Gas separation system and concentration control method

Abstract

The present invention stably supplies a product gas at a user-designated concentration even when the specific gas concentration of a gas grid varies across the user-designated concentration. In order to remix non-permeation gas and permeation gas discharged from a separation membrane module and control the specific gas concentration to be constant, the present invention comprises: a non-permeation gas pipe having a first adjustment valve for obtaining non-permeation gas from the non-permeation side of the separation membrane module; and a permeation gas pipe having a second adjustment valve for obtaining permeation gas from the permeation side of the separation membrane module. A plurality of control modes are set on the basis of the magnitude relationship between the concentration of the non-permeation gas supplied to the non-permeation side of the separation membrane module and the specific gas concentration of a target product gas, and the valve opening degrees of the first adjustment valve and the second adjustment valve are adjusted for each control mode.

Description

Gas separation system and concentration control method

[0001] The present invention relates to a gas separation system and a method for controlling the concentration of the gas.

[0002] One method for separating a specific gas from a mixture of multiple gases is to use a separation membrane that selectively permeates gases. Examples include molecular sieve membranes, such as ceramic membranes, which separate gases based on differences in molecular diameter, and polymer membranes that utilize differences in the solubility of gases in the membrane. These separation membranes also allow a certain amount of gases other than the specific gas to permeate. The side of the separation membrane before permeation is called the non-permeated side, and the side after permeation is called the permeated side.

[0003] The amount of gas permeated through a separation membrane is proportional to the difference between the partial pressure of the gas on the retentate side and the partial pressure of the gas on the permeate side multiplied by the membrane area. Polymer materials are relatively easy to process, and separation membrane modules have been put to practical use in which polymer materials in the form of hollow fibers or sheets are sealed in a container. Patent Document 1 describes a gas production method and gas production apparatus that use a gas separation membrane to control a specific gas to a required concentration.

[0004] Patent No. 5111829

[0005] The gas production apparatus described in Patent Document 1 increases the recovery rate while maintaining a constant concentration of the permeable gas by mixing the permeable gas with a bypassed feed gas. One factor that can cause changes in the concentration of the permeable gas is fluctuations in the flow rate of the feed gas supplied to the separation membrane module. For example, when the flow rate of the feed gas decreases, the partial pressure of the difficult-to-permeate gas increases near the outlet of the separation membrane module, increasing the amount of the difficult-to-permeate gas that permeates and decreasing the concentration of the permeable gas. In such cases, it is necessary to reduce the flow rate of the low-concentration feed gas that is bypassed to maintain the concentration of the permeable gas at a constant level or higher.

[0006] When hydrogen is mixed as a specific gas into an existing gas grid and transported, the hydrogen concentration required varies depending on the user, and therefore the hydrogen concentration in the gas grid fluctuates depending on the usage situation.

[0007] For example, if a user requires a hydrogen concentration of 20%, the hydrogen concentration of the permeable gas can be controlled to 20% with the gas production apparatus configuration described in Patent Document 1 if the hydrogen concentration in the gas grid is less than 20%. However, if the hydrogen concentration in the gas grid exceeds 20%, the hydrogen concentration of the gas permeating the separation membrane will be 20% or higher. In such a case, the hydrogen concentration of the bypass gas will also exceed 20%, so the gas production apparatus configuration described in Patent Document 1 cannot control the hydrogen concentration of the permeable gas to 20%.

[0008] In the gas production apparatus described in Patent Document 1, it is possible to control the hydrogen concentration of the retentate gas to 20% and extract it as product gas. However, in the gas production apparatus described in Patent Document 1, it is necessary to connect a pipe through which the retentate gas flows (retentate gas pipe) to a pipe through which the product gas flows (product gas pipe), and to install valves in the retentate gas pipe and the permeate gas pipe through which the permeate gas flows.

[0009] In the gas production apparatus described in Patent Document 1, when the hydrogen concentration in the gas grid fluctuates around 20%, it is necessary to switch the valve so that gas flows from the permeated gas pipe to the product gas pipe when the hydrogen concentration is 20% or less, and to extract the product gas by switching the valve so that gas flows from the retentate gas pipe to the product gas pipe when the hydrogen concentration is 20% or more.

[0010] For this reason, in the gas production apparatus described in Patent Document 1, it is necessary to discontinuously change the valve opening degree attached to the piping. Therefore, in the gas production apparatus described in Patent Document 1, when the hydrogen concentration in the gas grid fluctuates around the concentration specified by the user, it is necessary to discontinuously change the valve opening degree of the valve installed in the piping, which poses a problem of large fluctuations in the hydrogen concentration of the product gas supplied to the user.

[0011] The present invention has been made in consideration of the above circumstances, and aims to provide a gas separation system and a concentration control method that can continuously change the valve opening of a valve installed in a pipe, even when the concentration of a specific gas in a gas grid fluctuates around the concentration specified by the user, and can stably supply product gas at the concentration specified by the user.

[0012] To solve the above problems, for example, the configurations described in the claims are adopted. The present application includes multiple means for solving the above problems, and one example thereof is a gas separation system that remixes retentate gas and permeate gas discharged from a separation membrane module to control the concentration of a specific gas to a constant level, the system comprising: a retentate gas pipe having a first control valve for extracting the retentate gas from the retentate side of the separation membrane module; and a permeate gas pipe having a second control valve for extracting the permeate gas from the permeate side of the separation membrane module. The gas separation system of the present invention sets multiple control modes based on the magnitude relationship between the concentration of the retentate gas supplied to the retentate side of the separation membrane module and the specific gas concentration of the target product gas, and adjusts the valve openings of the first and second control valves for each control mode.

