JP7530282B2 - Nitrogen gas separation method and nitrogen gas separation device - Google Patents

Description

The present invention relates to a nitrogen gas separation method and a nitrogen gas separation device.

In recent years, nitrogen gas has been used in a wide variety of fields, from industrial gases used in heat treatment of metals, manufacturing of semiconductors, explosion-proof seals in chemical plants, etc., to filling gas for food preservation, and its usage is increasing year by year. A method for producing this nitrogen gas is the so-called Pressure Swing Adsorption (PSA) method, in which high-pressure air, which is the raw gas, is fed into an adsorption tower filled with molecular sieve carbon, which is a velocity separation type adsorbent, and oxygen gas is adsorbed by the adsorbent to separate nitrogen gas as a product gas. For example, the device described in Patent Document 1 is known as an apparatus that applies such a nitrogen gas separation method using the PSA method.

In the device described in Patent Document 1, when the ambient temperature of the adsorption tower is lower than a predetermined low temperature reference temperature, the time of the adsorption and removal process in which the product gas obtained in the adsorption tower is removed from the adsorption tower is extended.

Patent No. 5022785

The compressor for supplying the raw gas to the adsorption tower has the characteristic that the mass flow rate of the compressed air discharged from the compressor increases as the ambient temperature decreases. For this reason, at low temperatures, the pressure inside the adsorption tower is likely to increase as the mass flow rate of the raw gas supplied from the compressor increases. When the pressure inside the adsorption tower increases in this way, the purity of the product gas obtained in the adsorption tower may become excessively high.

In the device described in Patent Document 1, the time of the adsorption and removal process in the adsorption tower is extended in response to a drop in the ambient temperature, which makes it easier for the pressure in the adsorption tower to increase, and this makes it possible to prevent the purity of the product gas obtained in the adsorption tower from becoming excessively high. However, it cannot be said that this effectively utilizes the compressor's characteristic of increasing the mass flow rate of the raw material gas supplied from the compressor in response to a drop in the ambient temperature. Moreover, it cannot be said that the increased mass flow rate of the raw material gas can be effectively utilized in the adsorption tower to obtain product gas.

The present invention was made in consideration of these circumstances, and its purpose is to provide a nitrogen gas separation method and nitrogen gas separation device that can effectively utilize the raw material gas supplied from the compressor in the adsorption tower to obtain product gas while preventing the purity of the product gas from increasing excessively when the ambient temperature drops.

The nitrogen gas separation method according to the present invention is a method for separating nitrogen gas, which comprises pressurizing a raw gas containing nitrogen gas and oxygen gas and supplying the raw gas containing nitrogen gas and oxygen gas from a compressor to two or more adsorption towers filled with an adsorbent, and repeatedly performing an adsorption step, a pressure equalization step, a desorption step, and a pressure equalization step in each adsorption tower to separate nitrogen gas from the raw gas as a product gas and introduce the product gas into a product tank. In this nitrogen gas separation method, when the temperature of the raw gas sucked into the compressor is a first temperature, the product gas is discharged from the product tank at a first flow rate, and when the temperature of the raw gas sucked into the compressor is a second temperature lower than the first temperature, the product gas is discharged from the product tank at a second flow rate higher than the first flow rate.

According to this nitrogen gas separation method, when the ambient temperature of the compressor drops to a second temperature lower than the first temperature, the product gas is discharged from the product tank at a second flow rate higher than the first flow rate. Since the pressure in the product tank decreases due to an increase in the flow rate of the product gas discharged from the product tank, the pressure in the adsorption tower is less likely to increase, and an excessive increase in the pressure in the adsorption tower can be suppressed. This makes it possible to suppress an excessive increase in the purity of the product gas obtained in the adsorption tower. Furthermore, since the pressure in the adsorption tower is less likely to increase, the amount of raw gas supplied to the adsorption tower by the compressor can be increased. As a result, when the mass flow rate of the raw gas supplied from the compressor increases in response to a decrease in the ambient temperature, the increased amount of raw gas can be effectively utilized in the adsorption tower to obtain the product gas.

In addition, by increasing the flow rate of product gas flowing out of the product tank when the ambient temperature is low, it is possible to increase the amount of product gas provided to users who use product gas, for example, during the cold winter months or during times of the day when the temperature drops.

The nitrogen gas separation method according to the present invention is a method for separating nitrogen gas, which comprises pressurizing and supplying a raw gas containing nitrogen gas and oxygen gas from a compressor to two or more adsorption towers filled with an adsorbent, and repeatedly performing an adsorption step, a pressure equalization step, a desorption step, and a pressure equalization step in each adsorption tower to separate nitrogen gas from the raw gas as a product gas and introducing the product gas into a product tank. In this nitrogen gas separation method, the temperature of the raw gas sucked into the compressor is measured by a thermometer, and when the temperature measured by the thermometer is a first temperature, the product gas is discharged from the product tank at a first flow rate, and when the measured temperature is a second temperature lower than the first temperature, the product gas is discharged from the product tank at a second flow rate higher than the first flow rate.

According to this nitrogen gas separation method, when the temperature measured by the thermometer drops to a second temperature lower than the first temperature, the product gas is discharged from the product tank at a second flow rate greater than the first flow rate based on the measurement result of the thermometer. Since the pressure in the product tank decreases due to an increase in the outflow flow rate of the product gas from the product tank, the pressure in the adsorption tower is less likely to increase, and an excessive increase in the pressure in the adsorption tower can be suppressed. This makes it possible to suppress an excessive increase in the purity of the product gas obtained in the adsorption tower. Furthermore, since the pressure in the adsorption tower is less likely to increase, the amount of raw gas supplied to the adsorption tower by the compressor can be increased. As a result, when the mass flow rate of the raw gas supplied from the compressor increases in response to a decrease in the ambient temperature, the increased amount of raw gas can be effectively used in the adsorption tower to obtain the product gas.

In addition, by increasing the flow rate of product gas flowing out of the product tank in response to a decrease in temperature measured by the thermometer, the amount of product gas provided to the user who uses the product gas can be increased based on the measurement results of the thermometer.

In the nitrogen gas separation method described above, the adsorption and desorption times for the adsorption and desorption processes in each of the adsorption towers may be maintained constant.

In this embodiment, the adsorption/desorption time in each adsorption tower is maintained constant even when the ambient temperature of the compressor drops. This makes it possible to suppress fluctuations in the maximum pressure in each adsorption tower when the adsorption process is performed, compared to when the adsorption/desorption time is extended in response to a drop in the ambient temperature. This makes it possible to suppress fluctuations in the purity of the product gas obtained in each adsorption tower.

The nitrogen gas separation apparatus according to the present invention includes a compressor for pressurizing and supplying a raw gas containing nitrogen gas and oxygen gas, two or more adsorption towers filled with an adsorbent and for separating nitrogen gas as a product gas from the raw gas in response to the supply of the raw gas from the compressor, a product tank into which the product gas obtained in each of the adsorption towers is introduced, a flow rate adjustment unit for adjusting the flow rate at which the product gas is discharged from the product tank, a thermometer for measuring the temperature of the raw gas sucked by the compressor, and a control unit for controlling the repeated adsorption process, pressure equalization process, desorption process, and pressure equalization process so that the product gas is obtained in each of the adsorption towers. The control unit controls the flow rate adjustment unit so that the product gas flows out of the product tank at a first flow rate when the temperature measured by the thermometer is a first temperature, and so that the product gas flows out of the product tank at a second flow rate greater than the first flow rate when the measured temperature is a second temperature lower than the first temperature.

In the nitrogen gas separation device, the control unit may be configured to maintain a constant adsorption/desorption time for performing the adsorption process and the desorption process in each of the adsorption towers.

As described above, according to the present invention, when the ambient temperature drops, the purity of the product gas can be prevented from increasing excessively, and the raw gas supplied from the compressor can be effectively utilized in the adsorption tower to obtain the product gas.

1 is a diagram showing the configuration of a nitrogen gas separation device according to one embodiment of the present invention. FIG. 2 is a diagram showing the configuration of a flow rate adjusting unit provided in the nitrogen gas separation apparatus.

Hereinafter, the nitrogen gas separation method and nitrogen gas separation device according to an embodiment of the present invention will be described with reference to the drawings.

The nitrogen gas separation device 100 shown in FIG. 1 separates nitrogen gas from a raw material gas containing nitrogen gas and oxygen gas to obtain a product gas containing nitrogen gas. The raw material gas may be, for example, air, but is not limited to this, and may be any gas that contains at least nitrogen gas and oxygen gas.

The nitrogen gas separation device 100 includes a raw gas supply unit 1, a first adsorption tower 3A and a second adsorption tower 3B that constitute two or more adsorption towers, a product tank 4, a product gas flow rate adjustment unit 5, and a control unit 10.

The raw gas supply unit 1 has a compressor 2, a raw gas supply line L1 connected to the discharge port of the compressor 2, a first adsorption tower inlet line L1A connecting the raw gas supply line L1 to the inlet of the first adsorption tower 3A, and a second adsorption tower inlet line L1B connecting the raw gas supply line L1 to the inlet of the second adsorption tower 3B.

The compressor 2 draws in the raw material gas from the intake port, pressurizes the drawn in raw material gas, and discharges it from the discharge port, supplying the raw material gas at a predetermined pressure to the first and second adsorption towers 3A and 3B via the raw material gas supply line L1 and the first and second adsorption tower inlet lines L1A and L1B. When air is used as the raw material gas, the compressor 2 draws in air from the atmosphere. When a gas other than air is used as the raw material gas, the compressor 2 is connected to, for example, a raw material gas source in which the raw material gas is contained in a container.

