Abstract:
There is disclosed a fuel cell assembly comprising at least one horizontally arranged fuel cell stack that has numerous fuel cells, each comprising an anode, a cathode and an electrolyte situated between the anode and the cathode; combustible gas supply means for supplying combustible gas to the anodes of the fuel cells; anode gas withdrawal means for withdrawing the anode exhaust gas from the anodes; cathode gas supply means for supplying cathode gas to the cathodes of the fuel cells; cathode gas withdrawal means for withdrawing the cathode exhaust gas from the fuel cells; and recirculation means for recirculating at least one part of the anode exhaust gas and/or the cathode exhaust gas to cathodes of the fuel cells. The fuel cell assembly according to the invention is characterized in that the recirculation means comprise at least one catalytic burner with catalyst material for burning the remaining combustible gas contained in the anode exhaust gas, said burner being situated at the side of the fuel cell stack.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German patent applications DE 10 2008 047 920.9 filed on Sep. 19, 2008 and DE 10 2009 013 598.7 filed on Mar. 17, 2009 and PCT application PCT/EP2009/006701 filed on Sep. 16, 2009, which are hereby incorporated by reference in their entireties. 
     BACKGROUND 
     To generate electrical power by means of fuel cells a larger number of fuel cells are ordinarily arranged in the form of a stack, each fuel cell having an anode, a cathode and an electrolyte arranged in between. The individual fuel cells are each separated by bipolar plates and electrically contacted. Current collectors are provided on the anodes and cathodes, which serve for electrical contact of the anodes and cathodes, on the one hand, and to supply reaction gases to them, on the other. Sealing elements are provided in the edge area of the anode, cathode and electrolyte matrix, which form lateral sealing of the fuel cells and therefore the fuel cell stack from emergence of anode and cathode gas. 
     The electrolyte material in a molten carbonate fuel cell typically consists of binary or ternary alkali carbonate melts (for example, mixed melts of lithium and potassium carbonate), which are fixed in a porous matrix. Molten carbonate fuel cells typically reach working temperatures of about 650° C. during operation. A reaction of hydrogen with carbonate anions to water and carbon dioxide with release of electrons then occurs on the anode side. Oxygen reacts with carbon dioxide to carbonate ions on the cathode side with absorption of electrons. Heat is then released. The alkali carbonate melts used as electrolyte, on the one hand, supply the carbonate ions necessary for the anode half-reaction and, on the other hand absorb carbonate ions that form in the cathode half-reaction. A hydrocarbon-containing energy carrier, like methane, for example, which can come from natural gas or biogas, as well as water, are generally supplied in practice to the anode side of the fuel cell, from which hydrogen required for the anode half-reaction is produced by internal reforming. The anode waste gas is mixed with additionally supplied air and then oxidized catalytically to eliminate any residual components of the fuel gas. The formed gas mixture now contains carbon dioxide and oxygen, i.e., precisely the gases required for the cathode half-reaction so that anode waste gas can be introduced directly to the cathode half-cell after fresh air supply and catalytic oxidation. 
     The hot exhaust emerging at the cathode output is pollutant-free and can be further used for heat. The electrical efficiency of the molten carbonate fuel cell is already 45 to 50% and when the heat released in the overall process is used, an overall efficiency of about 90% can be achieved. 
     The known fuel cell arranged by the applicant is described in detail, for example, in the international patent applications WO 96/02951 A1 and WO 96/20506 A1 and in German patent application DE 195 48 297 A1, incorporated herein in their entirety. 
     The essential components of the known fuel cell arrangement are schematically depicted in  FIGS. 1 and 2  in a frontal and lateral cross-sectional view. The fuel cell arrangement designated overall with reference number  10  has a horizontally lying fuel cell stack  11 , i.e., consisting of vertically arranged, plate-like elements, which is arranged in a heat-insulated, gas-tight protective housing  12 . Fuel gas is supplied via a fuel gas line  13  into the interior of the gas-tight protective housing  12  and introduced into the anode chambers of the fuel cell stack  11  in a fuel gas distributor  16  arranged on the anode input  15  on the bottom of the fuel cell stack  11  via a heat exchanger  14 . The fuel gas flows through the anode chambers in essentially a vertical direction and emerges again on the anode output side  17  situated on the top of the fuel cell stack. The heat exchanger  14  is a gas/gas heat exchanger, which is traversed, on the one hand, by the fuel gas and, on the other hand, by a stream of cathode gas circulated within the gas-tight protective housing  12 . 
