GB2381306A

GB2381306A - Heat exchanger plates

Info

Publication number: GB2381306A
Application number: GB0218169A
Authority: GB
Inventors: Giovanni Sciarresi; Steffano Zanforlin; Gabriele Corsini; Severino Corsini
Original assignee: GRUPPO IMAR SpA
Current assignee: GRUPPO IMAR SpA
Priority date: 2001-08-09
Filing date: 2002-08-06
Publication date: 2003-04-30
Anticipated expiration: 2022-08-06
Also published as: DE10236665A1; GB2381306B; ITMI20011743A0; DE10236665B4; GB0218169D0; ITMI20011743A1

Abstract

A heat exchanger comprises a plurality of heat exchange plates 4 stacked on top of one another. The plates comprise a hollow cast metal body 18, an inlet (13, fig 4) and an outlet 15 at the same end 11, a plurality of parallel internal channels (fig 6) connected in series and separated by partition walls 31-34, a portion 19 having projecting members 20 to increase the heat exchange surface area, and an opening 21 through the hollow body 18 which allows the passage of gas. Projecting members 20 are preferably in a plurality of rows 20a - 20g and columns and are arranged on both sides of the plates 4. Rows 20a - 20c may be staggered with respect to rows 20d - 20g which allows the plates 4 to be interlocked with one another when the next plate 4 is turned upside down by one hundred and eighty degrees about the plates 4 longitudinal axis X-X. Interlocking of the projecting members 20 provides a gap 45. Tubular elements 40 extend from a wall 36 and aids manufacture and are sealed with caps (41, fig 6). Portion 19 may be tapered.

Description

: 1 2381 306

Title: Gas-liquid heat exchanger and boiler incorporating said heat exchanger DESCRIPTION

The present invention relates to a gas-liquid heat exchanger including a plurality of modular heat exchange plates adapted to effect a heat exchange between a gas and a 5 heat carrier liquid, which is preferably, but not [imitatively, used in boilers, such as for example pre-mixing boilers and condensation boilers.

This invention also relates to a boiler incorporating such a heat exchanger as well as to a modular heat exchange plate adapted to effect the aforementioned heat exchange.

As is known, in the field of gas-liquid or air-liquid heat exchangers in general, and in

10 particular in the field of gas-water heat exchangers for boilers, one of the most felt needs

is that of making highly efficient heat exchangers at reduced costs.

To this purpose, gas-liquid heat exchangers including a plurality of modular plates integrally made of cast iron by casting in a mould around a terracotta core, and package-

mounted together, have long been known. Each plate is essentially constituted by a body 15 including a plurality of structurally independent ducts extending parallel to each other between opposite ends of the plate. More particularly, said ducts convey the liquid from a liquid inlet opening into the plate defined in a manifold formed at a first end of the plate towards an outlet opening of the liquid from the plate defined in a manifold formed at the opposite end of the plate. Moreover, the ducts are generally provided with 2 0 fins for increasing the heat exchange surface between the gas and the liquid.

Heat exchangers of this type are generally used in boilers incorporating an atmospheric burner and are mounted above the latter. In this case, the gas is constituted by the combustion gases and the heat carrier liquid is water. In this way, a substantially zigzag liquid flowpath (whose horizontal sections are divided into a plurality of parallel 2 5 branches defined in the plate ducts) and a gas flowpath crossing the exchanger plates in a vertical direction from bottom to top are defined.

In the present description and in the subsequent claims, the terms "low" and "high",

"lower" and "upper", "under" and "over", "horizontal" and "vertical" will be attributed to the modular plates, to the heat exchanger and to the boiler, as well as to the components 3 0 thereof, with reference to their position once assembled.

In spite of the large heat exchange surface provided by the fins present on each plate,

- 2 heat exchangers of this type, and the boilers in which the same are incorporated, show a number of problems which have not been overcome yet.

Firstly, the parallel arrangement of the ducts for the liquid circulation in each heat exchange plate causes, on the one hand, a reduced liquid velocity with a corresponding 5 drop in heat exchange efficiency and, on the other hand, the possibility that local thermal changes may occur, for example overheatings, due to an uneven distribution of the liquid flow in the various ducts with negative consequences on the working life of the heat exchanger.

Secondly, gas-liquid heat exchangers constituted by plates such as those described 10 above have a large size due to the presence of the liquid manifolds formed at the aforementioned opposite ends of the plates.

Thirdly, the cleaning operations of the chemical type, normally deemed as being the most efficient, turned out to be extremely difficult to be carried out because the cleaning fluids employed tend to preferably flow into the ducts offering the minimum flowing 15 resistance, that is the least scaled ducts, to the detriment of the ducts which need more cleaning. The technical problem underlying the present invention is therefore that of providing a heat exchanger having a high thermal exchange efficiency which overcomes the drawbacks of the cited prior art.

