Plate heat exchanger, fuel cell system and manufacturing process of the plate heat exchanger

Abstract

Plate heat exchanger (14) for a fuel cell (12), comprising - a housing (16); - a plurality of embossed plates (34) arranged in the housing (16), which are arranged in pairs one behind the other in the direction of a body axis Y of the plate heat exchanger (14), - wherein a primary flow channel (44) for a heating medium H is formed between two immediately adjacent embossing plate pairs (36) and - wherein between the two embossing plates (34) of each pair of embossing plates (36) ◯ a first secondary flow channel (38) for a first medium M1 to be heated and ◯ a second secondary flow channel (40) is formed for a second medium M2 to be heated, wherein each of the secondary flow channels (38, 40) is designed in a meandering shape; - wherein at least some of the flow channels (38, 40, 44) have flow guide elements (46) which at least partially relocate the flow cross-section of the respective flow channel (38, 40, 44); - wherein a part of the flow guide elements (46) are embossed into the embossing plates (34) and - wherein at least some of the flow guiding elements (46) or all of the flow guiding elements (46) of the primary flow channels (44) are formed by guide plates (48) which are designed as separate components from the embossing plates (34).

Description

[0001] So-called solid oxide fuel cells (SOFCs) are high-temperature fuel cells that typically operate at temperatures between 800 and 1000 °C. These fuel cells are designed to achieve a system efficiency of 55–66%. In the long term, solid oxide fuel cells are intended to be used for decentralized energy supply. For example, a fuel cell system can generate hydrogen gas from natural gas using a reformer, which can produce electrical energy and heat through the electrochemical reaction.

[0002] When SOFC fuel cell systems are operated with hydrocarbon-based fuels, the fuel is typically first reformed and the reformate is fed into the fuel cell. Depending on the reforming process used, heat must be added or removed.

[0003] During the electrochemical conversion of the reformate in the fuel cell, the cell voltage decreases with increasing conversion. Therefore, the reformate is not fully converted in the fuel cell stack; instead, post-combustion takes place to utilize the remaining chemically bound energy. The electrochemical oxidation in the fuel cell and the post-combustion take place at high temperatures, so that the released thermal energy can be used for the reforming process. Heat exchangers are used for this purpose. The heat exchangers available on the market often have a compact and complex design to enable the connection of the media flowing through the heat exchanger.

[0004] From US 2014 / 0 231 048 A1 a heat exchanger with a plurality of heat transfer elements is known, wherein the heat transfer elements are designed to be separated by separators and joined together to form a stack.

[0005] EP 3 505 857 A1 discloses an ultrasonic flowmeter with a flow-optimized measuring tube. The ultrasonic flowmeter comprises plates with recesses for mounting a guide element.

[0006] DE 10 2013 218 278 A1 discloses a plate-shaped heat exchanger element for an ice storage system, consisting of two welded plate elements. The heat exchanger element has several spiral flow channels separated from each other in a gas-tight manner.

[0007] The object of the present invention is to provide a particularly compact and cost-effective plate heat exchanger for a fuel cell that can be easily scaled to the requirements of the fuel cell. Furthermore, the object of the invention is to provide a fuel cell system and a method for manufacturing the plate heat exchanger.

[0008] The object relating to the plate heat exchanger is achieved according to the invention by a plate heat exchanger having the features specified in claim 1. The fuel cell system according to the invention has the features specified in claim 12 and the method according to the invention has the features specified in claim 13.

[0009] The plate heat exchanger according to the invention is intended for an SOFC fuel cell and has a housing and a plurality of embossed plates arranged in the housing, which are arranged in pairs one behind the other in the direction of a body axis Y of the plate heat exchanger. Between two immediately adjacent pairs of embossed plates, a primary flow channel is formed for a heating medium H that can be guided through the plate heat exchanger, here for example the exhaust gas guided from the fuel cell. Between the two embossed plates of each pair of embossed plates, a first secondary flow channel for a first medium M1 to be heated, here for example the anode gas of the fuel cell, and a second secondary flow channel for a second medium M2 to be heated, here for example air to be supplied to the fuel cell, are formed.Each of the secondary flow channels is designed in a meandering pattern. The plate heat exchanger according to the invention can be manufactured particularly cost-effectively and simply from just two embossed plate designs and offers a particularly compact design. By integrating two secondary flow channels for media to be heated by the heating medium, the plate heat exchanger can be used even in particularly tight installation conditions. Due to its design, the plate heat exchanger can also be scaled particularly easily to the specific application requirements of the respective fuel cell.

