JP2016148599A - Method and system for removing radioactive cesium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of efficiently removing radioactive cesium by volatilization from incineration ash while suppressing an increase in energy consumption, in a radioactive cesium removing technique for removing radioactive cesium by volatilization from incineration ash by adding a cesium volatilization accelerator to the incineration ash and heating the incineration ash.SOLUTION: When executing addition processing for adding a cesium volatilization accelerator to incineration ash generated in association with incineration of waste and heat processing for heating the incineration ash to which the cesium volatilization accelerator has been added, a method for removing radioactive cesium executes crystallization processing for holding the incineration ash in a crystallization temperature range to crystallize an amorphous component before the addition processing of the cesium volatilization accelerator.SELECTED DRAWING: Figure 1

Description

  The present invention is a radioactive cesium removal that performs an addition process of adding a cesium volatilization accelerator to incineration ash generated with incineration of waste and a heating process of heating the incineration ash to which the cesium volatilization accelerator is added. The present invention relates to a method and a radioactive cesium removal system.

  In "Fukushima Prefecture's Policy on Disposal of Disaster Waste" (June 23, 2011, Ministry of the Environment), regarding the handling of incineration ash generated by incineration of disaster waste containing radioactive materials, the concentration of radioactive cesium ( If the total value of cesium 134 and cesium 137 (hereinafter referred to as “radioactivity concentration”) exceeds the standard value of 8,000 Bq / kg, storage in an intermediate storage facility is required. There is a policy that in some cases landfill is possible at a general waste final disposal site (managed final disposal site). However, in order to promote landfill disposal, it is required to remove radioactive cesium from such incinerated ash to further reduce the radioactive concentration of the incinerated ash.

  In addition, in the process of incineration of waste, most of the radioactive cesium in the waste moves to the exhaust gas and adheres to the fly ash, so the radioactivity concentration of the main ash is lower than that of the fly ash and is below the above standard value. Often. However, there is a possibility that the amount of main ash exceeding the above-mentioned standard value will increase in the future as volume reduction by incineration of decontamination waste in high-dose areas such as special decontamination areas is promoted. Therefore, in order to reduce the amount of main ash brought into intermediate storage facilities with limited storage capacity, it is necessary to remove radioactive cesium from such main ash and reduce the radioactivity concentration of main ash. It is done.

  As a conventional radioactive cesium removal technology that removes radioactive cesium from incineration ash, incineration ash is volatilized and removed from incineration ash by adding cesium volatilization accelerators such as chloride compounds and heating for a long time. The thing is known (for example, refer patent documents 1-3).

  In addition, there is a report that 95% of the radioactive cesium in the main ash is incorporated in the amorphous material (see, for example, Non-Patent Document 1).

JP 2014-174090 A JP 2013-120146 A JP2013-122440A

Anjo Tojo, Mikako Ishii, Takayuki Matsuo, Toshihiko Matsufuji, Takayuki Shimaoka, "Study on the existence and long-term stability of insoluble cesium in incinerator main ash", 25th Annual Conference of Japan Society for Waste Recycling Vol. D6-3, September 16-17, 2014, pp. 477-478

  As described above, most of the radioactive cesium incorporated into the amorphous material is hardly soluble because it is incorporated into the amorphous material, and is difficult to remove. On the other hand, in the conventional radioactive cesium removal technology, it was necessary to heat the incineration ash to a very high temperature (for example, more than 1200 ° C.). In this case, a large amount of energy is required. There is also a problem that the original properties are greatly changed and difficult to handle.

  In view of this situation, the main problem of the present invention is to increase the energy consumption in the radioactive cesium removal technology that volatilizes and removes radioactive cesium from the incinerated ash by adding a cesium volatilization accelerator to the incinerated ash and heating it. It is in the point of providing the technique which can volatilize and remove radioactive cesium from incineration ash efficiently.

The first characteristic configuration of the present invention includes an addition process for adding a cesium volatilization accelerator to the incineration ash generated with incineration of waste, and a heating process for heating the incineration ash to which the cesium volatilization accelerator is added. A method of removing radioactive cesium,
Before the addition process, a crystallization process is performed in which the incinerated ash is maintained in the crystallization temperature range and the amorphous component is crystallized.

  According to this feature configuration, the amorphous occupying most of the incinerated ash is changed to a crystal structure by crystallization treatment, and the radioactive cesium is efficiently volatilized and removed from the incinerated ash while suppressing an increase in energy consumption. it can.

