Gas purification method

Abstract

This invention provides a gas purification method using low-temperature adsorption that achieves energy savings. [Solution] The gas purification method includes an adsorption step in which a raw material gas containing the gas to be purified and impurities is passed through an adsorbent 1 contained inside an adsorption tower 2 to adsorb the impurities onto the adsorbent, and a product gas containing the gas to be purified at a higher purity than the raw material gas is extracted; and a regeneration step in which impurities are separated from the adsorbent 1 and the adsorbent 1 is regenerated. In the adsorption step, the adsorbent is cooled to below 0°C, and in the regeneration step, the adsorbent is at 0°C or higher and 40°C or lower.

Description

[Technical Field]

[0001] This disclosure relates to a gas purification method. [Background technology]

[0002] Patent Document 1 discloses a large-scale cryogenic gas purifier. This large-scale cryogenic gas purifier removes impurities from the gas to be purified by low-temperature adsorption using an adsorbent packed inside an adsorption tower housed in a cold box. This large-scale cryogenic gas purifier includes a first heat exchanger that cools the gas to be purified from room temperature to liquid nitrogen temperature level, a second heat exchanger that cools the gas to be purified with refrigerant nitrogen in front of multiple adsorption towers, a pre-cooling path that branches off from the purified gas outlet path leading out of the adsorption tower and connects to the purified gas inlet path of another adsorption tower, and a regenerated gas circulation path that branches off from the purified gas outlet path and rejoins the purified gas inlet path of the same adsorption tower via a blower and heater. In this large-scale cryogenic gas purifier, by providing a regenerated gas circulation path, the gas to be purified remaining in the adsorption tower can be circulated and used as a heating regeneration gas, thereby reducing the number of replacement vacuum evacuation cycles after regeneration, which reduces the amount of purified gas lost during replacement vacuum evacuation and shortens the vacuum evacuation time. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 9-323017 [Overview of the project] [Problems that the invention aims to solve]

[0004] In gas purification methods using so-called low-temperature adsorption, cooling of the adsorbent is necessary. However, in large-scale low-temperature gas purifiers and gas purification methods realized therein, such as those exemplified in Patent Document 1, it was necessary to heat the adsorbent and adsorption tower above room temperature for regeneration. Therefore, there was a problem of high energy consumption due to the back-and-forth between cooling during gas purification and heating during adsorbent regeneration. Thus, further energy conservation is required in gas purification methods using low-temperature adsorption.

[0005] This disclosure has been made in view of the above circumstances, and its purpose is to provide a gas purification method by low-temperature adsorption that achieves energy savings. [Means for solving the problem]

[0006] The gas purification method relating to this disclosure for achieving the above objective is: An adsorption step is performed by passing a raw material gas containing the gas to be purified and impurities through an adsorbent contained inside an adsorbent tower, thereby adsorbing the impurities onto the adsorbent, and extracting a product gas containing the gas to be purified at a higher purity than the raw material gas. The process includes a regeneration step of separating the impurities from the adsorbent and regenerating the adsorbent, In the adsorption step, the adsorbent is cooled to below 0°C. In the aforementioned regeneration process, the adsorbent is kept at a temperature between 0°C and 40°C. [Effects of the Invention]

[0007] According to this disclosure, a gas purification method using low-temperature adsorption that achieves energy savings can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] This is an explanatory diagram of a gas purification apparatus that implements the gas purification method according to this embodiment. [Modes for carrying out the invention]

[0009] The gas purification method according to the embodiment of this disclosure will be described below.

[0010] First, an overview of the gas purification method according to this embodiment will be described.

[0011] The gas purification method according to this embodiment includes an adsorption step in which a raw material gas containing the gas to be purified and impurities is passed through an adsorbent contained inside an adsorption tower to adsorb the impurities onto the adsorbent, and a product gas containing the gas to be purified at a higher purity than the raw material gas is extracted; and a regeneration step in which impurities are separated from the adsorbent and the adsorbent is regenerated. In the adsorption step, the adsorbent is cooled to below 0°C. In the regeneration step, the adsorbent is kept at a temperature between 0°C and 40°C.

[0012] The gas purification method according to this embodiment can achieve energy savings (reduction in energy consumption) in a gas purification method using low-temperature adsorption.

[0013] The gas purification method according to this embodiment will be described in detail below.

[0014] In this embodiment, the raw material gas is a gas that contains a certain amount of impurities, and the concentration of the gas to be purified is lower than the target concentration required for the product gas. Examples of gases to be purified include hydrogen, deuterium, and helium. Examples of impurities include nitrogen, oxygen, argon, carbon monoxide, carbon dioxide, and methane. It is preferable that the raw material gas has had sufficient moisture removed as an impurity beforehand. The amount of moisture that the raw material gas may contain is preferably 10 ppm by volume or less, and more preferably 1 ppm by volume or less. In the following description, when simply referred to as ppm, it means ppm by volume.

[0015] In this embodiment, gas purification means obtaining a product gas from a raw material gas, and removing impurities from the raw material gas.

[0016] Figure 1 shows apparatus 100 as an example of a gas purification apparatus that realizes the gas purification method according to this embodiment.

[0017] The apparatus 100 includes an adsorption tower 2 that houses an adsorbent 1 inside (inside the tower), a cold box 3 that houses the adsorption tower 2 and has a cooling mechanism for cooling the adsorption tower 2, a supply pipe 4 that supplies a raw material gas (gas G1) to the adsorption tower 2, a delivery pipe 5 that delivers a product gas (gas G2) from the adsorption tower 2 to the next process, and a vacuum pump 6 that evacuates the adsorption tower 2.

[0018] The apparatus 100 may be formed of a material that is not corroded by the gas to be purified or the refrigerant, and may be formed of a metal alloy such as stainless steel (ferroalloy) for example.

[0019] In the adsorption process, a raw material gas (gas G1) containing a gas to be purified and impurities is passed through the adsorbent 1 housed inside the adsorption tower 2 to adsorb the impurities onto the adsorbent 1, and a product gas G2 containing the gas to be purified with a higher purity than the raw material gas is taken out. In this adsorption process, the adsorbent 1 is cooled to below 0°C. That is, the adsorption process of the gas purification method in the present embodiment is a process for removing impurities that utilizes a method for purifying gas by low-temperature adsorption, so-called low-temperature adsorption method.

[0020] The regeneration process is a process for separating impurities from the adsorbent 1 and regenerating the adsorbent 1. In the regeneration process, the adsorbent 1 is set to 0°C or higher and 40°C or lower, preferably 5°C or higher and 35°C or lower. That is, in the regeneration process, a temperature-raising process for raising the temperature of the adsorbent 1 to 0°C or higher and 40°C or lower, preferably 5°C or higher and 35°C or lower is performed. In the regeneration process, by executing this temperature-raising process, the desorption (vaporization) of impurities from the adsorbent 1 proceeds, and thereby the adsorbent 1 is regenerated.

[0021] The temperature-raising process is preferably performed with the adsorption tower 2 sealed. In this case, in the temperature-raising process, the internal pressure of the adsorption tower 2 may be increased to 100 kPa or higher and 300 kPa or lower in gauge pressure.

[0022] After the heating process, a discharge process is performed. In the discharge process, residual gas remaining in the adsorption tower 2 is discharged from the adsorption tower 2. In this embodiment, residual gas refers to the gas (raw material gas and product gas) that was accumulated in the space inside the adsorption tower 2 at the start of the regeneration process and the gas that was desorbed from the adsorbent 1 during the heating process (hereinafter referred to as adsorbed gas). Furthermore, the adsorbed gas is a gas that contains the gas to be purified and impurities.

[0023] After the discharge process, a depressurization process may be performed to reduce the pressure of the adsorbent 1. This may improve the regeneration process. The depressurization process may be performed by reducing the pressure inside the adsorption tower 2.

[0024] The adsorption tower 2 is a container filled with adsorbent 1, having a raw material gas supply port and a product gas outlet. The adsorption tower 2 is formed, for example, in a cylindrical shape, and is positioned with its axis aligned vertically. In the adsorption tower 2, for example, a raw material gas supply port is located at the upper end, and a supply pipe 4 is connected to this supply port. Also, in the adsorption tower 2, for example, a product gas outlet is located at the lower end, and a discharge pipe 5 is connected to this outlet. The adsorption tower 2 has a sealed structure that allows the inside of the tower to be sealed. Here, sealing the inside of the adsorption tower 2, or sealing the adsorption tower 2, means closing (blocking) the supply port and outlet of the adsorption tower 2 or the pipes connected to these supply port and outlet. It is preferable that the adsorption tower 2 has a structure that can withstand a reduced pressure state of about minus 0.1 MPa (gauge pressure) to a pressurized state of about 0.5 MPa (gauge pressure) inside the tower.

[0025] Apparatus 100 is equipped with two adsorption towers, Adsorption Tower 2A and Adsorption Tower 2B, arranged in parallel. Adsorption and regeneration processes are repeated alternately (mutually) between Adsorption Tower 2A and Adsorption Tower 2B. Specifically, in apparatus 100, the regeneration process is performed in Adsorption Tower 2B during periods when the adsorption process is being performed in Adsorption Tower 2A, and the adsorption process is performed in Adsorption Tower 2B during periods when the regeneration process is being performed in Adsorption Tower 2A.

[0026] In the following description, matters common to both adsorption tower 2A and adsorption tower 2B will be described as adsorption tower 2, or adsorption tower 2A will be described as a representative of both adsorption tower 2A and adsorption tower 2B, and when it is necessary to distinguish between adsorption tower 2A and adsorption tower 2B, they will be described separately. In addition, each part and component of the apparatus 100 related to adsorption tower 2A or adsorption tower 2B will be described by adding the code A or code B to the code assigned to them. For example, the adsorbent 1 packed in adsorption tower 2A will be referred to as adsorbent 1A, and the adsorbent 1 packed in adsorption tower 2B will be referred to as adsorbent 1B.

[0027] The adsorbent 1 is not particularly limited in type, as long as it is capable of adsorbing the impurities exemplified above. Examples of particularly suitable adsorbents 1 (particularly suitable for adsorbing the impurities exemplified above) include activated carbon, molecular sieves, and activated alumina.

[0028] Cold box 3 is a containment container that houses the adsorption tower 2 and has a cooling mechanism for cooling the adsorption tower 2. The adsorbent 1 is cooled along with the cooling of the adsorption tower 2. Cold box 3 cools the contained adsorption tower 2 and adsorbent 1 to an extremely low temperature of, for example, minus 190°C. As a cooling mechanism, cold box 3 has a storage container for storing a refrigerant such as liquid nitrogen and refrigerant piping for cooling the adsorption tower with the refrigerant. In apparatus 100, adsorption tower 2A is housed in cold box 3A, which is cold box 3, and adsorption tower 2B is housed in cold box 3B, which is cold box 3.

[0029] A heat exchanger may be provided inside the cold box 3 to exchange heat between the raw material gas supplied to the adsorption tower 2 and the product gas discharged from the adsorption tower 2. This heat exchanger enables efficient cooling of the raw material gas and heating of the product gas to room temperature. Furthermore, it can also prevent condensation in the discharge piping 5, which will be described later.

[0030] Supply piping 4 is a gas piping that supplies the raw material gas supplied from the upstream process to the adsorption tower 2. In apparatus 100, adsorption tower 2A is supplied with raw material gas from supply piping 4A, which is supply piping 4, and adsorption tower 2B is supplied with raw material gas from piping 4B, which is supply piping 4. Supply piping 4A and 4B may be branches of supply piping 4 on the downstream side (closer to the adsorption tower 2 than the upstream process). Supply piping 4A and 4B may be provided with on-off valves 40A and 40B, such as stop valves, which are valve devices that switch between an open state that allows the flow of raw material gas and a closed state that prohibits the flow of raw material gas.

[0031] The discharge piping 5 is a gas piping that delivers the product gas purified in the adsorption tower 2 from the adsorption tower 2 to the next process. In the apparatus 100, the adsorption towers 2A and 2B deliver the product gas to the next process via the discharge piping 5A and 5B, which are the discharge piping 5. The discharge piping 5A and 5B may be merged into a single pipe on the downstream side (away from the adsorption tower 2). The discharge piping 5A and 5B may be equipped with on-off valves 50A and 50B, such as stop valves, which are valve devices that switch between an open state that allows the flow of product gas and a closed state that prohibits the flow of raw material gas.

