JP5032407B2 - Nitrogen production method and apparatus - Google Patents

Description

  The present invention relates to a nitrogen production method and apparatus, and more particularly to a nitrogen production method and apparatus for collecting product nitrogen gas by cryogenic liquefaction separation of compressed, purified and cooled raw material air.

  As a method of producing product nitrogen gas by cryogenic separation of air, basically, a method using a single rectifying column apparatus is widely used. In recent years, in order to improve product yield and power consumption rate. Various processes have been proposed. Among them, a process using two rectifying columns and using waste gas that was discarded in the conventional process as a raw material for the second rectifying column is a waste introduced into the second rectifying column as a raw material. Since the gas is not compressed or heated, there is an advantage that new compression power and a heat exchanger necessary for raising the temperature are basically unnecessary.

In such a two-column process, it may be necessary to raise a part of the product nitrogen gas obtained from the second rectification column to a predetermined pressure, but the required energy is minimized and the conventional energy is minimized. Compared with the process of a single rectification column, it is possible to greatly improve the product yield and the power unit (for example, refer to Patent Documents 1 and 2).
Japanese Patent No. 3738213 JP 2008-164236 A

  However, in the case of the above-mentioned two-column type, there is a lower limit of the apparatus operating pressure due to the nature of these processes, so when the product nitrogen gas pressure is low, take advantage of the characteristics of high product yield. Was difficult. For example, in the process described in Patent Document 1, the product nitrogen gas can be collected efficiently if the pressure of the product nitrogen gas is about 0.80 MPa, but the case where the pressure is lower than that can be handled. Was extremely difficult. Further, in the process described in Patent Document 2, product nitrogen gas can be efficiently collected if the pressure of the product nitrogen gas is about 0.60 MPa, but in the case of a pressure lower than that, for example, product nitrogen When the gas pressure was lowered to about 0.40 MPa, it was extremely difficult to cope with it.

  In addition, by changing the process in the double rectification process, which is generally used for oxygen and nitrogen production, from oxygen and nitrogen production to nitrogen production, the process is suitable for producing low-pressure nitrogen gas. Although it is possible to obtain the product nitrogen gas, there has been a problem that the power unit becomes higher than that in each of the above processes.

  Therefore, the present invention provides a nitrogen production method and apparatus that can efficiently collect product nitrogen gas even when the pressure required for the product nitrogen gas is low and can reduce the power consumption. It is an object.

In order to achieve the above object, the nitrogen production method of the present invention is a nitrogen production method for collecting product nitrogen by subjecting raw material air to cryogenic liquefaction separation, and the compressed, purified, cooled raw material air and the fourth oxygen enrichment described later. Indirect heat exchange with the liquefied fluid is performed to condense and liquefy a part of the raw material air to obtain gas-liquid two-phase air. At the same time, the fourth oxygen-enriched liquefied fluid is vaporized to obtain the fourth oxygen-enriched gas fluid. A first indirect heat exchange step, a first separation step in which the gas-liquid two-phase air is subjected to low-temperature distillation and separated into a first nitrogen gas and a first oxygen-enriched liquefied fluid, and the first oxygen-enriched liquefied fluid is decompressed A first separation step is performed by low-temperature distillation to separate the second nitrogen gas and the second oxygen-enriched liquefied fluid, and the second oxygen-enriched liquefied fluid and the first nitrogen gas are indirectly heat-exchanged for the first. Nitrogen gas is condensed and liquefied to obtain the first liquefied nitrogen and at the same time the second oxygen-enriched liquefied fluid is steamed. A second indirect heat exchange step to obtain a second oxygen-enriched gas stream to gasify the said second oxygen-enriched liquefied stream body unevaporated gasified in the second indirect heat exchange step was withdrawn remained liquid state A third separation step of low-temperature distillation of the 3 oxygen-enriched liquefied fluid to separate it into a third oxygen-enriched gas fluid and a 4th oxygen-enriched liquefied fluid, and the evaporative gasification in the first indirect heat exchange step withdrawing a fourth oxygen enriched liquefied stream body as a fifth oxygen-enriched liquefied fluid remains in a liquid state, the second liquefied nitrogen condensed and liquefied the second nitrogen gas indirect heat is exchanged with the second nitrogen gas after vacuum A third indirect heat exchange step for obtaining a fifth oxygen-enriched gas fluid by evaporating and gasifying the fifth oxygen-enriched liquefied fluid after decompression at the same time, and a product nitrogen gas after heat recovery of a part of the second nitrogen gas And a product recovery process to be collected.

  Furthermore, in the nitrogen production method of the present invention, in the nitrogen production method having the above-described configuration, a cold generation step of introducing the fifth oxygen-enriched gas fluid into an expansion turbine and expanding it in order to obtain the cold necessary for operation of the apparatus. The method includes any one of a cold generation step of introducing a part of the raw material air into an expansion turbine to expand and a liquefied gas injection step of supplying a liquefied gas from outside the system.

