Purified gas production system and method for producing purified gas

Abstract

To provide a production system of a refined gas and a production method of a refined gas, capable of reducing an energy consumption amount for cooling with a compact facility when producing a refined gas having the increased methane concentration from a biogas.SOLUTION: A production system (1) of a refined gas for obtaining a refined gas by concentrating methane in a biogas comprises: a separation device (40) that separates a biogas so as to obtain a refined gas in which the methane concentration is increased and a removed gas in which the carbon dioxide concentration is increased; a cooler that cools a biogas before being supplied to the separation device (40); a removed gas compressor (62) that compresses the removed gas discharged from the separation device; and an expansion valve (65) that expands the compressed removed gas, wherein latent heat followed by the expansion of the removed gas is used for cooling the biogas in the cooler.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a system for producing a purified gas and a method for producing a purified gas. [Background technology]

[0002] From the viewpoint of waste disposal and effective utilization of resources, methane-containing biogas is being generated by using methane fermentation from waste materials such as food waste from homes, cafeterias, restaurants, hotels, etc., livestock manure from farms and pig sties, and food waste from food factories.

[0003] In order to effectively use the methane in biogas as fuel for engines and boilers, it is necessary to increase the methane concentration by carrying out a purification process to remove carbon dioxide and other contaminants from the biogas. For the purification process, separation devices using a membrane separation method, a pressure swing adsorption method (hereinafter referred to as a "PSA method"), or the like are used (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-23211 A Summary of the Invention [Problem to be solved by the invention]

[0005] The membrane separation method used in purification processes uses a membrane separation device with a separation membrane, while the PSA method uses an adsorption tower filled with an adsorbent. Biogas is usually compressed before being supplied to these separators, but because separation membranes and adsorbents are sensitive to heat, the biogas that has been compressed to a high temperature is cooled in a cooler before being supplied to the separator. In addition, separation membranes and adsorbents have low resistance to moisture. Therefore, biogas with a high moisture content needs to be dehumidified in advance, and a cooler is used for this purpose as well.

[0006] However, cooling requires cooling equipment, which consumes energy. This requires space for the cooling equipment, and in addition to the initial and running costs of the cooling equipment, there is also the cost of energy consumption. The present invention has been made in consideration of the above circumstances, and provides a refined gas production system and a refined gas production method that can reduce energy consumption for cooling using compact equipment when producing refined gas with an increased methane concentration from biogas. [Means for solving the problem]

[0007] As a means for solving the above problem, the refined gas production system (1) described in claim 1 is a refined gas production system (1) that obtains a refined gas by concentrating methane in a biogas, and is characterized in that it includes a separation device (40) that separates biogas to obtain a refined gas with an increased methane concentration and a removed gas with an increased carbon dioxide concentration, a cooler that cools the biogas before it is supplied to the separation device (40), a removed gas compressor (62) that compresses the removed gas discharged from the separation device, and an expansion valve (65) that expands the compressed removed gas, and uses latent heat accompanying the expansion of the removed gas to cool the biogas in the cooler. According to this configuration, the removed gas, which has conventionally been discharged as is, can be used for cooling by simply compressing and then expanding it, so that the amount of energy consumed for cooling can be reduced with a compact facility.

[0008] The refined gas production system (1) described in claim 2 uses the latent heat accompanying the expansion of the removed gas to cool the biogas in the cooler by blowing the removed gas ejected from the expansion valve (65) into the cooler. According to this configuration, latent heat can be utilized for cooling with simple equipment.

[0009] In the refined gas production system (1) recited in claim 3, the cooler is a dehumidification cooler (12) that cools the biogas for dehumidification. According to this configuration, the latent heat of the removed gas can be utilized for cooling for dehumidification.

[0010] In the refined gas production system (1) recited in claim 4, the cooler is a cooler (23, 26) for cooling the compressed biogas. According to this configuration, the latent heat of the removed gas can be used to cool the biogas after compression.

