Conductivity and pH value measuring and verifying device

Abstract

The utility model relates to the technical field of power plant water sample detection, in particular to a conductivity and pH value measuring and verifying device. Comprising a sample introduction pipe, one end of which is connected with a power plant water sample; an inlet of the first three-way valve is communicated with the other end of the sample feeding pipe; an inlet of the second three-way valve is communicated with a first outlet of the first three-way valve. The inlet of the first three-way valve is communicated with the second outlet of the first three-way valve, the second outlet of the third three-way valve is communicated with the inlet of the third three-way valve, a water sample of the power plant can flow into the sample outlet pipe through the sample inlet pipe, and the standard conductivity meter can detect the conductivity of the water sample of the power plant.

Description

Technical Field

[0001] This utility model relates to the field of power plant water sample testing technology, specifically to a conductivity and pH value measurement and testing device. Background Technology

[0002] When measuring water samples from power plants, conductivity and pH values ​​need to be tested. Conductivity testing includes both conventional conductivity and hydrogen conductivity testing. Generally, these measurements can be performed using conductivity meters and pH meters. However, due to objective conditions such as wear and tear and temperature, the results from conductivity and pH meters may contain errors. Current methods for measuring power plant water samples lack proper instrument verification. Utility Model Content

[0003] In view of this, the present invention provides a conductivity and pH value measurement and testing device to solve the problem of the lack of instrument testing in the prior art.

[0004] This utility model provides a device for measuring and testing conductivity and pH value, comprising:

[0005] A sample inlet tube, one end of which is connected to a water sample from the power plant;

[0006] The first three-way valve has its inlet connected to the other end of the injection tube;

[0007] The second three-way valve has its inlet connected to the first outlet of the first three-way valve;

[0008] A mixing column, wherein the inlet of the mixing column is connected to the first outlet of the second three-way valve;

[0009] The hydrogen column has its inlet connected to the second outlet of the second three-way valve and the outlet of the mixing column, respectively.

[0010] The third three-way valve has its first outlet connected to the outlet of the hydrogen column, its second outlet connected to the second outlet of the second three-way valve, and its inlet connected to a sample outlet tube, on which a standard conductivity meter is installed.

[0011] The ammonia addition assembly is connected to the sample outlet tube and located between the third three-way valve and the standard conductivity meter.

[0012] This application allows for the connection of the inlet and second outlet of a first three-way valve, and the connection of the second outlet and inlet of a third three-way valve, to allow power plant water samples to flow through the inlet tube into the outlet tube. A standard conductivity meter can then be used to detect the conductivity of the power plant water sample. Alternatively, by connecting the inlet and first outlet of the first three-way valve, the inlet and second outlet of the second three-way valve, and the first outlet and inlet of the third three-way valve, the power plant water sample can flow through the inlet tube into a hydrogen column and then into the outlet tube. A standard conductivity meter can then be used to detect the hydrogen conductivity of the power plant water sample. The pH value of the power plant water sample can be calculated based on the conductivity and hydrogen conductivity.

[0013] Connect the inlet of the first three-way valve to its first outlet, connect the inlet of the second three-way valve to its first outlet, and connect the first outlet of the third three-way valve to its inlet. Add ammonia to the sample outlet tube using the ammonia addition assembly. Place a conductivity meter to be tested at the outlet of the sample outlet tube. Simultaneously record the measured values ​​of both the conductivity meter and the standard conductivity meter to verify the conductivity meter and obtain its measurement error. Similarly, a pH meter to be tested can be placed at the outlet of the sample tube, using the same connection method. Convert the measured value of the standard conductivity meter into a pH value to verify the pH meter and obtain its measurement error.

[0014] In one optional embodiment, the ammonia addition assembly includes:

[0015] The standard solution bottle is connected to the sample outlet tube via a dosing tube, and the standard solution bottle contains ammonia.

[0016] In one optional embodiment, the ammonia addition assembly further includes:

[0017] A dosing pump, installed on the dosing tube, is adapted to deliver ammonia water from the standard solution bottle to the sample outlet tube. This can accelerate the rate at which ammonia water flows into the sample outlet tube.

