EP0217320A2 - Heater for liquid or gaseous combustibles - Google Patents

Abstract

The heater consists of a water-bearing housing (16) with forward and return run connectors (18) and piping (1) which reaches through the housing horizontally, leads to a flue gas offtake (17), is equipped with a burner (15) and, in the free space of an internal ribbing of the piping formed from longitudinal ribs, contains a pot-like combustion chamber (2), the heat transfer surface on the off-flow side being dimensioned larger than in front. The pot-like combustion chamber (2), which is arranged in the rear region of the piping (1), is correspondingly dimensioned in its length to at most half the length of the piping (1). With at least approximate preservation of the entire effective rib surface in the piping (1), a part of the rib heat exchange surface in front of the combustion chamber (2) is arranged shifted into the region of the combustion chamber (2), and more particularly with correspondingly reduced distance (A) of the longitudinal ribs from one another there. The remaining longitudinal ribs (3') are provided in the region in front of the combustion chamber (2) in smaller number or with a lower height (H) than that of the longitudinal ribs (3) arranged in the region of the combustion chamber (2). <IMAGE>

Description

The invention relates to a boiler for liquid or gaseous fuels according to the preamble of the main claim and in particular for an operation in the so-called low or low temperature range.

A boiler of this type is known from DE-OS 33 27 354. Apart from this, almost every modern boiler today is basically designed in this way, which is therefore well known and in so far does not require any printed evidence. Such boilers differ only in their design variants, for which reference is made, for example, to DE-OS 32 O8 731 and FR-PS 23 2O 5O4, the prior art heating boilers according to these publications being particularly distinguished by the basic double-shell nature of their heat transfer surfaces.

In order to keep the flow resistance in the frame on the one hand and on the other hand to be able to accommodate a sufficiently effective heat exchange surface in the pipe pull, the longitudinal ribs were therefore practically continuous over the entire length of the burner side towards the discharge side with a correspondingly large fin spacing (approx. 20 mm) and in the space between this "all-round ribbing" is the pot-like combustion chamber, which, apart from a relatively short inflow area into the rib spaces or draft channels, also extends almost over the entire length of the longitudinal ribs. With this construction, the entire length of the burner flame burns into the pot-shaped combustion chamber, in which the heating gases are then deflected and flow back into the heating gas flues delimited by the ribs on the edge of the burner. The radiation emanating from the burner flame can practically only reach the water-cooled surface of the pipe run via the detour of the combustion chamber. which surrounds the combustion chamber and the heating gas flues. This also applies to the boiler according to DE-OS 33 27 354, in which the exhaust gases are to be better utilized by additional heat transfer surfaces arranged on the outflow side. Apart from the fact that such a boiler design does not provide direct heat radiation to the water-cooled transmission surface, this leads to an extremely hot combustion chamber over its entire length, which also results in the combustion of liquid or gaseous fuels, particularly in such a "hot" combustion chamber the so-called NOX content assumes values that do not occur in this order of magnitude, for example, if the combustion chamber itself were water-cooled. Such water-cooled combustion chamber designs are known, but understandably they are associated with a considerably greater outlay in terms of production and materials than is the case with a combustion chamber that is not water-cooled and only used in a pot-like manner.

In the boilers according to the aforementioned DE-OS 32 O8 731 and FR-PS 23 2O 5O4, short combustion chamber pots are provided, which take up only half the length of the tube, whereby in one case fins are only arranged in the area of the combustion chamber while in the other case, the ribs extend far into the actual combustion chamber.

In the boiler according to FR-PS 23 2O 5O4, the heat transfer in front of the combustion chamber takes place essentially by radiation and in the area of the combustion chamber by generating turbulence in the ring channel by means of sheet metal strips which are formed like ribs. If one imagined that the entire inner wall of this boiler, i.e. also in front of the combustion chamber, was covered with fins, and one wanted to concentrate the entire available finned heating surface only in the short burner pot area so that only the radiant heat could be effective in the front area this one unacceptable increase in resistance due to the associated rib concentration.

Since in the boiler according to DE-OS 32 O8 731 the longitudinal ribs are almost up to the flame-effective area in front of the combustion chamber pot, a direct heat radiation transfer to the inner wall of the pipe is only possible to a limited extent, if at all, and the completely free-standing ribs are heavily burdened accordingly.

In particular, the NOX value reduction to be taken into account is one of the following situations:
Boilers of the type mentioned at the beginning, which are operated with extremely hot combustion chamber pots, result in high NOX values. In the case of boilers according to FR-PS 23 2O 5O4, part of the flame heat is transferred directly by radiation in the front area of the combustion chamber, but if you do not want to increase the resistance in the ring channel extremely, this is done at the cost of reducing the effective rib transfer area which can be accommodated per se . Finally, in the boiler according to DE-OS 32 O8 731, only a relatively small part of the flame heat should be able to be transmitted by radiation, so that the combustion chamber pot itself remains correspondingly highly loaded.

Starting from the boiler according to DE-OS 33 27354, the invention is therefore based on the object of improving a boiler of the type mentioned in such a way that the heat transfer surface arrangement and heat transfer surface distribution with at least the same or less manufacturing effort to the actual type of heat supply in the pipe train under consideration one the greatest possible prevention of condensation should be adapted with the provision of an at least partial flow resistance laying from the front area in the downstream half of the pipe run, while maintaining or approximately maintaining the effective fin transfer surface, which is normally present in such boilers in the pipe run.

This object is achieved with a boiler of the type mentioned according to the invention by the features stated in the characterizing part of the main claim. Advantageous further developments and practical embodiments result from the subclaims.

In this solution according to the invention, the heat transfer area of the fins is therefore reduced in the front half of the pipe run and in the rear half, ie where the overall shortened pot-like combustion chamber is arranged, by concentration or "compression" enlarged, but without reducing the "normal" total transfer area. “Normal” ribbing is to be understood here as one in which the longitudinal ribs with the same height extend over almost the entire length of the pipe run. The entire heat transfer surface arrangement and distribution is thus made such that the heat transfer in the front area, unhindered by the combustion chamber, takes place essentially by radiation and in the area of the concentrated heat transfer surfaces by convection, which, as has been shown, is more appropriate to the actual heat transfer processes. than is the case with ribbing that runs uniformly from front to back. In view of the shortened combustion chamber and the reduction in the heat transfer area that is otherwise also present in the front area of the tube train, one can afford to increase the heat transfer area in the rear area without increasing the overall flow resistance. The temperature of the wall of the shortened and only in the back The combustion chamber arranged in the other area remains roughly the same, but the distance that the heating gases have to travel both inside and outside along the hot combustion chamber wall is correspondingly shorter, which has a favorable effect on the NOX balance, with correspondingly low emissions NOX values result in a way that can otherwise only be achieved with heating boilers with a water-cooled combustion chamber.

Since, according to the invention, only part of the fin heat exchange surface, which is otherwise also present in the front region of the tube train, is arranged in the region of the combustion chamber with a reduced spacing of the longitudinal ribs from one another there, the requirement that the available heat exchange surface in the front region be sufficiently large is also taken into account hold in order to be able to effectively counteract a condensate accumulation, which occurs when there is a smooth cylindrical and immediately water-cooled boundary wall in this area, as is the case with the previously known boiler according to FR-PS 23 2O 5O4. In addition, in this boiler there is no heat transfer surface concentration in the area of the combustion chamber pot in the sense of the solution according to the invention. Since this reduces the overall flow resistance in this boiler, there is also the risk that peripheral parts of the heating gases formed by the flame can flow directly into the heating gas flues. Since the increased heat transfer surface concentration according to the invention is associated with a certain build-up in the rear region of the tube train, this effect cannot occur and the heating gases enter, despite the extremely shortened combustion chamber, largely burned out into the spatially compressed longitudinal rib arrangement, in which the residual heat then essentially by convection to the there compacted transmission areas is released. Since this area heats up quickly due to the existing and dense ribbing (rib spacing to one another only in the order of magnitude of 12-15 mm) anyway in low-temperature mode of operation, this area is practically not at risk of condensate. The front Be rich, in which the heat is essentially transmitted by radiation, but in this regard and, as mentioned, is designed in such a way that no condensation can occur here either; in addition, however, a remaining part of the ribbing is left there, either with a reduced rib height and / or in a "thinned out" arrangement, ie with a smaller number in terms of its circumferential distribution. On the one hand, this makes this area of radiation transmission accessible and, in addition, the transmission area there is larger due to the remaining "residual ribs" than that of a completely non-ribbed area, as is the case with the boiler according to FR-PS 23 2O 5O4.

In view of the special rib arrangement, one embodiment of the boiler is that the double-shell wall is formed on the inside in the form of an inner shell formed from several cast rings. With this design, there is certainly the possibility of increasingly dimensioning the number of longitudinal ribs on the cast rings from the burner side to the discharge side, i.e. each subsequent ring towards the discharge side can have an increasingly larger number of longitudinal ribs. For manufacturing reasons, however, an embodiment is preferred in which the rings are divided into two groups, namely a combustion chamber group for the convective heat transfer and a group arranged in front of it with a smaller number of longitudinal ribs for the radiant heat transfer or with the same number of longitudinal ribs and their height then, however, is reduced. In summary, the design of the boiler according to the invention leads to the following:

At least half of the pipe run is made accessible to heat transfer by radiation while at the same time having a condensate-preventing design and a corresponding shortening of the combustion chamber. By reducing the resistance in the front half of the pipe, the possibility is ge manage to concentrate or enlarge the convection heating surface in the area of the shortened combustion chamber. The shortened path of the flame or heating gases along the short combustion chamber leads to a reduction in NOX. The known and proven principle of a double-shell design can be applied to the principle according to the invention without any problems, in various embodiments, in particular when the heating boiler is to be operated in low-temperature mode. Despite measures to prevent condensation over the entire length of the pipe run, at least in relation to boilers of the type mentioned at the beginning, there is a mass reduction in the front area with regard to the radiation-heat-effective transmission surfaces and a mass concentration in the area of the combustion chamber, which reductions or concentrations can be better recorded by control technology. Due to the "compressed" heating surfaces and the increased flow resistance in the convection area, a certain gas build-up is generated, which largely prevents heating or flame gases, without entering the combustion chamber and being sufficiently burned out, directly from the radiation area into the relatively narrow heating gas flues can flow in. The greater flow resistance in the convection area can only be provided because the resistance in the radiation area of the pipe run is greatly reduced. In addition, the convection surface compression has the advantage of being able to operate the boiler with a two-stage burner, especially if it is a boiler with a lower output, which does not mean that the exhaust gas temperature drops undesirably at a reduced output stage, because the exhaust gases flow more slowly through the concentrated convection surface at the lower power level and correspondingly reduced gas volume and give off less heat accordingly.

The solution according to the invention thus represents an advantageous compromise in which only part of the ribbing before The combustion chamber pot is installed in the area in order to meet the complex requirements, as explained.

The heating boiler according to the invention is explained in more detail below with reference to the drawing of exemplary embodiments.

• Fig. 1 im Schnitt die prinzipielle Ausführungsform des Heizungskessels;
• Fig. 2, 3 Schnitte durch den Rohrzug im Bereich der "ver­dichteten" Konvektionsheizfläche;
• Fig. 4 einen Schnitt durch einen Heizkessel im Sinne der Fig. 1 in einer besonderen Ausführungsform und
• Fig. 5 - 7 in Durchströmrichtung gesehen, Einzelteile des Heizungskessels gemäß Fig. 4.
  Wie aus Fig. 1 und 4 erkennbar, besteht der Heizkessel aus einem wasserführenden Gehäuse 16 mit Vor- und Rücklaufan­schlußstutzen 18 und einem an das Gehäuse 16 horizontal durchgreifenden, zu einem Rauchgasabzug 17 führenden und mit Brenner 15 bestückten Rohrzug 1, der im Freiraum einer aus Längsrippen gebildeten Rohrzuginnenverrippung eine topf­artige Brennkammer 2 enthält. Dieser Aufbau entspricht im wesentlichen der Grundkonzeption moderner Heizkessel dieser Art. Diese Grundkonzeption ist nun, wie ebenfalls aus den genannten Fig. erkennbar, derart verändert, daß die topfar­tige, im hinteren Bereich des Rohrzuges 1 angeordnete Brenn­kammer 2 in ihrer Länge maximal der halben Länge des Rohrzu­ges 1 entspricht, was an sich bekannt ist. Ein Teil der nor­malerweise vor der Brennkammer 2 vorhandenen Rippenwärme­tauschfläche ist in den Bereich der Brennkammer 2, bei dort reduziertem Abstand A der Längsrippen 3 zueinander, verlegt angeordnet. Um die Rippenanordnung zueinander mit ihrem re­duzierten Abstand A schon in Fig. 1 zu verdeutlichen, ist im Bereich der verkürzten Brennkammer 2 gestrichelt ein hal­ber Schnitt angedeutet. Die R ]duzierung der Wärmeübertra­gungsfläche im Strahlungsbereich 14 ist durch die Darstel­lung nur weniger und auch in ihrer Höhe reduzierten Längs­rippen 3 verdeutlicht. Durch die stehengelassenen "Restrip­pen" 3 wird das Wärmeaufnahmevermögen dieses Bereiches ei­nerseits so weit vergrößert, daß damit dem Kondensatanfall entgegengewirkt wird, andererseits wird aber durch der "reduzierten" Rippenbesatz dieser Bereich einer direkten Wärm estrahlungswirkung besser zugänglich gemacht.

It shows schematically

• Figure 1 shows in section the basic embodiment of the boiler.
• Fig. 2, 3 sections through the pipe in the area of the "compressed" convection heating surface.
• Fig. 4 shows a section through a boiler in the sense of FIG. 1 in a particular embodiment and
• 5 - 7 seen in the flow direction, individual parts of the heating boiler according to FIG. 4.
  As can be seen from FIGS. 1 and 4, the boiler consists of a water-carrying housing 16 with a supply and return connection piece 18 and a horizontally penetrating to the housing 16, leading to a flue gas discharge 17 and equipped with a burner 15 pipe 1, which in the free space one Longitudinal ribs formed tube inner ribbing contains a pot-like combustion chamber 2. This structure corresponds essentially to the basic concept of modern boilers of this type. This basic concept is now, as can also be seen from the above-mentioned figures, changed in such a way that the pot-like combustion chamber 2 arranged in the rear area of the pipe pull 1 has a maximum length of half the length of the Rohrzuges 1 corresponds to what is known per se. A part of the fin heat exchange surface normally present in front of the combustion chamber 2 is in the area of the combustion chamber 2, there reduced distance A of the longitudinal ribs 3 to each other, arranged laid. In order to illustrate the rib arrangement with respect to one another with its reduced spacing A in FIG. 1, a half-section is indicated in dashed lines in the region of the shortened combustion chamber 2. The reduction in the heat transfer surface in the radiation area 14 is illustrated by the illustration of only fewer and also reduced in height longitudinal ribs 3. By leaving the "residual ribs" 3, the heat absorption capacity of this area is increased on the one hand so much that it counteracts the accumulation of condensate, but on the other hand this area is made more accessible by the "reduced" ribbed area of a direct heat radiation effect.

With the same basic principle as explained, the boiler according to the embodiment shown in FIG. 2 is designed such that at least the wall of the pipe 1 extending in front of the combustion chamber 2 is designed as a double-walled wall 4. This two-shell wall 4 is formed on the inside in the form of an inner shell 5, which is in thermal contact with the inner wall surface 6 of the pipe run 1 at least in partial areas.

The effect of such double-walled walls with specifically arranged heat transfer bridges is known and does not require any further explanation. In particular in the convection area 13, the inner shell 5 according to FIG. 2 can also be formed from the base webs 6 'of tightly welded-on rib profiles 7, which, as shown, can be rectangular, U-shaped, rib-fold profiles or the like . 3, the inner shell 5 can also be formed in the region of the combustion chamber 2 or the convection in the form of a cylindrical insert 7, which is formed from several, each having a plurality of longitudinal ribs 8, correspondingly curved extruded profiles 9, which are joined together with longitudinal seams to form a cylindrical insert.

