JPH05192528A - Method for separating oxygen and nitrogen from gaseous mixture - Google Patents

Abstract

PURPOSE:To reduce a power unit and an amount of an adsorbent to a large extent by using two adsorbing towers packed with Na-X type zeolite adjusted to a specific properties and allowing a gaseous mixture to flow in one adsorbing tower under a definite condition and reducing the pressure of the other adsorbing tower. CONSTITUTION:Na-X type zeolite whose SiO2/Al2O3 ratio is adjusted to 2.0-2.5 is used as an adsorbent. Two adsorbing towers 8, 8' are packed with this zeolite and a gaseous mixture based on oxygen and nitrogen is allowed to flow in the adsorbing tower 8 at a low temp. equal to or lower than room temp. under atmospheric pressure of 3 ata or less. Whereupon, oxygen of high purity flows out of the upper part of the adsorbing tower 8. The adsorbing tower 8' after the completion of an adsorption process is reduced to 0.08-0.5 ata in pressure to regenerate the adsorbent 9' and nitrogen is discharged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating oxygen and nitrogen from a mixed gas containing oxygen and nitrogen as a main component by using an adsorbent which selectively adsorbs nitrogen.

[0002]

2. Description of the Related Art A method of separating oxygen and nitrogen from air by using a nitrogen adsorbent has a small size and a simple apparatus, requires almost no maintenance, and can be operated almost unattended. In recent years, the number of uses has increased as small and medium-sized devices of about 3000 Nm ³ O ₂ / Hr, and replacement of the case of transporting and using liquid oxygen produced by a cryogenic separation device is in progress.

An outline of a typical device of this type will be described. The device comprises two or more adsorption towers, an air compressor, and in some cases a vacuum pump. When compressed air is sent to one adsorption tower by an air compressor, nitrogen in the air is adsorbed by the nitrogen adsorbent filled in the tower, and high-pressure oxygen is discharged and recovered. The other column is decompressed by a vacuum pump, and if necessary, a part of product oxygen is caused to flow countercurrently to desorb nitrogen and regenerate the adsorbent. The adsorption step and the regeneration step are alternately repeated to continuously separate oxygen and nitrogen.

As the nitrogen adsorbent used here, a 60 to 70% Ca exchanger of Na-A type zeolite, which has been put into practical use by Union Carbint Co., is typical, and this nitrogen adsorbent is air. Co-adsorption of oxygen is estimated to be 10% or less of nitrogen adsorption under the conditions. The above device is 1
Power consumption 0.75 to 1 kW for producing Nm ³ oxygen
h is required, and the power consumption is 0.45 KWh, which is larger than the power consumption when manufacturing by the large-capacity cryogenic separation method. Further, it is said that the above apparatus has little economies of scale with respect to the increase of the apparatus capacity, and cannot compete with the cryogenic separation method in the region of 3000 Nm ³ (oxygen) / h or more.

[0005]

The drawbacks of the above device will be examined below. First, in order to reduce the power consumption, it is conceivable to lower the blast pressure and perform 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 increases significantly. Next, in order to increase the amount of adsorption, it is possible to carry out the adsorption operation under low temperature conditions, but since the adsorption / desorption rate decreases significantly, the product oxygen concentration at the same column length decreases rather than at room temperature. To do. In addition, since the oxygen co-adsorption amount at the time of nitrogen adsorption increases as the temperature decreases, the power consumption rate gradually increases. Therefore, the present invention intends to provide a method for separating oxygen and nitrogen under low temperature and low pressure adsorption conditions, which can solve the above-mentioned drawbacks and can significantly reduce the power consumption rate and the adsorbent amount. is there.

[0006]

The present invention is based on SiO ₂ /
Using at least two adsorption columns packed with Na-X type zeolite adjusted to an Al ₂ O ₃ ratio of 2.0 to 2.5,
A mixed gas containing oxygen and nitrogen as main components is caused to flow into one of the adsorption towers at a low temperature of room temperature or lower and a pressure of atmospheric pressure or more and 3 ata or less to selectively adsorb nitrogen from the mixed gas,
High-purity oxygen or oxygen-enriched gas is recovered, the other adsorption tower is decompressed to 0.08 to 0.5 ata to regenerate the adsorbent, and nitrogen is discharged. It is a method of separating.

[0007]

The inventors of the present invention have conducted an earnest study on a high-performance method for separating oxygen and nitrogen under low-temperature and low-pressure adsorption conditions.
₂ / Al ₂ O ₃ ratio adjusted to 2.0-2.5 Na-X
Type zeolite maintains a large amount of nitrogen adsorption and an adsorption rate in a practical range, and the decrease in selectivity of nitrogen adsorption is small, and for the first time in the present invention, the above zeolite is used to separate a mixed gas of oxygen and nitrogen. It is possible to significantly reduce the power consumption rate and the adsorbent amount of the gas separation device by applying to

The effectiveness of the present invention will be described below with reference to FIG. The air introduced from the inlet side line 1 is pressurized to 1.05 to 4 ata by the compressor 2 and is introduced into the dehumidification / decarbonation tower 4 through the flow path 3 to obtain extremely clean pressurized air. This pressurized air is introduced into the adsorption tower 8 through the flow path 3 ′, the open valve 5, the flow path 6, and the open valve 7. The pressurized air adsorbs and separates nitrogen by the adsorbent 9 in the adsorption tower 8 and increases the oxygen concentration as it flows upward. Then, the high-purity oxygen flows out from the upper part of the adsorption tower 8 to open the valve 1
It is stored in the oxygen product tank 13 through 0 and 11, and is collected through the valve 12 and the flow path 21 in the open state.

On the other hand, the adsorption tower 8'after the adsorption step is
Vacuum pump 18 through open valve 16 and flow path 17
Is connected to and the pressure is reduced. At that time, a part of the product oxygen flows countercurrently to the adsorption tower 8'through the pressure reducing valve 15 of the flow path 14 connecting the upper portions of the two adsorption towers, and the adsorbent 9'in the adsorption tower 8 '
It is possible to easily desorb the nitrogen adsorbed by the adsorbent 9 and regenerate the adsorbent 9 ′ in a short time. When the nitrogen adsorbent 9 in the adsorption tower 8 is saturated and the nitrogen adsorbent 9'in the adsorption tower 8'is regenerated, the inlet air flow path 6 is switched to the flow path 6 ', and the adsorption tower 8 is used in the regeneration step. The adsorption tower 8'is transferred to the adsorption step and the gas separation operation is continued, so that product oxygen can be continuously recovered.

It should be noted that the clean compressed air flow path 3'at the inlet
And a flow path 17 for the gas containing desorbed nitrogen as a main component, a heat exchanger 19 is arranged, and between the flow path 3 ′ and the product oxygen recovery flow path 21, By disposing the heat exchanger 22, the above pressurized air can be cooled. Further, by disposing the compression refrigerator 20 in the flow path 3 ', the compressed air can be cooled very efficiently, and the low temperature condition of the adsorption step can be secured. Further, the adsorption tower is not simply switched between the flow paths 6 and 6 ′ to prevent blow-in of the inlet air due to pressurization immediately after the switching, and to prevent oxygen remaining in the rear of the adsorption tower and the front side. In order to minimize the discharge of the pressurized air of the system out of the system, first, the valves 10, 15, 10 '
It is preferable to fully open and partially transfer the oxygen remaining behind the adsorption tower 8 immediately after adsorption to the adsorption tower 8 ′ immediately after regeneration.

At this time, the pressure in the adsorption tower 8 is changed to P ₀ (at
a), assuming that the pressure of the adsorption tower 8 ′ is P ₁ (ata), the pressure after equalization is about (P ₀ + P ₁ ) / 2 (ata).
After that, the adsorption tower 8 ′ is pressure-equalized with the product oxygen tank 13 by opening the valves 10 ′ and 11 ′, and can further fill high-pressure oxygen. The pressure P ₂ (ata) at the time of pressure equalization with the product oxygen tank 13 is V ₁ (liter) when the dead volume of the adsorption towers 8 and 8 ′ (volume of space not occupied by adsorbent in the adsorption tower) is V ₁ (liter). The volume of the oxygen tank is V ₂ (liter), and the pressure of the product oxygen tank 13 before pressure equalization is P _0.
Assuming that it is approximately equal to (ata), the pressure equalizing pressure P ₂ (a
ta) is roughly as follows. P ₂ = [((P ₀ + P
_{1) V 1/2) +} P 0 V 2 ] / [V ₁ + V _2] Therefore, simply P from P ₁ (ata) when switching the tower
Compared to the rapid boost to ₀ (ata), the above operation
P ₁ (ata), (P ₀ + P ₁ ) / 2 (ata), P ₂
(Ata) and P ₀ (ata) to raise the voltage gently,
It is possible to prevent blow-through of air during pressurization, and to minimize the release of residual oxygen and high-pressure air from the system during the desorption process.

