EXHAUST GAS DIFFUSER OF A GAS TURBINE

Abstract

An exhaust gas diffuser for a gas turbine includes a flow duct which widens towards a diffuser outlet. The flow duct includes an axially extending guide body, wherein the guide body, at least in an axial section of its longitudinal extent, has a plurality of recesses which are distributed over the circumference and arranged between guide elements. Each guide element extends along a spiral line along the longitudinal extent of the guide body. Further, a gas turbine plant with such an exhaust gas diffuser is provided.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2011/056210 filed Apr. 19, 2011, and claims the benefit thereof. The International Application claims the benefits of European Patent Application No. 10004244.9 EP filed Apr. 21, 2010. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to an exhaust gas diffuser for a gas turbine, having a flow duct which widens towards the diffuser outlet and in the center of which provision is made for an axially extending guide body.

BACKGROUND OF INVENTION

Such an exhaust gas diffuser serves for decelerating the exhaust gas flow of a gas turbine and for recuperating at least some of the dynamic pressure. In order to disclose an exhaust gas diffuser with a comparatively large opening angle of 10° and more, it is known from DE 198 05 115 A1, for example, to provide an axially extending guide body in the center of the diffuser duct. By using the guide body, the exhaust gas diffuser is designed as an annular diffuser. As a result, larger regions of backflow zones aft of the gas turbine hub are avoided, which has an advantageous effect upon the efficiency of the exhaust gas diffuser. It is disadvantageous, however, that the guide body is comparatively long and therefore has to be supported by additional struts on account of its length. In addition, the aerodynamic influences of the support struts are not taken into account.

Furthermore, an exhaust gas diffuser of a gas turbine with a central drum body, on the generated surface of which provision is made for a multiplicity of blades which are arranged in a rotation-resistant manner, is known from U.S. Pat. No. 5,791,136. The blades serve for homogenizing the exhaust gas flow of the gas turbine in the event of a small pressure drop.

SUMMARY OF INVENTION

It is an object to provide a space-saving exhaust gas diffuser for a gas turbine which for achieving an efficiency of the gas turbine which is as high as possible enables an improvement of the pressure recuperation. Also, the exhaust gas diffuser is to enable homogenization of the diffuser outflow so that in a heat recovery steam generator, which is connected downstream of the gas turbine, an inflow, which is as homogeneous as possible, of the hot exhaust gas from the gas turbine is effected.

This object is achieved by an exhaust gas diffuser as claimed in the claims. To this end, the guide body of the generic-type exhaust gas diffuser, at least in an axial section of its longitudinal extent, has a number of recesses which are distributed over the circumference and arranged between the guide elements, wherein each guide element extends along a spiral line.

The invention is based on the knowledge that the secondary flows which are initiated on the support struts of the rear bearing star in the event of swirled inflow are to be utilized in order to intensify the mixing-through aft of the hub end and so to further shorten the length of backflow zones aft of the hub. For this purpose, the guide body of the exhaust gas diffuser, which is designed as an essentially conical or cylindrical body, has recesses and guide elements which are distributed over the circumference in order to guide and to intensify the secondary flows in an optimum manner. The secondary flows guide fluid from the pressure side of the support struts onto spiral-like paths. By using recesses and guide elements, the secondary flows can therefore get closer to the center axis of the diffuser and the support body can be of a shorter design than in the case of the prior art without its efficiency being reduced in the process. As a result of the shortened length of the support body, this can also be of free-standing design. The particular advantage of the invention lies in the utilization of the secondary flows which are generated on the pitched and/or profiled support struts in order to guide fluid still closer to the hub axis with the aid of hub-side recesses in order to thus further reduce the size and especially the length of the backflow zone aft of the hub. This leads to further increased efficiency of the exhaust gas diffuser.

As a result of the pitched orientation of the guide elements (pitch) in relation to the center axis, both an exceptionally efficient and space-saving construction for de-swirling of the flow is disclosed. The pitch of the spiral line is comparatively large in this case so that the spiral lines are only slightly inclined in relation to the center axis of the exhaust gas diffuser. The pitch can also become smaller along its extent. Preferably, it increases, however, in order to obtain an outflow from the exhaust gas diffuser which has as little swirl as possible. This arrangement is particularly advantageous in the case of an axial exhaust gas diffuser in which the number of guide elements is the same as a number of support struts which are provided in the exhaust gas diffuser or directly upstream thereof for the turbine-side support of the gas turbine rotor.

In an advantageous embodiment, the guide body has a cross-sectional contour which is arranged perpendicularly to the center axis of the exhaust gas diffuser and which is in the shape of a star, the points of which are formed by the respective guide elements. By means of the star-shaped cross-sectional contour, significantly greater rigidity of the inner wall of the exhaust gas diffuser, now formed as an annular diffuser, can be achieved. The tendency of the guide body towards vibrating on account of the flow is significantly reduced as a result. Consequently, it is also possible to design the guide body in a way in which it is fastened on only one side so that its end facing the diffuser outlet overhangs in the exhaust gas diffuser in a freely suspended manner. An aerodynamically disturbing and cost-increasing outlet-side support of the guide body can consequently be avoided on account of the greater rigidity of the guide body.

In an expedient development, each guide element has an outer tip which projects radially outward from the center axis of the exhaust gas diffuser, the shortest distance of which to the center axis (that is to say in the cross section arranged perpendicularly to the center axis) reduces with decreasing axial distance to the diffuser outlet. In this case, each recess has a radially inward disposed base, the shortest distance of which to the center axis (that is to say in the cross section arranged perpendicularly to the center axis) also reduces with decreasing axial distance to the diffuser outlet. As a result of this, a widening of the flow cross section of the exhaust gas diffuser is also achieved on the hub side, which contributes to a further shortening of the overall axial length of the exhaust gas diffuser. The flow cross section increase must therefore be achieved not only via an increase of the diameter of the outer annular wall of the exhaust gas diffuser. This measure also reduces the overall axial length of the exhaust gas diffuser.

Each guide element—as seen in the flow direction of the exhaust gas diffuser—is preferably arranged in an aligning extension of the support struts. Particularly as a result of this, it is possible to utilize the secondary flows which are initiated on the support struts of the rear bearing star in the event of swirled inflow in order to intensify the mixing-through aft of the hub end and to achieve improved pressure recuperation. In particular, the secondary flow vortices along the pressure side of the support struts can then be directed in an aerodynamically especially favorable manner into the recess of the guide body, which brings along only comparatively low aerodynamic losses. In this case, it can be provided that in that axial section of the exhaust gas diffuser in which the support struts are arranged, the guide body, between the struts, already has an inner wall contour in the shape of an arc in the circumferential direction, the shortest distance of which to the center axis of the exhaust gas diffuser reduces with decreasing axial distance to the diffuser outlet. In other words, not just the guide body, which is connected to the support struts, can be of conical design but the inner wall of the annular exhaust gas diffuser in the axial section of the support struts can also already be of conical design, wherein its diameter also decreases to the outlet-side end of the exhaust gas diffuser. Especially in the case of a heat recovery steam generator, which is connected downstream of the gas turbine on the exhaust gas side via the exhaust gas diffuser, a saving in material is achieved by shortening associated steam lines to the heat recovery steam generator or heat recovery boiler.

A corresponding heat recovery steam generator or boiler in horizontal or vertical style of construction can then be designed with a relatively small heating surface since as a result of a comparatively homogeneous or more uniform inflow this is utilized better than before. In this way, the pressure loss of the boiler on the exhaust gas side reduces, which in turn results in an efficiency gain of the gas turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are explained in more detail with reference to a drawing.

FIG. 1 shows an exhaust gas diffuser of a gas turbine in a partially sectioned, partially perspective view with a guide body arranged in the center,

FIG. 2 shows the cross section through the guide body according to FIG. 1 in a first sectional view, and

FIG. 3 shows the guide body according to FIG. 1 in a second section.

DETAILED DESCRIPTION OF INVENTION

Shown in FIG. 1 is an exhaust gas diffuser 10 for a gas turbine in a longitudinal section, wherein the bearing star 12, which is arranged in the center of the exhaust gas diffuser 10, for the turbine-side support of the gas turbine rotor and of the guide body 14 which is arranged on the bearing star, is shown in perspective view. The exhaust gas diffuser 10 has a center axis 16 lying in its center, which extends from an inlet-side end 18 to an outlet-side end 20. Provision is made in the exhaust gas diffuser 10 for a flow duct 22, the cross section of which, being perpendicular to the center axis, has an annular contour. The flow duct 22 is delimited in this case by a radially outward disposed outer wall 24. The guide body 14 is arranged in the center of the exhaust gas diffuser 10, that is to say in the region of its center axis 16, and in this case constitutes the radially inward disposed boundary of the flow duct 22. The guide body 14 is supported in this case by five support struts 26 which are distributed evenly or unevenly around the circumference. In the axial section A of the exhaust gas diffuser 10, in which the support struts 26 are also arranged, the turbine-side end of the gas turbine rotor, which for reasons of clarity is not shown, terminates inside the guide body. Upstream of the section A, that is to say towards the inlet-side end 18, the guide body 14 is of cylindrical design. It is provided that in the section A the guide body 14 already does not have a cylindrical inner wall contour between the support struts 26 but that recesses 30 which become larger (deeper) are already provided there. Downstream of the section A, the recesses 30, which are distributed over the circumference of the guide body 14, are delimited by guide elements 32 so that recesses 30 and guide elements 32 are arranged in an alternating manner in the tangential direction. The number of guide elements 32 corresponds in this case to the number of support struts 26, five guide elements 32 and support struts 26 being provided in each case in the depicted exemplary embodiment. A greater or lesser number of guide elements 32 and support struts 26 can also be provided. If the support struts 26 are distributed unevenly over the circumference, the recesses 30 and guide elements 32 are distributed correspondingly unevenly on the inlet side. On the outlet side, their even distribution is preferred in any event. As is known, the support struts 26 are aerodynamically profiled. Therefore, the support struts 26 have a prespecified outflow angle, which is also known from turbine blades and compressor blades, in the aerodynamically aligning continuation of which the guide elements 32, being inclined in relation to the center axis, are twisted towards the outlet-side end 20 of the exhaust gas diffuser 10. Each guide element 32 has an outwardly projecting tip 36, the outermost point of which has a shortest distance to the center axis of the exhaust gas diffuser 10—for any chosen cross section which is perpendicular to the center axis 16—which distance reduces with decreasing axial distance of the cross section to the diffuser outlet 20. The same applies to each recess. The shortest distance of the radially inward disposed base 38 to the center axis 16 reduces with decreasing axial distance to the diffuser outlet. As a result, the guide body 14, downstream of its section A, altogether maintains a conical appearance which leads to the inner cross-sectional area of the guide body, through which exhaust gas does not flow, steadily reducing. At the end of the guide body, only a comparatively small cross section therefore remains, which can lead to backflow regions which are of a comparatively shorter and weaker form accordingly.

Shown in FIGS. 2 and 3 are the cross-sectional views, arranged perpendicularly to the center axis 16, of the guide body 14 according to the sections II and III from FIG. 1. In this case, identical features are provided with identical designations.

In all, the invention discloses an exhaust gas diffuser 10 for a gas turbine, having a flow duct 22 which widens towards the diffuser outlet 20, in the center of which provision is made for an axially extending guide body 14. In order to disclose a further shortened exhaust gas diffuser 10, the guide body 14 of which has a particularly high rigidity and the tendency of which towards flow-induced vibrations is reduced, it is provided that the guide body 14, at least in an axial section of its longitudinal extent, has a number of recesses 30 which are distributed over the circumference and arranged between guide elements 32.

Claims

1.-10. (canceled)

11. An exhaust gas diffuser for a gas turbine, comprising:

a flow duct which widens towards a diffuser outlet, the flow duct comprising an axially extending guide body,

wherein the guide body, at least in an axial section of its longitudinal extent, has a plurality of recesses which are distributed over the circumference and arranged between guide elements,

wherein each guide element extends along a spiral line along the longitudinal extent of the guide body.

12. The exhaust gas diffuser as claimed in claim 11, wherein the guide body has a cross-sectional contour which is arranged perpendicularly to a center axis of the exhaust gas diffuser, wherein the cross-sectional contour is in the shape of a star, and wherein the points of the star are formed by the guide elements.

13. The exhaust gas diffuser as claimed in claim 11, wherein each guide element has a tip which projects radially outward from a center axis of the exhaust gas diffuser, wherein the shortest distance of the tip to the center axis of the exhaust gas diffuser reduces with decreasing axial distance to the diffuser outlet.

14. The exhaust gas diffuser as claimed in claim 11, wherein each recess has a radially inward disposed base, wherein the shortest distance of the base to a center axis of the exhaust gas diffuser reduces with decreasing axial distance to the diffuser outlet.

15. The exhaust gas diffuser as claimed in claim 11, wherein an axial section of the guide body with recesses and guide elements extends over an entire axial extent of the guide body.

16. The exhaust gas diffuser as claimed in claim 11, wherein the plurality of guide elements corresponds to a number of support struts which are provided for the turbine-side support of the gas turbine rotor.

17. The exhaust gas diffuser as claimed in claim 16, wherein each guide element, as seen in a through flow direction of the exhaust gas diffuser, is arranged in an aligning extension of the support struts.

18. The exhaust gas diffuser as claimed in claim 16, wherein in an axial section of the support struts provision is made for an inner wall contour, which is in the shape of an arc in a circumferential direction, between the support struts, and wherein the shortest distance of the inner wall contour to a center axis of the exhaust gas diffuser reduces with decreasing axial distance to the diffuser outlet.

19. A gas turbine plant, comprising:

an exhaust gas diffuser, comprising: a flow duct which widens towards a diffuser outlet, the flow duct comprising an axially extending guide body, wherein the guide body, at least in an axial section of its longitudinal extent, has a plurality of recesses which are distributed over the circumference and arranged between guide elements, wherein each guide element extends along a spiral line along the longitudinal extent of the guide body.

20. The gas turbine plant as claimed in claim 19, further comprising a heat recovery steam generator which is connected downstream of the exhaust gas diffuser.