EP0225929B1 - Gas heated boiler plant and use thereof - Google Patents

Description

The invention relates to a gas-fired boiler system with a burner bed which takes up a surface and with heat exchange tubes arranged above the burner bed parallel to the surface, the heat exchange tubes having pipelines which have a plurality of essentially radially projecting, flat fins spaced apart from one another over the length of the heat exchange tubes are provided, which have bevels at their edges and furthermore the hot flue gas rising from the burner bed flows through the spaces formed by the ribs and the pipes.

Such a boiler system is known from DE-C 2 245 357.

The invention further relates to the use of such a boiler system.

In gas-fired boiler systems with a flat burner bed, care must be taken that both the convective heat transfer and the utilization of the radiant heat are optimized. Convective heat transfer is understood to be the transfer of heat from the hot air rising from the burner bed to the surfaces of a heat exchanger, while the radiant heat is exploited by the fact that the heat radiation emitted by the burner bed and the hot flue gas is essentially in the infrared range on surfaces of the heat exchanger is absorbed.

In order to be able to produce optimized boiler systems from these two points of view, so-called finned tubes have been used as heat exchange tubes in heat exchangers, as is known from the aforementioned DE-C 2 245 357. These finned tubes consist of a straight pipeline through which a heat exchange medium, for example water, flows, from which radially circular flat ribs project, which are arranged spirally around the pipeline and extruded out of it. The pipeline and fins are preferably made of a copper / beryllium alloy with particularly good thermal conductivity. These known finned tubes have a very large heat transfer surface and are therefore particularly suitable as convective heat exchangers. However, if several of these finned tubes lie parallel and close to one another in order to jointly form a heat exchanger above the burner bed, the fins are essentially perpendicular to the surface or to the radiation field of the burner bed, so that the heat exchanger, apart from the pipes for the infrared radiation of the radiant heat is practically completely permeable. As a result, a large part of the radiant heat of the burner emitted by the flames of the burner bed and the hot flue gases is lost. Particularly in the case of combustion chambers which are not or only partially cooled, the radiation component in the total heat development in the combustion chamber is relatively large due to the high combustion temperatures.

To remedy this problem, it is known from the aforementioned De-C-22 45 357 to place baffles on the side facing away from the burner bed of the heat exchanger consisting of several finned tubes on the protruding fins in order to pass through the fins to at least partially absorb the portion of the radiant heat that shines through.

However, these measures have proven to be insufficient in certain applications. This is essentially due to the fact that the deflection plates, as seen in the direction of flow of the hot flue gases, are arranged behind the heat exchanger, which acts essentially in a convective manner. The radiant heat collected in the baffle plates is therefore passed on to the flue gases that have already been removed and is lost if no further heat exchanger, in particular condensation heat exchanger in a condensing boiler, is provided.

In addition, because of the radially projecting arrangement of the ribs, the deflection plates can only rest on the narrow edges of the ribs, so that there is only a poor heat transfer between the deflection plates and the ribs, which in turn leads to the above-described emission of the radiant heat collected to the already cooled ones Flue gases are conveyed because the baffles cannot or only very poorly transfer their heat to the ribs due to the poor heat transfer.

Finally, it is known from DE-C-22 45 357 mentioned at the beginning to fold the radially projecting ribs to the side, the folds being perpendicular to the burner bed. The purpose of this measure is to be able to arrange adjacent heat exchange tubes closer together in a heat exchanger, which is made possible by the fact that the heat exchange tubes, viewed in front view, have the outer contour of a circle flattened on two sides. Although this measure reduces the "window" formed by the fins between the pipes of the heat exchange tubes, which is practically permeable to the radiant heat, it has been shown that this measure is also not sufficient to achieve particularly high efficiencies.

The invention is therefore based on the object of developing a gas-fired boiler system of the type mentioned in such a way that an even greater yield of radiant heat is possible while at the same time improving the convective heat transfer in order to be able to implement boiler systems with even higher efficiency.

This object is achieved in that the folds are inclined to the surface of the burner bed.

This measure completely solves the problem on which the invention is based from two points of view.

On the one hand, the bevels which are now arranged obliquely in the flow path of the rising hot flue gases result in a considerably enlarged area being available for absorbing the radiant heat, which is rigid, ie with optimal heat transfer is connected to the heat exchange tubes.

On the other hand, the oblique bevels arranged in the flow path of the rising smoke gases cause the rising smoke gases to be swirled considerably more, so that the convective heat transfer to the fins of the heat exchange tube is also considerably increased.

