Method and apparatus for reducing total pressure loss in a turbine engine

Abstract

A method and apparatus for reducing total pressure loss in the exhaust of a combustion device via an axial diffuser having no turning vanes, support struts, rods, or other obstructions to exhaust flow. The axial diffuser includes an inner wall and an outer wall each having a turn radius and forming an annular cross section having increasing cross-sectional area in the downstream direction of flow, the flow being transitioned from axial to radial direction thereby. The diffuser is supported in the plenum by rods, struts or a cradle; from a stand surrounding the axial diffuser via struts or rods; or from existing diffuser support structure by web stiffeners. The diffuser flow path turn radius of the outer wall ranges from about 50-95% of the radial distance from the inner wall to a wall of the exhaust plenum, and of the inner wall ranges from about 10-70% of this distance.

Description

This application claims priority from U.S. Provisional Application Ser. No. 60/473,442 filed May 28, 2003. The entirety of that provisional patent application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to turbine engine exhaust systems and more particularly to turbine engine exhaust systems containing axial diffusers that reduces pressure loss.

2. Background of the Technology

Typical combustion fired gas turbines consist of a compressor, combustion system, a power turbine, and an exhaust system, such as the exhaust system 1 shown in FIG. 1. A typical exhaust system 1 includes aerodynamic struts 2 (as further shown in closeup in FIG. 2) and a 90-degree axial to radial diffuser (axial to radial turn and support rods for a radial diffuser 30 are shown in FIG. 3) disposed within a plenum 4, followed by either a silencer 5 (plenum 4 and silencer 5 are further shown in FIG. 4) in a simple cycle system or a heat recovery steam generator in a combined cycle system. Also shown in FIG. 1 is a power turbine exit annulus/inlet to exhaust system 8. Note that the axial to radial turn and support rods, while contained within the exhaust system 1, are not visible in FIG. 1.

As shown in FIG. 3, the axial to radial diffuser 30 (also interchangeably referred to herein as an axial to radial turn) turns the flow from an axial direction to a radial direction to fill the plenum 4, as shown in FIG. 1. The axial to radial turns can be oriented in any direction, left right or top, depending upon the layout of the balance of the plant. Total pressure losses associated with these turns are irreversible and unrecoverable and therefore represent a reduction in the overall efficiency of the turbine. Further, the connection points and other features of the rods or struts and turning vanes associated with such exhaust systems often crack, requiring welding or similar repair, or require other maintenance.

Referring now to FIG. 5, a conventional axial to radial diffuser generally includes aerodynamic turning vanes 50 and support struts or rods 51. The support struts/rods 51 support both the turning vanes 50 and the outer radial wall 52 of the diffuser. The intent of the turning vanes 50 is to turn the flow from an axial direction A (as it leaves the power turbine last stage) to a radial direction B, such that the flow fills the plenum as efficiently as possible. Note that small, tight radius turns C are typically used for the turning vanes 50 of a conventional diffuser, as further shown in FIG. 6.

Attempts to improve upon conventional diffusers have been made. The prior state of the art [see, e.g., Norris, “Test Program for High Efficiency Turbine Diffuser—Project Summary (California Energy Commission Energy Innovations Small Grant Program, available at eisg.sdsu.edu/Fullsums/01-29.htm (last visited on May 19, 2003)] involves “inserting aerodynamic vanes and devices placed inside the exhaust diffuser” to “reduce backpressure on the turbine.” The small gains achieved using these techniques are not economically feasible to implement. Among other reasons, this approach does not work because it is impossible to match the orientation of the aerodynamic vanes to the flow for the full range of turbine operating conditions. Other attempts at improving the conventional exhaust system are illustrated in U.S. Pat. Nos. 5,188,510, 5,603,604, 5,813,828 and 5,340,276.

