NO322669B1 - A high temperature fuel cell system and method for operating it - Google Patents

Abstract

The invention concerns a method of operating a high-temperature fuel cell system (2) comprising a high-temperature fuel cell module (4) with an anode part (20) and a cathode part (22). The fuel gas necessary for the electrochemical reaction is generated by a gas reforming process, more hydrogen (H2) being generated than is consumed during the electrochemical reaction in the high-temperature fuel cell module (4). The hydrogen (H2) not consumed in the high-temperature fuel cell module (4) is made available for further use outside the high-temperature fuel cell module (4). Owing to this measure, the efficiency of the high-temperature fuel cell system (2) is optimized.

Description

The invention relates to a method for operating a high-temperature fuel cell plant and a high-temperature fuel cell plant.

To operate a high-temperature fuel cell plant, a carbon-hydrogen-containing fuel is used, such as natural gas, heating oil, naphtha or biogas. As a rule, these fuel types must be processed or regenerated in a suitable manner, i.e. be reformed, for the operation of the high-temperature fuel cells assembled into high-temperature fuel cell modules.

The carbon-hydrogen-containing fuel thereby undergoes a reformation process after moistening, whereby the reformation products CO, H2, CO2 and H2O in gaseous form occur, before the electrochemical reaction in the high-temperature fuel cell module. The gaseous reformation products, also referred to as reformate, further form the suitable fuel gas for the operation of the high-temperature fuel cell modules.

The reforming process can be external or internal, i.e. outside or inside the high-temperature fuel cell modules, with or without utilization of the heat content of an anode exhaust gas in the high-temperature fuel cell modules.

An internal reforming is known, for example, from the article "Verfahrenstechnik der Hochtemperaturbrennstoffzelle" by E. Riensche, VDI-Berichte 1174 (1995) pages 63-78, where the waste heat with a high heat content, which arises from the electrochemical combustion in the high-temperature fuel cell module, is used to the internal reforming of the fuel gases. If the reforming in the high-temperature fuel cell module takes place outside an anode part, this is termed indirect internal reforming. A reforming in the anode part is, in contrast, called direct internal reforming.

The well-known external reformer for an external reforming process, see especially the article "Erzeugung und Konditionerung von Gasen, fur den Einsatz in Brennstoffzellen", by K.H. van Heek, VDI-Berichte 1174 (1995), pages 97-116, is designed and constructed in such a way that the right amount of fuel gas is reformed, and is used for conversion in the high-temperature module fuel cell for the electrochemical combustion. This provision also applies to direct as well as indirect internal reformation.

Further fuel cell systems, which always consist of at least one fuel cell stack composed of individual cells, i.e. have a modular structure, and exhibit an anode and cathode part, whereby the fuel gas required for the electrochemical reaction is produced by means of a reforming process, are known from the German generally available publications 43 30 623 and 40 32 652, as well as the European patent application 0 430 017.

The high-temperature fuel cell systems known from the state of the art are consequently designed for an optimally high fuel gas utilization in the electrochemical reaction. The reformed fuel gas is therefore exclusively used for the purpose of utilization inside the high-temperature fuel cell plant.

With this design, there is a concentration drop in the fuel gas over the entire active surface for the electrochemical reaction inside the high-temperature fuel cell modules. This depletion or reduction of fuel gas over the active surface can amount to up to 80-90% at the output of the high-temperature fuel cell module. As a result of this reduction, a diffusion inhibition occurs inside the electrolyte of the high-temperature fuel cell modules, which in turn leads to a significant loss of the power density or in the vision of the high-temperature fuel cell modules.

The invention consequently aims to provide a method for operating or for operating a high-temperature fuel cell plant whereby the efficiency of the plant is optimised. In addition, a high-temperature fuel cell plant for carrying out the method is described.