[0018] In one alternative implementation, it further includes:

[0019] A pressure relief tube, one end of which is connected to the sample inlet tube;

[0020] A pressure relief valve is installed on the pressure relief pipe.

[0021] The pressure relief pipe is connected to the sample inlet pipe, which can reduce the water pressure in the sample inlet pipe. The water pressure in the sample inlet pipe can be adjusted by adjusting the opening of the pressure relief valve, thereby adjusting the flow rate of the power plant water sample in the entire water circuit.

[0022] In one optional embodiment, a first flow meter is provided on the inlet tube, and the first flow meter is located between the first three-way valve and the pressure relief pipe. The first flow meter can detect the flow rate of the power plant water sample in the inlet tube.

[0023] In one optional embodiment, a second flow meter is provided on the dosing pipe, located between the dosing pump and the third three-way valve. The second flow meter can detect the flow rate of the dosing agent in the dosing pipe.

[0024] In one alternative embodiment, a third flow meter is provided on the sample outlet tube, the third flow meter being located on the side of the standard conductivity meter away from the third three-way valve. The third flow meter is adapted to detect the total flow rate on the sample outlet tube.

[0025] In one alternative embodiment, the hydrogen column is filled with a cation exchange resin. The cation exchange resin allows hydrogen ions to dissociate from the power plant water sample.

[0026] In one alternative embodiment, the mixed column is filled with cation and anion resins. The cation and anion resins can absorb ions from the power plant water sample. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of this utility model or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the structure of an embodiment of the present utility model.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1. Injection tube; 2. First three-way valve; 3. Second three-way valve; 4. Mixing column; 5. Hydrogen column; 6. Third three-way valve; 7. Injection tube; 8. Standard conductivity meter; 9. Standard solution bottle; 10. Dosing tube; 11. Dosing pump; 12. Pressure relief tube; 13. Pressure relief valve; 14. First flow meter; 15. Second flow meter; 16. Third flow meter. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0032] Fixed online chemical instrument testing devices use the standard solution method to verify the basic error of online conductivity measuring instruments. Because standard solutions with low conductivity are easily affected by carbon dioxide in the air, causing changes in their conductivity values, standard solutions with a conductivity greater than 100 μS / cm are generally selected for verifying the basic error of conductivity measuring instruments. However, in reality, the conductivity of high-purity water samples in power plants is very low, generally not exceeding 0.2 μS / cm. The conductivity of the standard solution used for testing online conductivity measuring instruments in power plants is much greater than the conductivity value of the actual water sample during online measurement. Therefore, the accuracy of the actual measurement cannot be guaranteed. The "Inspection Procedure for Online Chemical Instruments in Power Plants" (DL / T 677-2018) requires that: for conductivity meters that measure water sample conductivity values ​​not exceeding 0.30 μS / cm, the water sample flow method should be used to inspect the overall machine operating error; for conductivity meters that measure conductivity values ​​exceeding 0.30 μS / cm, the water sample flow test method should be used to inspect the overall machine operating error, or the static standard solution offline test method can be used to inspect the overall machine reference error.

[0033] Online pH meter calibration typically employs a two-point calibration method, using two standard solutions: a pH 7 standard buffer and either a pH 9 or pH 4 standard buffer. First, the electrode is positioned using the pH 7 standard buffer. Then, the second standard buffer is selected based on the acidity or alkalinity of the solution being tested. If the solution is acidic, a pH 4 standard buffer is used; if it is alkaline, a pH 9 standard buffer is used. However, based on the principle of pH measurement, factors such as static charge, changes in liquid junction potential with the measured solution, and temperature variations during high-purity water pH measurement significantly impact the accuracy of high-purity water pH measurements in power plants. It is believed that some of these factors are difficult to completely eliminate. Therefore, simply using a two-point calibration with standard buffers cannot guarantee the accuracy of pH values ​​within a given range. The "Inspection Procedure for Online Chemical Instruments in Power Plants" (DL / T 677-2018) requires that for online pH meters measuring water sample conductivity values ​​not exceeding 100 μS / cm, the water sample flow test method should be used for online verification of the overall machine's operating error.

