Method for producing high-purity methane

Abstract

To provide a method for creating high-purity methane while reducing energy consumption.SOLUTION: A method for creating high-purity methane has: a cooling step of cooling adsorption containers to a liquefaction temperature of natural gas severally in a first adsorption container and a second adsorption container filled with adsorbent; an adsorption step of introducing liquefied natural gas into the cooled adsorption containers, and allowing the adsorbent to adsorb impurities in the liquefied natural gas in a liquid phase to obtain liquefied methane; and a regeneration step of introducing regeneration gas of a higher temperature than the liquefaction temperature into the adsorption containers after the adsorption step, desorbing impurities from the adsorbent in a vapor phase to regenerate the adsorbent, are sequentially repeated, and a both-containers adsorption step of performing a first state in which the regeneration step and the cooling step are performed in the second adsorption container while performing the adsorption step in the first adsorption container, and a second state in which the regeneration step and the cooling step are performed in the first adsorption container while performing the adsorption step in the second adsorption container, alternately in the first adsorption container and the second adsorption container, and adsorbing impurities between the first state and the second state by both of the first adsorption container and the second adsorption container.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing high-purity methane using liquefied natural gas as a raw material. By law This is related to. [Background technology]

[0002] Refined methane gas is used as fuel, semiconductors, carbon material raw material, etc. Natural gas is mainly used as a raw material for high-concentration methane gas. Such natural gas and city gas (13A, 12A, etc.) produced from natural gas contain methane as the main component and light hydrocarbons such as ethane, propane, butane, and isobutane. For example, the components of natural gas produced from oil fields in Japan (Niigata, Akita, etc.) are about 85-92% methane, about 4-7% ethane, about 1-4% propane, and about 1% butane and isobutane.

[0003] Until now, there has not been much demand for high-purity methane, but this is expected to increase in the future with advances in space development and other fields, and expectations are rising for technology that can efficiently produce high-purity methane.

[0004] The applicant is aware of the following Patent Documents 1 and 2 as prior art documents relating to such technology for refining methane from natural gas. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-024489 A [Patent Document 2] Special Publication No. 2014-509557

[0006] The above-mentioned Patent Document 1 relates to a technology for obtaining high-concentration methane from natural gas by distillation separation. The above-mentioned Patent Document 1 contains the following description.

[0012] An object of the present invention is to provide a method and apparatus capable of separating hydrocarbons such as ethane from liquefied natural gas with reduced energy consumption and low cost without impairing ease and reliability of operation.

[0013] According to the present invention, a) distilling a feed liquefied natural gas in a first distillation column to separate it into a fraction enriched in methane and a fraction enriched in components heavier than methane; b) distilling the fraction enriched in components heavier than methane in a second distillation column to separate the fraction enriched in ethane and the fraction enriched in components heavier than ethane; c) recovering the cold heat of the feed liquefied natural gas to be supplied to the first distillation column or the internal liquid of the first distillation column by a heat transfer medium; and d) cooling the overhead gas of the second distillation column with the heat transfer medium from which the cold heat has been recovered to condense at least a portion of the overhead gas of the second distillation column; A method for separating hydrocarbons from a liquefied natural gas having

[0007] The above-mentioned Patent Document 2 relates to a technology for obtaining high-concentration methane from natural gas by a temperature swing method using an adsorbent in a temperature range above room temperature. The above-mentioned Patent Document 2 contains the following description.

[0065] FIG. 1 herein is a schematic diagram of the PTSA process steps described above. A stream of natural gas fed to the swing adsorption unit A of the present invention via line 10 was modeled to flow into the feed input end of the adsorption bed within the swing adsorption unit. Feed gas was modeled to flow through the adsorption bed via the adsorption front from the feed inlet to the product outlet end of the adsorption bed. The swing adsorption unit described herein was a combined pressure / temperature swing adsorption (PTSA) unit modeled to be operated at high pressure during the adsorption step so that the adsorbed gas components can be desorbed and the adsorption bed can be regenerated at high temperature. As previously described, the adsorbent material used in the adsorption bed was modeled to be a 0.01% sorbent compared to methane. 2+The adsorption of hydrocarbons was modeled to be favored. The adsorption was modeled at a first pressure of 2 bara to 200 bara and a first temperature of 20°C to 150°C. During the adsorption process, C 2+ The hydrocarbon-depleted, methane-rich product stream was modeled to exit the product outlet end of the adsorbent bed via line 12, be sent to compressor P1 for compression to pipeline pressure, and exit via line 14.

[0066] The adsorption step was stopped and the adsorption bed was then depressurized, in this case by a series of equilibration discharge steps, cocurrent to the feed gas flow, to a second pressure lower than the pressure of the adsorption step. This second pressure ranged from about 1 bara to about 2 bara. The discharged effluent, in this case substantially pure methane, left the vessel via line 16 and was pressurized by sending a portion via line 17 to compressor P2 for use in a later stage as purge gas, where it was conveyed countercurrently through the adsorption bed during and / or after the heating / desorption step. A portion of the discharged effluent could optionally be conveyed via line 18 (preferably through compressor P3) to repressurize the adsorption bed if necessary.

