Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
1999-12-30
2001-09-18
Griffin, Steven P. (Department: 1754)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C588S253000, C588S253000
Reexamination Certificate
active
06291737
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for decomposing dioxins, and more particularly, to a method for effectively decomposing polychloro-p-dibenzodioxins (PCDD) and polychlorodibenzofurans (these compounds are hereinafter referred to as “dioxins”) contained in flyash and bottom ashes (these materials are hereinafter referred to as “incineration ashes”) discharged from various incineration plants such as an incineration plant for municipal solid waste, industrial waste and/or medical waste.
BACKGROUND OF THE INVENTION
In the incineration plants such as incineration plants for municipal solid waste, industrial waste and/or medical waste, the dioxides precursors including organic compounds such as phenols, benzene and acetylene, and chlorinated aromatic compounds such as chlorophenols and chlorobenzenes are formed during incineration. When flyash coexists in these precursors, the precursors change to dioxides under the catalytic action of flyash, and thus generated dioxins exist in incineration ashes.
Conventionally proposed methods for treating such dioxides-containing flyash are as follows. (1) To keep the dioxides-containing flash for 1-2 hours at a temperature between 320 and 400° C. under a reductive atmosphere (for instance, 2 hours at 320° C. or 1-1.5 hours at 340° C.) (Hagenmaier process, “ORGANOHALOGEN COMPOUNDS Vol. 27 (1996)” p. 147-152)
(2) A heat treatment of the dioxins-containing flash at 300-500° C. under the existence of a dioxins formation inhibitor (JPA 4-241880). It has been said that dioxins do not heat-decompose at a temperature lower than 300° C. This method is basically in accordance with the above mentioned theory, decomposing dioxides at above 300° C., and a dioxins formation inhibitor is added to the flash in order to prevent the formation of dioxins during the heat treatment in a temperature range in which dioxides decompose. For particulars, flyash is heated at 400° C. for 2 hours under the existence of pyridine vapor as the dioxins formation inhibitor.
The aforementioned conventional methods have a drawback in that their high treatment temperature and long treatment time require much energy and high cost. Especially, in the above mentioned method (1) it is required to perform the treatment under a reductive atmosphere such as nitrogen gas, bringing about complexity and a high cost.
DISCLOSURE OF THE INVENTION
The object of the present invention is to solve the problems of the prior art and to provide a method which makes it possible to decompose and eliminate the dioxins under a low temperature region in which dioxides have been thought not to decompose, and to perform the treatment even under the existence of oxygen.
According to the method of the present invention for decomposing dioxins, dioxins are decomposed by bringing dioxides or dioxides-containing materials into contact with at least one treating chemical selected from the group consisting of amine compounds and ammonium compounds at a temperature lower than 300° C.
According to the present invention, chlorines in dioxides react with the amine compound and/or the ammonium compound and this reaction causes quick dechlorination or replacement of chlorine atoms of dioxides and eventually, the detoxifications of dioxides at a temperature below 300° C., at which dioxides have been thought usually undecomposable.
Such effect of the amine compound and/or ammonium compound to decompose dioxins at a temperature below 300° C. has been hitherto unknown.
PREFERRED EMBODIMENT OF THE INVENTION
Dioxins to be treated according to the present invention may be contained in the exhaust gas discharged from various incineration plants such as municipal solid waste incineration plants, industrial wastes incineration plants, medical waste incineration plants and so on. The dioxins-containing materials are such as incineration ash which has dioxins adsorbed thereon, activated carbon powder used in the adsorption treatment of dioxins, and soil contaminated with dioxins.
The amine compound as the treating chemical may be at least one of alkanolamines such as monoethanolamine, diethanolamine, triethanolamin, methanolamine, and aminomethylpropanol, lower alkyl-derived amines such as diethylamine, propylamine, and ethylenediamine, and cyclic amines such as aniline. The preferred compounds among above mentioned are triethanolamine, diethanolamine, monoethanolamine, aniline, propylamine, ethylendiamine, and aminomethylpropanol.
The ammonium compound as the treating chemical may be at least one of ammonia, urea, and ammonium salts such as ammonium bicarbonate, ammonium carbonate, ammonium hydroxide, ammonium acetate. ammonium sulfate, ammonium phosphate, and ammonium hydrogen phosphate. The preferred compounds among above mentioned are ammonia, urea, ammonium bicarbonate, ammonium sulfate, and ammonium hydrogen phosphate, and the most preferred compound is ammonia.
When at least one treating material of the amine compounds and the ammonium compounds is brought into contact with the incineration ashes to decompose the dioxines, it is preferred that the treating chemical is added to the reaction system in a ratio of 0.1-10% by weight and especially 1-5% by weight to the amount of incineration ashes. The chemical is preferable to be added in a larger amount as the reaction temperature is lower.
The amine compounds and/or ammonium compounds to be added to the reaction system may be in the state of either gas, liquid, or aqueous solution. As the dioxins and the dioxins-containing materials are effectively decomposed when they are brought into contact with at least one of the gaseous amine compounds and the ammonium compounds, it is preferred that the amine compounds and the ammonium compounds have a sufficiently high vapor pressure at a temperature lower than 300° C.
In case that the liquid or the aqueous solution of the treating material is sprayed into the exhaust gas, or in case the material is preliminarily mixed with the incineration ashes, the material is preferable to have a vapor pressure that they are fully vaporized at a temperature lower than 300° C.
As to the method in which at least one of the amine compounds and the ammonium compounds is brought into contact with the dioxin-containing materials to be treated, either of the following methods A, B and C can be employed in case of the dioxin-containing materials are soil or incineration ashes.
A: The dioxins-containing materials and the amine compounds and /or ammonium compounds are mixed so that they are brought into contact at an ambient temperature. Otherwise, the mixture is heated to a temperature lower than 300° C. to gasify the amine compounds and/or ammonium compounds so that the amine compounds and/or ammonium compounds in gaseous form are brought into contact with dioxins. In these cases, it is preferable to previously dissolve the amine compounds and/or ammonium compounds into water or other solvents.
B: The amine compounds and/or ammonium compounds are heated to gasify at a temperature lower than 300° C., and a gas flow containing this resultant gas is brought into contact with the dioxins-containing materials.
C: The amine compounds and/or ammonium compounds are applied to a solid material and then, this solid material is mixed with, or placed on the dioxins-containing materials. After that, they are heated to a temperature lower than 300° C. In this case, preferably a gas flow is passed through the reaction system.
In a case dioxins or dioxins-containing materials exist in gaseous form or as floating small particles in a gas flow such as incineration exhaust gas, the following methods D, E, and F, for example, can be employed.
D: Vapor of the amine compounds and/or ammonium compounds or a gas containing this vapor is supplied into the above mentioned gas flow.
E: The amine compounds and/or ammonium compounds in liquid form are supplied into the gas flow in mist or in liquid drops.
F: A solution containing amine compounds and/or ammonium compounds dissolved in it is supplied into the gas flow in mist or in liquid drops.
In an incineration sy
Fujiwara Noboru
Fujiyoshi Naoaki
Izumikawa Hirofumi
Mashiko Mitsuhiro
Miyata Hiroshi
Griffin Steven P.
Kanesaka & Takeuchi
Kurita Water Industries Ltd.
Nave Eileen E.
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