The first-mentioned task is solved according to the invention by means of a method for operating a high-temperature fuel cell plant, in which heat content from the electrochemical reaction in the high-temperature fuel cell module by means of a reforming process of fuel gas is essentially used for the formation of the electrochemical reaction necessary hydrogen, as well as for additional hydrogen that is intended for utilization outside the high-temperature fuel cell module, the cells in the high-temperature fuel cell module each being operated with a cell voltage of less than 0.8 volts.

According to the invention, the second task is solved by means of a high-temperature fuel cell plant which comprises at least one high-temperature fuel cell module with an anode part, a cathode part, a reformer for reforming the fuel gas for the electrochemical reaction and a hydrogen separation device in a removal path in the anode part , which is arranged for the separation of hydrogen from the anode gas, where means are arranged for conducting essentially all the heat generated in the high-temperature fuel cell module to the reformer and that the reformer is dimensioned for the formation of more hydrogen than is used for the electrochemical the reaction.

Excess hydrogen H2 directly formed during reforming is, with the help of this storage, supplied, for example, to additional mobile or stationary plants that need hydrogen H2 for operation. Furthermore, hydrogen H2 can be fed directly to the user without the use of an additional storage. For the consumer, it can for example be about all possible applications in different branches of industry, for example in the chemical industry where hydrogen H2 is used. As the high-temperature fuel cell plant includes the storage or the consumer when dimensioning the efficiency, the efficiency, i.e. in other words the efficiency of the entire high-temperature fuel cell plant, is thus improved.

Moreover, at the same time, the power density of the high-temperature fuel cell modules is optimized, since due to the high concentration of the fuel gas over the entire active surface of the high-temperature fuel cell module, the electrical power density is higher than with the high-temperature fuel cell systems known from the state of the art, which are dimensioned for a high fuel gas utilization in the high temperature fuel cell module. With the known high-temperature fuel cell plants, due to the reduction of the fuel gases, which in a side path to the anode part can amount to between 80% and 90%, there is a diffusion inhibition which can lead to a significant performance reduction.

Moreover, in the method according to the invention, the high-temperature fuel cell module need not be designed with a high cell efficiency. It can instead, under circumstances of clearly lower cell voltage and thereby a significantly increased power density, be chosen as a high-temperature fuel cell plant optimized in terms of power generation, and instead have 0.5-0.7 V cell voltage instead of 0.8 V cell voltage. Due to both of these effects, a given electrical performance is also required with less active surface area than with the known high-temperature fuel cell plants. the increased waste heat resulting from the reduced electrical efficiency due to the lower cell voltage can then essentially be used for additional reforming in the present method. With the help of these measures, cooling of the high-temperature fuel cell modules, which with the known devices must be carried out with up to 10 times more excess air, can be reduced. The air flow is limited to the necessary amount for the electrochemical reaction in the high-temperature fuel cell module. Air flow, air heat exchange and air ducts can be dimensioned significantly smaller, whereby the need for equipment is reduced and additional costs are saved.

Preferably, at least 30% of the fuel gas effect is used to produce the unconsumed hydrogen H2. In particular, the heat content from the electrochemical combustion is supplied directly to the reformer without the use of external additional lines for transferring the heat content.

In a further embodiment, the fuel gas is reformed before introduction into the high-temperature fuel cell module. A reformer arranged outside the high-temperature fuel cell module is thereby heated with the heat content of an anode exhaust gas.

Preferably, for the reformation of the fuel gases for an electrochemical reaction, a reformer is arranged inside the high-temperature fuel cell module. This internal reformer is at least part of its scope in which the reforming takes place integrated in, for example, the anode part of the high-temperature fuel cell module. With these measures, an external reformer that is not arranged into the high-temperature fuel cell module is omitted.

In particular, at least one heat exchanger is arranged in the side path of the anode part for transferring the heat content of an anode exhaust gas over a side path on the inside of the high-temperature fuel cell module's arranged reformer.

In a further embodiment, a shift reactor is arranged to produce hydrogen H2. in the lateral path to the anode part. With the help of the shift reactor, additional hydrogen H2 is produced. Preferably, the shift reactor for producing hydrogen H2 is arranged between the two heat exchangers in the side path of the anode part.

In a further embodiment, at least one heat exchanger is arranged in a side path to the cathode part for releasing the heat content in a cathode exhaust gas.

Preferably, a reformer is arranged outside the high-temperature fuel cell module in a supply path for the anode part.

In particular, a side path or removal path is arranged on the reformer for the cathode part for transferring the heat content to a cathode exhaust gas.

In a further embodiment, a branch is arranged on the reformer in the side or removal path to the cathode part for transferring the heat content to a cathode exhaust gas.

Preferably, the removal path to the anode part is arranged on the external reformer for transferring the heat content to an anode exhaust gas.

For a further description of the invention, reference is made to the embodiment in the drawings.

Fig. 1 and 2 show a high-temperature fuel cell system according to the invention in a schematic position.

According to fig. 1 comprises a high temperature fuel cell plant (29 a high temperature fuel cell module (4) with a reformer (5) for reforming a fuel gas for the high temperature fuel cell module (4). the high temperature fuel cell module (4) comprises an anode (20) and a cathode part (22 ). the reformer (5) is also integrated in the anode part (20). In an embodiment not shown, the reformer (5) is located outside the anode part (20) but inside the high-temperature fuel cell module (4).

Furthermore, the high-temperature fuel cell plant (2) comprises an anode path (6), which in turn comprises a supply path (8) to the anode part (20) of the high-temperature fuel cell module (4) a side path or path away from the anode part (20) of the high-temperature fuel cell module (4) ), cathode path (12) comprising the feed path (14) to the cathode part of the high temperature fuel cell module (4) and a side path or path away (16) from the cathode part of the high temperature fuel cell module (4).

A carbon-hydrogen-containing fuel is fed via the supply path (8) to the anode path (6) and reformed in the reformer (5) of the high-temperature fuel cell module (4). The fuel gas produced by the reforming is fed into the high-temperature fuel cell module (4) and partially undergoes the electrochemical reaction.

During the reforming in the reformer (5), more fuel gas is reformed and consumed by the electrochemical reaction in the high-temperature fuel cell module (4). In total, at least 10-30% of the fuel gas effect becomes excess hydrogen H2. converted, especially at a cell voltage of less than 0.8 V. The theoretical upper limit is, for example, when reforming methane at 85-55% at a cell voltage of 0.5-0.8 V. An excess of hydrogen H2 is thereby produced. which is the road (10) to the anode road (6) to the anode part (20) is taken away and supplied to a device (70) for further use. The device (70) can be a storage or a consumer, which for example can again be a component of the overall high-temperature fuel cell plant.

In the supply path (8) a water injector (26) and a further heat exchanger (28) are arranged in order of a heat exchanger (24) in the flow direction. The carbon hydrogen-containing fuel is heated in the heat exchangers (24, 28) and moistened with water vapor from water injectors (26).

In the high-temperature fuel cell module (49 anode part (20) removal path or removal path (10), in the flow direction after the heat exchanger (28) there are sequentially arranged a shift reactor (30), an additional heat exchanger (32), a water cutter (34), the heat exchanger (24 ), a hydrogen decoupling device (36) and device (70).

The anode exhaust gas in the away path (10) essentially contains carbon monoxide CO, hydrogen H2., water H2O and carbon dioxide CO2. The proportion of carbon monoxide CO and hydrogen H2 in the anode exhaust typically has more than 10-30% of the heating value of the high-temperature fuel cell module (4) of the carbon hydrogen supplied by the fuel via the supply path (8).

The anode exhaust gas in the removal or removal path (10) to the anode part (20) transfers part of its heat content in the heat exchanger (28) to the fuel for the anode part (20) in the supply path (8) to the anode path (6). The water injector (26) in the supply path (8) is supplied with water via a line (50).

In the flow direction of the water, pumps (52), a further heat exchanger (44) and the heat exchanger (32) are arranged in the line 50.

In the shift reactor (30), which can also be integrated into the nearby heat exchangers (28, 32), a large part of the carbon monoxide CO with the water H2O in the anode exhaust gas is transformed into carbon dioxide CO2 and hydrogen H2O. A shift reaction for the transformation of carbon monoxide CO and water H2O into carbon dioxide CO2 and hydrogen H2 only takes place in the shift reactor (30), but also partially follows the entire length of the away path (10) to the anode part (20) for the supply of hydrogen H2 from the anode exhaust gas .

Finally, the anode gas in the heat exchanger (32) transfers a further part of its heat content to the water in the line (50).

A proportion of water is removed from the anode exhaust gas in the water cutter or brancher (34). A further proportion of its heat content transfers the anode exhaust gas in the heat exchanger (24) to the fuel in the supply path (8) for the anode part (20) of the high-temperature fuel cell module (4). In the hydrogen separation device (36) all the components that are present in the anode exhaust gas next to the hydrogen H2 are separated, so that in the last part of the away path (10) essentially only hydrogen H2 is present and which is finally supplied to the device (70) .

An oxidant, for example air or oxygen, is supplied via the supply path (14) to the cathode path (12) to the cathode part (22) of the high-temperature fuel cell module (4). In the flow calculation, a condenser (40) and an arm exchanger (42) are arranged in the supply path (14). The oxidant is compressed in the concentrator (40), whereby the flow rate of oxidant can be set, and finally heated in the heat exchanger (42).

After the reaction in the cathode part (22) of the high-temperature fuel cell module (4), the cathode exhaust gas via the removal path (16) of the cathode part (22), which is arranged in the heat exchanger (42, 44), is supplied to the outside air. In the heat exchanger (42), the heated cathode exhaust gas to the cathode part (22) transfers part of its heat content to the oxidant in the supply path (14) to the cathode part (22).

The introduction of the heat exchangers (24, 28, 32 and 44) means that the heat content of the cathode and anode exhaust gases of the high-temperature fuel cell module (4) can be used for preheating fuel and oxidant and thus for reforming.

In accordance with the high temperature fuel cell plant (2) in fig. 2, the supply path (8) for the anode part (20) in the flow direction behind the water injector (26) is arranged with a reformer (62) outside the high-temperature fuel cell module (4). The heat exchanger (24, 28) in the embodiment in fig. 1 has been removed. In contrast to the design in fig. 1, the fuel gas is no longer reformed inside the high-temperature fuel cell module (4), but in the external reformer (62), so that the fuel gas is at least partially reformed before it is fed into the anode part (20).

The exhaust gas from the anode part (29) emits part of its heat content via the away path (10) to the reformer (62). Behind the reformer (62), in the away path (10) to the anode part (20), an evaporator (64) is arranged in which the exhaust gas transfers a further part of its heat content to the water vapor for moistening the fuel for the reformer (62). finally, the exhaust gas passes through the hydrogen separation device (36) of the anode part (20), whereby after the hydrogen separation device (36) only hydrogen H2 is present in the anode exhaust gas, which is supplied to the device (70).

The cathode exhaust gas is supplied to the external reformer (62) via the away path (16) to the cathode part (22), in which the heat exchanger (42) is arranged. After giving off part of its heat content for reforming fuel gas for the anode part (20), the cathode exhaust gas passes through the evaporator (64), where a further part of its heat content is given off to the water for moistening the fuel for the reformer (62). Finally, the cathode exhaust gas, which essentially contains air, is emitted to the outside air.

From the away path (16) to the cathode part (22) there is a branch (72) between the cathode part (22) and the heat exchanger (42). The branch (72) feeds a portion of the cathode exhaust gas to the cathode section (22) to discharge its heat content directly into the external reformer (62). after part of its heat content has been released, this part of the cathode exhaust gas passes through the evaporator (64) and is finally also released into the outside air.

