Transcript Document

WELCOME
TO
PRESENTATION ON
SUPERCRITICAL BOILER
By
OPERATION TEAM
1
APML,TIRODA
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.
2
Rankine Cycle Subcritical Unit
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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 > Condensing
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
VARIATION OF LATENT HEAT
WITH PRESSURE
5
Absolute
Pressure
(Bar)
Saturation
Temperature
(oC)
Latent Heat
(K J/Kg.)
50
150
200
221
264
342
366
374
1640
1004
592
0
Departure from Nucleate Boiling
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.
DENSITY
WATER
STEAM
175 224
PRESSURE(ksc)
6
Supercritical Boiler Water Wall
Rifle Tube And Smooth Tube
7
Natural Circulation Vs. Once Through
System
8
5710C To HP
Turbine
Mixer Header
4230C
4620C
To IP
Turbine 5690C
5340C
5260C
Separator
FRH
4730C
FSH
Platen
Heater
From CRH Line
3240C
From FRS Line
NRV
3260C
2830C
2800C
Boiler
Recirculation Pump
LTRH
LTSH
4430C
Economizer
Phase 1
Bottom Ring
Header
Economizer
Phase 2
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)
10
Difference of Subcritical(500MW)
and Supercritical(660MW)
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COMPARISION OF SUPER CRITICAL & SUB CRITICAL
DESCRIPTION
SUPERCRITICAL
(660MW)
SUB-CRITICAL
(500MW)
Circulation Ratio
1
Feed Water Flow
Control
-Water to Fuel
Ratio
(7:1)
-OHDR(22-35 OC)
-Load Demand
Latent Heat Addition
Nil
Heat addition more
Sp. Enthalpy
Low
More
Sp. Coal consumption
Low
High
Air flow, Dry flu gas loss
Low
High
Once-thru=1
Assisted Circulation=3-4
Natural circulation= 7-8
Three Element Control
-Feed Water Flow
-MS Flow
-Drum Level
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
Continue..
DESCRIPTION
SUPERCRITICAL SUB-CRITICAL
(660MW)
(500MW)
Material / Infrastructure
(Tonnage)
Low
7502 MT
High
9200 MT
Start up Time
Less
More
Blow down loss
Nil
More
Water Consumption
Less
More
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Water Wall Design
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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.
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SPIRAL VS VERTICAL WALL
VERTICAL WALL
SPIRAL WALL
 Less ash deposition on wall
 More ash deposition
 Less mass flow
 More fluid mass flow
 More number of tubes
 Less number of tubes
 More boiler height for same
 Less boiler height
capacity
 No uniform heating of tubes and
heat transfer in all tubes of WW
 Uniform heat transfer and
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uniform heating of WW tubes
Furnace Arrangement
SPIRAL TYPE
VERTICAL TYPE
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Supercritical Sliding Pressure Boiler
Water Wall Design
Comparison of Vertical Wall and Spiral
Wall
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20
Ash accumulation on walls
Vertical water walls
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Spiral water walls
Super Critical Boiler
Materials
22
Advanced Supercritical Tube Materials
(300 bar/6000c/6200c)
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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
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Steam Water Cycle
Chemistry Controls
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S. Parameter
No.

Silica
< 20 ppb in feed water and steam, Standard value <15 ppb in the cycle
< 250 ppb in boiler drum
Expected value <10 ppb in the cycle
pH
9.0 - 9.5 for feed, steam &
condensate,
9.0 – 10.0 for Boiler drum
< 7 ppb for feed.
9.0 – 9.6 for AVT(All volatile treatment)
8.0 – 9.0 for CWT(Combine water
treatment)
< 7 ppb for feed in case of AVT
30 – 150 ppb for feed in case of CWT
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 By maintaining feed water quality Blow down possible till separators are
control
and
functioning (upto 30% load).
By operating CBD
2
3
4
5
Dissolved
Oxygen (DO)

LP and HP dosing. Or
All Volatile Treatment
(Hydrazine + Ammonia)
Super Critical
Type of Boiler
water
treatment
1
26
Sub Critical


No HP dosing
Combined water treatment (CWT).
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
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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
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Increase of Cycle Efficiency due to Steam
Parameters
Increase of efficiency [%]
10
6,77
9
4,81
7
3,74
4,26
6
5
3,44
3,37
4
2,64
3
2,76
1,47
2,42
2
600 / 620
1,78
0,75
1
580 / 600
566 / 566
0
300
Pressure [bar]
29
5,79
5,74
8
0
241
175
538 / 538
538 / 566
HP / RH outlet temperature [deg. C]
Sub. vs. Supercritical Cycle
Impact on Emissions
Plant Efficiency, %*
Plant Efficiency, Btu / kw-hr
Plant Efficiency, %
Fuel Consumption/Total Emissions
including CO2
30
* HHV Basis
Subcritical
34 - 37
10,000 - 9,200
Supercritical
37 - 41
9,200 - 8,300
34%
37%
41%
Base
Base-8%
Base-17%
Challenges of supercritical technology
 Water chemistry is more stringent in super critical once through
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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.
THANK YOU