Separation column for mixed ion exchange resins and method for separating mixed ion exchange resins using the same

Abstract

To provide a separation tower capable of separating mixed ion exchange resin used in an ion exchange device or the like with high accuracy.SOLUTION: A separation tower 1 for mixed ion exchange resin is provided with a water supply pipe 2 as a water injection part and a plurality of discharge nozzles 2A at the bottom part of the side 1A of a cylindrical separation tower body, and a drain pipe 3 as a discharge part is connected to the top part. A water collecting plate 4 is arranged on the upper side of the discharge nozzle 2A of the separation tower body 1A. An interface sensor 11 as detecting means for detecting the position of the interface between ion-exchange resin and the liquid is inserted from the top part of the separation tower body 1A, and a flow rate controller 12 as flow adjusting means is provided in the water supply pipe 2. Control means (not shown) such as a personal computer for controlling the flow rate controller 12 on the basis of the detection value of the interface sensor 11 is provided.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a separation column for separating mixed ion exchange resins used in an ion exchange device for use in a pure water production system, and a method for separating mixed ion exchange resins using the same. [Background technology]

[0002] Typically, pure water production systems remove impurities from raw water to improve its purity. To remove ionic impurities, i.e., anionic and cationic impurities, an ion exchange device packed with a mixture of anion exchange resin and cation exchange resin is commonly used. In this ion exchange device, once the ion exchange resin removes ions equivalent to its ion exchange capacity, any further ionic impurities cannot be removed and break through. Therefore, after treating a certain amount of water, the ion exchange resins are recovered from the ion exchange device and separated. They are then regenerated in a cation exchange resin regeneration tower and an anion exchange resin regeneration tower using sulfuric acid or caustic soda, respectively, and then re-filled into the ion exchange device for reuse.

[0003] The quality of treated water using mixed ion exchange resins is determined by the regeneration state of the ion exchange resins, but to maintain a high level of regeneration, it is necessary to minimize reverse regeneration. Reverse regeneration occurs when cation exchange resin contaminated with anion exchange resin is regenerated with an acid solution such as hydrochloric acid or sulfuric acid, resulting in the anion exchange resin being regenerated into Cl or SO4 form, or when anion exchange resin contaminated with cation exchange resin is regenerated with an alkaline solution such as sodium hydroxide, resulting in the cation exchange resin being regenerated into Na form.

[0004] To prevent this reverse regeneration, when regenerating a mixed ion exchange resin containing two or more types of ion exchange resins, it is necessary to separate the cation exchange resin and the anion exchange resin as completely as possible and to minimize the mixing of the anion exchange resin into the cation exchange resin and vice versa.

[0005] Therefore, a mixed ion exchange resin separation tower as shown in Figure 5 is used to separate the cation exchange resin and the anion exchange resin. In Figure 5, the mixed ion exchange resin separation tower 1 has a cylindrical separation tower body 1A. The bottom of the tower body 1A is provided with a water supply pipe 2 and multiple discharge nozzles 2A as a liquid inlet, and the top is connected to a drainage pipe 3 as a discharge. A water collecting plate 4 is disposed above the discharge nozzles 2A of the separation tower body 1A. An anion exchange resin withdrawal section (not shown) is provided near the middle of the separation tower 1 in the vertical direction, and a cation exchange resin withdrawal section (not shown) is provided below that. Separation tower 1 also has inlet and outlet ports at the bottom, and a fill port for used mixed resin and a sight glass on the upper side, but these are omitted for ease of explanation.

[0006] A method for accurately separating anion and cation exchange resins using such a mixed ion exchange resin separation tower 1 has been proposed: ion exchange resin R (a mixed resin of anion and cation exchange resins) used in a condensate demineralizer (a condensate demineralizer) is introduced into the cation exchange resin separation tower 1; water W is then injected; backwash water is passed upward from below to separate the mixed ion exchange resin into two layers, anion and cation exchange resin, due to the difference in specific gravity; the anion exchange resin in the upper layer is then selectively extracted and transferred to an anion exchange resin regeneration tower for regeneration with alkali. The cation exchange resin remaining in the cation exchange resin regeneration tower is then regenerated with acid in the cation exchange resin regeneration tower (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2019-181363 [Patent Document 2] Japanese Patent Publication No. 2020-75226 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in recent years, when a mixed ion exchange resin is used to produce high-purity pure water, there has been a demand for a more precise separation of anion exchange resin and cation exchange resin, but there are limitations to the conventional separation methods described in Patent Documents 1 and 2. In particular, when the mixed ion exchange resin contains a large amount of crushed resin, there is a problem in that the separation accuracy is low.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a separation column capable of separating with high precision mixed ion exchange resins used in ion exchange devices, etc. Another object of the present invention is to provide a separation method for mixed ion exchange resins capable of separating with high precision mixed ion exchange resins used in ion exchange devices, etc. [Means for solving the problem]

