JP2533669B2 - Chlorine demand meter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a chlorine demand meter for determining a chlorine injection amount in a water purification plant or the like, and in particular, accurately determines the amount of free chlorine without being affected by bound chlorine. It relates to a chlorine demand meter that can be measured.

[Conventional technology]

In general, discontinuous point chlorination method is used for chlorination. This discontinuous point chlorine treatment method will be described with reference to FIG. FIG. 4 shows changes in chlorine concentration when chlorine is injected into water, and is a diagram showing the relationship between the chlorine concentration in sample water and the chlorine injection amount. Characteristic line A in the figure is the case where chlorine is injected into pure water, and the injection amount becomes free chlorine as it is. Characteristic line B is the case where the water contains an organic or inorganic substance other than ammonia which is relatively easily oxidized by chlorine, and a part of the injection amount is consumed by the oxidation and the rest becomes free chlorine.

On the other hand, the characteristic line C is a case where ammonia nitrogen is contained in water. Monochloramine (NH ₂ C up to point p
Combined chlorine such as l) and dichloramine (NHCl ₂ ) is produced, but after the point p, the combined chlorine is consumed by the reaction of the following formula and the chlorine concentration decreases.

NH ₂ Cl + NHCl ₂ → N ₂ + 3HCl …… (1) NH ₂ Cl + NHCl ₂ + HClO → N ₂ O + 4HCl …… (2) After passing q point called discontinuity, free chlorine (HClO) increases with chlorine injection. To go. Such discontinuous point chlorine treatment method is generally adopted in water purification treatment because it is surely sterilized. At this time, the chlorine injection amount until the set free chlorine concentration is reached is called the chlorine demand amount.

As a device for automatically measuring such a chlorine demand, a chlorine demand meter as shown in FIG. 8 is conventionally known.

In FIG. 8, the chlorine generator 1 electrolyzes the sodium chloride solution in the reagent tank 2 to generate chlorine. In the reaction tank 3, this chlorine and sample water are mixed, and the UV lamp 4
The chlorine consumption reaction is promoted by the irradiation of ultraviolet rays from the above, and the polarographic free chlorine detector 5 further detects free chlorine in the sample water. The amplifier 6 amplifies the signal of the free chlorine detector 5 and sends it to the controller 7, which adjusts the electrolytic current of the chlorine generator 1 so that the free chlorine concentration detected by the free chlorine detector 5 becomes a set concentration. Adjust. The chlorine demand is measured by utilizing the fact that the electrolytic current at this time is proportional to the chlorine demand.

[Problems to be Solved by the Invention]

However, in the conventional chlorine demand meter, since a polarographic free chlorine detector is used to detect free chlorine, there is a problem that free chlorine cannot be accurately measured due to the influence of bound chlorine. The polarographic free chlorine detector applies an appropriate voltage between the electrodes to reduce the amount of free chlorine and measures the amount of free chlorine from its reduction current. This is because the bound chlorine, which is low, is also detected. When the combined chlorine is detected, the chlorine injection amount before the discontinuity point q may be determined as the required chlorine amount.

Particularly in recent years, pollution of environmental water such as rivers and lakes has increased, and the concentration of ammonia has increased, so that the amount of bound chlorine produced is large. For this reason, there is a situation in which free chlorine cannot be accurately measured due to interference with bound chlorine, and it is impossible to determine whether or not sterilization is sufficiently performed, which is a serious problem.

Further, since this detector is immersed in the sample water, there is a problem that the electrode surface is gradually contaminated and must be cleaned frequently.

The present invention has been made in view of the above points, and an object thereof is to provide a chlorine demand meter capable of accurately measuring free chlorine without detecting bound chlorine by improving a free chlorine detector.

