WO2019028487A1

WO2019028487A1 - Fuel cell system having at least one high-temperature fuel cell

Info

Publication number: WO2019028487A1
Application number: PCT/AT2018/060181
Authority: WO
Inventors: Martin HAUTH
Original assignee: Avl List Gmbh
Priority date: 2017-08-07
Filing date: 2018-08-07
Publication date: 2019-02-14
Also published as: DE112018004017A5; AT520263B1; AT520263A1

Abstract

The invention relates to a fuel cell system (10), comprising at least one high-temperature fuel cell (11), such as a solid oxide fuel cell or a molten carbonate fuel cell, which has an anode region (A) having an anode inlet (12) and an anode outlet (13), and comprising an anode gas supply line (14), which leads into the anode inlet (12) and in which a reformer (15) for reforming a hydrocarbon-containing fuel is arranged, and comprising an anode recirculation line (16), which proceeds from the anode outlet (13) and leads into the anode gas supply line (14) upstream of the reformer (15). In order to generate steam for the subsequent reforming during the start phase of the system, at least one oxidation catalyst (18, 19, 20) together with an upstream injector (21, 22) for an oxidant is arranged in the anode recirculation line (16) upstream of the junction (17) of the anode gas recirculation line into the anode gas supply line (14).

Description

Fuel cell system with at least one high-temperature fuel cell

The invention relates to a fuel cell system having at least one high-temperature fuel cell, which has an anode region with an anode inlet and an anode outlet, and with an anode gas supply line opening into the anode inlet, in which a reformer for the reforming of a hydrocarbon-containing fuel is arranged, as well as one from the anode outlet outgoing, upstream of the reformer in the anode gas supply line opening out the anode recirculation line. Furthermore, the invention relates to a method for starting a fuel cell system.

By a high temperature fuel cell is meant, for example, a Molten Carbonate Fuel Cell (MCFC) which operates at operating temperatures of about 580 ° C to 675 ° C. The electrolyte used in this type of fuel cell is usually an alkali metal carbonate mixed melt of lithium and potassium carbonate. Likewise, Solid Oxide Fuel Cells (SOFCs) are high temperature fuel cells operated at operating temperatures of about 650 ° C to 1000 ° C.

Such fuel cell systems are operated with a gaseous or liquid fuel, such as ethanol, methane, natural gas or diesel and gasoline, which are converted in a anode upstream reformer into a hydrogen and CO-containing synthesis gas. Via an anode recirculation line, the anode exhaust gases are at least partially recycled, wherein the recirculation line opens upstream of the reformer in the anode gas supply line. During operation of the fuel cell system, the reformer is also supplied with steam, which is contained in the anode exhaust gas.

During start-up operation of the fuel cell system before reaching the operating temperature, no water vapor is generated and must be supplied to the system during startup.

In this context, from WO 2015/090549 Al a solid oxide fuel cell system has become known, which is operated with gaseous or liquid hydrocarbon-containing fuels at an operating temperature between 500 ° C and 900 ° C. The system includes a reformer coupled to an anode of a solid oxide fuel cell via a fuel gas portion of a gas loop. The reformer uses a fuel section to Material supplied for treatment. Furthermore, the gas circuit has a recirculation section and a heat exchanger in which the fuel gas is heated by the recirculation before it enters the anode. Furthermore, water or water vapor can be supplied to the recirculation flow via an opening into the recirculation section of the gas circulation line by means of an ejector or a nozzle. The disadvantage here is that additional resources, such as water or steam, must be provided.

DE 10 2004 042 806 A1 describes a PEM fuel cell system which is operated with hydrogen and air, in which catalytic coatings are provided in the anode recirculation line at locations on the anode inlet or anode outlet. These serve to catalytically convert hydrogen which diffuses in the direction of the anode region when the fuel cell is at a standstill, when the anode region is filled with air or oxygen.

The object of the invention is to supply a fuel cell system having a reformer for the reforming of a hydrocarbon-containing fuel in a simple manner also in the starting mode with the water vapor required for the reforming.

According to the invention, this is achieved by arranging in the anode recirculation line upstream of its junction into the anode gas supply line at least one oxidation catalytic converter together with an upstream injector for an oxidizing agent for generating steam. Preferably, air is supplied as the oxidizing agent. In other words, at least one oxidation catalytic converter together with an upstream injector is thus provided upstream of the junction of an anode recirculation line in the anode gas supply line.

Through the oxidation catalyst and the injection of an oxidizing agent, water vapor can be generated from the hydrogen-containing fuel remaining in the anode exhaust gas. Thus, according to the invention, water vapor can be generated immediately when the fuel cell is started up without an external source of water or steam being necessary. Furthermore, it is possible to dispense with an additional evaporator and at the same time to ensure that the reformer is heated up quickly to its optimum operating temperature. When using methane-containing fuel gases, H ₂ O is immediately available for methane reforming and the avoidance of carbon deposits. These advantages also result in the regular operation of the fuel cell system, where after the anode, the reaction products of the fuel - when using a hydrocarbon-containing fuel in particular H ₂ and CO - are oxidized. Several positions are available for the arrangement of one or more oxidation catalysts in the anode circulation line:

According to a first variant of the invention, a waste heat from the anode recirculation line acted upon heat exchanger is arranged in the anode gas supply line before the anode inlet, wherein the oxidation catalyst is arranged in the heat exchanger and is passed through by the recycled material. The oxidation catalytic converter is preferably designed as a catalytic inner coating in the region of the heat exchanger acted upon by the anolyte recycle. Thus, no additional component is necessary, so that space and costs can be saved. In addition, more heat is generated by performing the catalytic reaction in the heat exchanger and transferred to the anode through the heat exchanger supplied anode gas.

A second variant provides that the oxidation catalyst is arranged in the hotter region of the anode recirculation line downstream of the anode outlet and upstream of a heat exchanger. Thereby, a compact construction and immediate conversion of the anode exhaust gas can be achieved.

Finally, according to a third variant, the oxidation catalyst can be arranged in the cooler region of the anode recirculation line upstream of the confluence with the anode gas supply line and downstream of a heat exchanger. The oxidation catalyst is preferably designed as a catalytic inner coating of the recirculation line. This embodiment allows a longer use of the catalyst components used, since they are arranged in cooler sections and thus exposed to lower thermal loads - this reduces wear and due to the rarer maintenance and operating costs.

To increase the oxidation rate, the individual variants can also be used in combination, ie oxidizing elements or layers can be used at several points.

In a further variant of the invention, the injector has a regulating device with which the supply of the oxidizing agent can be regulated as a function of operating parameters of the fuel cell or of the fuel cell system. The operating parameters may be, for example, the stack temperature, the steam-to-carbon ratio (in particular in a reformer) or the like.

A method according to the invention for starting the described fuel cell system provides the following steps: Starting the supply of the hydrocarbonaceous fuel to the fuel cell,

During the startup of the fuel cell system, supplying an oxidizing agent to the oxidation catalyst for generating steam for the subsequent reforming of the hydrocarbonaceous fuel, and

• Shutting off the supply of the oxidizing agent as soon as sufficient water vapor is generated by the operation of the fuel cell system.

According to the invention, the supply of the oxidizing agent can be regulated as a function of operating parameters of the fuel cell system. The operating parameters can be, for example, the temperature in the fuel cell or in the fuel cell stack, the water vapor content of the recyclate in the anode recirculation line or the steam-to-carbon ratio, in particular in a reformer element or reforming element of the fuel cell system.

In one variant of the invention, ambient air is used as the oxidizing agent.

The invention will be explained in more detail below with reference to non-limiting embodiments, which are illustrated in the figures. Show it :

1 shows a first embodiment of a fuel cell system according to the invention in a schematic representation;

FIG. 2 shows a second embodiment of a fuel cell system according to the invention in a schematic illustration; FIG. such as

3 shows a third embodiment of a fuel cell system according to the invention ms in a schematic representation.

