Patent Application
20100162705
This present application relates generally to methods, systems, and/or apparatus for improving the efficiency and/or operation of turbine engines. More specifically, but not by way of limitation, the present application relates to methods, systems, and/or apparatus pertaining to improved steam turbine diffusers and related components.
In conventional steam turbine design, the inner case of the steam turbine, which, for example, may be a double flow down exhaust unit, has an encompassing exhaust hood split vertically and extending along opposite sides and ends of the turbine. This large box-like structure houses the entire low pressure section of the turbine. The exhaust steam from the turbine flows downstream in a general axial direction. Then, the steam exhaust is redirected from an axial flow direction to a flow direction 90° relative to the axial flow direction. This 90° flow direction may be in any plane, downwardly, upwardly or transversely.
Generally, conventional exhaust hoods for steam turbines constitute large rectilinear structures at the exit end of the conical section for turning and diffusing the steam flow at right angles. The steam flow path was thus somewhat tortuous, which resulted in losses and adverse pressure drop. It will also be appreciated that access to various parts of the turbine, for example, the bearing for maintenance purposes was difficult in that it could necessitate the removal of the upper half of the exhaust hood. Further, it will be appreciated that the exhaust hood in conventional steam turbines typically supports the inner casing of the turbine and the associated steam path parts such as diaphragms and the like. Accordingly, there has been found a need to provide a new geometry to improve exhaust steam pressure recovery and overall performance of the turbine.
The present application thus describes an axial flow steam turbine flow path that includes a rotor and a casing defining the axial steam flow path; and a toroidal diffuser for diffusing the exhaust steam and turning the exhaust steam from a generally axial flow direction to a generally transverse or vertical and tangential direction; wherein the toroidal diffuser comprises a diffuser that, at least in part, incorporates the shape of a toroid or a section of a toroid; and wherein a toroid comprises the shape generated by revolving a circular or oval shape in three dimensional space about an axis coplanar with the circular or oval shape, which does not touch the circular or oval shape.
These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in con junction with the drawings and the appended claims.
These and other objects and advantages of this invention will be more completely understood and appreciated by careful study of the following more detailed description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:
Referring now to the drawings, particularly to
Also illustrated in
Referring now to
According to a preferred embodiment, the toroidal diffuser 40 generally includes a conical guide 45, which functions as the initial guide for the steam as it exits the last turbine section, a toroidal section 42, which, as illustrated, defines the upper half of the main body or chamber of the diffuser, and a rectilinear section 43, which defines the lower half of the main body or chamber of the diffuser and provides the flow path to an outlet 46. The toroidal section 42 may comprise approximately one half of a toroid shape, though other configurations are also possible. The toroidal section 42 engages and transitions to the rectilinear section 43 at a circumferential location that is approximately horizontal with the rotor 112. The axis of the toroid that forms the toroidal section 42 generally is the rotor 112.
The toroidal diffuser 40 may include other components that allow it to function in a more efficient and cost-effective manner. In some preferred embodiments, as already described, the toroidal diffuser 40 may include the conical guide 45. The upstream end of the conical guide 45, as illustrated, may be coupled to the inner casing 116 by a flexible joint 44. The conical guide 45 generally provides the outer radial boundary for steam exiting the final stage of the turbine. As illustrated, the conical guide 45 generally includes an expanding conical shape that has an axis along the rotor 112. Accordingly, the conical guide 45 has an increasing cross-sectional area, which allows the exiting steam to expand and, thereby, reduce its pressure. Particularly, the conical guide 45 has a cross-sectional diameter that increases as the distance from the flexible joint 44 increases. The conical guide 45 extends downstream and terminates at a flared lip 47. The flared lip 47 helps to smooth the flow and lessen the pressure of the steam into the toroidal section 42. As illustrated, the conical guide 45 may extend into the toroidal section 42 and/or rectilinear section 43. More specifically, the conical guide 45 may extend across approximately half the axial width of the toroidal section 42 and/or the rectilinear section 43. According to preferred embodiments, the inner boundary for the steam moving through the conical guide 45 may be provided by a cylindrical formed rotor plate 49. The cylindrical rotor plate 49 generally forms a smooth cylindrical shape that encloses the rotor and extends axially from the last stage of the turbine to the downstream wall of the toroidal diffuser 40. The axis of the rotor plate 49 also may be the rotor 112.
It has been discovered that the geometry of the toroidal section 42, according to the present invention, is effective at allowing the exiting steam to expand and reduce its pressure. These benefits are further enhanced by the combination of the toroidal section 42 and the conical guide 45. The toroidal diffuser 40, with the toroidal section 42 and/or the conical guide 45, is also effective at guiding the diffused steam to the outlet 46 with a minimum pressure loss. It will be appreciated that the outlet 46 need not be a down exhaust but can be a side or upwardly directed exhaust.
Apart from the increased performance due to the diffusion of the steam in a toroid on the steam exhaust side of the turbine, there are additional advantages. For example, the exhaust hood in prior conventional steam turbines is eliminated and there is no longer a need to support the inner casing and associated steam path parts, such as diaphragms from the exhaust hood. Cost reduction is also realized because an exhaust hood is no longer used to enclose the inner casing. Steam guides previously necessary are also entirely eliminated. Importantly, the inner casing and the toroidal diffuser of the turbine are each supported directly from the foundation of the turbine. To facilitate this, a flexible connection 44 (
From the above description of preferred embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof.
