The present invention relates to can combustors. In particular, the present invention relates to gaseous fuel-fired, impingement cooled, dry low emission can combustors for gas turbine engines.
Gas turbine combustion systems utilizing can type combustors are often prone to air flow mal-distribution. The problems caused by such anomalies are of particular concern in the development of low NOx systems. The achievement of low levels of oxides of nitrogen in combustors is closely related to flame temperature and its variation through the early parts of the reaction zone. Flame temperature is a function of the effective fuel-air ratio in the reaction zone which depends on the applied fuel-air ratio and the degree of mixing achieved before the flame front. These factors are obviously influenced by the local application of fuel and associated air and the effectiveness of mixing. Uniform application of fuel typically is under control in well designed injection systems but the local variation of air flow is often not, unless special consideration is given to correct mal-distribution.
The achievement of current levels of oxides of nitrogen set by regulations in some areas of the world calls for effective fuel-air ratio to be controlled to low standard deviations on the order of 10%. The cost of development of such combustion systems is high but can be significantly influenced by the right choice of configuration. However, the use of film cooling in these low flame temperature combustors generates high levels of carbon monoxide emissions. External impingement cooling of the flame tube (liner) can curtail such high levels. Moreover, in systems where high exit temperature is a performance requirement in addition to low NOx, the air flow to swirler/reaction zone is a large proportion of total air flow and therefore cooling and dilution air flows are limited. Hence there is considerable advantage in controlling these flows to optimize the overall flow conditions.
One such recent combustor design is that shown in U.S. Pat. No. 7,167,684 to Norster, assigned to the assignee of the present invention, the disclosure of which is hereby incorporated by reference. In the subject Norster combustor, essentially all the air flow for combustion is first separated from the dilution air stream and used for impingement cooling the portion of a combustor liner defining the combustion zone, and then channeled to swirl vanes for mixing with fuel. While the features of the Norster combustor may provide better control of the amount of air delivered to the swirl vanes, and thus the bulk fuel/air ratio, compared to previous impingement cooled combustors, further improvements in the aerodynamics of the combustion air flow to the swirl vanes may minimize local deviations in the fuel/air ratio. Improvements are also possible in the control of other cooling air flows in the combustor, which affect the level of emissions and the thermal efficiency of the combustor. Such improvements are set forth hereinafter.
In one aspect of the present invention, a gaseous fuel-fired can combustor for use with a gas turbine, for example in a gas turbine engine, includes a generally cylindrical housing having an interior, an axis, and a closed axial end. A generally cylindrical combustor liner is disposed coaxially within the housing interior and is configured to define with the housing a radial outer flow passage for combustion air. The liner also defines respective radially inner volumes for a combustion zone and a dilution zone, the dilution zone being axially distant the closed housing end relative to the combustion zone, and the combustion zone being axially adjacent the closed housing end. Mixing apparatus is disposed at the closed housing end and in flow communication with the combustion air passage. The mixing apparatus includes a plurality of vanes for mixing the gaseous fuel to be combusted with at least a part of the combustion air, and a mixing apparatus outlet for admitting the resulting fuel/air mixture to the combustion zone. An impingement cooling sleeve is coaxially disposed in the combustion air passage between the housing and the liner, the sleeve having a plurality of apertures sized and distributed to direct the combustion air against a radially outer surface of a portion of the liner defining the combustion zone, for impingement cooling the liner portion. Channeling apparatus is disposed in the combustion air passage for channeling the combustion air from an impingement cooling sleeve exit region to the inlet of the mixing apparatus. The channeling apparatus is configured to prevent flow separation and includes a diffuser section with an inlet flow area and an outlet flow area, wherein a ratio of the outlet flow area to the inlet flow area is in the range 1.3-1.5.
In another aspect of the present invention, the gaseous fuel can combustor for a gas turbine includes a generally cylindrical outer housing having an interior, an axis, and a closed end. A generally cylindrical combustor liner is disposed coaxially within the housing interior and is configured to define with the housing a radially outer flow passage for combustion air, with the liner having an interior defining a radially inner volume for a combustion zone proximate the housing closed end. Mixing apparatus including a plurality of swirl vanes is disposed at the housing closed end. The mixing apparatus has an inlet in flow communication with the combustion air flow passage and an axially directed outlet in flow communication with the combustion zone. The swirl vanes are arranged circumferentially spaced apart about the housing axis in a plane generally perpendicular to the axis. A gaseous fuel supply system is operatively connected to deliver gaseous fuel to the mixing apparatus in the vicinity of the swirl vanes for mixing with combustion air received from the combustion air flow passage. Adjacent ones of the circumferentially spaced apart vanes partly define generally radially inwardly directed mixing flow passages, wherein each the mixing flow passages has a substantially constant cross-sectional flow area and an increasing aspect ratio along a flow direction between the swirl vanes.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention.
