JP2013095727A - Methane concentration method and methane concentration device of biogas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly concentrate methane from a biogas and to further effectively utilize methane included in the biogas.SOLUTION: The biogas is pressurized and supplied to a first stage separation membrane module 1 via a supply tube 4 and a first compressor 5, a transmitted gas transmitted through the module 1 and containing carbon dioxide much is compressed by a second compressor 9 via a transmission gas tube 7 and cooled by a cooler 10 to liquefy and recover carbon dioxide and residual transmitted gas supplied to a gas engine 26 to be utilized. A non-transmitted gas which is not transmitted through the first stage separation membrane module 1 and contains methane much is supplied to a second stage separation membrane module 2 by residual pressure via a non-transmission gas tube 8 and a transmitted gas transmitted through the module 2 and containing carbon dioxide much is recycled to the first stage separation membrane module 1 via a recycle tube 11 and the supply tube 4 and a non-transmitted gas which is not transmitted through the second stage separation membrane module 2 and contains methane much is recovered as a methane concentrated gas in a recovering tube 12.

Description

  The present invention relates to a biogas methane concentration method and a methane concentration apparatus for concentrating and recovering methane from a biogas mainly composed of methane and carbon dioxide.

The composition of biogas is about 60% methane (CH ₄ ), about 40% carbon dioxide (CO ₂ ), 1000 ppm hydrogen sulfide (H ₂ S), trace amounts of oxygen (0 ₂ ), nitrogen (N ₂ ) And hydrogen (H ₂ ), and its calorific value is about half that of city gas (13A). In order to use this biogas as fuel for, for example, a natural gas vehicle (NGV), it is necessary to increase the calorific value. Therefore, it is necessary to refine the biogas and remove substances other than methane to increase the concentration of methane.

  Here, hydrogen sulfide can be removed by a desulfurizing agent, and oxygen can be removed by burning with hydrogen using an oxidation catalyst. On the other hand, the carbon dioxide removal method mainly includes a high pressure water absorption method, a PSA method, and a membrane separation method. In the membrane separation process, the methane recovery rate is lowered only by performing a one-stage membrane separation process (a process of passing the separation membrane once). Since carbon dioxide in biogas is permeated through a single separation membrane to separate it, it is necessary to lengthen the separation time, and in the process, some methane is also permeated at the same time as carbon dioxide, and methane is recovered. This is because the rate becomes low.

  Therefore, the following Patent Document 1 describes a technique for performing a two-stage membrane separation process. The apparatus shown in FIG. 2 includes front and rear separation membrane modules 51 and 52 arranged in series. A supply gas pipe 53 to which biogas is supplied is connected to an inlet of the first-stage separation membrane module 51 having a separation membrane, and a compressor 54 is provided in the supply gas pipe 53. An exhaust pipe 55 is connected to the permeate side outlet of the first-stage separation membrane module 51, and a vacuum pump 56 such as a vacuum pump is provided in the exhaust pipe 55. One end of a non-permeable gas pipe 57 is connected to the non-permeable side outlet of the first separation membrane module 51. The other end of the non-permeating gas pipe 57 is connected to the inlet of the second-stage separation membrane module 52 having a separation membrane. One end of a recycle pipe 58 is connected to the permeate side outlet of the second-stage separation membrane module 52. The other end of the recycle pipe 58 is connected to a supply gas pipe 53 upstream of the compressor 54. A product gas pipe 59 is connected to the non-permeate side outlet of the second separation membrane module 52.

  In the above apparatus, the supply gas pipe 53 is supplied with, for example, biogas having a methane concentration of 60% (after desulfurization). This gas is pressurized by the compressor 54 together with the gas joining from the recycle pipe 58 and is supplied to the first separation membrane module 51. In the first separation membrane module 51, the permeate side is decompressed by the decompression pump 56, so that carbon dioxide is efficiently removed and exhausted. On the non-permeate side of the first-stage separation membrane module 51, a gas enriched with methane is supplied to the second-stage separation membrane module 52 via the non-permeate gas pipe 57, and further methane is further added on the non-permeate side. Concentrated. The permeation side of the second-stage separation membrane module 52 is preferably at atmospheric pressure, but 20 to 40% of the amount of gas supplied to the second-stage separation membrane module 52 is supplied via the recycle pipe 58. Recycled to 53. That is, the methane remaining in the recycle off gas (permeate gas) of the second separation membrane module 52 is recycled for reconcentration without being exhausted as it is. As a result, the methane concentration at the non-permeation side outlet of the first separation membrane module 51 is 75 to 85%, and the methane concentration of the product gas at the non-permeation side outlet of the second separation membrane module 52 is 90% or more. Become. Further, the methane recovery rate is 85% or more.

