JP5498326B2 - Method and apparatus for treating boric acid-containing waste liquid - Google Patents

Description

  The present invention relates to a method for treating boric acid-containing waste liquid.

  Since the boric acid-containing waste liquid generated in a pressurized water reactor (PWR) or the like contains boric acid containing a radionuclide, it must finally be solidified with cement or the like. However, since boric acid prevents the cement from solidifying, there is a limit to the amount of boric acid that can be added to the cement. For this reason, a pretreatment is performed in which a boric acid-containing waste liquid is preliminarily added with a calcium compound such as calcium hydroxide to insolubilize boric acid and precipitate a borate such as calcium borate. A method is known in which an acid salt) is dried to be pulverized and cemented, thereby preventing boring acid from hindering cement solidification.

  However, the above-described method has a problem that the viscosity of the boric acid-containing waste liquid increases, and calcium borate settles and accumulates in a staying portion or the like in the pipe and the pipe is blocked. For this reason, an alkali metal element compound and an alkaline earth metal compound are added to a boric acid-containing waste liquid heated to 80 ° C., and the waste liquid is allowed to flow through the piping while being kept at a temperature equal to or higher than the precipitation temperature, and supplied to the dryer. There has been proposed a method of suppressing sedimentation or the like to a staying portion in a pipe by performing a drying process (for example, see Patent Document 1).

  On the other hand, the water vapor generated in the drying step contains borate such as calcium borate generated in the pretreatment step, and the borate settles and accumulates in the staying part in the piping, and the piping and condenser are There was a problem of blocking.

JP 2000-284092 A

  The present invention provides a novel boric acid-containing waste liquid treatment method and treatment apparatus capable of preventing the clogging of piping associated with drying treatment of borate produced by insolubilizing boric acid in the boric acid-containing waste liquid. The purpose is to provide.

  One aspect of the present invention is a method for treating a boric acid-containing waste liquid that solidifies cement, wherein the boric acid-containing waste liquid is hardly soluble in the first tank by precipitating insoluble borate. 1 step, the second step of transporting and storing the hardly soluble boric acid-containing waste liquid in a second tank having a stirrer, and the poorly soluble boric acid containing waste liquid being the second tank A third step in which the borate contained in the hardly-solubilized boric acid-containing waste liquid is dried and separated, and part of the borate produced in the dryer A fourth step of condensing the water vapor contained in the cooler to produce condensed water containing a portion of the borate, and a fifth step of removing a portion of the borate in the condensed water in a purifier. And supplying the washing water from the washing water tank Washed, characterized in that it comprises a sixth step of transferring into the second tank a cleaning liquid waste containing residues of the borate relates to a process for the treatment of boric acid-containing waste liquid.

  ADVANTAGE OF THE INVENTION According to this invention, the boric-acid waste liquid which can prevent the blockage of the piping accompanying the drying process of the borate produced | generated by insolubilizing the boric acid in a boric-acid containing waste liquid, and A processing device can be provided.

It is a figure which shows schematic structure of the processing apparatus of the boric acid containing waste liquid in embodiment. It is a flowchart which shows the processing method of a boric-acid containing waste liquid using the processing apparatus shown in FIG.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a boric acid-containing waste liquid treatment apparatus in the present embodiment. As shown in FIG. 1, the processing apparatus of this embodiment includes a pretreatment tank (first tank) 1 and a storage tank (second tank) 3 connected to the pretreatment tank 1 via a pipe 21. And have. Furthermore, it has a head tank 6 connected to the storage tank 3 via a pipe 22, and a dryer 7 connected to the head tank 6 via a pipe 23. Furthermore, the dryer 7 and the washing water tank 12 connected through the pipes 23 and 29 are provided.

  Moreover, it has the dryer 7, the condenser 26 connected via the piping 26 and the pressure gauge 5C, and the bleeder 13 connected via this condenser 11 and the piping 27. Furthermore, it has the condensed water storage tank 14 connected via the extraction apparatus 13 and the piping 28, and the purifier 15 connected via the condensed water storage tank 14 and the piping 35.

  A heater 1 </ b> A is installed on the side surface of the pretreatment tank 1. Moreover, the 1st stirrer 2 for accelerating | stimulating the poorly soluble process demonstrated below is provided in the pretreatment tank 1. FIG.

  The storage tank 3 is provided with a second stirrer 4 for stirring and refining the borate in the boric acid-containing waste liquid described below and the borate residue transferred from the dryer 7. It has been. In addition, the pipe 22 is provided with a pump 5, and pressure gauges 5 </ b> A and 5 </ b> B are arranged before and after the pump 5 to monitor the pressure before and after the pump 5 and to control the driving force of the pump 5.

