Air separation device

Abstract

The purpose of the present invention is to provide an air separation device in which the diameter of an argon column is reduced and a cold box can be made compact without reducing the recovery rate of argon. The present invention provides an air separation device (100) provided with an argon column for refining argon from air, the air separation device (100) including a low pressure column (600), wherein: the low pressure column (600) is a tray column; the argon column is a structured packed column; the structured packing with which the structured packed column is packed is a structure in which corrugated sheet pieces (81) made of corrugated metal are stacked and bundled such that the surfaces thereof run in the column axis direction of the argon column, and the specific surface area thereof is at least equal to 750 m2 / m3; a wave inclination angle, which is an angle between a line connecting the crests of the waves on the surface of the corrugated sheet pieces and a line perpendicular to the column axis of the argon column, is at most equal to 40°; and in a cross-sectional view in the thickness direction of the corrugated sheet pieces, the diameter of a curvature circle of the crest of each wave is at least equal to 60% of a peak height, which is the distance between the crest of the wave and the bottom of the wave.

Description

air separation unit

[0001] The present invention relates to an air separation unit having an argon column, and more particularly to an air separation unit that directly extracts argon without adding hydrogen.

[0002] In relatively small-scale air separation plants that extract argon without adding hydrogen, plate columns are used for the high-pressure and low-pressure columns, and a combination of plate columns and packed columns is used for the argon column. The use of plate columns in the argon column is intended to increase the recovery rate of argon by taking advantage of the high pressure drop caused by the plates to reduce pressure and increase the relative volatility of argon to oxygen in the packed column installed downstream.

[0003] Patent Documents 1 and 2 disclose air separation units that use such a plate column as an argon column. Figure 6 shows an example of the air separation units disclosed in Patent Documents 1 and 2. Air separation unit 101 includes a high-pressure column 500, a low-pressure column 600, and an argon column consisting of a crude argon column 711 and a deoxidation column 721. Plate columns are used in high-pressure column 500 and low-pressure column 600. A combination of a plate column and a structured packed column (a packed column packed with structured packing) is used in crude argon column 711.

[0004] A portion of the compressed and purified feed air is supplied to heat exchanger 201 via line 21. In heat exchanger 201, the purified feed air is cooled by heat exchange between nitrogen gas supplied via line 2 from the top of low-pressure column 600, exhaust gas supplied via line 3 from heat exchanger 202, and liquid oxygen supplied via line 1 from main condenser 300. The purified feed air is then supplied to the bottom of high-pressure column 500 via line 22. Another portion of the purified feed air is pressurized, supplied to heat exchanger 201 via line 11, liquefied, and supplied to the bottom of high-pressure column 500 via line 12.

[0005] Air supplied to the bottom of high-pressure column 500 via line 22 comes into gas-liquid contact with the reflux liquid flowing down inside high-pressure column 500, concentrating nitrogen, a low-boiling component, as it rises, producing nitrogen gas at the top of the column. The reflux liquid flowing down inside high-pressure column 500, which contains liquid air supplied via line 12 to the bottom of high-pressure column 500, is enriched in oxygen, a high-boiling component, as it descends, producing oxygen-enriched liquid air at the bottom of the column. The produced liquid air is withdrawn from the lower part of high-pressure column 500 via line 51.

[0006] Nitrogen gas produced in the high-pressure column is liquefied in the main condenser 300, and a portion of the liquefied nitrogen gas is supplied to the heat exchanger 202 via the line 61, cooled, and then reduced in pressure via the line 62, and then supplied to the top of the low-pressure column 600 as reflux liquid.

[0007] The oxygen-enriched liquid air produced at the bottom of the high-pressure column 500 is supplied to heat exchanger 202 via line 41, cooled, and reduced in pressure via line 42 before being introduced into argon condenser 400, which serves as the overhead condenser for deoxidation column 721. The introduced oxygen-enriched liquid air is evaporated and supplied to the low-pressure column 600. Meanwhile, liquid air withdrawn from the bottom of the high-pressure column 500 via line 51 is supplied to heat exchanger 202, cooled, and reduced in pressure via line 52 before being supplied to the low-pressure column 600 as reflux liquid. The reflux liquid supplied to the low-pressure column 600 flows downward through gas-liquid contact with the ascending gas within the column, concentrating oxygen, a high-boiling component, and producing liquid oxygen at the bottom of the column. Meanwhile, nitrogen, a low-boiling component, is concentrated in the ascending gas as it rises, producing nitrogen gas at the top of the column.

[0008] Furthermore, argon column feed gas having an argon concentration of 5% to 15% (the remaining components are almost entirely oxygen) is withdrawn from the intermediate portion of the low-pressure column 600 via line 31 and supplied to the bottom of the crude argon column 711. The supplied argon column feed gas rises while concentrating the low-boiling point argon component. It is then introduced from the crude argon column 711 into the bottom of the deoxidation column 721 and rises through the deoxidation column 721. Oxygen is removed during the rise, and the oxygen concentration in the ascending gas at the top of the deoxidation column 721 is 0.1 ppm to 10 ppm. The gas withdrawn from the top of the deoxidation column 721 is liquefied in the argon condenser 400, a portion of which is collected as product argon, and the remainder is returned to the deoxidation column 721 as reflux.

[0009] JP 04-222380 JP 04-214174

[0010] A structured packed column with low pressure loss is used as the deoxidation column 721. A structured packed column is used in the upper part of the crude argon column 711, while a plate column with high pressure loss is used in the lower part. Because a plate column is used in the lower part of the crude argon column 711, the pressure loss of the argon column feed gas supplied to the column bottom is large, and even a low-plate column reduces the pressure. The feed gas supplied to the argon column rises while its pressure is reduced in the plate column, and then the relative volatility of argon is increased in the upper part of the crude argon column 711 and the deoxidation column 721, which are structured packed columns, thereby concentrating the argon with high separation efficiency. A plate column has a larger column diameter for processing the same gas-liquid load than a structured packed column. As shown in FIG. 6, only the lower part of the crude argon column 711 is thicker, which causes the problem of an inefficiently large cold box for housing these columns and preventing heat input from the outside.

[0011] The present invention provides an air separation unit that allows the diameter of an argon column to be reduced and the cold box to be made compact without reducing the argon recovery rate.

[0012] In order to solve the above problems, the present invention provides the following air separation apparatus: [1] An air separation apparatus including an argon column for purifying argon from air, the air separation apparatus comprising a low-pressure column, the low-pressure column being a plate column, the argon column being a structured packed column, the structured packing packed in the structured packed column being a structure in which corrugated metal plate pieces are stacked with their surfaces aligned in the axial direction of the argon column, and the specific surface area of ​​the structured packing is 750 m ２ / m ３ an air separation apparatus according to [1], wherein the argon tower is divided into a first tower and a second tower, the first tower is a crude argon tower that concentrates argon in the argon tower feed gas from the low-pressure tower, and the second tower is a deoxidation tower that removes oxygen from the argon-enriched gas obtained in the crude argon tower, and further comprises a pipeline for supplying gas from the crude argon tower to the deoxidation tower, and the first and second towers are each the structured packed tower. [3] The air separation unit according to [2], wherein a pressure reducing valve is provided in the line for supplying argon-enriched gas from the crude argon column to the deoxidation column.

[0013] According to the air separation unit of the present invention, the diameter of the argon column can be reduced and the cold box can be made compact without reducing the argon recovery rate. Furthermore, because the air separation unit of the present invention uses a plate column as the low-pressure column, the pressure of the argon column feed gas supplied to the argon column is not significantly reduced. Therefore, a sufficient temperature difference can be ensured in the argon condenser to generate reflux liquid for the argon column.

[0014] 1 is a system diagram showing an example of an air separation unit of the present invention using a crude argon tower and a deoxidation tower which are structured packed towers. FIG. 2 is a diagram showing an example of structured packing used in the argon tower of the air separation unit of the present invention. FIG. 3 is a diagram showing corrugated sheet metal pieces constituting the structured packing provided in the argon tower of the air separation unit of the present invention, illustrating the wave inclination angle. FIG. 4 is a cross-sectional view of a corrugated sheet metal piece taken along line A-A' shown in FIG. 3, illustrating the apex curvature circle diameter ratio. FIG. 5 is a diagram showing the oxygen concentration distribution in the argon towers of Example 1 and Comparative Example 1. FIG. 6 is a system diagram showing a conventional air separation unit having a high-pressure tower, a low-pressure tower, and an argon tower.

[0015] An air separation unit according to one embodiment of the present invention will now be described in detail with reference to the drawings. The drawings used in the following description may show characteristic portions enlarged for ease of understanding, and the dimensional proportions of the components may not necessarily be the same as those in reality.

[0016] FIG. 1 shows an air separation unit using an argon column equipped with structured packing. The air separation unit 100 shown in FIG. 1 includes a high-pressure column 500, a low-pressure column 600, and an argon column having a crude argon column (first column) 710 and a deoxidation column (second column) 720. In the air separation unit 100 of this embodiment, a plate column is used as the low-pressure column 600. In the air separation unit 100 of this embodiment, the argon column is divided into a crude argon column 710 and a deoxidation column 720, and thus has two columns. However, the argon column may not be separated into two columns and may instead be composed of a single column. When composed of a single column, the crude argon column 710 and the deoxidation column 720 are integrated into a single tube without the use of pipes 73 and 74. However, in order to reduce the height of the cold box for holding these equipments operated at cryogenic temperatures, it is preferable to divide the argon column into two columns.

[0017] In this embodiment, it is preferable that the argon column does not include a plate column, which would increase the column diameter. If the argon column does not include a plate column, the column diameter of the argon column can be reduced. Generally, a plate column uses sieve trays, and gas comes into cross contact with liquid flowing perpendicularly to the column axis on the trays, thereby separating argon, a low-boiling-point component.

[0018] In the air separation unit 100 of this embodiment, the crude argon column 710 and the deoxidation column 720 that constitute the argon column are packed with the same structured packing, but they can also be packed with different structured packing. In this case, the structured packing should be selected in consideration of separation performance and pressure loss so that the argon column and cold box are compact.

[0019] The configuration of air separation unit 100 using the argon column will be described in detail below. A portion of the compressed and purified feed air is supplied to heat exchanger 201 via line 21. In heat exchanger 201, the purified feed air is cooled by heat exchange between nitrogen gas supplied from the top of low-pressure column 600 via line 2, exhaust gas supplied via line 3, and liquid oxygen supplied from main condenser 300 via line 1. The purified feed air is then supplied to the bottom of high-pressure column 500 via line 22. Another portion of the purified feed air is pressurized, supplied to heat exchanger 201 via line 11, liquefied, and supplied to the bottom of high-pressure column 500 via line 12.

[0020] Air supplied to the bottom of high-pressure column 500 via line 22 comes into gas-liquid contact with the reflux liquid flowing down inside high-pressure column 500, concentrating nitrogen, a low-boiling component, as it rises, producing nitrogen gas at the top of the column. The reflux liquid flowing down inside high-pressure column 500, which contains liquid air supplied to the bottom of high-pressure column 500 via line 12, is enriched in oxygen, a high-boiling component, as it descends, producing oxygen-enriched liquid air at the bottom of the column. The produced liquid air is withdrawn from the bottom of high-pressure column 500 via line 51.

[0021] Nitrogen gas produced in the high-pressure column 500 is liquefied in the main condenser 300, and a portion of the liquefied nitrogen gas is supplied to the heat exchanger 202 via the line 61, cooled, and then reduced in pressure via the line 62, and then supplied to the top of the low-pressure column 600 as reflux liquid.

