Method for operating upward-flow-type ion exchange tower

Abstract

Provided is a method for operating an upward-flow-type ion exchange tower for passing raw water in an upward flow, using a water-feeding pump, through an ion exchange tower having an ion-exchange-resin packed bed between a lower water-permeable partition plate and an upper water-permeable partition plate to produce deionized water, wherein the method for operating an upward-flow-type ion exchange tower includes: a fixed bed formation step for passing the raw water at a high LV into the ion exchange tower at the start of passing the raw water, pushing up the ion-exchange-resin packed bed within the ion exchange tower, and pressing the packed bed against the upper water-permeable partition plate to form an ion-exchange-resin fixed bed; and a steady operation step for subsequently passing the raw water through at a LV higher than a minimum LV at which the fixed bed is maintained and controlling the water flow rate of the raw water in accordance with a demand amount for the deionized water.

Description

Upflow ion exchange column operation method

[0001] The present invention relates to a method for operating an upflow ion exchange column, and more particularly to a method for operating an upflow ion exchange column in which the upflow water velocity (LV) is changed according to the demand for deionized water.

[0002] BACKGROUND ART As a method of operating an ion exchange column in which raw water is passed through a container containing ion exchange resin to obtain deionized water, there is an upward flow water method in which raw water is passed through the column in an upward direction.

[0003] When raw water is passed through an ion exchange column in an upward flow manner, the ion exchange resin may not be able to adsorb all the ions and may leak out. For this reason, an upward flow ion exchange column is often formed with a fixed bed (Patent Document 1).

[0004] In a typical upflow ion exchange column, a cylindrical container is installed with the axis of the cylinder oriented vertically. Permeable partition plates are provided at the top and bottom of the container, and ion exchange resin is housed between the partition plates. The ion exchange resin swells and shrinks as water is introduced and regenerated, increasing or decreasing its volume. Therefore, to ensure that the regenerating chemicals are uniformly passed through the resin layer, the container is housed with a certain height of freeboard space remaining.

[0005] When raw water is passed through such an ion exchange resin tower in an upward direction, the ion exchange resin is pushed up by the upward flow and becomes a fixed bed pressed against the upper permeable partition plate, and water is collected in this state. The treated water flows out from the outlet at the top of the container.

[0006] When the flow of raw water through the ion exchange tower is stopped, the force pushing up the ion exchange resin disappears, and the ion exchange resin that formed the fixed bed settles and falls to the lower permeable partition plate inside the container, returning to the state it was in before the water was passed through.

[0007] When the ion exchange resin settles and falls within the container, a collapsed portion of the ion exchange resin forms. This collapsed portion gradually moves upward, eventually reaching the top ion exchange resin, where the ion exchange resin stops falling. In this collapsed portion of the ion exchange resin, the ion exchange resin particles fall while mixing together. Therefore, if water sampling is stopped midway through operation (when raw water flow is stopped) when the ion exchange resin located at the lower end of the ion exchange resin packed bed has broken through but the ion exchange resin located at the upper end has not yet broken through, the broken-through resin at the lower end and the unbroken-through resin at the upper end may mix, resulting in a deterioration in treated water quality the next time water sampling is resumed.

[0008] Therefore, in an ion exchange column operated by the upward flow water system, once water sampling is started by the upward flow water, water is generally continuously passed through until the water sampling is completed (the next regeneration).

[0009] JP 2017-170419 A JP 2014-213263 A

[0010] As described above, in conventional upflow ion exchange columns, water is passed through at a rate above a certain level (high LV) at the start of water collection to form a fixed bed of ion exchange resin. After the fixed bed is formed, raw water is passed through at a constant flow rate to produce deionized water such as pure water.

[0011] However, the amount of water used at the pure water demand point is constantly changing depending on the operating status of the pure water demand point. Therefore, conventional pure water production systems equipped with ion exchange towers produce the maximum amount of pure water required by the pure water demand point, resulting in the production of surplus pure water. This surplus pure water is reused as feed water for the pure water production system.

[0012] In a pure water production system with a regenerative ion exchange column, the ion exchange resin in the ion exchange column is regenerated after a predetermined amount of pure water is drawn. When excess pure water is reused as feedwater as described above, the ionic load of the feedwater decreases, increasing the volume of water that can be drawn. However, since it is impossible to predict the amount of excess pure water, and it is unknown how much of the excess pure water will be reused as feedwater, a fixed volume of water drawn is set based on the ionic load of the raw water. Therefore, even if the actual ionic load is small, regeneration is performed when the water drawn reaches the fixed volume. This results in increased regeneration frequency and the use of excess regenerative chemicals.

[0013] An object of the present invention is to provide a method for operating an upflow ion exchange tower that can change the amount of deionized water produced in response to fluctuations in the amount of deionized water required at a site where deionized water is required.

[0014] The method for operating an upflow ion exchange column of the present invention is a method for producing deionized water by passing raw water upward through an ion exchange column having a packed bed of ion exchange resin between a lower permeable partition plate and an upper permeable partition plate, using a feed pump. The method comprises a fixed bed formation step in which, at the start of water flow, raw water is passed through the ion exchange column at a high LV to push up the packed bed of ion exchange resin in the ion exchange column and press it against the permeable partition plate above the packed bed to form a fixed bed of ion exchange resin; and a steady-state operation step in which raw water is then passed through the ion exchange column at an LV greater than the minimum LV at which the fixed bed can be maintained, and the amount of raw water passed through is controlled in accordance with the demand for deionized water.

[0015] In one aspect of the present invention, in the steady-state operation step, the method for operating an upflow ion exchange tower includes introducing deionized water from the ion exchange tower into a deionized water tank via a flow control valve and delivering the deionized water from the deionized water tank to a demand destination of the deionized water, and controlling the aperture of the flow control valve and / or the water supply pump so that the water level in the deionized water tank is within a predetermined range and so that a fixed bed in the ion exchange tower is maintained.

[0016] In one aspect of the present invention, the control frequency of the water supply pump is 7 times / min or less.

[0017] According to the method for operating an upflow ion exchange column of the present invention, the amount of deionized water produced can be changed in response to fluctuations in the amount of pure water required at the point of demand.

[0018] According to the method for operating an upflow ion exchange column of the present invention, the amount of water passing through the ion exchange column is controlled in accordance with the required amount of deionized water, thereby reducing the unit power consumption of the water supply pump and reducing the frequency of regeneration and replacement of the ion exchange resin.

[0019] FIG. 1 is a configuration diagram of a pure water production system to which a method for operating an upflow ion exchange column according to an embodiment is applied. FIG. 2 is a configuration diagram of a pure water production system to which a method for operating an upflow ion exchange column according to an embodiment is applied. FIG. 3 is a configuration diagram of an ion exchange device. FIG. 4 is a configuration diagram of an ion exchange device. FIG. 5 is a graph showing experimental results. FIG. 6 is a graph showing experimental results. FIG. 7 is a graph showing experimental results. FIG. 8 is a graph showing experimental results.

[0020] Hereinafter, an embodiment will be described with reference to the drawings.

[0021] 1 shows an example of a pure water production system to which the method of operating an upflow ion exchange column of the present invention can be applied. Raw water to be deionized is supplied to an ion exchange unit 3 via a first pump 1 and a pipe 2, and passes through the ion exchange column provided in the ion exchange unit 3. The water comes into contact with the ion exchange resin and is deionized to produce pure water (deionized water). The raw water flows upward through the ion exchange column of the ion exchange unit 3.

[0022] When starting to pass water through the ion exchange column, water is passed through the ion exchange column at a high LV to form a fixed bed.

[0023] The pure water from the ion exchange device 3 is introduced into a pure water tank 9 via a pipe 4, a second pump 5, a pipe 6, a flow control valve 7, and a pipe 8, and is then delivered to a pure water demand point via a pipe 10. A flow meter or pressure gauge 11 is installed in the pipe 6, and a water level gauge 12 is installed in the pure water tank 9, and the detection signals from each are input to a controller 13.

