Solid acid fuel cells

Abstract

To provide a solid oxide type fuel cell capable of preventing occurrence of a sudden boiling phenomenon by suppressing an increase in temperature of a vaporizer.SOLUTION: A solid oxide type fuel cell comprises: modified water supply means (14) of supplying modified water; a vaporizer (2) that vaporizes the modified water to a water vapor; a reformer (4) that to make a fuel gas react with the water vapor from the vaporizer (2) to reforms the water vapor; and a cell stack (6) that generates power by a fuel battery reaction of a reformed gas from the reformer (4) with air. The solid oxide type fuel cell further comprises cooling gas ejection means (48), and the cooling gas ejection means (48) ejects a cooling gas into the vaporizer (2) to cool it. The modified water supply means (14) includes a water supply pipe (10) for supplying the reformed water from a water supply pump (12) to the vaporizer (2). The cooling gas ejection means (48) ejects the cooling gas toward a drop region where the reformed water drops through the water supply pipe (10) at a bottom wall of the vaporizer (2).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a solid oxide fuel cell (hereinafter also referred to as "SOFC") provided with a vaporizer for vaporizing reformed water.

Background Art

[0002] As a solid oxide fuel cell (SOFC), for example, a fuel gas (e.g., city gas, etc.) is steam reformed to produce a reformed gas, and this reformed gas is supplied to the fuel electrode (anode) side of a cell stack. Also, air as an oxidant is supplied to the oxygen electrode (cathode) side of the cell stack, and power generation is performed by a fuel cell reaction in this cell stack. Such a solid oxide fuel cell includes a vaporizer for vaporizing reformed water and a reformer for steam reforming, the reformed water is supplied to the vaporizer, and the steam vaporized in the vaporizer is fed to the reformer. Further, the fuel gas is supplied to the reformer (or the vaporizer), and steam reforming of the fuel gas is performed using steam in this reformer.

[0003] In such an SOFC, when steam reforming of a hydrocarbon-based fuel gas (e.g., methane) is performed with steam under a high-temperature condition in a reformer, the fuel gas is converted into hydrogen and carbon monoxide by the following reaction.

[0004] CH4 + H2O → CO + 3H2 ···(1) On the other hand, when the fuel gas (e.g., methane) is heated without steam, the following reaction (Boudouard reaction) proceeds and carbon is deposited.

[0005] CH4 → C + 2H2 ···(2) Also, carbon is deposited from carbon monoxide by the following reaction using a metal such as nickel as a catalyst.

[0006] 2CO → C + CO2 ···(3) If carbon deposition progresses on the fuel electrode (anode) of the cell stack, it leads to a decrease in the power generation performance of the cell stack. Furthermore, if carbon deposition progresses in the reformer, it can cause blockage of the reformer and fouling of the reforming catalyst.

[0007] For these reasons, in order for steam reforming to occur as required in this reformer, a stable supply of steam is necessary. To achieve this, it is important that reformed water is supplied to the vaporizer to generate steam stably, and that the generated steam is then supplied to the reformer as required to react with the fuel gas.

[0008] Therefore, a SOFC has been proposed that stably generates water vapor in the vaporizer (evaporator) (see, for example, Patent Document 1). In this SOFC, the temperature is made to be high downstream of the fuel gas and vaporizer, while the temperature on the upstream side is not made to be excessively high, so that the temperature gradient in the vaporizer increases towards the downstream side. In such a vaporizer (evaporator), reformed water is supplied to the upstream side of the vaporizer, and the supplied reformed water flows downstream toward the high-temperature part, and by flowing in this manner, the reformed water is gradually heated and water vapor is generated. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Patent No. 6848104 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, the following problems may arise in this SOFC. Generally, the amount of reformed water used to generate the steam used in steam reforming is small, while the inside of the vaporizer (evaporator) is at a high temperature of several hundred degrees. Therefore, when the reformed water supplied to the vaporizer (supplied in droplet form) drips onto the contact surface (evaporation surface) of the vaporizer, it may vaporize, become superheated, and cause sudden boiling.

