alstom steam turbine and cycle design with integrated
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
Alstom Steam Turbine and Cycle Design with Integrated Boiler Feed Pump Drive for High
Efficiency Coal-Fired Power Plants
Heinrich Klotz1, Eric Pickering2, Christoph Brandt1
Alstom 1Mannheim, Germany
2Richmond, USA
Presented at the Power-Gen International Conference on 11-13 December 2007
ABSTRACT
The worldwide growing electricity demand increases the pressure to conserve both resources and
environment. Modern, high efficiency coal-fired power plants can significantly contribute to
fulfil these obligations. In this context, the steam cycle design and parameters play a major role.
In particular, increased turbine inlet pressures and temperatures contribute significantly to
improved efficiency of modern power plants.
The paper provides an overview of the Alstom steam turbine design for supercritical high
temperature (ultra-supercritical) applications as applied to the recently awarded projects in the
USA and Europe. Among them, there are the largest single shaft units worldwide. In addition to
sophisticated cycle parameters, advanced 3D blade design, effective sealing technologies, and
top performing large, last stage blades ensure outstanding efficiency levels. Furthermore, special
attention is given to operational aspects. Thermal elastic design enables short start-up times and
can cope with changing operation requirements over the lifetime of a power plant. Alstom’s
unique shrink ring high-pressure inner casing design and the welded rotor technology provide
maximum operational flexibility.
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
For maximum output a turbine driven boiler feed water pump is used. The performance and
operational flexibility of this drive and its integration in the main turbine system contribute
significantly to the economics of the power plant. Alstom’s integrated solution ensures overall
optimization and uses synergies in planning and during the erection and commissioning phase.
To minimize the specific investment cost a maximum unit output accompanied by a compact
turbine layout is required. Alstom’s current high capacity steam turbine generator sets in
combination with a turbine driven feed-water pump provide maximum possible power outputs of
approximately 1’000 MW in 60 Hz grids and 1’200 MW in 50 Hz grids in a single shaft
configuration. Large low-pressure exhaust areas and the single bearing design lead to a cost
effective, compact turbine layout. Maximum possible power output and compact design
combined with top class performance and low maintenance requirements enable lower electricity
generation costs while saving resources and minimizing environmental impact.
INTRODUCTION
Today, coal plays the most important role as fuel in electricity generation worldwide.
Approximately 39% of the electricity generation is based on coal-fired power plants. Especially
in countries with large local coal deposits, the contribution can be much higher, e.g. 95% in
Poland, 90% in South Africa, 85% in Australia, 80% in China (all values are approx., 2002 [1]).
Also in the USA (55%) and in Germany (50%) the share of coal as fuel in electricity generation
is very significant [2].
From today until the 2030s the electricity consumption will increase by more than 50%
worldwide [3]. Although the share of renewable energy sources and gas-fired power plants will
increase, the most important fuel for electricity generation worldwide will remain coal with a
nearly unchanged share of 38% [4]. Therefore, there is already great demand for new coal-fired
power plants not only to meet the growing electricity demand in emerging markets like China
and India, but also to replace old, less efficient coal-fired power plants in the USA and Europe.
The advantages of coal as fuel compared to other fossil fuels like oil or gas are the relatively low
price level, the long-term availability, and the diversity of sources around the world. The most
significant disadvantage of coal is the CO2 emission per electric work unit which is much higher
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
than for gas and renewable energy sources. Due to the latest discussions on climate change, the
necessity to reduce CO2 emissions of coal-fired power plants is of highest importance in order to
obtain regulatory and community acceptance. Because large scale CO2 capture technologies are
not yet available, increasing plant efficiency is today the most promising way to reduce the CO2
emissions of coal-fired power plants. Fortunately, in a certain range, efficiency gain correlates
well with economic gain, especially if the follow-up costs of the CO2 emissions are taken into
account. Today, coal-fired power plants with ultra-supercritical (USC) steam cycle parameters
and wet cooling tower can achieve efficiencies of approximately 46% for hard coal and 43% for
brown coal at typical Central European inland sites (efficiencies based on LHV). With direct
cooling, an additional percent improvement is possible.
