Gas recovery system and gas recovery method

Abstract

To provide a gas recovery system capable of suppressing fluctuations in the flow rate and properties of recovered gas discharged from a separation tank.SOLUTION: A gas recovery system 100 comprises: a raw material gas supply unit 10 configured to supply raw material gas; a separation tank 20 configured to separate carbon dioxide from the raw material gas; a first exhaust unit 30 configured to exhaust a first gas from the separation tank; a pressure control unit V31 provided in the first exhaust unit and configured to control a pressure inside the first exhaust unit; a second exhaust unit configured to exhaust a second gas having a higher carbon dioxide concentration than the first gas from the separation tank; a differential pressure drive mechanism 41 provided in the second exhaust unit 40; a return flow path L42 configured to return a portion of the gas on a discharge side of the differential pressure drive mechanism 41 to a suction side of the differential pressure drive mechanism 41; a flow rate control unit V41 provided in the return flow path L42 and configured to control a flow rate of the returned gas; a differential pressure detection unit configured to detect a differential pressure between the pressure of the gas on the supply side of the separation tank 20 and the pressure of the second gas; and a controller 210 configured to control the pressure control unit and the flow rate control unit based on the detected differential pressure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a gas recovery system and a gas recovery method. [Background technology]

[0002] A carbon dioxide separation and capture device is known that includes a carbon dioxide separator whose internal space is divided into a first space and a second space by a separation membrane that selectively permeates carbon dioxide, and a pump that generates a pressure difference between the first space and the second space by reducing the pressure in the second space (see, for example, Patent Document 1). A gas containing carbon dioxide is supplied to the first space. The permeated gas that has permeated the separation membrane flows from the second space to a permeated gas flow path. The non-permeated gas that has not permeated the separation membrane flows from the first space to a non-permeated gas flow path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-142336 Summary of the Invention [Problem to be solved by the invention]

[0004] In a system for separating and capturing carbon dioxide, fluctuations in the flow rate of the raw gas supplied to the separation tank cause fluctuations in the pressure difference in the separation tank, which in turn causes fluctuations in the flow rate and properties of the captured gas discharged from the separation tank.

[0005] An object of the present disclosure is to provide a gas recovery system that can suppress fluctuations in the flow rate and properties of the recovered gas discharged from a separation tank. [Means for solving the problem]

[0006] The gas recovery system according to the present disclosure includes a raw gas supply unit that supplies raw gas, a separation tank that separates carbon dioxide from the raw gas, a first discharge unit that discharges a first gas from the separation tank, a pressure control unit provided in the first discharge unit that controls the pressure inside the first discharge unit, a second discharge unit that discharges a second gas having a higher carbon dioxide concentration than the first gas from the separation tank, a differential pressure drive mechanism provided in the second discharge unit, a return flow path that returns a portion of the gas on the discharge side of the differential pressure drive mechanism to the suction side of the differential pressure drive mechanism, a flow rate control unit provided in the return flow path that controls the flow rate of the returned gas, a differential pressure detection unit that detects the differential pressure between the pressure of the gas on the supply side of the separation tank and the pressure of the second gas, and a controller that controls the pressure control unit and the flow rate control unit based on the differential pressure detected by the differential pressure detection unit. [Effects of the Invention]

[0007] The present disclosure can suppress fluctuations in the flow rate and properties of the recovered gas discharged from the separation tank. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating a gas recovery system according to a first embodiment. [Figure 2] 1 is a block diagram illustrating a hardware configuration of a gas recovery system according to a first embodiment. [Figure 3] 10 is a flowchart illustrating a procedure for a fluctuation suppression process in the gas recovery system. [Figure 4] FIG. 10 is a schematic diagram illustrating a gas recovery system according to a second embodiment. [Figure 5] FIG. 10 is a block diagram illustrating a hardware configuration of a gas recovery system according to a second embodiment. [Figure 6] 10 is a flowchart illustrating a procedure for a fluctuation suppression process in the gas recovery system. [Figure 7] FIG. 10 is a schematic diagram illustrating a gas recovery system according to a third embodiment. [Figure 8] FIG. 10 is a schematic diagram illustrating a gas recovery system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a gas recovery system according to an embodiment will be described with reference to the accompanying drawings. In this specification and the drawings, substantially identical components are designated by the same reference numerals, and redundant description may be omitted.

[0010] [Gas recovery system 100 according to the first embodiment] FIG. 1 is a schematic diagram illustrating a gas recovery system 100 according to a first embodiment. The gas recovery system 100 shown in FIG. 1 is a system that separates carbon dioxide contained in a raw material gas and recovers the carbon dioxide. The gas recovery system 100 may be, for example, a system that separates and recovers carbon dioxide from a raw material gas, which is a combustion exhaust gas discharged from a combustor. The raw material gas is not limited to the combustion exhaust gas discharged from a combustor, but may be a gas discharged from other equipment. The gas recovery system 100 is installed, for example, in a factory, a power plant, a ship, or the like. The installation location of the gas recovery system 100 is not particularly limited. The gas recovery system 100 is an example of a gas processing system.

[0011] The gas recovery system 100 includes a raw material gas supply unit 10, a separation tank 20, a first discharge unit 30, a second discharge unit 40, and a controller 210.

[0012] [Source gas supply unit 10] The raw material gas supply unit 10 supplies the raw material gas to the separation tank 20. The raw material gas supply unit 10 is connected to a source of raw material gas, such as a combustor. The raw material gas supply unit 10 includes a raw material gas supply pipe L11 for transporting the raw material gas. The raw material gas supply pipe L11 is connected to the separation tank 20.

[0013] The raw material gas supply unit 10 may include a blower that blows the raw material gas. The blower is connected to the raw material gas supply pipe L11. The raw material gas is blown by the blower, flows through the raw material gas supply pipe L11, and is supplied to the separation tank 20.

[0014] [Pressure Gauge 221] The raw material gas supply unit 10 has a pressure gauge 221 that detects the pressure P11 of the raw material gas upstream of the separation tank 20. The pressure gauge 221 is connected to the raw material gas supply pipe L11. Data related to the raw material gas pressure P11 detected by the pressure gauge 221 is input to the controller 210.