  That is, according to the configuration of the apparatus, carbon dioxide is separated in a short time by the first-stage separation membrane module 51 and the remaining carbon dioxide is separated by the second-stage separation membrane module 52. The transmission loss is reduced. Furthermore, the separation membrane module 52 in the second stage recycles the separated permeated gas (containing tens of percent of methane), thereby improving the methane recovery rate.

Japanese Patent Laid-Open No. 9-124514

  However, in the apparatus described in Patent Document 1, the concentration of carbon dioxide is high in the waste off-gas (permeate gas) in the first separation membrane module 51, and the methane recovery rate is extremely high when recycled (in-process recirculation). It will drop to. Therefore, the first separation membrane module 51 is discarded without being recycled like the recycle off-gas (permeated gas) in the second separation membrane module 52. As a result, methane (about “15%” of the total methane) contained in the permeated gas that has passed through the first-stage separation membrane module 51 is wasted. For this reason, it is required to further effectively use methane contained in biogas.

  The present invention has been made in view of the above circumstances, and its purpose is to highly concentrate methane from biogas and to make more effective use of methane contained in biogas. An object of the present invention is to provide a concentration method and a methane concentration apparatus.

  In order to achieve the above object, the invention described in claim 1 is a biogas methane concentration method for concentrating and recovering methane from biogas using a separation membrane. Pressurized supply to the separation membrane, compresses and cools the permeated gas containing a large amount of carbon dioxide that has passed through the first stage separation membrane, and liquefies and recovers the carbon dioxide in the permeated gas, and the remaining permeated gas Is supplied to a gas utilization device, and a non-permeate gas containing a large amount of methane that has not permeated through the first-stage separation membrane is supplied to the second-stage separation membrane by the residual pressure. The purpose is to recycle the permeated gas containing a large amount of permeated carbon dioxide to the first-stage separation membrane and recover the non-permeated gas containing a large amount of methane that has not permeated the second-stage separation membrane as a methane-enriched gas. To do.

  According to the configuration of the above invention, the biogas is pressurized and supplied to the first-stage separation membrane, whereby the components in the biogas are separated by the separation membrane. Then, the permeated gas containing a large amount of carbon dioxide that has passed through the first-stage separation membrane is compressed and cooled, whereby the carbon dioxide in the permeated gas is liquefied and recovered. Further, the remaining permeated gas containing methane is supplied to the gas utilization device for use. On the other hand, the non-permeate gas containing a large amount of methane that has not permeated through the first stage separation membrane is supplied to the second stage separation membrane by the residual pressure. Are further separated. The permeated gas containing a large amount of carbon dioxide that has permeated through the second stage separation membrane is recirculated to the first stage separation membrane. Further, the non-permeated gas containing a large amount of methane that has not permeated through the second-stage separation membrane is recovered as a methane-enriched gas. Accordingly, since carbon dioxide in the permeated gas that has passed through the first stage separation membrane is liquefied and recovered by compression and cooling, the carbon dioxide concentration in the remaining permeated gas is reduced, and the gas is a gas containing a large amount of methane. Used by equipment used. As a result, the methane-enriched gas can be obtained effectively, and the permeated gas that has permeated through the first-stage separation membrane, which has been conventionally discarded, is effectively used by the gas utilization device.

  In order to achieve the above object, according to a second aspect of the present invention, in the first aspect of the present invention, the gas utilization device is an energy generation device that generates energy from the remaining permeated gas. The purpose is to use the generated energy as an energy source of equipment for generating biogas.

  According to the configuration of the invention, in addition to the action of the invention according to claim 1, the energy generated by the energy generating device from the remaining permeated gas is used as the energy source of the facility for generating biogas. In order to generate biogas, methane contained in the permeate gas is effectively used.

