2. Types of Power Plants
(1)SUBCRITICAL
(2)SUPERCRITICAL
(3)ULTRA SUPERCRITICAL
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3. Water/steam circulation systems are divided
into two main classifications:
(1) Drum-Type Boiler
(2) Once-Through Boiler
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4. Use less coal per unit of production compared
with subcritical boilers.
Lower pollution levels.
Better efficiency.
A next step in the development of coal-based
power production technologies would be
carbon capture.
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6. The main technical challenge with
supercritical plants is that the higher steam
pressure and temperature require
components (superheaters, headers, water
tubes, steam chests, rotors and turbine
casings) which are produced from nickel-
based alloys.
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7. Nickel is an expensive commodity so that for
an increased use of SPF at lower costs further
developments are needed in new steels for
water and boiler tubes and high-alloy steels
that minimize corrosion.
Another operational aspect which would
support the market penetration of
supercritical and ultra-supercritical plants is
the development of advanced control
equipment and procedures (i.e. expert
systems, condition monitoring) to operate a
plant more flexibly.
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8. With respect to developing countries with a
high coal consumption, such as China and
India, SPF technology transfers could take
place by the sale of equipment, licensing, joint
ventures, co-operative production,
subcontracting of the manufacture of
components, and co-operative research and
development .
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9. Approximately 97% of global coal-base power
production capacity is based on pulverised
coal combustion.
Many conventional pulverised coal-fired
power plants have been improved by
upgrading the system so that emissions of
several pollutants could be reduced, but the
efficiency gains are minimal as the heat rates
can only be improved at existing plants by 3 to
5%-points at best.
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11. Steam cycle Subcritical Supercritical Ultra-supercritical
(best available)
Ultra-supercritical
(AD700)
Steam
conditions
180 bar (540oC) 250 bar (560oC) 300 bar (600oC) 350 bar (700oC)
Net output (MW) 458 458 456 458
Net efficiency (%) 40.2 42.0 43.4 50.6
CO2 emissions
(t/MWh-net)
0.83 0.80 0.77 0.73
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12. This analysis identifies optimized cycle
configurations and steam conditions for coal-
fired power project SC and USC designs that
will yield the best overall ST efficiency.
For a predetermined plant net power output of
600 MW, nominal matrices of thermal
performance and differential costs
were developed by varying the main steam
pressure and the main/reheat steam
temperatures.
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13. The pressure range was set from 3,500 psia
(240 bar) to 4,500 psia (310 bar), and main
steam/reheat temperatures from 1,000
°F/1,000°F (538 °C/538 °C) to 1,300 °F/1,300
°F (705°C/705 °C).
The heat balances were developed for a
variety of pressure and temperature
combinations using commercially available
simulation programs.
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14. As indicated in Figure 1, an increase in operating
pressure without a respective increase in
operating temperature is counterproductive.
The best results are achieved at the highest
pressure and temperature , an improvement of
0.39 percent compared with the base case.
The cycle optimization analysis indicates that the
higher the main steam throttle temperature,
when accompanied by a corresponding increase
in main steam pressure, thebetter the cycle
efficiency.
An increase in reheat temperatures also improves
the cycle efficiency, but to a lesser degree.
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15. The optimum approach is a thermal cycle
design that incorporates significant increases
in both main steam pressure and temperature.
A key aspect of the design is the determination
of the enthalpy end point (EEP) or moisture
level in the exhaust of the LP turbine.
A thermal cycle design that incorporates
significant increases in the operating pressure
of the ST without comparable
increases in temperature can lead to an EEP in
the wet zone of the LP exhaust greater than
the average of 10–12 percent.
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16. The high thermal efficiency of the SC and USC
steam power plants cannot be achieved without
the use of new alloys with higher creep strength
and improved oxidation resistance.
Operation above 1,000 °F was possible due to the
continuous development effort to improve the 9–
12 percent ferritic steels (T91/P91, T92/P92,
T112/P122), as well as some advanced austenitic
alloys (TP347, HFG, Super 304).
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17. It should be noted that the high temperature
strength of ferritic steels (P92, P122,E91) is
equal to that of the low-end austenitic alloys,
but their resistance to oxidation is lower.
The European material development program
AD 700 (named for its target of achieving
700°C [1,292 °F] as the MST)
includes research institutes and several major
ST manufacturers, including Siemens, Ansaldo,
and Alstom, which are actively collaborating
on this effort, despite being fierce commercial
competitors.
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18. To minimize thermal and operational stresses,
HP sections of USC equipment use triple-shell
construction.
With this type of arrangement, the outer
casing is not subject to elevated temperatures
and can be constructed of traditional CrMoV
material. The nozzle box is exposed to the
highest pressures
and temperatures and should be made of
forged 12CrMoVCbN steel.
