JPS6027607A - Preparation of nitrogen by pressure swing adsorption method - Google Patents

Abstract

PURPOSE:To improve yield of a product of nitrogen gas without lowering purity of the product, by sending the product of nitrogen gas to an adsorption column after regeneration and pressure equalizing processes, pressurizing the gas again, regenerating under reduced pressure an adsorption column after adsorption process. CONSTITUTION:A gas in the adsorption column 4a is fed to the top of the other adsorption column 4b after regeneration in vacuum, a raw material of air is sent to the adsorption column 4a until an outlet oxygen concentration reaches the same composition as that of air. The gas in the adsorption column 4a is released from a raw material inlet at the bottom of the column 4a, and introduced from the bottom of the adsorption column 4b to the column 4b. The valve 12 is closed, the valve 3b is opened, and the adsorption column 4a is regenerated by the vacuum pump 10. The raw material of the pressurized air introduced into 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 11. Similarly, the above-mentioned series of operations are repeated alternately in the adsorption columns 4a and 4b, so that the product of nitrogen gas is continuously prepared.

Description

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

2. Description of the Related 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 sieves. One such method for producing nitrogen gas is, for example, the method described in Japanese Patent Publication No. 1, No. 1, Showa 6-9QQ, shown in FIG. Raw air is sent to compressor 2 from pipe 1,
After being pressurized to about 1IKe/-, the switching valve 3a
After that, it is sent to one of the adsorption towers 4a and 4b of the λ group which is switched and used. The adsorption towers 4a+4b are filled with an adsorbent such as carbon sheeps that preferentially adsorbs oxygen, and oxygen in the feed air introduced under pressure is adsorbed, and the outlet of the adsorption tower 4a is filled with an adsorbent that preferentially adsorbs oxygen. Product nitrogen gas as a component is obtained.

This product nitrogen gas is sent to a supply destination via a pipe 5, a valve 6a, and a flow rate adjustment valve 7. (Adsorption process) Then, the adsorption tower 4a, which has adsorbed a predetermined amount of oxygen and is on the verge of saturation,
By switching a, the introduction of raw air is stopped, and the adsorption tower 4b is communicated with another adsorption tower 4b, which has completed the regeneration process and is under reduced pressure, 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 adsorption 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 is equipped with a vacuum pump 1.
o, the suction pressure is reduced, oxygen adsorbed on the adsorbent is desorbed, and the adsorbent is regenerated. (Regeneration Step) Similarly, product nitrogen gas is obtained by repeating this series of operations alternately for the adsorption towers 4a and 4b. The above steps are summarized in Table 1.

Table 7 By the way, the following drawbacks have been pointed out in the above-mentioned nitrogen production method, and a solution thereof is desired.

(b) In the above pressure equalization process, when the adsorption tower that has completed the adsorption operation is depressurized, the oxygen content of the gas released from this adsorption tower towards the other adsorption tower that has completed the regeneration process increases rapidly. Therefore, if sufficient pressure equilibrium is achieved, the oxygen contained in the gas released from one adsorption tower will be adsorbed by the adsorbent in the other adsorption tower that has completed the regeneration process, resulting in high purity. This becomes a hindrance when trying to obtain nitrogen (95% if 1+!l).

(b) In FIG. 7, the pipe 8 is in a state in which a part of the pipe 8 is shared with the pipe line for discharging the product toward the valves 6a+6b.

Therefore, the oxygen contained in the pressure equalized gas held in the pipe 8 remains in the product discharge pipe line, and oxygen gas is present in the product gas sent to the supply destination when product discharge is started. As a result, the purity of the initial product gas decreases.

For the reasons mentioned above (a) ←), in the conventional nitrogen production method, in order to generate high purity nitrogen, it is necessary to stop the pressure equalization process midway through the pressure equalization process without achieving sufficient stability. Then, you have to move on to the next process.

In this way, in conventional nitrogen production methods, the amount of recovered gas is limited by the desired product purity, so the disadvantage is that the yield drops significantly as the product purity is improved. be.

This invention was made in view of the above circumstances, and when producing nitrogen by pressure swing adsorption method,
The purpose of this invention is to propose a nitrogen production method that can increase the yield of product nitrogen gas without reducing the purity of the product nitrogen gas.

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 1 shows an example of a device 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 introduced into the adsorption tower 4& has oxygen adsorbed and removed to become a product nitrogen gas, which 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 above the desired product concentration, the valve 6a is closed and the valve 9 is opened, so that the gas in the adsorption tower 4a is transferred to the upper part of the other adsorption tower 4b which has been vacuum regenerated. Introduce.

At this time, raw air continues to be supplied to the adsorption tower 4a.

Then, feed air is continued to be supplied to the adsorption tower 4a until the outlet oxygen concentration reaches the same level as the air composition.

However, when obtaining high purity product nitrogen gas.

The supply of raw material air to the adsorption tower 4a is limited depending on the purity specifications of the product nitrogen gas to be obtained. In other words, the pressure equalization time is adjusted. In this operation, the valves other than valve 3a and valve 9 are in a closed state [pressure equalization (1) step].

When the outlet oxygen concentration from the adsorption tower 4a reaches a certain permissible value, the valves 3a and 9 are closed, and at the same time the valve 12 is closed.
is opened, the gas in the adsorption tower 4a is discharged from the lower raw material inlet of the tower 4a, and introduced into the tower 4b from the lower part of the adsorption tower 4b [pressure equalization (old process)].