[0034] Therefore, it is essential to develop an online device for the combined measurement and testing of (hydrogen) conductivity and pH value.

[0035] A Chinese patent, published on March 12, 2008, with publication number CN201035099Y, discloses a utility model patent for "A Mobile Online Conductivity Measuring Instrument Testing Device." This utility model discloses a mobile online conductivity measuring instrument testing device, including a water sample pipeline connected to a water sample. The water sample pipeline is connected to a flow meter and a standard conductivity measuring instrument via a water sample valve. An ion exchange column is also connected in series between the water sample pipeline and the flow meter. This utility model not only provides online testing and is simple and convenient to operate, but also includes an ion exchange column that can generate a conductivity standard solution and a hydrogen conductivity standard solution that match the actual conductivity measured by the conductivity measuring instrument. This makes the testing results of the high-purity water conductivity measuring instrument more accurate, overcomes the difficulties in conventional testing processes, and can test the hydrogen exchange column, which has a significant impact on hydrogen conductivity measurement, thereby ensuring the accuracy of the conductivity measuring instrument's values. However, this patent does not cover the measurement of pH values ​​in boiler condensate, feedwater, and steam, or the testing of online pH meters.

[0036] The purpose of this application is to overcome the shortcomings of the prior art and provide a method for accurate, convenient, and rapid online on-site measurement of the conductivity of all water samples (hydrogen) in a unit, and for online on-site direct measurement of the conductivity of boiler condensate, feedwater, and steam, thereby indirectly calculating the pH value. Simultaneously, it overcomes the deficiency of conductivity meters relying on single-point testing with standard solutions by preparing ammonia-containing water samples (high-purity water + ammonia) with the same conductivity as the conductivity meter for continuous testing using a flow method. Similarly, it prepares ammonia-containing water samples (high-purity water + ammonia) with the same conductivity as the pH meter, and converts the conductivity into pH value, thereby indirectly preparing water samples with continuously different pH values ​​to test the pH meter.

[0037] The following is combined Figure 1 The following describes embodiments of the present invention.

[0038] According to an embodiment of the present invention, a conductivity and pH value measuring and testing device is provided, comprising:

[0039] The sample inlet tube 1 is connected at one end to the power plant water sample. It should be noted that the power plant water sample has a certain pressure when it is introduced, so after being introduced into the sample inlet tube 1, it can flow directly along the sample inlet tube 1 to the connected pipeline.

[0040] The first three-way valve 2 has its inlet connected to the other end of the sample inlet tube 1. The inlets of the first three-way valve 2, the second three-way valve 3, and the third three-way valve 6 can all be selectively connected to either the first outlet or the second outlet. The first three-way valve 2 allows the sample inlet tube 1 to be connected to either the second three-way valve 3 or the third three-way valve 6.

[0041] The second three-way valve 3 has its inlet connected to the first outlet of the first three-way valve 2; the second three-way valve 3 can connect the injection tube 1 to the hydrogen column 5 or to the mixing column.

[0042] The mixing column 4 has its inlet connected to the first outlet of the second three-way valve 3; the mixing column 4 is suitable for absorbing ions in the power plant water sample.

[0043] The hydrogen column 5 has its inlet connected to the second outlet of the second three-way valve 3 and the outlet of the mixing column 4. The hydrogen column 5 can absorb cations in the power plant water sample and dissociate them into hydrogen ions, so that the power plant water sample contains hydrogen ions, which can be used to detect the hydrogen conductivity of the power plant water sample.

[0044] The third three-way valve 6 has its first outlet connected to the outlet of the hydrogen column 5, and its second outlet connected to the second outlet of the second three-way valve 3. The inlet of the third three-way valve 6 is connected to a sample outlet pipe 7, which is equipped with a standard conductivity meter 8. The conductivity and hydrogen conductivity of the power plant water sample can be detected using the standard conductivity meter 8, thereby determining the pH value of the power plant water sample. The standard conductivity meter 8 can be any standard conductivity meter. An instrument for measuring the conductivity or pH value to be measured can be installed at the outlet of the sample outlet pipe 7.

