US20050014102A1

US20050014102A1 - Recuperator burner including recuperator

Info

Publication number: US20050014102A1
Application number: US10/864,156
Authority: US
Inventors: Wolfgang Harbeck; Ingo Riehl; Karl Weiss
Original assignee: AICHELIN ENTWICKLUNGSZENTRUM UND AGGREGATEBAU GmbH
Current assignee: NOXMAT GmbH
Priority date: 2003-06-12
Filing date: 2004-06-09
Publication date: 2005-01-20
Also published as: EP1486728A3; EP1486728A2; EP1486728B1; DE10326951A1

Abstract

A recuperator burner comprising a recuperator is disclosed, comprising a tube section serving as a heat exchange surface with flowing fluids, the tube section having a plurality of pleats wound spirally about the longitudinal axis of the recuperator. The recuperator allows an intensive heat exchange between fluids streaming on the inner side and the outer side and can be manufactured using slip casting, due to its simple geometric shape.

Description

RELATED APPLICATIONS

This application claims Convention priority of German patent application serial no. 103 26 951.7 filed on Jun. 12, 2003.

BACKGROUND OF THE INVENTION

The invention relates to a ceramic recuperator for a recuperator burner, comprising a tube section, the inner surface and the outer surface of which serving as a heat exchanging surface with flowing fluid and that comprises a plurality of pleats.
In addition, the invention relates to a recuperator burner comprising a burner head, whereon a burner tube yielding into a burner chamber and an exhaust gas guide tube being coaxial to the burner tube are received, wherein between the burner tube and the exhaust gas guide tube a ceramic recuperator having a plurality of pleats is received.
Such a recuperator burner comprising such a recuperator is known from DE 40 11 190 A1.
In recuperator burners the efficiency is improved by increasing the heat exchange between the burner feed air and the exhaust gas current of the burner. To this end the recuperator is used that effects a heat exchange between the two flowing gases. In the recuperator burner as mentioned at the outset the recuperator is made of a ceramic material and, for increasing the heat exchange surface, comprises pleats that extend in longitudinal direction of the recuperator.
For effecting a further increase of the heat exchange according to EP 0 803 696 A2 a recuperator is used the heat exchange surface of which is increased by providing naps.
According to EP 0 773 407 A2 protrusions and recesses that are oriented in a certain manner are used for increasing the heat exchange surface.
All in all an effective heat exchange can be reached when using such recuperators. Due to the high thermal load such recuperators usually consist of a ceramic material. A manufacture using a cast process, in particular a slip cast process, is preferred because of the complicated shaped surface.
However, herein a problem arises with the generation of delicately structured surfaces, such as necessary for the known recuperators. Delicately structured outer surfaces became rounded more or less and loose their desired delicate structures.

