Gas separation system

Abstract

This disclosure provides a gas separation system that starts or stops while preventing damage to the separation membrane in the gas separation unit. [Solution] A gas separation system comprising: a first gas separation unit that separates a first permeate gas that permeates through a first separation membrane and a first impermeable gas that is discharged without permeating through the first separation membrane; a second gas separation unit that separates a second permeate gas that permeates through a second separation membrane and a second impermeable gas that is discharged without permeating through the second separation membrane; a first shut-off valve that shuts off the first permeate gas flowing from the first gas separation unit to the second gas separation unit; a first exhaust valve that shuts off the first permeate gas being exhausted to the outside from the first gas separation unit; a second shut-off valve that shuts off the second impermeable gas flowing to the recycling line; a second exhaust valve that shuts off the second impermeable gas being exhausted to the outside from the second gas separation unit; and a control unit that controls the opening and closing of the first shut-off valve, the first exhaust valve, the second shut-off valve, and the second exhaust valve, respectively.

Description

Technical Field

[0001] The present disclosure relates to a gas separation system.

Background Art

[0002] Patent Document 1 discloses a biogas enrichment system including a first gas separation unit having a separation membrane and a second gas separation unit having a separation membrane. Patent Document 1 discloses that the biogas enrichment system includes a permeate gas circulation line that returns the permeate gas of the second gas separation unit to upstream of a first compressor disposed in a raw material gas line that supplies raw material gas to the first gas separation unit.

[0003] Patent Document 2 discloses equipment for separating a gas including a feed stream separation stage, an unpermeate separation stage, and a permeate separation stage. Patent Document 2 discloses that the equipment for separating the gas separates, in the unpermeate separation stage, a first unpermeate stream in the feed stream separation stage into a second permeate stream and a second unpermeate stream. Further, Patent Document 2 discloses that the equipment for separating the gas separates, in the permeate separation stage, a first permeate stream in the feed stream separation stage into a third unpermeate stream and a third permeate stream. Furthermore, Patent Document 2 discloses that the equipment for separating the gas recycles the second permeate stream and the third unpermeate stream.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a gas separation system equipped with a gas separation unit using a separation membrane, it is desirable that the gas separation system be started or stopped in a manner that prevents damage to the separation membrane in the gas separation unit due to excessive pressure.

[0006] This disclosure provides a gas separation system that starts or stops while preventing damage to the separation membrane in the gas separation unit. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, a first gas separation unit is provided with a first separation membrane, to which a raw material gas is supplied, and to separate the supplied raw material gas into a first permeate gas that permeates through the first separation membrane and a first unpermeated gas that is discharged without permeating through the first separation membrane; a second gas separation unit is connected in series with the first gas separation unit, to which the first permeate gas is supplied, and to separate the supplied first permeate gas into a second permeate gas that permeates through the second separation membrane and a second unpermeated gas that is discharged without permeating through the second separation membrane; a raw material gas line is provided to supply the raw material gas to the first gas separation unit; a recycling line is provided to return the second unpermeated gas to the raw material gas line; and a first transfer is provided to supply the first permeate gas in the first gas separation unit to the second gas separation unit. The gas separation system is provided, comprising: a unit; a second transfer unit that discharges the second permeate gas from the second gas separation unit to the outside; a third transfer unit located in the recycling line that sends the second unpermeate gas to the raw material gas line; a first shut-off valve that shuts off the first permeate gas flowing from the first gas separation unit to the second gas separation unit; a first exhaust valve that shuts off the first permeate gas being exhausted from the first gas separation unit to the outside; a second shut-off valve that shuts off the second unpermeate gas flowing from the second gas separation unit to the recycling line; a second exhaust valve that shuts off the second unpermeate gas being exhausted from the second gas separation unit to the outside; and a control unit that controls the opening and closing of the first shut-off valve, the first exhaust valve, the second shut-off valve, and the second exhaust valve, respectively. [Effects of the Invention]

[0008] The gas separation system of this disclosure makes it possible to prevent damage to the separation membrane in the gas separation unit during startup or shutdown. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a diagram illustrating the schematic configuration of a gas separation system according to the first embodiment. [Figure 2] Figure 2 is a flowchart illustrating the startup process in the gas separation system according to the first embodiment. [Figure 3] Figure 3 is a flowchart illustrating the process during shutdown in the gas separation system according to the first embodiment. [Figure 4] Figure 4 is a diagram illustrating the schematic configuration of the gas separation system according to the second embodiment. [Figure 5] Figure 5 illustrates the calculations performed in the arithmetic unit of the gas separation system according to this embodiment. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described below with reference to the attached drawings. Note that, in the description and drawings of each embodiment, components having substantially the same or corresponding functional configurations may be denoted by the same reference numerals, thereby omitting redundant explanations. Furthermore, for ease of understanding, the scale of each part in the drawings may differ from that of actual parts.

[0011] A degree of deviation is permissible in directions such as parallel, right angles, orthogonal, horizontal, vertical, up and down, left and right, and front and back, as long as it does not impair the effects of the embodiment. The shape of the corners is not limited to right angles and may be rounded. Parallel, right angles, orthogonal, horizontal, and vertical may include approximately parallel, approximately right angles, approximately orthogonal, approximately horizontal, and approximately vertical, respectively.

[0012] For example, "approximately parallel" means that two lines or two planes can be treated as parallel to each other, even if they are not perfectly parallel, as long as it is within the limits of what is permissible in manufacturing. Similarly, "approximately right angle," "approximately perpendicular," "approximately horizontal," and "approximately vertical" are intended to apply as long as the relative positions of the two lines or planes are within the limits of what is permissible in manufacturing.

[0013] <First Embodiment> A gas separation system according to the first embodiment will now be described. The gas separation system according to the first embodiment includes a first gas separation unit equipped with a first separation membrane, to which a raw material gas is supplied, and which separates the supplied raw material gas into a first permeate gas that permeates through the first separation membrane and a first unpermeated gas that is discharged without permeating through the first separation membrane. The gas separation system according to the first embodiment also includes a second gas separation unit connected in series with the first gas separation unit and equipped with a second separation membrane. In the gas separation system according to the first embodiment, the second gas separation unit is supplied with a first permeate gas, and which separates the supplied first permeate gas into a second permeate gas that permeates through the second separation membrane and a second unpermeated gas that is discharged without permeating through the second separation membrane. Furthermore, the gas separation system according to the first embodiment includes a raw material gas line that supplies the raw material gas to the first gas separation unit and a recycling line that returns the second unpermeated gas to the raw material gas line. Furthermore, the gas separation system according to the first embodiment includes a first transfer unit that supplies the first permeate gas from the first gas separation unit to the second gas separation unit, and a second transfer unit that discharges the second permeate gas from the second gas separation unit to the outside. Furthermore, the gas separation system according to the first embodiment includes a third transfer unit located in the recycling line that sends the second unpermeated gas to the raw material gas line. Furthermore, the gas separation system according to the first embodiment includes a first shut-off valve that shuts off the flow of the first permeate gas from the first gas separation unit to the second gas separation unit, and a first exhaust valve that shuts off the exhaust of the first permeate gas from the first gas separation unit to the outside. The gas separation system according to the first embodiment includes a second shut-off valve that shuts off the flow of the second unpermeate gas from the second gas separation unit to the recycling line, and a second exhaust valve that shuts off the exhaust of the second unpermeate gas from the second gas separation unit to the outside. Furthermore, the gas separation system according to the first embodiment includes a control unit that controls the opening and closing of the first shut-off valve, the first exhaust valve, the second shut-off valve, and the second exhaust valve, respectively.

[0014] The gas separation system according to the first embodiment will be described in detail with reference to the drawings. Figure 1 is a diagram illustrating the schematic configuration of a gas separation system 1, which is an example of a gas separation system according to the first embodiment.

[0015] The gas separation system 1 separates carbon dioxide gas from the raw material gas Gm by a gas separation unit. Then, the gas separation system 1 concentrates the carbon dioxide gas by connecting a plurality of gas separation units in series. Note that the gas separation system 1 includes two gas separation units. And the gas separation system 1 discharges the concentrated carbon dioxide gas as the recovered gas Ge.

[0016] The raw material gas Gm is, for example, the exhaust gas of an engine that is a power source such as a ship. The carbon dioxide gas recovered as the recovered gas Ge is stored, for example, in a tank or the like.

[0017] The gas separation system 1 includes a gas separation unit 10 and a gas separation unit 20, transfer units 31, 32, and 33, and a control unit 80. Also, the gas separation system 1 includes a flow meter 41, a flow meter 42, and a flow meter 43, a pressure gauge 51, a pressure gauge 52, and a pressure gauge 53. Furthermore, the gas separation system 1 includes a raw material gas line 61, a connection line 62, an exhaust gas line 63, a gas recovery line 64, and a recycle line 65. Also, the gas separation system 1 includes a shut-off valve 71 and an exhaust valve 72, a shut-off valve 73, an exhaust valve 74, and a check valve 75.

[0018] Details of each component in the gas separation system 1 will be described.

[0019] (Gas separation unit 10 and gas separation unit 20) Each of the gas separation unit 10 and the gas separation unit 20 separates and discharges the permeated gas containing a large amount of carbon dioxide contained in the gas supplied through the separation membrane and the unpermeated gas that does not pass through the separation membrane and has a smaller amount of carbon dioxide than the permeated gas.

[0020] The gas separation unit 10 includes a separation membrane 11. Inside the gas separation unit 10, there are a non-permeation side space 10S1 and a permeation side space 10S2. The inside of the gas separation unit 10 is divided by the separation membrane

[0021] The impermeable space 10S1 in the gas separation unit 10 is connected to the raw material gas line 61 and the exhaust gas line 63. The permeable space 10S2 in the gas separation unit 10 is connected to the connection line 62.

[0022] The gas separation unit 10 is supplied with raw material gas Gm. More specifically, the gas separation unit 10 is supplied with a mixed gas Gc, which is a mixture of raw material gas Gm and recycled gas Gr.

[0023] The non-permeable space 10S1 of the gas separation unit 10 is supplied with raw material gas Gm, or more specifically, mixed gas Gc, which is a mixture of raw material gas Gm and recycled gas Gr. When a differential pressure is generated between the non-permeable space 10S1 and the permeable space 10S2, the separation membrane 11 selectively permeates the carbon dioxide gas contained in the mixed gas Gc (raw material gas Gm) supplied to the non-permeable space 10S1.

[0024] In the gas separation unit 10, the permeate gas Gp1 that has permeated through the separation membrane 11 is discharged into the connection line 62. In the gas separation unit 10, the unpermeated gas Gn1 that has not permeated through the separation membrane 11 is discharged into the exhaust gas line 63.