To date, Alstom has received orders for five USC steam turbines for the 50 Hz market and
awards for further eight. Most of them are located in Germany. Among them, there are the
world’s largest single shaft turbines, which will work with the most sophisticated steam cycle
parameters, i.e. main steam pressure of 3990 psia (27.5 MPa), main steam temperature of 1110°F
(600°C), and reheat temperature of 1150°F (620°C) at the turbine inlets. The latter temperature is
Figure 1: Recent orders and awards of Alstom USC steam turbine generator sets in Europe and USA
Europe Output up to
Main steam pressure up to Main steam temperature up to
Reheat steam temperature up to USA
Output up to Main steam pressure up to Main steam temperature up to Reheat steam temperature up to
13 units 12.3 GW 1,114 MW 3,990 psia 1,112 °F 1,148 °F 2 units 1.6 GW 965 MW 3,510 psia 1,112 °F 1,125 °F
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
close to the limit suitable for currently available ferritic/martensitic materials. In 2006, Alstom
received the first order for a 60 Hz USC steam turbine in the 700 MW class and expects further
orders to come soon for USC steam turbines up to 1’000 MW.
INCREASING STEAM CYCLE PARAMETERS
The increase of steam cycle
parameters is the most
promising way to improve the
efficiency of modern coal-fired
power plants. Raising the main
steam temperature by 18°F
(10 K) results in an plant
efficiency gain of
approximately 0.25%
(relative), whereas 18°F (10 K)
more in reheat temperature
leads to an approximately
0.2%-gain (relative) in plant
efficiency. On top of that, there
is a further efficiency gain by increasing the main steam pressure. Supercritical steam conditions
established at the end of last decade are a main pressure of approximately 3770 psia (26.0 MPa)
with temperatures of 1050°F (565°C) for the main steam and 1085°F (585°C) for the reheat.
Since the beginning of the new decade, these steam cycle parameters have been further
significantly raised due to the strongly increased pressure to serve both resources and
environment. Today, the temperatures have reached 1110°F (600°C) for the main steam and
1150°F (620°C) for the reheat steam. Together with the temperatures, the main steam pressure
has been increased up to 3990 psia (27.5 MPa) at turbine inlet and accordingly the reheat
pressure up to 870 psia (6.0 MPa). Steam cycle parameters with a main steam pressure above
3625 psia (25.0 MPa) and temperatures above 1050°F (565°C) are often called ultra-supercritical
(USC). Figure 2 shows the development of steam cycle parameters in the past and their impact
on the overall plant net efficiency.
Figure 2: Development of cycle parameters in the last years and their impact on the overall plant efficiency (relative)
2465 psia1000°F1000°F
+5.5%
3770 psia1050°F1085°F
3770 psia1110°F1110°F
3990 psia1110°F1150°F
5080 psia1290°F1330°F
subcriticalcycle
supercriticalcylce
USCcycle
1300°F/700°Ctechnology
state of the art
+6.2%
+11.5%
base line
+4.2%
chan
ge in
ove
rall
plan
t net
effi
cien
cy (r
elat
ive)
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
The Alstom steam turbine is capable to work with USC steam cycle parameters up to highest
power outputs. An Alstom STF100 (Alstom's largest turbine frame) together with the GIGATOP
generator can generate a power output up to 1’000 MW for 60 Hz or up to 1’200 MW for 50 Hz
applications. These turbine generator sets are the world’s largest tandem compound units for
USC applications. They contribute to cost efficient electricity generation while saving resources
and minimizing environmental impact.
MODULAR STEAM TURBINE DESIGN
Alstom’s modular steam turbine design has been well established in the market for many years.
Each turbine section can be selected from a wide range of volumetric variants and, for the low-
pressure section, of last stage blade lengths in order to cover a spectrum of 100 MW up to
1’200 MW power output with different cold end designs. The steam path in the high-pressure
(HP) and intermediate-pressure (IP) section is specifically adapted and optimized for each
project. The low-pressure (LP) steam path design is standardized. Thanks to the modular
concept, the materials of turbine parts such as the inner and outer casing can be adapted easily to
match the requirements of steam cycle parameters. This specific material selection is also
possible for the rotor sections because of its welded design. The utmost thermal flexible design is
able to cope with all changing operation requirements (e.g., change from base load to cycling
operation) during the lifetime of the unit, even with USC steam cycle parameters. Figure 3 shows
an HP and an IP turbine module with its valve arrangement.
Figure 3: HP and IP turbine modules
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
IMPROVING STEAM TURBINE PERFORMANCE
In parallel with increasing steam cycle parameters, it is necessary to improve the performance of
the steam turbine itself. There are at least three key features on which Alstom has worked in
recent years:
• advanced 3D blade design with minimized profile and secondary losses,
• improved sealing technologies to reduce sealing losses, and
• advanced top performing last stage blades in high strength steel and titanium to limit the
exhaust losses and/or to reduce the number of LP flows.
Advanced 3D blade design
Alstom uses reaction type blading with 3D state of the art profiles. This blading is adapted
specifically for the HP and IP turbine for each application. The blades are milled in one piece
from bar material with integrated shrouds and roots. They are assembled pre-twisted to form a
clearance-free ring with excellent vibration behaviour.
This well proven blade design has been
further improved in recent years,
particularly by minimizing secondary
losses, improving the aerodynamics at
the trailing edge and reducing the gap
and leakage flow interaction with the
main steam flow. To reduce the
secondary losses, special attention has
been given to the geometry at the
intersections of the airfoil with the
endwalls. Optimized compound radii
smooth these intersections in order to
reduce the endwall losses. A thin trailing edge improves the aerodynamics and reduces the
profile losses. However, the aerodynamic optimization is limited by the mechanics as well as by
the machining. The trailing edge thickness has been carefully optimized with respect to the
aerodynamics as well as with respect to the mechanical integrity and the manufacturability. The
gap and leakage flow interaction has been optimized by adaptations in the steam path geometry.
Figure 4: Alstom reaction type blading with 3D state of the art profiles
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
The stage efficiency gain of all three mentioned improvement measures can accumulate to
approximately 0.7%, depending on the aspect ratio. All three measures require high
manufacturing and quality standards. Figure 4 shows the Alstom reaction type blading with 3D
state of the art profiles.
Improved sealing technologies
For USC applications, the sealing of glands and pistons becomes more important, especially for
the HP turbine. Due to the higher-pressure differences, the driving forces for the leakage flow
become stronger and the leakage flow would increase with standard sealing technology. In
addition to standard fin-strip-sealing, Alstom has developed two advanced sealing technologies
in recent years in order to reduce the leakage flows.
The brush seal consists of a flexible
super alloy bristle pack, held within a
welded front plate-backing ring
assembly, which replaces some of fin-
strip-pairs in a standard sealing section.
The flexible bristle pack allows the
reduction of the clearance nearly to zero.
Brush seals evaluate especially well on
the HP piston and in the HP glands for
USC applications, although its appliance
is neither limited to USC applications
nor to the HP turbine piston and glands.
The brush seal itself and its arrangement
in a sealing section of a HP turbine is
shown in Figure 5.
Abradable coatings can be used to reduce the clearances in standard fin-strip-seals without the
risk of metal to metal rubbing. The coating consists of a thin layer of metallo-ceramic material
applied to the static surfaces in the sealing sections.
Figure 5: Brush seal itself (top, left) and arranged in asealing section of a HP turbine piston (top, right andbottom)
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
Advanced top performing last stage blades
The last stage blade (LSB) is of essential importance for the overall turbine efficiency. In
addition to the efficiency of the LSB itself, the exhaust area plays a central role because the
exhaust losses are much higher than for the HP and IP turbine and cannot be recovered.
Furthermore, the share of the LP turbine on the total turbine cost is superior. Therefore, a wide
spread of LSB with different exhaust areas is beneficial. It allows the optimization of the cold
end design with regard to both efficiency and economics. Using a larger exhaust area can reduce
the exhaust losses (improved efficiency) or eliminate the need for an extra LP casing (optimized
cost).
Currently, the Alstom LP turbine family includes
LSB from 25 in length up to 42 in for the 60 Hz
market and up to 49 in for the 50 Hz market. The
latest developments are the large steel LSB with a
length of 38 in for 60 Hz applications and 45 in for
50 Hz applications and the titanium LSB with a
length of 42 in and 49 in (Figure 6), respectively.
Today's high strength steel and lightweight titanium
give more freedom to design the airfoil, particularly
for longer blades. As a result, the stage efficiencies
of these new LSB have been increased remarkably.
In addition, the new LSB are equipped with
shrouds to reduce the leakage flow over the tip
compared to freestanding blades. At the same time
the shrouds, together with snubbers, enable a rigid
and robust blade ring with excellent vibration
behaviour. Following the latest LSB design, the
diffuser and the exhaust have been redesigned as
well in order to get best efficiencies over a wide
operating range. Naturally, the new LP turbines based on these LSB are also equipped with the
well-known 360° inlet scroll with radial-axial first stage. The LP turbines with advanced LSB
design have been well received by the market. The first units will be in operation in 2009.
Figure 6: 49 in titanium LSB (left) withdetailed shroud section (top, right) andintegrated optimization of diffuser andexhaust (bottom, right.
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
OPERATIONAL ASPECTS OF STEAM TURBINES FOR USC APPLICATIONS
USC steam cycle parameters with temperatures up
to 1110°F (600°C) for the main steam and 1150°F
(620°C) for the reheat steam together with a main
steam pressure up to 3990 psia (27.5 MPa) increase
the requirements on the turbine with regard to
operational aspects. Both the increase of the
absolute level and the differences of temperatures
and pressures along or across the turbine modules
often result in longer turbine modules and thicker
casing walls, even with the application of new
materials. All the mentioned points can result in
stronger casing distortions with negative impact on
long-term efficiency and reliability.
Shrink ring design of the HP turbine
The unique shrink ring design of the Alstom HP
turbine was introduced in the 1960s. It eliminates
bolt flanges on the inner casing and results in a
radially symmetrical structure with best thermo-
elasticity. Therefore, the shrink ring design
prevents casing distortions almost completely,
which is of essential importance for USC
applications. The benefits are long-term stable
clearances and sustained efficiencies combined
with long-term reliability and operational
flexibility. HP steam extraction in order to increase
the final feed water temperature can simply be done with a shrunk-on extraction chamber. Due to
the double shell design the outer casing is exposed to the exhaust steam only, which allows
relatively small flanges at the outer casing. The assembly of the HP turbine with its shrink rings
is shown in Figure 7.
Figure 7: Shrink ring design of the HPturbine (assembly of inner casing, shrinkring, outer casing)
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
Design features of the IP turbine
The standard Alstom IP turbine design is also of a double shell design. The lower pressure level
allows a horizontal split of the casings with conventional flanges. In order to minimize the casing
distortions for very high temperature applications the design of the inner casing has been
modified. This advanced design allows small and stable clearances also at highest temperatures,
which result in best and sustained efficiency levels. The material selection of the inner casing is
done accordingly to the requirements of pressure and temperature. Thanks to the inlet scrolls
with the integrated radial first stationary blade row and the welded rotor design a secondary
steam cooling with its negative impact on the efficiency is not required, not even for the highest
reheat temperatures of today.
Welded rotor design
The welded rotor design is a key feature of Alstom steam turbines since the 1930s. It allows the
material selection of each rotor section to match the respective temperature of the steam path.
Therefore, welded rotors can be easily adapted to USC steam cycle parameters. Because of the
cavity formed by the two welded rotor sections, the stress levels due to temperature differences
are lowered. This design allows a faster start-up and/or lower life consumption rates compared to
monoblock rotors. Further, the small forgings are easier to obtain on the market and to test than
big forgings for monoblock rotors.
COMPACT TURBINE LAYOUT TO SAVE SPECIFIC INVESTMENT COST
A compact turbine generator layout contributes to lower specific investment cost of the overall
power plant. A short length of the turbine generator set is especially important, because it
directly saves turbine hall length. The Alstom single bearing design, the large exhaust areas by
either long steel or titanium last stage blades, and the high capacity GIGATOP turbogenerator
enable a power output up to 1’000 MW in 60 Hz grids and up to 1’200 MW in 50 Hz grids with
top performance in a very compact layout. This compact turbine layout can be supported by
using a boiler feed pump turbine, which provides additional exhaust area.
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
Single bearing concept
The single bearing concept of Alstom steam turbine generators is well proven and worldwide
established since many years. It significantly reduces the steam turbine generator shaft length.
Additionally, the single bearing concept ensures a long-term smooth and stable operation. Due to
fewer bearings, maintenance costs are reduced.
Large exhaust area
Alstom’s largest steel LSB for 60 Hz applications is 38 in long and offers an exhaust area of
about 80 ft2 (7.4 m2) per flow. The corresponding 50 Hz LSB is 45 in long and offers 115 ft2
(10.7 m2) per flow. Alstom’s largest titanium LSB has a length of 42 in for 60 Hz and 49 in for
50 Hz applications. The corresponding exhaust areas are 99 ft² (9.2 m²) and 142 ft² (13.2 m²),
respectively. These large LSB can be used not only to improve the efficiency by reducing the
exhaust losses, but also to save a
LP casing. Using the 49 in LSB
for typical Central European
inland site conditions with a wet
cooling tower allows Alstom to
offer a 1’100 MW steam turbine
generator with only four casings
and a very competitive
efficiency level. The optimal
solutions for the 60 Hz market
are a 6 LP flow arrangement for
the 1’000 MW output class and
4 LP flow for the 700 MW
output class (Figure 8). Alstom
is well experienced with 6 LP
flow arrangements and has
several references with extensive
operating experience.
Figure 8: Steam turbine generator set with well proven 6 LP flowand extremely compact 4 LP flow arrangement
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
Boiler feed pump turbine
The compact turbine layout can be enhanced by a boiler feed pump turbine (BFPT). The BFPT
(Figure 9) extracts steam from the IP section of the main turbine and reduces the steam flow
through the LP turbine. The BFPT helps to keep the exhaust losses of the main turbine at a
satisfactory level by enlarging the total exhaust area and can therefore improve overall plant
efficiency. Since the BFPT drive does not draw power from the generator, the BFPT enables the
plant operator to provide the utmost power to the grid.
In contrast to the main turbine, the
BFPT has to cover a more or less
wide range of swallowing capacity.
For instance, at summer conditions
the condenser pressure of the BFTP
increases compared to average
conditions. The higher condenser
pressure reduces the length of the
expansion line whereas the needed
power output of the BFPT stays
constant. As a result, the BFPT
consumes more steam. If the
extraction point stays in the IP
section of the main turbine, the
needed swallowing capacity of the
BFPT increases. Therefore, the
summer conditions typically define
the design case for the swallowing capacity of the BFPT. In the best case (design case) of the
main turbine, which is normally at average conditions, the BFPT operates at part load and has to
be throttled to adapt its swallowing capacity. The efficiency of the BFPT decreases with
increasing throttling which can be more than 10%. As an alternative, the extraction point can be
switched to the cold reheat line. But the negative impact on the overall cycle efficiency is
enormous and normally overweighs the reduction of the BFPT efficiency by throttling.
Figure 9: 3D model and drawing of a BFPT
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
To get the best efficiency for the BFPT over a more or less wide range of swallowing capacity,
Alstom can offer two inlet configurations for the BFPT: with and without control stage. Whereas
the first offers better efficiencies at partial loads, the second has the better efficiency at full load.
Both types can be provided with steam from either the IP section of the main turbine or the cold
reheat line. A combination of both (dual admission) is also possible. Depending on the operating
mode of the main turbine, the selection of the inlet configuration in combination with the steam
extraction point must be optimized specifically for each application. To adapt the exhaust area of
the BFPT to different cooling conditions and power output ranges, the BFTP can be a single- or
double-flow with two different length of LSB. Moreover, the preferred 100% BFPT and pump
solution reduces the overall cost. Therefore, this solution is the optimal one for the largest power
output classes from both an economical and efficiency point of view. Of the fourteen steam
turbine generator sets for USC applications ordered/awarded to Alstom, seven will be equipped
with an Alstom BFPT.
GIGATOP TURBOGENERATOR
For full speed applications with high
output, Alstom has developed and
optimized the GIGATOP turbogenerator
(Figure 10) over the last decades. The
GIGATOP modular design matches
power output requirements from
500 MVA up to 1’400 MVA. Special
design features contribute to the
excellent performance values of Alstom
steam turbine generator for USC
applications.
The previously mentioned single bearing concept together with the use of static excitation design
results in a very short overall lengths. Further unique design features like stainless steel hollow
conductors within the stator bars, Micadur® insulation of the bars, and laminated press plates at
both ends of the stator core lead to outstanding availability and efficiency. These performance
Figure 10: GIGATOP turbogenerator in operation
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
figures are proven by the large operational experience of the Alstom GIGATOP fleet, which
includes the largest two-pole turbogenerators in operation worldwide (Lippendorf R&S). This
number one position is further extended with the 1’100 MW applications shown in Figure 1.
CONCLUSIONS
The worldwide growing electricity demand increases the pressure to conserve both resources and
environment. Modern high efficiency coal-fired power plants with USC steam cycle parameters
can significantly contribute to fulfil these obligations. Currently, the parameters have reached
3990 psia (27.5 MPa) for the main steam pressure, 1110°F (600°C) for the main steam
temperature, and 1150°F (620°C) for the reheat temperature. With these steam cycle parameters,
overall efficiencies of coal-fired power plants with wet cooling tower of approximately 46% for
hard coal and 43% for brown coal (both based on LHV) at typical Central Europe inland sites are
achievable. In parallel with increasing steam cycle parameters, Alstom has worked on three key
features to improve the steam turbine efficiency itself: advanced 3D blade and steam path design,
improved sealing technologies, and advanced top performing last stage blades with optimized
diffuser and exhaust. The higher requirements on steam turbines for USC applications
concerning operational aspects are met by well proven Alstom design features like the shrink
ring design of the HP inner casing and the welded rotor design. Additionally, some minor
adaptations of the standard design, e.g. as for the IP casing, have been implemented. The single
bearing concept together with large exhaust areas allow Alstom to offer a compact four-casing
1’100 MW steam turbine generator set for 50 Hz USC applications at a very competitive
efficiency level. An Alstom 100% boiler feed pump turbine can further improve such solutions.
Due to the reduced exhaust area available for LP turbines in 60 Hz applications, a 6 LP flow
arrangement is typically the superior solution for highest capacity units. This well proven
arrangement enables Alstom to build high efficient steam turbine generators set up to 1’000 MW
for 60 Hz grids in a tandem compound design. Such large steam turbine generator sets,
consisting of the Alstom steam turbine STF100 and the GIGATOP turbogenerator, allow low
electricity generation cost while saving resources and minimizing environmental impact.
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____________________________________________________________________________________________________________________ PowerGen International 2007 Klotz Pickering Brandt 11.-13. December 2007 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose.
REFERENCES
[1] W. Reichel, Langfristige Kohleverstromung in Deutschland trotz CO2-Restriktionen? Glückauf 140 (2004), Nr. 1/2, pp. 48-53.
[2] World Energy Outlook 2006, International Energy Agency.
[3] International Energy Outlook 2007,
Energy Information Administration. [4] The Coal Resource – A Comprehensive Overview of Coal
World Coal Institute, 2005. [5] A. Tremmel and D. Hartmann,
Efficient steam turbine technology for fossil fuel power plants in economically and ecologically driven markets, VGB Power Tech, 11/2004, pp. 38-43.
[6] A. Tremmel, H. Mandel, U. Klauke, C. Brandt
Modernste Turbinentechnologie mit höchsten Dampftemperaturen für das Kraftwerk Boxberg, Block R, VGB Power Tech, 12/2006, pp. 71-75.
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