JPS60171448A - Apparatus for measuring concentration of dissolved substance - Google Patents

Abstract

PURPOSE:To extend the continuously usable time of an obstruction component removal electrode by preventing the blocking of said electrode, by providing a plurality of obstruction component removal electrodes and forming each piercing hole of each removal electrode in a shape continuously or stepwise expanded toward the side of an opposed electrode. CONSTITUTION:A dissolved oxygen meter is constituted of a detector main body 16, a pressure resistant container 17 receiving said main body 16 and an external electric circuit system consisting of a voltmeter 15, an ammeter 12 and constant voltage power sources 13, 14. An oxygen pervious film 3 is provided to the surface of the detector main body 16 and an electrolyte 7 is sealed in said main body 16. An acting electrode 4 is constituted of a cathode having piercing holes. An obstruction component removal electrode having piercing holes is constituted of a post-stage cathode 6a and a front-stage cathode 6b, and both of them have piercing holes. Each piercing hole is formed so as to be expanded toward an anode 8. Specimen water is introduced from a specimen water inlet 19 and discharged from a specimen water outlet 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an apparatus for measuring the concentration of dissolved substances such as dissolved oxygen or dissolved hydrogen.

[Background of the invention]

A conventional device for measuring the concentration of dissolved substances, such as a dissolved oxygen meter, is described in Japanese Patent Application Laid-open No. 57-203945. This is shown in Fig. 1, in which the detector 16 is housed in a pressure-resistant container 17, and the sample water inlet 19 is
The sample water that has been introduced is passed through the entire interior of the pressure container through the water passage hole 5, and the entire detector is immersed in the high pressure sample water 18, and the pressure is maintained between the internal electrolyte 7 and the sample water, and the pressure is increased. In addition to improving the performance, the detector and selective (oxygen) permeable membrane 3 (hereinafter abbreviated as oxygen permeable membrane) are manufactured using heat-resistant resin.
This is intended to improve heat resistance by absorbing thermal expansion of the electrolyte with the bellows 10. moreover,
In order to prevent the oxygen permeable membrane from being damaged due to an increase in internal pressure due to the force of the bellows, the oxygen permeable membrane is inserted and supported by a porous cathode 4 (hereinafter abbreviated as cathode) and a metal filter 1, It reinforces the oxygen permeable membrane.

In the apparatus shown in FIG. 1, dissolved O2 in the sample water first passes through a metal filter and an oxygen permeable membrane and enters the detector. The cathode is made of Au, Pt, Ag, etc., and is connected to a constant potential power source B.
anode B made of silver through 14 and ammeter 12, 9
is connected to. The electrolyte contains K (J'll' alkaline aqueous reactor solution. The cathode is kept at a constant potential that is more negative than the anode B by a constant voltage power supply B14 and a potentiometer 15. According to formula (1), OH−
will be reduced to

02+2H20+4e-→40H-...-”・(1)
On the other hand, the reaction of formula (2) progresses on the anode, and the Ag
+C/=−−+AgC1+e−−−−−−・−(21
A current flows through. This current is detected by an ammeter 12, and the dissolved 02 concentration is determined from this current value.

In known dissolved oxygen meters, the lower surface of the cathode is exposed in the electrolyte and is susceptible to interference by dissolved 02, ions, etc. in the electrolyte, so these should be completely removed to prevent them from diffusing into the cathode. It is equipped with an interfering component removal electrode (hereinafter abbreviated as removal electrode) 6 for the purpose of this purpose. The removal electrode is Au
, A, G, Pt, or the like, and has a structure in which an electrolytic solution can be communicated only through the through hole, and is placed near a porous metal cathode. This removal electrode is connected to the anode A8 via a constant voltage power supply A13, and using this constant potential power supply A, the potential of the removal electrode with respect to the anode A is changed to the anode B.
The potential of the cathode is maintained at the same potential as the potential of the cathode. Interfering components such as dissolved O21 ions that diffuse from the anode A side to the cathode surface are
While the metal passes through the through-hole of the removal electrode, it is reduced and can be prevented from reaching the cathode and causing interference current. At this time, a reaction based on formula (2) proceeds on the anode A.

