KR20070053728A - Double separation method and double separation system for oxygen gas and nitrogen gas - Google Patents

Abstract

The present invention provides a method and system for separating and obtaining high purity oxygen gas from air or the like by means of a PSA gas separation device, and continuously and efficiently separating high purity nitrogen gas from a desorption gas continuously supplied from the PAS gas separation device. The purpose is to provide. The present invention includes a PSA gas separation process in the PSA gas separation device 1 and a membrane gas separation process in the membrane gas separator 2. In the PSA gas separation process, oxygen enrichment gas and nitrogen are mainly contained from oxygen-nitrogen-containing gas such as air by means of a pressure swing adsorption gas separation method using an adsorption tower filled with an adsorbent that preferentially adsorbs nitrogen. A desorption gas that also contains oxygen is taken. In the membrane gas separation process, the desorbed gas is not permeated with the gas that passes through the gas separation membrane 2A by the gas separation membrane 2A while reducing the permeation side of the gas separation membrane 2A that preferentially permeates oxygen to a pressure below atmospheric pressure. Do not separate into gas (nitrogen enriched gas).

Gas Separator, Oxygen Gas, Nitrogen Gas

Description

DOUBLE SEPARATION METHOD AND DOUBLE SEPARATION SYSTEM FOR OXYGEN GAS AND NITROGEN GAS}

The present invention relates to a method and system for parallel separation of oxygen gas and nitrogen gas from a mixed gas (eg air) comprising oxygen and nitrogen.

Oxygen and nitrogen gases, which can be obtained separately from air, have been used for various purposes. Oxygen gas has been used, for example, in waste melting furnaces, remelting furnaces, glass melting furnaces, for improving the combustion efficiency of steelmaking electric furnaces, oxidation reactions in chemical plants, oxygen aeration in wastewater treatment systems, and the like. On the other hand, nitrogen gas has been used, for example, in gas seals and purging in waste melting furnaces and chemical plants, atmosphere gas adjustment in heat treatment furnaces, gas seals for food packaging, and the like.

As one of practical methods for separating oxygen gas and nitrogen gas from air, a pressure swing adsorption method (PSA method) is known. In gas separation by the PAS method, a PAS gas separation device having an adsorption tower filled with an adsorbent for preferentially adsorbing a predetermined component can be used, and at least the adsorption step and the desorption step are performed in the adsorption tower. In the adsorption step, a mixed gas is introduced into the adsorption tower, and the reverse adsorption component in the mixed gas is adsorbed to the adsorbent under high pressure conditions, and a gas composed of a poor adsorption component is extracted from the adsorption tower. In the desorption step, the pressure in the column is lowered to desorb the reverse adsorption component from the adsorbent, and a gas mainly containing the reverse adsorption component is derived from the adsorption tower. For example, when an adsorbent capable of adsorbing nitrogen preferentially over oxygen is used and air is introduced into the adsorption tower as a mixed gas, oxygen is drawn out of the tower as a poor adsorption component in the adsorption process, and nitrogen is adsorbed as a reverse adsorption component. It is adsorbed by the adsorbent at and is taken out of the tower in the desorption process.

In the PSA method, the non-adsorption component gas that passes through the adsorption column in the adsorption step is more stable with respect to the gas concentration or the gas amount than the reverse adsorption component gas that is depressurized and desorbed in the desorption step and exits the column. Therefore, in the PSA method, it is easier to obtain the target gas more efficiently than the gas of the objective to be obtained as the poor adsorption component gas rather than the reverse adsorption component gas. Therefore, in the case of separating and acquiring oxygen from air by the PAS method, a nitrogen adsorption adsorbent is filled in an adsorption tower of a commonly used gas gas separation device, and the oxygen enriched gas from the adsorption tower is recovered as a product gas in the adsorption step. . When nitrogen is separated from the air by the PAS method, the oxygen adsorption adsorbent is generally filled in the adsorption tower, and the nitrogen enrichment gas derived from the adsorption tower in the adsorption step is recovered as the product gas.

However, there is a case where it is necessary to separate and acquire oxygen in the air, and to separate and acquire nitrogen in the air. In this case, a technology capable of separating and acquiring oxygen and nitrogen contained in the air in parallel in a single system is required. do.

Fig. 8 shows an oxygen / nitrogen parallel separation system X5 which is an example of a conventional system for separating oxygen and nitrogen in air in parallel. The oxygen / nitrogen parallel separation system X5 includes a PAS gas separator 81, a membrane gas separator 82, a storage tank 83, compressors 84, 85 and a vacuum pump 86. Connected via A plurality of automatic valves (not shown) are provided at a predetermined place in the piping, and when the system is in operation, the opening and closing states of the respective automatic valves are appropriately selected so that the flow of gas in the system can be changed. The PAS gas separator 81 includes an adsorption tower (not shown) filled with an adsorbent that preferentially adsorbs nitrogen over oxygen. The membrane gas separator 82 also has a gas separation membrane 82a for preferentially permeating oxygen. Such an oxygen-nitrogen parallel separation system is described, for example in following patent document 1.

[Patent Document 1] Japanese Patent Laid-Open No. 5-253438

At the time of operation of the oxygen-nitrogen parallel separation system X5, one cycle including an adsorption step and a desorption step is repeated in the adsorption tower of the PAS gas separation device 81, and oxygen-enriched gas is separated from the air. In the adsorption step, the compressor 84 operates to supply air to the adsorption tower of the PAS gas separation device 81, and adsorbs the reverse adsorption component (mainly containing nitrogen) in the air to the adsorbent while the tower is raised to a predetermined pressure. In this way, oxygen-enriched gas is derived from the adsorption tower or PAS gas separation device 81. This oxygen enrichment gas is used continuously for a predetermined use, for example. In the desorption process, the reverse adsorption component (mainly containing nitrogen) is desorbed from the adsorbent in the adsorption column in a state where the inside of the column is lowered to a predetermined pressure by the operation of the vacuum pump 86, and the oxygen is retained in the tower. The reverse adsorption component is discharged out of the tower or out of the PSA gas separation device 81 as the desorption gas. The oxygen concentration in the desorption gas is relatively high at the initial stage of the desorption process, and tends to gradually decrease with time.

