JPH05212236A - Method for recovering hydrogen sulfide of low concentration - Google Patents

Abstract

PURPOSE:To recover with high recovery rate the gas of high concentration using gas contg. hydrogen sulfide of low concentration as a raw material by returning outgoing gas in an adsorption process of the 2nd stage adsorber to the 1st stage adsorption process and returning outgoing gas in a concurrent purge process of the 2nd adsorber to an adsorption process of the 2nd stage adsorber. CONSTITUTION:Two adsorbers 6a, 6b at the 1st stage are each packed with a hydrogen sulfide adsorbent 5 and four adsorbers 16a-16d at the 2nd stage are each packed with tje hydrogen sulfide adsorbent 5. Gas recovered in the 1st stage vacuum countercurrent purge process is conducted from a passage 13 to a blower 14 to compress it. And, gas flowing from an adsorption process of the 2nd stage adsorbers 16a-16d is returned to an adsorption process of the 1st stage adsorbers 6a, 6b and gas flowing from a concurrent purge process of the 2nd stage adsorbers 16a-16d is returned to the adsorption process of the 2nd stage adsorbers 16a-16d. Further, if necessary, the gas is returned to a countercurrent pressure restoring process of the 2nd stage adsorbers 16a-16d. Thereby hydrogen sulfide of high concentration is obtained with high recovery rate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pressure swing adsorption method from a catalyst pretreatment gas in the chemical industry, or a low concentration hydrogen sulfide-containing gas after being used as a sulfur raw material, a sulfuric acid raw material, or an organic radical reaction terminator. The present invention relates to a method for recovering high-concentration hydrogen sulfide gas by using (hereinafter referred to as PSA method).

[0002]

2. Description of the Related Art FIG. 12 is a flow sheet of an apparatus for concentrating hydrogen sulfide by a conventional two-column pressure swing adsorption method (hereinafter referred to as PSA-I method). The adsorption tower 36 is filled with the hydrogen sulfide adsorbent 35, and the adsorption tower 36 in the adsorption step is
The valves 34a and 37a of a are opened. The hydrogen sulfide-containing gas 31 is pressurized to 3 atm by the blower 32, and the flow path 3
3, the gas is introduced into the adsorption tower 36a through the valve 34a, adsorbs hydrogen sulfide, and the hardly adsorbed component gas flows out of the system through the valve 37a and the flow path 38. (Adsorption step) In the adsorption tower 36b which has completed the adsorption step by moving the adsorption zone of hydrogen sulfide to the vicinity of the outlet of the tower, the valve 39b is opened to reduce the pressure inside the tower by the vacuum pump 40, and then the valve 42b is turned on. By opening the flow path 3 in the adsorption step
A part of the hardly adsorbed component gas flowing out from the pressure reducing valve 4
1. Introduced into the adsorption tower 36b via the valve 42b, countercurrent purge is performed, and hydrogen sulfide is desorbed from the adsorbent 35 and recovered. (Decompression countercurrent purge process)

The hydrogen sulfide concentration C ₂ of the gas recovered in the reduced pressure countercurrent purging step is determined by the amount of adsorbed hydrogen sulfide gas being G _H2S and the amount of hardly adsorbed component gas remaining in the adsorption tower being G 2
_COADS and countercurrent purge gas amount are Gp, they are expressed by the following equation. C ₂ = G _H2S / (G _H2S + G _COADS + Gp) ... Also, the required amount of Gp is according to the Skarstrom law,
It is expressed by the following equation. Gp = α (Pd / Pa) Go (however, α ≧ 1.2) ... _Further , the ratio between the adsorbed hydrogen sulfide gas amount G _H2S and the hardly adsorbed component gas amount G _COADS remaining in the adsorption tower is _calculated. Assuming selectivity β, it is expressed by the following equation. β = G _H2S / G _COADS ··· When the concentration of hydrogen sulfide in the feed gas and C _0, hydrogen sulfide concentration C ₂ in the recovered gas can be determined as the following formula from the above-equation. C ₂ = 1 / [1+ (1 / β) + (αPd / C ₀ Pa)] As is clear from this equation, hydrogen sulfide is regenerated as the selectivity β and the adsorption pressure Pa increase. The smaller the pressure Pd, the higher the recovery rate.

