JPS63100914A - Adsorption method for pressure swing - Google Patents

Abstract

PURPOSE:To increase gas collecting ratio by communicating an adsorption tower which has finished the washing process before desorption process with an adsorption tower which has finished the desorption process and guiding the gas remaining in the communication piping into an adsorption tower which has finished the desorption process. CONSTITUTION:Raw material gas is guided from a feed pipe 1 into respective adsorption towers 3a-3c to adsorb N2, and gas containing O2 as a major component is discharged out of a waste tube 4. After the adsorption process is over, the adsorption tower 3a proceeds to the washing process through the recovery process, and washed out with product gas N2 from a product gas holder 9. After the washing process is over, the adsorption tower 3a is communicated with the adsorption tower 3c which has finished the desorption process through a communication piping 10a, and impure gas in the piping 10a is guided into the adsorption tower 3c. After said process, the adsorption tower 3a is evacuated by a vacuum pump 6, and the desorbed N2 is recovered in the product gas holder 9.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pressure swing adsorption method used for the separation and production of high-purity gases, and in particular a method for eliminating impurity components in product gases to be desorbed and recovered as much as possible. The present invention relates to a pressure swing adsorption method for recovering high-purity product gas. The following is a representative example of N2 from a mixed gas of 02 and N2.
, will be described below, but the scope of application of the method of the present invention should not be construed as limited by this.

[Prior Art] Methods for concentrating and recovering N2 gas by introducing pressurized air into a pressure swing adsorption device (hereinafter simply referred to as a PSA device) can be roughly divided into two methods: a method in which 02 gas is adsorbed on an adsorbent and removed; There are two types of methods: methods in which N2 gas is adsorbed onto an adsorbent and then desorbed and recovered. The latter method uses a zeolite-based adsorbent and depressurizes the adsorption tower after adsorbing N2 gas using a vacuum pump or the like to desorb and recover high-purity N2 gas, and this method will be described below.

FIG. 2 is a schematic explanatory diagram showing a three-column type PSA device, and an automatic opening/closing valve (hereinafter simply a valve ) Vt to Vt, and 3c are connected thereto, and an exhaust gas waste pipe 4 is connected to the bottom of each tower via valves 4 to 6. In addition, from the middle of the exhaust gas waste pipe 4 (upstream of the valves V4 to V6 intervening points), the desorption pipes 5a and 5
b.

5c are branched, and they are joined downstream via valves V, ~■,. A vacuum pump 6 is provided in the merged desorption tube 5 and connected to a product gas holder 9. The product gas holder 9 is provided with a product gas recovery pipe 2 and a cleaning pipe 8 for extracting a part of the product gas for cleaning.
13 to V15 to the tops of adsorption towers 3a, 3b, and 3c. In addition, the connecting pipes 10a, 10b, 10c that connect the adsorption towers 3a, 3b, 3c in series are connected to valves ■1o to V1.
2, respectively.

Fig. 3 is a time schedule showing the operation process of one of the adsorption towers 3a, 3b, and 3c, and the entire operation from the start of the adsorption process to the start of the next adsorption process is considered to be one cycle. , one cycle consists of an adsorption step, a recovery step, a washing step, and a desorption step. First, in the adsorption process, the interior of the desorbed adsorption tower is pressurized, and the raw material gas is supplied under pressure from the supply pipe 1. N2 gas, the target component to be recovered, is adsorbed onto the adsorbent, and impure component gas (mainly 02 gas) is removed from the exhaust gas. Discharge from waste pipe 4. In the desorption process, the adsorption tower and the product gas holder 9 are communicated via the vacuum pump 6 and the desorption tube 5, and the pressure inside the adsorption tower is reduced to remove the N2 adsorbed by the adsorbent.
is removed and stored in the product gas holder 9.

Further, the recovery step and the washing step are illustrated in FIGS. 4(a) and 4(b), taking the case of the adsorption tower 3a as an example. That is, in the state shown in FIG. 4(a), the high-purity N2 gas supplied from the product gas holder 9 passes through the cleaning pipe 8 to expel the residual 02 in the adsorption tower 3C, and the adsorption tower 3a has completed the adsorption process. It is sent to via the connecting pipe 10c.

As a result, a recovery process is performed in the adsorption tower 3a, and the adsorption tower 3a
C, a cleaning process is performed. Next, in the state shown in FIG. 4(b), the adsorption tower 3a performs a cleaning process, and the adsorption tower 3b performs a recovery process.

After the cleaning step shown in FIG. 4(b) is completed, the adsorption tower 3a is then subjected to a desorption step.

[Problems to be solved by the invention] However, when desorbing and recovering N2 gas, the adsorption tower 3a
, 3b, and 3c are depressurized by the vacuum pump 6, we find that not only the gas in the adsorption tower where the desorption process is performed, but also the gas inside the pipe connected to the adsorption tower (however, the (up to the position where it is blocked by)
The remaining gas is also drawn into the vacuum pump 6 side (for example, when considering the adsorption tower 3a, the remaining gas in the piping surrounded by the broken line in FIG. 2 becomes a problem). Therefore, if low-purity N2 gas remains in the pipe,
This causes a problem in that the purity of the product N2 gas taken out into the product gas holder 9 decreases. In particular, the amount of low-purity N2 gas remaining in the connecting pipes used during the recovery process is large, and is therefore a major factor in reducing the purity of the product N2 gas.

Therefore, the present inventor developed a desorption preparation system in which impure component gases are removed in advance from around the adsorption tower where the next desorption process is scheduled, and only high-purity product gas is desorbed during desorption. As a result of various research aimed at this purpose, we succeeded in developing the method of the present invention.

[Means for Solving the Problems] The method of the present invention, which has achieved the above object, is that, after the cleaning step and before proceeding to the desorption step, the piping connected to the adsorption tower where the cleaning has been performed is already connected. The gist is to communicate with the adsorption tower after the desorption process is completed, and to introduce the gas remaining in the connected piping into the adsorption tower after the desorption process is completed using a pressure difference. .

[Function] In the present invention, the piping connected to the adsorption tower in which the cleaning process has been completed and the desorption process is to be performed next is connected to another adsorption tower in which the desorption process has already been completed and the internal pressure of the tower is in a reduced pressure state. The adsorption tower was connected to the adsorption tower, and the gas in the pipe was transferred to the other adsorption tower using the pressure difference. As a result, the impure component-containing gas in the pipe communicating with the adsorption tower that was scheduled for desorption was removed, making it possible to significantly reduce the concentration of impure components in the product gas extracted by desorption. .

Regarding the piping system for gas supply due to pressure difference,
In the embodiments described later, a case will be described as a representative case in which pipes are formed that bypass each other between the connecting pipes 10a to 10c, but the present invention is not limited at all, and may be formed by forming dedicated pipes or by other means. can also be adopted.

[Example] FIG. 1 is a schematic explanatory diagram showing a typical example of a PSA device used in the method of the present invention, and is similar to the conventional PSA device shown in FIG.
It has the following features compared to the SA device.

That is, in this device, each connection pipe IQa, 10b.

Pipes A, B, and C that mutually bypass 10c are provided, and each of the pipes A, B, and C is provided with valves 21 to Z, respectively.

As another example, as shown in FIG.
10-a+v11-a+ V 12-a and vlo
-b+ vII-b+ V 12-b may also be provided to provide for backflow prevention.

For example, as shown in Fig. 1, when the cleaning process in the adsorption tower 3a of the PSA device is completed, valve Z3 is opened and connected to the adsorption tower 3c (which is after the desorption process has been completed and is in a reduced pressure state). When the pipe 10a is brought into instantaneous communication (for several seconds), the gas in the connecting pipe 10a is moved along the arrow in FIG. 1 to the adsorption tower 3c. At this time, a portion of the gas in the adsorption tower 3b that has completed the recovery step is also transferred to the adsorption tower 3C.

Since the impure gas is removed after the cleaning step, this step will be referred to as a purification step hereinafter, but the recovered components in the impure gas will enter the adsorption tower 3C and constitute a part of the pressure increasing step.

That is, FIG. 5 is an explanatory diagram showing the process order of a certain adsorption tower, in which the above-mentioned purification step is set after the cleaning step is completed, and the connecting pipe is connected to another adsorption tower to remove low-purity N2 in the pipe.
Gas is released, and on the other hand, after the desorption step is completed, it forms part of the pressure increasing step as a receiver in the purification step of another adsorption tower.

The connection route between the connecting pipes 10a, 10b, 10c and the adsorption tower under reduced pressure after the completion of desorption is not limited to the embodiment shown in Fig. 1, but as described above, the embodiment shown in Fig. 6 is also adopted. can.

For example, in the purification process of the adsorption tower 3a, the connecting pipe 10a
The gas flows to the adsorption tower 3C along the arrow, but at this time, the gas in the adsorption tower 3b, which has completed the recovery process, passes through the on-off valve 10.
Since it is blocked by +o-b, it does not move to the adsorption tower 3C.

Trapho 1 Using the PSA device shown in Figure 1, N2 gas (79%) and 02 gas (21
An experiment was conducted in which N gas was selectively recovered from a mixed gas consisting of (%). The size of the adsorption tower is an inner diameter of 450III11.
A material with a height of 2000++ ua was used, and synthetic zeolite type 5A was used as the adsorbent.

The adsorption pressure was 4.0 kg/cm'G, and the raw material gas was 7.
Supplied to the adsorption tower at ONm'/h, desorption pressure is 0.1 k
g/cm2G, and one cycle of the adsorption tower process was 3 minutes.

On the other hand, when N and gas were recovered under the same conditions as above according to the conventional process sequence shown in Figure 3, the product N2 gas purity was 99.998%, but when the method of the present invention was used It has become possible to achieve a product N2 gas purity of 99.999%, which is approximately the same purity as when N2 gas is separated and recovered using a cryogenic separator.

Furthermore, the recovery rate of N2 gas by the method of the present invention was over 40%, which was almost unchanged compared to the recovery rate of the conventional method.

In the above example, an example of concentration and recovery of N2 gas was shown and explained, but the method of the present invention is also applicable to recovery of H2 gas, CO gas, etc.

[Effects of the Invention] Since the method of the present invention is configured as described above, it has become possible to separate and purify the target component gas to be recovered with high purity without reducing the recovery rate.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram showing a typical example of a PSA device used in the method of the present invention, and Fig. 2 is a schematic illustration of a typical PSA device used in the method of the present invention.
A schematic explanatory diagram showing an example of apparatus A, Fig. 3 is an explanatory diagram showing the conventional pressure swing adsorption process, and Figs. 4 (a) and (b).
) is an explanatory diagram showing the recovery process and cleaning process of the adsorption tower 3a,
FIG. 5 is an explanatory diagram showing the pressure swing adsorption step of the method of the present invention, and FIG. 6 is a schematic explanatory diagram showing another example of a PSA apparatus used in the method of the present invention.

Claims (1)

[Claims] In the separation and purification of easily adsorbable components in which at least the adsorption, washing, and desorption steps are performed using multiple pressure swing adsorption towers, after the washing step is completed and before moving on to the desorption step, the adsorption tower that has been washed is Connecting the connected piping to the adsorption tower after the desorption step has already been completed, and introducing the gas remaining in the connected piping to the adsorption tower after the desorption step has been completed by a pressure difference. A pressure swing adsorption method characterized by: