WO2024203281A1

WO2024203281A1 - Liquefied methane production method and liquefied methane production apparatus

Info

Publication number: WO2024203281A1
Application number: PCT/JP2024/009548
Authority: WO
Inventors: 沙紀藤井; 真子寺井; 智大西川
Original assignee: エア・ウォーター株式会社
Priority date: 2023-03-24
Filing date: 2024-03-12
Publication date: 2024-10-03
Also published as: JP2024136765A

Abstract

Provided is a method for producing liquefied methane from a biogas containing a methane gas, a carbon dioxide gas, a nitrogen gas, an oxygen gas, an argon gas and water or an enriched gas obtained by enriching the methane gas in the biogas, the method comprising a first step for separating the carbon dioxide gas and water from the biogas or the enriched gas to produce an intermediate gas and a second step for subjecting the intermediate gas to distillation separation using a distillation column to produce liquefied methane.

Description

Liquefied methane production method and liquefied methane production apparatus

This disclosure relates to a method for producing liquefied methane and an apparatus for producing liquefied methane.

Natural gas and liquefied natural gas have been attracting attention as clean energy sources that emit less carbon dioxide compared to fossil fuels such as coal and oil. However, even when natural gas or liquefied natural gas is used as an energy source, carbon dioxide is still emitted, and the amount of carbon dioxide emissions is steadily increasing. Therefore, there is a demand for alternative energy sources to replace natural gas and liquefied natural gas.

As such an alternative energy source, biogas derived from livestock manure such as dairy and beef cows, food waste, and sewage sludge is attracting attention. Biogas is composed of methane gas, carbon dioxide gas, nitrogen gas, etc., and is expected to be an alternative energy source to natural gas and liquefied natural gas.

When using biogas as energy, it is necessary to remove impurities such as carbon dioxide from the biogas and increase the concentration of methane gas. Patent Document 1 (JP 2018-188594 A) discloses a method for increasing the concentration of methane gas by removing carbon dioxide from biogas using a high-pressure water absorption method, Patent Document 2 (JP 2021-178269 A) discloses a method for increasing the concentration of methane gas by removing carbon dioxide from biogas using a chemical absorption method, and Patent Document 3 (JP 2013-534863 A) discloses a method for increasing the concentration of methane gas by removing carbon dioxide from biogas using a membrane separation method.

JP 2018-188594 A JP 2021-178269 A Special Publication No. 2013-534863

However, the method described in Patent Document 1 has problems such as the equipment becoming larger and being costly. Also, the methods described in Patent Documents 2 and 3 make it difficult to increase the purity of methane gas.

　Furthermore, overseas, liquefied methane derived from biogas is used as ship and truck fuel, and a supply system has been established. High-purity liquefied methane is also used as rocket fuel. As such, it is expected that demand will expand not only for methane gas, but also for liquefied methane.

The object of this disclosure is to provide a method and apparatus for producing liquefied methane from biogas.

[1] A method for producing liquefied methane from a biogas containing methane gas, carbon dioxide gas, nitrogen gas, oxygen gas, argon gas and moisture, or from a concentrated gas obtained by concentrating methane gas in the biogas, comprising:
A first step of separating carbon dioxide gas and moisture from the biogas or the concentrated gas to obtain an intermediate gas;
A second step of distilling and separating the intermediate gas in a distillation column to obtain liquefied methane.

[2] The method for producing liquefied methane described in [1], in which in the second step, liquid nitrogen is supplied as a refrigerant to a condenser connected to the top of the distillation column.

[3] The method for producing liquefied methane described in [2], in which the nitrogen gas produced in the condenser is reused as a refrigerant for cooling the intermediate gas in the second process.

[4] The method for producing liquefied methane described in any one of [1] to [3], wherein the first step includes a plurality of separation methods.

[5] The method for producing liquefied methane described in [4], in which separation is performed in the first step by membrane separation and temperature swing adsorption in this order.

[6] The method for producing liquefied methane described in any one of [1] to [5], wherein the biogas is a gas derived from at least one selected from the group consisting of livestock manure and food waste.

[7] A method for producing liquefied methane described in any one of [1] to [6], wherein the biogas contains 50% to 60% by volume of methane gas, 30% to 40% by volume of carbon dioxide gas, and 1% to 15% by volume of nitrogen gas.

