JP2994843B2 - Recovery method of low concentration carbon dioxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering CO ₂ which is a basic substance of the chemical industry by a pressure swing adsorption method (hereinafter referred to as PSA method).

[0002]

2. Description of the Related Art FIG. 12 is a flow sheet of a conventional two-column pressure swing adsorption method (hereinafter, referred to as PSA-I method) for concentrating CO ₂ . The adsorption tower 36 contains Na
-X zeolite (SiO ₂ / Al ₂ O ₃ = 2.7) or other CO ₂ adsorbent 35 is packed in the adsorption tower 3 in the adsorption step.
The valves 34a and 37a of 6a are opened. The CO ₂ -containing gas 31 is pressurized from 1 atm to 3 atm by the blower 32, introduced into the adsorption tower 36 a through the flow path 33 and the valve 34 a, adsorbs CO ₂ and removes the hardly adsorbable component gas into the valve 3.
7a, it flows out of the system through the flow path 38. (Adsorption Step) The adsorption tower 36b in which the adsorption step of CO ₂ has moved to the vicinity of the outlet of the tower and the adsorption step has been completed, opens the valve 39b, reduces the pressure inside the tower to a predetermined pressure by the vacuum pump 40, and then switches the valve 42b. By opening, the flow path 38
Part of the hardly adsorbable component gas flowing out of the pressure reducing valve 41,
The gas is introduced into the adsorption tower 36b through the valve 42b to perform countercurrent purge, and CO ₂ is desorbed from the adsorbent 35 and recovered.
(Depressurized countercurrent purge step)

[0003] The C of the gas recovered in the decompression countercurrent purge step
The O ₂ concentration C ₂ is represented by the following equation, where G _{CO2 is} the amount of CO ₂ adsorbed, G _{COADS is} the amount of the hardly adsorbable component gas remaining in the adsorption tower, and Gp is the amount of the countercurrent purge gas. C ₂ = G _CO2 / (G _CO2 + G _COADS + Gp) In addition, according to the test of the present inventors, the co-adsorbed nitrogen is CO ₂
Since the partial pressure is reduced in the desorption step, the required amount of Gp is
Since a value of about 0.4, which is considerably smaller than α = 1.2 proposed by the Karstrom rule, is good, it is expressed by the following equation. Gp = α (Pd / Pa) Go (where α ≧ 0.4) Also, if the ratio between the amount of CO ₂ G _CO2 and the amount of co-adsorbed component G _COADS is the selectivity β, it is expressed by the following equation. You. β = G _CO2 / G _COADS ... and the CO ₂ concentration in the raw material gas is C _0, and G _CO2 =
If Go · C ₀ , the CO ₂ concentration C ₂ in the recovered gas is
The following equation can be obtained from the above equations. C ₂ = 1 / [1+ (1 / β) + (αPd / C ₀ Pa)]... As is clear from this equation, CO ₂ is more regenerated as the selectivity β and the adsorption pressure Pa are larger. The smaller the pressure Pd, the higher the concentration rate.

In the method of FIG. 12 (PSA-I method),
As a CO ₂ adsorbent, Na-X zeolite (SiO ₂ /
When Al ₂ O ₃ = 2.7) is used, C ₀ is 10 vol.
% = Β = 1.5, Pa = 1.2 atm, Pd =
When 0.2 atm, C ₂ is about 42vol%. In this method, when the recovery rate of CO ₂ is set to be close to 100%, the CO ₂ concentration of the raw material gas suitable for processing is 40 vol.
% Relatively low concentration gas.

As a method suitable for treating a high-concentration gas having a CO ₂ concentration of more than 40 vol% in a raw material gas, there is a four-column pressure swing adsorption method (hereinafter, referred to as PSA-II method) shown in FIG. The four adsorption towers 56 are filled with Na-X zeolite (SiO ₂ / Al ₂ O ₃ = 2.7) 55, and the adsorption tower 56a in the adsorption step includes a valve 54a.
And the valve 57a are opened, and the raw material gas 51 containing high-concentration CO ₂ is compressed from 1 atm to 3 atm by the blower 52, and is adsorbed on the adsorption tower 56 through the flow path 53 and the valve 54a.
a, and adsorbs CO ₂ and releases the hardly adsorbable component gas out of the system through the valve 57 a and the flow path 58. CO ₂
The adsorption step is completed with the adsorption zone moved to the rear of the tower.

[0006] After the adsorption step, the adsorption tower 56b opens the valve 60b and the valve 62b, and allows the high-concentration CO ₂ -containing gas recovered in the next decompression recovery step to flow from the product holder 66 through the flow path 59 and the valve 60b. And introduced into the adsorption tower 56b, and the hardly adsorbable components remaining in the tower are purged in parallel, and discharged out of the system from the valve 62b and the flow path 63. After completion of the co-current purge step, the adsorption tower 56c opens the valve 64c, depressurizes the inside of the tower to 0.05 to 0.3 atm by the vacuum pump 65, desorbs CO ₂ from the adsorbent 55,
₂ Store the contained gas in the product holder 66. Then, a part thereof is collected from the flow path 67 as a product gas. The adsorption tower 56d which has completed regeneration of the adsorbent 55 in the reduced pressure recovery step has reached the maximum degree of vacuum. By opening the valve 69d, the raw material gas 51 is supplied through the flow path 68 and the valve 69d to the adsorption tower 56d. And return to atmospheric pressure.

Here, assuming that the gas amount recovered by the vacuum pump is Go and the gas amount used in the co-current purging step is Gp, the purge rate R (%) is defined as follows. R = (Gp / Go) × 100 Assuming that the CO ₂ concentration of the raw material gas is 65 vol% and the purging rate is three cases of 55%, 65% and 80%, the CO ₂ concentration of the product gas is 95 vol% , 99vol
%, 99.9 vol%. Thus, PSA-
Method II is an extremely high concentration method in which the product concentration reaches a maximum of 99.9 vol%. However, the recovery rate is 40-7
When the CO ₂ concentration of the inlet gas is lower than 40% by volume, the PSA performance cannot be maintained because the Skarstrom type countercurrent purge is not performed. Table 1 shows a comparative evaluation of the PSA-I method and the PSA-II method.
become that way.

[0008]

[Table 1]

[0009]

According to the above PSA-I method, a very high recovery rate can be obtained in a low concentration range, but when the product has a low CO ₂ concentration and is carried out on a high concentration side, desorption occurs. The amount of gas increases, it takes time to reach the maximum vacuum, and the desorption is sufficiently performed by this operation, so that countercurrent purging is not very effective. On the other hand, the PSA-II method can obtain a product with a very high CO ₂ concentration in a high concentration region, but has a low recovery rate, and does not employ a countercurrent purge when the process is performed on a low concentration side. Has a low playback rate,
Requires a large amount of adsorbent. Then, the product gas amount required for the cocurrent purge cannot be prepared. Thus, P
Even if SA-I method or PSA-II method is adopted, 40 vol%
It has been difficult to obtain a high-concentration gas of 90 vol% or more at a high recovery rate from the following low-concentration CO ₂ -containing gas. Therefore, the present invention solves the above-mentioned drawbacks, and can obtain a high-concentration gas of 90 vol% or more at a high recovery rate by using a low-concentration CO ₂ -containing gas of 40 vol% or less as a raw material.
It is an object of the present invention to provide a method for recovering CO ₂ using the method.

[0010]

SUMMARY OF THE INVENTION The present invention provides a method for recovering CO ₂ from a low-concentration CO ₂ -containing gas of 40 vol% or less by using an adsorption tower filled with a CO ₂ adsorbent in two stages. In the first-stage adsorption tower, (1) an adsorption step of supplying the above gas at a relatively low temperature and a high pressure to adsorb CO ₂ and recover accompanying low-adsorption gas from a rear portion of the tower; After the process, the pressure was reduced from the front of the adsorption tower, and then a part of the hardly adsorbable gas was introduced countercurrently to reduce the CO ₂ concentration to 40 V.
and the step of reducing and condensing to a volume of not less than ol% is alternately switched to continuously collect CO _2. Then, in the second stage adsorption tower, (3) the above-mentioned reduced and concentrated CO ₂ -containing gas is removed. An adsorption step of supplying CO ₂ at a relatively low temperature and a high pressure to adsorb CO ₂ and recovering an accompanying hardly adsorbable gas from a rear portion of the column;
(4) A highly concentrated CO ₂ -containing gas flows from the front part of the second-stage adsorption tower after the completion of the adsorption step in a parallel flow to discharge the hardly adsorbable gas remaining in the tower to the outside of the tower. Flow purge step, (5) reduced pressure recovery step of recovering highly concentrated CO ₂ -containing gas by reducing pressure from the front of the second-stage adsorption tower after completion of the co-current purge step, and (6) reduced pressure recovery step The step of returning the pressure by flowing the gas in countercurrent to the adsorption tower after completion is alternately switched to continuously recover the high-concentration CO ₂ gas, and the co-current flow of the above (4) of the second-stage adsorption tower is performed. The gas flowing from the purge step is subjected to the adsorption step of (3) or (6).
A method of recovering CO ₂ according to the pressure swing adsorption method and returning to the countercurrent pressure recovery process. In the above method, the gas flowing from the adsorption step (3) of the second-stage adsorption tower is returned to the adsorption step (1) of the first adsorption tower until the gas does not cause air pollution. Preferably, the CO ₂ concentration is reduced to facilitate direct release to the atmosphere.

[0011]

According to the present invention, the above-mentioned PSA-I method and PSA-II method are organically combined in two steps to provide 40 vol.
This makes it possible to recover a high-concentration CO ₂ gas from a low-concentration CO ₂ -containing gas of 1% or less at a high recovery rate.
That is, the gas flowing from the co-current purge step of the second-stage PSA-II method is returned to the second-stage adsorption step or the countercurrent pressure recovery step, which is a disadvantage of the conventional PSA-II method. By improving the low recovery rate and returning the gas flowing from the second PSA-II adsorption step to the first adsorption step, the recovery rate is further improved and the gas is discharged out of the system. The CO ₂ concentration in the gas is further reduced to enable disposal to the atmosphere.

[0012]

Using PSA apparatus according to Embodiment] FIG. 1, CO ₂ 1
0 vol%, 90 vol% nitrogen from raw material gas to C
It was concentrated O ₂ up to 99 vol%. Each of the first two adsorption towers 6 is filled with 500 kg of the CO ₂ adsorbent 5, the valves 4 a and 7 a of the adsorption tower 6 a in the adsorption step are opened, and the raw material gas 1 is blown by the blower 2 to 1 to 1. compressed into 5 atm, the flow path 3, adsorbed CO ₂ is introduced into the adsorption tower 6a past valve 4a, the valve 7a, to recover the flame adsorbable nitrogen gas through the flow path 8. And the CO ₂ adsorption zone is the adsorption tower 6
At the stage after the movement to the rear part of “a”, the adsorption step was completed.

The adsorption tower 6b, which has completed the adsorption step, opens the valves 9b and 12b and communicates with the vacuum pump 10 to allow a part of the nitrogen gas recovered in the adsorption step to flow while the pressure is reduced to 38 to 380 Torr. The gas was introduced into the adsorption tower 6b through the passage 8, the pressure reducing valve 11, and the valve 12b, and was subjected to countercurrent purge to desorb CO ₂ from the adsorbent 5 and was recovered from the valve 9b, the vacuum pump 10, and the flow path 13. The CO ₂ concentration in the recovered gas was set so as to be 40 vol% or more. After the counterflow purge step, the adsorption tower 6b opened only the valve 4b to introduce the raw material gas and returned to the atmospheric pressure.