     The cathode gas enters the fuel cell stack  11  at the cathode input  18  arranged laterally and leaves it at the cathode output  19  on the opposite side of the fuel cell stack. As can be deduced from  FIG. 1 , the flow directions of the cathode gas and fuel gas are perpendicular to each other. Maintenance of the gas streams in the protective housing  12  is accomplished by means of two fans  20 ,  21  arranged above the fuel cell stack  11 , each of which are driven by electric motors  22 ,  23 . A diffuser  24  and a static mixer  25  following it are arranged directly above the anode output  17  of the fuel cell stack  11 . The anode waste gas leaving the anode output  17  is mixed with the cathode gas stream circulating in the housing  12  in the static mixer  25 . Fresh air is also introduced to static mixer  24  via a line  26 . Under the action of fans  20 ,  21  the gas mixture of anode waste gas, circulated cathode gas and fresh air is fed into a catalytic burner  27  arranged above the static mixer  25 , in which combustible residual components of the anode waste gas are catalytically burned and converted to useful heat. The gas mixture leaving the catalytic burner, which now contains the main components of the cathode reaction with oxygen and carbon dioxide, is directed via fans  20 ,  21  to the cathode input  18 , where it then flows through horizontally to the fuel cell stack  11 . As mentioned above, after emergence at the cathode output  19 , a partial stream of the cathode gas is fed back to the static mixer  24 . A start heater  28  is preferably arranged in front of the cathode input  18 , which brings the process gases to the operating temperature of about 600° C. during startup of the fuel cell arrangement  10 . A diffuser  29  can also be arranged in front of the cathode input  18 , which is supposed to permit homogeneous flow against the cell stack together with additional internals provided between fans  20 ,  21  and the cathode input  18 . However, if, as in the depicted example, the heat exchanger  14  is also arranged in front of the cathode input  18 , homogeneous flow against the cell stack can also be guaranteed by an appropriate configuration of the heat exchanger so that the additional diffuser  29  can optionally be dispensed with. Excess cathode exhaust leaves the fuel cell stack  11  via a cathode exhaust line  30  shown only schematically here. 
     The fuel cell arrangement described here is marketed by the applicant under the name HM 300 in a circular cylindrical protective housing. 
     In this known design principle the static mixer, the catalytic burner and the fans connected to them are directly arranged above the anode output of the fuel cell stack, which imposes high flow requirements on the circulation fan, namely both with respect to suction behavior of the fan in order to guarantee uniform mixing of fresh air, anode waste gas and cathode exhaust in the static mixer, and with respect to outflow behavior of the fan in order to guarantee uniform flow against the cell stack by the gas mixture. These requirements can be guaranteed in the previous design only by rectifiers and internals in the flow path, which, however, lead to pressure losses, which again requires higher fan power. In cell stacks with several hundred individual cells several fans arranged along the cell stack are also required in order to achieve homogeneous flow behavior. 
     A further drawback of the previous design is that the catalytic burner is arranged above the cell stack between the static mixer and fan. The catalyst during the operating time, however, is exposed to soiling, which can lead to a deterioration in flow and additional pressure losses so that the catalyst must regularly be cleaned. In the previous arrangement, however, the complete cell stack must be disassembled for this purpose, which is connected with a very high work cost and can only be conducted by the manufacturer. 
     Another drawback of the known design is that the mixer must be designed very compact directly above the anode output because of the limited space available so that satisfactory mixing can only be achieved by numerous internals with correspondingly high pressure loss. The manufacturing costs of the previously used mixer are therefore high. 
     Finally, the previous fuel cell arrangement permits only a few design degrees of freedom. The ratio of height and width of the fuel cell stack and the additional components arranged in the protective housing is essentially stipulated by the use of a circular cylinder protective housing and the degrees of freedom with respect to arrangement and dimensioning of the components arranged in the protective housing are limited. The layout of individual components specifically adapted to each other also means that numerous components must be newly designed, depending on the power layout of the system. The assembly cost of the previously used fuel cell arrangement is also high. 
     BRIEF DESCRIPTION 
     In one embodiment of the present disclosure concerns a high temperature fuel cell arrangement, especially a molten carbonate fuel cell arrangement, as well as a method for operation of such a fuel cell arrangement. 
     The underlying technical problem of the present disclosure is therefore to further improve the described design principle of a fuel cell stack integrated in a protective housing with cathode gas stream circulating in the protective housing. 
     The applicant was able to integrate the fuel cell stack and all system components operating at high temperature in a common gas-tight protective housing. The efficiency of the system is therefore improved, on the one hand, and an arrangement could be achieved, on the other, in which the cathode gas stream can circulate freely in the internal space of the protective housing and the anode waste gas stream can be introduced freely into the circulating cathode gas stream. Whereas a gas distributor and gas collector are provided in ordinary fuel cell stacks at each anode input, anode output, cathode input and cathode output, which must be sealed relative to the fuel cell stack in costly fashion, in the known system of the applicant, owing to the cathode gas stream freely circulating in the protective housing, a gas distributor sealed relative to the fuel cell stack is provided at the anode input, but no gas distributor is necessary at the cathode input so that the overall design can be significantly simplified. 
     In one embodiment of the present disclosure solves these technical problems by providing a fuel cell arrangement with at least one horizontally arranged fuel cell stack, which has numerous fuel cells, each of which includes an anode, a cathode and an electrolyte arranged between the anode and cathode. At least one fuel gas feed device appears to feed fuel gas to the anodes of the fuel cells. An anode gas withdrawal device to withdraw the anode waste gas from the anodes, and a cathode gas feed device to feed cathode gas to the cathodes of the fuel cells. A cathode gas withdrawal device is present to withdraw cathode exhaust from the fuel cells and at least one return device to return at least part of the anode waste gas and/or cathode exhaust to the cathodes of the fuel cells. The return device has at least one catalytic burner with catalyst material for burning of residual combustible gas contained in the anode waste gas, which is arranged laterally next to the fuel cell stack. 
     It is proposed according to the one embodiment of the disclosure not to draw off the mixture of fresh air, anode waste gas and cathode exhaust after passing through the catalytic burner directly by the fan, but to collect it initially in a suction tube, which discharges into the fan. Mixing and catalytic burning of the drawn-in gas already occurs before the suction tube so that optimal suction by the fan is guaranteed. Because of flow guiding in a suction tube the fan can be arranged next to the protective housing and communicate with the internal space of the housing through standardized suction and discharge connectors. Since the protective housing and the flanged-on fan form two separate assemblies, both assemblies can be designed and optimized independently of each other. An optimized distributor for longitudinal distribution of the gas mixture coming from the fan can be arranged in the space gained above the cell stack so that the suction and outflow properties of the fan itself are not critical. Uniform flow against the cell stack is guaranteed without demanding rectifiers and internals by means of a flow distributor that tapers wedge-like in the longitudinal direction of the fuel cell stack so that pressure losses can be significantly reduced relative to the previous design. The power requirements on the fan are also reduced accordingly. It was surprisingly found that cell stacks with up to 600 individual units can be supplied with a single fan with the arrangement proposed according to the disclosure. 
     It is also proposed according to the disclosure to arrange the catalytic burner on the cathode output side between the fuel cell stack and the wall of the protective housing. Because of this arrangement the catalyst is more readily accessible so that maintenance for cleaning purposes is simplified. For example, cleaning/filling openings can be provided in the wall of the protective housing so that disassembly of the cell stack is no longer required. Cleaning of the catalyst can therefore be carried out by the user. In contrast to the previously used fuel cell arrangement the catalytic burner is traversed from the top down so that the use of pelletized catalysts is now also made possible. In the prior art pelletized catalysts could not be used, since suspension of the catalyst particles in the air stream occurs during flow from the bottom up, which entails strong mechanical wear on the catalyst elements. However, the previously preferably used honeycomb catalysts can likewise also be used in the present disclosure. 
     A simple gas mixer with lower pressure losses is also furnished according to the disclosure. The gas mixer has a first mixing zone in which cathode exhaust is mixed with fresh air, as well as a second mixing zone in which anode waste gas is introduced to the mixture of cathode exhaust and fresh air. The mixer is preferably arranged on the cathode output side between the cell stack and the wall of the protective housing above the catalytic burner also provided there. Long mixing zones can therefore be implemented so that fewer internals and mixing elements are required in order to guarantee homogeneous mixing of the cathode and anode waste gas streams and the fresh air. The pressure loss in the mixture relative to the known mixers arranged on the fuel cell stack is therefore significantly reduced. In addition, the mixer according to the disclosure can be made light and can be easily and cost effectively manufactured because of the simple sheet metal parts, which reduces the overall cost of the fuel cell arrangement. 
     The fuel cell arrangement according to the one embodiment of the disclosure is arranged in functional groups that can be dimensioned and optimized largely independently of each other. 
     One functional group then consists of a fuel cell stack with anode input gas distributor and the anode output gas collector. In contrast to the ordinary design in which the fuel cell stack also included components like the heat exchanger, static mixer and catalytic burner, the now proposed assembly can be constructed much more simply. Another functional group consists of the cathode gas feed with distributor channel, start heater and heat exchanger. This functional group can be preassembled completely outside the container and integrated before insertion of the stack. 
     Another functional group consists of the mixer and catalyst unit with sheet metal internals for mixing of fresh air, cathode exhaust and anode output gas, the catalyst housing and catalyst output flow collector with baffles. 
     Another functional group consists of the circulating fan with impeller housing and connections on the suction side via a suction tube to the catalyst output housing and on the pressure side to the cathode gas distributor channel. 
     It is proposed according to the disclosure to design the protective housing rectangular so that the design of the components of the fuel cell arrangement according to the disclosure is independent of the width to height ratio. 
     The functional group can be largely preassembled outside the module, which facilitates and accelerates assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The disclosure is further explained below with reference to a practical example depicted in the accompanying drawings. 
       In the drawings 
         FIG. 1  shows a frontal cross-sectional view of a fuel cell arrangement of the prior art; 
         FIG. 2  shows a lateral cross-sectional view of a fuel cell arrangement of the prior art; 
         FIG. 3  shows a frontal cross-sectional view of a fuel cell arrangement according to one variant of the disclosure; 
         FIG. 4  shows an enlarged detail view with an area of  FIG. 3  marked with circle IV; 
         FIG. 5  shows a lateral cross-sectional view of the fuel cell arrangement according to the disclosure depicted in  FIG. 2  along line V-V in  FIG. 3 ; 
         FIG. 6  shows a top cross section of the fuel cell arrangement according to the disclosure depicted in  FIG. 2  along line VI-VI of  FIG. 3 ; and 
         FIG. 7  shows a schematic perspective view of the gas-tight housing of a variant of the fuel cell arrangement of  FIGS. 3-6 . 
     
    
    
     DETAILED DESCRIPTION 
     The fuel cell according to the prior art was already described above in conjunction with  FIGS. 1 and 2 . 
     With reference to  FIGS. 3 to 7  two preferred variants of the fuel cell arrangement according to the disclosure are described below. Components that are identical to components of the fuel cell arrangement of the prior art or have the same or similar function are then referred to with the same reference numbers. 
     The fuel cell arrangement designed overall with reference number  10 , like the fuel cell arrangement of the prior art, has a horizontally lying fuel cell stack  11  consisting of vertically arranged plate-like elements, which is arranged in a heat-insulated, gas-tight protective housing  12 . In contrast to the protective housing of the fuel cell arrangement of the prior art, the protective housing of the fuel arrangement  10  according to the disclosure is designed essentially rectangular. The gas-tight protective housing  12  consists of individual metal plates  31  connected to each other, for example, welded to each other, which, as is especially recognizable in  FIG. 7 , are stabilized on the outside by steel supports  32 , which impart the necessary rigidity to the overall fuel cell arrangement  10 . An appropriate insulation material  100  for heat insulation of the internal space of the protective housing  12  is applied to the inside of metal plates  31 . The protective housing  12  can be easily adapted to the altered dimensions of the fuel cell stack, which thus permits cost-effective production of fuel cell arrangements with different power. 
     The fuel cell stack  11  again has a cathode input side  18 , cathode output side  19 , an anode input side  15  and an anode output side  17 . 