These two effects promote one another, so that the gas-fired boiler system according to the invention has a significantly higher efficiency than is possible according to the prior art. This aspect is of particular importance for modulating gas-fired boiler systems, in which the burner output is continuously and variably set depending on the respective heat requirement, in contrast to so-called on / off burners, which either run at full power or are switched off. If a modulating boiler system is operated at a low output, it is of particular importance to remove the heat generated by the burner bed as useful as possible. This results in a significantly improved efficiency on average over the year, which can certainly be measured against the very high efficiencies of so-called condensing boilers, in which the flue gases rising from the (first) heat exchanger are cooled by a downstream second condensation heat exchanger, the condensation heat thus obtained also serves to heat the boiler water.

However, it goes without saying that the gas-fired boiler system according to the invention can be equipped with only one heat exchanger and also with an additional condensation heat exchanger as a condensing boiler.

In a preferred embodiment of the invention, the bends to the surface of the burner bed run at an angle of approximately 45 °.

Although other angles also lead to satisfactory results, this angle has proven to be particularly advantageous because in this case, on the one hand, a relatively large receiving area is available for absorbing the radiant heat, and on the other hand, the rising smoke gases are optimally swirled when the bends are angled at 45 _° .

In a further embodiment of the invention, the heat exchange tubes, as is known per se, are arranged closely next to one another as heat exchangers, and according to the invention the ribs on the side of the heat exchanger facing the burner bed are provided with the inclined folds in sections.

This measure is of particular advantage from the point of view of optimal absorption of the radiant heat, because now the receiving surface formed by the bevels for the radiant heat is located directly above the burner bed and is therefore particularly suitable for absorbing the radiant heat. In the known boiler systems, this was not possible because the separate baffle plates, which were mentioned at the beginning, could not be arranged on the underside of the heat exchange tubes. Because of the poor heat transfer to the fins of the heat exchange tubes, which has also already been mentioned, these deflection plates would have been heated to an unacceptably high degree in the immediate vicinity of the burner bed. This is now avoided by the measure according to the invention mentioned above, because the area for absorbing the radiant heat, which consists of the folds, is in one piece with the fins of the heat exchange tubes and therefore optimal heat dissipation is ensured.

In a further embodiment of the invention, however, the folds can also be arranged on the side of the heat exchanger which faces away from the burner bed, this measure being particularly suitable for being used together with the measure mentioned above, so that the heat exchanger then has a total of folds is provided on both sides.

This has the advantage that a labyrinthine chamber system is created in the heat exchanger, through which the rising hot air passes through with particularly intensive swirling, so that the convective heat transfer is further promoted. The bevels arranged at the “outlet” of the heat exchanger also serve to practically completely absorb the radiant heat still emitted by the rising smoke gases, even as long as the smoke gases still flow through the heat exchanger.

In one embodiment of the invention, the ribs are provided with bends over part of their circumference.

This measure has the advantage that, as already explained, the radiant heat can be collected at the folded area, on the other hand the non-bent area of the ribs can be arranged in any way as inputs or outputs from the heat exchanger.

In this respect, an exemplary embodiment of the invention is particularly preferred in which the ribs are designed in the form of an annular disk in a manner known per se and the bevels are formed by bending edge regions of the ribs in the form of circular sections.

This measure has the advantage that conventional heat exchange tubes, which are designed as finned tubes, can be processed with known devices in order to produce the bent sections in the form of a circle.

In this context, an exemplary embodiment has proven to be particularly important in practice, in which the ribs are divided over their circumference into eight sections of approximately the same size, which with the exception of two diametrically opposite sections are provided with the folds. This applies in particular if the non-folded sections are in the installed state of the heat exchanger perpendicular to one another to the surface of the burner bed and form openings for the entry or exit of the flue gases rising from the burner bed into or out of the intermediate spaces.

This measure combines the advantages of the known heat exchangers of gas-fired boiler systems, as explained at the beginning, with the advantageous effects of the invention. On the one hand, the heat exchange tubes available as semi-finished products, which are designed as finned tubes, can be taken over unchanged along with their processing machines for folding the edge areas; on the other hand, the special configuration described above achieves an optimum with regard to the utilization of the radiant heat and the convective heat transfer. Due to the approximately octagonal shape of the heat exchange tubes with an inlet or outlet for the rising flue gases arranged at the top or bottom, a surface that absorbs heat radiation is achieved on the underside of the heat exchanger, which takes up almost two thirds of the surface of the heat exchanger the octagon shape achieves an approximately circular guidance of the flue gases in the heat exchanger around the water-filled pipelines, whereby a two-way reversal of direction occurs, which leads to particularly good turbulence and thus optimal convective heat transfer. The same applies on the outlet side of the heat exchanger, where the rising flue gases flow out like a chimney after passing through the pipes filled with the boiler water and flow past both bends in the exit area. This also optimizes the convective heat utilization as well as the utilization of the remaining radiant heat.

Furthermore, an embodiment of the invention is preferred in which, on the side of the heat exchanger facing away from the burner bed, inclined bends of adjacent heat exchanger tubes are connected to one another via axially extending baffle plates, as is known per se, but in addition there is that the baffle plates rest on the folds. In particular, if the bends run at 45 _° , the deflection plates can be designed as V-profiles with an internal angle of 90 _° .

This measure has the particular advantage that the flue gases flowing through the heat exchanger are used particularly well in the exit area, because the heat exchanger surface is closed except for narrow axial gaps. The fact that the baffle plates now rest on the bends also ensures a significantly improved heat transfer between the deflection areas and ribs than is the case in the prior art.

Finally, an embodiment of the invention is preferred, in which the boiler system is designed as a condensing boiler, the flue gases rising from the burner bed first passing through the heat exchange tubes provided with the oblique bends and then being fed to a further heat exchanger designed as a condensation heat exchanger.

Simultaneously or alternatively, the boiler system can be operated in a modulating manner in a preferred use.

The two last-mentioned measures each have, alone or in combination, the advantage described at the outset of the greatest possible optimization of the efficiency of the entire boiler system.

Further advantages result from the description and the attached drawing.

It goes without saying that the features mentioned above and those mentioned below can be used not only in the combination indicated in each case but also in other combinations or even on their own without departing from the scope of the present invention.

• Fig. 1 Eine schematische perspektivische Ansicht (teilweise aufgebrochen) einer erfindungsgemäßen gasbeheizten Kesselanlage;
• Fig. 2 und 3 zwei Ansichten von. Wärmetauschern nach dem Stand der Technik;
• Fig. 4 und 5 zwei Ansichten, ähnlich in Fig. 2 und 3, jedoch für ein Ausführungsbeispiel der Erfindung.

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail below on the basis of the description. Show it:

• Fig. 1 is a schematic perspective view (partially broken away) of a gas-fired boiler system according to the invention;
• 2 and 3 two views of. State of the art heat exchangers;
• 4 and 5 two views, similar to FIGS. 2 and 3, but for an embodiment of the invention.

In Fig. 1, 1 designates a gas-fired boiler system as can be used for buildings of all kinds. The boiler system 1 is provided with an air inlet 2, which reaches the area of a burner bed 10, which is composed of several burner rods 3. A regulated gas supply, not shown in FIG. 1, creates a flame bed above the burner bed 10, with possibly also regulated air inlet 2, so that hot air rises and reaches the area of a heat exchanger 60 there. The heat exchanger 60 has boiler water connections 4 for introducing or discharging the boiler water provided for the heating purposes. A flue gas 6 which has flowed through the heat exchanger 60 can escape to the outside via a trigger 5.

The heat exchanger 60 consists of a multiplicity of heat exchange tubes 61, which can be partially covered by baffle plates 80, as will be explained in more detail below with reference to FIGS. 4 and 5.

1 can also have a plurality of heat exchangers arranged one above the other, the first heat exchanger usually absorbing the radiant heat emanating from the burner bed 10 and also largely dissipating the heat contained in the rising flue gases by convective heat transfer and a second, downstream heat exchanger as a condensation heat exchanger cools the flue gas 6 by condensing the moisture contained therein and thus absorbs the heat of evaporation of this moisture. In these boiler systems, also known as condensing boilers, the cooling water first flows through the condensation heat build-up shear and then the heat exchanger 60 shown in detail in FIG. 1.

FIG. 2 shows a side view and FIG. 3 shows a top view of a heat exchanger 11 according to the prior art above the burner bed 10.

The heat exchanger 11 consists of a plurality of heat exchange tubes 15, 16 arranged in parallel next to one another, only two of which are shown completely in FIGS. 2 and 3.

The heat exchange tubes 15, 16 consist of a central pipeline 17, 18, from which radially circular ribs 19, 19a ... and 20, 20a ... respectively. The ribs 19 and 20 run spirally around the pipelines 17, 18 and are preferably extruded therefrom. The pipes 17, 18 and the fins 19, 20 consist of a good heat-conducting material, preferably a copper / beryllium alloy.

The pipelines 17, 18 are flowed through by water 21 of a building heating system.

The ribs 19, 19a ... and 20, 20a ... are laterally provided with bevels 23 and 24, respectively, in such a way that out of the circular disk-shaped surface of the ribs 19 and 20 edge-section-shaped edge regions are angled by 90 _° . The bevels 23, 24 are perpendicular to the surface of the burner bed 10. This, as can clearly be seen in FIG. 2, achieves that the heat exchange tubes 15, 16 can be arranged close to one another, but between the bevels 23, 24 of adjacent heat exchange tubes 15 , 16 still has a distance 26 of, for example, one millimeter.

On the upper side facing away from the burner bed 10, the heat exchange tubes 15, 16 are each covered in pairs with baffle plates 30, which cover the space between adjacent heat exchange tubes 15, 16. For the sake of clarity, only one deflection plate, partially broken off, is shown in FIG. 3.

When the burner bed 10 is ignited, flue gases 40 rise upwards and flow along a 41, essentially straight path indicated to slot-shaped openings 42 laterally delimited by the deflection plates 30 and then again out of the heat exchanger 11. as indicated by arrows 43. The flue gases 40 flow through spaces 44, 44a ..., which are delimited by the ribs 19, 19 a ..., the pipeline 17 and the bevels 23.

Although the baffle plates 30, seen from the burner bed 10, cover that "window" 48 between the pipes 17, 18, so that the baffle plates 30 absorb at least partially the radiant heat emanating from the burner bed 10 and the ascending smoke gases 40, but can be seen from FIG. 2 clearly that the interface 49 between the baffle plates 30 and the ribs 19, 19a ... or 20, 20a ... represents poor heat transfer because the ribs 19, 19a ... or 20, 20a ... only each abut the baffle plates 30 with their narrow side.

In contrast, FIGS. 4 and 5 show a heat exchanger 60, as already mentioned in FIG. 1, and how it is used for the present invention. The heat exchanger 60 in turn consists of heat exchange tubes 61, 62 arranged in parallel with one another, which are provided with pipes 63, 64 with radially projecting ribs 65, 65a ... and 66, 66a ..., respectively.

Although the heat exchange tubes used as semi-finished products in the exemplary embodiment according to FIGS. 4 and 5 correspond to those according to the prior art according to FIGS. 2 and 3, they are designed differently for use in the boiler system according to the invention.

4, the ribs 65 and 66 are divided on their circumference into eight circumferential regions of approximately the same length, of which apart from two diametrically opposed regions the other six regions with bevels 70, 71, 72, 73 , 74, 75 are provided. Because of this approximately octagonal configuration, mutually adjacent bevels, for example 70, 72, form an angle 76 of 135 _° with one another. The non-folded areas are arranged one above the other and vertically above the burner bed 10 in the installed state of the heat exchanger 60, so that in this installed state four of the six folds, namely the folds 70, 71, 74 and 75 at an angle 77 of 45 ° to Surface of the burner bed 10 run.

In this configuration, baffles 80 resting on two adjacent heat exchange tubes 61, 62 are formed on the upper side of the heat exchanger 60 as V-profiles with an internal angle of 90 °.

In this way, a chamber system is created inside the heat exchange tubes 60, 61 because the bevels 70, 72, 74 and 71, 73, 75 form side covers and leave only one passage from bottom to top. The ascending smoke gases, designated 82, first flow into this chamber system through an opening 83, which is formed by the lower edges of the folds 70 and 75. You now get into spaces 84, 84a ... which are formed by the ribs 65, 65a ..., the pipeline 63 and the bends 70 to 75. From these almost closed spaces 84, 84a ..., the flue gases 82 then flow out of the heat exchanger 60 through an opening 86, which is formed by the upper edges of the folds 71 and 74, in the direction of an arrow 87. They pass through a path indicated by 85, which runs almost circularly around the pipelines 63 and 64 and consequently runs three times at an angle because of the straight entry and exit at 82 and 87.

The upward seal is particularly good because the baffle plates 80 further reduce the openings 86 to an even narrower slot. The heat transfer between the baffle plates 80 and the ribs 65 and 66 is particularly good because the baffle plates 80 do not rest flat on the folds 71 and 74 on the narrow sides of the ribs 65 and 66, but rather.

From the point of view of convective heat transfer, the heat exchanger according to FIGS. 4 and 5 is clearly superior to that of FIGS. 2 and 3, because, as mentioned, the flue gases 82 are swirled on a multiple angled path in almost closed spaces 84, 84a ... so that the flue gases 82 transfer their heat almost completely to the surrounding surfaces or bends 70 to 75 of the ribs 65 or . 66 can deliver.

The utilization of the radiant heat is also significantly improved because the burner bed 10 has a receiving surface formed by the bevels 70 and 75 on a width 90, which makes up almost two thirds of the surface of the heat exchanger 60 compared to the burner bed 10.

It is understood that the exemplary embodiment illustrated with reference to FIGS. 4 and 5 is only to be understood as an example and that, of course, numerous modifications, in particular in the configuration of the ribs and the bevels, are possible without departing from the scope of the present invention.

For example, instead of circular disc-shaped ribs, square or rectangular ribs can also be used, a different polygon can be used instead of the octagonal shape of the folds, and the openings for the inlet and outlet of the flue gases can also be arranged off-center or offset, without this leaves the scope of the invention.

Claims (12)

1. A gas-fired boiler comprising a burner bed (10) extending over a flat surface and heat exchanger tubes (15, 16; 61, 62) arranged above the burner bed (10) parallel to the surface, the heat exchanger tubes (15,16; 61, 62) comprising pipes (17,18; 63, 64) equipped with a plurality of flat ribs (19, 19a ..., 20, 20a ...; 65, 65a ..., 66, 66a ...) extending substantially radially from the pipes (15, 16; 61, 62) and being arranged in spaced relationship to each other over the length of the heat exchanger tubes (15, 16; 61, 62), and being provided with bent-over edges (23, 24; 70, 71, 72, 73, 74, 75), the flue gases (40; 82) rising from the burner bed (10) flowing through the gaps (44, 44a ...; 84, 84a) formed between the ribs (19, 19a ..., 20, 20a ...; 65, 65a ..., 66, 66a ...) and pipes (17, 18; 63, 64), characterized in that said bent-over edges (70, 71, 74, 75) are inclined relative to the surface of the burner bed (10).

2. The boiler of claim 1, characterized in that the bent over edges (70, 71, 74, 75) extend under an angle (77) of about 45_° relative to the surface of the burner bed (10).

3. The boiler of claim 1 or 2, characterized in that the heat exchanger tubes (61, 62) are arranged as a heat exchanger (11) adjacent and parallel to each other and that the ribs (65, 65a ..., 66, 66a) are provided with the bent-over edges (70, 75) on sections of the heat exchanger (11) on that side facing the burner bed (10) .

4. The boiler of any of claims 1 through 3, characterized in that the heat exchanger tubes (61, 62) are arranged as a heat exchanger (11) adjacent and parallel to each other and that the ribs (65, 65a ..., 66, 66a) are provided with the bent-over edges (71, 74) on sections of the heat exchanger (11) on that side facing away from the burner bed (10).

5. The boiler of any of claims 1 through 4, characterized in that the ribs (65, 65a ..., 66, 66a ...) are provided with bent-over edges (70, 71, 72, 73, 74, 75) over a part of their periphery.

6. The boiler of claim 5, characterized in that the ribs (65, 65a ..., 66, 66a) are designed as circular rings and that the bent-over edges (70, 71, 72, 73, 74, 75) are made by bending over segments of the ribs (65, 65a ..., 66, 66a ...) having the shape of circular segments.

7. The boiler of claim 6, characterized in that the ribs (65, 65a ..., 66, 66a) are subdivided over their periphery into eight sections, being roughly of equal size and being provided with the bent-over edges (70, 71, 72, 73, 74, 75) with the exemption of two sections arranged diametrically vis-a-vis each other.

8. The boiler of claim 7, characterized in that the not bent-over edges are arranged above each other and above the surface of the burner bed (10) when the heat exchanger (11) is installed and form openings (83, 86) for the entry and exit, respectively, of hot air (82) rising from the burner bed (10) into the gaps (84, 84a...).

9. The boiler of any of claims 4 through 8, characterized in that bent-over edges (71, 74) of adjacent heat exchanger tubes (61, 62) are connected with each other via axially extending deviation sheets (80) on that side of the heat exchanger (11) facing away from the burner bed (10), the sheets being supported by the bent-off edges (71, 74).

10. The boiler of claims 2 and 9, characterized in that the deviation sheets (80) are made as V-shaped profiles having an inner angle of 90_°.

11. The boiler of any of claims 1 through 10, characterized in that the boiler (1) is designed as a condensing boiler where the flue gases (82) rising from the burner bed (10) initially pass the heat exchanger pipes (61, 62) equipped with the inclined bent-over edges (70, 71, 74, 75) and are then introduced to another heat exchanger designed as a condensing heat exchanger (50).

12. The use of a boiler according to any of claims 1 through 11, characterized in that the boiler (1) is run in a modulated mode of operation.

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