JPS5931391B2 - Waste liquid treatment method using centrifugal thin film dryer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating waste liquid using a centrifugal thin film dryer,
In particular, it prevents performance deterioration due to heat transfer surface scaling, etc.
The present invention relates to a waste liquid treatment method suitable for stabilizing operation.

It is generally known that when treating waste liquid, the volume of the waste should be reduced.

Particularly at nuclear power plants, where disposal costs and on-site storage space are issues, radioactive waste fluids such as ion exchange resin recycled waste fluids and floor drains are concentrated and dried, pulverized, compressed into granular pellets, and then stored in drums. It is considered to be stored.

The present invention relates to a method for treating waste liquid using a centrifugal thin film dryer, and will be explained below by taking the case of waste liquid treatment from a BWR power plant as an example.

Figure 1 is a flow sheet of a conventional treatment method, where 1 is a waste liquid tank, 2 is a centrifugal thin film dryer, 3 is a granulator, 4 is a drum filling machine, 5 is a solenoid valve, 6 is a stirrer, and 7 is a Liquid level gauge, 8
9 is a solenoid valve, 9 is a supply pump, 10 is a regulating valve, 11 is a flow meter, A is a waste liquid, and B is a cladding that is an insoluble component.

The composition of waste liquid A is Na2S0415-30% by weight
2O3 and S i O2 and cladding B such as resin are 1 to 4
% by weight and varies considerably.

The device operates as follows. The waste liquid A containing the cladding B is supplied to the waste liquid tank 1 via the solenoid valve 5.
It is supplied to the centrifugal thin film dryer 2 via a solenoid valve 8, a supply pump 9, a regulating valve 10, and a flow meter 11.

Here, the waste liquid A is evaporated to dryness and becomes powder,
The pellets are compression molded into granular pellets, and the pellets are filled into drums using a drum filling machine 4.

The centrifugal thin film dryer 2 has the advantage of being able to directly convert the waste liquid A into powder with a water content of approximately 1% by weight.

However, it has been experimentally revealed that the performance deteriorates depending on the composition and concentration of the waste liquid.

That is, insoluble component cladding B other than Na 2804
If the amount exceeds about 2% by weight, scaling may occur on the heat transfer surface, resulting in the production of undried powder due to a decrease in heat transfer efficiency, and abnormal wear and vibration of the rotor blades in the centrifugal thin film dryer.

Furthermore, if the produced powder contains cladding 8 and water, the mechanical strength of the molded pellets will be weak, and the pellet breakage rate will likely be high.

Furthermore, when the concentration of Na2SO4, which is a dissolved component, increases,
There is a risk that the amount of solids processed will be too large and products will adhere to and accumulate on heat transfer surfaces and rotor blades, resulting in the formation of undried powder and abnormal wear and vibration of equipment.

An object of the present invention is to provide a method for treating waste liquid in a centrifugal thin film dryer that can maintain stable performance even if the composition or concentration of the waste liquid changes.

The present invention has experimentally confirmed that the operating performance of a centrifugal thin film dryer is greatly affected by the composition and concentration of waste liquid, and that performance deterioration and troubles are likely to occur, and as a means to prevent this,
First, undissolved crud in the waste liquid is separated and removed, and then
The concentration of dissolved components is measured and the processing flow rate is determined according to the concentration.

The concentration is generally measured by the specific gravity method, and in order to improve measurement accuracy, it is necessary to separate and remove the cladding before measuring.

Further, the time required for cladding separation is determined by changes in radioactivity intensity.

That is, highly radioactive Co-60 and Mn-54
etc. are attached to the cladding, so the radioactive intensity of the liquid from which the cladding has been removed is low, and the liquid in which the cladding has accumulated becomes a dog.

Therefore, the separation state of the cladding can be detected by measuring the radioactivity intensity from the outside.

In addition, regarding the processing flow rate, we experimentally confirmed that centrifugal thin film dryers have the same performance when the solids processing amount is the same, and we adjusted the solids concentration to keep the solids processing amount below the specified value. The processing flow rate is determined based on the

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows an embodiment according to the present invention, in which 12 and 13 are radioactivity measuring instruments, 14 is an electromagnetic ball valve, 15 is a transfer pump,
16 is a cladding processing device, 17 is a concentration meter, 18 is a separation time determining device, and 19 is a processing flow rate determining device.

A radioactive waste liquid A containing Na 2 SO4 as a main component is supplied to a waste liquid tank 1, and when a specified amount of waste liquid A has entered the waste liquid tank 1, the waste liquid A is left to stand, and the insoluble cladding B is allowed to settle.