SUMMARY OF THE INVENTION

Therefore, it is a first object of the invention to provide a ceramic recuperator that effects a good heat transfer.
It is a second object of the invention to disclose a ceramic recuperator that allows a simple, precise and cost effective manufacture.
It is a third object of the invention to disclose a ceramic recuperator that is highly efficient as a heat exchanger.
It is a forth object of the invention to disclose a recuperator burner comprising a ceramic recuperator providing a high efficiency.
It is a fifth burner object of the invention to disclose a recuperator burner comprising a ceramic recuperator that allows a simple, precise and cost effective manufacture.
These and other objects of the invention are achieved by designing the pleats of a recuperator to be spirally wound about the longitudinal axis of the recuperator.
In addition, the object of the invention is achieved by a recuperator burner comprising a burner head, whereon a burner tube yielding into a burner chamber and an exhaust gas guide tube being coaxial to the burner tube are received, wherein between the burner tube and the exhaust gas tube a ceramic recuperator having a plurality of pleats is received, wherein the pleats are spirally wound about the longitudinal axis of the recuperator.
The object of the invention is thus fully achieved.
The recuperator according to the invention comprises a large heat exchange surface for the fluids transferring heat. The outer shape of the recuperator is designed in a simple way, thereby also it substantially duplicates the inner shape of the inner wall.
In this way the manufacture using a casting process, in particular a slip casting process, is particularly facilitated, wherein a precise design of the desired surface is guaranteed. By making the pleats spirally wound on the tube section of the recuperator serving as a heat exchange surface, the flow path of the media transferring heat is enlarged, thereby improving effiency.
Preferably, the pleats are bent gradually, in particular, are shaped undulated.
In this way a simple manufacture together with a large heat exchange surface can be guaranteed.
According to a further design of the invention the tube section together with an outer tube and an inner tube defines an outer space and an inner space for guiding the fluids, wherein at least between the outer tube and the pleats or between the inner and the pleats there remains a gap.
The gap which, preferably is formed between the outer tube and the pleats as well as between the inner tube and the pleats, preferably is at least 0.3 times the wall thickness of the tube section, preferably about half of the wall thickness of the tube section.
By these measures an increased turbulence is effected, whereby, the heat exchange is improved. When the fluids enter into the pleats, a part of the media flows along the wave troughs, while an other part flows above the wave crests through the remaining gap between the recuperator and the outer tube and the inner tube, respectively, thus through the respective area contractions that result at the crests. After the crests there are cross sectional enlargements, and thereby the current separates, and secondary currents are generated. This part also mixes with the part of the current that can be found within the next wave trough. In this way the generation of interface layers is considerably impaired, and the efficiency is considerably improved.
According to a further feature of the invention the pleats with respect to the longitudinal axis of the recuperator form a helix angle α that is between 5° and 85°, preferably between 30° and 80°.
Using such a helix angle depending on the current velocity of the flowing fluids an optimized heat transition can be reached. It will be understood that the helix may extend clockwise or counter clockwise with such a helix angle.
According to a further preferred embodiment of the invention the pleats define a distance L between a wave crest and an adjacent wave crest that is at least twice the thickness d of the tube section, preferably about four times the wall thickness d.
In addition, preferably the amplitude A defined by the difference between the radii of a circle touching the outer surface of the pleats and a circle touching the inner surface of the pleats is larger than the wall thickness of the tube section and is preferably about 2.5 times the wall thickness d.
In this way by designing the pleat shape the pleat number can be derived and depending thereon an optimized heat transfer can be reached.
According to a further preferred design of the invention for about 100 mm of an average circumference of the tube section, there is/there are provided at least one pleat, preferably at least two pleats, particularly preferred at least five pleats. Herein with an increase of the average diameter also the pleat number increases accordingly.
In this way by adjusting the pleat number and the rotation angle of the pleats depending thereon an optimized heat transfer can be reached.
Preferably, the recuperator is made of a SiC ceramic.
As mentioned before, preferably, the recuperator is designed as a cast part, particularly preferred as a slip cast part.
It will be understood that the above-mentioned and following features of the invention are not limited to the given combinations, but are applicable in other combinations or taken alone without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparent from the following description of a preferred embodiment taken in conjunction with the drawings. In the drawings show:
FIG. 1 a longitudinal sectional view through a recuperator burner according to the invention, shown in simplified representation;
