JP2569095B2 - Pressure swing adsorption method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention uses four adsorption towers to produce carbon monoxide (CO).
The present invention relates to a pressure swing adsorption method capable of separating and recovering high-purity CO from a mixed gas containing carbon.

(Prior art) Conventionally, as a pressure swing adsorption method for separating and recovering CO from a mixed gas containing CO, a cycle having a pressure increasing step, an adsorption step, a depressurizing step, a washing step, a pause step, and a desorption step is performed by a plurality of adsorption steps. It is known that CO is continuously desorbed and recovered by repeating the shift of each column in the tower so that once the desorption process of one adsorption tower is completed, the desorption process of another adsorption tower is started. ing.

The conventional pressure swing adsorption method is shown in FIGS.
The process explanatory diagram shown in the figure, and the four adsorption towers A, B, and
Based on one adsorption tower A based on the apparatus having C and D,
A description will be given from the state where the desorption process is completed. FIG. 5 shows each step of the adsorption tower A and the flow of gas in the above-mentioned apparatus.
Reference numerals are omitted for other steps.

The pressurizing step is divided into three stages. First, in the first pressurizing step, the adsorption tower A in which the desorption step is completed and in a depressurized state, and the adsorption tower B in which the adsorption step is completed and in a pressurized state are connected to a valve 31b. By connecting the valve by opening the valve 32a and guiding the decompressed exhaust gas from the adsorption tower B to the adsorption tower A through the circulation line 3, the pressure of the adsorption tower A is increased to almost the atmospheric pressure (0 kg / cm ² G). The pressure in the adsorption tower B is reduced to almost the atmospheric pressure. After the pressure reducing step, the adsorption tower B is supplied with the cleaning gas through the cleaning gas supply pipe 4 and enters the cleaning step.

In the second pressurization period, the exhaust gas for washing the adsorption tower B is supplied to the adsorption tower A through the circulation line 3 to collect CO in the exhaust gas for washing, and the remaining exhaust gas is opened by the valve 21a to open the exhaust line 2 for the exhaust gas. Released through

In the third stage of the pressure increase, the valve 21a and the valve 31b are closed, and the valve 31d is opened, so that the exhaust gas of the adsorption tower D in the latter half of the adsorption step is supplied to the adsorption tower A through the circulation line 3. , A predetermined adsorption pressure (2 kg / cm in FIG. 4)
Up to ² G). In addition, this adsorption pressure is 1-5 kg / cm
^It may be selected within a range of about ² G.

Next, in the adsorption step, the valve 11a and the valve 21a are opened, and the raw material gas compressor 10 is operated.
A mixed gas composed of CO ₂ , N ₂ and H ₂ is supplied to the adsorption tower A as a raw material gas. In the adsorption tower A, the most adsorbable CO (easy adsorbable component) in the raw material gas is adsorbed under pressure to an adsorbent obtained by impregnating a carrier such as zeolite with a copper compound, and N ₂ , CO ₂ And H ₂ (a poorly adsorbable component) are released into the atmosphere through the valve 21a and the exhaust gas discharge line 2 as the adsorbed exhaust gas.

Then, in the latter half of this adsorption step, the valve is set immediately before the CO concentration of the above-mentioned exhaust gas becomes equal to the CO concentration of the raw material gas.
The valve 21a is closed and the valve 31a and the valve 32c are opened, whereby the adsorption exhaust gas is used as the pressurized gas in the third stage of the pressure increase of the adsorption tower C.

When the adsorption step is completed, the adsorption tower A starts the pressure reduction step by opening the valves 31a and 32b of the circulation line 3. 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 in a reduced pressure state, and the pressure in the adsorption tower A is reduced to almost the atmospheric pressure, and the adsorption tower B is subjected to the first pressurization. .

Thereafter, the adsorption tower A enters a washing step. In this cleaning step, the valve 41a of the cleaning gas supply pipe 4 and the valve 3 of the circulation pipe 3 are connected.
1a, 32b and the valve 21b of the exhaust gas discharge line 2 are opened, and the CO component gas in the product gas storage tank 6 is introduced into the adsorption tower A. The poorly adsorbed components remaining in the adsorption tower A are purged by the CO component gas, and the purged exhaust gas is led to the adsorption tower B through the circulation pipe 3 and used in the second stage of the pressure increase of the adsorption tower B.