[0011] In the purified gas production system (1) recited in claim 5, the separation device (40) is a membrane separation device having a separation membrane. According to this configuration, it is easy to obtain a refined gas with a sufficiently increased methane concentration.

[0012] The refined gas producing system (1) recited in claim 6 further comprises a housing (70) that houses at least the outlet through which the removed gas is expanded by the expansion valve (65) and ejected, and the cooler. According to this configuration, the removal gas containing a high concentration of carbon dioxide is released into the housing (70), thereby improving the explosion-proofing properties of the housing.

[0013] The refined gas producing system (1) recited in claim 7 includes a concentration meter (71) that measures a methane concentration in the housing (70), and when the methane concentration measured by the concentration meter (71) exceeds a predetermined value, the removed gas is discharged from the expansion valve (65) to the outside of the housing (70). According to this configuration, when the methane concentration in the removed gas has not been sufficiently reduced, the removed gas continues to be discharged into the housing (70), thereby preventing the inside of the housing (70) from becoming a flammable atmosphere.

[0014] The method for producing a purified gas recited in claim 8 is a method for producing a purified gas by concentrating methane in a biogas to obtain a purified gas, in which a pre-cooled biogas is separated to obtain a purified gas having an increased methane concentration and a removed gas having an increased carbon dioxide concentration, and the removed gas is compressed and then expanded, and the latent heat associated with the expansion of the removed gas is used to cool the compressed biogas. According to this configuration, the removed gas, which has conventionally been discharged as is, can be used for cooling by simply compressing and then expanding it, so that the amount of energy consumed for cooling can be reduced with a compact facility.

[0015] The method for producing a purified gas recited in claim 9 is a method for producing a purified gas by concentrating methane in a biogas to obtain a purified gas, in which the biogas is dehumidified by cooling it, and the dehumidified biogas is separated to obtain a purified gas with an increased methane concentration and a removed gas with an increased carbon dioxide concentration, and the removed gas is compressed and then expanded, and latent heat accompanying the expansion of the removed gas is used to dehumidify the biogas. According to this configuration, the latent heat of the removed gas can be utilized for cooling for dehumidification.

[0016] The method for producing a purified gas recited in claim 10 is a method for producing a purified gas by concentrating methane in a biogas, in which the biogas is compressed and then cooled, and the cooled biogas is separated to obtain a purified gas with an increased methane concentration and a removed gas with an increased carbon dioxide concentration, and the removed gas is compressed and then expanded, and latent heat accompanying the expansion of the removed gas is used for cooling the biogas after compression. According to this configuration, the latent heat of the removed gas can be used to cool the biogas after compression.

[0017] In the method for producing a purified gas recited in claim 11, the biogas is separated by a membrane separation method using a separation membrane. According to this configuration, it is easy to obtain a refined gas with a sufficiently increased methane concentration. Effect of the Invention

[0018] According to the refined gas production system and refined gas production method of the present invention, when a refined gas having an increased methane concentration is produced from biogas, the amount of energy consumed for cooling can be reduced with compact equipment. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic configuration diagram of a purified gas production system 1 according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] FIG. 1 shows a schematic configuration of a manufacturing system 1 according to one embodiment of the present invention. The production system 1 is a purified gas production system that obtains purified gas by concentrating methane in biogas. The production system 1 is generally composed of a pretreatment section 10, a compression section 20, a separation device 40, a purified gas discharge section 50, a removed gas discharge section 60, a housing 70, and a concentration meter 71.

[0021] The biogas that is the raw material for the production system 1 is gas obtained by methane fermentation of waste materials such as food waste from homes, cafeterias, restaurants, and hotels, livestock manure from farms and pig farms, and food waste from food factories. Biogas is produced when organic matter in waste is decomposed by anaerobic microorganisms, and is mostly composed of methane and carbon dioxide, and also contains moisture due to the fermentation atmosphere.

[0022] The ratio of methane to carbon dioxide depends on the type of waste and fermentation conditions, but as an example, the proportion of methane is about 60% by volume, and the remaining 40% by volume is carbon dioxide. Therefore, in order to obtain high-purity methane, it is necessary to purify it by removing the carbon dioxide.

