JP2014174089A - Method for incinerating combustible waste containing radioactive cesium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for incinerating combustible waste that is capable of efficiently recovering radioactive cesium when incinerating combustible waste in an incinerator.SOLUTION: A method for incinerating combustible waste of the present invention includes: (1) an addition step for adding an inorganic calcium compound or an organic calcium compound generating calcium oxide in an oxidizing atmosphere of 500°C or more to combustible waste in an incinerator so that the ratio of the inorganic calcium compound or the organic calcium compound in a mixture of the combustible waste and the inorganic calcium compound or the organic calcium compound is 3 to 30 mass%, and further adding sodium chloride so that it is more than 0.5 mass% and 10 mass% or less to the mass of the mixture of the combustible waste and the inorganic calcium compound or the organic calcium compound; (2) an incineration step for incinerating the combustible waste in the incinerator; and (3) a recovery step for recovering radioactive cesium by collecting fly ash generated from main ash in the incineration step.

Description

The present invention relates to an incineration method in which combustible waste such as agricultural waste containing radioactive cesium (a radioactive cesium isotope such as ¹³⁴ Cs or ¹³⁷ Cs) is incinerated by an incinerator. The present invention relates to an incineration method in which a calcium compound and sodium chloride are added to waste in an incinerator and then incinerated to volatilize radioactive cesium and collect the radioactive cesium together with fly ash.

  In order to remove harmful organic components or combustible components from incineration ash generated after incineration of construction surplus soil or waste, incineration of organic components or combustible components is performed using a kiln. In Patent Document 1, the construction residual soil is continuously put into the rotary kiln by the feeder, and the residual soil thrown by the rotation of the kiln is gradually transferred to the discharge port provided on the opposite side of the feeder, and the organic matter in the residual soil is transferred. A high-temperature combustion gas with an air volume that conveys the ash produced by the combustion of the minute as fly ash is blown countercurrently into the rotary kiln, combusting the combustible organic components contained in the residual soil, and the ash with the above-mentioned combustion gas A method for firing construction residual soil is disclosed, in which the incombustible component in the remaining soil is fired and discharged by being exposed to the combustion gas while being discharged.

  In the firing method of Patent Document 1, combustible components contained in the residual soil or incinerated ash are combusted by the high-temperature combustion gas blown into the countercurrent, and incombustible components such as sand, rubble, and ash are exposed to the high-temperature combustion gas. Is fired. Sediment, rubble or ash fired in the rotary kiln is discharged from the rotary kiln as sterilized high-quality baked sand (fired earth) or ash that does not contain combustible components. It is possible to arrange the particle diameters by sorting and further sifting.

  On the other hand, in the case of radioactive waste, unlike an organic component or a combustible component, it cannot be decomposed even by heating, so that a unique treatment method is required. Patent Document 2 mainly uses sodium nitrate, which is characterized by heating a radioactive waste mainly composed of sodium nitrate, a reducing agent, and a vitrifying agent to produce a vitrified body without generating nitrogen oxides. A method for treating radioactive waste as a component is disclosed. In the treatment method of Patent Document 2, even when waste is buried and contacted with groundwater, radionuclide elution is small and the volatility of the radionuclide is low during denitration and vitrification treatment.

  In Patent Document 3, activated concrete generated by dismantling a nuclear power generation facility is cut into blocks, the concrete blocks are crushed in a sealed compartment, and coarse aggregate, fine aggregate, and fine powder having a predetermined particle size are classified. Then, the recycled material manufacturing process for manufacturing the recycled material, and the fine powder of the recycled material is supplied into the thermal decomposition furnace, heated to 700 ° C. or higher with the supplied high-temperature air, and contained in the fine powder. A heat treatment step for separating tritium and carbon-14, and a decontamination step for adsorbing and removing the tritium and carbon-14 contained in the high-temperature air on a path for circulating the high-temperature air from within the pyrolysis furnace; The recycling method for activated concrete is disclosed in which each recycled material is discharged from the sealed compartment after decontamination is confirmed. The recycling method of Patent Document 3 is said to be able to regenerate and manufacture recycled aggregates and the like by removing a predetermined radioactive substance adhering to the activated concrete.

