1 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 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 has designed the next generation USC steam turbine generator 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 1150F / 1180F), 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 and 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 USC project illustrates the latest design and technology capabilities of GE Energy and sets the standard for future 1000 MW USC applications. 1. INTRODUCTION 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 / 621C (4500 psi / 1150F). 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 / 600C / 610C (3626 psi / 1112F / 1130F). This 1000 MW USC steam turbine design is a natural evolution of GE’s USC technology. GE continues to develop and refine USC steam turbine technology. With the emerging interest in reducing emissions, including green house gases from coal
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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
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 has designed the next generation USC
steam turbine generator 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 1150F /
1180F), 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 and 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 USC project illustrates the latest design and technology capabilities of GE Energy and
sets the standard for future 1000 MW USC applications.
1. INTRODUCTION
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 / 621C (4500 psi / 1150F). 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 / 600C / 610C
(3626 psi / 1112F / 1130F). This 1000 MW USC steam turbine design is a natural evolution of GE’s
USC technology. GE continues to develop and refine USC steam turbine technology.
With the emerging interest in reducing emissions, including green house gases from coal
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fired power generation, GE Energy is striving to increase USC PC generation output and efficiency in
its 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 objective, GE Energy
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: 610C (1130F)
Reheat steam temperature: 621C (1150F)
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
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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.
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.
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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, and additional condenser, as well as a larger footprint for the 45” LP section.
These considerations resulted the selection of a 4-flow 45” LP section design. The overall
turbine configuration is shown in Figure 1.
Figure 1 - 4-casing, 4-flow LP Configuration
2.3 Evaluation of Ultra Super Critical Technology
The history of steam turbine development is 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 enabling 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: