JP4451438B2 - Nitrogen production method and apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for producing nitrogen, and more particularly to a method and apparatus for collecting product nitrogen (nitrogen gas, liquid nitrogen) by separating air by a cryogenic separation method.

As a method for producing product nitrogen by cryogenic separation of air, basically, a method using a single fractionator is widely used. In recent years, various methods have been used to improve product yield and power consumption. Process has been proposed. Among them, a process using two rectification towers and using waste gas that was discarded in the conventional process as a raw material for the second rectification tower is a waste that is introduced into the second rectification tower 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 this process, it may be necessary to boost some product nitrogen gas obtained from the second rectification column to a predetermined pressure, but the required energy is minimized and the product is compared with the conventional process. It is possible to greatly improve the yield and power consumption (for example, see Patent Document 1).
Japanese Patent No. 3738213

  However, since the above process has a lower limit of the apparatus operating pressure due to the nature of the process, it is an efficient apparatus when the product nitrogen pressure is about 0.8 MPa or more, and a low power unit can be expected. However, when the product pressure is 0.8 MPa or lower, it is difficult to cope with the feature of high product yield. In the present specification, the pressure {MPa} indicates an absolute pressure.

  Accordingly, an object of the present invention is to provide a nitrogen production method and apparatus capable of maintaining a high product yield even when the product nitrogen pressure is relatively low.

In order to achieve the above object, the first nitrogen production method of collecting the product nitrogen by cryogenic liquefaction separation of the raw material air of the present invention is the first nitrogen by low-temperature distillation of the compressed, purified and cooled first raw material air A first separation step of separating the gas into a first oxygen-enriched liquefied fluid and a second raw material by low-temperature distillation of the first oxygen-enriched liquefied fluid after depressurizing the first oxygen-enriched gas fluid described later A second separation step of separating the air into a second oxygen-enriched liquefied fluid, and a first nitrogen gas by indirectly exchanging a part of the second oxygen-enriched liquefied fluid and a part of the first nitrogen gas. A first indirect heat exchange step of obtaining a first oxygen-enriched gas fluid by evaporating and gasifying a part of the second oxygen-enriched liquefied fluid at the same time as obtaining the first liquefied nitrogen by condensing liquid, and the second raw material air A third separation step of low-temperature distillation to separate the second nitrogen gas and the third oxygen-enriched liquefied fluid; A part of the second nitrogen gas and the third oxygen-enriched liquefied fluid after decompression are indirectly heat-exchanged to condense and liquefy the second nitrogen gas to obtain second liquefied nitrogen, and at the same time, the third oxygen-enriched liquefied fluid A second indirect heat exchange step of evaporating the gas to obtain a second oxygen-enriched gas fluid, and the remaining portion of the second oxygen-enriched liquefied fluid is indirectly heat-exchanged with a part of the remaining portion of the first nitrogen gas after depressurization. A third indirect heat exchange step of condensing and liquefying the first nitrogen gas to obtain third liquefied nitrogen and simultaneously evaporating and gasifying the entire amount of the second oxygen-enriched liquefied fluid to obtain a third oxygen-enriched gas fluid; A first product recovery step for deriving the remainder of the first nitrogen gas as a first product nitrogen gas after heat recovery; and a second product recovery step for deriving the remainder of the second nitrogen gas as a second product nitrogen gas after heat recovery; In addition, the second separation step and the first indirect heat exchange To perform a process in a heat integrated rectification column, it is characterized by performing the cryogenic distillation of the second separation step in only one vapor-liquid equilibrium.

Moreover, the second nitrogen production method of the present invention includes a first separation step in which the compressed, purified, and cooled first raw material air is subjected to low-temperature distillation to separate the first nitrogen gas and the first oxygen-enriched liquefied fluid; A part of the first nitrogen gas and the first oxygen-enriched liquefied fluid after depressurization are indirectly heat exchanged to condense and liquefy the first nitrogen gas to obtain first liquefied nitrogen, and at the same time, the first oxygen-enriched liquefied A first indirect heat exchange step for obtaining a first oxygen-enriched gas-liquid mixed phase fluid by evaporating part of the fluid, and the second raw material by only one gas-liquid equilibrium for the first oxygen-enriched gas-liquid mixed phase fluid. A second separation step of separating the air into a second oxygen-enriched liquefied fluid, and a third separation step of separating the second raw material air into a second nitrogen gas and a third oxygen-enriched liquefied fluid by low-temperature distillation. The second nitrogen gas is condensed with the second nitrogen gas through indirect heat exchange between a part of the second nitrogen gas and the third oxygen-enriched liquefied fluid after decompression. The second indirect heat exchange step of obtaining the second oxygen-enriched gas fluid by evaporating and gasifying the third oxygen-enriched liquefied fluid at the same time as obtaining the second liquefied nitrogen, and the second oxygen-enriched liquefied fluid after decompression And the remaining part of the first nitrogen gas are indirectly heat-exchanged to condense and liquefy the first nitrogen gas to obtain third liquefied nitrogen, and at the same time evaporate and gasify the entire amount of the second oxygen-enriched liquefied fluid. 3 a third indirect heat exchange step for obtaining an oxygen-enriched gas fluid, a first product recovery step for deriving the remainder of the first nitrogen gas as a first product nitrogen gas after heat recovery, and a remainder of the second nitrogen gas. And a second product recovery step of deriving as second product nitrogen gas after heat recovery.

In addition, the first nitrogen production apparatus of the present invention that implements the first production method low-temperature distills the compressed, purified, and cooled first raw material air into the first nitrogen gas and the first oxygen-enriched liquefied fluid. a rectification column to carry out the first separation step of separating, the first oxygen-enriched liquefied fluid after decompression in decompression means, second feed air by cryogenic distillation with the total amount of the first oxygen-enriched gas stream below the A rectifying column that performs a second separation step for separating the oxygen-enriched liquefied fluid into a first fraction, and a part of the second oxygen-enriched liquefied fluid and a part of the first nitrogen gas are indirectly heat-exchanged to form a first A condenser for performing a first indirect heat exchange step of condensing and liquefying nitrogen gas to obtain first liquefied nitrogen and at the same time evaporating and gasifying a part of the second oxygen enriched liquefied fluid to obtain a first oxygen enriched gas fluid; the third separation engineering for separating the second feed air into a cryogenic distillation second nitrogen gas was a third oxygen-enriched liquefied fluid A rectification column to conduct, the third oxygen-enriched liquefied fluid and a second liquefied nitrogen condensed and liquefied the second nitrogen gas by indirect heat exchange after decompression part and pressure reducing means of the second nitrogen gas A condenser for performing a second indirect heat exchange step for obtaining a second oxygen-enriched gas fluid by evaporating and gasifying the third oxygen-enriched liquefied fluid at the same time, and reducing the remaining portion of the second oxygen-enriched liquefied fluid with a decompression means After decompression, the first nitrogen gas is indirectly heat exchanged with the remaining part of the first nitrogen gas to condense and liquefy the first nitrogen gas to obtain third liquefied nitrogen. At the same time, the entire amount of the second oxygen-enriched liquefied fluid is vaporized and gasified. A condenser for performing a third indirect heat exchange step for obtaining three oxygen-enriched gas fluids, a first product recovery path for deriving the remainder of the first nitrogen gas as a first product nitrogen gas after heat recovery by a heat recovery means, The remainder of the second nitrogen gas is introduced as second product nitrogen gas after heat recovery by the heat recovery means. A second product recovery path, that is provided with a characterized, furthermore, a condenser for performing the second separation step wherein the rectification column to carry out the first indirect heat exchange step is in heat integrated rectification column to The rectifying column that performs the second separation step is a gas-liquid separator that includes a condenser that performs the first indirect heat exchange step .

In addition, the second nitrogen production apparatus of the present invention that implements the second production method low-temperature distills the compressed, purified, and cooled first raw material air into the first nitrogen gas and the first oxygen-enriched liquefied fluid. The first nitrogen gas is condensed and liquefied by indirect heat exchange between the rectifying column for performing the first separation step to be separated, and a part of the first nitrogen gas and the first oxygen-enriched liquefied fluid after being depressurized by the decompression means. And a condenser for performing a first indirect heat exchange step for obtaining a first oxygen-enriched gas-liquid mixed phase fluid by evaporating and gasifying a part of the first oxygen-enriched liquefied fluid simultaneously with obtaining the first liquefied nitrogen, 1. A gas-liquid separator that performs a second separation step of gas-liquid separation of an oxygen-enriched gas-liquid mixed phase fluid into a second raw material air and a second oxygen-enriched liquefied fluid; and low-temperature distillation of the second raw material air a rectification column to carry out and the second nitrogen gas a third separation step of separating into a third oxygen-enriched liquefied fluid, the second nitrogen gas And the third oxygen-enriched liquefied fluid after being depressurized by the pressure reducing means are indirectly heat exchanged to condense and liquefy the second nitrogen gas to obtain second liquefied nitrogen, and at the same time evaporate the third oxygen-enriched liquefied fluid A condenser that performs a second indirect heat exchange step to obtain a second oxygen-enriched gas fluid, and a second oxygen-enriched liquefied fluid that has been depressurized by a depressurizing means and a part of the remainder of the first nitrogen gas. third indirect heat exchanger to obtain a third oxygen-enriched gas stream is evaporated gasifying the total amount of condensed and liquefied the first nitrogen gas by indirect heat exchange third obtains a liquefied nitrogen simultaneously the second oxygen-enriched liquefied fluid A condenser for performing the process, a first product recovery path for deriving the remainder of the first nitrogen gas as the first product nitrogen gas after heat recovery by the heat recovery means, and a heat recovery means for heating the remainder of the second nitrogen gas And a second product recovery path that leads out as second product nitrogen gas after recovery. It is characterized by a door.

  According to the present invention, product nitrogen having a relatively low pressure, for example, about 0.6 MPa can be obtained with a high yield and a low power unit.

  FIG. 1 is a system diagram of a nitrogen production apparatus showing a first embodiment of the present invention. This nitrogen production apparatus includes three towers, ie, a first rectification tower 11, a second rectification tower 12, and a third rectification tower 13, as rectification towers. Three units of a condenser 15 and a third condenser 16 are provided.

  Hereinafter, the process will be described in detail based on the gas-liquid flow. The first raw material air sucked from the filter 20, compressed by the raw material air compressor 21, removed from the compression heat by the after cooler 22, and purified and removed the water vapor and carbon dioxide contained in the purifier 23 is stored in the cold insulation outer tank. After being cooled to a predetermined temperature by the main heat exchanger 24, it is introduced into the lower part of the first rectifying column 11 through the path 25. In the first rectifying column 11, the first raw material air 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 (first separation step).

  A part of the first nitrogen gas extracted from the upper part of the first rectifying column 11 to the path 26 is branched into the path 27 and indirectly heat-exchanged with the first raw material air by the main heat exchanger 24. The temperature is raised and the first product nitrogen gas is led out from the first product recovery path 28 (first product recovery step).

  The first oxygen-enriched liquefied fluid led out from the lower part of the first rectifying column 11 to the path 29 is reduced to a predetermined pressure by the pressure reducing valve 30 and then introduced into the upper part of the second rectifying column 12. Is done. The second rectifying column 12 is a rectifying column provided with the first condenser 14 in the lower part. The first oxygen-enriched liquefied fluid descending the second rectifying column 12 undergoes low-temperature distillation with the ascending gas (first oxygen-enriched gas fluid described later) generated in the first condenser 14, and the first The oxygen-enriched liquefied fluid has a higher oxygen composition and becomes a second oxygen-enriched liquefied fluid that flows down below the second rectifying column 12, and the rising gas has a lower oxygen composition than the first oxygen-enriched liquefied fluid. It becomes 2nd raw material air, and raises to the upper part of the 2nd fractionator 12 (2nd separation process). The second oxygen-enriched liquefied fluid flowing down below the second rectifying column 12 immerses the first condenser 14 provided at the bottom of the second rectifying column 12 and serves as a cold fluid for the first condenser 14. Provided.

  In the first condenser 14, the second oxygen-enriched liquefied fluid and a part of the first nitrogen gas branched from the path 26 to the path 31 perform indirect heat exchange, and the first nitrogen gas is liquefied. At the same time as the first liquefied nitrogen, the second oxygen-enriched liquefied fluid becomes a first oxygen-enriched gas fluid that partially vaporizes and rises in the tower (first indirect heat exchange step). The first liquefied nitrogen is introduced as a descending liquid into the upper portion of the first rectifying column 11 through the path 32, and the first oxygen-enriched gas fluid rises up the second rectifying column 12 to enrich the first oxygen. Perform low-temperature distillation with the liquefied fluid. The remaining liquid (the fourth oxygen-enriched liquefied fluid described later) that is the remainder of the second oxygen-enriched liquefied fluid that has not been vaporized by the first condenser 14 is led to the path 33. In the present embodiment, the first oxygen-enriched gas fluid and the remaining liquid that is the remainder of the second oxygen-enriched liquefied fluid are in a gas-liquid equilibrium state, and therefore the second oxygen-enriched liquefaction flowing down in the second separation step. The composition of the fluid is fundamentally different from the composition of the staying liquid that is the remainder of the second oxygen-enriched liquefied fluid, and the staying that is the remainder of the second oxygen-enriched liquefied fluid rather than the oxygen composition of the second oxygen-enriched liquefied fluid The oxygen composition of the liquid is high.

  The second raw material air separated at the upper part of the second rectifying column 12 is extracted from the upper part of the tower to the path 34 and introduced into the lower part of the third rectifying tower 13. In the third fractionator 13, the second raw material air is distilled at a low temperature and separated into a second nitrogen gas at the top of the tower and a third oxygen-enriched liquefied fluid at the bottom of the tower (third separation step). A part of the second nitrogen gas extracted from the upper part of the third rectifying column 13 to the path 35 is branched to the path 36 and indirectly heat-exchanged with the first raw material air by the main heat exchanger 24. The temperature is raised and the second product nitrogen gas is led out from the second product recovery path 37 (second product recovery step). The second product nitrogen gas can be supplied to the supply destination at the derived pressure. However, when the second product nitrogen gas is joined to the first product nitrogen gas and supplied, the pressure is increased by the nitrogen compressor 38 and the aftercooler. What is necessary is just to make it merge with 1st product nitrogen gas after cooling by 39, and to supply to a supply destination as product nitrogen gas (GN2) from the product supply path 40.

The third oxygen-enriched liquefied fluid led out from the lower part of the third rectifying column 13 to the path 41 is depressurized to a predetermined pressure by the pressure reducing valve 42 and then introduced into the second condenser 15. The remaining portion of the second nitrogen gas branched from the path 35 to the path 43 is introduced into the second condenser 15, and the second nitrogen gas and the third oxygen-enriched liquefied fluid exchange heat indirectly, thereby 3 The oxygen-enriched liquefied fluid is vaporized to become a second oxygen-enriched gas fluid, and the second nitrogen gas is liquefied to become second liquefied nitrogen (second indirect heat exchange step). This second liquefied nitrogen is introduced as a descending liquid into the upper part of the third fractionator 13 through the path 44.

  The second oxygen-enriched gas fluid is led out from the second condenser 15 to the path 45, and is heated up by indirect heat exchange with the first raw material air in the main heat exchanger 24 and led out to the path 46. The refining device 23 is used for regeneration as necessary.

  On the other hand, the remaining liquid that is the remainder of the second oxygen-enriched liquefied fluid is led out to the passage 33 as the fourth oxygen-enriched liquefied fluid, and is reduced to a predetermined pressure by the pressure reducing valve 47, and then the third condenser 16 To be introduced. The remaining portion of the first nitrogen gas branched from the path 26 to the path 48 is introduced into the third condenser 16, and the first nitrogen gas and the fourth oxygen-enriched liquefied fluid perform indirect heat exchange, 4 The 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 (third indirect heat exchange step). The third liquefied nitrogen is led to the path 49 and merges with the first liquefied nitrogen flowing through the path 32, and is introduced into the upper portion of the first fractionator 11 as a descending liquid.

  The third oxygen-enriched gas fluid is led from the third condenser 16 to the path 50 and introduced into the main heat exchanger 24. A part of the third oxygen-enriched gas fluid branches as a turbine fluid into the passage 51 at an intermediate temperature, is introduced into the expansion turbine 52 and expands, generates cold necessary for operation of the apparatus, and passes through the passage 53 to It joins with the second oxygen-enriched gas fluid in the path 45 and is again introduced into the main heat exchanger 24. The remainder of the third oxygen-enriched gas fluid led out from the main heat exchanger 24 to the path 54 is decompressed by the pressure reducing valve 55 and then merges with the second oxygen-enriched gas fluid in the path 46.

  Further, a cold replenishment path 57 having a pressure reducing valve 56 is provided between the first rectifying column 11 and the third rectifying column 13, and the liquid fluid in the first rectifying column 11 is supplied with a pressure reducing valve. The pressure necessary for operation of the third rectifying column 13 is replenished by reducing the pressure at 56 and then introducing it into the third rectifying column 13 as a cold replenishing fluid.

  Further, as indicated by a broken line in FIG. 1, liquefied nitrogen from the outside of the apparatus is transferred from the path 58 to the first rectifying column 11 via the path 32, and from the path 59 to the third rectifying tower via the path 44. 13 is introduced as a cold source, or liquefied air from outside the apparatus is introduced as a cold source from the path 60 to the path 29 and from the path 61 to the path 41, thereby omitting the expansion turbine 52. be able to. In addition, the kind of fluid introduce | transduced as a cold source is not specifically limited, The introduction position can be suitably set according to the composition and pressure of a fluid. It is also possible to use an external fluid introduction and an expansion turbine together as a cold source.

  When the expansion turbine 52 is used as a cold source and the second product nitrogen gas in the second product recovery path 37 needs to be pressurized, the expansion turbine 52 is a brake blower type and the brake blower is a nitrogen compressor. It is also possible to use as.

  In the nitrogen production apparatus configured as described above, low-temperature distillation is performed in the second separation step of the second rectifying column 12, and part of the first condenser 14 is not vaporized in the first indirect heat exchange step. Is extracted with a liquid having a high oxygen composition, so that the oxygen composition of the second raw material air can be lowered and the operating pressure of the first fractionator can be lowered compared to the conventional case. The efficiency has improved, and efficient operation has become possible even in the product nitrogen pressure range where efficient operation has been difficult in the past.

  Here, the process of the present embodiment shown in FIG. 1 (hereinafter referred to as the present embodiment) is compared with the conventional process described in Patent Document 1 (hereinafter referred to as the conventional example) illustrated in FIG. The operational effects of will be described in detail. The configuration of the conventional example shown in FIG. 6 is basically the same as that described in Patent Document 1 although it is slightly different from the configuration described in Patent Document 1 in order to facilitate comparison with this embodiment. Further, in the description of the conventional example, constituent elements regarded as substantially the same as the constituent elements of the present embodiment example are denoted by reference numerals made up of numbers added with one hundred.

  First, in this embodiment and the conventional example, the lower limit of the apparatus operating pressure is governed by the vaporization temperature and vaporization pressure of the second oxygen-enriched gas fluid (paths 45 and 145) in the second condensers 15 and 115. That is, in the present embodiment and the conventional example, the second oxygen-enriched gas fluid vaporized by the second condensers 15 and 115 and led to the paths 45 and 145 is lost in the pressure loss in the main heat exchangers 24 and 124 and the like. It must have a pressure that can be released to the atmosphere after regenerating the purifiers 23 and 123.

  In the second condenser 15 in the present embodiment, the third oxygen-enriched liquefied fluid is vaporized by indirect heat exchange between the third oxygen-enriched liquefied fluid and the second nitrogen gas, so the dew point of the second nitrogen gas A predetermined temperature difference is required for the vaporization temperature of the second oxygen-enriched gas fluid, and when the temperature difference is determined, the second nitrogen gas pressure, i.e., the third, is determined from the required pressure of the second oxygen-enriched gas fluid. The minimum operating pressure of the rectifying column 13 is determined. Further, the operating pressure of the third rectifying column 13 becomes the operating pressure of the second rectifying column 12. Similarly, the minimum operating pressure of the first fractionator 11 is determined from the temperature difference required for indirect heat exchange in the first condenser 14. Therefore, if the oxygen composition of the second oxygen-enriched gas fluid can be lowered, the pressure of the second nitrogen gas, that is, the pressure of the first rectifying column 11 can be reduced.

  In the conventional example, the production of product nitrogen was performed in two stages of the first separation step (first rectification column 111) and the second separation step (third rectification column 113), whereas in the present embodiment, A new separation step (second separation step in the second rectifying column 12 in the present invention) is newly provided between the first separation step and the second separation step in the example, and the separation step is performed in three stages. The oxygen composition of the third oxygen-enriched liquefied fluid (path 41) from the process can be made lower than that of the conventional oxygen-enriched liquefied fluid (path 141).

  That is, in the conventional example, the source gas (path 125) is separated into the first product nitrogen gas (path 126) and the first oxygen-enriched liquefied fluid (path 129) in the first separation step (rectification column 111). After the entire amount of the first oxygen-enriched liquefied fluid is vaporized by the condenser 114, a part of the first oxygen-enriched liquefied fluid is introduced into the second separation step (rectifying column 113) as the raw material gas (path 134) of the second separation step It was. Therefore, the oxygen composition of the first oxygen-enriched liquefied fluid (path 129) and the oxygen composition of the raw material gas of the second separation step (rectification tower 113) were the same.

