JP6286237B2 - Pretreatment device and pretreatment method for air separation device - Google Patents

Description

  The present invention relates to a pretreatment device that supplies a raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and more particularly to a technique for accurately predicting the use limit of an adsorption tower.

Conventionally, oxygen and nitrogen are produced by using a cryogenic air separation device. The air separator cools and liquefies air, and separates oxygen and nitrogen by distillation using a difference in boiling points. Since air contains gases such as moisture (hereinafter referred to as “H ₂ O”) and carbon dioxide (hereinafter referred to as “CO ₂ ”) that solidify at low temperature, these are supplied before the air is supplied to the air separation device. If these are not removed, there arises a problem that they are solidified in the heat exchanger and the flow path is blocked. Therefore, a pre-treatment device that mainly removes H ₂ O and CO ₂ from the air and supplies the air to the air separation device is provided in the front stage of the air separation device.

As the pretreatment apparatus, a type in which mainly H ₂ O and CO ₂ are adsorbed by an adsorbent is widely used. For example, Patent Literature 1 includes an air liquefaction separation apparatus that includes a plurality of adsorption towers that are filled with an adsorbent that adsorbs and removes H ₂ O, CO _{2, and the} like from raw air and continuously purifies the raw air. A pre-processing method is disclosed.

  Referring to paragraph 0069 of Patent Document 1, an economically effective condition is found by optimizing an adsorption tower filled with a water adsorbent such as activated alumina and a carbon dioxide adsorbent such as X-type zeolite. In addition, it is described that the design of a pretreatment device under high-temperature air conditions has become possible.

  The used adsorption tower is regenerated by desorbing the adsorbed material using a high-temperature purge gas, and is used repeatedly.

The conventional pretreatment apparatus is designed on the assumption that the air containing 400 to 600 ppm of CO ₂ is used as a raw material, and the concentration of CO ₂ does not fluctuate outside this range. From the quantity, the timing for switching between adsorption and regeneration of the adsorption tower is obtained by a prior calculation. In addition to CO _2, the air contains about 0.35 ppm of moisture and slight nitrous oxide (hereinafter referred to as “N ₂ O”).

JP-A-9-38446

  In the conventional pretreatment equipment, the adsorption tower design is calculated using the upper limit value in the assumed range so that it can withstand the worst case assumed. Multiply safety factor. Therefore, in most cases, the adsorption tower is switched in a state where the adsorption capacity remains sufficiently in the adsorption tower. Even if the adsorbent has sufficient adsorption capacity, the same amount of heat is applied during regeneration as in the regeneration of the adsorption tower that has been adsorbed until saturation. Yes.

On the other hand, close to or the same site, steel, in the case that there is equipment to release a large amount of CO _2, such as chemical and power plants, such as CO ₂ in the air greatly exceeds the design value by wind, e.g. Since things exceeding 1000 ppm may occur, the conventional pretreatment apparatus cannot cope with the above.

The present invention has been made in view of the conventional problems as described above, and the adsorbent is effectively used so as not to switch between adsorption and regeneration in a state where the adsorption capacity remains sufficiently in the adsorption tower. It is an object of the present invention to provide a pretreatment device that can be used to suppress excessive consumption of regenerative energy and can cope with a case where CO _{2 in} the air greatly exceeds the design value.

The present invention is a pretreatment device that supplies a raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and passes H ₂ O, CO ₂ and N in the air through the air. At least two and an adsorption tower for removing _{2 O,} and a N _{2 O} sensor for measuring the concentration of N _{2 O} in the gas which has passed through one of the adsorption tower, measured by the N _{2 O} sensor N _The adsorption tower is switched when the concentration of ₂ O reaches a specified value.

The present invention is a pretreatment device that supplies a raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and passes H ₂ O, CO ₂ and N in the air through the air. At least two and an adsorption tower for removing _{2 O,} and a CO ₂ sensor for measuring the concentration of CO ₂ in the gas taken out from the adsorbent in the adsorption tower, measured by the CO ₂ sensor CO _When the concentration of ₂ reaches a specified value, the adsorption tower is switched.

