Transcript Measures to improve Plant Efficiency And / or Heat Rate of

Measures to improve Plant Efficiency
And / or Heat Rate of Supercritical
Units
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 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
Increase in Efficiency due to steam
parameters
SHO/RHO
Temp
Pressure
538 /
538
538 /
565
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
565 /
565
580 /
600
600 /
620
Effect of steam parameters on coal consumption
(500 MWe, 6500 h/a, LHV 13917 kJ/kg)
Coal consumption in kg/MWh
SH/RHTemp
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:
• 1990s:
• Today
Pressure increased from 175-180
bar to 225 bar ;temp mostly
around 540 deg C
Pressures raised to 285 bar; temp
raised to 565-580-600 Deg C
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
SH
ECO
STEAM TO
TURBINE
STEAM TO
TURBINE
SH
DRUM
DOWN
COMER
HEAT
HEAT
Water Wall
ORIFICE
ECO
Water Wall
CIRC. PUMP
Pressure
Steam Separation
Types
Burner Panel
Load Change
Cold Start
Hot Start
Super Critical Boilers
Sub critical
Drum
Natural / Assisted
Straight tube
Base
4-5 Hours
1-2 Hours
Sub & super Critical
Separator (Low loads)
(Sulzer) / (Benson)
Spiral Tube / Straight (MHI)
Faster
2 Hours
0.5 Hours
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 Boiler
Advantages:
•
•
•
•
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
Once -thru Boiler
Disadvantages :
• Higher feed pump auxiliary power
consumption
• Cannot operate under conditions of
condenser leak
Super Critical Boilers
Super Critical Boilers
Furnace Arrangement
SPIRAL TYPE
VERTICAL 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
Super Critical Boilers