[0011] Generally, the phenomenon in which bubbles are formed when a liquid reaches its boiling point is called boiling. However, there is a state in which bubbles are not formed even when a liquid reaches its boiling point. This state is called a superheated state, and if some stimulus (for example, vibration or the introduction of impurities) is applied to this superheated state, the liquid will suddenly boil explosively. This phenomenon is called bumping.

[0012] The vaporizer (part 2) becomes overheated, and if any stimulus acts on it in this overheated state, sudden boiling will occur. When this sudden boiling occurs, the pressure inside the vaporizer (evaporator) rises sharply, and fuel gas is not supplied to the vaporizer (evaporation chamber), which may lead to a phenomenon called fuel depletion.

[0013] The object of the present invention is to provide a solid oxide fuel cell that can prevent the vaporizer from rising to a high temperature and thus prevent the occurrence of sudden boiling. [Means for solving the problem]

[0014] The solid oxide fuel cell according to claim 1 of the present invention comprises a reformed water supply means for supplying reformed water, a vaporizer for vaporizing the reformed water into water vapor, a reformer for steam reforming by reacting a fuel gas with water vapor from the vaporizer, and a cell stack for generating electricity by a fuel cell reaction between the reformed gas from the reformer and air, The invention is characterized by being provided with a cooling gas injection means for injecting cooling gas into the vaporizer.

[0015] Furthermore, in the solid oxide fuel cell according to claim 2 of the present invention, the reformed water supply means includes a water supply pump for supplying reformed water and a water supply pipe for supplying reformed water from the water supply pump to the vaporizer, wherein the tip of the water supply pipe protrudes into the vaporizer, Cooling gas ejection means The invention is characterized by injecting a cooling gas into the dripping region at the bottom wall of the vaporizer, through the water supply pipe, where the reformed water drips.

[0016] Furthermore, in the solid oxide fuel cell according to claim 3 of the present invention, the cooling gas injection means includes a cooling gas supply pipe that supplies cooling gas to the vaporizer, and the cooling gas is injected through the cooling gas supply pipe toward the dripping region of the vaporizer, and the reformed water supply period in which reformed water is supplied by the reformed water supply means and the cooling gas supply period in which cooling gas is supplied by the cooling gas injection means do not overlap.

[0017] Furthermore, in the solid oxide fuel cell according to claim 4 of the present invention, the cooling gas supply pipe of the cooling gas injection means is provided with a gas flow rate adjustment valve for adjusting the flow rate of the cooling gas, and furthermore, the water supply pump and the Gas flow control valve A controller is provided to control the following: When the supply flow rate of reformed water from the water supply pump decreases, the controller... Gas flow control valve The opening of the valve is increased to control the flow rate of the cooling gas, and when the supply flow rate of reformed water from the water supply pump increases, the Gas flow control valve The method is characterized by controlling the flow rate of the cooling gas by reducing the opening of the valve.

[0018] Furthermore, the solid oxide fuel cell according to claim 5 of the present invention is characterized in that the cooling gas supplied by the cooling gas injection means is an oxygen-free gas. [Effects of the Invention]

[0019] According to the solid oxide fuel cell described in claim 1 of the present invention, the cooling gas injection means injects cooling gas into the vaporizer, so the temperature rise inside the vaporizer is suppressed by the injected cooling gas, and as a result the temperature of the reformed water rises gradually even if the supply amount is small, thus preventing the reformed water from boiling over.

[0020] Furthermore, according to the solid oxide fuel cell described in claim 2 of the present invention, reformed water is dripped into the dripping area of ​​the vaporizer through a water supply pipe. Cooling gas ejection meansSince the cooling gas is jetted toward this dropping region, this dropping region can be effectively cooled, and thereby, even if the dropping amount of the reformed water is small, a rapid temperature rise can be suppressed and the bumping of the reformed water can be prevented.

[0021] Further, according to the solid oxide fuel cell described in claim 3 of the present invention, since the supply period of the reformed water supplied through the water supply pipe and the supply period of the cooling gas supplied through the cooling gas supply pipe do not overlap, the cooling gas is not supplied when the reformed water dropped from the water supply pipe is evaporating. By performing supply control in this way, the dropping region of the vaporizer is not supercooled, and the generation delay of water vapor can be prevented.