The present invention is a pretreatment device that supplies a raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and passes H ₂ O, CO ₂ and N in the air through the air. ₂ at least two adsorption towers for removing ₂ O, and a temperature sensor for measuring two or more temperatures at intervals in the air flow direction in the adsorption tower. The adsorption tower is switched when the temperature difference at a location reaches a specified value.

The present invention relates to a pretreatment method in a pretreatment device for supplying a raw material gas to an air separation device for separating oxygen and nitrogen from the raw material gas, and the air passes through one of at least two adsorption towers. Removing the H ₂ O, CO ₂ and N ₂ O in the air, measuring the concentration of N ₂ O in the gas passed through one of the adsorption towers, and measuring the measured And a step of switching the adsorption tower when the concentration of N ₂ O reaches a specified value.

The present invention relates to a pretreatment method in a pretreatment device for supplying a raw material gas to an air separation device for separating oxygen and nitrogen from the raw material gas, and the air passes through one of at least two adsorption towers. Removing the H ₂ O, CO ₂ and N ₂ O in the air, measuring the concentration of CO _{2 in} the gas taken out from the adsorbent in the adsorption tower, and the CO _And a step of switching the adsorption tower when the concentration of CO ₂ measured by the step of measuring the concentration of ₂ reaches a specified value.

The present invention relates to a pretreatment method in a pretreatment device for supplying a raw material gas to an air separation device for separating oxygen and nitrogen from the raw material gas, and the air passes through one of at least two adsorption towers. And removing H ₂ O, CO ₂ and N ₂ O in the air, measuring the temperature at two or more locations in the adsorption tower at intervals in the air flow direction, And a step of switching the adsorption tower when the measured temperature difference at two or more locations reaches a specified value.

In the pretreatment apparatus and the pretreatment method of the present invention, when the concentration of N ₂ O in the gas that has passed through the adsorption tower reaches a specified value, the CO _{2 in} the gas taken out from the adsorbent in the adsorption tower. When the concentration reaches a specified value, or when the temperature difference between two or more locations in the adsorption tower reaches a specified value, the adsorption tower can be switched.

Thereby, the use limit of the adsorption tower can be accurately predicted, and the adsorption tower can be switched shortly before the use limit of the adsorption tower is exceeded. Therefore, it is possible to effectively use the adsorbent, to suppress the consumption of extra regeneration energy, and to cope with the case where the concentration of CO _{2 in} the air greatly exceeds the design value.

It is a functional block diagram which shows the outline of the cryogenic separation process containing the pre-processing apparatus which concerns on Embodiment 1 of this invention. It is the schematic which shows the detailed structure of the pre-processing apparatus which concerns on Embodiment 1 of this invention. It is a functional block diagram which shows the outline of the cryogenic separation process containing the pre-processing apparatus which concerns on Embodiment 2 of this invention. It is the schematic which shows the detailed structure of the pre-processing apparatus which concerns on Embodiment 2 of this invention. It is a functional block diagram which shows the outline of the cryogenic separation process containing the pre-processing apparatus which concerns on Embodiment 3 of this invention. It is the schematic which shows the detailed structure of the pre-processing apparatus which concerns on Embodiment 3 of this invention. It is a conceptual diagram which shows the adsorption | suction model in use. It is a conceptual diagram which shows the adsorption | suction model at the time of completion | finish of use.

  Hereinafter, the present invention will be described in more detail by way of embodiments of the present invention.However, the present invention is not limited by the following embodiments of the present invention, and appropriate modifications are made within a range that can be adapted to the purpose described above and below. In addition, it is of course possible to carry out them, all of which are included in the technical scope of the present invention.

<Embodiment 1>
The pretreatment device according to Embodiment 1 of the present invention is a pretreatment device that supplies the raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and passes the air through the air. Comprising at least two adsorption towers for removing H ₂ O, CO ₂ and N ₂ O of the gas, and an N ₂ O sensor for measuring the concentration of N ₂ O in the gas passing through one of the adsorption towers, The adsorption tower is switched when the concentration of N ₂ O measured by the N ₂ O sensor reaches a specified value.

A pretreatment method according to Embodiment 1 of the present invention is a pretreatment method in a pretreatment apparatus that supplies a raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and includes at least two adsorption towers Passing air through one of them to remove H ₂ O, CO ₂ and N ₂ O in the air, and determining the concentration of N ₂ O in the gas that has passed through one of the adsorption towers. And a step of switching the adsorption tower when the measured concentration of N ₂ O reaches a specified value.

