JP4894003B2 - Silica concentration measuring device - Google Patents

Description

  The present invention relates to a silica concentration measuring apparatus for measuring the silica concentration of a sample.

If the silica (silicon dioxide: SiO ₂ ) concentration in circulating water such as cooling towers and boilers exceeds a certain level, serious problems such as scale adhesion will occur. A silica concentration measuring device for measuring the silica concentration in the inside is provided.

  The silica concentration measurement method is also stipulated in Japanese Industrial Standard (JIS K 0101: 1998 44. Silica). Typical examples are molybdenum yellow absorptiometry (molybdenum yellow method) and molybdenum blue absorptiometry (molybdenum). Blue method).

  The molybdenum yellow absorptiometry is a method for quantifying silica by measuring the yellow absorbance of a heteropoly compound produced by reacting ionic silica with hexaammonium heptamolybdate. Molybdenum blue absorptiometry is a method in which the heteropoly compound produced by the reaction of ionic silica with hexaammonium heptamolybdate is reduced with L (+)-ascorbic acid to molybdenum blue, and the absorbance is measured. This is a method for quantifying silica.

Conventional silica concentration measuring devices are disclosed in, for example, the following patent documents.
JP-A-7-43306 Japanese Patent No. 3353096

  Patent Document 1 discloses a silica concentration measuring apparatus that can automatically switch between high-speed analysis by the molybdenum yellow method and high-precision analysis by the molybdenum blue method by switching a plurality of interference filters that transmit only a predetermined wavelength region. ing. Patent Document 2 discloses a silica concentration measuring device using a light emitting diode as a light source in molybdenum yellow absorptiometry.

  By the way, the conventional silica concentration measuring apparatus has a problem that the resolution decreases when the silica concentration increases. This is due to the fact that the amount of change in transmittance with respect to the change in silica concentration decreases as the silica concentration increases. In particular, when the concentration exceeds a certain level, the change in the transmittance with respect to the change in the silica concentration becomes extremely small, the resolution is greatly lowered, and the measurement accuracy is deteriorated.

  For example, since the silica concentration of the feed water supplied to the boiler and the boiler water differ greatly, if you try to measure both silica concentrations with a single silica concentration measuring device, the resolution when measuring boiler water with a high silica concentration In some cases, measurement was impossible. However, the conventional silica concentration measuring apparatus does not consider the decrease in resolution when the silica concentration is high.

  The present invention has been made in view of such a problem, and provides a silica concentration measuring apparatus capable of preventing the resolution from greatly fluctuating depending on the silica concentration in a sample and degrading the measurement accuracy. With the goal.

  In order to solve the above problems, a silica concentration measuring device according to the present invention is a silica concentration measuring device that measures the silica concentration of a sample from the transmittance or absorbance of a sample into which a reagent has been injected. A light emitting element capable of selectively emitting light, a light receiving element, and the low measurement wavelength in the low concentration region where the silica concentration is lower than the predetermined threshold, and the high measurement in the high concentration region higher than the predetermined threshold. And a control means for controlling the light emitting element so as to use a wavelength.

  Further, the silica concentration measurement method according to the present invention can selectively emit at least two types of measurement wavelengths in the silica concentration measurement method of measuring the silica concentration of the sample from the transmittance or absorbance of the sample into which the reagent is injected. Using the light emitting element and the light receiving element, measuring the transmittance of the sample, calculating the silica concentration of the sample using the measured transmittance, and using the low measurement wavelength In addition, when entering a high concentration region where the silica concentration is higher than a predetermined threshold, the step of switching the measurement wavelength to the high measurement wavelength, and when using the high measurement wavelength, the silica concentration is lower than the predetermined threshold. And a step of switching the measurement wavelength to the low measurement wavelength when entering a low low concentration region.

  According to the silica concentration measuring device according to the present invention, it is possible to provide a silica concentration measuring device capable of preventing the resolution from greatly fluctuating depending on the silica concentration in the sample and degrading the measurement accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, a case where the present invention is applied to the molybdenum yellow method will be described as an example. FIG. 1 is a cross-sectional view schematically showing a silica concentration measuring apparatus according to this embodiment. As shown in FIG. 1, the silica concentration measuring device 1 includes a transparent container 10, a liquid discharge device 11, a measuring device 20, a sample water supply line 30, and a discharge line 40.

  The transparent container 10 has a transparent cylindrical shape molded from an acrylic resin, and has a small hole 14 at the connection portion with the supply line 30 and a small hole 15 at the connection portion with the discharge line 40. A liquid discharge device 11 is disposed on the upper surface of the transparent container 10, and the discharge liquid of the liquid discharge device 11 is configured to be injected into the transparent container 10. The liquid discharge device 11 holds a reagent containing ammonium molybdate inside, and discharges and supplies a desired amount of reagent into the transparent container 10. Moreover, the stirring apparatus 12 is installed in the bottom part of the transparent container 10, and the sample in a container can be stirred and concentration etc. can be aimed at.

  The measuring device 20 includes a light emitting element 21, a light receiving element 22, and a control circuit 23 as a control unit that controls these and performs various calculations. The light emitting element 21 is a light emitting element whose emission wavelength can be switched under the control of the control circuit 23. In the present embodiment, light of two types of wavelengths of 430 nm (low measurement wavelength) and 450 nm (high measurement wavelength) is switched. Emits light. The reason why 430 nm and 450 nm are selected as the measurement wavelengths will be described later. The control circuit 23 stores a calibration curve described later in an internal memory for each measurement wavelength.

  The wavelength can be switched by preparing a plurality of LEDs (light emitting diodes) having different emission wavelengths and switching them mechanically. Alternatively, an interference filter having a different transmission wavelength may be prepared for a light emitting element having a predetermined emission band, and the measurement wavelength may be switched by switching the interference filter. The light receiving element (PD: Photodiode) 22 may be one as long as it is a light receiving element capable of receiving all the measurement wavelengths. A light receiving element may be arranged opposite to each LED, and an output may be selected.

  The output of the light receiving element 22 is transmitted to the control circuit 23, and the control circuit 23 calculates the silica concentration in the sample water, which is the sample, from the measured transmittance using the calibration curve. The calibration curve is prepared in advance as a relation line between the silica concentration and the transmittance using a silica standard solution, and is held in a memory in the control circuit 23.

  The supply line 30 supplies sample water such as boiler water or feed water as a sample into the transparent container 10, and supplies the sample water into the transparent container 10 through the small hole 14. The supply line 30 includes a solenoid valve 31. The discharge line 40 discharges the liquid in the transparent container 10 to the outside through the small hole 15.

Next, the reason why 430 nm and 450 nm are selected as the measurement wavelengths in this embodiment will be described. FIG. 2 is a graph showing the relationship (calibration curve) between silica concentration and transmittance for each measurement wavelength in the molybdenum yellow method, where the horizontal axis is silica concentration [mgSiO ₂ / l] and the vertical axis is transmittance [% T ] Is shown. As measurement wavelengths, seven measurement wavelengths of 410 nm, 420 nm, 430 nm, 440 nm, 450 nm, 460 nm, and 470 nm are shown. In FIG. 2, calibration curves are shown when the thick two-dot chain line is 410 nm, the thick short wave line is 420 nm, the two-dot chain line is 430 nm, the one-dot chain line is 440 nm, the short wave line is 450 nm, the wavy line is 460 nm, and the solid line is 470 nm. Yes.

As shown in the figure, the shorter the measurement wavelength, the larger the slope of the graph in the low concentration region (for example, 0 to 30 mg SiO ₂ / l), and the larger the change in transmittance when the concentration changes. That is, since the resolution is high, it is desirable to measure at a measurement wavelength with a short wavelength in the low concentration region. However, when the measurement wavelength is 410nm and 420nm from around beyond 60mgSiO ₂ / l, which rapidly decreases resolution, 410nm and 420nm of the calibration curve, the concentration measurement of 60mgSiO ₂ / l than is Not suitable.

On the other hand, at the measurement wavelengths of 450 nm and 460 nm, the calibration curve is inclined to some extent even in a high concentration region (for example, 100 to 200 mg SiO ₂ / l), and the desired resolution is maintained. Therefore, it is desirable to use a measurement wavelength having a long wavelength in the high concentration region.

  Thus, when the silica concentration is different, the wavelength suitable for the measurement is also different. Therefore, a desired resolution can be obtained by preparing a plurality of measurement wavelengths and selecting an appropriate measurement wavelength according to the silica concentration.

Therefore, the inventors selected a plurality of appropriate measurement frequencies with reference to FIG. FIG. 3 is a graph showing the transmittance at each silica concentration for each measurement wavelength. The horizontal axis represents the measurement wavelength, and the vertical axis represents the silica concentration (ppm = mgSiO ₂ / l. Hereinafter, mgSiO ₂ / l is expressed as ppm. In some cases, each mass that intersects indicates the transmittance [% T] at the measurement wavelength and silica concentration. In addition, on the right side of each transmittance, a difference in transmittance between the vertically adjacent cells, that is, a change amount of transmittance per 10 ppm [% T / 10 ppm] is shown.

  First, in selecting a low measurement wavelength, the present inventors focused on a low concentration region of 0 to 70 ppm, and considered that if the transmittance change amount / 10 ppm in this region is 4.5 or more, an appropriate resolution can be maintained. , 430 nm and 440 nm are listed as candidates. Since 430 nm has a larger amount of change in most of the low concentration region, 430 nm was selected as the low measurement wavelength.

  Subsequently, in selecting a high measurement wavelength, paying attention to the high concentration region of 70 to 200 ppm, it is considered that if the transmittance change amount / 10 ppm in this region is 2.0 or more, an appropriate resolution can be maintained. There is no measurement wavelength that satisfies a change rate of 2.0 or more at all 200 ppm, but if it is 450 nm and 460 nm, this condition is satisfied at 70 to 170 ppm or 70 to 180 ppm, and 450 and 460 nm are candidates for high measurement wavelength. did. Since 450 nm has more regions where the amount of change is larger, 450 nm was selected as the high measurement wavelength.

  In this way, in this embodiment, a light emitting element 21 having a 430 nm LED as a low wavelength light emitting element and a 450 nm LED as a high wavelength light emitting element is prepared and switched, thereby enabling a wide silica concentration range. High resolution is maintained and high measurement accuracy is achieved.

Of course, the wavelength of the light emitting element 21 is not limited to 430 nm and 450 nm, and any combination of wavelengths that can maintain high resolution in a wide silica concentration region (0 to ₂₀₀ mg SiO ₂ / l in the present embodiment) Other measurement wavelengths can be used as appropriate. Further, the range of the low concentration region using the low measurement wavelength and the range of the high concentration region using the high measurement wavelength can be appropriately set according to the selected measurement wavelength.

  For example, 410 nm may be selected as the low measurement wavelength in the low concentration region of 0 to 40 ppm, and 460 nm may be selected as the high measurement wavelength in the high concentration region of 40 to 200 ppm. Further, three measurement wavelengths of low, medium and high, or four or more measurement wavelengths may be set.

  In this embodiment, the measurement wavelength is set from the calibration curve of silica concentration and transmittance shown in FIGS. 2 and 3, but the measurement wavelength is determined with reference to the calibration curve of silica concentration and absorbance (Abs). You can also choose. The absorbance can be determined from the transmittance, and absorbance = −log (transmittance / 100). Therefore, the slope of the absorbance calibration curve also represents the resolution in the same way as the change in transmittance.

  Next, the timing of switching the measurement wavelength between the light emitting elements 21 will be described. The switching of the measurement wavelength is executed under the control of the control circuit 23. As described above, in the low concentration region where the silica concentration is 0 to 70 ppm, it is desirable from the aspect of resolution that the amount of change in transmittance [% T] per 10 ppm is 4.5 or more. At a low measurement wavelength of 430 nm, the silica concentration is In the region between 70 ppm and 80 ppm, that is, in the region where the transmittance [% T] is 16.84 to 13.13, the transmittance change amount [% T / 10 ppm] is 4.5 or less.

  Therefore, in this embodiment, when using a low measurement wavelength (430 nm), when the transmittance is 16.5 or less, the silica concentration is measured as a high concentration region higher than a predetermined threshold. The wavelength is switched to the high measurement wavelength (450 nm). Specifically, the control circuit 23 monitors the output of the light receiving element 22 and controls to switch the LED when the transmittance becomes 16.5 or less.

