FIELD OF THE INVENTION

The present invention relates to a fuel cell device and a method of operating a fuel cell device. BACKGROUND OF THE INVENTION

Fuel cells are electrochemical devices known as a promising alternative technology for clean power generation with potentially superior performance and little pollution. A fuel cell converts chemical energy of a fuel such as hydrogen, hydrocarbons, meth- anol etc. and an oxidant such as air into electricity. Especially promising fields of ap- plication are based on the use of fuel cells for portable power systems, such as for electronic devices, in particular mobile phones and laptops, mobile metering stations for environmental monitoring purposes, auxiliary power units for mobile homes, campers, sensing devices etc.

Fuel cells are usually named by the electrolyte material, such as for example the pro- ton exchange membrane fuel cell (PEMFC) utilizing polymer electrolyte membranes conducting protons, the alkaline fuel cell (AFC) with a solution of potassium hydrox- ide or sodium hydroxide used as an electrolyte. Besides the electrolyte material, the operating temperature is another parameter used to classify the various fuel cell types. The mentioned PEMFC and AFC for example, represent low-temperature fuel cells with typical operating temperatures between ca. 50°C and 100°C for PEMFCs or between ca. 60°C and 90°C for AFCs. Fuel cells operating at higher temperatures are classified as high temperature fuel cells, such as for example the solid oxide fuel cell (SOFC) using a solid material, typi- cally a ceramic material such as zirconium oxide, as an electrolyte. SOFCs typically operate between ca. 500°C and 1000°C.. High temperature fuel cells have, amongst others, advantages of higher reaction kinetics and that a noble metal catalyst is not required, higher resistance to impurities and that they are less subject to performance degradation due to carbon monoxide poisoning. The high operation temperatures, however, require a careful design in terms of thermal management such as thermal cycling and/or thermal shielding in order to provide efficient operation of the fuel cell. An example of a solid oxide fuel cell power system is shown in US2003/0054215 Al. The SOFC power system includes a fuel cell stack, two stages of heat exchange, and a thermal enclosure. The system includes a recuperator which exchanges heat between exhaust gas, heated by oxidizing unspent gases from the fuel cell stack in a combustion chamber, and incoming oxidant to pre-heat the oxidant. The solid oxide fuel cell stack has an internal manifold which exchanges heat between incoming fuel and the pre- heated oxidant. System components are enclosed by thermal insulation. The system may also include a catalytic partial oxidation reformer to pre-heat the fuel during start up. The system can also include an air compressor, fuel storage tank, and pressure relief valve, providing a portable power system. The air compressor can be used to pressurize the incoming oxidant to the SOFC stack, and to pressurize the fuel storage tank using the pressure relief valve as a pressure regulator.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a fuel cell device and a method of operating a fuel cell device which at least partially improves the prior art and avoids at least part of the disadvantages of the prior art. According to the present invention, this object is achieved by the features of the in- dependent claims. In addition, further advantageous embodiments follow from the dependent claims and the description as well as the figures.

According to an aspect of the invention, this object is particularly achieved by a fuel cell device comprising a fuel cell stack with a plurality of high temperature fuel cells stacked along a longitudinal axis, a first stack jacket laterally encompassing the fuel cell stack and arranged to define boundaries of a first and second compartment ar- ranged as a fuel agent inlet and outlet of the fuel cell stack, and of a third and fourth compartment arranged as an oxidizing agent inlet and outlet of the fuel cell stack, wherein the compartments are arranged to provide a cross-flow of the fuel agent and the oxidizing agent through the fuel cell stack, the fuel cell device further comprising a second stack jacket laterally encompassing the first stack jacket and arranged such that a fifth compartment extending around the first stack jacket is defined between the first stack jacket and the second stack jacket, wherein the first stack jacket com- prises a lateral opening connecting the third compartment with the fifth compartment in a manner that the oxidizing agent is guided from the fifth compartment to the third compartment through the lateral opening in order to enter the fuel cell stack.

The first compartment arranged as the fuel agent inlet of the fuel cell stack may be connected to an external fuel source by a piping. In particular, the first compartment may comprise a connector for the piping. The fuel agent may comprise pure hydrogen, natural gas, in particular methane, and/or similar agents. However, the operation of the fuel cell device according to the present invention is not specifically dependent on the particular choice of the fuel agent and may be applicable with any fuel agent suitable for fuel cell power generation. The fifth compartment may be fluidically connected to a source of an oxidizing agent, such as an air blower, ventilator or fan. In particular, the fifth compartment may be connected to the source of oxidizing agent via a heat exchanger, as described in more detail further below. The oxidizing agent may comprise air, pure oxygen, and/or sim- ilar oxidants. In particular, when using air as oxidizing agent, there is usually a stoi- chiometric excess of air compared to the fuel agent. Therefore, the thermal manage- ment of the oxidizing agent is of importance for improving the efficiency in operation of the fuel cell device.

The person skilled in the art understands that not all boundaries of the first, second, third or fourth compartment have to be defined by the first stack jacket. Typically, a portion of the boundaries of the respective compartment is defined by the first stack jacket and another portion of the boundaries is defined by a face of the fuel cell stack.

By arranging the second stack jacket to encompass the first stack jacket and furnishing the first stack jacket with the lateral opening connecting the third compartment with the fifth compartment, at least the part of the oxidizing agent entering the fifth com- partment in misalignment with the lateral opening can be guided to circulate around at least a portion of the first stack jacket in order to enter the fuel cell stack via the lateral opening and the third compartment. In particular, the first stack jacket and the second stack jacket are configured such that oxidizing agent from the fifth compart- ment may enter the third compartment only through the lateral opening of the first stack jacket. A portion of the oxidizing agent entering the fifth compartment in align- ment with the lateral opening of the first stack jacket, may directly enter the fuel cell stack without circulating around the first stack jacket. However, due to the localized passageway for entering the third compartment as provided by the lateral opening, a predominant portion of the oxidizing agent entering the fifth compartment can be guided to circulate around at least a portion of the fifth compartment or the first stack jacket, respectively, before entering the third compartment through the lateral open- ing of the first stack jacket.

During operation of the fuel cell stack, general heat transport within the fuel cell de- vice may be described as follows: Heat generated by the fuel cell stack is transferred to the first stack jacket encompassing the fuel cell stack, heating up the first stack jacket; the first stack jacket in turn transfers the heat into the fifth compartment, where the heat is largely absorbed by the oxidizing agent present in the fifth com- partment. By guiding the oxidizing agent to circulate around at least a portion of the first stack jacket in order to enter the fuel cell stack, an improved heat transfer to the oxidizing agent and, preferably more uniform, heat distribution can be achieved. Thus, a fuel cell device with a novel flow guidance structure for the oxidizing agent is provided which advantageously enables pre-heating of the oxidizing agent by using the heat generated by the fuel cell stack. Advantageously, this allows to reduce or even avoid the need for separately heating the fuel cell device in order to reach and/or keep the operating temperature, improving the efficiency of the fuel cell device.

Furthermore, the structure of the fuel cell device advantageously allows the oxidizing agent to flow from an exterior of the fuel cell device to the centrally arranged fuel cell stack through compartments defined by the stack jackets surrounding the fuel cell stack. Guiding the oxidizing agent to flow in such a manner from an exterior of the fuel cell device to a centrally arranged fuel cell stack has the advantage that the avail- able space to dimension and arrange the compartments is large compared to e.g. struc- tures where the oxidizing agent is guided to flow from the interior of the fuel cell stack into the fuel cells, which limits the available space for the flow channels. The comparatively large dimensioning of the compartments provides the effect that im- pedances for the flow of the oxidizing agent can be kept small, which has the ad- vantage that small blowers with low power, such as for example a computer fan, can be used to create a sufficient flow of the oxidizing agent through the fuel cell device. In particular, the use of a compressor may be avoided, which reduces costs and sim- plifies the design of the fuel cell device. Large dimensioning and low impedance of the compartments has furthermore the advantage that heat convection can be facili- tated, which improves the pre-heating of the oxidizing agent.

The first and/or second stack jacket may be made of an alloy based on nickel and chromium, such as for example Inconel.

In some embodiments, the second stack jacket comprises a plurality of inlet apertures for the oxidizing agent, the inlet apertures for the oxidizing agent arranged at a first longitudinal end portion of the second stack jacket.

By arranging the inlet apertures for the oxidizing agent at a longitudinal end portion of the second stack jacket, the oxidizing agent can be guided to spread from the lon- gitudinal end portion along the length of the fifth compartment while being guided to circulate around at least a portion of the first stack jacket, which further improves heat transfer and heat distribution while pre-heating the oxidizing agent.

In some embodiments, the inlet apertures for the oxidizing agent are arranged to be circumferentially distributed around the fifth compartment. Circumferential distribution of the inlet apertures for the oxidizing agent allows to increase uniform distribution of the oxidizing agent entering the fifth compartment from a longitudinal end portion of the second stack jacket, such that a more uniform pre-heating of the oxidizing agent can be achieved.

In some embodiments, the second stack jacket comprises one or more inlet apertures for the oxidizing agent, oppositely arranged to the lateral opening of the first stack jacket in a manner that the oxidizing agent is guided to circulate around at least a portion, preferably half, of the circumference of the fifth compartment before enter- ing the third compartment through the lateral opening of the first stack jacket.

The one or more inlet apertures may, in some embodiments, all be arranged oppositely to the lateral opening of the first stack jacket.

By arranging the inlet aperture for the oxidizing agent oppositely to the lateral open- ing of the first stack jacket, a more directed flow of the oxidizing agent when entering the fifth compartment may be achieved. Due to the opposite arrangement and the guiding of the oxidizing agent around at least a portion of the circumference of the fifth compartment or the first stack jacket, respectively, heat transfer and heat distri- bution can be increased further.

In some embodiments, the lateral opening extends along a longitudinal length of the first stack jacket. Thus, the oxidizing agent may enter the fuel cell stack along substantially the whole length of the fuel cell stack after being pre-heated by being guided around at least a portion of the first stack jacket.

Alternatively, the lateral opening may have a smaller length in longitudinal direction than the longitudinal length of the first stack jacket, such that a portion of the first stack jacket adjacent to the lateral opening forms a barrier for the impinging oxidizing agent. The portion of the stack jacket forming a barrier may then cause a part of the impinging oxidizing agent to be deflected and to further circulate around at least a portion of the first stack jacket.

In some embodiments, the lateral opening of the first stack jacket may be arranged at a second longitudinal end portion of the first stack jacket being oppositely arranged to the first longitudinal end portion of the second stack jacket. For the second stack jacket comprising an inlet aperture at a first longitudinal end portion of the second stack jacket, the oxidizing agent may then be guided to spread along the length of the fifth compartment to the lateral opening arranged at the second longitudinal end por- tion of the first stack jacket, which improves heat transfer and distribution.

In some embodiments, the fuel cell stack has a circular cross-section perpendicular to the longitudinal axis and the first stack jacket has a polygonal profile perpendicular to the longitudinal axis.

In some embodiments, the fuel cell stack has a polygonal cross-section perpendicular to the longitudinal axis and the first stack jacket has a circular profile perpendicular to the longitudinal axis.

In some embodiments, the fuel cell stack has a polygonal cross-section perpendicular to the longitudinal axis and the first stack jacket has a polygonal profile perpendicular to the longitudinal axis.

The polygonal profile of the first stack jacket perpendicular to the longitudinal axis may be one of: rectangular, hexagonal, octagonal.

The polygonal cross-section of the fuel cell stack perpendicular to the longitudinal axis may be one of: rectangular, hexagonal, octagonal.

Especially, the polygonal profile of the first stack jacket and the polygonal cross-sec- tion of the fuel cell stack may differ from each other. In an embodiment, for example, the fuel cell stack has a rectangular cross-section whereas the first stack jacket has an octagonal profile. In a further embodiment, the fuel cell stack has a rectangular cross- section whereas the first stack jacket has a hexagonal profile. In yet a further embod- iment, the fuel cell stack has an octagonal cross-section and the first stack jacket has a rectangular profile. The person skilled in the art understands that any combination of different polygons suitable for defining first, second, third and fourth compart- ments, may be used for the profile of the first stack jacket and the cross-section of the fuel cell stack.

Especially, the second stack jacket may have a geometrically similar profile perpen- dicular to the longitudinal axis as the first stack jacket. For example, the first stack jacket may have an octagonal profile perpendicular to the longitudinal axis of the fuel cell device and the second stack jacket may have an oc- tagonal profile perpendicular to the longitudinal axis with a larger area, wherein the two octagons may have a common center.

