JP7199703B2 - Gas production method and pollucite production method - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law 1. Website (1) Address https://www. fukushima-u. ac. jp/news/2018/06/005667. html https://www. fukushima-u. ac. jp/news/Files/2018/06/for4. pdf (2) Posting date on the website June 4, 2018 2. Press conference (1) Press conference name 114th Fukushima University regular press conference National University Corporation Fukushima University (2) Press conference date June 6, 2018 3-1. Publications (Proceedings) (1) Name of Publication Abstracts of the 7th Environmental Radioactivity Decontamination Research Conference (2) Publication date June 29, 2018 3-2. Publications (Proceedings) (1) Name of Publication Abstracts of the 7th Environmental Radioactivity Decontamination Research Presentation Conference (2) Publication date June 29, 2018 4-1. Meeting (conference/oral presentation) (1) Meeting name 7th Environmental Radioactivity Decontamination Research Presentation Meeting Environmental Radioactivity Decontamination Society (2) Release date July 4, 2018 4-2. Meeting (conference/poster presentation) (1) Meeting name 7th Environmental Radioactivity Decontamination Research Presentation Meeting Environmental Radioactivity Decontamination Society (2) Publication date July 4, 2018 5-1. Website (Proceedings) (1) Title of publication Web abstracts for the 67th Annual Meeting of the Japan Society for Analytical Chemistry (2) Date of publication on the website August 29, 2018 (3) Address http://www. j sac. or. jp/nenkai/nenkai67/program/contents/pdf/G3001. pdf 5-2. Meeting (conference/oral presentation) (1) Name of meeting The 67th Annual Meeting of the Japan Society for Analytical Chemistry Public Interest Incorporated Association The Japan Society for Analytical Chemistry (2) Release date September 14, 2018 6-1. Publications (Proceedings) (1) Name of publication: Proceedings of new technology briefing at Fukushima University Japan Science and Technology Agency (2) Publication date: September 27, 2018 6-2. Meeting (briefing session/oral presentation) (1) Name of Meeting Fukushima University New Technology Briefing Japan Science and Technology Agency National University Corporation Fukushima University (2) Release Date September 27, 2018

Application of Article 30, Paragraph 2 of the Patent Act 7-1. Publications (Proceedings) (1) Title of Publication Abstracts of the 54th X-ray Analysis Symposium Japan Society for Analytical Chemistry X-ray Analysis Research Gathering (2) Date of Publication October 25, 2018 7- 2. Meeting (conference/poster presentation) (1) Meeting name: The 54th X-ray Analysis Symposium The Japan Society for Analytical Chemistry, Social Gathering for X-ray Analysis Research (2) Release date: October 25 and October 26, 2018 8. Meeting (briefing session/oral presentation) (1) Name of meeting: Explanatory meeting for technology seeds from universities in the prefecture (2) Release date: November 7, 2018

The present invention relates to a method for producing gas and a method for producing pollucite.

Since the accident at the Fukushima Daiichi Nuclear Power Plant, the residential area has been decontaminated with radioactive cesium that has fallen. However, decontamination of forests, which cover about 70% of the area of Fukushima Prefecture, remains untouched. Furthermore, the current situation is that no specific policy has been established for the problem of disposal of radioactive waste after decontamination.

Japanese Patent Application Laid-Open No. 2007-126301

In order to decontaminate the remaining forests, a plan (chip decontamination) of laying wood chips in the forest and collecting radioactive cesium by adsorbing the radioactive cesium on the wood chips is being considered. A plan to cut down trees from the forest and use them is also being considered. However, effective solutions to the problem of disposal of radioactive waste such as collected wood chips and lumber have not yet been implemented.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a method of effectively utilizing a raw material containing a carbon-containing substance and cesium.
Another object of the present invention is to provide a method for producing pollucite, which is capable of synthesizing pollucite from the non-gas components obtained by the method.

In order to solve the above problems, the present inventors have made intensive studies, and as a result, have studied the use of energy from the above raw materials. The inventors have found that gasification is suitable as an energy utilization method for carbon-containing substances containing cesium, that is, that the efficiency is enhanced, and have completed the present invention.
That is, aspects of the present invention are the following gas production method and pollucite production method.