2 0 According to the first aspect of the invention, the aforementioned technical problem is solved by a gas-liquid heat exchanger including a plurality of modular heat exchanger plates adapted to effect a heat exchange between a gas and a heat carrier liquid, each modular plate comprising: a) a substantially plate-shaped hollow body integrally made of cast metal, said hollow 2 5 body comprising: al) an inlet opening and an outlet opening of the liquid into and from the hollow body, said inlet and outlet openings being formed at a proximal end of the modular plate; a2) at least one first channel extending along a first direction between said 30 proximal end and a distal end of the modular plate for conveying said heat carrier liquid from said inlet opening towards said distal end; e e _..... . _

l as) at least one second channel connected in series to said first channel and extending along said first direction between said distal end and said proximal end of the modular plate for conveying said heat carrier liquid from said distal end towards said outlet opening, 5 b) at least one portion provided with a plurality of heat exchange members extending in a cantilevered fashion from said hollow body for increasing the heat exchange surface between said gas and said heat carrier liquid; c) at least one opening for allowing a gas flow formed through said body aside to at least one part of said portion provided with heat exchange members, 10 wherein said modular plates are respectively package-mounted so as to form a liquid Towpath and a gas flowpath in said heat exchanger, said liquid and gas Towpaths being at least partially in crossbow with each other.

In the present description and in the subsequent claims, the expression "heat exchange

members" is used to indicate members cantilevered from the plates and having suitable 15 shape and size, adapted to increase the heat exchange surface between the gas and the liquid. As a non limitative example, suitable heat exchange members may be of frustoconical or cylindrical shape, or may be substantially fin-shaped.

In the present description and in the subsequent claims, the expressions "proximal" and

"distal" shall be used to indicate elements of the modular plate and of the heat 20 exchanger positioned near and, respectively, on opposite sides of the inlet and outle t openings of the liquid into and, respectively, from the plate.

Thanks to the fact that the first and second channels formed within the hollow body are connected in series to each other, it is advantageously possible to achieve a greater flowing velocity and a greater turbulence of the thermal carried liquid with respect to 2 5 those achieved in the heat exchangers of the prior art, with an ensuing increase of the

heat exchange coefficient on the liquid side and, as a result, of the overall heat exchange efficiency of the exchanger.

Moreover, the heat exchange efficiency is further improved with respect to that achievable by the heat exchangers of the prior art thanks to the fact that the liquid and

3 0 the gas Towpaths in the exchanger are at least in part essentially in crossflow relationship with each other. This increase in heat exchange efficiency can be attributed substantially to all the modular heat exchange plates constituting the heat exchanger,

with the partial exception of the plate which - in use - is the first to be lapped by the gas, for example by the combustion gases from a burner, since in such plate the gas flow is only partially crossed with respect to the flow of the heat carrier liquid.

Since the inlet and outlet openings of the liquid into and from each modular plate of the 5 exchanger according to the invention are formed at the same end of the plate (the proximal end), the heat exchanger of the invention advantageously includes a single series of manifolds for the heat carrier liquid, such manifolds being package-stacked at a single side (the proximal side) of the exchanger.

The heat exchanger of the invention is therefore more compact with respect to the 10 exchangers of the prior art having the same thermal power, which instead require two

series of manifolds at the opposite ends of the plate.

Advantageously, furthermore, the connection in series between the first and second channels formed within the hollow body of the plates allows to carry out an efficient cleaning of the chemical type of these channels using suitable cleaning fluids, such as 15 for example hydrochloric acid water solutions.

According to a preferred embodiment of the invention, the liquid flowpath in the heat exchanger is substantially extending according to a zigzag path between an inlet opening and an outlet opening of the heat carrier liquid into and from the heat exchanger and is at least partially extending in each modular plate along said first direction.

2 0 Preferably, the inlet and outlet openings of the liquid into and from said modular plates are defined in respective structurally independent inlet and outlet chambers separated in a liquid-tight manner and formed within a single manifold integrally extending from said proximal end of the modular plate.

In this way, it is advantageously possible to connect the modular plates to each other in 2 5 a very simply manner, that is by simply placing side by side the outlet opening of a plate and the inlet opening of an adjacent plate, at the proximal side of the exchanger.

Preferably, the modular plates are reciprocally associated in a fluidtight manner at said liquid manifolds and, still more preferably, also at their peripheral edges thanks to the use of suitable peripheral sealing means, such as for example gaskets interposed 3 0 between adjacent modular plates.

According to a preferred embodiment of the heat exchanger of the invention, the i , .... ...

- s - aforementioned at least one first channel is formed within the hollow body near a side wall thereof, while the second channel is formed within the hollow body near a side wall thereof opposite to the first channel.

Thanks to this combination of preferred features, it is advantageously possible to obtain 5 a fluid Towpath which not only makes maximum use of the volume available within the hollow body of each single heat exchange plate, but is also able to effect an excellent heat exchange with the gas lapping the plate.

Preferably, said hollow body further contains at least one intermediate channel connected in series to the first and second channels. The provision of an additional 10 intermediate channel allows to further increase the use of the available volume within the hollow body, while obtaining an extension of the liquid flowpath in each plate, with an ensuing improvement of the heat exchange efficiency of the exchanger.