[0025] The gas separation unit 20 includes a separation membrane 21. The gas separation unit 20 has an impermeable space 20S1 and a permeable space 20S2 inside. The inside of the gas separation unit 20 is divided into the impermeable space 20S1 and the permeable space 20S2 by the separation membrane 21.

[0026] The impermeable space 20S1 in the gas separation unit 20 is connected to the connection line 62 and the recycling line 65. The permeable space 20S2 in the gas separation unit 20 is connected to the gas recovery line 64.

[0027] The gas separation unit 20 is connected in series with the gas separation unit 10. The gas separation unit 20 is supplied with the permeate gas Gp1 that has permeated through the separation membrane in the gas separation unit 10.

[0028] The permeate gas Gp1 that has permeated through the separation membrane in the gas separation unit 10 is supplied to the impermeable space 20S1 of the gas separation unit 20. When a pressure difference is generated between the impermeable space 20S1 and the permeable space 20S2, the separation membrane 21 selectively allows carbon dioxide gas contained in the permeate gas Gp1 supplied to the impermeable space 20S1 to permeate.

[0029] In the gas separation unit 20, the permeate gas Gp2 that has permeated through the separation membrane 21 is discharged to the gas recovery line 64. In the gas separation unit 20, the unpermeated gas Gn2 that has not permeated through the separation membrane 21 is discharged to the recycling line 65.

[0030] Each of the separation membranes 11 and 21 is not particularly limited as long as it is a membrane capable of separating carbon dioxide. The material of each of the separation membranes 11 and 21 may be an organic membrane such as a polymer membrane, or an inorganic membrane such as a zeolite membrane or a silica-based amorphous membrane. The membrane shape of each of the separation membranes 11 and 21 may be a homogeneous membrane, a composite membrane consisting of a homogeneous membrane and a porous membrane, or a porous membrane. The configuration in which the separation membranes are housed in each of the gas separation units 10 and 20 may be a plate-and-frame type or a stacked sheet type, or a spiral type or a hollow fiber type.

[0031] (Transfer section 31, transfer section 32, and transfer section 33) Each of the transfer units 31, 32, and 33 transfers gas. Each of the transfer units 31, 32, and 33 is, for example, a pressure reducing pump, a blower, etc.

[0032] The transfer unit 31 supplies the permeate gas Gp1 that has permeated through the separation membrane 11 in the gas separation unit 10 to the gas separation unit 20. More specifically, the transfer unit 31 aspirates the permeate gas Gp1 that has permeated through the separation membrane 11 in the gas separation unit 10 and discharges it into the impermeable space 20S1 in the gas separation unit 20. The transfer unit 31 is located in the connection line 62.

[0033] The transfer unit 32 discharges the permeate gas Gp2 that has permeated through the separation membrane 21 in the gas separation unit 20 to the outside of the gas separation system 1 as recovered gas Ge. More specifically, the transfer unit 31 aspirates the permeate gas Gp2 that has permeated through the separation membrane 21 in the gas separation unit 20 and discharges it to the outside of the gas separation system 1 as recovered gas Ge. The transfer unit 32 is located in the gas recovery line 64.

[0034] The transfer unit 33 sends the unpermeable gas Gn2 that did not permeate the separation membrane 21 in the gas separation unit 20 to the raw material gas line 61. More specifically, the transfer unit 33 aspirates the unpermeable gas Gn2 that did not permeate the separation membrane 21 in the gas separation unit 20 and discharges it to the gas mixing header 70 in the raw material gas line 61. The transfer unit 33 is located in the recycling line 65.

[0035] (Flowmeter 41, Flowmeter 42 and Flowmeter 43) The gas separation system 1 is equipped with a flow meter 41 in the raw material gas line 61. The flow meter 41 is located downstream of the gas mixing header 70 in the raw material gas line 61. The flow meter 41 measures the flow rate of the mixed gas Gc flowing through the raw material gas line 61.

[0036] The gas separation system 1 is equipped with a flow meter 42 in the connection line 62. The flow meter 42 is located downstream of the transfer section 31 in the connection line 62. The flow meter 42 measures the flow rate of the permeate gas Gp1 flowing through the connection line 62.

[0037] The gas separation system 1 is equipped with a flow meter 43 in the recycling line 65. The flow meter 43 is located upstream of the transfer section 33 in the recycling line 65. The flow meter 43 measures the flow rate of the unpermeated gas Gn2 flowing through the recycling line 65.

[0038] Each of the flow meters 41, 42, and 43 is not limited in type as long as it can measure the flow rate of permeate gas Gp1 or impermeate gas Gn1. Each of the flow meters 41, 42, and 43 may be, for example, a differential pressure flow meter or a vortex flow meter. Alternatively, each of the flow meters 41, 42, and 43 may be used as a flow meter by converting the flow rate using a flow velocity meter.

[0039] (Pressure gauge 51, pressure gauge 52, and pressure gauge 53) The gas separation system 1 is equipped with a pressure gauge 51 in the raw material gas line 61. The pressure gauge 51 is located downstream of the gas mixing header 70 in the raw material gas line 61. The pressure gauge 51 measures the pressure of the mixed gas Gc flowing through the raw material gas line 61.

[0040] The gas separation system 1 is equipped with a pressure gauge 52 in the connection line 62. The pressure gauge 52 is located downstream of the transfer section 31 in the connection line 62. The pressure gauge 52 measures the pressure of the permeate gas Gp1 flowing through the connection line 62.