[Means for solving the problem]

According to the present invention, the above-mentioned object has a reaction tank 3, a metal oxide semiconductor gas sensor 11 containing In ₂ O ₃ as a main component, and a chlorine generator 1. The reaction tank comprises a reaction section 12 and an extraction section. 13, the reaction part irradiates ultraviolet rays to react free chlorine with the dissolved substances in the sample water, and the extraction part removes the free chlorine remaining in the carrier gas after the reaction with the dissolved substances in the reaction part. The metal oxide semiconductor gas sensor containing In ₂ O ₃ as the main component detects the amount of free chlorine transferred to the carrier gas, and the chlorine generator is an actuator for feedback control, and the electrolytic reaction To generate chlorine to maintain the free chlorine content of the sample water in the reaction tank at a specified value. At this time, the chlorine requirement is calculated so that the chlorine requirement can be calculated from the electrolytic current for chlorine generation and the flow rate of the sample water. Achieved by configuring a meter .

As a method of transferring free chlorine in the sample water into the carrier gas, a tubing method in which a porous tube is immersed in the sample water and the carrier gas is passed through this tube, a head space where the gas phase part above the sample water contacts Method, a bubbling method in which a gas is blown into the sample water.

The semiconductor gas sensor uses In ₂ O on the surface of the potential insulating substrate.
A metal oxide semiconductor thin film containing ₃ as a main component is formed, and the gas component is detected by the resistance change of the semiconductor thin film.

Both hypochlorous acid and bound chlorine in the sample water move into the carrier gas upon contact with the carrier gas. The metal oxide semiconductor gas sensor based on In ₂ O ₃ does not respond to bound chlorine. The hypochlorous acid transferred from the sample water into the carrier gas can be used as it is or in the decomposed state.
It is presumed that the resistance of the metal oxide semiconductor type gas sensor containing In ₂ O ₃ as a main component is changed.

[Action]

The metal oxide semiconductor gas sensor based on In ₂ O ₃ does not respond to bound chlorine. Since the metal oxide semiconductor gas sensor containing In ₂ O ₃ as a main component comes into contact with free chlorine in the carrier gas, the electrode surface is not contaminated.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings. First
FIG. 1 is a block diagram showing a chlorine demand meter according to a practical example of the present invention. It differs from the conventional chlorine demand meter in that the polarographic free chlorine detector 5 is replaced with an extraction unit 13 and a metal oxide semiconductor gas sensor 11 containing In ₂ O ₃ as a main component. The extraction unit 13 transfers free chlorine in the sample water into the carrier gas. Carrier gas is bubbled from the diffuser 10 and free chlorine (HC
lO) moves into the gas phase.

FIG. 7 is a diagram showing the pH dependence of the HClO existence ratio (%) in the sample water. Hypochlorous acid, which is free chlorine in sample water, is in the following dissociation equilibrium state. That is, HClOH ⁺ + ClO ⁻ (3) This hypochlorous acid HClO is produced by the reaction of chlorine and water as shown in equation (4).

Cl ₂ + H ₂ CHClO + HCl (4) The existence ratios of the hypochlorite HClO and the hypochlorite ion ClO ^{− in the} formula (3) differ depending on the pH of the sample water. For example, if the pH of the sample water is on the acidic side (region where the pH is less than 7), HClO
Occupies the majority, and less ClO ⁻ ions. On the other hand, on the alkaline side (region where the pH is greater than 7), the ratio of ClO ⁻ ions increases and the amount of HClO decreases. It is HClO hypochlorite that is transferred from the sample water to the carrier gas by vapor-liquid equilibrium. Hypochlorite ion ClO ^- can not migrate into the gas phase. It is necessary that the pH be constant when extracting free chlorine from sample water.

FIG. 6 shows a metal oxide semiconductor gas sensor containing In ₂ O ₃ as a main component, FIG. 6 (a) is a perspective view, and FIG. 6 (b).
Is a sectional view. A metal oxide semiconductor type gas sensor whose main component is In ₂ O ₃ is an electrically insulating substrate such as an alumina substrate.
21, In ₂ O ₃ formed on the surface of alumina substrate 21 by vapor deposition
Metal oxide semiconductor thin film 22 mainly composed of, semiconductor thin film 22
It is composed of a Pt film electrode 23 for measuring the change in resistance of the platinum film heater 24 and a platinum film heater 24 formed on the back surface of the alumina substrate 21 for avoiding deterioration of sensitivity with time due to water and oil in the gas phase.

The measurement of free residual chlorine by the metal oxide semiconductor type gas sensor containing In ₂ O ₃ as a main component is performed as follows. After mixing with chlorine in the reaction tank 3, the carrier gas is blown from the diffuser 10 into the sample water that has been irradiated with ultraviolet rays to accelerate the reaction and the chlorine consumption reaction has ended. Since free chlorine is volatile, it is volatilized in this carrier gas. At this time, the free chlorine in the gas is proportional to the concentration in the sample water. Free chlorine is then detected in the carrier gas by a metal oxide semiconductor gas sensor whose main component is In ₂ O ₃ .

In a metal oxide semiconductor type gas sensor containing In ₂ O ₃ as a main component, free chlorine is adsorbed on the metal oxide semiconductor thin film and changes the resistance of this semiconductor thin film. Since the degree of resistance change is proportional to the free chlorine concentration, the push button concentration in the carrier gas, and thus the free chlorine concentration in the sample water, can be measured.

FIG. 5 is a diagram showing the calibration relationship between the free chlorine concentration (mg / l) in the sample water and the sensor output of the metal oxide semiconductor gas sensor whose main component is In ₂ O ₃ . It can be seen that the logarithm of the sensor output is proportional to the logarithm of the free chlorine concentration. Again this
The metal oxide semiconductor type gas sensor containing In ₂ O ₃ as a main component did not detect the residual residual chlorine, and the sensor did not respond to both monochloramine: 4.9 mg / l and dichloramine: 7 mg / l.

The output of the metal oxide semiconductor gas sensor containing In ₂ O ₃ as a main component is amplified by the amplifier 6, and the electrolytic current of the chlorine generator 1 is adjusted by the controller 7 so that the difference from the set value becomes zero.
After converting the electrolysis current value into the chlorine generation amount M per hour, this M is divided by the flow rate N of the sample water flowing through the reaction tank 3.
When M / N is calculated, this is the chlorine demand per unit amount of sample water. The bubbling type chlorine demand meter is characterized by its excellent sensitivity and response.

FIG. 2 is a block diagram showing a chlorine demand meter according to another embodiment of the present invention. It differs from FIG. 1 in that the headspace method is used in the extraction section for transferring free chlorine into the carrier gas. Since the free chlorine in the sample water of the extraction unit 13 diffuses from the water surface to the gas phase, the free chlorine in the sample water is measured as in the device shown in FIG. The headspace type chlorine demand meter has the features that it can be adjusted to a medium level, with sensitivity and responsiveness.

FIG. 3 is a block diagram showing a chlorine demand meter according to a further different embodiment of the present invention. What is Fig. 1 and Fig. 2?
The difference is that tube 13 is used for tube 13. Tube 14
Is made of, for example, a porous fluororesin, and when the carrier gas flows through the tube, free chlorine in the sample water permeates the micropores of the porous tube and diffuses into the carrier gas. As a tube, for example, maximum pore diameter 2.0 μm, porosity 5
0%, inner diameter 2 mm, wall thickness 0.4 mm, length 600 mm. The tubing type chlorine demand meter has an advantage that the sensitivity can be changed by adjusting the fine pores.

〔The invention's effect〕

According to this invention, it has a reaction tank, a metal oxide semiconductor type gas sensor containing In ₂ O ₃ as a main component, and a chlorine generator, and the reaction tank is divided into a reaction section and an extraction section, and the reaction section The part is for irradiating ultraviolet rays to react free chlorine with the dissolved substance in the sample water, and the extraction part is for moving and extracting the free chlorine remaining after the reaction with the dissolved substance in the reaction part into the carrier gas, The metal oxide semiconductor type gas sensor whose main component is In ₂ O ₃ detects the amount of free chlorine transferred to the carrier gas, and the chlorine generator is a feedback control actuator, which generates chlorine by electrolytic reaction, The amount of free chlorine in the sample water inside is maintained at a specified value. At this time, the chlorine demand is calculated from the electrolytic current for chlorine generation and the flow rate of the sample water. Only free chlorine Is detected by a metal oxide semiconductor gas sensor containing In ₂ O ₃ as a main component, and a chlorine demand meter capable of accurately measuring free chlorine can be obtained. Further, since the metal oxide semiconductor gas sensor containing In ₂ O ₃ as a main component responds to free chlorine in the carrier gas, a chlorine demand meter with excellent reliability can be obtained without contaminating the sensor surface.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing a chlorine demand meter according to an embodiment of the present invention, and FIG. 2 is a configuration diagram showing a chlorine demand meter according to another embodiment of the present invention. FIG. 4 is a block diagram showing a chlorine demand meter according to still another embodiment of the present invention, FIG. 4 is a diagram showing the relationship between chlorine concentration in sample water and chlorine injection amount, and FIG. 5 is a bubbling type chlorine demand. Fig. 6 is a diagram showing the calibration relationship between the free chlorine concentration of the sample water and the sensor output for the meter, Fig. 6 shows the metal oxide semiconductor type gas sensor containing In ₂ O ₃ as the main component, and Fig. 6 (a). Is a perspective view, FIG. 6 (b) is a cross-sectional view, FIG. 7 is a diagram showing the relationship between the proportion of HClO present in sample water and pH of sample water, and FIG. 8 is a configuration diagram showing a conventional chlorine demand meter. Is. 1: Chlorine generator, 2: Reagent tank, 4: UV lamp, 5: Free chlorine detector, 6: Amplifier, 7: Controller, 8: Power supply, 10: Diffuser, 11: In ₂ O ₃ as main components Metal oxide semiconductor gas sensor, 21: alumina substrate, 22: semiconductor thin film, 23: Pt film electrode, 24: Pt film heater, 12: reaction part, 13: extraction part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Shinohara 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Inventor Yoshitaka Takada 2-5, Mitsuyanaka, Yodogawa-ku, Osaka-shi, Osaka No. 4 Inside New Cosmos Electric Co., Ltd. (72) Inventor Sakai Satoshi 2-5-4 Mitsuyachu, Yodogawa-ku, Osaka-shi, Osaka Prefecture Inside New Cosmos Electric Co., Ltd. (72) Toyoaki Aoki, Kusunoda Noda, Hirakata-shi, Osaka 37-32 (56) Reference JP-A-3-140855 (JP, A) JP-A-2-248851 (JP, A) JP-A-3-41360 (JP, A) JP-A-2-285260 ( JP, A) Actual Kaihei 3-81554 (JP, U) Japanese Patent Sho 53-3277 (JP, B2)

Claims (1)

(57) [Claims] 1. A reaction tank, a metal oxide semiconductor type gas sensor containing In ₂ O ₃ as a main component, and a chlorine generator. The reaction tank is divided into a reaction section and an extraction section. The part is for irradiating ultraviolet rays to react free chlorine with the dissolved substance in the sample water, and the extraction part is for moving and extracting the free chlorine remaining after the reaction with the dissolved substance in the reaction part into the carrier gas, The metal oxide semiconductor gas sensor containing In ₂ O ₃ as a main component detects the amount of free chlorine transferred to the carrier gas, the chlorine generator is a feedback control actuator, and generates chlorine by an electrolytic reaction. A chlorine demand meter for maintaining the free chlorine amount of sample water in a reaction tank at a predetermined value, wherein the chlorine demand amount is calculated from the electrolytic current of chlorine generation and the flow rate of sample water.