JPH0123164B2 - - Google Patents

Description

Detailed Description of the Invention This invention uses chemicals to clean a porous tube filter made of sintered fine stainless steel powder, which is the body of a parallel flow filtration device used for wastewater treatment in nuclear power plants, etc. Regarding how to.

Parallel flow equipment is used to filter and reuse treated water that does not contain crud from wastewater containing crud discharged from nuclear power plants, etc. An inlet chamber 3 is provided at one end of the interior of the filter 1 with a partition plate 2, and an outlet chamber 5 is provided with a partition plate 4 at the other end. Wastewater from a nuclear power plant or the like flowing into a circulation tank 7 is supported so as to be in communication with the circulation tank 7, and is force-fed to the inlet chamber 3 by a circulation pump 8.
While the waste water passes through each tube filter 6 and flows out into the outlet chamber 5, the treated water that does not contain cladding passes through the water chamber 9 between the two partition plates 2 and 4 and is collected outside. Concentrated wastewater with a high concentration of crud that has flowed out is returned to the circulation tank 7, and together with the wastewater that has newly flowed into the circulation tank, it is again forced into the inlet chamber 3 by the pump 8, and by circulating in this way, treated water is recovered. It is.

The differential pressure in this device is the average of the inlet pressure value _P1 indicated by the pressure gauge connected to the pipe from the inlet chamber 3 and the inlet pressure value _P2 indicated by the pressure gauge connected to the pipe from the outlet chamber 5. It is expressed as the difference between the treated water pressure value _P3 indicated by the pressure gauge connected to the pipe from the overwater chamber 9, and ΔP= _P1 + _P2 /2- _P3 . Therefore, the closer this excess pressure differential pressure ΔP is to 0,
A large amount of treated water can be recovered, and in this state, the inner surface of each tube filter has pores in the wastewater that are about the same size or larger than the pores (porous holes) of about 0.2 μm in the filter. A cake layer of crud is formed, with smaller cruds being trapped in the interstices of the larger cruds forming the cake layer, or flowing out into the outlet chamber for a stable filtration. The flow rate of wastewater passing through the tube filter is faster as it moves away from the inner surface of the filter, so when the cake layer grows and increases in thickness, the surface part comes into contact with the high-speed flow of wastewater and is peeled off, so the flow rate of wastewater increases. The cake layer can maintain a predetermined constant thickness depending on the conditions. However, as the operating time elapses, more fine cruds are captured in the gaps between the cruds of the cake layer, the gaps become clogged, and the cake layer becomes compacted. As a result, the differential pressure ΔP gradually increases, the amount of recovered treated water gradually decreases, and it becomes impossible to carry out filtration with a predetermined efficiency.

The wastewater used in nuclear power plant wastewater treatment contains CRAD, a highly radioactive SS consisting mainly of iron oxides, so it becomes radioactive waste and poses a problem in its disposal.

Therefore, when the excess pressure ΔP reaches a certain value,
Or at regular intervals regardless of the rise in differential pressure,
The filtration process is stopped for a few seconds, for example, 3 to 30 seconds, and during that time, filtrated water, compressed air, or a gas-liquid mixture is supplied to the filtration chamber and passed through the tube filter in the opposite direction to the water flow direction during the filtration process to perform backwashing. , the cake layer is loosened to remove the fine cruds clogging the gaps, and the tube filter is used for a long life (for example, about 30 years). However, due to backwashing errors or pump flow rate control errors, trouble may occur in which the excess pressure does not decrease to a predetermined value even after backwashing.

Therefore, an object of the present invention is to provide a method for chemically cleaning and renewing the tube filter using a cleaning chemical solution that dissolves the crud in such a case.

The cleaning chemical solution used in the present invention needs to contain an acid because the crud to be dissolved and removed is mainly composed of iron oxide as described above. A reducing agent is also added, because as mentioned above, the porous tube filter is a metal product made by sintering fine stainless steel powder, so washing it with acid will promote the dissolution of the iron oxide crud. At the same time, the eluted oxidizing ions promote passivation of the stainless steel surface of the porous tube filter, which is preferable. Furthermore, if necessary, an anticorrosive agent is included in the cleaning chemical solution.

Acids that can be used include oxalic acid, citric acid, acetic acid,
There are ethylenediaminetetraacetic acid (EDTA) and other organic acids, sulfuric acid, nitric acid, hydrochloric acid, phosphonic acid and other inorganic acids, and one or more of them are used. As the reducing agent, one or more of oxalic acid, erythorbic acid, ascorbic acid, hydrazine, other organic ring agents, and appropriate inorganic ring agents can be used.

In order to distribute the cleaning chemical liquid to the tube wall of each tube filter, there are two main methods: supplying it to the inlet chamber 3 or outlet chamber 5 of the over-shell as shown in FIG. 1, and supplying it to the over-chamber 9 of the over-shell as shown in FIG. There is a method shown in It is preferable to use these in combination, but only one of them may be used. In addition, in the case of combined use, in the explanation below, a pump or chemical tank is provided for each method, but this is for the sake of ease of explanation, and it is not possible to use multiple identical ones depending on piping and valve operation. This can be avoided.

