Patent Application
20250060158
This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to Japanese patent application No. JP 2023-131842, filed Aug. 14, 2023, which is herein incorporated by reference in its entirety.
The present invention relates to a nitrogen generating method and a nitrogen generating device. In particular, the present invention relates to a nitrogen generating method and device with which rapid variations in loads such as feed air are possible.
In recent years, there has been an increasing demand to synthesise ammonia without emitting carbon dioxide. In this regard, it is expected that ammonia will be obtained using hydrogen obtained by electrolysis of water using electric power generated by solar power or wind power, and nitrogen as starting materials. (Referred to as green ammonia.)
Cryogenic separation, with which it is possible to produce high-purity nitrogen on a large scale, is promising as a method for producing nitrogen. From the viewpoint of purity, in particular, it is desirable in terms of the efficiency of ammonia synthesis to control the amount of argon that can be contained in the nitrogen, and it is desirable to employ cryogenic separation since it is technically difficult to control the concentration of argon in nitrogen to an extremely low concentration using other nitrogen generation methods such as membrane separation and adsorption.
The power generation capacity of renewable energy sources such as solar power and wind power depends on environmental variables such as solar irradiance and wind speed, and therefore consumers must either increase and decrease the amount of electric power used in accordance with the fluctuating power generation capacity, or stabilize the power supply by means of electricity storage technologies such as storage batteries.
In relation to the supply of nitrogen by means of cryogenic air separation, a method has been proposed in which surplus nitrogen gas is liquefied and stored when demand is lower than the nitrogen gas production capacity, and conversely, the liquid nitrogen is vaporised to meet demand when demand is high. However, the cost of electricity obtained from renewable energy sources tends to be high when there is a shortage of electricity such that hydrogen cannot be generated and there is a low demand for nitrogen gas, and conversely, tends to be low when electricity is abundant and there is sufficient generation of hydrogen, giving rise to a high demand for nitrogen gas, and therefore this method in which nitrogen gas is liquefied when electricity costs are high and liquid nitrogen is vaporised when costs are low, thereby discarding cold energy, is irrational.
Therefore, a nitrogen generating device should have the capability of increasing or decreasing the nitrogen generation capacity in accordance with the power supply capacity, and more specifically, it is desirable for the amount of feed air to be increased or decreased rapidly in accordance with the nitrogen demand, but a rapid increase in the amount of feed air causes a deterioration in the purity and quality of the nitrogen deteriorate and is therefore problematic. This is because the amount of an oxygen-containing vapour stream within the nitrogen rectification column becomes greater than the amount of reflux liquid. Since a vapour stream supplied from the nitrogen rectification column is liquefied in a nitrogen condenser and is supplied as the reflux liquid, if a high boiling-point component reaches an upper portion of the nitrogen rectification column when there is an increase in the amount of nitrogen produced, the reflux liquid itself becomes contaminated with the high boiling-point component, making it impossible to maintain the purity of the nitrogen.
JP H8-226759 discloses the feature that compressed feed air is supplied to one rectification column, and a portion of nitrogen gas emitted from the rectification column is fractionated, liquefied, and recirculated to the rectification column.
Paragraph and FIG. 7 of JP H10-54658 indicate that excess liquefied air is stored in a storage tank disposed between a liquefaction device and a 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 part of the excess air is used during a second time period when power costs are relatively high.
JP 2012-145320 discloses a device for producing high-pressure nitrogen, the device comprising a high pressure distillation column, a condenser above the high pressure distillation column, a medium pressure distillation column, and a condenser above the medium pressure distillation column.
In order to resolve the abovementioned problems, an objective of the present disclosure is to provide a nitrogen generating method and a nitrogen generating device with which a reflux liquid that is in short supply can be introduced into a nitrogen rectification column when demand for product nitrogen increases. In addition, since excessive introduction of liquid nitrogen can make it difficult to maintain the process balance, another objective of the present disclosure is to provide a nitrogen generating method and a nitrogen generating device with which liquid nitrogen can be introduced while being appropriately managed.
Another objective of the present disclosure is to provide a nitrogen generating method and a nitrogen generating device with which product nitrogen can be supplied at a desired flow rate without disturbing the purity of the product nitrogen, even if a rate of increase or decrease in the amount of feed air increases in accordance with fluctuations in the supply capacity of a renewable energy source, for example.
A nitrogen generating device according to the present disclosure may comprise: 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 (first nitrogen condenser 3 connected to first nitrogen rectification column 2, second nitrogen condenser 5 connected to second nitrogen rectification column 4) which condenses (cools) a vapour stream fed from an upper gas phase portion of the at least one nitrogen rectification column and circulates the same to the upper gas phase portion; and a liquid nitrogen buffer (5, 9, 90) which is provided in the upper gas phase portion (upper gas phase portion of first nitrogen rectification column 2) or separately from the nitrogen rectification column (first nitrogen rectification column 2) and which stores liquid nitrogen (circulating liquid) that has been condensed by the nitrogen condenser (second nitrogen condenser 5).
The liquid nitrogen may be supplied to any of the nitrogen rectification columns (2, 4) from the liquid nitrogen buffer (9, 90) disposed outside and separate from the nitrogen rectification column (first nitrogen rectification column 2).