FIGS. 1 to 3 show different variants of the fuel cell system 10 according to the invention. The illustrated embodiments have at least one high-temperature fuel cell 11 or a stack or stack of high-temperature fuel cells, which have an anode region A and an electrolyte have cathode region K separated from the anode region.

The fuel cell system 10 is provided with an anode gas supply line 14 opening into an anode inlet 12 and one of an anode outlet 13 outgoing, opening into the anode gas supply line 14 Anodenrezirkula- tion line 16 equipped with a part of the anode exhaust gas of the anode A is supplied again. The remainder of the exhaust gas branches off at a branch point 29 from the anode recirculation line 16 and is discharged via an exhaust pipe 28, which is not described in more detail. In the following, the term "recycled material" is synonymously used for the anode exhaust gas, which includes both the gas mixture flowing upstream and downstream of the branching point.

In the gas circulation of the anode A, a recirculation fan 24 and a pressure measuring device 25 are arranged. Via the pressure measuring device 25, the recirculation rate can be determined in order to regulate the recirculation fan 24 accordingly.

In the illustrated embodiments, the recirculation fan 24 is arranged in the anode gas supply line 14 downstream of a junction 17 of the recirculation line 16, the pressure measuring device 25 is located between the anode outlet 13 and said junction 17.

In the illustrated embodiment, a reformer 15 for the reforming of a hydrocarbon-containing fuel is arranged in the anode gas supply line 14, but the reforming of the fuel can also take place directly in the anode-side region of the fuel cell 11 or the fuel cell stack. The control of the supply of anode gas or fuel via a control device 27th

A possible media guide to or through the cathode K is not shown in the figures for reasons of clarity and will not be explained further here.

As the hydrocarbonaceous fuels, for example, ethanol, methane, natural gas, diesel or gasoline can be used.

As shown in detail in the individual embodiments, in the anode recirculation line 16 upstream of the junction 17 in the anode gas supply line 14 at least at one point an oxidation catalyst including upstream injector arranged, with which an oxidizing agent for generating water vapor can be supplied. In other words, between the anode outlet 13 and the junction 17 of the anode recirculation line 16 in the anode gas supply line 14 at least one oxidation catalyst, including an upstream injector for an oxidizing agent is arranged. As shown in Fig. 1, in the anode gas supply line 14 in front of the anode inlet 12 with a waste heat from the anode recirculation line 16 acted heat exchanger 23 is arranged. The leading through the heat exchanger section 23 of the anode gas supply line 14 transports the anode A to be supplied anode gas, which is preheated by the waste heat of the fuel cell 11. The section of the anode recirculation line 16 extending in the heat exchanger 23 has the oxidation catalytic converter 20. The heat exchanger 23 is arranged in the illustrated embodiment with respect to the anode recirculation line 16 between the anode outlet 13 and the branch point 29 of the exhaust gas line 28.

In this case, the oxidation catalyst 20 may preferably be designed as a catalytic inner coating in the hot region of the heat exchanger 23 acted upon by the anode recycle.

The anode recirculation line 16 is subdivided into a hotter area T 1 between anode outlet 13 and heat exchanger 23, in which between 700 ° C.-900 ° C. may occur in the illustrated embodiment, and a cooler area T2 downstream of the heat exchanger 23, in which the temperatures are between 350 ° C and 700 ° C lie.

According to a variant of the invention, the heat exchanger 23 may additionally be provided on its cold side (the anode gas supply line 14) with a reformer function, so that the heat of the anode exhaust gas can be used for reforming. This allows a separate reformer 15, as he. As shown in Fig. 1, omitted or absorbed into the heat exchanger 23.

