Fuel cell system

Abstract

A fuel cell system according to the present disclosure comprises: a fuel cell having an anode and a cathode; a branch unit for branching an anode off-gas discharged from the anode into a branch gas and a recycle gas; a separation device having a plurality of separation units for separating a specific gas component from the branch gas; a compressor for boosting the branch gas; a pressure gauge for measuring the pressure of the branch gas introduced into the separation device; a pressure regulator for adjusting the pressure of the branch gas; a gas information acquisition unit for acquiring the composition and flow rate of the branch gas; and a distribution mechanism for distributing the branch gas to the plurality of separation units.

Description

fuel cell system

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

[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 properties that allow carbon dioxide and water to easily permeate, but are difficult to permeate other components. Therefore, the carbon dioxide concentration of the gas that permeates the separation membrane is higher than that of the anode off-gas. The remaining anode off-gas that does not permeate the separation membrane contains flammable components such as hydrogen. This gas is reused as regenerated fuel gas.

[0003] Japanese Patent Application Laid-Open No. 2019-139858

[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 decreases compared to when the fuel cell is operating at rated load. Other factors may also cause the flow rate of the anode off-gas introduced into the separation section to decrease. When the flow rate of the anode off-gas decreases, the area of ​​the separation membrane relative to the anode off-gas per unit flow rate increases. This increases the permeation rate of components that are less permeable to the separation membrane than carbon dioxide, such as hydrogen. This results in a problem of a decrease in the concentration of carbon dioxide contained in the recovered gas.

[0005] In view of the above circumstances, the present disclosure aims 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.

[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 anode off-gas discharged from the anode into a branched gas and a recycled gas, a separation device having a plurality of separation units that separate specific gas components from the branched gas, a compressor that pressurizes the branched gas, a pressure gauge that measures the pressure of the branched gas introduced into the separation device, a pressure regulator that adjusts the pressure of the branched gas, a gas information acquisition section that acquires the composition and flow rate of the branched gas, and a distribution mechanism that distributes the branched gas to the plurality of separation units.

[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.

[0008] Fig. 1 is a diagram showing the configuration of a fuel cell system according to embodiment 1. Fig. 2 is a diagram showing the configuration of a separation device of the fuel cell system shown in Fig. 1. Fig. 3 is a diagram showing a modified example of the configuration of the separation device according to embodiment 1. Fig. 4 is a diagram showing the configuration of a fuel cell system according to embodiment 2. Fig. 5 is a diagram showing the configuration of a fuel cell system according to embodiment 3. Fig. 6 is a diagram showing the configuration of a fuel cell system according to embodiment 4.

[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 can 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] As will be described in detail later, the gas separation device D (hereinafter simply referred to as separation device D) has the function of separating a process gas containing carbon dioxide 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. The process gas in this embodiment is anode off-gas discharged from the anode 4A of the fuel cell 4. However, the present disclosure may also be applied to process gases other than anode off-gas. In other words, the fuel cell system 100 may be applied to process gases other than that discharged from the fuel cell 4.

[0012] Other examples of process gases containing carbon dioxide include exhaust gas from factories and power plants. Also, exhaust gas from a reforming reaction system that produces hydrogen from a hydrocarbon fuel, such as the reformer 3, may be used as the process gas. In the present embodiment, the following description will be given taking "anode off-gas G" as an example of the process gas.

[0013] The supply path 1 supplies the raw material to the mixer 2. The raw material can be a carbon-containing material such as a hydrocarbon. An example of the hydrocarbon is methane. The following describes a case where the raw material is methane, but the raw material is not limited to methane. A raw material flow meter 1a is provided on the supply path 1. The raw material flow meter 1a measures the flow rate of the raw material supplied to the mixer 2. The measurement results of the raw material flow meter 1a may be input to, for example, the operating state acquisition unit 18 and the control device 19. A raw material supply system 2a is connected to the mixer 2. The raw material is mixed with a recycled gas G2 and steam, which will be described later, in the mixer 2, and is introduced into the reformer 3 via the raw material supply system 2a.

[0014] 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): CH ４ +H ２ O → CO + 3H ２ ...(I) CO+H ２ O → CO ２ +H ２The carbon dioxide reforming reaction follows, for example, the following formulas (III) and (IV): CH ４ +CO ２ → 2CO + 2H ２ ...(III) 2CO+2H ２ O → 2CO ２ +2H ２ ... (IV)

[0015] The reformer 3 preferably has at least one of a steam reforming catalyst and a carbon dioxide reforming catalyst. Furthermore, the reformer 3 more preferably 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.

[0016] 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.

[0017] 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. Temperature distributions suitable for both the steam reforming reaction and the carbon dioxide reforming reaction may be set inside the reformer 3 so that both reactions 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. The fuel for the combustor 3a can be the cathode offgas discharged from the cathode 4B, the regenerated fuel gas G12 discharged from the separation device D, or the like. The regenerated fuel gas G12 will be described later.

[0018] 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 ) The air supply system 5 is provided with an air supply blower 5a for flowing air toward the fuel cell 4. The air supply system 5 also has 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 makes it possible to use the exhaust heat from the combustor 3a to heat the air introduced into the cathode 4B.

[0019] 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 uses hydrogen (H ２ The reformed gas containing the fuel cell 4 reacts with air (an oxidant) to generate electricity, thereby generating electrical energy. The fuel cell system 100 including the fuel cell 4 can also be called a power generation system.

[0020] 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 the following formula (V), and the reaction at the cathode 4B follows the following formula (VI): H ２ +O ２－ →H ２ O + 2e － ...(V) 1 / 2O ２ +2e － →O ２－ ...(VI)

[0021] Anode off-gas G is discharged from the anode 4A of the fuel cell 4. The anode off-gas G may contain, for example, hydrogen (H ２ ), carbon dioxide (CO ２ ), water vapor (H ２ O), carbon monoxide (CO), and methane (CH ４ The anode off-gas system 6 extracts anode off-gas G from the anode 4A of the fuel cell 4 and directs it to a branching section 10. In the anode off-gas system 6, a steam generator 7, a heat recovery device 6a, and a condensation tank 9 are arranged in the portion between the fuel cell 4 and the branching section 10.