  That is, it is considered that most of the radioactive cesium in the incineration ash is taken into the amorphous material that occupies most of the incineration ash. Therefore, by maintaining the incineration ash before adding the cesium accelerator in the crystallization temperature range, crystallization of the incineration ash can be promoted, and incineration ash with a high degree of crystallinity can be obtained. Then, in the incinerated ash, most of the radioactive cesium exists not in the state of being taken into the hardly soluble amorphous material but in the state taken into the crystal structure generated by the crystallization treatment. Thus, unlike the amorphous structure, the crystal structure incorporating radioactive cesium is easily destroyed by adding a cesium volatilization accelerator and then performing a heat treatment. From this, in the heat treatment of the incinerated ash subjected to crystallization treatment, even when it is heated at a relatively low temperature or in a short time to suppress an increase in energy consumption, radioactive cesium is efficiently removed from the incinerated ash. Volatilization can be removed.

The second feature configuration of the present invention is the method for removing radioactive cesium provided with the first feature configuration described above, receiving incineration ash above the crystallization temperature range from an incinerator for incinerating waste,
In the crystallization treatment, the received incineration ash is maintained in a crystallization temperature range to crystallize an amorphous component.

  According to this characteristic configuration, when receiving incineration ash discharged from the incinerator at a temperature higher than the crystallization temperature range, the crystallization temperature is reduced by slowly cooling the received high-temperature incineration ash as it is in the crystallization process. The amorphous component can be crystallized while being held in the region. Therefore, there is no need for reheating to keep the incinerated ash in the crystallization temperature range, so that a significant reduction in energy consumption can be realized.

The third feature configuration of the present invention is the method for removing radioactive cesium having the first feature configuration described above, and accepts incinerated ash having a temperature lower than the crystallization temperature range,
In the crystallization process, the received incinerated ash is reheated and maintained in the crystallization temperature range.

  According to this characteristic configuration, even when incineration ash having a temperature lower than the crystallization temperature range is accepted, recrystallization of the incineration ash in the crystallization process keeps the incineration ash in the crystallization temperature range and crystallizes the amorphous component. Can be made. Even when reheating is necessary in this way, the crystallization temperature range, which is the target temperature for the reheating, is a melting temperature for melting incineration ash containing a large amount of amorphous material to volatilize and remove radioactive cesium. Therefore, the increase in energy consumption can be suppressed as a whole.

A fourth characteristic configuration of the present invention includes an addition processing unit that performs an addition process for adding a cesium volatilization accelerator to incineration ash generated incineration of waste, and an incineration ash to which the cesium volatilization accelerator is added. A radioactive cesium removal system including a heat treatment unit that performs heat treatment to heat,
Before the addition processing by the addition processing unit, a crystallization processing unit for performing a crystallization process for crystallizing an amorphous component while maintaining the incineration ash in a crystallization temperature range is provided.

  According to this characteristic configuration, since each processing unit for executing each process included in the radioactive cesium removal method having the first characteristic configuration described above is provided, the same operational effects as the radioactive cesium removal method are achieved, Even if the radioactive cesium taken in the amorphous which occupies most of the main ash can be volatilized and removed from the incinerated ash while suppressing an increase in energy consumption.

The fifth characteristic configuration of the present invention is configured as a waste incineration facility including an incinerator for performing an incineration process for incinerating waste in the radioactive cesium removal system having the first characteristic configuration described above.
The crystallization processing unit is configured to receive incineration ash having a temperature equal to or higher than the crystallization temperature range from the incinerator, and hold the received incineration ash in the crystallization temperature range to crystallize the amorphous component.

  According to this characteristic configuration, an incinerator is provided and configured as a waste incineration facility, and when the crystallization processing unit accepts incineration ash that is discharged from the incinerator or higher than the crystallization temperature range, the above-described first Similar to the method of removing radioactive cesium having two characteristic configurations, in the crystallization process executed by the crystallization process unit, the received high-temperature incineration ash is kept in the crystallization temperature range by slowly cooling it as it is, so that it is amorphous. The component can be crystallized. Therefore, there is no need for reheating to keep the incinerated ash in the crystallization temperature range, so that a significant reduction in energy consumption can be realized.

Schematic configuration diagram of the processing system of this embodiment The block diagram of the incinerator and crystallization process part in the processing system of this embodiment Graph showing the X-ray diffraction results of the main ash crystal structure before and after heat treatment

Embodiments of the present invention will be described with reference to the drawings.
The incineration ash treatment system 10 (an example of a radioactive cesium removal system) of the present embodiment shown in FIG. 1 is configured as a waste incineration facility including an incinerator 1 (an example of an incinerator) that incinerates waste. Furthermore, it is configured to remove radioactive cesium from the main ash (an example of the incineration ash) generated with the incineration of the waste containing the radioactive substance in the incinerator 1. For this reason, in this processing system 10, the addition process part 4 which performs the addition process which adds a cesium volatilization promoter to main ash, and the heat processing which heat the main ash to which the said cesium volatilization promoter was added are performed. A heat treatment unit 5 is provided.