[8] An apparatus for producing liquefied methane from a biogas containing methane gas, carbon dioxide gas, nitrogen gas, oxygen gas, argon gas and moisture, or from a concentrated gas obtained by concentrating methane gas in the biogas, comprising:
A separation device for separating carbon dioxide gas and moisture from the biogas or the concentrated gas to obtain an intermediate gas;
and a distillation apparatus for distilling and separating the intermediate gas to obtain liquefied methane.

[9] The distillation apparatus includes a distillation column and a condenser connected to the top of the distillation column,
The liquefied methane production apparatus according to claim 8, wherein liquid nitrogen is supplied to the condenser as a refrigerant.

[10] A main heat exchanger for cooling the intermediate gas,
The liquefied methane production apparatus according to claim 9, wherein nitrogen gas produced in the condenser is reused as a refrigerant in the main heat exchanger.

[11] The liquefied methane production apparatus according to any one of [8] to [10], wherein the separation device includes a plurality of separation devices.

[12] The liquefied methane production apparatus described in [11], wherein the separation device includes a membrane separation device and a temperature swing adsorption separation device.

The present disclosure provides a method and apparatus for producing liquefied methane from biogas.

FIG. 1 is a schematic diagram showing an example of the configuration of a liquefied methane production apparatus according to the present embodiment. FIG. 2 is a schematic diagram showing an example of a partial configuration of the liquefied methane production apparatus in this embodiment. FIG. 3 is a schematic diagram showing the configuration of the liquefied methane production apparatus used in Example 1. FIG. 4 is a schematic diagram showing the configuration of the liquefied methane production apparatus used in Example 2.

Embodiments of the present disclosure are described below. However, the following description is not intended to limit the scope of the claims.

<Method of producing liquefied methane>
The method for producing liquefied methane in this embodiment includes a first step of obtaining an intermediate gas by separating CO2 and _moisture from a biogas containing methane gas, carbon dioxide gas ( _CO2 ), nitrogen gas, oxygen gas, argon gas, and moisture, or from a concentrated gas obtained by concentrating methane gas in the biogas, and a second step of obtaining liquefied methane by distilling and separating the intermediate gas in a distillation column. Each step of the method for producing liquefied methane in this embodiment will be described below.

Biogas
In this embodiment, "biogas" refers to a gas containing methane gas, CO ₂ , nitrogen gas, oxygen gas, argon gas, and moisture. The biogas may be, for example, a gas derived from at least one selected from the group consisting of livestock manure and food residue. The concentrations of each gas in the biogas are, for example, methane gas is 50% by volume to 60% by volume, CO ₂ is 30% by volume to 40% by volume, nitrogen gas is 1% by volume to 15% by volume, oxygen gas is 0.1% by volume to 5% by volume, argon gas is 0.01% by volume to 1% by volume, and moisture is 0.01% by volume to 5% by volume. It is preferable that hydrogen sulfide is removed from the biogas in advance.

Concentrated Gas
In this embodiment, the term "concentrated gas" refers to a gas obtained by concentrating methane gas in biogas. The concentration of methane gas in the concentrated gas is, for example, 75% by volume or more and 97% by volume or less.

"Intermediate Gas"
In this embodiment, the term "intermediate gas" refers to a gas in which _CO2 and moisture have been separated from the biogas or concentrated gas, and the concentration of methane gas is higher than that of the biogas or concentrated gas. The concentration of methane gas in the intermediate gas is, for example, 80% by volume or more and 99% by volume or less.

<<First Step>>
This process is a process of obtaining intermediate gas by separating _CO2 and moisture from biogas or concentrated gas. By this process, the _CO2 concentration in the intermediate gas is reduced to 0.0001% by volume or less. By this process, the moisture in the intermediate gas is reduced to 0.0001% by volume or less. Examples of separation methods in this process include temperature swing adsorption and pressure swing adsorption. In addition, methods for mainly separating _CO2 include separation membrane separation, high-pressure water absorption, and chemical absorption.

(Temperature Swing Adsorption Method)
In this method, biogas or concentrated gas is introduced into an adsorption tower filled with an adsorbent that adsorbs _CO2 and moisture, and _CO2 and water are separated. In this method, for example, an adsorption cycle of (1) an adsorption step, (2) a thermal regeneration step, (3) a purging step, and (4) a pressure recovery step is repeated in sequence.