  Next, a boric acid-containing waste liquid treatment method using the treatment apparatus shown in FIG. 1 will be described with reference to the flowchart shown in FIG.

  First, the boric acid-containing waste liquid is introduced into the pretreatment tank 1, and the boric acid-containing waste liquid is insolubilized (S1). This poorly soluble treatment can be performed, for example, by adding an alkaline earth metal compound to the boric acid-containing waste liquid. As a result, insoluble borate, such as calcium borate, is precipitated in the boric acid-containing waste liquid, which makes the boric acid-containing waste liquid hardly soluble.

  An appropriate amount of the alkali metal compound can be added before and after the addition of the alkaline earth metal compound. In this case, sedimentation of the precipitate obtained as described above, that is, borate can be prevented.

  The addition amount of the alkali metal compound is set so that the molar ratio of the alkali metal in the alkali metal compound to boron in the boric acid-containing waste liquid is 0.25 to 0.35, preferably 0.3. For example, in the case of NaOH, Na / B (molar ratio) = 0.25 to 0.35, preferably 0.3, and in the case of KOH, K / B (molar ratio) = 0.25 to 0.35, preferably Is 0.3.

The addition amount in the case of an alkaline earth metal compound is such that the molar ratio of the alkaline earth metal in the alkaline earth metal compound to boron in the boric acid-containing waste liquid is 0.40 to 0.50, preferably 0.45. Set as follows. For example, in the case of Ca (OH) ₂ , Ca / B (molar ratio) = 0.40 to 0.50, preferably 0.45. As the alkaline earth metal compound, Mg (OH) ₂ can be used in addition to Ca (OH) ₂ .

  In the pretreatment tank 1, the side surface is heated to 95 ° C. or higher by the heater 1A so that the moisture in the boric acid-containing waste liquid does not adhere to the side wall.

  In addition, when the alkaline earth metal compound and further the alkali metal compound are added to make the solution hardly soluble, the boric acid-containing waste liquid is made slightly soluble by the first stirrer 2 provided in the pretreatment tank 1. Stir for several hours until

  Next, the boric acid-containing waste liquid that has been sparingly soluble in the pretreatment tank 1 is transferred to the storage tank 3 via the pipe 21 and stored (S2). Next, the pump 5 is transferred to the head tank 6 via the pipe 22 and once stored, and then transferred from the head tank 6 to the dryer 7 via the pipe 23 (S3).

  The head tank 6 is provided with a liquid level gauge (not shown) and holds the level of the hardly soluble boric acid-containing waste liquid in the head tank 6. A flow meter 8 is provided in the pipe 23, and the amount of hardly soluble boric acid-containing waste liquid to be supplied from the head tank 6 to the dryer 7 is controlled in consideration of the drying capacity of the dryer 7. . The head tank 6 is for supplying an appropriate flow rate, and a pump having the same function may be substituted.

  In the dryer 7, for example, borate is precipitated from the introduced hardly-solubilized boric acid-containing waste liquid by a heater, heating steam or the like (not shown), and dried and separated (S4). Since the separated borate becomes a dry powder, it is taken out from the dryer 7 through the three-way valve 7A, temporarily stored in the powder receiving hopper 9, and its weight is measured to derive the amount of cement required for cement solidification. After that, it is supplied to the cement solidifying system 10. The cement solidifying system 10 is supplied with the amount of cement derived as described above from a supply device (not shown), and is supplied with a predetermined amount of water from the washing water tank 12 through the pipe 32, whereby the boric acid is supplied. The dried salt powder is used for cement solidification.

  On the other hand, since the water in the waste liquid dried and separated by the dryer 7 evaporates to become water vapor, this water vapor is transferred to the condenser 11 via the pipe 26 and further extracted via the pipe 27. Transport to. In addition, the pressure gauge 5C is arrange | positioned at the piping 26, and it is comprised so that the obstruction | occlusion of the piping 26 may be detected by the rise in pressure. The bleeder 13 has a bleed tank and a bleed pump (not shown), and circulates and cools the water vapor transferred into the bleed tank by the bleed pump to produce condensed water. From this point of view, the extraction device 13 functions as a cooler for water vapor.

  The condensed water produced | generated as mentioned above is transferred to the condensed water storage tank 14 via the piping 28, and is stored (S5). Thereafter, the condensed water is transferred to the purifier 15 via the pipe 35 (S6).

  As described above, since water vapor contains borate such as calcium borate remaining in the dryer 7, the produced condensed water also contains borate. Therefore, in the purifier 15, the borate contained in the condensed water is removed.

  When removing the borate, for example, the pH of the condensed water in the purifier 15 can be adjusted to precipitate and remove the borate. That is, by adding an appropriate pH adjusting agent to the condensed water, a precipitate is obtained by reacting this pH adjusting agent with a borate, and this precipitate is removed. For example, sodium bicarbonate or carbon dioxide gas is reacted with calcium borate to obtain calcium carbonate, which is precipitated and removed.

  As the pH adjuster, for example, air, carbon dioxide gas, or a mixed gas thereof can be used. In this case, the pH of the condensed water shifts to the acidic side. Moreover, sodium hydrogencarbonate can be used as a pH adjuster, for example. In this case, the pH of the condensed water shifts to the alkaline side.

  The pH of the condensed water is preferably 10 or less, and more preferably in the range of 8 to 9.5. That is, by introducing a pH adjuster so that the pH value of the condensed water falls within the above range, the efficiency of producing precipitates by reacting the pH adjuster with the borate increases, and the concentration of boron in the condensed water increases. Removal of the acid salt can be performed efficiently.

  Furthermore, the temperature of the condensed water in the purifier 15 is preferably 40 ° C to 70 ° C. Thereby, since the solubility with respect to condensed water of borate, such as a calcium borate, becomes low, it becomes possible to efficiently remove the borate in condensed water as the above-described precipitate or the like.

  The purifier 15 includes at least one of a filtration membrane and a centrifuge, and the borate in the condensed water can be removed by filtration and / or centrifugation.

  The condensed water after the borate has been removed in the purifier 15 can be used as washing water. For example, the condensed water can be transferred to the washing water tank 12 via the pipe 31 by the pump 17 and used for washing the dryer 7. it can. Further, the removed borate can be used as a solidifying material, and can be transferred to the cement solidification system 10 via the pipe 33 and used for the cement solidification described above. Therefore, it is possible to reduce the amount of cleaning water and cement used.

  On the other hand, after carrying out the drying process in the dryer 7, washing water is introduced into the dryer 7 from the washing water tank 12 through the pipes 29 and 23 by the pump 18, and the inside of the dryer 7 is cleaned (S7). ).

  Since there is a residue of precipitated and dried borate in the dryer 7, the residue is included in the cleaning waste liquid generated after the dryer 7 is cleaned. Since this residue is radioactive, the cleaning waste liquid containing such a residue is transferred to the storage tank 3 via the pipe 25 (S8).

  Moreover, it is preferable that the washing water in the washing water tank 12 is saturated with carbon dioxide gas in advance. In this case, since the solubility of the calcium compound such as calcium borate in the washing water in the solid content adhering to the inner wall of the dryer 7 is increased, the inside of the dryer 7 is dissolved and washed with the calcium compound. The washing operation can be simplified.

  Thereafter, the residue is transferred to the dryer 7 again through the above-described steps together with the hardly-solubilized boric acid-containing waste liquid supplied from the pretreatment tank 1, and dried and separated.

  At this time, when the residue is relatively large, the pipe 25 may be blocked when the cleaning waste liquid containing the residue is transferred from the dryer 7 to the storage tank 3. Moreover, when transferring from the storage tank 3 to the dryer 7, the pipes 22 and 23 may be blocked. Therefore, in this embodiment, after the cleaning waste liquid containing the residue is transferred into the storage tank 3 (S8), the waste liquid stored in the storage tank 3 by the second stirrer 4 provided in the storage tank 3 is used. Stir and finely refine the residue (S9).

  Accordingly, at least when the residue is transferred from the storage tank 3 to the dryer 7 together with the hardly soluble boric acid-containing waste liquid, it is possible to prevent the pipes 22 and 23 from being blocked. In addition, even when the residue remains in the dryer 7 again, the residue is already finely divided, so that the cleaning waste liquid containing the residue is piped when the inside of the pipe 25 is transferred. 25 occlusions can be suppressed.

  As described above, by the stirring by the second stirrer 4 provided in the storage tank 3, not only the residue but also the insoluble in the hardly soluble boric acid-containing waste liquid supplied from the pretreatment tank 1 to the storage tank 3. Since borate can also be finely divided in advance, blockage of the pipes 22 and 23 due to the borate when initially transferred from the storage tank 3 to the dryer 7 can also be suppressed. Furthermore, since the size of the residue in the dryer 7 can be reduced as the borate is refined, the blockage of the pipe 25 during transfer from the dryer 7 to the storage tank 3 is also suppressed. can do.

The stirring speed of the storage tank 3 by the second stirrer 4 is preferably 155 times / minute or more. The stirring power of the second stirrer 4 can be 0.28 kW / m ³ or more. Thereby, the residue can be sufficiently refined by the second stirrer 4, and the original insoluble borate contained in the boric acid-containing waste liquid can be sufficiently refined.

In addition, although the stirring speed and stirring power of the 2nd stirrer 4 will not be specifically limited if it is more than the said lower limit, each upper limit can be 500 times / min and 1.10 kW / m < ³ >.

  In addition, when the processing conditions of the boric acid containing waste liquid shown in FIG. 1 were changed variously, the amount of boric acid containing water vapor generated could be reduced by about 30%.

  As mentioned above, although several embodiment of this invention was described, these embodiment was posted as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Pretreatment tank 1A Heater 2 First stirrer 3 Storage tank 4 Second stirrer 5, 17, 18 Pump 5A, 5B, 5C Pressure gauge 6 Head tank 7 Dryer 7A Three-way valve 8 Flow meter 9 Powder receiving hopper 10 Cement solidification system 11 Condenser 12 Washing water tank 13 Extraction device 14 Condensate storage tank 15 Purifier 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33 Piping

Claims (10)

A method for treating boric acid-containing waste liquid that solidifies into cement,
A first step of making the boric acid-containing waste liquid hardly soluble in the first tank by precipitating insoluble borate;
A second step of transporting and storing the hardly soluble boric acid-containing waste liquid into a second tank having a stirrer;
Transferring the hardly soluble boric acid-containing waste liquid from the second tank to a dryer, and drying and separating the borate contained in the hardly soluble boric acid-containing waste liquid; and
A fourth step of condensing water vapor containing a part of the borate produced in the dryer with a cooler to produce condensed water containing a part of the borate;
A fifth step of removing a portion of the borate in the condensed water in a purifier;
A sixth step of supplying cleaning water from a cleaning water tank to clean the dryer, and transferring cleaning waste liquid containing the borate residue into the second tank;
A method for treating boric acid-containing waste liquid, comprising:   The boric acid-containing product according to claim 1, wherein in the purifier, a part of the borate in the condensed water is precipitated and removed by controlling a pH of the condensed water to 10 or less. Waste liquid treatment method.   The said purifier WHEREIN: By controlling the pH of the said condensed water to 8-9.5, a part of said borate in the said condensed water is settled and removed, The characterized by the above-mentioned. Treatment method of boric acid-containing waste liquid.   The pH of the condensed water is adjusted by blowing air, carbonic acid, or a mixed gas thereof into the condensed water stored in the purifier. Treatment method of acid-containing waste liquid.   The pH of the boric acid-containing waste liquid is adjusted by adding sodium hydrogen carbonate to the condensed water stored in the purifier. Of boric acid containing waste liquid.   In the said purifier, the temperature of the said condensed water is hold | maintained at 40 to 70 degreeC, The processing method of the boric acid containing waste liquid as described in any one of Claims 1-5 characterized by the above-mentioned.   The said purifier removes a part of said borate in the said condensed water by at least one of a filtration membrane and a centrifuge, The processing method of the boric acid containing waste liquid of Claim 1 characterized by the above-mentioned.   In the said purifier, the said condensed water after a part of said borate is removed is used as a part of the said wash water, It is characterized by the above-mentioned. Treatment method of boric acid-containing waste liquid.   The method for treating a boric acid-containing waste liquid according to any one of claims 1 to 8, wherein a part of the borate removed in the purifier is used as a part of a cement solidifying material. An apparatus for treating boric acid-containing waste liquid that solidifies cement,
A first tank for making the boric acid-containing waste liquid hardly soluble by precipitating insoluble borate;
Storing the hardly-solubilized boric acid-containing waste liquid transferred from the first tank, a second tank having a stirrer and a pH adjusting agent injection nozzle;
A drier for drying and separating the borate contained in the hardly soluble boric acid-containing waste liquid transferred from the second tank;
A washing water tank for supplying washing water to the dryer for washing;
A condenser for condensing water vapor containing a part of the borate produced in the dryer to produce condensed water containing a part of the borate;
A purifier for removing a portion of the borate in the condensed water;
An apparatus for treating waste liquid containing boric acid, comprising:

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