Gas Turbine Online Monitoring
KEMA has developed several gas turbine online monitoring systems to avoid failure and performance loss
Combustion monitoring with FlameBeat
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. If such irregularities occur in a gas turbine the controls will trip the gas turbine, often accompanied by costly consequential damage. An unstable flame, leading to unacceptable combustion chamber vibrations, is one of the causes of such a trip. The KEMA "FlameBeat" on-line monitoring system is designed to prevent trips due to flame pulses and to timely recognize damage of hot gas path components. Large vibrations endanger the integrity of the gas turbine. The system is based on high temperature dynamic pressure probes on the combustion chamber(s). After start-up a "fingerprint" is taken. Through comparison of actual spectra with the "fingerprint" FlameBeat signals 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.
KEMA installed "FlameBeat" on the gas turbines of two power stations 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.
Blade temperature measurements with TurboTherm
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.
KEMA offers a system of blank contact temperature measurement. This has resulted in an operational method for 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.
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.
For a set of representative conditions, cost/benefit analysis indicates a net present value (NPV) of €/$ 3 million.
Remaining life monitoring with BladeLife
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.
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.
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.
Watch our FlameBeat video to get an idea of our on-line gas turbine combustion monitoring services!