In the case of FIG. 1, in order to supply chemical liquid to the inlet chamber 3, there is a liquid supply pipe 8' that supplies liquid from the circulation tank 7 to the conduit 3' to the inlet chamber 3 with a pump 8, a pump 11 from the chemical liquid tank 10, Chemical solution supply pipes 11' that supply cleaning chemicals through filters 12 are connected through valves. A conduit 5' leading to the outlet chamber 5 includes a circulation pipe 7' for returning the concentrated liquid obtained during the over-processing to the circulation tank 7, and a filter 13 for transporting the cleaning chemical solution discharged into the exit chamber during the cleaning process. Return pipes 10a, which are then returned to the chemical tank 10, are connected through valves, and a conduit 9' leading to the over-processing chamber 9 has a take-out pipe 14 for taking out over-treated water obtained during the over-processing process, and a take-out pipe 14 for taking out over-treated water obtained during the over-processing process. A second return pipe 10b for returning the cleaning chemical solution discharged into the cleaning chamber 9 to the chemical solution tank 10 through the filter 15 is connected to each via a valve. In order to supply a chemical solution to the outlet chamber 5 for cleaning, the chemical solution supply pipe 11' may be connected to the conduit 5', and the return pipe 10a may be connected to the conduit 3'.

In the case of FIG. 2, the chemical solution supply pipe 11' is connected to the conduit 9' via a valve in order to supply the chemical solution to the overchamber 9.
A return pipe 1 that returns to the chemical tank 10 that has undergone the cleaning action
0a and 10b are connected via valves to conduits 5' and 3'.

In either case, the valves in the stock solution supply pipe 8', the circulation pipe 7', and the take-out pipe 14 are opened, and the valves in the chemical solution supply pipe 11' and return pipes 10a and 10b are closed to perform the over-processing. When performing the cleaning process, the opening and closing of each of the above-mentioned valves can be reversed.

The cleaning pump 11 does not require high pressure or large capacity because the chemical solution only needs to flow inside the pipe.

The filters 12, 13, 15 provided in the chemical supply pipe 11' and the return pipes 10a, 10b collect detached solid crusts that may be contained in the chemical solution discharged from the tube filter after the cleaning action. Circulating the chemical solution prevents it from entering the tube filter again and causing clogging.

Further, since the cleaning chemical exhibits a great cleaning effect when the temperature is high to a certain extent, a heating device such as a heater 16 immersed in the chemical tank 10 is provided to heat the chemical inside.

When cleaning with the chemical solution is completed, and if necessary once or several times during the cleaning process, the above-mentioned backwashing is performed by supplying hydrogenated water, compressed air, or a gas-liquid mixture to the filter chamber to remove undissolved substances. The fine crud is discharged from the cake layer and separated by filters 12, 13, 15 or received in a separate storage tank for removal. still,
The effect is remarkable when the pressure during backwashing is set to a high pressure of about 10 kg/cm ² .

Example: Clad containing iron oxide as the main component at a concentration of approximately
Wastewater containing 400 ppm was circulated through a tube filter having pores of approximately 0.5 μm, and a filtration process was performed for 500 hours. As a result, the excess pressure ΔP of the tube filter was initially 0.3Kg/cm ² (400/m ² hr/each), but it increased to 3.7Kg/cm ² (same). Then, chemical cleaning using a cleaning chemical solution was performed as shown in FIG.

The cleaning chemical solution is 25% citric acid as an acid, 1.0% erythorbic acid as a reducing agent, and Ivit 30AR (trade name manufactured by Asahi Chemical Co., Ltd.) as a corrosion inhibitor.
The solution was adjusted by adding 0.3% of the solution, and the solution was placed in the chemical tank 10 and heated to 80°C. The amount of chemical liquid has an overarea of 0.045
Approximately 10 tubes per m ² tube filter.

Circulating the heated chemical solution at a rate of 0.1/min,
I washed it for hours. Next, the over-treated water obtained in the previous filtration process was pressurized to 10 kg/cm ² and backwashed, and then the wastewater filtration was restarted, and the excess pressure was reduced to the original 0.3 kg/cm ² (400/cm 2 ). ^m2・hr・per piece)
It was confirmed that it had been thoroughly cleaned.

[Brief explanation of drawings]

FIG. 1 is a flow sheet of an example of a parallel flow device in which the method of the present invention can be carried out, and FIG. 2 is a flow sheet of another example of the same, in which 6 is a porous tube filter, 10 is a tank for cleaning chemical solution, 11'
10a and 10b are chemical liquid supply pipes, and 10a and 10b are chemical liquid return pipes after cleaning.

Claims (1)

[Claims] 1 Wastewater containing radioactive waste is supplied from an inlet at one end parallel to the filtration surface, and circulated while being discharged from an outlet at the other end, and the filtered water is piped in a direction perpendicular to the flow of the wastewater. A method for cleaning a porous tube filter made by sintering fine stainless steel powder taken out from the wall, which is characterized by flowing a cleaning chemical solution containing an acid as a main component and a reducing agent through the tube wall. Method.