[0015] [Separation tank 20] The separation tank 20 separates carbon dioxide from the raw gas. The raw gas contains carbon dioxide. The separation tank 20 has, for example, a separation membrane and a container. The separation membrane is housed in the container. The separation tank 20 may have a separation membrane module. The separation membrane is a membrane that selectively permeates carbon dioxide relative to other components. The separation membrane includes a hollow fiber membrane. The separation membrane may have multiple spiral membranes or may have stacked flat membranes.

[0016] The raw material gas supplied to the separation tank 20 is separated into a permeated gas that has permeated the separation membrane and a retentate gas that has not permeated the separation membrane. The permeated gas has a higher carbon dioxide concentration than the retentate gas. The retentate gas has a lower carbon dioxide concentration than the permeated gas. The retentate gas is an example of a first gas, and the permeated gas is an example of a second gas.

[0017] Separation tank 20 may separate the raw material gas into a first gas and a second gas having a higher carbon dioxide concentration than the first gas. Separation tank 20 may separate at least a portion of the carbon dioxide contained in the raw material gas from the raw material gas.

[0018] [First discharge section 30] The first discharge section 30 includes a first discharge pipe L31 that discharges the retentate gas from the separation tank 20. The first discharge pipe L31 is connected to the separation tank 20. The retentate gas in the separation tank 20 flows through the first discharge pipe L31 and is discharged to the outside of the separation tank 20. The retentate gas may be released into the atmosphere.

[0019] [Pressure control valve V31] The gas recovery system 100 is provided with a pressure control valve V31 that is provided in the first discharge unit 30 and controls the pressure inside the first discharge unit 30. The pressure control valve V31 is connected to a first discharge pipe L31. The pressure control valve V31 is electrically connected to a controller 210. The pressure control valve V31 is driven in accordance with a command signal output from the controller 210. The controller 210 can control the valve opening degree of the pressure control valve V31. The pressure control valve V31 can control the pressure inside the first discharge pipe L31. The pressure control valve V31 is an example of a pressure control unit that controls the pressure inside the first discharge unit 30.

[0020] [Second discharge section 40] The second discharge section 40 includes a second discharge pipe L41 that discharges the permeable gas from the separation tank 20. The second discharge pipe L41 is connected to the separation tank 20. The permeable gas in the separation tank 20 flows through the second discharge pipe L41 and is discharged to the outside of the separation tank 20. The permeable gas is stored in, for example, a container and shipped as a product (carbon dioxide gas).

[0021] [Differential pressure drive mechanism 41] The second discharge section 40 is equipped with a differential pressure drive mechanism 41 connected to the second discharge pipe L41. The differential pressure drive mechanism 41 may be, for example, a vacuum pump. The differential pressure drive mechanism 41 generates a pressure difference between the front and rear of the separation membrane. The pressure of the permeated gas downstream of the separation membrane is lower than the pressure of the raw material gas upstream of the separation membrane. The differential pressure drive mechanism 41 is not limited to a vacuum pump, and may be a blower, an ejector, or another device. The carbon dioxide that has permeated the separation membrane flows through the second discharge pipe L41 and is stored in the product tank.

[0022] [Pressure Gauge 222] The second discharge section 40 has a pressure gauge 222 that detects the pressure P12 of the permeate gas downstream of the separation tank 20. The pressure gauge 222 is connected to the second discharge pipe L41. The pressure gauge 222 is provided on the second discharge pipe L41 between the separation tank 20 and the differential pressure drive mechanism 41. Data related to the pressure P12 of the permeate gas detected by the pressure gauge 222 is input to the controller 210.

[0023] [Return piping L42] The gas recovery system 100 includes a return pipe L42 that returns a portion of the gas on the discharge side of the differential pressure driving mechanism 41 to the suction side of the differential pressure driving mechanism 41. The return pipe L42 connects the second discharge pipe L41 downstream of the differential pressure driving mechanism 41 with the second discharge pipe L41 upstream of the differential pressure driving mechanism 41. The flow path inside the return pipe L42 is a return flow path.

[0024] [Flowmeter 223] The second discharge unit 40 has a flow meter 223 that detects the flow rate of the permeable gas flowing through the return pipe L42. The flow meter 223 is connected to the return pipe L42. Data related to the flow rate detected by the flow meter 223 is input to the controller 210.

[0025] [Flow control valve V41] The gas recovery system 100 is provided with a flow control valve V41 that is provided in the return pipe L42 and controls the flow rate of the returned gas. The flow control valve V41 is electrically connected to the controller 210. The flow control valve V41 is driven in accordance with a command signal output from the controller 210. The controller 210 can control the valve opening degree of the flow control valve V41. The flow control valve V41 can control the flow rate of the permeable gas flowing inside the return pipe L42. The flow control valve V41 can control the flow rate of the permeable gas flowing through the differential pressure driving mechanism 41 by controlling the flow rate of the permeable gas returned from the discharge side to the suction side of the differential pressure driving mechanism 41. The flow control valve V41 is provided in the return flow path and is an example of a flow rate control unit that controls the flow rate of the returned gas.

[0026] [Controller 210] Next, the controller 210 of the gas recovery system 100 will be described with reference to Fig. 2. Fig. 2 is a block diagram illustrating an example of the hardware configuration of the gas recovery system 100 according to the first embodiment. As shown in Fig. 2, the controller 210 is electrically connected to a pressure gauge 221, a pressure gauge 222, a flow meter 223, a pressure control valve V31, a flow control valve V41, and a differential pressure drive mechanism 41.

[0027] The controller 210 includes a CPU (Center Processing Unit) 211 and a storage unit 212. The CPU 211 is responsible for overall control of the gas recovery system 100. The CPU 211 receives input of various data detected by a pressure gauge 221, a pressure gauge 222, and a flow meter 223. Other sensors may be connected to the controller 210.

[0028] The storage unit 212 includes a ROM (Read Only Memory) 213 and a RAM (Random Access Memory) 214. The ROM 213 stores various programs for causing the CPU 211 to execute control processes, as well as various data necessary for operation of the gas recovery system 100. The RAM 214 temporarily stores data acquired from the sensor 220, etc.

