Stable Isotope Enrichment Method

Abstract

The object of the present invention is to provide a stable isotope enrichment method that can reduce equipment costs and power without lengthening the start-up time and can achieve efficient enrichment. The present invention provides a stable isotope enrichment method, which is a method for separating stable isotopes using a plurality of distillation columns (the first column to the m-th column; m is an integer of 2 or more) connected in cascade. One of gas and liquid is supplied from a position near the bottom of the (n-1)-th column to a position near the top of the n-th column (1 < n ≤ m), and the other of gas and liquid is returned from a position near the top of the n-th column to a position near the bottom of the (n-1)-th column. In each distillation column, when the flow rate of the gas rising in the column is set as the first flow rate and the flow rate of the gas or liquid supplied from the previous column or the next column is set as the second flow rate, the second flow rate is set to 4% by volume or more of the first flow rate.

Description

Technical Field

[0001] The present invention relates to a method for concentrating stable isotopes. Background Art

[0002] As methods for separating stable isotopes that exist only in extremely small amounts in nature, separation methods such as thermal diffusion separation, centrifugal force separation, laser separation, chemical exchange separation, and distillation separation are known. Among these separation methods, since distillation separation is for mass production of light elements, for example, as a method for separating stable isotopes of industrial oxygen, distillation separation of water or distillation separation of oxygen is adopted.

[0003] As a feature of the separation method of stable isotopes using distillation, since the separation coefficient is very close to 1, in order to obtain a high-concentration stable isotope, about several thousand theoretical plates are required. However, since the height of the distillation column is limited, it is necessary to divide the distillation column into multiple distillation columns and connect these multiple divided distillation columns in series (hereinafter, also referred to as "cascade connection"). In addition, since the natural abundance of stable isotopes is small, the amount of product is very small relative to the feed amount of the raw material.

[0004] Therefore, in the multiple distillation columns connected in series, the diameter of the column supplying the raw material is the largest, and as it approaches the end of the recovery / concentration section, the concentration of the product in the column becomes higher, so the column diameter can be reduced (also referred to as "step cascade"). Thereby, not only the equipment cost is reduced, but also the holdup is reduced, which is also helpful for shortening the start-up time. On the other hand, in order to reduce the column diameter, it is necessary to separately provide a condenser and a reboiler in the column with a reduced column diameter, and an increase in the number of condensers and reboilers results in an increase in power.

[0005] However, in order to connect multiple distillation columns, usually, a liquid is supplied from the bottom of the n-th distillation column to the top of the next column (the (n + 1)-th distillation column), and a gas is supplied from the top of the n-th distillation column to the bottom of the previous column (the (n - 1)-th distillation column). On the other hand, in Patent Document 1, when connecting multiple distillation columns, a gas is supplied from the bottom of the n-th distillation column to the top of the next column (the (n + 1)-th distillation column), and a liquid is supplied from the top of the n-th distillation column to the bottom of the previous column (the (n - 1)-th distillation column).

[0006] Patent Document 1: Japanese Patent No. 5132822 Gazette

[0007] As described above, in isotope separation, a very long distillation column is divided into a plurality of distillation columns, which are connected in series for separation. However, by providing a condenser and a reboiler in each column, the concentration can be increased, and by reducing the column diameter, the start-up time can be shortened without excessively increasing the required power. In order to reduce the required power, in addition to reducing the operating power of the reboiler for generating the rising gas and the condenser for generating the falling liquid in each column, it is also necessary to ensure the flow rate of the raw material required for connecting the columns. If this connection flow rate is too large, the energy consumption of the condenser and the reboiler will increase, and the pipeline will become larger, so the equipment cost will also increase. On the other hand, if the connection flow rate is insufficient, a concentration difference will occur between the distillation columns, and efficient concentration cannot be performed. Summary of the Invention

[0008] The present invention has been completed in view of the above circumstances, and its object is to provide a stable isotope concentration method that can reduce equipment costs and power without lengthening the start-up time and can achieve efficient concentration.

[0009] In order to achieve the above object, the present invention adopts the following configuration.

