JPH06233910A - Separation of mixed gas - Google Patents

Abstract

PURPOSE:To enhance the yield and purity of product gas to a large extent by smoothly advancing adsorption and desorption reaction by effectively utilizing the heat generated when mixed gas is separated by a pressure swing adsorbing method using a heat exchanger. CONSTITUTION:Raw material gas is supplied to two adsorbing towers 3,3a and a high pressure adsorbing process and a low pressure desorbing process are alternately repeated in the respective adsorbing towers to separate mixed gas. At this time, the heat exchange of the heating medium in the adsorbing tower 3 generating heat by heat of adsorption in the adsorbing process with the cooled exhaust gas from the adsorbing tower 3a in the desorbing process is performed by a heat exchanger 13. The heat exchange of the heating medium in the adsorbing tower 3a cooled by heat of desorption in the desorbing process with the raw material mixed gas pressurized by a compressor 1 to generate heat is performed by a heat exchanger 13a. These heat exchange processes are alternately repeated. By this constitution, the separation of mixed gas due to a pressure swing adsorbing method can be efficiently performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mixed gas separation method by a pressure swing adsorption method (hereinafter abbreviated as "PSA" method).

[0002]

2. Description of the Related Art In recent years, as a new gas separation / purification method, a mixed gas is supplied under pressure to an adsorption tower filled with an adsorbent having a selective adsorption ability, and a high pressure adsorption step and a low pressure desorption step are repeated to perform mixing. A gas separation method by the so-called PSA method for separating and purifying a specific gas component from a gas has been developed, and the method has been applied to practical use by separating oxygen or nitrogen in air, refining hydrogen, separating and recovering carbon dioxide, and the like. There is.

An example of this is, for example, Japanese Patent Publication No. 38-25.
Japanese Patent No. 969 discloses a so-called purge method in which a part of a product gas is allowed to flow back into the adsorption tower after the adsorption step so that the adsorbent is efficiently regenerated. Further, Japanese Patent Publication No. 62-13047 discloses that after two columns of adsorption towers are pressure-equalized, a gas having a high initial oxygen content flowing out from one tower which has entered the adsorption step is introduced into the atmosphere for 3 to 10 seconds. A method for obtaining highly pure nitrogen gas by releasing it into the atmosphere has been proposed. In addition, JP-A-1-234313 and 1-6.
No. 4714 discloses PSA using activated carbon as an adsorbent.
A method for producing carbon dioxide by the method is disclosed. Furthermore, JP-A-1-34422 discloses a method in which zeolite, activated carbon, activated alumina, or silica gel is applied in combination as an adsorbent, and the carbon dioxide adsorbed by these adsorbents is efficiently recovered. .

However, in spite of the selection of these suitable adsorbents and unit operation conditions, the existing PSA method is still insufficient in terms of purity and yield of the separated gas under the present circumstances.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have found that the existing P
In view of the above-mentioned problems of the SA method, the present invention has been completed as a result of intensive studies, and an object thereof is to provide an efficient method for separating a mixed gas by the PSA method. It is in. Further objects and effects will be apparent from the following description.

[0006]

The above object is to supply the raw material mixed gas to at least two or more adsorption towers and alternately repeat the high-pressure adsorption step and the low-pressure desorption step in each adsorption tower. In the pressure swing adsorption method for separating the heat transfer medium, the heat medium in the adsorption tower that has generated heat due to the heat of adsorption in the adsorption step and the cooled exhaust gas from the adsorption tower in the desorption step are exchanged, while in the desorption step. This is achieved by a method for separating a mixed gas, characterized in that heat is exchanged between the heat medium in the adsorption tower cooled by the heat of desorption and the raw material mixed gas which is heated by pressurization.

As used herein, the term "heat medium in the adsorption tower" means "gas in the tower and adsorbent". The apparatus used in the method for separating a mixed gas of the present invention is mainly filled with an adsorbent.
Adsorption tower above the tower, pressurized supply means for sending raw material gas such as blower / compressor to the adsorption tower, surge tank for storing product gas, piping connecting these components and automatic valve for controlling gas flow And its control system. The apparatus may be equipped with a vacuum pump, a flow controller, a gas concentration analyzer, and the like for performing decompression regeneration as required. Conventional P
In the method of separating a mixed gas by the SA method, heat is generated by pressurization, the heated raw material gas is cooled and dehumidified by a dryer or the like, while the cold heat of the exhaust gas cooled by expansion is released without being used. . However,
In a normal apparatus configuration and structure of an adsorption tower, heat is generated by adsorption heat during adsorption and cooling by desorption heat occurs during desorption, and heat is stored in the adsorption tower, which hinders smooth progress of adsorption / desorption reaction.

On the other hand, in the PSA apparatus for carrying out the present invention, a heat exchanger is attached to the bottom of the adsorption tower, one end of each heat exchanger is connected to the raw material gas supply line, and the other end is connected to the bottom of another adsorption tower. It is configured to be electrically connected, and the flow path can be appropriately switched by a valve. With this configuration, the adsorbent can exchange heat with the source gas or the exhaust gas. As the heat exchanger, for example, a metal hollow tube crimped in a spiral shape having good thermal conductivity, or a known heat exchanger such as a hollow tube laid around the bottom of the tower may be selected and used appropriately. .

The heat exchanger is preferably mounted on the bottom of the adsorption tower at about 1/2 to 1/3 of the height of the adsorption tower where the desorption reaction between the adsorbent and the gas occurs. When a hollow tube is installed as a heat exchanger at the bottom of the tower, it is preferable to increase the heat exchange efficiency by installing fins in a range that does not interfere with the gas flow in the adsorption tower.

Next, the present invention will be described with reference to the drawings. Figure 1
FIG. 3 is an explanatory diagram showing an example of an embodiment of the method for separating a mixed gas of the present invention. In the figure, 1 is a compressor, 2
2a is a drain drain, 3,3a is an adsorption tower, 4 is a surge tank, 5,5a, 6,6a, 7, 7a and 11 are valves,
8, 8a, 9, 9a and 10 are pipes 13 and 13a are heat exchangers.

In the two adsorption towers 3 and 3a, the high-pressure adsorption step and the low-pressure desorption step are alternately repeated in each adsorption tower. Here, the present invention will be described by taking the adsorption / desorption process operation in the adsorption tower 3 as an example.

The mixed gas raw material is pressurized by the compressor 1, and the valve 5a, the pipes 8a and 9a, the heat exchanger 13 are heated.
a, the drainage 2 is circulated, and the pressure is supplied to the adsorption tower 3,
In the adsorption tower 3, the high-pressure adsorption step proceeds, while the adsorption tower 3a
Inside, the low pressure desorption process is in progress. The adsorbent in the adsorption tower 3a is cooled by heat of desorption, but the cooled heat medium in the adsorption tower 3a is heat-exchanged with the raw material mixed gas heated by the compressor 1 in the heat exchanger 13a. The raw material gas is cooled by the cooled heat medium in the adsorption tower 3a and the water is removed by the drainage 2, and then the raw material gas is pressed into the adsorption tower 3.

The adsorption step is carried out in the adsorption tower 3, but heat of adsorption is generated at this time. Further, at this time, since the desorption process is performed in the adsorption tower 3a, the desorbed gas having a lowered temperature is passing through the pipe 9. Therefore, heat is exchanged through the pipe 9, and the heat of adsorption generated in the adsorption tower 3 is taken out of the system, and the adsorption process proceeds smoothly. The product gas produced in the adsorption process is taken out through the valve 6, the pipe 10, the surge tank 4, and the valve 11.

The adsorbing step is completed by closing the valves 5a, 6, 7 before the adsorbent in the adsorption tower 3 is saturated. When the adsorption process is completed, a pressure equalization process is performed.
The pressure equalization process includes methods such as pressure equalization at the top, pressure equalization at the bottom, cross pressure equalization, and simultaneous pressure equalization at the top and bottom. For example, in the case of pressure equalization at the top, the valve 12 is opened and the gas in the adsorption column 3 is opened. Is supplied into the adsorption tower 3a. This pressure equalizing step can be omitted. When the pressure equalizing step is completed, the desorption step is started. At this time, the adsorption tower 3a moves to the adsorption step. In the desorption process, the valves 7a, 5, 6a,
11 is opened.

The gas desorbed in the adsorption tower 3 is pipe 9a.
Through the valve 7a and discharged. This desorption gas is cooled because it deprives the heat of desorption. In the adsorption tower 3a, the adsorption process proceeds and the adsorption tower 3a stores heat due to the heat of adsorption. In the above process, heat exchange between the exhaust gas of the adsorption tower 3a and the heat medium in the adsorption tower 3a is performed by the heat exchanger 13a, and the adsorption step in the adsorption tower 3a proceeds smoothly.

Further, since the raw material gas is passing through the heat exchanger 13, heat is exchanged with the heat medium inside the adsorption tower of the adsorption tower 3 which is being cooled by desorption heat through the heat exchanger 13. The inside of the adsorption tower 3 is heated so that desorption proceeds smoothly.

When the method for separating a mixed gas of the present invention is carried out, the pressure difference between adsorption and desorption is preferably 3 kgf / cm ² or more, more preferably 5 kgf / cm ² or more. If this pressure difference is too small, the temperature change of the adsorbent is small and it is difficult to obtain a sufficient effect. Further, when the adsorption time is 100 seconds or more, the adsorbent undergoes a sufficient temperature change, and favorable results are obtained.

[0018]

According to the method of the present invention, the heat generated when the mixed gas is separated by the PAS method is effectively utilized by using the heat exchanger, so that the adsorption / desorption reaction can be smoothly progressed. A product gas with high purity can be obtained in high yield. In addition, the present invention uses a molecular sieve carbon
Activated carbon or zeolite can be used, and it can be applied to many gas separations such as separation of oxygen or nitrogen from air, purification of hydrogen, separation of carbon dioxide.

Example 1 An adsorption tower of a PSA apparatus equipped with two adsorption towers having an inner diameter of 300 mmφ × 850 mmL shown in FIG. 1 was filled with molecular sieving carbon for air separation, and operated in the operation cycle shown in Table 1. In this embodiment, the adsorption pressure is 8 kgf / cm ² G,
The desorption pressure was atmospheric pressure. FIG. 3 shows the relationship between the yield and the oxygen concentration when the product nitrogen extraction flow rate was changed.

[Table 1]

As a comparative example, the inner diameter is 3 as in Example 1.
FIG. 2 equipped with two adsorption towers of 00 mmφ × 850 mmL
The PSA apparatus shown in FIG. 1 was filled with the same molecular sieving carbon as that used in Example 1, and the operation cycle shown in Table 1 was applied to Example 1
The same experiment was performed. The results are also shown in FIG. It can be seen from FIG. 3 that product nitrogen gas with good purity can be obtained when the method for separating mixed gas of the present invention is carried out.

[Brief description of drawings]

FIG. 1 is an example of an apparatus used when implementing the present invention.
In FIG. 1, 1 ... Compressor, 2, 2a ... Drain drain, 3, 3a ... Adsorption tower, 4 ... Surge tank, 5, 5a,
6, 6a, 7, 7a, 11 ... Valves, 8, 8a, 9, 9
a, 10 ... Pipes, 13, 13a ... Heat exchangers. FIG. 2 is an example of a conventional PSA device. In FIG. 2, 1 ...
Air compressor, 2 ... Air dryer, 3, 3a ... Adsorption tower,
4,4a, 7,7a, 10,10a, 13,13a, 1
5 ... Valve, 5, 5a, 8, 9, 9a, 11, 12, 1
6 ... Pipe, 14 ... Surge tank. FIG. 3 is a diagram showing the relationship between the purity and yield of product nitrogen gas in Example 1 and Comparative Example. In the figure, the vertical axis represents the concentration of oxygen gas, which is an impurity in the product nitrogen gas, and the horizontal axis represents the nitrogen yield.

Claims (1)

[Claims] 1. A pressure swing adsorption method in which a raw material mixed gas is supplied to at least two adsorption towers and the high pressure adsorption step and the low pressure desorption step are alternately repeated in each adsorption tower to separate the mixed gas, While exchanging heat between the heat medium in the adsorption tower that has generated heat due to the heat of adsorption in the adsorption step and the cooled exhaust gas from the adsorption tower in the desorption step, inside the adsorption tower cooled by the desorption heat in the desorption step A method for separating a mixed gas, characterized in that heat exchange is performed between a heat medium and a raw material mixed gas that is heated by pressurization.