[0041] The gas separation system 1 is equipped with a pressure gauge 53 in the gas recovery line 64. The pressure gauge 53 is located upstream of the transfer section 32 in the gas recovery line 64. The pressure gauge 53 measures the pressure of the permeate gas Gp2 flowing through the gas recovery line 64.

[0042] (Raw material gas line 61) The raw material gas line 61 supplies raw material gas Gm to the gas separation unit 10 from outside the gas separation system 1. The raw material gas line 61 connects the gas separation unit 10 to external equipment, such as an engine that discharges exhaust gas. More specifically, the raw material gas line 61 is connected to the impermeable side space 10S1 in the gas separation unit 10. The raw material gas line 61 then supplies raw material gas Gm (mixed gas Gc) to the impermeable side space 10S1 in the gas separation unit 10.

[0043] The gas separation system 1 is equipped with a gas mixing header 70 in the raw gas line 61. The gas mixing header 70 mixes the raw gas Gm with the recycled gas Gr supplied from the recycling line 65. The gas mixing header 70 discharges the mixed gas Gc, which is a mixture of the raw gas Gm and the recycled gas Gr, to the gas separation unit 10.

[0044] (Connection line 62) The connection line 62 supplies the permeate gas Gp1 discharged from the gas separation unit 10 to the impermeable space 20S1 in the gas separation unit 20. The connection line 62 connects the gas separation unit 10 and the gas separation unit 20. More specifically, the connection line 62 connects the permeable space 10S2 in the gas separation unit 10 and the impermeable space 20S1 in the gas separation unit 20.

[0045] The gas separation system 1 includes a transfer unit 31 and a pressure gauge 52 on the connection line 62. The gas separation system 1 also includes a shut-off valve 71 and an exhaust valve 72 on the connection line 62.

[0046] (Exhaust gas line 63) The exhaust gas line 63 discharges the unpermeable gas Gn1 exhausted from the impermeable side space 10S1 in the gas separation unit 10 to the outside of the gas separation system 1. The exhaust gas line 63 is connected to, for example, a chimney. The unpermeable gas Gn1 flowing through the exhaust gas line 63 is gas that did not permeate the separation membrane 11, and therefore has a low carbon dioxide content.

[0047] (Gas recovery line 64) The gas recovery line 64 discharges the permeate gas Gp2 emitted from the gas separation unit 20 to the outside of the gas separation system 1. The gas recovery line 64 is connected to, for example, a tank that stores carbon dioxide gas. The gas recovery line 64 is connected to the permeate side space 20S2 in the gas separation unit 20.

[0048] The gas separation system 1 includes a transfer unit 32 in the gas recovery line 64.

[0049] (Recycling line 65) The recycling line 65 returns the unpermeated gas Gn2 discharged from the gas separation unit 20 back to the raw material gas line 61. More specifically, the recycling line 65 connects the impermeable side space 20S1 in the gas separation unit 20 to the gas mixing header 70 in the raw material gas line 61.

[0050] The gas separation system 1 includes a transfer section 33 in the recycling line 65. The gas separation system 1 also includes a shut-off valve 73, an exhaust valve 74, and a check valve 75 in the connection line 62.

[0051] (Shut-off valve 71 and shut-off valve 73) The gas separation system 1 is equipped with a shut-off valve 71 on the connection line 62. The shut-off valve 71 opens and closes to allow or block the flow of permeate gas Gp1 through the connection line 62. The opening and closing of the shut-off valve 71 is controlled by a calculator 81 in the control unit 80.

[0052] The gas separation system 1 is equipped with a shut-off valve 73 in the recycling line 65. The shut-off valve 73 opens and closes to allow or block the flow of unpermeable gas Gn2 through the recycling line 65. The opening and closing of the shut-off valve 73 is controlled by a calculator 82 in the control unit 80.

[0053] (Exhaust valves 72 and 74) The gas separation system 1 is equipped with an exhaust valve 72 on the connection line 62. The exhaust valve 72 opens and closes to allow or block the flow of permeate gas Gp1 exhausted from the connection line 62 to the outside. The opening and closing of the exhaust valve 72 is controlled by a calculator 81 in the control unit 80.

[0054] The gas separation system 1 is equipped with an exhaust valve 74 in the recycling line 65. The exhaust valve 74 opens and closes to allow or block the flow of unpermeable gas Gn2 exhausted from the recycling line 65 to the outside. The opening and closing of the exhaust valve 74 is controlled by a calculator 82 in the control unit 80.

[0055] (Check valve 75) The gas separation system 1 includes a check valve 75 between the recycle line 65 and the exhaust valve 74. The check valve 75 prevents gas from flowing into the recycle line 65 from outside the gas separation system 1.

[0056] (Control unit 80) The control unit 80 controls the gas separation system 1. Specifically, the control unit 80 controls the shut-off valve 71, exhaust valve 72, shut-off valve 73, and exhaust valve 74. The control unit 80 also acquires the flow rate measurements from the flow meters 41, 42, and 43. Furthermore, the control unit 80 acquires the pressure measurements from the pressure gauges 51, 52, and 53.

[0057] In the gas separation system 1, the control unit 80 controls the system to shut down the gas separation system 1 when the engine or other components stop and the supply of raw material gas stops, in order to prevent damage to the separation membrane 11 in the gas separation unit 10 and the separation membrane 21 in the gas separation unit 20.

[0058] The control unit 80 includes an arithmetic unit 81 and an arithmetic unit 82. Arithmetic unit 81 controls the opening and closing of the shut-off valve 71 and the exhaust valve 72, respectively. Arithmetic unit 82 controls the opening and closing of the shut-off valve 73 and the exhaust valve 74, respectively.

[0059] The arithmetic unit 81 acquires measurement results from the flow meters 41 and 42, and the pressure gauges 51 and 52. Based on the acquired measurement results, the arithmetic unit 81 controls the opening and closing of the shut-off valve 71 and the exhaust valve 72. The arithmetic unit 81 also outputs the results to the arithmetic unit 82 based on the acquired measurement results.

[0060] The arithmetic unit 82 obtains measurement results from the flow meter 43 and the pressure gauge 53. Based on the obtained measurement results and the calculation results from the arithmetic unit 81, the arithmetic unit 82 controls the opening and closing of the shut-off valve 73 and the exhaust valve 74.

[0061] First, the processing of the control unit 80 during startup of the gas separation system 1 will be described. Figure 2 is a flowchart illustrating the startup processing in the gas separation system 1, which is an example of a gas separation system according to the first embodiment.

[0062] (Step S10) First, the entire system is initialized. The control unit 80 controls shut-off valve 71, exhaust valve 72, shut-off valve 73, and exhaust valve 74 to close. Specifically, the arithmetic unit 81 in the control unit 80 controls shut-off valve 71 and exhaust valve 72 to close. In addition, the arithmetic unit 82 in the control unit 80 controls shut-off valve 73 and exhaust valve 74 to close. Note that exhaust valves 72 and 74 may be left open.

[0063] (Step S20) Next, the control unit 80 controls the exhaust valve 72 to open while the shut-off valve 71 is closed. Specifically, the arithmetic unit 81 in the control unit 80 controls the exhaust valve 72 to open. Note that if the exhaust valve 72 is opened in step S10, step S20 is omitted.

[0064] (Step S30) Next, the control unit 80 controls the transfer unit 31 to start up. When the transfer unit 31 is started up, the permeate gas Gp1 discharged from the permeate side space 10S2 in the gas separation unit 10 is discharged to the outside through the exhaust valve 72. On the other hand, since the shut-off valve 71 is closed, the permeate gas Gp1 does not flow into the gas separation unit 20. Therefore, the separation membrane 21 in the gas separation unit 20 can be protected without putting a load on it.

[0065] (Step S40) Next, the control unit 80 determines whether the flow rate of the permeate gas Gp1 in the gas separation unit 10 has stabilized. Specifically, the arithmetic unit 81 in the control unit 80 obtains the flow rate of the permeate gas Gp1 from the flow meter 42. Then, the arithmetic unit 81 in the control unit 80 determines whether the flow rate of the permeate gas Gp1 is above a predetermined flow rate and whether the flow rate has stabilized.

[0066] If the flow rate of permeate gas Gp1 is stable (YES in step S40), the control unit 80 proceeds to step S50. If the flow rate of permeate gas Gp1 is not stable, that is, if the flow rate of permeate gas Gp1 is in a transient state (NO in step S40), the control unit 80 returns to step S40 and repeats the process.

[0067] (Step S50) When the flow rate of permeate gas Gp1 stabilizes (YES in step S40), it is considered that the state of the gas flowing through the gas separation unit 10 has stabilized, and therefore, permeate gas Gp1 is supplied to the gas separation unit 20.

[0068] Before opening the shut-off valve 71 and supplying the permeate gas Gp1 to the gas separation unit 20, the control unit 80 controls the exhaust valve 74 to open while the shut-off valve 73 is closed. Specifically, the arithmetic unit 82 in the control unit 80 controls the exhaust valve 74 to open. If the exhaust valve 74 is opened in step S10, step S50 is omitted.

[0069] (Step S60) Next, in order to supply the permeate gas Gp1 to the gas separation unit 20, the control unit 80 controls the shut-off valve 71 to open. The control unit 80 also controls the exhaust valve 72 to close. Specifically, the arithmetic unit 81 in the control unit 80 controls the shut-off valve 71 to open and the exhaust valve 72 to close.

[0070] (Step S70) Next, the control unit 80 controls the transfer unit 32 to start up. When the transfer unit 32 is started up, the unpermeable gas Gn2 discharged from the impermeable space 20S1 in the gas separation unit 20 is discharged to the outside through the exhaust valve 74. On the other hand, since the shut-off valve 73 is closed, the unpermeable gas Gn2 does not flow into the transfer unit 33. By discharging the unpermeable gas Gn2 discharged from the impermeable space 20S1 in the gas separation unit 20 to the outside through the exhaust valve 74, the separation membrane 21 in the gas separation unit 20 can be protected without putting a load on it.

[0071] (Step S80) Next, the control unit 80 determines whether the flow rate of the unpermeated gas Gn2 in the gas separation unit 20 has stabilized. Specifically, the arithmetic unit 82 in the control unit 80 obtains the flow rate of the unpermeated gas Gn2 from the flow meter 43. Then, the arithmetic unit 82 in the control unit 80 determines whether the flow rate of the unpermeated gas Gn2 is within a predetermined flow rate range and whether the flow rate has stabilized.

[0072] If the flow rate of unpermeated gas Gn2 is stable (YES in step S80), the control unit 80 proceeds to step S90. If the flow rate of unpermeated gas Gn2 is not stable, that is, if the flow rate of unpermeated gas Gn2 is in a transient state (NO in step S80), the control unit 80 returns to step S80 and repeats the process.

[0073] (Step S90) When the flow rate of the unpermeated gas Gn2 stabilizes (YES in step S80), it is considered that the state of the gas flowing through the gas separation unit 20 has stabilized, so the transfer unit 33 is activated and the gas is sent to the recycling line 65.

[0074] The control unit 80 controls the shut-off valve 73 to open. The control unit 80 also controls the exhaust valve 74 to close. Specifically, the arithmetic unit 82 in the control unit 80 controls the shut-off valve 73 to open and the exhaust valve 74 to close.

[0075] (Step S100) Next, the control unit 80 controls the transfer unit 33 to start up. When the transfer unit 33 is started up, the unpermeable gas Gn2 discharged from the impermeable space 20S1 in the gas separation unit 20 passes through the recycling line 65 and is discharged into the gas mixing header 70 in the raw material gas line 61.

[0076] Next, the processing of the control unit 80 during the shutdown of the gas separation system 1 will be described. Figure 3 is a flowchart illustrating the processing during shutdown in the gas separation system 1, which is an example of a gas separation system according to the first embodiment.

[0077] (Step S110) The control unit 80 controls the exhaust valve 74 to open when the shut-off valve 73 is open. Specifically, the arithmetic unit 82 in the control unit 80 controls the exhaust valve 74 to open.

[0078] (Step S120) Next, the control unit 80 controls the transfer unit 33 to stop. When the transfer unit 33 stops, the flow of gas from the transfer unit 33 to the gas mixing header 70 in the recycling line 65 stops, but the unpermeated gas Gn2 from the gas separation unit 20 is discharged to the outside through the exhaust valve 74. Therefore, the separation membrane 21 in the gas separation unit 20 can be protected without being subjected to any load.

[0079] (Step S130) Next, the control unit 80 controls the transfer unit 31 and the transfer unit 32 to stop.

[0080] In step S110, by opening the exhaust valve 74 and then stopping the transfer unit 31 and the transfer unit 32, it is possible to prevent a transient increase in the discharge pressure in the transfer unit 31.

[0081] Furthermore, the gas separation system 1 is equipped with a check valve 75 upstream of the exhaust valve 74 to prevent outside air from being drawn in.

[0082] To combat global warming and reduce carbon dioxide emissions, the International Maritime Organization (IMO) introduced the Energy Efficiency Design Index (EEDI) regulation as a performance requirement for ships. The EEDI indicates the amount of carbon dioxide emissions per unit of transport. Under the EEDI regulation, a 30% reduction in carbon dioxide emissions is required in Phase 3, starting from 2025, compared to Phase 0, which was introduced in 2013.

[0083] In response to the situation described above, various efforts are being made to reduce carbon dioxide emissions from engine exhaust gases, which are the power source of ships. One of these efforts is carbon dioxide capture on board ships.

[0084] To reduce carbon dioxide emissions, it is crucial to achieve a high carbon dioxide capture rate. At the same time, in carbon dioxide capture systems on ships, space constraints necessitate removing gases other than carbon dioxide, separating carbon dioxide to a higher concentration, and compactly storing the captured carbon dioxide.

[0085] For example, existing technologies such as chemical absorption require excessive equipment, so there is a demand for carbon dioxide recovery using separation membranes that can save space.

[0086] In carbon dioxide capture systems using separation membranes, it is possible to increase the concentration of captured carbon dioxide by arranging the separation membranes in series in multiple stages. Furthermore, in multi-stage carbon dioxide capture systems, a recycling process is being considered in which the unpermeated gas from the downstream separation membrane, which has a higher carbon dioxide concentration, is mixed with the supply gas from the upstream separation membrane as a recycled gas, with the aim of increasing the carbon dioxide recovery rate.

[0087] For a gas separation membrane to perform optimally, a pressure difference must be maintained between the supply and permeate sides of the membrane as a driving force. Possible means of generating this pressure difference include pumping gas from the supply side or reducing pressure from the permeate side. For reducing system power consumption, pressure reduction is preferable. Furthermore, since the discharge pressure of a pressure reducing pump or blower is equivalent to atmospheric pressure, if a recycling process is applied to the unpermeated side of the separation membrane, a means of adding pressure for gas mixing, such as a recycling pump or blower, is necessary.

[0088] On the other hand, in ships, when the engine stops, the gas separation system must be shut down to prevent unnecessary pressure from being applied to the separation membrane.

[0089] According to the gas separation system of the first embodiment, the control unit controls the shut-off valve and the exhaust valve, thereby enabling safe startup or shutdown while preventing damage to the separation membrane in the gas separation unit.

[0090] Note that flowmeter 41 is an example of a first flowmeter, flowmeter 42 is an example of a second flowmeter, and flowmeter 43 is an example of a third flowmeter. Pressure gauge 51 is an example of a first pressure gauge, pressure gauge 52 is an example of a second pressure gauge, and pressure gauge 53 is an example of a third pressure gauge.

[0091] <Second Embodiment> The gas separation system according to the second embodiment further includes a shut-off valve and an exhaust valve in the line of the second permeate gas discharged from the second gas separation unit.

[0092] The gas separation system according to the second embodiment will be described in detail with reference to the drawings. Figure 4 is a diagram illustrating the schematic configuration of gas separation system 2, which is an example of the gas separation system according to the second embodiment.

