JP7784285B2 - 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 metal heat treatment, semiconductor manufacturing, and explosion-proof sealing in chemical plants, to filler gas for food preservation. Nitrogen gas is produced using the so-called pressure swing adsorption (PSA) method, in which high-pressure air (raw material) is fed into an adsorption tower filled with an adsorbent, and oxygen gas is adsorbed onto the adsorbent, resulting in nitrogen gas being separated as a product gas. An example of an apparatus that uses this PSA nitrogen gas separation method is described in Patent Document 1.

In the device described in Patent Document 1, the adsorption process is terminated when the total integrated value of the numerical value corresponding to the product nitrogen gas flow rate from the start of the adsorption process exceeds a predetermined value.

Patent No. 5559755

In the technology of Patent Document 1, the adsorption/desorption time during which each adsorption tower performs the adsorption process and desorption process is extended in response to a decrease in the product nitrogen gas flow rate. When the adsorption/desorption time is extended, the number of exhausts per unit time in the desorption process decreases, thereby reducing the amount of exhaust, thereby reducing the consumption of raw gas and achieving energy savings. However, simply setting the adsorption/desorption time based solely on the product nitrogen gas flow rate does not necessarily result in sufficient energy savings.

The present invention was made in light of these circumstances, and aims to provide a nitrogen gas separation method and nitrogen gas separation device that can obtain nitrogen gas with greater energy savings.

After extensive research, the inventors noticed that the adsorption and desorption characteristics of the adsorbent packed into the adsorption tower change in response to changes in the adsorbent's temperature. They discovered that by changing the adsorption and desorption time in response to changes in specific temperatures that can affect the adsorbent's temperature, it is possible to obtain nitrogen gas with less energy, leading to the completion of this invention.

Therefore, to solve the above problems, the present invention provides the following method and apparatus.

A nitrogen gas separation method according to the present invention includes supplying a feed gas containing nitrogen gas and oxygen gas under pressure by a compressor to two or more adsorption towers filled with an adsorbent, and each adsorption tower repeatedly performs an adsorption step, a pressure equalization step, a desorption step, and a pressure equalization step to separate nitrogen gas from the feed gas as a product gas and introduce the product gas into a product tank. In this nitrogen gas separation method, the adsorption and desorption times during which each adsorption tower performs the adsorption and desorption steps are extended relative to a reference adsorption and desorption time in response to a decrease in the flow rate of the product gas flowing out of the product tank below a reference flow rate. When a specific temperature, which is indicated by the temperature of the feed gas supplied by the compressor and which may affect the temperature of the adsorbent, is a first temperature, a first adsorption and desorption time is set longer than the reference adsorption and desorption time. When the specific temperature is a second temperature lower than the first temperature, a second adsorption and desorption time is set longer than the first adsorption and desorption time. The feed gas supply rate from the compressor is reduced as the specific temperature decreases from the first temperature to the second temperature .

According to this nitrogen gas separation method, the adsorption/desorption time during which each adsorption tower performs the adsorption and desorption processes is extended relative to the standard adsorption/desorption time in response to a decrease in the flow rate of the product gas flowing out of the product tank below the standard flow rate. When the flow rate of the product gas flowing out of the product tank decreases below the standard flow rate, the purity of the nitrogen gas obtained in the adsorption tower becomes higher than necessary. Therefore, the adsorption/desorption time during which each adsorption tower performs the adsorption and desorption processes is extended in response to a decrease in the flow rate of the product gas flowing out of the product tank. This allows a portion of the oxygen gas adsorbed by the adsorbent in the adsorption tower performing the adsorption process to be desorbed, thereby reducing the purity of the nitrogen gas, which had been increased more than necessary due to a decrease in the flow rate of the product gas flowing out of the product tank. This prevents an excessive increase in the purity of the nitrogen gas obtained in the adsorption tower performing the adsorption process. Furthermore, in the adsorption tower performing the desorption process, the number of exhausts per unit time decreases as the adsorption/desorption time is extended, thereby reducing the amount of exhaust, and therefore the supply amount of raw gas can be reduced. Therefore, nitrogen gas of the desired purity can be obtained with reduced energy consumption.

The adsorption/desorption characteristics of the adsorbent filled in the adsorption tower change with changes in the adsorbent temperature. The lower the specific temperature that can affect the adsorbent temperature, the slower the adsorbent's molecular motion, making it more difficult for oxygen gas adsorbed by the adsorbent to desorb. Focusing on these adsorption/desorption characteristics of the adsorbent, a first adsorption/desorption time longer than the reference adsorption/desorption time is set when the specific temperature is a first temperature, while a second adsorption/desorption time longer than the first adsorption/desorption time is set when the specific temperature is a second temperature lower than the first temperature. In this way, if the adsorbent exhibits characteristics that make it difficult to desorb oxygen gas as the specific temperature decreases, the adsorption/desorption time in the adsorption tower used in the adsorption process can be extended to increase the opportunities for oxygen gas to desorb from the adsorbent and prevent an excessive increase in the purity of the resulting nitrogen gas. Furthermore, by extending the adsorption/desorption time as the specific temperature decreases, the number of exhausts per unit time in the adsorption tower used in the desorption process is further reduced, thereby reducing the exhaust volume and enabling a smaller supply of raw gas. Therefore, when the flow rate of the product gas flowing out of the product tank decreases, nitrogen gas of the desired purity can be obtained with less energy in response to the decrease in the specific temperature.

A nitrogen gas separation method according to the present invention comprises supplying a feed gas containing nitrogen gas and oxygen gas under pressure by a compressor to two or more adsorption towers filled with an adsorbent, and each adsorption tower repeatedly performing an adsorption step, a pressure equalization step, a desorption step, and a pressure equalization step to separate nitrogen gas from the feed gas as a product gas. In this nitrogen gas separation method, a first adsorption/desorption time is defined as an adsorption/desorption time during which each adsorption tower performs the adsorption step and the desorption step when a specific temperature indicated by the temperature of the feed gas supplied by the compressor and which may affect the temperature of the adsorbent is a first temperature, and a second adsorption/desorption time is defined as a second adsorption/desorption time longer than the first adsorption/desorption time when the specific temperature is a second temperature lower than the first temperature, and the amount of the feed gas supplied from the compressor is reduced as the specific temperature decreases from the first temperature to the second temperature .

