+ economic ++ flexible +

+ innovative +

+ economic ++ flexible +

+ innovative +

Research & Development at the BENSON Test Rigby Siemens AG • Power Generation (PG)

BENSON BoilerBENSON Boiler

This booklet should remind you of the exhibitionin the monitoring room of the BENSON test rigin Erlangen, Germany, where the fundamentalresearch and development of Siemens/PGis performed on:

Siemens AG · Power Generation PG

BENSON test rig

Framatome ANP GmbH (A Framatome and Siemens company)Department FANP NT31Freyeslebenstraße 1D-91058 ErlangenGermany

Tel: +49 9131 18-93718Fax: +49 9131 18-92851

email: holger.schmidt@framatome-anp.de

BENSON license

Department PG W7Freyeslebenstraße 1D-91058 ErlangenGermany

Tel: +49 9131 18-6234Fax: +49 9131 18-6214

email: joachim.franke@erl11.siemens.de

2

heat transfer in boiler tubes• smooth• rifled

pressure loss in boiler tubes

thermoelastic design of water walls

feedwater treatment · erosion corrosion

vertical, inclined, horizontal

is licenserfor BENSON boilers

manufactures steamand gas turbines,generators,electrical equipmentand I&C

develops an improvedconcept withvertically tubedwater wallsfor BENSON boilers

designs andconstructs fossilfired power plants

The BENSON know-howallows for reliabledesign and ensurescustomer s benefitvia validated codesbased on extensiveinvestigations.

The BENSON know-howallows for reliabledesign and ensurescustomer s benefitvia validated codesbased on extensiveinvestigations.

3

Superheater

Evaporator

Economizer

Naturalcirculation (drum)

BENSON withsuperposed circulation

BENSON(once-through)

Principle

Operatingpressure

10 … 180 bar 20 … 180 bar 20 … 400 bar

Water walltubing

vertical vertical spiral or vertical

BENSON Boilersare the world-wide most often built once-through boilerswith approx. 1000 units:

steam pressure up to 310 bar

steam temperatures up to 650 °Csteam capacities up to 1232 kg/s (4435 t/h)

Evaporator systems for boilers by Siemens/PGEvaporator systems for boilers by Siemens/PG

4

Suitable for subcriticaland supercritical pressure

Highest efficiency of power plants

Wide scope in design (oversized combustionchamber, slag tap furnace)

Use of worldwide and difficult coals

Temperature

545 °C

Load

Main steam temperature independent of fueland degree of fouling . Low-stress start-up

Economical and low-stress operation Flexible operation mode

Rapid load changeswith sliding pressure operation

Time

4-6 %/min

Load

Enthalpy

Modes ofoperation

Criticalpoint

Pressure (load)

Improved concept with vertical tubed water wallsbased on R&D by Siemens/PG with additional advantages:

Simple design and easy maintenance of water wallssimilar to drum boilers

Low part-load of 20% with high steam temperatures

Simple start-up system without recirculation pump

Optimized flow chracteristic of water wall tubes (see next page)

Advantages of BENSON boilersAdvantages of BENSON boilers

Advantages of BENSON boilers with vertically tubed water wallsAdvantages of BENSON boilers with vertically tubed water walls

5

Once-through characteristicat high mass flux (approx. 1800 kg/m2s)

Pressure dropat constant mass flux

Nominalheated tube

Excessivelyheated tube

Hydrostatic

Friction

Natural circulation characteristicat low mass flux (approx. 1000 kg/m2s)

Pressure dropat constant mass flux

Nominalheated tube

Excessivelyheated tube

Hydrostatic

Hydrostatic

Friction

Systemof paralleltubes

Systemof paralleltubes

Optimized flow characteristic in case of excessive heat inputof water wall tubes due to low mass flux

Due to equal pressure dropin all parallel tubes:

Mass flow decreasesin the excessivelyheated tube

Mass flow increasesin the excessivelyheated tube

Due to equal pressure dropin all parallel tubes:

