JP2009242773A - Methane gas concentration device, method therefor, fuel gas production device and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a methane gas concentration device which can obtain a methane gas with a high concentration at a high recovery rate. <P>SOLUTION: The methane gas concentration device 1 where, from a mixed gas at least comprising a methane gas and carbon dioxide, the carbon dioxide is separated, so as to concentrate the methane gas, includes: a first concentration apparatus 11 where the methane gas is concentrated by a separation membrane allowing the carbon dioxide to preferentially permeate from the mixed gas; a second concentration apparatus 12 where the methane gas is further concentrated by a separation membrane allowing the carbon dioxide to preferentially permeate from a non-permeating gas in the first concentration apparatus 11; and a recovery apparatus 13 where the methane gas is recovered by a separation membrane allowing the carbon dioxide to further preferentially permeate from a permeating gas in the first concentration apparatus 11, thus, the methane gas with a high concentration can be obtained at a high recovery rate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a methane gas concentrating apparatus and method for concentrating methane gas by separating carbon dioxide from a mixed gas containing methane gas and carbon dioxide, and a fuel gas production apparatus and method including methane gas and a high calorific gas for heat quantity adjustment. Is.

  Conventionally, organic waste such as human waste, purified water sludge, sewage treatment sludge, livestock manure, and garbage is subjected to anaerobic fermentation treatment with methane fermentation bacteria to decompose organic waste mainly to produce methane gas and carbon dioxide. A technology has been developed to generate biogas containing methane and effectively use this biogas as energy.

  On the other hand, various recovery techniques for separating high-concentration methane and carbon dioxide from the generated biogas have been developed. In particular, a membrane separation method can be cited as a method that can be used for small to medium-sized facilities.

Such a membrane separation method uses a polymer membrane or the like to separate components based on the difference in permeation rate of gas components, and allows gas components to be separated simply by passing pressurized gas through the membrane. Select a separation membrane according to the type of gas, amount of processing gas, etc., and use a plurality of separation membranes in parallel as necessary (Patent Documents 1 to 3 below) or use in combination in series (Patent Document 4 below).
Japanese Patent Laid-Open No. 11-3723 JP 2001-949 A JP-T-2006-507385 JP 2007-254572 A

  However, if a plurality of separation membranes are simply used in parallel, the recovery rate can be increased to some extent, but there is a limit to obtaining a high concentration of methane gas. On the other hand, if a plurality of separation membranes are simply used in series, methane gas with a somewhat high concentration can be obtained, but there is a limit to increasing the recovery rate. Thus, the actual situation is that a methane gas concentrator capable of obtaining a high concentration methane gas with a high recovery rate has not been obtained. Further, when a fuel gas is obtained using a biogas mainly containing carbon dioxide and methane as a raw material, there is a problem that a sufficient amount of heat may not be obtained only with methane gas.

  The present invention has been made to solve such a problem, and provides a methane gas concentrating device and method and a fuel gas manufacturing device and method capable of obtaining a high concentration methane gas with a high recovery rate. Objective.

In order to achieve the above object, the methane gas concentrator of the present invention is a methane gas concentrator that separates carbon dioxide from a mixed gas containing at least methane gas and carbon dioxide to concentrate the methane gas,
A first concentrator for concentrating methane gas by a separation membrane that preferentially permeates carbon dioxide from the mixed gas;
A second concentrator that further concentrates methane gas by a separation membrane that preferentially permeates carbon dioxide from the non-permeate gas of the first concentrator;
The gist of the present invention is to provide a recovery device that recovers methane gas by a separation membrane that preferentially permeates carbon dioxide from the permeate gas of the first concentrator.