FIG. 2 a perspective view of the recuperator according to the invention, shown in FIG. 1;
FIG. 3 a longitudinal sectional view through the recuperator according to FIG. 2, shown in enlarged representation;
FIG. 4 a cross-sectional view through the recuperator according to FIGS. 3;
FIG. 5 a cross-sectional view through a pleat section; and
FIG. 6 a simplified representation of the recuperator, showing the definition of the helix angle α.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 a recuperator burner according to the invention is shown in longitudinal sectional view and designated in total with numeral 10.
The recuperator burner 10 comprises a burner head 12, whereon an air guide tube, the so-called burner tube 14, is supported at one end. The burner tube 14 yields into a burner chamber 16. An outer tube or exhaust gas guide tube 24 is supported by the burner head 12 coaxially to the burner tube 14. Between the burner tube 14 and the exhaust gas guide tube 24 a recuperator 30 is received.
Combustion air is fed to the burner head 12 via a lateral channel 26, as indicated by arrow 28 and passes into an inner space or cavity 32 defined between the burner tube and the recuperator, and finally, after passing there through, it reaches the burner chamber 16 via through openings (not shown) of the burner tube. Fuel is fed via a channel 22 arranged within the burner head 12 into a gas lens 20, as indicated by arrow 23, and reaches the burner chamber 16 via a swirl plate 21. In addition, for igniting the fuel/air mixture an igniting electrode 18 is provided which also protrudes with its free end into the burner chamber 16.
Between the recuperator 30 and the exhaust gas guide tube 24 an outer space or cavity 38 is defined. As shown by arrows 44, the combustion gases or flue gases flow through the outer space 38 into the exhaust gas channel 46 of the burner head 12 and thereby heat up the recuperator 30. The combustion air fed via channel 26 flows in opposite direction into the inner space between recuperator 30 and burner tube 14, as indicated by arrows 40. In this way there is a heat exchange between the combustion gases streaming within the outer space 38 and the combustion air streaming within the inner space 32, using the counter current principle.
As can be seen from FIGS. 2 to 6 in more detail, the recuperator comprises a tube section 50 serving as a heat exchange surface, whereon a plurality of pleats 36 are provided that are spirally wound about the longitudinal axis 58 of the recuperator. The tube section 50 which makes up about three quarters of the length of the recuperator 30 is received at its end facing the burner head 12 by a hollow cylindrical section 52 having a collar, and at the opposite end is also enclosed by a hollow cylindrical section 54 which tapers at its free end and wherein an opening 56 is provided. This opening 56 is designed so as to be able to receive the burner tube 14 at its exit end 49 for the flame gases.
As can be seen in particular from FIGS. 4 and 5, the pleats 36 are configured wave-shaped so that at the inner surface as well at the outer surface of the recuperator 30 alternatingly troughs and crests result.
The recuperator 30 consists of ceramic, for example of a SiC ceramic and is preferably prepared using a slip casting process.
The pleats 36 are shaped spirally or helically so that for a length of the tube section 50 of e.g. 400 mm they are rotated by 180°, this corresponding to a helix angle α of 65°.
The number of the pleats 36 and the helix angle α depend on the distance L between adjacent wave crests 59 and on the amplitude A (cf. FIG. 5), as well as on the respective case of application, in particular on the current velocity of the fluids, i.e. of the combustion air and of the exhaust gases.
When using an average recuperator diameter of about 120 mm, for example there could be provided 21 pleats. Herein the pleat distance L e.g. could be 24 mm using an amplitude A of 13 mm and a wall thickness d of 6 mm.
During operation hot flame gases exit from burner chamber 16 via its exit opening 49 and heat up the exhaust gas guide tube 24. From the end facing the burner combustion air streams into the helically located pleats 36 of the inner surface 32, while simultaneously flue gases enter into the spirally shaped pleats 36 of the outer space 38 from the outer end. Herein the helical arrangement effects an enlarged current path along the recuperator 30. In addition, continuously parts of the combustion air steam against the provided pleats on the inner side, as well as exhaust gases on the outer side. A portion of the media, respectively, flows through the gaps 34 and 39, respectively, between the pleats 36 and the burner tube 14 and the exhaust gas guide tube 24, respectively. Thus secondary currents are generated by the mixture between the media flowing along the spirally wound pleats 36 and of the media flowing through the gaps 34 and 39, respectively. To this end the gaps 34 and 39, respectively, may be dimensioned to have about half the wall thickness of the tube section, in the present case it could be about 3 mm for example. Thus a good mixture of the streaming media results and turbulences are generated so that the generation of stable interface layers is impeded or avoided to a large extent, respectively, thus leading to an intensive heat contact with the surfaces of the tube section 50.
In this way a very good heat exchange between the flue gases and the combustion air is reached.
Due to its simple geometrical shape the recuperator 30 can be manufactured with high precision using slip casting processing.