[0067] After the discharge step, the product end of the bed is sealed and the inlet stage is left open while the bed is externally heated and maintained at a pressure of about 1 bar to remove the adsorbed C from the adsorbent. 2+ At least a portion of the hydrocarbons are desorbed and removed from the bed, preferably using a countercurrent flow of purge gas provided by the product gas via line 18. 2+ The hydrocarbon stream is passed from the feed end of the adsorption bed via line 20 to a recovery processing unit R where it is separated, in this case by fractionation, specifically cryogenic distillation, into C2, C3, and C4. 4+A trace amount of C1 product could optionally be recovered in recovery processing unit R and sent via line 22 to compressor P4 (if necessary) and then to compressor P1, optionally compressed to pipeline pressure with methane-enriched product stream 12 obtained directly from the adsorption unit, and conveyed to the pipeline. Additionally or alternatively, C2, C3, and C4+, designated as C2, C3, and C4+, could be sent via line 22 to compressor P4 (if necessary) and then to compressor P1, optionally compressed to pipeline pressure with methane-enriched product stream 12 obtained directly from the adsorption unit, and conveyed to the pipeline. 4+ The stream could be collected as a product stream via recovery processing unit R for transport, sale, and / or further processing. Summary of the Invention [Problem to be solved by the invention]

[0008] The above-mentioned Patent Document 1 is a technology for separating and removing C2 or higher hydrocarbons from liquefied natural gas by distillation. For such distillation and separation, equipment such as a condenser and an evaporator is indispensable. In addition, these condensers and evaporators require large amounts of hot and cold heat. Therefore, there is a problem that the energy consumption for the hot and cold heat used by the condensers and evaporators is large. There is also a problem that purity defects are likely to occur due to the influence of composition fluctuations in the liquefied natural gas used as a raw material.

[0009] The above-mentioned Patent Document 2 is a technology for obtaining high-concentration methane by adsorbing impurities in natural gas in an adsorption bed. The adsorption of impurities in the adsorption bed is performed in a gas phase at room temperature, and the adsorption bed is regenerated in a high-temperature gas phase of 100 to 300°C. Therefore, in order to supply the heat required for the regeneration process, an electric heater, a steam heater, or the like must be installed. In addition, energy must be supplied to generate heat in the equipment, and, as with Patent Document 1, there is a problem of large energy consumption.

[0010] 〔the purpose〕 The present invention has been made in consideration of the above circumstances, and has the following objectives. A method for producing high-purity methane with reduced energy consumption Law provide. [Means for solving the problem]

[0011] In order to achieve the above object, the method for producing high purity methane according to claim 1 employs the following configuration. A method for producing high purity methane using liquefied natural gas as a raw material, comprising the steps of: providing at least a first adsorption vessel and a second adsorption vessel filled with an adsorbent; In each of the first and second adsorption vessels, a cooling step of cooling the adsorption vessel filled with the adsorbent to a temperature at which the natural gas is liquefied; an adsorption step of introducing liquefied natural gas into the cooled adsorption vessel and adsorbing impurities in the liquefied natural gas onto the adsorbent in a liquid phase to obtain high-purity liquefied methane; a regeneration step in which a regeneration gas having a temperature higher than the liquefaction temperature is introduced into the adsorption vessel after the adsorption step to remove the impurities from the adsorbent in the gas phase and regenerate the adsorbent; and a first state in which the regeneration step and the cooling step are performed in the second adsorption vessel while the adsorption step is being performed in the first adsorption vessel, and a second state in which the regeneration step and the cooling step are performed in the first adsorption vessel while the adsorption step is being performed in the second adsorption vessel, are alternately performed in the first adsorption vessel and the second adsorption vessel; Between the first state and the second state, a dual adsorption step is performed in which adsorption is performed in both the first adsorption vessel and the second adsorption vessel.

[0012] The method for producing high purity methane according to claim 2 employs the following features in addition to the features according to claim 1. In the first state, between the cooling step and the dual adsorption step, a piping cooling step is performed by discharging the liquefied methane filled in the second adsorption vessel through a piping, and in the second state, between the cooling step and the dual adsorption step, a piping cooling step is performed by discharging the liquefied methane filled in the first adsorption vessel through a piping. Effect of the Invention

[0013] The method for producing high purity methane according to claim 1 comprises: This method for producing high-purity methane using liquefied natural gas as a raw material includes preparing at least a first adsorption vessel and a second adsorption vessel filled with an adsorbent. A cooling step, an adsorption step, and a regeneration step are sequentially repeated in each of the first and second adsorption vessels. The cooling step cools the adsorption vessel filled with the adsorbent to the liquefaction temperature of natural gas. The adsorption step introduces liquefied natural gas into the cooled adsorption vessel and adsorbs impurities in the liquefied natural gas onto the adsorbent in the liquid phase, thereby obtaining high-purity liquefied methane. The regeneration step introduces a regeneration gas at a temperature higher than the liquefaction temperature into the adsorption vessel after the adsorption step, and removes the impurities from the adsorbent in the gas phase, thereby regenerating the adsorbent. The first and second adsorption vessels alternate between a first state in which the regeneration step and the cooling step are performed in the second adsorption vessel while the adsorption step is performed in the first adsorption vessel, and a second state in which the regeneration step and the cooling step are performed in the first adsorption vessel while the adsorption step is performed in the second adsorption vessel. Between the first and second states, a bi-adsorption step of adsorption is performed in both the first and second adsorption vessels. In this way, high-purity methane is obtained from liquefied natural gas by adsorption separation rather than distillation separation, so that equipment such as a condenser or evaporator is not required and there is no energy consumption due to them. In addition, the adsorption vessel filled with the adsorbent is cooled to the liquefaction temperature of natural gas, and impurities from the liquefied natural gas are adsorbed onto the adsorbent in the liquid phase. In addition, the adsorbent is regenerated in the gas phase by introducing a regeneration gas at a temperature higher than the liquefaction temperature into the adsorption vessel. Therefore, heat such as a heater or steam is not required to regenerate the adsorbent, and there is no energy consumption. Also, unlike distillation separation, purity defects due to the influence of composition fluctuations in the liquefied natural gas feedstock are unlikely to occur. In this way, high-purity methane can be produced with less energy consumption. Also, the adsorption process is carried out in one of the adsorption vessels to produce high-purity methane, and the regeneration process and cooling process are carried out in the other adsorption vessels, so that high-purity methane can always be produced.

[0014] The method for producing high purity methane according to claim 2 comprises the steps of: In the first state, between the cooling step and the dual adsorption step, a piping cooling step is carried out by discharging the liquefied methane filled in the second adsorption vessel through a piping to cool the piping, and in the second state, between the cooling step and the dual adsorption step, a piping cooling step is carried out by discharging the liquefied methane filled in the first adsorption vessel through a piping to cool the piping. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram showing an example of an apparatus used in the high-purity methane production method of the present invention. [Diagram 2] FIG. 1 is a process diagram illustrating one embodiment of the method for producing high-purity methane of the present invention. [Diagram 3] FIG. 1 shows Stage 1A. [Figure 4] FIG. 1B shows stage 1B. [Diagram 5] FIG. 1C shows stage 1C. [Figure 6] FIG. 1D shows stage 1D. [Figure 7] FIG. 1 shows stage 1E. [Figure 8] FIG. 1 shows stage 1F. [Figure 9] FIG. 1 shows stage 1G. [Figure 10] FIG. 1 shows stage 1H. [Figure 11] FIG. 1 shows stage T1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Next, the best mode for carrying out the present invention will be described.

[0017] [Overall structure] FIG. 1 shows the production of high purity methane according to the present invention. Use in a method Device one example 1 is a block diagram showing an example of the configuration shown in FIG. Book binding The apparatus uses liquefied natural gas as a raw material and removes impurities by adsorption separation in the liquid phase to obtain high-purity methane. With this apparatus, the method for producing high-purity methane of the present invention can be realized.

[0018] Book binding The apparatus comprises a raw material storage tank 10, a first adsorption vessel 20A and a second adsorption vessel 20B, a product methane storage tank 30, and a regenerated gas storage tank 40. Structures such as piping and valves connected to the raw material storage tank 10, the first adsorption vessel 20A and the second adsorption vessel 20B, the product methane storage tank 30, and the regenerated gas storage tank 40 function as the adsorption means, depressurization means, deliquification means, regeneration means, purging means, and cooling means of the present invention, and respectively realize the adsorption step, depressurization step, deliquification step, regeneration step, purging step, and cooling step of the present invention.

[0019] This embodiment Methodhas a plurality of adsorption vessels (two in the illustrated example, a first adsorption vessel 20A and a second adsorption vessel 20B), and realizes a cooling process by the cooling means, an adsorption process by the adsorption means, a regeneration process by the regeneration means, a depressurization process by the depressurization means, a deliquification process by the deliquification means, and a purging process by the purging means. These processes are alternately performed in the first adsorption vessel 20A and the second adsorption vessel 20B.

[0020] [Raw material storage tank 10] The raw material storage tank 10 stores liquefied natural gas, which is the raw material to be introduced into the first adsorption vessel 20A and the second adsorption vessel 20B.

[0021] The above-mentioned liquefied natural gas is made by cooling naturally occurring natural gas, a fossil fuel, to its liquefaction temperature of -162°C or lower. In addition to its main component methane, natural gas also contains other gases such as ethane, propane, and butane, and these gases are also liquefied during the liquefaction process, so the composition ratio of these hydrocarbons in liquefied natural gas also varies depending on the origin of the original natural gas.

[0022] The present invention is a technology for producing high purity methane using the above-mentioned liquefied natural gas as a raw material, and ethane, propane, butane, etc. other than methane will be described as impurities.

[0023] [First adsorption vessel 20A and second adsorption vessel 20B] The first adsorption vessel 20A and the second adsorption vessel 20B are filled with adsorbents 21A and 21B, respectively.

[0024] As the adsorbents 21A and 21B, for example, zeolite, activated carbon, organometallic complexes, etc., can be used. In the present invention, the "adsorbent" refers to an aggregate of granular materials made of the above-mentioned zeolite, activated carbon, organometallic complexes, etc.

[0025] In the present invention, the first adsorption vessel 20A and the second adsorption vessel 20B filled with the adsorbents 21A and 21B are cooled to a temperature below the liquefaction temperature of natural gas. The liquefied natural gas is introduced into the adsorption vessels 20A and 20B and brought into contact with the adsorbents 21A and 21B, and impurities other than methane are adsorbed and separated by the adsorbents 21A and 21B in the liquid phase. High-purity methane from which the impurities have been separated is then obtained and taken out of the first adsorption vessel 20A and the second adsorption vessel 20B.

[0026] As described above, in this example, the first adsorption vessel 20A and the second adsorption vessel 20B alternately perform an adsorption process by the adsorption means, a depressurization process by the depressurization means, a deliquification process by the deliquification means, a regeneration process by the regeneration means, a purging process by the purging means, and a cooling process by the cooling means. Specifically, while the first adsorption vessel 20A is performing an adsorption process, the second adsorption vessel 20B performs a depressurization process, deliquification process, regeneration process, purging process, and cooling process. Conversely, while the second adsorption vessel 20B is performing an adsorption process, the first adsorption vessel 20A performs a depressurization process, deliquification process, regeneration process, purging process, and cooling process.