[0024] The controller 13 adjusts the opening of the flow rate adjusting valve 7 by PID control or the like so that the water level detected by the water level gauge 12 falls within a predetermined range.

[0025] The amount of water sent from the pure water tank 9 to the pure water demand point varies depending on the amount of pure water used at the pure water demand point, and the water level in the pure water tank 9 changes accordingly, but by controlling the opening of the flow rate adjustment valve 7, the amount of raw water treated is controlled so that the water level in the pure water tank 9 remains within a predetermined range. In other words, the amount of water flowing to the ion exchange device 3 is controlled depending on the amount of water sent from the pure water tank 9 to the pure water demand point through the piping 10.

[0026] The controller 13 also inverter-controls the water supply rate (motor rotation speed) of the first pump 1 or the second pump 5 so that the flow rate or pressure detected by the flow meter or pressure meter 11 falls within a predetermined range after the opening of the flow control valve 7 has been adjusted. The predetermined range of the flow rate or pressure is set so as to achieve a flow rate at which a fixed bed is maintained in the ion exchange column of the ion exchange apparatus 3.

[0027] In the present invention, the amount of water passed through the ion exchange tower is controlled in accordance with the amount of pure water used at the point of demand and so as to maintain the fixed bed of the ion exchange tower.

[0028] This reduces the pump power consumption during operation of the ion exchange system, and also reduces the frequency of regeneration and replacement of the ion exchange resin.

[0029] FIG. 2 shows another example of a pure water production system to which the method of operating an upflow ion exchange column of the present invention is applied.

[0030] In the pure water production system of Figure 2, a flow meter or pressure gauge 11 is installed in the pipe 8, and a pressure gauge 14 is installed in the pipe 6, and the detection signals from each and the detection signal from the water level gauge 12 in the pure water tank 9 are input to the controller 13.

[0031] The other components of Fig. 2 are the same as those of Fig. 1, and the same reference numerals denote the same parts. In this water purification system, when water starts to flow through the ion exchange unit 3, water is passed through the ion exchange column at a high LV to form a fixed bed.

[0032] 2, the aperture of the flow control valve 7 is controlled so that the water level detected by the water level gauge 12 is within a predetermined range. Furthermore, the rotation speed of one or both of the first pump 1 and the second pump 5 is inverter-controlled so that the pressure detected by the pressure gauge 14 after the aperture of the flow control valve 7 is adjusted and either the flow rate or pressure detected by the flow meter or pressure gauge 11 or both are within a predetermined range (a range that maintains the fixed bed of the ion exchange column).

[0033] 2 also controls the amount of water flowing through the ion exchange unit 3 in accordance with the amount of water delivered from the pure water tank 9 to the point of demand through the piping 10, and so as to maintain the fixed bed of the ion exchange tower. This reduces the pump power consumption during operation of the pure water production unit, and also reduces the frequency of regeneration and replacement of the ion exchange resin.

[0034] In the present invention, it is preferable that the frequency of the flow rate adjustment operation of the first pump 1 or the second pump 5 is 7 times / min or less, and the range of flow rate fluctuation per operation is half the maximum flow rate or less.

[0035] The reason why the flow rate adjustment frequency is preferably set to 7 times / min or less is as follows.

[0036] Generally, the metal used in the pump is 2 x 10 ７ Assuming that the pump will be used for 5 years, the friction will cause wear and fatigue failure. ７ times / 5 years / 365 days / 24 hours / 60 minutes = 7.62 times / minute. Therefore, it is preferable to set the number of flow rate adjustments to 7 times / minute or less.

[0037] The water purifying apparatus of FIG. 1 or FIG. 2 is suitable for incorporation into a primary pure water system of an ultrapure water producing apparatus, but may also be used for other purposes.