Further, in order to achieve the above object, the methane gas concentration method of the present invention is a methane gas concentration method for concentrating methane gas by separating carbon dioxide from a mixed gas containing at least methane gas and carbon dioxide,
A first concentration step of concentrating methane gas by a separation membrane that preferentially permeates carbon dioxide from the mixed gas;
A second concentration step in which methane gas is further concentrated by a separation membrane that preferentially permeates carbon dioxide from the non-permeate gas in the first concentration step;
The present invention includes a recovery step of recovering methane gas by a separation membrane that preferentially permeates carbon dioxide from the permeate gas of the first concentration step.

In order to achieve the above object, a fuel gas production apparatus of the present invention is a fuel gas production apparatus containing methane gas and a high calorific gas for calorie adjustment,
A high calorific gas addition means for adding a high calorific gas to a biogas obtained by decomposing an organic substance to form a mixed gas of the biogas and the high calorific gas;
A first concentrator for concentrating methane gas and high calorific gas with a separation membrane that preferentially permeates carbon dioxide from the mixed gas;
The gist of the present invention is to provide a recovery device that recovers methane gas and high calorific gas by a separation membrane that preferentially permeates carbon dioxide from the permeate gas of the first concentrator.

In order to achieve the above object, a method for producing a fuel gas of the present invention is a method for producing a fuel gas containing methane gas and a high calorific gas for adjusting the calorific value,
A high calorific gas addition step of adding a high calorific gas to the biogas obtained by decomposing organic matter to make a mixed gas of the biogas and the high calorific gas,
A first concentration step of concentrating methane gas and high calorific gas with a separation membrane that preferentially permeates carbon dioxide from the mixed gas;
The present invention includes a recovery step of recovering methane gas and high calorific gas by a separation membrane that preferentially permeates carbon dioxide from the permeate gas of the first concentration step.

  The methane gas concentrating apparatus and method of the present invention removes carbon dioxide and concentrates the methane gas by two-stage concentration of the first stage and the second stage by the separation membrane, so that highly concentrated methane gas can be obtained. Further, since the permeated gas concentrated in the first stage is further separated into carbon dioxide by a separation membrane to recover methane gas, the recovery rate of methane gas can be dramatically improved. In this way, it is possible to obtain methane gas with a high recovery rate and high concentration. For example, the environment is such that a mixed gas having a methane gas content of less than 60% or an impurity gas such as air is mixed in the mixed gas. Even with this, it is possible to obtain a high concentration of methane gas with a high recovery rate. In addition, high-concentration carbon dioxide gas can be obtained as exhaust gas after recovering methane gas at a high recovery rate, and the function as a carbon dioxide recovery device is also exhibited at the same time.

  In the methane gas concentrating apparatus and method of the present invention, when the permeate gas of the second concentrator or process and the non-permeate gas of the recovery apparatus are refluxed to the introduction side of the first concentrator or process, the second concentrator or process is used. The carbon dioxide and methane gas permeated in step 1 are reintroduced into the first concentrator or process, and methane gas that has not permeated through the recovery unit is reintroduced into the first concentrator or process, thereby improving the concentration and recovery rate of methane gas. be able to.

  In the methane gas concentrating device and method of the present invention, when the areas of the separation membranes of the first concentrating device or step and the second concentrating device or step are substantially equal, the first concentrating device or step and the second concentrating device or step. By making the separation membranes substantially equal in area, it is possible to use the same separation membrane concentrator for the first concentrator and the second concentrator, which is advantageous in terms of equipment efficiency. In addition, since the difference between the introduction pressure of the first concentrator or the process and the introduction pressure of the second concentrator or the process is small, the first concentrator or the process is also the second concentrator or the process by making the area of the separation membrane substantially equal. In the process, substantially the same concentration performance is exhibited, and the concentration of methane gas and the recovery rate can be improved.

  In the methane gas concentrating device and method of the present invention, when the area of the separation membrane of the recovery device or process is smaller than the area of the separation membrane of the first concentration device or process, methane gas is used as the separation membrane of the recovery device or process. It becomes difficult to permeate, and the recovery efficiency of methane gas can be improved.

