Membrane separation system and method for evaluating deterioration of separation membrane

Abstract

To provide a membrane separation system and an evaluation method for degradation of a separation membrane, enabling the degradation state of the separation membrane to be inexpensively evaluated.SOLUTION: A membrane separation system comprises: a membrane separation device (10) which has a separation membrane (12); a multicomponent gas supply path (20) which supplies the multicomponent gas to the membrane separation device (10); a residual gas discharge path (30) which discharges the residual gas that flows out without passing through the separation membrane (12); a transmission gas discharge path (40) which discharges the transmission gas that transmits the separation membrane (12) and flows out; a residual gas flow meter (31) which measures a flow volume F1 of the residual gas discharge path (30); a transmission gas flow meter (41) which measures a flow rate F2 of the transmission gas discharge path (40); and a calculation control device (50). The calculation control device (50) obtains a ratio Rm of the flow rate F1 to the flow rate F2, and compares the obtained ratio Rm with a preset ratio Rk of the flow rate F1 to the flow rate F2 to thereby evaluate the degradation state of the separation membrane (12).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a membrane separation system and a method for evaluating deterioration of a separation membrane. [Background technology]

[0002] Membrane separation devices are a means for separating a multi-component gas into individual components. Membrane separation devices are a separation means that utilizes the fact that components permeate a separation membrane at different speeds, and are used, for example, to separate and recover methane from biogas. When a membrane separation device is used, the gas after separation is analyzed to confirm whether a gas of a desired purity has been obtained (Patent Documents 1 and 2). When gas of the target purity is no longer obtained, it is determined that the separation membrane has deteriorated, and measures such as replacing the separation membrane are taken. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2016-505354 [Patent Document 2] JP 2005-23211 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, as in Patent Documents 1 and 2, a gas concentration meter must be installed to analyze the gas after separation. Gas analysis is usually required at the inlet side of the membrane separation device as well, so gas concentration meters must be installed at three locations, including the two outlet locations. Although it depends on the type of gas to be analyzed, concentration meters are generally expensive. In addition, maintenance is also required to maintain the analytical accuracy. As a result, the costs of installing and maintaining the concentration meters are high. The present invention has been made in view of the above circumstances, and provides a membrane separation system and a method for evaluating deterioration of a separation membrane, which can inexpensively evaluate the deterioration state of a separation membrane. [Means for solving the problem]

[0005] As a means for solving the above problem, a membrane separation system (1) according to claim 1 includes a membrane separation device (10) having a separation membrane (12), a multicomponent gas supply path (20) for supplying a multicomponent gas containing at least two kinds of components to the membrane separation device (10), a residual gas discharge path (30) through which a residual gas that has flowed out of the membrane separation device (10) without permeating through the separation membrane (12) flows out, a permeated gas discharge path (40) through which a permeated gas that has flowed out of the membrane separation device (10) after permeating through the separation membrane (12) flows out, a residual gas flowmeter (31) provided in the residual gas discharge path (30) for measuring a flow rate F1 in the residual gas discharge path (30), a permeated gas flowmeter (41) provided in the permeated gas discharge path (40) for measuring a flow rate F2 in the permeated gas discharge path (40), and a gas supply system for supplying a gas containing at least two components to the membrane separation device (10), the residual gas flowmeter (31) and the residual gas flowmeter (41) and an arithmetic and control device (50) to which the signals F1 and F2 are input, the arithmetic and control device (50) calculating a ratio Rm between the flow rates F1 and F2 based on the input signals, and comparing the calculated ratio Rm with a preset ratio Rk between the flow rates F1 and F2, thereby evaluating a deterioration state of the separation membrane (12). According to this configuration, the deterioration state of the separation membrane (12) is evaluated based on a signal obtained from an inexpensive flow meter instead of an expensive concentration meter, thereby reducing costs.