[0010] [1] A stable isotope concentration method, which is a method of using a plurality of distillation columns (the first column to the mth column; m is an integer of 2 or more) connected in cascade to separate stable isotopes,

[0011] One of gas and liquid is supplied from a position near the bottom of the (n - 1)th column to a position near the top of the nth column (1 < n ≤ m), and the other of gas and liquid is returned from a position near the top of the nth column to a position near the bottom of the (n - 1)th column,

[0012] In each distillation column, when the flow rate of the gas rising in the column is set as the first flow rate and the flow rate of the gas or liquid supplied from the previous column or the next column is set as the second flow rate, the second flow rate is set to 4% by volume or more of the first flow rate.

[0013] [2] The stable isotope concentration method according to the previous item [1], wherein

[0014] The stable isotope is 18 O,

[0015] The second flow rate is set to 4% by volume or more of the first flow rate.

[0016] According to the stable isotope concentration method of the present invention, it is possible to reduce equipment costs and power without lengthening the start-up time and to achieve efficient concentration. Brief Description of the Drawings

[0017] Figure 1 It is a system diagram of a stable isotope enrichment device that can be applied to the stable isotope enrichment method involved in the embodiments of the present invention.

[0018] Figure 2 It is a graph for verifying the effects of the present invention.

[0019] Figure 3 It is a graph for verifying the effects of the present invention.

[0020] Figure 4 It is a graph for verifying the effects of the present invention.

[0021] Figure 5 It is a graph for verifying the effects of the present invention.

[0022] Figure 6 It is a graph for verifying the effects of the present invention.

[0023] Figure 7 It is a graph for verifying the effects of the present invention. Detailed Embodiments

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0025] In addition, for the convenience of understanding the features, in the accompanying drawings used in the following description, sometimes the parts as features are enlarged for convenience, and the dimensional ratios of the respective components are not necessarily the same as the actual ones.

[0026] <Stable Isotope Enrichment Device>

[0027] Figure 1 It is a system diagram of a stable isotope enrichment device that can be applied to the stable isotope enrichment method involved in the embodiments of the present invention.

[0028] The stable isotope enrichment device 300 of the present embodiment includes: a distillation column group formed by cascading 13 distillation columns 1 to 13, isotope scramblers 25, 13 condensers 21, 13 reboilers 22, a raw material supply line 30, a product derivation line 31, an isotope-enriched gas extraction line 36, and an isotope-enriched gas return line 37. The stable isotope enrichment device 300 of the present embodiment is a device for enriching the component of a stable isotope compound (hereinafter, sometimes simply referred to as "stable isotope") containing any stable isotope element contained in a raw material compound to a high concentration.

[0029] In addition, the stable isotope enrichment apparatus 300 is provided with a supply line 34 for supplying raw material from the previous column to the next column and a return line 35 for returning the raw material from the next column to the previous column between the respective distillation columns. On-off valves 23 are respectively provided on the supply line 34. On-off valves 24 are respectively provided on the return line 35.

[0030] Hereinafter, the n-th distillation column starting from the upstream end of the distillation column group will be referred to as the n-th distillation column.

[0031] In addition, in Figure 1 in the figure, considering the situation of the paper surface, only the first distillation column 1 and the ninth to thirteenth distillation columns 9 to 13 among the first to thirteenth distillation columns 1 to 13 to which the high-purity raw material compound (hereinafter, sometimes simply referred to as "raw material") is supplied are shown.

[0032] The first to thirteenth distillation columns 1 to 13 are cascade-connected in the order of the first distillation column 1, the second distillation column 2, the third distillation column 3, the fourth distillation column 4, the fifth distillation column 5, the sixth distillation column 6, the seventh distillation column 7, the eighth distillation column 8, the ninth distillation column 9, the tenth distillation column 10, the eleventh distillation column 11, the twelfth distillation column 12, and the thirteenth distillation column 13 (the distillation column at the downstream end of the distillation column group) to which the raw material is supplied.

[0033] Regarding the first to thirteenth distillation columns 1 to 13, by distilling the stable isotope compound containing the stable isotope element (performing a distillation cascade process), the stable isotope compound of the light component with a low boiling point is concentrated on the top side of the column, and the stable isotope compound of the heavy component with a high boiling point is concentrated on the bottom side of the column.

