JP6070970B2 - Ash processing equipment containing radioactive cesium oxide - Google Patents

Description

  The present invention relates to an apparatus capable of removing radioactive cesium from ash containing an oxide of radioactive cesium and further making effective use of this ash.

Combustible waste discharged from facilities that handle radioactive materials such as nuclear power plants is incinerated, and the incineration ash generated during the incineration contains radioactive materials. Since radioactive cesium has a long half-life of ¹³⁴ Cs for about 2 years and ¹³⁷ Cs for about 30 years, it must be carefully stored. In particular, recently, a large amount of radioactive material has been released due to an accident at a nuclear power plant in Fukushima Prefecture, causing pollution over a wide area, and the treatment of incinerated ash from combustible materials from the contaminated area has also become a problem.

  Therefore, the Ministry of the Environment has a guideline for incineration ash with radioactive cesium concentration exceeding 8,000 Bq / kg and 100,000 Bq / kg or less to make solidified by adding cement and covering the periphery of the cement solidified by landfill. (Non-Patent Document 1).

  Moreover, when solidifying the incinerated ash of radioactive waste with cement, a method of converting heavy metal chlorides such as lead chloride produced by incineration to a state having low solubility in water is also disclosed (Patent Document 1). ). For this conversion, an alkali metal hydroxide, an alkaline earth metal hydroxide, or the like is used.

JP 2008-256660 A

Ministry of the Environment, Abandoned Opportunity 110831001;

  Incinerated ash cement solids may have cracks. In such a case, when rainwater penetrates, radioactive cesium is eluted from the cracks. Therefore, conventional landfill methods include methods of changing the structure of the landfill disposal site to provide a partition wall layer, putting it in a concrete container, or treating waste water from the disposal site. However, it is necessary to pay close attention to prevent radioactive cesium from leaking out. Even if these methods are used, if there is an unexpected situation such as a trouble during transportation, a crack in the disposal site due to an earthquake, or a trouble in a wastewater treatment facility, There is concern that cesium may leak.

  In addition, when trying to use it as a cement raw material instead of landfill, it could not be used effectively because radioactive cesium remained and exceeded the clearance level of 100 Bq / kg which is the standard for effective use.

  An object of the present invention is to provide an apparatus capable of efficiently removing radioactive cesium from ash containing an oxide of radioactive cesium and effectively using the ash as a cement raw material.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that radioactive cesium contained in ash is present mainly in the form of an oxide or the like. And by heating it in a reducing gas atmosphere in the presence of chlorine, radioactive cesium can be converted into a chloride form to volatilize and concentrate on the fly ash side, and the remaining ash contains almost no radioactive cesium. I found out that it would be harmless.

  Furthermore, the ash is effectively used as a cement raw material, etc. by putting the carbonaceous material into the furnace to form a reducing gas atmosphere and removing radioactive cesium, and then burning and removing the remaining carbonaceous material. I found out that I can do it.

The present invention has been made on the basis of these findings, and includes an ash inlet containing radioactive cesium oxide, an in-furnace gas outlet, an ash outlet, and a chlorine source inlet. And a reduction volatilization furnace that volatilizes radioactive cesium as cesium chloride by reducing ash containing radioactive cesium oxide in a reducing gas atmosphere using a chlorine component present in the ash or an added chlorine source. An ash treatment apparatus containing radioactive cesium oxide,
The ash containing radioactive cesium oxide, wherein the chlorine content in the reduction volatilization furnace is equal to or greater than the sum of the equivalent of lead and the equivalent of zinc contained in the ash containing radioactive cesium oxide. there is provided a process equipment.

  According to the present invention, the ash containing the radioactive cesium oxide can be changed to the ash containing almost no radioactive cesium, and only the fly ash generated at that time has to be landfilled, so that the amount of landfill can be greatly reduced. it can. Moreover, the ash from which radioactive cesium has been removed can be effectively used as a cement raw material.

It is a figure which shows schematic structure of an example of the apparatus of this invention.

