JP3831485B2 - Method for measuring hydrazine concentration - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In this invention, a reagent tank in which a counter electrode and a reference electrode are installed is communicated with a liquid junction of a working electrode installed in a measurement cell, and the concentration of hydrazine contained in the sample water is measured by immersing the working electrode in the sample water. The present invention relates to a hydrazine concentration measurement method.
[0002]
[Prior art]
In a hydrazine concentration measuring apparatus using this type of method, a reagent solution (for example, a KCl solution) contained in a reagent tank as a supporting electrolyte flows into the boiler water while flowing into the boiler water, which is the sample water passing through the measurement cell. The concentration of hydrazine contained is measured.
[0003]
That is, as shown in FIG. 3, a flow path 54 of boiler water S having an inlet 52 and an outlet 53 is formed in the measurement cell 51, and the flow path 54 acts along the flow from upstream to downstream. The electrode 55 and the temperature compensation electrode 56 are provided, the outlet 53 is connected to the drain line 67, and the KCl solution 59 passes through the liquid junction 60 of the working electrode 55 from the upper end to the lower end through the communication path 58 with the reagent tank 57. The KCl solution 59 flows out to the position of the electrode portion 50 formed at the lower end. Note that an R-C electrode 63 composed of an electrode portion (R) of a comparison electrode and a cathode (C) of a counter electrode is installed in an upper part of the reagent tank 57 while being immersed in the KCl solution 59. Reference numeral 64 denotes a float switch.
[0004]
[Problems to be solved by the invention]
Conventionally, the sample water is monitored by setting the flow rate of the boiler water S passing through the measurement cell 51 (hereinafter referred to as the sample flow rate) to 250 mL / min. However, in the hydrazine concentration versus indicated value characteristic under this condition, as shown by the solid line in FIG. 4, when the hydrazine concentration exceeds about 250 ppb, which is the upper limit value of the linear response region R, a straight line as shown by the alternate long and short dash line Therefore, the measurement range of the apparatus could be expanded only to about 200 ppb. For this reason, it has been impossible to monitor sample water having a high hydrazine concentration, such as 20 ppm, which is generated when the boiler is started.
[0005]
Further, since the sample flow rate is large, a calibration liquid tank containing a calibration liquid having a predetermined concentration cannot be provided in the apparatus due to a large amount of calibration liquid used at the time of calibration. As shown in FIG. The calibrated solution a is diluted with the diluent A supplied from the diluent tank 66 outside the apparatus to obtain a calibrated solution having a predetermined concentration, and the calibrated solution is fed to the calibration line 61 that joins the boiler water S supply line 62. It was necessary to provide a calibration solution delivery means 68 for delivery.
[0006]
The present invention has been made in view of the above problems, and an object thereof is to provide a hydrazine concentration measurement method capable of extending the measurement range to sample water having a high hydrazine concentration.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the hydrazine concentration measuring method of the present invention comprises a reagent tank in which a counter electrode and a comparative electrode are installed and a liquid junction of a working electrode installed in a measurement cell, and the reagent is connected through the liquid junction. A hydrazine concentration measurement method for measuring a concentration of hydrazine contained in a sample water while allowing the reagent solution in the tank to flow into the sample water passing through the measurement cell, wherein the liquid junction of the working electrode is a working electrode holder The upper end protrudes upward from the upper end surface of the working electrode holder while being inserted and held in a through hole provided in the upper and lower rubber bushes, and the periphery of the upper end protruding portion is a heat shrinkable tube. The lower end protruding portion is covered with the electrode portion, and the concentration of hydrazine contained in the sample water is measured while flowing the reagent solution transmitted from the upper end to the lower end of the liquid junction portion into the electrode portion. The flow rate of the water sample passing through the measuring cell Utoki, characterized in that it is set to 10-50 ml / min.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0009]
FIG. 1 shows an apparatus for measuring hydrazine concentration used in one embodiment of the present invention, and FIG. 2 shows a straight line of hydrazine concentration corresponding to each sample flow rate when the sample flow rate of boiler water passing through the measurement cell is changed. Indicates the response area.
[0010]
In FIG. 1, reference numeral 1 denotes a reagent tank that stores a reagent solution (for example, KCl solution) 2 as a supporting electrolyte that flows into boiler water S that is sample water. On the upper part of the reagent tank 1, an R-C electrode 3 comprising an electrode part (R) of a comparison electrode and a cathode (C) of a counter electrode is installed in a state of being immersed in the KCl solution 2. A supply port 4 is provided at the bottom of the reagent tank 1 to supply the KCl solution 2 to the later-described measurement cell 6 side via the communication path 20. Reference numeral 5 denotes a float switch, which is juxtaposed with the R-C electrode 3 above the reagent tank 1.
[0011]
Reference numeral 6 denotes a measurement cell through which the boiler water S passes at a predetermined sample flow rate, in which a flow path F of the boiler water S having an inlet 40 and an outlet 41 is formed. A working electrode W and a temperature compensation electrode 7 are juxtaposed on the upper part of the measurement cell 6. An outlet 41 of the measurement cell 6 is connected to a drain line 42, and a packing 8 is fitted on the temperature compensation electrode 7.
[0012]
Reference numeral 43 denotes a calibration liquid tank containing a calibration liquid B having a predetermined concentration, and is provided in the apparatus 44 in the same manner as the reagent tank 1 and the measurement cell 6. The calibration line 45 from the calibration liquid tank 43 joins the boiler water S supply line 46.
[0013]
Further, the liquid junction portion 14 of the working electrode W is inserted and held through a pair of upper and lower rubber bushes in an insertion hole provided in the working electrode holder 13 in the vertical direction. And unlike the liquid junction part 60 of the working electrode 55 shown in FIG. 3, the upper end of the liquid junction part 14 is extended above the upper end surface of the working electrode holder 13, and this upper end protrusion part The periphery (side surface) of 14a is covered with a heat-shrinkable tube. An electrode part (anode) 15 is formed by winding the Pt wire around the lower end protruding part of the liquid junction part 14.
[0014]
During the measurement, the KCl solution sequentially transmitted to the reagent tank 1, the communication path 20, the upper end protruding portion 14 a of the liquid junction portion 14, and the lower end electrode portion 15 is caused to flow into the boiler water S passing through the flow path F. While measuring the concentration of hydrazine contained in the boiler water S.
[0015]
In this case, since the sample flow rate of the boiler water S passing through the flow path F of the measurement cell 6 is set to 10 to 50 mL / min, the linear response region can be increased from the conventional 250 ppb to, for example, 20 ppm. Yes, boiler water S with high hydrazine concentration can be monitored.
[0016]
For example, in FIG. 2, when the sample flow rate is set to 30 mL / min, for example, the upper limit of the linear response region R can be increased to about 10 ppm from the characteristic graph D, and the linearity between the hydrazine concentration and the indicated value can be increased. It can be seen that is improved.
[0017]
Similarly, even when the sample flow rate is set to, for example, 40 mL / min or 50 mL / min, the upper limit of the linear response region can be increased from the conventional 250 ppb indicated by the characteristic graph Q from each of the characteristic graphs P and T. It can be seen that the linearity is improved. The graph M is an ideal straight line.
[0018]
Thus, by reducing the sample flow rate from the conventional 250 mL / min to 10 to 50 mL / min, the linearity was maintained up to a high concentration and the upper limit of the linear response region could be increased for the following reason. Conceivable. That is, since the amount of hydrazine that reacts on the surface of the electrode unit 15 per unit time is determined, when the boiler water S having a large flow rate of 250 mL / min is passed as in the conventional case, for example, the hydrazine concentration increases when the boiler is activated. As a result, the amount of hydrazine exceeds the amount of reaction on the surface of the electrode portion 15, and the reaction rate is controlled, and the increase in the indicated value is slowed down.
However, when the sample flow rate is reduced as in the present invention, even if the hydrazine concentration is increased, the amount of hydrazine does not increase extremely, so that there is a margin in the reaction on the surface of the electrode portion 15. That is, if the sample flow rate is reduced, it becomes a diffusion-controlled state rather than a reaction-controlled state. If the sample flow rate is lowered, the sensitivity is lowered, but the reduced amount can be electrically processed and there is no problem.
[0019]
Further, in the present invention, the amount of the calibration liquid used can be reduced during calibration by reducing the sample flow rate. Further, a calibration liquid tank containing a calibration liquid of a predetermined concentration can be provided in the apparatus, and it is not necessary to provide a calibration liquid delivery means 68 as in the prior art, so that the cost can be reduced.
[0020]
In addition, in the present invention, the upper limit of the linear response region can be extended to about 30 ppm without using a multi-dimensional calibration curve or additional parts having a problem in accuracy or the like only by reducing the sample flow rate.
[0021]
【The invention's effect】
As described above, in the present invention, since the flow rate of the sample water passing through the measurement cell is set to 10 to 50 mL / min, the measurement range of the hydrazine apparatus can be extended to the high concentration side, such as when the boiler is started. Sample water with high hydrazine concentration can be monitored in a transient state. Also, it is possible to provide a small hydrazine device cheaper.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a hydrazine concentration measuring apparatus used in an embodiment of the present invention.
FIG. 2 is a characteristic diagram of hydrazine concentration versus indicated value for each sample flow rate.
FIG. 3 is a clear diagram of the overall configuration of a conventional hydrazine concentration measuring apparatus.
FIG. 4 is a diagram for explaining a conventional problem.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Reagent tank, 2 ... KCl solution, 3 ... RC electrode, 6 ... Measurement cell, 13 ... Working electrode holder, 14 ... Liquid junction part, 15 ... Electrode part, S ... Boiler water, W ... Working electrode.

Claims (1)

The reagent tank in which the counter electrode and the reference electrode are installed communicates with the liquid junction of the working electrode installed in the measurement cell, and the reagent solution in the reagent tank flows into the sample water passing through the measurement cell through the liquid junction. A hydrazine concentration measurement method for measuring the concentration of hydrazine contained in a sample water while allowing
The liquid junction portion of the working electrode is inserted and held in an insertion hole provided in the working electrode holder through a pair of upper and lower rubber bushes, and the upper end of the working electrode is protruded above the upper end surface of the working electrode holder. The periphery of the upper end protrusion is covered with a heat-shrinkable tube, and the lower end protrusion is formed on the electrode part. The reagent solution transmitted from the upper end to the lower end of the liquid junction part flows into the electrode part. A hydrazine concentration measuring method, wherein the flow rate of sample water passing through a measurement cell when measuring the concentration of hydrazine contained in sample water is set to 10 to 50 mL / min.

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