JP3302972B2 - Method for detecting impulse line blockage in air purge measurement system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for early and reliable detection of clogging occurring near the tip of a measuring pressure guiding tube used in an air purge measuring system.

[0002]

2. Description of the Related Art In nuclear facilities, an air purge measurement system is widely used to measure physical quantities such as liquid level, liquid density, and pressure. FIG. 6 shows an air purge type density meter as an example of the air purge measurement system. In this air purge type density meter, two impulse lines 2 and 3 are inserted into a liquid in a storage tank 1, air is supplied at a constant flow rate from an upper part of each impulse line by an air purge device 4, and bubbles are introduced from the end of each impulse line. Release. At this time, the air pressure in each pressure guiding tube is a pressure corresponding to the liquid depths H ₁ and H ₂ . The back pressures at the points a and b of the impulse tube tips are P ₁ and P ₂ respectively.
Back pressure to the _{P 1 = ρ · H 1 +} P 0 P 2 = ρ · H 2 + P 0 Thus _{ρ = (P 2 -P 1)} / (H 2 -H 1) . Therefore, the H ₂ -H ₁ as a constant and The density of the liquid can be determined by measuring P ₁ and P ₂ . Here, ρ: density of liquid H ₁ : height at point a H ₂ : height at point b P ₁ : back pressure in pressure guiding tube 2 P ₂ : back pressure in pressure guiding tube 3 P ₀ : inside storage tank 1 Pressure.

In FIG. 6, reference numeral 5 denotes a pressure detector, 6 denotes a recorder for recording the output from the pressure detector, and 7 denotes an alarm for issuing an alarm when the output from the pressure detector exceeds a predetermined value. Device.

In this air purge measurement system,
Clogging due to salt precipitation may occur near the tip of the impulse tube immersed in the liquid in the storage tank, and the back pressure in the impulse tube may increase, resulting in abnormal measurement values. As a conventional method for detecting such blockage of the impulse line, a method of measuring the natural frequency of the back pressure fluctuation time waveform in the impulse line and detecting the blockage from the rise in the natural frequency is known. It has been proposed (Japanese Patent Publication No. 8-7130).

[0005] The back pressure in the pressure guiding tube fluctuates minutely with the release of air from the pressure guiding tube tip. If the distal end of the pressure guiding tube is clogged, the diameter of the distal end is reduced, and the amount of released bubbles is reduced, the flow rate of the air purge is constant, and the discharge period of air is shortened. At this time, the natural frequency of the back pressure fluctuation time waveform corresponds to the air discharge cycle,
The natural frequency of the back pressure fluctuation time waveform also increases. As described above, if the back pressure fluctuation in the pressure guiding tube is measured, the clogging of the pressure guiding tube tip can be detected from the rise in the natural frequency.

[0006]

However, in the early stage of the impulse line clogging phenomenon, salt precipitation tends to occur slightly above the end of the impulse line. In such a case, the diameter of the leading end of the pressure guiding tube does not change, and therefore, the cycle of releasing bubbles does not change, so that the natural frequency of the back pressure fluctuation does not change. For this reason, in the initial stage of the clogging phenomenon, it is difficult to reliably detect the clogging of the pressure guiding tube by the above-described conventional method.

[0007] Further, when the liquid in the storage tank is circulated by a pump, the liquid level in the storage tank is constantly disturbed. In such a case, the pressure fluctuation in the impulse line due to the turbulence of the liquid level becomes larger than the minute back pressure fluctuation due to the discharge of air from the impulse line, and the natural vibration of the back pressure fluctuation in the impulse line Since the number cannot be reliably measured, the above-described conventional method cannot be applied.

Therefore, according to the present invention, a clogging phenomenon occurring near the leading end of a pressure guiding tube of an air purge measuring system can be reliably detected at an early stage even at an early stage, and the liquid in the storage tank is circulated by a pump. To provide a new and improved impulse line detection method capable of reliably detecting an impulse line clogging phenomenon even when there is a back pressure fluctuation in the impulse line due to a liquid level disturbance that occurs in some cases. It was made for the purpose of.

[0009]

That is, a method of detecting a blockage of a pressure guiding tube of an air purge measuring system according to the present invention is characterized in that the pressure guiding tube is purged when a certain amount of air is purged into the liquid through a measuring pressure guiding tube inserted into the liquid. A method for detecting clogging of the impulse line used in the air purge measurement system that measures the back pressure generated in the impulse line, wherein a back pressure fluctuation time waveform of the impulse line is measured, and a frequency analysis of the back pressure fluctuation time waveform The blockage of the pressure guiding tube is detected by the attenuation of the high frequency component in the power spectrum obtained by performing the operation.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an apparatus which can be preferably used in carrying out the method of the present invention. Since the air purge measurement system itself has the same configuration as that shown in FIG. 6, the same members as those in the system of FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. According to the apparatus shown in FIG. 1, the back pressure fluctuation time waveform in the pressure guiding tubes 2 and 3 of the air purge measurement system is measured by the pressure sensor 8 and input to the arithmetic unit 9. The arithmetic unit 9 performs frequency analysis to obtain a power spectrum.

FIG. 2 shows a state where the pressure guiding tube 2 or 3 is not clogged. FIG. 4A shows a back pressure fluctuation time waveform measured without such clogging, and FIG. 4B shows a power spectrum obtained by frequency analysis of the back pressure fluctuation time waveform.

On the other hand, FIG. 3 shows a state where there is a clogging with a salt precipitate 10 slightly above the tip of the pressure guiding tube 2 or 3. FIG. 5A shows a back pressure fluctuation time waveform measured in a state where there is such clogging, and FIG. 5B shows a power spectrum obtained by frequency analysis of this back pressure fluctuation time waveform.
Are shown below.

The measurement of the back pressure fluctuation time waveform and the power spectrum illustrated in FIGS.
Put 0% aqueous sodium chloride solution in the storage tank, inner diameter 14mm
Was introduced into the liquid so as to have a liquid immersion depth of 10 cm, and the purge air flow rate was set at 7 NL (liter) / h. In order to make the pressure guiding tube clogged as shown in FIG. 3, an orifice (3.5 m inner diameter) simulating the clogging was placed at a position 5 mm above the tip of the pressure guiding tube.
m, width 20 mm).

As can be seen from the power spectrum of FIG. 4B obtained by the impulse line without clogging, in this spectrum, there are two groups of peaks observed below 8 Hz and peaks observed between 8 and 35 Hz. Two peak groups appear. In the present invention, the “high frequency component” refers to the higher frequency of the two peak groups, that is, the component of 8 to 35 Hz in the illustrated example.

The position (frequency) of such a peak group varies depending on the inner diameter of the pressure guiding tube, the flow rate of the purge air, the surface tension and the density of the measurement solution, but the characteristic that two peak groups appear does not change. Also, the frequency range of the high frequency component is
It can be determined by actual measurement or calculation for each air purge measurement system to be measured.

The power spectrum of FIG. 5B obtained when the impulse line is clogged is compared with FIG. 4B.
It can be seen that high frequency components between 35 Hz and 35 Hz are attenuated. It is considered that such a high-frequency component attenuation is caused by a portion where the diameter of the impulse line becomes small due to clogging, which prevents transmission of a particularly high frequency component of the back pressure fluctuation in the impulse line.

The actual determination as to whether or not the signal is attenuated is preferably made by comparing values obtained by integrating power spectral densities in a range of high frequency components. The integral value can be obtained by the following equation.

[0018]

(Equation 1)

In the above equation, P (f) is the power at frequency f.
-The spectral density, f₁~ F _TwoIs the high frequency component
Frequency range. That is, this integral value is, for example,
And the area of the hatched portion shown in FIG. 5B. These integrals
5B (when the impulse line is clogged)
About 3 times as compared with FIG.
The value is 5% less.

Although the low frequency component of less than 8 Hz in the power spectrum of FIG. 5B is slightly attenuated as compared with FIG. 4B, the rate of attenuation is smaller than that of the high frequency component. Only the attenuation of the component needs to be determined.

In carrying out the method of the present invention, FIG.
By using a device such as described above, the power spectrum of the back pressure fluctuation time waveform of the impulse line can be continuously observed, and clogging of the impulse line can be detected early and reliably from the attenuation of the high frequency component.

Further, even when the liquid level in the storage tank is constantly disturbed, such as when the liquid in the storage tank is circulated by a pump, the pressure fluctuation caused by the liquid level disturbance is included. By measuring the back pressure fluctuation in the impulse line, and observing the power spectrum, when clogging of the impulse line occurs, high frequency components are similarly attenuated, so that the detection method of the present invention can be effectively applied. it can.

[0023]

As can be seen from the above description, according to the pressure guiding tube blockage detecting method of the present invention, the clogging phenomenon occurring near the tip of the pressure guiding tube can be detected earlier and more reliably than the conventional detection method. it can.

Furthermore, even when pressure fluctuations due to disturbances in the liquid level in the storage tank occur in the liquid, the clogging of the pressure guiding tube can be reliably detected.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of an apparatus for performing the method of the present invention.

FIG. 2 is an explanatory view showing a state in which a pressure guiding tube is not clogged.

FIG. 3 is an explanatory view showing a state where there is a clogging slightly above a pressure guiding tube tip.

FIG. 4A is an example of a back pressure fluctuation time waveform in a state where the pressure guiding tube is not clogged. FIG. 4B is a power spectrum obtained by frequency analysis of the back pressure fluctuation time waveform of FIG. 4A.

FIG. 5A is an example of a back pressure fluctuation time waveform in a state where clogging is present near the leading end of a pressure guiding tube. FIG. 5B is a power spectrum obtained by frequency analysis of the back pressure fluctuation time waveform of FIG. 5A.

FIG. 6 is an explanatory diagram of an air purge type density meter as an example of an air purge measurement system.

[Explanation of symbols]

 1: Storage tank 2, 3: Pressure guide tube 4: Air purge device 5: Pressure detector 6: Recorder 7: Alarm device 8: Pressure sensor 9: Operation device 10: Deposit

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI G01N 9/28 G01N 9/28 Z (56) References JP-A-2001-264228 (JP, A) JP-A-11-14528 (JP) , A) JP-A-7-159261 (JP, A) JP-A-4-198829 (JP, A) Takafumi Nakano et al., Development of diagnostic equipment for clogging of piping for measurement, Proceedings of Autumn Meeting of the Atomic Energy Society of Japan, Japan, Atomic Energy Society of Japan, Vol. 2001, 2nd volume, p320 Kazuhito Fukuda et al., Clogging prediction and removal equipment for measurement, JASDF, Japan, (former) Power Reactor Nuclear Fuel Development Corp., Vol. 96, p71-75 TANAKA N, et. al, Development of highly reliable air purge and declogging system at the Tokai Reprocessing Plant, Proc RECOD 91, Japan, Vol. 2, p. 863-868 (58) Fields investigated (Int. Cl. ⁷ , DB name) G01L 27/00 G01N 9/28 G01M 3/28 G01F 23/18 G01F 25/00 G01L 7/00 JICST file (JOIS)

Claims (1)

(57) [Claims] An air purge measurement system for measuring a back pressure generated in a pressure impulse pipe when a predetermined amount of air is purged into the liquid through a measurement pressure impulse pipe inserted into the liquid. A method for detecting, by measuring a back pressure fluctuation time waveform of the impulse line, and performing a frequency analysis of the back pressure fluctuation time waveform to reduce clogging of the impulse line due to attenuation of a high frequency component in a power spectrum obtained. A method for detecting pressure blockage in a pressure guiding tube of an air purge measurement system, comprising: