Method for producing oxygen-enriched gas

Abstract

To provide a method for producing an oxygen-enriched gas, which can efficiently increase the generation amount of the oxygen-enriched gas.SOLUTION: This method for producing an oxygen-enriched gas comprises: a nitrogen recovery step of introducing air to a first nitrogen oxygen separation tower among a plurality of nitrogen oxygen separation towers filled with oxygen selection-type adsorbents and recovering an oxygen-enriched gas derived therefrom; a pressure equalization / pressure reduction step of introducing pressure gas remaining in the first nitrogen oxygen separation tower into a second nitrogen oxygen separation tower; and an oxygen recovery step of eliminating oxygen adsorbed on the oxygen selection-type adsorbent to recover an oxygen-enriched gas derived from the first nitrogen oxygen separation tower. The nitrogen recovery step, the pressure equalization / pressure reduction step, the nitrogen recovery step, and the pressure equalization / pressure reduction step are sequentially switched to be executed. A specific perovskite-type oxide is used as the oxygen selection-type adsorbent, and a pressure equalization recovery rate represented by a specific expression when the pressure equalization / pressure reduction step is completed is set to over 0-30%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an oxygen-enriched gas. [Background technology]

[0002] Conventionally, methods for producing oxygen gas from air include cryogenic separation and PSA methods using zeolites, etc. In recent years, a PSA method using perovskite-type oxides has been disclosed as a method for efficiently producing oxygen gas from air (Patent Documents 1 and 2). A structure that enables effective use of the heat source used for adsorption has also been disclosed (Patent Document 3).

[0003] Patent Document 3 discloses an adsorption tower at least a portion of which is exposed to an atmosphere that is higher or lower than room temperature; a mixed gas supply unit that supplies a mixed gas containing multiple substances into the adsorption tower; an adsorbent that is provided in the adsorption tower and that, when it comes into contact with the mixed gas under a predetermined pressure and temperature environment, adsorbs the substances contained in the mixed gas and separates the substances in the mixed gas; a separated gas discharge unit that discharges a separated gas from the adsorption tower, resulting from the removal of the substances adsorbed by the adsorbent, from the mixed gas; and an adsorbed gas discharge unit that reduces the pressure inside the adsorption tower to desorb the adsorbed gas adsorbed on the adsorbent from the adsorbent and discharges it from the adsorption tower. The adsorption tower is characterized by having heat storage bodies that are provided both upstream and downstream of the adsorbent in the supply direction of the mixed gas, through which the mixed gas supplied into the adsorption tower from the mixed gas supply unit, the separated gas discharged from the adsorption tower by the separated gas discharge unit, and the adsorbed gas discharged from the adsorption tower by the adsorption gas discharge unit pass. and a gas separation method for separating substances from a mixed gas by bringing a mixed gas into contact with an adsorbent installed in an adsorption tower, at least a portion of which is exposed to an atmosphere higher or lower than room temperature, under a predetermined pressure and temperature environment, thereby adsorbing substances contained in the mixed gas onto the adsorbent, the method comprising: a supply step for supplying the mixed gas into the adsorption tower; an adsorption step for maintaining the adsorption tower in the predetermined pressure and temperature environment and adsorbing the substances contained in the mixed gas onto the adsorbent; a separated gas discharge step for discharging from the adsorption tower a separated gas in which the substances adsorbed by the adsorbent have been removed from the mixed gas; and an adsorbed gas discharge step for depressurizing the adsorption tower to desorb the adsorbed gas adsorbed on the adsorbent from the adsorbent and discharging it from the adsorption tower; the method is characterized in that in the supply step, the mixed gas is supplied from one end or the other end of the adsorption tower, whichever end the separated gas was discharged from in the previous separated gas discharge step.

[0004] Furthermore, in order to reduce the power required for operation of a conventional PSA unit, it has been proposed to provide a pressure equalization process between the adsorption and desorption processes, in which gas in an adsorption tower that has completed the adsorption process is circulated to an adsorption tower that has completed the desorption process, thereby reducing the power required for the compressor and enabling the PSA unit to operate efficiently. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4721967 [Patent Document 2] Patent No. 5298291 [Patent Document 3] Patent No. 5600336 Summary of the Invention [Problem to be solved by the invention]

[0006] There is a constant demand for reducing the initial and running costs of devices that separate specific components from mixed gases such as air. Patent Documents 1 and 2 describe oxygen production methods with low power consumption using perovskite oxides. However, they do not take into consideration the optimal operating conditions suited to the characteristics of perovskite oxides, and therefore are unable to minimize initial and running costs. In Patent Document 3, measures are taken to reduce running costs, but this requires a special adsorption tower structural design and increases the number of valves used, resulting in increased initial costs.

[0007] The present invention provides a method for producing an oxygen-rich gas that can efficiently increase the amount of oxygen-rich gas generated. [Means for solving the problem]

