US3176958A

US3176958A - Steam turbines

Info

Publication number: US3176958A
Application number: US253728A
Authority: US
Inventors: Ryall Michael Leslie
Original assignee: Pametrada
Current assignee: Pametrada
Priority date: 1962-02-12
Filing date: 1963-01-24
Publication date: 1965-04-06
Anticipated expiration: 1982-04-06
Also published as: GB1024844A; CH413867A

Description

M. L. RYALL STEAM TURBINES April 6, 1965 Filed Jan. 24, 1965 3 Sheets-Sheet 1 A ril 6, 1965 Filed Jan. 24, 1963 r M. L. RYALL STEAM TURBINES 3 Sheets-Sheet 2 April 6, 1965 M. L. RYALL 3,176,958

STEAM TURBINES Filed Jan. 24, 1965 3 Sheets-Sheet 3 United States Patent 3,17 6,958 STEAM TURBINES Michael Leslie Ryall, Glasgow, Scotland, assignor to Pametrada,-Wallsend, Northumberland, England Filed Jan. 24, 1963, Ser. No. 253,728 Claims priority, application Great Britain, Feb. 12, 1962, 5,340/ 62 5 Claims. (Cl. 253-39) This invention relates to steam turbine casings and diaphragms.

An object of the invention is to improve and simplify the construction of a turbine of the double-casing type, i.e. the type where in operation an annulus of steam surrounds an inner casing, and is in turn contained within an outer casing. Double casing turbines are frequently used in both land and marine practice, mainly to reduce distortion caused by difierential temperatures.

This invention consists in a steam turbine having an inner casing constituted by a piurality of axially abutting diaphragm rims and an outer casing surrounding the inner casing, wherein at least one passage, for instance a radial passage, is formed in one or more of the diaphragm rims leading from the interior of the inner casing to the exterior of the inner casing to provide communication with at least one steam bleed belt around the inner casing and within the outer casing.

The diaphragms may be formed in two parts with circumferentially abutting thickened rim and portions supported on axially-extending ledges in the outer casing, passageways being formed to provide communication between the upper and lower parts of the bleed belt. Using this arrangement, transverse alignment may be maintained by vertical'keys or webs on the vertical centre plane in the inside of the bottom part of the'outer casing. Axial alignment may be maintained by means of an annular flexible retaining seal ring fitted between a circumferential groove in the outer casing and the upstream face of the first diaphragm; this seal ring prevents the diaphragms from slidiiig'towardsthe inlet end of the turbine when the turbine is at rest whilst still allowing limited axial movement of the diaphragms due to thermal expansion, and also forms a pressure seal between the wheel-case pressure on the upstream side of the seal ring and the pressure within the space between the inner and outer casings on the downstream side of the seal ring.

The axially-extending ledges may be arranged such that, within certain limits, diaphragms of standard rim axial width and standard external diameter but embodying nozzles of any length may be fitted at any stage within the outer casing, whereby no modification of the outer casing is required regardless of the nozzle height in any given diaphragm. Thus, with very small alteration, if any, of the outer casing, a variety of turbine blade paths may be built up and a wide range of bleeding arrangements may be formed.

A proportion of said passages may be formed in the upper part of the diaphragm rim or rims and an exit opening provided in the lower part of the bleed belt so that the steam passes downwardly through the bleed belt.

The steam turbine may be provided with two or more bleed belts separated from one another by one or more annular seal rings in the annular space between the inner and outer casings. It is possible to nip the annular seal ring between the diaphragm rim so that the diaphragms abut each other by way of the seal ring, but the seal ring would have to dish sufiiciently to effect a seal at its periph ery whatever the transient distortion of the outer casing of the turbine. Thus it is found more convenient to lodge the inside edge of the seal ring in an annular groove defined between two adjacent diaphragm rims.

