JP2002331218A - Apparatus and method for gas separation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for gas separation improved in the ability of an adsorbent to yield the objective product and reduced in energy cost without sacrificing the feature, i.e., the simplicity of apparatus structure, of a rapid pressure swing adsorption system. SOLUTION: A gas separator to which a rapid pressure swing adsorption system is applied is provided. This separator is one provided with an adsorption cylinder (30) having an adsorbent, a gas feed path (31, etc.), which leads a raw material gas to the end of the inlet (34) of the cylinder, a gas withdrawal path (36, etc.), which withdraws a product gas rich in a difficultly adsorbable component from the end of the exit (35) of the cylinder, and a gas discharge path that discharges a discharge gas rich in a readily adsorbable component, wherein the gas discharge path has a first gas discharge path (40, etc.), that discharges the discharge gas spontaneously flowing out by the differential pressure between the discharge gas and the atmosphere and a second gas discharge path (53, etc.), arranged in a manner that the first gas discharge path can be switched to the second gas discharge path, provided with a vacuum pump (52), and forcibly discharging the discharge gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rapid pressure swing adsorption system (hereinafter sometimes abbreviated as the RPSA method), which is used to produce a gas mixture containing a component that can be selectively adsorbed. The present invention relates to a gas separation device and a gas separation method for separating components that are easily adsorbed, and more particularly, to a gas separation device and a gas having a mechanism for performing regeneration of an adsorbent under a pressure lower than atmospheric pressure using a vacuum pump. It relates to a separation method. As a specific application example, a device that separates nitrogen from air using zeolite as an adsorbent to obtain oxygen-enriched air, or
There is an apparatus for separating and recovering carbon dioxide from combustion exhaust gas using activated carbon as an adsorbent.

[0002]

BACKGROUND OF THE INVENTION The most important application of the present invention is gas separation, which uses the air around us as a raw material to separate nitrogen and extract an oxygen-rich gas mixture (hereinafter referred to as oxygen-enriched air). It is to provide a device. Therefore, if necessary, the conventional technology will be studied while citing a case in which oxygen in the air is concentrated as a specific example. Certain zeolites are known to preferentially adsorb nitrogen over oxygen. Utilizing this selective adsorption property of zeolite, nitrogen can be selectively adsorbed and removed from ordinary air, and oxygen-enriched air which is hardly adsorbed can be taken out. For such adsorption methods to be industrially successful, rather than disposable adsorbents,
It is important to have a way to quickly reproduce and reuse it repeatedly. At present, as such a method, a pressure swing adsorption method (pressure swing adsorption system) and a vacuum pressure swing adsorption method (vacuum swing adsorption system) are widely used (hereinafter, when there is no need to distinguish between the two methods, And collectively abbreviated as PSA method).
In these methods, usually an adsorption column filled with zeolite in the form of pellets or granules having a size of 1 to 3 mm is provided, and first, air is supplied to the adsorption column at a high pressure, and nitrogen is selectively adsorbed to form an oxygen-enriched air. Take out. Next, the partial pressure of nitrogen in the adsorption cylinder is reduced by reducing the total pressure in the adsorption cylinder or purging (scavenging and cleaning) the interior of the adsorption cylinder using a part of the generated oxygen-enriched air. Lower. The point of the PSA method is to desorb the nitrogen adsorbed on the adsorbent and regenerate the adsorbent by reducing the nitrogen partial pressure. Regeneration of the adsorbent allows repeated operation in which the adsorption step and the desorption step are one cycle, but oxygen-enriched air cannot be removed from the adsorption column during the desorption step. Therefore,
In order to continuously discharge oxygen-enriched air, as is well known, a plurality of adsorption cylinders are installed in parallel, and these are operated out of phase so that at least one adsorption cylinder always has oxygen-enriched air. The entire cycle is often configured to allow air to flow. In the case of such a multi-cylinder type, in order to obtain higher separation performance, several steps for transferring pressurized air or oxygen-enriched air between a plurality of adsorption cylinders (equalization step, etc.) are added. Can be In addition, an adsorbent having a relatively large particle size is used in order to minimize a pressure drop in the adsorption cylinder. As the particle size increases, more time is required for gas to enter and exit the particles to achieve adsorption equilibrium. For these reasons, the PSA method requires (1) one cycle to perform one cycle.
Minute to several minutes, and low adsorbent productivity (recovery amount of target component per unit amount of adsorbent and unit time)
(2) There is a problem that complicated piping and a large number of valves are required to switch the flow between the adsorption tubes.

On the other hand, as a method which does not have such a problem, a single adsorption column filled with fine adsorbent particles having a particle size of 20 mesh or less is provided, and one cycle is completed in several seconds to several tens of seconds. The pressure swing adsorption method (RPSA method) has already been devised. FIG.
FIG. 1 is a schematic diagram of the RPSA method disclosed in Japanese Patent Publication No. 1
0 is an adsorption column filled with an adsorbent, 14 and 15 are an inlet end and an outlet end of the adsorption column, 11 is a conduit for introducing a source gas, 12 is a compressor for pressurizing the source gas, and 1
3 is a gas supply valve, 16 is a conduit for guiding product gas, 17 is a product gas flow control valve for controlling the flow rate of product gas, 1
Reference numeral 9 denotes a gas discharge valve, and reference numeral 20 denotes a conduit for guiding the gas to be discharged.
Although not shown, a source gas surge tank is provided between the compressor 12 and the gas supply valve 13. The publication also discloses that, if necessary, a product gas surge tank 18 is provided between the product gas conduits 16 and a pump 21 for promoting the flow of the exhaust gas is provided between the exhaust gas conduits 20. It is written that it may be. One cycle of this method usually includes the following three steps. (A) Source gas introduction period t1 With the gas discharge valve closed, open the gas supply valve for a short time,
A high-pressure raw material gas is pulsed from the inlet end to the adsorption column. The introduced source gas moves toward the outlet end and forms a forward flow. Of the components in the source gas, the components that are easily adsorbed are selectively adsorbed by the adsorbent,
Components that are hardly adsorbed are more quickly flushed toward the outlet end. For this reason, as the gas passes between the adsorbent particles, the concentration of the easily adsorbed component decreases, the concentration of the hardly adsorbed component increases, and the product gas is gradually produced. Product gas flows out of the outlet end and is withdrawn through a product gas surge tank and a product gas flow control valve. The pressure of the product gas fluctuates somewhat during one cycle, but is much lower than the pressure of the feed gas. In the production of normal oxygen-enriched air, the pressure is adjusted to a pressure slightly higher than the atmospheric pressure by a product gas flow control valve. If the source gas pressure is the same,
The amount of source gas that can be processed in a cycle is determined by the length of the source gas introduction period. (B) Inlet end flow stop period t2 Close both the gas discharge valve and gas supply valve. The flow of the raw material gas into the inlet terminal stops, but in the adsorption column, the gas flows from the inlet terminal to the outlet terminal as in the raw gas introduction period, and the product gas flows out from the outlet terminal. The inlet end flow cessation phase is not essential. An appropriate length of inlet end flow stoppage allows time for the feed gas to penetrate deeper into the adsorption column and improves the recovery of poorly adsorbed components in the product gas. On the other hand, because the time required for one cycle is increased by this amount, an excessively long inlet terminal flow stop period reduces adsorbent productivity. (C) Reverse gas discharge period t3 Open the gas discharge valve with the gas supply valve closed. The high-pressure gas near the inlet end starts flowing out to the atmosphere side through the gas discharge valve due to a pressure difference from the pressure on the outlet side of the gas discharge valve (atmospheric pressure in the case where there is no pump 21). A reverse flow is formed in the cylinder that flows toward the inlet end. The starting point of the reverse flow, that is, the watershed boundary between the forward flow and the reverse flow (the position where the gas pressure in the adsorption column shows the maximum value) is initially at the inlet end, but as the gas discharge progresses, Gradually move towards the exit end. During this time, two flows in the forward direction and the reverse direction exist in the adsorption column, and the outflow of the product gas from the outlet end continues. Eventually, when the starting point of the reverse flow reaches the outlet end, the flow in the adsorption column becomes only the purge flow of the reverse flow. The subsequent purge flow will be driven by a slight pressure difference between the pressure of the product gas near the outlet end and the pressure at the inlet end (approximately atmospheric pressure in the normal case without the pump 21). In the reverse gas discharge period, the partial pressure of components that are easily adsorbed in the adsorption column is reduced by reducing the total pressure at the beginning and then purging with product gas, and the components that are easily adsorbed are adsorbed. And the adsorbent is regenerated. The gas containing a high concentration of desorbed easily adsorbed components forms a reverse flow and is discharged from the inlet end.

As described above, there is always a gas pressure gradient in the axial direction of the adsorption cylinder throughout one cycle, and during the period when the gas flow in the adsorption cylinder is only the forward flow, the two flows in the forward and reverse directions The PSA method shows that the three periods of repetition of the period in which the flow exists only in the reverse direction and the period in which the flow is only in the reverse direction are repeated, and the extraction of the product gas and the discharge of the exhaust gas are partially performed in parallel. This is a feature of the RPSA method which is different from the above. The RPSA method has high adsorbent productivity due to a short cycle time, and does not require complicated piping and a large number of valves because the purge step is performed in its own adsorption cylinder. It is said that providing a product gas surge tank has the advantage that a substantially continuous product gas flow can be obtained with a single adsorption column. However, the RPSA method is scarcely used except for applications requiring a particularly small device. This is because the RPSA method has the following problems. (3) Part of the adsorption cylinder is used for storing purge gas. Therefore, not all of the adsorbents are effectively used for the original purpose of adsorbing and collecting easily adsorbable components. (4) In the example of JP-A-55-5789 applied to the production of oxygen-enriched air having an oxygen concentration of 90 vol%, (i) when a short adsorption column is used, the oxygen recovery rate is low. When a long adsorption column is used, the recovery rate of oxygen is improved, but it is necessary to increase the pressure of the source gas. In any case, the energy cost for obtaining oxygen is high. (Ii) The length of the reverse gas discharge period is required to be at least twice as long as the source gas introduction period, usually 3 to 5 times. For example, a typical cycle time when a suction tube having a length of 1524 mm is used is t1 = 0.5 seconds, t2 = 1.0 seconds, and t3 = 15 seconds.
Seconds. The source gas introduction period, which determines the amount of gas that can be processed in one cycle, occupies only a small part of the total cycle time, and it cannot be said that the time is utilized sufficiently effectively. The adsorbent productivity decreases accordingly.