  FIG. 1 is a functional block diagram showing an outline of a cryogenic separation process including a pretreatment apparatus according to Embodiment 1 of the present invention. The cryogenic separation process shown in FIG. 1 includes an air compressor 1, a pretreatment device 2, an air separation device 3, and a control device A (not shown).

  The air compressor 1 takes in outside air, compresses it, cools it with water, and supplies compressed air whose pressure is adjusted to about 0.5 MPaG to the pretreatment device 2.

The pretreatment device 2 is a raw material obtained by removing at least H ₂ O, CO ₂ and N ₂ O from compressed air supplied from the air compressor 1 using an adsorbent such as activated alumina or X-type zeolite from the inlet side. Gas is generated and the raw material gas is supplied to the air separation device 3.

  The air separation device 3 is a deep-cooling type air separation device, which cools and liquefies the raw material gas supplied from the pretreatment device 2, and distills and separates oxygen and nitrogen using a boiling point difference.

FIG. 2 is a schematic diagram illustrating a detailed configuration of the preprocessing device 2 according to the first embodiment of the present invention. The pretreatment device 2 includes a first adsorption tower 4a, a second adsorption tower 4b, an N ₂ O sensor 5, and a heater 6.

The first adsorption tower 4a has an adsorbent such as activated alumina and X-type zeolite for removing H ₂ O, CO ₂ and N ₂ O. The 2nd adsorption tower 4b is the same composition as the 1st adsorption tower 4a, and has the same function as the 1st adsorption tower 4a.

  The second adsorption tower 4b is regenerated while the first adsorption tower 4a is used, and the first adsorption tower 4a is regenerated while the second adsorption tower 4b is used. Therefore, the adsorption tower is continuously switched and used. Driving is possible.

  When the controller A determines that the use limit of the adsorption tower is near while the first adsorption tower 4a is in use, the controller is switched to the second adsorption tower 4b. Similarly, when the controller A determines that the use limit of the adsorption tower is near while the second adsorption tower 4b is in use, the second adsorption tower 4b is switched to the first adsorption tower 4a.

  The first adsorption tower 4a and the second adsorption tower 4b are alternately used, and while one is being used, the other is heated and regenerated by the heater 6 and then cooled while waiting. Specifically, before the supply of compressed air to the first adsorption tower 4a is stopped, the supply of compressed air to the second adsorption tower 4b is started and before the supply of compressed air to the second adsorption tower 4b is stopped. In addition, by starting the supply of compressed air to the first adsorption tower 4a, continuous supply of the raw material gas to the air separation device 3 is enabled.

  Further, the adsorbent in the first adsorption tower 4a is regenerated during the supply of compressed air to the second adsorption tower 4b, and the adsorbent in the second adsorption tower 4b is supplied during the supply of compressed air to the first adsorption tower 4a. Play. Note that at least two adsorption towers are required, and three or more adsorption towers can be switched and used.

The N ₂ O sensor 5 measures the concentration of N ₂ O in the gas after passing through the first adsorption tower 4a and the second adsorption tower 4b. Since N ₂ O has a weaker binding force with the adsorbent than CO ₂ , the CO ₂ after a certain time has passed since the N ₂ O sensor 5 detects that the concentration of N ₂ O in the gas that has passed through the adsorption tower has increased. The concentration of ₂ increases. Thus, by measuring the concentration of N 2 _O, to switch the adsorption tower at an appropriate timing before predicting in advance the CO ₂ concentration increase in the adsorption tower outlet, the concentration of CO ₂ in the raw material gas begins to rise Is possible.

The controller A continuously determines whether or not the concentration of N ₂ O measured by the N ₂ O sensor 5 has reached a specified value. When the concentration of N ₂ O measured by the N ₂ O sensor 5 reaches a specified value, the control device A determines that the use limit of the adsorption tower is near, and another adsorption is performed to switch the adsorption tower. Start supplying compressed air to the tower. Note that even if N ₂ O is slightly detected in the raw material gas, the air separation device 3 is not adversely affected. It is preferable to switch the adsorption tower when the concentration of N ₂ O reaches about 0.1 ppm.