The first adsorption tower inlet line L1A is provided with a first intake valve CV1. The second adsorption tower inlet line L1B is provided with a second intake valve CV3. Furthermore, a first pressure equalization line L7 is provided that connects the first adsorption tower inlet line L1A and the second adsorption tower inlet line L1B. The first pressure equalization line L7 is provided with a first pressure equalization valve CV7. The first intake valve CV1, the second intake valve CV3, and the first pressure equalization valve CV7 are configured as valves that can be switched between open and closed.

The raw gas discharge line L2 is connected to the first and second adsorption tower inlet lines L1A and L1B. The raw gas discharge line L2 has a first discharge line L2A connected to the downstream side of the first intake valve CV1 on the first adsorption tower inlet line L1A, a second discharge line L2B connected to the downstream side of the second intake valve CV3 on the second adsorption tower inlet line L1B, and a discharge junction line L2C connected to the junction of the first discharge line L2A and the second discharge line L2B. The first discharge line L2A is provided with a first discharge valve CV2. The second discharge line L2B is provided with a second discharge valve CV4. The first discharge valve CV2 and the second discharge valve CV4 are configured as valves that can be switched between open and closed.

A thermometer 11 is provided near the compressor 2. The thermometer 11 measures the ambient temperature of the compressor 2. Specifically, the thermometer 11 is provided near the intake port of the compressor 2 and measures the temperature of the raw gas sucked in by the compressor 2 through the intake port.

The first and second adsorption towers 3A and 3B are filled with an adsorbent that adsorbs oxygen gas. When raw gas is supplied from the compressor 2, the first and second adsorption towers 3A and 3B separate nitrogen gas from the raw gas by adsorbing the oxygen gas in the raw gas with the adsorbent, and generate a product gas containing a high concentration of nitrogen gas. The adsorbent filled in the first and second adsorption towers 3A and 3B may be any material that can adsorb oxygen gas, and for example, molecular sieve carbon may be used.

Molecular sieve carbon is a wood-, coal-, resin-, or pitch-based adsorbent made by carbonizing raw materials with many pores, such as charcoal, coal, coke, coconut shells, resin, and pitch, at high temperatures to adjust the pore size to about 3 to 5 angstroms. Such molecular sieve carbon has the property of adsorbing oxygen gas more easily than nitrogen gas, and has the property of selectively adsorbing oxygen gas from a mixed gas containing nitrogen gas and oxygen gas, such as air. In addition, molecular sieve carbon has an increased ability to adsorb oxygen gas under high pressure conditions. Therefore, molecular sieve carbon can adsorb a large amount of oxygen gas by pressurizing the first and second adsorption towers 3A and 3B, and then the oxygen gas can be desorbed by depressurizing the first and second adsorption towers 3A and 3B.

The product gas generated in the first and second adsorption towers 3A and 3B flows through the product gas extraction line L3 and is introduced into the product tank 4. The product gas extraction line L3 has a first adsorption tower outlet line L3A connected to the outlet of the first adsorption tower 3A, a second adsorption tower outlet line L3B connected to the outlet of the second adsorption tower 3B, and a product gas merging line L3C where the first adsorption tower outlet line L3A and the second adsorption tower outlet line L3B join together and are connected to the product tank 4.

The first adsorption tower outlet line L3A is provided with a first extraction valve CV5. The second adsorption tower outlet line L3B is provided with a second extraction valve CV6. Furthermore, a second pressure equalization line L8 is provided, connecting the upstream side of the first extraction valve CV5 in the first adsorption tower outlet line L3A to the upstream side of the second extraction valve CV6 in the second adsorption tower outlet line L3B. The second pressure equalization line L8 is provided with a second pressure equalization valve CV8. The first extraction valve CV5, the second extraction valve CV6, and the second pressure equalization valve CV8 are configured with valves that can be switched between open and closed.

A cleaning gas flow rate adjustment line L9 is connected to the second pressure equalization line L8 so as to bypass the second pressure equalization valve CV8 in the second pressure equalization line L8. The cleaning gas flow rate adjustment line L9 is configured to have a smaller pipe diameter than the second pressure equalization line L8. In other words, since the cleaning gas flow rate adjustment line L9 is a line for cleaning gas, the flow rate of the cleaning gas flowing as part of the product gas is set to be smaller than the flow rate of the product gas flowing through the second pressure equalization line L8.

The cleaning gas flow rate adjustment valve CV9 is provided in the cleaning gas flow rate adjustment line L9. The cleaning gas flow rate adjustment valve CV9 is provided to send a portion of the product gas as cleaning gas from the adsorption tower undergoing the adsorption process to the adsorption tower undergoing the desorption process, and to promote the discharge of the raw material gas remaining in the adsorption tower undergoing the desorption process. The cleaning gas flow rate adjustment valve CV9 is configured to be able to adjust the opening degree of the cleaning gas flow rate adjustment line L9 under the control of the control unit 10 described below. Note that the cleaning gas flow rate adjustment valve CV9 and the cleaning gas flow rate adjustment line L9 may be omitted. In other words, a configuration may be adopted in which cleaning gas is not flowed.