[0023] The pretreatment section 10 is a section that pretreats the biogas prior to separation. The pretreatment section 10 includes a pretreatment line 11 that draws in the biogas from outside the production system 1, and is provided with a dehumidifying cooler 12, a desulfurizer 13, and a check valve 14, in that order from the upstream side. There is no particular limitation on the type of dehumidifying cooler 12, but a typical corrugated fin type or fin-tube type gas-liquid heat exchanger or the like can be used. A drain discharge line 15 is connected to the dehumidifying cooler 12, and the moisture dehumidified and removed by the dehumidifying cooler 12 can be discharged as drain outside the manufacturing system 1. The drain discharge line 15 is provided with an opening / closing valve 16.

[0024] The compression section 20 is provided with a first biogas compressor 22, a first cooler 23, an on-off valve 24, a second biogas compressor 25, and a second cooler 26 in this order from the upstream side on a first compression line 21. The upstream end of the first compression line 21 is connected to the downstream end of the pretreatment line 11, and the downstream end is connected to the separation device 40. In addition, a second compression line 27 that is connected directly to the separation device 40 without passing through a second biogas compressor 25 and a second cooler 26 branches off from between the first cooler 23 and the on-off valve 24 of the first compression line 21. An on-off valve 28 is provided on the second compression line 27.

[0025] The first biogas compressor 22 and the second biogas compressor 25 are provided to compress the pretreated biogas (dehumidified biogas) to a pressure required for treatment in the separation device 40. When the separator 40 is a membrane separator (a device using a membrane separation method), the biogas is supplied in a compressed state, so that a portion of the biogas can permeate the separation membrane. When the separation device 40 is a PSA (Pressure Swing Adsorption Method) device, the biogas can be passed through an adsorption tower filled with an adsorbent.

[0026] When the separation device 40 is a membrane separation device, the pressure of the biogas supplied to the separation device 40 is appropriately set according to the required methane concentration of the purified gas, etc. In order to obtain a purified gas containing a high concentration of methane, the pressure of the biogas supplied to the separation device 40 is set to a high level. In order to increase the yield of the purified gas, the pressure of the biogas supplied to the separation device 40 is set to a low level.

[0027] The first cooler 23 and the second cooler 26 are provided to cool the biogas whose temperature has increased due to compression, and to supply the biogas to the separation device 40 after it has been cooled to a temperature that can be processed in the separation device 40. The first cooler 23 cools the biogas whose temperature has increased as a result of being compressed by the first biogas compressor 22. The second cooler 26 cools the biogas whose temperature has increased as a result of being compressed by the second biogas compressor 25. There is no particular limitation on the type of the first cooler 23 and the second cooler 26, but a general corrugated fin type or fin-tube type gas-liquid heat exchanger or the like can be used.

[0028] A refrigerant is supplied to the first cooler 23 through a refrigerant inlet line 31, and the refrigerant cools the biogas passing through the first cooler 23. The refrigerant flowing out of the first cooler 23 is supplied to the second cooler 26 through a refrigerant transfer line 32, and cools the biogas passing through the second cooler 26. The refrigerant flowing out of the second cooler 26 is discharged from a refrigerant outlet line 33.

[0029] The type of refrigerant is not particularly limited, and any known refrigerant can be used as appropriate, such as long-life coolant (LLC), boiler cooling water using propylene glycol, simple water, fluorine-based refrigerants such as freon, etc. The digestive liquid generated during methane fermentation may also be used as the refrigerant.

[0030] When the separator 40 is a membrane separator, the temperature of the biogas supplied to the separator 40 is preferably 40 to 60°C, more preferably 45 to 55°C, although it depends on the material of the separation membrane. When the separation device 40 is a membrane separation device, deterioration of the separation membrane is easily suppressed if the temperature of the biogas supplied to the separation device 40 is equal to or lower than a preferable upper limit. If the temperature of the biogas supplied to the separation device 40 is equal to or higher than a preferable lower limit, moisture contained in the biogas is easily allowed to pass through the separation membrane as water vapor. In addition, a reduction in the effective area of ​​the separation membrane due to condensation is easily prevented.