[0038] In the present invention, there is no particular limitation on the configuration of the ion exchange device 3. An example of a configuration that can be adopted as the ion exchange device 3 is shown in FIGS.

[0039] 3 , a cylindrical cation exchange tower 21 and an anion exchange tower 23 are disposed within a housing 26. The cation exchange tower 21 and anion exchange tower 23 are installed so that the axial direction of the cylinders is vertical. Raw water from pipe 2 is introduced into cation exchange tower 21, where it flows upward and undergoes cation exchange treatment. It is then introduced into anion exchange tower 23 via pipe 25, where it flows upward and undergoes anion exchange treatment to become pure water, which then flows out into pipe 4.

[0040] The cation exchange tower 21 is provided with a packed bed 22 of strongly acidic cation exchange resin. Water-permeable partition plates 21a and 21b, each with a water-permeable portion, are horizontally installed above and below the packed bed 22. The water-permeable portions of the partition plates 21a and 21b are configured to allow water to pass through but not allow cation exchange resin particles to pass through. Under steady-state water flow, the packed bed 22 is pushed up and pressed against the upper partition plate 21b, forming a fixed bed. When water is not flowing, the distance between the top surface of the packed bed 22 and the water-permeable partition plate 21b is preferably 40% or more, particularly 50 to 70%, of the height (packed bed height) of the packed bed 22 when water is not flowing. The same applies to the anion exchange tower described below.

[0041] The cation exchange resin is regenerated by passing hydrochloric acid through it in a downward flow.

[0042] The anion exchange column 23 has a packed bed 24 of a strongly basic anion exchange resin. Permeable partition plates 23a and 23b, each having a water passage portion, are horizontally installed on the lower and upper sides of the packed bed 24. In a steady water flow state, the packed bed 24 is pushed up and pressed against the upper permeable partition plate 23b, forming a fixed bed.

[0043] The anion exchange resin is regenerated by passing an aqueous sodium hydroxide solution downward.

[0044] In the ion exchange apparatus 3' shown in Fig. 4, raw water from pipe 2 is introduced into cation exchange tower 30, where it flows upward and undergoes cation exchange treatment, and then is sent to decarbonation tower 40 via pipe 34 and is decarbonated. The decarbonated water is introduced into anion exchange tower 50 via pump 43 and pipe 44, where it flows upward and undergoes anion exchange treatment to become deionized water, which then flows out into pipe 4.

[0045] The cation exchange tower 30 is provided with packed beds 31 and 32 of strongly acidic cation exchange resin. Permeable partition plates 30a, 30b, and 30c, each having a water-permeable portion, are horizontally provided below the lower packed bed 31 and above and below the upper packed bed 32. The water-permeable partition plates 30a to 30c have water-permeable portions that allow water to pass through but not allow cation exchange resin particles to pass through. Under steady water flow conditions, the packed beds 31 and 32 are pushed up and pressed against the respective upper permeable partition plates 30b and 30c, forming fixed beds.

[0046] The cation exchange resin is regenerated by passing hydrochloric acid through it in a downward flow.

[0047] The decarbonation tower 40 has a packing layer 41. The pressure inside the decarbonation tower 40 is reduced by a vacuum pump (not shown). Dissolved carbon dioxide gas in the water is degassed as the water flows through the packing layer 41. The water that falls into the pit 42 is pumped by a pump 43.

[0048] The anion exchange tower 50 has packed beds 51 and 52 of a strong basic anion exchange resin. Permeable partition plates 50a, 50b, and 50c, each having a water passage portion, are horizontally installed below the lower packed bed 51 and above and below the upper packed bed 52. Under steady water flow conditions, the packed beds 51 and 52 are pushed up and pressed against the respective upper permeable partition plates 50b and 50c to form fixed beds.

[0049] The anion exchange resin is regenerated by passing an aqueous sodium hydroxide solution downward.

[0050] In the present invention, in the fixed bed formation step at the start of water flow into an ion exchange column containing ion exchange resins with an average particle size of about 500 to 700 μm, it is preferable to form a fixed bed by flowing water upward at an LV of 20 m / h or more, for example, 20 to 70 m / h, particularly about 20 to 50 m / h.

[0051] In the subsequent steady-state operation step, the water is passed upward at a smaller LV (but not less than the minimum LV that can maintain a fixed bed), and the amount of water passed is controlled in response to changes in the demand for deionized water. This minimum LV should be sufficient to maintain the floating of the ion exchange resin, and may be set appropriately, for example, between 6 m / h and 20 m / h.

[0052] [Experimental Example 1] A water flow test was carried out using an ion exchange apparatus 3 having a cation exchange tower 21 and an anion exchange tower 23 in one tower, as shown in Figure 3. The main conditions were as follows.

[0053] <Configuration of cation exchange tower 21> Inner diameter: 700 mm Height between partition plates 21a and 21b of cation exchange tower 21: 700 mm Height of fixed bed of cation exchange resin: 572 mm Average particle size of cation exchange resin: 650 μm <Configuration of anion exchange tower 23> Inner diameter: 700 mm Height between partition plates 23a and 23b of anion exchange tower 23: 1200 mm Height of fixed bed of anion exchange resin: 1105 mm Average particle size of anion exchange resin: 550 μm

[0054] <Water to be treated> Salt solution with a concentration of 8 mg / L (27°C)

[0055] <Fixed Bed Formation Step> Water was passed through the reactor at LV=20 m / h for 10 minutes to form a fixed bed.

[0056] <Steady-state operation step> After the fixed bed was formed, a steady-state operation step was carried out. In this steady-state operation step, the water flow rate was changed between LV = 42.9 m / h and LV = 90.9 m / h in 20-minute cycles. The water flow rate was linearly increased from LV = 42.9 m / h to LV = 90.9 m / h over 10 min, and then linearly decreased from LV = 90.9 m / h to LV = 42.9 m / h over 10 min. The total water flow time was 6 h.

[0057] <Results> The resistivity of deionized water remained constant (about 18 MΩ·cm) even when the LV was changed during the steady-state operation process.

[0058] [Experimental Example 2] <Experimental Method> A cation exchange tower 21 having the same configuration as that used in Experimental Example 1 was constructed.

[0059] A saline solution (27°C) with a concentration of 8 mg / L was passed through the pipe in an upward direction. The upward flow velocity (LV) was gradually increased from 0 m / h to 91.0 m / h over 30 minutes, and the change in differential pressure over time was measured. The results are shown in Table 1 and Figure 5.

[0060] After the upward flow velocity LV reached 91.0 m / h, it was gradually decreased to 0 m / h over 30 minutes, and the change in differential pressure over time was measured. The results are shown in Table 2 and Figure 6.

[0061] Tables 1 and 2 also show the value MPa / m (differential pressure per 1 m of packed bed) obtained by dividing the measured differential pressure (MPa) by the height (m) of the packed bed.

[0062]

[0063]

[0064] <Discussion> It was confirmed that the differential pressure changed almost in proportion to the change in LV, as shown in Tables 1 and 2 and Figures 5 and 6. Even when the LV changed near 20 m / h (LV during fixed bed formation in Experimental Example 1), the differential pressure changed almost in proportion to the change in LV.

[0065] [Experimental Example 3] <Experimental Method> An anion exchange tower 23 having the same configuration as that used in Experimental Example 1 was constructed.

[0066] A saline solution (27.6°C) with a concentration of 8 mg / L was passed through the pipe in an upward direction. The upward flow velocity (LV) was gradually increased from 0 m / h to 91.0 m / h over 30 minutes, and the change in differential pressure over time was measured. The results are shown in Table 3 and Figure 7.

[0067] After the upward flow velocity LV reached 91.0 m / h, it was gradually decreased to 0 m / h over 30 minutes, and the change in differential pressure over time was measured. The results are shown in Table 4 and Figure 8.

[0068] Tables 3 and 4 also show the value MPa / m (differential pressure per 1 m of packed bed) obtained by dividing the measured differential pressure (MPa) by the height (m) of the packed bed.

[0069]

[0070]

[0071] <Discussion> It was confirmed that the differential pressure changed almost in proportion to the change in LV, as shown in Tables 3 and 4 and Figures 7 and 8. Even when the LV changed near 20 m / h (LV during fixed bed formation in Experimental Example 1), the differential pressure changed almost in proportion to the change in LV.

[0072] [Experimental Examples 4-1 and 4-2] <Experimental Example 4-1> Two columns with an inner diameter of 40 mm and a height of 1000 mm were prepared. One column was packed with 500 mL of H-type cation resin (packed bed height ≈ 400 mm). The other column was packed with 1000 mL of OH-type anion resin (packed bed height ≈ 800 mm). These columns were connected by piping so that liquid was passed through the cation-packed column and then the anion-packed column in an upward flow manner. The H-type cation exchange resin was a regenerated Na-type cation exchange resin with an average particle size of 650 μm. The OH-type anion exchange resin was a regenerated Cl-type anion exchange resin with an average particle size of 550 μm.

[0073] Permeable partition plates were placed below and above the packed bed of cation exchange resin and below and above the packed bed of anion exchange resin. An 8 mg / L saline solution (27°C) was passed through each column at LV = 50 m / h for 10 min to push up the ion exchange resin beds and form fixed beds in each column. Then, saline solution was passed through each column at LV = 20 m / h to maintain the fixed beds. The change in resistivity over time after the start of water flow at LV = 20 m / h is shown in Figure 9.

[0074] <Experimental Example 4-2> In Experimental Example 4-1, the saline solution was passed through at LV=20 m / h without forming a fixed bed. The change in resistivity over time after the start of water passage is shown in FIG.

[0075] <Discussion> As shown in FIG. 9, it was confirmed that in Example 4-1 where a fixed bed was formed, the resistivity was about 1 MΩ·cm higher than in Example 4-2 where no fixed bed was formed.

[0076] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-127186, filed on August 3, 2023, and is incorporated by reference in its entirety.

[0077] 3, 3' Ion exchange device 7 Flow rate control valve 9 Pure water tank 11 Flow meter or pressure gauge 12 Water level gauge 13 Controller 14 Pressure gauge 21 Cation exchange tower 21a, 21b Water-permeable partition plate 22 Cation exchange resin 23 Anion exchange tower 23a, 23b Water-permeable partition plate 24 Anion exchange resin 30 Cation exchange tower 30a, 30b, 30c Water-permeable partition plate 31, 32 Cation exchange resin 40 Decarbonation tower 50 Anion exchange tower 50a, 50b, 50c Water-permeable partition plate 51, 52 Anion exchange resin

Claims

1. A method for operating an upflow ion exchange tower in which raw water is passed upward by a feed pump through an ion exchange tower having a packed bed of ion exchange resin between a lower permeable partition plate and an upper permeable partition plate to produce deionized water, the method comprising: a fixed bed formation step in which, at the start of water passage, raw water is passed through the ion exchange tower at a high LV to push up the packed bed of ion exchange resin in the ion exchange tower and press it against the upper permeable partition plate to form a fixed bed of ion exchange resin; and a steady operation step in which raw water is passed through the ion exchange tower at an LV higher than the minimum LV at which the fixed bed can be maintained, and the amount of raw water passed through is controlled in accordance with the demand for deionized water.

2. A method for operating an upward flow ion exchange tower, in which, in the steady operation step, deionized water from the ion exchange tower is introduced into a deionized water tank via a flow control valve and the deionized water is sent from the deionized water tank to a demand destination for the deionized water, wherein the opening of the flow control valve and / or the water supply pump are controlled so that the water level in the deionized water tank is within a predetermined range and the fixed bed of the ion exchange tower is maintained.

3. The method for operating an upflow ion exchange column according to claim 2, wherein the control frequency of the feed water pump is 7 times / min or less.

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