Gas circuit for a solid oxide fuel cell system and solid oxide fuel cell system

Abstract

Gas circuit (7) for a solid oxide fuel cell system (1), comprising an anode gas section (17) in which anode gas exiting from a gas space of an anode (3) of a solid oxide fuel cell (4) flows, and a recirculation section (9) for recirculating at least a portion of the anode gas back to a fuel gas conditioning unit (2) arranged in the gas circuit (7), in which fuel for the solid oxide fuel cell (4) is processed into fuel gas, wherein a conveying device (16) for recirculating the anode gas and a dividing device (18) which divides the anode gas into a recirculation stream and a residual gas stream to be discharged from the gas circuit (7) are arranged in the gas circuit (7), characterized in that the conveying device (16) is arranged upstream of the dividing device (18) in the anode gas section (17), and the fuel gas conditioning unit (2) has a desulfurization unit.

Description

[0001] The invention relates to a gas circuit for a solid oxide fuel cell system according to the preamble of claim 1 and to a solid oxide fuel cell system with at least one solid oxide fuel cell.

[0002] Solid oxide fuel cells (SOFCs) can be designed as high-temperature or low-temperature fuel cells and are essentially divided into tubular and planar solid oxide fuel cells according to their construction. Planar solid oxide fuel cells are particularly suitable for applications with high volumetric power densities. However, the reliability and service life of planar solid oxide fuel cells can be severely impaired by high pressure differentials between the air side (cathode) and the environment, as well as between the combustion side (anode) and the air side, which can arise, for example, from downstream heat exchangers.

[0003] When using hydrocarbon-containing fuels such as natural gas, LPG, diesel, or kerosene, fuel gas treatment is necessary to prevent carbon deposits within the solid oxide fuel cell. Steam reforming, along with partial oxidation and autothermal reforming, is the treatment method with the highest potential for efficiency. In addition to the steam required for the actual fuel reforming process, gases such as hydrogen, carbon monoxide, and carbon dioxide are advantageous, as they can generate methane via an exothermic reaction within the reformer.Since the reformate is not usually completely oxidized in the solid oxide fuel cell, it is known in the art to recirculate the gas exiting the anode back to the reformer in a gas circuit to provide the aforementioned gases hydrogen, carbon monoxide and carbon dioxide, which support the regeneration process.

[0004] Typically, a blower or ejector is used to recirculate the anode gas in the gas circuit, which is flowed through by the recirculated gas or a mixture of recirculated gas and primary fuel.

[0005] For example, EP 1 603 181 A2 discloses a solid oxide fuel cell system in which the division of the anode gas stream is carried out in front of the blower.

[0006] In US 2008 / 0 057 361 A1, an arrangement is further described in which the recirculation blower of the air side is located in the recirculation stream and thus also behind the division of the anode gas stream into a residual gas stream and a recirculation stream.

[0007] From DE 10 2012 218 648 A1 a solid oxide fuel cell system with H2O and CO2 separation is known.

[0008] A fuel cell power plant is known from EP 1 187 241 B1.

[0009] A fuel handling method is known from EP 1 603 181 A2.

[0010] In these SOFC system configurations known from the prior art, however, the pressure level of the anode is set correspondingly high above the pressure losses of the downstream components of the residual gas stream.

[0011] In this situation, the gas pressure at the anode can reach such a high level that it can lead to damage or failure of the fuel cell.

[0012] Therefore, it is an object of the present invention to provide a gas circuit for a solid oxide fuel cell system and a solid oxide fuel cell system according to which recirculation is enabled without excessively increasing the pressure in the gas space of the anode.

[0013] This problem is solved by a gas circuit for a solid oxide fuel cell system with the features according to claim 1 and by a solid oxide fuel cell system with the features according to claim 10. Advantageous embodiments of the invention are described in the dependent claims, the description, and the drawing. The features specified in the dependent claims and the description can, individually or in suitable combination, further develop the solution according to the invention.

[0014] According to the invention, a gas circuit for a solid oxide fuel cell system is provided, which has an anode gas section in which anode gas flows from a gas space of an anode of the solid oxide fuel cell, and a recirculation section for recirculating at least a part of the anode gas back to a fuel gas conditioning device arranged in the gas circuit, in which fuel for the solid oxide fuel cell is processed into fuel gas, wherein a gas conveying device for recirculating the anode gas and a dividing device, which divides the anode gas into a recirculation stream and a residual gas stream to be discharged from the gas circuit, are arranged in the gas circuit, wherein the conveying device is arranged upstream of the dividing device in the anode gas section.