[0031] When the separator 40 is an apparatus for the PSA method, the temperature of the biogas supplied to the separator 40 is preferably 30 to 60°C, and more preferably 40 to 50°C. When the separation device 40 is a PSA device, if the temperature of the biogas supplied to the separation device 40 is equal to or lower than a preferable upper limit, deterioration of the adsorbent is easily prevented. If the temperature of the biogas supplied to the separation device 40 is equal to or higher than a preferable lower limit, condensation is easily prevented.

[0032] When the on-off valve 24 is opened and the on-off valve 28 is opened, the biogas is compressed and cooled twice along the first compression line 21 . When the on-off valve 24 is closed and the on-off valve 28 is opened, the biogas passes from halfway through the first compression line 21 through the second compression line 27 and directly to the separation device 40, so that the biogas is compressed and cooled only once.

[0033] Which on-off valve is opened is appropriately selected depending on the flow rate and composition of the biogas, the required methane concentration of the refined gas, and the like. When the separation device 40 is a membrane separation device, the higher the flow rate of the biogas, the lower the methane concentration of the biogas, and the higher the methane concentration required in the purified gas, the higher the pressure of the biogas supplied to the separation device 40 needs to be.

[0034] When trying to increase the pressure of biogas using a single compressor, the temperature of the biogas becomes extremely high. This means that there is a risk of the compressor itself being damaged, and an expensive compressor that can handle high temperatures and pressures is required. In addition, a large-scale cooler following the compressor is also required.

[0035] In such cases, if the compression and cooling of the biogas is repeated two or more times, the burden on each compressor and each cooler will be reduced, making it possible to handle the situation with a normal compressor and cooler. Therefore, when the biogas pressure needs to be increased, the on-off valve 24 is opened so that compression and cooling are repeated twice, and when the biogas pressure does not need to be as high, the on-off valve 28 is opened so that compression and cooling are performed only once.

[0036] The separation device 40 may be a membrane separation device or a PSA method device. Among these, a membrane separation device is preferred because it is easy to obtain a purified gas with a sufficiently increased methane concentration and it is easy to make a compact device.

[0037] A membrane separation device is a separation device that has a separation membrane housed in a casing and utilizes the fact that components permeate the separation membrane at different speeds. Examples of the material for the separation membrane include polysulfone, cellulose acetate and polyamide, with polysulfone being particularly preferred.

[0038] For membranes made of these materials, the membrane permeation rate of carbon dioxide is high and the membrane permeation rate of methane is low. Therefore, the gas that does not permeate the separation membrane can be recovered as a purified gas with an increased methane concentration. Also, the gas that permeates the separation membrane can be used as a removed gas with an increased carbon dioxide concentration.

[0039] In addition, membranes made of these materials have high membrane permeability not only for carbon dioxide but also for water vapor, so the moisture concentration in the refined gas can be made lower than that in the biogas. However, moisture places a load on the separation membrane, so in this embodiment, the dehumidifying cooler 12 is used to prevent the biogas with a high moisture concentration from reaching the separation membrane.

[0040] The separation membrane may be in the form of a hollow tube or a flat membrane. Among them, a hollow tube-shaped separation membrane is preferred because of its high separation efficiency, and a bundle of a plurality of hollow tube-shaped separation membranes is more preferred. The dimensions of the hollow tube are not particularly limited, but it is preferable that the tube outer diameter is 0.4 to 0.9 mm, the tube inner diameter is 0.2 to 0.6 mm, and the membrane thickness is 0.2 to 0.3 mm.

[0041] In PSA equipment, methane and carbon dioxide are separated by the difference in the adsorption rate between methane and carbon dioxide in the adsorbent packed in the adsorption tower. The adsorbent used may be one that adsorbs carbon dioxide more easily than methane, or one that adsorbs methane more easily than carbon dioxide.