[0022] 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 and the control device 19.

[0023] The steam generator 7 heats the water supplied from the condensation tank 9 by heat exchange with the anode off-gas G. In this way, the steam generator 7 obtains steam. The steam generator 7 has an auxiliary heater 7a. The auxiliary heater 7a is, for example, a heater. If the amount of heat required to evaporate the water is insufficient through heat exchange with the anode off-gas G alone, the auxiliary heater 7a may be used to heat the water. The steam obtained by the steam generator 7 is introduced into the mixer 2 through a steam supply system 8.

[0024] The heat recovery unit 6a is located upstream of the condensation tank 9 and is capable of recovering heat from the anode off-gas G. This allows, for example, the anode off-gas G to be set at a temperature equal to or lower than the heat resistance temperature of a recycle gas blower 16a (described later). A branching unit 10 is disposed downstream of the condensation tank 9. At the branching unit 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.

[0025] The branching unit 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 unit 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 in the branching unit 10 to the flow path cross-sectional area to the branch gas system 11 and the recycle gas system 16. Furthermore, 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. The measurement result may also be input to, for example, the control device 19. However, the structure for changing the distribution ratio in the branching unit 10 is not limited to the above and can be changed as appropriate.

[0026] The recycle gas system 16 is provided with a recycle gas blower 16a and a recycle gas flow meter 16b. The recycle gas blower 16a generates power to flow the recycle gas G2 from the branching portion 10 toward the mixer 2. The recycle gas flow meter 16b measures the flow rate of the recycle gas G2 supplied to the mixer 2. In this manner, the recycle gas system 16 circulates the recycle gas G2 to the raw material supply system 2a. The mixer 2 may also be an ejector. In this case, the recycle gas G2 can be sucked in using steam as a driving fluid, eliminating the need for the recycle gas blower 16a and reducing the power required for auxiliary equipment.

[0027] The branch gas system 11 supplies at least a portion of the anode off-gas G as a branch gas G1 to the separation device D. 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 about the branch gas G1. The "information about the branch gas G1" includes, for example, the composition, flow rate, pressure, and temperature. The information about the composition of the branch gas G1 may include, for example, the partial pressure of carbon dioxide. Because the branch gas G1 is part of the anode off-gas G, it can also be said that the gas information acquisition unit 11a acquires information about the anode off-gas G.

[0028] The gas information acquiring unit 11a has sensors and the like according to the type of information to be acquired. For example, when acquiring a composition, the gas information acquiring unit 11a may have a near-infrared spectroscopic sensor. For example, when acquiring a flow rate, pressure, temperature, and the like, the gas information acquiring unit 11a may have a flow meter, a pressure gauge, a thermometer, and the like. The gas information acquiring unit 11a may have multiple types of sensors as described above. However, the gas information acquiring unit 11a may calculate the composition and flow rate of the branched gas G1 based on the operating state of the fuel cell 4 acquired by the operating state acquiring 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 branching unit 10.

[0029] The compressor 12 can increase the pressure of the branch gas G1 supplied to the separation device D. The compressor 12 may be, for example, a blower. The pressure of the branch gas G1 in the separation device 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 separation device D. The temperature regulator 13 can adjust the temperature of the branch gas G1 supplied to the separation device D.

[0030] In the example of FIG. 1 , the temperature regulator 13 includes a pump 13a and a heat exchanger 13b. In the heat exchanger 13b, heat exchange occurs between the refrigerant and the branch gas G1. The pump 13a generates power to cause the refrigerant to flow through the heat exchanger 13b. Changing the output of the pump 13a changes the flow rate of the refrigerant flowing through the heat exchanger 13b. Therefore, adjusting the output of the pump 13a can adjust the amount of heat exchanged between the refrigerant and the branch gas G1 in the heat exchanger 13b. This allows the temperature regulator 13 to adjust the temperature of the branch 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 branch gas G1.

[0031] In this embodiment, the separation apparatus D has a plurality of carbon dioxide separation units 14 (hereinafter simply referred to as separation units 14). As shown in FIG. 2 , this embodiment has four separation units 14. The four separation units 14 are referred to as a first separation unit 141, a second separation unit 142, a third separation unit 143, and a fourth separation unit 144, respectively. The separation units 14 are arranged in parallel. That is, when the branch gas G1 is introduced into each of the separation units 14, the introduced branch gas G1 is simultaneously separated. Each separation unit 14 has a separation membrane S that selectively allows carbon dioxide to permeate. Furthermore, the separation unit 14 has an introduction chamber R1 and a recovery chamber R2 that are partitioned by the separation membrane S. The separation membrane S is formed, for example, of a polymer. The number of separation units 14 included in the separation apparatus D is not limited to four, and may be two or more.

[0032] As shown in Fig. 2, the branched gas G1 flowing from the branch section 10 through the branched gas system 11 is distributed to a plurality of separation units 14 by a distribution mechanism DM. The distribution mechanism DM is controlled by a control device 19. The control device 19 controls the distribution mechanism DM based on information from a pressure gauge 20 and the gas information acquisition unit 11a to distribute the branched gas G1 to the plurality of separation units 14. The distribution mechanism DM includes a plurality of shut-off valves, and the control device 19 distributes the branched gas G1 to the separation units 14 by opening and closing the shut-off valves. More specifically, the distribution mechanism DM includes distribution shut-off valves Vi provided in each line introducing the branched gas G1 into the separation units 14, and recovery shut-off valves Vo provided in each line extracting gas from the introduction chamber R1 of the separation units 14. In the following description, the distribution shutoff valves Vi provided on the lines leading to the first to fourth separation units 141, 142, 143, and 144 will be referred to as first to fourth distribution shutoff valves V1i, V2i, V3i, and V4i, respectively, and the recovery shutoff valves Vo provided on the lines leading to the gas from the introduction chambers R1 of the first to fourth separation units 141, 142, 143, and 144 will be referred to as first to fourth recovery shutoff valves V1o, V2o, V3o, and V4o. The distribution gases GD introduced from the first to fourth distribution shutoff valves V1i, V2i, V3i, and V4i to each separation unit 14 will be referred to as first to fourth distribution gases GD1, GD2, GD3, and GD4, respectively.