[0045] An ammonia addition assembly is connected to the sample outlet pipe 7 and located between the third three-way valve 6 and the standard conductivity meter 8. Ammonia water can be added to the sample outlet pipe 7, and the value of the conductivity meter to be tested, set at the outlet position of the standard conductivity meter 8, can be recorded. This allows for the verification of the conductivity meter to be tested and the measurement error of the meter to be obtained. The detection value of the standard conductivity meter 8 is converted into a pH value, and a pH meter to be tested is set at the outlet position of the sample outlet pipe 7. This allows for the verification of the pH meter to be tested and the measurement error of the pH meter to be obtained.

[0046] This application allows power plant water samples to flow into the outlet pipe 7 via the inlet pipe 1 by connecting the inlet of the first three-way valve 2 to its second outlet, and the second outlet of the third three-way valve 6 to its inlet. The conductivity of the power plant water sample can then be detected by a standard conductivity meter 8. Alternatively, by connecting the inlet of the first three-way valve 2 to its first outlet, the inlet of the second three-way valve 3 to its second outlet, and the first outlet of the third three-way valve 6 to its inlet, the power plant water sample can flow into the hydrogen column 5 via the inlet pipe 1 and then into the outlet pipe 7. The hydrogen conductivity of the power plant water sample can then be detected by a standard conductivity meter 8. The pH value of the power plant water sample can be calculated based on the conductivity and hydrogen conductivity.

[0047] Connect the inlet of the first three-way valve 2 to its first outlet, connect the inlet of the second three-way valve 3 to its first outlet, and connect the first outlet of the third three-way valve 6 to its inlet. Add ammonia to the sample outlet tube 7 using the ammonia addition assembly. Place a conductivity meter to be tested at the outlet of the sample outlet tube 7. Simultaneously record the measured values ​​of both the conductivity meter to be tested and the standard conductivity meter 8. This completes the verification of the conductivity meter to be tested and obtains its measurement error. Similarly, a pH meter to be tested can be placed at the outlet of the sample outlet tube 7, using the same connection method. Convert the measured value of the standard conductivity meter 8 into a pH value to complete the verification of the pH meter to be tested and obtain its measurement error.

[0048] In one optional embodiment, the ammonia addition assembly includes: a standard solution bottle 9, which is connected to the sample outlet tube 7 via a dosing tube 10, and the standard solution bottle 9 contains ammonia water.

[0049] In an optional embodiment, the ammonia dosing assembly further includes a dosing pump 11, disposed on the dosing tube 10, wherein the dosing pump 11 is adapted to deliver ammonia water from the standard solution bottle 9 to the sample outlet tube 7. This can accelerate the rate at which ammonia water enters the sample outlet tube 7. It should be noted that the dosing pump 11 in this application is a unidirectional dosing pump, meaning that ammonia water can only flow from the standard solution bottle 9 to the sample outlet tube 7; ammonia water or power plant water samples located in the sample outlet tube 7 cannot flow to the standard solution bottle 9 via the dosing pump 11. The dosing pump 11 can be a variable frequency dosing pump.

[0050] In an optional embodiment, the system further includes: a pressure relief pipe 12, one end of which is connected to the sample inlet pipe 1; and a pressure relief valve 13 disposed on the pressure relief pipe 12. The pressure relief valve 13 can be a pressure relief valve. The pressure relief pipe 12 is connected to the sample inlet pipe 1, which can reduce the water pressure in the sample inlet pipe 1. By adjusting the opening of the pressure relief valve 13, the water pressure in the sample inlet pipe 1 can be adjusted, thereby adjusting the flow rate of the power plant water sample in the entire water circuit.

[0051] In one optional embodiment, a first flow meter 14 is provided on the sample inlet tube 1, and the first flow meter 14 is located between the first three-way valve 2 and the pressure relief pipe 12. The first flow meter 14 can detect the flow rate of the power plant water sample in the sample inlet tube 1.

[0052] In one optional embodiment, a second flow meter 15 is provided on the dosing pipe 10, and the second flow meter 15 is located between the dosing pump 11 and the third three-way valve 6. The second flow meter 15 can detect the flow rate of the dosing agent in the dosing pipe 10.