[0006] The membrane separation system (1) described in claim 2 includes a membrane separation device (10) having a separation membrane (12), a multicomponent gas supply line (20) for supplying a multicomponent gas containing at least two kinds of components to the membrane separation device (10), a residual gas discharge line (30) through which a residual gas that has flowed out of the membrane separation device (10) without permeating the separation membrane (12) flows out, a permeated gas discharge line (40) through which a permeated gas that has flowed out of the membrane separation device (10) after permeating the separation membrane (12) flows out, and a gas supply line (20) for supplying a multicomponent gas to the membrane separation device (10). a multicomponent gas flow meter (22) provided in the residual gas discharge path (30) for measuring a flow rate F0 (where F0=F1+F2) of the multicomponent gas supply path (20), a residual gas flow meter (31) provided in the residual gas discharge path (30) for measuring a flow rate F1 of the residual gas discharge path (30), or a permeable gas flow meter (41) provided in the permeable gas discharge path (40) for measuring a flow rate F2 of the permeable gas discharge path (40), and (41) and an arithmetic and control device (50) to which a signal of any one of the above is input, wherein the arithmetic and control device (50) calculates a ratio Rm of the flow rate F1 to the flow rate F2 based on the input signal, and compares the calculated ratio Rm with a preset ratio Rk of the flow rate F1 to the flow rate F2, thereby evaluating a deterioration state of the separation membrane (12).

[0007] According to this configuration, the deterioration state of the separation membrane (12) is evaluated based on a signal obtained from an inexpensive flow meter instead of an expensive concentration meter, thereby reducing costs. In the membrane separation system (1) recited in claim 2, when the system includes a residual gas flowmeter (31) but does not include a permeable gas flowmeter (41), the flow rate F2 is calculated from the signals of the multicomponent gas flowmeter (22) and the residual gas flowmeter (31). In addition, when the system does not include the residual gas flowmeter (31) but includes a permeable gas flowmeter (41), the flow rate F1 is calculated from the signals of the multicomponent gas flowmeter (22) and the permeable gas flowmeter (41).

[0008] In the membrane separation system (1) recited in claim 3, the arithmetic and control device (50) outputs an alarm when the ratio Rm and the ratio Rk deviate from each other by a value equal to or greater than a predetermined condition. According to this configuration, a user of the membrane separation system (1) can immediately know the deterioration of the membrane separation system (1).

[0009] The membrane separation system (1) recited in claim 4 further includes a pressure gauge (15) for measuring a supply pressure of a multi-component gas supplied to the membrane separation device (10), and the arithmetic and control device (50) controls the membrane separation system (1) so that the supply pressure is within a predetermined range. According to this configuration, fluctuations in the ratio Rm due to fluctuations in the supply pressure can be suppressed, and therefore the accuracy of evaluating the deterioration state of the separation membrane (12) is improved.

[0010] The membrane separation system (1) recited in claim 5 further includes a concentration meter (21) that analyzes the multi-component gas supplied to the membrane separation device (10), and the arithmetic and control device (50) resets the ratio Rk based on a signal input from the concentration meter (21). According to this configuration, the ratio Rk can be appropriately set based on the composition of the supplied multicomponent gas, thereby improving the accuracy of evaluation of the deterioration state of the separation membrane (12).

[0011] In the membrane separation system (1) described in claim 6, the multi-component gas contains two components, methane and carbon dioxide, as main components, and the concentration meter (21) is a methane concentration meter. According to this configuration, it is possible to inexpensively configure a membrane separation device (10) that separates and purifies methane from biogas that contains two main components, methane and carbon dioxide.

[0012] The method for evaluating deterioration of a separation membrane recited in claim 7 is a method for evaluating deterioration of a separation membrane (12) in a membrane separation device (10) that separates a multicomponent gas containing at least two types of components, in which, when the multicomponent gas is supplied to a membrane separation device (10) having the separation membrane (12), a ratio Rm of a flow rate F1 of a residual gas flowing out of the membrane separation device (10) without permeating the separation membrane (12) to a flow rate F2 of a permeated gas flowing out of the membrane separation device (10) after permeating the separation membrane (12) is calculated, and the calculated ratio Rm is compared with a preset ratio Rk of the flow rates F1 and F2, thereby evaluating a deterioration state of the separation membrane (12). According to this configuration, the deterioration state of the separation membrane (12) is evaluated using an inexpensive flow meter instead of an expensive concentration meter, thereby reducing costs.