  Of course, the measurement wavelength may be switched when the silica concentration is higher than a predetermined value based on the silica concentration calculated by the calibration curve from the transmittance. For example, in the present embodiment, 70 ppm may be used as a threshold, and the silica may be switched to a high measurement wavelength when the silica concentration exceeds 70 ppm. Similarly, the measurement wavelength may be switched based on the absorbance calculated from the transmittance.

  Regarding the switching from the high measurement wavelength to the low measurement wavelength, referring to FIG. 3, the transmittance [% T] at a silica concentration of 80 ppm at the measurement wavelength of 450 nm is 48.13. When the value becomes 48.5 or more, the LED is switched from 450 nm to 430 nm on the assumption that the silica concentration is a low concentration region lower than a predetermined threshold value.

  Of course, the switching from the high measurement wavelength to the low measurement wavelength may be performed based on the silica concentration. In this case, the same 70 ppm as in the case of switching from the low measurement wavelength to the high measurement wavelength can be set as the threshold value, and when the silica concentration becomes 70 ppm or less, the low measurement wavelength may be switched. Further, even when switching from the high measurement wavelength to the low measurement wavelength, it may be configured to switch based on the absorbance.

  The configuration of the silica concentration measuring device 1 according to the present embodiment has been described in detail above. Subsequently, the flow of processing when the silica concentration measuring device 1 measures the silica concentration will be described. FIG. 4 is a flowchart showing a processing flow in the silica concentration measurement according to the present embodiment. Here, a case where the measurement wavelength is switched based on the silica concentration will be described as an example, and it is assumed that a low measurement wavelength (430 nm) is set as the measurement wavelength in the initial setting.

  As shown in the figure, first, in S 10, the electromagnetic valve 31 is opened, and the sample water sample is caused to flow into the transparent container 10 from the supply line 30. Subsequently, in S <b> 11, a reagent is injected into the transparent container 10 from the liquid ejection device 11. In this embodiment, the silica concentration is measured by the molybdenum yellow method, and a reagent comprising an ammonium molybdate aqueous solution 10 w% and a 47% sulfuric acid solution 24 w% is used.

  After injecting the reagent in S11, the reagent is left for 10 minutes while stirring with the stirring device 12 (S12). Then, it progresses to S13 and the transmittance | permeability is measured. The light emitted from the light emitting element 21 and transmitted through the sample in the transparent container 10 is received by the light receiving element 22, and the transmittance is obtained in the control circuit 23 from the output of the light receiving element 22.

  In S14, the control circuit 23 calculates the silica concentration from the transmittance measured in S13 based on the calibration curve for the low measurement wavelength. In S16, it is determined whether or not the silica concentration calculated in S14 is greater than 70 ppm. In the case of 70 ppm or less, it is a low concentration region, and sufficient resolution can be obtained by measurement at a low measurement wavelength as described above. Therefore, the silica concentration calculated in S14 is used as a measurement value as it is, and the measurement ends.

  If the calculated concentration is larger than 70 ppm in S16, it is a high concentration region, and the resolution at the low measurement wavelength is not sufficient as described above. Therefore, the process proceeds to S17 and the measurement wavelength is controlled by the control circuit 23. Switch. That is, in the light emitting element 21, the measurement wavelength is switched from the low measurement wavelength to the high measurement wavelength by switching from the 430 nm LED to the 450 nm LED.

  Thereafter, the process proceeds to S18, where the transmittance is measured with a high measurement wavelength. In S19, the control circuit 23 calculates the silica concentration using the calibration curve from the transmittance measured in S18, and the measurement ends. Such processing is realized by the control circuit 23 executing a sequence program stored in a memory in the circuit.

  As described above, the silica concentration measuring apparatus 1 according to the present embodiment has been described in detail. However, according to the present embodiment, in the measurement of the silica concentration, the silica concentration measuring device 1 is divided into a low concentration region and a high concentration region. Since concentration measurement is performed by setting a measurement wavelength, high-accuracy measurement is possible in a wide concentration region. In particular, the conventional silica concentration measurement device that has only measured at one measurement wavelength has a problem with the measurement accuracy in the high concentration region, but in this embodiment, the measurement can be performed with high accuracy even in the high concentration region. It is.

