Fuel gas burner with low NOx content emissions

Details Fuel gas burner with low NOx content emissions Fuel gas burner with low NOx content emissions

2000-03-23

2001-07-17

Lateef, Marvin M. (Department: 3743)

Combustion

Mixer and flame holder

C431S350000, C431S181000

Reexamination Certificate

active

06261089

ABSTRACT:

The present invention relates to a fuel gas burner whose emissions have a low nitrogen oxide content (NO
x
).
As is known, during the combustion step, a sucked air fuel gas burner inevitably produces CO and NO
x
in combustion products.
This has led, in the more developed countries, and in particular in the European Union and the US, to the drawing up of norms that shall become in force, sooner or later, suitable to set severe limitations to the percentages (or, more exactly, to the parts per million—p.p.m.) of these products contained in the gaseous emissions originating from combustion.
It is also known that today the apparatuses running with fuel gas, such as boilers, water heaters, etc., require increasingly higher combustion powers; this requirement clashes with the other requirement constituted by the fact that the market requires that the spaces occupied by these apparatuses be increasingly smaller, to allow their housing in apartments that tend to have smaller sizes with respect to the past ones.
These two clashing requirements obviously create to the designer enormous difficulties in the realization of burners suitable to provide low emissions, in particular of NO
x
. However, in a period of a few years, a NO
x
reduction from 200 p.p.m. to 20-30 p.p.m. has been obtained.
The present sucked air, low NO
x
content burners, while working well, have all the same remarkable working limitations.
These limitations lie essentially in that:
they have—the combustion surface being the same—a power reduced by about 10% with respect to the usual suction burners of the hypostoichiometric type;
they cannot modulate the caloric power, as at about a half of their nominal power, the Venturi tube wherein the comburent air/gas mixing takes place has a reduced suction capacity; therefore, combustion that was of the hyperstoichiometric type at full power becomes hypostoichiometric, with the consequence that the burner head tends to become red-hot until it reaches the color of red steel, causing its destruction.
At present, the market requires burners having low NO
x
content in combustion products, high power, and being modulable, meaning that they should be able to work also in a regime far from maximum power.
This is not possible at present with the hyperstoichiometric burners of the known art. Object of this invention is to provide a burner of the so-called hyperstoichiometric type and as such able to cause reduced NO
x
emissions in combustion products, but also such as to be free from the above drawbacks.
This is achieved, according to the invention, by including in a burner of the hyperstoichiometric type a small fan, able to blow into the Venturi tube wherein the comburent air/fuel gas mixing takes place an air volume ranging from 1 to 30% with respect to the total volume necessary for combustion.
In this way, it is possible to obtain in the inside of the Venturi tube an introduction of air slightly greater with respect to that which would be obtained by the simple introduction of primary air sucked by the Venturi tube, which allows to burn more gas and to obtain very low NO
x
values (about 10-20 p.p.m.).
Thanks to the constant inlet of air coming from the fan of the Venturi tube, the flame remains always hyperstoichiometric, which prevents the very serious drawback of the abnormal heating of the burner head in low regime conditions.


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