[0034] Since the distillation load of the first distillation column 1 to which the raw material is supplied among the first to thirteenth distillation columns 1 to 13 is the largest, the column diameter is the largest. In addition, usually, since the abundance ratio of the heavy component stable isotope is small, the distillation load gradually decreases from the first distillation column 1 from the upstream end to the downstream end (the column diameter decreases).

[0035] In addition, a rectification (tray) section, regular packing materials, irregular packing materials, etc. (not shown) are respectively provided in the first to thirteenth distillation columns 1 to 13.

[0036] One end of the supply line 34 is connected to a position near the bottom of the (n - 1)-th distillation column (1 < n ≤ m; m is an integer of 2 or more). In addition, the other end of the supply line 34 is connected to a position near the top of the n-th distillation column. The gas in the (n - 1)-th distillation column is led out to the supply line 34. Regarding the raw material gas led out to the supply line 34, after the flow rate is controlled by the on-off valve 23, it is introduced into the n-th distillation column.

[0037] One end of the reflux line 35 is connected to a position near the top of the n-th distillation column. Further, the other end of the reflux line 35 is connected to a position near the bottom of the (n - 1)-th distillation column (1 < n ≤ m; m is an integer of 2 or more). The liquid in the n-th distillation column is led out to the reflux line 35. Regarding the feed liquid led out to the reflux line 35, after the flow rate is controlled by the on-off valve 24, it is introduced into the (n - 1)-th distillation column.

[0038] A condenser 21 is provided for each of the distillation columns (the 1st to 13th distillation columns 1 to 13).

[0039] The condenser 21 is provided in the circulation line 32, and both ends of the circulation line 32 are connected to different positions at the top of each distillation column. The condenser 21 has a function of liquefying the gas rising in the distillation column by heat exchange and making it fall again in the distillation column. The condenser 21 can reduce the top pressure of each column, thereby preventing a decrease in the separation coefficient caused by the pressure increase during series connection. In this example, a heat medium fluid circulation line 38 is provided for circulating the heat medium fluid through a plurality of condensers 21, and heat exchange is performed by the heat medium fluid circulating in the heat medium fluid circulation line 38.

[0040] A reboiler 22 is provided for each of the distillation columns.

[0041] The reboiler 22 is provided in the circulation line 33, and both ends of the circulation line 33 are connected to different positions at the bottom of each distillation column. The reboiler 22 has a function of vaporizing the liquid falling in the distillation column by heat exchange and making it rise again in the distillation column. In this example, a heat medium fluid circulation line 39 is provided for circulating the heat medium fluid through a plurality of reboilers 22, and heat exchange is performed by the heat medium fluid circulating in the heat medium fluid circulation line 39.

[0042] One end of the raw material supply line 30 is connected to the middle part of the 1st distillation column 1. The raw material supply line 30 is a line for supplying a high-purity raw material to the middle part of the 1st distillation column 1. A valve is provided on the raw material supply line 30.

[0043] The middle part of the distillation column means a position other than the top and bottom of the distillation column.

[0044] High-purity means that the total impurity concentration of the raw material is 0.001% or less.

[0045] In addition, the stable isotope compounds that can be concentrated by the stable isotope concentration method of the present embodiment are not particularly limited. Examples of the stable isotope compounds that can be concentrated include oxygen, water, carbon monoxide, nitric oxide, etc.

[0046] One end of the isotope enrichment gas extraction line 36 is connected to the middle part of the 10th distillation column 10, and the other end is connected to the isotope scrambler 25. A valve 26 is provided on the isotope enrichment gas extraction line 36.

[0047] When the valve 26 is in the open state, the isotope enrichment gas extraction line 36 extracts part or all of the raw material compounds from the 10th distillation column 10 and supplies them to the isotope scrambler 25.

[0048] The raw material compounds extracted from the 10th distillation column 10 contain stable isotope compounds concentrated by the 1st to 10th distillation columns 1 - 10.

[0049] The isotope scrambler 25 converts a stable isotope compound containing one stable isotope element into a stable isotope compound containing other stable isotope elements through an isotope exchange reaction (isotope scrambling). Thus, a concentrate with a further increased concentration of the stable isotope compound containing the desired stable isotope element can be obtained. The concentrate obtained by the isotope scrambler 25 is returned to the 10th distillation column 10 through the isotope enrichment gas return line 37.

[0050] One end of the isotope enrichment gas return line 37 is connected to the isotope scrambler 25, and the other end is connected to the 10th distillation column 10. A valve 27 is provided on the isotope enrichment gas return line 37.

[0051] When the valve 27 is in the open state, the isotope enrichment gas return line 37 returns the concentrate with a further increased concentration of the stable isotope compound containing the desired stable isotope element from the isotope scrambler 25 to the 10th distillation column 10.

[0052] The raw material compounds returned to the 10th distillation column 10 are distilled in the 11th to 13th distillation columns 11 - 13, and the stable isotope compound containing the desired stable isotope element is further concentrated.

[0053] The product export line (export line) 31 is a path for exporting the concentrated stable isotope compound containing the desired stable isotope element as a product. One end of the product export line 31 is connected to the lower part (position close to the bottom) of the 13th distillation column 13.

[0054] <Stable Isotope Enrichment Method>

[0055] Next, with reference to Figure 1 ,an explanation will be given of the stable isotope enrichment method according to the embodiment of the present invention. In this embodiment, the stable isotope enrichment device 300 shown in Figure 1 is used to enrich the stable isotope.

[0056] The stable isotope enrichment method of the present embodiment is a method for separating stable isotopes using a plurality of distillation columns (the first column to the m-th column; m is an integer of 2 or more) connected in cascade. Gas is supplied from a position near the bottom of the (n - 1)-th column to a position near the top of the n-th column (1 < n ≤ m), and liquid is returned from a position near the top of the n-th column to a position near the bottom of the (n - 1)-th column.

[0057] Moreover, in each distillation column (the second distillation column 2 to the thirteenth distillation column 13 in the stable isotope enrichment apparatus 300 shown in Figure 1 ), when the flow rate of the gas rising in the column is set as the first flow rate and the flow rate of the gas supplied from the previous column is set as the second flow rate, the second flow rate is set to be 4 vol% or more of the first flow rate.

[0058] Here, according to the stable isotope enrichment method of the present embodiment, by setting the second flow rate to be 4 vol% or more of the first flow rate, no concentration difference will occur in each column, so efficient enrichment can be achieved. Additionally, the second flow rate is more preferably 5 vol% or more of the first flow rate.

[0059] Furthermore, as described in the examples below, even when the stable isotope is 18 O, it is also preferable to set the second flow rate to be 4 vol% or more of the first flow rate. By operating the stable isotope enrichment apparatus 300 in this way, the abundance ratio of the stable isotope molecules of oxygen sent out from the bottom of the thirteenth distillation column 13 when the apparatus is stable can be set to 18 O of 97 atom% or more.

[0060] In addition, from the viewpoint of reducing the consumed energy, the upper limit value of the second flow rate is preferably 30 vol% or less of the first flow rate.

[0061] On the other hand, in the cascade process, a return line 35 to the previous column is also required. The flow rate of this needs to be approximately the same as the flow rate of the supply line 34. The size of the pipeline or on-off valve related to this flow path and the input energy of the reboiler or condenser can be minimized.

[0062] According to the stable isotope enrichment method of the present embodiment, by controlling the flow rate of the gas or liquid flowing between the distillation columns to be 4 - 30 vol% of the flow rate of the gas rising in the column (the first flow rate), the smooth connection of the concentrations between the columns can be maintained. Thereby, the energy consumed by the reboilers and condensers provided in each column can be reduced, and high-purity products can be collected.

[0063] As described above, according to the stable isotope enrichment method of the present embodiment, the equipment cost and power can be reduced without lengthening the start-up time of the stable isotope enrichment apparatus 300, and efficient enrichment can be achieved.

[0064] In addition, the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, the number of distillation columns (cascaded distillation columns) constituting the distillation column group of the stable isotope enrichment apparatus 300 is not limited to 13, and can be any number. The distillation column is not limited to a packed column filled with regular packing, and can also be a packed column filled with irregular packing or a plate column.

[0065] The distillation column connected to the isotope scrambler is not limited to the 10th distillation column 10, and can also be a distillation column other than the 10th distillation column 10. Among them, at least one of the distillation columns connected to the isotope scrambler 25 is a distillation column other than the distillation column disposed at the downstream end of the distillation column group. In addition, in the stable isotope enrichment apparatus 300 of the above-described embodiment, the configuration including the isotope scrambler 25 is described as an example, but the configuration may not require the isotope scrambler 25 depending on the fluid used.

[0066] In addition, in the stable isotope enrichment apparatus 300 of the above-described embodiment, the configuration in which the raw material supply column is the first column is described as an example, but it is not limited thereto, and the configuration may be a configuration other than the first column provided according to the composition of the raw material and the required yield.

[0067] In the above-described embodiment, the stable isotope enrichment apparatus 300 applied to the stable isotope enrichment method is described as an example in which condensers 21 and reboilers 22 are provided for each distillation column, but it is not limited thereto. For example, the configuration may be such that condensers 21 and reboilers 22 are provided for every several columns.

[0068] In addition, in the above-described embodiment, the stable isotope enrichment apparatus 300 applied to the stable isotope enrichment method is described as an example in which gas is supplied from a position near the bottom of the (n - 1)th column to a position near the top of the nth column (1 < n ≤ m), and liquid is returned from the position near the top of the nth column to the position near the bottom of the (n - 1)th column, but it is not limited thereto. The stable isotope enrichment apparatus may also be configured to supply liquid from a position near the bottom of the (n - 1)th column to a position near the top of the nth column (1 < n ≤ m), and return gas from the position near the top of the nth column to the position near the bottom of the (n - 1)th column. By adopting such a configuration, the capacities of the condensers 21 and reboilers 22 provided in each distillation column can be made small, but a liquid pump is required to supply liquid to the next column, so the consumed energy needs to be adjusted.

[0069] Examples

[0070] Hereinafter, the present invention will be described in detail through verification tests, but the present invention is not limited thereto.

[0071] <Verification Test 1>

[0072] (Test Example 1)

[0073] Use Figure 1 the stable isotope enrichment device 300 shown for 18 the enrichment of

[0074] O. The distillation column group consists of 13 distillation columns, and the distillation columns are packed columns. Liquid nitrogen is used as the cold source of the condenser 21, and liquid nitrogen is supplied to each condenser 21 from the heat medium fluid circulation line 38. Gaseous nitrogen is used as the heat source of the reboiler 22, and gaseous nitrogen is supplied to each reboiler 22 from the heat medium fluid circulation line 39.

[0075] In addition, an isotope scrambler 25 is provided in the stable isotope enrichment device 300. One end of the isotope enrichment gas extraction line 36 is connected to the 10th distillation column 10, and the other end is connected to the isotope scrambler 25. Part or all of the oxygen is extracted and supplied to the isotope scrambler 25. The oxygen that has undergone an isotope exchange reaction in the isotope scrambler 25 is returned from the isotope enrichment gas return line 37 to the 10th distillation column 10. 18 The composition of the raw material high-purity oxygen is the natural abundance ratio. The top pressure of each distillation column is 20 kPaG. The abundance ratio of the stable isotope molecules of the oxygen sent out from the bottom of the 13th distillation column 13 when the device is stable is set to

[0076] Figure 2 more than 97 atomic% for

[0077] As Figure 2 shown, according to Test Example 1, in the final column (the 13th distillation column 13), the target 18 O concentration is 97.5 atomic%.

[0078] (Test Example 2)

[0079] In Test Example 2, except that the flow rate of the gas and liquid connecting each column is set to 4% of the flow rate of the rising gas in each column, the other device configurations and operating conditions are the same as those in Test Example 1.

[0080] Figure 3 shows the concentration distribution of each distillation column in Test Example 2.

[0081] As Figure 3 shown, according to Test Example 2, in the final column (the 13th distillation column 13), the target 18The O concentration is 97.1 atomic %.

[0082] (Test Example 3)

[0083] In Test Example 3, except that the flow rates of the gas and liquid connecting each column were set to 3% of the flow rate of the rising gas in each column, the other conditions were the same as those in Test Example 1 in terms of the apparatus configuration and operating conditions.

[0084] Figure 4 It shows the concentration distribution of each distillation column in Test Example 3.

[0085] As Figure 4 shown, according to Test Example 3, in the final column (the 13th distillation column 13), the target 18 O concentration is 96.3 atomic %, slightly lower than the set value.

