Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
1999-04-07
2001-03-27
Verdier, Christopher (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With heating, cooling or thermal insulation means
Changing state mass within or fluid flow through working...
C416S22300B, C416S243000, C415S114000, C415S115000
Reexamination Certificate
active
06206637
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a blade for a gas turbine, and more particularly to a gas turbine blade adapted to be internally cooled by a coolant steam flowing through the interior of the gas turbine blade.
2. Description of the Related Art
A conventional gas turbine for a combined cycle is shown in
FIG. 5
to FIG.
7
. As is shown in
FIG. 5
, the gas turbine
1
includes a plurality of alternately disposed stationary blades
2
and moving blades
4
. A main gas flow of high temperature is fed to the gas turbine
1
from a combustor (not shown) to effect the moving blades
4
via the stationary blades
2
and rotate a rotor of the turbine at a high speed to thereby generate power.
Each of the stationary blades
2
of the turbine is provided with coolant steam pipes
3
. Further, a plurality of radial coolant steam flow path sections a are formed inside the stationary blade
2
, as can be seen in
FIG. 7
, wherein these coolant steam flow path sections are serially interconnected at a base end portion and a tip end portion of the stationary blade to thereby form a serpentine passage that extends from a leading edge side to a trailing edge side of the turbine stationary blade.
When the gas turbine is put into operation with the high temperature main gas being fed to the gas turbine, the stationary blade
2
is heated. In this case, however, the coolant steam is supplied to the coolant steam flow path section a formed inside of the stationary blade
2
of the turbine and located adjacent to the leading edge thereof to sequentially flow through the coolant steam flow path sections which form the serpentine passage. Hence, the stationary blade
2
of the turbine can be cooled from the internal surfaces thereof. Moreover, the coolant steam used for cooling the stationary blade
2
of the turbine is subsequently recovered through the coolant steam pipe
3
to be supplied to a succeeding system.
As can be seen from the above, in the combined cycle plant where the gas turbine is used in combination with a steam turbine, steam cooling has been proposed for cooling the gas turbine to enhance the thermal efficiency.
Next, a conventional air impingement cooling scheme is illustrated in
FIG. 8
to FIG.
10
. Inserts
5
a
,
5
b
and
5
c
are respectively disposed within radially partitioned compartments of a stationary blade
2
for a turbine, each insert having a predetermined gap relative to the inner wall surface of the compartment and a number of small holes
6
are formed therein. Additionally, a number of small holes
7
are also formed in the surface of the stationary blade
2
of the turbine in a predetermined pattern.
In the turbine stationary blade
2
of the structure mentioned above, the cooling air flowing into the inserts
5
a
,
5
b
and
5
c
is ejected through the individual small holes
6
formed in the inserts
5
a
,
5
b
and
5
c
to impinge on the inner wall surfaces of the stationary blade
2
of the turbine to thereby cool the stationary blade
2
from the inside (refer to FIG.
10
). Subsequently, the cooling air is ejected from the small holes
7
formed in the surface of the stationary blade to film cool the latter.
When impingement cooling using the cooling air, the ratio t/c of blade thickness t to chord length c of the stationary blade
2
of the turbine, as shown in
FIG. 7
, is ordinarily selected so as to be at least 0.2 in order to facilitate insertion of the inserts
5
a
-
5
c
into the interior of the stationary blade
2
of the turbine and ensure an uniform pressure distribution within the interiors of the individual inserts.
Nevertheless, a turbine stationary blade of a profile having the blade thickness/chord length ratio t/c mentioned above requires a large amount of coolant steam, e.g., a major proportion of the steam for the steam turbine of the combined cycle, because convection cooling must be adopted for steam cooling.
Furthermore, leakage of the coolant steam in the coolant steam piping will seriously affect the combined cycle (bottoming cycle), and possibly make the plant nonfunctional.
Also, the diameters of the pipes used in a complicated coolant steam piping system have to be increased due to the demand for a large amount of coolant steam, and this presents problems with respect to the cost and the space for installation of the coolant steam piping arrangement of individual pipes.
OBJECT OF THE INVENTION
In light of the state of the art described above, it is an object of the present invention to provide a blade for a combined cycle gas turbine that can be effectively cooled with a proper amount of steam, to thereby solve the problems mentioned above.
SUMMARY OF THE INVENTION
The present invention provides the following means for achieving the above object.
That is, a blade for a gas turbine according to the present invention includes an internally formed coolant steam passage for cooling the blade with coolant steam flowing through the coolant steam passage, and is characterized in that the ratio of blade thickness of the gas turbine blade to chord length thereof is not greater than 0.15.
By virtue of the structure of the gas turbine blade mentioned above, the flow velocity of the coolant steam flowing through the coolant steam passage increases as the ratio of the blade thickness to the chord length becomes smaller for a given constant flow rate of the coolant steam. Further, the heat transfer rate at the inner wall surface portion of the blade increases correspondingly.
Accordingly, by selecting the ratio t/c of the blade thickness to the chord length so as to be not greater than 0.15, which corresponds to a minimum heat transfer rate required in view of the required cooling performance of the turbine blade, not only can the turbine blade be cooled effectively, but also an appropriate steam flow rate for the combined cycle can also be maintained.
Thus, even when leakage of the coolant steam occurs in the coolant steam piping, the effects of such leakage on the plant's performance can be suppressed to a minimum because the inherent amount of coolant steam is small. Furthermore, due to the small amount of coolant steam required, the steam piping system can be implemented using pipes of small diameters. Thus, the cost and the space required for installation of the complicated piping system for the plant can be reduced.
Furthermore, it is preferred to implement the blade for the gas turbine according to the present invention such that the ratio of the blade thickness of the gas turbine blade to the chord length thereof falls within a range of 0.10 to 0.15.
Owing to the structure mentioned above, effective cooling of the turbine blade with the coolant steam is performed while ensuring effective reutilization of the recovered coolant steam.
REFERENCES:
patent: 3836283 (1974-09-01), Matsuki et al.
patent: 5536143 (1996-07-01), Jacala et al.
patent: 6004095 (1999-12-01), Waitz et al.
Aoki Sunao
Ito Eisaku
Mitsubishi Heavy Industries Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Verdier Christopher
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