Rotary kinetic fluid motors or pumps – Selectively adjustable vane or working fluid control means
Reexamination Certificate
1999-08-03
2001-07-17
Ryznic, John E. (Department: 3745)
Rotary kinetic fluid motors or pumps
Selectively adjustable vane or working fluid control means
C415S211200
Reexamination Certificate
active
06261055
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to steam turbines and more particularly to annular diffusers for the exhaust from such turbines. More particularly still, this invention relates to annular flow diffusers located at the exit from condensing steam turbines, such diffusers being defined in most cases by an outer flow guide and, for the most part, either a separate inner flow guide or a bearing cone beginning immediately after the last row of turbine blades and ending at the location of the entrance of the exhaust steam into the main structure of the exhaust hood. The inner or outer flow guides, or both, may be adjustable guide vanes.
2. Description of the Prior Art
In condensing steam turbines used in power generation, steam leaving the last row of turbine blades flows, generally, through an annular outwardly flared passage, known as a diffuser, positioned between the turbine enclosure, or casing, and the exhaust hood proper. Such diffuser is defined by an outwardly flared flow guide extending from the turbine casing, to which it is customarily fastened, for 360 degrees circumferentially about the turbine shaft, and an inner flow guide formed at least in part by the outer surface of the bearing cone or in some cases a separate flow guide, or in case of steam turbines equipped with an adjustable guide vane which at least partially surrounds the bearing cone, mainly by the outer surface of the adjustable guide vane. The steam passes from the diffuser into the body of a collector or “exhaust hood” and subsequently discharges from the exhaust hood into a condenser. The most prevalent type of exhaust hood is one located directly above the condenser, or a “downward-discharging” exhaust hood.
The so-called “diffuser” located between the exit from the last turbine blades and the exhaust hood per se is customarily formed from two annular surfaces which guide the exhausting steam from the turbine itself into the exhaust hood, meanwhile, in well-designed diffusers, because of its increasing cross-sectional areas, diffusing, or decelerating, the exhaust steam passing therethrough. This deceleration causes a decrease in the kinetic energy of the steam plus an increase in pressure, the net effect being that the inlet to the diffuser assumes the lowest pressure of the path from the turbine to the condenser so that the steam exhausts from the last turbine blades into a minimum pressure zone thus increasing the velocity of steam flowing through the blades and increasing the energy available to the turbine to do work.
In a typical arrangement, as indicated above, the upper surface of the bearing cone, or of the adjustable guide vane as the case may be, constitutes most of or the entire inner annular surface of the diffuser and the inner surface of an outer flow guide constitutes the outer annular surface having the overall contour or configuration necessary to direct steam into the exhaust hood. The length of a downward-discharging exhaust hood, measured along the axis of a steam turbine, is limited by the bearing span of the turbine. As a result, steam leaving the last row of blades of a turbine must have its direction changed from mainly horizontal to essentially vertical in a relatively short distance which varies about the circumferential extent of the diffuser, but is relatively short at all points. This places a limit on the length of the diffuser located at the turbine exit, since it is inadvisable to have sharp turns in a diffuser such as might be necessary particularly at the top of the turbine in order to extend the diffuser, because sharp turns are known to cause flow separation with resultant eddies and energy losses. In steam turbines built in the U.S.A. the ratio of the length of the diffuser to its height at inlet is customarily quite small, usually being close to one, and often even smaller. To produce a certain amount of diffusion, turbine designers build diffusers having rather large (inlet-to-exit) area ratios. Such designs are, in general, based on information available from studies of flow in diffusers having uniform and incompressible flow at the inlet.
It is desirable to have a large amount of diffusion, or pressure rise, in a diffuser of a steam turbine, because, for any given condenser pressure, there is then produced a lower pressure at the entrance to the diffuser and thus at the exit from the last row of turbine blades, thus increasing the energy available to the turbine to do work and also improving performance of the last row of blades when condenser pressure is higher than the pressure assumed in design of the turbine, thus increasing turbine efficiency. The amount of diffusion a diffuser can produce, however, is limited by the (longitudinal) pressure gradient, the average overall pressure gradient being the ratio of the pressure rise to the length of the diffuser. Such pressure rise in turn depends on the exit-to-inlet area ratio of the diffuser. If the pressure gradient becomes too large, i.e. the walls of the diffuser diverge to steeply, the steam flow will become separated from the walls of the diffuser and the amount of diffusion can be seriously reduced or even entirely eliminated.
Since a diffuser in a bottom condensing steam turbine is of necessity short relative to its height at its inlet, if it is not to be sharply curved, the amount of diffusion which it can produce is, therefore, correspondingly limited. This is especially so for diffusers in which the flow over a large portion is in predominantly an axial direction, that is, in the direction of the axis of the turbine, which as explained is usually desirable.
The flow entering a diffuser located downstream from a last blade row of a turbine has many wakes in it, these being necessarily formed at the trailing edges of blades by the deceleration of flow passing closely to the blade surfaces. Such wakes can be produced by both fixed blades of the turbine and the rotating blades (as well as shrouds on the blades plus any supporting struts interposed in the flow, or tie- or lacing-wires, if any). It is the wakes from the last rotating blades that exert most influence on the flow in the diffuser, any prior wakes having been largely dispersed into the general flow by such terminal blades. Each moving blade provides a wake, i.e. in the typical large turbine, as many as a hundred or more wakes are present. In this respect the actual flow in a diffuser located downstream of a condensing steam turbine differs from the rather thoroughly studied and relatively well understood diffuser flow in which flow at the inlet to the diffuser is uniform. In steam turbines these wakes are especially thick when the turbine operates at condenser pressures higher than the design condenser pressure because under such conditions the boundary layer flow passing over and from the surfaces of the last turbine blades is either on the verge of separation or is partially separated from the blade surfaces.
3. Description of Related Art
The following prior articles contain discussions or disclosures of phenomena and considerations having a bearing upon the present invention.
1. P. G. HILL, U. W. SCHAUB, Y. SENOO: “Turbulent Wakes in Pressure Gradient,” Transactions ASME, Journal of Applied Mechanics, vol. 85, Series E, pp.518-524, December 1963.
2. R. W. FOX, S. J. KLINE: “Flow Regimes in Curved Subsonic Diffusers” Transactions ASME, Journal of Basic Engineering, vol. 84, Series D, pp. 303-316, September 1962.
3. J. R. HENRY, C. C. WOOD, S. W. WILBUR: “Summary of Subsonic-Diffuser Data,” NACA RM L56F05, 1956.
4. G. SOVRAN, E. D. KLOMP: “Experimentally Determined Optimum Geometries for Rectilinear Diffusers With Rectangular, Conical or Annular Cross Section,” in: Fluid Mechanics of Internal Flow, Elsevier Publishing Company, Amsterdam, Netherlands, 1967, (FIG. 17 on page 291, and Appendix B on pages 311 and 312).
5. J. H. G. HOWARD, A. B. THORNTON-TRUMP, H. J. HENSELER: “Performance and Flow Regimes for Annular Diffusers,” ASME Paper 67-WA/FE-21, 1967.
6. M. Ye. DEICH, A. Ye. ZARYANKIN: “Gas Dynami
Ryznic John E.
Wilkinson Charles A.
LandOfFree
Exhaust flow diffuser for a steam turbine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exhaust flow diffuser for a steam turbine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exhaust flow diffuser for a steam turbine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2545940