[0032] The vacuum pump 6 is an exhaust device for reducing the pressure inside the adsorption tower 2 by exhausting residual gas (gas G3) remaining inside the tower. The vacuum pump 6 may be located in a pressure reducing pipe 7 that branches off from the supply pipe 4 and connected to the adsorption tower 2. In this embodiment, the upstream side of the pressure reducing pipe 7 (closer to the adsorption tower 2 than the vacuum pump 6) branches off to form pressure reducing pipes 7A and 7B, and these pressure reducing pipes 7A and 7B are shown as examples where they branch off from the downstream side (closer to the adsorption tower 2) of the supply pipes 4A and 4B, respectively, from the on-off valves 40A and 40B. The pressure reducing pipes 7A and 7B may be provided with on-off valves 70A and 70B, such as stop valves, which are valve devices that switch between an open state that allows the flow of residual gas and a closed state that prohibits the flow of residual gas.

[0033] A bypass pipe 71 that bypasses the vacuum pump 6 may be provided in the pressure reducing piping 7. The bypass pipe 71 may branch off from the pressure reducing piping 7 between the vacuum pump 6 and the on-off valves 70A and 70B. The bypass pipe 71 may rejoin the pressure reducing piping 7 downstream of the vacuum pump 6 (on the side opposite to the side closer to the adsorption tower 2). The bypass pipe 71 may have an on-off valve 73, such as a stop valve, as a valve device that switches between an open state that allows the flow of residual gas and a closed state that prohibits the flow of residual gas. Between the branching point of the vacuum pump 6 and the bypass pipe 71 in the pressure reducing piping 7, an on-off valve 72, such as a stop valve, may be provided as a valve device that switches between an open state that allows the flow of residual gas to the vacuum pump 6 and a closed state that prohibits the flow of residual gas.

[0034] In apparatus 100, when the adsorption process is performed in adsorption tower 2A, valves 40A and 50A are opened, and valves 40B, 50B, and 70A are closed. When the adsorption process is performed in adsorption tower 2B, valves 40B and 50B are opened, and valves 40A, 50A, and 70B are closed. Details of the open state of each valve during the adsorption process will be described later.

[0035] When the regeneration process is performed in adsorption tower 2A, at least valves 40A, 50A, and 70B are closed, and valves 70A, 72, and 73 are opened as the process progresses. When the regeneration process is performed in adsorption tower 2B, at least valves 40B, 50B, and 70A are closed, and valves 70B, 72, and 73 are opened as the process progresses. Details of the open state of each valve during the regeneration process will be described later.

[0036] In apparatus 100, the regeneration process is performed in adsorption tower 2B during periods that overlap with the period in which the adsorption process is performed in adsorption tower 2A, and the regeneration process is performed in adsorption tower 2A during periods that overlap with the period in which the adsorption process is performed in adsorption tower 2B. In adsorption towers 2A and 2B, the periods in which the adsorption process is performed and the periods in which the regeneration process is performed do not necessarily have to completely overlap. For example, while one adsorption tower 2 is performing either the adsorption process or the regeneration process, the other adsorption tower 2 may be in a stopped state, not performing either the adsorption process or the regeneration process.

[0037] The following describes the adsorption and regeneration processes performed in adsorption tower 2, using adsorption tower 2A as an example. The process is the same when performing the adsorption and regeneration processes in adsorption tower 2B as in the case of adsorption tower 2A.

[0038] The adsorption process begins when the adsorption tower 2A and adsorbent 1A are sufficiently cooled to cryogenic temperatures (e.g., 190°C) by the cold box 3A. During the adsorption process, with valves 40B, 50B, and 70A closed, valves 40A and 50A are opened, allowing the cryogenically cooled raw material gas (e.g., 190°C) to flow through the adsorption tower 2A, thereby bringing the raw material gas into contact with the adsorbent 1A. Through this contact, impurities and the gas to be purified are adsorbed onto the adsorbent 1A. The ratio of impurities adsorbed onto the adsorbent 1A to the gas to be purified is greater than the ratio of impurities to the gas to be purified in the raw material gas.

[0039] During the adsorption process, the cold box 3A cools the adsorption tower 2A and the supply piping 4 located inside the cold box 3A, thereby continuously cooling the adsorbent 1A and the raw material gas to extremely low temperatures. Before the adsorbent 1A breaks through, the flow of the raw material gas to the adsorption tower 2A is stopped, and the adsorption tower 2A is moved from the adsorption process to the regeneration process.

