JP6543487B2 - Method and apparatus for removing radioactive cesium - Google Patents

Description

  The present invention relates to a method and apparatus for removing radioactive cesium from waste containing radioactive cesium, and in particular, a waste containing radioactive cesium while removing the acid gas contained in the exhaust gas generated during the removal of radioactive cesium. It relates to the method etc. which aim at volume reduction of things.

  In order to remove radioactive cesium taken into wastes such as soil containing radioactive cesium and waste such as incineration ash, for example, in Patent Documents 1 and 2, the waste contaminated with radioactive cesium is heated together with a reaction accelerator. There is described a technique of volatilizing radioactive cesium in waste and obtaining a harmless fired product and using the fired product as an earthworking material or cement clinker.

  In the above technology, radioactive cesium in waste is volatilized in the heating furnace and discharged together with the exhaust gas, and the exhaust gas is cooled to solidify and collected by a bag filter or the like. Thereby, radioactive cesium is concentrated to a high concentration as a bag filter dust, volume reduction is achieved, and the burden of intermediate storage or final disposal can be reduced.

Unexamined-Japanese-Patent No. 2013-108782 Patent No. 5159971 gazette

In the radioactive cesium removal technology, the exhaust gas from the heating furnace contains acid gas such as HCl and SOx derived from the raw material and / or fuel, in addition to the radioactive cesium. Also, part of the calcium chloride added to chloride and volatilize the cesium decomposes into HCl. Therefore, a method is generally employed in which a Ca-based neutralizing agent such as calcium hydroxide (OH) ₂ is blown into the upstream side of the bag filter to neutralize and remove the acid gas. However, if this is done, the bag filter dust will contain reacted slaked lime that has reacted with the acid gas, and unreacted slaked lime, so the amount of dust generated will increase and the volume reduction intention Go against.

  Then, this invention is made in view of the said solution subject, Comprising: Volume reduction of the waste material containing a radioactive cesium, removing the acidic gas contained in the waste gas produced at the time of the removal of radioactive cesium. The aim is to

In order to achieve the above object, the present invention is a method for removing radioactive cesium, which comprises preparing radioactive cesium-contaminated waste, a calcium oxide source and a chlorine source, and heating the prepared raw material The radioactive cesium in the waste is volatilized, the gas generated by the heating is cooled and collected, and a neutralizing agent is added to the gas after the collection, and the collected gas is collected from the gas after the addition of the neutralizing agent. A calcium oxide source is added to the dust collected by the dust collection, the dust to which the calcium oxide source is added is used in the preparation, and the dust collected by the dust collection is used as a calcium oxide source of the neutralizing agent It is characterized by reuse .

According to the present invention, the gas generated by heating is cooled and collected to obtain dust enriched with radioactive cesium, thereby reducing the volume of waste contaminated with radioactive cesium and concentrating radioactive cesium Calcium oxide as a reaction accelerator for volatilizing removal of radioactive cesium by adding a neutralizing agent to the gas after removing dust to remove acid gas and removing dust collected from the gas after adding the neutralizing agent Operating cost can also be reduced because it can be reused as a source or chlorine source. In addition, since the calcium oxide source is added to the dust, the deliquescence of the dust can be suppressed to improve the handling property. Furthermore, the operation cost can be reduced by circulating and reusing part of the dust as a neutralizing agent.

  In the method for removing radioactive cesium, the neutralizing agent may include one or more selected from the group consisting of slaked lime, quick lime, dolomite, light-burned dolomite and dolomite hydroxide.

  Furthermore, the said blended material can be heated at 1200 degreeC or more and 1550 degrees C or less.

  In the method for removing radioactive cesium, the mixed material can be heated in an atmosphere having an oxygen partial pressure of 3% or more. When dust collected by dust collection from gas after addition of neutralizing agent is added to waste contaminated with radioactive cesium, there is a risk that the sulfur contained in the dust may be circulated and the SOx concentration of exhaust gas may gradually increase. However, by setting the oxygen partial pressure to 3% or more, the decomposition of the sulfur compound can be suppressed, and the circulation of sulfur can be suppressed. Further, by setting the calcium oxide concentration of the calcined product to 50% by mass or more, the sulfur content is retained in the calcined product, or collected as dust after cooling as a sulfur compound, the circulation of sulfur content is further enhanced. It can be further suppressed.

Further, the present invention is a radioactive cesium removal apparatus, which is a raw material mixing apparatus for mixing radioactive cesium-contaminated waste, a calcium oxide source, and a chlorine source, and a heating furnace for heating the mixed raw material A cooling tower for cooling the exhaust gas of the heating furnace, a first dust collector for collecting dust from the exhaust gas of the cooling tower, a neutralizing agent addition device for adding a neutralizing agent to the exhaust gas of the first dust collector, the neutralization Second dust collector to collect dust from exhaust gas after addition of agent, a route to return to the raw material blending device after adding a calcium oxide source to dust collected by the second dust collector, and dust collected by the second dust collector And a route for returning to the neutralizer addition device .

According to the present invention, dust collected from the exhaust gas of the cooling tower by the first dust collector is obtained to obtain dust enriched with radioactive cesium, thereby reducing the volume of waste contaminated with radioactive cesium and concentrating radioactive cesium A neutralizing agent is added to the gas after removing the dust to remove the acid gas adsorbed dust with a second dust collector, and the dust collected by the second dust collector is re-used as a calcium oxide source or chlorine source as a reaction accelerator As it can be used, the operating cost can be reduced while removing the acid gas. In addition, since the dust collected by the second dust collector is always returned as a raw material, even if the first dust collector fails, radioactive cesium can be collected by the second dust collector, and safety to avoid the outflow of radioactive cesium to the surrounding environment It becomes a measure. Furthermore, since the calcium oxide source is added to the dust, the deliquescence of the dust can be suppressed to improve the handling property. In addition, the operation cost can be reduced by circulating and reusing part of the dust as a neutralizing agent.

  As described above, according to the present invention, it is possible to reduce the volume of radioactive cesium-containing waste while removing the acid gas contained in the exhaust gas generated during the removal of radioactive cesium. .

It is the schematic which shows the reference example of the removal apparatus of the radioactive cesium which concerns on this invention. It is the schematic which shows one Embodiment of the removal apparatus of the radioactive cesium which concerns on this invention.

  Next, an embodiment for carrying out the present invention will be described in detail with reference to the drawings. In the following description, radioactive cesium is cesium 134 and cesium 137 which are radioactive isotopes of cesium.

FIG. 1 shows a reference example of the radioactive cesium removing apparatus according to the present invention, and the removing apparatus 1 is composed of a raw material preparation device 2, a baking device 3 and an exhaust gas treatment device 4.

  The raw material preparation device 2 includes a storage tank 21 for storing waste W such as soil contaminated with radioactive cesium and incinerated ash, and a storage tank 22 for storing a calcium oxide source (hereinafter referred to as "CaO source") as a reaction accelerator. And storage tank 23 for storing a chlorine source (hereinafter referred to as "Cl source") as a reaction accelerator, and a metering feeder for extracting and preparing waste W, CaO source and Cl source stored in storage tanks 21 to 23. (Not shown) and the storage tank 24 which stores the preparation raw material M are provided.

Materials containing limestone powder, calcium carbonate, quicklime, slaked lime, limestone, dolomite, blast furnace slag and the like can be used as the CaO source. Also, as a Cl source, there are calcium chloride (CaCl ₂ ), potassium chloride (KCl), sodium chloride (NaCl), waste plastic having chlorine, etc., among which CaCl ₂ can effectively remove radioactive cesium. So preferred.

  The baking apparatus 3 is comprised of a rotary kiln (heating furnace) 31 and a clinker cooler 32. The rotary kiln 31 is provided with an inlet 31a to which the blended raw material M from the raw material blending device 2 is supplied, and fossil fuel such as pulverized coal. A burner 31 b is provided to blow out and burn the mixed material M.

  The exhaust gas processing device 4 is disposed downstream of the sintering device 3 and includes a cooling tower 41 for cooling the exhaust gas G discharged from the rotary kiln 31, a cyclone 42 disposed downstream of the cooling tower 41, a first dust collector 43, and a second. It comprises a dust collector 44, a denitration device 45 for denitrifying exhaust gas G4 from which dust such as concentrated cesium salt has been removed by both the dust collectors 43 and 44, and a chimney 46 for exhausting exhaust gas G5 of the denitration device 45 out of the system.

  The cooling tower 41 is provided to cool the exhaust gas G of the rotary kiln 31 and recover radioactive cesium and the like volatilized from the waste W as a solid. Cooling of the exhaust gas G is performed by spraying water from a water sprinkler 41 a installed at the lower end portion of the cooling tower 41. In addition, this water sprinkler 41a should just be equipped with the function of making it adhere to the dust contained in waste gas G, making the volatilized cesium chloride solid, and collect | recovering it. Instead of water cooling, cooling may be performed by introducing cooling air into the cooling tower, or water and cooling air may be used in combination.

