 331 of the hole 33 of the first plate 3 will come to fit into the edge 431 of the hole 43 of the second plate 4.

As may be seen from the annexed figures, the coupling and union of the edges 321 and 421, projecting respectively from the surfaces of contact 31 and 41 with the second fluid, enables provision of a channel that will set two successive chambers 5 in communication, passing through the gaps 8.

In other words, the inlet header 6 for the first fluid is defined through the union of the edges 321 and 421. In the same way, the coupling and union of the edges 331 and 431 enables a further channel to be obtained, which sets two successive chambers 5 in communication, thus defining the outlet header 7 of the first fluid. The sealed fixing in a position corresponding to the edges can then be obtained with traditional techniques, for example welding or brazing. Advantageously, the heat exchanger according to the invention, in both of the embodiments 1 and 1 ', comprises a terminal closing plate 300, which closes one end of the headers 6 and 7. The other end of the headers is, instead, normally connected to the boiler system. Alternatively, according to one embodiment (not illustrated in the annexed figures), the headers 6 and 7 can be provided with closing means, for example threaded plugs, located at one end thereof. Preferably, in both of the embodiments 1 and 1 ' of the heat exchanger, it is envisaged that at least one of the plates 3-4 will be provided with ribbings. Said ribbings, which can be obtained, for example, by drawing, have the primary function of increasing the surface of heat exchange and of creating preferential paths of flow of the heat-exchange fluids. In the embodiments illustrated, the surfaces of the first plate 3 are substantially plane, whilst the surfaces of the second plate 4 are provided with a plurality of ribbings 450, oriented so as to maximize the heat exchange and create a preferential path, in particular for the first heat-exchange fluid within the chambers 5.

According to alternative embodiments (not illustrated) it is possible to equip also the surfaces of the plate 3 with appropriate ribbings so as to increase further the turbulence of the second fluid within the gaps 8, as well as the surface of heat exchange.

This solution is particularly simple and advantageous in so far as it reduces to a minimum the number of machining and other operations to be performed on one of the plates. There are obviously possible also alternative solutions in which the ribbings will be arranged on the plate according to modalities and geometries different from the ones illustrated, as likewise possible are solutions in which both of the plates may be equipped with ribbings.

It has been seen in practice that the heat exchanger 1 and 1 ' according to the present invention, in both of the embodiments proposed, enables the pre-set purposes to be achieved. The heat exchanger according to the present invention has a very simple structure that renders it easy and inexpensive to produce at an industrial level. The modularity of said structure moreover enables convenient sizing of the heat exchanger according to any type of boiler- system requirement.

The heat exchanger according to the invention at the same time ensures an effective heat exchange between combustion fumes and water thanks to the relatively large surface of heat exchange available and to the movement in counter-current of the two fluids. The passage of the second fluid through the gaps described previously enables, on the one hand, a considerable reduction in the head losses and on the other facilitates the integration of the device for recovery of heat in a boiler for domestic or industrial use.

It is moreover possible to carry out an effective collection of the condensate generated by the passage of the combustion fumes by simply providing a collection basin underneath the heat exchanger so as to collect the drips of condensate from the aforesaid gaps. Finally, it is possible to make the headers for the fumes of the boiler separately, with the possibility of choosing the materials and the structure of said headers according to a highly diversified range of design requirements.

As a whole, the foregoing enables a considerable simplification of the overall structure of the heat-recovery device that incorporates the heat exchanger according to the present invention.

The compact and simple structure of the heat exchanger according to the invention enables a considerable reduction in the costs for the materials used, as well as for machining and assembly in its industrial production as compared to traditional heat exchangers.

On the basis of the foregoing description, other characteristics, modifications or improvements are possible and evident to the average person skilled in the branch. Said characteristics, modifications and improvements are hence to be deemed as forming part of the present invention.

Claims

1. A plate heat exchanger (1, 1 '), characterized in that it comprises a plurality of heat- exchanger elements (2) defined by a first plate (3) and by a second plate (4) joined together to form a first chamber (5) for circulation of a first fluid and to define a portion of an inlet header (6) and a portion of an outlet header (7) for said first fluid, said plurality of heat-exchanger elements (2) being set alongside one another and joined together and defining a plurality of gaps (8) for passage of a second fluid, said heat exchanger (1) having an inlet section (10) and an outlet section (11) for said second fluid, which are substantially orthogonal to said first and second plates (3, 4).

2. The heat exchanger according to Claim 1, characterized in that said inlet header (6) and outlet header (7) develop along two mutually parallel axes perpendicular to said plates.

3. The heat exchanger according to one or more of the preceding claims, characterized in that said first, inlet, header (6) for the first fluid is positioned in the proximity of the outlet section (11) of the second fluid and said second, outlet, header (7) is positioned in the proximity of the inlet section (10) of the second fluid.

4. The heat exchanger according to one or more of the preceding claims, characterized in that said first plate (3) has a first (30) surface of contact with said first fluid and a second (31) surface of contact with said second fluid, and said second (4) plate has a third (40) surface of contact with said first fluid and a fourth (41) surface of contact with said second fluid.

5. The heat exchanger according to one or more of the preceding claims, characterized in that said first plate (3) has a first hole (32) and a second hole (33) for passage of said first fluid, and said second plate (4) has a third hole (42) and a fourth hole (43) for passage of said first fluid.

6. The heat exchanger according to Claim 5, characterized in that said first and third holes (32, 42) and said second and fourth holes (33, 43) of said first and second plates (3, 4) are, respectively, positioned in the proximity of first edges (310, 410) and second edges (320, 420) opposite to said first and second plates (3, 4).

7. The heat exchanger according to Claim 6, characterized in that said first edges (310, 410) define said outlet section (11) and said second edges (320, 420) define said inlet section (10).

8. The heat exchanger, one or more of the preceding claims, characterized in that said first and second plates (3, 4) comprise one or more edges (310, 320, 330, 340, 410, 420, 430, 440, 410a, 420a, 430a, 440a) coupled together by means of superposition.

9. The heat exchanger according to one or more of Claims 5 to 8, characterized in that said first hole (32) and said second hole (33) of said first plate (3) have, respectively, a first edge (321) and a second edge (331) that develop from said second surface (31) of contact with said second fluid, and said third hole (42) and fourth hole (43) have, respectively, a third edge (421) and a fourth edge (431) that develop from said fourth surface (41) of contact with said second fluid.

10. The heat exchanger according to Claim 9, characterized in that the first edge (321) of the first hole (32) and the second edge (331) of the second hole (33) are coupled together with the third edge (421) of the third hole (42) and with the fourth edge (431) of the fourth hole (43).

11. The heat exchanger according to one or more of the preceding claims, characterized in that at least one of said plates (3, 4) is provided with ribbings (450).

12. The heat exchanger according to Claim 11, characterized in that the surfaces of said first plate (3) are substantially plane, and the surfaces of said second plate (4) are provided with a plurality of ribbings (450).

13. The heat exchanger according to Claim 11, characterized in that the surfaces of said first plate (3) and the surfaces of said second plate (4) are provided with a plurality of ribbings (450).

14. The heat exchanger according to one or more of the preceding claims, characterized in that it comprises a terminal closing plate (300).

15. The heat exchanger according to one or more of the preceding claims, characterized in that said first fluid is constituted by water and said second fluid is constituted by combustion fumes of a boiler.

16. A device for heat recovery from the combustion fumes in a boiler for domestic or industrial use, characterized in that it comprises a heat exchanger according to one or more of the preceding claims.

17. A boiler for domestic or industrial use, characterized in that it comprises a heat exchanger according to one or more of Claims 1 to 15.