Gas separation system

Abstract

A gas separation system according to the present disclosure comprises: a gas separation device that separates a process gas containing carbon dioxide into a carbon dioxide-rich gas and a residual gas; a gas information acquisition unit that acquires gas information pertaining to the process gas; a pressure adjuster that adjusts the pressure of the process gas inside the gas separation device; a thermometer that measures the temperature of the process gas inside the gas separation device; a temperature adjuster that adjusts the temperature of the process gas inside the gas separation device; and a control device that controls the temperature adjuster on the basis of information from the thermometer and the gas information acquisition unit.

Description

Gas Separation Systems

[0001] The present disclosure relates to gas separation 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 gas separation 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 the gas separation system according to the present disclosure comprises a gas separation device that separates a process gas containing carbon dioxide into a carbon dioxide-rich gas having a higher carbon dioxide concentration than the process gas and a residual gas having a lower carbon dioxide concentration than the process gas, a gas information acquisition unit that acquires gas information related to the process gas, a pressure regulator that adjusts the pressure of the process gas inside the gas separation device, a thermometer that measures the temperature of the process gas inside the gas separation device, a temperature regulator that adjusts the temperature of the process gas inside the gas separation device, and a control device that controls the temperature regulator based on information from the thermometer and the gas information acquisition unit.

[0007] According to the gas separation system of the present disclosure, it is possible to 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.

[0008] FIG. 1 is a diagram showing the configuration of a gas separation system according to a first embodiment. FIG. 2 is a graph explaining the relationship between pressure and temperature and carbon dioxide permeability in a separation membrane. FIG. 3 is a graph explaining the relationship between pressure and temperature and carbon dioxide concentration in a separation membrane. FIG. 4 is a graph explaining the relationship between pressure and fuel cell load and carbon dioxide permeability in a separation membrane. FIG. 5 is a graph explaining the relationship between pressure and fuel cell load and carbon dioxide concentration in a separation membrane. FIG. 6 is a diagram showing the configuration of a separation device according to a second embodiment. FIG. 7 is a diagram showing the configuration of a separation device according to a first modified example of the second embodiment. FIG. 8 is a diagram showing the configuration of a separation device according to a second modified example of the second embodiment. FIG. 9 is a diagram showing the configuration of a separation device according to a third modified example of the second embodiment. FIG. 10 is a diagram showing the configuration of a gas separation system according to a third embodiment.

[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 gas separation system 100 according to embodiment 1. As shown in Fig. 1, the gas separation 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 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 a process gas other than anode off-gas. In other words, the gas separation system 100 does not need to be equipped with a fuel cell 4.

[0012] 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, an operating state acquisition unit 18 or a 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 ２ The 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 gas 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 (O ２ ) 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 gas separation system 100 including the fuel cell 4 can also be referred to as 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 / 2O２ +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 or 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 way, the recycle gas system 16 circulates the recycle gas G2 to the raw material supply system 2a.

[0027] The branch gas system 11 supplies at least a portion of the anode off-gas G as a branch gas G1 to the gas 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 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.

[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 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 used as the separation membrane S may be based on, for example, polyimide. Alternatively, the separation membrane S may have a structure in which a carrier is added to a water-absorbing polymer, which is called a facilitated transport membrane.

[0032] The branched gas G1 flowing 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.

[0033] In this specification, the gas that has permeated the separation membrane S from the inlet chamber R1 and moved to the recovery chamber R2 is referred to as the carbon dioxide-rich gas G11. The gas that does not permeate the separation membrane S and remains is referred to as the 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.

[0034] The carbon dioxide-rich gas G11 has a higher concentration of carbon dioxide than the branch gas G1 before separation by the carbon dioxide separation unit 14. The recycled fuel gas G12 has a lower concentration of carbon dioxide than the branch gas G1 before separation by the carbon dioxide separation unit 14. The recycled fuel gas G12 also contains combustible components such as hydrogen, carbon monoxide, and methane. Therefore, the recycled fuel gas G12 can be used as fuel. 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 introduction chamber R1. The combustor 3a is connected downstream of the recycled fuel gas system 14b. With this configuration, the recycled fuel gas G12 is supplied from the introduction chamber R1 to the combustor 3a and reused as fuel.

[0035] 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 arranged 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.

[0036] 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 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 carbon dioxide separation unit 14. Note that, as long as 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.

[0037] The thermometer 22 measures the temperature of the branched gas G1 in the 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.

[0038] 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.

[0039] As shown in Fig. 1, the gas separation 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.

[0040] Various types of information are 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 also control the distribution ratio of the branch gas G1 and the recycled gas G2 in the branching unit 10.

[0041] 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 carbon dioxide 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 carbon dioxide 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 creates the problem of a decrease in the power generation efficiency of the entire system.