[0053] In one alternative embodiment, a third flow meter 16 is provided on the sample outlet tube 7, the third flow meter 16 being located on the side of the standard conductivity meter 8 away from the third three-way valve 6. The third flow meter 16 is adapted to detect the total flow rate on the sample outlet tube 7.

[0054] In one alternative embodiment, the hydrogen column 5 is filled with a cation exchange resin. The cation exchange resin allows hydrogen ions to dissociate from the power plant water sample.

[0055] In one optional embodiment, the mixing column 4 is filled with cation and anion resins. The cation and anion resins can absorb ions from the power plant water sample.

[0056] Specifically, when measuring conductivity, the pressure relief valve 13 is fully opened, the dosing pump 11 is stopped, the inlet of the first three-way valve 2 is connected to the second outlet of the first three-way valve 2, and the second outlet of the third three-way valve 6 is connected to the inlet of the third three-way valve 6. The power plant water sample can flow into the outlet pipe 7 through the inlet pipe 1. The flow rates of the first flow meter 14 and the third flow meter 16 are observed. By adjusting the opening of the pressure relief valve 13, when the first flow meter 14 and the third flow meter 16 meet the requirements, the value displayed on the standard conductivity table 8 is the conductivity index SC of the measured power plant water sample.

[0057] When measuring hydrogen conductivity, fully open the pressure relief valve 13, stop the dosing pump 11, connect the inlet of the first three-way valve 2 to the first outlet of the first three-way valve 2, connect the inlet of the second three-way valve 3 to the second outlet of the second three-way valve 3, and connect the first outlet of the third three-way valve 6 to the inlet of the third three-way valve 6. The power plant water sample can flow into the hydrogen column 5 through the inlet pipe 1 and then into the outlet pipe 7. Observe the flow rate of the first flow meter 14 and the third flow meter 16. Adjust the opening of the pressure relief valve 13 until the first flow meter 14 and the third flow meter 16 meet the requirements. The value displayed on the standard conductivity table 8 is the hydrogen conductivity index CC of the measured water sample.

[0058] Regarding pH measurement, since the water sample to be tested is an ammonia-containing water sample from boiler condensate, feedwater, or steam, it can be calculated using the following formula: pH = 8.57 + Lg(SC - 1 / 3CC).

[0059] When testing the conductivity meter to be tested, a single-point testing method can be used: the same water sample is divided into two paths, one path is directly connected to the conductivity meter to be tested, and the other path is connected to the sample inlet tube 1. The measurement process is the same as the conductivity measurement described above. The test can be completed by comparing the conductivity measured by the two paths.

[0060] Alternatively, a multi-point testing method can be selected: fully open the pressure relief valve 13, stop the dosing pump 11, connect the inlet of the first three-way valve 2 to the first outlet of the first three-way valve 2, connect the inlet of the second three-way valve 3 to the first outlet of the second three-way valve 3, connect the first outlet of the third three-way valve 6 to the inlet of the third three-way valve 6, add ammonia to the sample outlet pipe 7 through the ammonia dosing assembly, set the conductivity meter to be tested at the outlet position of the sample outlet pipe 7, observe the flow rate of the first flow meter 14 and the third flow meter 16, adjust the opening of the pressure relief valve 13 until the first flow meter 14 and the third flow meter 16 meet the requirements, and record the reading SC1 of the standard conductivity meter 8 at this time. Start the dosing pump 11. By adjusting the frequency of the dosing pump 11 from low to high, the ammonia water in the standard solution bottle 9 flows through the dosing tube 10 to the sample outlet tube 7. At this time, record the readings of the standard conductivity meter 8, SC2, SC3, etc. Simultaneously, compare the recorded readings of the standard conductivity meter 8 with the readings of the conductivity meter to be tested at the outlet position of the sample outlet tube 7 to achieve multi-point testing.

[0061] When testing hydrogen conductivity, the same water sample can be divided into two paths: one path is directly connected to the online hydrogen conductivity device to be tested, and the other path is connected to the sample inlet tube 1. The measurement process is the same as that for hydrogen conductivity measurement. The test can be completed by comparing the hydrogen conductivity measured by the two paths.

