High-purity liquefied methane production equipment

Abstract

To provide a device that produces high-purity liquefied methane from liquefied natural gas, can be built near a place where a movable body with an internal combustion engine such as a rocket is arranged and can produce high-purity liquefied methane for the movable body including an internal combustion engine.SOLUTION: A device for producing high-purity liquefied methane for a movable body including an internal combustion engine from liquefied natural gas includes: a liquefied natural gas storage tank for storing liquefied natural gas; a rectification column for separating methane gas from the liquefied natural gas; a methane gas condenser for liquefying methane gas; and a liquefied methane storage tank for storing liquefied methane. In the production device for high-purity liquefied methane, an operating rate of the rectification column in the last one year is 60% or lower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus for producing high-purity liquefied methane from liquefied natural gas for moving bodies equipped with internal combustion engines. [Background Art]

[0002] Methane is used as a raw material for chemical processes, and ultra-high-purity liquefied methane with a purity of 99.9999% or higher is generally employed. The raw material for methane is liquefied natural gas (LNG), and methane is the main component of LNG. The methane concentration in LNG varies depending on the place of origin of the LNG: for example, Australian LNG contains approximately 87% methane, Indonesian and Malaysian LNG contain approximately 89% methane, and Alaskan LNG contains approximately 99% methane. Therefore, to use methane as a raw material for chemical processes, it is necessary to purify LNG to obtain ultra-high-purity liquefied methane with a methane purity of 99.9999% or higher.

[0003] Patent Documents 1 and 2 disclose apparatuses capable of producing ultra-high-purity methane with a methane purity of 99.9999% or higher by purifying LNG. Patent Document 1 describes an apparatus for producing ultra-high-purity methane comprising: a first distillation apparatus for separating high-boiling-point components, which is provided with a condenser and a reboiler and into which liquefied natural gas is introduced; a second distillation apparatus for separating low-boiling-point components, which is provided with a condenser and a reboiler and from which bottom liquid is recovered as ultra-high-purity methane; a transfer passage for extracting a mixed fluid of nitrogen and methane from the top of the first distillation apparatus and feeding the mixed fluid to the second distillation apparatus; and a condenser cooling passage for passing the liquid at the bottom of the first distillation apparatus through the condenser of at least one of the distillation apparatuses to be evaporated in this condenser. Patent Document 2 describes a purification apparatus for high-purity methane comprising a crude methane rectification column for roughly purifying natural gas, and a methane rectification column for further purifying the roughly purified methane obtained from the crude methane rectification column.

[0004] Methane is the main component of city gas and is also used as fuel for industrial and household purposes. Since the required methane concentration for city gas is around 90%, LNG can be used as is. However, if the methane concentration in LNG falls below the standard value, it needs to be purified to raise the methane concentration to around 90%.

[0005] Methane is used as a raw material in chemical processes and as an industrial and household fuel. In recent years, it has also been used as fuel for mobile vehicles equipped with internal combustion engines, such as rockets. High-purity liquefied methane with a purity of 99% or more is used as fuel for mobile vehicles equipped with internal combustion engines, such as rockets. Alaskan LNG contains about 99% methane, so if it is Alaskan LNG, it can be used as is, and there is no need to purify it to increase the purity of the methane. However, Alaskan LNG is not always available, and since LNG is a natural product, the methane concentration fluctuates and can fall below 99%. In such cases, it is necessary to purify LNG with a methane concentration of less than 99% to increase the methane concentration to about 99%. The apparatus described in the aforementioned Patent Documents 1 and 2 can be used to increase the methane concentration. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 4-225778 [Patent Document 2] Japanese Patent Publication No. 2010-275215 [Overview of the project] [Problems that the invention aims to solve]

[0007] The methane obtained by the apparatus described in Patent Documents 1 and 2 has an ultra-high purity of 99.9999% or more, making it over-specced for use as fuel for mobile vehicles equipped with internal combustion engines, such as rockets. Furthermore, the apparatus described in Patent Documents 1 and 2 requires a large rectification column to increase the methane purity to 99.9999% or more. The large size of the rectification column increases the time required for pre-cooling, etc., thus prolonging the production of high-purity liquefied methane. In addition, constructing a large apparatus requires a vast site, making it difficult to construct a rectification plant at each location where liquefied methane will be used. Therefore, it is necessary to load the liquefied methane, purified to the required purity at the refining facility, onto trucks or other vehicles and transport it to the location where the liquefied methane will be used.

