Boiler, in particular condensing boiler, comprising heat exchanger

Abstract

The invention relates to a boiler (10), in particular a condensing boiler (10), comprising: at least one combustion zone (13); a burner (11) arranged along a longitudinal axis (y) in correspondence with the combustion region (13); and at least one first heat exchanger (1) adapted to surround said burner (11) wherein an inner portion (7) of the first heat exchanger faces said burner (11) and is directly exposed to the flame of said burner (11) when said burner (11) is in use, said heat exchanger (1) being provided with a steel conduit having a helical profile, the invention relates to a heat exchanger (1) for a boiler (10), comprising a conduit (2), preferably made of stainless steel, and comprising a plurality of coils (2) having a common axis of symmetry (y), the axis of symmetry (y) of the first heat exchanger (1) coinciding with the longitudinal axis (y) of the boiler (10), an inner portion (7) of each coil (2) of the first heat exchanger (1) facing the axis of symmetry (y) has a continuous recess (9) along at least a portion of the helical profile.

Description

Technical Field

[0001] The present invention relates to a boiler, in particular to a condensing boiler.

[0002] More precisely, the invention relates to a boiler comprising a heat exchanger having a specific tubular profile. Background Art

[0003] In the prior art, heat exchangers for condensing boilers are known that have a serpentine pattern.

[0004] Some examples are described in the following patent titles EP 2 504 632 B1 or WO 2016 / 084109 A1, which relate to a heat exchanger for a condensing boiler, comprising a double serpentine circuit, specifically an inner circuit and an outer circuit.

[0005] In both known solutions, the outer surface of each coil S of the innermost exchanger facing the burner of the condensing boiler has a smooth and slightly convex surface (as shown in FIG. 4 ), with the bulge C facing the burner.

[0006] A disadvantage of this geometry is that the part of the heat exchanger facing the burner flame is more susceptible to corrosion due to material spalling phenomena.

[0007] This phenomenon is a typical characteristic of high temperature oxidation stainless steel.

[0008] When stainless steel is heated to a high temperature, an oxide layer and a scale layer (flake layer) are formed on the surface of the material.

[0009] The oxide scale and the metal substrate have different coefficients of thermal expansion, which affects its stability, especially when the material is subjected to frequent thermal cycling. Due to the different coefficients of thermal expansion, an excessive amount of oxide scale forms, which eventually breaks or fractures as the metal cools. This phenomenon occurs cyclically, with the surface becoming locally thinner, and cracks forming, leading to material failure.

[0010] Another disadvantage of this prior art geometry is that the inner wall of each coil of the internal heat exchanger generally has a relatively low temperature (typically between 30°C and 90°C) compared to the flame temperature of the burner 11 (approximately between 1600°C and 2000°C), and as shown in FIG8 , the oxidation of carbon monoxide to carbon dioxide is abruptly interrupted when the combustion flue gas reaches this wall. As a result, a large amount of pollutants is generated. Summary of the Invention

[0011] The object of the present invention is to resolve the disadvantages of the prior art.

[0012] In particular, one objective is to reduce, if not eliminate, the phenomenon of spalling of material forming the heat exchanger surfaces in the combustion zone corresponding to the burner.

[0013] Another object of the present invention is to reduce the amount of pollutants produced by the combustion process.

[0014] An object of the present invention is to provide a heat exchanger for a boiler, in particular a condensing boiler, the boiler comprising: at least one combustion zone; and a burner arranged along a longitudinal axis corresponding to the combustion zone, the heat exchanger being adapted to surround the burner of the boiler when inserted into the boiler, the heat exchanger being provided with a steel conduit having a spiral profile (preferably the conduit being made of stainless steel) and comprising a plurality of coils having a common axis of symmetry, wherein, in the heat exchanger, the inner portion of each coil facing the axis of symmetry has a continuous recess along at least a portion of the spiral profile.

