الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The use of stationary gas turbines for power generation has been growing rapidly with continuing trends predicted well into the future. Factors that are contributing to this growth include advances in turbine technology, operating and siting flexibility and low capital cost. Generally it may be more cost effective to install small distributed generation units (like gas turbines) within the grid rather than constructing large power plants in remote locations with extensive transmission and distribution systems. For the customer on-site generation will provide added reliability.
One of the key issues that is addressed in virtually every gas turbine application is emissions, particularly nitrogen oxides (NO and N02 shortly NOx) emissions, due to the rule of Ox in ozone depletion, global warning and the creation of photochemical smog. Emission limits from industrial gas turbines have become increasingly stricter during the past years, leading to increase research and development to reduce NOx levels emitted from gas turbines from uncontrolled levels.
The most common NOx control method for new gas turbine power plants is a Dry Low NOx (DLN) combustor to maintain NOx emission levels below allowed limits. DL combustors depend on lean premix technology. The philosophy behind lean premixed combustion is simple, the fuel and air are premixed prior to the flame in order to give a homogenous reaction temperature below the temperatures at which NOx production rates are high.
Dry low NOx (DLN) technology eliminated the need for water or steam injection in gas fired combustion turbines (CTs) by operating at lean fuel conditions. However DLN bumers are susceptible to dynamic pressure fluctuations in the combustion chamber. Severe hardware damage in the combustion chan1ber structure and potentially in the turbine can occur depending on the frequency and amplitude of these pressure fluctuations and if they are not quickly reduced.
Stable combustion in gas turbines is critical to guarantee the turbine’s reliability, availability and to attain maximum component endurance. Development of protective systems was necessary to ensure fast response to the onset of combustion dynamics. The protective systems compare some features of the pressure pulsations with pre-determined settings to trigger either a load shedding or trip the unit according to the severity of the fluctuations. These settings are typically excessive and conservative to ensure safe operation and may result in unnecessary interference by the protective system and disruption of efficient operation. Therefore the detem1ination of settings that activate alarms, induce load shedding or cause complete trip is very critical to the economical operation of the gas turbine. Automated control system would be much more effective in responding to combustion dynamics and minimize the occurrence of such events. Thus operators often need to remain proactive in preventing onset of excessive pressure oscillations and combustion induced vibrations and flame instabilities.
The phenomenon of combustion instability has afflicted a wide range of dry low NOx combustion systems. Today combustion instability is viewed as the major challenge facing the CT industry. In order to protect against combustor instabilities Mitsubishi developed an advanced monitoring and protection system known as the Advanced Combustor Pressure Fluctuation Monitoring (Advanced CPFM) system. This online monitoring and protection system automatically tunes the air bypass valve, main and pilot fuel flows to maintain appropriate fueVair ratio depending on the combustion chamber flame instability condition. The response to such actions successfully prevents flame out occurrence, combustion oscillation, and flame flash back under various modes as well as unexpected disturbances during the combustion process.