fuel cell system

Abstract

To provide a technique to simplify a system configuration of a fuel cell system that generates a fuel gas from liquid fuel and removes impurities from the generated fuel gas.SOLUTION: A fuel cell system comprises: a vaporizer that vaporizes liquid fuel through heat exchange with water reserved in a water tank; a reformer that reforms gaseous fuel vaporized by the vaporizer to generate fuel gas; a fuel cell that generates power by using the fuel gas generated by the reformer and air; and a remover that removes at least either an exhausted gas exhausted from the fuel cell or impurities included in the fuel gas generated by the reformer by using the water reserved in the water tank. A water tank of the vaporizer and a water tank of the remover share the water.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a fuel cell system. [Background technology]

[0002] Patent Document 1 discloses a fuel cell system including a vaporizer that vaporizes liquid ammonia, a reformer that reforms the vaporized ammonia to produce fuel gas, and a fuel cell that generates electricity using the produced fuel gas and air. In Patent Document 1, exhaust gas discharged from the fuel cell is heated and supplied to the vaporizer, and the liquid ammonia is vaporized by the heat of the exhaust gas.

[0003] Patent Document 2 discloses a fuel cell system including a reformer that reforms a feed gas containing hydrocarbons to produce a hydrogen-containing gas, a remover that removes ammonia from the hydrogen-containing gas, and a fuel cell that generates power using the hydrogen-containing gas from which the ammonia has been removed and air. In Patent Document 2, in order to reduce poisoning of a catalyst inside the fuel cell, the hydrogen-containing gas is brought into contact with water in the remover, thereby dissolving the ammonia in the water and removing the ammonia from the hydrogen-containing gas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-134278 [Patent Document 2] International Publication No. 2011 / 111400 Summary of the Invention [Problem to be solved by the invention]

[0005] In the fuel cell system of Patent Document 1, some of the vaporized ammonia may not be decomposed in the reformer and may remain in the fuel gas. That is, in the fuel cell system, the reformed fuel gas may contain impurities. Because such impurities may have various effects on the fuel cell system and the surrounding environment, it is desirable to remove impurities from the fuel gas and the exhaust gas emitted from the fuel cell.

[0006] Here, if a remover such as that in Patent Document 2 is applied to a fuel cell system that generates fuel gas from liquid fuel as in Patent Document 1, a large space is required and the system configuration becomes complicated. This specification provides a technology that further simplifies the system configuration in a fuel cell system that generates fuel gas from liquid fuel and removes impurities from the generated fuel gas, etc. [Means for solving the problem]

[0007] The fuel cell system disclosed in this specification includes a vaporizer that vaporizes liquid fuel through heat exchange with water stored in a water tank, a reformer that generates fuel gas by reforming the gaseous fuel vaporized by the vaporizer, a fuel cell that generates electricity using the fuel gas generated by the reformer and air, and a remover that removes impurities contained in at least one of exhaust gas emitted from the fuel cell and the fuel gas generated by the reformer using water stored in the water tank. The water tank of the vaporizer and the water tank of the remover share water.

[0008] In the above fuel cell system, liquid fuel is vaporized by heat exchange with water stored in a water tank of the vaporizer. The water tank of this vaporizer shares water with the water tank of the remover. That is, the water used to vaporize the liquid fuel and the water used to remove impurities are shared between the vaporizer and the remover. Because the exhaust gas discharged from the fuel cell and the fuel gas generated by the reformer are relatively high in temperature, introducing the exhaust gas or fuel gas into the remover not only removes impurities but also raises the temperature of the water stored in the water tank. This makes it possible to maintain the water temperature required for vaporizing the liquid fuel. In this way, the heat of the fuel gas and exhaust gas can be effectively utilized in the vaporizer and the remover. Therefore, the above configuration simplifies the system configuration and enables the system to operate efficiently.

[0009] The water tanks of the vaporizer and the remover may be configured to supply at least a portion of the water from the discharged water discharged from the fuel cell, thereby reducing the frequency of replenishing the water tanks with water.

[0010] The water tank of the vaporizer and the water tank of the remover may be integrated into one unit, which simplifies the system configuration because a single water tank serves both the vaporizer and the remover.

[0011] The water tank of the vaporizer and the water tank of the remover may be separate but connected. The exhaust gas discharged from the fuel cell or the fuel gas generated by the reformer may be configured to pass through the water stored in the water tank of the remover after heat exchange with water stored in the water tank of the vaporizer. In this configuration, the exhaust gas or the fuel gas is first introduced into the water tank for vaporizing the liquid fuel. In other words, the water temperature of the water tank of the vaporizer can be efficiently raised.