[0029] The controller 210 functions as a differential pressure detector that detects the differential pressure ΔP11 between the pressure P11 of the feed gas and the pressure P12 of the permeated gas. The feed gas pressure P11 is an example of a gas on the supply side of the separation tank 20. The permeated gas pressure P12 is an example of a second gas. The differential pressure ΔP11 is the differential pressure between the pressure P12 of the permeated gas on the downstream side of the separation tank 20 and the pressure P11 of the feed gas on the upstream side of the separation tank 20 (ΔP11 = P12 - P11). The pressure P11 is detected by a pressure gauge 221. The pressure P12 is detected by a pressure gauge 222.

[0030] The controller 210 can control the operation of the differential pressure driving mechanism 41 based on the differential pressure ΔP11.

[0031] [Pressure control by pressure control valve V31] The controller 210 can control the valve opening degree of the pressure control valve V31 based on the differential pressure ΔP11. The controller 210 can control the pressure control valve V31 according to whether the differential pressure ΔP11 is within the reference range. The lower limit value of the reference range may be, for example, the first determination threshold value Pth11. The upper limit value of the reference range may be, for example, the second determination threshold value Pth12. In this case, the reference range of the differential pressure ΔP11 is not less than the first determination threshold value Pth11 and not more than the second determination threshold value Pth12. The second determination threshold value Pth12 is a value larger than the first determination threshold value Pth11.

[0032] When the differential pressure ΔP11 is less than the first determination threshold value Pth11 (ΔP11 < Pth11), the controller 210 can control the pressure control valve V31 so as to increase the pressure P11 of the raw material gas. When the differential pressure ΔP11 is less than the first determination threshold value Pth11, the controller 210 can decrease the valve opening degree of the pressure control valve V31 to increase the pressure P11 of the raw material gas. As a result, the differential pressure ΔP11 can be increased.

[0033] When the differential pressure ΔP11 exceeds the second determination threshold value Pth12 (ΔP11 > Pth12), the controller 210 can control the pressure control valve V31 so as to decrease the pressure P11 of the raw material gas. When the differential pressure ΔP11 exceeds the second determination threshold value Pth12, the controller 210 can increase the valve opening degree of the pressure control valve V31 to decrease the pressure P11 of the raw material gas. As a result, the differential pressure ΔP11 can be decreased.

[0034] [Flow control by the flow control valve V41] The controller 210 can control the valve opening degree of the flow control valve V41 based on the differential pressure ΔP11.

[0035] When the differential pressure ΔP11 is less than the first determination threshold value Pth11 (ΔP11 < Pth11), the controller 210 can control the flow control valve V41 so as to decrease the pressure P12 of the permeated gas. When the differential pressure ΔP11 is less than the first determination threshold value Pth11, the controller 210 can decrease the valve opening degree of the pressure control valve V31 to decrease the flow rate of the permeated gas flowing through the return pipe L42. Thereby, the pressure P12 of the permeated gas can be decreased. As a result, the differential pressure ΔP11 can be increased.

[0036] When the differential pressure ΔP11 exceeds the second determination threshold value Pth12 (ΔP11 > Pth12), the controller 210 can control the flow control valve V41 so as to increase the pressure P12 of the permeated gas. When the differential pressure ΔP11 is higher than the first determination threshold value Pth11, the controller 210 can decrease the valve opening degree of the flow control valve V41 to decrease the flow rate of the permeated gas flowing through the return pipe L42. Thereby, the pressure P11 of the raw material gas can be decreased. As a result, the differential pressure ΔP11 can be decreased.

[0037] [Priority of Pressure Control and Flow Control] When the differential pressure ΔP11 is less than the first determination threshold value Pth11 (ΔP11 < Pth11), the controller 210 may control the pressure control valve V31 to increase the pressure P11 of the raw material gas and then control the flow control valve V41 to decrease the flow rate of the permeated gas flowing through the return pipe L42. The controller 210 can execute the pressure control by the pressure control valve V31 prior to the flow control by the flow control valve V41.

[0038] When the differential pressure ΔP11 exceeds the second determination threshold value Pth12 (ΔP11 > Pth12), the controller 210 may control the pressure control valve V31 to decrease the pressure P11 of the raw material gas and then control the flow control valve V41 to increase the flow rate of the permeated gas flowing through the return pipe L42. The controller 210 can execute the pressure control by the pressure control valve V31 prior to the flow control by the flow control valve V41.

[0039] The controller 210 may execute flow rate control using the flow rate control valve V41 while executing pressure control using the pressure control valve V31. Alternatively, the controller 210 may execute pressure control using the pressure control valve V31 after executing flow rate control using the flow rate control valve V41.

[0040] [Procedure of Fluctuation Control Processing in the Gas Recovery System 100 According to the First Embodiment] Next, the procedure of the fluctuation control process in the gas recovery system 100 will be described with reference to FIG. 3. FIG. 3 is a flowchart illustrating the procedure of the fluctuation suppression process in the gas recovery system 100. The fluctuation suppression control process may be a control process for suppressing fluctuations in the raw material gas pressure P11. A state in which the fluctuation suppression control process shown in FIG. 3 is not being executed is defined as a reference state. In this reference state, the pressure control valve V31 may be fully open. In the reference state, the flow control valve V41 may be fully closed. A case in which the differential pressure ΔP11 is within a reference range may be defined as the reference state. A range in which the differential pressure ΔP11 is equal to or greater than a first determination threshold Pth11 (lower limit value) and equal to or less than a second determination threshold Pth12 (upper limit value) can be defined as the reference range.

[0041] In the fluctuation suppression control process, first, the CPU 211 of the controller 210 determines whether or not the differential pressure ΔP11 is within a reference range (step S11). For example, if the load of the internal combustion engine, which is the source of the raw material gas, fluctuates significantly, the differential pressure ΔP11 may fall outside the reference range. The CPU 211 calculates the differential pressure ΔP11 based on the detection results of the pressure gauges 221 and 222, and determines whether or not the differential pressure ΔP11 is within the reference range. If the differential pressure ΔP11 is within the reference range (step S11; YES), the CPU 211 ends the process here. If the differential pressure ΔP11 is not within the reference range (step S11; NO), the CPU 211 executes the process of step S12.