[0013] In the method for evaluating deterioration of a separation membrane according to an eighth aspect of the present invention, the multi-component gas contains two components, namely, methane and carbon dioxide, as main components. According to this configuration, it is possible to inexpensively evaluate the deterioration of a separation membrane when methane is purified from biogas containing two main components, methane and carbon dioxide, by the membrane separation device (10). Effect of the Invention

[0014] According to the membrane separation system and the method for evaluating deterioration of a separation membrane of the present invention, the deterioration state of a separation membrane can be evaluated inexpensively. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic configuration diagram of a membrane separation system 1 according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] FIG. 1 shows a schematic configuration of a membrane separation system 1 according to one embodiment of the present invention. The membrane separation system 1 comprises a membrane separation device 10 having a separation membrane 12, a multicomponent gas supply path 20 that supplies a multicomponent gas to the membrane separation device 10, a residual gas discharge path 30 through which residual gas that flows out of the membrane separation device 10 without permeating the separation membrane 12 flows out, a permeated gas discharge path 40 through which permeated gas that flows out of the membrane separation device 10 after permeating the separation membrane 12 flows out, and an arithmetic and control device 50.

[0017] The membrane separation apparatus 10 is provided with a pressure gauge 15 for measuring the inlet pressure of the supply side space 13 (supply pressure of the multi-component gas). In the multi-component gas supply passage 20, a concentration meter 21, a multi-component gas flow meter 22, a compressor 23, and a cooler 24 are provided in this order from the upstream side. The residual gas discharge passage 30 is provided with a residual gas flow meter 31, and the permeable gas discharge passage 40 is provided with a permeable gas flow meter 41. Depending on the type of flowmeter, the flowmeter may be affected by changes in gas density due to temperature. In such cases, it is preferable to use a thermometer to perform temperature compensation.

[0018] The multi-component gas to be treated by the membrane separation system 1 contains at least two kinds of components. Although there is no particular limitation on the specific components, a gas containing two components, methane and carbon dioxide, as main components is preferable. Alternatively, the gas may contain two components, methane and hydrogen, as main components, or carbon monoxide and hydrogen, as main components. Here, containing two components as main components means that the total ratio of the two components to the entire multi-component gas is 50 volume % or more.

[0019] Examples of gases that contain the two main components, methane and carbon dioxide, include biogas and natural gas. Biogas is a gas obtained through the methane fermentation of waste materials such as food waste from homes, cafeterias, restaurants and hotels, livestock manure from farms and pig farms, and food waste from food factories.

[0020] Biogas is produced when organic matter in waste is decomposed by anaerobic microorganisms, and is mostly composed of methane and carbon dioxide, and also contains moisture due to the fermentation atmosphere. The ratio of methane to carbon dioxide depends on the type of waste and fermentation conditions, but as an example, the proportion of methane is about 60% by volume, and the remaining 40% by volume is carbon dioxide. Therefore, in order to obtain high-purity methane that can be used as fuel for engines and boilers, it is necessary to remove the carbon dioxide and purify it.

[0021] The membrane separation device 10 is configured to have a separation membrane 12 in a casing 11, and the casing 11 is divided into a supply side space 13 and a permeation side space 14 by the separation membrane 12. A multicomponent gas supply path 20 is connected to the inlet of this supply side space 13 to supply a multicomponent gas, and a residual gas discharge path 30 is connected to the outlet of the supply side space 13 to allow gas that has not permeated the separation membrane 12 to flow out. A permeate gas exhaust path 40 is connected to the permeate side space 14, so that the gas that has permeated the separation membrane 12 can flow out.

[0022] 1, the separation membrane 12 is shown as a flat membrane for convenience of illustration, but the separation membrane 12 is not limited to a flat membrane. The separation membrane 12 is preferably a hollow tubular separation membrane because of its high separation efficiency, and more preferably a bundle of a plurality of hollow tubular separation membranes. The dimensions of the hollow tube are not particularly limited, but it is preferable that the tube outer diameter is 0.4 to 0.9 mm, the tube inner diameter is 0.2 to 0.6 mm, and the membrane thickness is 0.2 to 0.3 mm.

