Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
2002-12-20
2004-11-09
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S740000
Reexamination Certificate
active
06813890
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a premix fuel nozzle for use in a gas turbine combustor and more specifically to a premix fuel nozzle that does not contain a fuel circuit dedicated to support a pilot flame.
2. Description of Related Art
The U.S. Government has enacted requirements for lowering pollution emissions from gas turbine combustion engines, especially nitrogen oxide (NOx) and carbon monoxide CO. These emissions are of particular concern for land based gas turbine engines that are used to generate electricity since these types of engines usually operate continuously and therefore emit steady amounts of NOx and CO. A variety of measures have been taken to reduce NOx and CO emissions including the use of catalysts, burning cleaner fuels such as natural gas, and improving combustion system efficiency. One of the more significant enhancements to land based gas turbine combustion technology has been the use of premixing fuel and compressed air prior to combustion. An example of this technology is shown in FIG.
1
and discussed further in U.S. Pat. No. 4,292,801.
FIG. 1
shows a dual stage dual mode combustor typically used in a gas turbine engine for generating electricity. Combustor
12
has first stage combustion chamber
25
and a second stage combustion chamber
26
interconnected by a throat region
27
, as well as a plurality of diffusion type fuel nozzles
29
. Depending on the mode of operation, combustion may occur in first stage combustion chamber
25
, second stage combustion chamber
26
, or both chambers. When combustion occurs in second chamber
26
, the fuel injected from nozzles
29
mixes with air in chamber
25
prior to ignition in second chamber
26
. As shown in
FIG. 1
, an identical fuel nozzle
29
is positioned proximate throat region
27
to aid in supporting combustion for second chamber
26
. While the overall premixing effect in first chamber
25
serves to reduce NOx and CO emissions from this type combustor, further enhancements have been made to the centermost fuel nozzle since fuel and air from this fuel nozzle undergo minimal mixing prior to combustion.
A combined diffusion and premix fuel nozzle, which is shown in
FIG. 2
, has been used instead of the diffusion type fuel nozzle shown proximate throat region
27
in FIG.
1
. Although an improvement was attained through premix nozzle
31
, this nozzle still contained a fuel circuit
32
that contained fuel that did not adequately mix with air prior to combusting and therefore contributed to elevated levels of NOx and CO emissions. As a result, this fuel nozzle was modified such that all fuel that was injected into a combustor was premixed with compressed air prior to combustion to create a more homogeneous fuel/air mixture that would burn more completely and thereby result in lower emissions. This improved fully premixed fuel nozzle is shown in FIG.
3
and discussed further in U.S. Pat. No. 6,446,439. Fuel nozzle
50
contains a generally annular premix nozzle
51
having a plurality of injector holes
52
and a premix pilot nozzle
53
with a plurality of feed holes
54
. In this pilot circuit embodiment, fuel enters a premix passage
55
from premix pilot nozzle
53
and mixes with air from air flow channels
56
to form a premixture. Fuel nozzle
50
is typically utilized along the centerline of a combustor similar to that shown in FIG.
1
and aids combustion in second chamber
26
. Although the fully premixed fuel nozzle disclosed in
FIG. 3
provides a more homogeneous fuel/air mixture prior to combustion than prior art fuel nozzles, disadvantages to the fully premixed fuel nozzle have been discovered, specifically relating to premix pilot nozzle
53
. More specifically, in order to maintain emissions levels in acceptable ranges, premix pilot feed holes
54
had to be adjusted depending on the engine type, mass flow, and operating conditions. This required tedious modifications to each nozzle either during manufacturing or during assembly and flow testing, prior to installation on the engine.
In order to simplify the fuel nozzle structure and further improve emissions, it is desirable to have a fuel nozzle that supports combustion in a second combustion chamber
26
without having a pilot circuit. Elimination of a pilot circuit, whether diffusion or premix, will further reduce emissions since the pilot circuit is always in operation whether or not it was actually needed to support combustion. Furthermore, eliminating the pilot circuit will simplify fuel nozzle design and manufacturing. The major concern with eliminating the pilot circuit is combustion stability in the second combustion chamber given the reduced amount of dedicated fuel flow to the secondary fuel nozzle. Experimental testing was conducted on a gas turbine combustor having first and second combustion chambers by blocking the premix pilot nozzle
53
of fuel nozzle
50
in accordance with FIG.
3
. The combustor was run through its entire range of operating conditions and positive results were obtained for maintaining a stable flame in the second combustion chamber. Changes in combustion dynamics or pressure fluctuations associated with the elimination of the pilot fuel circuit were found to be minimal and insignificant for typical operating conditions.
SUMMARY AND OBJECTS OF THE INVENTION
An improved fully premixed secondary fuel nozzle for use in a gas turbine combustor having multiple combustion chambers, in which the products of premixed secondary fuel nozzle are injected into the second combustion chamber, is disclosed. The improvement includes the elimination of the pilot fuel circuit, which previously served to support ignition and combustion in the second combustion chamber. The improved premix secondary fuel nozzle includes a first injector extending radially outward from the fuel nozzle body for injecting a fuel to mix with compressed air prior to combustion, a second injector located at the tip region of the fuel nozzle for injecting an additional fluid, either fuel or air, depending on mode of operation, and an air cooled tip having a swirler. In the preferred embodiment, the first injector is an annular manifold extending radially outward from the fuel nozzle by a plurality of support members and contains a plurality of first injector holes. Also in the preferred embodiment, the second injector is in fluid communication with a plurality of transfer tubes that transfer a fluid to the second injector from around the region of the fuel nozzle that contains the cooling air. In an alternate embodiment of the present invention, the first injector comprises a plurality of radially extending tubes and the second injector is in fluid communication with a generally annular passage that transfers a fluid to the second injector from upstream of the first injector.
It is an object of the present invention to provide an improved premix secondary fuel nozzle for use in a gas turbine combustor having a plurality of combustion chambers that does not contain a fuel circuit dedicated to the initiation and support of a pilot flame.
It is a further object of the present invention to provide a gas turbine combustor having stable combustion while producing lower NOx and CO emissions.
In accordance with these and other objects, which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings.
REFERENCES:
patent: 4292801 (1981-10-01), Wilkes et al.
patent: 4982570 (1991-01-01), Waslo et al.
patent: 5199265 (1993-04-01), Borkowicz
patent: 6282904 (2001-09-01), Kraft et al.
patent: 6446439 (2002-09-01), Kraft et al.
patent: 6698207 (2004-03-01), Wiebe et al.
patent: 2003/0024249 (2003-02-01), Akagi et al.
Kraft Robert J.
Mack Brian R.
Martling Vincent C.
Casaregola Louis J.
Mack Brian R.
Power Systems Mfg. LLC.
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