[0042] In step S12, the CPU 211 determines whether the differential pressure ΔP11 exceeds the upper limit of the reference range. If the differential pressure ΔP11 exceeds the upper limit of the reference range (step S12; YES), the CPU 211 executes the process of step S13. If the differential pressure ΔP11 does not exceed the upper limit of the reference range (step S12; NO), the CPU 211 executes the process of step S14.

[0043] In step S13, the CPU 211 determines whether or not control by the pressure control valve V31 is possible. If an operation to increase the valve opening degree (opening operation) can be performed in the pressure control valve V31, the CPU 211 can determine that control by the pressure control valve V31 is possible. If the pressure control valve V31 is in a fully open state or a state close to being fully open, the CPU 211 can determine that control by the pressure control valve V31 is impossible.

[0044] If control by the pressure control valve V31 is possible (step S13; YES), the CPU 211 executes the process of step S15. In step S15, the CPU 211 increases the valve opening of the pressure control valve V31. This allows the CPU 211 to reduce the differential pressure ΔP11. After executing the process of step S15, the CPU 211 executes the process of step S19.

[0045] If control by the pressure control valve V31 is not possible (step S13; NO), the CPU 211 executes the process of step S16. In step S16, the CPU 211 increases the valve opening of the flow control valve V41. The CPU 211 increases the flow rate of the permeate gas flowing through the return pipe L42, thereby increasing the pressure of the gas on the permeate side of the separation tank 20. This allows the CPU 211 to reduce the differential pressure ΔP11. After executing the process of step S16, the CPU 211 executes the process of step S19.

[0046] In step S14, the CPU 211 determines whether or not control by the flow control valve V41 is possible. If the flow control valve V41 can perform an operation to reduce the valve opening (closing operation), the CPU 211 can determine that control by the flow control valve V41 is possible. If the flow control valve V41 is in a fully closed state or a state close to being fully closed, the CPU 211 can determine that control by the flow control valve V41 is impossible.

[0047] If control by the flow control valve V41 is possible (step S14; YES), the CPU 211 executes the process of step S17. In step S17, the CPU 211 reduces the valve opening of the flow control valve V41. The CPU 211 reduces the flow rate of the permeate gas flowing through the return pipe L42, thereby lowering the pressure of the gas on the permeate side of the separation tank 20. This allows the CPU 211 to increase the differential pressure ΔP11. After executing the process of step S17, the CPU 211 executes the process of step S19.

[0048] If control by the flow control valve V41 is not possible (step S14; NO), the CPU 211 executes the process of step S18. In step S18, the CPU 211 reduces the valve opening of the pressure control valve V31. This allows the CPU 211 to increase the differential pressure ΔP11. After executing the process of step S18, the CPU 211 executes the process of step S19.

[0049] In step S19, the CPU 211 determines whether the differential pressure ΔP11 is within the reference range, similarly to step S11. If the differential pressure ΔP11 is within the reference range (step S19; YES), the CPU 211 ends the process here. If the differential pressure ΔP11 is not within the reference range (step S19; NO), the CPU 211 executes the process of step S12 again. If the differential pressure ΔP11 is outside the reference range, the processes of steps S11 to S19 are repeated until the differential pressure ΔP11 is within the reference range.

[0050] [Actions and Effects of the Gas Recovery System 100 According to the First Embodiment] The gas recovery system 100 according to the first embodiment includes a raw material gas supply unit 10 for supplying raw material gas, a separation tank 20 for separating carbon dioxide from the raw material gas, a first discharge unit 30 for discharging non-permeated gas from the separation tank 20, a pressure control valve (pressure control unit) V31 provided in the first discharge unit 30 for controlling the pressure inside the first discharge unit 30, a second discharge unit 40 for discharging permeated gas from the separation tank 20, a differential pressure drive mechanism 41 provided in the second discharge unit 40, and a pressure control valve (pressure control unit) V31 on the discharge side of the differential pressure drive mechanism 41. The system is equipped with a return pipe (return flow path) L42 that returns a portion of the gas to the suction side of the differential pressure drive mechanism 41, a flow control valve (flow control unit) V41 that is provided in the return pipe L42 and controls the flow rate of the permeated gas returned to the suction side, a differential pressure detection unit that detects the differential pressure ΔP11 between the pressure P11 of the raw material gas on the supply side of the separation tank 20 and the pressure P12 of the permeated gas, and a controller 210 that controls the pressure control valve V31 and the flow control valve V41 based on the differential pressure ΔP11 detected by the differential pressure detection unit.

[0051] According to the gas recovery system 100 of this embodiment, the pressure control valve V31 and the flow control valve V41 are controlled based on the pressure difference ΔP11 in the separation tank 20, thereby making it possible to keep the pressure difference ΔP11 within a certain range (for example, the above-mentioned reference range). In the gas recovery system 100, the pressure control valve V31 or the flow control valve V41 may be controlled so that the pressure difference ΔP11 falls within a certain range. In the gas recovery system 100, fluctuations in the pressure difference ΔP11 in the separation tank 20 can be suppressed. Therefore, in the gas recovery system 100, fluctuations in the flow rate and properties of the carbon dioxide gas (recovered gas) discharged from the separation tank 20 can be suppressed. In the gas recovery system 100, the carbon dioxide concentration contained in the recovered gas can be stabilized.

[0052] In the gas recovery system 100, when the differential pressure ΔP11 is less than a first determination threshold Pth11, the controller 210 may control the pressure control valve V31 to increase the pressure P11 of the raw material gas supplied to the separation tank 20, and when the differential pressure ΔP11 exceeds a second determination threshold Pth12 that is higher than the first determination threshold Pth11, the controller 210 may control the pressure control valve V31 to decrease the pressure P11 of the raw material gas supplied to the separation tank 20. In this way, in the gas recovery system 100, by controlling the pressure control valve V31 to control the pressure P11 of the raw material gas on the supply side, fluctuations in the differential pressure ΔP11 in the separation tank 20 can be suppressed.

