JP2989403B2 - Treatment method for cleaning wastewater discharged from nuclear power plants - 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 treating washing wastewater discharged from a nuclear power plant.

[0002]

2. Description of the Related Art Washing wastewater such as handwashing water, shower water and washing wastewater generated in a controlled area such as a nuclear power plant is a low-level radioactive waste and cannot be discharged as it is. Osmotic membrane (Reverse
Osmosis (RO). The conventional method will be specifically described with reference to FIG. In FIG. 3, the washing wastewater is first sent to the stock solution tank 1, passes through a prefilter 13 by a prefilter supply pump 12 to remove coarse suspended substances, and is supplied to a reverse osmosis device circulation tank 14. The water in the reverse osmosis device circulation tank 14 is pressurized by a reverse osmosis device supply pump 15 and is supplied to a reverse osmosis membrane module 16.
The permeated water from the reverse osmosis membrane from which radioactivity has been removed is discharged out of the system through the reverse osmosis treated water line 18. The concentrate of the reverse osmosis membrane passes through the reverse osmosis concentrated water circulation line 17 and returns to the reverse osmosis device circulation tank 14 again. Concentration is performed sequentially by the above-described route, and when a predetermined concentration ratio is reached, the apparatus is stopped, and the concentrated liquid passes through the reverse osmosis concentrated water discharge line 19 and is solidified by the existing waste liquid solidifying apparatus and stored at the site.

Further, as shown in FIG. 4, there has been proposed a processing apparatus in which an acrylonitrile ultrafiltration membrane and a spiral reverse osmosis membrane are combined (Japanese Patent Application Nos. Hei 3-100637).
issue). In FIG. 4, the washing wastewater is first sent to a stock solution tank 1 and sent to an ultrafiltration module 3 by an ultrafiltration supply pump 2. In the ultrafiltration module 3, there are two types of permeated water from which suspended substances are removed and a liquid in which suspended substances are concentrated.
0 and is transferred to the reverse osmosis device circulation tank 13. The concentrate is circulated to the stock solution tank 1 through the stock solution circulation line 4. After being pressurized by the reverse osmosis membrane supply pump 14 from the reverse osmosis apparatus circulation tank 13, the pressure is sent to the reverse osmosis membrane module 15, and the permeated water of the reverse osmosis membrane from which radioactivity has been removed passes through the reverse osmosis treated water line 18. It is discharged out of the system. The reverse osmosis membrane concentrate passes through the reverse osmosis membrane concentrated water circulation line 16,
Returning to the reverse osmosis device circulation tank 13 again, a part of the concentrated liquid is flow-adjusted through a return line 19 by a return flow control valve 20 and a return flow controller 21 in order to remove suspended substances generated by concentration by reverse osmosis. And the stock solution tank 1
Return to Concentration is performed sequentially by the above-described route, and when a predetermined concentration ratio is reached, the apparatus is stopped, and each concentrated liquid passes through the ultrafiltration concentrated liquid discharge line 5 and the reverse osmosis concentrated water discharge line 17 and is solidified by the existing waste liquid solidification device. Will be stored at the site. In the treatment apparatus of FIG. 4, the cleaning wastewater is of a type in which a polyacrylonitrile ultrafiltration membrane focuses on a small amount of organic matter adhering to the cleaning wastewater, and a longer-time durability is obtained. .

[0004]

Among the processing apparatuses using the combination of the ultrafiltration membrane and the reverse osmosis membrane shown in FIG. 4, the ultrafiltration membrane has the following problems. (1) A hollow fiber type is used for the ultrafiltration module for miniaturization, but since the inner diameter of the tube is only about 1 mm, the flow path is blocked by thread waste or the like. (2) Permeation flow rate decreases depending on the type of surfactant used for cleaning.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method capable of extending the life of an ultrafiltration membrane and reducing running costs.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for treating washing wastewater discharged from a nuclear power plant using a hollow fiber type ultrafiltration membrane. permeate of the ultrafiltration membrane by controlling the pressure of the permeate side of the membrane
And the pressure of the washing wastewater on the inlet side of the ultrafiltration membrane or the differential pressure between the washing wastewater on the inlet side and the outlet side of the ultrafiltration membrane is detected , and only when the pressure or the differential pressure rises, A method for treating washing wastewater discharged from a nuclear power plant, comprising reversing the flow direction of the washing wastewater flowing into the outer filtration membrane.

[0007]

Since the ultrafiltration membrane of the present invention uses a hollow fiber type, the diameter of the hollow fiber is as thin as 1 mm and the length is 1 mm.
m, the pressure loss is high, and the normal liquid flow rate is 1-3k
There is a pressure loss of about g / cm ² . Therefore, when pressure is not applied to the permeated water side, this pressure loss directly serves as a driving force for liquid permeation, and a large permeation flow rate can be obtained at the initial stage, but the contaminants adhere to the membrane quickly, and the amount of permeated liquid decreases rapidly. Cause.

