+ economic +
+ flexible +
+ innovative +
BENSON Boiler
Research & Development at the BENSON Test Rig
by Siemens AG • Power Generation (PG)
designs and
constructs fossil
fired power plants
manufactures steam
and gas turbines,
generators,
electrical equipment
and I&C
This booklet should remind you of the exhibition
in the monitoring room of the BENSON test rig
in Erlangen, Germany, where the fundamental
research and development of Siemens/PG
is performed on:
heat transfer in boiler tubes
• smooth
vertical, inclined, horizontal
• rifled
pressure loss in boiler tubes
thermoelastic design of water walls
feedwater treatment · erosion corrosion
is licenser
for BENSON boilers
develops an improved
concept with
vertically tubed
water walls
for BENSON boilers
The BENSON know-how
allows for reliable
design and ensures
customer´s benefit
via validated codes
based on extensive
investigations.
Siemens AG · Power Generation PG
BENSON license
BENSON test rig
Department PG W7
Freyeslebenstraße 1
D-91058 Erlangen
Germany
Framatome ANP GmbH (A Framatome and Siemens company)
Department FANP NT31
Freyeslebenstraße 1
D-91058 Erlangen
Germany
Tel:
Fax:
+49 9131 18-6234
+49 9131 18-6214
email: joachim.franke@erl11.siemens.de
Tel:
Fax:
+49 9131 18-93718
+49 9131 18-92851
email: holger.schmidt@framatome-anp.de
2
Evaporator systems for boilers by Siemens/PG
Principle
Natural
circulation (drum)
BENSON with
superposed circulation
BENSON
(once-through)
Superheater
Evaporator
Economizer
Operating
pressure
10 … 180 bar
20 … 180 bar
20 … 400 bar
Water wall
tubing
vertical
vertical
spiral or vertical
BENSON Boilers
are the world-wide most often built once-through boilers
with approx. 1000 units:
steam pressure up to 310 bar
steam temperatures up to 650 °C
steam capacities up to 1232 kg/s (4435 t/h)
3
Advantages of BENSON boilers
Highest efficiency of power plants
Use of worldwide and difficult coals
Enthalpy
Critical
point
Modes of
operation
Pressure (load)
Suitable for subcritical
and supercritical pressure
Wide scope in design (oversized combustion
chamber, slag tap furnace)
Economical and low-stress operation
Flexible operation mode
Temperature
Load
4-6 %/min
545 °C
Load
Time
Main steam temperature independent of fuel
and degree of fouling . Low-stress start-up
Rapid load changes
with sliding pressure operation
Improved concept with vertical tubed water walls
based on R&D by Siemens/PG with additional advantages:
Simple design and easy maintenance of water walls
similar 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)
4
Advantages of BENSON boilers with vertically tubed water walls
Once-through characteristic
at high mass flux (approx. 1800 kg/m2s)
Pressure drop
at constant mass flux
Friction
Due to equal pressure drop
in all parallel tubes:
System
of parallel
tubes
Hydrostatic
Hydrostatic
Nominal
heated tube
Mass flow decreases
in the excessively
heated tube
Excessively
heated tube
Optimized flow characteristic in case of excessive heat input
of water wall tubes due to low mass flux
Natural circulation characteristic
at low mass flux (approx. 1000 kg/m2s)
Pressure drop
at constant mass flux
Friction
Due to equal pressure drop
in all parallel tubes:
System
of parallel
tubes
Hydrostatic
Nominal
heated tube
Mass flow increases
in the excessively
heated tube
Excessively
heated tube
5
Milestones in the field of BENSON boilers
1924 Siemens buys the ”BENSON
Patent” from Mark Benson
1926 Siemens manufactures
to three BENSON boilers
1929 (30 t/h to 125 t/h)
BENSON boilers
licence since
– state: 2001
1937 Steinmüller
1933 Siemens introduces variablepressure operation
1939 Austrian Energy
1933 Siemens awards licences
to several boiler manufacturers
1950 Deutsche Babcock
1949 The world´s first once-through
boiler with high steam conditions
(175 bar/610 °C)
1954 The first BENSON boiler
with supercritical pressure
(300 bar/605 °C)
1963 The world´s first spiral-tubed water
walls in membrane design
1951 Mitsui Babcock
1954 Babcock & Wilcox
1954 Burmeister & Wain
1954 Kawasaki
1960 Babcock-Hitachi
1987 First hard-coal-fired boiler
>900 MW with spiral-tubed
water walls
1995 Ansaldo
2000 About 1000 BENSON boilers
with >700.000 t/h sold in total
1999 Bharat Heavy
Electricals Ltd.
(BHEL)
2000 First order of a BENSON boiler
with vertical tubed water walls
in low mass flux design
6
1996 Foster Wheeler
BENSON boiler
Boiler activities by Siemens/PG
Boiler concepts
Arrangement of heating surfaces
Thermal hydraulic design
New water wall/evaporator design
• Vertical tubed water walls
with optimized rifled tubes
• BENSON Boiler with superposed
circulation
• Horizontal evaporator tubes
for advanced power plants
with fluidized bed combustion
or coal gasification
Start-up systems
Increase of availability
Control concepts
Water chemistry
Interaction of boiler and turbine
R&D
Computer programs
• Reliable design based on extensive
knowledge of heat transfer
and flow stability
• Material preservation by thermal elastic
component design
• Prevention of pipe wall thinning
and resulting failures
Reduction of operating cost
• Low pressure loss and steady-state
flow condition in evaporator zones
and separators
• Optimized feedwater chemistry
7
BENSON test rig and range of parameters investigated
Test section
Spray
condenser
Pressurizer
Main heater
Preheater
Dosing pump
Technical data:
System pressure
Temperature
Mass flow
Heat capacity
Trickle
cooler
Circulation
pump
Feedwater
tank
Piston pump
330
600
28
2000
bar
°C
kg/s
kW
Main cooler
Reduction
valve
Tube Geometry
Number of
measurements
> 100.000
> 160.000
Heating
uniform
one-side
uniform
one-side
vertical
Tube
orientation
inclined
horizontal
Test parameter
Pressure
Mass flux
Test matrix for heat tansfer
and pressure drop investigations
8
25 ≤ p ≤ 280 bar
100 ≤ m ≤ 2500 kg/m2 s
Heat flux
0 ≤ q ≤ 950 kW/m2
Tube inner diameter
8≤d ≤
50 mm
Heat transfer and pressure drop in boiler tubes
Schematic course of wall temperature and pressure loss in an uniformly
heated vertical smooth evaporator tube
Heat transfer region
Steam
Convective heat transfer
to steam flow
Steam
quality
1.0
Post -CHF region/
Post-dryout region
Boiling
crisis
0.8
∆p
∆L
0.6
Wall
temperature
Convective heat transfer
through water film
Fluid
temperature
0.4
0.2
Saturated nucleate boiling
0
Subcooled boiling
Convective heat transfer to water flow
Pressure
loss gradient
Temperature
Water
9
Heat transfer in boiler tubes
Effect of gravity on heat transfer in inclined
and horizontal smooth tubes
Inner wall temperature (°C)
600
Inclined tube
Calculation with
WATHUN
500
Pressure
50
Mass flux
1000
Heat flux
400
Tube inner diameter
24.3
400
bar
kg/m2s
kW/m2
mm
300
200
0.40
0.45
0.50
Steam quality
0.55
0.60
15°
Inner wall temperature (°C)
600
Horizontal tube
Pressure
100 bar
Mass flux
500 kg/m2s
Heat flux
300 kW/m2
Tube inner diameter 24.3 mm
500
400
300
Fluid
200
0
0.2
0.4
0.6
Steam quality
10
0.8
1.0
Heat transfer in boiler tubes
Improvement in heat transfer by rifled tubes
Wall temperature in smooth and rifled tubes
Pressure
Mass flux
Heat flux
150 bar
500 kg/m2s
300 kW/m2
Steam quality
Fluid
1.0
Rifled
tube
0.8
Smooth
tube
0.6
0.4
10 0
Rifled tube
20 0
30 0
40 0
50 0
60 0
Inner wall temperature (°C)
Smooth tube
11
Heat transfer in boiler tubes
Wall temperatures in vertical rifled tubes at different loads
Inner wall temperature (°C)
High load
Pressure
Mass flux
Peak heat flux
212 bar
770 kg/m2s
310 kW/m2
400
Calculation with
WATHUN
375
Fluid
350
Pressure
Mass flux
Peak heat flux
Low load
325
Fluid
300
1600
1800
2000
2200
2400
2600
2800
Fluid enthalpy (kJ/kg)
12
100 bar
250 kg/m2s
200 kW/m2
Heat transfer in boiler tubes
Optimized rifled tubes reduce wall temperatures
or allow mass flux reduction
Inner wall temperature (°C)
Smooth tube
Mass flux 1000 kg/m2s
440
Standard rifled tube
Mass flux 1000 kg/m2s
420
400
Optimized rifled tube
Mass flux 1000kg/m2s
380
360
Calculation with
Pressure
WATHUN
212 bar
Peak heat flux 310 kW/m2
440
Standard rifled tube
Mass flux 1000 kg/m2s
Optimized rifled tube
