JPH0768042B2 - High-purity oxygen production method - Google Patents

Description

The present invention relates to a method for obtaining high-purity oxygen by using an adsorbent from a mixed gas containing oxygen and nitrogen as main components such as air.

[Conventional technology]

Oxygen and nitrogen adsorption separation method from air using nitrogen adsorbent has the advantages that the equipment is small and simple and requires almost no maintenance, which is similar to unmanned operation.
In recent years, the number of uses has increased as small and medium-sized devices of the order of m ³ −O ₂ / h, and replacement of the case of transporting and using liquid acid produced by a cryogenic separation device is in progress.

To give a brief description of a typical example of this apparatus, the apparatus is composed of an air compressor and two or more nitrogen adsorption columns, and optionally a vacuum pump or the like. In this apparatus, when compressed air is sent to one tower, nitrogen in the air is adsorbed and removed by the nitrogen adsorbent filled, and the remaining high-pressure oxygen flows out behind the adsorption tower and is collected. On the other hand, in the other column, the adsorbed nitrogen is released under reduced pressure (sometimes, a part of the product oxygen is caused to flow countercurrently, or a method of strongly removing nitrogen with a vacuum pump is used) for regeneration. By repeating this alternately, oxygen and nitrogen are continuously separated.

A typical nitrogen adsorbent filled in the adsorption tower is a 60 to 70% Ca exchanger of Na-A type zeolite which has been put into practical use by Union Carbide Co., and is a mixed gas of oxygen and nitrogen. From which nitrogen is selectively adsorbed,
Co-adsorption of oxygen under air conditions is estimated to be less than 10% of nitrogen adsorption.

[Problems to be Solved by the Invention]

The oxygen / nitrogen separation device by this adsorption is said to be advantageous in the small and medium-sized region, but it requires 0.75 to 1 Kwh to produce 1 Nm ³ of oxygen, and 0.39 Kwh of oxygen produced by the large capacity cryogenic separation method.
Power consumption is high compared to. In addition, it is said that there is little scale merit with respect to the increase in equipment capacity, and it cannot compete with the cryogenic separation method in the range of 3,000 Nm ³ -O ₂ / h or more.

Another problem is that argon, which is contained in the air in an amount of 0.9 vol%, behaves as a desorption / adsorption component in the same manner as oxygen with respect to the nitrogen adsorbent, so it is concentrated in product oxygen and the product oxygen concentration is approximately 94 vol% as the upper limit. And gas cutting of metal, oxygen-
It is difficult to apply oxygen for hydrogen combustion and oxidizers of the partial oxidation method for chemical raw materials, etc., and is supplied with liquid oxygen in a small size and high purity oxygen from a cryogenic separation method in a large capacity.

Therefore, various methods for improving these drawbacks are conceivable, but the following obstacles usually appear when the improving method is described in relation to the present invention.

First, in order to reduce the power consumption, it is conceivable to lower the blast pressure and carry out the adsorption operation at a low pressure, but since the nitrogen adsorption amount decreases almost in proportion to the pressure, the capacity of the device greatly increases. Next, in order to increase the adsorption amount, it is possible to carry out the adsorption operation under low temperature conditions. In this case, although the nitrogen adsorption amount increases, the adsorption / desorption rate decreases significantly, so that the same column length The product oxygen concentration is lower than at room temperature. Further, the amount of oxygen co-adsorbed at the time of nitrogen adsorption increases as the temperature decreases, so that the power consumption unit gradually increases.

In addition, when concentrating the product oxygen concentration to 94 vol% or more, first use the oxygen production device that uses the nitrogen adsorbent described above
Oxygen of 94 vol%, 5 vol% of nitrogen and 4.5 vol% of argon is produced, and oxygen is adsorbed by Molecule Sieves Carbon 4A (made by Bergbau Wolfsjung Co., Ltd.) with a window diameter of 3.8 Å that exhibits oxygen selective adsorption at room temperature. It is conceivable to release nitrogen and argon out of the system, but since the unit power consumption of the nitrogen adsorption tower in the previous stage is not so small, the combined use of the oxygen adsorption tower is further increased and 1 Kwh for 1 Nm ³ of oxygen production. Beyond the above, there is no hope of competition with the cryogenic method, and it will be applied to small and medium-sized applications. In addition, there is a limit to the adsorption capacity of the current nitrogen adsorbent and oxygen adsorbent at room temperature, and the maximum oxygen concentration is 98 vol%, which is slightly inferior to 99.5 vol% of the cryogenic separation method. Further, since both the nitrogen adsorption tower and the oxygen adsorption tower are operated at room temperature, the amount of the adsorbent used is large and the economy is rapidly lost due to scale up.