(1) A method for producing a gas, comprising heat-treating a raw material containing a carbon-containing substance and cesium to obtain a gas containing hydrogen gas.
(2) The gas production method according to (1) above, wherein the cesium contains radioactive cesium.
(3) The method for producing gas according to (1) or (2) above, wherein the carbon-containing substance includes woody biomass.
(4) The gas production method according to any one of (1) to (3), wherein the gas further contains carbon monoxide gas.
(5) Any one of (1) to (4) above, wherein the molar ratio (Cs/C) of carbon element (C) and cesium element (Cs) in the raw material is 0.0015 or more. gas production method.
(6) Any one of (1) to (5) above, wherein the molar ratio (Cs/C) of carbon element (C) and cesium element (Cs) in the raw material is 0.021 or less. gas production method.
(7) The gas production method according to any one of (1) to (6) above, wherein the cesium is a cesium compound.
(8) The gas production method according to (7) above, wherein the cesium compound is Cs ₂ CO ₃ .
(9) Any one of (1) to (8) above, wherein the cesium is a cesium compound, the carbon-containing substance contains woody biomass, and the proportion of the cesium compound in 100% by mass of the raw material exceeds 1% by mass. The gas production method according to 1.
(10) Any one of (1) to (9) above, wherein the cesium is a cesium compound, the carbon-containing substance contains woody biomass, and the ratio of the cesium compound to 100% by mass of the raw material is less than 15% by mass. 1. Gas production method according to one.
(11) The gas production method according to any one of (1) to (10) above, wherein the cold gas efficiency at a gasification temperature of 800° C. is 60% or more.
(12) A method for producing pollucite, comprising synthesizing pollucite from the non-gas component obtained by the gas production method according to any one of (1) to (11) above.
(13) The method for producing pollucite according to (12) above, which comprises removing calcium from the non-gas component.

According to the present invention, a highly efficient gas production method can be provided.
Moreover, according to the present invention, it is possible to provide a method for producing pollucite, which is capable of synthesizing pollucite from the non-gas components obtained by the method.

1 is a schematic configuration diagram of a gasifier used in Examples. FIG. FIG. 2 is a process chart explaining the production process of pollucite according to one embodiment of the present invention. 4 is a graph showing the gasification rate with respect to the addition ratio of Cs ₂ CO ₃ in Examples. 4 is a graph showing the cold gas efficiency with respect to the addition ratio of Cs ₂ CO ₃ in Examples. 4 is a graph showing changes in the amount of generated gas (gasification temperature 800° C.) with respect to the Cs ₂ CO ₃ addition ratio in Examples. 4 is a graph showing changes in the amount of generated gas (gasification temperature 900° C.) with respect to the Cs ₂ CO ₃ addition ratio in Examples. 4 is a graph showing changes in the amount of generated gas (gasification temperature 1000° C.) with respect to the Cs ₂ CO ₃ addition ratio in Examples. It is an image of adherents formed on the upper stage of the furnace due to the addition of Cs ₂ CO ₃ . 2 is a graph comparing the gasification rate of each Cs compound at a gasification temperature of 1000°C. It is a graph comparing the cold gas efficiency of each Cs compound at a gasification temperature of 1000°C. The residue (non-gaseous components including ash) obtained from the _Cs2CO3 addition gasification test was analyzed by an X _- ray absorption fine structure ₍ XAFS) spectrometer and compared with a standard _Cs2CO3 sample. is a graph showing 2 is a graph showing the results of wide-angle X-ray diffraction (XRD) analysis of the precipitates (#2 sample) obtained in Examples.

Embodiments of the gas production method and the pollucite production method of the present invention will be described below.

≪Gas production method≫
A gas production method of an embodiment includes heat-treating a raw material containing a carbon-containing substance and cesium to obtain a gas containing hydrogen gas.

A method of obtaining a gas containing hydrogen gas by heat-treating a carbon-containing substance as a raw material is conventionally known. In the gas production method of the embodiment, a method of gasifying a carbon-containing substance using water (H ₂ O) as a gasifying agent can be employed. The gas production method of the embodiment is preferably a method in which a raw material containing a carbon-containing substance and cesium is heat-treated and reacted with water vapor to obtain a gas containing hydrogen gas. This method is called "steam reforming" or "steam gasification" and is represented by the following reaction formula. The product gas includes hydrogen gas and carbon monoxide gas.
C + H ₂ O = H ₂ + CO … Steam gasification reaction

Hydrogen can be further produced by further reacting CO produced by the above steam gasification reaction with H ₂ O.
CO + H ₂ O = H ₂ + CO ₂ … water gas shift reaction

The carbon-containing substance is not particularly limited as long as it contains carbon and can be used for gasification, and may be coal, hydrocarbon oil, or the like. It is more preferable to contain an organic matter.
Examples of plant-derived organic matter include plant bodies, parts thereof, and processed products thereof. Examples include herbs such as Japanese pampas grass, bamboo grass, and Erianthus; agricultural residues such as rice straw, rice husks, and wheat straw; mentioned.

Plant-derived organic matter further includes woody biomass. Preferably, the carbonaceous material comprises woody biomass. Here, "woody biomass" refers to the lignified parts such as trunks and branches of plants or processed products thereof.
Woody biomass includes trees, lumber, sawdust, felled wood, thinned wood, pruned branches, construction waste, lumber waste, wood chips, wood chips, wood waste, and the like.
The tree species is not particularly limited, and may be either a coniferous tree or a broad-leaved tree, and examples thereof include cedar, cypress, cypress, cypress, Japanese red pine, Japanese black pine, larch, fir, Japanese white pine, sawtooth oak, oak, and the like. .

Examples of the types of treatments applied to the treated material include crushing treatment, crushing treatment, fragmentation treatment, heat treatment, drying treatment, and the like.

The shape, size, etc. of the carbon-containing substance are not particularly limited, but the average value based on the number of equivalent sphere diameters may be 0.05 to 500 mm, or 0.1 to 50 mm. It may be 1 to 10 mm.

The inclusion of plant-derived organic matter in the carbon-containing material, particularly the inclusion of woody biomass in the carbon-containing material, contributes to the above-described processing of forest decontamination waste and promotion of the use of renewable energy.

When the carbon-containing substance contains a plant-derived organic substance, the content of the plant-derived organic substance in 100% by mass of the carbon-containing substance may be 50% by mass or more, 70% by mass or more, or 90% by mass or more. and may be 95% by mass or more. The carbon-containing substance may consist of plant-derived organic matter.

When the carbon-containing substance contains woody biomass, the content of woody biomass in 100% by mass of the carbon-containing substance may be 50% by mass or more, 70% by mass or more, or 90% by mass or more. , 95% by mass or more. The carbonaceous material may consist of woody biomass.

It is known that woody biomass can be used as a raw material for useful gas. For example, Patent Literature 1 exemplifies the production of gas from woody biomass charcoal. Patent Document 1 exemplifies supporting a metal on a woody biomass carbide, but cesium is not exemplified, and it is not clear that the use of cesium increases gasification efficiency.
According to the gas production method of the embodiment, gasification efficiency can be improved by gasifying a raw material containing a carbon-containing substance and cesium.

As cesium, both radioactive cesium and non-radioactive cesium can be used, but from the viewpoint of contribution to the above-described cesium decontamination, cesium preferably contains radioactive cesium. Radioactive cesium includes cesium-137 and/or cesium-134.

The form of cesium contained in the raw material is not particularly limited, and may be in the form of metal cesium, cesium ions such as Cs ₂ and Cs ⁺ , cesium salts, and other complexes, and even cesium compounds. good. An inorganic compound is preferable as the cesium compound. Cesium compounds include oxides such as Cs ₂ O and CsO ₃ ; Cs ₂ CO ₃ , CsHCO ₃ , CsCl, CsBr, CsI, CsNO ₃ , Cs ₂ SO ₄ and CsOH. Among them, Cs ₂ CO ₃ is more preferable because the effect of improving the gasification rate and cold gas efficiency is particularly excellent.

It is assumed that cesium is preliminarily contained in or adhered to the above carbon-containing substances obtained by decontamination work or the like. That is, the raw material may contain a carbon-containing substance containing cesium or to which cesium is attached, or may contain a carbon-containing substance containing radioactive cesium or to which radioactive cesium is attached. Although this may be used as a raw material for gasification as it is, cesium can also be added to the raw material.

The molar ratio (Cs/C) between the carbon element (C) and the cesium element (Cs) in the raw material may be appropriately determined according to the type of the carbon-containing substance of the raw material, but it should be 0.001 or more. is preferably 0.0015 or more, more preferably 0.002 or more, still more preferably 0.0045 or more, and particularly preferably 0.01 or more. When the molar ratio (Cs/C) in the raw material satisfies the above value, the gasification rate and cold gas efficiency are further improved, and the gas can be produced more efficiently.

The molar ratio (Cs/C) between carbon element (C) and cesium element (Cs) in the raw material is preferably 0.021 or less, more preferably 0.02 or less, and 0.018 or less. is more preferable. As will be shown in the examples below, when the content of the cesium compound in the raw material increases, there are cases where deposits are generated in the furnace. The mechanism by which the deposits are generated inside the furnace is not clear, but it is speculated that the deposits are generated inside the furnace due to the reaction between the cesium or cesium compounds contained in the raw materials or the gasification residue and the metal walls inside the furnace. be done. When the molar ratio (Cs/C) in the raw material satisfies the above value, the generation of solid matter in the furnace is prevented, and the production line is stabilized, thereby more efficiently producing gas. is possible.

As an example of the numerical range of the above values, the molar ratio (Cs/C) between the carbon element (C) and the cesium element (Cs) in the raw material may be 0.001 or more and 0.021 or less. 0.0015 or more and 0.021 or less, 0.002 or more and 0.021 or less, 0.0045 or more and 0.02 or less, or 0.01 or more and 0.018 or less There may be.

When the cesium is a cesium compound and the carbon-containing substance contains woody biomass, the ratio of the cesium compound to 100% by mass of the raw material is preferably more than 1% by mass, preferably 1.5% by mass or more. , more preferably 3% by mass or more, more preferably 7.5% by mass or more, and particularly preferably 9% by mass or more. When the ratio of the cesium compound in the raw material satisfies the above values, the gasification rate and cold gas efficiency are further improved, and the gas can be produced more efficiently.

When the cesium is a cesium compound and the carbon-containing substance contains woody biomass, the ratio of the cesium compound to 100% by mass of the raw material is preferably less than 15% by mass, more preferably 13% by mass or less. , 11% by mass or less. When the ratio of cesium compounds in the raw material satisfies the above values, it is possible to produce gas more efficiently by preventing the occurrence of deposits in the furnace and stabilizing the production line. .

As an example of the numerical range of the above values, when the cesium is a cesium compound and the carbon-containing substance contains woody biomass, the ratio of the cesium compound to 100% by mass of the raw material is more than 1% by mass and less than 15% by mass. may be 1.5% by mass or more and 13% by mass or less, may be 3% by mass or more and 11% by mass or less, or may be 7.5% by mass or more and 11% by mass or less, 9 mass % or more and 11 mass % or less may be sufficient.

The temperature (gasification temperature) of the heat treatment of the gas raw material may be appropriately selected depending on the type of raw material and furnace. and may be from 750°C to 950°C.

The pressure (pressure in the gasification furnace) during the heat treatment of the gas raw material is not particularly limited, but is preferably less than 10 atmospheres, more preferably 1 atmosphere or more and less than 10 atmospheres, and 1 atmosphere or more and 5 atmospheres or less. More preferably, the pressure is 1 atmosphere or more and 2 atmospheres or less. The gas production method of the embodiment can achieve excellent gasification efficiency even when it is carried out near normal pressure as exemplified by the above numerical values. In addition, since the process is carried out at around normal pressure as exemplified by the above numerical values, the equipment and facilities required for treatment at high pressures above the above numerical range are not required, and gas can be produced at low cost.

Water vapor can be used as a gasifying agent during the heat treatment of the gas raw material, and an inert gas such as N ₂ , CO ₂ , Ar, He, etc., is contained as the atmospheric gas during the heat treatment of the gas raw material. is preferred. By using an inert gas, scattering of cesium contained in the gas raw material due to vaporization or the like can be suppressed. This means that it is possible to suppress the decrease in the Cs content in the non-gas components obtained after the heat treatment of the gas raw material. It is preferred that the atmosphere contains an inert gas.

A gasification rate is known as one of the indexes indicating the efficiency of gasification. The gasification rate indicates the rate at which the raw material is gasified using the carbon content as an index, and can be obtained by the formula (1) described in the Examples.
In the gas production method of the embodiment, the gasification rate at a gasification temperature of 800° C. is preferably 50% or higher, more preferably 60% or higher, and even more preferably 65% or higher. It is understood that the higher the gasification rate, the more efficiently the gas can be produced.

Cold gas efficiency is known as one of the indicators of gasification efficiency. The cold gas efficiency is an index for combustible gas among the produced gases, and can be obtained by formula (2) described in the Examples.
In the gas production method of the embodiment, the cold gas efficiency at a gasification temperature of 800° C. is preferably 60% or higher, more preferably 70% or higher, and even more preferably 75% or higher. It is understood that the higher the cold gas efficiency, the more efficiently the combustible gas can be produced.

The produced gas can be recovered by a known method, and may be further subjected to purification operations such as compression, gas-liquid phase separation, solid-liquid phase separation, adsorption separation, and the like. The recovered gas can be stored in a closed container such as a gas tank or gas cylinder.

According to the gas production method of the embodiment, since the raw material containing the carbon-containing substance further contains cesium, the gas can be produced with high efficiency.
The gas production method of the embodiment is particularly suitable as a method for treating woody biomass containing radioactive cesium. As a result, it is possible to produce energy for decontamination, waste treatment, etc., and furthermore, there is the advantage that the energy is renewable energy. By using woody biomass with attached radioactive cesium, it is possible to increase the utility value due to the attached radioactive cesium.
Conventional cesium treatment methods aimed at removing cesium. On the other hand, in the gas production method of the embodiment, cesium is intentionally used to solve the cesium problem.

