boiler and its structure related to supercritical technology and introduction to supercritical technology

1. SUPERCRITICAL BOILER
1
By
Ashvani Shukla
C&I
BGR ENERGY

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 o
C.

3. RANKIN CYCLE
SUBCRITICAL UNIT
 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 > HPT Work
 8 – 9 > Reheating
 9 – 10 > IPT Work
 10–11 > LPT Work
 11 – 1 > Condensing3

4. RANKINE CYCLE SUPERCRITICAL UNIT
 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
4

5. 5
AbsoluteAbsolute
PressurePressure
(Bar)(Bar)
SaturationSaturation
TemperatureTemperature
((oo
C)C)
Latent HeatLatent Heat
(K J/Kg.)(K J/Kg.)
5050
150150
200200
221221
264264
342342
366366
374374
16401640
10041004
592592
00
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 40
C TO 300
C.
6
Departure from Nucleate
Boiling
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
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

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 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

13. CONTINUE..
13
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

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
 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 the
WW tube and the fluid at high heat flux. 16

17. 17
SPIRAL VS VERTICAL WALL
VERTICAL WALL
 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 of WW
SPIRAL WALL
 More ash deposition
 More fluid mass flow
 Less number of tubes
 Less boiler height
 Uniform heat transfer
and uniform heating of
WW 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/6000
c/6200
c)

24. 24
MATERIAL COMPARISON
DescriptionDescription 660 MW660 MW 500 MW500 MW
Structural SteelStructural Steel Alloy SteelAlloy Steel Carbon SteelCarbon Steel
Water wallWater wall T22T22 Carbon SteelCarbon Steel
SH CoilSH Coil T23, T91T23, T91 T11, T22T11, T22
RH CoilRH Coil
T91,Super 304T91,Super 304
HH T22, T91,T11T22, T91,T11
LTSHLTSH T12T12 T11T11
EconomizerEconomizer SA106-CSA106-C Carbon SteelCarbon Steel
Welding Joints (Pressure Parts)Welding Joints (Pressure Parts) 42,000 Nos42,000 Nos 24,000 Nos24,000 Nos

25. 25
Steam Water Cycle
Chemistry Controls

26. 26
S.S.
No.No.
ParameterParameter Sub CriticalSub Critical Super CriticalSuper Critical
11
Type of BoilerType of Boiler
waterwater
treatmenttreatment
 LP and HP dosing. OrLP and HP dosing. Or
 All Volatile TreatmentAll Volatile Treatment
(Hydrazine + Ammonia)(Hydrazine + Ammonia)
 No HP dosingNo HP dosing
 Combined water treatment (CWT).Combined water treatment (CWT).
22
SilicaSilica < 20 ppb in feed water and steam,< 20 ppb in feed water and steam,
< 250 ppb in boiler drum< 250 ppb in boiler drum
Standard value <15 ppb in the cycleStandard value <15 ppb in the cycle
Expected value <10 ppb in the cycleExpected value <10 ppb in the cycle
33
pHpH 9.0 - 9.5 for feed, steam &9.0 - 9.5 for feed, steam &
condensate,condensate,
9.09.0 –– 10.0 for Boiler drum10.0 for Boiler drum
9.09.0 –– 9.6 for AVT(All volatile treatment)9.6 for AVT(All volatile treatment)
8.08.0 –– 9.0 for CWT(Combine water9.0 for CWT(Combine water
treatment)treatment)
44
DissolvedDissolved
Oxygen (DO)Oxygen (DO)
< 7 ppb for feed.< 7 ppb for feed. < 7 ppb for feed in case of AVT< 7 ppb for feed in case of AVT
3030 –– 150 ppb for feed in case of CWT150 ppb for feed in case of CWT
55
Cation (HCation (H++
))
ConductivityConductivity
<0.20<0.20 µµS/cm in the feed & steamS/cm in the feed & steam
cyclecycle
Standard value <0.15Standard value <0.15 µµS /cm in the cycleS /cm in the cycle
Expected value- <0.10Expected value- <0.10 µµS /cm in the cycleS /cm in the cycle
66 (CPU)(CPU) CPU is optionalCPU is optional CPU is essential for 100% flow.CPU is essential for 100% flow.
77
Silica and TDSSilica and TDS
controlcontrol
By maintaining feed water qualityBy maintaining feed water quality
andand
By operating CBDBy operating CBD
Blow down possible till separators areBlow down possible till separators are
functioning (upto 30% load).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