In the known dissolved oxygen meter, AgCt is generated and precipitated on the anodes A and B according to equation (2) as the dissolved O2 concentration is determined. The solubility of AgCt increases as the concentration increases, and at reactor water temperature it dissolves about 100 times as much as at room temperature, producing Ag+ ions.

This Ag+ ion is converted into AgA according to formula (3) at the cathode.
It is reduced to g"10e-→Ag (3), and this reduction current becomes an interference when measuring the 02 concentration. Therefore, at high temperatures, the Ag+ ions are removed. This is an important issue.Ag+ ions are electrodeposited as Ag in the removal electrode through-hole according to equation (3) and are removed.
At this time, the deposited Ag accumulates in the through-hole, and if measurements are carried out for a long period of time, the through-hole will be blocked and conduction between the cathode and anode 8 will be lost, making measurement impossible. there were.

[Purpose of the invention]

An object of the present invention is to provide a dissolved substance concentration measuring device that can be used continuously for a longer period of time.

[Summary of the invention]

The present invention relates to a measuring electrode consisting of a cathode and an anode having a through hole, one of which serves as a working electrode, an electrolytic solution sealed between the electrodes, a permselective membrane provided near the outside of the working electrode, and a permselective membrane provided near the outside of the working electrode. In a dissolved substance concentration measuring device whose main component is an interfering component removal electrode consisting of a cathode and an anode having a through hole arranged between measurement electrodes and arranged to have the same polarity as the measurement electrode,
The conventional removal electrode is characterized in that the through-hole of the interfering component removal electrode located on the working electrode side of the measurement electrode includes a shape that widens continuously or stepwise toward the counter electrode side. In order to remove interfering components at a high rate, a removal electrode having a small through-hole is used.

The removal rate of interfering components by the removal electrode (hereinafter abbreviated as removal rate) is determined only by the through-hole length, that is, the ratio of the removal electrode thickness to the through-hole radius, and does not depend on the temperature or the type of interfering component.

FIG. 2 shows the relationship between the ratio of the through hole length to the through hole radius and the removal rate. In Figure 2, the removal rate Y is calculated by the formula (
4), and the relationship between the removal rate and the ratio of the through-hole length to the through-hole radius is expressed by Equation 1% where Y represents the removal rate, and Ci and co represent the removal electrode inlet and outlet. represents the concentration of interfering components at Also Ro
is the through-hole radius, and L is the through-hole length. Figure 2 and formula (
5), as the ratio of the through-hole length to the through-hole radius increases, the removal rate increases. For example, in measuring the dissolved O2 concentration at high temperatures, it is required to remove a high concentration of Ag+ ions, so a removal electrode having a through-hole radius smaller than the through-hole length is used.

Ag+ ions diffusing from the anode side are reduced on the inner surface of this through-hole, precipitated as Ag, and captured, but for long-term measurements, it is necessary to take into account the decrease in the through-hole diameter due to accumulation of precipitated Ag.

As shown in FIG.
More than 9 pieces are removed and precipitated. Since the precipitated Ag reduces the radius of the through-hole, this region moves closer to the entrance of the through-hole with time. As a result, as shown in Figure 3, Ag
accumulates thickly at the entrance of the through-hole, further accelerating the blockage of the through-hole, and eventually the through-hole is completely blocked at the entrance, making it impossible to quantify the dissolved O2 concentration. In the present invention, it has been found through analysis that the change in the radius of the inlet portion over time is expressed by equation (6).

Here, t is the elapsed time, r is the entrance radius of the through hole at time t, Ro is the initial radius of the through hole at time O, M is the atomic weight of Ag, D and C are the diffusion coefficient and concentration of Ag + ions,
ρ represents the density of Ag.

