ONCE THROUGH STEAM GENERATORS

Benson boiler growthBenson boiler growth

• 1926 –Siemens maufactures 30–125t/h boilers• 1949 –First OT boiler with high steam conditions(175 bar/610 DegC

– Leverkusen)• 1963 – First spiral tube waterwall in membrane design(Rhodiaceta)• 1987- Largest hard coal fired boiler (Heyden 900 MWMore than 980 boilers with > 700000 t/h

CONTROLLED CIRCULATION (Vs) ONCE THRU’

CC OT

Once Through PrincipleComparison Natural Circulation /

Once-Through-System

Source: Siemens

Cumulative Steam Capacity of Ordered BENSON Boilers

BBP´s share about 44 %

Source: SiemensTotal Steam Output about 200.000 kg/s 220.000 MW

Once Through Boiler-Concept

Once through system

ONCE - THROUGH OPERATING RANGE

Increase of Cycle Efficiency due to Steam Parameters

300241

175 538 / 538

538 / 566

566 / 566

580 / 600

600 / 620

6,77

5,79

3,74

5,74

4,81

2,76

4,26

3,44

1,47

3,37

2,64

0,75

2,42

1,78

00

1

2

3

4

5

6

7

8

9

10

HP / RH outlet temperature [deg. C]Pressure [bar]

Increase of efficiency [%]

Comparison of Plant part load efficiency

30

40

46

30 40 50 60 70 80 90 100Load %

41,1 %

36,7 %

39,3 %40,5 %

43,2 %42,4 %

40,1 %

Pla

nt

net

eff

icie

ncy

Supercritical unitacc. Alternative 2255 bar 538°C / 538°C

Subcritical unitacc. Alternative 1166 bar 538°C / 538°C

43,6 %

Examples of Boiler ConceptsTwo-Pass Boilerwithout platen superheater

Two-Pass Boilerwith platen superheater

Tower Boiler

PS Heyden 4 - 920 MW el PS Kogan Creek - 700 MW elPS Staudinger 5 - 550 MW el

66,0 m

Comparison of Lignite, Coal and Oil Fired Units

PS Offleben (C), 325 MWel PS Farge, 320 MWel PS Doha West, 300 MWel

mHD = 1000 t/h; B = 16,4 m mHD = 1020 t/h; B = 16,5 m mHD = 1100 t/h; B = 14 m

Heat input / furnace area [kW/m²] 215 330 680 SH heating surfaces [m²] 17.781 6.791 10.953 RH heating surfaces [m²] 15.290 12.072 5.202 Bundel surfaces [m²] 33.071 18.863 16.155

Benson BoilerMain Configuration - Single-pass /

Two-pass

Source: Siemens

DRUM vs ONCE THROUGH DRUM vs ONCE THROUGH

Pressure Sub critical Sub & super Critical Steam Separation Drum Separator (Low loads) Types Natural / Assisted (Sulzer) / (Benson)

Burner Panel Straight tube Spiral Tube / Straight (MHI)Load Change Base FasterCold Start 4-5 Hours 2 HoursHot Start 1-2 Hours 0.5 Hours

SH

STEAM TOTURBINE

HEATDOWN

COMER

DRUMECO

Water Wall

ORIFICECIRC. PUMP

SH

STEAM TO TURBINE

ECO

HEAT

Water Wall

Drum type boiler• Steam generation takes place furnace water

walls

• Fixed evaporation end point - the drum

• Steam -water separation takes place in the drum

• Separated water mixed with incoming feed water

Once Through Boiler

• Once -through flow through all sections of boiler (economiser, water walls & superheater)

• Feed pump provides the driving head

• Suitable for sub critical & super critical pressures

Once -thru BoilerAdvantages:• Quick response to load changes• Shorter start up time• Better suited for sliding pressure operation• Steam temperature can be maintained over wider

load range under sliding pressure• Higher tolerance to varying coal quality• Suitable for sub critical & super critical pressures

ADVANTAGES OF ONCE THROUGH BOILERS

Once thru boiler enables :

• Peak power generation with better efficiency levels

• Quicker response to TG load changes

• Better heat rate of lower loads

Once -through BoilerCharacteristics :• Provides Quicker response to TG load changes• Supports achievement of better heat rate at lower

loads• Higher furnace wall pressure drop and consequent

higher feed pump auxiliary power consumption• Needs ultra pure quality feed water - Cannot

operate under conditions of condenser leak

Tower Vs Two passTower Vs Two pass

• For Indian Pit-head power station BBP preference is tower type ( to overcome flyash erosion)

• For power stations firing beneficiated Indian coals – Two pass boiler

• For coastal power stations firing imported coals – Two pass boiler

Flow Scheme of Membrane Walls for Two-Pass Boilers

3.) 1.)

