Gas separation system

Abstract

This disclosure provides a gas separation system capable of appropriately handling fluctuations in the flow rate of the supplied raw material gas. [Solution] A gas separation system comprising: a first gas separation unit equipped with a first separation membrane, to which 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 impermeable gas that is discharged without permeating through the first separation membrane; a second gas separation unit connected in series with the first gas separation unit, equipped with a second separation membrane, to which the supplied first permeate gas is supplied, and to which the supplied first permeate gas is separated into a second permeate gas that permeates through the second separation membrane and a second impermeable gas that is discharged without permeating through the second separation membrane; a raw material gas line that supplies raw material gas to the first gas separation unit; a recycling line that returns the second impermeable gas to the raw material gas line; a third transfer unit located in the recycling line that sends the second impermeable gas to the raw material gas line; and a control unit that controls the third transfer unit in response to fluctuations in the supply flow rate of the raw material gas.

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 supply stream separation stage, an unpermeate separation stage, and a permeate separation stage. Patent Document 2 discloses that the equipment for separating the gas separates a first unpermeate stream in the supply stream separation stage into a second permeate stream and a second unpermeate stream in the unpermeate separation stage. Further, Patent Document 2 discloses that the equipment for separating the gas separates a first permeate stream in the supply stream separation stage into a third unpermeate stream and a third permeate stream in the permeate separation stage. 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 gas separation systems using separation membranes, it is desirable to properly handle fluctuations in the flow rate of the supplied raw material gas.

[0006] This disclosure provides a gas separation system capable of appropriately handling fluctuations in the flow rate of the supplied raw material gas. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, 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 unpermeated gas that is discharged without permeating through the first separation membrane; a second gas separation unit connected in series with the first gas separation unit, comprising a second separation membrane, to which the first permeate gas is supplied, and to which the supplied first permeate gas is separated 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; and the first gas separation unit The gas separation system is provided, comprising: a raw material gas line that supplies the raw material gas; a recycling line that returns the second unpermeated gas to the raw material gas line; a first transfer unit that supplies the first permeated gas from the first gas separation unit to the second gas separation unit; a second transfer unit that discharges the second permeated gas from the second gas separation unit to the outside; a third transfer unit located in the recycling line that sends the second unpermeated gas to the raw material gas line; and a control unit that controls the third transfer unit in response to fluctuations in the supply flow rate of the raw material gas. [Effects of the Invention]

[0008] According to the gas separation system of this disclosure, even if the flow rate of the supplied raw material gas fluctuates, it can be processed appropriately. [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 diagram illustrating the schematic configuration of a gas separation system according to the second embodiment. [Figure 3] Figure 3 is a diagram illustrating the schematic configuration of a gas separation system according to the third embodiment. [Figure 4] Figure 4 is a diagram illustrating the schematic configuration of the gas separation system according to the fourth embodiment. [Figure 5] Figure 5 illustrates the calculations performed in the arithmetic unit of the gas separation system according to the fourth 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 to the first gas separation unit, equipped with a second separation membrane, to which the first permeate gas is supplied. The second gas separation unit in the gas separation system according to the first embodiment 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. The gas separation system according to the first embodiment also 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 control unit that controls the third transfer unit in response to fluctuations in the supply flow rate of the raw material gas.

[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 using a gas separation unit. The gas separation system 1 then concentrates the carbon dioxide gas by connecting multiple gas separation units in series. The gas separation system 1 is equipped with two gas separation units. Finally, the gas separation system 1 discharges the concentrated carbon dioxide gas as 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, a transfer unit 31, a transfer unit 32, and a transfer unit 33, and a control unit 80. Further, the gas separation system 1 includes a pressure gauge 51. 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.

[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 permeate 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. The gas separation unit 10 has a non-permeation side space 10S1 and a permeation side space 10S2 inside. The inside of the gas separation unit 10 is divided into a non-permeation side space 10S1 and a permeation side space 10S2 by the separation membrane 11.