Mass flux 770 kg/m2s
420
400
380
Smooth tube
Mass flux 1500 kg/m2s
360
1800
2000
2200
2400
Fluid enthalpy (kJ/kg)
13
Pressure loss in smooth and rifled boiler tubes
Pressure
Mass flux
Heat flux
Tube inner
diameter
Related pressure loss
100 bar
1000 kg/m2s
100 kW/m2
ca.13 mm
Location of boiling crisis
20
∆p wet steam
∆p water
16
12
Calculation with
DRUBEN
Rifled
tube
8
4
Smooth
tube
Wetted
surface
Unwetted
surface
0
0
0.2
0.4
0.6
0.8
1
Steam quality
Smooth tube
Water
14
Rifled tube
Steam
Thermoelastic design of water walls increases flexibility (1)
Rack plate
ϑ1
σ1
177
ϑ2
σ2
176,5
13,8
178
9,37
181
183
4,91
182
0,45
184
-4,01
186
188
190
192
8,47
8,44
12,9
191
194
4,01
-8,47
193
4,01
Temperature
field ϑ [°C]
Stress field σ
[N/mm2]
Measured values
Temperature and stress fields in a rack plate
at a gradient of 10 K/min, quasi-steady-state
conditions
15
Thermoelastic design of water walls increases flexibility (2)
Firing
500 °C
Stress analysis with WATHAN
based on R&D increases reliability
of water walls
380 °C
WATHAN
Input data: pressure, temperature, mass flux,
steam quality, heat flux, geometry
WATHUN-calculation (heat transfer coefficients)
Stress analysis
Fatigue analysis
(for p/pk < 1)
FEM-calculation
Temperature field
Thermal stress
Mechanical stress
FEM-calculation
Temperature field
Thermal stress differences
(Wetted and unwetted tube)
Stress assessment
Primary stress < Sm
∑ Primary and secondary stress < 3 Sm
Service life assessment
Thermal stress
Permissible
differences
range of stress
Height [m]
σax,T+P
60
qmax
50
.
q
Position
σax,W
TF
TW
σal
σef
Nomenclature
.
q
Average heat flux
.
qmax
Max. loc. heat flux
Fluid temperature
TF
TW
Wall temperature
40
30
σef
σax,T+P
σ1,T+P
σ2,T+P
σax,W
σal
20
10
σ2,T+P
σ1,T+P
0
100
300
Heat flux [kW/m2]
16
400
500
Temperature [°C]
0
400
500
Stress [N/mm2]
Effective stress
Axial stress (T+P)
Princ. stress1 (T+P)
Princ. stress2 (T+P)
Axial stress (weight)
Allowable stress
Feedwater treatment . Erosion-corrosion (1)
Appearance
Parameters of influence
Material (Cr-, Mo-, Cu-contents)
Geometry (pipe, bend, etc.)
Fluid velocity
Temperature
Steam quality
Feedwater chemistry (pH, O2)
Exposure time
Mechanism
Fe3 O4
Fe OH+
Oxide layer (magnetite)
protects against
erosion-corrosion
Metal loss caused by
erosion-corrosion
(mass transfer)
Fe (OH)2
Velocity profile
Steel
Wall adjacent
turbulent layer
Flow core
17
Feedwater treatment . Erosion-corrosion (2)
Effect of material composition
pH = 9,5; O2 = < 5ppb
pH = 7; O2 = < 5 ppb
pH = 7; O2 = 500ppb
Wall thinning mm/a
10
St 37.2
5
15 Mo3
2
1
Ferritic steel
15 NiCuMoNb 5
5
13 CrMo 4 4
2
10 CrMo 9 10
0.1
X10CrNiTi 18 9
Austenitic steel
5
St 37.2+5µm-Metco 33-coating
2
0.01
5
2
0.001
18
T = 180
v = 20
t = 200
°C
m/s
h
Feedwater treatment . Erosion-corrosion (3)
Effect of thermal hydraulic and water chemistry parameters
Measurement
v = 35 m/s
pH = 7
O2 ≤ 5 ppb
t = 200 h
Carbon steel
Measurement
T = 180 °C
pH = 7
O2 ≤ 5 ppb
t = 200 h
Carbon steel
Measurement
T = 120 °C
v = 35 m/s
pH ≤ 5 ppb
t = 200 h
Carbon steel
Measurement
T = 180 °C
v = 39 m/s
O2 ≤ 5 ppb
t = 200-400h
Carbon steel
Wall thinning mm/a
10
5
2
1
5
2
0,1
5
2
0,01
5
Calculation with
WATHEC
2
0,001
0
20
40
Fluid
velocity
(m/s)
0
100
200
Water
temperature
(°C)
6
8
10
pH
0
200
400
Oxygen
concentration
(ppb)
19
Research & development by Siemens/PG
allows reliable design of BENSON boilers
based on computer programs as:
WATHUN
Heat transfer
DRUBEN
Pressure drop
STADE
Flow distribution
in parallel tube systems
DEFA/DEFOS
Design of boilers
DYNASTAB
Dynamic stability
WATHAN
Material strength
WATHEC/COMSY
Erosion-corrosion
Printed by and copyright (2001):
Siemens Power Generation
Freyeslebenstaße 1
D-91058 Erlangen
Germany
Siemens Aktiengesellschaft
Subject to change without prior notice