[0042] Furthermore, the performance of the separation membrane S in the carbon dioxide separation unit 14 varies depending on the temperature 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 Figures 2 to 5. The horizontal axes in Figures 2 to 5 represent 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 carbon dioxide separation unit 14 corresponds to the horizontal axes in Figures 2 to 5.

[0043] 2 and 3 are graphs showing the relationship between gas temperature and the performance of separation membrane S. The vertical axis of FIG. 2 represents the carbon dioxide permeability through separation membrane S. The vertical axis of FIG. 3 represents the carbon dioxide concentration in the gas that has permeated separation membrane S. In FIGS. 2 and 3, temperature T0 (dashed line) is higher than temperature T1 (solid line). As can be seen from FIGS. 2 and 3, the higher the temperature, the higher the carbon dioxide permeability, but the lower the carbon dioxide concentration. The reason the carbon dioxide concentration decreases as the temperature increases is because the permeation amounts of components other than carbon dioxide, such as hydrogen, also increase.

[0044] 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 represents the carbon dioxide permeability through the separation membrane S. The vertical axis of FIG. 5 represents the carbon dioxide concentration in the gas that has permeated the separation membrane S. In FIGS. 4 and 5, the dashed lines represent the case where the fuel cell 4 is operating at rated output, and the solid lines represent 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 FIGS. 4 and 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.

[0045] 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.

[0046] As can be seen from FIGS. 2 to 5, the higher the pressure (horizontal axis) of the branched gas G1 in the carbon dioxide separation unit 14, the higher the carbon dioxide permeability and the lower the carbon dioxide concentration.

[0047] 2 to 5, the control device 19 in this embodiment performs control so that the separation performance of 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 obtained by the pressure gauge 20, the temperature obtained by the thermometer 22, the flow rate of the recycled gas G2 obtained by the recycled gas flow meter 16b, the operating state of the fuel cell 4 obtained by the operating state obtaining unit 18, and the like.

[0048] 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.

[0049] In the first example, the control device 19 reduces the temperature of the branch 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 removed from the branch gas G1 to the refrigerant, and the temperature of the branch gas G1 can be reduced.

[0050] 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, by increasing the aperture of the adjustment valve 21 serving as the pressure regulator Cp, the regenerated fuel gas G12 is made to flow more easily from the carbon dioxide separation unit 14 to the combustor 3a. Alternatively, by reducing 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 is reduced. As a result, the pressure of the branch gas G1 in the carbon dioxide separation unit 14 can be reduced.

[0051] 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-based control tends to have a small time constant, while temperature-based control tends to have a large time constant. In other words, pressure-based control tends to have a fast response speed, while temperature-based control tends to have a slow response speed. Taking these differences into consideration, feedback control may be performed so that the carbon dioxide concentration or recovery amount approaches a target value.

[0052] The gas 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 gas 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 gas separation device D may separate the process gas into a carbon dioxide-rich gas G11 with an increased carbon dioxide concentration and a residual gas with a reduced carbon dioxide concentration.

[0053] As described above, the gas separation system 100 of the present disclosure comprises a gas separation device D that separates a process gas (anode off-gas G) containing carbon dioxide into a carbon dioxide-rich gas G11 having a higher carbon dioxide concentration than the process gas and a residual gas (regenerated fuel gas G12) having a lower carbon dioxide concentration than the process gas, a gas information acquisition unit 11a that acquires gas information related to the process gas, a pressure regulator Cp that adjusts the pressure of the process gas inside the gas separation device D, a thermometer 22 that measures the temperature of the process gas inside the gas separation device D, a temperature regulator 13 that adjusts the temperature of the process gas inside the gas separation device D, and a control device 19 that controls the temperature regulator 13 based on information from the thermometer 22 and the gas information acquisition unit 11a.

[0054] According to the gas separation system 100 having such a configuration, when the flow rate of the process gas supplied to the gas separation device D changes, the temperature of the process gas can be adjusted by the temperature regulator 13 so that the carbon dioxide concentration of the carbon dioxide-rich gas G11 does not decrease.

[0055] The gas information acquired by the gas information acquiring unit 11a may also include information on at least the composition and flow rate of the process gas (branched gas G1) introduced into the gas separation apparatus D. In this case, the temperature of the process gas supplied to the gas separation apparatus D can be set to an appropriate value depending on the composition or flow rate of the process gas.

[0056] The gas separation system 100 may also include a fuel cell 4 having an anode 4A and a cathode 4B. The process gas may be anode off-gas G discharged from the anode 4A. The fuel cell 4 is a device that generates electricity using hydrogen and oxygen, and is highly efficient and has a low environmental impact. Combining such a fuel cell 4 with the gas separation system 100 of the present disclosure can further contribute to the challenge of reducing the environmental impact.

[0057] The gas separation system 100 may also include an operating state acquisition unit 18 that acquires the operating state of the fuel cell 4. The control device 19 may control the temperature regulator 13 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.