[0033] Next, a carbon dioxide separation method in each separation unit 14 will be described. First, a carbon dioxide separation method in the first separation unit 141 will be described when all distribution shutoff valves Vi and all recovery shutoff valves Vo are opened and the branched gas G1 is evenly distributed by the four distribution shutoff valves Vi. That is, in this case, ¼ of the branched gas G1 is distributed to each separation unit 14. The branched gas G1 is first introduced into the introduction chamber R1 of the first separation unit 141. 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.

[0034] In the first separation unit 141, the gas that passes through the separation membrane S from the introduction chamber R1 and moves to the recovery chamber R2 is referred to as the first carbon dioxide-rich gas GD11. The gas that does not pass through the separation membrane S and remains is referred to as the first regenerated fuel gas GD12. That is, the first separation unit 141 uses the separation membrane S to separate the first distributed gas GD1 into the first carbon dioxide-rich gas GD11 and the first regenerated fuel gas GD12. Similarly, the second to fourth separation units 142, 143, and 144 use the separation membrane S to separate the branched gas G1 into second to fourth carbon dioxide-rich gases GD21, GD31, and GD41 and second to fourth regenerated fuel gases GD22, GD32, and GD42.

[0035] In this specification, the gas that passes through the separation membrane S from the inlet chamber R1 of the first to fourth separation units 141, 142, 143, and 144 and moves to the recovery chamber R2 is referred to as the carbon dioxide-rich gas G11. Of the gases that remain in the first to fourth separation units 141, 142, 143, and 144 without passing through the separation membrane S, the gas that passes through the recovery shut-off valve Vo is referred to as the recycled fuel gas G12. In other words, the separation unit 14 uses the separation membrane S to separate the branched gas G1 into the carbon dioxide-rich gas G11 and the recycled fuel gas G12.

[0036] The carbon dioxide-rich gas G11 has a higher carbon dioxide concentration than the branch gas G1 before separation by the separation unit 14. The recycled fuel gas G12 has a lower carbon dioxide concentration than the branch gas G1 before separation by the separation unit 14. Furthermore, the recycled fuel gas G12 contains combustible components such as hydrogen, carbon monoxide, and methane. Therefore, the recycled fuel gas G12 can be used as fuel. As shown in FIGS. 1 and 2, in this embodiment, the recycled fuel gas G12 is used as fuel in the combustor 3a of the reformer 3. A recycled fuel gas system 14b is connected to the inlet chamber R1 of each separation unit 141-144. The first to fourth recycled fuel gases GD12, GD22, GD32, and GD42 discharged from each separation unit 141-144 pass through the recovery shutoff valve Vo from the inlet chamber R1 and are discharged to the recycled fuel gas system 14b. The combustor 3a is connected downstream of the recycled 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.

[0037] As shown in FIGS. 1 and 2, a carbon dioxide capture system 14a is connected to the recovery chamber R2 of each separation unit 141 to 144. The first to fourth carbon dioxide-rich gases GD11, GD21, GD31, and GD41 discharged from each separation unit 141 to 144 are 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 recovered in this manner may be reused for other purposes. The vacuum pump 15 does not necessarily have to be provided.

[0038] The pressure gauge 20 measures the pressure of the recycled fuel gas G12 in the recycled fuel gas system 14b between the separation unit 14 and the adjustment valve 21. The measurement result of the pressure gauge 20 makes it possible to indirectly know the pressure of the branched gas G1 supplied to the separation unit 14. Note that the position of the pressure gauge 20 can be changed as appropriate, provided that the pressure of the branched gas G1 supplied to the separation unit 14 can be measured directly or indirectly.

[0039] The thermometer 22 measures the temperature of the branched gas G1 in the branched gas system 11 between the temperature regulator 13 and the separation unit 14. 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 separation unit 14.

[0040] The adjustment valve 21 is provided in the recycled fuel gas system 14b. The pressure in the introduction chamber R1 can be adjusted by opening and closing the adjustment valve 21. For example, when the aperture of the adjustment valve 21 is increased, the recycled 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 adjustment valve 21 is decreased, the pressure in the introduction chamber R1 increases. Therefore, the adjustment valve 21 can function as a pressure regulator Cp that adjusts the pressure of the branch gas G1 in the introduction chamber R1.

[0041] 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.

[0042] The control device 19 receives various types of information from the pressure gauge 20, the thermometer 22, the recycled gas flow meter 16b, the operating state acquisition unit 18, an operation time acquisition unit 24 (described later), etc. Based on this information, the control device 19 controls the temperature regulator 13, the pressure regulator Cp, the distribution mechanism DM, etc. The control device 19 may also control the distribution ratio of the branch gas G1 and the recycled gas G2 in the branch unit 10.

[0043] Here, when the fuel cell 4 enters partial load operation, the flow rate of the anode off-gas G decreases. As a result, the flow rate of the branch gas G1 supplied to the separation unit 14 may decrease. When the flow rate of the branch gas G1 decreases, the area of ​​the separation membrane S per unit flow rate of the branch gas G1 in the separation unit 14 increases. As a result, hydrogen and other substances with 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 also causes a problem of reduced power generation efficiency in the entire system. Therefore, in this embodiment, when the flow rate of the branch gas G1 supplied to the separation unit 14 decreases, some of the multiple distribution shutoff valves Vi are closed depending on the flow rate, thereby adjusting the number of separation units 14 in use.

