supercritical technology

7/28/2019 SuperCritical technology

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CONCEPT OF

SUPER CRITICALCYCLE


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What is importance

History of this technology

Super Critical cycle details

Presentation Outline


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PERCAPITA ELECTRIC POWER CONSUMPTION

COUNTRY PERCAPITA ELECTRICPOWER CONSUMPTION KWH

INDIA 513CHINA 773

CANADA 16413

USA 13040

MEXICO 1439

NORWAY 24033

SWITZERLAND 7346

FRANCE 7069

UNITED KINGDOM 5968

SPAIN 4072

RUSSIA 5108

ITALY 4610

SWEDEN 15244

GERMANY 6406TURKEY 1259

JAPAN 7749

These are collected from Ststistics Organisation for Economic Cooperation and Development of I.E.A.


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Emerging Market Requirements For

Utility Units High Reliability & Availability Highest economically achievable plant

efficiency and heat rate

Suitable for differing modes ofoperation

Suitable for different quality of fuel

Ability to operate under adverse gridconditions / fluctuations Minimum emission of Pollutants

Lowest life cycle cost


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Thermal Power Generation

Higher cycle efficiency for: Conservation of fuel resources

Reduction of Atmospheric Pollutants

- SOX & NOX Reduction in CO2 emission (linked to

global warming)

Better economy in power generationwhere fuel costs are high and

pollution control requirements are

stringent


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GROWTH OF UNIT SIZES IN INDIA

RATING YEAR OF INTRODUCTION

60/70MW 1965

110/120MW 1966200/210MW 1972

250MW 1991

500MW 1979

660MW Commg

800 MW PROPOSAL STAGE


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AS THE UNIT SIZES GREW, BOILER SIZES SUPPLYING

STEAM TO SUCH TURBINES HAVE ALSO INCREASED

UNIT STEAM SHO SHO/RHO

SIZE FLOW PRESSURE TEMPERATURE

(T/H.) (KG/CM2) (DEG. C)

30MW 150 63 490

60/70MW 260 96 540

110/120MW 375 139 540/540

200/210MW 690 137/156 540/540

250MW 805 156 540/540

500MW 1670 179 540/540

600MW 2100 255 540/568

800 MW 2565 255 568/596


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Major Sulzer/Combustion Engineering

Innovations for Fossil Utility Boilers

First Sulzer Boiler

First Pulverized Coal Fired UtilityBoiler

Tangential Firing

First Commercial Monotube SteamGenerator

Controlled Circulation

First Commercial SupercriticalMonotube Steam Generator

1841

1912

1927

1931

1942

1954

Year of Introduction


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Major Sulzer/Combustion Engineering

Innovations for Fossil Utility Boilers

MHI Adopted as Monotube TechnologyLicensee

Highest Temperature and Pressure

Supercritical Boiler

Combined Circulation - Supercritical

Largest Oil/Gas Fired Supercritical Steam

Generator

Controlled Circulation Plus

Sliding Pressure Supercritical

1957

1960

1964

1970

1978

1980

Year of Introduction


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Fuels for Steam Power Plants

Coal & Lignite:

Abundant availability Lower cost

Will continue as the main fuels in many

countries


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Cycle Efficiency

Higher efficiency can be realised with

Higher live steam parameters Adoption of double reheat cycle

Reduction in condenser absolute pressure


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Measures to improve Plant Efficiency

and / or Heat Rate

Boiler side measures :

Minimum RH spray

Minimum SH spray (if tapped off before feed heaters)

Minimum flue gas temperature at AH outlet

Minimum excess air at AH outlet

Minimum unburnt Carbon loss

Reduced auxiliary power consumption


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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

0,752,42

1,78

00

1

2

3

4

5

6

7

8

9

10

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

Increase of efficiency [%]


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Approximate improvement in Cycle Efficiency

Pressure increase : 0.005 % per bar

Temp increase : 0.011 % per deg K


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500 MW Steam Generator

Coal Consumption and Emissions

Subcritical

Unit

Supercritical

Unit

Coal Saving t/year Base 68800

CO2 Reduction t/year Base 88270

SO2 Reduction t/year Base 385

Basis:

Cycle Efficiency % Base +1.0

No. of operating

hrs.

