JP4972467B2 - Low purity nitrogen gas generation method - Google Patents

Description

  The present invention relates to a low-purity nitrogen gas generation method, and in particular, the oxygen content rate is determined by using a nitrogen gas generator that separates nitrogen and oxygen in the air by a pressure fluctuation adsorption method using molecular sieve carbon as an adsorbent. The present invention relates to a method of generating 3 to 5% by volume of low purity nitrogen gas.

  There is known a method for separating and generating nitrogen gas (hereinafter also referred to simply as nitrogen, including nitrogen-rich gas) from air by pressure fluctuation adsorption method (PSA method) using molecular sieve carbon as an adsorbent. Yes. In the PSA method using molecular sieve carbon, typically, raw air pressurized to an appropriate pressure is introduced into two cylinders filled with molecular sieve carbon, and a predetermined amount of gas is introduced into the cylinder. Pressurizing process to make pressure, adsorbing preferentially adsorbed oxygen content to adsorbent, collecting nitrogen gas that is hard to adsorb and feeding it to the product tank (product extracting process), nitrogen content remaining in the cylinder Pressure reduction and pressure equalization process to send the adsorbent to the other adsorbing cylinder, the adsorbing cylinder is released to the atmosphere and the pressure is lowered to desorb the oxygen adsorbed on the adsorbent and regenerate the adsorbent, other adsorbing cylinder Nitrogen in the air is separated by alternately repeating each step of the pressure equalization step for receiving nitrogen from the inside by two adsorption cylinders.

  In this method, since the pressure can be changed in a relatively short operation cycle of about 1 minute, the amount of air treated per unit weight of the adsorbent can be increased. For this reason, since the apparatus configuration can be greatly simplified and the equipment cost is superior to the conventional cryogenic air separation method, a nitrogen gas generator (nitrogen PSA apparatus) based on such a PSA method can be used. ) Is widely used for small / medium nitrogen generation.

  For example, in a nitrogen PSA apparatus using two adsorption cylinders (A, B), each of the pressure equalization steps (the pressure reduction pressure equalization step and the pressure equalization step) is a valve between the A cylinder and the B cylinder. Is a step of making the pressures of both cylinders substantially equal, with the purpose of collecting the pressure of the suction cylinders with high pressure in the suction cylinders with low pressure. During this time, raw material air is not introduced into the adsorption cylinder, and product gas does not flow from the adsorption cylinder to the product tank. That is, during each pressure equalization process, the product gas is supplied with the residual pressure in the product tank. Furthermore, when the pressure equalization process is completed and the process proceeds to the pressurization process, the product gas is not supplied to the product tank until the pressure in the adsorption cylinder becomes higher than the pressure in the product tank.

  In general, when high-purity nitrogen gas is generated, the decrease in the pressure in the product tank is small because the amount of product gas supplied is small. However, when low purity nitrogen gas is generated, the product tank pressure is greatly reduced due to the large amount of product gas supplied. For this reason, when the time of the said pressure equalization process becomes long, there exists a possibility that the guarantee pressure which a customer requires cannot be maintained. In this case, it is possible to maintain the pressure above the guaranteed pressure by enlarging the product tank. However, an operation method with a long pressure equalization time is not applicable because the cost is increased or the apparatus becomes large. In addition, the purity tends to decrease as the pressure fluctuation width (maximum pressure and minimum pressure width) of the product tank increases.

  For example, in a nitrogen PSA apparatus that generates high-purity nitrogen gas with an oxygen content of less than 3% by volume, the pressure rise rate in the adsorption cylinder is 0.15 to 1.6 MPa / sec, and the pressure equalization time is 7 to 27 seconds. (For example, refer to Patent Document 1).

On the other hand, inert nitrogen gas is used as an explosion-proof purge gas and shield gas in ships such as LPG tankers and chemical tankers. Conventionally, as an apparatus for generating an inert gas such as a purge gas or a nitrogen gas serving as a shield gas, the IGG type using heavy oil combustion exhaust gas has been mainstream, but it contains a large amount of carbon dioxide, a global warming gas. In addition, the nitrogen PSA apparatus based on the PSA method, which requires frequent maintenance because it contains dirt (soot) and has a low maintenance frequency, has begun to attract attention, and the nitrogen PSA apparatus is increasingly mounted.
JP 2001-342013 A

  Nitrogen gas for use as an explosion-proof purge gas or seal gas in ships may be a relatively low-purity nitrogen gas containing up to 5% by volume of oxygen in the nitrogen gas in accordance with steel ship regulations. Unlike the nitrogen gas used in the above, high-purity nitrogen gas is not necessarily required. However, since the nitrogen PSA device must be housed in a ship, the size of the device, particularly the height, is limited, and it is required to efficiently generate nitrogen gas of a predetermined purity and pressure with a compact device. The

  Therefore, the present invention can efficiently generate low-purity nitrogen gas having an oxygen content of 3 to 5% by volume used as an explosion-proof purge gas or seal gas in a ship, and can reduce the size of a nitrogen PSA device. An object of the present invention is to provide a method for generating nitrogen gas.

In order to achieve the above object, the nitrogen gas generation method of the present invention includes steps of pressurization, product removal, decompression pressure equalization, regeneration, and pressure equalization for an adsorption cylinder filled with molecular sieve carbon as an adsorbent. In the method of generating low purity nitrogen gas having an oxygen content of 3 to 5% by volume from air by repeated pressure fluctuation adsorption method, the pressure of the raw material air to be introduced is set within a range of 0.7 to 1.0 MPa as a gauge pressure. And while setting the space velocity of the raw material air in the adsorption cylinder in the said pressurization process and the product extraction process in the range of 1500-2500 hr < ^-1 >, the extraction amount of the product nitrogen from an apparatus is 220-700 Nm < ³ > / hr. -It is characterized by setting in the range of ton.

Furthermore, in the low purity nitrogen gas generation method of the present invention, the molecular sieve carbon has an oxygen / nitrogen separation ratio α of 37.9 or more and an oxygen adsorption rate constant K (O ₂ ) of 8. It is characterized by being 5 × 10 ⁻² sec ⁻¹ or more.

  According to the nitrogen gas generation method of the present invention, low-purity nitrogen gas having an oxygen content of 3 to 5% by volume can be efficiently generated from the air by the nitrogen PSA method. It is possible to reduce the amount used and the equipment price.

  1 and 2 show an embodiment of a nitrogen PSA apparatus to which the nitrogen gas generation method of the present invention is applied. FIG. 1 is a system diagram of the nitrogen PSA apparatus, and FIG. 2 shows each process of the nitrogen PSA apparatus. It is explanatory drawing.

  The nitrogen PSA apparatus includes two adsorption cylinders A and B filled with molecular sieve carbon as an adsorbent, an air compressor 11 that compresses raw material air, an air storage tank 12 that stores raw material air, and a product that stores product gas. The first inlet valve 14a, the second inlet valve 14b, the first exhaust valve 15a, the second exhaust valve 15b, the purge valve 16, and the upper pressure equalizing valve that are opened and closed by a switching program for each process of the tank 13 and the adsorption cylinders A and B. 17, lower pressure equalizing valve 18, first check valve 19a, second check valve 19b, first mass flow controller 20 for adjusting the flow rate of the raw material air to a predetermined flow rate, and adjusting the product gas supply amount to a predetermined flow rate A second mass flow controller 21, a flow rate adjustment valve 22 for adjusting the flow rate of the purge gas to a predetermined flow rate, an inlet side pressure adjustment valve 23a, an outlet side pressure adjustment valve 23b, pressure gauges 24, 25, and 26, and an oxygen concentration meter 2 It is composed of a.