Each of the four adsorption towers 16 in the second stage is filled with 250 kg of the CO ₂ adsorbent 5 and the gas recovered in the first-stage depressurizing countercurrent purge step is passed through the flow path 13 through the blower 1.
4 and compress to 1-5 atm. The valves 15a and 17a of the adsorption tower 16a in the adsorption step are opened, and the recovered gas is introduced into the adsorption tower 16a via the valve 15a and C
O ₂ was adsorbed, and a hardly adsorbable nitrogen gas was recovered through the valve 17 a and the flow path 18. Since this recovered gas has a higher CO ₂ concentration than the gas flowing from the first adsorption step,
It cannot be released directly into the atmosphere. Then, this recovered gas is returned to just before the blower 2 through the flow path 18 and introduced into the adsorption tower 6a in the first adsorption step, whereby CO ₂ is adsorbed and separated to make the CO ₂ concentration extremely low. The nitrogen gas was recovered from the flow channel 8 and released to the atmosphere except for the portion used for the first stage countercurrent purge.

The CO ₂ adsorption zone moves to the rear of the adsorption tower,
The adsorption tower 16b that has completed the adsorption step shifts to the cocurrent purge step by opening the valve 20b and the valve 21b, and passes the highly concentrated CO ₂ from the product holder 27 through the flow path 19 and the valve 20b. By flowing in parallel to 16b, nitrogen gas remaining in the tower is purged and discharged out of the tower via the valve 21b and the flow path 22. Since this released gas had a considerably high CO ₂ concentration, it was returned immediately before the blower 14 and introduced into the adsorption tower 16a in the second adsorption step to recover CO ₂ .

The adsorption tower 16c which has completed the cocurrent purge step
Moves to a reduced pressure recovery step by opening the valve 25c, desorbs and recovers CO ₂ adsorbed on the adsorbent 5 by suctioning to a high vacuum of the regeneration pressure by the vacuum pump 26,
Stored in product holder 27. A part of the stored CO ₂ is taken out of the system as a product from the channel 28,
A part was returned to the adsorption tower 16c in the above-described cocurrent purge step and used for purging.

The adsorption tower 16d, which has completed the vacuum recovery step,
By opening the valve 24d, the process shifts to the countercurrent pressure recovery step, and a part of the gas released from the adsorption tower 16b in the cocurrent purge step is introduced into the adsorption tower 16d via the flow path 22 and the flow control valve 23. The pressure was restored to prepare for the next adsorption step. During this time, the sequence of the first-stage adsorption tower was as shown in FIG. 2, and the sequence of the second-stage adsorption tower was as shown in FIG. The unit of time required for each step is seconds.

In order to select an optimal adsorbent, a CO ₂ adsorbent shown in Table 2 was used, a gas having a CO ₂ concentration of 10 vol% and a nitrogen gas of 90% was used as a raw material, and the adsorption pressure of the first stage adsorption tower was adjusted. 1.2atm, adsorption temperature 50 ° C, regeneration pressure 0.2
atm, a purge rate α of 40%, and a cycle time of 5 minutes, the first-stage adsorption operation was performed, and the CO ₂ concentration (v
ol%) and the processing capacity (Nm ³ / Ton) of the raw material gas in terms of 1 Ton adsorbent are shown in Table 2. As apparent from Table 2, Na-X in the zeolite CO ₂ adsorbent, SiO ₂ / Al ₂ O ₃ ratio of the conventional 2.7 or more C
It can be seen that the X type, 2.5, which is the lowest practically, is superior to the O ₂ adsorbent. In addition, 30mo of Na
Ca-X zeolite (SiO
₂ / Al ₂ O ₃ = 2.7) is superior to those having a low Ca exchange rate.

[0019]

[Table 2]

Therefore, Na—X zeolite (SiO ₂ / Al ₂ O ₃ = 2.times.2) is used as the CO ₂ adsorbent in the first-stage adsorption tower.
5) as a CO ₂ adsorbent for the second-stage adsorption tower, Ca-X zeolite (SiO ₂ / Al ₂ O) having a Ca exchange rate of 60%
₃ = 2.5), the entire system was evaluated as follows.

For the first stage adsorption tower, the adsorption pressure is set to 1.
2 atm, regeneration pressure 0.2 atm, CO ₂ concentration of the raw material gas of the first stage adsorption column 10 vol%, purge rate 40%
And changing the adsorption temperature to reduce the CO in the recovered gas of the first stage.
₂ concentration (vol%) was measured, and the relationship between the adsorption temperature and the CO ₂ concentration is shown in FIG. The Na-X adsorbent is 25 to 12
Although it is applicable to a relatively low temperature range of 0 ° C., the above Ca
It can be seen that the -X adsorbent has applicability in a relatively high temperature range of 40 to 200C.

With respect to the first-stage adsorption tower, the adsorption temperature is set to 50 ° C. and the CO _{2 in} the first-stage inlet gas is set to 50 ° C.
CO _{2 in} the recovered gas of the first stage when changing the concentration
FIG. 5 shows the measured and compared concentrations. When an inlet gas having a CO ₂ concentration of 8 vol% is used, the CO ₂ concentration in the recovered gas in the first stage reaches 40 vol% and is 40 vol.
% Of the inlet gas was used, the CO ₂ concentration in the first stage recovered gas reached 80 vol%.

With respect to the first-stage adsorption tower, the adsorption temperature was set to 50 ° C., the purge rate was set to 40%, the CO ₂ concentration in the first-stage inlet gas was set to 10 vol%, and the first-stage regeneration pressure was set. CO _{2 in} the recovered gas of the first stage when changing
FIG. 6 shows the measured and compared concentrations. The purging gas amount can be reduced as the vacuum reaching pressure becomes higher, and purging at 1 Torr or less is theoretically possible. However, considering the efficiency of the vacuum pump and the leak of the valve,
About 30 Torr is the lower limit.

Regarding the first stage adsorption tower, of the above conditions, the regeneration pressure was 0.2 atm, the adsorption temperature was 50 ° C., the purge rate was 40%, and the CO ₂ concentration in the first stage inlet gas was 10 V.
FIG. 7 shows the results of comparison with the measurement of the CO ₂ concentration in the recovered gas in the first stage while changing the adsorption pressure in the first stage to ol%. As the adsorption pressure increases, the concentration of the purge gas can be reduced, and the concentration of the recovered gas can be improved. However, if the partial pressure of CO ₂ exceeds 1 atm, the adsorption amount tends to be saturated,
atm is the upper limit. In order to save energy, it is preferable to operate at an adsorption pressure of about 1.05 to 1.3 atm, which corresponds to the pressure loss of the adsorption tower.

For the second stage adsorption tower, the adsorption pressure is 1.2 atm, the regeneration pressure is 0.2 atm,
The adsorption temperature is 50 ° C and the CO ₂ concentration at the second stage inlet is 55 vo
When the second stage of adsorption and separation is performed in the same manner as described above, the relationship between the purge rate and the CO ₂ concentration of the recovered gas in the second stage is shown in FIG.
In both of the above Na-X and Ca-X, the purge rate was 60%, 70%, and 85%, and the C
O ₂ concentration is 95 vol%, 99 vol%, 99.9 vol
reached 1%.

With respect to the second stage adsorption tower, the adsorption pressure is 1.2 atm, the regeneration pressure is 0.2 atm,
The adsorption temperature was fixed at 50 ° C., the purge rate was fixed at 65%, the CO ₂ concentration at the second stage inlet was changed, and the CO
_The measurement of the _two concentrations is as shown in FIG. 9, and it can be seen that when the CO ₂ concentration at the inlet of the second stage exceeds 40 vol%, the CO ₂ concentration of the recovered gas in the second stage also exceeds 90 vol%.

Regarding the second stage adsorption tower, the adsorption pressure was fixed at 1.2 atm, the adsorption temperature was fixed at 50 ° C., the purge rate was fixed at 70%, and the CO ₂ concentration at the second stage inlet was 55 V.
ol%, the regeneration pressure was changed, and the CO ₂ concentration of the recovered gas in the second stage was measured, as shown in FIG.
As the regeneration pressure becomes higher, the CO2 of the recovered gas in the second stage increases.
_{(2) The} concentration increases, but if the concentration is 0.05 atm or less, the concentration increase slows down and the capacity of the vacuum pump also increases, which is not economical.

With respect to the second stage adsorption tower, the regeneration pressure was set to 0.2 atm, the adsorption temperature was set to 55 ° C., the purge rate was set to 70%, the CO ₂ concentration at the second stage inlet was set to 55 vol%, and the adsorption pressure was set. Was measured and the CO ₂ concentration of the second-stage recovered gas was measured, as shown in FIG. 11. The higher the adsorption pressure, the higher the CO ₂ concentration of the second-stage recovered gas, but exceeded 3 atm. It is not economical because of the power consumption of the blower.

(Example 1) After grasping the above tendency, CO ₂ was recovered under the following operating conditions, and the CO ₂ concentration of the recovered gas in the second adsorption tower and the CO ₂ recovery were compared. In case I, the effluent gas from the adsorption step of the second adsorption tower is returned to the previous stage of the blower of the first adsorption tower, introduced into the adsorption step together with the raw material gas, and subjected to the second-stage cocurrent purge. The effluent gas of the process was supplied countercurrently to the adsorption tower which had completed the second-stage adsorption tower after the decompression and recovery step, and the pressure was restored. In case II,
The effluent gas from the adsorption step of the second-stage adsorption tower and the effluent gas of the second-stage cocurrent purge step were directly discharged out of the system.

First stage adsorption tower Adsorbent Na-X (silica / alumina = 2.5) Adsorption pressure 1.2 atm Regeneration pressure 0.2 atm Countercurrent purge rate 40% Adsorption temperature 50 ° C. Inlet gas CO ₂ concentration 10 vol% outlet of the CO ₂ concentration of 2 vol% recovered gas in the gas CO ₂ concentration 43 vol% second stage adsorption tower adsorbent Na-X (silica / alumina = 2.5) adsorption pressure 1.2atm regeneration pressure 0.2atm cocurrent purge rate 75 % adsorption temperature 50 ° C. inlet CO ₂ concentration 99 vol% of CO ₂ concentration 43 vol% recovered gas in the gas (case I) the CO ₂ concentration 95 vol% of the recovered gas (case II) recovery of overall CO ₂ are cases I In contrast to 95%, Case II is 40%, indicating that Case I is extremely effective.

(Example 2) CO ₂ was recovered under the conditions of Example 1. In Case I, the effluent gas from the adsorption step of the second adsorption tower was returned to the stage preceding the blower of the first adsorption tower. Then, the gas was introduced into the adsorption step together with the raw material gas, and the effluent gas from the co-current purging step of the second adsorption tower was returned to the stage preceding the blower of the second adsorption tower and introduced into the second adsorption step. In Case II, the effluent gas from the adsorption step of the second-stage adsorption tower and the effluent gas of the second-stage cocurrent purge step were directly discharged out of the system. The CO ₂ concentration of the recovered gas in the second stage adsorption tower was
Is 98 vol% in case II and 90 vol% in case II. The total CO ₂ recovery is 90% in case I, but 40% in case II, and case I is extremely effective. You can see that there is.

[0032]

According to the present invention, the adsorption tower is used in two stages,
The effluent gas from the adsorption step of the two-stage adsorption tower is returned to the first adsorption step, or the effluent gas of the cocurrent purge step of the second adsorption tower is returned to the countercurrent depressurization step or the adsorption step of the second adsorption tower. The flow makes it possible to recover a high concentration of CO ₂ at a high recovery rate, which has the advantages of the conventional countercurrent purge method and the parallel flow purge method.

[Brief description of the drawings]

FIG. 1 is a flow sheet of an apparatus for performing the PSA method of the present invention.

FIG. 2 illustrates a sequence of a first-stage adsorption tower in an embodiment.

FIG. 3 illustrates a sequence of a second-stage adsorption tower in the embodiment.

FIG. 4 is a graph showing the relationship between the adsorption temperature and the CO ₂ concentration of the recovered gas in the first-stage adsorption tower in Examples.

FIG. 5 is a graph showing an example of C in the gas at the inlet of the first-stage adsorption tower in the embodiment.
5 is a graph showing the relationship between the O ₂ concentration and the CO ₂ concentration of the recovered gas of the first adsorption tower.

FIG. 6 shows the regeneration pressure of the first-stage adsorption tower and
CO recovered gas from the first stage adsorption tower _TwoShowed the relationship with the concentration
It is a graph.

FIG. 7 shows the adsorption pressure of the first-stage adsorption tower,
CO recovered gas from the first stage adsorption tower _TwoShowed the relationship with the concentration
It is a graph.

FIG. 8 shows a purge rate of a second-stage adsorption tower and
CO of recovered gas of second stage adsorption tower _TwoShowed the relationship with the concentration
It is a graph.

FIG. 9 is a graph showing the relationship between the concentration of hydrogen sulfide in the inlet gas of the second-stage adsorption tower and the concentration of CO _{2 in} the recovered gas of the second-stage adsorption tower in the example.

FIG. 10 shows the regeneration pressure of the second-stage adsorption tower in an example.
And CO in the recovered gas of the second stage adsorption tower _TwoShow relationship with concentration
It is the graph which did.

FIG. 11 shows the adsorption pressure of the second-stage adsorption tower in Examples.
And CO in the recovered gas of the second stage adsorption tower _TwoShow relationship with concentration
It is the graph which did.

FIG. 12 is a flow sheet of an apparatus for performing a conventional countercurrent purge method.

FIG. 13 is a flow sheet of an apparatus for performing a conventional cocurrent purge method.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuaki Oshima 1-1 Naganoura, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard (72) Inventor Hiroshi Nohara 1-1-1, Akunoura Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries Inside Nagasaki Shipyard Co., Ltd. (72) Inventor Kiichiro Ogawa 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Heavy Industries, Ltd. (56) References JP-A-5-238704 (JP, A) JP-A-5-212236 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 53/04

Claims (2)

(57) [Claims] 1. A method for recovering CO ₂ from a low-concentration CO ₂ -containing gas of 40 vol% or less using an adsorption tower filled with a CO ₂ adsorbent in two stages. The above gas is supplied at relatively low temperature and high pressure to produce CO ₂
(2) depressurizing from the front of the adsorption tower after the end of the adsorption step, and then countercurrently flowing a part of the hardly adsorbable gas. And the step of reducing the volume of CO ₂ to 40 vol% or more and recovering by concentrating and recovering the CO ₂ concentration alternately to continuously recover CO _2. Then, in the second stage adsorption tower, (3) the volume reduction An adsorption step in which the concentrated CO ₂ -containing gas is supplied at a relatively low temperature and a high pressure to adsorb CO ₂ , and the accompanying hardly adsorbable gas is recovered from the rear part of the column; and (4) after the adsorption step is completed. Second
A co-current purging step of passing a highly concentrated CO ₂ -containing gas through a co-current flow from the front of the adsorption tower and discharging the hardly adsorbable gas remaining in the column to the outside of the tower; (5) co-current flow A reduced pressure recovery step of recovering a highly concentrated CO ₂ -containing gas by reducing the pressure from the front of the second stage adsorption tower after the purging step, and (6) a gas flowing countercurrently to the adsorption tower after the completion of the reduced pressure recovery step. And the step of restoring the pressure by alternately switching the high pressure CO ₂
And recovering the gas flowing from the co-current purge step (4) of the second stage adsorption tower with the adsorption step (3),
Or, a method for recovering CO ₂ by the pressure swing adsorption method and returning to the counter-current pressure recovery step (6). 2. The method according to claim 1, wherein the gas flowing from the adsorption step (3) in the second adsorption tower is returned to the adsorption step (1) in the first adsorption tower. CO ₂ recovery method.