[0012] The hydrogen contained in the exhaust gas from which impurities have been removed by the remover may be supplied to the fuel cell as the fuel gas. In this configuration, the hydrogen in the exhaust gas can be effectively utilized.

[0013] The system may further include a neutralizer that neutralizes the water stored in the vaporizer water tank and the remover water tank. Impurities dissolve in the vaporizer and remover water tanks, causing the pH of the water in the tanks to fluctuate. In the above configuration, by including a neutralizer that neutralizes the water in the water tanks, corrosion of the system and unpleasant odors in the water can be suppressed. Note that the neutralizer may neutralize the water by, for example, using a neutralization reaction with an acid or a base, or by using the buffering action of a buffer solution.

[0014] The system may further include a heat exchanger that heat exchanges the gaseous fuel vaporized by the vaporizer through heat exchange with the exhaust gas discharged from the fuel cell. In this configuration, the vaporized gaseous fuel can be pre-heated before being introduced into the reformer. Furthermore, since the temperature of the exhaust gas is lowered, the water stored in the water tank can be prevented from being excessively heated. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing the configuration of a fuel cell system according to a first embodiment. [Figure 2] FIG. 10 is a schematic diagram showing the configuration of a fuel cell system according to a second embodiment. [Figure 3] FIG. 10 is a schematic diagram showing the configuration of a fuel cell system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Example 1 Hereinafter, a fuel cell system (hereinafter sometimes simply referred to as a system) 1 of Example 1 will be described with reference to the drawings. As shown in Fig. 1, the system 1 includes a liquid fuel tank 4, a pump 6, a vaporizer 12, a heat exchanger 14, a reformer 16, a fuel cell 20, a remover 22, and a nitrogen separation membrane 24.

[0017] The liquid fuel tank 4 stores the liquid fuel 5. In this embodiment, liquid ammonia (an example of a liquid fuel) is used as the liquid fuel 5. The liquid fuel tank 4 stores the liquid ammonia, for example, at room temperature (20 to 25°C) and at several atmospheres (8 to 10 atmospheres). Since the liquid fuel tank 4 stores the ammonia in a liquid state, the storage efficiency of the ammonia is high.

[0018] Pump 6 is disposed in liquid ammonia supply pipe 30 that connects liquid fuel tank 4 and vaporizer 12. Pump 6 sends out liquid ammonia stored in liquid fuel tank 4 toward vaporizer 12.

[0019] The vaporizer 12 is connected to a liquid ammonia supply pipe 30. The vaporizer 12 vaporizes the liquid ammonia flowing in from the liquid ammonia supply pipe 30 and sends it to the gaseous ammonia supply pipe 32. The vaporizer 12 has a water tank 12a and an evaporator 12b. Water 60 is stored in the water tank 12a. The temperature of the water 60 stored in the water tank 12a is approximately 70°C. As will be described later, in this embodiment, the water tank 12a of the vaporizer 12 and the water tank 22a of the remover 22 are integrated. That is, the water tank 12a and the water tank 22a share water. The liquid ammonia that flows into the vaporizer 12 is vaporized by heat exchange with the water 60 in the water tank 12a while passing through the evaporator 12b, and is sent to the gaseous ammonia supply pipe 32.

[0020] The heat exchanger 14 is disposed in a gaseous ammonia supply pipe 32 that connects the vaporizer 12 and the reformer 16. The heat exchanger 14 is provided to preheat the gaseous ammonia to be introduced into the reformer 16. The gaseous ammonia is heated to approximately 350 to 400°C by heat exchange with exhaust gas (described later) discharged from the fuel cell 20. The heated gaseous ammonia is sent to the reformer 16.

[0021] The reformer 16 is connected to a gaseous ammonia supply pipe 32. The reformer 16 generates fuel gas containing hydrogen by reforming gaseous ammonia. The reformer 16 has a heater (not shown), and by heating the ammonia with the heater, the ammonia is reformed and decomposed into hydrogen and nitrogen. Here, fuel gas heated to approximately 900°C is generated. The generated fuel gas is sent to a fuel gas supply pipe 34.