[0022] Oxygen-enriched liquid air produced at the bottom of the high-pressure column 500 is supplied to heat exchanger 202 via line 41, cooled, and reduced in pressure via line 42 before being introduced into argon condenser 400, the overhead condenser of the argon column. The introduced oxygen-enriched liquid air is evaporated and supplied to the low-pressure column 600. Meanwhile, liquid air withdrawn from the bottom of the high-pressure column 500 via line 51 is supplied to heat exchanger 202, cooled, and reduced in pressure via line 52 before being supplied to the low-pressure column 600 as reflux liquid. As the reflux liquid supplied to the low-pressure column 600 flows downward through gas-liquid contact with the ascending gas within the column, oxygen, a high-boiling component, is concentrated, producing liquid oxygen at the bottom of the column. As the ascending gas rises, nitrogen, a low-boiling component, is concentrated, producing nitrogen gas at the top of the column.

[0023] In addition, argon column feed gas having an argon concentration of 5% to 15% (the remaining components are mostly oxygen) is withdrawn from the intermediate portion of the low-pressure column 600 via line 31 and supplied to the bottom of the crude argon column 710. The supplied argon column feed gas rises while concentrating the low-boiling point argon component. It is then introduced from the top of the crude argon column 710 into the bottom of the deoxidation column 720 and rises through the deoxidation column 720. Oxygen is removed during the rise, and the oxygen concentration in the ascending gas at the top of the deoxidation column 720 is 0.1 ppm to 10 ppm. The gas withdrawn from the top of the deoxidation column 720 is liquefied in the argon condenser 400, a portion of which is collected as product argon, and the remainder is returned to the deoxidation column 720 as reflux.

[0024] When the argon column is divided into a crude argon column 710 and a deoxidation column 720, a pressure reducing valve 70 is preferably provided in a line 73 through which the gas obtained by concentrating argon in the crude argon column 710 is introduced from the top of the crude argon column 710 to the bottom of the deoxidation column 720. By providing the pressure reducing valve 70 in the line 73, even if the pressure loss in the crude argon column 710 decreases due to a turndown operation or the like, the pressure in the deoxidation column 720 can be adjusted and the argon recovery rate can be increased.

[0025] The structured packing packed in the crude argon column 710 and the deoxidation column 720 will be described below. FIG. 2 shows an example of structured packing used in the argon column of the air separation unit of the present invention. FIGS. 3A and 3B show corrugated sheet metal pieces constituting the structured packing provided in the argon column of the air separation unit of the present invention, and are diagrams illustrating the wave inclination angle. FIG. 4 is a cross-sectional view of the corrugated sheet metal piece taken along line A-A' shown in FIG. 3, and is a diagram for illustrating the apex curvature circle diameter ratio.

[0026] The structured packing is a structure obtained by stacking multiple corrugated sheet metal pieces 81 as shown in FIGS. 3A and 3B. The corrugated sheet metal pieces 81 may be metal sheets with corrugations. Here, "stacking" refers to a state in which the corrugated sheet metal pieces 81 are bundled together with their front and back sides alternately oriented with respect to the wave inclination angle α. Specifically, it refers to a state in which multiple corrugated sheet metal pieces 81 having the same wave inclination angle α are bundled together with their backs alternately stacked so as not to overlap each other. The bundled corrugated sheet metal pieces 81 do not all need to be the same size; different sizes of corrugated sheet metal pieces 81 may be bundled together. If the argon tower is cylindrical, as shown in FIG. 2, multiple different sizes of corrugated sheet metal pieces 81 may be stacked together and bound together with a frame around the stacked corrugated sheet metal pieces 81 to form a cylindrical shape. The shape is not limited to a cylindrical shape. It is preferable that multiple corrugated sheet metal pieces 81 can be stacked and handled as a block. Note that the method for bundling the corrugated sheet metal pieces 81 is not particularly limited. In this embodiment, metal bands are used as a frame. The corrugated sheet pieces 81 are preferably made of metal, and among metals, aluminum is particularly preferred.

