Field of the Invention
The present invention relates to a burner configuration for a firing installation, in particular a gas turbine combustion chamber, having a main burner and, disposed centrally within it, a primary pilot burner which is used for igniting and/or for stabilizing the combustion of the main burner. In addition, the present invention relates to a method of operating such a burner configuration.
Burner configurations of the generic type are often configured for different fuels and different modes of operation and, in view of the continually more strict regulations worldwide on the emission of pollutants, great efforts are being made to improve the configurations and modes of operation in such a way that the emission of pollutants is reduced.
Particularly environmentally friendly burners with a low emission of NOx are known from European Patent EP 0 108 361 B1 and European Patent EP 0 193 838 B1. Because the present invention deals precisely with a development of such burners, reference is made to the complete content of these two publications.
Published, Non-Prosecuted German Patent Application DE 196 10 930 A1 discloses a burner for a heat generator. In the burner, which consists essentially of a swirl generator for a combustion airflow and of a device for injecting a fuel into the combustion airflow, a mixing section is disposed downstream of the swirl generator mentioned. Within a first partial section, the mixing section has a number of transition ducts extending in the flow direction, which transition ducts ensure the continuous transfer of the flow formed in the swirl generator into a downstream mixing tube. The outlet plane of the mixing tube relative to the combustion chamber is configured with a final edge which serves to stabilize and increase a reverse-flow zone forming in the flow. A number of mixing elements, which serve to form a mixture of combustion air and a fuel, are provided concentrically with the mixing section. This mixture of the respective mixing elements then forms one pilot stage of the combustion chamber.
Although, in the known burner configurations, critical conditions of the burner can be substantially avoided by design measures and the mode of operation, there is nevertheless the possibilityxe2x80x94particularly when the burner configuration is operated in premixed operation, i.e. when fuel and air are already intensively mixed with one another before the combustion zonexe2x80x94that the combustion in a firing installation exhibits fluctuations and sometimes becomes unstable, which can, for example be expressed by a firing installation rumble. The flame can then also, on occasion, flash back into a partial region of one of the burners, which is undesirable because of the increases in temperature of burner components caused by it and because of an increased emission of pollutants which then occurs.
It is accordingly an object of the invention to provide a burner configuration with primary and secondary pilot burners which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which creates increased stabilization of the combustion and, helps avoid firing installation rumble due to unstable combustion and flashback of the flame into partial regions of the burner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a burner configuration for a firing installation such as a gas turbine combustion chamber. The burner configuration contains a main burner having an outlet region and a primary pilot burner disposed centrally within the main burner. The primary pilot burner ignites and stabilizes a combustion of the main burner. A fuel supply line and a secondary pilot burner having a peripheral annular duct with a plurality of outlet openings formed therein and disposed in the outlet region of the main burner, are provided. The peripheral annular duct is connected to the fuel supply line and is in connection with the outlet openings, the outlet openings being directed in a direction towards a center of the outlet region.
Such a burner configuration for a firing installation, in particular a gas turbine combustion chamber, has the main burner and, disposed centrally within it, a primary pilot burner which is used for igniting and/or for stabilizing the combustion of the main burner. Details of such burners, which are also called hybrid burners because of the different possibilities with respect to mode of operation and fuel supply, are described, for example, in European Patent EP 0 108 361 B1 and European Patent EP 0 193 838 B1. In the invention of the instant application, such a burner configuration is now additionally equipped with a secondary pilot burner, the latter exhibiting a plurality of outlet openings in the outlet region of the main burner. Because fuel, or a mixture of air and fuel, emerges from these outlet openings, a ring of flame is formed which surrounds the flame emerging from the main burner approximately as an annulus and, by this, additionally stabilizes the flame. Whereas the primary pilot burner supports the combustion centrally, more or less from the inside out, the secondary pilot burner can contribute to the stabilization from the outside without negatively affecting the principle of combustion with recirculation, which is possessed by the burners of the prior art. The outer recirculation region, which is important for stable combustion in the burner flame, is in fact strengthened by the secondary pilot burner.