According to a further pretested embodiment, the aforementioned intermediate channel is substantially zigzag-shaped and, still more preferably, is extending along the 15 transverse centre-line plane of the modular plate. In this way, the available volume within the hollow body is maximised, with an ensuing increase of the heat exchange efficiency. According to an alternative preferred embodiment, the aforementioned at least one first channel may be formed within the hollow body near a first face thereof, while the 20 second channel is preferably formed within the hollow body near the face thereof opposite to the first channel.

In this alternative embodiment, the first channel, the second channel, and the partition wall which separates the same preferably have a width substantially to the width of said at least one portion provided with heat exchange members of the modular plate. In this 25 way, the maximum heat exchange surface in relation to the size of the plate is advantageously achieved.

Preferably, the aforementioned at least one portion provided with a plurality of heat exchange members extends on opposite faces of the hollow body.

This preferred embodiment allows to achieve an advantageous increase of the heat 3 0 exchange surface available to the gas flowing between the plates of the exchanger as the gas crosses the latter.

. . . .. . .....

- 6 Preferably, the aforementioned at least one portion provided with a plurality of heat exchange members is inclined at a predetermined angle with respect to the transverse centre-line plane of the modular plate.

In this way, the downflow of possible condensation water along the plane defined by 5 each plate is advantageously facilitated, thus optimising the heat exchange and preserving the plates from the risk of corrosion.

Still more preferably, such angle is from about 2 to about 4 .

Preferably, the heat exchange members are pitchwise arranged in respective pluralities of rows substantially parallel to a longitudinal axis of said modular plate.

10 The pitch between the heat exchange members in each of the aforementioned rows is preferably from about 8 mm to about 20 mm.

In this way, it is advantageously possible to ensure a large heat exchange surface, while minimising the risk of local thermal gradients, thus ensuring a uniform distribution of the heat and an ensuing extension of the working life of the heat exchanger.

15 Preferably, the aforementioned rows are also pitchwise arranged along a direction substantially perpendicular to the longitudinal axis of the modular plate. Still more preferably, the pitch between the rows of heat exchange members is from about 8 mm to about 20 mm.

Preferably, the modular plates comprise a first and a second group of rows of heat 2 0 exchange members, which groups are arranged on opposite sides of the longitudinal axis of the modular plate.

In addition, the first group rows are preferably staggered with respect to second group rows, along a direction substantially parallel to the longitudinal axis of the modular plate, of a portion of length equal to half the pitch of the heat exchange members of the 2 5 second group.

Thanks to this arrangement of the heat exchange members, and as will be more clearly apparent from the following, it is advantageously possible to make the heat exchanger by package-mounting a plurality of structurally identical modular plates together: the aforementioned arrangement of the heat exchange members is in fact such as to allow 3 0 the insertion of such members between the members of an adjacent plate by turning over the plate about the longitudinal axis thereof. In other words, each plate is turned upside

down by an angle of 180 about its own longitudinal axis with respect to the adjacent plates. In this way, the heat exchanger of the invention allows to obtain an advantageous saving in production costs, while eliminating the need of stocking different types of plates.

5 Moreover, thanks to such arrangement, two further advantages can be simultaneously obtained which consist in the possibility of making an extremely compact heat exchanger and in the possibility of ensuring a uniform velocity of the gas flow. In other terms, it is advantageously possible to ensure a uniform heat distribution along each heat exchange member and, accordingly, an improvement both in the heat exchange 10 efficiency of the heat exchanger of the invention and in the reliability of the latter.

Preferably, the heat exchange members have a draft angle from about 2 to about 5 .

In the present description and the subsequent claims, the term: "draft angle" of a heat

exchange member is used to indicate the angle defined between the side surface of a heat exchange member and the line perpendicular to the plane defined by the body of the 15 modular plate.

According to a preferred embodiment of the invention, the heat exchange members have a substantially frustoconical shape.

Thanks to the manufacturing technology employed (sand casting), it is advantageously possible to reduce this draft angle down to the values described above, with an 2 0 advantageous reduction of the thickness of the gap formed between the heat exchange members belonging to adjacent modular plates.

According to a preferred embodiment, said gap forms part of the gas flowpath crossing the exchanger and has a substantial constant thickness.

Preferably, such gap has a thickness from about 1 to about 3 mm.

2 5 Thanks to the frustoconical shape of the heat exchange members, besides, the downflow of possible condensation water from one plate to another is facilitated, thus optimising the efficiency of the boiler and preserving, at the same time, the plates from the risk of corrosion. As a consequence, the heat exchanger of the invention can also be advantageously used to recover heat in condensation boilers.

3 0 Preferably, the aforementioned opening for allowing a gas flow through the hollow body . . .. id..

,

- 8 of the modular plates is formed near a side wall thereof.