[0040] When the adsorption process is finished, that is, when the regeneration process is started, the on-off valves 40A and 50A are closed. In other words, the adsorption tower 2A is sealed. This prevents contaminants (impurities) from the outside atmosphere from entering the adsorption tower 2A (hereinafter referred to as contamination prevention). Then, the cooling of the adsorption tower 2A by the cold box 3A is stopped, and a heating process is performed in which the temperature of the adsorption tower 2A (adsorbent 1A) is raised using the heat energy of the outside atmosphere (waiting for the temperature to rise).

[0041] In the heating process, the temperature of the adsorbent 1A rises as the temperature of the adsorption tower 2A increases. This causes the adsorbed gas that was adsorbed on the adsorbent 1A to desorb from the adsorbent 1A. In the heating process, the temperature of the residual gas containing this adsorbed gas rises as the temperature of the adsorption tower 2A rises. This rise in temperature promotes the desorption of impurities from the adsorbent 1A, prevents re-adsorption, and promotes the regeneration of the adsorbent 1A. In the heating process, it is preferable to keep the on-off valves 40A and 50A closed until the temperature of the adsorption tower 2A rises to between 0°C and 40°C (i.e., around room temperature).

[0042] In the heating step, the temperature of the adsorption tower 2A may be raised solely by heat transfer from the external atmosphere. In other words, no heating device or heat source is required in the heating step. Thus, in the gas purification method according to this embodiment, there is no need to raise the temperature above the temperature of the external atmosphere, so the energy consumption required in the heating step can be greatly reduced, and energy savings can be achieved. Furthermore, in the gas purification method according to this embodiment, if the temperature of the adsorption tower 2A is raised solely by heat transfer from the external atmosphere, the energy consumption required in the heating step can be further reduced, resulting in even greater energy savings. In the gas purification method according to this embodiment, as described above, the amount of moisture that the raw material gas may contain is preferably 10 ppm by volume or less, which eliminates the need to raise the temperature of the adsorption tower 2A to a temperature exceeding the temperature of the external atmosphere in the heating step.

[0043] During the heating process, the internal pressure of the adsorption tower 2 increases due to the desorption of adsorbed gas from the adsorbent 1A and the expansion of residual gas as its temperature rises. The internal pressure in the adsorption tower 2A during the heating process may be increased to a gauge pressure of 100 kPa to 300 kPa, preferably 100 kPa to 200 kPa. By increasing the internal pressure in the adsorption tower 2 to this pressure range, contamination can be prevented more effectively. Furthermore, a balance can be struck between contamination prevention and the regeneration of the adsorbent 1A (promotion of desorption of adsorbed gas from the adsorbent 1A).

[0044] The heating process may be terminated when the internal pressure inside the adsorption tower 2A reaches a predetermined value (e.g., 200 kPa) or when the adsorption tower 2A reaches a predetermined temperature (e.g., a temperature equivalent to the external atmosphere). If the termination conditions for the heating process are set as the internal pressure inside the adsorption tower 2A and the adsorption tower 2A itself, the heating process may be terminated when either condition is met.

[0045] After the heating process, a discharge process is performed in which valves 70A and 73 are opened with valves 70B and 72 closed, and residual gas (gas G3) is discharged from the adsorption tower 2A to the outside of the system. In this discharge process, residual gas containing a large amount of adsorbed gas desorbed from the adsorbent 1A during the heating process is discharged from the adsorption tower 2A to the outside of the system, thereby purging the adsorption tower 2A (discarding impurities adsorbed on the adsorbent 1A to the outside of the system of the adsorption tower 2A).

[0046] The discharge process may be carried out until the pressure inside the adsorption tower 2A drops completely, or it may be terminated when the internal pressure (gauge pressure) inside the adsorption tower 2A is slightly positive (for example, 1 kPa or more and 10 kPa or less). Terminating the discharge process means closing the on-off valve 70A or on-off valve 73 to seal the adsorption tower 2A. Contamination can be prevented by ending the discharge process when the adsorption tower 2A is slightly positive. Once the discharge process is complete, most of the impurities detached from the adsorbent 1A are discharged from the adsorption tower 2A, and the adsorbent 1A is regenerated to a degree that it can be reused (used again in the adsorption process) (hereinafter referred to as State 1).

