Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture
Patent
1997-12-24
1999-11-09
Straub, Gary P.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
4232453, 423246, 423393, 502300, 502325, 502506, 502514, 50252715, 5025272, B01D 5334, B05D 102, B01J 2300, B01J 3700
Patent
active
059808438
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention concerns a method to purify flue gases originating in incineration plants. It also concerns a catalyzer device for the implementation of such purification. The invention allows for an efficient purification or cleaning of the flue gases with respect to both carbon monoxide and light and heavy hydrocarbons. The method and the device according to the invention can also be used for other chemical reactions.
Flue gases from certain types of incineration plants contain unsafe contents of pollutants which are hazardous to our health and environment, such as carbon monoxide (CO), light hydrocarbons (VOC) and heavy aromatic hydrocarbons, poly aromatic hydrocarbons (PAH). Among these pollutants, the PAH exhaust is considered to be the most serious ones since they may give rise to cancer. The VOC hydrocarbons, on the other hand, contain more substances capable of forming a photochemical smog and contributing to the greenhouse effect. The greatest problem occurs in small plants that fire with solid fuels and where system solutions and operation control are often inadequate. The emissions can also be high if the fuel is low quality or contains lots of water. Examples of such fuels can be sludge from treatment plants, food industry refuse, waste from paper and pulp industries, and mixtures of water and organic substances from the chemical industry. The harmful compounds are formed because the energy content of the fuel is so low that the combustion temperature becomes too low to perform complete combustion.
STATE OF THE ART
Before the arrival of this invention, purification of flue gases with regard to CO, VOC, and PAH preferably occurred with catalyzers. These were based on pellets, monoliths or fibers which had been coated with catalytically active components. It is true that these catalyzer solutions yield an acceptable degree of purification but they do have some serious, diverse drawbacks which have often prevented the application. Beds of both pellets and fibers render too high of a pressure drop in most applications. Additionally, in the case of pellets, the catalyzer efficiency becomes very poor since the main part of the catalyzer is inaccessible for pollutants and oxygen due to diffusion effects during combustion. Monoliths are honeycomb-like structures with thousands of channels. Such structures are expensive, hard to clean of deposits (soot and ashes) and may crack during transient temperature intervals due to thermally induced tensions in the material.
By providing a net structure with a ceramic layer its activity can be increased to a considerable extent at the same time as consumption of precious metals can be reduced. Tests have therefore been conducted in which standard steel wire nets were submersed into suspensions of ceramic particles (slip casting) having high specific surface. Through a drying and calcination process it has become possible to make the ceramic layer adhere to the metal wires of the net, resulting in a ceramic layer of high specific surface. This layer has then been provided with an active material in a conventional impregnation process. Catalyzer designs of this type have been used to purify exhausts of hydrocarbons of different types and the result has been satisfactory. The existing problem is that the adhesion of the ceramic wash coat to the metal wires is inadequate, causing certain parts of the wash coat to gradually loosen. This process of disintegration is much more pronounced in net structures than in monoliths, because net structures are characterised by an inherent mobility and can made to vibrate by thrusts in the flow direction. In purifying dust-containing gases it is also essential that the net can be subject to mechanical cleaning through brushing or similar and that this is done with certain regularity. The wash coat might be loosely attached to the metal wires causing the layer, wholly or partially, to loosen from the net structure and, if this is the case, the catalyzer will lose its activity.
SUMMARY OF
REFERENCES:
patent: 3264226 (1966-08-01), Johnson
patent: 4465789 (1984-08-01), Lindsley
patent: 5061464 (1991-10-01), Cordonna, Jr. et al.
patent: 5266293 (1993-11-01), Fairey et al.
Katator AB
Straub Gary P.
Vanoy Timothy C
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