  In the methane gas concentrating device and method of the present invention, when the differential pressure before and after permeation of the separation membrane in the recovery device or process is 0.1 MPa or less, methane gas is more difficult to permeate the separation membrane of the recovery device or process. The methane gas recovery efficiency can be improved.

  The fuel gas production apparatus and method of the present invention add a high calorific gas to a biogas in advance to obtain a mixed gas of the biogas and the high calorific gas, and separate carbon dioxide from the mixed gas to obtain a methane gas and a high gas. Concentrate the calorific gas. In this way, a fuel gas having a predetermined calorific value in which methane gas and high calorific gas are mixed at a predetermined ratio can be obtained by preliminarily setting a mixing ratio with respect to biogas and adding a high calorific gas. In addition, a stable quality fuel gas can be obtained with a simple control with a sufficient amount of heat using biogas as a raw material.

  In the fuel gas production apparatus and method of the present invention, when the addition means adds a high calorific value gas to the biogas upstream of the boosting means for boosting the gas introduced into the first concentrator or the process, High calorific gas can be added to low pressure biogas to prevent liquefaction of high calorific gas. Thereby, the fluctuation | variation of the mixing ratio of methane gas and high calorie | heat amount gas after permeation | transmission of a separation membrane can be prevented, and stable quality fuel gas can be obtained by simple control.

  In the fuel gas production apparatus and method of the present invention, when the area of the separation membrane of the recovery device or process is smaller than the area of the separation membrane of the first concentration device or process, the separation membrane of the recovery device or process is used. It becomes difficult for methane gas to permeate, and the recovery efficiency of methane gas can be improved.

  Next, the best mode for carrying out the present invention will be described.

  FIG. 1 is a configuration diagram showing an example of a fuel gas production apparatus to which the present invention is applied.

  This fuel gas production apparatus includes a methane gas concentrator 1 that separates carbon dioxide from a mixed gas containing at least methane gas and carbon dioxide to concentrate the methane gas, and produces a fuel gas containing methane gas and a high calorific gas for heat quantity adjustment. To do.

  The fuel gas production apparatus uses biogas obtained by decomposing organic substances as a raw material gas. The biogas is generated in a digestion tank (not shown) that decomposes organic waste using anaerobic microorganisms such as methane bacteria in an anaerobic atmosphere. It is a gas containing carbon.

  For example, a cylindrical tank, a rectangular tank, an egg-shaped tank, or the like is used as the digestion tank. In addition, as the digester, a one-stage structure provided with a stirring device for circulating and stirring the generated digestion gas can be used, or a high-molecular organic substance such as a protein is organically treated by facultative anaerobic bacteria. It is also possible to use an acid fermentation tank that decomposes into low-molecular organic substances such as acids, a solubilization tank that decomposes and dissolves oils and fats at a high temperature, and the like in a two-stage structure.

  A propane gas addition passage 5 communicating with the LPG cylinder 4 is connected to the raw material gas introduction passage 3 for introducing the raw material gas into the methane gas concentrator 1, and a high calorific value gas is obtained with respect to the biogas obtained by decomposing organic matter. As a mixed gas of biogas and propane gas. The LPG cylinder 4 and the propane gas addition path 5 function as the high calorific gas addition means of the present invention. Instead of the propane gas addition path 5, a propane gas addition path 5a indicated by a chain line in the drawing may be provided so that the high calorific gas is added on the downstream side of the compressor 6.

  As the high calorific gas, not only propane gas but also ethane gas or butane gas can be used, and these can be used alone or in combination.

  In this way, a high calorific gas for calorie adjustment is added to the biogas containing methane gas and carbon dioxide at a predetermined ratio to obtain a mixed gas. And by separating carbon dioxide from this mixed gas, it is possible to obtain a fuel gas to which a high calorific gas is added at a predetermined ratio or more with respect to methane gas. Here, the addition ratio of the high calorific gas is set so that the calorific value of the finally obtained fuel gas matches the standard of, for example, city gas.

