News
European Turbine Network A.I.S.B.L.
Technology Watch - Advanced Sensor Technologies and Their Application in GT Monitoring
This short paper is written to raise awareness amongst ETN members of how the latest technologies in advanced sensors may assist in online monitoring of the performance and degradation of various components in gas turbines. Particular benefits can be gained from measurements taken within the hot gas path where the harsh environment has previously made it difficult to reliably install traditional instrumentation.
As examples of where advanced sensors can help with such issues:
1. The area of assessing whether turbine blades and stators have cooling passage blockages, deterioration in their thermal barrier coatings or are oxidising can be measured via Optical Pyrometry. This technique allows the temperature of the surface of the blade or vane to be measured by looking at the amount of infra-red radiation given off by that surface. By building up a picture of the blade or vane, hotspots can be identified which may indicate cooling blockages. Likewise, inspections performed at regular intervals under the same GT conditions can show deterioration to coatings. This technique therefore could reduce the need to perform boroscope inspections of gas turbines. The benefit would be reduced downtime and also provide foreknowledge of the kind of repairs that will be required to hot gas path components during the next planned maintenance outage
2. Another example is the safeguarding of the combustor system. If combustion becomes unstable, this can couple with the housing and cause damage to the combustor or potentially downstream of the combustor. Traditionally this has been monitored either by measuring the dynamic pressure fluctuations in the combustor or by mounting an accelerometer to the housing of the combustor. Advances within these types of sensors now allow them to be mounted far closer to the instabilities than before giving the best possible data and therefore allowing the user more information on how to react to humming or rumble issues within their GT equipment. As well as advanced acoustic sensors, optical sensors have also recently been developed, offering real time diagnostics, monitoring and detection of instability precursors. Improved understanding of the unsteady physics of instabilities would enable the best monitoring strategy to be determined. Application of either of these acoustic or optical sensors not only safeguards equipment during operation, but it also allows combustors to be effectively tuned and it can help with re-commissioning of equipment. Finally, as fuel quality widens and gas turbines have to operate at part loads whilst maintaining low emissions, these devices may enable "active control" systems to be realised.
3. A further example is the characterization and monitoring of blade vibrations. These are typically driven by upstream, downstream flow disturbances and hardware transmission. With the correct blade passing sensing technology, Blade Tip Timing can be successfully applied to determine the amplitude, frequency, phase and nodal diameter of blade responses. In a condition based monitoring application, this allows potentially dangerous vibrations to be detected or avoided and possibly extends the blade life or may protect the machine from catastrophic failure. Tip Timing Sensing technology has to not only reliably sense the blade passing events but also, be essentially non-intrusive and operate in harsh environments such as the hot sections. Advanced sensors are being applied to achieve this important field of turbo-machinery measurement.
It is also intended that this initiative should inspire and intensify further discussions among GT users, service providers, manufacturers and suppliers at the next ETN Workshop in October 2011. The discussion will be the first step for the eventual organization of a (European) project focused to improve knowledge of the main problems and to apply advanced sensors in gas turbines to provide significant pay-offs.
Key Business Problems
In order to reach 25,000 hours of operation without intervention, which has been identified as the vision of ETN’s Technology Committees 3 and 4, the following areas need to be addressed:
Compressor performance monitoring
Avoid compressor oil contamination
Online measurement of blade cracking/ erosion/creep
Online assessment of oxidation, cooling blockages and coating deterioration
Monitoring combustor instabilities
Internal oil leak monitoring or DOD
Fuel nozzle tip wear monitoring
Non-invasive measurement of static component cracks, blade rubs and bearing fatigue
Lube oil monitoring
Flame on/off detection
Seals/Secondary Airflow Monitoring
Monitoring Exhaust Dynamics
Measurement of turbine inlet temperature
Typically a gas turbine is operated based on the following measurements:
Temperatures and pressures at compressor inlet
Temperatures and pressures at compressor exit
Lube oil temperature
Bearing temperature
Fuel flow
Combustion instabilities monitoring
Temperature at the exhaust
Rotational shaft speed
Casing vibration/acceleration and
The power generated
These provide the means by which an operator or maintenance contractor can assess the performance, health and contractual features of a gas turbine in operation. Some of the latest generation of advanced sensors are intended to assist the operators and maintenance contractors in making decisions in engine health, performance, degradation, maintenance and warranty conditions.
Sensor technology continues to grow in its innovation and effectiveness to illuminate more information from previously inaccessible parts of the running Gas Turbine. It is felt that it would be valuable within ETN to explore further the needs and problems of users so that the sensor community can focus its efforts on providing solutions for the most pressing applications.
For further information please contact:
Karen Geris – Technical Project Officer, European Turbine Network
Tel: +32 2 646 15 77
Email: kg@etn-gasturbines.eu
Chris Dagnall – Cogsys Ltd and Chair of TC4 "Condition monitoring, Instrumentation and Controls"
Tel: +44 1925 283 868
Email: chris.dagnall@gl-group.com
Click here to download the press release