Nitrogen generating device and nitrogen generating method

Abstract

To provide a nitrogen generating method with which a reflux liquid that is in short supply can be introduced into a nitrogen rectification column when demand for product nitrogen increases.SOLUTION: The present invention provides a nitrogen generating method for producing product nitrogen using a nitrogen generating device, comprising a main heat exchanger for cooling feed air, a nitrogen rectification column into which the feed air cooled in the main heat exchanger is introduced, and a nitrogen condenser which condenses a vapor stream fed from the nitrogen rectification column and circulates the same to the nitrogen rectification column, the method including a control step for discharging liquid nitrogen condensed by the nitrogen condenser and stored in a liquid nitrogen buffer, which is provided in an upper gas phase portion of the nitrogen rectification column or separately from the nitrogen rectification column, to a rectification portion of the nitrogen rectification column in response to an increase in an amount of product nitrogen or an increase in a flow rate of the feed air.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a nitrogen generating method and a nitrogen generating apparatus, and more particularly to a method and an apparatus for generating nitrogen capable of rapidly varying the load of raw air or the like. [Background technology]

[0002] In recent years, there has been an increasing demand for synthesizing ammonia without emitting carbon dioxide. To achieve this, it is expected that ammonia can be obtained from hydrogen and nitrogen obtained by electrolysis of water using electricity generated by solar or wind power (known as green ammonia). As a method for producing nitrogen, the cryogenic separation method is promising because it can produce nitrogen on a large scale with high purity. In particular, from the viewpoint of purity, it is desirable to control the argon that may be contained in the nitrogen in terms of the efficiency of ammonia synthesis, but it is technically difficult to control the argon concentration in the nitrogen to an extremely low level using other nitrogen generation methods such as membrane separation and adsorption, so the application of the cryogenic separation method is desirable.

[0003] The power generation capacity of renewable energy sources such as solar power and wind power depends on environmental variables such as the amount of solar radiation and wind speed. Therefore, consumers need to either increase or decrease their power consumption in response to the fluctuating power generation capacity, or stabilize the power supply by using power storage technologies such as batteries. In the supply of nitrogen by cryogenic air separation, a method has been proposed in which surplus nitrogen gas is liquefied and stored when demand is low relative to the nitrogen gas production capacity, and liquid nitrogen is vaporized to meet demand when demand is high. However, the cost of electricity from renewable energy sources tends to be high when electricity is insufficient and hydrogen cannot be generated, so that demand for nitrogen gas is low, and low when electricity is abundant and hydrogen generation is sufficient, so that demand for nitrogen gas is high. Therefore, this method of liquefying nitrogen gas when electricity costs are high and vaporizing liquid nitrogen when costs are low to dispose of cold energy is irrational.

[0004] Therefore, the nitrogen generator should have the ability to increase or decrease the nitrogen generation capacity according to the power supply capacity, and more specifically, it is required to quickly increase or decrease the amount of feed air according to the nitrogen demand, but a rapid increase in the amount of feed air causes a problem of reducing the purity and quality of the nitrogen. This is because the amount of oxygen-containing vapor flow in the nitrogen rectification tower becomes greater than the reflux liquid. The reflux liquid is supplied by liquefying the vapor flow supplied from the nitrogen rectification tower in a nitrogen condenser, so if the high boiling point components reach the top of the nitrogen rectification tower when the nitrogen production volume is increased, the reflux liquid itself will be contaminated with the high boiling point components, and the purity of the nitrogen cannot be maintained.

[0005] Patent Document 1 discloses that compressed feed air is supplied to one rectification tower, and a portion of the nitrogen gas discharged from the rectification tower is separated, liquefied, and refluxed to the rectification tower. Paragraph 0047 and FIG. 7 of Patent Document 2 describe that excess liquefied air is stored in a storage tank disposed between the liquefaction device and the distillation column, and that the excess liquefied air is stored during a first time period when power costs are relatively low, and at least a portion of the excess air is used during a second time period when power costs are relatively high. Patent Document 3 discloses an apparatus for producing high-pressure nitrogen, which includes a high-pressure distillation column, an upper condenser of the high-pressure distillation column, a medium-pressure distillation column, and an upper condenser of the medium-pressure distillation column. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-226759 [Patent Document 2] Japanese Patent Application Publication No. 10-54658 [Patent Document 3] JP 2012-145320 A Summary of the Invention [Problem to be solved by the invention]

[0007] In order to solve the above problems, the present disclosure aims to provide a nitrogen generation method and a nitrogen generation apparatus that can inject a reflux liquid that is insufficient into a nitrogen rectification column when the demand for product nitrogen increases. In addition, since excessive injection of liquid nitrogen may make it difficult to maintain the process balance, the present disclosure aims to provide a nitrogen generation method and a nitrogen generation apparatus that can inject liquid nitrogen while properly managing it. Another object of the present disclosure is to provide a nitrogen generation method and nitrogen generation apparatus that can supply a desired flow rate of product nitrogen without compromising the purity of the product nitrogen, even when the amount of feed air increases or decreases rapidly in accordance with fluctuations in the supply capacity of renewable energy, for example. [Means for solving the problem]

[0008] The nitrogen generating device of the present disclosure comprises: A main heat exchanger (1); At least one nitrogen rectification column (first nitrogen rectification column 2, second nitrogen rectification column 4); At least one condenser (a first nitrogen condenser 3 connected to the first nitrogen rectification column 2, a second nitrogen condenser 5 connected to the second nitrogen rectification column 4) for condensing (cooling) a vapor stream sent from an upper vapor phase of at least one nitrogen rectification column and circulating it to the upper vapor phase; and a liquid nitrogen buffer (5, 9, 90) that is provided separately from the upper gas phase section (upper gas phase section of the first nitrogen rectification column 2) or the nitrogen rectification column (first nitrogen rectification column 2) and that stores the liquid nitrogen (circulating liquid) condensed in the nitrogen condenser (second nitrogen condenser 5). Liquid nitrogen may be supplied to any of the nitrogen rectification columns (2, 4) from a liquid nitrogen buffer (9, 90) disposed outside the nitrogen rectification column (first nitrogen rectification column 2) separately.