[Means for Solving the Problems]

Therefore, the inventors of the present invention have diligently studied a high-performance oxygen / nitrogen separation method under low-temperature and low-pressure adsorption conditions in which the above-mentioned drawbacks have been improved, and in the process of conducting experiments, weak nitrogen at room temperature with a window diameter of 4.1 to 4.5Å. It has been found that the molecular sieves carbon having selectivity exhibits oxygen selective adsorption at a low temperature, and the present invention has been completed based on the finding.

That is, the present invention has a window diameter of 4.1 to 4.5Å and shows weak nitrogen selective adsorption at room temperature, but shows oxygen selective adsorption at low temperature, but at least two adsorption columns filled with molecular sieves carbon showing oxygen selective adsorption at low temperature , A mixed gas of nitrogen and argon as a main component such as air at a temperature of 25 ° C or less and atmospheric pressure or more
The oxygen contained in the mixed gas is selectively adsorbed by flowing into the adsorption tower at 3 atm or less, and the nitrogen and the argon are released to the outside of the system, while the adsorption tower adsorbing oxygen has 0.08 atm or more 0.5
After decompressing to less than atm to recover oxygen-enriched air that does not contain argon, the recovered oxygen-enriched air is adsorbed in at least two or more towers packed with sodium fuadhasite represented by Na-X. It is introduced into the column, and at a temperature of 25 ° C or less, from the mixed gas containing oxygen and nitrogen as main components, the atmospheric pressure or more and 3 atm or more.
In the following, nitrogen is adsorbed and high-purity oxygen is allowed to flow out from the adsorption tower outlet, while an adsorption tower having adsorbed nitrogen is 0.08 atm or more.
It is a method for producing high-purity oxygen, which is characterized in that the pressure is reduced to 0.5 atm or less for regeneration.

That is, the present invention is a method for producing high-purity oxygen that uses an adsorbent that exhibits oxygen selective adsorption at a low temperature and a nitrogen selective adsorption adsorbent in combination, and that consumes less amount of adsorbent and consumes less power.

[Action]

The low-temperature oxygen-selective adsorptive adsorbent packed in the first-stage adsorption tower collected oxygen-enriched air containing almost no argon, which was then packed in the second-stage adsorption tower. Because the agent separates nitrogen to obtain oxygen,
High purity oxygen of 99.9vol% can be obtained.

The molecular sieves carbon is an activated carbon-like three-dimensional crosslinked product obtained by heat-treating a polystyrene granulated product at a temperature of 300 to 700 ° C in a nitrogen atmosphere to cause hydrogen desorption and styrene condensation. It is a structure. Cross-linked structure is 3
It has a uniform window of Å or more, and does not adsorb molecules larger than the window diameter, but has the effect of adsorbing molecules smaller than the window diameter. If the heat treatment time is kept long, the window diameter tends to shrink. The molecular sieves carbon having oxygen selectivity at a low temperature with a window diameter of 4.1 to 4.5Å used in the present invention can be obtained by heat-treating a polystyrene granulated product at 650 ° C for 3 hours in a nitrogen atmosphere.

Hereinafter, the method of the present invention will be described in detail with reference to Examples.

〔Example〕

In order to demonstrate the effectiveness of the present invention, in the air separation apparatus shown in FIG. 1, an oxygen selective adsorption adsorbent having a window diameter of 4.1 to 4.5Å, a molecular sieves carbon, and a nitrogen selective adsorption adsorbent, Na-X. Attempts were made to separate high-purity oxygen from air by using sodium phosphinasite.

Hereinafter, the contents implemented based on FIG. 1 will be described.

The air pressurized to 1.05 to 3ata by the compressor 2 through the inlet side line 1 enters the dehumidifying and CO ₂ removing column 4 from the flow path 3a and becomes extremely clean pressurized air. The valve 5 installed in the downstream of the flow path 3b is open, and the clean pressurized air enters the adsorption tower 8a through the flow path 6a. Oxygen is adsorbed and removed by the oxygen adsorbent 9a in the pressurized air that has entered the adsorption tower 8a, and the nitrogen concentration increases as it goes backward. After this, the pressurized air is released in the open valve.
Nitrogen and argon are discharged to the outside of the system through line 16 through 7a and 7b.