A nitrogen generating device (A1, A2, A3, A4, A5, B1) according to the present disclosure comprises: a main heat exchanger (1) for cooling feed air; a nitrogen rectification column (2) having a gas phase portion of a rectification portion (22) or a bottom portion (21) into which the feed air cooled in the main heat exchanger (1) is introduced; a nitrogen condenser (3) which condenses (cools) a vapour stream fed from an upper gas phase portion (23) of the nitrogen rectification column (2) (through a circulating liquid pipe L301) and circulates the same to the upper gas phase portion (23); an oxygen-enriched liquid pipeline (L21) for feeding oxygen-enriched liquid from the bottom portion (21) (to a refrigerant phase of the nitrogen condenser (3)) to be utilized as a refrigerant of the nitrogen condenser (3); a liquid nitrogen buffer (5, 9) which is provided in the upper gas phase portion (23) or separately from the nitrogen rectification column (2) (and is provided below the circulating liquid pipe L301) for storing the liquid nitrogen (circulating liquid) condensed by the nitrogen condenser (3); a liquid nitrogen discharge means (first discharge pipe L7, first regulating valve 7, second discharge pipe L72, second regulating valve 72, third discharge pipe L303, liquid feed pump 92, third regulating valve 93) for discharging the stored liquid nitrogen (reflux liquid) from the liquid nitrogen buffer (5, 9); and a control unit (8) for controlling the liquid nitrogen discharge means to discharge the liquid nitrogen (reflux liquid) from the liquid nitrogen buffer (5, 9) to the rectification portion (22) in response to an increase in an amount of product nitrogen or an increase in a flow rate of the feed air.
The nitrogen generating device (A1, A2, A3, A4, A5, B1) may be provided with a feed air pipeline (L1) for introducing the feed air via the main heat exchanger (1) into the nitrogen rectification column (2) having the gas phase portion of the rectification portion (22) or the bottom portion (21).
The liquid nitrogen buffer (5, 9) may be supplied with external liquid nitrogen other than the liquid nitrogen (circulating liquid) condensed by the nitrogen condenser (3).
The nitrogen generating device (A1, A2, A4, A5, B1) may be provided with a feed air flowmeter (F1) (provided in the feed air pipe L1 upstream or downstream of the main heat exchanger 1) for measuring a flow rate of the feed air.
The control unit (8) may control the liquid nitrogen discharge means to discharge the liquid nitrogen (reflux liquid) from the liquid nitrogen buffer (5, 9) to the rectification portion (22) in response to an increase in the flow rate of the feed air, as per a measured value from the feed air flowmeter (F1).
The amount of feed air is increased to increase the amount of product nitrogen, but since there is a temporary shortage of reflux liquid in this case, liquid nitrogen can be supplied from the liquid nitrogen buffer to the rectification portion, as described above, to eliminate the shortage of reflux liquid, thereby maintaining the product nitrogen purity.
The control unit (8) may control the amount of liquid nitrogen to be discharged from the liquid nitrogen buffer (5, 9) by calculating the required amount of reflux liquid using the amount of feed air (flow rate 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.
The amount of feed air can be calculated on the basis of the increase in the amount of product nitrogen, allowing the amount of reflux liquid to be calculated.
Increase in amount of feed air=increase in amount of product nitrogen×A (1)
Required amount of reflux liquid=increase in amount of feed air×B (2)
In formulas (1) and (2), the increase in the amount of feed air and the increase in the amount of product nitrogen are in a directly proportional relationship with respect to the required amount of reflux liquid.
The nitrogen generating device (A1, A2, A3, A4, A5, B1) may be provided with a product nitrogen flowmeter (F2) for measuring the flow rate of product nitrogen fed to a demand point, and the control unit (8) may control the amount of liquid nitrogen to be discharged from the liquid nitrogen buffer (5, 9) by calculating 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.
The control unit (8) may determine the amount of liquid nitrogen to be discharged from the liquid nitrogen buffer (5, 9) by calculating the required amount of reflux liquid using the amount of feed air (flow rate measured value, calculated value) as a variable, such that a reflux liquid to vapour stream ratio (L/V) does not drop below a predetermined control value (parameter determining nitrogen purity) when the amount of product nitrogen is increased.
The nitrogen generating device (A1, A2, A3, A4, A5) may be provided with a differential pressure gauge (6) for measuring a pressure difference between the upper gas phase portion (23) and a bottom portion of the liquid nitrogen buffer (5).
The control unit (8) may monitor the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer (5) on the basis of a measured value from the differential pressure gauge (6), and control the amount being discharged.
The nitrogen generating device (A1, A2, A3, A4, A5, B1) may be provided with distributors (201, 202), which are provided above the rectification portion (22) to distribute the reflux liquid or the liquid nitrogen evenly to the rectification portion (22).
Each distributor (201, 202) may be a structure that includes a plurality of storage portions, each storing a predetermined amount of liquid and having an overflow structure, and openings provided below the storage portions, such that liquid overflowing from each storage portion is fed to an adjacent storage portion.
As a result, although the descending reflux liquid tends to gather from a central portion of the rectification column toward an inner wall portion thereof so as to minimise the contact surface area with a counterflowing vapour stream, by disposing the distributors (201, 202) in the middle of the nitrogen rectification column (2), the reflux liquid can be effectively redistributed.
The nitrogen generating device (A1, A2, A3, A4, A5, B1) may be provided with a distributor differential pressure gauge (62) for measuring a pressure difference between an upper portion and a bottom portion of the distributor (202) and/or a rectification portion differential pressure gauge (not shown) for measuring a pressure difference between an upper portion and a lower portion of the rectification portion (22).
The control unit (8) may control the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer (5, 9) on the basis of a measured value from the distributor differential pressure gauge (62).
The nitrogen generating device (A1, A2, A3, A4, B1) may be provided with a waste gas pipeline (L31) for extracting gas discharged from an upper gas phase of the nitrogen condenser (3) as waste gas, via the main heat exchanger (1).