[0027] [Adsorption step and adsorption means] In the adsorption step in the first adsorption vessel 20A, liquefied natural gas in the raw material storage tank 10 is introduced into the lower part of the first adsorption vessel 20A via the raw material line 11 and raw material valve 11V, the first inlet line 12A and the first inlet valve 12AV. Product methane from which impurities have been adsorbed and separated by the adsorbent 21A is introduced into the product methane storage tank 30 via the first liquid outlet line 23A and the first liquid outlet valve 23AV, the product methane inlet line 31 and the product methane inlet valve 31V. In the adsorption step in the second adsorption vessel 20B, the liquefied natural gas in the raw material storage tank 10 is introduced into the lower part of the second adsorption vessel 20B via the raw material line 11 and raw material valve 11V, the second inlet line 12B and the second inlet valve 12BV. The product methane from which impurities have been adsorbed and separated by the adsorbent 21B is introduced into the product methane storage tank 30 via the second liquid outlet line 23B and the second liquid outlet valve 23BV, the product methane inlet line 31 and the product methane inlet valve 31V. The equipment such as piping and valves that are operating and functioning at this time function as the adsorption means of the present invention, and high-purity liquefied methane is obtained by introducing liquefied natural gas into the cooled adsorption vessel and adsorbing impurities in the liquefied natural gas onto the adsorbent in the liquid phase.

[0028] [Liquid phase and gas phase] In the first adsorption vessel 20A where the adsorption process is carried out, there are provided a liquid phase section where the liquefied natural gas becomes liquid during the adsorption process by the adsorption means, and a gas phase section where the liquefied natural gas becomes gaseous during the adsorption process. At least a part of the adsorbent 21A is present in the liquid phase section. Specifically, this is achieved by maintaining the temperature and pressure in the first adsorption vessel 20A within a predetermined range so that a gas phase section is formed in the upper part of the first adsorption vessel 20A where the adsorption process is carried out, and the lower part where the adsorbent 21A is present becomes liquid phase. The same is true for the second adsorption vessel 20B.

[0029] [Decompression step and decompression means] In a first depressurization step in the first adsorption vessel 20A, the gas present in the gas phase of the first adsorption vessel 20A is discharged via the first exhaust path 25A and the first exhaust valve 25AV, thereby reducing the pressure inside the first adsorption vessel 20A. In a second depressurization step performed after the deliquescence step described below, the gas remaining in the first adsorption vessel 20A is discharged via the lower exhaust path 27 and the first lower exhaust valve 27AV, thereby reducing the pressure inside the first adsorption vessel 20A. In a first depressurization step in the second adsorption vessel 20B, the gas present in the gas phase of the second adsorption vessel 20B is discharged via the second exhaust path 25B and the second exhaust valve 25BV, thereby reducing the pressure inside the second adsorption vessel 20B. In a second depressurization step performed after the deliquification step described below, the gas remaining in the second adsorption vessel 20B is discharged via the lower exhaust path 27 and the second lower exhaust valve 27BV, thereby reducing the pressure inside the second adsorption vessel 20B. The devices such as piping and valves that are operated and function at this time function as the pressure reducing means of the present invention, and the pressure inside the adsorption vessel is reduced by removing gas from the gas phase inside the adsorption vessel. After the adsorption step by the adsorption means, and before the regeneration step by the regeneration means, the pressure reducing step by the pressure reducing means is performed.

[0030] [Draining process and draining means] In the liquid removal step in the first adsorption vessel 20A, the liquid present in the liquid phase part of the first adsorption vessel 20A is discharged via the lower discharge path 27 and the first lower discharge valve 27AV, thereby removing liquid from the first adsorption vessel 20A. In the liquid removal step in the second adsorption vessel 20B, the liquid present in the liquid phase part of the second adsorption vessel 20B is discharged via the lower discharge path 27 and the second lower discharge valve 27BV, thereby removing liquid from the second adsorption vessel 20B. The equipment such as piping and valves that operate and function at this time function as the deliquation means of the present invention, which drains the liquid from the liquid phase in the adsorption vessel, and after the adsorption process, but before the regeneration process, a deliquation process is carried out by the deliquation means.

[0031] [Regeneration process and regeneration means] In the regeneration process in the first adsorption vessel 20A, the regeneration gas stored in the regeneration gas storage tank 40 is introduced into the upper part of the first adsorption vessel 20A via the regeneration gas inlet passage 41, the first upper flow passage 24A, and the first upper flow valve 24AV. The regeneration gas from which the impurities in the adsorbent 21A have been separated is discharged via the lower discharge passage 27 and the first lower discharge valve 27AV. In the regeneration process in the second adsorption vessel 20B, the regeneration gas stored in the regeneration gas storage tank 40 is introduced into the upper part of the second adsorption vessel 20B via the regeneration gas inlet passage 41, the second upper flow passage 24B, and the second upper flow valve 24BV. The regeneration gas from which the impurities in the adsorbent 21B have been separated is discharged via the lower discharge passage 27 and the second lower discharge valve 27BV. The equipment such as piping and valves that are in operation and function at this time function as the regeneration means of the present invention, and a regeneration gas having a temperature higher than the liquefaction temperature is introduced into the adsorption vessel after the adsorption step by the adsorption means to remove the impurities from the adsorbent in the gas phase, thereby regenerating the adsorbent. The regeneration gas may be, for example, an inert gas such as nitrogen gas or methane gas, and its temperature may be room temperature.