[0093] The gas separation system 2 is equipped with a shut-off valve 76, an exhaust valve 77, and a check valve 78 in the gas recovery line 64. Furthermore, the gas separation system 2 is equipped with a control unit 180 instead of the control unit 80 in the gas separation system 1. For configurations in the gas separation system 2 that are common to the gas separation system 1, please refer to the description of the gas separation system 1; a detailed explanation is omitted here.

[0094] (Shut-off valve 76) The gas separation system 2 is equipped with a shut-off valve 76 in the gas recovery line 64. The shut-off valve 76 opens and closes to allow or block the flow of permeate gas Gp2 through the gas recovery line 64. The opening and closing of the shut-off valve 76 is controlled by a calculator 182 in the control unit 180.

[0095] (Exhaust valve 77) The gas separation system 2 is equipped with an exhaust valve 77 in the gas recovery line 64. The exhaust valve 77 opens and closes to allow or block the flow of permeate gas Gp2 exhausted from the gas recovery line 64 to the outside. The opening and closing of the exhaust valve 77 is controlled by the arithmetic unit 182 in the control unit 180.

[0096] (Check valve 78) The gas separation system 2 includes a check valve 78 between the gas recovery line 64 and the exhaust valve 77. The check valve 78 prevents gas from flowing into the gas recovery line 64 from outside the gas separation system 1.

[0097] In the gas separation system 2, for example, until the flow rate of unpermeated gas Gn2 stabilizes, the exhaust valve 77 is opened and the shut-off valve 76 is shut off, thereby preventing the recovery of permeated gas Gp2, which has a low concentration of carbon dioxide, as recovered gas Ge.

[0098] [Regarding operations in arithmetic units] The calculations in the arithmetic unit of the gas separation system according to this embodiment will be described. Figure 5 is a diagram illustrating the calculations in the arithmetic unit of the gas separation system according to this embodiment. Figure 5 is a diagram illustrating the flow rate of gas passing through the gas separation unit SU.

[0099] The CTL calculator uses the flow rate Ff [mol / s] and pressure Ph [kPa] of the gas Gi flowing into the gas separation unit SU, and the pressure Pl [kPa] of the permeate gas Gpi that has permeated from the gas separation unit SU through the separation membrane MBR to calculate the flow rate. Note that sometimes the flow rate Ff is referred to as the supply gas flow rate, the pressure Ph as the supply gas pressure, and the pressure Pl as the permeate gas pressure.

[0100] For example, the flow rate Ff is measured by flow meter FM1, the pressure Ph by pressure gauge PG1, and the pressure Pl by pressure gauge PG2. The calculator CTL calculates the flow rate Fp [mol / s] measured by flow meter FM2. Note that the flow rate Fp is sometimes called the permeate flow rate. Furthermore, the calculator CTL also determines the flow rate Fi [mol / s] of the unpermeated gas Gni.

[0101] For example, suppose that the gas Gi flowing into the gas separation unit SU is composed of a first component gas Gi1 and a second component gas Gi2. The amount (composition) of the first component gas Gi1 relative to the total gas Gi is x0 (where x0 is a real number between 0 and 1). In other words, the amount (composition) of the second component gas Gi2 relative to the total gas Gi is (1-x0).

[0102] This section describes the intrinsic values ​​of the membrane material constituting the separation membrane MBR in the gas separation unit SU. For the separation membrane MBR in the gas separation unit SU, the permeability coefficient Q1 [mol·m / (m³)] of the first gas, gas Gi1, is described. 2 (·s·kPa), the permeability coefficient Q2 [mol·m / (m³)] of the second gas, gas Gi2. 2 Assume that (·s·kPa) is the case.

[0103] Furthermore, we will explain the specific values ​​in the gas separation unit SU. The membrane area of ​​the separation membrane MBR in the gas separation unit SU is A[m²]. 2 Let the film thickness be δ[m].

[0104] Here, we assume that the composition of the gas passing through the impermeable side of the separation membrane MBR in the gas separation unit SU changes as the gas flows from left to right in Figure 5. On the other hand, we assume that the gas passing through the permeable side of the separation membrane MBR in the gas separation unit SU is completely mixed, and the amount (composition) of the first component of the gas relative to the total gas is constant at yp (where yp is a real number between 0 and 1). In other words, here we will explain using a permeation model in which the supply side of the membrane (impermeable flow side) is plug flow (flow parallel to the membrane) and the permeable flow side is completely mixed.

[0105] Let F1 [mol / s] be the flow rate of the first gas passing through the impermeable side of the separation membrane MBR in the gas separation unit SU, x be the composition of the first gas, and F2 [mol / s] be the flow rate of the second gas. When the supply gas passes from left to right in Figure 5, the flow rates F1 and F2 in the minute section satisfy the following equations 1 and 2.

[0106] dF1 / dA = -(Q1 / δ)(ph x-pl yp) (Equation 1) dF2 / dA = -(Q2 / δ)(ph·(1-x)-pl·(1-yp)) ... (Formula 2)

[0107] Furthermore, composition x satisfies equation 3 below.

[0108] x = F1 / (F1+F2) (Formula 3)

[0109] Here, the flow rate Fi is obtained by integrating the flow rates F1 and F2 in the direction in which the gas flows through the separation membrane MBR, according to Equation 4. Then, the flow rate Fp is obtained using Equation 5.