On the other hand, the adsorption tower 8b is decompressed and pulled by a vacuum pump 13 connected through an open valve 11a and a flow path 12, and oxygen adsorbed on the adsorbent 9b in the adsorption tower 8b and co-adsorbed nitrogen. Is easily desorbed to recover the oxygen-enriched air, and the adsorbent 9b is regenerated in a short time.

When the oxygen adsorbent 9a of the adsorption tower 8a is saturated, while the oxygen and the co-adsorbed nitrogen are separated from the oxygen adsorbent 9b of the adsorption tower 8b and the recovery and regeneration are completed, the inlet air flow path 6a is switched to 6b, By alternately performing the above-mentioned methods, oxygen-enriched air containing no argon can be continuously recovered. In addition, between the flow path 3b of clean pressurized air at the inlet and the flow path 12 mainly composed of desorbed oxygen-enriched air, heat exchangers 15a and 15b are capable of exchanging heat, and a flow-through nitrogen line is provided. Heat exchange between the 16 and the flow path 3b is also possible by heat exchangers 17a and 17b. In addition, the compression type refrigerator 18 is provided in the flow path 3b.
Is installed, the adsorption towers 8a and 8b are extremely efficiently
Are cooled and set to low temperature conditions. In addition, when switching the adsorption tower, not only simply switching from the flow paths 6a to 6b (or vice versa), but also preventing blow-off of the inlet air due to pressurization immediately after switching, and advancing in the front. In order to minimize the release of compressed air to the outside of the system, first, the valves 7a and 10b are fully opened to partially transfer the residual air in the adsorption tower 8a immediately after adsorption to the adsorption tower 8b immediately after regeneration. At this time, the pressure of the adsorption tower 8a is changed to P ₀ (at
m) and the pressure in the adsorption tower 8b is P ₁ (atm), the pressure after equalization is Becomes P ₁ (atm) to P ₀ (at
Compared with the rapid pressure increase to m), P ₁ (atm), Since the pressure is gradually increased to P ₀ (atm), it is possible to take measures to minimize the release of high-pressure air to the outside of the system during the desorption process while preventing blow-through of air during pressure increase.

The oxygen-enriched air obtained in the above steps is adjusted to 1.05 to 3 atm so that the power consumption and the use of the nitrogen adsorbent are minimized, and the oxygen-enriched air thus adjusted is passed through the flow path 19. It enters the adsorption tower 22a through the valve 20 and the flow path 21a in the open state. The oxygen-enriched air that has entered the adsorption tower 22a has its nitrogen concentration adsorbed and removed by the nitrogen adsorbent 23a, and the oxygen concentration increases as it goes backward. After this, the pressurized air is recovered as product oxygen through the valves 24 and 25 in the open state. The adsorption tower 22b is decompressed and pulled by a vacuum pump 30 connected through an open valve 28a and a flow path 29, the nitrogen adsorbed by the adsorbent 23b in the adsorption tower 22b is easily released, and the adsorbent 23b is Play in a short time. When the nitrogen adsorbent 23a of the adsorption tower 22a is saturated, while nitrogen is separated from the nitrogen adsorbent 23b of the adsorption tower 22b and regeneration is completed, the inlet oxygen-enriching passage 21a is switched to the passage 21b. By alternately performing the above methods, product oxygen can be continuously recovered. In addition, between the flow path 19 of the oxygen-enriched air at the inlet and the gas flow path 29 mainly composed of desorbed nitrogen are heat exchangers 31a and 31b,
The heat can be exchanged, and the heat exchange between the product oxygen line 32 and the flow path 19 can also be performed by the heat exchangers 33a and 33b.
Further, since the compression refrigerator 34 is installed in the flow path 19, the adsorption towers 22a and 22b are cooled very efficiently and set to the cold temperature condition. In addition, when switching the adsorption tower, not only simply switching from the flow path 6a to the flow path 6b (or vice versa), but also by rapidly increasing the pressure around the tower after the adsorption step and the tower after the regeneration is completed. In order to prevent the above and to collect residual oxygen in the tower, the pressure equalization between the towers is performed in the same manner as in the oxygen adsorption towers 8a and 8b installed in the preceding stage. Further, both the oxygen adsorption towers 8a, 8b and the nitrogen adsorption towers 22a, 22b are installed in the cold storages 35, 36, and the invasion heat is suppressed to the minimum.

Air separation was performed by the air separation device shown in FIG. 1 by the above operation method. Table 1 shows the operating specifications of the device.

Oxygen and nitrogen were separated from air under the operating conditions shown in Table 1. The results at this time are summarized in FIG. The oxygen concentration of the high-purity oxygen produced in the above example was 99.5 vol% (remaining:
Argon).

FIG. 2 is a graph showing the relationship between the adsorption pressure of the oxygen adsorption tower and the power consumption rate. In FIG. 2, the horizontal axis represents the adsorption pressure P ₀ at.
m, vertical axis is 1 Nm ³ / h and the power consumption (K
W). The graph shows the adsorption pressure of 1.2 atm, the regeneration pressure of 0.2 atm, and the adsorption column temperature of -15 ° C. for the nitrogen adsorption tower of the latter stage, and the regeneration pressure of 0.15 atm for the oxygen adsorption column of the former stage.
Set the adsorption tower temperature to -30 ° C and set the oxygen adsorption tower pressure to 1.01 to 5a.
This is the power consumption when changing to tm. The alternate long and short dash line in the figure shows 0.39 KWh / Nm ³ -O ₂ of the power unit of the cryogenic separation method for producing oxygen with an oxygen concentration of 99.5 vol%.

As can be seen from FIG. 2, when the pressure in the oxygen adsorption tower is 3 atm or less, it is lower than the power unit of the cryogenic separation device, and especially about 50% of the cryogenic method in the vicinity of the atmospheric pressure of 1.01 to 1.2 atm.

FIG. 3 is a graph showing the relationship between the nitrogen adsorption tower pressure and the power consumption rate, and the notations in FIG. 3 are the same as those in FIG. Regarding the oxygen adsorption tower in the first stage, adsorption pressure 1.2atm, regeneration pressure 0.15at
m, adsorption tower temperature −30 ° C., regeneration pressure 0.2 atm for the nitrogen adsorption tower in the latter stage, and nitrogen adsorption tower pressure 1.01 ~
This is the result of checking the power consumption when changing to 5 atm. Third
As can be seen from the figure, the power consumption is about 50% of the deep-cooling method at low pressure around 1.01 to 1.2 atm as in FIG.

Next, the operating conditions of the nitrogen adsorption tower in the latter stage are the adsorption pressure 1.2at
m, regeneration pressure 0.2 atm, adsorption tower temperature -15 ° C, adsorption pressure 1.2 atm and adsorption tower temperature -30 ° for the oxygen adsorption tower in the previous stage, and the regeneration pressure for oxygen adsorption tower was changed from 0.1 to 1 atm. The units were measured and are shown in FIG. FIG. 4 is a graph showing the relationship between the regeneration pressure of the oxygen adsorption tower and the power consumption rate. In Fig. 4, the horizontal axis represents the regeneration pressure P ₁ (at
m), the vertical axis represents the power consumption rate when oxygen is produced at 1 Nm ³ / h. In the figure, the alternate long and short dash line is the power unit of the cryogenic method 0.39KWh / Nm ³
-O ₂ . There is a minimum point near the regeneration pressure of 0.15 atm and 0.1 to
It is less than the power consumption of the cryogenic method in the area of 0.5 atm.

Similarly, the above-mentioned examination was conducted for the nitrogen adsorption tower in the latter stage.
That is, the adsorption pressure 1.2 atm for the oxygen adsorption tower in the first stage,
The regeneration pressure is 0.15 atm, the adsorption tower temperature is -30 ° C, the nitrogen adsorption tower in the latter stage is set to 1.2 atm, the adsorption tower temperature is -15 ° C, and the regeneration pressure is changed from 0.1 to 1 atm for the nitrogen adsorption tower. The units were measured and are shown in FIG. FIG. 5 is a graph showing the relationship between the regeneration pressure of the nitrogen adsorption tower and the power consumption rate. The notation in FIG. 5 is the same as that in FIG. There is a minimum point near the regeneration pressure of 0.2 atm, which is lower than the power consumption of the cryogenic method in the region of 0.1 to 0.5 atm.