  The mixed gas in which propane gas is added at a predetermined ratio with respect to the biogas is boosted to a predetermined pressure of about 0.5 to 0.9 MPa (gauge pressure) by the compressor 6 and introduced into the methane gas concentrator 1. Therefore, in the present embodiment, the high calorific gas adding means adds the high calorific gas to the biogas upstream of the compressor 6 as a boosting means for boosting a gas to be introduced into the first concentrator 11 described later. It is like that.

  The methane gas concentrator 1 separates carbon dioxide from a mixed gas of methane gas and carbon dioxide and concentrates the methane gas. However, the mixed gas of the present embodiment is used as a high calorific gas in addition to methane gas and carbon dioxide. Propane gas is also added, and carbon dioxide is separated from this mixed gas to concentrate methane gas and high calorific gas. The mixed gas may contain other gases such as air in addition to methane gas, high calorific gas, and carbon dioxide.

  The methane gas concentrating device 1 includes a first concentrating device 11, a second concentrating device 12, and a recovery device 13 each having a separation membrane.

  The first concentrator 11 preferentially permeates carbon dioxide from the mixed gas through the separation membrane to concentrate the methane gas and the high calorific gas. The introduction pressure of the mixed gas to the first concentrator 11 is set to about 0.5 to 0.9 MPa (gauge pressure). The permeation gas of the separation membrane in the first concentrator 11 is a gas containing methane gas or high calorific gas that has permeated the separation membrane in carbon dioxide that has permeated the separation membrane, and is introduced into the recovery device 13. The non-permeate gas of the separation membrane in the first concentrator 11 is a gas in which some carbon dioxide that has not permeated the separation membrane is contained in the methane gas and the high calorific value gas, and is introduced into the second concentrator 12.

  The second concentrator 12 further concentrates the methane gas and the high calorific gas with a separation membrane that preferentially permeates carbon dioxide from the non-permeate gas of the first concentrator 11. The introduction pressure of the mixed gas to the second concentrator 12 is about 0.005 to 0.05 MPa lower than the introduction pressure to the first concentrator 11 unless the flow rate is adjusted. It is almost the same as the pressure. The permeated gas of the separation membrane in the second concentrator 12 is a gas in which methane gas or the like is contained in carbon dioxide that has permeated the separation membrane, and is refluxed to the introduction side of the first concentrator 11, that is, the upstream side of the compressor 6. It is again introduced into the first concentrator 11. Further, the non-permeate gas of the separation membrane in the second concentrator 12 is a mixed gas in which methane gas and high calorific gas are mixed at a predetermined ratio, and is sent as a product gas to a subsequent process.

  In this example, the separation membrane areas of the first concentrator 11 and the second concentrator 12 are set to be substantially equal. By doing in this way, the 1st concentrator 11 and the 2nd concentrator 12 can serve as the same separation membrane apparatus, and equipment efficiency is good.

  The recovery device 13 recovers methane gas and high calorific gas by a separation membrane that preferentially permeates carbon dioxide from the permeate gas of the first concentrator 11. That is, the gas introduced into the recovery device 13 is a gas containing carbon dioxide, methane gas, or high calorific gas that has passed through the separation membrane of the first concentration device 11 as described above, and priority is given to carbon dioxide from this gas. Permeate and separate to recover methane gas and high calorific gas.

  The non-permeate gas of the separation membrane in the recovery device 13 is a gas containing the recovered methane gas and high calorific gas, and is refluxed to the introduction side of the first concentrating device 11, that is, the upstream side of the compressor 6, and again the first concentration. Introduced into the device 11. The permeation gas of the separation membrane in the recovery device 13 is a gas mainly composed of high-concentration carbon dioxide and is discharged from the discharge path 14 or stored in the carbon dioxide tank 15 as product carbon dioxide.

  The introduction pressure of the gas introduced into the recovery device 13 is the pressure of the permeated gas of the first concentrating device 11 and is about 0.1 MPa (gauge pressure) or less. The differential pressure before and after permeation of the separation membrane in the recovery device 13 is preferably set to about 0.1 MPa or less.

