About Gas Turbines and how they can be monitored

1
About Gas Turbines and how they can be monitored

• The Gas turbine
• Compressor design
• Combustion design
• Common machine faults
• Instrumentation

2
Gas Turbine Fundamentals

• The gas turbine is a thermal machine, it
  coverts fuel energy into shaft work to drive a
  load e.g a generator.
• The gas turbine is a compact engine.
• The gas turbine is mechanically simple.- High
  reliability.
• The gas turbine cycle is complete within the
  flange to flange.
• Rapid start capability
• - Materials are sensitive to salt, chlorine and
  sulphor
• - Small power output gives high speed.

3
Flow Path in a Gas turbine
Conversions Station 0 - The atmosphere Station
1 - The compressor inlet Station 2 - The
compressor discharge Station 3 - The turbine
inlet Station 4 - The turbine discharge.
Flow Path
4
Efficiency of a Gas turbine
The efficiency of a gas turbine is improved by

• Inter-cooling of the compressor
• Pre-cooling before the compressor
• Exhaust heat recuperation by regenerators
• Re-heating the turbine (multistage burning).

5
Gas turbine Cycles
C
T
T
C
T
C
Simple open cycle with regenerator
Separated power turbine with regenerator
6
Gas turbine Cycles
C
T
T
C
Compound set HP drive
7
Types of Gas turbines
Single shaft, heavy duty gasturbine
8
Types of Gas turbines
Turbine driven
Compressor driven
9
Heavy Duty Gas turbines

• Wide power range 10 -100MW
• Not necessary combustion chambers all around the
  turbine cylinder.
• Can have one or two combustion chambers
• Small units (10-30MW) always roller bearing.
• Larger units always journal bearings.

10
Multi shaft Jet-derived Gas turbine
High Pressure
Load
Low Pressure
Power Turbine
11
Multi shaft Jet-derived Gas turbine
Aero-thermodynamical performance optimized
Generator
Constant speed
12
Multi shaft Jet-derived Gas turbine
Compressor
Independently Varied load speed
13
Jet-derived Gas turbines

• Light construction
• High speed
• No easy accesable roller bearings
• Several shafts at different speed

14
Axial and Centrifugal Compressors

• Two kind of compressors are used, centrifugal and
  axial flow.
• The Axial compressor is small in diameter and
  longer
• The centrifugal compressor is rugged
• The axial compressor has higher performance.

15
Combustor Design

• Combuster Design criteria
• Small.
• Temperature distribution uniform
• Combustion continuos and stable.

16
Gas turbine blade types
Impulse turbine
Reaction turbine
17
Gas turbine Failure Statistics
Main location of damage to turbines .
Munich reinsurance company
18
Gas turbine Failures

• 20 of the 42 rotating blade failures come from
  foreign bodies (i.e by combustion chamber parts)

• 30 of all cases were caused by thermal
  overloading
• 25 of all cases were caused by mechanical
  overloading
• 6 were caused by lack of lubricant

Munich reinsurance company
19
Gas turbine Failure Statistics
Distribution of 147 cases of damage versus
operating hours.
Munich reinsurance company
20
Gas turbine PFMs
Component Element Failure modes Loading
source Compressor Rotor Blades Fatigue,Erosion V
ibration Foreign Object Airborne
particles Rotor (disk) Fatigue,
Creep Centrifugal, Thermal Combustion Liner Fati
gue, Creep, Temperature Gradients Buckling
Casing Fatigue Pressure cycles Turbine Rotor
blades Creep, Fatigue Centrifugal,
vibration Corrosion, Erosion Exhaust
products, Thermal environments Rotor
(disk) Creep,rupture Centrifugal,
thermal Fatigue Stators Corrosion,erosion,
Thermal environments fatigue,
creep, pressure, buckling exhaust
products
21
Gas turbine Failures

• The life of gas-turbine blading and of combustion
  air or fuel-gas compressor blades, properly
  designed from the start, is determined namely by
  erosion-corrosions.
• In compressors the reason for erosion is normally
  dust from the blast-furnace gas and combustion's
  air.
• Increasing pollution has made corrosion problems
  in the combustion air compressors an increasing
  problem.
• Emergency power stations can have problems with
  sulfur compounds from contaminants in the fuel
  gas - due to out of service periods.
• Turbine has high temperature corrosion at the
  first stage(s).
• Corrosion and erosion is the main cause for blade
  cracks.

22
Gas turbine Failures
Particular responsible is the effect of alkalis
in conjunction with sulfur and vanadium. If over
600º C and heavy fuel oil is used measure must be
used for each stop . When blast-furnace gas is
used, the alkali-chloride can lower the melting
point of the surface on the blades to less than
operational temperature. The efficiency of the
turbine is highly invoked by deposits. The
turbine blades exhibit bladeprofile in the first
stage - followed by profile thickening at the
last stages.
23
Compressor Blade Erosion
The effect of compressor erosion is twofold. 1.
It causes blunting of leading edge. 2. It causes
thinning of the blade trailing edge.
The result is fatigue and degeneration of overall
performance. Modulations of air flow increased
24
Compressor Fouling
The cause of fouling is adhesive materials such
as Oil vapor, smoke, sea salt, industrial vapors.
The result is Less compressor efficiency Lower
compressor discharge pressure Reduced exhaust
temperature, Reduction in fuel efficiency. Higher
High Frq. broad band vibrations
EGT
DP/P
Vib
25
Tip Clang
The stall can be detected by a sudden change in
Low BP and diagnosed by autospectrum. The tip
clang raises the High BP dramatically as well.
26
Internal Cooling Blockage
5um finings
27
Blade Faults
In general

• Blade corrosion-erosion gives a poor efficiency.
• Many blade faults give a raise in the amplitude
  of the blade passing frequency and high BP.
• Most blade faults give a rise in envelope
  spectrum.

But the vibrations are highly with the Gas
Turbine Control!
28
Blade Corrosion

• Typical symptoms on blade corrosions due sulfur
  adhesive at the turbine end.
• Steady LProtor (N1) speeds
• Gas temperature (EGT) rise over some days but not
  more than 20-25C
• Decreasing Gas generator speed (N2) (1-2)
• Increasing fuel flow (EF)
• Front vibrations sudden increase,
• but no much
• Rear vibrations steady

All this could be normal operational variations,
but together they indicate a fault ! And the
performance goes down!
29
The Gas turbine
30
Performance Monitoring
The vibration pattern is varying highly with the
basic process parameters at station 0, 1, 2, 3, 4

Vibrations, in the best combination with
performance monitoring, can with a proper
instrumentation predict blade faults before it is
to late.
Vibrations, as the second best combined with
process parameters, can with a proper
instrumentation predict blade faults before it is
to late.
31
Instrumentation of Small Heavy Duty Gas turbines
Small heavy duty, go for

• Accelerometer near turbine inlet and/or intake
• Accelerometer on roll. bearings or integrated
  gears
• Phase reference on each rotor shaft
• EGT, Intake Temp, Fuel Flow, P2

32
Monitoring Small Heavy Duty Gas turbines
Small heavy duty, setup
Safety monitoring,running
BP tracking velocity RMS 1s avg. time 10Hz .. 10X
bp (or BP) acceleration RMS 10s 1KHz .. 20 kHz
Safety monitoring,run up, coast down
BP/P absolute velocity RMS 1s avg. time 10Hz ..
10 times max speed, bp (or BP) acceleration RMS
1s 1KHz .. 20 kHz
Predictive monitoring, running as, velocity
RMS. 10X, 30 avg. ass, acceleration RMS 30 avg.
center freq. b.p.f , freq.Span 10X cpb6
acceleration 0-20KHz ess, cep ..
33
Instrumentation of Large Heavy Duty Gas turbines
Larger heavy duty, go for

• Accelerometer Power turbine, intake
  combustion(s).
• Phase reference on each rotor shaft
• X,Y proximity probes on all bearings
• Bearing temperature
• EGT, Intake Temp, Fuel Flow, P2, P5

34
Monitoring Large Heavy Duty Gas Turbines
Larger duty, setups
Accelerometers
Safety monitoring,running
BP tracking velocity RMS 1s avg. time 10Hz .. 10X
bp (or BP) acceleration RMS 10s 1KHz .. 20 kHz
Safety monitoring,run up, coast down
BP/P absolute velocity RMS 1s avg. time 10Hz ..
10 times max speed, bp (or BP) acceleration RMS
1s 1KHz .. 20 kHz
Predictive monitoring, running as, velocity
RMS. 10X, 30 avg. as, acceleration RMS 30 avg.
center freq. b.p.f , freq.Span 10X cpb6
acceleration 0-20KHz es, cep ..
35
Monitoring Large Heavy Duty Gas Turbine
Larger duty, setups
Proximity probes
Safety monitoring,running
BP Peak-Peak 1s avg. time 10Hz .. 10shaft speed
and DC or Smax 2X and DC
Safety monitoring,run up, coast down
DC/P 1s avg. time 10Hz .. 10shaft speed BP/P
Peak-Peak 1s avg 10Hz - 10shaft speed or SMAX 2X
Predictive monitoring, running as peak-peak.
10X, 10 avg. Orbit 2Xkey phaser Smax 2X
36
Instrumentation of Jet Derived Gas turbines
Jet derived, go for

• Accelerometer near turbine inlet and/or intake
• Accelerometer on rol. el. bearings
• Phase reference on each rotor shaft
• EGT, Intake Temp, Fuel Flow, P2

37
Monitoring Jet Derived Gas turbine
Jet derived , setup
Safety monitoring,running
BP tracking velocity RMS 1s avg. time 10Hz .. 10X
bp (or BP) acceleration RMS 10s 1KHz .. 20 KHz
Safety monitoring,run up, coast down
BP/P absolute velocity RMS 1s avg. time 10Hz ..
10 times max speed, bp (or BP) acceleration RMS
10s 1KHz .. 20 KHz
Predictive monitoring, running as, velocity
RMS. 10X, 30 avg. as, acceleration RMS 30 avg.
center freq. b.p.f , freq.Span 10X cpb6
acceleration 0-20KHz es, cep ..
38
Example of Configurations
Example
Hispano-suiza THM
Acc
Acc
350C
TA
TA
39
Example of Configurations
Example
Solar Centaur
TA
Gear
40
Example of Configurations
Example
IHE/GE IM5000
Acc
350C
TA
TA
41
Example of Configurations
Example
ALSTROHM MS 50001 LA
Acc,T
Acc,T
TA
x,y
x,y
Ax1,Ax2
T1, T2
42
Example of Configurations
Example
NUOVO PIGNONE (GE)
Acc
TA
TA
43
An example of a Gas turbine