JPH1114541A - Cr densitometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Cr densitometer which improves the operability of maintenance operation for keeping clean transparent windows on the optical paths of detection light and reference light and has simpler constitution as a dip type Cr densitometer that adopts a two-wavelength absorptivity system. SOLUTION: In addition to a signal processor 33 which calculates hexavalent chromium density from the photodetection intensity values of the detection light S from a detection light source 15 and the reference light R from a reference light source 16, an abnormality occurrence monitor device 40 is provided which monitors variation in the photodetection intensity of the reference light R and generates an abnormality signal when the intensity decreases to a specific level. The frequency of cleaning operation for the transparent windows 17 and 19 can be minimized and the total operability is improved. Further, dirt is monitored by making use of the reference light R, so it is not necessary to specially provide an optical system etc. dedicated to dirt monitoring, thereby making the whole constitution simpler.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Cr concentration meter for measuring the concentration of hexavalent chromium contained in, for example, waste liquid treated in a waste liquid treatment facility in a plating factory.

[0002]

2. Description of the Related Art Chrome plating is frequently used in the steel, automobile, and electronics industries. Since hexavalent chromium in the waste liquid discharged from these plating plants is harmful to humans, its concentration when discharged into public waters has an environmental standard value of 0.05 according to the Water Pollution Control Law.
It is regulated to mg / liter (0.05 ppm) or less.

The present inventors have previously proposed a Cr concentration meter which can be used by directly immersing it in a waste liquid in such a waste liquid treatment facility such as a plating factory (see Japanese Patent Application Laid-Open No. 9-54036). This Cr concentration meter has a watertight housing for the light-emitting housing and the light-receiving housing that face each other, and the detection light source and the reference light source are arranged in the light-emitting housing, while the light-receiving housing supports each light source. In addition, a photodetector composed of a photodiode is provided. In addition, on the opposing outer wall surfaces of the light emitting housing and the light receiving housing, light emitting windows and light receiving windows made of transparent quartz glass are hermetically mounted on optical paths from each light source to the light receiver.

The Cr concentration meter having such a configuration is immersed in a waste liquid, and the intensity of the detection light and the reference light transmitted through the waste liquid between the light emitting window and the light receiving window is detected. Light having a center wavelength of 450 nm is emitted as detection light, and this light is attenuated in accordance with the concentration of hexavalent chromium when passing through the waste liquid. Also red
Light having a center wavelength of 850 nm is emitted from the LED, and this light hardly absorbs due to the concentration of hexavalent chromium in the waste liquid. A two-wavelength absorbance measurement method using the detection light and the reference light is employed to calculate the hexavalent chromium concentration in the waste liquid.

[0005] In particular, in the above, the light deviating toward the blue side from the wavelength (340 to 350 nm) in the near ultraviolet region where the absorbance in the hexavalent chromium solution peaks is used as the detection light, so that the hexavalent chromium concentration can be reduced to zero. It has a wide measurement range of ~ 4000 ppm.

[0006]

However, when the above-mentioned Cr concentration meter is immersed in the waste liquid and the continuous measurement is continued, the pollutants contained in the waste liquid are contaminated by the light transmitting window and the light receiving window. Gradually adheres to the outer surface, which impairs transparency and reduces measurement accuracy. Therefore, the worker
It is necessary to pull up the densitometer appropriately from the waste liquid tank, visually check the degree of fogging of the light emitting window and the light receiving window, and perform a cleaning operation according to the degree of fogging. This work
For example, it is a severe operation to be performed around the waste liquid tank while paying attention to the scattering of the waste liquid at the time of strong wind, and improvement of the workability is desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to perform maintenance work for maintaining the measurement accuracy of an immersion type Cr concentration meter applied to the above-mentioned waste liquid treatment equipment and the like. Cr that can improve the workability of the steel and make the overall structure simpler
It is to provide a densitometer.

[0008]

A Cr concentration meter according to the present invention for achieving the above object emits light having a wavelength at which the absorbance when passing through a hexavalent chromium solution changes according to the hexavalent chromium concentration. Light source, a reference light source that emits light of a wavelength that does not change with the hexavalent chromium concentration, and a detection light receiver and a reference light receiver that receive light from both light sources, respectively, are placed opposite to each other. Signal processing means for outputting a signal corresponding to the concentration of hexavalent chromium in the solution based on the intensity signal output in accordance with the amount of light received by each of the light receivers, the light receiving housing being housed in the light-tight housing and the light-receiving housing. And an abnormality occurrence monitoring means for comparing the intensity signal corresponding to the amount of light received by the reference light receiver with a reference value and issuing an abnormality signal when the intensity signal becomes equal to or less than the reference value.

According to such a configuration, the two housings having the watertight structure are directly immersed in the waste liquid, and the measurement of the hexavalent chromium concentration is continuously performed by the signal processing means based on the amounts of the detected light and the reference light received. At the same time, the change in the amount of received reference light is monitored by the abnormality occurrence monitoring means. In other words, if the light-emitting window or light-receiving window provided in the light-emitting housing or light-receiving housing becomes dirty, the amount of received reference light decreases, and when this falls below the reference value, an abnormal signal is generated. Then, for example, an alarm is generated.

Therefore, the worker only needs to clean the light-emitting window and the light-receiving window at this time, and the frequency of the maintenance work can be minimized. The performance is improved. Moreover, in the above,
It is a configuration that monitors the dirt on the light projecting window and the light receiving window using the reference light as described above. In this case, only by adding a signal processing circuit for the reference light, for example, an optical system dedicated to dirt monitoring is provided. Since there is no need to provide a separate configuration, the overall configuration can be simplified.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, an example of a waste liquid treatment facility for reducing and depositing hexavalent chromium in the waste liquid to harmless trivalent chromium will be described with reference to FIG. This equipment includes a concentrated plating wastewater tank 1 for storing high-concentration wastewater with a hexavalent chromium concentration of more than 1000 ppm as a tank for receiving a wastewater discharged from a surface treatment plant or a cold rolling plant at a steel mill, for example. A general plating wastewater tank 2 for storing a certain amount of waste liquid is provided. The waste liquid in the concentrated plating waste water tank 1 is sent little by little to the general plating waste water tank 2 and sent to the primary pH adjusting tank 3 together with the waste liquid in the waste water tank 2.

In this primary pH adjustment tank 3, the addition of sulfuric acid
The pH is adjusted to about 2 to 3, and then sodium bisulfite as a reducing agent is injected into the reducing tank 4 to reduce hexavalent chromium to trivalent chromium as shown in the following reaction formula. 4H ₂ CrO ₄ + 6NaHSO ₃ + 3H ₂ SO ₄ → 2Cr ₂ (SO ₄ ) ₃ + 3Na ₂ SO ₄
+ 10H ₂ O After that, neutralization treatment is performed with an alkaline agent such as sodium hydroxide in the secondary and tertiary pH adjusting tanks 5 and 6, and trivalent chromium is converted into water-insoluble chromium hydroxide as shown in the following formula. Becomes

Cr ₂ (SO ₄ ) ₃ + 6NaOH → 2Cr (OH) ₃ + 3Na ₂ SO ₄ An auxiliary agent is further injected to remove these precipitates, and chromium hydroxide is precipitated and separated in the next precipitation tank 7. You. The sedimented chromium compound is collected in a sludge storage tank together with other metals such as zinc and iron, and the supernatant water of the sedimentation tank 7 is sent to the next collecting raw water tank to confirm the final concentration. It is released at.

A Cr concentration meter 10 for detecting the concentration of hexavalent chromium in the waste liquid is installed in the primary pH adjusting tank 3 described above. Next, the configuration of the sensor head section 11 of the Cr concentration meter 10 will be described with reference to FIG. The sensor head section 11 includes a light emitting housing 13 and a light receiving housing 14 fixed on a substantially horizontal base plate 12 at predetermined intervals. These housings 13 and 14 have a watertight structure that prevents water from entering from outside.
A detection light source 15 composed of a blue light-emitting diode (hereinafter abbreviated as a blue LED) and a reference light source 16 composed of a red light-emitting diode (hereinafter abbreviated as a red LED) are housed in 13.

A light-transmitting window 17 made of transparent quartz glass is hermetically mounted on an outer wall surface of the light-transmitting housing 13 on the light-receiving housing 14 side, and a condenser lens is provided inside the light-transmitting window 17.
18 are arranged. The light emitted from each of the light sources 15 and 16 is converted into a substantially parallel light by the condenser lens 18 and then emitted from the light emitting window.
It is configured so as to pass through 17 to the light receiving housing 14 side.

On the other hand, the light receiving housing 19 is provided with a light receiving window 19 made of transparent quartz glass similarly to the above.
A light-scattering plate 20 and a condenser lens 21 are sequentially arranged inside the light-receiving window 19 along the side wall surface. Then, from the light emitting housing 13 side, the light receiving window 19 and the scattering plate
Reference is made to a detection light receiver 23 composed of a photodiode on an optical path which sequentially passes through the condenser lens 21 and travels straight, and on an optical path which is bent 90 ° by a half mirror 22 arranged in the middle of this optical path. An optical receiver 24 is provided.

An infrared light cut filter 25 is provided on the front surface of the detection light receiver 23, and a visible light cut filter 26 is provided on the front surface of the reference light receiver 24. Is the light from the detection light source 15,
Light from the reference light source 16 is incident on the reference light receiver 24, and a signal corresponding to the intensity of each incident light is output. The hexavalent chromium concentration is calculated based on the output signal corresponding to each of the incident lights as described later.
And as the reference light source 16, a blue LED and a red LED as described above.
The reason for selecting is described.

FIG. 4 shows the results of an examination of the light absorbance of the wastewater sent from the primary pH adjusting tank 3 to the reducing tank 4. The incoming wastewater, that is, wastewater with a “large” hexavalent chromium concentration before injecting the reducing agent, has a wavelength near 260 nm,
There are peaks of absorbance in the near ultraviolet region at 340 to 350 nm. Of these, the peaks are at 340-350nm, and
In the wavelength region extending to 500 nm, since the substances having an absorption band in this region are not contained in the waste liquid in the waste liquid treatment equipment except for hexavalent chromium, the wastewater during the reduction treatment (concentration “medium”) Also, as shown by the wastewater after the reduction treatment (concentration “small”), a change in absorbance corresponding to the hexavalent chromium concentration appears.

Therefore, on the assumption that the change in the absorbance in the above-mentioned absorption band is measured as the detection light source 15, in order to extend the measurement concentration range from 0 to several thousand ppm, the peak wavelength range from 340 to 350 nm is increased. A high-brightness blue LED having a peak at a wavelength of 450 nm which is shifted is used. On the other hand, the light having a wavelength of 500 nm or more is hardly affected by the change in the concentration of hexavalent chromium in the absorbance.
A red LED having a peak at 0 nm is used as the reference light source 16.

As described above, according to the two-color detection method of irradiating the detection light with the reference light, even if the light is scattered by dust or the like contained in the waste water, the decrease in the intensity of the transmitted light due to this is reduced by the detection light and the reference light Therefore, by comparing these, the effect of light scattering can be eliminated and high-precision measurement can be performed. FIG. 5 shows the blue LE described above.
The emission spectrum distributions of D and the red LED are shown.

Note that, as shown in FIG.
A circuit board 27 on which circuit elements constituting a signal processing device 33 and the like to be described later are mounted is provided on an upper side in the inside of the apparatus. Waterproof cords 28 and 29 are connected to upper ends of the light-receiving housing 14 and the light-emitting housing 13, respectively, through which power is supplied from outside and a detection signal is output. Further, an operation pipe for immersing the whole of the sensor head unit 11 in the waste liquid of the primary pH adjustment tank 3 and holding the sensor head unit 11 at a predetermined height position on a wall surface above the light receiving window 19 in the light receiving housing 14. 30 has been fixed.

Next, a control circuit formed on the circuit board 27 will be described with reference to FIG. First, a 3 kHz power supply 31 and a 10 k
A Hz power supply 32 is provided. The commercial power supplied from the outside is stepped down to a predetermined light emitting diode operating voltage by these high frequency power supplies 31 and 32, and applied to the detection light source 15 and the reference light source 16. Thereby, the detection light source 15
Blue light that blinks at 3 kHz, and infrared light that blinks at 10 kHz are emitted from the reference light source 16. As described above, by making the detection light and the reference light blink at a predetermined frequency, a decrease in detection accuracy due to disturbance light can be prevented even when used outdoors.

Light emitted from each of the light sources 15 and 16 driven as described above is applied to the detection light receiver 22 and the reference light receiver 24, respectively.
The signal from each of the light receivers 22 and 24 output according to the intensity of the incident light is sent to a signal processing device (signal processing means) 33. In this signal processing device 33, first, the output signal from the detection light receiver 22 is smoothed as a detection light signal A by a first band pass filter 34 that passes a frequency component of 3 kHz. Similarly, the output signal from the reference light receiver 24 is 10 kHz
Are passed through a second band-pass filter 35 which passes the frequency component of the reference light signal B and smoothed as a reference light signal B and sent to a divider 36.

From these two signals A and B, the hexavalent chromium concentration C in the waste liquid is calculated. That is, assuming that the intensity of the blue light emitted from the detection light source 15 is S and the optical path length in the waste liquid is d, for the detection light signal A, log (A / S) = − εCd, where ε: molar absorption The relationship of coefficient holds.

On the other hand, between the intensity R of the infrared light emitted from the reference light source 16 and the intensity B when the infrared light is detected by the reference light receiver 24 after passing through the waste liquid, there is a hexavalent value in the waste liquid. A relational expression is obtained, which is not affected by the chromium concentration C and attenuates depending on the optical path length d in the waste liquid. From these, the hexavalent chromium concentration C is calculated as follows: C = k1 + k2 · log (A / B) (1) However, k1 and k2 are obtained by constants.

Therefore, first, a divider 36 for performing A / B arithmetic processing and a logarithmic converter 37 for calculating the logarithm of the output signal and performing the calculation based on the equation (1) are included in the signal processing device 33. The logarithmic converter 37 outputs a voltage signal Vo corresponding to the concentration of hexavalent chromium in the waste liquid. FIG. 6 shows the result of measuring the relationship between the voltage signal (hereinafter referred to as sensor output) Vo and the concentration of hexavalent chromium. As shown in the figure, the sensor output Vo shows a steep change from 0 ppm to about 500 ppm, and then gradually changes gradually as the concentration increases. However, until the sensor output Vo exceeds 4000 ppm, the sensor output Vo becomes 6
It gradually increases with increasing chromium (VI) concentration. Therefore, 0
The sensor output Vo is 6 to 4000 ppm over a wide range.
It is possible to uniquely determine the chromium (VI) concentration.

The signal processing device 33 has a storage device 38 for storing calibration curve data corresponding to the sensor output-concentration curve shown in FIG. 6 over a range of 0 to 4000 ppm.
A density data converter 39 is further provided, which compares the sensor output Vo output from the logarithmic converter 37 with the above-mentioned calibration curve data at every predetermined sampling time, converts it into a digital value as a density value C and outputs it. I have. .

On the other hand, the reference light signal B smoothed through the second band-pass filter 35 is divided by the divider as described above.
In addition to being sent to 36, it is also sent to an abnormality occurrence monitoring device (an abnormality occurrence monitoring means) 40. This device 40 has a function of monitoring the degree of dirt on the surface of the light emitting window 17 and the light receiving window 19 described above. That is, the wastewater containing dust such as zinc and iron is sent to the above-mentioned primary pH adjustment tank 3, and the light-emission window 17 and the light-receiving window 19 are immersed in the wastewater containing these pollutants. (Hereinafter, the light projecting window 17 and the light receiving window 19 are collectively referred to as “transparent windows”). As a result, the light receiving sensitivity of the detection light and the reference light described above decreases, and the accuracy of the concentration value of hexavalent chromium output based on the detection light also decreases. Therefore, an abnormality occurrence monitoring device 40 that monitors the degree of dirt on the transparent window is provided.

This device 40 is provided with an average value calculator 41, an alarm level setter 42 and an alarm generator 43.
The average value calculator 41 is used for a predetermined time, for example, one day (24 hours)
The average value of the reference light signal B during the period is calculated every day. In other words, although the reference light signal B is not affected by the change in the concentration of hexavalent chromium in the waste liquid, light scattering occurs due to the dust floating in the waste liquid. During the processing of various types of waste liquid having different ratios, it varies in a short term according to the type of waste liquid. Therefore,
By calculating the average value over one day, the influence due to the change in the content ratio of the floating dust as described above is removed, and the change according to the degree of contamination of the transparent window surface is detected.

FIG. 7 shows an example of the output result from the average value calculator 41 described above. That is, on the basis of the day when the Cr concentration meter 10 was installed in the primary pH adjusting tank 3 with the surface of the transparent window being clean, the average of the day of the reference light signal B on this day was defined as the initial level (100%). In the graph, the average value of the reference light signal B gradually decreases with the progress of dirt on the surface of the transparent window. In the case of FIG. To the initial level
It is shown to have dropped to 90%.

As described above, the change in the reference light signal B is monitored, and the lowering level corresponding to the time when the above-described calculation result of the hexavalent chromium concentration cannot be maintained within the predetermined accuracy, for example, "90%" is alarmed. The set value is set in the alarm level setter 42 shown in FIG. In the alarm generator 43, an average calculator
The output from 41 is compared with the alarm set value, and when the output decreases to the set value, an alarm signal EM is generated. Thereby, an alarm such as a buzzer is issued in the operation monitoring room where the worker is resident.

The concentration of hexavalent chromium in the waste liquid flowing into the above-mentioned primary pH adjusting tank 3 is detected by the Cr concentration meter 10 having the above configuration. Depending on the detected concentration, the amount of waste liquid sent from the thick plating wastewater tank 1 to the general plating wastewater tank 2, the amount of wastewater sent from the general plating wastewater tank 2 to the primary pH adjustment tank 3, and further to the reduction tank 4 The injection amount of sodium bisulfite is adjusted.

The concentration of hexavalent chromium in the waste liquid flowing into the primary pH adjusting tank 3 varies over a wide range exceeding 1,000 ppm.
The Cr concentration meter 10 has a measurement range of 0 to 4000 ppm, and also employs a two-wavelength absorbance measurement method together with a method of flickering and modulating the light source itself and detecting transmitted light.
High-precision measurement that is not affected by disturbance light or other metal ions or complex ions such as zinc and iron contained in the plating waste liquid is possible.

The concentration of hexavalent chromium in the waste liquid in the primary pH adjusting tank 3 is continuously measured by the above-mentioned Cr concentration meter 10, but in this case, the transparent window becomes dirty and the predetermined accuracy is maintained. If no longer possible, the abnormality occurrence monitoring device 40 issues an alarm. Therefore, the worker only needs to perform the cleaning work of the transparent window at this time, and the frequency of maintenance work for this can be minimized, so that the overall workability and the operation rate are improved. .

Further, the Cr concentration meter 10 is configured to monitor the dirt on the transparent window as described above using the reference light in the two-wavelength absorbance measurement method. Just by adding a processing circuit, for example, there is no need to separately provide an optical system dedicated to dirt monitoring.
The overall configuration is also simpler. In the above description, the average calculator 41 calculates the average of the reference light signal B.
Therefore, the degree of dirt on the transparent window can be grasped more accurately without being affected by floating dust and the like in the waste liquid. Therefore, the Cr concentration meter according to the present embodiment is particularly suitable for use in a waste liquid treatment facility that treats waste liquid having various floating amounts of dust and the like.

The above embodiment does not limit the present invention, and various modifications can be made within the scope of the present invention. For example, in the above description, a method in which the light sources 15 and 16 are turned on and off to modulate the light is adopted. However, if it is assumed that the light source 15 and 16 are used in a facility where the influence of disturbance light is small, such a method is not necessarily required. The present invention can be applied to a Cr concentration meter having another configuration employing an absorbance measurement method. Further, in the above embodiment, the Cr concentration meter installed in the waste liquid treatment facility at the steel plant was described as an example, but for example, a waste liquid treatment facility such as a plating factory for automobiles and home appliance parts, and other plating processes. It is also possible to use it.

[0037]

As described above, the Cr concentration meter of the present invention measures the concentration of hexavalent chromium from the received light intensity of the detected light from the detected light source and the received light intensity of the reference light from the reference light source. Is continuously performed, and a decrease in the received light intensity of the reference light is monitored, and an abnormal signal is issued when the transparent window becomes dirty. Therefore, the worker only needs to perform the cleaning work of the transparent window at this time, and the frequency of the maintenance work for this can be minimized, so that the overall workability is improved. In addition, since such monitoring of the dirt on the transparent window is also performed using the reference light, it is not necessary to separately provide an optical system or the like dedicated to the dirt monitoring only by adding a signal processing circuit for the reference light. Thus, the overall configuration can be made simpler.

[Brief description of the drawings]

FIG. 1 is a control block diagram illustrating a configuration of a Cr concentration meter according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a waste liquid treatment facility provided with the Cr concentration meter.

FIG. 3 is a partially cutaway front view showing a sensor head of the Cr concentration meter.

FIG. 4 is a graph showing a measurement result of absorbance of a waste liquid in the waste liquid treatment facility.

FIG. 5 shows blue as a light source used in the Cr concentration meter.
4 is a graph showing emission spectrum distributions of an LED and a red LED.

FIG. 6 is a graph showing a relationship between a sensor output and a hexavalent chromium concentration in the Cr concentration meter.

FIG. 7 is a graph showing an example of a measurement result of a change in received light intensity of reference light in the Cr concentration meter.

[Explanation of symbols]

 10 Cr concentration meter 13 Light emitting housing 14 Light receiving housing 15 Detection light source 16 Reference light source 17 Light emitting window 19 Light receiving window 23 Detection light receiver 24 Reference light receiver 33 Signal processing device (signal processing means) 40 Abnormality monitoring device (Abnormality monitoring means)

Claims (1)

[Claims] 1. A detection light source which emits light having a wavelength whose absorbance changes according to the concentration of hexavalent chromium when passing through a hexavalent chromium solution, and a reference which emits light having a wavelength which does not change with the concentration of hexavalent chromium. A light source, a detection light receiver and a reference light receiver that respectively receive light from both of these light sources are housed in a light-tight housing and a light-receiving housing in which the light receiver and the reference light receiver are arranged opposite to each other. Signal processing means for outputting a signal corresponding to the concentration of hexavalent chromium in the solution based on the intensity signal output according to the amount of received light, and comparing the intensity signal corresponding to the amount of light received by the reference light receiver with a reference value And an abnormality occurrence monitoring means for generating an abnormality signal when the value falls below the reference value.
Densitometer.