Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1990-10-08
1996-04-30
Langel, Wayne
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
423240S, 4232453, B01D 5370
Patent
active
055122590
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method for reducing the emission of organic products from incomplete combustion, including poly-halogenated di-benzo-dioxines and di-benzo-furanes in the off-gases of incineration systems.
BACKGROUND OF THE ART
Incineration systems, especially trash and waste incineration systems, still emit organic compounds as products of incomplete combustion (PIC=Products of Incomplete Combustion), even after extensive purification of exhaust gas. A portion of these PICs consists of organic halogen compounds (chlorobenzoles, chloro-phenols, poly-chlorinated biphenyls, poly-halogenated (chlorine, bromine) di-benzo-dioxines and di-benzo-furanes, etc.). These compounds are toxic and are difficult to decompose. Therefore such compounds present in emitted incineration gasses pose a serious pollution problem. The effects of such pollutants are often delayed and thus great damage may be done before identification of the pollution problem.
From the point of view of the potential health risk of emissions from incineration systems, the poly-halogenated di-benzo-dioxines and di-benzo-furanes (all collected together under the brief name of "dioxines") are especially important. To reduce the emission of dioxines in off-gases, two methods are currently subjects of laboratory and pilot studies.
In a first method, prevention of the de novo synthesis of dioxines is accomplished by either poisoning the catalyst system that forms the dioxines, or by altering reaction temperatures.
It is disclosed in EP-A-87 110 006 that dioxines may arise at temperature ranges of from about 250.degree. C. to 400.degree. C., through a catalytic de novo synthesis on filter dusts which form in trash and waste incineration systems. One method for controlling this de novo synthesis comprises specifically poisoning the catalysts which are responsible for the de novo synthesis. Poisoning the catalyst may be accomplished by settling the crude gas dusts at high temperatures thereby causing the destruction of dioxin to predominate over the formation of dioxin.
In contrast, by settling the crude gas dusts at a temperature below 180.degree. C., de novo synthesis can not take place since it requires the higher temperatures discussed above. Current experiments with catalyst poisons aim exclusively at reducing the formation of dioxin. However, there are other problems which may occur when catalyst poisons are used which will not be discussed in detail here.
A second method of reducing dioxin emissions comprises settling dioxines on adsorption materials, such as activated charcoal. In this method, dioxines which are not completely removed by electro-filters or textile filters are adsorbed onto activated charcoal through which the off-gas is conducted. When activated charcoal is utilized to remove dioxines from exhaust gas emissions, there is a risk that, besides the dioxines, only a portion of the remaining PICs will be removed from the off-gas. Furthermore a follow-up treatment of the dioxin loaded activated charcoal is required in order to destroy the dioxines and other halogenated aromatic compounds, corresponding to the method described in the EP-A-87 110 006.
What is needed is a method for reducing the emission of organic products of incomplete combustion in the off-gas from incineration systems wherein the organic products are removed as thoroughly as possible.
SUMMARY OF THE INVENTION
Now in accordance with the present invention a method for substantially reducing organic products of incomplete combustion in off-gas from incineration systems is provided. In the present method, off-gas is directed through a denox catalyst under oxidative conditions whereby organic products contained within the off-gas are effectively degraded.
The organic products of incomplete combustion which are included in off-gas, and which are effectively degraded by the present method include organic halogen compounds such as halogenated aromatic compounds, e.g., chloro-benzoles, chloro-phenols, poly-chlorinated biphenyls, poly-halogenated (
REFERENCES:
patent: 4824360 (1989-04-01), Janka
patent: 5087430 (1992-02-01), Hanada et al.
patent: 5254797 (1993-10-01), Imoto et al.
patent: 5276250 (1994-01-01), Hagenmaier et al.
VDI Report 730, Report of the Meeting of the VDI Commission for Clean Air, "Progress in the Thermal, Catalytic, and Sorptive Purification of Off-Gas", Mar. 1-2, 1989, pp. 126, 250 and 251.
Hagenmaier Hanspaul
Mittelbach Gunther
Babcock Deutsche Babcock Anlagen AG
Hendrickson Stuart L.
Langel Wayne
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