The exemplary embodiments described so far are particularly intended for heating boilers whose pipe diameter is in the order of magnitude of approximately 60 cm. The embodiment according to FIG. 4 is particularly suitable for pipe runs 1 with a smaller diameter. Here, the double-shell wall 4 is formed on the inside in the form of an inner shell 5 formed from a plurality of cast rings 10. The number of longitudinal ribs 3 on the cast rings 10 from the burner side 11 to the discharge side 12 can be dimensioned increasingly, which is not particularly shown.

4, the boiler is designed in such a way that the rings 10 are divided into two groups, namely a combustion chamber group 13 (convection area) and a group 14 arranged in front (radiation area) ) with a smaller number of longitudinal ribs 13. The foremost ring 10 in the area of the combustion chamber 2 or in the convection area 13, as can be seen in FIG. 7, is very densely occupied with longitudinal ribs 3, the distance A of which is only about 12 is up to 15 mm, whereby the high concentration of heat transfer surface is achieved in this area. For the rings 10 located in front of them, ie the rings in the radiation region 14, a considerable "thinning" of the rib trim is provided, to be precise as far as can be seen from FIGS. 5, 6. Apart from an accelerated heating of these rings in this area, but also the inner surface 19 of the rings is more or less exempted for direct exposure to radiation and also the ribs 3 and 3 'have a stiffening function for the thin-walled cast rings and at the same time facilitate the insertion of the extremely shortened combustion chamber 2 in the convection chamber located in the rear half rich 13. Depending on the requirements and as can be seen from Fig. 6, 7, the length of the longitudinal ribs 3 may correspond to the height of the ribs of the rings 10 in the convection area 13 or may be reduced accordingly with respect to their height with an increased number, if necessary.

Claims (6)

1. Boiler for liquid or gaseous fuels, consisting of a water-bearing housing with flow and return connection piece and a horizontally reaching through the housing, leading to a flue gas discharge pipe and equipped with a burner, which contains a pot-like combustion chamber in the free space of a pipe rib formed by longitudinal ribs, the downstream side Heat transfer area is dimensioned larger than before, characterized in that the pot-like combustion chamber (2) arranged in the rear region of the pipe run (1) is dimensioned in its length at most half the length of the pipe run (1),
that while at least approximately maintaining the entire effective fin surface in the tube train (1), part of the fin heat exchange surface in front of the combustion chamber (2) is arranged in the region of the combustion chamber (2), with a correspondingly reduced distance (A) of the longitudinal fins to one another and
that the remaining longitudinal ribs (3 ') are provided in the area in front of the combustion chamber (2) with a smaller number or with a smaller height than that of the longitudinal ribs (3) arranged in the area of the combustion chamber (2). 2. Boiler according to claim 1, characterized in that at least the wall of the pipe run (1) extending in front of the combustion chamber (2) is designed as a double-walled wall (4), which at least in some areas with the inner wall surface (6) of the pipe run (1 ) is in thermal contact. 3. Boiler according to claim 1 or 2, characterized in that the inner shell (5) from the base webs (6 ') of rib profiles (7), such as right angle, U-shape, ribbed profiles or the like. Is formed. 4. Boiler according to one of claims 1 to 3, characterized in that the inner shell (5) in the region of the combustion chamber (2) in the form of a cylindrical insert (7) and this from several, each having a plurality of longitudinal ribs (8), correspondingly curved Extruded profiles (9) is formed. 5. A boiler according to claim 2, characterized in that the two-shell wall (4) extending over the entire length of the tube train is in the form of an inner shell (5) formed from a plurality of cast rings (10). 6. A boiler according to claim 5, characterized in that the number of longitudinal ribs (3) on the cast rings (1O) from the burner side (11) to the discharge side (12) is increasingly dimensioned.

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