Patent Publication Number: US-8528334-B2

Title: Flow conditioner for fuel injector for combustor and method for low-NOx combustor

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     This invention was made in part with the U.S. Government support under Contract DE-FC26-05NT42647 awarded by the Department of Energy to Precision Combustion Incorporated. The Government may have certain rights in this invention. 
    
    
     TECHNICAL FIELD 
     This patent disclosure relates generally to combustors and burners, and, more particularly to catalytic pilots for low emission gas turbine fuel injectors for use in combustors or burners. 
     BACKGROUND 
     Combustion is a major source of a class of pollutants including oxides of nitrogen, or NO x , (NO or nitric oxide, and NO 2  or nitrogen dioxide), which may contribute to acid rain, smog, and ozone depletion. NO x  emissions from combustion sources primarily consist of nitric oxide produced during combustion. When utilizing gaseous fuels, combustion processes that decrease the combustion temperature can greatly reduce the production of NO, and, accordingly, can have a significant effect on the overall production of NO x . 
     Various attempts have been made to re-engineer conventional non-premixed combustion systems to reduce emissions of oxides of nitrogen (NO x ). Flames in non-premixed combustion, that is, the combustion process wherein fuel and oxidizer (typically air) mix and burn concurrently, generally emit unacceptable levels of NO x , for example, over 200 parts-per-million (ppm), substantially higher than regulations allow for certain applications. The heating and power generation industries have recognized the need to develop cleaner, premixed combustion systems in which gaseous fuel and oxidizer (typically air) mix prior to burning. 
     The technical paper, Advanced Catalytic Pilot for Low NO x  Industrial Gas Turbines, by Karim, et al., Published by the Proceedings of ASME TURBO EXPO 2002, Jun. 3-6, 2002, Amsterdam, The Netherlands, GT-2002-30083, discloses a catalytic pilot for use in a gas turbine combustor. A catalytic pilot incorporates catalyst-coated tubes to convert part of the fuel gas into combustion products on the surfaces of the tubes. The remainder of the pilot fuel gas and oxidant gas exits the pilot and mixes with fuel gas and oxidant gas from a main swirler to complete the combustion process downstream of the injector. In contrast to traditional pilot injectors, a catalytic pilot allows the operation of the pilot at leaner equivalence ratios. As a result, the inclusion of a catalytic pilot, as opposed to a more traditional pilot injector, provides a reduction in overall NO x  levels. Additionally, the presence of a catalyst in the pilot may allow operation of the injector at overall leaner fuel-air ratios, resulting in lower flame temperatures, without combustion driven pressure oscillations. 
     Accordingly, there exists a need for alternative designs for fuel injectors that address the shortcomings of existing systems and/or that provide reduced NO x  emissions. Such designs would be particularly advantageous if they were relatively simple and economical to scale, manufacture and operate. 
     BRIEF SUMMARY OF THE INVENTION 
     The disclosure describes, in one aspect, an injector for a gas turbine combustor. The injector includes an inner wall, at least one catalyst coated surface disposed within the inner wall and forming at least one passage adapted to provide a feed gas flow through the injector, and at least one channel disposed within the inner wall and adapted for passage of an oxidant gas flow through the injector. At least one of the feed gas flow or the oxidant gas flow establishes an axial gas flow through the inner wall and to the combustor. The injector further includes a flow conditioner disposed within the axial gas flow. The flow conditioner includes an elongated body having a length, an upstream end, a downstream end, an exterior surface at least partially disposed within the inner wall, and an interior passage for passage of the axial gas flow. The interior passage extends along the length of the flow conditioner, opening into the upstream and downstream ends and including an interior diameter. The interior diameter of the flow conditioner substantially smoothly reduces and then increases from the upstream end to the downstream end. 
