ST Workshop Norrköping 2019 - Energiforsk€¦ · Ken Cotton, ”Evaluating and Improving Steam Turbine Performance”, 2nd ed. Lund University / Energy Sciences / Magnus Genrup

Lund University / Energy Sciences / Magnus Genrup / 2019-02-19 Page 1

MAGNUS GENRUP, ENERGY SCIENCES

Ångturbinseminariet 2019


Sedan sist…

• ASME IGTI

• PowerGen Int’l -18

• Ken Cotton Seminar

• Facklitteratur och fackpress


What is new?

• Combined cycle performance will (eventually) call for 650°C turbines- Maximum today is 605…650°C- Expensive HRSG and piping- Nu such CFB with biomass…

• Less than 30 minutes hot start-up time for the entire GTCC- 1400 MW in 28 minutes

• Maybe 700°C power plants – or?- 50 percent barrier still not breeched

• Flexibility

• AI (loads of IoT, ML,…)

• General Electric acquired Alstom -15

• Expected aerodynamic development - Retrofit capability

• ORC et al. is gaining momentum- Same old turbine?


Organic Rankine cycle – ORC

3 4

5

962

4 5

88

9

12

6

3

Alternator

Regenerator

Condenser

Sink

Pump

Evaporator

Heat source

Tem

pera

ture


Germany week 18 -16


German wind power – VGB

Courtesy of VGB, ”ELECTRICITY GENERATION 2017|2018 – Facts and Figures


German and European wind power – VGB

Courtesy of VGB, ”ELECTRICITY GENERATION 2018|2019 – Facts and Figures


Germany December -17


Flexibility steam turbines

VOC Improve Operability/Expand

operation range

ImprovementLoad following Capability

Grid Frequency Stabilization

Contents A Shorten startup durationB Maximum load operationC Minimum load operation

D Improve load change rateE improve load frequency control

F Grid Stabilizationcontrol

TechnicalRequirement

for Steam Turbine /

Generator

A Differential Expansion/Thermal Stress prediction and Optimization

B Over load valve, Heater Cutting Operation

C BFPT EHC, Auto changeover of main pump

D/E Stress prediction and optimization

• Overload valve • Sliding pressure control• Condensate stop operation• Heat cutting operation

F Fault Ride Through

A. Shorten Startup Duration

B. Max. Load operation

C. Min. Load Operation

E. Improve Load Frequency Control

D. Improve Load Change Rate F. Grid

Stabilization Control

Load

Time

• UK grid code requires constant output down to 49.5 Hz Stay on-line (i.e. no trip!) to 47 Hz (!!!)

with pro rata power output Brown-out capacity (0 V for 0.14 s) Rotor- and blading dynamics?

• Future Swedish requirements?• Operation without external grid?

Base

d on

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uma

& Ta

dash

i, “A

dvan

ces

in S

team

Tur

bine

s fo

r Mod

ern

Pow

er P

lant

s”


CSP – tower type

Figu

re c

ourte

sy to

Als

tom

Cold tank

Hot tank

Foto

by

Mon

ika

Tope

l, KT

H


CSP – tower type with direct steam generation

Figu

re c

ourte

sy to

Als

tom


• Turbine casing heating Used for CSP Lower-casing heating for long units

• Increased seal steam temperature Tricky

• Increased seal steam pressure Easy…

• Hot-air heating Effective but costly KKAB and Mälarenergi (+ new GE patent)

• Ventilation work• Stress controller

Start-up flexibility

2lenght expansion coefficient temperature difference16 casing diameter 2

h

Hot air


Fatigue

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


Turbine stress controller

Computer model for rotor temperature distribution f(T1,time)

ΔT=f(T1)

Evaluate real σ stress from σ=f(ΔT) and average rotor temp (Tavg)

Evaluate allowed stress and controllimits σLim=f(T1,Tavg) @design lifing

Evaluate relative stress σ/σlim

Loading and un-loading margins for turbine control

Turbine governor (speed and loading)

σ Tavg

σlim

T1

T1

Tavg

ΔT

Upprullningsregulator

Panntrycksbegränsare

Steg-/gradientbegränsare

Maxeffekt - generator

Maxeffekt - delturbin

Slagbegränsare

Frekvens/effektregulator

MIN

Väl

jare

MAXVK-2 Tryck

Minlast

Adm Tryck MIN

Ventilläges-regulator


Chemistry

• Typical issue when starting… However anyway always an issue…

• Must be within limits for the turbine!• Corrosion and deposits

Lower swallowing capacity and efficiency Vibration problems

• Always follow the turbine OEM recommendation• Some deposits requires rotor removal• Establish clear routines for N, AL1, AL2 and AL3

(cf. VGB R 450 Le) AL3 is shutdown within one hour!


Environment assisted crack

Materials

Stress

Environment

• SCC• Dynamic SCC• Corrosion fatigue

• Static stress• Repetitive stress• Vibration stress

• Strength – high is more suspicious for SCC

• Impurities etc.

Corrosive environment

• Temperature• Wetness*• Dissolved oxygen• Impurities in steam• Start-up and shutdown

*Wilson zone

Base

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& Ta

dash

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in S

team

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s”


Operational flexibility

• Swallowing capacity by-pass• Extra “arc” for turbines with c-stage

Always an efficiency penalty

• Top-heater(s) shut-down or by-pass Thrust forces may be an issue

• Condensate pump temporary shut-down Hotwell- and DEAE sizing?

• Extra top-heater for low-load operation Typically in concert with capacity by-pass

• Load changes in throttling mode

• Gas turbine in the preheating train


Operational flexibility – condensing tail

IP-DH LP

V1 V2

V3V1 V2 V3

Hea

t flu

x 0…

100%

Control 0…100%T

Q

1p

dTm cdQ

Min. flow• De-coupling power from heat load

Värtan, Västerås and Malmö Run overnight in heat mode

• Ultimate flexibility – fast!• Suitable sink necessary• Fourth-generation DH?• Unfortunately little possibility for retrofit• LPT ventilation protection

DHC1

DHC2

DHC2 DHC1


Extension to fourth generation DH

• 45°C DH feed temperature with DHC2 and DHC1• DHC3 and DHC2 for ”higher” DH feed

temperatures – potential risk for LP ventilation at hot return temperatures

• SSS-clutch between IPT and LPT

SSSIP-DH LP

V1 V2

V3

Min. flow

BFV

ORCSOLAR

City45…100 °CHeat Load

Local renewablesDHC3 DHC2 DHC1

Min Δp

Was

te h

eat

Heat


Boiler flexibility – HRSGs

B&W NEM

,nom

r pt

Alstom


NEM Drum Plus™


NEM Drum Plus™


Turbine technology


Refreshing the turbine technology – reaction vs. impulse

Large shaft trust

Impulse/Low-reaction*• High stage loading – low(er) stage count• Low axial trust on the rotor• High-turning robust blades• Low radius for diaphragms seals• Reduced tip leakage flow

Reaction• Low stage loading – high(er) stage

count• Higher (?) stage efficiency• High axial trust – balance piston

often required• Symmetrical vanes and blades• High radius for vane seals• Large rotor Δp

Balance hole

Some shaft trust

Low seal radius

Pres

sure

gra

dien

t

Pres

sure

gra

dien

t

Too low acceleration?

*Most impulse design retain a minimum level of rotor hub acceleration (i.e. a certain level of hub-reaction)

Very lossy!!!

