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Super Critical Boilers
SYSTEM STUDIES ON ADVANCED POWER GENERATION
TECHNOLOGIES FOR 21st CENTURY
Dr V K Sethi
Director MOP/ CEA
Super Critical Boilers
Fig.1 EFFICIENCY IMPROVEMENT FORECASTCONVENTIONAL Vs IGCC
60
55
50
45
40
35
301990 1995 2000 2005 2010
Year of commercial use
Net
The
rma
l Effi
cie
ncy
(%)
Ceramic gasturbine
566 Co 600 Co623 Co
1300 Co 1500 Co
540 Co
650 Co1184 Co
IGCC (15 C Amb)
IGCC (Indian Condition)
Super Critical PC Power Plant (15 C Amb.)o
Super Critical PC Power Plant (Indian Condition)o
Sub Critical PC Power Plant (Indian Condition)
Super Critical Boilers
0
20
40
60
80
100
SO Particulates
PULVERIZED COAL (PC)
PC+FGD
IGCC
Fig.2 COMPARISON OF EMISSIONS FROM VARIOUS
PE
RC
EN
TA
GE
OF
PC
PL
AN
TS
950*
200*
50*
800*
200*
100*
50* 50*
5*
2 NOx
mg/m 3*
COAL FIRED POWER PLANT
Super Critical Boilers
Measures to improve Plant Efficiency And / or Heat Rate
Turbine side measures :• Higher steam parameters (Pr. & Temp.)• Adoption of double reheat cycle• Enhancing Regenerative feed heating• Reduced Auxiliary power consumption• Increase in condenser vacuum
Boiler design to accommodate the first four requirements
Super Critical Boilers
Steam generation process
Super Critical Boilers
Sub-Critical vs Super CriticalSub-Critical vs Super Critical
Description Sub Critical Super Critical
Full Load Pressure <190 atm >240 atm
Flow in Water wall 2-Phase 1-Phase
Cycle efficiency Base + 2 - 3 % Approx
Fuel saving Base +8 - 10 % Approx
Boiler weight Base + 10 %
Stages of reheat 1 2 Preferred
Preference on date Maintaining Cyclic(Yet to start in India)
Super Critical Boilers
Super Critical Boilers
Super Critical Boilers
Super Critical Boilers
Super Critical Boilers
Increase in Efficiency due to steam parameters
SHO/RHOTempPressure
538 /538
538 /565
565 /565
580 /600
600 /620
175bar Base +0.75% +1.47% +2.76% +3.74%
235bar +1.72% +2.57% +3.36% +4.72% +5.69%
300bar +2.42% +3.37% +4.26% +5.74% +6.77%
Super Critical Boilers
Effect of steam parameters on coal consumption (500 MWe, 6500 h/a, LHV 13917 kJ/kg)
Coal consumption in kg/MWh
SH/RH-Temp
538 /538
538 /565
565 /565
580 /600
600 /620
175bar 567 572 579 583 587
235bar 556 561 568 572 576
300bar 551 556 563 567 571
Super Critical Boilers
Evolution of Higher steam parameters
• 1980s: Pressure increased from 175-180 bar to 225 bar ;temp mostly
around 540 deg C
• 1990s: Pressures raised to 285 bar; temp raised to 565-580-600 Deg C
• Today 255 bar 568/568 Deg C commonly used
300 bar & 620 Deg C under development
Super Critical Boilers
Super Critical Boilers
Super Critical Boilers
DRUM vs ONCE THROUGH DRUM vs ONCE THROUGH
Pressure Sub critical Sub & super Critical Steam Separation Drum Separator (Low loads) Types Natural / Assisted (Sulzer) / (Benson)
Burner Panel Straight tube Spiral Tube / Straight (MHI)Load Change Base FasterCold Start 4-5 Hours 2 HoursHot Start 1-2 Hours 0.5 Hours
SH
STEAM TOTURBINE
HEATDOWN
COMER
DRUMECO
Water Wall
ORIFICECIRC. PUMP
SH
STEAM TO TURBINE
ECO
HEAT
Water Wall
Super Critical Boilers
Drum type boiler
• Steam generation essentially 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 and fed back to ww lower drum by means of boiler water circulating pumps (BWCPs).
Super Critical Boilers
Drum type boiler
• Natural Circulation Boiler Circulation through water walls by thermo-siphon effect
• Controlled Circulation Boiler At higher operating pressures (just below critical pressure levels), thermo-siphon effect supplemented by pumps to ensure safety of furnace wall tubes.
Super Critical Boilers
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
Super Critical Boilers
Once Through Boiler-Concept
Once through system
Super Critical Boilers
Once Through Boiler
• Once -through forced flow through all sections of boiler (economiser, water walls & superheater)
• Feed pump provides the driving head
• Suitable for sub critical & super critical pressures
Super Critical Boilers
Once -thru BoilerAdvantages:• Quick response to load changes• Shorter start up time• Better suited for sliding pressure operation• Steam temperature can be maintained over wider
load range under sliding pressure• Higher tolerance to varying coal quality• Suitable for sub critical & super critical pressures
Super Critical Boilers
Once -through 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.
Super Critical Boilers
Once -through Boiler
Characteristics :• Provides Quicker response to TG load changes• Supports achievement of better heat rate at lower
loads• Higher furnace wall pressure drop and consequent
higher feed pump auxiliary power consumption• Needs ultra pure quality feed water - Cannot
operate under conditions of condenser leak
Super Critical Boilers
Super Critical Boilers
Once -thru Boiler
Disadvantages :
• Higher feed pump auxiliary power consumption
• Cannot operate under conditions of condenser leak
Super Critical Boilers
Furnace ArrangementFurnace Arrangement
VERTICAL TYPE
SPIRAL TYPE
Super Critical Boilers
Once -through Boiler Operating Range
Super Critical Boilers
Sliding Pressure Operation
Super Critical Boilers
Advantages of sliding pressure
• Higher efficiency
• Less auxiliary power
• Less fatigue of pressure parts