The oxygen concentration of the desorption gas from the PAS gas separation device 81 is constantly detected by an oxygen monitor, and the desorption gas having a relatively high oxygen concentration at the beginning of the desorption process is discarded out of the system as indicated by arrow G '. Then, when the oxygen concentration of the desorption gas falls to a predetermined value, the waste is stopped and the process is switched to the recovery of the desorption gas to the storage tank 83 to start the recovery of the desorption gas. Such desorption of the desorption gas and subsequent recovery are executed each time the desorption gas is discharged from the PAS gas separation device 81.

The desorption gas recovered in the storage tank 83 is supplied to the membrane gas separator 82 at a predetermined pressure by the operation of the compressor 85 and passes through the gas separation membrane 82a of the membrane gas separator 82. It is separated into a non-permeable gas that does not permeate. Oxygen in the desorption gas preferentially passes through the gas separation membrane 82a, whereby the nitrogen enrichment gas whose oxygen concentration is lowered and the nitrogen purity is high is discharged from the membrane type gas separator 82 as a non-permeable gas. This non-permeable gas is used continuously for a predetermined use, for example. According to oxygen-nitrogen parallel separation system X5, an oxygen enrichment gas and a nitrogen enrichment gas are isolate | separated and acquired from air as mentioned above.

In the oxygen / nitrogen parallel separation system X5, for example, all of the desorption gas from the PSA gas separation device 81 is not recovered to the storage tank 83 once, but is continuously passed through the compressor 85 through the membrane gas separator 82. If it is supplied to, the amount of nitrogen enriched gas discharged from the membrane gas separator 82 as a non-permeable gas fluctuates relatively large over time. This is because the oxygen partial pressure to oxygen concentration of the desorption gas supplied to the membrane gas separator 82 fluctuates relatively largely, and the driving force of oxygen permeation in the gas separation membrane 82a fluctuates relatively largely. The variation in the driving force results in a variation in the oxygen permeation amount or the non-permeation amount of oxygen to the gas separation membrane 82a, and hence in the variation of the amount of non-permeable gas (nitrogen-enriched gas) discharged from the membrane type gas separator 82. . Therefore, in the oxygen / nitrogen parallel separation system X5, when all the desorption gas from the PAS gas separation device 81 is not recovered to the storage tank 83 but is continuously supplied to the membrane gas separator 82 as a non-permeable gas. The nitrogen enrichment gas obtained cannot be used suitably as an inert gas because its supply amount is unstable.

On the other hand, in the oxygen-nitrogen parallel separation system X5 which operates in the original aspect as mentioned above, the disposal and collection | recovery of the desorption gas from the PAS gas separation apparatus 81 are switched at predetermined timing, and the predetermined | prescribed oxygen concentration area | region ( That is, the desorption gas of the nitrogen concentration region) is once recovered to the storage tank 83, and the desorption gas of the substantially constant oxygen concentration (i.e., the substantially constant nitrogen purity) is supplied from the storage tank 83 to the membrane gas separator 82. And since the fluctuation of the oxygen partial pressure (or oxygen concentration) of the desorption gas supplied to the membrane gas separator 82 is small, the fluctuation of oxygen permeation amount to the gas separation membrane 82a is small, and the membrane gas separator 82 is substantially constant. At the flow rate, the non-permeable gas (nitrogen-enriched gas) is discharged.

However, the conversion line configuration and the storage tank 83 for separating the flow of the desorption gas from the PAS gas separator 81 to the membrane gas separator 82 discontinuously separate and acquire the nitrogen-enriched gas. This is undesirable because it leads to system complexity. In addition, such a conversion line configuration and storage tank 83 are undesirable because they lead to a larger system. In addition, the storage tank 83 requires a larger capacity and is larger in size as the period for separating the flow of the desorption gas from the PAS gas separator 81 to the membrane gas separator 82 is long. For example, the desorption gas discharged in the initial and middle desorption periods of 20 seconds from the beginning of the desorption process (the oxygen concentration is relatively high and the nitrogen purity is relatively high between the desorption processes for 30 seconds in the adsorption tower of the PSA gas separation device 81). Low) is discarded out of the system, and the desorption gas (the oxygen concentration is relatively low and the nitrogen purity is relatively high) is discharged to the storage tank 83 at the end of the desorption for 20 to 30 seconds from the start of the desorption process. In the case of storage, since desorption gas is not stored in the storage tank 83 for 20 seconds of the initial stage and the middle stage of desorption, in order to supply gas from the storage tank 83 to the membrane type gas separator 82 therebetween, the storage tank 83 In this case, it is necessary to store the desorption gas discharged in the desorption process up to that point in advance without sending it to the membrane gas separator 82. At this time, it is necessary to introduce the desorption gas into the storage tank 83 at a corresponding pressure by the operation of the vacuum pump 86, but since the discharge pressure of the vacuum pump 86 has a certain limit, the storage tank 83 In order to introduce the desorption gas appropriately, the storage tank 83 needs a sufficient capacity. As long as the above-mentioned splitting time is long, the amount of desorption gas to be stored in advance in the storage tank 83 increases, so that the capacity required for the storage tank 83 also increases and the storage tank 83 becomes larger. .

Disclosure of the Invention

The present invention has been devised under such circumstances, and the high purity nitrogen gas is continuously obtained from the desorption gas continuously supplied from the PAS gas separation device while the high purity oxygen gas is separated and obtained from the oxygen / nitrogen mixed gas by the PAS gas separation device. It is an object of the present invention to provide a method and a system which can be efficiently separated and acquired.