[0012]

EXAMPLES To demonstrate the effectiveness of the present invention, SiO ₂
/ Al ₂ O ₃ ratio of 2.0 and N adjusted to 2.5
The a-X type zeolite was used as a nitrogen adsorbent and filled in the air separation apparatus of FIG. 1 to try to separate oxygen and nitrogen from the air.
For comparison, Na-X type zeolite is adjusted to SiO ₂ / Al ₂ O ₃ ratio 2.7 was also used. The specifications of the gas separation operation are as follows. Adsorption tower specifications: Diameter 60 mm, length 850 mm Adsorbent type: SiO ₂ / Al ₂ O ₃ ratio 2.
0 of _{Na-X SiO 2 / Al 2} O 3 ratio Na-X adsorbent filling amount of _{Na-X SiO 2 / Al 2} O 3 ratio of 2.7 2.5: 1.5 Kg / tower tower: 2 tower Switching time of tower: 1.5 minutes Adsorption tower pressure: 1-5 ata Regeneration tower pressure: 0.1-1 ata Adsorption tower temperature: 20-100 ° C. Outlet product flow rate: 2 N liters / minute According to the procedure.

The above three types of nitrogen adsorbents were compared for the results of separating oxygen and nitrogen from air under the above operating conditions. FIG. 2 is a graph showing the relationship between adsorption pressure and power consumption rate. The horizontal axis represents the adsorption pressure P ₀ (ata), and the vertical axis represents 1N.
Power consumption required to produce m ³ / h of oxygen (KWh /
It is Nm ³ (oxygen). And, the temperature of the adsorption tower is 20 ° C,
Desorption pressure P ₁ is 0.2 ata, tower space velocity U is 0.8 c
m / sec (outlet standard) and adsorption column pressure 1.5
The power consumption was examined by changing the power consumption to 4.5 ata. In the figure,
○ marks are Na-X with a SiO ₂ / Al ₂ O ₃ ratio of 2.7, Δ marks are Na-X with a SiO ₂ / Al ₂ O ₃ ratio of 2.5, and □ marks are S.
This is for Na-X having an iO ₂ / Al ₂ O ₃ ratio of 2.0. As is clear from FIG. 2 (the same applies to FIGS. 3 to 5), the zeolites (Δ mark and □ mark) in the range of the SiO ₂ / Al ₂ O ₃ ratio of the present invention are conventional (○).
It can be seen that oxygen can be separated from the air with a small power unit for the mark ().

FIG. 3 is a graph showing the relationship between desorption pressure and power consumption. The horizontal axis represents the desorption pressure P ₁ (ata), and the vertical axis represents the power consumption (KWh / Nm ³ (oxygen) required to produce ₁ Nm ³ / h of oxygen.
₀ is 1.5 at which the effectiveness is confirmed in FIG. 2, the tower space velocity U is 0.8 cm / sec (exit standard),
Set the temperature to 20 ° C and set the desorption pressure P ₁ to 0.1 to 0.5.
The power consumption was examined by changing to ata. As is clear from FIG. 3, the zeolite (Δ mark and □ mark) in the range of the SiO ₂ / Al ₂ O ₃ ratio of the present invention is the conventional one (◯ mark).
On the other hand, it can be seen that oxygen can be separated from air with a small power unit. Although no specific phenomenon was found in relation to desorption pressure, the lower limit of the power unit of oxygen production using a nitrogen adsorbent was around 0.25 KWh / Nm ³ (oxygen), and cryogenic separation The power consumption rate of oxygen production in the method is 0.
Considering that it is 45 to 0.6 KWh / Nm ³ (oxygen), the practical desorption pressure is 0.08 to 0.
It can be seen that 5 ata, especially 0.1 to 0.3 at around is preferable.

Next, the adsorption tower was introduced into a cooling condition to attempt adsorption separation under low temperature conditions. This is because the adsorption amount generally increases by setting the temperature at low temperature, so that the breakthrough zone at the time of adsorption is reduced, and miniaturization of the device and improvement of separation efficiency can be expected. The operating condition is that the adsorption pressure P ₀ is 1.5.
ata, regeneration pressure P ₁ is 0.2 ata, tower space velocity U is set to 0.8 cm / sec (outlet standard), power for producing 1 Nm ³ / h of oxygen by gradually lowering the adsorption tower temperature to a low temperature. I checked the basic unit. FIG. 4 is a graph showing the relationship between adsorption tower temperature and power consumption. The horizontal axis is the adsorption tower temperature (° C.), the vertical axis represents the power consumption necessary to produce the oxygen ^{1Nm 3 / h (KWh / Nm} 3 ( oxygen). As apparent from FIG. 4, the entire temperature range , SiO ₂ / Al of the present invention
Zeolite in the range of ₂ O ₃ ratio (marked with △ and □)
It can be seen that oxygen can be separated from air with a smaller power consumption unit than the conventional one (marked with ○). This means that it is possible to reduce the power consumption unit 0.25 KWh required for producing 1 Nm ³ / h of oxygen by the conventional zeolite by 40%. Further, the zeolite of the present invention was examined for power consumption in the adsorption tower temperature range up to -60 ° C, but there was no particular problem with respect to adsorption / separation of air, and according to the data of one component system, -100 ° C.
Even to a degree, its effectiveness is not lost. It should be noted that if the temperature is lower than that, co-adsorption of oxygen at the time of nitrogen adsorption cannot be ignored, which is not preferable. The cooling means has no problem particularly in this temperature range, and the cooling technology of the deep-chill separator can be used.

The above description has been mainly focused on the power cost, but next, the initial equipment cost will be considered. The operating conditions are as follows: adsorption pressure P ₀ is 1.5 ata, regeneration pressure P ₁ is 0.2 ata, column space velocity U is 0.8 cm / sec (outlet standard), and 1 Nm ³ / h of oxygen is produced. The amount of adsorbent required for the test was investigated. FIG. 5 is a graph showing the relationship between the adsorption tower temperature and the amount of the adsorbent, in which the horizontal axis represents the adsorption tower temperature and the vertical axis represents the adsorption required to produce 1 Nm ³ / h of oxygen. It is the dose (Kg). As is clear from FIG. 5, the conventional zeolite (circle) can save only about 45% of the adsorbent amount at room temperature even at a low temperature, while the Si of the present invention can be saved.
Zeolites in the range of O ₂ / Al ₂ O ₃ ratio (marked with Δ and □) can save about 65% at an adsorption tower temperature of −30 ° C. Since the adsorbent occupies a considerable part of the equipment cost, the above reduction is extremely effective.

As described above, according to the present invention, SiO ₂ / Al ₂
Using Na-X type zeolite adjusted to an O ₃ ratio of 2.0 to 2.5, the pressure of the adsorption step is set to 3 ata or less, and the pressure of the desorption step is set to 0.08 to 0.5 at a low pressure region at room temperature. If oxygen and nitrogen are separated from a mixed gas, such as air, by the pressure swing adsorption separation method in the following temperature range,
The power unit required for producing m ³ of oxygen is 0.45 to 0.6 kW in the deep-chill separation method, and 0.25 kW or more is required in the pressure swing adsorption separation method currently in use. It is possible to reduce to 0.15KW at once, and the amount of adsorbent used is 35% of the current method.
Could be reduced to.

[0018]

According to the present invention, by adopting the above-mentioned constitution, it becomes possible to greatly reduce the power consumption rate and the amount of the adsorbent as compared with the conventional pressure swing adsorption separation method.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an apparatus for carrying out the pressure swing adsorption separation method of the present invention.

FIG. 2 is a graph showing the relationship between adsorption pressure and power consumption rate in an example.

FIG. 3 is a graph showing a relationship between a desorption pressure and a power consumption unit in an example.

FIG. 4 is a graph showing a relationship between an adsorption temperature and a power consumption unit in an example.

FIG. 5 is a graph showing the relationship between the adsorption temperature and the amount of adsorbent required to produce 1 Nm ³ / h of oxygen in the examples.

[Explanation of symbols]

2 compressor, 4 dehumidification decarbonization tower, 8 adsorption tower, 13 product oxygen tank, 15 pressure reducing valve, 18
Vacuum pump, 19 heat exchanger, 20 compression refrigerator, 22 heat exchanger.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuaki Oshima 1-1 1-1 Atsunoura-machi, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard Co., Ltd.

Claims (1)

[Claims] 1. A SiO ₂ / Al ₂ O ₃ ratio of 2.0 to 2.5.
The mixed gas containing oxygen and nitrogen as main components is used at a low temperature not higher than room temperature and at a pressure not lower than atmospheric pressure for 3 atm by using at least two adsorption towers packed with Na-X type zeolite adjusted to
Flow into one adsorption tower at a pressure of a or less, selectively adsorb nitrogen from the mixed gas, recover high-purity oxygen or oxygen-enriched gas, and depressurize the other adsorption tower to 0.08 to 0.5 ata. Then, the adsorbent is regenerated and nitrogen is discharged, so that oxygen and nitrogen are separated from the mixed gas.