In the turbine shown in FIGURES 1 and 2, diaphragms' 1' are provided of the integral all-welded type, each made in two complementary parts with an external rim 2. The

rims in each part are dowelled so as to ensure that the upstream and downstream faces of the thickened portions 2- of the rims are accurately co-planar when assembled, and the parts are held together by two studs or bolts 3. The thickened parts of all the rims 2 are provided with radially projecting lugs 4a resting on a ledge 4 running axially along the inside of a cast outer casing 5. The lugs 4a ought ideally to have lower bearing surfaces in a plane containing the turbine axis in order to maintain alignment between the diaphragms and the rotor during temperature transients, but as the vertical thickness of the lugs 4a is small and as the temperature differences between the lugs 4a and the outer casing 5 are expected to be small, the lower bearing surfaces of the lugs 4:: may be somewhat displaced from a plane containing the turbine axis. Transverse alignment of the diaphragms is maintained by vertical keys 6 in the inside of the bottom half of the outer casing 5. The diaphragms are thus free to expand radially and axially, and when the turbine is running, the pressure drops across the diaphragms force the radial surfaces of the axially projecting rims of the diaphragms together to form a tight seal between each stage. The axial load applied from the sum of the pressure loadings across all the cliaphragms is carried bylan internal strengthened circumferential flange 7' on the cast outer casing.

The diaphragms are prevented from sliding axially towards the inlet end when the turbine is at rest by an annular seal ring 8 (made in two halves), which is carried in a circumferential groove in the outer casing; The seal ring is sufiiciently flexible to allow axial difierential expansion to occur between the diaphragm rims and the outer casing.

The seal ring 8 serves a second purpose, besides acting as an axial retainer for the diaphragms, by acting as a pressure seal between the steam in the casing upstream of the seal ring and the steam at some lower pressure in the annular space 9 downstream of the seal ring. The steam pressure in this annular space is the same as that of one stage downstream of the casing by virtue of a connection between the annular space and this stage provided by radial grooves 10 cut in the upstream side of the appropriate diaphragm rim. The steam bleed from any stage in the turbine may readily be obtained by cutting radial grooves in the upstream side of the rim of the diaphragm immediately downstream of the stage, to allow the bled steam to pass into the annular space 9, which will then be at the bled steam pressure. The bled steam can pass from the top half to the bottom half of the bleed belt through gaps or passages 4' through the lugs 4a on the rims, so that only one pipe connection 11 per bleed is necessary in the outer casing 5 and this connection 11 can be in the lower, fixed half of the casing 5.

When more than one bleed is required from the turbine, an extra annular seal ring or rings similar to 8 Patented Apr. 6, 1965 belt 9b through radial grooves and leaves the bleed belt 912 through a pipe connection 11b; steam is fed into the bleed belt 9a through radial grooves 10a and leaves the bleed belt 9a through a pipe connection 11a. The seal ring 8a is arranged to dish suificiently when steam pressure is applied to close a clearance, say of 0.002- 0.004 inch, between the inner edge portion of its downstream side and the upstream side of the downstream diaphragm rim. Otherwise, the steam turbine shown in FIGURE 3 is generally similar to that shown in FIG- URES 1 and 2, and the same reference numerals are used for like parts. a

The following are amongst the'advantageous features that can be achieved by arrangements embodying the present invention:

(1) The number of bleed belts can readily be altered to meet specific conditions of operation for which the turbine is designed.

(2) The outer casing diameter for a given mean blade diameter may be less' than that in double casing turbines with a horizontal joint, but not having the inner casing formed of a plurality of diaphragm rims. a

(3) No cast inner cylinder or inner cylinder insert are required and the amount of machining and fitting in the turbine can be reduced.

(4) The diaphragms are inherently stiff and virtually rigid at the outer rim due to the thick section of the outer rim and the horizontal joint, and this means that diaphragm deflections due to the steam loading are minimised.

(5) Distortion of the inner casing is minimised due to the composite nature of the casing.

