Recent Advances in Ultra Super Critical
Steam Turbine Technology
M. Boss T. Gadoury S. Feeny M. Montgomery
GE Energy, Steam Turbine Technology
1 River Road, Schenectady, NY 12345
Un‐Hak Nah Sung I. Cho Seong H. Yang
Doosan Heavy Industries & Construction Co., Ltd.
555 Gwigok‐Dong, Changwon, Gyeongnam, Korea
Abstract – With the continuing drive to reduce power plant emissions including green house
gases, coal fired power plants have been moving to higher ultra‐supercritical (USC) steam conditions in
addition to advances in technology. GE Energy and Doosan Heavy Industries are designing the next
generation USC power plant with a rating of 1000 MW to address the need for higher efficiency coal
fired power plants. With inlet steam conditions of 260 bar and 610ºC / 621ºC (3770 psi and 1150°F /
1180°F), the primary objective for the advanced technology USC 1000 MW steam turbine is high
efficiency. To achieve this higher cycle efficiency, the design utilizes advanced steam turbine technology
and system design, a longer last stage bucket design in addition to ultra supercritical steam conditions.
Performance enhancing technology is being applied to turbine buckets, nozzles and seals. In
addition to improvements to steam path components, performance gains are achieved by optimizing
stationary components such as valves, inlets and exhausts using advanced CFD tools.
This new USC project will illustrate the latest design and technology capabilities of GE Energy
and Doosan Heavy Industries and will set the standard for future 1000 MW USC applications in Korea,
as well as elsewhere in the world.
1. INTRODUCTION
After more than 100 years of progressive invention and improvement, the steam turbine
continues to be the most used prime mover of the world’s power generation industry. Innovations such
as Edison’s light bulb and Tesla’s induction motor resulted in a phenomenal demand for electric power
driven by steam turbines, which have exponentially grown to more than 56 GW of capacity in Korea and
almost 3,000 GW worldwide. Steam turbines generate more than 80% of the total electric power
throughout the world.
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GE Energy was an early entrant into USC steam turbine technology with the first unit shipped in
1956 with inlet steam conditions of 310 bar / 621°C (4500 psi / 1150°F). Since then, GE has shipped
77GW of steam turbines (125 units) with supercritical steam conditions. GE designed the world’s
most powerful USC steam turbine rated 1050 MW operating at 250 bar / 600°C / 610°C (3626 psi /
1112°F / 1130°F). Over the past five years, GE has co‐produced with Doosan Heavy Industries 16 units
with USC steam conditions. The 1000 MW USC steam turbine design is a nature evolution of GE’s USC
technology. GE continues to develop and refine USC steam turbine technology.
GE Energy has licensed its technology to Doosan Heavy Industries (formerly Korea Heavy
Industries and Construction Company) resulting in the development and installation of GE Energy steam
turbine and generator technology for the Korean power industry. During this period, the two
companies have designed, manufactured and installed:
16.1 GW of coal‐fired steam turbine generating capacity
2.4 GW of combined‐cycle steam turbine generating capacity
10.4 GW of nuclear turbine generating capacity.
To date, there are 70 GE Energy steam turbines and generators planned or installed for projects
in Korea, including combined‐cycle, nuclear, sub‐critical coal‐fired and supercritical coal‐fired steam
turbine applications. Fifty‐one of these steam turbines have been co‐produced with Doosan. Current
ongoing projects with planned commercial operation in 2006 thru 2008 include:
• 2 x 550MW USC Korea East‐West Power Co. (KEWESPO) Tangjin #7 & #8
• 2 x 550MW USC Korea Western Power Co. (KOWEPO) Taean #7 & #8
• 2 x 550MW USC Korea Midland Power Co. (KOMIPO) Poryeong #7 & #8
• 2 x 550MW USC Korea Southern Power Co. (KOSPO) Hadong #7 & #8
In addition to advanced steam turbine technology operating at steam conditions of 241 bar /
566°C / 593°C (3500 psi / 1050°F / 1100°F), these power plants also feature the latest technology in
once‐through USC boilers supplied by Doosan. These boilers will have improved heat efficiency to
further increase the plant’s capability to compete in the new Korean power market environment.
With the emerging interest to reduce emissions, including green house gases, from coal fired
power generation, GE Energy and Doosan are striving to increase USC PC generation output and
efficiency in its co‐development of this 1000MW USC PC platform. Every 1% improvement in plant
efficiency results in approximately 2.5% reduction in green house gas emissions. To satisfy this
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objective, both GE Energy and Doosan’s steam turbine technology and Doosan’s boiler technology is
looking to achieve the following advances in PC generation technologies:
MW rating: 1000MW MGR
HP throttle pressure: 260 bar (3770 psi)
HP throttle temperature: 610°C (1130°F)
Reheat steam temperature: 621°C (1150°F)
Condenser pressure: 1.5” Hg (NR Back Pressure: 2.5” Hg)
4 flow, 45 inch Last Stage Blade
Cycle: Single Reheat Regenerative
2. TECHNOLOGY of USC STEAM TURBINE
2.1 Cycle Overview
In the evaluation of steam conditions, the potential cycle efficiency gain from elevating steam
pressures and temperatures must be considered. Starting with the traditional 165 bar / 538°C (2400 psi
/ 1000°F) single reheat cycle, dramatic improvements in power plant performance can be achieved by
raising inlet steam conditions to levels up to 310 bar (4500 psi) and temperatures to levels in excess of
600°C (1112°F). Every 28°C (50°F) increase in throttle and reheat temperature results in approximately
1.5% improvement in heat rate.
The feedwater heater arrangement is designed to obtain the best heat rate for a given set of USC
steam conditions. In general, the selection of higher steam conditions will result in additional feedwater
heaters and a higher final feedwater temperature. The higher final feedwater temperature will have an
impact on the boiler cost. This then requires a system level optimization to determine the best
economical solution for the increase in final feedwater temperature. In many cases, the selection of a
heater above the reheat point (HARP) also is warranted. The use of a separate de‐superheater ahead of
the top heater for units with a HARP can result in additional gains in unit performance.
The selection of the cold reheat pressure is an integral part of any power plant design, but
becomes even more important for plants with advanced steam conditions. Comparing the heat rate at
the thermodynamic optimum, the improvement resulting from the use of a HARP can be about 0.6%.
However, economic considerations of the boiler design without a HARP tend to favor a lower reheater
pressure at the expense of a slight decrease in cycle performance. The resulting net heat rate gain is
usually larger, approaching 0.6‐0.7%. Changing the final feedwater temperature, adding a HARP, and
setting the reheater pressure obtain the best relative heat rate impact.
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The use of advanced reheat steam conditions strongly affects the inlet temperature to the low‐
pressure (LP) turbine section. An increase in hot reheat temperature translates into an almost equal
increase in crossover temperature for a given crossover pressure. However, the maximum allowable LP
inlet temperature is limited by material considerations associated with the rotor, crossover and hood
stationary components. In addition, the selection of hot reheat temperature (and corresponding effect
on LP inlet temperature) impacts the amount of moisture at the L‐0 bucket which factors into stress
corrosion cracking considerations.
Once the reheat steam conditions are established (pressure and temperature) then the LP steam
conditions can be determined. If the resulting crossover temperature is too high, the energy ratio
between the IP and the LP can be changed to lower this temperature. Increasing the energy on the IP
section will lower the crossover temperature, but it will also impact the cycle efficiency, increase the
number of IP stages, or the loading of the IP stages, increase the height of the final IP bucket, increase
the size of the crossover, or increase the pressure drop through the crossover.
2.2 Steam Turbine Configuration
The appropriate steam turbine configuration for a given USC application is largely a function of
the number of reheats selected, the unit rating, the site back pressure characteristics and any special
requirements such as district heating extractions. Specific design details will also determine the number
of flows in a turbine section, the number of stages and the last stage bucket (LSB) length.
In particular, the site ambient conditions and the condensing system will play a huge role in the
selection of the LSB and the number of LP section flows. The 38.1 mmHgA (1.5” HgA) would be for a
direct cooled condenser, or cooling towers in a cold environment. The 88.9 mmHgA (3.5” HgA) would
be for cooling towers in an area with warmer ambient temperatures.
