JP2569091B2 - Pressure swing adsorption method - Google Patents

Description

The present invention relates to a method for separating and recovering a specific component {for example, carbon monoxide (CO)} from a mixed gas in a high yield by using two or more adsorption towers. And a pressure swing adsorption method.

(Prior art) Conventionally, as a pressure swing adsorption method for separating and recovering CO from a mixed gas containing CO, for example, a pressure swing step, an adsorption step, a pressure equalization step, a washing step, and a desorption step are included. Instead of directly discarding the purge exhaust gas generated in the cleaning process, the purge exhaust gas is introduced into another adsorption tower, and the CO component in the purge exhaust gas is further adsorbed to remove CO.
There is known one that improves the recovery of components.

The conventional pressure swing adsorption method will be described with reference to one of the adsorption towers A based on a process explanatory view shown in FIG. 3 and an apparatus having two adsorption towers A and B as shown in FIG. First, in the pressurization step, CO, N ₂ , CO ₂ ,
The raw material gas, which is a mixed gas of H ₂ , is pressurized and supplied to the one adsorption tower A through the supply pipe 21 and the valve 31a.
Thereby, the pressure of the adsorption tower A is increased to a predetermined adsorption pressure.

Next, in the adsorption step, the raw material gas is supplied to the adsorption tower A following the above-described pressure increasing step, and the valve 32a is opened. As a result, highly adsorbable CO (easily adsorbable component) in the raw material gas is adsorbed to the adsorbent (for example, zeolite, activated carbon, or alumina) in the adsorption tower A under pressure, and N ₂ and H ₂ ( The hardly adsorbable component) is discharged line 22 and valve
Released into the atmosphere through 32a. This adsorption step is terminated by closing the valves 31a and 32a immediately before the CO concentration at the outlet of the adsorption tower A becomes the same as the CO concentration in the raw material gas at the inlet. It is blocked under the adsorption pressure.

While the adsorption tower A is in the pressure increasing step and the adsorption step, a desorption step is performed in the other adsorption tower B. In this desorption step, the CO component adsorbed up to the previous step is decompressed and desorbed by the vacuum pump 12. , This CO component is
And the product gas is introduced into the product gas storage tank 4 through the valve 33b.

When the above adsorption step is completed, the adsorption tower A is connected to the communication line 24a.
The pressure equalizing process is started by opening the valve 34a. As a result, the raw material gas in the adsorption tower A whose pressure has been increased to the adsorption pressure moves to the adsorption tower B in a reduced pressure state, and the pressure of the adsorption tower A is reduced to almost the atmospheric pressure, and the pressure of the adsorption tower B is increased to almost the atmospheric pressure.
The valve 34a is closed when the two adsorption towers A and B are almost equalized to the atmospheric pressure.

Thereafter, the adsorption tower A enters a washing step. In this cleaning step, the valve 35a of the cleaning gas supply pipe 25 and the valve of the communication pipe 24a
34a and the valve 32b of the discharge line 22 are opened, and the CO component gas in the product gas storage tank 4 is introduced into the adsorption tower A. The CO component gas purges the hardly adsorbable components remaining in the adsorption tower A, and the purge exhaust gas is sent to the other adsorption tower B, and a part of the CO component in the purge exhaust gas is converted into an adsorbent in the adsorption tower B. Is adsorbed. The remaining purged exhaust gas in which the CO component has been adsorbed by the adsorption tower B has almost the atmospheric pressure, and is released into the atmosphere by the exhaust gas compressor 13.

After closing the valves 35a, 34a, 32b opened in the washing step, the adsorption tower A enters a desorption step. In this desorption step, the CO component adsorbed in the adsorption tower A is desorbed under reduced pressure by opening the valve 33a of the absorption pipe 23 and operating the vacuum pump 12, and this CO component gas is absorbed in the product gas storage tank 4. Is done.

While the desorption step is being performed in the adsorption tower A, the other adsorption tower B is performing the pressure increasing step and the adsorption step.
When the other adsorption tower B enters the pressure equalizing step, the pressure of the adsorption tower A is raised to almost the atmospheric pressure.
Enters the washing step, a part of the CO component in the purge exhaust gas from the adsorption tower B is adsorbed in the adsorption tower A, and the remaining purge exhaust gas is discharged to the atmosphere through the discharge pipe 22. Thereafter, the adsorption tower A returns to the pressure increasing step, and the same steps are repeated thereafter.

In the conventional pressure swing adsorption method described above, for example, the cleaning gas supplied to the adsorption tower A in the cleaning step is a product gas having a high CO purity. Low but close to product gas
Has purity. Therefore, in the above-mentioned conventional method, the purged exhaust gas after the cleaning is sent to the other adsorption tower B, and the CO component in the purge exhaust gas is adsorbed by the adsorption tower B, but the supply from the product gas storage tank 4 is performed. Since the source pressure is relatively low, the recovery of the CO component in the other adsorption tower B is not sufficient. Therefore, a large amount of CO is contained in the purged exhaust gas discarded from the other adsorption tower B through the discharge line 22. Ingredients will be included. As a result, there is a problem that the recovery rate of the CO component cannot be sufficiently improved.

Therefore, in the pressure equalization step, the two adsorption towers A and B are not equalized with each other until the pressure becomes almost atmospheric pressure, and as shown by a dashed line in FIG. A method has also been proposed in which the other adsorption tower B is set to a pressure lower than the atmospheric pressure in a state where the pressure is reduced to a lower level (for example, see Japanese Patent Application Laid-Open No. 61-37970). According to this method, even if the cleaning step is performed with the valve 32b on the outlet side of the other adsorption tower B closed, the purged exhaust gas can be introduced from one adsorption tower A to the other adsorption tower B, As a result, the purge exhaust gas is stored without being discarded from the other adsorption tower B.

However, in this method, when the adsorption tower A during adsorption and the adsorption tower B during desorption are equalized in pressure, the adsorption pressure is reduced to normal pressure before the adsorption tower B returns to normal pressure. Values and desorption pressure values must be set, and setting these pressures is troublesome. Setting of equalizing time,
A great deal of labor is required for the adjustment, and the pressure inside the adsorption tower to be washed during the washing step gradually increases, which causes a problem that the washing effect is reduced.

It is also conceivable to make the supply pressure of the cleaning gas from the product gas storage tank 4 relatively high. However, in this case, since the cleaning pressure increases with time, the cleaning effect is deteriorated by the adsorption characteristics of the adsorbent, and as a result, the purity of the CO component gas to be desorbed and recovered is reduced.

In addition, it is conceivable that the purge exhaust gas from the discharge line 22 is introduced into the suction side of the raw material gas compressor 11, and the purge exhaust gas is reused as the raw material gas. However, in this case, it is necessary to increase the capacity of the raw material gas compressor 11 and the capacity of a not-shown pretreatment step (for example, removal of water) by the amount of reuse, which causes a problem of lack of economy. .

(Purpose of the Invention) The present invention has been made to solve such a conventional problem, and it is possible to easily and surely improve the recovery rate of a specific component, and to impair the purity and economic efficiency. The present invention is to provide a pressure swing adsorption method without any problem.

(Constitution of the Invention) The present invention has a pressure rising step, an adsorption step, a pressure equalizing step, a washing step, and a desorption step. In the pressure swing adsorption method for adsorbing and recovering a specific component, in the washing step, the specific component gas collected in the desorption step is introduced as a cleaning gas into the adsorption tower after the pressure equalization step. The outlet of another adsorption tower different from the adsorption tower is closed, and when the purge exhaust gas generated in the washing step is guided to the other adsorption tower, the purge exhaust gas is repressurized and sent to the other adsorption tower. is there.

According to the above configuration, even if the cleaning gas is supplied at a relatively small pressure in the cleaning step, the purge exhaust gas is repressurized when being sent from the adsorption tower in the cleaning step to another adsorption tower. The purged exhaust gas can be reliably introduced into another adsorption tower with the outlet closed, and the purged exhaust gas can be adsorbed to the adsorbent in a pressurized state. Thus, a larger amount of a specific component can be adsorbed and recovered than before.

(Embodiment) An apparatus for carrying out the present invention shown in FIG.
The apparatus shown in the figure is provided with a pressurized pipe 26 for pressurizing and sending purge exhaust gas generated in two adsorption towers A and B to one another from the conventional apparatus shown in the figure. The pressurized line 26 is provided with a purge exhaust gas compressor 14, and the outlets of the adsorption towers A and B are connected to the suction side of the purge exhaust gas compressor 14 via valves 36a and 36b. , B inlet valves 37a, 37b
Is connected to the discharge side of the purge exhaust gas compressor 14. Further, in the apparatus shown in FIG. 2, the exhaust gas compressor 13 provided in the conventional apparatus shown in FIG. 4 is omitted.

A feature of the embodiment shown in FIG. 1 is that the purge exhaust gas generated in the washing step of one adsorption tower is sent to the other adsorption tower, but the conventional method shown in FIG. twenty four
In this embodiment, the feed is performed through the pressurized pipe 26, whereas the feed is performed through the b.

That is, after equalizing the two adsorption towers A and B to almost the atmospheric pressure in the pressure equalizing step of one adsorption tower A, the valve of the communication line 24a is opened.
Close 34a. This allows all valves 31a-37a, 31b-3
7b, is closed. Thereafter, in the cleaning step of the one adsorption tower A, the valve 35a of the cleaning gas supply pipe 25 is opened, and the valve 36a on the outlet side of the adsorption tower A of the pressurization pipe 26 and the inlet of the other adsorption tower B are opened. Open side valve 37a and purge exhaust gas compressor 1
Activate 4. Then, the purge exhaust gas generated by washing the adsorption tower A is sucked from the adsorption tower A by the purge exhaust gas compressor 14, and the purge exhaust gas is pressurized and accumulated in the other adsorption tower B. Thereafter, the one adsorption tower A, which has completed the washing step, shifts to a desorption step, and the other adsorption tower B, in which the purged exhaust gas has been stored, shifts to a step of increasing the pressure by a raw material gas.

Therefore, in the other adsorption tower B, it is possible to perform the adsorption and recovery of the CO component in the purged exhaust gas at a pressure higher than the atmospheric pressure. It can be adsorbed and recovered. As a result, the yield in CO component recovery can be improved as compared with the conventional case. Further, since the purge exhaust gas which has been discarded up to now is accumulated in the other adsorption tower B as a part of the pressurizing gas without being discarded, the exhaust gas compressor 13 (for discharging the purge exhaust gas) in the conventional method is used. 4) can be omitted.

Further, since the purge exhaust gas is sucked from the adsorption tower A in the cleaning step by the purge exhaust gas compressor 14, even if the valve 32b on the discharge line 22 side of the other adsorption tower B is closed, the purge exhaust gas is removed. It can be reliably introduced into the other adsorption tower. Similarly, since the purge exhaust gas is supplied to the other adsorption tower B by the purge exhaust gas compressor 14, it is not necessary to set the adsorption tower B to a state lower than the atmospheric pressure in the pressure equalizing step.

Note in the above embodiment has described the case of separating and recovering the CO as a specific component from a feed gas containing CO, is not limited to this, for example, N _2, O ₂ and Ar particular from a feed gas consisting of a (argon) The present invention can also be applied to a case where, for example, N ₂ is separated and recovered as a component.

Further, in the above-described embodiment, an apparatus composed of two adsorption towers A and B is used.
In an apparatus composed of two adsorption towers, the steps may be shifted from each other to continuously operate.

(Examples) CO 70% by using the apparatus shown in FIG. 2, CO ₂ is 15%, N ₂
Was tested in accordance with the process shown in FIG. The adsorbent used was an activated alumina with a copper compound impregnated.

First, in one adsorption tower A, after performing a pressure raising step and an adsorption step at an adsorption pressure of 2 kg / cm ² G, the pressure in the adsorption tower A is reduced to atmospheric pressure by an equalizing step. Next, the adsorption tower A is depressurized.
The product gas is supplied from the product gas storage tank 4 to the adsorption tower A at a pressure of 0.1 kg / cm ² G to wash the adsorption tower A.
Purging exhaust gas compressor
The pressure is increased to 0.3 kg / cm ² G by 14 and the pressure is accumulated in the other adsorption tower B to adsorb and collect the CO component. After the washing, the adsorption tower A is depressurized to 50 Torr by the vacuum pump 12 to desorb and collect the CO component. After completion of the desorption step, the pressure of the adsorption tower A is raised to almost the atmospheric pressure by the pressure equalization step of the other adsorption tower B, and then the purge exhaust gas in the washing step of the other adsorption tower B is purged by the purge exhaust gas compressor 14 into the adsorption tower A. 0.3k
Increase the pressure to g / cm ² G. This completes one cycle, and returns to the above-described pressurizing step again, where the raw material gas compressor 11 performs the adsorption
Increase the pressure to 2kg / cm ² G.

