Combustion – Process of combustion or burner operation – Flame shaping – or distributing components in combustion zone
Reexamination Certificate
2001-11-01
2003-09-30
Yeung, James C. (Department: 3743)
Combustion
Process of combustion or burner operation
Flame shaping, or distributing components in combustion zone
C431S116000, C431S115000, C431S009000
Reexamination Certificate
active
06626661
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fuel ejectors and fuel ejection methods for burners used in process heaters, boilers, and other fired heating or incineration systems. More particularly, but not by way of limitation, the present invention relates to fuel ejectors and fuel ejection methods effective for reducing NO
x
emissions.
BACKGROUND OF THE INVENTION
A need presently exists for more efficient and economical burner systems capable of significantly reducing NO
x
emissions from heaters, furnaces, boilers, and other fired heating or incineration systems. One approach employed heretofore has been to precondition the burner fuel by mixing substantially inert flue gases therewith. As used herein, the phrase “flue gas” refers to the gaseous combustion products produced by the fired heating system. Diluting the fuel with flue gas reduces NO
x
emissions primarily by lowering burner flame temperatures.
As will be understood by those skilled in the art, some prior burner systems employ “free jet” fuel ejectors for entraining
5
flue gas in and mixing the flue gas with at least a portion of the burner fuel. The phrase “free jet” refers to a jet flow of a first fluid (i.e., fuel) issuing from a nozzle into a second fluid (i.e., flue gas) which, compared to the jet flow, is more at rest. Free jet fuel ejectors are sometimes positioned for discharging at least a portion of the burner fuel such that, prior to combustion, the fuel stream must travel through the flue gas environment existing within the interior of the fired heating system.
A free jet ejector
10
of a type heretofore employed in some burner systems is depicted in
FIGS. 1 and 2
. Ejector
10
comprises: a fuel pipe
12
which extends into the interior
20
of the heating system through a furnace wall or other structure
11
; an ejector tip or nozzle
15
secured on the distal end of fuel pipe
12
; a flow cavity
17
within ejector tip
15
in fluid communication with the flow passageway of fuel pipe
12
; and an ejector port
14
extending laterally from flow cavity
17
through the sidewall of ejector tip
15
. The lateral cross section of burner tip
15
will typically have a round shape, as depicted in FIG.
2
.
Ejector port
14
discharges a stream of fuel
16
toward a combustion zone (not shown) within the fired heating system. The fuel will typically be a fuel gas comprising natural gas or generally any other type of gas fuel or gas fuel blend employed in process heaters, furnaces, boilers, or other fired heating or incineration systems. The fuel stream
16
flows through and entrains flue gas present within the interior
20
of the fired heating system.
It is typically desired that as much flue gas as possible be entrained in and mixed with fuel stream
16
as it travels toward the combustion zone. However, such entrainment and conditioning must typically occur very quickly and over a relatively short distance.
Unfortunately, the fuel ejectors heretofore used in the art have not provided optimum or adequate flue gas entrainment in the fuel discharge region
18
immediately outside of the ejector port
14
. Because of the shape of ejector tip
15
, the furnace flue gas flowing into the ejector discharge region
18
must contact and interact with fuel stream
16
at a very abrupt angle (typically close to 90°). In addition, the flue gas
19
flowing into discharge region
18
around the exterior of ejector tip
15
must follow a very sharply curved flow path. As a result of these characteristics, eddies and currents are created in discharge region
18
which significantly reduce flue gas entrainment.
As will thus be apparent, a need exists for a fuel ejector which will provide significantly enhanced flue gas entrainment, particularly in the discharge region
18
of the fuel flow stream.
SUMMARY OF THE INVENTION
The present invention satisfies the needs and alleviates the problems discussed hereinabove. The present invention provides an improvement for an ejector having at least one port effective for delivering a flow of fuel into a heating system such that flue gas within the heating system is entrained in the flow of fuel. In one aspect, the inventive improvement comprises the ejector having an aerodynamic shape effective for increasing entrainment of the flue gas in the flow of fuel in the discharge region at the ejector port.
In another aspect, the inventive improvement comprises the cross-sectional shape of the ejector in a cross-sectional plane extending through the ejector port having: a discharge end wherein the port is provided; a major axis extending through the discharge end; a second end on the major axis opposite the discharge end; a total length along the major axis from the discharge end to the second end; and a maximum lateral width which is less than the total length. In addition, the lateral width of the cross-sectional shape preferably increases along the-major axis from the discharge end to the location of maximum lateral width.
In another aspect, the present invention provides a method of reducing NO
x
emissions from a heating system having flue gas therein. The inventive method comprises the step of ejecting a fuel into the heating system in free jet flow from at least one port of an ejector positioned in the heating system. The free jet flow has a region of discharge adjacent the port and the ejector has an aerodynamic shape effective for increasing entrainment of the flue gas in the free jet flow at the region of discharge.
In yet another aspect, the present invention provides a method of reducing NO
x
emissions from a heating system having a flue gas therein comprising the step of ejecting a fuel into the heating system in free jet flow from at least one port of an ejector positioned in the heating system. The cross-sectional shape of the ejector in a cross-sectional plane extending through the port includes: a discharge end wherein the port is provided; a major axis extending through the discharge end; a second end on the major axis opposite the discharge end; a total length along the major axis from the discharge end to the second end; and a maximum lateral width which is less than the total length. The maximum lateral width is located along the major axis at a location of maximum lateral width and the cross-sectional shape increases in lateral width from the discharge end to the location of maximum lateral width.
REFERENCES:
patent: 5060867 (1991-10-01), Luxton et al.
Isaacs Rex K.
Kirk Tim
Little Cody L.
McDonald John
Zink Darton J.
Fellers Snider Blankenship Bailey & Tippens, P.C.
Yeung James C.
Zeeco Inc.
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