[0053] In the gas recovery system 100, the controller 210 may control the flow control valve V41 to reduce the flow rate of the permeable gas flowing through the return pipe L42 when the differential pressure ΔP11 is less than the first determination threshold Pth11, and may control the flow control valve V41 to increase the flow rate of the permeable gas flowing through the return pipe L42 when the differential pressure ΔP11 exceeds a second determination threshold Pth12 that is higher than the first determination threshold Pth11. In this way, in the gas recovery system 100, by controlling the flow control valve V41 to control the flow rate of the permeable gas returned from the discharge side to the suction side of the differential pressure drive mechanism 41, fluctuations in the differential pressure ΔP11 in the separation tank 20 can be suppressed.

[0054] In the gas recovery system 100, when the differential pressure ΔP11 is less than the first determination threshold Pth11 (when it is equal to or less than the lower limit), the controller 210 may control the pressure control valve V31 to increase the pressure P11 of the raw material gas on the supply side of the separation tank 20, and then control the flow rate control valve V41 to reduce the flow rate of the permeable gas flowing through the return pipe L42. In this way, in the gas recovery system 100, control by the pressure control valve V31 may be performed first, and then control by the flow rate control valve V41 may be performed. In the gas recovery system 100, rough control can be performed by the pressure control valve V31, and then fine control can be performed by the flow rate control valve V41.

[0055] In the gas recovery system 100, when the differential pressure ΔP11 exceeds the second determination threshold Pth12 (when it is equal to or greater than the upper limit), the controller 210 may control the pressure control valve V31 to reduce the pressure P11 of the raw material gas on the supply side of the separation tank 20, and then control the flow rate control valve V41 to increase the flow rate of the permeable gas flowing through the return pipe L42. In this way, in the gas recovery system 100, control by the pressure control valve V31 may be performed first, and then control by the flow rate control valve V41 may be performed. In the gas recovery system 100, rough control can be performed by the pressure control valve V31, and then fine control can be performed by the flow rate control valve V41.

[0056] Furthermore, in the gas recovery system 100, even if a pressure fluctuation occurs such that the differential pressure ΔP11 in the separation tank 20 increases when the pressure control valve V31 is operated only slightly in the fully closed direction, the differential pressure ΔP11 can be reduced by controlling the flow control valve V41. In the gas recovery system 100, the differential pressure ΔP11 can be reduced by increasing the valve opening of the flow control valve V41.

[0057] Furthermore, in the gas recovery system 100, fluctuations in the differential pressure ΔP11 in the separation tank 20 can be suppressed, thereby suppressing the generation of condensed water in the flow paths. For example, in gas recovery systems according to conventional techniques, there is a risk that moisture condensed due to pressure fluctuations may be supplied to the separation tank 20. For example, when moisture entrained in the raw material gas is supplied to the separation tank 20 made of a material with a microporous structure, such as a polymer membrane (separation membrane), the moisture may clog the micropores. When the micropores are clogged, the separation performance in the separation tank 20 decreases. In the gas recovery system 100 according to this embodiment, pressure fluctuations in the raw material gas supplied to the separation tank 20 can be suppressed, thereby suppressing the generation of condensed water and suppressing a decrease in the separation performance in the separation tank 20. In the gas recovery system 100, the permeation performance of the separation membrane can be improved.

[0058] Furthermore, in a process in which separation membranes are connected in series in multiple stages, an increase in the pressure of the raw material gas can cause load fluctuations on the pump or blower that transports the raw material gas, which can lead to performance degradation and failure of the pump or blower. However, the gas recovery system 100 can suppress fluctuations in the differential pressure ΔP11 in the separation tank 20, thereby reducing the risk of performance degradation and failure of the pump or blower that supplies the raw material gas.

[0059] [Gas recovery system 100B according to the second embodiment] Next, a gas recovery system 100B according to a second embodiment will be described. FIG. 4 is a schematic diagram illustrating the gas recovery system 100B according to the second embodiment. The gas recovery system 100B according to the second embodiment shown in FIG. 4 differs from the gas recovery system 100 according to the first embodiment shown in FIG. 1 in that it includes a second-stage separation tank 20B, a recycle section 50 that returns the retentate gas in the separation tank 20B to the upstream side of the separation tank 20, and a gas mixing header 12. Note that in the description of the second embodiment, descriptions similar to those of the first embodiment may be omitted.

[0060] [Gas Mixing Header 12] The gas recovery system 100B includes a gas mixing header 12 provided upstream of the first-stage separation tank 20. The gas mixing header 12 is a mixing vessel that mixes the retentate gas discharged from the separation tank 20B with the raw material gas. The gas mixing header 12 is connected to a raw material gas supply pipe L11. The gas mixing header 12 is connected to a recycle pipe L51 that is connected to the separation tank 20B. The retentate gas discharged from the separation tank 20B flows through the recycle pipe L51 and is supplied to the gas mixing header 12. The retentate gas discharged from the separation tank 20B and the raw material gas are mixed in the gas mixing header 12 and supplied to the separation tank 20.

[0061] [Separation tank 20B] The gas recovery system 100B includes a separation tank 20B located downstream of the separation tank 20. The separation tank 20B is located in the second discharge section 40. The permeable gas discharged from the separation tank 20 is supplied to the separation tank 20B. The separation tank 20B is connected to the discharge side of a differential pressure driving mechanism 41. The separation tank 20B is connected to the differential pressure driving mechanism 41 via a second discharge pipe L41. A return pipe L42 branches off from the second discharge pipe L41 between the differential pressure driving mechanism 41 and the separation tank 20B. The permeable gas discharged from the separation tank 20 is supplied to the separation tank 20B via the second discharge pipe L41 and the differential pressure driving mechanism 41. The separation tank 20 is an example of a first separation tank, and the separation tank 20B is an example of a second separation tank.

[0062] [Recycling Department 50] The gas recovery system 100B includes a recycle section 50 that returns the retentate gas discharged from the separation tank 20B to the supply side of the separation tank 20. The recycle section 50 includes a recycle pipe L51 and a blower 51.

[0063] The recycle pipe L51 connects the separation tank 20B and the gas mixing header 12. The blower 51 is connected to the recycle pipe L51. The blower 51 blows the retentate gas discharged from the separation tank 20B and transfers it to the gas mixing header 12. The recycle unit 50 may include another transfer unit such as a pump instead of the blower 51. The recycle unit 50 may also include a flow control valve, a pressure control valve, a branch flow path, a pressure gauge, a flow meter, a container, and the like, connected to the recycle pipe L51.

