Patent Application
20110048022
The invention relates generally to gas turbine combustors, and more specifically to a system and method for controlling gas turbine combustion dynamics by varying fuel nozzle impedance among various nozzle groups.
Each can of a multi-can gas turbine combustion system typically includes 2-3 or more different fuel supply nozzle groups. These fuel supply nozzles in different groups are generally identical in geometry with differences relating only to the amount of fuel flow. The relative amount of fuel-flow to different nozzle groups is referred to as fuel split, which is one of the primary tools to control combustion dynamics. However, the best conditions for achieving lowest dynamics usually do not correspond to operating conditions suitable for minimum emissions and vice-versa.
The unsteady flame inside a combustor can, when coupled with the natural modes of the combustor establishes a feedback cycle and can lead to high amplitude pressure pulsations with potential damage to the hardware. These problems are more pronounced with modern lean premixed combustion systems that are used to generate lower emissions and have been addressed in various manners including modification of generation mechanisms, changes to combustor geometry, and active and passive control.
Since the interaction of various flame groups with each other in a multi-nozzle gas turbine combustion system can be a critical factor in causing/controlling the combustion dynamics of the combustor, it would be both advantageous and beneficial to provide a system and method for operating a gas turbine at even fuel-splits in a manner that achieves minimization of emissions while simultaneously lowering the combustion dynamics amplitude.
Briefly, in accordance with one embodiment, a combustor comprises a plurality of fuel nozzles, wherein at least one nozzle receives fuel from a first fuel line, and further wherein at least one different nozzle receives fuel from a second fuel line, each fuel line having a corresponding impedance such that the first fuel line impedance is fixedly or variably different from the second fuel line impedance. The impedance of the fuel lines is governed by the geometrical dimensions of nozzles and the fuel flow rate. The division of total fuel to various nozzles is referred to as the fuel split. When the amount of fuel per nozzle distributed among various nozzle groups is equal, the condition is referred to as even fuel-spilt.
According to another embodiment, a combustor comprises a plurality of fuel nozzles, wherein at least one nozzle receives fuel from a first fuel line, and further wherein at least one different nozzle receives fuel from a second fuel line, each nozzle comprising a fuel line impedance that is fixedly or variably different from at least one other nozzle fuel line impedance.
According to yet another embodiment, a combustor is configured to minimize combustion emissions at a lower level of combustion dynamics during combustor even fuel-split conditions by varying the fuel impedance through geometrical changes or inert addition in various nozzle groups than that achievable during combustor even fuel-split conditions with a multi-fuel nozzle combustor using nozzles with identical or similar impedance and high dynamics preventing attainment of the same low level of combustion emissions.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
While the above-identified drawing figures set forth alternative embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.
The interaction of various flame groups with one another in a multi-nozzle combustor system is known to be a critical factor in causing/controlling the combustion dynamics of the combustor. Therefore, fuel splitting has been successfully employed to control combustion dynamics. However, at even fuel split the characteristics of the various flame groups are very similar/identical, which inhibits operation to bring the emissions further lower. Since the fuel line impedance characterizes the response of a particular nozzle and plays a very important role in combustion dynamics, changing the fuel line impedance of one or more nozzle group(s) from one or more other nozzle groups can be used to alter the response of various flame groups to minimize emissions such as, without limitation, NOx, while simultaneously changing flame-acoustic interaction and lowering the combustion dynamics amplitude.
With continued reference to
According to particular embodiments, the fuel line impedance for each nozzle group 12, 20, 26 or a particular fuel nozzle 14, 16, 18, 22, 24, 28 can be varied by changing the size of its corresponding pre-orifice 36, corresponding post-orifice 38, fuel nozzle volume, combinations thereof or by addition of inert species in the fuel line of one of the nozzles. For example, the pre-orifice and post-orifice sizes for fuel nozzle group 12 may be different from the pre-orifice and post-orifice sizes for fuel nozzle group 20. In this manner, the fuel line impedance(s) vary from one nozzle group to another changing the behavior of one flame group from the other. Further depending on additional features inside the nozzle fuel flow passage, a change/alteration in those features can also be used to modify the nozzle fuel line impedance.
The differing fuel line impedance(s) among various nozzle groups may be achieved by fixed geometry variations or may be made variable/adjustable according to the requirements of a particular application, so long as the unwanted emissions are minimized and the combustion dynamics are simultaneously reduced during combustor even fuel split (fuel/air ratio) conditions in accordance with the principles described herein. This variation in fuel impedances among various nozzle groups allows most/all nozzles to operate at similar/identical equivalence ratio, which helps achieve the lowest emission for that gas turbine. Further the variable/adjustable impedance variation features can be used as part of an active or passive control strategy.
In summary, utilizing fuel impedance variations to operate a combustor with a multi-nozzle system at even fuel split conditions results in the least desirable highest combustion dynamics and the most desirable lowest emissions. Systems and methods described herein achieve reduced combustion dynamics below that achievable with combustor systems with similar/identical fuel line impedance, and helps attain the lowest emissions during combustor even fuel split conditions, making even fuel split combustor operation possible, a feature that is not achievable using existing combustor structures and techniques.
According to one embodiment, combustor 54 is a multi-fuel line combustor comprising a plurality of nozzle groups, wherein each nozzle group receives fuel from a corresponding fuel line, and further wherein at least one nozzle group fuel line has an impedance that is different from at least one other nozzle group fuel line impedance. According to another embodiment, a fuel powered machine 50 comprises a can or combustor 54, the can or combustor comprising a multi-fuel line manifold, wherein at least one fuel line has an impedance that is different from at least one other fuel line.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