The expected exhaust pressure of the plant at the time of maximum expected power production
should be considered in the design the LP section. At 1.5” HgA, and 1000 MW output, a 45” LSB and a
6‐flow LP section would achieve the best heat rate. At 3.5”HgA, and an output of 1000 MW, the 40” LSB
and a 4‐flow LP section would be the lowest heat rate choice. In either of these cases, the high pressure
(HP) and intermediate pressure (IP) sections would be essentially the same.
The turbine cost increases and plant cost increases would then be compared to the expected
kilowatt outputs to optimize the plant Cost of Electricity. In the case of the 3.5” HgA, the 4‐flow 40”
would be higher cost than the 4‐flow 33.5”, and the footprint of the 40” LP section would be larger also.
In the case of the 1.5” HgA chart, the 6‐flow LP section would require the additional LP turbine section,
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and additional condenser, as well as a larger footprint for the 45” LP section.
These considerations resulted in the selection of a 4‐flow 45” LP section design. The overall
turbine configuration is shown in Figure 1.
© 2007, General Electric Company
Figure 1 ‐ 4‐casing, 4‐flow LP Configuration
2.3 Evaluation of Ultra Super Critical Technology
The history of steam turbine development is basically an evolutionary advancement toward
greater power density and efficiency. Improvements in the power density of steam turbines have been
driven largely by the development of improved rotor and bucket alloys as well as improvements in the
design and analysis of the attachment devices for the vanes. This has increased the allowable stresses
and enabled the construction of longer last stage buckets for increased exhaust area per exhaust flow.
Increases in efficiency have been achieved largely through two kinds of advancements: (1)
improving expansion efficiency by reducing aerodynamic and leakage losses as the steam expands
through the turbine; and (2) improving the thermodynamic efficiency by increasing the temperature
and pressure at which heat is added to the power cycle. The latter improvement is the core of USC
technology.
The design of the Ultra Super Critical steam turbine for the present development will incorporate
the new technologies, which consist of:
i) Improvement of in the power density of steam turbines such as;
Increased number of stages
Decreased inner ring diameter
Optimized stage reaction levels
Optimized Stage energy levels
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ii) Mechanical design elements including:
Advanced sealing
Integral cover bucket (ICB)
Full Arc, hook diaphragm 1st stage
Advanced cooling scheme
iii) Improved HP/IP/LP shell design
iv) Advanced LP design with 45 inch last stage blade
3. HIGH/INTERMEDIATE PRESSURE TURBINE DESIGN
3.1 High Pressure (HP) Section Design
3.1.1 Section Design
Figure 2 shows the HP cross‐section. The HP section is designed in a single flow configuration.
This modern design eliminated the partial admission, control stage, and nozzle box. An overload
admission was added for frequency control and capacity margin. Main steam enters the section
through two pipes (top and bottom.) A heater above reheat point extraction is taken from the lower
half. The HP exhaust uses two cold‐reheat (CRH) pipes from the lower half arranged in the pant leg
configuration. Elimination of the nozzle box required that two inner shells be used. All shells are split
and bolted at their horizontal joints for ease of maintenance. In this arrangement, the inlet #1 inner
shell is subject to adjacent stage steam conditions on its’ inner surfaces and a downstream stage’s
steam pressure on its outer surface. The corresponding outer shell inner surface is subjected to steam
conditions at the same downstream steam pressure albeit with an enthalpy determined by the flow
balance of steam between the packing leakage and the split location. The exhaust #2 inner shell is
arranged in a manner similar to that for the full inner shell described above. The inner shell split
location is judiciously chosen to optimize the horizontal joint and bolting design of the outer, #1 inner,
and #2 inner shells. The outer and # 1 inner shell are cast 10Cr material. The #2 inner shell is cast
CrMoV material. The mono‐block rotor material is 12Cr. The Advancing steam conditions necessitated
the addition of inlet cooling for the rotating parts to allow the rotor design to stay 12Cr materials. Full
admission design alleviated the mechanical challenges associated with partial admission design and the
control stage. Thrust is balanced using the pressure difference across the rotor at the generator end of
the HP section. The rotor is supported by bearings in the front and middle standards. Both standards
slide in a manner conventional to GE 4 casing, 4‐flow turbine construction.