[0008] Rocket development was traditionally the domain of government agencies, but in recent years, private companies have also entered the field, and projects to transport civilians into space have already begun. In Japan, not only the Japan Aerospace Exploration Agency (JAXA) but also private companies are venturing into space development and the rocket industry. The fuel for these rockets and other mobile vehicles equipped with internal combustion engines needs to be liquefied methane, refined to a specified purity at a refinery, and then transported by truck or other means to the location where the vehicle is deployed. With the entry of private companies, the destinations for liquefied methane have expanded, and the transport distance has increased. When the transport distance increases, the liquefied methane vaporizes during transport, resulting in resource loss. Furthermore, the fuel for rockets and other mobile vehicles equipped with internal combustion engines is not needed on a regular basis, but is used irregularly as needed. Therefore, the liquefied methane transported to the location of the vehicle needs to be stored in a liquefied natural gas (LNG) storage tank until it is needed. Although the LNG stored in the LNG storage tank is in liquid form, if the temperature inside the tank changes, some of the components contained in the LNG vaporize, resulting in resource loss. Therefore, in order to reduce losses during transportation and storage, it is desirable to purify liquefied methane near the location where mobile vehicles equipped with internal combustion engines, such as rockets, are deployed.

[0009] The present invention has been made in view of the circumstances described above, and its purpose is to provide an apparatus for producing high-purity liquefied methane from liquefied natural gas, which can be constructed near the location of a mobile vehicle equipped with an internal combustion engine, such as a rocket, and which can produce high-purity liquefied methane for use in such a mobile vehicle. [Means for solving the problem]

[0010] The present invention is as follows: [1] A production apparatus for producing high-purity liquefied methane for a mobile vehicle equipped with an internal combustion engine from liquefied natural gas, comprising: a liquefied natural gas storage tank for storing the liquefied natural gas; a rectification column for separating methane gas from the liquefied natural gas; a methane gas condenser for liquefying the methane gas; and a liquefied methane storage tank for storing the liquefied methane, wherein the operating rate of the rectification column in the most recent year is 60% or less. [2] The manufacturing apparatus according to [1], wherein the liquefied methane storage tank is equipped with a reliquefaction device, the reliquefaction device is connected to a heat transfer medium supply path for supplying a heat transfer medium, and the reliquefaction device produces liquefied methane by heat exchange between the heat transfer medium and the methane gas in the liquefied methane storage tank. [3] The manufacturing apparatus according to [2], wherein the rectification column is equipped with a heat exchanger and has a path for supplying the heat transfer medium that has been heat-exchanged in the re-liquefaction device to the heat exchanger of the rectification column. [4] A manufacturing apparatus according to any one of [1] to [3], comprising a first boil-off gas supply path for supplying boil-off gas generated in the liquefied natural gas storage tank to the rectification column. [5] A manufacturing apparatus according to any one of [1] to [4], comprising a second boil-off gas supply path for supplying boil-off gas generated in the liquefied natural gas storage tank to the liquefied methane storage tank. [6] The manufacturing apparatus according to [5], wherein the second boil-off gas supply path is equipped with a device capable of determining the methane concentration in the second boil-off gas supply path. [7] The manufacturing apparatus according to [6], further comprising a first boil-off gas supply path for supplying boil-off gas generated in the liquefied natural gas storage tank to the rectification column. [8] The manufacturing apparatus according to [1] to [7], further comprising a liquefied natural gas supply route for supplying the liquefied natural gas in the liquefied natural gas storage tank to the rectification column. [9] A manufacturing apparatus according to any one of [1] to [8], comprising a discharge route for discharging boil-off gas generated in the liquefied natural gas storage tank.

[10] The manufacturing apparatus according to [9], wherein the boil-off gas generated in the liquefied natural gas storage tank contains nitrogen.

[11] A manufacturing apparatus according to any one of [1] to

[10] , comprising a discharge route for discharging boil-off gas generated in the liquefied methane storage tank.

[12] The manufacturing apparatus according to

[11] , wherein the boil-off gas generated in the liquefied methane storage tank contains nitrogen.

[13] The manufacturing apparatus according to any one of [1] to

[12] , wherein the purity of the high-purity liquefied methane is 99 mol% or higher.

[14] The manufacturing apparatus according to any one of [1] to

[13] , wherein the moving body is a rocket. [Effects of the Invention]

[0011] The high-purity liquefied methane production apparatus according to the present invention comprises a liquefied natural gas storage tank for storing liquefied natural gas, a rectification column for separating methane gas from the liquefied natural gas, a methane gas condenser for liquefying the methane gas, and a liquefied methane storage tank for storing the liquefied methane. Because the apparatus configuration is simple, the apparatus is relatively small and can be constructed near the location where the liquefied methane will be used. As a result, the transport distance of the purified liquefied methane can be shortened, thereby reducing transport losses. Furthermore, since high-purity liquefied methane can be easily produced from liquefied natural gas, the production apparatus only needs to be operated when high-purity liquefied methane is needed and does not need to be operated continuously. Therefore, the operating rate of the rectification column in the high-purity liquefied methane production apparatus according to the present invention is 60% or less over the past year. As a result, the running costs of the high-purity liquefied methane production apparatus can be reduced, and since there is no need to store the transported high-purity liquefied methane for a long period until it is needed, storage losses can be reduced. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram showing Embodiment 1 of the production apparatus for high-purity liquefied methane according to the present invention. [Figure 2] Figure 2 is a schematic diagram showing Embodiment 2 of the apparatus for producing high-purity liquefied methane according to the present invention. [Figure 3] Figure 3 is a schematic diagram showing Embodiment 3 of the apparatus for producing high-purity liquefied methane according to the present invention. [Modes for carrying out the invention]

[0013] The high-purity liquefied methane production apparatus according to the present invention is a production apparatus for high-purity liquefied methane for a mobile vehicle equipped with an internal combustion engine, comprising a liquefied natural gas storage tank for storing liquefied natural gas, a rectification column for separating methane gas from liquefied natural gas, a methane gas condenser for liquefying methane gas, and a liquefied methane storage tank for storing liquefied methane, wherein the operating rate of the rectification column in the most recent year is 60% or less.

[0014] The high-purity liquefied methane production apparatus according to the present invention has a simple configuration, making it relatively compact and allowing it to be constructed near the location where the liquefied methane will be used. As a result, the transport distance of the purified liquefied methane can be shortened, thereby reducing transport losses. Furthermore, since high-purity liquefied methane can be easily produced from liquefied natural gas, the production apparatus only needs to be operated when high-purity liquefied methane is needed and does not need to be operated continuously. Therefore, the rectification column in the high-purity liquefied methane production apparatus according to the present invention is designed to have an operating rate of 60% or less over the past year. As a result, the running costs of the high-purity liquefied methane production apparatus can be reduced, and since there is no need to store the transported liquefied methane for long periods until it is needed, storage losses can be reduced.

[0015] Hereinafter, an apparatus for producing high-purity liquefied methane according to the present invention will be specifically described with reference to the drawings showing embodiments, but the present invention is not limited to the illustrated examples. Modifications can be made within a range that conforms to the spirit described above and below, and all such modifications are included in the technical scope of the present invention.

[0016] (Embodiment 1) Embodiment 1 of the apparatus for producing high-purity liquefied methane according to the present invention will be described with reference to FIG. 1. The apparatus for producing high-purity liquefied methane in Embodiment 1 comprises: a liquefied natural gas storage tank 1 for storing liquefied natural gas; a rectification column 2 for separating methane gas from the liquefied natural gas; a methane gas condenser 3 for liquefying the methane gas; and a liquefied methane storage tank 4 for storing the liquefied methane.

[0017] The liquefied natural gas storage tank 1 is a vessel for storing liquefied natural gas. The methane concentration in the liquefied natural gas stored in the liquefied natural gas storage tank 1 is not particularly limited. For example, it may be less than 85 mol%, but 85 mol% or more is preferable. The methane concentration is more preferably 89 mol% or more, still more preferably 90 mol% or more. The upper limit of the methane concentration is not particularly limited, and may be, for example, 99.9 mol%.

[0018] The inside of the liquefied natural gas storage tank 1 is preferably controlled under conditions (i.e., temperature and pressure) that prevent liquefied methane contained in the liquefied natural gas from vaporizing. Specifically, it is preferable to control the temperature to be equal to or lower than the boiling point of methane (equal to or lower than -161°C under normal pressure). By controlling the temperature to be equal to or lower than the boiling point of methane, vaporization of methane contained in the liquefied natural gas can be suppressed.

[0019] The rectification column 2 is an apparatus for separating methane gas from liquefied natural gas. The rectification column 2 is preferably provided with a heat exchanger 13 at a lower portion thereof.

[0020] The methane gas condenser 3 is an apparatus that cools and liquefies the methane gas separated in the rectification column 2 to produce liquefied methane. The methane gas condenser 3 is provided in a vessel 3a.

