JPS6027606A - Preparation of nitrogen by pressure swing adsorption method - Google Patents

Abstract

PURPOSE:To improve yield of product of nitrogen gas without reducing its purity, by sending the product of nitrogen gas to a regenerated adsorption column adjusted to the same pressure as that of an adsorption column after adsorption, regenerating the adsorption column after adsorption process under reduced pressure. CONSTITUTION:A gas in the adsorption column 4a is made to flow in the bottom of the adsorption colum 4b after regeneration in vacuum. Simultaneously, at the initial stage, the valve 14 is opened, a product of nitrogen gas from the product tank 11 is fed to the top of the adsorption column 4b. When an outlet oxygen from the adsorption column 4a reaches a certain given tolerance value, the pressure of the adsorption column 4a and the adsorption column 4b is made equal through a pipe line passing through the valves 9, 12, and 13. In the operation, the valve 14 is in closed state. When the pressure of the two columns is made completely equilibrium in the operation, the valve 11 is closed, the valves 15 and 16 are opened, and the adsorption column 4a is regenerated by the vacuum pump 10. A raw material of pressurized air introduced in the adsorption column 4a is separated from oxygen which is adsorbed and removed, the raw material is made into the product of nitrogen gas, and sent to the product tank. The above- mentioned processes are repeated, consequently, the product of high-purity nitrogen gas is continuously prepared in high recovery ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method for separating and producing nitrogen gas from air by pressure swing adsorption.

BACKGROUND ART Conventionally, a method for producing nitrogen gas using a so-called pressure swing adsorption method is known, in which nitrogen gas is produced from air using an adsorbent that adsorbs oxygen such as carbon sheep. One such method for producing nitrogen gas is the method described in Japanese Patent Publication No. 56-9442 as shown in FIG. 1, for example. The raw material air is sent through the pipe 1 to the compressor 2, where it is pressurized to about 4 kg/d, and then passes through the switching valve 3a to one of the two adsorption towers 4a and 4b to be used. 4a is sent and received. The adsorption towers 4a and 4b are filled with an adsorbent that vaguely adsorbs oxygen, such as carbon sheep, and the oxygen in the feed air introduced under pressure is adsorbed, and at the outlet of the adsorption tower 4a, oxygen is adsorbed. Product nitrogen gas containing nitrogen as a main component is obtained.

This product nitrogen gas is sent to a supply destination via a pipe 5, a valve 6a, and a flow regulating valve 7. (Adsorption process)-7 Then, the adsorption tower 4a, which had adsorbed the specified amount of oxygen and was on the verge of exhaustion, stopped the introduction of raw air by switching the changeover valve 3a, and completed the regeneration process and was brought under reduced pressure. It is communicated with another adsorption tower 4b through a pipe 8 and a valve 9. By this operation, the nitrogen gas accumulated in the upper part of the adsorption tower 4a flows to the adsorption tower 4b, and the internal pressures of the two N absorption towers 4a and 4b become equal. (Pressure equalization step) Next, the raw air is sent to the adsorption tower 4b, and product nitrogen gas is produced in the same way. In addition, the adsorption tower 4a has a vacuum volume 1
It is connected to zero and the pressure is reduced by suction, the oxygen adsorbed on the adsorbent is desorbed, and the adsorbent is regenerated. (Regeneration Step) In the same manner, this series of operations is repeated for each of the M absorption towers 4a and 4b, thereby obtaining a product (pere gas). The above steps can be summarized as shown in Table 1.

Table 1 By the way, the following drawbacks have been pointed out in the nitrogen production method as described above, and a solution to these problems is desired.

That is, in the above-mentioned pressure equalization step, when the adsorption tower that has completed the adsorption operation is depressurized, the adsorbed oxygen is released from this adsorption tower toward the other low-pressure adsorption tower that has completed the regeneration step, so that adsorbed oxygen is desorbed. The amount of oxygen in the released gas increases rapidly. As a result, the deficient nitrogen in the gas released from one adsorption tower is adsorbed by the adsorbent in the other adsorption tower that has completed the regeneration process (contaminating the adsorption tower), resulting in high purity nitrogen. It becomes a hindrance when trying to obtain.

On the other hand, JP-A-57-132526 discloses an apparatus in which a product tank is provided between an adsorption tower and a supply destination of product phoneme gas, and a continuous process as shown in FIG. The company says it will be able to obtain pure nitrogen gas at a high yield and also save energy.

The feature of the method described in the above publication is that in step 2 or step 5 of the figure, in the heavy industry i1 or 4, the product nitrogen gas discharged from the adsorption tower still has a predetermined product quality. At this point, the product discharge is stopped, and the outflowing gas is then used to pressurize other columns.

However, in this method, after step 442 or 5, the adsorption tower that has completed adsorption enters the depressurization step (step 3.6) while maintaining the adsorption pressure. It is not possible to recover the gas present in the product, and as a result, it is not possible to increase the recovery rate of the product.

This invention was made in view of the above circumstances, and while nitrogen is produced by the pressure swing adsorption method,
The object of the present invention is to provide a method for using oxygen that can increase the yield of product nitrogen gas without reducing its purity.

Hereinafter, this invention will be explained with reference to the drawings. FIG. 3 shows an example of a device f, t suitable for carrying out the present invention, and parts common to the device shown in FIG. 1 are given the same reference numerals to simplify the explanation.

The pressurized raw material air and enzymes introduced into the adsorption tower 4aK are adsorbed and removed, and the product nitrogen gas is sent to the product tank 11 via the switching valve 6a and the pipe 5 (adsorption step).

When the oxygen concentration in the product nitrogen gas increases by more than product-1IA degrees, the valve 6a is closed and the valve 9.12.
13 is opened, and the gas in the adsorption tower 4a flows into the vacuum-regenerated adsorption tower 4b.

At the same time, at the beginning, the valve 14 is opened and the product nitrogen gas is supplied from the product tank 11 to the upper part of the adsorption tower 4b. In this operation, the valves other than valves 3a, 12, 13, and 14 are open (pressure equalization (step 11)).

When the outlet oxygen from the adsorption tower 4a reaches a certain predetermined peak value, the valve 3a is closed to stop the feed air supply, and the valve 9. 12. Adsorption tower 4a via a line passing through 13
and the adsorption tower 4b are made to be the same. At this time, valve 14it,
It is in a closed state (pressure equalization (■) work i).

After the two towers are brought to a completely balanced pressure by the above operation, the valve 11
is closed, valves 15 and 16 are opened, and the adsorption tower 4a is regenerated by the vacuum pump IO (regeneration step).

In the above (regeneration step), one adsorption tower 4b has a valve 3.
Pressurized feed air is introduced through d, and the adsorption tower 4b enters the adsorption stage. When this step is completed, valve 16 is closed at 1.44, valves 17 and 12.15 are opened, and the gas in the adsorption tower 4b flows into the lower part of the vacuum-regenerated g&adsorption tower 4a, and at the same time, the valve 18 is closed. The product nitrogen gas from the product ill is supplied to the upper part of the adsorption tower 4a through the pressure equalization (step 11).

Subsequently, the pressure equalization bending process is carried out with the adsorption towers 4a and 4b switched in position, and finally, only the valve 3a is opened, and the adsorption tower 4a is repressurized to the adsorption pressure with the feed air. (Raw material pressurization process).

Thereafter, the process returns to the adsorption process, and the process is repeated, whereby high-purity product nitrogen gas is continuously produced at a high recovery rate. The above steps are summarized as shown in Table 2 below.

Table 2 In this invention, the pressure equalization process is performed using two processes a (It and (11)).
By dividing the nitrogen gas into two parts, it is possible to improve the 9111 degree stability of the product nitrogen gas and its yield.

This will be explained with reference to Table 2 above.

Pressure equalization (In the IJ process, the raw material is supplied and the adsorption pressure is kept constant, but the product quality is low, but a mixed gas with a composition that is more concentrated in nitrogen gas than the raw material is obtained, and this is used for pressurization. It is sent as a gas to the adsorption tower that has been vacuum regenerated.At the beginning of this process, because the pressure difference between the two adsorption towers is large, the pressurizing gas flows in with an extremely large flow loss, and the gas for pressurization flows into the adsorption tower that has undergone vacuum regeneration. Since there is a risk that oxygen exceeding the product quality may be brought to the top of the adsorption tower, product nitrogen gas is supplied to the top of the regenerated adsorption tower to prevent the upper part of the adsorption tower from being contaminated with oxygen. ing.

Therefore, implementation of this step is not only effective in terms of product recovery, but also prevents the adsorbent in the tower from becoming fluidized by the gas flowing in from the bottom of the regenerated adsorption tower. There are also practical advantages.

Further, in the pressure equalization step (6) d, the upper part of the adsorption tower after the adsorption step is communicated with the lower part of the regenerated adsorption tower. Therefore, it is possible to recover a mixed gas that is somewhat more concentrated in nitrogen gas than the raw material held under adsorption pressure in the voids in the adsorption tower after the adsorption step, contributing to an improvement in the recovery rate.

The feature of this invention is that, as mentioned above, the pressure equalization (1) and the bending process are in step 2.3 or 6.7 in Table 2, so step 4.8 is not included. However, since this does not pose any particular problem to the process of the present invention, steps 4 and B may be omitted.

Next, examples of this invention will be shown.

〔Example〕

In the apparatus shown in FIG. 3 suitable for carrying out the invention,
When the adsorption towers 4a and 4b were filled with 8 o'clock carbon sheep and operated continuously, the most desirable operating conditions as shown in Table 3 could be obtained. As a result of this operation, a product nitrogen gas with a purity of 99.9- was obtained.

As explained above in Table 3, the method for producing nitrogen using the pressure swing adsorption method described in this invention is to provide a product tank between the adsorption tower and the supply destination of good quality nitrogen gas, and the adsorption tower that has completed one adsorption pole. At the same time, the nitrogen-rich gas in this adsorption tower flows into the lower part of another regenerated adsorption tower, and at the same time, the product nitrogen gas is supplied from the product tank to the upper part of this regenerated adsorption tower.゛After the pressure (1) step and the pressure equalization (1) step, the upper part of the adsorption tower after the completion of the first adsorption machine is communicated with the lower part of the regenerated adsorption tower to make both adsorption towers at the same pressure. Since the pressure equalization process is composed of the pressure equalization bending process, the yield of the product nitrogen gas can be significantly increased without reducing the purity of the product nitrogen gas.

[Brief explanation of the drawing]

jl (Figure 1 is a block diagram of a device used in an example of the conventional pressure swing adsorption method for producing nitrogen, Figure 2
The figure is a process diagram of another example of the conventional nitrogen production method using the pressure swing adsorption method, and FIG. 3 is a configuration diagram showing an example of an apparatus suitable for carrying out the present invention. 2...Compressor, 3a, 3a, 6a, 6b, 9 +13
．． 14,15,16.17.18...Switching valve, 4a,
4b...Adsorption tower, lO...Vacuum pump, 11...
Product tank. Appearance Person Japan tX8 Co., Ltd. Figure 1 (J Figure 2

Claims (1)

[Claims] A number of adsorption towers filled with an adsorbent that adsorbs oxygen in the raw air are used in each step of adsorption, pressure equalization, regeneration, pressure equalization, and product repressurization by using a switching valve. In the method of continuously producing nitrogen gas by switching sequentially, a product cylinder is provided between the adsorption tower and the supply destination of the product nitrogen gas, and the pressure equalization step and the adsorption step are completed. Feedstock air is supplied to the adsorption tower, and the nitrogen-rich gas discharged from this adsorption tower flows into the lower part of another adsorption tower that has been regenerated, and at the same time, the product nitrogen from the product tank is fed into the upper part of the regenerated adsorption tower. Pressure equalization for supplying gas (step 11); After completion of the pressure equalization (step 11), the introduction of raw air is stopped and the upper part of the adsorption tower after the adsorption step is communicated with the lower part of the regenerated adsorption tower. and a pressure equalization bending step to make both adsorption towers at the same pressure. A method for producing NMIAa using a pressure swing adsorption method, which is characterized in that the adsorption tower is regenerated under reduced pressure after the adsorption step.