[0044] Hereinafter, a method in this embodiment for controlling the number of separation units 14 in use so as not to degrade the separation performance of the separation units 14 when the output of the fuel cell 4 fluctuates will be specifically described. The branch gas G1 is distributed to all or some of the separation units 14 according to the pressure acquired by the pressure gauge 20 and information on the flow rate of the branch gas G1 from the gas information acquisition unit 11a. Specifically, the control unit 19 controls the open / close states of the distribution shutoff valves Vi and the recovery shutoff valves Vo using the distribution mechanism DM. This control may also be performed based on the temperature acquired by the thermometer 22, the flow rate of the recycled gas G2 acquired by the recycled gas flow meter 16b, the operating state of the fuel cell 4 acquired by the operating state acquisition unit 18, and the like.

[0045] For example, the control device 19 holds the carbon dioxide concentration or flow rate of the carbon dioxide-rich gas G11 obtained by the separation unit 14 as a target value. The control device 19 may control the open / close states of the distribution shutoff valves Vi and the recovery shutoff valves Vo of the distribution mechanism DM so as to satisfy these target values. As an example, first, when the flow rate of the branch gas G1 is equal to or greater than a first threshold, all of the distribution shutoff valves Vi are opened so that the branch gas G1 is introduced into all of the separation units 14. When the flow rate of the branch gas G1 is equal to or greater than the first threshold, the flow rate of the branch gas G1 includes, for example, the flow rate of the branch gas G1 when the fuel cell is in a rated output state. When the output of the fuel cell 4 decreases, the flow rate of the branch gas G1 decreases. To compensate for this decrease, the control device 19 may execute the following control.

[0046] When the flow rate of the branch gas G1 falls below a first threshold, one of the multiple distribution shutoff valves Vi is closed to prevent gas separation in one separation unit 14 connected to the closed distribution shutoff valve Vi. For example, the first threshold is determined based on a target value for the carbon dioxide concentration or flow rate of the carbon dioxide-rich gas G11, and may be, for example, ¾ of the flow rate of the branch gas G1 at rated output.

[0047] When the gas flow rate falls below the first threshold, for example, the fourth distribution shutoff valve V4i is closed, and the branched gas G1 is introduced into the first to third separation units 141 to 143. This makes it possible to prevent an excessive increase in the area of ​​the separation membrane S for the branched gas G1 per unit flow rate in the first to third separation units 141 to 143. This prevents an increase in the permeation amount of components that are less permeable through the separation membrane S than carbon dioxide, such as hydrogen, and prevents a decrease in the concentration of carbon dioxide contained in the carbon dioxide-rich gas G11.

[0048] In this way, when the flow rate of the branch gas G1 falls below the first threshold, one of the separation units 14 is shut off. Furthermore, when the flow rate of the branch gas G1 decreases, the number of separation units 14 to which the branch gas G1 is introduced is reduced. If the threshold value for the flow rate of the branch gas G1 when two of the separation units 14 are shut off is set as the second threshold, and the threshold value for the flow rate of the branch gas G1 when three separation units 14 are shut off is set as the third threshold, these thresholds satisfy the relationship of first threshold > second threshold > third threshold. For example, the second threshold may be 2 / 4 of the flow rate of the branch gas G1 at rated output, and the third threshold may be 1 / 4 of the flow rate of the branch gas G1 at rated output. Note that the second and third thresholds may be determined based on target values ​​for the carbon dioxide concentration or flow rate of the carbon dioxide-rich gas G11.

[0049] Based on these first to third thresholds, when the flow rate of the branched gas G1 falls below a corresponding threshold, the distribution shutoff valves Vi connected to the separation units 14, the number of which corresponds to the threshold, are closed. When the flow rate of the branched gas G1 is equal to or greater than a threshold, the distribution shutoff valves Vi connected to the separation units 14, the number of which corresponds to each threshold, are opened. The open / closed states of the recovery shutoff valves Vo may be controlled by the control device 19 in accordance with the opening and closing of the corresponding distribution shutoff valves Vi.

[0050] The control device 19 may perform the following control to change the pressure of the distribution gas GD in each separation unit 14. By increasing the aperture of the adjustment valve 21 serving as the pressure regulator Cp, the recycled fuel gas G12 can flow more easily from the separation unit 14 to the combustor 3a. Alternatively, by decreasing the rotation speed of the compressor 12 serving as the pressure regulator Cp, the pressure applied to the branch gas G1 in the branch gas system 11 can be reduced. As a result, the pressure of the branch gas G1 in the separation unit 14 (the total pressure of the distribution gas GD) can be changed.

[0051] In this way, the control device 19 controls the distribution mechanism DM and the pressure regulator Cp using the carbon dioxide concentration or flow rate of the carbon dioxide-rich gas G11 obtained by the separation unit 14 as a target value.

[0052] <Equalizing the Operation Times of the Separation Units 14 by the Operation Time Acquisition Unit 24> In the above example, the fourth separation unit 144 is shut off when the flow rate of the branch gas G1 falls below the first threshold. However, if the fourth separation unit 144 were always shut off when the flow rate of the branch gas G1 falls below the first threshold, the operation time of the first to third separation units 141 to 143 would be longer than the operation time of the fourth separation unit 144. The separation membrane S may need to be replaced when its specified usage time is exceeded, and there may be cases where only the separation membrane S of the first to third separation units 141 to 143 with the longest operation time needs to be replaced. Therefore, this embodiment includes an operation time acquisition unit 24 (see FIG. 2 ) that acquires the operation times of the multiple separation units 14. When the flow rate of the branch gas G1 falls below the threshold, the separation unit 14 to be shut off is switched based on information from the operation time acquisition unit 24, and control is performed so that the operation times of each separation unit 14 are equalized. The operation time acquisition unit 24 may be provided inside the control device 19, or the operation time acquisition unit 24 and the control device 19 may be realized by the same hardware.