Hrs./year 8000 8000


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Steam generation details


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Supercritical Cycles

Initially adopted in the late fifties and

sixties

Higher Steam temperature employed on

some units

Unit sizes also witnessed an increasing

trend

Slidi P S iti l D i


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Enthalpy Variations vs Pressure and Boiler Load

Sliding Pressure Supercritical Design


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Operating Experience

The first generation

supercritical units

Experienced increasedforced outages

Witnessed reduced plant

reliability and availability


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Comparison of Subcritical and

Supercritical

Cycle Availability (NERC)

0

2

4

6

8

10

12

14

EFOR %

Plant (Super) 13.347 12.077 9.668 7.685 7.534 7.482

Plant (Sub) 10.405 9.439 8.16 6.793 7.103 7.013

Blr (Super) 8.441 7.285 5.823 4.872 4.434 4.023

Blr (Sub) 5.928 5.464 4.344 3.811 3.926 4.018

1982-1984 1985-1987 1988-1990 1991-1993 1994-1996 1997


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Increased outages were caused

by

Inadequate experience while

extrapolating to the new designs

and the increased unit sizes.

Inadequate knowledge of high

temperature materials.


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The increased outages led to :

Reversal of steam pressures tosubcritical range

Lowering of steam temperatures to

540 Deg C


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Current Trends in Steam Parameters

1980s : Pressure increased from 175-180

bar to 225 bar; temp mostly

around 540 Deg C

1990 : Pressures raised to 285 bar;temp

raised to 565-580-600 Deg C

300 bar & 620 Deg C not unusual today

255 bar 568/568 Deg C commonly used presently


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Implications of higher steam

parameters on boiler design

Boiler type

Materials

Reliability and Availability


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Types of boilers

Drum type

Once-through type


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Drum type boiler

Steam generation takes place in furnace

water walls

Fixed evaporation end point - the drum Steam -water separation takes place in the

drum

Separated water mixed with incoming feedwater


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Drum type boiler

Natural Circulation Boiler Circulation thru water walls by

thermo-siphon effect

Controlled Circulation Boiler

At higher operating pressures

just below critical pressure levels,

thermo-siphon effect supplemented

by pumps


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Once Through Boiler-Concept


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THE CONCEPT

The mass flow rate thru all heat transfer circuits

from Eco. inlet to SH outlet is kept same except at

low loads wherein recirculation is resorted to

protect the water wall system


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COTROLLED CIRCULATION

(Vs) ONCE THRU

CC OT


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Once Through Boiler-Concept


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Once Through Boiler

Once -through flow through all

sections of boiler (economiser, water

walls & superheater) Feed pump provides the driving head

Suitable for sub critical & super

critical pressures


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Once-thru Boiler

Major differences from Drum type boiler :

Evaporator system

Low load circulation system

Separator


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Once -thru Boiler

Evaporator system : Formed by a number of parallel tubes

Tubes spirally wound around the

furnace to reduce number of tubes and

to increase the mass flow rate thru the

tubes

Small tube diameter

Arrangement ensures high mass

velocity thru the tubes


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Once -thru Boiler - Furnace Wall


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Furnace Arrangement

VERTICAL TYPE

SPIRAL TYPE


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ONCE - THROUGH OPERATING RANGE


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Once -thru Boiler

Low load circulation system :

At part loads once -thru flow not adequate tocool the tubes

To maintain required mass velocities boiler

operates on circulating mode at low loads

Excess flow supplied by feed pump or a

dedicated circulating pump

LOW LOAD SYSTEM WITH CIRC


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LOW LOAD SYSTEM WITH CIRC.

PUMP

LOW LOAD SYSTEM WITH HEAT


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LOW LOAD SYSTEM WITH HEAT

EXCHANGER


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Once - thru Boiler

Low load circulation system :

The excess flow over the once-thru

flow separated in separator and

Returned to the condenser thru a

heat exchanger

or

Recirculated back to the boilerdirectly by the dedicated circulating

pump


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Once -thru Boiler

Separator :

Separates steam and water during

the circulating mode operation Runs dry during once-thru flow

mode

Smaller in size compared to drum ina drum type boiler


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Typical Separator sizes

Number of separators 2 4

Inside diameterapprox

mm 850 600

Thickness mm 95 70


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Once -thru Boiler

Advantages: Better suited for sliding pressure operation

Steam temperature can be maintained over wider

load range under sliding pressure

Quick response to load changes

Shorter start up time

Higher tolerance to varying coal quality Suitable for sub critical & super critical pressures


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Sliding Pressure Operation


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Advantages of sliding pressure operation:

Lower thermal stresses in the turbine during loadchanges.

Control range of RH temp is extended.

Reduced pressure level at lower loads prolongsthe life span of the components.

Overall reduction in power consumption and

improved heat rate.


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Once -thru Boiler

Requirements : Stringent water quality

Sophisticated control system

Low load circulation system

Special design to support the spiral furnace

wall weight

High pressure drop in pressure parts Higher design pressure for components from

feed pump to separator

Ad d C l


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Advanced Cycles

Effect on Boiler Components

Evaporator (Furnace) walls

Superheaters Thickwalled boiler components

Steam piping


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Furnace walls

Increased operating pressureincreases the medium temperatures.

Increased regenerative feed heating

increases the fluid temp entering. Larger furnaces required for NOX

reduction, increase SH steam

temperature at furnace wall outlet.


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Superheaters

Tube metal temperatures in final

sections increase with outlet steam

temperature.

Susceptibility for high temperature

corrosion.

Susceptibility to steam side

oxidation


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Thick walled components

Higher pressure & temperature lead to

increased thickness of :

Shells of separator, start-up system

components, SHO header..

Main steam piping.

Higher thickness results in larger

temperature gradients across walls.

Changed heat release in the furnace


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Varying combustion and foulingbehaviour of different coals within awide range of coals cause varying

heat release and heat absorption inthe furnace

Benson boiler principle compensatesthese effects by shifting of the finalevaporation point without diminishingefficiency

Changed heat release in the furnace

by varying coal qualities


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D fi iti f S iti l D i


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Definition of Supercritical Design

Evaporator pressure (MCR) 222 bare SupercriticalDesign

Source: Siemens


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Varying combustion and foulingbehaviour of different coals within a

wide range of coals cause varying heatrelease and heat absorption in thefurnace

Benson boiler principle compensatesthese effects by shifting of the finalevaporation point.

Changed heat absorption in

furnace due to changes in coal

quality


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Fixed evaporation end point

For a drum type boiler the flue gases at the

combustion chamber outlet can not be cooled

below a certain value. Dimensioning of the heating surfaces of boilers

having fixed evaporation end point must be done

precisely.

Generation of steam and spraying quantity in theSH change substantially if the operating point

deviates from the design point.


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First Fire to Turbine Synch,

Minute without Bypass System


Minute with Bypass System

Hot Start Up, after 2 hr shutdown 40 30

Warm Start Up, after 8 hr shutdown

65

45

Cold Start Up, after 36 hr shutdown 130 90

Faster Start-up Time with Supercritical Design




Minute with Bypass SystemHot Start Up, after 2 hr shutdown 40 30

Warm Start Up, after 8 hr shutdown 65 - 90 45 - 70

Cold Start Up, after 36 hr shutdown 180 - 260 140 - 220

Once - Thru

Drum


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Present Trend in India

Unit

Size

MW

SHO

flow(t/hr)

SHO pr.

(Kg/Sq.cm)

SHOT

(C)

RHOT

(C)

660 2100 255 568 596

800 2565 255 568 596


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Minute with Bypass System

Hot Start Up, after 2 hr shutdown 40 30Warm Start Up, after 8 hr shutdown 65 45

Cold Start Up, after 36 hr shutdown 130 90

Faster Start-up Time with

Supercritical Design




Minute with Bypass SystemHot Start Up, after 2 hr shutdown 40 30

Warm Start Up, after 8 hr shutdown 65 - 90 45 - 70

Cold Start Up, after 36 hr shutdown 180 - 260 140 - 220

Once - Thru

Drum


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Typical Parameters

SH OutletSteam Temp.,

F

RH OutletSteam Temp.

F

Drum Type 3% per minute (30%-100% load) +/- 10 +/- 15 5% per minute (50% - 100% load) +/- 35 +/- 40Once-Through 3% per minute (30% - 100% load) +/-10 +/-10 5% per minute (50% - 100% load) +/-10 +/-12Note:Above values are based on sliding pressure mode and a 5 minute load ramp.

Tighter Control of Steam Temperatures


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