  The heater 6 heats the exhaust gas of the air separation device 3 and regenerates the used adsorption tower at a high temperature using this. After a certain period of time, the adsorbent regenerated at high temperature is put on standby with the exhaust gas bypassing the heater 6. In FIG. 2, the exhaust gas path of the air separation device 3 is indicated by a dotted line.

<Embodiment 2>
A pretreatment device according to Embodiment 2 of the present invention is a pretreatment device that supplies a raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and passes the air through the air. Comprising at least two adsorption towers for removing H ₂ O, CO ₂ and N ₂ O of the gas, and a CO ₂ sensor for measuring the concentration of CO _{2 in} the gas taken out from the adsorbent in the adsorption tower, The adsorption tower is switched when the concentration of CO ₂ measured by the CO ₂ sensor reaches a specified value.

A pretreatment method according to Embodiment 2 of the present invention is a pretreatment method in a pretreatment apparatus that supplies a raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and includes at least two adsorption towers Air is passed through one of them to remove H ₂ O, CO ₂ and N ₂ O in the air, and CO _{2 in} the gas taken out from the adsorbent in the adsorption tower. A step of measuring the concentration, and a step of switching the adsorption tower when the measured concentration of CO ₂ reaches a specified value.

  FIG. 3 is a functional block diagram showing an outline of a cryogenic separation process including a pretreatment apparatus according to Embodiment 2 of the present invention. The cryogenic separation process shown in FIG. 3 includes an air compressor 1, a pretreatment device 10, an air separation device 3, and a control device B (not shown). In addition, the same number is attached | subjected to the structure similar to Embodiment 1, and the description is abbreviate | omitted.

Similarly to the pretreatment device 2 of the first embodiment, the pretreatment device 10 uses at least H ₂ from compressed air supplied from the air compressor 1 using an adsorbent such as activated alumina and X-type zeolite from the inlet side. A raw material gas from which O, CO ₂ and N ₂ O are removed is generated, and the raw material gas is supplied to the air separation device 3.

FIG. 4 is a schematic diagram showing a detailed configuration of the preprocessing apparatus 10 according to the second embodiment of the present invention. The pretreatment device 10 includes a first adsorption tower 4 a, a second adsorption tower 4 b, a CO ₂ sensor 11 and a heater 6.

The CO ₂ sensor 11 measures the concentration of CO _{2 in} the gas taken out from the adsorbent in the first adsorption tower 4a and the second adsorption tower 4b. If the CO ₂ sensor 11 measures the concentration of CO ₂ in the gas of the adsorption tower outlet, when the concentration of CO ₂ detects that it has increased the concentration of CO ₂ in the feed gas is started to rise, The air separation device 3 is adversely affected. On the other hand, when the CO ₂ sensor 11 measures the concentration of CO _{2 in} the gas taken out from the adsorbent in the adsorption tower, the adsorption is performed after a certain period of time after the concentration of CO _{2 in} the raw material gas increases. The concentration of CO _{2 in} the gas at the tower outlet increases. Thus, by measuring the concentration of CO ₂ in the gas taken out from the adsorbent in the adsorption tower, the adsorption tower outlet of the CO ₂ concentration increases in the gas predicted in advance, the CO ₂ in the feed gas It is possible to switch the adsorption tower at an appropriate timing before the concentration starts to rise.

The control device B continuously determines whether or not the concentration of CO ₂ measured by the CO ₂ sensor 11 has reached a specified value. When the concentration of CO ₂ measured by the CO ₂ sensor 11 reaches a specified value, the control device B determines that the use limit of the adsorption tower is near and compresses the adsorption tower to another adsorption tower to switch the adsorption tower. Start supplying air. In the case where to retrieve the gas is near the adsorption tower outlet, when the concentration of CO ₂ reached about 1 ppm, it is preferable to switch the adsorption column.

<Embodiment 3>
A pretreatment device according to Embodiment 3 of the present invention is a pretreatment device that supplies a raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and passes the air through the air. And at least two adsorption towers for removing H ₂ O, CO ₂ and N ₂ O, and a temperature sensor for measuring two or more temperatures in the adsorption tower at intervals in the air flow direction. The adsorption tower is switched when the difference between two or more temperatures measured by the temperature sensor reaches a specified value. This utilizes the characteristic that when the CO ₂ is adsorbed on the adsorbent, the temperature of the adsorbent rises due to the heat of adsorption. A temperature sensor closer to the outlet side (hereinafter referred to as “outlet side temperature sensor”) When the temperature rises compared to the temperature sensor closer to the inlet side (hereinafter referred to as the “inlet side temperature sensor”), CO ₂ is between the inlet side temperature sensor installation position and the outlet side temperature sensor installation position. It has been moved to.

