•
92-GT-240
THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS
345 E. 47 St., Now York, N.Y. 10017
The Society shall not be responsible for statements or opinions advanced in papers or in discussion at meetings of the Society or of Its Divisions or Sections, or printed In its publications.
Discussion is printed only if the paper is published in an ASME Journal. Papers are available
Iron ASME for fifteen months alter the meeting.
Printed in USA.
Copyright © 1992 by ASME
New Advanced Cooling Technology and Material of the
1500°C Class Gas Turbine
H. MATSUZAKI, K. SHIMOMURA
Tohoku Electric Co., Inc.
Sendai, Japan
Y. FUKUYAMA, T. ARAKI, J. ISHII, M. YAMAMOTO, S. SHIBUYA, I. OKUHARA
Toshiba Corporation
Yokohama, Japan
1111111111,1 1 11)111111111
ABSTRACT
BASIC DESIGN OF COMBINED CYCLE SYSTEM
This paper describes the advanced cooling technology and materials (directionally solidified and
single-crystal superalloys) which are considered key
technological factors when developing the 1500 . 0 class
high temperature gas turbine.
Adopting a 1500 . 0 class gas turbine developed on
the basis of the new technology, a combined cycle plant
is likely to achieve a plant thermal efficiency of more
than 55% (LEV).
Selection of Cooling System
Fig. 1 shows comparison of combined cycle plant
thermal efficiency among several gas turbine cooling
systems. As shown in Fig. 1, employing a high temperature air-cooled gas turbine which uses an advanced
cooling technology and directionally solidified and
single crystal buckets will achieve high efficiency of
a combined-cycle plant. However, the joint research
project proved that a combination of high pressure
steam cooled (HP5C) nozzles and directionally solidi-
INTRODUCTION
From the viewpoint of energy saving and reduction
of environmentally damaging emissions (CO2 reduction in
particular), it has recently become important to increase the efficiency of thermal power plants. One
generally recognized solution to this problem is a
combined cycle with a high temperature gas turbine and
a steam turbine.
Tohoku Electric Power Co. and Toshiba Corp. began
a joint research project in May 1989 to carry out basic
design of an overall combined-cycle plant, and to
develop an advanced cooling technology including steam
cooling, and directionally solidified and single crystal buckets, etc. as elemental technologies for the
1500 . 0 class high temperature gas turbines (Saito and
Kano, 1990).
The ultimate goal of this project is to apply
such technologies to high temperature gas turbines to
achieve a combined cycle plant thermal efficiency of
55% (LEV) or higher.
This paper discusses basic design of combined
cycle systems including high temperature gas turbines.
Also discussed are advanced cooling technologies which
are applied to steam cooled nozzles and air-cooled
buckets as well as trial casting of directionally
solidified and single crystal buckets coupled, with
material evaluation.
a
, 60
high pressure steam cooling
!
an =I 'Ye
>,
t)
4.)
55
130eC Class CT
4>----- \
advanced air cooling
Li)
s— 50
cu
1100 °C Class CT
------ 7
CL
•
▪
45
1100
1200
1300
1400
1500
Turbine Inlet Temperature °C
(at 1st stage Nozzle Inlet )
Pig. 1 Comparison of cooling technology.
Presented at the International Gas Turbine and Aeroengine Congress and Exposition
Cologne, Germany June 1-4, 1992
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fied and single crystal buckets improved the efficiency
by about 1% over an advanced air cooled system (see
Fig. 1). By use of the HPSC system, it is possible to
increase gas turbine inlet temperature and reduce
cooling air effectively. Moreover, since the HPSC
system is closed circuit, all the cooling steam extracted from the high pressure superheater section of
the heat recovery steam generator can be fed back to
high pressure steam turbine inlet. As a result, energy
transferred to cooling steam can be effectively recovered. Based on the above mentioned factors, it is
possible to realize a high efficiency combined cycle
plant. High pressure steam cooling can also reduce gas
temperature drop through the first-stage nozzle (14).
Therefore, combustor outlet temperature can be decreased for the same 1st-stage bucket inlet temperature. This facilitates cooling design and NOx control
for combustors.
On the basis of these findings, a combination of
steam cooled nozzles (IN) and single crystal air-cooled
buckets (1B) using advanced cooling technology was
chosen as the study model for the joint research
project.
Combined Cycle System and Cycle Parameters
The objectives of selecting cycle parameters were
to achieve higher efficiency than combined cycle plants
with 1300"C class gas turbines.
For the gas turbine using single crystal and
directionally solidified buckets and advanced cooling
technology, 1450'C was chosen for the IN inlet gas
temperature. For the above inlet temperature, an
optimal pressure ratio of 18 was selected because it
maximized both combined-cycle thermal efficiency and
simple cycle specific output of the gas turbine alone
(see Fig. 2). Fig. 3 shows a diagram of the combinedcycle system. Through the application of a 200 MW
class gas turbine, the combined-cycle system, using a
three-pressure reheating type heat recovery steam
generator, is expected to achieve a thermal efficiency
of over 55% (LHV).
Basic Design of Scale Model Gas Turbine
The selection of cycle parameters mentioned above
was performed for a 200 MW class gas turbine. However,
a 50 MW class machine was planned for development of
key technologies of the 1500'C class high efficiency
gas turbine.
Ouiput
Fuel
Efficiency
ST Efteusf Gus
Fig. 3 A diagram of HPSC system.
The basic design of a next generation 1500C
class high efficiency scale model gas turbine was
carried out as a part of a joint research project.
This 1500*C class high efficiency scale model gas
turbine was called the Advanced Gas Turbine (AGT) in
the research project.
Fig. 4 shows a cross-section of the AGT.
It is a
single-shaft type machine and the use of reduction
gears enables it to drive a generator. The compressor
is a 17-stage axial type with high pressure ratio and
high flow rate. The combustion system consists of 10
combustors with effective cooling construction for high
firing-temperature operation and valid means for NOx
emission control. The turbine has three stages designed with advanced cooling and material technologies.
The 17-stage axial compressor of AGT achieves a
pressure ratio of 18 with high efficiency. Transonic
blades are used for the first and second stage rotor
blades. A portion of the compressor discharge air is
used to cool the first and second stage turbine buckets. This air is extracted from the compressor discharge and cooled by the external air cooler, then led
•
Combined Cycle
S I mple Cycle
36
—
5
Pressure rata-20
18
16
F2L__---0 ------°----- -.0-
_t
>,
o
5
1IN ..145CMC
Pressure ratio
0 2
35
0
0
•_
18
a
-
0 34
.c
610 620 630 640 650 660 670
Plant Specific Power ( kW/kg /s )
—TIN., 1450t
400
)
c1 16
410
420
G/T Specific Power (kW/kg/s )
Fig. 2 Selection of the optimum pressure ratio.
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Fig. 4 Cross-section of AGT.
S.
into the turbine to cool the buckets. Air is extracted
from the 11th and 14th stages to cool the 2nd and 3rd
stage nozzles. A variable inlet guide vane and 1st
stage stationary blade provide start-up surge control,
as well as improvement of partial load performance in
combined cycle operation.
The Dry Low NOx combustor (DLNC) is used for NOx
emission control. The combustion system is composed of
a pre-mix type combustor with pre-mix duct and a transition piece. To permit operation at a high firing
temperature, effective cooling construction has been
adopted for each part of the combustor. Compressor
discharge air flows into the space between the flow
sleeve and the combustion liner. For combustion liner
cooling, slot cooling (a kind of film cooling) is used
in combination with convection cooling by the external
flow sleeve. The transition piece is a double surface
structure and is cooled by impingement cooling, film
cooling and convection cooling.
The first stage turbine buckets and nozzles of
the AGT, which operate in especially high gas temperature conditions, are provided with advanced cooling
technologies. For the first stage nozzles, the HPSC
concept is used.
The first stage turbine bucket is
cooled by the advanced film cooling concept. The
cooling air for the turbine bucket is cooled by the
external air cooler system.
The cooling concepts for
the 2nd and 3rd stage nozzles and 2nd stage buckets are
similar to those of the 1300'C class gas turbine.
For turbine buckets, directionally solidified and
especially single crystal buckets are necessary from
the view point of high temperature strength and cooling
air reduction. Single crystal superalloy will be
adopted for the 1st stage bucket and directional solidification superalloy for 2nd and 3rd stage buckets.
The realization of the above mentioned concept is
required for AGT development. The realization of turbine element technologies, which are HPSC, advanced air
cooled bucket and manufacturing of single crystal and
directionally solidified buckets etc., are very important.
DEVELOPMENT OF ELEMENT TECHNOLOGIES
Turbine Bucket and Nozzle Cooling
Based on the preceding arguments on thermal cycle
analysis, an HPSC nozzle / advanced air film cooled
bucket combination was chosen as a primary cooling
concept for the 1st stage.
Table 1 summarizes the design conditions of the
1st stage nozzle and bucket.
The cooling configuration development studies are
briefly summarized in this section.
Table 1 Summary of design conditions of
first stage nozzle and bucket
Gas total temperature
Coolant
Coolant inlet temperature
Coolant outlet temperature
Coolant inlet pressure
Coolant outlet pressure
Coolant/gas mass flow rate
IN
1B
1450'C
Steam
389C
540 . 0
10.34 MPa
9.72 MPa
8.8 %
1288 . C4
Air
410 ° C
1.18 MPa
4.0 %
• Relative Total Temperature
.
Steam Cooled Nozzle. In the HPSC concept, steam
is introduced into the turbine nozzle from the high
pressure superheater section of the heat recovery steam
generator. Nozzles are used as a high pressure superheater and all the cooling steam is fed back to high
pressure steam turbine inlet for effective energy
conversion.
In the design of the HPSC nozzle, a small
straight hole configuration (similar to that of water
cooled nozzle (Blazek et al, 1980, Shilke et al, 1981,
Fukuyama et al, 1989)) was selected. The steam film
cooling was not applied because of a large loss of
thermal efficiency, which is caused by the steam injection into the moderate pressure hot gas path, and the
large amount of water consumption in the plant. Fig. 5
shows the designed cooling hole arrangement in the midspan cross section.
Thirty-two cooling holes are
distributed radially.
The selected diameter of the
cooling hole was 2.0 mm and was allocated 2.5 mm underneath the vane surface. In the trailing region of the
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The basic cooling design has been completed and
the practical application of the HPSC nozzle will be
evaluated on the basis of the thermal stress, precision
cast manufacturing, machining and fabrication.
Suction Side
Cooling Holes
(Group-i)
Leading Section.
Pressure Side
Cooling Hulce
(Grcup-2)
Trailing Section
Cooling Holes
(Group-3)
Fig. 5 Cooling hole arrangement in the mid-span
cross section of HPSC nozzle.
OUT
Po = 9.72 NPa
To = 540C
Outer
Endwall
7 Holes
IN
Pi = 10.34 t4Pa
Ti - 389 C
Channel-8
Channel-4
Channel
Group 3
11 Holes
Group 2
6 Holes
Group 1
15 Holes
Channel -5
Channel-3
Channel-2
Inner
Endwall
Advanced Air Cooled Bucket. The 1st stage bucket
is cooled by an advanced film cooling concept (Araki et
al, 1987). Fig. 7 shows the design cooling configuration. The configuration adopted for the 1st stage
bucket is a combination of a serpentine internal cooling circuit with transverse ribs, multi-row film cooling on both suction and pressure surfaces, the shower
head cooling on the leading edge and small blowing
holes for the trailing section.
The cooling air passages are formed with three
independent channels. The leading side passage serves
the impingement cooling to the inner surface and film
cooling to the outer surface of the leading edge region
of the bucket. The mid chord passage utilizes a 5-pass
serpentine configuration to enhance inner side heat
transfer and supply air to both suction and pressure
surface film cooling rows. The trailing side passage
is consisted of a 3-pass serpentine configuration which
delivers air to the small parallel air blowing holes to
cool the thin trailing section of the bucket.
Fig. 8 indicates the influence of cooling air
flow rate on the mid-span surface averaged cooling
effectiveness for the 1st stage bucket.
Precision cast design and manufacturing of test
buckets has also been completed. Fig. 9 shows the twodimensional experimental bucket with instrumentation
and the 4-bucket cascade to be tested in the high
temperature test rig.
Film Cooling
Shower Head
Cooling
Holes
Trail ing Edge
4—
Blowing
Fig. 6 Schematic diagram of HPSC nozzle cooling
flow circuit.
vane, holes of diameter 1.5, 1.6 and 1.8 mm were used
and ware placed near the center of the vane thickness.
Fig. 6 indicates the schematic diagram of a
nozzle cooling flow circuit. The vane and endwalls of
the nozzle are cooled by two parallel pass flow networks. Steam is supplied to and also collected from
the outer-endwall. The cooling circuit is composed of
6 distribution channels, connection ducts and parallel
cooling holes of the vane suction side, the vane pressure side, the vane trailing region, the inner endwall
and the outer endwall.