This nitrogen gas separation method focuses on the fact that the adsorption and desorption characteristics of the adsorbent filled in the adsorption tower change with changes in the adsorbent temperature. When a specific temperature that can affect the adsorbent temperature is a first temperature, the adsorption and desorption time during which each adsorption tower performs the adsorption and desorption processes is designated as a first adsorption and desorption time. When the specific temperature is a second temperature lower than the first temperature, the second adsorption and desorption time is set to be longer than the first adsorption and desorption time. As a result, if the adsorbent exhibits characteristics that make it difficult to desorb oxygen gas as the specific temperature decreases, the adsorption and desorption time in the adsorption tower performing the adsorption process is extended to increase the opportunities for oxygen gas to desorb from the adsorbent, thereby preventing an excessive increase in the purity of the resulting nitrogen gas. Furthermore, by extending the adsorption and desorption time as the specific temperature decreases, the number of exhausts per unit time in the adsorption tower performing the desorption process is reduced, thereby reducing the amount of exhaust, and therefore the amount of raw gas supplied. Therefore, nitrogen gas of the desired purity can be obtained with reduced energy as the specific temperature decreases.

In the above nitrogen gas separation method, the second adsorption/desorption time may be longer than the first adsorption/desorption time, but may be no longer than three times the first adsorption/desorption time.

In this aspect, when the specific temperature drops to a second temperature lower than the first temperature, each adsorption tower performs the adsorption and desorption processes for a second adsorption/desorption time that is longer than the first adsorption/desorption time but no more than three times the first adsorption/desorption time. This prevents the adsorption/desorption time from becoming unnecessarily long while maintaining the effect of obtaining nitrogen gas of the desired purity in an energy-saving manner in response to a drop in the specific temperature.

In the above-described nitrogen gas separation method, when a portion of the product gas obtained in an adsorption tower undergoing the adsorption process is discharged as cleaning gas to an adsorption tower undergoing the desorption process, the cleaning gas may be discharged at a first flow rate for a first cleaning time that is the same as the first adsorption/desorption time when the specific temperature is the first temperature, and the cleaning gas may be discharged at a second flow rate that is smaller than the first flow rate for a second cleaning time that is the same as the second adsorption/desorption time when the specific temperature is the second temperature.

In this embodiment, a portion of the product gas obtained in the adsorption tower undergoing the adsorption process is discharged as cleaning gas to the adsorption tower undergoing the desorption process. The cleaning gas promotes the discharge of gas remaining in the adsorption tower undergoing the desorption process. If cleaning gas is discharged at a constant flow rate for a cleaning time that is the same as the adsorption/desorption time, there is a risk that more product gas than necessary will be consumed as cleaning gas. Furthermore, the effect of reducing the supply amount of raw material gas by extending the adsorption/desorption time in response to a decrease in the specific temperature will be reduced as the product gas is consumed as cleaning gas.

When the specific temperature is the first temperature, the cleaning gas is discharged at a first flow rate for a first cleaning time that is the same as the first adsorption/desorption time, while when the specific temperature is the second temperature, the cleaning gas is discharged at a second flow rate that is smaller than the first flow rate for a second cleaning time that is the same as the second adsorption/desorption time. This prevents the product gas from being consumed as cleaning gas more than necessary while maintaining the effect of promoting the discharge of gas remaining in the adsorption tower by the discharge of cleaning gas. Furthermore, by reducing the consumption of product gas as cleaning gas, the supply amount of raw gas can be reduced. Therefore, when a portion of the product gas is discharged as cleaning gas, nitrogen gas of the desired purity can be obtained with reduced energy.

In the above-described nitrogen gas separation method, when a portion of the product gas obtained in an adsorption tower undergoing an adsorption process is discharged as cleaning gas to an adsorption tower undergoing a desorption process, the cleaning gas may be discharged in a first cleaning time that is shorter than the first adsorption/desorption time when the specific temperature is the first temperature, and the cleaning gas may be discharged in a second cleaning time that is shorter than the second adsorption/desorption time when the specific temperature is the second temperature.

In this aspect, when a portion of the product gas is discharged as cleaning gas, the cleaning gas is discharged for a first cleaning time that is shorter than the first adsorption/desorption time when the specific temperature is the first temperature, and the cleaning gas is discharged for a second cleaning time that is shorter than the second adsorption/desorption time when the specific temperature is the second temperature. This prevents the product gas from being consumed as cleaning gas more than necessary while maintaining the effect of promoting the discharge of gas remaining in the adsorption tower by the discharge of cleaning gas. Furthermore, by reducing the consumption of product gas as cleaning gas, the supply amount of raw gas can be reduced. Therefore, when a portion of the product gas is discharged as cleaning gas, nitrogen gas of the desired purity can be obtained with reduced energy.

The nitrogen gas separation apparatus according to the present invention comprises two or more adsorption towers filled with an adsorbent and configured to separate nitrogen gas as a product gas from a feed gas containing nitrogen gas and oxygen gas supplied under pressure by a compressor , a product tank into which the product gas obtained in each of the adsorption towers is introduced, a flowmeter for measuring the flow rate of the product gas flowing out of the product tank, a thermometer for measuring a specific temperature indicated by the temperature of the feed gas supplied by the compressor and which may affect the temperature of the adsorbent, and a control unit for controlling the repeated execution of an adsorption process, a pressure equalization process, a desorption process, and a pressure equalization process so as to obtain the product gas in each of the adsorption towers. The control unit performs adsorption/desorption control by extending the adsorption/desorption time during which each of the adsorption towers performs the adsorption and desorption processes relative to the standard adsorption/desorption time when the flow rate measured by the flowmeter decreases below a standard flow rate. In the adsorption/desorption control, the control unit performs control to set a first adsorption/desorption time that is longer than the reference adsorption/desorption time when the temperature measured by the thermometer is a first temperature, and to set a second adsorption/desorption time that is longer than the first adsorption/desorption time when the measured temperature is a second temperature that is lower than the first temperature, and reduces the amount of the raw material gas supplied from the compressor as the measured temperature decreases from the first temperature to the second temperature .