The nitrogen generating device (A1, A2, A3, A4, A5, B1) may be provided with a product nitrogen gas pipeline (L23) for extracting nitrogen gas discharged from the upper gas phase portion (23) as product nitrogen gas, via the main heat exchanger (1). With regard to the product nitrogen gas, if an indicated value of oxygen concentration from an oxygen analyser provided in an arbitrarily defined location in the product nitrogen gas pipeline or the nitrogen rectification column exceeds an oxygen concentration control value, the product nitrogen gas purity can be adjusted by supplying liquid nitrogen from the liquid nitrogen buffer (5, 9) to the rectification portion or by reducing the amount of product nitrogen gas introduced.
The nitrogen generating device (A5, B1) may be provided with: an expansion turbine (101) for expanding gas (oxygen-containing liquid evaporation gas) that has been discharged from above the nitrogen condenser (3) and that has been subjected to heat exchange (heated) by being passed through (extracted from an intermediate portion of) the main heat exchanger (1); and a waste gas pipeline (L31) for causing the gas (oxygen-containing liquid evaporation gas) discharged from above the nitrogen condenser (3) to pass through the main heat exchanger (1) and the expansion turbine (101), and then pass again through the main heat exchanger (1) and be extracted as waste gas.
The nitrogen generating device (A5, B1) may be provided with: a branch pipeline (L311) that branches off from the waste gas pipeline (L31) upstream of the expansion turbine (101) between the main heat exchanger (1) and the expansion turbine (101), and merges with the waste gas pipeline (L31) downstream of the expansion turbine (101) between the main heat exchanger (1) and the expansion turbine (101); and a flow rate regulating valve (102) provided in the branch pipeline (L311) to regulate a flow rate of gas diverted from the waste gas pipeline (L31) to the branch pipeline (L311).
The nitrogen generating device (A5, B1) may be provided with: an upper gas phase portion pressure gauge (61) for measuring the pressure in the upper gas phase portion (23); a waste gas pressure gauge (63) which is provided in the waste gas pipeline (L31) upstream of the expansion turbine (101) between the main heat exchanger (1) and the expansion turbine (101) or in the waste gas pipeline (L31) upstream of the branch pipeline (L311), to measure the gas pressure; and a waste gas supply pressure control unit (81) for opening and closing the flow rate regulating valve (102) or for performing flow rate control thereof, on the basis of measurement results from the upper gas phase portion pressure gauge (61) and the waste gas pressure gauge (63), so as to reduce the pressure of a waste gas stream on an inlet side of the expansion turbine (101) or to reduce the pressure on a low-temperature side (311) of the nitrogen condenser (3).
The nitrogen generating device (A5, B1) may be provided with: a rectification portion (4) provided above the nitrogen condenser (3); a recycle pipeline (L42) which allows gas (recycle gas) discharged from an upper part (42) of the rectification portion (4) to pass through the main heat exchanger (1) and merge with the feed air pipeline (L1) upstream of the main heat exchanger (1); and a recycle compressor (111) provided in the recycle pipeline (L42) to compress the gas (recycle gas) that has been discharged from the upper part (42) of the rectification portion (4) and that has been subjected to heat exchange (heating) by means of the main heat exchanger (1).
The nitrogen generating device (A5, B1) may be provided with a cooling means (112) provided in the recycle pipeline (L42) to cool the gas that has been 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 portion (21) of the nitrogen rectification column and oxygen-containing evaporation gas supplied from the nitrogen condenser (3).
The nitrogen generating device (B1) may be provided with: a circulating liquid branch pipe (L302) that branches off from the circulating liquid pipe (L301) leading out from the nitrogen condenser (3), to feed the liquid nitrogen (circulating liquid) to the liquid nitrogen buffer (9); and a differential pressure gauge (91) for measuring a pressure difference between a bottom portion and an upper portion of the liquid nitrogen buffer (9) in order to measure the amount of liquid nitrogen stored in the liquid nitrogen buffer (9).
The liquid nitrogen discharge means may be provided with: a third discharge pipe (L303) leading out from a bottom portion of the liquid nitrogen buffer (9); a liquid feed pump (92) provided in the circulating liquid branch pipe (L302) or the third discharge pipe (L303); and a third regulating valve (93) provided in the third discharge pipe (L303).
The control unit (8) may drive the liquid feed pump (92) and control opening and closing of the third regulating valve (93) and the flow rate thereof so as to discharge the liquid nitrogen (reflux liquid) from the liquid nitrogen buffer (9) to the rectification portion (22) in response to an increase in the amount of the product nitrogen or an increase in the measured value from the feed air flowmeter (F1) to or above a predetermined value.
The nitrogen generating device (A1, A2, A3, A4, A5, B1) is configured to increase the amount of feed air in response to an increased demand for the product nitrogen from the demand point.
There may be provided: a compressor for compressing the feed air; a purifying device for removing impurities (including moisture) from the compressed feed air; and a feed air flow rate control unit for controlling an output of the compressor to control the amount of feed air fed in to the main heat exchanger (1).
Another disclosed nitrogen generating device (B2) may comprise: a main heat exchanger (1) for cooling feed air; a first nitrogen rectification column (2) having a gas phase portion of a rectification portion (22) or a bottom portion (21) into which the feed air cooled in the main heat exchanger (1) is introduced; a first nitrogen condenser (3) which condenses (cools) a vapour stream fed from an upper gas phase portion (23) of the first nitrogen rectification column (2) (through a first circulating liquid pipe L231) and circulates the same to the upper gas phase portion (23); a product nitrogen extraction line (L23) which leads out from the upper gas phase portion (23) of the first nitrogen rectification column (2) to extract product nitrogen via the main heat exchanger (1); a second nitrogen rectification column (4) including a rectification portion (41, 421, 42) into which oxygen-enriched liquid is introduced from the bottom portion (21) of the first nitrogen rectification column (2) through the oxygen-enriched liquid pipeline L21; a second nitrogen condenser (5) which condenses (cools) a vapour stream fed from an upper gas phase portion (43) of the second nitrogen rectification column (4) (through a second circulating liquid pipe L43) and circulates the same to the upper gas phase portion (43); a liquid nitrogen buffer (90) to which condensate being returned to the upper gas phase portion (43) of the second nitrogen rectification column (4) is fed through a discharge pipe L302 (which branches off from the second circulating liquid pipe L43) to be stored; a waste gas extraction line (L51) which leads out from an upper gas phase portion (52) of the second nitrogen condenser (5) to extract waste gas via the main heat exchanger (1); a pipeline (L31) which leads out from a refrigerant phase of the first nitrogen condenser (3) to feed refrigerant liquid to a refrigerant phase of the second nitrogen condenser (5); a liquid nitrogen discharge means (third discharge pipe L303, liquid feed pump 902, third regulating valve 903) for discharging the stored liquid nitrogen (reflux liquid) from the liquid nitrogen buffer (90); and a control unit (80) for controlling the liquid nitrogen discharge means to discharge the liquid nitrogen (reflux liquid) from the liquid nitrogen buffer (90) to the upper gas phase portion (23) of the first nitrogen rectification column (2) or the rectification portion 22 (upstream of an intermediate portion thereof) in response to an increase in an amount of product nitrogen or an increase in a flow rate of the feed air.
A nitrogen generating method according to the present disclosure is a method for producing product nitrogen using a nitrogen generating device comprising a main heat exchanger (1) for cooling feed air, a nitrogen rectification column (2) into which the feed air cooled in the main heat exchanger (1) is introduced, and a nitrogen condenser (3) which condenses (cools) a vapour stream fed from the nitrogen rectification column (2) and circulates the same to the nitrogen rectification column (2), the method including a control step for discharging liquid nitrogen (circulating liquid) condensed by the nitrogen condenser (3) and stored in a liquid nitrogen buffer (5, 9), which is provided in an upper gas phase portion (23) of the nitrogen rectification column (2) or separately from the nitrogen rectification column (2), to a rectification portion of the nitrogen rectification column (2) in response to an increase in an amount of product nitrogen or an increase in a flow rate of the feed air.
The control step may involve controlling the amount of liquid nitrogen to be discharged from the liquid nitrogen buffer (5, 9) by calculating the required amount of reflux liquid using the amount of feed air (flow rate 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.
The control step may involve monitoring the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer (5) on the basis of a pressure difference between the upper gas phase portion (23) and a bottom portion of the liquid nitrogen buffer (5), and controlling the amount being discharged.
The control step may involve controlling the discharge amount (amount introduced into the distributor or the rectification portion) of the liquid nitrogen stored in the liquid nitrogen buffer (5, 9) on the basis of a pressure difference between an upper portion and a bottom portion of a distributor (202) for distributing the reflux liquid or a pressure difference between an upper part and a lower part of the rectification portion.
The “product nitrogen gas” has a nitrogen concentration of at least 99.999%. The “liquid nitrogen” (circulating liquid) has a nitrogen concentration of at least 99.999%. The nitrogen generating device (A1, A2, A3, A4, A5, B1) may include 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, and piping for connecting each element.
(1) The amount of product nitrogen produced can be increased while maintaining the product nitrogen purity, even if there is a rapid fluctuation in nitrogen demand.
(2) Although in the prior art it is typical for liquid nitrogen stored in advance to be vaporised and supplied when there is such a fluctuation in the nitrogen demand, since energy used to liquefy the nitrogen is emitted during the vaporisation at this time, energy consumption occurs in conjunction with both liquefaction and vaporisation of the nitrogen, but according to the present invention, a nitrogen liquefaction device is unnecessary, and energy consumption accompanying liquefaction and vaporisation of nitrogen is eliminated.
(3) The present invention is particularly useful for nitrogen generating devices for facilities in which the amount of supplied power fluctuates frequently (for green ammonia production, for example).
Other features and advantages of the invention will be further disclosed in the description that follows, and in several embodiments provided as non-limiting examples in reference to the appended schematic drawings, in which:
Several embodiments of the present invention will be described below. The embodiments described below are given as an example of the present disclosure. The present disclosure is in no way limited by the following embodiments, and also includes a number of variant modes which are implemented within a scope that does not alter the essential point of the present disclosure. It should be noted that not all the constituents described below are necessarily essential to the present disclosure. Upstream and downstream are based on a flow direction of a gas stream.
A nitrogen generating device A1 according to embodiment 1 will be described with reference to
In the main heat exchanger 1, feed air is introduced from a hot end and discharged from a cold end, and product nitrogen gas and waste gas are introduced from the cold end and discharged from the hot end. The feed air is fed to the main heat exchanger 1 after removal of predetermined impurities and moisture.
A feed air pipeline L1 is a pipeline for feeding the feed air to the main heat exchanger 1 and to the nitrogen rectification column 2.
A feed air flowmeter F1 is provided in the feed air pipeline L1 upstream of the main heat exchanger 1 to measure the flow rate of the feed air.
The nitrogen rectification column 2 includes a bottom portion 21 into which the feed air cooled in the main heat exchanger 1 is introduced, a rectification portion 22, and an upper gas phase portion 23. The rectification portion 22 may include a lower rectification portion 221 and an upper rectification portion 222.
An oxygen-enriched liquid pipeline L21 is a pipeline for feeding oxygen-enriched liquid discharged from the bottom portion 21 to a refrigerant phase of the nitrogen condenser 3. A valve V1 provided in the oxygen-enriched liquid pipeline L21 is opened or subjected to flow rate control to feed the oxygen-enriched liquid.
The nitrogen condenser 3 condenses a vapour stream (nitrogen-enriched gas) discharged from the upper gas phase portion 23 of the nitrogen rectification column 2, and circulates liquid nitrogen (circulating liquid) to the upper gas phase portion 23.
A circulating liquid pipe L301 is a pipeline into which the vapour stream from the upper gas phase portion 23 is introduced, and which returns the liquid nitrogen condensed by the nitrogen condenser 3 to the upper gas phase portion 23.
A waste gas pipeline L31 is a pipeline for extracting gas discharged from an upper gas phase 311 of the nitrogen condenser 3 via the main heat exchanger 1 as waste gas.
A product nitrogen gas pipeline L23 is a pipeline for extracting nitrogen gas discharged from the upper gas phase portion 23 via the main heat exchanger 1 as product nitrogen gas.
The liquid nitrogen buffer 5 is provided below an outlet of the circulating liquid pipe L301 inside the upper gas phase portion 23 of the nitrogen rectification column 2, and receives and stores liquid nitrogen.
The liquid nitrogen buffer 5 may have a configuration in which liquid nitrogen that has reached a storage capacity upper limit is fed to the rectification section 22 therebelow by means of an overflow structure. The liquid nitrogen buffer 5 may be configured to store excess liquid nitrogen (reflux liquid) up to the upper limit of the liquid nitrogen buffer 5 and allow the same to overflow during steady state operation of product nitrogen production and when the amount of product nitrogen produced is reduced. The liquid nitrogen buffer 5 may be configured such that, when the amount of product nitrogen being produced is reduced, the amount of feed air is not reduced for a prescribed period of time, and liquid nitrogen (reflux liquid) is stored up to the upper limit of the liquid nitrogen buffer 5.
The liquid nitrogen discharge means comprises a first discharge pipe L7 leading out from a bottom portion of the liquid nitrogen buffer 5, and a first regulating valve 7 provided in the first discharge pipe L7.
The control unit 8 controls the opening and closing of the first regulating valve 7, or controls the flow rate of the liquid nitrogen (reflux liquid) after the valve is opened, such that the liquid nitrogen (reflux liquid) is discharged from the liquid nitrogen buffer 5 to an upper distributor 202 of the rectification portion 22 in response to an increase in the flow rate of the feed air, as per a measured value from the feed air flowmeter F1.
For example, the control unit 8 calculates the required amount of reflux liquid using the amount of feed air (flow rate 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.
Increase in amount of feed air=increase in amount of product nitrogen×A (1)
Required amount of reflux liquid=increase in amount of feed air×B (2)
In formulas (1) and (2), the increase in the amount of feed air and the increase in the amount of product nitrogen are in a directly proportional relationship with respect to the required amount of reflux liquid.
The control unit (8) may, for example, determine the amount of liquid nitrogen to be discharged from the liquid nitrogen buffer 5 by calculating the required amount of reflux liquid using the amount of feed air (flow rate measured value, calculated value) as a variable, such that a reflux liquid to vapour stream ratio (L/V) does not drop below a predetermined control value (parameter determining nitrogen purity) when the amount of product nitrogen is increased.
A differential pressure gauge 6 measures a pressure difference between the upper gas phase portion 23 and the bottom portion of the liquid nitrogen buffer 5. The control unit 8 may, for example, monitor the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer 5 on the basis of a measured value from the differential pressure gauge 6, and control the amount being discharged.
It should be noted that a liquid level meter for measuring the liquid level position in the liquid nitrogen buffer 5 may be provided instead of the differential pressure gauge 6. The control unit 8 may, for example, monitor the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer 5 on the basis of a measured value from the liquid level meter, and control the amount being discharged.
A lower distributor 201 and the upper distributor 202 distribute the reflux liquid to the rectification portion 22 so as to be even. The lower distributor 201 and the upper distributor 202 are structures that include a plurality of storage portions, each storing a predetermined amount of liquid and having an overflow structure, and openings provided below the storage portions, such that liquid overflowing from each storage portion is fed to an adjacent storage portion.
A nitrogen generating device A2 according to embodiment 2 will be described with reference to
Reference signs that are the same as those in the nitrogen generating device A1 denote elements having the same functions, and therefore descriptions thereof are omitted or simplified.
The nitrogen generating device A2 includes, as the liquid nitrogen discharge means, the first discharge pipe L7, the first regulating valve 7, a second discharge pipe L72, and a second regulating valve 72.
The second discharge pipe L72 is a pipeline that branches off from the first discharge pipe L7 upstream of the first regulating valve 7 and introduces liquid nitrogen (reflux liquid) into the lower distributor 201. The second regulating valve 72 is provided in the second discharge pipe L72.
The control unit 8 controls the opening and closing of the first regulating valve 7 and the second regulating valve 72, or controls the flow rate of the liquid nitrogen (reflux liquid) after the valves are opened, such that the liquid nitrogen (reflux liquid) is discharged from the liquid nitrogen buffer 5 to the upper distributor 202 and the lower distributor 201 of the rectification portion 22.
A nitrogen generating device A3 according to embodiment 3 will be described with reference to
Reference signs that are the same as those in the nitrogen generating device A1 denote elements having the same functions, and therefore descriptions thereof are omitted or simplified. The nitrogen generating device A3 has a configuration that does not include the feed air flowmeter F1, and the control unit 8 has a configuration that does not utilize a measurement result from the feed air flowmeter F1.
The nitrogen generating device A3 is provided with a distributor differential pressure gauge 62. The distributor differential pressure gauge 62 measures a pressure difference between an upper portion and a bottom portion of the upper distributor 202.
The control unit 8 controls the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer 5 on the basis of a measured value (formula (3) below) from the distributor differential pressure gauge 62. An increase in the amount of product nitrogen is not necessarily constant, and may exhibit a nonlinear increase trend due to fluctuations in demand or external disturbances. In such cases, the required amount (amount to be introduced) of liquid nitrogen is determined in accordance with an increase in the amount of feed air, and in order to adjust the introduction flow rate thereof, the amount of liquid nitrogen introduced is adjusted such that the measured value of the differential pressure across the upper distributor 202 does not deviate from a predetermined differential pressure operation range.
The liquid level in the upper distributor 202 is determined by a balance between the reflux liquid supplied from the nitrogen condenser 3 or an 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 forms as a result of condensation of the vapour stream, and is therefore 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 continues to be introduced in an attempt to maintain a target value of the liquid level, the amount supplied may become excessive, causing an overflow of liquid in the upper distributor 202 or the bottom portion 21 of the nitrogen rectification column 2. To avoid this, the amount of liquid inside the nitrogen rectification column 2 can be calculated from a measured value obtained by a liquid level meter provided inside the nitrogen rectification column 2, and the amount of liquid nitrogen introduced can be limited such that the sum of said liquid amount and the amount of liquid nitrogen introduced does not exceed an allowable value.
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, and the liquid level in the distributor can be determined from the amount of reflux liquid passing through the distributor, a head pressure, which is determined from a differential pressure across a liquid flow path, and the density of the reflux liquid.
The liquid level can be obtained from a vertical differential pressure of the head and the liquid density. For a case in which the amount of product nitrogen is increasing, assume that it takes a time t to reach a target condition C2 from an initial condition C1. First, assuming an increase in the amount of feed air (ΔFair=Ac2−Ac1), since the reflux liquid is insufficient (ΔL=Lc2−Lc1) by an amount corresponding to the amount of increase of the feed air, liquid nitrogen must be introduced.
With regard to the introduction flow rate of liquid nitrogen, if A is a cross-sectional area of the flow path of the reflux liquid in the distributor:
F(liquid nitrogen=ln2)=ΔL(distributor liquid level difference)×A(flow path cross-sectional area)/t(increase time) (3),
that is, multiplying a liquid level height by the cross-sectional area of the flow path gives the required liquid volume, which is divided by the time t to calculate a volumetric flow rate. This makes it possible to maintain the nitrogen purity even if the amount of product nitrogen is increased simultaneously with an increase in the feed air flow rate.
A rectification portion differential pressure gauge (not shown) for measuring a pressure difference between a lower portion and an upper portion sandwiching the upper rectification portion 222 may be provided instead of the distributor differential pressure gauge 62.
In this case, the control unit 8 controls the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer 5 on the basis of a measurement value from the rectification portion differential pressure gauge.
The rectification portion 22 contains structured or random packing, and therefore a pressure difference arises as a result of contact between the feed air and the reflux liquid, and thus the differential pressure in the rectification portion can be utilized. If there is a shortage of reflux liquid, liquid on the surface of the rectification portion dries up and a turbulent flow mode at the gas-liquid contact surface disappears, causing the differential pressure to disappear. The control unit 8 may perform control to introduce reflux liquid so as to maintain the differential pressure in the rectification portion.
A nitrogen generating device A4 according to embodiment 4 will be described with reference to
Reference signs that are the same as those in the nitrogen generating devices A1 and A3 denote elements having the same functions, and therefore descriptions thereof are omitted or simplified. The nitrogen generating device A4 is provided with the feed air flowmeter F1.
The nitrogen generating device A4 is provided with the distributor differential pressure gauge 62. The distributor differential pressure gauge 62 measures the pressure difference between the upper portion and the bottom portion of the upper distributor 202.
The control unit 8 calculates the required amount of reflux liquid using the amount of feed air (flow rate measured value, calculated value) as a variable, and controls the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer 5 on the basis of the measured value from the distributor differential pressure gauge 62.
A rectification portion differential pressure gauge (not shown) for measuring a pressure difference between a lower portion and an upper portion sandwiching the upper rectification portion 222 may be provided instead of the distributor differential pressure gauge 62.
In this case, the control unit 8 calculates the required amount of reflux liquid using the amount of feed air (flow rate measured value, calculated value) as a variable, and controls the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer 5 on the basis of a measured value from the rectification portion differential pressure gauge.
The rectification portion 22 contains structured or random packing, and therefore a pressure difference arises as a result of contact between the feed air and the reflux liquid, and thus the differential pressure in the rectification portion can be utilized. If there is a shortage of reflux liquid, liquid on the surface of the rectification portion dries up and a turbulent flow mode at the gas-liquid contact surface disappears, causing the differential pressure to disappear. The control unit 8 may perform control to introduce reflux liquid so as to maintain the differential pressure in the rectification portion.
A nitrogen generating device A5 according to embodiment 5 will be described with reference to
Reference signs that are the same as those in the nitrogen generating devices A1 and A4 denote elements having the same functions, and therefore descriptions thereof are omitted or simplified.
The nitrogen generating device A5 is provided with a rectification portion 4, an expansion turbine 101, a recycle compressor 111, and a waste gas supply pressure control unit 81.
The waste gas pipeline L31 is a pipeline for passing gas (oxygen-containing liquid evaporation gas) discharged from above the nitrogen condenser 3 through the main heat exchanger 1 and the expansion turbine 101, and then once again through the main heat exchanger 1, and extracting the same as waste gas.
The expansion turbine 101 is provided in the waste gas pipeline L31 to compress the gas (oxygen-containing liquid evaporation gas) that has been discharged from the upper part 311 of the nitrogen condenser 3 and that has been extracted from an intermediate portion of the main heat exchanger 1 after being subjected to heat exchange (heating).
A branch pipeline L311 is a pipeline that branches off from the waste gas pipeline L31 upstream of the expansion turbine 101 between the main heat exchanger 1 and the expansion turbine 101, and merges with the waste gas pipeline L31 downstream of the expansion turbine 101 between the expansion turbine 101 and the main heat exchanger 1. A flow rate regulating valve 102 is provided in the branch pipeline L311 to regulate a flow rate of gas diverted from the waste gas pipeline L31 to the branch pipeline L311. An upper gas phase portion pressure gauge 61 measures the pressure in the upper gas phase portion 23. A waste gas pressure gauge 63 is provided in the waste gas pipeline L31 upstream of the branch pipeline L311 to measure the gas pressure.
The waste gas supply pressure control unit 81 opens and closes the flow rate regulating valve 102 or performs flow rate control thereof, on the basis of measurement results from the upper gas phase portion pressure gauge 61 and the waste gas pressure gauge 63, so as to reduce the pressure of a waste gas stream on an inlet side of the expansion turbine 101 or to reduce the pressure on a low-temperature side 311 of the nitrogen condenser 3.
With this configuration, the pressure at the expansion turbine inlet is controlled so as to maintain the pressure in the nitrogen rectification column 2. The expansion turbine pressure is coupled to a refrigerant side of the nitrogen condenser 3, and the evaporation pressure of the refrigerant can be adjusted by controlling the turbine inlet pressure. If liquid nitrogen is introduced as the reflux liquid, the liquid composition becomes nitrogen-enriched, and therefore if the pressure is the same, the liquid temperature drops as a result of gas-liquid equilibrium. Consequently, in some cases the temperature in the nitrogen condenser 3 drops excessively, causing the pressure in the nitrogen rectification column 2 to drop as a result of excessive nitrogen condensation, and resulting in a drop in the pressure of the product nitrogen. A drop in the nitrogen pressure can be avoided by controlling the turbine inlet pressure by opening and closing the flow rate regulating valve 102, for example, to increase the refrigerant side pressure in the nitrogen condenser 3.
The rectification portion 4 is provided above the nitrogen condenser (3).
A recycle pipeline L42 is a pipeline which allows gas (recycle gas) discharged from an upper part 42 of the rectification portion 4 to pass through the main heat exchanger 1 and merge with the feed air pipeline L1 upstream of the main heat exchanger 1.
The recycle compressor 111 is provided in the recycle pipeline L42 to compress the gas (recycle gas) that has been discharged from the upper part 42 of the rectification portion 4 and that has been subjected to heat exchange (heating) by means of the main heat exchanger 1.
A cooling means 112 is provided in the recycle pipeline L42 to cool the gas compressed by the recycle compressor 111.
With this configuration, a portion of the recycle gas (oxygen-containing evaporation gas) discharged from the upper part 42 of the rectification portion 4 is cooled in the main heat exchanger 1, is compressed by the recycle compressor 111 and then cooled again in the main heat exchanger 1, and is supplied once again to the nitrogen rectification column 2. Since the oxygen-containing liquid evaporation gas has been pressurized and also contains plenty of nitrogen, by subjecting the oxygen-containing liquid evaporation gas to cold recovery in the main heat exchanger 1 and then compressing the same using the recycle compressor 111 and rectifying the same in the nitrogen rectification column 2, the amount of product nitrogen can be increased using less energy than if air at atmospheric pressure is compressed. In the configuration of embodiment 5 (
A nitrogen generating device B1 according to embodiment 6 will be described with reference to
Reference signs that are the same as those in the nitrogen generating device A1 denote elements having the same functions, and therefore descriptions thereof are omitted or simplified.
The nitrogen generating device B1 differs from the nitrogen generating device A1 in that a liquid nitrogen buffer 9 is provided outside rather than inside the nitrogen rectification column 2.
A circulating liquid branch pipe L302 is a pipeline that branches off from the circulating liquid pipe L301 leading out from the nitrogen condenser 3 to feed the liquid nitrogen (circulating liquid) to a lower portion of the liquid nitrogen buffer 9. A third discharge pipe L303 is a pipeline that leads out from a bottom portion of the liquid nitrogen buffer 9. A liquid feed pump 92 is provided in the third discharge pipe L303. A third regulating valve 93 is provided in the third discharge pipe L303 downstream of the liquid feed pump 92. A differential pressure gauge 91 measures a pressure difference between the bottom portion and an upper portion 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 opening and closing of the third regulating valve 93 and the flow rate thereof so as to discharge the liquid nitrogen (reflux liquid) from the liquid nitrogen buffer 9 to the rectification portion 22 in response to an increase in the measured value from the feed air flowmeter F1 to or above a predetermined value.
The control unit 8 may control the discharge amount of the stored liquid nitrogen on the basis of the measured value from the differential pressure gauge 91. The control unit 8 may control the liquid feed pump 92 to stop and/or control the third regulating valve 93 to close when the amount of liquid nitrogen that can be discharged from the liquid nitrogen buffer 9 reaches a lower limit value.
Embodiment 6 may be provided with the rectification portion 4, the expansion turbine 101, the recycle compressor 111, the waste gas supply pressure control unit 81, and the like, having the same configuration as in embodiment 5.
Further, embodiment 6 may be provided with the same distributor differential pressure gauge as that in embodiments 3 and 4, and the control unit 8 may perform similar control.
A nitrogen generating device B2 according to embodiment 7 will be described with reference to
Reference signs that are the same as those in the nitrogen generating device B1 of embodiment 6 denote elements having the same functions, and therefore descriptions thereof are omitted or simplified.
The nitrogen generating device B2 differs from the nitrogen generating device B1 by being provided with a second nitrogen rectification column 4 and a second nitrogen condenser 5.
A liquid nitrogen buffer 90 is similarly provided outside rather than inside the first and second nitrogen rectification columns 2, 4.
The first nitrogen rectification column 2 includes a gas phase portion in the bottom portion 21, into which the feed air cooled in the main heat exchanger 1 is introduced, the rectification portion 22, and the upper gas phase portion 23.
The first nitrogen condenser 3 condenses (cools) a vapour stream fed through a first circulating liquid pipe L231 from the upper gas phase portion 23 of the first nitrogen rectification column 2, and circulates the same to the upper gas phase portion 23.
The second nitrogen rectification column 4 has a rectification portion (41, 421, 42) into which oxygen-enriched liquid is introduced from the bottom portion 21 of the first nitrogen rectification column 2 via the oxygen-enriched liquid pipeline L21. In the present embodiment, the oxygen-enriched liquid is introduced into an intermediate rectification portion 421.
The second nitrogen condenser 5 condenses (cools) a vapour stream discharged from an upper gas phase portion 43 of the second nitrogen rectification column 4 through a second circulating liquid pipe L43, and circulates the same to the upper gas phase portion 43.
The liquid nitrogen buffer 90 stores the condensate that is being returned to the upper gas phase portion 43 of the second nitrogen rectification column 4 through the second circulating liquid pipe L43. In the present embodiment, the condensate is fed to the liquid nitrogen buffer 90 via a discharge pipe L302 that branches off from the second circulating liquid pipe L43.
A product nitrogen extraction line L23 is a pipeline that leads out from the upper gas phase portion 23 of the first nitrogen rectification column 2 via the main heat exchanger 1 to extract product nitrogen. The first circulating liquid pipe L231 may branch off from the product nitrogen extraction line L23, or may be an independent pipeline.
A waste gas extraction line L51 is a pipeline that leads out from an upper gas phase portion 52 of the second nitrogen condenser section 5 to extract waste gas via the main heat exchanger 1.
A refrigerant pipeline L31 is a pipeline that leads out from a refrigerant phase 31 of the first nitrogen condenser 3 to feed refrigerant liquid to a refrigerant phase 51 of the second nitrogen condenser 5. This pipeline may be provided with a gate valve.
The third discharge pipe L303 is a pipeline that leads out from a bottom portion of the liquid nitrogen buffer 90. A liquid feed pump 902 is provided in the third discharge pipe L303. A third regulating valve 903 is provided in the third discharge pipe L303 downstream of the liquid feed pump 902. A differential pressure gauge 901 measures a pressure difference between the bottom portion and an upper portion of the liquid nitrogen buffer 90 in order to measure the amount of liquid nitrogen stored in the liquid nitrogen buffer 90.
A control unit 80 drives the liquid feed pump 902 and controls opening and closing of the third regulating valve 903 and the flow rate thereof so as to discharge the liquid nitrogen (reflux liquid) from the liquid nitrogen buffer 90 to the upper gas phase portion 23 of the first nitrogen rectification column 2 in response to an increase in the measured value from the feed air flowmeter F1 to or above a predetermined value.
The control unit 80 may control the discharge amount of the stored liquid nitrogen on the basis of a measured value from the differential pressure gauge 901. The control unit 80 may control the liquid feed pump 902 to stop and/or control the third regulating valve 903 to close when the amount of liquid nitrogen that can be discharged from the liquid nitrogen buffer 90 reaches a lower limit value.
The results of a physical simulation of the nitrogen generating device A1 according to embodiment 1 will be presented. Assume a nitrogen generating device that operates at a pressure of 9 barG (gauge pressure) and generates 167 Nm3/min of nitrogen. Assume that an internal reflux ratio of the nitrogen rectification column 2 is 0.6. To generate 167 Nm3/min of nitrogen, a vapour stream of 417 Nm3/h and a descending reflux liquid stream of 250 Nm3/min are required.
To increase the nitrogen production quantity by 10%/min, it is first necessary to increase the feed air by at least the same ratio, and if no liquid nitrogen is introduced, an increase from 250 Nm3/min to 275 Nm3/min is required in order to maintain the amount of reflux liquid so as to maintain the reflux liquid to vapour stream ratio (L/V) in order to maintain the purity.
In a conventional method (comparison example), in order for the nitrogen rectification column 2 to be operated stably even in the event of slight fluctuations or disturbances in the feed air, a margin of several percent is typically provided in the reflux liquid, and therefore an increase of approximately 1%/min in the amount of product nitrogen gas does not cause a purity failure, but if the rate of increase reaches approximately 10%/min, the amount of product nitrogen gas must be reduced to increase the reflux liquid in order to maintain the purity of the product nitrogen gas. As a result, it was necessary to reduce the amount of nitrogen generated to 142 Nm3/min.
In contrast, in the nitrogen generating device A1 of embodiment 1, liquid nitrogen can be introduced from the liquid nitrogen buffer, and thus the amount of nitrogen can be increased while maintaining the purity by supplying liquid nitrogen corresponding to the insufficient amount of reflux liquid, that is, (275 Nm3/min-250 Nm3/min)=25 Nm3/min.
Determining the introduction amount of liquid nitrogen to be added using solely 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 generating device A1 according to embodiment 1, the amount of liquid nitrogen to be introduced from the liquid nitrogen buffer when the amount of product nitrogen is increased is determined on the basis of the amount of liquid in the nitrogen distillation column 2, estimated from a material balance in the nitrogen distillation column 2 or the differential pressure in one or more nitrogen rectification columns 2. Furthermore, the problem discussed hereinabove is resolved by performing PID control to maintain a target control liquid level.
(1) Although not explicitly stated, pressure regulating devices and flow rate control devices, etc. may be installed in each pipeline in order to regulate pressure and regulate flow rate.
(2) Although not explicitly stated, control valves and gate valves, etc. may be installed in each line.
(3) Although not explicitly stated, pressure regulating devices and temperature measuring devices, etc. may be installed in each column in order to regulate pressure and regulate temperature.
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed.
Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP 2023-131842 | Aug 2023 | JP | national |