[0008] [1] A first nitrogen recovery step of introducing pressurized air into a first nitrogen oxygen separation tower among a plurality of nitrogen oxygen separation towers filled with an oxygen-selective adsorbent that selectively adsorbs and desorbs oxygen, and recovering nitrogen-enriched gas discharged from the first nitrogen oxygen separation tower by adsorbing oxygen contained in the air onto the oxygen-selective adsorbent heated to a predetermined temperature; a pressure equalization and depressurization step of introducing the pressurized gas remaining in the first nitrogen and oxygen separation tower after the nitrogen recovery step into a second nitrogen and oxygen separation tower; an oxygen recovery step of introducing a portion of the nitrogen-enriched gas recovered in the nitrogen recovery step into the first nitrogen-oxygen separation tower while reducing the pressure inside the first nitrogen-oxygen separation tower, and recovering the oxygen-enriched gas discharged from the first nitrogen-oxygen separation tower by desorbing the oxygen adsorbed by the oxygen-selective adsorbent; a second nitrogen recovery step of introducing pressurized air into a second nitrogen / oxygen separation tower among the plurality of nitrogen / oxygen separation towers, and adsorbing the oxygen contained in the air onto the oxygen-selective adsorbent heated to a predetermined temperature, thereby recovering a nitrogen-enriched gas discharged from the second nitrogen / oxygen separation tower; a pressure equalization step of introducing the pressurized gas remaining in the second nitrogen and oxygen separation tower after the second nitrogen recovery step into the first nitrogen and oxygen separation tower after the oxygen recovery step; Including, A method for producing an oxygen-enriched gas, in which the nitrogen-enriched gas and the oxygen-enriched gas are continuously recovered while sequentially switching between the nitrogen recovery step, the pressure equalization depressurization step, the oxygen recovery step, and the pressure equalization pressurization step using the plurality of nitrogen-oxygen separation towers, The oxygen-selective adsorbent has oxygen non-stoichiometry, and YBaCoO 7+δ (1.0≦δ≦1.5), CaAlMnO 5+δ (0≦δ≦0.5), La X Ba (1-X) CoO 3-δ (0.1≦σ≦0.5, 0.2≦X≦1), La X Sr (1-X)CoO 3-δ (0.1≦σ≦0.5, 0.2≦X≦1), Ba4CaFe3O 9+δ (0.1≦δ≦0.5), and YBa2Cu3O 7-δ (0≦δ≦1.0) Using any one or more perovskite oxides selected from the group P1: Pressure inside the first nitrogen and oxygen separation column at the end of the first nitrogen recovery step P2: Pressure inside the first nitrogen and oxygen separation column at the end of the oxygen recovery step P3: The pressure inside the first nitrogen and oxygen separation column at the end of the pressure equalization and depressurization step When the equalized pressure recovery rate is expressed by the formula below, the equalized pressure recovery rate is set to more than 0% and 30% or less. [2] The method for producing an oxygen-enriched gas according to [1], further comprising an air purification step for removing moisture and carbon dioxide from the air as a pretreatment of the air. [3] The method for producing an oxygen-enriched gas according to [1] or [2], wherein the amount of air used in the first nitrogen recovery step per hour is 600 to 1000 times the packed volume of the oxygen-selective adsorbent. [4] A method for producing an oxygen-enriched gas according to any one of [1] to [3], wherein after the first nitrogen recovery step is completed, the pressure equalization and depressurization step and the oxygen recovery step are completed, and the switching time until switching to the first nitrogen recovery step of the next cycle is 40 seconds or less. [Effects of the Invention]

[0009] According to the present invention, in the production of oxygen-rich gas using a perovskite-type oxide selected from a specific group having oxygen non-stoichiometry, by setting the pressure equalization recovery rate after completion of the pressure equalization and depressurization step to more than 0% to 30%, it is possible to obtain high-concentration oxygen gas while suppressing a decrease in the amount of oxygen-rich gas generated. [Brief explanation of the drawings]

[0010] [Figure 1]1 is a schematic diagram of an example of an oxygen-enriched gas production apparatus for carrying out the present invention. [Figure 2] 1 is a graph showing the relationship between the pressure-equalized recovery rate and the oxygen-enriched gas generation ratio in a test example. [Figure 3] 1 is a graph showing the relationship between the pressure equalization recovery rate and the oxygen recovery rate ratio in a test example. [Figure 4] 1 is a graph showing the relationship between pressure-equalized recovery rate and oxygen concentration ratio in a test example. DETAILED DESCRIPTION OF THE INVENTION

[0011] An example of an embodiment of the present invention will be described in detail below with reference to the drawings as appropriate. As an example applicable to the implementation of this embodiment, a schematic configuration of an oxygen production apparatus 1 is shown in FIG. 1. A specific example of producing an oxygen-enriched gas using air as a raw material gas using the oxygen production apparatus 1 will be described below. In this specification and claims, gas with an oxygen concentration of 22% by volume or more is referred to as "oxygen-enriched gas," gas with an oxygen concentration of 90% by volume or more is referred to as "oxygen gas," gas with a nitrogen concentration of 79% by volume or more is referred to as "nitrogen-enriched gas," and gas with a nitrogen concentration of 90% by volume or more is referred to as "nitrogen gas."

[0012] The oxygen production device 1 includes a TSA device 10 and a PSA device 20 connected thereto.

[0013] The TSA device 10 processes the raw air taken in by the compressor 51 using the TSA (Thermal Swing Adsorption) method to generate purified air from which water and carbon dioxide have been removed. The process for obtaining this purified air is a pretreatment of the raw air. The TSA device 10 includes a first adsorption tower 11a, a second adsorption tower 11b, a heater 54 for heating purified air from which water and carbon dioxide have been removed in the adsorption towers, gas flow paths L11, L12, L13, L14, L15, L16, L17, L18, L19, and L20, and valves V10, V11, V12, V13, V14, V15, V16, V17, V18, and V19.

[0014] The first adsorption tower 11a includes an adsorption tower main body 12a and a water / carbon dioxide adsorbent 13a packed therein. The second adsorption tower 11b has a configuration similar to that of the first adsorption tower 11a and includes an adsorption tower main body 12b and a water / carbon dioxide adsorbent 13b packed therein. Examples of the water / carbon dioxide adsorbent 13a (13b) include activated alumina, silica gel, zeolite, and activated carbon that adsorb water, and synthetic zeolite such as Na-X zeolite that adsorbs carbon dioxide. The activated alumina and zeolite may be a mixture, or one or more layers of activated alumina and one or more layers of zeolite may be stacked.