[0047] If a depressurization process is performed after the discharge process, the vacuum pump 6 is started with the on-off valves 72 and 73 closed, and then the on-off valve 72 is opened to depressurize the adsorption tower 2A. In the depressurization process, the adsorption tower 2A may be depressurized to a gauge pressure of -101 kPa or more and -20 kPa or less. This causes further adsorbed gas to desorb from the adsorbent 1A, resulting in a state where the adsorbent 1A is better regenerated (a state where regeneration is more advanced than in state 1). A state where the adsorbent 1A is better regenerated means that the recovery rate of the adsorption capacity of the adsorbent 1A is higher. In other words, it means that when reused, the breakthrough time (total usage time until the adsorbent breaks through) is longer due to regeneration.

[0048] When the depressurization process is complete, for example, the on-off valve 70A may be closed before stopping the vacuum pump 6. After the depressurization process, that is, after the regeneration process is completed, the production of the product gas using the adsorption tower 2A may be resumed.

[0049] As described above, the gas purification method according to this embodiment can achieve energy savings. [Examples]

[0050] The gas purification method according to this embodiment will be described below based on examples.

[0051] (Example 1) In this embodiment, a gas purification apparatus similar to the apparatus 100 shown in Figure 1 was used (however, only the adsorption tower corresponding to adsorption tower 2A was used), and an adsorption step for gas purification and a regeneration step for regenerating the adsorbent were performed according to the gas purification method of this embodiment. The adsorption capacity of the regenerated adsorbent for impurities (time until breakthrough), the time required for the regeneration step, the yield of the product gas, and the energy consumption of the gas purification apparatus per unit volume of product gas were evaluated.

[0052] In the adsorption process, the raw material gas used consisted mainly of deuterium gas, the gas to be purified, with the remainder being impurities. The composition and content of the impurities in the raw material gas were argon at 5 ppm, nitrogen at 50 ppm, oxygen at 5 ppm, and carbon dioxide at 5 ppm. This raw material gas had been dehumidified beforehand, and its moisture content was less than 1 ppm.

[0053] The adsorbent used to pack the adsorption tower was activated carbon granules, Shirasagi (manufactured by Osaka Gas Chemical Co., Ltd., model G2x 4 / 6-1G). The packed bed of the adsorbent in the adsorption tower had a diameter of 49.3 mm and a height of 984 mm.

[0054] After cooling the adsorption tower to -190°C, the source gas cooled to -190°C is then poured into a 3m³ chamber. 3 The adsorption process was carried out by passing the adsorbent through the packed bed at a supply rate of / h (where the volume flow rate is calculated at 1 atmosphere). The temperature of the adsorption tower was measured using a temperature sensor inserted into the packed bed of the packing material. Liquid nitrogen was used to cool the adsorption tower and the raw material gas. In this embodiment, no heat exchange was performed between the raw material gas and the product gas.

[0055] The adsorption process was carried out until the adsorbent broke through. In this embodiment, the adsorption process was continued for 600 hours until the adsorbent broke through.

[0056] After the adsorption process, a regeneration process consisting only of a heating process and a discharge process was performed. In the heating process, the adsorption tower was naturally heated to 25°C using the external atmosphere (28°C). At the end of the heating process, the internal pressure (gauge pressure) of the adsorption tower was approximately 180 kPa.

[0057] After the heating process, a discharge process was performed to remove the residual gas from the adsorption tower. During the discharge process, the adsorption tower was sealed when the internal pressure reached zero, and the regeneration process was terminated. The regeneration process took 24 hours.

[0058] After the regeneration process was completed, the adsorption process was performed again in the same manner as described above, and the time until the adsorbent broke through was measured. The breakthrough time was 530 hours. The required quality of the product gas was that the content of each impurity component in the product gas should be less than 0.1 ppm.

[0059] Furthermore, the yield of the product gas in these adsorption and regeneration processes was 98%. Note that the yield of the product gas (%) is calculated based on the amount of raw material gas supplied in the adsorption process (m³). 3 The amount of product gas recovered that meets the required quality (m³) 3 It refers to the percentage of ).

[0060] Here, whether or not the adsorbent had broken through was determined as follows: The product gas was measured every hour, and if the content of any of the impurities in the product gas exceeded 0.1 ppm, it was determined that the adsorbent had broken through. The content of impurities in the product gas was measured using a gas chromatograph (Shimadzu Corporation, model: GC-2014s).

