WO2011015571A1

WO2011015571A1 - Method for producing a heat transfer medium and heat transfer medium

Info

Publication number: WO2011015571A1
Application number: PCT/EP2010/061270
Authority: WO
Inventors: Roland Weiss; Andreas Lauer
Original assignee: Schunk Kohlenstofftechnik Gmbh
Priority date: 2009-08-04
Filing date: 2010-08-03
Publication date: 2011-02-10
Also published as: EP2462082A1; CN102803182A; DE102009026322A1

Abstract

The invention relates to a method for producing a heat transfer medium comprising molded parts having or bounding channels and made of ceramic material. In order to ensure good heat transfer and simple production, the invention proposes that preforms are made from paper comprising at least cellulose fibers and at least one filler material, and the paper preforms are then carbonized for forming the molded parts or segments thereof.

Description

Method for producing a heat exchanger and heat exchanger

The invention relates to a method for producing a heat exchanger comprising in particular fluid-carrying channels having or limiting shaped parts made of ceramic material. Furthermore, the invention relates to a heat exchanger with in particular fluid-carrying channels having or limiting molding parts of ceramic material, in particular heat exchangers such as cross-flow heat exchanger or rectifier.

DE-C-139 33 426 discloses a heat exchanger which consists of molded parts made of ceramic. The ceramic moldings are assembled before firing and connected by burning.

Heat exchangers serve the purpose of transferring heat from a stream of higher temperature to a stream of low temperature. In order to achieve optimum efficiency, it is necessary that the components separating the material streams have good heat conduction. Such is also necessary in rectifying apparatuses or apparatuses with which liquid mixtures are separated. This z. B. the liquid and the vapor of a mixture to be separated in countercurrent to each other, that touch both phases for material and heat exchange as intimately. For this purpose, the devices basically consist of a vertical tubular apparatus which contains internals in the form of plate elements with openings or packing elements arranged at intervals. From US-A-2002/0011683 a honeycomb body consisting of silicon carbide is known, which can be used as a soot filter for diesel engines. The honeycomb body is shaped by extension of a mixture containing silicon metal powder, resin and binder.

For the production of a high-temperature body such as heat exchangers, according to EP-A-1 284 251 a corrugated cardboard is used as the starting body, which is coated with slip or introduced into it. This is followed by drying and carbonization.

The subject of DE-A-197 13 068 is a hot gas filter element. For production, carbon fiber nonwoven or felt can be pressed or laminated onto a honeycomb material based on hard paper, in order then to pyrolyze the CFRP structure produced in this way.

In order to produce a heat exchanger according to JP-A-2005047014, a raw material in the form of a corrugated cardboard body is used, which is then laminated and coated with a slurry. Subsequently, a pyrolysis takes place.

Using cellulosic semi-finished molded parts which are pyrolyzed, according to DE-A-101 61 108 ceramic components are produced.

The present invention is based on the object, a method and a heat exchanger of the type mentioned in such a way that with simple production good heat conduction is ensured. It should also be possible to direct aggressive substances through the heat exchanger.

According to the invention, it is proposed by the method: Production of preforms of paper, containing at least cellulose fibers and at least one filler, with which the paper is loaded during its production, and

Pyrolysing the paper preforms to form the moldings or sections thereof.

In this case, the paper preforms forming the shaped parts and thus the sections of the heat exchanger can be assembled after or preferably before the pyrolysis or carbonization. Consequently, the preforms can be adhesively bonded as before being pulverized. It is also possible to join and bond the pyrolyzed preforms prior to a siliconizing process step.

The joining of the Papierpreformen before pyrolysis can be done by means of adhesive with high carbon yield. If the paper preforms are connected after pyrolysis and hence carbonization, this is preferably done in the context of the siliconizing of the pyrolyzed preforms.

According to the invention, a preform consisting of a ceramic paper is used, that is to say a paper which is already loaded with a filler during production.