  A cyclone 42 as a classifier is provided to collect fine powder containing high concentration radioactive cesium by the first dust collector 43 and return coarse powder C mainly composed of calcium and silica components to the rotary kiln 31.

  The first dust collector 43 is provided to collect dust D1 containing cesium salt and the like concentrated as described above from the exhaust gas G2 of the cyclone 42, and a bag filter or the like is used.

  The second dust collector 44 is provided to remove acid gas and the like contained in the exhaust gas G3 after removing the cesium salt and the like, and a neutralizer addition device (not shown) for the neutralizer N containing a calcium component , And recover the dust D2 adsorbed with acid gas and the like. A bag filter or the like is also used for the second dust collector 44.

The NOx removal device 45 is provided for injecting ammonia gas (NH ₃ ) into the exhaust gas G4 of the second dust collector 44 to reduce NOx to nitrogen and make it harmless.

  Next, the operation of the radioactive cesium removing apparatus 1 having the above configuration will be described with reference to FIG.

  In the raw material preparation device 2, the radioactive cesium-contaminated waste W, and the CaO source and the Cl source as reaction accelerators are drawn out from the storage tanks 21 to 23 and mixed to obtain the mixed raw material M. Here, the Cl source is prepared so as to be equivalent to or more than the radioactive cesium contained in the waste W.

  The raw material mixture M is put into the rotary kiln 31 from the storage tank 24 through the inlet 31a, and fired at 1200 ° C. or more and 1550 ° C. or less to obtain a fired product B. The fired product B can be effectively used as a cement mixture and an earthworking material. Here, the oxygen partial pressure in the rotary kiln 31 is 3% or more, preferably 5% or more. Thereby, the decomposition of the sulfur compound in the rotary kiln 31 is suppressed, and the circulation of the sulfur content is suppressed, so the increase in the amount of neutralizing agent used and the increase in the amount of coating adhesion on the rotary kiln 31 and the cooling tower 41 are suppressed. be able to.

  Moreover, it is preferable to perform the said preparation and baking so that the calcium oxide concentration of the baked product B may be 50 mass% or more. As a result, the sulfur content is held in the fired product B, or collected as the sulfur compound in the first dust collector 43 described later as the dust D1 of the exhaust gas G2, so that the circulation of the sulfur content can be further suppressed. .

  On the other hand, the radioactive cesium contained in the waste W of the mixed material M reacts with the chlorine generated from the Cl source in the rotary kiln 31 to volatilize as cesium chloride, and is contained in the exhaust gas G as a cooling tower It will be introduced in 41.

  The exhaust gas G is rapidly cooled by the water sprayed from the water sprinkler 41a in the cooling tower 41, and the cesium chloride contained in the exhaust gas G becomes a solid cesium salt and adheres to the fine powder of dust.

  The coarse powder C of the dust contained in the exhaust gas G1 of the cooling tower 41 is classified by the cyclone 42 and returned to the rotary kiln 31 because the radioactive cesium concentration is low.

  The exhaust gas G2 from the cyclone 42 containing the cesium salt is introduced into the first dust collector 43, and the dust D1 including the solid concentrated cesium salt is recovered. The recovered dust D1 can be further volume-reduced by compression, water washing, adsorption, etc. if necessary, and then sealed and stored in a container made of concrete etc. Wastes containing radioactive cesium can be stored externally The volume can be reduced and stored without leaking.

  On the other hand, since exhaust gas G3 after recovering concentrated cesium salt contains harmful gas such as acid gas, the second dust collector 44 is used after adding neutralizing agent N to exhaust gas G3 from the neutralizer addition device. The dust D2 adsorbed with an acid gas or the like is recovered from the exhaust gas G3. Here, as the neutralizer N, one containing one or more selected from the group consisting of slaked lime, quick lime, dolomite, light-burned dolomite and hydroxide dolomite can be used.

  Since the dust D2 collected by the second dust collector 44 is mainly composed of slaked lime, gypsum and calcium chloride, it is returned to the raw material preparation device 2 as a CaO source or a Cl source and added to the waste W for reuse.

  If the exhaust gas G4 of the second dust collector 44 contains NOx, the NOx removal device 45 removes the NOx. The cleaned exhaust gas G5 is exhausted out of the system through the chimney 46.

As described above, according to this reference example , dust D1 collected by radioactive cesium is obtained by collecting dust from exhaust gas G2 to achieve volume reduction of waste contaminated with radioactive cesium, and Since the additive N is added to remove the acid gas and the dust D2 collected from the exhaust gas G3 after the addition of the neutralizer N is reused as a CaO source or a Cl source as a reaction accelerator, the operation cost is reduced. It can be reduced.

  In addition, although soil and polluted ash polluted by radioactive cesium were illustrated as waste W polluted by radioactive cesium, in addition to these, felled wood, molten slag derived from waste, sewage sludge, sewage sludge dry powder, purified water Wastes such as sludge, construction sludge, sewage slag, shells, grasses, gravels, etc., including radioactive cesium, can be all targets, and one or two of these included in these groups The above can be used in combination. Furthermore, the radioactive cesium-concentrated intermediate treatment product, which is obtained by previously removing a portion (in the case of soil, sand or stone) which hardly contains radioactive cesium, is also a waste W contaminated with radioactive cesium according to the present invention include.

Although depending on the properties of the waste W, since the dust D2 collected by the second dust collector 44 is deliquescent, it is preferable to add a CaO source after being discharged from the second dust collector 44. Therefore, in the radioactive cesium removing apparatus 11 according to one embodiment of the present invention shown in FIG. 2, the Cl source, the dust D2 and the CaO source are put together into the storage tank 23, and a mixture of these is used as the Cl source. ing. Further, since the dust D2 collected by the second dust collector 44 contains an unreacted neutralizing agent, it can be reused as part of the neutralizing agent N added to the exhaust gas G3 of the first dust collector 43. In FIG. 2, the substance to be introduced into the storage tank 23, and the apparatus configuration and material flow other than reuse of the dust D2 as a part of the neutralizer N are the same as those in FIG. 1, and the description thereof will be omitted.

1, 11 Radioactive cesium removal device 2 Raw material blending device 21-24 Storage tank 3 Firing device 31 Rotary kiln 31a Input port 31b Burner 32 Clinker cooler 4 Exhaust gas processing device 41 Cooling tower 41a Watering device 42 Cyclone 43 1st dust collector 44 2nd dust collector 45 Denitrification Device 46 Chimney B Calcined product C Coarse powder D1, D2 Dust G, G1 to G5 Exhaust gas M Mixed raw material N Neutralizer W Waste contaminated with radioactive cesium

Claims (6)

Mix radioactive cesium contaminated waste, calcium oxide source and chlorine source,
Heating the compounded raw material to volatilize radioactive cesium in the waste;
After cooling the gas generated by the heating, dust is collected,
A neutralizing agent is added to the gas after the dust collection,
Dust is collected from the gas after the addition of the neutralizing agent,
A calcium oxide source is added to the dust collected by the dust collection, the dust to which the calcium oxide source is added is used in the preparation, and the dust collected by the dust collection is used again as the calcium oxide source of the neutralizing agent. method of removing radioactive cesium, characterized in that use.   The method for removing radioactive cesium according to claim 1, wherein the neutralizing agent comprises one or more selected from the group consisting of slaked lime, quick lime, dolomite, calcined dolomite and dolomite hydroxide. Method of removing radioactive cesium according to claim 1 or 2, characterized in that heating the formulation material at 1200 ° C. or higher 1550 ° C. or less. The method for removing radioactive cesium according to claim 1 , 2 or 3 , wherein the compounding material is heated under an atmosphere having an oxygen partial pressure of 3% or more. The method for removing radioactive cesium according to any one of claims 1 to 4 , wherein the calcium oxide concentration of the baked product obtained at the time of heating the mixed raw material is 50 mass% or more. A raw material preparation device for preparing radioactive cesium-contaminated waste, a calcium oxide source, and a chlorine source;
A heating furnace that heats the blended material;
A cooling tower for cooling the exhaust gas of the heating furnace;
A first dust collector for collecting dust from the exhaust gas of the cooling tower;
A neutralizer addition device for adding a neutralizer to the exhaust gas of the first dust collector;
A second dust collector for collecting dust from the exhaust gas after the addition of the neutralizing agent,
A route for adding a calcium oxide source to the dust collected by the second dust collector and returning it to the raw material preparation device ;
And a route for returning the dust collected by the second dust collector to the neutralizer addition device.

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