Nitrogen gas separation method and nitrogen gas separation unit

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 gas used in heat treatment of metals, manufacturing of semiconductors, explosion-proof seals in chemical plants, etc., to filled gas for food preservation. A method for producing nitrogen gas is known as a pressure swing adsorption (PSA) type production method, in which high-pressure air, which is a raw material gas, is fed into an adsorption tower filled with an adsorbent, oxygen gas is adsorbed by the adsorbent, and nitrogen gas is separated as a product gas. For example, the device described in Patent Document 1 is known as an apparatus that applies such a nitrogen gas separation method using the PSA system.

[0003] In such a PSA separation apparatus, as disclosed in Patent Document 1, the nitrogen concentration of the gas flowing out from 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 a predetermined value. Then, when 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, as the required nitrogen gas purity increases, it takes longer to reach the predetermined purity, so there is a demand for shortening the time required for the 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 in 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 increasing the nitrogen gas concentration flowing out from the adsorption tower more quickly. Meanwhile, Patent Document 2 discloses a method in which, in a purification operation performed before a steady-state operation, the gas flowing out from the adsorption tower is introduced into a product gas supply line through a bypass line that does not pass through the product tank, and at least a part of this gas is returned to the outlet side of the adsorption tower through a return line. In this method, the gas purity in the product tank is prevented from decreasing, and when the gas concentration from the adsorption tower reaches a predetermined concentration, the gas purity in the product tank is quickly increased by switching to introduce the gas into the product tank. [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, during preparatory operation until the nitrogen concentration reaches a predetermined value, the gas from the adsorption tower is not allowed to flow into the product tank, and the gas in the product tank is not discharged into the atmosphere. In other words, it can be said that these methods are performed on the premise that the nitrogen gas concentration of the gas in the product tank at the start of operation is maintained at a predetermined concentration. 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, so there is a demand for shortening the time required for preparatory operation while performing preparatory operations other than those disclosed in Patent Documents 1 and 2.

[0007] The present invention has been made in view of the above-mentioned conventional techniques, 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 that uses a nitrogen gas separation apparatus having two or more adsorption towers filled with an adsorbent and a product tank, supplies a raw material gas containing nitrogen gas and oxygen gas to the nitrogen gas separation apparatus under pressure, and stores the nitrogen gas obtained by each adsorption tower repeating an adsorption process, a pressure equalization process, a desorption process, and a pressure equalization process in the product tank as a product gas of a predetermined concentration. During 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, thereby causing the concentration of nitrogen gas in the product tank to reach a predetermined concentration, and during the preparatory operation, 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 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 preparatory operation is performed before a steady operation is performed. In this preparatory operation, an operation is performed in which nitrogen gas is separated from the raw gas in the adsorption tower while discharging the gas in the product tank. In this preparatory operation, the flow rate of the gas discharged from the adsorption tower is made smaller than the flow rate of the gas discharged from the adsorption tower during steady operation. Therefore, during the preparatory operation, the speed at which the raw gas passes through the adsorption tower is slowed (the time it takes to pass through the adsorption tower is lengthened), so that the nitrogen gas concentration of the gas discharged from the adsorption tower can be made higher. Therefore, since a gas with a higher nitrogen purity is supplied to the product tank, even if the flow rate of the gas discharged from the adsorption tower is reduced, the time (start-up time) required for the preparatory operation until the nitrogen gas concentration in the product tank reaches a predetermined concentration can be shortened as a result. Moreover, in the preparatory operation, since the gas in the product tank is discharged from the product tank, even if a gas with a low nitrogen gas concentration remains in the product tank, such a low-purity gas is prevented from remaining in the product tank.

[0010] In the preparatory operation, the gas may be caused to flow out from the adsorption tower at a flow rate that is 10% to 90% of the flow rate of the gas caused to flow out 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 operation. Moreover, the arrival time can be shortened whether or not nitrogen gas remains in the product tank when the nitrogen gas separation device is started up. Therefore, there is no need to check whether nitrogen gas remains in the product tank in order to ensure that the arrival time can be shortened.

[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 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 the gas discharged through the branch line during the preparatory operation is adjusted to a flow rate smaller than the flow rate of the gas supplied from the product tank to the demand side through the product gas line during the steady operation. Accordingly, the flow rate of the gas discharged from the adsorption tower during the preparatory operation is smaller than the flow rate of the gas discharged from the adsorption tower during the steady operation. In other words, the flow rate of the gas discharged from the adsorption tower can be limited by adjusting the flow rate of the gas discharged from the product tank. Therefore, the flow rate of the gas discharged from the adsorption tower can be reduced while accumulating pressure 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 raw gas containing nitrogen gas and oxygen gas and separate nitrogen gas from the raw 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 provided with an opening and closing mechanism and for supplying the product gas stored in the product tank to a demand side; a branch line branching off from a portion upstream of the opening and closing mechanism in the product gas line; and a control unit for controlling operation to repeatedly perform an adsorption process, a pressure equalization process, a desorption process, and a pressure equalization process in each adsorption tower, wherein, during a preparatory operation in which a process of separating nitrogen gas from the raw gas in the adsorption tower is performed with the product gas line closed by the opening and closing mechanism, so that the concentration of nitrogen gas in the product tank reaches a predetermined concentration, 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 operation in which the product gas in the product tank is supplied to the demand side.

[0015] In the nitrogen gas separation apparatus according to the present invention, a preparatory operation is performed before a steady operation is performed. In this preparatory operation, the adsorption tower separates nitrogen gas from the raw gas while discharging the gas in the product tank. In this preparatory operation, the flow rate of the gas discharged from the adsorption tower is made smaller than the flow rate of the gas discharged from the adsorption tower during steady operation. Therefore, during the preparatory operation, the speed at which the raw gas passes through the adsorption tower is slowed (the time it takes to pass through the adsorption tower is lengthened), so that the nitrogen gas concentration of the gas discharged from the adsorption tower can be made higher. Therefore, since a gas with a higher nitrogen purity is supplied to the product tank, even if the flow rate of the gas discharged from the adsorption tower is reduced, the time (start-up time) of the preparatory operation required for the nitrogen gas concentration in the product tank to reach a predetermined concentration can be shortened. Moreover, in the preparatory operation, since the gas in the product tank is discharged from the product tank, even if a 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 operation. Moreover, the arrival time can be shortened whether or not nitrogen gas remains in the product tank when the nitrogen gas separation device is started up. Therefore, there is no need to check whether nitrogen gas remains in the product tank in order to ensure that the arrival time can be shortened.

[0018] The branch line may, during the preparatory operation, release the gas in the product tank at a flow rate smaller than a flow rate of the product gas supplied to a demand side through the product gas line during the steady operation.

[0019] In this embodiment, the flow rate of the gas discharged through the branch line during the warm-up operation is adjusted to a flow rate smaller than the supply flow rate to the demand side through the product gas line during normal operation. Accordingly, the flow rate of the nitrogen gas discharged from the adsorption tower during the warm-up operation is smaller than the flow rate of the nitrogen gas discharged from the adsorption tower during normal operation. In other words, the flow rate of the gas discharged from the adsorption tower can be limited by adjusting the flow rate of the gas discharged from the product tank. Therefore, the flow rate of the gas discharged from the adsorption tower can be reduced while accumulating pressure in the product tank. Effect of the Invention

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

[0021] [Figure 1] 1 is a diagram illustrating a schematic configuration of a nitrogen gas separation device according to an embodiment. [Diagram 2]FIG. 2 is a diagram illustrating a schematic configuration of a nitrogen gas separation device according to another embodiment. [Diagram 3] FIG. 4 is a diagram showing the relationship between the blow amount and the arrival time in Examples 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0023] <Nitrogen gas separation equipment> The nitrogen gas separation device 1 shown in Fig. 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 may be, for example, air, but is not limited thereto, and may be any gas that contains 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 which 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 device 1 has 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 through 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 through 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 in which the raw material gas is placed in a container.

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

[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 downstream side of the first intake valve CV1 on the first adsorption tower inlet line L1A, a second discharge line L2B connected to the downstream side of the second intake valve CV3 on the second adsorption tower inlet line L1B, and a discharge junction line L2C connected to the junction of the first discharge line L2A and the second discharge line L2B. A first discharge valve CV2 is provided on the first discharge line L2A, and 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 by 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 raw material gas is supplied from the compressor 3, the first adsorption tower 1A and the second adsorption tower 1B separate nitrogen gas from the raw material gas by preferentially adsorbing oxygen gas in the raw material gas with the adsorbent, thereby generating 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] The molecular sieve carbon is a wood-based, coal-based, resin-based, pitch-based, or other adsorbent obtained by carbonizing raw materials such as charcoal, coal, coke, coconut shells, resin, and pitch, which have many pores, at high temperatures and adjusting the pore size to about 3 to 5 angstroms. Such molecular sieve carbon has a property of being more likely to adsorb oxygen gas than nitrogen gas, and has a property of selectively adsorbing oxygen gas from a mixed gas containing nitrogen gas and oxygen gas, such as air. In addition, the molecular sieve carbon has an increased adsorption capacity for oxygen gas under high pressure conditions. Therefore, the molecular sieve carbon can adsorb more oxygen gas by pressurizing the first and second adsorption towers 1A and 1B, and then the oxygen gas can be desorbed by depressurizing the first and second adsorption towers 1A and 1B.

[0031] The gas generated 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 has 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 junction line L3C where the first adsorption tower outlet line L3A and the second adsorption tower outlet line L3B join together and are connected to the product tank 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 equalizing line L7 is provided, which connects a portion of the first adsorption tower outlet line L3A upstream of the first extraction valve CV5 and a portion of the second adsorption tower outlet line L3B upstream of the second extraction valve CV6. The second equalizing line L7 is provided with a second equalizing valve CV7. The first extraction valve CV5, the second extraction valve CV6, and the second equalizing valve CV7 are each configured as a valve that can be switched between open and closed (ON / OFF valve).

[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. In other words, 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 towers 1A, 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 part of the gas from the adsorption towers 1A, 1B in the adsorption process to the adsorption towers 1B, 1A in the desorption process as a cleaning gas, and to promote the discharge of the raw material gas remaining in the adsorption towers 1B, 1A in 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 capable of adjusting the 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 the adsorption tower outlet lines L3A, L3B and the 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 demand destination through the product gas line L10.

[0037] An oxygen concentration meter 21, a flow meter 22, and an opening and 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] Flowmeter 22 measures the flow rate of the product gas flowing out from the product tank 2. Flowmeter 22 is disposed on the product gas line L10 between the oxygen concentration meter 21 and the opening and closing mechanism 10. Note that flowmeter 22 may also be disposed on the product gas line L10 between the product tank 2 and the 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 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 to discharge the product gas, but as shown in FIG. 2, the branch line L11 may be connected to the raw material gas inlet of the compressor 3 and the product gas discharged from the product tank 2 may be 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 raw material gas.

[0043] The branch line L11 is configured to flow the product gas at a flow rate smaller than the flow rate of the product gas supplied to the 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 smaller 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 from 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 from the adsorption towers 1A and 1B is smaller than that during the steady operation.

[0044] The flow rate adjustment mechanism 11 may be composed of a valve (on-off valve) that can be switched between opening and closing and an orifice, or may be composed of a valve that can adjust the opening degree. The branch line L11 may be formed to be thinner than the product gas line L10. In this case, the flow rate adjustment mechanism 11 is omitted and a valve that opens and closes the branch line L11 is 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 and closing mechanism 10 may be composed of a three-way valve. In this case, the flow rate adjustment mechanism 11 does not have the function of opening and closing the branch line L11, but only has the function of throttling the flow rate. The three-way valve is disposed at the branch portion of 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 opening / closing 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 opening / closing mechanism 10, and the flow rate adjusting mechanism 11 so as to perform a steady operation in which the first and second adsorption towers 1A and 1B are repeatedly subjected to an adsorption process, a pressure equalization process, a desorption process, and a pressure equalization process to obtain a product gas having a predetermined nitrogen gas concentration, and a preparatory operation which is performed prior to the steady operation when the nitrogen gas separation apparatus 1 is started up. 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 for moving a part of the gas in the first adsorption tower 1A to the second adsorption tower 1B after the first preparatory operation, and a second pressure equalization operation for moving a part of the gas in the second adsorption tower 1B to the first adsorption tower 1A after the second preparatory operation.

[0046] During steady-state operation, when the first adsorption tower 1A is subjected to the adsorption process and the second adsorption tower 1B is subjected to the desorption process, 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, 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 exhaust 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 exhaust valve CV2.

[0048] In addition, when the control unit 20 subjects the first and second adsorption towers 1A, 1B to the pressure equalization process, it closes the first intake valve CV1, the second intake valve CV3, the first exhaust valve CV2, the second exhaust 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 and 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 and closing mechanism 10 is configured as a three-way valve, the flow rate adjustment mechanism 11 is not subject to control.

[0050] On the other hand, in the first preparatory operation in the preparatory operation, the control unit 20 opens the first intake valve CV1, the first take-out valve CV5, and the second discharge valve CV4, and closes the second intake valve CV3, the second take-out valve CV6, the first discharge 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 in which gas can flow. In other words, the product gas in the product tank 2 is not supplied to the demand destination, but is set in a state in which it flows through the branch line L11. Also, in the first equalizing operation after the first preparatory operation, the control unit 20 closes the first intake valve CV1, the first take-out valve CV5, and the second discharge 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 in which gas can flow.

[0051] In 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 in which gas can flow. In other words, the product gas in the product tank 2 is not supplied to the demand destination, but is set in a state in which it flows through the branch line L11. In 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 in which gas can 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 operation performed after the nitrogen gas concentration in the product tank 2 reaches a predetermined value by the preparatory operation. 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 be performed first.

[0054] In the first preparatory operation, the first intake valve CV1, the first outlet valve CV5, and the second exhaust valve CV4 are opened, while the second intake valve CV3, the second outlet valve CV6, the first exhaust 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, and 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 the gas passing through the first adsorption tower 1A becomes slower than the gas flow rate during steady operation. As a result, the time that the raw material gas passes through the first adsorption tower 1A becomes longer, and 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 having 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 operation switches to the first pressure equalization operation. In the first pressure equalization operation, the first intake valve CV1, the first extraction valve CV5, and the second exhaust valve CV4 are closed, while the pressure equalization valves CV8 and CV7 are opened. This causes the gas in the first adsorption tower 1A to move to the second adsorption tower 1B through the first pressure equalization line L8 and the second pressure equalization line L7. Note that even in the first pressure equalization operation, the flow rate adjustment mechanism 11 is maintained in a state in which gas can 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 exhaust valve CV2 are opened, while the first intake valve CV1, the first outlet valve CV5, the second exhaust 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] In the second preparatory operation, the raw material gas discharged from the compressor 3 is supplied to the second adsorption tower 1B through the raw material gas supply line L1 and the second adsorption tower inlet line L1B. In the second adsorption tower 1B, oxygen gas is adsorbed by the adsorbent from the supplied raw material gas, so that a gas having a higher nitrogen gas concentration than the raw material gas is generated, and this gas is introduced into the product tank 2 through 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 through the product gas line L10 and the branch line L11. At this time, the gas flow rate that can flow through the product gas line L10 is limited by the flow rate adjustment mechanism 11 compared to that during steady operation, so that the gas flow rate flowing out from the second adsorption tower 1B is also reduced compared to that during steady operation. Therefore, the flow rate of the gas passing through the second adsorption tower 1B becomes slower than the gas flow rate during steady operation. As a result, the time that the raw material gas passes through the second adsorption tower 1B becomes longer, so that the nitrogen gas concentration of the gas flowing out from the second adsorption tower 1B can be increased.

[0061] 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, and therefore a portion of the gas in the first adsorption tower 1A (gas having 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 operation switches to the second pressure equalization operation. In the second pressure equalization operation, the second intake valve CV3, the second extraction valve CV6, and the first exhaust valve CV2 are closed, while the pressure equalization valves CV8 and CV7 are opened. This causes the gas in the second adsorption tower 1B to move to the first adsorption tower 1A through the first pressure equalization line L8 and the second pressure equalization line L7. Note that even in the second pressure equalization operation, the flow rate adjustment mechanism 11 is maintained in a state in which gas can flow.

[0063] The first preparatory operation, the first pressure equalizing operation, the second preparatory operation, and the second pressure equalizing operation are repeated, and when the concentration of nitrogen gas in product tank 2 reaches a predetermined concentration, the preparatory operation is terminated and a transition is made to steady operation.

[0064] In a steady-state operation, the adsorption process, the pressure equalization process, the desorption process, and the pressure equalization process are repeated in each of the adsorption towers 1A and 1B. However, the adsorption process and the 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 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 to the adsorbent from the adsorbent.

[0066] The adsorption process of the first adsorption tower 1A and the desorption process of the second adsorption tower 1B are initiated by opening the first intake valve CV1, the first extraction valve CV5, and the second exhaust 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 operation, the opening and closing mechanism 10 is opened, while the flow rate control 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, the raw material gas is supplied from the compressor 3 to the first adsorption tower 1A through the raw material gas supply line L1 and the first adsorption tower inlet line L1A. The raw material gas supplied to the first adsorption tower 1A is adsorbed by the adsorbent to separate nitrogen gas from the raw material gas, thereby generating a gas containing high-purity nitrogen gas. The gas generated in the first adsorption tower 1A is introduced as a product gas into the product tank 2 through 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 demand destination through the product gas line L10 by opening the opening / closing mechanism 10. A part of the product gas generated in the first adsorption tower 1A is sent as a cleaning gas to the second adsorption tower 1B through the cleaning gas line L9.

[0068] Meanwhile, in the desorption process of the second adsorption tower 1B, the gas in the second adsorption tower 1B is discharged together with the cleaning gas to the outside at a pressure lower than the pressure inside the second adsorption tower 1B via the second adsorption tower inlet line L1B, the second discharge line L2B, and the discharge junction line L2C due to the pressure difference. This reduces the pressure inside the second adsorption tower 1B, and the oxygen gas adsorbed to the adsorbent is desorbed from the adsorbent. The desorbed oxygen gas is discharged together with the cleaning gas from the second adsorption tower 1B. This regenerates the adsorbent in the second adsorption tower 1B.

[0069] After the adsorption and desorption processes are completed, a pressure equalization process is started to transfer the gas in the first adsorption tower 1A to the second adsorption tower 1B. The pressure equalization process is started by closing the first intake valve CV1, the first extraction valve CV5, and the second exhaust valve CV4, and opening the first and second equalization valves 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 pressure equalization line L8 and the second pressure 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 started 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 step of the second adsorption tower 1B, the raw gas discharged from the compressor 3 is supplied to the second adsorption tower 1B through the raw gas supply line L1 and the second adsorption tower inlet line L1B. At this time, oxygen gas in the raw gas is adsorbed by the adsorbent, and nitrogen gas is separated from the raw gas to generate a gas containing high-purity nitrogen gas. The gas generated in the second adsorption tower 1B is introduced as a product gas into the product tank 2 through 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 demand destination from the product tank 2 through the product gas line L10 by opening the opening / closing mechanism 10. A part of the product gas generated in the second adsorption tower 1B is sent as a cleaning gas to the first adsorption tower 1A through the cleaning gas line L9.

[0073] Meanwhile, in the desorption process of the first adsorption tower 1A, the gas in the first adsorption tower 1A is discharged together with the wash gas through the first adsorption tower inlet line L1A, the first discharge line L2A, and the discharge junction line L2C to the outside at a pressure lower than the pressure inside the first adsorption tower 1A due to the pressure difference. This reduces the pressure inside the first adsorption tower 1A, and the oxygen gas adsorbed to the adsorbent is desorbed from the adsorbent. The desorbed oxygen gas is discharged together with the wash gas from the first adsorption tower 1A. 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 performed again. Thereafter, the above cycle is repeated in the first and second adsorption towers 1A and 1B. EXAMPLES

[0076] Next, a specific example carried out 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, 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 so that each process is performed 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 nitrogen gas separation apparatus 1 used in Example 1 and the nitrogen gas separation apparatus 1 used in Example 2 have different capacities of the adsorption towers 1A, 1B and the product tank 2.

[0079] Using this nitrogen gas separation device 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, Tables 1 and 2. Table 1 shows the values ​​of the arrival time in the case of Example 1, and Table 2 shows the values ​​of the arrival time in the case of Example 2. The blow rate (%) represents the flow rate of the product gas during the warm-up operation relative to the flow rate of the product gas during the normal operation. In other words, the blow rate (%) represents the percentage of the flow rate of the product gas flowing into the branch line L11 while the opening / closing mechanism 10 is closed, based on the flow rate in a state in which the opening / closing mechanism 10 is open and the product gas flows into the product gas line L10, but the flow rate adjustment mechanism 11 prevents the product gas from flowing into the branch line L11. These flow rates are measured by the flow meter 22.

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

[0081] [Table 1]

[0082] [Table 2]

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

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

[0085] As described above, in the nitrogen gas separation method according to the present embodiment, a preparatory operation is performed before a steady operation is performed. In this preparatory operation, the adsorption towers 1A and 1B perform an operation of separating nitrogen gas from the raw gas while discharging the gas in the product tank 2. In this preparatory operation, the flow rate of the gas discharged from the adsorption towers 1A and 1B is set to be smaller than the flow rate of the gas discharged from the adsorption towers 1A and 1B during steady operation. Therefore, during the preparatory operation, the speed at which the raw gas passes through the adsorption towers 1A and 1B is slowed (the time it takes to pass through the adsorption towers 1A and 1B is lengthened), so that the nitrogen gas concentration of the gas discharged from the adsorption towers 1A and 1B can be made higher. Therefore, since a gas with a higher nitrogen purity is supplied to the product tank 2, even if the flow rate of the gas discharged from the adsorption towers 1A and 1B is reduced, 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 as a result. Furthermore, during the preparatory operation, the gas in the product tank 2 is released from the product tank 2, so that 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, in the preparatory operation, the gas may be discharged from the adsorption towers 1A, 1B at a flow rate that is 10% to 90% of the flow rate of the gas discharged from the adsorption towers 1A, 1B during steady 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 the case where the gas is discharged from the adsorption towers 1A, 1B at the same flow rate as the outflow gas flow rate during steady operation. Moreover, when the nitrogen gas separation apparatus 1 is started up, the arrival time can be shortened whether or not nitrogen gas remains in the product tank 2. Therefore, it is not necessary to check whether nitrogen gas remains in the product tank 2 in order to reliably shorten the arrival time.

[0087] In the above embodiment, in the preparatory 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 normal operation. Accordingly, in the preparatory operation, the flow rate of the gas flowing out from the adsorption towers 1A, 1B becomes smaller than the flow rate of the gas flowing out from the adsorption towers 1A, 1B during normal operation. That is, 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, it is possible to reduce the flow rate of the gas flowing out from the adsorption towers 1A, 1B 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 construed as limiting. The present invention is not limited to the above-described embodiments, and various modifications and improvements can be made 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 gas in the adsorption tower while gas is released from the product tank, so that the concentration of nitrogen gas in the product tank reaches a predetermined concentration; In the preparatory operation, the gas is discharged from the adsorption tower at a flow rate smaller than the flow rate of the gas discharged from the adsorption tower during steady-state operation in which the product gas in the product tank is supplied to a demand side.

2. 2. The nitrogen gas separation method according to claim 1, wherein in 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 discharged from the adsorption tower during steady-state operation.

3. 3. The nitrogen gas separation method according to claim 1 or 2, wherein during the preparatory operation, gas is released from the product tank through a branch line branching off from a product gas line that supplies product gas from the product tank to a demand side, at a flow rate smaller than the flow rate of product gas supplied to the demand side through the product gas line during steady-state operation.

4. two or more adsorption towers each filled with an adsorbent, the adsorption towers receiving a pressurized source gas containing nitrogen gas and oxygen gas and separating nitrogen gas from the source 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 of each adsorption tower to repeatedly perform an adsorption process, a pressure equalization process, a desorption process, and a pressure equalization process; Equipped with a nitrogen gas separation apparatus in which, during preparatory operation in which a process of separating nitrogen gas from a raw material gas in an adsorption tower is carried out with the product gas line closed by the opening and closing mechanism to bring the concentration of nitrogen gas in the product tank to a predetermined concentration, 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 the demand side.

5. 5. The nitrogen gas separation apparatus according to claim 4, wherein the branch line allows 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.

6. The nitrogen gas separation apparatus according to claim 4 or 5, wherein the branch line, during the preparatory operation, releases the gas in the product tank at a flow rate smaller than a flow rate of the product gas supplied to the demand side through the product gas line during the steady operation.

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