Patent Application
20110225974
The subject matter disclosed herein generally relates to turbomachines. More specifically, the subject disclosure relates to fuel and air passages through fuel nozzles for turbomachines.
As requirements for gas turbine emissions have become more stringent, one approach to meeting such requirements is to move from diffusion flame combustors to combustors utilizing lean fuel and air mixtures using a fully premixed operation mode to reduce emissions of, for example, NOx and CO. These combustors are known in the art as Dry Low NOx (DLN), Dry Low Emissions (DLE) or Lean Pre Mixed (LPM) combustion systems. These combustors typically include a plurality of primary nozzles which are ignited for low load and mid load operations of the combustor in a primary combustion zone. During fully premixed operations, the primary nozzles supply fuel to feed the secondary flame. The primary nozzles typically surround a secondary nozzle that is utilized for mid load up to fully premixed mode operations of the combustor, feeding a secondary combustion zone. An outer swirler is typically located surrounding the secondary nozzle between the primary and secondary combustion zones. The outer swirler includes a plurality of swirler passages through which air is injected into the secondary combustion zone. The swirler air creates a zone of lower fuel-to-air ratio between the primary and secondary combustion zones, and acts to quench the primary and secondary flames. This quenching results in combustion instabilities, higher emissions and lower turndown margins.
According to one aspect of the invention, a combustor for a turbomachine includes a plurality of primary fuel nozzles located in a combustor liner and a secondary fuel nozzle located in the combustor liner such that the plurality of primary fuel nozzles are arrayed about the secondary fuel nozzle. An outer swirler is positioned circumferentially around the secondary fuel nozzle between the secondary fuel nozzle and the plurality of primary fuel nozzles and includes a plurality of outer swirler channels for delivering fuel and/or air into an interior of the combustor.
According to another aspect of the invention, a method of operating a combustor includes delivering a primary fuel flow through a plurality of primary fuel nozzles toward a primary combustion zone and combusting the primary fuel flow in one or more of the primary combustion zone or a secondary combustion zone. A secondary fuel flow is delivered through a secondary fuel nozzle toward the secondary combustion zone and combusted therein. The secondary fuel nozzle is located such that the plurality of primary fuel nozzles are arrayed around the secondary fuel nozzle. An outer swirler is located between the plurality of primary fuel nozzles and the secondary fuel nozzle and includes a plurality of outer swirler channels extending therethrough. A flow of swirler fuel and/or air is delivered through the plurality of outer swirler channels into the combustor substantially between the primary combustion zone and the secondary combustion zone to stabilize combustion in the primary combustion zone and/or the secondary combustion zone.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
a-4d are schematic views of operational modes of an embodiment of a combustor.
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
Shown in
Shown in
Referring to
Surrounding the secondary fuel nozzle 32 is an outer swirler 40. Referring again to
The plurality of swirler channels 42 are connected to a fuel source 50, and in some embodiments, a passively fed air source 52. During operation of the combustor 14, a flow of swirler fuel 54 and a flow of air 56 is flowed from the fuel source 50 and the air source 52 and premixed in the plurality of swirler channels 42 before it is injected into the combustion chamber 36. In some embodiments, the flow of swirler fuel 54 and the flow of air 56 are injected in a directly axial direction into the combustion chamber 36, while in other embodiments, the plurality of swirler channels 42 are configured, for example, helically, such that the flow of swirler fuel 54 and the flow of air 56 are injected at an angle non-parallel to a combustor axis 58.
In effect, the flow of swirler fuel 54 and the flow of air 56 injected into the combustion chamber 36 via the plurality of swirler holes 44 acts as a premixed pilot to stabilize combustion in both the primary combustion zone 34 and the secondary combustion zone 38. For example, when the combustor 14 is operating in lean mode, there are combustion flames in both the primary combustion zone 34 and the secondary combustion zone 38. The presence of the flow of swirler fuel 54 and flow of air 56 injected into the combustion chamber 36 between the primary combustion zone 34 and the secondary combustion zone 38 increases the uniformity of fuel/air ratios between the primary combustion zone 34 and the secondary combustion zone 38, thus enhancing stability in both combustion zones 34/38.
To increase flexibility of the combustor 14, the flow of swirler fuel 54 may be linked to the a primary flow of fuel to the plurality of primary fuel nozzles 30 such that whenever fuel is supplied to the plurality of primary fuel nozzles 30, fuel is also supplied to the plurality of swirler channels 42. In some embodiments, the flow of swirler fuel 54 may be alternatively linked to a secondary flow of fuel to the secondary fuel nozzle 32 such that when fuel is supplied to the secondary fuel nozzle 32, fuel is also supplied to the plurality of swirler channels 42. Alternatively, the supply of fuel to the plurality of swirler channels 42 may be linked to a pilot circuit, independent of the primary fuel flow and the secondary fuel flow.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
