JP6013865B2 - Method and system for producing city gas - Google Patents

Description

  The present invention relates to a method and system for producing city gas, and more particularly to a method and system for producing city gas using methane fermentation gas obtained by methane fermentation treatment of organic waste.

  In recent years, methane fermentation gas obtained by subjecting organic waste such as excess sludge, raw garbage, and organic wastewater to methane fermentation has attracted attention as a new energy source. And as an example of the method of utilizing methane fermentation gas effectively as an energy source, using methane fermentation gas as a raw material of city gas is proposed.

Here, the methane fermentation gas obtained by the methane fermentation treatment contains about 60% by volume of methane gas, about 40% by volume of carbon dioxide gas, and a small amount of impurities (for example, hydrogen sulfide, siloxane, etc.).
Therefore, when preparing city gas using methane fermentation gas, after removing carbon dioxide and impurities from methane fermentation gas to obtain purified gas containing methane gas at a high concentration, the level required by city gas is obtained. It is necessary to adjust the composition (components and concentration) of the purified gas so as to satisfy it.

  Therefore, conventionally, as a city gas production system for producing city gas using methane fermentation gas, a methane fermentation apparatus that obtains methane fermentation gas by subjecting organic waste to methane fermentation, and purified gas by purifying methane fermentation gas A city gas production system has been proposed which has a purification device for obtaining a composition adjustment device for adjusting the composition of the purified gas to obtain a composition adjustment gas, and a calorific value adjustment device for adjusting the amount of heat of the composition adjustment gas (for example, (See Patent Documents 1 and 2.)

  However, here, in the above-described conventional purification apparatus for city gas production system, the methane fermentation gas is pressurized to 0.5 to 1.0 MPa (gauge pressure), and then the high pressure water absorption method or the pressure swing adsorption method (PSA method). Is used to remove carbon dioxide from methane fermentation gas. The “high pressure water absorption method” is a method of removing carbon dioxide from methane fermentation gas by bringing high pressure methane fermentation gas into contact with water and dissolving carbon dioxide in water. The “pressure swing adsorption method” is a gas separation method that utilizes the fact that the amount of gas adsorbed on the adsorbent varies depending on the gas species and the partial pressure of the gas. Methane fermentation gas is added to the adsorption tower packed with the adsorbent. An adsorption process to obtain purified gas enriched with methane gas by supplying under pressure and a desorption process to regenerate the adsorbent by desorbing the gas adsorbed by the adsorbent under a lower pressure than the adsorption process It is a method of obtaining purified gas by repeatedly performing.

  And in the refinement | purification apparatus of the said conventional city gas manufacturing system, after adjusting the composition adjustment and calorie | heat amount adjustment with respect to the refined gas whose pressure is 0.5-1.0MPa (gauge pressure), it prepared. The city gas is supplied through a city gas conduit after being set to a pressure suitable for supply, for example, less than 0.5 MPa (gauge pressure).

Japanese Patent No. 4934230 JP 2004-300206 A

However, in the conventional purification apparatus for city gas production system, the purified gas obtained by refining methane fermentation gas after pressurizing to 0.5 to 1.0 MPa (gauge pressure) Since the pressure is reduced to a pressure suitable for supply after the processing is performed, a part of energy required for gas pressure increase is wasted. Moreover, in the conventional purification apparatus of the city gas production system, since the methane fermentation gas containing carbon dioxide gas in addition to the methane gas which is the main raw material for city gas is pressurized, the volume of the pressurized gas is large and the gas pressure is increased. It took a lot of energy.
Therefore, the conventional city gas production system has room for improvement in that the energy required for producing city gas is large.

  Then, an object of this invention is to provide the manufacturing method and manufacturing system of city gas which reduced the energy required for manufacture of city gas.

An object of the present invention is to advantageously solve the above-mentioned problems, and the city gas production method of the present invention has been enriched by purifying methane fermentation gas containing methane gas and carbon dioxide gas. A method for producing city gas, comprising: a purification step for obtaining a purified gas; and a city gas preparation step for preparing a city gas having a predetermined composition, calorie, and pressure using the purified gas obtained in the purification step. The purification step includes at least a pressure swing adsorption step of separating carbon dioxide gas from methane fermentation gas using a pressure swing adsorption method. In the pressure swing adsorption step, the city gas obtained in the city gas preparation step is Carbon dioxide gas is separated from methane fermentation gas having a pressure lower than the pressure, and in the pressure swing adsorption step, a refinement provided with two or more adsorption towers packed with an adsorbent. In each adsorption tower using an apparatus, an adsorption step of supplying the methane fermentation gas to the adsorption tower to obtain the purified gas, and a gas adsorbed on the adsorbent in the adsorption step are desorbed under reduced pressure, A desorption step for regenerating the adsorbent, and the purification apparatus performs the desorption step in at least one of the remaining adsorption towers while performing the adsorption step in at least one adsorption tower. , At least a part of the desorption gas discharged from the adsorption tower that is performing the desorption process is circulated to the adsorption tower that is performing the adsorption process as a recycle gas , and at the end of the adsorption process in the at least one adsorption tower The concentration of methane gas and / or the concentration of carbon dioxide in the purified gas is measured, and the measured concentration of methane gas in the purified gas and / or carbon dioxide in the purified gas Is used to determine the maximum time during which the recycle gas can be circulated to the adsorption tower when the next adsorption step is performed in the at least one adsorption tower, and the measured methane gas in the purified gas is measured. When the concentration exceeds a predetermined concentration and / or when the concentration of carbon dioxide gas in the purified gas is less than a predetermined concentration, the recycle gas is circulated to the at least one adsorption tower in the adsorption step for the maximum time. Longer than the measured time, and when the measured concentration of methane gas in the purified gas is less than a predetermined concentration and / or when the concentration of carbon dioxide gas in the purified gas exceeds a predetermined concentration, the maximum time Is shorter than the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step, and the methane gas in the purified gas is measured. When the concentration is a predetermined concentration and / or when the concentration of carbon dioxide in the purified gas is a predetermined concentration, the maximum time is the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step. characterized by the following and be Rukoto. Thus, if carbon dioxide gas is separated from methane fermentation gas having a pressure lower than that of city gas in the pressure swing adsorption process, and the gas pressure is increased to a predetermined pressure in the city gas preparation process, methane fermentation gas is obtained. There is no need to pressurize the carbon dioxide contained therein to a high pressure. Further, it is not necessary to reduce the pressure of the gas once increased to a pressure suitable for supplying city gas. Accordingly, part of the energy required for gas pressure increase is not wasted, and the energy required for gas pressure increase can be reduced by reducing the volume of the pressurized gas. Therefore, the energy required for manufacturing city gas can be reduced. Further, when carbon dioxide gas is separated from low-pressure methane fermentation gas in the pressure swing adsorption process, the recovery rate of methane gas from methane fermentation gas (= (amount of methane gas in the purified gas obtained / in the supplied methane fermentation gas) The amount of methane gas) × 100%) tends to decrease. However, if at least part of the desorption gas discharged from the adsorption tower that is carrying out the desorption process is recycled to the adsorption tower that is carrying out the adsorption process, the methane gas contained in the desorption gas is recovered. , Ru can improve the recovery rate of methane from methane fermentation gas. In addition, the concentration of methane gas and / or carbon dioxide in the purified gas is used to determine the maximum time that the recycle gas can flow through the adsorption tower when performing the next adsorption step in at least one adsorption tower. For example, the methane gas contained in the desorption gas is sufficiently recovered to improve the recovery rate of the methane gas from the methane fermentation gas, and the concentration of the methane gas in the refined gas is suppressed from being lower than the desired concentration. be able to.

In the present invention, “predetermined composition, amount of heat and pressure” refers to a composition, amount of heat and pressure which are predetermined according to the level required by city gas.
In the present invention, the “predetermined concentration” can be determined in advance according to the performance of the adsorbent to be used, the required recovery rate of methane gas, and the allowable range of decrease in the concentration of methane gas in the purified gas. The “desired concentration” is a concentration determined in advance according to the level required by city gas prepared using purified gas.

And the manufacturing method of the city gas of this invention measures the density | concentration of the methane gas in the said desorption gas, and / or the density | concentration of a carbon dioxide gas, and is implementing the said next adsorption process when implementing the said next adsorption process. Determining the timing of stopping the circulation of the recycle gas to the adsorption tower that is performing the next adsorption step so that the concentration of the methane gas in the recycle gas to be circulated to the adsorption tower is equal to or higher than a predetermined concentration. Is preferred. Using the concentration of methane gas in the desorption gas and / or the concentration of carbon dioxide gas, the concentration of methane gas can be determined by determining when to stop the circulation of the recycle gas so that the concentration of methane gas in the recycle gas is equal to or higher than the predetermined concentration. This is because it is possible to effectively improve the recovery rate of methane gas from the methane fermentation gas by suppressing the low desorption gas from circulating as a recycle gas to the adsorption tower.
In the present invention, the “predetermined concentration of methane gas in the recycle gas” is appropriately determined according to the performance of the adsorbent used, the required recovery rate of methane gas, and the allowable range of decrease in the concentration of methane gas in the purified gas. Can be set.

Moreover, this invention aims at solving the said subject advantageously, and the manufacturing system of the city gas of this invention refine | purifies the methane fermentation gas containing methane gas and a carbon dioxide gas, and methane gas is enriched. A city gas production system comprising: a purification mechanism that obtains a purified gas, and a city gas preparation mechanism that uses the purified gas obtained by the purification mechanism to prepare a city gas having a predetermined composition, calorie, and pressure The purification mechanism includes at least a purification device that separates carbon dioxide gas from methane fermentation gas using a pressure swing adsorption method, and the purification device uses a pressure of the city gas obtained by the city gas preparation mechanism. The carbon dioxide gas is separated from the methane fermentation gas having a low pressure, and the purification apparatus includes two or more adsorption towers filled with an adsorbent, In the tower, an adsorption step of supplying the methane fermentation gas to the adsorption tower to obtain the purified gas, and a desorption step of regenerating the adsorbent by desorbing the gas adsorbed on the adsorbent in the adsorption step under reduced pressure The methane fermentation gas is supplied to at least one adsorption tower and the purified gas is produced to reduce the pressure in the adsorption tower with at least one of the remaining adsorption towers. A recycle gas supply configured to desorb the gas adsorbed on the at least one of the remaining adsorption towers and supplying at least a part of the desorption gas discharged from at least one of the remaining adsorption towers to the at least one adsorption tower as a recycle gas line and a supply interruption mechanism for blocking said at least one supply of recycle gas to the adsorption tower through the recycle gas supply lines, the refined gas A refined gas concentration meter that measures the concentration of tan gas and / or carbon dioxide, and a control device that controls the operation of the supply shut-off mechanism to control the time during which the recycle gas flows through the at least one adsorption tower; The control device performs the next adsorption step in the at least one adsorption tower using the measured concentration of methane gas in the refined gas and / or carbon dioxide gas concentration in the refined gas. Determining the maximum time during which the recycle gas can be circulated through the adsorption tower, and the concentration of methane gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower is a predetermined value. When the concentration is higher and / or when the concentration of carbon dioxide in the purified gas is less than a predetermined concentration, the maximum time is determined in the adsorption step. The operation of the supply cutoff mechanism is controlled so as to be longer than the time during which the recycle gas is circulated through the at least one adsorption tower, and measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower. When the concentration of methane gas in the purified gas is less than a predetermined concentration and / or when the concentration of carbon dioxide gas in the purified gas exceeds a predetermined concentration, the maximum time is the at least one in the adsorption step. The purified gas measured by the purified gas concentration meter at the end of the adsorption process in the at least one adsorption tower, controlling the operation of the supply shut-off mechanism so as to be shorter than the time when the recycle gas is circulated through the adsorption tower When the concentration of methane gas in the inside is a predetermined concentration and / or when the concentration of carbon dioxide in the purified gas is a predetermined concentration The maximum time is characterized that you control the operation of the supply shut off mechanism to be equal to or less than the at least one time by flowing through the recycle gas to the adsorption tower in the adsorption step. As described above, the purification apparatus is configured to separate the carbon dioxide gas from the methane fermentation gas having a pressure lower than that of the city gas. When the gas pressure is increased to a predetermined pressure in the city gas preparation mechanism, There is no need to pressurize the carbon dioxide contained in the fermentation gas to a high pressure. Further, it is not necessary to reduce the pressure of the gas once increased to a pressure suitable for supplying city gas. Accordingly, part of the energy required for gas pressure increase is not wasted, and the energy required for gas pressure increase can be reduced by reducing the volume of the pressurized gas. Therefore, the energy required for manufacturing city gas can be reduced. Furthermore, when carbon dioxide gas is separated from low-pressure methane fermentation gas in the refining apparatus, the recovery rate of methane gas from the methane fermentation gas tends to decrease. However, if a recycle gas supply line is provided, at least a part of the desorption gas is circulated to the adsorption tower as a recycle gas, and the methane gas contained in the desorption gas is recovered, improving the recovery rate of methane gas from the methane fermentation gas. Ru can be. In addition, the control device uses the measured value measured by the purified gas concentration meter at the end of the adsorption process, and the maximum recyclable gas can be circulated to the adsorption tower when performing the next adsorption process in at least one adsorption tower. If the time is determined, the concentration of methane gas in the purified gas will be lower than the desired concentration while sufficiently recovering the methane gas contained in the desorption gas and improving the recovery rate of methane gas from the methane fermentation gas. Can be suppressed.

In the present invention, “predetermined composition, amount of heat and pressure” refers to a composition, amount of heat and pressure which are predetermined according to the level required by city gas.
In the present invention, the “predetermined concentration” can be determined in advance according to the performance of the adsorbent to be used, the required recovery rate of methane gas, and the allowable range of decrease in the concentration of methane gas in the purified gas. The “desired concentration” is a concentration determined in advance according to the level required by city gas prepared using purified gas.

The city gas production system of the present invention further includes a desorption gas concentration meter that measures the concentration of methane gas and / or the concentration of carbon dioxide gas in the desorption gas, and the control device measures with the desorption gas concentration meter. The operation of the supply shut-off mechanism is controlled using the concentration of methane gas in the desorption gas and / or the concentration of carbon dioxide gas in the desorption gas, and the at least one adsorption is performed when performing the next adsorption step. It is preferable to shut off the supply of the recycle gas to the at least one adsorption tower so that the concentration of the methane gas in the recycle gas to be circulated to the tower is not less than a predetermined concentration. Using the concentration of methane gas and / or carbon dioxide in the desorption gas measured by the desorption gas concentration meter, the control device operates the supply shut-off mechanism so that the concentration of methane gas in the recycle gas exceeds the specified concentration. This is because it is possible to effectively improve the recovery rate of methane gas from methane fermentation gas by suppressing the desorption gas having a low concentration of methane gas from being supplied to the adsorption tower as a recycle gas.
In the present invention, the “predetermined concentration of methane gas in the recycle gas” is appropriately determined according to the performance of the adsorbent used, the required recovery rate of methane gas, and the allowable range of decrease in the concentration of methane gas in the purified gas. Can be set.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and manufacturing system of city gas which reduced the energy required for manufacture of city gas can be provided.

It is a block diagram which shows the structure of the manufacturing system of the typical city gas according to this invention. It is a figure which shows schematic structure of the refiner | purifier which can be used with the refinement | purification mechanism of the manufacturing system of the city gas shown in FIG. (A) shows the operation process table | surface of the refiner | purifier shown in FIG. 2, (b) shows the operation process table | surface of the refiner | purifier of a modification. It is a figure which shows the gas flow in the process 1 of the stage 1 of the driving | operation process table | surface shown to Fig.3 (a). It is a figure which shows the gas flow in the process 2 of the stage 1 of the driving | operation process table | surface shown to Fig.3 (a). It is a figure which shows the gas flow in the process 3 of the stage 1 of the driving | operation process table | surface shown to Fig.3 (a). It is a figure which shows the gas flow in the process 4 of the stage 1 of the driving | operation process table | surface shown to Fig.3 (a).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, what attached | subjected the same code | symbol in each figure shall show the same component.

  Here, the city gas production system of the present invention is used for producing city gas using methane fermentation gas obtained by subjecting surplus sludge, raw garbage, and organic waste such as organic wastewater to methane fermentation. Can be used. City gas has a composition (components and concentration), calorie, and pressure that satisfy a predetermined level. The “predetermined level” to be satisfied by city gas is, for example, “Biogas Purchasing Guidelines” (Tokyo Gas Co., Ltd.). Company).

  A city gas production system 1 shown in FIG. 1 includes a methane fermentation treatment device 2 that performs a methane fermentation treatment of organic waste, and a purification mechanism 3 that purifies the methane fermentation gas generated by the methane fermentation treatment device 2 to obtain a purified gas. And a city gas preparation mechanism 4 for preparing city gas using the purified gas obtained by the purification mechanism 3.

The methane fermentation treatment apparatus 2 is an apparatus for subjecting organic waste to methane fermentation using anaerobic microorganisms. Here, in the methane fermentation treatment apparatus 2, methane fermentation gas containing methane gas, carbon dioxide gas, and other impurities (for example, hydrogen sulfide, siloxane, etc.) and having a pressure P1 of 3 to 50 kPa (gauge pressure) is generated. Is done. The methane fermentation gas obtained by the methane fermentation treatment apparatus 2 is arbitrarily stored once in a methane fermentation gas tank (not shown) and then supplied to the purification mechanism 3.
The methane fermentation treatment apparatus 2 is not particularly limited, and a known methane fermentation tank can be used.