The profiles of the first and/or second stack jackets, respectively, may have clearances, such that the profile of the respective stack jacket does not occupy all sides of a poly- gon or the whole circumference of a circle. For example, the profile of the first stack jacket perpendicular to the longitudinal axis may only occupy seven sides of an octa- gon due to the lateral opening extending along one side of the octagon. First and/or second stack jackets, respectively, with polygonal profiles have the ad- vantage that the manufacturing can be simplified. For example, stack jackets with po- lygonal profiles may be produced by bending metal sheets.

In some embodiments, the fuel cell stack has a circular cross-section perpendicular to the longitudinal axis and the first stack jacket has a circular cross-section perpendic- ular to the longitudinal axis. The first to fourth compartments may be defined by ad- ditional separating walls arranged between the fuel cell stack and the first stack jacket.

In some embodiments, the first stack jacket abuts the fuel cell stack at four or more lateral positions of the fuel cell stack between adjacent compartments of the first, sec- ond, third or fourth compartment, wherein a seal is arranged at each of the lateral positions where the fuel cell stack and the first stack jacket abut on each other, the seals being configured to fluidically separate the first and second compartment from the third and fourth compartment.

In particular, the seals serve to fluidically separate the flow paths of the fuel agent and the oxidizing agent, especially in the respective compartments before entering and after exiting the fuel cell stack.

In some embodiments, the seals comprise or are made of a felt material, such as for example silica ceramic fibers. Due to comparatively large dimensioning of the com- partments and the resulting low impedances, as described above, seals made of felt provide a sufficient sealing between the compartments and the fuel cell stack to flu- idically separate the compartments of the fuel agent from the compartments of the oxidizing agent. Using seals made of felt has the advantage of reduced costs and that resistance to wear can be increased. Furthermore, the felt material has the advantage that mismatches in thermal expansion coefficients of adjoining materials, for example of portions of the fuel cell stack and the first stack jacket, can be accommodated, de- creasing potential stress occurring in the materials involved.

In some embodiments where the fuel cell stack has a rectangular cross-section and the first stack jacket has an octagonal profile perpendicular to the longitudinal axis, the first stack jacket may abut on the four edges of the fuel cell stack with every sec- ond face of the octagonal profile, such that the first, second, third and fourth com- partment may exhibit trapezoidal, preferably isosceles trapezoidal, profiles. For fur- ther polygonal profiles of the first stack jacket and/or cross-sections of the fuel cell stack, the first, second, third and/or fourth compartments may exhibit further profiles, such as for example triangular profiles.

In some embodiments, the fuel cell device further comprises a, preferably counter- flow, heat exchanger arranged next to the fifth compartment wherein the second stack jacket abuts a wall of the heat exchanger or forms at least partially a wall of the heat exchanger, the heat exchanger comprising one or more first channels for the oxidizing agent being in fluidic communication with the fifth compartment and one or more second channels for exhaust gas, wherein at least a portion of the first and second channels are alternating!/ arranged next to each other in a manner to provide heat exchange between the exhaust gas and the oxidizing agent and to pre-heat the oxidizing agent before entering the fifth compartment.

Using hot exhaust gas of the fuel cells of the fuel cell stack, a first stage pre-heating of the oxidizing agent before entering the fifth compartment may be provided by the heat exchanger. The circulation of the oxidizing agent in the fifth compartment may then provide a second stage pre-heating of the oxidizing agent.

In some embodiments, the first and the second channels are longitudinally arranged along the longitudinal axis of the fuel cell device. In some embodiments, the first and second channels have a, preferably equilateral, triangular transverse cross-section, wherein at least a part of neighboring first and second channels have mirrored triangular cross-sections abutting each other by an edge of the respective triangular cross-section.

First and second channels of the heat exchanger with triangular cross-sections abut- ting each other in a mirrored fashion provide an improved heat exchange since the surfaces where heat is released away from the heat exchanger can be reduced com- pared to a heat exchanger structure where the channels exhibit a rectangular cross- section and are arranged in a row. Instead, heat can be exchanged between two sides of a channel and two neighboring channels while only one side of the channel is free to release the heat away from the heat exchanger.

In some embodiments, the first and second channels are arranged that a face of the triangles of the cross-sections of the one or more second channels is facing towards the fifth compartment. In particular, the tips of the triangles of the cross-sections of the one or more first channels may be oriented towards the fifth compartment. This arrangement of the channels has the advantage that the heat released away from the one or more second channels and not directed to the one or more first channels can be absorbed by the oxidizing agent in the fifth compartment. In some embodiments, the heat exchanger laterally surrounds the fifth compartment.

By arranging the heat exchanger to surround the fifth compartment, the distribution of heat across the fifth compartment can he improved. The heat exchanger does not have to completely surround the fifth compartment with first and/or second channels, but may have recesses without first and/or second channels owing to the geometry of the fifth compartment, the second stack jacket and/or the heat exchanger. However, the second stack jacket or an inner wall of the heat exchanger may continuously lat- erally surround the fifth compartment. Each of the one or more first channels may end at a first outlet aperture arranged at a first longitudinal end portion of the heat exchanger and at a first inlet aperture ar- ranged at an opposite second longitudinal end portion of the heat exchanger.

The one or more first outlet apertures of the heat exchanger may be aligned or coin- cide with the one or more inlet apertures of the second stack jacket.

The fuel cell device may comprise an oxidizing agent source configured to feed the oxidizing agent into the first channels of the heat exchanger.

In particular, the oxidizing agent source may feed the oxidizing agent into the first channels of the heat exchanger through the one or more first inlet apertures. The oxidizing agent source may be a blower, a fan, for example a computer fan, a ventilator or other similar source of oxidizing agent, for example of air.

The oxidizing agent source may be arranged at the second longitudinal end portion of the heat exchanger.

Each of the one or more second channels may end at a second outlet aperture arranged at the second longitudinal end portion of the heat exchanger and at a second inlet aperture arranged at the first longitudinal end portion of the heat exchanger. In some embodiments, the fuel cell device further comprises a gas manifold closing the compartments and the fuel cell stack at a longitudinal end portion of the compart- ments, the gas manifold comprising a first manifold channel for exhaust oxidizing agent and a second manifold channel for exhaust fuel agent, the first manifold channel being in fluidic communication with the fourth compartment and the second mani- fold channel being in fluidic communication with the second compartment.