     Fuel gas arrives in the interior of the gas-tight protective housing  12  via fuel gas feed devices, which include a fuel gas line  13 , and is initially passed through a heat exchanger  14 , which, in contrast to the prior art, is arranged above the fuel cell stack  11 . The heat exchanger  14  is also designed as a gas/gas heat exchanger in the fuel cell arrangement  10  according to the disclosure, which is traversed on one side by the fuel gas and on the other side by a stream of cathode gas circulating within the gas-tight protective housing  12  so that the fuel gas is preheated before introduction into the fuel cell stack  11 . After passing through heat exchanger  14 , the heated fuel gas reaches a fuel gas distributor  16  arranged on the bottom of the fuel cell stack  11  via a line  33  arranged on the end of the fuel cell stack, which distributes the fuel gas to the anode chamber inputs of the individual fuel cells of the stack. In the depicted example the fuel gas, however, does not directly enter the anode chambers. Instead reformer elements designed plate-like are arranged between the cell elements of the fuel cell stack  11 , which reform at least part of the fuel gas before introduction into the anode chambers of the fuel cells in known fashion. The heated anode gas in the special variants of the disclosure depicted in  FIGS. 3 to 6  is supplied via line  33  initially into an edge strip formed as a hollow line  34  of the anode gas distributor  16 , which serves as longitudinal distributor. Along the hollow line  34  numerous distributor lines  35  branch off laterally, which supply the fuel gas into the inputs of the separate plate-like reformer units of the fuel cell stack via V-shaped distributor heads  36  arranged on the ends of the distributor lines. After passing through the reformer units, which can be arranged, for example, alternating with fuel cell elements in the fuel cell stack  11 , or which are provided after a certain number of fuel cell elements, for example, always after five fuel cell elements, the at least partially reformed fuel gas is returned into the interior of the fuel gas distributor  16  and goes from there to the anode inputs of the fuel cell elements of the stack. In a preferred variant of the fuel cell arrangement according to the disclosure, in addition to these separate reformer elements for the so-called indirect internal reforming, reformer catalyst for the so-called direct internal reforming is arranged in the anode chambers of the fuel cell elements. Sealing between the distributor lines  35  and the internal space of the fuel gas distributor  16  is therefore not critical because unreformed fuel gas that directly reaches the internal space of the fuel gas distributor  16  through possible leaks can also be directly reformed in the fuel cell elements. After flowing through the fuel cell stack  11  from the bottom up, the anode waste gas emerges at the anode output  17  on the top of the fuel cell stack  11  and is trapped by an anode waste gas collector  37  and fed laterally to a gas mixer  25 , which is apparent in  FIG. 3  and especially in the enlarged depiction in  FIG. 4  and is described in detail further below. 
     The cathode gas circulating in the gas-tight protective housing  12  enters the cathode chambers of the fuel cell elements on the open cathode input side  18  of the fuel cell stack  11  and leaves the stack on the cathode output side  19  after passing through the fuel cell stack essentially horizontally, on which a cathode exhaust collector  38  is arranged. The cathode exhaust collector  38  is connected via openings  39  to a cathode exhaust line  40 , via which excess cathode exhaust is taken off from the fuel cell arrangement  10 . Part of the cathode exhaust, however, also circulates in the protective housing  12  and, after mixing with the anode waste gas and the fresh air in the gas mixer  25  and subsequent after-burning in a catalytic burner  27  described further below, enters the fuel cell stack  11  again on the cathode input side  18  as so-called cathode gas. 
     The cathode exhaust collector  38  arranged on the cathode output side has a gap opening  42  extending essentially over the entire length of the fuel cell stack  11  in its upper area  41 , through which the circulating fraction of the cathode exhaust in the protective housing  12  reaches the downstream gas mixer  25 . The gas mixer  25  has a first mixing zone  43 , in which the cathode exhaust leaving the cathode exhaust collector via the gap opening  42  and fresh air are introduced. The fresh air is fed via a fresh air line  26  running essentially parallel to the fuel cell stack, which has at least one opening  44  along the mixer, for example, a gap opening running in the longitudinal direction, or several openings, through which fresh air can enter the first mixing zone  43 . The gas mixer  25  also has a second mixing zone  45  arranged downstream over the first mixing zone  43 , into which anode waste gas is introduced to the mixture of cathode exhaust and fresh air. The gas stream runs essentially horizontally in the first mixing zone  43 , whereas it is deflected downward in the transitional region  46  from the first to second mixing zone. The gas mixer  25  is also designed so that the flow cross section of the first mixing zone  43  and the flow cross section of the inflowing anode waste gas is tapered to the second mixing zone  45  so that the anode waste gas and the already premixed mixture of cathode exhaust fresh air are accelerated to the second mixing zone  45 . At the level of the first mixing zone and in the transitional region from the first to second mixing zones the anode gas stream and the stream of the mixture of cathode exhaust and fresh air run essentially parallel so that the anode waste gas stream is introduced essentially tangentially into the mixture of cathode exhaust and fresh air. In the region of the first mixing zone  43  the anode waste gas stream and the mixture of cathode exhaust and fresh air are separated by a baffle  47 , which ends in the transitional region from the first to second mixing zones. This end of the baffle  47  has a number of tongues  49 , which are bent upward or downward in alternation in the longitudinal direction and are welded to the top 50 or bottom  51  of the housing  52  of the gas mixer  25 . These tongues  49  ensure additional swirling of the gas mixture and guarantee homogeneous mixing of the anode waste gas, cathode exhaust and fresh air. In addition or as an alternative, other static mixing elements can be provided. The second mixing zone  45  also includes a distributor  53 , which widens from a first flow cross section at the input  54  of the distributor to a second flow cross section at the output  55  of the distributor, in which the flow cross section at the output of the distributor essentially corresponds to the surface of the inlet opening on the top of a catalytic burner  27  arranged after the gas mixer  25  for burning of the fuel gas contained in the anode waste gas. As is especially apparent from  FIG. 3 , the gas mixer  25  is arranged essentially between the fuel cell stack and a side wall  56  of the gas-tight protective housing enclosing the fuel cell stack. Relative to the prior art, longer mixing zones can therefore be implemented. More effective mixing can also be achieved without excessive use of numerous static mixing elements that increase flow resistance. 
     The catalytic burner  27  following the gas mixer  25  is also arranged laterally next to the fuel cell stack  11  on the side wall  56  of the gas-tight protective housing  12 . The catalytic burner  27  has a top with at least one inlet opening  57 , which communicates with the gas mixer  25  for mixing of anode waste gas, cathode exhaust and fresh air. The catalytic burner has at least one outlet opening  58  on its bottom, which communicates with a collector  59  for collection of the waste gases to be returned to the cathode input. The catalytic burner  27  can include, for example, a honeycomb catalyst. Due to flow guiding of the waste gas proposed according to the disclosure from the top down through the catalyst, the catalyst material is not exposed to increased abrasion so that the catalytic burner  27  according to the disclosure can be designed, in particular, as a pelletized catalyst. Owing to lateral arrangement next to the fuel cell stack, the catalytic burner  27  is situated in the immediate vicinity of a side wall  56  of the protective housing  12  of the fuel cell arrangement  10  according to the disclosure so that the catalyst material can be cleaned or replaced particularly simply. For this purpose, one or more cleaning openings are provided in the side wall  56  of the protective housing  12  of one or more cleaning openings  60  (see  FIG. 7 ). The cleaning openings  60  are recognizable, in particular, in the perspective view in  FIG. 7  of a variant in the version of  FIGS. 3 to 6 . Catalyst material can be drawn off through the cleaning openings  60  by means of a suction fan, for example. In contrast to the prior art, no demanding disassembly is therefore required. Access can be achieved directly to the catalyst material via the cleaning openings  60  and the side wall  56 , for example if the catalytic burner has a permanently opened access at a corresponding height and largely gas-tight sealing of the edge of the access is guaranteed with the inside of the side wall  56  of the protective housing  12 . As in the depicted variant, the catalytic burner  27  or the oblique section of the distributor  53  lying directly above it has a closable access opening  61  to the catalyst material at the level of cleaning opening  60  (cf.  FIG. 5 ). 
     To maintain circulation of the cathode gas, i.e., the mixture of cathode exhaust, anode waste gas and fresh air finely burned in the catalytic burner, return devices to return at least part of the anode waste gas and at least part of the cathode exhaust to the cathode inputs  18  and the cathode chambers of the fuel cells of stack  11  are provided. The return devices include at least one collection line  59  arranged on a longitudinal side of the fuel cell stack for collection of the return waste gases, which discharges into an inlet  62  of a feed device arranged on the front of the fuel cell stack, which includes circulation fan  20  and an electric motor  22 . The circulation fan has an outlet  63 , which communicates with the cathode gas feed devices, which supply the gas mixture to the input of the cathode chamber. 