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

[0022] The raw material gas Gm is supplied to the gas separation unit 10. More specifically, a mixed gas Gc in which the raw material gas Gm and the recycle gas Gr are mixed is supplied to the gas separation unit 10.

[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] (Pressure gauge 51) The pressure gauge 51 is installed between the transfer unit 31 and the gas separation unit 20 in the connection line 62. The pressure gauge 51 measures the pressure of the permeate gas Gp1 on the discharge side of the transfer unit 31. In other words, the pressure gauge 51 measures the pressure of the permeate gas Gp1 supplied to the impermeable space 20S1 in the gas separation unit 20.

[0036] (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.

[0037] 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.

[0038] (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.

[0039] The gas separation system 1 includes a transfer unit 31 and a pressure gauge 51 in the connection line 62.

[0040] (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.

[0041] (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.

[0042] The gas separation system 1 includes a transfer unit 32 in the gas recovery line 64.

[0043] (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.

[0044] The gas separation system 1 includes a transfer unit 33 in the recycling line 65.

[0045] (Control unit 80) The control unit 80 controls the gas separation system 1. Specifically, the control unit 80 controls the transfer unit 31, the transfer unit 32, and the transfer unit 33. The control unit 80 also acquires the pressure detected from the pressure gauge 51.

[0046] In the gas separation system 1, the control unit 80 controls the transfer unit 33 in response to fluctuations in the operating load. Specifically, the control unit 80 controls the output of the transfer unit 33 so that the pressure detected by the pressure gauge 51 is within a preset operating pressure range. The preset operating pressure range is, for example, a pressure range in which the transfer unit 31 can avoid failure. More specifically, it is a pressure range in which the pressure reducing pump or blower constituting the transfer unit 31 will not fail.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] On the other hand, in ships, engine load fluctuations occur during deceleration operations such as when entering or departing port. When engine load fluctuations occur, the exhaust gas flow rate and pressure (supply pressure) also fluctuate in accordance with the engine load fluctuations through adjustment operations. In membrane separation processes using separation membranes, fluctuations in the flow rate and pressure of the raw material gas cause fluctuations in the outlet gas flow rate (unpermeated gas flow rate, permeated gas flow rate). Since the recycled gas flow rate, which is the unpermeated flow through the separation membrane, also fluctuates, the recycling pump or blower also needs to adjust its operating load accordingly.

[0054] On the other hand, if the gas pressure on the discharge side of a pressure reducing pump or blower becomes too high, it can become overloaded, potentially leading to reduced pump performance or failure. Therefore, operational control of the recycling pump or blower is necessary to adjust the discharge pressure of the pressure reducing pump or blower within a certain range.

[0055] According to the gas separation apparatus of the first embodiment, even if the flow rate and pressure of the exhaust gas fluctuate, the process pressure can be stabilized in accordance with the load fluctuations of the supply gas. By stabilizing the process pressure, the gas separation apparatus of the first embodiment can avoid failures of equipment such as the pressure reducing pump or blower used as the transfer unit.

[0056] <Second Embodiment> A gas separation system according to the second embodiment will now be described. The gas separation system according to the second embodiment has a different pressure that is detected for control by the control unit in the gas separation system according to the first embodiment.

[0057] The gas separation system according to the second embodiment will be described in detail with reference to the drawings. Figure 2 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.

[0058] Gas separation system 2 is equipped with a pressure gauge 52 in place of the pressure gauge 51 in gas separation system 1. Furthermore, gas separation system 2 is equipped with a control unit 180 in place of the control unit 80 in gas separation system 1. For configurations in gas separation system 2 that are common to gas separation system 1, please refer to the description of gas separation system 1; a detailed explanation is omitted here.

[0059] (Pressure gauge 52) The pressure gauge 52 is installed between the gas separation unit 20 and the transfer unit 33 in the recycling line 65. The pressure gauge 52 measures the pressure of the impermeable gas Gn2 discharged from the impermeable side space 20S1 in the gas separation unit 20.

[0060] (Control unit 180) The control unit 180 controls the gas separation system 2. Specifically, the control unit 180 controls the transfer unit 31, the transfer unit 32, and the transfer unit 33. The control unit 180 also acquires the pressure detected from the pressure gauge 52.

[0061] In the gas separation system 2, the control unit 180 controls the transfer unit 33 in response to fluctuations in the operating load. Specifically, the control unit 180 controls the output of the transfer unit 33 so that the pressure detected by the pressure gauge 52 is within a range obtained by adding the pressure loss in the gas separation unit 20 to a preset operating pressure range. The preset operating pressure range is, for example, a pressure range in which the transfer unit 31 can avoid failure. More specifically, it is a pressure range in which the pressure reducing pump or blower constituting the transfer unit 31 will not fail.

[0062] According to the gas separation apparatus of the second embodiment, similar to the gas separation apparatus of the first embodiment, even if the flow rate and pressure of the exhaust gas fluctuate, the process pressure can be stabilized in accordance with the load fluctuations of the supply gas. By stabilizing the process pressure, the gas separation apparatus of the second embodiment can avoid failures of equipment such as the pressure reducing pump or blower used as the transfer unit.

[0063] <Third Embodiment> A gas separation system according to the third embodiment will now be described. The gas separation system according to the third embodiment detects pressure and flow rate for control by the control unit in the gas separation system according to the first embodiment.

[0064] The gas separation system according to the third embodiment will be described in detail with reference to the drawings. Figure 3 is a diagram illustrating the schematic configuration of gas separation system 3, which is an example of the gas separation system according to the third embodiment.

[0065] Gas separation system 3 further includes a flow meter 40 in addition to gas separation system 1. Furthermore, gas separation system 3 further includes pressure gauges 53, 54, and 55 in addition to gas separation system 1. Additionally, gas separation system 3 replaces the control unit 80 in gas separation system 1 with a control unit 280. For configurations common to gas separation system 1 in gas separation system 3, please refer to the description of gas separation system 1; a detailed explanation is omitted here.

[0066] (Flowmeter 40) The gas separation system 3 is equipped with a flow meter 40 in the raw material gas line 61. The flow meter 40 is installed upstream of the gas mixing header 70 in the raw material gas line 61. The flow meter 40 measures the flow rate of the raw material gas Gm flowing through the raw material gas line 61.

[0067] The flow meter 40 is not limited in type as long as it can measure the flow rate of the raw gas Gm. For example, the flow meter 40 may be a differential pressure flow meter or a vortex flow meter. Alternatively, a flow velocity meter may be used to convert the flow rate into a flow meter.

[0068] (Pressure gauge 53, pressure gauge 54, and pressure gauge 55) Pressure gauges 53, 54, and 55 each detect the pressure of the gas passing through the piping.

[0069] The pressure gauge 53 is installed between the gas mixing header 70 and the gas separation unit 10 in the raw gas line 61. The pressure gauge 53 measures the pressure of the mixed gas Gc supplied to the impermeable side space 10S1 in the gas separation unit 10.

[0070] The pressure gauge 54 is installed between the gas separation unit 10 and the transfer unit 31 in the connection line 62. The pressure gauge 54 measures the pressure of the permeate gas Gp1 discharged from the permeate side space 10S2 in the gas separation unit 10.

[0071] The pressure gauge 55 is installed between the gas separation unit 20 and the transfer unit 32 in the gas recovery line 64. The pressure gauge 55 measures the pressure of the permeate gas Gp2 discharged from the permeate side space 20S2 in the gas separation unit 20.

