Concept of Super Critcal technology
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Transcript of Concept of Super Critcal technology
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CONCEPT OF
SUPER CRITICALCYCLE
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What is importance
History of this technology
Super Critical cycle details
Presentation Outline
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PERCAPITA ELECTRIC POWER CONSUMPTION
COUNTRY PERCAPITA ELECTRICPOWER CONSUMPTION KWH
INDIA 513CHINA 773
CANADA 16413
USA 13040
MEXICO 1439
NORWAY 24033
SWITZERLAND 7346
FRANCE 7069
UNITED KINGDOM 5968
SPAIN 4072
RUSSIA 5108
ITALY 4610
SWEDEN 15244
GERMANY 6406TURKEY 1259
JAPAN 7749
These are collected from Ststistics Organisation for Economic Cooperation and Development of I.E.A.
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Emerging Market Requirements For Utility
Units
High Reliability & Availability
Highest economically achievable plant
efficiency and heat rate
Suitable for differing modes of operation Suitable for different quality of fuel
Ability to operate under adverse grid conditions
/ fluctuations
Minimum emission of Pollutants Lowest life cycle cost
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Thermal Power GenerationHigher cycle efficiency for: Conservation of fuel resources
Reduction of Atmospheric Pollutants - SOX& NOX
Reduction in CO2 emission (linked to
global warming)
Better economy in power generation where
fuel costs are high and pollution controlrequirements are stringent
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GROWTH OF UNIT SIZES IN INDIA
RATING YEAR OF INTRODUCTION
60/70MW 1965
110/120MW 1966200/210MW 1972
250MW 1991
500MW 1979
660MW Commg
800 MW PROPOSAL STAGE
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AS THE UNIT SIZES GREW, BOILER SIZES SUPPLYING
STEAM TO SUCH TURBINES HAVE ALSO INCREASED
UNIT STEAM SHO SHO/RHO
SIZE FLOW PRESSURE TEMPERATURE
(T/H.) (KG/CM2) (DEG. C)
30MW 150 63 490
60/70MW 260 96 540
110/120MW 375 139 540/540
200/210MW 690 137/156 540/540
250MW 805 156 540/540
500MW 1670 179 540/540
600MW 2100 255 540/568
800 MW 2565 255 568/596
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Major Sulzer/Combustion Engineering
Innovations for Fossil Utility Boilers
First Sulzer Boiler
First Pulverized Coal Fired Utility Boiler
Tangential Firing
First Commercial Monotube SteamGenerator
Controlled Circulation
First Commercial Supercritical MonotubeSteam Generator
1841
1912
1927
1931
1942
1954
Year of Introduction
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Major Sulzer/Combustion Engineering
Innovations for Fossil Utility Boilers
MHI Adopted as Monotube Technology Licensee
Highest Temperature and Pressure Supercritical
Boiler
Combined Circulation - Supercritical
Largest Oil/Gas Fired Supercritical Steam
Generator
Controlled Circulation Plus
Sliding Pressure Supercritical
1957
1960
1964
1970
1978
1980
Year of Introduction
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Fuels for Steam Power PlantsCoal & Lignite:
Abundant availability Lower cost
Will continue as the main fuels in many
countries
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Cycle EfficiencyHigher efficiency can be realised with
Higher live steam parameters
Adoption of double reheat cycle
Reduction in condenser absolute pressure
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Measures to improve Plant Efficiency and / or
Heat Rate
Boiler side measures :
Minimum RH spray
Minimum SH spray (if tapped off before feed heaters)
Minimum flue gas temperature at AH outlet
Minimum excess air at AH outlet
Minimum unburnt Carbon loss
Reduced auxiliary power consumption
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Increase of CycleEfficiency due to SteamParameters
300241
175 538 / 538
538 / 566
566 / 566
580 / 600
600 / 620
6,77
5,79
3,74
5,74
4,81
2,76
4,26
3,44
1,47
3,37
2,64
0,752,42
1,78
00
1
2
3
4
5
6
7
8
9
10
HP / RH outlet temperature [deg. C]Pressure [bar]
Increase of efficiency [%]
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Approximate improvement in Cycle Efficiency
Pressure increase : 0.005 % per bar
Temp increase : 0.011 % per deg K
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500 MW Steam Generator
Coal Consumption and Emissions
Subcritical
Unit
Supercritical
Unit
Coal Saving t/year Base 68800
CO2 Reduction t/year Base 88270
SO2 Reduction t/year Base 385
Basis:
Cycle Efficiency % Base +1.0
No. of operating
hrs.
Hrs./year 8000 8000
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Steam generation details
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Supercritical Cycles Initially adopted in the late fifties and sixties
Higher Steam temperature employed on some units
Unit sizes also witnessed an increasing trend
Slidi P S i i l D i
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Enthalpy Variations vs Pressure and Boiler Load
Sliding Pressure Supercritical Design
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Operating ExperienceThe first generation
supercritical units
Experienced increasedforced outages
Witnessed reduced plant
reliability and availability
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Comparison of Subcritical and
Supercritical
Cycle Availability (NERC)
0
2
4
6
8
10
12
14
EFOR %
Plant (Super) 13.347 12.077 9.668 7.685 7.534 7.482
Plant (Sub) 10.405 9.439 8.16 6.793 7.103 7.013
Blr (Super) 8.441 7.285 5.823 4.872 4.434 4.023
Blr (Sub) 5.928 5.464 4.344 3.811 3.926 4.018
1982-1984 1985-1987 1988-1990 1991-1993 1994-1996 1997
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Increased outages were caused
by Inadequate experience while extrapolating
to the new designs and the increased unit
sizes.
Inadequate knowledge of high
temperature materials.
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The increased outages led to :
Reversal of steam pressures to subcritical
range
Lowering of steam temperatures to 540
Deg C
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Current Trends in Steam Parameters
1980s : Pressure increased from 175-180
bar to 225 bar; temp mostly
around 540 Deg C
1990 : Pressures raised to 285 bar;temp
raised to 565-580-600 Deg C
300 bar & 620 Deg C not unusual today
255 bar 568/568 Deg C commonly used presently
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Implications of higher steam parameters on
boiler design
Boiler type
Materials
Reliability and Availability
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Types of boilers
Drum type
Once-through type
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Drum type boiler
Steam generation takes place in furnace water walls
Fixed evaporation end point - the drum
Steam -water separation takes place in the drum
Separated water mixed with incoming feed water
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Drum type boiler
Natural Circulation Boiler Circulation thru water walls by
thermo-siphon effect
Controlled Circulation Boiler
At higher operating pressures
just below critical pressure levels,
thermo-siphon effect supplemented
by pumps
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THE CONCEPT
The mass flow rate thru all heat transfer circuits
from Eco. inlet to SH outlet is kept same except at
low loads wherein recirculation is resorted to
protect the water wall system
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COTROLLED CIRCULATION
(Vs) ONCE THRU
CC OT
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Once Through Boiler-Concept
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Once Through Boiler
Once -through flow through all sections of
boiler (economiser, water walls &
superheater)
Feed pump provides the driving head
Suitable for sub critical & super critical
pressures
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Once-thru BoilerMajor differences from Drum type boiler :
Evaporator system
Low load circulation system Separator
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Once -thru BoilerEvaporator system : Formed by a number of parallel tubes
Tubes spirally wound around the furnace to
reduce number of tubes and to increase the massflow rate thru the tubes
Small tube diameter
Arrangement ensures high mass velocity thru the
tubes
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Once -thru Boiler - Furnace Wall
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Furnace Arrangement
VERTICAL TYPE
SPIRAL TYPE
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ONCE - THROUGH OPERATING RANGE
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Once -thru Boiler Low load circulation system :
At part loads once -thru flow not adequate to cool the tubes
To maintain required mass velocities boiler operates on
circulating mode at low loads
Excess flow supplied by feed pump or a dedicated circulating
pump
LOW LOAD SYSTEM WITH CIRC
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LOW LOAD SYSTEM WITH CIRC.
