Combustion – Process of combustion or burner operation – Flame shaping – or distributing components in combustion zone
Reexamination Certificate
2001-11-13
2003-05-06
Yeung, James C. (Department: 3743)
Combustion
Process of combustion or burner operation
Flame shaping, or distributing components in combustion zone
C431S075000, C431S351000, C431S354000, C060S737000, C060S748000
Reexamination Certificate
active
06558154
ABSTRACT:
FIELD OF THE INVENTION
The invention at hand relates to a burner system with staged fuel injection as well as an operating method associated with it. The burner system includes a burner with a swirl generator for a combustion air stream and means for introducing fuel into the combustion air stream, whereby the means for introducing fuel into the combustion air stream includes at least one first fuel supply means with a first group of fuel outlet openings for a first premix fuel amount and a second fuel supply means with a second group of fuel outlet openings downstream from the first group of fuel outlet openings for a second premix fuel amount. A preferred field of application for such a burner system is the gas and steam turbine technology.
BACKGROUND OF THE INVENTION
EP 0 321 809 B1 discloses a conical burner having several shells, a so-called double-cone burner. The conical swirl generator composed of several shells produces a closed swirl flow in the cone head, which, based on the increasing swirl, becomes instable along the cone tip and changes into an annular swirl flow with backflow in the core. The shells of the swirl generator are configured in such a way that tangential air inlet slits for the combustion air are formed along the burner axis. Along the cone shells' inflow edge created by this, supply means for the premix gas, i.e., the gaseous fuel, are provided, which have outlet openings for the premix gas distributed in the direction of the burner axis. The gas is injected transversely to the air inlet slit through the outlet openings or holes. In connection with the swirl of the combustion air/combustion gas flow generated in the swirl chamber, this injection results in a good mixing of the combustion or premix gas with the combustion air. In such premix burners, a good mixing is the prerequisite for low NO
x
values during the combustion process.
In order to further improve on such a burner, EP 0 780 629 A2 discloses a burner for a heat generator provided after the swirl generator with an additional mixing section for mixing fuel and combustion air. This mixing section, for example, could be realized as a subsequent pipe, into which the flow exiting the swirl generator is guided without any significant flow losses. This additional mixing section makes it possible to further increase the mixing efficiency and therefore to reduce noxious emissions.
FIG. 1
schematically shows an example for such burners, in which the fuel is mixed with the inflowing combustion air via outlet openings in supply channels arranged along the burner axis in the swirl body
1
. The figure hereby shows the conical swirl body
1
of the burner, on or in which the fuel supply means with outlet openings
2
arranged along the burner axis—shown in the figure by arrows symbolizing the injected fuel—extend. These fuel supply means usually are constructed as single channels with a fixed distribution of the fuel outlet openings
2
along the burner axis. The figure also shows a pilot lance
3
, through which the fuel is injected directly into the swirl chamber during the start-up of the burner. With an increasing load, a switchover from this pilot stage to the premix operation occurs, in which the fuel is mixed via the mentioned fuel outlet openings
2
with the inflowing combustion air.
Another known burner geometry of a premix burner is known from WO 93/17279. This arrangement uses a cylindrical swirl generator with an additional, conical internal body. The premix gas is also injected via supply means with corresponding outlet openings into the swirl chamber, the outlet openings being arranged along the axially extending air inlet slits. The pilot supply means of this burner is provided at the end of the conical internal body. The pilot operation results in increased NO
x
emissions, however, since this type of operation only allows an insufficient mixing with the combustion air.
All known burner systems are designed with a single-stage supply of the fuel during premix operation. Size, distribution, arrangement, spacing, as well number of the outlet openings of the fuel supply means along the burner axis must be optimized in order to fulfill the requirements regarding low emissions, extinction limit, backflash limit, as well as requirements for combustion stability. It is hereby almost impossible to also fulfill all of these requirements with a fixed distribution of the outlet openings under changing operating and environmental conditions. The characteristic of injection with respect to penetration depth and mixing-in of the gas jets as well as the fuel distribution along the air inlet slits or burner axis are established by the selection of the aforementioned parameters. A distribution of the outlet openings that are optimized for a particular type of system, for example with a ring combustion chamber, is no longer optimized for another type of system, for example one with a silo combustion chamber. Furthermore, the operating conditions of a system change over time, for example because leakage currents increase as a result of aging effects. A fixed distribution of the outlet openings is unable to compensate for such aging effects.
Another advantage of the known methods for operating premix burners is that they are optimized for low emissions and low combustion oscillations under full load conditions. An additional pilot stage is necessary for starting up the burner and gas turbine. At a certain operating load, at which the combustion can be maintained in premix operation, the burner is switched from the pilot to the premix stage. In the same manner, the shutting down of the gas turbine requires a switchover from premix operation to pilot operation. However, these switching processes cause strong combustion oscillations as well as large load oscillations. They furthermore require large amounts of an inert gas in order to flush the fuel supply means that are no longer in operation after the switchover. This is necessary in order to avoid an ignition of the unused fuel supply means through circulating hot gases.
Switchover processes from liquid to gaseous fuel, or vice versa, are also difficult to realize using existing fuel injection techniques because of the proximity of the injection nozzles to the inlet openings of the pilot system.
An aspect of the invention is a burner system as well as a method for operating a burner that do not have the above disadvantages and also permit optimized operation with changing operating and environmental conditions.
SUMMARY OF THE INVENTION
The burner system according to the invention includes a burner with a swirl generator for a combustion air stream and means for introducing fuel into the combustion air stream, whereby the means for introducing fuel into the combustion air stream includes at least one first fuel supply means with a first group of fuel outlet openings for a first premix fuel amount (first stage) and a second fuel supply means with a second group of fuel outlet openings (second stage) downstream from the first group of fuel outlet openings for a second premix fuel amount. Naturally, further groups of fuel outlet openings for further premix fuel amounts can be provided independently from the first and second group. Furthermore, several first and second fuel supply means for the respective stage are usually distributed with their outlet openings over the circumference of the swirl body, as is known already from the single-phased systems. The burner system also comprises a first measuring value probe that measures pulsations of a combustion initiated by the burner, and/or a second measuring value probe that measures the emission values of the combustion. The measuring value probes are connected to a control device that receives the measuring data from the measuring value probe(s) and controls the fuel supply by way of the first and second fuel supply means—as well as, if applicable, other fuel supply means—dependent on the measuring data provided by the measuring value probe(s). The control therefore adheres to the desired specifications.
Eroglu Adnan
Knoepfel Hans Peter
Paschereit Christian Oliver
Stuber Peter
Alstom (Switzerland Ltd
Burns Doane Swecker & Mathis L.L.P.
Yeung James C.
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