[0015] At least a portion of the moisture in the feed air taken in by the compressor 51 is removed by the refrigerator 53 before the feed air is introduced into the first adsorption tower 11a or the second adsorption tower 11b of the TSA unit .

[0016] The gas flow path L10 is a gas flow path that introduces air, which is a raw material gas, into the compressor 51. The gas flow path L11 is a gas flow path that connects the compressor 51, the valve V12, and the valve V13. The gas flow path L12 connects the valve V12, the valve V10, and the first adsorption tower 11a. The gas flow path L13 connects the valve V13, the valve V11, and the second adsorption tower 11b. The gas flow path L14 connects the first adsorption tower 11a with the valve V14, the valve V16, and the valve V18. The gas flow path L15 connects the second adsorption tower 11b with the valve V15, the valve V17, and the valve V19. The gas flow path L16 is a gas flow path that connects the valve V14 and the valve V15, and forms a pressure charging line. The gas flow path L17 is a gas flow path that connects the valve V16, the valve V17, and the heater 54. The gas flow path L18 is a gas flow path that connects the heater 54, the valve V18, and the valve V19, and shares a portion with the gas flow path L21. The gas flow path L19 is a gas flow path that connects the valve V10, the valve V11, and the gas outlet of the TSA device 10. The gas flow path L20 branches off from the gas flow path L21 and forms a pressure charging line that returns the gas in the gas flow path L21 to the gas flow path L16. The gas flow path L21 is a gas flow path that connects the valve V18, the valve V19, and the PSA device 20. A part of the gas flow path L21 is shared with the gas flow path L18.

[0017] The PSA unit 20 processes the purified air produced by the TSA unit 10 using a PSA (Pressure Swing Adsorption) method to produce high-purity product oxygen and product nitrogen. The PSA device 20 includes a first nitrogen-oxygen separation column 21a, a second nitrogen-oxygen separation column 21b, gas flow paths L21, L22, L23, L24, L25, L26, L27, L28, and L29, and valves V20, V21, V22, V23, V24, V25, V26, V27, V28, and V29.

[0018] The first nitrogen-oxygen separation tower 21a includes an adsorption tower body 22a and an oxygen-selective adsorbent 23a packed therein. The second nitrogen-oxygen separation tower 21b has the same configuration as the first nitrogen-oxygen separation tower 21a, and includes an adsorption tower body 22b and an oxygen-selective adsorbent 23b packed therein. The oxygen-selective adsorbents 23a and 23b are each independently: It has oxygen non-stoichiometry, and YBaCoO 7+δ (1.0≦δ≦1.5), CaAlMnO 5+δ (0≦δ≦0.5), La X Ba (1-X) CoO 3-δ (0.1≦σ≦0.5, 0.2≦X≦1), La X Sr (1-X) CoO 3-δ (0.1≦σ≦0.5, 0.2≦X≦1), Ba4CaFe3O 9+δ (0.1≦δ≦0.5), and YBa2Cu3O7-δ (0≦δ≦1.0) The present invention includes at least one perovskite oxide selected from the group consisting of:

[0019] The perovskite oxide can be obtained by the method disclosed in JP-A-2020-203816.

[0020] The "oxygen non-stoichiometry" of the perovskite oxides refers to the property of perovskite oxides and the like, where deviations in composition ratio occur due to oxygen deficiency in the crystal structure at high temperatures and low partial pressures of oxygen.

[0021] The oxygen-selective adsorbents 23a and 23b may each independently contain, in addition to the perovskite-type oxide, an oxygen ion conductor having oxygen non-stoichiometry, such as molecular sieves carbon (MSC). Examples of oxygen ion conductors include metal oxides having a Brownmillerite structure. When the oxygen-selective adsorbents 23a and 23b contain an oxygen ion conductor other than the perovskite-type oxide or MSC, the content should be within the scope of the present invention.

[0022] A vacuum pump 52, a gas flow path L30, and a product oxygen tank 31 for storing the generated oxygen are connected to the gas flow path L29 of the PSA device 20. A gas flow path L31 for extracting the product oxygen O2 is connected to the product oxygen tank 31. A nitrogen-enriched gas tank 32 for storing the generated nitrogen-enriched gas is connected to the gas flow path L28 of the PSA device 20. In addition, a gas flow path L27 for sending the stored nitrogen-enriched gas to the PSA device 20 as a rinse gas is connected to the nitrogen-enriched gas tank 32.

[0023] The gas flow path L21 is a gas flow path that connects the valve V18 and valve V19 of the TSA device 10 with the PSA device 20. A part of the gas flow path L21 is shared with the gas flow path L18 of the TSA device 10. The gas flow path L22 is a gas flow path that connects the valve V22, the valve V20, and the first nitrogen-oxygen separation column 21a. The gas flow path L23 is a gas flow path that connects the valve V23, the valve V21, and the second nitrogen-oxygen separation column 21b. The gas flow path L24 is a gas flow path that connects the first nitrogen-oxygen separation column 21a with the valve V24, the valve V26, and the valve V28. The gas flow path L25 is a gas flow path that connects the second nitrogen-oxygen separation column 21b with the valve V25, valve V27, and valve V29. The gas flow path L26 is a gas flow path that connects the valve V24 and the valve V25 and constitutes a pressure equalization line. The gas flow path L27 is a gas flow path that connects the valve V26, the valve V27, and the nitrogen-enriched gas tank 32. The gas flow path L28 is a gas flow path that connects the valve V28, the valve V29, and the nitrogen-enriched gas tank 32. The gas flow path L29 is a gas flow path that connects the valve V20, the valve V21, and the inlet side of the vacuum pump 52. The gas flow path L30 is a gas flow path that connects the outlet side of the vacuum pump 52 and the product oxygen tank 31. The gas flow path L31 is a gas flow path for extracting product oxygen from the product oxygen tank 31. The gas flow path L32 is a gas flow path for extracting nitrogen-enriched gas from the nitrogen-enriched gas tank 32.

