2. 2
What is Supercritical Pressure ?
Critical point in water vapour cycle is a
thermodynamic state where there is no clear
distinction between liquid and gaseous state
of water.
Water reaches to this state at a critical
pressure above 22.1 MPa and 374 o
C.
6. From CRH Line
From FRS Line
Boiler
Recirculation Pump
Economizer
Phase 1
Economizer
Phase 2
LTRH
LTSH
4430
C
FRH
Platen
Heater
Mixer Header
FSH
To HP
Turbine To IP
Turbine
Separator
Bottom Ring
Header
2830
C
3260
C
4230
C
4730
C
4620
C
5340
C
5260
C
5710
C
5690
C
3240
C
2800
C
NRV
7. 7
In Drum type Boiler Feed water flow control by
Three element controller
1.Drum level
2.Ms flow
3.Feed water flow.
Drum less Boiler Feed water control by
1.Load demand
2.Water/Fuel ratio(7:1)
3.OHD(Over heat degree)
9. DESCRIPTION SUPERCRITICAL
(660MW)
SUB-CRITICAL
(500MW)
Circulation Ratio 1 Once-thru=1
Assisted Circulation=3-4
Natural circulation= 7-8
Feed Water Flow
Control
-Water to Fuel
Ratio
(7:1)
-OHDR(22-35 O
C)
-Load Demand
Three Element Control
-Feed Water Flow
-MS Flow
-Drum Level
Latent Heat Addition Nil Heat addition more
Sp. Enthalpy Low More
Sp. Coal consumption Low High
Air flow, Dry flu gas loss Low High
10. DESCRIPTION SUPERCRITICAL
(660MW)
SUB-CRITICAL
(500MW)
Coal & Ash handling Low High
Pollution Low High
Aux. Power
Consumption
Low More
Overall Efficiency High
(40-42%)
Low
(36-37%)
Total heating
surface area Reqd
Low
(84439m2
)
High
(71582m2
)
Tube diameter Low High
10
12. 12
I ) Higher cycle efficiency means
Primarily
– less fuel consumption
– less per MW infrastructure investments
– less emission
– less auxiliary power consumption
– less water consumption
II ) Operational flexibility
– Better temp. control and load change flexibility
– Shorter start-up time
– More suitable for widely variable pressure operation
13. 13
ECONOMY
Higher Efficiency (η%)
•Less fuel input.
•Low capacity fuel handling system.
•Low capacity ash handling system.
•Less Emissions.
Approximate improvement in Cycle
Efficiency
Pressure increase : 0.005 % per bar
Temp increase : 0.011 % per deg K