Claims

1. A recuperator burner comprising:

a burner head;

a burner tube having a first and a second end, said first end being supported by said burner head;

a burner chamber provided at said second end of said burner tube;

an exhaust gas guide tube coaxially enclosing said burner tube from the outside and being supported by said burner head; and

a ceramic recuperator supported at one end thereof by said burner head and being located between said burner tube and said exhaust gas guide tube;

an outer gap defined between said exhaust gas guide tube and said recuperator;

an inner gap defined between said recuperator and said inner tube; and

a plurality of undulated pleats extending along a tube section of said recuperator along an outer surface thereof and along an inner surface thereof and being spirally wound about a longitudinal axis of said recuperator, said undulated pleats serving as a heat exchanger between said outer and said inner surfaces of said recuperator;

wherein at least one of said outer and inner gaps has a radial extension which corresponds to at least a wall thickness of said recuperator multiplied by 0.3.

2. The recuperator burner of claim 1, wherein at least one of said outer and inner gaps has a radial extension which substantially corresponds to half of a wall thickness of said recuperator.

3. The recuperator burner of claim 1, wherein said pleats of said recuperator define a helix angle with a longitudinal axis of said recuperator that is between 5° and 85°.

4. The recuperator burner of claim 1, wherein said pleats of said recuperator define a helix angle with a longitudinal axis of said recuperator that is between 30° and 80°.

5. The recuperator burner of claim 1, wherein adjacent wave crests of said undulated pleats define a distance that corresponds to at least twice the thickness of a wall of said tube section.

6. The recuperator burner of claim 1, wherein adjacent wave crests of said undulated pleats define a distance that corresponds to about for times the thickness of a wall of said tube section.

7. The recuperator burner of claim 1, wherein an amplitude defined by a difference between a radius of a circle touching an outer surface of the pleats and between a circle touching an inner surface of the pleats is larger than a thickness of a wall of said tube section.

8. The recuperator burner of claim 1, wherein an amplitude defined by a difference between a radius of a circle touching an outer surface of the pleats and between a circle touching an inner surface of the pleats is about 2.5 times the thickness of a wall of said tube section.

9. The recuperator burner of claim 1, wherein a ratio between the number of pleats provided along a circumference of said tube section and between an average circumference of said tube section is at least 2 per 100 millimeters.

10. The recuperator burner of claim 1, wherein a ratio between the number of pleats provided along a circumference of said tube section and between an average circumference of said tube section is at least 5 per 100 millimeters.

11. The recuperator burner of claim 1, wherein said recuperator is made of a SiC ceramic.

12. The recuperator burner of claim 1; wherein said recuperator is configured as a slip cast part.

13. A recuperator burner comprising:

a burner head;

a burner chamber provided at said second end of said burner tube;

an exhaust gas guide tube coaxially enclosing said burner tube from the outside and being supported by said burner head;

an outer gap defined between said exhaust gas guide tube and said recuperator;

an inner gap defined between said recuperator and said inner tube; and

a plurality of undulated pleats extending along a tube section of said recuperator along an outer surface thereof and along an inner surface thereof and being spirally wound about a longitudinal axis of said recuperator, said undulated pleats serving as a heat exchanger between said outer and said inner surfaces of said recuperator.

14. The recuperator burner of claim 13, wherein at least one of said outer and inner gaps has a radial extension which substantially corresponds to half of a wall thickness of said recuperator.

15. The recuperator burner of claim 13, wherein said pleats of said recuperator define a helix angle with a longitudinal axis of said recuperator that is between 5° and 85°.

16. The recuperator burner of claim 13, wherein said pleats of said recuperator define a helix angle with a longitudinal axis of said recuperator that is between 30° and 80°.

17. The recuperator burner of claim 13, wherein adjacent wave crests of said undulated pleats define a distance that corresponds to at least twice the thickness of a wall of said tube section.

18. The recuperator burner of claim 13, wherein adjacent wave crests of said undulated pleats define a distance that corresponds to about for times the thickness of a wall of said tube section.

19. The recuperator burner of claim 13, wherein an amplitude defined by a difference between a radius of a circle touching an outer surface of the pleats and between a circle touching an inner surface of the pleats is larger than a thickness of a wall of said tube section.

20. The recuperator burner of claim 13, wherein an amplitude defined by a difference between a radius of a circle touching an outer surface of the pleats and between a circle touching an inner surface of the pleats is about 2.5 times the thickness of a wall of said tube section.

21. The recuperator burner of claim 13, wherein a ratio between the number of pleats provided along a circumference of said tube section and between an average circumference of said tube section is at least 2 per 100 millimeters.

22. The recuperator burner of claim 13, wherein a ratio between the number of pleats provided along a circumference of said tube section and between an average circumference of said tube section is at least 5 per 100 millimeters.

23. The recuperator burner of claim 13, wherein said recuperator is made of a SiC ceramic.

24. The recuperator burner of claim 13, wherein said recuperator is configured as a slip cast part.

25. A recuperator burner comprising:

a burner head;

a burner chamber provided at said second end of said burner tube;

a ceramic recuperator supported at one end thereof by said burner head and being located between said burner tube and said exhaust gas guide tube; and

26. A recuperator arrangement for a recuperator burner, said recuperator arrangement comprising;

a ceramic recuperator, said ceramic recuperator comprising:

a first tubular end section and a second tubular end section, one of said first and second tubular end sections being configured for attachment to a burner head of said recuperator burner;

a tube section being arranged between said first and second end sections and serving as a heat exchanging surface between an outer surface and an inner surface of said recuperator; and

a plurality of pleats arranged along said tube section and being spirally wound about a longitudinal axis of said recuperator, said pleats being undulated at said outer and said inner surfaces, said inner and said outer surfaces replicating a contour of each other;

an outer tube enclosing said recuperator and being arranged at a distance to said recuperator defining an outer gap between said recuperator and said outer tube; and

an inner tube arranged within said recuperator at a distance there from and defining an inner gap between said recuperator and said inner tube.

27. The recuperator arrangement of claim 26, wherein at least one of said outer and inner gaps has a radial extension which corresponds to at least a wall thickness of said recuperator multiplied by 0.3.

28. The recuperator arrangement of claim 26, wherein said at least one of said outer and inner gaps have a radial extension which substantially corresponds to half of a wall thickness of said recuperator.

29. The recuperator arrangement of claim 26, wherein said pleats of said recuperator define a helix angle with a longitudinal axis of said recuperator that is between 5° and 85°.

30. The recuperator arrangement of claim 26, wherein said pleats of said recuperator define a helix angle with a longitudinal axis of said recuperator that is between 30° and 80°.

31. The recuperator arrangement of claim 26, wherein adjacent wave crests of said undulated pleats define a distance that corresponds to at least twice the thickness of a wall of said tube section.

32. The recuperator arrangement of claim 26, wherein adjacent wave crests of said undulated pleats define a distance that corresponds to about for times the thickness of a wall of said tube section.

33. The recuperator arrangement of claim 26, wherein an amplitude defined by a difference between a radius of a circle touching an outer surface of the pleats and between a circle touching an inner surface of the pleats is larger than a thickness of a wall of said tube section.

34. The recuperator arrangement of claim 26, wherein an amplitude defined by a difference between a radius of a circle touching an outer surface of the pleats and between a circle touching an inner surface of the pleats is about 2.5 times the thickness of a wall of said tube section.

35. The recuperator arrangement of claim 26, wherein the ratio between the number of pleats provided along a circumference of said tube section and between an average circumference of said tube section is at least 2 per 100 millimeters.

36. The recuperator arrangement of claim 26, wherein a ratio between the number of pleats provided along a circumference of said tube section and between an average circumference of said tube section is at least 5 per 100 millimeters.

37. The recuperator arrangement of claim 26, wherein said recuperator is made of a SiC ceramic.

38. The recuperator arrangement of claim 26, wherein said recuperator is configured as a slip cast part.

39. A ceramic recuperator for a recuperator burner, said ceramic recuperator comprising;

a plurality of pleats arranged along said tube section and being spirally wound about a longitudinal axis of said recuperator, said pleats being undulated at said outer and said inner surfaces, said inner and said outer surfaces replicating a contour of each other.

40. The recuperator of claim 39, wherein said pleats of said recuperator define a helix angle with a longitudinal axis of said recuperator that is between 5° and 85°.

41. The recuperator of claim 39, wherein said pleats of said recuperator define a helix angle with a longitudinal axis of said recuperator that is between 30° and 80°.

42. The recuperator of claim 39, wherein adjacent wave crests of said undulated pleats define a distance that corresponds to at least twice the thickness of a wall of said tube section.

43. The recuperator of claim 39, wherein adjacent wave crests of said undulated pleats define a distance that corresponds to about for times the thickness of a wall of said tube section.

44. The recuperator of claim 39, wherein an amplitude defined by a difference between a radius of a circle touching an outer surface of the pleats and between a circle touching an inner surface of the pleats is larger than a thickness of a wall of said tube section.

45. The recuperator of claim 39, wherein an amplitude defined by a difference between a radius of a circle touching an outer surface of the pleats and between a circle touching an inner surface of the pleats is about 2.5 times the thickness of a wall of said tube section.

46. The recuperator of claim 39, wherein the ratio between the number of pleats provided along a circumference of said tube section and between an average circumference of said tube section is at least 2 per 100 millimeters.

47. The recuperator of claim 39, wherein the ratio between the number of pleats provided along a circumference of said tube section and between an average circumference of said tube section is at least 5 per 100 millimeters.

48. The recuperator of claim 39, wherein said recuperator is made of a SiC ceramic.

49. The recuperator of claim 39, wherein said recuperator is configured as a slip cast part.

50. A ceramic recuperator for a recuperator burner, said ceramic recuperator comprising;

a plurality of pleats arranged along said tube section and being spirally wound about a longitudinal axis of said recuperator, said pleats being bent gradually.