TECHNICAL FIELD

[0001] The invention relates to apparatus and methods for normalizing exhaust gas flow in exhaust systems for gas turbine engines. More particularly, the invention relates to flow normalization in exhaust systems for gas turbine engines, by incorporation of one or more flow control inserts within their volute passages.

BACKGROUND

[0002] Gas turbine engines are used to generate power for driving loads, such as generators and compressors. The engines convert thermal energy released during combustion to mechanical power, as combustion gas flows past shaft-mounted turbine blades. After spinning the turbine blades, the energy depleted combustion gas leaves the turbine section as exhaust gas via an exhaust outlet of the engine. An exhaust system transports the exhaust gas away from the turbine engine installation to an exhaust conduit, such as a chimney. Ideally, the exhaust system does not modify the flow velocity of exhaust gas departing the engine’s exhaust outlet, allowing the exhaust gas to expand gradually to ambient pressure and temperature, with uniform, cross-sectional flow velocity, and low backpressure.

[0003] Many gas-turbine engine installations cannot accommodate idealized exhaust system designs, due to existing equipment spatial limitations, and/or need to route exhaust gas into existing balance-of-plant (BoP) exhaust conduits. For example, a gas turbine engine driving a compressor or generator load, via a drive shaft, cannot accommodate an idealized exhaust system, due to limitations on engine to load shaft length. In such exhaust systems, an exhaust hood turns the exhaust-gas flow path perpendicular to the central axis of the engine shaft and the exhaust system’s annular diffuser. The rapid, sharp turn in the exhaust flow path from the exhaust annular diffuser to the exhaust hood imparts variations in exhaust flow velocity, direction, and speed, about the diffuser’s exit. In some exhaust systems, a circumferential volute is interposed between the annular diffuser exit and the exhaust hood, in order to achieve a more gradual change in exhaust gas velocity. BoP exhaust conduits have different backpressure properties downstream of the turbine exhaust that is influenced by aerodynamic properties of the conduits or downstream heat recovery systems. Backpressure variations in a plant also influence engine performance.

[0004] Past attempts to normalize variations in exhaust gas-flow velocity within exhaust systems have focused on placement of flow-control vanes between or intermediate the engine exhaust outlet and the entrance of the annular diffuser of the exhaust system. Intermediate located, flow-control vanes have not significantly improved exhaust gas flow uniformity exiting the exhaust hood to the BoP exhaust conduits.

SUMMARY

[0005] In exemplary embodiments described herein, exhaust gas flow within a turbine engine exhaust is normalized by incorporation of flow control inserts within the volute passage, between the exhaust diffuser and the exhaust hood. The flow control inserts alter localized variations in exhaust gas flow within the volute and/or exhaust hood passages of the exhaust system. Exemplary localized variations in exhaust gas flow are caused by swirling or counter-swirling exhaust-flow variations imparted by turbine blades within the turbine section of the engine. Other localized variations in exhaust gas flow are caused by backpressure restrictions in the balance-of-plant (BoP), exhaust conduit system, including downstream heat recovery systems. Exemplary exhaust flow variations that are remedied by placement of flow control inserts include normalization of swirling or counter-swirling flows about the circumference of the exhaust volute within the volute passage and in the transitional flow from the volute into the exhaust hood. Modular flow-control inserts enable localized exhaust flow normalization in existing exhaust system configurations, during initial fabrication or during subsequent maintenance. The modular flow-control inserts facilitate localized flow control normalization, for different engine and engine installation configurations.

[0006] Exemplary embodiments of the invention feature an exhaust system for a gas turbine engine. The exhaust system has an annular diffuser, having: a central axis; an entrance; an exit radially outwardly directed relative to the central axis; inner and outer diffuser walls. A diffuser passage is formed between the inner and outer diffuser walls, which defines a first flow path for passage of exhaust gas there through. The exhaust system includes a volute circumscribing the outer diffuser wall and the exit of the annular diffuser. A volute passage is formed between the outer diffuser wall and the volute, which defines a second flow path for passage of exhaust gas therein that is in fluid communication with the first flow path. A flow control insert is interposed in fixed orientation within the volute passage, for selectively altering the second flow path and flow velocity of exhaust gas therein. An exhaust hood is coupled to the volute and extends radially outwardly relative to the diffuser’s central axis; it has an exhaust hood passage, which defines a third flow path, for passage of exhaust gas therein. The second and third flow paths are in communication with each other.

[0007] Other exemplary embodiments of the invention feature an exhaust system for a gas turbine engine installation. The installation includes a gas turbine engine, having an exhaust outlet. An entrance of an annular diffuser is coupled to the exhaust outlet of the gas turbine engine. The annular diffuser also has a central axis; an exit radially outwardly directed relative to the central axis; inner and outer diffuser walls; and a diffuser passage formed between the inner and outer diffuser walls. The diffuser passage defines a first flow path for passage of exhaust gas generated by the gas turbine engine there through. The exhaust system includes a volute, which circumscribes the outer diffuser wall and the exit of the annular diffuser. A volute passage is formed between the outer diffuser wall and the volute; it defines a second flow path for passage of exhaust gas generated by the gas turbine engine therethrough. The first and second flow paths are in fluid communication with each other. A flow control insert is selectively interposed in fixed orientation within the volute passage, for selectively altering within the volute passage the second flow path and flow velocity of exhaust gas generated by the gas turbine engine. An exhaust hood is coupled to the volute; it extends radially outwardly relative to the central axis of the diffuser. The exhaust hood has an exhaust hood passage, which defines a third flow path for passage of exhaust gas generated by the gas turbine engine therethrough. The second and third flow paths are in fluid communication with each other. In some embodiments, while the flow control insert is selectively interposed in fixed orientation within the volute passage, it selectively alters within the volute passage the third flow path and flow velocity of exhaust gas exiting the volute into the third passage.

[0008] Additional exemplary embodiments of the invention feature methods for altering exhaust gas flow in an exhaust system for a gas turbine engine. In practicing one of the exemplary methods, an exhaust outlet of a gas turbine engine is coupled to a diffuser entrance of an exhaust system of the type having an annular diffuser, a volute, and an exhaust hood. More particularly, the annular diffuser has a central axis; the aforementioned entrance; an exit radially outwardly directed relative to the central axis; inner and outer diffuser walls; and a diffuser passage formed between the inner and outer diffuser walls. The diffuser passage defines a first flow path for passage of exhaust gas generated by the gas turbine engine there through. The volute circumscribes the outer diffuser wall and the exit of the annular diffuser. A volute passage is formed between the outer diffuser wall and the volute, which defines a second flow path for passage of exhaust gas generated by the gas turbine engine there through. The first and second flow paths are in fluid communication with each other. The exhaust hood is coupled to the volute and extends radially outwardly relative to the central axis of the diffuser. The exhaust hood has an exhaust hood passage, which defines a third flow path for passage of exhaust gas generated by the gas turbine engine there through. The second and third flow paths in fluid communication with each other. When practicing this exemplary method of exhaust gas-flow alteration, a flow control insert is selectively interposed in fixed orientation within the volute passage. This selective insert placement alters the second flow path and flow velocity of exhaust gas generated by the gas turbine engine within the volute passage. Flow control insert placement is determined by observing generated exhaust gas flow velocity within the second and/or third flow paths. During observation, one or more localized variations in exhaust gas-flow velocity within the second and/or third flow paths that deviate from desired gas flow velocity therein are identified. At least one flow control insert is placed in fixed orientation within the volute passage, at a location that alters at least one of the one or more identified deviations from desired gas flow velocity. In some embodiments, the gas-flow velocity deviation is a swirling or counter-swirling pattern in the second or third flow paths.

[0009] The respective features of the exemplary embodiments of the invention that are described herein may be applied jointly or severally in any combination or sub combination.

BRIEF DESCRIPTION OF DRAWINGS

[0010] The exemplary embodiments of the invention are further described in the following detailed description in conjunction with the accompanying drawings, in which:

[0011] FIG. 1 is an elevational view, in partial axial cross section, of a gas turbine engine installation that includes an exhaust system, in accordance with an embodiment disclosed herein;

[0012] FIG. 2 is an elevational view, in radial cross section, of the gas turbine engine installation of FIG. 1, taken along 2-2 thereof;

[0013] FIG. 3 is a schematic elevational view, in radial cross section, showing an embodiment of exhaust system with a circumferentially oriented, plate- or planar baffle- type, flow control insert, in accordance with an embodiment disclosed herein;

[0014] FIG. 4 is a cross sectional view of the exhaust system of FIG. 3, taken along 4-4 thereof; [0015] FIG. 5 is a schematic elevational view, in radial cross section, showing an embodiment of exhaust system with a radially oriented, plate- or planar baffle-type, flow control insert, in accordance with an embodiment disclosed herein;

[0016] FIG. 6 is a cross sectional view of the exhaust system of FIG. 5, taken along 6-6 thereof;

[0017] FIG. 7 is a schematic elevational view, in radial cross section, showing an embodiment of exhaust system with a type of flow control insert that alters a cross section of the second flow path in the volute passage, in accordance with an embodiment disclosed herein;

[0018] FIG. 8 is a cross sectional view of the exhaust system of FIG.7, taken along 8-8 thereof; and

[0019] FIG. 9 is a fragmentary, exploded view, in radial cross section, showing another embodiment of the flow control insert of FIGs. 7 and 8 prior to its affixation to the volute of the exhaust system.

[0020] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale.

DESCRIPTION OF EMBODIMENTS

[0021] Exemplary embodiments of the invention are utilized in exhaust systems for gas turbine engines. Exhaust gas flow within a turbine engine exhaust is normalized by incorporation of flow control inserts within the volute passage of the exhaust system, between the exhaust diffuser and the exhaust hood. The flow control inserts alter localized variations in exhaust gas flow within the volute and/or exhaust hood passages of the exhaust system, such as swirling or counter-swirling exhaust-flow variations imparted by turbine blades within the turbine section of the engine. In some embodiments, modular flow-control inserts enable localized exhaust flow normalization in existing exhaust system configurations, during initial fabrication or during subsequent maintenance. The modular, flow-control inserts facilitate localized flow control normalization, for different engine and engine installation configurations. In some embodiments, multiple types of engine specification and/or installation configurations share a common-design exhaust system, which reduces design, manufacture and inventory costs. Sharing a common-design exhaust system among different engine specifications and installation configurations also reduces service and maintenance costs, as fewer types of replacement components and maintenance procedures are needed in the field.

[0022] FIGs. 1 and 2 show a gas turbine installation 20, with a gas turbine engine 22. The gas turbine engine 22 is of known construction, and includes a compressor section 24, a combustion section 26 for generating hot combustion gas, a turbine section 28 with turbine blades 30 mounted to a rotating engine shaft 32. The shaft 32 drives a load 34, such as a known generator or compressor or pump or other known, powered equipment. The engine 22 is fluidly coupled to an exhaust system 40. The exhaust system 40 includes an annular diffuser 42, for receiving engine exhaust gas E, and an exhaust hood 54 for passage of engine exhaust gas to an exhaust conduit in the balance-of-plant installation. A volute 60 is oriented intermediate the annular diffuser 42 and the exhaust hood 54.

[0023] Exhaust gas E flows from the exhaust outlet 36 of the gas turbine engine 22 to an entrance 44 of the annular diffuser 42. The annular diffuser 42 has a central axis CA, which in this embodiment is coaxial with that of the engine shaft 32. An annular diffuser exit 46 is outwardly directed, radially, relative to the central axis CA. The annular diffuser has radially spaced and opposed inner 48 and outer 50 diffuser walls, which form a diffuser passage 52 between them. In some embodiments, the inner 48 and outer 50 diffuser walls diverge from the entrance 44 to the exit 46. The diffuser passage 52 defines a first flow path for passage of exhaust gas E generated by the gas turbine engine 22 therethrough.

[0024] The exhaust hood 54 has a shaft passage 56 for passage of the engine shaft 32, through the inner diffuser wall 48, sidewalls 57 and 58, and a circumferential wall 59. The exhaust hood 54 incorporates the volute 60. A volute inner wall 62 circumscribes the outer diffuser wall 50 and the exit 46 of the annular diffuser 42. A symmetric cross section, volute passage 64 is defined within, and bounded by a structural surface comprising: the outer diffuser wall 50, the volute inner wall 62, the exhaust hood sidewalls 57, 58, and the exhaust hood circumferential wall 59. In some embodiments, the exhaust hood volute 60 does not include the volute inner wall 62, in which case the volute passage 64 is defined within, and bounded by a structural surface comprising: the outer diffuser wall 50, the exhaust hood sidewalls 57, 58, and the exhaust hood circumferential wall 59. In other embodiments, the volute passage 64 is asymmetrical. The volute passage 64 defines a second flow path for passage of exhaust gas generated by the gas turbine engine therethrough. The first and second flow paths are in fluid communication with each other, so that exhaust gas E leaving the diffuser exit 46 turns from parallel to the diffuser central axis CA to radially outwardly into the toroidal shaped, volute passage 64; exhaust gas then circulates circumferentially within the volute passage/second flow path.

[0025] The exhaust hood 54 is coupled to and in common fluid communication with the volute passage 64 of the volute 60, and the transition 74 and its downstream cylindrical pipe 72 of the balance-of-plant exhaust network by the exhaust hood passage 76. The exhaust hood passage 76 defines a third flow path for passage of exhaust gas E generated by the gas turbine engine 22 therethrough. The second and third flow paths of the respective volute passage 64 and the exhaust hood passage 76 are in fluid communication with each other.

