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April 11, 2023 PMI Revision 00 1
CONCEPT OF SUPER CRITICAL
CYCLE
April 11, 2023 PMI Revision 00 2
• What is importance • History of this technology• Super Critical cycle details
Presentation Outline
April 11, 2023 PMI Revision 00 3
PERCAPITA ELECTRIC POWER CONSUMPTION
COUNTRY PERCAPITA ELECTRICPOWER CONSUMPTION –KWH
INDIA 513CHINA 773CANADA 16413USA 13040MEXICO 1439NORWAY 24033SWITZERLAND 7346FRANCE 7069UNITED KINGDOM 5968SPAIN 4072RUSSIA 5108
ITALY 4610SWEDEN 15244GERMANY 6406TURKEY 1259JAPAN 7749
These are collected from Ststistics Organisation for Economic Cooperation and Development of I.E.A.
April 11, 2023 PMI Revision 00 4
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
April 11, 2023 PMI Revision 00 5
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 control requirements are stringent
April 11, 2023 PMI Revision 00 6
GROWTH OF UNIT SIZES IN INDIA
RATING YEAR OF INTRODUCTION
60/70MW 1965
110/120MW 1966
200/210MW 1972
250MW 1991
500MW 1979
660MW Commg
800 MW PROPOSAL STAGE
April 11, 2023 PMI Revision 00 7
AS THE UNIT SIZES GREW, BOILER SIZES SUPPLYING STEAM TO SUCH TURBINES HAVE ALSO INCREASED
UNIT STEAM SHO SHO/RHOSIZE 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
April 11, 2023 PMI Revision 00 8
Major Sulzer/Combustion EngineeringInnovations for Fossil Utility Boilers
• First Sulzer Boiler
• First Pulverized Coal Fired Utility Boiler
• Tangential Firing
• First Commercial Monotube Steam Generator
• Controlled Circulation
• First Commercial Supercritical Monotube Steam Generator
1841
1912
1927
1931
1942
1954
Year of Introduction
April 11, 2023 PMI Revision 00 9
Major Sulzer/Combustion EngineeringInnovations 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
April 11, 2023 PMI Revision 00 10
Fuels for Steam Power PlantsCoal & Lignite:
• Abundant availability• Lower cost• Will continue as the main fuels in many
countries
April 11, 2023 PMI Revision 00 11
Cycle EfficiencyHigher efficiency can be realised with
• Higher live steam parameters • Adoption of double reheat cycle• Reduction in condenser absolute pressure
April 11, 2023 PMI Revision 00 12
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
April 11, 2023 PMI Revision 00 13
Increase of Cycle Efficiency due to Steam
Parameters
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
0,75
2,42
1,78
00
1
2
3
4
5
6
7
8
9
10
HP / RH outlet temperature [deg. C]Pressure [bar]
Increase of efficiency [%]
April 11, 2023 PMI Revision 00 14
Approximate improvement in Cycle Efficiency
Pressure increase : 0.005 % per bar
Temp increase : 0.011 % per deg K
April 11, 2023 PMI Revision 00 15
500 MW Steam GeneratorCoal Consumption and Emissions
SubcriticalUnit
SupercriticalUnit
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 operatinghrs.
Hrs./year 8000 8000
April 11, 2023 PMI Revision 00 16
Steam generation details
April 11, 2023 PMI Revision 00 17
Supercritical Cycles• Initially adopted in the late fifties and sixties • Higher Steam temperature employed on some units • Unit sizes also witnessed an increasing trend
April 11, 2023 PMI Revision 00 18
Enthalpy Variations vs Pressure and Boiler Load
Sliding Pressure Supercritical DesignSliding Pressure Supercritical Design
April 11, 2023 PMI Revision 00 19
Operating Experience
The first generation supercritical units
• Experienced increased forced outages
• Witnessed reduced plant reliability and availability
April 11, 2023 PMI Revision 00 20
Comparison of Subcritical and SupercriticalCycle 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
April 11, 2023 PMI Revision 00 21
Increased outages were caused by
• Inadequate experience while extrapolating to the new designs and the increased unit sizes.
• Inadequate knowledge of high temperature materials.
April 11, 2023 PMI Revision 00 22
The increased outages led to :
• Reversal of steam pressures to subcritical range
• Lowering of steam temperatures to 540 Deg C
April 11, 2023 PMI Revision 00 23
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
April 11, 2023 PMI Revision 00 24
Implications of higher steam parameters on boiler design
Boiler type
Materials
Reliability and Availability
April 11, 2023 PMI Revision 00 25
Types of boilers
Drum type
Once-through type
April 11, 2023 PMI Revision 00 26
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
April 11, 2023 PMI Revision 00 27
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
April 11, 2023 PMI Revision 00 28
Once Through Boiler-Concept
April 11, 2023 PMI Revision 00 29
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
April 11, 2023 PMI Revision 00 30
COTROLLED CIRCULATION (Vs) ONCE THRU’
CC OT
April 11, 2023 PMI Revision 00 31
Once Through Boiler-Concept
April 11, 2023 PMI Revision 00 32
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
April 11, 2023 PMI Revision 00 33
Once-thru Boiler
Major differences from Drum type boiler :
• Evaporator system• Low load circulation system• Separator
April 11, 2023 PMI Revision 00 34
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 mass flow rate thru’ the tubes
• Small tube diameter• Arrangement ensures high mass velocity thru the
tubes
April 11, 2023 PMI Revision 00 35
Once -thru Boiler - Furnace Wall
April 11, 2023 PMI Revision 00 36
Furnace ArrangementFurnace Arrangement
VERTICAL TYPE
SPIRAL TYPE
April 11, 2023 PMI Revision 00 37
ONCE - THROUGH OPERATING RANGE
April 11, 2023 PMI Revision 00 38
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
April 11, 2023 PMI Revision 00 39
LOW LOAD SYSTEM WITH CIRC. PUMP
April 11, 2023 PMI Revision 00 40
LOW LOAD SYSTEM WITH HEAT EXCHANGER
April 11, 2023 PMI Revision 00 41
Once - thru’ BoilerLow load circulation system :
The excess flow over the once-thru flow separated in separator and– Returned to the condenser thru’ a heat
exchanger
or– Recirculated back to the boiler directly
by the dedicated circulating pump
April 11, 2023 PMI Revision 00 42
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
April 11, 2023 PMI Revision 00 43
Typical Separator sizes
Number of separators 2 4
Inside diameter approx mm 850 600
Thickness mm 95 70
April 11, 2023 PMI Revision 00 44
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
April 11, 2023 PMI Revision 00 45
Sliding Pressure Operation
April 11, 2023 PMI Revision 00 46
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.
April 11, 2023 PMI Revision 00 47
April 11, 2023 PMI Revision 00 48
Once -thru BoilerRequirements : 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
April 11, 2023 PMI Revision 00 49
Advanced CyclesEffect on Boiler Components
• Evaporator (Furnace) walls• Superheaters• Thickwalled boiler components• Steam piping
April 11, 2023 PMI Revision 00 50
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.
April 11, 2023 PMI Revision 00 51
Superheaters
• Tube metal temperatures in final sections increase with outlet steam temperature.
• Susceptibility for high temperature corrosion.
• Susceptibility to steam side oxidation
April 11, 2023 PMI Revision 00 52
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.
April 11, 2023 PMI Revision 00 53
• Varying combustion and fouling behaviour of different coals within a wide range of coals cause varying heat release and heat absorption in the furnace
• Benson boiler principle compensates these effects by shifting of the final evaporation point without diminishing efficiency
Changed heat release in the furnace
by varying coal qualities
April 11, 2023 PMI Revision 00 54
April 11, 2023 PMI Revision 00 55
April 11, 2023 PMI Revision 00 56
Definition of Supercritical DesignEvaporator pressure (MCR) 222 bar Supercritical
Design
Source: Siemens
April 11, 2023 PMI Revision 00 57
April 11, 2023 PMI Revision 00 58
April 11, 2023 PMI Revision 00 59
• Varying combustion and fouling behaviour of different coals within a wide range of coals cause varying heat release and heat absorption in the furnace
• Benson boiler principle compensates these effects by shifting of the final evaporation point.
Changed heat absorption in furnace due to changes in coal
quality
April 11, 2023 PMI Revision 00 60
Fixed evaporation end point
• For a drum type boiler the flue gases at the combustion chamber outlet can not be cooled below a certain value.
• Dimensioning of the heating surfaces of boilers having fixed evaporation end point must be done precisely.
• Generation of steam and spraying quantity in the SH change substantially if the operating point deviates from the design point.
April 11, 2023 PMI Revision 00 61
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 System
Hot 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
April 11, 2023 PMI Revision 00 62
April 11, 2023 PMI Revision 00 63
April 11, 2023 PMI Revision 00 64
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
April 11, 2023 PMI Revision 00 65
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 System
Hot 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
April 11, 2023 PMI Revision 00 66
Typical Parameters SH Outlet
Steam Temp.,°F
RH OutletSteam Temp.
°F Drum Type
3% per minute (30%-100% load) +/- 10 +/- 15 5% per minute (50% - 100% load) +/- 35 +/- 40 Once-Through
3% per minute (30% - 100% load) +/-10 +/-10 5% per minute (50% - 100% load) +/-10 +/-12
Note:Above values are based on sliding pressure mode and a 5 minute load ramp.
Tighter Control of Steam Temperatures
April 11, 2023 PMI Revision 00 67
THANK YOU