Pressure Parts 500MW Boiler

CONSTRUCTION OF 500 MW BOILER (PRESSURE PARTS)

BY ABHAY D. KHOBRAGADEA. E. (CHANDRAPUR PROJECT)

CONTENTS• WHY TO GO HIGHER CAPACITY

BOILER• SPECIFICATION OF 500 MW BOILER• SPECIAL FEATURE OF 500 MW

BOILER• NEED FOR ASSISTED CIRCULATION /

FORCED CIRCULATION

• DESIGN FACTORS

• CONSTRUCTION OF• WATER WALL TUBE, SUPER HEATER,

REAHEATER

• CONSTRUCTION OF BOILER DRUM

WHY TO GO FOR HIGHER CAPACITY BOILER

1

23

4

T

S

1’

P1

P2

2’

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.

Theoretically rankine Cycle is the ldeal cycle. But it is having practical difficulties.

For steam power plant, practically thermal cycle used is modified rankine cycle.

The maximum efficiency between two limits of the working fluid as given by the Rankine cycle is

Efficiency = (T1 – T2)/T1where T1 and T2 are max. and min absolute temp.

Now as T2 is limited by ambient conditions so T1 must be as high as possible.

Thus from the efficiency point of view, the largest gain can be obtained by the use of higher temperature. i.e to increase T1

SPECIFICATION OF BOILER 500 MW

FURNACE TYPE: Balanced Draft Wall: Fusion welded Bottom: Dry Tube arrangement: Membrane Explosion / Implosion withstand Capacity at 67% yield

point : +/- 660mmhg Residence time for fuel particles in the furnace : 3 sec. Effective volume used to calculate residence time: 14580

m3

Furnace height(from center of ring header to centre of roof inlet header) : 61.168 meter.

Depth : 15.289 meter

Width : 18.034 meter Furnace Volume : 14580 m3

Design Code: IBR Type of Firing: Tilting Tangential

SPECIFICATION OF BOILER 500 MW

SPECIAL FEATURES OF 500 MW 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.

4 Nos. of bisector air pre heater, two for primary air and two for

secondary air.

8 Nos. of XRP 1043 bowl mills.

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

Density difference is the driving force for the steam and water mixture.

Circulation takes place at such a rate that the driving force and the frictional resistance are balance.

But as the pressure increases, the difference in density between the water and steam reduces.

Hydrostatic head available may not be able to overcome the frictional resistance for the flow corresponding to the minimum requirement of cooling of water wall tubes.

Therefore, natural circulation is limited to Boiler with the drum operating pressure around 175 kg/cm2

Above 175 kg/cm2 of pressure, circulation is to be assisted with mechanical pumps, to overcome the frictional losses.

To regulate the flow through various tubes orifice plates are used.

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 methods

Scaling resistance

Maintenance

CONSTRUCTION OF PRESSURE PARTS

ECONOMIZER TUBESTUBE DETAILS All economizer tube are of Ø 51mm X 5mm. Located in the boiler back pass. It is composed of three banks of 130 parallel

tube elements arranged in horizontal rows. Each row is in line with the row above and

below. All tube circuit originate from the inlet

header and terminate at the outlet header.

ECO OUTLET HDR Ø406.4

EC0 FEED PIPE

ECO MIDDLE BANK

ECO UPPER BANK

ECO LOWER BANK

ECO INLET HDR Ø508

WATER WALL TUBES

TUBEE DETAILSDescription Tube Size Material

Riser Tube Ø 159 X 15 SA – 106 Gr-C

Water wall panel tubes

Ø51 X 5.6 SA – 210 Gr-C

Extended side water wall tube

Ø 63.5 X 7.1 SA – 210 Gr-A1

W. W. Hanger tubes

Ø63.5 X 11 SA – 210 Gr-C

W. W. Screen tubes Ø63.5 X 7.1 SA – 210 Gr-A1

Rear Arch Tubes i. Ø51 X 5.6ii. Ø63.5 X 7.1iii. Ø63.5 X 7.1

SA – 210 Gr-CSA – 210 Gr-CSA – 210 Gr-A1

FURN REAR HDR , Ø914.4

FURN SIDEHDR , Ø914.4

FURN FRONT WALL TUBES Ø51

FURN REAR WALL TUBES Ø51

FURN SIDE WALL TUBES Ø51

SUCTION MANIFOLD , Ø508

BCW PUMP

BOILER DRUMØ1778

REAR WALL HGR TUBES Ø63.5

SCREN TUBES Ø63.5

FUR UPPER SIDE WW HDR Ø273 FUR UPPER REAR

WW HDR Ø273

FUR REAR HGR TUBE O/L HDR Ø273

RISER TUBES, Ø 159

WATER WALL DETAILS AND CYCLE

SUPER HEATER TUBES

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

SUPER HEATER TUBESDescription 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 CSA 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 CSA 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, TP347HSA 213, T11SA 210, Gr CSA 213, T11SA 210, Gr C

SUPER HEATER TUBES

Super heater tubes is composed of three basic stages of section.Finishing

pendent platen super heater

A Low Temperature

Section

Divisional Panel Section

The finishing section is located on the horizontal gas path above the furnace rear arch tubes.

The divisional panel section are located in the furnace between the front wall and the pendent platen section.

It consist of 6 front and 6 rear assemblies. The low temperature section are located in the

furnace rear back pass above the economizer section.

They are composed of 116 assemblies spaced on across the furnace width.

The back pass wall and roof section forms the side, front, rear wall and roof of the vertical gas pass.