[0022] Further, according to the solid oxide fuel cell described in claim 4 of the present invention, a gas flow rate adjustment valve is provided in the cooling gas supply pipe, and the controller reduces the opening degree of the gas flow rate adjustment valve to reduce the jet flow rate of the cooling gas when the supply flow rate of the reformed water from the water supply means increases, and increases the opening degree of the gas flow rate adjustment valve to increase the jet amount of the cooling gas when the supply flow rate of the reformed water decreases. Therefore, the temperature of the dropping region of the vaporizer can be managed as desired regardless of the flow rate of the reformed water.

[0023] Furthermore, according to the solid oxide fuel cell described in claim 5 of the present invention, since the cooling gas is a gas that does not contain oxygen, oxidation of the fuel electrode of the cell stack can be prevented.

Brief Description of the Drawings

[0024] [Figure 1] A schematic view showing a first embodiment of a solid oxide fuel cell according to the present invention. [Figure 2] A partial cross-sectional view showing a vaporizer of the solid oxide fuel cell of FIG. 1 and related configurations. [Figure 3] A diagram showing a supply pattern of reformed water, where FIG. 3(a) is a diagram showing a supply pattern when the supply amount of reformed water is small, FIG. 3(b) is a diagram showing a supply pattern when the supply amount of reformed water is medium, and FIG. 3(c) is a diagram showing a supply pattern when the supply amount of reformed water is large. [Figure 4] A simplified cross-sectional view showing a part of a second embodiment of a solid oxide fuel cell according to the present invention. [Figure 5] A diagram showing the relationship between the supply rate of reformed water and the supply rate of cooling gas. [Modes for carrying out the invention]

[0025] Hereinafter, embodiments of a solid oxide fuel cell according to the present invention will be described with reference to the attached drawings. First, a first embodiment of a solid oxide fuel cell according to the present invention will be described with reference to Figures 1 to 3.

[0026] In Figure 1, the illustrated solid oxide fuel cell (SOFC) comprises a vaporizer 2 that vaporizes reformed water, a reformer 4 that steam reforms fuel gas (e.g., city gas), and a solid oxide cell stack 6 that generates electricity through a fuel cell reaction. In this embodiment, a water supply source 8, which is composed of, for example, a water tank, is connected to the vaporizer 2 via a water supply pipe 10 (which constitutes a water supply channel), and a water supply pump 12 is installed in this water supply pipe 10. When the water supply pump 12 is operated, water from the water supply source 8 is supplied to the vaporizer 2 as reformed water through the water supply pipe 10, and the water supply source 8, water supply pump 12, and water supply pipe 10 (water supply channel) constitute a water supply means 14 that supplies reformed water to the vaporizer 2.

[0027] Furthermore, a fuel gas supply source 16, which consists of, for example, a fuel tank and buried pipes, is connected to a reformer 4 via a fuel gas supply pipe 18 (which constitutes a fuel gas supply path), and a fuel gas supply pump 20 is installed in this fuel gas supply pipe 18. When this fuel gas supply pump 20 is activated, fuel gas from the fuel gas supply source 16 is supplied to the reformer 4 through the fuel gas supply pipe 18, and this fuel gas supply source 16, fuel gas supply pump 20, and fuel gas supply pipe 18 (fuel gas supply path) constitute a fuel gas supply means 22 that supplies fuel gas to the reformer 4.

[0028] The vaporizer 2 vaporizes the reformed water into steam, and the steam generated in the vaporizer 2 is supplied to the reformer 4 through the steam supply channel 24 (which consists of, for example, a steam supply pipe). The reformer 4 is filled with a reforming catalyst, and in this reformer 4, the steam from the vaporizer 2 is used to steam reform the fuel gas supplied from the fuel gas supply means 22.

[0029] The reformed gas, steam reformed in the reformer 4, is supplied to the fuel electrode (anode) side of the cell stack 6 through the reformed gas supply channel 26 (for example, consisting of a reformed gas supply pipe). In addition, air is supplied to the oxygen electrode (cathode) side of the cell stack 6 as an oxidizing gas. An air supply pipe 28 (which constitutes an air supply channel) is connected to the oxygen electrode side of the cell stack 6, and an air blower 30 is installed in this air supply pipe 28. When the air blower 30 is activated, air from the atmosphere is supplied to the cell stack 6 through the air supply pipe 28, and this air blower 30 and air supply pipe 28 constitute an air supply means 32 that supplies air to the cell stack 6.