  The nitrogen PSA apparatus separates nitrogen in the air by repeating the steps shown in FIG. 2, and collects product nitrogen gas. Note that FIG. 2 is a schematic diagram, and only shows a path through which gas flows in the valve-open state in each step. Hereinafter, each process is demonstrated in order of a process.

  FIG. 2A shows a state in which the adsorption cylinder A is performing the pressurizing process and the adsorption cylinder B is performing the first half of the regeneration process, and the first inlet valve 14a of the adsorption cylinder A is opened, and a predetermined pressure is set in the adsorption cylinder A. The raw material air is introduced and the inside of the cylinder is pressurized. At this time, the purge valve 16 and the second exhaust valve 15b of the adsorption cylinder B are opened, and the flow rate of the nitrogen gas derived from the outlet of the adsorption cylinder A is adjusted by the flow rate adjustment valve 22, passes through the purge valve 16 and the adsorption cylinder B The gas is sent to the outlet, the gas in the adsorption cylinder B is released from the inlet, and the purge in the cylinder is performed.

  FIG. 2B shows a state in which the adsorption cylinder A is in the adsorption (product take-out) process and the adsorption cylinder B is in the latter half of the regeneration process, and the pressure in the adsorption cylinder A rises above the pressure in the product tank 13. Thus, the outlet gas of the adsorption cylinder A passes through the first check valve 19a and flows into the product tank 13. The outlet gas of the adsorption cylinder A is nitrogen concentrated to a predetermined oxygen content because oxygen is adsorbed by the adsorbent (molecular sieve carbon) filled in the cylinder. On the other hand, in the adsorption cylinder B, the in-cylinder gas is continuously released and purged.

  FIG. 2C shows a state in which the adsorption cylinder A is switched from the adsorption process to the pressure-reducing and pressure equalizing process, and the adsorption cylinder B is switched from the regeneration process to the pressure-equalizing and equalizing process, and the first inlet valve 14a of the adsorption cylinder A, The second exhaust valve 15b and the purge valve 16 of the adsorption cylinder B are closed, and the upper pressure equalizing valve 17 and the lower pressure equalizing valve 18 are opened. In this pressure equalization process, the nitrogen-rich gas in the adsorption cylinder A having a relatively high in-cylinder pressure after completion of the adsorption process is recovered in the adsorption cylinder B having a relatively low in-cylinder pressure after the regeneration process is completed. As a result, the suction cylinder A is depressurized and the suction cylinder B is pressurized.

  FIG. 2 (D) shows a state in which the adsorption cylinder A is switched to the regeneration process and the adsorption cylinder B is switched to the pressurization process, the first exhaust valve 15a of the adsorption cylinder A is opened, and the in-cylinder gas is released into the atmosphere. As a result, oxygen adsorbed on the adsorbent is desorbed and released out of the cylinder. Further, the purge valve 16 is opened, and purge gas (nitrogen gas) from the adsorption cylinder B is introduced into the outlet of the adsorption cylinder A to further wash out oxygen. Further, in the adsorption cylinder B, the second inlet valve 14b is opened, and the raw material air is introduced into the cylinder and pressurized.

  FIG. 2E shows a state in which the adsorption cylinder A continues the regeneration process, and the adsorption cylinder B is switched from the pressurization process to the adsorption process. In the adsorption cylinder A, the introduction of the purge gas from the adsorption cylinder B, 1 The gas discharge from the exhaust valve 15a is continued. Further, when the in-cylinder pressure of the adsorption cylinder B is increased, the product nitrogen gas is collected from the adsorption cylinder B to the product tank 13 through the second check valve 19b.

  FIG. 2F shows a state in which the adsorption cylinder A is switched from the regeneration process to the pressurization and pressure equalization process, and the adsorption cylinder B is switched from the adsorption process to the decompression and pressure equalization process, and the second inlet valve 14b of the adsorption cylinder B, The first exhaust valve 15a and the purge valve 16 of the adsorption cylinder A are closed, and both the pressure equalizing valves 17 and 18 are opened. In this pressure equalization process, the nitrogen-rich gas in the adsorption cylinder B that has completed the adsorption process is collected in the adsorption cylinder A that has completed the regeneration process.

