JPH0243916A - Method and apparatus for pressure swing adsorbing - Google Patents

Abstract

PURPOSE:To enhance the purity of product gas by a method wherein component gas to be recovered at high purity is initially introduced into an adsorbing tower after the finish of a desorbing process up to 150-300mmHg and raw material gas is supplied to said tower on the side opposite to the initial introducing port to start an adsorbing process. CONSTITUTION:The air compressed by a compressor 9 enters a pretreatment apparatus 2 to remove H2O and CO2 while the pretreated air is introduced into an adsorbing tower 3a to adsorb N2 being a component to be recovered and impure component gas is discharged through a waste gas disposal pipe 4a. Subsequently, the adsorbing tower 3a is washed with the washing gas sent through a washing pipe 8 and subsequently reduced in pressure by a vacuum pump 6 and N2 is desorbed to be recovered and stored in a product gas holder 20. Thereafter, high purity N2 is initially introduced into an adsorbing tower 3a from the tank 20 up to 150-300mmHg and raw material gas is supplied to said tower on the opposite side and an adsorbing process is started. This process is successively repeated in adsorbing towers 3a-3c.

Description

Detailed Description of the Invention [Field of Application in Industry A] The present invention relates to a pressure swing adsorption method and device (hereinafter referred to as a PSA method and a PSA device) used in the production of high-purity gas, and more particularly, The present invention relates to a PSA method and a PSA device that can obtain product gas with higher purity by suppressing the remaining impurity components in the column as much as possible.

In the following, a PSA device and a PSA method for recovering N2 gas with high purity from raw material air will be described as a representative example, but the scope of application of the present invention should not be construed as limited by this.

[Prior art] Methods for concentrating and recovering N2 gas by introducing raw air into a PSA device can be roughly divided into two methods: a method in which 02 gas is adsorbed on an adsorbent and removed, and a method in which N2 gas is adsorbed on an adsorbent and further desorbed. There are two types of collection methods. Among these, the latter is a method in which a zeolite-based adsorbent is loaded into an adsorption tower and the pressure of the adsorption tower is reduced after N2 gas adsorption, thereby desorbing and recovering high-purity N2 gas. PS used for this method below
Device A will be explained.

FIG. 3 is a schematic explanatory diagram of an apparatus for selectively recovering N2 gas by supplying the 02/N2 mixed gas from which N20 and Co2 have been removed by the pretreatment apparatus 2 to a three-column PSA apparatus.

The air pressurized by the compressor 9 is sent to the pretreatment device 2, where the adsorbent adsorbs and removes N20 and CO2 components, and the 0□/N2 mixed gas that has passed through this is used as the raw material gas for the PSA device. Send it into the supply pipe 1a. Raw material gas supply pipe 1
A is connected to the top of adsorption towers 3a, 3b and 3c via automatic on-off valves (hereinafter referred to as valves) 3, and exhaust gas waste pipe 4a is connected to the bottom of each adsorption tower via valves V4 to V6. be done. Furthermore, desorption pipes 5a, 5b, and 5c are provided at the bottoms of the adsorption towers 3a, 3b, and 3c, and the pipes are merged downstream from the pipes via valves (1) to (v9), respectively. The combined desorption tube 5 is provided with a vacuum pump 6 and connected to the product gas holder 20, and stores the high-purity N2 gas desorbed and recovered from the adsorption towers 3a, 3b, and 3c. The product gas holder 20 is provided with a cleaning pipe 8 for extracting a part of the product gas for cleaning the adsorption tower, and after the cleaning pipe 8 is branched, a valve V
Adsorption towers 3a, 3b via I3-VIS.

3c. In addition, each adsorption tower 3a.

3b and 3c are connected in series by connecting pipes 10a, 10b, and 10c, and each connecting pipe is provided with valves VIO to v1□.

Figure 4 is a time schedule (time progresses from left to right) showing the operating process of one of the adsorption towers 3a, 3b, and 3c, and shows the operating process from the start of the adsorption process to the end of the desorption process. It is one process cycle. As shown in the figure, this one-step cycle consists of an adsorption step, a recovery step, a washing step, and a desorption step. First, in the adsorption process, as an operation to increase the pressure inside the adsorption tower, which has been depressurized in the desorption process, 02/N2 mixed gas is supplied under pressure from the supply pipe 1a, and the N of the target component to be recovered is
2 gases are adsorbed by the adsorbent, and impure component gases (mainly 0.2 gases) are released through the exhaust gas waste pipe 4a. In the desorption step, the adsorption tower is depressurized by the vacuum pump 6, and the N2 component adsorbed by the adsorbent in the tower is desorbed and collected and stored in the product gas holder 20 through the desorption pipe 5.

Next, the recovery process and the washing process will be explained using the case of the adsorption tower 3a in FIG. 3 as an example.

That is, high-purity N2 gas from the product gas holder 2o side is introduced into the adsorption tower 3c through the cleaning pipe 8 as shown by arrow A, replacing impurity components remaining in the adsorption tower 3a with N2 components, The gas thus expelled is sent via the connecting pipe 10a to the adsorption tower 3b where the adsorption process has been completed, as shown by arrow B. Therefore, at this time, a cleaning process is performed in the adsorption tower 3a, and a N2 recovery process is performed in the adsorption tower 3b.

[Problems to be Solved by the Invention] FIGS. 5(a) to 5(d) are schematic explanatory diagrams showing the N2 gas adsorption state in each step of the adsorption tower 3a. Note that the shaded area indicates a high concentration adsorption area of N2. When the raw material gas, cleaning gas, etc. are supplied from the top side of the adsorption tower 3a as shown in the figure,
Adsorption or replacement of the N2 component proceeds from the upper side of the adsorption tower, and in the lower part, the impure component, the 0□ component, remains until the start of the desorption process (02 in the adsorbent).
The component may remain adsorbed without being replaced by the N2 component, or may remain in the loading gap of the adsorbent).

In particular, as mentioned above, when the 02/N2 mixed gas is supplied from the top side of the adsorption tower in the adsorption process, the adsorption of the N2 component proceeds from above the loaded adsorbent, and in the lower part of the adsorption tower there is no
2 rich of the mixed gas will come into contact with each other, increasing the proportion of the 02 component remaining.

As a result, the concentration of N2 gas recovered in the desorption process was 9
The upper limit is 9.9%, and higher purity N2
Gas recovery was considered impossible.

Therefore, the present inventors have completed the present invention as a result of repeated research aimed at obtaining a component gas to be recovered with a high purity of 99.9% or more.

[Means for Solving the Problems] The method of the present invention, which achieves the above object, supplies high-purity recovery target component gas to an adsorption tower after the desorption step is 150 to 300 mm.
The gist is to initially introduce up to Hg, and then to perform the adsorption step by supplying the raw material gas from the opposite side of the initial introduction port of the adsorption tower.

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

[Operations and Examples] FIG. 1(A) is a schematic explanatory diagram showing an example of a typical PSA device of the present invention. The characteristic configuration different from the conventional device shown in FIG.
a, llb, llc are arranged, and each initial introduction pipe 11a, j
lb and llc are connected to each adsorption tower 3a and 3b via automatic on-off valves via to via.

It is located at the point connected to the bottom of 3c. That is, in each adsorption tower, the initial introduction pipes 11a, llb, and llc are connected to the upper and lower sides opposite to the connection position of the raw material gas supply pipe 1a.

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

As shown in FIG. 2(A), immediately before the desorption process is completed and the adsorption process is started, high-purity N2 gas in the product gas holder 20 is introduced into the tower from the bottom side of the adsorption tower 3a through the initial introduction pipe 11a. The N2 component is mainly introduced into the column and adsorbed on the adsorbent loaded in the lower part of the column. Thereafter, the valve is switched to proceed to the adsorption step, and the 02/N2 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 N2 component onto the adsorbent proceeds from the upper part of the adsorption tower 3a, and in addition to the initial introduction of N2 before this step, the N2 supplied in this step is adsorbed onto the adsorbent in the tower, and the adsorption step is completed. As a result, the number of 0□ components adsorbed by the adsorbent is reduced compared to the conventional method, and at this point, a reduction in the impurity component concentration is already achieved. This is because 0 during the adsorption process.
This is because the adsorbent that comes into contact with the O2-rich gas has already adsorbed N2 upon initial introduction, and the rate of O2 adsorption will be very low.

After the slightly remaining impurity component gas is almost completely expelled by the recovery process and cleaning process shown in FIGS. 2(C) and 2(D), high-purity N2 gas is recovered in the desorption process.

As mentioned above, by introducing high-purity N2 gas from the side opposite to the feed gas introduction direction in the adsorption tower immediately before the adsorption process, it is possible to prevent impurity components from remaining in the tower until the desorption process. The purity of the recovered N2 gas is 99
．． You will be able to achieve 99% or more.

