Construction of 500 mw boiler

by Vaibhav G. Paydelwar ( Project Engineer) Sunil Hi-Tech Engineers Limited

Boiler means any closed vessel exceeding 22.75 Ltr. in capacity used for steam generation under pressure. The first boiler was developed in 1725 and its working pressure was 10 kg/ cm2.

Boiler can be regarded as a number of interconnected heat exchangers arranged in such manner that heat available by burning of fuel is transferred to convert water into steam in most efficient manner.

WHAT DO YOU MEAN BY BOILER ?

FUNCTION OF BOILER

To produce the steam at the desired

rate at desired pressure and temperature

with use of resources such as oil, coal &

water for generating the power.

Types of BoilersNatural circulation Boiler :- Drum to down comer - to main ring header – to ww tubes and back -to drum. Due to difference in density of water and steam this types of circulation takes place.

Forced circulation (Assisted circulation) Boiler :- As per operating pressure of the boiler approaches to the critical pressure, additional pumps are required to install in down comers, because at this pressure there is no appreciable density difference between water and steam to have natural circulation of water.

NEED FOR ASSISTED CIRCULATION

80 100 120 140 160 180 200 220 2400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Pressure (Kg/cm2)

Density of Water

Density of Steam

Critical Point

According to working pressure

Sub critical pressure boiler : when working pressure of boiler is between 130 to 180 kg/ cm2

critical boiler : when working pressure of boiler is 225.56 kg/ cm2

Super critical boiler : when working pressure of boiler is 240.10 kg/ cm2

Why to go for higher capacity ?

1’-2’ = Work done in turbine from P1 – P2

2’-3 = Heat Rejection in condenser

3-4 = Water pumped to boiler

4-1 = Heat addition in eco and boiler.

SPECIAL FEATURES OF 500MW BOILER

Controlled circulation of feed water in water walls with the help of 3 Nos. of boiler circulating water pumps installed on down comers. Rifled bore water wall tubes as against smooth bore tubes in 210 MW boiler.

Provision of Orifices for equal distribution of water in water wall tubes from bottom ring header.

All down comers are connected to front header of the bottom ring header.

DESIGN FACTORFor the construction of boiler parts subjected to pressure and their integral attachment, the designer takes into account several factors Relative Cost Mechanical Properties Manufacturing Method Scaling Resistance Maintenance

Various parts of BoilerBOILER IS DIVIDED INTO TWO PASS:- FIRST PASS SECOND PASS

First pass of the boiler consists of:-

Furnace water wall.

Divisional super heater pendent assembly.

Final Super heater pendent assembly.

Reheater front pendent assembly. (CRH)

Reheater rear pendent assembly. (HRH)

Rear Arch Panel.

Water Wall screen tubes.

Second pass of the boiler consists of:-

Steam cooled wall.

Economizer lower bank coils.

Economizer middle bank coils.

Economizer upper bank coils.

LTSH lower bank coils

LTSH upper bank coils

Eco. Hanger tubes.

LTSH terminal tubes.

ECONOMISER Requirement why ? Advantages• As the economiser recover the heat in the flue gas that leaves the boiler

and transfer to working fluid there will be saving in fuel consumption.• As the feed water is preheated in the economiser and enter the boiler

tube at an elevated temperature( near to saturation temp.) the heat transfer area required for the evaporation surface required will be reduce considerably. As the size of boiler also will be reduced.

Types of Economiser Steaming Non steaming• Plain tube economiser• Fin-tube economiser

Plain tubes Direction of Gas Flow

Direction of Gas Flow

 

Inline Arrangement Staggered Arrangement

 

Fin-tube Eonomiser

Tube size and spacing The tubes can be made any length and diameter with 38mm to 52mm

OD. The side spacing and back spacing can be arranged for good cleaning, absorption of heat and less draught loss. Spacing about 90mm to 140mm.

It is composed of three banks of 130 parallel tube elements arranged in horizontal rows in such a manner that each row is in line with the row above and below.

Drum & Drum Internals Requirement Separation of saturated steam from the steam-water mixture produced by the

evaporating tubes Mixing feed water from economiser and water separated from steam – water

mixture, and re-circulate through the evaporating tubes. Carrying out blow down for reduction of boiler water salt concentration. Treatment of Boiler water by chemicals

construction of drum

1 11111

BOILER DRUM: Construction: Fusion weldedMaterial specification: SA299Design pressure: 204.9 kg/cm2

Maximum operating press: 193 kg/cm2

Thickness for straight portion: 195/165 mmOverall length of drum : 22070 mmOutside dia. Of Drum : 2138 mmInternal dia. Of Drum :1778 mmElevation of drum centre above ground level: 71.583 meterNo. of distribution headers : 6No. of cyclonic separator :92No. of secondary dryers : 92No. of final dryers : 124Maximum permissible DT between any two parts of Drum : 50 0C

Connection to Boiler Drum Main connection• Feed lines • Down comers • Up risers• Super heater supply tubes

Auxiliary connection• Blow down line• Chemical dosing line• Instrumentation tapping• Air vents• Safety valves• Nitrogen filling line• High and low level trips

Drum InternalsFeed headerAnti vortex spiderSteam separatorSteam dryers or scrubbersC.B.D. line E.B.D. line chemical dosing line

Water Walled Furnace Requirement Advantages In furnace not only combustion but also heat transfer is taking place

simultaneously. The maintenance work involved in repairing the firebricks (which is

otherwise necessary) is completely eliminated. Due to heat transfer in the furnace, temperature of the flue gas leaving

the furnace is reduced to the acceptable level of the superheating surfaces.

Higher heat loading in the furnace is possible, as heat is being simultaneously removed by heat transfer, and hence economy in surfacing.

Providing a Gas tight seal to the combustion chamber to prevent air infiltration.

Water Wall Furnace Constuction

Expansion and Sealing

330 mm

36mm

29mm

53mm

174mm

58mm

Buckstay and Furnace Guides

Superheaters Requirement?

By increasing the temperature of the steam, the useful energy that can be recovered economically increases thus the efficiency of the cycle also as can be seen in Fig.3.40.

Superheating of steam eliminates the condensation of steam during transporting of steam in pipelines and inside the early stages of turbines which is harmful to the turbine blades and pipe lines.

Limits the work done by turbine stages to avoid excessive erosion of blades

Types of superheater radiant superheater convective superheater

Relationship in SH DesignThe steam temperature desiredThe super heater surface area requiredThe rate of steam flow through the tubes (mass

flow)The material best suited for the super heater

tubesThe gas temperature zones where the surfaces

are to be locatedThe arrangement of surfaces to meet the

characteristics of the fuel to be used with specific reference to the spacing of tubes