≪Method for producing pollucite≫
A method for producing pollucite according to an embodiment includes synthesizing pollucite from non-gas components obtained by the method for producing gas according to the present invention.

_Polucite is a _compound represented by _CsAlSi2O6 or _{( Cs} , _Na ) _{2Al2Si4O12.2H2O} . As shown in the above structural formula, the pollucite raw material includes a Cs source containing Cs, an Al source containing Al, a Si source containing Si, and an O source containing O.
Since the non-gas component obtained by the gas production method of the embodiment contains cesium derived from the cesium contained in the raw material for gasification, in the method for producing pollucite of the embodiment, the non-gas component is used as a Cs source It is used as

The method for producing pollucite of the embodiment comprises synthesizing pollucite from a composition (corresponding to the second composition described later) containing the non-gas component containing Cs, Al, Si, and O. include.
In the method for producing pollucite according to the embodiment, a composition (corresponding to a second composition described later) containing the non-gas component containing Cs, Al, Si, and O is heat-treated to produce pollucite. Including synthesizing.

The non-gas component may contain ash, which is a processing residue from gasification. Examples of the ash include bottom ash and fly ash. Since ash usually contains the O element, the ash can serve as both a Cs source and an O source.

Any Al source may be used as long as it contains Al, and aluminum oxides are preferred, such as NaAlO ₂ , Al(O—CH(CH ₃ ) ₂ ), AlCl ₃ , Al(OH) ₃ , Al ₂ O ₃ , AlO(OH), Al(NO ₃ ) ₃ and the like can be exemplified. Note that the oxide of aluminum can serve as an O source as well as an Al source.

Any Si source may be used as long as it _{contains Si ,} and _oxides of _{silicon are} preferable. I can give an example. In addition, the oxide of silicon can serve as an O source as well as a Si source.

Also, the Al source and the Si source may contain both Al and Si. mordenite ₍ Ca, K2, _Na2 )[ _AlSi5O12 ] _2.7H2O ), _bentonite , which is a layered mineral containing Al and Si, _{clinoptilolite} , etc. Aluminosilicate and the like can be exemplified. In addition, these can serve also as an O source with an Al source and a Si source.

The O source may be one containing O, and as exemplified above, it may also serve as a Cs source, an Al source, or a Si source. Oxygen can also be exemplified.

The non-gas component may be previously pretreated before being used as the porcite raw material. Such treatments include carbon removal (calcination) and/or calcium removal. In this specification, as long as Cs is included, a treated product derived from a non-gas component obtained by subjecting a non-gas component to any treatment is also treated as a non-gas component. An embodiment in which these pretreatments are performed will be described below with reference to the drawings.

FIG. 2 is a process drawing explaining the manufacturing process of pollucite according to the embodiment.

First, carbon removal is performed from non-gas components. Carbon removal can employ calcination. Carbon dioxide can be generated and carbon can be removed from the non-gaseous components by calcining the non-gaseous components. Excessive carbon content in the pollucite raw material may hinder the synthesis of pollucite, so calcination of the non-gas component can increase the efficiency of pollucite synthesis. Note that it is not necessary to remove all the carbon contained in the non-gas components.
Since ash has a relatively high carbon content, in the production of pollucite using ash as a non-gas component, removal of carbon is particularly effective in improving the efficiency of pollucite synthesis.
The calcination temperature may be appropriately determined depending on the type of non-gas component, but it is preferably a temperature lower than the melting point of the substance constituting the non-gas component. you can
The calcination time may be appropriately determined according to the type of non-gas component and the like, and may be 1 to 48 hours as an example.

Calcium removal is then performed from the non-gas components after calcination. Since calcium may be an inhibitory factor for pollucite synthesis, removal of calcium can increase the efficiency of pollucite synthesis. Note that it is not necessary to remove all of the calcium contained in the non-gas components.
Since ash has a relatively high content of calcium, removal of calcium is particularly effective in improving the efficiency of pollucite synthesis when producing pollucite using ash as a non-gas component.
Methods for removing calcium include synthesizing a calcium compound and removing the resulting calcium compound.
Synthesis of the calcium compound is not particularly limited, but hydrothermal synthesis can be employed. The hydrothermal synthesis includes synthesizing a calcium compound from the first composition containing the non-gas component and hydroxide by hydrothermal synthesis. The first composition can contain water.
From the viewpoint of reaction efficiency, hydroxides of alkali metals or alkaline earth metals are preferable, and examples thereof include NaOH, KOH, and CsOH.
By heat-treating the first composition, for example, oxidation of residual carbon and non-gas components after calcination (for example, K ₂ Ca(CO ₃ ) ₂ (Fairchildite) contained in calcined woody biomass) The combination with the contained carbonate component is accelerated to synthesize calcium carbonate. The calcium carbonate obtained here can be easily separated from the supernatant containing non-gas components as a solid content.