[0042] When an adsorbent that adsorbs carbon dioxide more easily than methane is used, the gas that flows out without being adsorbed by the adsorbent becomes the purified gas, and the gas that is adsorbed by the adsorbent and then desorbed from the adsorbent becomes the removed gas. When an adsorbent that adsorbs methane more easily than carbon dioxide is used, the gas that flows out without being adsorbed by the adsorbent becomes the removed gas, and the gas that is adsorbed by the adsorbent and then desorbed from the adsorbent becomes the purified gas. The desorption from the adsorbent can be carried out by reducing the pressure.

[0043] The purified gas discharge section 50 is a section that discharges the purified gas, whose methane concentration has been increased in the separation device 40, to the outside of the production system 1. The purified gas discharge section 50 is composed of a purified gas discharge line 51 whose upstream end is connected to the separation device 40 and whose downstream end is connected to a purified gas tank 80 provided outside the production system 1, and an on-off valve 52 provided in the purified gas discharge line 51.

[0044] A purified gas extraction line 81 is connected to the purified gas tank 80, and an on-off valve 82 is provided on the purified gas extraction line 81. The purified gas stored in the purified gas tank 80 can be extracted by opening the on-off valve 82 provided on the purified gas extraction line 81.

[0045] The removed gas discharge section 60 is a section for discharging the removed gas in which the carbon dioxide concentration has increased in the separation device 40 . In the removed gas discharge section 60, a removed gas compressor 62, a removed gas tank 63, an expansion valve 65, and an on-off valve 66 are provided in a removed gas ejection line 61 in this order from the upstream side. The removed gas ejection line 61 has an upstream end connected to the separation device 40 and a downstream end opening near the surface of the dehumidifying cooler 12. In addition, a second discharge line 67 is provided branching off from between the expansion valve 65 and the on-off valve 66 of the removed gas ejection line 61, and the downstream end of the second discharge line 67 is disposed outside the production system 1. The second discharge line 67 is provided with an on-off valve 68.

[0046] The removed gas compressor 62 compresses the removed gas with an increased carbon dioxide concentration. The compressed removed gas is stored in a removed gas tank 63. By opening an expansion valve 65 and an on-off valve 66 and closing an on-off valve 68, the high-pressure removed gas stored in the removed gas tank 63 is ejected while expanding from the downstream end (outlet) of the removed gas ejection line 61, and is sprayed onto the dehumidifying cooler 12. There is no particular limitation on the specific location to which the air is sprayed, but depending on the structure of the dehumidifying cooler 12, the air can be sprayed onto the surface of the case of the dehumidifying cooler 12, or onto fins, tubes, etc. inside the case.

[0047] As a result, the biogas passing through the dehumidifying cooler 12 is cooled by the latent heat accompanying the expansion of the removed gas. If an opening / closing valve 66 capable of adjusting its opening is used, the amount of removal gas blown to the dehumidifying cooler 12 can be adjusted to appropriately control the degree of cooling by the removal gas.

[0048] The production system 1 is entirely housed in a housing 70. However, the pretreatment line 11 and the refrigerant inlet line 31 are arranged such that their upstream ends are exposed to the outside of the housing 70. In addition, the drain discharge line 15, the refrigerant outlet line 33, the purified gas discharge line 51, and the second release line 67 are arranged such that their downstream ends are exposed to the outside of the housing 70.

[0049] The removal gas contains a high concentration of carbon dioxide. Therefore, when the removal gas exhaust unit 60 accommodated in the housing 70 releases the removal gas inside the housing 70, the carbon dioxide concentration inside the housing 70 increases. This improves the explosion-proofing properties inside the housing 70. The removal gas released into the housing 70 passes through gaps in the housing 70 and is released into the atmosphere.

[0050] In addition, by discharging the pressurized removal gas into the housing 70, the pressure inside the housing 70 becomes slightly higher than the pressure outside the housing 70. This also has the effect of preventing dust from entering the housing 70 from the outside. Furthermore, when the pressurized gas is discharged, a certain amount of noise is generated, but when the gas is discharged into the housing 70, the housing 70 provides sound insulation, so that noise to the outside can be suppressed. If the pressurized removal gas is blown into the case of a cooler such as the dehumidifying cooler 12, the noise suppression effect is further improved.

[0051] In this embodiment, a concentration meter 71 for measuring the methane concentration is provided in the housing 70 . The amount of methane contained in the removed gas is usually small. However, if a situation occurs in which the methane concentration in the removed gas is not sufficiently reduced due to a malfunction of the separation device 40 or the like, the release of the removed gas unintentionally increases the methane concentration in the housing 70, creating a flammable atmosphere, which is undesirable. Therefore, it is preferable to monitor the methane concentration in the housing 70 using the concentration meter 71.

[0052] If the concentration meter 71 detects that the methane concentration inside the housing 70 exceeds a predetermined value, the expansion valve 65 and the on-off valve 68 are opened, and the on-off valve 66 is closed. As a result, the high-pressure removal gas stored in the removal gas tank 63 is directly released outside the housing 70 from the downstream end of the second release line 67. The predetermined value is determined according to the required explosion-proof performance. If the methane concentration inside the housing 70 exceeds a predetermined value, the on-off valve 68 is opened and the on-off valve 66 is closed, an alarm may be output.

[0053] The downstream end of the second discharge line 67 may be open to the atmosphere, or may be connected to a tank to store the removed gas in the tank. The stored removed gas contains a large amount of carbon dioxide and can be used as a raw material for chemical processing products. The carbon dioxide can be used, for example, together with hydrogen, for fuel synthesis.

[0054] In the above embodiment, the biogas in the dehumidifying cooler 12 is cooled only by the latent heat due to the expansion of the removed gas. However, a refrigerant may also be used in combination to cool the biogas in the dehumidifying cooler 12. Further, the latent heat generated by the expansion of the removed gas may be used to cool the biogas (compressed biogas) in the first cooler 23 or the second cooler 26 instead of cooling the biogas in the dehumidifying cooler 12. Additionally, the latent heat from the expansion of the rejected gas may be utilized to cool the biogas in two or more coolers.

[0055] When a housing 70 is provided, it is preferable that the housing 70 accommodates at least the outlet of the removal gas ejection line 61 through which the removal gas expands and is ejected by the expansion valve 65, and the cooler to be cooled (the dehumidifying cooler 12 in the above embodiment). It is particularly preferable that the housing 70 accommodates almost the entire manufacturing system 1 as in the above embodiment, from the viewpoint of ensuring the explosion-proofness of the entire system by utilizing a removal gas.

[0056] The outlet of the removal gas ejection line 61 and some or all of the components other than the cooler to be cooled may be disposed outside the housing 70. For example, the entire concentration meter 71 does not have to be housed in the housing 70. Specifically, only the sensor unit may be housed in the housing 70, with the concentration meter body being disposed outside the housing 70. The entire concentration meter may be disposed outside the housing 70, with only the upstream end of the sampling tube being inserted into the housing 70.

[0057] Furthermore, there is no particular limitation on the specific configuration of the pretreatment unit 10. For example, the desulfurizer 13 may be omitted depending on the composition of the biogas. Furthermore, the specific configuration of the compression section 20 is not particularly limited. For example, the second biogas compressor 25 and the second cooler 26 of the compression section 20 may be omitted, and the compression and cooling of the biogas may always be performed only once each. Furthermore, a further compressor and cooler may be added, and the compression and cooling of the biogas may be repeated three or more times. In addition, if the degree of compression by the compression section is small and the temperature of the biogas after compression is sufficiently low, the cooler may be omitted.

[0058] Also, a vacuum pump may be disposed in the purified gas discharge line 51. When a vacuum pump is disposed in the purified gas discharge line 51, the entire compression section 20 may be omitted. In addition, in the case where a vacuum pump is provided in the purified gas discharge line 51 and the compression section 20 is entirely omitted, a heater may be provided to heat the biogas to a temperature suitable for treatment in the separation device 40 .

