JPH0254918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Purpose and Background) The present invention provides a method for preparing a slurry containing settleable particles at a constant concentration.
This invention relates to a quantitative supply device. Although the present invention was invented to treat waste liquid discharged from nuclear power plants, it can be applied to all other slurries that need to be supplied at a constant concentration and quantity.

However, as a specific example, a slurry-like waste liquid containing sedimentary particles discharged from a nuclear power plant will be explained here. Nuclear power plants discharge a water slurry containing soluble salts as well as settleable particles such as sand, iron oxide, and ion exchange resins, but since this contains trace amounts of radioactivity, it can be heated and concentrated. The material must be reduced in volume, dried, and then subjected to solidification treatments such as cement solidification, asphalt solidification, plastic solidification, etc., and then stored as a stable solidified product for a long period of time. The properties of the above-mentioned solidified material vary greatly depending on the components of the waste, the mixing ratio with the solidifying material, etc., so in order to obtain a solidified material with constant quality and stable over a long period of time, it is necessary to keep the waste liquid at a constant concentration.
It is important to feed the volume reduction treatment equipment and other equipment at a constant rate. However, if the waste liquid is a slurry containing settleable particles, if there is a dead space in the entire supply line, including the supply tank, the settleable particles will settle there, resulting in changes in the uniformity of the slurry. It becomes impossible to maintain a constant concentration. In addition, the deposits scale and cause blockage of pipes and other troubles.

As a method conventionally used as a countermeasure for such a case, there is a method shown in the attached FIGS. 1 and 2. In the method shown in Figure 1, the slurry extracted from the supply tank 1 is passed through the circulation pump 2 and the circulation line 3.
The slurry in the supply tank is constantly stirred to make the slurry concentration uniform, and
This is a method in which slurry is extracted from the middle of the circulation line 3 using a branch pump 4. In this method, fluctuations in the level of the supply tank 1 appear as fluctuations in the discharge pressure of the circulation pump 2. Fluctuations in the discharge pressure of the circulation pump 2 due to this reason and others appear as fluctuations in the blowing pressure of the branch pump 4, and therefore affect the quantitative performance of the branch pump 4.

In addition, in the method shown in Fig. 2, a head tank 5 is installed in the middle of the circulation line 3, the slurry overflows from this head tank to maintain a constant level in the head tank, and piping is installed to draw out the branched liquid from the bottom of the head tank. A constant suction pressure is applied to the branch pump 4 so that the quantitative performance of the branch pump can be maintained. This method maintains constant concentration during continuous operation;
Although it is easy to maintain quantitative properties, nuclear waste liquid treatment equipment is often operated intermittently, and in that case, the second
In the device shown in the figure, when the operation of the branch pump 4 is stopped, the sedimentary particles in the residual slurry in the head tank 5 are deposited, and when the operation of the branch pump is started next, the deposited particle layer is placed first. There is a drawback that the concentration becomes non-uniform due to suction.

(Structure) The present invention aims to eliminate the drawbacks of these conventional methods. A circulation line that extracts slurry from the lower part of the supply tank and returns it to the upper part of the supply tank via a branch, and a circulation pump. This slurry supply device has a structure in which a circulating slurry inlet pipe is provided on the side and a circulating slurry overflow pipe is provided on the side.

To explain this with reference to FIG. 3, 1 is a supply tank containing a slurry containing sedimentary particles, 6
3 is a circulation line that takes slurry from the bottom of the supply tank and returns it to the top of the supply tank via branch 6; 2 is a circulation pump; The vessel is provided with a branch pump suction pipe 61 inserted from above, a circulating slurry inlet pipe 62 at the bottom, and a circulating slurry overflow pipe 63 on the side.

When the circulation pump 2 is operated in this device,
The slurry in the supply tank 1 is passed from the circulation line 3 to the branch 6 through an inlet pipe 62 provided at the bottom of the branch.
It overflows from the overflow pipe 63 provided on the side of the branch and returns to the supply tank 1. This circulating flow mixes the slurry within the supply tank to maintain a uniform composition. Conversely, a circulation pump with a capacity that can maintain a uniform slurry concentration in the supply tank by circulating flow is installed. Such circulating flow maintains uniform slurry concentration in the supply tank as well as in the branching device.
Furthermore, since the liquid level in the branch is kept constant by the overflow pipe 63, the water pressure in the suction section of the branch pump suction pipe 61 is kept constant. This suction pipe is connected to a branch pump, and the branched slurry is sent to a dryer or other post-treatment system via a branch pipe 8. Note that FIG. 3 shows a state in which a vertical pump 7 is installed inside the suction pipe as a branch pump.
9 indicates the drive motor of the vertical pump. Branch pipe 8
is sloped downward in the direction of flow of the branched liquid until it reaches the after-treatment device to prevent settling particles from settling in the middle of the pipe.

As mentioned above, since the pressure on the suction side of the branch pump is kept constant, the quantitative performance of the branch pump is maintained well. If even stricter quantitative performance is required, an automatic flow rate control system can be freely installed on the outlet side of the branch pump.

Because the after-treatment equipment is operated intermittently, even if the branch pump is stopped, the slurry in the branch 6 is always in a circulating state while the circulation pump 2 is in operation, so the slurry concentration in the supply tank is always the same as the slurry concentration in the supply tank. remains the same. Therefore, even if the operation of the branch pump is restarted, there will be no change in the slurry concentration in the branch flow.

Furthermore, even if the circulation pump 2 is stopped arbitrarily or due to reasons such as a power outage, the circulation pump can be restarted first, and after the slurry concentration in the supply tank has become completely uniform, the branch pump can be operated to increase the concentration of the branched flow. No change occurs.

Note that in FIG. 3, reference numeral 10 is a pressure equalization line connecting the supply tank 1 and the gas phase portion of the branching device 6. This pressure equalization line is not necessary if the supply tank and branch are each open to the atmosphere, or if the circulation line 3 has a large diameter and also functions as a pressure equalization line, but it is not necessary for the treatment of radioactive waste. In order to avoid each part of the system being exposed to the atmosphere, it is better to provide a pressure equalization line so that the supply tank and the branch are under the same pressure so that the flow of the circulating fluid is not obstructed.

Although the basic configuration of the present invention has been described above, the pump suction pipe may be extracted from the branching machine for cleaning or repair. At this time, it will be easier to do the rest of the work if the outside surface of the pump suction pipe is clean. This is particularly important when handling radioactive waste slurries.

FIG. 5 shows a structure for this purpose, and will be explained in comparison with the basic type shown in FIG. 4. In the basic type shown in FIG. 4, a branch pump suction pipe 61 is inserted into the branch 6 from above, a circulating slurry inlet pipe 62 is provided at the bottom, and a circulating slurry overflow pipe 63 is provided at the side. 64 is a gas inlet and outlet pipe for the pressure equalization line. Further, 65 is a branch liquid extraction pipe, to which a pump may be connected, or a branch pump suction pipe 6
1 may be a suction pipe of a vertical pump.

The improved type shown in FIG. 5 is the same in that the branch pump suction pipe 61 is inserted from above the branch 6, but the outer pipe 66 is fixed to the cover 67 of the branch and the branch pump is mounted above it. The branch pump suction pipe 61 is inserted into the outer pipe 66 from the upper part, and its lower end is watertightly and removably fitted to the lower end of the outer pipe. 68 is a watertight gasket. With this structure, the outer surface of the branch pump suction pipe 61 does not come into contact with the slurry, so cleaning is not only easy, especially when handling radioactive slurry, but also
The amount of waste liquid will not be increased unnecessarily.

In either structure shown in FIG. 4 or FIG. 5, it is a matter of course that the circulation slurry passage is set within a range that provides a flow rate that does not allow the particles in the slurry to settle.

(Effects) (1) Slurry does not stagnate in the branch, so a constant concentration can be ensured and no blockage occurs.

(2) A constant concentration can be maintained even during intermittent operation.

(3) Quantitativeness can be ensured because there is no change in the suction pressure of the branch pump.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams of the conventional device;
The figure is an explanatory diagram of the device of the present invention, and FIGS. 4 and 5 are structural diagrams of a turnout used in the present invention.

Claims (1)

[Scope of Claims] 1. A supply tank containing slurry containing sedimentary particles, a branching device for receiving the slurry in the supply tank and branching out the fixed amount, and extracting the slurry from the lower part of the supply tank and supplying it through the branching device. Consisting of a circulation line returning to the upper part of the tank and a circulation pump, the branching device is provided with a suction pipe for the branch pump inserted from above, a circulation slurry inlet pipe at the bottom, and a circulation slurry overflow pipe at the side. A slurry supply device with a structure that 2. The slurry supply device according to claim 1, wherein a pressure equalization line is provided between the supply tank and the branch. 3 A structure in which a double pipe consisting of a branch pump suction pipe and an outer pipe is inserted from above the branch, the outer pipe is fixed to the cover of the branch, and an insertion port for the branch pump suction pipe is provided at the top. 3. The slurry supply device according to claim 1, wherein the pump suction pipe is inserted into the outer tube from the upper part, and its lower end is watertightly and removably fitted to the lower end of the outer tube. 4. The slurry supply device according to claim 1, 2 or 3, which is equipped with a vertical pump as a branch pump.