Combustion – Fuel disperser installed in furnace – Disperser feeds into permeable mass – e.g. – checkerwork – etc.
Patent
1996-05-02
1998-09-22
Price, Carl D.
Combustion
Fuel disperser installed in furnace
Disperser feeds into permeable mass, e.g., checkerwork, etc.
431 7, 431326, 431328, F23D 1412, F23D 2100, F23C 600
Patent
active
058105778
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
The present application claims priority under 35 U.S.C. .sctn. 119 of German Patent Application No. P 43 30 130.4, filed Sep. 6, 1993
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a two-stage catalytic burner, in which the first combustion stage is designed in the form of a diffusion burner.
Similarly to flame burners, catalytic burners can be classified according to the type of mixture formation. A distinction is drawn between burners without and with pre-mixing.
2. Discussion of Background Information
In contrast to flame burners, the stability ranges with catalytic combustion are clearly wider, and therefore conversion is not so easily disturbed by operational fluctuations. Particularly when hydrogen is used, this advantage becomes very noticeable, so that catalytic H.sub.2 burners can be relatively simple in construction. For this reason also, and also due to the extreme ease of oxidation of hydrogen on catalysing contacts, catalytic burners are eminently suitable for use within the framework of hydrogen technology.
Catalytic burners without pre-mixing, also called diffusion burners, are used for special applications. Technical appliances are on the market for use in the leisure area and as infra-red dryers. In addition to their use as infra-red dryers, catalytic burners are mainly used as heating appliances for camping, boats, holiday houses and as mobile heating appliances.
In this case the catalytic burner is so constructed that the pure fuel gas, after it has been distributed in a chamber, flows at a homogeneous speed through a planar porous catalyst. The atmospheric oxygen necessary for combustion then diffuses out of the environment into the catalyst structure and catalytic combustion takes place in the zone close to the surface. The reaction heat is emitted by reflection and radiation.
Such a diffusion burner for operation with hydrogen is described in the article by K. Ledjeff "Use of hydrogen through catalytic combustion, BWK, Volume 39 (1987), No. 7/8, pages 370-374. This diffusion burner has an approximately tubular supply for the fuel gas and connected therewith a chamber for the fuel gas whose walls are constructed from a sintered metal. These sintered metals, made for example from special steel, are commercial products.
This burner, however, is unsuitable for operation with fuel gases containing hydrocarbons. The catalytic combustion of hydrocarbons is considerably more difficult than the combustion of hydrogen, as the fuel gases present in a gaseous form are extremely stable. For example, methane is so stabilised by its molecular structure that catalytic activation even on platinum begins only from extremely high temperatures of at least approximately 300.degree. C. In order to obtain total catalytic combustion of methane or natural gas, which consists mainly of methane, it is necessary to use highly-active catalysts, e.g. noble metals on ceramic carriers. These catalysts, however, are subject to ageing, the conversion rates deteriorating in time and the burners emitting increasing amounts of contaminants. This is the reason why the burner described above is unsuitable in particular for fuel gases containing hydrocarbons, as incomplete combustion results with high emissions or even with unconsumed fuel gas.
A further diffusion burner is described in EP 0 389 652 A1. This diffusion burner is so constructed that the fuel gas firstly passes through a diffusion layer with a relatively high flow resistance and then enters a catalytically active layer, which is placed on the diffusion layer. In this case the catalytically active layer has zones of differing activity.
This burner is indeed intended for hydrogen and for fuel gases containing hydrocarbons. Here also it has become apparent that the disadvantages described above are not totally removed, so that in this case also only incomplete combustion results, with high emissions.
There is known from P42 04 320.4 a water heater, which has two combustion stages, i.e. via
REFERENCES:
patent: 3912443 (1975-10-01), Revault et al.
patent: 3975140 (1976-08-01), Placek
patent: 4878837 (1989-11-01), Otto
patent: 5160254 (1992-11-01), Bell et al.
patent: 5395235 (1995-03-01), Lan-Sun Hung
LEDJEFF, K., "Wasserstoffnutzung Durch Katalytische Verbrennung" BWK, vol. -8, pp. 370-374 (1987).
English Language Abstract of JP-61-93307.
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Price Carl D.
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