(6) A wide range of diaphragms may be fitted within the outer casing with virtually no modification to the casing, thus providing'an ideal design for a standard turbine to cover a range of horse-powers, steam conditions and bleeding requirements;

I claim:

. 1. A steam turbine comprising an outer casing, axially extending ledges in the outer casing, a plurality of diaphragms supported in saidouter casing and having axially projecting rims providing abutting radial surfaces defining an inner casing and a steam zone between said outer and inner casings and isolated from a steamizone within said inner casing, each of said diaphragms being formed of two complementary parts, each of said parts having a flange mating with the flange of the correspond-; ing complementary part, said flanges having radially projecting abutting lugs slidably supported in said axially extending ledges, said abutting lugs having passages providing communication betweenthe portions of the outer steam zone on opposite sides of said lugs, means for transversely aligning the diaphragms, means providing communication between said inner and outer steam zones at a preselected stage and means for bleeding steam from said outer steam zone.

2. A steam turbine as claimed in claim 1, in which each of the rims includes a pair of oppositely axially directed projecting radial faces, the parts of said faces on one complementary part of a diaphragm being coplanar With the part of the corresponding face on the other complementary part of the said diaphragm and also with the cooperating abutting radial face of the adjacent diaphragm.

3. A steam turbine as claimed in claim 1, wherein the axially extending ledges are equidistant from each other and from the joint plane of the diaphragms whereby diaphragms of standardized diameter and lug thickness but embodying nozzles of any length, within a limited range, may be fitted at any stage within the outer casing so that no modification of the outer casing is required to accommodate nozzles of diiferent length.

4. A steam turbine as claimed in claim 1, comprising passages formed in the axially projecting diaphragm rims to allow communication between the outer steam zone and the inner steam zone, and an annular sealing ring in the outer steam zone to divide the same into steam bleed belts each connected by a separate passage to a separate stage of the turbine, and means in said outer casing for bleeding steam from said bleed belts.

5. A steam turbine as claimed in claim 4, comprising a groove in the outer casing and wherein the annular seal ring has its outer periphery located in the said groove and its inner periphery confined between adjacent diaphragm rims and is elastically deformable, so that its outer periphery seals by conforming to one or other edge of the groove. 7

References Cited by the Examiner UNITED STATES PATENTS 1,692,537 11/28 Baumann 253-69 2,247,378 7/41 Hinrichs 25 378 2,247,387 7/41 Johnson et al. 253-78 FOREIGN PATENTS 896,203 4/ 44 France. 726,982 10/42 Germany. 290,097 7/53 Switzerland.

JOSEPH H. BRANSON, IR., Primary Examiner.

Claims

1. A STEAM TURBINE COMPRISING AN OUTER CASING AXIALLY EXTENDING LEDGES IN THE OUTER CASING, A PLURALITY OF DIAPHRAGMS SUPPORTED IN SAID OUTER CASING AND HAVING AXIALLY PROJECTING RIMS PROVIDING ABUTTING RADIAL SURFACES DEFINING AN INNER CASING AND A STEAM ZONE BETWEEN SAID OUTER AND INNER CASINGS AND ISOLATED FROM A STEAM ZONE WITHIN SAID INNER CASING, EACH OF SAID DIAPHRAGMS BEING FORMED OF TWO COMPLEMENTARY PARTS, EACH OF SAID PARTS HAVING A FLANGE MATING WITH THE FLANGES OF THE CORRESPONDING COMPLEMENTARY PART, SAID FLANGES HAVING RADIALLY PROJECTING ABUTTING LUGS SLIDABLY SUPPORTED IN SAID AXIALLY EXTENDING LEDGES, SAID ABUTTING LUGS HAVING PASSAGES PROVIDING COMMUNICATION BETWEEN THE PORTIONS OF THE OUTER STEAM ZONE ON OPPOSITE SIDES OF SAID LUGS, MEANS FOR TRANSVERSELY ALIGNING THE DIAPHRAGMS, MEANS PROVIDING COMMUNICATION BETWEEN SAID INNER AND OUTER STEAM ZONES