US2511130A - Exhaust head of steam turbines - Google Patents

Description

June 13, 1950 M. H. L. SEDILLE ET AL 2,511,130

EXHAUST HEAD OF STEAM TURBINES Filed Aug. 9, 1945 2 Sheets-Sheet l INVENTOR m. 3141'"; SM 1 vwki. 1.5

June 13, 1950 M. H. 1.. SEDILLE ET AL 2,511,130

EXHAUST HEAD OF STEAM TURBINES Filed Aug. 9, 1945 2 Sheets-Sheet 2 Patented June 13, 1950 EXHAUST HEAD OF STEAM TURBINES Marcel Henri Louis Sdille and Marcel Georges Schwarz, Paris, France, assignors to Societc Rateau (Societe Anonyme), Paris, France, a

company of France Application August 9, 1945, Serial No. 609,870 In France July 16, 1942 2 Claims.

The connection between the last expansion stage of a steam turbine and the condenser under vacuum is effected generally by a curved member of complex shape providing for the passage of the turbine shaft and carrying fluid-tight packings. In the most general case the flow of steam elfects in the corresponding exhaust head a change in direction of 90 towards the bottom, going round the obstacle created by the packing box and the turbine shaft. It is of importance in order that the output of the turbine be not affected by this, that the flow of steam in the exhaust head be effected with a minimum of pressure losses between the outlet of the last wheel of the turbine and the inlet to the condenser. To this end numerous devices have been proposed comprising generally highly developed screens intended to canalise the different portions of the steam flow, or again an extension of the exhaust head in the axial direction in order to increase the radius of curvature of the fluid streams.

Exhaust heads constructed on these bases involve nevertheless substantial pressure losses, by reason of the increase in the frictional surfaces; they involve, moreover, increases in weight and in net cost which are often considerable.

The present invention eliminates to a large extent these difficulties, reduces the coefi'icient of pressure loss of an exhaust head of given dimensions, and ensures greater homogeneity of the fluid jet in the plane of the outlet flange of the head. It consists essentially in the provision of a row of deflecting blades disposed in the lower part of the head, in the zone where the radius of curvature of the fluid streams should be a minimum.

The following description having regard to the accompanying drawings will explain how the invention may be carried into effect.

Fig. 1 illustrates an exhaust head of current construction and Fig. 2 a section thereof through the horizontal joint, that is to say on the line IIII of Fig. 1.

Fig. 3 illustrates the distribution of the velocities in the plane of the outlet flange of an exhaust head of current construction, and Fig. 4 that of an exhaust head provided with an intermediate screen.

Fig. 5 illustrates the provision of a row of defleeting blades in conformity with a first constructional form of the invention, Figure 5a is a secillustrated in vertical section in Fig. 1 and in section through the horizotal joint in Fig. 2, will first be considered. The exhaust steam leaves the last wheel I) of the turbine following the direction of the arrows F, F by forming a jet of annular section; it is deflected by an elbow constituted by the walls of the exhaust head and leaves the latter through the horizontal flange a following the arrows F in the direction of the condenser. In its travel the fluid jet encounters different obstacles, in particular the shaft 0 of the turbine, as well as the indentation of the wall of the elbow intended for housing the packing box it and for the bearing 0. The fluid streams issuing from the upper part of the exhaust head, at F, cannot flow away in the vertical plane of symmetry, and must necessarily go around the housing of the shaft and of the packing box following the arrows F, F and F, F (Fig. 2). At the lower part, on the contrary the streams which follow the direction of the arrow F do not encounter any obstacle and tend to escape horizontally whilst coming away from the interior wall a of the elbow, then vertically. In a general way the fluid jet in the exhaust head does not have the characteristics of a flow in a, simple elbow at 90 of circular section, by reason of the obstacles which it encounters.

Experience shows that the distribution of the velocities in the plane of the outlet flange is very irregular, the equivelocity curves, numbered from 1 to 9.5 affecting generally the shape of a horseshoe as shown in Fig. 3; it is even very frequently the case that the inner part of the horseshoe comprises a zone of negative velocities (indicated at A by cross-hatching on Fig. 3) showing that a portion of the flow takes place in the opposite direction with the formation of a vortex (indicated schematically at F on Fig. 1). The shape of the field of velocities is explained by the presence of the obstacle encountered by the streams coming from the upper part, on the one hand, and by the defective curvature of the streams coming from the lower part, on the other hand. In these conditions, therefore, the desired damping of the velocity is not obtained, since the mean velocity in the section actually utilised of the exhaust flange is greater than would be obtained with a uniform distribution in the whole of the available outlet section. It likewise follows from this that the static pressure at the outlet of the turbine wheel is generally greater than that which prevails in the plane of the outlet flange of the exhaust head, when, by reason of the sections an exhaust headaof usual construction such as of passage altered. a less static pressure should be discounted, by reason of the damping of velocity which can be obtained.