[0015] In particular, according to the present invention, the cross section of the conduit of each coil may have a concave portion defined between two inflection points arranged at an inner portion of the coil.

[0016] More specifically, according to the invention, the depth of the recess may be between 4% and 50% of the width of the cross section of the conduit of the corresponding coil.

[0017] Furthermore, according to the invention, the height of the recess may be between 43% and 81% of the height of the cross section of the conduit of the corresponding coil, wherein the height of the recess is measured as the distance between the two inflection points.

[0018] Still, according to the invention, the cross section of the conduit of each coil may have two mutually opposite and parallel sides substantially transverse to the axis of symmetry, so as to form a plurality of parallel channels between adjacent coils.

[0019] Furthermore, according to the present invention, the cross section of the conduit of each coil may be circular, triangular, or approximately pentagonal, and the inner side of the cross section may include the concave portion.

[0020] Furthermore, an object of the present invention is to provide a boiler comprising: at least one combustion zone; a burner arranged along a longitudinal axis corresponding to the combustion zone; and a first heat exchanger as described above, the first heat exchanger surrounding the burner, the axis of symmetry of the first heat exchanger coinciding with the longitudinal axis of the boiler, wherein, in the boiler, the inner portion of each coil of the first heat exchanger facing the burner has the continuous recess along a spiral profile corresponding at least to the combustion zone.

[0021] Specifically, according to the present invention, the boiler may include a second heat exchanger provided with a conduit having a spiral profile and comprising a plurality of coils, the axes of symmetry of the coils coinciding with the longitudinal axis, the radius of the coils of the second heat exchanger being greater than the radius of the coils of the first heat exchanger so as to surround the first heat exchanger from the outside.

[0022] More specifically, according to the present invention, each coil of the second heat exchanger may be arranged between two coils of the first heat exchanger, thereby being staggered and forming an additional channel for the combustion flue gas to pass through.

[0023] Preferably, according to the present invention, the cross section of the conduit of each coil of the first heat exchanger and the second heat exchanger may have an edge with an acute angle between 30° and 90°, preferably, the acute angle is equal to 90°, and the edge of each coil of each heat exchanger faces the gap between two adjacent coils of the other heat exchanger.

[0024] Furthermore, according to the present invention, the cross-section of the conduit of each coil of the second heat exchanger may have the same shape as that of the conduit of each coil of the first heat exchanger, the two cross-sections being mirror images relative to an imaginary plane parallel to the longitudinal axis.

[0025] Finally, according to the invention, the boiler may be a condensing boiler comprising a condensation zone adjacent to the combustion zone along the longitudinal axis and separated from the combustion zone by an internal partition member. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] For purposes of illustration and not limitation, the present invention will now be described with particular reference to the several figures of the accompanying drawings, in which:

[0027] Figure 1 shows a top view of a condensing boiler including a pair of spiral heat exchangers according to the present invention;

[0028] Figure 2 Shown along Figure 1 A cross-sectional view of the condensing boiler taken along plane II-II';

[0029] Figure 3 Shown Figure 2 Details in III;

[0030] FIG4 shows a cross-sectional view of a conduit of a prior art heat exchanger;

[0031] Figure 5 Shown Figure 1 A cross-sectional view of a conduit of one of two heat exchangers of a condensing boiler;

[0032] Figure 6 A cross-sectional view showing a conduit of a heat exchanger according to a second variant of the invention;

[0033] Figure 7 Shown Figure 2 Detail VII in which the dynamics of the combustion gas flow corresponding to the combustion zone are shown;

[0034] FIG8 shows a cross-sectional view of a detail of a prior art heat exchanger having conduits similar to those in FIG4 , showing the different hot zones;

[0035] Figure 9 Shown Figure 1 A cross-sectional view of a heat exchanger in FIG. 1 showing different heat zones;

[0036] Figure 10 shows a cross-sectional view of a condensing boiler according to the present invention corresponding to the combustion region in a variation of the first embodiment;

[0037] Figures 11a to 11c each showing a cross-sectional view of a condensing boiler according to the invention corresponding to a condensing region according to three different embodiments; and

[0038] Figure 12 A cross-sectional view of a condensing boiler according to another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0039] refer to Figure 1 and Figure 2 , it can be seen that the condensing boiler 10 according to a preferred embodiment of the present invention includes a pair of heat exchangers 1, 1'.

[0040] The condensing boiler 10 further includes a burner 11 arranged corresponding to the combustion region 13 , and an inner partition wall 12 arranged between the combustion region 13 and the condensation region 14 .

[0041] Each heat exchanger 1 , 1 ′ is suitable for passing a heat transfer fluid which is heated by exchanging heat with the condensing fluid corresponding to the condensation zone 14 and with the combustion fumes corresponding to the combustion zone 13 .

[0042] Specifically, each heat exchanger 1, 1' has a spiral pattern, and one heat exchanger 1' is concentric with respect to the other heat exchanger 1. The axis of symmetry of these heat exchangers 1, 1' coincides with the longitudinal axis of symmetry y of the boiler 10. Specifically, the longitudinal axis y is a vertical axis arranged in a vertical direction relative to the apparent horizontal support plane x.

[0043] In other embodiments, such as Figure 12In the embodiment shown in , the symmetry axis y of the boiler 10 can be oriented transversely to the vertical axis, in other words, the symmetry axis y of the boiler can be substantially parallel to the horizontal support plane x or slightly inclined to the horizontal support plane. Figure 12 As shown in , the angle of inclination is 4°.

[0044] Each heat exchanger 1 , 1 ' comprises a conduit having a helical profile. The conduit is made of steel, preferably stainless steel.

[0045] Specifically, it can be seen that the first spiral heat exchanger 1 includes a plurality of coils 2, and the inner portion 7 of each coil 2 faces the burner 11. The second spiral heat exchanger 1' also includes a plurality of coils 2', and the radius of the second spiral heat exchanger is larger than that of the first heat exchanger 1 so as to surround the first heat exchanger from the outside.

[0046] Furthermore, each coil 2, 2' of each heat exchanger 1, 1' has a cross section approximately in the shape of a pentagon, specifically as shown in FIG. Figure 3 and Figure 5 Specifically, a shape approximately pentagonal refers to a geometric figure having five sides, however, the sides and the angles between the sides are not necessarily exactly the same.

[0047] Specifically, as in Figure 5 The coils of both the first heat exchanger 1 and the second heat exchanger 1 ' shown by way of example in the figure have a substantially pentagonal cross section with a first side 3 and a second side 4 opposite each other, the two sides being substantially parallel to each other and substantially transverse to the longitudinal axis y. In addition, the substantially pentagonal cross section of each coil 2 has a third side 7 for connecting the two opposite sides 3 and 4, and the cross section has two inclined sides 5 in a position opposite the third side 7, the two inclined sides forming an edge 6 with an acute angle α. The acute angle α is between 30° and 90°, preferably between 90° and 100°. Figure 5 In the embodiment of the present invention, the acute angle is equal to 90°.

[0048] In each heat exchanger 1, a channel 16 is formed between the first side 3 and the second side 4 of adjacent coils 2 of the same heat exchanger 1. The channel is used to allow the combustion flue gas corresponding to the combustion area 13 to pass through, or to allow the condensed liquid corresponding to the condensation area 14 to pass through. The fact that the first side 3 and the second side 4 of each coil 2 are parallel allows for better heat exchange. However, in other embodiments, they may not even be parallel.

[0049] Furthermore, when two spiral heat exchangers 1, 1' are arranged side by side, they are arranged so that the edge 6 of the respective coil 2, 2' faces the edge 6 of the coil 2', 2 of the other spiral heat exchanger 1', 1 and fits between the inclined sides 5 of the two side-by-side coils 2 of the same spiral heat exchanger 1, as Figure 3 As shown in , they are thus staggered with each other.