The product gas obtained in the first and second adsorption towers 3A, 3B is introduced into the product tank 4 via the product gas junction line L3C. The product tank 4 is composed of a container having a temporary storage space for appropriately storing the introduced product gas, and is used to level out the nitrogen gas concentration in the product gas stored in the product tank 4. A product gas outlet line L10 is connected to the product tank 4. The product gas stored in the product tank 4 flows out from the product tank 4 through the product gas outlet line L10. The product gas flowing out from the product tank 4 is used by the user.

The product gas outflow line L10 is provided with an oxygen concentration meter 12, a flow meter 13, and a product gas flow rate adjustment unit 5.

The oxygen concentration meter 12 measures the concentration of oxygen gas contained in the product gas flowing out from the product tank 4. The control unit 10, which will be described later, calculates the concentration of nitrogen gas in the product gas based on the oxygen gas concentration measured by the oxygen concentration meter 12, and calculates the nitrogen purity of the product gas based on the calculation result. The oxygen concentration meter 12 is located downstream of the product tank 4 on the product gas outflow line L10.

The flowmeter 13 measures the flow rate of the product gas flowing out from the product tank 4. The flowmeter 13 is disposed between the oxygen concentration meter 12 and the product gas flow rate adjustment unit 5 on the product gas outflow line L10. The flowmeter 13 may also be disposed between the product tank 4 and the oxygen concentration meter 12 on the product gas outflow line L10.

The product gas flow rate adjustment unit 5 is for adjusting the flow rate of the product gas stored in the product tank 4 that flows out from the product tank 4. The flow rate of the product gas that flows out from the product tank 4 is set based on the ambient temperature of the compressor 2. The product gas flow rate adjustment unit 5 will be described with reference to FIG. 2. The product gas flow rate adjustment unit 5 may have the configuration shown in FIG. 2(A) or the configuration shown in FIG. 2(B).

In the example shown in FIG. 2(A), the product gas flow rate adjustment unit 5 is composed of a product gas flow rate adjustment valve 51 whose opening is adjustable. By adjusting the opening of the product gas flow rate adjustment valve 51, the flow rate of the product gas flowing out from the product tank 4 can be adjusted.

In the example shown in FIG. 2(B), the product gas flow rate adjustment unit 5 is composed of multiple product gas outlet valves 52 that can be switched between open and closed. The multiple product gas outlet valves 52 are arranged in parallel on the product gas outlet line L10. By adjusting the number of valves that are opened among the multiple product gas outlet valves 52, the flow rate of the product gas flowing out from the product tank 4 can be adjusted.

The control unit 10 is electrically connected to the valves CV1 to CV8, the cleaning gas flow rate control valve CV9, and the product gas flow rate control unit 5. The control unit 10 controls the opening and closing of the valves CV1 to CV8 and the opening degree of the cleaning gas flow rate control valve CV9, and also controls the product gas flow rate control unit 5, so that the adsorption process, pressure equalization process, desorption process, and pressure equalization process can be repeatedly performed in the first and second adsorption towers 3A and 3B.

Specifically, when the first adsorption tower 3A is put into the adsorption process and the second adsorption tower 3B is put into the desorption process, the control unit 10 opens the first intake valve CV1, the first extraction valve CV5, and the second exhaust valve CV4, and closes the second intake valve CV3, the second extraction valve CV6, and the first exhaust valve CV2.

When the control unit 20 subjects the first adsorption tower 3A to the desorption process and the second adsorption tower 3B to the adsorption process, it closes the first intake valve CV1, the first extraction valve CV5, and the second exhaust valve CV4, and opens the second intake valve CV3, the second extraction valve CV6, and the first exhaust valve CV2.

When subjecting the first and second adsorption towers 3A and 3B to the pressure equalization process, the control unit 20 closes the first intake valve CV1, the second intake valve CV3, the first extraction valve CV5, and the second extraction valve CV6, and opens the first equalization valve CV7 and the second equalization valve CV8.

When the nitrogen gas separation apparatus 100 is started, the control unit 20 controls the valves CV1 to CV8 to maintain their open/closed states so that each process is performed for a preset time. In addition, when the nitrogen gas separation apparatus 100 is started, the control unit 20 controls the cleaning gas flow rate adjustment valve CV9 to a preset opening during the desorption process.

The control unit 10 also controls the product gas flow rate adjustment unit 5 based on the ambient temperature of the compressor 2 measured by the thermometer 11. This makes it possible to adjust the flow rate at which the product gas stored in the product tank 4 flows out of the product tank 4 based on the ambient temperature of the compressor 2.

Next, we will explain the nitrogen gas separation method using the nitrogen gas separation device 100 configured as described above.

First, when the nitrogen gas separation device 100 is started, the adsorption process, pressure equalization process, desorption process, and pressure equalization process are repeated for a preset time. At this time, the opening of the cleaning gas flow control valve CV9 during the adsorption process is also adjusted to a preset opening.

