JP2573442B2 - Operation method of centrifugal clarifier - 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 operating a centrifugal clarifier, for example, in nuclear fuel reprocessing.

[0002]

2. Description of the Related Art In a spent fuel reprocessing facility, spent fuel is disassembled and cut and then dissolved using nitric acid.
In this case, small amounts of useful nuclides, in particular uranium, plutonium, some of the fission products and chips of the Zircaloy fuel cladding remain as insoluble sludge.

By the way, it is necessary to remove this particulate sludge before extracting uranium and plutonium with an organic solvent, and a centrifugal fining machine has been developed as a fining process for solid-liquid separation of the sludge. I have. This centrifugal clarifier performs centrifugal separation by the difference in specific gravity between the sludge and the lysis solution, and has the advantage that collection, washing, and discharge of the sludge can be easily performed by a centrifugal operation. Here, the configuration of the centrifugal clarifier will be described with reference to FIG.

[0004] In FIG. 3, reference numeral 1 denotes a concrete shielding wall, and a motor 3 of a driving mechanism is mounted on a top of the shielding wall 1 via a gantry 2. A rotating shaft 5 is connected to the motor 3 via a coupling 4. The lower end of the rotating shaft 5 penetrates through the shielding wall 1 and is connected to an upper end plate 7 of a rotating body 6 installed below the shielding wall 1. A lower end plate 9 having an opening 8 is connected to a lower end of the rotating body 6. A liquid supply nozzle 10 and a cleaning nozzle 11 are inserted inside the rotating body 6.

[0005] The outer periphery of the rotating body 6 is surrounded by a casing 13, and an annular receiving container 14 is provided on the upper outer surface of the casing 13. The guide plate 1 is provided on the inner surface of the upper portion of the receiving container 14 such that the clarified liquid flowing out of the clarified liquid discharging hole 12 falls into the receiving container 14 without scattering upward.
5 are provided. A lower part of the casing 13 is formed in a conical shape, and an insoluble scrap discharge pipe 16 is connected to a lower end. The vibration of the rotating body 6 is suppressed by the bearing 17. The motor 3 is driven by a motor drive power supply 18, and the rotation speed is detected by a tachometer 19.

In the centrifugal fining machine having the above-described configuration, the normal operation is to supply the lysate having undergone analysis (insoluble scrap concentration or the like) from the liquid supply nozzle 10 to the rotating body 6 maintained at the rated rotation speed. The clarified liquid is continuously discharged from the clarified liquid outlet pipe 18, and the undissolved scrap is collected as sludge on the lower end plate 9. Since this sludge has strong radioactivity, the measurement of its collection amount has been calculated indirectly in the past,
Calculation from the concentration of the analysis value and the operation time is one of them.

[0007]

In the centrifugal fining machine having such a structure, the amount of collected and deposited sludge is estimated from the sludge concentration of the processing solution, the volume of the separation chamber of the rotating body, and the operation time. However, this method has a problem that the amount of sludge does not coincide with the actual amount of sludge accumulated in the rotating body, such as when sludge is accumulated in the liquid transfer path after the concentration measurement.

Indirectly, the rotation of the rotating shaft
A method of associating the displacement with the weight of the rotating body (for example, see
No. 5164) and radionuclides in separated sludge (
¹⁰⁶ Estimation of sludge weight in rotating body by gamma measurement of Ru)
(For example, JP-A-59-195194).
However, both methods require large-scale measurement equipment.
You.

Since this type of centrifugal fining machine is installed in a radiation environment, it is desired to reduce the number of measuring instruments from the viewpoint of easy maintenance, and the centrifugal fining machine normally operates continuously. It is desired that the sludge weight can be measured in a short time when necessary. An object of the present invention is to provide an operation method of a centrifugal clarifier that can easily measure the weight of sludge in a rotating body and can grasp an operation state.

[0010]

In order to achieve the above object, the present invention operates a centrifugal fining machine which rotates a rotator by a motor and separates sludge from the rotator from a fining liquid by utilizing the centrifugal force. In the method, the motor current is detected by slightly changing the rotation speed, and the operation is performed while estimating the sludge accumulation amount based on the correlation between the motor current and the sludge amount obtained in advance from the detected value of the motor current. It is in.

[0011]

[Function] In the operation method of such a centrifugal clarifier,
When the rotation speed is changed during the fining operation, the motor current changes in proportion to the completion moment of the rotating body when the rotation speed is accelerated or decelerated. On the other hand, when sludge accumulates in the rotating body, the moment of inertia increases, that is, there is a correlation between the motor current and the amount of sludge accumulation.

Therefore, the rotation speed is slightly reduced and accelerated with a constant rotation speed change, and the sludge accumulation amount can be estimated from the motor current at that time based on the correlation between the motor current and the sludge amount.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. Since the structure of the centrifugal fining machine is the same as that shown in FIG. 3, the description thereof will be omitted, and here, only the operation method will be described with reference to FIGS.

As shown in FIG. 1, in the configuration of this embodiment,
The motor current is measured by an ammeter 20 provided on an electric path connecting the motor 3 connected to the rotating body 6 via the rotating shaft 5 and a motor drive power supply 18 for supplying a motor current to the motor 3. Is detected by the tachometer 19, and the motor current measured by the ammeter 20 and the rotation speed detected by the tachometer 19 are input to the detection circuit 21, respectively. The detection circuit 21 changes the rotation speed of the motor 3 (deceleration, acceleration), and changes the acceleration current I _Acc at that time.
The accelerating current detected by the detecting circuit 21 is supplied to the determining unit 22 to estimate the amount of insoluble sludge from the accelerating current, and to determine whether to continue or stop the operation of the motor 3.

FIG. 2 shows the relationship between the acceleration current _{Acc of the} motor 3 and the amount of insoluble sludge. From this relationship, the amount of insoluble sludge is estimated to determine whether to continue or stop the operation of the motor 3. In the configuration shown in FIG. 1, during the operation of the finer, the rotational speed of the motor 3 is forcibly reduced intermittently to about 5% of the rated value and further accelerated to the rated value. Now, when ΔN / Δt = constant and the speed is changed, the following equation is established. I _p · (ΔN / Δt) = T−T _L (1) where I _p : moment of inertia of the rotating body, ΔN / Δt:
Speed change rate, T: motor generated torque, _TL : mechanical loss torque Even if sludge is deposited, the mechanical loss torque _TL is almost invariant to the amount of sludge because the loss of the rolling bearing changes minutely. On the other hand, I _p is the mass Δm of the rotating body,
Assuming that the radius of rotation of m is r, I _p = Δmr ² …… (2)

Therefore, when the amount of sludge increases, I
_p also increases. When _Ip increases and ΔN / Δt = constant and the speed is changed, the torque T increases in proportion to _Ip .

When the motor torque T increases, the current increases (the voltage has the same pattern every time). That is, if the acceleration current is detected, the insoluble sludge accumulation amount can be estimated from the sludge amount estimation curve obtained in advance.

It is not necessary to carry out the measurement of the sludge amount many times in detail.
Performed at 1/20 hour intervals. The range of deceleration was about 5% of the rating. The reason for setting it to 5% is as follows.

At present, the insolubility of micro-order
To remove ludge, centrifugal force of several thousand g is required
I have. For this reason, several thousand rpm is required as the rotation speed.
You. Centrifugation of the specific gravity difference between sludge and lysate
The minimum particle size that can be obtained, that is, the critical particle size dP is: dP = {18 · μ · Q / ΔP · g ·}^1/2  Where Σ is the centrifugal sedimentation area Σ = 2 π ・ l ・ ω^Two (R_Two ^Two -R₁ ^Two ) / G · [l_nr_Two/ R₁Where r₁: Extraction radius, r_Two: Bowl radius, l: Rotation
Body length, ω: Number of rotations of rotating body, μ: Viscosity of solution (treatment solution)
Degree, Q: processing flow rate, ΔP: specific gravity difference.

The centrifugal sedimentation area has the same shape of the rotating body (r ₁ , r ₂ , l) and the same throughput (μ, Q, ΔP).
Then, it depends only on the rotation speed of the rotating body, and eventually ΔP is proportional to ω. For example, if the rated rotation speed is several thousand rpm, a constant speed
Free down to 95%. The effect on fining is dP ₁ / dP ₂ = ω ₁ / ω ₂ = ω ₁ /0.95ω ₁ = 1.05 from the previous equation, which is a 5% increase in the minimum particle diameter on the order of microns, but since the time is short, Not a problem.

In the present embodiment, the calculation procedure of the sludge collection amount was shown at one time during the fining operation. However, the collection amount confirmation after stopping the supply of the processing liquid, and the next operation after the rinsing operation, when the next fining operation is started. It can also be used to check the difference in the weight of the rotating body.

[0022]

As described above, according to the operation method of the finer according to the present invention, the amount of collected sludge can be accurately confirmed in a short time at any time during the fine operation.
There is no need to bring new equipment into the area as a measurement system, and the measurement system can be simplified. In addition, it is easy to check the rated collection of the rotating body, which leads to an improvement in the reliability of the centrifugal clarifier when operating for a long period of time. Check for fluctuations.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining an operation method of a centrifugal clarifier according to the present invention.

FIG. 2 is a curve diagram showing a correlation between a motor acceleration current and a sludge amount in the embodiment.

FIG. 3 is a longitudinal sectional view showing a configuration example of a centrifugal clarifier.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Shield wall, 2 ... Stand, 3 ... Motor, 4 ... Coupling, 5 ... Rotating shaft, 6 ... Rotating body, 7 ... Upper end plate, 8 ... Opening, 9 ... Lower end plate, 10 ... Liquid supply nozzle , 11 ... washing nozzle, 12 ... clarified liquid discharge hole, 13 ... casing, 14 ...
Receiving container, 15: guide plate, 16: insoluble sludge discharge pipe, 17: bearing, 18: motor drive power supply, 19: tachometer, 20: ammeter, 21: detection circuit, 22: determination unit.

Claims (1)

(57) [Claims] 1. A method of operating a centrifugal fining machine in which a rotating body is rotated by a motor and centrifugal force is used to separate sludge from the rotating body from a fining solution. By slightly changing the speed, the motor current at that time is detected, and the centrifugal fining machine is operated while estimating the sludge accumulation amount based on the correlation between the motor current and the sludge amount obtained in advance from the detected value of the motor current. An operation method of a centrifugal fining machine, which is operated.