In the method of FIG. 12 (PSA-I method),
When polymerized phosphoric acid-containing activated alumina is used as the hydrogen sulfide adsorbent, C _{0 is set} to 3 vol% and β = 10, P
If a = 1.05 atm and Pd = 0.03 atm,
C ₂ is about 45 vol%. In this method, when the hydrogen sulfide recovery rate is set to near 100%, the hydrogen sulfide concentration of the raw material gas suitable for the treatment becomes a relatively low concentration gas of 40 vol% or less.

As a method suitable for treating a high-concentration gas in which the hydrogen sulfide concentration of the source gas exceeds 40 vol%, a method shown in FIG.
4 tower type pressure swing adsorption method (hereinafter referred to as PSA-
II method). The four adsorption towers 56 are filled with a hydrogen sulfide adsorbent 55 such as polymerized phosphoric acid-containing alumina. The adsorption tower 56a in the adsorption step opens the valve 54a and the valve 57a to release a high concentration of hydrogen sulfide. The raw material gas 51 contained therein is compressed by the blower 52 from 1 atm to 3 atm, and is passed through the flow path 53 and the valve 54 a to the adsorption tower 56 a.
And adsorbs hydrogen sulfide to release the hardly adsorbed component gas to the outside of the system via the valve 57a and the flow path 58. The adsorption process is terminated with the hydrogen sulfide adsorption zone moving to the rear of the column.

In the adsorption tower 56b which has completed the adsorption process, the valves 60b and 62b are opened, and the high-concentration hydrogen sulfide-containing gas recovered in the next reduced pressure recovery process is passed from the product holder 66 through the flow path 59 and the valve 60b. Is introduced into the adsorption tower 56b, the hardly adsorbed component remaining in the tower is cocurrently purged, and is discharged from the system through the valve 62b and the flow passage 63. In the adsorption tower 56c after completion of the co-current purging step, the valve 64c is opened and the inside of the tower is depressurized to 0.01 to 0.3 atm by the vacuum pump 65 to desorb hydrogen sulfide from the adsorbent 55 and to remove high-concentration sulfide. The hydrogen-containing gas is stored in the product holder 66. And
A part of the product gas is collected from the flow channel 67 as a product gas. The adsorption tower 56d, which has completed the regeneration of the adsorbent 55 in the reduced pressure recovery step,
When the maximum degree of vacuum is reached and the valve 69d is opened, the source gas 51 is introduced into the adsorption tower 56d through the flow path 68 and the valve 69d, and returned to atmospheric pressure.

Here, when the amount of gas collected by the vacuum pump is Go and the amount of gas used in the co-current purging step is Gp, the purge rate R (%) is defined as follows. R = (Gp / Go) × 100 If the hydrogen sulfide concentration of the source gas is 55 vol%,
Assuming three cases of purge rates of 55%, 65%, and 80%, the hydrogen sulfide concentration of the product gas is 95 vol%, 99%.
and reach 99.9 vol%. Thus, P
The SA-II method is an extremely high concentration method in which the product concentration reaches a maximum of 99.9 vol%. However, the recovery rate is 4
0 to 70%, the hydrogen sulfide concentration of the inlet gas is 40v
When it is less than ol%, PSA performance cannot be maintained because Skarstrom type countercurrent purging is not performed. Table 1 shows a comparative evaluation of the PSA-I method and the PSA-II method.

[0008]

[Table 1]

[0009]

The above-mentioned PSA-I method can obtain a very high recovery rate in a low concentration range, but the product concentration is low, and when it is carried out on the high concentration side, the amount of desorption gas is small. However, it takes a long time to reach the maximum degree of vacuum, and since desorption is sufficiently performed by this operation, the effect of countercurrent purging cannot be achieved. On the other hand, the PSA-II method is
Very high product concentration can be obtained in the high concentration range,
The recovery rate is low, and when it is carried out on the low concentration side, since the countercurrent purge is not adopted, the regeneration rate is low and a large amount of adsorbent is required. Then, the amount of product gas required for the cocurrent purge cannot be prepared. As described above, even if the PSA-I method or the PSA-II method is adopted, it is difficult to obtain a high-concentration gas of 90 vol% or more from a low-concentration hydrogen sulfide-containing gas of 40 vol% or less with a high recovery rate. .. Therefore, the present invention solves the above-mentioned drawbacks and uses a low concentration hydrogen sulfide containing gas of 40 vol% or less as a raw material to obtain a high concentration gas of 90 vol% or more with a high recovery rate. It is intended to provide a recovery method.