The purification mechanism 3 is a mechanism for purifying the methane fermentation gas (mixed gas containing methane gas and carbon dioxide gas) obtained by the methane fermentation treatment apparatus 2 to obtain a purified gas enriched in methane gas. And the refinement | purification mechanism 3 of this example manufacturing system 1 uses the 1st compressor 5 which compresses and pressurizes methane fermentation gas, and the methane fermentation pressurized with the 1st compressor 5 using the pressure swing adsorption method. And a purifier 6 for separating carbon dioxide from the gas.
The refining mechanism 3 includes a mist separator (not shown) that removes excess water from the methane fermentation gas, a hydrogen sulfide removal device (not shown) that removes hydrogen sulfide from the methane fermentation gas, and a methane fermentation gas. You may have the siloxane removal apparatus (not shown) which removes siloxane. Incidentally, the mist separator, the hydrogen sulfide removing device and the siloxane removing device are not particularly limited, and known mist separators, hydrogen sulfide removing devices and siloxane removing devices can be used. Further, the mist separator, the hydrogen sulfide removing device, and the siloxane removing device can be provided at any position in the purification mechanism 3, for example, closer to the methane fermentation treatment device 2 than the purification device 6.

The first compressor 5 of the purification mechanism 3 is a device that compresses the methane fermentation gas at the pressure P1 obtained by the methane fermentation treatment apparatus 2 and pressurizes the methane fermentation gas to the pressure P2. The pressure P2 is a pressure equal to or lower than the pressure P3 of the city gas produced and supplied using the production system 1, and the pressure P2 can be set to, for example, 5 to 100 kPa (gauge pressure).
The first compressor 5 is not particularly limited, and a known blower or the like can be used.
Incidentally, in the city gas production system of the present invention, the methane fermentation gas obtained by the methane fermentation treatment apparatus may be supplied to the purification apparatus 6 as it is for purification without providing a compressor in the purification mechanism.

The purification device 6 of the purification mechanism 3 has an adsorption tower filled with an adsorbent such as activated carbon, molecular sieve charcoal, or zeolite. And in the refiner | purifier 6, the refined gas enriched in methane gas is manufactured by supplying methane fermentation gas to the adsorption tower filled with the adsorbent, and making the adsorbent adsorb the carbon dioxide gas in methane fermentation gas. . Further, in the refining device 6, when the amount of gas adsorbed on the adsorbent approaches the saturated adsorption amount, the gas adsorbed on the adsorbent is desorbed under reduced pressure (under a pressure lower than the pressure during adsorption) to adsorb the adsorbent. Play.
That is, in the adsorption tower of the purification device 6, an adsorption process for supplying purified gas by supplying methane fermentation gas to the adsorption tower, and the gas adsorbed by the adsorbent in the adsorption process are under reduced pressure (lower pressure than the adsorption process). And the desorption step of regenerating the adsorbent by desorption in step 1 and 2 are alternately repeated.

  Here, as the purification apparatus 6, any purification apparatus capable of obtaining a purified gas having a methane gas concentration suitable for the production of city gas can be used. In addition, it is preferable to use the refiner | purifier 100 demonstrated in detail later as a refiner | purifier of a refinement | purification mechanism from a viewpoint of raising the recovery rate of methane gas from methane fermentation gas.

  The city gas preparation mechanism 4 is a mechanism for preparing a city gas having a composition (components and concentration), a calorific value, and a pressure that satisfy a predetermined level by using the purified gas obtained by the purification mechanism 3. And the city gas preparation mechanism 4 of the manufacturing system 1 of this example adjusts the composition of the second compressor 7 that compresses and pressurizes the refined gas, and the composition of the refined gas that is pressurized by the second compressor 7. It has the composition adjustment apparatus 8 which obtains gas, and the calorie | heat amount adjustment apparatus 9 which adjusts the calorie | heat amount of a composition adjustment gas.

The second compressor 7 of the city gas preparation mechanism 4 functions as a pressure adjusting device that compresses the purified gas obtained by the purification mechanism 3 and pressurizes the purified gas to a pressure suitable for supply of the city gas. In the second compressor 7, the purified gas having the pressure P <b> 2 obtained by the purification mechanism 3 is pressurized to a pressure P <b> 3 equal to the city gas supplied using the manufacturing system 1. The pressure P3 can be set to 0.4 MPa (gauge pressure), for example. Incidentally, in the above description, it was assumed that the pressure loss in the city gas preparation mechanism 4 was almost negligible, and the purified gas was pressurized to a pressure P3 equal to the city gas supply pressure. However, when the pressure loss in the city gas preparation mechanism 4 is large, the purified gas can be pressurized to a pressure larger than the pressure P3 equal to the supply pressure of the city gas by a pressure loss.
The second compressor 7 is not particularly limited, and a known blower or the like can be used.
Incidentally, in the city gas production system of the present invention, the compressor of the city gas preparation mechanism may be provided on the rear side of the composition adjusting device and the calorific value adjusting device.

  The composition adjustment device 8 of the city gas preparation mechanism 4 adds hydrogen to the refined gas pressurized by the second compressor 7 and removes oxygen from the refined gas to satisfy a predetermined level required by the city gas. This is an apparatus for obtaining a composition-adjusting gas having (component and concentration). Here, in the composition adjusting device 8, the composition of the purified gas is adjusted using a known composition adjusting means such as a hydrogen addition device or an oxygen removal catalyst tower so that a composition adjusting gas having a pressure P3 can be obtained.

  The calorific value adjustment device 9 of the city gas preparation mechanism 4 mixes LP gas or the like with the composition adjustment gas obtained by the composition adjustment device 8 to satisfy the predetermined level required by the city gas for the amount of heat of the composition adjustment gas. This is a device for obtaining city gas having a predetermined pressure P3. Here, in the calorific value adjusting device 9, a known calorific value adjusting means, for example, an LP gas vaporizing device and a vaporized LP gas adding device, etc. are used so as to obtain a city gas of a pressure P3 having a predetermined calorific value. The city gas is prepared by adjusting the amount of heat of the composition adjustment gas.

  In the city gas production system 1 of the above example, the purification mechanism 3 purifies the methane fermentation gas containing methane gas and carbon dioxide gas to obtain a purified gas enriched in methane gas. Specifically, in the refining process, after pressurizing the methane fermentation gas to the pressure P2 using the first compressor 5, the pressure at which the carbon dioxide gas is separated from the methane fermentation gas using the pressure swing adsorption method in the refining device 6. At least the swing adsorption process is performed. In the refining process, a water removal process for removing excess water from the methane fermentation gas, a hydrogen sulfide removal process for removing hydrogen sulfide from the methane fermentation gas, and a siloxane removal process for removing siloxane from the methane fermentation gas. And may be implemented.

  In the city gas production system 1 of the above example, the city gas preparation mechanism 4 that uses the purified gas obtained by the purification mechanism 3 to prepare the city gas having a predetermined composition, calorie, and pressure is the city gas preparation mechanism 4. Implemented in Specifically, in the city gas preparation step, the pressure adjustment step of pressurizing the purified gas to the pressure P3 suitable for the supply of city gas using the second compressor 7 and the composition of the purified gas using the composition adjustment device 8 Adjustment step for adjusting the amount of heat of the composition adjustment gas to the amount of heat satisfying the predetermined level required by the city gas using the heat amount adjusting device 9 To prepare city gas.

In the manufacturing system 1 of the above example, the purification device 6 of the purification mechanism 3 performs pressure swing adsorption under a pressure P2 lower than the pressure P3 of the city gas, and separates carbon dioxide from the methane fermentation gas. There is no need to pressurize the carbon dioxide gas contained in the methane fermentation gas to a high pressure (eg, pressure P3 or higher). In addition, when the gas is pressurized to a pressure P3 suitable for city gas supply, compared to the conventional technique in which the methane fermentation gas is pressurized to a pressure P3 suitable for city gas supply before the pressure swing adsorption is performed. The volume of the gas to be pressurized can be reduced, and the energy required for boosting the gas can be reduced. Furthermore, in the manufacturing system 1 of the above example, the second compressor 7 is used to pressurize the refined gas to a pressure P3 suitable for supplying city gas, and keep the pressure (that is, without greatly reducing the pressure). Since the gas is prepared, it is not necessary to reduce the pressure of the gas once increased to a pressure suitable for supplying city gas.
Therefore, in the manufacturing system 1, part of the energy required for gas pressure increase is not wasted, and the energy required for gas pressure increase can be reduced by reducing the volume of the pressurized gas. Therefore, the energy required for manufacturing city gas can be reduced.

As mentioned above, although the manufacturing system and manufacturing method of the city gas of this invention were demonstrated using an example, the manufacturing system and manufacturing method of this invention are not limited to the said example, The manufacturing system and manufacturing method of this invention Can be appropriately modified.
Specifically, in the production system 1 of the above example, in order to separate the carbon dioxide from the low-pressure methane fermentation gas having the pressure P2, the recovery rate of methane gas from the methane fermentation gas (in the pressure swing adsorption process performed in the purifier 6) ( = (Amount of methane gas in the purified gas obtained / Amount of methane gas in the supplied methane fermentation gas) × 100%) is likely to decrease. Therefore, in the city gas production system of the present invention, for example, a purifier 100 as described in detail below may be used.

<Purification equipment>
2 includes two or more (three in the illustrated example) adsorption towers 10, 20, and 30 filled with an adsorbent. And in the refiner | purifier 100, the methane fermentation gas containing methane gas and a carbon dioxide gas is refine | purified using a pressure swing adsorption method, and the refined gas enriched in methane gas is manufactured. Specifically, in the purification apparatus 100, methane gas was enriched by supplying methane fermentation gas to the adsorption tower and adsorbing most of the carbon dioxide and part of the methane gas with the adsorbent in the adsorption tower. Purified gas is produced. The adsorbent that adsorbs carbon dioxide gas and methane gas is appropriately regenerated by desorbing the gas adsorbed on the adsorbent under reduced pressure (pressure lower than the pressure during adsorption).

  Here, as shown in FIG. 2, the purification apparatus 100 includes a first adsorption tower 10, a second adsorption tower 20, and a third adsorption tower 30 that are connected in parallel to each other. Each of the adsorption towers 10, 20, and 30 is filled with a known adsorbent that can be used for purification of methane fermentation gas using the pressure swing adsorption method, such as activated carbon, molecular sieve charcoal, zeolite, and the like. ing.

Moreover, the refiner | purifier 100 is common with the 1st methane fermentation gas line 11 which connects the common methane fermentation gas line 40 into which methane fermentation gas flows in from the outside of the apparatus, the common methane fermentation gas line 40, and the 1st adsorption tower 10, and. A second methane fermentation gas line 21 connecting the methane fermentation gas line 40 and the second adsorption tower 20; and a third methane fermentation gas line 31 connecting the common methane fermentation gas line 40 and the third adsorption tower 30. ing.
The first methane fermentation gas line 11 is provided with a first methane fermentation gas valve 12, the second methane fermentation gas line 21 is provided with a second methane fermentation gas valve 22, and a third methane fermentation gas valve 21 is provided. The gas line 31 is provided with a third methane fermentation gas valve 32.

Furthermore, the purification apparatus 100 includes a common purification gas line 50 that flows the purified gas flowing out from each adsorption tower to the outside of the apparatus, and a first purification gas line 13 that connects the first adsorption tower 10 and the common purification gas line 50. The second purification gas line 23 that connects the second adsorption tower 20 and the common purification gas line 50 and the third purification gas line 33 that connects the third adsorption tower 30 and the common purification gas line 50 are provided. . The common purified gas line 50 is provided with a first carbon dioxide gas sensor 51 as a purified gas concentration meter that measures the concentration of carbon dioxide in the purified gas flowing out from the purification apparatus 100.
The first purified gas line 13 is provided with a first purified gas valve 14, the second purified gas line 23 is provided with a second purified gas valve 24, and the third purified gas line 33 is provided with A third purified gas valve 34 is provided.

The purifier 100 also includes a first pressure equalizing line 15 extending from the first purified gas line 13, a second pressure equalizing line 25 extending from the second purified gas line 23, and a third purification. And a third pressure equalizing line 35 extending from the gas line 33. The first pressure equalizing line 15, the second pressure equalizing line 25, and the third pressure equalizing line 35 are connected to each other via a common pressure equalizing line 60.
The first pressure equalizing line 15 branches from the first purified gas line 13 between the first adsorption tower 10 and the first purified gas valve 14, and the second pressure equalizing line 25 is the second pressure equalizing line 25. The second purification gas line 23 is branched between the adsorption tower 20 and the second purification gas valve 24, and the third pressure equalizing line 35 is provided between the third adsorption tower 30 and the third purification gas valve 34. Branches from the third purified gas line 33. The first pressure equalizing line 15 is provided with a first pressure equalizing valve 16, the second pressure equalizing line 25 is provided with a second pressure equalizing valve 26, and the third The pressure equalization line 35 is provided with a third pressure equalization valve 36.

Further, the purification apparatus 100 has a common desorption gas line 70 for flowing the desorption gas generated when the adsorbent in each adsorption tower is desorbed under reduced pressure to regenerate the adsorbent. doing. The common desorption gas line 70 includes a first desorption gas line 17 extending from the first methane fermentation gas line 11, a second desorption gas line 27 extending from the second methane fermentation gas line 21, and a third methane. A third desorption gas line 37 extending from the fermentation gas line 31 is connected.
The first desorption gas line 17 branches from the first methane fermentation gas line 11 between the first methane fermentation gas valve 12 and the first adsorption tower 10, and the second desorption gas line 27 is the second desorption gas line 27. The methane fermentation gas valve 22 and the second adsorption tower 20 branch from the second methane fermentation gas line 21, and the third desorption gas line 37 includes a third methane fermentation gas valve 32, a third adsorption tower 30, and the like. Is branched from the third methane fermentation gas line 31. The first desorption gas line 17 is provided with a first desorption gas valve 18, the second desorption gas line 27 is provided with a second desorption gas valve 28, and a third desorption gas line 37 is provided. Is provided with a third desorption gas valve 38.

  Here, the common desorption gas line 70 includes a vacuum pump 71 as a depressurization device used for depressurization in each adsorption tower from the connection side with the third desorption gas line 37 toward the outside of the apparatus, and a desorption gas. A second carbon dioxide gas sensor 72 as a desorption gas concentration meter for measuring the carbon dioxide gas concentration and a common desorption gas valve 73 are sequentially arranged.

The purification apparatus 100 also has a recycle gas line 80 having one end connected to the common methane fermentation gas line 40 and the other end connected to the common desorption gas line 70.
Here, one end of the recycle gas line 80 is a common methane fermentation gas between the inlet of the methane fermentation gas to the refining device 100 and the connection portion between the common methane fermentation gas line 40 and the first methane fermentation gas line 11. Connected to line 40. The other end of the recycle gas line 80 is connected to the common desorption gas line 70 between the second carbon dioxide gas sensor 72 and the common desorption gas valve 73.
The recycle gas line 80 includes a recycle gas valve 81 as a supply shut-off mechanism that blocks the flow of the recycle gas from the other end side to the one end side, and a recycle gas pump 82 that pressurizes and sends the recycle gas. They are arranged sequentially.

And in the refiner | purifier 100 which has the structure mentioned above, the common methane fermentation gas line 40, the 1st methane fermentation gas line 11, the 2nd methane fermentation gas line 21, and the 3rd methane fermentation gas line 31 are each adsorption towers 10. , 20, 30 can function as a methane fermentation gas supply line for supplying methane fermentation gas.
Moreover, the 1st refinement gas line 13, the 2nd refinement gas line 23, the 3rd refinement gas line 33, and the common refinement gas line 50 carry out the refinement gas which flowed out from each adsorption tower 10,20,30 out of an apparatus. It can function as a flowing purified gas line.
Further, a part of the first purified gas line 13 (from the first adsorption tower 10 to a portion where the first pressure equalizing line 15 branches), the first pressure equalizing line 15, and one of the second purified gas lines 23. Part (from the second adsorption tower 20 to the portion where the second pressure equalization line 25 branches), the second pressure equalization line 25, and a part of the third purified gas line 33 (from the third adsorption tower 30 to the third The pressure equalization line 35, the third pressure equalization line 35, and the common pressure equalization line 60 communicate with each other to equalize the pressure in the adsorption tower. It can function as a conversion line.
Further, a part of the first methane fermentation gas line 11 (from the first adsorption tower 10 to a part where the first desorption gas line 17 branches), a part of the first desorption gas line 17 and the second methane fermentation gas line 21 ( From the second adsorption tower 20 to the portion where the second desorption gas line 27 branches), the second desorption gas line 27, and a part of the third methane fermentation gas line 31 (from the third adsorption tower 30 to the third desorption gas line). 37) and the third desorption gas line 37 and the common desorption gas line 70 can function as a desorption gas line for flowing the desorption gas flowing out from each of the adsorption towers 10, 20, 30 to the outside of the apparatus. .
Furthermore, the recycle gas line 80, the common methane fermentation gas line 40, the first methane fermentation gas line 11, the second methane fermentation gas line 21, and the third methane fermentation gas line 31 are adsorption towers that are regenerating the adsorbent. It can function as a recycle gas supply line for supplying at least a part of the desorption gas flowing out from the recycle gas to other adsorption towers. In the recycle gas supply line of the purification apparatus 100, the recycle gas is supplied to the adsorption towers 10, 20, and 30 in a state of being mixed with the methane fermentation gas. May be supplied directly.

  Note that the purification apparatus 100 supplies the methane fermentation gas to at least one adsorption tower to produce purified gas, and at least one of the remaining adsorption towers reduces the pressure in the adsorption tower to form an adsorbent. It is operated to desorb the adsorbed gas. The operation of the refining apparatus 100 may be performed manually or automatically using a control panel (not shown).

  In the refining device 100, at least a part of the desorption gas discharged from at least one of the remaining adsorption towers is supplied to the at least one adsorption tower as a recycle gas. Incidentally, the amount of the desorption gas supplied to the adsorption tower as a recycle gas can be controlled using the control device 90 that controls the operations of the common desorption gas valve 73, the recycle gas valve 81 and the recycle gas pump 82. Here, the control device 90 of the purification apparatus 100 uses the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 and the concentration of carbon dioxide in the desorption gas measured by the second carbon dioxide sensor 72, As will be described in detail later, this device controls the operation of the common desorption gas valve 73, the recycle gas valve 81, and the recycle gas pump 82.

<Pressure swing adsorption process>
Purification of methane fermentation gas using the purification apparatus 100 shown in FIG. 2 can be performed according to the operation process chart as shown in FIG. Specifically, in the refiner 100, the methane fermentation gas is continuously refined by sequentially repeating the stages 1 to 3 shown in FIG. 3A, and a refined gas containing a high concentration of methane gas is obtained. Can be obtained.
In addition, it is preferable that the density | concentration of the methane gas in refined gas is more than desired density | concentration. Here, the “desired concentration” of methane gas in the purified gas is a concentration determined in advance according to the level required by the city gas prepared using the purified gas, and is, for example, 99.5% by volume. If the concentration of methane gas in the purified gas is lower than the desired concentration, the concentration of methane gas exceeds the desired concentration by mixing with another purified gas containing methane gas above the desired concentration or by refining the purified gas again. It is necessary to use it as a raw material for city gas.

  Here, as shown in FIG. 3 (a), in this example of the method for purifying methane fermentation gas, in each of the first adsorption tower 10, the second adsorption tower 20, and the third adsorption tower 30, methane fermentation is performed in the adsorption tower. An adsorption process for supplying a purified gas by supplying gas and a desorption process for regenerating the adsorbent by desorbing the gas adsorbed by the adsorbent in the adsorption process under a reduced pressure (lower pressure than the adsorption process) are repeated. To be implemented. In this example of the purification method, as shown in FIG. 3 (a), while the adsorption process is performed in one adsorption tower, the desorption process is performed in one of the remaining adsorption towers.

  As is clear from FIG. 3 (a), in this example purification method, the methane fermentation gas is continuously purified by sequentially switching the adsorption tower for performing the adsorption step for each stage. Accordingly, those skilled in the art can understand that stage 2 and stage 3 can be implemented in the same manner as stage 1. Therefore, in the following, using FIG. 4A to FIG. 4D, the operation contents of the purification apparatus 100 in the stage 1 after the second start from the start of the purification of the methane fermentation gas (that is, after performing the stages 1 to 3 at least once). And the description of the operation of the purification apparatus 100 in stages 2 and 3 is omitted. In FIG. 4A to FIG. 4D, the gas flow is displayed using thick arrows.

Here, at the start of stage 1 for the second and subsequent times after the start of purification of methane fermentation gas, each adsorption tower 10, 20, 30 is in a state where step 4 of stage 3 has been completed. Therefore, as apparent from FIG. 3A, the third adsorption tower 30 is in a state where carbon dioxide gas or the like is adsorbed on the adsorbent.
And in the stage 1, the following processes 1-4 are implemented sequentially.

(Process 1)
As shown in FIG. 4A, in the process 1 of the stage 1, only the first methane fermentation gas valve 12, the first purified gas valve 14, the second pressure equalizing valve 26, and the third pressure equalizing valve 36 are opened. The valve is closed and the vacuum pump 71 and the recycle gas pump 82 are stopped.

  And in the process 1 of the stage 1, methane fermentation gas is supplied to the 1st adsorption tower 10 via a part of common methane fermentation gas line 40 and the 1st methane fermentation gas line 11. FIG. Here, in the first adsorption tower 10, most of the carbon dioxide gas contained in the supplied methane fermentation gas and a part of the methane gas are adsorbed by the adsorbent. As a result, the purified gas enriched with methane gas flows out from the first adsorption tower 10, and the purified gas that flows out from the first adsorption tower 10 passes through the first purified gas line 13 and the common purified gas line 50 to be a device. It flows out.

Note that the methane fermentation gas is supplied to the first adsorption tower 10 at a relatively low pressure P2: 5 to 100 kPa (gauge pressure). Therefore, from the viewpoint of sufficiently adsorbing carbon dioxide gas to the adsorbent, carbon dioxide gas can be sufficiently adsorbed to the adsorbent by increasing the amount of adsorbent packed in the adsorption tower and decreasing the space velocity SV. . Specifically, when molecular sieve charcoal is used as the adsorbent, the carbon dioxide gas can be sufficiently adsorbed by the adsorbent by setting the space velocity SV to 300 h ⁻¹ or less. Here, the space velocity SV can be calculated using the following equation (1).
SV = (Methane fermentation gas supply rate [m ³ / h] / adsorbent volume [m ³ ]) (1)

  Moreover, in the process 1 of the stage 1, the 2nd adsorption tower 20 and the 3rd adsorption tower 30 are connected via the 2nd pressure equalization line 25, the common pressure equalization line 60, and the 3rd pressure equalization line 35. And by equalizing the pressure in the second adsorption tower 20 and the pressure in the third adsorption tower 30, the pressure in the second adsorption tower can be increased in the subsequent process, Reduce the energy required to reduce pressure.

That is, in the process 1 of the stage 1, in the first adsorption tower 10, an adsorption process is performed in which the methane fermentation gas is supplied to the adsorption tower to obtain purified gas, and in the second adsorption tower 20 and the third adsorption tower 30, the adsorption is performed. A pressure equalization step is performed to equalize the pressure between the columns.
In addition, the implementation time of the process 1 can be sufficient time to make the pressure of the 2nd adsorption tower 20 and the 3rd adsorption tower 30 uniform.

(Process 2)
In step 2 performed after step 1, as shown in FIG. 4B, the first methane fermentation gas valve 12 and the first purified gas valve 14 remain open, while the second pressure equalizing valve 26 and the second pressure equalizing valve 26 are maintained. The three pressure equalizing valve 36 is closed. In step 2, the third desorption gas valve 38 and the recycle gas valve 81 are opened, and the vacuum pump 71 and the recycle gas pump 82 are operated. The other valves remain closed.

  Here, in step 2 of stage 1, the inside of the third adsorption tower 30 is decompressed using the vacuum pump 71, and the gas adsorbed by the adsorbent in the third adsorption tower is desorbed to regenerate the adsorbent. Further, the desorption gas flowing out from the third adsorption tower 30 is recycled using a recycle gas pump 82, a part of the third methane fermentation gas line 31, the third desorption gas line 37, a part of the common desorption gas line 70 and the recycle gas. It flows into the common methane fermentation gas line 40 via the line 80. That is, in step 2, the desorption gas flowing out from the third adsorption tower 30 is supplied to the first adsorption tower 10 together with the methane fermentation gas as a recycle gas.

  And in the process 2 of the stage 1, the mixed gas of methane fermentation gas and recycle gas supplied to the 1st adsorption tower 10 via a part of common methane fermentation gas line 40 and the 1st methane fermentation gas line 11 is obtained. And purified in the first adsorption tower 10. That is, in the first adsorption tower 10, most of the carbon dioxide gas contained in the mixed gas of methane fermentation gas and recycle gas and a part of the methane gas are adsorbed by the adsorbent and the methane gas is enriched. Gas flows out. Note that the purified gas flowing out of the first adsorption tower 10 flows out of the apparatus through the first purified gas line 13 and the common purified gas line 50.

  That is, in the process 2 of the stage 1, in the 1st adsorption tower 10, the adsorption process which supplies methane fermentation gas and recycle gas to an adsorption tower, and obtains purified gas is implemented. Further, in the third adsorption tower 30, a desorption process for regenerating the adsorbent by desorbing the gas adsorbed by the adsorbent is performed, and the desorption gas generated in the desorption process is performed by the adsorption process. A recycling process for supplying the 1 adsorption tower 10 as a recycled gas is performed. In addition, in the 2nd adsorption tower 20, the holding process which maintains the state after completion | finish of the process 1 is implemented.

  Here, in the adsorption step, most of the carbon dioxide gas contained in the methane fermentation gas and a part of the methane gas are adsorbed by the adsorbent. In addition, at the end of the adsorption step, purified gas containing high-concentration methane gas remains in the voids in the adsorption tower. Therefore, the gas (desorption gas) discharged from the adsorption tower in the desorption step contains both carbon dioxide gas and methane gas. Therefore, when the desorption gas is supplied to the first adsorption tower 10 as a recycle gas, the methane gas in the desorption gas can be effectively recovered as a purified gas, so that the entire amount of the desorption gas is exhausted outside the apparatus. The methane gas recovery rate can be improved.

However, here, the concentration of methane gas contained in the desorption gas is low (for example, about 20% by volume at maximum), and the desorption gas contains a relatively high concentration of carbon dioxide gas.
In addition, the adsorbent used in the pressure swing adsorption method usually adsorbs carbon dioxide more easily than methane gas, but more easily desorbs methane gas than carbon dioxide. Further, the purified gas remaining in the adsorption tower at the end of the adsorption process is discharged immediately after the start of the desorption process. Therefore, the concentration of methane gas contained in the desorption gas becomes maximum immediately after the start of the desorption process, and then gradually decreases.
Therefore, when the desorption gas is continuously supplied to the first adsorption tower 10 as the recycle gas, the amount of carbon dioxide flowing into the first adsorption tower 10 increases. When the amount of carbon dioxide gas flowing into the first adsorption tower 10 increases, the amount of gas adsorbed by the adsorbent approaches the saturated adsorption amount, and in the purified gas during the adsorption process, particularly at the end of the adsorption process. There is a risk that the concentration of carbon dioxide gas increases (that is, the concentration of methane gas decreases). When the concentration of carbon dioxide in the refined gas increases, it becomes impossible to obtain a purified gas having a methane gas concentration higher than the desired concentration.

Therefore, in the purification apparatus 100, the process 2 is ended as follows, and the supply of the recycled gas to the first adsorption tower 10 is stopped.
That is, in the refining apparatus 100, the stage 1 (hereinafter, referred to as “previous stage 1”) performed one time before the stage 1 (hereinafter, sometimes referred to as “current stage 1”) currently being performed may be referred to. .)) At the end of the adsorption step (that is, at the end of step 4), using the carbon dioxide gas concentration in the purified gas measured using the first carbon dioxide sensor 51, step 2 of the current stage 1 is performed. The maximum time to be obtained is determined, and the process 2 is completed between the start of the process 2 and the elapse of the maximum time. Specifically, in the refining device 100, when a predetermined maximum time has elapsed from the start of step 2, the control device 90 closes the recycle gas valve 81 and stops the operation of the recycle gas pump 82, so that the first adsorption tower The supply of the recycle gas to 10 is cut off, and the process 2 is finished.

Here, the maximum time during which step 2 can be performed is the following (I) to (I) using the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 at the end of step 4 of the previous stage 1. It can be determined as in III).
(I) When the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 is less than a predetermined concentration, the time during which the recycle gas is circulated through the first adsorption tower 10 in the adsorption process of the previous stage 1 ( That is, the time is longer than the previous execution time of step 2.
(II) When the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 exceeds a predetermined concentration, the time during which the recycle gas is circulated through the first adsorption tower 10 in the adsorption process of the previous stage 1 ( That is, the time is shorter than the previous execution time of step 2).
(III) When the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 is equal to the predetermined concentration, the time during which the recycle gas is circulated through the first adsorption tower 10 in the adsorption process of the previous stage 1 ( In other words, the time is equal to or less than the previous execution time of the step 2, preferably the same time as the previous execution time of the step 2.

Here, the “predetermined concentration” when determining the maximum time during which the step 2 can be performed is the permissible range of the performance of the adsorbent used, the required recovery rate of methane gas, and the decrease in concentration of methane gas in the purified gas The concentration is determined according to Specifically, the “predetermined concentration” can be determined experimentally, for example, within a range in which the concentration of methane gas in the purified gas does not become less than a desired concentration until the end of stage 1. In the purification of methane fermentation gas, the total of the methane gas concentration and the carbon dioxide gas concentration in each gas can be approximated to 100% by volume. Therefore, the “predetermined concentration” is more specifically 0, for example, than the concentration of carbon dioxide when the concentration of methane gas in the purified gas is a desired concentration (hereinafter referred to as “limit carbon dioxide concentration”). The concentration may be lower by 2 to 2.0% by volume. If the predetermined concentration is lower than the limit carbon dioxide concentration by 0.2% by volume or more, the concentration of methane gas in the refined gas becomes less than the desired concentration when the maximum time is set longer than the previous execution time of step 2. This is because it can be sufficiently suppressed. If the predetermined concentration is lower than the limit carbon dioxide concentration within a range of 2.0% by volume or less, the probability that the maximum time is set shorter than the execution time of the previous step 2 is reduced, and methane gas It is because it can suppress that a recovery rate falls.
It should be noted that how long (or short) the maximum time with respect to the execution time of the previous step 2 is determined using a known method such as proportional control, differential control, integral control, PID control. Can do. Specifically, how long (or shorter) the maximum time is accumulated using PID control or the like by accumulating data on the past execution time of step 2 and carbon dioxide concentration at the end of step 4 Can be determined.

Here, as described above, the concentration of methane gas contained in the desorption gas becomes maximum immediately after the start of the desorption process, and then gradually decreases. Therefore, when ending the process 2 at the elapse of the maximum time determined by using the carbon dioxide gas concentration in the refined gas at the end of the process 4 of the previous stage 1, the concentration of methane gas particularly in the latter half of the process 2 There is a possibility that a desorption gas having a very low value will be supplied to the first adsorption tower 10 as a recycle gas.
Therefore, in this purification apparatus 100, from the viewpoint of suppressing the supply of the desorption gas containing almost no methane gas to the first adsorption tower 10 as the recycle gas, the concentration of the carbon dioxide gas contained in the desorption gas is also reduced. It is preferable to use and determine the timing to end the process 2 of the current stage 1.
That is, in the purification apparatus 100, the carbon dioxide concentration in the desorption gas is continuously measured using the second carbon dioxide sensor 72 in the process 2 of the present stage 1 and the measured carbon dioxide concentration in the desorption gas is used. It is preferable to determine the timing for ending step 2. Specifically, the carbon dioxide concentration in the desorption gas is continuously measured during the step 2, and only the desorption gas having a methane gas concentration equal to or higher than a predetermined concentration is supplied to the first adsorption tower 10 as a recycle gas. In addition, it is preferable to determine the timing for ending step 2.

  More specifically, in the refining device 100, even before the maximum time elapses, if the concentration of carbon dioxide in the desorption gas measured by the second carbon dioxide sensor 72 becomes a predetermined value or more, the control is performed. It is preferable that the apparatus 90 closes the recycle gas valve 81 and stops the operation of the recycle gas pump 82 to shut off the supply of the recycle gas to the first adsorption tower 10 and end the step 2. If the concentration of the carbon dioxide gas in the desorption gas does not become a predetermined value or more before the maximum time elapses, the process 2 is terminated when the maximum time elapses.

Here, the “predetermined value of the concentration of carbon dioxide in the desorption gas” for ending Step 2 can be appropriately set according to the performance of the adsorbent used and the required recovery rate of methane gas.
Specifically, the “predetermined value of the concentration of carbon dioxide in the desorption gas” can be set, for example, within a range of 40% by volume to 80% by volume. This is because if the predetermined value is 40% by volume or more, the recovery rate of methane gas can be sufficiently increased. Further, if the predetermined value is 80% by volume or less, the desorption gas containing almost no methane gas is suppressed from being supplied to the first adsorption tower 10 as a recycle gas while sufficiently increasing the methane gas recovery rate. Because you can.

In the above example, the process 2 is ended when the maximum time has elapsed from the start of the process 2 or when the concentration of carbon dioxide in the desorption gas is equal to or higher than a predetermined value, but the process 2 is ended. The timing may be determined by a method other than the above example.
Specifically, the timing for ending Step 2 is when the maximum time has elapsed since the start of Step 2 and when the predetermined time has elapsed since the concentration of carbon dioxide in the desorption gas has reached a predetermined value. It may be any earlier timing. The “predetermined time” can be determined by conducting an experiment in advance.

(Process 3)
In step 3 performed after step 2, as shown in FIG. 4C, the first methane fermentation gas valve 12, the first purified gas valve 14, and the third desorption gas valve 38 are kept open, and the vacuum pump 71 is Continue driving. On the other hand, the control device 90 closes the recycle gas valve 81. In step 3, the control device 90 opens the common desorption gas valve 73 and stops the operation of the recycle gas pump 82. The other valves remain closed.

  Here, in the process 3 of the stage 1, the pressure reduction in the third adsorption tower 30 using the vacuum pump 71 is continued. In the third adsorption tower, the gas adsorbed on the adsorbent is desorbed to regenerate the adsorbent. On the other hand, the desorption gas that has been desorbed from the adsorbent and has flowed out of the third adsorption tower 30 is not supplied to the first adsorption tower 10 as a recycle gas, but a part of the third methane fermentation gas line 31, the third desorption. The gas is discharged outside the apparatus through the gas line 37 and a part of the common desorption gas line 70.

  And in the process 3 of the stage 1, like the process 1, the methane fermentation gas supplied to the 1st adsorption tower 10 via the part of the common methane fermentation gas line 40 and the 1st methane fermentation gas line 11 is 1st. Purification is performed in one adsorption tower 10. Note that the purified gas flowing out of the first adsorption tower 10 flows out of the apparatus through the first purified gas line 13 and the common purified gas line 50.

That is, in the process 3 of the stage 1, in the 1st adsorption tower 10, the adsorption process which supplies methane fermentation gas to an adsorption tower and obtains refined gas is implemented. Further, in the third adsorption tower 30, a desorption process for regenerating the adsorbent by desorbing the gas adsorbed by the adsorbent is performed, and an exhaust process for discharging the desorbed gas generated in the desorption process to the outside of the apparatus. carry out. In the second adsorption tower 20, the holding process is continued.
In addition, the timing which complete | finishes the process 3 can be made into the timing from which gas is fully desorbed from the adsorbent in the 3rd adsorption tower 30 (namely, adsorbent fully reproduce | regenerates). Specifically, the timing at which the pressure in the third adsorption tower 30 becomes, for example, −80 kPa (gauge pressure) can be set.

(Process 4)
In step 4 performed after step 3, as shown in FIG. 4D, the first methane fermentation gas valve 12, the first purified gas valve 14, and the third desorption gas valve 38 are kept open, and the vacuum pump 71 is Continue driving. On the other hand, the common desorption gas valve 73 is closed. In step 4, the second purified gas valve 24, the third purified gas valve 34, and the recycled gas valve 81 are opened, and the recycled gas pump 82 is operated. The other valves remain closed.

  Here, in step 4 of stage 1, a part of the purified gas flowing out from the first adsorption tower 10 is supplied to the second adsorption tower 20 via the second purification gas line 23, and the inside of the second adsorption tower 20 Pressurize. And the pressure in the 2nd adsorption tower 20 is raised to the pressure substantially equal to the pressure of refined gas, and it prepares for implementation of the adsorption process in the 2nd adsorption tower 20 in process 1 of stage 2.

  In step 4 of stage 1, a part of the purified gas flowing out from the first adsorption tower 10 is supplied to the third adsorption tower 30 via the third purification gas line 33, and the inside of the third adsorption tower 30 is The atmosphere is replaced with purified gas, and the desorption gas remaining in the third adsorption tower 30 is caused to flow out of the third adsorption tower 30. The gas flowing out from the third adsorption tower 30 (hereinafter referred to as “substitution gas”) has almost the same composition as the purified gas, and contains methane gas at a high concentration. Therefore, the replacement gas is not exhausted, and the common methane fermentation gas line passes through a part of the third methane fermentation gas line 31, the third desorption gas line 37, a part of the common desorption gas line 70, and the recycle gas line 80. 40 is supplied to the first adsorption tower 10.

  And in the process 4 of the stage 1, the mixed gas of the methane fermentation gas and the replacement gas supplied to the first adsorption tower 10 via the part of the common methane fermentation gas line 40 and the first methane fermentation gas line 11 is Purification is performed in the first adsorption tower 10. That is, in the first adsorption tower 10, most of the carbon dioxide gas contained in the mixed gas of the methane fermentation gas and the replacement gas and a part of the methane gas are adsorbed by the adsorbent and the methane gas is enriched. Gas flows out.

That is, in the process 4 of the stage 1, in the 1st adsorption tower 10, the adsorption process which supplies methane fermentation gas and substitution gas to an adsorption tower, and obtains purified gas is implemented. Moreover, in the 2nd adsorption tower 20, the pressurization process with which the adsorption process implemented next is implemented by pressurizing the inside of an adsorption tower previously is implemented. Further, in the third adsorption tower 30, a substitution step is performed in which the inside of the adsorption tower is substituted with a purified gas and the adsorbent is sufficiently regenerated.
It should be noted that the timing at which the step 4 is completed, that is, the timing at which the stage 1 is terminated can be a timing at which a predetermined time has elapsed from the start of the stage 1.
Incidentally, at the end of the step 4, the first carbon dioxide sensor 51 measures the concentration of carbon dioxide in the purified gas. The measured concentration of carbon dioxide gas is used to determine the maximum time during which the process 2 can be performed in the next stage 1 (that is, the stage 1 after performing the stages 2 and 3).

  Then, according to the purification method of the above example using the purification apparatus 100, in the step 2 of each stage, the adsorption step is performed using at least a part of the desorption gas discharged from the adsorption tower performing the desorption step as a recycle gas. Since it is made to distribute | circulate to the inside adsorption tower, the methane gas contained in desorption gas can be collect | recovered as refined gas. Therefore, even when low-pressure methane fermentation gas is used, the recovery rate of methane gas from methane fermentation gas can be improved.

In the purification method of the above example, the maximum time during which the process 2 of each stage can be performed is determined by using the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 at the end of the process 4 of the previous stage. Has been decided. Therefore, the methane gas contained in the desorption gas is sufficiently recovered to improve the recovery rate of the methane gas from the methane fermentation gas, and the concentration of the methane gas in the refined gas is suppressed from being lower than the desired concentration. be able to.
Specifically, when the concentration of carbon dioxide gas in the purified gas measured by the first carbon dioxide sensor 51 is less than a predetermined concentration, that is, at the end of the previous step 4, there is a sufficient margin for adsorbing carbon dioxide gas to the adsorption tower. In the case where it remains, the recovery time of methane gas can be further improved by setting the maximum time to be longer than the previous execution time of step 2.
Further, when the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 exceeds a predetermined concentration, that is, when there is not enough room to adsorb carbon dioxide in the adsorption tower at the end of the previous step 4. In this case, the maximum time is set to be shorter than the previous execution time of step 2, and the concentration of methane gas in the purified gas can be suppressed from becoming lower than the desired concentration.
Furthermore, when the concentration of carbon dioxide gas in the purified gas measured by the first carbon dioxide sensor 51 is a predetermined concentration, the maximum time is set to be less than the execution time of the previous step 2 and the purification rate of methane gas is improved while improving the recovery rate. It can suppress that the density | concentration of the methane gas in gas becomes lower than a desired density | concentration.

  In the purification method of the above example, if the circulation of the recycle gas is also stopped using the concentration of the carbon dioxide gas in the desorption gas, the desorption gas having a low concentration of methane gas is suppressed from flowing to the adsorption tower as the recycle gas. Thus, the recovery rate of methane gas from methane fermentation gas can be effectively improved.

In the above example, a carbon dioxide gas sensor is provided and control is performed by measuring a carbon dioxide concentration that is easier to measure than the methane gas concentration. However, in the purification apparatus 100, methane gas is used instead of (or in addition to) the carbon dioxide gas sensor. Control may be performed by providing a sensor and measuring the methane gas concentration instead of (or in addition to) the carbon dioxide gas concentration. More specifically, the maximum time during which Step 2 of the above example can be performed may be determined by measuring the concentration of methane gas in the purified gas in Step 4 of the previous stage and using the measured methane gas concentration. In addition, when using the methane gas density | concentration in the refined gas measured in the process 4, maximum time can be determined like following (IV)-(VI).
(IV) When the concentration of methane gas in the purified gas measured by the methane gas sensor exceeds a predetermined concentration, the time during which the recycle gas is circulated through the adsorption tower in the adsorption process of the previous stage (ie, implementation of the previous process 2) Time).
(V) When the concentration of the methane gas in the purified gas measured by the methane gas sensor is less than the predetermined concentration, the time during which the recycle gas is circulated through the adsorption tower in the adsorption process of the previous stage (that is, the execution of the previous process 2) Time).
(VI) When the concentration of methane gas in the purified gas measured by the methane gas sensor is equal to the predetermined concentration, the time during which the recycle gas is circulated through the adsorption tower in the adsorption process of the previous stage (ie, implementation of the previous process 2) Time) The following time, preferably the same time as the previous execution time of step 2.
Further, step 2 in the above example may be terminated when the concentration of methane gas in the desorption gas is measured in step 2 and the concentration of methane gas in the desorption gas becomes a predetermined value or less. In the above example, the sum of the methane gas concentration and the carbon dioxide gas concentration can be approximated to 100% by volume. Therefore, when the control is performed using the methane gas concentration, the above approximation is used to indicate “methane gas in purified gas”. And the “predetermined value of the concentration of methane gas in the desorption gas” can be determined.
Moreover, the process 1 and the process 3 of the driving | operation process table | surface of the said example may not be implemented.
Further, in the purification apparatus 100, the execution time of step 1, the total execution time of step 2 and step 3, and the execution time of step 4 are determined in advance, and the execution time of step 2 is set to the total of step 2 and step 3. You may change within the range of implementation time.
Further, when purification is performed using two adsorption towers, the purification can be performed according to an operation process chart as shown in FIG. 3B, for example.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and manufacturing system of city gas which reduced the energy required for manufacture of city gas can be provided.