[0032] [Purging process and purging means, cooling process and cooling means] In the purging step in the first adsorption vessel 20A, product methane in the product methane storage tank 30 is introduced into the lower part of the first adsorption vessel 20A via the cooling path 32, the liquid accumulation path 28, the first liquid accumulation valve 28AV, and the first lower flow passage 22A. In addition, the regeneration gas remaining in the first adsorption vessel 20A is purged via the first exhaust path 25A and the first exhaust valve 25AV. During this purging step, the inside of the first adsorption vessel 20A is cooled, and the purging step also serves as a cooling step. In the purging step in the second adsorption vessel 20B, product methane in the product methane storage tank 30 is introduced into the lower part of the second adsorption vessel 20B via the cooling path 32, the liquid accumulation path 28, the second liquid accumulation valve 28BV, and the second lower flow passage 22B. In addition, the regeneration gas remaining in the second adsorption vessel 20B is purged via the second exhaust path 25B and the second exhaust valve 25BV. During this purging step, the inside of the second adsorption vessel 20B is cooled, and the purging step also serves as a cooling step. The equipment such as piping and valves that operate and function at this time function as the purging means and cooling means of the present invention. The cooling means cools the adsorption vessels by introducing the liquefied methane obtained by the adsorption means into the adsorption vessels in a cooling step performed after the regeneration step by the regeneration means. In this cooling step, the adsorption vessels 20A, 20B are cooled to the liquefaction temperature of natural gas. At the same time, the liquefied methane is introduced into the liquid phase in the adsorption vessels, and the regeneration gas is purged from the adsorption vessels and piping. In this way, a purging step by the purging means is performed in the cooling step performed after the regeneration step. The first exhaust valve 25AV and the second exhaust valve 25BV are pressure regulating valves, and the pressure inside the first adsorption vessel 20A and the second adsorption vessel 20B during the purging step can be adjusted by setting them.

[0033] [Pipe Cooling Process and Pipe Cooling Means] In the piping cooling step in first adsorption vessel 20A, the liquefied methane filling first adsorption vessel 20A is discharged via first liquid outlet passage 23A, first upper discharge valve 26AV, and upper discharge passage 26, thereby cooling the piping. In the piping cooling step in second adsorption vessel 20B, the liquefied methane filling second adsorption vessel 20B is discharged via second liquid outlet passage 23B, second upper discharge valve 26BV, and upper discharge passage 26, to cool the piping. At this time, the pipes, valves, and other equipment that are in operation and function function as the pipe cooling means.

[0034] Reference numeral 29A denotes a first pressure gauge 29A, which detects the pressure inside the first adsorption vessel 20A. Reference numeral 29B denotes a second pressure gauge 29B, which detects the pressure inside the second adsorption vessel 20B.

[0035] [Process Description] FIG. 2 is a process diagram showing one embodiment of the method for producing high purity methane of the present invention.

[0036] Using the first adsorption vessel 20A and the second adsorption vessel 20B, steps 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, T1, 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H, and T2 are carried out in sequence, and then repeated.

[0037] In stages 1A to 1H, the first adsorption vessel 20A performs the adsorption process, while the second adsorption vessel 20B sequentially performs the processes of first depressurization, deliquoring, second depressurization, regeneration, pressurization standby, purging / cooling, pressurization, and piping cooling.

[0038] Stage 1A involves an adsorption step in a first adsorption vessel 20A and a first depressurization step in a second adsorption vessel 20B. In stage 1B, an adsorption step is carried out in the first adsorption vessel 20A, and a deliquation step is carried out in the second adsorption vessel 20B. Stage 1C involves an adsorption step in the first adsorption vessel 20A and a second depressurization step in the second adsorption vessel 20B. Stage 1D involves an adsorption step in the first adsorption vessel 20A and a regeneration step in the second adsorption vessel 20B. In stage 1E, an adsorption step is performed in the first adsorption vessel 20A, and a pressurization standby step is performed in the second adsorption vessel 20B. Stage 1F includes an adsorption step in first adsorption vessel 20A and a purge / cool step in second adsorption vessel 20B. Stage 1G involves an adsorption step in the first adsorption vessel 20A and a pressurization step in the second adsorption vessel 20B. In stage 1H, an adsorption step is performed in first adsorption vessel 20A, and a pipe cooling step is performed in second adsorption vessel 20B.

[0039] Stage T1 involves performing an adsorption process in both the first adsorption vessel 20A and the second adsorption vessel 20B.

[0040] In stages 2A to 2H, the second adsorption vessel 20B performs the adsorption process, while the first adsorption vessel 20A sequentially performs the processes of first depressurization, deliquoring, second depressurization, regeneration, pressurization standby, purging / cooling, pressurization, and piping cooling.

[0041] Stage 2A involves an adsorption step in the second adsorption vessel 20B and a first depressurization step in the first adsorption vessel 20A. Stage 2B involves an adsorption step in the second adsorption vessel 20B and a deliquation step in the first adsorption vessel 20A. Stage 2C involves an adsorption step in the second adsorption vessel 20B and a second depressurization step in the first adsorption vessel 20A. Stage 2D involves an adsorption step in second adsorption vessel 20B and a regeneration step in first adsorption vessel 20A. In stage 2E, an adsorption step is performed in the second adsorption vessel 20B, and a pressurization standby step is performed in the first adsorption vessel 20A. Stage 2F involves an adsorption step in second adsorption vessel 20B and a purge / cool step in first adsorption vessel 20A. Stage 2G involves an adsorption step in the second adsorption vessel 20B and a pressurization step in the first adsorption vessel 20A. In stage 2H, an adsorption step is carried out in second adsorption vessel 20B, and a pipe cooling step is carried out in first adsorption vessel 20A.

[0042] Stage T2 involves performing an adsorption process in both the first adsorption vessel 20A and the second adsorption vessel 20B.

[0043] 3 to 11, the flow of liquid and gas in each of stages 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, and T1 will be described. Unless otherwise specified, pipes through which liquid or gas flows are shown with thick lines, and valves in those pipes are open. Similarly, pipes through which liquid or gas does not flow are shown with thin lines, and valves in those pipes are closed.