Milestones in the field of BENSON boilers

6

Milestones in the field of BENSON boilers

BENSON boilerslicence since– state: 2001

1924 Siemens buys the ”BENSON Patent” from Mark Benson

1926 Siemens manufactures to three BENSON boilers1929 (30 t/h to 125 t/h)

1933 Siemens introduces variable-pressure operation

1933 Siemens awards licencesto several boiler manufacturers

1949 The world´s first once-throughboiler with high steam conditions(175 bar/610 °C)

1954 The first BENSON boilerwith supercritical pressure(300 bar/605 °C)

1963 The world´s first spiral-tubed waterwalls in membrane design

1987 First hard-coal-fired boiler>900 MW with spiral-tubedwater walls

2000 About 1000 BENSON boilerswith >700.000 t/h sold in total

2000 First order of a BENSON boilerwith vertical tubed water wallsin low mass flux design

1937 Steinmüller

1939 Austrian Energy

1950 Deutsche Babcock

1951 Mitsui Babcock

1954 Babcock & Wilcox

1954 Burmeister & Wain

1954 Kawasaki

1960 Babcock-Hitachi

1995 Ansaldo

1996 Foster Wheeler

1999 Bharat HeavyElectricals Ltd.(BHEL)

BENSON Boiler activities by Siemens/PGBENSON boiler activities by Siemens/PG

7

New water wall/evaporator design• Vertical tubed water walls

with optimized rifled tubes• BENSON Boiler with superposed

circulation• Horizontal evaporator tubes

for advanced power plantswith fluidized bed combustionor coal gasification

Increase of availability• Reliable design based on extensive

knowledge of heat transferand flow stability

• Material preservation by thermal elasticcomponent design

• Prevention of pipe wall thinningand resulting failures

Reduction of operating cost• Low pressure loss and steady-state

flow condition in evaporator zonesand separators

• Optimized feedwater chemistry

Boiler concepts

Arrangement of heating surfaces

Thermal hydraulic design

Start-up systems

Control concepts

Water chemistry

Interaction of boiler and turbine

R&D

Computer programs

BENSON test rig and range of parameters investigated

8

BENSON test rig and range of parameters investigated

Reductionvalve

Technical data:System pressure 330 barTemperature 600 °CMass flow 28 kg/sHeat capacity 2000 kW

Tube Geometry

Number ofmeasurements > 100.000

Tubeorientation

vertical

inclined

horizontal

Heating

Test parameter

uniform one-side uniform one-side

Test matrix for heat tansferand pressure drop investigations

> 160.000

Spraycondenser

Main cooler

Pressurizer

Main heater

Preheater

Feedwatertank

Circulationpump

Tricklecooler

Piston pump

Test section

Dosing pump

Pressure 25 ≤ p ≤ 280 bar

Mass flux 100 ≤ m ≤ 2500 kg/m2s

Heat flux 0 ≤ q ≤ 950 kW/m2

Tube inner diameter 8 ≤ d ≤ 50 mm

Heat transfer and pressure drop in boiler tubesHeat transfer and pressure drop in boiler tubes

Steam

∆p

∆L

Heat transfer region

1.0

0.8

0.6

0.4

0.2

0

Convective heat transferto steam flow

Post -CHF region/Post-dryout region

Convective heat transferthrough water film

Saturated nucleate boiling

Subcooled boiling

Convective heat transfer to water flow

Pressureloss gradient

Temperature Water

Walltemperature

Fluidtemperature

Boilingcrisis

Steamquality

Schematic course of wall temperature and pressure loss in an uniformlyheated vertical smooth evaporator tube

9

Heat transfer in boiler tubes

10

Effect of gravity on heat transfer in inclinedand horizontal smooth tubes

15°

600

500

400

300

2000 0.2 0.4 0.6 0.8

Steam quality

Horizontal tube

Inner wall temperature (°C)

Fluid

600

500

400

300

2000.40 0.45 0.50 0.55 0.60

Inner wall temperature (°C)

Inclined tube

Pressure 100 barMass flux 500 kg/m2sHeat flux 300 kW/m2

Tube inner diameter 24.3 mm

Pressure 50 barMass flux 1000 kg/m2sHeat flux 400 kW/m2

Tube inner diameter 24.3 mm

1.0

Calculation withWATHUN

Heat transfer in boiler tubes

Steam quality

11

Wall temperature in smooth and rifled tubes

PressureMass fluxHeat flux

150 bar500 kg/m2s300 kW/m2

100 200 300 400 500 600

Inner wall temperature (°C)Rifled tube

0.6

0.8

1.0

Steam quality

0.4

Smoothtube

Rifledtube

Fluid

Improvement in heat transfer by rifled tubes

Heat transfer in boiler tubesHeat transfer in boiler tubes

Smooth tube

Heat transfer in boiler tubesHeat transfer in boiler tubes

400

375

350

325

3001600 1800 2000 2200 2400 2600 2800

Inner wall temperature (°C)

Fluid

Fluid

Fluid enthalpy (kJ/kg)

Calculation withWATHUN

Pressure 212 barMass flux 770 kg/m2s

Peak heat flux 310 kW/m2

Wall temperatures in vertical rifled tubes at different loads

High load

Low load

Pressure 100 barMass flux 250 kg/m2s

Peak heat flux 200 kW/m2

12

13

Optimized rifled tubes reduce wall temperaturesor allow mass flux reduction

Heat transfer in boiler tubesHeat transfer in boiler tubes

1800

Inner wall temperature (°C)

440

420

400

380

360

2000 2400

Fluid enthalpy (kJ/kg)

2200

Standard rifled tubeMass flux 1000 kg/m2s

Standard rifled tubeMass flux 1000 kg/m2s

Smooth tubeMass flux 1500 kg/m2s

Optimized rifled tubeMass flux 1000kg/m2s

Calculation withWATHUN

440

420

400

380

360

Smooth tubeMass flux 1000 kg/m2s

Optimized rifled tubeMass flux 770 kg/m2s

Pressure 212 barPeak heat flux 310 kW/m2

Pressure loss in smooth and rifled boiler tubesPressure loss in smooth and rifled boiler tubes

14

Water Steam

0 0.2 0.4 0.6 0.8 1

Steam quality

Wettedsurface

Smoothtube

Unwettedsurface

Rifledtube

Related pressure loss

∆p wet steam

∆p water

Smooth tube

Rifled tube

20

16

12

8

4

0

Location of boiling crisis

Pressure 100 bar

Mass flux 1000 kg/m2s

Heat flux 100 kW/m2

Tube innerdiameter ca. 13 mm

Calculation withDRUBEN

Rack plate

ϑ1

ϑ2

σ2

σ1

Thermoelastic design of water walls increases flexibility (1)

15

Thermoelastic design of water walls increases flexibility (1)

Measured values

Temperaturefield ϑ [°C]

Temperature and stress fields in a rack plateat a gradient of 10 K/min, quasi-steady-stateconditions

Stress field σ[N/mm2]

178

177 176,5

13,8

9,37

4,91

0,45

-4,01

181

182

184

186188

190192

191

194

1934,01

-8,47

4,01

12,9

8,44

8,47

183

16

WATHANInput data: pressure, temperature, mass flux,

steam quality, heat flux, geometry

WATHUN-calculation (heat transfer coefficients)

q.

q

max

Position

Firing

500 °C

380 °C

Stress analysis

FEM-calculationTemperature fieldThermal stressMechanical stress

Stress assessmentPrimary stress < Sm∑ Primary and secondary stress < 3 Sm

Fatigue analysis (for p/pk < 1)

FEM-calculationTemperature fieldThermal stress differences(Wetted and unwetted tube)

Service life assessmentThermal stress Permissibledifferences range of stress

60

50

40

30

20

10

0

100 300 400 500Heat flux [kW/m2] Temperature [°C]

0 400 500Stress [N/mm2]

Height [m]

TFTW

σef

σ1,T+P σ2,T+P

σax,Wσal

σax,T+P

Stress analysis with WATHANbased on R&D increases reliabilityof water walls

Thermoelastic design of water walls increases flexibility (2)Thermoelastic design of water walls increases flexibility (2)

Nomenclature

q Average heat flux

q

max Max. loc. heat flux

TF Fluid temperature

TW Wall temperature

σef Effective stress

σax,T+P Axial stress (T+P)

σ1,T+P Princ. stress1 (T+P)

σ2,T+P Princ. stress2 (T+P)

σax,W Axial stress (weight)

σal Allowable stress

.

.

Feedwater treatment . Erosion-corrosion (1)

17

Feedwater treatment . Erosion-corrosion (1)

Material (Cr-, Mo-, Cu-contents)

Geometry (pipe, bend, etc.)

Fluid velocity

Temperature

Steam quality

Feedwater chemistry (pH, O2)

Exposure time

Appearance Parameters of influence

Metal loss caused byerosion-corrosion(mass transfer)

Oxide layer (magnetite)protects againsterosion-corrosion

Wall adjacentturbulent layer

Flow core

Velocity profile

Steel

Fe OH+

Fe (OH)2

Fe3 O4

Mechanism

Feedwater treatment . Erosion-corrosion (2)Feedwater treatment . Erosion-corrosion (2)

18

pH = 7; O2 = < 5ppb pH = 9,5; O2 = < 5ppb

pH = 7; O2 = 500ppb

10

10 CrMo 9 10

T = 180 °Cv = 20 m/st = 200 h

St 37.25

2

1

5

2

0.1

5

2

0.01

5

2

0.001

15 Mo3

13 CrMo 4 4

15 NiCuMoNb 5

X10CrNiTi 18 9

St 37.2+5µm-Metco 33-coating

Ferritic steel

Austenitic steel

Wall thinning mm/a

Effect of material composition

19

Oxygenconcentration

(ppb)

Fluidvelocity

(m/s)

Watertemperature

(°C)

pH

0 20 40 0 100 200 6 8 10 0 200 400

MeasurementT = 120 °Cv = 35 m/spH ≤ 5 ppbt = 200 hCarbon steel

MeasurementT = 180 °CpH = 7O2 ≤ 5 ppbt = 200 hCarbon steel

Measurementv = 35 m/spH = 7O2 ≤ 5 ppbt = 200 hCarbon steel

MeasurementT = 180 °Cv = 39 m/sO2 ≤ 5 ppbt = 200-400hCarbon steel

10

5

2

1

5

2

0,1

5

2

0,01

5

2

0,001

Wall thinning mm/a

Effect of thermal hydraulic and water chemistry parameters

Feedwater treatment . Erosion-corrosion (3)Feedwater treatment . Erosion-corrosion (3)

Calculation withWATHEC

Subject to change without prior noticeSiemens Aktiengesellschaft

Printed by and copyright (2001):Siemens Power GenerationFreyeslebenstaße 1D-91058 ErlangenGermany

Research & development by Siemens/PGallows reliable design of BENSON boilersbased on computer programs as:

WATHUN

DRUBEN

STADE

DEFA/DEFOS

DYNASTAB

WATHAN

WATHEC/COMSY

Heat transfer

Pressure drop

Flow distributionin parallel tube systems

Design of boilers

Dynamic stability

Material strength

Erosion-corrosion