A pretreatment method according to Embodiment 3 of the present invention is a pretreatment method in a pretreatment apparatus that supplies a raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, and includes at least two adsorption towers Passing air through one of them to remove H ₂ O, CO ₂ and N ₂ O in the air, and in the adsorbing tower, spaced in the direction of the air flow, at two locations A step of measuring the above temperature, and a step of switching the adsorption tower when a difference between the measured temperatures at two or more locations reaches a specified value.

  FIG. 5 is a functional block diagram showing an outline of a cryogenic separation process including a pretreatment apparatus according to Embodiment 3 of the present invention. The cryogenic separation process shown in FIG. 5 includes an air compressor 1, a pretreatment device 20, an air separation device 3, and a control device C (not shown). In addition, the same number is attached | subjected to the structure similar to Embodiment 1, and the description is abbreviate | omitted.

Similar to the pretreatment device 2 of the first embodiment, the pretreatment device 20 uses at least H ₂ from compressed air supplied from the air compressor 1 using an adsorbent such as activated alumina and X-type zeolite from the inlet side. The raw material gas from which O, CO ₂ and N ₂ O have been removed is supplied to the air separation device 3.

FIG. 6 is a schematic diagram showing a detailed configuration of the preprocessing apparatus 20 according to the third embodiment of the present invention. The pretreatment device 20 includes a first adsorption tower 4a, a second adsorption tower 4b, a temperature sensor 21, and a heater 6.
The temperature sensor 21 measures two or more temperatures at intervals in the air flow direction in the adsorption tower. For example, the temperature sensor 21 includes a first temperature sensor 21a and a second temperature sensor 21b.

  The control device C continuously determines whether or not the difference between two or more temperatures measured by the temperature sensor 21 has reached a specified value. When the temperature difference between two or more locations reaches a specified value, the control device C determines that the use limit of the adsorption tower is near and supplies compressed air to another adsorption tower to switch the adsorption tower. Start.

<Description of the principle for determining that the use limit of the adsorption tower is near>
FIG. 7 is a conceptual diagram showing an adsorption model in use. FIG. 8 is a conceptual diagram showing an adsorption model at the end of use. The adsorption model shown in FIGS. 7 and 8 shows a state in which H ₂ O, CO ₂ and N ₂ O are adsorbed on the adsorbent bed. Here, the adsorbent bed refers to a mass of adsorbent packed in the first adsorption tower 4a and the second adsorption tower 4b. The “bed length” described in FIGS. 7 and 8 refers to the length of the adsorbent bed in the air flow direction.

H ₂ O has the strongest binding force with the adsorbent when adsorbed on the adsorbent bed, and the binding strength with the adsorbent becomes weaker in the order of CO _{2 and} N ₂ O. Therefore, when shifting from the state of FIG. 7 to the state of FIG. 8, first, H ₂ O in the flowing air is adsorbed by expelling the already adsorbed CO ₂ . Next, the expelled CO ₂ and the flowing CO ₂ are adsorbed by expelling the already adsorbed N ₂ O. Next, the expelled N ₂ O and the flowing N ₂ O are adsorbed in a region where nothing is adsorbed.

In the adsorption model, the adsorbent bed in the direction of air flow, for each adsorbate, a saturated zone where the adsorbent is saturated, and a mass transfer zone that adsorbs the adsorbate but remains adsorbed , The adsorbate can be divided into unused zones that do not adsorb at all. Specifically, paying attention to N ₂ O, in FIG. 7, the adsorbent bed can be divided into a saturation zone A1, a mass transfer zone A2, and an unused zone A3. In FIG. Can be divided into a saturation zone A4 and a mass transfer zone A5, and there is no unused zone. Further, focusing attention on CO ₂ , in FIG. 7, the adsorbent bed can be divided into a saturation zone B1, a mass transfer zone B2, and an unused zone B3. In FIG. It can be divided into a mass transfer zone B5 and an unused zone B6. Therefore, as the adsorption time advances, the saturation zone, the mass transfer zone, and the unused zone move to the outlet side, and the unused zone decreases and the saturation zone increases.

Here, by measuring the concentration of N ₂ O, it can be determined that the use limit of the adsorption tower is near.
N ₂ O is usually contained in the air in an amount of about 0.35 ppm, and if it is about 0.1 ppm, there is no problem in the operation of the air separation device. The adsorbent bed shown in FIG. 8 shows that the N ₂ O transfer zone moved to the outlet side and decreased, and the N ₂ O concentration in the gas at the outlet of the adsorption tower increased to about 0.1 ppm. Show. If it is used for a while, the CO ₂ unused zone does not exist, and the concentration of CO ₂ in the gas that has passed through the adsorption tower starts to rise.

As described above, since N ₂ O has a weaker binding force with the adsorbent than CO ₂ , there is an unused zone of CO ₂ by measuring the concentration of N ₂ O in the gas that has passed through the adsorption tower. It is possible to accurately predict the timing at which the CO ₂ concentration starts to increase. Therefore, the supply of air to the adsorption tower can be stopped before the CO ₂ concentration starts to increase.

On the other hand, instead of measuring the concentration of N ₂ O, it is possible to determine that the use limit of the adsorption tower is near by directly measuring the concentration of CO ₂ . CO ₂ is usually contained in the air in an amount of about 400 to 600 ppm, and if it is not removed to about 1 ppm, there is a possibility that a problem occurs in the air separation device.

By directly measuring the concentration of CO _{2 in} the gas taken out from the adsorbent, it is possible to predict the movement of the CO ₂ transfer zone in advance and switch the adsorption tower at an appropriate timing.

On the other hand, it is also possible to determine that the use limit of the adsorption tower is near by measuring the temperature at two or more locations with an interval in the air flow direction in the adsorption tower. When the adsorption tower adsorbs molecules, heat of adsorption is generated. Therefore, since a temperature difference occurs between the mass transfer zone and the unused zone, CO ₂ is measured by measuring two or more temperatures in the air flow direction and comparing the temperature difference or analyzing the temperature distribution. It is possible to accurately predict the timing at which the concentration of water starts to rise. Therefore, it is possible to predict the CO ₂ concentration increase in the gas at the outlet of the adsorption tower in advance and switch the adsorption tower at an appropriate timing.

As described above, in the pretreatment apparatuses 2, 10, and 20 according to the present invention, the use limit of the adsorption tower can be accurately predicted, and the adsorption tower can be switched at an appropriate timing. Therefore, it is possible to effectively use the adsorbent, to suppress the consumption of extra regeneration energy, and to cope with the case where the concentration of CO _{2 in} the air greatly exceeds the design value.

1 air compressor 2 preprocessing device 3 the air separation unit 4a first adsorption tower 4b second adsorption tower 5 N ₂ O sensor 6 heater 10 pre-processor 11 CO ₂ sensor 20 pretreatment unit 21 temperature sensor 21a first temperature sensor 21b Second temperature sensor

Claims (2)

A pretreatment device for supplying the raw material gas to an air separation device for separating oxygen and nitrogen from the raw material gas,
At least two adsorption towers through which air is passed to remove H ₂ O, CO ₂ and N ₂ O in the air;
An N ₂ O sensor that measures the concentration of N ₂ O in the gas that has passed through one of the adsorption towers;
The adsorption tower includes an adsorbent having a binding force with N ₂ O lower than that with CO ₂ ,
A pretreatment apparatus that switches the adsorption tower when the concentration of N ₂ O measured by the N ₂ O sensor reaches a specified value. A pretreatment method in a pretreatment device for supplying the raw material gas to an air separation device for separating oxygen and nitrogen from the raw material gas,
Passing air through one of the at least two adsorption towers to remove H ₂ O, CO ₂ and N ₂ O in the air;
Measuring the concentration of N ₂ O in the gas that has passed through one of the adsorption towers;
Switching the adsorption tower when the measured concentration of N ₂ O reaches a specified value ,
In the adsorption tower, an adsorbent having a binding force with N ₂ O lower than that with CO ₂ is used .

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