Further, the nitrogen production apparatus of the present invention is a nitrogen production apparatus that collects product nitrogen by cryogenic liquefaction separation of raw material air, and indirectly supplies the compressed, purified, and cooled raw material air and a fourth oxygen-enriched liquefied fluid described later. A first indirect heat exchanger for obtaining a fourth oxygen-enriched gas fluid by evaporating and gasifying the fourth oxygen-enriched liquefied fluid at the same time as obtaining a gas-liquid two-phase air by condensing and liquefying part of the raw material air A first rectifying column that separates the gas-liquid two-phase air into a first nitrogen gas and a first oxygen-enriched liquefied fluid by low-temperature distillation, and the first oxygen-enriched liquefied fluid is subjected to low-temperature distillation after depressurization. The second rectification column that separates the second nitrogen gas and the second oxygen-enriched liquefied fluid, and the second oxygen-enriched liquefied fluid and the first nitrogen gas are indirectly heat-exchanged to exchange the first nitrogen gas. Condensed liquefaction to obtain first liquefied nitrogen and at the same time second oxygen-enriched liquefied fluid is evaporated and gasified to second oxygen-enriched A second indirect heat exchanger to obtain a scan fluid was withdrawn while the second oxygen-enriched liquefied stream body unevaporated gasified in the second indirect heat exchanger from the bottom of the second fractionator the liquid state A third rectification column for low-temperature distillation of the third oxygen-enriched liquefied fluid to separate it into a third oxygen-enriched gas fluid and a fourth oxygen-enriched liquefied fluid; and evaporative gasification by the first indirect heat exchanger the fourth oxygen enriched liquefied stream body the third rectification column fifth oxygen-enriched liquefied fluid second nitrogen the second nitrogen gas and allowed to indirect heat exchange after vacuum was extracted remain in the liquid state from the bottom of the A second indirect heat exchanger for condensing and liquefying gas to obtain second liquefied nitrogen and at the same time evaporating gas after depressurizing the fifth oxygen-enriched liquefied fluid to obtain a fifth oxygen-enriched gas fluid; Including a product recovery route for collecting part of the gas as product nitrogen gas after heat recovery That. Further, the second rectifying tower and the third rectifying tower may be a single tower type in which the third rectifying tower is integrated with a lower part of the second rectifying tower.

  According to the present invention, when the pressure of the product nitrogen gas is low, the product nitrogen gas can be efficiently collected even when the pressure is about 0.40 MPa, for example, and the power consumption can be reduced.

  FIG. 1 is a system diagram showing a first embodiment of a nitrogen production apparatus capable of performing the nitrogen production method of the present invention. This nitrogen production apparatus includes a first rectifying column 11, a second rectifying column 12, a third rectifying column 13, a first indirect heat exchanger 14, a second rectifying column 14 provided at the lower part of the third rectifying column 13. The second indirect heat exchanger 15 provided in the lower part of the rectifying column 12 and the third indirect heat exchanger 16 provided in the upper part of the second rectifying column 12 and a cooling necessary for the operation of the apparatus are obtained. An expansion turbine 17 and a main heat exchanger 19 for exchanging heat between the gas (raw material air) introduced into the cold insulation outer tank 18 and the gas (product nitrogen gas and waste gas) led out from the cold insulation outer tank 18 are provided. Yes.

  In the following, the apparatus configuration and process will be described in detail based on a method for collecting product nitrogen by cryogenic liquefaction separation of raw material air. First, the raw material air (AIR) is compressed to a predetermined pressure by the air compressor 21 and cooled to near normal temperature by the air precooler 22, and then impurities such as moisture and carbon dioxide in the raw material air are purified by the purifier 23. It is removed by adsorption and purified. The purified compressed raw material air is introduced into the cold insulation outer tub 18 from the path 24, and indirectly heat exchanged with the gas (product nitrogen gas, waste gas) derived from the cold insulation outer tub 18 by the main heat exchanger 19. And cool to near dew point.

  The raw air cooled by the main heat exchanger 19 is introduced into the first indirect heat exchanger 14 from the path 25, and the first indirect heat exchanger 14 performs a first indirect heat exchange process. In this first indirect heat exchange step, the fourth oxygen-enriched liquefied fluid separated in the lower part of the third rectifying column 13 and the source air perform indirect heat exchange, and a part of the source air is condensed and liquefied. Simultaneously with the liquid two-phase air, the fourth oxygen-enriched liquefied fluid is evaporated and gasified to become the fourth oxygen-enriched gas fluid.

  The gas-liquid two-phase air obtained in the first indirect heat exchange step is introduced from the first indirect heat exchanger 14 through the path 26 to the lower portion of the first rectifying column 11, and in the first rectifying column 11. A first separation step is performed on the gas phase part (raw material air) of gas-liquid two-phase air. In this first separation step, the gas component in the gas-liquid two-phase air becomes the rising gas of the first rectifying column 11 and the gas from the first liquefied nitrogen flowing down from the upper part of the first rectifying column 11 as the reflux liquid. Low temperature distillation is performed by liquid contact, and nitrogen in the raw material air is concentrated at the upper part of the first rectifying column 11 to separate the first nitrogen gas, and oxygen in the raw material air is concentrated at the lower part of the first rectifying column 11. The first oxygen-enriched liquefied fluid is separated by mixing with the liquid phase part of the gas-liquid two-phase air. The first oxygen-enriched liquefied fluid is led out from the lower part of the first rectifying column 11 to the path 27, is decompressed by the pressure reducing valve 28, and is then introduced into the middle part of the second rectifying tower 12 via the path 29. The

  The first nitrogen gas is led out from the upper part of the first rectifying column 11 to the path 30 and introduced into the second indirect heat exchanger 15, and the second indirect heat exchanger 15 performs the second indirect heat exchange. A process is performed. In the second indirect heat exchange step, the second oxygen-enriched liquefied fluid separated in the lower part of the second rectifying column 12 and the first nitrogen gas exchange heat indirectly, and the entire amount of the first nitrogen gas is condensed and liquefied. At the same time as the first liquefied nitrogen, the second oxygen-enriched liquefied fluid is evaporated and gasified to become the second oxygen-enriched gas fluid. The first liquefied nitrogen led out from the second indirect heat exchanger 15 to the path 31 branches into a path 32 and a path 33, and the first liquefied nitrogen branched into the path 32 is introduced into the upper part of the first rectifying column 11. Then, it becomes the descending liquid (reflux liquid) of the first rectifying column 11. The first liquefied nitrogen branched into the path 33 is depressurized by the pressure reducing valve 34 and then introduced into the upper part of the second rectifying column 12 via the path 35 to become the reflux liquid of the second rectifying column 12.

  In the second rectification column 12, a second separation step is performed on the first oxygen-enriched liquefied fluid introduced from the path 29 into the middle of the column. In this second separation step, the first oxygen-enriched liquefied fluid, the first liquefied nitrogen introduced to the upper part of the tower from the path 35, and the second oxygen evaporated and gasified by the second indirect heat exchanger 15 are used. The enriched gas fluid, the second liquefied nitrogen introduced from the third indirect heat exchanger 16 at the upper part of the second rectifying tower 12 via the path 36, and the upper part of the third rectifying tower 13 introduced via the path 37 The low-temperature distillation is performed by gas-liquid contact with the third oxygen-enriched gas fluid, and the nitrogen component in the first oxygen-enriched liquefied fluid is concentrated on the upper part of the second rectifying column 12 to generate the second nitrogen gas. The oxygen component in the first oxygen-enriched liquefied fluid is concentrated in the lower part, and the second oxygen-enriched liquefied fluid is separated.

  The second nitrogen gas is led out from the upper part of the second rectifying column 12 to the path 38 and branches into the path 39 and the path 40. The second nitrogen gas branched into the path 39 proceeds to the product recovery process, and is recovered from the heat by exchanging heat with the raw material air in the main heat exchanger 19, and then led out from the cold insulation outer tank 18 through the product recovery path 41. And collected as product nitrogen gas (GN).

  The second nitrogen gas branched into the path 40 is introduced into the third indirect heat exchanger 16, and a third indirect heat exchange process is performed in the third indirect heat exchanger 16. In the third indirect heat exchange step, a fifth oxygen-rich state is introduced into the path 42 from the lower part of the third rectifying column 13 and is decompressed by the pressure reducing valve 43 and introduced into the third indirect heat exchanger 16 from the path 44. The liquefied liquefied fluid and the second nitrogen gas exchange heat indirectly, and the entire amount of the second nitrogen gas is condensed and liquefied to become second liquefied nitrogen. At the same time, the fifth oxygen-enriched liquefied fluid is evaporated and gasified. Becomes an oxygen-enriched gas fluid. The second liquefied nitrogen is introduced into the upper part of the second rectifying column 12 via the path 36 and becomes the reflux liquid of the second rectifying column 12.

  A part of the second oxygen-enriched liquefied fluid separated at the lower part of the second rectifying column 12 is led out to the path 45 to become a third oxygen-enriched liquefied fluid and introduced into the upper part of the third rectifying column 13. As a result, the third rectification column 13 is refluxed, and the third separation step is performed on the third oxygen-enriched liquefied fluid. In the third separation step, the fourth oxygen-enriched gas fluid evaporated and gasified in the first indirect heat exchange step in the first indirect heat exchanger 14 becomes the rising gas, and the third oxygen-enriched fluid that is a reflux liquid. The third oxygen-enriched gas fluid that has been cryogenically distilled by gas-liquid contact with the liquefied liquefied fluid, and the nitrogen content of the third oxygen-enriched liquefied fluid increased in the upper part of the third rectifying column 13 is separated, The fourth oxygen-enriched liquefied fluid in which the oxygen content in the third oxygen-enriched liquefied fluid has increased is separated at the lower part of the 3 rectifying column 13.

  The third oxygen-enriched gas fluid is led out from the upper part of the third rectifying column 13 to the path 37 and is introduced into the lower part of the second rectifying column 12 as a rising gas. In addition, a part of the fourth oxygen-enriched liquefied fluid is led out as a fifth oxygen-enriched liquefied fluid from the lower part of the third rectifying column 13 to the passage 42 and is decompressed by the pressure reducing valve 43 to be the third It is introduced into the indirect heat exchanger 16. In the third indirect heat exchange step in the third indirect heat exchanger 16, the entire amount of the fifth oxygen-enriched liquefied fluid is evaporated and gasified to become the fifth oxygen-enriched gas fluid, and the path 46 from the third indirect heat exchanger 16 To be derived.

  The fifth oxygen-enriched gas fluid led to the path 46 branches from the path 46 to the path 47 and the path 48, and the fifth oxygen-enriched gas fluid branched to the path 47 proceeds to the cold generation process, and the main heat exchange Part of the heat is recovered by exchanging heat with the raw material air in the vessel 19, and then led out to the passage 49 from the intermediate portion of the main heat exchanger 19, introduced into the expansion turbine 17, and expanded in the expansion turbine 17. As a result, the cold necessary for the operation of the apparatus is generated and led out from the expansion turbine 17 to the path 50.

  The fifth oxygen-enriched gas fluid branched into the path 48 is decompressed by the pressure reducing valve 51, and then merges with the fifth oxygen-enriched gas fluid after expansion of the path 50, and the raw heat exchanger 19 After heat is recovered by exchanging heat with air, it is led out as waste gas (WG) from the cold insulation outer tub 18 via the path 52, and a part is used as regeneration gas of the purifier 23.

  FIG. 2 is a system diagram showing a second embodiment of a nitrogen production apparatus capable of performing the nitrogen production method of the present invention. In the following description, the same components as those of the nitrogen production apparatus shown in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, a rectifying tower (hereinafter referred to as a fourth rectifying tower for convenience) 61 in which the second rectifying tower (12) and the third rectifying tower (13) in the first embodiment are integrated. The fourth rectifying column 61 includes a second rectifying column portion 61a that performs the same second separation step as the second rectifying column (12), and the third rectifying column. A third rectifying tower 61b that performs the same third separation step as the tower (13), and the third rectifying tower 61b is connected to the lower part of the second rectifying tower 61a. It is an integrated one. Furthermore, the 1st indirect heat exchanger 14 which performs the said 1st indirect heat exchange process is provided in the lower part of the 3rd rectification tower part 61b, The 2nd rectification tower part 61a, the 3rd rectification tower part 61b, Is provided with a second indirect heat exchanger 15 for performing the second indirect heat exchange step, and a third indirect heat for performing the third indirect heat exchange step is provided above the second rectifying tower 61a. An exchanger 16 is provided.