[0072] (Control unit 280) The control unit 280 controls the gas separation system 3. Specifically, the control unit 280 controls the transfer unit 31, the transfer unit 32, and the transfer unit 33. The control unit 280 also obtains the flow rate detected from the flow meter 40. Furthermore, the control unit 280 obtains the pressure detected from the pressure gauges 51, 53, 54, and 55.

[0073] The control unit 280 includes arithmetic units 281, 282, and 283.

[0074] The arithmetic unit 281 controls the transfer unit 31 so that a predetermined differential pressure is generated in the separation membrane 11 of the gas separation unit 10. The arithmetic unit 281 obtains the pressure value of the mixed gas Gc supplied to the separation membrane 11 (separation membrane supply gas pressure value) from the pressure gauge 53. The arithmetic unit 281 also obtains the pressure value of the permeate gas Gp1 discharged from the separation membrane 11 (separation membrane permeate flow pressure value) from the pressure gauge 54. The arithmetic unit 281 controls the output of the transfer unit 31 so that the differential pressure between the pressure value of the mixed gas Gc and the pressure value of the permeate gas Gp1 becomes a predetermined set pressure (separation membrane differential pressure set value).

[0075] The arithmetic unit 282 controls the transfer unit 32 so that a predetermined differential pressure is generated in the separation membrane 21 of the gas separation unit 20. The arithmetic unit 282 obtains the pressure value of the permeate gas Gp1 supplied to the separation membrane 21 (separation membrane supply gas pressure value) from the pressure gauge 51. The arithmetic unit 282 also obtains the pressure value of the permeate gas Gp2 discharged from the separation membrane 21 (separation membrane permeate flow pressure value) from the pressure gauge 55. The arithmetic unit 282 controls the output of the transfer unit 32 so that the differential pressure between the pressure value of permeate gas Gp1 and the pressure value of permeate gas Gp2 becomes a predetermined set pressure (separation membrane differential pressure set value).

[0076] The arithmetic unit 283 controls the transfer unit 33 in response to fluctuations in the operating load. The arithmetic unit 283 obtains the flow rate of the raw material gas Gm from the flow meter 40. The arithmetic unit 283 stores in the database the flow rate of the permeate gas Gp1 when the differential pressure of the separation membrane 11 in the gas separation unit 10 relative to the flow rate of the raw material gas Gm is a predetermined set pressure (separation membrane differential pressure set value). The arithmetic unit 283 also stores in the database the flow rate of the unpermeated gas Gn2 when the differential pressure of the separation membrane 21 in the gas separation unit 20 relative to the flow rate of the raw material gas Gm is a predetermined set pressure (separation membrane differential pressure set value). Then, based on the database, the arithmetic unit 283 controls the output of the transfer unit 33 so that the flow rate of the unpermeated gas Gn2 becomes a predetermined flow rate.

[0077] According to the gas separation apparatus of the third embodiment, similar to the gas separation apparatus of the first embodiment, even if the flow rate and pressure of the exhaust gas fluctuate, the process pressure can be stabilized in accordance with the load fluctuations of the supply gas. By stabilizing the process pressure, the gas separation apparatus of the third embodiment can avoid failures of equipment such as the pressure reducing pump or blower used as the transfer unit.

[0078] <Fourth Embodiment> A gas separation system according to the fourth embodiment will now be described. The gas separation system according to the fourth embodiment detects pressure and flow rate for control by the control unit in the gas separation system according to the first embodiment.

[0079] The gas separation system according to the fourth embodiment will be described in detail with reference to the drawings. Figure 4 is a diagram illustrating the schematic configuration of a gas separation system 4, which is an example of a gas separation system according to the fourth embodiment.

[0080] Gas separation system 4 is further equipped with a flow meter 40 in addition to gas separation system 1. Furthermore, gas separation system 4 replaces the pressure gauge 51 in gas separation system 1 with pressure gauges 53, 54, and 55. Additionally, gas separation system 4 replaces the control unit 80 in gas separation system 1 with a control unit 380. For configurations in gas separation system 4 that are common to gas separation system 1 or gas separation system 3, please refer to the description of gas separation system 1 or gas separation system 3; a detailed explanation is omitted here.

[0081] (Control unit 380) The control unit 380 controls the gas separation system 4. Specifically, the control unit 380 controls the transfer unit 31, the transfer unit 32, and the transfer unit 33. The control unit 380 also obtains the flow rate detected from the flow meter 40. Furthermore, the control unit 380 obtains the pressure detected from the pressure gauges 53, 54, and 55.

[0082] The control unit 380 includes an arithmetic unit 381 and an arithmetic unit 383.

[0083] The arithmetic unit 381 predicts the flow rate of permeate gas Gp1 discharged from the gas separation unit 10. The arithmetic unit 381 obtains the flow rate of the raw material gas Gm from the flow meter 40. The arithmetic unit 381 also obtains the pressure value of the mixed gas Gc supplied to the separation membrane 11 (separation membrane supply gas pressure value) from the pressure gauge 53. The arithmetic unit 381 also obtains the pressure value of the permeate gas Gp1 discharged from the separation membrane 11 (separation membrane permeate flow pressure value) from the pressure gauge 54. Furthermore, the arithmetic unit 381 obtains the flow rate of unpermeated gas Gn2 discharged from the gas separation unit 20 from the arithmetic unit 383. Then, the arithmetic unit 381 estimates the flow rate of permeate gas Gp1 permeating through the separation membrane 11 in the gas separation unit 10 according to the calculation formula, based on the differential pressure between the pressure value of the mixed gas Gc and the pressure value of the permeate gas Gp1, the flow rate of the raw material gas Gm, and the estimated flow rate of the unpermeated gas Gn2. The arithmetic unit 381 outputs the estimated flow rate of permeate gas Gp1 to the arithmetic unit 383.

[0084] The arithmetic unit 383 controls the transfer unit 33 in response to fluctuations in the operating load. The arithmetic unit 383 obtains the flow rate of permeate gas Gp1 discharged from the gas separation unit 10 specified by the arithmetic unit 381 from the arithmetic unit 381. The arithmetic unit 383 obtains the pressure value of permeate gas Gp2 discharged from the separation membrane 21 (separation membrane permeate flow pressure value) from the pressure gauge 55. Then, the arithmetic unit 383 estimates the flow rate of unpermeated gas Gn2 that does not permeate the separation membrane 11 in the gas separation unit 20 according to the calculation formula, based on the flow rate of permeate gas Gp1 and the pressure value of permeate gas Gp2. The arithmetic unit 383 outputs the estimated flow rate of unpermeated gas Gn2 to the arithmetic unit 381.

[0085] Calculators 381 and 383 repeat calculations until the flow rate of unpermeated gas Gn2 converges to a constant value. As described above, Calculators 381 and 383 calculate the flow rate of unpermeated gas Gn2 based on the flow rate of the raw material gas Gm and the pressure values ​​of the mixed gas Gc, permeated gas Gp1, and permeated gas Gp2. Once the flow rate of unpermeated gas Gn2 converges to a constant value, Calculator 383 controls the output of the transfer unit 33 to match the calculated flow rate of unpermeated gas Gn2.

[0086] Furthermore, the control unit 380 may maintain a database of flow rate patterns for recycled gas Gr corresponding to the flow rate of the raw material gas Gm and the pressure values ​​of the mixed gas Gc, permeate gas Gp1, and permeate gas Gp2, based on the calculations described above. The output of the transfer unit 33 may then be controlled based on the flow rate patterns of recycled gas Gr in the database.

[0087] [Regarding operations in arithmetic units] The calculations in the arithmetic unit of the gas separation system according to the fourth embodiment will be described. Figure 5 is a diagram illustrating the calculations in the arithmetic unit of the gas separation system according to the fourth embodiment. Figure 5 is a diagram illustrating the flow rate of gas passing through the gas separation unit SU.