The can combustor of the present invention, generally designated by the numeral 10 in the figures, is intended for use in combusting gaseous fuel with compressed air from compressor 6, and delivering combustion gases to gas turbine 8, e.g., for work-producing expansion such as in a gas turbine engine. See
In accordance with the present invention, as embodied and broadly described herein, the can combustor may include a generally cylindrical housing having an interior, an axis, and a closed axial end. As embodied herein, and with reference to
In accordance with the present invention, the combustor also includes a generally cylindrical combustor liner disposed coaxially within the housing and configured to define with the housing respective radial outer passage for combustion air. The liner also defines respective radially inner volumes for a combustion zone and a dilution zone. The dilution zone is axially distant the closed housing end relative to the combustion zone, and the combustion zone is axially adjacent the closed housing end.
As embodied herein, and with continued reference to
The interior of liner 20 also defines combustion zone 32 axially adjacent closed end 18, where the swirling combustion air and fuel mixture is combusted to produce hot combustion gases. In conjunction with mixing apparatus 40 at closed end 18 (to be discussed hereinafter) liner portion 20a is configured to provide stable recirculation in region 34 of combustion zone 32, in a manner known to those skilled in the art. The interior of liner 20 further defines dilution zone 36 where combustion gases are mixed with dilution air from dilution ports 30 to lower the temperature of the combustion gases, before work-producing expansion in turbine 8.
Also, in accordance with the present invention, the combustor includes apparatus having a plurality of vanes for mixing at least a part of the combustion air with gaseous fuel, the mixing apparatus having an outlet for admitting the resulting fuel/air mixture to the combustion zone. As embodied herein, and with continued attention to
With reference now to
Further, and as best seen in
Table 1 presents a particularly preferred set of design parameter ranges for the profile and orientation of vanes 44, in relation to the depiction in
Still further in accordance with the present invention, as embodied and broadly described herein, the can combustor may further include an impingement cooling sleeve coaxially disposed between the housing and the combustion liner and extending axially from the closed housing end for a substantial length of the combustion zone. The impingement cooling sleeve may have a plurality of apertures sized and distributed to direct combustion air against the radially outer surface of the portion of the combustor liner defining the combustion zone, for impingement cooling.
As embodied herein, and with reference to
Significantly, in the embodiment depicted in
Still further in accordance with the invention, as embodied and broadly described herein, the can combustor includes apparatus for channeling the combustion air from an exit region downstream of the impingement cooling sleeve to an inlet of the mixing apparatus. The channeling apparatus is configured to prevent flow separation and includes a diffuser section with an inlet flow area and an outlet flow area, with the ratio of the outlet flow area to the inlet flow area being in the range 1.3-1.5 or greater.
As embodied herein, and with reference to
It may specifically be preferred to use a radius of curvature r that satisfies the following relations:
where H1 is the height of vane 44 at trailing edge 70, and R1, is the radial distance from axis 16 to inner surface 96 of housing 18 at the beginning of guide section 94 (location B). See
Returning to diffuser section 92, diffuser flow area 98 in the depicted embodiment is the space between the conical inside surface 100 of housing 14 between locations “A” and “B”, and the conical outside surface 104 of wall 114 of toroidal spacer member 102. These two conical surfaces are sized and configured to provide a continuously increasing annular diffuser flow area from the diffuser section inlet (location “A”) to diffuser section outlet (location “B”) to provide an expansion ratio of the outlet flow area to the inlet flow area in the range of 1.3-1.5, via a smooth, continuous expansion. The consequent lowering of the average velocity may provide a more optimum velocity ratio between the combustion air entering mixing apparatus 40 and the fuel injected from nozzles 50, thus providing more uniform mixing.
One skilled in the art would understand from the above that the configuration of the surfaces defining diffuser section 92 need not both be conical to provide the desired expansion ratio. That is, wall 114 with outer surface 104 of toroidal spacer member 102 could be cylindrical while inner surface 100 of diffuser section 42 of housing 14 could be conical, or vice versa. While each of these alternatives may result in a more radially compact combustor, each would increase the severity of hydraulic losses in guide section 94 due to the sharper turn (smaller radius of curvature) proximate mixing apparatus inlet 46, and hence may not be preferred. In the
It may also be preferred that a small fraction (˜14%) of the combustion air from the diffuser section 92 be used to cool the “head” end of liner 20, namely, liner part 20a surrounding portion 34 of the combustion zone, where the recirculated combustion gases can create high heat loading. In the
Still further and as best seen in
It may be further preferred to use another small fraction (˜1%) of the combustion air to prevent flow separation at the diffuser inlet A. As best seen in
As a consequence of the features of the can combustor described above, and in addition to the advantage of the more uniform air flow to the swirl vanes discussed previously, the can combustor may provide more uniform pre-mixing in the swirl vanes and, consequently, a higher effective fuel-air ratio for a given NOx and CO requirement. Also, the above-described can combustor may provide a higher margin of stable burning, in terms of providing a more stable recirculation pattern and may also minimize temperature deviations (“spread”) in the combustion products delivered to the turbine. Finally, the can combustor disclosed above may also maximize the effectiveness of the cooling air and provide optimum liner wall metal temperatures.
It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed impingement cooled can combustor, without departing from the teachings contained herein. Although embodiments will be apparent to those skilled in the art from consideration of this specification and practice of the disclosed apparatus, it is intended that the specification and examples be considered as exemplary only, with the true scope being indicated by the following claims and their equivalents.