[0005] Many of these problems are related to the purge step of regenerating the adsorbent. For example, it is considered that the cause of the longer reverse gas discharge period is that the flow rate of the purge flow is not sufficient because the purge flow is driven by a slight pressure difference between the product gas and the atmosphere. Therefore, it is considered that there is room for improving the adsorbent productivity and energy cost of the RPSA method by devising the regeneration step.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and further improves the adsorbent productivity while maintaining the characteristics of the rapid pressure swing adsorption method, which is a simple apparatus configuration. An object of the present invention is to provide a gas separation device and a gas separation method to which a rapid pressure swing adsorption method with improved energy cost is applied.

[0007]

In order to achieve the above object, a gas separation apparatus according to the present invention is a gas separation apparatus to which a rapid pressure swing adsorption method is applied. A gas supply path for introducing a raw material gas to the inlet end of the adsorption column, and a product gas resulting from selectively adsorbing and removing components easily adsorbed by the adsorbent from the raw material gas, from the outlet end of the adsorption column. A gas take-out passage for taking out the product gas from the raw material gas, and a gas discharge passage for discharging the exhaust gas remaining in the adsorption column from the end of the inlet after taking out the product gas from the raw material gas; A first gas discharge path for discharging the gas to be discharged, which flows out at its own pressure due to a pressure difference from the atmospheric pressure, and a switchable switch disposed between the first gas discharge path and the first discharge path; And having a second gas discharge passage for forcibly exhausting the scan by the vacuum pump.
Further, a shutoff valve is provided in the gas extraction path, and is capable of preventing the product gas from flowing back into the adsorption column. Further, the gas separation method of the present invention is a gas separation method based on a rapid pressure swing adsorption method, wherein one cycle comprises at least a high-pressure raw material gas flowing from the inlet end of an adsorption column having an adsorbent therein into the adsorption column. The source gas introduction step to introduce in a pulse, and remains after extracting a product gas rich in a component that is difficult to be adsorbed by the selective adsorption action of the adsorbent from the source gas,
An exhausted gas exhausting step of exhausting the exhausted gas rich in a component that is easily adsorbed from the adsorption column, wherein the exhausted gas exhausting step includes a high-pressure exhaust gas through a first gas exhaust passage provided at the inlet end. The exhaust gas is caused to flow out at its own pressure by a pressure difference from the atmospheric pressure, and a reverse gas discharging step of reducing the pressure to near the atmospheric pressure, and provided at the inlet end so as to be switchable with the first gas discharging path. A vacuum regeneration step of forcibly exhausting the low-pressure exhaust gas by a vacuum pump through the second gas exhaust path.

In the rapid pressure swing adsorption method using the gas separation apparatus of the present invention, after the above three steps (a) to (c), desorption is performed under a pressure lower than atmospheric pressure using a vacuum pump. (D) Add a vacuum regeneration period t4 and add one cycle, usually with (a)
To (d). The vacuum regeneration is also described in claim (16) in the Japanese Patent Application Laid-Open No. 55-5789. However, when a vacuum pump is installed between the exhaust gas conduits as shown in FIG. 2, high-pressure exhaust gas that does not need to be exhausted by the vacuum pump must be exhausted through the pump. Therefore, in order to increase the effect of the vacuum regeneration, it is necessary to take an excessively long inlet end gas discharge period t3 or to provide a vacuum pump having an excessive exhaust capacity, and the actual effect is doubtful.
In the apparatus of the present invention, separate gas discharge paths are provided for each of the steps (c) and (d). For the step (c), the exhaust gas conduit is opened to the atmosphere with the shortest length, and the high pressure gas near the inlet end remaining immediately after the step (b) is exhausted in the shortest time. So that Thereafter, when the pressure of the exhaust gas near the inlet end decreases to near the atmospheric pressure, and the exhaust speed by itself decreases, the process immediately proceeds to the step (d). In the step (d), the gas pressure in the adsorption column is reduced by forced evacuation by the vacuum pump, and the purge flow in the reverse flow is strengthened to promote the regeneration of the adsorbent. An exhaust gas surge tank is provided upstream of the vacuum pump in the gas discharge path used in the step (d), and the exhaust gas that has flown out of the capacity of the vacuum pump during the step (d) is temporarily stored. And steps (a) to
It is desirable to be discharged during (c). As described above, by providing two gas exhaust passages optimized for each of the steps (c) and (d), it is possible to improve the effect of the vacuum regeneration with the vacuum pump having a relatively small exhausting capacity, And (d) are combined to shorten the exhaust gas discharge step period and improve adsorbent productivity.

Further, a shut-off valve is provided at a position as close as possible to the outlet end of the adsorption cylinder in the product gas take-out path, and the pressure in the adsorption cylinder near the end of the exit becomes lower than the pressure in the gas take-out path in the vacuum regeneration period. At this time, the connection between the adsorption cylinder and the gas extraction path is disconnected. As a result, it is possible to prevent the product gas from being lost as the purge gas and to reduce the recovery rate of the component that is hardly adsorbed, and to regenerate all the adsorbents in the adsorption column in vacuum.

[0010]

FIG. 1 is a schematic diagram showing an embodiment of the present invention. 30 is an adsorption cylinder filled with an adsorbent, 3
4 and 35 are the inlet end and outlet end of the adsorption column, respectively. A source gas conduit 31 for guiding the source gas is provided with a compressor 32 for pressurizing the source gas, a source gas surge tank 32a for temporarily storing the source gas, and a gas supply valve 33 for opening and closing the introduction of the source gas. Constitutes a gas supply path. A product gas conduit 36 for guiding the product gas has a product gas flow control valve 37 for adjusting the flow rate of the product gas, a product gas surge tank 38 for temporarily storing the product gas, the adsorption column 30 and the product gas. Surge tank 3
A shut-off valve 54 for opening and closing the connection of the valves 8 is provided. The first exhaust gas conduit 40 that guides the exhaust gas is provided with a first gas exhaust valve 39 that opens and closes the exhaust of a high-pressure exhaust gas that flows out at its own pressure due to a pressure difference from the atmospheric pressure. These together constitute a first gas discharge path. A second exhaust gas conduit 53 for leading the exhaust gas has a second gas exhaust valve 50 for opening and closing the forced exhaust of the low-pressure exhaust gas, an exhaust gas surge tank 51 for temporarily storing the exhaust gas, and an exhaust gas. A vacuum pump 52 for forcibly exhausting the gas is provided, and these constitute a second gas exhaust passage as a whole. The gas supply valve 33, the first gas discharge valve 39, the second gas discharge valve 50, and the shutoff valve 54 are electromagnetic valves whose opening and closing can be electrically controlled. The control device 60 is connected to these solenoid valves, and is configured to open and close these solenoid valves at a predetermined timing. These valves may be mechanical valves driven by a common camshaft, in which case the control device 60 becomes unnecessary. When the use conditions such as the temperature and the supply gas pressure fluctuate greatly, it is desirable to attach a pressure sensor to the side wall of the adsorption cylinder 30 near the outlet end 35 and control the opening and closing of the closing valve 54 while detecting the output. . The shut-off valve 54 can be a check valve (a check valve), in which case no control is required for this valve. The particle size of the adsorbent filled in the adsorption column 30 is 20 mesh or less, preferably 40 mesh or less, which is considerably smaller than the particle size in the PSA method.

One cycle of the rapid pressure swing adsorption method in the present invention comprises at least the following steps (a), (c) and (d), and usually includes four steps including the step (b). Be composed. (A) Source gas introduction period t1 With the first gas discharge valve 39 and the second gas discharge valve 50 closed, the gas supply valve 33 is opened for a short time, and the high pressure source gas is pulsed from the inlet end 34 to the adsorption column 30. Introduction. The introduced source gas moves in the direction of the outlet end 35 and forms a forward flow. Of the components in the source gas, the components that are easily adsorbed are selectively adsorbed by the adsorbent, whereas the components that are not easily adsorbed are more quickly swept toward the outlet end 35. For this reason, as the gas passes between the adsorbent particles, the concentration of the easily adsorbed component decreases, the concentration of the hardly adsorbed component increases, and the product gas is gradually produced. Product gas is supplied to the outlet end 3
5, shut-off valve 54, product gas surge tank 3
8. It is taken out through the product gas flow control valve 37. The pressure of the product gas fluctuates slightly during one cycle,
Much lower than the source gas pressure. In normal production of oxygen-enriched air, the pressure is adjusted by the product gas flow control valve 37 to a pressure slightly higher than the atmospheric pressure. If the pressure of the source gas is the same, the amount of the source gas that can be processed by the apparatus in one cycle is determined by the length of the source gas introduction period. (B) Inlet end flow stop period t2 The first gas discharge valve 39, the second gas discharge valve 50, and the gas supply valve 33 are all closed. The flow of the raw material gas into the inlet end 34 is stopped, but in the adsorption column 30, the gas flows from the inlet end 34 to the outlet end 35, and the product gas flows from the outlet end 35, as in the raw gas introduction period. Outflow continues. The inlet end flow cessation phase is not essential. An appropriate length of the inlet end flow stop period provides time for the feed gas to penetrate deeper into the adsorption column 30 to improve the recovery of less adsorbed components in the product gas. On the other hand, because the time required for one cycle is increased by this amount, an excessively long inlet terminal flow stop period reduces adsorbent productivity. (C) Reverse gas discharge period t3 The first gas discharge valve 39 is opened while the gas supply valve 33 and the second gas discharge valve 50 are closed. The high-pressure gas near the inlet end 34 begins to flow out to the atmosphere through the first gas discharge valve 39, and a reverse flow is formed in the adsorption column 30 flowing toward the inlet end 34. The origin of the reverse flow is initially at the inlet end 34, but gradually moves toward the outlet end 35 as gas evacuation proceeds. Immediately after the start of step (c),
High pressure gas near the inlet end 34 is rapidly discharged. When the pressure of the gas to be discharged near the inlet end 34 decreases to near the atmospheric pressure and the discharge speed by itself decreases, the process immediately proceeds to the step (d). (D) Vacuum regeneration period t4 With the gas supply valve 33 closed, the first gas discharge valve 39 is closed, the second gas discharge valve 50 is opened, and the pressure at the inlet end 34 is set close to the pressure in the discharge gas surge tank 51. To lower. Due to the forced evacuation by the vacuum pump 52, the adsorption cylinder 3
The gas pressure in 0 is rapidly reduced, and the backward flow in the adsorption cylinder 30 is promoted. Until the starting point of the reverse flow reaches the outlet end 35, two flows in the forward direction and the reverse direction exist in the adsorption column 30, and the outflow of the product gas from the outlet end 35 continues. When the starting point of the reverse flow reaches the outlet end 35, the flow in the adsorption column 30 becomes only the purge flow of the reverse flow, and the product gas surge tank 38
Starts flowing back to the adsorption column 30. Shortly thereafter, the gas pressure in the entire area of the adsorption cylinder 30 including the vicinity of the outlet end 35 decreases to the atmospheric pressure or less. When the shut-off valve 54 is an electromagnetic valve, the controller 6 may be controlled at an appropriate time before or after the time when the product gas starts to flow back to the adsorption column.
The shut-off valve 54 is closed by a command from 0, and the connection between the adsorption cylinder 30 and the product gas surge tank 38 is cut off. As a result, it is possible to prevent the product gas from being lost as the purge gas and to reduce the recovery rate of the component that is hardly adsorbed, and to regenerate all the adsorbents in the adsorption column in vacuum. The timing of closing the shut-off valve 54 may be predetermined, but in order to appropriately cope with fluctuations in operating conditions such as temperature and supply gas pressure, a pressure sensor is provided on the side wall of the adsorption cylinder 30 near the outlet end 35. It is desirable to control the opening and closing of the closing valve 54 while mounting and detecting the output.
When the closing valve 54 is a check valve (check valve), the valve automatically closes when the backflow from the product gas surge tank 38 starts, so that control of the closing valve 54 is unnecessary. During the total discharge period including (c) and (d), the total pressure is reduced and purging with the product gas is performed.
The partial pressure of the easily adsorbed component in the adsorption column 30 is reduced, the easily adsorbed component is desorbed from the adsorbent, and the adsorbent is regenerated. The gas containing a high concentration of the desorbed easily adsorbed components forms a reverse flow, and the gas flows into the inlet end 34.
Is discharged from.

[0012] Up to this point, the gas flowing out from the outlet end has been assumed to be mainly composed of a zeolite that selectively adsorbs nitrogen rather than oxygen as an adsorbent and oxygen-enriched air as a product gas. Gas and gas exhausted from the inlet end have been referred to as exhaust gas. However, "product gas",
The name "exhaust gas" is for convenience of explanation, and the product gas is always collected as product gas, and the exhaust gas is always discarded as unnecessary. That doesn't mean that
I want you to be careful. For example, in the case of separating and recovering carbon dioxide from flue gas using activated carbon as an adsorbent,
The product gas containing a large amount of oxygen and nitrogen which is hardly adsorbed and flowing out of the outlet end is discarded, and the exhaust gas containing a large amount of carbon dioxide which is easily adsorbed and discharged from the inlet end is collected as a product gas. In some cases, both the gas flowing out of the inlet terminal and the gas flowing out of the outlet terminal may be collected and used as product gas.

[0013]

EXAMPLE An experiment for concentrating oxygen in the air was performed using the gas separation apparatus based on the rapid pressure swing adsorption method shown in FIG. Room temperature was approximately 15 ° C. As the raw material air, dry air (oxygen: 21 vo
(1%, nitrogen: 79 vol%) was adjusted to 0.14 MPa by a pressure regulator, and the compressor 32 was omitted in the experiment. The pressure of the raw material air in the raw material gas surge tank 32a ranges from 0.14MPa to 0.1% during the raw gas introduction period t1.
It fluctuates between 09MPa, but is on average about 0.10MPa. The inside diameter of the adsorption cylinder 30 was 50 mm, and the inside of the adsorption cylinder 30 was filled with a fine synthetic zeolite having a particle size of 60 to 80 mesh and a molecular sieve 5A. In the experiment,
The influence of the length of the source gas introduction period t1 and the vacuum regeneration period t4;
The change when the length of the adsorption cylinder was changed to 400 mm, 300 mm, and 200 mm was examined. The results of the experiment are shown in Table 1 and FIG. Table 1 shows the cycle time, the flow rate (L / min) of the extracted oxygen-enriched air, and the oxygen concentration (vol%) for each example. Generally, as the flow rate of the oxygen-enriched air taken out increases, the oxygen concentration in the oxygen-enriched air decreases. As an index that allows comparison of the separation performance of experiments in which the flow rate of oxygen-enriched air is variously different, the following equation is obtained: oxygen flow rate (L / min) = ((oxygen-enriched oxygen concentration-21) / 100) * (oxygen-rich (L / min) (1) The obtained oxygen flow rate was defined by (1), and the values are also shown in Table 1. The first term of the equation (1) is an increase in the volume fraction of oxygen when the oxygen-enriched air is compared with the raw air. Therefore, the acquired oxygen flow rate obtained by the equation (1) is the total oxygen amount (L / L) in the oxygen-enriched air extracted during the unit time (1 minute).
min) minus the amount of oxygen (L / min) originally contained in the raw material air of the same volume as the oxygen-enriched air. Amount per unit time (1 minute) (L / min)
(Here, the amount of gas is changed to room temperature, 0.1 MPa
Under the volume (L). In Table 1 and FIG. 3, in order to show the effect of the present invention, the same adsorption cylinder as used in Examples 01 to 08 was used, and a conventional R without vacuum regeneration was used.
Experimental results of oxygen concentration by the PSA method are shown as comparative examples.

[Table 1]

The results are summarized as follows. 1. Comparative Examples 1 and 2, Examples 07 to 09, Examples 14 and 1
5, the cycle times are the same as each other. The result is different because the opening of the product gas flow control valve was changed.If the opening of the valve was reduced and the flow rate of the oxygen-enriched air taken out was restricted, the oxygen concentration increased,
Acquired oxygen flow is reduced. Further, as can be seen by comparing Examples 11 to 19, the flow rate of the oxygen-enriched air taken out also decreases by increasing the vacuum regeneration period t4,
The oxygen concentration of the oxygen-enriched air increases, but the acquired oxygen flow decreases. These facts can be explained as follows. RP
In oxygen enrichment by the SA method, a product gas in which oxygen is enriched in an adsorption column flows out as a pulsed gas flow having a certain size of space and time in each cycle. It is considered that the oxygen concentration in the pulse flow of the product gas is not uniform, and the gas flowing out earlier has a higher oxygen concentration, and the gas flowing out later has a lower oxygen concentration. For this reason, the narrower the degree of opening of the product gas flow control valve, the more the gas to be taken out is limited to the gas that flows out earlier, the higher the oxygen concentration in the oxygen-enriched air taken out, but at the same time, Since part of the product gas having a higher oxygen concentration than the source gas is not recovered, the obtained oxygen flow rate is reduced. It is considered that the effect of increasing the vacuum regeneration period t4 is partially similar to the flow restriction by the valve operation. In other words, if the vacuum regeneration period t4 is lengthened, regeneration of the adsorbent proceeds, and the amount of gas adsorbed and collected in the next cycle increases. Therefore, the amount of gas flowing out as product gas is reduced by opening the valve. As in the case of
As a result, only a product gas having a high oxygen concentration corresponding to the initial effluent of the pulsed gas stream is extracted, and the oxygen concentration of the oxygen-enriched air increases, but the obtained oxygen flow rate decreases. It is thought that. Assuming that the above concept is correct, the oxygen concentration of 75 vol% in Example 19 having the lowest flow rate of the oxygen-enriched air among Examples 11 to 19 is the earliest outflow of the pulsed product gas flow. It is considered to be representative of the oxygen concentration of the coming gas. The flow rate of 1.35 L / min in Example 19 is 8.25 L / min in Example 11.
16%. On the other hand, the vacuum regeneration period t4 is shortened,
The larger the flow rate of oxygen-enriched air taken out, the more
This means that the gas flowing out later in the pulse flow is extracted. When comparing Example 11 with 14,
In Example 11, although the flow rate increased by 3.5 L / min, the increase in the acquired oxygen flow rate was extremely small at 0.06 L / min. In other words, the oxygen concentration in the 3.5 L / min gas was not much different from the oxygen concentration in the raw air. 3.5 L / min corresponds to 42% of the flow rate in Example 11. Integrating these inferences and recognizing that it is somewhat violent consideration, and estimating the distribution of oxygen concentration in the pulse flow of the product gas flowing out in each cycle in Example 11, The initial effluent, which accounts for about 16% of the total volume, is highly enriched oxygen-enriched air with an oxygen concentration of around 75vol%, and the oxygen concentration of the intermediate effluent, which accounts for about 42% of the total volume, is around 75vol%. 21vol%
The last effluent, which dropped sharply to about 42% of the total volume, can be said to be a gas with an oxygen concentration of just over 21 vol%, which is not much different from the feed air. From the discussion using FIG. 3 described below, in the oxygen enrichment by the RPSA method, the higher the separation performance of the adsorption column, the higher the oxygen concentration in the initial effluent, and the greater the contribution of the initial effluent to the obtained oxygen flow rate. On the other hand, the contribution of the intermediate effluent to the acquired oxygen flow rate is reduced, and the product gas pulse flow is bipolarized into an initial effluent with a high oxygen concentration and a late effluent with an oxygen concentration that is not much different from the feed air. Can be estimated to approach. 2. FIG. 3 shows the oxygen concentration of the oxygen-enriched air with respect to the reciprocal of the flow rate. Equation (1) is: oxygen-enriched air oxygen concentration (vol%)-21 (vol%) = (100 * (acquired oxygen flow rate (L / min))) * (1 / (oxygen-enriched air flow rate (L / min) ))) ... (2) Since the obtained oxygen flow rate is constant, the points representing the respective examples are arranged on one straight line starting from the point (0, 21) on the vertical axis. Should be. Referring to FIG. 3, in the region of high flow rate and low oxygen concentration, all the examples are arranged on the same straight line indicated by the dotted line, and the influence of the length of the adsorption cylinder is not seen. However, when moving to a region with a high oxygen concentration with a reduced flow rate,
Reflecting the decrease in the obtained oxygen flow rate, in any of the examples, the shift from the dotted line to the lower right direction, and the shorter the length of the adsorption column, the earlier the shift from the dotted line appears, and the degree of the shift is large. I understand. The fact is that the length of the adsorption cylinder is short,
The lower the separation performance, the more insufficient the bipolar differentiation of the oxygen concentration in the product gas pulse stream described above, and the greater the contribution of the intermediate effluent to the obtained oxygen flow rate. It can be explained that it appears quickly and large. The point representing the comparative example is greatly shifted to the lower right as compared with the example, indicating that the separation performance of the comparative example is remarkably inferior and the effect of vacuum regeneration in the example is large. 3. Comparing Examples 21 to 23, it can be seen that when the source gas introduction period t1 is increased, the obtained oxygen flow rate is slightly improved, but the effect is small. When the source gas introduction period is lengthened, the amount of the source gas that can be processed in one cycle can be increased. On the other hand, in order to maintain the required oxygen concentration despite the increase in the source gas, the vacuum regeneration period t4 also needs to be long, and the total cycle time increases with the increase in t1 and t4, and Cycle number is reduced. Since the former positive effect is partially offset by the latter negative effect, it is considered that an increase in the feed gas introduction period is not as effective in improving the obtained oxygen flow rate as expected.

According to the present invention, the gas discharge path of the gas separation apparatus to which the rapid pressure swing adsorption method is applied is the first gas discharge for discharging the gas to be discharged, which flows out at its own pressure due to the pressure difference from the atmospheric pressure. And a second gas exhaust path, which is provided so as to be switchable with the first gas exhaust path, is provided with a vacuum pump, and forcibly exhausts the exhaust gas by the vacuum pump, so that the vacuum pump has a relatively small exhaust capacity. Thus, the period of the regeneration step can be shortened and the adsorbent productivity can be improved while enhancing the effect of vacuum regeneration.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of a gas separation device of the present invention to which a rapid pressure swing adsorption method is applied.

FIG. 2 is a schematic diagram showing one embodiment of a conventional gas separation device to which a rapid pressure swing adsorption method is applied.

FIG. 3 is a graph showing a relationship between an oxygen-enriched air flow rate and an oxygen concentration in an experiment of an example.

[Explanation of symbols]

 Reference Signs List 30 adsorption cylinder 31 raw material gas conduit 32 compressor 32a raw material gas surge tank 33 gas supply valve 34 inlet terminal 35 outlet terminal 36 product gas conduit 37 product gas flow control valve 38 product gas surge tank 39 first gas discharge valve 40 One exhausted gas conduit 50 Second gas exhaust valve 51 Exhausted gas surge tank 52 Vacuum pump 53 Second exhausted gas conduit 54 Shut-off valve 60 Controller

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[Procedure amendment]

[Submission date] May 10, 2001 (2001.5.1
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

The results are summarized as follows. 1. Comparative Examples 1 and 2, Examples 06 to 08, Examples 14 and 1
5, the cycle times are the same as each other. The result is different because the opening of the product gas flow control valve was changed.If the opening of the valve was reduced and the flow rate of the oxygen-enriched air taken out was restricted, the oxygen concentration increased,
Acquired oxygen flow is reduced. Further, as can be seen by comparing Examples 11 to 19, the flow rate of the oxygen-enriched air taken out also decreases by increasing the vacuum regeneration period t4,
The oxygen concentration of the oxygen-enriched air increases, but the acquired oxygen flow decreases. These facts can be explained as follows. RP
In oxygen enrichment by the SA method, a product gas in which oxygen is enriched in an adsorption column flows out as a pulsed gas flow having a certain size of space and time in each cycle. It is considered that the oxygen concentration in the pulse flow of the product gas is not uniform, and the gas flowing out earlier has a higher oxygen concentration, and the gas flowing out later has a lower oxygen concentration. For this reason, the narrower the degree of opening of the product gas flow control valve, the more the gas to be taken out is limited to the gas that flows out earlier, the higher the oxygen concentration in the oxygen-enriched air taken out, but at the same time, Since part of the product gas having a higher oxygen concentration than the source gas is not recovered, the obtained oxygen flow rate is reduced. It is considered that the effect of increasing the vacuum regeneration period t4 is partially similar to the flow restriction by the valve operation. In other words, if the vacuum regeneration period t4 is lengthened, regeneration of the adsorbent proceeds, and the amount of gas adsorbed and collected in the next cycle increases. Therefore, the amount of gas flowing out as product gas is reduced by opening the valve. As in the case of
As a result, only a product gas having a high oxygen concentration corresponding to the initial effluent of the pulsed gas stream is extracted, and the oxygen concentration of the oxygen-enriched air increases, but the obtained oxygen flow rate decreases. It is thought that. Assuming that the above concept is correct, the oxygen concentration of 75 vol% in Example 19 having the lowest flow rate of the oxygen-enriched air among Examples 11 to 19 is the earliest outflow of the pulsed product gas flow. It is considered to be representative of the oxygen concentration of the coming gas. The flow rate of 1.35 L / min in Example 19 is 8.25 L / min in Example 11.
16%. On the other hand, the vacuum regeneration period t4 is shortened,
The larger the flow rate of oxygen-enriched air taken out, the more
This means that the gas flowing out later in the pulse flow is extracted. When comparing Example 11 with 14,
In Example 11, although the flow rate increased by 3.5 L / min, the increase in the acquired oxygen flow rate was extremely small at 0.06 L / min. In other words, the oxygen concentration in the 3.5 L / min gas was not much different from the oxygen concentration in the raw air. 3.5 L / min corresponds to 42% of the flow rate in Example 11. Integrating these inferences and recognizing that it is somewhat violent consideration, and estimating the distribution of oxygen concentration in the pulse flow of the product gas flowing out in each cycle in Example 11, The initial effluent, which accounts for about 16% of the total volume, is highly enriched oxygen-enriched air with an oxygen concentration of around 75vol%, and the oxygen concentration of the intermediate effluent, which accounts for about 42% of the total volume, is around 75vol%. 21vol%
The last effluent, which dropped sharply to about 42% of the total volume, can be said to be a gas with an oxygen concentration of just over 21 vol%, which is not much different from the feed air. From the discussion using FIG. 3 described below, in the oxygen enrichment by the RPSA method, the higher the separation performance of the adsorption column, the higher the oxygen concentration in the initial effluent, and the greater the contribution of the initial effluent to the obtained oxygen flow rate. On the other hand, the contribution of the intermediate effluent to the acquired oxygen flow rate is reduced, and the product gas pulse flow is bipolarized into an initial effluent with a high oxygen concentration and a late effluent with an oxygen concentration that is not much different from the feed air. Can be estimated to approach. 2. FIG. 3 shows the oxygen concentration of the oxygen-enriched air with respect to the reciprocal of the flow rate. Equation (1) is: oxygen-enriched air oxygen concentration (vol%)-21 (vol%) = (100 * (acquired oxygen flow rate (L / min))) * (1 / (oxygen-enriched air flow rate (L / min) ))) ... (2) Since the obtained oxygen flow rate is constant, the points representing the respective examples are arranged on one straight line starting from the point (0, 21) on the vertical axis. Should be. Referring to FIG. 3, in the large flow rate and low oxygen concentration region, all the examples are arranged on the same straight line indicated by the dotted line, and the influence of the length of the adsorption cylinder is not seen. However, when moving to a region with a high oxygen concentration with a reduced flow rate,
Reflecting the decrease in the obtained oxygen flow rate, in any of the embodiments, the shift from the dotted line to the lower right direction, and the shift from the dotted line appears earlier and the degree of the shift is larger as the length of the adsorption cylinder is shorter. I understand. The fact is that the length of the adsorption cylinder is short,
The lower the separation performance, the more insufficient the bipolar differentiation of the oxygen concentration in the product gas pulse stream described above, and the greater the contribution of the intermediate effluent to the obtained oxygen flow rate. It can be explained that it appears quickly and large. The point representing the comparative example is greatly shifted to the lower right as compared with the example, indicating that the separation performance of the comparative example is remarkably inferior and the effect of vacuum regeneration in the example is large. 3. Comparing Examples 21 to 23, it can be seen that when the source gas introduction period t1 is increased, the obtained oxygen flow rate is slightly improved, but the effect is small. When the source gas introduction period is lengthened, the amount of the source gas that can be processed in one cycle can be increased. On the other hand, in order to maintain the required oxygen concentration despite the increase in the source gas, the vacuum regeneration period t4 also needs to be long, and the total cycle time increases with the increase in t1 and t4, and Cycle number decreases. Since the former positive effect is partially offset by the latter negative effect, it is considered that an increase in the feed gas introduction period is not as effective in improving the obtained oxygen flow rate as expected.

According to the present invention, the gas discharge path of the gas separation apparatus to which the rapid pressure swing adsorption method is applied is the first gas discharge for discharging the gas to be discharged, which flows out at its own pressure due to the pressure difference from the atmospheric pressure. And a second gas exhaust path, which is provided so as to be switchable with the first gas exhaust path, is provided with a vacuum pump, and forcibly exhausts the exhaust gas by the vacuum pump, so that the vacuum pump has a relatively small exhaust capacity. Thus, the period of the regeneration step can be shortened and the adsorbent productivity can be improved while enhancing the effect of vacuum regeneration.

Claims (3)

[Claims] 1. A gas separation apparatus to which a rapid pressure swing adsorption method is applied, comprising: an adsorption cylinder having an adsorbent therein; a gas supply path for leading a raw material gas to an inlet end of the adsorption cylinder; A gas take-out path for taking out a product gas resulting from selectively adsorbing and removing a component which is easily adsorbed by the adsorbent from an outlet end of the adsorption cylinder; and, after taking out the product gas from the raw material gas, the adsorption cylinder A gas discharge path for discharging the gas to be discharged remaining inside from the inlet end, wherein the gas discharge path flows out at its own pressure due to a pressure difference from the atmospheric pressure, and discharges the gas to be discharged. A first gas discharge path, and a second gas discharge path that is provided so as to be switchable with the first gas discharge path, is provided with a vacuum pump, and forcibly exhausts the gas to be discharged by the vacuum pump. A gas separation device. 2. The gas separation device according to claim 1, further comprising a shut-off valve provided in the gas take-out path and capable of preventing the product gas from flowing back into the adsorption column. 3. A gas separation method according to a rapid pressure swing adsorption method, wherein one cycle comprises a step of pulsing a high-pressure raw material gas into the adsorption column at least from an inlet end of the adsorption column having an adsorbent therein. Introducing the source gas to be introduced, and removing the exhaust gas rich in the easily adsorbed component remaining after extracting the product gas rich in the component which is hardly adsorbed by the selective adsorption action of the adsorbent from the source gas. An exhausted gas exhausting step of exhausting the exhausted gas from a cylinder, wherein the exhausted gas exhausting step comprises: A reverse gas discharge step of reducing the pressure to near atmospheric pressure, and a second gas discharge path provided at the inlet end so as to be switchable with the first gas discharge path. Te, gas separation method, wherein the the more the vacuum regeneration step of forcibly exhausted by the exhaust gas of a vacuum pump.