SUPER CRITICAL SUPER CRITICAL TECHNOLOGY IN TECHNOLOGY IN

NTPCNTPC

PRESENTATION CONTENTSPRESENTATION CONTENTS

What is critical condition??What is critical condition?? Types of boilers.Types of boilers. Major differences between drum type & once Major differences between drum type & once

through boilers.through boilers. Advantages of once through boiler.Advantages of once through boiler. Effect of advanced cycles on boiler Effect of advanced cycles on boiler

components.components. Conclusion.Conclusion.

Definition of critical Condition

CRITICAL CONDITION IS THERMODYNAMIC

EXPRESSION DESCRIBING THE STATE OF A

SUBSTANCE BEYOUND WHICH THERE IS NO

CLEAR DISTINCTION BETWEEN THE LIQUID

AND GASEOUS PHASE.

SUPERCRITICAL PARAMETERSSUPERCRITICAL PARAMETERS

Tem

per

a tu

re (

C)

Entropy

Critical Point

Pr = 225.56 kg/cm2

T = 374.15 Deg.C

538 Deg C

Subcritical

Supercritical

Types of boilersTypes of boilers

Drum typeDrum type

Once-through typeOnce-through type

Design TypesDesign Types

NATURAL

STEAM DRUM

FURNACEWALLS

ECON.

CONTROLLED

TO SUPERHEATER

CIRC.PUMP

SEPARATOR

CIRC.PUMP

ECON.

DISTRIB.HEADER

ONCE THROUGH

• Natural circulation - well suited for < 175 kg/cm2

• Controlled circulation - optimum solution for reliable high-pressure subcritical operation• Once-through technology

• Suitable for sub and supercritical cycles

Drum type boilerDrum type boiler Natural Circulation BoilerNatural Circulation Boiler

Circulation thru water walls by Circulation thru water walls by

thermo-siphon effectthermo-siphon effect

Controlled Circulation BoilerControlled Circulation Boiler

At higher operating pressures At higher operating pressures

just below critical pressure levels, just below critical pressure levels,

thermo-siphon effect supplementedthermo-siphon effect supplemented

by pumpsby pumps

Drum type boilerDrum type boiler

Steam generation takes place in furnace Steam generation takes place in furnace

water walls. water walls.

Steam -water separation takes place in Steam -water separation takes place in

the drum.the drum.

Separated water mixed with incoming Separated water mixed with incoming

feed water. feed water.

Supercritical Boilers in NTPC Supercritical Boilers in NTPC

SIPAT(3x660 SIPAT(3x660 MW)MW)

BARH (3x660 BARH (3x660 MW) MW)

SupplierSupplier Doosan, KoreaDoosan, Korea TPE, RussiaTPE, Russia

TypeType Two pass,spiral-Two pass,spiral-walledwalled

Two pass,spiral-Two pass,spiral-walledwalled

CapacityCapacity 2225T/hr.2225T/hr. 2225T/hr.2225T/hr.

Steam ParametersSteam Parameters(at boiler outlet)(at boiler outlet)

256kg/cm2/540/568 256kg/cm2/540/568 deg.Cdeg.C

256kg/cm2/540/568 256kg/cm2/540/568 deg.Cdeg.C

Coal Firing Coal Firing Tangential firedTangential fired Front & Rear firedFront & Rear fired

OrderOrder March, 2004March, 2004 March, 2005March, 2005

CommissioningCommissioning 20072007 20082008

Once -thru BoilerOnce -thru Boiler

Requirements :Requirements : Stringent water quality Stringent water quality

Sophisticated control systemSophisticated control system

Low load circulation system Low load circulation system

Special design to support the spiral Special design to support the spiral

furnace wall weightfurnace wall weight

Higher design pressure for components Higher design pressure for components

from feed pump to separator from feed pump to separator

Once Through BoilerOnce Through Boiler

Water flowing through water walls gets Water flowing through water walls gets

converted into steam in one circulation. converted into steam in one circulation.