[0010] According to a particularly preferred development of the invention, the first secondary flow channel of each embossed plate pair encompasses the second secondary flow channel of the respective embossed plate pair at least partially, i.e., in sections. This is preferably done on three sides. This allows the plate heat exchanger to be realized in a particularly compact manner. At the same time, the respective inlets and outlets of the first and second secondary flow channels of the embossed plate pairs can be arranged more easily on the plate heat exchanger, in particular on one and the same side of the plate heat exchanger.

[0011] According to a preferred development of the invention, the first secondary flow channel of each embossing plate pair is longer than the respectively associated second secondary flow channel of the respective embossing plate pair. This enables a media guide through the plate heat exchanger that is tailored to the mass flow of the two gases to be heated. If every second secondary flow channel is associated with the inlet-side end of the primary flow channel for the heating medium, i.e. if it runs essentially between the inlet-side channel segments of two immediately adjacent primary flow channels, this makes it possible to achieve a particularly large heat input into the second medium to be heated. A shorter length of the second secondary flow channel compared to the first secondary flow channel can thus be at least partially compensated for.

[0012] According to a particularly preferred embodiment of the invention, the primary flow channels each have a length which substantially corresponds to the cumulative length of the first and second secondary flow channels of each pair of dies.

[0013] The embossed plates of the plate heat exchanger preferably each have embossings, i.e., embossed or formed areas, particularly in the form of embossed flanges, via which the respective embossed plates of a pair of embossed plates abut one another. The embossed plates of a respective pair of embossed plates can be welded together in the area of ​​these embossings. The respective welds are preferably designed to be fluid-tight and pressure-tight up to a specified test pressure in order to ensure reliable separation of the media flowing through the primary / secondary flow channels within the plate heat exchanger during operation.

[0014] According to a particularly preferred embodiment of the plate heat exchanger, the inlet and / or outlet of each first and each second secondary flow channel are each arranged on the same side of the plate heat exchanger. This allows for particularly simple supply and removal of the media to be heated to / from the plate heat exchanger. This also allows for an even more compact design of the plate heat exchanger. Complex external piping and the like for the media to be heated can be eliminated if necessary.

[0015] According to the invention, the inlets and outlets of the primary flow channels are arranged on different sides of the plate heat exchanger. This minimizes the size of the plate heat exchanger while simultaneously providing a sufficiently large inlet and outlet connection cross-section for the primary flow channels of the plate heat exchanger.

[0016] According to the invention, the primary and / or first secondary flow channels and / or second secondary flow channels of the plate heat exchanger each have one or more flow guide elements. The flow guide elements at least partially redirect the flow cross-section of the respective flow channel. This allows for flow guidance and, if necessary, turbulence of the medium conveyed through the respective flow channel to be achieved in order to ensure particularly efficient heat transfer from the heating medium to the first and second medium to be heated.

[0017] According to the invention, some of the flow guide elements are embossed into the stamping plates. This offers manufacturing advantages.

[0018] In addition, the flow guide elements of the primary flow channels are at least partially formed by guide plates, which are designed as separate components from the embossed plates. At least some of the guide plates extend through recesses in the embossed plate pairs of the plate heat exchanger in a direction axial to the body axis Y of the plate heat exchanger. The guide plates can be attached, in particular welded, to the housing and / or to one or more of the embossed plate pairs of the plate heat exchanger.

[0019] The plate heat exchanger or its housing is preferably designed hexahedrally. This simplifies the manufacture of the plate heat exchanger and allows for a particularly simple connection of the fuel cell to the plate heat exchanger.

[0020] According to the invention, each individual embossed plate or even the entire plate heat exchanger can be made of stainless steel. This allows for a particularly long service life of the plate heat exchanger, even when exposed to corrosive media.

[0021] The fuel cell system comprises a fuel cell, in particular a so-called SOFC fuel cell, and a plate heat exchanger as described above. The fuel cell system can be implemented in a particularly compact and cost-effective manner.

[0022] The method according to the invention for producing the plate heat exchanger explained above comprises the following process steps: - Punching the embossing plates out of a sheet metal; - embossing impressions into the dies to form the first and second secondary flow channels; - Forming the embossing plate pairs by placing two of the embossing plates on top of each other and welding them together; - Punching of recesses in each pair of stamping plates for flow guide elements in the form of guide plates; - Mounting the guide plates in the recesses of the embossing plate pairs; and - Arranging the embossing plate pairs in the housing.

[0023] The method according to the invention allows a particularly simple and cost-effective production of the plate heat exchanger.