[0024] Next, a method for producing an oxygen-enriched gas using the oxygen production apparatus 1 of FIG. 1 (hereinafter, also simply referred to as an "oxygen production method") will be described. The oxygen production method of this embodiment includes a process of removing water and carbon dioxide from air to produce purified air (hereinafter also referred to as the "air purification process"), and a process of producing oxygen-enriched gas and nitrogen-enriched gas from the purified air (hereinafter also referred to as the "oxygen generation process").

[0025] <Air purification process> In an air purification process, TSA device 10 is used to remove water and carbon dioxide from air to produce purified air. In the air purification process, the first adsorption tower 11a and the second adsorption tower 11b are switched between alternately and continuously performing adsorption of water and carbon dioxide onto the water / carbon dioxide adsorbent and desorption of water and carbon dioxide from the water / carbon dioxide adsorbent (regeneration of the adsorbent). Specifically, in the first adsorption tower 11a, the moisture and carbon dioxide contained in the pressurized feed air are adsorbed onto the adsorbent to produce purified air (adsorption process), while in the second adsorption tower 11b, the moisture and carbon dioxide adsorbed onto the adsorbent in the preceding cycle are desorbed, thereby regenerating and cooling the adsorbent in the second adsorption tower 11b (regeneration and cooling process).

[0026] In the following, the adsorption of water and carbon dioxide to the water / carbon dioxide adsorbent in the first adsorption tower 11a and the desorption of water and carbon dioxide from the water / carbon dioxide adsorbent will be described in more detail.

[0027] (Adsorption process) The adsorption process in the TSA unit 10 involves sending a raw gas into an adsorption tower, removing impurities such as moisture and carbon dioxide by adsorbing them onto an adsorbent, and extracting a purified gas. Air (feed air), which is the raw gas, is taken in by a compressor 51 through a gas flow path L10 and sent to the TSA unit 10 through a gas flow path L11. A refrigerator 53 is installed in the gas flow path L11, and at least a portion of the moisture contained in the raw air passing through the refrigerator 53 is removed. The air that has passed through the refrigerator 53 is sent to the TSA unit 10 and introduced into the first adsorption tower 11a (valve V10 closed, valve V12 open, valve V13 closed). When the air passes through the first adsorption tower 11a, the water and carbon dioxide in the air are adsorbed by the water / carbon dioxide adsorbent 13a and removed. The air (purified air) from which water and carbon dioxide have been removed in the first adsorption tower 11a is extracted from the top of the first adsorption tower 11a, and a portion of it is used to regenerate the second adsorption tower 11b. The rest is supplied to the PSA device 20 through gas flow paths L14 and L21 and used as raw material gas for the oxygen generation step (valve V14 closed, valve V16 closed, valve V18 open, valve V19 closed).

[0028] During the adsorption process in the first adsorption tower 11a, the second adsorption tower 11b performs a regeneration and cooling process for the water / carbon dioxide adsorbent 13b that has adsorbed water and carbon dioxide in the preceding cycle in order to operate the TSA device 10 efficiently.

[0029] (Depressurization process) An example of the depressurization step in the TSA device 10 is a step of discharging the pressurized gas remaining in the first adsorption tower 11a after the adsorption step has been completed to the outside of the first adsorption tower 11a. After the adsorption step in the first adsorption tower 11a is completed, valve V18 is closed and only the depressurization valve on gas flow path L12 is opened. The gas in the first adsorption tower 11a is released through gas flow paths L12 and L19, and the pressure in the first adsorption tower 11a is reduced to near atmospheric pressure (valve V10 is open, valve V11 is closed, and valve V12 is closed).

[0030] (Regeneration / cooling process) An example of a regeneration / cooling process in the TSA device 10 is a process in which heated purified air (also referred to as regeneration gas) is introduced into the first adsorption tower 11a, which has been depressurized to near atmospheric pressure in the depressurization process, to regenerate the adsorbent. A portion of the purified air is introduced into a heater 54 through gas flow path L18 and heated. The purified air (regeneration gas) heated by the heater 54 is introduced into the upper part of the first adsorption tower 11a through gas flow path L17 and gas flow path L14 (valve V14 closed, valve V15 closed, valve V16 open, valve V17 closed, valve V18 closed, valve V19 open). In the first adsorption tower 11a, the moisture and carbon dioxide desorbed from the water / carbon dioxide adsorbent 13a diffuse into the regeneration gas, thereby regenerating the water / carbon dioxide adsorbent 13a. The regeneration gas containing the desorbed moisture and carbon dioxide is then exhausted through L19 (V10 open, V11 closed, V12 closed). Next, room temperature or cooled purified air is introduced into the first adsorption tower 11a, and the water / carbon dioxide adsorbent 13a, which was heated by the regeneration gas during regeneration, is cooled to room temperature, completing the adsorbent regeneration and cooling process.

[0031] (Charging process) An example of a pressurization process in the TSA device 10 is a process of introducing pressurized gas remaining in another adsorption tower that has completed the adsorption process, such as the second adsorption tower 11b, into another adsorption tower that has completed the regeneration and cooling process, such as the first adsorption tower 11a. After the regeneration and cooling steps in the first adsorption tower 11a are completed, valves V10 and V16 are closed, and valve V14 on gas flow path L16 (pressurization line) is opened. A portion of the purified air flowing through gas flow path L21 is introduced into the first adsorption tower 11a via gas flow paths L20, L16, and L14, and is pressurized to the operating pressure for the next adsorption step. After the above-mentioned pressurizing step is performed, the valve V14 is closed and the valves V12 and V18 are opened again, thereby starting a new cycle in the first adsorption tower 11a, starting from the adsorption step.

[0032] The operations of the adsorption step, depressurization step, regeneration / cooling step, and pressurization step described above are repeated alternately in the first adsorption tower 11a and the second adsorption tower 11b, so that removal of moisture and carbon dioxide from the feed air and regeneration / cooling of the adsorbent in the adsorption towers 11a and 11b are continuously carried out.

[0033] The purified air obtained in the air purification step is introduced into a nitrogen / oxygen separation tower set at a predetermined temperature for use in the subsequent oxygen production step. From the viewpoint of balancing the operating speeds of the air purification step and the oxygen generation step, the amount of purified air treated per hour in the oxygen generation step is preferably 600 to 1000 times the total volume of adsorbents provided in all adsorption towers used in the oxygen generation step.

[0034] <Oxygen generation process> In the oxygen production step, nitrogen and oxygen are continuously recovered by sequentially switching between a nitrogen recovery step and an oxygen recovery step described below using the PSA device 20, and oxygen-enriched gas and nitrogen-enriched gas are produced from purified air. In the oxygen generation process, the purified air is introduced into the first nitrogen-oxygen separation tower 21a and the second nitrogen-oxygen separation tower 21b, and oxygen is adsorbed onto the oxygen-selective adsorbent and desorbed from the oxygen-selective adsorbent in an alternating and continuous manner. Specifically, in the first nitrogen-oxygen separation tower 21a, oxygen contained in the pressurized purified air is adsorbed onto an oxygen-selective adsorbent to produce a nitrogen-enriched gas (nitrogen recovery step). Meanwhile, in parallel with this, in the second nitrogen-oxygen separation tower 21b, the oxygen adsorbed onto the oxygen-selective adsorbent in the preceding cycle is desorbed to recover an oxygen-enriched gas (oxygen recovery step). In the oxygen recovery step, the oxygen-selective adsorbent in the second nitrogen-oxygen separation tower 21b is regenerated.

[0035] In the following, adsorption of oxygen to and desorption of oxygen from the oxygen-selective adsorbent in the first nitrogen-oxygen separation column 21a will be described.

[0036] (Nitrogen recovery process) The purified air pressurized by compressor 51 is sent to PSA unit 20 and introduced into first nitrogen-oxygen separation column 21a (valve V20 closed, valve V22 open, valve V23 closed). At this time, oxygen-selective adsorbent 23a packed in first nitrogen-oxygen separation column 21a is preheated to a predetermined temperature by separation column heater 24a. In this state, oxygen contained in the pressurized purified air passing through first nitrogen-oxygen separation column 21a is adsorbed by oxygen-selective adsorbent 23a. Thereafter, the nitrogen-enriched gas separated from the oxygen is discharged from the top of first nitrogen-oxygen separation column 21a (valve V24 closed, valve V26 closed, valve V28 open, valve V29 closed).

[0037] The first nitrogen-oxygen separation column 21a is heated by a separation column heater 24a. Heating improves the oxygen adsorption and desorption performance of the perovskite-type oxidant constituting the oxygen-selective adsorbent 23a. The temperature to which the first nitrogen-oxygen separation column 21a is heated is preferably 200 to 500°C, more preferably 300 to 400°C, and even more preferably 320 to 360°C.

[0038] The nitrogen-enriched gas taken out from the top of the first nitrogen-oxygen separation column 21a is sent to the nitrogen-enriched gas tank 32 via the gas flow path L28 and stored therein. The nitrogen-enriched gas stored in the nitrogen-enriched gas tank 32 becomes product nitrogen gas, but a portion of it can be extracted when needed and sent to the second nitrogen-oxygen separation tower 21b via gas flow path L25, and can also be used as a rinse gas. The rinse gas sent to the second nitrogen-oxygen separation column 21b is used to desorb the oxygen adsorbed on the oxygen-selective adsorbent 23b.

[0039] (Pressure equalization and decompression process) An example of the pressure equalization and depressurization process is a process of introducing the pressurized gas remaining in the first nitrogen and oxygen separation tower 21a after the nitrogen recovery process has been completed into another nitrogen and oxygen separation tower, for example, the second nitrogen and oxygen separation tower 21b. Specifically, in the nitrogen recovery step, purified air is introduced into the first nitrogen-oxygen separation tower 21a and pressurized to adsorb oxygen onto the oxygen-selective adsorbent. At least a portion of the resulting pressurized nitrogen-enriched gas is introduced into the unpressurized or depressurized second nitrogen-oxygen separation tower 21b via gas flow path L26, which is a pressure equalization line (valve V22 closed, valve V24 open, valve V25 open, valve V28 closed). As a result, the pressure inside the first nitrogen-oxygen separation tower 21a is reduced and the pressure inside the second nitrogen-oxygen separation tower 21b is increased, so that the pressures in both towers 21a and 21b approach an equilibrium state. In other words, while the first nitrogen-oxygen separation tower 21a performs the pressure equalization depressurization step, the second nitrogen-oxygen separation tower 21b performs the pressure equalization pressurization step.