Feed pump provides the driving headFeed pump provides the driving head

Suitable for sub critical & super critical Suitable for sub critical & super critical

pressurespressures

Once-thru BoilerOnce-thru Boiler

Major differences from Drum type boiler :Major differences from Drum type boiler :

Evaporator systemEvaporator system Low load circulation systemLow load circulation system SeparatorSeparator

Once -thru BoilerOnce -thru Boiler

Evaporator systemEvaporator system : :

Formed by a number of parallel tubesFormed by a number of parallel tubes Tubes spirally wound around the Tubes spirally wound around the

furnace to reduce number of tubes and furnace to reduce number of tubes and to increase the mass flow rate thru’ the to increase the mass flow rate thru’ the tubestubes

Small tube diameterSmall tube diameter Arrangement ensures high mass Arrangement ensures high mass

velocity thru the tubesvelocity thru the tubes

Once - thru BoilerOnce - thru Boiler

Low load circulation system :Low load circulation system :

The excess flow over the once-The excess flow over the once-thru flow separated in separator .thru flow separated in separator .

Recirculated back to the boiler Recirculated back to the boiler directly by the dedicated circulating directly by the dedicated circulating pump.pump.

LOW LOAD SYSTEM WITH CIRCIRCULATION PUMP

Once -thru BoilerOnce -thru Boiler

Separator :Separator :

Separates steam and water during Separates steam and water during

the circulating mode operationthe circulating mode operation

Runs dry in once through flow Runs dry in once through flow

mode.mode.

Smaller in size compared to drum in Smaller in size compared to drum in

a drum type boilera drum type boiler

Once -through BoilerOnce -through Boiler

Advantages :-Advantages :-

Better suited for sliding pressure operationBetter suited for sliding pressure operation

Steam temperature can be maintained over Steam temperature can be maintained over

wider load range under sliding pressurewider load range under sliding pressure

Conservation of fuel resources.Conservation of fuel resources.

Shorter start up timeShorter start up time

Improvement in EfficiencyImprovement in Efficiency

Advanced CyclesAdvanced CyclesEffect on Boiler ComponentsEffect on Boiler Components

Evaporator (Furnace) wallsEvaporator (Furnace) walls SuperheatersSuperheaters Thickwalled boiler componentsThickwalled boiler components

Furnace wallsFurnace walls

Increased operating pressure increases Increased operating pressure increases the medium temperatures.the medium temperatures.

Increased regenerative feed heating Increased regenerative feed heating increases the fluid temp entering.increases the fluid temp entering.

Larger furnaces required for NOLarger furnaces required for NOXX

reduction, increase SH steam reduction, increase SH steam temperature at furnace wall outlet.temperature at furnace wall outlet.

SuperheatersSuperheaters

Tube metal temperatures in final Tube metal temperatures in final sections increase with outlet steam sections increase with outlet steam temperature.temperature.

Susceptibility for high temperature Susceptibility for high temperature corrosion. corrosion.

Susceptibility to steam side oxidationSusceptibility to steam side oxidation

Thick walled componentsThick walled components

Higher pressure & temperature lead to Higher pressure & temperature lead to increased thickness of :increased thickness of : Shells of separator, start-up system Shells of separator, start-up system

components, SHO header..components, SHO header.. Main steam piping.Main steam piping.

Higher thickness results in larger Higher thickness results in larger temperature gradients across walls.temperature gradients across walls.

Subcritical Vs SupercriticalSubcritical Vs Supercritical(A Comparison)(A Comparison)

500 MW Unit Size500 MW Unit Size

(Subcritical)(Subcritical)

660 MW Unit Size660 MW Unit Size

(Supercritical)(Supercritical)

Steam ParametersSteam Parameters

(ata / Deg.C/ Deg.C)(ata / Deg.C/ Deg.C)

169/538/538169/538/538 246/538/566246/538/566

Cost of Boiler & Cost of Boiler & Turbine Generator Turbine Generator BlockBlock

BaseBase 1.5%1.5%

Coal ConsumptionCoal Consumption BaseBase 2.1%2.1%

Plant EfficiencyPlant Efficiency BaseBase 2.1%2.1%

COCO22 Emissions Emissions BaseBase 2.1%2.1%

SOSO22 Emissions Emissions BaseBase 2.1%2.1%

Supercritical Technology - StatusSupercritical Technology - Status• More than 500 Units of various sizes operating

worldwide

• Material technology matured up to 600 Deg.C

temperature

• Availability of the order of 88 – 90% which is

comparable with that of subcritical units

• European union working on program “AD 700” which

aims at temperature up to 700-720 Deg.C and

efficiency target of 50%

• First supercritical unit in India has commissioned in

2007 by NTPC in sipat.

Thank YouThank You