JPH01151920A - Pressure-swing absorption method - Google Patents

Abstract

PURPOSE:To elevate recovery efficiency of particular gases, by carrying out the processes of pressure elevation, absorption pressure equalization, cleaning, desorption, using a component gas recovered by the desorption process for cleaning, and sending a purged waste gas, which is produced in the cleaning process and re-compressed, to another absorption tower. CONSTITUTION:Raw material gases contg. CO, CO2 and N2 are pressured by a compressor 11, supplied to an adsorption column A, compressed to a defined pressure, and then CO in the gases is adsorbed by opening valve 32a and other gases are exhausted to air. Then, the adsorption column A and B are put in pressure-equalizing process, a valve 34a is opened so as to lower the pressure of the adsorption column A, and the column A is purged with CO from a prod uct gas storage tank 4. The waste gas produced in the purging process is pres sured by a compressor 14 and sent to the adsorption column B to be used for pressure-elevation. And then, in the tower A, CO is desorpted by a vacuum pump 12, recovered, and sent to product gas storage tank 4. Thus, these processes are repeated in the tower A and B.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention is directed to the separation and recovery of specific components (e.g. carbon oxide (Go)) from a mixed gas using two or more adsorption towers in high yield. The present invention relates to a pressure swing adsorption method that allows for

(Conventional technology) Conventionally, c from a mixed gas containing CO, for example.

The pressure swing adsorption method involves a pressure raising process, an adsorption process, a pressure equalization process, a cleaning process, and a desorption process. The purge gas is introduced into another adsorption tower to further adsorb the CO acid component in the purge gas.

Some devices are known that improve the recovery rate of components.

The above conventional pressure swing adsorption method will be explained based on the process diagram shown in FIG. 3 and an apparatus having two adsorption towers A and B as shown in FIG. 4, focusing on one adsorption tower Δ. First, in the pressure increasing step, the raw material gas compressor 11
2, CO2, N2 f7) The raw material gas, which is a mixed gas, is pressurized and supplied to one of the adsorption towers A through the supply pipe 21 and the valve 31a. As a result, the adsorption tower A is pressurized to a predetermined adsorption pressure.

Next, in the adsorption step, the raw material gas is supplied to the adsorption tower A following the pressure increasing step, and the valve 32a is opened. As a result, highly adsorbable Go (an easily adsorbable component) in the raw gas is adsorbed by the adsorbent (e.g. zeolite, activated carbon, or alumina) in the adsorption tower A under pressure, and N2 and N2 (a component that is difficult to adsorb) are adsorbed under pressure. component) is discharge pipe 2
2 and into the atmosphere through valve 32a. In this adsorption step, the valve 31
The process is completed by closing the valve 32a and the adsorption tower A, thereby sealing the adsorption tower A with its interior still at the adsorption pressure.

While the adsorption tower A is in the pressure increasing step and adsorption step,
In the other adsorption tower B, a desorption step is being carried out, and in this desorption step, the CO acid component adsorbed in the previous step is desorbed under reduced pressure by the vacuum pump 12, and the product gas is passed through the CO acid component recovery pipe 23 and valve 33b. It is introduced into the storage tank 4 as a product gas.

When the above adsorption step is completed, the adsorption tower A is connected to the connecting pipe 24a.
The pressure equalization process begins by opening the valve 34a. As a result, the raw material gas in the adsorption tower A, which has been pressurized to the adsorption pressure, moves to the adsorption tower B, which is in a reduced pressure state, and the adsorption tower A is reduced in pressure to approximately atmospheric pressure, and the pressure in the adsorption tower B is increased to approximately atmospheric pressure. The valve 34a is closed when the pressures of the two adsorption towers A and B are equalized to approximately atmospheric pressure.

After this, adsorption tower A enters a cleaning process. In this cleaning process, the valve 35a of the cleaning gas supply pipe 25 and the connecting pipe 24 are
The valve 34a of a and the valve 32b of the discharge pipe 22 are opened, and the CO component gas in the product gas storage tank 4 is introduced into the adsorption tower A. This CO component gas purges the poorly adsorbed components remaining in the adsorption tower A, and this purge exhaust gas is sent to the other adsorption tower B, where a part of the CO acid component in the purge exhaust gas is transferred to the adsorbent in the adsorption tower B. is adsorbed to. The remaining purge exhaust gas from which the CO acid component has been adsorbed in the adsorption tower B has approximately atmospheric pressure, and is therefore discharged into the atmosphere by the exhaust gas compressor 13.

After closing the valves 35a, 34a, and 32b that were opened in the cleaning process, the adsorption tower A enters the desorption process. In this desorption step, by opening the valve 33a of the recovery pipe 23 and operating the vacuum pump 12, the CO acid component adsorbed in the adsorption tower A is desorbed under reduced pressure, and this CO component gas is recovered into the product gas storage tank 4. be done.

While this desorption step is being performed in adsorption tower A, the other adsorption tower B is performing a pressure increasing step and an adsorption step. Then, as the local adsorption tower B enters the pressure equalization process, the pressure of the adsorption tower A is increased to almost atmospheric pressure, and as the other adsorption tower B enters the cleaning process, the adsorption tower B
A portion of the CO acid component in the purge exhaust gas from the purge gas is adsorbed, and the remaining purge gas is discharged to the atmosphere through the exhaust pipe 22. After this, the adsorption tower A returns to the pressure increasing process, and the same process is repeated thereafter.

In the above-mentioned conventional pressure swing adsorption method, the cleaning gas supplied to the adsorption tower in the cleaning step is a product gas with high CO purity, so the purge exhaust gas after cleaning of the adsorption tower A is higher than the product gas. C low but close to its product gas
It has O purity.

Therefore, in the conventional method described above, the purge exhaust gas after cleaning is sent to the other adsorption tower B, and this adsorption tower B adsorbs the cobalt acid component in the purge exhaust gas. Because the original pressure is relatively low, the recovery of the CO acid component in the other adsorption tower B is not sufficient, and therefore a large amount of CO is contained in the purge gas discharged from the other adsorption tower B through the discharge pipe 22. It will contain acid components.

As a result, there is a problem that the CO acid component recovery rate cannot be sufficiently improved.

Therefore, in the pressure equalization process, two adsorption towers A are used.

Instead of equalizing the pressure between B and B until it reaches almost atmospheric pressure, the adsorption tower A after the adsorption process is
A method has also been proposed in which the pressure of the other adsorption tower B is set to be lower than atmospheric pressure while the adsorption tower B is reduced to atmospheric pressure (see, for example, Japanese Patent Application Laid-open No. 37970/1983). 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 purge 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 disposed of from the other adsorption tower B.

However, in this method, when equalizing the pressure between adsorption tower A during adsorption and adsorption tower B during desorption, the adsorption pressure is adjusted such that adsorption tower A is reduced to normal pressure before adsorption tower B returns to normal pressure. It is necessary to set the desorption pressure value and the desorption pressure value, and setting these pressures requires time and effort. Further, there is another problem in that a great deal of effort is required to set and adjust the pressure equalization time, and the pressure inside the adsorption tower that is cleaned during the cleaning step gradually increases, thereby reducing the cleaning effect.

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, as the cleaning pressure increases over time, the cleaning effect deteriorates accordingly due to the adsorption properties of the adsorbent, and as a result, the purity of the CO component gas desorbed and recovered decreases.

In addition, it is also conceivable to introduce the purge exhaust gas from the discharge pipe 22 into the suction side of the raw material gas compressor 11 and reuse the purge exhaust gas as the raw material gas. However,
In this case, it is necessary to increase the raw material gas compression capacity *ii and the capacity of a pretreatment process (for example, water removal, etc.) not shown in the drawings to account for the reuse, and therefore there is a problem that it is uneconomical.

(Purpose of the invention) This invention was made in order to solve such conventional problems, and it is possible to easily and reliably improve the recovery rate of specific components, and it is possible to easily and reliably improve the recovery rate of specific components. This provides a pressure swing adsorption method that does not cause problems.

(Structure of the Invention) This invention has a pressure increasing step, an adsorption step, a pressure equalization step, a washing step, and a 182nd adsorption step, and the mixed gas is In the pressure swing adsorption method for adsorbing and recovering specific components in the water, in the cleaning process, the specific component gas recovered in the desorption process is introduced as a cleaning gas into the adsorption tower after the pressure equalization process, and in the cleaning process of a certain adsorption tower, The outlets of this adsorption tower and another adsorption tower different from each other are closed, and when the purge exhaust gas generated in the cleaning process is guided to the other adsorption tower, the purge exhaust gas is repressurized and sent to the other adsorption tower. It is something.

According to the above configuration, even if the cleaning gas is supplied at a relatively low pressure in the cleaning process, the purge exhaust gas is repressurized when being fed from the adsorption tower in the cleaning process to other adsorption towers. , the purge exhaust gas can be reliably introduced into the other adsorption tower with the outlet narrowed, and the purge exhaust gas can be adsorbed onto the adsorbent under pressure. It is possible to adsorb and recover more specific components than before without having to discard them.

