Combustion – Process of combustion or burner operation – Flame shaping – or distributing components in combustion zone
Reexamination Certificate
2001-09-07
2004-09-28
Cocks, Josiah (Department: 3743)
Combustion
Process of combustion or burner operation
Flame shaping, or distributing components in combustion zone
C431S175000, C431S284000, C431S285000
Reexamination Certificate
active
06796790
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of industrial burners and in particular to radiant wall burners which operate to heat the surrounding portions of a wall of a furnace or the like, which often consist of a burner tile, and these heated surrounding portions then distribute heat by radiation in the furnace. Even more particularly, the invention relates to methodology and apparatus whereby the efficiency and capacity and NO
x
reduction capabilities of radiant burners is enhanced.
2. The State of the Prior Art
Reduction and/or abatement of NO
x
in radiant burners has always been a desirable aim. Moreover, it has always been a desirable aim in the industry to increase the heat production of known burners which use a primary premix produced by inducing a flow of air with fluid fuel but previous burners have not been capable of producing fuel-air premixes containing less than about 80% of the total fuel. Such premixes combust at high temperatures resulting in excessive production of NO
x
and other contaminants. Moreover, the amount of secondary fuel available for other purposes such as carrying flue gas into the flame has been extremely limited because the primary fuel-air premix includes the bulk of the fuel needed for combustion. Accordingly the industry has needed means for improving the efficiency of burners for radiant burner applications such that the primary pre-mix is leaner in fuel whereby a large mass of air is available during the initial combustion to reduce the combustion temperature and a large amount of secondary fuel is available for circulating in the furnace space away from the flame so as to premix with a large amount of flue gas to further reduce combustion temperatures. The industry has also needed radiant burners with greater heat production capacities.
SUMMARY OF THE INVENTION
The present invention alleviates the problems discussed above and enhances radiant burner installations by providing a high capacity, low NO
x
radiant wall burner assembly wherein the primary fuel-air premix has a much higher air content and a correspondingly much lower fuel content than previously thought possible by those skilled in the art. The burner of the invention is also capable of generating greater amounts of heat than previously known burners. In accordance with the concepts and principles of the invention, a high capacity radiant burner is provided which includes a burner tube structure comprising an elongated burner conduit having spaced inlet and outlet ends. The conduit is adapted and arranged for directing a fuel lean gaseous mixture comprising a portion of the total fluid fuel to be combusted and oxygen therealong from the inlet end to the outlet end. A main burner nozzle is provided at the outlet end of the conduit, and such burner nozzle has a central axis, a wall extending around a centrally located chamber therein, and a downstream end spaced from the outlet end of the conduit. The main burner nozzle is arranged and adapted for receiving the fuel lean fuel-air mixture from the conduit in the chamber and redirecting the same without substantial recirculation and with minimal pressure drop through a plurality of apertures in the wall and into a combustion zone in a direction transverse to the axis and at a velocity which is greater than the flame speed of the gaseous mixture. The apertures are distributed around the wall, whereby the fuel-air mixture directed into the combustion zone through the apertures is generally in the form of a round flat pattern which is detached from the nozzle, surrounds the wall and extends outwardly across a radiant surface of a burner tile. Ideally, the fuel lean gaseous mixture includes all of the oxygen needed for combusting the total fuel delivered to the furnace.
The burner of the invention also includes an elongated fuel tube that extends in a direction generally parallel to the axis of the nozzle. The fuel tube has a downstream end portion and a secondary fuel nozzle including at least one secondary fuel port is positioned on the downstream end portion of the fuel tube. Each secondary fuel port is located and arranged so as to deliver secondary fuel to a location in the furnace which is on the opposite side of the round flat pattern from the radiant surface and is sufficiently remote from the combustion zone to permit the same to become intermixed with flue gases before entering the combustion zone.
In accordance with the invention, the elongated fuel tube may be located externally of the main fuel nozzle and each secondary fuel port may be located and arranged so as to deliver secondary fuel at a velocity and in a direction such that at least a portion of the secondary fuel pierces the pattern to reach the proper location described above. Alternatively, the elongated fuel tube may extend through the main fuel nozzle and protrude through the downstream end thereof to deliver the secondary fuel directly to the location which is on the opposite side of the fuel-air pattern from the radiant surface.
Preferably, the burner tube structure may comprise a venturi tube which uses a flow of the gaseous fuel to induce a flow of air, whereby to create the fuel lean fuel-air mixture. Ideally, the mixture may comprise a mixture of a gaseous fuel and air.
In another form of the invention, the burner tube structure may comprise a plurality of venturi tubes arranged for parallel flow, each of the venturis being adapted and arranged to use a flow of the gaseous fuel to induce a flow of air, whereby to generate the mixture as an ultra fuel lean mixture of fuel and air.
In a more specific sense, the high capacity, low NO
x
radiant wall burner according to the invention may include an elongated nozzle arrangement adapted for installation in a central passageway of a refractory burner tile inserted in a wall of a furnace adjacent a combustion zone. The tile may preferably have a radiant surface surrounding the passageway and located adjacent the combustion zone. The nozzle arrangement may include an elongated burner tube including an elongated downstream portion configured to extend through the passageway and an elongated upstream portion, such portions may have respective centrally disposed, longitudinally extending axes. The nozzle arrangement may also include a fuel-air mixture supply system providing a source of a fuel lean combustible fuel-air mixture for introduction into the burner tube, an upstream end of the upstream portion of the burner tube being connected in fluid communication with the fuel supply system for receiving the fuel lean combustible fuel-air mixture, the burner tube providing a conduit for flow of the fuel lean combustible fuel-air mixture therealong from the upstream end to a downstream end of the downstream portion of the burner tube.
The nozzle arrangement of the invention may further include a main nozzle positioned at the downstream end of the downstream portion of the burner tube adjacent the radiant surface, the main nozzle having an internal chamber that is in fluid communication with the downstream end of the downstream portion of the burner tube for receiving the fuel lean combustible fuel-air mixture flowing along the tube. The main nozzle is arranged and configured to redirect the fuel-air mixture in the chamber and cause it to flow without substantial recirculation in a direction radially outwardly relative to the axis of the downstream portion of the burner tube, into the combustion zone, and generally across the radiant surface. The main nozzle has a wall extending around the chamber and a series of radially extending openings in the wall. The openings are arranged and configured to dispense the combustible fuel-air mixture in a radial direction at an initial velocity which exceeds the flame speed of the mixture and in a circular pattern which essentially surrounds the nozzle in a radial direction, whereby a detached round flame is created when the mixture is combusting. Finally, the burner arrangement may desirably include a secondary fuel nozzle
Bussman Wesley Ryan
Chambers Jesse S.
Hayes Ralph Robert
Poe Roger L.
Venizelos Demetris T.
Cocks Josiah
John Zink Company LLC
Marsh, Jr. James H.
Stinson Morrison & Hecker LLP
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