[0015] The basic idea of ​​the present invention is to arrange the conveying device upstream of the dividing device in the anode gas section. By dividing the anode gas flow only after the conveying device, the conveying device is supplied with all the gas exiting the anode gas chamber. This allows the pressure level in the anode gas chamber to be kept low despite high pressure losses in the residual gas flow. The power consumption of the conveying device will be higher compared to conventional anode gas recirculation known from the prior art, since the volume flow can double. However, this only results in a decrease in electrical efficiency of a maximum of 1%.

[0016] According to a preferred embodiment, the gas conveying device is a blower.

[0017] According to an alternative preferred embodiment, the gas conveying device can also be an ejector.

[0018] Preferably, the fuel gas conditioning unit comprises a reformer in which the conditioning of the fuel gas is carried out.

[0019] Furthermore, it is advantageous if the fuel gas conditioning device is designed to carry out fuel gas conditioning at different temperatures, at different pressures and / or with different catalysts.

[0020] Furthermore, the fuel gas treatment plant may include facilities for carrying out partial oxidation, autothermal reforming or steam reforming.

[0021] According to a preferred embodiment, the fuel gas conditioning device includes a desulfurization device, so that sulfur-containing fuels can also be used.

[0022] It is also advantageous if the residual gas stream can be fed to a residual gas burner for oxidizing the residual gas with air or oxygen. Preferably, the gas circuit also includes a fuel gas section which leads from the fuel gas device to the gas space of the anode.

[0023] According to the invention, a solid oxide fuel cell system is further provided, comprising at least one solid oxide fuel cell and a gas circuit as described above. The solid oxide fuel cell system according to the invention, which is equipped with a gas circuit as described above, offers the advantage of high reliability and a long service life, since large pressure differentials or excessive pressure increases in the gas space of the anode are avoided.

[0024] The invention is explained in more detail below with reference to an embodiment illustrated in the drawing. The drawing shows: Fig. 1 the schematic structure of a solid oxide fuel cell system according to a first embodiment; Fig. 2 the schematic structure of a solid oxide fuel cell system according to a second embodiment; Fig. 3 the schematic structure of a solid oxide fuel cell system according to a further embodiment; and Fig. 4 the schematic structure of a solid oxide fuel cell system according to yet another embodiment.

[0025] Fig. Figure 1 shows the schematic structure of a solid oxide fuel cell system 1 with the gas circuit according to one embodiment, which can be operated, for example, with hydrocarbon-containing fuels such as natural gas, LPG, diesel, gasoline, kerosene, methanol, or ethanol at an operating temperature between 500 °C and 900 °C. The solid oxide fuel cell system 1 has a fuel gas conditioning unit 2 in the form of a reformer, which is coupled to an anode 3 of a solid oxide fuel cell 4 via a fuel gas section 6 of the gas circuit 7. The fuel gas conditioning unit 2 is designed to operate under heated, cooled, or adiabatic conditions at temperatures from 250 °C to 1000 °C. Fuel is supplied to the fuel gas conditioning unit 2 for conditioning via a fuel section 15.

[0026] The solid oxide fuel cell 4 can be designed as a low- or high-temperature fuel cell, which is proton- or oxygen-conducting. Furthermore, the solid oxide fuel cell 4 can consist of several cells or cell stacks connected in series or parallel on the gas side, which are not shown in detail here. Separated from the anode 3 by a solid electrolyte, for example, a ceramic one, the cathode 14 of the solid oxide fuel cell 4 is arranged next to the anode 3.

[0027] The solid oxide fuel cell system 1 further comprises a heat exchanger 5, through which fuel gas processed by the fuel gas conditioning unit 2 is passed in the fuel gas section 6 of the gas circuit 7 of the solid oxide fuel cell system 1 on its way to the anode 3, and a further heat exchanger 8, which is arranged in a recirculation section 9 of the gas circuit 7, in which recirculated gas flows, and which brings the gas to the required inlet temperature of the reformer 2 and the solid oxide fuels 4.

[0028] Furthermore, the solid oxide fuel cell system 1 comprises an oxidation unit 10 with a residual gas burner. The oxidation unit 10 is arranged in a residual gas section 11, through which residual gas to be discharged from the gas circuit 7 flows. The residual gas is supplied to the oxidation unit 10 together with air 12 in order to oxidize the residual gas and exit the oxidation unit 10 as exhaust gas 13. To prevent a pressure increase in the gas space of the anode 3, a gas supply device 16, designed here as a blower and serving to recirculate a portion of the anode gas exiting the anode 3, is arranged in an anode gas section 17, such that the entire anode gas flows through the gas supply device 16. Downstream of the gas supply device 16, a dividing device 18, for example designed as a valve, is arranged, which divides the anode gas into a recirculation flow, which flows in the recirculation section 9, and a residual gas flow to be discharged from the gas circuit, which flows in the residual gas section 11.

[0029] Fig. Figure 2 shows the schematic structure of a solid oxide fuel cell system 1 according to a second embodiment, which differs from the one in Fig. The embodiment shown in Figure 1 differs in that a further solid oxide fuel cell 4 is arranged in the residual gas section 11 upstream of the oxidation unit 10 and downstream of the partitioning device 18. More than one further solid oxide fuel cell can also be arranged in this section. By providing one or more additional solid oxide fuel cells 4 in the residual gas section 11, the fuel conversion rate is increased.

[0030] Fig. Figure 3 shows the schematic structure of a solid oxide fuel cell system 1 according to a further embodiment, which differs from the one shown in Fig. The embodiment shown in 1 differs in that a further medium, such as water or steam, is supplied to the recirculation flow in the recirculation section 9 via a line 19 opening into the recirculation section 9 by means of an ejector, a nozzle or a jet scrubber not shown here.

[0031] Fig. Figure 4 shows the schematic structure of a solid oxide fuel cell system 1 according to yet another embodiment, which differs from the one shown in Fig. The embodiment shown in Figure 3 differs in that the additional medium, such as water or steam, is introduced into the anode gas section 17, i.e. downstream of the anode 3 and upstream of the gas conveying device 16. Reference symbol list 1 Solid oxide fuel cell system 2 Fuel gas processing (reformer) 3' Anode of the solid oxide fuel cell 4, 4' solid oxide fuel cell 3, 5 heat exchangers 6 Fuel gas section 7 Gas cycle 8 heat exchangers 9 Recirculation section 10 oxidation units 11 Residual gas section 12 Air 13 Exhaust gas 14, 14 Cathode 15 Fuel section 16 Gas supply equipment 17 Anode gas section 18 Division device 19 Management for further medium

Claims

[1] Gas circuit (7) for a solid oxide fuel cell system (1), which has an anode gas section (17), in which anode gas emerging from a gas space of an anode (3) of a solid oxide fuel cell (4) flows, and a recirculation section (9) for recirculating at least a portion of the anode gas back to a fuel gas processing device (2) arranged in the gas circuit (7), in which fuel for the solid oxide fuel cell (4) is processed into fuel gas, wherein a conveying device (16) for recirculating the anode gas and a dividing device (18) which divides the anode gas into a recirculation stream and a residual gas stream to be discharged from the gas circuit (7) are arranged in the gas circuit (7), characterized by that the conveying device (16) is arranged upstream of the distribution device (18) in the anode gas section (17), and the fuel gas processing device (2) has a desulfurization device. [2] Gas circuit (7) according to claim 1, characterized by that the conveying device (16) is a blower. [3] Gas circuit (7) according to claim 1, characterized by that the conveying device (16) is an ejector. [4] Gas circuit (7) according to one of claims 1 to 3, characterized by that the fuel gas processing device (2) comprises a reformer. [5] Gas circuit (7) according to one of claims 1 to 4, characterized by that the fuel gas processing device (2) is designed to carry out the fuel gas processing at different temperatures, at different pressures and / or with different catalysts. [6] Gas circuit (7) according to one of claims 1 to 5, characterized by that the fuel gas processing device (2) has devices for carrying out partial oxidation, autothermal reforming or steam reforming. [7] Gas circuit (7) according to one of claims 1 to 6, characterized by that the residual gas stream can be fed to an oxidation unit (10) with a residual gas burner for oxidizing the residual gas with air or oxygen. [8] Gas circuit (7) according to one of claims 1 to 7, characterized by that the gas circuit (7) further comprises a fuel gas section (15) which leads from the fuel gas device (2) to the gas space of the anode (3). [9] Solid oxide fuel cell system (1) comprising at least one solid oxide fuel cell (4, 4') and a gas circuit (7) according to one of claims 1 to 8.

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