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© 2007, General Electric Company
Figure 2 ‐ HP Section Arrangement
3.1.2 High Pressure Steam Path
The HP steam path has 10 stages. The first stage is full‐arc admission. The HP staging is
designed in a manner typical for GE’s proven designs using Dense PackTM steampath components. The
buckets of the first four stages are made of nickel‐based material due to the high temperature creep
requirements. The remaining buckets are conventional 12Cr materials. All 10 stages will utilize integral
cover buckets (ICB) with advanced tip seals. Figure 3 shows a typical GE ICB design. The wheel spaces of
the first two stages are cooled using external cooling steam. The first five stages of diaphragms utilize
10Cr materials. The remaining five stages of diaphragms use 12Cr web and ring material. A combination
of brush, variable clearance, and conventional shaft seals are used in the HP section.
© 2007, General Electric Company
Figure 3 ‐ Typical GE ICB Design
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3.2 Intermediate Pressure (IP) Section
3.2.1 Section Design
Figure 4 shows the intermediate‐pressure cross‐section. The IP section is designed in a double
flow configuration. Steam enters the section through two pipes in the lower half. Two feed water
heater extractions are taken from the lower half. The IP exhaust uses two cross over connections from
the upper half arranged in the manner conventional to GE 4 casing, 4‐flow turbine construction. Single
shell construction is used. The shell is split and bolted at its horizontal joint to minimize clearances
and reduce manufacturing cost. The shell is cast 10Cr material. The mono‐block rotor material is 12Cr.
The advancing steam conditions necessitated the addition of inlet cooling for the rotating parts. The
rotor is supported by bearings in the middle standard and LPA standards. Both standards slide in a
manner conventional to GE 4 casing, 4‐flow turbine construction.
© 2007, General Electric Company
Figure 4 ‐ IP Section Arrangement
3.2.1 Steam Path Design
The IP steam path has 8 stages. The IP staging is designed in a manner typical for GE’s proven
designs using Dense PackTM components. The buckets of the first three stages are made of nickel‐based
material due to high temperatures. The remaining buckets are conventional 12Cr materials. All 8 stages
will utilize integral cover buckets (ICB) with advanced tip seals. The wheel spaces of the first two stages
are cooled using cooling steam, from HP section. The first two stages of diaphragms utilize 10Cr
materials. The remaining six stages of diaphragms use 12Cr web and ring material. A combination of
variable clearance and conventional shaft seals are used in the IP section.
3.3 Aerodynamic Design
3.3.1 Advanced Aero Design
The biggest advance in steam turbines in recent years has been Aerodynamics. GE has
continued to develop advance aerodynamic vane shapes based on 100 years of experience coupled
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with 3D CFD (computational fluid dynamics) and GE’s HP test facility. The addition of CFD in the last 10‐
15 years has resulted in great strides in steam turbine aerodynamics. Figure 5 shows the evolution of
aerodynamic shapes over the years.