The oxidation catalyst 20 is preceded by an injector 21 with which an oxidizing agent is introduced into the anode recirculation line 16. For this example, air can be used. In other words, an injector 21 is thus provided between the anode outlet 13 and the oxidation catalytic converter 20.

By introducing or injecting the oxidant, the hydrogen (H ₂ ), hydrocarbon and / or carbon monoxide (CO) present in the anode exhaust gas is converted into water vapor and carbon dioxide and recirculated into the anode gas supply line 14, whereby the reforming process of the fuel supplied to the anode A can be improved , At the same time, the generation of water vapor prevents the formation of carbon deposits. These advantages are independent of the operating state of the fuel cell system 10 - in the starting phase, where the fuel in the anode is not or insufficiently implemented, the fuel can be oxidized, while in normal operation, the anode exhaust gas, which in particular includes H ₂ and CO, is implemented. According to the variant illustrated in FIG. 2, the oxidation catalyst 18 is arranged to generate steam in the hotter area T 1 (about 650 ° C. to 900 ° C.) of the anode recirculation line 16 downstream of the anode outlet 13 and upstream of the heat exchanger 23. The oxidation catalyst 18 in this embodiment is thus arranged upstream of the branch point 29 of the exhaust pipe 28.

The nozzle or the injector 21 for the metered addition of the oxidizing agent (preferably ambient air) is arranged in the variants according to FIG. 1 and FIG. 2 upstream of the oxidation catalytic converter 18 or 20, but can also be located directly on the input side into, for example, a separate component open present oxidation catalyst 18.

The injector 21 has a control device 26, with which the supply of the oxidant depending on operating parameters of the fuel cell (for example pressure, temperature, steam-to-carbon ratio, in particular in a reformer element, etc.) adjustable and can be switched off when stable operating conditions of the fuel cell system. The regulation of the supply of the oxidizing agent is aimed in particular at ensuring that sufficient water vapor is present in the reformer in order to support the reforming reaction and to avoid the deposition of carbon. In one of the possible variants, the necessary amount of oxidant is defined via the steam-to-carbon ratio, taking into account the reformer temperature and, if appropriate, the recirculation rate. When using natural gas as fuel, a ratio of one part of CH ₄ to two parts of H ₂ 0 is aimed in particular.

Finally, according to another embodiment shown in FIG. 3, the oxidation catalyst 19 may be located in the cooler region T2 (about 350-650 ° C.) of the anode recirculation line 16 upstream of the junction 17 into the anode gas supply line 14 and downstream of the heat exchanger 23 his. In particular, the oxidation catalyst 19 in this embodiment is located downstream of the branch 29 of the exhaust conduit 28 in the anode recirculation conduit 16. In this variant, a second injector 22 may also be located in the cooler region downstream of the heat exchanger 23, either in addition to the injector 21 immediately near the anode outlet 13 or This injector 21 may be arranged. The injector 21 is therefore shown in Fig. 3 by dashed lines. This embodiment has the advantage that the oxidizing agent is introduced only after the branch point 29 of the exhaust pipe 28 in the anode recirculation line 16 and thus is completely available for steam generation and not partially unused escapes into the environment. also For example, the oxidation catalyst 19 is subjected to a lower thermal load than in the other embodiments, which allows less wear and longer operating life.

The oxidation catalysts 18, 19 may be designed, for example, as a catalytic inner coating of the recirculation line 16, but it is also possible to use conventional catalysts together with the housing and the internal, catalytically coated support structure.

The method according to the invention for operating such a fuel cell system 10 is advantageously used especially when starting the fuel cell system 10. Here, it is particularly important to quickly raise the temperature of the system and its components to higher levels in order to be ready for use.

The supply of an oxidizing agent such as air is essentially necessary in the start-up operation of the fuel cell system, since sufficient steam is provided by the fuel cell itself during normal operation. Should this not be so, the supply of oxidant can also be done in regular operation to provide the steam for the reforming and prevention of carbon deposits.

When used during start-up of the fuel cell system 10, according to the invention, after the start of the supply of the fuel, the oxidizing agent is supplied to generate water vapor in the anode recirculation line 16 for the reforming of the fuel. The supply of the oxidant can be adjusted if the fuel cell system itself generates sufficient water vapor. This time can be determined, for example map-controlled by monitoring certain operating parameters of the fuel cell system. Optionally, even during operation, for. B. during longer periods of low load, an additional generation of water vapor may be necessary, which is easily possible by activating the oxidant supply. The supply of the oxidant - both in terms of quantity and duration or start and stop - can generally be regulated as a function of operating parameters of the fuel cell system. Suitable parameters are, for example, the temperature of the fuel cell 11 and / or the water vapor content of the recycled material in the anode recirculation line 16 and / or the steam-to-carbon ratio, in particular in a reformer element.

Claims

PATENT APPLICATIONS

1. Fuel cell system (10) with at least one high-temperature fuel cell (11), which has an anode region (A) with an anode input (12) and an anode output (13), and with an anode gas supply line (14) opening into the anode inlet (12). in which a reformer (15) for the reforming of a hydrocarbon-containing fuel is arranged, and with an anode recirculation line (16) emanating from the anode outlet (13) upstream of the reformer (15) into the anode gas supply line (14), characterized in that the anode recirculation line (16) upstream of the junction (17) in the anode gas supply line (14) at least one oxidation catalyst (18, 19, 20) including upstream injector (21, 22) for an oxidizing agent, preferably air, is arranged to generate water vapor.

2. fuel cell system (10) according to claim 1, characterized in that in the anode gas supply line (14) in front of the anode inlet (12) with the waste heat from the anode recirculation line (16) acted upon heat exchanger (23) is arranged, wherein the oxidation catalyst (20 ) is arranged in the heat exchanger.

3. fuel cell system (10) according to claim 2, characterized in that the oxidation catalyst (20) is designed as a catalytic inner coating in the area acted upon by the Anodenrezyklat the heat exchanger (23).

4. Fuel cell system (10) according to claim 1, characterized in that the oxidation catalyst (18) in the hotter area of the anode recirculation line (16) downstream of the anode outlet (13) and upstream of a heat exchanger (23) is arranged.

5. Fuel cell system (10) according to claim 1, characterized in that the oxidation catalyst (19) in the cooler region of the anode recirculation line (16) upstream of the junction (17) in the anode gas supply line (14) and downstream of a heat exchanger (23) is arranged.

6. Fuel cell system (10) according to claim 4 or 5, characterized in that the oxidation catalyst (18, 19) is designed as a catalytic inner coating of the recirculation line (16).

7. Fuel cell system (10) according to any one of claims 1 to 6, characterized in that the injector (21, 22) has a control device (26), with which the supply of the oxidizing agent can be regulated depending on operating parameters of the fuel cell.

8. A method for starting a fuel cell system (10) with at least one high-temperature fuel cell (11) with an anode gas supply line (14), in which a reformer (15) is arranged for the reforming of a hydrocarbon-containing fuel, and with an anode recirculation line (16) discharging into the anode gas supply line (16) is provided, wherein at least one oxidation catalyst (18, 19, 20) together with upstream one in the anode recirculation line (16) upstream of the junction (17) in the anode gas supply line (14) Injector (21, 22) is arranged for an oxidizing agent, with the steps:

Starting the supply of the hydrocarbonaceous fuel to the fuel cell (11),

During the startup of the fuel cell system, supplying an oxidant to the oxidation catalyst (18, 19, 20) for generating water vapor for the subsequent reforming of the hydrocarbonaceous fuel, as well as

• Shutting off the supply of the oxidizing agent as soon as sufficient steam is generated by the operation of the fuel cell system (10).

9. The method according to claim 8, characterized in that the supply of the oxidizing agent is regulated depending on operating parameters of the fuel cell system.

10. The method according to claim 8 or 9, characterized in that ambient air is used as the oxidizing agent.