Suitable fillers are those which are carbonizable. But ceramic fillers such as Al ₂ O ₃ or ZrO ₂ can be used to load the paper accordingly. Another preferred filler is carbon black.

Furthermore, additives in the form of binders such as phenolic resin and / or cellulose can be added to the paper to be pyrolyzed.

The weight fraction of the filler is preferably from 30% by weight to 95% by weight, in particular from 60% by weight to 90% by weight, based on the paper's paper stock and filler dry matter, with additives being included. According to the invention, provision is made in particular for the pyrolyzed, ie the carbonized, paper to be silicided. This can be done with hyperpure silicon, working in excess or deficiency. The siliciding is carried out by conventional methods. In particular, however, the pyrolyzed paper is contacted with a silicon melt for siliconization, e.g. B. by wicks, transfer plates or similar techniques.

The pyrolyzed paper is preferably silicided in a reaction space at a reduced pressure which should be in a range from 50 mbar to 0.05 mbar, in particular in the range of 0.1 mbar, in each case absolute. After the reaction of C with Si to SiC, the reaction space is then vented with an inert gas atmosphere to provide the possibility that excess silicon may be formed on the siliconized ceramic substrate as a Si layer.

If a corresponding Si layer is desired, the process should be controlled such that the Si layer has a thickness d of 0.5 μm <d <50 μm, in particular 10 μm <d <20 μm.

The siliconizing takes place in a temperature range of 1350 ⁰ C <T <2000 ⁰ C, in particular in the range of 1650 ⁰ C <T <1700 ⁰ C instead.

As preform, in particular one or more corrugated board having paper layers are used. In this case can be used as a preform one such that comprises three layers with an inner first layer, a bonded as this bonded as a wave geometry having intermediate layer and connected with this as glued and the intermediate layer covering level third layer. In this case, the first and the second layers are spaced over the intermediate layer.

However, it is also possible to choose paper layers embossed as a preform, which are assigned to one another in such a way and supported on one another and connected to one another that the desired channel formation is present, if one is required becomes. Other geometries, in particular required for plate elements as molding for rectification, can also be produced as stamped.

According to the teaching according to the invention, the preform is shaped by the paper itself, which has been loaded with at least one filler during production. The shaped paper is then carbonized. Due to the fact that the preform is shaped by the paper itself, any desired geometries for the heat exchanger can be generated, a possibility that z. B. is not possible during extrusion for molding.

Furthermore, the invention provides that the pyrolyzed and optionally silicated intermediate layer has a thickness d _{z of} 50 μm <d _z <1000 μm. The webs providing the webs in the true sense of the first and second layer provides a good heat transfer with a corresponding thickness, wherein the media flowing through the channels can have a temperature up to 1400 ⁰ C, without causing damage. If silicon-free pyrolyzed preforms are used as molded parts for the heat exchanger, the fluids may have even higher temperatures.

Regardless of this, the material to be used for the preform should be one which shrinks up to 60% during the pyrolysis and / or has a coke content in the range between 20% and 60% after carbonization. The shrinkage should be 0 <shrinkage <60%. The coke yield range, based on the total weight of the body, should be between 20% and 60%.

End plates and / or funnels of the heat exchanger or possibly between individual layers of the moldings extending stabilizing plates can be made of cellulose and / or lignocellulose particles existing plate-shaped moldings, the conclusion under air at a temperature T with 400 ⁰ C <T <2000 ⁰ C, in particular 800 ⁰ C <T <1600 ⁰ C pyrolyzed. In particular, moldings should be used which are produced from wood fibers and / or vegetable fibers such as flax, hemp, sisal, miscanthus or nettle and, after pyrolysis. have a density between 500 kg / m ³ and 900 kg / m ³ . For this purpose, medium density fibreboards or high density fiberboards are preferably used as starting moldings to be pyrolyzed.

In that regard, recourse is made to carbon or ceramic components, as can be deduced from WO-A-03/050058, to the disclosure of which reference is expressly made.