[0044] FIG. 3 shows a diagram illustrating stage 1A. In stage 1A, an adsorption step is performed in a first adsorption vessel 20A and a first depressurization step is performed in a second adsorption vessel 20B.

[0045] In the adsorption process in the first adsorption vessel 20A, the liquefied natural gas in the raw material storage tank 10 is introduced into the lower part of the first adsorption vessel 20A via the raw material line 11, the raw material valve 11V, the first inlet line 12A and the first inlet valve 12AV. The introduced liquefied natural gas is brought into contact with the adsorbent 21A, and impurities are adsorbed by the adsorbent 21A in the liquid phase. This results in the production of product methane from which the impurities have been adsorbed and separated. The product methane is introduced into the product methane storage tank 30 via the first liquid outlet line 23A, the first liquid outlet valve 23AV, the product methane inlet line 31 and the product methane inlet valve 31V. The pressure inside the first adsorption vessel 20A in the adsorption process can be set to, for example, about 0.40 MPaG.

[0046] The first depressurization step in the second adsorption vessel 20B reduces the pressure inside the second adsorption vessel 20B, in which the adsorption step had been carried out up until then. The gas present in the gas phase of the second adsorption vessel 20B is discharged via the second exhaust path 25B and the second exhaust valve 25BV, thereby reducing the pressure inside the second adsorption vessel 20B. By the first depressurization step, the pressure inside the second adsorption vessel 20B, which was, for example, about 0.40 MPaG during the adsorption step, can be reduced to, for example, about 0.20 MPaG.

[0047] FIG. 4 illustrates stage 1B. In stage 1B, an adsorption step is carried out in the first adsorption vessel 20A, and a deliquation step is carried out in the second adsorption vessel 20B. The adsorption step in the first adsorption vessel 20A is similar to stage 1A. In the deliquescence step in the second adsorption vessel 20B, the liquid present in the liquid phase of the second adsorption vessel 20B after the above-mentioned first depressurization step is discharged via the lower discharge path 27 and the second lower discharge valve 27BV, thereby deliquescence is removed from the second adsorption vessel 20B. The pressure in the second adsorption vessel 20B after the deliquescence step is, for example, about 0.20 MPaG.

[0048] FIG. 5 shows a diagram illustrating stage 1C. In stage 1C, an adsorption step is carried out in the first adsorption vessel 20A, and a second depressurization step is carried out in the second adsorption vessel 20B. The adsorption step in the first adsorption vessel 20A is similar to stage 1A. In the second depressurization step in the second adsorption vessel 20B, the gas remaining in the second adsorption vessel 20B after the above-mentioned deliquescence step is discharged via the lower discharge path 27 and the second lower discharge valve 27BV, thereby reducing the pressure inside the second adsorption vessel 20B. The pressure inside the second adsorption vessel 20B after the second depressurization step is, for example, 0.20 MPaG or less.

[0049] FIG. 6 illustrates stage 1D. Stage 1D involves an adsorption step in the first adsorption vessel 20A and a regeneration step in the second adsorption vessel 20B. The adsorption step in the first adsorption vessel 20A is similar to Stage 1A. In the regeneration step in the second adsorption vessel 20B, the regeneration gas stored in the regeneration gas storage tank 40 is introduced into the upper part of the second adsorption vessel 20B after the second depressurization step via the regeneration gas inlet line 41, the second upper flow passage 24B, and the second upper flow valve 24BV. By introducing the regeneration gas, the inside of the second adsorption vessel 20B is heated to room temperature, and the impurities adsorbed by the adsorbent 21B are desorbed. The regeneration gas containing the desorbed impurities is discharged via the lower discharge line 27 and the second lower discharge valve 27BV. The pressure inside the second adsorption vessel 20B during the regeneration step is atmospheric pressure (0 MPaG).

[0050] FIG. 7 shows a diagram illustrating stage 1E. In stage 1E, an adsorption step is performed in the first adsorption vessel 20A, and a pressurization standby step is performed in the second adsorption vessel 20B. The adsorption step in the first adsorption vessel 20A is similar to stage 1A. The pressurization standby step in the second adsorption vessel 20B involves closing the second upper flow valve 24BV to stop the introduction of regeneration gas into the second adsorption vessel 20B, and closing the second lower discharge valve 27BV to stop the discharge of regeneration gas from the second adsorption vessel 20B.

[0051] FIG. 8 shows stage 1F. Stage 1F involves an adsorption step in the first adsorption vessel 20A and a purge / cool step in the second adsorption vessel 20B. The adsorption step in the first adsorption vessel 20A is similar to Stage 1A. In the purging / cooling step in the second adsorption vessel 20B, the product methane in the product methane storage tank 30 is introduced into the lower part of the second adsorption vessel 20B via the cooling path 32, the liquid accumulation path 28, the second liquid accumulation valve 28BV, and the second lower flow passage 22B. The introduction of the product methane cools the inside of the second adsorption vessel 20B to the liquefaction temperature of natural gas, and the liquefied natural gas gradually accumulates in the second adsorption vessel 20B. In addition, the regeneration gas remaining in the second adsorption vessel 20B and the piping is purged via the second exhaust path 25B and the second exhaust valve 25BV. This purging step purges the second adsorption vessel 20B and the second lower flow passage 22B. The pressure in the second adsorption vessel 20B during the purging / cooling step can be set to, for example, about 0.20 MPaG by setting the second exhaust valve 25BV.

