JPH0691925B2 - Pressure swing adsorption method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a pressure swing adsorption method and apparatus (hereinafter simply referred to as PSA method and PSA apparatus) used for producing high-purity gas.
Regarding, in detail, PS that can obtain the product gas in higher purity by suppressing the residual of the impure component in the adsorption tower as much as possible
A method and PSA device.

Hereinafter, a PSA apparatus and a PSA method for recovering N ₂ gas from a raw material air to a high purity will be described as a typical example thereof, but the application target of the present invention should not be limitedly interpreted by this.

[Prior art] The method of introducing raw material air into the PSA device and concentrating and recovering N ₂ gas is roughly divided into a method of adsorbing O ₂ gas to an adsorbent and a method of adsorbing N ₂ gas to an adsorbent. It is further classified into two methods of desorption and recovery. Among the latter the adsorbent zeolite system was loaded into the adsorption tower, by depressurizing the adsorption tower after the N ₂ gas adsorption, a method of desorbing recover high-purity N ₂ gas. The PSA device used in this method will be described below.

Figure 3 is a schematic of an apparatus for selectively recovering O ₂ / N ₂ mixed gas 3 is supplied to the tower of the PSA unit N ₂ gas after the removal of H ₂ O and CO ₂ by the preprocessing unit 2 FIG.

The air pressurized by the compressor 9 is sent to the pretreatment device 2, and the H ₂ O and CO ₂ components are adsorbed and removed by the adsorbent,
The O ₂ / N ₂ mixed gas that has passed through this is fed into the raw material gas supply pipe 1a of the PSA device. Source gas supply pipe 1a adsorption tower 3a via the automatic opening and closing valve (hereinafter simply referred to as a valve) V ₁ ~V _3, 3b, connected to 3c top, via the valve V ₄ ~V ₆ are each in the bottom of the adsorption tower The exhaust gas disposal pipe 4a is connected. Also each of the adsorption columns 3a, 3b, 3c of the bottom pipe adsorbing the section 5a, 5b, 5c are arranged, are merged from it via respective valves V ₇ ~V ₉ downstream. Desorption tube 5 merged
Is provided with a vacuum pump 6 and is connected to a product gas holder 20 to store the high-purity N ₂ gas desorbed and collected from the adsorption towers 3a, 3b, 3c. Adsorption wherein the product gas holder 20, cleaning pipe 8 for extracting a portion of the product gas for the cleaning of the adsorption tower is disposed, the cleaning tube 8 via the Koben V ₁₃ ~V ₁₅ which is branched It is connected to the tops of the towers 3a, 3b, 3c. Each adsorption tower 3a, 3b,
3c is connected in series by connecting pipes 10a, 10b, 10c,
Valves V _{10 to} V ₁₂ are provided in each connecting pipe.

FIG. 4 is a time schedule (the time progresses from left to right) showing the operation process of one of the adsorption towers 3a, 3b, 3c, showing the operation process from the start of the adsorption process to the end of the desorption process. It is a one-step cycle. This one-step cycle is composed of an adsorption step, a recovery step, a washing step and a desorption step as shown in the figure. First, in the adsorption step, as an operation to increase the pressure inside the adsorption tower depressurized in the desorption step, an O ₂ / N ₂ mixed gas is pressure-supplied from the supply pipe 1a to adsorb N ₂ gas as a recovery target component to the adsorbent and impure. Exhaust gas waste pipe 4a for component gas (mainly O ₂ gas)
To be released via. In the desorption process, the pressure of the adsorption tower is reduced by the vacuum pump 6, the N ₂ component adsorbed by the adsorbent in the tower is desorbed, and collected and stored in the product gas holder 20 through the desorption tube 5.

Next, the recovery process and the cleaning process will be described by taking the case of the adsorption tower 3a in FIG. 3 as an example.

That is, the high-purity N ₂ gas from the product gas holder 20 side is introduced into the adsorption tower 3c through the cleaning pipe 8 as shown by arrow A, and the impure component remaining in the adsorption tower 3a is replaced with the N ₂ component. Then, the gas expelled by this is sent to the adsorption tower 3b, for which the adsorption process has been completed, through the connecting pipe 10a as shown by the arrow B. Therefore, at this time, the washing step is performed in the adsorption tower 3a,
In the adsorption tower 3b, a N ₂ recovery process is performed.

