JP6062464B2 - Radiocesium removal method and radioactive cesium removal system - Google Patents

Description

  The present invention includes a pulverization process for pulverizing a processing object such as incineration ash and soil generated with incineration of waste, an addition process for adding a cesium volatilization accelerator to the processing object after the pulverization process, The present invention relates to a radioactive cesium removal method and a radioactive cesium removal system for performing a heat treatment for heating an object to be treated after the addition treatment.

  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 and soil and other treatment objects, the incineration ash is heated from the incineration ash by adding a cesium volatilization accelerator such as a chloride compound. One that volatilizes and removes radioactive cesium is known (see, for example, Patent Documents 1 to 4).

JP 2014-174090 A JP 2013-120146 A JP2013-122440A JP 2014-014802 A

  In the conventional radioactive cesium removal technology, it is necessary to heat the object to be processed to a very high temperature (for example, more than 1200 ° C.). In this case, a large amount of energy is required, and further, the object to be processed is slagged. There was also a problem that the original properties changed greatly and became difficult to handle.

  In view of this situation, the main problem of the present invention is to add a cesium volatilization accelerator to the object to be processed and then heat it to remove the radioactive cesium from the object to be processed by volatilization and removal. An object of the present invention is to provide a technique that can efficiently volatilize and remove radioactive cesium from a processing object while increasing the scale and saving energy.

The first characteristic configuration of the present invention is a pulverization process for pulverizing a processing object, an addition process for adding a cesium volatilization accelerator to the processing object after the pulverization process, and heating the processing object after the addition process. A method for removing radioactive cesium by performing heat treatment,
Dispose of the object to be processed after the pulverization process to the airflow conveyance path, and carry the airflow through the airflow conveyance path,
While the addition process is a process of supplying a cesium volatilization accelerator to the airflow conveyance path, and injecting the cesium volatilization accelerator separately from the processing object into the conveyance airflow flowing through the airflow conveyance path. ,
It exists in the point which performs the separation process which isolate | separates a process target object from the conveyance airflow after the said addition process, and uses for the said heat processing.

  In the radioactive cesium removal method of heating the treatment object pulverized by the pulverization treatment by the heat treatment, in order to volatilize and remove radioactive cesium from the treatment object efficiently, a cesium volatilization accelerator is added to the treatment object. It is necessary to mix well. However, in order to promote the mixing of the cesium volatilization accelerator with the object to be treated, the processing capacity of the grinding process is increased and a cesium volatilization accelerator is added to the object to be treated during the grinding process, or the cesium volatilization accelerator is added. If measures such as separately providing an agitator for agitating the object to be treated are added, the system becomes large-scale and energy efficiency decreases.

Therefore, according to the present characteristic configuration, the cesium volatilization accelerator is introduced into the carrier airflow in which the object to be treated is dispersed substantially uniformly by the addition process. Similar to the object to be processed, it is dispersed substantially uniformly using the carrier airflow. Furthermore, in the carrier airflow after the cesium volatilization accelerator is introduced, mixing of the object to be processed and the cesium volatilization accelerator is promoted by the turbulent flow generated in the airflow. Therefore, when the object to be processed is separated from the carrier airflow by the above separation process, not only the object to be treated but also the cesium volatilization accelerator can be separated from the carrier airflow in a substantially uniformly dispersed state, and the object to be separated is separated. Since the mixing of the product and the cesium volatilization accelerator is promoted, the cesium volatilization accelerator is uniformly mixed in the object to be subjected to the heat treatment after the separation. For this reason, it is not necessary to expand the processing capacity of the pulverization treatment for promoting the mixing of the cesium volatilization promoter and to install a separate stirring device, and the system can be reduced in size and energy can be saved.
In addition, by crushing the object to be processed by the above pulverization process, it becomes possible to carry the object to be processed in a suitable air flow, so that the mixing of the cesium volatilization accelerator into the object to be processed is realized by introducing it into the air flow. It becomes easy to do.

  Furthermore, the processing object separated by the separation process is in a state in which much of the radioactive cesium incorporated therein is exposed by being pulverized by the pulverization process. Therefore, the uniformly mixed cesium volatilization promoter comes into good contact with the exposed radioactive cesium. For this reason, even if this treatment target is heated at a relatively low temperature or in a short time to suppress an increase in energy consumption, the radioactive cesium is efficiently volatilized and removed from the treatment target. be able to.

  The 2nd characteristic structure of this invention exists in the point which performs the drying process which dries the process target object before the said addition process.

  According to this characteristic configuration, by drying the object to be processed before the addition process by the drying process, not only the water content of the object to be processed is lowered, but also the cesium volatilization accelerator is added by the addition process. The humidity of the conveying airflow can be kept low. Therefore, in the conveying airflow, the aggregation of the processing object itself due to the moisture of the pulverized processing object is suppressed, and the agglomeration due to moisture absorption and deliquescence is also suppressed for the cesium volatilization accelerator that is input. Become. Thus, even when processing a processing object having a high water content or when using a cesium volatilization accelerator having deliquescence, it was pulverized by the pulverization process in the carrier airflow after the addition process. Both the object to be treated and the cesium volatilization promoter introduced by the addition treatment are in a state of being more uniformly dispersed in a state in which aggregation is suppressed, and as a result, separated by the separation treatment and subjected to the heat treatment. In the object to be treated, the cesium volatilization accelerator can be more uniformly mixed.

  The third characteristic configuration of the present invention is that exhaust heat of the heat treatment is used as a heat source of the drying treatment.

  According to this characteristic configuration, since the exhaust heat of the heat treatment is used as a heat source for the drying treatment, it is possible to suppress deterioration in energy efficiency due to the addition of the drying treatment.

  The 4th characteristic structure of this invention exists in the point which performs the collection | recovery process which isolate | separates the coarse particle part of a process target object from the conveyance airflow before the said addition process, and returns to the said grinding | pulverization process.

  According to this characteristic configuration, the recovery process separates the coarse particles having a relatively large particle diameter after the pulverization process from the conveying air flow and returns to the pulverization process. The object to be processed to be processed can be surely and sufficiently finely pulverized. Thereby, the fall of the removal efficiency of the radioactive cesium by the processing target object of the coarse grain inadequately grind | pulverized remaining in the processing target object provided to the said heat processing can be suppressed.

A fifth characteristic configuration of the present invention includes a pulverization processing unit that performs a pulverization process for pulverizing a processing target, and an addition processing unit that performs an addition process for adding a cesium volatilization accelerator to the processing target after the pulverization process. , A radioactive cesium removal system comprising a heat treatment unit for performing a heat treatment to heat the treatment object after the addition treatment,
An air flow conveyance path for carrying out air flow conveyance of the processed object after the processing object after the pulverization process has been paid out;
In the form in which the addition processing unit supplies the cesium volatilization accelerator to the airflow conveyance path, the cesium volatilization promoter is charged separately from the processing object into the conveyance airflow flowing through the airflow conveyance path. As well as
It is in the point provided with the separation processing part which performs the separation processing which separates a processing object from the conveyance air current after the addition processing, and supplies it to the heat processing part.

  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, It is possible to efficiently volatilize and remove radioactive cesium from an object to be processed while reducing the size and energy of the system.

Schematic configuration diagram of the processing system of the first embodiment

An embodiment of the present invention will be described with reference to FIG.
A processing system 10 (an example of a radioactive cesium removal system) for incineration ash (an example of an object to be processed) according to the present embodiment shown in FIG. 1 is a main ash (an incineration ash) generated when incineration of waste containing radioactive materials is performed. One example) is supplied as a raw material from an incinerator 1a, a main ash storage 1b, or the like, and is configured to remove radioactive cesium from the main ash. For this reason, in this processing system 10, the addition process part 5 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 were added are performed. A heat treatment unit 7 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.

  Specifically, as the cesium volatilization accelerator, 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, or An organic calcium compound that generates calcium oxide under an oxidizing atmosphere of 500 ° C. or higher and sodium chloride are added to the incineration ash.

  The addition amount of the inorganic compound or the organic calcium compound is adjusted so that the ratio of the inorganic compound or the organic calcium compound in the mixture of the incinerated ash and the inorganic compound or the organic calcium compound is 3% by mass or more and 50% by mass or less. Next, the incineration ash to which the inorganic calcium compound or the organic calcium compound is added to the incineration ash containing the radioactive cesium-containing incineration ash and the inorganic calcium compound or the organic calcium compound exceeds 0.5% by mass and is 10% by mass or less. Sodium chloride is added so that

  From the viewpoint of reducing the amount of hydrogen chloride derived from sodium chloride, the amount of sodium chloride added may be 10% by mass or less based on the total amount of the mixture of the radioactive cesium-containing incinerated ash and the inorganic calcium compound or the organic calcium compound. preferable. Moreover, from a viewpoint of volatilizing radioactive cesium from incineration ash reliably, the addition amount of sodium chloride shall be 1 mass% or more with respect to the total amount of the mixture of radioactive cesium containing incineration ash and an inorganic calcium compound or an organic calcium compound. It is preferably 3% by mass or more, more preferably 5% by mass or more. In addition, calcium chloride, potassium chloride, etc. can be utilized instead of sodium chloride.

  Although the heat processing part 7 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 7 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 7 will be a thing by which the radiation density | concentration was fully reduced, it thinks that the volume reduction of the contaminated main ash contaminated with radioactive cesium is attained. It is done.

  The above is the basic configuration of the incineration ash treatment system 10, but the incineration ash treatment system 10 and the radioactive cesium removal method executed by the incineration ash treatment system 10 according to the present embodiment achieves downsizing and energy saving of the system. Even most of the radioactive cesium incorporated in the main ash is capable of being efficiently volatilized and removed from the incinerated ash, and the detailed configuration will be described below.

  The processing system 10 is provided with a pulverization processing unit 3 that executes a pulverization process for pulverizing the main ash supplied from the incinerator 1a, the main ash storage 1b, and the like. The pulverization processing unit 3 is not particularly limited, and includes a known dry pulverization apparatus such as a rolling ball mill pulverizer, a vertical roller mill pulverizer, a jet mill pulverizer, and a grinding pulverizer. In addition, about the operating conditions of this grinding | pulverization process part 3, it can set suitably so that the particle diameter of the main ash after grinding | pulverization may become a desired particle diameter of about 10 micrometers, for example. And the pulverization process by the pulverization processing unit 3 is executed, whereby the amorphous in the main ash is suitably pulverized, and most of the radioactive cesium incorporated in the amorphous is exposed. Then, the main ash after the pulverization processing by the pulverization processing unit 3 is discharged to the airflow conveyance path 9 together with the supply air supplied by the suction force of the blower 8, and is conveyed in the airflow through the airflow conveyance path 9. In addition, about the flow velocity of the conveyance airflow in the airflow conveyance path 9, it is generally set within the range of 10 m / s to 30 m / s, preferably within the range of 20 m / s to 30 m / s.

  The addition processing unit 5 provided in the processing system 10 performs cesium volatilization in the transport airflow flowing through the airflow transport path 9 as an addition processing for adding a cesium volatilization accelerator to the incinerated ash after the pulverization processing by the pulverization processing unit 3 Execute the process of charging the accelerator. Although this addition process part 3 is not specifically limited, It can be comprised with the fixed_quantity | feed_rate supply apparatus etc. which supply a cesium volatilization promoter to the airflow conveyance path 9 quantitatively. Moreover, about the injection | throwing-in method of a cesium volatilization promoter, various injection | throwing-in methods, such as injection using gravity air etc. and gravity fall, are employable. Furthermore, it is desirable to set the particle diameter of the cesium volatilization accelerator introduced into the transport airflow by the addition processing unit 5 within a range that can be transported by the transport airflow with the incinerated ash, for example, within a range of 10 μm to 1000 μm, Preferably, it can set in the range of 50 micrometers-500 micrometers. In this embodiment, the particle diameter of calcium carbonate added as a cesium volatilization accelerator is set to about 80 μm, and the sodium chloride supplied as a cesium volatilization accelerator is set to about 400 μm.

  Further, a separation processing unit 6 that performs a separation process for separating the main ash from the transport airflow is provided downstream of the addition processing unit 5 in the airflow transport path 9. The separation processing unit 6 is not particularly limited, but can be configured by a known powder separation device that separates powder from the airflow. In this embodiment, main ash having a relatively small particle size is separated from the carrier airflow. It consists of a possible bag filter type separation device. Then, the main ash separated by the separation processing unit 6 is subjected to a heat treatment by the heat treatment unit 7 as a heating target main ash.

  Thus, since the cesium volatilization accelerator is introduced into the carrier airflow by the addition processing unit 5, the pulverized main ash and the introduced cesium volatilization accelerator are both uniformly dispersed in the carrier airflow. It becomes a state. Therefore, the main ash to be heated separated by the separation processing unit 6 on the downstream side is in a state where the cesium volatilization accelerator is uniformly mixed. For this reason, it is not necessary to expand the processing capacity of the pulverization process for promoting the mixing of the cesium volatilization promoter or to install a separate stirring device, and as a result, the system can be reduced in size and energy can be saved. Become.

  Since the main ash to be heated is the main ash pulverized by the pulverization processing unit 3, most of the radioactive cesium incorporated therein is exposed. Since the uniformly mixed cesium volatilization accelerator is in good contact with the exposed radioactive cesium, the main ash is heated at a relatively low temperature or in a short time by the heat treatment of the heat treatment unit 7. Even when the increase in energy consumption is suppressed, radioactive cesium is efficiently volatilized and removed from the main ash.

  The processing system 10 is provided with a drying processing unit 2 that executes a drying process for drying the main ash of the raw material charged into the pulverization processing unit 3. Although this drying process part 2 is not specifically limited, It can be comprised with a well-known drying apparatus, and in this embodiment, it is comprised so that main ash may be exposed to hot air and dried. Furthermore, as the heat source of the drying processing unit 2, the exhaust heat of the heat processing unit 7 is used, thereby suppressing the deterioration of energy efficiency due to the drying processing.

  Since the main ash before the addition treatment by the addition treatment unit 5 is dried by the drying treatment by the drying treatment unit 2, not only the water content of the main ash is lowered, but also the addition treatment unit in the air flow path 9. The humidity of the conveying airflow that flows through 5 is kept low. Therefore, in the transport airflow, the aggregation of the main ash itself due to the water of the main ash pulverized by the pulverization processing unit 3 is suppressed, and the cesium volatilization accelerator introduced by the addition processing unit 5 also aggregates due to moisture absorption and deliquescence. Will be suppressed. Thus, in the transport airflow downstream of the addition processing unit 5 of the airflow transport path 9, both the main ash and the cesium volatilization accelerator are more uniformly dispersed in a state where aggregation is suppressed, As a result, the cesium volatilization promoter is more uniformly mixed in the main ash to be heated separated by the separation processing unit 6.

  On the upstream side of the addition processing unit 5 of the airflow conveyance path 9, the coarse particles of main ash are separated from the conveyance airflow before the addition of the cesium volatilization accelerator in the addition processing unit 5 and returned to the pulverization processing unit 3. A collection processing unit 4 that executes the collection process is provided. Specifically, the recovery processing unit 4 is not particularly limited, but can be configured by a known powder separation device that separates powder from an air current. In this embodiment, main ash having a relatively large particle size is used. It consists of a cyclonic separator that can be separated from the carrier airflow.

  That is, the main ash that is pulverized by the pulverization processing unit 3 and is conveyed in the airflow conveyance path 9 may have coarse ash of about several tens to several hundreds μm that is insufficiently pulverized. . As described above, the coarse ash with insufficient pulverization is separated as recovered main ash by the recovery processing unit 4, returned to the pulverization processing unit 3, and pulverized again. In the collection processing unit 4, the separation particle size of the recovered main ash can be set as appropriate. For example, the main ash exceeding 30 μm, preferably 15 μm, more preferably 10 μm can be separated as the recovered main ash and pulverized again. desirable.

  Therefore, most of the main ash to be heated separated by the separation processing unit 6 on the downstream side becomes the main ash of fine particles that are surely and sufficiently finely pulverized, and as a result, the main ash of coarse particles that are insufficiently pulverized Therefore, the decrease in the removal efficiency of radioactive cesium due to the remaining of the cesium is suppressed. In addition, since the main ash in the transport airflow flowing through the recovery processing unit 4 is dried by the drying processing unit 2, aggregation is suppressed. 4 is prevented from being collected as a coarse particle and pulverized again, and the enlargement of the pulverization processing unit 3 due to the recovery of such extra main ash is avoided.

[Another embodiment]
(1) In the above embodiment, the example in which the incineration ash that is the target of the volatilization removal process 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.

(2) In the above embodiment, the drying processing unit 2 is provided on the upstream side of the pulverization processing unit 3 so as to dry the main ash of the raw material charged into the pulverization processing unit 3. The main ash after the powder treatment may be dried by using, for example, low-humidity dry air supplied to the air 9. Moreover, you may abbreviate | omit suitably the drying process by this drying process part.

(3) In the above embodiment, the exhaust heat of the heat treatment by the heat treatment unit 7 is used as the heat source of the dry treatment by the dry treatment unit 2, but naturally, another heat source is used as the heat source of the drying treatment. It doesn't matter.

(4) In the above embodiment, the main ash coarse particles are separated from the transport air flow for transporting the main ash by the cyclone separator, etc. For example, the coarse particles may be separated from the main ash before airflow conveyance by a sieving device and returned to the pulverization processing unit 3. Moreover, in the said embodiment, such a collection | recovery process part 4 is provided in the upstream rather than the addition process part 5 in the airflow conveyance path 9, and the coarse grain of main ash from the conveyance airflow before a cesium volatilization promoter is thrown in. However, the recovery processing unit 4 may be omitted, and a cesium volatilization accelerator may be added to the entire main ash and heat treatment may be performed.

(5) In the above embodiment, the example in which the processing object for removing radioactive cesium is incinerated ash has been described, but in addition to the incinerated ash, various soils such as construction residual soil and other substances containing radioactive cesium are processed. It does not matter as an object.

2 Drying processing unit 3 Grinding processing unit 4 Recovery processing unit 5 Addition processing unit 6 Separation processing unit 7 Heat processing unit 9 Airflow conveyance path 10 Processing system (radioactive cesium removal system)

Claims (5)

Radioactive cesium removal that performs pulverization processing for pulverizing the processing target, addition processing for adding a cesium volatilization promoter to the processing target after the pulverization processing, and heating processing for heating the processing target after the addition processing A method,
Dispose of the object to be processed after the pulverization process to the airflow conveyance path, and carry the airflow through the airflow conveyance path,
While the addition process is a process of supplying a cesium volatilization accelerator to the airflow conveyance path, and injecting the cesium volatilization accelerator separately from the processing object into the conveyance airflow flowing through the airflow conveyance path. ,
A method for removing radioactive cesium, wherein a separation object is separated from a carrier airflow after the addition treatment and subjected to a heat treatment.   The radioactive cesium removal method of Claim 1 which performs the drying process which dries the process target object before the said addition process.   The method for removing radioactive cesium according to claim 2, wherein exhaust heat of the heat treatment is used as a heat source for the drying treatment.   The radioactive cesium removal method of any one of Claims 1-3 which performs the collection | recovery process which isolate | separates the coarse particle content of a process target object from the conveyance airflow before the said addition process, and returns to the said grinding | pulverization process. A pulverization processing unit that performs a pulverization process for pulverizing the processing target, an addition processing unit that performs an addition process for adding a cesium volatilization accelerator to the processing target after the pulverization process, and a processing target after the addition process A radioactive cesium removal system comprising a heat treatment unit for performing a heat treatment for heating
An air flow conveyance path for carrying out air flow conveyance of the processed object after the processing object after the pulverization process has been paid out;
In the form in which the addition processing unit supplies the cesium volatilization accelerator to the airflow conveyance path, the cesium volatilization promoter is charged separately from the processing object into the conveyance airflow flowing through the airflow conveyance path. As well as
The radioactive cesium removal system provided with the separation process part which performs the separation process which isolate | separates a process target object from the conveyance airflow after the said addition process, and supplies to the said heat processing part.

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