(1) Adsorption process The adsorption process is a process in which the biogas or concentrated gas is supplied to an adsorption tower and the _CO2 and moisture are adsorbed by an adsorbent, thereby separating the _CO2 and moisture from the biogas or concentrated gas. In this process, the temperature of the supplied biogas or concentrated gas is adjusted to be, for example, 40°C or lower.

The adsorbent is a regenerative adsorbent that can adsorb _CO2 and moisture and can recover its adsorption performance by being heated to release the adsorbed _CO2 and moisture. Examples of such adsorbents include activated alumina, silica gel, and hydrophobic zeolite.

(2) Thermal regeneration process The thermal regeneration process is a process in which a gas inert to the adsorbent (hereinafter simply referred to as "inert gas") is heated and supplied to the adsorption tower after the adsorption process, or the adsorbent is directly heated, thereby desorbing _CO2 and moisture from the adsorbent. In other words, the thermal regeneration process is a process in which the adsorbent filled in the adsorption tower is made reusable.

Examples of inert gases include gases from which _CO2 and moisture have been removed by the adsorption process from biogas or concentrated gas, and nitrogen gas. Such gases are heated and brought into contact with the adsorbent filled in the adsorption tower, thereby increasing the temperature of the adsorbent surface and desorbing the _CO2 and moisture adsorbed to the adsorbent. The adsorbent is regenerated by this process. The heating temperature is, for example, 170°C or higher.

As the inert gas, nitrogen gas is preferably used. In this case, it is preferable to reuse the nitrogen gas used in the second step described below. In this way, the nitrogen gas is used efficiently and the amount of nitrogen gas used throughout this manufacturing method is reduced.

(3) Purge step The purge step is a step of removing the inert gas in the adsorption tower after the heating regeneration step. In this step, the inert gas is removed by introducing a gas into the adsorption tower. When the inert gas is nitrogen gas, the gas introduced is, for example, a gas obtained by removing _CO2 and moisture from the biogas or concentrated gas by the adsorption step. This step is preferably performed multiple times until the inert gas is completely removed. Note that when the inert gas is a gas obtained by removing _CO2 and moisture from the biogas or concentrated gas by the adsorption step, this step is not necessary.

(4) Pressure Reinstatement Step In the pressure reinstatement step, for example, a high-pressure gas is introduced into the adsorption tower after the desorption step to restore the pressure to the pressure required for the adsorption step. For example, the high-pressure gas used may be a gas from which _CO2 and moisture have been removed by the adsorption step.

In this method, it is preferable to use a plurality of adsorption towers. For example, when two adsorption towers are used, while an adsorption step is being performed in one adsorption tower, a heating regeneration step, a purging step, and a pressure recovery step are being performed in the other adsorption tower, and by operating the two adsorption towers while switching in this manner, it is possible to continuously and efficiently separate _CO2 and water from the biogas or concentrated gas.

(Pressure Swing Adsorption)
In this method, biogas or concentrated gas is introduced into an adsorption tower filled with an adsorbent that adsorbs _CO2 and moisture, and _CO2 and water are separated. In this method, an adsorption cycle of (1) adsorption step, (2) purging step, (3) desorption step, and (4) pressure recovery step is repeated in sequence. Note that the (2) purging step and (4) pressure recovery step are the same as the (3) purging step and (4) pressure recovery step in the above-mentioned temperature swing adsorption method, so a description thereof will be omitted.

The adsorption process is a process in which biogas or concentrated gas is supplied to an adsorption tower, and _CO2 and moisture are adsorbed by an adsorbent, thereby separating _CO2 and moisture from the biogas or concentrated gas. This process is carried out, for example, under a pressure of 0.7 MPaG or more. The adsorbent is the same as the adsorbent that can be used in the above-mentioned temperature swing adsorption method, so a description thereof is omitted.

The desorption process is a process in which the adsorption tower after the adsorption process is depressurized to atmospheric pressure (0 MPaG) and the CO ₂ and moisture adsorbed by the adsorbent are desorbed. In this process, for example, the pressure in the adsorption tower may be reduced to -0.1 MPaG by a vacuum pump.

(Membrane separation method)
In this method, biogas or concentrated gas is introduced into a separation membrane that selectively allows _CO2 to permeate, and _CO2 is separated. In this method, biogas or concentrated gas is compressed and introduced, and separation proceeds due to the partial pressure difference between the membranes. Examples of separation membranes include hollow fiber polymer membranes and those made of inorganic materials such as zeolite. In this method, it is preferable to compress to 0.8 MPaG or more. Since the _CO2 separated by this method may contain methane gas, the separated _CO2 may be separated again into _CO2 and methane gas by this method, and the methane gas may be recovered and recycled.

(High pressure water absorption method)
In this method, _CO2 is separated by absorbing _CO2 into water under high pressure conditions. In this method, biogas or concentrated gas is compressed and introduced, and separation proceeds due to the difference in solubility in water. In this method, it is preferable to compress it to 0.9 MPaG or more.

(Chemical absorption method)
In this method, biogas or concentrated gas is introduced into a chemical absorption liquid and _CO2 is separated by chemical reaction. In this method, separation proceeds by reacting an alkaline compound in the chemical absorption liquid with _CO2 in the biogas or concentrated gas. An example of the alkaline compound is an amine compound.

The first step preferably includes at least one method selected from the group consisting of temperature swing adsorption and pressure swing adsorption. It is more preferable that the first step includes a plurality of separation methods. For example, when the first step includes two separation methods, it is preferable that the combination of one method selected from the group consisting of temperature swing adsorption and pressure swing adsorption and one method selected from the group consisting of membrane separation, high pressure water absorption, and chemical absorption is used. Of these, it is more preferable that separation by membrane separation and temperature swing adsorption is performed in this order. Note that when an intermediate gas is obtained from a concentrated gas, it is sufficient that the first step includes at least one method selected from the group consisting of temperature swing adsorption and pressure swing adsorption.

<<Second step>>
This process involves distilling the intermediate gas in a distillation column to obtain liquefied methane. This process includes (1) a cooling process, (2) a distillation process, and (3) a condensation process.

(1) Cooling Step The cooling step is a step of cooling the intermediate gas obtained in the first step. The temperature of the intermediate gas supplied to the cooling step is preferably 40° C. or lower. The pressure of the intermediate gas during the cooling step is, for example, 0.1 to 0.8 MPaG. A part of the methane gas contained in the intermediate gas may be liquefied by the cooling step. The cooling step may be performed only once or may be performed multiple times. In addition, the nitrogen gas in the condensation step described below may be reused as a cooling means in this step.

The pressure of the intermediate gas after this process may be adjusted before it is introduced into the distillation process described below. The pressure during this process is usually higher than the pressure during the distillation process, so it is preferable to reduce the pressure.

(2) Distillation Step The distillation step is a step in which the intermediate gas is introduced into a distillation column and distilled. The pressure in the distillation column during the distillation step is, for example, 0.1 to 0.9 MPaG.

In this process, the nitrogen gas (boiling point at atmospheric pressure: -195.8°C), oxygen gas (boiling point at atmospheric pressure: -183°C), and argon gas (boiling point at atmospheric pressure: -185.8°C) contained in the intermediate gas are separated from methane gas (boiling point at atmospheric pressure: -161.6°C) due to their difference in boiling points. The separated methane gas is converted into liquefied methane by heat exchange with a reboiler that is usually installed at the bottom of the distillation tower.

(3) Condensation Step The condensation step is a step in which the methane gas that was not liquefied in the distillation step is condensed in a condenser to obtain liquefied methane.

The condenser is connected to the top of the distillation tower, and methane gas is introduced into the condenser from the top of the tower. The methane gas introduced into the condenser is condensed, and at least a portion of it becomes liquefied methane. The liquefied methane is returned to the distillation tower and recovered.

The methane gas introduced into the condenser is condensed, for example, by heat exchange with a refrigerant. For example, liquid nitrogen is used as the refrigerant, and this process is carried out by supplying liquid nitrogen to the condenser. The liquid nitrogen is introduced into the condenser under pressure, for example, of about 0.5 MPaG.

Part of the liquid nitrogen is vaporized and becomes nitrogen gas through heat exchange with the methane gas. The nitrogen gas obtained in this process is preferably reused, for example, as a refrigerant for cooling the intermediate gas in the cooling process. The reused nitrogen gas is also preferably reused in the purging process of the temperature swing adsorption method described above. In this way, the nitrogen gas is used effectively, and the amount of nitrogen gas used throughout this production method is reduced.

In this process, the nitrogen gas, oxygen gas, and argon gas in the intermediate gas separated in the distillation process are also introduced into the condenser. Since these nitrogen gas, oxygen gas, and argon gas are not liquefied, they may be discharged or reused as a refrigerant to cool the intermediate gas in the cooling process.