[0021] The liquefied methane storage tank 4 is a container for storing the liquefied methane obtained from the methane gas condenser 3. It is preferable to maintain conditions (i.e., temperature and pressure) inside the liquefied methane storage tank 4 that prevent the liquefied methane from vaporizing. Specifically, it is preferable to maintain the temperature below the boiling point of methane (below -161°C at normal pressure). By maintaining the temperature below the boiling point of methane, the vaporization of methane can be suppressed.

[0022] Preferably, the liquefied methane storage tank 4 is connected to a path for supplying the liquefied methane stored in the liquefied methane storage tank 4 to the fuel tank of the internal combustion engine provided on the mobile unit. The liquefied methane may be supplied directly from the liquefied methane storage tank 4 to the fuel tank of the internal combustion engine, or it may be transferred to a container such as a lantern and supplied indirectly to the fuel tank of the internal combustion engine.

[0023] The apparatus for producing high-purity liquefied methane according to the present invention preferably further includes a heat transfer medium storage tank 5. The heat transfer medium storage tank 5 is a container for storing a heat transfer medium at a temperature lower than the boiling point of methane. The form of the heat transfer medium at a temperature lower than the boiling point of methane is preferably a liquid, and specifically, examples include liquids such as oxygen, argon, nitrogen, and helium. Among these, liquid nitrogen is preferred in terms of safety and cost.

[0024] The liquefied natural gas (LNG) storage tank 1 and the rectification column 2 are connected by a LNG supply path 103 that supplies LNG from the LNG storage tank 1 to the rectification column 2. The rectification column 2 and the methane gas condenser 3 are connected by a path 114, and the methane gas condenser 3 and the LNG storage tank 4 are connected by a path 116. The heat transfer medium storage tank 5 and the heat exchanger 13 installed in the rectification column 2 are connected by a path 111. This path 111 branches off midway, and the branch path 115 is connected to a container 3a equipped with the methane gas condenser 3.

[0025] The liquefied natural gas stored in the liquefied natural gas storage tank 1 is supplied to the rectification column 2 via the liquefied natural gas supply path 103. The liquefied natural gas supplied to the rectification column 2 undergoes heat exchange with a heat transfer medium supplied from a path 111 connected to the heat exchanger 13 in the rectification column 2.

[0026] The temperature of the heat transfer medium supplied to the heat exchanger 13 via path 111 is preferably above the boiling point of methane. By setting the temperature of the heat transfer medium above the boiling point of methane, the methane contained in the liquefied natural gas supplied to the rectification column 2 can be vaporized. Specifically, the temperature of the heat transfer medium should be controlled to -161°C or higher. On the other hand, there is no particular upper limit to the temperature of the heat transfer medium, but it is preferable to control the temperature of the heat transfer medium to, for example, 35°C or lower. The temperature of the heat transfer medium may also be controlled to be below the boiling point of ethane (specifically, below -88°C). By setting the temperature of the heat transfer medium below the boiling point of ethane, the vaporization of hydrocarbons with more carbon atoms than methane contained in the liquefied natural gas supplied to the rectification column 2 can be suppressed, thereby increasing the purity of the methane discharged from the rectification column 2.

[0027] In order to control the temperature of the heat transfer medium supplied to the heat exchanger 13 within the above range, it is preferable to place a vaporizer 7 in the middle of the path 111 connecting the heat transfer medium storage tank 5 and the heat exchanger 13 provided in the rectification column 2, which vaporizes the liquid supplied from the heat transfer medium storage tank 5. In the vaporizer 7, the temperature of the heat transfer medium can be controlled within the above range by exchanging heat between the heat transfer medium supplied from the heat transfer medium storage tank 5 and the atmosphere.

[0028] The heat transfer medium is supplied to the heat exchanger 13 of the rectification column 2 via path 111, and after heat exchange in the heat exchanger 13, it can be discharged out of the system via path 113. The heat transfer medium discharged from path 113 can be used, for example, as an instrumentation gas or a process purge gas.

[0029] The gas obtained by heat exchange and vaporization in the heat exchanger 13 rises within the rectification column 2 and accumulates at the top of the rectification column 2. An outlet for removing the gas produced within the rectification column 2 is provided at the top of the rectification column 2. A passage 114 is connected to this outlet, and this passage 114 is connected to the methane gas condenser 3.

[0030] A heat transfer medium is supplied to a container 3a equipped with a methane gas condenser 3 from a heat transfer medium storage tank 5 via a branch line 115. In the methane gas condenser 3, heat exchange occurs between the heat transfer medium supplied via the branch line 115 and the gas supplied via path 114. The methane gas contained in the heat-exchanged gas is cooled and liquefied, and the resulting liquefied methane is supplied to a liquefied methane storage tank 4 via path 116 and stored there.

[0031] Preferably, the container 3a is provided with an outlet for removing the gas accumulated at the top of the container 3a. A path 118 is connected to this outlet, and preferably, the path 118 is connected downstream of the vaporizer 7 located in the path 111 that connects the heat transfer medium storage tank 5 and the heat exchanger 13 of the rectification column 2, and upstream of the heat exchanger 13. By supplying the gas accumulated at the top of the container 3a to the heat exchanger 13 of the rectification column 2 via paths 118 and 111, the gas accumulated at the top of the container 3a can be reused as a heat transfer medium.

[0032] The liquid containing hydrocarbons heavier than methane separated in the rectification column 2 descends within the rectification column 2 and accumulates at the bottom of the rectification column 2. Preferably, an outlet is provided at the bottom of the rectification column 2 for removing the liquid accumulated at the bottom of the rectification column 2. A passage 112 is connected to this outlet, and the liquid accumulated at the bottom of the rectification column 2 is discharged out of the system through the passage 112. The liquid discharged through the passage 112 can be used, for example, as fuel for other equipment.

[0033] The operating rate of the rectification column 2 in the high-purity liquefied methane production apparatus according to the present invention over the past year is 60% or less (excluding 0%). Since the high-purity liquefied methane production apparatus according to the present invention is an apparatus for producing high-purity liquefied methane for a mobile vehicle equipped with an internal combustion engine, the apparatus only needs to be operated when high-purity liquefied methane is used. Therefore, the operating time of the high-purity liquefied methane production apparatus according to the present invention is approximately 60% or less of the year, and the time during which it is not operated is very long. Whether the high-purity liquefied methane production apparatus is operating can be determined by whether the rectification column 2 is operating. Whether the rectification column 2 is operating can be determined by whether liquefied methane is being supplied to the liquefied methane storage tank 4 through the path 116, and the operating rate can be calculated based on the time that liquefied methane is being supplied to the liquefied methane storage tank 4. The operating rate of the rectification column 2 over the past year may be, for example, 50% or less.

[0034] In the apparatus for producing high-purity liquefied methane according to the present invention, the number of rectification columns 2 may be multiple, but one is sufficient.

[0035] It is preferable that the rectification column 2 is equipped with a rectification means inside. Examples of rectification means include rectification shelves and packing materials. Examples of packing materials include regular packing materials and irregular packing materials.

[0036] The high-purity liquefied methane production apparatus according to the present invention may include a gas-liquid separator 6 in the middle of the path 116 connecting the methane gas condenser 3 and the liquefied methane storage tank 4. In the gas-liquid separator 6, the liquid supplied from the methane gas condenser 3 via the path 116 is separated into gas and liquid, and by separating the gas from the liquid, the purity of the methane contained in the liquid can be further increased. On the other hand, the gas separated from the liquid in the gas-liquid separator 6 can be discharged out of the system through a path 121 connected to an outlet provided at the top of the gas-liquid separator 6.

[0037] It is preferable to control the temperature inside the gas-liquid separator 6 so that it is higher than the boiling point of the heat transfer medium supplied to the container 3a, and below the boiling point of methane. This allows substances with lower boiling points than methane (such as nitrogen) contained in the liquefied methane to be vaporized, thereby increasing the purity of the methane.

[0038] The path 116 connecting the gas-liquid separator 6 and the liquefied methane storage tank 4 may be branched along the way, and if it is branched, it is preferable that the branch path 117 is connected to the rectification column 2. The liquid separated in the gas-liquid separator 6 is returned to the rectification column 2 via the branch path 117, and the purity of the liquefied methane can be further increased by purifying it again in the rectification column 2.

[0039] As described above, the conditions inside the liquefied methane storage tank 4 are controlled to prevent the liquefied methane from vaporizing (i.e., temperature and pressure). However, boil-off gas can still be generated inside the liquefied methane storage tank 4. Boil-off gas is the gas that is produced when some of the liquefied methane stored in the liquefied methane storage tank 4 evaporates and vaporizes. Conventionally, the boil-off gas generated inside the liquefied methane storage tank 4 was exhausted into the atmosphere.

[0040] In the high-purity liquefied methane production apparatus according to the present invention, the liquefied methane storage tank 4 is equipped with a reliquefaction device 12, and it is preferable that a heat medium supply path 119 for supplying a heat medium is connected to the reliquefaction device 12. The heat medium supply path 119 is a path that connects the heat medium storage tank 5 and the reliquefaction device 12 provided in the liquefied methane storage tank 4. For example, the heat medium supply path 119 may be a branched path that branches off from the path 111 connecting the heat medium storage tank 5 and the heat exchanger 13 of the rectification column 2.