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19. The choice of material for bolting appears to
be relatively easy. The major requirements are
high resistance to stress relaxation, thermal
expansion compatibility, and low notch
sensitivity.
As with ST rotating blades, the experience
accumulated from the use of identical
materials in large industrial gas turbines
operating at high temperatures is also relevant
for these applications.
The status of material development for ST
parts used in various high pressure and high
temperature applications is given in Table .
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21. COBALT:-
Cobalt is resistant to stress and corrosion
at high temperatures.
CHROMIUM :-
Chromium is helpful in high corrosion
resistance and hardness.
TITANIUM :-
It optimizes special properties such as
fracture toughness, fatigue strength, and high-
temperature creep strength.
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23. Element
Material
Ni Cr Co Mo Other
INCONEL
625
63.5 21.5 0 9 Al,Ti,Mb
INCONEL
617
52 22 12 9.5 Al,Ti
INCONEL
263
51 20 20 6 Al,Ti
INCONEL
740
50 24 20 0.5 Al,Ti,Nm
Sanicro 25 25 22 1.5 0 W,Cu,Fe
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24. The new AD700 technology of coal-fired
power plants supports the aim of the Kyoto-
protocol to reduce the CO2 emission in a mid-
term perspective under the target for a secure
and stable energy price.
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25. The previous graph shows that as efficiency
increases, specific carbon dioxide emissions
decrease from 1100g/kWh at 30% net plant
efficiency to 650g/kWh at 50% efficiency. This
equates to a reduction in carbon dioxide
emissions of 41%. Coal is similarly reduced
and clearly illustrates the benefits of efficiency
increase with regard to potential
environmental protection.
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27. In parallel with an ongoing R&D programme
aimed at the development of a high
temperature, solid solution nickel alloy (Alloy
617) for application to both pipe work and
superheater tubes, the AD700 programme
investigated precipitation-hardening nickel
alloys (Alloy 263 and Alloy 740).
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28. The high cost of nickel, however, prohibits its
extensive use in tubes, and so the boiler
materials programme also set out to develop a
high temperature austenitic steel with average
stress rupture properties of 100MPa following
100,000 hours operation at 700°C.
The austenitic material developed, Sanicro 25,
has been successfully produced in commercial
quantities and is has undergone extensive
testing as part of the phase 3 programme.
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29. Nickel-based Alloys 617 and 625
were the main candidates for many turbine
components and their characterization in
terms of creep, creep/fatigue crack growth,
low cycle fatigue for castings, forgings and
welds was successfully completed.
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30. Due to difficulties experienced with the
castability of Alloy 617, most of the effort has
been focussed on the casting of Alloy 625.
Both 617 and Alloy 625 have been successfully
forged and considered suitable for HP and IP
rotor forgings.
Welded rotor will be a key feature of AD700
turbine technology. Prototype joints have been
manufactured successfully by welding 10%
Chrome steel to the nickel-based alloy.
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32. TURBINE INLET VALVE:The Component Test
Facility (including the Goodwin alloy 625
valve) is installed in the coalfired
power plant “Scholven F” located in
Gelsenkirchen (Germany). The valve casting
has been in service operating at 705’C
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33. The AD700 Programme Phase 2 project
participants are listed below:
# Tech-wise A/s
# ALSTOM (Switzerland) Ltd
# ALSTOM Power Boiler GmbH
# ALSTOM Power Ltd
# ALSTOM Power
# Ansaldo Caldei
# Ansaldo Ricerche
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34. # Babcock-Hitachi Europe GmbH
# BOHLER Edelstahl GmbH & Co KG
# Burmeister & Wain Energy A/S
# Cantro Sviluppo Materiali S.p.A
# CESI Spa
# Doncasters FVC Ltd
# EDF R&D
# EDF-SEPTEN
# Eindhoven University of Technology
# ENEA CRF
# Energi E2 A/S
# EPPSA
# Fortum Power and Heat Oy
# Goodwin Steel Castings Ltd
# GRUPO EDP - Electricidade de Portugal
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35. Development of an AD700 power plant
supports the European commitments for
emission reduction made in the Kyoto Treaty.
The resources are protected through more
efficient utilisation of the fuel coal. The
competitive situation of the energy industry
will be strengthened and secured with regard
to both operators and manufacturers.
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36. These technologies can combust pulverised
coal and produce steam at higher
temperatures and under a higher pressure, so
that an efficiency level of 50% can be reached
(ultra-supercritical plants). Supercritical and
ultra supercritical power plants have become
the system of choice in most industrialised
countries.
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37. We must
# Adopt Super Critical technology and work for
Ultra Super Critical Technology.
# Put efforts for inducting Clean Technologies
# Revise its energy mix by including non-fossil
fuel based generation such as those from
hydro, nuclear and renewable energy in its
portfolio.
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