Fuel Cell Systems

Abstract

The fuel cell system according to the present disclosure includes a fuel cell having an anode and a cathode, a branching section that branches an anode off-gas discharged from the anode into a branched gas and a recycled gas, a gas separation device that separates the branched gas into a carbon dioxide-rich gas having a higher carbon dioxide concentration than the branched gas and a residual gas having a lower carbon dioxide concentration than the branched gas, a pressure regulator that adjusts the pressure of the anode off-gas inside the gas separation device, a pressure gauge that acquires the pressure of the branched gas, a gas information acquisition section that acquires gas information relating to at least the composition and flow rate of the branched gas, and a control device that controls the pressure regulator based on the pressure acquired by the pressure gauge and the gas information acquired by the gas information acquisition section.

Description

[Technical field]

[0001] The present disclosure relates to fuel cell systems. [Background technology]

[0002] Patent Document 1 discloses a technology for separating carbon dioxide from anode off-gas discharged from the anode of a fuel cell. Specifically, the anode off-gas is introduced into a separation section having a separation membrane. The separation membrane in Patent Document 1 has the property of being easily permeable to carbon dioxide and water, but being difficult to permeate other components. Therefore, the carbon dioxide concentration of the gas that has permeated the separation membrane is higher than that of the anode off-gas. The remaining gas of the anode off-gas that has not permeated the separation membrane contains combustible components such as hydrogen. This gas is reused as regenerated fuel gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-139858 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, when the fuel cell is operating at partial load, the flow rate of the anode off-gas introduced into the separation section is reduced compared to when the fuel cell is operating at rated load. Other factors may also reduce the flow rate of the anode off-gas introduced into the separation section. When the flow rate of the anode off-gas is reduced, the area of ​​the separation membrane for the anode off-gas per unit flow rate increases relatively. This causes an increase in the permeation amount of components that are less likely to permeate the separation membrane than carbon dioxide, such as hydrogen. As a result, a problem occurs in that the concentration of carbon dioxide contained in the recovered gas is reduced.

[0005] In view of the above circumstances, an object of the present disclosure is to provide a fuel cell system that can suppress a decrease in the carbon dioxide concentration of the separated gas when the flow rate of the gas introduced into the separation membrane changes. [Means for solving the problem]

[0006] One aspect of a fuel cell system according to the present disclosure includes a fuel cell having an anode and a cathode, a branching section that branches an anode off-gas discharged from the anode into a branched gas and a recycled gas, a gas separation device that separates the branched gas into a carbon dioxide-rich gas having a higher carbon dioxide concentration than the branched gas and a residual gas having a lower carbon dioxide concentration than the branched gas, a pressure regulator that adjusts the pressure of the anode off-gas inside the gas separation device, a pressure gauge that acquires the pressure of the branched gas, a gas information acquisition section that acquires gas information regarding at least the composition and flow rate of the branched gas, and a control device that controls the pressure regulator based on the pressure acquired by the pressure gauge and the gas information acquired by the gas information acquisition section. Effect of the Invention

[0007] According to the fuel cell system of the present disclosure, when the flow rate of the gas introduced into the separation membrane changes, it is possible to suppress a decrease in the carbon dioxide concentration of the separated gas. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram showing a configuration of a fuel cell system according to a first embodiment. [Diagram 2] 1 is a graph illustrating the relationship between pressure and temperature and the carbon dioxide permeability in a separation membrane. [Diagram 3] 1 is a graph illustrating the relationship between pressure and temperature and the concentration of carbon dioxide in a separation membrane. [Figure 4] 1 is a graph illustrating the relationship between pressure and fuel cell load and the carbon dioxide permeability in a separation membrane. [Diagram 5]4 is a graph illustrating the relationship between pressure and fuel cell load and the concentration of carbon dioxide in a separation membrane. [Figure 6] FIG. 11 is a diagram showing a configuration of a separation device according to a second embodiment. [Figure 7] FIG. 11 is a diagram showing a configuration of a separation device according to a first modified example of the second embodiment. [Figure 8] FIG. 13 is a diagram showing a configuration of a separation device according to a second modified example of the second embodiment. [Figure 9] FIG. 13 is a diagram showing a configuration of a separation device according to a third modified example of the second embodiment. [Figure 10] FIG. 11 is a diagram showing the configuration of a fuel cell system according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the scope of the present disclosure is not limited to the following embodiments, and may be modified as desired within the scope of the technical concept of the present disclosure.

[0010] Embodiment 1 Fig. 1 is a schematic diagram of a fuel cell system 100 according to embodiment 1. As shown in Fig. 1, the fuel cell system 100 includes a supply path 1, a raw material flow meter 1a, a mixer 2, a reformer 3, a fuel cell 4, a steam generator 7, a condensation tank 9, a branching section 10, a compressor 12, a temperature regulator 13, a control device 19, a pressure gauge 20, a control valve 21, a thermometer 22, and a gas separation device D.

[0011] Although details will be described later, the fuel cell 4 discharges an anode off-gas G containing carbon dioxide. A part of the anode off-gas G is supplied as branch gas G1 to a gas separation device D. The gas separation device D has a function of separating the branch gas G1 into a carbon dioxide-rich gas G11 having a high carbon dioxide concentration and a regenerated fuel gas G12 having a low carbon dioxide concentration.

[0012] The supply path 1 supplies the raw material to the mixer 2. As the raw material, a carbon-containing material such as a hydrocarbon can be used. An example of the hydrocarbon is methane. In the following, the case where the raw material is methane will be described, but the raw material is not limited to methane. The supply path 1 is provided with a raw material flow meter 1a. The raw material flow meter 1a measures the flow rate of the raw material supplied to the mixer 2. The measurement result of the raw material flow meter 1a may be input to, for example, the operating state acquisition unit 18 or the control device 19. A raw material supply system 2a is connected to the mixer 2. The raw material is mixed with a recycle gas G2 and steam described later in the mixer 2, and is introduced into the reformer 3 via the raw material supply system 2a.

[0013] The reformer 3 generates a reformed gas by a steam reforming reaction or a carbon dioxide reforming reaction. The reformed gas contains hydrogen. The steam reforming reaction follows, for example, the following formulas (I) and (II). CH4 + H2O → CO + 3H2 (I) CO+H2O→CO2+H2 (II) The carbon dioxide reforming reaction follows, for example, the following formulas (III) and (IV). CH4 + CO2 → 2CO + 2H2 (III) 2CO+2H2O → 2CO2+2H2...(IV)

[0014] The reformer 3 preferably has at least one of a steam reforming catalyst and a carbon dioxide reforming catalyst. In addition, it is more preferable that the reformer 3 has both a steam reforming catalyst and a carbon dioxide reforming catalyst. The steam reforming catalyst promotes the steam reforming reaction. The carbon dioxide reforming catalyst promotes the carbon dioxide reforming reaction. Examples of the steam reforming catalyst include Ni-supported alumina and Ru-supported alumina. Examples of the carbon dioxide reforming catalyst include Ni-supported yttria and Pt-supported yttria.

[0015] The steam reforming catalyst and the carbon dioxide reforming catalyst may be mixed and packed into the reformer 3. The steam reforming catalyst and the carbon dioxide reforming catalyst may form different layers and be packed into the reformer 3. The steam reforming catalyst and the carbon dioxide reforming catalyst may be packed into the reformer 3 so that they are located in appropriate temperature zones for the respective catalysts to function, for example.

[0016] The temperature inside the reformer 3 is set so that at least one of the steam reforming reaction and the carbon dioxide reforming reaction proceeds. A temperature distribution suitable for each reaction may be set inside the reformer 3 so that both the steam reforming reaction and the carbon dioxide reforming reaction proceed. A combustor 3a is thermally connected to the reformer 3. The combustor 3a burns fuel to generate heat so that the inside of the reformer 3 is in an appropriate temperature range. As fuel for the combustor 3a, the cathode offgas discharged from the cathode 4B, the regenerated fuel gas G12 discharged from the gas separation device D, etc. can be used. The regenerated fuel gas G12 will be described later.

[0017] The air supply system 5 supplies air to the fuel cell 4. The air supplied from the air supply system 5 is an oxygen-containing gas. The oxygen-containing gas contains oxygen (O2) as an oxidant. The air supply system 5 is provided with an air supply blower 5a for causing the air to flow toward the fuel cell 4. The air supply system 5 is also provided with a heat exchanger 17. The heat exchanger 17 exchanges heat between the air flowing in the air supply system 5 and the combustion off-gas discharged from the combustor 3a. This allows the air introduced into the cathode 4B to be heated by utilizing the exhaust heat from the combustor 3a.

[0018] The fuel cell 4 has an anode 4A and a cathode 4B. The reformed gas obtained in the reformer 3 is supplied to the anode 4A of the fuel cell 4. Air supplied from an air supply system 5 is supplied to the cathode 4B of the fuel cell 4. The fuel cell 4 generates electricity by reacting the reformed gas containing hydrogen (H2) with air (oxidant), thereby generating electrical energy. The fuel cell system 100 can also be called a power generation system.

[0019] The fuel cell 4 may be, for example, a solid oxide fuel cell. In the case of a solid oxide fuel cell, the reaction at the anode 4A follows formula (V) below, and the reaction at the cathode 4B follows formula (VI) below. H2+O 2- →H2O+2e - (V) 1 / 2O2+2e - →O 2- (VI)

[0020] Anode off-gas G is discharged from the anode 4A of the fuel cell 4. The anode off-gas G contains, for example, hydrogen (H2), carbon dioxide (CO2), water vapor (H2O), carbon monoxide (CO), and methane (CH4). The anode off-gas system 6 extracts the anode off-gas G from the anode 4A of the fuel cell 4 and guides it to a branching section 10. In the anode off-gas system 6, a water vapor generator 7, a heat recovery device 6a, and a condensation tank 9 are arranged in a portion between the fuel cell 4 and the branching section 10.

[0021] The condensation tank 9 can condense a portion of the water vapor contained in the anode off-gas G. The water obtained in the condensation tank 9 is supplied to the water vapor generator 7 via a pump 23a and a flow rate controller 23. The pump 23a generates power for causing the water to flow from the condensation tank 9 toward the water vapor generator 7. The flow rate controller 23 controls the flow rate of the water supplied to the water vapor generator 7. The measurement result of the flow rate controller 23 may be input to, for example, the operating state acquisition unit 18 or the control device 19.

[0022] The water vapor generator 7 heats the water supplied from the condensation tank 9 by heat exchange with the anode off-gas G. As a result, the water vapor generator 7 obtains water vapor. The water vapor generator 7 has an auxiliary heater 7a. The auxiliary heater 7a is, for example, a heater. When the amount of heat required for evaporating water is insufficient only through heat exchange with the anode off-gas G, the auxiliary heater 7a may be used to heat the water. The water vapor obtained by the water vapor generator 7 is introduced into the mixer 2 from a water vapor supply system 8.

[0023] The heat recovery device 6a is located upstream of the condensation tank 9 and can recover heat from the anode off-gas G. This allows, for example, the anode off-gas G to be set to a temperature equal to or lower than the heat-resistant temperature of a recycle gas blower 16a (described later). A branching section 10 is disposed downstream of the condensation tank 9. At the branching section 10, the anode off-gas system 6 branches into a branch gas system 11 and a recycle gas system 16. The recycle gas system 16 supplies at least a portion of the anode off-gas G to the mixer 2 as a recycle gas G2.