Thanks to this feature, the assembly of the plates according to the method described above (i.e. by turning upside down the plates by 180 with respect to the adjacent plates) allows to obtain a substantially zigzag gas Towpath within the exchanger which directs 5 the gas flow along a direction substantially in crossbow with respect to the direction of the heat carrier liquid Towpath, increasing to the maximum extent the heat exchange between the gas passing between the plates and the liquid flowing within the same.

Preferably, furthermore, the gas Towpath is at least partially extending between adjacent modular plates along a second direction substantially perpendicular to the direction of 10 the first and second channels defined in the modular plates.

Thanks to the direction of the gas Towpath, the drainage of any condensates which may form is advantageously facilitated.

According to a second aspect thereof, the invention provides a boiler including a burner and a heat exchanger as described above.

15 Preferably, the burner is of the so-called pre-mixing type, and the heat exchanger is supported below the burner, so that the latter is preserved from the risk of coming in contact with possible condensates.

Preferably, the modular plates of the exchanger are obtained by casting metal materials having different heat resistances, and are mounted in such a way that the modular plates 2 0 of metal material having the greater heat resistance are positioned closer to the burner.

Preferably, the modular plates of the exchanger are obtained by casting metal materials having different corrosion resistances and are mounted in such a way that the modular plates of material having the lower corrosion resistance are positioned closer to the burner. 2 5 According to the latter two preferred embodiments of the boiler of the invention, it is advantageously possible to reduce the cost of the materials using the highest quality materials - possessing increased high temperature or corrosion resistance - only where necessary. Preferably, the boiler of the invention further comprises a manifold for collecting the 3 0 condensate, said manifold being positioned downstream of the exchanger.

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According to a third aspect thereof, the invention provides a modular heat exchange plate, adapted to effect a heat exchange between a gas and a heat carrier liquid, having the features described above.

Additional features and advantages of the present invention will be more clearly 5 apparent from the following description of a preferred embodiment thereof, given by

way of illustration and not of limitation with reference to the accompanying drawings, in which the same references identify identical or equivalent components.

In the drawings: - Figure 1 shows a schematic cross-section view of a boiler comprising a heat exchanger 10 according to the invention; - Figure 2 shows a perspective view of a modular plate of the heat exchanger of Figure 1; - Figure 3 shows a top view of the modular plate of Figure 2; Figure 4 shows a transversal cross-section, made according to line I-I of Figure 3, of 15 the modular plate of Figure 2; - Figure S shows a side view, in partial cross-section, made according to line II-II of Figure 3, of the modular plate of Figure 2; - Figure 6 shows a cross- section, made according to line III-III of Figure S. of the modular plate of Figure 2; 20 - Figure 7 shows a cross-section of a portion of the heat exchanger of Figure 1 comprising a couple of modular plates sectioned according to line IV-IV of Figure 3.

With reference to figure 1, a boiler incorporating a burner 2, such as for example a burner of the pre-mixing type, below which a heat exchanger 3 according to a preferred embodiment of the invention is supported in a manner known per se, is generally 2 5 indicated at 1.

The heat exchanger 3 comprises a plurality of structurally identical modular plates 4 package-mounted together. The modular plates 4 carry out a heat exchange between the combustion gases coming from the burner 2 and a suitable heat carrier liquid, such as for example water.

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- 10 As shown in Figure 1, the boiler 1 comprises a combustion zone 5 downstream of the burner 2. The combustion zone S is fed with combustion air from a blower 6 and with combustible gas from a pipe 7 provided with an on-off valve 8. The combustion air and the combustible gas are intimately mixed by a Venturi tube 9.

5 In Figure 1, the heat exchanger 3 comprises three modular plates 4 reciprocally associated in a fluid-tight manner at respective manifolds 10 for distributing and collecting the heat carrier liquid into and from the plates 4. Each manifold 10 integrally extends from a proximal end 11 of each modular plate 4 and comprises an inlet opening 13 and an outlet opening 15 of the liquid into and from the plate 4 itself.

10 Moreover, each modular plate 4 comprises an opening 21 for allowing a gas flow which will be described more in detail in the following. A gap 45 is defined between each pair of adjacent modular plates 4, such gap 45 being intended for allowing a gas flow and forming part of a gas Towpath G defined within the exchanger 3 (figure 7).

A return duct 12 for conveying the heat carrier liquid back to the heat exchanger 3 is 15 connected, in a way known per se, to the heat exchanger 3, the return duct 12 being in fluid communication with the inlet opening 13 of the modular plate 4 arranged at the lowest position. A delivery duct 14 for delivering the heat carrier liquid from the heat exchanger 3 is in fluid communication with the outlet opening 15 of the modular plate 4 arranged at the highest position.

2 0 The boiler 1 further comprises a discharge duct 16 for discharging the combustion gases from the heat exchanger 3 and a manifold 17 for collecting the condensate. The discharge duct 16 and the manifold 17 are arranged downstream of the heat exchanger 3.