[0030] In the cell stack 6, electricity is generated by a fuel cell reaction between the reformed gas (reformed fuel gas) from the reformer 4 and the air (oxygen contained in the air) from the air supply means 32. The reformed gas (fuel off-gas) that flows through the fuel electrode of the cell stack 6 and the air off-gas that flows through the air electrode flow into the fuel region 34 above the cell stack 6, where the fuel off-gas (containing fuel gas) is burned by the air off-gas (containing air).

[0031] In this SOFC, the vaporizer 2, reformer 4, and cell stack 6 are housed within an insulated module 36, with the vaporizer 2 and reformer 4 positioned above the cell stack 6. With this configuration, the vaporizer 2 and reformer 4 are heated by combustion in the combustion zone 34 and kept at a high temperature, and this combustion heat is used to keep the inside of the insulated module 36 at a high temperature as well.

[0032] The combustion exhaust gas from within the insulated module 36 is discharged through a combustion gas discharge channel 38 (which consists of, for example, a combustion gas discharge pipe). The combustion gas discharge channel 38 is provided with a combustion section 40, which is equipped with, for example, a combustion catalyst. The combustion exhaust gas from within the insulated module 36 is completely combusted by the catalytic reaction in the combustion section 40 before being discharged to the outside through the combustion gas discharge channel 38.

[0033] In this SOFC, to prevent the reformed water from boiling over in the vaporizer 2, it is further configured as follows: Referring to Figure 2 as well as Figure 1, the water supply pipe 10 penetrates the side wall 42 of the vaporizer 2 and protrudes inward. The reformed water supplied through this water supply pipe 10 is dripped from its tip toward the dripping area S of the bottom wall 44 of the vaporizer 2, as indicated by arrow 46, and the dripped reformed water spreads along the surface of this bottom wall 44 and evaporates.

[0034] At this time, if the dripping region S of the vaporizer 2 is in a high-temperature state (for example, 130°C or higher) due to the combustion heat from the combustion region 34 (is this temperature acceptable as an example?), the reformed water dripped from the tip of the water supply pipe 10 into the dripping region S may be rapidly heated and become overheated. To prevent this overheating, a cooling gas injection means 48 is provided to inject cooling gas into the vaporizer 2.

[0035] To explain further, the illustrated cooling gas injection means 48, as shown in Figure 1, comprises a cooling gas supply source 50, which is for example composed of a cooling tank, and a cooling gas supply pipe 52 (which constitutes a cooling gas supply path) that supplies cooling gas from the cooling gas supply source 50 to the vaporizer 2. A cooling gas supply pump 54 is installed in this cooling gas supply pipe 52, and when this cooling gas supply pump 54 is operated, cooling gas from the cooling gas supply source 50 is supplied to the vaporizer 2 through the cooling gas supply pipe 52.

[0036] It is preferable to use an oxygen-free gas as the cooling gas, as this prevents oxidation of the fuel electrode of the cell stack 6. For example, nitrogen gas can be used as the cooling gas.

[0037] In this embodiment, as shown in Figure 2, the tip end (downstream end) of the cooling gas supply pipe 52 penetrates the side wall 42 of the vaporizer 2 and protrudes inward, protruding somewhat further inward than the tip of the reformed water pipe 10, and this tip extends downward toward the dripping region S of the bottom wall 44 of the vaporizer 2. With this configuration, the cooling gas supplied through the cooling gas supply pipe 10 is ejected toward the dripping region S, as indicated by arrow 56, thereby effectively cooling the dripping region S with the cooling gas and preventing it from becoming hot.

[0038] In this embodiment, the reformed water supplied from the water supply means 14 and the cooling gas supplied from the cooling gas injection means 48 are supplied at the timings shown in Figure 3. For example, when the supply amount of reformed water is small, as shown in Figure 3(a), the reformed water is supplied only once during the time X of one cycle T, and the cooling gas is supplied during the period when reformed water is not supplied. When the supply amount of reformed water is moderate, as shown in Figure 3(b), the reformed water is supplied twice during the time X of one cycle T, and the cooling gas is supplied during the period when reformed water is not supplied. Furthermore, when the supply amount of reformed water is large, as shown in Figure 3(c), the reformed water is supplied four times during the time X of one cycle T, and the cooling gas is supplied during the period when reformed water is not supplied, as described above.

[0039] By timing the supply of reformed water and cooling gas in this way, during the period when reformed water is supplied, the dripping region S of the vaporizer 2 is cooled by the vaporization of the reformed water, and during the period when reformed water is not supplied, it is cooled by the cooling gas ejected from the cooling gas ejection means 48. Therefore, it is possible to prevent the dripping region S from becoming excessively hot and to prevent the boiling of the reformed water. Furthermore, since the reformed water supply period and the cooling gas supply period do not overlap, the dripping region S of the vaporizer 2 is not cooled simultaneously by the reformed water and cooling gas, thereby preventing the dripping region S from becoming overcooled.

[0040] Next, a second embodiment of the solid oxide fuel cell according to the present invention will be described with reference to Figures 4 and 5. In this second embodiment, the amount of cooling gas supplied is controlled according to the amount of reformed water supplied. In this second embodiment, the same numbers are used for components as in the first embodiment described above, and their descriptions are omitted.

[0041] In Figure 4, which shows a part of a solid oxide fuel cell, in this second embodiment, the controller 62 that controls the solid oxide fuel cell includes a fuel gas supply amount calculation means 64, a reformed water supply amount calculation means 66, an air supply amount calculation means 68, and a cooling gas supply amount calculation means 70. The fuel gas supply amount calculation means 64 calculates the amount of fuel gas to be supplied according to the power output of the cell stack (not shown), and the controller 62 controls the rotation speed of the fuel gas pump (not shown) based on this supply amount, thereby controlling the amount of fuel gas supplied from the fuel gas supply means (not shown). The reformed water supply amount calculation means 66 calculates the amount of reformed water to be supplied according to the power output of the cell stack (not shown), and the controller 62 controls the rotation speed of the water supply pump 12 based on this supply amount, thereby controlling the amount of reformed water supplied from the water supply means 14. Furthermore, the air supply amount calculation means 68 calculates the amount of air to be supplied according to the power generation output of the cell stack (not shown), and the controller 62 controls the rotation speed of the air blower (not shown) based on this supply amount, thereby controlling the amount of air supplied from the air supply means (not shown).

[0042] Furthermore, the cooling gas supply amount calculation means 70 calculates the cooling gas supply amount as follows. In this embodiment, the controller 62 further includes a memory means 72, which stores, for example, the reformed water-cooling gas supply map shown in Figure 5, and the cooling gas supply amount is calculated based on this reformed water-cooling gas supply map which shows the relationship between the amount of reformed water supplied and the amount of cooling gas supplied.

[0043] Referring also to Figure 5, when the supply amount of reformed water increases, a lot of heat is consumed in the vaporization of the reformed water, causing the temperature of the dripping region S of the vaporizer 2 to tend to decrease. Therefore, the supply amount of cooling gas from the cooling gas injection means 48A is controlled to decrease. When the supply amount of reformed water decreases, less heat is consumed in the vaporization of the reformed water, causing the temperature of the dripping region S to tend to increase. Therefore, the supply amount of cooling gas from the cooling gas injection means 48A is controlled to increase.

[0044] To control the supply amount of cooling gas in this manner, a gas flow rate control valve 74 is provided in the cooling gas supply pipe 52. This gas flow rate control valve 74 is located downstream of the cooling gas supply pump 54 and controls the supply amount of cooling gas supplied through the cooling gas supply pipe 52 as described later. The other configurations of the solid oxide fuel cell in this second embodiment are the same as those of the first embodiment shown in Figures 1 to 3.