A heat exchanger of the type mentioned above is characterized in that the molded parts consist of ceramized Papierpreformen. Standard papers or paperboard as starting material for the preform are included. In this case, the cellulose fibers and at least one filler-containing paper is carbonized. The filler should be selected from the group of carbon black, SiC, Si, ceramic filler such as Al ₂ O ₃ or ZiO ₂ . Car- bonizable fillers are also suitable.

The ceramized paper preform may consist of SiC-converted paper loaded with the filler and / or SiC.

In particular, the preform has a corrugated cardboard geometry, wherein the preform can comprise three layers with a planar first layer, a corrugated intermediate layer joined thereto and a planar second layer covering and joining the latter, the intermediate layer comprising the first and second layers forming the channels limited.

The intermediate layer can consist of sections which have an S-shaped, V-shaped, U-shaped or circular section-shaped section in section. It is also possible to use stamped paper to form the moldings, without necessarily the first and second layer are provided. In this case, the embossed papers are aligned with each other so that they provide the desired channel formation. Furthermore, the heat exchanger can have intermediate or end plates as well as fluid inlet or outlet elements in the form of a respective ceramic component which is produced by pyrolysis of a cellulosic semi-finished molded part. As a cellulose-containing semi-finished molded part is in particular a medium density fiberboard with an initial density between 600 kg / m ³ and 850 kg / m ³ or a high density fiberboard with an initial density between 850 kg / m ³ and 1050 kg / m ³ in question, which the pyrolysis have a density between 500 kg / m ³ and 700 kg / m ³ or 700 kg / m ³ and 900 kg / m ³ . The semifinished product should also be silicided after pyrolysis or carbonization.

For more details, advantages and features of the invention will become apparent not only from the claims, the features to be taken these features - alone and / or in combination - but also from the following description of the drawing to be taken preferred embodiments.

Show it:

1 is a first view of a cross-flow heat exchanger,

2 of the cross-flow heat exchanger according to FIG. 1 rotated by 90 °,

3 shows a section of a first embodiment of a molded part,

Fig. 4 shows a detail of a second embodiment of a molded part and

Fig. 5 shows a detail of a third embodiment of a molded part.

The teaching according to the invention will be described below with reference to a cross-flow heat exchanger or molded parts which are used for producing the cross-flow heat exchanger, without thereby restricting the teaching according to the invention. Rather, this can also be used for other heat exchangers, which also include rectifiers that are not necessarily limiting channels Contain molded parts, which are flowed through by fluids. Rather, the teaching of the invention applies to all heat-transmitting moldings.

In Figs. 1 and 2, a cross-flow heat exchanger 10 is shown, by means of which the heat from a substance Ström higher temperature is transferred to a material Ström low temperature. Each material stream has its own delimited flow path, wherein the material flows are guided at right angles to each other. Typical applications of corresponding cross-flow heat exchangers are pipe registers or finned tube registers for heating and cooling tasks.

The flow directions of the fluids flowing through the cross-flow heat exchanger 10 are symbolized in FIGS. 1 and 2 by the arrows 12 and 14, the flow direction of the one substance in FIG. 1 extending perpendicular to the plane of the drawing.

The individual channels of the cross-flow heat exchanger 10 are characterized by pyrolyzed, d. H. carbonized Papierpreformen formed, which are optionally silicided. Consequently, ceramic preforms are used which form the ducts forming or delimiting molded parts of the heat exchanger 10.

As materials for Papierpreformen also standard papers and cardboard in question.

The paper preforms may be those of different geometries, portions of which are shown in FIGS. 3-5. Thus, in Fig. 3, a portion of a preform 16 is shown having a corrugated cardboard geometry. In this case, the preform 16 consists of a first and second planar layer 18, 20, between which a section having a wave geometry and the first and second layer 18, 20 spaced intermediate layer 22 extends. The intermediate layer 22 consists of juxtaposed sections that show an S-geometry.

A corresponding preform 16 extends over the effective heat exchanger length of the heat exchanger 10, with corresponding preforms 16 spaced from one another are arranged. In the intermediate spaces preferably geometrically identical preforms are arranged, which, however, run rotated by 90 ° to the first preforms to allow the desired cross flow.

4, a section of molded parts 20 of a cross-flow heat exchanger is shown, wherein the individual molded parts consist of semicircular embossed sections 22, 24 of paper, which are joined together in their edges. This is indicated by the thickened regions 26, 28. Corresponding embossed sections 22, 24 forming a tube geometry on average are strung together to form a first series of channels. Above this are corresponding rows of embossed paper preforms rotated 90 degrees to form the intersecting channels of the heat exchanger. The adjacent channels rotated by 90 ° are identified by reference numerals 30, 32.

But other geometries for forming the moldings or the fluids leading channels are possible. This will be clarified with reference to FIG. 5. Thus, V-shaped embossed paper strips 34, 36 are joined together (joints 38, 40) and lined up to form channels. The adjacent channels rotated by 90 ° have the reference numerals 42, 44.

In addition to the three exemplified geometries of preforms or sections of these, however, z. B. U-geometries or an open oval-shaped embossed papers or paper webs or strips possible to form molded parts of a heat exchanger.

The moldings forming the channels consist fiction, according to at least cellulose-containing paper such as standard paper or paperboard and at least one filler. This may be carbon black, a carbonizable filler, a reactive filler such as boron or Si or a ceramic filler. Carbon black or A ₂ O ₃ or ZrO _{2 may} be mentioned as ceramic fillers as preferred fillers.

The paper may also be loaded with SiC or Si + SiC. Regardless of this, the weight fraction of the filler should be from 30% by weight to 95% by weight, based on the paper's paper content and filler's dry matter in the paper. Also, other additives such. As binders such as phenolic resin or cellulose are added.

The paper already loaded with a filler in the production is also called ceramic paper which, after carbonization, is a ceramized paper preform forming a shaped part of the heat exchanger.

A corresponding preform, as shown in FIG. 3 can be found or formed by embossing of paper webs or strips and composite preforms z. B. according to FIGS. 4 and 5, are then pyrolyzed in a temperature range between 800 ⁰ C and 1400 ⁰ C, ie carbonized. Subsequently, a siliconizing of the carbonized paper in a temperature range between 1350 ⁰ C and 2000 ⁰ C, in particular between 1650 ⁰ C and 1700 ⁰ C take place. In particular, siliconizing by means of a wick with a silicon melt is preferred. In siliconizing, the carbonized preform should be arranged in a reaction space in which a negative pressure in the range of 0.1 mbar prevails.

The preforms, which also include embossed papers such as paper sections or strips or strips, can be combined before the pyrolysis or after the pyrolyzing. If the latter happens, the preforms are joined together during siliciding.

If the preforms are connected to one another prior to pyrolysis, this is done preferably by means of an adhesive with a high C yield.

As is apparent from Figs. 1 and 2, the cross-flow heat exchanger 10 at its opposite ends fluid inlet and -austritthaler 44, 46 which are bounded by flanges 48, 50, through which the cross-flow heat exchanger 10 installed in a system and in this can be fixed. Both the funnels 44, 46 and the flanges 48, 50 can consist of appropriately cut or shaped medium-density or high-density cellulosic, in particular lignocellulose-containing semi-finished molded parts, which are ceramized by pyrolysis carried out in a non-oxidizing gas atmosphere. In this case, the pyrolyzed, ie carbonized semi-finished molded parts are in particular siliconized such that the ceramic component is a SiSiC ceramic component with a defined free C content. Thus ceramic components are used for the flanges 48, 50 and the funnel-shaped end portions 44, 46, which are made according to the teaching of WO-A-03/050058, the disclosure of which is referred to. The connection between the channels delimiting the molded parts of the cross-flow heat exchanger 10 and the funnel-shaped components 44, 46 can take place in a siliconizing process. It is also possible to connect components by means of adhesive with high C-yield prior to the siliconizing process.

