JP2016128368A - Refractory coating method and refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refractory coating method capable of effectively preventing impregnation of harmful components, especially radioactive materials into a refractory by applying coating to the refractory.SOLUTION: The refractory coating method includes applying a coat agent consisting of 2:1 type laminar silicate mineral of 30 to 70 wt.% and a binder of 30 to 70 wt.% to a refractory surface.SELECTED DRAWING: None

Description

  The present invention relates to a method for coating a refractory for construction of an incinerator in order to prevent a radioactive material from entering a fire wall of an incinerator for treating radioactive waste, and a refractory coated using the coating method. About.

  For the purpose of protection and durability of refractories, various refractory coating agents are known that differ in material, particle size, viscosity, film thickness, construction method, and the like. For example, Patent Document 1 discloses a coating agent for forming a coating layer on the surface of a refractory body, which contains 70 to 96% by weight of zirconium oxide and 4 to 30% by weight of a silicon compound. .

  However, the invention of Patent Document 1 is intended to improve the corrosion resistance of the refractory (the problem to be solved by the invention), and it is mentioned in Patent Document 1 that the penetration of radioactive substances into the refractory is prevented. Absent.

  When radioactive materials permeate and accumulate in the refractory, there is a problem in that the workers in the furnace are exposed to the risk of exposure when repairing or dismantling the incinerator.

  Cesium (Cs), which is a radioactive substance, is an alkali metal and is considered to behave similarly to Na, K and the like. Strontium (Sr) is an alkaline earth metal and is considered to behave similarly to Mg, Ca and the like. It has been reported that the penetration of Cs into the refractory shows a positive correlation with the porosity (Non-patent Document 1, C4-7). Electroformed bricks are super dense with a porosity of 0 to 2% and have high gas barrier properties. However, this is disadvantageous in that the radioactive material easily permeates from the joint and is vulnerable to thermal fluctuations, so that it cannot be used in an incinerator with large thermal fluctuations. For this reason, amorphous refractories and fired bricks are employed instead of electroformed bricks, but there is a problem that their porosity is higher than that of electroformed bricks.

  In addition, it is conceivable to prevent penetration of radioactive materials into the refractory by applying a dense thermal spray coating on the refractory surface. If the thickness of the thermal spray coating is increased, it is possible to prevent the penetration of radioactive materials. However, in general, thermal spraying is expensive, and application to the entire surface of the refractory in the incinerator is impractical.

JP 2009-155124 A

Proceedings of the 24th Annual Meeting of Japan Society for Waste Resource Circulation 2013C4-3. Investigation of cesium penetration into refractories in pdf incineration facilities (2nd report) -Elution characteristics of cesium- (Germany) National Institute for Environmental Studies Mizuhara et al. C4-6. pdf Survey of radionuclides and air dose rates accumulated in general waste incineration facilities Kyoto University Graduate School Oshita et al. C4-7. pdf About the penetration of radioactive cesium into refractories Kubota Co., Ltd. Uebayashi et al., National Institute for Environmental Studies Mizuhara et al.

  An object of the present invention is to provide a refractory coating method and a coating method that can effectively prevent the penetration of radioactive materials into the refractory by coating the refractory in view of the above-mentioned problems of the prior art. It is to provide a refractory coated using.

  As a result of intensive studies to achieve the above object, the present inventors have found a method for effectively preventing penetration of radioactive materials into the refractory in the incinerator and have completed the present invention.

  That is, the present invention is a refractory coating method characterized in that a coating agent comprising 30 to 70% by weight of a 2: 1 type layered silicate mineral and 30 to 70% by weight of a binder is applied to the refractory surface.

  Typical examples of 2: 1 type layered silicate minerals are muscovite and illite.

  The average particle diameter of the 2: 1 type layered silicate mineral is preferably 1 to 30 μm.

  The thickness of the coating layer formed on the refractory surface by applying the coating agent is preferably 100 to 1000 μm.

  The viscosity of the coating agent is preferably 500 to 2000 mPa · s.

  The coating agent is preferably applied by selecting at least one of brush coating, spatula coating and spraying.

  It is preferable to include a mesh in the refractory coating layer.

  The present invention also provides a refractory coated using the refractory coating method described above.

According to the refractory coating method of the present invention, a coating layer having a high barrier property is formed on the surface of the refractory. Therefore, in a radioactive waste incinerator constructed using such a refractory, the radioactive material is contained in the incinerator. Intrusion into the furnace wall can be effectively prevented. Therefore, the radioactive material does not enter and accumulate in the furnace wall of the incinerator, and there is no possibility that the worker is exposed to the risk of exposure to the radioactive material when repairing or dismantling the incinerator.
Generally, a refractory material infiltrated with a radioactive material becomes a radioactive waste after the furnace is dismantled. The radioactive waste is only the coating layer portion, and a significant volume reduction of the radioactive waste can be achieved.

  Although the coating layer does not peel off at the extent of dust or ash collision, it can be easily peeled off by applying a force to the coating layer to generate cracks when the furnace is dismantled, so that the dismantling work can be reduced.

It is a test outline figure showing an embodiment of the invention. It is a figure which shows the cutting point of a fireproof test block. It is a figure which shows the result of the element mapping by a scanning electron microscope.

  In the coating agent composed of 30 to 70% by weight of 2: 1 type layered silicate mineral and 30 to 70% by weight of binder, the ratio of 2: 1 type layered silicate mineral is preferably 30 to 70% by weight. When the ratio of the 2: 1 type layered silicate mineral is less than 30% by weight, the effect of preventing the penetration of radioactive substances is weakened. Moreover, when it exceeds 70 weight%, the adhesiveness with respect to a refractory cannot be maintained.

Layered silicates such as 2: 1 type layered silicates have the property (cleavage) that each layer is easy to peel off in parallel. This is a crystal structure in which three oxygen atoms of a silicate having a tetrahedral structure surrounded by four oxygen atoms are shared with the adjacent silicate tetrahedron (SiO ₄ ) and connected in a plane. to cause. This planar connection of tetrahedrons is called a tetrahedron sheet. Furthermore, the octahedral net-like connection in which this tetrahedral sheet is combined with aluminum oxide, magnesium oxide, or the like is called an octahedral sheet. The mica mineral has a structure (2: 1 type mineral) in which an octahedral sheet is sandwiched from above and below by two tetrahedral sheets. Since cesium is the same size as this layer, it has the property of sinking and filling between layers.

  The coating agent mainly composed of a 2: 1 type layered silicate mineral further exhibits an effect of preventing cesium permeation by overlapping each particle composed of a scaly (foil-like) layer in parallel with the coating surface.

  As the binder, an inorganic hydraulic binder or the like is preferably used. Examples of the inorganic hydraulic binder include zircon cement and alumina cement. Moreover, you may use the patching material (indeterminate form refractory) used at the time of refractory repair as a binder. When an inorganic hydraulic binder or patching material is used, it is exposed to a high temperature of 700 ° C. to 1200 ° C. in the furnace, and the moisture is released and sintered, whereby adhesion to the refractory can be maintained. In addition, an organic water-soluble binder may be used. For example, an ethanol-based water-soluble binder and an acrylic water-soluble binder can be used. The organic water-soluble binder evaporates at the time of drying and is exposed to a high temperature in the furnace, thereby forming a coating layer with good adhesion containing a large amount of 2: 1 type layered silicate mineral.

  The average particle size of the 2: 1 type layered silicate mineral is preferably 1 to 30 μm. When the average particle diameter is smaller than 1 μm, the particles having the characteristic scale-like (foil-like) layer are overlapped with each other, and the effect of preventing penetration of the radioactive substance is reduced. Moreover, since workability will fall when it becomes larger than 30 micrometers, 30 micrometers or less are preferable. The average particle diameter here is the median diameter (d50) calculated from the particle size distribution obtained by the laser diffraction / scattering method.

  The thickness of the coating layer formed on the surface of the refractory by application of the coating agent is preferably 100 to 1000 μm, more preferably 300 to 700 μm. If the thickness of the coating layer is in such a range, the coating layer will not be peeled off at the extent of dust or ash collision, but can be easily peeled off when the furnace is dismantled. If the thickness of the coating layer is less than 100 μm, the effect of preventing penetration of radioactive material may be weakened. Moreover, when it exceeds 1000 micrometers, there exists a possibility that the adhesiveness with respect to a refractory material cannot be maintained.

The viscosity of the coating agent is preferably 500 to 2000 mPa · s, more preferably 1000 to 1500 mPa · s. If the coating agent has a viscosity in such a range, the thickness of the coating layer can be easily made uniform during construction. When the viscosity is less than 500 mPa · s, there is a possibility that unevenness occurs in the thickness of the coating layer during the application of the coating. If it exceeds 2000 mPa · s, it may be difficult to control the thickness of the coating layer during coating. The viscosity here is calculated by reading the resistance that the rotating body receives from the fluid from the rotational torque.

  The coating agent is preferably applied by brush coating, spatula coating or spraying.

  It is preferable to include a mesh in the coating layer. As the mesh, for example, a wire mesh made of a ceramic fiber sheet or a corrosion-resistant metal is preferably used. The wire diameter of the mesh is preferably 1 to 500 μm, more preferably 10 to 300 μm. The mesh opening is preferably 10 to 1000 μm, more preferably 30 to 500 μm. By forming the coating layer including the mesh, the peeling resistance and adhesion of the coating layer are improved. In particular, by using a wire mesh made of a corrosion-resistant metal, the adhesion of the coating layer to the refractory is reinforced by the thermal expansion during the heat. Moreover, by removing the mesh at the time of furnace dismantling, the generation of dust can be suppressed, the work of removing the coating layer can be simplified, and the risk of exposure to the operator can be further reduced.

  The refractory coated using the coating method according to the present invention is suitably used for incinerator construction.

Next, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.
Example 1
a) Formation of Coating Layer A test block of 60 mm × 60 mm × 60 mm was made of a refractory using mullite aggregate (hereinafter referred to as “fireproof test block”).

  This fireproof test block was heated to 1000 ° C. in a static air atmosphere in an electric furnace, held for 3 hours, and pre-fired.

  The ash adhering to the inner wall of the stoker-type municipal waste incinerator is collected and classified with a sieve with a mesh opening of 2 mm. The resulting fine particles are cesium chloride with a stable cesium source concentration of 100 g / kg. And mixed well to homogenize (hereinafter referred to as “prepared ash”).

A coating agent composed of 60% by weight of mica and 40% by weight of an ethanol-based water-soluble binder was brushed on the upper surface of the fireproof test block (1), and the coating film was dried to form a coating layer (2) having a thickness of 300 μm. The average particle diameter of mica in the coating agent was 30 μm, and the viscosity of the coating agent was 1500 mPa · s.
b) Test With the coating layer (2) of the fireproof test block (1) facing up, the block (1) is placed in a box-type electric furnace and prepared on the coating layer (2) as shown in FIG. The ash (3) was placed thereon, and the prepared ash (3) was covered with a transparent cup (4) in order to prevent the prepared ash (3) from flowing out. In this state, the test block (1) and the prepared ash (3) were heated to 1000 ° C. in the atmosphere and further maintained at this temperature for 6 hours, and then gradually cooled gradually.

  The appearance of the fireproof test block (1) after the test was observed, and the deposit on the upper surface was removed with a brush. As shown in FIG. 2, penetration marks (6) remained on the upper surface of the fireproof test block (1). After marking (5) at one corner of the same upper surface, the fireproof test block (1) was divided into left and right parts, and the cross section of the divided piece with the mark (5) was observed. The other divided piece was divided into two pieces in the vertical direction, and the upper divided piece was further cut into three pieces of upper, middle, and lower pieces with a thickness of 10 mm. Each of these cut pieces (a), (b), and (c) was pulverized by a mill, and each cut piece was subjected to elemental analysis by fluorescent X-ray analysis.

  The test was performed in two ways: without a coating layer and with a coating layer.

  Table 1 shows the results of elemental analysis. In the table, the detected concentration is the weight% of each element with respect to each divided piece.

In addition, the vicinity of the coating layer was observed with a scanning electron microscope (SEM). The obtained elemental mapping is shown in FIG. FIG. 3 shows that cesium (Cs) is captured in the coating layer, and the coating layer prevents penetration into the refractory block.
From the results of element mapping and elemental analysis, it was confirmed that the impregnation of cesium derived from the prepared ash was not observed in the fireproof test block under the conditions of this test, and the penetration was prevented by the coating layer.

Claims (8)

2. A refractory coating method comprising applying a coating agent comprising 30 to 70% by weight of a 2: 1 type layered silicate mineral and 30 to 70% by weight of a binder to a refractory surface. The refractory coating method according to claim 1, wherein the 2: 1 type layered silicate mineral is muscovite or illite. The refractory coating method according to claim 1 or 2, wherein the 2: 1 type layered silicate mineral has an average particle size of 1 to 30 µm. The refractory coating method according to any one of claims 1 to 3, wherein the coating layer formed on the refractory surface by application of the coating agent has a thickness of 100 to 1000 µm. The refractory coating method according to any one of claims 1 to 4, wherein the viscosity of the coating agent is 500 to 2000 mPa · s. The refractory coating method according to any one of claims 1 to 5, wherein the coating agent is applied by selecting at least one of brush coating, spatula coating, and spraying. The refractory coating method according to claim 1, wherein a mesh is included in the refractory coating layer. A refractory coated by using the refractory coating method according to any one of claims 1 to 7.