et 2008 steam circulation system

7/31/2019 ET 2008 Steam Circulation System

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STEAM CIRCULATIONSTEAM CIRCULATION

SYSTEMSYSTEM


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Steam circuit diagramSuper HeaterDe-super heater /

AttemperatorRe-heaterIBR

Super Critical Boiler


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Pendant typeHorizontal type

Radiant SuperheaterConvectionSuperheaterCombined

Superheater

Types of SuperHeaters


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M.S

FROM F.R.S

Sh 1Sh 1


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M.S

FROM F.R.S

SH 2SH 2


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M.S

FRM F.R.S

LTSHLTSH


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M.S

FROM F.R.S

Final SHFinal SH


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M.S

H.

R.

HC.R.H

FROM F.R.S


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Super heater heats the high-

pressure steam from itssaturation temperature to ahigher specified temperature.

Super heaters are often dividedinto more than one stage.

Super heaters

Super heater heats the high-

pressure steam from itssaturation temperature to ahigher specified temperature.

Super heaters are often dividedinto more than one stage.

Super heater heats the

high-pressure steamfrom its saturationtemperature to a

higher specifiedtemperature.

Super heaters are oftendivided into more than

Super heater heats thehigh-pressure steam

from its saturationtemperature to a higherspecified temperature.

Super heaters are oftendivided into more thanone stage.

Super heater heats thehigh-pressure steamfrom its saturation

temperature to ahigher specifiedtemperature.

Super heaters are oftendivided into more than

one stage.


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Transfer of EnergyTransfer of Energy

Hot Flue

GasThermal Structure

SH

Steam

Convection &

Radiation HT

Convection HT

Drop in Enthalpy

of Flue Gas

Rise in Enthalpy of

Steam

Mechanism of Heat Transfer

Source/Supply Thermal Structure Sink /Demand


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Mechanism of Heat Transfer :Mechanism of Heat Transfer :

Rate of heat transfer from hot gas toRate of heat transfer from hot gas to

cold steam is proportional to:cold steam is proportional to:

Surface area of heat transferSurface area of heat transfer

Mean Temperature differenceMean Temperature differencebetween Hot Gas and Cold Steam.between Hot Gas and Cold Steam.

Thot gas,in

Tcold steam,in

Thot gas,out

Tcold steam,out


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Thot gas,in

Tcold steam,in

Thot gas,out

Tcold steam,out

Thot gas,in

Tcold steam,in

Thot gas,out

Tcold steam,out


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Mechanism of Heat Transfer :Mechanism of Heat Transfer :

Rate of heat transfer from hot gas toRate of heat transfer from hot gas to

cold steam is proportional to:cold steam is proportional to:

Surface area of heat transferSurface area of heat transfer

Mean Temperature differenceMean Temperature differencebetween Hot Gas and Cold Steam.between Hot Gas and Cold Steam.

Thot gas,in

Tcold steam,in

Thot gas,out

Tcold steam,out


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Platen SuperheaterPlaten Superheater Platen Superheater : FlatPlaten Superheater : Flat

panels of tubes located in thepanels of tubes located in theupper part of the furnace,upper part of the furnace,

where the gas temperature iswhere the gas temperature is

high.high.

The tubes of the platen SHThe tubes of the platen SH

receive very high radiation asreceive very high radiation aswell as a heavy dust burden.well as a heavy dust burden.

Mechanism of HT : HighMechanism of HT : High

Radiation & Low convectionRadiation & Low convection

Thermal Structure:Thermal Structure:

No. of platensNo. of platens No. of tubes in a platenNo. of tubes in a platen

Dia of a tubeDia of a tube

Length of a tubeLength of a tube


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Geometry of Thermal Structure :Geometry of Thermal Structure :

Platen SHPlaten SH

The outer diameter of platen SH isThe outer diameter of platen SH is

in the range of 32 42 mm.in the range of 32 42 mm.

The platens are usually widelyThe platens are usually widely

spaced, Sspaced, S11 = 500 900 mm.= 500 900 mm. The number of parallel tubes in aThe number of parallel tubes in a

platen is in the range of 15 35.platen is in the range of 15 35.

Design Constraints: Max. allowableDesign Constraints: Max. allowable

steam flow rates.steam flow rates.


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WAYS TO IMPROVEWAYS TO IMPROVE

EFFICIENCYEFFICIENCY

SUPERHEATINGSUPERHEATING

REHEATINGREHEATING

REGENERATIONREGENERATION


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REHEATING


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Rankine Cycle Efficiency

net workn = --------------

Qin

Cycle thermal efficiency is improved by increasing the

mean temperature of heat addition process. This

temperature is increased because the boiler inletpressure sets the saturation temperature in Rankine

cycle.

Total fuel input

Heat Rate =------------------

Electrical generation (KW)


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It effects improvement andIt effects improvement and

economy in the following wayseconomy in the following ways

It increases capacity of plant.It increases capacity of plant.

It eliminates errosion of the lastIt eliminates errosion of the last

stage of the turbine.stage of the turbine.

It reduces the steamIt reduces the steam

consumption of the turbine.consumption of the turbine.


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Horizontal SuperheaterHorizontal Superheater


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How it increases efficiency?How it increases efficiency?


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Rankine Cycle Efficiency

net workn = --------------

Qin

Cycle thermal efficiency is improved by increasing the

mean temperature of heat addition process. This

temperature is increased because the boiler inletpressure sets the saturation temperature in Rankine

cycle.