[0053] For example, when a certain time has elapsed since the fourth separation unit 144 was shut off, the distribution shutoff valve V4i of the fourth separation unit 144 is opened, and the distribution shutoff valve Vi of the separation unit 14 with the longest cumulative operating time is closed. Thereafter, every time a certain time has elapsed, the distribution shutoff valve Vi of the separation unit 14 that was shut off is opened, and the distribution shutoff valve Vi of the separation unit 14 with the longest cumulative operating time is closed. Similarly, in the case where multiple separation units 14 are shut off, the control device 19 switches the open / close state of the distribution shutoff valve Vi of the separation unit 14 into which the branch gas G1 is introduced based on the operating times of the multiple separation units 14 acquired by the operating time acquisition unit 24, thereby controlling the operation times of each separation unit 14 to be uniform. Specifically, the control device 19 controls the distribution mechanism DM based on the operating times of the multiple separation units 14 acquired by the operating time acquisition unit 24 so that the operating times of each separation unit 14 are uniform, thereby controlling the opening and closing of the distribution shutoff valve Vi described above.

[0054] <Adjusting the Operating Pressure of Separation Units When the Distribution Shutoff Valve Vi is Opened or Closed> When the flow rate of the branch gas G1 falls below the first threshold and the distribution shutoff valve V4i is closed, the flow rate of the gas flowing through the fourth separation unit 144 changes, for example, from one-quarter of the flow rate of the branch gas G1 to zero. When the distribution shutoff valve V4i is controlled between two patterns, open and closed, a sudden decrease in flow rate may occur in the fourth separation unit 144. Furthermore, a sudden increase in flow rate may occur in the first to third separation units 141 to 143 other than the fourth separation unit 144. Hereinafter, a condition in which such a sudden change in flow rate occurs and the operating pressure of the separation unit 14 changes suddenly is referred to as a discontinuous condition. Under a discontinuous condition, the separation capacity of the separation unit 14 may decrease. Therefore, in this embodiment, the pressure regulator Cp is controlled, and the control device 19 controls the distribution mechanism DM so that the change in flow rate in the separation unit 14 is gradual. For example, when the first to third separation units 141 to 143 are operating, if the control device 19 detects that the flow rate of the branched gas G1 measured by the gas information acquisition unit 11a exceeds a first threshold value and starts introducing the branched gas G1 into the fourth separation unit 144, the control device 19 may perform the following first or second example of control.

[0055] In the first example, before opening the fourth distribution shutoff valve V4i, the operating pressure in the first to third separation units 141 to 143 is first increased by controlling the pressure regulator Cp. Then, the aperture of the fourth distribution shutoff valve V4i is gradually increased. The aperture of the fourth distribution shutoff valve V4i may be increased continuously from 0% to 100% within a certain period of time, or may be increased in steps of several percent. As the aperture of the fourth distribution shutoff valve V4i increases and the operating pressure in the fourth separation unit 144 increases, the amount of gas flowing to the first to third separation units 141 to 143 decreases, and the operating pressure in the first to third separation units 141 to 143 decreases to a certain pressure. After the operating pressures of the four separation units 14 become equal, the pressure regulator Cp may be controlled as necessary to reduce the pressure of the branch gas G1.

[0056] In the second example, the fourth distribution shutoff valve V4i is opened, and at the same time, the pressure regulator Cp is controlled to reduce the operating pressures in the first to third separation units 141 to 143. Thereafter, the operating pressures of the first to fourth separation units 141 to 144 are increased to a constant pressure. After the operating pressures of the four separation units 14 become equal, the pressure regulator Cp may be controlled as necessary to increase the pressure of the branched gas G1.

[0057] In the first and second examples, by controlling the operating pressure of the separation unit 14 with the pressure regulator Cp, it is possible to distribute the branched gas G1 to the plurality of separation units 14 according to a threshold value while suppressing a decrease in separation capacity due to a sudden change in the operating pressure in the separation unit 14. Note that even when one of the distribution shutoff valves Vi is closed, the pressure regulator Cp can be controlled based on the first or second example to prevent a discontinuous state.

[0058] <Serial Arrangement of Separation Units 14> The separation apparatus D is provided with a mechanism for introducing gas discharged from one separation unit 14 into another separation unit 14, thereby providing multiple separation units 14 in series. In this embodiment, a check valve NV is provided for introducing gas discharged from the inlet chamber R1 into another separation unit 14. As a result, a portion of the branched gas G1 undergoes gas separation processing sequentially by the multiple separation units 14. As such, in the example shown in FIG. 2 , in addition to providing multiple separation units 14 in parallel, multiple separation units 14 are also provided in series. As shown in FIG. 2 , a check valve NV is provided connected from the inlet chamber R1 of one separation unit 14 to the line of the distributed gas GD leading to the inlet chamber R1 of another separation unit 14. Thus, the gas in the inlet chamber R1 is introduced into the inlet chamber R1 of the other separation unit 14 through the check valve NV.

[0059] More specifically, in the example shown in Figure 2, there are provided a first check valve NV1 connected from the inlet chamber R1 of the first separation unit 141 to the line of the distribution gas GD2 introduced into the second separation unit 142, a second check valve NV2 connected from the inlet chamber R1 of the second separation unit 142 to the line of the distribution gas GD3 introduced into the third separation unit 143, and a third check valve NV3 connected from the inlet chamber R1 of the third separation unit 143 to the line of the distribution gas GD4 introduced into the fourth separation unit 144.

[0060] For example, a case will be described in which the first distribution shutoff valve V1i is open, the second to fourth distribution shutoff valves V2i, V3i, and V4i are closed, the first to third recovery shutoff valves V1o, V2o, and V3o are closed, and the fourth recovery shutoff valve V4o is open. A portion of the first regenerated fuel gas GD12 delivered from the first check valve NV1 of the first separation unit 141 is further gas-separated in the second to fourth separation units 142 to 144 and is discharged toward the fourth recovery shutoff valve V4o or the inlet line for the carbon dioxide-rich gas G11.

[0061] In this way, when multiple separation units 14 are arranged in series, a portion of the first to third regenerated fuel gases GD12 to GD32 is again subjected to gas separation processing using the separation membrane S. This makes it possible to further increase the carbon dioxide concentration contained in the carbon dioxide-rich gas G11 discharged from the separation device D, and to further increase the concentration of hydrogen and other components contained in the regenerated fuel gas G12.

[0062] Note that the provision of the check valve NV is not essential, and the check valve NV may be omitted and the multiple separation units 14 may be arranged only in parallel, not connected in series, as shown in Fig. 3. Furthermore, at least two or more of the multiple separation units 14 may be connected by the check valve NV.

[0063] The separation device D in this embodiment separates the process gas (anode off-gas G) into a carbon dioxide-rich gas G11 and a regenerated fuel gas G12. However, the process gas to be separated by the separation device D does not need to contain flammable components such as hydrogen. Therefore, the residual gas remaining after the carbon dioxide-rich gas G11 is separated from the process gas does not need to contain flammable components. In other words, the separation device D may separate the process gas into a carbon dioxide-rich gas G11 with an increased carbon dioxide concentration and a regenerated fuel gas G12 with a reduced carbon dioxide concentration and an increased hydrogen concentration.

[0064] 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 separation device D having a plurality of separation units 14 that separate specific gas components from the branched gas G1, a compressor 12 that pressurizes the branched gas G1, a pressure gauge 20 that measures the pressure of the branched gas G1 introduced into the separation device D, a pressure regulator Cp that adjusts the pressure of the branched gas G1, a gas information acquisition section 11a that acquires the composition and flow rate of the branched gas G1, and a distribution mechanism DM that distributes the G1 branched gas to the plurality of separation units 14.

[0065] According to the fuel cell system 100 configured as described above, when the flow rate of the process gas supplied to the separation device D changes, the flow rate of the process gas distributed to each separation unit 14 by the distribution mechanism DM can be adjusted so that the carbon dioxide concentration of the carbon dioxide-rich gas G11 does not decrease. Therefore, it is possible to adjust the operating pressure of the gas separation process in the separation unit 14. Control based on flow rate and pressure has a small time constant, that is, control based on flow rate and pressure has a high response speed. Therefore, by controlling the gas separation process by dividing the branch gas G1 among multiple separation units 14 as in this embodiment, it is possible to suitably bring the carbon dioxide concentration or recovery amount close to a target value.

[0066] The system further includes a control device 19 that controls the distribution mechanism DM, and the control device 19 controls the distribution mechanism DM based on information from the pressure gauge 20 and the gas information acquisition unit 11a to distribute the branched gas G1 to the plurality of separation units 14. This allows the branched gas G1 to be distributed and introduced into the plurality of separation units 14, enabling gas separation processing at an appropriate flow rate and pressure of the branched gas G1 in each separation unit 14.

[0067] Furthermore, the plurality of separation units 14 are arranged in parallel, the distribution mechanism DM includes a distribution shutoff valve Vi, and the control device 19 distributes the branched gas G1 to the separation units 14 by opening and closing the distribution shutoff valve Vi. Because the plurality of separation units 14 are arranged in parallel, it is possible to perform gas separation processing simultaneously in the plurality of separation units 14. Furthermore, by opening and closing the distribution shutoff valve Vi according to the flow rate of the branched gas G1, it is possible to perform gas separation processing at an appropriate flow rate and pressure of the branched gas G1 in each separation unit 14.

[0068] Furthermore, at least two separation units 14 included in the separation unit 14 are arranged in series. This allows a portion of the branched gas G1 to be treated multiple times by the separation membrane S, thereby making it possible to further increase the concentration of the gas to be recovered in the carbon dioxide-rich gas G11 and the regenerated fuel gas G12.

[0069] Furthermore, the distribution mechanism DM distributes the branched gas G1 to all of the separation units 14 when the flow rate of the branched gas G1 acquired by the gas information acquisition unit 11a is equal to or greater than a threshold value, and distributes the branched gas G1 to some of the separation units 14 when the flow rate of the branched gas G1 acquired by the gas information acquisition unit 11a is below the threshold value. This allows the number of separation units 14 to which the branched gas G1 is introduced to be adjusted based on the threshold value. This makes it possible to prevent an excessive increase in the area of ​​the separation membrane S for the branched gas G1 per unit flow rate in the separation unit 14. This prevents an increase in the permeation amount of components that are less permeable through the separation membrane S than carbon dioxide, such as hydrogen, and prevents a decrease in the concentration of carbon dioxide contained in the carbon dioxide-rich gas G11.

[0070] The control device 19 further includes an operation time acquisition unit 24 that acquires the operation times of the plurality of separation units 14, and controls the distribution mechanism DM so that the operation times of the plurality of separation units 14 are uniform, based on the operation times of the plurality of separation units 14 acquired by the operation time acquisition unit 24. This makes it possible to equalize the usage times of the separation membranes S included in each of the plurality of separation units 14. Therefore, the timing of replacement or maintenance of the separation membranes S based on the cumulative usage time of the separation membranes S can be synchronized.

[0071] Furthermore, by controlling the pressure regulator Cp to change the pressure of the branch gas G1, the operating pressure of the separation unit 14 is adjusted when the open / close state of the distribution shutoff valve Vi is changed. This prevents the operating pressure of the separation unit 14 from changing suddenly when the distribution shutoff valve Vi is opened or closed. This prevents a decrease in the gas separation capacity of the separation unit 14 due to a sudden change in the operating pressure.