[0064] [Flowmeter 224] A flow meter 224 is connected to the recycle pipe L51. The flow meter 224 has a flow meter 224 that detects the flow rate of the retentate gas flowing through the recycle pipe L51. Data related to the flow rate detected by the flow meter 224 is input to the controller 210.

[0065] [Fourth discharge section 40B] The gas recovery system 100 includes a fourth discharge unit 40B. The fourth discharge unit 40B includes a second discharge pipe L41B that discharges the permeable gas from the separation tank 20B. The second discharge pipe L41B is connected to the separation tank 20B. The permeable gas in the separation tank 20B flows through the second discharge pipe L41B and is discharged to the outside of the separation tank 20B. The permeable gas is stored, for example, in a container and shipped as a product (carbon dioxide gas). The carbon dioxide that has permeated the separation membrane flows through the second discharge pipe L41B and is stored in a product tank.

[0066] [Differential pressure drive mechanism 41B] The fourth discharge unit 40B includes a differential pressure driving mechanism 41B connected to the second discharge pipe L41B. The differential pressure driving mechanism 41B is the same as the second discharge unit 40 described above.

[0067] [Controller 210] Next, the controller 210 of the gas recovery system 100B will be described with reference to Fig. 5. Fig. 5 is a block diagram illustrating an example of the hardware configuration of the gas recovery system 100B according to the second embodiment. As shown in Fig. 5, the controller 210 is electrically connected to a pressure gauge 221, a pressure gauge 222, a flow meter 223, a pressure control valve V31, a flow control valve V41, a differential pressure drive mechanism 41, a flow meter 224, and a blower 51.

[0068] As described above, the controller 210 functions as a differential pressure detector that detects the differential pressure ΔP11 between the pressure P11 of the feed gas in the separation vessel 20 and the pressure P12 of the permeated gas.

[0069] [Flow rate control in the recycle flow path] The controller 210 can control the operation of the blower 51 based on the recycle flow rate Q51. The recycle flow rate Q51 is the flow rate of the retentate gas flowing through the recycle pipe L51. The flow meter 224 detects the flow rate of the retentate gas flowing through the recycle pipe L51 and outputs the detected flow rate to the controller 210.

[0070] The controller 210 can control the recycle flow rate Q51 depending on whether the recycle flow rate Q51 is lower than before the load change. Before the load change may be before the processing of steps S12 to S19 shown in Fig. 3 is performed. The gas recovery system 100B can detect the recycle flow rate Q51 before the load change and store it in the memory unit 212.

[0071] The controller 210 can control the operation of the blower 51 so as to increase the recycle flow rate Q51 when the recycle flow rate Q51 is lower than before the load change. The controller 210 can control the operation of the blower 51 so as to decrease the recycle flow rate Q51 when the recycle flow rate Q51 is higher than before the load change. The controller 210 can output a command signal to the blower 51 to control the rotation speed of the blower 51.

[0072] The controller 210 may control the operation of the blower 51 based on the difference ΔQ51 between the recycle flow rate Q51 before the load change and the recycle flow rate Q51 after the load change.

[0073] [Procedure of Fluctuation Control Processing in the Gas Recovery System 100B According to the Second Embodiment] Next, the procedure of the fluctuation control process in the gas recovery system 100B will be described with reference to Fig. 6. Fig. 6 is a flowchart illustrating the procedure of the fluctuation suppression process in the gas recovery system 100B. The fluctuation suppression control process may be a control process for suppressing fluctuations in the pressure of the raw material gas. Fig. 6 shows the procedure for controlling the recycle flow rate. In the fluctuation suppression control process according to the second embodiment, the processes shown in Figs. 3 and 6 are executed.

[0074] The control of the recycle flow rate shown in Fig. 6 is performed after the processing of steps S15 to S18 shown in Fig. 3 is performed and before the processing of step S19 is performed. Note that Fig. 6 contains some overlapping descriptions with Fig. 3 (step S19).

[0075] After executing the processes of steps S15 to S18, CPU 211 executes the process of step S21. In step S21, CPU 211 determines whether or not the recycle flow rate Q51 after the load change is equal to a specified value. The specified value may be, for example, a determination threshold value for determining whether or not to control the flow rate by blower 51. The specified value may also be the recycle flow rate Q51 before the load change.

[0076] If the recycle flow rate Q51 is the designated value (step S21; YES), the CPU 211 performs the process of step S19. The process of step S19 is the same as the process of step S19 shown in Fig. 3. If the recycle flow rate Q51 is not the designated value (step S21; NO), the CPU 211 performs the process of step S23.

[0077] In step S23, the CPU 211 determines whether the current recycle flow rate Q51 is lower than the recycle flow rate Q51 before the load change. If the current recycle flow rate Q51 is lower than the recycle flow rate Q51 before the load change (step S23; YES), the CPU 211 executes the process of step S24. If the current recycle flow rate Q51 is not lower than the recycle flow rate Q51 before the load change (step S23; NO), the CPU 211 executes the process of step S25.

[0078] In step S24, the CPU 211 controls the blower 51 to increase the recycle flow rate Q51, and in step S25, the CPU 211 controls the blower 51 to decrease the recycle flow rate Q51.

[0079] After the process of step S24 or step S25, the CPU 211 executes the process of step S19 again.

[0080] In the process of step S19 again, if the CPU 211 determines that the differential pressure ΔP11 is within the reference range, the process ends here. In the process of step S19, if the CPU 211 determines that the differential pressure ΔP11 is not within the reference range, the process returns to step S12 shown in FIG.

[0081] [Actions and Effects of the Gas Recovery System 100B According to the Second Embodiment] The gas recovery system 100B according to the second embodiment also provides the same effects as the gas recovery system 100 according to the first embodiment.