[0026] The transition portion 74 of the exhaust hood 54 extends radially outwardly and vertically relative to the central axis CA of the diffuser 42, in order to conserve floor space around the gas turbine installation 20. In alternative embodiments, shown in phantom lines in FIG. 2, the transition extends radially and laterally left or right.

[0027] Having described the first, second, and third exhaust-gas flow paths in the exhaust system 40, of FIGs. 1 and 2, specific, exemplary flow-control insert embodiments are shown in the respective exhaust system embodiments 140, 240 and 340, of FIGs. 3-9. Each of the exhaust systems 140, 240 and 340 have similar structures of: inner 48 and outer 50 diffuser walls and diffuser passages 52; volute inner walls 62 and volute passages 64; and exhaust hood 54 circumferential walls 59, side walls 57, 58 and exhaust hood passages 76.

[0028] In FIGs. 3-6, the respective flow control inserts are depicted schematically as a circumferentially oriented, planar baffle 80 of exhaust system 140, and a radially oriented, planar baffle 90 of exhaust system 240. The baffles 80 and 90, respectively, are shown schematically as bent and cut, flat metal sheets. In other embodiments, the baffles have varying three-dimensional profiles, such as airfoils or wedges. The circumferentially oriented, planar baffle 80 has an opposed pair of outer faces 82 and baffle edges 84. The baffle 80 is retained in fixed orientation within the volute passage 64 by a plurality of struts 86. In some embodiments, the stmts 86 are affixed to the baffle edges 84 and the sidewalls 57, 58 of the exhaust hood 54. The radially oriented, planar baffle 90 has an opposed pair of outer faces 92. The baffle 90 is retained in fixed orientation within the volute passage 64 by a baffle mounting plate 94 and stmts 98. The baffle mounting plate 94 is affixed to the circumferential wall 59 of the exhaust hood 54 by a peripheral weld bead 96. The struts 98 are affixed to the outer faces 92 of the baffle 90 and the sidewalls 57, 58 of the exhaust hood 54. While the outer faces 92 of the planar baffle 90 is shown in FIGs. 5 and 6 as oriented perpendicular to the central axis of the annular diffuser 42, in other embodiments, the outer faces are oriented parallel to or skewed relative to the diffuser’s central axis.

[0029] Use of struts 86, 98 or welded mounting plates 94, or a combination of both, for affixation of the baffles 80, 90, or other types of flow control inserts is determined, inter alia, by aerodynamic and thermal-mechanical factors. Strut placement can lower aerodynamic efficiency of exhaust gas flow within the volute passage 64. Struts and planar baffles are also susceptible to warpage or thermo-mechanical failure, caused by exposure to hot exhaust gas E. Direct weldment of baffles or other types of flow control inserts to the structural walls forming the volute passage 64, such as the baffle mounting plate 94 of FIG. 6, facilitates higher aerodynamic efficiency, and offers enhanced thermo mechanical stress distribution over struts alone. In some flow-control insert mounting applications, combinations of welded mounting plates and struts provide better aerodynamic efficiency and thermo-mechanical outcomes than either type of mounting structure alone.

[0030] In FIGs. 7-9 the flow control insert embodiments 100, 120 selectively restrict local cross section of the second flow path within the volute passage 64. These local flow path restrictions selectively alter exhaust gas velocity direction and/or speed. The flow control insert 100 has an outer face 102 that projects into the volute passage 64. The flow control insert 100 has a peripheral edge 104 that is affixed, by a peripheral weld bead 106, to some of the surfaces of the exhaust system that define the volute passage 64: namely the side walls 57, 58 and circumferential wall 59 of the exhaust hood 54..In alternative embodiments the insert 100 is affixed to the volute inner wall 62, alone or in combination with any of the other surfaces that define the volute passage 64. The outer face 102 insert 100 has a three-dimensional profile, with convex 108 and concave 110 surface features, for selective alteration of gas flow velocity in the volute passage 64. As shown in the exploded view of FIG. 9, the flow control insert 120 comprises a three dimensional insert, such as a metal casting, having integrally formed convex 124 and concave 126 surface features. In the embodiment of FIGs. 7 and 8, the flow control insert 100 alters exhaust gas flow velocity by changing the throat depth between its outer face 102 and the opposing volute inner wall 62 at different circumferential locations 130, 132, 134. For example, if it is desired to increase speed of exhaust gas flow in the volute passage 64 in the region 132, in order to normalize it with the gas flow speed at other circumferential locations within the volute passage, the throat depth is decreased, by orienting the outer surface 102 of the insert 100 toward the volute inner wall 62. [0031] Selective orientation of one or more flow control inserts, such as the insert embodiments 80, 90, 100, 120 of FIGs. 3-9, in the volute passage 64 alters velocity (direction and/or speed) of exhaust gas E within the second flow path of the volute 60. In some embodiments, such selective insert placement alters velocity of exhaust gas in the third flow path of the exhaust hood 54. In other embodiments, such selective insert placement alters velocity of exhaust gas as it turns radially outwardly from the second to the third flow path. In some embodiments, selective insert placement alters velocity of exhaust gas in any one or more of the second, third or transition from second to third flow paths in the exhaust system. In some embodiments, the flow control inserts are flat or three-dimensional, varying profde, planar baffles, having an outer face (or multiple outer faces) that is oriented parallel to and/or perpendicular to and/or skewed relative to central axis of the diffuser. The planar baffles alter exhaust-gas flow direction, and/or isolate variations in exhaust-gas flow velocity. In other embodiments, the planar baffle-type flow control inserts 80, 90 selectively alter localized cross section of, and/or split exhaust gas flow within the volute passage 64, by changing baffle thickness and/or orientation within the volute passage. In other embodiments, such as the flow control inserts 100 and 120 of FIGs. 7-9, the insert is affixed to a surface of the exhaust system that defines the volute passage 64, which varies the latter’s throat depth and/or profile. Selectively varying the volute passage’s throat depth or profile selectively alters the localized exhaust gas velocity direction and/or speed.

[0032] Referring generally to FIGs. 1-9 exhaust gas flow E in the exhaust systems 40, 140, 240, and 340 are altered by observing generated exhaust gas flow velocity within the respective second and/or third flow paths in the volute passage 64 and in the exhaust hood passage 76. Exemplary exhaust flow paths are referenced as E in the figures. One or more localized variations V in exhaust gas flow velocity within the second and/or third flow paths that deviate from desired gas flow velocity therein are identified, based on any one or more of empirical observation of actual exhaust flow, and/or virtual or lab bench flow-modeling, and/or forensic examination of actual exhaust system components during periodic maintenance service of the engine. At least one flow control insert, or more, is selectively placed in fixed orientation within the volute passage. Flow control insert placement alters at least one of the identified deviations V from desired gas flow velocity.

[0033] In some embodiments, the identified variation VI or V2 in exhaust gas flow- velocity is where the exhaust gas leaves the exit 46 of the annular diffuser 42, where it turns sharply in a radially outwardly direction and circulates circumferentially in the volute passage 64. In some engines and exhaust systems, exhaust gas flow E in the annular diffuser 42 has a spinning velocity component that is imparted in the exhaust gas by the spinning turbine blades 30. Selective placement of one or more flow control inserts in the volute passage 64 counteracts the spinning velocity component of the exhaust gas as it leaves the exit 46 of the annular diffuser 42; this normalizes exhaust gas flow velocity, such as VI or V2, leaving the diffuser exit.

[0034] In other embodiments, the identified, variation in exhaust gas flow-velocity has a localized, slower exhaust gas-flow speed in the second flow path within the volute passage 64, such as the variation VI shown in FIG. 2. Referring again to FIGs. 7-9, the slower-speed flow variation VI is normalized by selectively restricting cross section of the second flow path by placing the flow control insert 100 or 120 in fixed orientation in the zone with the slower speed variation V 1. Placement of the flow control inserts 100 or 120, or a suitably thick cross section profile baffle 80 or 90 in slower flow zone speeds up and normalizes gas flow as it passes through the restricted cross section of the volute passage 64

[0035] In other embodiments, the identified, variation in exhaust gas flow-velocity is in the third flow path within the exhaust hood passage 76, such as the spiral exhaust flows V3 and V4 of FIG. 2. Selective placement of a flow control insert in the volute passage 64 alters the flow velocity variations V3 and V4, and facilitates normalized upward flow E through the exhaust hood passage 76, to the exhaust conduit 72.

[0036] Although various embodiments that incorporate the invention have been shown and described in detail herein, others can readily devise many other varied embodiments that still incorporate the claimed invention. The invention is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out m various ways. In addition, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of“including,” “comprising,” or“having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms“mounted”,“connected”,“supported”, and“coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical, mechanical, or electrical connections or couplings.