[0050] In this way, the two spiral heat exchangers 1 , 1 ′, which are concentric with each other, are particularly compact and form additional channels 17 for the passage of combustion flue gases or condensed liquid.

[0051] Finally, still observe Figure 5 A recess 9 is formed at a position corresponding to the third side 7 , and the recess 9 is formed along the entire wall of the third side 7 of the coil 2 .

[0052] Each spiral heat exchanger 1 therefore has a continuous recess 9 along its entire wall, which recess corresponds to the respective third side 7 following the spiral profile of the heat exchanger 1 .

[0053] Specifically, in the first heat exchanger 1, the recessed portion 9 faces the inner portion of the condensing boiler 10. In the combustion area 13, the recessed portion 9 faces the burner 11 and is directly exposed to the flame of the burner 11 when the boiler 10 is in use.

[0054] This recess 9 is obtained by machining a tubular profile which initially has this third convex side 7 (such as shown in the prior art in FIG. 4 ), thereby obtaining the recess 9 shown in the accompanying drawings.

[0055] The depth P of the recess 9 is preferably 4% of the width L of the coil 2 .

[0056] In other embodiments, the depth P of the recess 9 may be between 4% and 50% of the width L of the coil 2, as shown in the following formula:

[0057]

[0058] Figure 6 A variant of the coil 2 according to the invention is shown in which the depth P of the recess 9 is equal to 50% of the width L of the coil 2 .

[0059] Furthermore, the height H9 of the recess 9 is substantially 61% of the height H2 of the coil 2 .

[0060] The height H9 of the recess 9 is measured as the distance between the inflection points of the recess 9 arranged corresponding to the third side 7 .

[0061] In other embodiments, the height H9 of the recess 9 may be between 43% and 81% of the height H2 of the coil 2, as shown in the following formula:

[0062]

[0063] For example, in Figure 6 In the variant, the height H9 of the recess 9 is substantially 81% of the height H2 of the coil 2 .

[0064] In the second heat exchanger 1', the recessed portion 9 instead faces the outside of the condensing boiler 10. In other embodiments, the second heat exchanger 1' may not have the recessed portion.

[0065] Furthermore, in other embodiments, the first heat exchanger 1 may have the concave portion 9 which is continuous along its spiral profile and corresponds only to the combustion region 13 .

[0066] The recessed portion 9 formed in each coil 2 of the first heat exchanger 1 and corresponding to the combustion zone 13 advantageously improves product reliability. The inner portion 7 of the coil 2 of the first heat exchanger 1 is compressed when directly exposed to the flame of the burner 11, which enhances corrosion resistance. This prevents material spalling, thereby extending the product's lifespan.

[0067] Furthermore, due to the presence of the recess 9 corresponding to the third side 7 of each coil 2 of the first heat exchanger 1, combustion can be advantageously improved, such as Figure 7 The concave shape 9 on the surface of the third side 7 makes it possible to form a stagnation area or recirculation area of ​​the combustion gases, such as Figure 9 . The flame of the burner 11 is kept away from the cold walls of the coil 2 of the first exchanger 1 and burns cleanly: in fact, the oxidation of carbon monoxide to carbon dioxide is not interrupted by direct contact with the wall of the coil 2, so the presence of the recess 9 allows the combustion flow to have a longer path, thus slowing down the oxidation of CO to CO2.

[0068] This phenomenon can be seen from Figure 8 and Figure 9 This is particularly evident in the contrast of FIG. 1 , where, in the grayscale image, the darker colors represent the temperature of the combustion gases from the burner 11 , and the gradually lighter color gradient represents areas where the temperature gradually cools toward the surface of the coil 2 .

[0069] Specifically, in Figures 8 and Figure 9 In the diagram, the various regions represent the following average temperatures:

[0070] - Darker areas: average T° = 1700°C;

[0071] - Next area: average T° = 1400°C;

[0072] - Next area: average T° = 950°C;

[0073] - Next region: average T° = 440°C; and

[0074] - Lighter-colored areas: average T° = 100°C.

[0075] As can be seen in the solution according to the invention, due to the presence of the recess 9, the low temperature zone is further away from the burner 11 than in the solution of the prior art shown in Figure 8. Therefore, the material is in a state of compression when directly exposed to the flame (the oxides are subject to compressive stress and therefore tend to adhere to the surface), which enhances the corrosion resistance.

[0076] The benefits of this solution become more pronounced the larger the surface of the recess 9 facing the flame of the burner 11. The extent of the recess is limited by the deformation of the coil, which must not be too great to avoid malfunction. In practice, it is necessary to adhere to a minimum bending radius determined by the absolute dimensions of the coil and the material used.

[0077] Furthermore, excessively deep recesses 9 may increase the hydraulic resistance of the fluid flowing through the coil 2 tubes by reducing the passage cross-section. To limit this increase in hydraulic resistance, the depth of recess 9 needs to be evaluated for each specific application. This hydraulic resistance depends on the passage cross-section. This resistance affects boiler flow rate and the choice of circulator. The depth of the recess should be optimized based on a cost-benefit assessment.

[0078] In other embodiments, the first spiral heat exchanger 1 may have a cross-section different from the described pentagonal or approximately pentagonal heat exchanger, for example the first spiral heat exchanger may have a circular or triangular cross-section, as long as it has at least the recessed portion 9 corresponding to the combustion zone 13.

[0079] In a variant embodiment of the boiler 10 according to the invention, the heat exchanger 1 , 1 ′ can be surrounded by a grooved jacket 18 corresponding to the combustion zone 13 and / or the condensation zone 14 .

[0080] The slotted jacket refers to a baffle provided with openings (e.g. slots and / or holes). The slotted jacket 18 can be arranged outside the serpentine heat exchanger in the combustion zone and correspondingly inside and / or outside the heat exchanger in the condensation zone.

[0081] The opening of the partition is preferably located between two consecutive coils, whereby heat exchange and flue gas circulation can be significantly improved.

[0082] Specifically, Figure 10 A slotted jacket 18 is shown corresponding to the combustion area 13, and Figure 11a and Figure 11c A slotted jacket 18 corresponding to the condensation area 14 is also shown.

[0083] In addition, if Figure 11a and Figure 11b As shown in FIG, a second slotted jacket 19 may be provided, which is arranged inside the heat exchangers 1 , 1 ′, specifically surrounded by these heat exchangers, corresponding to the condensation area 14 .

[0084] exist Figure 11a In the variant, two slotted sheaths are provided, namely an outer slotted sheath 18 and an inner slotted sheath 19, while in Figure 11b In the variant, only the inner grooved sheath 19 is present.

[0085] The opening of the slotted jacket 18 or 19 can be constant or variable, corresponding to the combustion zone 13, in order to balance the flow of the combustion fumes between the internal exchanger 1 and the external exchanger 1 ', thereby balancing and optimizing the heat exchange.

[0086] Having variable openings allows for balanced passage of combustion flue gases, resulting in better heat exchange.

[0087] The balance of openings depends not only on the heat exchanger but also on the structure and distribution of the burners.

[0088] The solution according to the invention is integrated into a condensing boiler, but it can also be provided in a boiler having only a combustion zone, thereby maintaining the technical advantages of the invention. Thus, it can be integrated into a boiler (not necessarily a condensing boiler) configured for heating liquids (e.g. domestic hot water).

[0089] Advantageously, thanks to the solution according to the invention, the time for the oxidation of CO to CO 2 is prolonged, thereby reducing the amount of pollutants produced.

[0090] Furthermore, thanks to the invention, the phenomena of spalling of the material forming the heat exchanger surfaces in the combustion zone are reduced.

