JPH0372326B2 - - Google Patents

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. As a typical example, a method for recovering N ₂ with high purity from a mixed gas of O ₂ and N ₂ will be described below, but the scope of application of the method of the present invention should not be construed as limited by this.

[Conventional technology] Pressurized air is transferred to a pressure swing adsorption device (hereinafter simply referred to as
The methods for concentrating and recovering _N2 gas by introducing it into a PSA device can be roughly divided into two methods: one is to adsorb _O2 gas to an adsorbent and remove it, and the other is to adsorb _N2 gas to an adsorbent and then desorb and recover it. It is classified into two methods.
The latter uses a zeolite-based adsorbent,
This is a method of desorbing and recovering high-purity N ₂ gas by reducing the pressure of the adsorption tower after adsorbing N ₂ gas using a vacuum pump or the like, and this method will be explained below.

The second is a schematic explanatory diagram showing a three-column type PSA device, in which an automatic opening/closing valve (hereinafter simply referred to as a valve) is installed in a raw material gas (pressurized air) supply pipe 1 connected to the outlet side of a pretreatment device (not shown). ) Adsorption towers 3a, 3b, 3c are connected via V ₁ to V ₃ , and a valve is installed at the bottom of each tower.
An exhaust gas waste pipe 4 is connected via V ₄ to V ₆ .
In addition, desorption pipes 5a, 5b, and 5c are branched from the middle of the exhaust gas waste pipe 4 (upstream from the valves _V4 to _V6 intervening points), and these are connected to the downstream side via the valves _V7 to _V9 . will be joined at. And the merged detachment tube 5
A vacuum pump 6 is installed in the product gas holder 9.
connected to. The product gas holder 9 is provided with a product gas recovery pipe 2 as well as a cleaning pipe 8 for extracting a part of the product gas for cleaning, and the cleaning pipe 8 is branched and then connected to valves V ₁₃ to V ₁₅ . It is connected to the tops of adsorption towers 3a, 3b, and 3c via. Incidentally, connection pipes 10a, 10b, 10c connecting the adsorption towers 3a, 3b, 3c in series are provided respectively via valves _V10 to _V12 .

FIG. 3 is a time schedule showing the operation process of the adsorption towers 3a, 3b, and 3c. When the entire operation from the start of the adsorption process to the start of the next adsorption process is defined as one cycle, one cycle is the adsorption process. It consists of a process, a recovery process, a cleaning process, and a desorption process. First, in the adsorption process, the interior of the adsorption tower after desorption is pressurized, and the raw material gas is supplied under pressure from the supply pipe 1, and the N ₂ gas, which is the target component to be recovered, is adsorbed on the adsorbent, and the impure component gas (mainly O ₂ gas) is is released from the exhaust gas waste pipe 4. In addition, in the desorption process, the adsorption tower and the product gas holder 9 are communicated via the vacuum pump 6 and the desorption pipe 5, and the pressure inside the adsorption tower is reduced to desorb the N ₂ adsorbed by the adsorbent and store it in the product gas holder 9. do.

Further, the recovery step and the washing step will be explained using the adsorption tower 3a as an example, as shown in FIGS. 4a and 4b. That is, in the state shown in FIG. 4a, high-purity N ₂ gas supplied from the product gas holder 9 passes through the cleaning pipe 8 to expel the residual O ₂ in the adsorption tower 3c, and the adsorption tower after the adsorption process is removed. 3a via the connecting pipe 10c. As a result, a recovery process is performed in the adsorption tower 3a, and a cleaning process is performed in the adsorption tower 3c. Furthermore, in the state shown in Figure 4b,
The adsorption tower 3a performs a cleaning process, and the adsorption tower 3b performs a recovery process.

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

[Problem to be solved by the invention] However, when desorbing and recovering _N2 gas, one of the adsorption towers 3a, 3b, and 3c is operated by the vacuum pump 6.
If we look in more detail at the situation when the pressure is reduced 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 N ₂ gas remains in the pipe, a problem arises in that the purity of the product N ₂ gas taken out to the product gas holder 9 decreases. In particular, low-purity _N2 gas remaining in the connecting pipes used in the recovery process and cleaning process is
Since the amount is large, it is a major factor in reducing the purity of the product N ₂ gas. That is, in the example of FIG. 2, when the adsorption tower 3a is desorbed, the downstream portion of the valve V ₁₂ of the connecting pipe 10c and the valve V ₁₀ of the connecting pipe 10a are
A large amount of low-purity _N2 gas remains in the upstream portion of the gas, and this will be mixed into the product gas.

Therefore, the present inventor conducted various research with the aim of developing a desorption preparation system in which impurity gases are removed from the connecting pipes before the desorption process, and only high-purity product gas is desorbed during the desorption process. As a result of repeated efforts, we succeeded in developing the method of the present invention.

[Means for Solving the Problems] The method of the present invention that has achieved the above object uses three or more pressure swing adsorption towers, each adsorption tower is connected in series by a connecting pipe, and each adsorption tower is In a method for separating easily adsorbable components in which at least the steps of adsorption, recovery, washing, and desorption are carried out in sequence, the column is used to connect the connecting piping used in the recovery step in the adsorption tower immediately before the desorption step and the connection piping used in the recovery step in the adsorption tower immediately before the desorption step, and the connection piping used in the recovery step in the adsorption tower immediately before the desorption step, and Another adsorption tower after the completion of the desorption step is connected through a bypass pipe, and gas remaining in the connecting pipe is introduced into the other adsorption tower after the completion of the desorption step through a purification step. This is a summary.

[Function] In the present invention, the connecting pipe used in the recovery process and the cleaning process is connected via a bypass pipe to an adsorption tower in which the desorption process has already been completed and the internal pressure of the tower is in a reduced pressure state, and the connecting pipe is It was decided to move the gas to the adsorption tower in the reduced pressure state using the pressure difference. As a result, when the adsorption tower is desorbed, the contamination of gas containing impure components is reduced, making it possible to significantly reduce the concentration of impure components in the product gas taken out by desorption.

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

That is, in this device, each connection pipe 10a, 10b,
10c and each adsorption tower 3a to 3c are provided separately, and each bypass pipe A,
Valves Z ₁ to _{Z 3} are disposed midway between B and C, respectively. As shown in FIG. 6, other configurations of this embodiment include the most upstream end (lower side of each adsorption tower 3a to 3c) and the most downstream end (top side of each adsorption tower 3a to 3c) of the connecting pipes 10a to 10c. ) on each of the on-off valves V _10-a ,
Similarly _{, bypass pipe A} ,
B, C and valves Z ₁ to _{Z 3} can also be provided.

For example, as shown in Figure 1, the adsorption tower 3 of a PSA device
When the cleaning step a is completed, the valve _Z3 is opened to instantaneously (several seconds) communicate the adsorption tower 3c (which is in a reduced pressure state after the desorption step) and the connecting pipe 10a. When the connecting pipe 10a
The gas therein is moved to the adsorption tower 3c along the arrow in FIG. 7a. If the valve Z ₃ is opened before closing the valve V ₁₀ , the gas remaining in either the upstream or downstream portion of the valve V ₁₀ in the connecting pipe 10a will be transferred to the adsorption tower 3c. . In other words, the purification of the upstream portion assists in increasing the concentration during the desorption step of the adsorption tower 3a, and the purification of the downstream portion is performed by the adsorption tower 3b, which performs the desorption step after the cleaning step.
This promotes high concentration of the components, and the components to be recovered can be obtained with high purity overall. At this time, a small amount of high-purity gas in the adsorption towers 3a and 3b also moves to the adsorption tower 3c.

After the cleaning step, the impure gas is removed, so this step will be referred to as a purification step hereinafter, and the components to be recovered in the impure gas enter the adsorption tower 3c and are adsorbed by the adsorbent. Figures 7a to 7c show each connecting pipe 10a to 10.
FIG. 3 is an explanatory diagram showing a state when adsorption towers 3a to 3c are connected to adsorption towers 3a to 3c after the desorption process.