Stea
m P
ath
Effic
ienc
y %
Free -Vortex• Uniform Radial
Controlled -Vortex• Non-Uniform Radial Flow• Straight Trailing Edge
Advanced -Vortex• Compound Lean • Bowed Nozzle
Partitions
1960’sFree -
VortexDesign
1970’sImproved
Vane Profiles
1980’sControlVortexDesign
1990’sAV1, adv
RTSS
Late 1990’sAV2, ICBs,
opt. clearance
2000’sDense Pack
2000’sDense Pack ™
w/adv sealing
Free -Vortex• Uniform Radial
Flow
Controlled- Vortex• Non Uniform Radial Flow• Straight Trailing Edge• Optim ized Reaction
Advanced - Vortex• Compound Lean • Bowed Nozzle
Partit ions
-
Stea
m P
ath
Effic
ienc
y %
Free -Vortex• Uniform Radial
Controlled -Vortex• Non-Uniform Radial Flow• Straight Trailing Edge
Advanced -Vortex• Compound Lean • Bowed Nozzle
Partitions
1960’sFree -
VortexDesign
1970’sImproved
Vane Profiles
1980’sControlVortexDesign
1990’sAV1, adv
RTSS
Late 1990’sAV2, ICBs,
opt. clearance
2000’sDense Pack
2000’sDense Pack ™
w/adv sealing
Free -Vortex• Uniform Radial
Flow
Controlled- Vortex• Non Uniform Radial Flow• Straight Trailing Edge• Optim ized Reaction
Advanced - Vortex• Compound Lean • Bowed Nozzle
Partit ions
- New Design
Adv Sealing
Stea
m P
ath
Effic
ienc
y %
Free -Vortex• Uniform Radial
Controlled -Vortex• Non-Uniform Radial Flow• Straight Trailing Edge
Advanced -Vortex• Compound Lean • Bowed Nozzle
Partitions
1960’sFree -
VortexDesign
1970’sImproved
Vane Profiles
1980’sControlVortexDesign
1990’sAV1, adv
RTSS
Late 1990’sAV2, ICBs,
opt. clearance
2000’sDense Pack
2000’sDense Pack ™
w/adv sealing
Free -Vortex• Uniform Radial
Flow
Controlled- Vortex• Non Uniform Radial Flow• Straight Trailing Edge• Optim ized Reaction
Advanced - Vortex• Compound Lean • Bowed Nozzle
Partit ions
-
Stea
m P
ath
Effic
ienc
y %
Free -Vortex• Uniform Radial
Controlled -Vortex• Non-Uniform Radial Flow• Straight Trailing Edge
Advanced -Vortex• Compound Lean • Bowed Nozzle
Partitions
1960’sFree -
VortexDesign
1970’sImproved
Vane Profiles
1980’sControlVortexDesign
1990’sAV1, adv
RTSS
Late 1990’sAV2, ICBs,
opt. clearance
2000’sDense Pack
2000’sDense Pack ™
w/adv sealing
Free -Vortex• Uniform Radial
Flow
Controlled- Vortex• Non Uniform Radial Flow• Straight Trailing Edge• Optim ized Reaction
Advanced - Vortex• Compound Lean • Bowed Nozzle
Partit ions
- New Design
Adv Sealing
© 2007, General Electric Company
Figure 5 ‐ Evolution of Steam Turbine Aerodynamics
GE’s designs using Dense PackTM components further improve efficiency by addressing the major
sources or aerodynamic loss in impulse steam turbines. This is achieved via:
• Higher bucket reaction ‐> Decreased nozzle velocity/turning ‐>Decreased nozzle profile and
secondary losses
• Reduced nozzle and bucket counts ‐> Decreased friction loss
• Decreased root diameter ‐> Increase bucket active length ‐> Improved bucket efficiency
In addition, the higher reaction and decreased root diameter result in additional stages (in
order to keep optimum wheel velocity ratio). These additional stages improved section efficiency.
3.3.2 High Pressure Turbine 1st Stage
Older steam turbine designs utilized a control stage to control pressure and load during
transient conditions. The mechanical design requirements of this stage, having to withstand partial arc
stimulus, often result in a very large and in‐efficient 1st stage design that can be 5‐10% lower efficiency
than the other HP stages. Although there have been many improvements to control stage design in
recent years as part of GE’s products using Dense PackTM components, the efficiency still lags other
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group stages. Therefore, for the new Korea 1000 MW USC standard GE and Doosan chose to implement
a full arc 1st stage design, which is much higher reaction and lower aspect ratio to a traditional control
stage. This enables the first stage design to rival the efficiency of other stages. To allow this however,
changes need to be made to allow the turbine to quickly and efficiently respond to load swings.
Therefore, GE and Doosan will utilize an overload valve that will bypass the 1st stage and allow
additional flow/load response. GE has utilized such a design previously and has a patent in this area.
3.3.3 High Pressure and Intermediate Pressure Cooling
As throttle temperatures increase, cooling becomes extremely important. For the new Korean
1000 MW USC standard, GE utilizes traditional type IP Cooling, and also HP cooling, which was utilized
on GE’s 1st USC machine in 1958. HP cooling takes lower enthalpy steam from the boiler and floods the
HP 1st stage wheel and N2 packing areas. This method has minimal performance penalty since lower
enthalpy steam feeds the leakage circuit and the high enthalpy steam stays in the steampath. In
addition, the IP cooling steam is mixed from 2 different sources, allowing better control of temperature,
minimizing flow and performance loss.
4. LOW PRESSURE TURBINE DESIGN TECHNOLOGY
4.1 Wheel and Diaphragm Configuration Structure
m© 2007, General Electric Co pany
Figure 6 ‐ Wheel and Diaphragm Configuration
As shown in Figure 6, the LP design for the 1000 MW consists of 5 stages with 4 extractions for
the feed water cycle. The last 3 stages (L‐0, L‐1, and L‐2) are designed as a system and the L‐0 utilizes
the new GE 45” Titanium LSB design. This provides the maximum annulus area for a 4‐flow
configuration. Titanium material is required due to the large load. In addition, advanced curved axial
entry dovetails have been developed to minimize stresses. High strength LP rotor material, similar to
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that used on GE’s 40” steel bucket is also used to control stress.
The first 2 LP stages (L‐3 and L‐4) utilize high reaction stage design for optimal efficiency. In
addition, advance brush seals are utilized to reduce leakage losses.
4.2 Exhaust Hood Design
The LP turbine section is a complex system, which requires a careful optimization to get the
proper balance of performance, cost, robust operability, and ease of maintenance. The elements of this
LP turbine section are: the outer exhaust hood, the inner casing, the stationary steam path, and the
rotor.
As the steam paths get larger, with the introduction of longer last stage buckets, the challenges
of the exhaust hood design become more critical. The exhaust hood must contain the vacuum
established in the condenser, it must support the rotor bearings, as well as the inner casing, and it must
have a design that allows for the proper diffusion of the steam leaving the last stage.
Three‐dimensional (3D) solid models of all of the components of the LP turbine allow for state‐
of‐the‐art analysis techniques, with respect to finite stress calculations, transient heat transfer
calculations, component response to heating and loading, and Computational Fluid Dynamic (CFD)
Analysis. The critical movements of the interfaces of the various components need to be understood to
be able to optimize the clearance calculation throughout the LP turbine. The required axial and radial
clearances can be calculated with the transient loading conditions for start‐up and shut down of the
machine. This together with a statistical analysis on the expected variation from the stack‐up,
manufacturing tolerances, and calculation uncertainty, yields the clearances for the machines. Figure 7
shows the exhaust hood outer model, which is a part of this analysis.
© 2007, General Electric Company
Figure 7 ‐ LP Exhaust Hood Model
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The LP exhaust hood directs the flow from the last stage bucket exit annulus to the condenser. The high
volumetric flows associated with the low exhaust pressure result in high exit Mach numbers making the
recovery of this exit kinetic energy or “Leaving Loss” an important feature of the LP turbine. To
maximize the recovery of the exit kinetic energy, the exhaust hood is designed using an unstructured
CFD mesh. Inlet boundary conditions are set to model the effects of the LSB exit flow profile.
Results of this model, shown in Figure 8, are used to refine the geometric definition of the
exhaust hood shape such that the flow losses are reduced and the leaving loss is recovered to the
maximum extent possible. In the exhaust, the placement and shapes of the butterfly plates, Herzog
plates and steam guides were design for the best performance. These changes reduced the high
velocity regions, minimized separations, and reduced flow turning resulting in reduced inlet and
exhaust pressure losses, contributing to the overall improved performance of the LP turbine.
© 2007, General Electric Company
Figure 8 ‐LP casing Model and CFD results
The LP inner casing inlet duct transitions flow from the crossover pipe to the annular inlets of
the steam path. 3D CFD analysis of the inlet region is employed to minimize the losses in this transition.
Results from this analysis provided the inlet boundary condition for the turbine analysis including both
radial and circumferential variation.
4.3 LP Inlet Design
In addition to the CFD work used to optimize LP Exhaust, similar methods are used for LP Inlets.
Although the velocities are much lower in the inlets, meaning that less performance is lost than in the
exhaust, some improvements can be made. Aside from the basic area rules of crossover to LP inlet to
1st stage used to avoid acceleration, the LP inlet shape can be designed to reduce pressure drop. Figure
9 shows a CFD analysis of an LP inlet before and after aerodynamic optimization. The colors represent
areas of different velocity. (red is high, blue is low)
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© 2007, General Electric Company
Figure 9 ‐ LP Inlet Optimization
5. ADVANCED SEAL DESIGN TECHNOLOGY
One of the biggest issues with increased reaction is the need for improved seals over the
bucket tips due to the higher pressure drops. In addition, to further efficiency improvements, improved
seals are also applied to diaphragms. GE’s wheel and diaphragm construction lends itself well to
application of a variety of advanced seals.
5.1 Elliptical Clearance Packing
The first, most basic advanced seal used is a standard hi‐lo or slant tooth packing with elliptical
packing. Elliptical packing has been shown through experience to be the best solution to minimize
leakage area while preventing most rubs. Clearances tend to be larger at the vertical position as
opposed to the horizontal position due to rotor and stationary part movements. Recent CFD analyses as
well as component testing has shown that rubbed packing shapes have a much higher leakage than a
sharp toothed packing (see Figure 10).
© 2007, General Electric Company
Figure 10 ‐ Rubbed packing CFD
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Elliptical clearances are used in conjunction with other advanced seals in most areas.
5.2 Variable Clearance Positive Pressure Packing
In the 1990’s GE introduced its proprietary variable clearance positive pressure packing
(VCPPP). This design provides improved rub resistance, as the packing is “open” while the turbine is
starting up. Unlike conventional packing where the spring pushes the packing ring toward the rotor, the
spring on VCPPP packing pushed the ring away from the rotor by a prescribed amount. Once the
turbine starts to increase in load, pressure builds up and “closes” the ring against the hook. This is
beneficial as the rotor has already gone through its critical speeds and much of the thermal transient
conditions that lead to rubbing have passed. GE applies VCPPP where pressure drops are large enough
to close the rings.
5.3 Brush Seals
Brush seals have been used in GE steam turbines since the 1990’s and have proven to be very
beneficial. Brush seals, unlike traditional packing, are designed to contact during normal operation. The
“bristle” material is designed for heavy wear, thus resulting in a minimal clearance during the life of the
turbine. Brush seals are most effective where there are large pressure drops, however there is some
limitations on pressure drop based on backplate stress. Brush seal usage is also limited based on rotor
dynamics criteria. Since the seals are designed to rub, there is heat generation in the rotor locally to the
rub. This rub causes a thermal bow that can cause the rotor instability. Therefore, brush seals are
limited in number based on the rotor dynamics characteristics of a given rotor.
6. CONCLUSIONS
As global fuel prices are making coal‐fired fossil steam turbine generators increasingly more
attractive in the world generation market, the increased efficiency / reduction in emissions is of
paramount importance to the environment. USC steam conditions enable high efficiency designs that
reduce the amount of fuel required for generation and help reduce green house gas emissions.
GE Energy and Doosan are currently developing the next generation 1000 MW fossil PC steam
turbine generator platform, a design that includes will set a new standard for power plant performance
and economics, using state of the art analysis and technology.
REFERENCES
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1. J. Michael Hill, Sanjay Goel, “Development of the Dense Pack Steam turbine: A New Design
Methodology for Increased Efficiency”, Proceedings of 2000 International Joint Power Generation
Conference, 2000
2. Eichiro Watanabe, Yoshinori Tanaka, “Development of New High Efficiency Steam Turbine”,
Mitsubishi Heavy Industries, Ltd., Technical Review Vol. 40 No.4., Aug. 2003
3. Tom Logan, Un‐Hak Nah, James Donohue, “GE and Doosan bring Ultra Super Critical Steam Turbine
Technology to Korea”, Proceedings of 2003 Power Gen Asia, 2003.
4. Daniel Cornell, Klaus Retzlaff, Sean Talley, “DX2 (Dense Pack) Steam Turbines”, GER‐4202 GE Power
Systems.
5. Mujezinovic, A., Hofer, D., Barb, K., Kaneko, J, Tanuma, T. and Okuno, K, “Introduction of 40/48 Inch
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