     The disclosure further describes an injector for a gas turbine combustor wherein the injector comprises an inner wall, at least one catalyst coated surface disposed within the inner wall and forming at least one passage adapted to provide a feed gas flow through the injector, and at least one channel disposed within the inner wall and adapted for passage of an oxidant gas flow through the injector. At least one of the feed gas flow or the oxidant gas flow establishes an axial gas flow through the inner wall and to the combustor. The injector further includes a flow conditioner disposed within the axial gas flow. The flow conditioner includes an elongated body having a length, an upstream end, a downstream end, and an exterior surface along the length. At least a portion of the exterior surface is spaced away from and disposed within the inner wall, the exterior surface of the flow conditioner and the inner wall of the injector defining at least one substantially longitudinally extending channel for passage of the axial gas flow. The flow conditioner further includes an interior passage for passage of the axial gas flow. The interior passage extends along the length, and opens into the upstream and downstream ends and includes an interior diameter. The interior diameter substantially smoothly reduces and then increases from the upstream end to the downstream end. 
     Also disclosed is a method of conditioning gas flow through an injector assembly by establishing a flow of a feed gas through at least one pilot passage including at least one catalyst coated surface into a mix zone, establishing a flow of oxidant gas through at least one pilot channel into the mix zone, and establishing a flow of feed and oxidant gases from the mix zone through a flow conditioner. Establishing the flow of feed and oxidant gases from the mix zone through the flow conditioner includes establishing a flow of feed and oxidant gases from the mix zone through a plurality of vane channels formed between a plurality of substantially longitudinally extending vanes in an exterior surface of a flow conditioner, and establishing an axial flow of feed and oxidant gases from the mix zone through an interior passage along a length of the flow conditioner wherein the axial gas flow through the interior passage increases in velocity as an interior diameter of the interior passage substantially smoothly reduces, and the axial gas flow then decreases in velocity as the interior diameter substantially smoothly increases and then opens into a flame zone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an embodiment of an injector assembly according to the disclosure. 
         FIG. 2  is an enlarged, fragmentary, cross-sectional view of the catalytic pilot of  FIG. 1  including the flow conditioner. 
         FIG. 3  is an enlarged, isometric view of the catalytic pilot of  FIG. 2  without the flow conditioner. 
         FIG. 4  is an end view of the catalytic pilot of  FIG. 3 . 
         FIG. 5  is an isometric view of the flow conditioner of  FIG. 2 . 
         FIG. 6  is a side elevational view of the flow conditioner of  FIG. 5 . 
         FIG. 7  is a cross-sectional view of the flow conditioner of  FIGS. 5 and 6  taken along line  7 - 7  in  FIG. 6 . 
         FIG. 8  is a partially cross-sectioned side view of a test rig incorporating an exemplary combustor including the injector assembly of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings, there is shown a cross-section of a fuel injector assembly  10  including a main injector  12  and a catalytic pilot  14  including a flow conditioner  16 . 
     More specifically, in the illustrated embodiment, the injector  12  includes a housing  18  that forms at least one gas flow channel  20 , or main swirl injector, having at least one upstream opening  22  and a downstream outlet  24  to a flame zone  26 . The injector  12  itself may be of any appropriate design, including, for example, angled vanes to impart a swirl to the gasses flowing therethrough. The illustrated embodiment is adapted to utilize fuel gas or liquid fuel. In this regard, the housing  18  supports a plurality of nozzles  28  through which a liquid fuel may be provided. Alternately, fuel gas may be provided to the interior of the injector  12  by way of a supply line  27 , which provides fuel to a circumferentially disposed plenum  29 . The plenum  29  is fluidly connected to a plurality of radially disposed fuel supply spokes  30 , which include a plurality of orifices  31 . In this way, a flow of feed gas is provided from the supply line  27 , through the plenum  29 , spokes  30 , and orifices  31  to the interior of the injector  12 . A flow of oxidant gas is provided through the upstream opening  22  into the gas flow channel  20  where it is mixed with a flow of feed gas provided through the orifices  31  or the liquid fuel provided through the nozzles  28  before reaching the flame zone  26 . 