Advantageously, the first and second manifold channels are configured to laterally spread the exhaust oxidizing agent and the exhaust fuel agent towards a combustion chamber. The gas manifold provides the advantage that exhaust oxidizing agent and exhaust fuel agent which may not have reacted within the fuel cell stack can be used to pre- heat incoming oxidizing agent. For this purpose, a mixture of exhaust oxidizing agent and exhaust fuel agent may be combusted in the combustion chamber producing hot exhaust gas which may be fed into the one or more second channels of the heat ex- changer. Laterally spreading the exhaust oxidizing agent and the exhaust fuel agent has the effect that the heat of the exhaust gas can be substantially isotropically spread, which may be especially advantageous for a heat exchanger surrounding the fifth compartment. Furthermore, exhaust oxidizing agent and exhaust fuel agent may be mixed after being laterally spread towards the combustion chamber, such that the potential ignition sites of the mixture of exhaust oxidizing agent and exhaust fuel agent may be increased. The combustion chamber may therefore be arranged to sur- round the gas manifold. In some embodiments, part of the laterally spreading flow path of the exhaust oxidizing agent and/or the exhaust fuel agent may be arranged within the combustion chamber. In some embodiments, the gas manifold comprises a ring burner circumferentially arranged around a central axis of the gas manifold and configured to brum a mixture of exhaust oxidizing agent and exhaust fuel agent.

Especially, the ring burner may be arranged adjacent to the combustion chamber. In combination with the lateral spreading of the exhaust oxidizing agent and the exhaust fuel agent, the ring burner can provide optimally arranged ignition sites for the mix- ture of exhaust oxidizing agent and exhaust fuel agent. Furthermore, the geometry and the arrangement of the ring burner provide the advantage that the exhaust gas produced by combustion can emerge in a substantially isotropic fashion from the ring burner, which may especially be advantageous for a heat exchanger surrounding the fifth compartment and comprising circumferentially arranged second inlet apertures of the one or more second channels.

In some embodiments, the first manifold channel comprises a first constriction ar- ranged such that exhaust oxidizing agent is guided through the first constriction to a first side of the ring burner and the second manifold channel comprises a second con- striction arranged such that exhaust fuel agent is guided through the second con- striction to a second side of the ring burner, wherein the ring burner comprises a plurality of, preferably circumferentially arranged, apertures at which the exhaust ox- idizing agent and the exhaust fuel agent are mixed for combusting at the ring burner and producing exhaust gas.

The ring burner may comprise a wall with a first side and a second side and apertures formed within the wall. In some embodiments, the ring burner may be shaped to have a circular or polygonal, for example rectangular, hexagonal or octagonal, profile. The ring burner may have a geometrically similar profile as the profile of the first stack jacket, the second stack jacket or as the cross-section of the fuel cell stack.

During operation of the fuel cell device, exhaust fuel agent and exhaust oxidizing agent may continuously be supplied via the gas manifold and mixed and combusted at the apertures of the ring burner.

In some embodiments, the first side of the ring burner is oriented towards the com- bustion chamber and facing away from an interior of the gas manifold, wherein the second side of the ring burner is oriented towards the interior of the gas manifold and facing away from the combustion chamber. In some embodiments, the first constriction and the second constriction are aligned on top of each other. The second constriction may be arranged below the first con- striction.

The first constriction may be arranged at the central axis of the gas manifold. Alternatively or in addition, the second constriction may be arranged at the central axis of the gas manifold.

In some embodiments, the first constriction and/or the second constriction may be arranged eccentrically with respect to the central axis of the gas manifold.

In some embodiments, the first and/or second constriction may be arranged at the central axis of the gas manifold and the second and/or first constriction may be ar- ranged eccentrically with respect to the central axis of the gas manifold.

In some embodiments, the gas manifold comprises transverse walls delimiting inlet and/or outlet compartments for the first and/or second constrictions. The transverse walls delimiting the inlet and/or outlet compartments for the first and/or second con- strictions may be configured to laterally spread the exhaust fuel agent and/or the ex- haust oxidizing agent towards the combustion chamber.

In some embodiments, the first or the second constriction is arranged at a top cover of the gas manifold. The fuel cell device may comprise a cap which covers the gas manifold and the first longitudinal end portion of the heat exchanger and forms a boundary of the combustion chamber. In particular, the combustion chamber may be delimited by the cap, the gas manifold and a cover portion of heat exchanger. The cap may comprise a transverse cover which is arranged on top of the first or second con- striction and configured to laterally spread exhaust oxidizing agent or exhaust fuel agent flowing out of the first or second constriction.

In some embodiments, the combustion chamber is arranged adjacent to the first or second side of the ring burner and comprises a plurality of exhaust apertures in fluidic communication with the second channel of the heat exchanger. In some embodiments, the exhaust apertures are aligned or coincide with the second inlet apertures of the heat exchanger. The exhaust gas may therefore exit the combus- tion chamber through the exhaust apertures and enter the one or more second chan- nels of the heat exchanger. In some embodiments, the cap comprises a flange arranged adjacent to the first longitudinal end portion of the heat exchanger and comprising the plurality of exhaust apertures. The flange may be oppositely arranged to the trans- verse cover of the cap. In some embodiments, a cover flange of the heat exchanger forms a lower closure of the combustion chamber with the plurality of second inlet apertures of the heat exchanger forming the plurality of exhaust apertures of the com- bustion chamber. Preferably, the high temperature fuel cells are solid oxide fuel cells (SOFCs). In some embodiments, the fuel cell device comprises a reformer, e.g. a catalytic partial oxidation or a thermal partial oxidation reformer, for the fuel agent.