[0024] Further advantages of the invention will become apparent from the description and the drawings. The embodiments shown and described are not intended to be exhaustive, but rather serve as examples for describing the invention. Detailed description of the invention and drawing

[0025] The drawing shows: Fig. 1 shows a plate heat exchanger according to the invention in a perspective view; Fig. 2 the plate heat exchanger according to Fig. 1 with a partially removed housing and in a perspective view of one of the embossing plates with a third and a fourth flow channel for the first and second media to be heated; Fig. 3 a plan view of the top of the plate heat exchanger according to Fig. 1 with inlet and outlet openings; Fig. 4 an enlarged detail of the plate heat exchanger according to. Fig. 3; Fig. 5 a sectional view of the plate heat exchanger according to Fig. 1 showing the secondary flow channels defined by a pair of die plates; Fig. 6 a sectional view of the plate heat exchanger according to Fig. 1 showing the primary flow channel formed between a pair of dies; Fig. 7 two embossed plates of the plate heat exchanger according to Fig. 1 before their assembly to form a pair of embossing plates and in a view of their surfaces facing each other in the assembled state; and Fig. 8 a pair of embossed plates of the plate heat exchanger according to Fig. 1 showing the welding points through which both dies of the die pair are welded fluid- and pressure-tight; Fig. 9 a pair of embossed plates of the plate heat exchanger according to Fig. 1 showing recesses for the inclusion of flow guide elements (in Fig. 9 not shown), by which the primary flow channels are partially limited; and Fig. 10 a block diagram with individual process steps of the method according to the invention for producing the plate heat exchanger.

[0026] Fig. 1 shows a fuel cell system 10 comprising a fuel cell 12 in the form of a so-called SOFC stack, shown with a dashed line, and a plate heat exchanger 14. The fuel cell 12 is arranged here above the plate heat exchanger 14 in the direction of the vertical axis Z of the plate heat exchanger 14.

[0027] The fuel cell 12 advantageously has additional modules such as a known afterburner and / or a regenerator for the respective hydrocarbon-containing energy source used, for example methane (CH4), which are Fig. 1 are not shown.

[0028] The plate heat exchanger 14 has a housing 16 with an overall hexahedral design. The plate heat exchanger 14 or the housing 16 comprises a top side 14a, a bottom side 14b, a front and rear side 14c, 14d, and a right and left side 14e, 14f. The housing 16 can be provided with various fastening points 18 for directly or indirectly attaching the plate heat exchanger 14 to the fuel cell 12.

[0029] An inlet 20 for the heating medium H, here the exhaust gas from the fuel cell 12, is arranged on the upper side 14a of the plate heat exchanger 14. The inlet 20 is fluidically connected to first or primary flow channels for the heating medium formed in the housing 16 of the plate heat exchanger 14. The primary flow channels are fluidically connected to an outlet 22, which is arranged (in each case) on the right side 14e of the plate heat exchanger 14 or housing 16.

[0030] The first inlet 20 can be provided with a first air baffle 24. The first air baffle 24 extends along the body axis Y of the plate heat exchanger 14, which is orthogonal to the vertical axis Z, and forms an acute angle a with the vertical axis Z ( Fig. 2).

[0031] Furthermore, second and third inlets 26, 28 and second and third outlets 30, 32 for a first medium to be heated and a second medium to be heated are arranged on the top side 14a of the plate heat exchanger 14. The first medium to be heated is the anode gas of the fuel cell stack, while the second medium to be heated is the air to be supplied to the fuel cell. In the embodiment shown in the drawing, the inlet and outlet of each first and each second secondary flow channel are therefore all arranged on the same side, here the top side 14a, of the plate heat exchanger.

[0032] In Fig. 2, the plate heat exchanger 14 is shown in a cut-out perspective view and with the housing 16 partially removed. Fig. 3 shows the plate heat exchanger 14 in a plan view of its top side 14a, while Fig. 4 a correspondingly enlarged detail of the plate heat exchanger 14 according to Fig. 3 shows.

[0033] The plate heat exchanger 14 comprises a plurality of embossed plates 34. The embossed plates 34 can all be made of stainless steel. The embossed plates 34 are manufactured according to the Fig. 3 and Fig. 4 are arranged in pairs one behind the other in the direction of the body axis Y. Two embossing plates 34 form a pair of embossing plates 36. Between the immediately adjacent embossing plates 34 of one and the same pair of embossing plates 36, Fig. 2, a first secondary flow channel 38 for the first medium to be heated (anode gas) and—fluidically separated therefrom—a second secondary flow channel 40 for the second medium to be heated (air) are arranged. The embossing plates 34 of one and the same embossing plate pair 36 each have edge-side embossing flanges 42, via which the directly adjacent embossing plates 34 rest against one another. The embossing plates 34 of each embossing plate pair 36 are connected to one another in this region in a fluid-tight and preferably pressure-tight manner, in particular welded.

