Super-critical Boiler

1. 1
WELCOME
TO
PRESENTATION ON
SUPERCRITICAL BOILER
By
OPERATION TEAM
APML,TIRODA

2. 2
Introduction to Supercritical
Technology
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 oC.

3. Rankine Cycle Subcritical Unit
3
 1 - 2 > CEP work
 2 - 3 > LP Heating
 3 - 4 > BFP work
 4 - 5 > HP Heating
 5 – 6 > Eco,WW
 6 – 7 > Superheating
 7 – 8 > HPTWork
 8 – 9 > Reheating
 9 – 10 > IPTWork
 10–11 > LPTWork
 11 – 1 > Condensing

4. Rankine Cycle Supercritical Unit
4
 1 - 2 > CEP work
 2 – 2s > Regeneration
 2s - 3 > Boiler Superheating
 3 – 4 > HPT expansion
 4 – 5 > Reheating
 5 – 6 > IPT & LPT Expansion
 6 – 1 > Condenser Heat rejection

5. 5
Absolute
Pressure
(Bar)
Saturation
Temperature
(oC)
Latent Heat
(K J/Kg.)
50
150
200
221
264
342
366
374
1640
1004
592
0
VARIATION OF LATENT HEAT
WITH PRESSURE

6. Nucleate boiling is a type of boiling that takes place when the surface temp is
hotter than the saturated fluid temp by a certain amount but where heat flux
is below the critical heat flux. Nucleate boiling occurs when the surface
temperature is higher than the saturation temperature by between 40C to
300C.
6
Departure from Nucleate Boiling
PRESSURE(ksc)
DENSITY
WATER
STEAM
175 224

7. 7
Supercritical Boiler Water Wall
Rifle Tube And Smooth Tube

8. Natural Circulation Vs. Once Through
System
8

9. From CRH Line
From FRS Line
Boiler
Recirculation Pump
Economizer
Phase 1
Economizer
Phase 2
LTRH
LTSH
4430C
FRH
Platen
Heater
Mixer Header
FSH
To HP
Turbine To IP
Turbine
Separator
Bottom Ring
Header
2830C
3260C
4230C
4730C
4620C
5340C
5260C
5710C
5690C
3240C
2800C
NRV

10. 10
Feed water control
 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)

11. 11
Difference of Subcritical(500MW)
and Supercritical(660MW)

12. COMPARISION OF SUPER CRITICAL & SUB CRITICAL
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 OC)
-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

13. Continue..
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
13

14. Continue..
DESCRIPTION SUPERCRITICAL
(660MW)
SUB-CRITICAL
(500MW)
Material / Infrastructure
(Tonnage)
Low
7502 MT
High
9200 MT
Start up Time Less More
Blow down loss Nil More
Water Consumption Less More
14

15. 15
Water Wall Design

16. WATER WALL ARRANGEMENT
16
 Bottom spiral & top vertical tube furnace arrangement
 Once through design feature is used for boiler water wall design
 The supercritical water wall is exposed to the higher heat flux
 Spiral tube wall design (wrapped around the unit) with high mass flow
& velocity of steam/water mixture through each spiral
 Higher mass flow improves heat transfer between theWW tube and
the fluid at high heat flux.

17. 17
SPIRAL VS VERTICAL WALL
VERTICALWALL
 Less ash deposition on wall
 Less mass flow
 More number of tubes
 More boiler height for same
capacity
 No uniform heating of tubes and
heat transfer in all tubes ofWW
SPIRAL WALL
 More ash deposition
 More fluid mass flow
 Less number of tubes
 Less boiler height
 Uniform heat transfer and
uniform heating ofWW tubes

18. 18
Furnace Arrangement
VERTICAL TYPE
SPIRAL TYPE

19. 19
Supercritical Sliding Pressure Boiler
Water Wall Design
Comparison of Vertical Wall and Spiral
Wall

20. 20

21. 21
Ash accumulation on walls
Vertical water walls Spiral water walls

22. 22
Super Critical Boiler
Materials

23. 23
Advanced Supercritical Tube Materials
(300 bar/6000c/6200c)

24. 24
Material Comparison
Description 660 MW 500 MW
Structural Steel Alloy Steel Carbon Steel
Water wall T22 Carbon Steel
SH Coil T23, T91 T11, T22
RH Coil
T91,Super 304
H T22, T91,T11
LTSH T12 T11
Economizer SA106-C Carbon Steel
Welding Joints (Pressure Parts) 42,000 Nos 24,000 Nos

25. 25
Steam Water Cycle
Chemistry Controls

26. 26
S.
No.
Parameter Sub Critical Super Critical
1
Type of Boiler
water
treatment
 LP and HP dosing. Or
 All Volatile Treatment
(Hydrazine + Ammonia)
 No HP dosing
 Combined water treatment (CWT).
2
Silica < 20 ppb in feed water and steam,
< 250 ppb in boiler drum
Standard value <15 ppb in the cycle
Expected value <10 ppb in the cycle
3
pH 9.0 - 9.5 for feed, steam &
condensate,
9.0 – 10.0 for Boiler drum
9.0 – 9.6 for AVT(All volatile treatment)
8.0 – 9.0 for CWT(Combine water
treatment)
4
Dissolved
Oxygen (DO)
< 7 ppb for feed. < 7 ppb for feed in case of AVT
30 – 150 ppb for feed in case of CWT
5
Cation (H+)
Conductivity
<0.20 µS/cm in the feed & steam
cycle
Standard value <0.15 µS /cm in the cycle
Expected value- <0.10 µS /cm in the cycle
6 (CPU) CPU is optional CPU is essential for 100% flow.
7
Silica and TDS
control
By maintaining feed water quality
and
By operating CBD
Blow down possible till separators are
functioning (upto 30% load).

27. 27
Advantages of SC Technology
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

28. 28
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

29. 29
Increase of Cycle Efficiency due to Steam
Parameters
300
241
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
0
0
1
2
3
4
5
6
7
8
9
10
HP / RH outlet temperature [deg. C]
Pressure [bar]
Increase of efficiency [%]

30. 30
Sub. vs. Supercritical Cycle
Impact on Emissions
Plant Efficiency, %*
Plant Efficiency, %
Fuel Consumption/Total Emissions
including CO2
Subcritical Supercritical
34 - 37 37 - 41
Plant Efficiency, Btu / kw-hr 10,000 - 9,200 9,200 - 8,300
34%
Base
37%
Base-8%
41%
Base-17%
* HHV Basis

31. 31
Challenges of supercritical technology
 Water chemistry is more stringent in super critical once through
boiler.
 Metallurgical Challenges
 More complex in erection due to spiral water wall.
 More feed pump power is required due to more friction losses in
spiral water wall.
 Maintenance of tube leakage is difficult due to complex design of
water wall.
 Ash sticking tendency is more in spiral water wall in comparison
of vertical wall.

32. THANK YOU