(Example) The apparatus for carrying out the present invention shown in FIG. 2 has two adsorption towers A in contrast to the conventional apparatus shown in FIG.

A pressurizing pipe line 26 is provided for pressurizing and feeding the purge exhaust gas generated in B from one side to the other. A purge exhaust gas compressor 14 is installed in this pressurizing pipe 26, and the outlets of the adsorption towers A and B are connected to valves 36a.

The inlets of the adsorption towers A, B are connected to the suction side of the purge exhaust gas compressor 14 through the valve 37a.
, 37b to the discharge side of the purge exhaust gas compressor 1114. Furthermore, the exhaust gas compression e113 provided in the conventional device shown in FIG. 4 is omitted in the device shown in FIG. 2.

The feature of the embodiment shown in FIG. 1 is that in order to send purge exhaust gas generated in the cleaning process of one adsorption tower to the other adsorption tower, in the conventional method shown in FIG.
24b, whereas in this embodiment, it is fed through the pressurized pipe line 26.

That is, after the pressure of the two adsorption towers A and B is equalized to almost atmospheric pressure by the pressure equalization process of one adsorption tower A, the connecting pipe 24a is
Close the valve 34a. As a result, all valves 31a
~37a, 31b ~37b.

is stolen. After that, in the cleaning process for one of the adsorption towers, the valve 35a of the cleaning gas supply pipe 25 is opened, and the valve 36a of the pressurization pipe 26 on the outlet side of the adsorption tower A and the inlet of the other adsorption tower B are The side valve 37a is opened to operate the purge exhaust gas compressor 14. Then, the purge exhaust gas generated by cleaning 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 stored in the other adsorption tower B. After this,
One adsorption tower A, which has completed the cleaning process, moves to a desorption process, and the other adsorption tower B, in which the pressure of the purge exhaust gas has been accumulated, moves to a pressure increasing process using raw material gas.

Therefore, in this other adsorption tower B, the CO acid component in the purge exhaust gas can be adsorbed and recovered under a pressure higher than atmospheric pressure, so a larger amount of CO acid component can be absorbed than in the conventional case where the CO acid component is adsorbed under atmospheric pressure. It can be collected by adsorption. As a result, the yield in CO component recovery can be improved compared to the conventional method.

In addition, the purge exhaust gas that has been discarded up to now is not disposed of but is stored in the other adsorption tower B as part of the pressurizing gas, so the exhaust gas compressor 13 ( (see FIG. 4) can be omitted.

In addition, since the purge exhaust gas compressor 14 sucks the purge exhaust gas from the adsorption tower A in the cleaning process, even if the valve 32b on the discharge pipe 22 side of the other adsorption tower B is closed, the purge gas will still be removed. The exhaust gas can be reliably introduced into the other adsorption tower. Similarly purge exhaust gas compression 1f
Since the purge exhaust gas is fed to the other adsorption tower B by i14, there is no need to set the adsorption tower B to a state lower than atmospheric pressure in the pressure equalization step.

In the above embodiment, a case was explained in which CO is separated and recovered as a specific component from a raw material gas containing CO, but the present invention is not limited to this. For example, it can be applied to the case where N2 is separated and recovered.

Further, in the above embodiment, there are two adsorption towers A.

Although a device consisting of B is used, it is not limited to this.
For example, in an apparatus consisting of four adsorption towers, the processes may be shifted from each other and operated continuously.

(Specific example) Using the apparatus shown in Figure 2, CO is 70% and CO2 is 15%.
A test was conducted in accordance with the process shown in FIG. 1 for the case where CO was separated and recovered from a raw material gas having a composition of 15% and N2. The adsorbent used was activated alumina impregnated with a copper compound.

First, a pressure raising step and an adsorption step are performed in one adsorption tower A at an adsorption pressure of 2 D/ciG, and then the pressure of the adsorption tower A is reduced to atmospheric pressure in a pressure equalization step.

Next, the product gas from the product gas storage tank 4 is flowed into the reduced pressure adsorption tower A at a pressure of 0.1 phantom/dG to clean the adsorption tower A, and after cleaning, the pressure becomes atmospheric and comes out from the outlet of the adsorption tower A. The purge exhaust gas is reduced to 0.3 by the purge exhaust gas compressor 14.
The pressure is increased to dG, the pressure is accumulated in the other adsorption tower B, and the CO acid component is adsorbed and recovered.

