steam turbine seminar -17 open vacuum breaker about 15 minutes for hogging/vacuum pull no corrosion...

Steam Turbine Seminar -17Lund University

Lund University / LTH / Energy Sciences / TPE / Magnus Genrup / 2017-10-25

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condenser pressure have been replaced by 2/3 measuring devices (and trips)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


Trip logic – non exhaustive principle

Lube oil pres

≥2

≥2

≥2

≥2

Vibrations

≥2

≥2

≥2

≥2

≥2

N.N

.

≥1H

igh exhtem

p

≥1

≥1

2oo31oo2

≥1

≥1

≥1

High brg

temp

PLC

Bus

≥1

≥1

≥1

N.N

.

Speed <m

ax

Speed < max

Trip

blo

ck 2

oo3

Hard-wired

Speed <m

ax

Pcond < m

ax

Pcond <

max

Pcond < m

ax

Ch.1

Ch.2

Ch.3

≥1

≥1

≥1


Trip block – two out of three logic

Manual trip valve

Pressure switch

PI

ESV

Hydraulic supply unit

Channel A Channel B Channel C

) (


Trip block – test

Pressure switch

PI

ESV

Manual trip valve


Tripped channel

) (


Trip block – trip

Pressure switch

PI

ESV

Manual trip valve


Tripped channel Tripped channelNo pressure!

) (


The ”Duck-Curve”…

4.3 GW/h

California

Sweden


Flexibility

Star

t Steady state Active generation control

Spinning reserve off-peak turndown

SS

Shut

dow

n

Load

LF

Load

Cou

rtesy

of S

iem

ens


Start-up transient stress

Courtesy of John Gülen, “Gas Turbine Combined Cycle Fast Start: The Physics Behind the Concept”


Turbine pressures vs. flow (load)

CondSteamSteam

outCW,inCW,CWp,CW

hhmQ

TTcmQLMTDAUQ

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


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 pressureLinearExtraction #1 pressurePressure ratio

Condenser pressure vs. flow (load)

Relative flow [-]

Rel

ativ

e pr

essu

re [-

]

Sect

ion

pres

sure

ratio

[-]

Turbine load

CondSteamSteam

outCW,inCW,CWp,CW

hhmQ

TTcmQLMTDAUQ

SteamSteam mh

SteamCondCond mmh

CWp,CW c,m


The proof…


Grid codes


Grid stability

1 2⁄ · ·1 2⁄ · 2 · · · ⁄

The inertia constant:

The inertia constant is typically within the range of 5 and 10 seconds:

Nominal power = 500 MW5 s. 2500 MJ10 s. 5000 MJ

500048 ·

10.4 260

Energy required during a start @ 5000 MJ, as 48 MJ/kg natural gas:

This is equivalent of some 280000 cups of tea!


Grid stability

1 2 109876543

Grid demand (4500 MW)

10 units á 500 MW running at 90 % load – 4500 MW

∆· ·

0.0010.0020.0030.0040.0050.0060.00

0 20 40 60 80 100 120Freq

uenc

y

Time

Speed/frequency vs. time @tau=10 s.

@

∆2 · · ·


Grid stability

@

∆2 · · ·

∆ 100 · ·

· ·1

2 · ·


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…


Heating blankets


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


Background


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


Shaft glands

Courtesy to Siemens


Gland system – Increased pressureNo 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


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


Enhanced flexibility

HP

LPG

FWT/DEAE

Capacity by-pass

HP-FV by-pass0.7

m

m

FW

bypass

• HP-FWH bypass• Capacity bypass• Top-heater for

constant FW-temp


Rotor stress – temperature gradients

T

r

TCenter

TAverage

TSteam

TSurface

ΔT

y

i i

r

r

r

r2

i2y

2i

2

2r drrTdrrTrrrr

rμ1Eαrσ

y

i i

r

r

r

r

22

i2y

2i

2

2θ TrdrrTdrrTrrrr

rμ1Eαrσ

rim

r

0

r

022

rimr r

r13ΔTEαdrrT

r1drrT

r1Eαrσ

rim

rim

r

0

r

022

rimθ r

r213ΔTEαTdrrT

r1drrT

r1Eαrσ

rim

Temperature induced stresses (radial and hoop):

Simplified equations for a case without a bore:

α = 1.8∙105 °C-1

E = 6.9∙104 MPaΔT = 55 °Cσ@r=0 = 46 MPa

Example


Rotor stress – temperature gradients

Control mode ΔT first stage ΔT exhaustPartial 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

Enth

alpy

Entropy31

36.812.3


Fatigue – low or high?

Life cycles, [n]

Stre

ss a

mpl

itude

, [σ a

]

Low-cycle fatigue High-cycle fatigue

Fatigue limit

σσa

σa

Time

Stre

ss

Failure

No failure – no crack initiation

105…7

Wöhler- or σ,N curve

Base

d on

Tan

uma

& Ta

dash

i, “A

dvan

ces

in S

team

Tur

bine

s fo

r Mod

ern

Pow

er P

lant

s”


Casing wall temperature probe


Avancerad turbinregulator

T

r

TCenter

TAverage

TSteam

TSurface

ΔT


Aged deterioration – failures M

ater

ial

Perf

orm

ance

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

Base

d on

Tan

uma

& Ta

dash

i, “A

dvan

ces

in S

team

Tur

bine

s fo

r Mod

ern

Pow

er P

lant

s”


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

Base

d on

Tan

uma

& Ta

dash

i, “A

dvan

ces

in S

team

Tur

bine

s fo

r Mod

ern

Pow

er P

lant

s”


Turbine damage – erosion


Solid particle erosion (SPE)

Ken Cotton, ”Evaluating and Improving Steam Turbine Performance”, 2nd ed.

N.B. This is a very design specific problem!!!


Turbine damage – rubbing

steam turbine seminar -17 open vacuum breaker about 15 minutes for hogging/vacuum pull no corrosion...

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