FIG. 1(B) shows the initial introduction tubes 11a and llb.

Amount of N2 gas supplied to the adsorption tower by 11c (indicated by partial pressure)
It is a graph showing the relationship between and product gas purity. That is, the size of the adsorption tower is 80 mm in diameter and 1000 mm in height.
0.5 to 0.1 kg/c of raw material supply in the adsorption process
m”G, and the desorption process was carried out at 100 mG using a vacuum pump.
Desorption was performed under reduced pressure to ~50 m+nHg. As a result, the introduction of high-purity N2 gas just before the adsorption process was 150~3
It was found that it was necessary to keep the temperature within the range of 00 mmHg.

This is because if it is less than 150 mmHg, even if N2 gas is initially introduced, it cannot be expected to have much effect on improving the recovered gas concentration compared to the conventional method, and if it is more than 300 mmHg, the amount of N2 adsorbed in the adsorption process will decrease. This is because the recovery rate will decrease.

(Comparative Experimental Example) Using the PSA apparatus having the structure shown in FIG. 1(A) and FIG. 3, N2 gas recovery experiments were conducted under the following conditions to examine the concentration of each recovered gas. Note that the PS shown in Figure 1 (A)
When using A, high purity N2 gas was introduced for 2 seconds immediately before the start of the adsorption process.

The inner diameter of each adsorption tower is 80 mm, the height is Zoo + m,
Synthetic zeolite type 5A was used as the adsorbent to be filled.

Raw material gas supply pressure: 0.2 kg/cm"G, desorption pressure: 70 Torr, 1 process cycle of 1 column = 1 minute, Raw material air supply amount to compressor 9: 320ONIL/h, N2 gas recovery amount: 800 NfL/h.

Experiments were conducted under the following conditions.

As a result of this experiment, the concentration of N2 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 N2 concentration could be increased to 99.997%.

In each adsorption tower, high purity N is supplied from the side opposite to the feed gas supply side.
The method of introducing the two gases immediately before the adsorption process is not limited to the embodiment shown in FIG.
A separate N2 gas holder may be provided and the initial introduction pipe may be connected from the holder to the adsorption tower, or the initial introduction pipe may be connected to the outlet side of the vacuum pump 6 or branched from the product gas holder 20. It doesn't matter if it's something you do.

[Effects of the Invention] The method of claim (1) makes it possible to reduce the concentration of impurity components remaining in the adsorption tower until the start of the desorption process. Furthermore, the apparatus of claim (2) makes it possible to accurately introduce a predetermined partial pressure of the component to be recovered into the adsorption tower immediately before the adsorption step.

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

[Brief Description of the Drawings] Figure 1 (A) is a schematic explanatory diagram showing a typical embodiment of the PSA device of the present invention, and Figure 1 (B) shows the relationship between the initially introduced gas partial pressure and the product gas purity. Graph, Figure 2 (A) to (D)
is a schematic explanatory diagram showing the process status of one column using the PSA device of FIG. 1 (^), FIG. 3 is a schematic explanatory diagram showing the conventional PSA device, and FIG. figure,
FIG. 5 is a schematic explanatory diagram showing a process state of one column using a conventional PSA apparatus. la... Raw material gas supply pipe 2... Pretreatment device 3a
, 3b, 3c...Adsorption tower 5...Desorption tube 6.
・・Vacuum pump 8・Cleaning pipe 9・Compressor

Claims (2)

[Claims] (1) In the adsorption step, the raw material gas is introduced into the adsorption tower and the target component gas to be recovered is adsorbed on the adsorbent, and in the desorption step, the target component gas to be recovered is desorbed and recovered, and the above adsorption and desorption steps are repeated. In the pressure swing adsorption method, a high-purity recovery target component gas is initially introduced to the adsorption tower after the desorption step is completed to a pressure of 150 to 300 mmHg, and then a raw material gas is supplied from the opposite side of the initial introduction port in the adsorption tower. A pressure swing adsorption method characterized by starting an adsorption process. (2) In a pressure swing adsorption device in which a raw material gas supply pipe, a desorption pipe, and a cleaning pipe are connected to an adsorption tower, a side opposite to the raw material gas supply pipe connection side of the adsorption tower is connected to the cleaning pipe from the cleaning pipe. A pressure swing adsorption device characterized by connecting branched initial introduction pipes.