[0045] In this second embodiment, when the reformed water supply amount calculation means 66 calculates the amount of reformed water to be supplied, the cooling gas supply amount calculation means 70 calculates the amount of cooling gas to be supplied based on the cooling water-cooling gas supply map registered in the memory means 72, and the controller 62 controls the amount of cooling gas supplied from the cooling gas ejection means 48A by controlling the opening of the gas flow rate control valve 74. The cooling gas supply amount calculation means 70 calculates to reduce (or increase) the amount of cooling gas supplied based on the reformed water-cooling gas supply map if the amount of reformed water supplied from the water supply means 14 is large (or small), and as a result the controller 62 reduces (or increases) the amount of cooling gas supplied by making the opening of the gas flow rate control valve 74 smaller (or larger), and by controlling the amount of cooling gas supplied in relation to the amount of reformed water supplied in this way, the temperature of the dripping region S of the vaporizer 2 can be kept at an appropriate temperature (for example, around 100°C). In this second embodiment as well, it is preferable that the supply period of reformed water and the supply period of cooling gas do not overlap.

[0046] Although embodiments of solid oxide fuel cells according to the present invention have been described above, the present invention is not limited to these embodiments, and various changes and modifications are possible without departing from the scope of the present invention.

[0047] For example, in the above-described embodiment, the vaporizer 2 and the reformer 4 are configured separately, but the invention is not limited to this configuration and can be similarly applied to a configuration in which the vaporizer 2 and the reformer 4 are configured as a single unit.

[0048] Furthermore, in the embodiment described above, the cooling gas supply means 48 (48A) includes a cooling gas supply pump 54. However, if, for example, cooling gas at a predetermined pressure can be supplied from a cooling gas supply source 50, a supply on-off valve (not shown) may be provided instead of the cooling gas supply pump 54. In this case, when the supply on-off valve is opened, cooling gas is supplied through the cooling gas supply pipe 52, and when the supply on-off valve is closed, the supply of cooling gas is stopped. [Explanation of Symbols]

[0049] 2. Vaporizer 4. Reformer 6-cell stack 10 Water supply pipes 14 Water supply means 22 Fuel gas supply means 32 Air supply means 48,48A Cooling gas ejection means 52 Cooling gas supply pipe 62 Controllers 66. Means for calculating the amount of treated water supplied 70 Cooling gas supply amount calculation means 74 Gas flow control valve S Dripping area

Claims

1. A solid oxide fuel cell comprising: a reformed water supply means for supplying reformed water; a vaporizer for vaporizing the reformed water into steam; a reformer for steam reforming fuel gas by reacting it with the steam from the vaporizer; and a cell stack for generating electricity through a fuel cell reaction between the reformed gas from the reformer and air, A solid oxide fuel cell is characterized in that a cooling gas injection means for injecting cooling gas into the vaporizer is provided.

2. The solid oxide fuel cell according to claim 1, wherein the reformed water supply means includes a water supply pump for supplying reformed water and a water supply pipe for supplying reformed water from the water supply pump to the vaporizer, the tip of the water supply pipe protruding into the vaporizer, and the cooling gas ejection means ejects cooling gas toward a dripping region on the bottom wall of the vaporizer through the water supply pipe where the reformed water drips.

3. The solid oxide fuel cell according to claim 2, wherein the cooling gas ejection means includes a cooling gas supply pipe that supplies cooling gas to the vaporizer, and the cooling gas is ejected through the cooling gas supply pipe toward the dripping region of the vaporizer, and the reformed water supply period during which reformed water is supplied by the reformed water supply means and the cooling gas supply period during which cooling gas is supplied by the cooling gas ejection means do not overlap.

4. The cooling gas supply pipe of the cooling gas ejection means is provided with a gas flow rate control valve for adjusting the flow rate of the cooling gas, and further, a controller is provided for controlling the water supply pump and the gas flow rate control valve, wherein the controller controls the opening of the gas flow rate control valve to increase the flow rate of the cooling gas when the supply flow rate of reformed water from the water supply pump decreases, and controls the opening of the gas flow rate control valve to decrease the flow rate of the cooling gas when the supply flow rate of reformed water from the water supply pump increases.

5. The solid oxide fuel cell according to claim 1, characterized in that the cooling gas supplied by the cooling gas injection means is an oxygen-free gas.

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