  In the portion of the second indirect heat exchanger 15, the second oxygen-enriched liquefied fluid flowing down from the gas-liquid contact portion of the second rectifying tower portion 61a and the first nitrogen gas perform indirect heat exchange, and the first At the same time as the nitrogen gas is condensed and liquefied to become the first liquefied nitrogen, a part of the second oxygen-enriched liquefied fluid is vaporized to become the second oxygen-enriched gas fluid, and the rising gas of the second rectifying tower 61a Become. In addition, the second oxygen-enriched liquefied fluid that has not been evaporated and gasified in the second indirect heat exchanger 15 flows into the third oxygen-enriched liquefied fluid in a liquid state toward the third rectifying tower 61b below. And becomes the reflux liquid of the third fractionator 61b. Further, the third oxygen-enriched gas fluid that has risen from the gas-liquid contact portion of the third rectifying tower 61b passes through the portion of the second indirect heat exchanger 15 and rises to the second rectifying tower 61a. Ascending gas.

  Also in the nitrogen production apparatus shown in the second embodiment, the same first separation step, second separation step, third separation step, first indirect heat exchange step, second indirect heat exchange step as in the first embodiment, A third indirect heat exchange step, a product recovery step, and a cold generation step are performed, and product nitrogen gas (GN) is collected from the product recovery path 41.

  FIG. 3 is a system diagram showing a third embodiment of a nitrogen production apparatus capable of performing the nitrogen production method of the present invention. In this embodiment, a part of the raw air is used in place of the fifth oxygen-enriched gas fluid instead of the fluid that generates cold in the cold generation step.

  The raw material air (AIR) compressed by the air compressor 21 and purified by the purifier 23 via the air precooler 22 is introduced from the path 24 to the main heat exchanger 19 in the cold insulation outer tub 18 and the main heat exchange. A part of the raw air is branched into a path 71 at an intermediate portion of the vessel 19 and is introduced into the expansion turbine 17 to perform a cold generation process. Part of the raw air expanded by the expansion turbine 17 is introduced as a rising gas into the middle part of the third rectifying column 13 via the path 72 and is supplied to the third separation step together with the third oxygen-enriched liquefied fluid.

  The remaining raw material air is cooled to near the dew point in the main heat exchanger 19 and then introduced into the first indirect heat exchanger 14 from the path 25 in the same manner as in the first and second embodiments. Hereinafter, similarly to the first embodiment and the second embodiment, the first separation step, the second separation step, the third separation step, the first indirect heat exchange step, the second indirect heat exchange step, and the third indirect heat exchange. A process and a product recovery process are performed, and product nitrogen gas (GN) is collected from the product recovery path 41. Further, the fifth oxygen-enriched gas fluid evaporated and gasified in the third indirect heat exchanger 16 is entirely introduced into the main heat exchanger 19 through the path 46 without performing the cold generation process, and heat recovery is performed. After that, it is derived from the path 52 as waste gas (WG).

  In addition, a part of the raw air expanded by the expansion turbine 17 may be introduced as an ascending gas from the path 73 into the middle of the second rectifying column 12 instead of being introduced into the third rectifying column 13. it can. Also in this case, the second separation step is performed together with the first oxygen-enriched liquefied fluid introduced from the route 29 to the middle part of the second rectification column 12, and the other steps are performed in the same manner as described above, thereby the product recovery route. From 41, product nitrogen gas (GN) is collected.

  FIG. 4 is a system diagram showing a fourth embodiment of a nitrogen production apparatus capable of performing the nitrogen production method of the present invention. In the present embodiment, as in the third embodiment, the fluid that performs the cold generation process in the expansion turbine 17 is a part of the raw material air, and the second separation process is performed in the same manner as in the second embodiment. A fourth rectifying column 61 in which a second rectifying column unit 61a and a third rectifying column unit 61b performing a third separation step are integrated is used.

  A part of the raw material air branched from the path 72 to the fourth path is branched from the path 72 to the path 71 at the middle portion of the main heat exchanger 19 and expanded by the expansion turbine 17 to perform a cold generation process. A rising gas is introduced into the middle part of the third rectifying column 61b of the rectifying column 61, and the third separation step is performed together with the third oxygen-enriched liquefied fluid in the same manner as described above. Or it introduce | transduces as rising gas to the 2nd rectification tower | column part 61a of the 4th rectification tower | column 61 from the path | route 73, and a 2nd separation process is performed with a 1st oxygen enriched liquefied fluid similarly to the above.

  Also in this embodiment, the first separation step, the second separation step, the third separation step, the first indirect heat exchange step, the second indirect heat exchange step, the third indirect heat exchange step, and the respective embodiment examples, Product nitrogen gas (GN) is collected from the product collection path 41 by performing the product collection process.

  In each of the above embodiments, in the first embodiment and the second embodiment, the entire amount of the raw material air is subjected to indirect heat exchange in the first indirect heat exchanger 14 and the second indirect heat exchanger 15, Compared to the third embodiment and the fourth embodiment, the amount of exchange heat in the first indirect heat exchanger 14 and the second indirect heat exchanger 15 is increased, and the rising gas in the second rectifying column 12 and the third rectifying column 13 is increased. Since the amount increases, the yield of product nitrogen gas can be increased.

  On the other hand, in the third embodiment and the fourth embodiment, since it is not necessary to expand the fifth oxygen-enriched gas fluid by the expansion turbine 17, the pressure of the fifth oxygen-enriched gas fluid is set to the first embodiment and the second embodiment. It can be lowered compared to the example. Thereby, since the operating pressure of each rectification column 11, 12, 13 can be made low, the pressure of product nitrogen gas can be made low compared with the 1st form example and the 2nd form example. That is, when the pressure of the product nitrogen gas to be recovered is a relatively low pressure of, for example, about 0.40 to 0.55 MPa, the pressure of the raw material air is reduced by performing a cold generation process using a part of the raw material air. Since the power consumption of the air compressor 21 can be reduced, the product nitrogen gas can be produced more efficiently, and the power consumption rate can be further reduced.

