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SUPER CRITICAL

TECHNOLOGYBy- Arvind Kumar Yadav

(Executive Trainees-09)Employee No -101917

Operation Group - 3

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Te mp e ra t u re (

0 C )

Enthalpy

Critical point (221.25 bar, 374.15 0 C)

S a t u r a t e d v a p o u r l i n e

Wet Region

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Reasons for changeover from Sub

Critical to Super critical Higher Cycle efficiency. Conservation of fuel resources (Coal)

Reduction of Pollutants - SO X& NO X

Reduction in CO 2 emission (linked to globalwarming)

Better economy in power generation where fuel costsare high and pollution control requirements arestringent

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Steam Generation Process

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Super critical Operation

SC Steam generator Boiler Steam Pressure above the critical point Critical Point

221 bar, 374 c

S

T

1

2

3

4

Entropy

Temperatu

1 - 2 Feed Water Pumping Process 2 - 3 He at addition in the Feed

Water Heaters & Boiler 3 - 4 Expansion in HP Turbine 4 - 5 Reheating in Boiler 5 - 6 Expansion in IP & LP Turbine 6 - 1 Heat rejection in Condenser

5

6

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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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SUPERCRITICAL ADVANTAGESEnhancements Plant efficiency 0.69% to 1.64% Fuel tolerance More tolerant to coal quality changes

Reductions Coal Consumption Ash production CO 2

SO 2

NoxImprovements Startup time Sliding Pressure Operation Load following capability

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Reduction in CO 2, SO 2 and NO x between 1.79% to4.24%

Reduction for 500 MW at 68.5% PLF per year is- CO

278300 tons

- SO 2 365 tons

- No x 71 tons

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Critical PipMain Stea

Si

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Steam TuCasings

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TurbineBoiler F

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Types of Boilers

Drum type

Once Through

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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

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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 belowcritical pressure levels, thermo-siphon effectsupplemented by pumps

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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.

THE CONCEPT

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Major differences from Drum type boiler :

Evaporator system Low load circulation system

Separator

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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 ratethru the tubes

Small tube diameter Arrangement ensures high mass velocity thru the

tubes

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VERTICAL TYPE

SPIRAL TYPE

Furnace Arrangement

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Spiral wall arrangement

Advantage1.By spiraling around the furnace, every tube is part of all four walls

which means that not only the difference in the length of the paralleltube is minimized but also the heat pick up of individual tubes isparticularly equalized.

2.At low load also sufficient cooling of the tubes can be assured.

Disadvantage Complicated manufacturing, construction of tubes. Greater ash accumulation on water walls.

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Straight Tube Wall vs. Spiral Tube Wall

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Low load circulation system : At part loads once -thru flow not adequate to cool the

tubes.

To maintain required mass velocities boiler operates oncirculating mode at low loads.

Excess flow supplied by feed pump or a dedicatedcirculating pump.

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LOW LOAD SYSTEM WITH CIRC. PUMP

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Separator

Separates steam and water during thecirculating mode operation

Runs dry during once-thru flow mode Smaller in size compared to drum in a

drum type boiler

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EATURES OF SUPER CRITICAL BOILEREATURES OF SUPER CRITICAL BOILER ::

FEEDWATER

PUMPECONOMISER WATER WALL/

EVAPORATORSEPERATOR SUPERHEATER

STORAGETANK

RECIRCULATION

PUMP

CONSTANT WATER WALL FLOW

FEEDWATER

PUMPECONOMISER

WATER WALL/EVAPORATOR

SEPERATOR SUPERHEATER

ONCE THROUGH FLOW OPERATION

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ONCE - THROUGH OPERATING

RANGE

540C, 255 Ksc

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HPT

IPTLPTCONDENSER

FEED WATER

FRS

STORAGE

TANK

SEPARATOR

BWRP

Spira

l wate

r walls

MS LINE

HRH LINE

VERTICAL WW

ECO I/L

ECOJUNCTION

HDR

ECO HGRO/L HDR

FUR LOWER HDR

FUR ROOFI/L HDR

DIV PANELS SH PLATENSH

FINALRH

FINAL SH

LTRH

ECONOMISER

290C, 302 KSC

411C,277Ksc

411C,275 Ksc

492C, 260 Ksc

3 0 5 C , 49 Ks c

457C, 49 Ksc

568C, 47Ksc

GLPT

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The sliding pressure operation is a control system in which the main steamis controlled by sliding pressure in proportion to the generation output.Steam quality at the turbine inlet can be changed at constant volume flowswhile keeping the turbine governing valve open. Utilizing sliding pressure,the thermal efficiency of the steam turbine is improved at partial operatingloads through decreasing thermodynamic efficiency as follows, bycomparison with constant pressure type operation:

(1) A smaller governing value loss enables improvement of high pressureturbine internal efficiency(2) Decrease of feed water pump throughput

(3) Boiler reheat steam temperature can be maintained at higher levelsbecause of higher temperatures in high-pressure turbine exhaust steam.

Sliding Pressure Operation

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Enthalpy Variations vs Pressure andBoiler Load

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Sliding pressure V/s Constant

pressureIn sliding operation, turbine inlet valves remains fully open duringnormal operation. As a result the live.Advantages

lower thermal stresses

Reduce pressure level at low loads prolong the life span of plantcomponents.

Overall reduction in power consumption

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Pressure Operation Mod

140

160

180

200

220

240

260

280

30 50 70 90 110

Boiler Load (%

Pressure(bar)

Constant pressure mode

Sliding pressureModified Sloding pressur

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REQUIREMENT OF WATER QUALITY

The contents of dissolved and undissolved solids and other materialshould be practically zero.

In order to maintain above conditions continuous purification of thereturn condensate by means of CPU is mandatory.

It employ the use of all volatile treatment in order to maintain thelow TDS in water.

O.T. Is recent method employed for the treatment of water/steamcycle

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Super Critical Technology in NTPCs Plant

Plants in advance stage of construction

3x660MWSipatSTPPStage-I 3x660MWBarhSTPPStage-I

Upcoming Plants

Barh-II,Bihar2x660MW

NorthKaranpura,Jharkhand3x660MW Darlipali,Orissa4x800MW Lara,Chattisgarh5x800MW Cheyyur,Tamilnadu3x800MW

Marakanam,Tamilnadu4x800MW Tanda-II,UttarPradesh-2x660MW Meja,UttarPradesh-2x660MW

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Thankyou !