  In order to achieve the above object, the invention according to claim 3 is the invention according to claim 1 or 2, wherein when the remaining permeate gas is supplied to the gas utilization device and used, the city gas is used as the permeate gas. Is intended to be mixed.

  According to the structure of the said invention, in addition to the effect | action of the invention of Claim 1 or 2, since city gas is mixed with permeation | transmission gas, permeation | transmission gas is utilized more efficiently.

  In order to achieve the above object, the invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the dehumidification is performed before the permeated gas that has permeated through the first separation membrane is cooled. The purpose is to do.

  According to the configuration of the invention, in addition to the operation of the invention according to any one of claims 1 to 3, the permeated gas that has permeated the first-stage separation membrane is dehumidified before being cooled. Moisture is removed from the water, and a permeated gas that does not contain water is used for cooling.

  In order to achieve the above object, the invention described in claim 5 is a biogas methane concentrator for concentrating and recovering methane from biogas using a separation membrane, wherein biogas is supplied. A pipe, a first-stage separation membrane module connected to the supply pipe, a first compressor provided in the supply pipe, and a permeated gas containing a large amount of carbon dioxide permeated through the first-stage separation membrane module A non-permeating gas flow through which the non-permeating gas containing a large amount of methane that has not permeated through the first separation membrane module flows. A gas pipe, a second compressor and a cooler sequentially provided in series with the permeate gas pipe from the upstream side, a second-stage separation membrane module connected to the non-permeate gas pipe, and a second-stage separation membrane Many carbon dioxide permeated through the module The purpose of the present invention is to provide a recirculation pipe that recirculates the permeated gas to the supply pipe and a recovery pipe that collects a non-permeated gas containing a large amount of methane that has not permeated through the second separation membrane module as a methane-enriched gas. And

  According to the configuration of the invention, the biogas is supplied to the supply pipe, and the biogas is compressed by the first compressor, whereby the pressurized biogas is supplied to the first separation membrane module. Supplied. In the first separation membrane module, components in the supplied biogas are separated. The permeated gas containing a large amount of carbon dioxide permeated through the first-stage separation membrane module flows to the permeate gas pipe, and the non-permeated gas containing a large amount of methane that did not permeate the first-stage separation membrane module It flows into the tube. The permeate gas that has flowed to the permeate gas pipe is compressed by the second compressor and cooled by the cooler, whereby carbon dioxide in the permeate gas is liquefied and recovered. Further, the remaining permeate gas containing methane further flows through the permeate gas pipe, is guided to the outside, and is used by the gas utilization device. On the other hand, the non-permeate gas containing a large amount of methane that has not permeated through the first-stage separation membrane module is supplied to the second-stage separation membrane module via the non-permeate gas pipe due to the residual pressure. In the second separation membrane module, the components in the non-permeating gas are further separated. Then, the permeated gas containing a large amount of carbon dioxide that has passed through the second-stage separation membrane module is recirculated to the supply pipe via the recirculation pipe, and is supplied again to the first-stage separation membrane module. On the other hand, the non-permeate gas containing a large amount of methane that has not permeated through the second separation membrane module flows to the recovery pipe and is recovered as a methane concentrated gas. Therefore, since carbon dioxide in the permeate gas that has passed through the first separation membrane module is liquefied and recovered by compression and cooling, the concentration of carbon dioxide in the remaining permeate gas decreases, and the permeate gas containing a large amount of methane. It is used for gas utilization equipment. As a result, the methane-enriched gas can be obtained effectively, and the permeated gas that has permeated through the first-stage separation membrane module that has been conventionally discarded can be effectively used by the gas utilization device.

  In order to achieve the above object, according to a sixth aspect of the present invention, in the fifth aspect of the invention, the gas utilization device is an energy generation device that generates energy from the permeated gas guided to the outside, and the energy The purpose is to use the energy generated by the generating device as an energy source of the facility for generating biogas.

  According to the configuration of the above invention, in addition to the action of the invention according to claim 5, the energy generated by the energy generating device from the remaining permeated gas is used as an energy source of the facility for generating biogas. In order to generate biogas, methane contained in the permeate gas is effectively used.

  In order to achieve the above object, the invention according to claim 7 is the invention according to claim 5 or 6, wherein when the permeate gas is used by a gas utilization device, the city gas is mixed with the permeate gas. The purpose.