[0091] In the foregoing, preferred embodiments have been described and variations of the present invention have been proposed, but it should be understood that modifications and variations can be made by those skilled in the art without departing from the scope of protection defined by the appended claims.

Claims

1. A boiler (10), in particular a condensing boiler (10), the boiler (10) comprising: at least one combustion zone (13); a burner (11) arranged along the longitudinal axis (y) corresponding to the combustion zone (13); and at least one first heat exchanger (1) surrounding the burner (11), wherein an inner portion (7) of the first heat exchanger faces the burner (11) and is directly exposed to the flame of the burner (11) when the burner (11) is in use, The heat exchanger (1) is provided with a steel conduit having a spiral profile, preferably made of stainless steel, and comprises a plurality of coils (2) having a common axis of symmetry (y), The symmetry axis (y) of the first heat exchanger (1) coincides with the longitudinal axis (y) of the boiler (10), Characterized in that, in the boiler (10), the inner portion (7) of each coil (2) of the first heat exchanger (1) facing the symmetry axis (y) has a continuous recess (9) along at least the portion of the spiral profile corresponding to the combustion zone (13) of the boiler (10).

2. The boiler (10) according to the preceding claim, wherein The cross section of the duct of each coil (2) of the first heat exchanger (1) has a concave portion (9) defined by two inflection points arranged at the inner portion (7) of the coil (2).

3. The boiler (10) according to the preceding claim, wherein: The depth (P) of the recess (9) is between 4% and 50% of the width (L) of the cross section of the conduit of the corresponding coil (2).

4. The boiler (10) according to claim 2 or 3, wherein: The height (H9) of the recess (9) is between 43% and 81% of the height (H2) of the cross section of the conduit of the corresponding coil (2), wherein the height (H9) of the recess (9) is measured as the distance between the two inflection points.

5. The boiler (10) according to any one of claims 2 to 4, wherein: The cross section of the conduit of each coil (2) has two mutually opposite and parallel sides (3, 4) substantially transverse to the axis of symmetry (y) to form a plurality of parallel channels (16) between adjacent coils (2).

6. The boiler (10) according to any one of claims 2 to 5, wherein: The cross section of the conduit of each coil (2) is circular, triangular or approximately pentagonal, and the inner side (7) of the cross section includes the concave portion (9).

7. The boiler (10) according to any one of the preceding claims, wherein: The boiler (10) comprises a second heat exchanger (1'), which is provided with a conduit having a spiral profile and comprises a plurality of coils (2'), the symmetry axes of which coincide with the longitudinal axis (y), the radius of the coils (2') of the second heat exchanger (1') being larger than the radius of the coils (2) of the first heat exchanger (1) so as to surround the first heat exchanger from the outside.

8. Boiler (10) according to the preceding claim, wherein Each coil (2') of the second heat exchanger (1') is arranged between two coils (2) of the first heat exchanger (1), so as to be staggered and form an additional channel (17) for the combustion flue gas to pass through.

9. Boiler (10) according to the preceding claim, wherein The cross section of the duct of each coil (2; 2') of the first heat exchanger (1) and the second heat exchanger (1') has an edge (6) having an acute angle (α) between 30° and 90°, preferably equal to 90°, the edge (6) of each coil (2; 2') of each heat exchanger (1; 1') facing two adjacent coils (2; 2').

10. The boiler (10) according to any one of claims 8 or 9, wherein: The shape of the cross section of the conduit of each coil (2') of the second heat exchanger (1') is the same as the shape of the cross section of the conduit of each coil (2) of the first heat exchanger (1), and the two cross sections are mirror images relative to an imaginary plane parallel to the longitudinal axis (y).

11. The boiler (10) according to any one of the preceding claims, wherein: The boiler (10) is a condensing boiler (10) comprising a condensation zone (14) which is adjacent to the combustion zone (13) along the longitudinal axis (y) and which is separated from the combustion zone by an internal partition member (12).

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