JPS6086010A - Concentration of nitrogen - Google Patents

Abstract

PURPOSE:To prepare high-purity nitrogen with the desired concentration, by introducing a raw material gas containing nitrogen into one of two adsorption columns packed with zeolite so that it has high pressure, with the other at low pressure, communicating both the columns. CONSTITUTION:The two adsorption columns 10 and 20 are packed with zeolite, a raw material gas containing nitrogen is sent from the feed pipe 1 through the valve 13 and the pipe 11 to the column 10, the pressure of which is raised to the desired pressure. Then, the valve 13 is closed, the valve 14 is opened, a treated gas rich in oxygen is exhausted from the pipe 2, and a gas rich in nitrogen is left in the column 10. Meanwhile the column 20 is evacuated and made in vacuum at 50-600 Torr through the pipe 21 and the valve 26 by the vacuum circuit pipe 3. Then, when the column 10 is made at atmospheric pressure, it is communicated through the pipe 12, the valve 15, and the pipe 21 with the column 20. Consequently, oxygen in the column 10 is preferentially transferred to the column 20, and an adsorption gas in the column 10 has nitrogen with high concentration. A nitrogen product with the desired purity is obtained by adjustment of the communication period and the filler.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for concentrating nitrogen by 11 Il from a nitrogen-containing mixed gas by pressure swing adsorption (hereinafter referred to as PSA).

PSA is widely used as a gas separation method for removing moisture from the air, purifying hydrogen to high purity, concentrating oxygen from the atmosphere, and the like.

To separate components in a mixed gas: 1) Utilizing the difference in adsorption selectivity between the components, strongly adsorbing components are concentrated on the adsorbent side, and weakly adsorbing components are concentrated on the gas side.

2) Strongly adsorbed components selectively captured and concentrated on the adsorbent side,
The pressure around the adsorbent is reduced and the adsorbent is desorbed.

This is usually done by filling a tower or column with a strong absorbent agent and passing gas through it using a fixed bed method.

When feed gas is overcharged from one end of the adsorption tower, a gas stream rich in weakly adsorbable components is obtained from the other end at a pressure approximately equal to the feeding pressure of the feed gas.

On the other hand, strongly adsorptive components are recovered after being reduced to a pressure lower than the adsorption pressure. The purity of each of these components depends on the adsorption selectivity exhibited by the adsorbent used, and the larger the difference in selectivity, the better the separation performance, that is, the higher the purity of the gas can be obtained.

If the required purity of the product gas is particularly high, a so-called purge step is provided in which a portion of the product gas is sent back into the plant. When the product gas is a weakly adsorptive component, the purge step is placed before the raw material gas is excessively supplied, and when the product is a strongly adsorbent component, it is generally performed immediately before the product gas recovery, that is, the depressurization step. In either case, the product gas used for purging is no longer as pure as the product, so its disappearance results in product loss.

In order to obtain a high-purity product, a larger amount of purging is required, resulting in a decrease in yield.

When obtaining nitrogen from air using conventional technology, air is passed through the tower at atmospheric pressure and then purged with product nitrogen at equal pressure (equity 47-509!16), atmosphere) 1 or more. There are methods such as continuing to purge this feed at higher pressure (share 57-42367).

Although these methods can obtain nitrogen with high purity, the amount of product gas consumed in purging is a non-negligible amount, making it difficult to obtain a sufficiently high yield.

The present invention provides a method for obtaining a highly pure strongly adsorptive component without reducing the product gas recovery rate, in particular a method for recovering nitrogen gas from a gas containing 7 elements such as air. The adsorption selectivity between two gases is planned by the distribution ratio of each component to the adsorption phase and the gas phase, and the coefficient ratio is called the selectivity coefficient or specific volatility of absorption and is calculated by the following formula. can.

a= ((1+/p+)/(Q2/1)2) where a
: Selectivity coefficient q; @W stool of each component p: Partial pressure of each component (subscript 1: strongly adsorbed component, 2: weakly adsorbed component) For example,
Mordenite-type zeolite (adsorbent) for nitrogen and oxygen
a for 335A type zeolite is 2
8 (total pressure 760 toor, 25 degrees Celsius, respectively). These values vary depending on the total pressure; 2 for 5A type; 23.4 for /cjG; 20 for g/l:iG; aII decreases as pressure increases.

The present inventors conducted detailed research on the characteristics of zeolite as an adsorbent, discovered the following facts, and continued research to effectively utilize the decrease in the a value to efficiently achieve nitrogen concentration. This led to the establishment of an excellent nitrogen separation method.

The atIi between nitrogen and oxygen in the theorides such as mordenite and 5A mentioned above tends to become larger under atmospheric pressure; taking mordenite as an example, it is 31 at 400[OQr] and 39 at 200toor. . but,
At 100t00r, it is 3.2.

altl, which determines the product gas purity, depends not on the feeding pressure of the raw material gas but on the internal pressure of the column immediately before starting vacuum recovery of nitrogen. Therefore, in carrying out vacuum recovery, it is preferable to reduce the internal pressure of the tower to below atmospheric pressure, preferably in the range of 250 to 6 ootoor, by some method after feeding the raw material gas.

A simple method for reducing the pressure inside the column is suction and exhaust using a vacuum pump. Although this method has the advantage of being able to freely select the level of pressure within the column to be achieved, it is difficult to avoid loss of nitrogen during exhaust gas. When the raw ore is delivered to the tower after the reduced pressure recovery of the product gas, it is effective to increase the pressure inside the tower in advance in order to avoid excessive gas movement caused by the pressure difference.

In view of the above, the present inventors have established a method for transferring gas within J5 through communication with a vacuum-depressurized tower as a method for reducing the pressure in the plant. If the pressure in the tower is higher than atmospheric pressure, it is effective to reduce the pressure inside the tower to atmospheric pressure in advance. The nitrogen abundance ratio of is extremely high.

By increasing the communication time, the pressure between the two units becomes equal. In the case of mordenite, the equalization pressure is approximately 20011Qll [l
It is.

After reducing the internal pressure of the column to the target level, pressurization with product nitrogen is performed to drive out trace amounts of impurity nitrogen still remaining in the column and to partially increase the pressure before feeding the raw material. This improves product purity and improves I+I. It is possible to shorten the partial pressurization time in the column to which the feed is to be fed, and to control the composition of the components in the column when the pressure is completed.

All steps of the present invention will be explained in detail below.

FIG. 1 is a diagram showing the relationship of the apparatus of the present invention.

Two adsorption groups jM io, 20 are filled with a zeolite, for example mordenai 1-. Each adsorption tower has two gas inlet and outlet pipes 11. +2.21.22, the raw material gas is fed from the nitrogen-containing raw material gas feed pipe 1 to 10 via the valve 13 and the pipe 11, and the pressure is increased to a predetermined pressure point. Subsequently, the valve 13 is closed, the valve 14 is opened, and the process gas is discharged from the whistle 12 through the valve 14 and the exhaust pipe 2 to bring the tower 10 to atmospheric pressure.
The exhaust gas at this time reaches the lli element.

On the other hand, the adsorption tower 20 is previously vacuum depressurized through the pipe 21, the valve 26, and the vacuum recovery pipe 3, and the pressure inside the tower is 50 to 60 tons.
00" and buy it.

The column 10 that has reached atmospheric pressure and the column 20 that has been evacuated are then communicated via a valve 15. At this time, all other valves +at are closed, and the gas inside the column 10 is pipe 12 valve +stg2+
is transferred to the tower 20 by. Although the gas composition in j'iiO before communication is rich in nitrogen, a slight amount of @ wire remains.

However, as a result of the forward movement of oxygen from the IO to the column 20, the adsorbed gas in the column 10 and the gas present in the interstices between the adsorbents have a very high concentration of nitrogen.

The adsorption tower 10 is depressurized to below atmospheric pressure through communication.

Column 20 is pressurized with transfer gas. If communication is continued for a sufficiently long time, the pressures in columns 10 and 20 will become equal. It is also possible to shorten the communication period and stop the transfer from the column 10 to the column 20 midway through, and the amount of communication transfer to be taken depends on the equilibrium relationship of the packed adsorbent with respect to nitrogen and oxygen. It is also determined depending on the desired purity of the product nitrogen.

Particularly when producing high-purity nitrogen, the towers 10 and 20 are communicated and transferred until the pressure angles become equal, and then the product nitrogen is returned @ 4 through the valve 11 to the pipe 11 with the valve 15 open.
A more suitable nitrogen gas, such as product nitrogen, is introduced. Further gas transfer from the column 10 to the column 20 is carried out through the opening valve 15 for introducing a predetermined amount of nitrogen product.Transfer of the product nitrogen to the column 10;
After completing the communication transfer associated with this, the rear piece 15.11 is closed, and the pressure of the continuation tower 20 is increased by feeding the raw material gas through the passage 1.23.21.

On the other hand, the gas in the column 10 passes through the valve 16 and the pipe 3 and is reduced in pressure by a vacuum pump. The extracted gas is a high MIR product nitrogen gas. By repeating the series of steps between the columns 10 and 20, high purity nitrogen can be obtained from the tube 3.

Next, the present invention will be explained in detail with reference to Examples.

The adsorbent used in the present invention is preferably a common crystalline aluminosilicate, ie, zeolite.

The present invention obtains high purity nitrogen in high yield by a simple method.

Example Using the VRW shown in Figure 1, mordenite type zeolite was packed into towers 10 and 20 in an amount of 9 kll each. Pour 2k of air into the bong from 1 (1/cmG 1' 13) (First, shift pressure of 10 was applied. At the beginning, close valve 13 and open valve 14 to release it to the atmosphere to make atmospheric pressure. Already reduced to 50 toor) The gas in column 10 was transferred from valve 15 to J1320, which equalized the pressure in both columns.The ultimate pressure was -47 cmH.
There was q'C-. 4.17 with valve 15 open.
After 11 hours, 336 hours of product nitrogen was delivered. After the pressure in the basin 10 reached 128 clIIHg, the valve 15 was closed to stop communication. Then, open the valve 16 and connect the pipe 13 to the column 1.
Instead of drawing out 0 gas, 794 gas was obtained. The oxygen concentration of this gas was O,+X. Nitrogen has a yield of 47
It was recovered with good results of χ.

[Brief explanation of the drawing]

Figure 1 shows an example of the device u for attaching the present invention to the tip.
0 indicates the suction tower 1, 2□3 indicates the gas inlet/outlet, respectively. Patent applicant: Toyo Kaidat Kogyo Co., Ltd.

Claims (1)

[Claims] 1. In separating and concentrating nitrogen in a nitrogen-containing gas by pressure fluctuation adsorption using a plurality of adsorption towers, (1
) Step of pressurizing the first column with raw material gas, (2) Step of discharging the gas inside the first column in parallel flow to lower the pressure inside the column, (3)
(4) a step of communicating a first tower and a second adsorption tower at a lower pressure and transferring a part of the gas from the first tower to the second adsorption tower;
A step of supplying nitrogen-rich gas to the first tower while maintaining communication between the first tower and the second tower to increase the pressure inside the first tower and the second tower;
(5) A method characterized by the steps of stopping the communication between the first column and the second column, recovering the gas in the first column as a product, and pressurizing the second column with raw material gas, and repeating these steps in sequence. 2 At the end of the process of communicating the first column and the second unit and transferring a part of the gas from the first column to the second unit, the pressure of the first column is increased to 250 to 6
The method according to claim 1, which is ootoor.