  According to the structure of the said invention, in addition to the effect | action of the invention of Claim 5 or 6, since a city gas is mixed with a permeation | transmission gas, a permeation | transmission gas is utilized more efficiently.

  In order to achieve the above object, an invention according to an eighth aspect is the invention according to any one of the fifth to seventh aspects, wherein the first-stage separation membrane module and the second compressor are provided. The purpose of this is to provide a dehumidifier in the permeating gas pipe.

  According to the configuration of the invention, in addition to the action of the invention according to any one of claims 5 to 7, the permeated gas that has permeated the first separation membrane module is cooled by the cooler in the permeated gas pipe. Since the moisture is dehumidified by the dehumidifier before the water is removed, moisture is removed from the permeated gas, and the permeated gas not containing water is used for cooling by the cooler.

  According to invention of Claim 1, while being able to highly concentrate methane from biogas, the methane contained in biogas can be utilized still more effectively.

  According to the invention described in claim 2, in addition to the effect of the invention described in claim 1, methane contained in the biogas can be effectively used for generating the biogas.

  According to the invention described in claim 3, in addition to the effect of the invention described in claim 1 or 2, energy can be used more efficiently for the permeated gas.

  According to the invention described in claim 4, in addition to the effect of the invention described in any one of claims 1 to 3, it is possible to prevent moisture in the permeate gas from freezing during cooling by the cooler, Inhibitory factors for methane concentration can be eliminated.

  According to invention of Claim 5, while being able to highly concentrate methane from biogas, the methane contained in biogas can be utilized still more effectively.

  According to the invention described in claim 6, in addition to the effect of the invention described in claim 5, methane contained in the biogas can be effectively used for generating the biogas.

  According to the invention described in claim 7, in addition to the effect of the invention described in claim 5 or 6, energy can be used more efficiently per permeated gas.

  According to the invention described in claim 8, in addition to the effect of the invention described in any one of claims 5 to 7, it is possible to prevent moisture in the permeate gas from freezing during cooling by the cooler, Inhibitory factors for methane concentration can be eliminated.

The schematic block diagram which concerns on one Embodiment and shows a methane concentration apparatus. The schematic block diagram which shows a methane concentration apparatus in connection with a prior art.

  Hereinafter, an embodiment embodying a biogas methane concentration method and a methane concentration apparatus according to the present invention will be described in detail with reference to the drawings.

In FIG. 1, the methane concentration apparatus of this embodiment is shown with a schematic block diagram. As shown in FIG. 1, this methane concentrator uses a separation membrane to concentrate and recover methane (CH ₄ ) from biogas, and is a two-stage separation membrane module 1 arranged in series. , 2 are provided. The first-stage separation membrane module 1 and the second-stage separation membrane module 2 are each configured by accommodating a separation membrane 3 inside the case. Any type of separation membrane 3 can be used without limitation as long as it is a separation membrane that does not easily permeate methane and easily permeates carbon dioxide, such as polyamide, polyimide, and zeolite. The separation membrane 3 is separated into a permeate gas containing a large amount of carbon dioxide (CO ₂ ) and a non-permeate gas containing a large amount of methane (CH ₄ ) that did not permeate the separation membrane by allowing the biogas to permeate through the separation membrane 3. Can do.

  A supply pipe 4 to which biogas is supplied is connected to the inlet side of the first-stage separation membrane module 1. A methane fermentation tank 21, a desulfurization tower 22, and a gas holder 23 are sequentially provided in the upstream portion of the supply pipe 4 in series. The methane fermentation tank 21 is adapted to ferment methane and generate carbon dioxide and the like by introducing various types of biomass (for example, food waste). Then, biogas including methane and a carbon dioxide tower flows from the methane fermentation tank 21 to the supply pipe 4. In the process of passing through the desulfurization tower 22, the sulfur component is removed from the biogas that has flowed to the supply pipe 4. The biogas from which the sulfur component has been removed is temporarily stored in the gas holder 23 and flows from the gas holder 23 to the downstream portion of the supply pipe 4. The methane fermentation tank 21 described above corresponds to the facility for generating the biogas of the present invention, and includes various devices (not shown) such as a predetermined stirrer, a liquid feed pump, and a heat exchanger. These agitators, liquid feed pumps, and the like operate upon receipt of electricity, and the heat exchanger functions upon receipt of heat.

