Furnaces – Process – Treating fuel constituent or combustion product
Patent
1996-02-27
1997-10-14
Bennett, Henry A.
Furnaces
Process
Treating fuel constituent or combustion product
110190, 110215, 422111, 422168, 122 4D, 423235, F23J 1100
Patent
active
056760710
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and a device for introducing a liquid or gaseous treatment medium into a flue gas flow. In particular, this invention relates to the introduction of a nitrogen oxide removal medium or a dioxin inhibitor into the flue gas flow of a furnace in order to reduce the nitrogen oxide components or dioxins being generated in the flue gas during the combustion process.
2. Description of Prior Art
Various gaseous compounds harmful to the environment and health are known to be generated in furnaces. It is, thus, desirable to remove as much as possible of said compounds from the flue gas. Emission threshold limits are prescribed by lawful regulations and may not be exceeded in any way. Although the description which follows relates generally to nitrogen oxides (NOx), it should be pointed out here that the problems in general and the proposals for their solution are described herein are also applicable to the treatment of other chemical compounds.
Nitrogen oxide removal from flue gases is mostly performed today by catalytic reduction, that is by splitting the nitrogen oxides into nitrogen and water vapor with the addition of ammonia in the presence of a catalyst. The ammonia is added in the form of "aqueous ammonia", or in the form of solid ammonia compounds dissolved in water, to the flue gas flow. Although the desired chemical reaction takes place over a relatively wide temperature range, the degree of reduction is only satisfactory within a narrow temperature range. It is therefore necessary to assure that the ammonia molecules mix with the nitrogen oxide molecules within this temperature range. If the process is not optimally performed, the emission of nitrogen oxides and/or unused ammonia rapidly attains unsatisfactory values. Furthermore, excessive amounts of treatment medium are used up in the course of a non-optimal performance of the process. Finally, the thermal efficiency of the furnace is also lowered by excessively large amounts of supplied treatment medium, in particular excess amounts of supplied water in which the actually effective substances are dissolved.
One method for controlling the amount of a treatment medium supplied for nitrogen oxide removal from flue gas is taught by German Patent DE 41 39 862 A1, wherein the addition of the treatment medium is controlled as a function of the concentration of ammonia in the exhaust gas, and taking into consideration the nitrogen oxide content in the exhaust gas. Fairly satisfactory results can be obtained depending on the type of the furnace controlled in this way. However, it has been shown that improvements are required, particularly in larger furnaces with correspondingly larger flue gas conduits.
One method for introducing a treatment medium into a flue gas flow is taught by German Patent DE 39 35 400 C1, which also relates to the removal of nitrogen oxide from flue gas. In accordance with this known method, treatment medium is introduced into the flue gas at only those locations where it has been determined by the use of an optical sensor that there is no flame present at the time, because it has been found that the injected chemicals are always destroyed at the places where a flame actually licks up into the flow chamber. However, this method also does not provide completely satisfactory results.
To assure the optimal feeding of treatment media, a special form of nozzles is disclosed by German patent reference DE 39 35 401 A1 and DE 39 35 402 A1, through which the treatment medium is intended to be sprayed into the flue gas conduit. It is respectively proposed in these publications to perform the mixing of the actually effective substance with the carrier substance (water) as closely as possible to the nozzle opening. However, no optimal results can be achieved by this either.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a method for introducing a treatment medium into flue gases in such a way that it is possible to achieve improved emis
REFERENCES:
patent: 4440100 (1984-04-01), Michelfelder et al.
patent: 5103742 (1992-04-01), Valentino
patent: 5260042 (1993-11-01), Martin
patent: 5326536 (1994-07-01), Carter
patent: 5478542 (1995-12-01), Chawla et al.
Horler Stefan
Kemter Andreas
Nikolaus Thomas
Bennett Henry A.
Techform Engineering AG
Tinker Susanne C.
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