<Liquefied methane production equipment>
The liquefied methane production apparatus in this embodiment includes a separation device for obtaining an intermediate gas by separating _CO2 and moisture from a biogas containing methane gas, _CO2 , nitrogen gas, oxygen gas, argon gas, and moisture, or from a concentrated gas obtained by concentrating methane gas in the biogas, and a distillation device for distilling and separating the intermediate gas to obtain liquefied methane.

FIG. 1 is a schematic diagram showing an example of the configuration of a liquefied methane production apparatus in this embodiment. The liquefied methane production apparatus 30 will be described below. Note that any explanation that overlaps with the contents explained in the above <Liquefied methane production method> will be omitted.

Separation Device
This device is a device for separating _CO2 and moisture from biogas or concentrated gas to obtain an intermediate gas. Examples of separation devices include temperature swing adsorption separation devices and pressure swing adsorption separation devices. Devices that mainly separate _CO2 include membrane separation devices, high-pressure water absorption devices, and chemical absorption devices. Note that FIG. 1 shows a membrane separation device 1 and a temperature swing adsorption device 10 as separation devices.

(Temperature Swing Adsorption Separation Device)
This apparatus is equipped with an adsorption tower 11 that adsorbs _CO2 and moisture contained in the biogas or concentrated gas. The adsorption tower 11 is filled with an adsorbent for adsorbing _CO2 and moisture. Using this apparatus, each step of the temperature swing adsorption method described above is performed, thereby separating _CO2 and moisture from the biogas or concentrated gas.

The present apparatus is preferably equipped with a heating means 12. The heating means 12 heats the inert gas used in the above-mentioned thermal regeneration process to such an extent that the adsorbent filled in the adsorption tower can be reused. There are no particular limitations on the heating means 12, but examples include a heater.

Temperature swing adsorption separation apparatus 10 preferably includes a plurality of adsorption towers 11. In Fig. 1, temperature swing adsorption separation apparatus 10 is configured with two adsorption towers (adsorption tower 11a, adsorption tower 11b), and biogas or concentrated gas is alternately discharged to adsorption tower 11a and adsorption tower 11b, thereby enabling continuous and efficient separation of _CO2 and moisture from the biogas or concentrated gas.

(Pressure Swing Adsorption Separation Device)
This apparatus (not shown) is equipped with an adsorption tower that adsorbs _CO2 and moisture contained in the biogas or concentrated gas. The adsorption tower is filled with an adsorbent for adsorbing _CO2 and moisture. Using this apparatus, each step of the pressure swing adsorption method described above is performed, thereby separating _CO2 and moisture from the biogas or concentrated gas.

(Membrane separation device)
This device is equipped with a separation membrane module (not shown) for selectively allowing _CO2 contained in the biogas or concentrated gas to permeate. The biogas or concentrated gas is discharged to the separation membrane module by a compressor (not shown), and the _CO2 contained in the biogas or concentrated gas is separated by the separation membrane. Since the _CO2 separated by the membrane separation device may contain methane gas, the separated _CO2 may be separated again by the membrane separation device into _CO2 and methane gas, and the methane gas may be recovered and recycled.

(High pressure water absorption device)
This apparatus (not shown) is equipped with a high-pressure absorption tower that absorbs the _CO2 contained in the biogas or concentrated gas. The high-pressure absorption tower contains water for absorbing the _CO2 . The biogas or concentrated gas is delivered to the high-pressure absorption tower by a compressor, and the _CO2 contained in the biogas or concentrated gas is separated.

(Chemical absorption device)
This apparatus (not shown) is equipped with an absorption tower that absorbs the _CO2 contained in the biogas or concentrated gas. The absorption tower contains a treatment liquid for absorbing the _CO2 . The biogas or concentrated gas is led to the absorption tower, and the _CO2 contained in the biogas or concentrated gas is separated.

It is preferable that the separation device includes at least one device selected from the group consisting of a temperature swing adsorption separation device and a pressure swing adsorption separation device. It is more preferable that the separation device includes multiple separation devices. For example, when the separation device includes two separation devices, it is preferable that the separation device is a combination of one device selected from the group consisting of a temperature swing adsorption separation device and a pressure swing adsorption separation device and one device selected from the group consisting of a membrane separation device, a high-pressure water absorption device, and a chemical absorption device. Of these, it is more preferable that separation using the membrane separation device and the temperature swing adsorption separation device is performed in this order. Note that when an intermediate gas is obtained from a concentrated gas, it is sufficient that the separation device includes at least one separation device selected from the group consisting of a temperature swing adsorption separation device and a pressure swing adsorption separation device.

Distillation Apparatus
In this production apparatus, the intermediate gas is separated by distillation to obtain liquefied methane. Fig. 2 is a schematic diagram showing an example of the configuration of the distillation apparatus. The following description will be given with reference to Fig. 2.

The intermediate gas obtained by the separation device is cooled, for example, by the main heat exchanger 21. In the main heat exchanger 21, it is preferable to reuse nitrogen gas, which will be described later, as a refrigerant. In addition, as will be described later, the nitrogen gas, oxygen gas, and argon gas that are separated in the distillation column 23 and not condensed in the condenser 24 may also be reused as refrigerants. Note that the pressure of the intermediate gas cooled by the main heat exchanger 21 may be adjusted, for example, by a pressure reducing valve (not shown) before being introduced into the distillation column 23.

The intermediate gas cooled by the main heat exchanger 21 is introduced into the distillation tower 23 and distilled. From the viewpoint of increasing the efficiency of distillation, it is preferable that the intermediate gas is introduced into the distillation tower 23 from the center of the tower by providing an inlet at the center of the tower. The liquefied methane distilled and separated in the distillation tower 23 is taken out from the bottom of the distillation tower 23 and sent to the storage tank 25.

Before being introduced into the distillation tower 23, the intermediate gas cooled by the main heat exchanger 21 is usually introduced into the distillation tower 23 through a reboiler 22 installed at the bottom of the distillation tower 23. As the intermediate gas is cooled in the reboiler 22, some of the methane gas in the intermediate gas is liquefied, and the intermediate gas and liquefied methane are introduced into the distillation tower 23 in a mixed state.

The methane gas that is not liquefied in the distillation tower 23 is condensed by the condenser 24 connected to the top of the distillation tower 23, and at least a portion of it becomes liquefied methane. The liquefied methane is returned to the distillation tower 23 and sent to the storage tank 25.

The methane gas introduced into the condenser 24 is condensed, for example, by heat exchange with a refrigerant. For example, liquid nitrogen is used as the refrigerant.

Part of the liquid nitrogen is vaporized and becomes nitrogen gas through heat exchange with the methane gas. The nitrogen gas is preferably reused, for example, as a refrigerant for cooling the intermediate gas in the main heat exchanger 21. In addition, the nitrogen gas reused in the main heat exchanger 21 is preferably reused in the temperature swing adsorption separation device 10 described above.

The nitrogen gas, oxygen gas, and argon gas in the intermediate gas separated by the distillation column 23 are also introduced into the condenser 24. These non-liquefied gases such as nitrogen gas, oxygen gas, and argon gas may be exhausted or reused as a refrigerant to cool the intermediate gas in the main heat exchanger 21.

The distillation apparatus may include a tank 26 for holding liquid nitrogen. The melting point of liquefied methane is -182.5°C, whereas the liquid nitrogen used in this embodiment is introduced into the condenser 24 under a pressure of about 0.5 MPaG. The liquid nitrogen in this case is hotter than normal liquid nitrogen (e.g., -180 to -175°C) and is close to the melting point of liquefied methane. If the pressure of the liquid nitrogen drops, there is a risk that the liquefied methane will solidify in the condenser 24. Therefore, by installing a tank 26 for storing liquid nitrogen to suppress a drop in the temperature of the liquid nitrogen in the condenser 24, it is possible to prevent the condenser 24 from overcooling.

The following examples are provided. However, the following examples are not intended to limit the scope of the claims.

Example 1
A liquefied methane production apparatus having the configuration shown in FIG. 3 was prepared. Biogas derived from livestock manure was prepared. The concentrations of each gas in the biogas are as shown in point 1 of Table 1. In this embodiment, in the above-mentioned production method, the first step was performed in the order of membrane separation method and temperature swing adsorption method, and then the second step was performed. In the membrane separation device, a hollow fiber membrane was used as the separation membrane, and in the temperature swing adsorption separation device, zeolite was used as the adsorbent. As the refrigerant in the main heat exchanger, nitrogen gas obtained by vaporizing a part of the liquid nitrogen that was heat exchanged with methane gas in the condenser, and nitrogen gas, oxygen gas, and argon gas separated by distillation were used. Note that the biogas at point 1 is compressed by a compressor.