By the above operation, the pressures of the two towers are completely brought to equilibrium.

When this pressure equalization step is completed, the valve 12 is closed and the valve 3b is opened, and the adsorption tower 4a is regenerated by the vacuum pump 10 [regeneration step].

On the other hand, in the adsorption tower 4b, the valve 6b is opened and the short poem 1&'
1. The product nitrogen from the product tank 11 is caused to flow back, flushing out the product outlet line and preparing for the adsorption step. The amount of pressurization of the product gas at this time is effective from above the equilibrium pressure due to pressure equalization to the start pressure of adsorption [product pressurization step].

When this product pressurization step is completed, the valve 3c is opened and the adsorption tower 4b proceeds to the adsorption step.

Hereinafter, the above series of operations are carried out in the same manner as in the adsorption towers 4a and 4b.
By repeating the steps alternately, the product nitrogen gas is continuously obtained. The above steps can be summarized as shown in the table below.

Table 2 In this invention, by dividing the pressure equalization process into one process and incorporating a new product pressurization process, it is possible to improve the stability of the purity of the product nitrogen gas and increase its yield. is made of. This will be explained in more detail using the above-mentioned section No. 2.

In the pressure equalization (1) step, while supplying raw air to the adsorption tower that has already completed the adsorption step, nitrogen-rich gas in the tower is made to flow into the upper part of the regenerated adsorption tower. This is due to the drawback of the conventional pressure equalization, that is, when the adsorption tower is depressurized after the adsorption process, the oxygen adsorbed on the adsorbent (carbon sheep) becomes more concentrated than nitrogen due to the characteristics of the adsorbent (carbon sheep) itself. This is intended to improve the drawback that a sufficient amount of pressure equalization recovery cannot be obtained because the pressure is quickly desorbed. That is,
Is the pressure equalization (I) process reduced pressure? The purpose of this is to recover the nitrogen-rich gas inside the tower into optical components by pushing out the gas inside the tower with air supplied to the lower part of the adsorption tower.

In addition, the pressure equalization (old process) was aimed at keeping the regenerated adsorption bed as clean as possible. The pressure is made equal.This allows sufficient pressure recovery to be performed and increases the yield of product nitrogen gas.Furthermore, after the product pressure equalization process is completed, the product pressurization process moves to the adsorption process. Pressurization is carried out in the opposite direction to the discharge direction using the product nitrogen gas from the previous adsorption tower VCg product tank.As a result, product nitrogen is supplied to the discharge pipe at the top of the adsorption tower in the pressure equalization (I) step. Highly concentrated nitrogen-containing gas (product nitrogen gas) indicates that gas with a higher oxygen content than the purity of the gas is stagnant.
At the same time, the oxygen recovered in the pressure equalization (n) step and rising up the adsorption bed without being adsorbed is pushed back to the bottom of the adsorption bed with product nitrogen gas and adsorbed, thereby increasing the stability of product purity. This is what made it possible.

Next, examples of this invention will be shown.

〔Example〕

Table 3 shows the operating conditions in which the adsorption towers 4m and 4b were filled with gKf of carbon sheep in the equipment +rt4 shown in FIG. 1, which is suitable for carrying out the present invention. As a result, 92.95 g of highly pure fu nitrogen gas could be obtained.

Table 3 Note that the J&4 operating conditions of the present invention were determined by this example. I showed 7L to the evening crowd.

(12) ・ (;0 As explained above, in the nitrogen production method using the pressure swing adsorption method according to the present invention, the pressure equalization step is performed by using air supplied to the lower part of the adsorption tower without almost reducing the pressure. Pressure equalization (1) in which the nitrogen-rich gas in the column is recovered into the regenerated adsorption tower by extrusion.
It consists of a pressure equalization (II) step in which both adsorption towers that have completed the process are communicated to completely equalize the pressure, and then a product pressurization step in which product nitrogen gas is repressurized. The yield of product nitrogen gas can be significantly increased without reducing the purity of the gas.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus used in a conventional pressure swing adsorption method for producing nitrogen, and FIGS. 2A and 2B are block diagrams showing an example of a suitable apparatus for carrying out the present invention. 2...Compressor, 3a-3b, 3c, 3d, 6a
, 6b, 9.12-...Switching valve, 4a, 4b...
...Adsorption tower, lO...Vacuum pump, 11.
...Product tank. Applicant Nippon e-So Co., Ltd.

Claims (1)

[Claims] A plurality of adsorption towers filled with an adsorbent that adsorbs oxygen in raw air are sequentially switched to the following processes using a switching valve: adsorption, pressure equalization, regeneration, pressure equalization, and product repressurization. In this method, the pressure equalization step is performed by supplying raw air to an adsorption tower that has already completed the adsorption step, and converting the nitrogen-rich gas in the adsorption tower into another regenerated gas. It consists of a pressure equalization step (1) in which the material flows into the upper part of the adsorption tower, and then a pressure equalization step (II) in which the supply of the raw material is stopped and the two adsorption towers are communicated with each other to have the same pressure. The product nitrogen gas is sent from the product tank installed between the product nitrogen gas supply destination to the adsorption tower that has been regenerated and has undergone the pressure equalization process and is repressurized, while the adsorption tower that has completed the adsorption process is depressurized and regenerated. A method for producing nitrogen by pressure swing adsorption method, which is characterized by: