JP4719598B2 - Pretreatment method and apparatus in air liquefaction separation - Google Patents

Description

  The present invention relates to a pretreatment method and apparatus in air liquefaction separation, and more specifically, adsorbs impurities such as moisture, carbon dioxide, and dinitrogen monoxide contained in raw air introduced into a cryogenic separation part of the air liquefaction separation apparatus. The present invention relates to a pretreatment method and apparatus in air liquefaction separation to be removed.

  In an air liquefaction separation device that produces product gases such as oxygen, nitrogen, and argon by liquefying raw material air, impurities such as moisture and carbon dioxide that solidify at a low temperature in the cryogenic separation section are removed in advance by pretreatment. The impurities are adsorbed and separated from the raw air using an adsorber filled with an adsorbent that adsorbs the impurity components.

Among impurities in the raw material air, dinitrogen monoxide (N ₂ O) is present in the atmosphere at about 0.3 ppm, and its concentration tends to increase. This dinitrogen monoxide is adsorbed on the zeolite that adsorbs carbon dioxide, but when carbon dioxide in the raw material air comes into contact with the zeolite on which dinitrogen monoxide is adsorbed, the carbon dioxide is adsorbed and dinitrogen monoxide is absorbed. Since a substitution phenomenon released into the raw material air occurs, it has been difficult to sufficiently remove dinitrogen monoxide with a conventional general adsorber.

For this reason, by removing moisture and carbon dioxide in the raw air completely and then removing nitrous oxide by adsorption, it is possible to prevent substitution by carbon dioxide or to selectively use nitrous oxide over carbon dioxide. Dinitrogen monoxide, such as using an adsorbent to remove by adsorption, using an adsorbent with a large amount of adsorbed dinitrogen monoxide, or using a composite adsorbent that is a physical mixture of several adsorbents Various proposals have been made regarding the removal of adsorbed water (for example, see Patent Documents 1 to 9).
Japanese Patent No. 3308248 JP 2001-129342 A JP 2002-126436 A JP 2003-275532 A JP 2004-975 A JP 2004-148315 A JP 2000-140550 A Japanese Patent No. 2967871 JP 2002-143628 A

  However, in order to remove dinitrogen monoxide with a general adsorbent, it is necessary to adsorb and remove dinitrogen monoxide in a state where carbon dioxide in the raw material air is almost completely removed. In this case, it is most convenient to increase and fill the adsorbent for removing nitrous oxide downstream of the carbon dioxide adsorbent of the existing adsorber. Since the main purpose is to remove carbon, not only is it difficult to optimize the design to adsorb and remove dinitrogen monoxide, but adsorbers for removing dinitrogen monoxide are packed into adsorbers with a large column diameter. Therefore, a large amount of adsorbent for removing dinitrogen monoxide is required, and the adsorber becomes large.

  In addition, if a special adsorbent that selectively adsorbs and removes nitrous oxide over carbon dioxide is used, the manufacturer of this adsorbent is limited, and there is a concern that the price is high. Anxiety remains from the point.

  Furthermore, if a composite adsorbent that is physically mixed with several types of adsorbents is used, the adsorbents are separated due to the difference in specific gravity of the adsorbents over a long period of time, making it impossible to maintain an appropriate mixed state. It was necessary to take measures such as remixing. In addition, when the nitrous oxide is newly removed with the existing pretreatment apparatus, it is necessary to modify the adsorber itself, which is a large-scale operation and a great problem in terms of cost.

  Therefore, the present invention provides a pretreatment method and apparatus in air liquefaction separation that can reliably adsorb and remove dinitrogen monoxide with a simple configuration and can be easily applied to an existing pretreatment apparatus. It is aimed.

In order to achieve the above object, the pretreatment method in the air liquefaction separation of the present invention is a pretreatment method of raw material air in the air liquefaction separation, in which moisture and carbon dioxide in the raw material air are adsorbed and removed and dinitrogen monoxide is removed. a first adsorber which temporarily adsorbs, the downstream of the first adsorber, the second adsorption for adsorbing and removing the dinitrogen monoxide desorbed after being temporarily adsorbed by the first adsorber And a regeneration step and an adsorption step of the second adsorber are performed during the adsorption step of the first adsorber. Furthermore, the raw material air led out from the first adsorber is cooled and then introduced into the second adsorber.

The pretreatment apparatus for air liquefaction separation according to the present invention includes a plurality of first adsorbers for alternately performing an adsorption step and a regeneration step in the raw air pretreatment apparatus for air liquefaction separation, and the first adsorber One second adsorber provided on the downstream side, and the plurality of first adsorbers adsorb and remove moisture and carbon dioxide in the raw material air and temporarily adsorb dinitrogen monoxide. It is filled with an adsorbent, and the second adsorber is filled with an adsorbent that adsorbs and removes the dinitrogen monoxide adsorbed and removed after being temporarily adsorbed by the first adsorber. A cooler is provided for cooling the raw material air led out from the first adsorber and then introducing it into the second adsorber.

  According to the present invention, dinitrogen monoxide is temporarily adsorbed by the first adsorber that removes moisture and carbon dioxide, so that the dinitrogen monoxide provided on the downstream side of the first adsorber is adsorbed and removed. In the second adsorber, the raw material air may be purified intermittently. For this reason, it is possible to continuously purify the raw air only by providing one second adsorber. In addition, since the second adsorber for adsorbing and removing only dinitrogen monoxide is provided, dinitrogen monoxide can be reliably adsorbed and removed under optimum conditions.

  Furthermore, the amount of adsorbent for removing nitrous oxide can be set according to the amount of dinitrogen monoxide in the raw air, so the minimum amount of adsorbent is sufficient and the cost required for the adsorber and adsorbent can be reduced. I can plan. Further, since only one small adsorber needs to be installed, it can be easily added to an existing pretreatment device. Furthermore, the removal efficiency of dinitrogen monoxide can be significantly improved by removing dinitrogen monoxide after cooling the raw material air.

  FIG. 1 is a system diagram showing an example of a pretreatment apparatus for carrying out a pretreatment method for an air liquefaction separation apparatus according to the present invention, and FIG. 2 is a diagram showing an operating state of each adsorber.

  This pretreatment apparatus includes a pair of first adsorbers 11A and 11B and one second adsorber 12 provided on the downstream side thereof. The first adsorbers 11A and 11B mainly include raw material air. An adsorbent, for example, activated alumina 13a for adsorbing and removing moisture therein, and an adsorbent, for example, zeolite 13b, mainly for adsorbing and removing carbon dioxide in the raw material air are provided in two layers. The second adsorber 12 is filled with a dinitrogen monoxide adsorbent 13c capable of adsorbing and removing dinitrogen monoxide in the raw material air.

  In the first adsorbers 11A and 11B, each adsorber alternately repeats an adsorption process and a regeneration process for a predetermined time, and when one of the first adsorbers is performing the adsorption process, the other first adsorber By performing the regeneration process, the raw material air is continuously purified. In addition, the second adsorber 12 starts the regeneration process when any one of the first adsorbers starts the adsorption process when alternately performing the adsorption process and the regeneration process. The regeneration process is switched to the adsorption process within the adsorption process time of the apparatus, and the second adsorber 12 is set to complete the adsorption process at the end of the adsorption process of the first adsorber. Therefore, in the second adsorber 12, an adsorption process for adsorbing and removing dinitrogen monoxide in the raw material air is intermittently performed.

  The first adsorber is filled with an adsorbent for removing water and removing carbon dioxide. As described above, X-type zeolite used as an adsorbent for removing carbon dioxide also adsorbs dinitrogen monoxide, but is substituted and desorbed by carbon dioxide. Due to the nature of the carbon dioxide adsorbent, in the first half of the adsorption process in the first adsorber, the concentration of nitrous oxide in the raw air derived from the first adsorber is such that it does not cause a problem in the cryogenic separation unit. Low. However, in the latter half of the adsorption process in the first adsorber, the derived raw material air contains a higher concentration of dinitrogen monoxide than in the atmosphere. This is considered that the dinitrogen monoxide was concentrated in the first adsorber. The present invention utilizes this phenomenon, and it is possible to efficiently remove dinitrogen monoxide by providing one second adsorber 12 downstream of the plurality of first adsorbers 11A and 11B. Become.

  This pretreatment apparatus continuously adsorbs and removes impurities in the raw material air supplied to the cryogenic separation section by operating each adsorber as shown in FIG. First, when one first adsorber 11A is performing an adsorption process and the other first adsorber 11B is performing a regeneration process, the second adsorber 12 performs a regeneration process and an adsorption process.

  The raw material air compressed to a predetermined pressure by the raw material air compressor 21 is freed of compression heat by the aftercooler 22 and condensed water is removed by the drain separator 23, and then passes through the inlet valve 24a to the first adsorber 11A. To be introduced. If necessary, a refrigerator 25 can be provided downstream of the aftercooler 22 to cool the raw material air.

  Moisture, which is an impurity in the raw air introduced into the first adsorber 11A, is adsorbed and removed by the activated alumina 13a, and carbon dioxide and dinitrogen monoxide are adsorbed and removed by the zeolite 13b. Dinitrogen monoxide is adsorbed on the zeolite 13b at the start of the adsorption process, but when carbon dioxide comes into contact with the zeolite 13b that adsorbs dinitrogen monoxide, the substitution phenomenon of carbon dioxide and dinitrogen monoxide causes the dinitrogen monoxide to be absorbed. The carbon dioxide is adsorbed by desorption from the zeolite 13b, and the dinitrogen monoxide repeats sequential adsorption and desorption on the zeolite 13b, and gradually becomes concentrated in the zeolite 13b located on the downstream side.

  The raw material air from which impurities are removed by adsorption with the activated alumina 13a and the zeolite 13b is led out from the first adsorber 11A through the outlet valve 26a, and after the heat of adsorption is removed by the cooler 27, the first supply valve 28 is passed through. It is supplied to a cryogenic separation unit (not shown). Further, a measuring device 29 for measuring the concentration of dinitrogen monoxide is provided on the downstream side of the cooler 27, and the dinitrogen monoxide in the raw material air derived from the first adsorber in the adsorption process is continuous. Has been measured.

  On the other hand, in the other first adsorber 11B performing the regeneration process, the regeneration gas heated to a predetermined temperature by the first heater 30 is introduced from the outlet side through the regeneration inlet valve 31b, and the zeolite 13b. In addition, by heating the activated alumina 13a with a high-temperature regeneration gas, carbon dioxide and moisture adsorbed on these adsorbents in the previous adsorption step are desorbed, and accompanied by the regeneration gas, on the inlet side of the first adsorber 11B. Is discharged through the regeneration outlet valve 32b.

  In the first half of the adsorption process of the first adsorber 11A and the regeneration process of the first adsorber 11B, the second adsorber 12 performs the regeneration process, and the regeneration gas heated to a predetermined temperature by the second heater 33 is It is introduced from the outlet side of the second adsorber 12 through the second adsorber regeneration inlet valve 34, and adsorbs in the previous adsorption step by heating the nitrous oxide adsorbent 13 c in the second adsorber 12. The dinitrogen monoxide adsorbed on the agent 13c is desorbed, is accompanied by the regeneration gas, and is discharged from the inlet side through the second adsorber regeneration outlet valve 35.

  Usually, in the regeneration process of each adsorber, the decompression stage, the heating regeneration purge stage, the cooling stage, and the charging stage are performed for a predetermined time. In the above-described operation state, each valve shown in FIG. 1 is opened in the above description, and the other valves are closed.

  After the adsorption process of the first adsorber 11A is performed for a predetermined time or when dinitrogen monoxide is detected by the measuring device 29, the second adsorber 12 is switched from the regeneration process to the adsorption process. In the adsorption process of the second adsorber 12, the first supply valve 28, the second adsorber regeneration inlet valve 34, and the second adsorber regeneration outlet valve 35 are closed, and the second adsorber inlet valve 36 and the second adsorber regeneration valve 35 are closed. The adsorber outlet valve 37 is opened. Thereby, the flow of the raw material air derived from the first adsorber 11 </ b> A performing the adsorption process is switched to a path passing through the second adsorber 12 downstream of the cooler 27.

  Accordingly, the raw air derived from the first adsorber 11A is introduced into the second adsorber 12 through the second adsorber inlet valve 36, and supplied to the cryogenic separation section through the second adsorber outlet valve 37. Is done. At this time, dinitrogen monoxide once adsorbed on the zeolite 13b of the first adsorber 11A, substituted with carbon dioxide and desorbed is introduced from the first adsorber 11A to the second adsorber 12 along with the raw material air. Then, it is adsorbed by the filler 13c in the second adsorber 12 and removed from the raw material air.

  The first adsorber 11A is switched from the adsorption process to the regeneration process before the zeolite 13b breaks through and the carbon dioxide flows out of the first adsorber 11A. At the same time, the other first adsorber 11B is adsorbed from the regeneration process. The second adsorber 12 is switched from the adsorption process to the regeneration process. That is, after the depressurization stage of the first adsorber 11A and the second adsorber 12, the inlet valve 24a, the outlet valve 26a, the regeneration inlet valve 31b, the regeneration outlet valve 32b, the second adsorber inlet valve 36, and the second adsorber outlet. The valve 37 is closed, the inlet valve 24b, the outlet valve 26b, the regeneration inlet valve 31a, the regeneration outlet valve 32a, the second adsorber regeneration inlet valve 34 and the second adsorber regeneration outlet valve 35 are opened, and the first heater 30 and The second heater 33 is activated.

  In the first half of the adsorption process of the first adsorber 11B, the compressed raw material air passes through the first adsorber 11B and adsorbs and removes impurities such as moisture, carbon dioxide, and dinitrogen monoxide in the packed beds 13a and 13b. It is supplied to the cryogenic separator as it is, and the regeneration process is performed in the first adsorber 11A and the second adsorber 12. In the second half of the adsorption process of the first adsorber 11B, the second adsorber 12 is switched to the adsorption process, and the raw material air derived from the first adsorber 11B passes through the second adsorber 12 and dinitrogen monoxide. It is removed by adsorption and supplied to the cryogenic separation unit.

  Hereinafter, by switching the operation state of each adsorber as shown in FIG. 2, impurities such as moisture, carbon dioxide, and dinitrogen monoxide in the raw material air can be adsorbed and removed by each adsorbent. Then, dinitrogen monoxide is used in the second adsorber 12 because the second adsorber 12 may be used to adsorb and remove what flows out from the first adsorbers 11A and 11B in the second half of the adsorption process by substitution with carbon dioxide. The amount of the adsorbent can be set according to the concentration of dinitrogen monoxide contained in the raw air, and the diameter of the second adsorber 12 can be formed in accordance with conditions suitable for adsorption of dinitrogen monoxide.

  Further, since the second adsorber 12 only needs to perform the adsorption process in the second half of the adsorption process of the first adsorber, the regeneration process of the second adsorber 12 can be performed in the first half of the adsorption process of the first adsorber. Yes, only one second adsorber 12 needs to be installed. Furthermore, the amount of the adsorbent for dinitrogen monoxide charged in the second adsorber 12 can be reduced as compared with the case where the adsorber is filled with the carbon dioxide adsorbed zeolite. Therefore, it is possible to efficiently remove dinitrogen monoxide in the raw material air only by adding one small adsorber.

  Since the adsorbent for adsorbing nitrous oxide used in the second adsorber 12 has sufficiently removed moisture and carbon dioxide in the raw material air in the first adsorber, the adsorbent after nitrous oxide is adsorbed There is no need to consider substitution with carbon dioxide, and any one can be selected as long as it can adsorb and remove dinitrogen monoxide in the raw material air. Therefore, the adsorbent cost can be greatly reduced as compared with the case where an expensive and special adsorbent is used.

Example 1
In the process of the present invention in FIG. 1, an example in which moisture, carbon dioxide, and dinitrogen monoxide in the raw air are removed is shown below.

The feed air containing about 0.3 ppm of dinitrogen monoxide (flow rate 3850 Nm ³ / h) was pressurized to about 0.6 MPa by the feed air compressor 21 and cooled to about 15 ° C. by the aftercooler 22 and the refrigerator 25. Thereafter, the drain was removed by the drain separator 23 and introduced into the first adsorber (11A or 11B) performing the adsorption process. The lower part of the first adsorber was filled with activated alumina 13a, and the upper part thereof was filled with Na-X zeolite 13b. Moisture and carbon dioxide are removed from the raw air introduced into the first adsorber and introduced into the second adsorber 12. In this example, the cooling device 27 introduced the second adsorber without cooling. The second adsorber was filled with 0.3 m ³ of Mg-X zeolite 13c as a dinitrogen monoxide adsorbent.

  A change in the concentration of dinitrogen monoxide in the raw material air at the outlet of the first adsorber measured by the measuring device 29 is indicated by a triangular mark in FIG. Under these conditions, dinitrogen monoxide broke through about 60 minutes after the start of the adsorption process in the first adsorber.

  The adsorption process and the regeneration process of the first adsorber were 240 minutes each, and one cycle was 480 minutes. The adsorption process of the second adsorber was started after 60 minutes from the start of the adsorption process of the first adsorber, and was performed for 180 minutes. The regeneration process (decompression, heating, cooling, charging) time of the second adsorber was 60 minutes, and one cycle of the second adsorber was 240 minutes.

  Finally, the entire amount of dinitrogen monoxide contained in the raw air could be removed.

Comparative Example 1
For comparison, an example of removal of dinitrogen monoxide by a conventional method is shown. In the apparatus shown in FIG. 4, the raw air containing about 0.3 ppm of dinitrogen monoxide (flow rate 3850 Nm ³ / h) is boosted to about 0.6 MPa by the raw air compressor 21, and the aftercooler 22, the refrigerator 25, After cooling to about 15 ° C., the drain is removed by the drain separator 23 and introduced into the adsorber (111A or 111B) performing the adsorption process. Each adsorber was filled with activated alumina 13a and Na-X zeolite 13b in the same amount as in the first adsorber of Example 1 from the bottom, and further laminated with Mg-X zeolite 13c.

Similar to the first adsorber of Example 1, the adsorption process and the regeneration process of the adsorber were performed for 240 minutes, and one cycle was 480 minutes. In order to adsorb and remove the entire amount of dinitrogen monoxide contained in the raw air, 0.3 m ^{3 of} Mg-X zeolite 13c was required for each adsorber, for a total of 0.6 m ³ . In Comparative Example 1, the second adsorber is not used, but each adsorber is filled with Mg-X zeolite 13c, so that each adsorber is higher than the first adsorber of Example 1. About 26% larger, and twice as much adsorbent for nitrous oxide was required.

Example 2
Using the apparatus shown in FIG. 1, the raw material air (flow rate 3850 Nm ³ / h) containing about 0.3 ppm of dinitrogen monoxide is pressurized to about 0.6 MPa by the raw material air compressor 21, and about 40 by the after cooler 22. After cooling to ° C., the drain was removed without using the refrigerator 25 and introduced into the first adsorber (11A or 11B) performing the adsorption process. The lower part of the first adsorber was filled with activated alumina 13a, and the upper part thereof was filled with Na-X zeolite 13b.

Moisture and carbon dioxide were removed from the raw air introduced into the first adsorber, cooled by the cooler 27, and then introduced into the second adsorber 12. The second adsorber was filled with 0.3 m ³ of Mg-X zeolite 13c as a dinitrogen monoxide adsorbent.

  The change in the concentration of dinitrogen monoxide in the raw material air at the outlet of the first adsorber measured by the measuring device 29 is indicated by a circle in FIG. Under these conditions, dinitrogen monoxide broke through about 30 minutes after the start of the adsorption process in the first adsorber.

  One cycle of the first adsorber was 240 minutes. The adsorption process of the second adsorber was started 60 minutes after the start of the adsorption process of the first adsorber, and was performed for 60 minutes. The second adsorber regeneration process (depressurization, overheating, cooling, charging) time was 60 minutes, and one cycle of the second adsorber was 120 minutes. Finally, about 80% of the dinitrogen monoxide contained in the raw air could be removed.

Comparative Example 2
In the apparatus shown in FIG. 4, the feed air containing about 0.3 ppm of dinitrogen monoxide (flow rate 3850 Nm ³ / h) is pressurized to about 0.6 MPa by the feed air compressor 21, and is heated to about 40 ° C. by the aftercooler 22. After cooling, the drain is removed by the drain separator 23 and introduced into the adsorber (111A or 111B) performing the adsorption process. Each adsorber was filled with activated alumina 13a and Na-X zeolite 13b in the same amount as in the first adsorber of Example 2 from the bottom, and further laminated with Mg-X zeolite 13c.

As with the first adsorber of Example 2, one cycle of the adsorber was 240 minutes. In order to remove 80% of dinitrogen monoxide contained in the raw air, 0.55 m ^{3 of} Mg-X zeolite 13c was required for each adsorber, for a total of 1.10 m ³ . Each adsorber was approximately 30% higher in height than the first adsorber of Example 2, and the adsorbent for dinitrogen monoxide was required 3.7 times.

  In Example 2, the amount of the nitrous oxide adsorbent is reduced by improving the adsorption conditions of nitrous oxide in addition to using a single nitric oxide adsorber. That is, in Comparative Example 2, the temperature of the air from which moisture and carbon dioxide have been adsorbed and removed by the adsorbers (111A, 111B) increases by several tens of degrees Celsius due to the heat of adsorption. For this reason, dinitrogen monoxide must be removed by adsorption under this temperature condition. On the other hand, according to the present invention, since the adsorption temperature of dinitrogen monoxide can be greatly lowered by the cooler 27 installed downstream of the first adsorber, the adsorption conditions in the second adsorber are improved, The amount of nitrous oxide adsorbent required can be reduced.

It is a systematic diagram which shows one example of the pretreatment apparatus which implements the pretreatment method in the air liquefaction separation of this invention. It is a figure which shows the driving | running state of each adsorption device. It is a figure which shows the density | concentration change of the dinitrogen monoxide exit of the 1st adsorption device in Example 1 and Example 2. FIG. It is a systematic diagram which shows the pretreatment apparatus used in Comparative Examples 1 and 2.

Explanation of symbols

  11A, 11B ... first adsorber, 12 ... second adsorber, 13a ... activated alumina, 13b ... zeolite, 13c ... adsorbent for dinitrogen monoxide, 21 ... feed air compressor, 22 ... after cooler, 23 ... drain Separator, 24a, 24b ... inlet valve, 25 ... refrigerator, 26a, 26b ... outlet valve, 27 ... cooler, 28 ... first supply valve, 29 ... measuring instrument, 30 ... first heater, 31a, 31b ... Regeneration inlet valve, 32a, 32b ... regeneration outlet valve, 33 ... second heater, 34 ... second adsorber regeneration inlet valve, 35 ... second adsorber regeneration outlet valve, 36 ... second adsorber inlet valve, 37 ... Second adsorber outlet valve

Claims (4)

In the pretreatment method for feed air in cryogenic air separation, water of said feed air, a first adsorber which temporarily adsorbs nitrogen monoxide with adsorbing and removing carbon dioxide, downstream of the first adsorber A second adsorber for adsorbing and removing the dinitrogen monoxide that has been temporarily adsorbed by the first adsorber and then desorbed , and during the adsorption process of the first adsorber, A pretreatment method in air liquefaction separation, comprising performing an adsorber regeneration step and an adsorption step.   The pretreatment method in air liquefaction separation according to claim 1, wherein the raw material air led out from the first adsorber is cooled and then introduced into the second adsorber. In the raw material air pretreatment apparatus in the air liquefaction separation, a plurality of first adsorbers for alternately performing an adsorption step and a regeneration step, and one second adsorber provided on the downstream side of the first adsorber The plurality of first adsorbers are filled with an adsorbent that adsorbs and removes moisture and carbon dioxide in the raw material air and temporarily adsorbs dinitrogen monoxide , and the second adsorber includes: A pretreatment apparatus in air liquefaction separation, which is filled with an adsorbent for adsorbing and removing the dinitrogen monoxide adsorbed and removed after being temporarily adsorbed by the first adsorber .   The pretreatment apparatus for air liquefaction separation according to claim 3, further comprising a cooler for cooling the raw material air led out from the first adsorber and then introducing the air into the second adsorber.

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