[0022] The fuel cell 20 is a solid oxide fuel cell (SOFC). The fuel cell 20 has a stack structure in which a plurality of cells are stacked. Each cell has an anode 20a, a cathode 20b, and an electrolyte layer (not shown) disposed between the anode 20a and the cathode 20b. The anode 20a is connected to the reformer 16 via a fuel gas supply pipe 34. The anode 20a is supplied with fuel gas reformed by the reformer 16. The cathode 20b is connected to an air blower 26 via an air supply pipe 35. Air is supplied from the atmosphere to the cathode 20b by the air blower 26. The fuel cell 20 generates electricity using the fuel gas produced by the reformer 16 and the air supplied from the air blower 26.

[0023] When the fuel cell 20 generates power, it discharges exhaust gas containing unreacted fuel gas and other components, along with water (exhaust water) produced by a chemical reaction between hydrogen in the fuel gas and oxygen in the air. The temperature of the exhaust gas at this time is approximately 700°C. The exhaust gas and exhaust water are introduced into the heat exchanger 14 through the discharge pipe 36. In the heat exchanger 14, the exhaust gas and exhaust water are cooled by heat exchange with the gaseous ammonia vaporized by the vaporizer 12. The cooled exhaust gas and exhaust water are introduced into the remover 22 through the discharge pipe 36.

[0024] The fuel gas generated by the reformer 16 may contain residual ammonia (an example of an impurity) that remains without being reformed (decomposed) in the reformer 16. The residual ammonia contained in the fuel gas is discharged directly from the fuel cell 20 and contained in the exhaust gas. The remover 22 removes the residual ammonia contained in the exhaust gas by dissolving it in water. The remover 22 has a water tank 22a in which water 60 is stored. In this embodiment, the water tank 22a of the remover 22 and the water tank 12a of the vaporizer 12 are integrated. That is, the water 60 used to vaporize the liquid ammonia is also used to remove the residual ammonia. The discharge pipe 36 extends into the water 60 in the water tank 22a, and the exhaust gas and discharged water flowing through the discharge pipe 36 flow into the water 60 in the water tank 22a through multiple discharge holes 36a provided at the tip of the discharge pipe 36. The discharged water is used as the water 60 in the water tank 22a. Furthermore, residual ammonia contained in the exhaust gas is removed from the exhaust gas by dissolving it in water 60. Most of the exhaust gas (more specifically, the mixed gas of hydrogen and nitrogen) from which the residual ammonia has been removed is introduced into separation tube 38.

[0025] The nitrogen separation membrane 24 is connected to the remover 22 via a separation pipe 38. The nitrogen separation membrane 24 separates nitrogen from a mixed gas of hydrogen and nitrogen. When the mixed gas passes through the nitrogen separation membrane 24, only nitrogen is adsorbed by the nitrogen separation membrane 24, while hydrogen permeates the nitrogen separation membrane 24. The hydrogen that has permeated the nitrogen separation membrane 24 is sent to a hydrogen supply pipe 40. The hydrogen supply pipe 40 is connected to the anode 20a of the fuel cell 20, and the hydrogen is supplied to the anode 20a as fuel gas.

[0026] The system 1 also includes a neutralizer 28. As described above, when the system 1 is operated, ammonia dissolves in the water 60 stored in the water tanks 12a and 22a. Therefore, as the system 1 continues to operate, the water 60 becomes basic. Furthermore, because discharge water from the fuel cell 20 is supplied to the water tanks 12a and 22a, the amount of water 60 in the water tanks 12a and 22a increases. As shown in FIG. 1 , the neutralizer 28 neutralizes the water 62 that overflows from the water tanks 12a and 22a. Specifically, the neutralizer 28 neutralizes the water 62 by adding citric acid to the water 62 in which the ammonia has dissolved, utilizing a neutralization reaction. The neutralized water 62 is treated as wastewater.

[0027] As described above, in the system 1 of this embodiment, the water tank 12a of the vaporizer 12 and the water tank 22a of the remover 22 are integrated. That is, the water tank 12a that stores the water 60 used for vaporizing the liquid ammonia and the water tank 22a that stores the water 60 used for removing the residual ammonia are both used as a single water tank, which simplifies the system configuration. Furthermore, since the exhaust gas discharged from the fuel cell 20 has a relatively high temperature (approximately 700°C), when the exhaust gas is introduced into the water 60 stored in the water tanks 12a and 22a, the residual ammonia is removed and the temperature of the water 60 is raised. In this way, by integrating the water tanks 12a and 22a, the removal of the residual ammonia and the supply of energy to maintain the water temperature required for vaporizing the liquid ammonia can be performed simultaneously. Therefore, in this embodiment, the system configuration can be simplified and the system can be operated efficiently.