  By repeating these steps of pressurization, product removal, reduced pressure equalization, regeneration, and pressure equalization, nitrogen is separated from air and product nitrogen gas is obtained. An on-off valve may be used in place of the reversely supported valves 19a and 19b, or an orifice may be used in place of the purge valve 16 and the flow rate adjusting valve 22. In addition, by using a multi-cylinder PSA apparatus provided with three or more adsorption cylinders, it is possible to reduce the size of the adsorption cylinder, in particular, to lower the cylinder height and to stabilize the product purity and the product tank pressure. In the regeneration step, the inside of the cylinder may be evacuated by a vacuum pump as necessary.

  In the PSA operation in which such a process is repeated, it is necessary to appropriately set the process switching time. When the flow rate of the raw material air and the flow rate of the product nitrogen gas are fixed, if the switching time is too short, the in-cylinder pressure Adsorbent performance cannot be fully achieved without reaching the feed air supply pressure, and if the adsorption time is too long, the amount of feed air introduced will increase, so the adsorbent oxygen adsorption will saturate and oxygen will break through. As a result, the purity of the product nitrogen gas decreases. It is also important to select an appropriate switching time depending on the oxygen adsorption rate and nitrogen adsorption rate of the adsorbent used. That is, when an adsorbent having a high oxygen adsorption rate is used, it is necessary to set an earlier switching time. Therefore, by setting an optimal switching time according to the supply amount of the product nitrogen gas, the amount of raw material air, and the performance of the adsorbent, it is possible to efficiently generate the product nitrogen gas having a predetermined flow rate and a predetermined purity.

  First, four types of molecular sieve carbon (MSC-I, II, III, IV) were prepared as samples, and the adsorption rates of oxygen and nitrogen in each sample were measured. The adsorption rate was measured by measuring the time-dependent change in pressure due to adsorption in a constant volume container using a commercially available constant volume method measuring device (Bell Soap 28 manufactured by Nippon Bell Co., Ltd.). About 1 g of each sample is accurately weighed, heated to 100 ° C. in 30 minutes under vacuum, and then subjected to pretreatment for 2 hours, followed by measurement at a temperature of about 25 ° C. and an introduction pressure of 200 Torr. went.

Based on the pressure change data obtained from the measurement, a pressure change curve over time is created, and the theoretical pressure change curve obtained from the LDF adsorption speed model (Linear Driving Force Model) is used to absorb 50% of the equilibrium adsorption amount. The adsorption rate constant K was determined so as to agree with the amount. Table 1 shows the measurement results of oxygen adsorption rate constant K (O ₂ ) and nitrogen adsorption rate constant K (N ₂ ) in each sample (MSC-I, II, III, IV) and their ratio (K (O ₂ ) / K (N ₂ ), separation ratio α).

From these measurement results, two types of adsorbents, MSC-I, which has a relatively high oxygen adsorption rate and MSC-III, which has a relatively low oxygen adsorption rate, are used in the nitrogen PSA apparatus having the configuration shown in FIG. An experiment to generate nitrogen gas was performed. In the experiment, in MSC-I, the raw material air pressure is 0.7 MPa (gauge pressure, the same applies hereinafter), the space velocity (SV value: the ratio of the amount of air introduced per hour and the amount of adsorbent charged) is 1500 hr ⁻¹ , the product The flow rate is set to 27 NL / min (converted to the standard state), MSC-III sets the raw material air pressure to 0.70 MPa (gauge pressure, the same applies hereinafter), SV = 1500 hr ⁻¹ , and the product flow rate of 18 NL / min. Was fixed at 1 second, and the switching time, which is the total time of the pressurization step, the adsorption step, and the pressure equalization time, was changed, and the purity of the product nitrogen gas obtained in each experiment was measured. The results are shown in Table 2 (MSC-I) and Table 3 (MSC-III), respectively.

From the results of Tables 2 and 3, the switching time when the purity of the product nitrogen gas is the best is 43 seconds for MSC-I, which has a high oxygen adsorption rate, and 55 seconds for MSC-III, which has a slow oxygen adsorption rate. there were. Therefore, it can be seen that it is necessary to set an optimum PSA operating condition according to the performance of the adsorbent used (adsorption rate constants K (O ₂ ), K (N ₂ ) and separation ratio (α).

For each of the adsorbents MSC-I to IV, an experiment was performed on the influence of the ratio (SV value) between the raw material air introduction amount per unit time and the adsorbent filling amount. The switching time at each SV value was adjusted from the optimum switching time obtained in Example 1 so that the product of the air introduction time (switching time-pressure equalizing time) and the SV value during the switching time was constant. . That is, the SV value, if you change from SV = 1000 hr ^-1 to SV = 2000 hr ^-1, the air introduction time during switching time is half.

For example, in MSC-I in Example 1, based on the product of the switching time of 43 seconds and SV = 1500 hr ⁻¹ , the flow rate is adjusted and the conditions for product purity of 95, 96, and 97% by volume are selected. The capacity of each adsorbent was estimated based on the conditions. The results are shown in FIGS. FIG. 3 shows the case where the oxygen concentration in the product nitrogen gas is 3% by volume, FIG. 4 shows the same 4% by volume, FIG. 5 shows the same 5% by volume, and the raw material air pressure is 0.98 MPa. When the pressure was 0.7 MPa.

From the result when the oxygen concentration in the product nitrogen gas is 3% by volume (FIG. 3), the maximum capacity when the raw material air pressure is 0.98 MPa (the amount of product gas generated per ton of adsorbent filled in the nitrogen PSA device) ^{[Nm 3 / hr · ton]} ) ^{is, 490Nm 3 / hr · ton,} 380Nm 3 in ^{MSC-II 550Nm 3 / hr ·} ton, in ^{MSC-III 370Nm 3 / hr ·} ton, in MSC-IV in MSC-I / Hr · ton. Moreover, it turns out that each adsorbent has shown the maximum value in SV = 2000-2250hr- ¹ vicinity. Maximum capacity when the raw material air pressure 0.70MPa is, 350 Nm in ^{MSC-I 3 / hr · ton} , 400Nm 3 / hr · ton at MSC-II, MSC-III in ^{260Nm 3 / hr · ton, MSC} -IV 290 Nm ³ / hr · ton. Moreover, it turns out that each adsorbent shows the maximum value near SV = 1250-1500 hr ⁻¹ .

Moreover, when the result of FIG. 3 is seen, compared with the adsorption agent (MSC-III) used conventionally, a high performance agent (MSC-II) has the capability of 1.5 times or more. Recognize. This is due to the fact that the oxygen adsorption rate constant is large and the separation ratio α is large, which is an expected result. On the other hand, although the adsorption rate constant K (O ₂ ) of oxygen is larger than that of the conventional agent (MSC-III), the adsorbent (MSC-I) with a poor separation ratio has a conventional oxygen concentration of 0.1%. Under the condition of less than 1%, the separation ratio was low, and although no significant improvement in performance was observed, it was predicted compared with the conventional agent (MSC-III) when the oxygen concentration was 3%. The above significant capacity improvement became apparent. Since the oxygen concentration is high, the influence of the low separation performance is small, and the high oxygen adsorption rate is considered to have improved the performance. In addition, the separation ratio α is the same as that of the conventional agent (MSC-III), but the adsorbent (MSC-IV), which has a slightly higher oxygen adsorption rate constant, has a greater capacity than the conventional agent (MSC-III). However, the improvement is small. From these results, it can be seen that there is a threshold value in the oxygen adsorption rate constant K (O ₂ ) in addition to the large separation ratio α for improving the capacity in the low purity nitrogen gas generation method.

