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On-line diagnostics of gas turbines
Blade temperature measurements with TurboTherm, Burner monitoring with FlameBeat, Remaining life assessment with BladeLife
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Combustion monitoring with FlameBeat
Challenge
If irregularities occur in a gas turbine, then the control software will ensure that the gas turbine shuts down to prevent operational failure, often accompanied by costly consequential damage. The gas turbine trips. An unstable flame, leading to unacceptable combustion chamber vibrations, is one of the causes of such a trip. And time is money, standstills cost money. The KEMA "FlameBeat" permanent on-line monitoring system is designed to prevent trips due to flame pulses and to timely recognise damage of hot gas path components. It saves money.
Solution
In modern gas turbines, a reduction of the NOx-emissions is achieved with Dry Low NOx-burners using a pre-mixture of fuel with a large excess of air. The flame of lean premix burners easily turns unstable. This gives rise to acoustic oscillations that may couple to the structure of the combustion chamber. Large vibrations endanger the integrity of the gas turbine and the safety system will trip the machine.
The KEMA "FlameBeat" on-line combustion monitoring system is based on high temperature dynamic pressure probes, installed directly on the combustion chamber. The spectra of the acoustical vibrations that occur during normal use are stored in a database as "the fingerprint" of the combustion chamber. Through comparison of the actual spectra with the "fingerprint" FlameBeat signals the occurrence of defects or component degradation at an early stage. In this way, it provides information about fissures in combustion chambers, leakage of gaskets, burner damage or variations in fuel quality. It also helps to predict and prevent turbine trips caused by large amplitude vibrations.
Advantages
With the KEMA "FlameBeat" on-line combustion monitoring system:
- you can save a lot of money because it gives you an early indication about defects and therefore prevents major failures
- you can perform condition based maintenance rather than random repair work
- you gain an insight into the degradation process of liners and hot gas components, so that you can anticipate their lifetime
- you can prevent turbine trips due to flame instabilities
- you can tune the burners at any time you want more easily.
Example
KEMA installed "FlameBeat" on the gas turbines of the Lage Weide and Diemen power stations of Reliant Energy Power Generation Benelux in the Netherlands. Variations in the level and frequency of the flame pulses in one of these units suggested a crack in the combustion chamber. A temporary repair was made and the unit was started again. The combustion chamber was replaced during the next scheduled overhaul.
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[download] FlameBeat Turbomachinery International March 2002 (.pdf 303 kb)
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[download] FlameBeat video (.avi 20.297 kb)
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[download] Project references FlameBeat 0402 (.pdf 136 kb)
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On-line diagnostics
"For your peace of mind" Having knowledge of the condition of the components in an
installation is of great importance for a reliable operation. In a
time in which broad commercial interests are linked to the
reliability and predictability of, for example, the supply of
energy, this will only become very important. Large amounts of money can be saved by monitoring the critical
components, for maintenance to take place at the most suitable
moments in time. This so-called condition based maintenance
requires the right equipment to be able to determine the actual
condition of the components. This may be equipment that measures
vibration, temperature, pressure, et cetera. Saving just one set of
blades on the lifetime of a gas turbine is keeping millions of
EURO’s in your pocket! Furthermore, on-line diagnostics can be of great help in
preventing machines from tripping. These trips disturb the
reliability of the supply and they will seriously shorten the life
of hot gas path-components. Apart from the commercial implications
resulting from not being able to meet the terms of delivery, the
costs of large gas turbine trip may rise to EUR 50,000 -
100,000. How can this be avoided?
KEMA can supply the following systems for on-line
diagnostics: - TurboTherm for blade temperatures
- FlameBeat for combustion monitoring
- BladeLife for remaining life assessment.
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Blade temperature measurements with TurboTherm
Avoid catastrophic failures and forced outages with KEMA’s
Improved temperature measurements on turbine blades. Challenge
In modern gas turbines, there is a major difference
between the intake temperature of the turbine and the allowable
metal temperature of the blades. For this reason, the blades are
cooled. Disruption in the cooling will rise blade temperature and,
eventually, lead to premature failure of the blades. That kind of
damage is extremely costly. Solution
KEMA offers a system of blank contact temperature
measurement. This has resulted in an operational method for e.g.
tracing cooling problems. Moreover, blade temperature influences
coating oxidation, fatigue and creep of the gas turbine blades and
is therefore of major concern in blade life. Advantages
From the 'fingerprint' of the blade temperatures of a
stage, blades with a temperature deviating from the mean value are
immediately identified. Replacement of excessively hot blades
reduces the risk of severe damage. In turbines with non-cooled
rotor blades, pyrometry permits adjustment of the inlet temperature
for an optimal balance between turbine efficiency and blade life.
An important feature of the method is the fact that the temperature
can be measured while the turbine is in normal operation, which
means that the operational process is not affected. Benefits
Blade temperature monitoring: - minimises the risk of failure of rotor blades from
overheating
- permits detection of blocking of cooling-ducts (trend
analysis).
For a set of representative conditions, cost/benefit analysis
indicates a net present value (NPV) of 3 million euro.
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Remaining life monitoring with BladeLife
Challenge
Components in the hot gas path of gas turbines have a limited life. Replacement is carried out according to guidelines supplied by the manufacturer. These are often conservative and do not take the individual operational conditions into account. The costs of replacement may rise to a third of the original investment. Solution
KEMA has developed BladeLife: lifecycle management systems, for various types of gas turbines. The systems include factors such as creep, fatigue and degradation of the coating. The remaining life is determined based on historical operational data. Simulations permit an assessment of the effect of operational parameters. Besides, from the knowledge packed into the models, acceptance criteria like coating and wall thickness can be derived. Advantages
BladeLife permits optimal lifecycle management and gives a clear insight into the effect of the operational parameters, so that adverse conditions can be avoided. Remaining life may be considerably longer than indicated by the manufacturer. For more information please contact us.
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Combustion monitoring with FlameBeat
Read more
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