For the dimensioning of the molded parts is to indicate that they can have a planar extension of easily 1 m, so the length or cross section of the cross-flow heat exchanger can pretend. The wall thicknesses of the mold parts delimiting the channels can be less than 100 μm due to the preform made of paper, so that a good heat transfer is ensured. Preferred thicknesses of the paper layers are between 50 μm and 1000 μm after carbonization and optionally siliconizing.

The paper layer itself should have a weight of 50 g / m to 1000 g / m.

The invention will be further elucidated below on the basis of three examples, from which characteristics and / or combinations of features emerge which characterize the invention.

Example 1:

It is a paper web with a basis weight of 200 g / m used, which is loaded with a carbon black filler. The weight fraction of the filler is about 75%, based on the consisting of cellulose fibers and filler dry matter of the paper. The thus loaded paper is then further processed into a paper semi-finished product, which has a corrugated cardboard geometry and wound into a preform and glued. The resulting preform is pyrolyzed in an inert atmosphere at a temperature between 800 ⁰ C and 1400 ⁰ C. Then, a siliconization of the carbonized paper by means of a wick with a silicon melt, at a temperature in the range between 1650 ⁰ C and 1700 ⁰ C. In the reaction chamber itself, there is a negative pressure in the range between 1650 ⁰ C and 1700 ⁰ C. In the Reaction space itself prevails a negative pressure in the range of 0.1 mbar absolute. The siliconizing takes place with excess of silicon. After reaction of the silicon with carbon to form SiC, the reaction space is vented to avoid that the excess silicon is discharged. As a result, an Si layer is formed on the ceramic substrate, the process being controlled such that the thickness is in the range between 10 .mu.m and 20 .mu.m. The solidified layer is then remelted at a temperature just above the melting point of silicon and recrystallized. For the silicization itself hyperpure silicon is used.

It resulted in a thin-walled highly stable structure. Micrographs show that the substrate consists essentially of free silicon surrounding SiC. Unreacted C can be contained to a negligible extent.

The ceramic can be used as a heat exchanger such as cross-flow heat exchanger or rectifier.

Example 2:

A paper web with a weight per unit area of 200 g / m ^{2 is} used, which is loaded with a filler consisting of SiC powder. The weight fraction of the filler is about 75%, based on the consisting of cellulose fibers and filler dry matter of the paper. The thus loaded paper is then further processed into a paper semi-finished product, which has a corrugated cardboard geometry and wound into a preform and glued. The resulting preform is in an inert atmosphere at a Temperature pyrolyzed between 800 ⁰ C and 1400 ⁰ C. Then, the carbonized paper is siliconized by means of a wick with a silicon melt, at a temperature in the range between 1650 ⁰ C and 1700 ⁰ C. In the reaction chamber itself, there is a negative pressure in the range of 0.1 mbar absolute. The siliconizing takes place with excess of silicon. After reaction of the silicon with carbon to form SiC, the reaction space is vented to avoid that the excess silicon is discharged. As a result, an Si layer is formed on the ceramic substrate, the process being controlled such that the thickness is in the range between 10 .mu.m and 20 .mu.m. The solidified layer is then remelted at a temperature just above the melting point of silicon and recrystallized. For siliconizing itself, solar grade poly-silicon is used.