[0027] The corrugated sheet 81 will be described in detail below. As shown in Figures 3A and 3B, the surface of the corrugated sheet 81 is corrugated and further provided with through-holes 82. The corrugations are formed so that the wave inclination angle α, which is the angle between the line connecting the crests of the corrugations and a line perpendicular to the axis of the argon column, is 40° or less. In other words, the line connecting the crests of the waves on the corrugated sheet 81 is perpendicular or inclined at an angle of 50° or more to the axis of the argon column. Figure 3A shows a corrugated sheet 81 having a wave inclination angle α of 40° or less in a counterclockwise direction relative to a line perpendicular to the axis of the argon column, while Figure 3B shows a corrugated sheet 81 having a wave inclination angle α of 40° or less in a clockwise direction relative to a line perpendicular to the axis of the argon column. The reflux liquid descending in the argon column flows along the corrugated sheet 81, and the ascending gas flows between the corrugated sheet 81 along which the reflux liquid flows, resulting in gas-liquid contact. The through holes 82 allow gas and liquid to move in the radial direction of the column and suppress drift. Here, if the inclination angle α of the waves provided on the corrugated sheet pieces 81 is 40° or less, the resistance to the gas flowing upward between the corrugated sheet pieces 81 in the argon column is increased, resulting in a pressure drop that is sufficiently high to increase the relative volatility of argon, and allowing the diameter of the argon column to be reduced without reducing the argon recovery rate.

[0028] Furthermore, when the corrugated sheet 81 is viewed in cross section in the thickness direction, the distance between the crest and the bottom of the wave is defined as the crest height. The ratio of the diameter of the circle of curvature of each crest of the wave in the cross section in the thickness direction of the corrugated sheet 81 to the crest height (hereinafter, sometimes referred to as the "crown diameter of curvature ratio") is 60% or more. A crest diameter of curvature ratio of 100% means that the wave slope of the corrugated sheet 81 is zero. Therefore, to achieve a corrugated shape, the crest diameter of curvature must be less than 100%. If the crest diameter of curvature ratio is 60% or more, high separation performance can be obtained even when high pressure loss occurs, and the diameter of the argon column can be reduced without increasing the height of the argon column.

[0029] The specific surface area of ​​the corrugated sheet 81 is 750 m ２ / m ３ The specific surface area is 750 m ２ / m ３ If the separation efficiency in the argon column is 920 m or more, it is possible to improve the separation efficiency in the argon column.２ / m ３ The specific surface area of ​​the corrugated sheet 81 is 750 m ２ / m ３ If the ratio is above this, the gas ascending in the argon column and the fluid descending in the argon column will be in sufficient contact with each other, and the diameter of the argon column can be reduced without reducing the argon recovery rate. The specific surface area of ​​the corrugated sheet metal pieces 81 can be adjusted by adjusting the apex curvature diameter ratio. By setting the apex curvature diameter ratio to 60% or more, the specific surface area of ​​the corrugated sheet metal pieces 81 can be easily increased to 750 m ２ / m ３ It can be more than that.

[0030] In this embodiment, any corrugated sheet piece 81 can be used as long as the wave inclination angle α and the apex curvature circle diameter ratio are within the above ranges.

[0031] The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

[0032] Reference Example 1 Table 1 shows a column diameter of 300 mm, a packing height of 1500 mm, and a specific surface area of ​​750 m ２ / m ３ An argon-oxygen total reflux distillation test was carried out using a structured packed column equipped with structured packing a750_α40D80, which had a wave inclination angle α of 40° and a top curvature circle diameter ratio of 80%, and the HETP and pressure loss obtained at different gas loads (factor based on superficial velocity: fs) are shown in Table 1. Table 1 also shows the HETP and pressure loss obtained at different gas loads (factor based on superficial velocity: fs) for comparative packing a750_α45D50 (specific surface area: 750 m ２ / m ３ The values ​​in the table are the measured HETP values ​​for the comparative packing with fs = 1.7 m / s (kg / m) for the packing of 1.7 m / s (kg / m) and the wave inclination angle of 45° and the top curvature circle diameter ratio of 50%. HETP is the packing height per theoretical plate, and was calculated by dividing the packing height by the number of theoretical plates calculated from the measured oxygen concentrations at the top and bottom of the column. ３ ) ０．５ The pressure loss is the pressure difference per unit packed height, and was calculated by dividing the value measured by a differential pressure gauge between the top and bottom of the column by the packed height. The values ​​in the table are for pressure loss when the comparative packing has an fs of 1.7 m / s (kg / m ３) ０．５ The pressure loss is normalized by the pressure loss at

[0033]

[0034] The comparative packing a750-α45D50 is used in the conventional argon column. Compared to the comparative packing, the practical packing achieves high separation performance with high pressure drop, as shown in Table 1. It can also be seen that increasing the load on the comparative packing increases pressure drop, but the separation performance remains unchanged, failing to reach the separation performance of the practical packing.

[0035] (Example 1) Structured packing a750_α40D80 (specific surface area: 750 m ２ / m ３ A simulator used in the design of structured packed columns in air separation plants was used to calculate the separation behavior of a structured packed column using a structured packing with a wave inclination angle of 40° and a top curvature circle diameter ratio of 80%. The simulator calculates separation behavior from the heat and mass transfer rate across the gas-liquid interface. By incorporating the separation performance obtained from tests, the simulator can be applied to changes in the structured packing (specific surface area, wave inclination angle, and top curvature circle diameter ratio). A pressure drop calculation formula based on tests was also incorporated. Figure 5 shows the results of a simulation of the separation behavior of the crude argon column and deoxidation column using structured packing a750_α40D80 in the air separation unit shown in Figure 1.

[0036] (Comparative Example 1) In the air separation unit shown in FIG. 6, a plate column was installed in the lower part and the above-mentioned comparative packing a750_α45D50 (specific surface area: 750 m) was installed in the upper part. ２ / m ３ A simulation was conducted to compare the separation behavior of an argon column comprising a crude argon column using a packing of 45°, a wave inclination angle of 45°, and a top curvature circle diameter ratio of 50%), and a deoxidation column using the comparative packing a750_α45D50. The results are shown in Figure 5.

[0037] 5, the vertical axis represents the vapor phase oxygen concentration, and the horizontal axis represents the packing height (the top of the tower is set to 0) when the packing height of the argon tower in Comparative Example 1 is set to 1. The horizontal axis (packing height) for the plate tower is calculated by dividing the distance between plates by the plate efficiency and integrating this up to the theoretical number of plates.

[0038] In Fig. 5, the solid line represents the oxygen concentration distribution in the argon tower of Example 1, and the dashed line represents the oxygen concentration distribution in the argon tower of Comparative Example 1. As shown in Fig. 5, it was found that argon containing 1 ppm of oxygen can be obtained at approximately the same filling height in the argon tower of Example 1 and the argon tower of Comparative Example 1. This indicates that the argon recovery rate in Example 1 is not reduced compared to Comparative Example 1.

[0039] 5 also shows the column diameter of the crude argon column (the column diameter of the plate column is defined as 1). It was found that the column diameter of the crude argon column in Example 1 could be reduced by 25% or more compared to the column diameter of the plate column portion in Comparative Example 1. This allows the cold box to be made more compact.

[0040] (Example 2) The argon column was composed of a deoxidation column and a crude argon column, and structured packing a750_α35D80 (specific surface area: 750 m ２ / m ３ A simulation of the separation behavior of the argon column was carried out in the same manner as in Example 1, except that the air separation unit shown in Figure 1 was used, in which the column was filled with a sieve having a wave inclination angle of 35° and a top curvature circle diameter ratio of 80%, and a pressure reducing valve 70 was provided in line 73 connecting the two columns. The results are shown in Table 2 below.

[0041] (Example 3) The argon column was composed of a deoxidation column and a crude argon column, and structured packing a920_α40D80 (specific surface area: 920 m ２ / m ３ A simulation of the separation behavior of the argon column was carried out in the same manner as in Example 1, except that the air separation unit shown in Figure 1 was used, in which the column was filled with a sieve having a wave inclination angle of 40° and a top curvature circle diameter ratio of 80%, and a pressure reducing valve 70 was provided in a line 73 connecting the two columns. The results are shown in Table 2 below.

