EP0156619B1

EP0156619B1 - Blade ring for a steam turbine

Info

Publication number: EP0156619B1
Application number: EP85301915A
Authority: EP
Inventors: Lewis J. Miller
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1984-03-23
Filing date: 1985-03-19
Publication date: 1988-09-28
Also published as: JPH0373721B2; KR850007838A; ES541438A0; JPS60212604A; ES8607476A1; EP0156619A1; IN162366B; DE3565299D1; KR930008675B1

Description

This invention relates to steam turbines and in particularto steam turbines with inner casings and blade rings.
High pressure steam turbines are built with an outer casing, an inner casing disposed within the outer casing and supported from the outer casing, and blade rings supported within the inner casing.
An inner casing is provided to better accommodate the high pressures and temperature of the inlet steam which are especially high near the inlet axial end of the steam expansion path. Although such intermediate inner casing greatly reduces the stresses to which the turbine casing is exposed, it does require a substantial amount of space necessitating a larger-diameter outer casing and therefore is relatively expensive.
As shown for example in DE-A-2003954, the blade ring structure is generally diverging in steam flow direction to provide an increasing steam flow passage as the steam is expanding during its flow through the turbine. In turbines accommodating large steam pressure differentials the expansion stages and in accordance therewith the blade ring structures are relatively long and therefore of substantial outer diameter at their downstream ends and as a result the inner casings in which the blade ring structures are generally supported and also, of course the outer casings in which the inner casings are supported need to be of relatively large diameters.
It is, however, also known from Swiss Patent No. 435,319 to provide in a steam turbine a blade ring structure which slightly project by and the inner housing and the projecting end portion is directly supported by the outer housing.
It is the principal object of the present invention to provide a turbine design with inner casing and a blade ring within the inner casing which has the advantages of a turbine without inner casing as well as the reduced stress exposure of turbines with inner casing.
With this object in view, the present invention resides in a steam turbine comprising an outer horizontally split cylindrical casing, an inner cylindrical casing disposed within the outer casing and supported from the outer casing and a blade ring partly disposed within the inner casing and surrounding a turbine rotor, said blade ring having a lower pressure end portion projecting axially from said inner casing and a higher pressure and portion disposed within said inner casing, said axially projecting lower pressure blade ring portion being provided with integral support arms which extend radially outward to, and are directly supported on the outer casing, characterized in that said inner cylindrical casing is horizontally split and said blade ring is a divergent one and only the higher pressure end portion of said blade ring which is of a relatively small diameter is disposed in said inner casing.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a prior art steam turbine with upper casings, and various upper rings removed;
Figure 2 is a partial sectional view taken on line II-II of Figure 1;
Figure 3 is a partial plan view of a steam turbine, with upper casings and various upper rings partially removed, made in accordance with this invention; and
Figure 4 is a partial sectional view taken on line IV-IV of Figure 3.

Figures 1 and 2 are indicated as prior art and show a steam turbine 103 which is designed for the same operating temperature, pressure and steam throughput as the turbine 3 shown in Figures 3 and 4 and made in accordance with this invention. Reference numerals with a 100 prefix in the prior art, Figs. 1 and 2 indicate parts similar to those indicated by the reference numeral without the prefix in Figs. 3 and 4.
The turbine 3 comprises a horizontally split cylindrical outer housing or casing 5 held together by bolts 7, a horizontally split cylindrical inner housing or casing 9 held together by bolting 11 and disposed within the outer casing 5 and supported from the outer casing 5 by supports 13. Disposed partially within the inner casing 9 and partially within the outer casing 5 is a longitudinally split blade ring 15 which is also held together by bolting 17. The blade ring 15 is supported on an arm 19 which extends outwardly to and is supported by the outer casing 5. The blade ring 15 has a plurality of circumferential grooves 21 which receive annular arrays of stationary blades forming rows of stationary blades 23.
A rotor 25 having a plurality of annular arrays of rotating blades forming rows of rotating blades 27 is disposed within the blade ring 15 and the rows of rotating blades 27 interdigitate with the rows of stationary blades 23.
A nozzle block 29 and nozzle chamber 31 are disposed on one end of the blade ring 15 and within the inner casing 9for admitting steam to the blade path. Also disposed within the inner casing 9 is a dummy ring 33 which cooperates with an integral balance disc 35 on the rotor to balance the thrust produced by the steam acting on the rotating blades and rotor.
Supporting the blade ring 15 from the outer casing 5 rather than from the inner casing advantageously increases the resisting momentum acting on the blade ring thus reducing the stresses, support is moved to a lower temperature region lowering the material requirements and raising the allowable stresses; reduces inner and outer casing overall diameter, wall thickness and bolting requirements; and reduces inner casing support size as loading from the blade ring is transmitted directly to the outer casing, thus producing savings in material, manufacturing and handling.

Claims

A steam turbine comprising an outer horizontally split cylindrical casing (5), an inner cylindrical casing (9) disposed within the outer casing (5) and supported from the outer casing (5), and a blade ring (15) partly disposed within the inner casing (9) and surrounding a turbine rotor (25), said blade ring (15) having a lower pressure end portion projecting axially from said inner casing (9) and a higher pressure end portion disposed within said inner casing, said axially projecting lower pressure blade ring portion being provided with integral support arms (19) which extend radially outward to, and are directly supported on the outer casing (5), characterized in that said inner cylindrical casing (9) is horizontally split and said blade ring (15) is a divergent one and only the higher pressure end portion of said blade ring (15) which is of a relatively small diameter is disposed in said inner casing (9).