  Further, in an environment where a low-temperature liquefied gas can be used, the liquefied gas is injected into a path corresponding to the composition of the liquefied gas and a liquefied gas injection step is performed, which is necessary for the operation of the apparatus. Can compensate for cold. In this case, the entire amount of the raw material air can be used for indirect heat exchange in the first indirect heat exchanger 14 and the second indirect heat exchanger 15, and the pressure of the fifth oxygen-enriched gas fluid can be lowered. Since the yield of product nitrogen gas can be increased and the basic unit of power can be reduced, it is effective when the cost of the liquefied gas to be injected is low.

Process value in each path when the nitrogen production apparatus shown in the first embodiment is used, the raw material air flow rate is 100, the product nitrogen gas pressure is 0.60 MPa, and the allowable oxygen concentration in the product nitrogen gas is 0.1 ppm. Was simulated. Raw material air having a pressure of 1.00 MPa is separated into each separation step and each of the first rectifying column 11 having a pressure of 0.97 MPa, the second rectifying column 12 having a pressure of 0.61 MPa, and the third rectifying column 13 having a pressure of 0.63 MPa. By performing each indirect heat exchange step with the indirect heat exchangers 14, 15, and 16, respectively, product nitrogen gas having a flow rate of 68, a pressure of 0.60 MPa, and an oxygen concentration of 0.1 ppm is recovered. In addition, the fifth oxygen-enriched gas fluid having a flow rate of 32, a pressure of 0.21 MPa, and an oxygen concentration of 66% is mostly used for generating cold in the expansion turbine 10 and recovered, and then regenerated in the purifier 23. Used as gas. Table 1 shows the process values for each route.

  Process value in each path when the nitrogen production apparatus shown in the third embodiment is used, the raw material air flow rate is 100, the product nitrogen gas pressure is 0.40 MPa, and the allowable oxygen concentration in the product nitrogen gas is 0.1 ppm. Was simulated.

Raw material air having a pressure of 0.66 MPa is separated into each separation step and each of the first rectifying column 11 having a pressure of 0.64 MPa, the second rectifying column 12 having a pressure of 0.41 MPa, and the third rectifying column 13 having a pressure of 0.43 MPa. By performing each indirect heat exchange process with the indirect heat exchangers 14, 15, and 16, product nitrogen gas having a flow rate of 64, a pressure of 0.40 MPa, and an oxygen concentration of 0.1 ppm is recovered. The fifth oxygen-enriched gas fluid having a flow rate of 36, a pressure of 0.13 MPa, and an oxygen concentration of 58% is used as a regeneration gas for the purifier 23 after heat recovery. Table 2 shows the process value of each route.

  Further, the nitrogen production apparatus described in Patent Document 1 shown in FIG. 5 (Comparative Example 1), the nitrogen production apparatus described in Patent Document 2 shown in FIG. 6 (Comparative Example 2), and the double precision apparatus shown in FIG. A nitrogen production apparatus (Comparative Example 3) in which a fluid to be expanded in an expansion turbine for nitrogen production is a part of waste gas, and a fluid to be expanded in an expansion turbine for nitrogen production in FIG. In each of the nitrogen production apparatuses (Comparative Example 4) as a part of the raw material air, the power unit when the product nitrogen gas pressure is 0.80 MPa, 0.60 MPa and 0.40 MPa and the allowable oxygen concentration is 0.1 ppm, and The raw material air pressure was calculated.

  The nitrogen production apparatus shown in FIG. 5 is a two-column type equipped with two rectification columns, and includes a first rectification column 101, a second rectification column 102, a first condenser 103, a second condenser 104, An expansion turbine 105, a main heat exchanger 106, and a product nitrogen compressor 107 are provided.

  The raw material air cooled by the main heat exchanger 106 through the air compressor 21, the air precooler 22, and the purifier 23 is introduced into the lower part of the first rectifying column 101 and is subjected to low-temperature distillation, and the first nitrogen in the upper part of the tower. Separation into gas and first oxygen-enriched liquefied fluid at the bottom of the tower. The first nitrogen gas and the first oxygen-enriched liquefied fluid respectively derived from the first rectifying column 101 are subjected to indirect heat exchange in the first condenser 103, whereby the first nitrogen gas is condensed and liquefied. At the same time as the first liquefied nitrogen, the first oxygen-enriched liquefied fluid is evaporated and gasified to become the first oxygen-enriched gas fluid. The first liquefied nitrogen is introduced into the upper part of the first rectifying column 101 and becomes the reflux liquid of the first rectifying column 101.

  A part of the first oxygen-enriched gas fluid is introduced into the lower part of the second rectifying column 102 and distilled at a low temperature, and separated into a second nitrogen gas at the upper part of the tower and a second oxygen-enriched liquefied fluid at the lower part of the tower. To do. The second nitrogen gas and the second oxygen-enriched liquefied fluid respectively derived from the second rectifying column 102 are subjected to indirect heat exchange in the second condenser 104, whereby the second nitrogen gas is condensed and liquefied. Simultaneously with the second liquefied nitrogen, the second oxygen-enriched liquefied fluid is evaporated and gasified to become a second oxygen-enriched gas fluid.

  A part of the first nitrogen gas led out from the first rectifying column 101 is recovered by the main heat exchanger 106 and then led out to the path 108 as the first product nitrogen gas. Further, a part of the second nitrogen gas led out from the second rectifying column 102 is also recovered by the main heat exchanger 106 and then led out to the passage 109 as the second product nitrogen gas. The pressure is increased to the same pressure as that of the first product nitrogen gas. The first product nitrogen gas in the path 108 and the second product nitrogen gas boosted by the product nitrogen compressor 107 merge and are collected as product nitrogen gas (GN).

  The remaining portion of the first oxygen-enriched gas fluid is partially recovered by the main heat exchanger 106 and then introduced into the expansion turbine 105, where it expands in the expansion turbine 105 to generate the cold necessary for the operation of the apparatus. To do. Further, the second oxygen-enriched gas fluid joins with the expanded first oxygen-enriched gas fluid and is recovered by the main heat exchanger 106, and then is discharged as waste gas (WG).

  The nitrogen production apparatus shown in FIG. 6 is a three-column type including three rectifying columns, and includes a first rectifying column 111, a second rectifying column 112, a third rectifying column 113, and a first condenser 114. , Second condenser 115, third condenser 116, expansion turbine 117, main heat exchanger 118, and product nitrogen compressor 119.

  The raw material air cooled by the main heat exchanger 118 through the air compressor 21, the air precooler 22, and the purifier 23 is introduced into the lower part of the first rectifying column 111 and subjected to low-temperature distillation, and the first nitrogen in the upper part of the tower. Separation into gas and first oxygen-enriched liquefied fluid at the bottom of the tower. The first nitrogen gas derived from the upper part of the first rectifying column 111 is branched into three paths, and the first nitrogen gas branched into the first path is recovered by the main heat exchanger 118, The first product nitrogen gas is led to the path 120.

  The first oxygen-enriched liquefied fluid led out from the first rectifying column 111 is introduced into the upper part of the second rectifying column 112 after decompression and distilled at a low temperature, so that the oxygen composition is higher than that of the first oxygen-enriched liquefied fluid. The second raw material air having a low oxygen content is separated in the upper part of the tower, and the second oxygen-enriched liquefied fluid having a higher oxygen composition than the first oxygen-enriched liquefied fluid is separated in the lower part of the tower. Part of the second oxygen-enriched liquefied fluid undergoes indirect heat exchange with the first nitrogen gas branched into the second path and the first condenser 114 to evaporate and gas, and the rising gas of the second rectification column 112 Become. Further, the first nitrogen gas is liquefied and introduced into the upper part of the first rectifying column 111, and becomes a reflux liquid of the first rectifying column 111.

  The second raw material air derived from the second rectification column 112 is introduced into the lower part of the third rectification column 113 and is distilled at a low temperature, and the second nitrogen gas at the upper part of the tower and the third oxygen-enriched liquefaction at the lower part of the tower. Separate into fluid. A part of the second nitrogen gas led out from the third rectifying column 113 is recovered by the main heat exchanger 118 and then led out as a second product nitrogen gas to the path 121, where a product nitrogen compressor 119 is obtained. The pressure is increased to the same pressure as that of the first product nitrogen gas. The first product nitrogen gas in the path 120 and the second product nitrogen gas pressurized by the product nitrogen compressor 119 are merged and collected as product nitrogen gas (GN).

  The third oxygen-enriched liquefied fluid derived from the third rectifying column 113 is introduced into the second condenser 115 after decompression, and indirect heat exchange is performed with the remainder of the second nitrogen gas. The liquefied fluid is evaporated and gasified to become a second oxygen-enriched gas fluid, and the second nitrogen gas is liquefied to become second liquefied nitrogen. This second liquefied nitrogen is introduced into the upper part of the third rectifying column 113 and becomes the reflux liquid of the third rectifying column 13.

  The remaining portion of the second oxygen-enriched liquefied fluid is led out from the second rectification column 112 and introduced into the third condenser 116, and indirectly heat exchanges with the remaining portion of the first nitrogen gas branched into the third path. The second oxygen-enriched liquefied fluid is vaporized to become a third oxygen-enriched gas fluid, and the first nitrogen gas is liquefied to become third liquefied nitrogen. The third liquefied nitrogen merges with the first liquefied nitrogen liquefied by the first condenser 114 and is introduced into the upper portion of the first rectifying column 111 as a reflux liquid.

  The third oxygen-enriched gas fluid is partially recovered by the main heat exchanger 118, and then introduced into the expansion turbine 117. The third oxygen-enriched gas fluid expands in the expansion turbine 117, thereby generating cold necessary for the operation of the apparatus. The expanded third oxygen-enriched gas fluid joins with the second oxygen-enriched gas fluid, is introduced into the main heat exchanger 118, is heat-recovered, and is then led out as waste gas (WG).

  The nitrogen production apparatus comprising the double rectification process shown in FIG. 7 includes a double rectification column having a first rectification column (high pressure column) 131, a second rectification column (low pressure column) 132, and a main condensing evaporator 133; An expansion turbine 134 using waste gas as an expanding fluid, a main heat exchanger 135, a supercooler 136, and a product nitrogen compressor 137 are provided.

  The raw material air introduced into the main heat exchanger 135 through the air compressor 21, the air precooler 22, and the purifier 23 is introduced into the lower part of the first rectifying column 131 and subjected to low-temperature distillation, and the first nitrogen in the upper part of the tower. Separation into gas and first oxygen-enriched liquefied fluid at the bottom of the tower. The first oxygen-enriched liquefied fluid is cooled by the supercooler 136, then depressurized, introduced into the middle part of the second rectifying column 132, and subjected to low-temperature distillation. Separate into 2 oxygen enriched liquefied fluid.

  A part of the first nitrogen gas is introduced into the main condensing evaporator 133 to evaporate and gasify the second oxygen-enriched liquefied fluid into liquefied nitrogen, and part of the first nitrogen gas is second rectifying tower. The upper part of 132 is introduced as a reflux liquid, and the remaining part is introduced as an upper part of the first fractionator 131 as a reflux liquid. A part of the oxygen-enriched gas fluid evaporated and gasified by the main condensing evaporator 133 becomes the rising gas of the second rectifying column 142.