2.)

4.)5.)Detail:Ties for Spiral Tubing

Temperature differencebetween the wall systems(Example Studstrup Power Plant)

Boiler LoadLocation 100% 35%

1.) 2 K 1 K2.) 7 K 1 K3.) 13 K 1 K4.) 2 K 3 K5.) 7 K 17 K

Flow Scheme of Membrane WallsFlow Scheme of Membrane Wallsfor Tower Boilersfor Tower Boilers

Transition from Spiral Tubing to Vertical Tubing

Start-Up Times [min] of Power Plants

Plants with BENSON Boiler250 bar / 540°C / 560°C

Plants with Drum Boiler167 bar / 538°C / 538°C

first steamto Turbine

full load

From ignition to:

first steamto Turbine

full load

From ignition to:

20 - 30

40 - 60

150 - 210

150 - 210

60 - 80

80 - 100

300 - 350

450 - 600

20 - 30

30 - 40

60 - 80

60 - 80

30 - 40

50 - 60

150 - 200

400 - 600

After shutdown hours

<1

8

48

>48

Modern Coal-Fired Power PlantKWU 99 152d

Page 23

EV 2 / ; NTPC Presentation.ppt

BOILERS - DISCUSSED AT BBP

MAJUBA 660 MW TOWER 192 bar 555 C 19286x19286SCHKOPAU 450 MW TOWER 262 bar 545 C 17846x17846VOERDE 700 MW TWO PASS 206 bar 530 C 23668x15773

BOXBERG 900 MW TOWER 266 bar 545 C 24086X24086ELKRAFT 300 MW TWO PASS 250 bar 545 C 12720X14280

MAJUBA,SCHKOPAU,VOERDE : WITH VERTICAL TUBE HOPPER BOXBERG: WITH SPIRAL TUBE HOPPER ELKRAFT: WITH SPIRAL HOPPER & SPIRAL IN FRONT/REAR , HORIZONTAL IN SIDES

Once -thru Boiler - Furnace Wall

Furnace ArrangementFurnace Arrangement

VERTICAL TYPE

SPIRAL TYPE

FURNACE WALL ARRANGEMENT

BOILER PRESSURE PARTS WEIGHT

BOILER TYPE PIPES TUBES

210 MW 315 MT 1100 MT

250 MW 410 MT 1440 MT

500 MW 695 MT 2870 MT

660 MW** 1070 MT 5080 MT

** Worked out based on the Alstom BOM supplied

for SIPAT boiler.

Technology Acquisition Thru Collaboration – Status

•BHEL entered into a TCA with M/S Babcock Borsig Power(BBP), Grmany in 1999.

•First phase of training provided by BPP in 2001.

•BBP has become insolvent in July 2002 & further training planned during the execution of the first contract and technology transfer was not possible.

•Subsequently a new Engg company , Babcock Borsig Power Systems (BBPS), owned by Babcock Hitachi, Japan was formed.

•BBPS was found acceptable for Technical collaboration after “due deligence” exercises. But the collaboration route with BBPS could not be utilised for Sipat tender as NTPC spec required the collaborator to provide financial guarantees.

SIPAT 3x660MW – Joint Bidding with Alstom

•In the original bid submitted in Oct 2003, BHEL-Alstom joint bid was placed at L3, with Dossan/Korea as L1 and TPE/Russia as L2.

•In Dec 2003, NTPC invited snap bids to be submitted by all the three bidders by 9 Jan 2003

•The new requirements (with increased steam flow & for vacating certain deviations) called for a total redesign by Alstom with estimated three months time. Accordingly BHEL sought extension till 05 March 2004 for submitting the revised bid.

•However since the request for extension was not granted by NTPC, the snap bid could not be submitted by BHEL

Immediate OTB projects

•NTPC – BARH 3x660MW

Tender due in May 2004. QR same as Sipat project.

•APGENCO, Vijayawada 1X660MW

Four companies (Alstom, Siemens/Doosan,Sumitomo/Babcock Hitachi & TPE/Russia) have been pre-qualified for EPC