[0040] In the pressure equalization / depressurization step, the pressurized gas remaining in the first nitrogen / oxygen separation tower 21a after the nitrogen recovery step is introduced into the second nitrogen / oxygen separation tower 21b, thereby performing the pressure equalization / depressurization step in the first nitrogen / oxygen separation tower 21a and the pressure equalization / pressurization step in the second nitrogen / oxygen separation tower 21b. As a result, the pressures in both nitrogen / oxygen separation towers can eventually be made uniform (a pressure equalization ratio of 100%, as described below). Furthermore, if the pressure equalization / depressurization step is completed before the pressures are made uniform, the pressure equalization ratio, as described below, can be adjusted to a desired range, for example, from greater than 0% to 30% or less. Furthermore, the pressurized gas introduced into the second nitrogen / oxygen separation tower 21b is used as a rinse gas for desorbing oxygen. By performing the pressure equalization / depressurization step, in which pressure is released from the first nitrogen / oxygen separation tower 21a to the second nitrogen / oxygen separation tower 21b, the power required to depressurize the first nitrogen / oxygen separation tower 21a using a vacuum pump can be reduced, resulting in reduced running costs.

[0041] However, considering the objective of obtaining a larger amount of oxygen-enriched gas containing a high concentration of oxygen, the pressure equalization and depressurization step results in a disadvantage in that some oxygen is desorbed from the oxygen-selective adsorbent 23a, reducing the amount of oxygen-enriched gas recovered later. Specifically, when the pressurized gas remaining in the first nitrogen-oxygen separation tower 21a after the nitrogen recovery step is introduced into the second nitrogen-oxygen separation tower 21b, the pressure in the first nitrogen-oxygen separation tower 21a decreases, causing some oxygen to desorb from the oxygen-selective adsorbent 23a. The desorbed oxygen is introduced into the second nitrogen-oxygen separation tower 21b via the gas flow path L26, which is a pressure equalization line, and is recovered as nitrogen-enriched gas in the subsequent nitrogen recovery step of the second nitrogen-oxygen separation tower 21b. As a result, the amount of oxygen-enriched gas obtained decreases.

[0042] In order to alleviate the above-mentioned inconveniences, in the present invention, the pressure equalization recovery rate in the pressure equalization depressurization step is set to a range of more than 0% to 30%, thereby increasing the amount of oxygen-enriched gas obtained and suppressing a decrease in the oxygen concentration of the product oxygen-enriched gas. If the pressure equalization recovery rate in the pressure equalization depressurization step exceeds 30%, the amount of oxygen-enriched gas obtained will decrease. If the pressure equalization recovery rate is set to 0%, that is, if the pressure equalization depressurization step (and pressure equalization pressurization step) are not performed, the oxygen concentration in the obtained oxygen-enriched gas will decrease. In this embodiment, the pressure equalization recovery rate is preferably greater than 0% and equal to or less than 30%. Within this range, the lower limit of the pressure equalization recovery rate may be 5%, 10%, 15%, or 20%. The upper limit of the pressure equalization recovery rate may be 25%, 20%, 15%, or 10%.

[0043] The "pressure equalization recovery rate" is calculated using the following formula:

[0044]

number

[0045] For example, if the pressure P1 inside the tower at the end of the nitrogen recovery step is 20 kPaG and the pressure P2 inside the tower at the end of the oxygen recovery step is -90 kPaG, the pressure P3 inside the tower when the process is completed with complete pressure equalization as in the past (100% pressure equalization recovery rate) will be -35 kPaG, as shown in Table 1. Here, the positive and negative values ​​of the pressure inside the tower are defined as positive when the side higher than atmospheric pressure is used as the reference pressure and negative when the side lower than atmospheric pressure is used as the reference pressure.

[0046] [Table 1]

[0047] On the other hand, when the pressure equalization recovery rate is set to 10%, the pressure P3 inside the column is 14.5 kPaG, as shown in Table 2.

[0048] [Table 2]

[0049] The "pressure equalization recovery rate" can be controlled within a desired range by adjusting the time of the pressure equalization decompression process by opening and closing valves 24V and 25V, changing the piping diameter of pressure equalization line L26, or adjusting the gas flow rate through pressure equalization line L26.

[0050] In the nitrogen recovery step, the first nitrogen / oxygen separation column 21a is heated by a separation column heater 24a. The temperature to which the first nitrogen / oxygen separation column 21a is heated is preferably 200 to 500°C, more preferably 300 to 400°C, and even more preferably 320 to 360°C.

[0051] (Oxygen recovery process) After the pressure equalization and depressurization step is completed, the oxygen adsorbed by the oxygen-selective adsorbent 23a in the first nitrogen-oxygen separation tower 21a (oxygen that remains undesorbed in the pressure equalization and depressurization step) is recovered into the product oxygen tank 31 via the vacuum pump 52 and gas flow path L30 (valve V22 closed, valve V20 open, valve V21 closed, valve V24 closed, valve V25 closed).

[0052] In the oxygen recovery step, a portion of the nitrogen-enriched gas in the nitrogen-enriched gas tank 32 may be introduced as a rinse gas into the first nitrogen-oxygen separation tower 21a. By introducing the rinse gas, the oxygen adsorbed on the oxygen-selective adsorbent 23a in the first nitrogen-oxygen separation tower 21a can be efficiently desorbed (valve V20 open, valve V21 closed, valve V22 closed, valve V26 open, valve V27 closed, valve V28 closed). By introducing the rinse gas, the oxygen partial pressure around the oxygen-selective adsorbent decreases, and the oxygen previously adsorbed on the oxygen-selective adsorbent is efficiently extracted.

[0053] In the oxygen recovery step, the first nitrogen-oxygen separation column 21a is heated by a separation column heater 24a. Heating improves the oxygen adsorption and desorption performance of the perovskite-type oxidant constituting the oxygen-selective adsorbent 23b. The temperature to which the first nitrogen-oxygen separation column 21a is heated is preferably 300 to 500°C, more preferably 300 to 400°C, and even more preferably 320 to 360°C.

[0054] (Equal pressure process) An example of the pressure equalization step is a step of introducing pressurized gas in the second nitrogen and oxygen separation tower 21b, in which the nitrogen recovery step has been completed, into the first nitrogen and oxygen separation tower 21a, in which the oxygen recovery step has been completed. Specifically, the first nitrogen-oxygen separation tower 21a is depressurized by vacuum pump 52, and at least a portion of the nitrogen-enriched gas obtained from the second nitrogen-oxygen separation tower 21b after the nitrogen recovery step is introduced into the first nitrogen-oxygen separation tower 21a, which is now in a depressurized state, via gas flow path L26, which is an equalization line, to perform a pressure equalization and depressurization step (valve V20 closed, valve V24 open, valve V25 open, valve V26 closed). While the first nitrogen-oxygen separation tower 21a is performing the pressure equalization and pressurization step, the second nitrogen-oxygen separation tower 21b is performing the pressure equalization and depressurization step.

[0055] After carrying out the pressure equalization process of the first nitrogen-oxygen separation tower 21a, purified air can be introduced into the first nitrogen-oxygen separation tower 21a via gas flow path L21, and the nitrogen recovery process of the first nitrogen-oxygen separation tower 21a can be started (valve V22 open, valve V23 closed, valve V20 closed, valve V24 closed, valve V25 closed, valve V26 closed, valve V28 open, valve V29 closed).

[0056] The operations of the nitrogen recovery process (adsorption process), pressure equalization decompression process, oxygen recovery process (desorption process), and pressure equalization pressurization process described above are repeated alternately in the first nitrogen-oxygen separation tower 21a and the second nitrogen-oxygen separation tower 21b, thereby continuously producing oxygen-enriched gas.

[0057] <Action and effect> In conventional methods for producing oxygen-enriched gas, when a pressure equalization step is performed after a nitrogen recovery step for the purpose of reducing running costs, the pressure equalization recovery rate has not been particularly considered, and it has naturally been performed so that it is 100%. A pressure equalization recovery rate of 100% poses a problem in that oxygen is desorbed from the adsorbent during the pressure equalization step, reducing the amount of oxygen-enriched gas. In contrast, as explained in this embodiment, by setting the pressure equalization recovery rate within the range of more than 0% to 30%, most of the oxygen-enriched gas remaining after the nitrogen recovery step in the first nitrogen-oxygen separation tower can be recovered in the subsequent oxygen recovery step, thereby efficiently increasing the amount of oxygen-enriched gas generated while suppressing a decrease in oxygen concentration. [Example]

[0058] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the examples described below, and various modifications are possible without departing from the gist of the present invention.

[0059] [Examples and Comparative Examples] Using the oxygen production apparatus 1 of FIG. 1, continuous operation was carried out for 8 hours at a temperature of 25° C. under atmospheric pressure under the following operating conditions. (1) Raw material gas Air was used. The amount of air introduced into the air purification process was 1 L / min. (2) TSA device The adsorption tower was configured as follows: Alumina, which removes water from the raw air supplied from the compressor 51, is packed as an adsorbent in the lower part, and zeolite, which removes carbon dioxide, is packed as an adsorbent in the upper part. Adsorbent regeneration temperature: 150 to 200°C. Regeneration gas introduction ratio: 20 to 50% of the gas at the outlet of the TSA device 10 was used as regeneration gas. Cycle time setting: 120 to 240 minutes. (3)PSA device The nitrogen and oxygen separation column had the following configuration: Oxygen-selective adsorbent: A metal oxide with oxygen non-stoichiometry and the following perovskite structure was used. This metal oxide (YBaCoO 7+δ (1.0≦δ≦1.5)) has a perovskite structure and was synthesized by the method disclosed in JP 2020-203816 A. Heating temperature of oxygen-selective adsorbent: 340°C. Pressure in the nitrogen / oxygen separation column: 120 kPaA during adsorption, 10-25 kPaA during desorption Nitrogen recovery process time: 27 seconds Time for pressure equalization / decompression process and pressure equalization / pressure process: Over 0 seconds to 3 seconds each Total adsorbent volume in all adsorption towers: 80.3 cm 3 Oxygen recovery process time: 27 seconds Switching time: 30 seconds

[0060] The pressure equalization recovery rate was varied in the range of 0 to 90% by adjusting the time for the pressure equalization decompression step and the pressure equalization pressurization step and by changing the piping diameter of the pressure equalization line. The results are shown in Figures 2 to 4. 2 refers to the oxygen-enriched gas generation rate ratio, which is the flow rate of oxygen-enriched gas generated per weight of perovskite-type oxide packed in the first nitrogen-oxygen separation tower 21a and the second nitrogen-oxygen separation tower 21b, and represents the ratio when the highest value of the oxygen gas flow rate obtained when the pressure-equalized recovery rate is changed is set to 1. Here, the ratio was measured using an integrating flow meter attached to the gas flow path L31. 3 refers to the volumetric ratio of oxygen gas recovered from the perovskite oxide in the first nitrogen-oxygen separation tower 21a and the second nitrogen-oxygen separation tower 21b by drawing a vacuum with the vacuum pump 52 to the oxygen gas contained in the purified air introduced into the first nitrogen-oxygen separation tower 21a and the second nitrogen-oxygen separation tower 21b, and represents a ratio where the highest ratio obtained when the pressure-equalized recovery rate is changed is set to 1. Here, the ratio was measured using an integrating flow meter attached to the gas flow path L31. 4 indicates the ratio of the highest oxygen concentration in the product gas recovered in the product oxygen tank 31 when the pressure equalization recovery rate is changed, with the highest value set as 1. Here, the oxygen concentration was measured using a zirconia oxygen concentration meter (LC750 manufactured by Toray Engineering D Solutions Co., Ltd.) attached to the gas flow path L31.

[0061] When the pressure equalization frequency was changed from 0 to 90% by adjusting the time of the pressure equalization decompression process and pressure equalization pressurization process and by changing the piping diameter of the pressure equalization line, almost no change was observed in the oxygen recovery rate ratio (Figure 3). On the other hand, the amount of oxygen-enriched gas generated decreased when the equalized pressure recovery rate exceeded 30%, as shown in Figure 2, and the oxygen concentration ratio decreased when the equalized pressure recovery rate was 0%, as shown in Figure 4. Therefore, it was found that by setting the equalized pressure recovery rate within the range of over 0% to 30%, it was possible to achieve both an increase in the amount of oxygen-enriched gas generated and an increase in the oxygen concentration in the product oxygen-enriched gas. [Explanation of symbols]

[0062] 1...oxygen production device, 10...TSA device, 11a...first adsorption tower, 11b...second adsorption tower, 12a, 12b...adsorption tower body, 13a, 13b...water / carbon dioxide adsorbent, 20...PSA device, 21a...first nitrogen / oxygen separation tower, 21b...second nitrogen / oxygen separation tower, 22a, 22b...adsorption tower body, 23a, 23b...oxygen-selective adsorbent, 24a, 24b...separation tower heater, 31...product oxygen tank, 32...nitrogen-enriched gas tank, 51...compressor, 52...vacuum pump, 53...refrigerator, 54...heater L10, L11, L12, L13, L14, L15, L16, L17, L18, L19, L20, L21, L22, L23, L24, L25, L26, L27, L28, L29, L30, L31, L32...Gas flow path, V10, V11, V12, V13, V14, V15, V16, V17, V18, V19, V20, V21, V22, V23, V24, V25, V26, V27, V28, V29...Valve, AIR...Source air, O2...Oxygen-enriched gas, N2...Nitrogen-enriched gas

Claims

1. a first nitrogen recovery step of introducing pressurized air into a first nitrogen / oxygen separation tower among a plurality of nitrogen / oxygen separation towers filled with an oxygen-selective adsorbent that selectively adsorbs and desorbs oxygen, and recovering nitrogen-enriched gas discharged from the first nitrogen / oxygen separation tower by adsorbing oxygen contained in the air onto the oxygen-selective adsorbent heated to a predetermined temperature; a pressure equalization and depressurization step of introducing the pressurized gas remaining in the first nitrogen and oxygen separation tower after the nitrogen recovery step into a second nitrogen and oxygen separation tower; an oxygen recovery step of introducing a portion of the nitrogen-enriched gas recovered in the nitrogen recovery step into the first nitrogen-oxygen separation tower while reducing the pressure inside the first nitrogen-oxygen separation tower, and recovering the oxygen-enriched gas discharged from the first nitrogen-oxygen separation tower by desorbing the oxygen adsorbed by the oxygen-selective adsorbent; a second nitrogen recovery step of introducing pressurized air into a second nitrogen / oxygen separation tower among the plurality of nitrogen / oxygen separation towers, and adsorbing oxygen contained in the air onto the oxygen-selective adsorbent heated to a predetermined temperature, thereby recovering nitrogen-enriched gas discharged from the second nitrogen / oxygen separation tower; a pressure equalization step of introducing the pressurized gas remaining in the second nitrogen and oxygen separation tower after the second nitrogen recovery step into the first nitrogen and oxygen separation tower after the oxygen recovery step; Including, A method for producing an oxygen-enriched gas, in which the nitrogen-enriched gas and the oxygen-enriched gas are continuously recovered while sequentially switching between the nitrogen recovery step, the pressure equalization depressurization step, the oxygen recovery step, and the pressure equalization pressurization step using the plurality of nitrogen-oxygen separation towers, The oxygen-selective adsorbent has oxygen non-stoichiometry, and YBaCo ４ O ７＋δ (1.0≦δ≦1.5)、 Ca ２ AllMnO ５＋δ (0≦δ≦0.5), No Ｘ No （１－Ｘ） Yes ３－δ (0.1≦σ≦0.5,0.2≦X≦1), L Ｘ Sr （１－Ｘ） Yes ３－δ (0.1≦σ≦ 0.5, 0.2≦X≦1), Ba ４ CaFe ３ O ９＋δ (0.1≦δ≦0.5), and YB ２ Cổ ３ O ７－δ (0≦δ≦1.0) Using any one or more perovskite oxides selected from the group P １ : Pressure inside the first nitrogen and oxygen separation column at the end of the first nitrogen recovery step P ２ : Pressure inside the first nitrogen and oxygen separation column at the end of the oxygen recovery step P ３ : the pressure inside the first nitrogen and oxygen separation column at the end of the pressure equalization and depressurization step When the pressure equalization recovery rate is expressed by the following formula, [Equation 1] The pressure equalization recovery rate is more than 0% to 30% or less. A method for producing oxygen-enriched gas.

2. 2. The method for producing an oxygen-enriched gas according to claim 1, further comprising an air purification step of removing moisture and carbon dioxide from the air as a pretreatment of the air.

3. 3. The method for producing an oxygen-enriched gas according to claim 2, wherein the hourly processing amount of the air used in the first nitrogen recovery step is 600 to 1000 times the packed volume of the oxygen-selective adsorbent.

4. 4. The method for producing an oxygen-enriched gas according to claim 3, wherein after the first nitrogen recovery step is completed, the pressure equalization step and the oxygen recovery step are completed, and the switching time until switching to the first nitrogen recovery step of the next cycle is 40 seconds or less.

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