[0028] In this embodiment, the water tanks 12a and 22a are supplied with water discharged from the fuel cell 20. This prevents the water 60 in the water tanks 12a and 22a from decreasing due to evaporation or the like, reducing the frequency with which water needs to be replenished in the water tanks 12a and 22a.

[0029] In this embodiment, nitrogen is separated from the exhaust gas (a mixed gas of hydrogen and nitrogen) from which residual ammonia has been removed by the nitrogen separation membrane 24, and the hydrogen that has permeated the nitrogen separation membrane 24 is supplied as fuel gas to the fuel cell 20. Therefore, the hydrogen in the exhaust gas can be effectively utilized.

[0030] This embodiment also includes a neutralizer 28 that neutralizes the water 60 stored in the water tanks 12a and 22a. The water 60 containing dissolved ammonia can be neutralized by the neutralizer 28, which can suppress corrosion of the system and unpleasant odors in the water. Furthermore, the neutralized water 62 is approximately neutral, so it can be easily treated as wastewater.

[0031] In this embodiment, the heat exchanger 14 lowers the temperature of the exhaust gas discharged from the fuel cell 20, and also raises the temperature of the gaseous ammonia vaporized by the vaporizer 12. This allows the temperature of the gaseous ammonia to be raised in advance before being introduced into the reformer 16. Furthermore, because the temperature of the exhaust gas is lowered, it is possible to prevent the temperature of the water 60 stored in the water tanks 12a and 22a from being raised excessively.

[0032] Example 2 2, the fuel cell system 100 of the second embodiment differs from the first embodiment in that fuel gas, instead of exhaust gas, is introduced into the remover 22. The other configurations are the same as those of the first embodiment.

[0033] In the second embodiment, as shown in FIG. 2 , the reformer 16 is connected to the remover 22 via a fuel gas supply pipe 134. That is, after gaseous ammonia is reformed into fuel gas by the reformer 16, the fuel gas is introduced into the remover 22 via the heat exchanger 14. In the heat exchanger 14, the temperature of the fuel gas is lowered by heat exchange with the gaseous ammonia before being introduced into the reformer 16. The fuel gas supply pipe 134 extends into the water 60 in the water tank 22a, and the fuel gas flowing through the fuel gas supply pipe 134 flows into the water 60 in the water tank 22a through a plurality of discharge holes 134a provided at the tip of the fuel gas supply pipe 134. As described in the first embodiment, residual ammonia may be present in the fuel gas. In this embodiment, the residual ammonia contained in the fuel gas is removed by the remover 22. The fuel gas from which the residual ammonia has been removed is introduced into the separation pipe 38.

[0034] The fuel gas (i.e., a mixed gas of hydrogen and nitrogen) from which the residual ammonia has been removed is separated into hydrogen and nitrogen by the nitrogen separation membrane 24. Then, the hydrogen that has permeated the nitrogen separation membrane 24 is supplied to the anode 20a of the fuel cell 20 as the fuel gas.

[0035] In the system 100 of the present embodiment, residual ammonia is removed from the fuel gas generated by the reformer 16 before it is supplied to the fuel cell 20. In the first embodiment, a solid oxide fuel cell was used as the fuel cell 20, but it is known that, for example, a polymer electrolyte fuel cell (PEFC) is prone to deterioration due to impurities such as ammonia. For this reason, the system 100 of the second embodiment is particularly useful when using a type of fuel cell (for example, a polymer electrolyte fuel cell) that has a relatively low tolerance for impurities.

[0036] In the second embodiment, similarly to the first embodiment, the exhaust gas and discharged water discharged from the fuel cell 20 may be introduced into the remover 22. With this configuration, the unreacted fuel gas (hydrogen) and discharged water in the fuel cell 20 can be effectively utilized.

[0037] Example 3 3, in a fuel cell system 200 of the third embodiment, a water tank 112a of the vaporizer 112 and a water tank 122a of the remover 122 are separate bodies. The water tanks 112a and 122a are connected by a communication pipe 114. That is, water in the water tanks 112a and 122a can circulate through the communication pipe 114. The other configurations are the same as those of the first embodiment.

[0038] In the third embodiment, the discharge pipe 36 passes through the water 60 in the water tank 112a of the vaporizer 112, and then is introduced into the water tank 122a of the remover 122. That is, the discharge pipe 36 first enters the water tank 112a, passes through the communication pipe 114, and is then introduced into the water tank 122a. The discharge hole 36a of the discharge pipe 36 is provided so as to be located inside the water tank 122a of the remover 122.