For example, when the adsorption process is performed in the first adsorption tower 3A, the desorption process is performed in the second adsorption tower 3B. The adsorption process is a process of separating nitrogen gas from the raw material gas to produce a product gas containing nitrogen gas. The desorption process is a process of regenerating the adsorbent by desorbing the oxygen gas adsorbed to the adsorbent from the adsorbent.

The adsorption process of the first adsorption tower 3A and the desorption process of the second adsorption tower 3B are initiated by opening the first intake valve CV1, the first extraction valve CV5, the second exhaust valve CV4, and the cleaning gas flow control valve CV9, and closing the first exhaust valve CV2, the second intake valve CV3, the second extraction valve CV6, and the first and second pressure equalization valves CV7 and CV8.

In the adsorption process of the first adsorption tower 3A, first, the raw gas is supplied from the compressor 2 to the first adsorption tower 3A through the raw gas supply line L1 and the first adsorption tower inlet line L1A. The raw gas supplied to the first adsorption tower 3A is adsorbed by the adsorbent, and nitrogen gas is separated from the raw gas to generate a product gas containing nitrogen gas. The product gas generated in the first adsorption tower 3A is introduced into the product tank 4 through the first adsorption tower outlet line L3A and the product gas merging line L3C. The product gas introduced into the product tank 4 is discharged from the product tank 4 through the product gas outflow line L10 with the flow rate adjusted by the product gas flow rate adjustment unit 5. A part of the product gas generated in the first adsorption tower 3A is sent to the second adsorption tower 3B as a cleaning gas through the cleaning gas flow rate adjustment line L9.

Meanwhile, in the desorption process of the second adsorption tower 3B, the raw material gas in the second adsorption tower 3B is discharged to the outside, which is lower than the pressure inside the second adsorption tower 3B, together with the cleaning gas via the second adsorption tower inlet line L1B, the second discharge line L2B, and the discharge junction line L2C, due to the pressure difference. This reduces the pressure inside the second adsorption tower 3B, and the oxygen gas adsorbed to the adsorbent is desorbed from the adsorbent. The desorbed oxygen gas is discharged from the second adsorption tower 3B together with the raw material gas and the cleaning gas. This regenerates the adsorbent in the second adsorption tower 3B.

When the adsorption and desorption processes are completed, the pressure equalization process is started to move the gas in the first adsorption tower 3A to the second adsorption tower 3B. The pressure equalization process is started by closing the first intake valve CV1, the first extraction valve CV5, and the second exhaust valve CV4, and opening the first and second equalization valves CV7 and CV8.

In the pressure equalization process, the gas that filled the first adsorption tower 3A moves to the second adsorption tower 3B through the first pressure equalization line L7 and the second pressure equalization line L8.

When the pressure equalization process is completed, the desorption process of the first adsorption tower 3A and the adsorption process of the second adsorption tower 3B are carried out. The desorption process of the first adsorption tower 3A and the adsorption process of the second adsorption tower 3B are started by opening the first exhaust valve CV2, the second intake valve CV3, the second extraction valve CV6, and the cleaning gas flow rate control valve CV9, and closing the first and second pressure equalization valves CV7 and CV8.

In the adsorption process of the second adsorption tower 3B, the raw gas is supplied from the compressor 2 through the raw gas supply line L1 and the second adsorption tower inlet line L1B to the second adsorption tower 3B. At this time, oxygen gas in the raw gas is adsorbed by the adsorbent, and nitrogen gas is separated from the raw gas to generate a product gas containing nitrogen gas. The product gas generated in the second adsorption tower 3B is introduced into the product tank 4 through the second adsorption tower outlet line L3B and the product gas merging line L3C. The product gas introduced into the product tank 4 is discharged from the product tank 4 through the product gas outflow line L10 with the flow rate adjusted by the product gas flow rate adjustment unit 5. A part of the product gas generated in the second adsorption tower 3B is sent to the first adsorption tower 3A as a cleaning gas through the cleaning gas flow rate adjustment line L9.

Meanwhile, in the desorption process of the first adsorption tower 3A, the raw material gas in the first adsorption tower 3A is discharged to the outside, which is lower than the pressure inside the first adsorption tower 3A, together with the cleaning gas through the first adsorption tower inlet line L1A, the first discharge line L2A, and the discharge junction line L2C, due to the pressure difference. This reduces the pressure inside the first adsorption tower 3A, and the oxygen gas adsorbed to the adsorbent is desorbed from the adsorbent. The desorbed oxygen gas is discharged from the first adsorption tower 3A together with the raw material gas and the cleaning gas. This regenerates the adsorbent in the first adsorption tower 3A.

When the desorption process in the first adsorption tower 3A and the adsorption process in the second adsorption tower 3B are completed, a pressure equalization process is carried out to move the gas in the second adsorption tower 3B to the first adsorption tower 3A.

When the pressure equalization process is completed, the adsorption process in the first adsorption tower 3A and the desorption process in the second adsorption tower 3B are carried out. After that, the above cycle is repeated in the first and second adsorption towers 3A and 3B.

Here, the compressor 2 for supplying the raw gas to the first and second adsorption towers 3A and 3B has a characteristic that the mass flow rate of the raw gas discharged from the compressor 2 increases as the ambient temperature decreases. The reason why the mass flow rate of the raw gas discharged from the compressor 2 increases with a decrease in the ambient temperature is because the gas density increases when the intake gas temperature of the compressor 2 decreases. In this way, when the mass flow rate of the raw gas discharged from the compressor 2 increases with a decrease in the ambient temperature, the pressure in the first and second adsorption towers 3A and 3B to which the raw gas is supplied tends to increase. When the pressure in the first and second adsorption towers 3A and 3B increases, the amount of oxygen gas adsorbed by the adsorbent increases, and the nitrogen purity of the product gas obtained in the first and second adsorption towers 3A and 3B may become excessively high.

In the nitrogen gas separation device 100, the pressure in the product tank 4 is adjusted by adjusting the volumetric flow rate of the product gas flowing out from the product tank 4 using the product gas flow rate adjustment unit 5 based on the ambient temperature of the compressor 2. At this time, the volumetric flow rate of the product gas flowing out from the product tank 4 is adjusted so that the nitrogen purity of the product gas flowing out from the product tank 4 becomes a predetermined target purity (e.g., 99.9%) in the range of, for example, 99% to 99.999%.

Specifically, when the ambient temperature of the compressor 2 is a first temperature (a temperature within a preset range), the product gas is discharged from the product tank 4 at a first flow rate. On the other hand, when the ambient temperature of the compressor 2 is a second temperature lower than the first temperature, the product gas is discharged from the product tank 4 at a second flow rate higher than the first flow rate. In this case, the second flow rate is set according to the ambient temperature of the compressor 2 so that the nitrogen purity of the product gas does not change from the nitrogen purity when discharged at the first flow rate, or, if it does change, it falls within a specified range. Therefore, the volumetric flow rate of the product gas discharged from the product tank 4 is adjusted to be larger the lower the ambient temperature of the compressor 2.

As described above, in this embodiment, when the ambient temperature of the compressor 2 drops to a second temperature lower than the first temperature, the product gas is discharged from the product tank 4 at a second flow rate greater than the first flow rate. Since the pressure in the product tank 4 decreases due to an increase in the flow rate of the product gas from the product tank 4, the pressure in the first and second adsorption towers 3A and 3B is less likely to increase, and an excessive increase in the pressure in each of the adsorption towers 3A and 3B can be suppressed. This makes it possible to suppress an excessive increase in the purity of the product gas obtained in the first and second adsorption towers 3A and 3B. Moreover, since the pressure in the first and second adsorption towers 3A and 3B is less likely to increase, the amount of raw material gas supplied to each of the adsorption towers 3A and 3B by the compressor 2 can be increased. As a result, when the mass flow rate of the raw material gas supplied from the compressor 2 increases in response to a decrease in the ambient temperature, the increased amount of raw material gas can be effectively used in each of the adsorption towers 3A and 3B to obtain the product gas.

In addition, by increasing the volumetric flow rate of the product gas flowing out of the product tank 4 when the ambient temperature is low, it is possible to increase the amount of product gas provided to users who use the product gas, for example, during the cold winter months or during times of the day when the temperature drops.

The volumetric flow rate of the product gas discharged from the product tank 4 is set based on flow rate index data that correlates the ambient temperature of the compressor 2, the volumetric flow rate of the raw material gas discharged from the compressor 2, and the amount of product gas with a predetermined target purity produced in the first and second adsorption towers 3A and 3B. The flow rate index data is data that represents the relationship between the volumetric flow rate of the raw material gas and the amount of product gas produced for each ambient temperature. Based on this flow rate index data, the amount of product gas produced in the first and second adsorption towers 3A and 3B using the raw material gas supplied from the compressor 2 can be grasped for each ambient temperature of the compressor 2. Then, based on the amount of product gas produced in the first and second adsorption towers 3A and 3B, the volumetric flow rate of the product gas discharged from the product tank 4 can be calculated for each ambient temperature.

In addition, experimental data showing the relationship between the volumetric flow rate of the product gas flowing out of the product tank 4 and the ambient temperature may be obtained in advance, and the volumetric flow rate of the product gas flowing out of the product tank 4 may be set based on the experimental data.

In this embodiment, the pressure in the product tank 4 is adjusted by adjusting the volumetric flow rate of the product gas flowing out from the product tank 4 using the product gas flow rate adjustment unit 5 based on the measurement result of the thermometer 11 installed near the compressor 2. Specifically, when the temperature measured by the thermometer 11 is a first temperature, the product gas is flowed out from the product tank 4 at a first flow rate. On the other hand, when the temperature measured by the thermometer 11 is a second temperature lower than the first temperature, the product gas is flowed out from the product tank 4 at a second flow rate higher than the first flow rate. In this case, the second flow rate is set according to the temperature measured by the thermometer 11 so that the nitrogen purity of the product gas does not change from the nitrogen purity when it is flowed out at the first flow rate, or, if it does change, it falls within a predetermined range. Therefore, the volumetric flow rate of the product gas flowing out from the product tank 4 is adjusted to be larger as the temperature measured by the thermometer 11 is lower.

When the temperature measured by the thermometer 11 drops to a second temperature lower than the first temperature, the product gas is discharged from the product tank 4 at a second flow rate higher than the first flow rate based on the measurement result of the thermometer 11. Since the pressure in the product tank 4 decreases due to an increase in the flow rate of the product gas flowing out from the product tank 4, the pressure in the first and second adsorption towers 3A and 3B is less likely to increase, and an excessive increase in the pressure in each of the adsorption towers 3A and 3B can be suppressed. As a result, it is possible to suppress an excessive increase in the purity of the product gas obtained in the first and second adsorption towers 3A and 3B. Moreover, since the pressure in the first and second adsorption towers 3A and 3B is less likely to increase, the amount of raw material gas supplied to each of the adsorption towers 3A and 3B by the compressor 2 can be increased. As a result, when the mass flow rate of the raw material gas supplied from the compressor 2 increases in response to a decrease in the ambient temperature, the increased amount of raw material gas can be effectively used in each of the adsorption towers 3A and 3B to obtain the product gas.

In addition, by increasing the flow rate of the product gas flowing out of the product tank 4 in response to a decrease in temperature measured by the thermometer 11, the amount of product gas provided to the user who uses the product gas can be increased based on the measurement results of the thermometer 11.

In addition, in the nitrogen gas separation apparatus 100, the control unit 10 may perform control to maintain constant the adsorption/desorption time for performing the adsorption process and the desorption process in the first and second adsorption towers 3A, 3B even when the ambient temperature of the compressor 2 drops. This makes it possible to suppress fluctuations in the maximum pressure in each of the adsorption towers 3A, 3B when performing the adsorption process in each of the first and second adsorption towers 3A, 3B, compared to a case in which the adsorption/desorption time is extended in response to a drop in the ambient temperature. This makes it possible to suppress fluctuations in the purity of the product gas obtained in each of the adsorption towers 3A, 3B.

It is desirable that the adsorption/desorption times in the first and second adsorption towers 3A, 3B be maintained constant, but they may be adjusted to vary within a predetermined tolerance range relative to a predetermined reference adsorption/desorption time. For example, the adsorption/desorption times in the first and second adsorption towers 3A, 3B are permitted to vary within a tolerance range of 80% to 120% of the reference adsorption/desorption time.

Although the nitrogen gas separation device 100 always adjusts the outflow rate of the product gas from the product tank 4 according to the measurement result of the thermometer 11, this is not limited to the above. For example, the nitrogen gas separation device 100 may be configured to be able to switch between the first mode and the second mode, and adjust the outflow rate of the product gas from the product tank 4 only when the device is switched to the second mode. That is, in the first mode, the volumetric flow rate of the product gas flowing out from the product tank 4 is maintained constant even if the ambient temperature of the compressor 2 changes. On the other hand, in the second mode, the volumetric flow rate of the product gas flowing out from the product tank 4 is adjusted according to the ambient temperature of the compressor 2, as described above.

Below, we will explain a specific example that was implemented using the nitrogen gas separation device 100 shown in Figure 1.

Example 1
In Example 1, the compressor 2 was set so that the volumetric flow rate of air as the raw material gas supplied from the compressor 2 to the first and second adsorption towers 3A, 3B was 2.2 ^m3 /min and the pressure was 0.9 MPa. The flow rate of the product gas discharged from the product tank 4 was changed to increase from 24 Nm3 ^/ h, 28 Nm3/h, ³⁰ Nm3/h, ³² Nm3/h, ³⁴ Nm3/h, and 35 Nm3/h as the ambient temperature of the compressor 2 was changed to decrease from 45°C, 35°C, 30°C, ^{20°C, 5 °} C, and 0°C. The adsorption and desorption time for performing the adsorption step and the desorption step in the first and second adsorption towers 3A, 3B was maintained constant at 40 sec.

(Comparative Example 1)
Comparative Example 1 differs from Example 1 in that the flow rate of the product gas discharged from the product tank 4 was kept constant at 24 ^Nm3 /h and the adsorption/desorption times of the first and second adsorption towers 3A, 3B were extended to 40 sec, 50 sec, 60 sec, 60 sec, 80 sec, and 80 sec, respectively, as the ambient temperature of the compressor 2 was decreased to 45° C., 35° C., 30° C., 20° C., 5° C., and 0° C. The other conditions of Comparative Example 1 were the same as those of Example 1.