  For example, in the conventional example, the oxygen composition of the first oxygen-enriched liquefied fluid from the first separation step and the raw material gas in the second separation step are both about 38%. As a result, the oxygen composition of the second oxygen-enriched liquefied fluid (path 141) from the second separation step is about 55%. On the other hand, in the present embodiment, the first oxygen-enriched liquefied fluid (path 29) from the first separation step is introduced into the second separation step, from which a fluid with a low oxygen composition (second raw material air: path 34). Is taken out and introduced into the third separation step as the second source gas.

  Therefore, in this embodiment, even if the oxygen composition of the first oxygen-enriched liquefied fluid from the first separation step is about 38%, the oxygen composition of the second raw material air taken out from the second separation step is, for example, 20 %. As a result, the oxygen composition of the third oxygen-enriched liquefied fluid 41 from the third separation step is about 36%.

  At this time, even when the evaporation pressure of the second oxygen-enriched gas fluid in the second condenser 15 is the same as that in the conventional example, in this embodiment, the evaporation temperature is lowered by an amount corresponding to the lower oxygen composition in the third oxygen-enriched liquefied fluid. It has become. For this reason, even if the temperature difference between the second nitrogen gas and the second oxygen-enriched gas fluid in the second condensers 15 and 115 is the same, the operating pressure of the third rectifying column 13 is lowered as compared with the conventional example. be able to. Furthermore, since the operating pressure of the third rectifying column 13 is lowered, the operating pressure of the first rectifying column 11 can be lowered.

  That is, in this embodiment, it is possible to lower the operating pressure of the entire apparatus including the third fractionator 13 by lowering the oxygen composition of the third oxygen-enriched liquefied fluid introduced into the second condenser 15. Become. As a result, it is possible to supply the product nitrogen gas in a low unit by a lower pressure than the conventional example.

  Further, in the present embodiment, the remaining portion of the second oxygen-enriched liquefied fluid that has not been vaporized by the first condenser 14 is extracted as the fourth oxygen-enriched liquefied fluid (path 33), whereby the first condenser 14 is cooled. The evaporation temperature of the second oxygen-enriched liquefied fluid, which is a fluid, can be lowered, and efficient operation is possible even in the product nitrogen pressure range, which has been difficult to operate efficiently in the past.

  That is, as shown in FIG. 2 (a), the second oxygen-enriched liquefied fluid is extracted from the passage 33 with a liquid having an oxygen composition of 55% and the other oxygen-enriched liquid is vaporized by the first condenser. As shown in FIG. 2 (b), the vaporization temperature of the liquefied fluid is obtained when the second oxygen-enriched liquefied fluid is completely vaporized and then a part thereof is extracted from the passage 33a with a gas having an oxygen composition of 55%. We are taking advantage of being lower than that. In the former case, the vaporization temperature of the second oxygen-enriched liquefied fluid is the vapor-liquid equilibrium temperature of a fluid having a liquid-phase oxygen composition of 55% (gas-phase oxygen composition is 29%, for example). This is because the vaporization temperature is the vapor-liquid equilibrium temperature of a fluid having a gas phase oxygen composition of 55% (liquid phase oxygen composition is more than 55%).

  Therefore, as shown in FIG. 2A, by extracting a part of the second oxygen-enriched liquefied fluid with the liquid, the vaporization temperature of the first condenser 14 is lowered, and as a result, the first condenser 14 is compared with the conventional example. The operating pressure required for one rectification column 11, 111 can be lowered. In the above comparison, the liquid or gas having the same oxygen composition of 55% is extracted because the oxygen composition of the second raw material air derived from the upper part of the second fractionator 12 is the same.

  That is, the present embodiment reduces the operating pressure of the third rectifying column 13 by reducing the oxygen composition of the second oxygen-enriched gas fluid that is the cold fluid of the second condenser 15, and the second oxygen A process capable of dealing with the production of product nitrogen having a relatively low pressure, which was not possible with the conventional example, by extracting the remainder of the enriched liquefied fluid as a liquid and consequently lowering the operating pressure of the first fractionator 11 It has become.

  FIG. 3 is a system diagram of a nitrogen production apparatus showing a second embodiment of the present invention. In the following description, the same components as those shown in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The nitrogen production apparatus shown in the present embodiment is called an internal heat exchange rectification column (hereinafter referred to as HIDiC) instead of the second rectification column 12 and the first condenser 14 in the first embodiment. ) 17 is shown. Part of the first nitrogen gas led out from the upper part of the first rectifying column 11 to the path 26 and branched into the path 31 is introduced into the upper part of the warm fluid passage 17a of the HIDiC 17 and from the lower part of the first rectifying column 11 The first oxygen-enriched liquefied fluid led to the path 29 and decompressed by the pressure reducing valve 30 is introduced into the upper part of the cold fluid passage 17b of the HIDiC 17.

First nitrogen gas to lower the temperature the fluid passage 17 a is a part in indirect heat exchange with the first oxygen-enriched liquefied fluid down the cold fluid passage 17b is a first liquefied nitrogen and liquefied, hot fluid passage 17 It is led out from the lower part of a to the path 32 and introduced into the upper part of the first rectifying column 11. The first nitrogen gas not liquefied is the temperature derived from the lower portion of the fluid passage 17 a to the path 27, after raising the temperature to room temperature in the main heat exchanger 24, the first product from the first product recovery path 28 Derived as nitrogen gas.

  The first oxygen-enriched liquefied fluid descending the cold fluid passage 17b undergoes partial heat vaporization and low temperature rectification by indirect heat exchange with the first nitrogen gas, and from the lower portion of the cold fluid passage 17b. , The second oxygen-enriched liquefied fluid having an oxygen composition of 55%, for example, is withdrawn into the passage 33 and decompressed by the pressure reducing valve 47 and then introduced into the third condenser 16. The entire amount is vaporized by heat exchange with the first nitrogen gas branched from the first to the channel 48 and introduced into the main heat exchanger 24. On the other hand, from the upper part of the cold fluid passage 17b, the second raw material air whose oxygen composition is lower than that of the first oxygen-enriched liquefied fluid, for example, as low as the atmospheric composition, is led out to the passage 34, where It is introduced into the lower part of the distillation column 13.

  As described above, even if the second rectifying column 12 and the first condenser 14 in the first embodiment are replaced with the internal heat exchange rectifying column (HIDiC) 17, the same effects as those in the first embodiment can be obtained. It is done. It is also possible to incorporate the third condenser 16 into the HIDiC 17 integrally.

  FIG. 4 is a system diagram of a main part of a nitrogen production apparatus showing a third embodiment of the present invention. The present embodiment shows an example in which the second rectifying column 12 and the first condenser 14 in the first embodiment are replaced with a gas-liquid separator 18 incorporating the first condenser 14.

  The first oxygen-enriched liquefied fluid led out from the lower part of the first rectifying column 11 to the path 29 and decompressed by the pressure reducing valve 30 is introduced into the gas-liquid separator 18 having the first condenser 14 at the lower part. By the gas-liquid separation in the stage, the second raw material air having a low oxygen composition can be obtained from the upper part of the gas-liquid separator 18. In this way, by performing the second separation step in one vapor-liquid equilibrium, the second raw material air having a lower oxygen composition than in the conventional example can be led out to the path 34 and introduced into the third rectification column. it can. In addition, the second oxygen-enriched liquefied fluid is extracted from the lower part of the gas-liquid separator 18 to the path 33, decompressed by the decompression valve 47, and then introduced into the third condenser 16.

  FIG. 5 is a system diagram of a main part of a nitrogen production apparatus showing a fourth embodiment of the present invention. The present embodiment shows an example in which the second rectifying column 12 in the first embodiment is replaced with a gas-liquid separator 19.

  The first oxygen-enriched liquefied fluid led out from the lower part of the first rectifying column 11 to the passage 29 and decompressed by the pressure reducing valve 30 is introduced into the first condenser 14 and indirectly heat exchanged with the first nitrogen gas. A part of the gas is vaporized to become a first oxygen-enriched gas-liquid mixed phase fluid in a gas-liquid mixed state, and is introduced into the gas-liquid separator 19. In the gas-liquid separator 19, the second raw material air having an oxygen composition lower than that of the first oxygen-enriched liquefied fluid is separated into the gas phase based on the gas-liquid equilibrium, and the liquid phase is separated from the first oxygen-enriched liquefied fluid. The second oxygen-enriched liquefied fluid having a high oxygen composition is separated. Further, the second raw material air is led out from the upper part of the gas-liquid separator 19 to the path 34 and introduced into the lower part of the third rectification column 13, and the second oxygen-enriched liquefied fluid is To the path 33, the pressure is reduced by the pressure reducing valve 47, and then introduced into the third condenser 16.

  In the nitrogen production apparatus having the configuration shown in the first embodiment of FIG. 1, the simulation was performed by setting the product nitrogen gas pressure to 0.6 MPa and the allowable oxygen composition in the product nitrogen gas to 0.1 ppm.

  The raw material air is introduced into the main heat exchanger 24 at 0.63 MPa and 40 ° C. and cooled to the vicinity of the dew point, and then introduced into the first rectifying column 11 from the path 25, and the upper first nitrogen gas and the lower part Is separated into a first oxygen-enriched liquefied fluid having an oxygen composition of 38%. The product yield of the first rectifying column 11 is about 44%. The first oxygen-enriched liquefied fluid derived from the lower part of the first rectifying column 11 is introduced into the upper part of the second rectifying column 12, and the oxygen composition is obtained by the action of the second rectifying column 12 and the first condenser 14. A 19% second feed air and a fourth oxygen-enriched liquefied fluid with an oxygen composition of 55% are obtained. The second raw material air is introduced into the third fractionator 13 and separated into the upper second nitrogen gas and the lower oxygen enriched liquefied fluid having a lower oxygen composition of 36%. The product yield of the third rectification column 13 is about 50%, and when the first nitrogen gas is combined, the product yield of the entire process is 57%.

Table 1 shows the process value of each path when the flow rate of the raw material air is 100. The first rectifying column 11, the second rectifying column 12, and the third rectifying column 13 are assumed to be shelf-type rectifying columns. However, a packed column using an irregular packing material or a regular packing material is used. When used, the pressure loss of the rectifying column is reduced, so that the power cost can be improved.

In the nitrogen production apparatus having the configuration shown in the second embodiment of FIG. 3, simulation was performed under the conditions of the same product specifications. Table 2 shows the process value of each path when the flow rate of the raw material air is 100.

  When Example 1 and Example 2 are compared, it turns out that the operating pressure of the 3rd fractionator 13 in Example 2 is about 0.04 MPa high. This is because the first condenser 14 needs to secure a predetermined temperature difference (several degrees Celsius) in the first embodiment, whereas the HIDiC17 employed in the second embodiment can be operated even with a smaller temperature difference. It is due to that. For this reason, in Example 2, the second product nitrogen gas having a pressure higher by about 0.04 MPa than in Example 1 can be collected, and when it is necessary to increase the pressure of the second product nitrogen gas, nitrogen compression is performed. Reduction of power of the machine 38 can be expected.

In addition, it is possible to further reduce the operating pressure of the second oxygen-enriched vaporized fluid, and in Example 2, it is possible to cope with sampling of product nitrogen gas at a lower pressure. Table 3 shows a comparison between Example 2 and the conventional example when the power unit of Example 1 is 100. Note that, under the conditions of this comparison, when the product pressure was 0.6 MPa, the conventional example did not hold.

  Furthermore, it was confirmed that the HIDiC used in Example 2 has a predetermined performance with an axial length of about 1000 to 2000 mm. As a result, the apparatus can be reduced in size and piping can be simplified as compared with the case where the rectifying stage type or regular packed type second rectifying column 12 and the first condenser 14 of the plate fin type heat exchanger are used. can do.

1 is a system diagram of a nitrogen production apparatus showing a first embodiment of the present invention. It is explanatory drawing of the 2nd fractionator part provided with the 1st condenser. It is a systematic diagram of the nitrogen manufacturing apparatus which shows the 2nd form example of this invention. It is a systematic diagram of the principal part of the nitrogen manufacturing apparatus which shows the 3rd form example of this invention. It is a systematic diagram of the principal part of the nitrogen manufacturing apparatus which shows the 4th example of this invention. It is a systematic diagram of the nitrogen manufacturing apparatus which shows an example of a conventional process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... 1st rectification tower, 12 ... 2nd rectification tower, 13 ... 3rd rectification tower, 14 ... 1st condenser, 15 ... 2nd condenser, 16 ... 3rd condenser, 17 ... Internal heat exchange Type rectification column (HIDiC), 18 ... gas-liquid separator with built-in first condenser, 19 ... gas-liquid separator, 20 ... filter, 21 ... feed air compressor, 22 ... after cooler, 23 ... purifier, 24 ... main heat exchanger, 28 ... first product recovery path, 30 ... pressure reducing valve, 37 ... second product recovery path, 38 ... nitrogen compressor, 39 ... after cooler, 40 ... product supply path, 42 ... pressure reducing valve, 47 ... Pressure reducing valve, 52 ... Expansion turbine, 55 ... Pressure reducing valve, 56 ... Pressure reducing valve, 57 ... Cold supply route

Claims (8)

In a nitrogen production method for collecting product nitrogen by cryogenic liquefaction separation of raw material air, the first raw material air that has been compressed, purified and cooled is subjected to low-temperature distillation to be separated into a first nitrogen gas and a first oxygen-enriched liquefied fluid. After depressurizing the first separation step and the first oxygen-enriched liquefied fluid, it is separated into the second raw material air and the second oxygen-enriched liquefied fluid by low-temperature distillation with the whole amount of the first oxygen-enriched gas fluid described later. At the same time as the second separation step, the first nitrogen gas is condensed and liquefied by indirect heat exchange between a part of the second oxygen-enriched liquefied fluid and a part of the first nitrogen gas to obtain first liquefied nitrogen. A first indirect heat exchange step of evaporating part of the second oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas fluid; and low-temperature distillation of the second source air to produce second nitrogen gas and third oxygen A third separation step for separating into an enriched liquefied fluid, a part of the second nitrogen gas, and before decompression Indirect heat exchange with the third oxygen-enriched liquefied fluid to condense and liquefy the second nitrogen gas to obtain second liquefied nitrogen, and simultaneously evaporate and gasify the third oxygen-enriched liquefied fluid to obtain the second oxygen-enriched gas fluid. A second indirect heat exchanging step for obtaining the second oxygen-enriched liquefied fluid, and a second portion of the second oxygen-enriched liquefied fluid is subjected to indirect heat exchange with a part of the remaining portion of the first nitrogen gas after depressurization to condense and liquefy the first nitrogen gas. A third indirect heat exchange step for obtaining a third oxygen-enriched gas fluid by evaporating and gasifying the entire amount of the second oxygen-enriched liquefied fluid at the same time as obtaining liquefied nitrogen, and a first after the heat recovery of the remainder of the first nitrogen gas A method for producing nitrogen, comprising: a first product recovery step derived as product nitrogen gas; and a second product recovery step wherein the remainder of the second nitrogen gas is derived as a second product nitrogen gas after heat recovery. The method for producing nitrogen according to claim 1, wherein the second separation step and the first indirect heat exchange step are performed in an internal heat exchange rectification column. The method for producing nitrogen according to claim 1, wherein the low-temperature distillation in the second separation step is performed only by one vapor-liquid equilibrium. In a nitrogen production method for collecting product nitrogen by cryogenic liquefaction separation of raw material air, the first raw material air that has been compressed, purified and cooled is subjected to low-temperature distillation to be separated into a first nitrogen gas and a first oxygen-enriched liquefied fluid. Simultaneously obtaining a first liquefied nitrogen by condensing and liquefying the first nitrogen gas by indirect heat exchange between the first separation step and a part of the first nitrogen gas and the first oxygen-enriched liquefied fluid after decompression A first indirect heat exchange step of evaporating and gasifying a part of the first oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas-liquid mixed phase fluid; A second separation step for separating the second raw material air and the second oxygen-enriched liquefied fluid only by equilibrium, and the second raw material air is subjected to low-temperature distillation to separate into a second nitrogen gas and a third oxygen-enriched liquefied fluid. Indirect heat of the third separation step, a part of the second nitrogen gas and the third oxygen-enriched liquefied fluid after decompression A second indirect heat exchange step of condensing and liquefying the second nitrogen gas to obtain second liquefied nitrogen and simultaneously evaporating and gasifying the third oxygen enriched liquefied fluid to obtain a second oxygen enriched gas fluid; The second oxygen-enriched liquefied fluid and the remaining portion of the first nitrogen gas are indirectly heat-exchanged to condense and liquefy the first nitrogen gas to obtain third liquefied nitrogen, and at the same time, the second oxygen-enriched A third indirect heat exchange step for evaporating and gasifying the entire amount of the liquefied fluid to obtain a third oxygen-enriched gas fluid; and a first product recovery step for deriving the remainder of the first nitrogen gas as the first product nitrogen gas after heat recovery And a second product recovery step of deriving the remainder of the second nitrogen gas as a second product nitrogen gas after heat recovery. A nitrogen production apparatus for carrying out a method for collecting product nitrogen by cryogenic liquefaction separation of raw material air according to claim 1, wherein the first raw material air that has been compressed, purified and cooled is subjected to low temperature distillation to produce first nitrogen gas and first oxygen. A rectifying column that performs a first separation step for separating the enriched liquefied fluid into the liquefied fluid, and after depressurizing the first oxygen enriched liquefied fluid by a decompression means, by low-temperature distillation with the total amount of the first oxygen enriched gas fluid described later A rectifying column that performs a second separation step for separating the second raw material air and the second oxygen-enriched liquefied fluid, and indirectly a part of the second oxygen-enriched liquefied fluid and a part of the first nitrogen gas. 1st indirect heat exchange which heat-exchanges and liquefies 1st nitrogen gas to obtain 1st liquefied nitrogen, and at the same time evaporates and gasifies a part of 2nd oxygen enriched liquefied fluid, and obtains 1st oxygen enriched gas fluid a condenser for performing step, the second feed air to cryogenic distillation to second nitrogen gas and the third oxygen-enriched Third and rectification column to carry out the separation step, the third oxygen-enriched liquefied fluid and allowed to indirect heat exchange with the second nitrogen gas after depressurization part and pressure reducing means of the second nitrogen gas is separated into a fluids A condenser for performing a second indirect heat exchange step for obtaining a second oxygen-enriched gas fluid by evaporating and gasifying the third oxygen-enriched liquefied fluid at the same time to obtain second liquefied nitrogen by condensing and liquefying the second oxygen The remainder of the enriched liquefied fluid is decompressed by the decompression means and indirectly heat exchanged with a part of the remainder of the first nitrogen gas to condense and liquefy the first nitrogen gas to obtain third liquefied nitrogen, and at the same time, the second oxygen enrichment A condenser for performing a third indirect heat exchange step for evaporating and gasifying the entire amount of the liquefied fluid to obtain a third oxygen-enriched gas fluid, and a first product nitrogen gas after heat recovery of the remainder of the first nitrogen gas by a heat recovery means The first product recovery path derived as the second nitrogen gas and the remaining portion of the second nitrogen gas are heated by the heat recovery means. After a second product recovery path for deriving a second product nitrogen gas, and a thing nitrogen producing apparatus according to claim. 6. The nitrogen production apparatus according to claim 5, wherein the rectifying column for performing the second separation step and the condenser for performing the first indirect heat exchange step are internal heat exchange rectifying columns. 6. The nitrogen production apparatus according to claim 5 , wherein the rectification column that performs the second separation step is a gas-liquid separator that includes a condenser that performs the first indirect heat exchange step . 5. A nitrogen production apparatus for carrying out the method for collecting product nitrogen by cryogenic liquefaction separation of the raw material air of claim 4, wherein the first raw material air that has been compressed, purified and cooled is subjected to low temperature distillation to produce a first nitrogen gas and a first oxygen. A rectifying column for performing a first separation step to separate the enriched liquefied fluid, a part of the first nitrogen gas and the first oxygen enriched liquefied fluid after being decompressed by the decompression means to indirectly heat-exchange performing a first indirect heat exchanger to obtain a first oxygen-enriched gas-liquid mixed phase fluid one nitrogen gas evaporated gasifying a portion of the condensed and liquefied by the first liquefied nitrogen obtained at the same time the first oxygen-enriched liquefied fluid A gas-liquid separator for performing a second separation step of separating the first oxygen-enriched gas-liquid mixed phase fluid into a second raw material air and a second oxygen-enriched liquefied fluid by separating the first oxygen-enriched gas-liquid mixed phase fluid into the second source air and the second oxygen-enriched liquefied fluid; line a third separation step of separating the 2 feed air to cryogenic distillation to second nitrogen gas and the third oxygen-enriched liquefied fluid Obtaining a rectification column, the third oxygen-enriched liquefied fluid and a second liquefied nitrogen condensed and liquefied the second nitrogen gas by indirect heat exchange after decompression part and pressure reducing means of the second nitrogen gas At the same time , a condenser that performs a second indirect heat exchange step for evaporating and gasifying the third oxygen-enriched liquefied fluid to obtain a second oxygen-enriched gas fluid, and the second oxygen-enriched liquefied fluid that has been depressurized by the depressurizing means, The remaining part of the first nitrogen gas is indirectly heat-exchanged to condense and liquefy the first nitrogen gas to obtain third liquefied nitrogen, and at the same time evaporate and gasify the entire amount of the second oxygen-enriched liquefied fluid. A condenser for performing a third indirect heat exchange step for obtaining an oxygen-enriched gas fluid, a first product recovery path for deriving the remainder of the first nitrogen gas as a first product nitrogen gas after heat recovery by a heat recovery means, The remainder of the second nitrogen gas is extracted as second product nitrogen gas after heat recovery by the heat recovery means. Nitrogen producing apparatus characterized in that it comprises a product recovery path, the.

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