[0041] The reliquefaction device 12 is a device that generates liquefied methane by exchanging heat between a heat transfer medium supplied to the reliquefaction device 12 and methane gas generated in the liquefied methane storage tank 4. By reliquefying the methane gas generated in the liquefied methane storage tank 4, the loss of liquefied methane stored in the liquefied methane storage tank 4 can be reduced.

[0042] The liquefied methane storage tank 4 may be equipped with a discharge path 105 for discharging boil-off gas generated within the liquefied methane storage tank 4. Preferably, the discharge path 105 is connected to an outlet provided at the top of the liquefied methane storage tank 4. By discharging the boil-off gas from the discharge path 105 to the outside of the system, the methane purity in the liquefied methane stored in the liquefied methane storage tank 4 can be increased.

[0043] The boil-off gas discharged from the discharge path 105 preferably contains a substance with a boiling point lower than that of methane, and preferably contains nitrogen, for example.

[0044] The heat transfer medium that has undergone heat exchange in the reliquefaction unit 12 can be discharged out of the system via a path 120 connected to the reliquefaction unit 12. The path 120 may be connected to, for example, a heat exchanger 13 in the rectification column 2, or, as shown in Figure 1, the path 120 may be connected to a path 111 that connects the vaporizer 7 and the heat exchanger 13 of the rectification column 2. The heat transfer medium can be reused by supplying the heat transfer medium that has undergone heat exchange in the reliquefaction unit 12 to the heat exchanger 13 in the rectification column 2 via the path 120.

[0045] (Embodiment 2) Next, Embodiment 2 of the high-purity liquefied methane production apparatus according to the present invention will be described with reference to Figure 2. In Figure 2, the same reference numerals are used for parts that overlap with Figure 1 to avoid redundant explanations.

[0046] As described above, the liquefied natural gas (LNG) storage tank 1 is controlled to maintain conditions (i.e., temperature and pressure) that prevent the liquefied methane contained in the LNG from vaporizing. However, boil-off gas is generated within the LNG storage tank 1. Boil-off gas is the gas that vaporizes when a portion of the LNG stored in the LNG storage tank 1 evaporates. Conventionally, the boil-off gas generated within the LNG storage tank 1 was exhausted into the atmosphere.

[0047] Embodiment 2 of the present invention includes a first boil-off gas supply path 101 that supplies boil-off gas generated in the liquefied natural gas storage tank 1 to the rectification column 2. The first boil-off gas supply path 101 is connected to a boil-off gas outlet located at the top of the liquefied natural gas storage tank 1. The boil-off gas generated in the liquefied natural gas storage tank 1 is supplied to the rectification column 2 via the first boil-off gas supply path 101, and is purified in the rectification column 2, separating the methane gas contained in the boil-off gas from a liquid containing hydrocarbons heavier than methane. As a result, the methane contained in the boil-off gas can be effectively utilized.

[0048] The liquefied natural gas (LNG) storage tank 1 may also be equipped with a discharge route 104 for discharging boil-off gas generated within the LNG storage tank 1 to the outside of the system, separate from the first boil-off gas supply route 101. Preferably, the discharge route 104 is connected to an outlet provided at the top of the LNG storage tank 1. By discharging boil-off gas from the discharge route 104 to the outside of the system, the methane purity in the LNG stored in the LNG storage tank 1 can be increased.

[0049] The boil-off gas discharged from the discharge path 104 preferably contains a substance with a boiling point lower than that of methane, and preferably contains nitrogen, for example.

[0050] (Embodiment 3) Next, Embodiment 3 of the production apparatus for high-purity liquefied methane according to the present invention will be described with reference to Figure 3. In Figure 3, the same reference numerals are used for parts that overlap with Figures 1 and 2 to avoid redundant explanations.

[0051] Embodiment 2 is equipped with the first boil-off gas supply path 101, whereas Embodiment 3 differs from Embodiment 2 in that it is equipped with a second boil-off gas supply path 102 that supplies boil-off gas generated in the liquefied natural gas storage tank 1 to the liquefied methane storage tank 4. If the methane concentration in the boil-off gas generated in the liquefied natural gas storage tank 1 is high, the boil-off gas can be effectively utilized as liquefied methane by supplying it to the liquefied methane storage tank 4 instead of supplying it to the rectification column 2 as in Embodiment 2. The boil-off gas generated in the liquefied natural gas storage tank 1 may be supplied to the liquefied methane storage tank 4 in a gaseous state and liquefied in the reliquefaction device 12 provided in the liquefied methane storage tank 4 to produce liquefied methane, or a methane gas condenser (not shown) may be provided in the middle of the second boil-off gas supply path 102 to convert it into a liquid state and supply it to the liquefied methane storage tank 4. Furthermore, the second boil-off gas supply route 102 only needs to be connected to a boil-off gas outlet located at the top of the liquefied natural gas storage tank 1.