Claims (17)

1. Procedure for operating a high temperature fuel cell plant (2) with a high temperature fuel cell model (4), characterized in that the heat content from the electrochemical reaction in the high-temperature fuel cell module (4) by means of a reforming process of fuel gas is essentially used for the formation of the hydrogen required for the electrochemical reaction, as well as for additional hydrogen that is intended for further utilization outside of high temperature -the fuel cell module (4), the cells of the high-temperature fuel cell module (4) each being operated with a cell voltage of less than 0.8 V. 2. Method according to claim 1, characterized in that the cells of the high-temperature fuel cell module are each operated with a cell voltage between 0.5 and 0.7 V. 3. Method according to claim 1 or 2, characterized by at least 30% of the fuel gas effect being used for the formation of the unconsumed hydrogen (H2) 4. Method according to one of claims 1-3, characterized in that by the fuel gas being reformed inside the high-temperature fuel cell module (4). 5- Method according to one of claims 1-3, characterized in that the fuel gas is reformed before introduction into the high-temperature fuel cell module (4). 6. High-temperature fuel cell plant (2) has the method carried out according to one of claims 1-5, characterized in that it comprises at least one high-temperature fuel cell module (4) with an anode part (29), a cathode part (22), a reformer (5) for reforming the fuel gas for the electrochemical reaction, and a hydrogen separation device (36) in a removal path ( 10) on the anode part (20), which is arranged for the separation of hydrogen from the anode exhaust gas, in that it arranged means for conducting substantially all the heat generated in the high-temperature fuel cell module (4) to the reformer (5) and that the reformer (5) is designed for the formation of more hydrogen than is used for the electrochemical reaction. 7. High-temperature fuel cell plant (2) according to claim 6, characterized in that a device (70) is arranged in a removal path (10) on the anode part (20) as a storage for the hydrogen that is not used in the high-temperature fuel cell module (4). 8. High-temperature fuel cell plant (2) according to claim 6, characterized in that a device (70) is arranged in a removal path (10) on the anode part (20) as a consumer for the hydrogen that is not consumed in the high-temperature fuel cell module (4). 9. High-temperature fuel cell plant (2) according to one of claims 6-8, characterized in that the reformer (5) is arranged inside the high-temperature fuel cell module 4. 10. High-temperature fuel cell plant (2) according to one of claims 6-9, characterized in that it arranged at least one heat exchanger (24, 28, 32) in the removal path to the anode part (20) for transferring the heat content of an anode exhaust gas over a supply path (8) to the reformer (5) arranged inside the high-temperature fuel cell module (4). 11. High-temperature fuel cell plant (2) according to one of claims 6-10, characterized in that a shift reactor (30) is arranged for the formation of hydrogen (H2) in the removal path (10) to the anode part (20). 12. High-temperature fuel cell plant (2) according to one of claims 11, characterized in that the shift reactor (30) is arranged between the two heat exchangers (28, 32) in the removal path (10) to the anode part (20). 13. High-temperature fuel cell plant (2) according to one of claims 6-12, characterized in that at least in the heat exchanger (42, 44) a removal path (16) is arranged to the cathode part (22) in order to give off the heat content of a cathode exhaust gas. 14. High-temperature fuel cell plant (2) according to one of claims 6-8, characterized in that a reformer (62) is arranged outside the high-temperature fuel cell module (4) in the supply path (8) for the anode part (20). 15. High-temperature fuel cell plant (2) according to claim 14, characterized in that the removal path (16) on the cathode part (22) is arranged for transferring the heat content from a cathode exhaust gas to the reformer (62). 16. High-temperature fuel cell plant (2) according to claim 15. characterized in that a branch (72) is arranged in the removal path 16 to the cathode part (22) for the transfer of heat content from a cathode exhaust gas to the reformer (62). 17. High-temperature fuel cell plant (2) according to claim 14, characterized in that the removal path (10) to the anode part (20) is arranged to transfer the heat content from an anode exhaust gas to the reformer (62).