The temperature of the heat treatment (synthesis temperature of the calcium compound) when hydrothermally synthesizing the calcium compound is not particularly limited, but may be relatively low, and may be 100 to 374°C. It may be 130 to 300°C or 150 to 250°C.

The pressure during the heat treatment in the hydrothermal synthesis of the calcium compound (synthesis pressure of the calcium compound) is not particularly limited, but is preferably a pressure exceeding normal pressure, and may be more than 1 atmosphere and 218 atmospheres or less. 0.7 to 85 atmospheres, 4.7 to 39 atmospheres, or 4.7 to 20 atmospheres.

Next, the synthesis of pollucite is carried out from non-gas components after calcium removal. A hydrothermal synthesis method can be employed for the synthesis of pollucite. The hydrothermal synthesis of pollucite includes synthesizing pollucite by hydrothermally synthesizing a second composition containing the non-gas component containing Cs, Al, Si, and O. The second composition can contain water.
The ratio of the non-gas component may be 10% by mass or more and 80% by mass or less, or may be 15% by mass or more and 50% by mass or less with respect to 100% by mass of the components excluding water from the composition.

The temperature of heat treatment in hydrothermal synthesis of pollucite (synthesis temperature of pollucite) is not particularly limited; It may be 300°C, or 150 to 250°C.

The pressure during the heat treatment in the hydrothermal synthesis of pollucite (synthesis pressure of pollucite) is not particularly limited, but is preferably a pressure exceeding normal pressure, and may be more than 1 atmosphere and 218 atmospheres or less. 0.7 to 85 atmospheres, 4.7 to 39 atmospheres, or 4.7 to 20 atmospheres.

According to the method for producing pollucite of the embodiment, pollucite can be synthesized from the non-gas components obtained by the method for producing gas according to the present invention.

In the method for producing pollucite exemplified above, carbon removal and calcium removal from non-gas components were carried out, but these are not essential steps in the method for producing pollucite. Alternatively, for example, only calcium removal may be performed without removing carbon from non-gas components. When both carbon removal and calcium removal are performed, there is no restriction on the order of performing these steps, and carbon removal may be performed after calcium removal. Calcium removal may also be performed on the first composition.

In addition to the non-gas component containing Cs, a Cs source may also be used. For example, a Cs source may be added to the first composition and a Cs source may be added to the second composition. By using Cs sources other than non-gaseous components, cesium collected by other methods can also be polcite.

Polucite is a kind of zeolite mineral. Many zeolites have ion-exchange ability, but since Cs in pollucite is a non-ion-exchange site, cesium is insoluble, and theoretically, cesium does not elute from pollucite. Therefore, pollucite is very suitable as a final disposal form of radioactive cesium.

In conventional gas production methods, in order to avoid increasing the amount of incinerated ash, the goal has been to increase the efficiency of gasification by using as few additives as possible. Including cesium at the stage of the gas feedstock is rather advantageous if the synthesis is to be the final stage, since it improves the efficiency of gas production.
For example, by converting the non-gas components containing radioactive cesium obtained by the gas production method according to the present invention into pollucite, the problem of disposal of radioactive cesium residue produced by the gas production method of the embodiment can be solved. In this way, the utilization of energy using woody biomass containing radioactive cesium and the fixation of combustion residue containing radioactive cesium by mineralization are integrated to further promote the spread of the gas production method of the embodiment. can be done.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

1. 1. Gasification of Woody Biomass 1.1 Specimens/Materials As a woody biomass, cedar sawdust with a particle size of 2 to 4 mm from the southern region of Fukushima Prefecture was prepared.
The following cesium compounds were used as additives containing cesium.
Cs ₂ CO ₃ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., model number 034-06542) _,
CsCl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., model number 035-01952) _,
CsNO ₃ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., model number 039-12462) _,
Cs ₂ SO ₄ (manufactured by Fujifilm Wako Pure Chemical Industries, model number 032-12452)

The analysis results of the sawdust are shown below.
Table 1 shows industrial analysis values of wet weight of sawdust.
Table 2 shows the elemental analysis values in the dry mass (dry, ash free: DAF) that does not contain ash of sawdust.

・Sample preparation By the following procedure, the content ratio of the additive (Cs compound) to 100% by mass of the sample is added to the sawdust so that it is approximately 1% by mass, 2% by mass, 5% by mass, or 10% by mass. agent was sprayed. The term "sample" as used herein includes sawdust and additives.

(Preparing sawdust)
1) After drying cedar sawdust (produced in the southern area of Fukushima Prefecture) at 105°C for 24 hours, vacuum drying was performed for 24 hours.
2) The dried sawdust was classified with a 2 mm sieve and a 2.8 mm sieve, and sieved to a particle size of more than 2.0 mm and 2.8 mm or less.
3) 12.5 g of sawdust was measured.

(solution spraying)
₄ ) 5 ml of distilled water was weighed out and the required amount (0.125, 0.25, 0.65, 1.45 g) of Cs compounds _{( Cs2CO3 ,} CsCl, _CsNO3 , Cs2SO4) was dissolved therein. Table 3 shows the Cs compound concentration in the aqueous solution, and Table 4 shows the Cs concentration in the aqueous solution.
5) Using an atomizer, the entire amount of the prepared aqueous solution was sprayed onto the sawdust.
6) 2 ml of distilled water was put into a spray container and washed, and the entire amount was sprayed on the sawdust.
7) The operation of 6) above was performed again.

(dry)
8) After drying the sawdust sprayed with the Cs compound at 105°C for 24 hours, it was vacuum-dried for 24 hours to obtain a sample.

1.2 Gasification Experiment FIG. 1 is a schematic configuration diagram of a gasification apparatus 1 used in Examples.
The sample was quantitatively fed into the gasification furnace 15 using the screw feeder 11 . Nitrogen (N ₂ ) was supplied from the front stage of the gasification furnace 15 while controlling the flow rate with a needle valve and a mass flow meter. Distilled water was sent by a plunger pump 12, heated to 200° C. by a preheater 13, turned into steam, and then supplied into the gasification furnace 15. After the temperature of the tubular electric furnace 14 was raised to the set temperature, the supply of the sample and steam was started. The generated gas was gas-liquid separated by the impinger 17 and recovered by the gas bag 18 . The gas volume was measured by a dry integrating flowmeter 19 . Non-gas components including the generated ash were deposited on the alumina balls 16 .
The experimental conditions were the temperature inside the gasifier of 800°C, 900°C or 1000°C under normal pressure conditions. The feed gas was nitrogen and the set flow rate was 200 mL/min. Regarding the amount of steam, the molar ratio (S/C ratio) of the amount of steam to the amount of carbon in the feedstock was set to 1.0. The sample was fed at 0.7 g/min for 18 minutes.

1.3 Evaluation method In order to evaluate gasification performance, gasification rate and cold gas efficiency were defined.
The gasification rate was defined as shown in the following formula (1), and obtained by the ratio of the amount of carbon substance in the produced gas to the amount of carbon substance in the sample. In addition, since the added Cs ₂ CO ₃ contains carbon, the amount of this substance was also calculated by adding it to the amount of carbon contained in the feedstock.

The cold gas efficiency is defined as shown in the following formula _{( 2} ) and obtained by the ratio of the lower calorific value of the combustible gases H2, CO, and CH4 in the produced gas to the calorific value of the raw material sawdust. .

1.4 Results Table 5 shows the temperature in the gasification furnace (gasification temperature), the type of additive, the amount of additive added, the content ratio of additive to 100% by mass of sample (mass%), The elemental ratio of Cs and C in the sample (Cs/C), the amount of sample supplied to the gasification furnace, the amount of each produced gas, the total amount of all produced gases, the cold gas efficiency, and the gasification rate are shown, respectively.

3 to 9 show graphs of some of the data in Table 5 above.
FIG. 3 shows a graph of the gasification rate versus the Cs ₂ CO ₃ addition ratio. Figure 4 shows the change in cold gas efficiency with respect to the Cs ₂ CO ₃ addition ratio. Figures 5 to 7 show changes in the amount of generated gas with respect to the Cs ₂ CO ₃ addition ratio for each gasification temperature (Figure 5: 800°C, Figure 6: 900°C, Figure 7: 1000°C). In addition, this time, tests were also conducted with the addition amount of Cs ₂ CO ₃ of 20 and 30 wt%. In addition, instead of adding Cs ₂ CO ₃ , K ₂ CO ₃ is added, and the additive is added to the sawdust so that the content ratio is about 10% by mass with respect to 100% by mass of the sample. After adjusting the sample by spraying, gasification experiments were conducted at a temperature of 800°C inside the gasification furnace. 9 and 10 show the results of comparing the gasification efficiency and cold gas efficiency of Cs ₂ CO ₃ and Cs compounds other than Cs ₂ CO ₃ at a gasification temperature of 1000° C., respectively.

From the above results, it can be seen that in the gasification of sawdust (woody biomass), the gasification rate and cold gas efficiency can be improved by adding a cesium compound to sawdust (woody biomass). It is also found that the addition of a cesium compound can achieve an excellent gasification rate and cold gas efficiency even at a relatively low gasification temperature. In particular, among the cesium compounds, the addition of Cs ₂ CO ₃ made it possible to achieve a very good gasification rate and cold gas efficiency.

1.5 XAFS analysis of gasification residue (non-gas components including ash) Gasification of the above woody biomass (gasification temperature: 800°C, 900°C, 1000°C, additive: _{Cs2CO3 ,} additive amount: about 5% by mass) and the residue (non-gas components including ash) and standard _Cs2CO3 samples _were analyzed with an X-ray absorption fine structure (XAFS) measurement device (SAGA-LS, BL06 (Kyushu University beam line)).
The results are shown in FIG. The peaks detected with non-gas components and standard Cs ₂ CO ₃ were identical. From this, after the addition of Cs ₂ CO ₃ and the gasification reaction, the state of Cs remaining at 800 ° C to 1000 ° C is Cs ₂ CO ₃ , and Cs ₂ CO ₃ is the active point.

2. 2. Synthesis of pollucite 2.1 Experiment of pollucite conversion Wood pellet fuel obtained by drying and compressing cedar sawdust from the southern region of Fukushima Prefecture is supplied to a demonstration-scale direct gasification furnace (fixed-bed downdraft type). Gasification was carried out under conditions of limited air supply (reducing atmosphere) so that partial combustion proceeded (reaction pressure: about 1 atm, reaction temperature: about 700°C to about 1000°C). 10.0 g of gasification residue (non-gas components including woody biomass ash) remaining after gasification was heat-treated (calcined) at 550° C. for 24 hours. To 1 g of the calcined residue obtained, 6 ml of 50% by weight ¹³³ CsOH aqueous solution and 40 ml of H ₂ O were added to obtain a first composition, which was treated at 180° C. and 9.9 atm for 41 hours ( Hydrothermal synthesis) produced 0.57 g of a precipitate (#1 sample). As a result of measuring this precipitate (#1 sample) by wide-angle X-ray diffraction (XRD), this precipitate (#1 sample) contained calcite (calcite, composition: calcium carbonate). . To the filtrate from which the precipitate (#1 sample) was removed, 1.85 g of _Na2SiO3 and 0.36 g of _NaAlO2 were added to obtain a _second composition, which was heated at 180°C and 9.9 atm. After 63 hours of treatment (hydrothermal synthesis), a precipitate (#2 sample) was obtained.

2.2 Results The precipitate obtained above (#2 sample) was washed three times by decantation, set in a wide-angle X-ray diffraction (XRD) device (RIGAKU, RINT-ultima-III), and Cu-Kα Measurement was performed under the conditions of line, 40 kV/40 mA, scan speed of 5 degrees/minute, and scan range of 10 to 80 degrees. As a result, the peak of pollucite shown in FIG. 12 was observed, confirming the presence of pollucite in the precipitate (#2 sample).
From the above, it was shown that pollucite can be synthesized using non-gas components including woody biomass ash and cesium as raw materials.

Each configuration and combination thereof in each embodiment is an example, and addition, omission, replacement, and other modifications of the configuration are possible without departing from the scope of the present invention. Moreover, the present invention is not limited by each embodiment, but is limited only by the scope of the claims.

1 Gasifier 11 Screw Feeder 12 Plunger Pump 13 Preheater 14 Tubular Electric Furnace 15 Gasifier 16 Alumina Ball 17 Impinger 18 Gas Bag 19 Dry Integrated Flow Meter

Claims (7)

A gas production method comprising heat-treating a raw material containing a carbon-containing substance, radioactive cesium, and water vapor in an inert gas atmosphere to obtain a gas containing hydrogen gas,
The molar ratio (Cs/C) of carbon element (C) and cesium element (Cs) in the raw material is 0.0075 or more and 0.017 or less,
A gas production method , wherein the heat treatment temperature is 900 to 1000°C . 2. The gas production method according to claim 1, wherein said cesium is a cesium compound. _3. The gas production method according to claim 2 , wherein the cesium compound is _Cs2CO3 . The gas production method according to any one of claims 1 to 3 , wherein the carbon-containing substance includes woody biomass. The gas production method according to any one of claims 1 to 4 , wherein the gas further contains carbon monoxide gas. A method for producing pollucite, comprising synthesizing pollucite from non-gas components obtained by the gas production method according to any one of claims 1 to 5 . 7. A method of producing pollucite according to claim 6 , comprising removing calcium from said non-gas components.

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