From equation (6), the time T until the through hole closes is given by equation (7)
It is expressed as

That is, T increases in proportion to the square of the through hole radius,
It decreases in inverse proportion to the first power of Ag+ ion concentration. Therefore, a removal electrode having a through-hole with a small diameter has an extremely short usage time, and the usage time of a high-temperature, high-pressure type dissolved oxygen meter is mainly determined by this time T. - As an example, equation (6)
1 mob/L K at reactor water temperature (285tZ'), Ag+ saturated in CL aqueous solution
caused by ions, 0.025 (?F71
The change over time of the entrance radius of a through hole having an initial radius of is shown in FIG. The through hole becomes clogged in about 30 days, and this value is shorter than the life span determined by the consumption of Ct- ions in the electrolyte, deterioration of the oxygen permeable membrane, and the like.

The present invention solves this problem and provides a high-efficiency and long-life removal electrode. According to equation (7), the occlusion time T can be increased by increasing the radius or decreasing the Ag + ion concentration. Focusing on one thing, we provided a plurality of removal electrodes, installed a small through hole entrance close to the cathode, and installed a removal electrode with the aim of removing all interfering components such as Ag+ ions at a high rate. , close to the anode, with a large through-hole, to remove interfering components such as Ag + ions at a low rate,
After reducing the concentration, the interfering components are diffused to the high-rate removal electrode placed on the cathode side, and the high-rate removal 1 (11) prevents clogging of the electrode and spreads itself over the large-diameter through-hole. Therefore, the high-temperature, high-pressure type dissolution is characterized by being placed on the removal electrodes that are difficult to block, and applying the same potential to them at the same time to prevent any of the removal electrodes from clogging while performing measurements for removing interfering components at a high rate. He came up with the idea of an oxygen meter.

The characteristics of the present invention are that an electrolytic solution is filled inside a container, an oxygen permeable membrane is broken down on the surface of the container in contact with sample water, and a cathode is placed near the oxygen permeable membrane in the electrolytic solution. A structure in which a cathode anode is installed in the liquid, deep inside the cathode, and connected to this via a constant potential power source and an ammeter, and a through hole is provided through which this electrolyte can pass? A plurality of interfering component removal electrodes (removal electrodes) made of a conductive material are installed closer to the anode for the cathode than the removal electrodes, and the constant potential power supply is fully turned on to connect the removal electrodes and the removal electrodes. In a diaphragm-type dissolved oxygen meter that has an anode for a removal electrode that is connected, a through hole having a radius smaller than the length of the through hole is provided close to the cathode side, and formula (4) and formula ( 5)
High interference obtained by (10) A removal electrode having a component removal rate is arranged, and a through-hole with a radius larger than that provided in the removal electrode located close to the anode and the above-mentioned cathode. A voltage is simultaneously applied to these electrodes by a constant potential power source, and the dissolved O2 concentration is measured while removing interfering components.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 5 to 10. FIG. 5 is a schematic diagram of the dissolved oxygen meter of this embodiment. The dissolved oxygen meter of the embodiment includes a detector body 16, a pressure-resistant container 17 that houses the detector body, a voltmeter 15, and an ammeter 1.
2. It is composed of an external electric circuit system connected to the electrodes inside the detector body, such as a constant pressure source A13, a constant voltage power source B14, etc. An oxygen permeable membrane 3 is installed on the surface of the detector body, and an electrolytic solution 7 is sealed inside. The working electrode 4 is composed of a cathode having a through hole. Further, the interfering component removing electrode (hereinafter referred to as a removal electrode) having a through hole has a rear stage cathode 6a (hereinafter referred to as a rear stage removal electrode) and a front stage cathode 6b (hereinafter referred to as a rear stage removal electrode).
(abbreviated as "pre-stage removal electrode") or (11). 9 is an anode in the measurement electrode, and 8 is an anode that forms a pair with the above-mentioned removal electrode. In addition, the detector is equipped with a device aimed at improving the durability of the detector for measuring high-temperature sample water. That is, the detector is equipped with a bellows 10 that communicates with the electrolyte to absorb thermal expansion of the electrolyte.

However, the oxygen permeable membrane is inserted and supported by a porous metal filter 1 and a porous cathode to improve the durability of the oxygen permeable membrane. ! ! io, to prevent the oxygen permeable membrane from being damaged due to an increase in internal pressure.

In addition, the sample water enters the pressure container from the sample water inlet 19.
The sample water flows out from the sample water outlet 11. Since the pressure container is filled with sample water and the entire detector is immersed in it, a pressure balance is always maintained between the sample water and the electrolyte, preventing damage to the detector body and oxygen permeable membrane. There is no. With these devices, the detector can perform measurements without being damaged even in high-temperature, high-pressure sample water. The main body of the detector is made of heat-resistant materials such as tetrafluoroethylene resin and polyimide resin.
2) Resin is used. A heat-resistant resin with a large oxygen permeability coefficient, such as tetrafluoroethylene resin, is used for the oxygen permeable membrane. The cathode, the first-stage removal electrode, and the second-stage removal electrode are manufactured using metals that are less corrosive even at high temperatures, such as gold, platinum, and silver. For the anodes A and B, Ag/AgC4 electrodes are used, which do not decompose even at high temperatures and are stable, reversible, and highly reliable. Along with this, the electrolyte contains an alkaline solution containing Ct- ions, for example, KCl 1 mot/
An aqueous solution containing 1 mot/l of KOH is used.

The cathode is connected to the anode B via a constant voltage power supply B and an ammeter, and
The front removal electrode and the rear removal electrode are connected to the anode A via a constant voltage power supply A, and by these constant voltage power supplies, the cathode potential with respect to the anode B and the potential of the front removal electrode and the rear removal electrode with respect to the anode A are as follows. , respectively the same potential,
Preferably, the reactor water temperature is maintained at about -0.8V.

02 in the sample water passes through the oxygen permeable membrane and enters the electrolyte in the cathode hole, and while it diffuses inside the electrode hole, the formula (
1) will be refunded. At this time, the reaction of formula (2) progresses on the anode B, and a current flows between the two electrodes. This current is detected by an ammeter, and the dissolved 02 concentration is determined from this current. At this time, Agct generated on the anode B according to equation (2) is dissolved at high temperature and generates Ag'' ions.This Ag+ ion is reduced at the cathode and generates a disturbance current, so the former removal electrode and the latter removal electrode This is reduced and removed using

Since the purpose of the first-stage removal electrode is to remove Ag+ at a high rate, the radius of the through hole is smaller than the length of the through hole, that is, the thickness of the removal electrode, and is preferably manufactured to be 115 mm or less. Ru. At this time, the removal electrode removes 99.999% or more of the interfering components within its through hole. By reducing the radius of the through hole, the electrical resistance of the electrolyte inside the through hole increases, so this is reduced by providing a large number of through holes.

Since this pre-stage removal electrode has a small through-hole diameter, Equation (6) 1
A precipitated as expected from equation (7) and FIG.
g, the through hole is easily blocked and the usage time is short. In order to solve this problem, in this embodiment, a post-removal electrode is installed in the inspection (14) utility area. The rear removal electrode is installed between the front removal electrode, anode A and anode B,
It is held at the same potential as the previous removal electrode and used at the same time as the previous removal electrode. The second-stage removal electrode removes interfering components such as Ag+ ions that diffuse from the anode electrolyte toward the cathode at a low rate as well as the first-stage removal electrode, and after reducing the concentration, the second-stage removal electrode It has the function of spreading to the side. The removal rate of the post-removal electrode is relatively small, and preferably about 95 electrodes are used. Therefore, the diameter of the through hole is relatively large, preferably about 1.25 times the length of the through hole. As shown in equation (7), the closure time of the through hole increases in proportion to the square of the through hole radius,
It increases in inverse proportion to the first power of the ion concentration. Therefore, by using the rear removal electrode and the front removal electrode at the same time, the usage time of the former is greatly extended due to the effect of increasing the through hole radius, and the latter is due to the effect of decreasing the Ag + ion concentration, respectively. And, the removal rate is Ag+
It is sometimes possible to remove interfering components such as ions (15). Figure 6 shows a radius of 0.2 cm and a thickness of 0.
．． A rear removal electrode with a 25 cm through hole and a radius of 0.
025 saw and a pre-stage removal electrode having a through-hole diameter of 0.125 m in thickness are used at the same time at an incorrect reactor water temperature, and the change over time in the through-hole radius of each electrode is shown.

The use time of the post-stage removal electrode is 2000 days or more, and the use time of the pre-stage removal electrode is 600 days or more, that is, the use time is more than 20 times that of the known example removal electrode shown in FIG.

In this example, in addition to the front stage removal electrode, only one rear stage removal electrode was used, but as shown in FIG. It is also possible to do so. In FIG. 7, the rear removal electrode A6C has a larger through hole than the front removal electrode, and is closer to the anode B8 than the front removal electrode, and the rear removal electrode B6d has an even larger penetration hole than the rear removal electrode A. It has a hole and is arranged closer to the anode B than the post-removal electrode A,
These are held at the same potential by a constant voltage power supply 13 and used simultaneously. When this electrode system is used, (16) it is possible to further extend the usage time of each electrode. Although two rear stage electrodes are used in FIG. 7, it is also possible to use a larger number of rear stage electrodes. In addition, in the example shown in Figure 7, the independent front-stage removal electrode and rear-stage removal electrode are used while being held at the same potential at the same time, but as shown in Figure 8, they are brought into direct contact with each other and used as a single electrode. or on the same metal plate as shown in Figure 9.
Provide a through hole whose radius decreases stepwise from the anode side to the cathode side, and use an electrode that has the same function as when using the same electrode as a front stage removal electrode and a plurality of rear stage removal electrodes, and As the electrode plate, it is also possible to use an electrode having a through hole whose radius changes continuously as shown in FIG. 10.

In this example, Ag/A is used as anode A and anode B.
Although an example using a GCT electrode has been described, the method of removing interfering components such as Ag+ ions using the front-stage removal electrode and the rear-stage removal electrode of the present invention is stable at other high temperatures,
Reversible and reliable electrodes, e.g. Ag/AgBr,
Ag/AgI, Ag/AgaPO4, Pb/PbS
It is also effective when using electrodes such as O4, Ag/, Ag2SO4, etc.

As described above, according to this embodiment, the continuous measurable time of the high-temperature, high-pressure dissolved oxygen meter is reduced from the conventional 20 to 30 days to 20 days.
This has the effect of making it possible to extend the period by more than double, that is, to more than 600 days.

Other examples of the removal electrode arranged on the working electrode side of the measurement electrode are shown in FIGS. 11-14. Further, although not shown in the drawings, the cross-sectional shape of the through hole may be triangular, quadrangular, or any other shape other than circular.

In this embodiment, the same explanation has been given for the 03 concentration measuring device, but the present invention can also be applied to a concentration measuring device for measuring other dissolved substances such as H2, 1428° H2O2, or metal ions. In addition, in this example, the cathode was used as the working electrode, but 0
For dissolved substances other than 2, it is also possible to use the anode as a working electrode.

〔Effect of the invention〕

In the case of the high-temperature, high-pressure dissolved oxygen meter using the device of one embodiment of the present invention, the continuous measurement time can be extended from the conventional 20 to 30 days to more than 600 days, so continuous measurement can be performed for about 200 days to one year. It will be possible to apply the high-temperature, high-pressure dissolved oxygen meter as a measurement device for actual plants such as light water reactors and heavy water reactors, where it is essential to have the highest possible performance, and to put it into practical use.