[0013] According to the present invention, even when the concentration of a specific gas in the gas grid fluctuates around the concentration specified by the user, it is possible to stably supply product gas at the concentration specified by the user without discontinuously switching the valves installed in the piping. Problems, configurations, and effects other than those described above will become clear from the description of the following embodiments.

[0014] FIG. 1 is a schematic configuration diagram of a gas separation system according to a first embodiment of the present invention. FIG. 2 is a diagram showing a method of operating a control valve according to the first embodiment of the present invention. FIG. 3 is a diagram showing an example of the opening degree of a control valve when the hydrogen concentration in the gas supplied to the gas separation system according to the first embodiment of the present invention changes between 5% and 40%. FIG. 4 is a schematic configuration diagram of a gas separation system according to a second embodiment of the present invention. FIG. 5 is a schematic configuration diagram of a gas separation system according to a third embodiment of the present invention. FIG. 6 is a schematic configuration diagram of a gas separation system according to a fourth embodiment of the present invention. FIG. 7 is a schematic configuration diagram of a gas separation system according to a fifth embodiment of the present invention. FIG. 8 is a schematic configuration diagram of a gas separation system according to a sixth embodiment of the present invention. FIG. 9 is a diagram showing an example of an image output to a display device by a visualization device 570 according to the sixth embodiment of the present invention.

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that common components in the following drawings will be assigned the same reference numerals and redundant explanations will be omitted.

[0016] 1 is a schematic diagram of a gas separation system according to a first embodiment. The gas separation system according to this embodiment is a system that controls the hydrogen concentration of a product gas to a constant concentration designated by a user, even if the hydrogen concentration of the supply gas varies around a concentration designated by a user (a concentration of 20% (vol %) in this embodiment), for a supply gas that is a mixture of hydrogen and methane.

[0017] First, the configuration of a gas separation system 1 of this embodiment will be described. As shown in Figure 1, the gas separation system (hydrogen separation system) 1 is configured to continuously change the valve openings installed in the retentate gas supply pipe 14 and the permeate gas supply pipe 16 even when the hydrogen concentration of the supply gas fluctuates around 20%. In other words, the gas separation system 1 is configured to remix appropriate amounts of the retentate gas and permeate gas separated by the separation membrane module 10 in order to maintain a constant hydrogen concentration of the product gas at 20%.

[0018] A mixed gas is supplied to the gas separation system 1 from a supply gas pipe 11 branched from a main pipe of a gas grid (not shown). The gas separation system 1 is provided with a separation membrane module 10. The separation membrane module 10 is divided into a non-permeated side 31 and a permeated side 32 by a separation membrane 30. In this embodiment, a polymer membrane is used as the hydrogen separation membrane. Note that a ceramic or carbon-based hydrogen separation membrane may be used instead of the polymer membrane.

[0019] The permeation amount of each gas is calculated by multiplying the permeation rate of each gas and the partial pressure difference between each gas on the retentate side 31 and permeate side 32 by the membrane area of ​​the separation membrane 30. Because the permeation rate of hydrogen is higher than that of methane through the separation membrane 30, hydrogen permeates more easily. Therefore, the hydrogen concentration on the permeate side 32 is higher than that of the feed gas. On the other hand, the hydrogen concentration on the retentate side 31 is lower than that of the feed gas because hydrogen is the remaining gas (retentate gas) after more hydrogen has permeated than methane.

[0020] The gas separation system 1 is arranged with a retentate gas pipe 12 connected to the retentate side 31 of the separation membrane module 10 and discharging the retentate gas, a permeate gas pipe 15 connected to the permeate side 32 of the separation membrane module 10 and discharging the permeate gas, and a product gas pipe 18 for supplying the product gas. Furthermore, the retentate gas pipe 12 branches into a retentate gas return pipe 13 that returns the retentate gas to the mother pipe, and a retentate gas supply pipe 14 that connects to the product gas pipe 18. Similarly, the permeate gas pipe 15 branches into a permeate gas supply pipe 16 that connects to the product gas pipe 18, and a permeate gas return pipe 17 that returns the permeate gas to the mother pipe.

[0021] The retentate gas return pipe 13, the retentate gas supply pipe 14, the permeate gas supply pipe 16, and the permeate gas return pipe 17 are each equipped with control valves 20, 21, 22, and 23, respectively, to control the hydrogen concentration of the product gas to a constant value specified by the user.

[0022] The retentate gas return pipe 13 is equipped with a compressor 40 for increasing the pressure of the retentate gas downstream of the control valve 20 (third control valve) and returning it to the mother pipe when the pressure of the retentate gas downstream of the control valve 20 (third control valve) is lower than that of the mother pipe. Similarly, the permeate gas return pipe 17 is equipped with a compressor 41 for increasing the pressure of the permeate gas downstream of the control valve 23 (fourth control valve) and returning it to the mother pipe when the pressure of the permeate gas downstream of the control valve 23 (fourth control valve) is lower than that of the mother pipe.

[0023] The state of the gas separation system 1 is monitored by a hydrogen concentration meter C1 (first specified gas concentration meter) installed in the supply gas pipe 11, a pressure gauge P1 (first pressure gauge) installed in the retentate gas pipe 12, a pressure gauge P2 (second pressure gauge) installed in the permeate gas pipe 15, and a hydrogen concentration meter C2 (second specified gas concentration meter) installed in the product gas pipe 18.

[0024] The gas separation system 1 also includes a control device 50. The control device 50 receives state quantities of the system from the supply gas hydrogen concentration meter C1, the pressure gauge P1 on the retentate side 31, the pressure gauge P2 on the permeate side 32, and the product gas hydrogen concentration meter C2, and calculates the valve opening degree that keeps the hydrogen concentration of the product gas constant from the state quantities to generate a control signal.

[0025] Furthermore, the gas separation system 1 includes a control signal transmitter 51 that transmits control signals from the control device 50 to the control valves 20, 21, 22, and 23. Lines that transmit signals to the control device 50 are indicated by dashed lines, and lines that transmit signals from the control signal transmitter 51 to the control valves 20, 21, 22, and 23 are indicated by dashed lines. In this embodiment, the control signal transmitter 51 is described as a block separate from the control device 50, but the control signal transmitter 51 may also be included as an internal configuration of the control device 50. The same applies to the second to sixth embodiments shown in Figures 4 to 8. Note that the "control device" described in the claims is described as a control device that also includes the control device 50 and the control signal transmitter 51 of Figure 1, etc.

[0026] Next, a concentration control method using the gas separation system 1 will be described. Figure 2 is a diagram showing a method for operating the control valves 20, 21, 22, and 23. In Figure 2, Cin represents the specific gas concentration in the supply gas (hydrogen concentration in this embodiment), Crq represents the gas concentration specified by the user for the product gas (hydrogen concentration 20% in this embodiment), and ΔC represents the allowable value for the gas concentration fluctuation range for the product gas. ΔC is a value determined by the limit on gas concentration fluctuations in the equipment that uses the product gas.

[0027] An example of a method for determining the allowable value ΔC of the gas concentration fluctuation range will be described below. The gas separation system 1 of this embodiment controls the concentration of hydrogen in the product gas, which is a mixture of hydrogen and methane.

[0028] It should be noted that publicly known information indicates that there is no safety issue with equipment that uses product gas if the calorific value fluctuation of the gas is 2% or less. For a product gas with a hydrogen concentration of 20%, the hydrogen concentration fluctuation should be 2.5% or less to keep the calorific value fluctuation to 2% or less, so ΔC = 2.5% is determined. In this embodiment, the allowable value ΔC of the gas concentration fluctuation range is determined based on the limit on the calorific value fluctuation of the gas, but ΔC may also be determined based on other limits.

[0029] 2, the control device 50 classifies the supply gas concentration conditions into three conditions based on the magnitude relationship between the specific gas concentration (hydrogen concentration) Cin in the supply gas and the gas concentration Crq (hydrogen concentration 20%) specified by the user for the product gas. The control device 50 then determines a control mode for operating the regulator valves 20, 21, 22, and 23 for each condition, and controls the specific gas concentration in the product gas to a constant concentration specified by the user.

[0030] Next, a method for controlling the hydrogen concentration of the product gas to 20% when the hydrogen concentration Cin in the supply gas supplied to the gas separation system 1 varies between 5% and 40% will be described. In this embodiment, the values ​​of Cin, Crq, and ΔC shown in Figure 2 are Cin = 5% to 40%, Crq = 20%, and ΔC = 2.5%, respectively.

[0031] First, under the condition that the hydrogen concentration Cin in the supply gas satisfies Cin<Crq-ΔC (Cin<17.5%), the control device 50 calculates the valve openings of the control valves 20, 21, 22, and 23 in control mode A in Fig. 2. In control mode A, in order to maximize the flow rate of the product gas, the control device 50 fully closes the control valve 23 (fourth control valve) and sends the entire amount of permeable gas passing through the control valve 22 (second control valve) to the product gas pipe 18.

[0032] Furthermore, based on a hydrogen concentration meter C2 installed in the product gas pipe 18, the control device 50 adjusts the aperture of the control valve 21 (first control valve) to send a portion of the retentate gas to the product gas pipe 18 so that the hydrogen concentration of the product gas is 20%. That is, the control device 50 controls the hydrogen concentration of the product gas based on the hydrogen concentration meter C2 using the control valve 21. The remaining retentate gas is returned to the mother pipe through the retentate gas return pipe 13. Note that when the pressure downstream of the control valve 20 (third control valve) is lower than that of the mother pipe, the compressor 40 is started, and the pressure downstream of the control valve 20 is increased and returned to the mother pipe.

[0033] As described above, the flow rate of each gas permeating through the separation membrane 30 is calculated by multiplying the permeation rate of each gas and the partial pressure difference between the retentate side 31 and the permeate side 32 by the membrane area of ​​the separation membrane. The permeation rate of each gas and the membrane area of ​​the separation membrane are values ​​(fixed values) specific to the separation membrane module 10. Therefore, the flow rate permeating through the separation membrane 30 can be adjusted by adjusting the aperture of the control valve 21 and the control valve 22 (second control valve) to set the partial pressure difference between the retentate side 31 and the permeate side 32 to an appropriate value.

[0034] Specifically, the aperture of the control valve 20 is adjusted based on a pressure gauge P1 (first pressure gauge) installed in the retentate gas pipe 12 so that the pressure on the retentate side 31 becomes an appropriate value, and the aperture of the control valve 22 is adjusted based on a pressure gauge P2 (second pressure gauge) installed in the permeate gas pipe 15 so that the pressure on the permeate side 32 becomes an appropriate value. That is, the control valve 20 controls the pressure on the retentate side 31 based on the pressure gauge P1, and the control valve 22 controls the pressure on the permeate side 32 based on the pressure gauge P2. In this embodiment, the control valve 20 controls the pressure on the retentate side 31 to be 0.8 MPaG, and the control valve 22 controls the pressure on the permeate side 32 to be 0.1 MPaG.