[0052] In Embodiment 3, the liquefied methane storage tank 4 is equipped with a reliquefaction device 12, and a heat medium supply path 119 for supplying a heat medium is connected to the reliquefaction device 12. In the reliquefaction device 12, heat exchange occurs between the heat medium supplied to the reliquefaction device 12 and the methane gas generated in the liquefied methane storage tank 4 and the boil-off gas supplied from the second boil-off gas supply path 102 to produce liquefied methane. By reliquefying the methane gas generated in the liquefied methane storage tank 4 and the boil-off gas supplied from the second boil-off gas supply path 102, the loss of liquefied methane stored in the liquefied methane storage tank 4 can be reduced, and the boil-off gas supplied from the liquefied natural gas storage tank 1 can be effectively utilized as a resource.

[0053] Preferably, the second boil-off gas supply path 102 is equipped with a device that can determine the methane concentration in the boil-off gas supplied to the liquefied methane storage tank 4 via the second boil-off gas supply path 102. If the methane concentration in the boil-off gas falls below a predetermined value, the supply of boil-off gas from the liquefied natural gas storage tank 1 to the liquefied methane storage tank 4 can be stopped. This prevents boil-off gas with a methane concentration below a predetermined value from flowing into the liquefied methane storage tank 4, thereby maintaining the purity of liquefied methane in the liquefied methane storage tank 4. When the methane concentration in the boil-off gas falls below a predetermined value, the boil-off gas can be discharged outside the system.

[0054] The configuration of the device capable of determining the methane concentration is not particularly limited; it may be a concentration meter capable of measuring the methane concentration in boil-off gas, or a concentration meter capable of measuring the concentration of other gases (for example, the concentration of impurity gases such as nitrogen) in boil-off gas. If a concentration meter capable of measuring the concentration of other gases in boil-off gas is used, the methane concentration in the boil-off gas can be calculated by subtracting the concentration of other gases measured by the concentration meter from 100 mol%.

[0055] The threshold methane concentration for deciding whether or not to stop the supply of boil-off gas from the liquefied natural gas storage tank 1 to the liquefied methane storage tank 4 is preferably, for example, 99 mol%. If the methane concentration is 99 mol% or higher, it is preferable to continue supplying boil-off gas from the liquefied natural gas storage tank 1 to the liquefied methane storage tank 4, and if the methane concentration is less than 99 mol%, it is preferable to stop supplying boil-off gas from the liquefied natural gas storage tank 1 to the liquefied methane storage tank 4. If the methane concentration is less than 99 mol%, it is preferable to, for example, discharge the boil-off gas generated in the liquefied natural gas storage tank 1 to the outside of the system via the discharge path 104 to increase the methane gas concentration in the boil-off gas within the liquefied natural gas storage tank 1. The threshold methane concentration may also be, for example, 98 mol%, 97 mol%, or 99.5 mol%.

[0056] The location of the device capable of determining the methane concentration is not particularly limited and may be at the connection point between the liquefied natural gas storage tank and the second boil-off gas supply path 102, or at the connection point between the second boil-off gas supply path 102 and the liquefied methane storage tank 4. Of course, it may also be located somewhere along the second boil-off gas supply path 102.

[0057] If the second boil-off gas supply path 102 is equipped with a device capable of determining the methane concentration in the boil-off gas supplied to the liquefied methane storage tank 4, it is preferable that the high-purity liquefied methane production apparatus further includes a first boil-off gas supply path 101a.

[0058] The first boil-off gas supply route 101a may be provided, for example, as a route connecting the liquefied natural gas storage tank 1 and the rectification column 2, separate from the second boil-off gas supply route 102, but it is preferable to provide it as a branch of the second boil-off gas supply route 102 that connects the liquefied natural gas storage tank 1 and the liquefied methane storage tank 4. When the first boil-off gas supply route 101a is provided as a branch of the second boil-off gas supply route 102, it is preferable to place a valve 122 at the connection point between the second boil-off gas supply route 102 and the first boil-off gas supply route 101a. When the methane concentration detected by a device capable of determining the methane concentration in the boil-off gas falls below a threshold, the valve 122 is switched, and the boil-off gas in the liquefied natural gas storage tank 1 is supplied to the rectification column 2, where it is purified to increase the methane concentration.

[0059] As described above, while Embodiment 2 and Embodiment 3 differ in the destination of the boil-off gas generated in the liquefied natural gas storage tank 1, they are similar in that they effectively utilize the boil-off gas generated in the liquefied natural gas storage tank 1.

[0060] According to the apparatus for producing high-purity liquefied methane according to the present invention, high-purity liquefied methane with a methane purity of 99 mol% or higher can be produced. The methane purity is more preferably 99.9 mol% or higher, even more preferably 99.99 mol% or higher, and particularly preferably 99.999 mol% or higher. For example, a methane purity of less than 99.9999 mol% is preferred.

[0061] The high-purity liquefied methane produced by the high-purity liquefied methane production apparatus according to the present invention can be used as fuel for a mobile vehicle equipped with an internal combustion engine, such as a rocket.

[0062] The high-purity liquefied methane production apparatus according to the present invention can reduce the amount of boil-off gas (BOG) released into the atmosphere and produce high-purity liquefied methane from liquefied natural gas (LNG) in high yield. Therefore, it can reduce greenhouse gas emissions and contribute to some of the Sustainable Development Goals (SDGs). [Explanation of Symbols]

[0063] 1. Liquefied natural gas storage tank 2 Rectification tower 3. Methane gas condenser 3a container 4. Liquefied methane storage tank 5. Heat transfer medium storage tank 6 Gas-liquid separator 7. Vaporizer 12 Reliquefaction equipment 13 Heat exchanger 101 First boil-off gas supply path 102 Second boil-off gas supply route 103 Liquefied Natural Gas Supply Routes 104, 105 Emission routes Routes 111-114, 116, 118, 120 115, 117 Junction 119 Heat transfer medium supply path

Claims

1. A production apparatus for high-purity liquefied methane for mobile vehicles equipped with internal combustion engines, derived from liquefied natural gas, A liquefied natural gas storage tank for storing the aforementioned liquefied natural gas, A rectification column for separating methane gas from a liquid containing hydrocarbons heavier than methane gas, A methane gas condenser that liquefies methane gas, A liquefied methane storage tank for storing liquefied methane, It is equipped with, A production apparatus for high-purity liquefied methane, wherein the operating rate of the aforementioned rectification column over the past year has been 60% or less.

2. The aforementioned liquefied methane storage tank is equipped with a reliquefaction device, The aforementioned reliquefaction device is connected to a heat transfer medium supply path for supplying a heat transfer medium. The manufacturing apparatus according to claim 1, wherein the reliquefaction apparatus generates liquefied methane by heat exchange between the heat transfer medium and the methane gas in the liquefied methane storage tank.

3. The aforementioned rectification column is equipped with a heat exchanger, The manufacturing apparatus according to claim 2, further comprising a path for supplying the heat transfer medium, which has been heat-exchanged in the re-liquefaction apparatus, to the heat exchanger of the rectification column.

4. The manufacturing apparatus according to claim 1, further comprising a first boil-off gas supply path for supplying boil-off gas generated in the liquefied natural gas storage tank to the rectification column.

5. The manufacturing apparatus according to claim 1, further comprising a second boil-off gas supply path for supplying boil-off gas generated in the liquefied natural gas storage tank to the liquefied methane storage tank.

6. The manufacturing apparatus according to claim 5, wherein the second boil-off gas supply path is equipped with a device capable of determining the methane concentration within the second boil-off gas supply path.

7. The manufacturing apparatus according to claim 6, further comprising a first boil-off gas supply path for supplying boil-off gas generated in the liquefied natural gas storage tank to the rectification column.

8. The manufacturing apparatus according to claim 1, further comprising a liquefied natural gas supply path for supplying the liquefied natural gas in the liquefied natural gas storage tank to the rectification column.

9. The manufacturing apparatus according to claim 1, further comprising a discharge path for discharging boil-off gas generated in the liquefied natural gas storage tank.

10. The manufacturing apparatus according to claim 9, wherein the boil-off gas generated in the liquefied natural gas storage tank contains nitrogen.

11. The manufacturing apparatus according to claim 1, further comprising a discharge path for discharging boil-off gas generated in the liquefied methane storage tank.

12. The manufacturing apparatus according to claim 11, wherein the boil-off gas generated in the liquefied methane storage tank contains nitrogen.

13. The manufacturing apparatus according to claim 1, wherein the purity of the high-purity liquefied methane is 99 mol% or more.

14. The manufacturing apparatus according to claim 1, wherein the moving body is a rocket.

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