[0052] FIG. 9 shows a diagram illustrating stage 1G. In stage 1G, an adsorption step is carried out in the first adsorption vessel 20A, and a pressurization step is carried out in the second adsorption vessel 20B. The adsorption step in the first adsorption vessel 20A is similar to stage 1A. In the pressurization step in the second adsorption vessel 20B, the setting value of the second exhaust valve 25BV is changed to increase the pressure inside the second adsorption vessel 20B after the purging / cooling step. By the pressurization step, the pressure inside the second adsorption vessel 20B can be increased to, for example, about 0.40 MPaG. At this time, the liquid remaining in the liquid pool passage 28 and the cooling passage 32 is discharged from the liquid drain passage 33 and the liquid drain valve 33V.

[0053] FIG. 10 shows step 1H. In stage 1H, an adsorption step is performed in the first adsorption vessel 20A, and a piping cooling step is performed in the second adsorption vessel 20B. The adsorption step in the first adsorption vessel 20A is similar to stage 1A. In the piping cooling step in the second adsorption vessel 20B, the liquefied methane filled in the second adsorption vessel 20B is discharged via the second liquid outlet passage 23B, the second upper discharge valve 26BV, and the upper discharge passage 26, thereby cooling the piping. At this time, the pressure inside the second adsorption vessel 20B is, for example, about 0.40 MPaG.

[0054] FIG. 11 shows stage T1. Stage T1 involves performing an adsorption process in both the first adsorption vessel 20A and the second adsorption vessel 20B. The adsorption process in first adsorption vessel 20A is similar to stage 1A. In the adsorption step in the second adsorption vessel 20B, the liquefied natural gas in the raw material storage tank 10 is introduced into the lower part of the second adsorption vessel 20B via the raw material line 11 and raw material valve 11V, the second inlet line 12B and the second inlet valve 12BV. The product methane from which impurities have been adsorbed and separated by the adsorbent 21B is introduced into the product methane storage tank 30 via the second liquid outlet line 23B and the second liquid outlet valve 23BV, the product methane inlet line 31 and the product methane inlet valve 31V.

[0055] Stage 2A, stage 2B, stage 2C, stage 2D, stage 2E, stage 2F, stage 2G, stage 2H, and stage T2 are respectively the same as stage 1A, stage 1B, stage 1C, stage 1D, stage 1E, stage 1F, stage 1G, stage 1H, and stage T1, and are operated with the left and right sides swapped. Since they are the same except for the left and right sides, the explanation will be omitted.

[0056] [Effects of the embodiment] The above embodiment is explained. The way The method has the following effects:

[0057] The method for producing high-purity methane according to the present embodiment is a method for producing high-purity methane using liquefied natural gas as a raw material, and at least a first adsorption vessel and a second adsorption vessel are prepared as adsorption vessels filled with an adsorbent. A cooling step, an adsorption step, and a regeneration step are sequentially repeated in each of the first adsorption vessel and the second adsorption vessel. The cooling step cools the adsorption vessel filled with the adsorbent to the liquefaction temperature of natural gas. The adsorption step introduces liquefied natural gas into the cooled adsorption vessel, and adsorbs impurities in the liquefied natural gas onto the adsorbent in the liquid phase, thereby obtaining high-purity liquefied methane. The regeneration step introduces a regeneration gas having a temperature higher than the liquefaction temperature into the adsorption vessel after the adsorption step, and removes the impurities from the adsorbent in the gas phase, thereby regenerating the adsorbent. The first and second adsorption vessels alternate between a first state in which the regeneration step and the cooling step are performed in the second adsorption vessel while the adsorption step is performed in the first adsorption vessel, and a second state in which the regeneration step and the cooling step are performed in the first adsorption vessel while the adsorption step is performed in the second adsorption vessel. Between the first and second states, a bi-adsorption step of adsorption is performed in both the first and second adsorption vessels. In this way, high-purity methane is obtained from liquefied natural gas by adsorption separation rather than distillation separation, so that equipment such as a condenser or evaporator is not required and there is no energy consumption due to them. In addition, the adsorption vessel filled with the adsorbent is cooled to the liquefaction temperature of natural gas, and impurities from the liquefied natural gas are adsorbed onto the adsorbent in the liquid phase. In addition, the adsorbent is regenerated in the gas phase by introducing a regeneration gas at a temperature higher than the liquefaction temperature into the adsorption vessel. Therefore, heat such as a heater or steam is not required to regenerate the adsorbent, and there is no energy consumption. Also, unlike distillation separation, purity defects due to the influence of composition fluctuations in the liquefied natural gas feedstock are unlikely to occur. In this way, high-purity methane can be produced with less energy consumption. Also, the adsorption process is carried out in one of the adsorption vessels to produce high-purity methane, and the regeneration process and cooling process are carried out in the other adsorption vessels, so that high-purity methane can always be produced.

[0058] In the method for producing high-purity methane of the present embodiment, in the first state, between the cooling step and the dual adsorption step, a piping cooling step is carried out by discharging the liquefied methane filled in the second adsorption vessel through a piping to cool the piping, and in the second state, between the cooling step and the dual adsorption step, a piping cooling step is carried out by discharging the liquefied methane filled in the first adsorption vessel through a piping to cool the piping.

[0059] In this embodiment, a liquid phase section and a gas phase section are provided in the adsorption vessel. In the liquid phase section, the liquefied natural gas becomes a liquid phase during the adsorption process. In the gas phase section, the liquefied natural gas becomes a gas phase during the adsorption process. At least a part of the adsorbent is present in the liquid phase section. This allows impurities from the liquefied natural gas to be adsorbed by the adsorbent in the liquid phase section. In addition, the pressure generated in the gas phase section can be made to contribute to the delivery of liquid from the liquid phase section.

[0060] In this embodiment, a deliquification step is performed after the adsorption step and before the regeneration step. In the deliquification step, liquid is removed from the liquid phase in the adsorption vessel. This deliquification allows a smooth transition to the regeneration step.