Table 1 shows the maximum pressure in the first and second adsorption towers 3A and 3B, the nitrogen purity of the product gas calculated from the oxygen gas concentration measured by the oxygen concentration meter 12, and the consumption rate of the raw material gas supplied to the first and second adsorption towers 3A and 3B by the compressor 2 in the above Example 1 and Comparative Example 1. The raw material gas consumption rate is expressed as a percentage of the amount of raw material gas actually generated by the compressor 2 to obtain the product gas in the first and second adsorption towers 3A and 3B, relative to the maximum amount of raw material gas that the compressor 2 can generate (the amount of raw material gas supplied to the first and second adsorption towers 3A and 3B at the maximum capacity of the compressor 2).

As shown in Table 1, in Comparative Example 1, the nitrogen purity of the product gas was maintained constant at a predetermined target purity of 99.9% by extending the adsorption/desorption time in the first and second adsorption towers 3A and 3B in response to a decrease in the ambient temperature of the compressor 2, which makes it easier for the maximum pressure in the first and second adsorption towers 3A and 3B to increase. However, the consumption rate of the raw material gas supplied to the first and second adsorption towers 3A and 3B by the compressor 2 decreased in response to a decrease in the ambient temperature of the compressor 2. This is thought to be because, in Comparative Example 1, although the mass flow rate of the raw material gas supplied from the compressor 2 increases in response to a decrease in the ambient temperature, the increased amount of raw material gas could not be effectively utilized in the first and second adsorption towers 3A and 3B to obtain the product gas.

In contrast, in Example 1, the flow rate of the product gas flowing out of the product tank 4 was adjusted to increase in response to a decrease in the ambient temperature of the compressor 2, thereby maintaining the nitrogen purity of the product gas constant at a predetermined target purity of 99.9%. Furthermore, even when the ambient temperature of the compressor 2 changed, the consumption rate of the raw material gas supplied by the compressor 2 to the first and second adsorption towers 3A and 3B was 100%. From this, it can be seen that in Example 1, even when the ambient temperature of the compressor 2 decreases, the product gas can be obtained by effectively utilizing the raw material gas supplied from the compressor 2 in the first and second adsorption towers 3A and 3B while preventing the nitrogen purity of the product gas from increasing excessively.

Reference Signs List 1 Raw material gas supply section 2 Compressor 3A First adsorption tower 3B Second adsorption tower 4 Product tank 5 Product gas flow rate adjustment section 10 Control section 11 Thermometer 100 Nitrogen gas separation apparatus

Claims (5)

A nitrogen gas separation method comprising the steps of: supplying a feed gas containing nitrogen gas and oxygen gas under pressure from a compressor to two or more adsorption towers filled with an adsorbent; separating nitrogen gas from the feed gas as a product gas by repeatedly performing an adsorption step, a pressure equalization step, a desorption step, and a pressure equalization step in each adsorption tower; and introducing the product gas into a product tank,
A nitrogen gas separation method, comprising: when the temperature of the raw material gas sucked into the compressor is a first temperature, causing the product gas to flow out of the product tank at a first flow rate; and when the temperature of the raw material gas sucked into the compressor is a second temperature lower than the first temperature, causing the product gas to flow out of the product tank at a second flow rate higher than the first flow rate. A nitrogen gas separation method comprising the steps of: supplying a feed gas containing nitrogen gas and oxygen gas under pressure from a compressor to two or more adsorption towers filled with an adsorbent; separating nitrogen gas from the feed gas as a product gas by repeatedly performing an adsorption step, a pressure equalization step, a desorption step, and a pressure equalization step in each adsorption tower; and introducing the product gas into a product tank,
Measure the temperature of the raw material gas sucked by the compressor with a thermometer;
A nitrogen gas separation method, comprising: when the temperature measured by the thermometer is a first temperature, causing the product gas to flow out of the product tank at a first flow rate; and when the measured temperature is a second temperature lower than the first temperature, causing the product gas to flow out of the product tank at a second flow rate higher than the first flow rate. The nitrogen gas separation method according to claim 1 or 2, wherein the adsorption and desorption times for performing the adsorption and desorption steps in each of the adsorption towers are maintained constant. a compressor for pressurizing and supplying a raw material gas containing nitrogen gas and oxygen gas;
two or more adsorption towers each filled with an adsorbent, and configured to separate nitrogen gas as a product gas from the raw material gas in response to the raw material gas being supplied from the compressor;
a product tank into which the product gas obtained in each of the adsorption towers is introduced;
a flow rate adjusting unit that adjusts the flow rate of the product gas flowing out from the product tank;
a thermometer that measures the temperature of the raw material gas sucked by the compressor;
a control unit that controls the adsorption step, the pressure equalization step, the desorption step, and the pressure equalization step to be repeatedly performed in each of the adsorption towers so as to obtain the product gas,
The control unit controls the flow rate adjustment unit so that the product gas flows out of the product tank at a first flow rate when the temperature measured by the thermometer is a first temperature, and so that the product gas flows out of the product tank at a second flow rate greater than the first flow rate when the measured temperature is a second temperature lower than the first temperature. The nitrogen gas separation device according to claim 4, wherein the control unit maintains constant adsorption/desorption times for performing the adsorption process and the desorption process in each of the adsorption towers.

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