24044811 supercritical technology in boilers
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SUPER CRITICAL TECHNOLOGY
Presented By:Amit Joshi
UPES Dehradun,India
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Introduction "Supercritical" is a thermodynamic expression
describing the state of a substance where there is noclear distinction between the liquid and the gaseousphase.
Supercritical Power plants operate at highertemperatures & higher pressure resulting in higher
efficiencies i.e., up to 46 percent for supercriticalplants and lower emissions than traditional(subcritical) coal-fired plants.
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WHAT IS A SUPERCRITICAL BOILER? Supercritical steam generators (also known as Benson boilers) are
frequently used for the production of electric power.
In contrast to a "subcritical boiler", a supercritical steam generatoroperates at such a high pressure (over 3,200 psi/22.06 MPa 3,200
psi/220.6 bar that actual boiling ceases to occur, and the boiler has nowater - steam separation.
There is no generation of steam bubbles within the water, because thepressure is above the "critical pressure" at which steam bubbles canform.
It passes below the critical point as it does work in the high pressureturbine and enters the generator's condenser.
This is more efficient, resulting in slightly less fuel use. The term"boiler" should not be used for a supercritical pressure steam generator,as no "boiling" actually occurs in this device.
http://wapedia.mobi/en/Supercritical_fluidhttp://wapedia.mobi/en/Mark_Benson_(engineer)http://wapedia.mobi/en/Mark_Benson_(engineer)http://wapedia.mobi/en/Supercritical_fluid -
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WHAT IS SUPERCRITICAL TECHNOLOGY? Above 221 bars, two phase mixtures of water and steam cease to exist
They are replaced by a single supercritical fluid.
This eliminates the need for water/steam separation in drums duringoperation
Thus allowing a simpler separator to be employed during start-up
conditions. The transition to steam temperatures of 600C and higher is now a
further major development step, which decisively affects many aspectsof the design of the power plant, especially of the boiler
Critical Point
22.1MPa-373C
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Special feature of supercritical boilers Capacity to operate under low load.
Suitability for continuous variable loads.
Suitability for cyclic operations. Suitability for two shift operations.
Quicker start up and shut down capability.
Larger unit size.
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Advantages of Supercritical technology
Today supercritical units can achieve thermalefficiency of more than 45 percent, compared with atypical subcritical plants 30-38 percent.
Higher firing temperatures and pressures translateinto better efficiency, defined as more electricitygenerated per BTU of coal consumed.
super critical technology will result in saving of about
4% of fuel and correspondingly less emission. The Benson design offers a number of advantages,
including simplified start up and the ability to operatein sliding pressure mode.
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LIMITATIONS Economy of scale.
Problem with the metallurgical limit .
An increase in steam temperature (>700 C) is possible but
without NICKEL based materials it is not possible to obtain
more than 10K to 20K.
Double reheating is required to prevent Inlet pressure
turbine exhaust wetness
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Extremelyhigh initial build cost.
More complicated to operate.
Much higher O&M costs.
Not very flexible, generation changes are slowand minimal, usually only for "base-load"generation.
Environmental considerations.
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1960s 1970s 1980s 1990s 2000s 2010s
Mature
Technology
R&D-
Advance
USCSubcritical
170/540oC/540o
Super critical 245/540/540
245/540/565
245-580/600
285-600-620
285-630/650
382-700/720
ULTRA SUPERCRITICAL
Year
SUPERCRITICALSUB-
CRITICAL
Und
erInduction
Alread
yInducted
International Scenario of Supercritical Technology
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CO2 Reduction Scenarios
0
200
400
600
800
1000
1200
1400
30 35 40 45 50 55 60
Plant Net Efficiency
CO2
Emissionskg/MWh
USCA-USC
Super Critical
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Capacity addition based on Supercriticaltechnology
11 number supercritical units totaling to 7,540 MW
under construction during 11th Plan.
20 number supercritical units totaling to 14,000 MWordered so far for 12th Plan
13 number UMPP, each of about 4,000 MW capacity,based on supercritical technology planned. Four UMPPalready awarded
About 62 number supercritical units totaling to44,000 MW likely to be added during 12th Plan.
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Super Critical Technology in NTPC
UPCOMING PLANTS
North Karanpura, Jharkhand 3x660 MW
Darlipali, Orissa 4x800 MW
Lara, Chattisgarh 5x800 MW
Marakanam, Tamilnadu 4x800 MW
Tanda-II, Uttar Pradesh - 2x660 MW
Meja, Uttar Pradesh - 2x660 MW
Sholapur 2x660 MW
New Nabinagar-3x660 MW
Many more projects including 800 MW ultra super critical units
under consideration