[0058] 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 reduce the pressure of the anode off-gas G inside the gas separation device D. By reducing 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.

[0059] The gas separation system 100 may also include a reformer 3 that produces hydrogen from hydrocarbons and a combustor 3a thermally connected to the reformer 3. The residual gas obtained in the gas separation device D may be a regenerated fuel gas G12 having a higher hydrogen concentration than the process gas, and this regenerated fuel gas G12 may be supplied to the combustor 3a. With this configuration, the regenerated fuel gas G12, which has a lower carbon dioxide concentration and a higher hydrogen concentration than the process gas, can be reused as fuel for the combustor 3a. This can further improve the power generation efficiency of the entire system.

[0060] The gas separation system 100 may also include a branching section 10 that branches the process gas into a branched gas G1 and a recycled gas G2, a branched gas system 11 that supplies the branched gas G1 to the gas separation device D, and a recycled gas system 16 that supplies the recycled gas G2 to the mixer 2. With this configuration, carbon dioxide is separated from a portion of the process gas in the gas separation device D, and the remaining portion of the process gas can be reused as a raw material for power generation in the fuel cell 4. The mixer 2 may also be an ejector. In this case, the recycled gas G2 can be sucked in using water vapor as a driving fluid, eliminating the need for a blower 16a and reducing the power required for auxiliary equipment.

[0061] 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 process gas 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, the operation of the system can be optimized in terms of both carbon dioxide separation in the gas separation device D and power generation in the fuel cell 4.

[0062] The gas separation 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. 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 achieve high efficiency for the separation membrane S and to prevent the phenomenon in which carbon dioxide permeation stagnates due to a high carbon dioxide concentration in the recovery chamber R2.

[0063] Second Embodiment Next, a gas separation system 100A according to a second embodiment will be described with reference to Figure 6. The basic configuration of the gas separation system 100A is similar to that of the gas separation system 100 of the first embodiment, and therefore differences will be mainly described. Although not shown in Figure 6, a branch section 10 and the like (see Figure 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.

[0064] As shown in FIG. 6 , the gas separation apparatus D in the gas separation system 100A according to this embodiment includes, in addition to the carbon dioxide separation unit 14, a hydrogen separation unit 14H, an intermediate system 24, a circulation system 25, a second pressure gauge 20A, and a second adjustment valve 21A. The hydrogen separation unit 14H has a second separation membrane SH, a second inlet chamber R3, and a second recovery chamber R4. The second inlet 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, for example, from a polymer. The second separation membrane SH is formed from 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 permeates based on molecular size.

[0065] 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, the hydrogen contained in the branched gas G1 permeates the second separation membrane SH and moves to the second recovery chamber R4. A recycled fuel gas system 14b is connected to the second recovery chamber R4. The gas that permeates the second separation membrane SH has a higher hydrogen concentration 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 recycled fuel gas system 14b as recycled fuel gas G12. This recycled fuel gas G12 can also be used as fuel for the combustor 3a, as in the first embodiment.

[0066] 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. 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.

[0067] The separation unit 14 shown in Fig. 6 separates carbon dioxide contained in the intermediate gas Gm using a separation membrane S and discharges it as a carbon dioxide-rich gas G11 to the 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.

[0068] 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 the 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 measurement results of the pressure gauge 20, the second pressure gauge 20A, the thermometer 22, etc.

[0069] 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 using the temperature regulator 13, the compressor 12, 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 using 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.

[0070] FIG. 7 shows a first modified example of the gas separation 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 temperature of the gas introduced into the introduction chamber R1 and the second introduction chamber R3 can be adjusted by the control device 19 controlling the temperature regulator 13. Furthermore, the pressure of the gas introduced into the introduction chamber R1 and the second introduction chamber R3 can be adjusted by the control device 19 controlling the adjustment valve 21. Furthermore, the simple configuration contributes to cost reduction.

[0071] FIG. 8 shows a second modified example of the gas separation 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 branch gas G1 introduced into the inlet chamber R1 of the upstream carbon dioxide separation unit 14 using the temperature regulator 13, the compressor 12, and the like. Furthermore, the pressure of the intermediate gas Gm introduced into the second inlet chamber R3 of the downstream hydrogen separation unit 14H can be controlled using the second adjustment valve 21A and the like. The control device 19 can perform control so that the hydrogen utilization efficiency and the carbon dioxide recovery efficiency approach target values.

[0072] Furthermore, as shown in a third modified example in FIG. 9, the second pressure gauge 20A and the second adjusting valve 21A may be omitted.

[0073] As described above, in the gas separation system 100A (FIGS. 6 to 8) according to the second embodiment, the gas separation apparatus D has a plurality of separation units 14, 14A. The plurality of separation units 14, 14H includes a carbon dioxide separation unit 14 that separates carbon dioxide and a hydrogen separation unit 14H that separates hydrogen. This configuration can further improve the carbon dioxide recovery efficiency and hydrogen utilization efficiency. The gas separation apparatus D may have three or more separation units.

[0074] Third Embodiment Next, a gas separation system 100B according to a third embodiment will be described with reference to Fig. 10. The basic configuration of the gas separation system 100B is similar to that of the gas separation system 100 of the first embodiment, and therefore differences will be mainly described.

[0075] 10 , the gas separation 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 3 a. The carbon dioxide capture unit 26 may include, for example, an adsorbent capable of adsorbing carbon dioxide.

[0076] 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 materials other than those listed above may be used. The adsorbent may be in a granular form (e.g., bead-like (spherical) or pellet-like (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.

[0077] 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, too, the carbon dioxide contained in the combustion off-gas can be separated using the separation membrane S before being released into the atmosphere. Therefore, the concentration and amount of carbon dioxide released into the atmosphere can be reduced.

[0078] 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.

[0079] 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. Furthermore, the gas separation system 100 may not include the branching section 10, and the entire amount of the anode off-gas G may be supplied directly to the gas separation device D.

[0080] 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.

[0081] Furthermore, 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 an external source. 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), which is a hydrocarbon fuel. Carbon recycling can be achieved by generating a synthetic fuel based on the carbon components used as raw materials in the fuel cell 4.

[0082] In addition, the above-described embodiments and modifications may be combined as appropriate. For example, the gas separation system 100B described in the third embodiment may include a gas separation device D as shown in FIGS.

[0083] DESCRIPTION OF SYMBOLS 2...Mixer 3...Reformer 3a...Combustor 4...Fuel cell 4A...Anode 4B...Cathode 10...Branch 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...Operating state acquisition section 19...Control device 22...Thermometer 26...Carbon dioxide recovery section 100, 100A, 100B...Gas separation system Cp...Pressure regulator D...Gas separation device G...Anode off-gas (process gas) G1...Branched gas G2...Recycled gas G11...Carbon dioxide-rich gas G12...Regenerated fuel gas (residual gas)

Claims

1. A gas separation system comprising: a gas separation device that separates a process gas containing carbon dioxide into a carbon dioxide-rich gas having a higher carbon dioxide concentration than the process gas and a residual gas having a lower carbon dioxide concentration than the process gas; a gas information acquisition unit that acquires gas information regarding the process gas; a pressure regulator that adjusts the pressure of the process gas inside the gas separation device; a thermometer that measures the temperature of the process gas inside the gas separation device; a temperature regulator that adjusts the temperature of the process gas inside the gas separation device; and a control device that controls the temperature regulator based on information from the thermometer and the gas information acquisition unit.

2. The gas separation system of claim 1, wherein the gas information includes information regarding at least the composition and flow rate of the process gas.

3. The gas separation system according to claim 1 or 2, further comprising a fuel cell having an anode and a cathode, wherein the process gas is an anode off-gas discharged from the anode.

4. The gas separation system according to claim 3, further comprising an operating state acquisition unit that acquires an operating state of the fuel cell, and the control device controls the temperature regulator based on the operating state.

5. The gas separation system described in claim 4, wherein the control device controls the pressure regulator so as to reduce the pressure of the anode off-gas inside the gas separation device when it determines, based on the operating state, that the output of the fuel cell has decreased.

6. The gas separation system according to claim 4 or 5, further comprising: a branching section that branches the process gas into a branched gas and a recycled gas; a branched gas system that supplies the branched gas to the gas separation device; and a recycled gas system that supplies the recycled gas to a mixer.

7. The gas separation system described in claim 6, wherein the control device controls the distribution ratio of the branched gas and the recycled gas in the branching section based on the pressure of the process gas inside the gas separation device, the temperature acquired by the thermometer, and the operating state acquired by the operating state acquisition section.

8. A gas separation system according to any one of claims 1 to 7, further comprising a vacuum pump that sucks the carbon dioxide-rich gas separated in the gas separation device.

9. The gas separation system according to any one of claims 1 to 8, wherein the gas separation apparatus has a plurality of separation units, and the plurality of separation units includes a carbon dioxide separation unit that separates carbon dioxide.

10. The gas separation system of claim 9, wherein the plurality of separation units includes a hydrogen separation unit that separates hydrogen.

11. A gas separation system according to any one of claims 1 to 10, further comprising: a reformer that produces hydrogen from hydrocarbons; and a combustor thermally connected to the reformer, wherein the residual gas is a recycled fuel gas having a higher concentration of hydrogen than the process gas, and the recycled fuel gas is supplied to the combustor.

12. The gas separation system according to claim 11, further comprising a carbon dioxide recovery section that recovers carbon dioxide from the combustion off-gas discharged from the combustor.

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