[0062] When performing pH testing, a single-point testing method can be used: the same water sample is divided into two paths, one directly connected to the pH meter to be tested, and the other connected to the sample inlet tube 1. The measurement process is the same as the pH measurement described above. The test can be completed by comparing the pH values ​​measured by the two paths.

[0063] Alternatively, a multi-point testing method can be selected: fully open the pressure relief valve 13, stop the dosing pump 11, connect the inlet of the first three-way valve 2 to the first outlet of the first three-way valve 2, connect the inlet of the second three-way valve 3 to the first outlet of the second three-way valve 3, and connect the first outlet of the third three-way valve 6 to the inlet of the third three-way valve 6. Observe the flow rate of the first flow meter 14 and the third flow meter 16. Adjust the valve opening of the pressure relief valve 13 until the first flow meter 14 and the third flow meter 16 meet the requirements. At this time, the reading SC1 of the standard conductivity meter 8 can be recorded. When the standard conductivity meter 8 reading SC1 decreases to approximately 0.055 μS / cm, start the dosing pump 11. By adjusting the frequency of the dosing pump 11 from low to high, the ammonia water in the standard solution bottle 9 flows through the dosing tube 10 to the sample outlet tube 7. At this time, record the standard conductivity meter 8 readings SC2, SC3, etc. Since the CC of the water sample can be ignored at this time, use the formula pH = 8.57 + Lg(SC) and compare it with the reading of the instrument for the pH value to be tested to achieve multi-point testing.

[0064] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A device for measuring and testing conductivity and pH value, characterized in that, include: A sample inlet tube (1) is provided, one end of which is connected to the water sample from the power plant. The first three-way valve (2) has its inlet connected to the other end of the sample inlet tube (1); The inlet of the second three-way valve (3) is connected to the first outlet of the first three-way valve (2); Mixing column (4), the inlet of which is connected to the first outlet of the second three-way valve (3); Hydrogen column (5), the inlet of which is connected to the second outlet of the second three-way valve (3) and the outlet of the mixing column (4); The third three-way valve (6) has its first outlet connected to the outlet of the hydrogen column (5), its second outlet connected to the second outlet of the second three-way valve (3), and its inlet connected to a sample outlet tube (7), which is equipped with a standard conductivity meter (8). The ammonia addition assembly is connected to the sample outlet tube (7) and located between the third three-way valve (6) and the standard conductivity meter (8).

2. The conductivity and pH value measuring and testing device according to claim 1, characterized in that, The ammonia addition assembly includes: The standard solution bottle (9) is connected to the sample outlet tube (7) through the dosing tube (10), and the standard solution bottle (9) contains ammonia water.

3. The conductivity and pH value measuring and testing device according to claim 2, characterized in that, The ammonia addition assembly also includes: A dosing pump (11) is installed on the dosing tube (10), and the dosing pump (11) is adapted to deliver ammonia water in the standard solution bottle (9) to the sample outlet tube (7).

4. The conductivity and pH value measuring and testing device according to claim 1, characterized in that, Also includes: A pressure relief tube (12) is provided, one end of which is connected to the sample inlet tube (1). A pressure relief valve (13) is installed on the pressure relief pipe (12).

5. The conductivity and pH value measuring and testing device according to claim 4, characterized in that, The sample inlet tube (1) is equipped with a first flow meter (14), which is located between the first three-way valve (2) and the pressure relief pipe (12).

6. The conductivity and pH value measuring and testing device according to claim 3, characterized in that, A second flow meter (15) is installed on the dosing pipe (10), and the second flow meter (15) is located between the dosing pump (11) and the third three-way valve (6).

7. The conductivity and pH value measuring and testing device according to claim 1, characterized in that, A third flow meter (16) is provided on the sample outlet tube (7), and the third flow meter (16) is located on the side away from the third three-way valve (6) from the standard conductivity meter (8).

8. The conductivity and pH value measuring and testing device according to claim 1, characterized in that, The hydrogen column (5) is filled with cation resin.

9. The conductivity and pH value measuring and testing device according to claim 1, characterized in that, The mixed column (4) is filled with cation and anion resins.

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