[0088] The CTL calculator adjusts the output of the BW transfer unit using 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. 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.

[0089] 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.

[0090] 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).

[0091] 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.

[0092] 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].

[0093] 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.

[0094] 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.

[0095] dF1 / dA = -(Q1 / δ)(ph x-pl yp) (Equation 1) dF2 / dA = -(Q2 / δ)(ph·(1-x)-pl·(1-yp)) ... (Formula 2)

[0096] Furthermore, composition x satisfies equation 3 below.

[0097] x = F1 / (F1+F2) (Formula 3)

[0098] 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.

[0099] Fi = F1 + F2 ... (Equation 4) Fp = Ff-Fi = Ff -(F1+F2) (Formula 5)

[0100] 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.

[0101] By performing the calculations described above, arithmetic units 381 and 383 calculate the flow rate. Note that the transmission model used above is just one example, and different calculation formulas may be used by applying a different transmission model.

[0102] According to the gas separation apparatus of the fourth embodiment, similar to the gas separation apparatus of the first embodiment, even if the flow rate and pressure of the exhaust gas fluctuate, the process pressure can be stabilized in accordance with the load fluctuations of the supply gas. By stabilizing the process pressure, the gas separation apparatus of the fourth embodiment can avoid failures of equipment such as the pressure reducing pump or blower used as the transfer unit.

[0103] Note that gas separation unit 10 is an example of a first gas separation unit, separation membrane 11 is an example of a first separation membrane, gas separation unit 20 is an example of a second gas separation unit, and separation membrane 21 is an example of a second separation membrane. Furthermore, unpermeated gas Gn1 is an example of a first unpermeated gas, permeated gas Gp1 is an example of a first permeated gas, unpermeated gas Gn2 is an example of a second unpermeated gas, and permeated gas Gp2 is an example of a second permeated gas.

[0104] In the embodiment described above, the gas separation apparatus comprises two gas separation units, but the number of gas separation units is not limited to two. The gas separation apparatus of this disclosure may comprise three or more gas separation units.

[0105] 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]

[0106] 1, 2, 3, 4 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 40 Flow meter 51, 52, 53, 54, 55 Pressure gauges 61. Raw material gas line 62 connection lines 63 Exhaust gas line 64 Gas recovery line 65 Recycling Line 70 Gas Mixing Header 80, 180, 280, 380 Control Unit 281, 282, 283, 381, 383 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 control unit that controls the third transfer unit in response to fluctuations in the supply flow rate of the raw material gas, Equipped with, Gas separation system.

2. The system further includes a flow meter for detecting the flow rate of the gas flowing through the aforementioned raw material gas line. The gas separation system according to claim 1.

3. The operating load in the first transfer unit is controlled according to the respective pressures of the raw material gas and the first permeate gas in the first gas separation unit, and the operating load in the second transfer unit is controlled according to the respective pressures of the first permeate gas and the second permeate gas in the second gas separation unit. The gas separation system according to claim 2.

4. The system has a flow rate pattern for the raw material gas and a recycled gas flow rate pattern corresponding to the pressure in the raw material gas, the first permeate gas, and the second permeate gas, and controls the operating load in the third transfer unit based on this pattern. The gas separation system according to claim 3.

5. Based on the flow rate of the raw material gas, the pressures in the raw material gas, the first permeate gas, and the second permeate gas, the flow rate of the second unpermeated gas is calculated, and the operating load in the third transfer unit is controlled based on the calculated flow rate of the second unpermeated gas. The gas separation system according to claim 3.

6. A first gas separation unit comprising 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 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 includes 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 to the second gas separation unit, 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 control unit that controls the third transfer unit in response to the pressure of the first permeate gas, Equipped with, Gas separation system.

7. The system includes a pressure gauge for measuring the pressure of the first permeate gas, The gas separation system according to claim 6.

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