  The embodiment of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, the case where the present invention is applied to the molybdenum yellow absorptiometry is described as an example, but the present invention can also be applied to other silica concentration measuring apparatuses such as a molybdenum blue absorptiometry. In this case, the setting of a plurality of measurement wavelengths and the threshold value that is the boundary of the concentration region for wavelength switching need to be appropriately set with reference to the calibration curve of each measurement method.

(Modification 1)
Subsequently, Modification 1 of the present embodiment will be described. FIG. 5 is a diagram schematically showing the configuration of the dilution unit 50 according to the first modification. In the first modification, the molybdenum yellow method according to the present embodiment is difficult to measure the silica concentration when the silica concentration exceeds 200 mg SiO ₂ / l. It is characterized in that a dilution unit for diluting the sample water is additionally installed in the silica concentration measuring apparatus 1 so as to be within the range of 0 to ₂₀₀ mg SiO ₂ / l).

  As shown in FIG. 5, the dilution unit 50 includes a multi-way valve 51, a syringe 52, and prefilters 53 and 54, and is connected and arranged on the upstream side of the electromagnetic valve 31 of the supply line 30 in FIG. Sample water is supplied to the upstream pipe of the pre-filter 53, and dilution water is supplied to the upstream pipe of the pre-filter 54.

  As dilution water, supply water (for example, raw water, soft water, feed water into which chemicals are not added), drain water, or the like on the primary side of equipment that condenses water such as a cooling tower or a boiler can be used. Further, the dilution unit 50 may be configured to incorporate dilution water. In addition, when diluting water is incorporated, it is possible to prevent generation of bacteria in the diluting water by using the diluting water to which sodium hypochlorite is added.

  In such a configuration, by using the multi-way valve 51 and the syringe 52, the sample supplied into the transparent container 10 is a sample water only, a dilution water only, a sample water mixed with a desired amount of dilution water, And can be switched easily.

  In the measurement, first, the silica concentration of only the dilution water is measured, and then the silica concentration of the mixed sample of the sample water and the dilution water is measured. Then, the silica concentration of the sample water can be calculated by subtracting the silica concentration of the dilution water from the silica concentration of the mixed sample according to the mixing ratio.

The mixing ratio of the dilution water may be diluted so as to be not more than a measurable upper limit silica concentration (200 mg SiO ₂ / l in the present embodiment). For example, in the case of boiler water with a control value of 600 mg SiO ₂ / l, the sample water (boiler water) may be set to be diluted 10 times from the beginning. If the application to which the silica concentration measuring apparatus according to the first modification is applied is fixed, the dilution rate is fixed, and the silica concentration of the reagent water is adjusted by applying a correction coefficient to the silica concentration of the mixed sample. What is necessary is just to comprise so that it may measure.

  According to the first modification, the silica concentration can be measured even with sample water having a high silica concentration, which is difficult to measure with the silica concentration measuring apparatus according to the embodiment. Further, it is possible to measure a high concentration of sample water by a simple improvement such as adding the dilution unit 50 before the supply line 30 of the silica concentration measuring apparatus 1 without greatly improving the apparatus.

  In the case of a sample having a high silica concentration, such as boiler water, it is desirable to always perform measurement by diluting about 10 times using the dilution unit according to the first modification.

(Modification 2)
Then, the modification 2 of this embodiment is demonstrated. This modification 2 is characterized in that temperature correction is performed on the measured silica concentration in order to eliminate measurement errors due to water temperature. When the temperature of the sample water or the reagent is low, the reaction between silicic acid and molybdic acid is slow, so the formation of silicomolybdic acid complex becomes dull and it takes a long time to reach the maximum coloration. Therefore, if the transmittance is measured without sufficient time, an error may occur in the measurement result.

  For this reason, in the second modification, when a temperature sensor is installed in the transparent container 10 and the water temperature of the sample is low, the measurement time is constant, and the measurement value is multiplied by a correction factor considering the water temperature. This prevents the measurement accuracy from being lowered.

  Specifically, with respect to a water temperature of 15 ° C. or less, a calibration curve for each temperature measured in a state where a sufficient time has elapsed since the injection of the reagent, and a state in which 10 minutes have passed in the same manner as in S12 of the above embodiment. A temperature correction coefficient for each temperature is obtained in advance from a calibration curve for each temperature. In the measurement, as in the above embodiment, the measurement is performed 10 minutes after the reagent is injected, and the final silica concentration is obtained by multiplying the measured value by the temperature correction coefficient of the temperature.

  If the water temperature is too low, such as 10 ° C. or lower, the maximum color may not be reached even after a sufficient time has elapsed since the reagent was injected. In such a case, an appropriate temperature correction coefficient can be obtained by using a calibration curve measured by heating.

  In this way, by performing temperature correction for the measured value in consideration of the water temperature of the sample, when measuring a low-temperature sample that takes a long time to react, or even when sufficient time has passed, the maximum color is not reached. Even when measuring a sample having such a water temperature, it is possible to measure the silica concentration with high accuracy in a short time.

(Modification 3)
Then, the modification 3 of this embodiment is demonstrated. The third modification is characterized in that a heating device for heating the sample is added. As described above, when the water temperature of the sample is low, it may take a very long time to reach the maximum coloration. Further, when the water temperature of the sample is too low, the maximum color may not be reached even after a sufficient time has elapsed.

  In order to solve such a problem, the silica concentration measuring device according to the third modification has a heater as a heating device in the transparent container 10, and in the stirring / leaving step of S12, for example, It is comprised so that it may heat to 40 degreeC. Therefore, according to the third modification, even when the water temperature of the sample is low, the problem that the maximum color is not reached does not occur, and the silica concentration can be measured with high accuracy in a short time.

FIG. 1 is a diagram schematically illustrating a configuration of a silica concentration measuring apparatus according to an embodiment. FIG. 2 is a diagram illustrating a calibration curve for each wavelength according to the embodiment. FIG. 3 is a diagram illustrating the transmittance at each silica concentration for each measurement wavelength according to the embodiment. FIG. 4 is a flowchart showing a flow of processing in the silica concentration measurement according to the embodiment. FIG. 5 is a diagram schematically illustrating a configuration of a dilution unit according to the first modification of the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silica density | concentration measuring apparatus 10 Transparent container 11 Liquid discharge apparatus 12 Stirring apparatus 14,15 Small hole 20 Measuring device 21 Light emitting element 22 Light receiving element 23 Control circuit 30 Supply line 31 Solenoid valve 40 Discharge line

Claims (5)

In the silica concentration measuring device that measures the silica concentration of the sample from the transmittance or absorbance of the sample injected with the reagent,
A light emitting device capable of selectively emitting at least two types of measurement wavelengths,
A light receiving element;
Control means for controlling the light emitting element to use the low measurement wavelength in a low concentration region where the silica concentration is lower than a predetermined threshold, and to use the high measurement wavelength in a high concentration region higher than the predetermined threshold;
A silica concentration measuring device comprising:   The control means has a calibration curve for calculating the silica concentration from the transmittance or absorbance of the sample for each measurement wavelength, and the calibration curve is switched according to the switching of the measurement wavelength. The silica concentration measuring device according to claim 1. The silica concentration measuring device is a measuring device for measuring silica concentration by molybdenum yellow absorptiometry,
3. The silica concentration measuring apparatus according to claim 1, wherein the low measurement wavelength is a wavelength between 410 nm and 440 nm, and the high measurement wavelength is a wavelength between 450 nm and 460 nm.   The silica concentration measuring device according to any one of claims 1 to 3, further comprising a diluting device for diluting the sample. In the silica concentration measurement method for measuring the silica concentration of the sample from the transmittance or absorbance of the sample injected with the reagent,
A step of measuring the transmittance of the sample using a light emitting element and a light receiving element capable of selectively emitting at least two types of measurement wavelengths;
Calculating the silica concentration of the sample using the measured transmittance;
When using the low measurement wavelength, when entering a high concentration region where the silica concentration is higher than a predetermined threshold, switching the measurement wavelength to the high measurement wavelength;
When using the high measurement wavelength, when entering a low concentration region where the silica concentration is lower than a predetermined threshold, switching the measurement wavelength to the low measurement wavelength;
A method for measuring silica concentration, comprising:

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