[0082] The gas recovery system 100B includes a separation tank (first separation tank) 20, a separation tank (second separation tank) 20B that separates carbon dioxide from a permeated gas (second gas) discharged from a differential pressure drive mechanism 41, a recycle pipe (recycle flow path) L51 that returns at least a portion of the retentate gas (third gas) that is discharged from the separation tank 20B and has a lower carbon dioxide concentration than the permeated gas (second gas) to the supply side of the separation tank 20, a blower 51 that pressurizes the retentate gas flowing through the recycle pipe L51, a fourth discharge section 40B that discharges the permeated gas (fourth gas) from the separation tank 20B, and a differential pressure drive mechanism 41B provided in the fourth discharge section 40B.

[0083] The gas recovery system 100B can increase the concentration of recovered carbon dioxide gas by including multiple separation tanks 20, 20B. In addition, the gas recovery system 100B can increase the concentration of recovered carbon dioxide gas by returning the retentate gas in the separation tank 20B to the supply side of the separation tank 20.

[0084] Furthermore, in the gas recovery system 100B, the flow rate Q51 of the retentate gas flowing through the recycle pipe L51 may be controlled based on the differential pressure ΔP11 in the separation tank 20. This makes it possible to suppress fluctuations in the differential pressure ΔP11.

[0085] Furthermore, in the gas recovery system 100B, the controller 210 can compare the recycle flow rate Q51 before the load change with the recycle flow rate Q51 after the load change and control the operation of the blower 51. This allows operation to be stabilized so that the recycle flow rate Q51 is the same as before the load change. As a result, fluctuations in the differential pressure ΔP11 in the separation tank 20 can be suppressed.

[0086] [Gas recovery system 100C according to the third embodiment] Next, a gas recovery system 100C according to a third embodiment will be described. FIG. 7 is a schematic diagram illustrating the gas recovery system 100C according to the third embodiment. The gas recovery system 100C according to the third embodiment shown in FIG. 7 differs from the gas recovery system 100 according to the first embodiment shown in FIG. 1 in that it does not include a pressure control valve V31. Note that in the description of the third embodiment, explanations similar to those of the first embodiment may be omitted.

[0087] In this way, the gas recovery system 100C does not need to include the pressure control valve V31. The gas recovery system 100C controls the flow rate of the returned retentate gas, and does not need to control the pressure inside the first discharge part 30.

[0088] [Actions and Effects of the Gas Recovery System 100C According to the Third Embodiment] The gas recovery system 100C according to the third embodiment includes a raw material gas supply unit 10 for supplying raw material gas, a separation tank 20 for separating carbon dioxide from the raw material gas, a first discharge unit 30 for discharging retentate gas from the separation tank 20, a second discharge unit 40 for discharging permeated gas from the separation tank 20, a differential pressure drive mechanism 41 provided in the second discharge unit 40, a return pipe (return flow path) L42 for returning a portion of the gas on the discharge side of the differential pressure drive mechanism 41 to the suction side of the differential pressure drive mechanism 41, a flow control valve (flow control unit) V41 provided in the return pipe L42 for controlling the flow rate of the returned permeated gas, a differential pressure detection unit for detecting a differential pressure ΔP11 between the pressure P11 of the raw material gas on the supply side of the separation tank 20 and the pressure P12 of the permeated gas, and a controller 210 for controlling the flow control valve V41 based on the differential pressure ΔP11 detected by the differential pressure detection unit.

[0089] According to the gas recovery system 100C of this embodiment, the flow control valve V41 is controlled based on the pressure difference ΔP11 in the separation tank 20, thereby making it possible to keep the pressure difference ΔP11 within a certain range. This makes it possible to suppress fluctuations in the flow rate and properties of the carbon dioxide gas (recovered gas) discharged from the separation tank 20. The gas recovery system 100C can stabilize the carbon dioxide concentration contained in the recovered gas.

[0090] [Gas recovery system 100D according to the fourth embodiment] Next, a gas recovery system 100D according to a fourth embodiment will be described. FIG. 8 is a schematic diagram illustrating the gas recovery system 100D according to the fourth embodiment. The gas recovery system 100D according to the fourth embodiment shown in FIG. 8 differs from the gas recovery system 100 according to the first embodiment shown in FIG. 1 in that it does not include a flow control valve V41. Note that in the description of the fourth embodiment, descriptions similar to those of the first embodiment may be omitted.

[0091] In this way, the gas recovery system 100D does not need to be equipped with the flow control valve V41. The gas recovery system 100D controls the pressure inside the first discharge part 30 using the pressure control valve V31, and does not need to control the flow rate of the returned retentate gas.

[0092] [Actions and Effects of the Gas Recovery System 100D According to the Fourth Embodiment] The gas recovery system 100D according to the fourth embodiment includes a raw material gas supply unit 10 that supplies raw material gas, a separation tank 20 that separates carbon dioxide from the raw material gas, a first discharge unit 30 that discharges unpermeated gas from the separation tank 20, a pressure control valve (pressure control unit) V31 provided in the first discharge unit 30 and that controls the internal pressure of the first discharge unit 30, a second discharge unit 40 that discharges permeated gas from the separation tank 20, a differential pressure drive mechanism 41 provided in the second discharge unit 40, a differential pressure detection unit that detects the differential pressure between the raw material gas pressure P11 and the permeated gas pressure P12 in the separation tank 20, and a controller 210 that controls the pressure control valve V31 based on the differential pressure ΔP11 detected by the differential pressure detection unit.

[0093] According to the gas recovery system 100D of this embodiment, the pressure control valve V31 is controlled based on the pressure difference ΔP11 in the separation tank 20, thereby making it possible to keep the pressure difference ΔP11 within a certain range. This makes it possible to suppress fluctuations in the flow rate and properties of the carbon dioxide gas (recovered gas) discharged from the separation tank 20. The gas recovery system 100D can stabilize the carbon dioxide concentration contained in the recovered gas.

[0094] It should be noted that the present invention is not limited to the configurations shown here, and other embodiments may be possible in which other components are combined with the configurations described in the above embodiments. In this regard, the present invention can be modified within the scope of the present invention, and can be appropriately determined depending on the application form.

[0095] In the gas recovery system 100 according to the embodiment, the number of separation tanks 20 is not limited. The gas recovery system 100 may include a plurality of separation tanks 20, 20B. Furthermore, in the gas recovery system 100, a separation tank 20 may be provided in the first discharge section 30. The first discharge section 30 may include a second-stage separation tank 20 to which the retentate gas discharged from the first-stage separation tank 20 is supplied.

