Combustion – Process of combustion or burner operation – In a porous body or bed – e.g. – surface combustion – etc.
Reexamination Certificate
1998-06-12
2001-08-07
Lazarus, Ira S. (Department: 3743)
Combustion
Process of combustion or burner operation
In a porous body or bed, e.g., surface combustion, etc.
C431S009000, C431S116000, C431S170000, C431S328000, C431S011000, C431S247000, C060S738000, C060S750000
Reexamination Certificate
active
06270337
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus and method for increasing the reactivity of a fuel/air mixture prior to homogenous combustion of the mixture. More specifically, the present invention is a pilot for a gas turbine combustor which utilizes the heat of combustion within the pilot to increase the reactivity of a portion of the fuel/air mixture utilized by the pilot.
2. Brief Description of the Related Art
Known dry low NOx combustion systems for gas turbines can achieve relatively low emissions levels; however, the use of continuous pilot systems, as distinguished from starter systems, is required to stabilize combustion over a wide range of gas turbine operational conditions and minimize emission levels.
U.S. Pat. No. 5,634,784 represents a state-of-the-art continuous pilot. The patent teaches a catalytic pilot that will make a portion of the fuel/air mixture destined for the pilot's combustion zone more reactive by passing it through a catalytic centerbody. The patent also teaches that by recirculating hot combustion gas products back on to the catalytic centerbody the catalytic centerbody can use the heat of combustion within the pilot to assure that the catalytic component of the centerbody is at a suitably high operating temperature.
The structure of the catalytic centerbody design previously taught has several shortcomings. In particular, no method is provided to limit the temperature of the centerbody, thus the surface temperature could reach the adiabatic flame temperature of the fuel/air mixture, generally above th e centerbody's material failure temperature. In addition, a catalyst is required.
It has now been found that a stabilizing pilot can be created without the use of a catalyst. By utilizing the fuel/air mixture passing through the centerbody more fully, a more versatile pilot can be created. The invention accomplishes this by increasing the channel length for the fuel/air mixture within the centerbody, and by utilizing the fuel/air mixture entering the centerbody for cooling the centerbody structure, increasing the temperature and overall combustibility of the fuel/air mixture, and allowing the centerbody to be exposed to greater temperatures, even temperatures above the material limit of the centerbody.
SUMMARY OF THE INVENTION
The Dry, Low NOx Pilot (hereinafter “pilot”) is a continuously operating pilot that stabilizes the combustion within a gas turbine combustor. The basic pilot utilizes two fuel/air flows. One fuel/air flow enters a centerbody, and by passing through the centerbody obtains a temperature rise by extracting heat from the centerbody. The second fuel/air flow passes through a flow condition er capable of creating a recirculation zone to provide heat to the centerbody.
The centerbody and flow conditioner are parts of an integrated assembly. In the pilot of the present invention, the combustion zone is maintained downstream of the centerbody. The flow conditioner has the dual functions of contacting the second fuel/air mixture with heated fuel/air exiting the centerbody, and creating a recirculation zone such that hot combustion gases, either through radiation or conduction, impart a temperature rise to the centerbody. The flow conditioner can be any structure capable of accomplishing these functions, such as a swirler, a bluff body, a dump, opposed flow jets, or a combination of any of the above.
The centerbody is attached to the flow conditioner. During operation, a portion of the centerbody is simultaneously exposed to the heat of the recirculation zone on one surface and the fuel/air mixture entering the centerbody on an opposite surface (or backside). The entering fuel/air mixture sufficiently interacts with this opposite surface to obtain a temperature rise thereby lowering the temperature of the centerbody. This backside cooling of the centerbody can allow the temperature of the recirculation gases to exceed the material limit of the centerbody. Backside cooling allows for an increased temperature rise to be imparted to the fuel/air mixture; as the temperature of the recirculation gases contacting the centerbody are increased the temperature rise imparted to the fuel/air mixture is increased for any given flow.
The centerbody can be of numerous three dimensional configurations, such as cylindrical or elliptical; symmetry is not required.
The centerbody should have a high thermal conductivity. Preferably, the thermal conductivity of the cap should allow for a uniform distribution of the heat imparted to the cap from the recirculating gases so the temperature of the cap is approximately uniform.
The centerbody can incorporate a fuel/air channel. The fuel/air channel is placed within the centerbody such that the fuel/air mixture enters the space between the centerbody and the fuel/air channel, forcing the fuel/air mixture to be turned by, and to interact with, the cap. The fuel/air channel is placed within the centerbody such that a minority of the exits from the centerbody are above the exit of the fuel/air channel. The term “above” refers to a direction parallel to (and in the same direction as) the flow of the fuel/air mixture in the fuel/air channel. For the present invention structures, the centerbody is attached to the fuel/air channel by securing the base of the centerbody directly to the fuel/air channel, thereby forming a baffle and forcing all the fuel/air entering the centerbody to enter through the fuel/air channel.
For the present invention two fuel/air mixture flows are required—a fuel/air mixture flow through the flow conditioner and a fuel/air mixture flow through the centerbody. The fuel/air mixture can either be a single flow split between the flow conditioner and the centerbody based on the flow characteristics of both, or separate fuel/air flows with different characteristics. If separate fuel/air flows are provided, flow conditions could vary significantly, such as different fuel/air mixture ratios (even to the degree that one is rich and the other lean), different flow velocities, or different fuels. It is also possible to split a single fuel/air mixture but provide additional fuel injection to one or both of the two resulting fuel/air streams, thereby varying flow conditions, fuel/air mixture ratios, or fuel composition. These design alternatives can be done by those skilled in the art.
REFERENCES:
patent: 3030773 (1962-04-01), Johnson
patent: 3417978 (1968-12-01), Suzukawa et al.
patent: 3430443 (1969-03-01), Richardson
patent: 4160640 (1979-07-01), Maev et al.
patent: 4262482 (1981-04-01), Roffe et al.
patent: 4374466 (1983-02-01), Sotheran
patent: 4629413 (1986-12-01), Michelson et al.
patent: 4643667 (1987-02-01), Fleming
patent: 5346389 (1994-09-01), Retallick et al.
patent: 5624252 (1997-04-01), Charles, Sr. et al.
patent: 5634784 (1997-06-01), Pfefferle et al.
Etemad Shahrokh
Karim Hasan Ul
Pfefferle William C.
Cocks Josiah C.
Lazarus Ira S.
McCormick Paulding & Huber LLP
Precision Combustion Inc.
LandOfFree
Dry, low NOx pilot does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dry, low NOx pilot, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dry, low NOx pilot will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2510587