[Problems to be Solved by the Invention] FIGS. 5A to 5D are schematic explanatory views showing N ₂ gas adsorption states in respective steps of the adsorption tower 3a. The shaded area indicates the high-purity N ₂ adsorption portion. When the raw material gas, the cleaning gas, etc. are supplied from the top side of the adsorption tower 3a as shown in the figure, the adsorption or substitution of the N ₂ component proceeds from the upper side of the adsorption tower, and the lower portion is an impure component. The O ₂ component remains until the start of the desorption process (the O ₂ component in the adsorbent remains adsorbed without being replaced with the N ₂ component, or remains in the adsorbent loading gap. To go). In particular, when the O ₂ / N ₂ mixed gas is supplied from the top side of the adsorption tower in the adsorption step as described above, adsorption of the N ₂ component proceeds from above the loaded adsorbent,
In the lower part of the adsorption tower, the O ₂ -rich mixed gas comes into contact with each other, and the proportion of O ₂ component remaining increases.

As a result, the concentration of N ₂ gas recovered in the desorption process was 99.9.
However, it was considered impossible to recover N ₂ gas of higher purity.

Therefore, the present inventors have completed the present invention as a result of repeated research for the purpose of obtaining a target gas for recovery with a high purity of 99.9% or more.

[Means for Solving the Problems] In the method of the present invention which has achieved the above object, a high-purity recovery target component gas is initially introduced to an adsorption tower after the desorption step up to 150 to 300 mmHg, and then the initial stage of the adsorption tower. The gist is to perform the adsorption step by supplying the raw material gas from the side opposite to the inlet.

Further, the pressure swing adsorption device used in the above method is characterized in that an initial introduction pipe branched from the cleaning pipe is connected to a side of the adsorption tower facing the raw material gas supply pipe connection side. is there.

[Operation and Embodiment] FIG. 1A is a schematic explanatory view showing an embodiment of a typical PSA device of the present invention. A characteristic configuration different from the conventional device shown in FIG. 3 is that the cleaning pipe 6 is branched and the initial introduction pipes 11a, 11
b, 11c are installed, and each initial introduction pipe 11a, 11b, 11c is an automatic opening / closing valve
It is a point connected to the bottom of each adsorption tower 3a, 3b, 3c through V _{16 to} V ₁₈ . That is, in each adsorption tower, the initial introduction pipes 11a, 11b, 11c are connected to the upper and lower sides of the connection position of the raw material gas supply pipe 1a.

2 (A) to (D) are schematic explanatory views sequentially showing from immediately before the adsorption step to immediately before the desorption step in the adsorption tower 3a by the PSA apparatus shown in FIG. 1 (A).

As shown in FIG. 2 (A), immediately before the desorption process is finished and the adsorption process is started, the high-purity N ₂ gas in the product gas holder 20 is passed through the initial introduction pipe 11a from the bottom side of the adsorption column 3a. The N ₂ component is adsorbed in the column and is mainly adsorbed on the adsorbent loaded in the lower part of the column. After that, the valve is switched to shift to the adsorption step, and the O ₂ / N ₂ mixed gas is introduced from the top side of the adsorption tower 3a through the raw material gas supply pipe 1a [FIG. 2 (B)].
At this time, the adsorption of the N ₂ component to the adsorbent proceeds from the upper part of the adsorption tower 3a, and in addition to the initial introduction of N ₂ before the step, the N ₂ supplied in this step is adsorbed by the adsorbent in the tower to perform the adsorption step. finish. As a result, the O ₂ component adsorbed on the adsorbent is reduced as compared with the conventional one, and at this point, the concentration of the impure component is already reduced.
Because already N ₂ by the initial introduction into the adsorbent is contacted with O ₂ rich gas during the adsorption step are adsorbed, O ₂
This is because the adsorption rate is extremely low.

Then, after the slightly remaining impure component gas is almost completely expelled by the recovery process and the cleaning process shown in FIGS. 2C and 2D, high-purity N ₂ gas is recovered in the desorption process.

Immediately before the adsorption step as described above, by introducing high-purity N ₂ gas from the opposite side to the raw material gas introduction direction in the adsorption tower, it is possible to prevent impurities from remaining in the tower until the desorption step. And the purity of the recovered N ₂ gas is 99.99%.
You will be able to achieve the above.