[0072] The separation device D also has a vacuum pump that sucks in the carbon dioxide-rich gas G11 discharged from the separation device D. This configuration makes it possible to increase the pressure ratio between the inlet chamber R1 and the recovery chamber R2, thereby improving the performance of the separation membrane S. Furthermore, it is possible to prevent the carbon dioxide-rich gas G11 from accumulating in the recovery chamber R2. Therefore, it is possible to prevent the phenomenon in which carbon dioxide permeation through the separation membrane S stagnates due to a high carbon dioxide concentration in the recovery chamber R2.

[0073] Second Embodiment Next, a fuel cell system 100A according to a second embodiment will be described with reference to Fig. 4. The basic configuration of the fuel cell system 100A is similar to that of the fuel cell system 100 according to the first embodiment, and therefore differences will be mainly described.

[0074] 4, the fuel cell system 100A according to this embodiment further includes a temperature detection mechanism 30 provided in the combustor 3a. The temperature detection mechanism 30 measures the temperature of the combustor 3a. Temperature information from the temperature detection mechanism 30 is input to the control device 19.

[0075] The combustor 3a burns fuel to generate heat so that the temperature inside the reformer 3 is within an appropriate range. As described above, the fuel for the combustor 3a is the recycled fuel gas G12 discharged from the separation device D. In this embodiment, the temperature detection mechanism 30 measures the combustion temperature of the combustor 3a, and the control device 19 estimates the amount of gas separated in the separation device D (the amount of recycled fuel gas G12) based on the temperature information from the temperature detection mechanism 30. The amount of gas separated in the separation device D is then controlled according to the estimated amount of gas separated. The amount of gas separated in the separation device D is controlled by the distribution mechanism DM or the pressure regulator 21. For example, if the combustion temperature is lower than a target value, the control device 19 may control the distribution mechanism DM or the pressure regulator 21 to increase the amount of recycled fuel gas G12, thereby increasing the amount of gas separated in the separation device D. If the combustion temperature is higher than a target value, the control device 19 may control the distribution mechanism DM or the pressure regulator 21 to decrease the amount of recycled fuel gas G12, thereby decreasing the amount of gas separated in the separation device D.

[0076] The fuel cell system 100A of this embodiment includes a reformer 3 that generates hydrogen from a hydrocarbon fuel and a combustor 3a thermally connected to the reformer. Regenerated fuel gas G12, which is discharged from a separation device D and has a higher hydrogen concentration than branched gas G1, is supplied to the combustor 3a. The distribution mechanism DM or pressure regulator 21 is controlled based on information from a temperature detection mechanism 30 provided in the combustor 3a. This configuration allows the regenerated fuel gas G12, which has a lower carbon dioxide concentration and a higher hydrogen concentration than the process gas, to be efficiently reused as fuel for the combustor 3a. This further increases the power generation efficiency of the entire system.

[0077] Third Embodiment Next, a fuel cell system 100B according to a third embodiment will be described with reference to Fig. 5. The basic configuration of the fuel cell system 100B is similar to that of the fuel cell system 100 according to the first embodiment, and therefore differences will be mainly described.

[0078] As shown in Fig. 5, the fuel cell system 100B further includes a fuel synthesis reaction mechanism 40 that produces synthetic fuel from carbon dioxide. Carbon dioxide-rich gas G11, which has been separated from the branch gas G1 by the separation device D and introduced into the carbon dioxide capture system 14a, is supplied to the fuel synthesis reaction mechanism 40 together with hydrogen gas supplied from an external source. The hydrogen gas supplied from an external source may be hydrogen produced separately by water electrolysis, or hydrogen stored and transported by another production method. Carbon and hydrogen in the carbon dioxide-rich gas G11 react to produce synthetic fuel (e.g., methane), which is a hydrocarbon fuel.

[0079] The fuel cell system 100B in this embodiment further includes a fuel synthesis reaction mechanism 40 that produces synthetic fuel from carbon dioxide, and a carbon dioxide capture system 14a that supplies the carbon dioxide-rich gas G11 separated from the branch gas G1 by the separation device D to the fuel synthesis reaction mechanism 40. This allows synthetic fuel to be synthesized using the carbon dioxide-rich gas G11 discharged from the separation device D.

[0080] Embodiment 4 Next, a fuel cell system 100C according to embodiment 3 will be described with reference to Fig. 6. The basic configuration of the fuel cell system 100C is similar to that of the fuel cell system 100B according to embodiment 3, and therefore differences will be mainly described.

[0081] 6 , the fuel cell system 100C further includes a co-electrolytic cell 50 between the carbon dioxide capture system 14a and the fuel synthesis reaction mechanism 40. The carbon dioxide-rich gas G11, which has been separated from the branched gas G1 by the separation device D and introduced into the carbon dioxide capture system 14a, is introduced into the co-electrolytic cell 50. The co-electrolytic cell 50 produces a synthesis gas containing hydrogen and carbon monoxide from the carbon dioxide-rich gas G11. The synthesis gas is introduced into the fuel synthesis reaction mechanism 40, where a synthetic fuel (e.g., methane or higher hydrocarbons) is produced from the synthesis gas containing hydrogen and carbon monoxide.

[0082] According to this embodiment, a co-electrolytic cell 50 that produces synthesis gas containing hydrogen and carbon monoxide is further provided between the carbon dioxide capture system 14a and the fuel synthesis reaction mechanism 40. This allows the fuel synthesis reaction mechanism 40 to use hydrogen produced in the co-electrolytic cell 50, instead of the hydrogen supplied from an external source in the third embodiment.

[0083] Carbon recycling can be achieved by turning the carbon components used as raw materials into synthetic fuel.

[0084] The technical scope of the present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure.