The adsorption tower A after the completion of the washing step is connected to the valve 41a and the valve 31a.
Is closed and stopped at the atmospheric pressure until the desorption step of the adsorption tower D is completed. At the same time when the desorption step of the adsorption tower D is completed, the valve 51a of the desorption gas recovery pipe 5 is opened, and the vacuum pump 50 is continuously operated, whereby the adsorption tower A enters the desorption step. In this desorption step, the CO component adsorbed in the adsorption tower A is desorbed under reduced pressure, and this CO component gas is collected in the product gas storage tank 6.

The desorption step in the adsorption tower A includes an adsorption step in the adsorption tower B,
The pressure-reducing, washing and resting steps are performed in the adsorption tower C, and the pressure-increasing step is performed in the adsorption tower D.

By this desorption step, the pressure in the adsorption tower A is finally reduced to approximately −1 kg / cm ² . This completes one cycle, after which the adsorption tower A returns to the pressure increasing step, and the same steps are repeated thereafter.

In the above conventional pressure swing adsorption method, in order to improve the recovery rate, CO in the exhaust gas of the adsorption step, the depressurization step, and the cleaning step is collected by another adsorption tower, and the power of the vacuum pump is effectively used. Therefore, it is set so that one of the adsorption towers is always in the desorption step. For this reason, the adsorption tower after the washing step has to wait until the next desorption step, and there is a problem that a pause step always occurs during this time.

In addition, since a chemical adsorbent obtained by impregnating a carrier such as zeolite with a copper compound is used as an adsorbent, CO is strongly adsorbed to the chemical adsorbent as compared with a case where a physical adsorbent such as zeolite is used. For this reason, the CO
Has a problem that it is difficult to detach.

In order to solve this problem, it is conceivable to increase the capacity of the vacuum pump for desorption and recovery to lower the pressure during desorption. However, when the adsorption power is strong, even if the desorption pressure is lowered, the desorption reaction is rate-determining, so it is not desorbed immediately but is gradually desorbed, so the CO desorption amount in the entire desorption process does not increase much . In addition, if you lower the desorption pressure,
Since impurities that are hardly adsorbed components easily reach adsorption equilibrium, the amount of the impurities desorbed increases according to the desorption pressure, and CO
There is a problem that the purity is reduced.

It is also conceivable to increase the temperature at the time of desorption to facilitate desorption. However, in this case, if the desorption temperature is increased, the adsorption temperature is relatively increased, and as a result, the adsorption capacity is reduced. It is also conceivable to lengthen the time of one cycle and thereby lengthen the time of the desorption step. However, the amount of CO desorbed per unit time decreases because the amount of CO desorbed does not increase with the desorption time due to the characteristics of the desorption reaction.

For this reason, in the pressure swing adsorption method using a strong adsorbent, the adsorbed CO is efficiently desorbed and collected,
In addition, there is a demand for the development of a method that can effectively use time and increase the amount of recovery.

(Object of the Invention) The present invention has been made to solve such a conventional problem, and a pressure swing capable of easily and surely increasing the amount of CO desorbed and recovered and improving the purity. The present invention provides an adsorption method.

(Constitution of the Invention) The present invention comprises a pressure boosting step, an adsorption step, a decompression step, a washing step, and a desorption step, and the above-mentioned step is carried out by using four pressure swing adsorption towers filled with an adsorbent impregnated with a copper compound. In a pressure swing adsorption method for separating and recovering carbon monoxide from a mixed gas containing carbon monoxide by repeating the above steps, a part of the desorption step of one adsorption tower and a part of the desorption step of another adsorption tower overlap each other. In this way, a plurality of adsorption towers can be simultaneously desorbed.

According to the above configuration, the desorption step of one adsorption tower and the desorption step of another adsorption tower are partially overlapped with each other, so that the unit desorption step of the adsorption tower can be performed without increasing the time per cycle. The desorption continuation time per unit and the total desorption time in the total operation time can be increased.

In addition, since the adsorption tower where desorption has been performed to some extent and the adsorption tower where desorption starts are simultaneously desorbed, at the beginning of desorption,
The pressures of the two adsorption towers are equalized, and the adsorption tower where desorption has begun instantaneously drops to a pressure value effective for desorption, and the pressure inside the adsorption tower is maintained at a pressure value effective for desorption during the desorption process. Time is increased.

Thus, the amount of desorbed and recovered can be increased as compared with the conventional method. In addition, since a plurality of adsorption towers are simultaneously decompressed and desorbed by one vacuum pump, the final desorption pressure in the desorption step is higher than in the case where one conventional adsorption tower is depressurized and desorbed. Is also reduced.

