Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Plural distributing means immediately upstream of runner
Reexamination Certificate
1999-04-23
2001-03-20
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Plural distributing means immediately upstream of runner
C415S195000, C415S213100, C415S216100, C415S221000, C415S229000
Reexamination Certificate
active
06203274
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a steam turbine and, in particular, to a high-temperature, high-pressure, high-output, high/low-pressure integrated steam turbine.
DESCRIPTION OF RELATED ART
Prior-Art Technique (1)
Technical difficulties, particularly those relating to countermeasures against shaft rotation, ensure that it is not yet possible to implement a practicable high/low-pressure integrated steam turbine which has a rated power of at least 100 MW under steam conditions of a primary steam pressure of at least 100 kg/cm
2
and a primary steam temperature of at least 500° C., and which has a downward-exhaust type of turbine exhaust with rotor blades of an effective blade length of at least 36 inches rotating at 3000 rpm or rotor blades of an effective blade length of at least 33.5 inches rotating at 3600 rpm (hereinafter referred to as “high-temperature, high-pressure, high-output conditions”); and which also has a high-pressure portion, an intermediate-pressure portion, and a low-pressure portion (or just a high-pressure portion and a low-pressure portion) on a turbine rotor formed of a single rotor shaft supported by two journal bearings, wherein all of these components are accommodated within an integral casing (hereinafter referred to as “single turbine rotor condition”).
A prior-art high/low-pressure integrated steam turbine that satisfies the “high-temperature, high-pressure, high-output conditions” but does not satisfy the “single turbine rotor condition” utilizes a method such that a rotor
111
of high- and intermediate-pressure portions
103
and
104
, or a single high-pressure portion, and a rotor
112
of a low-pressure portion
105
are each formed separately and each is accommodated within separate casings
106
and
107
, and these rotors
111
and
112
are joined together by a coupling
113
, as shown in
FIGS. 11 and 13
.
With a prior-art high/low-pressure integrated steam turbine that does not satisfy the “high-temperature, high-pressure, high-output conditions” but does satisfy the “single turbine rotor condition,” it is possible to set a comparatively high stiffness for the shaft linkage, so that two bearings
1
and
11
can be disposed each on foundation portions
10
and
12
, as shown in FIG.
12
.
Prior-Art Technique (2)
With a prior-art high/low-pressure integrated steam turbine that does not satisfy the “high-temperature, high-pressure, high-output conditions” but does satisfy the “single turbine rotor condition,” the output power is small because of the lower primary steam pressure and temperature, so the bearing span is comparatively short and therefore the bearing load is distributed suitably between the front bearing disposed at the high-pressure side of the high/low-pressure integrated steam turbine and the rear bearing disposed at the low-pressure side thereof, which means that it is possible to design a turbine that is stable with respect to shaft vibration.
Prior-Art Technique (3)
As previously mentioned, the technical difficulties involved with a high/low-pressure integrated steam turbine that satisfies both the “high-temperature, high-pressure, high-output conditions” and the “single turbine rotor condition” ensure that it is not yet possible to implement such a turbine in practice.
A prior-art steam turbine has a multiple casing formed of a plurality of casings, as shown in
FIG. 11
, with each of the high/intermediate-pressure rotor (or high-pressure rotor) and the low-pressure rotor having two bearings. Alternatively, three bearings are provided for the two rotors which are in a coupled state, as shown in FIG.
13
. In such a multiple-casing steam turbine, the bearing span of each rotor is shorter than that of a high/low-pressure integrated steam turbine and thus the stiffness thereof is extremely high, so it is possible to ensure favorable characteristics for shaft vibration, even when the number of turbine stages configured of paired static and rotating turbine blades is increased and thus the bearing span increases slightly.
Prior-Art Technique (4)
As previously mentioned, the configuration of a steam turbine in the prior art that satisfies the “high-temperature, high-pressure, high-output conditions” is as shown in
FIG. 11
or FIG.
13
. Alternatively, a downward-exhaust type of high/low-pressure integrated steam turbine has a conical shape of the exhaust chamber that is of a form called a linear circular-cone shape, as shown in FIG.
12
.
Prior-Art Technique (5)
The configuration of another steam turbine in the prior art that satisfies the “high-temperature, high-pressure, high-output conditions” has a conical shape of the exhaust chamber that is of a form called a linear circular-cone shape (see FIG.
12
), wherein the axial length L of the exhaust chamber is increased so that the shape of the exhaust chamber is such that the ratio L/D is greater than 0.5, as shown in
FIG. 17
, with the object of ensuring the exhaust efficiency.
Prior-Art Technique (6)
The configuration of yet another steam turbine in the prior art that satisfies the “high-temperature, high-pressure, high-output conditions” has a conical shape of the exhaust chamber that has a vertical cross-section of a form called a linear circular-cone shape, as shown in FIG.
12
.
Technical Problem (1)
With a turbine wherein the conditions of the steam flowing into the steam turbine are a high temperature and a high pressure generally leads to an increase in the number of stages, increasing the output power generally causes an increase in the number of stages. This means that, with a high/low-pressure integrated steam turbine using a single turbine rotor supported by two journal bearings, the bearing span generally increases as the power output increases.
With a high/low-pressure integrated steam turbine, all of the stages from the high-pressure side to the low-pressure side are provided on a single rotor, so the length of that single rotor is increased. If the rated output is increased by making the steam conditions of the in-flowing primary steam (main steam) a high temperature and a high pressure, therefore, which makes the design difficult from the vibration viewpoint because the ratio S/Do of the bearing span S and the outer diameter Do of the rotor shaft increases, leading to a reduction in the stiffness of the shaft and a tendency for the eigenvalue of the shaft assembly to drop. In addition, the steam flowrate also generally increases, so that the lengths of the longer blades in the final stages increase, thus increasing the additional weight which is a factor in the drop of the eigenvalue of the shaft assembly, which means that a high level of technical skill is necessary to ensure favorable vibration characteristics.
In particular, when it comes to implementing a high-temperature, high-pressure, high-output, high/low-pressure integrated steam turbine that satisfies both the “high-temperature, high-pressure, high-output conditions” and the “single turbine rotor condition” in practice, problems occur in the use of the prior art without modifications, because the bearing span increases and thus the critical speeds fall, with the secondary critical speed in particular approaching the rated speed so that detuning is insufficient, or the secondary critical speed matching the rated speed, so it is difficult to achieve stable operation.
Increasing the diameter of the rotor shaft is an effective method of solving these problems in the prior art, but the resultant narrowing of clearance dimensions in the radial direction between the static portions and the rotating portions causes difficulties from the viewpoint of preventing rubbing, so that thickening the rotor diameter causes an increase in the clearance area, which leads to an increase in leakage losses and a deterioration in efficiency. In addition, if the diameter of the blade attachment portions (turbine wheel) is increased by a thickening of the rotor shaft assembly, the blade length becomes shorter and secondary flow losses increase, which also leads to a deterioration in efficiency. Therefore,
Kikuchi Masataka
Matsuyama Kenzo
Oda Ryou
Okita Nobuo
Sakuma Akira
Foley & Lardner
Kabushiki Kaisha Toshiba
Look Edward K.
Nguyen Ninh
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