As a result of operating the above cycle for 8 minutes, the CO purity of the product gas was 99.7% and the CO recovery was 85% in about 80 minutes after the start of the operation.

(First Comparative Example) Using a conventional apparatus shown in FIG. 4, a test was conducted in accordance with the conventional process shown in FIG. 3 in the case of separating and recovering CO from a raw material gas having the same composition as the above specific example. In this case, as the washing step, the product gas is supplied from the product gas storage tank 4 to the adsorption tower A at a pressure of 0.2 kg / cm ² G to wash the adsorption tower A, and
The purge gas discharged from the outlet of the adsorption tower A at a pressure of 0.1 kg / cm ² G flows into the other adsorption tower B to adsorb and recover the CO component. The discharged exhaust gas is disposed of by the exhaust gas compressor 13.

As a result, the CO purity of the product gas was 98.9%, and the CO recovery was 78%.

(Second Comparative Example) The other adsorption tower B was used as a washing step in the first comparative example.
The operation was performed with the valve 32b on the outlet side of the valve closed. For this reason, the product gas is supplied to the adsorption tower A from the product gas storage tank 4 at a pressure of 0.4 kg / cm.
^The adsorption tower A was washed by flowing at ² G, and the purged exhaust gas coming out of the outlet of the adsorption tower A was flowed into the other adsorption tower B to adsorb and collect the CO component. In this case, the pressure of the purged exhaust gas coming out of the outlet of the adsorption tower A at the beginning of the washing step is relatively low, but the pressure increases with the passage of time and finally reaches 0.4 kg / cm ² G. .

As a result, the CO purity of the product gas was 98.5%, and the CO recovery was 84%.

(Effect of the Invention) According to the pressure swing adsorption method of the present invention, even if the cleaning gas is supplied to the adsorption tower at a relatively small pressure, the purge exhaust gas from the adsorption tower is supplied to another adsorption tower. At the time of re-pressurization, it can be reliably introduced into another adsorption tower with the outlet closed, and since the other adsorption tower has its outlet closed, the above-mentioned purged exhaust gas is stored in the adsorption tower. Is held in a pressurized state. For this reason, the other adsorption towers can adsorb and recover a larger amount of specific components in the purged exhaust gas than in the conventional apparatus without discarding the purged exhaust gas.

Therefore, there is no need to set the other adsorption tower to a pressure lower than the atmospheric pressure in the pressure equalization step, and the recovery rate of the specific component can be easily and reliably improved with the adsorbent having ordinary adsorption performance, and the purity is also improved. It does not hurt the economy.

[Brief description of the drawings]

FIG. 1 is a process explanatory diagram showing the steps of the embodiment of the present invention and the qualitative pressure in the adsorption tower with time, FIG. 2 is a schematic configuration diagram of an apparatus for performing the process of FIG. FIG. 3 is a process explanatory view showing each step of the conventional method and the qualitative pressure in the adsorption tower with time, and FIG. 4 is a schematic configuration diagram of an apparatus for performing the process of FIG. A, B …… Adsorption tower (pressure swing adsorption tower).

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Taku Aogata 366, Hasuike, Myohoji, Suma-ku, Kobe City, Hyogo Prefecture Dihiko 376-1, Kako, Inami-cho, Kako-gun, Hyogo (72) Inventor Toshiaki Tsuji 145 Minaminakaokamoto, Izumisano-shi, Osaka

Claims (1)

(57) [Claims] 1. A method comprising a step of increasing pressure, an adsorption step, a pressure equalization step, a washing step and a desorption step, wherein at least two or more pressure swing adsorption towers are repeated with the above steps shifted from each other to remove specific components in the mixed gas. In the pressure swing adsorption method of adsorbing and recovering, in the washing step, the specific component gas collected in the desorbing step is introduced as a washing gas into the adsorption tower after the pressure equalization step. Closing the outlet of another different adsorption tower, and introducing the purge exhaust gas generated in the washing step to the other adsorption tower, re-pressurizing the purge exhaust gas and feeding it to the other adsorption tower. Pressure swing adsorption method.