  On the other hand, a first compressor 5 is provided downstream of the supply pipe 4. A permeate gas pipe 7 is connected to the outlet side of the separation membrane module 1 at the first stage. Further, a non-permeable gas pipe 8 through which a non-permeable gas containing a large amount of methane that has not permeated through the separation membrane module 1 flows is connected to the outlet side of the separation membrane module 1 at the first stage. The permeate gas pipe 7 guides a permeate gas (off gas) containing a large amount of carbon dioxide permeated through the first-stage separation membrane module 1 to the outside. One end of the permeate gas pipe 7 is connected to a gas engine 26 provided outside. The gas engine 26 corresponds to a gas utilization device of the present invention that uses a permeated gas guided from the permeate gas pipe 7 to the outside, and also corresponds to an energy generating device that generates energy from the permeate gas. The gas engine 26 is configured to supplement the permeated gas with city gas in an auxiliary manner when the permeated gas supplied is used as fuel in the gas engine 26. The gas engine 26 operates by burning the mixed permeated gas and city gas as fuel, and generates electricity and heat as energy. These electricity and heat are supplied to various devices provided in the methane fermentation tank 21 as energy sources.

  Here, the gas engine 26 uses city gas mixed with permeated gas from the viewpoint of more efficient use of energy, but the permeated gas can also be used alone. In this embodiment, as described above, the permeated gas is converted into energy of electricity and heat by the gas engine 26 and used for biogas fermentation, so that high energy utilization efficiency from the methane fermentation process to the biogas separation process is achieved. Can be achieved.

  The permeate gas pipe 7 is provided with a second compressor 9 and a cooler 10 in series from the upstream side in order to recover carbon dioxide. A dehumidifier 13 is provided in the permeate gas pipe 7 between the first-stage separation membrane module 1 and the second compressor 9. Further, the permeate gas pipe 7 downstream from the cooler 10 is provided with a pressure reducing valve 16 for depressurizing the permeated gas. One end of the non-permeating gas pipe 8 is connected to the inlet side of the separation membrane module 2 at the second stage. A recirculation pipe 11 is connected to the outlet side of the separation membrane module 2 at the second stage. The recirculation pipe 11 is configured to recirculate the permeated gas containing a large amount of carbon dioxide permeated through the second-stage separation membrane module 2 to the supply pipe 4. One end of the recirculation pipe 11 is connected to the supply pipe 4 on the upstream side of the first compressor 5. Connected to the outlet side of the separation membrane module 2 at the second stage is a recovery pipe 12 that collects a non-permeated gas containing a large amount of methane that has not permeated the separation membrane module 2 as a methane concentrated gas (purified methane).

In this embodiment, the gas supply pressure by the first compressor 5 is preferably set to “0.5 to 0.98 (MPa)”. The gas supply pressure by the second compressor 9 is preferably set to “0.9 to 3 (MPa)”. The cooling temperature of the cooler 10 is preferably “−
20 to −50 (° C.) ”.

Next, an example of the methane concentration method performed using the above methane concentration apparatus will be described. In this embodiment, about 30 (Nm ³ / h) of biogas that has been desulfurized and dehydrated is supplied to the supply pipe 4.

  In this embodiment, a biogas methane concentration method is performed in which methane is concentrated and recovered from biogas using the first and second separation membrane modules 1 and 2 having the separation membrane 3. Specifically, the biogas is pressurized and supplied to the first-stage separation membrane module 1, and the permeated gas containing a large amount of carbon dioxide that has passed through the first-stage separation membrane module 1 is compressed and cooled. The carbon dioxide in the gas is liquefied and recovered, and the remaining permeated gas is supplied to the gas engine 26 as fuel and used. A non-permeated gas containing a large amount of methane that has not permeated through the first-stage separation membrane module 1 is supplied to the second-stage separation membrane module 2 by residual pressure, and carbon dioxide that has permeated through the second-stage separation membrane module 2 is supplied. The permeated gas containing a large amount is recirculated to the first-stage separation membrane module 1, and the non-permeated gas containing a large amount of methane that has not permeated the second-stage separation membrane module 2 is recovered as a methane-enriched gas.

That is, at the position shown in FIG. 1A, biogas of “30 (Nm ³ / h)” is supplied to the supply pipe 4. This biogas is compressed to about “0.5 to 0.98 (MPa)” by the first compressor 5 and supplied to the first separation membrane module 1. Then, by allowing the biogas to permeate through the first-stage separation membrane module 1, the components in the biogas are separated.

Here, at a position shown in FIG. 1C, a permeated gas containing a large amount of carbon dioxide that has permeated through the first separation membrane module 1 flows through the permeate gas pipe 7. In this permeate gas, carbon dioxide occupies “80 (%)” or more, the remainder is mostly methane, and also contains trace amounts of hydrogen (H ₂ ), oxygen (0 ₂ ), and nitrogen (N ₂ ). . On the other hand, at the position shown in FIG. 1 (d), a non-permeate gas containing a large amount of methane that has not permeated through the first separation membrane module 1 flows through the non-permeate gas pipe 8. As for the properties of this non-permeating gas, methane accounts for “70 (%)” or more, the remainder is mostly carbon dioxide, and also contains trace amounts of hydrogen, oxygen and nitrogen.

  At the position shown in FIG. 1 (c), the permeate gas contains carbon dioxide (“80 (%)”) or more, so it is difficult to use it as fuel, and it is returned to the first-stage separation membrane module 1 for recycling. Then, the separation efficiency of the first-stage separation membrane module 1 is extremely lowered. Therefore, in the prior art, the permeated gas has been discarded.

  Therefore, in this embodiment, the permeated gas that has permeated the first separation membrane module 1 is compressed again by the second compressor 9 and cooled by the cooler 10, so that the position shown in FIG. The carbon dioxide is liquefied and recovered. Thereby, the remaining gas after liquefaction flows through the permeating gas pipe 7 at the position shown in FIG. Regarding the properties of this gas, carbon dioxide occupies “40 to 60 (%)”, and methane becomes “40 to 60 (%)”. In this way, by reducing the concentration of carbon dioxide in the permeate gas from “80 (%)” or more to “40 to 60 (%)”, the separation efficiency of the first separation membrane module 1 is reduced. Instead, the permeated gas that has permeated through the first-stage separation membrane module 1 can be supplied to the gas engine 26 and used as fuel. Furthermore, the pressure of the permeate gas used is increased by the second compressor 9 to be equal to or higher than the pressure of the first compressor 5. Therefore, in this embodiment, the permeated gas can be supplied to the gas engine 26 after the pressure is reduced by the pressure reducing valve 16 provided in the permeated gas pipe 7.

  Here, when the carbon dioxide is liquefied and recovered, the permeated gas contains moisture at the position shown in FIG. If this moisture is contained at a rate equal to or higher than the dew point of the cooling temperature of the permeate gas, the water in the permeate gas may freeze during cooling by the cooler 10 and become an obstacle. Therefore, in this embodiment, before the permeate gas flowing through the permeate gas pipe 7 is cooled by the cooler 10, the moisture is removed by the dehumidifier 13.

  The non-permeate gas that has not permeated through the first-stage separation membrane module 1 flows to the non-permeate gas pipe 8 at the position shown in FIG. 1D and is supplied to the second-stage separation membrane module 2. . The separation membrane module 2 in the second stage is divided into a permeation gas and a non-permeation gas as in the first separation membrane module 1. The non-permeating gas at this time flows to the recovery pipe 12 at the position shown in FIG. 1 (g), and is recovered as highly concentrated high-purity methane concentrated gas (product gas (purified methane)). On the other hand, the permeated gas that has permeated through the separation membrane module 2 at the second stage flows into the recirculation pipe 11 and recirculates to the supply pipe 4 at the position shown in FIG. The properties of the permeated gas are “about 60 (%)” for methane and “about 40 (%)” for carbon dioxide. Therefore, the permeated gas can be recycled without reducing the separation efficiency of the first-stage separation membrane module 1. Since this permeated gas is in an atmospheric pressure state, it is returned to the supply pipe 4 in the preceding stage of the first compressor 5.

  As described above, in this embodiment, the permeated gas that has passed through the first separation membrane module 1 that was discarded in the prior art can be used as fuel for the gas engine 26. Further, the methane concentration gas (purified methane) recovered in the recovery pipe 12 can be set to “98 (%)” or more, and the final methane recovery rate can be improved. In addition, since carbon dioxide can be liquefied and recovered, the amount of carbon dioxide generated from the biogas purification process can be greatly reduced.

  According to the biogas methane concentration method and methane concentration apparatus in this embodiment described above, the biogas is supplied to the supply pipe 4, and the biogas is compressed by the first compressor 5. Pressurized biogas is supplied to the separation membrane module 1 of the eye. In the 1st separation membrane module 1, the component in the supplied biogas is isolate | separated. Then, the permeated gas containing a large amount of carbon dioxide permeated through the first-stage separation membrane module 1 flows to the permeate gas pipe 7, and the non-permeated gas containing a large amount of methane that did not pass through the first-stage separation membrane module 1 is It flows to the non-permeating gas pipe 8.

  The permeate gas that has flowed to the permeate gas pipe 7 is compressed by the second compressor 9 and cooled by the cooler 10, whereby carbon dioxide in the permeate gas is liquefied and recovered. Further, the remaining permeated gas containing methane is supplied to the gas engine 26 as fuel in a state of being depressurized via the permeate gas pipe 7 and the pressure reducing valve 16 and used. On the other hand, the non-permeated gas containing a large amount of methane that has not permeated through the first-stage separation membrane module 1 is supplied to the second-stage separation membrane module 2 through the non-permeate gas pipe 8 due to the residual pressure.

  In the separation membrane module 2 at the second stage, the components in the non-permeating gas are further separated. Then, the permeated gas containing a large amount of carbon dioxide that has passed through the second-stage separation membrane module 2 is recirculated to the supply pipe 4 via the recirculation pipe 11 and supplied again to the first-stage separation membrane module 1. . On the other hand, the non-permeate gas containing a large amount of methane that has not permeated through the separation membrane module 2 in the second stage flows to the recovery pipe 12 and is recovered as a highly concentrated and highly purified methane enriched gas (product gas (purified methane)). Is done.

  Accordingly, since carbon dioxide in the permeate gas that has passed through the first separation membrane module 1 is liquefied and recovered by compression and cooling, the concentration of carbon dioxide in the remaining permeate gas is reduced and contains a large amount of methane. The gas is supplied to the gas engine 26 and used as fuel. As a result, the methane-enriched gas can be obtained effectively, and the permeated gas that has permeated through the first-stage separation membrane module 1 that has been conventionally discarded is effectively used by the gas engine 26. For this reason, while being able to highly concentrate methane from biogas, the methane contained in biogas can be utilized still more effectively.

  In this embodiment, city gas is mixed with permeated gas and used as fuel in the gas engine 26. Therefore, the permeate gas is used more efficiently. For this reason, energy can be utilized more efficiently per permeated gas. Here, since the flow rate of city gas can generally be easily adjusted by a valve or the like, the gas engine 26 can be stabilized by adjusting the flow rate of city gas even when the amount of permeated gas generated becomes unstable. Can be operated automatically.

In this embodiment, the amount of permeated gas generated by the first separation membrane module 1 is, for example, “about 3.8 (m ³ / h)”, and city gas is, for example, “about 5.6 (m ³ / h). h) ”is mixed and used, and the gas engine 26 (power generation efficiency: 30%, heat recovery efficiency: 50%) of“ 25 (kW) ”can be operated. The energy (electricity, heat) obtained by the gas engine 26 is calculated to be able to supplement all of the amount of heat with “about 50%” or more of the amount of power required by the equipment such as the methane fermentation tank 21, and the energy balance As well as a balanced system.

  In this embodiment, electricity or heat energy generated by the gas engine 26 from the permeate gas remaining in the first separation membrane module 1 is used as an energy source for equipment such as the methane fermentation tank 21 for generating biogas. Use. Therefore, methane contained in the permeate gas is effectively used to generate biogas. For this reason, methane contained in the biogas can be effectively used to generate the biogas. In other words, high energy utilization efficiency can be achieved in the entire system from the methane fermentation process to the biogas separation process.

  In this embodiment, the permeated gas that has permeated through the first separation membrane module 1 is dehumidified by the dehumidifier 13 before being cooled by the cooler 10 in the permeate gas pipe 7. Moisture is removed from the permeated gas, and the permeated gas not containing water is supplied to the cooler 10 for cooling. For this reason, it is possible to prevent the moisture in the permeate gas from freezing during cooling by the cooler 10, and to eliminate an obstruction factor for methane concentration.

  In addition, this invention is not limited to the said embodiment, A part of structure can also be changed suitably and implemented in the range which does not deviate from the meaning of invention.

  For example, although the dehumidifying device 13 is provided in the embodiment, it may be omitted depending on circumstances.

  In the above embodiment, the gas engine 26 is provided as the gas utilization device of the present invention, but a device such as a fuel cell or a gas boiler may be provided instead of the gas engine 26.

  In the above embodiment, city gas is mixed with permeated gas and supplied to the gas engine 26 for use. However, since the permeated gas itself has a relatively large amount of heat, it can be used as fuel as it is.

  The present invention can be used in a biogas system that effectively utilizes methane by concentrating and recovering methane from biogas.

1 1st stage separation membrane module 2 2nd stage separation membrane module 3 Separation membrane 4 Supply pipe 5 1st compressor 7 Permeate gas pipe 8 Non-permeate gas pipe 9 2nd compressor 10 Cooler 11 Recirculation pipe 12 Recovery pipe 13 Dehumidification processor 21 Methane fermentation tank (equipment for generating biogas)
26 Gas engine (gas-using equipment, energy-generating equipment)

Claims (8)

A method for concentrating and recovering methane from biogas by using a separation membrane,
Pressurize and supply the biogas to the first stage separation membrane,
By compressing and cooling the permeated gas containing a large amount of carbon dioxide that has passed through the first-stage separation membrane, the carbon dioxide in the permeated gas is liquefied and recovered, and the remaining permeated gas is supplied to the gas utilization device. And use
Supplying a non-permeating gas containing a large amount of methane that has not permeated through the first separation membrane to the second separation membrane by residual pressure;
Recirculating the permeated gas containing a large amount of carbon dioxide permeated through the second stage separation membrane to the first stage separation membrane;
A biogas methane concentration method, wherein non-permeate gas containing a large amount of methane that has not permeated through the second-stage separation membrane is recovered as methane concentrated gas.   The gas utilization device is an energy generation device that generates energy from the remaining permeated gas, and uses the energy generated by the energy generation device as an energy source of a facility for generating the biogas. The method for concentrating methane in biogas according to claim 1.   3. The biogas methane concentration method according to claim 1, wherein when the remaining permeate gas is supplied to the gas utilization device and used, city gas is mixed with the permeate gas.   The method of concentrating biogas according to any one of claims 1 to 3, wherein the permeated gas that has passed through the first-stage separation membrane is dehumidified before being cooled. A biogas methane concentrator that concentrates and recovers methane from biogas using a separation membrane,
A supply pipe to which biogas is supplied;
A first-stage separation membrane module connected to the supply pipe;
A first compressor provided in the supply pipe;
A permeate gas pipe for guiding a permeate gas containing a large amount of carbon dioxide permeated through the first stage separation membrane module to the outside;
A gas utilization device for utilizing the permeated gas guided from the permeate gas pipe to the outside;
A non-permeating gas pipe through which a non-permeating gas containing a large amount of methane that has not permeated the first-stage separation membrane module flows;
A second compressor and a cooler sequentially provided in series from the upstream side to the permeate gas pipe;
A second separation membrane module connected to the non-permeating gas pipe;
A recirculation pipe for recirculating a permeated gas containing a large amount of carbon dioxide permeated through the second stage separation membrane module to the supply pipe;
A biogas methane concentration apparatus comprising: a recovery pipe that recovers a non-permeate gas containing a large amount of methane that has not permeated through the second-stage separation membrane module as a methane concentrated gas.   The gas using device is an energy generating device that generates energy from the permeated gas guided to the outside, and uses the energy generated by the energy generating device as an energy source of a facility for generating the biogas. The biogas methane concentrator according to claim 4.   The biogas methane concentrator according to claim 5 or 6, wherein when the permeate gas is used by the gas utilization device, a city gas is mixed with the permeate gas.   The biogas according to any one of claims 5 to 7, wherein a dehumidifier is provided in the permeate gas pipe between the first stage separation membrane module and the second compressor. Methane concentrator.

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