At this time, the surface dose rate of the radiation measuring devices 12 and 13 provided on the side and bottom surfaces of the waste liquid tank 1 changes as shown in FIG.

Characteristic 20 shows the surface dose rate at the bottom of the tank, and characteristic 21 shows the surface dose rate at the side of the tank.

That is, at the bottom of the tank, Co-60 and Mn
The surface dose rate increases because the crud to which radioactive substances such as -54 are attached gathers, and when the sedimentation is almost complete, the surface dose rate becomes saturated.

On the side of the tank, the opposite is true. Therefore, by inputting the change in surface dose rate into the separation time determination device 18, the required time H for cladding sedimentation separation is determined.

Next, the concentration of the supernatant liquid from which cladding B has been removed is measured using a densitometer 17.

If the waste liquid contains crud as mentioned above,
Since the error in the concentration measurement is significant, the concentration measurement is necessarily performed after the clad separation.

The processing flow rate is determined by the processing flow rate determining device 19 based on the concentration measurement result, and the supernatant liquid is supplied to the waste liquid tank 1 by the pump 9 and the regulating valve 1.
0, supplied to the centrifugal thin film dryer 2 via the flow meter 11.

The relationship between concentration and processing flow rate is shown in Figure 4.

Figure 4 shows heat transfer area 2? ? These are experimental results obtained using the Z2 centrifugal thin film dryer, and the stable operation region E is divided by two straight lines.

In other words, the waste liquid treatment flow rate is 10
oKg/rr?・H or less is required, and the solid content processing amount is based on the experimental results') 18Ky/rr? - Must be less than h.

The centrifugal thin film dryer 2 and subsequent parts operate in the same manner as before.

On the other hand, the cladding b includes the electromagnetic ball valve 14 and the transfer pump 15.
is supplied to the cladding processing device 16 for processing.

According to this embodiment, even if the composition and concentration of the waste liquid fluctuates, it is possible to prevent scaling of the heat transfer surface of the centrifugal thin film dryer 2 and abnormalities in equipment such as the rotor blades, thereby stabilizing the operation and improving the operating rate. realizable.

Furthermore, since the resulting powder contains extremely little crud, which is an impurity, the pellet breakage rate is greatly reduced.

Furthermore, since the radioactivity intensity of the produced pellets can be uniform and reduced, the drum packing efficiency can be doubled or more, and storage becomes easy.

In the embodiment shown in FIG. 2, the concentration of the supernatant liquid was measured using the densitometer 17, but the concentration may also be detected using the radioactivity measuring device 12.

In other words, during steady operation of a BWR power plant, the Na
2 SO4 concentration and specific radioactivity are almost proportional.

Therefore, the surface dose rate measured by the radioactivity measuring device 12 after the clad sedimentation and separation is approximately proportional to the concentration, as shown in FIG. 5, and the concentration can be measured by the radioactivity measuring device 12.

According to this embodiment, the same effects as those shown in the above-mentioned embodiments can be obtained, and the densitometer becomes unnecessary, so that the apparatus becomes simple.

However, when various waste liquids are mixed in, such as during regular inspections, it is difficult to measure the concentration using the radioactivity measuring device 12 because the chemical concentration and specific radioactivity are not proportional.

According to the present invention, the following effects can be achieved.

(1) Trouble caused by scaling of centrifugal thin film dryers can be prevented, and operational performance can be stabilized and operation rates improved.

(2) The breakage rate of the granulated pellets can be reduced, and the radioactivity intensity of the pellets can be uniformly reduced, so the drum packing efficiency can be increased and storage becomes easy.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a processing device to which a conventional method is applied, Fig. 2 is a system diagram of a processing device to which a preferred embodiment of the present invention is applied, and Fig. 3 shows the temporal change in surface dose rate. FIG. 4 is a characteristic diagram showing the relationship between Na 2 SO 4 concentration and processing flow rate, and FIG. 5 is a characteristic diagram showing the relationship between surface dose rate and Na 2 SO 4 concentration. 2... Centrifugal thin film dryer, 12, 13...
・Radiation measuring device, 16... Cladding processing device,
17... Concentration meter, 18... Separation time determining device, 19... Processing flow rate determining device.

Claims (1)

[Claims] 1. In a method of pulverizing waste liquid using a centrifugal thin film dryer, a means for separating the crud and dissolved components in the waste liquid;
A method for treating waste liquid using a centrifugal thin film dryer, comprising means for subsequently measuring the concentration of dissolved components and determining a processing flow rate of the waste liquid to be supplied into the centrifugal thin film dryer according to the concentration.