Example 3:

It is a paper web with a basis weight of 100 g / m used, which is loaded with a carbon black filler. The weight fraction of the filler is about 50% based on the consisting of cellulose fibers and filler dry matter of the paper. The thus loaded paper is then further processed into a paper semi-finished product, which has a corrugated cardboard geometry and wound into a preform and glued. The resulting preform is pyrolyzed in an inert atmosphere at a temperature between 800 ⁰ C and 1400 ⁰ C. Then, the carbonized paper is siliconized by means of a wick with a silicon melt, at a temperature in the range between 1650 ⁰ C and 1700 ⁰ C. In the reaction chamber itself, there is a negative pressure in the range of 0.1 mbar absolute. The siliconizing takes place with excess of silicon. After reaction of the silicon with carbon to form SiC, the reaction space is vented to avoid that the excess silicon is discharged. As a result, an Si layer is formed on the ceramic substrate, the process being controlled such that the thickness is in the range between 10 .mu.m and 20 .mu.m. The solidified layer is then remelted at a temperature just above the melting point of silicon and recrystallized. For siliconizing itself, solar grade poly-silicon is used.

Claims

A method for producing a heat exchanger and heat exchanger

1. A method for producing a heat exchanger comprising in particular fluid-carrying channels having or delimiting molded parts made of ceramic material, characterized by

the process steps:

Production of preforms of paper containing at least cellulose fibers and at least one filler, and

Carbonizing the paper preforms to form the moldings or sections thereof.

2. The method according to claim 1,

characterized,

the paper preforms are joined before or after carbonization to form the heat exchanger or at least part of it.

3. The method according to claim 1 or 2,

characterized,

that the carbonized Papierpreform is silicided.

4. The method according to at least one of the preceding claims,

characterized,

in that a carbonizable filler is used as the filler.

5. The method according to at least one of the preceding claims,

characterized,

that carbon black is used as the filler.

6. The method according to at least one of the preceding claims, characterized

in that a reactive filler such as Si or B ₄ C is used as the filler.

7. The method according to at least one of the preceding claims,

characterized,

that a ceramic filler such as Al ₂ O ₃ or ZrO _{2 is} used as filler.

8. The method according to at least one of the preceding claims,

characterized,

in that a binder such as phenolic resin and / or cellulose is added to the paper to be carbonized as an additive.

9. The method according to at least one of the preceding claims,

characterized,

that the filler with a weight proportion G with 30 wt.% <G <95 wt.%, In particular 60 wt.% <G <90 wt.%, Based on the consisting of cellulose fibers and the filler dry matter of the paper in the production of the paper is introduced into this.

10. The method according to at least one of the preceding claims,

characterized,

that the carbonized Papierpreform is siliconized with hyperpure silicon.

11. The method according to at least one of the preceding claims,

characterized,

that the pyrolyzed Papierpreform is siliconized with hyperpure silicon in excess or undershot.

12. The method according to at least one of the preceding claims, characterized in that

that the carbonized Papierpreform is siliconized by means of a silicon melt.

13. The method according to at least one of the preceding claims,

characterized,

the pyrolized paper preform is silicided in a reaction space at a pressure p of 50 mbar <p <0.05 mbar, preferably p in about 0.1 mbar.

14. The method according to at least one of the preceding claims,

characterized,

that the reaction of the carbonized Papierpreform with Si to SiC at a temperature T with 1350 ⁰ C <T <2000 ⁰ C, preferably with 1650 ° <T <1700 ⁰ C is performed.

15. The method according to at least one of the preceding claims,

characterized,

in that a paper corrugated paper or paper layers are used as the paper preform.

16. The method according to at least one of the preceding claims,

characterized,

that a paper embossed paper is used as Papierpreform.

17. The method according to at least one of the preceding claims,

characterized,

in that a paper preform is used which comprises three layers with a flat first layer, an intermediate layer having a wave geometry connected thereto and a planar third layer connected thereto and covering same.

18. The method according to at least one of the preceding claims, characterized

in that the paper used for the preform is one which shrinks by up to 60% during pyrolysis and / or has a coke yield between 20% and 60%.

19. The method according to at least one of the preceding claims,

characterized,

that the heat exchanger ends z. B. is provided with a funnel-shaped supply or discharge opening, which consists of a ceramic component, which is ceramized by pyrolyzing a cellulosic, in particular lignocellulosic semi-finished molding, preferably in the form of a fiberboard.