[0061] In this embodiment, the energy consumption of the gas purification apparatus during the regeneration process and the second adsorption process was determined. The energy consumption of the gas purification apparatus was evaluated as the energy consumption per unit volume of the obtained product gas. The energy consumption of the gas purification apparatus was calculated as the sum of the amount of electricity consumed for driving and controlling each part of the gas production apparatus and the amount of electricity obtained by converting the amount of nitrogen used for cooling into the amount of electricity required for the production of the liquid nitrogen.

[0062] In the evaluation of Example 2 and Comparative Example 1 described later, the relative evaluation was based on the energy consumption of the gas purification apparatus during the regeneration process and the second adsorption process in this example.

[0063] (Example 2) Example 2 differs from Example 1 in that a depressurization process is carried out after the discharge process, but otherwise it is the same as Example 1.

[0064] The depressurization process followed the discharge process. The depressurization process involved gradually reducing the pressure in the adsorption tower until the internal pressure reached -101 kPa. At that point, the adsorption tower was sealed, and the regeneration process was completed. The regeneration process took 32 hours.

[0065] After the regeneration process was completed, the adsorption process was performed again, and the time until the adsorbent broke through was measured. The breakthrough time was 560 hours.

[0066] Furthermore, the yield of the product gas in these adsorption and regeneration processes was over 99%. Note that the yield of the product gas (%) is calculated based on the amount of raw material gas supplied in the adsorption process (m³). 3 The amount of product gas recovered that meets the required quality, substantially recovered through these adsorption and regeneration processes (m³) 3 It is the percentage of ).

[0067] In this embodiment, the energy consumption of the gas purification apparatus during the regeneration process and the second adsorption process was 1.5 times that of Example 1.

[0068] (Comparative Example 1) Comparative Example 1 differs from Example 1 in its regeneration process, but is otherwise the same as Example 1.

[0069] In this comparative example, a regeneration process was performed to regenerate the adsorbent as follows.

[0070] After the adsorption process is complete, deuterium gas (product gas) at 300°C is introduced at a flow rate of 0.6 m³. 3 The adsorption tower was run at a rate of 0.75 / h for 20 hours (hereinafter referred to as the high-temperature treatment). The deuterium gas used in this adsorption process was the product gas produced in the adsorption process performed immediately before this one. The impurities contained in this deuterium gas (product gas) were argon, nitrogen, oxygen, and carbon dioxide, each at a concentration of less than 0.1 ppm.

[0071] After passing the deuterium gas at 300 °C, the adsorption tower was sealed. Then, it was allowed to cool (naturally cooled) until the temperature of the adsorption tower reached 40 °C, and the regeneration process was completed. The required time for the regeneration process was 44 hours.

[0072] After the completion of the regeneration process, the adsorption process was carried out again, and the time until breakthrough of the adsorbent was measured. As a result, the breakthrough time was 560 hours.

[0073] Also, the yield of the product gas in this adsorption process was 80%. The yield of the product gas (%) is the percentage of the recovered amount (m 3 ) of the product gas that meets the required quality, which was substantially recovered through these adsorption and regeneration processes, with respect to the supply amount (m 3 ) of the raw material gas supplied in the adsorption process. Supplementary note: In this example, the recovered amount (m 3 ) of the product gas that meets the required quality recovered in the adsorption process minus the usage amount (m 3 ) of the deuterium gas (product gas) used in the adsorption process, and the recovered amount (m 3 ) of the product gas that meets the required quality, which was substantially recovered through these adsorption and regeneration processes, was calculated.

[0074] In this comparative example, the energy consumption of the gas purification device during the execution process of the regeneration process and the second adsorption process was 1.9 times that in the case of Example 1. The energy consumption of the gas purification device in this comparative example was calculated as the total value of the amount of electric power consumed for driving and controlling each part of the gas production device, the amount of electric power obtained by converting the amount of heat required for the production of deuterium gas at 300 °C into electric power, and the amount of electric power obtained by converting the usage amount of nitrogen required for cooling into the amount of electric power required for the production of the liquid nitrogen.

[0075] Table 1 shows the breakthrough time, the required time for the regeneration process (regeneration time in Table 1), the yield of the product gas, and the energy consumption in Example 1, Example 2, and Comparative Example 1.