DESCRIPTION OF SYMBOLS 1 City gas manufacturing system 2 Methane fermentation processing apparatus 3 Purification mechanism 4 City gas preparation mechanism 5 1st compressor 6 Purification apparatus 7 2nd compressor 8 Composition adjustment apparatus 9 Calorific value adjustment apparatus 10 1st adsorption tower 11 1st methane fermentation Gas line 12 First methane fermentation gas valve 13 First purified gas line 14 First purified gas valve 15 First pressure equalization line 16 First pressure equalization valve 17 First desorption gas line 18 First desorption gas valve 20 Second Adsorption tower 21 Second methane fermentation gas line 22 Second methane fermentation gas valve 23 Second purification gas line 24 Second purification gas valve 25 Second pressure equalization line 26 Second pressure equalization valve 27 Second desorption gas line 28 2 Desorption gas valve
30 Third adsorption tower 31 Third methane fermentation gas line 32 Third methane fermentation gas valve 33 Third purification gas line 34 Third purification gas valve 35 Third pressure equalization line 36 Third pressure equalization valve 37 Third desorption gas Line 38 Third desorption gas valve 40 Common methane fermentation gas line 50 Common refining gas line 51 First carbon dioxide sensor 60 Common pressure equalization line 70 Common desorption gas line 71 Vacuum pump 72 Second carbon dioxide sensor 73 Common desorption gas valve 80 Recycle gas Line 81 Recycle gas valve 82 Recycle gas pump 90 Controller 100 Purifier

Claims (4)

A purification process for purifying methane fermentation gas containing methane gas and carbon dioxide gas to obtain a purified gas enriched in methane gas;
Using the purified gas obtained in the purification step, a city gas preparation step of preparing a city gas having a predetermined composition, calorie and pressure,
A method for producing city gas including
The purification step includes at least a pressure swing adsorption step of separating carbon dioxide from methane fermentation gas using a pressure swing adsorption method,
In the pressure swing adsorption step, carbon dioxide gas is separated from methane fermentation gas having a pressure lower than the pressure of the city gas obtained in the city gas preparation step,
In the pressure swing adsorption process,
Using a purification device equipped with two or more adsorption towers packed with an adsorbent,
In each adsorption tower, an adsorption step of supplying the methane fermentation gas to the adsorption tower to obtain the purified gas, and a gas adsorbed on the adsorbent in the adsorption step are desorbed under reduced pressure to regenerate the adsorbent. Repeat the desorption process,
In the purification apparatus,
While the adsorption process is being performed in at least one adsorption tower, the desorption process is performed in at least one of the remaining adsorption towers, and at least the desorption gas discharged from the adsorption tower in which the desorption process is being performed Distribute a part of the adsorption process to the adsorption tower as a recycle gas ,
Measuring the concentration of methane gas and / or carbon dioxide gas in the purified gas at the end of the adsorption step in the at least one adsorption tower;
Using the measured concentration of methane gas in the purified gas and / or concentration of carbon dioxide gas in the purified gas, the recycle gas is supplied to the adsorption tower when the next adsorption step is performed in the at least one adsorption tower. Determine the maximum time for circulation,
When the measured concentration of methane gas in the purified gas exceeds a predetermined concentration and / or when the concentration of carbon dioxide gas in the purified gas is less than a predetermined concentration, the maximum time is set at the adsorption step in the at least the adsorption step. It is longer than the time when the recycle gas is circulated through one adsorption tower, and when the measured concentration of methane gas in the purified gas is less than a predetermined concentration and / or the concentration of carbon dioxide gas in the purified gas is a predetermined value. In the case of exceeding the concentration, the maximum time is made shorter than the time when the recycle gas is circulated through the at least one adsorption tower in the adsorption step, and the measured concentration of methane gas in the purified gas is a predetermined concentration. And / or if the concentration of carbon dioxide in the purified gas is a predetermined concentration, the maximum time is set to the at least the adsorption step. One of the you less time to flow through the recycle gas to the adsorption tower,
A method for producing city gas. Measure the concentration of methane gas and / or the concentration of carbon dioxide gas in the desorption gas,
When the next adsorption step is performed, the next adsorption step is performed so that the concentration of the methane gas in the recycle gas that is circulated to the adsorption tower that is performing the next adsorption step is equal to or higher than a predetermined concentration. 2. The method for producing city gas according to claim 1 , wherein the timing for stopping the circulation of the recycled gas to the adsorption tower is determined. A purification mechanism for purifying methane fermentation gas containing methane gas and carbon dioxide gas to obtain a purified gas enriched in methane gas;
A city gas preparation mechanism that uses the purified gas obtained by the purification mechanism to prepare a city gas having a predetermined composition, amount of heat, and pressure;
A city gas manufacturing system including
The purification mechanism includes at least a purification device for separating carbon dioxide from methane fermentation gas using a pressure swing adsorption method,
The purification apparatus is configured to separate carbon dioxide gas from methane fermentation gas having a pressure lower than the pressure of the city gas obtained by the city gas preparation mechanism,
The purification device is
Equipped with two or more adsorption towers filled with adsorbent,
In each adsorption tower, an adsorption step of supplying the methane fermentation gas to the adsorption tower to obtain the purified gas, and a gas adsorbed on the adsorbent in the adsorption step are desorbed under reduced pressure to regenerate the adsorbent. Repeat the desorption process,
While supplying the methane fermentation gas to at least one adsorption tower to produce purified gas, at least one of the remaining adsorption towers depressurizes the adsorption tower to reduce the gas adsorbed on the adsorbent. Configured to desorb,
A recycle gas supply line for supplying at least a part of the desorption gas discharged from at least one of the remaining adsorption towers to the at least one adsorption tower as a recycle gas ;
A supply shut-off mechanism for shutting off the supply of the recycle gas to the at least one adsorption tower via the recycle gas supply line;
A purified gas concentration meter for measuring the concentration of methane gas and / or the concentration of carbon dioxide in the purified gas;
A control device for controlling the operation of the supply shut-off mechanism to control the time for circulating the recycle gas to the at least one adsorption tower;
With
The controller is
Using the measured concentration of methane gas in the purified gas and / or concentration of carbon dioxide gas in the purified gas, the recycle gas is supplied to the adsorption tower when the next adsorption step is performed in the at least one adsorption tower. Determine the maximum time for circulation,
When the concentration of methane gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower exceeds a predetermined concentration and / or the concentration of carbon dioxide gas in the purified gas is predetermined. If the concentration is less than the concentration, the operation of the supply cutoff mechanism is controlled so that the maximum time is longer than the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step,
When the concentration of methane gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower is less than a predetermined concentration and / or the concentration of carbon dioxide gas in the purified gas is predetermined. If the concentration exceeds, the operation of the supply cutoff mechanism is controlled so that the maximum time is shorter than the time during which the recycled gas is circulated through the at least one adsorption tower in the adsorption step.
When the concentration of methane gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower is a predetermined concentration and / or the concentration of carbon dioxide gas in the purified gas is a predetermined concentration In the case of concentration, the operation of the supply cutoff mechanism is controlled so that the maximum time is equal to or less than the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step.
A city gas production system characterized by that. A desorption gas concentration meter for measuring the concentration of methane gas and / or the concentration of carbon dioxide gas in the desorption gas;
The controller controls the operation of the supply cutoff mechanism using the concentration of methane gas in the desorption gas and / or the concentration of carbon dioxide gas in the desorption gas measured by the desorption gas concentration meter;
When carrying out the next adsorption step, the recycle gas to the at least one adsorption tower is adjusted so that the concentration of the methane gas in the recycle gas to be circulated to the at least one adsorption tower is not less than a predetermined concentration. 4. The city gas production system according to claim 3 , wherein the supply is cut off.

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