In some embodiments, the fuel cell stack, the first stack jacket and the second stack jacket are arranged concentrically. According to a further aspect, the present invention is also directed to a method of operating a fuel cell device, comprising the steps of: providing a fuel cell device ac- cording to the present invention; supplying a fuel agent to a first compartment of the fuel cell device; supplying an oxidizing agent to a third compartment of the fuel cell device by guiding the oxidizing agent from a fifth compartment of the fuel cell device to the third compartment through a lateral opening of a first stack jacket of the fuel cell device laterally encompassing a fuel cell stack of the fuel cell device; guiding the oxidizing agent from the third compartment and the fuel agent from the first com- partment in a cross-flow through the fuel cell stack such that exhaust oxidizing agent from the fuel cell stack enters a fourth compartment of the fuel cell device and exhaust fuel agent from the fuel cell stack enters a second compartment of the fuel cell device; combusting a mixture of exhaust fuel agent and exhaust oxidizing agent in a combus- tion chamber of the fuel cell device to produce exhaust gas; guiding the exhaust gas through a heat exchanger such that the exhaust gas exchanges heat with the oxidizing agent which flows through the heat exchanger before entering the fifth compartment. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained in more detail, by way of exemplary embod- iments, with reference to the schematic drawings, in which:

Fig. 1 shows an exploded perspective view of an embodiment of a fuel cell de- vice;

Fig. 2 shows a perspective view of the fuel cell device of Figure 1;

Fig. 3 shows a perspective view of the fuel cell device of Figure 2 with removed cap;

Fig. 4 shows a perspective view of the fuel cell device of Figure 3 with removed first plate of the gas manifold;

Fig. 5 shows a perspective view of the fuel cell device of Figure 4 with removed gas manifold;

Fig. 6 shows a perspective view of the fuel cell device of Figure 5 with removed heat exchanger; Fig. 7 shows a cut view of the fuel cell device of Figure 2;

Fig. 8 shows a further cut view of the fuel cell device of Figure 2; Fig. 9 shows a further cut view of the fuel cell device of Figure 2;

Fig. 10 shows a cut view of a further embodiment of a fuel cell device. DESCRIPTION OF EXEMPLARY EMBODIMENTS

Figure 1 shows an exploded perspective view of an embodiment of a fuel cell de- vice 100. The fuel cell device 100 comprises a fuel cell stack 1 with a plurality of high temperature fuel cells 11, which are stacked along a longitudinal axis A coinciding with the central axis of the fuel cell device 100. in the shown embodiment, the high temperature fuel cells 11 are solid oxide fuel cells (SOFCs). The fuel cell stack 1 has a rectangular cross section perpendicular to the longitudinal axis A and, accordingly, exhibits four lateral faces across which the flow paths of a fuel agent and of an oxidiz- ing agent may be provided in a cross-flow configuration. At the four edges of the fuel cell stack 1, there are arranged four elongate 12 seals configured to seal the positions where the edges of the fuel cell stack 1 abut on the first stack jacket 2. As a fuel agent, methane is used. It is, however, also possible to use pure hydrogen, natural gas and/or similar agents as a fuel agent. The fuel cell stack 1 further comprises a sealing plate 13 arranged at a top of the fuel cell stack 1. In some embodiments, the sealing plate 13 may comprise electronic components, such as for example a current collector of the fuel cell stack 1.

The fuel cell device 100 further comprises a first stack jacket 2 with an octagonal pro- file perpendicular to the longitudinal axis A and laterally encompassing the fuel cell stack 1. It can be recognized from Figure 1 that “lateral” is understood with respect to the longitudinal axis A. The first stack jacket 2 abuts the four edges of the fuel cell stack 1 with every second face of the octagonal profile at the positions of the four elongate seals 12. The first stack jacket 2 is arranged to define boundaries of a first and second compartment arranged as a fuel agent inlet and outlet of the fuel cell stack 1, and of a third and fourth compartment arranged as an oxidizing agent inlet and outlet of the fuel cell stack 1, as will be presented by the further Figures in more detail. The seals 12 are made of a felt material and are arranged between the four lateral edges of the fuel cell stack 1 and the respective faces of the first stack jacket 2 in order to flu- idically separate the compartments of the fuel agent from the compartments of the oxidizing agent. In some embodiments, the seals 12 may comprise or be made of a plastic material. In some embodiments, the seals 12 may comprise a rigid core at least partially covered with a soft sealing material, such as a felt. The person skilled in the art understands that fluidic separation in this context is meant as a fluidic separation of fuel agent and oxidizing agent except potential ionic exchange across electrolytes within the fuel cells. The first stack jacket 2 comprises a lateral opening 21 in the form of a clearance which extends over a face of the octagonal profile of the first stack jacket 2. Therefore, the profile of the first stack jacket 2 perpendicular to the longitu- dinal axis A only occupies seven faces of an octagon due to the lateral opening 21 extending along one face of the octagon.

The fuel cell device 100 further comprises a second stack jacket 3 forming an inner wall 43 of a heat exchanger 4. The heat exchanger 4 surrounds the first stack jacket 2 such that a fifth compartment is defined between the first stack jacket 2 and the sec- ond stack jacket 3. The heat exchanger 4 operates in a counterflow fashion comprising a plurality of first channels for the oxidizing agent and a plurality of second channels for exhaust gas, wherein the oxidizing agent and the exhaust gas are flowing in oppo- site directions through the heat exchanger 4. At least a portion of the first channels and the second channels are alternatingly arranged next to each in a manner that heat exchange between the exhaust gas and the oxidizing agent is provided in order to pre- heat the oxidizing agent before entering the fifth compartment. The first and second channels are longitudinally arranged parallel to the longitudinal axis A. The heat ex- changer 4 comprises eight channel components 44 arranged at the faces of the octag- onal profile of the heat exchanger 4, Each channel component 44 comprises three first channels for the oxidizing agent and two second channels for the exhaust gas which are alternatingly arranged next to each other within a channel component 44. Be- tween neighboring channel components 44, the heat exchanger 4 comprises recesses 45 where no first and/or second channel is arranged. However, the inner wall 43 or the second stack jacket 3, respectively, is surrounding the first stack jacket 2 in a con- tinuous fashion.

The first channels end at first outlet apertures 41.1 for the oxidizing agent arranged at a first longitudinal end portion of the heat exchanger 4 and at first inlet apertures for the oxidizing agent arranged at an opposite second longitudinal end portion (not vis- ible in Figure 1) of the heat exchanger 4. The first outlet apertures 41.1 of the heat exchanger 4 form inlet apertures 31 of the second stack jacket 3. The second channels end at second inlet apertures 42.1 for the exhaust gas arranged at the first longitudinal end portion of the heat exchanger 4 and at second outlet apertures 42.2 for the exhaust gas arranged at the second longitudinal end portion of the heat exchanger 4.

The fuel cell device 100 further comprises a blower 51 acting as a source of oxidizing agent such as, for the shown example, air. The blower 51 is arranged at the second longitudinal end portion of the heat exchanger 4, and mounted on a blower plate 54 which supports the heat exchanger 4. The blower plate 54 comprises a central opening 541 through which the oxidizing agent is blown from the blower 51 into the first inlet apertures of the heat exchanger 4. Further, a piping 52 connecting the first compart- ment arranged as the fuel agent inlet of the fuel cell stack 1 to an external fuel source is fed through an aperture of the blower plate 54. The piping 52 is further fed through an aperture of a base plate 53 supporting the fuel cell stack 1 and the first stack jacket 2. The base plate 53 is configured to fit into the inner space of the heat exchanger 4 by abutting the inner wall 43 of the heat exchanger 4.

The fuel cell device 100 further comprises a gas manifold 6 closing the compartments and the fuel cell stack 1 at a longitudinal end portion of the compartments or the fuel cell stack 1, respectively. The gas manifold 6 comprises a first manifold channel for exhaust oxidizing agent and a second manifold channel for exhaust fuel agent, as will be shown in further Figures of the present application. The gas manifold 6 comprises a first plate 64 forming a top cover of the gas manifold 6 and comprising an eccentri- cally arranged opening 613 and a second plate 65 forming a lower cover of the gas manifold 6. The second plate 65 comprises a centrally arranged opening 621 and an eccentrically arranged opening 612. The eccentrically arranged opening 612 of the second plate 65, the eccentrically arranged opening 613 of the first plate 64, and a hollow cylindrical connector 66 connecting the eccentric openings 612 and 613, form a first constriction of the first manifold channel. The central opening 621 of the sec- ond plate 65 forms a second constriction of the second manifold channel. The gas manifold 6 further comprises a ring burner 63 circumferentially arranged around a central axis of the gas manifold 6 which coincides with the longitudinal axis A. The ring burner 63 is arranged between the first plate 64 and the second plate 65. The ring burner 63 has an octagonal profile and comprises a plurality of circumferentially ar~ ranged apertures 631 formed in a wall of the ring burner 63 and configured to act as ignition sites for the mixture of exhaust oxidizing agent and exhaust fuel agent. The central opening 621 of the second plate 65 is arranged such that the exhaust fuel agent is guided therethrough to a second, inner side of the ring burner 63. The eccentrically arranged openings 612 and 613 and the cylindrical connector 66 are arranged such that the exhaust oxidizing agent is guided therethrough to a first, outer side of the ring burner 63. The exhaust fuel agent and the exhaust oxidizing agent are mixed at the apertures 631 for combusting at the ring burner 63 and producing exhaust gas. The fuel cell device 100 further comprises a cap 7.1 covering the gas manifold 6 and con- figured to laterally spread exhaust oxidizing agent flowing out of the eccentric open- ing 613. The cap 7.1 comprises a side wall with an octagonal profile and a transverse cover. The person skilled in the art understands that the role of the exhaust fuel agent and the exhaust oxidizing agent may be interchanged with respect to the first and second manifold channels.

Figure 2 shows a perspective view of the fuel cell device 100 of Figure 1 in an assem- bled state. The cap 7.1, heat exchanger 4, the blower plate 54 and the blower 51 are visible in the shown configuration. Furthermore, the second outlet apertures 42.2 for the exhaust gas arranged at the second longitudinal end portion of the heat exchanger 4 can be recognized. The exhaust gas escapes from the fuel cell device 100 through the second outlet apertures 42.2. The fuel cell device 100 may comprise, in some em- bodiments, an additional outer housing (not shown in Figure 2) which may encompass the heat exchanger 4 and optionally the blower 51. In particular, the outer housing may be thermally insulating.

Figure 3 shows a perspective view of the fuel cell device 100 of Figure 2 with removed cap such that the interior of the combustion chamber delimited by the cap, the gas manifold 6 and a cover flange 46 of the heat exchanger 4 is laid open. The cover flange 46 of the heat exchanger 4 forms a lower closure of the combustion chamber with the plurality of second inlet apertures 42.1 of the heat exchanger 4 forming the plurality of exhaust apertures of the combustion chamber. Exhaust oxidizing agent flows out of the gas manifold 6 through the eccentric opening 613 of the first plate 64 and into the combustion chamber towards the outer, first side of the ring burner 63. At the aper- tures 631 of the ring burner 63, the exhaust oxidizing agent is mixed with the fuel agent flowing out of the gas manifold from the inner, second side of the ring burner 63 through the apertures 631 of the ring burner 63. The mixture of the exhaust oxi- dizing agent and the exhaust fuel agent is combusted in the combustion chamber pro- ducing hot exhaust gas. The exhaust gas then flows into the plurality of second chan- nels of the heat exchanger 4 through the second inlet apertures 42.1. The ignition of the mixture of exhaust oxidizing agent and exhaust fuel agent is performed by a piezo igniter arranged within the combustion chamber.

Figure 4 shows a perspective view of the fuel cell device 100 of Figure 3 with removed first plate of the gas manifold 6, such that the central opening 621 and the eccentric opening 612 of the second plate 65 are visible. The hollow, cylindrical connector 66 connecting the eccentric opening 612 with the eccentric opening of the first plate for forming the first constriction is also visible. In some embodiments, the cylindrical connector 66 may he formed integrally with the first and/or second plate of the gas manifold 6. Exhaust fuel agent flowing out of the central opening 621 is guided along the surface of the second plate 65 towards the inner, second side 63.2 of the ring burner 63 until reaching the apertures 631 of the ring burner 63. As already described, exhaust oxidizing agent flows from the eccentric opening of the first plate of the gas manifold via the combustion chamber towards the outer, first side 63.1 of the ring burner 63 until reaching the apertures 631.