According to a first aspect of the present invention, a method for parallel separation of oxygen gas and nitrogen gas from a mixed gas comprising oxygen and nitrogen is provided. This parallel separation method includes a pressure swing adsorption gas separation process and a membrane gas separation process. In the pressure swing adsorption gas separation process, a mixed gas is introduced into the adsorption tower at a relatively high pressure in the adsorption tower by a pressure swing adsorption gas separation method using an adsorption tower packed with an adsorbent for preferentially adsorbing nitrogen, and nitrogen in the mixed gas. Is adsorbed to the adsorbent to derive an oxygen enriched gas from the adsorption column, and desorbs nitrogen from the adsorbent in a relatively low pressure in the adsorption tower, and desorbs the oxygen remaining in the adsorption tower and the oxygen-containing desorption gas containing the nitrogen to the adsorption tower. Derived from In the membrane-type gas separation process, the permeate side of the gas separation membrane for preferentially permeating oxygen to a pressure below atmospheric pressure, while the oxygen-containing desorption gas passes through the gas separation membrane and the non-permeable nitrogen enrichment gas does not permeate through the gas separation membrane. To separate.

Preferably, the parallel separation method further includes a compression process for compressing the oxygen-containing desorption gas before the oxygen-containing desorption gas is added to the membrane gas separation process. In this case, it is preferable to compress the oxygen-containing desorption gas to a pressure of 0.6 MPa or more in the compression step.

Preferably, the decompression in the adsorption tower when derivatizing the oxygen-containing desorption gas from the adsorption tower in the pressure swing adsorption gas separation process and the decompression on the permeate side in the membrane gas separation process are realized by a single decompression means. .

Preferably, in the membrane gas separation process, a portion of the oxygen-containing desorption gas is configured to be introduced into the permeate side of the gas separation membrane without passing through the gas separation membrane.

According to a second aspect of the present invention, a system for parallel separation of oxygen gas and nitrogen gas from a mixed gas comprising oxygen and nitrogen is provided. This parallel separation system comprises a pressure swing adsorption gas separator, a membrane gas separator and a decompression means. The pressure swing adsorption gas separation device has an adsorption tower filled with an adsorbent for preferentially adsorbing nitrogen, and the mixed gas is introduced into the adsorption tower in a relatively high pressure state by a pressure swing adsorption gas separation method using the adsorption tower. And adsorbing nitrogen in the mixed gas to the adsorbent, deriving oxygen enrichment gas from the adsorption column, and desorbing nitrogen from the adsorbent in a state of relatively low pressure in the adsorption tower, and containing oxygen and the nitrogen remaining in the adsorption tower. The oxygen-containing desorption gas is for deriving from the adsorption tower. The membrane type gas separator has a gas separation membrane for preferentially permeating oxygen, and is intended to separate and derive an oxygen-containing desorption gas into a permeate gas that passes through the gas separation membrane and a non-permeable nitrogen enrichment gas that does not permeate. The decompression means is for depressurizing the permeate side in the gas separation membrane of the membrane type gas separator to a pressure below atmospheric pressure. According to this parallel separation system, the method of the 1st aspect of this invention can be performed suitably.

Preferably, the parallel separation system further comprises a compression means for compressing the oxygen-containing desorption gas before the oxygen-containing desorption gas is supplied to the membrane gas separator.

Preferably, the decompression means also functions as a means for depressurizing the inside of the adsorption tower when derivatizing the oxygen-containing desorption gas from the adsorption tower of the pressure swing adsorption gas separation device.

Preferably, the parallel separation system further includes bypass means for bypassing a portion of the oxygen-containing desorption gas and introducing it to the permeate side of the gas separation membrane without passing through the gas separation membrane.

Best Mode for Carrying Out the Invention

1 shows an oxygen / nitrogen parallel separation system X1 according to a first embodiment of the present invention. The oxygen / nitrogen parallel separation system X1 is a pressure swing adsorption (PSA) gas separator 1, a membrane gas separator 2, a source gas supply device 3, a pump 4, 5 and a silencer. (6), a compressor (7), a gas-liquid separator (8), an oxygen concentration control mechanism (9) and a pipe connecting them, and oxygen enrichment gas and nitrogen enrichment from air (oxygen-nitrogen-containing source gas). The gas must be separated in parallel, and it is configured to carry out the oxygen-nitrogen parallel separation method including pressure swing adsorption gas separation process, compression process and membrane gas separation process.

The PSA gas separation device 1 mainly includes at least one adsorption tower (not shown) filled with an adsorbent for preferentially adsorbing nitrogen, and is oxygen-nitrogen-containing raw material by a pressure swing adsorption gas separation method performed using the adsorption tower. Oxygen-enriched gas can be taken from the gas (air in this embodiment). As the adsorbent to be filled in the adsorption column, a Li-X zeolite molecular sieve, a Ca-X zeolite molecular sieve, a Ca-A zeolite molecular sieve and the like can be used. A single adsorption column may be filled with one type of adsorbent or may be filled with a plurality of types of adsorbents.

In the pressure swing adsorption gas separation method performed in the PSA gas separation device 1, one cycle including an adsorption step, a desorption step, and a regeneration step is repeated for a single adsorption tower. The adsorption process introduces air into an adsorption tower in which the inside of the tower is at a predetermined high pressure, adsorbs nitrogen and other components (carbon dioxide, moisture, etc.) in the source gas to the adsorbent, and derives the oxygen enriched gas from the adsorption tower. It is a process for doing this. The desorption step is a step for desorbing nitrogen from the adsorbent by depressurizing the inside of the adsorption tower and discharging the nitrogen to the outside of the tower. The regeneration process needs to prepare an adsorption tower again in an adsorption process, for example, it is a process for restoring the adsorption performance of the adsorbent with respect to nitrogen by making a washing gas flow through the inside of a tower. As such PAS gas separation apparatus 1, a well-known PAS oxygen separation apparatus can be used.

The membrane gas separator 2 has an inlet 2a and outlets 2b, 2c and has a gas separation membrane 2A which preferentially permeates oxygen. A predetermined gas flow path (specifically, not shown) is provided inside the membrane gas separator 2, and the introduction port 2a and the discharge port 2b communicate with each other via a part of the gas flow path. Further, a gas separation membrane 2A is provided at a predetermined place in the gas flow path from the inlet port 2a to the outlet port 2c. The gas separation membrane 2A is a porous resin membrane made of, for example, polyimide, polysulfone, or the like. As such a porous resin film, UFIRECKSPT (made by U.S. Corporation) can be used.

The source gas supply device 3 is for supplying air, which is an oxygen-nitrogen-containing source gas, to the adsorption tower of the PAS gas separation device 1, for example, an air blower. The pump 4 is for sucking and depressurizing the inside of the adsorption tower of the PAS gas separation device 1, for example, a vacuum pump. In addition, the pump 5 is for suction-pressure reduction of the permeate side (gas flow path from the gas separation membrane 2A to the outlet port 2c) of the gas separation membrane 2A in the membrane type gas separator 2, for example. It is a vacuum pump.

The silencer 6 is for discharging the remainder of the gas from the pump 4 to the outside of the system while guiding a part of the gas from the pump 4 to the compressor 7, and discharges the gas from the pump 4 to the compressor 7. ) And a gas flow path for discharging the gas from the pump 4 to the outside of the system while noise is audible.

The compressor 7 is for compressing the gas via the silencer 6 and supplying it to the gas-liquid separator 8. In addition, the gas-liquid separator 8 has a discharge port 8a, and is for separating water contained in the gas sent from the compressor 7 into the gas. The outlet 8a is for discharging the water recovered in the gas-liquid separator 8 to the outside of the gas-liquid separator 8.

The oxygen concentration control mechanism 9 consists of an oxygen sensor 9a and an automatic valve 9b installed in a pipe L1 attached to the outlet 2b of the membrane gas separator 2, and inside the pipe L1. The oxygen concentration of the gas is adjusted by adjusting the flow rate of the gas (that is, the amount of gas that does not penetrate the gas separation membrane 2A of the membrane gas separator 2) according to the oxygen concentration of the gas flowing through the gas. Is to adjust. The oxygen sensor 9a is for detecting the oxygen concentration of the gas flowing through the inside of the pipe L1 at all times. In the oxygen concentration control mechanism 9, the opening degree of the automatic valve 9b is adjusted as desired according to the detection result of the oxygen sensor 9a.

When the oxygen-nitrogen parallel separation system X1 having the above structure is operated, air is supplied from the source gas supply device 3 to the PSA gas separation device 1 by the operation of the source gas supply device 3.

In the PAS gas separation device 1, air is added to the pressure swing adsorption gas separation process. Specifically, in the PAS gas separator 1, one cycle including an adsorption step, a desorption step, and a regeneration step is repeated for each adsorption tower by a pressure swing adsorption gas separation method.

In the adsorption step, air is introduced into the adsorption tower in which the inside of the tower is in a predetermined high pressure state. In the adsorption tower, nitrogen and other components (carbon dioxide, moisture, etc.) contained in the air are adsorbed and removed by the adsorbent, and high-purity oxygen gas (oxygen-enriched gas) is drawn out of the tower. This high-purity oxygen gas exits the oxygen / nitrogen parallel separation system X1 through a predetermined pipe.

In the desorption process, the adsorption tower is depressurized by the operation of the pump 4, nitrogen and other components are desorbed from the adsorbent, and the oxygen-containing desorption gas containing oxygen and the desorption components remaining inside the tower is separated from the tower or the PAS gas separator. (1) It is discharged to the outside. The graph which shows an example of the time change of the pressure in the oxygen-containing desorption gas discharged | emitted from the adsorption tower in a desorption process is shown in FIG. In the graph of FIG. 2, the horizontal axis represents the desorption time (elapsed time from the start of the desorption process) in the adsorption tower, and the vertical axis represents the desorption pressure (pressure of the oxygen-containing desorption gas). In the example of this pressure change, the pressure at the start of the desorption process is atmospheric pressure, the pressure at the time of 10 seconds is 0.0611 Mpa, and the pressure at the time of 30 seconds is 0.0332 Mpa. FIG. 2 also shows the oxygen concentration (volume ratio of oxygen) of the oxygen-containing desorption gas at the start of the desorption step, at the time of 10 seconds and at the time of 30 seconds.

In the regeneration process, for example, the cleaning gas is flowed into the tower, whereby the adsorption performance of the adsorbent to nitrogen is mainly restored. In the adsorption tower after the regeneration process, the above adsorption is performed again.

In the PAS gas separation device 1, as the above-described pressure swing adsorption gas separation step is performed, high purity oxygen gas is taken and oxygen-containing desorption gas is taken. The high purity oxygen gas is used continuously for a predetermined purpose or stored in a predetermined tank, for example. On the other hand, the oxygen-containing desorption gas discharged from the adsorption tower in the desorption step to the outside of the PAS gas separation device 1 is sent to the silencer 6 through a predetermined pipe and pump 4. Part of the oxygen-containing desorption gas passes through the silencer 6 to reach the compressor 7. The remainder of the oxygen-containing desorption gas is discharged out of the system in the silencer 6.

The oxygen-containing desorption gas passing through the silencer 6 is compressed in the compressor 7 (compression process) and supplied to the membrane gas separator 2 via the gas-liquid separator 8. Preferably, the oxygen-containing desorption gas is compressed by the compressor 7 to a pressure of 0.6 MPa or more. In the gas-liquid separator 8, water is separated from the oxygen-containing desorption gas. This water is discharged from the gas-liquid separator 8 to the outside via the discharge port 8a.

In the membrane gas separator 2, the oxygen-containing desorption gas is added to the membrane gas separation process. Specifically, the oxygen-containing desorption gas G1 introduced into the membrane gas separator 2 from the inlet 2a is formed by the gas separation membrane 2A provided in the gas flow path of the membrane gas separator 2. It is separated into permeate gas G2 that passes through 2A) and non-permeable gas G3 that does not permeate. The permeant gas G2 is an oxygen enriched gas having an increased oxygen concentration based on the permeation characteristics of the gas separation membrane 2A, and the non-permeable gas G3 is a high purity nitrogen gas having a high nitrogen concentration based on the permeation characteristics of the gas separation membrane 2A. (Nitrogen-enriched gas).