In addition to 02, I4 is present in the reactor water in light water reactors and heavy water reactors.
202 is present and during the sample water cooling operation) Jios is 02
Pyrolyzed into O! Since the concentration changes, it is important for reactor water quality management to directly measure the 02 concentration without cooling the sample water. According to the present invention, in an actual plant,
It has become possible to provide a practical detector that can achieve this purpose, and it is extremely effective in controlling the quality of reactor water and injecting H2 into the reactor water to reduce the dissolved O2 concentration in the reactor water. can provide the means.

[Brief explanation of drawings]

Figure 1 is a schematic longitudinal cross-sectional view showing the basic structure of a conventional high-temperature, high-pressure dissolved oxygen analyzer, and Figure 2 is a graph showing the ratio of the removal electrode through-hole length to the through-hole radius and the removal rate of interfering components in the through-hole. be. FIG. 3 is a cross-sectional view of the removed electrode showing the pattern of Ag crowding in the removed (19) electrode through-hole, and FIG. 4 is a graph showing the change over time in the radius of the through-hole entrance of the removed electrode. FIG. 5 is a schematic cross-sectional view showing the structure of a concentration measuring device according to an embodiment of the present invention, and FIG. 6 is a diagram of the entrance radius of the shell through-hole of the front-stage removal electrode and the rear-stage removal electrode over time when this embodiment is used. It is a figure showing a change. 7 to 14 are cross-sectional views showing the structure of the removal electrode used in the measuring device of the present invention. DESCRIPTION OF SYMBOLS 1...Metal filter, 2...Pedestal, 3...Selective (oxygen) permeable membrane, 4...Cathode, 5...Water hole, 6...
... Electrode for removing interference components (removal electrode), 6a... Electrode after the electrode for removing interference components (removal electrode), 6b...
・Pre-stage electrode of the interfering component removal electrode (pre-stage removal electrode), 6
C... Post-stage removal electrode A, 6d... Post-stage removal electrode B,
7... Electrolyte, 8... Anode A, 9... Anode B11
0...Bellows, 11...Sample water outlet, 12...
Ammeter, 13... Constant potential power source A114... Constant potential power source B115... Voltmeter, 16... Detector body, 17
...Pressure vessel, 18...Sample water, 19...Sample water inlet, 20...Through hole, 21...Analysis (20) Steel tapping. 911 Potato II! 1 躬 2 口(Arc e Saikan Jl sau/(" stone complete hole 10 i wo) Imo 3 Zurod 4 Sen o 10 20 30 40 Light Tsu" FM (Japanese Ugi k Diagram No. 6 system i Dashi day to day (day) Figure 9↑ ↑ Ari + Ari 1 Potato 10 Figure ↑ I A5 + Eight 1 Py-nol Figure I γ Yokokai Ikari ￥; ノ2fi I乍目] O →Continued from page 1 of Iriri lamp, Mutai Li

Claims (1)

[Claims] 1. A measuring electrode consisting of a cathode and an anode having a through hole, one of which serves as a working electrode, an electrolytic solution sealed between the electrodes, and a selection electrode provided near the outside of the working electrode. Concentration of dissolved substances whose main component is an interfering component removal electrode consisting of a permeable membrane and an anode and a cathode that is provided between the measurement electrode and has a through hole arranged so as to have the same polarity as the measurement electrode. In the measuring device, the through hole of the interfering component removing electrode located on the working electrode side of the measuring electrode has a shape that expands continuously or stepwise toward the counter electrode side. concentration measuring device. 2. The dissolved substance concentration measuring device according to claim 1, wherein the interfering component removing electrode disposed on the working electrode side is an integrally molded product. 3. The dissolved substance concentration measuring device according to claim 1, wherein the interfering component removing electrode disposed on the working electrode side is constructed by a combination of a plurality of molded products.