The addition of two inwardly curved median partitions such as shown in dotted lines at f in Fig. 1 does not improve the above results, if this is a shape slightly different from the return zone of the fluid in the plane of the outlet flange of the head and of the equivelocity curves; Fig. 4 illustrates the results obtained in these conditions.

In conformity with the invention the uniform supply of the outlet section of the exhaust head, or at least the suppression or the return zones of the fluid, is obtained by arranging in the lower part only of the exhaust head an oblique grid or row comprising two or more blades disposed perpendicularly to the vertical plane of symmetry of the exhaust head, these blades having in section an inwardly curved aerodynamic profile. Fig. 5 illustrates schematically this arrangement, the deflecting blades g of the row being illustrated in section following the vertical plane of symmetry of the exhaust head, the angle [1, the pitch 1: and the width Z of the blades 9 of the grid being determined by known methods, taking into account the lift of the profile and the deflection diagram to be produced.

For a deflection of 90? which is necessary in the most frequent case, it may be necessary to utilise substantial coeflicients of lift, which may involve therisk of break-down of the flow along the blades; asecond form of construction of the deflecting-grid may, in conformity with Fig. 6 which is a view analogous to Fig. 5, be constituted by a series of deflection rows, for example 1 three, each one comprising a series of blades g g g each rowproviding for a part of the total deflection of the fluid.

Finally, a third form of construction of the deflecting grid may be constitutedby a succession of inwardly curved blades 9 offset in the direction of flow of the fluid as shown in Fig. 7, the angular position and the final position of the blades being, regulated by means of experiments with a model blower, in such a way that the distribution of velocities is uniform in the plane of the outlet flange of the exhaust head.

Experience shows that in this, way auniform distribution is obtained and,'providing there is a sufliciently large ratio of the section of the outlet flange to'the section of the fluid inlet, there is not only a decrease in the pressure losses in the head but also a recovery of the speed at the outlet of the last wheel'such that the static pressure in the outlet plane of the head is less than the 7 static pressure at the outlet of the last wheel of the turbine.

The general reduction in the pressure losses for the different streams of fluid passing through the head, likewise renders more uniform the static pressure at the different outlet points of the last turbine wheel; the result is therefore an improvement in the flow of steam in this latter, improving the thermodynamic output of the corresponding stage.

Independently of these first advantages, the condenser tubes, in the case of a surface condensation, are supplied in a uniform manner instead of being supplied by an irregular flux the section of which reproduces the field of velocities at the exhaust of usual exhaust heads; the result of this is an improvement in thermal exchanges between the steam to be condensed and the cooling water of the condenser. Finally, when the connecting sleeve between the exhaust head and the admission flange to the condenser is of diverging shape, there is obtained a better diffusion in this sleeve than if the flow at the inlet into the latter is not homogeneous.

Finally, the device in conformity with the invention permits for a given absolute pressure to the condenser, of increasing the usable thermal drop in the turbine, by reduction of the static pressure at the outlet of the last turbine wheel, and consequently an increase in the thermal output of this latter.

It is evident that modifications in detail may be made to the device above described without thereby departing from the scope of the invention.

What we claim is:

1. An exhaust head for conducting steam from a steam turbine to a condenser disposed laterally of said turbine, said head comprising an elbow conduit having an, inlet opening defining a plane perpendicular to the turbine axis and an outlet opening defining a plane parallel to the turbine axis, said conduit being formed to provide a reentrant boss extending toward said inlet opening, said boss having an opening to receive the turbine shaft, and a plurality of blades of airfoil section extending transversely of the turbine axis and being located adjacent that side only of the boss which is nearest the outlet opening, whereby said blades deflect only that part of the exhaust steam which follows the path of least radius in flowing from the inlet opening to the outletopening, said blades being arranged in a plurality of rows, spaced in the direction of flow of steam.

2. An exhaust head for conducting exhaust steam from a steam turbine to a condenser disposed laterally of said turbine, said head comprising an elbow conduit having an inlet opening in a plane substantially perpendicular to the turbine axis and adapted to deflect laterally the flow of exhaust steam, said conduit being formed to provide a reentrant boss extending towards said inlet opening, said boss having an opening to receive the turbine shaft, and a plurality of curved blades of airfoil section extending transversely of the turbine axis and spaced apart in that portion solely of said conduit which is confined between the innermost portion of said boss and the curved wall of least radius of the said conduit which faces said innermost portion of said boss, so as to leave a wholly unobstructed zone in the other portions of said conduit which extend on bothsides of said boss. I

MARCEL HENRI Lou s SED ILLE. MARCEL GEORGES SCHWARZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number I Name Date 1,269,998 Baurnann June 18, 1918 1,302,282 Baumann Apr. 29, 1919 1,626,849 Luclie May 3, 1927 1,723,104 Warren et a1 Aug.'6, 1929 1,723,110 Wirt Aug. 6, 1929 1,814,629 Hanzlik July 14, 1931 2,296,023 Dauenbach et al. -sept. 15, 1942

Images