[0010] In view of the above object, the present invention first provides a mixed ion exchange resin separation column for separating a mixed ion exchange resin of two or more types of ion exchange resins, which has a liquid inlet at the bottom and a liquid outlet at the top, and which has a detection means for detecting the position of an interface between the mixed ion exchange resin and a liquid in the separation column when a liquid is passed through the separation column in an upward direction from the liquid inlet (Invention 1).

[0011] In the above invention (Invention 1), it is preferable to have a flow rate adjusting means capable of adjusting the amount of liquid passing through the liquid injection section, and a control means for controlling the flow rate adjusting means based on the interface position data between the ion exchange resin and the liquid detected by the detection means (Invention 2).

[0012] According to the inventions (Inventions 1 and 2), the inventors investigated the factors behind the limited separation accuracy of mixed ion exchange resins even when separating each ion exchange resin by specific gravity. To reuse mixed ion exchange resins, the inventors generally pass the resin through the liquid in an upward flow direction to separate the resins by utilizing the difference in sedimentation velocity due to the difference in specific gravity. However, when a large amount of crushed resin is contained, the crushed resin changes its sedimentation velocity, making it impossible to separate the resins by specific gravity. Therefore, by monitoring the interface between the ion exchange resin and the liquid in the separation tower and controlling the amount of liquid passing through the liquid injection port so that the mixed ion exchange resin reaches the top of the separation tower but does not reach the discharge port, and only the crushed resin, which tends to float, is discharged from the discharge port, the crushed ion exchange resin can be removed and the anion exchange resin and cation exchange resin can be clearly separated.

[0013] In the above invention (Invention 2), the mixed ion exchange resin of two or more types of ion exchange resins preferably contains at least one type of anion exchange resin and one or more types of cation exchange resin (Invention 3).

[0014] According to this invention (Invention 3), mixed resins of anion exchange resin and cation exchange resin are widely used, and the two are easy to separate by taking advantage of the difference in specific gravity, making them suitable for application to the separation tower of Invention 2.

[0015] In the above inventions (Inventions 1 to 3), it is preferable that the detection means for detecting the interface position between the ion exchange resin and the liquid in the separation column is an ultrasonic or optical interface sensor (Invention 4).

[0016] According to this invention (Invention 4), the position of the interface between the ion exchange resin and the liquid in the separation column can be monitored simply and accurately.

[0017] In the above inventions (Inventions 1 to 3), it is preferable that the separation tower has a window through which the inside of the separation tower can be seen from the outside, and that the detection means for detecting the position of the interface between the ion exchange resin and the liquid in the separation tower is an image analysis means capable of checking the resin interface through the window (Invention 5).

[0018] According to this invention (Invention 5), the position of the interface between the ion exchange resin and the liquid in the separation column can be monitored simply and accurately.

[0019] Secondly, the present invention provides a method for separating mixed ion exchange resins, in which a mixed ion exchange resin of two or more types is filled in a mixed ion exchange resin separation column having a liquid inlet at the bottom and a liquid outlet at the top, and the liquid is passed through the separation column in an upward direction from the liquid inlet, and the position of the interface between the mixed ion exchange resin and the liquid in the separation column is detected, and the amount of liquid passed through the liquid inlet is controlled based on the detected position of the interface (Invention 6).

[0020] According to this invention (Invention 6), the position of the interface between the ion exchange resin and the liquid in the separation tower is monitored, and the amount of liquid passing through the liquid injection section is controlled so that the mixed ion exchange resin reaches the top of the separation tower but does not reach the discharge section when the liquid is passed through in an upward flow, and only the crushed resin that is likely to float is discharged from the discharge section, thereby making it possible to remove the crushed ion exchange resin and clearly separate the anion exchange resin and the cation exchange resin.

[0021] In the above invention (Invention 6), the mixed ion exchange resin of two or more types of ion exchange resins preferably contains at least one type of anion exchange resin and one or more types of cation exchange resin (Invention 7).

[0022] According to this invention (Invention 7), mixed resins of anion exchange resin and cation exchange resin are widely used, and the two are easy to separate by taking advantage of the difference in specific gravity, making them suitable for applying the separation method of Invention 6.

[0023] In the above inventions (Inventions 6 and 7), it is preferable that the interface position between the ion exchange resin and the liquid in the separation column is detected by an ultrasonic or optical interface sensor (Invention 8).

[0024] According to this invention (Invention 8), the position of the interface between the ion exchange resin and the liquid in the separation column can be monitored simply and accurately.

[0025] In the above inventions (Inventions 6 and 7), it is preferable that the separation tower has a window through which the inside of the separation tower can be seen from the outside, and that the position of the interface between the ion exchange resin and the liquid in the separation tower is detected by an image analysis means that can be seen through the window (Invention 9).

[0026] According to the above invention (Invention 9), the position of the interface between the ion exchange resin and the liquid in the separation column can be monitored simply and accurately. [Effects of the Invention]

[0027] The mixed ion exchange resin separation column of the present invention has a detection means for detecting the position of the interface between the ion exchange resin and the liquid in the separation column when the liquid is passed through the column in an upward flow from the liquid injection section. Therefore, by monitoring the position of the interface between the ion exchange resin and the liquid in the separation column and controlling the amount of liquid passing through the liquid injection section so that the mixed ion exchange resin reaches the top of the separation column but does not reach the discharge section when the liquid is passed through in an upward flow, and only the crushed resin that is likely to float is discharged from the discharge section, the crushed ion exchange resin can be removed and the anion exchange resin and the cation exchange resin can be clearly separated. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic diagram showing a separation column for mixed ion exchange resins according to a first embodiment of the present invention. FIG. [Figure 2] FIG. 2 is a schematic diagram showing a backwashing step of the mixed ion exchange resin using a separation column according to the embodiment. [Figure 3] FIG. 3 is an enlarged view showing a backwashing step of the mixed ion exchange resin using a separation column according to the embodiment. [Figure 4] FIG. 2 is a schematic diagram showing a separation column for mixed ion exchange resins according to a second embodiment of the present invention. [Figure 5] FIG. 1 is a schematic diagram showing a conventional mixed ion exchange resin separation column. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, one embodiment of a separation column for mixed ion exchange resins according to the present invention will be described in detail with reference to the accompanying drawings.

[0030] [Mixed ion exchange resin separation column] FIG. 1 shows a mixed ion exchange resin separation column according to a first embodiment of the present invention. In FIG. 1, the mixed ion exchange resin separation column 1 includes a cylindrical separation column body 1A. The bottom of the column body 1A is provided with a water supply pipe 2 and multiple discharge nozzles 2A as a liquid inlet, and the top is connected to a drainage pipe 3 as a discharge port. A water collecting plate 4 is disposed above the discharge nozzle 2A of the separation column body 1A. In this embodiment, an interface sensor 11 is inserted from the top of the separation column body 1A as a detection means for detecting the interface position between the ion exchange resin and the liquid, and a flow controller 12 is provided in the water supply pipe 2 as a flow rate adjustment means. A control means (not shown), such as a personal computer, is also provided to control the flow controller 12 based on the detection value of the interface sensor 11. An ultrasonic or optical sensor can be used as the interface sensor 11. An anion exchange resin outlet (not shown) is provided near the vertical center of the separation column 1, and a cation exchange resin outlet (not shown) is provided below that. In addition, although inlet and outlet ports are provided at the bottom of the separation tower 1, their description will be omitted for convenience.