Thus, in the heat exchanger 3 are defined a liquid flowpath L substantially extending in a zigzag manner between the inlet opening 13 and the outlet opening 15 of the heat 25 carrier liquid into and from the exchanger 3 and the aforementioned gas flowpath G. also substantially extending in a zigzag manner and substantially crossing the liquid Towpath L defined between the plates 4. More particularly, the liquid flowpath L is at least partially extending in each plate 4 along a direction substantially parallel to the longitudinal axis X-X of the plate 4: such portion of the liquid Towpath L is generally 3 0 indicated with the letter L' in figure 6.

Thanks to the arrangement of the heat exchanger 3 in the boiler 1, possible condensates are easily drained through the exchanger 3 and collected in the manifold 17.

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- 11 Preferably, the modular plates 4 of the heat exchanger 3 are obtained by casting metal materials having different thermal and corrosion resistances. Still more preferably, the modular plates 4 made of metal materials having the higher thermal resistance, such as for example cast iron, are mounted near the burner 2, while the modular plates 4 of 5 highest quality metal materials, as such having the higher corrosion resistance, such as for example aluminium, are mounted furthest from the burner 2, where the risk of corrosion is greater.

Figure 2 shows a perspective view of the modular heat exchange plate 4.

According to the invention, the modular plate 4 comprises a substantially plate-shaped 10 hollow body 18 integrally made of cast metal, such as for example cast iron, obtained by casting the metal according the so-called "sand casting" technique in a mould around a core preferably comprising a conventional mixture of sand and resin.

The modular plate 4 further comprises at least one portion 19 provided with a plurality of heat exchange members 20 extending in a cantilevered fashion from the hollow body 15 18 for increasing the heat exchange surface between the combustion gases and the heat carrier liquid, and the aforementioned opening 21 for allowing a gas flow formed through the hollow body 18 aside the portion 19.

According to the invention and as described in detail in figures 4 and 5, the inlet opening 13 and the outlet opening 15 of the liquid into and from the hollow body 18 are 2 0 formed at the proximal end 11 of the modular plate 4.

As shown in figure 6, the hollow body 18 comprises at least one first channel 22 extending, in a first direction substantially parallel to the longitudinal axis X-X of the plate 4, between the proximal end 1 1 and a distal end 23 of the plate 4 for conveying the heat carrier liquid from the inlet opening 13 towards the distal end 23, and at least one 2 5 second channel 24, connected in series to the first channel 22, also extending along the aforementioned direction between the distal end 23 and the proximal end 11 for conveying the heat carrier liquid from the distal end 23 to the outlet opening 1 S. According to the preferred embodiment illustrated in figure 6, the first channel 22 is formed within the hollow body 18 near a side wall 25 thereof between said wall 25 and 3 0 an inner wall 26.

The second channel 24 is preferably formed in the hollow body 18 near a side wall 27 thereof opposite to the first channel 22.

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- 12 In the preferred embodiment illustrated, the second channel 24 is defined between the side wall 27 and a partition wall 28 extending within the hollow body 18.

At the proximal end 11, the aforementioned first channel 22 and second channel 24 are separated in a liquid-tight manner by a wall 29 extending between the wall 27 and the 5 partition wall 28.

According to the preferred embodiment described in Figure 6, the hollow body 18 further comprises an intermediate channel 30 connected in series to the first channel 22 and to the second channel 24, such intermediate channel 30 advantageously allowing to extend the liquid Towpath L' in each plate 4 and to increase the heat exchange 10 efficiency of the heat exchanger 3.

Preferably, the intermediate channel 30 is substantially zigzag-shaped along the transverse centre-line line of the modular plate 4 thanks to a plurality of inner partition walls 31-34 having a predetermined length, said partition walls 31-34 being all parallel to the longitudinal axis XX and alternatively extending from an inner proximity wall 35 15 and from an inner distal wall 36 of the hollow body 18.

Preferably, in order to maximise the heat exchange surface, the channel constituted by the first channel 22 and by the intermediate channel 30 arranged in series with the same have a total width substantially equal to the width of the portion 19 provided with the heat exchange members 20 of the modular plate 4.

2 0 According to this preferred embodiment of the invention and as illustrated in figures 4 and 5, the inlet opening 13 and the outlet opening 15 of the liquid into and from the modular plate 4 are defined in respective structurally independent inlet and outlet chambers 37, 38 separated in a liquid-tight manner, for example by a partition wall 39, and formed within the manifold 10 of the modular plate 4.

2 5 Preferably, the modular plate 4 comprises a plurality of tubularelements 40, cantilevered from the wall 36 and formed during the casting around supporting elements of the core (known in the field by the term "core supports") adapted to allow the

manufacture of the modular plate 4. The tubular elements 40 carry out the function of facilitating the extraction of the modular plate 4 from the manufacturing mould and the 30 subsequent removal of the core from the modular plate 4. When the manufacturing process is completed, the tubular elements 40 are suitably sealed with caps 41, schematically shown in figure 3.