[0024] The branching section 10 can change the distribution ratio of the anode off-gas G to the branch gas system 11 and the recycle gas system 16. The branching section 10 may have, for example, a control valve for changing the distribution ratio. More specifically, the control valve may change the ratio of the flow path cross-sectional area to the branch gas system 11 and the flow path cross-sectional area to the recycle gas system 16 in the branching section 10. In addition, a thermocouple may be provided inside the condensation tank 9 to measure the condensation temperature, thereby making it possible to know the amount of water vapor in the gas. In addition, the measurement result may be input to, for example, the control device 19. However, the structure for changing the distribution ratio in the branching section 10 is not limited to the above and can be appropriately changed.

[0025] The recycled gas system 16 is provided with a recycled gas blower 16a and a recycled gas flowmeter 16b. The recycled gas blower 16a generates power to cause the recycled gas G2 to flow from the branching portion 10 toward the mixer 2. The recycled gas flowmeter 16b measures the flow rate of the recycled gas G2 supplied to the mixer 2. In this manner, the recycled gas system 16 circulates the recycled gas G2 to the raw material supply system 2a.

[0026] The branch gas system 11 supplies at least a portion of the anode off-gas G to the gas separation device D as a branch gas G1. The branch gas system 11 is provided with a gas information acquisition unit 11a, a compressor 12, and a temperature regulator 13. The gas information acquisition unit 11a acquires information on the branch gas G1. The "information on the branch gas G1" is, for example, the composition, flow rate, pressure, temperature, etc. The information on the composition of the branch gas G1 may include, for example, the partial pressure of carbon dioxide. Since the branch gas G1 is a part of the anode off-gas G, it can also be said that the gas information acquisition unit 11a acquires information on the anode off-gas G.

[0027] The gas information acquisition unit 11a has a sensor or the like according to the type of information to be acquired. For example, when acquiring a composition, the gas information acquisition unit 11a may have a near-infrared spectroscopic sensor. For example, when acquiring a flow rate, pressure, temperature, or the like, the gas information acquisition unit 11a may have a flowmeter, a pressure gauge, a thermometer, or the like. The gas information acquisition unit 11a may have a plurality of types of sensors as described above. However, the gas information acquisition unit 11a may calculate the composition and flow rate of the branch gas G1 based on the operating state of the fuel cell 4 acquired by the operating state acquisition unit 18, the raw material flow rate acquired by the raw material flow meter 1a, the condensation temperature in the condensation tank 9, and the distribution ratio of the anode off-gas G in the branch unit 10.

[0028] The compressor 12 can increase the pressure of the branch gas G1 supplied to the gas separation apparatus D. The compressor 12 may be, for example, a blower. The pressure of the branch gas G1 in the gas separation apparatus D can be changed by adjusting the output of the compressor 12. Therefore, the compressor 12 can function as a pressure regulator Cp that adjusts the pressure of the branch gas G1 in the gas separation apparatus D. The temperature regulator 13 can adjust the temperature of the branch gas G1 supplied to the gas separation apparatus D.

[0029] In the example of FIG. 1, the temperature regulator 13 has a pump 13a and a heat exchanger 13b. In the heat exchanger 13b, heat exchange is performed between the refrigerant and the branched gas G1. The pump 13a generates power for the refrigerant to flow in the heat exchanger 13b. By changing the output of the pump 13a, the flow rate of the refrigerant flowing in the heat exchanger 13b changes. Therefore, by adjusting the output of the pump 13a, the amount of heat exchanged between the refrigerant and the branched gas G1 in the heat exchanger 13b can be adjusted. This allows the temperature regulator 13 to adjust the temperature of the branched gas G1. However, the configuration of the temperature regulator 13 is not limited to the above, and can be changed as appropriate as long as it can adjust the temperature of the branched gas G1.

[0030] In this embodiment, the gas separation apparatus D has one carbon dioxide separation unit 14. The carbon dioxide separation unit 14 has a separation membrane S that selectively allows carbon dioxide to permeate. The carbon dioxide separation unit 14 also has an introduction chamber R1 and a recovery chamber R2 that are partitioned by the separation membrane S. The separation membrane S is formed of, for example, a polymer. The polymer as the separation membrane S may be, for example, polyimide-based. Alternatively, the separation membrane S may have a structure in which a carrier is added to a water-absorbent polymer, which is a so-called facilitated transport membrane.

[0031] The branched gas G1 that flows from the branching section 10 through the branched gas system 11 is first introduced into the introduction chamber R1. Inside the introduction chamber R1, the branched gas G1 comes into contact with the separation membrane S. The branched gas G1 comes into contact with the separation membrane S at a pressure adjusted by the pressure regulator Cp. As a result, carbon dioxide contained in the branched gas G1 permeates the separation membrane S and moves to the recovery chamber R2. Depending on conditions such as the type and pressure of the separation membrane S, components other than carbon dioxide may also permeate the separation membrane S.

[0032] In this specification, the gas that has permeated the separation membrane S from the introduction chamber R1 and moved to the recovery chamber R2 is referred to as a carbon dioxide-rich gas G11. Also, the gas that does not permeate the separation membrane S and remains is referred to as a regenerated fuel gas G12. That is, the carbon dioxide separation unit 14 uses the separation membrane S to separate the branched gas G1 into the carbon dioxide-rich gas G11 and the regenerated fuel gas G12.

[0033] The carbon dioxide rich gas G11 has a higher carbon dioxide concentration than the branch gas G1 before being separated by the carbon dioxide separation unit 14. The regenerated fuel gas G12 has a lower carbon dioxide concentration than the branch gas G1 before being separated by the carbon dioxide separation unit 14. The regenerated fuel gas G12 also contains combustible components such as hydrogen, carbon monoxide, and methane. Therefore, the regenerated fuel gas G12 can be used as a fuel. In this embodiment, the regenerated fuel gas G12 is used as a fuel in the combustor 3a of the reformer 3. The regenerated fuel gas system 14b is connected to the introduction chamber R1. The combustor 3a is connected to the downstream side of the regenerated fuel gas system 14b. With this configuration, the regenerated fuel gas G12 is supplied from the introduction chamber R1 to the combustor 3a and reused as fuel.

[0034] A carbon dioxide capture system 14a is connected to the recovery chamber R2. The carbon dioxide rich gas G11 is discharged from the recovery chamber R2 to the carbon dioxide capture system 14a. A vacuum pump 15 is disposed in the carbon dioxide capture system 14a. The vacuum pump 15 sucks the carbon dioxide rich gas G11 in the recovery chamber R2 through the carbon dioxide capture system 14a. The carbon dioxide rich gas G11 thus recovered may be reused for other purposes. The vacuum pump 15 may not be provided.

[0035] The pressure gauge 20 measures the pressure of the regenerated fuel gas G12 in the portion of the regenerated fuel gas system 14b between the carbon dioxide separation unit 14 and the regulating valve 21. According to the measurement result of the pressure gauge 20, it is possible to indirectly know the pressure of the branched gas G1 supplied to the carbon dioxide separation unit 14. Note that, if the pressure of the branched gas G1 supplied to the carbon dioxide separation unit 14 can be measured directly or indirectly, the position of the pressure gauge 20 can be changed as appropriate.

[0036] The thermometer 22 measures the temperature of the branched gas G1 in a portion between the temperature regulator 13 and the carbon dioxide separation unit 14 in the branched gas system 11. The position of the thermometer 22 can be changed as appropriate as long as it can measure the temperature of the branched gas G1 supplied to the carbon dioxide separation unit 14.

[0037] The regulating valve 21 is provided in the regenerated fuel gas system 14b. The pressure in the introduction chamber R1 can be adjusted by opening and closing the regulating valve 21. For example, when the aperture of the regulating valve 21 is increased, the regenerated fuel gas G12 flows more easily from the introduction chamber R1 to the combustor 3a. As a result, the pressure in the introduction chamber R1 decreases. Conversely, when the aperture of the regulating valve 21 is decreased, the pressure in the introduction chamber R1 increases. Therefore, the regulating valve 21 can function as a pressure regulator Cp that adjusts the pressure of the branched gas G1 in the introduction chamber R1.

[0038] As shown in Fig. 1, the fuel cell system 100 includes an operating state acquisition unit 18 and a control device 19. The operating state acquisition unit 18 acquires the operating state of the fuel cell 4. The operating state is, for example, the state of the output of the fuel cell 4 relative to the rated output. The operating state acquisition unit 18 may include, for example, an ammeter and a voltmeter for measuring the output of the fuel cell 4. The operating state acquisition unit 18 inputs the operating state of the fuel cell 4 to the control device 19.

[0039] Various information is input to the control device 19 from the pressure gauge 20, the thermometer 22, the recycled gas flow meter 16b, the operating state acquisition unit 18, etc. Based on this information, the control device 19 controls the temperature regulator 13, the pressure regulator Cp, etc. The control device 19 may control the distribution ratio of the branch gas G1 and the recycled gas G2 in the branching unit 10.

[0040] Here, when the fuel cell 4 is in partial load operation, the flow rate of the anode off-gas G decreases. As a result, the flow rate of the branched gas G1 supplied to the carbon dioxide separation unit 14 may decrease. When the flow rate of the branched gas G1 decreases, the area of ​​the separation membrane S per unit flow rate of the branched gas G1 increases in the carbon dioxide separation unit 14. As a result, hydrogen and other substances having a smaller permeability coefficient than carbon dioxide also easily permeate the separation membrane S, and the carbon dioxide concentration in the carbon dioxide-rich gas G11 decreases. Furthermore, the amount of combustible components such as hydrogen contained in the regenerated fuel gas G12 decreases, which causes a problem of a decrease in the power generation efficiency of the entire system.

[0041] Furthermore, the performance of the separation membrane S in the carbon dioxide separation unit 14 varies depending on the temperature, pressure, and flow rate of the gas in contact with the separation membrane S. Examples of the performance of the separation membrane S will be described with reference to Figs. 2 to 5. The horizontal axis in Figs. 2 to 5 represents the pressure of the gas to be separated, in contact with the separation membrane S. In this embodiment, the pressure of the branched gas G1 in the introduction chamber R1 of the carbon dioxide separation unit 14 corresponds to the horizontal axis in Figs. 2 to 5.

[0042] Figures 2 and 3 are graphs showing the relationship between gas temperature and the performance of separation membrane S. The vertical axis in Figure 2 is the carbon dioxide permeability through separation membrane S. The vertical axis in Figure 3 is the carbon dioxide concentration in the gas that has permeated through separation membrane S. In Figures 2 and 3, temperature T0 (dashed line) is higher than temperature T1 (solid line). As can be seen from Figures 2 and 3, the higher the temperature, the higher the carbon dioxide permeability, but the lower the carbon dioxide concentration. The reason that the carbon dioxide concentration decreases with increasing temperature is because the permeation amount of components other than carbon dioxide, such as hydrogen, also increases.

[0043] 4 and 5 are graphs showing the relationship between the gas flow rate and the performance of the separation membrane S. The vertical axis of FIG. 4 is the carbon dioxide permeability of the separation membrane S. The vertical axis of FIG. 5 is the carbon dioxide concentration in the gas that has permeated the separation membrane S. In FIG. 4 and FIG. 5, the dashed lines indicate the case where the fuel cell 4 is operating at rated output, and the solid lines indicate the case where it is operating at partial load. When the fuel cell 4 is operating at partial load, the flow rate of the anode off-gas G is reduced compared to when it is operating at rated output. Therefore, in FIG. 4 and FIG. 5, "rated" represents the case where the gas flow rate is high, and "partial load" represents the case where the gas flow rate is low.

[0044] 4 and 5, when the operating state of the fuel cell 4 changes from rated load to partial load, the carbon dioxide permeability increases but the carbon dioxide concentration decreases. This is because the flow rate of the gas supplied to the separation membrane S decreases and the area of ​​the separation membrane S per unit flow rate of the gas increases.

[0045] As can be seen from FIGS. 2 to 5, as the pressure (horizontal axis) of the branched gas G1 in the introduction chamber R1 of the carbon dioxide separation unit 14 increases, the transmittance of carbon dioxide increases and the concentration of carbon dioxide decreases.

[0046] 2 to 5, the control device 19 in this embodiment performs control so that the separation performance in the carbon dioxide separation unit 14 does not decrease even if the output of the fuel cell 4 fluctuates. Specifically, the control device 19 controls the temperature regulator 13 and the pressure regulator Cp. This control is performed based on the pressure acquired by the pressure gauge 20, the temperature acquired by the thermometer 22, the flow rate of the recycled gas G2 acquired by the recycled gas flowmeter 16b, the operating state of the fuel cell 4 acquired by the operating state acquisition unit 18, and the like.

[0047] For example, the control device 19 holds the carbon dioxide concentration or flow rate of the carbon dioxide rich gas G11 obtained by the carbon dioxide separation unit 14 as a target value. The control device 19 may control the temperature regulator 13 and the pressure regulator Cp so as to satisfy these target values. As an example, when the output of the fuel cell 4 decreases, the carbon dioxide concentration in the carbon dioxide rich gas G11 decreases. To compensate for this decrease, the control device 19 may execute the control in the following first or second example.

[0048] In the first example, the control device 19 reduces the temperature of the branched gas G1 supplied to the carbon dioxide separation unit 14. More specifically, the flow rate of the refrigerant supplied to the heat exchanger 13b is increased by, for example, increasing the rotation speed of the pump 13a of the temperature regulator 13. As a result, in the heat exchanger 13b, more heat is transferred from the branched gas G1 to the refrigerant, and the temperature of the branched gas G1 can be reduced.

[0049] In the second example, the control device 19 reduces the pressure of the branch gas G1 in the carbon dioxide separation unit 14. More specifically, the opening of the regulating valve 21 serving as the pressure regulator Cp is increased to facilitate the flow of the regenerated fuel gas G12 from the carbon dioxide separation unit 14 to the combustor 3a. Alternatively, the rotation speed of the compressor 12 serving as the pressure regulator Cp is reduced to reduce the pressure applied to the branch gas G1 in the branch gas system 11. As a result, the pressure of the branch gas G1 in the carbon dioxide separation unit 14 can be reduced.

[0050] The first and second examples described above may be combined. That is, the control device 19 may change both the temperature and pressure of the branched gas G1 in the carbon dioxide separation unit 14 by controlling both the temperature regulator 13 and the pressure regulator Cp. Furthermore, pressure control tends to have a small time constant, while temperature control tends to have a large time constant. In other words, pressure control tends to have a fast response speed, while temperature control tends to have a slow response speed. Taking such differences into consideration, feedback control may be performed so that the carbon dioxide concentration or recovery amount approaches the target value. Alternatively, the control device 19 may control only the pressure regulator Cp without controlling the temperature regulator 13.

[0051] As described above, the fuel cell system 100 of the present disclosure includes a fuel cell 4 having an anode 4A and a cathode 4B, a branching section 10 that branches the anode off-gas G discharged from the anode 4A into a branched gas G1 and a recycled gas G2, a gas separation device D that separates the branched gas G1 into a carbon dioxide-rich gas G11 having a higher carbon dioxide concentration than the branched gas G1 and a residual gas having a lower carbon dioxide concentration than the branched gas G1, a pressure regulator Cp that adjusts the pressure of the anode off-gas G inside the gas separation device D, a pressure gauge 20 that acquires the pressure of the branched gas G1, a gas information acquisition unit 11a that acquires gas information regarding at least the composition and flow rate of the branched gas G1, and a control device 19 that controls the pressure regulator Cp based on the pressure acquired by the pressure gauge 20 and the gas information acquired by the gas information acquisition unit 11a.

[0052] According to the fuel cell system 100 having such a configuration, when the flow rate of the anode off-gas G supplied to the gas separation device D changes, it is possible to adjust the pressure of the anode off-gas G (branched gas G1) by the pressure regulator Cp so that the carbon dioxide concentration of the carbon dioxide-rich gas G11 does not decrease.

[0053] Furthermore, a temperature regulator 13 for adjusting the temperature of the branched gas G1 may be disposed between the branching section 10 and the gas separation device D. With this configuration, the temperature regulator 13 can adjust the temperature of the branched gas G1 supplied to the gas separation device D. By adjusting not only the pressure but also the temperature of the branched gas G1, it is possible to more reliably suppress a decrease in the carbon dioxide concentration in the carbon dioxide-rich gas G11 when the flow rate of the anode off-gas G changes.

[0054] Furthermore, the fuel cell system 100 may include an operating state acquisition unit 18 that acquires the operating state of the fuel cell 4. The control device 19 may control the pressure regulator Cp based on the operating state. With this configuration, when the operating state of the fuel cell 4 changes from rated output to partial load, it is possible to suppress a decrease in the concentration of carbon dioxide contained in the carbon dioxide rich gas G11.

[0055] The fuel cell system 100 may also include a branch gas system 11 that supplies the branch gas G1 to the gas separation device D, and a recycled gas system 16 that supplies the recycled gas G2 to the mixer 2. The control device 19 may also control the distribution ratio of the branch gas G1 and the recycled gas G2 in the branching section 10 based on the pressure of the branch gas G1 inside the gas separation device D, the temperature acquired by the thermometer 22, and the operating state acquired by the operating state acquisition section 18. With this configuration, carbon dioxide is separated from the branch gas G1, which is a part of the anode offgas G, in the gas separation device D, and at the same time, the recycled gas G2, which is the remaining part of the anode offgas G, can be reused as a raw material for power generation in the fuel cell 4. Furthermore, the operation of the fuel cell system 100 can be optimized in terms of both the separation of carbon dioxide in the gas separation device D and the power generation in the fuel cell 4. Moreover, the mixer 2 may be an ejector. In this case, since the recycled gas G2 can be sucked in using steam as a driving fluid, the blower 16a becomes unnecessary, and the power of the auxiliary equipment can be reduced.

[0056] The fuel cell system 100 may further include a vacuum pump 15 that sucks in the carbon dioxide-rich gas G11 separated in the gas separation device D. With this configuration, the pressure ratio between the inlet chamber R1 and the recovery chamber R2 can be increased, and the performance of the separation membrane S can be improved. Furthermore, the carbon dioxide-rich gas G11 can be prevented from accumulating in the recovery chamber R2. Therefore, the efficiency of the separation membrane S can be increased, and the phenomenon in which the permeation of carbon dioxide stagnates due to a high carbon dioxide concentration in the recovery chamber R2 can be prevented.

[0057] Furthermore, when the control device 19 determines that the output of the fuel cell 4 has decreased based on the operating state acquired by the operating state acquisition unit 18, the control device 19 may control the pressure regulator Cp to decrease the pressure of the anode off-gas G inside the gas separation device D. By decreasing the pressure in this manner, it is possible to suppress a decrease in the concentration of carbon dioxide contained in the carbon dioxide-rich gas G11.

[0058] The fuel cell system 100 may also include a reformer 3 that produces hydrogen from hydrocarbons, and a combustor 3a that is thermally connected to the reformer 3. The residual gas obtained in the gas separation device D may be supplied to the combustor 3a as regenerated fuel gas G12 having a higher hydrogen concentration than the anode off-gas G. With this configuration, the regenerated fuel gas G12, which has a lower carbon dioxide concentration and a higher hydrogen concentration than the anode off-gas G, can be reused as fuel for the combustor 3a. This can further increase the power generation efficiency of the entire system.

[0059] Embodiment 2 Next, a fuel cell system 100A according to a second embodiment will be described with reference to Fig. 6. The basic configuration of the fuel cell system 100A is similar to that of the fuel cell system 100 according to the first embodiment, so differences will be mainly described. Although not shown in Fig. 6, a branching section 10 and the like (see Fig. 1) are arranged upstream of the branch gas system 11. A combustor 3a and the like are arranged downstream of the regenerated fuel gas system 14b.

[0060] As shown in FIG. 6, the gas separation device D in the fuel cell system 100A according to this embodiment includes a hydrogen separation unit 14H, an intermediate system 24, a circulation system 25, a second pressure gauge 20A, and a second adjustment valve 21A in addition to the carbon dioxide separation unit 14. The hydrogen separation unit 14H has a second separation membrane SH, a second introduction chamber R3, and a second recovery chamber R4. The second introduction chamber R3 and the second recovery chamber R4 are partitioned by the second separation membrane SH. The second separation membrane SH selectively allows hydrogen to permeate. The second separation membrane SH is formed of, for example, a polymer. The second separation membrane SH is formed of a material that is more permeable to hydrogen and less permeable to carbon dioxide than the separation membrane S of the carbon dioxide separation unit 14. The second separation membrane SH may also be an inorganic molecular sieve membrane that selectively allows permeation based on the size of the molecule.

[0061] In this embodiment, the branched gas G1 is introduced into the second introduction chamber R3 of the hydrogen separation unit 14H. In the hydrogen separation unit 14H, hydrogen contained in the branched gas G1 permeates the second separation membrane SH and moves to the second recovery chamber R4. The second recovery chamber R4 is connected to the regenerated fuel gas system 14b. The gas that permeates the second separation membrane SH has a higher hydrogen concentration than the branched gas G1 and a lower carbon dioxide concentration than the branched gas G1. In this embodiment, the gas that permeates the second separation membrane SH and moves to the second recovery chamber R4 is discharged to the regenerated fuel gas system 14b as the regenerated fuel gas G12. This regenerated fuel gas G12 can also be used as fuel for the combustor 3a, as in the first embodiment.

[0062] The intermediate system 24 connects the second inlet chamber R3 of the hydrogen separation unit 14H and the inlet chamber R1 of the carbon dioxide separation unit 14. The hydrogen separation unit 14H is located upstream of the carbon dioxide separation unit 14. The gas that does not permeate the second separation membrane SH and remains in the second inlet chamber R3 is introduced into the inlet chamber R1 through the intermediate system 24. In this embodiment, the gas flowing through the intermediate system 24 in this manner is referred to as intermediate gas Gm. The intermediate gas Gm has a lower hydrogen concentration and a higher carbon dioxide concentration than the branch gas G1 before being separated by the hydrogen separation unit 14H.

[0063] The separation unit 14 shown in Fig. 6 separates the carbon dioxide contained in the intermediate gas Gm using a separation membrane S, and discharges it as a carbon dioxide-rich gas G11 to a carbon dioxide recovery system 14a. The circulation system 25 circulates the gas that does not permeate the separation membrane S and remains in the introduction chamber R1 as a circulation gas Gc to the branch gas system 11. The circulation gas Gc contains hydrogen and carbon dioxide that were not separated by the carbon dioxide separation unit 14 and the hydrogen separation unit 14H. By circulating the circulation gas Gc to the branch gas system 11, the carbon dioxide recovery efficiency and the hydrogen utilization efficiency can be improved.

[0064] The second pressure gauge 20A and the second adjustment valve 21A are disposed in the intermediate system 24. The pressure in the introduction chamber R1 changes depending on the opening degree of the second adjustment valve 21A. Therefore, the second adjustment valve 21A can also function as a pressure regulator Cp. The pressure gauge 20 and the adjustment valve 21 are disposed in the circulation system 25. Although not shown in FIG. 6, the control device 19 (see FIG. 1) may control the temperature regulator 13, the adjustment valve 21, and the second adjustment valve 21A based on the gas information acquired by the gas information acquisition unit 11a, the measurement results of the pressure gauge 20, the second pressure gauge 20A, the thermometer 22, etc.

[0065] More specifically, the control device 19 can adjust the temperature and pressure of the branched gas G1 introduced into the second inlet chamber R3 of the upstream hydrogen separation unit 14H by the temperature regulator 13, the second regulating valve 21A, etc. Also, the control device 19 can control the pressure of the intermediate gas Gm introduced into the inlet chamber R1 of the downstream carbon dioxide separation unit 14 by the regulating valve 21, etc. The control device 19 can perform control so that the hydrogen utilization efficiency and the carbon dioxide recovery efficiency approach target values.

[0066] FIG. 7 shows a first modified example of the fuel cell system 100A according to the second embodiment. As shown in FIG. 7, the second pressure gauge 20A and the second adjustment valve 21A may be omitted. In this case, the controller 19 controls the temperature regulator 13 to adjust the temperature of the gas introduced into the introduction chamber R1 and the second introduction chamber R3. The controller 19 controls the adjustment valve 21 to adjust the pressure of the gas introduced into the introduction chamber R1 and the second introduction chamber R3. Furthermore, the simple configuration contributes to cost reduction.

[0067] FIG. 8 shows a second modified example of the fuel cell system 100A according to the second embodiment. As shown in FIG. 8, the hydrogen separation unit 14H may be disposed downstream of the carbon dioxide separation unit 14. With this configuration, the control device 19 can adjust the temperature and pressure of the branched gas G1 introduced into the inlet chamber R1 of the upstream carbon dioxide separation unit 14 by the temperature regulator 13, the second adjustment valve 21A, etc. Also, the pressure of the intermediate gas Gm introduced into the second inlet chamber R3 of the downstream hydrogen separation unit 14H can be controlled by the adjustment valve 21, etc. The control device 19 can perform control so that the hydrogen utilization efficiency and the carbon dioxide recovery efficiency approach target values.

[0068] Furthermore, as shown in a third modified example in FIG. 9, the second pressure gauge 20A and the second adjustment valve 21A may be omitted.

[0069] As described above, in the fuel cell system 100A according to the second embodiment (FIGS. 6 to 8), the gas separation apparatus D has a plurality of separation units 14, 14A. The plurality of separation units 14, 14H include a carbon dioxide separation unit 14 that separates carbon dioxide, and a hydrogen separation unit 14H that separates hydrogen. With this configuration, it is possible to further improve the efficiency of recovering carbon dioxide and the efficiency of using hydrogen. The gas separation apparatus D may have three or more separation units.

[0070] In the examples of FIG. 6 and FIG. 8, the fuel cell system 100A further includes a second pressure gauge 20A that measures the pressure of the branch gas (intermediate gas Gm) upstream of the pressure gauge 20. The pressure regulator Cp includes a regulation valve 21 and a second regulation valve 21A arranged upstream of the regulation valve 21. The control device 19 may control the regulation valve 21 based on the measurement result of the pressure gauge 20 and the gas information from the gas information acquisition unit 11a. Furthermore, the control device 19 may control the second regulation valve 21A based on the measurement result of the second pressure gauge 20A and the gas information from the gas information acquisition unit 11a. With this configuration, the pressure of the gas in the multiple separation units 14, 14A can be adjusted more flexibly. Therefore, it is possible to optimize the concentrations of the components of the carbon dioxide rich gas G11 and the regenerated fuel gas G12, which are the products obtained in the respective separation units 14, 14A.

[0071] Embodiment 3 Next, a fuel cell system 100B according to a third embodiment will be described with reference to Fig. 10. The basic configuration of the fuel cell system 100B is similar to that of the fuel cell system 100 of the first embodiment, and therefore differences will be mainly described.

[0072] 10, the fuel cell system 100B includes a carbon dioxide capture unit 26. The carbon dioxide capture unit 26 captures carbon dioxide from the combustion off-gas discharged from the combustor 3a. The carbon dioxide capture unit 26 may have, for example, an adsorbent capable of adsorbing carbon dioxide.

[0073] Examples of materials for the adsorbent include amine, zeolite, silica gel, diatomaceous earth, alumina, and activated carbon. A plurality of materials may be selected from the above, or a material other than the above may be used. The adsorbent may be granular (e.g., bead-shaped (spherical), pellet-shaped (cylindrical)). Alternatively, a powdered adsorbent may be used. In this case, the powdered adsorbent may be supported on the surface of a substrate. The substrate may be, for example, honeycomb-shaped.

[0074] According to this configuration, the amount of carbon dioxide released into the atmosphere can be reduced by recovering carbon dioxide from the combustion off-gas using the carbon dioxide recovery section 26. Note that the carbon dioxide recovery section 26 may have a separation membrane S similar to that of the carbon dioxide separation unit 14, instead of an adsorbent. In this case as well, the carbon dioxide contained in the combustion off-gas can be separated using the separation membrane S and then released into the atmosphere. Therefore, the concentration and amount of carbon dioxide released into the atmosphere can be reduced.

[0075] The technical scope of the present disclosure is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present disclosure.

[0076] For example, in the first embodiment, the compressor 12 and the regulating valve 21 function as the pressure regulator Cp. However, the function of the pressure regulator Cp may be realized by only one of the compressor 12 and the regulating valve 21.

[0077] In the above embodiment, the control device 19 controls the temperature regulator 13 and the pressure regulator Cp. The functions of the control device 19 are realized by a processor such as a CPU (Central Processing Unit) executing a program stored in a program memory. Some or all of these functions may be realized by hardware such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programmable Gate Array), or may be realized by software and hardware working together. The functions of the control device 19 may be realized by one piece of hardware. Alternatively, the hardware that controls the temperature regulator 13 may be different from the hardware that controls the pressure regulator Cp.

[0078] In addition, the carbon dioxide rich gas G11 separated from the branch gas G1 by the separation device D and introduced into the carbon dioxide capture system 14a may be supplied to a fuel synthesis reaction mechanism (not shown) together with hydrogen gas supplied from the outside. The hydrogen gas supplied to the fuel synthesis reaction mechanism may be generated, for example, by water electrolysis, or may be stored and transported by other generation methods. In the fuel synthesis reaction mechanism, the carbon dioxide and hydrogen in the carbon dioxide rich gas G11 may be reacted to generate a synthetic fuel (e.g., methane, etc.) which is a hydrocarbon fuel. Carbon recycling can be realized by generating a synthetic fuel based on the carbon component used as a raw material in the fuel cell 4.

[0079] In addition, the above-described embodiments and modifications may be combined as appropriate. For example, the fuel cell system 100B described in the third embodiment may include a gas separation device D as shown in FIGS. [Explanation of symbols]

[0080] 2...mixer 3...reformer 3a...combustor 4...fuel cell 4A...anode 4B...cathode 10...branching section 11...branched gas system 11a...gas information acquisition section 13...temperature regulator 14...carbon dioxide separation unit 14H...hydrogen separation unit 15...vacuum pump 16...recycled gas system 18...operation status acquisition section 19...control device 20...pressure gauge 20A...second pressure gauge 21...regulating valve 21A...second regulating valve 22...thermometer 26...carbon dioxide recovery section 100, 100A, 100B...fuel cell system Cp...pressure regulator D...gas separation device G...anode off-gas G1...branched gas G2...recycled gas G11...carbon dioxide-rich gas G12...regenerated fuel gas (residual gas)

Claims

1. A fuel cell having an anode and a cathode, A branching section that splits the anode off-gas discharged from the anode into branched gas and recycled gas, A gas separation device that separates the branched gas into a carbon dioxide-rich gas with a higher carbon dioxide concentration than the branched gas and a residual gas with a lower carbon dioxide concentration than the branched gas, A carbon dioxide recovery system in which the carbon dioxide-rich gas moved from the gas separation device is discharged and recovered, A pressure regulator for adjusting the pressure of the anode off-gas inside the gas separation device, A pressure gauge for obtaining the pressure of the aforementioned branched gas, A gas information acquisition unit that acquires gas information relating at least the composition and flow rate of the branched gas, A fuel cell system comprising: a control device that controls the pressure regulator based on the pressure acquired by the pressure gauge and the gas information acquired by the gas information acquisition unit.

2. The fuel cell system according to claim 1, wherein a temperature regulator for adjusting the temperature of the branched gas is arranged between the branching section and the gas separation device.

3. The system further includes an operating state acquisition unit that acquires the operating state of the fuel cell, The fuel cell system according to claim 1 or 2, wherein the control device controls the pressure regulator based on the operating state.

4. The fuel cell system according to claim 3, wherein the control device, based on the operating state, determines that the output of the fuel cell has decreased, and controls the pressure regulator so that the pressure of the anode off-gas inside the gas separation device decreases.

5. A branch gas system that supplies the branch gas to the gas separation device, The system further comprises a recycled gas system that supplies the aforementioned recycled gas to a mixer, The fuel cell system according to claim 3, wherein the control device controls the distribution ratio of the branched gas and the recycled gas in the branch section based on the pressure of the branched gas inside the gas separation device and the operating state acquired by the operating state acquisition unit.

6. The gas separation apparatus has a plurality of separation units, The fuel cell system according to claim 1 or 2, wherein the plurality of separation units include a carbon dioxide separation unit for separating carbon dioxide.

7. The fuel cell system according to claim 6, wherein the plurality of separation units include a hydrogen separation unit for separating hydrogen.

8. The system further includes a second pressure gauge for measuring the pressure of the branched gas upstream of the aforementioned pressure gauge. The pressure regulator includes a control valve and a second control valve located upstream of the control valve. The fuel cell system according to claim 6, wherein the control device controls the regulating valve based on the measurement result of the pressure gauge and the gas information, and controls the second regulating valve based on the measurement result of the second pressure gauge and the gas information.

9. The fuel cell system according to claim 1 or 2, further comprising a vacuum pump for sucking up the carbon dioxide-rich gas separated by the gas separation device.

10. A reformer that produces hydrogen from hydrocarbons, The reformer is further comprising a combustor that is thermally connected to the reformer, The residual gas is a regenerated fuel gas with a higher hydrogen concentration than the branched gas. The fuel cell system according to claim 1 or 2, wherein the regenerative fuel gas is supplied to the combustor.

11. The fuel cell system according to claim 10, further comprising a carbon dioxide recovery unit for recovering carbon dioxide from the combustion off-gas discharged from the combustor.

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