Figure 5 shows a perspective view of the fuel cell device 100 of Figure 4 with removed gas manifold. It can be recognized that the first stack jacket 2 laterally encompasses the fuel cell stack 1 in a manner to define boundaries of a first compartment 10 ar- ranged as a fuel agent inlet and of a second compartment 20 arranged as a fuel agent outlet of the fuel cell stack 1, and of a third compartment 30 arranged as an oxidizing agent inlet and of a fourth compartment 40 arranged as an oxidizing agent outlet of the fuel cell stack 1. The compartments 10, 20 and 30, 40 are therefore arranged to provide a cross-flow of the fuel agent and the oxidizing agent through the fuel cell stack 1. The third compartment 30 is fluidically connected to a fifth compartment 50 via the lateral opening 21 of the first stack jacket 2, the fifth compartment 50 being defined between the first stack jacket 2 and the second stack jacket 3, which at least partially forms an inner wall 43 of the heat exchanger 4. The inner wall 43 of the heat exchanger 4 comprises first outlet apertures 41.1 arranged at the first longitudinal end portion of the heat exchanger 4, which first outlet apertures 41.1 simultaneously form inlet, apertures 31 of the second stack jacket 3. Oxidizing agent flowing into the fifth compartment 50 via the inlet apertures 31 can enter the third compartment 30 only via the lateral opening 21 of the first stack jacket 2. Therefore, oxidizing agent flowing into the fifth compartment 50 via inlet apertures 31 not directly facing the lateral opening 21 is guided to circulate around at least a portion of the first stack jacket 2 and in doing so, absorbing heat released by the fuel cell stack 1. Next to the first channels of the heat exchanger 4, which end at the first outlet apertures 41.1, there are arranged second channels 42 for the exhaust gas which end at second inlet aper- tures 42.1 arranged at the first longitudinal end portion of the heat exchanger 4. On top of the fuel cell stack 1, the sealing plate 13 is arranged, which is configured to seal the space between the top of the fuel cell stack 1 and the bottom of the gas manifold. In particular, the sealing plate 13 seals possible passages between first and second manifold channel of the gas manifold, which may arise in the space between the top of fuel cell stack 1 and the bottom of the gas manifold. Figure 6 shows a perspective view of the fuel cell device 100 of Figure 5 with removed heat exchanger. The first stack jacket 2 with the octagonal profile is arranged around the fuel cell stack 1 with the rectangular cross-section in a manner that the four edges of the fuel cell stack 1 abut on every second face of the octagonal profile of the first stack jacket 2. Due to this arrangement, the first compartment 10, second compart- ment 20, third compartment 30 and the fourth compartment 40 exhibit isosceles trap- ezoidal profiles perpendicular to the longitudinal axis of the fuel cell device. The lat- eral opening 21 extends along the longitudinal length of the first stack jacket 2 at a face of the octagonal profile such that the profile of the first stack jacket 2 only occu- pies seven sides of an octagon. Accordingly, the trapezoidal profile of the third com- partment 30 exhibits a cleared face along the short base of the trapezoidal profile. The arrangement of the first stack jacket 2 and the fuel cell stack 1 provides fluidic sepa- ration of the first compartment 10 and the second compartment 20 from the third compartment 30 and the fourth compartment 40. Therefore, the flow paths of fuel agent and oxidizing agent in the respective compartments are fluidically separated before entering the fuel cell stack 1 and the flow paths of exhaust fuel agent and ex- haust oxidizing agent in the respective compartments are fluidically separated after exiting the fuel cell stack 1.

Figure 7 shows a cut view of the fuel cell device 100 taken along a plane as indicated by Cl in Figure 1. The plane is defined by the axis A and the dashed line Cl. The viewing direction is indicated by the two dashed arrows at the ends of the dashed line Cl . The flow of the oxidizing agent, for example air, and of the exhaust gas is indicated by arrows with hollow tips. Oxidizing agent from a blower 51 flows into first channels 41 of the heat exchanger 4 through first inlet apertures 41.2 arranged at the second longitudinal end portion of the heat exchanger 4, as indicated by the arrows AF1. At the first longitudinal end portion of the heat exchanger 4, the first channels 41 end at first outlet apertures 41.1, which form the inlet apertures 31 of the second stack j acket 3. The second stack jacket 3 at least partially forms an inner wall 43 of the heat ex- changer 4. The oxidizing agent flows along the first channels 41, as indicated by the arrows AF2.1 and AF2.2, until entering the fifth compartment 50 via the first outlet apertures 41.1 or the inlet apertures 31, respectively. The fifth compartment 50 is de- fined between the second stack jacket 3 and the first stack jacket 2, and delimited by the base plate 53 and the gas manifold 6. Oxidizing agent which enters the fifth com- partment 50 through inlet apertures 31 facing the lateral opening 21 of the first stack jacket 2 may directly enter the third compartment 30 without substantial circulation, as indicated by the arrow AF2.1. In contrast, oxidizing agent which enters the fifth compartment 50 through inlet apertures 31 not directly facing the lateral opening 21, is guided to circulate around at least a portion of the first stack jacket 2 through the fifth compartment 50 before reaching the lateral opening 21 and entering the third compartment 30, as indicated by the arrows AF2.2, AF3.1 and AF3.2. The arrows AF2.2, AF3.1 and AF3.2 show an example where the oxidizing agent is guided to cir- culate around half of the circumference of the first stack jacket 2 before entering the third compartment 30 via the lateral opening 21. The third compartment 30 is ar- ranged as an oxidizing agent inlet from which the oxidizing agent flows through the fuel cell stack 1, as indicated by the arrow AF4. Exhaust oxidizing agent flowing out of the fuel cell stack 1, enters the fourth compartment 40, which is thus arranged as an oxidizing agent outlet of the fuel cell stack 1. The exhaust oxidizing agent flows from the fourth compartment 40 through the first manifold channel 61 of the gas manifold 6, as indicated by the arrow AF5. The exhaust oxidizing agent flows out of the gas manifold 6 via the eccentric opening 613 and enters the combustion chamber 7.2. A transverse cover portion of the cap 7.1 arranged on top of the eccentric opening

