Liquid heaters and vaporizers – Stand boiler – Fluid fuel burner
Patent
1995-11-27
1998-01-20
Bennett, Henry A.
Liquid heaters and vaporizers
Stand boiler
Fluid fuel burner
431328, 1223671, F22B 500
Patent
active
057091749
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a hot water heater with an inlet for liquid fuels, a plurality of inlets for fresh air, an inlet for a fluid to be heated, at least two combustion stages which are traversed by the fuel-air mixture and have catalytic combustion chambers surrounded at least partially by at least one fluid chamber filled with fluid, and with an offgas heat exchanger for the fluid to be heated, which is traversed by the offgas escaping from the combustion chambers.
A hot water heater as generally described above is known for example from German Patent document DE-OS 33 32 572. In addition, a hot water heater is likewise described in German Patent document 42 04 320.4 wherein the heater, in particular has a first advantageous combustion stage. This reference provides background information on the first and second combustion stages. For improved clarity, the reference numerals in this application partially correspond to those in German Patent document 42 04 3204.
When fossil fuels are burned, in addition to the greenhouse gas carbon dioxide, additional pollutants such as sulfur dioxide and oxides of nitrogen are produced. In conventional flame burners, the reduction possibilities, primarily for the oxides of nitrogen, are limited by flame stability and the formation of carbon monoxide. A definite reduction in the emission of oxides of nitrogen can be achieved in flameless combustion on oxidation catalysts (platinum for example) as a result of the low reaction temperature. Catalytic burners also offer the advantage that mixtures of fuels with different energy densities can be reacted stably over a wide range of mixing ratios.
Burners for gasoline, diesel fuel, or methanol for example, are available today only as conventional flame burners. Because of the high reaction temperature (flame temperature) such burners have high nitrogen oxide emissions. There are ways in which emissions can be reduced even in such burners, for example by flame cooling or changing the percentage of air, but this causes the flame stability to decrease and the carbon monoxide emissions to increase.
This prior art has the disadvantage that it is not especially suitable for liquid fuels. Hence, there is therefore needed an improved hot water heater such that liquid fuels can be used without significant cracking.
The present invention meets this need by providing a hot water heater with an inlet for liquid fuels, a plurality of inlets for fresh air, an inlet for a fluid to be heated, at least two combustion stages which are traversed by the fuel-air mixture and have catalytic combustion chambers surrounded at least partially by at least one fluid chamber filled with fluid, and with an offgas heat exchanger for the fluid to be heated, which is traversed by the offgas escaping from the combustion chambers. The first combustion stage has an evaporation chamber which has at least partially on its outer surface, a catalyst layer of a catalytic combustion chamber of the first combustion stage. The invention makes it possible to thermally couple the first stage of the two-stage catalytic burner to the evaporation chamber.
One advantageous improvement on the catalytic cracking burner is that the first catalytic combustion chamber of the first combustion stage is designed as a catalytic cracking burner.
It is also advantageous for the evaporation chamber to be designed as a combustion chamber, for which purpose it has an ignition device. A bypass for the feed for the liquid fuel can serve as the igniting flame for example. In addition, the hot water heater has a supply of primary air for the combustion chamber for this purpose.
It is further advantageous if the fuel is supplied in isolation so that the fuel enters the combustion chamber without cracking.
It is also advantageous to provide a nozzle or other devices for atomizing the fuel.
It can also be advantageous to recycle a portion of the offgas from the first stage into the evaporation chamber, since the liquid fuel is then evaporated more easily
Gieshoff Juergen
Ledjeff Konstantin
Schuler Alexander
Bennett Henry A.
Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung
Wilson Gregory A.
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