032

2

2 1 tan

cos2 2 1s

hu

uh

Loading equations:

~2%


Skoda steam turbine technology – low reaction

Control stageHP stages

Balance holes

Inner casing

Riveted shrouds

Honeycomb seals

• Pin-type blade attachment C-stage• Low-radii HP-section for tall blades

Reduce need for two-casings design• Balance holes

Lower shaft thrust• Riveted shrouds• Honeycomb shroud seals

De-swirling vanes for reduced mixing loss• Traditional casing flanges


Speed level – geared vs. direct drive

U ω r 1 12 2

1 1 1 1

60sin sin sinm m m

V u c V u cm vld c d u d n

21 UU

2

1

@ 90

cos2 1is

uc

High

Low

l

dm

dm

mArea d l


Skoda MTD40

Courtesy of Skoda


SKODA MTD30


Industrial low-reaction HP-turbineVAX II or SST-700

Courtesy to Siemens

• Geared design• No horizontal flange (barrel mount)• 170…230 m/s blade speed*

Thrust bearing

Radial bearing

Radial bearing

Shaft seal

Shaft seal

Extraction

Extraction

*48…87 kJ/kg per stage @ U/Cs = 0.55

0.9* 7.2 Reksc


Industrial LP-turbineVAX II or SST-700

Courtesy to Siemens

• Horizontal flange• 210…300 m/s blade speed*

*73…148 kJ/kg per stage @ U/Cs = 0.55


Industrial IP-turbineSST-900

Courtesy to Siemens

L-1 Temperature probe

Extractions


Turbine blades

• Advanced three-dimensional blading Short vs. tall blades C-shaping

• Both CFD and testing is required• Bang for the buck?

Other losses such as leakage etc. are often more important

Siemens

Skoda


Advanced seals


Stage flow model

Seal

Seal

Hole21

01

mh

31

02,gap

mh

2 3

Gap C.V.

1 ,3 1

01 ,3 1

gap i

gap i

m m

h h

TE 22

0 X

mh

Stage C.V.

,3

,3

gap i

gap i

m

h

2m 3m

p2 p3

23

0 X

mh

21 22 23

1n nX X

X

E m m mEp p Ep


Partial arc admission

TS #1

Arc #1

TS #2

ESV

CV1

CV2

CV3

CV4

Rot

or #

1

Control stage

Arc #4

Arc #3

Arc #2


Partial arc admission – stage loading4 arcs – design 2 arcs ~ 50 percent flow

Arc #1

TS #2

ESV

CV1

CV2

CV3

CV4

Rot

or #

1 p2

p11

p12

p13

p14

Arc #2

Arc #3

Arc #4

TS #1

2 2

, -i j

T i ji i

p pm C

p v

M1=0.65M1=1.16

Ψ=3.4Ψ=1.5

ClosedVWO

PRTS=1.36PRTS=2.38

Δη≈12 %-units

Higher aero-loading at part load!

M1,rel=0.30 M1,rel=0.78

2188 kW 2828 kW


Hybrid control mode

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


Monitoring


Monitoring plan

• Gradual or abrupt?

• Efficiency- Only dry steam

• Swallowing capacity

• Leakage flows- Steam traps etc.

• Heat exchangers

• Vibrations- Valves

• Machine learning (ML)


Typical turbine damage mechanisms'

StilleståndskorrosionDeposits Stand-still corrosion Corrosion fatigue

Stress corrosion Pitting

In-adequate conservation


Typical turbine failure modesM

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

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& Ta

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s”


Swallowing capacity

ii

2j

2i

jiT,2

j

ii

ijiT,ji vp

ppC

pp

11vpCm

pi

pj

CT,i-j

vi

i

ii

ijiT,ji

TpKm

pzRTv

vpCm

The Stodola cone rule can be written as:

If pi>>pj then the simpler form appears:

Logarithmic differentiation yields1):

TΔT

21

pΔp

mmΔ

1) N.B. Only if superheated – i.e. an ideal gas!!!