[0096] The gas recovery systems 100C and 100D may include a separation tank 20B provided in the second discharge section 40. The gas recovery systems 100C and 100D may include a recycle section 50, which controls the flow rate of the retentate gas flowing through the recycle pipe L51.

[0097] There are no particular limitations on the number and arrangement of pressure meters and flow meters in the gas recovery system 100. The judgment thresholds in the control process are set appropriately based on past operating data, test data, and the like. [Explanation of symbols]

[0098] 100, 100B, 100C, 100D: gas recovery system, 10: raw material gas supply unit, 20, 20B: separation tank, 30: first discharge unit, 40: second discharge unit, 40B: fourth discharge unit, 41: differential pressure drive mechanism, 50: recycle unit, 51: blower, 210: controller (differential pressure detection unit), 221: pressure gauge, 222: pressure gauge, 223: flow meter, 224: flow meter, L42: return piping (return flow path), L51: recycle piping (recycle flow path), V31: pressure control valve (pressure control unit), V41: flow control valve (flow control unit).

Claims

1. a raw material gas supply unit that supplies a raw material gas; a separation tank for separating carbon dioxide from the raw material gas; a first discharge section that discharges a first gas from the separation tank; a pressure control unit provided in the first discharge unit and configured to control a pressure inside the first discharge unit; a second discharge section that discharges a second gas having a higher carbon dioxide concentration than the first gas from the separation tank; a differential pressure driving mechanism provided in the second discharge section; a return flow path that returns a portion of the gas on the discharge side of the differential pressure driving mechanism to the suction side of the differential pressure driving mechanism; a flow rate control unit provided in the return flow path to control a flow rate of the returned gas; a differential pressure detection unit that detects a differential pressure between the pressure of the gas on the supply side of the separation tank and the pressure of the second gas; a controller that controls the pressure control unit and the flow rate control unit based on the differential pressure detected by the differential pressure detection unit.

2. The controller When the pressure difference is less than a first determination threshold, the pressure control unit is controlled to increase the pressure of the gas on the supply side of the separation tank; The gas recovery system according to claim 1, wherein when the differential pressure exceeds a second judgment threshold that is higher than the first judgment threshold, the pressure control unit is controlled to reduce the pressure of the gas on the supply side of the separation tank.

3. The controller When the differential pressure is less than a first determination threshold, the flow rate control unit is controlled to reduce the flow rate of the gas flowing through the return flow path; The gas recovery system according to claim 1 , wherein the flow rate control unit is controlled to increase the flow rate of the gas flowing through the return flow path when the differential pressure exceeds a second determination threshold that is higher than the first determination threshold.

4. The controller 3. The gas recovery system of claim 2, wherein when the differential pressure is less than the first judgment threshold, the pressure control unit is controlled to increase the pressure of the gas on the supply side of the separation tank, and then the flow rate control unit is controlled to reduce the flow rate of the gas flowing through the return flow path.

5. The controller A gas recovery system as described in claim 2, wherein when the differential pressure exceeds the second judgment threshold, the pressure control unit is controlled to reduce the pressure of the gas on the supply side of the separation tank, and then the flow rate control unit is controlled to increase the flow rate of the gas flowing through the return flow path.

6. a first separation tank which is the separation tank; a second separation tank that separates carbon dioxide from the second gas discharged from the differential pressure driving mechanism; a recycle flow path that returns at least a portion of a third gas that is discharged from the second separation tank and has a lower carbon dioxide concentration than the second gas to the supply side of the first separation tank; a fourth discharge section that discharges a fourth gas having a higher carbon dioxide concentration than the third gas from the second separation tank; The gas recovery system according to claim 1 or 2, further comprising: a differential pressure drive mechanism provided in the fourth discharge section.

7. a raw material gas supply unit that supplies a raw material gas; a separation tank for separating carbon dioxide from the raw material gas; a first discharge section that discharges a first gas from the separation tank; a pressure control unit provided in the first discharge unit and configured to control a pressure inside the first discharge unit; a second discharge section that discharges a second gas having a higher carbon dioxide concentration than the first gas from the separation tank; a differential pressure driving mechanism provided in the second discharge section; a differential pressure detection unit that detects a differential pressure between the pressure of the gas on the supply side of the separation tank and the pressure of the second gas; a controller that controls the pressure control unit based on the differential pressure detected by the differential pressure detection unit.

8. a raw material gas supply unit that supplies a raw material gas; a separation tank for separating carbon dioxide from the raw material gas; a first discharge section that discharges a first gas from the separation tank; a second discharge section that discharges a second gas having a higher carbon dioxide concentration than the first gas from the separation tank; a differential pressure driving mechanism provided in the second discharge section; a return flow path that returns a portion of the gas on the discharge side of the differential pressure driving mechanism to the suction side of the differential pressure driving mechanism; a flow rate control unit provided in the return flow path to control a flow rate of the returned gas; a differential pressure detection unit that detects a differential pressure between the pressure of the gas on the supply side of the separation tank and the pressure of the second gas; a controller that controls the flow rate control unit based on the differential pressure detected by the differential pressure detection unit.

9. a separation step of supplying a raw material gas to a separation tank, separating the raw material gas into a first gas and a second gas having a carbon dioxide concentration higher than that of the first gas, and separately discharging the first gas and the second gas; a pressure control step of controlling the pressure of the first gas discharged from the separation tank; a differential pressure driving step of operating a differential pressure driving mechanism that generates a differential pressure between the gas on the supply side of the separation tank and the second gas, thereby generating the differential pressure; a returning step of returning the gas on the discharge side of the differential pressure driving mechanism to the suction side of the differential pressure driving mechanism; a flow rate control step of controlling a flow rate of the gas returned to the suction side of the differential pressure drive mechanism in the returning step; a differential pressure detection step of detecting a differential pressure between the pressure of the gas on the supply side of the separation tank and the pressure of the second gas, the pressure control step controls the pressure of the first gas based on the differential pressure detected in the differential pressure detection step; In the flow rate control step, the flow rate of the gas returned to the suction side of the differential pressure drive mechanism is controlled based on the differential pressure detected in the differential pressure detection step.

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