JPH0576576B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for measuring hydrazine concentration, which polarographically measures the hydrazine concentration contained in a liquid to be measured.

<Prior Art> In high-temperature and high-pressure plants, deoxidation treatment is performed by injecting hydrazine, a reducing substance, into water supply in addition to deaeration. Therefore, measuring the residual hydrazine concentration can indicate whether there are low levels of dissolved oxygen. Further, if the amount of hydrazine to be injected is controlled by feeding back the measured concentration signal, excessive injection of hydrazine can be prevented, which is also suitable for energy saving measures. From these viewpoints, hydrazine concentration meters are widely used.

However, the conventional hydrazine concentration meter has a major drawback in that when the pH value of the liquid to be measured changes, the sensitivity of the detection current changes, resulting in an error in reading. Additionally, when the liquid to be measured comes into contact with oxygen such as dissolved oxygen in the measurement container, hydrazine is oxidized and decomposed, resulting in a concentration change, and a concentration value different from the hydrazine concentration initially contained in the liquid to be measured is detected. There was also a drawback.

<Object of the Invention> The present invention has been made in view of the above drawbacks, and its purpose is to suppress hydrazine concentration changes caused by air oxidation and reading fluctuations caused by PH value fluctuations of the liquid to be measured, and to suppress hydrazine concentration changes caused by air oxidation. An object of the present invention is to provide a method for measuring hydrazine concentration that allows the concentration to be measured with high accuracy.

<Means for Solving the Problems> In order to achieve this object, the present invention mixes a reagent consisting of a solution containing potassium chloride, acetic acid, and sodium acetate with a liquid to be measured at a fixed ratio, and adjusts the pH of the mixed liquid. Based on the magnitude of the oxidation current detected when an indicator electrode made of a rotating platinum electrode and a counter electrode made of a silver chloride electrode are immersed in the mixed solution and a constant voltage is applied between these electrodes, This method employs the hydrazine concentration measurement method of measuring the hydrazine concentration in the liquid to be measured.

<Example> Hereinafter, the present invention will be described in detail using the drawings.

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the present invention.

In the figure, 1 is a tank in which a liquid to be measured 2 such as boiler water is stored, and 3 is a tank containing, for example, 10 g of sodium acetate (CH ₃ COONa) and 10 milliliters of acetic acid (CH ₃ COOH) (with a purity of 95% or more). acetic acid),
and 25g of potassium chloride (KCl) in pure water ( _H2
A tank 5 stores a reagent 4 with a pH of 4.7 adjusted to 1 liter by dissolving it in O.
Dual pump that pumps liquid while mixing at 100:3),
6 is a measuring container in which the liquid (mixed liquid) 7 mixed and sent by the dual pump 5 is stored, 8 is an indicator electrode made of a rotating platinum electrode immersed in the mixed liquid 7, and 9 is, for example, 4 mol/liter. a counter electrode consisting of a silver chloride electrode immersed in the mixture 7 with a potassium chloride solution as an internal liquid; 10 a DC power source that applies a constant voltage (for example, +0.6 V) between the indicator electrode 8 and the counter electrode 9; 11
12 is a galvanometer that detects the oxidation current flowing between the indicator electrode 8 and the counter electrode 9;
This is a waste liquid tank to which the above-mentioned mixed liquid 7 (flow) is introduced.

In the embodiment of the present invention having the above configuration, 2
When the continuous pump 5 is driven, the liquid to be measured 2 in the tank 1 and the reagent 4 in the tank 3 are mixed at a constant ratio (for example,
The liquid is supplied into the measurement container 6 while being mixed at a ratio of 100:3), and the overflow from the measurement container 6 is led to the waste liquid tank 12. On the other hand, a constant voltage (for example, +0.6V) is applied between the indicator electrode 8 and the counter electrode 9 by a DC power supply 10, and an oxidation current corresponding to the hydrazine concentration in the liquid mixture 7 is applied between these electrodes. is starting to flow. This oxidation current is detected by a galvanometer 11, and the hydrazine concentration in the liquid to be measured 2 is determined from the value of the detected current.

FIG. 2 shows the above mixed solution 7 using the embodiment of the present invention.
For cases where the PH _{values of} It is a program. In this polarogram, when the PH value is 9.0, the output (μA) shows a larger fluctuation than in other cases. This is because when the liquid mixture 7 becomes alkaline, hydrazine is easily oxidized and decomposed and is greatly affected by air oxidation. Therefore, in order to eliminate the influence of such air oxidation, it is necessary to maintain the PH value of the mixed liquid 7 on the acidic side, and in the example of the present invention, the PH value of the reagent 4 is adjusted to 4.7. Figure 3 shows
A solution containing 0.32 ppm hydrazine (N ₂ H ₄ ) is used as the liquid to be measured 2, and the indicator electrode 8
9 is a graph showing the relationship between the PH value and the output when a DC voltage of +0.6 V is applied between the electrode 9 and the counter electrode 9. FIG. This graph shows that when the PH value of the mixed liquid 7 changes greatly, the output (μA) also changes.
Therefore, in order to prevent such output fluctuations, it is necessary to keep the pH value of the mixed liquid 7 constant, and in the embodiment of the present invention, an acetic acid-sodium acetate solution having buffering properties is used as the reagent 4. ing. In addition, in the reagent 4, for example, 10 to 40 g of potassium chloride (KCl) is dissolved in order to increase the electrical conductivity of the mixed liquid 7 and prevent applied voltage shifts due to IR drop (current/resistance drop). I'm making it 1 liter.

Figure 4 shows an example of the present invention (the above applied voltage is +
0.6V), the hydrazine concentration (ppm) contained in the liquid to be measured 2 was varied, and the relationship between the concentration and the output (μA) was investigated. As is clear from this graph, good linearity is obtained for low concentration hydrazine of 0 to 0.8 ppm when measured using the example of the present invention. still,
The present invention is not limited to the above-described embodiments, and can be modified in various ways. For example, glass beads, ceramic beads, etc. are placed in the measurement container 6, and the iron content in the liquid to be measured 2 is placed between the electrodes 8 and 9. It is also possible to prevent the sensitivity of the detection current from decreasing due to adhesion.

<Effects of the Invention> According to the embodiment of the present invention as described in detail above, a buffered acetic acid-sodium acetate solution (reagent 4) is mixed with the liquid to be measured 2, and the PH value of the mixed liquid is measured. Since this is a method that keeps the temperature constant, the temperature of the measured liquid 2
There is an advantage that even if the PH value fluctuates, the indication does not fluctuate as in the conventional example. In addition, since the PH value of the above mixture is maintained on the acidic side by mixing reagent 4,
The influence of air oxidation as in the conventional example is eliminated, and the hydrazine concentration in the liquid to be measured can be measured accurately.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing the configuration of the embodiment of the present invention, FIG. 2 is a polarogram created using the embodiment of the present invention, and FIG. 3 is a graph showing the relationship between the PH value of the mixed liquid and the output. FIG. 4 is a diagram showing the relationship between hydrazine concentration and output. 1, 12... Tank, 2... Liquid to be measured, 3...
Reagent, 5...double pump, 6...measuring container, 8...
...Indicator electrode, 9...Counter electrode, 10...Power supply, 11...
Galvanometer.

Claims (1)

[Claims] 1. A reagent consisting of a solution containing potassium chloride, acetic acid, and sodium acetate is mixed with a liquid to be measured at a fixed ratio to make the pH of the mixed liquid acidic, and the mixed liquid is heated with a rotating platinum electrode. From the magnitude of the oxidation current detected when an indicator electrode and a counter electrode made of a silver chloride electrode are immersed and a constant voltage is applied between these electrodes,
A method for measuring hydrazine concentration in the liquid to be measured. 2. The reagent has a hydrazine concentration according to claim 1, which is a solution prepared by dissolving 10 g of sodium acetate, 10 milliliters of acetic acid, and 25 g of potassium chloride in pure water to make a total of 1 liter. Measuring method.