PUMP
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Once - thru Boiler
Low load circulation system :
The excess flow over the once-thru flow
separated in separator and
Returned to the condenser thru a heatexchanger
or
Recirculated back to the boiler directlyby the dedicated circulating pump
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Once -thru BoilerSeparator :
Separates steam and water during the
circulating mode operation
Runs dry during once-thru flow mode
Smaller in size compared to drum in a
drum type boiler
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Typical Separator sizes
Number of separators 2 4
Inside diameter approx mm 850 600
Thickness mm 95 70
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Once -thru Boiler
Advantages: Better suited for sliding pressure operation
Steam temperature can be maintained over wider load range
under sliding pressure
Quick response to load changes
Shorter start up time
Higher tolerance to varying coal quality
Suitable for sub critical & super critical pressures
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Sliding Pressure Operation
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Advantages of sliding pressure operation:
Lower thermal stresses in the turbine during load changes. Control range of RH temp is extended.
Reduced pressure level at lower loads prolongs the life
span of the components.
Overall reduction in power consumption and improved heat
rate.
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Once -thru Boiler
Requirements : Stringent water quality
Sophisticated control system
Low load circulation system
Special design to support the spiral furnace wall weight
High pressure drop in pressure parts
Higher design pressure for components from feed pump
to separator
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Advanced Cycles
Effect on Boiler Components Evaporator (Furnace) walls
Superheaters Thickwalled boiler components
Steam piping
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Furnace walls Increased operating pressure increases
the medium temperatures.
Increased regenerative feed heating
increases the fluid temp entering.
Larger furnaces required for NOX
reduction, increase SH steam temperature
at furnace wall outlet.
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Superheaters
Tube metal temperatures in final sections
increase with outlet steam temperature.
Susceptibility for high temperaturecorrosion.
Susceptibility to steam side oxidation
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Thick walled components Higher pressure & temperature lead to
increased thickness of :
Shells of separator, start-up system
components, SHO header.. Main steam piping.
Higher thickness results in larger temperature
gradients across walls.
Changed heat release in the furnace
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Varying combustion and fouling behaviour ofdifferent coals within a wide range of coalscause varying heat release and heat
absorption in the furnace
Benson boiler principle compensates theseeffects by shifting of the final evaporation
point without diminishing efficiency
Changed heat release in the furnace
by varying coal qualities
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Definition of Supercritical DesignEvaporator pressure (MCR) 222 bar e SupercriticalDesign
Source: Siemens
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First Fire to Turbine Synch,
Minute without Bypass System
First Fire to Turbine Synch,
Minute with Bypass System
Hot Start Up, after 2 hr shutdown 40 30
Warm Start Up, after 8 hr shutdown
65
45
Cold Start Up, after 36 hr shutdown 130 90
Faster Start-up Time with Supercritical Design
First Fire to Turbine Synch,
Minute without Bypass System
First Fire to Turbine Synch,
Minute with Bypass SystemHot Start Up, after 2 hr shutdown 40 30
Warm Start Up, after 8 hr shutdown 65 - 90 45 - 70
Cold Start Up, after 36 hr shutdown 180 - 260 140 - 220
Once - Thru
Drum
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Present Trend in IndiaUnit Size
MW
SHO
flow(t/hr)
SHO pr.
(Kg/Sq.cm)
SHOT
(C)
RHOT
(C)
660 2100 255 568 596
800 2565 255 568 596
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Typical Parameters
SH OutletSteam Temp.,
F
RH OutletSteam Temp.
F
Drum Type 3% per minute (30%-100% load) +/- 10 +/- 15 5% per minute (50% - 100% load) +/- 35 +/- 40Once-Through 3% per minute (30% - 100% load) +/-10 +/-10 5% per minute (50% - 100% load) +/-10 +/-12Note:Above values are based on sliding pressure mode and a 5 minute load ramp.
Tighter Control of Steam Temperatures
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