As can be understood from FIG. 6 showing the relationship between the separation ratio α and the adsorption rate constant K (O ₂ ) of oxygen in each of the adsorbents MSC-I to IV shown in Table 1, an arrow heading from MSC-III to MSC-IV As described above, a sufficient effect cannot be obtained if the oxygen adsorption rate constant K (O ₂ ) is slightly increased. As indicated by arrows from MSC-III and MSC-IV to MSC-II, The adsorption rate constant K (O ₂ ) is only slightly increased, but when the separation ratio α is increased, the ability of the low-purity nitrogen gas generation method is greatly improved. Further, from MSC-III and MSC-IV to MSC As shown by the arrow toward -I, the separation ratio α is slightly inferior, but when the oxygen adsorption rate constant K (O ₂ ) is large, the ability in the low-purity nitrogen gas generation method is improved.

Therefore, by using an adsorbent having an oxygen / nitrogen separation ratio α of 37.9 or more and an oxygen adsorption rate constant of 8.5 × 10 ⁻² sec ⁻¹ or more, SV = 1500 to 2500 hr. ⁻¹ , it becomes possible to achieve a product nitrogen extraction capacity of 220 Nm ³ / hr or more from the PSA apparatus, and the nitrogen generation efficiency can be further increased. Although it is possible to use MSC-III or MSC-IV, since the amount of adsorbent increases, the adsorbent price and the adsorption cylinder price increase, and the size of the apparatus increases. Is inappropriate.

Next, regarding the SV value, if the SV value is excessively increased, the switching time is shortened, so that the regeneration time is also shortened, resulting in insufficient regeneration. Conversely, if the SV value is excessively decreased, the maximum pressure (adsorption pressure) during the switching time is reached. Since the maximum value) does not reach the raw material air pressure, it is necessary to select an optimum range for the SV value. Table 4 shows the result of measuring the maximum value of the adsorption pressure in each adsorbent when the raw material air pressure is 0.98 MPa and the SV value is changed.

From this result, in the case of MSC-I and MSC-II, when it becomes smaller than SV = 1750 hr ⁻¹ , the maximum adsorption pressure value gradually decreases and significantly decreases from SV = 1250 hr ⁻¹ . For this reason, in order to sufficiently exhibit the performance of the adsorbent, the SV value is suitably in the range of 1500 to 2500 hr ⁻¹ , and the raw material air pressure is set to 0.7 MPa or more, particularly 0.9 MPa or more. It can be seen that the maximum adsorption pressure should be increased sufficiently. In addition, as for MSC-III and MSC-IV, since the adsorption rate constant of O ₂ is small, it is difficult for oxygen to be adsorbed by the adsorbent, and oxygen breaks through to the product nitrogen gas side, so that the adsorption pressure is increased. However, the purity of nitrogen is lowered. In addition, when the raw material air pressure is set to a pressure exceeding 1.0 MPa, the pressure resistance of the apparatus must be taken into account, which is uneconomical.

In addition, since the PSA nitrogen generator has the characteristic that the nitrogen purity decreases when a large amount of product is taken out and the nitrogen purity increases when it is reduced, there is an optimal amount of product extracted according to the oxygen concentration in the product. When the oxygen concentration in the product is 3% by volume, 220 to 550 Nm ³ / hr · ton, similarly when the oxygen concentration is 4% by volume, 280 to 630 Nm ³ / hr · ton, and similarly when the oxygen concentration is 5% by volume, 340 ˜700 Nm ³ / hr · ton is the optimum product removal amount from the apparatus.

Therefore, as a method for operating a nitrogen PSA apparatus for supplying low purity nitrogen gas having an oxygen concentration of 3 to 5% by volume used as an explosion-proof purge gas or seal gas in a ship, the adsorption pressure maximum value is sufficiently increased. Therefore, the raw material air pressure is set in the range of 0.7 to 1.0 MPa, preferably in the range of 0.9 to 1.0 MPa, and the SV value is set in the range of 1500 to 2500 hr ⁻¹ in order to obtain an appropriate switching time. and sets, product take-off (ability) from devices, 220~550Nm ³ / hr · ton when the oxygen concentration in the product is 3% by volume, also when the oxygen concentration of 4 vol% 280~630Nm ³ / hr Ton, similarly, when the oxygen concentration is 5% by volume, by setting within the range of 340 to 700 Nm ³ / hr Purity nitrogen gas can be generated efficiently, and the size of the nitrogen PSA device can be reduced, the amount of molecular sieve carbon used can be reduced, and the device price can be reduced.

PSA device made by Taiyo Nippon Sanso Co., Ltd. filled with MSC-I as an adsorbent (adsorbent filling amount 200 kg / cylinder) and two compressors (Atlas Copco GA37AFF and Hitachi OSPN-22) Experiments on a scale were performed. The raw material air pressure was set to 0.9 MPa, the SV value was set to 1720 hr ⁻¹ , and the switching time was set to 30 seconds. The nitrogen generation capacity when the oxygen concentration in the product nitrogen gas was 5% by volume was 635 Nm ³ / hr · ton.

It is a systematic diagram which shows one example of a nitrogen PSA apparatus to which the nitrogen gas generation method of this invention is applied. It is explanatory drawing which shows each process of a nitrogen PSA apparatus. It is a figure which shows the relationship between SV value when the oxygen concentration in product nitrogen gas is 3 volume%, and the capability of adsorption agent. It is a figure which shows the relationship between SV value when the oxygen concentration in product nitrogen gas is 4 volume%, and the capability of adsorption agent. It is a figure which shows the relationship between SV value when the oxygen concentration in product nitrogen gas is 5 volume%, and the capability of adsorption agent. Is a view showing the relationship between the adsorbent separation ratio in MSC-I-IV alpha and oxygen adsorption rate constant K (O _2).

Explanation of symbols

  A, B ... Adsorption cylinder, 11 ... Air compressor, 12 ... Air storage tank, 13 ... Product tank, 14a ... First inlet valve, 14b ... Second inlet valve, 15a ... First exhaust valve, 15b ... Second exhaust valve , 16 ... purge valve, 17 ... upper pressure equalizing valve, 18 ... lower pressure equalizing valve, 19a ... first check valve, 19b ... second check valve, 20 ... first mass flow controller, 21 ... second mass flow controller, 22 ... Flow rate adjusting valve, 23a ... Inlet side pressure adjusting valve, 23b ... Outlet side pressure adjusting valve, 24, 25, 26 ... Pressure gauge, 27 ... Oxygen concentration meter

Claims (2)

Oxygen content of 3 to 5 volumes from air by pressure fluctuation adsorption method that repeats the steps of pressurization, product removal, decompression pressure equalization, regeneration, and pressure equalization for an adsorption cylinder filled with molecular sieve carbon as an adsorbent % Of low-purity nitrogen gas is generated, the pressure of the raw material air to be introduced is set within a range of 0.7 to 1.0 MPa as a gauge pressure, and the inside of the adsorption cylinder in the pressurizing step and the product removing step is set. The low-purity nitrogen gas is characterized in that the space velocity of the raw material air is set in a range of 1500 to 2500 hr ^{−1 and} the amount of product nitrogen extracted from the apparatus is set in a range of 220 to 700 Nm ³ / hr · ton. How it occurs. The molecular sieve carbon has an oxygen / nitrogen separation ratio α of 37.9 or more and an oxygen adsorption rate constant K (O ₂ ) of 8.5 × 10 ⁻² sec ⁻¹ or more. The low-purity nitrogen gas generation method according to claim 1, wherein

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