Italian power generation market is living today a period of substantial changes due to the liberalization process, climate issues, natural gas price fluctuation and the uncertain future of nuclear and coal. In this framework, many gas turbine power plants, originally designed to operate mainly at base load, feel the necessity to be flexibly and profitably operated into the dispatch and ancillary energy service market. In particular, many operators ask for the possibility to operate their gas turbines intermittently, frequently cycling and quickly ramping up and down to satisfy energy demand. Such using drafts new trade off between profitability and maintenance cost. From this point of view it’s not unusual to shut down the engine when the power demand is low if the unit cannot be cost effectively parked at a suitable low load and then quickly ramped up to base load when the power demand is higher. The main barrier against lowering the minimum load of the gas turbines is the increase of the CO emission. When the engine operates close to its turndown load the compressor airflow is such that the heat released by the flame cannot properly support the conversion of CO into CO2. In such a condition, the power plant will not comply with the environmental legislation and must be operated at a higher load or, worse, shut down. An operating strategy has been devised to face up such problem. It is based on the adjustment of compressor IGV (Inlet Guide Vanes) and the optimisation of cooling air consumption in order to keep the proper amount of combustion air close to the turndown load. This paper shows the feasibility check, the installation and final field tests of the low load turndown upgrade on a AE64.3A gas turbine which allowed to operate the unit in a more cost effective way even when the power demand is low.

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