613 has the effect that the exhaust oxidizing agent flowing out of the eccentric open- ing 613 is guided to laterally spread within the combustion chamber 7.2 until reaching an outer, first side of the ring burner 63, as indicated by the arrows AF6.1. A piezo igniter 7.3 is arranged in the combustion chamber 7.2 and is configured to ignite the mixture of exhaust oxidizing agent and exhaust fuel agent, which flows through the second manifold channel 62, at the apertures 631 of the ring burner 63, as indicated by the stars F. The mixture of exhaust oxidizing agent and exhaust fuel agent is com- busted in the combustion chamber 7.2 to produce hot exhaust gas, which flows out of the combustion chamber 7.2 through the second inlet apertures 42.1 of the heat ex- changer 4, forming exhaust apertures of the combustion chamber 7,2, as indicated by the arrows EF1. The hot exhaust gas flowing out of the combustion chamber 7.2 through the second inlet apertures 42.1, flows through the second channels of the heat exchanger 4 and transfers heat to oxidizing agent flowing through neighboring first channels 41 before leaving the heat exchanger 4 via the second outlet apertures (not visible in Figure 7). Figure 8 shows a further cut view of the fuel cell device 100 taken along a plane as indicated by C2 in Figure 1. The plane is defined by the axis A and the dashed line C2. The viewing direction is indicated by the two dashed arrows at the ends of the dashed line C2. The fuel agent, for example methane, enters the first compartment 10 through a piping 52, as indicated by the arrow FF1. The piping 52 fluidically connects the first compartment 10 with a fuel source (not shown in Figure 8) and reaches into the first compartment 10. The first compartment 10 is thus arranged as a fuel agent inlet of the fuel cell stack 1 from which the fuel agent is flows through the fuel cell stack 1, as indicated by the arrow FF2. Exhaust fuel agent flowing out of the fuel cell stack 1 enters the second compartment 20, which is thus arranged as a fuel agent outlet of the fuel cell stack 1. From the second compartment 20, the exhaust fuel agent flows into the second manifold channel 62 of the gas manifold 6, as indicated by the arrow FF3. The second manifold channel 62 comprises a second constriction which is formed by the central opening 621. The exhaust fuel agent flows out of the central opening 621 into an outlet compartment 622 of the second constriction in which the exhaust fuel agent is laterally spread towards the inner, second side of the ring burner 63, as indi- cated by the arrows FF4, The ignition of the mixture of the exhaust fuel agent and exhaust oxidizing agent at the apertures of the ring burner 63 is again symbolized by the star F.

Figure 9 shows a further cut view of the fuel cell device 100 of Figure 2, taken along a plane, as indicated by the dashed line C3 in Figure 2. The viewing direction is indi- cated by the two dashed arrows at the ends of the dashed line C3. The fuel agent enters the first compartment 10 arranged as the fuel agent inlet through the piping 52 and flows through the fuel cell stack 1 such that exhaust fuel agent reaches the second compartment 20 arranged as the fuel agent outlet of the fuel cell stack 1 , as indicated by the arrow FF5. The arrows AF7 indicate the circulation of the oxidizing agent within the fifth compartment 50 defined between the first stack jacket 2 and the sec- ond stack jacket 3 (or the inner wall 43, respectively). The shown arrows AF7 indicate for example a flow path where the oxidizing agent enters the fifth compartment 50 through inlet apertures of the second stack jacket 3 arranged opposite to the lateral opening 21. As indicated by the two arrows AF8, the oxidizing agent enters the third compartment 30 via the lateral opening 21 after being circulated around at least a portion of the first stack jacket 2. From the third compartment 30, arranged as an oxidizing agent inlet, the oxidizing agent flows through the fuel stack 1 such that exhaust oxidizing agent reaches the fourth compartment 40. The heat exchanger 4 comprises eight channel components 44, wherein each channel component 44 com- prises three first channels 41 and two second channels 42 alternatingly arranged next to each other. Due to the octagonal profile of the heat exchanger 4, recesses 45 are arranged between neighboring channel components 44. In some embodiments, the recesses 45 may be occupied by additional first and/or second channels of the heat exchanger.

Figure 10 shows a cut view of a further embodiment of a fuel cell device 100’, similar to the cut view of the embodiment shown in Figure 9. As compared to the embodi- ment shown in Figure 9, the first stack jacket 2’ of the fuel cell device 100’ encom- passing the fuel cell stack 1' exhibits a hexagonal profile. Due to the hexagonal profile, the first compartment 10’ and the second compartment 20’ exhibit triangular profiles perpendicular to the longitudinal axis, whereas the third compartment 30’ and the fourth compartment 40’ exhibit trapezoidal profiles perpendicular to the longitudinal axis of the fuel cell device 100’. Each of the four lateral edges of the fuel cell stack 1’ abut a face of the hexagonal profile of the first stack jacket 2’. Seals (not visible in Figure 10) are arranged between each lateral edge of the fuel cell stack 1' and the respective abutting face of the first stack jacket 2’ in a manner to fluidically separate neighboring compartments of the first, second, third and fourth compartments 10’, 20’, 30’, 40’ from each other. For example, the seals serve to fluidically separate the first compartment 10’ from the third compartment 30’ and the fourth compartment 40’. Similarly, the seals serve to fluidically separate the second compartment 20’ from the third compartment 30’ and the fourth compartment 40’. The first stack jacket 2’ comprises a lateral opening 2G which extends over a face of the hexagonal profile of the first stack jacket 2’, such that the profile of the first stack jacket 2’ only occupies only five sides of a hexagon. Accordingly, the trapezoidal profile of the third compart- ment 30’ exhibits a cleared face along the short base of the trapezoidal profile.

Similar to Figure 9, the flow paths of the oxidizing agent are indicated by the arrows AF7, AF8 with hollow tips and the flow path of the fuel agent is indicated by the arrow FF5 with filled tip. The heat exchanger 4’ surrounding the fifth compartment 50’ also exhibits a hexagonal profile. The second stack jacket 3’ is formed by an inner wall 43’ of the heat exchanger 4’ and exhibits a hexagonal profile, geometrically sim- ilar to the first stack jacket 2’. The heat exchanger 4’ comprises first channels 4G and second channels 42’ with equilateral triangular cross-sections. The triangular cross- sections of neighboring first channels 4G and second channels 42’ are mirrored and abut each other by an edge of the respective triangular cross-section. It can be recog- nized that the triangular cross-sections of the first channels 4G and the second chan- nels 42’ provide an improved packing structure. For example, recesses between neigh- boring channel components, as shown in Figure 9, can he avoided, which improves the efficiency of heat exchange. Furthermore, heat can be exchanged between two sides of a channel and two neighboring channels and only one side of the channel is free to release heat away from the heat exchanger 4’. The second channels 42’ are each arranged such that a base of the triangular cross-sections of the second channels 42’ is facing towards the fifth compartment 50’ and a tip of the triangular cross-sections is oriented towards the outside of the fuel cell device 100’. At the faces of the hexagonal profile, first channels 4G and second channels 42’ are alternatingly arranged, whereas at the corners of the hexagonal profile, two first channels 41' are arranged next to each other, owing to the hexagonal profile of the heat exchanger 4’.

The fuel cell device 100, 100’ is particularly advantageous for portable applications, especially for power ranges in the order of ca. 100 W, as the improved and integrated structures for thermal management allow to realize an efficient, compact and com- paratively cheap fuel cell device.

LIST OF DESIGNATIONS