The design point cooling steam over gas mass flow
rate [Gc/Gg x 100] is 6.6%, where Gc is cooling steam
flow and Gg is inlet gas flow, and the nozzle surface
mean cooling effectiveness v c of mid-span cross section
is expected to be 0.7, where , c is defined as below.
Impingement
Cooling
Turbulence
Promoter
--
Trailing Edge
Blowing Holes
n e r (Tg-Tm)/(Tg-Tc)
Tg:1N inlet gas temperature
Tm:metal temperature
Tc:coolant inlet temperature
Fig. 7 Cooling configuration of 1st stage
air-cooled bucket.
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I 0
0. 6
r,
II
0.6
(a) Two - dimensional experimental bucket with
instrumentation.
ra g
0,
8
0.2
0.0
4
a
6
Cooling Flow Rate GOR6
LO
Ix]
Fig. 8 Influence of cooling air flow rate on
cooling effectiveness for 1st stage bucket.
(b) Four-blade cascade in the high temperature
test rig.
Fig. 9 Photographs of experimental bucket.
Material Study
To realize high temperature gas turbines of the
1500 . 0 class, materials having higher temperature
capability are required for hot parts such as buckets
and nozzles, in addition to the application of the
advanced cooling technologies mentioned above. Single
crystal and directional solidification superalloys can
meet such demand for bucket materials in this advanced
gas turbine, which have much higher creep and stress
rupture strength and thermal fatigue life, comparing to
conventional casting superalloys used in current gas
turbines. Especially, single crystal superalloys are
most promising for first stage buckets in advanced gas
turbines from the viewpoint of high temperature
strength. However, it is necessary to establish the
production technologies for large size hollow buckets
and verify mechanical properties of large size
products, since land base gas turbine buckets are much
larger than those of aero jet engine parts which have
much more production experience.
Several steps of the bucket casting trial have
been performed under cooperation with the casting
supplier, in order to establish the production parameters for large size single crystal and directionally
solidified buckets having complex serpentine internal
cooling circuits of the 50 MW class and larger gas
turbines. For bucket materials used in this study,
CMS/C-2 single crystal (Harris et al, 1983) and CM247LC
directional solidification superalloys (Erickson, 1985)
were chosen because they have the highest level of
creep and stress rupture strength among the same kind
of superalloys. In these casting trials, various
casting parameters have been adjusted, that is,
o
o
o
process parameters such as pouring temperature,
mold temperature and withdrawal rate
core and mold materials selection
configurational modification for bucket producibility
The first steps of the bucket casting trials were made
by a high rapid solidification process for existing
first stage hollow buckets of the 1300 . C-15 MW class
gas turbine developed by Toshiba (Yamamoto et al, 1987,
Hijikata et al, 1990). Fig. 10 and Fig. 11 show single
crystal and directionally solidified buckets, indicating that both buckets can be made by good crystal or
columnar grain growth without any abnormal equiaxed
grain growth and other casting defects such as freckling, etc. Moreover, there was no recrystallization
after solution treatment in both buckets. From microscopic observation in cross section and nondestructive
examination of buckets, the distribution of porosity
and shrinkage was clarified. In the next step, solid
first stage buckets of the 50 MW class were made before
the complex hollow bucket production in order to check
the process parameters in larger buckets about twice
the size of the first casting trial. Fig. 12 shows
that single crystal and directionally solidified solid
buckets were successfully made. Based on solid buckets
production experiences, hollow buckets for 50 KW class
first stage have been manufactured, of which configuration is as described in Fig. 7. Directionally solidified hollow bucket production has been established as
shown in Fig. 13, which has good columnar-grain structure and cooling passage configuration. Casting trial
—5—
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50 arr.
100
■■
•
• 152.
7":
Fig. 10 Single crystal (right), directionally solidi-
Fig. 11 Internal cooling passages are exposed by
grinding away half the single crystal
(right) and directionally solidified (left)
buckets of 15 MW class gas turbine.
fied (middle) and conventional casting (left)
buckets of 15 MW class gas turbine.
Fig. 12
Fig. 13 Directionally solidified hollow bucket for
50 MW class first stage.
Single crystal (right) and directionally
solidified (left) first stage solid buckets
of 50 MW class advanced gas turbine.
of single crystal hollow bucket is also progressed.