[0039] In the system 200 of the third embodiment, the exhaust gas discharged from the fuel cell 20 is first introduced into the water tank 112a for vaporizing the liquid ammonia. Since the exhaust gas, which is at a relatively high temperature, is introduced into the water tank 112a before the water tank 122a, the water temperature required for vaporizing the liquid ammonia can be efficiently maintained by heat exchange between the exhaust gas and the water 60 in the water tank 112a.

[0040] In the third embodiment, the configuration of the second embodiment (that is, the configuration in which the fuel gas generated in the reformer 16 is introduced into the remover 22) may be applied to the third embodiment.

[0041] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. Modifications of the above-described embodiments are listed below.

[0042] (Variation) In the above-described embodiment, an example in which liquid ammonia is used as the liquid fuel has been described, but for example, a compound containing hydrocarbons, alcohol, or the like may also be used as the liquid fuel.

[0043] Furthermore, instead of using a neutralization reaction to neutralize the water 62 in the neutralizer 28, a buffer solution may be introduced and the buffering action of the buffer solution may be used to neutralize the water 62. For example, a phosphate buffer solution may be used as the buffer solution.

[0044] In the first and third embodiments, the components for separating nitrogen from a mixed gas of hydrogen and nitrogen and reusing the hydrogen (i.e., the separation tube 38, the nitrogen separation membrane 24, and the hydrogen supply tube 40) may not be provided. Also, in each embodiment, the heat exchanger 14 and the neutralizer 28 may not be provided.

[0045] Furthermore, in each embodiment, a pressure-boosting mechanism for increasing the pressure of hydrogen may be provided in the hydrogen supply pipe 40. For example, an ejector, a blower, or the like may be provided in the hydrogen supply pipe 40 to supply pressurized hydrogen to the fuel cell 20. With such a configuration, fuel gas (hydrogen) can be efficiently supplied to the fuel cell 20.

[0046] The technical elements described in this specification or drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of those objectives is itself technically useful. [Explanation of symbols]

[0047] 1: Fuel cell system 4: Liquid fuel tank 5:Liquid fuel 6: Pump 12: Vaporizer 12a: Aquarium 12b: Evaporator 14: Heat exchanger 16: Reformer 20: Fuel cell 22: Remover 22a: Aquarium 24: Nitrogen separation membrane 28: Neutralizer 60:Water

Claims

1. 1. A fuel cell system, comprising: a vaporizer that vaporizes the liquid fuel by heat exchange with water stored in a water tank; a reformer that generates fuel gas by reforming the gaseous fuel vaporized by the vaporizer; a fuel cell that generates electricity using the fuel gas produced by the reformer and air; a remover that removes impurities contained in at least one of the exhaust gas discharged from the fuel cell and the fuel gas generated by the reformer using water stored in a water tank; Equipped with The water tank of the vaporizer and the water tank of the remover share water. Fuel cell system.

2. 2. The fuel cell system according to claim 1, A fuel cell system configured such that at least a portion of the water stored in the water tank of the vaporizer and the water tank of the remover is supplied from the discharged water discharged from the fuel cell.

3. 3. The fuel cell system according to claim 1, A fuel cell system, wherein the vaporizer water tank and the remover water tank are integrated.

4. 3. The fuel cell system according to claim 1, The water tank of the vaporizer and the water tank of the remover are separate bodies but communicate with each other, A fuel cell system configured such that the exhaust gas discharged from the fuel cell or the fuel gas generated by the reformer is heat exchanged with water stored in the water tank of the vaporizer and then passes through the water stored in the water tank of the remover.

5. The fuel cell system according to any one of claims 1 to 4, The fuel cell system is configured so that hydrogen contained in the exhaust gas from which impurities have been removed by the remover is supplied to the fuel cell as the fuel gas.

6. The fuel cell system according to any one of claims 1 to 5, The fuel cell system further comprises a neutralizer that neutralizes the water stored in the water tank of the vaporizer and the water tank of the remover.

7. 7. The fuel cell system according to claim 6, The neutralizer neutralizes water by utilizing a neutralization reaction with an acid or a base.

8. 7. The fuel cell system according to claim 6, The neutralizer neutralizes water by utilizing the buffering action of a buffer solution.

9. The fuel cell system according to any one of claims 1 to 8, The fuel cell system further comprises a heat exchanger that raises the temperature of the gaseous fuel vaporized by the vaporizer through heat exchange with the exhaust gas discharged from the fuel cell.

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