JP6508830B2 - 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 method for reducing the volume of radioactive cesium-containing waste and reducing the concentration of radioactive cesium in a heated product, etc. About.

  In order to remove radioactive cesium taken into the soil, for example, Patent Document 1 heats the soil contaminated with radioactive cesium with a rotary kiln, cools the kiln exhaust gas to produce fine powder containing radioactive cesium, and produces the kiln exhaust gas A technique is disclosed that collects the coarse powder inside and returns it to the rotary kiln to collect fine powder from the kiln exhaust gas. By this technology, radioactive cesium is concentrated to a high concentration as fine powder to reduce the volume, the burden of intermediate storage or final disposal can be alleviated, and a baked product with a reduced concentration of radioactive cesium can be obtained. .

Unexamined-Japanese-Patent No. 2013-19734

  In the above radioactive cesium removal technology, the coarse powder contained in the kiln exhaust gas is recovered and returned to the rotary kiln, but this coarse powder is radioactive radioactive cesium of higher concentration than the original waste although it is not as high as fine powder. It is possible to cause the concentration of radioactive cesium in the baked product to increase by circulating and concentrating it. In addition, alkali chlorine compounds such as NaCl and KCl are also contained in a large amount, so they are easily melted, and this melting prevents the volatilization of radioactive cesium in the coarse powder, which is also a factor that increases the concentration of radioactive cesium in baked products. It can be As a result, there is a possibility that they will be an obstacle in using the fired product for earthwork materials and the like.

  In order to avoid the above problems, if the coarse powder is recovered together with the fine powder without being returned to the rotary kiln, the radioactive cesium concentration of the fired product can be reduced, but the radioactive cesium of recovered matter (fine powder and coarse powder) from the kiln exhaust gas This is against the intention of reducing the volume of radioactive cesium-containing waste as the concentration decreases and the amount of recovered material also increases.

  Therefore, the present invention has been made in view of the above-mentioned problems, and the radioactive cesium concentration of the heated product (baked product) generated in the volume reduction of radioactive cesium-containing waste is reduced to a low level. The purpose is to reduce the volume of radioactive cesium-containing waste while maintaining it.

  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, heating the preparation to produce the waste The radioactive cesium in the substance is volatilized, the gas generated by heating the above-mentioned preparation is cooled, the dust contained in the gas after cooling is classified into coarse powder and fine powder, and the coarse powder after classification is washed with water to solidify It is characterized in that the solid side containing the coarse powder after liquid separation and solid-liquid separation is heated together with the preparation.

  According to the present invention, the crude powder obtained by classifying the gas after cooling is washed with water to dissolve and remove an alkali chlorine compound such as NaCl or KCl contained in the coarse powder, whereby the water after washing is obtained. It is possible to prevent the melting of the coarse powder itself and to prevent the coarse powder from being mixed with the blended material and becoming easy to melt, thereby promoting volatilization of the radioactive cesium. In addition, by dissolving and removing water-soluble radioactive cesium such as CsCl, it is possible to suppress circulating concentration of radioactive cesium, so the radioactive cesium is contained while maintaining the radioactive cesium concentration of the heating product at a low level. It is possible to reduce the volume of waste. The solid-liquid separation after the coarse powder washing does not have to be strict. That is, a part of the filtrate may be mixed to some extent on the solid side to form a slurry, and conversely, coarse powder may be mixed to some extent in the filtrate.

In the method for removing radioactive cesium, water is added to the coarse powder after classification to form a slurry, and then the slurry is separated by solid-liquid separation to perform the water washing to obtain a dewatered cake as the solid side containing the coarse powder. be able to. As a result, it is possible to more reliably remove the water-soluble radioactive cesium such as alkali chlorine compounds and CsCl contained in the coarse powder. In addition, when the specific surface area of the dewatered cake is reduced compared to the coarse powder before water washing, melting can be prevented when heating the dewatered cake, and volatilization of radioactive cesium can be promoted.

  Moreover, the filtrate after the solid-liquid separation can be used to cool the gas generated by the heating. Thereby, the water content of the filtrate can be evaporated, and CsCl or the like dissolved in the filtrate can be recovered as solid radioactive cesium. In addition, the amount of cooling water used can be reduced, and since it is not necessary to separately provide a wastewater treatment facility, costs can be reduced.

  After the calcium source is added to the coarse powder after classification, the water washing can be performed, whereby the melting of the coarse powder itself after the water washing can be prevented more reliably. In addition, solid-liquid separation of the washed coarse powder is facilitated.

Furthermore, the present invention is a radioactive cesium removal apparatus, which comprises: a raw material preparation apparatus for preparing radioactive cesium-contaminated waste, a calcium oxide source, and a chlorine source; and heating a preparation from the preparation apparatus. Heating furnace, a cooling tower for cooling the exhaust gas of the heating furnace, a classifier for classifying dust contained in the exhaust gas of the cooling tower into coarse powder and fine powder, and washing the coarse powder classified by the classifier , A solid-liquid separator for solid-liquid separation of the coarse powder washed by the water-washing apparatus, and a solid side containing the coarse powder separated by the solid-liquid separator to the heating furnace And a supply device.

  According to the present invention, the crude powder obtained by classifying the gas after cooling is washed with water to dissolve and remove an alkali chlorine compound such as NaCl or KCl contained in the coarse powder, whereby the water after washing is obtained. It is possible to prevent the melting of the coarse powder itself and prevent the coarse powder from being mixed with the blended material and becoming easy to melt, thereby promoting volatilization of the radioactive cesium, and further, to use a water-soluble radioactive cesium such as CsCl. By dissolving and removing it, it is possible to prevent the circulating concentration of radioactive cesium, so it is possible to reduce the volume of radioactive cesium-containing waste while maintaining the radioactive cesium concentration of the heated product at a low level. . The solid-liquid separation in the solid-liquid separator does not have to be strict. That is, a part of the filtrate may be mixed to some extent on the solid side to form a slurry, and conversely, coarse powder may be mixed to some extent in the filtrate.

  In the radioactive cesium removal apparatus, the supply device can supply a dewatered cake including the coarse powder from the solid-liquid separator to the heating furnace. As a result, it is possible to more reliably remove the water-soluble radioactive cesium such as alkali chlorine compounds and CsCl contained in the coarse powder. In addition, when the specific surface area of the dewatered cake is reduced compared to the coarse powder before water washing, melting can be prevented when heating the dewatered cake, and volatilization of radioactive cesium can be promoted.

  The cooling tower can be equipped with a spray device for charging the filtrate from the solid-liquid separator. Thereby, the water content of the filtrate can be evaporated, and CsCl or the like dissolved in the filtrate can be recovered as solid radioactive cesium. In addition, the amount of cooling water used can be reduced, the heat generated by the removing device can be effectively used, and since the cesium dust recovery device provided in the removing device is also utilized, it is not necessary to separately provide a wastewater treatment facility. Cost can be reduced.

  An addition device for adding a calcium source to the coarse powder classified by the classifier can be provided, and the addition of the calcium source can more reliably prevent the melting of the coarse powder itself after water washing.

  As described above, according to the present invention, the volume of radioactive cesium-containing waste is reduced while maintaining the radioactive cesium concentration of the heated product generated during the volume reduction of radioactive cesium-containing waste at a low level. Can be implemented.

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 an embodiment of the radioactive cesium removing apparatus according to the present invention, and the radioactive cesium 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.

As the CaO source, a material containing calcium carbonate, quick lime, slaked lime, limestone, dolomite, blast furnace slag and the like can be used. 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 composed of a rotary kiln (heating furnace) 31 and a cooler 32. The rotary kiln 31 ejects an injection port 31a to which the blended material M is supplied from the raw material blending apparatus 2 and fossil fuel such as pulverized coal. And a burner 31 b for firing the mixed material M and the like.

  The exhaust gas processing device 4 is disposed downstream of the firing device 3 and is recovered by the cooling tower 41 for cooling the exhaust gas G discharged from the rotary kiln 31, the cyclone 42 disposed downstream of the cooling tower 41, and the cyclone 42. A storage tank 43 for storing the coarse powder C, a water washing device 44 for washing the coarse powder C1, a solid-liquid separator 45 for solid-liquid separation of the slurry S from the water washing device 44, a first dust collector 46, and a second dust collector 47 A denitration device 48 denitrates the exhaust gas G4 from which dust such as concentrated cesium salt has been removed by both dust collectors 46 and 47, and a chimney 49 exhausts the exhaust gas G5 of the denitration device 48 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 or a filtrate F described later 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 cooling and recovering radioactive cesium, such as cesium chloride volatilized, until it becomes solid. 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 46 and recover coarse powder C mainly composed of calcium and silica components.

  The storage tank 43 is provided to store a coarse powder C1 by adding a calcium source (hereinafter referred to as "Ca source") to the coarse powder C supplied from the cyclone 42. As a source of Ca, calcium carbonate, quick lime, slaked lime, limestone, dolomite, blast furnace slag and the like can be used. This Ca source has the effect of preventing the melting of the dehydrated cake DC described later.

  The water washing device 44 is provided to wash the coarse powder C1 supplied from the storage tank 43 and dissolve the alkali chlorine compound such as NaCl and KCl and the like and the water-soluble radioactive cesium such as CsCl contained in the coarse powder C1. Water is added to the powder C1 to form a slurry, and a stirring tank having a stirring blade for stirring is used.

  The solid-liquid separator 45 is provided to separate the slurry S from the water washing device 44 into the dewatered cake DC and the filtrate F, and is an alkali chlorine compound such as NaCl or KCl contained in the coarse powder C1, CsCl, etc. By removing the water-soluble radioactive cesium in the filtrate F side, it is possible to promote the volatilization of the radioactive cesium by preventing the melting of the dewatering cake DC itself and the melting of the compounding material by mixing it with the compounding material, And prevent the cyclic concentration of radioactive cesium. Further, the specific surface area of the dewatered cake DC is reduced as compared to the coarse powder C1 before the water washing, thereby preventing the melting when heating the dewatered cake DC and promoting volatilization of the radioactive cesium. Here, if the particle size of the dewatered cake DC is larger than 100 mm, the supply device of the dewatered cake DC becomes excessive and cost increases, while if it is less than 1 mm, the specific surface area is undesirably increased. It is preferable to carry out crushing and granulation of the dewatered cake DC as necessary so as to be within the above.

  The first dust collector 46 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 47 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 47.

The NOx removal device 48 is provided for injecting ammonia gas (NH ₃ ) into the exhaust gas G4 of the second dust collector 47 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 46 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 and the filtrate F sprayed from the water sprinkler 41 a in the cooling tower 41, and the cesium chloride contained in the exhaust gas G becomes a solid cesium salt.

The dust contained in the exhaust gas G1 of the cooling tower 41 is classified by the cyclone 42, and the coarse powder C obtained by classification is temporarily stored in the storage tank 43, and a Ca source is added to form coarse powder C1. Here, it is preferable to add a Ca source so that the relationship between CaO, SiO ₂ and MgO in the coarse powder C1 becomes (CaO + 1.39 × MgO) / SiO ₂ = 1.0 to 3.0. When the mass ratio of the left side is less than 1, the coarse powder C1 is easily melted as the baking temperature becomes high, and the volatilization of radioactive cesium is inhibited. On the other hand, if the above mass ratio exceeds 3, free lime (free lime) contained in the obtained baked product B will increase, which may cause expansion failure or the like.

  The coarse powder C1 after the addition of the Ca source is washed with water by the water washing device 44, and then supplied as the slurry S to the solid-liquid separator 45 to be solid-liquid separated. The obtained dewatered cake DC is returned to the rotary kiln 31.

  The filtrate F from the solid-liquid separator 45 is sprayed via the water sprinkler 41 a to evaporate the water content of the filtrate F and recover solid radioactive cesium as dust D1 by the first dust collector 46 described later .

  On the other hand, the exhaust gas G2 from the cyclone 42 containing the cesium salt is introduced into the first dust collector 46, and the dust D1 containing 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.

  Exhaust gas G3 after recovering the concentrated cesium salt contains noxious gas such as acid gas, so after adding the neutralizing agent N to the exhaust gas G3 from the neutralizer addition device, the second dust collector 47 Dust D2 adsorbed with acid gas etc. is recovered from 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 47 is mainly composed of slaked lime, gypsum and calcium chloride, it is returned to the raw material blending device 2 as a CaO source, Cl source and Ca source and added to the waste W for reuse it can.

  If NOx is contained in the exhaust gas G4 of the second dust collector 47, it is removed by the NOx removal device. The cleaned exhaust gas G5 is exhausted out of the system through the chimney 49.

  As described above, according to the present embodiment, the waste gas collected from the exhaust gas G2 to obtain the dust D1 enriched with radioactive cesium and to reduce the volume of the waste W contaminated with the radioactive cesium After washing the coarse powder C in G1 with water and solid-liquid separation, alkaline chlorine compounds such as NaCl and KCl and water-soluble radioactive cesium such as CsCl are removed to the filtrate F side, and as a result, the rotary kiln 31 is used. The radioactive cesium concentration of the baked product B can be reduced by preventing melting to promote volatilization of the radioactive cesium and preventing circulation and concentration of the radioactive cesium.

  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 more of these may be included alone or in combination. Can be combined. 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.

  Moreover, although the case where the filtrate F from the solid-liquid separator 45 was supplied to the cooling tower 41 was demonstrated in the said embodiment, you may add this filtrate F to waste gas G2 of the cyclone 42. FIG. When the filtrate F is supplied to the cooling tower 41, there is a possibility that the radioactive cesium contained in the filtrate F adheres to the coarse powder C side of the cyclone 42 and is circulated, but the radioactive cesium is added by being added to the exhaust gas G2. Circulation can be reliably prevented. In this case, the cooling tower does not necessarily have to cool to a temperature at which the radioactive cesium becomes solid, and the first dust collector 46 may cool to a temperature at which the radioactive cesium becomes solid. As a result, the radioactive cesium concentration of the coarse powder C1 is low, and the radioactive cesium can be more concentrated in the dust D1.

  Furthermore, it is not necessary to strictly carry out solid-liquid separation in the solid-liquid separator 45, for example, a part of the filtrate F is somewhat mixed in the dewatering cake DC as in centrifugal separation or sedimentation separation. It may be done. Conversely, some coarse powder may be mixed in the filtrate F. A filter press is preferably used as the solid-liquid separator 45.

  In addition, in the said embodiment, when heating the compounding material M, although the baking apparatus 3 provided with the rotary kiln 31 and the cooler 32 was used, another heating furnace etc. can also be used. Even in such a case, the dust contained in the gas after cooling the gas discharged from the heating furnace or the like is classified into coarse powder and fine powder, and the coarse powder after classification is washed with water and then returned to the heating furnace. It prevents the melting of itself and prevents the raw material from being mixed with the raw material and becomes easy to melt, thereby promoting volatilization of the radioactive cesium and dissolving and removing the water-soluble radioactive cesium such as CsCl. As a result, it is possible to reduce the volume of radioactive cesium-containing waste while maintaining the radioactive cesium concentration of the heat product at a low level.

DESCRIPTION OF SYMBOLS 1 Radioactive cesium removal apparatus 2 Raw material preparation apparatus 21-24 Storage tank 3 Firing apparatus 31 Rotary kiln 31a Input port 31b Burner 32 Cooler 4 Exhaust gas processing apparatus 41 Cooling tower 41a Water sprinkling apparatus 42 Cyclone 43 Storage tank 44 Water washing apparatus 45 Solid-liquid separator Dust collector 47 Second dust collector 48 Denitrification apparatus 49 Chimney B Calcined product C, C1 Coarse powder D1, D2 Dust DC Dewatered cake F Filtrate liquid G, G1 to G5 Exhaust gas M Mixed raw material N Neutralizer S Slurry W Waste)

Claims (8)

Mix radioactive cesium contaminated waste, calcium oxide source and chlorine source,
Heating the formulation to volatilize radioactive cesium in the waste;
Cooling the gas generated by heating the formulation;
Classify the dust contained in the cooled gas into coarse powder and fine powder,
The coarse powder after classification is washed with water and solid-liquid separated,
A method of removing radioactive cesium, comprising heating the solid side containing the coarse powder after solid-liquid separation together with the preparation.   Water is added to the coarse powder after classification to form a slurry, and then the slurry is subjected to solid-liquid separation to carry out the water washing to obtain a dewatered cake as the solid side containing the coarse powder. The removal method of radioactive cesium as described in.   The method for removing radioactive cesium according to claim 1 or 2, wherein the filtrate after the solid-liquid separation is used to cool the gas generated by the heating.   The method for removing radioactive cesium according to claim 1, 2 or 3, wherein the washing with water is carried out after adding a calcium source to the coarse powder after classification. A raw material preparation device for preparing radioactive cesium-contaminated waste, a calcium oxide source, and a chlorine source;
A heating furnace for heating the preparation from the preparation device;
A cooling tower for cooling the exhaust gas of the heating furnace;
A classifier that classifies dust contained in the exhaust gas of the cooling tower into coarse powder and fine powder;
A water washing apparatus for washing the coarse powder classified by the classifier;
A solid-liquid separator for solid-liquid separation of the coarse powder washed by the water washing apparatus;
And a feeder for feeding the solid side containing the coarse powder separated by the solid-liquid separator to the heating furnace.   The apparatus for removing radioactive cesium according to claim 5, wherein the supply device supplies a dewatered cake containing the coarse powder from the solid-liquid separator to the heating furnace.   The said cooling tower is equipped with the spraying apparatus which injects the filtrate from the said solid-liquid separator, The removal apparatus of the radioactive cesium of Claim 5 or 6 characterized by the above-mentioned.   The removal apparatus of the radioactive cesium of Claim 5, 6 or 7 provided with the addition apparatus which adds a calcium source to the coarse powder classified by the said classifier.

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