The flow rate, pressure, temperature, and composition at points 1 to 6 in Figure 3 are shown in Table 1. The composition at each point was analyzed by gas chromatography (GAS5000F HPID, manufactured by J Science Labs, Inc.).

Example 2
A liquefied methane production apparatus having the configuration shown in Fig. 4 was prepared. A concentrated gas was prepared by concentrating the methane gas in the biogas used in Example 1. The concentrations of each gas in the concentrated gas are as shown in point 1 of Table 2. In this example, in the above-mentioned production method, the first step was performed in the order of the temperature swing adsorption method, and then the second step was performed. The same temperature swing adsorption separation apparatus in the first step and the distillation apparatus in the second step were used as in Example 1. The concentrated gas at point 1 was compressed by a compressor.

The flow rate, pressure, temperature, and composition at points 1 to 5 in Figure 4 are shown in Table 2. The composition at each point was analyzed by gas chromatography in the same manner as in Example 1.

As shown in Table 1, in Example 1, liquefied methane with a purity of 99.99% or more was obtained from biogas containing 50% by volume of methane gas. In addition, the recovery rate of the liquefied methane was 95% by volume.

As shown in Table 2, in Example 2, liquefied methane with a purity of 99.99% or more was obtained from the concentrated gas obtained by concentrating the methane gas in the same biogas as in Example 1. In addition, the recovery rate of the liquefied methane was 95% by volume.

In this way, by using the liquefied methane production method and production apparatus described in this disclosure, high-purity liquefied methane can be produced from biogas. In addition, this disclosure makes effective use of livestock manure that would otherwise be discarded, which can contribute to some of the activities of the Sustainable Development Goals (SDGs).

The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 separation membrane device, 10 temperature swing adsorption separation device, 11, 11a, 11b adsorption tower, 12 heating means, 20 distillation device, 21 main heat exchanger, 22 reboiler, 23 distillation tower, 24 condenser, 25 storage tank, 26 tank, 30 liquefied methane production device.

Claims

A method for producing liquefied methane from a biogas containing methane gas, carbon dioxide gas, nitrogen gas, oxygen gas, argon gas and moisture, or from a concentrated gas obtained by concentrating methane gas in the biogas, comprising:
A first step of separating carbon dioxide gas and moisture from the biogas or the concentrated gas to obtain an intermediate gas;
A second step of distilling and separating the intermediate gas in a distillation column to obtain liquefied methane.
The method for producing liquefied methane according to claim 1, wherein in the second step, liquid nitrogen is supplied as a refrigerant to a condenser connected to the top of the distillation column.
The method for producing liquefied methane according to claim 2, wherein the nitrogen gas produced in the condenser is reused as a refrigerant for cooling the intermediate gas in the second step.
The method for producing liquefied methane according to any one of claims 1 to 3, wherein the first step includes a plurality of separation methods.
The method for producing liquefied methane according to claim 4, wherein in the first step, separation is performed in this order by membrane separation and temperature swing adsorption.
The method for producing liquefied methane according to any one of claims 1 to 5, wherein the biogas is derived from at least one selected from the group consisting of livestock manure and food waste.
The method for producing liquefied methane according to any one of claims 1 to 6, wherein the biogas contains 50% to 60% by volume of methane gas, 30% to 40% by volume of carbon dioxide gas, and 1% to 15% by volume of nitrogen gas.
An apparatus for producing liquefied methane from a biogas containing methane gas, carbon dioxide gas, nitrogen gas, oxygen gas, argon gas and moisture, or from a concentrated gas obtained by concentrating methane gas in the biogas, comprising:
A separation device for separating carbon dioxide gas and moisture from the biogas or the concentrated gas to obtain an intermediate gas;
and a distillation apparatus for distilling and separating the intermediate gas to obtain liquefied methane.
The distillation apparatus includes a distillation column and a condenser connected to the top of the distillation column;
The liquefied methane production apparatus according to claim 8 , wherein liquid nitrogen is supplied to the condenser as a refrigerant.
a main heat exchanger for cooling the intermediate gas;
The liquefied methane production apparatus according to claim 9, wherein nitrogen gas produced in the condenser is reused as a refrigerant in the main heat exchanger.
The liquefied methane production apparatus according to any one of claims 8 to 10, wherein the separation device includes a plurality of separation devices.
The liquefied methane production apparatus according to claim 11, wherein the separation device includes a membrane separation device and a temperature swing adsorption separation device.