  Here, “incinerated ash” means municipal waste, agricultural and forestry by-products (for example, rice straw or wheat straw), sawmill waste, dewatered sewage sludge cake, pruned branches, dead leaves, grass, paper, plastics, decontamination It means ash generated by incineration of various types of waste such as combustible waste such as tyvek or clothing used for work, disaster waste such as disaster debris, etc.

  Known types of cesium volatilization accelerators and heating conditions can be used. For example, if an inorganic calcium compound or an organic calcium compound and a chloride compound are added as cesium volatilization accelerators to the main ash, the heat treatment is relatively easy. By heating at a low temperature of 900 ° C. to 1200 ° C. and a relatively short time of 120 minutes or less, preferably 10 minutes or more and 60 minutes or less, radioactive cesium in the main ash can be volatilized well.

  As the inorganic calcium compound, use at least one inorganic calcium compound selected from the group consisting of calcium oxide, calcium carbonate, calcium hydroxide, calcium phosphate, calcium silicate, calcium cyanamide, calcium sulfate and calcium nitrate. Can do. Moreover, as an organic calcium compound, the organic calcium compound which produces | generates a calcium oxide in the oxidation atmosphere of 500 degreeC or more can be utilized. Moreover, as a chlorinated compound, although sodium chloride can be utilized suitably, calcium chloride, potassium chloride, etc. can also be utilized.

  Although the addition process part 4 which adds a cesium volatilization promoter with respect to main ash is not specifically limited, It is comprised with a well-known blender, a screw feeder, etc. FIG. And this addition process part 4 adds a cesium volatilization promoter with respect to main ash in the form which sprinkles a cesium volatilization promoter with respect to the main ash, conveying main ash to the heat processing part 5 side. . The main ash and the cesium volatilization accelerator can be mixed in advance with a mixer or the like. The cesium volatilization accelerator may be added in a solid state (powder), but can also be supplied in a liquid state (solution). When supplied in a liquid state, the fine powder in the main ash The effect which suppresses scattering can be acquired.

  Although the heat processing part 5 which heats main ash is not specifically limited, It is comprised with well-known heating furnaces, such as a rotary kiln. And this heat processing part 5 discharges | emits the combustion exhaust gas containing the volatilized radioactive cesium while discharging | emitting the main ash from which radioactive cesium was volatilized and removed by heat processing as a processed main ash.

  Thus, since the processed main ash discharged | emitted from the heat processing part 5 becomes a thing by which the radiation concentration was fully reduced, it thinks that the volume reduction of the contaminated main ash contaminated with radioactive cesium is attained. It is done.

  On the other hand, the combustion exhaust gas discharged from the heat treatment unit 5 contains fine powder scattered from the main ash as fly ash, and volatilized radioactive cesium adheres to the fly ash. As described above, fly ash having radioactive cesium attached thereto and having a high radioactive concentration is collected by the bag filter 6 and stored in an intermediate storage facility or the like.

  The above is the basic configuration of the incineration ash processing system 10. However, the incineration ash processing system 10 and the radioactive cesium removal method executed by the incineration ash processing system 10 of the present embodiment suppress the increase in energy consumption and Even most of the radioactive cesium incorporated in the amorphous material is configured so that it can be efficiently volatilized and removed from the incinerated ash, and the detailed configuration will be described below.

  Prior to the addition processing by the addition processing unit 4, a crystallization processing unit 2 is provided that performs a crystallization process for crystallizing an amorphous component while maintaining the main ash in the crystallization temperature range. As will be described in detail later, this crystallization processing unit 2 accepts main ash having a temperature higher than the crystallization temperature range from the incinerator 1 and keeps the received high-temperature incineration ash in the crystallization temperature range by slowly cooling it. Thus, the amorphous component is crystallized. Hereinafter, specific configurations of the incinerator 1 and the crystallization processing unit 2 will be described.

  As shown in FIG. 2, the incinerator 1 is configured as a well-known stoker furnace, and incinerates the input waste while stirring and transporting it on the grate 1a, and the main ash which is the unburned residue of the incineration Are dropped from the main ash discharge part 1b on the rear end side of the grate 1a and discharged. And the main ash discharged | emitted by this main ash discharge part 1b contains many amorphous | non-crystalline forms formed at the time of high temperature incineration, and the radioactive cesium contained in waste is taken in in this amorphous | non-crystalline substance. It is thought that there is.

  Below the main ash discharge part 1b, there is provided a main ash storage part 2a for storing the main ash discharged from the main ash discharge part 1b above the crystallization temperature range. A main ash conveyor 2 b is provided for conveying the stored main ash to the ash pit 3. And these main ash accommodating part 2a and main ash conveyor 2b function as the crystallization process part 2 which hold | maintains main ash in the crystallization temperature range, and crystallizes an amorphous component.

  That is, the main ash container 2a and the main ash conveyor 2b store and convey main ash, and although not shown, the outer wall is covered with a heat insulating material, so that the main ash received at, for example, about 800 ° C. The cooling of the main ash received at a high temperature is made slow, such as cooling over 3 hours to less than 24 hours. Further, the main ash conveyor 2b includes a drive motor 2d capable of adjusting the transport speed of the main ash, a temperature sensor 2c for detecting the temperature of the transported main ash, and a drive motor 2d based on the detection result of the temperature sensor 2c. And a control unit 2e including a computer or the like for controlling the conveying speed of the main ash so that the temperature of the main ash is maintained in the crystallization temperature range. Specifically, when the temperature of the main ash detected by the temperature sensor 2c is higher than the crystallization temperature range, the control unit 2e increases the rotation speed of the drive motor 2d to increase the main ash conveyance speed, When the temperature of the main ash detected by the sensor 2c is lower than the crystallization temperature range, the rotational speed of the drive motor 2d is decreased to lower the main ash transport speed, and when the temperature of the main ash is low In the main ash conveyor 2b, the main ash is reheated using exhaust heat generated from the incinerator 1 or a new heat source. Moreover, the arrangement | positioning location and number of the temperature sensors 2c on the main ash conveyor 2b can be set suitably. The main ash conveyor 2b is not limited to a conveyor as long as it transports the main ash, and may be a device such as a rotary kiln.

  In the crystallization treatment unit 2, in order to crystallize the amorphous component of the main ash, the main ash is held in a crystallization temperature range within a range of 900 to 1200 ° C. (for example, about 1100 ° C.). Although necessary, for example, in addition to this, a crystal nucleating agent such as iron sulfide or sodium sulfate is added, and before being held in the crystallization temperature range, it is 700 slightly lower than the crystallization temperature range. It is considered that the crystallization of main ash can be further promoted by maintaining the crystal nucleation temperature range within a range of ˜900 ° C. (for example, about 800 ° C.).

  With these configurations, the high-temperature main ash discharged from the incinerator 1 is discharged for a desired time from when it is discharged to the main ash accommodating portion 2a until it is conveyed to the ash pit 3 by the main ash conveyor 2b. , And maintained in a desired crystallization temperature range. As a result, most of the amorphous contained in the main ash changes to a crystal structure. Therefore, most of the radioactive cesium contained in the main ash discharged into the ash pit 3 is not in a state in which it is incorporated into a hardly soluble amorphous material, but in a state in which it is incorporated into the crystal structure generated by the crystallization process. Will exist.

For example, in order to confirm the crystal structure of the main ash discharged from the incinerator 1 before the addition of cesium volatilization accelerator and heat treatment, and the main ash after the treatment, As a result of analysis, the results shown in FIG. 3 were obtained. That is, the crystal structure of plagioclase (NaAlSi ₃ O ₈ —CaAl ₂ Si ₂ O ₈ ) indicated by the arrow A is mostly contained in the main ash before addition of the cesium volatilization accelerator and heat treatment. It was confirmed that the main ash after treatment was hardly contained.

Since the concentration of cesium is very low, the crystal structure containing cesium cannot be directly confirmed by X-ray diffraction. However, the sodium contained in plagioclase has similar chemical characteristics to cesium, which is the same alkali metal, and therefore may be replaced with porcite (CsAlSi ₂ O ₆ ), which is a crystal structure containing cesium. Is known, and plagioclase behavior can be approximated to that of porcite. Therefore, it is presumed that the porcite crystal structure containing cesium also disappeared because the plagioclase crystal structure disappeared by the addition of the cesium volatilization accelerator and the heat treatment.

On the other hand, for the galenite (Ca ₂ Al (AlSi) O ₇ ) having the crystal structure indicated by arrow B and the larnite (Ca ₂ SiO ₄ ) having the crystal structure indicated by arrow C, the addition of a cesium volatilization accelerator and Although the amount of main ash before heat treatment was small, it was confirmed that the amount of main ash after the heat treatment increased significantly. From this, it is considered that the plagioclase contained in the main ash discharged from the incinerator 1 has undergone a structural change to gehlenite or larnite by the addition of a cesium volatilization accelerator and heat treatment.

  As described above, it is considered that the cesium-containing porsite is changed in crystal structure by addition of a cesium volatilization accelerator and heat treatment, and cesium is volatilized when the structural change occurs.

  Then, as shown in FIG. 1, the main ash discharged from the ash pit 3 is supplied to the addition processing unit 4 and added with the cesium volatilization accelerator, and then supplied to the heat processing unit 5 to be subjected to the heat treatment. Will be given. Unlike the amorphous structure, the crystal structure incorporating the radioactive cesium contained in the main ash is easily destroyed by adding a cesium volatilization accelerator and then performing a heat treatment. From this, in the heat treatment of the main ash subjected to the crystallization treatment, even when the increase in energy consumption is suppressed by heating at a relatively low temperature or in a short time, radioactive cesium is efficiently removed from the main ash. It is thought that it is volatilized and removed.

[Another embodiment]
(1) In the above embodiment, the incineration ash treatment system 10 is configured as a waste incineration facility including the incinerator 1, and the crystallization processing unit 2 accepts main ash from the incinerator 1 over the crystallization temperature range. However, it is configured as a separate treatment facility from the waste incineration facility including the incinerator and accepts the main ash stored in the storage area below the crystallization temperature range and crystallizes. You may comprise so that a process may be performed. In this case, in the crystallization process, the low-temperature main ash received from the waste incineration facility can be reheated and held in the crystallization temperature range.

(2) In the above embodiment, the example in which the incineration ash that is the target of the volatilization removal processing of radioactive cesium is the main ash (burning husk) has been described, but the incineration ash such as fly ash (dust) other than the main ash is the processing target It does not matter. In addition, in the present application, the types of wastes that are the source of incineration ash (city waste, agricultural and forestry by-products, etc.) and the types of incinerators (stoker furnace, fluidized bed furnace, kiln furnace, etc.) are particularly limited. It is not a thing.

DESCRIPTION OF SYMBOLS 1 Incinerator 2 Crystallization processing part 4 Addition processing part 5 Heat processing part 10 Processing system (radioactive cesium removal system)

1st characteristic structure of this invention is the incineration ash which added the cesium volatilization promoter to the incineration ash discharged | emitted from the incinerator which incinerates a waste, and the said cesium volatilization promoter was added A method for removing radioactive cesium, comprising:
Before the addition treatment, a crystallization treatment is performed in which the incinerated ash discharged from the incinerator is kept in a crystallization temperature range to crystallize an amorphous component.

A fourth characteristic configuration of the present invention includes an addition processing unit that performs an addition process for adding a cesium volatilization accelerator to incineration ash discharged from an incinerator that performs an incineration process for incinerating waste, and the cesium volatilization accelerator. A radioactive cesium removal system comprising a heat treatment unit for performing a heat treatment for heating the incinerated ash to which is added,
Before the addition treatment by the addition treatment unit, a crystallization process is performed in which the incinerated ash discharged from the incinerator is kept in the crystallization temperature range and the amorphous component is crystallized. The processing unit is provided.

Claims (5)

A radioactive cesium removal method that performs an addition process of adding a cesium volatilization accelerator to incineration ash generated by incineration of waste and a heating process of heating the incineration ash to which the cesium volatilization accelerator is added. ,
A method for removing radioactive cesium, wherein a crystallization process is performed to crystallize an amorphous component while maintaining the incineration ash in a crystallization temperature range before the addition process. Accept incineration ash above the crystallization temperature range from an incinerator that incinerates waste,
The method for removing radioactive cesium according to claim 1, wherein in the crystallization treatment, the received incinerated ash is held in a crystallization temperature range to crystallize an amorphous component. Accept incineration ash below the crystallization temperature range,
The method for removing radioactive cesium according to claim 1, wherein in the crystallization treatment, the received incinerated ash is reheated and maintained in a crystallization temperature range. Heat treatment for performing an addition treatment unit for performing an addition process for adding a cesium volatilization accelerator to incineration ash generated by incineration of waste, and a heating process for heating the incineration ash to which the cesium volatilization accelerator is added A radioactive cesium removal system comprising:
The radioactive cesium removal system provided with the crystallization process part which performs the crystallization process which hold | maintains incineration ash in the crystallization temperature range and crystallizes an amorphous component before the addition process by the said addition process part. It is configured as a waste incineration facility with an incinerator that performs incineration processing to incinerate waste,
The said crystallization process part receives incineration ash more than a crystallization temperature range from the said incinerator, hold | maintains the received incineration ash in a crystallization temperature range, and crystallizes an amorphous component. Radiocesium removal system.

Images