[0085] For example, a shift reaction section 61 that converts carbon monoxide into carbon dioxide and a shift reaction heat exchange section 62 that exchanges heat between the heat of the shift reaction section and steam may be provided between the branch section 10 and the compressor 12 that pressurizes the branch gas G1 supplied to the separation unit D. The steam used for the heat exchange may be steam supplied to the reformer 3. In the shift reaction section 61 and the shift reaction heat exchange section 62, the shift reaction causes changes in the concentrations of each gas in the branch gas G1. For this reason, the shift reaction section 61 and the shift reaction heat exchange section 62 are preferably located upstream of the gas information acquisition section 11a. Furthermore, in the shift reaction section 61, a higher steam partial pressure promotes the reaction toward carbon dioxide production, so it is more preferable to provide the shift reaction section 61 in an appropriate temperature range between the steam generator 7 and the condensation tank 9. The shift reaction reduces the carbon monoxide concentration and increases the concentrations of carbon dioxide and hydrogen in the branch gas G1 before it is introduced into the separation unit D. Therefore, it is possible to further increase the concentration of carbon dioxide or hydrogen in the carbon dioxide-rich gas G11 and the regenerated fuel gas G12 discharged from the separation device D.

[0086] In addition, 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. In addition, the fuel cell system 100 may not include the branching unit 10, and the entire amount of the anode off-gas G may be supplied directly to the separation device D.

[0087] In the above embodiment, the control device 19 controls the temperature regulator 13, the pressure regulator Cp, and the like. 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 a combination of software and hardware. The functions of the control device 19 may also be realized by a single piece of hardware. Alternatively, the hardware that controls the temperature regulator 13 may be different from the hardware that controls the pressure regulator Cp.

[0088] In addition, the above-described embodiments and modifications may be combined as appropriate.

[0089] 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...Separation unit 14a...Carbon dioxide recovery system 15...Vacuum pump 18...Operating state acquisition section 19...Control device 22...Thermometer 24...Operating time acquisition section 30...Temperature detection mechanism 40...Fuel synthesis reaction mechanism 50...Co-electrolysis cell 61...Shift reaction section 62...Shift reaction heat exchange section 100, 100A, 100B, 100C...Fuel cell system Cp...Pressure regulator D...Separator DM...Distribution mechanism G...Anode off-gas (process gas) G1...Branched gas G2...Recycled gas G11...Carbon dioxide-rich gas G12...Regenerated fuel gas (residual gas) Vi...Distribution shut-off valve NV...Check valve

Claims

1. A fuel cell system comprising: a fuel cell having an anode and a cathode; a branching section that branches anode off-gas discharged from the anode into a branch gas and a recycled gas; a separation device having a plurality of separation units that separate specific gas components from the branched gas; a compressor that pressurizes the branched gas; a pressure gauge that measures the pressure of the branched gas introduced into the separation device; a pressure regulator that adjusts the pressure of the branched gas; a gas information acquisition section that acquires the composition and flow rate of the branched gas; and a distribution mechanism that distributes the branched gas to the plurality of separation units.

2. The fuel cell system of claim 1, further comprising a control device that controls the distribution mechanism, wherein the control device controls the distribution mechanism based on information from the pressure gauge and the gas information acquisition unit, and distributes the branched gas to the multiple separation units.

3. The fuel cell system according to claim 2, wherein the plurality of separation units are arranged in parallel, the distribution mechanism includes a distribution shutoff valve, and the control device distributes the branched gas to the separation units by opening and closing the distribution shutoff valve.

4. The fuel cell system according to claim 3, wherein at least two separation units included in said separation unit are arranged in series.

5. A fuel cell system as described in any one of claims 1 to 4, wherein the distribution mechanism distributes the branched gas to all of the plurality of separation units when the flow rate of the branched gas acquired by the gas information acquisition unit is equal to or greater than a threshold value, and distributes the branched gas to some of the plurality of separation units when the flow rate of the branched gas acquired by the gas information acquisition unit is below a threshold value.

6. A fuel cell system as described in any one of claims 1 to 5, further comprising an operation time acquisition unit that acquires the operation times of the plurality of separation units, and a control device that controls the distribution mechanism controls the distribution mechanism based on the operation times of the plurality of separation units acquired by the operation time acquisition unit so that the operation times of the plurality of separation units are uniform.

7. The fuel cell system according to claim 3, wherein the pressure regulator is controlled to change the pressure of the branched gas, thereby adjusting the operating pressure of the separation unit when the open / closed state of the distribution shutoff valve is changed.

8. A fuel cell system according to any one of claims 1 to 7, comprising a reformer that generates hydrogen from hydrocarbon fuel, and a combustor that is thermally connected to the reformer, wherein a regenerated fuel gas having a higher hydrogen concentration than the branched gas discharged from the separation device is supplied to the combustor, and the distribution mechanism or the pressure regulator is controlled based on information from a temperature detection mechanism provided in the combustor.

9. A fuel cell system according to any one of claims 1 to 8, further comprising: a fuel synthesis reaction mechanism that produces synthetic fuel from carbon dioxide; and a carbon dioxide recovery system that supplies carbon dioxide-rich gas separated from the branch gas by the separation device to the fuel synthesis reaction mechanism.

10. The fuel cell system of claim 9, further comprising a co-electrolysis cell between the carbon dioxide capture system and the fuel synthesis reaction mechanism for producing a synthesis gas comprising hydrogen and carbon monoxide.

11. A fuel cell system according to any one of claims 1 to 10, comprising a shift reaction section between the branching section and a compressor that pressurizes the branched gas supplied to the separation device, which converts carbon monoxide into carbon dioxide, and a shift reaction heat exchange section that exchanges heat between the heat of the shift reaction section and steam, wherein the steam used in the heat exchange is steam supplied to a reformer that generates hydrogen from a hydrocarbon fuel.

12. The fuel cell system according to any one of claims 1 to 11, further comprising a vacuum pump for sucking the carbon dioxide-rich gas discharged from the separation device.

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