JP4891166B2 - Exhaust gas treatment method for radioactive waste melting furnace - Google Patents

Description

  The present invention relates to an exhaust gas treatment method for melting radioactive waste generated when melting incombustible miscellaneous solid waste discharged from a radioactive material handling facility represented by a nuclear power plant.

  Incombustible miscellaneous solid waste discharged from nuclear facilities generally includes iron, stainless steel, concrete, heat insulating materials, filters, and the like. Since these are waste, complete separation is difficult, and some zinc and vinyl chloride may be mixed.

  As a method for reducing the volume of these noncombustible miscellaneous solid wastes, conventionally, a radioactive solidification method and apparatus disclosed in Patent Document 1 have been widely used. This method of melting and solidifying radioactive waste is a treatment method in which non-combustible miscellaneous solid waste is heated and melted by an induction heating coil provided in a melting furnace to reduce the volume.

  When non-combustible miscellaneous solid waste is melted by this method, the melting temperature exceeds 1500 ° C. because the metal and concrete contained in the non-combustible miscellaneous solid waste are melted. , High-temperature molten exhaust gas containing chlorides and metals is discharged. The molten waste gas from the radioactive waste melting furnace is guided to a ceramic filter having excellent heat resistance and durability, and the particulate matter contained in the molten exhaust gas is collected. Further, an HEPA filter (High Efficiency Particulate Air Filter) is used. ), Fine particulate matter contained in the molten exhaust gas is collected and released.

When melting incombustible miscellaneous solid waste, zinc and vinyl chloride contained in the incombustible miscellaneous solid waste are melted in a melting furnace to produce zinc chloride (ZnCl ₂ ), It will contain. Since the melting point of zinc chloride contained in the molten exhaust gas is about 280 ° C., if this zinc chloride is collected on the ceramic filter, it will melt on the surface of the ceramic filter and cause clogging. Is generally operated at 250 ° C. or lower. Since the outlet of the melting furnace is usually about 1000 ° C., conventionally, cooling air is mixed in the flue leading the exhaust gas from the melting furnace to the ceramic filter, and the ceramic filter is operated at a temperature of 250 ° C. or lower. I was going to do that.

  However, even with this method, clogging of the ceramic filter occurs in a short period (100 operations). When the inventors analyzed this clogging material, it was found to be fine zinc oxide (ZnO, melting point 1725 ° C.), which, as mentioned above, normally melted non-combustible miscellaneous solid waste. Since the melting furnace to be operated is operated at a high temperature of about 1500 ° C., when zinc having a boiling point of 907 ° C. is introduced, it immediately becomes zinc vapor and volatilizes and shifts to a molten exhaust gas system. It has been found that when this zinc vapor comes into contact with the cooling air, it becomes fine zinc oxide, which penetrates into the ceramic filter and clogs the ceramic filter.

  Therefore, in order to solve such a problem, an exhaust gas treatment method for a radioactive waste melting furnace as shown in Patent Document 2 has been proposed. In this radioactive waste melting furnace exhaust gas treatment method, the molten exhaust gas is mixed with air or air and water at the position closest to the outlet of the melting furnace and cooled to 600 ° C. or lower, and zinc in the molten exhaust gas is converted into zinc oxide particles. Is condensed as a core, air is further supplied to the front stage of the ceramic filter, and cooled to 250 ° C. or lower before being led to the ceramic filter. In other words, the molten exhaust gas is cooled by supplying air in the first stage, thereby generating zinc oxide at 600 ° C. or lower and agglomerating zinc therein or agglomerating zinc oxides to increase the particle size. The aim was to further increase the particle size of zinc oxide by cooling with the supply of eye air, and to make the temperature of the molten exhaust gas not higher than 250 ° C. below the melting point temperature of zinc chloride.

  However, even the method disclosed in Patent Document 2 is not sufficient because the lifetime of the ceramic filter is only about 1.5 times that of the conventional method. This is because fine zinc oxide is generated by the supply of air in the first stage, but zinc does not easily aggregate in the fine zinc oxide. It was found that the cause was that it was difficult to aggregate even if it was large.

As described above, when the ceramic filter is clogged in a short period of time, the operating rate of the melting furnace is lowered. Therefore, there has been a demand for the development of a molten exhaust gas treatment method capable of further extending the life of the ceramic filter.
Japanese Patent Publication No. 3-2440 JP 2005-127767 A

  By solving the above problems, a method for treating exhaust gas from a radioactive waste melting furnace that can be used for a long time without clogging of a ceramic filter is provided.

  The present invention, which has been made to solve the above-mentioned problems, sprays water in a no-oxygen or low-oxygen state on a high-temperature molten exhaust gas discharged from a radioactive waste melting furnace for treating radioactive waste containing zinc. It is characterized in that zinc in the molten exhaust gas is condensed on the surface of the spray water to increase the particle size and then led to a ceramic filter.

  In addition, it is preferable to cool molten exhaust gas to 250 degrees C or less by spraying water, and to guide | induced to a ceramic filter.

  Further, it is preferable that the molten exhaust gas is cooled to 550 ° C. to 420 ° C. by spraying water, and then further supplied with air to be cooled to 250 ° C. or lower and led to the ceramic filter.

  In addition, it is preferable to maintain the said molten exhaust gas more than the boiling point of zinc until it heats up the molten exhaust gas discharged | emitted from a radioactive waste melting furnace exit, and sprays water.

  Water is sprayed in the oxygen-free or low-oxygen state to the high-temperature molten exhaust gas discharged from the radioactive waste melting furnace that treats radioactive waste containing zinc, and the zinc in the molten exhaust gas is condensed on the surface of this spray water. Since it was led to a ceramic filter after it was made larger in size, it did not supply new air, so almost no zinc oxide that was not easily aggregated was produced, and it was agglomerated between liquid or solid zinc that was easily aggregated As a result, the particle size of zinc can be made sufficiently large. For this reason, it is possible to prevent zinc from entering the ceramic filter and causing clogging, and the ceramic filter can be used for a long time. Further, since the gaseous zinc is rapidly cooled on the surface of the water droplet and condensed and condensed, it is possible to suppress the gaseous zinc from condensing on the wall surface of the flue. As a result, the adhesion of zinc to the downstream flue sprayed with water is reduced, the frequency of cleaning the flue can be reduced, and not only the operation efficiency is improved, but also the exposure of workers is reduced. It becomes possible.

  If the molten exhaust gas is cooled to 250 ° C. or less by spraying water and led to the ceramic filter, the molten exhaust gas is at a temperature lower than the melting point of zinc chloride. Without entering the filter, it is possible to prevent the ceramic filter from being blocked.

  Further, when the molten exhaust gas is cooled to 550 ° C. to 420 ° C. by spraying water, and further supplied with air and cooled to 250 ° C. or less, the molten exhaust gas is led to the ceramic filter. It is possible to reduce the amount of water contained in the water to such an extent that acid dew point corrosion does not occur. Further, since the molten exhaust gas is at a temperature lower than the melting point of zinc chloride, the zinc chloride does not melt and enter the ceramic filter, which can prevent the ceramic filter from being clogged. .

  If the molten exhaust gas discharged from the radioactive waste melting furnace outlet is heated to a temperature equal to or higher than the boiling point of zinc until it is sprayed with water, zinc will condense on the inner wall surface of the flue. It becomes possible to prevent the flue from being blocked.

(Configuration of the first embodiment)
Hereinafter, a preferred embodiment (first embodiment) of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a first embodiment of the present invention. In the figure, reference numeral 1 denotes a radioactive waste melting furnace for melting low-level radioactive waste discharged from a nuclear power plant or the like. For example, a melting furnace having an induction heating coil as shown in Patent Document 1 is used. It is done. This type of radioactive waste melting furnace 1 is capable of injecting radioactive waste into a canister, performing induction heating by high frequency, cooling it as it is, and obtaining a solidified body stored in the canister. It is adopted in. However, in the present invention, the type of the radioactive waste melting furnace 1 is not particularly limited. In addition, the radioactive waste melt-processed by this invention may contain the chloride derived from zinc, vinyl chloride, etc.

  Reference numeral 2 denotes a flue made of a refractory, one end connected to the outlet of the radioactive waste melting furnace 1 and the other end connected to the ceramic filter 3. In the present embodiment, the flue 2 has a substantially cylindrical shape, and the inner diameter is, for example, 100 mm to 300 mm, and is 150 mm in the present embodiment. The length of the flue 2 is 5 m to 20 m, and is 10 m in this embodiment. The ceramic filter 3 is made of porous ceramic, and is for collecting particulate matter contained in the molten exhaust gas.

In the present invention, the spraying device 4 is provided at a position near the outlet of the radioactive waste melting furnace 1. This spraying device 4 sprays water. In this embodiment, the average particle diameter of water sprayed from the spraying device 4 is 10 μm to 30 μm. The average particle diameter here means the Sauter average particle diameter. (Sauter average particle diameter: particle diameter having the same surface area to volume ratio as the total volume of all particles relative to the total surface area of the previous particles DS = Σ (n · d ³ ) i / Σ (n · d2) i, where DS: Sauter Average particle diameter, n: number of particles, d: diameter)

  It is preferable that the spraying device 4 be as close to the outlet of the radioactive waste melting furnace 1 as possible. However, when water enters the radioactive waste melting furnace 1, the temperature in the furnace decreases, so the spraying device 4 is used for the radioactive waste. It is necessary to install on the outlet side of the melting furnace 1. In the present invention, the distance is preferably within 1 m from the furnace outlet.

  Moreover, it is preferable to install the spraying device 4 so as to face the inner wall surface of the flue 2, so that the water sprayed from one spraying device 4 does not adhere to the wall surface of the other side flue 2, that is, It is preferable to adjust the average particle diameter and spray amount of water sprayed from the spray device 4 so that water evaporates before reaching the side surface of the other side flue 2. This is because the corrosive gas is contained in the molten exhaust gas, so that water adheres to the wall surface of the flue 2 and the corrosive gas is dissolved in this water to prevent the flue 2 from corroding. is there.

  A HEPA filter 7 (abbreviation of High Efficiency Particulate Air Filter) is provided at the subsequent stage of the ceramic filter 3. The ceramic filter 3 and the HEPA filter 7 are connected by a flue 8. The HEPA filter 7 is made of a glass fiber non-woven fabric and the like, and is for collecting fine particulate matter contained in the molten exhaust gas.

  A post-processing device 9 is provided following the HEPA filter 7. The HEPA filter 7 and the post-processing device 9 are connected by a flue 10. A chimney 11 is provided at the subsequent stage of the post-processing device 9. The aftertreatment device 9 and the chimney 11 are connected by a flue 12.

  When chloride or sulfide is generated in the molten exhaust gas, it reacts with water vapor to form hydrochloric acid vapor or sulfuric acid vapor. When the molten exhaust gas falls below the acid dew point (temperature at which hydrochloric acid vapor, sulfuric acid vapor, etc. condense), the hydrochloric acid vapor and sulfuric acid vapor condense and become a hydrochloric acid aqueous solution and a sulfuric acid aqueous solution. For this reason, the molten exhaust gas that has passed through the HEPA filter 7 is guided to the post-processing device 9, and post-processing is performed to prevent the flue 12 and the chimney 11 from being corroded by the chloride or sulfide. I have to. This post-treatment is, for example, a treatment in which molten exhaust gas containing hydrochloric acid vapor or sulfuric acid vapor is heated by the post-treatment device 9, and the molten exhaust gas flowing through the flue 12 and the chimney 11 is maintained at a temperature equal to or higher than the acid dew point. In this way, the flue 12 and the chimney 11 are prevented from being corroded. Alternatively, the post-treatment may be a treatment in which hydrochloric acid vapor or sulfuric acid vapor contained in the molten exhaust gas is condensed by the post-treatment device 9 to remove chloride and sulfide from the molten exhaust gas.

(Operation of the first embodiment)
Next, the operation of the first embodiment will be described. In order to melt metal and concrete contained in radioactive waste, the melting temperature of the radioactive waste melting furnace 1 usually reaches 1500 ° C., which is a high temperature containing dust, chloride and metals ( 700 ° C. to 1100 ° C.) Molten exhaust gas is generated. Since radioactive waste contains zinc (Zn, melting point 420 ° C., boiling point 907 ° C.) and chloride, zinc chloride (ZnCl ₂ , melting point approximately 280 ° C., boiling point 730 ° C.) is generated. FIG. 2 shows the vapor pressure curve of zinc. As shown in FIG. 2, since the molten exhaust gas discharged from the radioactive waste melting furnace 1 has a high temperature, zinc and zinc chloride contained in the molten exhaust gas are gaseous.

  The high-temperature molten exhaust gas flows through the flue 2 and is guided to the ceramic filter 3. In this embodiment, the high-temperature molten exhaust gas is added to the high-temperature molten exhaust gas discharged from the radioactive waste melting furnace 1. By spraying water at the position closest to the outlet, the molten exhaust gas is lowered to 250 ° C. or less at once. That is, the spray amount of water sprayed from the spray device 4 is a spray amount sufficient to lower the molten exhaust gas to 250 ° C. or lower. The temperature of the molten exhaust gas flowing through the flue 2 is measured by a thermometer provided on the downstream side of the spraying device 4, and the spray amount is adjusted so that the molten exhaust gas becomes 250 ° C. or less.

  Thus, when water is sprayed onto the molten exhaust gas flowing through the flue 2 and the molten exhaust gas is brought to 250 ° C. or less, the zinc contained in the molten exhaust gas is rapidly cooled on the surface of the sprayed water droplets and condensed.・ Set. At this time, liquid or solid zinc aggregates to increase the particle size of zinc.

  Here, the flue 2 is sealed and the supply of air is shut off. Usually, the radioactive waste is batch-fed into the radioactive waste melting furnace 1, but when the radioactive waste containing zinc is charged into the radioactive waste melting furnace 1, the boiling point of zinc is low, so it takes a short time. Zinc becomes a gas, and the oxygen concentration in the flue 2 when a large amount of gaseous zinc is generated is about 5 to 15%. For this reason, when gaseous zinc condenses and condenses, since the inside of the flue 2 is a low oxygen state, zinc is hardly oxidized and zinc oxide (ZnO) which is hard to aggregate is hardly produced | generated. For this reason, zinc contained in the molten exhaust gas flowing through the flue 2 condenses and condenses in the state of zinc, and liquid or solid zinc aggregates to increase the particle size of zinc.

  On the other hand, when zinc becomes liquid or solid, the oxygen concentration in the flue 2 increases, and the residual air in the exhaust gas comes into contact with the air in the flue 2 and the ceramic filter 3, so that the melting point temperature is high and stable. Zinc oxide (melting point: 1725 ° C.).

  As described above, gaseous zinc contained in the molten exhaust gas condenses and aggregates on the surface of the water droplets, so that almost no condensation occurs on the wall surface of the flue 2, and zinc adheres to the wall surface of the flue 2. Is reduced.

  Since zinc is made sufficiently large in size and then brought into contact with air to form zinc oxide, the average particle size of zinc oxide contained in the molten exhaust gas before being led to the ceramic filter 3 is 10 μm to Since the particle size is 30 μm and the zinc oxide is sufficiently large, most of the zinc oxide particles are collected on the surface of the ceramic filter 3. For this reason, the zinc oxide particles hardly penetrate into the ceramic filter 3, and the clogging of the ceramic filter 3 can be suppressed. Thus, since zinc oxide particles hardly penetrate into the ceramic filter 3, it is possible to easily recover the pressure loss by backwashing.

  Further, since the temperature of the molten exhaust gas is 250 ° C. or lower, zinc chloride contained in the molten exhaust gas is solid, and liquid zinc chloride enters the ceramic filter 3 to block the ceramic filter 3. Nor.

  The molten exhaust gas in which particulate matter such as zinc oxide and zinc chloride is collected by the ceramic filter 3 flows through the flue 8 and fine particulate matter is collected by the HEPA filter 7. The molten exhaust gas 9 that has passed through the HEPA filter 7 flows through the flue 10 and is guided to the post-treatment device 9. After the post-treatment is performed by the post-treatment device 9 as described above, it is discharged from the chimney 11 through the flue 12. To do.

(Configuration of Second Embodiment)
FIG. 3 shows a block diagram of the second embodiment, and the configuration of the second embodiment will be described below. The radioactive waste melting furnace 1, the flue 2, the ceramic filter 3, the spray device 4, the HEPA filter 7, the flue 8, and the chimney 11 of the second embodiment are the same as those in the first embodiment. is there. In the second embodiment, an air supply pipe 5 is connected to the front stage of the ceramic filter 3. Air is supplied to the air supply pipe 5 from an air supply device 6 such as a blower. Further, in the second embodiment, the post-processing device 9 is not necessary, and a chimney 11 is provided at the subsequent stage of the HEPA filter 7, and the HEPA filter 7 and the chimney 11 are connected by a flue 15.

(Operation of Second Embodiment)
Next, the operation of the second embodiment will be described. The high temperature molten exhaust gas flows through the flue 2 and is guided to the ceramic filter 3. In this embodiment, the high temperature molten exhaust gas discharged from the radioactive waste melting furnace 1 is added to the outlet of the radioactive waste melting furnace 1. The molten exhaust gas is lowered to 420 ° C. to 550 ° C. by spraying water at the nearest position. That is, the spray amount of water sprayed from the spray device 4 is a spray amount necessary and sufficient to lower the molten exhaust gas to 420 ° C. to 550. The temperature of the molten exhaust gas flowing through the flue 2 is measured by a thermometer provided on the downstream side of the spraying device 4, and the spray amount is adjusted so that the molten gas becomes 420 ° C to 550 ° C.

  Thus, when water is sprayed on the molten exhaust gas flowing through the flue 2 to bring the molten exhaust gas to 420 ° C. to 550 ° C., most of the zinc contained in the molten exhaust gas is obtained as shown in FIG. From gas to liquid. That is, gaseous zinc is rapidly cooled and condensed on the surface of the sprayed water droplets. At this time, liquid zinc aggregates to increase the particle size of zinc.

  Since the flue 2 is sealed and the supply of air is blocked up to the portion where the air supply pipe 5 is connected, since it is in a low oxygen state, zinc is hardly oxidized and hardly aggregated. Little zinc oxide is produced. For this reason, zinc contained in the molten exhaust gas flowing through the flue 2 is condensed in the state of zinc, and liquid zinc aggregates to increase the particle size of zinc.

  As described above, the gaseous zinc contained in the molten exhaust gas condenses on the surface of the water droplets, so that it is suppressed from condensing almost on the wall surface of the flue 2, and zinc adheres to the wall surface of the flue 2. Is reduced.

  Zinc having a large particle size contained in the molten exhaust gas flowing through the flue 2 comes into contact with the air supplied from the air supply pipe 5 and becomes zinc oxide.

  The molten exhaust gas flowing through the flue 2 is cooled by the air supplied from the air supply pipe 5 and reaches 250 ° C. or less at the inlet of the ceramic filter 3. That is, the amount of air supplied from the air supply pipe 5 is sufficient to make the temperature of the molten exhaust gas guided to the ceramic filter 3 250 ° C. or less.

  Since zinc is made sufficiently large in size and then brought into contact with air to form zinc oxide, the average particle size of zinc oxide contained in the molten exhaust gas before being led to the ceramic filter 3 is 10 μm to It becomes 30 μm, and zinc oxide becomes a sufficiently large particle. For this reason, as described in the first embodiment, the zinc oxide particles hardly penetrate into the ceramic filter 3, and the clogging of the ceramic filter 3 can be suppressed. Further, pressure loss can be easily recovered by backwashing.

  Further, since the temperature of the molten exhaust gas is 250 ° C. or lower, zinc chloride contained in the molten exhaust gas is solid, and liquid zinc chloride enters the ceramic filter 3 to block the ceramic filter 3. Nor.

  In the second embodiment, the molten exhaust gas flowing in the flue 2 is cooled to 420 ° C. to 550 ° C. higher than the melting point of zinc by water spraying, and air supplied from the air supply pipe 5 is used. Thus, the temperature of the molten exhaust gas led to the ceramic filter 3 is cooled to 250 ° C. or less. For this reason, compared to the first embodiment, the amount of water sprayed is reduced, and the amount of water contained in the molten exhaust gas can be 10%. As the amount of water contained in the molten exhaust gas increases, the acid dew point increases. However, in the second embodiment, the amount of water contained in the molten exhaust gas can be reduced to 10% or less, so the acid dew point is high. The molten exhaust gas does not become below the acid dew point until it is discharged from the chimney 11, and corrosive substances such as aqueous hydrochloric acid and aqueous sulfuric acid are not generated. For this reason, it is not necessary to post-process the molten exhaust gas discharged from the HEPA filter 7 as in the first embodiment, and the post-processing device 9 is not necessary.

(Configuration of Third Embodiment)
Next, the configuration of the third embodiment will be described. The structure of 3rd Embodiment is a structure which provided the burner (not shown) in the radioactive waste melting furnace 1 exit of 2nd Embodiment. This burner raises the temperature of the molten exhaust gas discharged from the radioactive waste melting furnace 1.

(Operation of the third embodiment)
Next, the operation of the third embodiment will be described. When the temperature of the molten exhaust gas discharged from the radioactive waste melting furnace 1 is low, zinc is condensed in the flue 2 near the outlet of the radioactive waste melting furnace 1 and the flue 2 is blocked. For this reason, in the third embodiment, the molten exhaust gas discharged from the radioactive waste melting furnace 1 is heated by the burner before the water is sprayed, and the spraying device 4 is connected from the outlet of the radioactive waste melting furnace 1. By maintaining the temperature of the molten exhaust gas flowing above the boiling point of zinc up to the position where it is provided (until water is sprayed on the molten exhaust gas flowing through the flue 2), Condensation and adhesion are prevented, and the flue 2 is prevented from being blocked with zinc.

  Further, since water is sprayed on the molten exhaust gas at the downstream side of the spraying device 4, gaseous zinc is condensed on the surface of the sprayed water droplets, and the gaseous zinc is suppressed from condensing on the inner wall of the flue 2. The adhesion of zinc to the inner wall surface of the flue 2 is reduced.

  As described above in detail in the first to third embodiments, the molten exhaust gas discharged from the radioactive waste melting furnace 1 is sprayed with water in an oxygen-free or low-oxygen state, and the molten exhaust gas is applied to the surface of the spray water. The zinc inside was condensed to increase the particle size, and then contacted with air to generate zinc oxide. For this reason, it becomes possible to make the particle diameter of the zinc oxide led to the ceramic filter 3 sufficiently large, and it becomes possible to suppress the blockage of the ceramic filter 3.

  Although the present invention has been described above in connection with the most practical and preferred embodiments at the present time, the present invention is not limited to the embodiments disclosed herein. The invention can be changed as appropriate without departing from the spirit or concept of the invention that can be read from the claims and the entire specification, and the exhaust gas treatment method for a radioactive waste melting furnace accompanied by such a change is also included in the technical scope. Must be understood as being.

It is a block diagram which shows 1st Embodiment. It is a graph which shows the vapor pressure curve of zinc. It is a block diagram which shows 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radioactive waste melting furnace 2 Flue 3 Ceramic filter 4 Spraying device 5 Air supply pipe 6 Air supply device 7 HEPA filter 8 Flue 9 Aftertreatment device 10 Flue 11 Chimney 12 Flue 15 Flue

Claims (4)

  Water is sprayed in the oxygen-free or low-oxygen state to the high-temperature molten exhaust gas discharged from the radioactive waste melting furnace that treats radioactive waste containing zinc, and the zinc in the molten exhaust gas is condensed on the surface of this spray water. An exhaust gas treatment method for a radioactive waste melting furnace characterized in that the particle size is increased and then led to a ceramic filter.   The method for treating an exhaust gas in a radioactive waste melting furnace according to claim 1, wherein the molten exhaust gas is cooled to 250 ° C or lower by spraying water and led to a ceramic filter.   The molten exhaust gas is cooled to 550 ° C. to 420 ° C. by spraying water, and further supplied with air to be cooled to 250 ° C. or lower and led to the ceramic filter. The radioactive waste melting furnace exhaust gas treatment method as described.   The molten exhaust gas discharged from the exit of the radioactive waste melting furnace is maintained at a temperature equal to or higher than the boiling point of zinc until the temperature is raised and water is sprayed. An exhaust gas treatment method for a radioactive waste melting furnace.

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