     In the illustrated embodiment, the housing  18  further surrounds the catalytic pilot  14 . The catalytic pilot  14  includes an annular pilot housing  32  having an upstream oxidant inlet  34 , and a downstream outlet  36  through a gas flow channel  38 . Although any appropriate design may be provided, in the illustrated embodiment, a plurality of longitudinally extending tubes  40 , the exterior surfaces of which are catalyst coated, are disposed within the gas flow channel  38  to receive a flow of oxidant gas, typically air, from the upstream inlet  34  and to supply the same to a mix zone  42  downstream. 
     To supply a feed gas to the catalytic pilot  14 , a plenum  44 , here, an annular plenum, is provided, which fluidly connects a feed gas supply passage  46  in a supply line  48  with longitudinally extending passages  50  surrounding the catalyst-coated tubes  40  in the interior of the catalytic pilot  14 . Flow of fuel gas into the supply line  48  is provided through a fitting  51 , which includes a plurality of openings  52  into supply passage  46 . Oxidant gas is further provided to the supply passage  46  by way of a plurality of openings  53  into the supply line  48 . In this way, the fuel and oxidant gases mix within the supply passage  46  to yield the feed gas that flows to the plenum  44  by way of at least one opening  54 . The feed gas within the plenum  44  flows on to the longitudinally extending passages  50  by way of at least one opening  55  in the interior of the catalytic pilot  14 . Thus, the feed gas supply passage  46 , the opening  54 , the annular plenum  44 , the plurality of openings  55 , and the longitudinally extending passages  50  surrounding the tubes  40  in the interior of the catalytic pilot  14  together form a plurality of passages that supply feed gas to the mix zone  42  in the interior of the catalytic pilot  14  before flowing to the flame zone  26 . 
     As the fuel gas flows along the catalyst-coated tubes, a portion of the fuel gas is converted into combustion products on the exterior surface of the tubes before reaching the mix zone  42  where it is combined with the oxidant gas flowing through the tubes  40 . In the illustrated embodiment, the internal diameter of the mix zone  42  generally narrows, and then extends at a constant diameter before opening into the flame zone  26 . 
     The arrangement of the catalytic pilot  14  is provided by way of example, however, and alternate arrangements are within the purview of the disclosure. By way of example only, although a pilot housing  32  of a generally circular cross-section is illustrated, the housing may have an alternate design or cross-section, such as an oval or octagonal cross-section. By way of further example, although a fuel gas is supplied to the supply passage  46  where it is mixed with oxidant gas supplied through the supply line  48 , a premix of feed gas may be provided. 
     Gas flow through and from the pilot  14  is at least partially controlled by a flow conditioner  16  disposed downstream within the channel  38 , as illustrated in  FIGS. 1 and 2 . As may be best seen in  FIGS. 5-7 , the flow conditioner  16  includes an elongated body  60  from which at least one vane  62  extends outwardly therefrom. In the illustrated embodiment, the elongated body  60  acts as a hub from which a plurality of vanes  62  extend. The radially outermost surfaces of the vanes  62  generally conform to the inner surface of the downstream end of the pilot housing  32  such that a plurality of elongated flow channels  64  are formed between the vanes  62 , the pilot housing  32 , and the elongated body  60 . Alternate structures are envisioned to provide the elongated channels  64 , however. In an alternate embodiment, for example, the vanes may be disposed to generally conform to a surface  66  (see  FIG. 1 ) of an inner wall  67  of the injector housing  18 , such that the channels are formed between the vanes  62  and the elongated body  60  of the flow conditioner  16 , and the surface  66  of the injector housing  18 . In order to impart an angular momentum or swirl to the gas flow exiting the flow channels  64 , the vanes  62  are disposed in a generally spiral arrangement about the body  60 . In this way, the flow through the elongated channels  64  allows the pilot flow to expand and mix with the flow from the injector channel  20 . 
     Any appropriate number of vanes  62  may be provided, and the vanes  62  may have any appropriate structure and be disposed at any appropriate angle, so long as the vanes impart the desired angular momentum to the gas as it flows from the flow conditioner  16 . In the embodiment illustrated in  FIGS. 5-7 , ten axial curved vanes  62  are disposed at a vane angle on the order of 10° to 25°, here, 15°. 
     A further flow of gas from the pilot  14  is provided through an interior passage  68  extending axially through the elongated body  60  of the flow conditioner  16 . The interior passage  68  has an interior diameter and a length extending from an upstream end  70  to a downstream end  72 . The diameter of the interior passage  68  generally decreases, and then increases along the length from to the upstream end  70  to the downstream end  72 . In this way, the geometry of the interior passage  68  allows relatively high flow velocities at the core of the flow conditioner  16 , and inhibits flame from the flame zone  26  from flashing back into the pilot  16 , while the reduced flow velocity at the downstream end  72 , where the flow expands, inhibits blow off in transient conditions. 
     The flow conditioner  16  may be constructed from metal, ceramic, or other rigid materials capable of withstanding the conditions. 
     The fuel gas may be any appropriate gas, such as, for example, natural gas. Likewise, the oxidant gas may be any appropriate gas, such as, for example, air. Further, the feed gas may be in the form of either pure fuel gas, or a mix or premix of fuel gas and oxidant gas. 
     The gas flow may be provided to the pilot  14  by any appropriate arrangement. For example, a oxidant gas or premix of fuel gas and oxidant gas may be provided to the upstream inlet  34  to the pilot housing  32  and/or to the inlet  22  to the housing  18 . Alternately, separate fuel gas and oxidant gas may be provided to the housings  18 ,  32 , or a combination of the same. In an embodiment, oxidant gas, typically air, is supplied to the housings  18 ,  32  through upstream openings  22 ,  34 . Fuel gas may be introduced at any appropriate opening or location to mix with the oxidant gas, so long as adequate residence time is provided within the injector  12  and pilot  15  for efficient and effective oxidant gas/fuel gas mixing. Fuel gas may be provided through one or more passages or the like into the housings  18 ,  32 . 
     INDUSTRIAL APPLICABILITY 
     An injector assembly  10  according to the disclosure may be utilized to achieve ultra-low NO x  emissions in, for example, an industrial gas turbine. The injector assembly  10  may provide the advantages of an assembly including a catalytic pilot  14 , while the flow conditioner  16  may yield a stable, compact pilot flame. The fuel injector assembly  12  including the catalytic pilot  14  and flow conditioner  16  may additionally provide acceptable radial profile and pattern factor at the inlet to the turbine. 
     Embodiments of the flow conditioner  16  for use in the assembly  10  may additionally inhibit or prevent flashback of the flame into the pilot  14  module. Embodiments of the flow conditioner  16  for use in the assembly  10  may additionally provide low pressure loss across the conditioner  16 . In some embodiments, either or both of the catalytic pilot and the flow conditioner  16  may be provided as modules that may be readily replaced and/or serviced as necessary. Additionally, the flow conditioner  16  may be efficiently and economically manufactured and readily assembled into the injector assembly  10 . 
     Turning to  FIG. 8 , a test rig incorporating the disclosed fuel injector assembly  10  within a combustor  80  is illustrated. The fuel injector assembly  10  is disposed within a combustor housing  82  to which oxidant or air flow may be provided through an air inlet  84 . In turn, exhaust gas may be expelled to outlet  86 . In use, the gas flow exiting the main injector  12  and the catalytic pilot injector  14  interact at the flame zone  26 . Upon ignition, a flame may be stabilized just downstream of the injector exit plane at the downstream outlet  24 ,  36 . 
     The velocities of unburnt fuel gas and oxidant gas exiting a catalytic pilot injector not including flow conditioner  16  can be relatively high, which can result in a long and/or unstable flame. Gas flow through the interior passage  68  of the flow conditioner  16  of the catalytic pilot injector  14  of the disclosure, however, increases in velocity as the interior diameter of the interior passage  68  decreases, and then the velocity decreases as the interior diameter of the interior passage  68  increases before the flow enters the flame zone  26 . Thus, in use, the flow conditioner  16  may inhibit or prevent the flame from flashing back into the catalytic pilot injector  14 , while inhibiting blow-off during transient periods. 
     It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the invention or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the invention more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the invention entirely unless otherwise indicated. 
     Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. 
     Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.