Total fuel input

Heat Rate =------------------

Electrical generation (KW)


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Superheated cycleSuperheated cycle


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Based on the position of headerBased on the position of header

1.Vertical superheater.1.Vertical superheater.2.Horizontal superheater.2.Horizontal superheater.


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Based on heat receiving capacityBased on heat receiving capacity

Convective superheaterConvective superheater

Radiant superheaterRadiant superheater


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STEAM OUTLETSTEAM OUTLET

TEMPERATURETEMPERATURE

RESPONSE OFRESPONSE OFDIFFERENTDIFFERENT

SUPRHEATERSSUPRHEATERS


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Radiant SH & Convective SH each hasRadiant SH & Convective SH each has

different steam outlet temp response.different steam outlet temp response.

As demand for steam increases withAs demand for steam increases with

increase in load, fuel and airflow andincrease in load, fuel and airflow and

hence combustion gas flow arehence combustion gas flow areincreased.increased.


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Load response of SHLoad response of SH


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In CSH heat transfer co-efficient (Hi&Ho)In CSH heat transfer co-efficient (Hi&Ho)

increases both outside & inside due toincreases both outside & inside due toincrease in gas flow rate and increase inincrease in gas flow rate and increase in

steam flow rate respectively.steam flow rate respectively.

In case of RSH since furnace temperatureIn case of RSH since furnace temperatureand hence the amount of available heatand hence the amount of available heat

from radiation does not rise as rapidly asfrom radiation does not rise as rapidly as

the steam flow rate it has fallingthe steam flow rate it has fallingcharacteristic.characteristic.


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In CSH steam O/T Temp.In CSH steam O/T Temp.

increases with incease in steamincreases with incease in steam

flow rate while in RSH itflow rate while in RSH it

decreases with steam flow rate.decreases with steam flow rate. Hence combination of RSHHence combination of RSH

&CSH is used in series which&CSH is used in series which

gives a relatevely flat curve forgives a relatevely flat curve forsteam O/T temp. and is thussteam O/T temp. and is thus

insensetive to load change.insensetive to load change.


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Basically the control of temperature is to protect the

superheater by preventing the metal temperatures

reaching a dangerously high level reducing mechanical

strength and leading to failure. Water flowing through atube conducts heat away much more effectively than

steam due to its higher specific heat capacity. This

means that tubes carrying water have a metal

temperature much closer to the fluid passing through it.

For superheat temperatures alloys of chromemolybdenum steels are used (upto 560oC)

Superheat temperature control is therefore fitted to

ensure superheat temperature does not exceed design

limits

Superheater Temperature Control


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Reheater and DesuperheaterReheater and Desuperheater


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Reheat pressure for optimumReheat pressure for optimum

efficiencyefficiency


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Reheater in 500 MW plantReheater in 500 MW plant


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M.S

FROM F.R.S

RHRH


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CRHCRHpressure 43.5 KSCpressure 43.5 KSC

temperature 340temperature 340 CC

HRHHRHpressure 41.5 KSCpressure 41.5 KSC

temperature 535temperature 535 CC


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ATTEMPERATIONATTEMPERATION


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What is the purpose of attemperation andWhat is the purpose of attemperation and

its location in power plant?its location in power plant?


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Direct contact DesuperheaterDirect contact Desuperheater


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Enthalpy

538

Expansion Line

170 kg/cm2

240 kg/cm2

Condensation

EFFECT OF SUPERCRITICAL PARAMETERSEFFECT OF SUPERCRITICAL PARAMETERS

Critical Point 225 kg/cm2


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Enhancements

Plant efficiency 0.69% to 1.64%Fuel tolerance More tolerant to

coal quality changes

Reductions

Coal Consumption

Ash productionCO2

SO2

Nox

Improvements

Startup timeSliding Pressure Operation

Load following capability

SUPERCRITICAL ADVANTAGESSUPERCRITICAL ADVANTAGES

SELECTEDPARAMETERS

MSP 246 kg/cm2

MST 538 0C

RST 566 0C


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Sliding pressure V/s Constant pressure

In sliding operation, turbine inlet valves

remains fully open during normal

operation. As a result the live.

Advatages

lower thermal stresses

The control range of the reheater final

steam is extended.

Reduce pressure level at low loads prolong

the life span of plant components.

Overall reduction in power consumption


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Type Supercritical, suitable for variable pressure operation with spiralor rifled/plain water wall tubing Tower type or two pass type

Rating Flow (T/Hr) Temperature Deg CPressureKg/Cm2(a)

At SH Outlet 2225 540 256

At RH Outlet 1740 568 52.0

Flue gas temperature at air-heater outlet- 125 Deg C

Fuel GCV range 3000 to 4000 Kcal/kg with 10-16% moisture and 32 to 48%ash

Start upsystem

Start up system with one no. circulating pump is with alternate drainflow to condenser through flash tank .

Salient Features of the Steam Generator


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Indian Boiler Regulations

Scope (cover regulations on): Electric-Resistance-Welded

Steel Boiler And Super-Heater

Tubes

Boiler Tubes Subject To External

Pressure The Working Pressure To Be

Allowed On Various Parts Of

Boilers

Welded And Seamless ForgedDrums For Water Tube Boilers

And Super Heaters Requisite Mountings, Fittings

and Auxiliaries


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Boiler And Super Heater

Tubes, Headers And Other

Pressure Parts TubesSteam-Pipes And Fittings

Registration Of Boilers And

Inspection Of BoilersSafety Of Persons Inside

BoilersQualification Tests For

Welders Engaged In Welding

Of Boilers

et 2008 steam circulation system

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