[0023] When the separation membrane 12 is a hollow tubular separation membrane or a bundle thereof, the inside of the hollow tube becomes the supply side space 13, the inlet of which is connected to a multicomponent gas supply channel 20, and the outlet of which is connected to a residual gas discharge channel 30. The outside of the hollow tube becomes the permeation side space 14, to which a permeation gas discharge channel 40 is connected. As the material for the separation membrane 12, known materials can be used depending on the components to be separated.

[0024] When the multi-component gas to be separated is biogas, there is no particular limitation on the material of the separation membrane, and either an inorganic membrane or an organic membrane may be used. Examples of inorganic membranes include composite membranes of a support such as ceramic and zeolite. Organic membranes include, for example, polysulfone, cellulose acetate, or polyamide, with polysulfone being particularly preferred. For membranes made of these materials, the membrane permeation rate of carbon dioxide is high and the membrane permeation rate of methane is low, so this difference can be utilized to separate and recover methane as residual gas.

[0025] Furthermore, membranes made of these materials have high membrane permeability not only for carbon dioxide but also for water vapor, so the water in the biogas can be separated from the methane along with the carbon dioxide. However, when the biogas contains a large amount of moisture, in order to reduce the load on the separation membrane 12, it is preferable to dehumidify the biogas before supplying it to the membrane separation device 10.

[0026] The concentration meter 21 provided in the multi-component gas supply passage 20 measures the concentration of one of at least two components contained in the multi-component gas to be separated. For example, when the multi-component gas is biogas, the concentration meter 21 is a methane concentration meter.

[0027] The compressor 23 provided in the multi-component gas supply path 20 makes the supply pressure of the multi-component gas supplied to the supply side space 13 higher than the pressure on the permeation side space 14 side (atmospheric pressure in this embodiment), thereby allowing a portion of the multi-component gas supplied to the supply side space 13 to permeate the separation membrane 12.

[0028] It is preferable that the arithmetic and control device 50 controls the compressor 23 based on the measurement value of the pressure gauge 15 so that the supply pressure of the multi-component gas is within a preset range. The higher the supply pressure, the higher the proportion of permeated gas and the lower the proportion of residual gas. For example, when the multi-component gas is biogas, the target gas, methane, is obtained as residual gas. The higher the supply pressure of the multi-component gas, the higher the proportion of permeable gas, so the yield of methane obtained as residual gas decreases, but the purity of methane in the residual gas increases. It is preferable that the supply pressure of the multi-component gas is controlled to be within a predetermined pressure range, since this suppresses fluctuations in the ratio Rm caused by fluctuations in the supply pressure, thereby improving the accuracy of the deterioration evaluation of the separation membrane 12.

[0029] Therefore, the supply pressure of the multi-component gas is set in consideration of the target yield and purity of the target gas. The purity of methane in the residual gas tends to be higher as the methane concentration in the biogas increases. Therefore, the supply pressure of the multi-component gas is set in consideration of the target gas concentration in the multi-component gas measured by concentration meter 21 and the desired yield and purity of the target gas.

[0030] The cooler 24 cools the multi-component gas, the temperature of which has been increased by being pressurized by the compressor 23, to a temperature at which the multi-component gas can be treated by the membrane separation device 10. The temperature of the multi-component gas supplied to the membrane separation device 10 depends on the material of the separation membrane 12, but is preferably 40 to 55°C, and more preferably 45 to 50°C.

[0031] When the temperature of the multicomponent gas supplied to the membrane separation apparatus 10 is equal to or lower than the preferred upper limit, it is easy to suppress deterioration of the separation membrane 12. When the temperature of the multicomponent gas supplied to the membrane separation apparatus 10 is equal to or higher than the preferred lower limit, if moisture is contained in the multicomponent gas, it is easy to pass the separation membrane 12 as water vapor. It is also easy to prevent a reduction in the effective area of ​​the separation membrane 12 due to condensation.

[0032] A multicomponent gas flow meter 22 provided in the multicomponent gas supply passage 20 measures the flow rate F0 of the multicomponent gas. A residual gas flow meter 31 provided in the residual gas discharge passage 30 measures the flow rate F1 of the residual gas. A permeable gas flow meter 41 provided in the permeable gas discharge passage 40 measures the flow rate F2 of the permeable gas.

[0033] The signal of the multicomponent gas flowmeter 22 (multicomponent gas flow rate F0), the signal of the residual gas flowmeter 31 (residual gas flow rate F1) and the signal of the permeable gas flowmeter 41 (permeable gas flow rate F2) are input to the arithmetic and control device 50. Here, the flow rate F0 of the multicomponent gas is equal to the sum of the flow rate F1 of the residual gas and the flow rate F2 of the permeable gas. Therefore, by confirming that the flow rate F0 measured by the multicomponent gas flowmeter 22 is the sum of the flow rates F1 and F2, the reliability of the signals from the residual gas flowmeter 31 and the permeable gas flowmeter 41 can be confirmed.

[0034] The arithmetic and control device 50 calculates the ratio Rm of the residual gas flow rate F1 to the permeable gas flow rate F2 based on the signals input from the residual gas flow rate meter 31 and the permeable gas flow rate meter 41, and compares the calculated ratio Rm with a preset ratio Rk to evaluate the deterioration state of the separation membrane 12. In other words, the separation membrane evaluation method of the present invention is carried out. In addition, when the downstream ends of both the residual gas discharge channel 30 and the permeate gas discharge channel 40 are open to the atmosphere, the ratio of the flow rates F1 and F2 is equal to the ratio of the volume of the residual gas to the volume of the permeate gas obtained by the membrane separation device 10.

[0035] In the present invention, the ratios Rm and Rk are not limited to the value [F1 / F2] obtained by dividing the flow rate F1 by the flow rate F2, and may be any value that substantially indicates [F1 / F2]. For example, the ratios Rm and Rk may be the value [F2 / F1] obtained by dividing the flow rate F2 by the flow rate F1, the value [F1 / (F1+F2)=F1 / F0] obtained by dividing the flow rate F1 by the sum of the flow rates F1 and F2, or the value [F2 / (F1+F2)=F2 / F0] obtained by dividing the flow rate F2 by the sum of the flow rates F1 and F2.

[0036] The inventors noticed that even if the composition, flow rate, and other conditions of the multi-component gas supplied to the supply side space 13 are constant, as the deterioration of the separation membrane 12 progresses, the pressure in the supply side space 13 of the separation membrane 12 fluctuates, causing the ratio Rm to fluctuate and deviate from the ratio Rk. The inventors then conceived that the deterioration state of separation membrane 12 can be evaluated by comparing ratio Rm with ratio Rk. When the difference between the ratios Rm and Rk is large, it can be evaluated that the deterioration is advanced, whereas when the difference is small or there is no difference, it can be evaluated that the degree of deterioration is small or that there is no deterioration.

[0037] There is no particular limitation on the evaluation index for the degree of deviation between the ratio Rm and the ratio Rk. For example, the evaluation index can be the degree to which the ratio of the two [Rm / Rk] or [Rk / Rm] is different from 1. Also, the evaluation index can be the degree to which the absolute value of the difference between the two [|Rm-Rk|] or the ratio of the absolute value of the difference between the two and the ratio Rk [|Rm-Rk| / Rk] has increased.

[0038] When the arithmetic and control device 50 determines, based on the evaluation index, that the ratio Rm and the ratio Rk have deviated beyond a predetermined condition (alarm condition), it can output an alarm to notify the operator of the deterioration of the separation membrane 12. As an alarm output means, one or more known means such as an alarm sound, an alarm display, or external transmission of an alarm signal can be appropriately adopted. The alarm conditions may be appropriately set based on the required quality of the residual gas or permeated gas, etc.

[0039] Note that the system may be configured to inform the operator that the condition has not yet reached the alarm condition but has come close to the alarm condition to some extent, thereby enabling the operator to predict when separation membrane 12 needs to be replaced. Furthermore, when the difference between the ratio Rm and the ratio Rk is not so large, the pressure in the supply side space 13 may be adjusted so that the ratio Rm approaches the ratio Rk.

[0040] Furthermore, when the calculation and control device 50 determines that the ratio Rm and the ratio Rk have deviated by more than a predetermined condition, instead of or in addition to outputting an alarm, it may take appropriate measures, such as stopping operation of the membrane separation system 1.

[0041] The ratio Rk can be set based on the required quality of the residual gas or permeate gas, the composition of the multi-component gas, and the like. For example, if the multi-component gas is biogas, the residual gas will be a methane-rich gas and the permeate gas will be a carbon dioxide-rich gas.

[0042] In this case, the larger the ratio Rk indicated by [F1 / F2], the higher the yield of residual gas containing a large amount of methane, but the lower the methane concentration of the residual gas. Therefore, the higher the desired purity of methane, the smaller the ratio Rk indicated by [F1 / F2] must be set. However, if you want to increase the yield even if the purity of methane is relatively low, you should set the ratio Rk indicated by [F1 / F2] to a larger value. Furthermore, when the residual gas is further purified by another membrane separation system 1, the ratio Rk may be set to a value that assumes a purity lower than the final required purity.

[0043] In addition, even if the ratio Rk is the same, the compositions of the residual gas and the permeated gas change depending on the composition of the multicomponent gas supplied. Therefore, it is preferable to adjust the ratio Rk according to the composition of the multicomponent gas. For example, when the multi-component gas is biogas, if the methane concentration of the supplied biogas is high, the methane concentration of the residual gas will be high even if the ratio Rk represented by [F1 / F2] is the same. Therefore, when the methane concentration of the supplied biogas is high, the ratio Rk represented by [F1 / F2] can be lowered to a certain degree compared to when the methane concentration of the supplied biogas is low.

[0044] In this embodiment, a signal from the concentration meter 21 is input to the arithmetic and control device 50. It is preferable that the arithmetic and control device 50 resets the ratio Rk based on the signal input from the concentration meter 21. Note that the ratio Rk can be reset constantly when the concentration meter 21 outputs the analysis results of the multi-component gas in real time, or whenever a result is output when the concentration meter 21 outputs the analysis results of the multi-component gas intermittently (for example, every hour). However, for the sake of system stability, it is preferable to reset the frequency at an appropriate time, such as once a day, at the time of regular maintenance, or when new waste material that will be used as biogas raw material is input.

[0045] The arithmetic and control device 50 may issue an alarm when it receives a signal from the concentration meter 21 indicating that the composition of the multi-component gas has significantly deviated from the initially assumed composition, in addition to resetting the ratio Rk based on the signal input from the concentration meter 21, or without resetting the ratio Rk. In addition, in this case, instead of or in addition to outputting an alarm, appropriate measures such as stopping the operation of the membrane separation system 1 may be taken.

[0046] The arithmetic and control device 50 controls the entire membrane separation system 1 so that the ratio Rm satisfies the set ratio Rk in the initial stage of operation. In particular, it controls the flow rates of the multicomponent gas flowing through the compressor 23 and the multicomponent gas supply path 20. As the pressure in the supply space 13 (the supply pressure of the multi-component gas) is increased by the compressor 23, the flow rate F1 of the residual gas flowing through the residual gas discharge path 30 decreases and the flow rate of the permeable gas flowing through the permeable gas discharge path 40 increases. Furthermore, as the flow rate of the multicomponent gas flowing through the multicomponent gas supply channel 20 is increased, the flow rate F1 of the residual gas flowing through the residual gas discharge channel 30 increases and the flow rate F2 of the permeable gas flowing through the permeable gas discharge channel 40 decreases.

[0047] Therefore, the arithmetic and control device 50 sets the operating conditions of the compressor 23, the flow rate of the multi-component gas, and the like so as to satisfy the ratio Rk, and controls the membrane separation system 1 under the set conditions. Then, while continuing to maintain the control conditions, the ratio Rm is obtained, and the deterioration state of the separation membrane 12 is evaluated by the above-mentioned method. Then, if necessary, a necessary response such as issuing an alarm can be taken.

[0048] In the above embodiment, the ratio Rm is calculated based on the signals from the residual gas flowmeter 31 and the permeable gas flowmeter 41, but the ratio Rm may be calculated based on the signals from the multicomponent gas flowmeter 22 and the residual gas flowmeter 31. In that case, the flow rate F2 of the permeable gas flowing through the permeable gas discharge path 40 can be calculated from the difference between the flow rate F0 measured by the multicomponent gas flowmeter 22 and the flow rate F1 measured by the residual gas flowmeter 31, so the permeable gas flowmeter 41 may be omitted.

[0049] Alternatively, the ratio Rm may be calculated based on signals from the multicomponent gas flowmeter 22 and the permeable gas flowmeter 41. In this case, the flow rate F1 of the residual gas flowing through the residual gas discharge path 30 can be calculated from the difference between the flow rate F0 measured by the multicomponent gas flowmeter 22 and the flow rate F2 measured by the permeable gas flowmeter 41, so the residual gas flowmeter 31 may be omitted. When the residual gas flow meter 31 and the permeation gas flow meter 41 are used, the multicomponent gas flow meter 22 may be omitted.

[0050] In the above embodiment, the outlet side of the supply side space 13 and the permeate side space 14 are at atmospheric pressure, but instead of providing the compressor 23 in the multicomponent gas supply path 20, suction pumps may be provided in the residual gas discharge path 30 and the permeate gas discharge path 40. In addition to providing the compressor 23 in the multicomponent gas supply path 20, suction pumps may be provided in the residual gas discharge path 30 and the permeate gas discharge path 40.

[0051] In the above embodiment, the cooler 24 is provided, but if the degree of pressurization by the compressor 23 is small and the temperature of the multi-component gas after passing through the compressor 23 is sufficiently low, the cooler 24 may be omitted. Furthermore, when a suction pump is provided in the residual gas discharge path 30 and the permeate gas discharge path 40 instead of providing a compressor 23 in the multicomponent gas supply path 20, a heater may be used instead of the cooler 24 to heat the mixture to a temperature appropriate for treatment in the membrane separation device 10.

[0052] Furthermore, if the composition of the multi-component gas is stable, the concentration meter 21 may be omitted. Furthermore, if the supply pressure of the multi-component gas is stable, the pressure gauge 15 may be omitted. When the residual gas discharge channel 30 and the permeate gas discharge channel 40 are provided with suction pumps, a pressure gauge may be provided in the permeate side space 14 .

[0053] In addition, the residual gas flowing out from the residual gas discharge channel 30 may be further treated in another membrane separation system. In this case, the permeate gas obtained by treating in the further membrane separation system may be returned to the multicomponent gas supply channel 20 of the membrane separation system 1. In addition, the permeate gas flowing out from the permeate gas discharge channel 40 may be further treated in another membrane separation system. In this case, the residual gas obtained by treating the permeate gas in the another membrane separation system may be returned to the multicomponent gas supply channel 20 of the membrane separation system 1. The membrane separation system and the method for evaluating deterioration of a separation membrane of the present invention can be modified in various ways without impairing the effects of the present invention. [Explanation of symbols]

[0054] 1. Membrane separation system 10 Membrane separation equipment 11 Casing 12 Separation membrane 13 Supply side space 14 Transmission side space 15 Pressure gauge 20 Multi-component gas supply line 21 Densitometer 22 Multi-component gas flowmeter 23 Compressor 24 Cooler 30 Residual gas exhaust path 31 Residual gas flow meter 40 Permeation gas exhaust passage 41 Permeation gas flow meter 50 Arithmetic and control device