The nitrogen gas separation apparatus according to the present invention comprises two or more adsorption towers filled with an adsorbent and configured to separate nitrogen gas as a product gas from a feed gas containing nitrogen gas and oxygen gas supplied under pressure by a compressor , a thermometer configured to measure a specific temperature indicated by the temperature of the feed gas supplied by the compressor and capable of affecting the temperature of the adsorbent, and a control unit configured to control each of the adsorption towers to repeatedly perform an adsorption process, a pressure equalization process, a desorption process, and a pressure equalization process so as to obtain the product gas. The control unit controls each of the adsorption towers to perform the adsorption and desorption processes in a manner that a first adsorption/desorption time is set as an adsorption/desorption time when the temperature measured by the thermometer is a first temperature, and a second adsorption/desorption time is set as an adsorption/desorption time longer than the first adsorption/desorption time when the measured temperature is a second temperature lower than the first temperature, and reduces the amount of the feed gas supplied from the compressor as the measured temperature decreases from the first temperature to the second temperature .

In the above-mentioned nitrogen gas separation device, the control unit may be configured to control the second adsorption/desorption time to be longer than the first adsorption/desorption time, but not longer than three times the first adsorption/desorption time.

The nitrogen gas separation apparatus may further include a cleaning gas outlet line for discharging a portion of the product gas obtained in the adsorption tower undergoing the adsorption process as cleaning gas to the adsorption tower undergoing the desorption process, and a flow rate adjustment unit for adjusting the flow rate of the cleaning gas flowing through the cleaning gas outlet line. In this case, the control unit controls the flow rate adjustment unit so that when the measured temperature is the first temperature, the cleaning gas flows out of the cleaning gas outlet line at a first flow rate for a first cleaning time that is the same as the first adsorption/desorption time, and so that when the measured temperature is the second temperature, the cleaning gas flows out of the cleaning gas outlet line at a second flow rate that is smaller than the first flow rate for a second cleaning time that is the same as the second adsorption/desorption time.

The nitrogen gas separation apparatus may further include a cleaning gas outlet line for discharging a portion of the product gas obtained in the adsorption tower undergoing the adsorption process as cleaning gas to the adsorption tower undergoing the desorption process, and a flow path opening/closing unit for opening and closing the flow path of the cleaning gas outlet line. In this case, the control unit controls the flow path opening/closing unit so that when the measured temperature is the first temperature, the cleaning gas flows out of the cleaning gas outlet line in a first cleaning time that is shorter than the first adsorption/desorption time, and so that when the measured temperature is the second temperature, the cleaning gas flows out of the cleaning gas outlet line in a second cleaning time that is shorter than the second adsorption/desorption time.

As explained above, according to the present invention, nitrogen gas can be obtained with greater energy savings.

1 is a diagram showing the configuration of a nitrogen gas separation device according to one embodiment of the present invention.

The nitrogen gas separation method and nitrogen gas separation apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

The nitrogen gas separation device 1 shown in Figure 1 is a device that 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 can be, for example, air, but is not limited to this, and can be any gas that contains at least nitrogen gas and oxygen gas.

The nitrogen gas separation device 1 includes a first adsorption tower 1A and a second adsorption tower 1B, which constitute two or more adsorption towers, a product tank 2, a control unit 20, and a thermometer 23. A compressor 3 is also connected to the nitrogen gas separation device 1.

The compressor 3 draws in raw gas through an inlet, pressurizes the drawn-in raw gas, and discharges it from an outlet. The compressor 3 discharges the raw gas so that the discharge pressure is constant. A raw gas supply line L1 is connected to the discharge port of the compressor 3. The raw gas supply line L1 is connected to the inlet of the first adsorption tower 1A via the first adsorption tower inlet line L1A, and to the inlet of the second adsorption tower 1B via the second adsorption tower inlet line L1B. The compressor 3 supplies raw gas at a predetermined pressure to the first and second adsorption towers 1A and 1B via the raw gas supply line L1 and the first and second adsorption tower inlet lines L1A and L1B. When air is used as the raw gas, the compressor 3 draws air from the atmosphere. When a gas other than air is used as the raw gas, the compressor 3 is connected to a raw gas source, for example, a container containing the raw gas.

A first intake valve CV1 is provided in the first adsorption tower inlet line L1A. A second intake valve CV3 is provided in the second adsorption tower inlet line L1B. Furthermore, a first pressure equalization line L8 is provided connecting the first adsorption tower inlet line L1A and the second adsorption tower inlet line L1B. A first pressure equalization valve CV8 is provided in the first pressure equalization line L8. The first intake valve CV1, second intake valve CV3, and first pressure equalization valve CV8 are configured as valves that can be switched between open and closed states.

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

The first adsorption tower 1A and the second adsorption tower 1B are filled with an adsorbent that adsorbs oxygen gas. When raw gas is supplied from the compressor 3, the first adsorption tower 1A and the second adsorption tower 1B separate nitrogen gas from the raw gas by adsorbing the oxygen gas in the raw gas with the adsorbent, and produce a product gas containing a high concentration of nitrogen gas. The adsorbent filled in the first and second adsorption towers 1A and 1B may be any material that can adsorb oxygen gas, such as molecular sieve carbon.

Molecular sieve carbon is a wood-, coal-, resin-, or pitch-based adsorbent made by carbonizing pores at high temperatures from materials with numerous pores, such as charcoal, coal, coke, coconut shells, resin, and pitch, to adjust the pore size to approximately 3 to 5 angstroms. Such molecular sieve carbon has the property of adsorbing oxygen gas more easily than nitrogen gas, and is capable of selectively adsorbing oxygen gas from mixed gases containing nitrogen gas and oxygen gas, such as air. Furthermore, molecular sieve carbon's oxygen gas adsorption capacity increases under high-pressure conditions. Therefore, molecular sieve carbon can adsorb large amounts of oxygen gas by pressurizing the first and second adsorption towers 1A and 1B, and then desorb the oxygen gas by depressurizing the first and second adsorption towers 1A and 1B.

The product gas produced in the first and second adsorption towers 1A and 1B flows through the product gas withdrawal line L3 and is introduced into the product tank 2. The product gas withdrawal line L3 includes a first adsorption tower outlet line L3A connected to the outlet of the first adsorption tower 1A, a second adsorption tower outlet line L3B connected to the outlet of the second adsorption tower 1B, and a product gas confluence line L3C where the first adsorption tower outlet line L3A and the second adsorption tower outlet line L3B join and are connected to the product tank 2.

A first extraction valve CV5 is provided in the first adsorption tower outlet line L3A. A second extraction valve CV6 is provided in the second adsorption tower outlet line L3B. Furthermore, a second equalization line L7 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. A second equalization valve CV7 is provided in the second equalization line L7. The first extraction valve CV5, second extraction valve CV6, and second equalization valve CV7 are each composed of valves that can be switched on and off.

A cleaning gas outflow line L9 is connected to the second equalizing line L7 so as to bypass the second equalizing valve CV7 on the second equalizing line L7. The cleaning gas outflow line L9 is configured to have a smaller pipe diameter than the second equalizing line L7. In other words, because the cleaning gas outflow 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 equalizing line L7.

A cleaning gas flow rate adjustment valve CV9 is provided in the cleaning gas outlet 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, thereby facilitating the discharge of raw material gas remaining in the adsorption tower undergoing the desorption process. The cleaning gas flow rate adjustment valve CV9 is configured to adjust the aperture of the cleaning gas outlet line L9 under the control of the control unit 20, described below. The cleaning gas flow rate adjustment valve CV9 functions as a flow rate adjustment unit that adjusts the flow rate of the cleaning gas flowing through the cleaning gas outlet line L9 by adjusting the aperture of the cleaning gas outlet line L9. The cleaning gas flow rate adjustment valve CV9 also functions as a flow path opening/closing unit that opens and closes the flow path of the cleaning gas outlet line L9.

The product gas obtained in the first and second adsorption towers 1A and 1B is introduced into the product tank 2 via the product gas merging line L3C. The product tank 2 is composed of a container with a temporary storage space that appropriately stores the introduced product gas, and equalizes the nitrogen gas concentration in the product gas stored in the product tank 2. A product gas outlet line L10 is connected to the product tank 2. The product gas stored in the product tank 2 is discharged from the product tank 2 through the product gas outlet line L10. The product gas discharged from the product tank 2 is used by the user.

The product gas outflow line L10 is equipped with an oxygen concentration meter 21, a flow meter 22, and a product gas outflow valve 10.

The oxygen concentration meter 21 measures the concentration of oxygen gas contained in the product gas flowing out from the product tank 2. The control unit 20, described below, calculates the concentration of nitrogen gas in the product gas based on the oxygen gas concentration measured by the oxygen concentration meter 21, and calculates the nitrogen purity of the product gas based on the calculation result. The oxygen concentration meter 21 is located downstream of the product tank 2 on the product gas outflow line L10.

The flow meter 22 measures the flow rate of the product gas flowing out from the product tank 2. The flow meter 22 is disposed on the product gas outflow line L10 between the oxygen concentration meter 21 and the product gas outflow valve 10. The flow meter 22 may also be disposed on the product gas outflow line L10 between the product tank 2 and the oxygen concentration meter 21.

The product gas outlet valve 10 is a valve for discharging the product gas stored in the product tank 2 from the product tank 2. The product gas outlet valve 10 is composed of a valve that can be switched between open and closed.

The thermometer 23 measures a specific temperature that may affect the temperature of the adsorbent filled in the first and second adsorption towers 1A and 1B. The specific temperature may be, for example, the ambient temperature of the nitrogen gas separation apparatus 1, the ambient temperature of the compressor 3, the temperature inside the first and second adsorption towers 1A and 1B, or the temperature of the raw gas supplied by the compressor 3. If the thermometer 23 is installed in the space where the nitrogen gas separation apparatus 1 is installed, the thermometer 23 measures the ambient temperature of the nitrogen gas separation apparatus 1 as the specific temperature. If the thermometer 23 is installed in the space where the compressor 3 is installed, the thermometer 23 measures the ambient temperature of the compressor 3 as the specific temperature. If the thermometer 23 is installed so that its temperature measuring section is inserted into the first and second adsorption towers 1A and 1B, the thermometer 23 measures the temperature inside the first and second adsorption towers 1A and 1B as the specific temperature. If a thermometer 23 is installed near the intake or discharge port of the compressor 3, the thermometer 23 measures the temperature of the raw material gas supplied by the compressor 3 as a specific temperature.

The range of change in the specific temperature assumes the environment in which the nitrogen gas separation device 1 is installed, ranging from the summer ambient temperature (e.g., approximately 40°C) to the winter ambient temperature in cold regions (e.g., temperatures below freezing).

The control unit 20 is electrically connected to the valves CV1 to CV9 and the product gas outlet valve 10. The control unit 20 controls the opening and closing of the valves CV1 to CV9 in response to the opening and closing of the product gas outlet valve 10 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 1A and 1B.

Specifically, when the first adsorption tower 1A is put into the adsorption process and the second adsorption tower 1B is put into the desorption process, the control unit 20 opens the first intake valve CV1, the first extraction valve CV5, and the second discharge valve CV4, and closes the second intake valve CV3, the second extraction valve CV6, the first discharge valve CV2, the first equalizing valve CV8, and the second equalizing valve CV7.

When the first adsorption tower 1A is put into the desorption process and the second adsorption tower 1B is put into the adsorption process, the control unit 20 closes the first intake valve CV1, the first extraction valve CV5, the second discharge valve CV4, the first equalizing valve CV8, and the second equalizing valve CV7, and opens the second intake valve CV3, the second extraction valve CV6, and the first discharge valve CV2.

When subjecting the first and second adsorption towers 1A and 1B to the pressure equalization process, the control unit 20 closes the first intake valve CV1, the second intake valve CV3, the first discharge valve CV2, the second discharge valve CV4, the first extraction valve CV5, and the second extraction valve CV6, and opens the first equalization valve CV8 and the second equalization valve CV7.

By controlling the opening and closing of valves CV1 to CV8, the control unit 20 controls the adsorption and desorption times during which the first and second adsorption towers 1A, 1B perform the adsorption and desorption processes, as well as the pressure equalization time during which the first and second adsorption towers 1A, 1B perform the pressure equalization process. Furthermore, by controlling the cleaning gas flow rate adjustment valve CV9 during the desorption process, the control unit 20 adjusts the outflow flow rate of the cleaning gas and controls the cleaning time according to the outflow of the cleaning gas.

The control unit 20 controls the adsorption/desorption time in the first and second adsorption towers 1A and 1B, as well as the outflow flow rate of the cleaning gas or the cleaning time, based on the outflow flow rate of the product gas from the product tank 2 measured by the flow meter 22 in response to the opening and closing of the product gas outflow valve 10, and a specific temperature measured by the thermometer 23 that may affect the temperature of the adsorbent.

Next, we will explain the nitrogen gas separation method using the nitrogen gas separation device 1 configured as described above.

When the adsorption process is performed in the first adsorption tower 1A, the desorption process is performed in the second adsorption tower 1B. The adsorption process is a process in which nitrogen gas is separated from the feed gas to produce a product gas containing nitrogen gas. The desorption process is a process in which the adsorbent is regenerated by desorbing the oxygen gas adsorbed on the adsorbent from the adsorbent.

The adsorption process in the first adsorption tower 1A and the desorption process in the second adsorption tower 1B are initiated by opening the first intake valve CV1, the first extraction valve CV5, the second discharge 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 equalizing valves CV8 and CV7.

In the adsorption process of the first adsorption tower 1A, raw material gas is first supplied from the compressor 3 to the first adsorption tower 1A via the raw material gas supply line L1 and the first adsorption tower inlet line L1A. The oxygen gas in the raw material gas supplied to the first adsorption tower 1A is adsorbed by the adsorbent, causing nitrogen gas to be separated from the raw material gas and producing a product gas containing nitrogen gas. The product gas produced in the first adsorption tower 1A is introduced into the product tank 2 via the first adsorption tower outlet line L3A and the product gas merging line L3C. The product gas introduced into the product tank 2 is discharged from the product tank 2 through the product gas outlet line L10 by opening the product gas outlet valve 10. A portion of the product gas produced in the first adsorption tower 1A is sent as cleaning gas to the second adsorption tower 1B via the cleaning gas outlet line L9.

Meanwhile, during the desorption process in the second adsorption tower 1B, the gas inside the second adsorption tower 1B, along with the cleaning gas, is discharged via the second adsorption tower inlet line L1B, the second discharge line L2B, and the discharge junction line L2C to the outside at a pressure lower than the pressure inside the second adsorption tower 1B due to the pressure difference. This reduces the pressure inside the second adsorption tower 1B, and the oxygen gas adsorbed on the adsorbent is desorbed from the adsorbent. The desorbed oxygen gas is discharged from the second adsorption tower 1B together with the cleaning gas. This regenerates the adsorbent inside the second adsorption tower 1B.

Once the adsorption and desorption processes are completed, the pressure equalization process begins, which transfers the gas in the first adsorption tower 1A to the second adsorption tower 1B. The pressure equalization process begins 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 CV8 and CV7.

During the pressure equalization process, the gas that filled the first adsorption tower 1A moves to the second adsorption tower 1B through the first pressure equalization line L8 and the second pressure equalization line L7.

Once the pressure equalization process is complete, the desorption process in the first adsorption tower 1A and the adsorption process in the second adsorption tower 1B begin. The desorption process in the first adsorption tower 1A and the adsorption process in the second adsorption tower 1B begin by opening the first exhaust valve CV2, second intake valve CV3, second extraction valve CV6, and cleaning gas flow control valve CV9, and closing the first and second pressure equalization valves CV8 and CV7.

During the adsorption process in the second adsorption tower 1B, the raw material gas is supplied from the compressor 3 to the second adsorption tower 1B via the raw material gas supply line L1 and the second adsorption tower inlet line L1B. At this time, oxygen gas in the raw material gas is adsorbed by the adsorbent, and nitrogen gas is separated from the raw material gas to produce a product gas containing nitrogen gas. The product gas produced in the second adsorption tower 1B is introduced into the product tank 2 via the second adsorption tower outlet line L3B and the product gas merging line L3C. The product gas introduced into the product tank 2 is discharged from the product tank 2 through the product gas outlet line L10 by opening the product gas outlet valve 10. A portion of the product gas produced in the second adsorption tower 1B is sent to the first adsorption tower 1A as cleaning gas via the cleaning gas outlet line L9.

Meanwhile, during the desorption process in the first adsorption tower 1A, the gas inside the first adsorption tower 1A, along with the cleaning gas, is discharged to the outside at a pressure lower than the pressure inside the first adsorption tower 1A via 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 1A, and the oxygen gas adsorbed on the adsorbent is desorbed from the adsorbent. The desorbed oxygen gas is discharged from the first adsorption tower 1A together with the cleaning gas. This regenerates the adsorbent inside the first adsorption tower 1A.

Once the desorption process in the first adsorption tower 1A and the adsorption process in the second adsorption tower 1B are completed, a pressure equalization process is carried out to transfer the gas in the second adsorption tower 1B to the first adsorption tower 1A.

Once the pressure equalization process is complete, the adsorption process in the first adsorption tower 1A and the desorption process in the second adsorption tower 1B are carried out. The above cycle is then repeated in the first and second adsorption towers 1A and 1B.

Here, compressor 3 has the characteristic that the efficiency of raw material gas production improves as a specific temperature, including the ambient temperature of compressor 3, decreases. Therefore, as the specific temperature decreases, compressor 3 generates more raw material gas, which makes it easier for the pressure in first and second adsorption towers 1A, 1B, to which raw material gas is supplied from compressor 3, to increase. If the pressure in first and second adsorption towers 1A, 1B increases, the purity of the nitrogen gas obtained in first and second adsorption towers 1A, 1B may become higher than necessary.

Furthermore, the adsorption and desorption characteristics of the adsorbent filled in the first and second adsorption towers 1A and 1B change in response to changes in the adsorbent temperature. The lower the specific temperature that can affect the adsorbent temperature, the slower the adsorbent's molecular motion, making it more difficult for oxygen gas adsorbed by the adsorbent to be desorbed. The nitrogen gas separation device 1 of this embodiment focuses on the adsorption and desorption characteristics of the adsorbent as described above, and changes the adsorption and desorption time in the first and second adsorption towers 1A and 1B in response to changes in the specific temperature measured by the thermometer 23. In this case, regardless of the product gas outflow flow rate from the product tank 2 measured by the flowmeter 22, the adsorption and desorption time in the first and second adsorption towers 1A and 1B is changed in response to changes in the specific temperature measured by the thermometer 23. Therefore, the installation of the flowmeter 22 may be omitted.

Specifically, the control unit 20 controls the adsorption/desorption time in the first and second adsorption towers 1A and 1B to be the first adsorption/desorption time when the specific temperature measured by the thermometer 23 is the first temperature, and to be the second adsorption/desorption time, which is longer than the first adsorption/desorption time, when the specific temperature is the second temperature, which is lower than the first temperature. As a result, if the adsorbent exhibits characteristics that make it difficult to desorb oxygen gas as the specific temperature decreases, the adsorption/desorption time in the adsorption towers performing the adsorption process is extended to increase the opportunities for oxygen gas to desorb from the adsorbent, thereby preventing an excessive increase in the purity of the resulting nitrogen gas. Furthermore, by extending the adsorption/desorption time as the specific temperature decreases, the number of exhausts per unit time in the adsorption towers performing the desorption process is reduced, thereby reducing the amount of exhaust, and therefore the amount of raw gas supplied from the compressor 3. Therefore, nitrogen gas of the desired purity can be obtained with reduced energy as the specific temperature decreases.

Furthermore, in the nitrogen gas separation apparatus 1, if the flow rate of the product gas flowing out of the product tank 2 decreases below the reference flow rate, the purity of the nitrogen gas obtained in the first and second adsorption towers 1A and 1B will be higher than necessary.

Therefore, in the nitrogen gas separation apparatus 1 according to this embodiment, the adsorption and desorption times in the first and second adsorption towers 1A and 1B are controlled based on the outflow flow rate of the product gas from the product tank 2 measured by the flow meter 22 and a specific temperature that may affect the temperature of the adsorbent measured by the thermometer 23.

Specifically, the control unit 20 performs adsorption/desorption control to extend the adsorption/desorption time in the first and second adsorption towers 1A and 1B relative to the reference adsorption/desorption time in response to a decrease in the product gas outflow rate from the product tank 2 measured by the flowmeter 22 compared to the reference flow rate. As a result, in the adsorption towers performing the adsorption process, a portion of the oxygen gas adsorbed by the adsorbent is desorbed, thereby reducing the purity of the nitrogen gas, which was increased more than necessary due to the decrease in the product gas outflow rate from the product tank 2. This prevents excessive increases in the purity of the nitrogen gas obtained in the adsorption towers performing the adsorption process. Furthermore, in the adsorption towers performing the desorption process, the number of exhausts per unit time decreases as the adsorption/desorption time increases, thereby reducing the exhaust volume, allowing the amount of raw gas supplied by the compressor 3 to be reduced. Therefore, nitrogen gas of the desired purity can be obtained with reduced energy consumption.

Furthermore, during adsorption/desorption control, the control unit 20 sets a first adsorption/desorption time longer than the reference adsorption/desorption time when the specific temperature measured by the thermometer 23 is a first temperature, and sets a second adsorption/desorption time longer than the first adsorption/desorption time when the specific temperature is a second temperature lower than the first temperature. As a result, if the adsorbent exhibits characteristics that make it difficult to desorb oxygen gas as the specific temperature decreases, the adsorption/desorption time in the adsorption tower used in the adsorption process is lengthened to increase the opportunities for oxygen gas to desorb from the adsorbent, thereby preventing an excessive increase in the purity of the resulting nitrogen gas. Furthermore, by lengthening the adsorption/desorption time as the specific temperature decreases, the number of exhausts per unit time in the adsorption tower used in the desorption process is further reduced, thereby reducing the amount of exhaust, and thereby reducing the amount of raw gas supplied by the compressor 3. Therefore, when the flow rate of product gas flowing out of the product tank 2 decreases, nitrogen gas of the desired purity can be obtained with greater energy savings as the specific temperature decreases.

Furthermore, during adsorption/desorption control, the control unit 20 controls the second adsorption/desorption time to be longer than the first adsorption/desorption time but not more than three times the first adsorption/desorption time. In this case, when the specific temperature measured by the thermometer 23 drops to a second temperature lower than the first temperature, the first and second adsorption towers 1A, 1B perform the adsorption and desorption processes for a second adsorption/desorption time that is longer than the first adsorption/desorption time but not more than three times the first adsorption/desorption time. This prevents the adsorption/desorption time from becoming unnecessarily long while maintaining the effect of obtaining nitrogen gas of the desired purity in an energy-saving manner in response to a drop in the specific temperature.

In addition, in the nitrogen gas separation apparatus 1 according to this embodiment, a portion of the product gas obtained in the adsorption tower undergoing the adsorption process is discharged as cleaning gas via the cleaning gas outlet line L9 to the adsorption tower undergoing the desorption process. The cleaning gas promotes the discharge of gas remaining in the adsorption tower undergoing the desorption process.

If the cleaning gas is discharged at a constant flow rate for a cleaning time that is the same as the adsorption/desorption time, there is a risk that more product gas than necessary will be consumed as cleaning gas. Furthermore, the effect of reducing the amount of raw material gas supplied by lengthening the adsorption/desorption time in response to a decrease in the specific temperature measured by the thermometer 23 will be reduced as the product gas is consumed as cleaning gas.

Therefore, the control unit 20 controls the cleaning gas flow rate adjustment valve CV9 so that when the specific temperature measured by the thermometer 23 is the first temperature, the cleaning gas flows out of the cleaning gas outlet line L9 at a first flow rate during the first cleaning time, which is the same as the first adsorption/desorption time. When the specific temperature is the second temperature, the cleaning gas flows out of the cleaning gas outlet line L9 at a second flow rate, which is smaller than the first flow rate, during the second cleaning time, which is the same as the second adsorption/desorption time. This prevents the product gas from being consumed more than necessary as cleaning gas, while maintaining the effect of promoting the discharge of gas remaining in the adsorption tower by the flow of cleaning gas into the adsorption tower undergoing the desorption process. Furthermore, by reducing the consumption of product gas as cleaning gas, the amount of raw gas supplied by the compressor 3 can be reduced. Therefore, when a portion of the product gas is discharged as cleaning gas, nitrogen gas of the desired purity can be obtained with reduced energy consumption.

In this case, the control unit 20 may control the cleaning gas flow control valve CV9 so that when the specific temperature measured by the thermometer 23 is the first temperature, the cleaning gas flows out of the cleaning gas outlet line L9 for a first cleaning time shorter than the first adsorption/desorption time, and when the specific temperature is the second temperature, the cleaning gas flows out of the cleaning gas outlet line L9 for a second cleaning time shorter than the second adsorption/desorption time. In this case, the outflow flow rate of the cleaning gas in the cleaning gas outlet line L9 is maintained constant at a reference cleaning gas flow rate set corresponding to the reference adsorption/desorption time. The first and second cleaning times may be the same, or the second cleaning time may be shorter than the first cleaning time. By shortening the cleaning time compared to the adsorption/desorption time while maintaining a constant outflow flow rate of the cleaning gas, the effect of promoting the discharge of gas remaining in the adsorption tower by the outflow of cleaning gas into the adsorption tower undergoing the desorption process can be maintained, while suppressing the unnecessary consumption of product gas as cleaning gas. Furthermore, by reducing the consumption of product gas as cleaning gas, the amount of raw gas supplied by compressor 3 can be reduced. Therefore, when a portion of the product gas is discharged as cleaning gas, nitrogen gas of the desired purity can be obtained with less energy.

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

Example 1
In Example 1, as shown in Table 1 below, when the flow rate of the product gas flowing out of product tank 2 was the standard flow rate of 20 Nm ³ /h, the adsorption/desorption time in the first and second adsorption towers 1A and 1B was set to the standard adsorption/desorption time of 40 seconds, the flow rate of the cleaning gas was set to the standard cleaning gas flow rate of 4.0 Nm ³ /h, and the cleaning time with the cleaning gas was set to the standard cleaning time of 40 seconds. Then, as the flow rate of the product gas flowing out of product tank 2 decreased from the standard flow rate of 20 Nm ³ /h to 15 Nm ³ /h, 10 Nm ³ /h, and 7 Nm ³ /h, the adsorption/desorption time in the first and second adsorption towers 1A and 1B was extended from the standard adsorption/desorption time of 40 seconds, the flow rate of the cleaning gas was maintained constant at the standard cleaning gas flow rate, and the cleaning time was set to the same as the extended adsorption/desorption time. Furthermore, when the flow rate of the product gas flowing out of the product tank 2 decreased relative to the reference flow rate, the adsorption/desorption time in the first and second adsorption towers 1A and 1B was lengthened in accordance with the specific temperature measured by the thermometer 23 decreasing to 35°C, 20°C, and 5°C.

(Comparative Example 1)
In Comparative Example 1, as shown in Table 2 below, when the flow rate of the product gas flowing out of product tank 2 decreased relative to the reference flow rate, the adsorption and desorption times in first and second adsorption towers 1A and 1B were maintained constant even when the specific temperature measured by thermometer 23 decreased to 35° C., 20° C., and 5° C. Comparative Example 1 differs from Example 1 in that, except for this, the same procedures were followed as in Example 1.

Tables 1 and 2 show the raw gas volume, which indicates the amount of raw gas supplied by compressor 3, and the product gas nitrogen concentration, which indicates the nitrogen purity of the product gas, calculated from the oxygen gas concentration measured by oxygen concentration meter 21. A comparison of Tables 1 and 2 reveals that in Example 1, compared to Comparative Example 1, when the flow rate of product gas flowing out of product tank 2 decreases, the amount of raw gas supplied by compressor 3 is smaller while maintaining the nitrogen purity of the product gas at the desired purity (99.99%). This shows that in Example 1, when the flow rate of product gas flowing out of product tank 2 decreases, nitrogen gas of the desired purity can be obtained with less energy in accordance with a decrease in the specific temperature.

Example 2
In Example 2, as shown in Table 3 below, when the flow rate of the product gas flowing out of product tank 2 decreased to 15 Nm ³ /h from the reference flow rate of 20 Nm ³ /h, the adsorption/desorption times in first and second adsorption towers 1A and 1B were increased in response to the specific temperature measured by thermometer 23 decreasing to 35°C, 20°C, and 5°C, and the flow rate of the cleaning gas was decreased while keeping the cleaning time with the cleaning gas the same as the adsorption/desorption time.

As with Table 1, Table 3 shows the raw gas volume, which indicates the amount of raw gas supplied by compressor 3, and the product gas nitrogen concentration, which indicates the nitrogen purity of the product gas, calculated from the oxygen gas concentration measured by oxygen concentration meter 21. As is clear from a comparison of Tables 1 and 3, in Example 2, when a portion of the product gas is discharged as cleaning gas, if the flow rate of the product gas discharged from product tank 2 decreases, the flow rate of the cleaning gas can be reduced in accordance with the decrease in the specific temperature, thereby reducing the amount of raw gas supplied by compressor 3 while maintaining the nitrogen purity of the product gas at the desired purity (99.99%). This shows that in Example 2, when a portion of the product gas is discharged as cleaning gas, nitrogen gas of the desired purity can be obtained with reduced energy.

Example 3
In Example 3, as shown in Table 4 below, when the flow rate of the product gas flowing out of product tank 2 decreased to 15 Nm ³ /h from the reference flow rate of 20 Nm ³ /h, the adsorption/desorption times in first and second adsorption towers 1A, 1B were changed to be longer in response to the specific temperature measured by thermometer 23 decreasing to 35°C, 20°C, and 5°C, and the cleaning time using the cleaning gas was made shorter than the adsorption/desorption time while the flow rate of the cleaning gas was maintained constant at the reference cleaning gas flow rate of 4.0 Nm ³ /h. Other than this, the same procedure as in Example 1 was followed.

As with Table 1, Table 4 shows the raw gas volume, which indicates the amount of raw gas supplied by compressor 3, and the product gas nitrogen concentration, which indicates the nitrogen purity of the product gas, calculated from the oxygen gas concentration measured by oxygen concentration meter 21. As is clear from a comparison of Tables 1 and 4, in Example 3, when a portion of the product gas is discharged as cleaning gas, if the flow rate of the product gas discharged from product tank 2 decreases, the amount of raw gas supplied by compressor 3 can be reduced while maintaining the nitrogen purity of the product gas at the desired purity (99.99%) by shortening the cleaning time with cleaning gas compared to the adsorption/desorption time. This shows that in Example 3, when a portion of the product gas is discharged as cleaning gas, nitrogen gas of the desired purity can be obtained with reduced energy.

1 Nitrogen gas separation apparatus 1A First adsorption tower 1B Second adsorption tower 2 Product tank 20 Control unit 22 Flow meter 23 Thermometer CV9 Cleaning gas flow rate adjustment valve (flow rate adjustment unit, flow path opening/closing unit)
L9 Cleaning gas outflow line

Claims (10)

A nitrogen gas separation method comprising: supplying a feed gas containing nitrogen gas and oxygen gas under pressure by 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,
an adsorption/desorption time during which each of the adsorption towers performs an adsorption step and a desorption step is extended relative to the standard adsorption/desorption time in response to a decrease in the flow rate of the product gas flowing out of the product tank compared to a standard flow rate;
a first adsorption/desorption time longer than the reference adsorption/desorption time when a specific temperature , which is indicated by the temperature of the raw material gas supplied by the compressor and which may affect the temperature of the adsorbent, is a first temperature; a second adsorption/desorption time longer than the first adsorption/desorption time when the specific temperature is a second temperature lower than the first temperature; and an amount of the raw material gas supplied from the compressor is reduced as the specific temperature decreases from the first temperature to the second temperature . A nitrogen gas separation method comprising: supplying a feed gas containing nitrogen gas and oxygen gas under pressure by a compressor to two or more adsorption towers filled with an adsorbent; and 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;
a first adsorption/desorption time is an adsorption/desorption time during which each adsorption tower performs an adsorption process and a desorption process when a specific temperature , which is indicated by the temperature of the raw material gas supplied by the compressor and which may affect the temperature of the adsorbent, is a first temperature; and a second adsorption/desorption time is a second adsorption/desorption time that is longer than the first adsorption/desorption time when the specific temperature is a second temperature that is lower than the first temperature, and the amount of the raw material gas supplied from the compressor is reduced as the specific temperature decreases from the first temperature to the second temperature . The nitrogen gas separation method described in claim 1 or 2, wherein the second adsorption/desorption time is longer than the first adsorption/desorption time and is no more than three times the first adsorption/desorption time. The nitrogen gas separation method according to any one of claims 1 to 3, wherein when a portion of the product gas obtained in an adsorption tower undergoing an adsorption step is discharged as cleaning gas to an adsorption tower undergoing a desorption step, the cleaning gas is discharged at a first flow rate for a first cleaning time that is the same as the first adsorption/desorption time when the specific temperature is the first temperature, and the cleaning gas is discharged at a second flow rate that is smaller than the first flow rate for a second cleaning time that is the same as the second adsorption/desorption time when the specific temperature is the second temperature. The nitrogen gas separation method according to any one of claims 1 to 3, wherein when a portion of the product gas obtained in an adsorption tower undergoing an adsorption step is discharged as cleaning gas to an adsorption tower undergoing a desorption step, the cleaning gas is discharged for a first cleaning time shorter than the first adsorption/desorption time when the specific temperature is the first temperature, and the cleaning gas is discharged for a second cleaning time shorter than the second adsorption/desorption time when the specific temperature is the second temperature. two or more adsorption towers filled with an adsorbent, each of which separates nitrogen gas as a product gas from a raw material gas containing nitrogen gas and oxygen gas in response to the raw material gas being supplied under pressure by a compressor ;
a product tank into which the product gas obtained in each of the adsorption towers is introduced;
a flow meter that measures the flow rate of the product gas flowing out of the product tank;
a thermometer for measuring a specific temperature indicated by the temperature of the raw material gas supplied by the compressor and which may affect the temperature of the adsorbent;
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
In response to the flow rate measured by the flow meter decreasing below the reference flow rate, an adsorption/desorption control is performed to extend the adsorption/desorption time during which each of the adsorption towers performs the adsorption step and the desorption step relative to the reference adsorption/desorption time;
The adsorption/desorption control is performed by setting a first adsorption/desorption time that is longer than the reference adsorption/desorption time when the temperature measured by the thermometer is a first temperature, and setting a second adsorption/desorption time that is longer than the first adsorption/desorption time when the measured temperature is a second temperature that is lower than the first temperature, and by reducing the amount of the raw material gas supplied from the compressor as the measured temperature decreases from the first temperature to the second temperature . two or more adsorption towers filled with an adsorbent, each of which separates nitrogen gas as a product gas from a raw material gas containing nitrogen gas and oxygen gas in response to the raw material gas being supplied under pressure by a compressor ;
a thermometer for measuring a specific temperature indicated by the temperature of the raw material gas supplied by the compressor and which may affect the temperature of the adsorbent;
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 adsorption/desorption time, during which each adsorption tower performs the adsorption process and the desorption process, to be a first adsorption/desorption time when the temperature measured by the thermometer is a first temperature, and to be a second adsorption/desorption time that is longer than the first adsorption/desorption time when the measured temperature is a second temperature that is lower than the first temperature, and reduces the amount of the raw material gas supplied from the compressor as the measured temperature decreases from the first temperature to the second temperature . The nitrogen gas separation apparatus according to claim 6 or 7, wherein the control unit controls the second adsorption/desorption time to be longer than the first adsorption/desorption time and not more than three times the first adsorption/desorption time. a cleaning gas outflow line for allowing a portion of the product gas obtained in the adsorption tower subjected to the adsorption step to flow as cleaning gas to the adsorption tower subjected to the desorption step;
a flow rate adjusting unit that adjusts the flow rate of the cleaning gas flowing through the cleaning gas outflow line,
The nitrogen gas separation apparatus according to any one of claims 6 to 8, wherein the control unit controls the flow rate adjustment unit so that the cleaning gas flows out of the cleaning gas outflow line at a first flow rate during a first cleaning time that is the same as the first adsorption/desorption time when the measured temperature is the first temperature, and so that the cleaning gas flows out of the cleaning gas outflow line at a second flow rate that is smaller than the first flow rate during a second cleaning time that is the same as the second adsorption/desorption time when the measured temperature is the second temperature. a cleaning gas outflow line for allowing a portion of the product gas obtained in the adsorption tower subjected to the adsorption step to flow as cleaning gas to the adsorption tower subjected to the desorption step;
a flow path opening/closing unit that opens and closes a flow path of the cleaning gas outflow line,
The nitrogen gas separation apparatus according to any one of claims 6 to 8, wherein the control unit controls the flow path opening and closing unit so that the cleaning gas flows out of the cleaning gas outflow line in a first cleaning time that is shorter than the first adsorption/desorption time when the measured temperature is the first temperature, and so that the cleaning gas flows out of the cleaning gas outflow line in a second cleaning time that is shorter than the second adsorption/desorption time when the measured temperature is the second temperature.