FIG. 2 shows the results obtained by measuring the membrane life of the simulated washing wastewater with the ultrafiltration membrane by controlling the permeation flow rate of the simulated washing wastewater variously according to the permeate pressure. As is clear from FIG. 2, it has been found that controlling the permeation flow rate increases not only the life of the membrane but also the integrated permeable water amount.

Next, the flow path is blocked by lint. Most of lint (fiber) at the time of washing is a short fiber, and therefore, many of the lint cannot be caught by a net. Requires a filter, but the filter plugs more directly with dirt and the like. As a result of various measures, if the membrane flow path (hollow fiber inlet) is clogged with yarn waste, the pressure loss will inevitably increase.
It is effective to supply the circulating water from the existing circulating water outlet side and to blow off the existing inlet-side obstruction by switching the valve by detecting the rise in the differential pressure between the washing drainage on the mouth side and the outlet side. It has been found. Further, since the flow path blockage solidifies with dirt and the like and becomes coarse, it can be removed with a net size. When the flow path is blocked, the effective membrane area is reduced. Therefore, even if the amount of the permeated liquid is controlled, the permeation flux per membrane area increases, which causes a contaminant to adhere.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to FIG. In FIG. 1, 1 is a stock tank, 2 is an ultrafiltration supply pump, 3 is an ultrafiltration module, 4 is a stock solution circulation line, 5 is an ultrafiltration concentrate discharge line, 6 is a differential pressure alarm, and 7 is a flow A path switching valve, 8 is an ultrafiltration water flow control valve, 9 is an ultrafiltration water flow controller, and 10 is an ultrafiltration water discharge line.

The washing wastewater enters a stock solution tank 1 and is transferred from the washing solution tank 1 to an ultrafiltration module 3 by an ultrafiltration membrane supply pump 2, where it is converted into a liquid from which suspended solids have been removed and a concentrated liquid. The liquid from which suspended substances have been removed is sent to the outside of the system or to a reverse osmosis device (not shown) through the ultrafiltration water discharge line 10. At this time, the amount of permeated water of the ultrafiltration membrane is adjusted to an optimum flow rate by the ultrafiltration water flow rate control valve 8 and the ultrafiltration water flow rate controller 9.

Since the degree of lint or the like clogging the inlet of the ultrafiltration hollow fiber is determined from the differential pressure measured by the differential pressure alarm 6 of the ultrafiltration module 3, when the differential pressure rises, the flow path switching valve 7 is used. The flow path is set to the opposite direction. The concentrate is returned to the stock tank 1 through the stock solution circulation line 4.

Concentration is performed sequentially by the above-described route, and when the concentration reaches a predetermined concentration ratio, the apparatus is stopped. Each concentrated liquid passes through the ultrafiltration concentration line 5 and is solidified by an existing waste liquid solidifying apparatus (not shown) and stored at the site. Is done.

[0014]

As described above, washing drainage such as washing water , hand washing water , shower water , etc. in a controlled area such as a nuclear power plant,
Oite wastewater treatment that is treated with an ultrafiltration membrane of hollow fiber type made of polyacrylonitrile, a mechanism for changing the flow direction of the raw water flow path of the ultrafiltration by detecting the increase or the like of the inlet pressure to, limit Since the flow rate of the permeated water is controlled by controlling the pressure on the raw water side and the permeated water side in the external filtration, the blockage of the ultrafiltration membrane is less likely to occur and the replacement of the membrane is not required for a long time, so running Costs are reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is a chart showing measurement results of the lifetime of a membrane when the permeation flow rate is controlled by an ultrafiltration membrane in one embodiment of the present invention.

FIG. 3 is an explanatory view of one embodiment in which washing wastewater discharged from a conventional nuclear power plant is treated by a reverse osmosis membrane module.

FIG. 4 is an explanatory view of an embodiment in which washing wastewater discharged from a conventional nuclear power plant is treated using a combination of an acrylonitrile ultrafiltration membrane and a spiral reverse osmosis membrane.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B01D 65/08 B01D 65/08 (72) Inventor Hiroshi Sagawa 1-1-1, Wadazakicho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries Kobe Shipyard Co., Ltd. (56) References JP-A-60-166006 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G21C 9/06

Claims (1)

(57) [Claims] 1. The cleaning wastewater discharged from a nuclear power plant
A method of treatment using the hollow fiber type ultrafiltration membrane, the flux of permeate inlet pressure and the membrane of the permeate side ultrafiltration membrane by controlling the pressure of the ultrafiltration membrane And the pressure or inlet pressure of the washing wastewater on the inlet side of the ultrafiltration membrane.
Detecting the differential pressure of the washing drainage port side and the outlet side, the pressure or
A method for treating washing wastewater discharged from a nuclear power plant, comprising reversing the flow direction of the washing wastewater flowing into the ultrafiltration membrane when the differential pressure rises.