  The area of the separation membrane of the recovery device 13 can be the same as the area of the separation membrane of the first concentration device 11. By doing in this way, the collection | recovery apparatus 13 and the 2nd concentration apparatus 12 can serve as the same separation membrane apparatus, and equipment efficiency is good.

  Further, the area of the separation membrane of the recovery device 13 may be set smaller than the area of the separation membrane of the first concentration device 11. By doing in this way, it becomes difficult for methane gas to permeate | transmit the separation membrane of the collection | recovery apparatus 13, and the collection | recovery efficiency of the methane gas in the collection | recovery apparatus 13 can be improved.

  Separation membranes used in the first concentrating device 11, the second concentrating device 12, and the recovery device 13 are mainly polymers such as a polyimide membrane, a polysulfone membrane, a cellulose triacetate membrane, a polytetrafluoroethylene membrane, and a polyethersulfone membrane. Gas separation membranes, carbon membranes, microporous glass composite membranes, etc. can be used, but among these, polyimide membranes have a high separation factor between methane gas and carbon dioxide and are also resistant to hydrogen sulfide. Is preferable.

  In this way, as the non-permeate gas of the second concentrator 12, the fuel gas, which is a mixed gas in which the methane gas and the high calorific gas are mixed at a predetermined ratio, is purified and led out from the product gas lead-out path 16.

  As described above, by separating carbon dioxide from a mixed gas obtained by adding a high calorific gas to a biogas containing methane gas and carbon dioxide at a predetermined ratio, the high calorific gas was added at a predetermined ratio to the methane gas. Obtain fuel gas. The ratio of the methane gas and the high calorific gas in the fuel gas, which is the product gas, is determined by the addition ratio of the high calorific gas that is initially added to the biogas, and this addition ratio is provided in the propane gas addition path 5. It adjusts with the flow regulator 26.

  Here, the raw material gas introduction path 3 is provided with a concentration detector 17 for detecting the methane gas concentration in the biogas which is the raw material gas, and when the methane gas concentration in the raw material gas is reduced below a certain ratio, The raw material valve 18 of the gas introduction path 3 and the propane valve 19 of the propane gas addition path 5 are closed, and the introduction of the mixed gas to the methane gas concentrator 1 is stopped. When the methane gas concentration in the raw material gas becomes a certain ratio or more again, the raw material valve 18 and the propane valve 19 are opened, and the introduction of the mixed gas into the methane gas concentrating device 1 is resumed. As a result, the ratio of the high calorific gas to the methane gas in the fuel gas that is the product gas is kept above a certain level.

  Here, instead of providing the concentration detector 17 in the raw material gas introduction path 3, a concentration detector 17 a may be provided in the product gas outlet path 16 downstream of the methane gas concentrator 1. In this case, when the methane gas concentration in the product gas is out of the predetermined range, the raw material valve 18 of the raw material gas introduction path 3 and the propane valve 19 of the propane gas addition path 5 are closed to introduce the mixed gas into the methane gas concentrator 1. Is stopped, and the high pressure tank 7 is prevented from being filled with product gas whose calorific value is outside the proper range.

  The product gas outlet path 16 is provided with a flow rate regulator 27 for adjusting the flow rate of the purified gas, and an odor gas cylinder 20 and an odor gas addition path for adding odor gas to the purified fuel gas. 21 is connected to a buffer tank 22 for temporarily storing product gas to which odorous gas is added. The product gas stored in the buffer tank 22 is compressed by the compressor 23 and stored in each high-pressure tank 7 of the high-pressure gas tank unit 24.

  The fuel gas stored in each of the high-pressure tanks 7 is individually filled in the fuel cylinder 8 and carried to a place where it is used as a predetermined fuel, or from the supply nozzle 9 as fuel to a vehicle with an internal combustion engine. Supplied.