LTSH LWR BANK Ø 47.63

LTSH UPPE BANK Ø 47.63

SH & ECO SUPP TUBES, Ø 51

SH C

ON

N T

UBE

S,

Ø 5

9

SH R

OO

F O

/L

HD

R, Ø

406

.4

BP U

PPER

REA

R H

DR,

Ø 2

73LT

SH I/

L H

DR,

Ø

323.

9

BP LWR REAR HDR, Ø 323.9

BP LWR SIDE REAR HDR, Ø 323.9

BP LWR SIDE REAR HDR, Ø 406.4

BP LWR FRONT HDR, Ø 406.4

MAIN STEAM

SH DESH Ø 508, 2 NOS.

SH V

ERT

PLAT

EN

ASSY

, Ø 5

1, 6

ASS

Y

SH DIV. PANELETTE, Ø 44.5, 6 ASSY

DIV PANEL O/L LINK Ø 508, 2 NOS.

REHEATER

TUBE DETAILS

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

REHEATER The re heater section is composed of

three stages or section.

Finishing section

Radiant wall sectio

n

Front Platen Sectio

n

REHEATER

The finishing section is located above he furnace arch between the furnace screen tubes and the super heater tubes.

It consists of 46 tubes assemblies. The reheater front and side radiant wall

is composed of tangent tubes on 63.5 centres across the furnace width.

SH C

ON

N T

UBE

S,

Ø 5

9

SH R

OO

F O

/L

HD

R, Ø

406

.4

RH V

ERT

PLAT

EN

I/L

HD

R, Ø

457

.2

RH V

ERT

PLAT

EN

O/L

HD

R, Ø

558

.8

MAIN STEAM

COMPLETE CYCLE 500 MW

RH V

ERT

PLAT

EN

I/L

HD

R, Ø

457

.2

RH V

ERT

PLAT

EN

O/L

HD

R, Ø

558

.8

BOILER DRUM

The function of the boiler drum internals is to separate the water from the steam generated in the furnace walls.

To reduce the dissolved solid contents of the steam to below the prescribed level.

BOILER DRUM

Separation is generally performed in three stages.

Dry Saturated Steam

IIIrd Stage Screen Dryers

Ist stage

Spinner Blades

IInd StageCorrugated

sheets

Boiler Drum Internals

Baffle

Turbo separator

Screen Dryer

Anti Vortex Spider

Boiler Internals Mainly Consists of: -

Separating Chamber From the riser tube steam and

water mixture flows into the Drum through a narrow annulus formed by a shroud extending along the length of the Drum Shell called the Separating Chamber.

This is a welded construction formed by Baffles.

These surfaces direct the flow of substances either to prevent or o improve it’s flow.

It directs the steam and water mixture entering the drum to the turbo separator.

Turboseparator

From the lower end of the separating chamber the steam and water mixture is forced upward in the turboseparator.

Turbo separator is a main separating device.

Cans

Spinner Blades

Primary stage The primary stage is formed by two concentric cans

and a spinner blade located inside the inner can. The fixed spinner blade of turbo separator which is

located inside the inner can imparts a centrifugal motion to the mixture of steam and water flowing upward through the inner can.Secondary stage

The secondary stage consists of two opposed banks of closely spaced thin corrugated sheets.

It directs the steam through a curved path and separates the remaining entrained water.

Since the velocity is relatively low this water is not picked up again but runs down the plate and flows down to the drum water.

This stage of separation is called secondary separation or steam scrubbing.

Third stage

The third and final stage of steam/water separation takes place in the screen dryer.

It removes residual moisture from the steam leaving turbo separator.

The screen dryer box consists of wire mesh of different gauges.

Exterior meshes are of thicker wire rod, which have better mechanical rigidity to the screen box.

The steam passing between the strips making one or more sharp changes of direction and throwing the heavier water particle coming in contact with the strips.

Chemical Composition of tubes used in 500 MW

boilerSr. No.

Materila spec.

C Mn P S Si Ni Cr Mo V Cb Used in

1 SA 210, Gr- A1

0.27 0.93 0.048

0.058 0.10

Extended side WW tube, WW screen tube arch tube

2. SA 210, Gr C

0.35 0.29 to 1.06

0.048

0.058 0.10

WW Panel & corner transition tube, hanger tubes, rear arch tube, Eco tube, steam cooled wall, rear roof, SH hanger tube, LTSH divisional Panel loose tube.

3. SA 213, T11

0.15 0.30 to 0.60

0.03 0.03 0.5 to 1.0

1.0 to 1.5

0.44 to 0.65

Radiant roof pendent coil divisional panel, S, C, spacer, SH Platen coil, re heater wall , re heater coil.

4. SA 213, T91

0.15 0.3 to 0.6

0.03 0.03 0.5 1.9 to 2.6

0.87 to 1.13

Divisional Panel, SH Platen coil, RH Platen Coil, RH rear coil.

5. SA 213, T91

0.08 to 0.12

0.3 to 0.6

0.02 0.01 0.2 to 0.5

0.4 8.0 to 9.5

0.85 to 1.05

0.18 to 0.25

0.06 to 0.10

Platen SH coil, platen RH Coil.

6. SA 213 TP 304-H

0.04 to 0.10

2.0 0.04 0.03 0.75

8.0 to 11.0

18.0 to 20.0

- - - Divisional Panel, RH platen coil.

7 SA 213, TP 304-H

0.04 2.0 0.04 0.03 0.75

9.0 to 13.0

17.0 to 20.0

Divisional panel, SH platen coil, steam cooled spacer.

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