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According to the preferred embodiment illustrated, the portion 19 provided with the heat exchange members 20 extends on opposite faces 42, 43 of the hollow body 18 for increasing the heat exchange surface.

Moreover, the portion 19 provided with the heat exchange members 20 is preferably 5 inclined at an angle a equal to about 3 with respect to the transverse centre-line plane of the modular plate 4, in order to facilitate the downflow of possible condensation water. The heat exchange members 20 are preferably pitchwise spaced apart from each other, according to a pitch p', in respective pluralities of rows 20a-20g substantially parallel to 1 0 the longitudinal axis X-X of the modular plate 4, in order to permit a heat distribution as uniform as possible.

More in detail, according to a preferred embodiment, the modular plates 4 comprise a first 20' and a second 20" group of rows of heat exchange members 20 arranged on--

opposite sides of the longitudinal axis X-X, the rows 20a-20c of the first group 20' 1 5 being staggered parallel to the longitudinal axis X-X with respect to the rows 20d-20g of the second group 20" of a portion of length "s" substantially equal to half the pitch p' of the heat exchange members 20 of the second group 20" (figure 3).

Such arrangement of the heat exchange members 20 advantageously allows to mount side by side a plurality of modular plates 4 of the same type.

20 Preferably, also the rows 20a-20g of the heat exchange members 20 are pitchwise spaced apart from each other along a direction substantially perpendicular to the longitudinal axis X-X of the modular plate 4: in figure 3 this pitch between the rows 20a-20g is indicated with the letter p".

As shown in figure 7, which illustrates a portion of the heat exchanger 3 comprising two 2 5 modular plates 4 arranged side by side, the latter can be package-mounted together by placing a first modular plate 4 and then placing a second structurally identical plate 4, previously turned upside down by 180 around its own longitudinal axis X-X, next to the first plate 4.

In this way, it is advantageously possible to reciprocally insert the heat exchange 30 members 20 of adjacent plates 4 in order to create a gap 45 having a substantially constant thickness.

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- 14 Preferably, the opening 21 for allowing a gas flow is formed near a side wall, in the case illustrated the wall indicated with 25, of the hollow body 18 of the modular plates 4.

Accordingly, two Towpaths essentially in crossbow with each other are defined between adjacent plates 4, a liquid Towpath L substantially extending in a zigzag manner 5 between the inlet opening 13 and the outlet opening 15 of the liquid into and from the heat exchanger 3 with portions extending in a direction substantially parallel to the longitudinal axis X-X, and a gas Towpath G also generally extending substantially in a zigzag manner in the heat exchanger 3, and comprising the gap 45 defined between the heat exchange members 20 of adjacent modular plates 4.

10 According to the preferred embodiment illustrated, the gas Towpath G at least partially extends between adjacent modular plates 4 along a second direction Y-Y substantially perpendicular to the direction X-X.

Thanks to the fact that the liquid Towpath L and the gas Towpath G are partially essentially crossed with each other, the heat exchange efficiency is advantageously 15 improved with respect to the efficiency obtainable with the heat exchangers of the prior art. Advantageously, then, the portion of the liquid Towpath L' is also substantially extending according to a zigzag path within the hollow body 18 of each plate 4, thus contributing to optimise the heat exchange efficiency between the gas and the liquid.

2 0 Clearly, a man skilled in the art may introduce changes and variants to the invention described hereinabove in order to satisfy specific and contingent application requirements, variants and changes which anyhow fall within the scope of protection as defined by the following claims.

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Claims

- 15 CLAIMS

1. A gas-liquid heat exchanger (3) including a plurality of modular heat exchange plates (4) adapted to effect a heat exchange between a gas and a heat carrier liquid, each modular plate (4) comprising: 5 a) a substantially plate-shaped hollow body (18) integrally made of cast metal, said hollow body (18) comprising: al) an inlet opening (13) and an outlet opening (15) of the liquid into and from the hollow body (18), said inlet (13) and outlet (15) openings being formed at a proximal end ( 11) of the modular plate (4); 10 a2) at least one first channel (22) extending along a first direction between said proximal end (11) and a distal end (23) of the modular plate (4) for conveying said heat carrier liquid from said inlet opening (13) towards said distal end (23); a3) at least one second channel (24) connected in series to said first channel (22) and extending along said first direction between said distal end (23) and said 15 proximal end (11) of the modular plate (4) for conveying said heat carrier liquid from said distal end (23) towards said outlet opening (15); b) at least one portion (19) provided with a plurality of heat exchange members (20) extending in a cantilevered fashion from said hollow body (18) for increasing the heat exchange surface between said gas and said heat carrier liquid; 2 0 c) at least one opening (21) for allowing a gas flow formed through said body (18) aside to at least one part of said portion (19) provided with heat exchange members (20), wherein said modular plates (4) are respectively package-mounted so as to form a liquid Towpath (L) and a gas flowpath (G) in said heat exchanger (3), said liquid (L) and gas (G) Towpaths being at least partially in crossflow with each other.