Material for SHASME CODE NOMINAL

COMPOSITION

TEMP.LIMIT 0C

SA 213 CARBON STEEL 450

SA 213 T1 C-1/2 Mo. 470

SA 213 T11 11/4 Cr. –1/2 Mo. 550

SA 213 T22 21/4 Cr.-1 Mo. 580

SA 213 T9 9 Cr.-1 Mo. 635

SA 213 TP 304 H 18 Cr.-8 Ni. 705

SA 213 TP 347 H 18 Cr.-10 Ni. 705

SA 213 TP 316 H 16 Cr.-12 Ni.-2 Mo. 705

Description Tube Size Material

Radiant Roof Tubes i. Ø 63.5 X 6.3 ii. Ø 57 X 5.6

SA 213, T11SA 213, T11

Steam Cooled Side wall tubes

i. Ø 63.5 X 6.3ii. Ø 51 X 5iii. Ø 76.1 X 10

SA 210, Gr CSA 210, Gr CSA 210, Gr C

Steam Cooled front wall tubes

i. Ø 51 X 5ii. Ø 63.5 X 6.3iii. Ø 44.5 X 7.1

SA 210, Gr CSA 210, Gr CSA 210, Gr C

Front Wall Hanger Tubes Ø 51 X 5.0 SA 210, Gr C

Rear Roof Tubes i. Ø 51 X 5ii. Ø 44.5 X 7.1

SA 210, Gr CSA 210, Gr C

Eco and LTSH Support tubes

Ø 47.63 X 8.6 SA 210, Gr C

Description Tube Size Material

Steam Cooled Side Wall tubes Ø 51 X 5 SA 210, Gr C

Bifurcate Tubes (Bottom Header) Ø 51 X 5 SA 210, Gr C

LTSH Horizontal Tubes i. Ø 51 X 5ii. Ø 51 X 5.6

SA 210, Gr C SA 210, Gr C

Pendent Coil Tubes i. Ø 51 X 5ii. Ø 51 X 5.6

SA 213, T11SA 213, T11

Divisional Panel inlet loose tubes i. Ø 51 X 6ii. Ø 44.5 X 4.5

SA 210, Gr C SA 210, Gr C

Divisional Panel Outlet loose tubes i. Ø 51 X 6 SA 213, T11

Steam Cooled Spacer i. Ø 63.5 X 8ii. Ø 51 X 5.6iii. Ø 63.5 X 6.5iv. Ø63.5 X 7.1v. Ø 63.5 X 7.1vi. Ø 51 X 5.0vii. Ø 51 X 5.0

SA 213, T11SA 213, TP347HSA 213, TP347H SA 213, T11 SA 210, Gr C SA 213, T11 SA 210, Gr C

Reheater

Requirement?

Description Tube Size Material

Reheater Wall tubes Ø 60.3 X 4 SA 313, T11

Cross over tubes Ø 54 X 3.6 SA 213, T11

Sr

.

N

o.

Type

Heating Surface

Area in m2

1 Radiant roof, steam cooled wall LTSH

Horizontal and pendent.

9620

2 Super Heater Divisional Panel 1361

3 Final Super heater Platen 1458

4 Reheater radiant wall front and side,

front platen, rear platen.

5075

Total Heating Surface 17514 M2

Sr.

No.

Parameters Rating

1 Super heater system flow 1681 TPH2 Reheater System Flow 1430.64 TPH3 Pressure at super heater outlet 179 Kg/cm2

4 Temperature at super heater outlet 540 oC5 Pressure at reheater inlet 44.88 Kg/cm2 (g)6 Temperature at reheater inlet 342.7 oC7 Pressure at reheater outlet 42.68 Kg/cm2 (g)8 Temperature of reheater outlet 540 oC 9 Feed Water temperature 255 oC10 Ambient air temperature 28 oC11 Combustion air temperature secondary 335 oC12 Fuel Quantity 330 TPH13 Air Quantity (Total Combustion air) 2030 TPH14 Temperature of Gas at boiler exit 142 oC15 Total Heat output of the system 1076 Kcal/Hr

A B

PLSH RH FSH

LTSH

ECO

APH

ESP

MAX-134 ºC

1135-1020 ºC

1020-793 ºC

758-726 ºC 720 ºC

461 ºC

355 ºC

147 ºC 137 ºC

DRUM

1300-1400

BOILER AIR & FLUE GAS TEMPERATURES

1100-1250

SA-318 ºC PA-313 ºC

143 ºC

A B

PLSH RH FSH

LTSH

ECO

APH

ESP

DRUM

BOILER WATER & STEAM TEMPERATURE

243-286 ºC

286-349 ºC

349-426 ºC426-520 ºC

520-540 ºC

344-540

1300-1400

BOTTOM RNG HDR WW PANELS & 1ST PASS W.W.

1ST PASS W.W O/L HDRS ROOF I/L HEADER

2ND PASS UPPER C-HDR 2nd PASS LOWER C-HDRS

LTSH I/L HEADER LTSH & O/L HEADER

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

FINAL S.H. R.H.HEADER

2ND PASS ROOF O/L HDR(REAR ECONOMISER

M.S

H.R.HC.R.H

FROM F.R.S

500MW BOILER

BCW Pump

Thank You