[0035] Next, under the condition that the hydrogen concentration Cin in the supply gas satisfies Crq-ΔC≦Cin≦Crq+ΔC (17.5%≦Cin≦22.5%), the control device 50 calculates the valve openings of the control valves 20, 21, 22, and 23 in control mode B in FIG. 2. In control mode B, the hydrogen concentration of the supply gas is within the allowable gas concentration fluctuation range (=2.5%) for the product gas, based on the gas concentration (=20%) specified by the user. Therefore, the retentate gas and permeate gas separated by the separation membrane module 10 may be entirely mixed and supplied as the product gas.

[0036] At this time, the retentate-side control valve 20 and the permeate-side control valve 23 are fully closed, so the gas flow rate returned to the mother pipe becomes zero. In addition, control valve 21 controls the pressure on the retentate side 31 based on pressure gauge P1, and control valve 22 controls the pressure on the permeate side 32 based on pressure gauge P2.

[0037] Next, under the condition that the hydrogen concentration Cin in the supply gas satisfies Cin > Crq + ΔC (Cin > 22.5%), the control device 50 calculates the valve apertures of the control valves 20, 21, 22, and 23 in control mode C in Fig. 2. In control mode C, in order to maximize the flow rate of the product gas, the control device 50 fully closes the control valve 20 and sends all of the retentate gas passing through the control valve 21 to the product gas pipe 18. Furthermore, based on the hydrogen concentration meter C2, the control device 50 adjusts the aperture of the control valve 22 to send a portion of the permeate gas to the product gas pipe 18 so that the hydrogen concentration of the product gas is 20%.

[0038] That is, control valve 22 controls the hydrogen concentration of the product gas based on hydrogen concentration meter C2. The remaining permeate gas is returned to the mother pipe through permeate gas return pipe 17. When the pressure downstream of control valve 23 is lower than that of the mother pipe, compressor 41 is started, and the pressure downstream of control valve 23 is increased and returned to the mother pipe. Furthermore, control valve 21 controls the pressure on retentate side 31 based on pressure gauge P1, and control valve 23 controls the pressure on permeate side 32 based on pressure gauge P2.

[0039] In order to control the pressure on the retentate side 31 using the control valve 20 (control mode A) or the control valve 21 (control modes B and C), the control device 50 calculates the valve opening degree of the control valve 20 or the control valve 21 from the deviation between the pressure measurement value on the retentate side 31 received from the pressure gauge P1 and the pressure set value on the retentate side 31, for example, using PID control, which is a well-known technique.

[0040] Similarly, in order to control the hydrogen concentration of the product gas using the control valve 21 (control mode A) or the control valve 22 (control mode C), the control device 50 uses PID control to calculate the valve opening degree of the control valve 21 or the control valve 22 from the deviation between the measured hydrogen concentration value of the product gas received from the hydrogen concentration meter C2 and the set hydrogen concentration value of the unproduct gas.

[0041] Furthermore, in order to control the pressure on the permeate side 32 with the control valve 22 (control modes A and B) or the control valve 23 (control mode C), the control device 50 uses PID control to calculate the valve aperture of the control valve 22 or the control valve 23 from the deviation between the pressure measurement value on the permeate side 32 received from the pressure gauge P2 and the pressure set value on the permeate side 32. In this embodiment, the valve aperture of the control valve is calculated using PID control, but the control device 50 may also calculate the valve aperture of the control valve using other control methods such as model predictive control or AI control.

[0042] Figure 3 is a diagram showing an example of the apertures of the control valves 20, 21, 22, and 23 when the hydrogen concentration Cin in the gas supplied to the gas separation system 1 varies between 5% and 40%. In Figure 3, the aperture of each control valve is shown by a different line type, and the number of each line corresponds to the number of the control valve in Figure 1. That is, the aperture of the control valve 20 is shown by a solid line, the aperture of the control valve 21 by a fine dashed line, the aperture of the control valve 22 by a coarse dashed line, and the aperture of the control valve 23 by a dashed line.

[0043] When the supply gas hydrogen concentration Cin is less than 17.5%, the control valve 23 is fully closed to maximize the product gas flow rate. As the supply gas hydrogen concentration Cin increases, the hydrogen partial pressure on the retentate side 31 increases, and the amount of hydrogen permeating through the separation membrane 30 increases, increasing the hydrogen concentration on the permeate side and the permeate gas flow rate.

[0044] 3 , the controller 50 increases the aperture of the control valve 22 as the feed gas hydrogen concentration Cin increases in order to maintain a constant pressure on the permeate side 32. Furthermore, in order to maintain the hydrogen concentration of the product gas at 20%, the controller 50 increases the aperture of the control valve 21 to increase the retentate gas flow rate and send it to the product gas pipe 18. Since an increase in the amount of retentate gas sent to the product gas pipe 18 reduces the retentate gas flow rate returned to the mother pipe, the controller 50 decreases the aperture of the control valve 20 in order to maintain a constant pressure on the retentate side 31.

[0045] When the hydrogen concentration Cin in the feed gas is 17.5%≦Cin≦22.5%, the controller 50 fully closes the retentate-side control valve 20 and the permeate-side control valve 23 to set the gas flow rate returned to the mother pipe to zero. As the hydrogen concentration Cin in the feed gas increases, the hydrogen partial pressure on the retentate side 31 increases, and the amount of hydrogen permeating through the separation membrane 30 increases, increasing the hydrogen concentration on the permeate side. This increases the permeate gas flow rate and decreases the retentate gas flow rate.