[0031] In this mixed ion exchange resin separation column 1, the space above the water collecting plate 4 of the separation column main body 1A is filled with used mixed ion exchange resin R to occupy approximately 40 to 70% by volume. In this embodiment, the mixed ion exchange resin R is a mixed resin containing at least one anion exchange resin and one cation exchange resin. The ratio (volume ratio) of anion exchange resin to cation exchange resin in this mixed ion exchange resin is not particularly limited, but is approximately 30:70 to 70:30. Furthermore, the average particle size of the smaller ion exchange resin is preferably 50 to 2000 μm (as swollen). Furthermore, the anion exchange resin and the cation exchange resin are preferably porous ion exchange resins. The anion exchange resin and the cation exchange resin are each set at their respective positions depending on the packed amount (volume) of the mixed ion exchange resin, the ratio of anion exchange resin to cation exchange resin, and a safety factor.

[0032] [Method for separating mixed ion exchange resins] Next, a method for separating a mixed ion exchange resin using the mixed ion exchange resin separation column 1 of this embodiment having the above-described configuration will be described.

[0033] First, the used mixed ion exchange resin R packed in the ion exchange device is removed and packed into the mixed ion exchange resin separation tower 1 through the packing port. Then, water (pure water) W is poured into the separation tower 1 through the inlet / outlet at the bottom of the separation tower 1 to fill the separation tower 1 with water.

[0034] Next, in the backwashing process, liquid water (pure water) W is discharged from the multiple discharge nozzles 2A and passed through in an upward flow to backwash the used ion exchange resin R. As a result, as shown in Figure 2, the mixed ion exchange resin R occupies approximately 40 to 70% by volume of the space above the water collecting plate 4, and so is dispersed throughout the entire space above the water collecting plate 4. At this time, the interface position between the ion exchange resin R and the pure water W in the separation tower 1 is monitored by an interface sensor 11, and the amount of pure water W discharged from the discharge nozzles 2A is controlled by a flow rate controller 12 to prevent the mixed ion exchange resin R from flowing out of the drainage pipe 3 due to the upward flow.

[0035] As time passes, the crushed ion exchange resin rises to the top, so the interface position between the ion exchange resin R and the pure water W in the separation tower 1 is continuously monitored by the interface sensor 11, and the amount of pure water W discharged from the discharge nozzle 2A is controlled by the flow rate controller 12 so that the mixed ion exchange resin R does not flow out of the drainage pipe 3 due to the upward flow of water, but only the crushed resin is discharged from the drainage pipe 3 together with the wastewater W1. As a result, as shown in Figure 3, normal anion exchange resin A and cation exchange resin C do not flow out, and only the crushed ion exchange resin can be removed from the drainage pipe 3 together with the wastewater W1.

[0036] The longer the time for this upward backwashing process, the more crushed ion exchange resin can be removed, which is preferable, but if it is too long, the work efficiency will decrease, so it is preferably about 30 to 120 minutes. In particular, in the backwashing process for the time described above, by performing the upward backwashing at a water flow rate in the range of, for example, about LV3 m / h to 15 m / h while controlling the discharge rate of pure water W with flow rate controller 12 so that the crushed ion exchange resin rises to the top due to the stirring effect, the crushed fine resin can be reliably and efficiently discharged from drainage pipe 3 of separation tower 1.

[0037] After backwashing, the crushed ion exchange resins are discharged and allowed to stand, allowing the remaining intact ion exchange resins R to settle. Because anion exchange resins A and cation exchange resins C have different specific gravities, they can be separated by specific gravity. Generally, cation exchange resins have a higher specific gravity than anion exchange resins, so the cation exchange resins settle at the bottom and the anion exchange resins settle at the top. After backwashing, pure water may be discharged and injected through the bottom inlet and outlet, allowing a separate ion exchange resin separation process to be performed using a known method. The separated anion exchange resins and cation exchange resins are then extracted from the anion exchange resin extraction section and the cation exchange resin extraction section, respectively, and regenerated in their respective regeneration towers. To improve the separation accuracy of the anion and cation exchange resins, it is preferable to leave a certain range of resins from the separation boundary between the anion and cation exchange resins without separating them, taking into account a safety factor. This remaining ion exchange resin can be removed and used for the next separation of a mixed anion and cation exchange resin.

[0038] The present invention has been described above based on the above-described embodiments with reference to the accompanying drawings. However, the present invention is not limited to these embodiments and various modifications are possible. For example, while the above-described embodiment uses an interface sensor 11 as a detection means, as shown in FIG. 4, a window (sight glass) 13 through which the interior of the separation column 1 can be viewed may be provided at the top of the separation column 1. A camera 14 for image analysis may be installed as a detection means through which the interior of the separation column 1 can be viewed from the outside through the sight glass 13, thereby detecting the interface between the pure water W and the resin R and controlling the flow rate of the pure water flowing upward. Furthermore, while the above-described embodiment describes the use of two types of resins, an anion exchange resin and a cation exchange resin, the present invention is also applicable to the use of multiple types of anion exchange resins and cation exchange resins of different grades or properties. Furthermore, in the present invention, the ion exchange resin is not limited to anion exchange resins and cation exchange resins, but also includes catalyst resins in which catalytic metals are supported on these ion exchange resins, boron-selective adsorption resins, and the like. Furthermore, the present invention is characterized in that when separating a mixture of multiple types of ion exchange resins, the ion exchange resins that have been crushed in advance are excluded. There are no particular restrictions on the subsequent separation steps, and it goes without saying that various known separation methods can be applied. [Example]

[0039] The present invention will be further illustrated by the following specific examples. [Example 1] In the ion exchange resin separation column 1 shown in FIG. 1, 2 m of a mixed resin of anion exchange resin and cation exchange resin (anion exchange resin:cation exchange resin = 50:50 (volume ratio)) was placed. 3The separation tower was filled with pure water W, and a mechanism for controlling the discharge rate of pure water W from the discharge nozzle 2A based on the interface position detected by the interface sensor 11 was used. The flow rate of pure water W was controlled to maintain a constant resin interface at the top of the tower at a standard flow rate of LV10 m / h in an upward flow direction for one hour. After water flow was stopped, the settled anion exchange resin and cation exchange resin were separated, and the separated anion exchange resin and cation exchange resin were each extracted and the contamination rate of other ion exchange resins was measured. The contamination rates of cation exchange resin in the anion exchange resin and anion exchange resin in the cation exchange resin were each 0.01%. Furthermore, the amount of intact resin flowing from the separation tower into the wastewater tank after one hour of water flow was confirmed, and the loss of intact resin from separation tower 1 was 0%. These results, along with the backwash conditions, are shown in Table 1.

[0040] [Example 2] In the ion exchange resin separation column 1 shown in FIG. 4, 2 m of a mixed resin of anion exchange resin and cation exchange resin (anion exchange resin:cation exchange resin=50:50 (volume ratio)) was placed. 3 The separation tower 1 was filled with pure water W, and a mechanism was used to control the discharge rate of pure water W from the discharge nozzle 2A based on the interface position detected by the image analysis camera 14 through the window (sight glass) 13 of the separation tower 1. The flow rate of pure water W was controlled to maintain a constant resin interface at the top of the tower at a standard flow rate of LV10 m / h in an upward flow direction for one hour. After water flow was stopped, the settled anion exchange resin and cation exchange resin were separated, and the separated anion exchange resin and cation exchange resin were each extracted and the contamination ratio of other ion exchange resins was measured. The contamination ratios of cation exchange resin in the anion exchange resin and anion exchange resin in the cation exchange resin were found to be 0.01%, respectively. Furthermore, the amount of intact resin flowing from the separation tower to the wastewater tank after one hour of water flow was confirmed, and the loss of intact resin from separation tower 1 was found to be 0%. These results, along with the backwash conditions, are shown in Table 1.

[0041] [Comparative Example 1] In the mixed ion exchange resin separation column 1 shown in FIG. 5, 2 m of a mixed resin of anion exchange resin and cation exchange resin (anion exchange resin: cation exchange resin = 50:50 (volume ratio)) was placed. 3 The column was filled with water and passed through it in an upward direction at a rate of 5 m / h for one hour. After the water flow stopped, the settled anion and cation exchange resins were separated, and the separated anion and cation exchange resins were each removed to measure the contamination rate of other ion exchange resins. The contamination rates of cation exchange resin in the anion exchange resin and anion exchange resin in the cation exchange resin were both 0.1%. Furthermore, the amount of intact resin flowing into the wastewater tank from separation tower 1 after one hour of water flow was checked, and the loss of intact resin from the separation tower was 0%. These results, along with the backwash conditions, are shown in Table 1.