The adsorption tower A after washing is heated to 50 Torr by the vacuum pump 12.
The CO acid component is desorbed and recovered by reducing the pressure to r. The pressure of the adsorption tower A after the desorption step is increased to approximately atmospheric pressure by the pressure equalization step of the other adsorption tower B, and then the purge exhaust gas from the cleaning step of the other adsorption tower B is transferred to the adsorption tower A by the purge exhaust gas compressor 14. to raise the pressure of adsorption tower A to 0.3 Kg/aJG. This completes one cycle and returns to the pressure increasing step again to increase the adsorption pressure to 2 kg by the raw material gas compressor 11.
/cd G.

As a result of operating the above one cycle for 8 minutes, the Co purity of the product gas reached 99.7% approximately 80 minutes after the start of operation, and the 00 recovery rate was able to be maintained at 85%.

(First Comparative Example) Using the conventional apparatus shown in FIG. 4, a test was conducted in accordance with the conventional process shown in FIG. 3 for separating and recovering Co from a raw material gas having the same composition as in the above specific example. In this case, the cleaning step is to flow the product gas from the product gas storage tank 4 into the adsorption tower A at a pressure of 0.2Ky/cdG to clean the adsorption term 8, and after cleaning, the pressure becomes 0.1Kg/dG and the product gas is supplied to the adsorption tower A. The purge exhaust gas coming out from the outlet of C flows into the other adsorption tower B.
The O component was adsorbed and recovered, and the exhaust gas coming out at atmospheric pressure from the outlet of the other adsorption tower was disposed of by the exhaust gas compressor 13.

As a result, the CO purity of the product gas was 98.9%, which was 0.
The zero recovery rate was 78%.

(Second Comparative Example) The cleaning step in the first comparative example was carried out with the valve 32b on the outlet side of the other adsorption tower B being closed.

Therefore, the product gas is supplied to the absorption tower A from the product gas storage tank 4 at a pressure of 0.4! Clean adsorption tower A by flowing with F/cjG,
The purge exhaust gas coming out of the outlet of the adsorption tower A was made to flow into the other adsorption tower B, where the CO acid component was adsorbed and recovered. In this case, the pressure of the purge exhaust gas coming out of the outlet of adsorption tower A at the beginning of the cleaning process is relatively low, but the pressure increases with the passage of time and eventually reaches 0.4 to 9.
/cdG becomes.

As a result, the CO purity of the product gas was 98.5%, which was 0.
The zero recovery rate was 84%.

(Effects 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 low pressure, the purge exhaust gas from the adsorption tower is sent to other adsorption towers. Since it is repressurized at the same time, it can be reliably introduced into other adsorption towers whose outlets are closed, and since the other adsorption towers have their exits closed, the purge exhaust gas is not contained within the adsorption tower. is held under pressure. Therefore, in the other adsorption towers mentioned above, it is possible to adsorb and recover a larger amount of the specific component in the purge gas than before without discarding the purge gas.

Therefore, there is no need to set the other adsorption towers at a pressure lower than atmospheric pressure in the pressure equalization process, and it is possible to easily and reliably improve the recovery rate of specific components using an adsorbent with normal adsorption performance. There is no loss in economic efficiency.

[Brief explanation of the drawing]

FIG. 1 is a process explanatory diagram showing each process and qualitative pressure in the suction 11 over time in an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of an apparatus for carrying out the process of FIG. 1. FIG. 3 is a process explanatory diagram showing each step of the conventional method and the qualitative pressure in the adsorption tower over time, and FIG. 4 is a schematic diagram of an apparatus for carrying out the process of FIG. 3. A, B... Adsorption tower (pressure swing adsorption tower).

Claims (1)

[Claims] 1. It has a pressure raising step, an adsorption step, a pressure equalization step, a washing step, and a desorption step, and adsorbs specific components in the mixed gas by repeating the above steps in at least two or more pressure swing adsorption towers with a shift from each other. In the pressure swing adsorption method for recovery, in the above-mentioned cleaning process, the specific component gas recovered in the desorption process is introduced as a cleaning gas into the adsorption tower after the pressure equalization process, and in the cleaning process of a certain adsorption tower, a gas different from this adsorption tower is used. Pressure characterized in that when the outlet of the other adsorption tower is closed and the purge exhaust gas generated in the cleaning process is guided to the other adsorption tower, the purge exhaust gas is re-pressurized and sent to the other adsorption tower. Swing suction method.