[0046] Furthermore, in order to maintain a constant pressure on the permeate side 32, the controller 50 increases the aperture of the control valve 22 as the hydrogen concentration Cin in the feed gas increases. Furthermore, in order to maintain a constant pressure on the retentate side 31, the controller 50 decreases the aperture of the control valve 21 as the hydrogen concentration Cin in the feed gas increases.

[0047] When the hydrogen concentration Cin in the feed gas is greater than 22.5%, the control device 50 fully closes the control valve 20 to maximize the flow rate of the product gas. As the hydrogen concentration Cin in the feed gas increases, the hydrogen partial pressure on the retentate side 31 increases, increasing the amount of hydrogen permeating through the separation membrane 30 and increasing the hydrogen concentration on the permeate side. This increases the permeate gas flow rate and decreases the retentate gas flow rate.

[0048] Furthermore, in order to maintain a constant pressure on the non-permeated side 31, the controller 50 reduces the aperture of the control valve 21 as the hydrogen concentration Cin in the feed gas increases. Furthermore, in order to control the hydrogen concentration of the product gas to 20%, the controller 50 reduces the aperture of the control valve 22 to decrease the permeate gas flow rate and send it to the product gas piping 18. Since the reduction in the amount of permeate gas sent to the product gas piping 18 increases the permeate gas flow rate returned to the mother pipe, the controller 50 increases the aperture of the control valve 23 in order to maintain a constant pressure on the permeate side 32.

[0049] 3, even if the hydrogen concentration of the supply gas fluctuates around the concentration specified by the user, the valve openings of the regulator valves 20, 21, 22, and 23 can be continuously changed to stably supply the product gas at the concentration specified by the user. Furthermore, by controlling the regulator valves so that the controlled objects of the three control modes A, B, and C do not overlap, interference between the control modes does not occur, and therefore the hydrogen concentration can be stably controlled.

[0050] As described above, according to this embodiment, even when the concentration of a specific gas in the gas grid fluctuates around the concentration specified by the user, the product gas can be stably supplied at the concentration specified by the user without discontinuously switching the valves installed in the piping.

[0051] <Second Embodiment> Fig. 4 is a schematic diagram of a gas separation system 101 according to a second embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals as in Fig. 1, and redundant explanations will be omitted.

[0052] The difference between this embodiment and the first embodiment is that the gas separation system 101 has a control valve 124 (fifth control valve), a compressor 142, a control device 150, a control signal transmission device 151, a buffer tank 160, and a flow meter F2 instead of the control device 50 and control signal transmission device 51 that the gas separation system 1 shown in Figure 1 has.

[0053] A compressor 142, a buffer tank 160, a control valve 124, and a flow meter F2 are installed downstream of the hydrogen concentration meter C2 in the product gas pipe 18. The product gas supplied from the retentate gas supply pipe 14 and the permeate gas supply pipe 16 to the product gas pipe 18 is pressurized by the compressor 142 and stored in the buffer tank 160.

[0054] In addition to the functions of control device 50, control device 150 has the function of receiving the product gas flow rate from flow meter F2, calculating the valve opening of adjustment valve 124 so that the product gas flow rate matches the flow rate specified by the user, and generating a control signal. In order to control the product gas flow rate with adjustment valve 124, control device 150 calculates the valve opening of adjustment valve 124 from the deviation between the product gas flow rate measurement value received from flow meter F2 and the flow rate set value, for example, using PID control, which is a well-known technique. Control signal transmitter 151 has the function of transmitting a control signal from control device 150 to adjustment valve 124, in addition to the functions of control signal transmitter 51.

[0055] The gas separation system 101 of this embodiment can supply product gas at a flow rate specified by the user by controlling the product gas flow rate with the control valve 124. Because the control target of the control valve 124 is the product gas flow rate, there is no overlap with the control targets of the control valves 20, 21, 22, and 23, such as the pressure on the retentate side 31, the pressure on the permeate side 32, and the product gas hydrogen concentration, and no interference occurs between the controls. Therefore, the gas separation system 101 of this embodiment can more stably control the product gas hydrogen concentration and flow rate.

[0056] Furthermore, since the product gas supplied from the retentate gas supply pipe 14 and the permeate gas supply pipe 16 to the product gas pipe 18 is temporarily stored in the buffer tank 160, the gas separation system 101 of this embodiment can further reduce the fluctuation range of the hydrogen concentration of the product gas relative to fluctuations in the hydrogen concentration of the supply gas, compared to the first embodiment.

[0057] As described above, in addition to the effects obtained in the first embodiment, the present embodiment can supply product gas at a flow rate specified by the user by controlling the product gas flow rate with the control valve 124. Furthermore, even when the concentration of a specific gas in the gas grid fluctuates, the gas separation system 101 of the present embodiment can more stably supply product gas at the concentration specified by the user.

[0058] <Third Embodiment> Fig. 5 is a schematic diagram of a gas separation system 201 according to a third embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals as in Fig. 1, and redundant explanations will be omitted.

[0059] The difference between this embodiment and the first embodiment is that the gas separation system 201 has a supply gas branch pipe 219, a control valve 225 (sixth control valve), a control device 250, and a control signal transmission device 251 instead of a control device 50 and a control signal transmission device 51.

[0060] The gas separation system 201 of this embodiment is provided with a supply gas branch pipe 219 branched from the supply gas pipe 11, and supplies a part of the supply gas as a dilution gas to the permeation side 32 of the separation membrane module 10. The supply gas branch pipe 219 is provided with a control valve 225 for adjusting the flow rate of the dilution gas.

[0061] In addition to the functions of the control device 50, the control device 250 has a function of calculating the valve opening degree of the adjustment valve 225 and generating a control signal. In addition to the functions of the control signal transmission device 51, the control signal transmission device 251 has a function of sending a control signal from the control device 250 to the adjustment valve 225.

[0062] When the gas partial pressure difference between the retentate side 31 and the permeate side 32 is large, the flow rate of gas permeating through the separation membrane 30 increases. The gas separation system 201 of this embodiment supplies a dilution gas with a low hydrogen concentration to the permeate side 32, which has permeated through the separation membrane 30 and has a high hydrogen concentration, to lower the hydrogen concentration on the permeate side 32 in the separation membrane module 10. In this way, the gas separation system 201 increases the hydrogen gas partial pressure difference between the retentate side 31 and the permeate side 32, thereby increasing the amount of hydrogen permeating through the separation membrane 30.

[0063] When the hydrogen concentration in the supply gas is lower than the concentration specified by the user, supplying a dilution gas to the permeation side 32 increases the amount of hydrogen permeating the separation membrane 30, improving the hydrogen recovery rate. That is, the proportion of hydrogen recovered as product gas relative to the amount of hydrogen contained in the supply gas increases. In other words, the lower the hydrogen concentration in the supply gas, the greater the proportion of hydrogen recovery rate achieved by supplying a dilution gas.

[0064] As a result, when the hydrogen concentration in the supply gas is lower than the concentration specified by the user, the control device 250 increases the hydrogen concentration in the supply gas and reduces the valve opening of the control valve 225. Furthermore, when the hydrogen concentration in the supply gas is higher than the concentration specified by the user, the control device 250 continuously adjusts the valve opening so that the control valve 225 is fully closed. Alternatively, the control device 250 may maintain the valve opening of the control valve 225 at a constant opening.

[0065] In this embodiment, by supplying a portion of the supply gas as a dilution gas to the permeation side 32 of the separation membrane module 10, the amount of hydrogen permeating the separation membrane 30 increases, and the hydrogen recovery rate improves under conditions where the hydrogen concentration in the supply gas is lower than the concentration specified by the user. Furthermore, under conditions where the hydrogen concentration in the supply gas is lower than the concentration specified by the user, the control device 250 either decreases the valve opening of the control valve 225 as the hydrogen concentration in the supply gas increases, or sets the valve opening of the control valve 225 to a constant opening.

[0066] Furthermore, when the hydrogen concentration in the supply gas is higher than the concentration specified by the user, the control device 250 continuously adjusts the valve opening so as to fully close the control valve 225. As a result, the gas separation system 201 of this embodiment does not overlap with the pressure on the retentate side 31, the pressure on the permeate side 32, and the product gas hydrogen concentration, which are controlled by the control valves 20, 21, 22, and 23, and no interference occurs between the controls, so the product gas hydrogen concentration can be stably controlled.

[0067] As described above, in this embodiment, in addition to the effects obtained in the first embodiment, by supplying a portion of the supply gas as a dilution gas to the permeation side 32 of the separation membrane module 10, it is possible to improve the hydrogen recovery rate under conditions where the hydrogen concentration in the supply gas is lower than the concentration specified by the user.

[0068] <Fourth embodiment> Fig. 6 is a schematic diagram of a gas separation system 301 according to a fourth embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals as in Fig. 1, and redundant explanations will be omitted.

[0069] This embodiment differs from the first embodiment in that the gas separation system 301 includes a separation membrane module 310 , a supply gas pipe 311 , a retentate gas pipe 312 , and a permeate gas pipe 315 .

[0070] The separation membrane module 310 of this embodiment is installed in parallel to the separation membrane module 10 used in the first embodiment, and a mixed gas from a supply gas pipe 311 branched from the supply gas pipe 11 is supplied to the separation membrane module 310. As with the separation membrane module 10, the interior of the separation membrane module 310 is divided into a non-permeated side 331 and a permeated side 332 by the separation membrane 330.

[0071] In this embodiment, a polymer membrane is used as the hydrogen separation membrane, but a ceramic or carbon-based hydrogen separation membrane may also be used. A retentate gas pipe 312 is disposed on the retentate side 331 of the separation membrane module 310, from which the retentate gas from the separation membrane module 310 is discharged and merges with the retentate gas pipe 12. Furthermore, a permeate gas pipe 315 is disposed on the permeate side 332 of the separation membrane module 310, from which the permeate gas from the separation membrane module 310 is discharged and merges with the permeate gas pipe 15.

[0072] In the gas separation system 301 of this embodiment, the separation membrane module 10 and the separation membrane module 310 are arranged in parallel, and the supply gas from the gas grid is branched and supplied to the separation membrane module 10 and the separation membrane module 310. This enables the gas separation system 301 to increase the flow rate of the product gas. For example, if the separation membrane module 10 and the separation membrane module 310 have the same gas permeation rate and membrane area, the gas separation system 301 of this embodiment can double the flow rate of the product gas compared to the gas separation system 1 of the first embodiment.

[0073] On the other hand, the placement conditions of the control valves 20, 21, 22, 23, pressure gauges P1, P2, and hydrogen concentration meters C1, C2 related to the concentration control described in the first embodiment are the same in both the first and present embodiments, and therefore, in this embodiment, as in the first embodiment, product gas can be stably supplied at the concentration specified by the user even if the hydrogen concentration of the supply gas fluctuates around the concentration specified by the user.

[0074] As described above, in addition to the effects obtained in the first embodiment, the flow rate of the product gas can be increased by arranging the separation membrane module 10 and the separation membrane module 310 in parallel. Note that, although the example of arranging two separation membrane modules in parallel has been described in the present embodiment, the number of separation membrane modules arranged in parallel may be three or more.