Claims

1. A membrane separation device (10) having a separation membrane (12); a multicomponent gas supply line (20) for supplying a multicomponent gas containing at least two components to the membrane separation device (10); a residual gas discharge channel (30) through which the residual gas flowing out of the membrane separation device (10) without permeating the separation membrane (12) flows; a permeation gas discharge channel (40) through which a permeation gas that has permeated the separation membrane (12) and flowed out of the membrane separation device (10) flows out; a residual gas flowmeter (31) provided in the residual gas discharge passage (30) for measuring a flow rate F1 of the residual gas discharge passage (30); a permeation gas flowmeter (41) provided in the permeation gas discharge path (40) for measuring a flow rate F2 of the permeation gas discharge path (40); a calculation control device (50) to which signals from the residual gas flow meter (31) and the residual gas flow meter (41) are input, The arithmetic and control device (50) calculates a ratio Rm between the flow rate F1 and the flow rate F2 based on the input signal, The membrane separation system (1) is characterized in that the deterioration state of the separation membrane (12) is evaluated by comparing the calculated ratio Rm with a preset ratio Rk of the flow rate F1 and the flow rate F2.

2. A membrane separation device (10) having a separation membrane (12); a multicomponent gas supply line (20) for supplying a multicomponent gas containing at least two components to the membrane separation device (10); a residual gas discharge channel (30) through which the residual gas flowing out of the membrane separation device (10) without permeating the separation membrane (12) flows; a permeation gas discharge channel (40) through which a permeation gas that has permeated the separation membrane (12) and flowed out of the membrane separation device (10) flows out; either a residual gas flow meter (31) provided in the residual gas discharge path (30) for measuring a flow rate F1 of the residual gas discharge path (30), or a permeable gas flow meter (41) provided in the permeable gas discharge path (40) for measuring a flow rate F2 of the permeable gas discharge path (40); a multicomponent gas flowmeter (22) provided in the multicomponent gas supply passage (20) for measuring a flow rate F0 (where F0=F1+F2) of the multicomponent gas supply passage (20); a calculation and control device (50) to which a signal from either one of the residual gas flow meter (31) or the residual gas flow meter (41) and a signal from the multi-component gas flow meter (22) are input, The arithmetic and control device (50) calculates a ratio Rm between the flow rate F1 and the flow rate F2 based on the input signal, The membrane separation system (1) is characterized in that the deterioration state of the separation membrane (12) is evaluated by comparing the calculated ratio Rm with a preset ratio Rk of the flow rate F1 and the flow rate F2.

3. 3. The membrane separation system according to claim 1, wherein the arithmetic and control device outputs an alarm when the ratio Rm and the ratio Rk deviate from each other by a predetermined condition or more.

4. The membrane separation apparatus further includes a pressure gauge (15) for measuring a supply pressure of the multi-component gas supplied to the membrane separation apparatus (10), The membrane separation system (1) according to any one of claims 1 to 3, wherein the arithmetic and control device (50) controls the membrane separation system (1) so that the supply pressure is within a predetermined range.

5. The membrane separation apparatus further includes a concentration meter (21) for analyzing the multi-component gas supplied to the membrane separation apparatus (10), The membrane separation system (1) according to any one of claims 1 to 4, wherein the arithmetic and control device (50) resets the ratio Rk based on a signal input from the concentration meter (21).

6. 6. The membrane separation system (1) according to claim 5, wherein the multi-component gas contains two components, methane and carbon dioxide, as main components, and the concentration meter (21) is a methane concentration meter.

7. A method for evaluating deterioration of a separation membrane (12) in a membrane separation device (10) that separates a multi-component gas containing at least two components, comprising: When the multi-component gas is supplied to a membrane separation device (10) having the separation membrane (12), A ratio Rm of a flow rate F1 of a residual gas flowing out from the membrane separation device (10) without permeating the separation membrane (12) to a flow rate F2 of a permeated gas flowing out from the membrane separation device (10) after permeating the separation membrane (12) is calculated; The method for evaluating deterioration of a separation membrane includes comparing the determined ratio Rm with a preset ratio Rk of the flow rate F1 and the flow rate F2 to evaluate a deterioration state of the separation membrane (12).

8. The method for evaluating deterioration of a separation membrane according to claim 7 , wherein the multi-component gas contains two components, methane and carbon dioxide, as main components.

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