The ash to which the apparatus of the present invention is applied is an ash containing an oxide of radioactive cesium, for example, incineration ash generated when incinerated combustibles containing radioactive cesium and its main ash are melted to form slag For example, molten fly ash generated during the process. The incineration ash generated when combustibles containing radioactive cesium are incinerated are collected by the main ash that is the bottom ash collected at the bottom of the incinerator and collected by a dust collector such as a bag filter contained in the combustion exhaust gas. There is fly ash. There is also a molten fly ash that is generated when the main ash is heated and melted in a melting furnace to be slag and collected by a dust collector such as a bag filter. The cesium content of these fly ash is usually about 0.1 to 10 ppm, of which the radioactive cesium content varies depending on the radioactivity concentration, but the initial ash radiation concentration is equal to ¹³⁴ Cs and ¹³⁷ Cs, For example, if each of them is 500 Bq / kg (that is, 1,000 Bq / kg in total), ¹³⁴ Cs is about 10 pg / kg and ¹³⁷ Cs is about 155 pg / kg, which is a very small amount.

  The apparatus of the present invention comprises a reduction volatilization furnace for reducing and volatilizing ash containing radioactive cesium oxide.

  In a reduction volatilization furnace, carbonaceous material is added in a reducing gas atmosphere to heat the ash, cesium oxide in the ash is reduced, and cesium chloride is obtained using a chlorine component present in the ash or an added chlorine source. Moreover, about cesium chloride which originally exists in ash, oxidation can be suppressed by making it a reducing gas atmosphere. In this way, the radioactive cesium oxide is volatilized as cesium chloride, and the carbon content in the ash is burned and removed in the combustion furnace of the next step.

  Chlorine changes cesium oxide into a form of cesium chloride during heating, and a wide variety can be used. The ash containing radioactive cesium oxide often contains 0.4 to 2% by weight of chlorine component, and if the chlorine component content is less than 0.4% by weight, a chlorine source is added. There is a need.

  Examples of the chlorine source include vinyl chloride resins, alkali metal chlorides, alkaline earth metal chlorides, and the like. Examples of the alkali metal chloride include sodium chloride and potassium chloride, and examples of the alkaline earth metal chloride include calcium chloride and magnesium chloride.

  The chlorine content is preferably at least the sum of the equivalents of lead and zinc contained in the ash containing the radioactive cesium oxide. This is because lead and zinc are easily chlorinated and more volatile than cesium. In addition, each equivalent of lead and zinc can be calculated by double the amount of each substance (number of moles) of lead and zinc. If chlorine component is contained in ash, this is also calculated as chlorine content. You may calculate including.

  The furnace for heating the ash may be any furnace that can heat the powder and granules to about 1000 ° C., but is preferably a closed type and equipped with a stirring mechanism. In addition, an inlet for ash and chlorine sources, charcoal, etc., an exhaust port for furnace gas, and an ash outlet from which radioactive cesium has been removed are necessary. Examples of furnaces to which the present invention can be applied include rotary kilns and stoker furnaces.

  In a reduction volatile furnace, in order to make the inside of the furnace a reducing gas atmosphere, the furnace gas is composed of carbon monoxide gas, carbon dioxide gas, hydrogen gas, nitrogen gas, water and oxygen gas of less than 1% by volume. Is preferred.

  When carbon monoxide gas is used as a reducing gas atmosphere, a carbon material may be put into the furnace and incompletely combusted, or liquid fuel or gaseous fuel may be incompletely combusted.

  As the carbon material, coke, anthracite, graphite, or the like can be used. As the liquid fuel, heavy oil, waste oil, or the like can be used, and as the gaseous fuel, liquefied natural gas, liquefied petroleum gas, or the like can be used.

The concentration of the carbon monoxide gas is preferably about 5 to 40% by volume, and more preferably about 20 to 30% by volume. Furthermore, the concentration ratio (CO / CO ₂ ) between carbon monoxide gas and carbon dioxide gas is preferably about 0.1 to 100, and more preferably about 0.5 to 20.

  When the concentration of the carbon monoxide gas is less than 5% by volume, the oxidization is strengthened, so that cesium chlorination does not proceed. On the other hand, when the concentration of carbon monoxide gas exceeds 40% by volume, the effect of cesium chloride is hardly changed.

Further, when the concentration ratio (CO / CO ₂ ) between the carbon monoxide gas and the carbon dioxide gas is less than 0.1, the oxidization becomes stronger, so that cesium chlorination does not proceed. On the other hand, when the concentration ratio (CO / CO ₂ ) between carbon monoxide gas and carbon dioxide gas exceeds 100, the effect of cesium chloride is hardly changed.

  The inside of the reduction volatilization furnace is preferably set to 700 ° C. or more and about 800 to 1100 ° C. in order to reduce the radioactive cesium oxide to react with chlorine to form cesium chloride and volatilize it.

  Volatilized cesium chloride is discharged out of the furnace by a gas supplied into the furnace, for example, a combustion gas supplied from a burner for heating, mixed with the gas discharged from the combustion furnace, and air is blown into the combustion furnace. By burning carbon monoxide and hydrogen in the gas.

  Since the exhausted gas may contain dioxins, the exhaust gas is heated to 850 ° C. or higher in a combustion furnace with a residence time of 2 seconds or longer if necessary using a burner. After cooling to about 200 ° C., it is collected by a dust collector together with fly ash. As the dust collector, one that collects dust from the flue can be used, and for example, a bug filter can be used.

  Thus, in the ash from which radioactive cesium has been removed, when a reducing gas atmosphere is formed using a carbon material, the carbon material may remain. Therefore, when the remaining carbon material hinders the subsequent effective use of ash, it is necessary to remove it beforehand. For example, when the heat loss of ash is 5% by weight or more, it is preferable to burn away the remaining carbon. Here, the heat loss of ash is a value that represents the weight percent of unburned residue remaining in the waste incineration residue when ignited at 600 ° C. for 3 hours. The smaller the heat loss, the better the combustion. It was possible.

  The combustion furnace is preferably performed in a furnace different from the above reduction volatile furnace. Both furnaces may be separate bodies, or one furnace may be divided into two chambers. Combustion is performed by supplying oxygen so that the carbon content is sufficiently combusted. This supply of oxygen can be performed by blowing air.

The composition of the ash used was as follows: Si: 10 wt%, Al: 9 wt%, Ca: 20 wt%, Na: 4 wt%, K: 1 wt%, Cl: 1 wt%, Pb: 0.1 wt% Zn: 0.4% by weight, and the concentration of radioactive cesium (total of ¹³⁴ Cs and ¹³⁷ Cs) is 10,000 Bq / kg.

The furnace shown in FIG. 1 was used. This furnace is composed of a two-stage rotary kiln and is continuously charged into the furnace at 1 kg / hr of ash, 0.03 kg / hr of coke and 0.01 kg / hr of CaCl ₂ from the leftmost inlet of the reduction volatilization furnace. did. A flame was blown from the burner at the right end of the reducing volatile furnace and heated in a reducing gas atmosphere. The CO concentration in this atmosphere was 30% by volume, and the temperature in the furnace was 1000 ° C. The average residence time of the ash in the furnace was 1 hour. The exhaust gas discharged from the gas exhaust port of the reduction volatile furnace is mixed with the exhaust gas discharged from the combustion furnace, burned with carbon monoxide in the combustion furnace, cooled, and a bag filter (in the middle of the flue) (It is not shown in the figure) and collected in the atmosphere. The concentration of radioactive cesium in the collected fly ash was 500,000 Bq / kg.

  The ash discharged from the reduction volatilization furnace was transferred to the combustion furnace, where it was further heated by the burner flame supplied with the combustion air, and the remaining carbon was burned and removed. The temperature in the furnace was 1000 ° C., and the average residence time of the ash in the furnace was 1 hour.

  The concentration of radioactive cesium in the obtained ash was 50 Bq / kg, and it was found that there was no problem even if it was used as a raw material for cement as it was.

  According to the present invention, since radioactive cesium can be almost completely removed from ash containing radioactive cesium oxide, only the fly ash separated at that time can be significantly reduced, and the ash from which radioactive cesium has been removed can be saved. Can be effectively used as a raw material for cement and the like, and can be used for treating ash containing various radioactive cesium oxides.

Claims (1)

An ash inlet containing radioactive cesium oxide, a furnace gas exhaust, an ash outlet, and a chlorine source inlet, and containing ash containing radioactive cesium oxide in the ash An apparatus for treating ash containing oxide of radioactive cesium with a reduction volatilization furnace that reduces chlorine in a reducing gas atmosphere using a chlorine component present in or added chlorine source and volatilizes radioactive cesium as cesium chloride. ,
The ash containing radioactive cesium oxide, wherein the chlorine content in the reduction volatilization furnace is equal to or greater than the sum of the equivalent of lead and the equivalent of zinc contained in the ash containing radioactive cesium oxide. Processing equipment.

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