  As described above, the methane gas concentrating apparatus 1 and the method of the present embodiment concentrates methane gas by removing carbon dioxide by two-stage concentration of the first stage and the second stage by the separation membrane. Can be obtained. Further, since the permeated gas concentrated in the first stage is further separated into carbon dioxide by a separation membrane to recover methane gas, the recovery rate of methane gas can be dramatically improved. In this way, it is possible to obtain methane gas with a high recovery rate and high concentration. For example, the environment is such that a mixed gas having a methane gas content of less than 60% or an impurity gas such as air is mixed in the mixed gas. Even with this, it is possible to obtain a high concentration of methane gas with a high recovery rate. In addition, high-concentration carbon dioxide gas can be obtained as exhaust gas after recovering methane gas at a high recovery rate, and the function as a carbon dioxide recovery device is also exhibited at the same time.

  In addition, the fuel gas production apparatus and method of the present embodiment add a high calorific gas to the biogas in advance to obtain a mixed gas of the biogas and the high caloric gas, and separate carbon dioxide from the mixed gas. Concentrate methane gas and high calorific gas. In this way, a fuel gas having a predetermined calorific value in which methane gas and high calorific gas are mixed at a predetermined ratio can be obtained by preliminarily setting a mixing ratio with respect to biogas and adding a high calorific gas. In addition, a stable quality fuel gas can be obtained with a simple control with a sufficient amount of heat using biogas as a raw material.

  Further, when the permeate gas of the second concentrator 12 or the process and the non-permeate gas of the recovery device 13 are refluxed to the introduction side of the first concentrator 11 or the process, the permeated CO 2 permeated in the second concentrator 12 or the process. Introducing carbon and methane gas again into the first concentrator 11 or process, and introducing methane gas that has not permeated through the recovery device 13 into the first concentrator 11 or process again, thereby improving the concentration and recovery rate of methane gas. Can do.

  Further, when the area of the separation membrane of the first concentrator 11 or the process and the second concentrator 12 or the process is substantially equal, the separation membrane of the first concentrator 11 or the process and the second concentrator 12 or the process is separated. By making the areas substantially equal, it is possible to use the same separation membrane concentrator for the first concentrator 11 and the second concentrator 12, which is advantageous in terms of equipment efficiency. Further, since the difference between the introduction pressure of the first concentrator 11 or the process and the introduction pressure of the second concentrator 12 or the process is small, the first concentrator 11 or the process is also the second by making the area of the separation membrane substantially equal. The concentration device 12 or the process also exhibits substantially the same concentration performance, and can improve the concentration concentration and recovery rate of methane gas.

  Further, when the area of the separation membrane of the recovery device 13 or the process is made smaller than the area of the separation membrane of the first concentrating device 11 or the process, methane gas is less likely to permeate the separation membrane of the recovery device 13 or the process. The methane gas recovery efficiency can be improved.

  Further, when the differential pressure before and after the permeation of the separation membrane in the recovery device 13 or process is set to 0.1 MPa or less, the methane gas is more difficult to permeate through the separation membrane of the recovery device 13 or the process, and the recovery efficiency of methane gas is improved. Can be improved.

  In addition, when the high-calorific gas is added to the biogas upstream of the compressor 6 which is a pressure-increasing means for boosting the gas to be introduced into the first concentrator 11 or the process, the adding means is a low-pressure biogas. High calorific gas can be added to prevent liquefaction of high calorific gas. Thereby, the fluctuation | variation of the mixing ratio of methane gas and high calorie | heat amount gas after permeation | transmission of a separation membrane can be prevented, and stable quality fuel gas can be obtained by simple control.

Using the fuel gas production apparatus, methane gas was concentrated from a mixed gas of 55 to 60% methane gas, 5% nitrogen gas, and the remaining carbon dioxide. The example which concentrated using the methane gas concentration apparatus 1 mentioned above as an Example is shown, the example concentrated only by the 1st concentration apparatus 11 as the comparative example 1, and the first concentration apparatus 11 and the 2nd concentration apparatus 12 as the comparative example 2. An example of concentration is shown. Incidentally, the introduction pressure of the respective gas mixture 0.6 MPa, 0.65 MPa, 0.7 MPa and varied, by varying each further the flow rate of the purified gas ^{4m 3 / Hr, 5m 3 /} Hr, and ^{6 m} 3 / Hr. The recovery rate of methane gas at each time is shown in Table 1 below. The flow rate was adjusted by opening and closing a valve (not shown) provided in the product gas lead-out path 16, and the introduction pressure was adjusted by the number of rotations of the compressor 6 at each flow rate.

  As can be seen from Table 1 above, the recovery rate of the examples was 99% or more, which was higher than those of Comparative Examples 1 and 2.

Further, for the above example, 0.6 MPa the introduction pressure of a gas mixture, 0.65 MPa, 0.7 MPa and changing, further flow of ^4m 3 ^/ Hr, respectively the purified gas, 5 m 3 / Hr, and a ^{6 m} 3 / Hr The measurement result of the methane gas concentration of the concentrated gas when changed is shown in Table 2 below.

  In Table 2 above, gas generated from a biogas plant is used as a raw material, and air is contained in addition to methane and carbon dioxide. Therefore, nitrogen gas is mixed in the produced gas, and the measured value is 90% or less. Take a value of degree. Therefore, the methane gas concentration was calculated without considering the nitrogen gas caused by air.

First, the composition of the purified gas was measured when the introduction pressure of the mixed gas was 0.6 MPa and the flow rates of the purified gas were 1 m ³ / Hr and 6 m ³ / Hr. The results are shown in Table 3 below. Table 3 also shows the measurement results of the composition of the raw material gas.

According to Table 3 above, when the introduction pressure of the mixed gas is 0.6 MPa and the purified gas flow rate is 1 m ³ / Hr, the methane concentration is 95.29%, the nitrogen concentration is 4.71%, and the purified gas flow rate is At 6 m ³ / Hr, the methane concentration was 82.72% and the nitrogen concentration was 11.65%.

Based on this result, the relationship between the methane concentration and the residual nitrogen concentration is plotted as the separation performance of the separation membrane when the purified gas flow rate is changed. It can be seen that the following equation (1) holds between the residual nitrogen concentrations.
y (residual nitrogen concentration) = − 0.5521x (methane concentration) +57.32 (1)

Table 4 below shows values obtained by applying the actual measurement values in Table 2 to the above formula (1) and calculating the residual nitrogen concentration and residual carbon dioxide concentration in each purified gas. In addition, since the permeation | transmission speed | rate of permeate gas component is represented by following formula (2), if the partial pressure difference of permeate gas component changes, separation performance will also change. However, since the gas permeability coefficient of the separation membrane is an eigenvalue corresponding to the gas component, even if the introduction pressure of the mixed gas changes if the methane concentration of the purified gas is the same, the effect on the separation performance of the separation membrane Is considered extremely small. Therefore, the above formula (1) was also applied to the actually measured values of the introduction pressures of 0.65 MPa and 0.7 MPa.
F = {P · (P1-P2)} / L (2)
F: Permeation rate of gas component P: Permeation coefficient of gas component P1-P2: Partial pressure difference of permeate gas component L: Thickness of separation membrane

  Furthermore, Table 5 below shows the result of calculating the methane gas concentration without considering residual nitrogen from the results of Table 4 above.

  As can be seen from the results in Table 5, it can be seen that the methane gas can be concentrated until the methane gas concentration becomes 94% or more as long as the raw material gas does not contain air as the purification ability of the methane gas in the examples. Thus, according to the fuel gas production apparatus of the embodiment, methane gas can be recovered at a high recovery rate of 99% or more while ensuring sufficient methane gas separation performance.

