Combustion – Process of combustion or burner operation – Flame shaping – or distributing components in combustion zone
Reexamination Certificate
2003-04-11
2004-08-03
Yeung, James C. (Department: 3749)
Combustion
Process of combustion or burner operation
Flame shaping, or distributing components in combustion zone
C431S012000, C431S350000, C431S354000, C060S737000
Reexamination Certificate
active
06769903
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of operating a burner, which has at least one first fuel supply conduit with a first group of fuel outlet openings, essentially arranged in the direction of a burner longitudinal axis, for the introduction of a first premix fuel quantity into a swirl space and one or a plurality of second fuel supply conduits with a second group of fuel outlet openings essentially arranged in the direction of the burner longitudinal axis, it being possible to admit fuel to the second fuel supply conduits independently of the first fuel supply conduit. The invention also relates to a burner which can be advantageously operated by means of the method. The combustion spaces of gas turbines are a preferred field of employment for such burners; in addition such burners are, for example, also employed in atmospheric boiler firing systems.
RELATED ART
A conical burner consisting of a plurality of shells, a so-called double-cone burner, is known from EP 0 321 809. A swirl flow in the interior space of the cone enclosed by the conical partial shells is generated by the conical swirl generator composed of a plurality of shells. Because of a cross-sectional step at a combustion-space end of the burner, the swirl flow becomes unstable and merges into an annular swirl flow with reverse flow at the core. This reverse flow permits stabilization of a flame front at the burner outlet. The shells of the swirl generator are combined in such a way that tangential air inlet slots for combustion air are formed along the burner longitudinal axis. Supply conduits for a gaseous premix fuel are provided at the inlet flow edge of the conical shells formed by this means. These supply conduits have outlet openings, distributed in the direction of the burner longitudinal axis, for the premix gas. The gas is injected transverse to the air inlet gap through the outlet openings or holes. In association with the swirl, generated in the swirl space, of the flow of combustion air and fuel gas flow, this injection leads to good mixing of the fuel gas or premix gas with the combustion air. In such premix burners, good mixing is the precondition for low NO
x
values during the combustion process.
For further improvement to such a burner, a burner for a heat generator is known from EP 0 780 629, which burner has an additional mixing section, which abuts the swirl generator, for further mixing of fuel and combustion air. This mixing section can, for example, be embodied as a downstream tube, into which the flow emerging from the swirl generator is transferred without appreciable flow losses. By means of this additional mixing section, the degree of mixing can be further increased and, therefore, the pollutant emissions reduced.
WO 93/17279 shows a further known premix burner, in which a cylindrical swirl generator with an additional conical inner body is employed. In this burner, the premix gas is likewise injected into the swirl space by means of supply conduits with corresponding outlet openings, which are arranged along the axially extending air inlet slots. In the conical inner body, this burner has, in addition, a central supply conduit for fuel gas, which can be injected for pilot operation into the swirl space near the outlet opening of the burner. This additional pilot stage is used for starting the burner. The supply of the pilot gas in the outlet region of the burner leads, however, to increased NO
x
emissions because it is only inadequate mixing with the combustion air which can take place in this region.
EP 0918191 A1 shows a burner, of the generic type, for operating a heat generator which, parallel to a first supply conduit for fuel, also has a second supply conduit for another type of fuel, which supply conduit is matched to the other type of fuel. The two supply conduits can be initiated independently of one another. By means of this design, the burner can be operated, without modification, on different types of fuel.
In all the burners presented, the injection of the premix gas in the air inlet gap takes place by means of supply conduits with outlet openings essentially arranged in the direction of the burner longitudinal axis. In consequence, the characteristics of the injection are predetermined with respect to penetration depth, mixing of the gas jets and the fuel distribution along the air inlet slots or the burner longitudinal axis. The arrangement of the outlet openings has therefore already determined the quality of mixing of the gas and the combustion air and the fuel distribution at the burner outlet. These parameters are, in turn, decisive for the NO
x
emissions, for the flame-out and flash-back limits and for the stability of the burner with respect to combustion pulsations.
In the case of different loads, gas qualities or gas preheat temperatures, however, different upstream gas pressures occur at the outlet openings and these, in turn, lead to different premixing conditions and mixture qualities at the fuel outlet. The different premixing conditions then result in different emission values and stability conditions, which depend on the load, the gas quality and the gas preheating. The known burners can therefore only be operated optimally for quite specific value ranges of these parameters.
A problematic feature in the operation of premix burners, particularly in gas turbines, is the part-load range because, in this range, the combustion air is mixed with only comparatively small fuel quantities. In the case of the complete mixing of the fuel with the whole of the air, however, a mixture occurs which is no longer capable of being ignited, particularly in the lower part-load range, or is only capable of forming a very unstable flame. This can lead to damaging combustion pulsations or to the flame becoming completely extinguished.
In order to match the known burners to certain emission values or to a certain stability window in the case of different loads, environmental conditions, gas qualities and preheat temperatures, the possibility currently exists of, on the one hand, staging the premix gas supply to individual burner groups in cases where multiple burner arrangements are employed. This, however, is only possible in the case of multi-row burner arrangements. In the case of single-row annular combustion chambers, this technology has the disadvantage that a temperature profile, which is non-uniform in the peripheral direction, appears at the combustion chamber outlet.
Another possibility, as already sketched above, is to equip burners with a so-called pilot fuel supply. The burners are then operated as diffusion burners at very high excess air numbers. This results, on the one hand, in superior flame stability but, on the other, in high emission values and further technical disadvantages in operation.
The object of the present invention consists in providing a burner operating method and a burner, by means of which the burner can, as far as possible, be stably operated in premix operation at approximately constant NO
x
emission values, even in the case of changes to the load, the gas quality or the gas preheat temperature.
SUMMARY OF THE INVENTION
The object is achieved by means of the method according to claims 1 and 7 and the burner according to claim 8. Advantageous designs and developments of the burner and the method are the subject matter of the subclaims.
In the present method, a burner with swirl body and swirl space is employed which has at least one first fuel supply conduit, with a first group of fuel outlet openings essentially arranged in the direction of a burner longitudinal axis, for the introduction of a first premix fuel quantity into the swirl space and one or a plurality of second fuel supply conduits with a second group of fuel outlet openings essentially arranged in the direction of the burner longitudinal axis, it being possible to admit fuel to the second fuel supply conduits independently of the first fuel supply conduit. In order to operate the burner, the supply of the fuel via the first fuel supply cond
Eroglu Adnan
Hellat Jaan
Stuber Peter
Alstom Technology LTD
Cermak Adam J.
Yeung James C.
LandOfFree
Method for operating a burner and burner with stepped premix... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for operating a burner and burner with stepped premix..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for operating a burner and burner with stepped premix... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3345339