(Example) The steps shown in FIG. 1 and FIG.
The pause step in the conventional cycle shown in the figure is eliminated, and the time is included in the desorption step, thereby extending the time of the desorption step without increasing the time required for one cycle (12 minutes). Therefore, one cycle is constituted by the steps of pressure increase, adsorption, decompression, washing, and desorption, and the desorption step has three stages, ie, the first desorption, depending on the relationship with other adsorption towers.
Phase, the second phase of desorption and the third phase of desorption.

For example, regarding the adsorption tower A, two of the adsorption tower A in the first stage of desorption and the adsorption tower D in the third stage of desorption are decompressed and desorbed by the vacuum pump 50. Next, in the second phase of desorption, only the adsorption tower A is decompressed and desorbed by the vacuum pump 50. In the third phase of desorption, the adsorption tower A and the adsorption tower C in the first phase of desorption are used.
Are decompressed and desorbed by the vacuum pump 50. Therefore, the desorption process in the four adsorption towers A, B, C, and D is continuously repeated while the beginning and end thereof overlap with each other. FIG. 2 shows each step of the adsorption tower A and the flow of gas in the apparatus shown in FIG. 3. In the apparatus, main symbols are assigned only to the first stage of the pressure increase, and symbols are omitted for other steps. doing.

1, 2 and 3, the adsorption tower A has a pressure of 2 kg / cm ² G in the process from the first stage to the third stage in the same manner as the conventional process shown in FIG. The pressure is increased, and then the adsorption process is started while maintaining the adsorption pressure. After this,
In the pressure reduction step, the valve 31a of the circulation line 3 is opened, and the pressure in the adsorption tower A is reduced to the atmospheric pressure. Then, in the cleaning step, the product gas from the product gas storage tank 6 is passed as a cleaning gas to the adsorption tower A to purge the hardly adsorbable components, and to fill the voids of the adsorbent with the high-purity CO component gas. The cleaning process is performed in the same manner as the conventional process shown in FIG. 4, and the adsorption tower A at the end of the cleaning process is almost at atmospheric pressure.

The cleaning process is completed by closing the valves 41a, 31a, 32b, and 21b, and subsequently, the valve 51a of the recovery line 5 is opened, so that the adsorption tower A enters the first stage of desorption in the desorption process. Immediately before entering the first phase of desorption, the adsorption tower D is in the second phase of desorption, and the adsorption tower D is independently decompressed and decompressed by the vacuum pump 50 through the valve 51d. Therefore, when the adsorption tower A enters the first stage of desorption, the two of the adsorption tower A and the adsorption tower D are simultaneously depressurized and desorbed by the vacuum pump 50, and the adsorption tower D enters the third stage of desorption. Adsorption tower A is desorbed first
During the period when the adsorption tower D is in the third phase of desorption, the adsorption tower B
In the third stage, the adsorption step is performed in the adsorption tower C.

The valve 51d of the recovery line 5 is closed, and the third desorption of the adsorption tower D is performed.
Even after the end of the period, the adsorption tower A is continuously desorbed under reduced pressure. As a result, the adsorption tower A enters the second stage of desorption and is decompressed alone, so that the pressure in the adsorption tower A decreases rapidly as compared with the first phase of desorption and is reduced to almost the final pressure. During the second stage of the desorption, the other adsorption tower B performs the adsorption step, the adsorption tower C
, The pressure reduction step and the washing step are performed, and the adsorption tower D is subjected to the second pressure raising phase.

After that, the adsorption tower C after the washing step is returned to the recovery line 5.
When the valve 51b is opened, the first stage of the desorption process is started. As a result, the adsorption tower A is moved from the second stage of desorption to 2
The third stage of desorption, in which two adsorption towers are simultaneously desorbed under reduced pressure, is entered.
In the third stage of the desorption, the adsorption tower A is continuously operated by the vacuum pump 50.
However, since the same vacuum pump 50 simultaneously suctions the two adsorption towers and the other adsorption tower C is suctioned from the atmospheric pressure, the pressure in the adsorption tower A and the pressure in the adsorption tower C are different from each other. The pressure is equalized at a pressure slightly higher than the pressure at the end of the second stage of desorption of the adsorption tower A. As a result, the pressure in the adsorption tower C can be instantaneously reduced to a certain degree or less, instead of being gradually reduced. After this, the above 2
One of the adsorption towers A and C is further depressurized, but the final pressure of the entire desorption step is the same as in the conventional method when the desorption steps of each adsorption tower A, B, C and D are independently depressurized by the vacuum pump 50. Slightly higher than

With the end of the adsorption step of the adsorption tower B, the desorption step of the adsorption tower A is also ended, whereby one cycle in the adsorption tower A is ended, and the adsorption tower A enters the pressure increasing step again and enters the next cycle.

According to the above method, the decompression state in the desorption step is changed to the fourth state.
Since it can be continued for a longer time than the conventional method shown in FIG. 5 and FIG.
CO can be desorbed and recovered. In addition, since the time required for one cycle is the same as that of the conventional method, the amount of desorbed and recovered per total operating time and per unit time can be increased as compared with the conventional method. In addition, since the final pressure in the desorption step is higher than in the conventional method, the amount of desorbed impurities is reduced by that amount, thereby improving the CO purity.

(Examples) The 3 CO using the apparatus shown in figure 70%, CO ₂ is 15%, N ₂
Was tested according to the steps shown in FIGS. 1 and 2 for the case of separating and recovering CO from a raw material gas having a composition of 15%. As a result of repeating one cycle for 12 minutes, the CO purity of the product gas was constant at 99.8% 80 minutes after the start of operation, and the CO recovery rate was
Maintain 50%, and the amount of CO desorbed per cycle is 1.
It was 5m ^3. The adsorbent used was an activated alumina with a copper compound impregnated.

(Comparative Example) A test was performed according to the conventional method shown in FIGS. 4 and 5 using the same apparatus and the same source gas as in the above specific example. As a result of repeating the same cycle time as the above example, the CO purity of the product gas was constant at 99.5% in 80 minutes after the start of operation, and the recovery rate was almost the same, but the amount of CO desorbed gas was 1.2 m ³ Met.

That is, in the specific example based on the embodiment shown in FIGS. 1 and 2, the amount of CO desorbed gas could be increased by 25% as compared with the comparative example based on the conventional method. Also, as the amount of desorption increased, the amount of impurities desorbed decreased compared with the conventional method, so that the CO purity was improved by 0.3%.

(Effects of the Invention) According to the pressure swing adsorption method of the present invention, the desorption step of a certain adsorption tower and the desorption step of another adsorption tower are performed by partially overlapping each other to reduce the time per cycle. It is possible to increase the desorption duration per unit desorption step of the adsorption tower and the total desorption time in the total operation time without increasing the amount of CO, thereby easily and reliably increasing the amount of CO desorbed and recovered compared with the conventional method. Can be. Moreover, since a plurality of adsorption towers are simultaneously decompressed and depressurized by one vacuum pump, the final desorption pressure in the desorption step is higher than in the conventional method, and thus the amount of impurities desorbed is smaller than in the conventional method, so that the purity can be improved. it can.

[Brief description of the drawings]

FIG. 1 is a process explanatory diagram showing each step of the embodiment of the present invention and the pressure in the adsorption tower with time, FIG. 2 is a process explanatory diagram showing each process of FIG. 1 and a gas flow, FIG. 3 is a schematic configuration diagram of an apparatus for performing each step of FIG. 1 and each step of FIG. 4, and FIG. 4 is a description of each step of the conventional method and the pressure over time in the adsorption tower. FIG. 5 is a process explanatory view showing each process of FIG. 4 and the flow of gas. A, B, C, D ... pressure swing adsorption tower, 1 ... source gas supply line, 2 ... exhaust gas discharge line, 3 ... circulation line, 4 ...
Cleaning gas supply line, 5 ... Desorption gas recovery line, 6 ...
Product gas storage tank.

Continued on the front page (72) Inventor Taku Aogata 366, Hasuike, Myohoji, Suma-ku, Kobe-shi, Hyogo Prefecture Inventor Jintaro Yokoe 8-8-101 Hanazono-cho, Nishinomiya-shi, Hyogo (72) Inventor Toshiaki Tsuji 145 Minaminakaokamoto, Izumisano-shi, Osaka

Claims (1)

(57) [Claims] 1. A pressure swinging step, an adsorbing step, a depressurizing step, a washing step, and a desorbing step, wherein the above steps are shifted from each other by using four pressure swing adsorption towers filled with an adsorbent to which a copper compound is impregnated. In a pressure swing adsorption method for separating and recovering carbon monoxide from a mixed gas containing carbon monoxide by repeating, a desorption step of one adsorption tower and a desorption step of another adsorption tower are partially overlapped with each other by a plurality of steps. A pressure swing adsorption method, wherein the steps of desorbing the adsorption tower are performed simultaneously.