Combustion – Combustion products return structure
Patent
1997-01-15
1998-12-08
Dority, Carroll B.
Combustion
Combustion products return structure
431175, 431166, F23D 1144
Patent
active
058460675
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a low-NOx burner. More particularly, in combustion using air preheated utilizing exhaust gas by direct heat exchange between exhaust gas and combustion air using a regenerator, the present invention relates to a low-NOx burner that is effective for reduction in NOx in a mid-temperature range which was conventionally difficult to be realized, as well as a high-temperature range.
BACKGROUND OF THE INVENTION
In order to reduce NOx in a burner, there has been conventionally adopted such a two-stage fuel combustion method as shown in FIG. 8 that is disclosed in, for example, Japanese patent-laid open publication No. 6-50508 (U.S. Pat. No. 5,403,181). According to this two-stage fuel combustion method, fuel is supplied from a primary nozzle 102 and a secondary nozzle 103 to combustion air A flowing in a burner throat 101 at two stages, and a primary flame is formed using the primary fuel and the full quantity of the combustion air while a secondary flame is formed by a reaction of mixture of the secondary fuel and the high-temperature combustion gas of the primary flame. Since a density of oxygen is low in the vicinity of the secondary fuel nozzle, NOx of the primary flame can be reduced by a reducing reaction.
However, in the burner adopting this two-stage fuel combustion method, since a direction of injection of the secondary fuel forming the main flame is substantially parallel with a flow of the combustion air, stability of the secondary flame is lowered when a temperature is low, and the flame can not be therefore stabilized unless the combustion air is preheated above approximately 1000.degree. C. When a direction of injection of the fuel is changed to be closer to a direction perpendicular to a flow of the combustion air to stabilize the secondary flame at a low temperature, the flame is stabilized but local combustion occurs to locally rise a temperature, thereby increasing NOx. In this manner, stabilization of the flame and reduction in NOx have been difficult to be simultaneously realized.
Therefore, as in the case where the burner is used as a heat source for a molten aluminum holding furnace, stabilization of the flame is deteriorated when operating in a mid-temperature range in which a relatively-low temperature of approximately 700.degree. to 800.degree. C. is obtained or when starting the furnace at a low temperature, and the prior art two-stage fuel combustion method is hence difficult to effect. Further, since a direction of injection of the fuel forming the main flame is substantially parallel to a flow of the combustion air, a very long flame can be obtained and it is difficult to use-the method when combustion is performed in a narrow space such as around a crucible of the molten aluminum holding furnace or under the crucible.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a low-NOx burner that improves stability of the flame and is effective for reduction in NOx in a mid-temperature range which was conventionally difficult to be realized as well as in a high-temperature range, in combustion using preheated air obtained by direct heat exchange with combustion exhaust gas utilizing a regenerator.
To this end, according to the present invention, in a low-NOx burner for preheating combustion air by a direct heat exchange that alternately flows exhaust gas and combustion air through a regenerator to inject fuel from the circumference of a flow of the combustion air, there are provided at an outlet of an air throat for injecting the preheated combustion air a burner tile having an enlarged diameter portion whose diameter is larger than that of the throat and a fuel nozzle for injecting fuel obliquely with respect to a flow of the combustion air from the enlarged diameter portion of the burner tile.
In this low-NOx burner, a flow of the combustion air injected from the air throat produces a negative pressure inside the enlarged diameter portion of the burner tile around this flow of the combustion air, i
REFERENCES:
patent: 2822864 (1958-02-01), Black
patent: 3180395 (1965-04-01), Reed
patent: 3217779 (1965-11-01), Reed et al.
patent: 4175920 (1979-11-01), Guerre et al.
patent: 5180300 (1993-01-01), Houis et al.
patent: 5284438 (1994-02-01), McGill et al.
patent: 5403181 (1995-04-01), Tanaka et al.
patent: 5431147 (1995-07-01), Tanaka et al.
Matsuo Mamoru
Mitani Kazuhisa
Nishiyama Tomohiko
Tanaka Ryoichi
Dority Carroll B.
Nippon Furnace Koayo Kabushiki Kaisha
Toyota Jidosha & Kabushiki Kaisha
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