  Here, after the explosion accident at TEPCO and Fukushima Daiichi NPS in March 2011, radioactive cesium has been detected from soil in a wide area centering on Fukushima Prefecture. . For decontamination treatment of soil contaminated with radioactive cesium, many methods such as water washing, acid treatment under heating, topsoil removal, high pressure washing, or high temperature treatment in the presence of calcium salt have been studied. However, a processing method at a level that can be adopted on a practical scale has not been developed. The main cause is that the existence form of cesium in the soil, the chemical and physical properties of the cesium compound, and the reaction behavior between the cesium compound and the soil component have not been clarified.

  As a technique for removing radioactive cesium from contaminated soil containing radioactive cesium, Non-Patent Document 1 adds two types of calcium compounds as cesium volatilization promoters to contaminated soil and heat-treats them at 1350 ° C. Discloses a 99.9% volatilization removal method from soil. Non-Patent Document 2 discloses that when calcium chloride is added to soil, cesium hardly volatilizes even when the soil is heated to 1000 ° C. or higher.

JP 2002-79234 A JP 2002-221593 A Japanese Patent No. 4471110

March 1, 2012 Asahi Shimbun article, http://www.asahi.com/national/update/0301/TKY201203010146.html The National Institute of Agricultural and Food Research, February 22, 2012, press release, "Development of technology for removing dry cesium from contaminated soil containing radioactive materials" http: //www.naro.affrc. go.jp/publicity_report/press/laboratory/narc/027564.html

  Although the baking method of patent document 1 can be utilized as a method of removing organic content or combustible content from the soil and regenerating the soil, inorganic materials such as cesium compounds are not targeted for removal.

  The radioactive waste processing method of Patent Document 2 is a method of fixing radioactive waste as a vitrified body, and does not describe volatilization and removal of cesium in combustible materials.

  The recycling method of Patent Document 3 is intended for removal of tritium or carbon-14, and is not intended for removal of radioactive cesium in combustible materials.

  It is said that the radioactive cesium removal method of Non-Patent Document 1 can remove the radioactive cesium in the soil almost completely, but it is necessary to heat the object to be treated to 1300 ° C or higher, and the energy consumption is large. It is.

  In addition, combustible waste is usually incinerated using an incinerator, but some of the radioactive cesium contained in the combustible waste is transferred to fly ash released from the incinerator along with the exhaust gas. Some have been reported to burn or remain in the main ash without moving to fly ash. For this reason, it is necessary to collect radioactive cesium not only from the fly ash in the exhaust gas discharged from the incinerator but also from the burnt ash or the main ash.

  An object of this invention is to provide the incineration method of the combustible waste which can collect | recover radioactive cesium efficiently when incinerating a combustible waste in an incinerator.

  When the present inventors incinerate combustible waste containing radioactive cesium in an incinerator, if the inorganic calcium compound or organic calcium compound and sodium chloride are added and incinerated, the radioactive cesium volatilizes and fly ash Found to move to.

  Therefore, the present inventors reduced the amount of sodium chloride added and reduced flammability by combining inorganic calcium compounds or organic calcium compounds and sodium chloride as an additive that promotes cesium volatilization during incineration of combustible waste. A method to remove a small amount of radioactive cesium from the main ash of waste was investigated. As a result, the inventors have at least one selected from the group consisting of calcium oxide, calcium carbonate, calcium hydroxide, calcium phosphate, calcium silicate, calcium cyanamide, calcium sulfate and calcium nitrate. It has been found that the above-mentioned problems can be solved by using sodium chloride in combination with an inorganic calcium compound or an organic calcium compound that generates calcium oxide in an oxidizing atmosphere of 500 ° C. or higher, and the present invention has been completed. It was.