     Collection line  59  is an essentially horizontally running collection line that extends over essentially the entire length of the fuel cell stack  11  in the foot area of the fuel cell stack  11 . Numerous baffles  64  are arranged in the collection line  59 , which deflect the vertical gas stream coming from the gas mixer  25  and catalytic burner  27  into a horizontal gas stream along the longitudinal axis of collection line  59 . The baffles  64  are designed as bent sheets and are arranged offset relative to each other in the horizontal and vertical direction so that uniform horizontal flow without additional swirling is generated. The baffles are preferably arranged on a space diagonal that runs from the lower end of the horizontal section of the collection line  59  away from the inlet  62  of the circulation fan  20  to the upper end of the horizontal section of collection line  59  directed toward the inlet  62 . Baffles  65  are again arranged on the end of the horizontal section of collection line  59 , which divert the gas stream upward into an essentially vertical line section  66  to the inlet  62  of circulation fan  20 . At the outlet  63  of the circulation fan  20  the gas distributor  67  is connected, which extends essentially over the entire length of the fuel cell stack in the head area of the fuel cell stack. The gas distributor  67  has lateral outlet opening  68  arranged parallel to its longitudinal axis, through the gas mixture can flow into a heating device  28  serving as start heater arranged after the outlet openings of the gas distributor. As is apparent especially in  FIG. 6 , the cross-sectional surface oriented perpendicular to the longitudinal axis of the internal space of gas distributor  67  tapers from its end arranged at the outlet  63  of the circulation fan  20  to its opposite end so that the amount of gas emerging laterally from the outlet opening  68  is essentially constant over the entire length of the gas distributor  67 . The start heater  28  arranged after the gas distributor  67  during startup of the fuel cell arrangement  10  heats the circulating gas mixture to the operating temperature. The already mentioned heat exchanger  14  is connected directly to the start heater  28 , in which the circulating cathode gas is brought into thermal contact with the fuel gas introduced to the protective housing  12 . After flowing through the heat exchanger  14 , the circulating cathode gas flows freely through the internal space  69  of the protective housing  12  back to the input  18  of the fuel cell stack  11  on the cathode side. 
     The variant of the fuel cell arrangement according to the disclosure depicted in  FIG. 7  differs from the variant depicted in  FIGS. 3 to 6  only in that in the variant according to  FIG. 7  the fuel cell line  13  discharges linearly at the level of the heat exchanger  14  (see  FIG. 6 ) into the protective housing  12 , whereas the fuel cell line  13  in the variant of  FIGS. 4-6  discharges into the protective housing beneath the fresh air line  26  and, as is especially apparent in  FIG. 5 , is deflected upward in the direction of the heat exchanger  14  within the protective housing. 
     As can be deduced in the variants depicted in the figures, the fuel cell arrangement according to the disclosure favors a modular design from largely independent assemblies that communicate with each other via standardized interfaces. 
     In a fuel cell arrangement according to the disclosure a first assembly includes the fuel cell stack  11  with the fuel gas feed devices, especially the fuel gas line  13  and the fresh air feed line, and the anode gas withdrawal devices, especially the anode waste gas collector  37 . The anode gas collector  37  is tightened by means of a clamping device  70  in the housing with the fuel cell stack and the fuel gas distributor  16  arranged at the anode input. 
     The second assembly includes the cathode gas feed device with cathode gas distributor  67 , start heater  28  and heat exchanger  14 , which are mounted in an assembly frame  71  on the bottom of the cover  72  of the protective housing  12 . 
     The third assembly includes the cathode exhaust collector  38 , a cathode exhaust line  40 , a gas mixer  25  for mixing of fresh air, cathode exhaust and anode waste gases, a catalytic burner  27  and a collection line  59  of the return device. In the depicted variant the third assembly is divided into a first subassembly, which includes the cathode exhaust collector  38  and the cathode exhaust line  40 , as well as a second subassembly, which includes the gas mixer  25 , the catalytic burner  27  and the collection line  59  of the return device. 
     Finally a fourth assembly includes the feed device of the return device, which consists of a circulation fan  20  with an impeller housing and connections on the suction side (e.g., outlet  63 ), which communicate with the collection line  59  of the third assembly, and connections on the pressure side (e.g., inlet  64 ), which communicate with the cathode gas distributor  67  of the second assembly, as well as the electric motor  22  to drive the circulation fan  20 . 
     The assemblies are arranged in the interior of the gas-tight protective housing  12 , in which the protective housing has an essentially cuboid general shape. 
     A particular advantage of the arrangement according to the one embodiment of the disclosure is seen in the fact that the second and fourth assemblies can be connected beforehand to the inside walls of the protective housing before the first and third assemblies are inserted. 
     Those skilled in the art recognize the words used are words of description, and not words of limitation. Many variations and embodiments will be apparent without departing from the scope and spirit of the invention as set forth in the appended claims.