[0110] Fi = F1 + F2 ... (Equation 4) Fp = Ff-Fi = Ff -(F1+F2) (Formula 5)

[0111] If the composition yp is undetermined, the calculation is performed by making appropriate assumptions about the composition yp, and the composition yp is determined from the results of the calculation based on these assumptions. Then, the calculation is repeated using the newly calculated composition yp until the results stabilize.

[0112] Regarding pressure, for example, the pressure may be corrected by adjusting the pressure gauge readings before and after the transfer section to account for the pressure increase in the transfer section.

[0113] By performing the above calculations, each of the calculators 81, 82, and 182 can calculate the flow rates of the permeate and unpermeated gases using the supply gas flow rate, supply gas pressure, permeate gas pressure, and supply gas composition supplied to the gas separation unit. Note that the permeate model used above is just one example, and different calculation formulas may be used by applying a different permeate model.

[0114] For example, by combining the above calculations, the control unit 80 or control unit 180 can estimate the flow rate of permeate gas Gp1 measured by flow meter 42 based on the measurement results of flow meter 41, pressure meter 51, and pressure meter 52. Furthermore, the control unit 80 or control unit 180 can estimate the flow rate of unpermeate gas Gn2 measured by flow meter 43 based on the measurement results of flow meter 41, pressure meter 51, pressure meter 52, and pressure meter 53. The control unit 80 or control unit 180 may use the estimated flow rates to control the shut-off valve and exhaust valve.

[0115] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The above embodiments may be omitted, replaced, or modified in various ways without departing from the scope and spirit of the appended claims. [Explanation of Symbols]

[0116] 1. Gas separation system 10, 20 Gas Separation Units 10S1, 20S1 Non-transparent side space 10S2, 20S2 Transmission side space 11, 21 Separation membrane 31, 32, 33 Transfer section 41, 42, 43 flowmeter 51, 52, 53 Pressure gauges 61. Raw material gas line 62 connection lines 63 Exhaust gas line 64 Gas recovery line 65 Recycling Line 66 Recovery gas line 70 Gas Mixing Header 71, 73 Shut-off valves 72, 74 Exhaust valve 75 Check valve 80 Control Unit 81, 82 Arithmetic unit Gc mixed gas G-recovered gas Gm raw material gas Gn1, Gn2 Unpermeable Gas Gp1, Gp2 permeable gas Gr Recycled Gas

Claims

1. A first gas separation unit comprising a first separation membrane, to which a raw material gas is supplied, and to which the supplied raw material gas is separated into a first permeate gas that permeates through the first separation membrane and a first unpermeate gas that is discharged without permeating through the first separation membrane, A second gas separation unit is connected in series with the first gas separation unit, and is equipped with a second separation membrane, to which the first permeate gas is supplied, and which separates the supplied first permeate gas into a second permeate gas that permeates through the second separation membrane and a second unpermeated gas that is discharged without permeating through the second separation membrane, A raw material gas line that supplies the raw material gas to the first gas separation unit, A recycling line that returns the second unpermeated gas to the raw material gas line, A first transfer unit that supplies the first permeate gas in the first gas separation unit to the second gas separation unit, The second gas separation unit includes a second transfer unit that discharges the second permeate gas to the outside, A third transfer unit is located in the recycling line and sends the second unpermeated gas to the raw material gas line, A first shut-off valve that shuts off the first permeate gas flowing from the first gas separation unit to the second gas separation unit, A first exhaust valve that shuts off the first permeate gas being exhausted to the outside from the first gas separation unit, A second shut-off valve that shuts off the second unpermeable gas flowing from the second gas separation unit to the recycling line, A second exhaust valve that shuts off the second impermeable gas being exhausted to the outside from the second gas separation unit, A control unit that controls the opening and closing of the first shut-off valve, the first exhaust valve, the second shut-off valve, and the second exhaust valve, Equipped with, Gas separation system.

2. The system further includes a first flow meter for measuring the flow rate of the first permeate gas, The control unit controls the opening and closing of the first shut-off valve and the first exhaust valve, respectively, based on the flow rate measured by the first flow meter. The gas separation system according to claim 1.

3. The system further includes a second flow meter for measuring the flow rate of the second unpermeated gas, The control unit controls the opening and closing of the second shut-off valve and the second exhaust valve, respectively, based on the flow rate measured by the second flow meter. The gas separation system according to claim 2.

4. A third flow meter for measuring the flow rate of the supply gas supplied to the first gas separation unit, A first pressure gauge for measuring the pressure of the supply gas, The system further comprises a second pressure gauge for measuring the pressure of the first permeate gas, The control unit controls the opening and closing of the first shut-off valve and the first exhaust valve, respectively, based on the flow rate measured by the third flow meter, the pressure measured by the first pressure gauge, and the pressure measured by the second pressure gauge. The gas separation system according to claim 1.

5. The system further includes a third pressure gauge for measuring the pressure of the second permeate gas, The control unit controls the opening and closing of the second shut-off valve and the second exhaust valve, respectively, based on the flow rate measured by the third flow meter, the pressure measured by the first pressure gauge, the pressure measured by the second pressure gauge, and the pressure measured by the third pressure gauge. The gas separation system according to claim 4.

6. A third shut-off valve that shuts off the second permeate gas flowing from the second gas separation unit to the gas recovery line, A third exhaust valve that shuts off the second permeate gas being exhausted to the outside from the second gas separation unit, Furthermore, The control unit further controls the opening and closing of the third shut-off valve and the third exhaust valve, respectively. A gas separation system according to any one of claims 1 to 5.

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