[0061] In the present embodiment, in the cooling step performed after the regeneration step, the adsorption vessel is cooled by introducing the liquefied methane obtained in the adsorption step into the adsorption vessel. In this manner, by utilizing the liquefied methane obtained in the adsorption step in the cooling step performed after the regeneration step, it is possible to save equipment and energy required for cooling.

[0062] In the present embodiment, in the cooling step performed after the regeneration step, the liquefied methane is introduced into the liquid phase in the adsorption vessel, and the regeneration gas is purged from the adsorption vessel and piping. In this manner, by purging the regeneration gas with the liquefied methane, it is possible to prevent recontamination of the separated impurities.

[0063] Summary In this embodiment, the liquefied natural gas is introduced into the adsorption vessel as a liquid, and the adsorbent is C 2+ The temperature inside the vessel is low at about -162°C during the adsorption process, and the C adsorbed in the adsorbent is released from the top of the vessel. 2+ The hydrocarbons are separated from the adsorbent. The adsorption and regeneration steps are alternately repeated in the first and second adsorption vessels to continuously obtain liquefied methane.

[0064] In the adsorption process, the temperature inside the adsorption vessel is the same as that of liquefied natural gas, which is -162°C. In the regeneration process, nitrogen gas at room temperature is introduced into the adsorption vessel, and the temperature inside the adsorption vessel is raised to above 0°C. By heating the inside of the adsorption vessel, the hydrocarbons adsorbed by the adsorbent are released, and the adsorption vessel can be regenerated into a state where it can adsorb hydrocarbons again.

[0065] In the purge / cooling process, liquefied natural gas is used to cool the adsorption vessel, and the gasified natural gas can then be used as fuel in the cogeneration system.

[0066] In the distillation separation method as in Patent Document 1, cold energy is required in the condenser and hot energy is required in the evaporator, resulting in a large amount of energy consumption. In Patent Document 2, adsorption and separation are performed at a temperature swing between room temperature and high temperature, so a high-temperature heat source is required. In contrast, the present invention performs adsorption and separation at a temperature swing between low and normal temperatures, and the low-temperature raw LNG is introduced directly into the adsorption vessel and C 2+ Hydrocarbons are adsorbed and desorbed (regenerated) with nitrogen gas at room temperature. Therefore, no heat source is required. In addition, while distillation separation as shown in Patent Document 1 is susceptible to fluctuations in the composition of the raw LNG, adsorption separation is less susceptible.

[0067] [Modifications] Although the above describes a particularly preferred embodiment of the present invention, the present invention is not intended to be limited to the illustrated embodiment, but can be modified and embodied in various forms, and the present invention is intended to encompass various modified embodiments. [Explanation of symbols]

[0068] 10: Raw material storage tank 11: Raw material path 11V: Feed valve 12A: 1st introduction path 12AV: First introduction valve 12B:Second introduction path 12BV: Second introduction valve 20A: 1st adsorption container 20B:Second adsorption container 21A: Adsorbent 21B: Adsorbent 22A: 1st lower flow passage 22B: 2nd lower flow passage 23A: 1st liquid outlet 23AV: 1st liquid outlet valve 23B: 2nd liquid outlet 23BV: 2nd liquid outlet valve 24A: 1st upper flow passage 24AV: First upper flow valve 24B: 2nd upper flow passage 24BV: 2nd upper flow valve 25A: First exhaust passage 25AV: First exhaust valve 25B: Second exhaust passage 25BV: Second exhaust valve 26: Upper discharge channel 26AV: First upper discharge valve 26BV: 2nd upper exhaust valve 27: Lower discharge channel 27AV: First lower discharge valve 27BV: Second lower discharge valve 28:Liquid reservoir 28AV: First reservoir valve 28BV:Second reservoir valve 29A: First pressure gauge 29B: Second pressure gauge 30: Product methane storage tank 31: Product methane inlet 31A: Product methane inlet valve 32: Cooling path 33: Drainage channel 33V: Drain valve 40: Regenerated gas storage tank 41: Regenerative gas inlet

Claims

1. A method for producing high purity methane using liquefied natural gas as a raw material, comprising the steps of: providing at least a first adsorption vessel and a second adsorption vessel filled with an adsorbent; In each of the first and second adsorption vessels, a cooling step of cooling the adsorption vessel filled with the adsorbent to a temperature at which the natural gas is liquefied; an adsorption step of introducing liquefied natural gas into the cooled adsorption vessel and adsorbing impurities in the liquefied natural gas onto the adsorbent in a liquid phase to obtain high-purity liquefied methane; a regeneration step in which a regeneration gas having a temperature higher than the liquefaction temperature is introduced into the adsorption vessel after the adsorption step to remove the impurities from the adsorbent in the gas phase and regenerate the adsorbent; and a first state in which the regeneration step and the cooling step are performed in the second adsorption vessel while the adsorption step is being performed in the first adsorption vessel, and a second state in which the regeneration step and the cooling step are performed in the first adsorption vessel while the adsorption step is being performed in the second adsorption vessel, are alternately performed in the first adsorption vessel and the second adsorption vessel; Between the first state and the second state, a dual adsorption step is performed in which adsorption is performed in both the first adsorption vessel and the second adsorption vessel. A method for producing high purity methane.

2. In the first state, a piping cooling step is performed between the cooling step and the dual adsorption step by discharging the liquefied methane filled in the second adsorption vessel through a piping; In the second state, a piping cooling step is performed between the cooling step and the dual adsorption step by discharging the liquefied methane filled in the first adsorption vessel through a piping. The method for producing high purity methane according to claim 1.

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