It is a figure which shows one Embodiment of the methane gas concentration apparatus and fuel gas manufacturing apparatus to which this invention was applied. It is the diagram which plotted the relationship between methane density | concentration and residual nitrogen density | concentration as the separation performance of a separation membrane.

Explanation of symbols

1: Methane gas concentrator 3: Raw material gas introduction path 4: LPG cylinder 5: Propane gas addition path 5a: Propane gas addition path 6: Compressor 7: High pressure tank 8: Fuel cylinder 9: Supply nozzle 11: First concentrator 12 : Second concentrator 13: recovery device 14: discharge path 15: carbon dioxide tank 16: product gas outlet path 17: concentration detector 17a: concentration detector 18: raw material valve 19: propane valve 20: odor gas cylinder 21: attached Odor gas addition path 22: buffer tank 23: compressor 24: high pressure gas tank unit 26: flow rate regulator 27: flow rate regulator

Claims (9)

A methane gas concentrator that separates carbon dioxide from a mixed gas containing at least methane gas and carbon dioxide to concentrate the methane gas,
A first concentrator for concentrating methane gas by a separation membrane that preferentially permeates carbon dioxide from the mixed gas;
A second concentrator that further concentrates methane gas by a separation membrane that preferentially permeates carbon dioxide from the non-permeate gas of the first concentrator;
A methane gas concentrating device comprising: a recovery device that recovers methane gas by a separation membrane that preferentially permeates carbon dioxide from the permeated gas of the first concentrating device.   The methane gas concentrator according to claim 1, wherein the permeate gas of the second concentrator and the non-permeate gas of the recovery unit are recirculated to the introduction side of the first concentrator.   The methane gas concentrator according to claim 1 or 2, wherein areas of the separation membranes of the first concentrator and the second concentrator are substantially equal.   The methane gas concentrator according to any one of claims 1 to 3, wherein an area of the separation membrane of the recovery device is smaller than an area of the separation membrane of the first concentrator. A methane gas enrichment method for concentrating methane gas by separating carbon dioxide from a mixed gas containing at least methane gas and carbon dioxide,
A first concentration step of concentrating methane gas by a separation membrane that preferentially permeates carbon dioxide from the mixed gas;
A second concentration step in which methane gas is further concentrated by a separation membrane that preferentially permeates carbon dioxide from the non-permeate gas in the first concentration step;
And a recovery step of recovering the methane gas by a separation membrane that preferentially permeates carbon dioxide from the permeate gas of the first concentration step. An apparatus for producing a fuel gas containing methane gas and a high calorific gas for adjusting the calorific value,
A high calorific gas addition means for adding a high calorific gas to a biogas obtained by decomposing an organic substance to form a mixed gas of the biogas and the high calorific gas;
A first concentrator for concentrating methane gas and high calorific gas with a separation membrane that preferentially permeates carbon dioxide from the mixed gas;
An apparatus for producing fuel gas, comprising: a recovery device for recovering methane gas and high calorific gas by a separation membrane that preferentially permeates carbon dioxide from the permeate gas of the first concentrator.   7. The fuel gas production apparatus according to claim 6, wherein the adding means adds a high calorific gas to the biogas upstream of the boosting means for boosting the gas introduced into the first concentrator.   The fuel gas production apparatus according to claim 6 or 7, wherein the area of the separation membrane of the recovery device is smaller than the area of the separation membrane of the first concentrator. A method for producing a fuel gas containing methane gas and a high calorie gas for heat quantity adjustment,
A high calorific gas addition step of adding a high calorific gas to the biogas obtained by decomposing organic matter to make a mixed gas of the biogas and the high calorific gas,
A first concentration step of concentrating methane gas and high calorific gas with a separation membrane that preferentially permeates carbon dioxide from the mixed gas;
A fuel gas production method comprising: a recovery step of recovering methane gas and high calorific gas with a separation membrane that preferentially permeates carbon dioxide from the permeate gas of the first concentration step.

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