Specifically, the present invention
An incineration method in which combustible waste containing radioactive cesium is incinerated in an incinerator,
Oxidized into combustible waste so that the proportion of inorganic calcium compound or organic calcium compound in the mixture of combustible waste and inorganic calcium compound or organic calcium compound is 3% by mass or more and 30% by mass in the incinerator. At least one inorganic calcium compound selected from the group consisting of calcium, calcium carbonate, calcium hydroxide, calcium phosphate, calcium silicate, calcium cyanamide, calcium sulfate and calcium nitrate, or calcium oxide in an oxidizing atmosphere of 500 ° C or higher An addition step of adding the calcium compound to be generated, and further adding sodium chloride so as to be more than 0.5 mass% and 10 mass% or less with respect to the mass of the mixture of the combustible waste and the inorganic calcium compound or the organic calcium compound; ,
An incineration process in which combustible waste is incinerated at a temperature of 900 ° C to 1200 ° C for 30 minutes to 120 minutes in an incinerator;
A collection process for collecting radioactive cesium by collecting fly ash generated in the incineration process,
The present invention relates to a method for incinerating combustible waste.

In the present invention, calcium oxide, calcium carbonate, calcium hydroxide, calcium phosphate (lime phosphate), calcium silicate (lime silicate), calcium cyanamide (lime nitrogen: CaCN ₂ ), calcium sulfate (gypsum) ) And at least one inorganic calcium compound selected from the group consisting of calcium nitrate (lime nitrate), or an organic calcium compound that generates calcium oxide in an oxygen atmosphere of 500 ° C. or higher, and is conventionally used as a cesium removal accelerator. By using in combination with sodium chloride, which is cheaper than the calcium chloride that has been used, incineration treatment of 900 ° C to 1200 ° C, which is lower than 1300 ° C in Non-Patent Document 1, for 30 minutes or more and 120 minutes or less, from combustible waste, radioactive cesium Can be efficiently removed. A specific example of the organic calcium compound that generates calcium oxide in an oxidizing atmosphere of 500 ° C. or higher is calcium acetate.

  This is because radioactive cesium is desorbed from burning combustible waste by adding an inorganic calcium compound or an organic calcium compound that generates calcium oxide in an oxidizing atmosphere of 500 ° C. or higher to the combustible waste. It is surmised that the desorbed radioactive cesium is combined with chlorine atoms derived from sodium chloride, and the radioactive cesium contained in the combustible waste is volatilized as (radioactive) cesium chloride. As the inorganic calcium compound, at least one inorganic calcium compound selected from the group consisting of calcium oxide, calcium carbonate, and calcium hydroxide is particularly preferable.

  Here, the “organic calcium compound that generates calcium oxide in an oxidizing atmosphere of 500 ° C. or higher” may be an organic calcium compound that generates calcium oxide in an oxidizing atmosphere of 500 ° C. or higher, and is less than 500 ° C. (for example, Also included are organic calcium compounds that produce calcium oxide in an oxidizing atmosphere at 300 ° C.

  By burning the combustible waste in the incinerator, the radioactive cesium contained in the combustible waste is volatilized, but the volatilized radioactive cesium moves with the fly ash. For this reason, if the generated fly ash is collected, radioactive cesium can be efficiently recovered and the amount of radioactive cesium remaining in the main ash can be reduced.

  In the method for removing radioactive cesium of the present invention, the addition amount of the sodium chloride in the addition step is 1% by mass to 10% by mass with respect to the mass of the mixture of the combustible waste and the inorganic calcium compound or the organic calcium compound. Preferably there is.

  A part of the added sodium chloride is decomposed or volatilized by the influence of moisture or the like in the combustible waste due to the heating accompanying combustion of the combustible waste, and does not react with the radioactive cesium. For this reason, 1 mass% or more of sodium chloride is added with respect to the mass of the mixture of a combustible waste and an inorganic calcium compound or an organic calcium compound from a viewpoint of volatilizing radioactive cesium in a combustible waste more reliably. It is preferable. On the other hand, some of the chlorine atoms derived from sodium chloride that do not react with radioactive cesium react with water volatilized from combustible waste or water generated by the pyrolysis reaction of organic substances contained in combustible waste. Since hydrogen chloride is generated, from the viewpoint of suppressing the generation of hydrogen chloride, sodium chloride is 5% by mass or less, more preferably 3% by mass with respect to the mass of the mixture of combustible waste and inorganic calcium compound or organic calcium compound. It is preferable to add at% or less.

  According to the present invention, the main ash can be handled safely by reducing the amount of radioactive cesium remaining in the main ash after incineration of combustible waste containing radioactive cesium. Moreover, it is possible to efficiently recover the volatilized radioactive cesium together with the fly ash.

  Embodiments of the present invention will be described. The present invention is not limited to the following description.

<Addition process>
Combustible waste containing radioactive cesium, at least one inorganic calcium compound selected from the group consisting of calcium oxide, calcium carbonate, calcium hydroxide, calcium phosphate, calcium silicate, calcium cyanamide, calcium sulfate and calcium nitrate, Alternatively, an organic calcium compound that generates calcium oxide under an oxidizing atmosphere of 500 ° C. or higher is added. The addition amount of the inorganic compound is adjusted so that the proportion of the inorganic compound in the mixture of the combustible waste and the inorganic compound is 3% by mass or more and 30% by mass or less. At this time, the mass of the combustible waste is based on the dry mass.

  Next, the amount of the combustible waste to which the inorganic calcium compound or the organic calcium compound is added exceeds 0.5% by mass with respect to the total amount of the mixture of the combustible waste containing radioactive cesium and the inorganic calcium compound or the organic calcium compound. Sodium chloride is added so that it may become 10 mass% or less. At this time, the mass of the combustible waste is based on the dry mass.

  Specific examples of combustible waste include agricultural waste (for example, rice straw or wheat straw), sawmill waste, sewage sludge dehydrated cake, pruned branches, dead leaves, grass, papers, plastics, Tyvek used for decontamination work Or, if it is a combustible waste such as clothing, but contaminated with radioactive cesium, the type is not limited.

  The combustible waste is preferably crushed as necessary before being put into the incinerator for easy combustion in the incinerator.

  From the viewpoint of reducing the amount of hydrogen chloride generated in the incinerator, the amount of sodium chloride added is 5 with respect to the total amount of the mixture of combustible waste containing radioactive cesium and inorganic calcium compounds or organic calcium compounds. The mass is not more than mass%, preferably not more than 3 mass%. By reducing the amount of hydrogen chloride generated, not only reducing furnace corrosion due to hydrogen chloride, but also reducing the amount of exhaust gas treatment agent (eg, slaked lime or sodium bicarbonate) added in the exhaust gas treatment process. Can do. Moreover, from the viewpoint of surely volatilizing radioactive cesium from combustible waste, the amount of sodium chloride added to the total amount of the mixture of combustible waste containing radioactive cesium and inorganic calcium compound or organic calcium compound It is preferable to set it as 1 mass% or more.

  When the addition amount of sodium chloride is about 1% by mass, most of the added sodium chloride is decomposed or volatilized in the heating step, and is taken out from the heating apparatus together with the exhaust gas.

  When an inorganic calcium compound or an organic calcium compound is added, the amount added to the combustible waste containing radioactive cesium is more preferably 10% by mass or less in order to reduce the amount of heat treatment after the addition.

  From the viewpoint of easy availability of a large amount of drug itself and easy handling, it is preferable to use calcium carbonate as the inorganic calcium compound.

  Note that the order of addition to the combustible waste may be either sodium chloride and the inorganic calcium compound or the organic calcium compound, and both may be added to the combustible waste at the same time.

  A general blender or a screw feeder can be used for mixing the combustible waste, the inorganic calcium compound or the organic calcium compound, and sodium chloride.

  If there is no hindrance to the operation of the incinerator, sodium chloride and an inorganic calcium compound or an organic calcium compound may be charged into the incinerator during the incineration process.

<Incineration process>
The combustible waste to which sodium chloride and an inorganic calcium compound or an organic calcium compound are added is supplied to an incinerator. Specific examples of the incinerator are a fluidized bed incinerator, a gasification melting furnace, a stoker furnace, or a circulating fluidized bed furnace. Incineration of combustible waste is preferably performed at a furnace temperature of 900 ° C. or higher and 1200 ° C. or lower for a period of 30 minutes or longer and 120 minutes or shorter. When the combustible waste is incinerated, radioactive cesium is volatilized from the combustible waste to which the inorganic calcium compound or the organic calcium compound and sodium chloride are added.

  In order to volatilize radioactive cesium, it is necessary to set the inside of the incinerator to 900 ° C. or higher during the incineration process, and to increase the volatilization efficiency and shorten the heat treatment time, it is necessary to set the temperature to 950 ° C. or higher. In order to sufficiently volatilize radioactive cesium from the main ash, it is preferable to continue the incineration process for 30 minutes or more.