[0076]

Table 1

[0077] From the comparison of Example 1, Example 2, and Comparative Example 1 described above, the following can be seen.

[0078] As shown in Examples 1 and 2, by following the gas purification method according to this embodiment, it is possible to regenerate the adsorbent to a level close to or equivalent to that achieved with high-temperature treatment as in Comparative Example 1, without requiring the high-temperature treatment seen in Comparative Example 1. Furthermore, the energy consumption per unit volume of product gas is significantly lower in Examples 1 and 2 compared to Comparative Example 1, indicating superior energy efficiency. In addition, from the perspective of process time, Examples 1 and 2 have shorter process times compared to Comparative Example 1, demonstrating their superiority.

[0079] In particular, comparing Example 1 and Example 2, the reduced pressure process allows for better regeneration (the breakthrough time of the regenerated adsorbent is extended), so from the perspective of adsorbent regeneration ability, the case with the reduced pressure process as in Example 2 is superior. However, from the perspective of energy saving, Example 1 is superior to Example 2, which includes the reduced pressure process, so the reduced pressure process can be evaluated as not being essential. Furthermore, from the perspective of process time, the reduced pressure process can also be evaluated as not being essential.

[0080] As described above, a gas purification method using low-temperature adsorption that achieves energy savings can be provided.

[0081] The embodiments disclosed herein are illustrative and not limited to those described herein. They may be modified as appropriate without departing from the purpose of this disclosure. [Industrial applicability]

[0082] This disclosure is applicable to gas purification methods. [Explanation of Symbols]

[0083] 100: Equipment 1: Adsorbent 1A: Adsorbent 1B: Adsorbent 2:Adsorption tower 2A: Adsorption tower 2B: Adsorption tower 3: Cold box 3A: Cold Box 3B: Cold Box 4: Supply piping 4A: Supply piping 4B: Supply piping 40A: Shut-off valve 40B: Shut-off valve 5: Delivery piping 5A: Delivery piping 5B: Delivery piping 50A: Shut-off valve 50B: Shut-off valve 6: Vacuum pump 7: Piping for pressure reduction 7A: Piping for pressure reduction 7B: Piping for pressure reduction 70A: Shut-off valve 70B: Shut-off valve 71: Bypass piping 72: Shut-off valve 73: Shut-off valve G1: Gas (raw material gas) G2: Gas (product gas) G3: Gas (residual gas)

Claims

1. An adsorption step is performed by passing a raw material gas containing the gas to be purified and impurities through an adsorbent contained inside an adsorbent tower, thereby adsorbing the impurities onto the adsorbent, and extracting a product gas containing the gas to be purified at a higher purity than the raw material gas. The process includes a regeneration step of separating the impurities from the adsorbent and regenerating the adsorbent, In the adsorption step, the adsorbent is cooled to below 0°C. In the regeneration step, the adsorbent is heated to a temperature of 0°C or higher and 40°C or lower in this gas purification method.

2. The aforementioned regeneration process is, A heating step in which the adsorbent is heated to a temperature of 0°C or higher and 40°C or lower while the adsorption tower is sealed, The process includes a discharge step of discharging the adsorbed gas that was adsorbed on the adsorbent from the adsorption tower, The gas purification method according to claim 1, wherein the discharge step is performed after the heating step.

3. The gas purification method according to claim 2, wherein the regeneration step further comprises a depressurization step of reducing the pressure of the adsorbent.

4. The gas purification method according to claim 2, wherein the adsorbed gas is a gas containing the gas to be purified and the impurities.

5. The gas purification method according to claim 2, wherein in the heating step, the internal pressure of the adsorption tower is increased to 100 kPa or more and 300 kPa or less in gauge pressure.

6. The gas purification method according to claim 2, wherein in the adsorption step, the raw material gas, which has been dehumidified to 10 ppm by volume or less, is passed through the adsorbent.

7. In the adsorption step, the adsorption tower is cooled to cool the adsorbent, The gas purification method according to any one of claims 1 to 6, wherein the cooling of the adsorption tower is stopped and the adsorbent is heated in the regeneration step.

8. The gas purification method according to any one of claims 1 to 6, wherein the impurity comprises at least one of nitrogen, oxygen, argon, carbon monoxide, carbon dioxide, and methane.

9. The gas purification method according to any one of claims 1 to 6, wherein the gas to be purified is deuterium.

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