  The remainder of the oxygen-enriched gas fluid is partially recovered by the main heat exchanger 135 and then introduced into the expansion turbine 134, where it expands in the expansion turbine 134 to generate the cold necessary for the operation of the apparatus. The expanded oxygen-enriched gas fluid is recovered as heat in the main heat exchanger 135, and is then discharged as waste gas (WG).

  The remaining portion of the first nitrogen gas led out from the upper part of the first rectifying column 131 is recovered by the main heat exchanger 135 and then led out to the path 138 as the first product nitrogen gas. The second nitrogen gas derived from the upper part of the second rectifying column 132 is recovered by the supercooler 136 and the main heat exchanger 135, and then is led to the path 139 as the second product nitrogen gas. The product nitrogen compressor 137 is pressurized to the same pressure as the first product nitrogen gas. The first product nitrogen gas in the path 138 and the second product nitrogen gas pressurized by the product nitrogen compressor 137 merge and are collected as product nitrogen gas (GN).

  The nitrogen production apparatus comprising the double rectification process shown in FIG. 8 includes a double rectification column having a first rectification column (high pressure column) 141, a second rectification column (low pressure column) 142, and a main condensation evaporator 143, An expansion turbine 144 using a part of the raw air as an expanding fluid, a main heat exchanger 145, a supercooler 146, and a product nitrogen compressor 147 are provided.

  Part of the raw air introduced into the main heat exchanger 145 through the air compressor 21, the air precooler 22, and the purifier 23 is branched into the middle of the main heat exchanger 145 and introduced into the expansion turbine 144. Then, after generating the cold necessary for the operation of the apparatus, it is introduced into the middle of the second rectifying column 142. Most of the remaining raw material air is introduced into the lower part of the first rectifying column 141 and is distilled at a low temperature, and separated into a first nitrogen gas at the upper part of the tower and a first oxygen-enriched liquefied fluid at the lower part of the tower. The first oxygen-enriched liquefied fluid is cooled in the supercooler 146, then decompressed and introduced into the middle part of the second rectifying column 142, and is cryogenically distilled together with a part of the raw material air after expansion, The second nitrogen gas and the second oxygen-enriched liquefied fluid at the bottom of the column are separated.

  A part of the first nitrogen gas is introduced into the main condensing evaporator 143 to evaporate and gasify the second oxygen-enriched liquefied fluid and to liquefy it into liquefied nitrogen, and a part thereof is the second rectifying column. 142 is introduced as a reflux liquid in the upper part, and the remainder is introduced as a reflux liquid in the upper part of the first rectifying column 141. A part of the oxygen-enriched gas fluid evaporated and gasified by the main condensing evaporator 143 becomes the rising gas of the second rectifying column 142. The remainder of the oxygen-enriched gas fluid is recovered as heat in the main heat exchanger 145 and then discharged as waste gas (WG).

  The remaining portion of the first nitrogen gas derived from the upper part of the first rectifying column 141 is recovered by the main heat exchanger 145 and then led to the path 148 as the first product nitrogen gas. The second nitrogen gas derived from the upper part of the second rectifying column 142 is recovered by the supercooler 146 and the main heat exchanger 145, and then is led to the path 149 as the second product nitrogen gas. The product nitrogen compressor 147 is pressurized to the same pressure as the first product nitrogen gas. The first product nitrogen gas in the path 148 and the second product nitrogen gas boosted by the product nitrogen compressor 147 merge and are collected as product nitrogen gas (GN).

Table 3 shows the power unit in each example and each comparative example, and the raw material air pressure in parentheses. The numerical value of the power basic unit is a relative value when the power basic unit is 100 when the product nitrogen gas is sampled at 0.80 MPa in Example 1.

  In Table 3, the nitrogen production apparatus of Comparative Example 1 produces product nitrogen gas having a pressure of 0.60 MPa and 0.40 MPa, and the nitrogen production apparatuses of Example 1, Comparative Example 2 and Comparative Example 3 have a pressure of 0.00. Production of 40 MPa product nitrogen gas was not achieved in the process.

  In addition, when the product nitrogen pressure is 0.60 MPa or less, the nitrogen production apparatuses of Examples 1 and 2 are more suitable for producing product nitrogen gas at each pressure than the nitrogen production apparatuses of Comparative Examples 2 to 4. It can be seen that the power unit can be greatly reduced in any of the cases.

  Furthermore, in any case, since the raw material air pressure in Examples 1 and 2 is higher than that in the respective comparative examples, when a general adsorption type purifier is used as the purifier (23), the raw material air is used. Since the pressure is high, the purifier can be made smaller and the amount of adsorbent can be reduced, which is advantageous in terms of apparatus cost, and the amount of necessary regenerated gas can be reduced. In particular, when producing 0.40 MPa product nitrogen gas in the nitrogen production apparatus of Comparative Example 4, since the raw material air pressure becomes considerably low, the size of the purifier increases and the amount of adsorbent increases significantly. Not only the cost of the apparatus increases, but also the amount of product nitrogen gas may be sacrificed to secure the regeneration gas.

  Further, in both examples, it is not necessary to provide a nitrogen compressor, but in each comparative example, the product nitrogen gas is derived from a rectifying column operated at a pressure corresponding to the product nitrogen pressure and is operated at a low pressure. Since the low-pressure nitrogen gas is also derived from the rectification column, and the low-pressure nitrogen gas is pressurized and merged with the product nitrogen gas, it is necessary to provide a nitrogen compressor separately from the air compressor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram showing a first embodiment of a nitrogen production apparatus capable of performing the nitrogen production method of the present invention. It is a systematic diagram which shows the 2nd form example of the nitrogen manufacturing apparatus which can implement the nitrogen manufacturing method of this invention. It is a systematic diagram which shows the 3rd form example of the nitrogen manufacturing apparatus which can implement the nitrogen manufacturing method of this invention. It is a systematic diagram which shows the 4th example of a nitrogen manufacturing apparatus which can implement the nitrogen manufacturing method of this invention. 2 is a system diagram of a nitrogen production apparatus used as Comparative Example 1. FIG. 5 is a system diagram of a nitrogen production apparatus used as Comparative Example 2. FIG. 6 is a system diagram of a nitrogen production apparatus used as Comparative Example 3. FIG. 6 is a system diagram of a nitrogen production apparatus used as Comparative Example 4. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... 1st rectification tower, 12 ... 2nd rectification tower, 13 ... 3rd rectification tower, 14 ... 1st indirect heat exchanger, 15 ... 2nd indirect heat exchanger, 16 ... 3rd indirect heat exchanger , 17 ... Expansion turbine, 18 ... Cold storage outer tank, 19 ... Main heat exchanger, 21 ... Air compressor, 22 ... Air precooler, 23 ... Purifier, 28, 34, 43, 51 ... Pressure reducing valve, 41 ... Product Recovery route, AIR ... Raw material air, GN ... Product nitrogen gas, WG ... Waste gas

Claims (6)

In a nitrogen production method for collecting product nitrogen by cryogenic liquefaction separation of raw material air, indirect heat exchange is performed between the compressed, purified, and cooled raw material air and a fourth oxygen-enriched liquefied fluid, which will be described later, to obtain a part of the raw material air. A first indirect heat exchange step of condensing and liquefying to obtain gas-liquid two-phase air and simultaneously evaporating and gasifying the fourth oxygen-enriched liquefied fluid to obtain a fourth oxygen-enriched gas fluid; A first separation step of distilling to separate the first nitrogen gas and the first oxygen-enriched liquefied fluid; and the second oxygen gas and second oxygen-enriched by low-temperature distillation after depressurizing the first oxygen-enriched liquefied fluid. At the same time as obtaining a first liquefied nitrogen by condensing and liquefying the first nitrogen gas by indirect heat exchange between the second oxygen-enriched liquefied fluid and the first nitrogen gas, and a second separation step of separating into a liquefied fluid Second indirect heat for obtaining a second oxygen-enriched gas fluid by evaporating the second oxygen-enriched liquefied fluid Conversion step and the third oxygen-enriched liquefied fluid cryogenic distillation to third oxygen enriched the second oxygen-enriched liquefied stream body unevaporated gasification in the second indirect heat exchange step was withdrawn remained liquid state the third separation step and the fifth oxygen remains the fourth oxygen enriched liquefied stream body liquid state that did not first evaporation gasification in indirect heat exchange step is separated into a gaseous fluid and the fourth oxygen-enriched liquefied fluid Extracted as an enriched liquefied fluid, indirectly heat-exchanged with the second nitrogen gas after decompression to condense and liquefy the second nitrogen gas to obtain second liquefied nitrogen, and at the same time evaporate the fifth oxygen enriched liquefied fluid after decompression And a third indirect heat exchange step for obtaining a fifth oxygen-enriched gas fluid, and a product recovery step for collecting a part of the second nitrogen gas as product nitrogen gas after heat recovery. Method.   The method for producing nitrogen according to claim 1, further comprising a cold generation step of introducing the fifth oxygen-enriched gas fluid into an expansion turbine and expanding the fluid.   The method for producing nitrogen according to claim 1, further comprising a cold generation step of introducing a part of the raw material air into an expansion turbine to expand the raw material air.   The method for producing nitrogen according to claim 1, further comprising a liquefied gas injection step of supplying liquefied gas from outside the system to compensate for the refrigeration necessary for the operation of the apparatus. In a nitrogen production system that collects product nitrogen by cryogenic liquefaction separation of raw material air, the raw material air that has been compressed, purified, and cooled is indirectly heat-exchanged with a fourth oxygen-enriched liquefied fluid described later to obtain part of the raw material air. A first indirect heat exchanger for obtaining a fourth oxygen-enriched gas fluid by evaporating and gasifying a fourth oxygen-enriched liquefied fluid at the same time as condensing and liquefying to obtain gas-liquid two-phase air; A first rectifying column that is distilled to separate it into a first nitrogen gas and a first oxygen-enriched liquefied fluid; and a low-temperature distillation of the first oxygen-enriched liquefied fluid after depressurization and a second nitrogen gas and a second oxygen-enriched fluid. A second rectifying column that is separated into a liquefied fluid, the second oxygen-enriched liquefied fluid, and the first nitrogen gas are indirectly heat exchanged to condense and liquefy the first nitrogen gas to obtain first liquefied nitrogen. At the same time, the second indirect heat exchanger for obtaining the second oxygen-enriched gas fluid by evaporating the second oxygen-enriched liquefied fluid The third oxygen-enriched liquefied fluid extracted remain in the liquid state the second oxygen-enriched liquefied stream body unevaporated gasified in the second indirect heat exchanger from the bottom of the second rectification column by cryogenic distillation Te and a third oxygen-enriched gas stream and a third rectification column is separated into a fourth oxygen-enriched liquefied fluid, the fourth oxygen enriched liquefied stream body unevaporated gasification in a first indirect heat exchanger The fifth oxygen-enriched liquefied fluid extracted from the bottom of the third rectifying column in a liquid state is subjected to indirect heat exchange with the second nitrogen gas after depressurization to condense and liquefy the second nitrogen gas to obtain second liquefied nitrogen. A third indirect heat exchanger that obtains a fifth oxygen-enriched gas fluid by evaporating and gasifying the fifth oxygen-enriched liquefied fluid after decompression and a product nitrogen gas after recovering a part of the second nitrogen gas. And a product recovery route to be collected as a nitrogen production apparatus.   6. The nitrogen producing apparatus according to claim 5, wherein the second rectifying tower and the third rectifying tower are integrated with the third rectifying tower at a lower portion of the second rectifying tower.

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