High temperature material testing has been carried out to verify the strength levels of large size
parts, using single crystal and directionally solidified slabs up to 150 mm and 300 mm in length, respectively, as shown in Fig. 14. Typical stress rupture
test results are summarized in Fig. 15, where test
specimens were sampled in longitudinal direction from
various locations of slabs. Compared to typical conventional casting superalloy IN738LC and Mar-M247, both
directionally solidified and single crystal slabs have
much higher rupture strength which are almost the same
levels as reported (Harris, K., 1983, Erickson, G.L.
1985). Stress rupture elongation of both slabs are
extremely high. In Fig. 15, stress rupture test result
of a specimen machined from airfoil of the 50 MW class
first stage solid bucket is also plotted.
It is confirmed that bucket casting possesses as high a strength
as those of a slab.
In addition, various kinds of mechanical testing
have been performed, including low and high cycle
fatigue tests, tensile test and physical property
measurements such as elastic modulus and thermal expansion, etc at elevated temperatures. It was found that
low cycle fatigue life in longitudinal direction of
directionally solidified slab is several times longer
than that of conventional casting alloy, but single
crystal slabs have still longer life.
As for nozzles, casting productivity of the steam
cooled nozzles mentioned above will be studied in
future programs.
- 6 -
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CONCLUSION
Basic design of combined cycle systems has been
completed. The HPSC system is one of the attractive
cooling concepts for 1500C class gas turbines. The
HPSC system adopted for gas turbines results in achieving about 1% improvement of combined-cycle efficiency
over advanced air cooling system.
Also the basic design of advanced cooling technology and the study of material for the AGT has been
almost finished.
As a result of the above mentioned study, a large
amount of data was obtained, which is leading to attainment of the ultimate goal, realization of a high
efficiency combined-cycle plant.
ACKNOWLEDGMENT
Authors express thanks to Mr. Sudo, Mr. Morikuni,
Mr. Makita of Tohoku Electric Power Co. for giving us
the opportunity to carry out the development of the
AGT.
REFERENCES
Fig. 14 Single crystal (right) and directionally
solidified (left) large size slabs.
0 C1747LC Longitudinal
100 - • 012471X Machined fro, airfoil of 51111 class tol d bucket
60 -0 052 -2
lithin 10 • of [0011 orientsticm
80 . A Mai-11247 Ccoventionsl cut rig
rit 70
Mar-M247
-\..\401247LC
60
50
0
40
/,
\
ao
- CMSX-2
1N738LC
L'
ai‘NN
20
Araki, T. et al, 1987, "High Temperature Wind Tunnel
Testing of Film Cooled Blade", The 1987 Tokyo International Gas Turbine Congress, 87-TOKYO-IGTC-63.
Blazek, W.S., Schiling, W.F., and Schilke, P.W.
1980, "Water-Cooled Gas Turbine Monometallic Nozzle
Development", ASME Paper 80-GT-97.
Erickson, G.L., 1985, "Directionally Solidified DS
CM247LC-Optimized Mechanical Properties Resulting from
Extensive Solutioning,", ASME Paper 85-GT-107.
Fukuyama, Y., and Araki, T., 1989, "Testing of
Water-Cooled Nozzle for High Temperature Gas Turbine",
Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics, pp. 1019-1026.
Harris, K., Erickson, G.L., and Schwer, RE., 1983,
"Development of The Single Crystal Alloys CMSX-2 and
CMSX-3 for Advanced Technology Turbine Engines,", ASME
Paper 83-GT-244.
HiJikata, T. et al, 1990, "Cooling Characteristic of
Air Cooled Nozzle and Bucket in Test Rig for High
Temperature Turbine", GTSJ Conference, SENDAI, JAPAN.
Saito, T., and Kano, K., 1990, "Development of Next
Generation High Efficiency Gas Turbine Technology",
Journal of the GTSJ, Vol. 18, No. 69.
Schilke, P.W., and DeGeorge, C.L., 1981, "WaterCooled Gas Turbine Monometallic Nozzle Fabrication and
Testing", ASME Paper 81-GT-162.
Yamamoto, H., Okamura, T., and Kobayashi, T., 1987,
"Gas Turbine Development", Toshiba Review, Vol. 42, No.
6.
00 0 0
23
24
25
20
77
28
29
30
P=1. (20+log tr) x10'
Fig. 16 Stress rupture test results of single
crystal and directionally solidified
slabs and solid buckets.
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