In the membrane gas separation process, the permeate side of the gas separation membrane 2A is reduced to a pressure below atmospheric pressure by the operation of the pump 5. The decompression pressure by the pump 5 is 0.02-0.05 Mpa, for example. Permeate gas G2 is led out of membrane-type gas separator 2 from outlet 2c and then discharged out of the system via pump 5.

In addition, in the membrane gas separation process, the amount of non-permeable gas is directly controlled by the operation of the oxygen concentration control mechanism 9, and the oxygen concentration of the non-permeable gas G3 is kept constant. The oxygen sensor 9a of the oxygen concentration control mechanism 9 constantly detects the oxygen concentration with respect to the non-permeable gas G3 which is led out of the membrane gas separator 2 from the outlet port 2b and passes through the pipe L1. do. When the detected concentration exceeds the desired value, the opening degree of the automatic valve 9b becomes small, and the flow rate of the non-permeable gas G3 passing through the pipe L1, and further, the membrane type in the membrane type gas separator 2 The amount of non-permeable gas (G3) generated in the gas separation process (the amount generated per unit time) is reduced. On the other hand, when the detection concentration is lower than the desired value, the opening degree of the automatic valve 9b becomes large, and the flow rate of the non-permeable gas G3 passing through the pipe L1, and further, the membrane type gas separation process in the membrane type gas separator 2 The amount of non-permeable gas (G3) occurring at is increased. Since the purity and oxygen concentration of the non-permeable gas G3 in the membrane type gas separation process may vary depending on the amount of the non-permeable gas G3 generated, the non-permeable gas G3 is controlled by adjusting the flow rate of the non-permeable gas G3. Control the oxygen concentration.

In the membrane gas separator 2, as the membrane gas separation process as described above is performed, high purity nitrogen gas is taken while oxygen concentration control is performed. This high purity nitrogen gas is continuously used for a predetermined use or stored in a predetermined tank, for example.

According to oxygen-nitrogen parallel separation system X1, high purity oxygen gas and high purity nitrogen gas can be separated and separated from air as mentioned above.

In the oxygen / nitrogen parallel separation method by the oxygen / nitrogen parallel separation system X1, a pressure swing adsorption gas separation process is performed. The oxygen partial pressure (oxygen concentration represented by the amount of material per volume) of the oxygen-containing desorbed gas G1 discharged from the adsorption tower of the PSA gas separator 1 and added to the membrane gas separation process in the membrane gas separator 2, The oxygen-containing desorption gas G1 has a permeate side of the gas separation membrane 2A below atmospheric pressure with respect to the oxygen partial pressure (oxygen concentration represented by the amount of material per volume) of the permeate gas G2 separated by the gas separation membrane 2A. A sufficient difference can be made by depressurizing to desired pressure of. The compression process in the compressor 7 also contributes to a sufficient difference between the oxygen partial pressure of the oxygen-containing desorption gas G1 from the adsorption tower and the oxygen partial pressure of the permeate gas G2 separated by the gas separation membrane 2A. Doing. Even when the oxygen partial pressure (to oxygen concentration) of the oxygen-containing desorption gas G1 is varied, a sufficient difference is obtained for both oxygen partial pressures, thereby ensuring sufficient driving force for oxygen permeation in the gas separation membrane 2A. At the same time, the rate of change of the driving force can be suppressed, and therefore, a sufficient amount of oxygen permeation to the gas separation membrane 2A can be obtained and at the same time a change in the amount of permeation can be suppressed. As the oxygen permeation amount in the gas separation membrane 2A is large, the nitrogen permeation amount in the gas separation membrane 2A tends to be small, and therefore, the non-permeable gas (high purity nitrogen) in the membrane gas separation process in the membrane gas separator 2 is high. The amount of generation of the gas (G3) tends to be large. On the other hand, since the rate of change of the oxygen permeation amount in the gas separation membrane 2A is small, the rate of change in the amount of generation of the non-permeable gas (high purity nitrogen gas) G3 in the membrane gas separation process tends to be small.

As described above, according to the oxygen-nitrogen-nitrogen parallel separation method by the oxygen-nitrogen parallel separation system X1 according to the present invention, a large amount of non-permeable nitrogen-enriched gas can be supplied at a stable flow rate. Therefore, according to this parallel separation method, high purity oxygen gas is separated and acquired from air by the PAS gas separation device 1, and high purity nitrogen gas is continuously supplied from the oxygen-containing desorption gas continuously supplied from the PAS gas separation device 1. It is possible to separate and acquire continuously and efficiently. Therefore, according to this parallel separation method, it is not necessary to use the tank etc. for storing the oxygen-containing desorption gas from the PSA gas separation apparatus 1 once.

In the present invention, with respect to the oxygen-containing desorption gas G1 introduced into the membrane gas separator 2, the pressure is P ₁ (MPa), the oxygen concentration (volume ratio of oxygen) is X ₁ , and the gas amount is Q ₁ (Nm ³ / hour), the pressure (ie, the pressure on the permeate side of the gas separation membrane 2A) with respect to the permeate gas G2 derived from the membrane gas separator 2 is P ₂ (MPa), the oxygen concentration is X ₂ , and the gas amount. Is Q ₂ (Nm ³ / hour), the oxygen concentration is X ₃ and the gas quantity is Q ₃ (Nm ³ / hour) for the non-permeable gas (high purity nitrogen gas) G3 derived from the membrane gas separator (2). If the area and thickness of the gas separation membrane 2A are set to S (m ² ) and L (m), and the oxygen permeation coefficient of the gas separation membrane 2A is set to K (Nm ² / hour · Mpa), the gas separation membrane is The following equations (1) to (3) are theoretically established for gas separation by (2A). Equation (1) shows the gas amount balance, Equation (2) shows the oxygen amount balance, and Equation (3) shows the oxygen permeation characteristics of the gas separation membrane 2A.

[Equation]

For example, as the gas separation membrane 2A, Eupirex PPT (manufactured by U.S. Co., Ltd.), which is a porous polyimide membrane, is employed to set the value of S (L / S) in formula (3) to 186, and the PSA gas The oxygen-containing desorption gas having an oxygen concentration (X ₁ ) of 20.6% at the start of the desorption process (e.g., initial desorption), which is discharged from the separator 1 as shown in FIG. 2, is 0.79MPa (by the compressor 7). P ₁ ) and introduced into the membrane gas separator 2 at a feed rate of 125 Nm ³ / hour (Q ₁ ), and the pressure on the permeate side of the gas separation membrane 2A was reduced to 0.0332Mpa (P ₂ ) to maintain the residual oxygen concentration. When adjusting the flow rate of the non-permeable gas by the oxygen concentration control mechanism 9 to obtain a non-permeable gas (high-purity nitrogen gas) having (X ₃ ) of 1%, three unknowns X ₂ , Q ₂ , and Q ₃ are obtained from the above equation ( It can be found as a solution of the system of simultaneous equations consisting of 1) to (3). In the initial stage of desorption, a permeate gas having an oxygen concentration (X ₂ ) of 88.9% is generated at 27.9 Nm ³ / hour (Q ₂ ), and the non-permeable gas amount Q ₃ is found to be 97.1 Nm ³ / hour. These values in the initial stage of desorption are shown in the table of FIG.

Oxygen concentration of the oxygen-containing desorption gas (X ₁ ) 10 seconds after the desorption process starts (desorption medium stage) while maintaining the values of K (S / L), P ₁ , Q ₁ , P ₂ , and X ₃ constant. ) it has the formula (1) ~ X _2, standing solutions of simultaneous equations formed from (3) Q _2, the art removable medium, the oxygen concentration (X ₂ by calculating the Q ₃ when reached to 10.0%, as shown in Figure 2 52. It is found that 2% of permeated gas is generated at 22.0 Nm ³ / hour (Q ₂ ), and the non-permeable gas amount Q ₃ is 103.2 Nm ³ / hour. These values in desorption medium are also shown in the table of FIG.

Oxygen concentration of the oxygen-containing desorption gas (X ₁ ) 30 seconds after the desorption process starts (end of desorption) while maintaining the values of K (S / L), P ₁ , Q ₁ , P ₂ , and X ₃ constant. 2) reaches 5.0% as shown in FIG. 2, by obtaining X ₂ , Q ₂ , Q ₃ as a solution of the system of equations formed from the above formulas (1) to (3). X ₂ ) It is found that 35.7% of permeated gas is generated in an amount Q ₂ of 14.4 Nm ³ / hour, and the non-permeable gas amount Q ₃ is 110.6 Nm ³ / hour. These values at the end of desorption are also shown in the table of FIG. 3.

On the other hand, the oxygen-containing desorption gas can be discharged from the PAS gas separation device 1 as shown in FIG. 2 except that the permeate side of the gas separation membrane 2A is set at atmospheric pressure (0.101 MPa) without depressurizing. In the case of desorption initial stage, desorption intermediate stage, and desorption stage, X ₂ , Q ₂ and Q ₃ are obtained based on the formulas (1) to (3), the results are as shown in the table of FIG. 4.

As can be understood from the comparison of the table of FIG. 3 and the table of FIG. 4, when the permeate side of the gas separation membrane 2A is not depressurized in the membrane gas separation process (see FIG. 4), the amount of permeated gas Q ₂ is desorbed. The amount of non-permeable gas Q ₃ is relatively small from the initial stage to the end of the desorption period from the initial stage to the end stage of desorption. In addition, the amount of change of the permeated gas amount Q ₂ (to the rate of change) due to the decrease in the oxygen concentration (X ₁ ) of the oxygen-containing desorption gas is large, and therefore, the amount of change of the non-permeable gas amount Q ₃ (to the rate of change) is also large. In contrast, when the permeate side of the gas separation membrane 2A is depressurized to less than atmospheric pressure in the membrane type gas separation process (see FIG. 3), the permeation gas amount Q ₂ is relatively small from the initial stage of desorption to the end of the desorption, and thus, the non-permeability The amount of gas Q ₃ is relatively large from the beginning of desorption to the end of desorption. In addition, the amount of change (or the rate of change) of the amount of permeated gas Q ₂ caused by the decrease in the oxygen concentration (X ₁ ) of the oxygen-containing desorption gas is small, and therefore the amount of change (or the rate of change) of the amount of non-permeable gas Q ₃ is also small. . From the above, it can be understood that according to the membrane gas separation process in the oxygen-nitrogen parallel separation system X1, a large amount of high-purity nitrogen gas can be supplied at a stable flow rate.

5 shows an oxygen / nitrogen parallel separation system X2 according to a second embodiment of the present invention. The oxygen / nitrogen parallel separation system X2 has no pump 5 and a pipe L2 connecting the outlet 2c of the membrane type gas separator 2 and the suction side of the pump 4 to the point where it is provided. Is different from the oxygen / nitrogen parallel separation system X1.

The pump 4 in the oxygen / nitrogen parallel separation system X2 functions as a decompression means for depressurizing the inside of the adsorption tower of the PAS gas separation device 1, and the gas separation membrane 2A in the membrane type gas separator 2. It also functions as a decompression means for depressurizing the permeate side of the. This configuration is desirable while at the same time building the system compactly.

At the time of operation of the oxygen / nitrogen parallel separation system X2, the pressure gas adsorption-type gas separation process is performed in the PAS gas separation system 1 as described above for the oxygen / nitrogen parallel separation system X1, thereby desorbing high purity oxygen gas and oxygen-containing. Gas is taken. In the membrane gas separator 2, a high purity nitrogen gas is taken by performing a membrane gas separation process in the same manner as described above with respect to the oxygen-nitrogen parallel separation system X1 except for the decompression method on the permeate side of the gas separation membrane 2A. . In the membrane type gas separation process in the present embodiment, the permeate side of the gas separation membrane 2A is depressurized to a pressure below atmospheric pressure by the operation of the pump 4. For example, by the operation of the pump 4, the inside of the adsorption tower in the adsorption process is sucked and depressurized, and the permeate side of the gas separation membrane 2A is also decompressed.

Therefore, according to the oxygen-nitrogen parallel separation method by oxygen-nitrogen parallel separation system X2, in addition to being able to supply high-purity oxygen gas in the same way as oxygen-nitrogen parallel separation system X1, a large amount of high-purity nitrogen gas is stable. It can be supplied at a flow rate.

6 shows an oxygen / nitrogen parallel separation system X3 according to a third embodiment of the present invention. The oxygen / nitrogen parallel separation system X3 is an inlet port 2d provided on the permeate side of the gas separation membrane 2A in the membrane gas separator 2, an upstream side of the compressor 7 and an inlet port of the membrane gas separator 2. It differs from oxygen-nitrogen parallel separation system X2 in the point which further provided the piping L3 which connects (2d), and the flow regulating valve 10 provided in the piping L3.

The pipe L3 in the oxygen / nitrogen parallel separation system X3 is discharged from the adsorption tower of the PAS gas separation device 1 in the desorption process, and a part of the oxygen-containing desorption gas flowing toward the membrane gas separator 2 is separated from the gas separation membrane ( A portion which functions as a bypass means for bypassing 2A) without introducing it and introducing it to the permeate side of the gas separation membrane 2A.

At the time of operation of the oxygen / nitrogen parallel separation system X3, the pressure gas adsorption-type gas separation process is performed in the PAS gas separation system 1 in the same manner as described above for the oxygen / nitrogen parallel separation system X1. Desorption gas is taken. In the membrane type gas separation process in this embodiment, similarly to the oxygen / nitrogen parallel separation system X2, the pump 4 is operated so that the permeate side of the gas separation membrane 2A is depressurized to a predetermined pressure less than atmospheric pressure. In this embodiment, since the upstream side of the compressor 7 and the inlet port 2d of the membrane gas separator 2 are connected to each other by the pipe L3, the membrane 7 is discharged from the adsorption tower of the PAS gas separation device 1, A part of the oxygen-containing desorption gas directed to the gas separator 2 is introduced to the permeate side of the gas separation membrane 2A via the pipe L3 and the inlet 2d. In other words, a part of the oxygen-containing desorption gas (hereinafter referred to as gas for reducing oxygen partial pressure G4) is bypassed without passing through the gas separation membrane 2A and supplied to the permeate side of the gas separation membrane 2A. Here, since the permeate side of the gas separation membrane 2A is depressurized, supply to the permeate side of the gas separation membrane 2A via the pipe L3 of the oxygen partial pressure reducing gas G4 is continuously and stably performed. In addition, the supply amount of the oxygen partial pressure reducing gas G4 to the permeate side of the gas separation membrane 2A is adjusted as desired by the flow regulating valve 10.

On the permeate side of the gas separation membrane 2A, the oxygen partial pressure reduction with a relatively low oxygen concentration bypassed without permeating the gas permeate gas G2 having passed through the gas separation membrane 2A and the gas separation membrane 2A without passing through the gas separation membrane 2A. The gaseous gas G4 merges (Hereinafter, the said combined gas is called merged gas G5.). Therefore, the oxygen concentration of the confluence gas G5 becomes lower than the oxygen concentration of the permeate gas G2. On the other hand, since the permeate side of the gas separation membrane 2A is depressurized to a predetermined pressure less than atmospheric pressure, the oxygen partial pressure of the combined gas G5 is lower than the oxygen partial pressure of the permeate gas G2.

Therefore, according to the oxygen-nitrogen parallel separation method by the oxygen-nitrogen parallel separation system X3, while reducing the permeation | transmission side of the gas separation membrane 2A to predetermined | prescribed pressure below atmospheric pressure, the oxygen partial pressure reduction gas G4 is decomposed. The oxygen partial pressure of the oxygen-containing desorption gas (G1) from the adsorption tower and the gas (permeation) that is present on the permeate side separated from the oxygen-containing desorption gas (G1) by the gas separation membrane (2A) by introducing into the permeation side of (2A) A larger difference can be made with respect to the oxygen partial pressure of the combined gas G5 consisting of the gas G2 and the gas for reducing the oxygen partial pressure G4. This also contributes to increasing the driving force for oxygen permeation in the gas separation membrane 2A to increase the amount of non-permeable gas (high purity nitrogen gas) G3.

7 shows the oxygen / nitrogen parallel separation system X4 according to the fourth embodiment of the present invention. The oxygen / nitrogen parallel separation system X3 differs from the oxygen / nitrogen parallel separation system X3 in that the pipe L4 is provided instead of the pipe L3 and the pressure control valve 11 is further provided. The piping L4 is comprised so that the downstream side of the compressor 7 and the inlet port 2d of the membrane type gas separator 2 may be connected. The pipe L4 is discharged from the adsorption tower of the PAS gas separation device 1 in the desorption process and flows toward the membrane-type gas separator 2 similarly to the pipe L3 of the oxygen / nitrogen parallel separation system X3. A part (gas for reducing oxygen partial pressure G4) is bypassed without passing through the gas separation membrane 2A and introduced into the permeate side of the gas separation membrane 2A. In addition, the pipe L4 is provided with a flow regulating valve 10 similarly to the oxygen / nitrogen parallel separation system X3. The pressure control valve 11 is provided between the compressor 7 and the membrane type gas separator 2 and is used to adjust the pressure of the oxygen-containing desorption gas G1 introduced into the membrane type gas separator 2 as desired. will be.

In the oxygen / nitrogen parallel separation system X4, since the downstream side of the compressor 7 and the inlet port 2d of the membrane gas separator 2 are connected by the pipe L4, the membrane gas at the time of system operation In the separation step, the oxygen partial pressure reducing gas G4 is supplied to the permeate side of the gas separation membrane 2A via the pipe L4. On the permeate side of the gas separation membrane 2A, a relatively high oxygen concentration permeate gas G2 that has passed through the gas separation membrane 2A, and a relatively low oxygen partial pressure that bypasses the gas separation membrane 2A without permeation. Since the gas for reducing G4 joins, the oxygen concentration of this confluence gas G5 becomes lower than the oxygen concentration of the permeate gas G2. On the other hand, since the permeate side of the gas separation membrane 2A is depressurized to a predetermined pressure of less than atmospheric pressure, the oxygen partial pressure of the combined gas G5 is lower than the oxygen partial pressure of the permeate gas G2.

Therefore, according to the oxygen-nitrogen parallel separation method by the oxygen-nitrogen parallel separation system X4, while reducing the permeation | transmission side of the gas separation membrane 2A to predetermined | prescribed pressure below atmospheric pressure, the oxygen partial pressure reduction gas G4 is decomposed. By introducing to the permeate side of 2A, the oxygen partial pressure of the oxygen-containing desorption gas G1 from the adsorption column and the gas containing the oxygen-containing desorption gas G1 on the permeate side separated by the gas separation membrane 2A (permeation) A larger difference can be made with respect to the oxygen partial pressure of the combined gas G5 consisting of the gas G2 and the gas for reducing the oxygen partial pressure G4. This also contributes to increasing the driving force for oxygen permeation in the gas separation membrane 2A, thereby increasing the amount of non-permeable gas (high purity nitrogen gas) G3.

1 shows a schematic configuration of an oxygen / nitrogen parallel separation system according to a first embodiment of the present invention.

FIG. 2 shows an example of time change in pressure with respect to the oxygen-containing desorption gas discharged from the pressure swing adsorption gas separation device shown in FIG. 1.

FIG. 3 relates to a membrane gas separation process in the oxygen / nitrogen parallel separation method of the present invention, which is performed using the oxygen / nitrogen parallel separation system shown in FIG. 1, and as shown in FIG. It is a table | surface which summarized an example of each physical quantity change from the initial stage of desorption (at the start of a desorption process), the middle stage of desorption (at 10 second), and the last stage of desorption (at the time of 30 seconds) when oxygen-containing desorption gas is discharged.

FIG. 4 relates to a membrane gas separation process performed without depressurizing the permeate side of the gas separation membrane in the membrane gas separator of the oxygen / nitrogen parallel separation system shown in FIG. 1, and as shown in FIG. The following table summarizes examples of changes in physical quantities from the initial stage of desorption (at the start of desorption process), the middle stage of desorption (at 10 seconds) and the end of desorption (at 30 seconds) when the oxygen-containing desorption gas is discharged.

5 shows a schematic configuration of an oxygen / nitrogen parallel separation system according to a second embodiment of the present invention.

6 shows a schematic configuration of an oxygen / nitrogen parallel separation system according to a third embodiment of the present invention.

7 shows a schematic configuration of an oxygen / nitrogen parallel separation system according to a fourth embodiment of the present invention.

8 shows a schematic configuration of a conventional oxygen-nitrogen parallel separation system.

Claims (9)

In a method for parallel separation of oxygen gas and nitrogen gas from a mixed gas containing oxygen and nitrogen, The mixed gas is introduced into the adsorption tower in a relatively high pressure state by a pressure swing adsorption gas separation method using an adsorption tower packed with an adsorbent for preferentially adsorbing nitrogen, and nitrogen in the mixed gas is introduced into the adsorbent. Oxygen enriched gas is derived from the adsorption tower, and the nitrogen remaining in the adsorption tower and oxygen containing the nitrogen are desorbed from the adsorbent in a state of relatively low pressure in the adsorption tower. A pressure swing adsorption gas separation process for deriving the containing desorption gas from the adsorption tower, The oxygen-containing desorption gas is separated into a permeate gas that passes through the gas separation membrane and a non-permeable nitrogen enrichment gas that is permeated by the gas separation membrane while reducing the permeation side of the gas separation membrane for preferentially permeating oxygen to a pressure below atmospheric pressure. A parallel separation method of oxygen gas and nitrogen gas, including a membrane gas separation process for performing the same. The parallel separation method according to claim 1, further comprising a compression step for compressing the oxygen-containing desorption gas before the oxygen-containing desorption gas is added to the membrane gas separation process. The parallel separation method according to claim 2, wherein in the compression step, the oxygen-containing desorption gas is compressed to a pressure of 0.6 MPa or more. 2. The pressure reduction adsorption column in the adsorption tower when the oxygen-containing desorption gas is derived from the adsorption tower in the pressure swing adsorption gas separation process, and the pressure reduction side on the permeate side in the membrane gas separation process, A parallel separation method realized by a single decompression means. The parallel separation method according to claim 1, wherein in the membrane gas separation process, a part of the oxygen-containing desorption gas is introduced to the permeate side of the gas separation membrane without passing through the gas separation membrane. A system for parallel separation of oxygen gas and nitrogen gas from a mixed gas containing oxygen and nitrogen, The mixed gas is introduced into the adsorption tower in a relatively high pressure state by a pressure swing adsorption gas separation method using an adsorption tower packed with an adsorbent for preferentially adsorbing nitrogen, and nitrogen in the mixed gas is introduced into the adsorbent. Oxygen-derived gas is extracted from the adsorption tower by adsorbing to the adsorption column, and in the state where the adsorption tower is relatively low pressure, the nitrogen is desorbed from the adsorbent to desorb the oxygen-containing oxygen containing the nitrogen and the nitrogen remaining in the adsorption tower. A pressure swing adsorption gas separation device for drawing gas from the adsorption tower, A membrane type gas separator having a gas separation membrane for preferentially permeating oxygen, and separating and deriving the oxygen-containing desorption gas into a permeate gas that passes through the gas separation membrane and a non-permeable nitrogen enrichment gas that does not permeate; A parallel separation system of oxygen gas and nitrogen gas provided with decompression means for depressurizing the permeate side to a pressure below atmospheric pressure in the gas separation membrane of the membrane type gas separator. The parallel separation system according to claim 6, further comprising compression means for compressing the oxygen-containing desorption gas before the oxygen-containing desorption gas is supplied to the membrane gas separator. 7. The parallel separation system according to claim 6, wherein the decompression means also functions as a means for depressurizing the inside of the adsorption tower when deriving the oxygen-containing desorption gas from the adsorption tower of the pressure swing adsorption gas separation device. 7. The parallel separation system according to claim 6, further comprising bypass means for bypassing a portion of said oxygen-containing desorption gas and introducing it to the permeate side of said gas separation membrane without permeating said gas separation membrane.

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