Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Plural rigidly related blade sets
Reexamination Certificate
2001-12-26
2004-08-03
Verdier, Christopher (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Plural rigidly related blade sets
C415S200000, C416S190000, C416S191000, C416S22300B, C416S24100B, C416S243000, C416SDIG002, C416SDIG005
Reexamination Certificate
active
06769869
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to steam turbines. In particular, the invention relates to the configuration of the turbine blades for a steam turbine.
DESCRIPTION OF THE RELATED ART
With recent turbines, there has been a tendency to use longer blades in the final turbine stage and in the turbine stages upstream of the final stage to economise on fuel and operate more efficiently.
For example,
FIG. 10
shows a 700,000 kW-output class steam turbine in which long blades have been adopted in the final turbine stage and the turbine stages upstream of the final turbine stage. This is an axial flow type turbine in which multiple stages
5
are located serially in the turbine-driving steam flow along the axial direction of turbine shaft
2
that is housed in turbine casing
1
. Each stage
5
comprises a set of fixed turbine nozzle blades
3
, and a downstream adjacent set of turbine moving blades
4
.
The turbine nozzle blades
3
of each stage are aligned in the circumferential direction around the turbine shaft
2
with their outer ends supported by an outer diaphragm
6
, which is fixed in the turbine casing
1
, and their inner ends supported by an inner diaphragm
7
adjacent the turbine shaft
2
. A seal
7
a
carried by the inner diaphragm
7
seals inner diaphragm
7
to rotating shaft
2
.
The turbine moving blades
4
of each stage are circumferentially aligned around turbine shaft
2
, adjacent and downstream of the turbine nozzle blades
3
of that stage. Each turbine moving blade extends radially from the shaft
2
and has a blade embedded portion
8
embedded in the shaft
2
, a blade effective portion
9
from root to tip and a blade tip connecting portion
10
. The blade effective portion
9
is the part of the blade that does the actual work (generates rotational torque) when the turbine driving steam passes through the turbine moving blades.
The turbine moving blades
4
are provided with intermediate connectors
11
in the intermediate parts of the blade effective portions
9
, which serve to stabilize the effective portions
9
of the entire set of blades. The intermediate connectors
11
comprise, as shown in
FIG. 11
, bosses
11
a
and
11
b
on the respective backs (“suction side” or “suction surface” as it is commonly called),
9
c
and
9
d
, and bellies (“pressure side” or “pressure surface” as it is commonly called),
9
e
and
9
f
, of one blade effective portion
9
a
and the adjacent blade effective portion
9
b
. A linking sleeve
11
c
pivotally interconnects bosses
11
a
and
11
b
via lugs (not shown) provided at both ends of bosses
11
a
and
11
b
. Thus, vibration of the intermediate portions, induced by such factors as fluctuations over time of the jet force of the turbine driving steam flowing from the turbine nozzle blades
3
, and turbine shaft vibration, is suppressed to a low level.
The tips of turbine moving blades
4
are stabilized by blade tip connectors
10
which are formed, for example, as so-called “snubber type” plate-shaped extension pieces
10
a
and
10
b
integrally cut from the blade effective portion
9
, as shown in FIG.
12
. During operation, blade tip vibration is suppressed using the mutual contact friction of the extension pieces
10
a
and
10
b.
The above-described arrangement of intermediate connectors
11
and blade tip connectors
10
provides effective countermeasures against vibration induced by such factors as variation over time of the turbine driving steam jet force, in turbines having long blades. However, in a prior art steam turbines (shown in FIG.
10
), with long blades in which the blade effective portions
9
of the turbine moving blades
4
exceed 1 m, many other problems arise because of the blade length. One of these is that, during operation, the throat•pitch ratio (S/T) varies as a consequence of deformation of the blade warp configuration due to centrifugal force, resulting in a reduction of aerodynamic efficiency.
Attempts have been made in the prior art to address this problem by adopting the so-called “simplified three-dimensional blade design method”. In this method, the cross-sectional shape of the turbine moving blade is varied to correspond to the fact that the equivalent velocity diagram had been largely changed in the height direction of the passage. However, if the turbine moving blades
4
of the steam turbine are long, as shown in
FIG. 13
, the inlet flow angle of the turbine driving steam relative to the turbine blade will vary greatly along the blade effective portion
9
from the blade root to the blade mean diameter (pitch circle diameter), to the blade tip.
In
FIG. 13
, &agr; indicates the inlet flow angle of the turbine driving steam to the turbine moving blade
4
, BV the turbine driving steam inlet flow speed vector flowing into the turbine moving blade
4
, SV the turbine driving steam outlet flow speed vector flowing out of the turbine nozzle blades (not shown) and U the peripheral speed, respectively. Also, the subscripts R, P and T indicate the respective blade root, blade mean diameter (pitch circle diameter) and blade tip position.
In this case, there is a requirement to modify the blade cross-sectional shapes at each of the blade root, the blade mean diameter and the blade tip positions of the blade effective portion
9
to correspond to the turbine driving steam inlet flow angles &agr;
R
, &agr;
P
and &agr;
T
at each position. However, as a prerequisite for that, first there is a requirement to find turbine driving steam inlet flow speed vectors BV
R
, BV
P
and BV
T
at each position.
Turbine driving steam inlet flow speed vectors BV
R
, BV
P
and BV
T
at each position can be found from equivalent velocity diagrams composed of outlet flow speeds SV
R
, SV
P
and SV
T
of the turbine driving steam flowing out from the blade root, the blade mean diameter and the blade tip positions of the turbine nozzle blades, and the circumferential speed vector (the turbine shaft circumferential speed component) determined by the radius and angular rotational speed at each position (the angular rotational speed of course being constant, independent of radial position).
For turbine driving steam inlet flow speed vectors BV
R
, BV
P
and BV
T
at the various positions found from equivalent velocity diagrams, the inlet flow angles can vary. For example, the inlet flow angle &agr;
R
at the blade root typically is in the range of about 30° to about 50° while the inlet flow angle &agr;
T
at the blade tip typically is in the range of about 140° to about 170°, and their angular difference may be a maximum of about 140°. This large angular difference is due to the fact that the radial position of the blade tip (measured from the turbine shaft axis of rotation) is at least twice that of the blade root, and, proportionally, the circumferential speed component at the blade tip is at least twice that at the blade root.
If the turbine moving blade is not modified to compensate for this large variation in the inlet flow angle in the radial direction, aerodynamic loss will markedly increase. Therefore, prior art steam turbines were modified by varying the twist angle of the blade cross-section to conform it to the turbine driving steam inlet flow angles &agr;
R
, &agr;
P
and &agr;
T
at the various positions on the blade effective portion
9
; and, moreover, the blade cross-sectional shape close to the leading edge was modified in the direction of the inlet flow speed vector.
FIG. 14
is a drawing of a circumferential direction cross-section at any height of the turbine moving blade row, developed on a plane, and shows the configuration of the turbine moving blade steam passage. S is the throat, and indicates the width of the narrowest part in the inter-blade steam passage formed between the back of one blade and the belly of the next turbine moving blade. T is the pitch, that is the gap between turbine moving blades in the circumferential direction. The throat•pitch ratio (S/T) is an aerodynamic design parameter that does not depend on the size of the stea
Sakamoto Taro
Tanuma Tadashi
Foley & Lardner LLP
Verdier Christopher
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