SUMMARY OF THE INVENTION

The present invention overcomes the above mentioned problems with the prior art, as well as others, by providing a method and apparatus for reducing total pressure loss in the exhaust portion of a combustion system. An embodiment of the method and apparatus include one or more of the following features: 1) removing the axial to radial turning vanes and any other devices of the prior art for conditioning or improving the flow field between the hub wall and outer radial wall of the axial diffuser aft of the main exhaust struts; 2) removing any support struts or rods and any other blockages or obstructions that interact with the flow between the hub wall and outer radial wall of the axial diffuser aft of the exhaust struts; and 3) transitioning the axial diffuser flow path from an axial to a radial direction using a radius turn.

In an embodiment of the present invention, the transitioned axial diffuser flow path includes a turn radius in an inner wall (also interchangeably referred to herein as “the hub surface”) of the axial diffuser ranging preferably between about 50% and 95% of the radial distance from the hub surface of the axial diffuiser to the nearest wall of the exhaust plenum. In an embodiment of the present invention, the flow path also includes a turn radius in the outer radial surface of the axial diffuser, the turn radius of the inner radial surface being preferably between about 10% and 70% of that of the outer radial turn. Depending on particular advantages for each embodiment, the turn radius of the hub surface of the axial diffuser may or may not be concentric with the turn radius of the outer radial surface of the axial diffuser.

In embodiments of the present invention, the end of the outer surface of the axial diffuser with the aforementioned turn radius is supported via a support structure in any number of ways, including: a) from the exhaust plenum floor by rods, struts or a cradle; b) from a stand surrounding the axial diffuser by one or more struts or rods; or c) from the existing diffuser support structure by web stiffeners attached to the outside surface of the diffuser wall.

The approach of the present invention performs better than in the prior art at least in part because the resultant static pressure in the exhaust plenum reaches a value equal to the static pressure that occurs at the inside of the turn from the axial to radial direction at the exit of the turn. The flow rate and the radius of curvature of the turn set the pressure at this location. The larger the radius of the turn, the higher the resultant pressure and the greater the pressure recovery.

Using the present invention, turbine efficiency and output can be improved on the order of 1 percent. This amount of improvement is economically feasible to achieve, given the lack of expensive aerodynamically shaped hardware. The only hardware required to implement this design is a new smooth radius axial to radial turn, which is an inexpensive part to manufacture and install in the turbine or other combustion device.

In addition, the present invention reduces maintenance and repair associated with the struts or rods and turning vanes of prior art axial diffusers.

Additional advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become more apparent to those skilled in the art upon examination of the following or upon learning by practice of the invention.

BRIEF DESCRIPTION OF THE FIGURES

In the drawings:

FIG. 1 shows an exemplary exhaust system for a typical combustion fired gas turbine, the turbine consisting of a compressor, combustion system, a power turbine, and an exhaust system;

FIG. 2 contains a view of an exemplary aerodynamic strut section for the exhaust system of FIG. 1;

FIG. 3 presents a view of axial to radial turn and support rod features for an exemplary diffuser for use with the exhaust system of FIG. 1;

FIG. 4 shows a view of an exemplary plenum and silencer for the exhaust system of FIG. 1;

FIG. 5 presents a view of a conventional axial to radial diffuser that includes aerodynamic turning vanes and support struts or rods;

FIG. 6 contains a view of a conventional diffuser, showing the small, tight radius turns that are typically used for turning vanes;

FIG. 7 is a cutaway view of an exemplary diffuser in accordance with an embodiment of the present invention;

FIG. 8 shows a closeup view of the turn radius of the inner radial of the diffuser of FIG. 7;

FIG. 9 contains a closeup view of the turn radius of the outer radial of the diffuser of FIG. 7;

FIG. 10 is a cutaway view the diffuser of FIG. 7;

FIG. 11 shows a cross-sectional view of a diffuser, in accordance with an embodiment of the present invention;

FIG. 12 contains another view of the diffuser of FIG. 11, with the hub wall of the diffuser indicated;

FIG. 13 presents a view of the diffuser of FIG. 11, with the outer wall of the diffuser indicated;

FIG. 14 is another view of the diffuser of FIG. 11, with perpendicular distance from the hub of the diffuser to the nearest parallel wall of the exhaust plenum indicated;

FIG. 15 shows the radius turn of the hub wall of the diffuser, in accordance with an embodiment of the present invention;

FIG. 16 shows the radius turn of the outer wall of the diffuser, in accordance with an embodiment of the present invention;

FIGS. 17-19 present views of the end of the outer surface of the axial diffuser supported from the exhaust plenum floor by rods, struts or a cradle, in accordance with an embodiment of the present invention;

FIGS. 20-22 show views of the end of the outer surface of the axial diffuser supported from a stand surrounding the axial diffuser by one or more struts or rods, in accordance with an embodiment of the present invention; and

FIGS. 23-25 contain views of the end of the outer surface of the axial diffuser supported from the existing diffuser support structure by web stiffeners attached to the outside surface of the diffuser wall, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The method and apparatus of one embodiment of the present invention, which reduces the total pressure loss in the exhaust portion of a turbine or other combustor includes one or more of the following features: 1) completely removed axial to radial turning vanes and any other devices used for or intended to condition or improve the flow field between the hub wall and outer radial wall of the axial diffuser aft of the main exhaust struts; 2) completely removed support struts or rods and any other blockages or obstructions that interfere or otherwise interact with the flow between the hub wall and outer radial wall of the axial diffuser aft of the exhaust struts; and 3) transitioning of the axial diffuser flow path from an axial to a radial direction using a large radius turn.

In particular, in one embodiment, the transitioned axial diffuser flow path includes a turn radius in an inner wall (also interchangeably referred to herein as “the hub surface”) of the axial diffuser ranging preferably between about 50% and 95% of the radial distance from the hub surface of the axial diffuser to the nearest wall of the exhaust plenum. In an embodiment of the present invention, the flow path also includes a turn radius in the outer radial surface of the axial diffuser, the turn radius of the inner radial surface being preferably between about 10% and 70% of that of the outer radial turn. Depending on particular advantages for each embodiment, the turn radius of the hub surface of the axial diffuser may or may not be concentric with the turn radius of the outer radial surface of the axial diffuser.

References will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

One embodiment of a diffuser according to the present invention is illustrated in FIGS. 7-16. In the embodiment of FIGS. 7-16, both the turning vanes and the support struts/rods have been removed and large radius turns have been included on both the hub and outer walls of the diffuser. As discussed above, not all features are present in all embodiments of the invention. For example, in some embodiments, the turning vanes are removed without removing the support struts. In other embodiments, the turning vanes and the struts are removed, while one or both of the diffuser surfaces are provided with a small radius, rather than a large radius. Other combinations of the features set forth above are also possible in other embodiments of the present invention.

As shown in FIG. 7, in an embodiment of the present invention, a rotor shaft 71 traverses the center of an axial diffuser 70. The shaft 71, which is driven, for example, by exhaust flow via one or more blades connected to the shaft 71, rotates and is optionally connected to an output device, such as a generator. The diffuser 70 includes a diffuser inner radial wall 72 and a diffuser outer radial wall 73.

As shown in the closeup of the diffuser 70 contained in FIG. 8, the present invention includes a diffuser inner wall 72 having a radius turn R₁, such as a large turn radius. Similarly, as shown in FIG. 9, the outer wall 73 of the diffuser 70 also has a radius turn R₂, such as a large turn radius. As a result of the features shown in FIGS. 7-9, this embodiment of the present invention removes or reduces the need for axial to radial turning vanes, support struts, rods, or gussets, etc., of the prior art (see, e.g., FIG. 5), and provides for an unobstructed, “clean” flow path between the inner and outer walls 72, 73 of the diffuser 70.

FIG. 10 shows another cutaway view of a diffuser 70, in accordance with an embodiment of the present invention. In the cross-sectional view of the diffuser 70 shown in FIG. 11, the axial diffuser inlet 110 is annular in a cross section perpendicular to the direction of the exhaust centerline C, with the inlet 110 widening in cross-sectional area downstream of flow direction F, as flow proceeds from the exhaust of the power turbine or other combustion device into the plenum.

FIG. 12 contains another view of the diffuser 70 of FIG. 11, with a central portion of the inner wall 120 of the diffuser 70, indicated. FIG. 13 presents a view of the diffuser 70 of FIG. 1, with the outer wall 73 of the diffuser 70 indicated.

As shown in FIG. 14, in an embodiment of the present invention, the radial distance D extends from the portion of hub wall 120 of the axial diffuser 70, which is approximately parallel to the direction of the centerline C, to the nearest cross-sectionally approximately parallel wall 140 of the exhaust plenum. In one embodiment of the present invention, the nearest such wall 140 is the bottom side of the exhaust plenum, as shown in FIG. 14.

FIG. 15 shows the radius turn RI of the hub wall 72 of the diffuser 70. The radius of hub wall radius turn R₁, for example, is between about 50% and 95% of D.

Similarly, as shown in FIG. 16, the radius turn R₂ of the outer wall 73 of the diffuser 70, together with the hub wall 72, form a flow path that allows the exhaust system to transition the exhaust flow from an axial direction AD to a radial direction RD via the radius turns. The radius of inner wall radius turn R₁, for example, is between about 10% and 70% of the radius of outer wall radius turn R₂.

The end of the outer surface of the axial diffuser with the aforementioned turn radius can be supported any number of ways, including: a) from the exhaust plenum floor by rods, struts or a cradle as shown in FIGS. 17-19; b) from a stand surrounding the axial diffuser by one or more struts or rods as shown in FIGS. 20-22; or c) from the existing diffuser support structure by web stiffeners attached to the outside surface of the diffuser wall as shown in FIGS. 23-25; or by any combination of the above. In addition, in some variations, the outer surface is supported by rods or struts, absent turning vanes. The outer surface is also supported, in other variations, by a non-attached external mechanism, such as a portion of a turbine abutting or otherwise supporting the outer surface. These various combinations of support features, collectively and individually, are interchangeably referred to herein as “a support mechanism.”

FIGS. 17-19 show cutaway views of an axial diffuser 170 supported by an exemplary bottom cradle 172. Similarly, one or more elements of the diffuser 170 may be supported by rods or struts. FIGS. 20-22 contain cutaway views of an axial diffuser 200 supported by an exemplary full cradle 201. FIGS. 23-25 present cutaway views of an axial diffuser 230 supported by an existing diffuser support structure 231 (the indicated structure in FIGS. 23-25, having opposite end [not shown] is attached to the opposite wall of the plenum at the inlet to the exhaust system) by web stiffeners 232 attached to the outside surface of the diffuser wall 233.

Example embodiments of the present invention have now been described in accordance with the above advantages. It will be appreciated that these examples are merely illustrative of the invention. Many variations and modifications will be apparent to those skilled in the art.

Claims

1. An axial diffuser, comprising:

an inner wall connected to an exhaust plenum, the inner wall having an inner wall radius turn;

an outer wall having an outer wall radius turn; and

a support mechanism supporting the outer wall;

wherein the inner wall and the outer wall form a flow path free of turning vanes.

2. The diffuser of claim 1, wherein has a circular cross-sectional shape.

3. The diffuser of claim 2, wherein the inner wall has an opening, and wherein a shaft is receivable in the inner wall opening in a direction along a centerline within the opening in the inner wall.

4. The diffuser of claim 3, wherein the inner wall includes a first inner wall portion, the first inner wall portion extending in a direction generally parallel to the centerline.

5. The diffuser of claim 1, wherein the outer wall radius turn is a large radius turn.

6. The diffuser of claim 5, wherein the large radius turn of the inner wall has a radius between about 50% and 95% of a perpendicular distance from the first inner wall portion to a wall of the exhaust plenum.

7. The diffuser of claim 6, wherein the perpendicular distance is a minimum.

8. The diffuser of claim 1, wherein the outer wall has a circular cross-sectional shape.

9. The diffuser of claim 6, wherein the outer wall radius turn is a large radius turn.

10. The diffuser of claim 9, wherein the large radius turn of the inner wall has a radius between about 10% and 70% of the radius of the outer radial turn.

11. The diffuser of claim 1, wherein the support mechanism comprises a connection between a wall of the exhaust plenum and the outer wall.

12. The diffuser of claim 11, wherein the connection comprises one selected from a group consisting of rods, struts, or a cradle.

13. The diffuser of claim 11, wherein the connection comprises a stand surrounding the axial diffuser.

14. The diffuser of claim 11, wherein the connection comprises at least one web stiffener attached to a wall of the axial diffuser.

15. The diffuser of claim 1, wherein the support mechanism is external to the flow path.

16. The diffuser of claim 1, wherein the support mechanism comprises an extension from turbine.

17. The diffuser of claim 1, wherein the cross-sectional area of the flow path increases in size in a downstream direction of exhaust flow through the flow path.

18. The diffuser of claim 3, wherein the cross-sectional area of the flow path increases in size in a downstream direction of exhaust flow through the flow path, and wherein the shaft is a rotor shaft.

19. The diffuser of claim 18, wherein the rotor shaft is rotated by the exhaust flow.

20. The diffuser of claim 19, wherein the rotor has at least one attached blade.

21. The diffuser of claim 1, wherein the inner wall radius turn is concentric with the outer wall radius turn.

22. The diffuser of claim 1, wherein the flow path is unobstructed by at least one selected from a group consisting of radial turning vanes, support struts, and rods.

23. The diffuser of claim 1, wherein the annular flow path transitions the exhaust flow from an axial direction to a radial direction.

24. The diffuser of claim 1, wherein the flow path has a generally annular cross-sectional shape.

25. An axial diffuser for a combustion device exhaust component, the exhaust component including an exhaust plenum having at least a first plenum wall and a second plenum wall, the diffuser comprising:

an outer diffuser wall having a circular cross-sectional shape;

an inner diffuser wall attached to the first plenum wall, the inner diffuser having a circular cross-sectional shape and an inner opening, wherein the inner diffuser wall is situated such that the inner diffuser wall and the outer diffuser wall form a flow path therebetween, the flow path being unobstructed by turning vanes.

26. The axial diffuser of claim 25, wherein the flow path has a generally annular cross-sectional shape and cross-sectional area, the area of the annular cross-sectional area increasing with downstream direction of exhaust flow in the flow path

27. The axial diffuser of claim 25, further comprising:

a rotor extending through the inner opening of the inner diffuser wall.

28. The diffuser of claim 26, wherein the inner wall includes a first inner wall portion and a second inner wall portion, the second inner wall portion including a radius turn.

29. The axial diffuser of claim 28, wherein the radius turn of the inner wall is a large radius turn having a radius between about 50% and 95% of a perpendicular distance from the first inner wall portion to the second plenum wall.

30. The diffuser of claim 28, wherein the outer wall includes a radius turn.

31. The diffuser of claim 30, wherein the inner wall radius turn and the outer wall radius turn cooperate to transition the exhaust flow from an axial direction to a radial direction.

32. The diffuser of claim 29, wherein the outer wall includes a large radius turn, the large radius turn of the inner wall having a radius between about 10% and 70% of radius turn of the inner wall large radius turn.

33. A method for reducing total pressure loss in the exhaust flow of a combustion device having an exhaust plenum, the method comprising:

forming a flow path unobstructed by turning vanes, the flow path being located within an axial diffuser in the exhaust plenum, wherein the flow path has an increasing cross-sectional area in downstream direction of flow therethrough, wherein the axial diffuser includes an inner wall having a radius turn and an outer wall having a radius turn, the inner wall being attached to a wall of the exhaust plenum and the outer wall being attached to the exhaust plenum via a support mechanism external to the flow path;

transmitting the exhaust flow through the axial diffuser; and

transitioning the exhaust flow from an axial direction to a radial direction.