A particularly preferred configuration is for the secondary pilot burner to be formed by a peripheral annular duct in the outlet region of the main burner, which annular duct is connected to a fuel supply line and is in connection with the outlet openings. The peripheral annular duct surrounds the outlet region of the main burner more or less like a collar in which the outlet openings are disposed, preferably directed toward the inside in the direction of the center of the outlet region.
To avoid any limitation to the number or the cross-sectional area of the outlet openings, the peripheral annular duct is subdivided, in a particularly preferred embodiment example, into a lower annular duct and an upper annular duct, which are connected together by a throttle location, the upper annular duct being connected to the fuel supply line and the lower annular duct being in connection with the outlet openings. In this way, the fuel quantity for the secondary pilot burner is determined by the throttle location and not by the cross section of the outlet openings and their number. In this way, the lower annular duct acts as a resonance chamber so that the fuel quantity emerging at the outlet openings is influenced by the external pressure which, given appropriate design and dimensioning of this lower annular duct, acts in a strongly damping manner in the case of pressure vibrations, i.e. during burner configuration rumble for example.
According to the invention, the outlet openings can preferably be disposed in a ring, at approximately equal distances apart, in the outlet region of the main burner. This configuration is symmetrical to all sides and leads to uniform stabilization on all sides.
As an alternative, it is also possible to dispose the outlet openings in a ring, at different distances apart, in the outlet region of the main burner, this being useful, particularly in the case of combustion chamber configurations with a plurality of burners, in order to avoid accumulations of outlet openings in regions in which two burners come very close together. In addition, a non-uniform distribution of the outlet openings has a smaller tendency to vibration, and therefore to instabilities, than a uniform distribution because, in the case of pressure shocks, different pressure wave traverse times to or from the individual outlet nozzles occur due to different distances and this leads, at least partially, to mutual extinguishing of such pressure waves and therefore damps instabilities.
There is also a large degree of freedom with respect to the shape of the outlet openings. Particularly preferred, according to the invention, are round or oval outlet openings, which are particularly easy to manufacture.
Depending on the burner geometry, however, the outlet openings can have a polygonal edge, in particular in the form of a triangle with an apex pointing in the gas flow direction. The burner configuration with the secondary pilot burner is configured, according to the invention, in such a way that between 0 and 10% of the fuel quantity required at base load of the burner configuration can be supplied to the outlet openings, in particular in the form of fuel gas. Depending on the mode of operation of the burner configurations, it can be useful to appropriately throttle the fuel supply to the central primary pilot burner, which is now supported, according to the invention, by the secondary pilot burner, in order not to unduly increase the proportion of fuel which is supplied by the pilot burners overall.
In the burner configurations of the prior art, it is known art for the main burner and the primary pilot burner to be operated in premixed operation, in diffusion operation or in a mixed operation of both types of operation, it being also possible to configure the main burner and the primary pilot burner for optional operation with liquid and gaseous fuels. All these modes of operation are also possible in the case of a burner configuration according to the present invention. In addition, it is also possible to operate the secondary pilot burner as a premixing burner with a premixed mixture of fuel and air, which particularly contributes to reducing the generation of oxides of nitrogen.
The invention also relates to a method of operating the burner configuration, in particular to avoid instabilities in the combustion chamber, the associated rumble and the possible flashback of the flame in partial regions of the burner, the burner configuration having the main burner stabilized by the primary pilot burner and, according to the invention, the flame of the main burner being additionally stabilized by the secondary pilot burner, the secondary pilot burner having a plurality of outlet openings distributed around the outlet region of the main burner, which outlet openings are supplied separately, using open-chain control or closed-loop control, with fuel or fuel mixture. This method according to the invention provides a further parameter for the particularly reliable and environmentally friendly control of a burner configuration. The stabilization of the flame of the main burner by the outer secondary pilot burner inhibits unstable operating conditions such as rumble in the firing installation and, therefore, also inhibits flashback of the flame in partial regions of a burner.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a burner configuration with primary and secondary pilot burners, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.