Steam Turbine Seminar -17
Lund University
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 2
Something on hydraulics…
N.B. This is an old setup with 1 of 2 – the state-
of-the-art is 2 out of 3 trip redundancy (both the
protection system and the hydraulics)
• The safety system works like a three-way
valve
• The trip system will simply de-pressurize the
hydraulics system
• Most “direct” trips such as speed and
condenser pressure have been replaced by
2/3 measuring devices (and trips)
• The 2/3 philosophy makes it possible to
“test” the trip all the way to the hydraulics
• ESV movability test
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 3
Trip logic – non exhaustive principle
Lube oil pres
≥2
≥2
≥2
≥2
Vibrations
≥2
≥2
≥2
≥2
≥2
N.N.
≥1
High exh temp
≥1
≥1
2oo3
1oo2
≥1
≥1
≥1
High brg temp
PLC
Bus
≥1
≥1
≥1
N.N.
Speed < max
Speed < max
Trip block 2oo3
Hard-wired
Speed < max
P
cond
< max
P
cond
<max
P
cond
< max
Ch.1
Ch.2
Ch.3
≥1
≥1
≥1
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 4
Trip block – two out of three logic
Manual
trip valve
Pressure
switch
PI
ESV
Hydraulic
supply unit
Channel A Channel B Channel C
) (
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 5
Trip block – test
Pressure
switch
PI
ESV
Manual
trip valve
Hydraulic
supply unit
Tripped channel
) (
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 6
Trip block – trip
Pressure
switch
PI
ESV
Manual
trip valve
Hydraulic
supply unit
Tripped channel
Tripped channel
No pressure!
) (
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 7
The ”Duck-Curve”…
4.3 GW/h
California
Sweden
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 8
Flexibility
Start
Steady state
Active generation
control
Spinning reserve
off-peak
turndown
SS
Shutdown
Load
LF
Load
Courtesy of Siemens
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 9
Start-up transient stress
Courtesy of John Gülen, “Gas Turbine Combined Cycle Fast Start: The Physics Behind the Concept”
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 10
Turbine pressures vs. flow (load)


CondSteamSteam
outCW,inCW,CWp,CW
hhmQ
TTcmQ
LMTDAUQ
SteamSteam
mh
SteamCondCond
mmh
CWp,CW
c,m
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Normalisedpressure[‐]
Normalisedflow[‐]
Linear CV
Extr#5 Extr#4
Extr#3 Extr#2
Extr#1 Cond
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 11
0
2
4
6
8
10
12
14
16
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Condenserpressure
Linear
Extraction#1pressure
Pressureratio
Condenser pressure vs. flow (load)
Relative flow [-]
Relative pressure [-]
Section pressure ratio[-]
Turbine load


CondSteamSteam
outCW,inCW,CWp,CW
hhmQ
TTcmQ
LMTDAUQ
SteamSteam
mh
SteamCondCond
mmh
CWp,CW
c,m
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 12
The proof…
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 13
Grid codes
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 14
Grid stability

12
⁄
·
·

1 2
⁄
· 2··
·



⁄

The inertia constant:
The inertia constant is typically within the range of 5 and 10 seconds:
Nominal power = 500 MW
5 s. 2500 MJ
10 s. 5000 MJ
5000
48
·
1
0.4
260
Energy required during a start @ 5000 MJ, as 48 MJ/kg natural gas:
This is equivalent of some 280000 cups of tea!
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 15
Grid stability
1 2
10
9876543
Grid demand (4500 MW)
10 units á 500 MW running at 90 % load – 4500 MW


∆

·

·
0.00
10.00
20.00
30.00
40.00
50.00
60.00
0 20406080100120
Frequency
Time
Speed/frequency vs. time @tau=10 s.


@
∆
2·
·

·

Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 16
Grid stability


@
∆
2·
·

·



∆
100
·

·






·

·
1
2··
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 17
Increased flexibility – starting
• Stress controller
– State-of-the
• Blankets
– Since the 80s – mature if OEM involved
• Hot air
– High initial cost
– Very effective
• High-speed barring
– Risky…
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 18
Heating blankets
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 19
Hot-air ST warming
Hot air
• Used by Karlshamnsverket (KKAB) since 1980s
Large 340MW HP-IP-LP Alstom (BBC) utility turbines
• Flanges for blower/heater
• Open vacuum breaker
About 15 minutes for hogging/vacuum pull
No corrosion risk since RH<<60 percent
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 20
Background
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 21
High-speed barring
• Both ventilation and disk friction feed energy into the
trapped steam.
– Scales with speed cubed and density
– Normal barring speed is approx. 200 rpm
• Potential risk of uneven temperature
– More work with longer blades and stage diameter
– LSB spray cooling
– Pipe and valve from HP-extraction to condenser
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 22
Shaft glands
Courtesy to Siemens
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 23
Gland system – Increased pressure
No or low load
FAN
Low P. Low P.
Spray
Sep.
1.1...1.3 bar(a)
0.98 bar(a)
Controlling
Closed
• The mass flow of seal steam
into the turbine(s) follow a
Fanno line
• Steaming seals should be
avoided
• Steam into the HPT through
seal off-load pipe(s)
• Steam supply must be
available
• No hard-ware modifications
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 24
Increased flexibility – in operation
• Capacity bypass
– Loss one in use
• Extra arc
– Small loss when not used
• Top-heater shut-down
– Thrust force
• Condensate pump shut-down – sliding pressure mode
– Caveat! Drum- and hot well levels
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 25
Enhanced flexibility
HP
LP
G
FWT/DEAE
Capacity by-pass
HP-FV by-pass
• HP-FWH bypass
• Capacity bypass
• Top-heater for
constant FW-temp
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 26
Rotor stress – temperature gradients
T
r
T
Center
T
Average
T
Steam
T
Surface
ΔT



y
ii
r
r
r
r
2
i
2
y
2
i
2
2
r
drrTdrrT
rr
rr
rμ1
Eα
rσ



y
ii
r
r
r
r
2
2
i
2
y
2
i
2
2
θ
TrdrrTdrrT
rr
rr
rμ1
Eα
rσ
  

rim
r
0
r
0
22
rim
r
r
r
1
3
ΔTEα
drrT
r
1
drrT
r
1
Eαrσ
rim
  

rim
r
0
r
0
22
rim
θ
r
r
21
3
ΔTEα
TdrrT
r
1
drrT
r
1
Eαrσ
rim
Temperature induced stresses (radial and hoop):
Simplified equations for a case without a bore:
α = 1.8∙10
5
°C
-1
E = 6.9∙10
4
MPa
ΔT = 55 °C
σ
@r=0
= 46 MPa
Example
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 27
Rotor stress – temperature gradients
Control mode ΔT first stage ΔT exhaust
Partial arc 94°C 61°C
Throttle 46°C 28°C
Sliding 3°C 18°C
• The HPT-example shows a load change
from full to 1/3 load
• IPT swallowing capacity and re-heater
temperature controls the HPT back-
pressure
3°C
46°C
94°C
18°C
28°C
61°C
Enthalpy
Entropy
3
1
36.8
12.3
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 28
Fatigue – low or high?
Life cycles, [n]
Stress amplitude, [σ
a
]
Low-cycle fatigue High-cycle fatigue
Fatigue limit
σ
σ
a
σ
a
Time
Stress
Failure
No failure – no crack initiation
10
5…7
Wöhler- or σ,N curve
Based on Tanuma & Tadashi, “Advances in Steam Turbines for Modern Power Plants”
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 29
Casing wall temperature probe
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 30
Avancerad turbinregulator
T
r
T
Center
T
Average
T
Steam
T
Surface
ΔT
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 31
Aged deterioration – failures
MaterialPerformance
Creep
Embrittlement
Fatigue
Environment
assisted crack
Thermal
fatigue
Low-cycle
fatigue
Fretting
Dynamic SCC*
Static SCC*
Corrosion
fatigue
Crack
Crack
Crack
Crack
Crack
Crack
Crack
Brittle fracture
Softening
Creep
Wear/rubbing
Erosion/FAC
Scale deposition
Type of deterioration
Mode of deterioration
Damage or incidence
Loosening
Deformation
Efficiency decrease
Efficiency decrease
Efficiency decrease,
stick, rubbing
HP/IP shroud, blade groove, HP/IP casing,
main pipes, main valves
HP/IP rotor
HP/IP heat groove, bottom of blade root
groove
LP last blades groove of LP rotor, HP/IP
casings
HP/IP blade groove of rotor
Blade groove of LP rotor
Blade groove of LP rotor
Blade root and groove, shroud and profile
Casing bolts (high temperature)
HP/IP diaphragm nozzle plate (impulse),
HP/IP rotor and inner casings (leak)
Seals, bearings, valve shafts
Control stage nozzle and LP last stages
HP/IP nozzles and blades, main valves
Typical damaged portion
*Stress corrosion cracking
Based on Tanuma & Tadashi, “Advances in Steam Turbines for Modern Power Plants”
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 32
Environment assisted crack
Corrosive environment
Materials
Stress
Environment
•SCC
• Dynamic SCC
• Corrosion fatigue
• Static stress
• Repetitive stress
• Vibration stress
• Strength – high is more
suspicious for SCC
• Impurities etc.
• Temperature
• Wetness*
• Dissolved oxygen
• Impurities in steam
• Start-up and shutdown
*Wilson zone
Based on Tanuma & Tadashi, “Advances in Steam Turbines for Modern Power Plants”
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 33
Turbine damage – erosion
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 34
Solid particle erosion (SPE)
Ken Cotton, ”Evaluating and Improving Steam Turbine Performance”, 2
nd
ed.
N.B. This is a very design
specific problem!!!
Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25 Page 35
Turbine damage – rubbing