[0034] The primary flow channels 44 each extend at least partially between the embossing plate pairs 36. It should be noted that each of the aforementioned flow channels 38, 40, 44 is designed to be meander-shaped, at least in sections, to ensure the most efficient heat transfer possible.

[0035] According to Fig. 2, every second secondary flow channel 40 of the plate heat exchanger 14 is shorter than the respectively associated first secondary flow channel 38. The second secondary flow channel 40 has a length of less than 40%, in particular less than 25% of the length of the first secondary flow channel 38.

[0036] According to the exemplary embodiment illustrated in the drawing, the second secondary flow channel 40 can also have a smaller flow cross-section than the first secondary flow channel 38. It should be noted that every second secondary flow channel 40, in its axial projection along the body axis Y, is assigned to the inlet-side channel segment of at least one primary flow channel 44 carrying the heating medium or coincides with it (in the projection). During operational use of the plate heat exchanger 14, this enables particularly effective heat transfer from the heating medium 22 flowing into the plate heat exchanger 14 to the second medium to be heated flowing through the second secondary flow channel 40. The shorter course and the smaller flow cross-section of the second secondary flow channel 40 compared to the first secondary flow channel 38 can thus be at least partially functionally compensated.

[0037] The primary, first secondary, and second secondary flow channels 44, 38, 40 each have flow guide elements 46, as shown. In the case of the primary flow channel, the flow guide elements 46 are formed by guide plates 48 that are designed separately from the embossed plates and extend in the direction of the body axis Y through corresponding recesses 50 in the embossed plates. Corresponding recesses 50 of the embossed plate pairs 36 are arranged in alignment with one another along the Y-axis. These guide plates 48 can each be connected, in particular welded, to the housing 16 and / or to embossed plate pairs. It should be noted that, according to an embodiment of the plate heat exchanger 14 not shown in the drawing, the flow guide elements 46 of the primary flow channels 44 can also be formed on the outside (in multiple parts) of the embossed plates 34.

[0038] The flow guide elements 46 inside the embossed plate pairs 36, i.e., in the respective first and second secondary flow channels 38, 40, are embossed into one of the two respective embossed plates 34 or into both embossed plates 34, i.e., designed as embossed recesses in one or both embossed plates 34 of a embossed plate pair 36. This offers manufacturing advantages and allows particularly simple free scaling of the plate heat exchanger in the direction of its body axis Y.

[0039] In Fig. Figure 5 shows the flow pattern of the media within a respective pair of die plates 36 of the first and one of the second secondary flow channels 38, 40. The flow patterns of the first medium to be heated (anode gas) and the second medium to be heated (air) are each represented by arrows. The flow patterns here are in the same direction (relative to the body axis Y).

[0040] Fig. 6 shows the flow path of the heating medium H within one of the first flow channels 44. In the projection of the second secondary flow channel 40 along the body axis Y, the heating medium H is guided in the same direction in the first flow channel 38. The inlet-side channel segment 52 of the primary flow channel 44 coincides in the projection with the respectively assigned second secondary flow channel(s) 40 of the respectively immediately adjacent embossing plate pair(s) 36.

[0041] In the projection of the first secondary flow channel 40, the heating medium H in the primary flow channel 44 is guided in the opposite direction to the first medium M1 to be heated.

[0042] In Fig. 7 shows two embossing plates 34 as an example, which together form a pair of embossing plates 36 (see Fig. 2 and Fig. 3). The embossing plates 34 are placed on top of each other during the production of the embossing plate pair 36.

[0043] Fig. 8 shows the embossing plates 34 of a pair of embossing plates 36 in the superimposed state together with the welded connection 54, via which the two embossing plates 34 are permanently, fluid-tightly and pressure-tightly connected to one another.

[0044] In Fig. 9 is a (welded) pair of stamping plates 36 with punched recesses 50 for the guide plates 48 (cf. Fig. 5 and Fig. 6). 56 denotes a material bridge of the embossing plates 34 of the embossing plate pair 36.

[0045] The method 100 for producing the plate heat exchanger 14 comprises the Fig. 10 reproduced procedural steps.

[0046] In a first step 102, the embossing plates 34 are punched out of a sheet metal panel 58 and simultaneously or subsequently in step 104 are embossed or deep-drawn to form the first and second secondary flow channels 38, 40.

[0047] In a further step 106, the embossing plate pairs 36 are formed by placing two embossing plates 34 on top of each other and, for example, by forming the Fig. 8 shown welded joint 54.

[0048] In a further step 108, the recesses 50 of each pair of stamping plates for the guide plates 48 (cf. Fig. 2) punched out if necessary.

[0049] In step 110, the guide plates 48 are arranged, in particular inserted, into the recesses 50 of the embossing plate pairs 36.

[0050] In step 112, the embossed plate pairs 36 are arranged in the housing 16 to form the plate heat exchanger.

Claims

[1] Plate heat exchanger (14) for a fuel cell (12), comprising - a housing (16); - a plurality of embossed plates (34) arranged in the housing (16), which are arranged in pairs one behind the other in the direction of a body axis Y of the plate heat exchanger (14), - wherein a primary flow channel (44) for a heating medium H is formed between two immediately adjacent embossing plate pairs (36) and - wherein between the two embossing plates (34) of each pair of embossing plates (36) ◯ a first secondary flow channel (38) for a first medium M1 to be heated and ◯ a second secondary flow channel (40) is formed for a second medium M2 to be heated, wherein each of the secondary flow channels (38, 40) is designed in a meandering shape; - wherein at least some of the flow channels (38, 40, 44) have flow guide elements (46) which at least partially relocate the flow cross-section of the respective flow channel (38, 40, 44); - wherein a part of the flow guide elements (46) are embossed into the embossing plates (34) and - wherein at least some of the flow guiding elements (46) or all of the flow guiding elements (46) of the primary flow channels (44) are formed by guide plates (48) which are designed as separate components from the embossing plates (34). [2] Plate heat exchanger (14) according to claim 1, characterized by that the first secondary flow channel (38) of each embossing plate pair (36) partially encompasses the second secondary flow channel (40) of the respective embossing plate pair (36). [3] Plate heat exchanger (14) according to claim 1 or 2, characterized bythat the first secondary flow channel (38) of each embossing plate pair (36) is longer than the respectively associated second secondary flow channel (40). [4] Plate heat exchanger (14) according to one of the preceding claims, characterized by that the two embossing plates (34) of each embossing plate pair (36) each have embossings (42), in particular an embossing flange, via which the embossing plates (34) each bear against one another. [5] Plate heat exchanger (14) according to one of the preceding claims, characterized by that the two embossing plates (34) of each pair of embossing plates (36) are welded together. [6] Plate heat exchanger (14) according to one of the preceding claims, characterized by that the inlet (20, 26, 28) and / or the outlet (22, 30, 32) of each first and each second secondary flow channel (38, 40) are each arranged on the same side of the plate heat exchanger (14). [7] Plate heat exchanger (14) according to one of the preceding claims, characterized by that the inlet (20, 26, 28) and the outlet (22, 30, 32) of the respective primary flow channels (44) are arranged on different sides of the plate heat exchanger (14). [8] Plate heat exchanger (14) according to one of the preceding claims, characterized by that at least some of the guide plates (48) extend through recesses (50) of the embossed plate pairs (36) in a direction axial to the body axis Y of the plate heat exchanger (14). [9] Plate heat exchanger (14) according to one of the preceding claims, characterized by that at least some of the guide plates (48) are fastened, in particular welded, to the housing (16) of the plate heat exchanger (14) and / or to embossed plate pairs (36). [10] Plate heat exchanger (14) according to one of the preceding claims, characterized in that the plate heat exchanger (14) is designed hexahedrally. [11] Plate heat exchanger (14) according to one of the preceding claims, characterized by that each pair of embossed plates (36) or the entire plate heat exchanger (14) is made of stainless steel. [12] Fuel cell system (10) comprising a fuel cell (12) and a plate heat exchanger (14) according to one of the preceding claims 1 to 11. [13] Method for producing a plate heat exchanger (14) according to one of claims 1 to 11, characterized by the following procedural steps: - producing (102) the embossing plates (34) by punching (104) the embossing plates (34) out of a flat product (58) and, preferably simultaneously, embossing (106) the first and second secondary flow channels (38, 40) into the embossing plates (34); - forming (108) the pairs of embossing plates (36) by placing two of the embossing plates (34) on top of each other and welding them together; - arranging (110) the embossing plate pairs (36) on a housing plate (16a), in particular by inserting the embossing plate pairs (36) into recesses (60) of the housing plate (16a); - mounting (112) guide plates (48) for the primary flow channels (44) in the recesses (50) of the embossing plate pairs (36); - front-side welding (114) of the embossing plate pairs (36) to the housing plate (16a); and - Mount (116) the remaining housing (16).

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