[0075] <Fifth Embodiment> Fig. 7 is a schematic diagram of a gas separation system 401 according to a fifth embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals as in Fig. 1, and redundant explanations will be omitted.

[0076] This embodiment differs from the first embodiment in that the gas separation system 401 includes a separation membrane module 410 , a retentate gas pipe 412 , and a permeate gas pipe 415 .

[0077] The separation membrane module 410 is disposed in series with the separation membrane module 10, and a mixed gas from a supply gas pipe 11 is supplied to the separation membrane module 410. As with the separation membrane module 10, the separation membrane module 410 is divided into a non-permeated side 431 and a permeated side 432 by the separation membrane 430.

[0078] In the gas separation system 401 of this embodiment, a polymer membrane is used as the hydrogen separation membrane, but a ceramic or carbon-based hydrogen separation membrane may also be used. A retentate gas pipe 412 is disposed on the retentate side 431 of the separation membrane module 410, which discharges the retentate gas from the separation membrane module 410 and supplies it to the separation membrane module 10. In addition, a permeate gas pipe 415 is disposed on the permeate side 432 of the separation membrane module 410, which discharges the permeate gas from the separation membrane module 410 and merges with the permeate gas pipe 15.

[0079] In the gas separation system 401 of this embodiment, by arranging the separation membrane module 10 and the separation membrane module 410 in series, the flow rate of the product gas can be increased, as in the gas separation system 301 of the fourth embodiment. For example, if the separation membrane module 10 and the separation membrane module 410 have the same gas permeation rate and membrane area, the gas separation system 401 of this embodiment can double the flow rate of the product gas compared to the gas separation system 1 of the first embodiment.

[0080] On the other hand, the placement conditions of the control valves 20, 21, 22, 23, pressure gauges P1, P2, and hydrogen concentration meters C1, C2 related to the concentration control described in the first embodiment are the same in both the first embodiment and this embodiment, so the gas separation system 401 of this embodiment, like the gas separation system 1 of the first embodiment, can stably supply product gas at the concentration specified by the user even if the hydrogen concentration of the supply gas fluctuates around the concentration specified by the user.

[0081] As described above, in this embodiment, by arranging the separation membrane module 10 and the separation membrane module 410 in series, the flow rate of the product gas can be increased in addition to the effects obtained in the first embodiment.

[0082] Although the present embodiment has been described as an example in which two separation membrane modules are arranged in series, the number of separation membrane modules arranged in series may be three or more. Furthermore, in combination with the fourth embodiment, a plurality of separation membrane modules may be arranged in a combination of parallel and series.

[0083] 8 is a schematic diagram of a gas separation system 501 according to a sixth embodiment. The same components as those in the first embodiment are denoted by the same reference numerals as in FIG. 1, and redundant explanations will be omitted.

[0084] This embodiment differs from the first embodiment in that the gas separation system 501 of this embodiment has a control device 550 and a visualization device 570 instead of the control device 50. In addition to the functions of the control device 50, the control device 550 has a function of sending a generated control signal to the visualization device 570.

[0085] The visualization device 570 is composed of a computer and a display device such as a liquid crystal display, plasma display, organic EL display, or cathode ray tube, and receives the control signal generated by the control device 550 as input and outputs the contents of the control signal to the display device.

[0086] 9 is a diagram showing an example of an image output to a display device by the visualization device 570 for the method of operating the regulator valve shown in FIG. 2 in the first embodiment. As shown in FIG. 9, concentration control information 571 and regulator valve information 572 are displayed on the display device of the visualization device 570.

[0087] The concentration control information 571 is data relating to the current concentration control, and is composed of the supply gas hydrogen concentration (Cin), the target product gas hydrogen concentration value (Crq), the allowable product gas hydrogen concentration fluctuation value (ΔC), the product gas hydrogen concentration, and the current value of the control mode.

[0088] The control valve information 572 is information relating to the current state of the control valves, and is data configured from the operation methods and current valve opening values ​​of the control valves 20, 21, 22, and 23. The concentration control information 571 shown in Fig. 9 indicates that the control device 550 is calculating the valve openings of the control valves in control mode A.

[0089] Correspondingly, the control valve information 572 indicates, in accordance with the contents shown in Figure 2, that the control valve 20 controls the pressure of the retentate side 31 based on the pressure gauge P1, the control valve 21 controls the product gas hydrogen concentration based on the hydrogen concentration meter C2, the control valve 22 controls the pressure of the permeate side 32 based on the pressure gauge P2, and the control valve 23 is in a fully closed state.

[0090] In the gas separation system 501 of this embodiment, the visualization device 570 displays concentration control information 571 and regulating valve information 572 on the display device, allowing the current concentration control information and regulating valve state to be confirmed.

[0091] As described above, in this embodiment, the visualization device 570 displays the concentration control information 571 and the adjustment valve information 572 on the display device, so that in addition to the effects obtained in the first embodiment, the current concentration control information and the adjustment valve status can be confirmed.

[0092] The above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the described configurations, but may be applied to other configurations as appropriate. Furthermore, some or all of the configurations and processes described in one embodiment may be combined with other embodiments.

[0093] 1 to 8, only control lines and information lines that are considered necessary for explanation are shown, and not all control lines and information lines in the product are necessarily shown. In reality, it can be assumed that almost all components are interconnected.

[0094] 1, 101, 201, 301, 401, 501: Gas separation system (hydrogen separation system) 10, 310, 410, 510: Separation membrane module 11, 311: Supply gas piping 12, 312, 412: Retent gas piping 13: Retent gas return piping 14: Retent gas supply piping 15, 315, 415: Permeate gas piping 16: Permeate gas supply piping 17: Permeate gas return piping 18: Product gas piping 219: Supply gas branch piping 20, 21, 22, 23, 124, 225: Control valve 30, 330, 430: Separation membrane 31, 331, 431: Retent side 32, 332, 432: Permeate side 40, 41, 142: Compressor 50, 150, 250, 550: Control device 51, 151, 251: Control signal transmitter 160: Buffer tank 570: Visualization device 571: Concentration control information 572: Control valve information C1: Hydrogen concentration meter (first specified gas concentration meter, first hydrogen concentration meter) C2: Hydrogen concentration meter (second specified gas concentration meter, second hydrogen concentration meter) P1: Pressure meter (first pressure meter) P2: Pressure meter (second pressure meter) F2: Flow meter

Claims

1. A gas separation system that remixes retentate gas and permeate gas discharged from a separation membrane module to control the concentration of a specific gas to a constant level, comprising: a retentate gas pipe having a first control valve that extracts the retentate gas from the retentate side of the separation membrane module; and a permeate gas pipe having a second control valve that extracts the permeate gas from the permeate side of the separation membrane module, wherein a plurality of control modes are set based on the magnitude relationship between the concentration of the retentate gas supplied to the retentate side of the separation membrane module and the specific gas concentration of the target product gas, and the valve opening degree of the first control valve and the second control valve is adjusted for each control mode.

2. The gas separation system according to claim 1, comprising: a product gas pipe where the retentate gas pipe and the permeate gas pipe join and connect downstream of the first control valve and the second control valve; a first specified gas concentration meter that measures the gas concentration of the supply gas; a first pressure gauge that measures the pressure on the retentate side of the separation membrane module; a second pressure gauge that measures the pressure on the permeate side of the separation membrane module; a second specified gas concentration meter that measures the gas concentration in the product gas pipe; and a control device that calculates and controls the valve openings of the first control valve and the second control valve based on information on measurement values from the first specified gas concentration meter, the first pressure gauge, the second pressure gauge, and the second specified gas concentration meter.

3. The gas separation system according to claim 2, further comprising: a retentate gas return pipe branching off from the retentate gas pipe upstream of the first control valve and having a third control valve; and a permeate gas return pipe branching off from the permeate gas pipe upstream of the second control valve and having a fourth control valve, wherein the control device controls the valve openings of the third control valve and the fourth control valve based on information on measurement values from the first specified gas concentration meter, the first pressure gauge, the second pressure gauge, and the second specified gas concentration meter.

4. The gas separation system according to claim 3, wherein the control device classifies the specific gas concentration conditions of the supply gas into three conditions based on the magnitude relationship between the specific gas concentration of the supply gas and the specific gas concentration of the target product gas, and determines a control mode for operating the first control valve, the second control valve, the third control valve, and the fourth control valve for each of the three conditions to calculate the valve opening degree.

5. The gas separation system described in claim 4, further comprising, downstream of the second specified gas concentration meter, a compressor for pressurizing the product gas, a buffer tank for storing the product gas, a fifth control valve, and a flow meter for measuring the product gas flow rate, and the control device calculates the valve opening of the fifth control valve based on the measurement value information of the flow meter, generates a control signal, and controls the valve opening of the fifth control valve.

6. The gas separation system according to claim 5, further comprising a supply gas branch pipe having a sixth control valve that supplies a portion of the supply gas to the permeation side of the separation membrane module, and wherein the control device controls the valve opening of the sixth control valve to a constant value.

7. The gas separation system described in claim 6, wherein the control device controls the sixth control valve so that when the concentration of the specific gas in the supply gas is lower than the concentration of the specific gas in the target product gas, the opening of the sixth control valve is reduced when the concentration of the specific gas in the supply gas increases, and the opening of the sixth control valve is increased when the concentration of the specific gas decreases, and the opening of the sixth control valve is set to zero when the concentration of the specific gas in the supply gas is equal to or higher than the concentration of the specific gas in the target product gas.

8. The gas separation system according to any one of claims 1 to 7, comprising two or more separation membrane modules installed in parallel, a retentate gas pipe through which the retentate gas is taken out from each of the retentate sides of the two or more separation membrane modules and merges with the retentate gas pipe, and a permeate gas pipe through which the permeate gas is taken out from each of the permeate sides of the two or more separation membrane modules and merges with the permeate gas pipe.

9. The gas separation system according to any one of claims 1 to 7, comprising two or more separation membrane modules installed in series, a retentate gas pipe that removes the retentate gas from the retentate side of the upstream separation membrane module and supplies it to the retentate side of the downstream separation membrane module, and a permeate gas pipe that removes the permeate gas from the permeate side of the upstream separation membrane module and joins the permeate gas pipe on the downstream side.

10. A gas separation system according to any one of claims 1 to 7, further comprising a visualization device that receives the control signal generated by the control device as input and outputs the contents of the control signal to a display device.

11. A concentration control method for controlling a specific gas concentration to a constant level by remixing retentate gas and permeate gas discharged from a separation membrane module, comprising the steps of: withdrawing the retentate gas from the separation membrane module through a retentate gas pipe having a first control valve; withdrawing the permeate gas from the separation membrane module through a permeate gas pipe having a second control valve; and setting a plurality of control modes based on the magnitude relationship between the concentration of the retentate gas supplied to the retentate side of the separation membrane module and the specific gas concentration of the target product gas, and adjusting the valve opening of the first control valve and the second control valve for each control mode.

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