Nitrogen gas separation method and nitrogen gas separation device

Abstract

To shorten the time required for the preparation drive of a PSA type separation unit.SOLUTION: A separation unit 1 comprises: absorption towers 1A, 1B; a product tank 2; a product gas line L10, provided with an open / close mechanism 10 to supply a product gas reserved in the product tank 2 to the demand side; a branch line L11 branching from the product gas line L10; and a control part 20, which makes drive control for repeating an adsorption process, a pressure equalization process, a desorption process, the pressure equalization process in each adsorption tower. In a preparation drive for making the concentration of the nitrogen gas in the product tank 2 reach a predetermined concentration by executing the process for separating the nitrogen gas from the raw material gas in the adsorption towers 1A, 1B in the state that the open / close mechanism 10 is closed, the branch line L11 discharges the gas in the product tank 2 so that a gas of a flow rate smaller than the flow rate of the gas flowing out of the adsorption towers 1A, 1B can flow out of the adsorption towers 1A, 1B on steady drive.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nitrogen gas separation method and a nitrogen gas separation apparatus. [Background technology]

[0002] In recent years, nitrogen gas has been used in a wide variety of fields, from industrial gases used in the heat treatment of metals, the manufacture of semiconductors, and explosion-proof seals in chemical plants to filled gases for food preservation. Nitrogen gas is produced by a so-called pressure swing adsorption (PSA) method, in which high-pressure air, a raw material gas, is fed into an adsorption tower filled with an adsorbent, and oxygen gas is adsorbed onto the adsorbent, resulting in the separation of nitrogen gas as a product gas. For example, a device using this PSA-based nitrogen gas separation method is known, as described in Patent Document 1.

[0003] In such a PSA separation apparatus, as disclosed in Patent Document 1, the nitrogen concentration of the gas flowing out of the adsorption tower does not reach a predetermined value at the start of operation of the apparatus, so the gas in the product tank is discharged into the atmosphere until the nitrogen concentration reaches the predetermined value. Once it is confirmed that the predetermined purity has been reached, the discharge of the gas in the product tank is stopped and the gas is supplied to the consumer as product gas. However, with this method, the higher the required nitrogen gas purity, the longer it takes to reach the predetermined purity, so there is a need to shorten the time required for warm-up operation performed at the start of operation of the separation apparatus.

[0004] Therefore, in Patent Document 1, at the start of operation, the pressure inside the adsorption tower is increased by repeating a predetermined cycle of adsorption and regeneration with the communication between the adsorption tower and the product tank closed, thereby more quickly increasing the concentration of nitrogen gas flowing out of the adsorption tower. Meanwhile, Patent Document 2 discloses a method in which, during a purification operation performed before steady-state operation, gas flowing out of the adsorption tower is introduced into a product gas supply line through a bypass that does not pass through the product tank, and at least a portion of this gas is returned to the outlet side of the adsorption tower through a reflux line. This method prevents a decrease in the gas purity in the product tank, and quickly increases the gas purity in the product tank by switching to introducing gas into the product tank when the gas concentration from the adsorption tower reaches a predetermined concentration. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 6-93967 [Patent Document 2] Patent No. 6231363 Summary of the Invention [Problem to be solved by the invention]

[0006] In the nitrogen gas separation methods disclosed in Patent Documents 1 and 2, gas from the adsorption tower is prevented from flowing into the product tank during warm-up operation until the nitrogen concentration reaches a predetermined value, and the gas in the product tank is not discharged into the atmosphere. In other words, these methods are performed under the assumption that the nitrogen gas concentration of the gas in the product tank is maintained at a predetermined concentration at the start of operation. However, in actual use, the nitrogen gas concentration of the gas in the product tank is not necessarily maintained at a predetermined concentration at the start of operation of the separation device. Therefore, there is a need to perform warm-up operation methods other than those disclosed in Patent Documents 1 and 2, and to shorten the time required for warm-up operation.

[0007] The present invention has been made in view of the above-mentioned prior art, and an object of the present invention is to shorten the time required for warm-up operation of a PSA type separation device. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides a nitrogen gas separation method using a nitrogen gas separation apparatus having two or more adsorption towers filled with adsorbent and a product tank, in which a raw material gas containing nitrogen gas and oxygen gas is supplied to the nitrogen gas separation apparatus under pressure, and each adsorption tower repeats an adsorption process, a pressure equalization process, a desorption process, and a pressure equalization process, thereby obtaining nitrogen gas which is stored in the product tank as a product gas of a predetermined concentration.When the nitrogen gas separation apparatus is started up, a preparatory operation is performed in which nitrogen gas is separated from the raw material gas in the adsorption towers while gas is released from the product tank, so that the concentration of nitrogen gas in the product tank reaches a predetermined concentration, and during the preparatory operation, gas is discharged from the adsorption towers at a flow rate lower than the gas flow rate discharged from the adsorption towers during steady-state operation in which the product gas in the product tank is supplied to the demand side.

[0009] In the nitrogen gas separation method according to the present invention, a warm-up operation is performed before steady-state operation. During this warm-up operation, nitrogen gas is separated from the feed gas in the adsorption tower while the gas in the product tank is discharged. During this warm-up operation, the flow rate of the gas discharged from the adsorption tower is set lower than the flow rate of the gas discharged from the adsorption tower during steady-state operation. Therefore, during the warm-up operation, the feed gas passes through the adsorption tower at a slower rate (the time it takes to pass through the adsorption tower increases), thereby increasing the nitrogen gas concentration of the gas discharged from the adsorption tower. Therefore, even if the flow rate of the gas discharged from the adsorption tower is reduced, the time required for the warm-up operation (start-up time) until the nitrogen gas concentration in the product tank reaches a predetermined concentration can be shortened. Furthermore, since the gas in the product tank is discharged from the product tank during the warm-up operation, even if gas with a low nitrogen gas concentration remains in the product tank, the low-purity gas is prevented from remaining in the product tank.

[0010] In the preparatory operation, the gas may be discharged from the adsorption tower at a flow rate that is 10% to 90% of the flow rate of the gas discharged from the adsorption tower during steady-state operation.

[0011] In this embodiment, the time required for the nitrogen gas concentration in the product tank to reach a predetermined concentration (arrival time) can be halved compared to when gas is discharged from the adsorption tower at the same flow rate as the outflow gas flow rate during steady-state operation. Moreover, the arrival time can be shortened whether or not nitrogen gas remains in the product tank during startup of the nitrogen gas separation apparatus. Therefore, there is no need to check whether nitrogen gas remains in the product tank in order to reliably shorten the arrival time.

[0012] During the preparatory operation, gas may be released from the product tank through a branch line branching off from the product gas line that supplies product gas from the product tank to the demand side at a flow rate that is smaller than the flow rate of product gas supplied to the demand side through the product gas line during steady-state operation.

[0013] In this embodiment, the flow rate of gas released through the branch line during warm-up operation is adjusted to a flow rate smaller than the flow rate of gas supplied from the product tank to the demand side through the product gas line during steady-state operation. Accordingly, the flow rate of gas released from the adsorption tower during warm-up operation is smaller than the flow rate of gas released from the adsorption tower during steady-state operation. In other words, by adjusting the flow rate of gas released from the product tank, it is possible to limit the flow rate of gas released from the adsorption tower. Therefore, the flow rate of gas released from the adsorption tower can be reduced while pressure is accumulated in the product tank.

[0014] The present invention provides a nitrogen gas separation apparatus comprising: two or more adsorption towers, each filled with an adsorbent, which are supplied with a pressurized feed gas containing nitrogen gas and oxygen gas and which separate nitrogen gas from the feed gas; a product tank for storing the nitrogen gas flowing out of the adsorption towers as a product gas of a predetermined concentration; a product gas line equipped with an opening and closing mechanism and which supplies the product gas stored in the product tank to a demand side; a branch line branching off from the product gas line at a position upstream of the opening and closing mechanism; and a control unit for controlling operation to repeatedly perform an adsorption step, a pressure equalization step, a desorption step, and a pressure equalization step in each adsorption tower, wherein, during preparatory operation in which the adsorption tower separates nitrogen gas from the feed gas with the product gas line closed by the opening and closing mechanism, the branch line releases gas in the product tank so that the gas flows out of the adsorption tower at a flow rate smaller than the flow rate of gas flowing out of the adsorption tower during steady-state operation in which the product gas in the product tank is supplied to a demand side.

[0015] In the nitrogen gas separation apparatus according to the present invention, a warm-up operation is performed before steady-state operation. During this warm-up operation, nitrogen gas is separated from the feed gas in the adsorption tower while the gas in the product tank is released. During this warm-up operation, the flow rate of the gas flowing out of the adsorption tower is set lower than the flow rate of the gas flowing out of the adsorption tower during steady-state operation. Therefore, during the warm-up operation, the feed gas passes through the adsorption tower at a slower rate (the time it takes to pass through the adsorption tower increases), thereby increasing the nitrogen gas concentration of the gas flowing out of the adsorption tower. Therefore, even if the flow rate of the gas flowing out of the adsorption tower is reduced, the warm-up operation time (start-up time) required for the nitrogen gas concentration in the product tank to reach a predetermined concentration can be shortened. Furthermore, since the gas in the product tank is released from the product tank during the warm-up operation, even if gas with a low nitrogen gas concentration remains in the product tank, the low-purity gas is prevented from remaining in the product tank.

[0016] The branch line may allow the gas to flow out from the adsorption tower at a flow rate that is 10% to 90% of the flow rate of the gas flowing out from the adsorption tower during the steady operation.

[0017] In this embodiment, the time required for the nitrogen gas concentration in the product tank to reach a predetermined concentration (arrival time) can be halved compared to when gas is discharged from the adsorption tower at the same flow rate as the outflow gas flow rate during steady-state operation. Moreover, the arrival time can be shortened whether or not nitrogen gas remains in the product tank during startup of the nitrogen gas separation apparatus. Therefore, there is no need to check whether nitrogen gas remains in the product tank in order to reliably shorten the arrival time.

[0018] During the warm-up operation, the branch line may release the gas in the product tank at a flow rate that is smaller than the flow rate of the product gas supplied to the demand side through the product gas line during the steady operation.

[0019] In this embodiment, during warm-up operation, the flow rate of gas released through the branch line is adjusted to a flow rate smaller than the supply flow rate to the demand side through the product gas line during steady-state operation. Accordingly, during warm-up operation, the flow rate of nitrogen gas released from the adsorption tower is smaller than the flow rate of nitrogen gas released from the adsorption tower during steady-state operation. In other words, by adjusting the flow rate of gas released from the product tank, it is possible to limit the flow rate of gas released from the adsorption tower. Therefore, the flow rate of gas released from the adsorption tower can be reduced while pressure is accumulated in the product tank. [Effects of the Invention]

[0020] As described above, according to the present invention, it is possible to reduce the time required for the warm-up operation of a PSA separation device. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a diagram illustrating a schematic configuration of a nitrogen gas separation device according to an embodiment. [Figure 2]FIG. 10 is a diagram schematically illustrating the configuration of a nitrogen gas separation device according to another embodiment. [Figure 3] FIG. 10 is a diagram showing the relationship between the blow amount and the arrival time in Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0023] <Nitrogen gas separation device> The nitrogen gas separation apparatus 1 shown in Fig. 1 is an apparatus for separating 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 thereto, and may be any gas containing at least nitrogen gas and oxygen gas.

[0024] The nitrogen gas separation apparatus 1 includes a first adsorption tower 1A and a second adsorption tower 1B that constitute two or more adsorption towers, a product tank 2, and a control unit 20.

[0025] A compressor 3 is connected to the nitrogen gas separation apparatus 1. The compressor 3 pressurizes and discharges the raw material gas. The compressor 3 discharges the raw material gas so that the discharge pressure is constant, for example.

[0026] The nitrogen gas separation apparatus 1 includes a raw material gas supply line L1 connected to the discharge port of the compressor 3, a first adsorption tower inlet line L1A connecting the raw material gas supply line L1 to the inlet of the first adsorption tower 1A, and a second adsorption tower inlet line L1B connecting the raw material gas supply line L1 to the inlet of the second adsorption tower 1B. The raw material gas discharged from the compressor 3 is supplied to the first adsorption tower 1A via the raw material gas supply line L1 and the first adsorption tower inlet line L1A, and is also supplied to the second adsorption tower 1B via the raw material gas supply line L1 and the second adsorption tower inlet line L1B. When air is used as the raw material gas, the compressor 3 draws air from the atmosphere. When a gas other than air is used as the raw material gas, the compressor 3 is connected to, for example, a raw material gas source containing the raw material gas in a container.

[0027] The first adsorption tower inlet line L1A is provided with a first intake valve CV1, and the second adsorption tower inlet line L1B is provided with a second intake valve CV3. Furthermore, a first equalizing line L8 is provided connecting the first adsorption tower inlet line L1A and the second adsorption tower inlet line L1B. The first equalizing line L8 is provided with a first equalizing valve CV8. The first intake valve CV1, the second intake valve CV3, and the first equalizing valve CV8 are configured as valves that can be switched between open and closed (ON / OFF valves).

[0028] 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. The first discharge line L2A is provided with a first discharge valve CV2, and 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 (ON / OFF valves).

[0029] The first adsorption tower 1A and the second adsorption tower 1B are filled with an adsorbent that adsorbs oxygen gas more quickly than nitrogen gas. When the raw material gas is supplied from the compressor 3, the first adsorption tower 1A and the second adsorption tower 1B use the adsorbent to preferentially adsorb oxygen gas in the raw material gas, thereby separating nitrogen gas from the raw material gas and producing a gas containing nitrogen gas at a higher concentration than the raw material gas. The adsorbent filled in the first and second adsorption towers 1A and 1B may be any material that can adsorb oxygen gas, and for example, molecular sieve carbon may be used.

[0030] Molecular sieve carbon is a wood-, coal-, resin-, or pitch-based adsorbent made by carbonizing a pore-rich raw material, such as charcoal, coal, coke, coconut shell, resin, or pitch, at high temperatures to adjust the pore size to approximately 3 to 5 angstroms. Such molecular sieve carbon has the property of more easily adsorbing oxygen gas than nitrogen gas, and thus selectively adsorbs oxygen gas from a gas mixture containing nitrogen gas and oxygen gas, such as air. Furthermore, the oxygen gas adsorption capacity of molecular sieve carbon increases under high-pressure conditions. Therefore, molecular sieve carbon can adsorb more 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.

[0031] The gas produced in the first and second adsorption towers 1A, 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.

[0032] The first adsorption tower outlet line L3A is provided with a first extraction valve CV5, and the second adsorption tower outlet line L3B is provided with a second extraction valve CV6. Furthermore, a second equalization line L7 is provided, connecting a portion of the first adsorption tower outlet line L3A upstream of the first extraction valve CV5 with a portion of the second adsorption tower outlet line L3B upstream of the second extraction valve CV6. The second equalization line L7 is provided with a second equalization valve CV7. The first extraction valve CV5, the second extraction valve CV6, and the second equalization valve CV7 are configured as valves that can be switched between open and closed (ON / OFF valves).

[0033] A cleaning gas line L9 is connected to the second equalizing line L7 so as to bypass the second equalizing valve CV7 in the second equalizing line L7. The cleaning gas line L9 is configured to have a smaller pipe diameter than the second equalizing line L7. That is, since the cleaning gas line L9 is a line for cleaning gas, the flow rate of the cleaning gas flowing as part of the gas flowing out from the adsorption columns 1A and 1B is configured to be smaller than the flow rate of the gas flowing through the second equalizing line L7.

[0034] The cleaning gas line L9 is provided with a cleaning gas flow rate adjusting member CV9. The cleaning gas flow rate adjusting member CV9 is provided to send a portion of the gas from the adsorption towers 1A, 1B performing the adsorption process to the adsorption towers 1B, 1A performing the desorption process as cleaning gas, thereby facilitating the discharge of the raw material gas remaining in the adsorption towers 1B, 1A performing the desorption process. The cleaning gas flow rate adjusting member CV9 is configured with a valve capable of adjusting the aperture of the cleaning gas line L9. Note that the cleaning gas flow rate adjusting member CV9 is not limited to a valve with an adjustable aperture, and may be configured with, for example, an orifice.

[0035] The gas obtained in the first and second adsorption towers 1A, 1B is introduced into the product tank 2 via adsorption tower outlet lines L3A, L3B and product gas merging line L3C. The product tank 2 is composed of a container having a temporary storage space for appropriately storing the introduced gas, and the nitrogen gas concentration in the gas stored in the product tank 2 is leveled. As a result, gas having a predetermined nitrogen gas concentration is stored in the product tank 2 as the product gas.

[0036] A product gas line L10 is connected to the product tank 2. The product gas stored in the product tank 2 is supplied from the product tank 2 to a consumer via the product gas line L10.

[0037] An oxygen concentration meter 21, a flow meter 22, and an opening / closing mechanism 10 are provided on the product gas line L10.

[0038] Oxygen concentration meter 21 measures the concentration of oxygen gas contained in the product gas flowing out from product tank 2. Control unit 20, which will be described later, calculates the concentration of nitrogen gas in the product gas based on the oxygen gas concentration measured by oxygen concentration meter 21, and calculates the nitrogen purity of the product gas based on the calculation result.

[0039] Flow meter 22 measures the flow rate of the product gas flowing out from product tank 2. Flow meter 22 is disposed on product gas line L10 between oxygen concentration meter 21 and opening / closing mechanism 10. Note that flow meter 22 may also be disposed on product gas line L10 between product tank 2 and oxygen concentration meter 21.

[0040] The opening and closing mechanism 10 is disposed on the product gas line L10 downstream of the oxygen concentration meter 21 and the flow meter 22. The opening and closing mechanism 10 switches between a state in which the product gas stored in the product tank 2 is supplied to a demand destination and a state in which it is not supplied to a demand destination, and in this embodiment is configured by a valve (on / off valve) that can be switched between open and closed states.

[0041] The opening and closing mechanism 10 is connected to the control unit 20 so as to be able to send and receive signals, and is switched between open and closed states by signals from the control unit 20. The opening and closing mechanism 10 opens the product gas line L10 during steady operation, which will be described later, and closes the product gas line L10 during preparatory operation, which will be described later. The opening and closing mechanism 10 may also be configured to be manually switched between open and closed states.

[0042] A branch line L11 is connected to the product gas line L10 at a location downstream of the oxygen concentration meter 21 and the flow meter 22 and upstream of the opening and closing mechanism 10. The branch line L11 is a line for discharging the product gas flowing through the product gas line L10 from the product gas line L10 (or the product tank 2) when the opening and closing mechanism 10 is closed. In FIG. 1, the end of the branch line L11 is open so that the product gas can be discharged. However, as shown in FIG. 2, the branch line L11 may be connected to the feed gas inlet of the compressor 3 so that the product gas discharged from the product tank 2 is returned to the adsorption towers 1A and 1B. In this case, the product gas discharged from the product tank 2 can be reused as part of the feed gas.

[0043] The branch line L11 is configured to allow the product gas to flow at a flow rate lower than the flow rate of the product gas supplied to a demand destination through the product gas line L10. Specifically, in this embodiment, the branch line L11 is provided with a flow rate adjustment mechanism 11 that adjusts the flow rate of the product gas flowing through the branch line L11. The flow rate adjustment mechanism 11 limits the flow rate of the product gas so that the flow rate of the product gas flowing through the branch line L11 is lower than the flow rate of the product gas flowing through the product gas line L10 when the opening and closing mechanism 10 is open. Therefore, the flow rate of the product gas flowing out of the product tank 2 is reduced during the preparatory operation described below when the opening and closing mechanism 10 is closed, compared to the steady operation described below when the opening and closing mechanism 10 is open. Therefore, during the preparatory operation, the flow rate of the gas flowing out of the adsorption towers 1A and 1B is lower than the steady operation.

[0044] The flow rate adjustment mechanism 11 may be configured with a valve (on / off valve) that can be switched between on and off and an orifice, or may be configured with a valve that can adjust the opening size. The branch line L11 may be narrower than the product gas line L10. In this case, the flow rate adjustment mechanism 11 may be omitted, and a valve that opens and closes the branch line L11 may be provided. That is, the flow rate of the branch line L11 may be adjusted by the branch line L11 itself, rather than by the flow rate adjustment mechanism 11. The opening / closing mechanism 10 may be configured with a three-way valve. In this case, the flow rate adjustment mechanism 11 does not have the function of opening or closing the branch line L11, but only has the function of throttling the flow rate. The three-way valve is located at the branch point between the product gas line L10 and the branch line L11, and is configured to switch between a state in which the product gas stored in the product tank 2 flows to the demand side through the product gas line L10 and a state in which the product gas is released through the branch line L11.

[0045] The control unit 20 is electrically connected to the valves CV1 to CV8, the flow rate adjusting member CV9, the on-off mechanism 10, and the flow rate adjusting mechanism 11. The control unit 20 controls the valves CV1 to CV8, the flow rate adjusting member CV9, the on-off mechanism 10, and the flow rate adjusting mechanism 11 so that the nitrogen gas separation apparatus 1 can perform a steady operation in which the first and second adsorption towers 1A and 1B repeatedly perform an adsorption process, a pressure equalization process, a desorption process, and a pressure equalization process to obtain a product gas with a predetermined nitrogen gas concentration, and a preparatory operation that is performed prior to the steady operation when starting up the nitrogen gas separation apparatus 1. The preparatory operation includes a first preparatory operation for starting up the first adsorption tower 1A and a second preparatory operation for starting up the second adsorption tower 1B. The preparatory operation also includes a first pressure equalization operation in which a portion of the gas in the first adsorption tower 1A is transferred to the second adsorption tower 1B after the first preparatory operation, and a second pressure equalization operation in which a portion of the gas in the second adsorption tower 1B is transferred to the first adsorption tower 1A after the second preparatory operation.

[0046] During steady-state operation, 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.

[0047] In addition, when the control unit 20 subjects the first adsorption tower 1A to the desorption process and the second adsorption tower 1B to the adsorption process, it 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.

[0048] In addition, when the first and second adsorption towers 1A, 1B are subjected 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.

[0049] During the above steady-state operation, in any of the adsorption process, pressure equalization process, and desorption process, the control unit 20 controls the opening / closing mechanism 10 and the flow rate adjustment mechanism 11 so that the product gas in the product tank 2 is supplied to the demand destination and the product gas does not flow through the branch line L11. Note that if the opening / closing mechanism 10 is configured as a three-way valve, the flow rate adjustment mechanism 11 is not subject to control.

[0050] Meanwhile, in the first preparatory operation of the preparatory operation, the control unit 20 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, the first exhaust valve CV2, the first equalizing valve CV8, the second equalizing valve CV7, and the opening / closing mechanism 10. At this time, the control unit 20 sets the flow rate adjustment mechanism 11 in a state where gas can flow. In other words, the product gas in the product tank 2 is not supplied to a demand destination, but flows through the branch line L11. Furthermore, in the first equalizing operation after the first preparatory operation, the control unit 20 closes the first intake valve CV1, the first extraction valve CV5, and the second exhaust valve CV4, and opens the equalizing valves CV8 and CV7. At this time, the control unit 20 maintains the flow rate adjustment mechanism 11 in a state where gas can flow.

[0051] Furthermore, during the second preparatory operation, the control unit 20 closes the first intake valve CV1, the first extraction valve CV5, the second exhaust valve CV4, the first equalizing valve CV8, the second equalizing valve CV7, and the opening / closing mechanism 10, and opens the second intake valve CV3, the second extraction valve CV6, and the first exhaust valve CV2. At this time, the control unit 20 sets the flow rate adjustment mechanism 11 in a state that allows gas to flow. In other words, the product gas in the product tank 2 flows through the branch line L11 rather than being supplied to a demand destination. Furthermore, during the second equalizing operation after the second preparatory operation, the control unit 20 closes the second intake valve CV3, the second extraction valve CV6, and the first exhaust valve CV2, and opens the equalizing valves CV8 and CV7. At this time, the control unit 20 maintains the flow rate adjustment mechanism 11 in a state that allows gas to flow.

[0052] <Nitrogen gas separation method> Next, a nitrogen gas separation method using the nitrogen gas separation apparatus 1 configured as above will be described.

[0053] The nitrogen gas separation method includes a preparatory operation performed when starting up the nitrogen gas separation apparatus 1 and a steady-state operation performed after the preparatory operation has caused the nitrogen gas concentration in the product tank 2 to reach a predetermined value. The preparatory operations include a first preparatory operation for starting up the first adsorption tower 1A, a first pressure equalization operation performed after the first preparatory operation, a second preparatory operation for starting up the second adsorption tower 1B, and a second pressure equalization operation performed after the second preparatory operation. The first preparatory operation, the first pressure equalization operation, the second preparatory operation, and the second pressure equalization operation are performed in this order and are repeated. Note that, although the first preparatory operation is performed first here, the second preparatory operation may also be performed first.

[0054] In the first preparatory operation, the first intake valve CV1, the first outlet valve CV5, and the second outlet valve CV4 are opened, while the second intake valve CV3, the second outlet valve CV6, the first outlet valve CV2, the first equalizing valve CV8, the second equalizing valve CV7, and the opening / closing mechanism 10 are closed. At this time, the flow rate adjustment mechanism 11 is set to a state in which gas can flow through the branch line L11.

[0055] Therefore, the raw material gas discharged from the compressor 3 is supplied to the first adsorption tower 1A through the raw material gas supply line L1 and the first adsorption tower inlet line L1A. In the first adsorption tower 1A, oxygen gas is adsorbed by the adsorbent from the supplied raw material gas, producing a gas with a higher nitrogen gas concentration than the raw material gas. This gas is introduced into the product tank 2 through the first adsorption tower outlet line L3A and the product gas merging line L3C. Accordingly, the product gas in the product tank 2 is discharged through the product gas line L10 and the branch line L11.

[0056] At this time, the flow rate of gas that can flow through the product gas line L10 is limited by the flow rate adjustment mechanism 11 compared to that during steady operation, and therefore the flow rate of gas flowing out of the first adsorption tower 1A is also reduced compared to that during steady operation. As a result, the flow rate of gas passing through the first adsorption tower 1A is slower than the gas flow rate during steady operation. This increases the time that the raw material gas passes through the first adsorption tower 1A, and therefore the nitrogen gas concentration of the gas flowing out of the first adsorption tower 1A can be increased.

[0057] A portion of the gas flowing out from the first adsorption tower 1A is introduced into the second adsorption tower 1B through the cleaning gas line L9, and therefore a portion of the gas in the second adsorption tower 1B (gas with a relatively high oxygen gas concentration) is exhausted through the second exhaust line L2B and the exhaust junction line L2C.

[0058] After the first preparatory operation has been performed for a predetermined time, the system switches to first pressure equalization operation. In the first pressure equalization operation, the first intake valve CV1, the first extraction valve CV5, and the second discharge valve CV4 are closed, while the pressure equalization valves CV8 and CV7 are opened. This causes gas in the first adsorption tower 1A to move to the second adsorption tower 1B through the first equalization line L8 and the second equalization line L7. Note that even in the first pressure equalization operation, the flow rate adjustment mechanism 11 remains in a state that allows gas to flow.

[0059] After the first pressure equalization operation has been performed for a predetermined time, the operation switches to the second preparatory operation. In the second preparatory operation, the second intake valve CV3, the second outlet valve CV6, and the first discharge valve CV2 are opened, while the first intake valve CV1, the first outlet valve CV5, the second discharge valve CV4, the first equalization valve CV8, the second equalization valve CV7, and the opening / closing mechanism 10 are closed. In the second preparatory operation, as in the first preparatory operation, the flow rate adjustment mechanism 11 is set to a state in which gas can flow through the branch line L11.

[0060] During the second warm-up operation, the feed gas discharged from the compressor 3 is supplied to the second adsorption tower 1B via the feed gas supply line L1 and the second adsorption tower inlet line L1B. In the second adsorption tower 1B, oxygen gas is adsorbed onto the adsorbent from the supplied feed gas, producing a gas with a higher nitrogen gas concentration than the feed gas. This gas is then introduced into the product tank 2 via the second adsorption tower outlet line L3B and the product gas merging line L3C. Accordingly, the product gas in the product tank 2 is discharged via the product gas line L10 and the branch line L11. Because the gas flow rate through the product gas line L10 is limited by the flow rate control mechanism 11 compared to that during steady-state operation, the gas flow rate out of the second adsorption tower 1B is also reduced compared to that during steady-state operation. Therefore, the flow rate of the gas passing through the second adsorption tower 1B is slower than that during steady-state operation. This increases the time the feed gas spends passing through the second adsorption tower 1B, thereby increasing the nitrogen gas concentration of the gas outflowing from the second adsorption tower 1B.

[0061] Since a portion of the gas flowing out from the second adsorption tower 1B is introduced into the first adsorption tower 1A through the cleaning gas line L9, a portion of the gas in the first adsorption tower 1A (gas with a relatively high oxygen gas concentration) is exhausted through the first exhaust line L2A and the exhaust junction line L2C.

[0062] After the second preparatory operation has been performed for a predetermined time, the system switches to second pressure equalization operation. In the second pressure equalization operation, the second intake valve CV3, the second extraction valve CV6, and the first discharge valve CV2 are closed, while the pressure equalization valves CV8 and CV7 are opened. This causes gas in the second adsorption tower 1B to move to the first adsorption tower 1A through the first equalization line L8 and the second equalization line L7. Note that even during the second pressure equalization operation, the flow rate adjustment mechanism 11 remains in a state that allows gas to flow.

[0063] The first preparatory operation, the first pressure equalization operation, the second preparatory operation, and the second pressure equalization operation are repeated, and when the concentration of nitrogen gas in the product tank 2 reaches a predetermined concentration, the preparatory operation is terminated and the system transitions to steady-state operation.

[0064] In steady-state operation, the adsorption process, pressure equalization process, desorption process, and pressure equalization process are repeated in each of the adsorption towers 1A and 1B, but the adsorption process and desorption process are alternately performed in each of the adsorption towers 1A and 1B.

[0065] That is, when the adsorption step is performed in the first adsorption tower 1A, the desorption step is performed in the second adsorption tower 1B. The adsorption step is a step of separating nitrogen gas by adsorbing oxygen gas contained in the raw material gas onto an adsorbent, thereby producing a gas containing high-purity nitrogen gas. The desorption step is a step of regenerating the adsorbent by desorbing the oxygen gas adsorbed on the adsorbent from the adsorbent.

[0066] 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, and the second discharge valve CV4, 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. During steady-state operation, the opening / closing mechanism 10 is open, while the flow rate adjustment mechanism 11 is in a state that does not allow gas to flow.

[0067] In the adsorption step of the first adsorption tower 1A, first, a raw material gas is 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, whereby nitrogen gas is separated from the raw material gas, producing a gas containing high-purity nitrogen gas. The gas produced in the first adsorption tower 1A is introduced as a product gas 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 sent from the product tank 2 to a consumer via the product gas line L10 by opening the opening / closing mechanism 10. A portion of the product gas produced in the first adsorption tower 1A is sent as a cleaning gas to the second adsorption tower 1B via the cleaning gas line L9.

[0068] Meanwhile, during the desorption process in the second adsorption tower 1B, the gas in the second adsorption tower 1B, together 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 in the second adsorption tower 1B.

[0069] After the adsorption and desorption processes are completed, the pressure equalization process begins, in which the gas in the first adsorption tower 1A is transferred 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 discharge valve CV4, and opening the first and second equalization valves CV8 and CV7.

[0070] In the pressure equalization step, the gas that filled the first adsorption tower 1A moves to the second adsorption tower 1B through the first equalization line L8 and the second equalization line L7.

[0071] After the pressure equalization step is completed, the desorption step in the first adsorption tower 1A and the adsorption step in the second adsorption tower 1B are performed. The desorption step in the first adsorption tower 1A and the adsorption step in the second adsorption tower 1B are initiated by opening the first exhaust valve CV2, the second intake valve CV3, and the second extraction valve CV6 and closing the first and second equalization valves CV8 and CV7.

[0072] In the adsorption process of the second adsorption tower 1B, the raw material gas discharged from the compressor 3 is supplied 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, producing a gas containing high-purity nitrogen gas. The gas produced in the second adsorption tower 1B is introduced as product gas 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 supplied to a consumer from the product tank 2 via the product gas line L10 by opening the opening / closing mechanism 10. A portion of the product gas produced in the second adsorption tower 1B is sent as cleaning gas to the first adsorption tower 1A via the cleaning gas line L9.

[0073] Meanwhile, during the desorption process in the first adsorption tower 1A, the gas in the first adsorption tower 1A, together with the cleaning gas, is discharged to the outside at a pressure lower than the pressure inside the first adsorption tower 1A 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 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 in the first adsorption tower 1A.

[0074] After the desorption step in the first adsorption tower 1A and the adsorption step in the second adsorption tower 1B are completed, a pressure equalization step is carried out to transfer the gas in the second adsorption tower 1B to the first adsorption tower 1A.

[0075] After the pressure equalization step is completed, the adsorption step in the first adsorption tower 1A and the desorption step in the second adsorption tower 1B are carried out again, and the above cycle is then repeated in the first and second adsorption towers 1A and 1B. [Example]

[0076] Next, a specific example implemented using the nitrogen gas separation apparatus 1 shown in FIG. 1 will be described.

[0077] In Example 1, the nitrogen gas separation apparatus 1 is set to perform each process so that the nitrogen gas concentration of the product gas stored in the product tank 2 is 99.99% during steady operation, and the flow rate of the product gas flowing out from the product tank 2 during steady operation is 20 Nm 3 / h. In Example 1, a nitrogen gas separation apparatus 1 is used in which the capacity of each of the adsorption towers 1A and 1B is 150 L and the capacity of the product tank 2 is 180 L.

[0078] In Example 2, the nitrogen gas separation apparatus 1 is set to perform each process so that the nitrogen gas concentration of the product gas stored in the product tank 2 is 99.99% during steady operation, and the flow rate of the product gas flowing out from the product tank 2 during steady operation is 2.4 Nm 3 / h. In Example 2, a nitrogen gas separation apparatus 1 is used in which the capacity of each of the adsorption towers 1A, 1B is 1 L and the capacity of the product tank 2 is 1 L. That is, the capacities of the adsorption towers 1A, 1B and the product tank 2 are different between the nitrogen gas separation apparatus 1 used in Example 1 and the nitrogen gas separation apparatus 1 used in Example 2.

[0079] Using this nitrogen gas separation apparatus 1, operation was performed with the opening / closing mechanism 10 closed and the gas flow rate (blow rate) by the flow rate adjustment mechanism 11 varied, and the time until the nitrogen gas concentration in the product tank 2 reached a predetermined value (99.99%) was measured in each case. The results are shown in FIG. 3 and Tables 1 and 2. Table 1 shows the arrival time values ​​for Example 1, and Table 2 shows the arrival time values ​​for Example 2. The blow rate (%) represents the product gas flow rate during warm-up operation relative to the product gas flow rate during steady operation. In other words, the blow rate (%) represents the percentage of the flow rate of product gas flowing into branch line L11 while the opening / closing mechanism 10 is closed, relative to the flow rate when the opening / closing mechanism 10 is open and product gas flows into product gas line L10, but the flow rate adjustment mechanism 11 prevents product gas from flowing into branch line L11. These flow rates are measured by flowmeter 22.

[0080] Example 1 shows the results when the nitrogen gas separation apparatus 1 was started up with nitrogen gas filled in the product tank 2, and Example 2 shows the results when the nitrogen gas separation apparatus 1 was started up with nitrogen gas not filled in the product tank 2.

[0081] [Table 1]

[0082] [Table 2]

[0083] In both Examples 1 and 2, the arrival time was shortened when the blow rate was reduced compared to when the blow rate was 100%, i.e., when the gas flow rate during warm-up operation was the same as the gas flow rate during steady operation. That is, when the gas flow rate that can flow through the flow rate control mechanism 11 is limited compared to steady operation, the gas flow rate flowing out of the adsorption towers 1A and 1B is also reduced compared to steady operation, and the time it takes for the raw material gas to pass through the adsorption towers 1A and 1B becomes longer. This allows the nitrogen gas concentration of the gas flowing out of the adsorption towers 1A and 1B to be increased, which can be said to shorten the arrival time.

[0084] In particular, if the blow rate is in the range of 10% to 90%, the arrival time can be halved compared to when the blow rate is 100%. Moreover, since the results are the same whether the nitrogen gas separation apparatus 1 is started up with the product tank 2 filled with nitrogen gas or with the product tank 2 not filled with nitrogen gas, the arrival time can be halved when starting up the nitrogen gas separation apparatus 1, even without checking whether nitrogen gas remains in the product tank 2. Furthermore, the arrival time can be further shortened when the blow rate is in the range of 20% to 80%, and even further shortened when the blow rate is in the range of 40% to 70%.

[0085] As described above, in the nitrogen gas separation method according to this embodiment, a preparatory operation is performed before steady-state operation. During this preparatory operation, nitrogen gas is separated from the feed gas in the adsorption towers 1A and 1B while the gas in the product tank 2 is discharged. During this preparatory operation, the flow rate of the gas flowing out of the adsorption towers 1A and 1B is set lower than the flow rate of the gas flowing out of the adsorption towers 1A and 1B during steady-state operation. Therefore, during the preparatory operation, the feed gas passes through the adsorption towers 1A and 1B at a slower rate (the time it takes to pass through the adsorption towers 1A and 1B is longer), thereby increasing the nitrogen gas concentration of the gas flowing out of the adsorption towers 1A and 1B. Therefore, because gas with a higher nitrogen purity is supplied to the product tank 2, the time (start-up time) required for the preparatory operation until the nitrogen gas concentration in the product tank 2 reaches a predetermined concentration can be shortened, even if the flow rate of the gas flowing out of the adsorption towers 1A and 1B is reduced. Furthermore, during the preparatory operation, the gas in the product tank 2 is released from the product tank 2, so even if gas with a low nitrogen gas concentration remains in the product tank 2, such low-purity gas is prevented from remaining in the product tank 2.

[0086] In the above embodiment, during the warm-up operation, gas may be discharged from the adsorption towers 1A, 1B at a flow rate that is 10% to 90% of the flow rate of gas discharged from the adsorption towers 1A, 1B during steady-state operation. In this case, the time required for the nitrogen gas concentration in the product tank 2 to reach a predetermined concentration (arrival time) can be halved compared to when gas is discharged from the adsorption towers 1A, 1B at the same flow rate as the outflow gas flow rate during steady-state operation. Moreover, during start-up of the nitrogen gas separation apparatus 1, the arrival time can be shortened whether or not nitrogen gas remains in the product tank 2. Therefore, there is no need to check whether nitrogen gas remains in the product tank 2 in order to ensure that the arrival time can be shortened.

[0087] In the above embodiment, during the warm-up operation, the flow rate of the gas released through the branch line L11 is adjusted to a flow rate smaller than the flow rate supplied from the product tank 2 to the demand side through the product gas line L10 during steady-state operation. Accordingly, during the warm-up operation, the flow rate of the gas flowing out from the adsorption towers 1A, 1B is smaller than the flow rate of the gas flowing out from the adsorption towers 1A, 1B during steady-state operation. In other words, by adjusting the flow rate of the gas released from the product tank 2, it is possible to set a limit on the flow rate of the gas flowing out from the adsorption towers 1A, 1B. Therefore, the flow rate of the gas flowing out from the adsorption towers 1A, 1B can be reduced while accumulating pressure in the product tank 2.

[0088] It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The present invention is not limited to the above-described embodiments, and various modifications and improvements are possible without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0089] 1: Nitrogen gas separator 1A: 1st adsorption tower 1B:Second adsorption tower 2:Product tank 10: Opening and closing mechanism 11:Flow rate adjustment mechanism 20: Control section L10: Product gas line L11: Branch line

Claims

1. A nitrogen gas separation method using a nitrogen gas separation apparatus having two or more adsorption towers filled with an adsorbent and a product tank, supplying a raw material gas containing nitrogen gas and oxygen gas under pressure to the nitrogen gas separation apparatus, and storing the nitrogen gas obtained by repeating an adsorption step, a pressure equalization step, a desorption step, and a pressure equalization step in each adsorption tower as a product gas of a predetermined concentration in the product tank, At the start-up of the nitrogen gas separation apparatus, a preparatory operation is performed in which nitrogen gas is separated from the raw material gas in the adsorption tower while gas is released from the product tank, and the concentration of nitrogen gas in the product tank reaches a predetermined concentration; In the preparatory operation, gas is released from the product tank at a flow rate smaller than the flow rate of the product gas supplied to the demand side through the product gas line during steady-state operation in which the product gas in the product tank is supplied to the demand side through a branch line branching off from the product gas line that supplies the product gas from the product tank to the demand side, and gas is discharged from the adsorption tower at a flow rate smaller than the gas flow rate discharged from the adsorption tower during steady-state operation.

2. 2. The nitrogen gas separation method according to claim 1, wherein, during the preparatory operation, the gas is discharged from the adsorption tower at a flow rate that is 10% to 90% of the gas flow rate that is discharged from the adsorption tower during the steady operation.

3. A nitrogen gas separation apparatus, two or more adsorption towers, each filled with an adsorbent, to which a raw material gas containing nitrogen gas and oxygen gas is supplied under pressure and which separate nitrogen gas from the raw material gas; a product tank for storing the nitrogen gas flowing out from the adsorption tower as a product gas of a predetermined concentration; a product gas line that is provided with an opening / closing mechanism and that supplies the product gas stored in the product tank to a demand side; a branch line branching off from a portion of the product gas line upstream of the opening and closing mechanism; a control unit that controls operation for a preparatory operation when starting up the nitrogen gas separation apparatus and a steady-state operation that is performed after the nitrogen gas concentration in the product tank has reached a predetermined value through the preparatory operation, in which an adsorption step, a pressure equalization step, a desorption step, and a pressure equalization step are repeatedly performed in each adsorption tower; Equipped with a nitrogen gas separation apparatus in which, during the preparatory operation in which a process of separating nitrogen gas from a raw material gas is carried out in an adsorption tower to bring the concentration of nitrogen gas in the product tank to a predetermined concentration, the control unit closes the product gas line using the opening and closing mechanism, and the branch line releases gas in the product tank so that gas flows out of the adsorption tower at a flow rate smaller than the flow rate of gas flowing out of the adsorption tower during steady-state operation in which the product gas in the product tank is supplied to a demand side.

4. 4. The nitrogen gas separation apparatus according to claim 3, wherein the branch line allows the gas to flow out of the adsorption tower at a flow rate that is 10% to 90% of the flow rate of the gas flowing out of the adsorption tower during the steady operation.

5. 5. The nitrogen gas separation apparatus according to claim 3, wherein the branch line releases the gas in the product tank at a flow rate during the preparatory operation that is smaller than the flow rate of the product gas supplied to the demand side through the product gas line during the steady-state operation.

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