[0009] The nitrogen generation apparatus (A1, A2, A3, A4, A5, B1) disclosed herein is A main heat exchanger (1) for cooling the feed air; a nitrogen rectification column (2) having a rectification section (22) or a gas phase section at a bottom (21) into which the feed air cooled in the main heat exchanger (1) is introduced; a nitrogen condenser (3) for condensing (cooling) a vapor stream sent from the upper vapor phase (23) of the nitrogen rectification column (2) (through a circulating liquid pipe L301) and circulating the vapor stream to the upper vapor phase (23); an oxygen-enriched liquid piping line (L21) for conveying oxygen-enriched liquid from the bottom (21) (to the refrigerant phase of the nitrogen condenser (3)) for use as a refrigerant in the nitrogen condenser (3); a liquid nitrogen buffer (5, 9) provided separately from the upper gas phase section (23) or the nitrogen rectification column (2) (and provided below the circulating liquid pipe L301), for storing the liquid nitrogen (circulating liquid) condensed in the nitrogen condenser (3); liquid nitrogen discharge means (first discharge pipe L7, first control valve 7, second discharge pipe L72, second adjustment valve 72, third discharge pipe L303, liquid feed pump 92, third control valve 93) for discharging the liquid nitrogen (reflux liquid) stored in the liquid nitrogen buffer (5, 9); a control unit (8) for controlling the liquid nitrogen discharge means so as to discharge liquid nitrogen (reflux liquid) from the liquid nitrogen buffer (5, 9) to a rectification unit (22) in response to an increase in the amount of product nitrogen or an increase in the flow rate of the feed air; Equipped with. The nitrogen generating apparatus (A1, A2, A3, A4, A5, B1) is The system may further include a feed air piping line (L1) for introducing the feed air through the main heat exchanger (1) into a nitrogen rectification column (2) having a gas phase portion in the rectification section (22) or the bottom (21). The liquid nitrogen buffer (5, 9) may be supplied with external liquid nitrogen other than the liquid nitrogen (circulating liquid) condensed in the nitrogen condenser (3).

[0010] The nitrogen generating apparatus (A1, A2, A4, A5, B1) A feed air flow meter (F1) for measuring the flow rate of the feed air (installed in the feed air pipe L1 on the upstream or downstream side of the main heat exchanger 1) may be provided. The control unit (8) may control the liquid nitrogen discharge means to discharge liquid nitrogen (reflux liquid) from the liquid nitrogen buffers (5, 9) to the rectification unit (22) in response to an increase in the flow rate of the feed air as measured by the feed air flow meter (F1).

[0011] As a result, when the amount of product nitrogen is increased, the amount of feed air is increased, but since there is a temporary shortage of reflux liquid, liquid nitrogen can be supplied to the rectification section from the liquid nitrogen buffer, thereby resolving the shortage of reflux liquid and maintaining the purity of the product nitrogen.

[0012] The control unit (8) may calculate the required amount of reflux liquid using the amount of feed air (measured flow rate value, calculated value) as a variable so as to maintain the purity of the product nitrogen when the amount of product nitrogen is increased, and control the amount of liquid nitrogen to be led out from the liquid nitrogen buffers (5, 9). The amount of feed air is calculated based on the increase in product nitrogen, and the amount of reflux liquid can be calculated. Increase in feed air = Increase in product nitrogen x A (1) Required amount of reflux liquid = Increase in feed air x B (2) In equations (1) and (2), the increase in feed air and the increase in product nitrogen are directly proportional to the required amount of reflux liquid.

[0013] The nitrogen generators (A1, A2, A3, A4, A5, B1) are a product nitrogen flow meter (F2) for measuring the flow rate of product nitrogen sent to the demand point; The control unit (8) may calculate the required amount of reflux liquid using the amount of product nitrogen (measured value, calculated value) as a variable so as to maintain the purity of the product nitrogen when the amount of product nitrogen is increased, and control the amount of liquid nitrogen to be drawn off from the liquid nitrogen buffers (5, 9). The control unit (8) may calculate the required amount of reflux liquid using the amount of feed air (measured flow rate value, calculated value) as a variable so that the reflux liquid to vapor flow ratio (L / V) does not fall below a preset control value (parameter that determines the nitrogen purity) when increasing the amount of product nitrogen, and may determine the amount of liquid nitrogen to be derived from the liquid nitrogen buffers (5, 9).

[0014] The nitrogen generators (A1, A2, A3, A4, A5) are A differential pressure gauge (6) may be provided to measure the pressure difference between the upper gas phase (23) and the bottom of the liquid nitrogen buffer (5). The control unit (8) may monitor the amount of liquid nitrogen stored in the liquid nitrogen buffer (5) that is discharged based on the measurement value of the differential pressure gauge (6), and control the amount of liquid nitrogen that is discharged.

[0015] The nitrogen generators (A1, A2, A3, A4, A5, B1) are The system may further comprise distributors (201, 202) disposed above the rectifying section (22) for uniformly distributing the reflux liquid or the liquid nitrogen to the rectifying section (22). The distributor (201, 202) may have a plurality of storage sections each having an overflow structure and capable of storing a predetermined amount of liquid, and an opening provided below the storage section, so that liquid overflowing from the storage section is sent to the adjacent storage section. As a result, the descending reflux liquid tends to gather from the center of the distillation column toward the inner wall in order to minimize the contact area with the countercurrent vapor flow, but by disposing the distributors (201, 202) in the middle of the nitrogen distillation column (2), the reflux liquid can be effectively redistributed.

[0016] The nitrogen generators (A1, A2, A3, A4, A5, B1) are a distributor differential pressure gauge (62) for measuring the pressure difference between the top and bottom of the distributor (202); and / or A rectifying section differential pressure gauge (not shown) for measuring the pressure difference between the upper and lower parts of the rectifying section (22) may be provided. The control unit (8) may control the amount of liquid nitrogen stored in the liquid nitrogen buffers (5, 9) to be discharged based on a measurement value of the distributor differential pressure gauge (62).

[0017] The nitrogen generators (A1, A2, A3, A4, B1) are The system may be provided with a waste gas piping line (L31) for extracting the gas discharged from the upper gas phase of the nitrogen condenser (3) as waste gas via the main heat exchanger (1). The nitrogen generators (A1, A2, A3, A4, A5, B1) are The system may be provided with a product nitrogen gas piping line (L23) for extracting the nitrogen gas discharged from the upper gas phase section (23) as product nitrogen gas via the main heat exchanger (1). When the oxygen concentration reading of an oxygen analyzer provided in the product nitrogen gas piping line or at any position in the nitrogen rectification column exceeds the oxygen concentration control value, the purity of the product nitrogen gas can be adjusted by supplying liquid nitrogen from the liquid nitrogen buffers (5, 9) to the rectification section or by reducing the amount of product nitrogen gas introduced.

[0018] The nitrogen generator (A5, B1) an expansion turbine (101) in which a gas (oxygen-containing liquid evaporated gas) discharged from above the nitrogen condenser (3) is heat-exchanged (heated) through the main heat exchanger (1) (taken out from an intermediate portion) and then expanded; a waste gas piping line (L31) for passing a gas (oxygen-containing liquid evaporated gas) discharged from above the nitrogen condenser (3) through the main heat exchanger (1) and the expansion turbine (101) again through the main heat exchanger (1) and extracting the gas as waste gas; The device may include: The nitrogen generator (A5, B1) a branch piping line (L311) which is located upstream of the expansion turbine (101) and branches off from the exhaust gas piping line (L31) between the main heat exchanger (1) and the expansion turbine (101) and which merges with the exhaust gas piping line (L31) located downstream of the expansion turbine (101) and between the main heat exchanger (1) and the expansion turbine (101); A flow rate control valve (102) may be provided in the branch piping line (L311) to control the flow rate of gas diverted from the waste gas piping line (L31) to the branch piping line (L311). The nitrogen generator (A5, B1) an upper gas phase pressure gauge (61) for measuring the pressure of the upper gas phase (23); an exhaust gas pressure gauge (63) that is provided in the exhaust gas piping line (L31) between the main heat exchanger (1) and the expansion turbine (101) upstream of the expansion turbine (101) or in the exhaust gas piping line (L31) upstream of the branch piping line (L311) and measures a gas pressure; The exhaust gas supply pressure control section (81) may be provided which opens and closes the flow rate regulating valve (102) or controls the flow rate, based on the measurement results of the upper gas phase pressure gauge (61) and the exhaust gas pressure gauge (63), so as to reduce the pressure of the exhaust gas flow on the inlet side of the expansion turbine (101) or to reduce the pressure of the low-temperature side (311) of the nitrogen condenser (3).

[0019] The nitrogen generator (A5, B1) a rectification section (4) provided above the nitrogen condenser (3); a recycle piping line (L42) for allowing a gas (recycle gas) discharged from an upper portion (42) of the rectification section (4) to flow through the main heat exchanger (1) into a feed air piping line (L1) located upstream of the main heat exchanger (1); a recycle compressor (111) that is provided in the recycle piping line (L42) and compresses a gas (recycle gas) discharged from an upper portion (42) of the rectification section (4) after the gas has been heat exchanged (heated) in the main heat exchanger (1); The device may include: The nitrogen generator (A5, B1) The recycle piping line (L42) may further include a cooling means (112) for cooling the gas compressed by the recycle compressor (111). The "recycle gas" is a gas in which nitrogen has been concentrated by gas-liquid contact between the oxygen-enriched liquid supplied from the bottom (21) of the nitrogen rectification column and the oxygen-containing evaporated gas supplied from the nitrogen condenser (3).

[0020] The nitrogen generator (B1) is a circulating liquid branch pipe (L302) that branches off from a circulating liquid pipe (L301) extending from the nitrogen condenser (3) and that sends the liquid nitrogen (circulating liquid) to the liquid nitrogen buffer (9); a differential pressure gauge (91) for measuring the pressure difference between the bottom and the top of the liquid nitrogen buffer (9) in order to measure the amount of liquid nitrogen stored in the liquid nitrogen buffer (9); The device may include: The liquid nitrogen discharge means is a third outlet pipe (L303) extending from the bottom of the liquid nitrogen buffer (9); a liquid feed pump (92) provided in the circulating liquid branch pipe (L302) or the third outlet pipe (L303); a third control valve (93) provided in the third outlet pipe (L303); The device may include: The control section (8) may drive the liquid feed pump (92) and control the opening and closing of the third control valve (93) and the flow rate thereof so as to deliver liquid nitrogen (reflux liquid) from the liquid nitrogen buffer (9) to the rectification section (22) in response to an increase in the amount of the product nitrogen or an increase in the measurement value of the feed air flow meter (F1) of equal to or greater than a predetermined amount.

[0021] The nitrogen generators (A1, A2, A3, A4, A5, B1) are The system is configured to provide increased amounts of feed air in response to increased requests for product nitrogen from demand points. A compressor for compressing the raw air; A purification device that removes impurities (including moisture) from the compressed raw air; a feed air flow rate control unit that controls the output of the compressor and controls the amount of feed air sent to the main heat exchanger (1); The device may include:

[0022] Another disclosed nitrogen generator (B2) comprises: A main heat exchanger (1) for cooling the feed air; a first nitrogen rectification column (2) having a rectification section (22) or a gas phase section at a bottom (21) into which the feed air cooled in the main heat exchanger (1) is introduced; a first nitrogen condenser (3) that condenses (cools) a vapor stream sent from the upper vapor phase section (23) of the first nitrogen rectification column (2) (through a first circulating liquid pipe L231) and circulates the vapor stream to the upper vapor phase section (23); a product nitrogen withdrawal line (L23) for withdrawing nitrogen from the upper gas phase portion (23) of the first nitrogen rectification column (2) and passing through the main heat exchanger (1) to be withdrawn as product nitrogen; a second nitrogen rectification column (4) having a rectification section (41, 421, 42) into which an oxygen-enriched liquid is introduced from a bottom (21) of the first nitrogen rectification column (2) via an oxygen-enriched liquid piping line L21; a second nitrogen condenser (5) that condenses (cools) a vapor stream sent from the upper vapor phase (43) of the second nitrogen rectification column (4) (through a second circulating liquid pipe L43) and circulates the vapor stream to the upper vapor phase (43); a liquid nitrogen buffer (90) for storing the condensate returning to the upper gas phase portion (43) of the second nitrogen rectification column (4) through an outlet pipe L302 (branched from the second circulating liquid pipe L43); a waste gas withdrawal line (L51) for leading out the waste gas from the upper gas phase section (52) of the second nitrogen condenser section (5) and withdrawing it as waste gas via the main heat exchanger (1); a piping line (L31) for delivering a refrigerant liquid from the refrigerant phase of the first nitrogen condenser (3) to the refrigerant phase of the second nitrogen condenser (5); a liquid nitrogen discharge means (a third discharge pipe L303, a liquid feed pump 902, a third control valve 903) for discharging the liquid nitrogen (reflux liquid) stored in the liquid nitrogen buffer (90); a control unit (80) for controlling the liquid nitrogen discharge means so as to discharge liquid nitrogen (reflux liquid) from the liquid nitrogen buffer (90) to an upper gas phase section (23) or a rectification section 22 (upstream of the intermediate section) of the first nitrogen rectification column (2) in response to an increase in the amount of product nitrogen or an increase in the flow rate of the feed air; The device may include:

[0023] The nitrogen generation method of the present disclosure includes: A method for producing product nitrogen using a nitrogen generation apparatus comprising: a main heat exchanger (1) for cooling feed air; a nitrogen rectification column (2) into which the feed air cooled by the main heat exchanger (1) is introduced; and a nitrogen condenser (3) for condensing (cooling) a vapor stream sent from the nitrogen rectification column (2) and circulating the vapor stream to the nitrogen rectification column (2), comprising the steps of: The method includes a control step of conducting the liquid nitrogen (circulating liquid) condensed in the nitrogen condenser (3), which is stored in the upper gas phase part (23) of the nitrogen rectification column (2) or in a liquid nitrogen buffer (5, 9) provided separately from the nitrogen rectification column (2), to the rectification part of the nitrogen rectification column (2) in response to an increase in the amount of product nitrogen or an increase in the flow rate of the feed air. The control step may calculate the required amount of reflux liquid using the amount of feed air (measured flow rate value, calculated value) as a variable and control the amount of liquid nitrogen led out from the liquid nitrogen buffer (5, 9) so as to maintain the purity of the product nitrogen when the amount of the product nitrogen is increased. The control step may include monitoring the amount of liquid nitrogen stored in the liquid nitrogen buffer (5) that is discharged based on the pressure difference between the upper gas phase (23) and the bottom of the liquid nitrogen buffer (5) and controlling the amount of liquid nitrogen that is discharged. The control step may control the amount of liquid nitrogen stored in the liquid nitrogen buffer (5, 9) that is discharged (the amount of liquid nitrogen that is fed to the distributor or the rectification section) based on the pressure difference between the top and bottom of a distributor (202) for distributing the reflux liquid, or the pressure difference between the top and bottom of the rectification section.

[0024] "Product nitrogen gas" has a nitrogen concentration of 99.999% or more. "Liquid nitrogen (circulating liquid)" has a nitrogen concentration of 99.999% or more. The nitrogen generators (A1, A2, A3, A4, A5, B1) are Various measuring instruments such as flow rate measuring instruments, pressure measuring instruments, temperature measuring instruments, and liquid level measuring instruments, Various valves such as control valves and gate valves, Piping that connects each element;

[0043]

[0025] (Action and effect) (1) Even if there is a rapid change in nitrogen demand, the amount of product nitrogen produced can be increased while maintaining the purity of the product nitrogen. (2) In conventional technology, when there was a fluctuation in nitrogen demand, it was common to vaporize liquid nitrogen that had been stored in advance and supply it. However, in this case, the energy used to liquefy the nitrogen was released during the vaporization process, resulting in energy consumption associated with the liquefaction and vaporization of nitrogen. According to the present invention, a nitrogen liquefaction device is not required, and the energy consumption associated with the liquefaction and vaporization of nitrogen is also eliminated. (3) It is particularly useful for nitrogen generators for facilities where the power supply fluctuates frequently (e.g., for green ammonia production). [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a diagram showing a nitrogen generating apparatus according to a first embodiment. [Diagram 2] FIG. 1 is a diagram showing a nitrogen generating apparatus according to a second embodiment. [Diagram 3] FIG. 11 is a diagram showing a nitrogen generating apparatus according to a third embodiment. [Figure 4] FIG. 11 is a diagram showing a nitrogen generating apparatus according to a fourth embodiment. [Diagram 5] FIG. 13 is a diagram showing a nitrogen generating apparatus according to a fifth embodiment. [Figure 6] FIG. 13 is a diagram showing a nitrogen generating apparatus according to a sixth embodiment. [Figure 7] FIG. 13 is a diagram showing a nitrogen generating apparatus according to a seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Several embodiments of the present disclosure will be described below. The embodiments described below are examples of the present disclosure. The present disclosure is not limited to the following embodiments, and includes various modified forms implemented within the scope of the present disclosure. Note that not all of the configurations described below are essential configurations of the present disclosure. Upstream and downstream are based on the flow direction of the gas flow.

[0028] (Embodiment 1) The nitrogen generating apparatus A1 of the first embodiment will be described with reference to FIG. The nitrogen generation apparatus A1 includes a main heat exchanger 1, a nitrogen rectification column 2, a nitrogen condenser 3, a liquid nitrogen buffer 5, a liquid nitrogen discharge means, and a control unit 8. In the main heat exchanger 1, raw air is introduced from the hot end and discharged from the cold end, while product nitrogen gas and waste gas are introduced from the cold end and discharged from the hot end. The raw air is sent to the main heat exchanger 1 after certain impurities and moisture are removed. The feed air piping line L1 is a piping line for sending the feed air to the main heat exchanger 1 and then to the nitrogen rectification column 2. The feed air flow meter F1 is provided in the feed air piping line L1 upstream of the main heat exchanger 1, and measures the flow rate of the feed air.

[0029] The nitrogen rectification column 2 has a bottom portion 21 into which the feed air cooled in the main heat exchanger 1 is introduced, a rectification section 22, and an upper gas phase section 23. The rectification section 22 may have a lower rectification section 221 and an upper rectification section 222. The oxygen-enriched liquid piping line L21 is a piping line that sends the oxygen-enriched liquid discharged from the bottom 21 to the refrigerant phase of the nitrogen condenser 3. A valve V1 provided in the oxygen-enriched liquid piping line L21 is opened or the flow rate is controlled when sending the oxygen-enriched liquid.

[0030] The nitrogen condenser 3 condenses the vapor flow (nitrogen-enriched gas) led out from the upper vapor phase section 23 of the nitrogen rectification column 2, and circulates liquid nitrogen (circulating liquid) to the upper vapor phase section 23. The circulating liquid pipe L301 is a pipe line for introducing a vapor flow from the upper gas phase part 23 and returning the liquid nitrogen condensed in the nitrogen condenser 3 to the upper gas phase part 23.

[0031] The waste gas piping line L31 is a piping line for taking out the gas discharged from the upper gas phase 311 of the nitrogen condenser 3 via the main heat exchanger 1 as waste gas. The product nitrogen gas piping line L23 is a piping line for taking out the nitrogen gas discharged from the upper gas phase section 23 via the main heat exchanger 1 as product nitrogen gas.

[0032] The liquid nitrogen buffer 5 is provided below the outlet of the circulating liquid pipe L301 inside the upper gas phase section 23 of the nitrogen rectification column 2, and receives and stores liquid nitrogen. The liquid nitrogen buffer 5 may be configured such that when the liquid nitrogen reaches the upper limit of its storage volume, it is sent to the rectification section 22 below by an overflow structure. The liquid nitrogen buffer 5 may be configured such that, during steady operation of the product nitrogen production and during volume reduction, excess liquid nitrogen (reflux liquid) is stored up to the upper limit of the liquid nitrogen buffer 5 and allowed to overflow. The liquid nitrogen buffer 5 may be configured such that, during volume reduction of the product nitrogen production, the liquid nitrogen (reflux liquid) is stored up to the upper limit of the liquid nitrogen buffer 5 without reducing the amount of feed air for a predetermined period of time.

[0033] The liquid nitrogen discharge means includes a first discharge pipe L7 extending from the bottom of the liquid nitrogen buffer 5, and a first control valve 7 provided on the first discharge pipe L7. The control unit 8 controls the opening and closing of the first control valve 7 so that liquid nitrogen (reflux liquid) is discharged from the liquid nitrogen buffer 5 to the upper distributor 202 of the rectification section 22 in response to an increase in the flow rate of the feed air as measured by the feed air flow meter F1, or controls the flow rate of the liquid nitrogen (reflux liquid) after the valve is opened.

[0034] For example, the control unit 8 calculates the required amount of reflux liquid using the amount of feed air (measured flow rate, calculated value) as a variable so as to maintain the purity of the product nitrogen when the amount of product nitrogen is increased. Increase in feed air = Increase in product nitrogen x A (1) Required amount of reflux liquid = Increase in amount of feed air × B (2) In equations (1) and (2), the increase in feed air and the increase in product nitrogen are directly proportional to the required amount of reflux liquid.

[0035] For example, when increasing the amount of product nitrogen, the control unit 8 may calculate the required amount of reflux liquid using the amount of feed air (flow rate measurement value, calculated value) as a variable so that the reflux liquid to vapor flow ratio (L / V) does not fall below a preset control value (parameter that determines the nitrogen purity), and determine the amount of liquid nitrogen to be derived from the liquid nitrogen buffer 5.

[0036] The differential pressure gauge 6 measures the pressure difference between the upper gas phase 23 and the bottom of the liquid nitrogen buffer 5 . The control unit 8 may monitor the amount of liquid nitrogen stored in the liquid nitrogen buffer 5 being discharged based on the measurement value of the differential pressure gauge 6, for example, and control the amount of liquid nitrogen being discharged. Note that a liquid level gauge for measuring the liquid level of the liquid nitrogen buffer 5 may be provided instead of the differential pressure gauge 6. The control unit 8 may monitor the amount of liquid nitrogen stored in the liquid nitrogen buffer 5 being discharged and control the amount of liquid nitrogen being discharged, for example, based on the measurement value of the liquid level gauge.

[0037] The lower distributor 201 and the upper distributor 202 distribute the reflux liquid so as to be uniform to the rectification section 22. The lower distributor 201 and the upper distributor 202 each have a plurality of storage sections each having an overflow structure and capable of storing a predetermined amount of liquid, and an opening provided below the storage section, and are configured such that liquid overflowing from a storage section is sent to the adjacent storage section.

[0038] (Embodiment 2) The nitrogen generation device A2 of the second embodiment will be described with reference to FIG. The same reference numerals as those in the nitrogen generating apparatus A1 have the same functions, and therefore the explanation thereof will be omitted or simplified. The nitrogen generation apparatus A2 is equipped with a first outlet pipe L7, a first adjustment valve 7, a second outlet pipe L72, and a second adjustment valve 72 as liquid nitrogen outlet means. The second outlet pipe L72 is a pipe line that branches off from the first outlet pipe L7 upstream of the first control valve 7 and introduces liquid nitrogen (reflux liquid) to the lower distributor 201. The second adjustment valve 72 is provided in the second outlet pipe L72. The control unit 8 controls the opening and closing of the first control valve 7 and the second control valve 72 so as to guide liquid nitrogen (reflux liquid) from the liquid nitrogen buffer 5 to the upper distributor 202 and the lower distributor 201 of the rectification section 22, or controls the flow rate of liquid nitrogen (reflux liquid) after the valves are opened.

[0039] (Embodiment 3) The nitrogen generating apparatus A3 of the third embodiment will be described with reference to FIG. The same reference numerals as those in nitrogen generator A1 have the same functions, and therefore their explanation will be omitted or simplified. Nitrogen generator A3 is configured without a feed air flow meter F1, and control unit 8 is configured without using the measurement results of feed air flow meter F1. The nitrogen generator A3 is equipped with a distributor differential pressure gauge 62. The distributor differential pressure gauge 62 measures the pressure difference between the top and bottom of the upper distributor 202. The control unit 8 controls the amount of liquid nitrogen stored in the liquid nitrogen buffer 5 to be discharged based on the measurement value (the following formula (3)) of the distributor differential pressure gauge 62. The increase in the amount of product nitrogen is not necessarily constant, and may show a nonlinear increase tendency due to fluctuations in demand or disturbances. In such a case, the required amount of liquid nitrogen (input amount) is determined by the increase in the feed air, and the input flow rate is adjusted by adjusting the input amount of liquid nitrogen so that the differential pressure measurement value in the upstream distributor 202 does not deviate from a preset differential pressure operation range.

[0040] The liquid level in the upper distributor 202 is determined by the balance between the reflux liquid supplied from the nitrogen condenser 3 or the upper stage of the nitrogen rectification column 2, the liquid nitrogen supplied from the liquid nitrogen buffer 5, and the amount of liquid descending from the upper distributor 202. The reflux liquid supplied from the nitrogen condenser 3 or the upper stage of the nitrogen rectification column 2 is brought about by condensation of the vapor flow, and is reflected in the liquid level of the upper distributor 202 with a delay compared to the liquid nitrogen supplied from the liquid nitrogen buffer 5. Therefore, if liquid nitrogen is continued to be added to maintain the target liquid level, the supply amount may become excessive, causing liquid overflow at the upper distributor 202 or the bottom 21 of the nitrogen rectification column 2. To avoid this, the liquid volume inside the nitrogen rectification column 2 can be calculated from the measurement value of the liquid level gauge installed inside the nitrogen rectification column 2, and the amount of liquid nitrogen added can be limited so that the sum of the liquid volume and the amount of liquid nitrogen added does not exceed the allowable value.

[0041] In a steady state, there is a positive correlation between the amount of feed air, the amount of product nitrogen, and the amount of reflux liquid. The liquid level in the distributor can be determined by the head pressure, which is determined by the amount of reflux liquid passing through the distributor and the pressure difference in the liquid flow path, and the reflux liquid density. The liquid level can be calculated from the pressure difference between the top and bottom of the head and the liquid density. When increasing the amount of product nitrogen, assume that the initial condition C1 is reached at time t before the target condition C2 is reached. First, the amount of feed air is increased (ΔF air =A c2 -A c1 ) and the reflux liquid is insufficient by the increase in the feed air (ΔL = L c2 -L c1 ) so liquid nitrogen must be added. The flow rate of liquid nitrogen is calculated by the cross-sectional area A of the return liquid of the distributor. F(liquid nitrogen=l n2 ) = ΔL (distributor liquid level difference) × A (flow path cross-sectional area) / t (increase time) (3) In other words, the required liquid volume is calculated by multiplying the liquid level by the cross-sectional area of ​​the flow path, and then divided by the time t to calculate the volumetric flow rate. This makes it possible to maintain the nitrogen purity even if the product nitrogen volume is increased at the same time as the feed air flow rate is increased.

[0042] (Another embodiment) Instead of the distributor differential pressure gauge 62, a rectifying section differential pressure gauge (not shown) that measures the pressure difference between the lower and upper parts of the upper rectifying section 222 may be provided. In this case, the control unit 8 controls the amount of liquid nitrogen stored in the liquid nitrogen buffer 5 to be discharged based on the measurement value of the rectification section differential pressure gauge. Since the rectification section 22 contains ordered or random packing, a pressure difference occurs due to contact between the feed air amount and the reflux liquid, and the pressure difference in the rectification section can be utilized. When the reflux liquid is insufficient, the liquid on the surface of the rectification section dries up, and the turbulent flow mode of the gas-liquid contact surface disappears, so that the pressure difference disappears. The control unit 8 may control the introduction of reflux liquid so as to maintain the pressure difference in the rectification section.

[0043] (Embodiment 4) A nitrogen generating apparatus A4 according to the fourth embodiment will be described with reference to FIG. The same reference numerals as those in the nitrogen generators A1 and A3 have the same functions, and therefore the explanation will be omitted or simplified. The nitrogen generator A4 is equipped with a feed air flow meter F1. The nitrogen generator A4 is equipped with a distributor differential pressure gauge 62. The distributor differential pressure gauge 62 measures the pressure difference between the top and bottom of the upper distributor 202. The control unit 8 calculates the required amount of reflux liquid using the amount of raw air (flow rate measurement value, calculated value) as a variable, and controls the amount of liquid nitrogen stored in the liquid nitrogen buffer 5 to be discharged based on the measurement value of the distributor differential pressure gauge 62.

[0044] (Another embodiment) Instead of the distributor differential pressure gauge 62, a rectifying section differential pressure gauge (not shown) that measures the pressure difference between the lower and upper parts of the upper rectifying section 222 may be provided. In this case, the control unit 8 calculates the required amount of reflux liquid using the amount of feed air (flow rate measurement value, calculated value) as a variable, and controls the amount of liquid nitrogen stored in the liquid nitrogen buffer 5 to be discharged based on the measurement value of the rectification section differential pressure gauge. Since the rectification section 22 contains ordered or random packing, a pressure difference occurs due to contact between the feed air amount and the reflux liquid, and the pressure difference in the rectification section can be utilized. When the reflux liquid is insufficient, the liquid on the surface of the rectification section dries up, and the turbulent flow mode of the gas-liquid contact surface disappears, so that the pressure difference disappears. The control unit 8 may control the introduction of reflux liquid so as to maintain the pressure difference in the rectification section.

[0045] (Embodiment 5) A nitrogen generating apparatus A5 according to the fifth embodiment will be described with reference to FIG. The same reference numerals as those in the nitrogen generators A1 and A4 have the same functions, and therefore the explanation thereof will be omitted or simplified. The nitrogen generation apparatus A5 includes a rectification section 4, an expansion turbine 101, a recycle compressor 111, and a waste gas supply pressure control section 81.

[0046] The waste gas piping line L31 is a piping line for passing the gas (oxygen-containing liquid evaporated gas) discharged from above the nitrogen condenser 3 through the main heat exchanger 1 and the expansion turbine 101 again, and extracting it as waste gas. The expansion turbine 101 is provided in the waste gas piping line L31, and takes out the gas (oxygen-containing liquid evaporated gas) discharged from the upper part 311 of the nitrogen condenser 3 from the middle part of the main heat exchanger 1, exchanges heat (heats) and then expands. The branch piping line L311 is a piping line that branches off from the waste gas piping line L31 between the main heat exchanger 1 and the expansion turbine 101 on the upstream side of the expansion turbine 101 and joins the waste gas piping line L31 between the expansion turbine 101 and the main heat exchanger 1 on the downstream side of the expansion turbine 101. The flow rate control valve 102 is provided in the branch piping line L311 and adjusts the gas flow rate diverted from the waste gas piping line L31 to the branch piping line L311. The upper gas phase pressure gauge 61 measures the pressure of the upper gas phase 23. The waste gas pressure gauge 63 is provided in the waste gas piping line L31 upstream of the branch piping line L311 and measures the gas pressure. The waste gas supply pressure control unit 81 opens and closes the flow control valve 102 or controls the flow rate based on the measurement results of the upper gas phase pressure gauge 61 and the waste gas pressure gauge 63, so as to reduce the pressure of the waste gas flow on the inlet side of the expansion turbine 101 or to reduce the pressure on the low-temperature side 311 of the nitrogen condenser 3.

[0047] With this configuration, the pressure at the expansion turbine inlet is controlled to maintain the pressure of the nitrogen rectification tower 2. The expansion turbine pressure is connected to the refrigerant side of the nitrogen condenser 3, and the evaporation pressure of the refrigerant can be adjusted by controlling the turbine inlet pressure. When liquid nitrogen is introduced as the reflux liquid, the composition of the liquid is enriched with nitrogen, so that the liquid temperature drops at the same pressure due to gas-liquid equilibrium. This may result in an excessive drop in the temperature of the nitrogen condenser 3, which may cause the nitrogen to be excessively condensed, resulting in a drop in the pressure of the nitrogen rectification tower 2 and a drop in the pressure of the product nitrogen. The drop in nitrogen pressure can be avoided by controlling the turbine inlet pressure, for example by opening and closing the flow control valve 102, so as to increase the refrigerant side pressure of the nitrogen condenser 3.

[0048] The rectification section 4 is provided above the nitrogen condenser (3). The recycle piping line L42 is a piping line that allows gas (recycle gas) discharged from the upper part 42 of the rectification section 4 to flow through the main heat exchanger 1 and join the feed air piping line L1 upstream of the main heat exchanger 1. The recycle compressor 111 is provided in the recycle piping line L42, and compresses the gas (recycle gas) discharged from the upper part 42 of the rectification section 4 after the gas has been heat exchanged (heated) through the main heat exchanger 1. The cooling means 112 is provided in the recycle piping line L42 and cools the gas compressed by the recycle compressor 111.

[0049] With this configuration, a part of the recycled gas (oxygen-containing evaporated gas) discharged from the upper part 42 of the rectification section 4 is cooled by the main heat exchanger 1, compressed by the recycle compressor 111, cooled again by the main heat exchanger 1, and resupplied to the nitrogen rectification column 2. The oxygen-containing evaporated gas is pressurized and contains a sufficient amount of nitrogen, so that it is recovered by refrigeration in the main heat exchanger 1, compressed by the recycle compressor 111, and rectified in the nitrogen rectification column 2, thereby increasing the amount of product nitrogen with less energy than compressing air at atmospheric pressure. In the configuration of the fifth embodiment (Fig. 5), the rectification section 4 composed of structured packing, trays, etc. is provided above the nitrogen condenser 3, and the oxygen-enriched liquid supplied from the bottom 21 of the nitrogen rectification column 2 and the oxygen-containing evaporated gas supplied from the nitrogen condenser 3 are brought into gas-liquid contact. In this way, the gas in which nitrogen is concentrated can be discharged as recycled air from further above 42 of the rectification section 4 above 311 of the nitrogen condenser 3, and the product nitrogen can be recovered more efficiently.

[0050] (Embodiment 6) A nitrogen generating apparatus B1 according to the sixth embodiment will be described with reference to FIG. The same reference numerals as those in the nitrogen generating apparatus A1 have the same functions, and therefore the explanation thereof will be omitted or simplified. Nitrogen generator B1 differs from nitrogen generator A1 in that liquid nitrogen buffer 9 is provided outside nitrogen rectification column 2 rather than inside it. The circulating fluid branch pipe L302 is a pipe line that branches off from the circulating fluid pipe L301 leading out from the nitrogen condenser 3, and sends liquid nitrogen (circulating fluid) to the lower part of the liquid nitrogen buffer 9. The third outlet pipe L303 is a pipe line leading out from the bottom of the liquid nitrogen buffer 9. The liquid feed pump 92 is provided in the third outlet pipe L303. The third control valve 93 is provided in the third outlet pipe L303 downstream of the liquid feed pump 92. The differential pressure gauge 91 measures the pressure difference between the bottom and top of the liquid nitrogen buffer 9 in order to measure the amount of liquid nitrogen stored in the liquid nitrogen buffer 9. The control unit 8 drives the liquid feed pump 92 and controls the opening and closing and flow rate of the third control valve 93 so as to draw liquid nitrogen (reflux liquid) from the liquid nitrogen buffer 9 to the rectification unit 22 in response to an increase in the measurement value of the feed air flow meter F1 exceeding a predetermined amount. The control unit 8 may control the amount of stored liquid nitrogen to be discharged based on the measurement value of the differential pressure gauge 91. The control unit 8 may control the liquid feed pump 92 to stop and / or the third control valve 93 to close when the amount of liquid nitrogen that can be discharged from the liquid nitrogen buffer 9 reaches a lower limit.

[0051] (Another embodiment) The sixth embodiment may include a rectification section 4, an expansion turbine 101, a recycle compressor 111, a waste gas supply pressure control section 81, and the like, which are configured similarly to the fifth embodiment. Moreover, the sixth embodiment may include a distributor differential pressure gauge similar to those in the third and fourth embodiments, and the control unit 8 may perform similar control.

[0052] (Embodiment 7) The nitrogen generating apparatus B2 of the seventh embodiment will be described with reference to FIG. The same reference numerals as those in the nitrogen generating apparatus B1 of the sixth embodiment have the same functions, and therefore the description thereof will be omitted or simplified. The nitrogen generator B2 is different from the nitrogen generator B1 in that it is provided with a second nitrogen rectifier 4 and a second nitrogen condenser 5. Similarly, the liquid nitrogen buffer 90 is provided outside the first and second nitrogen rectification columns 2, 4, rather than inside them. The first nitrogen rectification column 2 has a gas phase section at the bottom 21 into which the feed air cooled in the main heat exchanger 1 is introduced, a rectification section 22, and an upper gas phase section . The first nitrogen condenser 3 condenses (cools) the vapor flow sent from the upper vapor phase part of the first nitrogen rectification column 2 through the first circulating liquid pipe L231, and circulates the vapor flow to the upper vapor phase part . The second nitrogen rectification column 4 has rectification sections (41, 421, 42) to which the oxygen-enriched liquid is introduced from the bottom 21 of the first nitrogen rectification column 2 via the oxygen-enriched liquid piping line L21. In this embodiment, the oxygen-enriched liquid is introduced into the rectification section 421 in the middle section. The second nitrogen condenser 5 condenses (cools) the vapor flow discharged from the upper vapor phase section 43 of the second nitrogen rectification column 4 through the second circulating liquid pipe L43, and circulates the vapor flow to the upper vapor phase section 43. The liquid nitrogen buffer 90 stores the condensate that returns to the upper gas phase section 43 of the second nitrogen rectification column 4 through the second circulation liquid pipe L43. In this embodiment, the condensate is sent to the liquid nitrogen buffer 90 through an outlet pipe L302 branched off from the second circulation liquid pipe L43. The product nitrogen extraction line L23 is a piping line that leads out from the upper gas phase section 23 of the first nitrogen rectification column 2 and passes through the main heat exchanger 1 to extract product nitrogen. The first circulating liquid piping L231 may be branched off from the product nitrogen extraction line L23 or may be an independent piping line. The waste gas withdrawal line L51 is a piping line that leads out from the upper gas phase section 52 of the second nitrogen condenser section 5 and passes through the main heat exchanger 1 to withdraw the waste gas. The refrigerant piping line L31 is a piping line that is led out from the refrigerant phase 31 of the first nitrogen condenser 3 and is used to deliver refrigerant liquid to the refrigerant phase 51 of the second nitrogen condenser 5. This piping line may be provided with a gate valve. The third outlet pipe L303 is a piping line leading out from the bottom of the liquid nitrogen buffer 90. The liquid feed pump 902 is provided in the third outlet pipe L303. The third control valve 903 is provided in the third outlet pipe L303 downstream of the liquid feed pump 902. The differential pressure gauge 901 measures the pressure difference between the bottom and top of the liquid nitrogen buffer 90 in order to measure the amount of liquid nitrogen stored in the liquid nitrogen buffer 90. The control unit 80 drives the liquid feed pump 902 and controls the opening and closing and flow rate of the third control valve 903 so as to draw liquid nitrogen (reflux liquid) from the liquid nitrogen buffer 90 to the upper gas phase section 23 of the first nitrogen rectification column 2 in response to an increase in the measurement value of the feed air flow meter F1 exceeding a predetermined amount. The control unit 80 may control the amount of stored liquid nitrogen to be discharged based on the measurement value of the differential pressure gauge 901. The control unit 80 may control the liquid feed pump 902 to stop and / or the third control valve 903 to close when the amount of liquid nitrogen that can be discharged from the liquid nitrogen buffer 90 reaches a lower limit.

[0053] (Example) 4 shows the results of a physical simulation of the nitrogen generation apparatus A1 of the first embodiment. Operating at 9 barG (gauge pressure), 167 Nm 3 The nitrogen generator generates nitrogen at 167 Nm / min. The internal reflux ratio of the nitrogen rectification column 2 is 0.6. 3 To generate nitrogen at 417Nm / min 3 / h steam flow and 250Nm 3 A reflux rate of 1 / min is required. When increasing the nitrogen production rate by 10% / min, it is necessary to first increase the feed air by the same ratio or more. However, if liquid nitrogen is not being added, the reflux liquid to vapor flow ratio (L / V) must be maintained at 250 Nm to maintain the reflux liquid in order to maintain purity. 3 / min to 275Nm 3 / min. In the conventional method (comparison example), in order to stably operate the nitrogen rectification column 2 even when there are slight fluctuations in the feed air or disturbances, a margin of several percent is provided in the reflux liquid. Therefore, if the amount of product nitrogen gas is increased by about 1% / min, a purity defect does not occur. However, if the increase rate is about 10% / min, it is necessary to reduce the amount of product nitrogen gas and increase the amount of reflux liquid in order to maintain the purity of the product nitrogen gas. As a result, the amount of nitrogen generated is reduced to 142 Nm 3 The dose had to be reduced to / min. In contrast, in the nitrogen generator A1 of the first embodiment, liquid nitrogen can be introduced from the liquid nitrogen buffer, and the shortage of reflux liquid, i.e., (275 Nm 3 / min-250Nm 3 / min)=25Nm 3 / min, the amount of nitrogen can be increased while maintaining purity. Determining the amount of liquid nitrogen to be added based solely on the reflux liquid flow rate before the increase in the amount of product nitrogen may result in losses due to excessive liquid supply to the nitrogen rectification column 2, or poor nitrogen purity due to insufficient liquid supply. In the nitrogen generation apparatus A1 of the first embodiment, the amount of liquid nitrogen to be introduced from the liquid nitrogen buffer when the product nitrogen is increased is determined based on the liquid amount in the nitrogen rectification column 2 estimated from the material balance of the nitrogen rectification column 2 or the differential pressure in one or more of the nitrogen rectification columns 2. Furthermore, the above-mentioned problem is solved by performing PID control so that the target control liquid level is maintained.

[0054] (Another embodiment) (1) Although not specifically stated, pressure regulators, flow control devices, etc. may be installed in each piping line to adjust the pressure or flow rate. (2) Although not specifically stated, control valves, gate valves, etc. may be installed on each line. (3) Although not specifically stated, each tower may be equipped with a pressure regulator, a temperature measuring device, etc., for pressure or temperature regulation. [Explanation of symbols]

[0055] 1 heat exchanger 2 Nitrogen rectification tower 3 Nitrogen condenser 4. Rectification section 5. Liquid Nitrogen Buffer 8. Control Unit 9. Liquid Nitrogen Buffer

Claims

1. a main heat exchanger for cooling the feed air; at least one nitrogen rectification column into which the feed air cooled by the main heat exchanger is introduced; at least one nitrogen condenser for condensing and circulating a vapor stream passed from said at least one nitrogen rectification column; a liquid nitrogen buffer provided separately from the nitrogen rectification column or the nitrogen rectification column, for storing the liquid nitrogen condensed by the at least one nitrogen condenser; A liquid nitrogen discharge means for discharging the liquid nitrogen stored in the liquid nitrogen buffer; a control unit that controls the liquid nitrogen discharge means so as to discharge the liquid nitrogen from the liquid nitrogen buffer to the at least one nitrogen rectification column in response to an increase in the amount of product nitrogen; A nitrogen generating apparatus comprising:

2. a feed air flow meter for measuring a flow rate of the feed air, the control unit controls the liquid nitrogen discharge means to discharge the liquid nitrogen from the liquid nitrogen buffer to the rectifying unit in response to an increase in the flow rate of the feed air as measured by the feed air flow meter. The nitrogen generating apparatus of claim 1.

3. 3. The nitrogen generating apparatus according to claim 1, wherein the control unit calculates the required amount of reflux liquid using the amount of feed air as a variable so that the reflux liquid to vapor flow ratio (L / V) does not fall below a preset control value when increasing the amount of product nitrogen, and determines the amount of liquid nitrogen to be drawn off from the liquid nitrogen buffer.

4. A differential pressure gauge is provided to measure the pressure difference between the upper gas phase of the nitrogen rectification column and the bottom of the liquid nitrogen buffer. The nitrogen generating apparatus according to claim 1 or 2.

5. 3. The nitrogen generating apparatus according to claim 1, further comprising a distributor disposed above the rectifying section for uniformly distributing the reflux liquid or the liquid nitrogen to the rectifying section.

6. a distributor provided above the rectifying section for distributing the reflux liquid or the liquid nitrogen evenly over a flat area of ​​the rectifying section; a distributor differential pressure gauge for measuring the pressure difference between the top and bottom of the distributor; The nitrogen generating apparatus according to claim 1 or 2, comprising:

7. A rectification section differential pressure gauge is provided to measure the pressure difference between the upper and lower parts of the rectification section. The nitrogen generating apparatus according to claim 1 or 2.

8. an expansion turbine in which the gas discharged from above the nitrogen condenser is heat exchanged through the main heat exchanger and then expanded; a waste gas piping line for passing the gas discharged from above the nitrogen condenser through the main heat exchanger and the expansion turbine, and then through the main heat exchanger again, and extracting the gas as waste gas; a branch piping line that is branched off from the exhaust gas piping line between the main heat exchanger and the expansion turbine on an upstream side of the expansion turbine and that joins the exhaust gas piping line between the expansion turbine and the main heat exchanger on a downstream side of the expansion turbine; a flow rate control valve provided in the branch piping line for controlling a flow rate of gas diverted from the waste gas piping line to the branch piping line; an upper gas phase pressure gauge for measuring the pressure of the upper gas phase of the nitrogen rectification column; an exhaust gas pressure gauge that is provided in the exhaust gas piping line between the main heat exchanger and the expansion turbine and upstream of the expansion turbine, or in the exhaust gas piping line upstream of the branch piping line, for measuring a pressure of gas; an exhaust gas supply pressure control unit that opens and closes the flow control valve or controls the flow rate based on the measurement results of the upper gas phase pressure gauge and the exhaust gas pressure gauge so as to reduce the pressure of the exhaust gas flow on the inlet side of the expansion turbine or reduce the pressure on the low temperature side of the nitrogen condenser; Equipped with The nitrogen generating apparatus according to claim 1 or 2.

9. A rectification section provided above the nitrogen condenser; a recycle piping line for allowing the gas discharged from above the rectification section to flow through the main heat exchanger and join a feed air piping line upstream of the main heat exchanger; a recycle compressor provided in the recycle piping line for compressing the gas discharged from above the rectification section after the gas has been heat exchanged through the main heat exchanger; Equipped with The nitrogen generating apparatus according to claim 1 or 2.

10. a circulating liquid branch pipe that branches off from a circulating liquid pipe extending from the nitrogen condenser and that sends the liquid nitrogen to the liquid nitrogen buffer that is provided separately from the nitrogen rectification column; a differential pressure gauge for measuring a pressure difference between a bottom and an upper portion of the liquid nitrogen buffer in order to measure an amount of liquid nitrogen stored in the liquid nitrogen buffer; The liquid nitrogen discharge means is a third outlet pipe extending from a bottom of the liquid nitrogen buffer; a liquid feed pump provided in the circulating liquid branch pipe or the third outlet pipe; 2. The nitrogen generation apparatus according to claim 1, further comprising: a third control valve provided in the third outlet pipe.

11. a main heat exchanger for cooling the feed air; a first nitrogen rectification column having a rectification section or a bottom gas phase section into which the feed air cooled by the main heat exchanger is introduced; a first nitrogen condenser for condensing a vapor stream sent from an upper vapor phase of the first nitrogen rectification column and circulating the vapor stream to the upper vapor phase; a second nitrogen rectification column having a rectification section into which an oxygen-enriched liquid is introduced from the bottom of the first nitrogen rectification column; a second nitrogen condenser for condensing a vapor stream sent from the upper vapor phase of the second nitrogen rectification column and circulating the vapor stream to the upper vapor phase; a liquid nitrogen buffer for storing condensate returning to the upper vapor phase of the second nitrogen rectification column; A liquid nitrogen discharge means for discharging the liquid nitrogen stored in the liquid nitrogen buffer; a control unit for controlling the liquid nitrogen discharge means so as to discharge liquid nitrogen from the liquid nitrogen buffer to an upper gas phase section or a rectification section of the first nitrogen rectification column in response to an increase in the amount of product nitrogen or an increase in the flow rate of the feed air; Equipped with Nitrogen generator.

12. 1. A method for producing product nitrogen using a nitrogen generation apparatus comprising: a main heat exchanger for cooling feed air; a nitrogen distillation column into which the feed air cooled by the main heat exchanger is introduced; and a nitrogen condenser for condensing a vapor stream sent from the nitrogen distillation column and circulating the vapor stream to the nitrogen distillation column, comprising the steps of: The method includes a control step of conducting the liquid nitrogen condensed in the nitrogen condenser, which is stored in the upper gas phase part of the nitrogen rectification column or in a liquid nitrogen buffer provided separately from the nitrogen rectification column, to the rectification part of the nitrogen rectification column in response to an increase in the amount of product nitrogen or an increase in the flow rate of the feed air. Nitrogen generation methods.

13. 13. The nitrogen generation method according to claim 12, wherein the control step calculates the required amount of reflux liquid using the amount of feed air (flow rate measurement value, calculated value) as a variable and controls the amount of liquid nitrogen drawn off from the liquid nitrogen buffer so as to maintain the purity of the product nitrogen when the amount of product nitrogen is increased.

14. 13. The nitrogen generation method according to claim 12, wherein the control step comprises monitoring the amount of liquid nitrogen stored in the liquid nitrogen buffer that is discharged based on a pressure difference between the upper gas phase and a bottom of the liquid nitrogen buffer, and controlling the amount of liquid nitrogen that is discharged.

15. 13. The nitrogen generation method according to claim 12, wherein the control step controls the amount of liquid nitrogen stored in the liquid nitrogen buffer to be discharged based on a pressure difference between the top and bottom of a distributor for distributing a reflux liquid, or a pressure difference between the top and bottom of a rectification section.

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