  After the incineration process is completed, the main ash removed from the incinerator can be landfilled as general waste when the radioactivity concentration is measured and confirmed to be less than 8000 Bq / kg. .

<Recovery process>
The radioactive cesium volatilized in the incineration process is transferred to the fly ash contained in the exhaust gas during the incineration process, and is discharged from the incinerator. This exhaust gas is supplied to a cooling tower as necessary and cooled, and then a dry collection means such as a bag filter, a cyclone, a HEPA filter or an electrostatic precipitator, or a wet collection such as a wet scrubber. Supplied to the means. Since radioactive cesium is contained in the fly ash contained in the exhaust gas, the radioactive cesium released from the incinerator is recovered by collecting the fly ash by dry collection means or wet collection means. It becomes possible.

  A dry collection means and a wet collection means may be used in combination, or a dry collection means such as a bag filter may be used in combination with an exhaust gas treatment agent (for example, slaked lime, baking soda or activated carbon). . The exhaust gas that has passed through the collecting means is subjected to advanced treatment such as denitration treatment as necessary, and then exhausted to the atmosphere.

  When fly ash containing radioactive cesium is collected by a dry collection means such as a bag filter, the collected material and the filters attached to the collected material are stored in a container together with other harmful substances. Alternatively, it may be buried in a shielded management-type disposal site, or may be vitrified by melting and contained so as not to elute, and similarly buried in a management-type disposal site. Further, after being mixed with concrete and solidified, it may be buried in a managed disposal site.

  The volatilized radioactive cesium is volatilized as a compound that is easily dissolved in water, such as cesium chloride, and the fly ash collected by dry collection means is washed with water to decontaminate the fly ash. However, it may be rendered harmless. In this case, since radioactive cesium elutes in the washing waste water, the radioactive cesium can be fixed by adsorbing the dissolved radioactive cesium using an adsorbent (for example, bitumen or zeolite). Moreover, you may make it adsorb | suck a radioactive cesium to an adsorbent, after concentrating washing wastewater using a concentrating means like a reverse osmosis membrane apparatus or an evaporative concentration apparatus as needed.

  Even if wet collection means such as a wet scrubber is used, it is possible to dissolve radioactive cesium contained in fly ash in water. For example, wet scrubber wash water is filtered to separate solid components that do not dissolve in water, and radioactive cesium compounds in the wash water are concentrated by a reverse osmosis membrane device or separated by an adsorption treatment using an adsorbent. May be. By performing the concentration or adsorption treatment, the amount of radioactive waste that needs final disposal can be reduced. As in the case of recovering radioactive cesium in a dry manner, the adsorbent may be stored in a container, subjected to a solidification process using a melting process or concrete, and may be buried in a managed disposal site.

  The combustible waste incineration method of the present invention is useful in the field of waste treatment.

Claims (2)

An incineration method in which combustible waste containing radioactive cesium is incinerated in an incinerator,
Oxidized into combustible waste so that the proportion of inorganic calcium compound or organic calcium compound in the mixture of combustible waste and inorganic calcium compound or organic calcium compound is 3% by mass or more and 30% by mass in the incinerator. At least one inorganic calcium compound selected from the group consisting of calcium, calcium carbonate, calcium hydroxide, calcium phosphate, calcium silicate, calcium cyanamide, calcium sulfate and calcium nitrate, or calcium oxide in an oxidizing atmosphere of 500 ° C or higher Addition step of adding sodium chloride so that the organic calcium compound to be generated is added, and more than 0.5 mass% and 10 mass% or less with respect to the mass of the mixture of flammable waste and inorganic calcium compound or organic calcium compound When,
An incineration process in which combustible waste is incinerated at a temperature of 900 ° C to 1200 ° C for 30 minutes to 120 minutes in an incinerator;
A collection process for collecting radioactive cesium by collecting fly ash generated in the incineration process,
An incineration method for combustible waste. The combustible of Claim 1 whose addition amount of the said sodium chloride in the said addition process is 1 to 3 mass% with respect to the mass of the mixture of a combustible waste and an inorganic calcium compound or an organic calcium compound. Of incineration of radioactive waste.