FIG. 1 (B) is a graph showing the relationship between the N ₂ gas supply amount (indicated by the partial pressure) to the adsorption tower by the initial introduction pipes 11a, 11b, 11c and the product gas purity. That is, the size of the adsorption tower is 80 mm in diameter,
The height is 1000 mm and the raw material supply in the adsorption process is 0.5 to 0.1.
Kg / cm ² G is used, and the desorption process is performed by a vacuum pump at 100
Desorption was performed by reducing the pressure to -50 mmHg. As a result, it was found that the introduction of high-purity N ₂ gas just before the adsorption step should be in the range of 150 to 300 mmHg. Because, if it is less than 150 mmHg, even if N ₂ gas is initially introduced, the effect of improving the concentration of the recovered gas cannot be expected so much compared to the conventional case, and if it exceeds 300 mmHg, the N ₂ adsorption amount in the adsorption process decreases. This is because the recovery rate will decrease.

(Comparative Experimental Example) Using the PSA apparatus having the structure shown in FIGS. 1 (A) and 3, N ₂ gas recovery experiments were conducted under the following conditions to examine the concentration of each recovered gas. In using the PSA shown in FIG. 1 (A), high-purity N ₂ gas was introduced for 2 seconds immediately before the start of the adsorption step.

The inner diameter of each adsorption tower was 80 mm, the height was 1000 mm, and the adsorbent to be filled was synthetic zeolite 5A type.

Source gas supply pressure: 0.2 kg / cm ² G, Desorption pressure: 70 Torr, 1 tower 1 step cycle: 1 minute, Source air supply amount to compressor 9: 3200 Nl / h, N ₂ gas recovery amount: 800 Nl / The experiments were carried out under the conditions of h and.

As a result of this experiment, the concentration of the N ₂ component recovered in the product gas holder 20 by the conventional device (shown in FIG. 3) was 99.9%, whereas in the case of the PSA device of the present invention, the N ₂ concentration was 99.
I was able to increase it to 997%.

High-purity N ₂ from the side opposite to the source gas supply side in each adsorption tower
The method of introducing the gas immediately before the adsorption step is not limited to the embodiment shown in FIG. 1 (A), and an N ₂ gas holder different from the product gas holder 20 is provided and an initial introduction pipe is introduced from the holder to the adsorption tower. It may be connected, or may be branched from the outlet side of the vacuum pump 6 or the product gas holder 20 to connect the initial introduction pipe.

[Advantages of the Invention] By the method of claim (1), the concentration of the impure component remaining in the adsorption tower can be reduced until the desorption step is started. Further, the apparatus of claim (2) enables the predetermined partial pressure of the recovery target component to be accurately introduced into the adsorption tower immediately before the adsorption step.

As a result, the concentration of the target component gas recovered as the product gas can be made higher than before.

[Brief description of drawings]

FIG. 1 (A) is a schematic explanatory view showing a typical embodiment of the PSA device of the present invention, FIG. 1 (B) is a graph showing the relationship between the initial introduced gas partial pressure and the product gas purity, and FIG. 2 (A). ) To (D) are schematic explanatory views showing a process state of one tower by the PSA apparatus of FIG. 1 (A), FIG. 3 is a schematic explanatory view showing a conventional PSA apparatus, and FIG. 4 is one adsorption tower. FIG. 5 is an explanatory view showing a process sequence, and FIG. 5 is a schematic explanatory view showing a process state of one tower by a conventional PSA device. 1a ... Raw material gas supply pipe, 2 ... Pretreatment device 3a, 3b, 3c ... Adsorption tower, 5 ... Desorption pipe 6 ... Vacuum pump, 8 ... Cleaning pipe 9 ... Compressor 11a, 11b, 11c ... Initial introduction pipe

Claims (2)

[Claims] 1. A raw material gas is introduced into an adsorption tower in an adsorption step to adsorb a recovery target component gas to an adsorbent, and a desorption step desorbs and recovers the recovery target component gas. The adsorption step and the desorption step In the pressure swing adsorption method in which the above steps are repeated, a high-purity recovery target component gas is supplied to the adsorption tower after the desorption process.
A pressure swing adsorption method characterized in that the adsorption step is started by initially introducing up to 150 to 300 mmHg and then supplying a raw material gas from the opposite side of the initial introduction port in the adsorption tower. 2. A pressure swing adsorption apparatus in which a raw material gas supply pipe, a desorption pipe and a cleaning pipe are connected to an adsorption tower, wherein the cleaning is provided on the side of the adsorption tower facing the raw material gas supply pipe connection side. A pressure swing adsorption device characterized in that an initial introduction pipe branched from a pipe is connected.