[0059] Furthermore, it is also possible to provide a plurality of separation devices 40. For example, the purified gas flowing out from the separation device 40 may be further treated in another separation device 40 to increase the methane concentration of the purified gas. Also, the removed gas flowing out from the separation device 40 may be returned to the separation device 40 for processing, thereby recovering methane remaining in the removed gas. The purified gas production system and the purified gas production method of the present invention can be modified in various ways without impairing the effects of the present invention.

[0060] Furthermore, the removal gas ejection line 61 of the removal gas discharge section 60 may be provided with a discharge line upstream of the removal gas compressor 62 for discharging the removal gas into or outside the housing 70. In this case, when the pressure in the removal gas tank 63 reaches or exceeds a certain level, the excess removal gas can be discharged without being compressed. This allows only the amount of removal gas required for cooling to be compressed, minimizing the energy required for compression. [Explanation of symbols]

[0061] 1. Manufacturing System 10 Pretreatment section 12 Dehumidification cooler 13 Desulfurizer 20 Compression section 22 First biogas compressor 23 1st cooler 25 Second biogas compressor 26 Second cooler 40 Separation device 50 Refined gas exhaust section 60 Removal gas exhaust section 62 Removal gas compressor 63 Removal Gas Tank 65 Expansion valve 70 Housing 71 Densitometer 80 Refined Gas Tank

Claims

1. A system (1) for producing purified gas, which concentrates methane in a biogas to obtain a purified gas, comprising: a separation device (40) for separating the biogas to obtain a purified gas having an increased concentration of methane and a rejected gas having an increased concentration of carbon dioxide; a cooler for cooling the biogas before it is fed to the separation device (40); a rejection gas compressor (62) for compressing the rejection gas discharged from the separation device; an expansion valve (65) for expanding the compressed removal gas; The removal gas ejected from the expansion valve (65) is sprayed onto the cooler, thereby utilizing latent heat accompanying the expansion of the removal gas for cooling the biogas in the cooler.

2. The system (1) for producing purified gas according to claim 1, wherein the cooler is a dehumidification cooler (12) for cooling biogas for dehumidification.

3. The system (1) for producing purified gas according to claim 1 or 2, wherein the cooler is a cooler (23, 26) for cooling biogas after compression.

4. The system (1) for producing a purified gas according to any one of claims 1 to 3, wherein the separation device (40) is a membrane separation device having a separation membrane.

5. The system (1) for producing a purified gas according to any one of claims 1 to 4, further comprising a housing (70) for accommodating at least the outlet through which the removal gas is expanded by the expansion valve (65) and ejected, and the cooler.

6. The refined gas producing system (1) according to claim 5, further comprising a concentration meter (71) for measuring a methane concentration in the housing (70), and when the methane concentration measured by the concentration meter (71) exceeds a predetermined value, the removed gas is discharged from the expansion valve (65) to the outside of the housing (70).

7. A method for producing purified gas, comprising the steps of: concentrating methane in a biogas to obtain a purified gas, The biogas is dehumidified by cooling it. The dehumidified biogas is separated to obtain a purified gas having an increased methane concentration and a removed gas having an increased carbon dioxide concentration. compressing and then expanding the removal gas; A method for producing a purified gas, comprising the steps of: dehumidifying the biogas by utilizing latent heat accompanying the expansion of the removed gas;

8. A method for producing purified gas, comprising the steps of: concentrating methane in a biogas to obtain a purified gas, Biogas is compressed and cooled, The cooled biogas is separated to obtain a purified gas having an increased methane concentration and a removed gas having an increased carbon dioxide concentration. compressing and then expanding the removal gas; A method for producing a purified gas, characterized in that latent heat accompanying the expansion of the removed gas is utilized for cooling the biogas after compression.

9. The method for producing a purified gas according to claim 7 or 8, wherein the separation of the biogas is carried out by a membrane separation method using a separation membrane.

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