U.S. patent application number 11/243974 was filed with the patent office on 2007-04-12 for steam turbine exhaust diffuser.
This patent application is currently assigned to General Electric Company. Invention is credited to Edward Sharrow.
Application Number | 20070081892 11/243974 |
Document ID | / |
Family ID | 37395898 |
Filed Date | 2007-04-12 |
United States Patent
Application |
20070081892 |
Kind Code |
A1 |
Sharrow; Edward |
April 12, 2007 |
Steam turbine exhaust diffuser
Abstract
An axial flow steam turbine includes an exhaust diffuser in the
form of a volute for diffusing the exhaust steam and turning the
exhaust steam from a generally axial flow direction to a generally
radial direction. The volute exit may be at the bottom or to one
side of the steam turbine. The volute and casing are independently
mounted relative to one another on a foundation with a flexible
joint therebetween.
Inventors: |
Sharrow; Edward; (Scotia,
NY) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
37395898 |
Appl. No.: |
11/243974 |
Filed: |
October 6, 2005 |
Current U.S.
Class: |
415/211.2 |
Current CPC
Class: |
F01D 25/28 20130101;
F05D 2220/31 20130101; F01D 25/30 20130101 |
Class at
Publication: |
415/211.2 |
International
Class: |
F01D 9/00 20060101
F01D009/00 |
Claims
1. An axial flow steam turbine flow path comprising: a rotor and a
casing defining the axial steam flow path; and an exhaust diffuser
for the turbine including a volute for diffusing the exhaust steam
and turning the exhaust steam from a generally axial flow direction
to a generally transverse and tangential direction.
2. A flow path according to claim 1 wherein said volute has an axis
generally parallel to an axis of the flow path.
3. A flow path according to claim 1 wherein said exhaust diffuser
and said casing are independently mounted relative to one another
on a foundation.
4. A flow path according to claim 1 including a flexible joint
between said exhaust diffuser and said casing.
5. A flow path according to claim 1 wherein said volute has an axis
generally parallel to an axis of the flow path, said volute
terminating in an outlet facing in a downward, upward or transverse
direction.
6. A flow path according to claim 1 wherein said volute has an axis
generally parallel to an axis of the flow path, said exhaust
diffuser and said casing being independently mounted relative to
one another on a foundation.
7. A flow path according to claim 6 including a flexible joint
between said exhaust diffuser and said casing.
Description
[0001] The present invention relates to steam turbines and
particularly relates to an exhaust diffuser in the shape of a
volute.
BACKGROUND OF THE INVENTION
[0002] In prior steam turbines, the inner case of the steam
turbine, for example 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 outlet from the turbine is generally conically
shaped and the steam exhaust is redirected from a generally axial
extending flow direction to a flow direction 90.degree. relative to
the axial flow direction. This 90.degree. flow direction may be in
any plane, downwardly, upwardly or transversely. Thus the prior
exhaust hoods for steam turbines constitute a large rectilinear
structure at the exit end of the conical section for turning and
diffusing the steam flow at right angles. The steam flow path was
thus tortuous resulting 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 necessitated 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.
BRIEF DESCRIPTION OF THE INVENTION
[0003] In a preferred embodiment of the invention, there is
provided an axial flow steam turbine flow path comprising: a rotor
and a casing defining the axial steam flow path; and an exhaust
diffuser for the turbine including a volute for diffusing the
exhaust steam and turning the exhaust steam from a generally axial
flow direction to a generally transverse and tangential
direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a fragmentary schematic illustration of half of a
double flow down exhaust steam turbine according to the prior
art.
[0005] FIG. 2 is a fragmentary side cross-sectional view of a steam
turbine illustrating an exhaust diffuser having a volute
configuration; and
[0006] FIGS. 3 and 4 are axial end views of two embodiments of
volutes which may be employed to receive the exhaust steam from the
steam turbine.
DETAILED DESCRIPTION OF THE INVENTION
[0007] Referring now to the drawings, particularly to FIG. 1 there
is illustrated a portion of a steam turbine, generally designated
10, including a rotor 12 mounting a plurality of turbine buckets
14. An inner casing 16 is also illustrated mounting a plurality of
diaphragms 18. A centrally disposed generally radial steam inlet 20
applies steam to each of the turbine buckets and stator blades on
opposite axial sides of the turbine to drive the rotor. The stator
vanes of the diaphragms 18 and the axially adjacent buckets 14 form
the various stages of the turbine forming a flow path and it will
be appreciated that the steam is exhausted from the final stage of
the turbine for flow into a condenser not shown.
[0008] Also illustrated in FIG. 1 is an outer exhaust hood 22 which
surrounds and supports the inner casing of the turbine as well as
other parts such as the bearings. In the illustration of FIG. 1,
the turbine includes steam guides 24 for guiding the steam
exhausting from the turbine into an outlet 26 for flow to one or
more condensers. With the use of an exhaust hood supporting the
turbine, bearings and ancillary parts, the exhaust steam path is
tortuous and subject to pressure losses with consequent reduction
in performance and efficiency.
[0009] Referring now to FIG. 2, there is illustrated an aspect of
the present invention wherein like reference numerals as in FIG. 1
are applied to like parts preceded by the numeral 1. As
illustrated, the exhaust hood 22 of the prior art is completely
eliminated in favor of a volute diffuser 40. The diffuser 40
includes a diffusing conical section 42 coupled to the inner casing
116 by a flexible joint 44. The volute 40 has an axis parallel to
the axis of rotation of the rotor 112. The axis of volute 40 is
generally perpendicular to the direction of the general spiral flow
about the axis and through the volute. Consequently, the exhaust
steam flowing substantially in an axial direction from the final
stage of the turbine flows into the volute 40 where it changes its
flow direction by about 90.degree.. Additionally, by using the
volute 40, the geometry of the volute enables the steam to expand
reducing its pressure. The volute 40 also guides the diffused steam
through an outlet 46 coupled to one or more condensers, not shown.
As illustrated in FIG. 3, the volute 40 includes an internal
passage 48 which increases in cross-sectional area in a direction
toward the outlet 46 thereby diffusing the exhaust steam. It will
be appreciated that the exit or outlet 46 need not be a down
exhaust but can be a side or upwardly directed exhaust. In either
configuration, a single volute can exhaust a single flow steam
turbine or a pair of volutes may exhaust steam from double flow
steam turbines. In FIG. 4, a double walled volute is illustrated
having a divider wall 50 forming a pair of diffuser exit
passages.
[0010] Apart from the increased performance due to the diffusion of
the steam in a volute on the steam exhaust side of the turbine,
there are additional advantages. For example, the exhaust hood in
prior conventional steam turbines is entirely 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. Also the overall dimensions of
the turbine are reduced. Steam guides previously necessary are also
entirely eliminated. Importantly, the inner casing and the volute
of the turbine are each supported directly from the foundation of
the turbine. To facilitate this, a flexible connection 44 (FIG. 2)
is provided between the inner casing and the volute 40. The
flexible connection may be of many different types such as an
expansion bellows to allow for differential thermal expansion.
Further, the previously utilized exhaust hood is no longer
necessary for the support of the turbine bearings. As illustrated
in FIG. 2, the bearings 54 may be supported on stanchions 56 in
turn directly supported by the foundation of the turbine. Thus, the
stanchions provide a rigid support for the bearings with improved
turbine reliability as a result. The volute may be formed of a
composite material, steel plate or pipe, structural steel,
fiber-reinforced plastic or any combination of these materials to
obtain the required structural integrity and desired steam flow
diffusion characteristics.
[0011] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
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