[0042] Comparative Example 2 In the mixed ion exchange resin separation column 1 shown in FIG. 5, 2 m of a mixed resin of anion exchange resin and cation exchange resin (anion exchange resin: cation exchange resin = 50:50 (volume ratio)) was placed. 3 The column was filled with water and passed through it in an upward direction at LV20m / h for one hour. After the water flow stopped, the settled anion exchange resin and cation exchange resin were separated, and the separated anion exchange resin and cation exchange resin were each removed to measure the contamination rate of other ion exchange resins. The contamination rates of cation exchange resin in the anion exchange resin and anion exchange resin in the cation exchange resin were each 0.05%. Furthermore, the amount of intact resin flowing into the wastewater tank from separation tower 1 after one hour of water flow was checked, and the loss rate of intact resin from the separation tower was found to be 30%. These results, along with the backwash conditions, are shown in Table 1.

[0043] [Table 1] [Explanation of symbols]

[0044] 1. Mixed ion exchange resin separation column 1A Separation tower body 2 Water supply pipe 2A discharge nozzle 3 Drainage piping 4 Water collection board 11 Interface sensor (detection means) 12 Flow controller (flow rate adjusting means) 13 Window (sight glass) 14 Image analysis camera (detection means) R Mixed Ion Exchange Resin A Anion Exchange Resin C cation exchange resin W Pure water (liquid) W1 Effluent water

Claims

1. A mixed ion exchange resin separation column for separating a mixed ion exchange resin of two or more kinds of ion exchange resins, the column having a liquid inlet at a bottom and a discharge port at a top, the mixed ion exchange resin comprises crushed resin; a detection means for detecting an interface position between the mixed ion exchange resin and a liquid in the separation column when the liquid is passed through the liquid injection port into the separation column in an upward flow manner; a flow rate adjusting means capable of adjusting the amount of liquid passing through the liquid injecting portion; a control means for controlling the flow rate adjusting means based on data on the interface position between the mixed ion exchange resin and the liquid detected by the detection means; The control means controls the flow rate adjusting means so that the crushed resin is discharged from the discharge section by an upward flow from the injection section during backwashing of the mixed ion exchange resin.

2. 2. The mixed ion exchange resin separation column according to claim 1, wherein the mixed ion exchange resin of two or more types of ion exchange resins contains at least one type of anion exchange resin and one or more types of cation exchange resin.

3. 3. The mixed ion exchange resin separation column according to claim 1, wherein the detection means for detecting the interface position between the mixed ion exchange resin and the liquid in the separation column is an ultrasonic or optical interface sensor.

4. 3. A mixed ion exchange resin separation tower according to claim 1, wherein the separation tower has a window through which the inside of the separation tower can be seen from the outside, and the detection means for detecting the position of the interface between the mixed ion exchange resin and the liquid in the separation tower is an image analysis means capable of checking the resin interface through the window.

5. A method for separating a mixed ion exchange resin of two or more types of ion exchange resins, comprising: the mixed ion exchange resin comprises crushed resin; Filling a mixed ion exchange resin separation column having a liquid inlet at the bottom and a discharge port at the top with the mixed ion exchange resin; detecting an interface position between the mixed ion exchange resin and the liquid in the separation tower after the liquid is passed through the liquid injection port in an upward direction into the separation tower; and controlling the amount of liquid passing through the liquid injection unit based on the detected interface position, The controlling step includes controlling the amount of liquid passing through the liquid injection section so that the crushed resin is discharged from the discharge section by an upward flow from the liquid injection section during backwashing of the mixed ion exchange resin.

6. 6. The method for separating a mixed ion exchange resin according to claim 5, wherein the mixed ion exchange resin of two or more types of ion exchange resins contains at least one type of anion exchange resin and one or more types of cation exchange resin.

7. 7. The method for separating a mixed ion exchange resin according to claim 5, wherein the position of the interface between the mixed ion exchange resin and the liquid in the separation column is detected by an ultrasonic or optical interface sensor.

8. 7. The method for separating a mixed ion exchange resin according to claim 5 or 6, wherein the separation tower has a window through which the inside of the separation tower can be viewed from the outside, and the position of the interface between the mixed ion exchange resin and the liquid in the separation tower is detected by an image analysis means that can be viewed through the window.

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