WELCOME TO PRESENTATION ON SUPERCRITICAL BOILER By OPERATION - - PowerPoint PPT Presentation

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WELCOME

TO PRESENTATION ON

SUPERCRITICAL BOILER

By OPERATION TEAM

APML,TIRODA

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In Intr trod

• duc

ucti tion

• n to S
• Sup

uper ercri criti tical cal Tec echnolog nology

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

• f water.

Water reaches to this state at a critical pressure above 22.1 MPa and 374 oC.

Ra Rank nkin ine e Cycl cle e Subc ubcrit ritic ical al Unit 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

Ra Rank nkin ine e Cycl cle e Super upercriti critical cal Unit Unit

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 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

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Absolute Pressure (Bar) Saturation Temperature (oC) Latent Heat (K J/Kg.) 50 150 200 221 264 342 366 374 1640 1004 592

VAR ARIA IATION ION OF OF LA LATENT ENT H HEA EAT WIT ITH PR PRES ESSURE SURE

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.

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De Depar artur ture e from

• m Nuc

ucleat leate e Bo Boil ilin ing

PRESSURE(ksc) DENSITY WATER STEAM 175 224

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Sup uper ercritical critical Bo Boiler ler Water er Wall l Rifle fle Tub ube e And nd Smo mooth th Tub ube

Natural tural Circulation culation Vs.

• s. On

Once e Through

• ugh

Syst stem em

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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

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Fee eed d wat ater er co contr ntrol

• l

 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)

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Di Differe erenc nce e of

• f Sub

ubcri criti tical cal(50 (500M 0MW) W) an and S d Sup uper ercri criti tical(6 cal(660 60MW) MW)

COMPAR ARISION SION OF OF SUP UPER CRITICAL ICAL & SUB UB CRITICAL CAL

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..

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

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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

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Wat ater er Wall all De Desi sign gn

WATER ER WAL ALL ARR L ARRAN ANGEMENT GEMENT

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• 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 RAL VS VS VERT ERTICAL ICAL 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

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Fur urnace nace Arrang rrangemen ement

VERTICAL TYPE SPIRAL TYPE

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Sup uper ercritical critical Sliding iding Press essure ure Bo Boiler ler Water er Wall l De Desi sign gn Compa parison rison of Ver ertic tical al Wall l and nd Spi piral ral Wall

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As Ash ac accu cumulat mulation ion on

• n wal

alls

Vertical water walls Spiral water walls

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Super Critical Boiler Materials

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

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Mat ater eria ial l Com

• mparis

arison

• n

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. 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).

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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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EC ECONOMY NOMY

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 crease of Cycl cle e Efficiency ciency due e to Steam Par Paramet ameter ers

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

1 2 3 4 5 6 7 8 9 10

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

Increase of efficiency [%]

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Sub

• ub. vs. Sup

uper ercriti critical cal Cycle cle

Impact act on Em Emissions sions

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

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Chall lleng enges es of sup uper ercrit critical ical tec echnolo nology

 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

• f vertical wall.

TH THANK ANK YOU OU