Method and apparatus for controlling the combustion in a gas turbine

A method for controlling the combustion in a gas turbine comprising at least one compressor, capable of compressing air introduced therein through an inlet duct, at least one combustion chamber, in which said compressed air is mixed with a gaseous fuel coming from a supply duct, and at least one turbine, capable of transforming energy of the gas coming from said combustion chamber into work energy which is exploited for activating one or more operating machines, the method comprising:

• measuring, with one or more measurement instruments, the temperature, calorific value and relative density of said gaseous fuel in order to determine a Wobbe index, Iw, said Wobbe index being defined as:
• I
• w
• =
• PC
• T
• G
• *
• G
• s
• where PC is an upper or lower calorific value of said gaseous fuel, TG is the temperature of said gaseous fuel, and GS is the specific gravity of said gaseous fuel;
• comparing the Wobbe index value measured with a predefined Wobbe index value for said gaseous fuel;
• regulating the temperature of said gaseous fuel with at least one heat exchanger in order to reach said predefined Wobbe index value;
• and
• changing, based on said Wobbe index value, a functioning of the gas turbine from a diffusive flame to a premixed flame, wherein the diffusive flame is present during an ignition phase of the gas turbine while the premixed flame is present during normal functioning of the gas turbine.