[0010]

According to the present invention, an adsorption column filled with a hydrogen sulfide adsorbent is used in two stages, and 40 vol%
In the following method for recovering hydrogen sulfide from a low-concentration hydrogen sulfide-containing gas, in the first-stage adsorption tower, (1) the above gas is supplied at a relatively low temperature and high pressure to adsorb hydrogen sulfide, and the accompanying difficulty adsorption An adsorption step for collecting gas from the rear part of the tower,
(2) A step of decompressing from the front part of the adsorption tower after the end of the adsorption step, then introducing a part of the above-mentioned difficult-to-adsorb gas into a countercurrent to reduce the concentration of hydrogen sulfide to 40 vol% or more, and concentrate and recover. , And the hydrogen sulfide is continuously recovered by switching alternately, and then, in the second-stage adsorption tower, (3) the hydrogen sulfide-containing gas concentrated and reduced in volume is supplied at a relatively low temperature and high pressure to adsorb hydrogen sulfide. And the adsorbing step for collecting the accompanying hardly adsorbing gas from the rear part of the tower, and (4) flowing the highly concentrated hydrogen sulfide-containing gas in parallel flow from the front part of the second adsorption tower after the end of the adsorbing step. The co-current purging step of discharging the hardly adsorbed gas remaining in the tower to the outside of the tower, and (5) the second step after the co-current purging step is completed.
A reduced pressure recovery step of recovering the highly concentrated hydrogen sulfide-containing gas by depressurizing it from the front part of the stage adsorption tower; and (6) a step of flowing gas countercurrently to the adsorption tower after completion of the reduced pressure recovery step to restore pressure. Are alternately switched over to continuously collect a high-concentration hydrogen sulfide gas, and the gas flowing from the adsorption step (3) of the second-stage adsorption tower is passed through the above-mentioned (1) of the first-stage adsorption tower. And the gas flowing from the co-current purging step (4) of the second stage adsorption tower is returned to the adsorption step (3) of the second stage adsorption tower. This is a method for recovering hydrogen sulfide by the swing adsorption method. In the above method, the gas flowing from the cocurrent flow purging step (4) of the second stage adsorption tower may be used as the recompression gas to be returned in the countercurrent recompression step (6).

[0011]

The present invention organically combines the above-mentioned PSA-I method and PSA-II method in two steps to obtain 40 vo
It is possible to recover a high-concentration hydrogen sulfide-containing gas at a high recovery rate from a low-concentration hydrogen sulfide-containing gas of 1% or less. That is, the gas flowing from the adsorption step of the second-stage PSA-II method is returned to the adsorption step of the first-stage PSA-I method, and the co-current purge of the second-stage PSA-II method is performed. It is possible to improve the low recovery rate, which is a drawback of the conventional PSA-II method, by returning the gas flowing from the process to the second adsorption process and, if necessary, the countercurrent recompression process. It was done.

Examples of the adsorbent used in the adsorption separation of the present invention include activated alumina, silicalite, and Na-X type zeolite (having a silica / alumina ratio of 2.7). However, when the adsorption temperature is 40 ° C. or higher and oxygen is present in the atmosphere, a Claus-like reaction is likely to occur, and the generated sulfur may be deposited on the surface of the adsorbent to lower the adsorption performance. It is preferable to use activated alumina containing polymerized phosphoric acid in the range of ˜2% by weight, particularly 0.5 to 1% by weight. It was confirmed that increasing the acidity by adding polymerized phosphoric acid in the above range is effective in avoiding the Claus-like reaction. If the content of polymerized phosphoric acid is less than 0.1% by weight, the amount of sulfur deposited will increase, which may block the pores of activated alumina and reduce the adsorption performance. It is not preferable because the amount is reduced.