25 2. Heat exchanger (3) according to claim 1, wherein said liquid Towpath (L) is substantially extending according to a zigzag path between an inlet opening (13) and an outlet opening (15) of the heat carrier liquid into and from the heat exchanger (3) and is at least partially extending in each modular plate (4) along said first direction.

3. Heat exchanger (3) according to claim 1, wherein the inlet (13) and the outlet (15) .

- 16 openings of the liquid into and from said modular plates (4) are defined in respective structurally independent inlet (37) and outlet (38) chambers separated in a liquid-tight manner and formed within a manifold (10) integrally extending from said proximal end (11) of the modular plate (4).

5 4. Heat exchanger (3) according to claim 3, wherein said modular plates (4) are reciprocally associated in a fluid-tight manner at said manifolds (10).

5. Heat exchanger (3) according to claim 1, wherein said at least one first channel (22) is formed within said hollow body (18) near a side wall (25) thereof.

6. Heat exchanger (3) according to claim 5, wherein said at least one second channel 10 (24) is formed within said hollow body (18) near a side wall (27) thereof opposite to said at least one first channel (22).

7. Heat exchanger (3) according to claim 1, wherein said at least one first channel (22) is formed within said hollow body (18) near a first face (43) thereof.

8. Heat exchanger (3) according to claim 7, wherein said at least one second channel 1 5 (24) is formed within said hollow body (18) near a face (42) thereof opposite to said at least one first channel. (22).

9. Heat exchanger (3) according to claim 7 or 8, wherein said at least one first (22) and second (24) channels have a width substantially equal to the width of said at least one portion (19) provided with heat exchange members (20) of the modular plate (4).

20 10. Heat exchanger (3) according to claim 1, wherein said hollow body (18) further comprises at least one intermediate channel (30) connected in series to said at least one first channel (22) and to said at least one second channel (24).

11. Heat exchanger (3) according to claim 10, wherein said intermediate channel (30) is substantially zigzag-shaped along the transverse centreline plane (a) of the modular 2 5 plate (4).

12. Heat exchanger (3) according to claim 1, wherein said at least one portion (19) provided with a plurality of heat exchange members (20) extends on opposite faces (42, 43) of said hollow body (18).

13. Heat exchanger (3) according to claim 1, wherein said at least one portion (19) 3 0 provided with a plurality of heat exchange members (20) is inclined at a predetermined : .....

angle (or) with respect to the transverse centre-line plane ( c) of the modular plate (4).

14. Heat exchanger (3) according to claim 1, wherein said heat exchange members (20) are pitchwise arranged in respective pluralities of rows (20a-20g) substantially parallel to a longitudinal axis (X-X) of said modular plate (4).

5 15. Heat exchanger (3) according to claim 14, wherein said rows (20a20g) are pitchwise arranged along a direction substantially perpendicular to said longitudinal axis (X-X) of the modular plate (4).

16. Heat exchanger (3) according to claim 14 or 15, wherein said modular plates (4) comprise a first (20') and a second group (20") of rows (20a20g) of heat exchange 10 members (20), wherein said first (20') and second (20") groups of rows (20a-20g) are arranged on opposite sides of said longitudinal axis (X-X) of the modular plate (4) and wherein the rows (20a-20c) of the first group (20') are staggered along a direction substantially parallel to the longitudinal axis (X-X) with respect to the rows (20d-20g) of the second group (20") of a portion of length (s) substantially equal to half of the 15 pitch (p') of the heat exchange members (20) of the second group (20").

17. Heat exchanger (3) according to claim 1, wherein said heat exchange members (20) have a substantially frustoconical shape having a draft angle from about 2 to about 5 .

18. Heat exchanger (3) according to claim 1, wherein said gas Towpath (G) comprises a gap (45), having a substantially constant thickness, defined between the heat exchange 2 0 members (20) of adjacent modular plates (4).

l9. Heat exchanger (3) according to claim 18, wherein said gap (45) has a thickness from about 1 to about 3 mm.

20. Heat exchanger (3) according to claim 1, wherein said opening (21) for allowing a gas flow is formed near a side wall (25) of the hollow body (18) of said modular plates 2 5 (4)

21. Heat exchanger (3) according to claim 1, wherein said gas Towpath (G) is a substantially zigzag path.

22. Heat exchanger (3) according to claim 1 or 21, wherein said gas Towpath extends at least partially between adjacent modular plates (4) along a second direction (Y-Y) 3 0 substantially perpendicular to a longitudinal axis (X-X) of said modular plate (4).

- 18 23. Heat exchanger (3) according to claim 1, further comprising a plurality of peripheral sealing means positioned between adjacent modular plates (4).

24. Boiler (1) including a burner (2) and a heat exchanger (3) according to any one of the preceding claims 1-23.

5 25. Boiler (1) according to claim 24, wherein the modular plates (4) of the heat exchanger (3) are obtained by casting metal materials having a different heat resistance, and are mounted in such a way that the modular plates (4) made of metal materials having a higher heat resistance are positioned closest to said burner (2).

26. Boiler (1) according to claim 24, wherein the modular plates (4) of the heat 10 exchanger (3) are obtained by casting metal materials having a different corrosion resistance and are mounted in such a way that the modular plates (4) made of metal materials having a lower corrosion resistance are positioned closest to said burner.

27. Boiler (1) according to claim 24, further comprising a manifold (17) for collecting condensate positioned downstream of said heat exchanger (3) .

1 5 28. A modular heat exchange plate (4) adapted to effect a heat exchange between a gas and a heat carrier liquid, said modular plate comprising: a) a substantially plate-shaped hollow body (18) integrally made of cast metal, said hollow body (18) comprising: al) an inlet opening (13) and an outlet opening (IS) of the liquid into and from 20 the hollow body (18), said inlet (13) and outlet (15) openings being formed at a proximal end (11) of the modular plate (4); a2) at least one first channel (22) extending along a first direction between said proximal end (11) and a distal end (23) of the modular plate (4) for conveying said heat carrier liquid from said inlet opening (13) towards said distal end (23); 2 5 a3) at least one second channel (24) connected in series to said first channel (22) and extending along said first direction between said distal end (23) and said proximal end (11) of the modular plate (4) for conveying said heat carrier liquid from said distal end (23) towards said outlet opening (15); b) at least one portion (19) provided with a plurality of heat exchange members (20) 30 extending in a cantilevered fashion from said hollow body (18) for increasing the heat

- 19 exchange surface between said gas and said heat carrier liquid, c) at least one opening (21) for allowing a gas flow formed through said body (18) aside to at least one part of said portion (19) provided with heat exchange members (20).

29. Modular plate (4) according to claim 28, wherein the inlet (13) and the outlet (15) 5 openings of the liquid into and from said modular plate (4) are defined in respective structurally independent inlet (37) and outlet (38) chambers separated in a liquid-tight manner and formed within a manifold (lO) integrally extending from said proximal end (11) of the modular plate (4).

30. Modular plate (4) according to claim 28, wherein said at least first channel (22) is 1 0 formed in said hollow body (18) near a side wall (25) thereof.

31. Modular plate (4) according to claim 30, wherein said at least one second channel (24) is formed in said hollow body (18) near a side wall (27) thereof opposite to said at least one first channel. (22).

32. Modular plate (4) according to claim 28, wherein said at least one first channel (22) 1 5 is formed in said hollow body (18) near a first face (43) thereof.

33. Modular plate (4) according to claim 32, wherein said at least one second channel (24) is formed in said hollow body (18) near a face (42) thereof opposite to said at least one first channel (22).

34. Modular plate (4) according to claim 32 or 33, wherein said at least one first channel 2 0 (22) and said at least one second channel (24) have a width substantially equal to the width of said at least one portion (l9) provided with heat exchange members (20) of the modular plate (4).

35. Modular plate (4) according to claim 28, wherein said hollow body (18) further comprises at least one intermediate channel (30) connected in series to said at least one 2 5 first channel (22) and to said at least one second channel (24).

36. Modular plate (4) according to claim 35, wherein said intermediate channel (30) is substantially zigzag-shaped along the transverse centreline plane (a) of the modular plate (4).

37. Modular plate (4) according to claim 28, wherein said at least one portion (19) 3 0 provided with a plurality of heat exchange members (20) extends on opposite faces (42, ... i. v ..

l - 20 43) of said hollow body (18).

38. Modular plate (4) according to claim 28, wherein said at least one portion (19) provided with a plurality of heat exchange members (20) is inclined at a predetermined angle with respect to the transverse centreline plane (a) of the modular plate (4).

5 39. Modular plate (4) according to claim 28, wherein said heat exchange members (20) are pitchwise arranged in respective pluralities of rows (20a-20g) substantially parallel to a longitudinal axis (X-X) of said modular plate (4).

40. Modular plate (4) according to claim 39, wherein said rows (20a-20g) are pitchwise arranged along a direction substantially perpendicular to said longitudinal axis (X-X) of 1 0 the modular plate (4).

41. Modular plate (4) according to claim 39 or 40, comprising a first group (20') and a second group (20") of rows (20a-20g) of heat exchange members (20), wherein said first (20') and second (20") groups of rows (20a-20g) are arranged on opposite sides of said longitudinal axis (X-X) of the modular plate (4) and wherein the rows (20a-20c) of 15 the first group (20') are staggered along a direction substantially parallel to the longitudinal axis (X-X) with respect to the rows (20d-20g) of the second group (20") of a portion of length (s) substantially equal to half the pitch (p') of the heat exchange members (20) of the second group (20").

42. Modular plate (4) according to claim 28, wherein said heat exchange members (20) 2 0 have a substantially frustoconical shape having a draft angle from about 2 to about 5 .

43. Modular plate (4) according to claim 28, wherein said opening (21) for allowing a gas flow is formed near a side wall (25) of the hollow body (18) of said modular plates (4) . j..