Next, the operating conditions of the nitrogen adsorption tower in the latter stage are the adsorption pressure 1.2at
m, regeneration pressure 0.2 atm, adsorption tower temperature -15 ℃, set adsorption pressure 1.2 atm and regeneration pressure 0.15 atm for the oxygen adsorption tower in the previous stage, and the adsorption tower temperature for oxygen adsorption tower from 25 ℃ to -10
The power consumption rate was measured by changing the temperature to 0 ° C. and shown in FIG. FIG. 6 is a graph showing the relationship between the temperature of the oxygen adsorption tower and the power consumption rate. In FIG. 6, the horizontal axis shows the oxygen adsorption tower temperature (° C.), and the vertical axis shows the power consumption rate during production of oxygen (99.5 vol%) 1 Nm ³ / h. In the figure, the alternate long and short dash line is the power unit of the cryogenic method
A 0.39KWh / Nm ³ -O _2. There is a minimum point near the tower temperature of -30 ° C, and it falls below the power unit of the cryogenic method in the region of 5 to -50 ° C. At 10 ° C or higher, the adsorbent exhibits weak nitrogen selectivity and oxygen-enriched air cannot be obtained, and at -50 ° C or lower, the power consumption of the refrigerator significantly increases.

Similarly, the above-mentioned examination was conducted for the nitrogen adsorption tower in the latter stage.
That is, the adsorption pressure 1.2 atm for the oxygen adsorption tower in the first stage,
The regeneration pressure was 0.15 atm and the adsorption tower temperature was -30 ° C. The nitrogen adsorption tower in the latter stage was set to 1.2 atm adsorption pressure and the regeneration pressure was 0.2 atm, and the adsorption temperature was changed from 25 ° C to -100 ° C for the nitrogen adsorption tower. The power consumption unit was measured and is shown in FIG. 7.
FIG. 7 is a graph showing the relationship between the tower temperature of the nitrogen adsorption tower and the power consumption rate. The notation in FIG. 7 is the same as that in FIG. There is a minimum point near the tower temperature of -30 ° C, and it falls below the power unit of the cryogenic method in the range of 10 to -30 ° C.

In FIG. 1 showing the above-mentioned embodiment, the nitrogen adsorption tower 22 at the latter stage is shown.
The oxygen concentration in the waste gas desorbed from a and 22b is 30 to 45 vol%, which is higher than the atmospheric oxygen concentration of 21 vol%. Also, from the viewpoint of the mass balance of all devices, about 30% of oxygen in the inlet air is lost and it is useless as it is. Therefore, it is preferable to return the flow rate from the flow path 37 to the flow path 3b to increase the oxygen concentration in the inlet air and further improve the oxygen recovery rate to further reduce the power consumption rate.

〔The invention's effect〕

According to the present invention, the required power consumption is lower than that of the conventional adsorbent method, and the oxygen concentration that cannot be produced by the conventional method is 9
High-purity oxygen of 5.5% or more can be produced.

[Brief description of drawings]

FIG. 1 is an exemplary view of a high-purity oxygen production apparatus for explaining an embodiment of the present invention, FIG. 2 is a graph showing a relationship between adsorption pressure of an oxygen adsorption tower and power consumption, and FIG. 3 is a nitrogen adsorption tower. A graph showing the relationship between the adsorption pressure and the power consumption unit, FIG. 4 is a graph showing the relationship between the oxygen adsorption tower regeneration pressure and the power consumption unit, and FIG. 5 is a graph showing the relationship between the nitrogen adsorption tower regeneration pressure and the power consumption unit,
FIG. 6 is a graph showing the relationship between the oxygen adsorption tower temperature and the power consumption unit, and FIG. 7 is a graph showing the relationship between the nitrogen adsorption tower temperature and the power consumption unit.

Claims (1)

[Claims] 1. Oxygen in at least two adsorption columns packed with molecular sieves carbon having a window diameter of 4.1 to 4.5Å and weak nitrogen selective adsorption at room temperature but oxygen selective adsorption at low temperature. A mixed gas such as air containing nitrogen and argon as a main component at a temperature of 25 ° C. or lower, is allowed to flow into an adsorption tower at atmospheric pressure or higher and 3 atm or lower to selectively adsorb the oxygen contained in the mixed gas, The nitrogen and the argon are released to the outside of the system, while the adsorption tower that has adsorbed oxygen is decompressed to 0.08 atm or more and 0.5 atm or less to recover argon-free oxygen-enriched air, and then the recovered oxygen-enriched air At least 2 air filled with sodium phosphinasite represented by Na-X
Lead to an adsorption tower above the column, and adsorb nitrogen from the mixed gas containing oxygen and nitrogen as the main components at a temperature of 25 ° C. or lower at atmospheric pressure or higher and 3 atm or lower to cause high-purity oxygen to flow out from the outlet of the adsorption tower. On the other hand, the adsorption tower that adsorbed nitrogen was 0.08 atm or more and 0.5 atm
A method for producing high-purity oxygen, which comprises regenerating under reduced pressure as follows.