steam circulation system of pulverized coal fired boiler

8/12/2019 Steam Circulation System of pulverized coal fired boiler.

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24 March 2014 PMI Revision 00 1

SteamCirculation

System


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Presentation Plan Steam circuit diagram

Super Heater

De-superheater /Attemperator

Re-heater

IBR

Super Critical Boiler


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FROM BFP

DISCHARGE

DRUM

500MW WATER AND

STEAM CIRCUIT

CC

Pump

Bank I

Bank II

Economizer


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BOTTOM RNG HDR & Z-PANEL 1STPASS W.W

1STPASS W.W O/L HDRS ROOF I/L HEADER

2NDPASS UPPER C-HDR 2ndPASS LOWER C-HDRS

LTSH I/L HEADER LTSH O/L HEADER

D.P.I/L HEADER D.P.O/L HEADER

S.H. HEADER R.H.HEADER2NDPASS ROOF O/L HDR(REAR ECONOMISER

M.S

H.

R.

HC.R.H

FROM F.R.S


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Types of Super Heaters Pendant type

Horizontal type

Radiant Superheater

ConvectionSuperheater

CombinedSuperheater


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SUPER HEATER

WATER IS HEATED TO RAISE STEAM TO HIGHER TEMPERATURE

ARRANGED IN 3 STAGES

LTSH LOCATED ABOVE ECONAMISER

RADIANT PENDENT TYPE (DIV PANEL)

ABOVE FURNACE

CONVECTIVE FINAL SUPER HEATERABUVE FURNACE IN CONV PATH


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Super heaters

Super heater heats the high-pressure steam from itssaturation temperature to a higher specified

temperature.

Super heaters are often divided into more than one

stage. The enthalpy rise of steam in a given section should

not exceed

250420 kJ/kg for High pressure. > 17 MPa

< 280 kJ/kg for medium pressure. 7 Mpa17MPa

< 170 kJ/kg for low pressure. < 7 MPa


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Transfer 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 :

Rate of heat transfer from hot gas to cold steam is

proportional to:

Surface area of heat transfer

Mean Temperature difference between Hot Gas and ColdSteam.

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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Platen Superheater Platen Superheater : Flat panels

of tubes located in the upper part

of the furnace, where the gas

temperature is high.

The tubes of the platen SH

receive very high radiation as

well as a heavy dust burden.

Mechanism of HT : HighRadiation & Low convection

Thermal Structure:

No. of platens

No. of tubes in a platen

Dia of a tube

Length of a tube


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Geometry of Thermal Structure :Platen SH The outer diameter of platen SH is in the range of 3242

mm.

The platens are usually widely spaced, S1= 500900

mm.

The tubes within a platen are closely spaced, S2/d = 1.1.

The number of parallel tubes in a platen is in the range of

1535.

Design Constraints: Max. allowable steam flow rates.


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Convective SuperheaterPendant) Convective super heaters are vertical

type (Pendant ) or horizontal types.

The Pendant SH is always arranged

in the horizontal crossover duct.

Pendant SH tubes are widely spaceddue to high temperature and ash is

soft.

Transverse pitch : S1/d > 4.5

Longitudinal pitch : S2/d > 3.5.

The outside tube diameter : 3251mm

Tube thickness : 37mm

S1S2


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Convective Superheater Horizontal) The horizontal SH are located in the back pass.

The tubes are arranged in the in-line configuration.

The outer diameter of the tube is 3251 mm.

The tube thickness of the tube is 37 mm.

The transverse pitch : S1/d = 23.

The longitudinal pitch :S2/d = 1.62.5.

The tubes are arranged in multiple parallel sets.

The desired velocity depends on the type of SH and operating steam

pressures. The outside tube diameter : 3251mm

Tube thickness : 37mm

S1S2


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CRH FROM

HPT

MS TO HPT HRH TO IPT

DRUM

PLATEN SH1

PRI. SH

ECONOMISER

ECONOMISER


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SuperheaterTemperature Control Basically the control of temperature is to protect the

superheater by preventing the metal temperatures reachinga dangerously high level reducing mechanical strength andleading to failure. Water flowing through a tube conductsheat away much more effectively than steam due to itshigher specific heat capacity. This means that tubescarrying water have a metal temperature much closer to thefluid passing through it.

For superheat temperatures alloys of chrome molybdenumsteels are used (upto 560oC), difficulties in welding means

that there use is restricted to only within the highesttemperature zone and a transition piece fitted to connect toremaining mild steel tubing.

Superheat temperature control is therefore fitted to ensuresuperheat temperature does not exceed design limits.


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Locating the desuperheater The preferred location of

desuperheater, especially fortemperature above 450 deg C isbetween sections of superheater. Thesteam is first passed through a

primary superheater where it is raisedto intermediate temperature. It is thenpassed through the desuperheater andits temperature reduction is controlledso that, after continuing through thesecondary or final stage of the

superheater, the required constantconditions are maintained at the outlet.


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Reheater Purpose: RE-HEAT THE STEAM FROM HP TURBINE TO

540 DEG

COMPOSED OF THREE SECTIONS

RADIANT WALL REHEATER ARRANGED IN FRONT& SIDE WATER WALLS

REAR PENDANT SECTION ARRANGED ABOVE

GOOSE NECK

FRONT SECTION ARRANGED BETWEEN UPERHEATER PLATEN & REAR WATER WALL HANGER

TUBES


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Reheater


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Procedure to DetermineOptimum Reheat Pressure Calculate the efficiency of Rankine cycle, Rankine.

Calculate mean effective temperature of heat

addition, Tm,inusing

Find out pressure corresponding to Tm,inand

entropy at HP turbine inlet. Add reheating at this pressure and calculate

efficiency of the Reheat Cycle.

Repeat above steps for few iterations.

inm

cCarnotEqRankine

TT

,

. 1hh


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Arrangement andConstruction

The arrangement and construction of a re-

heater is similar to that of a super-heater. In

large modern boiler plant, the reheat sections

are mixed equally with super-heater sections.


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Reheater

The pressure drop inside re-heater tubes has an importantadverse effect on the efficiency of turbine.

Pressure drop through the re-heater should be kept as lowas possible.

The tube diameter : 4260mm.

The design is similar to convective super-heaters.

Overall Heat Transfer Coefficient : 90110 W/m2K.


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Safety ValvesDevice attached to a boiler for

automatically relieving the pressure

of steam before it becomes great

enough to cause bursting. Thecommon spring-loaded type is held

closed by a spring designed to open

the valve when the internal pressure

reaches a point in excess of the

calculated safe load of the boiler.Safety valves are installed on

boilers according to strict safety

norms and IBR recommendation


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Safety Valve Settings of aTypical 200 MW BoilerLocacation Set

Pressure

(Kg/sq cm

Reliving

Capacity

T/Hr

Drum 175.8 177.1179.3 180.6

181.1 182.5

Super Heater 163.3 154.0Re-heater inlet 45.0

45.5

46.3

Re-heateroutlet 42.70


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Indian Boiler Regulations History

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 Forged Drums For Water TubeBoilers And Super Heaters

Requisite Mountings, Fittings and Auxiliaries


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Indian Boiler RegulationsContinued)

Boiler And Super Heater Tubes, HeadersAnd Other Pressure Parts Tubes

Steam-Pipes And Fittings

Registration Of Boilers And Inspection OfBoilers

Safety Of Persons Inside Boilers

Qualification Tests For Welders Engaged InWelding Of Boilers

Feed Water For Boiler


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WHY SUPERCRITICAL

PRESSURE Increasing the pressure will mean increase in saturation

temperature at which steam evaporates thus increasing

the average temperature of heat addition.

A Boiler operating at a pressure above critical point iscalled SUPERCRITICAL BOILER

A point where boiling water and dry saturated lines

meet so that associated latent heat is zero, this point

is called Critical Point.


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CRITICAL CONDITION

Definition

CRITICAL is a thermodynamic expressiondescribing the state of a substance beyond

which there is no clear distinction between theliquid and gaseous phase.

The critical pressure & temperature for water are

Pressure = 225.56 Kg / cm2

Temperature = 374.15 C
http://d/UTSAV/STAGE1/CRITICAL.ppthttp://d/UTSAV/STAGE1/CRITICAL.ppt


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T S DIAGRAM

Entropy KJ / Kg K

Temperatu

re(0C

)

-2730

240c

A

B C

D

E

F

OUTPUT INCREASE Basic Rankine Cycle


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0

100

200

300

400

500

600 540C568C

ENTROPY

TEMP

SUPER CRITICAL

BOILER CYCLE WITH

SH, RH & Regeneration

of SIPAT 3 x 660 MW

Steam flow :2225 T/Hr

Steam temp : 540 c

Steam Pres : 256 kg/cm2

RH pre : 51.6 Kg/cm2

RH Temp : 568c

Feed water Temp : 291c


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SUPERCRITICAL BOILER

Supercritical pressure boiler has no drumand heat absorbing

surface being, in effect, one continuous tube, hence called

once through Supercritical pressure boilers.

The water in boiler is pressurized by Boiler Feed Pump, sensible

heat is added in feed heaters, economizer and furnace tubes,

until water attains saturation temperature and flashes

instantaneously to dry saturated steam and super heating

commences.


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Pressure Parts Material

SA210C, T12, T23Reheater

Tube

Final

Section

Economizer Tube SA210C

Spiral SA213T22EvaporatorTube/Water

Wall Vertical SA213T22

Primary SA213T23, T91

Secondary SA213T12, T23, T91Superheater

Tube

Final SA213T23, T91, T92

Primary

SA213T23, T91

SUPER304H

Separator SA302C

SH outlet SA335P91Header

RH outlet SA335P91

SIPAT 500 MW PlantMaterial Oxidation

Criteria,

SA-210C 454

SA-213T2 482

SA-213T12 552

SA-213T22 593

SA-213T23 593

SA-213T91 649

SA-T92 649

SUPER304H 760


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THANK YOU

steam circulation system of pulverized coal fired boiler

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