FIG. 5 is an explanatory diagram showing the process order of each adsorption tower in a three-column PSA device, and the above-mentioned purification process is performed after the cleaning process is completed when connecting the connecting piping with other adsorption towers in a reduced pressure state. An example is shown in which a process is set, the connecting pipe is connected to another adsorption tower, and low-purity N ₂ gas in the pipe is released.
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. The connecting pipes 10a to 10c are connected to the adsorption towers 3a to 3c via bypass pipes A, B, and C. In this example, in the purification process of the adsorption tower 3a, the gas in the connecting pipe 10a moves along the arrow to the adsorption tower 3c via the valve Z ₃ and the bypass pipe C, but at this time, the valve V _10-b is closed. If this is done, the gas in the adsorption tower 3b after the recovery process is blocked by the valve _1010-b , so that it can be prevented from moving to the adsorption tower 3c.

Experimental example Using the PSA device shown in Figure 1, N ₂ gas (79%) and O ₂ gas were added along the process sequence shown in Figure 5.
An experiment was conducted to selectively recover N ₂ gas from a mixed gas consisting of (21%) gas. The adsorption tower used had an inner diameter of 450 mm and a height of 2000 mm, and synthetic zeolite type 5A was used as the adsorbent.

The adsorption pressure is 4.0Kg/cm ² G, and the raw material gas is 70N.
m ³ /h to the adsorption tower, and the desorption pressure is 0.1Kg/cm ²
G, and one cycle of the adsorption tower process was set to 3 minutes.

On the other hand, if _N2 gas is recovered under the same conditions as above according to the conventional process order shown in Figure 3,
The product _N2 gas purity was 99.998%, but when the method of the present invention was used, the product _N2 gas purity was 99.999%.
%, using a cryogenic separator
It has become possible to obtain a product with almost the same purity as by separating and recovering N ₂ gas. Furthermore, the recovery rate of N ₂ 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 N ₂ gas was shown and explained, but the method of the present invention can also be applied to H ₂ gas, CO
It is also applied to the recovery of gas, etc., and is used in PSA equipment that has three or more adsorption towers.

[Effect of the invention] Since the method of the present invention is configured as described above,
Since the low-purity gas remaining in the connecting pipe is no longer mixed into the product gas, it is now possible to separate and purify the high-purity component gas to be recovered. At this time, the recovery rate of the component to be recovered is not reduced.

[Brief explanation of drawings]

Figure 1 shows a typical PSA used in the method of the present invention.
Fig. 2 is a schematic explanatory diagram showing an example of a PSA device used in a conventional method; Fig. 3 is an explanatory diagram showing a conventional pressure swing adsorption process; Fig. 4 a, b 5 is an explanatory diagram showing the recovery process and washing process of the adsorption tower 3a, FIG. 5 is an explanatory diagram showing the pressure swing adsorption process of the method of the present invention, and FIG. 6 is an example of another PSA device used in the method of the present invention. Schematic explanatory diagrams 7a to 7c are explanatory diagrams showing the connection between the connecting pipe and the adsorption tower in the apparatus shown in FIG. 1. 1... Raw material gas supply pipe, 2... Product gas extraction pipe, 3a, 3b, 3c... Adsorption tower, 4... Exhaust gas disposal pipe, 5... Desorption pipe, 6... Vacuum pump, 8
...Cleaning pipe, 9...Product gas holder, 10a,
10b, 10c...Connection piping, _V1 to _V16 , _V10-a ,
V _11-a , V _12-a , V _10-b , V _11-b , V _12-b , Z ₁ to _{Z 3} …
...Automatic on-off valve.

Claims (1)

[Claims] 1 Three or more pressure swing adsorption towers are used, and each adsorption tower is connected in series through connecting piping, and each adsorption tower is capable of absorbing easily adsorbable components that perform at least the steps of adsorption, recovery, washing, and desorption in sequence. In the separation method, the connecting pipe used for the recovery process in the adsorption tower immediately before the desorption process is communicated with another adsorption tower after the desorption process has already been completed via a bypass pipe, and A pressure swing adsorption method comprising a purification step of introducing gas remaining in the adsorption column into another adsorption tower after the completion of the desorption step using a pressure difference.