20. The method according to at least one of the preceding claims,

characterized,

that a medium density fiberboard is used as the fiberboard.

21. The method according to at least one of the preceding claims,

characterized,

that a high-density fiberboard is used as the fiberboard.

22. The method according to at least one of the preceding claims,

characterized,

in that the medium density or high density fiberboard has a starting density of in particular 600 kg / m ³ to 850 kg / m ³ for the medium density fiberboard or in particular 850 kg / m ³ to 1050 kg / m ³ for the high density fiberboard and that the semi-finished molded parts after pyrolyzing a density between 500 kg / m ³ and 700 kg / m m ³ and 900 kg / m ³ ³ bzw.700 kg /.

23. Heat exchanger (10) comprising in particular fluid-carrying channels having or limiting molding parts (16, 20, 33) of ceramic material, in particular heat exchangers such as cross-flow heat exchanger or rectifier, characterized

the molded parts (16, 20, 33) consist of ceramised paper preforms.

24. Heat exchanger according to claim 23,

characterized,

that the paper of the preform contains at least cellulose fibers and at least one filler.

25. Heat exchanger according to at least one of claims 23 or 24,

characterized,

the filler is a reactive filler such as silicon or boron.

26. Heat exchanger according to at least one of claims 23 to 25,

characterized,

that the filler from the group carbon black, SiC, Si, B and ceramic filler such as Al ₂ O ₃ or ZrO ₂ is selected.

27. Heat exchanger according to at least one of claims 23 to 26,

characterized,

in that the ceramised paper preform is SiC-converted paper loaded with the filler and / or SiC.

28. Heat exchanger according to at least one of claims 23 to 27,

characterized,

that the preform has a corrugated cardboard geometry.

29. Heat exchanger according to at least one of claims 23 to 28, characterized

in that the preform comprises three layers (18, 20, 22) with a flat first layer (18), an intermediate layer (22) connected thereto and a flat second layer (20) connected thereto, the intermediate layer comprising the first and second layers Layer spaced over web-like sections.

30. Heat exchanger according to at least one of claims 23 to 29,

characterized,

in that the intermediate layer (22) consists in section of sections of an S-shaped, V-shaped, U-shaped or circular section-shaped geometry.

31. Heat exchanger according to at least one of claims 23 to 30,

characterized,

in that the preform (20) consists of embossed paper (22, 24, 34, 36).

32. Heat exchanger according to at least one of claims 23 to 31,

characterized,

that the preform consists on average of circular section-shaped, triangular-shaped or U-shaped and / or oval-shaped sections of paper such as paper strips.

33. Heat exchanger according to at least one of claims 23 to 32,

characterized,

the heat exchanger has intermediate and / or end plates, such as bottom plates or cover plates, in the form of a ceramic component which is produced by pyrolysis of a cellulosic semi-finished molded part.

34. Heat exchanger according to at least one of claims 23 to 33,

characterized,

that the semi-finished molded part is siliconized.

35. Heat exchanger according to at least one of claims 23 to 34, characterized

the heat exchanger preferably has funnel-shaped openings (44, 46) on opposite end faces, which openings are made of a ceramized cellulosic semi-finished molded part.

36. Heat exchanger according to at least one of claims 23 to 35,

characterized,

the semi-finished molded part is a medium-density or high-density and to the desired extent machined or formed fiber board.

37. Heat exchanger according to at least one of claims 23 to 36,

characterized,

that the carbonized or ceramised semi-finished molded part has a density between 600 kg / m ³ and 700 kg / m ³ or 700 kg / m ³ and 900 kg / m ³ .

38. Heat exchanger according to at least one of claims 23 to 37,

characterized,

in that the preferably funnel-shaped end section (44, 46) merges at the end into a flange plate (48, 50) which consists of a cellulosic, in particular lignocellulose-containing, semifinished molded part which has been ceramised.