[0042] (Example 4) The argon tower was composed of a deoxidation tower and a crude argon tower, and the deoxidation tower was filled with structured packing a750-α40D60 (specific surface area: 750 m ２ / m ３ The crude argon column was packed with structured packing a750_α35D80 (specific surface area: 750 m), wave inclination angle: 40°, top curvature circle diameter ratio: 60%). ２ / m ３A simulation of the separation behavior of the argon column was carried out in the same manner as in Example 1, except that the air separation unit shown in Figure 1 was used, in which the column was filled with a sieve having a wave inclination angle of 35° and a top curvature circle diameter ratio of 80%, and a pressure reducing valve 70 was provided in line 73 connecting the two columns. The results are shown in Table 2 below.

[0043] (Example 5) The argon tower was composed of a deoxidation tower and a crude argon tower, and the deoxidation tower was filled with structured packing a750_α40D70 (specific surface area: 750 m ２ / m ３ The crude argon column was packed with structured packing a920_α40D80 (specific surface area: 920 m), wave inclination angle: 40°, top curvature circle diameter ratio: 70%). ２ / m ３ A simulation of the separation behavior of the argon column was carried out in the same manner as in Example 1, except that the air separation unit shown in FIG. 1 was used, in which the column was filled with a sieve having a wave inclination angle of 40° and a top curvature circle diameter ratio of 80%, and a pressure reducing valve 70 was provided in a line 73 connecting the two columns. The results are shown in Table 2 below. Table 2 below also shows the results of Example 1.

[0044]

[0045] As shown in Table 2 above, it was found that argon containing 1 ppm of oxygen could be obtained in all Examples at a packing height that was approximately the same as or smaller than Comparative Example 1. It was also found that Examples 2, 3, 4, and 5 could reduce the diameter of the argon column to the same extent as Example 1. It was also found that the larger the specific surface area and the smaller the wave inclination angle α, the lower the packing height could be. However, since pressure loss increases, the temperature difference in the argon condenser decreases and the surface area increases. Therefore, the structured packing is selected so that the cold box can be made compact, taking into account the arrangement of equipment within the cold box.

[0046] According to the air separation unit of the present invention, the diameter of the argon column can be reduced and the cold box can be made compact without reducing the argon recovery rate. The air separation unit of the present invention is useful as a relatively small-scale air separation unit.

[0047] 1, 2, 3, 11, 12, 21, 22, 31, 51, 61, 73 Pipe 70 Pressure reducing valve 81 Corrugated sheet metal piece 82 Through hole 100, 101 Air separation unit 201 Heat exchanger 300 Main condenser 400 (Argon column) overhead condenser 500 High pressure column 600 Low pressure column 710, 711 Crude argon column 720, 721 Deoxidation column

Claims

1. An air separation unit equipped with an argon tower for purifying argon from air, comprising a low-pressure tower, the low-pressure tower being a plate tower, the argon tower being a structured packed tower, the structured packing packed in the structured packed tower being a structure in which corrugated metal plate pieces are layered and bundled together so that their surfaces are aligned along the axial direction of the argon tower, and the specific surface area of ​​the structured packed tower is 750 m ２ / m ３ an air separation unit, wherein the wave inclination angle, which is the angle between a line connecting the crests of the waves on the surface of the corrugated sheet and a line perpendicular to the axis of the argon tower, is 40° or less, and when viewed in cross section in the thickness direction of the corrugated sheet, the diameter of the circle of curvature of each wave crest is 60% or more of the crest height, which is the distance between the crest and bottom of the wave.

2. The air separation unit according to claim 1, wherein the argon tower is divided into a first tower and a second tower, the first tower is a crude argon tower for concentrating argon in the argon tower feed gas from the low pressure tower, the second tower is a deoxidation tower for removing oxygen from the argon-concentrated gas obtained in the crude argon tower, and further comprising a gas supply line for supplying gas from the crude argon tower to the deoxidation tower, and the first and second towers are each structured packed towers.

3. The air separation unit according to claim 2, wherein a pressure reducing valve is provided in the gas supply line for supplying argon-enriched gas from the crude argon column to the deoxidation column.

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