JPS6355420A - Dip tube - Google Patents

Abstract

PURPOSE:To exactly and stably obtain a result of measurement even when a downflow is generated in a liquid to be measured, by providing a stagnation container having a large fluid resistance against the downflow of the liquid to be measured, on the periphery of an air bubble discharge part of the tip of a dip tube. CONSTITUTION:An air bubble which has been discharged from an air bubble discharge part 30a of a dip tube tip 30 ascends in a stagnation container 31, and since the upper part of the container 31 opens large, the air bubble does not remain but ascends to the upper part of the container 31. Therefore, it does not join an air bubble being on the way of growth in the tip 30, and exerts no bad influence on a measuring signal. Also, a downflow of a liquid to be measured 6 is obstructed by a stagnant liquid in the container 31 and takes a roundabout route, therefore, it does not reach the discharge part 30a, a roundabout route, therefore, it does not reach the discharge part 30a, an obstruction to discharge of the air bubble is avoided. When a liquid surface of the liquid 6 lowers downward from the upper face of the container 31, a small hole 33 which is opened at the left side of a bottom plate 31a of the container 31 allows the liquid in the container 31 to flow out. Also, extremely a part of the downflow of the liquid from the upper part of the container 31 flows out of the hole 33, but since the hole 33 is placed at the opposite side of the discharge part 30a and the quantity is extremely small, no influence is exerted on discharge of the air bubble.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to a dip tube used in a purge type liquid level gauge or a purge type density meter in a spent nuclear fuel reprocessing plant, and particularly The present invention relates to a dip tube that allows accurate measurement results to be easily obtained even when a downward flow occurs in a liquid to be measured in which the tip of the dip tube is immersed.

(Prior technology) In spent nuclear fuel reprocessing plants that handle large quantities of highly radioactive solutions, purge type liquid level gauges and purge type density meters measure liquid levels and densities in towers and tanks with high accuracy and reliability. It is widely used as a measuring instrument.

Fig. 3 shows this type of conventional purge type liquid level gauge and purge type density meter. In the figure, symbols 1 and 2 are differential pressure detectors, and the input side of both differential pressure detectors 1 and 2 is shown. The first, second,
The proximal ends of the third tubular dip tubes 3, 4, and 5 are connected to each other. Further, the tip openings of the first and second dip tubes 3 and 4 are immersed in the liquid to be measured 6 at immersion depths H, H2, and the third dip tube 5 is immersed in the liquid to be measured 6.
The tip opening of is located above the liquid level of the measuring liquid 6.

Each of these dip tubes 3, 4.5 is equipped with a purge set 10 that adjusts the purge flow rate to a constant level, as shown in FIG.
．． 11.12 are connected via piping 7, 8.9, respectively, and each purge set 1.0, 11゜12 receives pressurized air of 1 to 2 kg/aJG from a pressure air source via piping 13. It is now being supplied.

In the above configuration, a small flow rate of several Q/h of purge gas is supplied from each pipe 7, 8.9 into each dip tube 3°4.5. This purge gas is supplied to each dip tube 3, 4. .
(ρ: density of the liquid 6 to be measured, g: gravitational acceleration). Further, inside the second dip tube 4, a pressure equal to the pressure applied from the gas phase above the liquid level of the liquid to be measured 6 and the liquid pressure ρKHz of the liquid to be measured 6 up to the tip opening is exhibited. . Further, inside the third dip tube 5, a pressure equal to the pressure exerted from the gas phase above the liquid level of the liquid to be measured 6 is exhibited. Therefore, if the differential pressure detector 1 detects the differential pressure between the purge gas pressure generated in the first dip tube 3 and the purge gas pressure generated in the second dip tube 4, this differential pressure will be 9 g (H2-H
t), and since H2-H□ has been determined in advance, the density ρ of the liquid to be measured 6 can be determined from this measured value.

Furthermore, if the differential pressure detector 2 detects the differential pressure between the purge gas pressure generated in the second dip tube 4 and the purge gas pressure generated in the third dip tube 5, this differential pressure will be ρKH
z, and from this value, the liquid level position H2 can be determined using the density ρ of the liquid to be measured 6.

Generally, a spent nuclear fuel reprocessing plant is equipped with several evaporators for concentrating the solution, one of which is the plutonium nitrate evaporator shown in FIG. This evaporator heats the plutonium nitrate solution to boiling in two heating sections 14, 15 by means of steam flowing through the steam jacket 16, 17. The steam generated at this time is led to an unillustrated waste gas treatment system through steam relief pipes 18 and 19.

On the other hand, the heated solution whose density has been reduced flows into the circulation section 22 through the upper communication pipes 20 and 21, where it is mixed with a liquid having a slightly lower plutonium concentration and its temperature is lowered. In addition, in order to supplement the solution that has flowed into the circulation section 22, a low temperature solution flows from the circulation section 22 into the heating sections 14 and 15 via the lower communication pipes 23 and 24. Therefore, a downward flow of the solution occurs in the circulation section 22 .

By the way, purge gas is released in the form of small bubbles from the tips of the dip tubes 3 and 4 in which the liquid to be measured 6 is immersed. It is thought that the size of the bubble is determined by the relationship between the buoyant force acting on the bubble and the surface tension acting on the bubble surface.

The relationship between the size of the released bubbles and the purge flow rate determines the range of vertical fluctuation of the interface between the purge gas and the liquid to be measured 6 that is repeated at the tips of the dip tubes 3 and 4, and this size is around 5 wn H, 0. There is, and the fluctuation period is usually around 1 second. This fluctuation usually occurs in the differential pressure detectors 1 and 2.
Since the output signals of are input to the integrating circuit and averaged, the fluctuation width can be suppressed to less than 2×H20.

(Problems to be Solved by the Invention) However, in an evaporator such as the plutonium nitrate evaporator described above, the dip tubes 3 and 4 immersed in the liquid to be measured 6 are
A downward flow occurs in the liquid to be measured 6 at the tip installation portion of the dip tubes 3, 4, and this downward flow obstructs the release (rising) of bubbles from the tips of the dip tubes 3, 4.
Bubble growth continues at the 4-tip, and the size of each ejected bubble increases. For this reason, the width of the vertical fluctuation of the interface between the purge gas and the liquid to be measured 6 that is repeated at the tip of the dip tube 3.degree. 4 becomes large, and the period of fluctuation becomes long. The magnitude of the above-mentioned vertical fluctuation range is around 10 wn H2O, and the fluctuation period is so long that a normal integration circuit cannot increase the average value, and the fluctuation range is as high as 7 to 8 +nm H20.

To solve this problem, 1. It is possible to average by using an integrating circuit with a sufficiently larger time constant than the normally used integrating circuit, but in this case, it is not a problem because the time response becomes poor. be.

In addition, liquid is normally supplied to the evaporator from the liquid supply piping 25 so that the liquid level measured with a purge type liquid level gauge is constant, and this control includes ρ
is used.

However, as described above, due to the influence of the downward flow, the obtained liquid level signal and density signal vary greatly, making it impossible to accurately control the liquid level position, which may impair stable operation of the evaporator. Additionally, if the time constant of the integrating circuit is lengthened to reduce the fluctuation width, the delay in liquid level measurement will increase.
Again, the accuracy of liquid level position control is impaired.

In addition, since the concentration level of the solution in the evaporator is controlled by the density ρ and the concentration end point is detected, accurate measurement is required.
There is no guarantee that the flow velocity of the downward flow of the liquid to be measured 6 at the tip positions of both dip tubes 3 and 4 is the same, so the density signal obtained by the differential pressure detector 1 is averaged by an integrating circuit with a long time constant. However, accurate density cannot be obtained. In this case, the end point of concentration cannot be accurately detected, resulting in insufficient or overconcentration, which may impair the safe operation of subsequent steps.

The present invention has been made in consideration of these points, and when measuring the liquid level position or density of the liquid to be measured in an evaporator or other towers and tanks in a spent nuclear fuel reprocessing plant, it is possible to Even if there is a downward flow in the measured liquid,
The purpose is to provide a dip tube that provides accurate and stable measurement results.

[Structure of the invention]

(Means for Solving the Problems) The present invention is a dip tube that is used in a purge type liquid level meter or a purge type density meter, and whose tip part that releases air bubbles is immersed in a liquid to be measured. A stagnation container having a large fluid resistance against the downward flow of the liquid to be measured is provided around the bubble discharge part at the tip of the tube.

(Function) Due to the presence of the stagnation container, the bubbles released from the dip tube into the liquid to be measured are not affected by the downward flow of the liquid to be measured. Therefore, bubbles can be discharged stably, and the accuracy of the purge type liquid level gauge or purge type density meter can be improved.

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, reference numeral 22 is a circulation section similar to that shown in FIG. The tips of the first and second dip tubes 3 and 4 are immersed.

The dip tube tips 30 of these dip tubes 3 and 4 are cut diagonally at an angle of 45 degrees with respect to the axis as shown in FIG. The liquid is always emitted from the emitting part 30a.

As shown in FIGS. 1 and 2, a stagnation container 31 is fixed to the dip tubes 3 and 4 via a support plate 32 so as to wrap around the tip 30 of the dip tube. The stagnation container 31 has a bottom plate 31a, and the bottom plate 31a has a side (
A small hole 33 is bored in the left side of FIG. As shown by the arrow in FIG. 1, the downward flow of the liquid to be measured 6 is blocked by the liquid in the stagnation container 31 and takes a detour, so that the downward flow does not have an adverse effect on the bubble discharge part 30a of the dip tube tip 30. ing.

Next, the operation of this embodiment will be explained.

The bubbles released from the bubble release part 30a of the dip tube tip 30 rise within the stagnation container 31, and
The upper part is wide open, and the air bubbles rise to the upper part of the stagnation container 31a without stagnation. Therefore, it does not merge with the bubbles that are in the process of growing at the dip tube tip 30, and there is no adverse effect on the measurement signal.

Further, the downward flow of the liquid to be measured 6 is blocked by the stagnant liquid in the stagnation container 31 and detours as shown by the arrow in FIG.
0a is not reached, and interference with bubble release is avoided. A small hole 33 opened on the left side of the bottom plate 31a of the stagnation container 31 in FIG. This is what I did.

From the upper part of the stagnation container 31, a small portion of the downward flow of the liquid to be measured 6 flows into the stagnation container 31 and flows out through the small hole 33, but the position of the small hole 33 is on the opposite side from the bubble discharge part 30a. Since the measuring liquid 6 is installed in a small area and the amount of inflow is extremely small, the downward flow of the liquid to be measured 6 does not affect bubble release.

In this way, even when there is a downward flow in the liquid 6 to be measured, bubbles are released as stably as when there is no downward flow, and the liquid level position and density can be measured accurately and stably using the purge method. can be done.

Safe and stable operation of spent nuclear fuel reprocessing plants will be ensured.

〔Effect of the invention〕

As explained above, the present invention is provided with a stagnation container that inhibits the inflow of the downward flow of the liquid to be measured at a position surrounding the bubble discharge section at the tip of the dip tube, so that the bubble discharge is not adversely affected by the downward flow. It's fleeting. For this reason, when measuring the liquid level or density of the liquid to be measured in the evaporator or other towers and tanks at a spent nuclear fuel reprocessing plant, it is stable and accurate even when there is a downward flow in the liquid to be measured. This will ensure safe and stable operation of the spent nuclear fuel reprocessing plant.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a main part showing an embodiment of the present invention, Fig. 2 is a perspective view of the tip of the dip tube, and Fig. 3 is an overall configuration of a conventional purge type liquid level gauge and purge type density meter. It is a diagram. 3.4... Dip tube 6... Liquid to be measured, 30... Dip tube 30a...
...bubble release part, 31...stagnation container 31a...bottom
Board, 33...Mr. Koko, Patent Attorney, Noriyuki Chika, Yudo, Hirofumi Mitsumata, Fig. 1, Fig. 2

Claims (2)

[Claims] (1) In a dip tube used in a purge type liquid level gauge or a Parsi type density meter, the tip of which releases bubbles is immersed in the liquid to be measured. A dip tube characterized in that it is provided with a stagnation container that has a large fluid resistance against the downward flow of liquid. (2) The bubble discharge section at the tip of the dip tube opens in a certain horizontal direction, and the stagnation container is a cylindrical container with an open top having a bottom plate, and the bottom plate has an opening direction of the bubble discharge section. 2. The dip tube according to claim 1, wherein the dip tube has a small hole on the opposite side.