super critical boiler.ppt

7/22/2019 Super Critical Boiler.ppt

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1

WELCOME TO

PRESENTATION ON

SUPERCRITICALBOILERBy

OPERATION TEAM

APML,TIRODA



2

Introduction to Supercritical

Technology

What is Supercritical Pressure ?

Critical point in water vapour cycle is a

thermodynamic state where there is no cleardistinction between liquid and gaseous state

of water.

Water reaches to this state at a critical

pressure above 22.1 MPa and 374 oC.



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 > HPT Work

8 – 9 > Reheating

9 –

10 > IPT Work 10 –11 > LPT Work

11 – 1 > Condensing



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

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



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 thesurface temperature is higher than the saturation temperature by between

40C to 300C.

6

Departure from Nucleate

Boiling

PRESSURE(ksc)

D E N S I T Y

WATER

ST

EAM

175 224



7

Supercritical Boiler Water Wall

Rifle Tube And Smooth Tube



Natural Circulation Vs. Once

Through System

8



From CRH Line

From FRS Line

BoilerRecirculation Pump

Economizer

Phase 1Economizer

Phase 2

LTRH

LTSH

4430C

FRH

Platen

Heater

Mixer Header

FSH

To HP

TurbineTo IP

Turbine

Separator

Bottom Ring

Header

2830C

3260C

4230C

4730C

4620C

5340C5260C

5710C

5690C

3240C

2800C

NRV



10

Feed water control

In Drum type Boiler Feed water flow control byThree 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

Difference of

Subcritical(500MW) and

Supercritical(660MW)



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



Continue..


(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..


(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

Water Wall Design



WATER WALL ARRANGEMENT

16

Bottom spiral & top vertical tube furnace arrangement

Once through design feature is used for boiler water walldesign

The supercritical water wall is exposed to the higher heatflux

Spiral tube wall design (wrapped around the unit) withhigh mass flow & velocity of steam/water mixture througheach spiral

Higher mass flow improves heat transfer between the

WW tube and the fluid at high heat flux.



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 oftubes 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

Furnace Arrangement

VERTICAL TYPE

SPIRAL TYPE



19

Supercritical Sliding Pressure Boiler

Water Wall Design

Comparison of Vertical Wall andSpiral Wall



20



21

Ash accumulation on wallsVertical water walls Spiral water walls



22

Super Critical BoilerMaterials



23

Advanced Supercritical Tube Materials

(300 bar/6000c/6200c)



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

http://localhost/var/www/apps/conversion/tmp/AppData/Local/AppData/Local/Local%20Settings/Temporary%20Internet%20Files/Desktop/New%20Folder6/New%20Folder%20(3)/Tata%20Power%20Presentation/WORLD%20OF%20SUPER%20CRITICAL_PRESENTATION%20ON%2006.08.04/Supercrical_material.doc



25

Steam Water CycleChemistry Controls



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).

2Silica < 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

3pH 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)

4Dissolved

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

Advantages of SC Technology

I ) Higher cycle efficiency meansPrimarily

– 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

ECONOMY

Higher Efficiency (η%)•Less fuel input.

•Low capacity fuel handling system.

•Low capacity ash handling system.

•Less Emissions.

Approximate improvement in Cycle

EfficiencyPressure increase : 0.005 % per bar

Temp increase : 0.011 % per deg K



29

Increase of Cycle Efficiency due to Steam

Parameters

300241

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

00

1

2

3

4

5

6

7

8

9

10

HP / RH outlet temperature [deg. C]Pressure [bar]

Increase of efficiency [%]



30

Sub. vs. Supercritical CycleImpact on Emissions

Plant Efficiency, %*

Plant Efficiency, %

Fuel Consumption/Total Emissions

including CO2

Subcritical Supercritical34 - 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

technology

Water chemistry is more stringent in super criticalonce 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.



THANK YOU

super critical boiler.ppt

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