1)

1)


The summation rule of turbine constants

TS #1

p1

TS #2 TS #3 TS #n

p2 p3 pn pn+1

11

2

21,

22

21 vp

CmppT

22

2

32,

23

22 vp

CmppT

33

2

43,

24

23 vp

CmppT

nn

nnTnn vp

Cmpp

2

1,

21

2

2

11,

112

12

1,

22

1,2

43,

332

32,

222

21,

112

1

21

221

21 ...

nT

n

i iiT

ii

nnT

nn

TTT

n

iiin

Cvpm

Cvpm

Cvp

Cvp

Cvp

Cvpmpppp

n

i iiT

ii

nT Cvp

Cvp

12

1,2

11,

11

11

2

11,

21

21 vp

CmppnT

n

n

i iiT

iiiExtr

nT Cvp

mm

Cvp

12

1,

2,

211,

11 1


The Cotton method

Condition Flow pc-stage pHRH pX-O ηHP ηIP

Increase A HPT, c-stageIncrease A IPT, stg #1Decrease A HPT, c-stageDecrease A IPT, stg #1Decrease A HPT, stg#2Increase A HPT, stg#2Decrease A LPT

pc-stage

pHRHpX-O


The STAL-LAVAL K0 method

1el0 x

i adm

PKp T

0 1 0 1 2 0

1

01

1 1

... 1

I II III

mel ext adm m

jj

h h hP m

h

The power output can be written as:

~ ~ xadm i im m p

The relation between flow and pressure may be written as:

The ratio between power and stage pressure can hence be thought of as a gauge of the efficiency and capacity.

Ref: STAL-LAVAL Service Information, Preventive Checks on Smaller Range of Condensing Turbo-Alternators, STAL-Laval, 1967


Steam traps

ThermodynamicMechanical

Thermostatic

Simple to monitor by simple temperature measurements!


Repair technology


Balance hole cracking – weld repairing

• Two discs with balance hole cracks• Weld repair – disk build-up!

Blade attachments?

Courtesy of TG Advisers


Blade lift

Suction side

Pressure side

Suction side

Pressure side

+

+

+

-

-

Compressor Turbine

Stagnation point, p1=p0,1

Stagnation point, p1=p0,1plocal-p1

L

D

L

Dplocal-p1


Turbine profiling

*Thin boundary layers

Maexit

MaSS,max (<1.2 if possible)

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0Axial distance (x/b)

Mac

h #

MaPS,min

Mainlet

Smooth accelerations*

N.B. Schematic

Throat

Avoid LE over-speed(s) Marchal quality factor:

<0.6∙Mss,max

𝐷𝑀𝑎 , 𝑀𝑎

𝑀𝑎 ,0.20 … 0.25 𝐷

𝑀𝑎 𝑀𝑎 ,𝑀𝑎 0.45

𝑅𝑎𝑡𝑒 𝑝𝑎𝑟𝑎𝑚𝑒𝑡𝑒𝑟𝐷

∆𝑙 𝑙⁄ 0.6

𝑄 1𝑥

𝑠𝑏𝑠

∆𝑝1 2⁄ 𝜌𝑐


Performance test


Guarantee test

LPG

FWT/DEAE

Mixing heater

Gea

r

Gea

r

HPc-stage

• Contractual agreement stipulates the test code DIN 1943 IEC ASME

• Bring in a consultant with real experience!!!

• No testing with operational instruments!!!

• Calibrated devices• Follow the check list• Operation as intended?• Remember the prosciutto and

the scale!

Heat balance


Uncertainty – an introduction

Prob

abilit

y de

nsity Standard deviation confidence

level = 68.269%

2σ confidence level = 95%

True

val

ue

Dur

atio

n

Mea

sure

d av

erag

e

+σ-σ+2σ-2σ

1

1 n

ii

x xn

2

1

1

n

ii

x

x xs

n

• With an infinite number of readings the estimatedstandard deviation will be approach the true standarddeviation S – with a confidence level of 68.269%

• For a finite value of n (i.e. n ≤ ∞), the Student t-factor isintroduced as:

• This is normally referred to as the “two sigma” valuebecause it is 1.960 times the standard deviation at n ≤ ∞

• The 2σ-value quantifies the component of testuncertainty which is due to precision (random) errors

• Bias errors are mitigated by calibration!

ixx

st s t

n

x

x


Documents

ST Workshop Norrköping 2019 - Energiforsk€¦ · Ken Cotton, ”Evaluating and Improving Steam Turbine Performance”, 2nd ed. Lund University / Energy Sciences / Magnus Genrup