[0086] In Test Examples 1 - 2, the flow rates of the gas and liquid connecting each column were 4% or more of the flow rate of the rising gas in each column, the equipment was of an appropriate size, and the energy consumption was also optimal.

[0087] On the other hand, in Test Example 3, the flow rates of the gas and liquid connecting each column were less than 4% of the flow rate of the rising gas in each column, resulting in a gap in the concentration distribution of each column and making it impossible to collect a high - concentration product.

[0088] <Verification Test 2>

[0089] (Test Example 4)

[0090] Using Figure 1 the stable isotope enrichment device 300 shown for 18 O enrichment. Except that 18 O was set to 98 atomic % or more, the other conditions were the same as those in Test Example 1. That is, the flow rates of the gas and liquid connecting each column were 5% of the flow rate of the rising gas in each column.

[0091] Figure 5 It shows the concentration distribution of each distillation column in Test Example 4.

[0092] As Figure 5 shown, according to Test Example 4, in the final column (the 13th distillation column 13), the target 18 O concentration is 98.2 atomic %.

[0093] (Test Example 5)

[0094] In Test Example 5, except that the flow rates of the gas and liquid connecting each column were set to 4% of the flow rate of the rising gas in each column, the other conditions were the same as those in Test Example 4 in terms of the apparatus configuration and operating conditions.

[0095] Figure 6Shows the concentration distribution of each distillation column in Test Example 5.

[0096] As Figure 6 shown, according to Test Example 5, in the final column (the 13th distillation column 13), the target 18 O concentration is 98.0 atomic %.

[0097] (Test Example 6)

[0098] In Test Example 6, except that the flow rates of the gas and liquid connecting each column were set to 3% of the flow rate of the rising gas of each column, the other conditions were the same as those in Test Example 4 in terms of the device configuration and operating conditions.

[0099] Figure 7 Shows the concentration distribution of each distillation column in Test Example 6.

[0100] As Figure 7 shown, according to Test Example 6, in the final column (the 13th distillation column 13), the target 18 O concentration is 97.6 atomic %, which is lower than the set value.

[0101] In Test Examples 4 to 5, the flow rates of the gas and liquid connecting each column were 4% or more of the flow rate of the rising gas of each column, the equipment was of an appropriate size, and the energy consumption was also optimal.

[0102] On the other hand, in Test Example 6, the flow rates of the gas and liquid connecting each column were less than 4% of the flow rate of the rising gas of each column, resulting in a gap in the concentration distribution of each column and making it impossible to collect a high-concentration product.

[0103] According to the results of Verification Tests 1 and 2, when the specifications of the 18 O that becomes the product satisfy multiple conditions (98 atomic % or more, 97 atomic % or more), by setting the flow rates of the gas and liquid connecting each column to 4% or more of the flow rate of the rising gas of each column, it is possible to collect a high-concentration product.

[0104] Industrial Applicability

[0105] The stable isotope enrichment method using a distillation apparatus having a distillation column group formed by connecting (cascading) a plurality of distillation columns in series to concentrate a stable isotope containing a stable isotope atom has applicability.

[0106] Explanation of Reference Numerals

[0107] 1, 9, 10, 11, 12, 13... Distillation columns

[0108] 21... Condenser

[0109] 22... Reboiler

[0110] 23, 24... On-off valve

[0111] 25... Isotope scrambler

[0112] 30... Feedstock supply line

[0113] 31... Product export line (export line)

[0114] 34... Supply line

[0115] 35... Return line

[0116] 300... Stable isotope enrichment device

Claims

1. A method for concentrating stable isotopes, which is a method for separating stable isotopes using a plurality of distillation columns connected in cascade, wherein, The plurality of distillation columns include a first column to an m-th column, where m is an integer of 2 or more. One of a gas and a liquid is supplied from a position near the bottom of the (n - 1)-th column to a position near the top of the n-th column, and the other of the gas and the liquid is returned from the position near the top of the n-th column to the position near the bottom of the (n - 1)-th column, where n satisfies 1 < n ≤ m. In each distillation column, when the flow rate of the gas rising in the column is defined as a first flow rate and the flow rate of the gas or liquid supplied from the previous column or the next column is defined as a second flow rate, the second flow rate is 4% by volume or more of the first flow rate.

2. The stable isotope enrichment method according to claim 1, wherein The stable isotope is 18 O.

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