[0013]

EXAMPLES Using the PSA apparatus shown in FIG. 1, hydrogen sulfide was concentrated to 99 vol% from a raw material gas containing 3 vol% hydrogen sulfide and 97 vol% nitrogen. The two first-stage adsorption towers 6 are each filled with 500 kg of hydrogen sulfide adsorbent 5, the valves 4a and 7a of the adsorption tower 6a in the adsorption step are opened, and the raw material gas 1 is blower 1 to 5a
After being compressed to tm, it was introduced into the adsorption tower 6a through the flow path 3 and the valve 4a to adsorb hydrogen sulfide, and the hardly adsorbed nitrogen gas was recovered through the valve 7a and the flow path 8. Then, the adsorption step was completed at the stage when the hydrogen sulfide adsorption zone moved to the rear part of the adsorption tower 6a.

In the adsorption tower 6b which has completed the adsorption process, the valves 9b and 12b are opened to communicate with the vacuum pump 10 and a part of the nitrogen gas recovered in the adsorption process is flowed while the pressure is reduced to 5 to 230 Torr. It 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 purging to desorb hydrogen sulfide from the adsorbent 5, and was recovered from the valve 9b, the vacuum pump 10, and the passage 13. The concentration of hydrogen sulfide in the recovered gas was set to be 40 vol% or more. In the adsorption tower 6b having completed the countercurrent purging step, only the valve 4b was opened to introduce the raw material gas, and the atmospheric pressure was restored.

The four adsorption towers 16 of the second stage are each filled with 250 kg of the hydrogen sulfide adsorbent 5, and the gas recovered in the depressurizing countercurrent purging step of the first stage is introduced from the flow passage 13 to the blower 14. To compress. The valves 15a and 17a of the adsorption tower 16a in the adsorption step are opened, the above-mentioned recovered gas is introduced into the adsorption tower 16a through the valve 15a to adsorb hydrogen sulfide, and the hardly adsorbed nitrogen is admitted through the valve 17a and the flow path 18. The gas was recovered. Since this recovered gas has a higher hydrogen sulfide concentration than the gas flowing from the first-stage adsorption step, it cannot be released into the atmosphere as it is. Therefore, this recovered gas is returned immediately before the blower 2 via the flow path 18 and introduced into the adsorption tower 6a in the first-stage adsorption step, whereby hydrogen sulfide is adsorbed and separated to make the hydrogen sulfide concentration extremely low. Nitrogen gas was recovered from the flow path 8 and discharged into the atmosphere except for the amount used for the countercurrent purging in the first stage.

The hydrogen sulfide adsorption zone moves to the rear part of the adsorption tower, and the adsorption tower 16b, which has completed the adsorption process, has a valve 20b.
And the valve 21b is opened to shift to the cocurrent flow purging step, and the highly concentrated hydrogen sulfide from the product holder 27 is cocurrently flowed to the adsorption tower 16b through the flow path 19 and the valve 20b. The nitrogen gas staying inside is purged and discharged to the outside of the tower through the valve 21b and the flow path 22. Since this released gas has a considerably high hydrogen sulfide concentration, it was returned immediately before the blower 14 and introduced into the adsorption tower 16a in the second stage adsorption step to recover hydrogen sulfide.

Adsorption tower 16c which has completed the co-current purging process
Opens the valve 25c and shifts to the reduced pressure recovery step, and the vacuum pump 26 sucks up to a high vacuum of the regeneration pressure to desorb and recover the hydrogen sulfide adsorbed on the adsorbent 5, and the product holder 27 Stored. Part of the stored hydrogen sulfide was taken out of the system as a product from the flow path 28, and part of the stored hydrogen sulfide was returned to the adsorption tower 16c in the above-mentioned parallel flow purging step and used for purging.

The adsorption tower 16d which has completed the reduced pressure recovery step is
By opening the valve 24d, the countercurrent decompression process is started, and a part of the gas released from the adsorption tower 16b in the cocurrent purge step is introduced into the adsorption tower 16d through the flow path 22 and the flow control valve 23. Then, the pressure was restored to prepare for the next adsorption step. The sequence of the first-stage adsorption tower during this period 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 the optimum adsorbent, the hydrogen sulfide adsorbents shown in Tables 2 and 3 were used, and the hydrogen sulfide concentration was 3 v.
Using a gas of ol% and 97% nitrogen as the raw material, the adsorption pressure of the first stage adsorption tower is 1.05 atm, the adsorption temperature is 25 ° C., the regeneration pressure is 0.03 atm, the purge rate α is 120%, and the cycle time is 5 minutes. The concentration of hydrogen sulfide in the outlet gas of the adsorption step was set to 150 ppm, and the first-stage adsorption operation was performed, and the concentration of hydrogen sulfide in the recovered gas (vol%) and the processing capacity of the raw material gas (Nm ³ / Ton) is shown in Table 2. In addition, the adsorption pressure of the second stage adsorption tower is 1.05a.
tm, adsorption temperature 25 ° C., regeneration pressure 0.02 atm,
Second with a purge rate α of 75% and a cycle time of 4 minutes
The adsorption operation of the stage is performed, and the hydrogen sulfide concentration (vol
%) And the treatment capacity (Nm ³ / Ton) of the raw material gas converted into an adsorbent of 1 Ton are shown in Table 3. As is clear from Table 2 and Table 3, activated alumina containing 0.5 to 1 wt% of polymerized phosphoric acid, activated alumina, and silicalite are
It turns out to be excellent. However, it should be noted that activated alumina causes a Claus reaction when the adsorption temperature is 40 ° C. or higher and oxygen is present in the atmosphere.

[0020]

[Table 2]

[0021]

[Table 3]

Regarding the first-stage adsorption tower, the hydrogen sulfide concentration (vol%) in the first-stage recovered gas was measured by changing the adsorption temperature among the above conditions, and the relationship between the adsorption temperature and the hydrogen sulfide concentration was measured. It is shown in FIG. Activated alumina containing 0.5 wt% of polymerized phosphoric acid gave a high hydrogen sulfide concentration in a wide adsorption temperature range of 0 to 300 ° C, while silicalite contained 0-1.
It can be seen that the method is applicable only in a relatively low temperature range of 50 ° C.

Regarding the first-stage adsorption tower, the hydrogen sulfide concentration in the recovered gas of the first stage when the concentration of hydrogen sulfide in the inlet gas of the first stage was changed among the above conditions was measured and compared. Is shown in FIG. When the inlet gas having a hydrogen sulfide concentration of 2 vol% is used, the hydrogen sulfide concentration in the recovered gas of the first stage reaches 40 vol%, and when the inlet gas of 40 vol% is used, the recovered gas of the first stage is The hydrogen sulfide concentration reached 90 vol%.

With respect to the first-stage adsorption tower, the regeneration pressure of the first-stage among the above conditions was changed, and the concentration of hydrogen sulfide in the recovered gas of the first-stage was measured and compared. As the ultimate vacuum pressure becomes higher, the amount of purge gas can be reduced, and theoretically purging at 1 Torr or less can be considered. However, considering the efficiency of the vacuum pump and the leak of the valve, the lower limit is about 10 Torr. ..

With respect to the first-stage adsorption tower, the adsorption pressure of the first-stage of the above conditions was changed, and the concentration of hydrogen sulfide in the recovered gas of the first-stage was measured and compared. The amount of purge gas can be reduced and the recovery concentration can be improved as the adsorption pressure increases, but the partial pressure of hydrogen sulfide is 1 atm.
If it exceeds m, the adsorption amount tends to be saturated, so 3 atm is the upper limit. In order to save energy, it is preferable to operate at an adsorption pressure of 1.05 to 1.1 atm, which corresponds to the pressure loss of the adsorption tower.

With respect to the second stage adsorption tower, the adsorption pressure was 1.
2 atm, regeneration pressure 0.2 atm, hydrogen sulfide concentration at the inlet of the second stage was 55 vol%, adsorption temperature was 25 ° C., and the adsorption rate of the second stage was the same as above, the purge rate and recovery of the second stage The relationship with the hydrogen sulfide concentration of the gas is as shown in FIG. 8, and the activated alumina containing 0.5% of polymerized phosphoric acid was used, and the purge rates were 55%, 65%, and 80%. Hydrogen sulfide concentration of the recovered gas is 95vol%, 99vol
% And 99.9 vol%. In addition, when silicalite is used, the purging rate is 60%, 70%, and 85%, and
The hydrogen sulfide concentration of the recovered gas in the stage is 95 vol%, 99 vo
It reached 1% and 99.9 vol%.

Regarding the second-stage adsorption tower, the purge rate was fixed at 65% among the above conditions, the hydrogen sulfide concentration at the inlet of the second stage was changed, and the hydrogen sulfide concentration of the recovered gas of the second stage was measured. However, as shown in FIG. 9, it can be seen that when the hydrogen sulfide concentration at the inlet of the second stage exceeds 40 vol%, the hydrogen sulfide concentration of the recovered gas at the second stage also exceeds 90 vol%.

Regarding the second-stage adsorption tower, the purge rate is fixed at 65% among the above conditions, the hydrogen sulfide concentration at the second-stage inlet is set to 55 vol%, the regeneration pressure is changed, and the recovery gas of the second stage is changed. As shown in FIG. 10, the hydrogen sulfide concentration of the second stage recovered gas increased as the regeneration pressure became higher, but the concentration increased at 0.05 atm or less. In addition, the capacity of the vacuum pump increases, which is not economical.

Regarding the second-stage adsorption tower, the purge rate is fixed to 65% among the above conditions, the hydrogen sulfide concentration at the second-stage inlet is set to 55 vol%, the adsorption pressure is changed, and the recovered gas of the second stage is changed. The hydrogen sulfide concentration was measured as shown in Fig. 11. The hydrogen sulfide concentration of the recovered gas in the second stage increased as the adsorption pressure increased, but it slowed down when it exceeded 3 atm, and the power consumption of the blower also increased. It is not economical.

(Example 1) After grasping the above tendency, hydrogen sulfide was recovered under the following operating conditions, and the hydrogen sulfide concentration of the recovered gas of the second stage adsorption tower and the hydrogen sulfide recovery rate were compared. In case I, the outflow gas from the adsorption step of the second-stage adsorption tower is returned to the previous stage of the blower of the first-stage adsorption tower and introduced into the adsorption step together with the raw material gas in the second-stage co-current purging step. The effluent gas was countercurrently supplied to the adsorption tower after the decompression recovery process of the second-stage adsorption tower was completed to restore the pressure. In case II,
The effluent gas from the adsorption step of the second stage adsorption tower and the effluent gas of the second stage co-current purging step were directly discharged to the outside of the system.

First-stage adsorption tower Adsorbent Adsorbent: 0.5 wt% polymerized phosphoric acid activated alumina Adsorption pressure 1.05 atm Regeneration pressure 0.03 atm Countercurrent purge rate 120% Adsorption temperature 25 ° C. Hydrogen sulfide concentration in inlet gas 3 vol% Outlet gas Hydrogen sulfide concentration of 44 vol% 2nd stage adsorption tower adsorbent polymerized phosphoric acid 0.5 wt% activated alumina containing adsorption pressure 1.2 atm regeneration pressure 0.2 atm cocurrent purge rate 75% adsorption temperature 25 ° C hydrogen sulfide concentration of inlet gas 44 vol % Hydrogen sulfide concentration of outlet gas 99 vol% Hydrogen sulfide concentration of outlet gas is 99 vol% in both Case I and Case II, but the overall hydrogen sulfide recovery rate is 95% in Case I. , Case II is 60
%, Indicating that Case I is extremely effective.

(Example 2) Hydrogen sulfide was recovered under the conditions of Example 1, and in case I, the outflow gas from the adsorption step of the second stage adsorption tower was returned to the stage before the blower of the first stage adsorption tower. Was introduced into the adsorption step together with the raw material gas, and the outflow gas from the co-current purging step of the second-stage adsorption tower was returned to the front stage of the blower of the second-stage adsorption tower and introduced into the second-stage adsorption step. Case II
Then, the outflow gas from the adsorption step of the second stage adsorption tower, and
The effluent gas from the second stage co-current purging step was directly discharged to the outside of the system. The hydrogen sulfide concentration of the outlet gas is 98 vo in case I
The total hydrogen sulfide recovery rate is 95% in Case I, whereas it is 60% in Case II, and Case I is extremely effective. I understand.

[0033]

The present invention uses the adsorption tower in two stages,
The effluent gas from the adsorption step of the two-stage adsorption tower is returned to the first-stage adsorption step, and the effluent gas from the co-current purging step of the second-stage adsorption tower is returned to the adsorption step of the second-stage adsorption tower, and countercurrent as necessary. By returning to the re-pressurization step, it became possible to recover high-concentration hydrogen sulfide with a high recovery rate, which has the advantages of the conventional countercurrent purge method and the parallel flow purge method.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a sequence of a first-stage adsorption tower in an example.

FIG. 3 is a diagram showing the sequence of the second-stage adsorption tower in the examples.

FIG. 4 is a graph showing the relationship between the adsorption temperature and the hydrogen sulfide concentration of the recovered gas in the first stage adsorption tower in the examples.

FIG. 5 is a graph showing the relationship between the hydrogen sulfide concentration of the inlet gas of the first-stage adsorption tower and the hydrogen sulfide concentration of the recovered gas of the first-stage adsorption tower in the examples.

FIG. 6 shows the regeneration pressure of the first-stage adsorption tower in Examples,
It is the graph which showed the relationship with the hydrogen sulfide concentration of the recovery gas of the 1st stage adsorption tower.

FIG. 7 shows the adsorption pressure of the first-stage adsorption tower in the example,
It is the graph which showed the relationship with the hydrogen sulfide concentration of the recovery gas of the 1st stage adsorption tower.

FIG. 8 shows the purge rate of the second-stage adsorption tower in Examples,
It is the graph which showed the relationship with the hydrogen sulfide concentration of the recovery gas of the 2nd stage adsorption tower.

FIG. 9 is a graph showing the relationship between the hydrogen sulfide concentration of the inlet gas of the second-stage adsorption tower and the hydrogen sulfide concentration of the recovered gas of the second-stage adsorption tower in the examples.

FIG. 10 is a graph showing the relationship between the regeneration pressure of the second-stage adsorption tower and the hydrogen sulfide concentration of the recovered gas of the second-stage adsorption tower in the examples.

FIG. 11 is a graph showing the relationship between the adsorption pressure of the second-stage adsorption tower and the hydrogen sulfide concentration of the recovered gas of the second-stage adsorption tower in the examples.

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

FIG. 13 is a flow sheet of an apparatus for performing a conventional co-current purging method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Araki 5-717-1, Fukahori-cho, Nagasaki-shi, Nagasaki Sanryo Heavy Industries Co., Ltd. Nagasaki Shipyard

Claims (1)

[Claims] 1. A method for recovering hydrogen sulfide from a low-concentration hydrogen sulfide-containing gas of 40 vol% or less by using an adsorption tower filled with a hydrogen sulfide adsorbent in two stages, wherein the first-stage adsorption tower comprises (1) An adsorption step in which the above gas is supplied at a relatively low temperature and a high pressure to adsorb hydrogen sulfide and the accompanying hardly adsorbed gas is recovered from the rear part of the tower, and (2) from the front part of the adsorption tower after the adsorption step is completed. The pressure is reduced, and then a part of the hardly adsorbed gas is introduced in a counterflow to reduce the concentration of hydrogen sulfide to 40 vol% or more for concentration and recovery, and are alternately switched to continuously recover hydrogen sulfide. Then, in the second-stage adsorption tower, (3) the reduced volume concentrated hydrogen sulfide-containing gas is supplied at a relatively low temperature and high pressure to adsorb hydrogen sulfide, and the accompanying hardly adsorbed gas is adsorbed to the rear part of the tower. Adsorption process to collect more, and (4) second adsorption after the adsorption process A co-current purging step of flowing a highly concentrated hydrogen sulfide-containing gas in co-current from the front part of the tower to discharge the hardly adsorbed gas remaining in the tower to the outside of the tower, and (5) co-current purging step. After the end, the decompression recovery step of decompressing from the front part of the second-stage adsorption tower to recover the highly concentrated hydrogen sulfide-containing gas, and (6) flowing the gas countercurrently into the adsorption tower after the completion of the decompression recovery step And the step of recovering pressure is alternately switched to continuously collect high-concentration hydrogen sulfide gas, and the gas flowing through from the adsorption step (3) of the second stage adsorption tower
It is characterized by returning to the adsorption step (1) of the two-stage adsorption tower and returning the gas flowing from the parallel flow purging step (4) of the second adsorption tower to the adsorption step (3). Method for recovering hydrogen sulfide by pressure swing adsorption method.